Simulations of blood flow through a stenosed carotid artery

NASA Astrophysics Data System (ADS)

Lundin, Staffan; Meder, Samuel; Metcalfe, Ralph

2000-11-01

The human carotid artery is often the site of the formation of atherosclerotic lesions that can lead to severe reduction of blood flow to the brain, frequently resulting in a stroke. There is strong evidence that hemodynamic variables such as the wall shear stress and its spatial and temporal derivatives play a role in fostering atherosclerosis. To investigate the potential of these effects, we have performed unsteady, three-dimensional numerical simulations of blood flow through the carotid bifurcation in the presence of stenoses of varying degrees and eccentricities. The simulations indicate that regions of low maximum and minimum shear stress correlate better with lesion prone sites than low average wall shear stress. As the degree of stenosis increases, it is found that the downstream flow changes drastically for stenoses greater than about 25Downstream eddies are generated during systole that create local shear stress peaks on the internal carotid artery wall, resulting in significant reduction in flow rates through the internal carotid artery. Large secondary flows develop, and there are also periods of flow reversal during the systolic/diastolic cycle.

Patient specific 3-d modeling of blood flow in a multi-stenosed left coronary artery.

PubMed

Kamangar, Sarfaraz; Badruddin, Irfan Anjum; Ameer Ahamad, N; Soudagar, Manzoor Elahi M; Govindaraju, Kalimuthu; Nik-Ghazali, N; Salman Ahmed, N J; Yunus Khan, T M

2017-01-01

The current study investigates the effect of multi stenosis on the hemodynamic parameters such as wall pressure, velocity and wall shear stress in the realistic left coronary artery. Patients CT scan image data of normal and diseased left coronary artery was chosen for the reconstruction of 3D coronary artery models. The diseased 3D model of left coronary artery shows a narrowing of more than 70% and 80% of area stenosis (AS) at the left main stem (LMS) and left circumflex (LCX) respectively. The results show that the decrease in pressure was found downstream to the stenosis as compared to the coronary artery without stenosis. The maximum pressure drop was noted across the 80% AS at the left circumflex branch. The recirculation zone was also observed immediate to the stenosis and highest wall shear stress was found across the 80% area stenosis. Our analysis provides an insight into the distribution of wall shear stress and pressure drop, thus improving our understanding on the hemodynamics in realistic coronary artery.

Experimental and numerical investigation of low-drag intervals in turbulent boundary layer

NASA Astrophysics Data System (ADS)

Park, Jae Sung; Ryu, Sangjin; Lee, Jin

2017-11-01

It has been widely investigated that there is a substantial intermittency between high and low drag states in wall-bounded shear flows. Recent experimental and computational studies in a turbulent channel flow have identified low-drag time intervals based on wall shear stress measurements. These intervals are a weak turbulence state characterized by low-speed streaks and weak streamwise vortices. In this study, the spatiotemporal dynamics of low-drag intervals in a turbulent boundary layer is investigated using experiments and simulations. The low-drag intervals are monitored based on the wall shear stress measurement. We show that near the wall conditionally-sampled mean velocity profiles during low-drag intervals closely approach that of a low-drag nonlinear traveling wave solution as well as that of the so-called maximum drag reduction asymptote. This observation is consistent with the channel flow studies. Interestingly, the large spatial stretching of the streak is very evident in the wall-normal direction during low-drag intervals. Lastly, a possible connection between the mean velocity profile during the low-drag intervals and the Blasius profile will be discussed. This work was supported by startup funds from the University of Nebraska-Lincoln.

The effects of recirculation flows on mass transfer from the arterial wall to flowing blood.

PubMed

Zhang, Zhiguo; Deng, Xiaoyan; Fan, Yubo; Guidoin, Robert

2008-01-01

Using a sudden tubular expansion as a model of an arterial stenosis, the effect of disturbed flow on mass transfer from the arterial wall to flowing blood was studied theoretically and tested experimentally by measuring the dissolution rate of benzoic acid disks forming the outer tube of a sudden tubular expansion. The study revealed that mass transfer from vessel wall to flowing fluid in regions of disturbed flow is independent of wall shear rates. The rate of mass transfer is significantly higher in regions of disturbed flow with a local maximum around the reattachment point where the wall shear rate is zero. The experimental study also revealed that the rate of mass transfer from the vessel wall to a flowing fluid is much higher in the presence of microspheres (as models of blood cells) in the flowing fluid and under the condition of pulsatile flow than in steady flow. These results imply that flow disturbance may enhance the transport of biochemicals and macromolecules, such as plasma proteins and lipoproteins synthesized within the blood vessel wall, from the blood vessel wall to flowing blood.

In vivo vascular flow profiling combined with optical tweezers based blood routing

NASA Astrophysics Data System (ADS)

Meissner, Robert; Sugden, Wade W.; Siekmann, Arndt F.; Denz, Cornelia

2017-07-01

In vivo wall shear rate is quantified during zebrafish development using particle image velocimetry for biomedical diagnosis and modeling of artificial vessels. By using brightfield microscopy based high speed video tracking we can resolve single heart-beat cycles of blood flow in both space and time. Maximum blood flow velocities and wall shear rates are presented for zebrafish at two and three days post fertilization. By applying biocompatible optical tweezers as an Optical rail we present rerouting of red blood cells in vivo. With purely light-driven means we are able to compensate the lack of proper red blood cell blood flow in so far unperfused capillaries.

Turbulence significantly increases pressure and fluid shear stress in an aortic aneurysm model under resting and exercise flow conditions.

PubMed

Khanafer, Khalil M; Bull, Joseph L; Upchurch, Gilbert R; Berguer, Ramon

2007-01-01

The numerical models of abdominal aortic aneurysm (AAA) in use do not take into account the non-Newtonian behavior of blood and the development of local turbulence. This study examines the influence of pulsatile, turbulent, non-Newtonian flow on fluid shear stresses and pressure changes under rest and exercise conditions. We numerically analyzed pulsatile turbulent flow, using simulated physiological rest and exercise waveforms, in axisymmetric-rigid aortic aneurysm models (AAMs). Discretization of governing equations was achieved using a finite element scheme. Maximum turbulence-induced shear stress was found at the distal end of an AAM. In large AAMs (dilated to undilated diameter ratio = 3.33) at peak systolic flow velocity, fluid shear stress during exercise is 70.4% higher than at rest. Our study provides a numerical, noninvasive method for obtaining detailed data on the forces generated by pulsatile turbulent flow in AAAs that are difficult to study in humans and in physical models. Our data suggest that increased flow turbulence results in increased shear stress in aneurysms. While pressure readings are fairly uniform along the length of an aneurysm, the kinetic energy generated by turbulence impacting on the wall of the distal half of the aneurysm increases fluid and wall shear stress at this site. If the increased fluid shear stress results in further dilation and hence further turbulence, wall stress may be a mechanism for aneurysmal growth and eventual rupture.

Mining data from hemodynamic simulations for generating prediction and explanation models.

PubMed

Bosnić, Zoran; Vračar, Petar; Radović, Milos D; Devedžić, Goran; Filipović, Nenad D; Kononenko, Igor

2012-03-01

One of the most common causes of human death is stroke, which can be caused by carotid bifurcation stenosis. In our work, we aim at proposing a prototype of a medical expert system that could significantly aid medical experts to detect hemodynamic abnormalities (increased artery wall shear stress). Based on the acquired simulated data, we apply several methodologies for1) predicting magnitudes and locations of maximum wall shear stress in the artery, 2) estimating reliability of computed predictions, and 3) providing user-friendly explanation of the model's decision. The obtained results indicate that the evaluated methodologies can provide a useful tool for the given problem domain. © 2012 IEEE

In vitro shear stress measurements using particle image velocimetry in a family of carotid artery models: effect of stenosis severity, plaque eccentricity, and ulceration.

PubMed

Kefayati, Sarah; Milner, Jaques S; Holdsworth, David W; Poepping, Tamie L

2014-01-01

Atherosclerotic disease, and the subsequent complications of thrombosis and plaque rupture, has been associated with local shear stress. In the diseased carotid artery, local variations in shear stress are induced by various geometrical features of the stenotic plaque. Greater stenosis severity, plaque eccentricity (symmetry) and plaque ulceration have been associated with increased risk of cerebrovascular events based on clinical trial studies. Using particle image velocimetry, the levels and patterns of shear stress (derived from both laminar and turbulent phases) were studied for a family of eight matched-geometry models incorporating independently varied plaque features - i.e. stenosis severity up to 70%, one of two forms of plaque eccentricity, and the presence of plaque ulceration). The level of laminar (ensemble-averaged) shear stress increased with increasing stenosis severity resulting in 2-16 Pa for free shear stress (FSS) and approximately double (4-36 Pa) for wall shear stress (WSS). Independent of stenosis severity, marked differences were found in the distribution and extent of shear stress between the concentric and eccentric plaque formations. The maximum WSS, found at the apex of the stenosis, decayed significantly steeper along the outer wall of an eccentric model compared to the concentric counterpart, with a 70% eccentric stenosis having 249% steeper decay coinciding with the large outer-wall recirculation zone. The presence of ulceration (in a 50% eccentric plaque) resulted in both elevated FSS and WSS levels that were sustained longer (∼20 ms) through the systolic phase compared to the non-ulcerated counterpart model, among other notable differences. Reynolds (turbulent) shear stress, elevated around the point of distal jet detachment, became prominent during the systolic deceleration phase and was widely distributed over the large recirculation zone in the eccentric stenoses.

Suppressing wall turbulence by means of a transverse traveling wave

PubMed

Du; Karniadakis

2000-05-19

Direct numerical simulations of wall-bounded flow reveal that turbulence production can be suppressed by a transverse traveling wave. Flow visualizations show that the near-wall streaks are eliminated, in contrast to other turbulence-control techniques, leading to a large shear stress reduction. The traveling wave can be induced by a spanwise force that is confined within the viscous sublayer; it has its maximum at the wall and decays exponentially away from it. We demonstrate the application of this approach in salt water, using arrays of electromagnetic tiles that produce the required traveling wave excitation at a high efficiency.

Research on wall shear stress considering wall roughness when shear swirling flow vibration cementing

NASA Astrophysics Data System (ADS)

Cui, Zhihua; Ai, Chi; Feng, Fuping

2017-01-01

When shear swirling flow vibration cementing, the casing is revolving periodically and eccentrically, which leads to the annulus fluid in turbulent swirling flow state. The wall shear stress is more than that in laminar flow field when conventional cementing. The paper mainly studied the wall shear stress distribution on the borehole wall when shear swirling flow vibration cementing based on the finite volume method. At the same time, the wall roughness affected and changed the turbulent flow near the borehole wall and the wall shear stress. Based on the wall function method, the paper established boundary conditions considering the wall roughness and derived the formula of the wall shear stress. The results showed that the wall roughness significantly increases the wall shear stress. However, the larger the wall roughness, the greater the thickness of mud cake, which weakening the cementing strength. Considering the effects in a comprehensive way, it is discovered that the particle size of solid phase in drilling fluid is about 0.1 mm to get better cementing quality.

Effect of solid boundaries on swimming dynamics of microorganisms in a viscoelastic fluid

PubMed Central

Li, G. -J.; Karimi, A.

2015-01-01

We numerically study the effect of solid boundaries on the swimming behavior of a motile microorganism in viscoelastic media. Understanding the swimmer-wall hydrodynamic interactions is crucial to elucidate the adhesion of bacterial cells to nearby substrates which is precursor to the formation of the microbial biofilms. The microorganism is simulated using a squirmer model that captures the major swimming mechanisms of potential, extensile, and contractile types of swimmers, while neglecting the biological complexities. A Giesekus constitutive equation is utilized to describe both viscoelasticity and shear-thinning behavior of the background fluid. We found that the viscoelasticity strongly affects the near-wall motion of a squirmer by generating an opposing polymeric torque which impedes the rotation of the swimmer away from the wall. In particular, the time a neutral squirmer spends at the close proximity of the wall is shown to increase with polymer relaxation time and reaches a maximum at Weissenberg number of unity. The shear-thinning effect is found to weaken the solvent stress and therefore, increases the swimmer-wall contact time. For a puller swimmer, the polymer stretching mainly occurs around its lateral sides, leading to reduced elastic resistance against its locomotion. The neutral and puller swimmers eventually escape the wall attraction effect due to a releasing force generated by the Newtonian viscous stress. In contrast, the pusher is found to be perpetually trapped near the wall as a result of the formation of a highly stretched region behind its body. It is shown that the shear-thinning property of the fluid weakens the wall-trapping effect for the pusher squirmer. PMID:26855446

The effect of shear wall location in resisting earthquake

NASA Astrophysics Data System (ADS)

Tarigan, J.; Manggala, J.; Sitorus, T.

2018-02-01

Shear wall is one of lateral resisting structure which is used commonly. Shear wall gives high stiffness to the structure so as the structure will be stable. Applying shear wall can effectively reduce the displacement and story-drift of the structure. This will reduce the destruction comes from lateral loads such as an earthquake. Earlier studies showed that shear wall gives different performance based on its position in structures. In this paper, seismic analysis has been performed using response spectrum method for different Model of structures; they are the open frame, the shear wall at core symmetrically, the shear wall at periphery symmetrically, and the shear wall at periphery asymmetrically. The results are observed by comparing the displacement and story-drift. Based on the analysis, the placement of shear wall at the core of structure symmetrically gives the best performance to reduce the displacement and story-drift. It can reduce the displacement up to 61.16% (X-dir) and 70.60% (Y-dir). The placement of shear wall at periphery symmetrically will reduce the displacement up to 53.85% (X-dir) and 47.87% (Y-dir) while the placement of shear wall at periphery asymmetrically reducing the displacement up to 59.42% (X-dir) and 66.99% (Y-dir).

Deformation Behaviors of Geosynthetic Reinforced Soil Walls on Shallow Weak Ground

NASA Astrophysics Data System (ADS)

Kim, You-Seong; Won, Myoung-Soo

In this study, the fifteen-month behavior of two geosynthetic reinforced soil walls, which was constructed on the shallow weak ground, was measured and analyzed. The walls were backfilled with clayey soil obtained from the construction site nearby, and the safety factors obtained from general limit equilibrium analysis were less than 1.3 in both wall. To compare with the measured data from the real GRS walls and unreinforced soil mass, a series of finite element method (FEM) analyses on two field GRS walls and unreinforced soil mass were conducted. The FEM analysis results showed that failure plane of unreinforced soil mass was consistent with the Rankine active state, but failure plane did not occur in GRS walls. In addition, maximum horizontal displacements and shear strains in GRS walls were 50% smaller than those found in unreinforced soil mass. Modeling results such as the maximum horizontal displacements, horizontal pressure, and geosynthetic tensile strengths in GRS wall have a god agreement with the measured data. Based on this study, it could be concluded that geosynthetic reinforcement are effective to reduce the displacement of the wall face and/or the deformation of the backfill soil even if the mobilized tensile stress after construction is very small.

Significance of Shear Wall in Multi-Storey Structure With Seismic Analysis

NASA Astrophysics Data System (ADS)

Bongilwar, Rajat; Harne, V. R.; Chopade, Aditya

2018-03-01

In past decades, shear walls are one of the most appropriate and important structural component in multi-storied building. Therefore, it would be very interesting to study the structural response and their systems in multi-storied structure. Shear walls contribute the stiffness and strength during earthquakes which are often neglected during design of structure and construction. This study shows the effect of shear walls which significantly affect the vulnerability of structures. In order to test this hypothesis, G+8 storey building was considered with and without shear walls and analyzed for various parameters like base shear, storey drift ratio, lateral displacement, bending moment and shear force. Significance of shear wall has been studied with the help of two models. First model is without shear wall i.e. bare frame and other another model is with shear wall considering opening also in it. For modeling and analysis of both the models, FEM based software ETABS 2016 were used. The analysis of all models was done using Equivalent static method. The comparison of results has been done based on same parameters like base shear, storey drift ratio, lateral displacement, bending moment and shear force.

Steel Shear Walls, Behavior, Modeling and Design

NASA Astrophysics Data System (ADS)

Astaneh-Asl, Abolhassan

2008-07-01

In recent years steel shear walls have become one of the more efficient lateral load resisting systems in tall buildings. The basic steel shear wall system consists of a steel plate welded to boundary steel columns and boundary steel beams. In some cases the boundary columns have been concrete-filled steel tubes. Seismic behavior of steel shear wall systems during actual earthquakes and based on laboratory cyclic tests indicates that the systems are quite ductile and can be designed in an economical way to have sufficient stiffness, strength, ductility and energy dissipation capacity to resist seismic effects of strong earthquakes. This paper, after summarizing the past research, presents the results of two tests of an innovative steel shear wall system where the boundary elements are concrete-filled tubes. Then, a review of currently available analytical models of steel shear walls is provided with a discussion of capabilities and limitations of each model. We have observed that the tension only "strip model", forming the basis of the current AISC seismic design provisions for steel shear walls, is not capable of predicting the behavior of steel shear walls with length-to-thickness ratio less than about 600 which is the range most common in buildings. The main reasons for such shortcomings of the AISC seismic design provisions for steel shear walls is that it ignores the compression field in the shear walls, which can be significant in typical shear walls. The AISC method also is not capable of incorporating stresses in the shear wall due to overturning moments. A more rational seismic design procedure for design of shear walls proposed in 2000 by the author is summarized in the paper. The design method, based on procedures used for design of steel plate girders, takes into account both tension and compression stress fields and is applicable to all values of length-to-thickness ratios of steel shear walls. The method is also capable of including the effect of overturning moments and any normal forces that might act on the steel shear wall.

Seismic anisotropy in the vicinity of the Alpine fault, New Zealand, estimated by seismic interferometry

NASA Astrophysics Data System (ADS)

Takagi, R.; Okada, T.; Yoshida, K.; Townend, J.; Boese, C. M.; Baratin, L. M.; Chamberlain, C. J.; Savage, M. K.

2016-12-01

We estimate shear wave velocity anisotropy in shallow crust near the Alpine fault using seismic interferometry of borehole vertical arrays. We utilized four borehole observations: two sensors are deployed in two boreholes of the Deep Fault Drilling Project in the hanging wall side, and the other two sites are located in the footwall side. Surface sensors deployed just above each borehole are used to make vertical arrays. Crosscorrelating rotated horizontal seismograms observed by the borehole and surface sensors, we extracted polarized shear waves propagating from the bottom to the surface of each borehole. The extracted shear waves show polarization angle dependence of travel time, indicating shear wave anisotropy between the two sensors. In the hanging wall side, the estimated fast shear wave directions are parallel to the Alpine fault. Strong anisotropy of 20% is observed at the site within 100 m from the Alpine fault. The hanging wall consists of mylonite and schist characterized by fault parallel foliation. In addition, an acoustic borehole imaging reveals fractures parallel to the Alpine fault. The fault parallel anisotropy suggest structural anisotropy is predominant in the hanging wall, demonstrating consistency of geological and seismological observations. In the footwall side, on the other hand, the angle between the fast direction and the strike of the Alpine fault is 33-40 degrees. Since the footwall is composed of granitoid that may not have planar structure, stress induced anisotropy is possibly predominant. The direction of maximum horizontal stress (SHmax) estimated by focal mechanisms of regional earthquakes is 55 degrees of the Alpine fault. Possible interpretation of the difference between the fast direction and SHmax direction is depth rotation of stress field near the Alpine fault. Similar depth rotation of stress field is also observed in the SAFOD borehole at the San Andreas fault.

A multi-component parallel-plate flow chamber system for studying the effect of exercise-induced wall shear stress on endothelial cells.

PubMed

Wang, Yan-Xia; Xiang, Cheng; Liu, Bo; Zhu, Yong; Luan, Yong; Liu, Shu-Tian; Qin, Kai-Rong

2016-12-28

In vivo studies have demonstrated that reasonable exercise training can improve endothelial function. To confirm the key role of wall shear stress induced by exercise on endothelial cells, and to understand how wall shear stress affects the structure and the function of endothelial cells, it is crucial to design and fabricate an in vitro multi-component parallel-plate flow chamber system which can closely replicate exercise-induced wall shear stress waveforms in artery. The in vivo wall shear stress waveforms from the common carotid artery of a healthy volunteer in resting and immediately after 30 min acute aerobic cycling exercise were first calculated by measuring the inner diameter and the center-line blood flow velocity with a color Doppler ultrasound. According to the above in vivo wall shear stress waveforms, we designed and fabricated a parallel-plate flow chamber system with appropriate components based on a lumped parameter hemodynamics model. To validate the feasibility of this system, human umbilical vein endothelial cells (HUVECs) line were cultured within the parallel-plate flow chamber under abovementioned two types of wall shear stress waveforms and the intracellular actin microfilaments and nitric oxide (NO) production level were evaluated using fluorescence microscope. Our results show that the trends of resting and exercise-induced wall shear stress waveforms, especially the maximal, minimal and mean wall shear stress as well as oscillatory shear index, generated by the parallel-plate flow chamber system are similar to those acquired from the common carotid artery. In addition, the cellular experiments demonstrate that the actin microfilaments and the production of NO within cells exposed to the two different wall shear stress waveforms exhibit different dynamic behaviors; there are larger numbers of actin microfilaments and higher level NO in cells exposed in exercise-induced wall shear stress condition than resting wall shear stress condition. The parallel-plate flow chamber system can well reproduce wall shear stress waveforms acquired from the common carotid artery in resting and immediately after exercise states. Furthermore, it can be used for studying the endothelial cells responses under resting and exercise-induced wall shear stress environments in vitro.

Seismic Performance of Composite Shear Walls Constructed Using Recycled Aggregate Concrete and Different Expandable Polystyrene Configurations.

PubMed

Liu, Wenchao; Cao, Wanlin; Zhang, Jianwei; Qiao, Qiyun; Ma, Heng

2016-03-02

The seismic performance of recycled aggregate concrete (RAC) composite shear walls with different expandable polystyrene (EPS) configurations was investigated. Six concrete shear walls were designed and tested under cyclic loading to evaluate the effect of fine RAC in designing earthquake-resistant structures. Three of the six specimens were used to construct mid-rise walls with a shear-span ratio of 1.5, and the other three specimens were used to construct low-rise walls with a shear-span ratio of 0.8. The mid-rise and low-rise shear walls consisted of an ordinary recycled concrete shear wall, a composite wall with fine aggregate concrete (FAC) protective layer (EPS modules as the external insulation layer), and a composite wall with sandwiched EPS modules as the insulation layer. Several parameters obtained from the experimental results were compared and analyzed, including the load-bearing capacity, stiffness, ductility, energy dissipation, and failure characteristics of the specimens. The calculation formula of load-bearing capacity was obtained by considering the effect of FAC on composite shear walls as the protective layer. The damage process of the specimen was simulated using the ABAQUS Software, and the results agreed quite well with those obtained from the experiments. The results show that the seismic resistance behavior of the EPS module composite for shear walls performed better than ordinary recycled concrete for shear walls. Shear walls with sandwiched EPS modules had a better seismic performance than those with EPS modules lying outside. Although the FAC protective layer slightly improved the seismic performance of the structure, it undoubtedly slowed down the speed of crack formation and the stiffness degradation of the walls.

Seismic Performance of Composite Shear Walls Constructed Using Recycled Aggregate Concrete and Different Expandable Polystyrene Configurations

PubMed Central

Liu, Wenchao; Cao, Wanlin; Zhang, Jianwei; Qiao, Qiyun; Ma, Heng

2016-01-01

The seismic performance of recycled aggregate concrete (RAC) composite shear walls with different expandable polystyrene (EPS) configurations was investigated. Six concrete shear walls were designed and tested under cyclic loading to evaluate the effect of fine RAC in designing earthquake-resistant structures. Three of the six specimens were used to construct mid-rise walls with a shear-span ratio of 1.5, and the other three specimens were used to construct low-rise walls with a shear-span ratio of 0.8. The mid-rise and low-rise shear walls consisted of an ordinary recycled concrete shear wall, a composite wall with fine aggregate concrete (FAC) protective layer (EPS modules as the external insulation layer), and a composite wall with sandwiched EPS modules as the insulation layer. Several parameters obtained from the experimental results were compared and analyzed, including the load-bearing capacity, stiffness, ductility, energy dissipation, and failure characteristics of the specimens. The calculation formula of load-bearing capacity was obtained by considering the effect of FAC on composite shear walls as the protective layer. The damage process of the specimen was simulated using the ABAQUS Software, and the results agreed quite well with those obtained from the experiments. The results show that the seismic resistance behavior of the EPS module composite for shear walls performed better than ordinary recycled concrete for shear walls. Shear walls with sandwiched EPS modules had a better seismic performance than those with EPS modules lying outside. Although the FAC protective layer slightly improved the seismic performance of the structure, it undoubtedly slowed down the speed of crack formation and the stiffness degradation of the walls. PMID:28773274

Measurements in the near-wall region of a relaxing three-dimensional low speed turbulent air boundary layer

NASA Technical Reports Server (NTRS)

Hebbar, K. S.; Melnik, W. L.

1976-01-01

An experimental investigation was conducted at selected locations of the near-wall region of a three dimensional turbulent air boundary layer relaxing in a nominally zero external pressure gradient behind a transverse hump (in the form of a 30 deg swept, 5-foot chord wing-type model) faired into the side wall of a low speed wind tunnel. Wall shear stresses measured with a flush-mounted hot-film gage and a sublayer fence were in very good agreement with experimental data obtained with two Preston probes. With the upstream unit Reynolds number held constant at 325,000/ft. approximately one-fourth of the boundary layer thickness adjacent to the wall was surveyed with a single rotated hot-wire probe mounted on a specially designed minimum interference traverse mechanism. The boundary layer (approximately 3.5 in thick near the first survey station where the length Reynolds number was 5.5 million) had a maximum crossflow velocity ratio of 0.145 and a maximum crossflow angle of 21.875 deg close to the wall.

Streaming potential of superhydrophobic microchannels.

PubMed

Park, Hung Mok; Kim, Damoa; Kim, Se Young

2017-03-01

For the purpose of gaining larger streaming potential, it has been suggested to employ superhydrophobic microchannels with a large velocity slip. There are two kinds of superhydrophobic surfaces, one having a smooth wall with a large Navier slip coefficient caused by the hydrophobicity of the wall material, and the other having a periodic array of no- shear slots of air pockets embedded in a nonslip wall. The electrokinetic flows over these two superhydrophobic surfaces are modelled using the Navier-Stokes equation and convection-diffusion equations of the ionic species. The Navier slip coefficient of the first kind surfaces and the no-shear slot ratio of the second kind surfaces are similar in the sense that the volumetric flow rate increases as these parameter values increase. However, although the streaming potential increases monotonically with respect to the Navier slip coefficient, it reaches a maximum and afterward decreases as the no-shear ratio increases. The results of the present investigation imply that the characterization of superhydrophobic surfaces employing only the measurement of volumetric flow rate against pressure drop is not appropriate and the fine structure of the superhydrophobic surfaces must be verified before predicting the streaming potential and electrokinetic flows accurately. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Statistical field estimators for multiscale simulations.

PubMed

Eapen, Jacob; Li, Ju; Yip, Sidney

2005-11-01

We present a systematic approach for generating smooth and accurate fields from particle simulation data using the notions of statistical inference. As an extension to a parametric representation based on the maximum likelihood technique previously developed for velocity and temperature fields, a nonparametric estimator based on the principle of maximum entropy is proposed for particle density and stress fields. Both estimators are applied to represent molecular dynamics data on shear-driven flow in an enclosure which exhibits a high degree of nonlinear characteristics. We show that the present density estimator is a significant improvement over ad hoc bin averaging and is also free of systematic boundary artifacts that appear in the method of smoothing kernel estimates. Similarly, the velocity fields generated by the maximum likelihood estimator do not show any edge effects that can be erroneously interpreted as slip at the wall. For low Reynolds numbers, the velocity fields and streamlines generated by the present estimator are benchmarked against Newtonian continuum calculations. For shear velocities that are a significant fraction of the thermal speed, we observe a form of shear localization that is induced by the confining boundary.

Near-wall similarity in a pressure-driven three-dimensional turbulent boundary layer

NASA Technical Reports Server (NTRS)

Pierce, F. J.; Mcallister, J. E.

1980-01-01

Mean velocity, measured wall pressure and wall shear stress fields were made in a three dimensional pressure-driven turbulent boundary layer created by a cylinder with trailing edge placed normal to a flat plate floor. The direct force wall shear stress measurements were made with floating element direct force sensing shear meter that responded to both the magnitude and direction of the local wall shear stress. The ability of 10 near wall similarity models to describe the near wall velocity field for the measured flow under a wide range of skewing conditions and a variety of pressure gradient and wall shear vector orientations was used.

Experimental and numerical investigations of higher mode effects on seismic inelastic response of reinforced concrete shear walls

NASA Astrophysics Data System (ADS)

Ghorbanirenani, Iman

This thesis presents two experimental programs together with companion numerical studies that were carried out on reinforced concrete shear walls: static tests and dynamic (shake table) tests. The first series of experiments were monotonic and cyclic quasi-static testing on ductile reinforced concrete shear wall specimens designed and detailed according to the seismic provisions of NBCC 2005 and CSA-A23.3-04 standard. The tests were carried out on full-scale and 1:2.37 reduced scale wall specimens to evaluate the seismic design provisions and similitude law and determine the appropriate scaling factor that could be applied for further studies such as dynamic tests. The second series of experiments were shake table tests conducted on two identical 1:2.33 scaled, 8-storey moderately ductile reinforced concrete shear wall specimens to investigate the effects of higher modes on the inelastic response of slender walls under high frequency ground motions expected in Eastern North America. The walls were designed and detailed according to the seismic provisions of NBCC 2005 and CSA-A23.3-04 standard. The objectives were to validate and understand the inelastic response and interaction of shear, flexure and axial loads in plastic hinge zones of the walls considering the higher mode effects and to investigate the formation of second hinge in upper part of the wall due to higher mode responses. Second mode response significantly affected the response of the walls. This caused inelastic flexural response to develop at the 6th level with approximately the same rotation ductility compared to that observed at the base. Dynamic amplification of the base shear forces was also observed in both walls. Numerical modeling of these two shake table tests was performed to evaluate the test results and validate current modeling approaches. Nonlinear time history analyses were carried out by the reinforced concrete fibre element (OpenSees program) and finite element (VecTor2 program) methods using the shake table feedback signals as input. Good agreement was generally obtained between numerical and experimental results. Both computer programs were able to predict the natural frequency of the walls in the undamaged and damaged conditions. Both modeling techniques could predict that the maximum bending moment at the base of the walls reached the actual wall moment capacity. The inelastic response and the dual plastic hinge behaviour of the walls could be adequately reproduced using the fibre element and finite element analysis programs. The fibre element method is a good alternative in terms of computing time. It produces reasonable results in comparison with the finite element method, although particular attention needs to be given to the selection of the damping ratios. The different parametric analyses performed in this thesis showed that, for both models, adding a small amount of global viscous damping in combination with a refined reinforced concrete hysteretic model could predict better the seismic behaviour of the tested structures. For the VecTor2 program, a viscous damping of 1% led to reasonable results for the studied RC walls. For the OpenSees program, 2% damping resulted in a good match between test and predictions for the 100% EQ test on the initially undamaged wall. When increasing the earthquake intensities, the damping had to be reduced between 1.5% and 1% to achieve good results for a damaged wall with elongated vibration periods. According to the experimental results and numerical analyses on reinforced concrete shear walls subjected to ground motions from Eastern North America earthquakes, there is a high possibility of having a second plastic hinge forming in the upper part of walls in addition to the one assumed in design at the base. This second hinge could dissipate the earthquake energy more effectively and decrease the force demand on the wall. A dual plastic hinge design approach in which the structures become plastic in the upper wall segment as well as the base could be therefore more appropriate. Preliminary design recommendations considering higher mode effects on dual hinge response and base shear forces for ductile slender shear walls are given in this thesis. (Abstract shortened by UMI.)

Flow and wall shear stress characterization after endovascular aneurysm repair and endovascular aneurysm sealing in an infrarenal aneurysm model.

PubMed

Boersen, Johannes T; Groot Jebbink, Erik; Versluis, Michel; Slump, Cornelis H; Ku, David N; de Vries, Jean-Paul P M; Reijnen, Michel M P J

2017-12-01

Endovascular aneurysm repair (EVAR) with a modular endograft has become the preferred treatment for abdominal aortic aneurysms. A novel concept is endovascular aneurysm sealing (EVAS), consisting of dual endoframes surrounded by polymer-filled endobags. This dual-lumen configuration is different from a bifurcation with a tapered trajectory of the flow lumen into the two limbs and may induce unfavorable flow conditions. These include low and oscillatory wall shear stress (WSS), linked to atherosclerosis, and high shear rates that may result in thrombosis. An in vitro study was performed to assess the impact of EVAR and EVAS on flow patterns and WSS. Four abdominal aortic aneurysm phantoms were constructed, including three stented models, to study the influence of the flow divider on flow (Endurant [Medtronic, Minneapolis, Minn], AFX [Endologix, Irvine, Calif], and Nellix [Endologix]). Experimental models were tested under physiologic resting conditions, and flow was visualized with laser particle imaging velocimetry, quantified by shear rate, WSS, and oscillatory shear index (OSI) in the suprarenal aorta, renal artery (RA), and common iliac artery. WSS and OSI were comparable for all models in the suprarenal aorta. The RA flow profile in the EVAR models was comparable to the control, but a region of lower WSS was observed on the caudal wall compared with the control. The EVAS model showed a stronger jet flow with a higher shear rate in some regions compared with the other models. Small regions of low WSS and high OSI were found near the distal end of all stents in the common iliac artery compared with the control. Maximum shear rates in each region of interest were well below the pathologic threshold for acute thrombosis. The different stent designs do not influence suprarenal flow. Lower WSS is observed in the caudal wall of the RA after EVAR and a higher shear rate after EVAS. All stented models have a small region of low WSS and high OSI near the distal outflow of the stents. Copyright © 2016 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.

Augmentative effect of pulsatility on the wall shear stress in tube flow.

PubMed

Nakata, M; Tatsumi, E; Tsukiya, T; Taenaka, Y; Nishimura, T; Nishinaka, T; Takano, H; Masuzawa, T; Ohba, K

1999-08-01

Wall shear stress (WSS) has been considered to play an important role in the physiological and metabolic functions of the vascular endothelial cells. We investigated the effects of the pulse rate and the maximum flow rate on the WSS to clarify the influence of pulsatility. Water was perfused in a 1/2 inch transparent straight cylinder with a nonpulsatile centrifugal pump and a pulsatile pneumatic ventricular assist device (VAD). In nonpulsatile flow (NF), the flow rate was changed 1 to 6 L/min by 1 L/min increments to obtain standard values of WSS at each flow rate. In pulsatile flow (PF), the pulse rate was controlled at 40, 60, and 80 bpm, and the maximum flow rate was varied from 3.3 to 12.0 L/min while the mean flow rate was kept at 3 L/min. The WSS was estimated from the velocity profile at measuring points using the laser illuminated fluorescence method. In NF, the WSS was 12.0 dyne/cm2 at 3 L/min and 33.0 dyne/cm2 at 6 L/min. In PF, the pulse rate change with the same mean, and the maximum flow rate did not affect WSS. On the other hand, the increase in the maximum flow rate at the constant mean flow rate of 3 L/min augmented the mean WSS from 13.1 to 32.9 dyne/cm2. We concluded that the maximum flow rate exerted a substantial augmentative effect on WSS, and the maximum flow rate was a dominant factor of pulsatility in this effect.

Optimisation of tool path for improved formability of commercial pure aluminium sheets during the incremental forming process

NASA Astrophysics Data System (ADS)

Prasad, Moyye Devi; Nagarajan, D.

2018-05-01

An axisymmetric dome of 70 mm in diameter and 35 mm in depth was formed using the ISF process using varying proportions (25, 50 and 75%) of spiral (S) and helical (H) tool path combinations as a single tool path strategy, on a 2 mm thickness commercially pure aluminium sheets. A maximum forming depth of ˜30 mm was observed on all the components, irrespective of the different tool path combinations employed. None of the components were fractured for the different tool path combinations used. The springback was also same and uniform for all the tool path combinations employed, except for the 75S25H which showed slightly larger springback. The wall thickness reduced drastically up to a certain forming depth and increased with the increase in forming depth for all the tool path combinations. The maximum thinning occurred near the maximum wall angle region for all the components. The wall thickness improved significantly (around 10-15%) near the maximum wall angle region for the 25S75H combination than that of the complete spiral and other tool path strategies. It is speculated that this improvement in wall thickness may be mainly due to the combined contribution of the simple shear and uniaxial dilatation deformation modes of the helical tool path strategy in the 25S75H combination. This increase in wall thickness will greatly help in reducing the plastic instability and postpone the early failure of the component.

Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal

NASA Technical Reports Server (NTRS)

Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III

1996-01-01

The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

Small-bubble transport and splitting dynamics in a symmetric bifurcation.

PubMed

Qamar, Adnan; Warnez, Matthew; Valassis, Doug T; Guetzko, Megan E; Bull, Joseph L

2017-08-01

Simulations of small bubbles traveling through symmetric bifurcations are conducted to garner information pertinent to gas embolotherapy, a potential cancer treatment. Gas embolotherapy procedures use intra-arterial bubbles to occlude tumor blood supply. As bubbles pass through bifurcations in the blood stream nonhomogeneous splitting and undesirable bioeffects may occur. To aid development of gas embolotherapy techniques, a volume of fluid method is used to model the splitting process of gas bubbles passing through artery and arteriole bifurcations. The model reproduces the variety of splitting behaviors observed experimentally, including the bubble reversal phenomenon. Splitting homogeneity and maximum shear stress along the vessel walls is predicted over a variety of physical parameters. Small bubbles, having initial length less than twice the vessel diameter, were found unlikely to split in the presence of gravitational asymmetry. Maximum shear stresses were found to decrease exponentially with increasing Reynolds number. Vortex-induced shearing near the bifurcation is identified as a possible mechanism for endothelial cell damage.

An investigation on near wall transport characteristics in an adiabatic upward gas-liquid two-phase slug flow

NASA Astrophysics Data System (ADS)

Zheng, Donghong; Che, Defu

2007-08-01

The near-wall transport characteristics, inclusive of mass transfer coefficient and wall shear stress, which have a great effect on gas-liquid two-phase flow induced internal corrosion of low alloy pipelines in vertical upward oil and gas mixing transport, have been both mechanistically and experimentally investigated in this paper. Based on the analyses on the hydrodynamic characteristics of an upward slug unit, the mass transfer in the near wall can be divided into four zones, Taylor bubble nose zone, falling liquid film zone, Taylor bubble wake zone and the remaining liquid slug zone; the wall shear stress can be divided into two zones, the positive wall shear stress zone associated with the falling liquid film and the negative wall shear stress zone associated with the liquid slug. Based on the conventional mass transfer and wall shear stress characteristics formulas of single phase liquid full-pipe turbulent flow, corrected normalized mass transfer coefficient formula and wall shear stress formula are proposed. The calculated results are in good agreement with the experimental data. The shear stress and the mass transfer coefficient in the near wall zone are increased with the increase of superficial gas velocity and decreased with the increase of superficial liquid velocity. The mass transfer coefficients in the falling liquid film zone and the wake zone of leading Taylor bubble are lager than those in the Taylor bubble nose zone and the remaining liquid slug zone, and the wall shear stress associated falling liquid film is larger than that associated the liquid slug. The mass transfer coefficient is within 10-3 m/s, and the wall shear stress below 103 Pa. It can be concluded that the alternate wall shear stress due to upward gas-liquid slug flow is considered to be the major cause of the corrosion production film fatigue cracking.

Electrochemical wall shear rate microscopy of collapsing bubbles

NASA Astrophysics Data System (ADS)

Reuter, Fabian; Mettin, Robert

2018-06-01

An electrochemical high-speed wall shear raster microscope is presented. It involves chronoamperometric measurements on a microelectrode that is flush-mounted in a submerged test specimen. Wall shear rates are derived from the measured microelectrode signal by numerically solving a convection-diffusion equation with an optimization approach. This way, the unsteady wall shear rates from the collapse of a laser pulse seeded cavitation bubble close to a substrate are measured. By planar scanning, they are resolved in high spatial resolution. The wall shear rates are related to the bubble dynamics via synchronized high-speed imaging of the bubble shape.

Wall shear stress measurement in blade end-wall corner region

NASA Technical Reports Server (NTRS)

Bhargava, R.; Raj, R.; Boldman, D. R.

1987-01-01

The magnitude and the direction of wall shear stress and surface pressure in the blade end-wall corner region were investigated. The measurements were obtained on a specially designed Preston tube, the tip of which could be concentrically rotated about its axis of rotation at the measurement location. The magnitude of wall shear stress in the vicinity of the corner was observed to increase significantly (170 percent) compared to its far-upstream value; the increase was consistently higher on the blade surface compared to the value on the plate surface of the blade end-wall corner. On both surfaces in the blade end-wall corner, the variation of the wall shear stress direction was found to be more predominant in the vicinity of the blade leading-edge location. The trend of the measured wall shear stress direction showed good agreement with the limiting streamline directions obtained from the flow visualization studies.

Effects of Combined Shear and Thermal Forces on Destruction of Microbacterium lacticum

PubMed Central

Bulut, S.; Waites, W. M.; Mitchell, J. R.

1999-01-01

A twin-screw extruder and a rotational rheometer were used to generate shear forces in concentrated gelatin inoculated with a heat-resistant isolate of a vegetative bacterial species, Microbacterium lacticum. Shear forces in the extruder were mainly controlled by varying the water feed rate. The water content of the extrudates changed between 19 and 45% (wet weight basis). Higher shear forces generated at low water contents and the calculated die wall shear stress correlated strongly with bacterial destruction. No surviving microorganisms could be detected at the highest wall shear stress of 409 kPa, giving log reduction of 5.3 (minimum detection level, 2 × 104 CFU/sample). The mean residence time of the microorganism in the extruder was 49 to 58 s, and the maximum temperature measured in the end of the die was 73°C. The D75°C of the microorganism in gelatin at 65% water content was 20 min. It is concluded that the physical forces generated in the reverse screw element and the extruder die rather than heat played a major part in cell destruction. In a rotational rheometer, after shearing of a mix of microorganisms with gelatin at 65% (wt/wt) moisture content for 4 min at a shear stress of 2.8 kPa and a temperature of 75°C, the number of surviving microorganisms in the sheared sample was 5.2 × 106 CFU/g of sample compared with 1.4 × 108 CFU/g of sample in the nonsheared control. The relative effectiveness of physical forces in the killing of bacteria and destruction of starch granules is discussed. PMID:10508076

Shear-induced desorption of isolated polymer molecules from a planar wall

NASA Astrophysics Data System (ADS)

Dutta, Sarit; Dorfman, Kevin; Kumar, Satish

2014-03-01

Shear-induced desorption of isolated polymer molecules is studied using Brownian dynamics simulations. The polymer molecules are modeled as freely jointed bead-spring chains interacting with a planar wall via a short-range potential. The simulations include both intrachain and chain-wall hydrodynamic interactions. Shear flow is found to cause chain flattening, resulting at low shear rates in an increased fraction of chain segments bound to the wall. However, above a critical shear rate the chains desorb completely. The desorption process is nucleated by random protrusions in the shear gradient direction which evolve under the combined effect of drag, hydrodynamic interaction, and vorticity-induced rotation, and subsequently lead to recapture. Above the critical shear rate, these protrusions grow in length until the entire chain is peeled off the wall. For free-draining chains, the protrusions are not sustained and no desorption is observed even at shear rates much higher than the critical value. These simulations can help in interpreting experiments on shear-induced desorption of polymer films and brushes.

Experimental investigation of compliant wall surface deformation in a turbulent channel flow

NASA Astrophysics Data System (ADS)

Zhang, Cao; Wang, Jin; Katz, Joseph

2016-11-01

The dynamic response of a compliant wall under a turbulent channel flow is investigated by simultaneously measuring the time-resolved, 3D flow field (using tomographic PIV) and the 2D surface deformation (using interferometry). The pressure distributions are calculated by spatially integrating the material acceleration field. The Reynolds number is Reτ = 2300, and the centerline velocity (U0) is 15% of the material shear speed. The wavenumber-frequency spectra of the wall deformation contain a non-advected low-frequency component and advected modes, some traveling downstream at U0 and others at 0.72U0. Trends in the wall dynamics are elucidated by correlating the deformation with flow variables. The spatial pressure-deformation correlations peak at y/ h 0.12 (h is half channel height), the elevation of Reynolds shear stress maximum in the log-layer. Streamwise lagging of the deformation behind the pressure is caused in part by phase-lag of the pressure with decreasing distance from the wall, and in part by material damping. Positive deformations (bumps) are preferentially associated with ejections, which involve spanwise vortices located downstream and quasi-streamwise vortices with spanwise offset, consistent with hairpin-like structures. The negative deformations (dents) are preferentially associated with pressure maxima at the transition between an upstream sweep to a downstream ejection. Sponsored by ONR.

Wall shear measurement in sand-water mixture flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yucel, O.; Grad, W.H.

1975-07-01

The wall shear stress was measured in clear-water and sand-water mixture flows with the use of a flush-mounting hot-film shear-sensor. Data were obtained with 2 shear-sensors and 2 different sands (d50 = 0.45 mm and d50 = 0.88 mm) with solids concentrations of up to Cmax = 1.6% by vol, and for flow Reynolds number of 10/sup 5/ < RD < 6 x 10/sup 5/. The measured sensor wall shear stresses were compared with the true wall shear stresses obtained with the energy head loss measurements conducted in a pipeline system. The results of the tests in the clear-water flowsmore » confirmed the relationship between the sensor power output, Ps, and the wall shear stress, tauo, given by tauo1/3 = APs + B, in which A and B are calibration coefficients. The tests with the low-concentration sand-water mixtures in a vertical pipe indicated that for the present range of experiments, sensor power outputs with the mixtures exceeded those for clear-water by an average of 5%. It is shown that the shear sensors are delicate but accurate instruments that can be used for the measurement of the wall shear stress. (13 refs.)« less

On investigating wall shear stress in two-dimensional plane turbulent wall jets

NASA Astrophysics Data System (ADS)

Mehdi, Faraz; Johansson, Gunnar; White, Christopher; Naughton, Jonathan

2012-11-01

Mehdi & White [Exp Fluids 50:43-51(2011)] presented a full momentum integral based method for determining wall shear stress in zero pressure gradient turbulent boundary layers. They utilized the boundary conditions at the wall and at the outer edge of the boundary layer. A more generalized expression is presented here that uses just one boundary condition at the wall. The method is mathematically exact and has an advantage of having no explicit streamwise gradient terms. It is successfully applied to two different experimental plane turbulent wall jet datasets for which independent estimates of wall shear stress were known. Complications owing to experimental inaccuracies in determining wall shear stress from the proposed method are also discussed.

Measurement of Wall Shear Stress in High Speed Air Flow Using Shear-Sensitive Liquid Crystal Coating.

PubMed

Zhao, Jisong

2018-05-17

Wall shear stress is an important quantity in fluid mechanics, but its measurement is a challenging task. An approach to measure wall shear stress vector distribution using shear-sensitive liquid crystal coating (SSLCC) is described. The wall shear stress distribution on the test surface beneath high speed jet flow is measured while using the proposed technique. The flow structures inside the jet flow are captured and the results agree well with the streakline pattern that was visualized using the oil-flow technique. In addition, the shock diamonds inside the supersonic jet flow are visualized clearly using SSLCC and the results are compared with the velocity contour that was measured using the particle image velocimetry (PIV) technique. The work of this paper demonstrates the application of SSLCC in the measurement/visualization of wall shear stress in high speed flow.

Measurement of Wall Shear Stress in High Speed Air Flow Using Shear-Sensitive Liquid Crystal Coating

PubMed Central

Zhao, Jisong

2018-01-01

Wall shear stress is an important quantity in fluid mechanics, but its measurement is a challenging task. An approach to measure wall shear stress vector distribution using shear-sensitive liquid crystal coating (SSLCC) is described. The wall shear stress distribution on the test surface beneath high speed jet flow is measured while using the proposed technique. The flow structures inside the jet flow are captured and the results agree well with the streakline pattern that was visualized using the oil-flow technique. In addition, the shock diamonds inside the supersonic jet flow are visualized clearly using SSLCC and the results are compared with the velocity contour that was measured using the particle image velocimetry (PIV) technique. The work of this paper demonstrates the application of SSLCC in the measurement/visualization of wall shear stress in high speed flow. PMID:29772822

Effect of exercise on hemodynamic conditions in the abdominal aorta.

PubMed

Taylor, C A; Hughes, T J; Zarins, C K

1999-06-01

The beneficial effect of exercise in the retardation of the progression of cardiovascular disease is hypothesized to be caused, at least in part, by the elimination of adverse hemodynamic conditions, including flow recirculation and low wall shear stress. In vitro and in vivo investigations have provided qualitative and limited quantitative information on flow patterns in the abdominal aorta and on the effect of exercise on the elimination of adverse hemodynamic conditions. We used computational fluid mechanics methods to examine the effects of simulated exercise on hemodynamic conditions in an idealized model of the human abdominal aorta. A three-dimensional computer model of a healthy human abdominal aorta was created to simulate pulsatile aortic blood flow under conditions of rest and graded exercise. Flow velocity patterns and wall shear stress were computed in the lesion-prone infrarenal aorta, and the effects of exercise were determined. A recirculation zone was observed to form along the posterior wall of the aorta immediately distal to the renal vessels under resting conditions. Low time-averaged wall shear stress was present in this location, along the posterior wall opposite the superior mesenteric artery and along the anterior wall between the superior and inferior mesenteric arteries. Shear stress temporal oscillations, as measured with an oscillatory shear index, were elevated in these regions. Under simulated light exercise conditions, a region of low wall shear stress and high oscillatory shear index remained along the posterior wall immediately distal to the renal arteries. Under simulated moderate exercise conditions, all the regions of low wall shear stress and high oscillatory shear index were eliminated. This numeric investigation provided detailed quantitative data on the effect of exercise on hemodynamic conditions in the abdominal aorta. Our results indicated that moderate levels of lower limb exercise are necessary to eliminate the flow reversal and regions of low wall shear stress in the abdominal aorta that exist under resting conditions. The lack of flow reversal and increased wall shear stress during exercise suggest a mechanism by which exercise may promote arterial health, namely with the elimination of adverse hemodynamic conditions.

Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms

PubMed Central

Avrahami, Idit; Kersh, Dikla

2016-01-01

Arterial wall shear stress (WSS) parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity—known as the pulsatility index (PI)—which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV). The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%]), oscillating shear index (OSI) and the ratio of minimum to maximum shear stress rates (min/max), are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS. PMID:27893801

Wall shear stress in intracranial aneurysms and adjacent arteries☆

PubMed Central

Wang, Fuyu; Xu, Bainan; Sun, Zhenghui; Wu, Chen; Zhang, Xiaojun

2013-01-01

Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations between hemodynamic parameters and the formation and growth of intracranial aneurysms, the present study constructed a computational model of a case with an internal carotid artery aneurysm and an anterior communicating artery aneurysm, based on the CT angiography findings of a patient. To simulate the formation of the anterior communicating artery aneurysm and the growth of the internal carotid artery aneurysm, we then constructed a model that virtually removed the anterior communicating artery aneurysm, and a further two models that also progressively decreased the size of the internal carotid artery aneurysm. Computational simulations of the fluid dynamics of the four models were performed under pulsatile flow conditions, and wall shear stress was compared among the different models. In the three aneurysm growth models, increasing size of the aneurysm was associated with an increased area of low wall shear stress, a significant decrease in wall shear stress at the dome of the aneurysm, and a significant change in the wall shear stress of the parent artery. The wall shear stress of the anterior communicating artery remained low, and was significantly lower than the wall shear stress at the bifurcation of the internal carotid artery or the bifurcation of the middle cerebral artery. After formation of the anterior communicating artery aneurysm, the wall shear stress at the dome of the internal carotid artery aneurysm increased significantly, and the wall shear stress in the upstream arteries also changed significantly. These findings indicate that low wall shear stress may be associated with the initiation and growth of aneurysms, and that aneurysm formation and growth may influence hemodynamic parameters in the local and adjacent arteries. PMID:25206394

Low-drag events in transitional wall-bounded turbulence

NASA Astrophysics Data System (ADS)

Whalley, Richard D.; Park, Jae Sung; Kushwaha, Anubhav; Dennis, David J. C.; Graham, Michael D.; Poole, Robert J.

2017-03-01

Intermittency of low-drag pointwise wall shear stress measurements within Newtonian turbulent channel flow at transitional Reynolds numbers (friction Reynolds numbers 70 - 130) is characterized using experiments and simulations. Conditional mean velocity profiles during low-drag events closely approach that of a recently discovered nonlinear traveling wave solution; both profiles are near the so-called maximum drag reduction profile, a general feature of turbulent flow of liquids containing polymer additives (despite the fact that all results presented are for Newtonian fluids only). Similarities between temporal intermittency in small domains and spatiotemporal intermittency in large domains is thereby found.

Determination of wall shear stress from mean velocity and Reynolds shear stress profiles

NASA Astrophysics Data System (ADS)

Volino, Ralph J.; Schultz, Michael P.

2018-03-01

An analytical method is presented for determining the Reynolds shear stress profile in steady, two-dimensional wall-bounded flows using the mean streamwise velocity. The method is then utilized with experimental data to determine the local wall shear stress. The procedure is applicable to flows on smooth and rough surfaces with arbitrary pressure gradients. It is based on the streamwise component of the boundary layer momentum equation, which is transformed into inner coordinates. The method requires velocity profiles from at least two streamwise locations, but the formulation of the momentum equation reduces the dependence on streamwise gradients. The method is verified through application to laminar flow solutions and turbulent DNS results from both zero and nonzero pressure gradient boundary layers. With strong favorable pressure gradients, the method is shown to be accurate for finding the wall shear stress in cases where the Clauser fit technique loses accuracy. The method is then applied to experimental data from the literature from zero pressure gradient studies on smooth and rough walls, and favorable and adverse pressure gradient cases on smooth walls. Data from very near the wall are not required for determination of the wall shear stress. Wall friction velocities obtained using the present method agree with those determined in the original studies, typically to within 2%.

Fluid Mechanics Optimising Organic Synthesis

NASA Astrophysics Data System (ADS)

Leivadarou, Evgenia; Dalziel, Stuart

2015-11-01

The Vortex Fluidic Device (VFD) is a new ``green'' approach in the synthesis of organic chemicals with many industrial applications in biodiesel generation, cosmetics, protein folding and pharmaceutical production. The VFD is a rapidly rotating tube that can operate with a jet feeding drops of liquid reactants to the base of the tube. The aim of this project is to explain the fluid mechanics of the VFD that influence the rate of reactions. The reaction rate is intimately related to the intense shearing that promotes collision between reactant molecules. In the VFD, the highest shears are found at the bottom of the tube in the Rayleigh and the Ekman layer and at the walls in the Stewardson layers. As a step towards optimising the performance of the VFD we present experiments conducted in order to establish the minimum drop volume and maximum rotation rate for maximum axisymmetric spreading without fingering instability. PhD candidate, Department of Applied Mathematics and Theoretical Physics.

Research Status on Bonding Behavior of Prefabricated Concrete Shear Wall

NASA Astrophysics Data System (ADS)

Wang, Donghui; Liu, Xudong; Wang, Sheng; Li, Shanshan

2018-03-01

Prefabricated shear wall structure adapts to the development and requirements of China’s residential industrialization. The key to the prefabricated concrete shear wall structure is the connection between the prefabricated members, where the reliability of the connection of the concrete joint is related to the overall performance and seismic effect of the structure. In this paper, the microstructures of the joint surface and shear properties are analysed, and the formula for calculating the shear strength of the joint is obtained.

Impact of wall shear stress on initial bacterial adhesion in rotating annular reactor

PubMed Central

Saur, Thibaut; Morin, Emilie; Habouzit, Frédéric; Bernet, Nicolas

2017-01-01

The objective of this study was to investigate the bacterial adhesion under different wall shear stresses in turbulent flow and using a diverse bacterial consortium. A better understanding of the mechanisms governing microbial adhesion can be useful in diverse domains such as industrial processes, medical fields or environmental biotechnologies. The impact of wall shear stress—four values ranging from 0.09 to 7.3 Pa on polypropylene (PP) and polyvinyl chloride (PVC)—was carried out in rotating annular reactors to evaluate the adhesion in terms of morphological and microbiological structures. A diverse inoculum consisting of activated sludge was used. Epifluorescence microscopy was used to quantitatively and qualitatively characterize the adhesion. Attached bacterial communities were assessed by molecular fingerprinting profiles (CE-SSCP). It has been demonstrated that wall shear stress had a strong impact on both quantitative and qualitative aspects of the bacterial adhesion. ANOVA tests also demonstrated the significant impact of wall shear stress on all three tested morphological parameters (surface coverage, number of objects and size of objects) (p-values < 2.10−16). High wall shear stresses increased the quantity of attached bacteria but also altered their spatial distribution on the substratum surface. As the shear increased, aggregates or clusters appeared and their size grew when increasing the shears. Concerning the microbiological composition, the adhered bacterial communities changed gradually with the applied shear. PMID:28207869

Triglyceride glucose index and common carotid wall shear stress.

PubMed

Tripolino, Cesare; Irace, Concetta; Scavelli, Faustina B; de Franceschi, Maria S; Esposito, Teresa; Carallo, Claudio; Gnasso, Agostino

2014-02-01

Alterations in wall shear stress contribute to both clinical and subclinical atherosclerosis. Several conditions such as hypertension, diabetes, and obesity can impair shear stress, but the role of insulin resistance has never been investigated. The present study was designed to investigate whether insulin resistance assessed by TyG Index associates with wall shear stress in the common carotid artery. One hundred six individuals were enrolled. Blood pressure, lipids, glucose, and cigarette smoking were evaluated. TyG Index was calculated as log[fasting triglycerides × fasting glucose / 2]. Subjects underwent blood viscosity measurement and echo-Doppler evaluation of carotid arteries to calculate wall shear stress. The association between TyG Index and carotid wall shear stress was assessed by simple and multiple regression analyses. TyG Index was significantly and inversely associated with carotid wall shear stress both in simple (r = -0.44, P < 0.001) and multiple regression analyses accounting for age, sex, and major cardiovascular risk factors. The association was further confirmed after exclusion of subjects with diabetes, dyslipidemia, fasting blood glucose greater than 100 mg/dL, and triglycerides greater than 150 mg/dL. The present findings suggest that increasing insulin resistance, as assessed by TyG Index, associates with atherosclerosis-prone shear stress reduction in the common carotid artery.

In vivo wall shear measurements within the developing zebrafish heart.

PubMed

Jamison, R Aidan; Samarage, Chaminda R; Bryson-Richardson, Robert J; Fouras, Andreas

2013-01-01

Physical forces can influence the embryonic development of many tissues. Within the cardiovascular system shear forces resulting from blood flow are known to be one of the regulatory signals that shape the developing heart. A key challenge in investigating the role of shear forces in cardiac development is the ability to obtain shear force measurements in vivo. Utilising the zebrafish model system we have developed a methodology that allows the shear force within the developing embryonic heart to be determined. Accurate wall shear measurement requires two essential pieces of information; high-resolution velocity measurements near the heart wall and the location and orientation of the heart wall itself. We have applied high-speed brightfield imaging to capture time-lapse series of blood flow within the beating heart between 3 and 6 days post-fertilization. Cardiac-phase filtering is applied to these time-lapse images to remove the heart wall and other slow moving structures leaving only the red blood cell movement. Using particle image velocimetry to calculate the velocity of red blood cells in different regions within the heart, and using the signal-to-noise ratio of the cardiac-phase filtered images to determine the boundary of blood flow, and therefore the position of the heart wall, we have been able to generate the necessary information to measure wall shear in vivo. We describe the methodology required to measure shear in vivo and the application of this technique to the developing zebrafish heart. We identify a reduction in shear at the ventricular-bulbar valve between 3 and 6 days post-fertilization and demonstrate that the shear environment of the ventricle during systole is constantly developing towards a more uniform level.

Large scale structures in a turbulent boundary layer and their imprint on wall shear stress

NASA Astrophysics Data System (ADS)

Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

2015-11-01

Experiments were performed on a turbulent boundary layer developing on a flat plate model under zero pressure gradient flow. A MEMS differential capacitive shear stress sensor with a 1 mm × 1 mm floating element was used to capture the fluctuating wall shear stress simultaneously with streamwise velocity measurements from a hot-wire anemometer traversed in the wall normal direction. Near the wall, the peak in the cross correlation corresponds to an organized motion inclined 45° from the wall. In the outer region, the peak diminishes in value, but is still significant at a distance greater than half the boundary layer thickness, and corresponds to a structure inclined 14° from the wall. High coherence between the two signals was found for the low-frequency content, reinforcing the belief that large scale structures have a vital impact on wall shear stress. Thus, estimation of the wall shear stress from the low-frequency velocity signal will be performed, and is expected to be statistically significant in the outer boundary layer. Additionally, conditionally averaged mean velocity profiles will be presented to assess the effects of high and low shear stress. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

Study on Shear Performance of Cold-formed Steel Composite Wall with New Type of stud

NASA Astrophysics Data System (ADS)

Wang, Chungang; Yue, Sizhe; Liu, Hong; Zhang, Zhuangnan

2018-03-01

The shear resistance of single oriented-strand board wall and single gypsum board wall can be improved in different degrees by increasing strength of steel. The experimental data of literatures were used, and the test specimens had been simulated and validated by ABAQUS finite element analysis. According to the research, it showed that the compressive bearing capacity of the new stud composite wall was much better than the common stud composite wall, so the establishment and research of all models had been based on the new section stud. The analysis results show that when using new type of stud the shear resistance of the single oriented-strand board wall can be improved efficiently by increasing strength of steel, but the shear resistance of the single gypsum wall can be increased little.

Calculation Method of Lateral Strengths and Ductility Factors of Constructions with Shear Walls of Different Ductility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamaguchi, Nobuyoshi; Nakao, Masato; Murakami, Masahide

2008-07-08

For seismic design, ductility-related force modification factors are named R factor in Uniform Building Code of U.S, q factor in Euro Code 8 and Ds (inverse of R) factor in Japanese Building Code. These ductility-related force modification factors for each type of shear elements are appeared in those codes. Some constructions use various types of shear walls that have different ductility, especially for their retrofit or re-strengthening. In these cases, engineers puzzle the decision of force modification factors of the constructions. Solving this problem, new method to calculate lateral strengths of stories for simple shear wall systems is proposed andmore » named 'Stiffness--Potential Energy Addition Method' in this paper. This method uses two design lateral strengths for each type of shear walls in damage limit state and safety limit state. Two lateral strengths of stories in both limit states are calculated from these two design lateral strengths for each type of shear walls in both limit states. Calculated strengths have the same quality as values obtained by strength addition method using many steps of load-deformation data of shear walls. The new method to calculate ductility factors is also proposed in this paper. This method is based on the new method to calculate lateral strengths of stories. This method can solve the problem to obtain ductility factors of stories with shear walls of different ductility.« less

Unified description of the slip phenomena in sheared polymer films: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Priezjev, Nikolai

2010-03-01

The dynamic behavior of the slip length in shear flow of polymer melts past atomically smooth surfaces is investigated using MD simulations. The polymer melt was modeled as a collection of FENE-LJ bead-spring chains. We consider shear flow conditions at low pressures and weak wall-fluid interaction energy so that fluid velocity profiles are linear throughout the channel at all shear rates examined. In agreement with earlier studies we confirm that for shear- thinning fluids the slip length passes through a local minimum at low shear rates and then increases rapidly at higher shear rates. We found that the rate dependence of the slip length depends on the lattice orientation at high shear rates. The MD results show that the ratio of slip length to viscosity follows a master curve when plotted as a function of a single variable that depends on the structure factor, contact density and temperature of the first fluid layer near the solid wall. The universal dependence of the slip length holds for a number of parameters of the interface: fluid density and structure (chain length), wall-fluid interaction energy, wall density, lattice orientation, thermal or solid walls.

Structure of high and low shear-stress events in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Gomit, G.; de Kat, R.; Ganapathisubramani, B.

2018-01-01

Simultaneous particle image velocimetry (PIV) and wall-shear-stress sensor measurements were performed to study structures associated with shear-stress events in a flat plate turbulent boundary layer at a Reynolds number Reτ≈4000 . The PIV field of view covers 8 δ (where δ is the boundary layer thickness) along the streamwise direction and captures the entire boundary layer in the wall-normal direction. Simultaneously, wall-shear-stress measurements that capture the large-scale fluctuations were taken using a spanwise array of hot-film skin-friction sensors (spanning 2 δ ). Based on this combination of measurements, the organization of the conditional wall-normal and streamwise velocity fluctuations (u and v ) and of the Reynolds shear stress (-u v ) can be extracted. Conditional averages of the velocity field are computed by dividing the histogram of the large-scale wall-shear-stress fluctuations into four quartiles, each containing 25% of the occurrences. The conditional events corresponding to the extreme quartiles of the histogram (positive and negative) predominantly contribute to a change of velocity profile associated with the large structures and in the modulation of the small scales. A detailed examination of the Reynolds shear-stress contribution related to each of the four quartiles shows that the flow above a low wall-shear-stress event carries a larger amount of Reynolds shear stress than the other quartiles. The contribution of the small and large scales to this observation is discussed based on a scale decomposition of the velocity field.

Wall shear stress estimates in coronary artery constrictions

NASA Technical Reports Server (NTRS)

Back, L. H.; Crawford, D. W.

1992-01-01

Wall shear stress estimates from laminar boundary layer theory were found to agree fairly well with the magnitude of shear stress levels along coronary artery constrictions obtained from solutions of the Navier Stokes equations for both steady and pulsatile flow. The relatively simple method can be used for in vivo estimates of wall shear stress in constrictions by using a vessel shape function determined from a coronary angiogram, along with a knowledge of the flow rate.

Manufacture of high aspect ratio micro-pillar wall shear stress sensor arrays

NASA Astrophysics Data System (ADS)

Gnanamanickam, Ebenezer P.; Sullivan, John P.

2012-12-01

In the field of experimental fluid mechanics the measurement of unsteady, distributed wall shear stress has proved historically challenging. Recently, sensors based on an array of flexible micro-pillars have shown promise in carrying out such measurements. Similar sensors find use in other applications such as cellular mechanics. This work presents a manufacturing technique that can manufacture micro-pillar arrays of high aspect ratio. An electric discharge machine (EDM) is used to manufacture a micro-drilling tool. This micro-drilling tool is used to form holes in a wax sheet which acts as the mold for the micro-pillar array. Silicone rubber is cast in these molds to yield a micro-pillar array. Using this technique, micro-pillar arrays with a maximum aspect ratio of about 10 have been manufactured. Manufacturing issues encountered, steps to alleviate them and the potential of the process to manufacture similar micro-pillar arrays in a time-efficient manner are also discussed.

Aerodynamic study of time-trial helmets in cycling racing using CFD analysis.

PubMed

Beaumont, F; Taiar, R; Polidori, G; Trenchard, H; Grappe, F

2018-01-23

The aerodynamic drag of three different time-trial cycling helmets was analyzed numerically for two different cyclist head positions. Computational Fluid Dynamics (CFD) methods were used to investigate the detailed airflow patterns around the cyclist for a constant velocity of 15 m/s without wind. The CFD simulations have focused on the aerodynamic drag effects in terms of wall shear stress maps and pressure coefficient distributions on the cyclist/helmet system. For a given head position, the helmet shape, by itself, obtained a weak effect on a cyclist's aerodynamic performance (<1.5%). However, by varying head position, a cyclist significantly influences aerodynamic performance; the maximum difference between both positions being about 6.4%. CFD results have also shown that both helmet shape and head position significantly influence drag forces, pressure and wall shear stress distributions on the whole cyclist's body due to the change in the near-wake behavior and in location of corresponding separation and attachment areas around the cyclist. Copyright © 2017 Elsevier Ltd. All rights reserved.

A time dependent difference theory for sound propagation in ducts with flow. [characteristic of inlet and exhaust ducts of turbofan engines

NASA Technical Reports Server (NTRS)

Baumeister, K. J.

1979-01-01

A time dependent numerical solution of the linearized continuity and momentum equation was developed for sound propagation in a two dimensional straight hard or soft wall duct with a sheared mean flow. The time dependent governing acoustic difference equations and boundary conditions were developed along with a numerical determination of the maximum stable time increments. A harmonic noise source radiating into a quiescent duct was analyzed. This explicit iteration method then calculated stepwise in real time to obtain the transient as well as the steady state solution of the acoustic field. Example calculations were presented for sound propagation in hard and soft wall ducts, with no flow and plug flow. Although the problem with sheared flow was formulated and programmed, sample calculations were not examined. The time dependent finite difference analysis was found to be superior to the steady state finite difference and finite element techniques because of shorter solution times and the elimination of large matrix storage requirements.

Diagnostic Techniques to Elucidate the Aerodynamic Performance of Acoustic Liners

NASA Technical Reports Server (NTRS)

June, Jason; Bertolucci, Brandon; Ukeiley, Lawrence; Cattafesta, Louis N., III; Sheplak, Mark

2017-01-01

In support of Topic A.2.8 of NASA NRA NNH10ZEA001N, the University of Florida (UF) has investigated the use of flow field optical diagnostic and micromachined sensor-based techniques for assessing the wall shear stress on an acoustic liner. Stereoscopic particle image velocimetry (sPIV) was used to study the velocity field over a liner in the Grazing Flow Impedance Duct (GFID). The results indicate that the use of a control volume based method to determine the wall shear stress is prone to significant error. The skin friction over the liner as measured using velocity curve fitting techniques was shown to be locally reduced behind an orifice, relative to the hard wall case in a streamwise plane centered on the orifice. The capacitive wall shear stress sensor exhibited a linear response for a range of shear stresses over a hard wall. PIV over the liner is consistent with lifting of the near wall turbulent structure as it passes over an orifice, followed by a region of low wall shear stress.

Spatio-temporal characteristics of large scale motions in a turbulent boundary layer from direct wall shear stress measurement

NASA Astrophysics Data System (ADS)

Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

2016-11-01

Particle image velocimetry (PIV) and fluctuating wall shear stress experiments were performed on a flat plate turbulent boundary layer (TBL) under zero pressure gradient conditions. The fluctuating wall shear stress was measured using a microelectromechanical 1mm × 1mm floating element capacitive shear stress sensor (CSSS) developed at the University of Florida. The experiments elucidated the imprint of the organized motions in a TBL on the wall shear stress through its direct measurement. Spatial autocorrelation of the streamwise velocity from the PIV snapshots revealed large scale motions that scale on the order of boundary layer thickness. However, the captured inclination angle was lower than that determined using the classic method by means of wall shear stress and hot-wire anemometry (HWA) temporal cross-correlations and a frozen field hypothesis using a convection velocity. The current study suggests the large size of these motions begins to degrade the applicability of the frozen field hypothesis for the time resolved HWA experiments. The simultaneous PIV and CSSS measurements are also used for spatial reconstruction of the velocity field during conditionally sampled intense wall shear stress events. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

Shake-table testing of a self-centering precast reinforced concrete frame with shear walls

NASA Astrophysics Data System (ADS)

Lu, Xilin; Yang, Boya; Zhao, Bin

2018-04-01

The seismic performance of a self-centering precast reinforced concrete (RC) frame with shear walls was investigated in this paper. The lateral force resistance was provided by self-centering precast RC shear walls (SPCW), which utilize a combination of unbonded prestressed post-tensioned (PT) tendons and mild steel reinforcing bars for flexural resistance across base joints. The structures concentrated deformations at the bottom joints and the unbonded PT tendons provided the self-centering restoring force. A 1/3-scale model of a five-story self-centering RC frame with shear walls was designed and tested on a shake-table under a series of bi-directional earthquake excitations with increasing intensity. The acceleration response, roof displacement, inter-story drifts, residual drifts, shear force ratios, hysteresis curves, and local behaviour of the test specimen were analysed and evaluated. The results demonstrated that seismic performance of the test specimen was satisfactory in the plane of the shear wall; however, the structure sustained inter-story drift levels up to 2.45%. Negligible residual drifts were recorded after all applied earthquake excitations. Based on the shake-table test results, it is feasible to apply and popularize a self-centering precast RC frame with shear walls as a structural system in seismic regions.

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

NASA Astrophysics Data System (ADS)

Dong, Hongying; Cao, Wanlin; Wu, Haipeng; Zhang, Jianwei; Xu, Fangfang

2013-12-01

A composite shear wall concept based on concrete filled steel tube (CFST) columns and steel plate (SP) deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements: CFST columns; SP deep beams; and reinforced concrete (RC) strips. The RC strips are intended to allow the core structural elements — the CFST columns and SP deep beams — to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

Computational Fluid Dynamic simulations of pipe elbow flow.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Homicz, Gregory Francis

2004-08-01

One problem facing today's nuclear power industry is flow-accelerated corrosion and erosion in pipe elbows. The Korean Atomic Energy Research Institute (KAERI) is performing experiments in their Flow-Accelerated Corrosion (FAC) test loop to better characterize these phenomena, and develop advanced sensor technologies for the condition monitoring of critical elbows on a continuous basis. In parallel with these experiments, Sandia National Laboratories is performing Computational Fluid Dynamic (CFD) simulations of the flow in one elbow of the FAC test loop. The simulations are being performed using the FLUENT commercial software developed and marketed by Fluent, Inc. The model geometry and meshmore » were created using the GAMBIT software, also from Fluent, Inc. This report documents the results of the simulations that have been made to date; baseline results employing the RNG k-e turbulence model are presented. The predicted value for the diametrical pressure coefficient is in reasonably good agreement with published correlations. Plots of the velocities, pressure field, wall shear stress, and turbulent kinetic energy adjacent to the wall are shown within the elbow section. Somewhat to our surprise, these indicate that the maximum values of both wall shear stress and turbulent kinetic energy occur near the elbow entrance, on the inner radius of the bend. Additional simulations were performed for the same conditions, but with the RNG k-e model replaced by either the standard k-{var_epsilon}, or the realizable k-{var_epsilon} turbulence model. The predictions using the standard k-{var_epsilon} model are quite similar to those obtained in the baseline simulation. However, with the realizable k-{var_epsilon} model, more significant differences are evident. The maximums in both wall shear stress and turbulent kinetic energy now appear on the outer radius, near the elbow exit, and are {approx}11% and 14% greater, respectively, than those predicted in the baseline calculation; secondary maxima in both quantities still occur near the elbow entrance on the inner radius. Which set of results better reflects reality must await experimental corroboration. Additional calculations demonstrate that whether or not FLUENT's radial equilibrium pressure distribution option is used in the PRESSURE OUTLET boundary condition has no significant impact on the flowfield near the elbow. Simulations performed with and without the chemical sensor and associated support bracket that were present in the experiments demonstrate that the latter have a negligible influence on the flow in the vicinity of the elbow. The fact that the maxima in wall shear stress and turbulent kinetic energy occur on the inner radius is therefore not an artifact of having introduced the sensor into the flow.« less

Thinner regions of intracranial aneurysm wall correlate with regions of higher wall shear stress: a 7.0 tesla MRI

PubMed Central

Blankena, Roos; Kleinloog, Rachel; Verweij, Bon H.; van Ooij, Pim; ten Haken, Bennie; Luijten, Peter R.; Rinkel, Gabriel J.E.; Zwanenburg, Jaco J.M.

2016-01-01

Purpose To develop a method for semi-quantitative wall thickness assessment on in vivo 7.0 tesla (7T) MRI images of intracranial aneurysms for studying the relation between apparent aneurysm wall thickness and wall shear stress. Materials and Methods Wall thickness was analyzed in 11 unruptured aneurysms in 9 patients, who underwent 7T MRI with a TSE based vessel wall sequence (0.8 mm isotropic resolution). A custom analysis program determined the in vivo aneurysm wall intensities, which were normalized to signal of nearby brain tissue and were used as measure for apparent wall thickness (AWT). Spatial wall thickness variation was determined as the interquartile range in AWT (the middle 50% of the AWT range). Wall shear stress was determined using phase contrast MRI (0.5 mm isotropic resolution). We performed visual and statistical comparisons (Pearson’s correlation) to study the relation between wall thickness and wall shear stress. Results 3D colored AWT maps of the aneurysms showed spatial AWT variation, which ranged from 0.07 to 0.53, with a mean variation of 0.22 (a variation of 1.0 roughly means a wall thickness variation of one voxel (0.8mm)). In all aneurysms, AWT was inversely related to WSS (mean correlation coefficient −0.35, P<0.05). Conclusions A method was developed to measure the wall thickness semi-quantitatively, using 7T MRI. An inverse correlation between wall shear stress and AWT was determined. In future studies, this non-invasive method can be used to assess spatial wall thickness variation in relation to pathophysiologic processes such as aneurysm growth and –rupture. PMID:26892986

Impact of Age and Aerobic Exercise Training on Conduit Artery Wall Thickness: Role of the Shear Pattern.

PubMed

Tanahashi, Koichiro; Kosaki, Keisei; Sawano, Yuriko; Yoshikawa, Toru; Tagawa, Kaname; Kumagai, Hiroshi; Akazawa, Nobuhiko; Maeda, Seiji

2017-01-01

Hemodynamic shear stress is the frictional force of blood on the arterial wall. The shear pattern in the conduit artery affects the endothelium and may participate in the development and progression of atherosclerosis. We investigated the role of the shear pattern in age- and aerobic exercise-induced changes in conduit artery wall thickness via cross-sectional and interventional studies. In a cross-sectional study, we found that brachial shear rate patterns and brachial artery intima-media thickness (IMT) correlated with age. Additionally, brachial artery shear rate patterns were associated with brachial artery IMT in 102 middle-aged and older individuals. In an interventional study, 39 middle-aged and older subjects were divided into 2 groups: control and exercise. The exercise group completed 12 weeks of aerobic exercise training. Aerobic exercise training significantly increased the antegrade shear rate and decreased the retrograde shear rate and brachial artery IMT. Moreover, changes in the brachial artery antegrade shear rate and the retrograde shear rate correlated with the change in brachial artery IMT. The results of the present study indicate that changes in brachial artery shear rate patterns may contribute to age- and aerobic exercise training-induced changes in brachial artery wall thickness. © 2017 S. Karger AG, Basel.

Experimental Verification of Same Simple Equilibrium Models of Masonry Shear Walls

NASA Astrophysics Data System (ADS)

Radosław, Jasiński

2017-10-01

This paper contains theoretical fundamentals of strut and tie models, used in unreinforced horizontal shear walls. Depending on support conditions and wall loading, we can distinguish models with discrete bars when point load is applied to the wall (type I model) or with continuous bars (type II model) when load is uniformly distributed at the wall boundary. The main part of this paper compares calculated results with the own tests on horizontal shear walls made of solid brick, silicate elements and autoclaved aerated concrete. The tests were performed in Poland. The model required some modifications due to specific load and static diagram.

An Automatic Braking System That Stabilizes Leukocyte Rolling by an Increase in Selectin Bond Number with Shear

PubMed Central

Chen, Shuqi; Springer, Timothy A.

1999-01-01

Wall shear stress in postcapillary venules varies widely within and between tissues and in response to inflammation and exercise. However, the speed at which leukocytes roll in vivo has been shown to be almost constant within a wide range of wall shear stress, i.e., force on the cell. Similarly, rolling velocities on purified selectins and their ligands in vitro tend to plateau. This may be important to enable rolling leukocytes to be exposed uniformly to activating stimuli on endothelium, independent of local hemodynamic conditions. Wall shear stress increases the rate of dissociation of individual selectin–ligand tether bonds exponentially (1, 4) thereby destabilizing rolling. We find that this is compensated by a shear-dependent increase in the number of bonds per rolling step. We also find an increase in the number of microvillous tethers to the substrate. This explains (a) the lack of firm adhesion through selectins at low shear stress or high ligand density, and (b) the stability of rolling on selectins to wide variation in wall shear stress and ligand density, in contrast to rolling on antibodies (14). Furthermore, our data successfully predict the threshold wall shear stress below which rolling does not occur. This is a special case of the more general regulation by shear of the number of bonds, in which the number of bonds falls below one. PMID:9885254

An automatic braking system that stabilizes leukocyte rolling by an increase in selectin bond number with shear.

PubMed

Chen, S; Springer, T A

1999-01-11

Wall shear stress in postcapillary venules varies widely within and between tissues and in response to inflammation and exercise. However, the speed at which leukocytes roll in vivo has been shown to be almost constant within a wide range of wall shear stress, i.e., force on the cell. Similarly, rolling velocities on purified selectins and their ligands in vitro tend to plateau. This may be important to enable rolling leukocytes to be exposed uniformly to activating stimuli on endothelium, independent of local hemodynamic conditions. Wall shear stress increases the rate of dissociation of individual selectin-ligand tether bonds exponentially (, ) thereby destabilizing rolling. We find that this is compensated by a shear-dependent increase in the number of bonds per rolling step. We also find an increase in the number of microvillous tethers to the substrate. This explains (a) the lack of firm adhesion through selectins at low shear stress or high ligand density, and (b) the stability of rolling on selectins to wide variation in wall shear stress and ligand density, in contrast to rolling on antibodies (). Furthermore, our data successfully predict the threshold wall shear stress below which rolling does not occur. This is a special case of the more general regulation by shear of the number of bonds, in which the number of bonds falls below one.

Velocity and pressure fields associated with near-wall turbulence structures

NASA Technical Reports Server (NTRS)

Johansson, Arne V.; Alfredsson, P. Henrik; Kim, John

1990-01-01

Computer generated databases containing velocity and pressure fields in three-dimensional space at a sequence of time-steps, were used for the investigation of near-wall turbulence structures, their space-time evolution, and their associated pressure fields. The main body of the results were obtained from simulation data for turbulent channel flow at a Reynolds number of 180 (based on half-channel height and friction velocity) with a grid of 128 x 129 x and 128 points. The flow was followed over a total time of 141 viscous time units. Spanwise centering of the detected structures was found to be essential in order to obtain a correct magnitude of the associated Reynolds stress contribution. A positive wall-pressure peak is found immediately beneath the center of the structure. The maximum amplitude of the pressure pattern was, however, found in the buffer region at the center of the shear-layer. It was also found that these flow structures often reach a maximum strength in connection with an asymmetric spanwise motion, which motivated the construction of a conditional sampling scheme that preserved this asymmetry.

Modeling Force Transfer around Openings in Wood-Frame Shear Walls

Treesearch

Minghao Li; Frank Lam; Borjen Yeh; Tom Skaggs; Doug Rammer; James Wacker

2012-01-01

This paper presented a modeling study on force transfer around openings (FTAO) in wood-frame shear walls detailed for FTAO. To understand the load transfer in the walls, this study used a finite-element model WALL2D, which is able to model individual wall components, including framing members, sheathing panels, oriented panel-frame nailed connections, framing...

Quantification of wall shear stress in large blood vessels using Lagrangian interpolation functions with cine phase-contrast magnetic resonance imaging.

PubMed

Cheng, Christopher P; Parker, David; Taylor, Charles A

2002-09-01

Arterial wall shear stress is hypothesized to be an important factor in the localization of atherosclerosis. Current methods to compute wall shear stress from magnetic resonance imaging (MRI) data do not account for flow profiles characteristic of pulsatile flow in noncircular vessel lumens. We describe a method to quantify wall shear stress in large blood vessels by differentiating velocity interpolation functions defined using cine phase-contrast MRI data on a band of elements in the neighborhood of the vessel wall. Validation was performed with software phantoms and an in vitro flow phantom. At an image resolution corresponding to in vivo imaging data of the human abdominal aorta, time-averaged, spatially averaged wall shear stress for steady and pulsatile flow were determined to be within 16% and 23% of the analytic solution, respectively. These errors were reduced to 5% and 8% with doubling in image resolution. For the pulsatile software phantom, the oscillation in shear stress was predicted to within 5%. The mean absolute error of circumferentially resolved shear stress for the nonaxisymmetric phantom decreased from 28% to 15% with a doubling in image resolution. The irregularly shaped phantom and in vitro investigation demonstrated convergence of the calculated values with increased image resolution. We quantified the shear stress at the supraceliac and infrarenal regions of a human abdominal aorta to be 3.4 and 2.3 dyn/cm2, respectively.

Circulatory shear flow alters the viability and proliferation of circulating colon cancer cells

NASA Astrophysics Data System (ADS)

Fan, Rong; Emery, Travis; Zhang, Yongguo; Xia, Yuxuan; Sun, Jun; Wan, Jiandi

2016-06-01

During cancer metastasis, circulating tumor cells constantly experience hemodynamic shear stress in the circulation. Cellular responses to shear stress including cell viability and proliferation thus play critical roles in cancer metastasis. Here, we developed a microfluidic approach to establish a circulatory microenvironment and studied circulating human colon cancer HCT116 cells in response to a variety of magnitude of shear stress and circulating time. Our results showed that cell viability decreased with the increase of circulating time, but increased with the magnitude of wall shear stress. Proliferation of cells survived from circulation could be maintained when physiologically relevant wall shear stresses were applied. High wall shear stress (60.5 dyne/cm2), however, led to decreased cell proliferation at long circulating time (1 h). We further showed that the expression levels of β-catenin and c-myc, proliferation regulators, were significantly enhanced by increasing wall shear stress. The presented study provides a new insight to the roles of circulatory shear stress in cellular responses of circulating tumor cells in a physiologically relevant model, and thus will be of interest for the study of cancer cell mechanosensing and cancer metastasis.

Correlation between vortices and wall shear stress in a curved artery model under pulsatile flow conditions

NASA Astrophysics Data System (ADS)

Cox, Christopher; Plesniak, Michael W.

2017-11-01

One of the most physiologically relevant factors within the cardiovascular system is the wall shear stress. The wall shear stress affects endothelial cells via mechanotransduction and atherosclerotic regions are strongly correlated with curvature and branching in the human vasculature, where the shear stress is both oscillatory and multidirectional. Also, the combined effect of curvature and pulsatility in cardiovascular flows produces unsteady vortices. In this work, our goal is to assess the correlation between multiple vortex pairs and wall shear stress. To accomplish this, we use an in-house high-order flux reconstruction Navier-Stokes solver to simulate pulsatile flow of a Newtonian blood-analog fluid through a rigid 180° curved artery model. We use a physiologically relevant flow rate and generate results using both fully developed and uniform entrance conditions, the latter motivated by the fact that flow upstream to a curved artery may not be fully developed. Under these two inflow conditions, we characterize the evolution of various vortex pairs and their subsequent effect on several wall shear stress metrics. Supported by GW Center for Biomimetics and Bioinspired Engineering.

Shear zone junctions: Of zippers and freeways

NASA Astrophysics Data System (ADS)

Passchier, Cees W.; Platt, John P.

2017-02-01

Ductile shear zones are commonly treated as straight high-strain domains with uniform shear sense and characteristic curved foliation trails, bounded by non-deforming wall rock. Many shear zones, however, are branched, and if movement on such branches is contemporaneous, the resulting shape can be complicated and lead to unusual shear sense arrangement and foliation geometries in the wall rock. For Y-shaped shear zone triple junctions with three joining branches and transport direction at a high angle to the branchline, only eight basic types of junction are thought to be stable and to produce significant displacement. The simplest type, called freeway junctions, have similar shear sense in all three branches. The other types show joining or separating behaviour of shear zone branches similar to the action of a zipper. Such junctions may have shear zone branches that join to form a single branch (closing zipper junction), or a single shear zone that splits to form two branches, (opening zipper junction). All categories of shear zone junctions show characteristic foliation patterns and deflection of markers in the wall rock. Closing zipper junctions are unusual, since they form a non-active zone with opposite deflection of foliations in the wall rock known as an extraction fault or wake. Shear zipper junctions can form domains of overprinting shear sense along their flanks. A small and large field example are given from NE Spain and Eastern Anatolia. The geometry of more complex, 3D shear zone junctions with slip parallel and oblique to the branchline is briefly discussed.

Analysis of Slab-column Shearwall Structure of 6000 Tons Cold Storage

NASA Astrophysics Data System (ADS)

He, Dongqing; Song, Pengwei; Jie, Pengyu

2018-05-01

Combining with the functional requirements, the site conditions and the 6000 tons load characteristics of cold storage, so determine its structure system for the slab-column-shear wall structure. The paper recommends the design of foundation, the settings of column cap, the arrangement of shear wall, the punching shear of floor slab and the analysis and calculation results of main structure. By addition shear wall in slab-column structure to increase the overall stiffness of structure and improve the seismic performance of structure. Take the detached form between the main structure and the external wall insulation, while set anchorage beam between in the main floor and the ring beam along the axis of the column grid to enhance the overall stability of the external wall insulation.

Breaking symmetry in non-planar bifurcations: distribution of flow and wall shear stress.

PubMed

Lu, Yiling; Lu, Xiyun; Zhuang, Lixian; Wang, Wen

2002-01-01

Non-planarity in blood vessels is known to influence arterial flows and wall shear stress. To gain insight, computational fluid dynamics (CFD) has been used to investigate effects of curvature and out-of-plane geometry on the distribution of fluid flows and wall shear stresses in a hypothetical non-planar bifurcation. Three-dimensional Navier-Stokes equations for a steady state Newtonian fluid were solved numerically using a finite element method. Non-planarity in one of the two daughter vessels is found to deflect flow from the inner wall of the vessel to the outer wall and to cause changes in the distribution of wall shear stresses. Results from this study agree to experimental observations and CFD simulations in the literature, and support the view that non-planarity in blood vessels is a factor with important haemodynamic significance and may play a key role in vascular biology and pathophysiology.

Extremely high wall-shear stress events in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Pan, Chong; Kwon, Yongseok

2018-04-01

The present work studies the fluctuating characteristics of the streamwise wall-shear stress in a DNS of a turbulent boundary layer at Re τ =1500 from a structural view. The two-dimensional field of the fluctuating friction velocity u‧ τ (x,z) is decomposed into the large- and small-scale components via a recently proposed scale separation algorithm, Quasi-bivariate Variational Mode Decomposition (QB-VMD). Both components are found to be dominated by streak-like structures, which can be regarded as the wall signature of the inner-layer streaks and the outer-layer LSMs, respectively. Extreme positive/negative wall-shear stress fluctuation events are detected in the large-scale component. The former’s occurrence frequency is nearly one order of magnitude higher than the latter; therefore, they contribute a significant portion of the long tail of the wall-shear stress distribution. Both two-point correlations and conditional averages show that these extreme positive wall-shear stress events are embedded in the large-scale positive u‧ τ streaks. They seem to be formed by near-wall ‘splatting’ process, which are related to strong finger-like sweeping (Q4) events originated from the outer-layer positive LSMs.

Application of mean wall shear stress boundary condition to complex turbulent flows using a wall-modeled large eddy simulation

NASA Astrophysics Data System (ADS)

Cho, Minjeong; Lee, Jungil; Choi, Haecheon

2012-11-01

The mean wall shear stress boundary condition was successfully applied to turbulent channel and boundary flows using large eddy simulation without resolving near-wall region (see Lee, Cho & Choi in this book of abstracts). In the present study, we apply this boundary condition to more complex flows where flow separation and redeveloping flow exist. As a test problem, we consider flow over a backward-facing step at Reh = 22860 based on the step height. Turbulent boundary layer flow at the inlet (Reθ = 1050) is obtained using inflow generation technique by Lund et al. (1998) but with wall shear stress boundary condition. First, we prescribe the mean wall shear stress distribution obtained from DNS (Kim, 2011, Ph.D. Thesis, Stanford U.) as the boundary condition of present simulation. Here we give no-slip boundary condition at flow-reversal region. The present results are in good agreements with the flow statistics by DNS. Currently, a dynamic approach of obtaining mean wall shear stress based on the log-law is being applied to the flow having flow separation and its results will be shown in the presentation. Supported by the WCU and NRF programs.

A new simplified methodology for studying the coupled fluid-structure interaction in a weakened basilar artery.

PubMed

Montanino, A; Fortunato, A; Angelillo, M

2016-07-01

In this paper, we study the fluid-structure interaction in a weakened basilar artery. The aim is to study how the wall shear stress changes in space and time because of the weakening, because spatial and temporal changes are thought to be possible causes of aneurysm and vascular deseases. The arterial wall, in its natural configuration, is modeled as a hyperelastic cylinder, inhomogeneous along its axis, in order to simulate the axis-symmetric weakening. The fluid is studied exploiting a recent approach for quasi-one-dimensional flows in slowly varying ducts, which allows to write the averaged equations of mass and energy balance on the basis of the velocity profile in a straight duct. The unknowns are the wall pressure, the average velocity, and the wall radial displacement. The problem is solved in two parts: first, the stationary non-linear coupled problem is solved, and an intermediate configuration is obtained. Then, we study the variation of the basic unknowns about the intermediate configuration, considering time dependence over the cardiac cycles. The results suggest that, with a 10% reduction of the main elastic modulus, the shear stress in the weakened zone changes its sign and doubles the maximum stress value detected in the healthy zone. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Computational modelling of flow and tip variations of aortic cannulae in cardiopulmonary bypass procedure

NASA Astrophysics Data System (ADS)

Thomas, Siti A.; Empaling, Shirly; Darlis, Nofrizalidris; Osman, Kahar; Dillon, Jeswant; Taib, Ishkrizat; Khudzari, Ahmad Zahran Md

2017-09-01

Aortic cannulation has been the gold standard for maintaining cardiovascular function during open heart surgery while being connected onto the heart lung machine. These cannulation produces high velocity outflow which may lead to adverse effect on patient condition, especially sandblasting effect on aorta wall and blood cells damage. This paper reports a novel design that was able to decrease high velocity outflow. There were three design factors of that was investigated. The design factors consist of the cannula type, the flow rate, and the cannula tip design which result in 12 variations. The cannulae type used were the spiral flow inducing cannula and the standard cannula. The flow rates are varied from three to five litres per minute (lpm). Parameters for each cannula variation included maximum velocity within the aorta, pressure drop, wall shear stress (WSS) area exceeding 15 Pa, and impinging velocity on the aorta wall were evaluated. Based on the result, spiral flow inducing cannulae is proposed as a better alternatives due to its ability to reduce outflow velocity. Meanwhile, the pressure drop of all variations are less than the limit of 100 mmHg, although standard cannulae yielded better result. All cannulae show low reading of wall shear stress which decrease the possibilities for atherogenesis formation. In conclusion, as far as velocity is concerned, spiral flow is better compared to standard flow across all cannulae variations.

Discussion on the installation checking method of precast composite floor slab with lattice girders

NASA Astrophysics Data System (ADS)

Chen, Li; Jin, Xing; Wang, Yahui; Zhou, Hele; Gu, Jianing

2018-03-01

Based on the installation checking requirements of China’s current standards and the international norms for prefabricated structural precast components, it proposed an installation checking method for precast composite floor slab with lattice girders. By taking an equivalent composite beam consisted of a single lattice girder and the precast concrete slab as the checking object, compression instability stress of upper chords and yield stress of slab distribution reinforcement at the maximum positive moment, tensile yield stress of upper chords, slab normal section normal compression stress and shear instability stress of diagonal bars at the maximum negative moment were checked. And the bending stress and deflection of support beams, strength and compression stability bearing capacity of the vertical support, shear bearing capacity of the bolt and compression bearing capacity of steel tube wall at the bolt were checked at the same time. Every different checking object was given a specific load value and load combination. Application of installation checking method was given and testified by example.

Bubble transport in bifurcations

NASA Astrophysics Data System (ADS)

Bull, Joseph; Qamar, Adnan

2017-11-01

Motivated by a developmental gas embolotherapy technique for cancer treatment, we examine the transport of bubbles entrained in liquid. In gas embolotherapy, infarction of tumors is induced by selectively formed vascular gas bubbles that originate from acoustic vaporization of vascular droplets. In the case of non-functionalized droplets with the objective of vessel occlusion, the bubbles are transported by flow through vessel bifurcations, where they may split prior to eventually reach vessels small enough that they become lodged. This splitting behavior affects the distribution of bubbles and the efficacy of flow occlusion and the treatment. In these studies, we investigated bubble transport in bifurcations using computational and theoretical modeling. The model reproduces the variety of experimentally observed splitting behaviors. Splitting homogeneity and maximum shear stress along the vessel walls is predicted over a variety of physical parameters. Maximum shear stresses were found to decrease with increasing Reynolds number. The initial bubble length was found to affect the splitting behavior in the presence of gravitational asymmetry. This work was supported by NIH Grant R01EB006476.

Sustained expression of MCP-1 by low wall shear stress loading concomitant with turbulent flow on endothelial cells of intracranial aneurysm.

PubMed

Aoki, Tomohiro; Yamamoto, Kimiko; Fukuda, Miyuki; Shimogonya, Yuji; Fukuda, Shunichi; Narumiya, Shuh

2016-05-09

Enlargement of a pre-existing intracranial aneurysm is a well-established risk factor of rupture. Excessive low wall shear stress concomitant with turbulent flow in the dome of an aneurysm may contribute to progression and rupture. However, how stress conditions regulate enlargement of a pre-existing aneurysm remains to be elucidated. Wall shear stress was calculated with 3D-computational fluid dynamics simulation using three cases of unruptured intracranial aneurysm. The resulting value, 0.017 Pa at the dome, was much lower than that in the parent artery. We loaded wall shear stress corresponding to the value and also turbulent flow to the primary culture of endothelial cells. We then obtained gene expression profiles by RNA sequence analysis. RNA sequence analysis detected hundreds of differentially expressed genes among groups. Gene ontology and pathway analysis identified signaling related with cell division/proliferation as overrepresented in the low wall shear stress-loaded group, which was further augmented by the addition of turbulent flow. Moreover, expression of some chemoattractants for inflammatory cells, including MCP-1, was upregulated under low wall shear stress with concomitant turbulent flow. We further examined the temporal sequence of expressions of factors identified in an in vitro study using a rat model. No proliferative cells were detected, but MCP-1 expression was induced and sustained in the endothelial cell layer. Low wall shear stress concomitant with turbulent flow contributes to sustained expression of MCP-1 in endothelial cells and presumably plays a role in facilitating macrophage infiltration and exacerbating inflammation, which leads to enlargement or rupture.

Numerical design and optimization of hydraulic resistance and wall shear stress inside pressure-driven microfluidic networks.

PubMed

Damiri, Hazem Salim; Bardaweel, Hamzeh Khalid

2015-11-07

Microfluidic networks represent the milestone of microfluidic devices. Recent advancements in microfluidic technologies mandate complex designs where both hydraulic resistance and pressure drop across the microfluidic network are minimized, while wall shear stress is precisely mapped throughout the network. In this work, a combination of theoretical and modeling techniques is used to construct a microfluidic network that operates under minimum hydraulic resistance and minimum pressure drop while constraining wall shear stress throughout the network. The results show that in order to minimize the hydraulic resistance and pressure drop throughout the network while maintaining constant wall shear stress throughout the network, geometric and shape conditions related to the compactness and aspect ratio of the parent and daughter branches must be followed. Also, results suggest that while a "local" minimum hydraulic resistance can be achieved for a geometry with an arbitrary aspect ratio, a "global" minimum hydraulic resistance occurs only when the aspect ratio of that geometry is set to unity. Thus, it is concluded that square and equilateral triangular cross-sectional area microfluidic networks have the least resistance compared to all rectangular and isosceles triangular cross-sectional microfluidic networks, respectively. Precise control over wall shear stress through the bifurcations of the microfluidic network is demonstrated in this work. Three multi-generation microfluidic network designs are considered. In these three designs, wall shear stress in the microfluidic network is successfully kept constant, increased in the daughter-branch direction, or decreased in the daughter-branch direction, respectively. For the multi-generation microfluidic network with constant wall shear stress, the design guidelines presented in this work result in identical profiles of wall shear stresses not only within a single generation but also through all the generations of the microfluidic network under investigation. The results obtained in this work are consistent with previously reported data and suitable for a wide range of lab-on-chip applications.

Runge-Kutta method for wall shear stress of blood flow in stenosed artery

NASA Astrophysics Data System (ADS)

Awaludin, Izyan Syazana; Ahmad, Rokiah@Rozita

2014-06-01

A mathematical model of blood flow through stenotic artery is considered. A stenosis is defined as the partial occlusion of the blood vessels due to the accumulation of cholesterols, fats and the abnormal growth of tissue on the artery walls. The development of stenosis in the artery is one of the factors that cause problem in blood circulation system. This study was conducted to determine the wall shear stress of blood flow in stenosed artery. Modified mathematical model is used to analyze the relationship of the wall shear stress versus the length and height of stenosis. The existing models that have been created by previous researchers are solved using fourth order Runge-Kutta method. Numerical results show that the wall shear stress is proportionate to the length and height of stenosis.

Importance of Tensile Strength on the Shear Behavior of Discontinuities

NASA Astrophysics Data System (ADS)

Ghazvinian, A. H.; Azinfar, M. J.; Geranmayeh Vaneghi, R.

2012-05-01

In this study, the shear behavior of discontinuities possessing two different rock wall types with distinct separate compressive strengths was investigated. The designed profiles consisted of regular artificial joints molded by five types of plaster mortars, each representing a distinct uniaxial compressive strength. The compressive strengths of plaster specimens ranged from 5.9 to 19.5 MPa. These specimens were molded considering a regular triangular asperity profile and were designed so as to achieve joint walls with different strength material combinations. The results showed that the shear behavior of discontinuities possessing different joint wall compressive strengths (DDJCS) tested under constant normal load (CNL) conditions is the same as those possessing identical joint wall strengths, but the shear strength of DDJCS is governed by minor joint wall compressive strength. In addition, it was measured that the predicted values obtained by Barton's empirical criterion are greater than the experimental results. The finding indicates that there is a correlation between the joint roughness coefficient (JRC), normal stress, and mechanical strength. It was observed that the mode of failure of asperities is either pure tensile, pure shear, or a combination of both. Therefore, Barton's strength criterion, which considers the compressive strength of joint walls, was modified by substituting the compressive strength with the tensile strength. The validity of the modified criterion was examined by the comparison of the predicted shear values with the laboratory shear test results reported by Grasselli (Ph.D. thesis n.2404, Civil Engineering Department, EPFL, Lausanne, Switzerland, 2001). These comparisons infer that the modified criterion can predict the shear strength of joints more precisely.

Experimental, numerical, and analytical studies on the seismic response of steel-plate concrete (SC) composite shear walls

NASA Astrophysics Data System (ADS)

Epackachi, Siamak

The seismic performance of rectangular steel-plate concrete (SC) composite shear walls is assessed for application to buildings and mission-critical infrastructure. The SC walls considered in this study were composed of two steel faceplates and infill concrete. The steel faceplates were connected together and to the infill concrete using tie rods and headed studs, respectively. The research focused on the in-plane behavior of flexure- and flexure-shear-critical SC walls. An experimental program was executed in the NEES laboratory at the University at Buffalo and was followed by numerical and analytical studies. In the experimental program, four large-size specimens were tested under displacement-controlled cyclic loading. The design variables considered in the testing program included wall thickness, reinforcement ratio, and slenderness ratio. The aspect ratio (height-to-length) of the four walls was 1.0. Each SC wall was installed on top of a re-usable foundation block. A bolted baseplate to RC foundation connection was used for all four walls. The walls were identified to be flexure- and flexure-shear critical. The progression of damage in the four walls was identical, namely, cracking and crushing of the infill concrete at the toes of the walls, outward buckling and yielding of the steel faceplates near the base of the wall, and tearing of the faceplates at their junctions with the baseplate. A robust finite element model was developed in LS-DYNA for nonlinear cyclic analysis of the flexure- and flexure-shear-critical SC walls. The DYNA model was validated using the results of the cyclic tests of the four SC walls. The validated and benchmarked models were then used to conduct a parametric study, which investigated the effects of wall aspect ratio, reinforcement ratio, wall thickness, and uniaxial concrete compressive strength on the in-plane response of SC walls. Simplified analytical models, suitable for preliminary analysis and design of SC walls, were developed, validated, and implemented in MATLAB. Analytical models were proposed for monotonic and cyclic simulations of the in-plane response of flexure- and flexure-shear-critical SC wall piers. The model for cyclic analysis was developed by modifying the Ibarra-Krawinler Pinching (IKP) model. The analytical models were verified using the results of the parametric study and validated using the test data.

Development of a shear stress sensor to analyse the influence of polymers on the turbulent wall shear stress.

PubMed

Nottebrock, Bernardo; Grosse, Sebastian; Schröder, Wolfgang

2011-05-11

The drag reducing effect of polymers in a channel flow is well known and it is assumed that the polymer filaments interfere with the turbulent structures in the very near-wall flow. To analyse their precise effect, a micro-pillar shear stress sensor (MPS³) measurement system is developed which allows the detection of wall shear stress at high spatial and temporal resolutions. Different manufacturing techniques for the required micro-pillars are discussed and their influence on the flow is investigated evidencing the non-intrusive character of the pillars. Subsequently, a complete calibration is presented to relate the recorded deflection to wall shear stress values and to assure the correct detection over the whole expected frequency spectrum. A feasibility study about the ability to visualize the two-dimensional wall shear stress distribution completes the discussion about the validity of MPS³. In the last step, the drag reduction of a polymer filament grafted on a micro-pillar compared to a plain pillar and the application of MPS³ in an ocean-type polymer solution are investigated. The results confirm the expected behaviour found in the literature.

Investigation of Wall Shear Stress Behavior for Rough Surfaces with Blowing

NASA Astrophysics Data System (ADS)

Helvey, Jacob; Borchetta, Colby; Miller, Mark; Martin, Alexandre; Bailey, Sean

2014-11-01

We present an experimental study conducted in a turbulent channel flow wind tunnel to determine the modifications made to the turbulent flow over rough surfaces with flow injection through the surfaces. Hot-wire profile results from a quasi-two-dimensional, sinusoidally-rough surface indicate that the effects of roughness are enhanced by momentum injection through the surface. In particular, the wall shear stress was found to show behavior consistent with increased roughness height when surface blowing was increased. This observed behavior contradicts previously reported results for regular three-dimensional roughness which show a decrease in wall shear stress with additional blowing. It is unclear whether this discrepancy is due to differences in the roughness geometry under consideration or the use of the Clauser fit to estimate wall shear stress. Additional PIV experiments are being conducted for a three-dimensional fibrous surface to obtain Reynolds shear stress profiles. These results provide an additional method for estimation of wall-shear stress and thus allow verification of the use of the Clauser chart approach for flows with momentum injection through the surface. This research is supported by NASA Kentucky EPSCoR Award NNX10AV39A, and NASA RA Award NNX13AN04A.

Interaction of thermal and mechanical processes in steep permafrost rock walls: A conceptual approach

NASA Astrophysics Data System (ADS)

Draebing, D.; Krautblatter, M.; Dikau, R.

2014-12-01

Degradation of permafrost rock wall decreases stability and can initiate rock slope instability of all magnitudes. Rock instability is controlled by the balance of shear forces and shear resistances. The sensitivity of slope stability to warming results from a complex interplay of shear forces and resistances. Conductive, convective and advective heat transport processes act to warm, degrade and thaw permafrost in rock walls. On a seasonal scale, snow cover changes are a poorly understood key control of the timing and extent of thawing and permafrost degradation. We identified two potential critical time windows where shear forces might exceed shear resistances of the rock. In early summer combined hydrostatic and cryostatic pressure can cause a peak in shear force exceeding high frozen shear resistance and in autumn fast increasing shear forces can exceed slower increasing shear resistance. On a multiannual system scale, shear resistances change from predominantly rock-mechanically to ice-mechanically controlled. Progressive rock bridge failure results in an increase of sensitivity to warming. Climate change alters snow cover and duration and, hereby, thermal and mechanical processes in the rock wall. Amplified thawing of permafrost will result in higher rock slope instability and rock fall activity. We present a holistic conceptual approach connecting thermal and mechanical processes, validate parts of the model with geophysical and kinematic data and develop future scenarios to enhance understanding on system scale.

Magnetoelectric domain wall dynamics and its implications for magnetoelectric memory

DOE PAGES

Belashchenko, K. D.; Tchernyshyov, O.; Kovalev, Alexey A.; ...

2016-03-30

Domain wall dynamics in a magnetoelectric antiferromagnet is analyzed, and its implications for magnetoelectric memory applications are discussed. Cr 2O 3 is used in the estimates of the materials parameters. It is found that the domain wall mobility has a maximum as a function of the electric field due to the gyrotropic coupling induced by it. In Cr 2O 3, the maximal mobility of 0.1 m/(s Oe) is reached at E≈0.06 V/nm. Fields of this order may be too weak to overcome the intrinsic depinning field, which is estimated for B-doped Cr 2O 3. These major drawbacks for device implementationmore » can be overcome by applying a small in-plane shear strain, which blocks the domain wall precession. Domain wall mobility of about 0.7 m/(s Oe) can then be achieved at E = 0.2 V/nm. Furthermore, a split-gate scheme is proposed for the domain-wall controlled bit element; its extension to multiple-gate linear arrays can offer advantages in memory density, programmability, and logic functionality.« less

49 CFR 230.27 - Maximum shearing strength of rivets.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false Maximum shearing strength of rivets. 230.27 Section 230.27 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD... Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing strength...

49 CFR 230.27 - Maximum shearing strength of rivets.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 4 2010-10-01 2010-10-01 false Maximum shearing strength of rivets. 230.27 Section 230.27 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD... Appurtenances Strength of Materials § 230.27 Maximum shearing strength of rivets. The maximum shearing strength...

Response of hot element flush wall gauges in oscillating laminar flow

NASA Technical Reports Server (NTRS)

Giddings, T. A.; Cook, W. J.

1986-01-01

The time dependent response characteristics of flush-mounted hot element gauges used as instruments to measure wall shear stress in unsteady periodic air flows were investigated. The study was initiated because anomalous results were obtained from the gauges in oscillating turbulent flows for the phase relation of the wall shear stress variation, indicating possible gauge response problems. Flat plate laminar oscillating turbulent flows characterized by a mean free stream velocity with a superposed sinusoidal variation were performed. Laminar rather than turbulent flows were studied, because a numerical solution for the phase angle between the free stream velocity and the wall shear stress variation that is known to be correct can be obtained. The focus is on comparing the phase angle indicated by the hot element gauges with corresponding numerical prediction for the phase angle, since agreement would indicate that the hot element gauges faithfully follow the true wall shear stress variation.

Fluid, solid and fluid-structure interaction simulations on patient-based abdominal aortic aneurysm models.

PubMed

Kelly, Sinead; O'Rourke, Malachy

2012-04-01

This article describes the use of fluid, solid and fluid-structure interaction simulations on three patient-based abdominal aortic aneurysm geometries. All simulations were carried out using OpenFOAM, which uses the finite volume method to solve both fluid and solid equations. Initially a fluid-only simulation was carried out on a single patient-based geometry and results from this simulation were compared with experimental results. There was good qualitative and quantitative agreement between the experimental and numerical results, suggesting that OpenFOAM is capable of predicting the main features of unsteady flow through a complex patient-based abdominal aortic aneurysm geometry. The intraluminal thrombus and arterial wall were then included, and solid stress and fluid-structure interaction simulations were performed on this, and two other patient-based abdominal aortic aneurysm geometries. It was found that the solid stress simulations resulted in an under-estimation of the maximum stress by up to 5.9% when compared with the fluid-structure interaction simulations. In the fluid-structure interaction simulations, flow induced pressure within the aneurysm was found to be up to 4.8% higher than the value of peak systolic pressure imposed in the solid stress simulations, which is likely to be the cause of the variation in the stress results. In comparing the results from the initial fluid-only simulation with results from the fluid-structure interaction simulation on the same patient, it was found that wall shear stress values varied by up to 35% between the two simulation methods. It was concluded that solid stress simulations are adequate to predict the maximum stress in an aneurysm wall, while fluid-structure interaction simulations should be performed if accurate prediction of the fluid wall shear stress is necessary. Therefore, the decision to perform fluid-structure interaction simulations should be based on the particular variables of interest in a given study.

Shear stress and flow dynamics of the femoral vein among obese patients who qualify for bariatric surgery.

PubMed

Wiewiora, Maciej; Piecuch, Jerzy; Glűck, Marek; Slowinska-Lozynska, Ludmila; Sosada, Krystyn

2013-01-01

The aim of this study was to evaluate the effects of obesity on wall shear stress and its relationship to erythrocyte aggregation. We studied 35 morbidly obese patients who were qualified for bariatric surgery. The control group consisted of 20 non-obese people. Blood rheological measurements were performed using the Laser-assisted Optical Rotational Cell Analyzer (Mechatronics, the Netherlands) and a cone-plate viscometer (Brookfield DV-II). The venous flow dynamics were assessed using a duplex ultrasound. The shear rate was estimated from the measured blood flow velocity and the diameter of the femoral vein. Venous wall shear stress was calculated from the whole blood viscosity and the shear rate. The shear rate (P < 0.005) and the venous wall shear stress (P < 0.05) were significantly lower in obese patients compared with the controls. The aggregation index (P < 0.001), syllectogram amplitude - AMP (P < 0.05) and Tslow (P < 0.001) were significantly higher in the obese patients; the aggregation half-time (P < 0.001) and Tfast (P < 0.001) were decreased compared with the control group. Multivariate regression analyses found waist circumference (β -0.31, P < 0.05), thigh circumference (β 0.33, P < 0.05) and Tslow (β -0.47, P < 0.005) to be variables that independently influenced the shear rate. Nevertheless, the AMP (β 0.34, P < 0.05) and Tslow (β -0.47, P < 0.01) were independent predictors that influenced the wall shear stress. This study indicates that there is a relationship between wall shear stress in the femoral vein and the rheological impairment of the RBC among obese patients, but further studies are necessary to confirm this suggestion.

Effect of heart rate on the hemodynamics of bileaflet mechanical heart valves' prostheses (St. Jude Medical) in the aortic position and in the opening phase: A computational study.

PubMed

Jahandardoost, Mehdi; Fradet, Guy; Mohammadi, Hadi

2016-03-01

To date, to the best of the authors' knowledge, in almost all of the studies performed around the hemodynamics of bileaflet mechanical heart valves, a heart rate of 70-72 beats/min has been considered. In fact, the heart rate of ~72 beats/min does not represent the entire normal physiological conditions under which the aortic or prosthetic valves function. The heart rates of 120 or 50 beats/min may lead to hemodynamic complications, such as plaque formation and/or thromboembolism in patients. In this study, the hemodynamic performance of the bileaflet mechanical heart valves in a wide range of normal and physiological heart rates, that is, 60-150 beats/min, was studied in the opening phase. The model considered in this study was a St. Jude Medical bileaflet mechanical heart valve with the inner diameter of 27 mm in the aortic position. The hemodynamics of the native valve and the St. Jude Medical valve were studied in a variety of heart rates in the opening phase and the results were carefully compared. The results indicate that peak values of the velocity profile downstream of the valve increase as heart rate increases, as well as the location of the maximum velocity changes with heart rate in the St. Jude Medical valve model. Also, the maximum values of shear stress and wall shear stresses downstream of the valve are proportional to heart rate in both models. Interestingly, the maximum shear stress and wall shear stress values in both models are in the same range when heart rate is <90 beats/min; however, these values significantly increase in the St. Jude Medical valve model when heart rate is >90 beats/min (up to ~40% growth compared to that of the native valve). The findings of this study may be of importance in the hemodynamic performance of bileaflet mechanical heart valves. They may also play an important role in design improvement of conventional prosthetic heart valves and the design of the next generation of prosthetic valves, such as percutaneous valves. © IMechE 2016.

Studies in turbulence

NASA Technical Reports Server (NTRS)

Gatski, Thomas B. (Editor); Sarkar, Sutanu (Editor); Speziale, Charles G. (Editor)

1992-01-01

Various papers on turbulence are presented. Individual topics addressed include: modeling the dissipation rate in rotating turbulent flows, mapping closures for turbulent mixing and reaction, understanding turbulence in vortex dynamics, models for the structure and dynamics of near-wall turbulence, complexity of turbulence near a wall, proper orthogonal decomposition, propagating structures in wall-bounded turbulence flows. Also discussed are: constitutive relation in compressible turbulence, compressible turbulence and shock waves, direct simulation of compressible turbulence in a shear flow, structural genesis in wall-bounded turbulence flows, vortex lattice structure of turbulent shear slows, etiology of shear layer vortices, trilinear coordinates in fluid mechanics.

Temporal and spatial intermittencies within Newtonian turbulence

NASA Astrophysics Data System (ADS)

Kushwaha, Anubhav; Graham, Michael

2015-11-01

Direct numerical simulations of a pressure driven turbulent flow are performed in a large rectangular channel. Intermittent high- and low-drag regimes within turbulence that have earlier been found to exist temporally in minimal channels have been observed both spatially and temporally in full-size turbulent flows. These intermittent regimes, namely, ''active'' and ''hibernating'' turbulence, display very different structural and statistical features. We adopt a very simple sampling technique to identify these intermittent intervals, both temporally and spatially, and present differences between them in terms of simple quantities like mean-velocity, wall-shear stress and flow structures. By conditionally sampling of the low wall-shear stress events in particular, we show that the Maximum Drag Reduction (MDR) velocity profile, that occurs in viscoelastic flows, can also be approached in a Newtonian-fluid flow in the absence of any additives. This suggests that the properties of polymer drag reduction are inherent to all flows and their occurrence is just enhanced by the addition of polymers. We also show how the intermittencies within turbulence vary with Reynolds number. The work was supported by AFOSR grant FA9550-15-1-0062.

Shear-layer structures in near-wall turbulence

NASA Technical Reports Server (NTRS)

Johansson, A. V.; Alfredsson, P. H.; Kim, J.

1987-01-01

The structure of internal shear layer observed in the near-wall region of turbulent flows is investigated by analyzing flow fields obtained from numerical simulations of channel and boundary-layer flows. It is found that the shear layer is an important contributor to the turbulence production. The conditionally averaged production at the center of the structure was almost twice as large as the long-time mean value. The shear-layer structure is also found to retain its coherence over streamwise distances on the order of a thousand viscous length units, and propagates with a constant velocity of about 10.6 u sub rho throughout the near wall region.

Linear Mechanisms and Pressure Fluctuations in Wall Turbulence

NASA Astrophysics Data System (ADS)

Septham, Kamthon; Morrison, Jonathan

2014-11-01

Full-domain, linear feedback control of turbulent channel flow at Reτ <= 400 via vU' at low wavenumbers is an effective method to attenuate turbulent channel flow such that it is relaminarised. The passivity-based control approach is adopted and explained by the conservative characteristics of the nonlinear terms contributing to the Reynolds-Orr equation (Sharma et al .Phys .Fluids 2011). The linear forcing acts on the wall-normal velocity field and thus the pressure field via the linear (rapid) source term of the Poisson equation for pressure fluctuations, 2U'∂v/∂x . The minimum required spanwise wavelength resolution without losing control is constant at λz+ = 125, based on the wall friction velocity at t = 0 . The result shows that the maximum forcing is located at y+ ~ 20 , corresponding to the location of the maximum in the mean-square pressure gradient. The effectiveness of linear control is qualitatively explained by Landahl's theory for timescales, in that the control proceeds via the shear interaction timescale which is much shorter than both the nonlinear and viscous timescales. The response of the rapid (linear) and slow (nonlinear) pressure fluctuations to the linear control is examined and discussed.

Jetting of a ultrasound contrast microbubble near a rigid wall

NASA Astrophysics Data System (ADS)

Sarkar, Kausik; Mobadersany, Nima

2017-11-01

Micron sized gas-bubbles coated with a stabilizing shell of lipids or proteins, are used as contrast enhancing agents for ultrasound imaging. However, they are increasingly being explored for novel applications in drug delivery through a process called sonoporation, the reversible permeabilization of the cell membrane. Under sufficiently strong acoustic excitations, bubbles form a jet and collapse near a wall. The jetting of free bubbles has been extensively studied by boundary element method (BEM). Here, for the first time, we implemented a rigorous interfacial rheological model of the shell into BEM and investigated the jet formation. The code has been carefully validated against past results. Increasing shell elasticity decreases the maximum bubble volume and the collapse time, while the jet velocity increases. The shear stress on the wall is computed and analyzed. A phase diagram as functions of excitation pressure and wall separation describes jet formation. Effects of shell elasticity and frequency on the phase diagram are investigated. Partially supported by National Science Foundation.

Seismic performance of RC shear wall structure with novel shape memory alloy dampers in coupling beams

NASA Astrophysics Data System (ADS)

Mao, Chenxi; Dong, Jinzhi; Li, Hui; Ou, Jinping

2012-04-01

Shear wall system is widely adopted in high rise buildings because of its high lateral stiffness in resisting earthquakes. According to the concept of ductility seismic design, coupling beams in shear wall structure are required to yield prior to the damage of wall limb. However, damage in coupling beams results in repair cost post earthquake and even in some cases it is difficult to repair the coupling beams if the damage is severe. In order to solve this problem, a novel passive SMA damper was proposed in this study. The coupling beams connecting wall limbs are split in the middle, and the dampers are installed between the ends of the two cantilevers. Then the relative flexural deformation of the wall limbs is transferred to the ends of coupling beams and then to the SMA dampers. After earthquakes the deformation of the dampers can recover automatically because of the pseudoelasticity of austenite SMA material. In order to verify the validity of the proposed dampers, seismic responses of a 12-story coupled shear wall with such passive SMA dampers in coupling beams was investigated. The additional stiffness and yielding deformation of the dampers and their ratios to the lateral stiffness and yielding displacements of the wall limbs are key design parameters and were addressed. Analytical results indicate that the displacement responses of the shear wall structure with such dampers are reduced remarkably. The deformation of the structure is concentrated in the dampers and the damage of coupling beams is reduced.

Inverse Interscale Transport of the Reynolds Shear Stress in Plane Couette Turbulence

NASA Astrophysics Data System (ADS)

Kawata, Takuya; Alfredsson, P. Henrik

2018-06-01

Interscale interaction between small-scale structures near the wall and large-scale structures away from the wall plays an increasingly important role with increasing Reynolds number in wall-bounded turbulence. While the top-down influence from the large- to small-scale structures is well known, it has been unclear whether the small scales near the wall also affect the large scales away from the wall. In this Letter we show that the small-scale near-wall structures indeed play a role to maintain the large-scale structures away from the wall, by showing that the Reynolds shear stress is transferred from small to large scales throughout the channel. This is in contrast to the turbulent kinetic energy transport which is from large to small scales. Such an "inverse" interscale transport of the Reynolds shear stress eventually supports the turbulent energy production at large scales.

Preferential particle concentration in wall-bounded turbulence with zero skin friction

NASA Astrophysics Data System (ADS)

Yang, Kun; Zhao, Lihao; Andersson, Helge I.

2017-11-01

Inertial particles dispersed in turbulence distribute themselves unevenly. Besides their tendency to segregate near walls, they also concentrate preferentially in wall-parallel planes. We explore the latter phenomenon in a tailor-made flow with the view to examine the homogeneity and anisotropy of particle clustering in the absence of mean shear as compared with conventional, i.e., sheared, wall turbulence. Inertial particles with some different Stokes numbers are suspended in a turbulent Couette-Poiseuille flow, in which one of the walls moves such that the shear rate vanishes at that wall. The anisotropies of the velocity and vorticity fluctuations are therefore qualitatively different from those at the opposite non-moving wall, along which quasi-coherent streaky structures prevail, similarly as in turbulent pipe and channel flows. Preferential particle concentration is observed near both walls. The inhomogeneity of the concentration is caused by the strain-vorticity selection mechanism, whereas the anisotropy originates from coherent flow structures. In order to analyse anisotropic clustering, a two-dimensional Shannon entropy method is developed. Streaky particle structures are observed near the stationary wall where the flow field resembles typical wall-turbulence, whereas particle clusters near the moving friction-free wall are similar to randomly oriented clusters in homogeneous isotropic turbulence, albeit with a modest streamwise inclination. In the absence of mean-shear and near-wall streaks, the observed anisotropy is ascribed to the imprint of large-scale flow structures which reside in the bulk flow and are global in nature.

Convection of wall shear stress events in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Pabon, Rommel; Mills, David; Ukeiley, Lawrence; Sheplak, Mark

2017-11-01

The fluctuating wall shear stress is measured in a zero pressure gradient turbulent boundary layer of Reτ 1700 simultaneously with velocity measurements using either hot-wire anemometry or particle image velocimetry. These experiments elucidate the patterns of large scale structures in a single point measurement of the wall shear stress, as well as their convection velocity at the wall. The wall shear stress sensor is a CS-A05 one-dimensional capacitice floating element from Interdisciplinary Consulting Corp. It has a nominal bandwidth from DC to 5 kHz and a floating element size of 1 mm in the principal sensing direction (streamwise) and 0.2 mm in the cross direction (spanwise), allowing the large scales to be well resolved in the current experimental conditions. In addition, a two sensor array of CS-A05 aligned in the spanwise direction with streamwise separations O (δ) is utilized to capture the convection velocity of specific scales of the shear stress through a bandpass filter and peaks in the correlation. Thus, an average wall normal position for the corresponding convecting event can be inferred at least as high as the equivalent local streamwise velocity. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

Simultaneous wall-shear-stress and wide-field PIV measurements in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Gomit, Guillaume; Fourrie, Gregoire; de Kat, Roeland; Ganapathisubramani, Bharathram

2015-11-01

Simultaneous particle image velocimetry (PIV) and hot-film shear stress sensor measurements were performed to study the large-scale structures associated with shear stress events in a flat plate turbulent boundary layer at a high Reynolds number (Reτ ~ 4000). The PIV measurement was performed in a streamwise-wall normal plane using an array of six high resolution cameras (4 ×16MP and 2 ×29MP). The resulting field of view covers 8 δ (where δ is the boundary layer thickness) in the streamwise direction and captures the entire boundary layer in the wall-normal direction. The spatial resolution of the measurement is approximately is approximately 70 wall units (1.8 mm) and sampled each 35 wall units (0.9 mm). In association with the PIV setup, a spanwise array of 10 skin-friction sensors (spanning one δ) was used to capture the footprint of the large-scale structures. This combination of measurements allowed the analysis of the three-dimensional conditional structures in the boundary layer. Particularly, from conditional averages, the 3D organisation of the wall normal and streamwise velocity components (u and v) and the Reynolds shear stress (-u'v') related to a low and high shear stress events can be extracted. European Research Council Grant No-277472-WBT.

Influence of packing density and surface roughness of vertically-aligned carbon nanotubes on adhesive properties of gecko-inspired mimetics.

PubMed

Chen, Bingan; Zhong, Guofang; Oppenheimer, Pola Goldberg; Zhang, Can; Tornatzky, Hans; Esconjauregui, Santiago; Hofmann, Stephan; Robertson, John

2015-02-18

We have systematically studied the macroscopic adhesive properties of vertically aligned nanotube arrays with various packing density and roughness. Using a tensile setup in shear and normal adhesion, we find that there exists a maximum packing density for nanotube arrays to have adhesive properties. Too highly packed tubes do not offer intertube space for tube bending and side-wall contact to surfaces, thus exhibiting no adhesive properties. Likewise, we also show that the surface roughness of the arrays strongly influences the adhesion properties and the reusability of the tubes. Increasing the surface roughness of the array strengthens the adhesion in the normal direction, but weakens it in the shear direction. Altogether, these results allow progress toward mimicking the gecko's vertical mobility.

Non-invasive vascular radial/circumferential strain imaging and wall shear rate estimation using video images of diagnostic ultrasound.

PubMed

Wan, Jinjin; He, Fangli; Zhao, Yongfeng; Zhang, Hongmei; Zhou, Xiaodong; Wan, Mingxi

2014-03-01

The aim of this work was to develop a convenient method for radial/circumferential strain imaging and shear rate estimation that could be used as a supplement to the current routine screening for carotid atherosclerosis using video images of diagnostic ultrasound. A reflection model-based correction for gray-scale non-uniform distribution was applied to B-mode video images before strain estimation to improve the accuracy of radial/circumferential strain imaging when applied to vessel transverse cross sections. The incremental and cumulative radial/circumferential strain images can then be calculated based on the displacement field between consecutive B-mode images. Finally, the transverse Doppler spectra acquired at different depths along the vessel diameter were used to construct the spatially matched instantaneous wall shear values in a cardiac cycle. Vessel phantom simulation results revealed that the signal-to-noise ratio and contrast-to-noise ratio of the radial and circumferential strain images were increased by 2.8 and 5.9 dB and by 2.3 and 4.4 dB, respectively, after non-uniform correction. Preliminary results for 17 patients indicated that the accuracy of radial/circumferential strain images was improved in the lateral direction after non-uniform correction. The peak-to-peak value of incremental strain and the maximum cumulative strain for calcified plaques are evidently lower than those for other plaque types, and the echolucent plaques had higher values, on average, than the mixed plaques. Moreover, low oscillating wall shear rate values, found near the plaque and stenosis regions, are closely related to plaque formation. In conclusion, the method described can provide additional valuable results as a supplement to the current routine ultrasound examination for carotid atherosclerosis and, therefore, has significant potential as a feasible screening method for atherosclerosis diagnosis in the future. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Shear flow of dense granular materials near smooth walls. I. Shear localization and constitutive laws in the boundary region.

PubMed

Shojaaee, Zahra; Roux, Jean-Noël; Chevoir, François; Wolf, Dietrich E

2012-07-01

We report on a numerical study of the shear flow of a simple two-dimensional model of a granular material under controlled normal stress between two parallel smooth frictional walls moving with opposite velocities ± V. Discrete simulations, which are carried out with the contact dynamics method in dense assemblies of disks, reveal that, unlike rough walls made of strands of particles, smooth ones can lead to shear strain localization in the boundary layer. Specifically, we observe, for decreasing V, first a fluidlike regime (A), in which the whole granular layer is sheared, with a homogeneous strain rate except near the walls, then (B) a symmetric velocity profile with a solid block in the middle and strain localized near the walls, and finally (C) a state with broken symmetry in which the shear rate is confined to one boundary layer, while the bulk of the material moves together with the opposite wall. Both transitions are independent of system size and occur for specific values of V. Transient times are discussed. We show that the first transition, between regimes A and B, can be deduced from constitutive laws identified for the bulk material and the boundary layer, while the second one could be associated with an instability in the behavior of the boundary layer. The boundary zone constitutive law, however, is observed to depend on the state of the bulk material nearby.

Experimental research on the seismic behavior of CSPSWs connected to frame beams

NASA Astrophysics Data System (ADS)

Guo, Lanhui; Ma, Xinbo; Li, Ran; Zhang, Sumei

2011-03-01

The seismic performance of composite steel plate shear walls (CSPSWs) that consist of a steel plate shear wall (SPSW) with reinforced concrete (RC) panels attached to one or both sides by means of bolts or connectors is experimentally studied. The shear wall is connected to the frame beams but not to the columns. This arrangement restrains the possible out-of-plane buckling of the thin-walled steel plate, thus significantly increasing the bearing capacity and ductility of the overall wall, and prevents the premature overall or local buckling failure of the frame columns. From a practical viewpoint, these solutions can provide open space in a floor as this type of composite shear walls with a relatively small aspect ratio can be placed parallel along a bay. In this study, four CSPSWs and one SPSW were tested and the results showed that both CSPSWs and SPSW possessed good ductility. For SPSW alone, the buckling appeared and resulted in a decrease of bearing capacity and energy dissipation capacity. In addition, welding stiffeners at corners were shown to be an effective way to increase the energy dissipation capacity of CSPSWs.

A strategy for enhancing shear strength and bending strength of FRP laminate using MWCNTs

NASA Astrophysics Data System (ADS)

Rawat, Prashant; Singh, K. K.

2016-09-01

Multi-wall carbon nanotubes (MWCNTs) promises to enhance mechanical properties exceptionally when it is doped with fiber reinforced polymer (FRP) composite. Glass fiber symmetrical laminate with eight layers of 4.0 mm thickness was fabricated by hand lay-up technique assisted by vacuum bagging method. Ply orientations for symmetrical laminate used [(0,90)/(+45,-45)/(+45,-45)/(0,90)//(90,0)/(+45,-45)/(+45,-45)/(90,0)]. MWCNTs reinforced three different samples (0 wt.%, 0.5 wt.% and 0.75 wt.% by weight) were tested on universal testing machine (UTM). Short beam strength test and inter laminar shear strength (ILSS) calculation have been done according to ASTM D2344 and ASTM D7264. UTM having maximum load capacity of 50 KN with loading rate of 0.1 mm/min to 50 mm/min was used for mechanical testing. Testing results justified that by adding 0.50 wt.% MWCNTs in symmetrical GFRP laminate can enhance inter laminar shear strength by 13.66% and bending strength by 44.22%.

Development of a MEMS dual-axis differential capacitance floating element shear stress sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnard, Casey; Griffin, Benjamin

A single-axis MEMS wall shear stress sensor with differential capacitive transduction method is produced. Using a synchronous modulation and demodulation interface circuit, the system is capable of making real time measurements of both mean and fluctuating wall shear stress. A sensitivity of 3.44 mV/Pa is achieved, with linearity in response demonstrated up to testing limit of 2 Pa. Minimum detectable signals of 340 μPa at 100 Hz and 120 μPa at 1 kHz are indicated, with a resonance of 3.5 kHz. Multiple full scale wind tunnel tests are performed, producing spectral measurements of turbulent boundary layers in wind speeds rangingmore » up to 0.5 Ma (18 Pa of mean wall shear stress). The compact packaging allows for minimally invasive installation, and has proven relatively robust over multiple testing events. Temperature sensitivity, likely due to poor CTE matching of packaged materials, is an ongoing concern being addressed. These successes are being directly leveraged into a development plan for a dual-axis wall shear stress sensor, capable of producing true vector estimates at the wall.« less

Seismic behavior of outrigger truss-wall shear connections using multiple steel angles

NASA Astrophysics Data System (ADS)

Li, Xian; Wang, Wei; Lü, Henglin; Zhang, Guangchang

2016-06-01

An experimental investigation on the seismic behavior of a type of outrigger truss-reinforced concrete wall shear connection using multiple steel angles is presented. Six large-scale shear connection models, which involved a portion of reinforced concrete wall and a shear tab welded onto a steel endplate with three steel angles, were constructed and tested under combined actions of cyclic axial load and eccentric shear. The effects of embedment lengths of steel angles, wall boundary elements, types of anchor plates, and thicknesses of endplates were investigated. The test results indicate that properly detailed connections exhibit desirable seismic behavior and fail due to the ductile fracture of steel angles. Wall boundary elements provide beneficial confinement to the concrete surrounding steel angles and thus increase the strength and stiffness of connections. Connections using whole anchor plates are prone to suffer concrete pry-out failure while connections with thin endplates have a relatively low strength and fail due to large inelastic deformations of the endplates. The current design equations proposed by Chinese Standard 04G362 and Code GB50011 significantly underestimate the capacities of the connection models. A revised design method to account for the influence of previously mentioned test parameters was developed.

Sudden Relaminarization and Lifetimes in Forced Isotropic Turbulence.

PubMed

Linkmann, Moritz F; Morozov, Alexander

2015-09-25

We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. We perform direct numerical simulations of isotropic turbulence forced at large scales at moderate Reynolds numbers and observe sudden transitions from a chaotic dynamics to a spatially simple flow, analogous to the laminar state in wall bounded shear flows. We find that the survival probabilities of turbulence are exponential and the typical lifetimes increase superexponentially with the Reynolds number. Our results suggest that both isotropic turbulence and wall-bounded shear flows qualitatively share the same phase-space dynamics.

Shear localization and effective wall friction in a wall bounded granular flow

NASA Astrophysics Data System (ADS)

Artoni, Riccardo; Richard, Patrick

2017-06-01

In this work, granular flow rheology is investigated by means of discrete numerical simulations of a torsional, cylindrical shear cell. Firstly, we focus on azimuthal velocity profiles and study the effect of (i) the confining pressure, (ii) the particle-wall friction coefficient, (iii) the rotating velocity of the bottom wall and (iv) the cell diameter. For small cell diameters, azimuthal velocity profiles are nearly auto-similar, i.e. they are almost linear with the radial coordinate. Different strain localization regimes are observed : shear can be localized at the bottom, at the top of the shear cell, or it can be even quite distributed. This behavior originates from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. Then we study the effective friction at the cylindrical wall, and point out the strong link between wall friction, slip and fluctuations of forces and velocities. Even if the system is globally below the sliding threshold, force fluctuations trigger slip events, leading to a nonzero wall slip velocity and an effective wall friction coefficient different from the particle-wall one. A scaling law was found linking slip velocity, granular temperature in the main flow direction and effective friction. Our results suggest that fluctuations are an important ingredient for theories aiming to capture the interface rheology of granular materials.

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 2: Wall shear stress

NASA Technical Reports Server (NTRS)

Liou, M. S.; Adamson, T. C., Jr.

1979-01-01

An analysis is presented of the flow in the two inner layers, the Reynolds stress sublayer and the wall layer. Included is the calculation of the shear stress at the wall in the interaction region. The limit processes considered are those used for an inviscid flow.

Determination of seismic performance factors for CLT shear wall systems

Treesearch

M. Omar Amini; John W. van de Lindt; Douglas Rammer; Shiling Pei; Philip Line; Marjan Popovski

2016-01-01

This paper presents selected results of connector testing and wall testing which were part of a Forest Products Lab-funded project undertaken at Colorado State University in an effort to determine seismic performance factors for cross laminated timber (CLT) shear walls in the United States. Archetype development, which is required as part of the process, is also...

Turbulent shear stresses in compressible boundary layers

NASA Technical Reports Server (NTRS)

Laderman, A. J.; Demetriades, A.

1979-01-01

Hot-wire anemometer measurements of turbulent shear stresses in a Mach 3 compressible boundary layer were performed in order to investigate the effects of heat transfer on turbulence. Measurements were obtained by an x-probe in a flat plate, zero pressure gradient, two dimensional boundary layer in a wind tunnel with wall to freestream temperature ratios of 0.94 and 0.71. The measured shear stress distributions are found to be in good agreement with previous results, supporting the contention that the shear stress distribution is essentially independent of Mach number and heat transfer for Mach numbers from incompressible to hypersonic and wall to freestream temperature ratios of 0.4 to 1.0. It is also found that corrections for frequency response limitations of the electronic equipment are necessary to determine the correct shear stress distribution, particularly at the walls.

Pulsatile flows and wall-shear stresses in models simulating normal and stenosed aortic arches

NASA Astrophysics Data System (ADS)

Huang, Rong Fung; Yang, Ten-Fang; Lan, Y.-K.

2010-03-01

Pulsatile aqueous glycerol solution flows in the models simulating normal and stenosed human aortic arches are measured by means of particle image velocimetry. Three transparent models were used: normal, 25% stenosed, and 50% stenosed aortic arches. The Womersley parameter, Dean number, and time-averaged Reynolds number are 17.31, 725, and 1,081, respectively. The Reynolds numbers based on the peak velocities of the normal, 25% stenosed, and 50% stenosed aortic arches are 2,484, 3,456, and 3,931, respectively. The study presents the temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall-shear stress during the systolic and diastolic phases. It is found that the flow pattern evolving in the central plane of normal and stenosed aortic arches exhibits (1) a separation bubble around the inner arch, (2) a recirculation vortex around the outer arch wall upstream of the junction of the brachiocephalic artery, (3) an accelerated main stream around the outer arch wall near the junctions of the left carotid and the left subclavian arteries, and (4) the vortices around the entrances of the three main branches. The study identifies and discusses the reasons for the flow physics’ contribution to the formation of these features. The oscillating wall-shear stress distributions are closely related to the featured flow structures. On the outer wall of normal and slightly stenosed aortas, large wall-shear stresses appear in the regions upstream of the junction of the brachiocephalic artery as well as the corner near the junctions of the left carotid artery and the left subclavian artery. On the inner wall, the largest wall-shear stress appears in the region where the boundary layer separates.

Turbulent boundary layer on a convex, curved surface

NASA Technical Reports Server (NTRS)

Gillis, J. C.; Johnston, J. P.; Kays, W. M.; Moffat, R. J.

1980-01-01

The effects of strong convex curvature on boundary layer turbulence were investigated. The data gathered on the behavior of Reynolds stress suggested the formulation of a simple turbulence model. Three sets of data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 deg of turning, and then onto a flat recovery surface. The geometry was adjusted so that, for both rigs, the pressure gradient along the test surface was zero - thus avoiding any effects of streamwise acceleration on the wall layers. Results show that after a sudden introduction of curvature, the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. In contrast, when the surface suddenly becomes flat again, the wall shear and shear stress profiles recover very slowly towards flat wall conditions.

The Fluid Mechanics of a Wavy-Wall Bioreactor

NASA Astrophysics Data System (ADS)

Sucosky, Philippe; Bilgen, Bahar; Aleem, Alexander; Neitzel, Paul; Barabino, Gilda

2004-11-01

Bioreactors are devices used for the production of mammalian tissue in vitro. Although mixing has been shown to stimulate the growth of cartilage constructs, high shear-stress levels can damage the cells. In order to enhance mixing while minimizing shear, a wavy-wall bioreactor (WWB) featuring a sinusoidal internal profile has been designed. The turbulent hydrodynamic environment produced in this device is investigated experimentally using particle-image velocimetry. A model bioreactor made of acrylic and filled with an index-matching solution of zinc iodide is used to compensate for the refraction of light at the walls. The flow observed in different planes is shown to be periodic, spatially dependent, and dominated by mean-shear rather than Reynolds stresses in the vicinity of constructs. Finally, a comparison between the mean-shear stresses obtained in the WWB and in a standard spinner flask reveals similar stress levels near the construct walls.

Evaluation of Extended Wall OSB Sheathing Connection under Combined Uplift and Shear Loading for 24-inch Heel Trusses

Treesearch

Vladimir Kochkin; Andrew DeRenzis; Xiping Wang

2014-01-01

This study was designed to evaluate the performance of the extended wall structural panel connection in resisting combined uplift and shear forces at the roof-to-wall interface with a focus on a truss heel height of 24 in. to address the expected increases in the depth of attic insulation used in Climate Zones 5 and higher. Five full-size roof-wall assemblies were...

Navier-Stokes Computations With One-Equation Turbulence Model for Flows Along Concave Wall Surfaces

NASA Technical Reports Server (NTRS)

Wang, Chi R.

2005-01-01

This report presents the use of a time-marching three-dimensional compressible Navier-Stokes equation numerical solver with a one-equation turbulence model to simulate the flow fields developed along concave wall surfaces without and with a downstream extension flat wall surface. The 3-D Navier- Stokes numerical solver came from the NASA Glenn-HT code. The one-equation turbulence model was derived from the Spalart and Allmaras model. The computational approach was first calibrated with the computations of the velocity and Reynolds shear stress profiles of a steady flat plate boundary layer flow. The computational approach was then used to simulate developing boundary layer flows along concave wall surfaces without and with a downstream extension wall. The author investigated the computational results of surface friction factors, near surface velocity components, near wall temperatures, and a turbulent shear stress component in terms of turbulence modeling, computational mesh configurations, inlet turbulence level, and time iteration step. The computational results were compared with existing measurements of skin friction factors, velocity components, and shear stresses of the developing boundary layer flows. With a fine computational mesh and a one-equation model, the computational approach could predict accurately the skin friction factors, near surface velocity and temperature, and shear stress within the flows. The computed velocity components and shear stresses also showed the vortices effect on the velocity variations over a concave wall. The computed eddy viscosities at the near wall locations were also compared with the results from a two equation turbulence modeling technique. The inlet turbulence length scale was found to have little effect on the eddy viscosities at locations near the concave wall surface. The eddy viscosities, from the one-equation and two-equation modeling, were comparable at most stream-wise stations. The present one-equation turbulence model is an effective approach for turbulence modeling in the near solid wall surface region of flow over a concave wall.

Effect of TurboSwirl Structure on an Uphill Teeming Ingot Casting Process

NASA Astrophysics Data System (ADS)

Bai, Haitong; Ersson, Mikael; Jönsson, Pär

2015-12-01

To produce high-quality ingot cast steel with a better surface quality, it would be beneficial for the uphill teeming process if a much more stable flow pattern could be achieved in the runners. Several techniques have been utilized in the industry to try to obtain a stable flow of liquid steel, such as a swirling flow. Some research has indicated that a swirl blade inserted in the horizontal and vertical runners, or some other additional devices and physics could generate a swirling flow in order to give a lower hump height, avoid mold flux entrapment, and improve the quality of the ingot products, and a new swirling flow generation component, TurboSwirl, was introduced to improve the flow pattern. It has recently been demonstrated that the TurboSwirl method can effectively reduce the risk of mold flux entrapment, lower the maximum wall shear stress, and decrease velocity fluctuations. The TurboSwirl is built at the elbow of the runners as a connection between the horizontal and vertical runners. It is located near the mold and it generates a tangential flow that can be used with a divergent nozzle in order to decrease the axial velocity of the vertical flow into the mold. This stabilizes flow before the fluid enters the mold. However, high wall shear stresses develop at the walls due to the fierce rotation in the TurboSwirl. In order to achieve a calmer flow and to protect the refractory wall, some structural improvements have been made. It was found that by changing the flaring angle of the divergent nozzle, it was possible to lower the axial velocity and wall shear stress. Moreover, when the vertical runner and the divergent nozzle were not placed at the center of the TurboSwirl, quite different flow patterns could be obtained to meet to different requirements. In addition, the swirl numbers of all the cases mentioned above were calculated to ensure that the swirling flow was strong enough to generate a swirling flow of the liquid steel in the TurboSwirl.

An Experimental Study on the Shear Hysteresis and Energy Dissipation of the Steel Frame with a Trapezoidal-Corrugated Steel Plate

PubMed Central

Shon, Sudeok; Yoo, Mina; Lee, Seungjae

2017-01-01

The steel frame reinforced with steel shear wall is a lateral load resisting system and has higher strength and shear performance than the concrete shear wall system. Especially, using corrugated steel plates in these shear wall systems improves out-of-plane stiffness and flexibility in the deformation along the corrugation. In this paper, a cyclic loading test of this steel frame reinforced with trapezoidal-corrugated steel plate was performed to evaluate the structural performance. The hysteresis behavior and the energy dissipation capacity of the steel frame were also compared according to the corrugated direction of the plate. For the test, one simple frame model without the wall and two frame models reinforced with the plate are considered and designed. The test results showed that the model reinforced with the corrugated steel plate had a greater accumulated energy dissipation capacity than the experimental result of the non-reinforced model. Furthermore, the energy dissipation curves of two reinforced frame models, which have different corrugated directions, produced similar results. PMID:28772624

An Experimental Study on the Shear Hysteresis and Energy Dissipation of the Steel Frame with a Trapezoidal-Corrugated Steel Plate.

PubMed

Shon, Sudeok; Yoo, Mina; Lee, Seungjae

2017-03-06

The steel frame reinforced with steel shear wall is a lateral load resisting system and has higher strength and shear performance than the concrete shear wall system. Especially, using corrugated steel plates in these shear wall systems improves out-of-plane stiffness and flexibility in the deformation along the corrugation. In this paper, a cyclic loading test of this steel frame reinforced with trapezoidal-corrugated steel plate was performed to evaluate the structural performance. The hysteresis behavior and the energy dissipation capacity of the steel frame were also compared according to the corrugated direction of the plate. For the test, one simple frame model without the wall and two frame models reinforced with the plate are considered and designed. The test results showed that the model reinforced with the corrugated steel plate had a greater accumulated energy dissipation capacity than the experimental result of the non-reinforced model. Furthermore, the energy dissipation curves of two reinforced frame models, which have different corrugated directions, produced similar results.

SIP Shear Walls: Cyclic Performance of High-Aspect-Ratio Segments and Perforated Walls

Treesearch

Vladimir Kochkin; Douglas R. Rammer; Kevin Kauffman; Thomas Wiliamson; Robert J. Ross

2015-01-01

Increasing stringency of energy codes and the growing market demand for more energy efficient buildings gives structural insulated panel (SIP) construction an opportunity to increase its use in commercial and residential buildings. However, shear wall aspect ratio limitations and lack of knowledge on how to design SIPs with window and door openings are barriers to the...

Experimenatal analysis of the effect of cartilaginous rings on human tracheobronchial flow

NASA Astrophysics Data System (ADS)

Montoya Segnini, Jose; Bocanegra Evans, Humberto; Castillo, Luciano

2016-11-01

We present a set of high-resolution PIV experiments carried out in a refractive index-matched model of a trachea with cartilage rings at Re 2800. Results show a higher vorticity along the walls of the trachea in the model with cartilaginous rings as well as small recirculation areas on the upstream side of the wall cavities created by the rings. Furthermore, the ringed model experiences higher shear stress in the trachea due to the sudden change in the wall position created by the rings. Additionally, small recirculation areas are identified in the cavities between rings. For the smooth model, a stronger separation bubble is observed at the bronchi entrance, generating a stronger shear layer and increasing the wall shear stress on the bottom bronchi wall. The differences observed go against the notion that the main airway, i.e. trachea and main bronchi, may be modeled as smooth. Our results suggest that cartilage rings will have an impact on the wall shear stress and may affect particle deposition, which is of importance in inhaled drug delivery and pollutant deposition in the airway. Additionally, the effects introduced by the rings may change the flow characteristics in further generations.

High shear microfluidics and its application in rheological measurement

NASA Astrophysics Data System (ADS)

Kang, Kai; Lee, L. James; Koelling, Kurt W.

2005-02-01

High shear rheology was explored experimentally in microchannels (150×150 μm). Two aqueous polymer solutions, polyethylene oxide (viscoelastic fluid) and hydroxyethyl cellulose (viscous fluid) were tested. Bagley correction was applied to remove the end effect. Wall slip was investigated with Mooney’s analysis. Shear rates as high as 106 s-1 were obtained in the pressure-driven microchannel flow, allowing a smooth extension of the low shear rheological data obtained from the conventional rheometers. At high shear rates, polymer degradation was observed for PEO solutions at a critical microchannel wall shear stress of 4.1×103 Pa. Stresses at the ends of the microchannel also contributed to PEO degradation significantly.

Hydraulic properties of 3D rough-walled fractures during shearing: An experimental study

NASA Astrophysics Data System (ADS)

Yin, Qian; Ma, Guowei; Jing, Hongwen; Wang, Huidong; Su, Haijian; Wang, Yingchao; Liu, Richeng

2017-12-01

This study experimentally analyzed the influence of shear processes on nonlinear flow behavior through 3D rough-walled rock fractures. A high-precision apparatus was developed to perform stress-dependent fluid flow tests of fractured rocks. Then, water flow tests on rough-walled fractures with different mechanical displacements were conducted. At each shear level, the hydraulic pressure ranged from 0 to 0.6 MPa, and the normal load varied from 7 to 35 kN. The results show that (i) the relationship between the volumetric flow rate and hydraulic gradient of rough-walled fractures can be well fit using Forchheimer's law. Notably, both the linear and nonlinear coefficients in Forchheimer's law decrease during shearing; (ii) a sixth-order polynomial function is used to evaluate the transmissivity based on the Reynolds number of fractures during shearing. The transmissivity exhibits a decreasing trend as the Reynolds number increases and an increasing trend as the shear displacement increases; (iii) the critical hydraulic gradient, critical Reynolds number and equivalent hydraulic aperture of the rock fractures all increase as the shear displacement increases. When the shear displacement varies from 0 to 15 mm, the critical hydraulic gradient ranges from 0.3 to 2.2 for a normal load of 7 kN and increases to 1.8-8.6 for a normal load of 35 kN; and (iv) the Forchheimer law results are evaluated by plotting the normalized transmissivity of the fractures during shearing against the Reynolds number. An increase in the normal load shifts the fitted curves downward. Additionally, the Forchheimer coefficient β decreases with the shear displacement but increases with the applied normal load.

Haemodynamic predictors of a penetrating atherosclerotic ulcer rupture using fluid–structure interaction analysis

PubMed Central

D'Ancona, Giuseppe; Amaducci, Andrea; Rinaudo, Antonino; Pasta, Salvatore; Follis, Fabrizio; Pilato, Michele; Baglini, Roberto

2013-01-01

We present preliminary data on the flow-induced haemodynamic and structural loads exerted on a penetrating atherosclerotic aortic ulcer (PAU). Specifically, one-way fluid–structure interaction analysis was performed on the aortic model reconstructed from a 66-year-old male patient with a PAU that evolved into an intramural haematoma and rupture of the thoracic aorta. The results show that elevated blood pressure (117 mmHg) and low flow velocity at the aortic wall (0.15 m/s2) occurred in the region of the PAU. We also found a low value of time-averaged wall shear stress (1.24 N/m2) and a high value of the temporal oscillation in the wall shear stress (oscillatory shear index = 0.13) in the region of the PAU. After endovascular treatment, these haemodynamic parameters were distributed uniformly on the luminal surface of the stent graft. These findings suggest that wall shear stress could be considered one of the major haemodynamic factors indicating the structural fragility of the PAU wall, which ultimately lead to PAU growth and rupture. PMID:23736658

Evolution of the Die-Wall Pressure during the Compression of Biconvex Tablets: Experimental Results and Comparison with FEM Simulation.

PubMed

Mazel, Vincent; Diarra, Harona; Busignies, Virginie; Tchoreloff, Pierre

2015-12-01

Capping is a classical manufacturing problem for tablets, which is known to affect more biconvex tablets than flat-faced ones. One reason could be the development of a higher residual die-wall pressure during unloading. Unfortunately, contradictory results were published on the subject. In this work, the evolution of the die-wall pressure during the compaction of biconvex tablets was studied experimentally and using finite element method (FEM) modeling. It was compared with the case of flat-faced tablets. Experimental and numerical results showed that during the compression of biconvex tablet, a lower maximum die-wall pressure and a higher residual die-wall pressure were obtained compared with the case of flat-faced tablet. Moreover, both approaches showed, for biconvex tablets, a temporary increase of the die-wall pressure at the end of the unloading phase. FEM demonstrated that this phenomenon was due to a gradual loss of contact between the punch and the tablet from the side to the center. This complex unloading behavior causes the temporary increase of the die-wall pressure and the development of a shear stress between the convex part and the land of the tablet. This could explain the capping tendency of biconvex tablets. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Literature Review of Shear Performance of Light-weight Steel Framing Wall Panels

NASA Astrophysics Data System (ADS)

Zhang, Zhuangnan; Liu, Shen; Liu, Hong

2018-03-01

In this paper, a comprehensive review of light-weight steel framing wall panels was carried out. The structure and force characteristics of light-weight steel framing wall panels were introduced. The testing and theoretical research results on the shear behaviour of light-weight steel framing wall panels were summarized in the domestic and foreign. And combined with the existing standards in China, the author's views and ideas are put forward to the problems in the research field of this kind of structural system.

Can regurgitant flow damage the left atrial endothelium in patients with prosthetic mechanical heart valves?

PubMed

Milo, Simcha; Zarandi, Mehrdad; Gutfinger, Chaim; Gharib, Morteza

2005-05-01

Previous in-vitro studies of mechanical heart valves (MHVs) in the closed position demonstrated the formation of regurgitant flows, with bubbles and jets forming vortices during each systole. The study aim was to determine whether the regurgitant flow observed in patients with MHVs can damage the left atrial endothelium, due to shear stresses exerted on the endothelial layers. This objective has been accomplished by appropriate in-vitro simulation experiments. In these experiments, leakage flow through several commercial MHVs was investigated. The geometry of the set-up closely resembled that of the left atrial anatomy. Water was forced through the slit of a closed MHV and directed toward the hemispherical cup coated with fluorescent paint. The flow field between the valve and the cup was photographed using high-speed videography, from which local velocities were measured, using digital particle imaging velocimetry. Qualitative damage to the surface of the cup was assessed from the amount of fluorescent paint removed from the cup. The experimental results and calculations indicated that flows through the gaps of the closed valves were sufficient to generate strong vortices, with velocities near the atrial wall in the range of 0.5 to 4.0 m/s, depending on the valve. This led to high shear stresses on the left atrial wall, which far exceeded physiologically acceptable levels. The calculated shear stresses exceeded by orders of magnitude the maximum physiologically tolerated stresses. This suggests that shear stresses associated with regurgitant jets in MHVs may damage the endothelial cells, leading to the activation of the inflammatory reaction, enhanced procoagulation, platelet activation and aggregation, and mechanical cell denudation.

Reynolds number invariance of the structure inclination angle in wall turbulence.

PubMed

Marusic, Ivan; Heuer, Weston D C

2007-09-14

Cross correlations of the fluctuating wall-shear stress and the streamwise velocity in the logarithmic region of turbulent boundary layers are reported over 3 orders of magnitude change in Reynolds number. These results are obtained using hot-film and hot-wire anemometry in a wind tunnel facility, and sonic anemometers and a purpose-built wall-shear stress sensor in the near-neutral atmospheric surface layer on the salt flats of Utah's western desert. The direct measurement of fluctuating wall-shear stress in the atmospheric surface layer has not been available before. Structure inclination angles are inferred from the cross correlation results and are found to be invariant over the large range of Reynolds number. The findings justify the prior use of low Reynolds number experiments for obtaining structure angles for near-wall models in the large-eddy simulation of atmospheric surface layer flows.

Experimental study on the bed shear stress under breaking waves

NASA Astrophysics Data System (ADS)

Hao, Si-yu; Xia, Yun-feng; Xu, Hua

2017-06-01

The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1:15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.

Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model.

PubMed

Raben, Jaime S; Hariharan, Prasanna; Robinson, Ronald; Malinauskas, Richard; Vlachos, Pavlos P

2016-03-01

We present advanced particle image velocimetry (PIV) processing, post-processing, and uncertainty estimation techniques to support the validation of computational fluid dynamics analyses of medical devices. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Experimental measurements were performed using time-resolved PIV at five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2000, 5000, and 8000. Images included a twofold increase in spatial resolution in comparison to the previous study. Data was processed using ensemble correlation, dynamic range enhancement, and phase correlations to increase signal-to-noise ratios and measurement accuracy, and to resolve flow regions with large velocity ranges and gradients, which is typical of many blood-contacting medical devices. Parameters relevant to device safety, including shear stress at the wall and in bulk flow, were computed using radial basis functions. In addition, in-field spatially resolved pressure distributions, Reynolds stresses, and energy dissipation rates were computed from PIV measurements. Velocity measurement uncertainty was estimated directly from the PIV correlation plane, and uncertainty analysis for wall shear stress at each measurement location was performed using a Monte Carlo model. Local velocity uncertainty varied greatly and depended largely on local conditions such as particle seeding, velocity gradients, and particle displacements. Uncertainty in low velocity regions in the sudden expansion section of the nozzle was greatly reduced by over an order of magnitude when dynamic range enhancement was applied. Wall shear stress uncertainty was dominated by uncertainty contributions from velocity estimations, which were shown to account for 90-99% of the total uncertainty. This study provides advancements in the PIV processing methodologies over the previous work through increased PIV image resolution, use of robust image processing algorithms for near-wall velocity measurements and wall shear stress calculations, and uncertainty analyses for both velocity and wall shear stress measurements. The velocity and shear stress analysis, with spatially distributed uncertainty estimates, highlights the challenges of flow quantification in medical devices and provides potential methods to overcome such challenges.

Small hydrogen/oxygen rocket flowfield behavior from heat flux measurements

NASA Technical Reports Server (NTRS)

Reed, Brian D.

1993-01-01

The mixing and heat transfer phenomena in small rocket flow fields with fuel film cooling is not well understood. An instrumented, water-cooled chamber with a gaseous hydrogen/gaseous oxygen injector was used to gather steady-state inner and outer wall temperature profiles. The chamber was tested at 414 kPa (60 psia) chamber pressure, from mixture ratios of 3.41 to 8.36. Sixty percent of the fuel was used for film cooling. These temperature profiles were used as boundary conditions in a finite element analysis program, MSC/NASTRAN, to calculate the local radial and axial heat fluxes in the chamber wall. The normal heat fluxes were then calculated and used as a diagnostic of the rocket's flow field behavior. The normal heat fluxes determined were on the order of 1.0 to 3.0 MW/meters squared (0.6 to 1.8 Btu/sec-inches squared). In the cases where mixture ratio was 5 or above, there was a sharp local heat flux maximum in the barrel section of the chamber. This local maximum seems to indicate a reduction or breakdown of the fuel film cooling layer, possibly due to increased mixing in the shear layer between the film and core flows. However, the flow was thought to be completely laminar, as the throat Reynolds numbers were below 50,000 for all the cases. The increased mixing in the shear layer in the higher mixture ratio cases appeared not to be due to the transition of the flow from laminar to turbulent, but rather due to increased reactions between the hydrogen film and oxidizer-rich core flows.

The impact of wall shear stress and pressure drop on the stability of the atherosclerotic plaque.

PubMed

Li, Zhi-Yong; Taviani, Valentina; Gillard, Jonathan H

2008-01-01

Rupture of vulnerable atheromatous plaque in the carotid and coronary arteries often leads to stroke and heart attack respectively. The mechanism of blood flow and plaque rupture in stenotic arteries is still not fully understood. A three dimensional rigid wall model was solved under steady state conditions and unsteady conditions by assuming a time-varying inlet velocity profile to investigate the relative importance of axial forces and pressure drops in arteries with asymmetric stenosis. Flow-structure interactions were investigated for the same geometry and the results were compared with those retrieved with the corresponding 2D cross-section structural models. The Navier-Stokes equations were used as the governing equations for the fluid. The tube wall was assumed hyperelastic, homogeneous, isotropic and incompressible. The analysis showed that the three dimensional behavior of velocity, pressure and wall shear stress is in general very different from that predicted by cross-section models. Pressure drop across the stenosis was found to be much higher than shear stress. Therefore, pressure may be the more important mechanical trigger for plaque rupture other than shear stress, although shear stress is closely related to plaque formation and progression.

Debonding Stress Concentrations in a Pressurized Lobed Sandwich-Walled Generic Cryogenic Tank

NASA Technical Reports Server (NTRS)

Ko, William L.

2004-01-01

A finite-element stress analysis has been conducted on a lobed composite sandwich tank subjected to internal pressure and cryogenic cooling. The lobed geometry consists of two obtuse circular walls joined together with a common flat wall. Under internal pressure and cryogenic cooling, this type of lobed tank wall will experience open-mode (a process in which the honeycomb is stretched in the depth direction) and shear stress concentrations at the junctures where curved wall changes into flat wall (known as a curve-flat juncture). Open-mode and shear stress concentrations occur in the honeycomb core at the curve-flat junctures and could cause debonding failure. The levels of contributions from internal pressure and temperature loading to the open-mode and shear debonding failure are compared. The lobed fuel tank with honeycomb sandwich walls has been found to be a structurally unsound geometry because of very low debonding failure strengths. The debonding failure problem could be eliminated if the honeycomb core at the curve-flat juncture is replaced with a solid core.

Gas Near a Wall: Shortened Mean Free Path, Reduced Viscosity, and the Manifestation of the Knudsen Layer in the Navier-Stokes Solution of a Shear Flow

NASA Astrophysics Data System (ADS)

Abramov, Rafail V.

2018-06-01

For the gas near a solid planar wall, we propose a scaling formula for the mean free path of a molecule as a function of the distance from the wall, under the assumption of a uniform distribution of the incident directions of the molecular free flight. We subsequently impose the same scaling onto the viscosity of the gas near the wall and compute the Navier-Stokes solution of the velocity of a shear flow parallel to the wall. Under the simplifying assumption of constant temperature of the gas, the velocity profile becomes an explicit nonlinear function of the distance from the wall and exhibits a Knudsen boundary layer near the wall. To verify the validity of the obtained formula, we perform the Direct Simulation Monte Carlo computations for the shear flow of argon and nitrogen at normal density and temperature. We find excellent agreement between our velocity approximation and the computed DSMC velocity profiles both within the Knudsen boundary layer and away from it.

Axial compression behavior and partial composite action of SC walls in safety-related nuclear facilities

NASA Astrophysics Data System (ADS)

Zhang, Kai

Steel-plate reinforced concrete (SC) composite walls typically consist of thick concrete walls with two exterior steel faceplates. The concrete core is sandwiched between the two steel faceplates, and the faceplates are attached to the concrete core using shear connectors, for example, ASTM A108 steel headed shear studs. The shear connectors and the concrete infill enhance the stability of the steel faceplates, and the faceplates serve as permanent formwork for concrete placement. SC composite walls were first introduced in the 1980's in Japan for nuclear power plant (NPP) structures. They are used in the new generation of nuclear power plants (GIII+) and being considered for small modular reactors (SMR) due to their structural efficiency, economy, safety, and construction speed. Steel faceplates can potentially undergo local buckling at certain locations of NPP structures where compressive forces are significant. The steel faceplates are usually thin (0.25 to 1.50 inches in Customary units, or 6.5 to 38 mm in SI units) to maintain economical and constructional efficiency, the geometric imperfections and locked-in stresses induced during construction make them more vulnerable to local buckling. Accidental thermal loading may also reduce the compressive strength and exacerbate the local buckling potential of SC composite walls. This dissertation presents the results from experimental and numerical investigations of the compressive behavior of SC composite walls at ambient and elevated temperatures. The results are used to establish a slenderness limit to prevent local buckling before yielding of the steel faceplates and to develop a design approach for calculating the compressive strength of SC composite walls with non-slender and slender steel faceplates at ambient and elevated temperatures. Composite action in SC walls is achieved by the embedment of shear connectors into the concrete core. The strength and stiffness of shear connectors govern the level of composite action. This level of partial composite action can influence the behavior and stiffness of SC composite walls. This dissertation presents numerical investigations of the level of partial composite action and its influence on the flexural stiffness of SC walls. The results are used to propose design criteria for steel headed shear studs, such as their size, spacing, and strength.

Influence of Zero-Shear on Yeast Development

NASA Technical Reports Server (NTRS)

McGinnis, Michael R.

1997-01-01

The objective of the research was to begin evaluating the effect of zero-shear on the development of the cell wall of Saccharomyces cerevisiae employing the High Aspect Rotating-Wall Vessel (HARV) NASA bioreactor. This particular yeast has enormous potential for research as a model eukaryotic system on the International Space Station, as well as the production of food stuffs' at the future lunar colony. Because the cell wall is the barrier between the cell and the environment, its form and function as influenced by microgravity is of great importance. Morphologic studies revealed that the circularity and total area of the individual yeast cells were essentially the same in both the control and test HARV's. The growth rates were also essentially the same. In zero-shear, the yeast grew in clumps consisting of rudimentary pseudohyphae in contrast to solitary budding cells in the control. Based upon mechanical and sonic shear applied to the yeast cells, those grown in zero-shear had stronger cell walls and septa. This suggests that there are structural differences, most likely related to the chitin skeleton of the cell wall. From this research further NASA support was obtained to continue the work. Investigations will deal with gene expression and ultrastructure. These will lead to a clearer assessment of the value of S. cerevisiae eukaryotic as a model for space station research.

Role of Wall Shear Stress in Cryptosporidium parvum Oocyst Attachment to Environmental Biofilms.

PubMed

Luo, Xia; Jedlicka, Sabrina S; Jellison, Kristen L

2017-12-15

This study investigated Cryptosporidium parvum oocyst deposition onto biofilms as a function of shear stress under laminar or turbulent flow. Annular rotating bioreactors were used to grow stabilized stream biofilms at shear stresses ranging from 0.038 to 0.46 Pa. These steady-state biofilms were then used to assess the impact of hydrodynamic conditions on C. parvum oocyst attachment. C. parvum deposition onto biofilms followed a pseudo-second-order model under both laminar (after a lag phase) and turbulent flows. The total number of oocysts attached to the biofilm at steady state decreased as the hydrodynamic wall shear stress increased. The oocyst deposition rate constant increased with shear stress but decreased at high shear, suggesting that increasing wall shear stress results in faster attachment of Cryptosporidium due to higher mass transport until the shear forces exceed a critical limit that prevents oocyst attachment. These data show that oocyst attachment in the short and long term are impacted differently by shear: higher shear (to a certain limit) may be associated with faster initial oocyst attachment, but lower shear is associated with greater numbers of oocysts attached at equilibrium. IMPORTANCE This research provides experimental evidence to demonstrate that shear stress plays a critical role in protozoan-pathogen transport and deposition in environmental waters. The data presented in this work expand scientific understanding of Cryptosporidium attachment and fate, which will further influence the development of timely and accurate sampling strategies, as well as advanced water treatment technologies, to target protozoan pathogens in surface waters that serve as municipal drinking water sources. Copyright © 2017 American Society for Microbiology.

Shear-Sensitive Liquid Crystal Coating Method Applied Through Transparent Test Surfaces

NASA Technical Reports Server (NTRS)

Reda, Daniel C.; Wilder, Michael C.

1999-01-01

Research conducted at NASA Ames Research Center has shown that the color-change response of a shear-sensitive liquid crystal coating (SSLCC) to aerodynamic shear depends on both the magnitude of the local shear vector and its direction relative to the observer's in-plane line of sight. In conventional applications, the surface of the SSLCC exposed to aerodynamic shear is illuminated with white light from the normal direction and observed from an oblique above-plane view angle of order 30 deg. In this top-light/top-view mode, shear vectors with components directed away from the observer cause the SSLCC to exhibit color-change responses. At any surface point, the maximum color change (measured from the no-shear red or orange color) always occurs when the local vector is aligned with, and directed away from, the observer. The magnitude of the color change at this vector-observer-aligned orientation scales directly with shear stress magnitude. Conversely, any surface point exposed to a shear vector with a component directed toward the observer exhibits a non-color-change response, always characterized by a rusty-red or brown color, independent of both shear magnitude and direction. These unique, highly directional color-change responses of SSLCCs to aerodynamic shear allow for the full-surface visualization and measurement of continuous shear stress vector distributions. The objective of the present research was to investigate application of the SSLCC method through a transparent test surface. In this new back-light/back-view mode, the exposed surface of the SSLCC would be subjected to aerodynamic shear stress while the contact surface between the SSLCC and the solid, transparent wall would be illuminated and viewed in the same geometrical arrangement as applied in conventional applications. It was unknown at the outset whether or not color-change responses would be observable from the contact surface of the SSLCC, and, if seen, how these color-change responses might relate to those observed in standard practice.

Turbulent structures of non-Newtonian solutions containing rigid polymers

NASA Astrophysics Data System (ADS)

Mohammadtabar, M.; Sanders, R. S.; Ghaemi, S.

2017-10-01

The turbulent structure of a channel flow of Xanthan Gum (XG) polymer solution is experimentally investigated and compared with water flow at a Reynolds number of Re = 7200 (based on channel height and properties of water) and Reτ = 220 (based on channel height and friction velocity, uτ0). The polymer concentration is varied from 75, 100, and 125 ppm to reach the point of maximum drag reduction (MDR). Measurements are carried out using high-resolution, two-component Particle Image Velocimetry (PIV) to capture the inner and outer layer turbulence. The measurements showed that the logarithmic layer shifts away from the wall with increasing polymer concentration. The slopes of the mean velocity profile for flows containing 100 and 125 ppm XG are greater than that measured for XG at 75 ppm, which is parallel with the slope obtained for deionized water. The increase in slope results in thickening buffer layer. At MDR, the streamwise Reynolds stresses are as large as those of the Newtonian flow while the wall-normal Reynolds stresses and Reynolds shear stresses are significantly attenuated. The sweep-dominated region in the immediate vicinity of the wall extends further from the wall with increasing polymer concentration. The near-wall skewness intensifies towards positive streamwise fluctuations and covers a larger wall-normal length at larger drag reduction values. The quadrant analysis at y + 0 = 25 shows that the addition of polymers inclines the principal axis of v versus u plot to almost zero (horizontal) as the joint probability density function of fluctuations becomes symmetric with respect to the u axis at MDR. The reduction of turbulence production is mainly associated with the attenuation of the ejection motions. The spatial-correlation of the fluctuating velocity field shows that increasing the polymer concentration increases the spatial coherence of u fluctuations in the streamwise direction while they appear to have the opposite effect in the wall-normal direction. The proper orthogonal decomposition of velocity fluctuations shows that the inclined shear layer structure of Newtonian wall flows becomes horizontal at the MDR and does not contribute to turbulence production.

Effects of wall curvature on turbulence statistics

NASA Technical Reports Server (NTRS)

Moser, R. D.; Moin, P.

1985-01-01

A three-dimensional, time-dependent, direct numerical simulation of low-Reynolds number turbulent flow in a mildly curved channel was performed, and the results examined to determine the mechanism by which curvature affects wall-bounded turbulent shear flows. A spectral numerical method with about one-million modes was employed, and no explicit subgrid scale model was used. The effects of curvature on this flow were determined by comparing the concave and convex sides of the channel. The observed effects are consistent with experimental observations for mild curvature. The most significant difference in the turbulence statistics between the concave and convex sides is in the Reynolds shear stress. This is accompanied by significant differences in the terms of the Reynolds shear stress balance equations. In addition, it was found that stationary Taylor-Goertler vortices were present and that they had a significant effect on the flow by contributing to the mean Reynolds shear stress, and by enhancing the difference between the wall shear stresses.

Small Scale Mass Flow Plug Calibration

NASA Technical Reports Server (NTRS)

Sasson, Jonathan

2015-01-01

A simple control volume model has been developed to calculate the discharge coefficient through a mass flow plug (MFP) and validated with a calibration experiment. The maximum error of the model in the operating region of the MFP is 0.54%. The model uses the MFP geometry and operating pressure and temperature to couple continuity, momentum, energy, an equation of state, and wall shear. Effects of boundary layer growth and the reduction in cross-sectional flow area are calculated using an in- integral method. A CFD calibration is shown to be of lower accuracy with a maximum error of 1.35%, and slower by a factor of 100. Effects of total pressure distortion are taken into account in the experiment. Distortion creates a loss in flow rate and can be characterized by two different distortion descriptors.

Application of kinematic vorticity and gold mineralization for the wall rock alterations of shear zone at Dungash gold mining, Central Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Kassem, Osama M. K.; Abd El Rahim, Said H.; El Nashar, EL Said R.; AL Kahtany, Kaled M.

2016-11-01

The use of porphyroclasts rotating in a flowing matrix to estimate mean kinematic vorticity number (Wm) is important for quantifying the relative contributions of pure and simple shear in wall rocks alterations of shear zone at Dungash gold mine. Furthermore, it shows the relationship between the gold mineralization and deformation and also detects the orientation of rigid objects during progressive deformation. The Dungash gold mine area is situated in an EW-trending quartz vein along a shear zone in metavolcanic and metasedimentary host rocks in the Eastern Desert of Egypt. These rocks are associated with the major geologic structures which are attributed to various deformational stages of the Neoproterozoic basement rocks. We conclude that finite strain in the deformed rocks is of the same order of magnitude for all units of metavolcano-sedimentary rocks. The kinematic vorticity number for the metavolcanic and metasedimentary samples in the Dungash area range from 0.80 to 0.92, and together with the strain data suggest deviations from simple shear. It is concluded that nappe stacking occurred early during the underthrusting event probably by brittle imbrication and that ductile strain was superimposed on the nappe structure during thrusting. Furthermore, we conclude that disseminated mineralization, chloritization, carbonatization and silicification of the wall rocks are associated with fluids migrating along shearing, fracturing and foliation of the metamorphosed wall rocks.

Distinct molecular and cellular contributions to stabilizing selectin-mediated rolling under flow

PubMed Central

Yago, Tadayuki; Leppänen, Anne; Qiu, Haiying; Marcus, Warren D.; Nollert, Matthias U.; Zhu, Cheng; Cummings, Richard D.; McEver, Rodger P.

2002-01-01

Leukocytes roll on selectins at nearly constant velocities over a wide range of wall shear stresses. Ligand-coupled microspheres roll faster on selectins and detach quickly as wall shear stress is increased. To examine whether the superior performance of leukocytes reflects molecular features of native ligands or cellular properties that favor selectin-mediated rolling, we coupled structurally defined selectin ligands to microspheres or K562 cells and compared their rolling on P-selectin. Microspheres bearing soluble P-selectin glycoprotein ligand (sPSGL)-1 or 2-glycosulfopeptide (GSP)-6, a GSP modeled after the NH2-terminal P-selectin–binding region of PSGL-1, rolled equivalently but unstably on P-selectin. K562 cells displaying randomly coupled 2-GSP-6 also rolled unstably. In contrast, K562 cells bearing randomly coupled sPSGL-1 or 2-GSP-6 targeted to a membrane-distal region of the presumed glycocalyx rolled more like leukocytes: rolling steps were more uniform and shear resistant, and rolling velocities tended to plateau as wall shear stress was increased. K562 cells treated with paraformaldehyde or methyl-β-cyclodextrin before ligand coupling were less deformable and rolled unstably like microspheres. Cells treated with cytochalasin D were more deformable, further resisted detachment, and rolled slowly despite increases in wall shear stress. Thus, stable, shear-resistant rolling requires cellular properties that optimize selectin–ligand interactions. PMID:12177042

Extrema principles of entrophy production and energy dissipation in fluid mechanics

NASA Technical Reports Server (NTRS)

Horne, W. Clifton; Karamcheti, Krishnamurty

1988-01-01

A survey is presented of several extrema principles of energy dissipation as applied to problems in fluid mechanics. An exact equation is derived for the dissipation function of a homogeneous, isotropic, Newtonian fluid, with terms associated with irreversible compression or expansion, wave radiation, and the square of the vorticity. By using entropy extrema principles, simple flows such as the incompressible channel flow and the cylindrical vortex are identified as minimal dissipative distributions. The principal notions of stability of parallel shear flows appears to be associated with a maximum dissipation condition. These different conditions are consistent with Prigogine's classification of thermodynamic states into categories of equilibrium, linear nonequilibrium, and nonlinear nonequilibrium thermodynamics; vortices and acoustic waves appear as examples of dissipative structures. The measurements of a typical periodic shear flow, the rectangular wall jet, show that direct measurements of the dissipative terms are possible.

Fluid dynamics during Random Positioning Machine micro-gravity experiments

NASA Astrophysics Data System (ADS)

Leguy, Carole A. D.; Delfos, René; Pourquie, Mathieu J. B. M.; Poelma, Christian; Westerweel, Jerry; van Loon, Jack J. W. A.

2017-06-01

A Random Positioning Machine (RPM) is a device used to study the role of gravity on biological systems. This is accomplished through continuous reorientation of the sample such that the net influence of gravity is randomized over time. The aim of this study is to predict fluid flow behavior during such RPM simulated microgravity studies, which may explain differences found between RPM and space flight experiments. An analytical solution is given for a cylinder as a model for an experimental container. Then, a dual-axis rotating frame is used to mimic the motion characteristics of an RPM with sinusoidal rotation frequencies of 0.2 Hz and 0.1 Hz while Particle Image Velocimetry is used to measure the velocity field inside a flask. To reproduce the same experiment numerically, a Direct Numerical Simulation model is used. The analytical model predicts that an increase in the Womersley number leads to higher shear stresses at the cylinder wall and decrease in fluid angular velocity inside the cylinder. The experimental results show that periodic single-axis rotation induces a fluid motion parallel to the wall and that a complex flow is observed for two-axis rotation with a maximum wall shear stress of 8.0 mPa (80 mdyne /cm2). The experimental and numerical results show that oscillatory motion inside an RPM induces flow motion that can, depending on the experimental samples, reduce the quality of the simulated microgravity. Thus, it is crucial to determine the appropriate oscillatory frequency of the axes to design biological experiments.

Bayesian decision and mixture models for AE monitoring of steel-concrete composite shear walls

NASA Astrophysics Data System (ADS)

Farhidzadeh, Alireza; Epackachi, Siamak; Salamone, Salvatore; Whittaker, Andrew S.

2015-11-01

This paper presents an approach based on an acoustic emission technique for the health monitoring of steel-concrete (SC) composite shear walls. SC composite walls consist of plain (unreinforced) concrete sandwiched between steel faceplates. Although the use of SC system construction has been studied extensively for nearly 20 years, little-to-no attention has been devoted to the development of structural health monitoring techniques for the inspection of damage of the concrete behind the steel plates. In this work an unsupervised pattern recognition algorithm based on probability theory is proposed to assess the soundness of the concrete infill, and eventually provide a diagnosis of the SC wall’s health. The approach is validated through an experimental study on a large-scale SC shear wall subjected to a displacement controlled reversed cyclic loading.

Log-layer mismatch and modeling of the fluctuating wall stress in wall-modeled large-eddy simulations

NASA Astrophysics Data System (ADS)

Yang, Xiang I. A.; Park, George Ilhwan; Moin, Parviz

2017-10-01

Log-layer mismatch refers to a chronic problem found in wall-modeled large-eddy simulation (WMLES) or detached-eddy simulation, where the modeled wall-shear stress deviates from the true one by approximately 15 % . Many efforts have been made to resolve this mismatch. The often-used fixes, which are generally ad hoc, include modifying subgrid-scale stress models, adding a stochastic forcing, and moving the LES-wall-model matching location away from the wall. An analysis motivated by the integral wall-model formalism suggests that log-layer mismatch is resolved by the built-in physics-based temporal filtering. In this work we investigate in detail the effects of local filtering on log-layer mismatch. We show that both local temporal filtering and local wall-parallel filtering resolve log-layer mismatch without moving the LES-wall-model matching location away from the wall. Additionally, we look into the momentum balance in the near-wall region to provide an alternative explanation of how LLM occurs, which does not necessarily rely on the numerical-error argument. While filtering resolves log-layer mismatch, the quality of the wall-shear stress fluctuations predicted by WMLES does not improve with our remedy. The wall-shear stress fluctuations are highly underpredicted due to the implied use of LES filtering. However, good agreement can be found when the WMLES data are compared to the direct numerical simulation data filtered at the corresponding WMLES resolutions.

Pressure and wall shear stress in blood hammer - Analytical theory.

PubMed

Mei, Chiang C; Jing, Haixiao

2016-10-01

We describe an analytical theory of blood hammer in a long and stiffened artery due to sudden blockage. Based on the model of a viscous fluid in laminar flow, we derive explicit expressions of oscillatory pressure and wall shear stress. To examine the effects on local plaque formation we also allow the blood vessel radius to be slightly nonuniform. Without resorting to discrete computation, the asymptotic method of multiple scales is utilized to deal with the sharp contrast of time scales. The effects of plaque and blocking time on blood pressure and wall shear stress are studied. The theory is validated by comparison with existing water hammer experiments. Copyright © 2016. Published by Elsevier Inc.

Power Doppler Ultrasonography and Shear Wave Elastography as Complementary Imaging Methods for Suspected Local Breast Cancer Recurrence.

PubMed

Jales, Rodrigo Menezes; Dória, Maira Teixeira; Serra, Kátia Piton; Miranda, Mila Meneguelli; Menossi, Carlos Alberto; Schumacher, Klaus; Sarian, Luis Otávio

2018-06-01

To prospectively investigate the diagnostic accuracy and clinical consequences of power Doppler morphologic criteria and shear wave elastography (SWE) as complementary imaging methods for evaluation of suspected local breast cancer recurrence in the ipsilateral breast or chest wall. Thirty-two breast masses with a suspicion of local breast cancer recurrence on B-mode ultrasonography underwent complementary power Doppler and SWE evaluations. Power Doppler morphologic criteria were classified as avascular, hypovascular, or hypervascular. Shear wave elastography was classified according to a 5-point scale (SWE score) and SWE maximum elasticity. Diagnostic accuracy was assessed by the sensitivity, specificity, and area under the curve. A decision curve analysis assessed clinical consequences of each method. The reference standard for diagnosis was defined as core needle or excisional biopsy. Histopathologic examinations revealed 9 (28.2%) benign and 23 (71.8%) malignant cases. Power Doppler ultrasonography (US) had sensitivity of 34.8% (95% confidence interval [CI], 6.6%-62.9%) and specificity of 45.4% (95% CI, 19.3%-71.5%). The SWE score (≥3) had sensitivity of 87.0% (95% CI, 66.4%-97.2%) and specificity of 44.4% (95% CI, 13.7%-78.8%). The SWE maximum elasticity (velocity > 6.5cm/s) had sensitivity of 87% (95% CI, 66.4%-97.2%) and specificity of 77.8% (95% CI, 40.0% to 97.2%). The areas under the curves for the SWE score and SWE maximum elasticity were 0.71 (95% CI, 0.53-0.87) and 0.82 (95% CI, 0.64-0.93), respectively (P = .32). Power Doppler US is unsuitable for discrimination between local breast cancer recurrence and fibrosis. Although the SWE score and SWE maximum elasticity can make this discrimination, the use of these methods to determine biopsy may lead to poorer clinical outcomes than the current practice of performing biopsies of all suspicious masses. © 2017 by the American Institute of Ultrasound in Medicine.

Direct and Large Eddy Simulation of non-equilibrium wall-bounded turbulent flows

NASA Astrophysics Data System (ADS)

Park, Hee-Jun

2005-11-01

The performance of several existing SGS models in non-equilibrium wall-bounded turbulent flows is investigated through comparisons of LES and DNS. The test problem is a shear-driven three-dimensional turbulent channel flow at base Reτ˜210 established by impulsive motion of one of the channel walls in the spanwise direction with a spanwise velocity equal to 3/4 of the bulk mean velocity in the channel. The DNS and LES are performed using pseudo-spectral methods with resolutions of 128x128x129 and 32x64x65, respectively. The SGS models tested include the nonlinear Interactions Approximation model (NIA) [Haliloglu and Akhavan (2004)], the Dynamic Smagorinsky model (DSM) [Germano et al. (1991)], and the Dynamic Mixed Model (DMM) [Zang et al. (1993)]. The results show that NIA gives the best overall agreement with DNS. Both DMM and DSM over-predict the decay of the mean streamwise wall shear stress on the moving wall, while NIA gives results in close agreements with DNS. Similarly, NIA gives the best agreement with DNS in the prediction of the mean velocity, the higher-order turbulence statistics, and the lag angle between the mean shear and the turbulent shear stress. These results suggest that non-equilibrium wall-bounded turbulent flows can be accurately computed by LES with NIA as the SGS model.

Irrigation dynamics associated with positive pressure, apical negative pressure and passive ultrasonic irrigations: a computational fluid dynamics analysis.

PubMed

Chen, José Enrique; Nurbakhsh, Babak; Layton, Gillian; Bussmann, Markus; Kishen, Anil

2014-08-01

Complexities in root canal anatomy and surface adherent biofilm structures remain as challenges in endodontic disinfection. The ability of an irrigant to penetrate into the apical region of a canal, along with its interaction with the root canal walls, will aid in endodontic disinfection. The aim of this study was to qualitatively examine the irrigation dynamics of syringe irrigation with different needle tip designs (open-ended and closed-ended), apical negative pressure irrigation with the EndoVac® system, and passive ultrasonic-assisted irrigation, using a computational fluid dynamics model. Syringe-based irrigation with a side-vented needle showed a higher wall shear stress than the open-ended but was localised to a small region of the canal wall. The apical negative pressure mode of irrigation generated the lowest wall shear stress, while the passive-ultrasonic irrigation group showed the highest wall shear stress along with the greatest magnitude of velocity. © 2013 The Authors. Australian Endodontic Journal © 2013 Australian Society of Endodontology.

Characterisation of minimal-span plane Couette turbulence with pressure gradients

NASA Astrophysics Data System (ADS)

Sekimoto, Atsushi; Atkinson, Callum; Soria, Julio

2018-04-01

The turbulence statistics and dynamics in the spanwise-minimal plane Couette flow with pressure gradients, so-called, Couette-Poiseuille (C-P) flow, are investigated using direct numerical simulation. The large-scale motion is limited in the spanwise box dimension as in the minimal-span channel turbulence of Flores & Jiménez (Phys. Fluids, vol. 22, 2010, 071704). The effect of the top wall, where normal pressure-driven Poiseuille flow is realised, is distinguished from the events on the bottom wall, where the pressure gradient results in mild or almost-zero wall-shear stress. A proper scaling of turbulence statistics in minimal-span C-P flows is presented. Also the ‘shear-less’ wall-bounded turbulence, where the Corrsin shear parameter is very weak compared to normal wall-bounded turbulence, represents local separation, which is also observed as spanwise streaks of reversed flow in full-size plane C-P turbulence. The local separation is a multi-scale event, which grows up to the order of the channel height even in the minimal-span geometry.

Stability of carotid artery under steady-state and pulsatile blood flow: a fluid-structure interaction study.

PubMed

Saeid Khalafvand, Seyed; Han, Hai-Chao

2015-06-01

It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid-structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17-23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo.

Stability of Carotid Artery Under Steady-State and Pulsatile Blood Flow: A Fluid–Structure Interaction Study

PubMed Central

Saeid Khalafvand, Seyed; Han, Hai-Chao

2015-01-01

It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid–structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17–23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo. PMID:25761257

Structural state diagram of concentrated suspensions of jammed soft particles in oscillatory shear flow

NASA Astrophysics Data System (ADS)

Khabaz, Fardin; Cloitre, Michel; Bonnecaze, Roger T.

2018-03-01

In a recent study [Khabaz et al., Phys. Rev. Fluids 2, 093301 (2017), 10.1103/PhysRevFluids.2.093301], we showed that jammed soft particle glasses (SPGs) crystallize and order in steady shear flow. Here we investigate the rheology and microstructures of these suspensions in oscillatory shear flow using particle-dynamics simulations. The microstructures in both types of flows are similar, but their evolutions are very different. In both cases the monodisperse and polydisperse suspensions form crystalline and layered structures, respectively, at high shear rates. The crystals obtained in the oscillatory shear flow show fewer defects compared to those in the steady shear. SPGs remain glassy for maximum oscillatory strains less than about the yield strain of the material. For maximum strains greater than the yield strain, microstructural and rheological transitions occur for SPGs. Polydisperse SPGs rearrange into a layered structure parallel to the flow-vorticity plane for sufficiently high maximum shear rates and maximum strains about 10 times greater than the yield strain. Monodisperse suspensions form a face-centered cubic (FCC) structure when the maximum shear rate is low and hexagonal close-packed (HCP) structure when the maximum shear rate is high. In steady shear, the transition from a glassy state to a layered one for polydisperse suspensions included a significant induction strain before the transformation. In oscillatory shear, the transformation begins to occur immediately and with different microstructural changes. A state diagram for suspensions in large amplitude oscillatory shear flow is found to be in close but not exact agreement with the state diagram for steady shear flow. For more modest amplitudes of around one to five times the yield strain, there is a transition from a glassy structure to FCC and HCP crystals, at low and high frequencies, respectively, for monodisperse suspensions. At moderate frequencies, the transition is from glassy to HCP via an intermediate FCC phase.

Assessment of shear stress related parameters in the carotid bifurcation using mouse-specific FSI simulations.

PubMed

De Wilde, David; Trachet, Bram; Debusschere, Nic; Iannaccone, Francesco; Swillens, Abigail; Degroote, Joris; Vierendeels, Jan; De Meyer, Guido R Y; Segers, Patrick

2016-07-26

The ApoE(-)(/)(-) mouse is a common small animal model to study atherosclerosis, an inflammatory disease of the large and medium sized arteries such as the carotid artery. It is generally accepted that the wall shear stress, induced by the blood flow, plays a key role in the onset of this disease. Wall shear stress, however, is difficult to derive from direct in vivo measurements, particularly in mice. In this study, we integrated in vivo imaging (micro-Computed Tomography-µCT and ultrasound) and fluid-structure interaction (FSI) modeling for the mouse-specific assessment of carotid hemodynamics and wall shear stress. Results were provided for 8 carotid bifurcations of 4 ApoE(-)(/)(-) mice. We demonstrated that accounting for the carotid elasticity leads to more realistic flow waveforms over the complete domain of the model due to volume buffering capacity in systole. The 8 simulated cases showed fairly consistent spatial distribution maps of time-averaged wall shear stress (TAWSS) and relative residence time (RRT). Zones with reduced TAWSS and elevated RRT, potential indicators of atherosclerosis-prone regions, were located mainly at the outer sinus of the external carotid artery. In contrast to human carotid hemodynamics, no flow recirculation could be observed in the carotid bifurcation region. Copyright © 2015 Elsevier Ltd. All rights reserved.

Aortic dissection simulation models for clinical support: fluid-structure interaction vs. rigid wall models.

PubMed

Alimohammadi, Mona; Sherwood, Joseph M; Karimpour, Morad; Agu, Obiekezie; Balabani, Stavroula; Díaz-Zuccarini, Vanessa

2015-04-15

The management and prognosis of aortic dissection (AD) is often challenging and the use of personalised computational models is being explored as a tool to improve clinical outcome. Including vessel wall motion in such simulations can provide more realistic and potentially accurate results, but requires significant additional computational resources, as well as expertise. With clinical translation as the final aim, trade-offs between complexity, speed and accuracy are inevitable. The present study explores whether modelling wall motion is worth the additional expense in the case of AD, by carrying out fluid-structure interaction (FSI) simulations based on a sample patient case. Patient-specific anatomical details were extracted from computed tomography images to provide the fluid domain, from which the vessel wall was extrapolated. Two-way fluid-structure interaction simulations were performed, with coupled Windkessel boundary conditions and hyperelastic wall properties. The blood was modelled using the Carreau-Yasuda viscosity model and turbulence was accounted for via a shear stress transport model. A simulation without wall motion (rigid wall) was carried out for comparison purposes. The displacement of the vessel wall was comparable to reports from imaging studies in terms of intimal flap motion and contraction of the true lumen. Analysis of the haemodynamics around the proximal and distal false lumen in the FSI model showed complex flow structures caused by the expansion and contraction of the vessel wall. These flow patterns led to significantly different predictions of wall shear stress, particularly its oscillatory component, which were not captured by the rigid wall model. Through comparison with imaging data, the results of the present study indicate that the fluid-structure interaction methodology employed herein is appropriate for simulations of aortic dissection. Regions of high wall shear stress were not significantly altered by the wall motion, however, certain collocated regions of low and oscillatory wall shear stress which may be critical for disease progression were only identified in the FSI simulation. We conclude that, if patient-tailored simulations of aortic dissection are to be used as an interventional planning tool, then the additional complexity, expertise and computational expense required to model wall motion is indeed justified.

Time-dependent rheological behavior of natural polysaccharide xanthan gum solutions in interrupted shear and step-incremental/reductional shear flow fields

NASA Astrophysics Data System (ADS)

Lee, Ji-Seok; Song, Ki-Won

2015-11-01

The objective of the present study is to systematically elucidate the time-dependent rheological behavior of concentrated xanthan gum systems in complicated step-shear flow fields. Using a strain-controlled rheometer (ARES), step-shear flow behaviors of a concentrated xanthan gum model solution have been experimentally investigated in interrupted shear flow fields with a various combination of different shear rates, shearing times and rest times, and step-incremental and step-reductional shear flow fields with various shearing times. The main findings obtained from this study are summarized as follows. (i) In interrupted shear flow fields, the shear stress is sharply increased until reaching the maximum stress at an initial stage of shearing times, and then a stress decay towards a steady state is observed as the shearing time is increased in both start-up shear flow fields. The shear stress is suddenly decreased immediately after the imposed shear rate is stopped, and then slowly decayed during the period of a rest time. (ii) As an increase in rest time, the difference in the maximum stress values between the two start-up shear flow fields is decreased whereas the shearing time exerts a slight influence on this behavior. (iii) In step-incremental shear flow fields, after passing through the maximum stress, structural destruction causes a stress decay behavior towards a steady state as an increase in shearing time in each step shear flow region. The time needed to reach the maximum stress value is shortened as an increase in step-increased shear rate. (iv) In step-reductional shear flow fields, after passing through the minimum stress, structural recovery induces a stress growth behavior towards an equilibrium state as an increase in shearing time in each step shear flow region. The time needed to reach the minimum stress value is lengthened as a decrease in step-decreased shear rate.

Turbulent flows over superhydrophobic surfaces with shear-dependent slip length

NASA Astrophysics Data System (ADS)

Khosh Aghdam, Sohrab; Seddighi, Mehdi; Ricco, Pierre

2015-11-01

Motivated by recent experimental evidence, shear-dependent slip length superhydrophobic surfaces are studied. Lyapunov stability analysis is applied in a 3D turbulent channel flow and extended to the shear-dependent slip-length case. The feedback law extracted is recognized for the first time to coincide with the constant-slip-length model widely used in simulations of hydrophobic surfaces. The condition for the slip parameters is found to be consistent with the experimental data and with values from DNS. The theoretical approach by Fukagata (PoF 18.5: 051703) is employed to model the drag-reduction effect engendered by the shear-dependent slip-length surfaces. The estimated drag-reduction values are in very good agreement with our DNS data. For slip parameters and flow conditions which are potentially realizable in the lab, the maximum computed drag reduction reaches 50%. The power spent by the turbulent flow on the walls is computed, thereby recognizing the hydrophobic surfaces as a passive-absorbing drag-reduction method, as opposed to geometrically-modifying techniques that do not consume energy, e.g. riblets, hence named passive-neutral. The flow is investigated by visualizations, statistical analysis of vorticity and strain rates, and quadrants of the Reynolds stresses. Part of this work was funded by Airbus Group. Simulations were performed on the ARCHER Supercomputer (UKTC Grant).

Laminar flow in a microchannel with superhydrophobic walls exhibiting transverse ribs

NASA Astrophysics Data System (ADS)

Davies, J.; Maynes, D.; Webb, B. W.; Woolford, B.

2006-08-01

One approach recently proposed for reducing the frictional resistance to liquid flow in microchannels is the patterning of microribs and cavities on the channel walls. When treated with a hydrophobic coating, the liquid flowing in the microchannel wets only the surfaces of the ribs, and does not penetrate the cavities, provided the pressure is not too high. The net result is a reduction in the surface contact area between channel walls and the flowing liquid. For microribs and cavities that are aligned normal to the channel axis (principal flow direction), these micropatterns form a repeating, periodic structure. This paper presents results of a study exploring the momentum transport in a parallel-plate microchannel with such microengineered walls. The investigation explored the entire laminar flow Reynolds number range and characterized the influence of the vapor cavity depth on the overall flow field. The liquid-vapor interface (meniscus) in the cavity regions is treated as flat in the numerical analysis and two conditions are explored with regard to the cavity region: (1) The liquid flow at the liquid-vapor interface is treated as shear-free (vanishing viscosity in the vapor region), and (2) the liquid flow in the microchannel core and the vapor flow within the cavity are coupled by matching the velocity and shear stress at the interface. Regions of slip and no-slip behavior exist and the velocity field shows distinct variations from classical laminar flow in a parallel-plate channel. The local streamwise velocity profiles, interfacial velocity distributions, and maximum interfacial velocities are presented for a number of scenarios and provide a sound understanding of the local flow physics. The predictions and accompanying measurements reveal that significant reductions in the frictional pressure drop (enhancement in effective fluid slip at the channel walls) can be achieved relative to the classical smooth-channel Stokes flow. Reductions in the friction factor and enhancements in the fluid slip are greater as the cavity-to-rib length ratio is increased (increasing shear-free fraction) and as the channel hydraulic diameter is decreased. The results also show that the slip length and average friction factor-Reynolds number product exhibit a flow Reynolds dependence. Furthermore, the predictions reveal the global impact of the vapor cavity depth on the overall frictional resistance.

Large-scale structures in turbulent Couette flow

NASA Astrophysics Data System (ADS)

Kim, Jung Hoon; Lee, Jae Hwa

2016-11-01

Direct numerical simulation of fully developed turbulent Couette flow is performed with a large computational domain in the streamwise and spanwise directions (40 πh and 6 πh) to investigate streamwise-scale growth mechanism of the streamwise velocity fluctuating structures in the core region, where h is the channel half height. It is shown that long streamwise-scale structures (> 3 h) are highly energetic and they contribute to more than 80% of the turbulent kinetic energy and Reynolds shear stress, compared to previous studies in canonical Poiseuille flows. Instantaneous and statistical analysis show that negative-u' structures on the bottom wall in the Couette flow continuously grow in the streamwise direction due to mean shear, and they penetrate to the opposite moving wall. The geometric center of the log layer is observed in the centerline with a dominant outer peak in streamwise spectrum, and the maximum streamwise extent for structure is found in the centerline, similar to previous observation in turbulent Poiseuille flows at high Reynolds number. Further inspection of time-evolving instantaneous fields clearly exhibits that adjacent long structures combine to form a longer structure in the centerline. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2014R1A1A2057031).

The Thin Oil Film Equation

NASA Technical Reports Server (NTRS)

Brown, James L.; Naughton, Jonathan W.

1999-01-01

A thin film of oil on a surface responds primarily to the wall shear stress generated on that surface by a three-dimensional flow. The oil film is also subject to wall pressure gradients, surface tension effects and gravity. The partial differential equation governing the oil film flow is shown to be related to Burgers' equation. Analytical and numerical methods for solving the thin oil film equation are presented. A direct numerical solver is developed where the wall shear stress variation on the surface is known and which solves for the oil film thickness spatial and time variation on the surface. An inverse numerical solver is also developed where the oil film thickness spatial variation over the surface at two discrete times is known and which solves for the wall shear stress variation over the test surface. A One-Time-Level inverse solver is also demonstrated. The inverse numerical solver provides a mathematically rigorous basis for an improved form of a wall shear stress instrument suitable for application to complex three-dimensional flows. To demonstrate the complexity of flows for which these oil film methods are now suitable, extensive examination is accomplished for these analytical and numerical methods as applied to a thin oil film in the vicinity of a three-dimensional saddle of separation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dechant, Lawrence J.

We examine the role of periodic sinusoidal free-stream disturbances on the inner law law-of-the-wall (log-law) for turbulent boundary layers. This model serves a surrogate for the interaction of flight vehicles with atmospheric disturbances. The approximate skin friction expression that is derived suggests that free-stream disturbances can cause enhancement of the mean skin friction. Considering the influence of grid generated free stream turbulence in the laminar sublayer/log law region (small scale/high frequency) the model recovers the well-known shear layer enhancement suggesting an overall validity for the approach. The effect on the wall shear associated with the lower frequency due to themore » passage of the vehicle through large (vehicle scale) atmospheric disturbances is likely small i.e. on the order 1% increase for turbulence intensities on the order of 2%. The increase in wall pressure fluctuation which is directly proportional to the wall shear stress is correspondingly small.« less

The dynamics and control of fluctuating pressure loads in the reattachment region of a supersonic free shear layer

NASA Technical Reports Server (NTRS)

Smits, A. J.

1990-01-01

The primary aim is to investigate the mechanisms which cause the unsteady wall-pressure fluctuations in shock wave turbulent shear layer interactions. The secondary aim is to find means to reduce the magnitude of the fluctuating pressure loads by controlling the unsteady shock motion. The particular flow proposed for study is the unsteady shock wave interaction formed in the reattachment zone of a separated supersonic flow. Similar flows are encountered in many practical situations, and they are associated with high levels of fluctuating wall pressure. Wall pressure fluctuations were measured in the reattachment region of the supersonic free shear layer. The free shear layer was formed by the separation of a Mach 2.9 turbulent boundary layer from a backward facing step. Reattachment occurred on a 20 deg ramp. By adjusting the position of the ramp, the base pressure was set equal to the freestream pressure, and the free shear layer formed in the absence of a separation shock. An array of flush-mounted, miniature, high-frequency pressure transducers was used to make multichannel measurements of the fluctuating wall pressure in the vicinity of the reattachment region. Contrary to previous observations of this flow, the reattachment region was found to be highly unsteady, and the pressure fluctuations were found to be significant. The overall behavior of the wall pressure loading is similar in scale and magnitude to the unsteadiness of the wall pressure field in compression ramp flows at the same Mach number. Rayleigh scattering was used to visualize the instantaneous shock structure in the streamwise and spanwise direction. Spanwise wrinkles on the order of half the boundary layer thickness were observed.

Modelling Force Transfer Around Openings of Full-Scale Shear Walls

Treesearch

Tom Skaggs; Borjen Yeh; Frank Lam; Minghao Li; Doug Rammer; James Wacker

2011-01-01

Wood structural panel (WSP) sheathed shear walls and diaphragms are the primary lateralload-resisting elements in wood-frame construction. The historical performance of lightframe structures in North America has been very good due, in part, to model building codes that are designed to preserve life safety. These model building codes have spawned continual improvement...

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. II - Wall shear stress

NASA Technical Reports Server (NTRS)

Liou, M. S.; Adamson, T. C., Jr.

1980-01-01

Asymptotic methods are used to calculate the shear stress at the wall for the interaction between a normal shock wave and a turbulent boundary layer on a flat plate. A mixing length model is used for the eddy viscosity. The shock wave is taken to be strong enough that the sonic line is deep in the boundary layer and the upstream influence is thus very small. It is shown that unlike the result found for laminar flow an asymptotic criterion for separation is not found; however, conditions for incipient separation are computed numerically using the derived solution for the shear stress at the wall. Results are compared with available experimental measurements.

Direct measurements of wall shear stress by buried wire gages in a shock-wave boundary-layer interaction region

NASA Technical Reports Server (NTRS)

Murthy, V. S.; Rose, W. C.

1977-01-01

Detailed measurements of wall shear stress (skin friction) were made with specially developed buried wire gages in the interaction regions of a Mach 2.9 turbulent boundary layer with externally generated shocks. Separation and reattachment points inferred by these measurements support the findings of earlier experiments which used a surface oil flow technique and pitot profile measurements. The measurements further indicate that the boundary layer tends to attain significantly higher skin-friction values downstream of the interaction region as compared to upstream. Comparisons between measured wall shear stress and published results of some theoretical calculation schemes show that the general, but not detailed, behavior is predicted well by such schemes.

Research Status on Reinforcement Connection Form of Precast Concrete Shear Wall Structure

NASA Astrophysics Data System (ADS)

Zhang, Zhuangnan; Zhang, Yan

2018-03-01

With the rapid development of Chinese economy and the speeding up the process of urbanization, housing industrialization has been paid more and more attention. And the fabricated structure has been widely used in China. The key of precast concrete shear wall structure is the connection of precast components. The reinforcement connection can directly affect the entirety performance and seismic behavior of the structure. Different reinforcement connections have a great impact on the overall behavior of the structure. By studying the characteristics of the reinforcement connection forms used in the vertical connection and horizontal connection of precast concrete shear wall, it can provide reference for the research and development of the reinforcement connection forms in the future.

Production of functional proteins: balance of shear stress and gravity

NASA Technical Reports Server (NTRS)

Kaysen, James Howard (Inventor); Hammond, Timothy Grant (Inventor); Goodwin, Thomas John (Inventor)

2011-01-01

A method for the production of functional proteins including hormones by renal cells in a three dimensional culturing process responsive to shear stress uses a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-.alpha.-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D.sub.3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating an in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

Deformation and failure mechanism of secondary cell wall in Spruce late wood

NASA Astrophysics Data System (ADS)

Adusumalli, Ramesh-Babu; Raghavan, Rejin; Ghisleni, Rudy; Zimmermann, Tanja; Michler, Johann

2010-08-01

The deformation and failure of the secondary cell wall of Spruce wood was studied by in-situ SEM compression of micropillars machined by the focused ion beam technique. The cell wall exhibited yield strength values of approximately 160 MPa and large scale plasticity. High resolution SEM imaging post compression revealed bulging of the pillars followed by shear failure. With additional aid of cross-sectional analysis of the micropillars post compression, a model for deformation and failure mechanism of the cell wall has been proposed. The cell wall consists of oriented cellulose microfibrils with high aspect ratio embedded in a hemicellulose-lignin matrix. The deformation of the secondary wall occurs by asymmetric out of plane bulging because of buckling of the microfibrils. Failure of the cell wall following the deformation occurs by the formation of a shear or kink band.

A numerical simulation of peristaltic motion in the ureter using fluid structure interactions.

PubMed

Vahidi, Bahman; Fatouraee, Nasser

2007-01-01

An axisymmetric model with fluid-structure interactions (FSI) is introduced and solved to perform ureter flow and stress analysis. The Navier-Stokes equations are solved for the fluid and a linear elastic model for ureter is used. The finite element equations for both the structure and the fluid were solved by the Newton-Raphson iterative method. Our results indicated that shear stresses were high around the throat of moving contracted wall. The pressure gradient magnitude along the ureter wall and the symmetry line had the maximum value around the throat of moving contracted wall which decreased as the peristalsis propagates toward the bladder. The flow rate at the ureter outlet at the end of the peristaltic motion was about 650 mm3/s. During propagation of the peristalsis toward the bladder, the inlet backward flow region was limited to the areas near symmetry line but the inner ureter backward flow regions extended to the whole ureter contraction part. The backward flow was vanished after 1.5 seconds of peristalsis propagation start up and after that time the urine flow was forward in the whole ureter length, so reflux is more probable to be present at the beginning of the wall peristaltic motion.

Evaluation of Aortic Blood Flow and Wall Shear Stress in Aortic Stenosis and Its Association With Left Ventricular Remodeling.

PubMed

von Knobelsdorff-Brenkenhoff, Florian; Karunaharamoorthy, Achudhan; Trauzeddel, Ralf Felix; Barker, Alex J; Blaszczyk, Edyta; Markl, Michael; Schulz-Menger, Jeanette

2016-03-01

Aortic stenosis (AS) leads to variable stress for the left ventricle (LV) and consequently a broad range of LV remodeling. The aim of this study was to describe blood flow patterns in the ascending aorta of patients with AS and determine their association with remodeling. Thirty-seven patients with AS (14 mild, 8 moderate, 15 severe; age, 63±13 years) and 37 healthy controls (age, 60±10 years) underwent 4-dimensional-flow magnetic resonance imaging. Helical and vortical flow formations and flow eccentricity were assessed in the ascending aorta. Normalized flow displacement from the vessel center and peak systolic wall shear stress in the ascending aorta were quantified. LV remodeling was assessed based on LV mass index and the ratio of LV mass:end-diastolic volume (relative wall mass). Marked helical and vortical flow formation and eccentricity were more prevalent in patients with AS than in healthy subjects, and patients with AS exhibited an asymmetrical and elevated distribution of peak systolic wall shear stress. In AS, aortic orifice area was strongly negatively associated with vortical flow formation (P=0.0274), eccentricity (P=0.0070), and flow displacement (P=0.0021). Bicuspid aortic valve was associated with more intense helical (P=0.0098) and vortical flow formation (P=0.0536), higher flow displacement (P=0.11), and higher peak systolic wall shear stress (P=0.0926). LV mass index and relative wall mass were significantly associated with aortic orifice area (P=0.0611, P=0.0058) and flow displacement (P=0.0058, P=0.0283). In this pilot study, AS leads to abnormal blood flow pattern and peak systolic wall shear stress in the ascending aorta. In addition to aortic orifice area, normalized flow displacement was significantly associated with LV remodeling. © 2016 American Heart Association, Inc.

Behaviour of Masonry Walls under Horizontal Shear in Mining Areas

NASA Astrophysics Data System (ADS)

Kadela, Marta; Bartoszek, Marek; Fedorowicz, Jan

2017-12-01

The paper discusses behaviour of masonry walls constructed with small-sized elements under the effects of mining activity. It presents some mechanisms of damage occurring in such structures, its forms in real life and the behaviour of large fragments of masonry walls subjected to specific loads in FEM computational models. It offers a constitutive material model, which enables numerical analyses and monitoring of the behaviour of numerical models as regards elastic-plastic performance of the material, with consideration of its degradation. Results from the numerical analyses are discussed for isolated fragments of the wall subjected to horizontal shear, with consideration of degradation, impact of imposed vertical load as well as the effect of weakening of the wall, which was achieved by introducing openings in it, on the performance and deformation of the wall.

Analysis of flow disturbance in a stenosed carotid artery bifurcation using two-equation transitional and turbulence models.

PubMed

Tan, F P P; Soloperto, G; Bashford, S; Wood, N B; Thom, S; Hughes, A; Xu, X Y

2008-12-01

In this study, newly developed two-equation turbulence models and transitional variants are employed for the prediction of blood flow patterns in a diseased carotid artery where the growth, progression, and structure of the plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, the laminar-turbulent transition in the poststenotic zone can alter the separation zone length, wall shear stress, and pressure distribution over the plaque, with potential implications for stresses within the plaque. Following the validation with well established experimental measurements and numerical studies, a magnetic-resonance (MR) image-based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using realistic patient-specific conditions. Laminar flow, a correlation-based transitional version of Menter's hybrid k-epsilon/k-omega shear stress transport (SST) model and its "scale adaptive simulation" (SAS) variant were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress, and turbulence intensity were conducted. In general, the transitional version of SST and its SAS variant are shown to give a better overall agreement than their standard counterparts with experimental data for pulsatile flow in an axisymmetric stenosed tube. For the patient-specific case reported, the wall shear stress analysis showed discernable differences between the laminar flow and SST transitional models but virtually no difference between the SST transitional model and its SAS variant.

The Relationship Between Pulsatile Flow Impingement and Intraluminal Thrombus Deposition in Abdominal Aortic Aneurysms.

PubMed

Lozowy, Richard J; Kuhn, David C S; Ducas, Annie A; Boyd, April J

2017-03-01

Direct numerical simulations were performed on four patient-specific abdominal aortic aneurysm (AAA) geometries and the resulting pulsatile blood flow dynamics were compared to aneurysm shape and correlated with intraluminal thrombus (ILT) deposition. For three of the cases, turbulent vortex structures impinged/sheared along the anterior wall and along the posterior wall a zone of recirculating blood formed. Within the impingement region the AAA wall was devoid of ILT and remote to this region there was an accumulation of ILT. The high wall shear stress (WSS) caused by the impact of vortexes is thought to prevent the attachment of ILT. WSS from impingement is comparable to peak-systolic WSS in a normal-sized aorta and therefore may not damage the wall. Expansion occurred to a greater extent in the direction of jet impingement and the wall-normal force from the continuous impact of vortexes may contribute to expansion. It was shown that the impingement region has low oscillatory shear index (OSI) and recirculation zones can have either low or high OSI. No correlation could be identified between OSI and ILT deposition since different flow dynamics can have similar OSI values.

Full-scale shear wall tests for force transfer around openings

Treesearch

Tom Skaggs; Borjen Yeh; Frank Lam; Douglas Rammer; James Wacker

2010-01-01

Wood structural panel sheathed shear walls and diaphragms are the primary lateral-load resisting elements in wood-frame construction. The historical performance of light-frame structures in North America are very good due, in part, to model building codes that are designed to preserve life safety, as well as the inherent redundancy of wood-frame construction using wood...

Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow

NASA Astrophysics Data System (ADS)

Alam, Meheboob; Arakeri, V. H.; Nott, P. R.; Goddard, J. D.; Herrmann, H. J.

2005-01-01

Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a "plug" near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an "imperfection", thus destroying the "perfect" bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of "isolas", with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a "floating" plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under "microgravity" conditions.

Effects of biaxial oscillatory shear stress on endothelial cell proliferation and morphology.

PubMed

Chakraborty, Amlan; Chakraborty, Sutirtha; Jala, Venkatakrishna R; Haribabu, Bodduluri; Sharp, M Keith; Berson, R Eric

2012-03-01

Wall shear stress (WSS) on anchored cells affects their responses, including cell proliferation and morphology. In this study, the effects of the directionality of pulsatile WSS on endothelial cell proliferation and morphology were investigated for cells grown in a Petri dish orbiting on a shaker platform. Time and location dependent WSS was determined by computational fluid dynamics (CFD). At low orbital speed (50 rpm), WSS was shown to be uniform (0-1 dyne/cm(2)) across the bottom of the dish, while at higher orbital speed (100 and 150 rpm), WSS remained fairly uniform near the center and fluctuated significantly (0-9 dyne/cm(2)) near the side walls of the dish. Since WSS on the bottom of the dish is two-dimensional, a new directional oscillatory shear index (DOSI) was developed to quantify the directionality of oscillating shear. DOSI approached zero for biaxial oscillatory shear of equal magnitudes near the center and approached one for uniaxial pulsatile shear near the wall, where large tangential WSS dominated a much smaller radial component. Near the center (low DOSI), more, smaller and less elongated cells grew, whereas larger cells with greater elongation were observed in the more uniaxial oscillatory shear (high DOSI) near the periphery of the dish. Further, cells aligned with the direction of the largest component of shear but were randomly oriented in low magnitude biaxial shear. Statistical analyses of the individual and interacting effects of multiple factors (DOSI, shear magnitudes and orbital speeds) showed that DOSI significantly affected all the responses, indicating that directionality is an important determinant of cellular responses. Copyright © 2011 Wiley Periodicals, Inc.

Analysis of wall shear stress around a competitive swimmer using 3D Navier-Stokes equations in CFD.

PubMed

Popa, C V; Zaidi, H; Arfaoui, A; Polidori, G; Taiar, R; Fohanno, S

2011-01-01

This paper deals with the flow dynamics around a competitive swimmer during underwater glide phases occurring at the start and at every turn. The influence of the head position, namely lifted up, aligned and lowered, on the wall shear stress and the static pressure distributions is analyzed. The problem is considered as 3D and in steady hydrodynamic state. Three velocities (1.4 m/s, 2.2 m/s and 3.1 m/s) that correspond to inter-regional, national and international swimming levels are studied. The flow around the swimmer is assumed turbulent. The Reynolds-averaged Navier-Stokes (RANS) equations are solved with the standard k-ω turbulent model by using the CFD (computational fluid dynamics) numerical method based on a volume control approach. Numerical simulations are carried out with the ANSYS FLUENT® CFD code. The results show that the wall shear stress increases with the velocity and consequently the drag force opposing the movement of the swimmer increases as well. Also, high wall shear stresses are observed in the areas where the body shape, globally rigid in form, presents complex surface geometries such as the head, shoulders, buttocks, heel and chest.

Measurement of the near-wall velocity profile for a nanofluid flow inside a microchannel

NASA Astrophysics Data System (ADS)

Kanjirakat, Anoop; Sadr, Reza

2015-11-01

Hydrodynamics and anomalous heat transfer enhancements have been reported in the past for colloidal suspensions of nano-sized particles dispersed in a fluid (nanofluids). However, such augmentations may manifest itself by study of fluid flow characteristics near in the wall region. Present experimental study reports near-wall velocity profile for nanofluids (silicon dioxide nanoparticles in water) measured inside a microchannel. An objective-based nano-Particle Image Velocimetry (nPIV) technique is used to measure fluid velocity within three visible depths, O(100nm), from the wall. The near-wall fluid velocity profile is estimated after implementing the required corrections for optical properties and effects caused by hindered Brownian motion, wall-particle interactions, and non-uniform exponential illumination on the measurement technique. The fluid velocities of nanofluids at each of the three visible depths are observed to be higher than that of the base fluid resulting in a higher shear rate in this region. The relative increase in shear rates for nanofluids is believed to be the result of the near-wall shear-induced particle migration along with the Brownian motion of the nanoparticles. This research is funded by NPRP grant # 08-574-2-239 from the Qatar National Research Fund (a member of Qatar Foundation).

Large-Eddy Simulations of Noise Generation in Supersonic Jets at Realistic Engine Temperatures

NASA Astrophysics Data System (ADS)

Liu, Junhui; Corrigan, Andrew; Kailasanath, K.; Taylor, Brian

2015-11-01

Large-eddy simulations (LES) have been carried out to investigate the noise generation in highly heated supersonic jets at temperatures similar to those observed in high-performance jet engine exhausts. It is found that the exhaust temperature of high-performance jet engines can range from 1000K at an intermediate power to above 2000K at a maximum afterburning power. In low-temperature jets, the effects of the variation of the specific heat ratio as well as the radial temperature profile near the nozzle exit are small and are ignored, but it is not clear whether those effects can be also ignored in highly heated jets. The impact of the variation of the specific heat ratio is assessed by comparing LES results using a variable specific heat ratio with those using a constant specific heat ratio. The impact on both the flow field and the noise distributions are investigated. Because the total temperature near the nozzle wall can be substantially lower than the nozzle total temperature either due to the heating loss through the nozzle wall or due to the cooling applied near the wall, this lower wall temperature may impact the temperature in the shear layer, and thus impact the noise generation. The impact of the radial temperature profile on the jet noise generation is investigated by comparing results of lower nozzle wall temperatures with those of the adiabatic wall condition.

Computational Study of a Vortex-Ring Pair Interacting with a Constant-Temperature Heated Wall

NASA Astrophysics Data System (ADS)

Jabbar, Hussam; Naguib, Ahmed

2017-11-01

Impinging jets are used widely in industrial and manufacturing processes because of their ability to increase the heat transfer rate from the impingement surface. The vortical structures of these jets have an important influence on the heat transfer; by affecting the thermal boundary layer (TBL) during their interaction with the wall. In order to better understand the physics of this interaction, particularly when pairing of two vortices happens near the wall, a simplified model problem of two isolated vortex rings interacting with a flat wall is investigated computationally using ANSYS FLUENT 17.1. Observations of the vorticity field, the temperature field, the wall shear stress, the TBL and the Nusselt number (Nu) provide insight into the association of local Nu maxima/minima with different flow features. The results provide physical understanding of the flow processes leading to enhancement/deterioration of Nu due to vortex-wall interaction. Additionally, the characteristics of the vortical structures are quantified, and possible correlations between the temporal development of these characteristics and the evolution of the maximum/minimum Nu are investigated. The results are compared to those involving a single vortex ring in order to understand the effect of vortex pairing. This work is supported by NSF Grant Number CBET-1603720. Hussam Jabbar also acknowledges the fellowship support from Higher Committee for Education Development in Iraq (HCED).

Mathematical modeling of power law and Herschel - Buckley non-Newtonian fluid of blood flow through a stenosed artery with permeable wall: Effects of slip velocity

NASA Astrophysics Data System (ADS)

Chitra, M.; Karthikeyan, D.

2018-04-01

A mathematical model of non-Newtonian blood flow through a stenosed artery is considered. The steadynon-Newtonian model is chosen characterized by the generalized power-law model and Herschel-Bulkley model incorporating the effect of slip velocity due to steanosed artery with permeable wall. The effects of slip velocity for non-Newtonian nature of blood on velocity, flow rate and wall shear stress of the stenosed artery with permeable wall are solved analytically. The effects of various parameters such as slip parameter (λ), power index (m) and different thickness of the stenosis (δ) on velocity, volumetric flow rate and wall shear stress are discussed through graphs.

Evolution and dynamics of shear-layer structures in near-wall turbulence

NASA Technical Reports Server (NTRS)

Johansson, Arne V.; Alfredsson, P. H.; Kim, John

1991-01-01

Near-wall flow structures in turbulent shear flows are analyzed, with particular emphasis on the study of their space-time evolution and connection to turbulence production. The results are obtained from investigation of a database generated from direct numerical simulation of turbulent channel flow at a Reynolds number of 180 based on half-channel width and friction velocity. New light is shed on problems associated with conditional sampling techniques, together with methods to improve these techniques, for use both in physical and numerical experiments. The results clearly indicate that earlier conceptual models of the processes associated with near-wall turbulence production, based on flow visualization and probe measurements need to be modified. For instance, the development of asymmetry in the spanwise direction seems to be an important element in the evolution of near-wall structures in general, and for shear layers in particular. The inhibition of spanwise motion of the near-wall streaky pattern may be the primary reason for the ability of small longitudinal riblets to reduce turbulent skin friction below the value for a flat surface.

Behavior of Steel-Sheathed Shear Walls Subjected to Seismic and Fire Loads.

PubMed

Hoehler, Matthew S; Smith, Christopher M; Hutchinson, Tara C; Wang, Xiang; Meacham, Brian J; Kamath, Praveen

2017-07-01

A series of tests was conducted on six 2.7 m × 3.7 m shear wall specimens consisting of cold-formed steel framing sheathed on one side with sheet steel adhered to gypsum board and on the opposite side with plain gypsum board. The specimens were subjected to various sequences of simulated seismic shear deformation and fire exposure to study the influence of multi-hazard interactions on the lateral load resistance of the walls. The test program was designed to complement a parallel effort at the University of California, San Diego to investigate a six-story building subjected to earthquakes and fires. The test results reported here indicate that the fire exposure caused a shift in the failure mode of the walls from local buckling of the sheet steel in cases without fire exposure, to global buckling of the sheet steel with an accompanying 35 % reduction in lateral load capacity after the wall had been exposed to fire. This behavior appears to be predictable, which is encouraging from the standpoint of residual lateral load capacity under these severe multi-hazard actions.

Spatial variations in shear stress in a 3-D bifurcation model at low Reynolds numbers.

PubMed

Rouhanizadeh, Mahsa; Lin, Tiantian C; Arcas, Diego; Hwang, Juliana; Hsiai, Tzung K

2005-10-01

Real-time wall shear stress is difficult to monitor precisely because it varies in space and time. Microelectromechanical systems sensor provides high spatial resolution to resolve variations in shear stress in a 3-D bifurcation model for small-scaled hemodynamics. At low Reynolds numbers from 1.34 to 6.7 skin friction coefficients (C(f)) varied circumferentially by a factor of two or more within the bifurcation. At a Reynolds number of 6.7, the C(f) value at the lateral wall of the bifurcation along the 270 degree plane was 7.1, corresponding to a shear stress value of 0.0061 dyn/cm(2). Along the 180 degree plane, C(f) was 13 or 0.0079 dyn/cm(2), and at the medial wall along the 90 degree plane, C(f) was 10.3 or 0.0091 dyn/cm(2). The experimental skin friction coefficients correlated with values derived from the Navier-Stokes solutions.

Pulmonary blood flow and pulmonary hypertension: Is the pulmonary circulation flowophobic or flowophilic?

PubMed Central

Kulik, Thomas J.

2012-01-01

Increased pulmonary blood flow (PBF) is widely thought to provoke pulmonary vascular obstructive disease (PVO), but the impact of wall shear stress in the lung is actually poorly defined. We examined information from patients having cardiac lesions which impact the pulmonary circulation in distinct ways, as well as experimental studies, asking how altered hemodynamics impact the risk of developing PVO. Our results are as follows: (1) with atrial septal defect (ASD; increased PBF but low PAP), shear stress may be increased but there is little tendency to develop PVO; (2) with normal PBF but increased pulmonary vascular resistance (PVR; mitral valve disease) shear stress may also be increased but risk of PVO still low; (3) with high PVR and PBF (e.g., large ventricular septal defect), wall shear stress is markedly increased and the likelihood of developing PVO is much higher than with high PBF or PAP only; and (4) with ASD, experimental and clinical observations suggest that increased PBF plus another stimulus (e.g., endothelial inflammation) may be required for PVO. We conclude that modestly increased wall shear stress (e.g., ASD) infrequently provokes PVO, and likely requires other factors to be harmful. Likewise, increased PAP seldom causes PVO. Markedly increased wall shear stress may greatly increase the likelihood of PVO, but we cannot discriminate its effect from the combined effects of increased PAP and PBF. Finally, the age of onset of increased PAP may critically impact the risk of PVO. Some implications of these observations for future investigations are discussed. PMID:23130101

Orbitally shaken shallow fluid layers. II. An improved wall shear stress model

NASA Astrophysics Data System (ADS)

Alpresa, Paola; Sherwin, Spencer; Weinberg, Peter; van Reeuwijk, Maarten

2018-03-01

A new model for the analytical prediction of wall shear stress distributions at the base of orbitally shaken shallow fluid layers is developed. This model is a generalisation of the classical extended Stokes solution and will be referred to as the potential theory-Stokes model. The model is validated using a large set of numerical simulations covering a wide range of flow regimes representative of those used in laboratory experiments. It is demonstrated that the model is in much better agreement with the simulation data than the classical Stokes solution, improving the prediction in 63% of the studied cases. The central assumption of the model—which is to link the wall shear stress with the surface velocity—is shown to hold remarkably well over all regimes covered.

Investigation of the seismic resistance of interior building partitions, phase 1

NASA Astrophysics Data System (ADS)

Anderson, R. W.; Yee, Y. C.; Savulian, G.; Barclay, B.; Lee, G.

1981-02-01

The effective participation of wood-framed interior shear wall partitions when determining the ultimate resistance capacity of two- and three-story masonry apartment buildings to seismic loading was investigated. Load vs. deflection tests were performed on 8 ft by 8 ft wall panel specimens constructed of four different facing materials, including wood lath and plaster, gypsum lath and plaster, and gypsum wallboard with joints placed either horizontally or vertically. The wood lath and plaster construction is found to be significantly stronger and stiffer than the other three specimens. Analyses of the test panels using finite element methods to predict their static resistance characteristics indicates that the facing material acts as the primary shear-resisting structural element. Resistance of shear wall partitions to lateral loads was assessed.

The shear-lag effect of thin-walled box girder under vertical earthquake excitation

NASA Astrophysics Data System (ADS)

Zhai, Zhipeng; Li, Yaozhuang; Guo, Wei

2017-03-01

The variation method based on the energy variation principle is proved to be accurate and valid for analyzing the shear lag effect of box girder under static and dynamic load. Meanwhile, dynamic problems gradually become the key factors in engineering practice. Therefore, a method for calculating the shear lag effect in thin-walled box girder under vertical seismic excitation is proposed by applying Hamilton Principle in this paper. The Timoshenko shear deformation is taken into account. And a new definition of shear lag ratio for box girder is given. What's more, some conclusions are drawn by analysis of numerical example. The results show that small amplitude of earthquake ground motion can generate high stress and obvious shear lag, especially in the region of resonance. And the influence of rotary inertia cannot be ignored for analyzing the shear lag effect. With the increase of span to width ratio, shear lag effect becomes smaller and smaller. These research conclusions will be useful for the engineering practice and enrich the theoretical studies of box girders.

Periodic Viscous Shear Heating Instability in Fine-Grained Shear Zones: Mechanism for Intermediate Depth Earthquakes

NASA Astrophysics Data System (ADS)

Coon, E.; Kelemen, P.; Hirth, G.; Spiegelman, M.

2005-12-01

Kelemen and Hirth (Fall 2004 AGU) presented a model for periodic, viscous shear heating instabilities along pre-existing, fine grained shear zones. This provides an attractive alternative to dehydration embrittlement for explaining intermediate-depth earthquakes, especially those in a narrow thermal window within the mantle section of subducting oceanic plates (Hacker et al JGR03). Ductile shear zones with widths of cm to m are common in shallow mantle massifs and peridotite along oceanic fracture zones. Pseudotachylites in a mantle shear zone show that shear heating temperatures exceeded the mantle solidus (Obata & Karato Tectonophys95). Olivine grain growth in shear zones is pinned by closely spaced pyroxenes; thus, once formed, these features do not `heal' on geological time scales in the absence of melt or fluid (Warren & Hirth EPSL05). Grain-size sensitive creep will be localized within these shear zones, in preference to host rocks with olivine grain size from 1 to 10 mm. Inspired by the work of Whitehead & Gans (GJRAS74), we proposed that such pre-existing shear zones might undergo repeated shear heating instabilities. This is not a new concept; what is new is that viscous deformation is limited to a narrow shear zone, because grain boundary sliding, sensitive to both stress and grain size, may accommodate creep even at high stress and high temperature. These new ideas yield a new result: simple models for a periodic shear heating instability. Last year, we presented a 1D numerical model using olivine flow laws, assuming that viscous deformation remains localized in shear zones, surrounded by host rocks undergoing elastic deformation. Stress evolves due to elastic strain and drives viscous deformation in a shear zone of specified width. Shear heating and thermal diffusion control T. A maximum of 1400 C (substantial melting of peridotite ) was imposed. Grain size evolves due to recrystallization and diffusion. For strain rates of E-13 to E-14 per sec and initial T of 600 to 850 C, this produced periodic viscous shear heating events with periods of 100's to 1000's of years. Strain rates during these events approach 1 per second as temperatures reach 1400. Cooling between events returns the shear zone almost to its initial temperature, though ultimately shear zone temperature between events exceeds 850 C resulting in stable viscous creep. Analysis shows that our system of equations jumps from one steady state to another, depending on a non-dimensional number relating the rate of shear heating to the rate of diffusive cooling. This year, Kelemen and Hirth show that the rate of stress drop during shear heating events is greater than the rate of elastic stress relaxation, so that shear heating events are a runaway instability. Rather than capping the temperature at 1400 C, we parameterize melt fraction as a function of T, and shear viscosity as a function of melt fraction. A problem with our 1D model is that predicted displacements are too large (1 to 20 m) during shear heating events, essentially because there is no resistance at shear zone ends. To address this, Coon and Spiegelman have embarked on a 3D model, incorporating a pre-existing fine-grained, tabular shear zone of finite extent, with a visco-elastic rheology for both shear zone and wall rocks. Preliminary 1D models using this approach show that the more complicated rheology yields the same result as the simpler model. We will present preliminary results, and determine the Maxwell time for this problem, since low strain rates could produce viscous relaxation in both shear zone and wall rocks with negligible shear heating.

Optimal energy growth in a stably stratified shear flow

NASA Astrophysics Data System (ADS)

Jose, Sharath; Roy, Anubhab; Bale, Rahul; Iyer, Krithika; Govindarajan, Rama

2018-02-01

Transient growth of perturbations by a linear non-modal evolution is studied here in a stably stratified bounded Couette flow. The density stratification is linear. Classical inviscid stability theory states that a parallel shear flow is stable to exponentially growing disturbances if the Richardson number (Ri) is greater than 1/4 everywhere in the flow. Experiments and numerical simulations at higher Ri show however that algebraically growing disturbances can lead to transient amplification. The complexity of a stably stratified shear flow stems from its ability to combine this transient amplification with propagating internal gravity waves (IGWs). The optimal perturbations associated with maximum energy amplification are numerically obtained at intermediate Reynolds numbers. It is shown that in this wall-bounded flow, the three-dimensional optimal perturbations are oblique, unlike in unstratified flow. A partitioning of energy into kinetic and potential helps in understanding the exchange of energies and how it modifies the transient growth. We show that the apportionment between potential and kinetic energy depends, in an interesting manner, on the Richardson number, and on time, as the transient growth proceeds from an optimal perturbation. The oft-quoted stabilizing role of stratification is also probed in the non-diffusive limit in the context of disturbance energy amplification.

High-pressure high-temperature rheological studies of colloidal suspensions with carbon nanotube

NASA Astrophysics Data System (ADS)

Baby, Anoop; Sadr, Reza; Yarc, Rommel; Amani, Mahmood

2017-11-01

Selection of the drilling fluid, drilling mud, is vital in minimizing the cost and time required for the drilling in oil fields. Drilling mud aids in cooling, lubricating drilling bit, removing the debries from the drill bore and maintaining the wellbore stability. Owing to the enhanced thermo-physical properties and stable nature, suspensions of nanoparticles have been suggested for drilling fluids. High-pressure and high-temperature rheology of a nanomud suspension (nano particles suspended in a mud solution) is studied here. The nanomud is prepared by dispersing a water-based drilling mud suspension (water with 1% Bentonite and 7% Barite particles) with multi-walled carbon nanotubes, MWCNT. The effect of pressure, temperature, and shear rate are independently studied for the various particle loading of the nanoparticles. Viscosity values are measured at a maximum pressure of 170MPa with temperatures ranging from ambient to 180oC. The effect of MWCNT concentration and variation in shear rate are also investigated A shear thinning non-Newtonian behavior is observed for the basemud and the nanomud samples for all cases. The basemud showed an increase in viscosity with an increase in pressure. However, with MWCNT particle addition, this trend is observed to have reversed.

Thrust Slip Rates as a Control on the Presence and Spatial Distribution of High Metamorphic Heating Rates in Collisional Systems: The "Hot Iron" Model Revisited

NASA Astrophysics Data System (ADS)

Thigpen, R.; Ashley, K. T.; Law, R. D.; Mako, C. A.

2017-12-01

In natural systems, two key observations indicate that major strain discontinuities such as faults and shear zones should play a fundamental role in orogenic thermal evolution: (1) Large faults and shear zones often separate components of the composite orogen that have experienced broadly different thermal and deformational histories, and (2) quantitative metamorphic and diffusional studies indicate that heating rates are much faster and the duration of peak conditions much shorter in natural collisional systems than those predicted by numerical continuum deformation models. Because heat transfer processes such as conduction usually operate at much slower time scales than rates of other tectonic processes, thermal evolution is often transient and thus can be strongly influenced by tectonic disturbances that occur at rates much faster than thermal relaxation. Here, we use coupled thermal-mechanical finite element models of thrust faults to explore how fault slip rate may fundamentally influence the thermal evolution of individual footwall and hanging wall thrust slices. The model geometry involves a single crustal-scale thrust with a dip of 25° that is translated up the ramp at average velocities of 20, 35, and 50 km Myr-1, interpreted to represent average to relatively high slip rates observed in many collisional systems. Boundary conditions include crustal radioactive heat production, basal mantle heat flow, and surface erosion rates that are a function of thrust rate and subsequent topography generation. In the models, translation of the hanging wall along the crustal-scale detachment results in erosion, exhumation, and retrograde metamorphism of the emerging hanging wall topography and coeval burial, `hot iron' heating, and prograde metamorphism of the thrust footwall. Thrust slip rates of 20, 35, and 50 km Myr-1 yield maximum footwall heating rates ranging from 55-90° C Myr-1 and maximum hanging wall cooling rates of 138-303° C Myr-1. These relatively rapid heating rates explain, in part, the presence of chemical diffusion profiles in metamorphic minerals that are indicative of high heating rates. Additionally, the relatively high cooling rates explain preservation of chemical zoning, as rapid cooling prevents diffusive profiles from being substantially modified during exhumation.

Production of functional proteins: balance of shear stress and gravity

NASA Technical Reports Server (NTRS)

Kaysen, James Howard (Inventor); Hammond, Timothy Grant (Inventor); Goodwin, Thomas John (Inventor)

2004-01-01

The present invention provides a method for production of functional proteins including hormones by renal cells in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-a-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

Production of functional proteins: balance of shear stress and gravity

NASA Technical Reports Server (NTRS)

Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor); Goodwin, Thomas John (Inventor)

2007-01-01

The present invention provides a method for production of functional proteins including hormones by renal cells in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-a-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.

Drainage Asperities on Subduction Megathrusts

NASA Astrophysics Data System (ADS)

Sibson, R. H.

2012-12-01

Geophysical observations coupled with force-balance analyses suggest that the seismogenic shear zone interface of subduction megathrusts is generally fluid-overpressured to near-lithostatic values (λv = Pf/σv > 0.9) below the forearc hanging-wall, strongly modulating the profile of frictional shear resistance. Fluid sources include the accretionary prism at shallow levels and, with increasing depth, metamorphic dehydration of material entrained within the subduction shear zone together with progressive metamorphism of oceanic crust in the downgoing slab. Solution transfer in fine-grained material contained within the deeper subduction shear zone (150 < T < 350°C) likely contributes to hydrothermal sealing of fractures. A dramatic difference may therefore exist between low prefailure permeability surrounding the megathrust and high postfailure fracture permeability along the rupture zone and adjacent areas of aftershock activity. Observed postseismic changes in the velocity structure of the fore-arc hanging-wall led Husen and Kissling (2001) to propose massive fluid loss across the subduction interface following the 1995 Antofagasta, Chile, Mw8.0 megathrust rupture. Such trans-megathrust discharges represent a variant of 'fault-valve' action in which the subduction interface itself acts as a seal trapping overpressured fluids derived from metamorphic dehydration beneath. In low-permeability assemblages the maximum sustainable overpressure is limited by the activation or reactivation of brittle faults and fractures under the prevailing stress state. Highest overpressures tend to occur at low differential stress in compressional stress regimes. Loci for fluid discharge are likely determined by stress heterogeneities along the megathrust (e.g. the hangingwall of the rupture at its downdip termination). Discharge sites may be defined by swarm aftershocks defining activated fault-fracture meshes. However, fluid loss across a subduction interface will be enhanced when the stress-state in the forearc hanging-wall switches from compressional reverse-slip faulting before failure to extensional normal-slip faulting postfailure, as occurred during the 2011 Mw9.0 Tohoku megathrust rupture. Mean stress and fault-normal stress then change from being greater than vertical stress prefailure, to less than vertical stress postfailure. Postfailure reductions in overpressure are expected from a combination of poroelastic effects and fluid loss through fault-fracture networks, enhancing vertical permeability. Mineralised fault-fracture meshes in exhumed fore-arc assemblages (e.g. the Alaska-Juneau Au-quartz vein swarm) testify to the episodic discharge of substantial volumes of hydrothermal fluid (< tens of km3). Localized drainage from the subduction interface shear zone increases frictional strength significantly, giving rise to a postfailure strength asperities. Anticipated strength increases from such fluid discharge depends on the magnitude of the drop in overpressure but are potentially large (< hundreds of MPa). Time to the subsequent failure is then governed by reaccumulation of fluid overpressure as well as shear stress along the subduction interface.

Stability numerical analysis of soil cave in karst area to drawdown of underground water level

NASA Astrophysics Data System (ADS)

Mo, Yizheng; Xiao, Rencheng; Deng, Zongwei

2018-05-01

With the underground water level falling, the reliable estimates of the stability and deformation characteristics of soil caves in karst region area are required for analysis used for engineering design. Aimed at this goal, combined with practical engineering and field geotechnical test, detail analysis on vertical maximum displacement of top, vertical maximum displacement of surface, maximum principal stress and maximum shear stress were conducted by finite element software, with an emphasis on two varying factors: the size and the depth of soil cave. The calculations on the soil cave show that, its stability of soil cave is affected by both the size and depth, and only when extending a certain limit, the collapse occurred along with the falling of underground water; Additionally, its maximum shear stress is in arch toes, and its deformation curve trend of maximum displacement is similar to the maximum shear stress, which further verified that the collapse of soil cave was mainly due to shear-failure.

Oscillatory motion based measurement method and sensor for measuring wall shear stress due to fluid flow

DOEpatents

Armstrong, William D [Laramie, WY; Naughton, Jonathan [Laramie, WY; Lindberg, William R [Laramie, WY

2008-09-02

A shear stress sensor for measuring fluid wall shear stress on a test surface is provided. The wall shear stress sensor is comprised of an active sensing surface and a sensor body. An elastic mechanism mounted between the active sensing surface and the sensor body allows movement between the active sensing surface and the sensor body. A driving mechanism forces the shear stress sensor to oscillate. A measuring mechanism measures displacement of the active sensing surface relative to the sensor body. The sensor may be operated under periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor measurably changes the amplitude or phase of the motion of the active sensing surface, or changes the force and power required from a control system in order to maintain constant motion. The device may be operated under non-periodic excitation where changes in the nature of the fluid properties or the fluid flow over the sensor change the transient motion of the active sensor surface or change the force and power required from a control system to maintain a specified transient motion of the active sensor surface.

Velocity shear, turbulent saturation, and steep plasma gradients in the scrape-off layer of inner-wall limited tokamaks

DOE PAGES

Halpern, Federico D.; Ricci, Paolo

2016-12-19

The narrow power decay-length (λ q), recently found in the scrape-off layer (SOL) of inner wall limited (IWL) discharges in tokamaks, is studied using 3D, flux-driven, global two fluid turbulence simulations. The formation of the steep plasma profiles is found to arise due to radially sheared E×B poloidal flows. A complex interaction between sheared flows and parallel plasma currents outflowing into the sheath regulates the turbulent saturation, determining the transport levels. We quantify the effects of sheared flows, obtaining theoretical estimates in agreement with our non-linear simulations. As a result, analytical calculations suggest that the IWL λ q is roughlymore » equal to the turbulent correlation length.« less

Characteristics of sources and sinks of momentum in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Fiscaletti, D.; Ganapathisubramani, B.

2018-05-01

In turbulent boundary layers, the wall-normal gradient of the Reynolds shear stress identifies momentum sources and sinks (T =∂ [-u v ]/∂ y ). These motions can be physically interpreted in two ways: (1) as contributors to the turbulence term balancing the mean momentum equation, and (2) as regions of strong local interaction between velocity and vorticity fluctuations. In this paper, the space-time evolution of momentum sources and sinks is investigated in a turbulent boundary layer at the Reynolds number (Reτ) = 2700, with time-resolved planar particle image velocimetry in a plane along the streamwise and wall-normal directions. Wave number-frequency power spectra of T fluctuations reveal that the wave velocities of momentum sources and sinks tend to match the local streamwise velocity in proximity to the wall. However, as the distance from the wall increases, the wave velocities of the T events are slightly lower than the local streamwise velocities of the flow, which is also confirmed from the tracking in time of the intense momentum sources and sinks. This evidences that momentum sources and sinks are preferentially located in low-momentum regions of the flow. The spectral content of the T fluctuations is maximum at the wall, but it decreases monotonically as the distance from the wall grows. The relative spectral contributions of the different wavelengths remains unaltered at varying wall-normal locations. From autocorrelation coefficient maps, the characteristic streamwise and wall-normal extents of the T motions are respectively 60 and 40 wall units, independent of the wall distance. Both statistics and instantaneous visualizations show that momentum sources and sinks have a preferential tendency to be organized in positive-negative pairs in the wall-normal direction.

Surface temperatures and glassy state investigations in tribology, part 2

NASA Technical Reports Server (NTRS)

Bair, S. S.; Winer, W. O.

1979-01-01

Measurements of lubricant shear rheological behavior in the amorphous solid region and near the liquid solid transition are reported. Elastic, plastic and viscous behavior was observed. The maximum yield shear stress (limiting shear stress) is a function of temperature and pressure and is believed to be the property which determines the maximum traction in elastohydrodynamic contacts such as traction drives. A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is Maxwell model modified with a limiting shear stress. Three material properties are required: low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure.

Post-Treatment Hemodynamics of a Basilar Aneurysm and Bifurcation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortega, J; Hartman, J; Rodriguez, J

2008-01-16

Aneurysm re-growth and rupture can sometimes unexpectedly occur following treatment procedures that were initially considered to be successful at the time of treatment and post-operative angiography. In some cases, this can be attributed to surgical clip slippage or endovascular coil compaction. However, there are other cases in which the treatment devices function properly. In these instances, the subsequent complications are due to other factors, perhaps one of which is the post-treatment hemodynamic stress. To investigate whether or not a treatment procedure can subject the parent artery to harmful hemodynamic stresses, computational fluid dynamics simulations are performed on a patient-specific basilarmore » aneurysm and bifurcation before and after a virtual endovascular treatment. The simulations demonstrate that the treatment procedure produces a substantial increase in the wall shear stress. Analysis of the post-treatment flow field indicates that the increase in wall shear stress is due to the impingement of the basilar artery flow upon the aneurysm filling material and to the close proximity of a vortex tube to the artery wall. Calculation of the time-averaged wall shear stress shows that there is a region of the artery exposed to a level of wall shear stress that can cause severe damage to endothelial cells. The results of this study demonstrate that it is possible for a treatment procedure, which successfully excludes the aneurysm from the vascular system and leaves no aneurysm neck remnant, to elevate the hemodynamic stresses to levels that are injurious to the immediately adjacent vessel wall.« less

Finite element analyses for seismic shear wall international standard problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Y.J.; Hofmayer, C.H.

Two identical reinforced concrete (RC) shear walls, which consist of web, flanges and massive top and bottom slabs, were tested up to ultimate failure under earthquake motions at the Nuclear Power Engineering Corporation`s (NUPEC) Tadotsu Engineering Laboratory, Japan. NUPEC provided the dynamic test results to the OECD (Organization for Economic Cooperation and Development), Nuclear Energy Agency (NEA) for use as an International Standard Problem (ISP). The shear walls were intended to be part of a typical reactor building. One of the major objectives of the Seismic Shear Wall ISP (SSWISP) was to evaluate various seismic analysis methods for concrete structuresmore » used for design and seismic margin assessment. It also offered a unique opportunity to assess the state-of-the-art in nonlinear dynamic analysis of reinforced concrete shear wall structures under severe earthquake loadings. As a participant of the SSWISP workshops, Brookhaven National Laboratory (BNL) performed finite element analyses under the sponsorship of the U.S. Nuclear Regulatory Commission (USNRC). Three types of analysis were performed, i.e., monotonic static (push-over), cyclic static and dynamic analyses. Additional monotonic static analyses were performed by two consultants, F. Vecchio of the University of Toronto (UT) and F. Filippou of the University of California at Berkeley (UCB). The analysis results by BNL and the consultants were presented during the second workshop in Yokohama, Japan in 1996. A total of 55 analyses were presented during the workshop by 30 participants from 11 different countries. The major findings on the presented analysis methods, as well as engineering insights regarding the applicability and reliability of the FEM codes are described in detail in this report. 16 refs., 60 figs., 16 tabs.« less

Repair and Strengthening by Use of Superficial Fixed Laminates of Cracked Masonry Walls Sheared Horizontally-Laboratory Tests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kubica, Jan; Kwiecien, Arkadiusz; Zajac, Boguslaw

2008-07-08

There are many methods of crack repairing in masonry structures. One of them is repair and strengthening by using of superficial fixed laminates, especially in case of masonry walls with plastering on their both sides. The initial laboratory tests of three different types of strengthening of diagonal cracked masonry wallettes are presented. Tests concerned three clay brick masonry walls subjected to horizontal shearing with two levels of precompression and strengthened by flexible polymer injection, superficial glass fixed by polymer fibre laminate plates and using of CRFP strips stiff fixed to the wall surface by polymer and stiff resin epoxy fixingmore » are presented and discussed.« less

A law of the wall for turbulent boundary layers with suction: Stevenson's formula revisited

NASA Astrophysics Data System (ADS)

Vigdorovich, Igor

2016-08-01

The turbulent velocity field in the viscous sublayer of the boundary layer with suction to a first approximation is homogeneous in any direction parallel to the wall and is determined by only three constant quantities — the wall shear stress, the suction velocity, and the fluid viscosity. This means that there exists a finite algebraic relation between the turbulent shear stress and the longitudinal mean-velocity gradient, using which as a closure condition for the equations of motion, we establish an exact asymptotic behavior of the velocity profile at the outer edge of the viscous sublayer. The obtained relationship provides a generalization of the logarithmic law to the case of wall suction.

Numerical Investigation of Oxygenated and Deoxygenated Blood Flow through a Tapered Stenosed Arteries in Magnetic Field.

PubMed

Abdollahzadeh Jamalabadi, M Y; Akbari Bidokhti, Amin Ali; Khak Rah, Hamid; Vaezi, Siavash; Hooshmand, Payam

2016-01-01

Current paper is focused on transient modeling of blood flow through a tapered stenosed arteries surrounded a by solenoid under the presence of heat transfer. The oxygenated and deoxygenated blood are considered here by the Newtonian and Non-Newtonian fluid (power law and Carreau-Yasuda) models. The governing equations of bio magnetic fluid flow for an incompressible, laminar, homogeneous, non-Newtonian are solved by finite volume method with SIMPLE algorithm for structured grid. Both magnetization and electric current source terms are well thought-out in momentum and energy equations. The effects of fluid viscosity model, Hartmann number, and magnetic number on wall shear stress, shearing stress at the stenosis throat and maximum temperature of the system are investigated and are optimized. The current study results are in agreement with some of the existing findings in the literature and are useful in thermal and mechanical design of spatially varying magnets to control the drug delivery and biomagnetic fluid flows through tapered arteries.

A Computational Model for Biomechanical Effects of Arterial Compliance Mismatch

PubMed Central

He, Fan; Hua, Lu; Gao, Li-jian

2015-01-01

Background. Compliance mismatch is a negative factor and it needs to be considered in arterial bypass grafting. Objective. A computational model was employed to investigate the effects of arterial compliance mismatch on blood flow, wall stress, and deformation. Methods. The unsteady blood flow was assumed to be laminar, Newtonian, viscous, and incompressible. The vessel wall was assumed to be linear elastic, isotropic, and incompressible. The fluid-wall interaction scheme was constructed using the finite element method. Results. The results show that there are identical wall shear stress waveforms, wall stress, and strain waveforms at different locations. The comparison of the results demonstrates that wall shear stresses and wall strains are higher while wall stresses are lower at the more compliant section. The differences promote the probability of intimal thickening at some locations. Conclusions. The model is effective and gives satisfactory results. It could be extended to all kinds of arteries with complicated geometrical and material factors. PMID:27019580

Transient response of nonideal ion-selective microchannel-nanochannel devices

NASA Astrophysics Data System (ADS)

Leibowitz, Neta; Schiffbauer, Jarrod; Park, Sinwook; Yossifon, Gilad

2018-04-01

We report evidence of variation in ion selectivity of a fabricated microchannel-nanochannel device resulting in the appearance of a distinct local maximum in the overlimiting chronopotentiometric response. In this system consisting of shallow microchannels joined by a nanochannel, viscous shear at the microchannel walls suppresses the electro-osmotic instability and prevents any associated contribution to the nonmonotonic response. Thus, this response is primarily electrodiffusive. Numerical simulations indicate that concentration polarization develops not only within the microchannel but also within the nanochannel itself, with a local voltage maximum in the chronopotentiometric response correlated with interfacial depletion and having the classic i-2 Sands time dependence. Furthermore, the occurrence of the local maxima is correlated with the change in selectivity due to internal concentration polarization. Understanding the transient nonideal permselective response is essential for obtaining fundamental insight and for optimizing efficient operation of practical fabricated nanofluidic and membrane devices.

Clinical, morphological, and hemodynamic independent characteristic factors for rupture of posterior communicating artery aneurysms.

PubMed

Zhang, Ying; Jing, Linkai; Liu, Jian; Li, Chuanhui; Fan, Jixing; Wang, Shengzhang; Li, Haiyun; Yang, Xinjian

2016-08-01

To identify clinical, morphological, and hemodynamic independent characteristic factors that discriminate posterior communicating artery (PCoA) aneurysm rupture status. 173 patients with single PCoA aneurysms (108 ruptured, 65 unruptured) between January 2012 and June 2014 were retrospectively collected. Patient-specific models based on their three-dimensional digital subtraction angiography images were constructed and analyzed by a computational fluid dynamic method. All variables were analyzed by univariate analysis and multivariate logistic regression analysis. Two clinical factors (younger age and atherosclerosis), three morphological factors (higher aspect ratio, bifurcation type, and irregular shape), and six hemodynamic factors (lower mean and minimum wall shear stress, higher oscillatory shear index, a greater portion of area under low wall shear stress, unstable and complex flow pattern) were significantly associated with PCoA aneurysm rupture. Independent factors characterizing the rupture status were identified as age (OR 0.956, p=0.015), irregular shape (OR 6.709, p<0.001), and minimum wall shear stress (OR 0.001, p=0.038). We combined clinical, morphological, and hemodynamic characteristics analysis and found the three strongest independent factors for PCoA aneurysm rupture were younger age, irregular shape, and low minimum wall shear stress. This may be useful for guiding risk assessments and subsequent treatment decisions for PCoA aneurysms. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

Morphotype-Dependent Flow Characteristics in Bicuspid Aortic Valve Ascending Aortas: A Benchtop Particle Image Velocimetry Study

PubMed Central

McNally, Andrew; Madan, Ashish; Sucosky, Philippe

2017-01-01

The bicuspid aortic valve (BAV) is a major risk factor for secondary aortopathy such as aortic dilation. The heterogeneous BAV morphotypes [left-right-coronary cusp fusion (LR), right-non-coronary cusp fusion (RN), and left-non-coronary cusp fusion (LN)] are associated with different dilation patterns, suggesting a role for hemodynamics in BAV aortopathogenesis. However, assessment of this theory is still hampered by the limited knowledge of the hemodynamic abnormalities generated by the distinct BAV morphotypes. The objective of this study was to compare experimentally the hemodynamics of a normal (i.e., non-dilated) ascending aorta (AA) subjected to tricuspid aortic valve (TAV), LR-BAV, RN-BAV, and NL-BAV flow. Tissue BAVs reconstructed from porcine TAVs were subjected to physiologic pulsatile flow conditions in a left-heart simulator featuring a realistic aortic root and compliant aorta. Phase-locked particle image velocimetry experiments were carried out to characterize the flow in the aortic root and in the tubular AA in terms of jet skewness and displacement, as well as mean velocity, viscous shear stress and Reynolds shear stress fields. While all three BAVs generated skewed and asymmetrical orifice jets (up to 1.7- and 4.0-fold increase in flow angle and displacement, respectively, relative to the TAV at the sinotubular junction), the RN-BAV jet was out of the plane of observation. The LR- and NL-BAV exhibited a 71% increase in peak-systolic orifice jet velocity relative to the TAV, suggesting an inherent degree of stenosis in BAVs. While these two BAV morphotypes subjected the convexity of the aortic wall to viscous shear stress overloads (1.7-fold increase in maximum peak-systolic viscous shear stress relative to the TAV-AA), the affected sites were morphotype-dependent (LR-BAV: proximal AA, NL-BAV: distal AA). Lastly, the LR- and NL-BAV generated high degrees of turbulence in the AA (up to 2.3-fold increase in peak-systolic Reynolds shear stress relative to the TAV) that were sustained from peak systole throughout the deceleration phase. This in vitro study reveals substantial flow abnormalities (increased jet skewness, asymmetry, jet velocity, turbulence, and shear stress overloads) in non-dilated BAV aortas, which differ from those observed in dilated aortas but still coincide with aortic wall regions prone to dilation. PMID:28203207

Impact of competitive flow on wall shear stress in coronary surgery: computational fluid dynamics of a LIMA-LAD model.

PubMed

Nordgaard, Håvard; Swillens, Abigail; Nordhaug, Dag; Kirkeby-Garstad, Idar; Van Loo, Denis; Vitale, Nicola; Segers, Patrick; Haaverstad, Rune; Lovstakken, Lasse

2010-12-01

Competitive flow from native coronary vessels is considered a major factor in the failure of coronary bypass grafts. However, the pathophysiological effects are not fully understood. Low and oscillatory wall shear stress (WSS) is known to induce endothelial dysfunction and vascular disease, like atherosclerosis and intimal hyperplasia. The aim was to investigate the impact of competitive flow on WSS in mammary artery bypass grafts. Using computational fluid dynamics, WSS was calculated in a left internal mammary artery (LIMA) graft to the left anterior descending artery in a three-dimensional in vivo porcine coronary artery bypass graft model. The following conditions were investigated: high competitive flow (non-significant coronary lesion), partial competitive flow (significant coronary lesion), and no competitive flow (totally occluded coronary vessel). Time-averaged WSS of LIMA at high, partial, and no competitive flow were 0.3-0.6, 0.6-3.0, and 0.9-3.0 Pa, respectively. Further, oscillatory WSS quantified as the oscillatory shear index (OSI) ranged from (maximum OSI = 0.5 equals zero net WSS) 0.15 to 0.35, <0.05, and <0.05, respectively. Thus, high competitive flow resulted in substantial oscillatory and low WSS. Moderate competitive flow resulted in WSS and OSI similar to the no competitive flow condition. Graft flow is highly dependent on the degree of competitive flow. High competitive flow was found to produce unfavourable WSS consistent with endothelial dysfunction and subsequent graft narrowing and failure. Partial competitive flow, however, may be better tolerated as it was found to be similar to the ideal condition of no competitive flow.

Characteristics of time-varying intracranial pressure on blood flow through cerebral artery: A fluid-structure interaction approach.

PubMed

Syed, Hasson; Unnikrishnan, Vinu U; Olcmen, Semih

2016-02-01

Elevated intracranial pressure is a major contributor to morbidity and mortality in severe head injuries. Wall shear stresses in the artery can be affected by increased intracranial pressures and may lead to the formation of cerebral aneurysms. Earlier research on cerebral arteries and aneurysms involves using constant mean intracranial pressure values. Recent advancements in intracranial pressure monitoring techniques have led to measurement of the intracranial pressure waveform. By incorporating a time-varying intracranial pressure waveform in place of constant intracranial pressures in the analysis of cerebral arteries helps in understanding their effects on arterial deformation and wall shear stress. To date, such a robust computational study on the effect of increasing intracranial pressures on the cerebral arterial wall has not been attempted to the best of our knowledge. In this work, fully coupled fluid-structure interaction simulations are carried out to investigate the effect of the variation in intracranial pressure waveforms on the cerebral arterial wall. Three different time-varying intracranial pressure waveforms and three constant intracranial pressure profiles acting on the cerebral arterial wall are analyzed and compared with specified inlet velocity and outlet pressure conditions. It has been found that the arterial wall experiences deformation depending on the time-varying intracranial pressure waveforms, while the wall shear stress changes at peak systole for all the intracranial pressure profiles. © IMechE 2015.

Measurements of wall shear stress in a planar turbulent Couette flow with porous walls

NASA Astrophysics Data System (ADS)

Beuther, Paul

2013-11-01

Measurements of drag on a moving web in a multi-span festoon show a stronger than expected dependency on the porosity of the web. The experiments suggest a wall shear stress 3-4 times larger than non-porous webs or historical Couette flow data for solid walls. Previous DNS studies by Jimenez et al. (JFM Vol 442) of boundary layers with passive porous surfaces predict a much smaller increase in wall shear stress for a porous wall of only 40%. Other DNS studies by Quadrio et al. (JFM Vol 576) of porous walls with periodic transpiration do show a large increase in drag under certain periodic conditions of modest amplitude. Although those results are aligned in magnitude with this study, the exact reason for the observed high drag for porous webs in this present study is not understood because there was no external disturbance applied to the web. It can be hypothesized that natural flutter of the web results in a similar mechanism shown in the periodic DNS study, but when the natural flutter was reduced by increasing web tension, there was only a small decrease of the drag. A key difference in this study is that because of the multiple parallel spans in a festoon, any transpiration in one layer must act in the opposite manner on the adjacent span.

Stent implantation influence wall shear stress evolution

NASA Astrophysics Data System (ADS)

Bernad, S. I.; Totorean, A. F.; Bosioc, A. I.; Petre, I.; Bernad, E. S.

2016-06-01

Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. The impact of flow alterations around struts vary as the strut geometrical parameters change. Our results provide data regarding the hemodynamic parameters for the blood flow in both stenosed and stented coronary artery under physiological conditions, namely wall shear stress and pressure drop.

The Effects of Single-Wall Carbon Nanotubes on the Shear Piezoelectricity of Biopolymers

NASA Technical Reports Server (NTRS)

Lovell, Conrad; Fitz-Gerald, James M.; Harrison, Joycelyn S.; Park, Cheol

2008-01-01

Shear piezoelectricity was investigated in a series of composites consisting of increased loadings of single-wall carbon nanotubes (SWCNTs) in poly (gamma-benzyl-L-glutamate), or PBLG. The effects of the SWCNTs on this material property in PBLG will be discussed. Their influence on the morphology of the polymer (degree of orientation and crystallinity), and electrical and dielectric properties of the composite will be reported

Influence of morphology and hemodynamic factors on rupture of multiple intracranial aneurysms: matched-pairs of ruptured-unruptured aneurysms located unilaterally on the anterior circulation.

PubMed

Zhang, Ying; Yang, Xinjian; Wang, Yang; Liu, Jian; Li, Chuanhui; Jing, Linkai; Wang, Shengzhang; Li, Haiyun

2014-12-31

The authors evaluated the impact of morphological and hemodynamic factors on the rupture of matched-pairs of ruptured-unruptured intracranial aneurysms on one patient's ipsilateral anterior circulation with 3D reconstruction model and computational fluid dynamic method simulation. 20 patients with intracranial aneurysms pairs on the same-side of anterior circulation but with different rupture status were retrospectively collected. Each pair was divided into ruptured-unruptured group. Patient-specific models based on their 3D-DSA images were constructed and analyzed. The relative locations, morphologic and hemodynamic factors of these two groups were compared. There was no significant difference in the relative bleeding location. The morphological factors analysis found that the ruptured aneurysms more often had irregular shape and had significantly higher maximum height and aspect ratio. The hemodynamic factors analysis found lower minimum wall shear stress (WSSmin) and more low-wall shear stress-area (LSA) in the ruptured aneurysms than that of the unruptured ones. The ruptured aneurysms more often had WSSmin on the dome. Intracranial aneurysms pairs with different rupture status on unilateral side of anterior circulation may be a good disease model to investigate possible characteristics linked to rupture independent of patient characteristics. Irregular shape, larger size, higher aspect ratio, lower WSSmin and more LSA may indicate a higher risk for their rupture.

CFD simulation of hemodynamics in sequential and individual coronary bypass grafts based on multislice CT scan datasets.

PubMed

Hajati, Omid; Zarrabi, Khalil; Karimi, Reza; Hajati, Azadeh

2012-01-01

There is still controversy over the differences in the patency rates of the sequential and individual coronary artery bypass grafting (CABG) techniques. The purpose of this paper was to non-invasively evaluate hemodynamic parameters using complete 3D computational fluid dynamics (CFD) simulations of the sequential and the individual methods based on the patient-specific data extracted from computed tomography (CT) angiography. For CFD analysis, the geometric model of coronary arteries was reconstructed using an ECG-gated 64-detector row CT. Modeling the sequential and individual bypass grafting, this study simulates the flow from the aorta to the occluded posterior descending artery (PDA) and the posterior left ventricle (PLV) vessel with six coronary branches based on the physiologically measured inlet flow as the boundary condition. The maximum calculated wall shear stress (WSS) in the sequential and the individual models were estimated to be 35.1 N/m(2) and 36.5 N/m(2), respectively. Compared to the individual bypass method, the sequential graft has shown a higher velocity at the proximal segment and lower spatial wall shear stress gradient (SWSSG) due to the flow splitting caused by the side-to-side anastomosis. Simulated results combined with its surgical benefits including the requirement of shorter vein length and fewer anastomoses advocate the sequential method as a more favorable CABG method.

Scaled-Up Fabrication of Thin-Walled ZK60 Tubing using Shear Assisted Processing and Extrusion (ShAPE)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whalen, Scott A.; Joshi, Vineet V.; Overman, Nicole R.

Shear Assisted Processing and Extrusion (ShAPE) has been scaled-up and applied to direct extrusion of thin-walled magnesium tubing. Using ShAPE, billets of ZK60A-T5 were directly extruded into round tubes having an outer diameter of 50.8 mm and wall thickness of 1.52 mm. The severe shearing conditions inherent to ShAPE resulted in microstructural refinement with an average grain size of 3.8μm measured at the midpoint of the tube wall. Tensile testing per ATSM E-8 on specimens oriented parallel to the extrusion direction gave an ultimate tensile strength of 254.4 MPa and elongation of 20.1%. Specimens tested perpendicular to the extrusion directionmore » had an ultimate tensile strength of 297.2 MPa and elongation of 25.0%. Due to material flow effects resulting from the simultaneous linear and rotational shear intrinsic to ShAPE, ram force and electrical power consumption during extrusion were just 40 kN and 11.5 kW respectively. This represents a significant reduction in ram force and power consumption compared to conventional extrusion. As such, there is potential for ShAPE to offer a scalable, lower cost extrusion option with potentially improved bulk mechanical properties.« less

Development of a wall-shear-stress sensor and measurements in mini-channels with partial blockages

NASA Astrophysics Data System (ADS)

Afara, Samer; Medvescek, James; Mydlarski, Laurent; Baliga, Bantwal R.; MacDonald, Mark

2014-05-01

The design, construction, operation and validation of a wall-shear-stress sensor, and measurements obtained using this sensor in air flows downstream of partial blockages in a mini-channel are presented. The sensor consisted of a hot wire mounted over a small rectangular slot and operated using a constant-temperature anemometer. It was used to investigate flows similar to those within the mini-channels inside notebook computers. The overall goal of the present work was to develop a sensor suitable for measurements of the wall-shear stress in such flows, which can be used to validate corresponding numerical simulations, as the latter are known to be often surprisingly inaccurate. To this end, measurements of the wall-shear stress, and the corresponding statistical moments and power spectral densities, were obtained at different distances downstream of the partial blockage, with blockage ratios of 39.7, 59.2, and 76.3 %. The Reynolds number (based on average velocity and hydraulic diameter) ranged from 100 to 900. The results confirmed the presence of unsteadiness, separation, reattachment, and laminar-turbulent transition in the ostensibly laminar flow of air in mini-channels with partial blockages. The present results demonstrate why accurate numerical predictions of cooling air flows in laptop and notebook computers remain a challenging task.

An effective simplified model of composite compression struts for partially-restrained steel frame with reinforced concrete infill walls

NASA Astrophysics Data System (ADS)

Sun, Guohua; Chuang-Sheng, Walter Yang; Gu, Qiang; DesRoches, Reginald

2018-04-01

To resolve the issue regarding inaccurate prediction of the hysteretic behavior by micro-based numerical analysis for partially-restrained (PR) steel frames with solid reinforced concrete (RC) infill walls, an innovative simplified model of composite compression struts is proposed on the basis of experimental observation on the cracking distribution, load transferring mechanism, and failure modes of RC infill walls filled in PR steel frame. The proposed composite compression struts model for the solid RC infill walls is composed of α inclined struts and main diagonal struts. The α inclined struts are used to reflect the part of the lateral force resisted by shear connectors along the frame-wall interface, while the main diagonal struts are introduced to take into account the rest of the lateral force transferred along the diagonal direction due to the complicated interaction between the steel frame and RC infill walls. This study derives appropriate formulas for the effective widths of the α inclined strut and main diagonal strut, respectively. An example of PR steel frame with RC infill walls simulating simulated by the composite inclined compression struts model is illustrated. The maximum lateral strength and the hysteresis curve shape obtained from the proposed composite strut model are in good agreement with those from the test results, and the backbone curve of a PR steel frame with RC infill walls can be predicted precisely when the inter-story drift is within 1%. This simplified model can also predict the structural stiffness and the equivalent viscous damping ratio well when the inter-story drift ratio exceeds 0.5%.

Dynamics of liquid slug using particle image velocimetry technique

NASA Astrophysics Data System (ADS)

Siddiqui, M. I.; Aziz, A. Rashid A.; Heikal, M. R.

2016-11-01

Two phase liquid-gas slug flow is a source of vibration and fatigue on pipe walls and downstream equipment. This paper examines the effect of inlet conditions on the stream-wise velocity profiles and on the shear stresses induced by the liquid phase on the pipe wall during the slug flow. Instantaneous velocity vector fields of the liquid-gas (water-air) slug flow regime were obtained using particle image velocimetry (PIV) technique at various inlet conditions. A 6-m long Plexiglas pipe having an internal diameter 74-mm with a slight inclination of about 1.16° was considered for the visualization of the flow pattern. Test section was employed at a point 3.5m from the inlet, mounted with optical correction box filled with water to minimize the curvature effect of pipe on the PIV snapshots. Stream-wise velocity profiles are obtained at the wake of the liquid slug and the effect of inlet conditions were analyzed. A direct relationship was observed in between superficial gas velocity and the liquid stream-wise velocity at wake section of the slug flow. Further, the lower wall shear stresses were obtained using PIV velocity profiles at liquid film and the slug wake sections in a unit slug. The wall shear stress remained higher in the liquid slugy body as compared to the liquid film. Moreover, an increase in the wall shear stress was observed by increasing the gas superficial velocities.

Impact of Wall Shear Stress and Pressure Variation on the Stability of Atherosclerotic Plaque

NASA Astrophysics Data System (ADS)

Taviani, V.; Li, Z. Y.; Sutcliffe, M.; Gillard, J.

Rupture of vulnerable atheromatous plaque in the carotid and coronary arteries often leads to stroke and heart attack respectively. The mechanism of blood flow and plaque rupture in stenotic arteries is still not fully understood. A three dimensional rigid wall model was solved under steady and unsteady conditions assuming a time-varying inlet velocity profile to investigate the relative importance of axial forces and pressure drops in arteries with asymmetric stenosis. Flow-structure interactions were investigated for the same geometry and the results were compared with those retrieved with the corresponding one dimensional models. The Navier-Stokes equations were used as the governing equations for the fluid. The tube wall was assumed linearly elastic, homogeneous isotropic. The analysis showed that wall shear stress is small (less than 3.5%) with respect to pressure drop throughout the cycle even for severe stenosis. On the contrary, the three dimensional behavior of velocity, pressure and wall shear stress is in general very different from that predicted by one dimensional models. This suggests that the primary source of mistakes in one dimensional studies comes from neglecting the three dimensional geometry of the plaque. Neglecting axial forces only involves minor errors.

In-shoe plantar tri-axial stress profiles during maximum-effort cutting maneuvers.

PubMed

Cong, Yan; Lam, Wing Kai; Cheung, Jason Tak-Man; Zhang, Ming

2014-12-18

Soft tissue injuries, such as anterior cruciate ligament rupture, ankle sprain and foot skin problems, frequently occur during cutting maneuvers. These injuries are often regarded as associated with abnormal joint torque and interfacial friction caused by excessive external and in-shoe shear forces. This study simultaneously investigated the dynamic in-shoe localized plantar pressure and shear stress during lateral shuffling and 45° sidestep cutting maneuvers. Tri-axial force transducers were affixed at the first and second metatarsal heads, lateral forefoot, and heel regions in the midsole of a basketball shoe. Seventeen basketball players executed both cutting maneuvers with maximum efforts. Lateral shuffling cutting had a larger mediolateral braking force than 45° sidestep cutting. This large braking force was concentrated at the first metatarsal head, as indicated by its maximum medial shear stress (312.2 ± 157.0 kPa). During propulsion phase, peak shear stress occurred at the second metatarsal head (271.3 ± 124.3 kPa). Compared with lateral shuffling cutting, 45° sidestep cutting produced larger peak propulsion shear stress (463.0 ± 272.6 kPa) but smaller peak braking shear stress (184.8 ± 181.7 kPa), of which both were found at the first metatarsal head. During both cutting maneuvers, maximum medial and posterior shear stress occurred at the first metatarsal head, whereas maximum pressure occurred at the second metatarsal head. The first and second metatarsal heads sustained relatively high pressure and shear stress and were expected to be susceptible to plantar tissue discomfort or injury. Due to different stress distribution, distinct pressure and shear cushioning mechanisms in basketball footwear might be considered over different foot regions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Intracranial Vascular Disease Evaluation With Combined Vessel Wall Imaging And Patient Specific Hemodynamics

NASA Astrophysics Data System (ADS)

Samson, Kurt; Mossa-Basha, Mahmud; Yuan, Chun; Canton, Maria De Gador; Aliseda, Alberto

2017-11-01

Intracranial vascular pathologies are evaluated with angiography, conventional digital subtraction angiography or non-invasive (MRI, CT). Current techniques present limitations on the resolution with which the vessel wall characteristics can be measured, presenting a major challenge to differential diagnostic of cerebral vasculopathies. A new combined approach is presented that incorporates patient-specific image-based CFD models with intracranial vessel-wall MRI (VWMRI). Comparisons of the VWMRI measurements, evaluated for the presence of wall enhancement and thin-walled regions, against CFD metrics such as wall shear stress (WSS), and oscillatory shear index (OSI) are used to understand how the new imaging technique developed can predict the influence of hemodynamics on the deterioration of the aneurysmal wall, leading to rupture. Additionally, histology of each resected aneurysm, evaluated for inflammatory infiltration and wall thickness features, is used to validate the analysis from VWMRI and CFD. This data presents a solid foundation on which to build a new framework for combined VWMRI-CFD to predict unstable wall changes in unruptured intracranial aneurysms, and support clinical monitoring and intervention decisions.

An analytical study of the effects of transverse shear deformation and anisotropy on buckling loads of laminated cylinders. M.S. Thesis - George Washington Univ.

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.

1987-01-01

Buckling loads of thick-walled orthotropic and anisotropic simply supported circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of buckling loads predicted by the conventional first-order transverse-shear deformation theory and the higher-order theory show that the additional allowance for transverse shear deformation has a negligible effect on the predicted buckling loads of medium-thick metallic isotropic cylinders. However, the higher-order theory predicts buckling loads which are significantly lower than those predicted by the first-order transverse-shear deformation theory for certain short, thick-walled cylinders which have low through-the-thickness shear moduli. A parametric study of the effects of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 45 degree plies are most sensitive to transverse-shear deformation effects. Interaction curves for buckling loads of cylinders subjected to axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are as sensitive to transverse-shear deformation effects as buckling loads due to axial compressive loadings. The effects of anisotropy are important over a much wider range of cylinder geometries than the effects of transverse shear deformation.

Experimental Tests of Nonlocal Rheology in Dense Granular Flows

NASA Astrophysics Data System (ADS)

Tang, Zhu; Brzinski, Ted; Shearer, Michael; Daniels, Karen

Several nonlocal granular rheology models have been proposed to address shortcomings in local rheology models. One such model, developed by Kamrin & Koval, is based on extending a local Bagnold-type granular flow law by including a Laplacian term that accounts for the grain size and cooperative effects. We perform experiments to test this model in a quasi-2D annular shear geometry with a fixed outer wall and a rotating inner wall. We obtain the speed profile by particle tracking. We measure the inner wall torque, and calculate the pressure and shear stress on the outer wall using deformable laser-cut leaf springs. This allows us to calculate the relationship between the stress ratio μ and the inertial number I at different inner wall rotation speeds and packing fractions. The results are compared with nonlocal models.

Wall shear stress fixed points in blood flow

NASA Astrophysics Data System (ADS)

Arzani, Amirhossein; Shadden, Shawn

2017-11-01

Patient-specific computational fluid dynamics produces large datasets, and wall shear stress (WSS) is one of the most important parameters due to its close connection with the biological processes at the wall. While some studies have investigated WSS vectorial features, the WSS fixed points have not received much attention. In this talk, we will discuss the importance of WSS fixed points from three viewpoints. First, we will review how WSS fixed points relate to the flow physics away from the wall. Second, we will discuss how certain types of WSS fixed points lead to high biochemical surface concentration in cardiovascular mass transport problems. Finally, we will introduce a new measure to track the exposure of endothelial cells to WSS fixed points.

Fluid Mechanics, Arterial Disease, and Gene Expression.

PubMed

Tarbell, John M; Shi, Zhong-Dong; Dunn, Jessilyn; Jo, Hanjoong

2014-01-01

This review places modern research developments in vascular mechanobiology in the context of hemodynamic phenomena in the cardiovascular system and the discrete localization of vascular disease. The modern origins of this field are traced, beginning in the 1960s when associations between flow characteristics, particularly blood flow-induced wall shear stress, and the localization of atherosclerotic plaques were uncovered, and continuing to fluid shear stress effects on the vascular lining endothelial) cells (ECs), including their effects on EC morphology, biochemical production, and gene expression. The earliest single-gene studies and genome-wide analyses are considered. The final section moves from the ECs lining the vessel wall to the smooth muscle cells and fibroblasts within the wall that are fluid me chanically activated by interstitial flow that imposes shear stresses on their surfaces comparable with those of flowing blood on EC surfaces. Interstitial flow stimulates biochemical production and gene expression, much like blood flow on ECs.

Nonlinear Reynolds stress model for turbulent shear flows

NASA Technical Reports Server (NTRS)

Barton, J. Michael; Rubinstein, R.; Kirtley, K. R.

1991-01-01

A nonlinear algebraic Reynolds stress model, derived using the renormalization group, is applied to equilibrium homogeneous shear flow and fully developed flow in a square duct. The model, which is quadratically nonlinear in the velocity gradients, successfully captures the large-scale inhomogeneity and anisotropy of the flows studied. The ratios of normal stresses, as well as the actual magnitudes of the stresses are correctly predicted for equilibrium homogeneous shear flow. Reynolds normal stress anisotropy and attendant turbulence driven secondary flow are predicted for a square duct. Profiles of mean velocity and normal stresses are in good agreement with measurements. Very close to walls, agreement with measurements diminishes. The model has the benefit of containing no arbitrary constants; all values are determined directly from the theory. It seems that near wall behavior is influenced by more than the large scale anisotropy accommodated in the current model. More accurate near wall calculations may well require a model for anisotropic dissipation.

Wall shear stress measurements using a new transducer

NASA Technical Reports Server (NTRS)

Vakili, A. D.; Wu, J. M.; Lawing, P. L.

1986-01-01

A new instrument has been developed for direct measurement of wall shear stress. This instrument is simple and symmetric in design with small moving mass and no internal friction. Features employed in the design of this instrument eliminate most of the difficulties associated with the traditional floating element balances. Vibration problems associated with the floating element skin friction balances have been found to be minimized by the design features and optional damping provided. The unique design of this instrument eliminates or reduces the errors associated with conventional floating-element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Measurement made in three different tunnels show good agreement with theory and data obtained by the floating element devices.

Kinetics of the head-neck complex in low-speed rear impact.

PubMed

Stemper, Brian D; Yoganandan, Naryan; Pintar, Frank A

2003-01-01

A comprehensive characterization of the biomechanics of the cervical spine in rear impact will lead to an understanding of the mechanisms of whiplash injury. Cervical kinematics have been experimentally described using human volunteers, full-body cadaver specimens, and isolated and intact head-neck specimens. However, forces and moments at the cervico-thoracic junction have not been clearly delineated. An experimental investigation was performed using ten intact head-neck complexes to delineate the loading at the base of the cervical spine and angular acceleration of the head in whiplash. A pendulum-minisled apparatus was used to simulate whiplash acceleration of the thorax at four impact severities. Lower neck loads were measured using a six-axis load cell attached between the minisled and head-neck specimens, and head angular motion was measured with an angular rate sensor attached to the lateral side of the head. Shear and axial force, extension moment, and head angular acceleration increased with impact severity. Shear force was significantly larger than axial force (p < 0.0001). Shear force reached its maximum value at 46 msec. Maximum extension moment occurred between 7 and 22 msec after maximum shear force. Maximum angular acceleration of the head occurred 2 to 18 msec later. Maximum axial force occurred last (106 msec). All four kinetic components reached maximum values during cervical S-curvature, with maximum shear force and extension moment occurring before the attainment of maximum S-curvature. Results of the present investigation indicate that shear force and extension moment at the cervico-thoracic junction drive the non-physiologic cervical S-curvature responsible for whiplash injury and underscore the importance of understanding cervical kinematics and the underlying kinetics.

Cosmic shear measurement with maximum likelihood and maximum a posteriori inference

NASA Astrophysics Data System (ADS)

Hall, Alex; Taylor, Andy

2017-06-01

We investigate the problem of noise bias in maximum likelihood and maximum a posteriori estimators for cosmic shear. We derive the leading and next-to-leading order biases and compute them in the context of galaxy ellipticity measurements, extending previous work on maximum likelihood inference for weak lensing. We show that a large part of the bias on these point estimators can be removed using information already contained in the likelihood when a galaxy model is specified, without the need for external calibration. We test these bias-corrected estimators on simulated galaxy images similar to those expected from planned space-based weak lensing surveys, with promising results. We find that the introduction of an intrinsic shape prior can help with mitigation of noise bias, such that the maximum a posteriori estimate can be made less biased than the maximum likelihood estimate. Second-order terms offer a check on the convergence of the estimators, but are largely subdominant. We show how biases propagate to shear estimates, demonstrating in our simple set-up that shear biases can be reduced by orders of magnitude and potentially to within the requirements of planned space-based surveys at mild signal-to-noise ratio. We find that second-order terms can exhibit significant cancellations at low signal-to-noise ratio when Gaussian noise is assumed, which has implications for inferring the performance of shear-measurement algorithms from simplified simulations. We discuss the viability of our point estimators as tools for lensing inference, arguing that they allow for the robust measurement of ellipticity and shear.

Pseudotachylyte formation vs. mylonitization - repeated cycles of seismic fracture and aseismic creep in the middle crust (Woodroffe Thrust, Central Australia)

NASA Astrophysics Data System (ADS)

Wex, Sebastian; Mancktelow, Neil; Hawemann, Friedrich; Camacho, Alfredo; Pennacchioni, Giorgio

2014-05-01

The Musgrave Ranges in Central Australia provide excellent exposure of the shallowly south-dipping Woodroffe Thrust, which placed ~1200 Ma granulites onto amphibolite facies gneisses. This ~400 km long E-W structure developed under mid-crustal conditions during the intracratonic Petermann Orogeny around 550 Ma. From field observations and measurements, the shortening direction is constrained to be N-S and the movement sense top-to-north. Ductile deformation during this process almost entirely localized in the footwall rocks, developing a zone of mylonites, ultramylonites and sheared pseudotachylytes, several hundred metres wide, with pseudotachylyte abundance rapidly decreasing further into the footwall. In contrast, the hanging wall behaved in a predominantly brittle manner, producing significant volumes of pseudotachylyte breccia and isolated veins, but was otherwise mostly unaffected and only weakly foliated. The difference in rheological behaviour is reflected in the pseudotachylyte fabric, which is dominantly sheared in the footwall and largely unsheared in the hanging wall. Low-strain domains in the footwall show that localized shearing initiated along pseudotachylyte veins and that shear zones and mylonitic foliations were in turn exploited by subsequent pseudotachylyte veins. Neither phyllonitization nor synkinematic growth of new muscovite is observed. In contrast to models with a simple brittle-to-viscous transition, these observations show that a continuous cycle of brittle fracturing and shearing is active in dry mid-crustal environments. The products of multiple earthquakes and ductile overprint, repeatedly exploiting the same structural discontinuity, are composite layers of sheared pseudotachylyte. In the Woodroffe Thrust, these layers are numerous and frequently observed parallel to the foliation in the footwall mylonites. The thickest of these sheared pseudotachylyte horizons (~15 m thick) mark the immediate contact to the hanging wall and almost entirely consist of pseudotachylyte matrix. Particularly in the footwall, but locally also in the hanging wall, shear strain can additionally be concentrated along the margins of dolerite dykes, whose mineral assemblages will be studied to determine the metamorphic conditions that were active during development of the Woodroffe Thrust.

Characterization of ignition transient processes in kerosene-fueled model scramjet engine by dual-pulse laser-induced plasma

NASA Astrophysics Data System (ADS)

Li, Xipeng; Liu, Weidong; Pan, Yu; Yang, Leichao; An, Bin; Zhu, Jiajian

2018-03-01

Dual-pulse laser-induced plasma ignition of kerosene in cavity at model scramjet engine is studied. The simulated flight condition is Ma 6 at 30 km, and the isolator entrance has a Mach number of 2.92, a total pressure of 2.6 MPa and a stagnation temperature of 1650 K. Two independent laser pulses at 532 nm with a pulse width of 10 ns, a diameter of 12 mm and a maximum energy of 300 mJ are focused into cavity for ignition. The flame structure and propagation during transient ignition processes are captured by simultaneous CH* and OH* chemiluminescence imaging. The entire ignition process of kerosene can be divided into five stages, which are referred as turbulent dissipation stage, quasi-stable state, combustion enhancement stage, reverting stage and combustion stabilization stage. A local closed loop of propagations of the burning mixtures from the shear layer into the recirculation zone of cavity is revealed, which the large-scale eddy in the shear layer plays a key role. The enhancement of mass exchange between shear layer and the recirculation zone of cavity could promote the flame propagation process and enhance the ignition capability as well as extend the ignition limits. A cavity shear-layer stabilized combustion of kerosene is established in the supersonic flow roughly 3.3 ms after the laser pulse. Chemical reactions mainly occur in the shear layer and the near-wall zone downstream of the cavity. The distribution of OH* is thicker than CH* at stable combustion condition.

Computer Modeling of Thermal Convection in Melts to Explain Glass Formation in Low Gravity and on Earth

NASA Technical Reports Server (NTRS)

Ray, Chandra S.; Ramachandran, Narayanan

2006-01-01

Experiments conducted up to this time on glass forming melts in the low gravity environment of space show that glasses prepared in low-g are more chemically homogeneous and more resistant to crystallization than the comparable glasses prepared at 1-g on Earth. This result is somewhat surprising and opposite to the accepted concept on glass formation for a melt. A hypothesis based on "shear thinning" of a melt, a decrease in viscosity with increasing shear stress, is proposed as an explanation for the observed low-gravity results. This paper describes detailed simulation procedures to test the role of thermal convection in introducing shear stress in glass forming melts, using a lithium disilcate melt as a model. The simulation system in its idealized version consists of a cylinder that is heated at one end and cooled at the other with gravity acting in a transverse direction to the thermal gradient. The side wall of the cylinder is assumed to be insulating. The governing equations of motion and energy are solved using variable properties for viscosity (Arrehenius and non-Arrehenius behaviors) and density (constant and temperature dependent). Other parametric variables in the calculations include gravity level and gravity vector orientation. The shear stress in the system are then computed as a function of gravity from the calculated values of maximum melt velocity, and its effect on melt viscosity (shear thinning) is predicted. Also included and discussed are the modeling efforts related to other potential convective processes in glass forming melts and their possible effects on melt viscosity.

Fluid-structure interaction modeling of aneurysmal arteries under steady-state and pulsatile blood flow: a stability analysis.

PubMed

Sharzehee, Mohammadali; Khalafvand, Seyed Saeid; Han, Hai-Chao

2018-02-01

Tortuous aneurysmal arteries are often associated with a higher risk of rupture but the mechanism remains unclear. The goal of this study was to analyze the buckling and post-buckling behaviors of aneurysmal arteries under pulsatile flow. To accomplish this goal, we analyzed the buckling behavior of model carotid and abdominal aorta with aneurysms by utilizing fluid-structure interaction (FSI) method with realistic waveforms boundary conditions. FSI simulations were done under steady-state and pulsatile flow for normal (1.5) and reduced (1.3) axial stretch ratios to investigate the influence of aneurysm, pulsatile lumen pressure and axial tension on stability. Our results indicated that aneurysmal artery buckled at the critical buckling pressure and its deflection nonlinearly increased with increasing lumen pressure. Buckling elevates the peak stress (up to 118%). The maximum aneurysm wall stress at pulsatile FSI flow was (29%) higher than under static pressure at the peak lumen pressure of 130 mmHg. Buckling results show an increase in lumen shear stress at the inner side of the maximum deflection. Vortex flow was dramatically enlarged with increasing lumen pressure and artery diameter. Aneurysmal arteries are more susceptible than normal arteries to mechanical instability which causes high stresses in the aneurysm wall that could lead to aneurysm rupture.

Localized modelling and feedback control of linear instabilities in 2-D wall bounded shear flows

NASA Astrophysics Data System (ADS)

Tol, Henry; Kotsonis, Marios; de Visser, Coen

2016-11-01

A new approach is presented for control of instabilities in 2-D wall bounded shear flows described by the linearized Navier-Stokes equations (LNSE). The control design accounts both for spatially localized actuators/sensors and the dominant perturbation dynamics in an optimal control framework. An inflow disturbance model is proposed for streamwise instabilities that drive laminar-turbulent transition. The perturbation modes that contribute to the transition process can be selected and are included in the control design. A reduced order model is derived from the LNSE that captures the input-output behavior and the dominant perturbation dynamics. This model is used to design an optimal controller for suppressing the instability growth. A 2-D channel flow and a 2-D boundary layer flow over a flat plate are considered as application cases. Disturbances are generated upstream of the control domain and the resulting flow perturbations are estimated/controlled using wall shear measurements and localized unsteady blowing and suction at the wall. It will be shown that the controller is able to cancel the perturbations and is robust to unmodelled disturbances.

Wall shear stress characterization of a 3D bluff-body separated flow

NASA Astrophysics Data System (ADS)

Fourrié, Grégoire; Keirsbulck, Laurent; Labraga, Larbi

2013-10-01

Efficient flow control strategies aimed at reducing the aerodynamic drag of road vehicles require a detailed knowledge of the reference flow. In this work, the flow around the rear slanted window of a generic car model was experimentally studied through wall shear stress measurements using an electrochemical method. The mean and fluctuating wall shear stress within the wall impact regions of the recirculation bubble and the main longitudinal vortex structures which develop above the rear window are presented. Correlations allow a more detailed characterization of the recirculation phenomenon within the separation bubble. In the model symmetry plane the recirculation structure compares well with simpler 2D configurations; specific lengths, flapping motion and shedding of large-scale vortices are observed, these similarities diminish when leaving the middle plane due to the strong three-dimensionality of the flow. A specific attention is paid to the convection processes occurring within the recirculation: a downstream convection velocity is observed, in accordance with 2D recirculations from the literature, and an upstream convection is highlighted along the entire bubble length which has not been underlined in some previous canonical configurations.

Characteristics of Mach 10 transitional and turbulent boundary layers

NASA Technical Reports Server (NTRS)

Watson, R. D.

1978-01-01

Measurements of the mean flow properties of transitional and turbulent boundary layers in helium on 4 deg and 5 deg wedges were made for flows with edge Mach numbers from 9.5 to 11.3, ratios of wall temperature to total temperature of 0.4 to 0.95, and maximum length Reynolds numbers of one hundred million. The data include pitot and total temperature surveys and measurements of heat transfer and surface shear. In addition, with the assumption of local similarity, turbulence quantities such as the mixing length were derived from the mean flow profiles. Low Reynolds number and precursor transition effects were significant factors at these test conditions and were included in finite difference boundary layer predictions.

Dynamics of model blood cells in shear flow

NASA Astrophysics Data System (ADS)

Podgorski, Thomas; Callens, Natacha; Minetti, Christophe; Coupier, Gwennou; Dubois, Frank; Misbah, Chaouqi

The dynamics of a vesicle suspension in shear flow was investigated by digital holographic microscopy [1] in parabolic flights and in the MASER 11 sounding rocket. Vesicles are lipid membranes which mimic the mechanical behaviour of cells, such as red blood cells in flow. In a simple shear flow between parallel walls, a lift force of purely viscous origin pushes vesicles away from walls. Our parabolic flight experiments [2] reveal that the lift velocity in a dilute suspen-sion is well described by theoretical predictions by Olla. As vesicles gather near the center of the flow chamber due to lift forces from both walls, one expects hydrodynamic interactions of pairs of vesicles to result in shear induced diffusion in the suspension. The BIOMICS experi-ment in the MASER 11 sounding rocket revealed a complex spatial structure of a polydisperse vesicle suspension due to the interplay between lift forces from the walls and hydrodynamic interactions. These phenomena have a strong impact on the structure and rheology of blood in small vessels, and a precise knowledge of the dynamics of migration and diffusion of soft particles in flow can lead to alternative ways to separate and sort blood cells. 1. Dubois, F., Schockaert, C., Callens, N., Yourrassowsky, C., "Focus plane detection criteria in digital holography microscopy by amplitude analysis", Opt. Express, Vol. 14, pp 5895-5908, 2006 2. Callens, N., Minetti, C., Coupier, G., Mader, M.-A., Dubois, F., Misbah, C., Podgorski, T., "Hydrodynamics lift of vesicles under shear flow in microgravity", Europhys. Lett., Vol. 83, p. 24002, 2008

The Effects of Acoustic Treatment on Pressure Disturbances From a Supersonic Jet in a Circular Duct

NASA Technical Reports Server (NTRS)

Dahl, Milo D.

1996-01-01

The pressure disturbances generated by an instability wave in the shear layer of a supersonic jet are studied for an axisymmetric jet inside a lined circular duct. For the supersonic jet, locally linear stability analysis with duct wall boundary conditions is used to calculate the eigenvalues and the eigenfunctions at each axial location. These values are used to determine the growth rates and phase velocities of the instability waves and the near field pressure disturbance patterns. The study is confined to the dominant Kelvin-Helmholtz instability mode and to the region just downstream of the nozzle exit where the shear layer is growing but is still small in size compared to the radius of the duct. Numerical results are used to study the effects of changes in the outer flow, growth in the shear layer thickness, wall distance, and wall impedance, and the effects of these changes on non-axisymmetric modes. The primary results indicate that the effects of the duct wall on stability characteristics diminish as the outer flow increases and as the jet azimuthal mode number increases. Also, wall reflections are reduced when using a finite impedance boundary condition at the wall; but in addition, reflections are reduced and growth rates diminished by keeping the imaginary part of the impedance negative when using the negative exponential for the harmonic dependence.

Mixing and segregation of microspheres in microchannel flows of mono- and bidispersed suspensions

NASA Astrophysics Data System (ADS)

Gao, C.; Xu, B.; Gilchrist, J. F.

2009-03-01

We investigate the mixing and segregation of mono- and bidispersed microsphere suspensions in microchannel flows. These flows are common in biological microelectromechanical systems (BioMEMS) applications handling blood or suspensions of DNA. Suspension transport in pressure driven flows is significantly hindered by shear-induced migration, where particles migrate away from the walls and are focused in the center due to multibody hydrodynamic interactions. The microchannels used in this study have geometries that induce chaotic advection in Newtonian fluids. Our results show that mixing in straight, herringbone and staggered herringbone channels depends strongly on volume fraction. Due to this complex interplay of advection and shear-induced migration, a staggered herringbone channel that typically results in chaotic mixing is not always effective for dispersing particles. The maximum degree of segregation is observed in a straight channel once the maximum packing fraction is reached at channel center. We modify a one-dimensional suspension balance model [R. Miller and J. Morris, J. Non-Newtonian Fluid Mech. 135, 149 (2006)] to describe the behavior at the center of the straight channel. The degree of mixing is then calculated as a function of bulk volume fraction, predicting the volume fraction that results in the maximum degree of segregation. In bidispersed suspension flow, it is shown that mixing of the larger species is enhanced in straight and staggered herringbone channels while segregation is enhanced at moderate volume fractions in herringbone channels. This suggests mixing and separations can be tailored by adjusting both the suspension properties and the channel geometry.

Anisotropic shear stress patterns predict the orientation of convergent tissue movements in the embryonic heart

PubMed Central

2017-01-01

Myocardial contractility and blood flow provide essential mechanical cues for the morphogenesis of the heart. In general, endothelial cells change their migratory behavior in response to shear stress patterns, according to flow directionality. Here, we assessed the impact of shear stress patterns and flow directionality on the behavior of endocardial cells, the specialized endothelial cells of the heart. At the early stages of zebrafish heart valve formation, we show that endocardial cells are converging to the valve-forming area and that this behavior depends upon mechanical forces. Quantitative live imaging and mathematical modeling allow us to correlate this tissue convergence with the underlying flow forces. We predict that tissue convergence is associated with the direction of the mean wall shear stress and of the gradient of harmonic phase-averaged shear stresses, which surprisingly do not match the overall direction of the flow. This contrasts with the usual role of flow directionality in vascular development and suggests that the full spatial and temporal complexity of the wall shear stress should be taken into account when studying endothelial cell responses to flow in vivo. PMID:29183943

A modification of Murray's law for shear-thinning rheology.

PubMed

McGah, Patrick M; Capobianchi, Massimo

2015-05-01

This study reformulates Murray's well-known principle of minimum work as applied to the cardiovascular system to include the effects of the shear-thinning rheology of blood. The viscous behavior is described using the extended modified power law (EMPL), which is a time-independent, but shear-thinning rheological constitutive equation. The resulting minimization problem is solved numerically for typical parameter ranges. The non-Newtonian analysis still predicts the classical cubic diameter dependence of the volume flow rate and the cubic branching law. The current analysis also predicts a constant wall shear stress throughout the vascular tree, albeit with a numerical value about 15-25% higher than the Newtonian analysis. Thus, experimentally observed deviations from the cubic branching law or the predicted constant wall shear stress in the vasculature cannot likely be attributed to blood's shear-thinning behavior. Further differences between the predictions of the non-Newtonian and the Newtonian analyses are highlighted, and the limitations of the Newtonian analysis are discussed. Finally, the range and limits of applicability of the current results as applied to the human arterial tree are also discussed.

Modeling Periodic Adiabatic Shear Bands Evolution in a 304L Stainless Steel Thick-Walled Cylinder

NASA Astrophysics Data System (ADS)

Liu, Mingtao; Hu, Haibo; Fan, Cheng; Tang, Tiegang

2015-06-01

The self-organization of multiple shear bands in a 304L stainless steel thick-walled cylinder (TWC) was numerically studied. The microstructures of material lead to the non-uniform distribution of local yield stress, which plays a key role in the formation of spontaneous shear localization. We introduced a probability factor satisfied Gauss distribution into the macroscopic constitutive relationship to describe the non-uniformity of local yield stress. Using the probability factor, the initiation and propagation of multiple shear bands in TWC were numerically replicated in our 2D FEM simulation. Experimental results in the literature indicate that the machined surface at the internal boundary of a 304L stainless steel cylinder provides a work-hardened layer (about 20 μm) which has significantly different microstructures from base material. The work-hardened layer leads to the phenomenon that most shear bands are in clockwise or counterclockwise direction. In our simulation, periodic oriented perturbations were applied to describe the grain orientation in the work-hardened layer, and the spiral pattern of shear bands was successfully replicated.

Correlation between Reynolds number and eccentricity effect in stenosed artery models.

PubMed

Javadzadegan, Ashkan; Shimizu, Yasutomo; Behnia, Masud; Ohta, Makoto

2013-01-01

Flow recirculation and shear strain are physiological processes within coronary arteries which are associated with pathogenic biological pathways. Distinct Quite apart from coronary stenosis severity, lesion eccentricity can cause flow recirculation and affect shear strain levels within human coronary arteries. The aim of this study is to analyse the effect of lesion eccentricity on the transient flow behaviour in a model of a coronary artery and also to investigate the correlation between Reynolds number (Re) and the eccentricity effect on flow behaviour. A transient particle image velocimetry (PIV) experiment was implemented in two silicone based models with 70% diameter stenosis, one with eccentric stenosis and one with concentric stenosis. At different times throughout the flow cycle, the eccentric model was always associated with a greater recirculation zone length, maximum shear strain rate and maximum axial velocity; however, the highest and lowest impacts of eccentricity were on the recirculation zone length and maximum shear strain rate, respectively. Analysis of the results revealed a negative correlation between the Reynolds number (Re) and the eccentricity effect on maximum axial velocity, maximum shear strain rate and recirculation zone length. As Re number increases the eccentricity effect on the flow behavior becomes negligible.

Measurement of wall shear stress in chick embryonic heart using optical coherence tomography

NASA Astrophysics Data System (ADS)

Ma, Zhenhe; Dou, Shidan; Zhao, Yuqian; Wang, Yi; Suo, Yanyan; Wang, Fengwen

2015-03-01

The cardiac development is a complicated process affected by genetic and environmental factors. Wall shear stress (WSS) is one of the components which have been proved to influence the morphogenesis during early stages of cardiac development. To study the mechanism, WSS measurement is a step with significant importance. WSS is caused by blood flow imposed on the inner surface of the heart wall and it can be determined by calculating velocity gradients of blood flow in a direction perpendicular to the wall. However, the WSS of the early stage embryonic heart is difficult to measure since the embryonic heart is tiny and beating fast. Optical coherence tomography (OCT) is a non-invasive imaging modality with high spatial and temporal resolution, which is uniquely suitable for the study of early stage embryonic heart development. In this paper, we introduce a method to measure the WSS of early stage chick embryonic heart based on high speed spectral domain optical coherence tomography (SDOCT). 4D (x,y,z,t) scan was performed on the outflow tract (OFT) of HH18 (~3 days of incubation) chick embryonic heart. After phase synchronization, OFT boundary segmentation, and OFT center line calculation, Doppler angle of the blood flow in the OFT can be achieved (This method has been described in previous publications). Combining with the Doppler OCT results, we calculate absolute blood flow velocity distribution in the OFT. The boundary of the OFT was segmented at each cross-sectional structural image, then geometrical center of the OFT can be calculated. Thus, the gradients of blood flow in radial direction can be calculated. This velocity gradient near the wall is termed wall shear rate and the WSS value is proportional to the wall shear rate. Based on this method, the WSS at different heart beating phase are compare. The result demonstrates that OCT is capable of early stage chicken embryonic heart WSS study.

Brownian dynamics simulations of polyelectrolyte adsorption in shear flow with hydrodynamic interaction

NASA Astrophysics Data System (ADS)

Hoda, Nazish; Kumar, Satish

2007-12-01

The adsorption of single polyelectrolyte molecules in shear flow is studied using Brownian dynamics simulations with hydrodynamic interaction (HI). Simulations are performed with bead-rod and bead-spring chains, and electrostatic interactions are incorporated through a screened Coulombic potential with excluded volume accounted for by the repulsive part of a Lennard-Jones potential. A correction to the Rotne-Prager-Yamakawa tensor is derived that accounts for the presence of a planar wall. The simulations show that migration away from an uncharged wall, which is due to bead-wall HI, is enhanced by increases in the strength of flow and intrachain electrostatic repulsion, consistent with kinetic theory predictions. When the wall and polyelectrolyte are oppositely charged, chain behavior depends on the strength of electrostatic screening. For strong screening, chains get depleted from a region close to the wall and the thickness of this depletion layer scales as N1/3Wi2/3 at high Wi, where N is the chain length and Wi is the Weissenberg number. At intermediate screening, bead-wall electrostatic attraction competes with bead-wall HI, and it is found that there is a critical Weissenberg number for desorption which scales as N-1/2κ-3(lB∣σq∣)3/2, where κ is the inverse screening length, lB is the Bjerrum length, σ is the surface charge density, and q is the bead charge. When the screening is weak, adsorbed chains are observed to align in the vorticity direction at low shear rates due to the effects of repulsive intramolecular interactions. At higher shear rates, the chains align in the flow direction. The simulation method and results of this work are expected to be useful for a number of applications in biophysics and materials science in which polyelectrolyte adsorption plays a key role.

Correlation of laser-Doppler-velocity measurements and endothelial cell shape in a stenosed dog aorta.

PubMed

Liepsch, D W; Levesque, M; Nerem, R M; Moravec, S T

1988-01-01

Laser-Doppler-velocity measurements were carried out in an elastic 1:1 true-to-scale silicone rubber model of a dog aorta with stenosis. The model was constructed from a cast of a severely stenosed dog aorta (71% of its area). The stenosis in the dog aorta was prepared by wrapping a cotton band around the aorta. This band was tightened until the presence of a thrill or a bruit was felt distal to the band. Twelve weeks later the animal was sacrificed and a cast was prepared from the aorta. From this vascular cast, the cross-sectional area was calculated. Endothelial cell geometry and orientation was studied using computerized analysis to determine the cell area and shape index. An elastic silicone rubber model was prepared from the cast to measure the velocity profiles and to estimate the local wall shear stress. Velocity measurements were done at steady and pulsatile flow using a Newtonian aqueous-glycerol solution and a non-Newtonian blood-like fluid. From those velocity measurements the velocity gradients near the wall were determined and the shear stress calculated. The flow distal to the stenosis separates from the wall at physiological conditions. The endothelial cells are smaller and more elongated in the throat; distal to the stenosis they are larger and rounder. The shape index distribution along the stenosed aorta is correlated with the level of wall shear stress. It is shown that even low changes in the wall shear stress have an influence on the orientation of the endothelial cells.

The Amount and Preferred Orientation of Simple-shear in a Deformation Tensor: Implications for Detecting Shear Zones and Faults with GPS

NASA Astrophysics Data System (ADS)

Johnson, A. M.; Griffiths, J. H.

2007-05-01

At the 2005 Fall Meeting of the American Geophysical Union, Griffiths and Johnson [2005] introduced a method of extracting from the deformation-gradient (and velocity-gradient) tensor the amount and preferred orientation of simple-shear associated with 2-D shear zones and faults. Noting the 2-D is important because the shear zones and faults in Griffiths and Johnson [2005] were assumed non-dilatant and infinitely long, ignoring the scissors- like action along strike associated with shear zones and faults of finite length. Because shear zones and faults can dilate (and contract) normal to their walls and can have a scissors-like action associated with twisting about an axis normal to their walls, the more general method of detecting simple-shear is introduced and called MODES "method of detecting simple-shear." MODES can thus extract from the deformation-gradient (and velocity- gradient) tensor the amount and preferred orientation of simple-shear associated with 3-D shear zones and faults near or far from the Earth's surface, providing improvements and extensions to existing analytical methods used in active tectonics studies, especially strain analysis and dislocation theory. The derivation of MODES is based on one definition and two assumptions: by definition, simple-shear deformation becomes localized in some way; by assumption, the twirl within the deformation-gradient (or the spin within the velocity-gradient) is due to a combination of simple-shear and twist, and coupled with the simple- shear and twist is a dilatation of the walls of shear zones and faults. The preferred orientation is thus the orientation of the plane containing the simple-shear and satisfying the mechanical and kinematical boundary conditions. Results from a MODES analysis are illustrated by means of a three-dimensional diagram, the cricket- ball, which is reminiscent of the seismologist's "beach ball." In this poster, we present the underlying theory of MODES and illustrate how it works by analyzing the three- dimensional displacements measured with the Global Positioning System across the 1999 Chi-Chi earthquake ground rupture in Taiwan. In contrast to the deformation zone in the upper several meters of the ground below the surface detected by Yu et al. [2001], MODES determines the orientation and direction of shift of a shear zone representing the earthquake fault within the upper several hundred or thousand meters of ground below the surface. Thus, one value of the MODES analysis in this case is to provide boundary conditions for dislocation solutions for the subsurface shape of the main rupture during the earthquake.

Evolution of hairpin vortices in a shear flow

NASA Technical Reports Server (NTRS)

Hon, T.-L.; Walker, J. D. A.

1988-01-01

Recent experimental studies suggest that the hairpin vortex plays an important (and perhaps dominant) role in the dynamics of turbulent flows near walls. In this study a numerical procedure is developed to allow the accurate computation of the trajectory of a 3-D vortex having a small core radius. For hairpin vortices which are convected in a shear flow above a wall, the calculated results show that a 2-D vortex containing a small 3-D disturbance distorts into a complex shape with subsidiary hairpin vortices forming outboard of the original hairpin vortex. As the vortex moves above the wall, it induces unsteady motion in the viscous flow near the wall: numerical solutions suggest that the boundary-layer flow near the wall will ultimately erupt in response to the motion of the hairpin vortex and in the process a secondary hairpin vortex will be created. The computer results agree with recent experimental investigations.

Towards the evaluation of the pathological state of ascending thoracic aneurysms: integration of in-vivo measurements and hemodynamic simulations

NASA Astrophysics Data System (ADS)

Boccadifuoco, Alessandro; Mariotti, Alessandro; Celi, Simona; Martini, Nicola; Salvetti, Maria Vittoria

2016-11-01

Ascending thoracic aortic aneurysms are cardiovascular diseases consisting in a dilation of the ascending thoracic aorta. Since indicating a weakness of the arterial wall, they can lead to major complications with significant mortality rate. Clinical decisions about surgery are currently based on the maximum aortic diameter, but this single index does not seem a reliable indicator of the pathological state of the aorta. Numerical simulations of the blood flow inside the aneurysm may give supplementary information by quantifying important indices that are difficult to be measured, like the wall shear stress. Our aim is to develop an efficient platform in which in-vivo measurements are used to perform the hemodynamic simulations on a patient-specific basis. In particular, we used real geometries of thoracic aorta and focused on the use of clinical information to impose accurate boundary conditions at the inlet/outlets of the computational model. Stochastic analysis was also performed, to evaluate how uncertainties in the boundary parameters affect the main hemodynamic indicators, by considering both rigid and deformable walls. Stochastic calibration of numerical parameters against clinical data is in progress and results will be possibly shown.

Computational analysis of the effectiveness of blood flushing with saline injection from an intravascular diagnostic catheter

PubMed Central

Ghata, Narugopal; Aldredge, Ralph C.; Bec, Julien; Marcu, Laura

2015-01-01

SUMMARY Optical techniques including fluorescence lifetime spectroscopy have demonstrated potential as a tool for study and diagnosis of arterial vessel pathologies. However, their application in the intravascular diagnostic procedures has been hampered by the presence of blood hemoglobin that affects the light delivery to and the collection from the vessel wall. We report a computational fluid dynamics model that allows for the optimization of blood flushing parameters in a manner that minimizes the amount of saline needed to clear the optical field of view and reduces any adverse effects caused by the external saline jet. A 3D turbulence (k−ω) model was employed for Eulerian–Eulerian two-phase flow to simulate the flow inside and around a side-viewing fiber-optic catheter. Current analysis demonstrates the effects of various parameters including infusion and blood flow rates, vessel diameters, and pulsatile nature of blood flow on the flow structure around the catheter tip. The results from this study can be utilized in determining the optimal flushing rate for given vessel diameter, blood flow rate, and maximum wall shear stress that the vessel wall can sustain and subsequently in optimizing the design parameters of optical-based intravascular catheters. PMID:24953876

Effect of end-wall riblets on radial turbine performance

NASA Astrophysics Data System (ADS)

Khader, M. A.; Sayma, A. I.

2017-08-01

This paper presents a detailed study of the impact of manufacturing residual riblets at the rotor hub surface of a radial inflow turbine on the flow within the rotor passages and their contribution to drag reduction. Numerical analysis has been used to study the effects of those features at design point conditions. Riblets with different height and spacing have been examined to determine the riblet geometry where the maximum drag reduction is achieved. The relative height of the riblets to rotor inlet blade height was introduced to generalise the results. At the end of this study the results were compared with the available data in literature. It was found that the introduction of riblets could reduce the wall shear stress at the hub surface, while they contribute to increasing the streamwise vorticity within the rotor passage. For the geometries tested, the minimum drag was achieved using riblets with relative height hrel = 2.5% equivalent to 19.3 wall units. The results revealed that the spacing between riblets have a minor effect on their performance, this is due to the size of the streamwise vortex above the hub surface which will be discussed in this work.

An Experimental Investigation of the Risk of Triggering Geological Disasters by Injection under Shear Stress

PubMed Central

Liu, Yixin; Xu, Jiang; Peng, Shoujian

2016-01-01

Fluid injection has been applied in many fields, such as hazardous waste deep well injection, forced circulation in geothermal fields, hydraulic fracturing, and CO2 geological storage. However, current research mainly focuses on geological data statistics and the dominating effects of pore pressure. There are only a few laboratory-conditioned studies on the role of drilling boreholes and the effect of injection pressure on the borehole wall. Through experimental phenomenology, this study examines the risk of triggering geological disasters by fluid injection under shear stress. We developed a new direct shear test apparatus, coupled Hydro-Mechanical (HM), to investigate mechanical property variations when an intact rock experienced step drilling borehole, fluid injection, and fluid pressure acting on the borehole and fracture wall. We tested the peak shear stress of sandstone under different experimental conditions, which showed that drilling borehole, water injection, and increased pore pressure led to the decrease in peak shear stress. Furthermore, as pore pressure increased, peak shear stress dispersion increased due to crack propagation irregularity. Because the peak shear stress changed during the fluid injection steps, we suggest that the risk of triggering geological disaster with injection under shear stress, pore, borehole, and fluid pressure should be considered. PMID:27929142

An Experimental Investigation of the Risk of Triggering Geological Disasters by Injection under Shear Stress.

PubMed

Liu, Yixin; Xu, Jiang; Peng, Shoujian

2016-12-08

Fluid injection has been applied in many fields, such as hazardous waste deep well injection, forced circulation in geothermal fields, hydraulic fracturing, and CO 2 geological storage. However, current research mainly focuses on geological data statistics and the dominating effects of pore pressure. There are only a few laboratory-conditioned studies on the role of drilling boreholes and the effect of injection pressure on the borehole wall. Through experimental phenomenology, this study examines the risk of triggering geological disasters by fluid injection under shear stress. We developed a new direct shear test apparatus, coupled Hydro-Mechanical (HM), to investigate mechanical property variations when an intact rock experienced step drilling borehole, fluid injection, and fluid pressure acting on the borehole and fracture wall. We tested the peak shear stress of sandstone under different experimental conditions, which showed that drilling borehole, water injection, and increased pore pressure led to the decrease in peak shear stress. Furthermore, as pore pressure increased, peak shear stress dispersion increased due to crack propagation irregularity. Because the peak shear stress changed during the fluid injection steps, we suggest that the risk of triggering geological disaster with injection under shear stress, pore, borehole, and fluid pressure should be considered.

ESTIMATION OF EFFECTIVE SHEAR STRESS WORKING ON FLAT SHEET MEMBRANE USING FLUIDIZED MEDIA IN MBRs

NASA Astrophysics Data System (ADS)

Zaw, Hlwan Moe; Li, Tairi; Nagaoka, Hiroshi; Mishima, Iori

This study was aimed at estimating effective shear stress working on flat sheet membrane by the addition of fluidized media in MBRs. In both of laboratory-scale aeration tanks with and without fluidized media, shear stress variations on membrane surface and water phase velocity variations were measured and MBR operation was conducted. For the evaluation of the effective shear stress working on membrane surface to mitigate membrane surface, simulation of trans-membrane pressure increase was conducted. It was shown that the time-averaged absolute value of shear stress was smaller in the reactor with fluidized media than without fluidized media. However, due to strong turbulence in the reactor with fluidized media caused by interaction between water-phase and media and also due to the direct interaction between membrane surface and fluidized media, standard deviation of shear stress on membrane surface was larger in the reactor with fluidized media than without media. Histograms of shear stress variation data were fitted well to normal distribution curves and mean plus three times of standard deviation was defined to be a maximum shear stress value. By applying the defined maximum shear stress to a membrane fouling model, trans-membrane pressure curve in the MBR experiment was simulated well by the fouling model indicting that the maximum shear stress, not time-averaged shear stress, can be regarded as an effective shear stress to prevent membrane fouling in submerged flat-sheet MBRs.

Behavior of Rapidly Sheared Bubble Suspensions

NASA Technical Reports Server (NTRS)

Sangani, A. S.; Kushch, V. I.; Hoffmann, M.; Nahra, H.; Koch, D. L.; Tsang, Y.

2002-01-01

An experiment to be carried out aboard the International Space Station is described. A suspension consisting of millimeter-sized bubbles in water containing some dissolved salt, which prevents bubbles from coalescing, will be sheared in a Couette cylindrical cell. Rotation of the outer cylinder will produce centrifugal force which will tend to accumulate the bubbles near the inner wall. The shearing will enhance collisions among bubbles creating thereby bubble phase pressure that will resist the tendency of the bubbles to accumulate near the inner wall. The bubble volume fraction and velocity profiles will be measured and compared with the theoretical predictions. Ground-based research on measurement of bubble phase properties and flow in vertical channel are described.

Simulation of High-Speed Droplet Impact Against Dry Substrates with Partial Velocity Slip

NASA Astrophysics Data System (ADS)

Kondo, Tomoki; Ando, Keita

2017-11-01

High-speed droplet impact can be used to clean substrates such as silicon wafers. Radially spreading shear flow after the impact may allow for mechanically removing contaminant particles at substrate surfaces. Since it is a big challenge to experimentally explore such complicated flow that exhibits contact line motion and water hammer, its flow feature is not well understood. Here, we aim to numerically evaluate shear flow caused by the impact of a spherical water droplet (of submillimeter sizes) at high speed (up to 50 m/s) against a dry rigid wall. We model the flow based on compressible Navier-Stokes equations with Stokes' hypothesis and solve them by a high-order-accurate finite volume method equipped with shock and interface capturing. To treat the motion of a contact line between the three phases (the droplet, the rigid wall, and the ambient air) in a robust manner, we permit velocity slip at the wall with Navier's model, for wall slip is known to come into play under steep velocity gradients that can arise from high-speed droplet impact. In our presentation, we will examine radially spreading flow after the droplet impact and the resulting wall shear stress generation from the simulation. This work was supported by JSPS KAKENHI Grant Number JP17J02211.

Experimental study of shear rate dependence in perpetually sheared granular matter

NASA Astrophysics Data System (ADS)

Liu, Sophie Yang; Guillard, François; Marks, Benjy; Rognon, Pierre; Einav, Itai

2017-06-01

We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called "3D Stadium Shear Device" which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm) and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10-6 to 10-2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.

The cause and resolution of log-layer mismatch in wall-modeled LES: a new perspective and its implication in complex flows

NASA Astrophysics Data System (ADS)

Park, George; Yang, Xiang; Moin, Parviz

2017-11-01

Log-layer mismatch (LLM) refers to the erroneous shifts of the mean velocity profile in the log-law region when wall models are coupled to the LES solution at the first off-wall grid points. It is often believed that the discretization error and subgrid-scale modeling error in the highly under resolved near-wall region contaminates the first off-wall LES solution, thereby providing inaccurate input to wall models resulting in inaccurate wall shear stress. Placing the LES/wall-model interface a couple of cells away from the wall has been recommended to avoid LLM. However, its non-local nature render this method impractical for flows involving complex geometry, by incurring significant overhead in LES mesh preparation and wall-model implementation. We propose an alternative remedy for LLM which warrants the removal of LLM while utilizing the first off-wall LES data. The method is based on filtering the wall-model input either in space or in time. It is simple, easy to implement, and would be particularly well suited for unstructured-grid LES involving complex geometries. We also demonstrate that LLM is caused by excessive correlation between the wall-model input and its wall shear stress output. This research is sponsored by NASA (NNX15AU93A) and ONR (FA9550-16-1-0319).

Experimental data and model for the turbulent boundary layer on a convex, curved surface

NASA Technical Reports Server (NTRS)

Gillis, J. C.; Johnson, J. P.; Moffat, R. J.; Kays, W. M.

1981-01-01

Experiments were performed to determine how boundary layer turbulence is affected by strong convex curvature. The data gathered on the behavior of the Reynolds stress suggested the formulation of a simple turbulence model. Data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 deg of turning and then onto a flat recovery surface. The geometry was adjusted so that, for both rigs, the pressure gradient along the test surface was zero. Two experiments were performed at delta/R approximately 0.10, and one at weaker curvature with delta/R approximately 0.05. Results show that after a sudden introduction of curvature the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. When the surface suddenly becomes flat again, the wall shear and shear stress profiles recover very slowly towards flat wall conditions. A simple turbulence model, which was based on the theory that the Prandtl mixing length in the outer layer should scale on the velocity gradient layer, was shown to account for the slow recovery.

The Use of Fluid Mechanics to Predict Regions of Microscopic Thrombus Formation in Pulsatile VADs.

PubMed

Topper, Stephen R; Navitsky, Michael A; Medvitz, Richard B; Paterson, Eric G; Siedlecki, Christopher A; Slattery, Margaret J; Deutsch, Steven; Rosenberg, Gerson; Manning, Keefe B

2014-03-01

We compare the velocity and shear obtained from particle image velocimetry (PIV) and computational fluid dynamics (CFD) in a pulsatile ventricular assist device (VAD) to further test our thrombus predictive methodology using microscopy data from an explanted VAD. To mimic physiological conditions in vitro , a mock circulatory loop is used with a blood analog that matched blood's viscoelastic behavior at 40% hematocrit. Under normal physiologic pressures and for a heart rate of 75 bpm, PIV data is acquired and wall shear maps are produced. The resolution of the PIV shear rate calculations are tested using the CFD and found to be in the same range. A bovine study, using a model of the 50 cc Penn State V-2 VAD, for 30 days at a constant beat rate of 75 beats per minute (bpm) provides the microscopic data whereby after the 30 days, the device is explanted and the sac surface analyzed using scanning electron microscopy (SEM) and, after immunofluorescent labeling for platelets and fibrin, confocal microscopy. Areas are examined based on PIV measurements and CFD, with special attention to low shear regions where platelet and fibrin deposition are most likely to occur. Data collected within the outlet port in a direction normal to the front wall of the VAD shows that some regions experience wall shear rates less than 500 s -1 , which increases the likelihood of platelet and fibrin deposition. Despite only one animal study, correlations between PIV, CFD, and in vivo data show promise. Deposition probability is quantified by the thrombus susceptibility potential, a calculation to correlate low shear and time of shear with deposition.

On the asymmetric distribution of shear-relative typhoon rainfall

NASA Astrophysics Data System (ADS)

Gao, Si; Zhai, Shunan; Li, Tim; Chen, Zhifan

2018-02-01

The Tropical Rainfall Measuring Mission (TRMM) 3B42 precipitation, the National Centers for Environmental Prediction (NCEP) Final analysis and the Regional Specialized Meteorological Center (RSMC) Tokyo best-track data during 2000-2015 are used to compare spatial rainfall distribution associated with Northwest Pacific tropical cyclones (TCs) with different vertical wind shear directions and investigate possible mechanisms. Results show that the maximum TC rainfall are all located in the downshear left quadrant regardless of shear direction, and TCs with easterly shear have greater magnitudes of rainfall than those with westerly shear, consistent with previous studies. Rainfall amount of a TC is related to its relative position and proximity from the western Pacific subtropical high (WPSH) and the intensity of water vapor transport, and low-level jet is favorable for water vapor transport. The maximum of vertically integrated moisture flux convergence (MFC) are located on the downshear side regardless of shear direction, and the contribution of wind convergence to the total MFC is far larger than that of moisture advection. The cyclonic displacement of the maximum rainfall relative to the maximum MFC is possibly due to advection of hydrometeors by low- and middle-level cyclonic circulation of TCs. The relationship between TC rainfall and the WPSH through water vapor transport and vertical wind shear implies that TC rainfall may be highly predictable given the high predictability of the WPSH.

Development of a MEMS shear stress sensor for use in wind tunnel applications

NASA Astrophysics Data System (ADS)

Barnard, Casey; Meloy, Jessica; Sheplak, Mark; Interdisciplinary Microsystems Group Team

2013-11-01

The measurement of mean and fluctuating wall shear-stress in laminar, transitional, and turbulent boundary layers and channel flows has applications both in industry and the scientific community. Currently there is no method for time resolved, direct measurement of wall shear stress at the spatial and temporal scales of turbulent flow structures inside model testing facilities. To address this need, a silicon micromachined differential capacitance shear stress sensor system has been developed. Mean measurements are enabled by custom synchronous modulation/demodulation circuitry, which allows for measurement of both magnitude and phase of incident wall shear stress. Sizes of the largest device features are on the order of relevant viscous length scales, to minimize flow disturbance and provide a hydraulically smooth sensing surface. Static calibration is performed in a flow cell setup, and an acoustic plane wave tube is used for dynamic response data. Normalized sensitivity of 1.34 mV/V/Pa has been observed over a bandwidth of 4.8 kHz, with a minimum detectable signal of 6.5 mPa. Initial results show qualitative agreement with contemporary measurement techniques. The design, fabrication, support electronics, characterization, and preliminary experimental performance of this sensor will be presented. The support of NASA SFW-NRA NNX11AI30A, AFOSR grant #FA 9550-12-1-0469, and Sandia Campus Executive Fellowship are gratefully acknowledged.

Seismic Response Of Masonry Plane Walls: A Numerical Study On Spandrel Strength

DOE Office of Scientific and Technical Information (OSTI.GOV)

Betti, Michele; Galano, Luciano; Vignoli, Andrea

2008-07-08

The paper reports the results of a numerical investigation on masonry walls subjected to in-plane seismic loads. This research aims to verify the formulae of shear and flexural strength of masonry spandrels which are given in the recent Italian Standards. Seismic pushover analyses have been carried out using finite element models of unreinforced walls and strengthened walls introducing reinforced concrete (RC) beams at the floor levels. Two typologies of walls have been considered distinguished for the height to length ratio h/l of the spandrels: a) short beams (h/l = 1.33) and b) slender beams (h/l = 0.5). Results obtained formore » the unreinforced and the strengthened walls are compared with equations for shear and flexural strength provided in Standards [1]. The numerical analyses show that the reliability of these equations is at least questionable especially for the prediction of the flexural strength. In the cases in which the axial force has not been determined by the structural analysis, Standards seems to overestimate the flexural strength of short spandrels both for the unreinforced and the strengthened wall.« less

Computation of turbulent boundary layers employing the defect wall-function method. M.S. Thesis

NASA Technical Reports Server (NTRS)

Brown, Douglas L.

1994-01-01

In order to decrease overall computational time requirements of spatially-marching parabolized Navier-Stokes finite-difference computer code when applied to turbulent fluid flow, a wall-function methodology, originally proposed by R. Barnwell, was implemented. This numerical effort increases computational speed and calculates reasonably accurate wall shear stress spatial distributions and boundary-layer profiles. Since the wall shear stress is analytically determined from the wall-function model, the computational grid near the wall is not required to spatially resolve the laminar-viscous sublayer. Consequently, a substantially increased computational integration step size is achieved resulting in a considerable decrease in net computational time. This wall-function technique is demonstrated for adiabatic flat plate test cases from Mach 2 to Mach 8. These test cases are analytically verified employing: (1) Eckert reference method solutions, (2) experimental turbulent boundary-layer data of Mabey, and (3) finite-difference computational code solutions with fully resolved laminar-viscous sublayers. Additionally, results have been obtained for two pressure-gradient cases: (1) an adiabatic expansion corner and (2) an adiabatic compression corner.

Seismic Response Of Masonry Plane Walls: A Numerical Study On Spandrel Strength

NASA Astrophysics Data System (ADS)

Betti, Michele; Galano, Luciano; Vignoli, Andrea

2008-07-01

The paper reports the results of a numerical investigation on masonry walls subjected to in-plane seismic loads. This research aims to verify the formulae of shear and flexural strength of masonry spandrels which are given in the recent Italian Standards [1]. Seismic pushover analyses have been carried out using finite element models of unreinforced walls and strengthened walls introducing reinforced concrete (RC) beams at the floor levels. Two typologies of walls have been considered distinguished for the height to length ratio h/l of the spandrels: a) short beams (h/l = 1.33) and b) slender beams (h/l = 0.5). Results obtained for the unreinforced and the strengthened walls are compared with equations for shear and flexural strength provided in Standards [1]. The numerical analyses show that the reliability of these equations is at least questionable especially for the prediction of the flexural strength. In the cases in which the axial force has not been determined by the structural analysis, Standards [1] seems to overestimate the flexural strength of short spandrels both for the unreinforced and the strengthened wall.

Hemodynamic simulations in coronary aneurysms of a patient with Kawasaki Disease

NASA Astrophysics Data System (ADS)

Sengupta, Dibyendu; Marsden, Alison; Burns, Jane

2010-11-01

Kawasaki Disease is the leading cause of acquired pediatric heart disease, and can cause large coronary artery aneurysms in untreated cases. A simulation case study has been performed for a 10-year-old male patient with coronary aneurysms. Specialized coronary boundary conditions along with a lumped parameter heart model mimic the interactions between the ventricles and the coronary arteries, achieving physiologic pressure and flow waveforms. Results show persistent low shear stress in the aneurismal regions, and abnormally high shear at the aneurysm neck. Correlation functions have been derived to compare wall shear stress and wall shear stress gradients with recirculation time with the idea of localizing zones of calcification and thrombosis. Results are compared with those of an artificially created normal coronary geometry for the same patient. The long-term goal of this work is to develop links between hemodynamics and thrombotic risk to assist in clinical decision-making.

Magnetic resonance imaging 4-D flow-based analysis of aortic hemodynamics in Turner syndrome.

PubMed

Arnold, Raoul; Neu, Marie; Hirtler, Daniel; Gimpel, Charlotte; Markl, Michael; Geiger, Julia

2017-04-01

Cardiovascular surveillance is important in Turner syndrome because of the increased risk of aortic dilation and dissection with consecutively increased mortality. To compare 4-D flow MRI for the characterization of aortic 3-D flow patterns, dimensions and vessel wall parameters in pediatric patients with Turner syndrome and age-matched controls. We performed 4-D flow MRI measuring in vivo 3-D blood flow with coverage of the thoracic aorta in 25 patients with Turner syndrome and in 16 female healthy controls (age mean ± standard deviation were 16 ± 5 years and 17 ± 4 years, respectively). Blood flow was visualized by time-resolved 3-D path lines. Visual grading of aortic flow in terms of helices and vortices was performed by two independent observers. Quantitative analysis included measurement of aortic diameters, quantification of peak systolic wall shear stress, pulsatility index and oscillatory shear index at eight defined sites. Patients with Turner syndrome had significantly larger aortic diameters normalized to BSA, increased vortices in the ascending aorta and elevated helix flow in the ascending and descending aorta compared to controls (all P<0.03). Patients with abnormal helical or vortical flow in the ascending aorta had significantly larger diameters of the ascending aorta (P<0.03). Peak systolic wall shear stress, pulsatility index and oscillatory shear index were significantly lower in Turner patients compared to controls (p=0.02, p=0.002 and p=0.01 respectively). Four-dimensional flow MRI provides new insights into the altered aortic hemodynamics and wall shear stress that could have an impact on the development of aortic dissections.

Turbulent structures in wall-bounded shear flows observed via three-dimensional numerical simulators. [using the Illiac 4 computer

NASA Technical Reports Server (NTRS)

Leonard, A.

1980-01-01

Three recent simulations of tubulent shear flow bounded by a wall using the Illiac computer are reported. These are: (1) vibrating-ribbon experiments; (2) study of the evolution of a spot-like disturbance in a laminar boundary layer; and (3) investigation of turbulent channel flow. A number of persistent flow structures were observed, including streamwise and vertical vorticity distributions near the wall, low-speed and high-speed streaks, and local regions of intense vertical velocity. The role of these structures in, for example, the growth or maintenance of turbulence is discussed. The problem of representing the large range of turbulent scales in a computer simulation is also discussed.

A three-dimensional turbulent separated flow and related mesurements

NASA Technical Reports Server (NTRS)

Pierce, F. J.

1985-01-01

The applicability of and the limits on the applicability of 11 near wall similarity laws characterizing three-dimensional turbulent boundary layer flows were determined. A direct force sensing local wall shear stress meter was used in both pressure-driven and shear-driven three-dimensional turbulent boundary layers, together with extensive mean velocity field and wall pressure field data. This resulted in a relatively large number of graphical comparisons of the predictive ability of 10 of these 11 similarity models relative to measured data over a wide range of flow conditions. Documentation of a complex, separated three-dimensional turbulent flow as a standard test case for evaluating the predictive ability of numerical codes solving such flows is presented.

Seismic performance evaluation of RC frame-shear wall structures using nonlinear analysis methods

NASA Astrophysics Data System (ADS)

Shi, Jialiang; Wang, Qiuwei

To further understand the seismic performance of reinforced concrete (RC) frame-shear wall structures, a 1/8 model structure is scaled from a main factory structure with seven stories and seven bays. The model with four-stories and two-bays was pseudo-dynamically tested under six earthquake actions whose peak ground accelerations (PGA) vary from 50gal to 400gal. The damage process and failure patterns were investigated. Furthermore, nonlinear dynamic analysis (NDA) and capacity spectrum method (CSM) were adopted to evaluate the seismic behavior of the model structure. The top displacement curve, story drift curve and distribution of hinges were obtained and discussed. It is shown that the model structure had the characteristics of beam-hinge failure mechanism. The two methods can be used to evaluate the seismic behavior of RC frame-shear wall structures well. What’s more, the NDA can be somewhat replaced by CSM for the seismic performance evaluation of RC structures.

Responses of a 58-story RC dual core shear wall and outrigger frame building inferred from two earthquakes

USGS Publications Warehouse

Çelebi, Mehmet

2016-01-01

Responses of a dual core shear-wall and outrigger-framed 58-story building recorded during the Mw6.0 Napa earthquake of 24 August 2014 and the Mw3.8 Berkeley earthquake of 20 October 2011 are used to identify its dynamic characteristics and behavior. Fundamental frequencies are 0.28 Hz (NS), 0.25 Hz (EW), and 0.43 Hz (torsional). Rigid body motions due to rocking are not significant. Average drift ratios are small. Outrigger frames do not affect average drift ratios or mode shapes. Local site effects do not affect the response; however, response associated with deeper structure may be substantial. A beating effect is observed from data of both earthquakes but beating periods are not consistent. Low critical damping ratios may have contributed to the beating effect. Torsion is relatively larger above outriggers as indicated by the time-histories of motions at the roof, possibly due to the discontinuity of the stiffer shear walls above level 47.

Fluid Structure Interaction Analysis on Sidewall Aneurysm Models

NASA Astrophysics Data System (ADS)

Hao, Qing

2016-11-01

Wall shear stress is considered as an important factor for cerebral aneurysm growth and rupture. The objective of present study is to evaluate wall shear stress in aneurysm sac and neck by a fluid-structure-interaction (FSI) model, which was developed and validated against the particle image velocimetry (PIV) data. In this FSI model, the flow characteristics in a straight tube with different asymmetric aneurysm sizes over a range of Reynolds numbers from 200 to 1600 were investigated. The FSI results agreed well with PIV data. It was found that at steady flow conditions, when Reynolds number above 700, one large recirculating vortex would be formed, occupying the entire aneurysm sac. The center of the vortex is located at region near to the distal neck. A pair of counter rotating vortices would however be formed at Reynolds number below 700. Wall shear stresses reached highest level at the distal neck of the aneurysmal sac. The vortex strength, in general, is stronger at higher Reynolds number. Fluid Structure Interaction Analysis on Sidewall Aneurysm Models.

Propose a Wall Shear Stress Divergence to Estimate the Risks of Intracranial Aneurysm Rupture

PubMed Central

Zhang, Y.; Takao, H.; Murayama, Y.; Qian, Y.

2013-01-01

Although wall shear stress (WSS) has long been considered a critical indicator of intracranial aneurysm rupture, there is still no definite conclusion as to whether a high or a low WSS results in aneurysm rupture. The reason may be that the effect of WSS direction has not been fully considered. The objectives of this study are to investigate the magnitude of WSS (|WSS|) and its divergence on the aneurysm surface and to test the significance of both in relation to the aneurysm rupture. Patient-specific computational fluid dynamics (CFD) was used to compute WSS and wall shear stress divergence (WSSD) on the aneurysm surface for nineteen patients. Our results revealed that if high |WSS| is stretching aneurysm luminal surface, and the stretching region is concentrated, the aneurysm is under a high risk of rupture. It seems that, by considering both direction and magnitude of WSS, WSSD may be a better indicator for the risk estimation of aneurysm rupture (154). PMID:24191140

Endovascular Treatment of Thoracic Aortic Dissection: Hemodynamic Shear Stress Study

NASA Astrophysics Data System (ADS)

Tang, Yik Sau; Lai, Siu Kai; Cheng, Stephen Wing Keung; Chow, Kwok Wing

2012-11-01

Thoracic Aortic Dissection (TAD), a life threatening cardiovascular disease, occurs when blood intrudes into the layers of the aortic wall, creating a new artificial channel (the false lumen) beside the original true lumen. The weakened false lumen wall may expand, enhancing the risk of rupture and resulting in high mortality. Endovascular treatment involves the deployment of a stent graft into the aorta, thus blocking blood from entering the false lumen. Due to the irregular geometry of the aorta, the stent graft, however, may fail to conform to the vessel curvature, and would create a ``bird-beak'' configuration, a wedge-shaped domain between the graft and the vessel wall. Computational fluid dynamics analysis is employed to study the hemodynamics of this pathological condition. With the `beaking' configuration, the local hemodynamic shear stress will drop below the threshold of safety reported earlier in the literature. The oscillating behavior of the shear stress might lead to local inflammation, atherosclerosis and other undesirable consequences. Supported by the Innovation and Technology Fund of the Hong Kong Government.

A viscoplastic shear-zone model for episodic slow slip events in oceanic subduction zones

NASA Astrophysics Data System (ADS)

Yin, A.; Meng, L.

2016-12-01

Episodic slow slip events occur widely along oceanic subduction zones at the brittle-ductile transition depths ( 20-50 km). Although efforts have been devoted to unravel their mechanical origins, it remains unclear about the physical controls on the wide range of their recurrence intervals and slip durations. In this study we present a simple mechanical model that attempts to account for the observed temporal evolution of slow slip events. In our model we assume that slow slip events occur in a viscoplastic shear zone (i.e., Bingham material), which has an upper static and a lower dynamic plastic yield strength. We further assume that the hanging wall deformation is approximated as an elastic spring. We envision the shear zone to be initially locked during forward/landward motion but is subsequently unlocked when the elastic and gravity-induced stress exceeds the static yield strength of the shear zone. This leads to backward/trenchward motion damped by viscous shear-zone deformation. As the elastic spring progressively loosens, the hanging wall velocity evolves with time and the viscous shear stress eventually reaches the dynamic yield strength. This is followed by the termination of the trenchward motion when the elastic stress is balanced by the dynamic yield strength of the shear zone and the gravity. In order to account for the zig-saw slip-history pattern of typical repeated slow slip events, we assume that the shear zone progressively strengthens after each slow slip cycle, possibly caused by dilatancy as commonly assumed or by progressive fault healing through solution-transport mechanisms. We quantify our conceptual model by obtaining simple analytical solutions. Our model results suggest that the duration of the landward motion increases with the down-dip length and the static yield strength of the shear zone, but decreases with the ambient loading velocity and the elastic modulus of the hanging wall. The duration of the backward/trenchward motion depends on the thickness, viscosity, and dynamic yield strength of the shear zone. Our model predicts a linear increase in slip with time during the landward motion and an exponential decrease in slip magnitude during the trenchward motion.

Turbulent Boundary Layer on a Cylinder in Axial Flow

DTIC Science & Technology

1988-09-29

finding the wall shea stress. Finally, ft ;hould be noted that the wall shear stress can be found from the streamwrwise gradient of the mornsntum...somewhat butter collapse than inner scaling, suggesting that the outer flow affects events at the wall. By comparison, the burst frequency in a planar

Tangent-ogive nose cones

NASA Technical Reports Server (NTRS)

Wing, L. D.

1976-01-01

Program calculates aerodynamic heating and shear stresses at wall for tangent-ogive noses that are slender enough to maintain an attached nose shock during portion of flight when heat transfer from boundary layer to wall is significant.

Predicting the size-dependent tissue accumulation of agents released from vascular targeted nanoconstructs

NASA Astrophysics Data System (ADS)

de Tullio, Marco D.; Singh, Jaykrishna; Pascazio, Giuseppe; Decuzzi, Paolo

2014-03-01

Vascular targeted nanoparticles have been developed for the delivery of therapeutic and imaging agents in cancer and cardiovascular diseases. However, at authors' knowledge, a comprehensive systematic analysis on their delivery efficiency is still missing. Here, a computational model is developed to predict the vessel wall accumulation of agents released from vascular targeted nanoconstructs. The transport problem for the released agent is solved using a finite volume scheme in terms of three governing parameters: the local wall shear rate , ranging from to ; the wall filtration velocity , varying from to ; and the agent diffusion coefficient , ranging from to . It is shown that the percentage of released agent adsorbing on the vessel walls in the vicinity of the vascular targeted nanoconstructs reduces with an increase in shear rate , and with a decrease in filtration velocity and agent diffusivity . In particular, in tumor microvessels, characterized by lower shear rates () and higher filtration velocities (), an agent with a diffusivity (i.e. a 50 nm particle) is predicted to deposit on the vessel wall up to of the total released dose. Differently, drug molecules, exhibiting a smaller size and much higher diffusion coefficient (), are predicted to accumulate up to . In healthy vessels, characterized by higher and lower , the largest majority of the released agent is redistributed directly in the circulation. These data suggest that drug molecules and small nanoparticles only can be efficiently released from vascular targeted nanoconstructs towards the diseased vessel walls and tissue.

Wall to membrane linkers, stretch activated channels, and the detection of tension, voltage, temperature, auxin, and pH

NASA Technical Reports Server (NTRS)

Pickard, B. G.

1992-01-01

Introduction. The higher plant is a heterogeneous, mechanically prestressed structure continually subject to shifting forces. When a cell grows in a plant at gravitropic equilibrium, it must create localized maxima of shear in walls of neighboring cells. Such mechanical stress and strain are likely detected in a variety of ways. However, tension-sensitive ion channels are of particular interest because it appears that they are elaborately evolved for sensory function. We hypothesize that 1) the patchy patterns of high shear are focused via wall-to-membrane linkers onto the plasma membrane, where 2) they are translated by mechanosensory cation channels into corresponding patterns of high cytosolic Ca2+, which 3) initiate local enhancement of wall expansion. Further, we hypothesize that the local promotion of enhancement is achieved at least in part by local intensification of auxin transport across the plasma membrane. By implication, when an organ is asymmetrically pressed, rubbed, or bent or when it is displaced in the gravitational field, the net asymmetry of shear stress occurring across the organ would lead to asymmetric redistribution of auxin and corrective asymmetric growth. We shall describe a representative mechanosensitive Ca(2+) -selective cation channel (MCaC) with susceptibilities to xenobiotics implicating it as a force transducer in thigmo- and gravitropism. Then, we shall consider whether a putative wall-to-membrane linker (WML) could be a key feature of the molecular architecture permitting the stress distributed in the wall system to be focused on the channels.

Effect of vortical structures on velocity and turbulent fields in the near region of an impinging turbulent jet

NASA Astrophysics Data System (ADS)

Yadav, Harekrishna; Agrawal, Amit

2018-03-01

This experimental study pertains to the formation of a secondary peak in heat transfer distribution for an axisymmetric turbulent impinging submerged jet. The analysis of instantaneous fields is undertaken at various Reynolds numbers based upon the bulk velocity and nozzle diameter (Re = 1300-10 000) and surface spacings (L/D = 0.25-6). Our analysis shows that flow separation and reattachment correspond to decrease/increase in local pressure and are caused by primary vortices; these are further linked to the location of maxima in streamwise and cross-stream velocities. It is further observed that the locations of maxima and minima in velocities are linked to fluctuations in rms velocities and thickening/thinning of the boundary layer. The vortices transported along the surface either coalesce among themselves or combine with other eddies to form a primary vortex. The primary vortex while getting convected downstream makes multiple interactions with the inner shear layer and causes waviness in instantaneous flow fields. In their later stage, the primary vortex moves away from the wall and accelerates, while the flow decelerates in the inner shear layer. The accelerated fluid in the outer shear layer pulls the downstream fluid from the inner shear layer and leads to the formation of a secondary vortex. After a certain distance downstream, the secondary vortex rolling between the primary vortex and the wall eventually breaks down, while the flow reattaches to the wall. The behavior of time average and instantaneous velocity fields suggests that unsteadiness in the heat transfer is linked to the location of maximum streamwise velocity, location of flow attachment, location of rms velocity, and thickness of the boundary layer. The instantaneous velocity fields show that for a given surface spacing, the chances for the appearance of the secondary vortex reduce with an increase in Reynolds number because of the reduction in space available for the secondary vortex to develop. It is further deduced that the strength of the secondary vortex is primarily dependent upon the strength of the primary vortex. However, the velocity field estimated using the linear stochastic estimation technique shows a tendency for the formation of the secondary vortex at higher Reynolds number, suggesting that most measurements do not resolve them well. Our analysis explains the reason for the appearance of the secondary peak in heat transfer distribution and helps resolve the contradictions in the literature regarding this phenomenon.

NMRI Measurements of Flow of Granular Mixtures

NASA Technical Reports Server (NTRS)

Nakagawa, Masami; Waggoner, R. Allen; Fukushima, Eiichi

1996-01-01

We investigate complex 3D behavior of granular mixtures in shaking and shearing devices. NMRI can non-invasively measure concentration, velocity, and velocity fluctuations of flows of suitable particles. We investigate origins of wall-shear induced convection flow of single component particles by measuring the flow and fluctuating motion of particles near rough boundaries. We also investigate if a mixture of different size particles segregate into their own species under the influence of external shaking and shearing disturbances. These non-invasive measurements will reveal true nature of convecting flow properties and wall disturbance. For experiments in a reduced gravity environment, we will design a light weight NMR imager. The proof of principle development will prepare for the construction of a complete spaceborne system to perform experiments in space.

A numerical study of multiple adiabatic shear bands evolution in a 304LSS thick-walled cylinder

NASA Astrophysics Data System (ADS)

Liu, Mingtao; Hu, Haibo; Fan, Cheng; Tang, Tiegang

2017-01-01

The self-organization of multiple shear bands in a 304L stainless steel(304LSS) thick-walled cylinder (TWC) was numerically studied. The microstructures of material lead to the non-uniform distribution of the local yield stress, which play a key role in the formation of spontaneous shear localization. We introduced a probability factor satisfied the Gaussian distribution into the macroscopic constitutive relationship to describe the non-uniformity of local yield stress. Using the probability factor, the initiation and propagation of multiple shear bands in TWC were numerically replicated in our 2D FEM simulation. Experimental results in the literature indicated that the machined surface at the internal boundary of a 304L stainless steel cylinder provides a work-hardened layer (about 20˜30μm) which has significantly different microstructures from the base material. The work-hardened layer leads to the phenomenon that most shear bands propagate along a given direction, clockwise or counterclockwise. In our simulation, periodical single direction spiral perturbations were applied to describe the grain orientation in the work-hardened layer, and the single direction spiral pattern of shear bands was successfully replicated.

The Pinto shear zone; a Laramide synconvergent extensional shear zone in the Mojave Desert region of the southwestern United States

USGS Publications Warehouse

Wells, M.L.; Beyene, M.A.; Spell, T.L.; Kula, J.L.; Miller, D.M.; Zanetti, K.A.

2005-01-01

The Pinto shear zone is one of several Late Cretaceous shear zones within the eastern fringe of the Mesozoic magmatic arc of the southwest Cordilleran orogen that developed synchronous with continued plate convergence and backarc shortening. We demonstrate an extensional origin for the shear zone by describing the shear-zone geometry and kinematics, hanging wall deformation style, progressive changes in deformation temperature, and differences in hanging wall and footwall thermal histories. Deformation is constrained between ???74 and 68 Ma by 40Ar/39Ar thermochronology of the exhumed footwall, including multi-diffusion domain modeling of K-feldspar. We discount the interpretations, applied in other areas of the Mojave Desert region, that widespread Late Cretaceous cooling results from refrigeration due to subduction of a shallowly dipping Laramide slab or to erosional denudation, and suggest alternatively that post-intrusion cooling and exhumation by extensional structures are recorded. Widespread crustal melting and magmatism followed by extension and cooling in the Late Cretaceous are most consistent with production of a low-viscosity lower crust during anatexis and/or delamination of mantle lithosphere at the onset of Laramide shallow subduction. ?? 2005 Elsevier Ltd. All rights reserved.

Skin Friction Reduction Through Large-Scale Forcing

NASA Astrophysics Data System (ADS)

Bhatt, Shibani; Artham, Sravan; Gnanamanickam, Ebenezer

2017-11-01

Flow structures in a turbulent boundary layer larger than an integral length scale (δ), referred to as large-scales, interact with the finer scales in a non-linear manner. By targeting these large-scales and exploiting this non-linear interaction wall shear stress (WSS) reduction of over 10% has been achieved. The plane wall jet (PWJ), a boundary layer which has highly energetic large-scales that become turbulent independent of the near-wall finer scales, is the chosen model flow field. It's unique configuration allows for the independent control of the large-scales through acoustic forcing. Perturbation wavelengths from about 1 δ to 14 δ were considered with a reduction in WSS for all wavelengths considered. This reduction, over a large subset of the wavelengths, scales with both inner and outer variables indicating a mixed scaling to the underlying physics, while also showing dependence on the PWJ global properties. A triple decomposition of the velocity fields shows an increase in coherence due to forcing with a clear organization of the small scale turbulence with respect to the introduced large-scale. The maximum reduction in WSS occurs when the introduced large-scale acts in a manner so as to reduce the turbulent activity in the very near wall region. This material is based upon work supported by the Air Force Office of Scientific Research under Award Number FA9550-16-1-0194 monitored by Dr. Douglas Smith.

Fatigue design of a mechanically biocompatible lattice for a proof-of-concept femoral stem.

PubMed

Arabnejad Khanoki, Sajad; Pasini, Damiano

2013-06-01

A methodology is proposed to design a spatially periodic microarchitectured material for a two-dimensional femoral implant under walking gait conditions. The material is composed of a graded lattice with controlled property distribution that minimizes concurrently bone resorption and interface failure. The periodic microstructure of the material is designed for fatigue fracture caused by cyclic loadings on the hip joint as a result of walking. The bulk material of the lattice is Ti6AL4V and its microstructure is assumed free of defects. The Soderberg diagram is used for the fatigue design under multiaxial loadings. Two cell topologies, square and Kagome, are chosen to obtain optimized property gradients for a two-dimensional implant. Asymptotic homogenization (AH) theory is used to address the multiscale mechanics of the implant as well as to capture the stress and strain distribution at both the macro and the microscale. The microstress distribution found with AH is also compared with that obtained from a detailed finite element analysis. For the maximum value of the von Mises stress, we observe a deviation of 18.6% in unit cells close to the implant boundary, where the AH assumption of spatial periodicity of the fluctuating fields ceases to hold. In the second part of the paper, the metrics of bone resorption and interface shear stress are used to benchmark the graded cellular implant with existing prostheses made of fully dense titanium implant. The results show that the amount of initial postoperative bone loss for square and Kagome lattice implants decreases, respectively, by 53.8% and 58%. In addition, the maximum shear interface failure at the distal end is significantly reduced by about 79%. A set of proof-of-concepts of planar implants have been fabricated via Electron Beam Melting (EBM) to demonstrate the manufacturability of Ti6AL4V into graded lattices with alternative cell size. Optical microscopy has been used to measure the morphological parameters of the cellular microstructure, including cell wall thickness and pore size, and compared them with the nominal values. No sign of fracture or incomplete cell walls was observed, an assessment that shows the satisfactory metallurgical bond of cell walls and the structural integrity of the implants. Copyright © 2013 Elsevier Ltd. All rights reserved.

Shear thinning effects on blood flow in straight and curved tubes

NASA Astrophysics Data System (ADS)

Cherry, Erica M.; Eaton, John K.

2013-07-01

Simulations were performed to determine the magnitude and types of errors one can expect when approximating blood in large arteries as a Newtonian fluid, particularly in the presence of secondary flows. This was accomplished by running steady simulations of blood flow in straight and curved tubes using both Newtonian and shear-thinning viscosity models. In the shear-thinning simulations, the viscosity was modeled as a shear rate-dependent function fit to experimental data. Simulations in straight tubes were modeled after physiologically relevant arterial flows, and flow parameters for the curved tube simulations were chosen to examine a variety of secondary flow strengths. The diameters ranged from 1 mm to 10 mm and the Reynolds numbers from 24 to 1500. Pressure and velocity data are reported for all simulations. In the straight tube simulations, the shear-thinning flows had flattened velocity profiles and higher pressure gradients compared to the Newtonian simulations. In the curved tube flows, the shear-thinning simulations tended to have blunted axial velocity profiles, decreased secondary flow strengths, and decreased axial vorticity compared to the Newtonian simulations. The cross-sectionally averaged pressure drops in the curved tubes were higher in the shear-thinning flows at low Reynolds number but lower at high Reynolds number. The maximum deviation in secondary flow magnitude averaged over the cross sectional area was 19% of the maximum secondary flow and the maximum deviation in axial vorticity was 25% of the maximum vorticity.

Numerical investigation of MHD flow of blood and heat transfer in a stenosed arterial segment

NASA Astrophysics Data System (ADS)

Majee, Sreeparna; Shit, G. C.

2017-02-01

A numerical investigation of unsteady flow of blood and heat transfer has been performed with an aim to provide better understanding of blood flow through arteries under stenotic condition. The blood is treated as Newtonian fluid and the arterial wall is considered to be rigid having deposition of plaque in its lumen. The heat transfer characteristic has been analyzed by taking into consideration of the dissipation of energy due to applied magnetic field and the viscosity of blood. The vorticity-stream function formulation has been adopted to solve the problem using implicit finite difference method by developing well known Peaceman-Rachford Alternating Direction Implicit (ADI) scheme. The quantitative profile analysis of velocity, temperature and wall shear stress as well as Nusselt number is carried out over the entire arterial segment. The streamline and temperature contours have been plotted to understand the flow pattern in the diseased artery, which alters significantly in the downstream of the stenosis in the presence of magnetic field. Both the wall shear stress and Nusselt number increases with increasing magnetic field strength. However, wall shear stress decreases and Nusselt number enhances with Reynolds number. The results show that with an increase in the magnetic field strength upto 8 T, does not causes any damage to the arterial wall, but the study is significant for assessing temperature rise during hyperthermic treatment.

Particle Trajectories in Rotating Wall Cell Culture Devices

NASA Technical Reports Server (NTRS)

Ramachandran N.; Downey, J. P.

1999-01-01

Cell cultures are extremely important to the medical community since such cultures provide an opportunity to perform research on human tissue without the concerns inherent in experiments on individual humans. Development of cells in cultures has been found to be greatly influenced by the conditions of the culture. Much work has focused on the effect of the motions of cells in the culture relative to the solution. Recently rotating wall vessels have been used with success in achieving improved cellular cultures. Speculation and limited research have focused on the low shear environment and the ability of rotating vessels to keep cells suspended in solution rather than floating or sedimenting as the primary reasons for the improved cellular cultures using these devices. It is widely believed that the cultures obtained using a rotating wall vessel simulates to some degree the effect of microgravity on cultures. It has also been speculated that the microgravity environment may provide the ideal acceleration environment for culturing of cellular tissues due to the nearly negligible levels of sedimentation and shear possible. This work predicts particle trajectories of cells in rotating wall vessels of cylindrical and annular design consistent with the estimated properties of typical cellular cultures. Estimates of the shear encountered by cells in solution and the interactions with walls are studied. Comparisons of potential experiments in ground and microgravity environments are performed.

Role of endothelium sensitivity to shear stress in noradrenaline-induced constriction of feline femoral arterial bed under constant flow and constant pressure perfusions.

PubMed

Kartamyshev, Sergey P; Balashov, Sergey A; Melkumyants, Arthur M

2007-01-01

The effect of shear stress at the endothelium in the attenuation of the noradrenaline-induced constriction of the femoral vascular bed perfused at a constant blood flow was investigated in 16 anesthetized cats. It is known that the adrenergic vasoconstriction of the femoral vascular bed is considerably greater at a constant pressure perfusion than at a constant blood flow. This difference may depend on the ability of the endothelium to relax smooth muscle in response to an increase in wall shear stress. Since the shear stress is directly related to the blood flow and inversely related to the third power of vessel diameter, vasoconstriction at a constant blood flow increases the wall shear stress that is the stimulus for smooth muscle relaxation opposing constriction. On the other hand, at a constant perfusion pressure, vasoconstriction is accompanied by a decrease in flow rate, which prevents a wall shear stress increase. To reveal the effect of endothelial sensitivity to shear stress, we compared noradrenaline-induced changes in total and proximal arterial resistances during perfusion of the hind limb at a constant blood flow and at a constant pressure in vessels with intact and injured endothelium. We found that in the endothelium-intact bed the same concentration of noradrenaline at a constant flow caused an increase in overall vascular peripheral resistance that was half as large as at a constant perfusion pressure. This difference is mainly confined to the proximal arterial vessels (arteries and large arterioles) whose resistance at a constant flow increased only 0.19 +/- 0.03 times compared to that at a constant pressure. The removal of the endothelium only slightly increased constrictor responses at the perfusion under a constant pressure (noradrenaline-induced increases of both overall and proximal arterial resistance augmented by 12%), while the responses of the proximal vessels at a constant flow became 4.7 +/- 0.4 times greater than in the endothelium-intact bed. A selective blockage of endothelium sensitivity to shear stress using a glutaraldehyde dimer augmented the constrictor responses of the proximal vessels at a constant flow 4.6-fold (+/-0.3), but had no significant effect on the responses at a constant pressure. These results are consistent with the conclusion that the difference in constrictor responses at constant flow and pressure perfusions depends mainly on the smooth muscle relaxation caused by increased wall shear stress. Copyright (c) 2007 S. Karger AG, Basel.

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 1: Pressure distribution. Part 2: Wall shear stress. Part 3: Simplified formulas for the prediction of surface pressures and skin friction

NASA Technical Reports Server (NTRS)

Adamson, T. C., Jr.; Liou, M. S.; Messiter, A. F.

1980-01-01

An asymptotic description is derived for the interaction between a shock wave and a turbulent boundary layer in transonic flow, for a particular limiting case. The dimensionless difference between the external flow velocity and critical sound speed is taken to be much smaller than one, but large in comparison with the dimensionless friction velocity. The basic results are derived for a flat plate, and corrections for longitudinal wall curvature and for flow in a circular pipe are also shown. Solutions are given for the wall pressure distribution and the shape of the shock wave. Solutions for the wall shear stress are obtained, and a criterion for incipient separation is derived. Simplified solutions for both the wall pressure and skin friction distributions in the interaction region are given. These results are presented in a form suitable for use in computer programs.

A two-system, single-analysis, fluid-structure interaction technique for modelling abdominal aortic aneurysms.

PubMed

Kelly, S C; O'Rourke, M J

2010-01-01

This work reports on the implementation and validation of a two-system, single-analysis, fluid-structure interaction (FSI) technique that uses the finite volume (FV) method for performing simulations on abdominal aortic aneurysm (AAA) geometries. This FSI technique, which was implemented in OpenFOAM, included fluid and solid mesh motion and incorporated a non-linear material model to represent AAA tissue. Fully implicit coupling was implemented, ensuring that both the fluid and solid domains reached convergence within each time step. The fluid and solid parts of the FSI code were validated independently through comparison with experimental data, before performing a complete FSI simulation on an idealized AAA geometry. Results from the FSI simulation showed that a vortex formed at the proximal end of the aneurysm during systolic acceleration, and moved towards the distal end of the aneurysm during diastole. Wall shear stress (WSS) values were found to peak at both the proximal and distal ends of the aneurysm and remain low along the centre of the aneurysm. The maximum von Mises stress in the aneurysm wall was found to be 408kPa, and this occurred at the proximal end of the aneurysm, while the maximum displacement of 2.31 mm occurred in the centre of the aneurysm. These results were found to be consistent with results from other FSI studies in the literature.

An Axial-Torsional, Thermomechanical Fatigue Testing Technique

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Bonacuse, Peter J.

1995-01-01

A technique for conducting strain-controlled, thermomechanical, axial-torsional fatigue tests on thin-walled tubular specimens was developed. Three waveforms of loading, namely, the axial strain waveform, the engineering shear strain waveform, and the temperature waveform were required in these tests. The phasing relationships between the mechanical strain waveforms and the temperature and axial strain waveforms were used to define a set of four axial-torsional, thermomechanical fatigue (AT-TMF) tests. Real-time test control (3 channels) and data acquisition (a minimum of 7 channels) were performed with a software program written in C language and executed on a personal computer. The AT-TMF testing technique was used to investigate the axial-torsional thermomechanical fatigue behavior of a cobalt-base superalloy, Haynes 188. The maximum and minimum temperatures selected for the AT-TMF tests were 760 and 316 C, respectively. Details of the testing system, calibration of the dynamic temperature profile of the thin-walled tubular specimen, thermal strain compensation technique, and test control and data acquisition schemes, are reported. The isothermal, axial, torsional, and in- and out-of-phase axial-torsional fatigue behaviors of Haynes 188 at 316 and 760 C were characterized in previous investigations. The cyclic deformation and fatigue behaviors of Haynes 188 in AT-TMF tests are compared to the previously reported isothermal axial-torsional behavior of this superalloy at the maximum and minimum temperatures.

Skin friction measurements by laser interferometry in swept shock wave/turbulent boundary-layer interactions

NASA Technical Reports Server (NTRS)

Kim, Kwang-Soo; Settles, Gary S.

1988-01-01

The laser interferometric skin friction meter was used to measure wall shear stress distributions in two interactions of fin-generated swept shock waves with turbulent boundary layers. The basic research configuration was an unswept sharp-leading-edge fin of variable angle mounted on a flatplate. The results indicate that such measurements are practical in high-speed interacting flows, and that a repeatability of + or - 6 percent or better is possible. Marked increases in wall shear were observed in both swept interactions tested.

Shearing of nanoscopic bridges in two-component thin liquid layers between chemically patterned walls.

PubMed

Hemming, C J; Patey, G N

2004-10-01

Bridge phases associated with a phase transition between two liquid phases occur when a two-component liquid mixture is confined between chemically patterned walls. In the bulk the liquid mixture with components A, B undergoes phase separation into an A-rich phase and a B-rich phase. The walls bear stripes attractive to A. In the bridge phase A-rich and B-rich regions alternate. Grand canonical Monte Carlo studies are performed with the alignment between stripes on opposite walls varied. Misalignment of the stripes places the nanoscopic liquid bridges under shear strain. The bridges exert a Hookean restoring force on the walls for small displacements from equilibrium. As the strain increases there are deviations from Hooke's law. Eventually there is an abrupt yielding of the bridges. Molecular dynamics simulations show the bridges form or disintegrate on time scales which are fast compared to wall motion and transport of molecules into or from the confined space. Some interesting possible applications of the phenomena are discussed. (c) 2004 American Institute of Physics

Numerical study of wall shear stress-based descriptors in the human left coronary artery.

PubMed

Pinto, S I S; Campos, J B L M

2016-10-01

The present work is about the application of wall shear stress descriptors - time averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residence time (RRT) - to the study of blood flow in the left coronary artery (LCA). These descriptors aid the prediction of disturbed flow conditions in the vessels and play a significant role in the detection of potential zones of atherosclerosis development. Hemodynamic descriptors data were obtained, numerically, through ANSYS® software, for the LCA of a patient-specific geometry and for a 3D idealized model. Comparing both cases, the results are coherent, in terms of location and magnitude. Low TAWSS, high OSI and high RRT values are observed in the bifurcation - potential zone of atherosclerosis appearance. The dissimilarities observed in the TAWSS values, considering blood as a Newtonian or non-Newtonian fluid, releases the importance of the correct blood rheologic caracterization. Moreover, for a higher Reynolds number, the TAWSS values decrease in the bifurcation and along the LAD branch, increasing the probability of plaques deposition. Furthermore, for a stenotic LCA model, very low TAWSS and high RRT values in front and behind the stenosis are observed, indicating the probable extension, in the flow direction, of the lesion.

Mathematical modeling of pulsatile flow of non-Newtonian fluid in stenosed arteries

NASA Astrophysics Data System (ADS)

Sankar, D. S.; Lee, Usik

2009-07-01

The pulsatile flow of blood through mild stenosed artery is studied. The effects of pulsatility, stenosis and non-Newtonian behavior of blood, treating the blood as Herschel-Bulkley fluid, are simultaneously considered. A perturbation method is used to analyze the flow. The expressions for the shear stress, velocity, flow rate, wall shear stress, longitudinal impedance and the plug core radius have been obtained. The variations of these flow quantities with different parameters of the fluid have been analyzed. It is found that, the plug core radius, pressure drop and wall shear stress increase with the increase of yield stress or the stenosis height. The velocity and the wall shear stress increase considerably with the increase in the amplitude of the pressure drop. It is clear that for a given value of stenosis height and for the increasing values of the stenosis shape parameter from 3 to 6, there is a sharp increase in the impedance of the flow and also the plots are skewed to the right-hand side. It is observed that the estimates of the increase in the longitudinal impedance increase with the increase of the axial distance or with the increase of the stenosis height. The present study also brings out the effects of asymmetric of the stenosis on the flow quantities.

Effect of low shear modeled microgravity on phenotypic and central chitin metabolism in the filamentous fungi Aspergillus niger and Penicillium chrysogenum.

PubMed

Sathishkumar, Yesupatham; Velmurugan, Natarajan; Lee, Hyun Mi; Rajagopal, Kalyanaraman; Im, Chan Ki; Lee, Yang Soo

2014-08-01

Phenotypic and genotypic changes in Aspergillus niger and Penicillium chrysogenum, spore forming filamentous fungi, with respect to central chitin metabolism were studied under low shear modeled microgravity, normal gravity and static conditions. Low shear modeled microgravity (LSMMG) response showed a similar spore germination rate with normal gravity and static conditions. Interestingly, high ratio of multiple germ tube formation of A. niger in LSMMG condition was observed. Confocal laser scanning microscopy images of calcofluor flurophore stained A. niger and P. chrysogenum showed no significant variations between different conditions tested. Transmission electron microscopy images revealed number of mitochondria increased in P. chrysogenum in low shear modeled microgravity condition but no stress related-woronin bodies in fungal hyphae were observed. To gain additional insight into the cell wall integrity under different conditions, transcription level of a key gene involved in cell wall integrity gfaA, encoding the glutamine: fructose-6-phosphate amidotransferase enzyme, was evaluated using qRT-PCR. The transcription level showed no variation among different conditions. Overall, the results collectively indicate that the LSMMG has shown no significant stress on spore germination, mycelial growth, cell wall integrity of potentially pathogenic fungi, A. niger and P. chrysogenum.

Numerical simulation of adverse-pressure-gradient boundary layer with or without roughness

NASA Astrophysics Data System (ADS)

Mottaghian, Pouya; Yuan, Junlin; Piomelli, Ugo

2014-11-01

Large-eddy and direct numerical simulations are carried out on flat-plate boundary layer over smooth and rough surfaces, with adverse pressure gradient.The deceleration is achieved by imposing a wall-normal freestream velocity profile, and is strong enough to cause separation at the wall. The Reynolds number based on momentum thickness and freestream velocity at inlet is 600. Numerical sandgrain roughness is applied based on an immersed boundary method, yielding a flow that is transitionally rough. The turbulence intensity increases before separation, and reaches a higher value for the rough case, indicating stronger mixing. Roughness also causes higher momentum deficit near the wall, leading to earlier separation. This is consistent with previous observation made on rough-wall flow separation over a ramp. In both cases, the turbulent kinetic energy peaks inside the shear layer above the detachment region, with higher values in the rough case; it then decreases approaching the reattachment region. Near the wall inside the separation bubble, the near-zero turbulent intensity indicates that the turbulent structures are lifted up in the separation region. Compared with the smooth case, the shear layer is farther from the wall and the reattachment length is longer on the rough wall.

Inflectional instabilities in the wall region of bounded turbulent shear flows

NASA Technical Reports Server (NTRS)

Swearingen, Jerry D.; Blackwelder, Ron F.; Spalart, Philippe R.

1987-01-01

The primary thrust of this research was to identify one or more mechanisms responsible for strong turbulence production events in the wall region of bounded turbulent shear flows. Based upon previous work in a transitional boundary layer, it seemed highly probable that the production events were preceded by an inflectional velocity profile which formed on the interface between the low-speed streak and the surrounding fluid. In bounded transitional flows, this unstable profile developed velocity fluctuations in the streamwise direction and in the direction perpendicular to the sheared surface. The rapid growth of these instabilities leads to a breakdown and production of turbulence. Since bounded turbulent flows have many of the same characteristics, they may also experience a similar type of breakdown and turbulence production mechanism.

Heating and current drive requirements towards steady state operation in ITER

NASA Astrophysics Data System (ADS)

Poli, F. M.; Bonoli, P. T.; Kessel, C. E.; Batchelor, D. B.; Gorelenkova, M.; Harvey, B.; Petrov, Y.

2014-02-01

Steady state scenarios envisaged for ITER aim at optimizing the bootstrap current, while maintaining sufficient confinement and stability to provide the necessary fusion yield. Non-inductive scenarios will need to operate with Internal Transport Barriers (ITBs) in order to reach adequate fusion gain at typical currents of 9 MA. However, the large pressure gradients associated with ITBs in regions of weak or negative magnetic shear can be conducive to ideal MHD instabilities, reducing the no-wall limit. The E × B flow shear from toroidal plasma rotation is expected to be low in ITER, with a major role in the ITB dynamics being played by magnetic geometry. Combinations of H/CD sources that maintain weakly reversed magnetic shear profiles throughout the discharge are the focus of this work. Time-dependent transport simulations indicate that, with a trade-off of the EC equatorial and upper launcher, the formation and sustainment of quasi-steady state ITBs could be demonstrated in ITER with the baseline heating configuration. However, with proper constraints from peeling-ballooning theory on the pedestal width and height, the fusion gain and the maximum non-inductive current are below the ITER target. Upgrades of the heating and current drive system in ITER, like the use of Lower Hybrid current drive, could overcome these limitations, sustaining higher non-inductive current and confinement, more expanded ITBs which are ideal MHD stable.

Hydrothermal quartz formation during fluctuations of brittle shear-zone activity and fluid flow: grain growth and deformation structures of the Pfahl shear zone (Germany)

NASA Astrophysics Data System (ADS)

Yilmaz, T.; Prosser, G.; Liotta, D.; Kruhl, J. H.

2012-12-01

The Bavarian Pfahl shear zone is a WNW-ESE trending dextral strike-slip shear zone at the SW margin of the Bohemian Massif (Central Europe). It was discontinuously active during decreasing PT-conditions, i.e. from ductile to brittle, from the late-Carboniferous to the late-Cretaceous - Paleocene times. Triassic hydrothermal activity produced a 150 km long and 30-100 m wide quartz dyke along the main fault, surrounded by sheared basement rocks. Within a zone of >10 m metasomatism transformed the wall rocks to mostly kaolinite, chlorite and phyllosilicates. The quartz dyke exhibits a layered to lenticular and partly symmetric structure with different types of quartz masses, transected by a complex quartz vein network. This already indicates pulses of fluid flux and fragmentation during the lifetime of the shear zone. Analyses by optical microscopy, cathodoluminescence (CL) and SEM-EDX reveal at least four subsequent stages of quartz crystallization and fragmentation. (i) The oldest generation of quartz is represented by a homogeneous dark grey to reddish quartz mass made up by ~10-20 μm-sized crystals. It contains mm- to cm-sized angular wall-rock fragments, completely altered to kaolinite, indicating intense wall-rock alteration prior to the earliest event of silica precipitation. This rules out the possibility that the quartz mass developed from silicification of the wall rocks. This first type of quartz occurs as cm- to dm-large angular fragments in (ii) a light grey to pink quartz mass formed by ~10-50 μm-sized crystals. The different colours result from variable types and amounts of inclusions. Quartz of both generations shows random crystallographic orientations and complex inclusion structures. It probably developed during two fragmentation events and possibly from a silica gel precursor that crystallized after precipitation. (iii) The third quartz generation formed as a set of mm- to dm-wide veins roughly parallel to the trend of the Pfahl zone, crosscutting the first generations of fine-grained quartz mass and the wall rocks, in connection to intense fracturing and brecciation. The complex geometry of the vein sets points to multiple fluid injections and brecciation, as additionally indicated by coarse quartz with different inclusion and CL intensity. Temporal changes of strain rate are indicated by crystal plastic deformation structures in quartz, which overprint brittle structures. (iv) The fourth quartz generation occurs in mm- to dm-thick quartz veins, partly open as geodes, filling N-S oriented cm- to dm-spaced fractures that crosscut the earlier quartz masses and veins and extend at least several meters into the wall rock. They indicate the last activity of the shear-zone in a constant kinematic framework. Summarizing, the Pfahl shear zone shows brittle-ductile deformation during the long-term activity of a large-scale hydrothermal system. Consequently, it represents an excellent example where different generations of quartz precipitation can be connected to fluctuations of fluid flow and strain rate.

Scaling study of the combustion performance of gas—gas rocket injectors

NASA Astrophysics Data System (ADS)

Wang, Xiao-Wei; Cai, Guo-Biao; Jin, Ping

2011-10-01

To obtain the key subelements that may influence the scaling of gas—gas injector combustor performance, the combustion performance subelements in a liquid propellant rocket engine combustor are initially analysed based on the results of a previous study on the scaling of a gas—gas combustion flowfield. Analysis indicates that inner wall friction loss and heat-flux loss are two key issues in gaining the scaling criterion of the combustion performance. The similarity conditions of the inner wall friction loss and heat-flux loss in a gas—gas combustion chamber are obtained by theoretical analyses. Then the theoretical scaling criterion was obtained for the combustion performance, but it proved to be impractical. The criterion conditions, the wall friction and the heat flux are further analysed in detail to obtain the specific engineering scaling criterion of the combustion performance. The results indicate that when the inner flowfields in the combustors are similar, the combustor wall shear stress will have similar distributions qualitatively and will be directly proportional to pc0.8dt-0.2 quantitatively. In addition, the combustion peformance will remain unchanged. Furthermore, multi-element injector chambers with different geometric sizes and at different pressures are numerically simulated and the wall shear stress and combustion efficiencies are solved and compared with each other. A multielement injector chamber is designed and hot-fire tested at several chamber pressures and the combustion performances are measured in a total of nine hot-fire tests. The numerical and experimental results verified the similarities among combustor wall shear stress and combustion performances at different chamber pressures and geometries, with the criterion applied.

Numerical Investigation of the Effect of the Location of Critical Rock Block Fracture on Crack Evolution in a Gob-side Filling Wall

NASA Astrophysics Data System (ADS)

Li, Xuehua; Ju, Minghe; Yao, Qiangling; Zhou, Jian; Chong, Zhaohui

2016-03-01

Generation, propagation, and coalescence of the shear and tensile cracks in the gob-side filling wall are significantly affected by the location of the fracture of the critical rock block. The Universal Discrete Element Code software was used to investigate crack evolution characteristics in a gob-side filling wall and the parameter calibration process for various strata and the filling wall was clearly illustrated. The cracks in both the filling wall and the coal wall propagate inward in a V-shape pattern with dominant shear cracks generated initially. As the distance between the fracture and the filling wall decreases, the number of cracks in the filling wall decreases, and the stability of the filling wall gradually improves; thus, by splitting the roof rock at the optimal location, the filling wall can be maintained in a stable state. Additionally, we conducted a sensitivity analysis that demonstrated that the higher the coal seam strength, the fewer cracks occur in both the filling wall and the coal wall, and the less failure they experience. With the main roof fracturing into a cantilever structure, the higher the immediate roof strength, the fewer cracks are in the filling wall. With the critical rock block fracturing above the roadway, an optimal strength of the immediate roof can be found that will stabilize the filling wall. This study presents a theoretical investigation into stabilization of the filling wall, demonstrating the significance of pre-splitting the roof rock at a desirable location.

Diffusion of microspheres in shear flow near a wall: use to measure binding rates between attached molecules.

PubMed Central

Pierres, A; Benoliel, A M; Zhu, C; Bongrand, P

2001-01-01

The rate and distance-dependence of association between surface-attached molecules may be determined by monitoring the motion of receptor-bearing spheres along ligand-coated surfaces in a flow chamber (Pierres et al., Proc. Natl. Acad. Sci. U.S.A. 95:9256-9261, 1998). Particle arrests reveal bond formation, and the particle-to-surface distance may be estimated from the ratio between the velocity and the wall shear rate. However, several problems are raised. First, data interpretation requires extensive computer simulations. Second, the relevance of standard results from fluid mechanics to micrometer-size particles separated from surfaces by nanometer distances is not fully demonstrated. Third, the wall shear rate must be known with high accuracy. Here we present a simple derivation of an algorithm permitting one to simulate the motion of spheres near a plane in shear flow. We check that theoretical predictions are consistent with the experimental dependence of motion on medium viscosity or particle size, and the requirement for equilibrium particle height distribution to follow Boltzman's law. The determination of the statistical relationship between particle velocity and acceleration allows one to derive the wall shear rate with 1-s(-1) accuracy and the Hamaker constant of interaction between the particle and the wall with a sensitivity better than 10(-21) J. It is demonstrated that the correlation between particle height and mean velocity during a time interval Deltat is maximal when Deltat is about 0.1-0.2 s for a particle of 1.4-microm radius. When the particle-to-surface distance ranges between 10 and 40 nm, the particle height distribution may be obtained with a standard deviation ranging between 8 and 25 nm, provided the average velocity during a 160-ms period of time is determined with 10% accuracy. It is concluded that the flow chamber allows one to detect the formation of individual bonds with a minimal lifetime of 40 ms in presence of a disruptive force of approximately 5 pN and to assess the distance dependence within the tens of nanometer range. PMID:11423392

Paleomagnetic, structural, and seismological evidence for oblique-slip deformation in fault-related folds in the Rocky Mountain Foreland, Colorado Plateau, and central Coast Ranges

NASA Astrophysics Data System (ADS)

Tetreault, Joya Liana

The two geologic questions I address in this research are: do fault-related folds accommodate oblique-slip shortening, and how is oblique-slip deformation absorbed within the folded strata? If the strata is deforming as a strike-slip shear zone, then we should be able to observe material rotations produced by strike-slip shear by measuring paleomagnetic vertical-axis rotations. I have approached these problems by applying paleomagnetic vertical-axis rotations, minor fault analyses, and focal mechanism strain inversions to identify evidence of strike-slip shear and to quantify oblique-slip deformation within fault-related folds in the Rocky Mountain Foreland, Colorado Plateau, and the central Coast Ranges. Clockwise paleomagnetic vertical-axis rotations and compressive paleostress rotations of 15-40º in the forelimb of the Grayback Monocline, northeastern Front Range Colorado, indicate that this Laramide fold is absorbing right-lateral shear from a N90E regional shortening direction. This work shows that paleomagnetic vertical-axis rotations in folded strata can be used to identify strike-slip motion on an underlying fault, and that oblique-slip deformation is localized in the forelimb of the fold. I applied the same paleomagnetic methods to identify oblique-slip on the underlying faults of the Nacimiento, East Kaibab, San Rafael, and Grand Hogback monoclines of the Colorado Plateau. The absence of paleomagnetic rotations and structural evidence for small displacements at the Nacimiento and East Kaibab monoclines indicate minor (<1km) right-lateral slip is being accommodated in these folds. Paleomagnetic vertical-axis rotations are found in the forelimbs of the San Rafael and Grand Hogback monoclines, yielding strike-slip displacements of ˜5km within these two folds. These results are consistent with a northeast Laramide compressive stress direction. In the Coalinga anticline, central Coast Ranges, California, clockwise paleomagnetic rotations and an 8º counterclockwise deflection of the maximum shortening direction (derived from focal mechanisms strain inversions of the upper 7km) are compatible with right-lateral shear. The maximum shortening direction in the area of the mainshock rupture is fold-normal, indicating that strike-slip displacement is confined to the main fault plane and not distributed to the hanging wall. The San Andreas Fault is therefore partitioning a small amount of strike-slip to the Coalinga anticline.

Bicuspid aortic valves are associated with increased wall and turbulence shear stress levels compared to trileaflet aortic valves.

PubMed

Saikrishnan, Neelakantan; Mirabella, Lucia; Yoganathan, Ajit P

2015-06-01

Congenital bicuspid aortic valves (BAVs) are associated with accelerated disease progression, such as leaflet calcification and ascending aorta dilatation. Although common underlying genetic factors have been implicated in accelerated disease in BAV patients, several studies have suggested that altered hemodynamics also play a role in this disease process. The present study compares turbulence and wall shear stress (WSS) measurements between various BAV and trileaflet aortic valve (TAV) models to provide information for mechanobiological models of BAV disease. BAV and TAV models were constructed from excised porcine aortic valves to simulate parametric variations in BAV stenosis, hemodynamics and geometry. Particle image velocimetry experiments were conducted at physiological pressure conditions to characterize velocity fields in the ascending aorta. The velocity fields were post-processed to calculate turbulence, viscous and wall shear stresses in the ascending aorta. Stenosed BAV models showed the presence of eccentric systolic jets, causing increased WSS. Lower cardiac output resulted in a narrower jet, lower turbulence and lower viscous shear stress (VSS). The specific severe stenosis BAV model studied here showed reduced WSS due to reduction in non-fused leaflet mobility. Dilation of the aorta did not affect any turbulence or VSS, but reduced the WSS. In comparison with BAVs, TAVs have similar VSS values, but much smaller WSS and turbulence levels. These increased turbulence  and WSS levels in BAVs may play a key role in amplifying the biological responses of the ascending aorta wall and valvular leaflets, and support the hemodynamic underpinnings of BAV disease processes.

Shear stress along the conduit wall as a plausible source of tilt at Soufrière Hills volcano, Montserrat

NASA Astrophysics Data System (ADS)

Green, D. N.; Neuberg, J.; Cayol, V.

2006-05-01

Surface deformations recorded in close proximity to the active lava dome at Soufrière Hills volcano, Montserrat, can be used to infer stresses within the uppermost 1000 m of the conduit system. Most deformation source models consider only isotropic pressurisation of the conduit. We show that tilt recorded during rapid magma extrusion in 1997 could have also been generated by shear stresses sustained along the conduit wall; these stresses are a consequence of pressure gradients that develop along the conduit. Numerical modelling, incorporating realistic topography, can reproduce both the morphology and half the amplitude of the measured deformation field using a realistic shear stress amplitude, equivalent to a pressure gradient of 3.5 × 104 Pa m-1 along a 1000 m long conduit with a 15 m radius. This shear stress model has advantages over the isotropic pressure models because it does not require either physically unattainable overpressures or source radii larger than 200 m to explain the same deformation.

Shear-banding and superdiffusivity in entangled polymer solutions

NASA Astrophysics Data System (ADS)

Shin, Seunghwan; Dorfman, Kevin D.; Cheng, Xiang

2017-12-01

Using high-resolution confocal rheometry, we study the shear profiles of well-entangled DNA solutions under large-amplitude oscillatory shear in a rectilinear planar shear cell. With increasing Weissenberg number (Wi), we observe successive transitions from normal Newtonian linear shear profiles to wall-slip dominant shear profiles and, finally, to shear-banding profiles at high Wi. To investigate the microscopic origin of the observed shear banding, we study the dynamics of micron-sized tracers embedded in DNA solutions. Surprisingly, tracer particles in the shear frame exhibit transient superdiffusivity and strong dynamic heterogeneity. The probability distribution functions of particle displacements follow a power-law scaling at large displacements, indicating a Lévy-walk-type motion, reminiscent of tracer dynamics in entangled wormlike micelle solutions and sheared colloidal glasses. We further characterize the length and time scales associated with the abnormal dynamics of tracer particles. We hypothesize that the unusual particle dynamics arise from localized shear-induced chain disentanglement.

Quantifying colloidal particle bands and their formation in combined electroosmotic and Poiseuille flow

NASA Astrophysics Data System (ADS)

Yee, Andrew; Cevheri, Necmettin; Yoda, Minami

2015-11-01

Recently, we have shown that suspended radii a = 245 nm particles flowing through a microchannel driven by the combination of a dc electric field and pressure gradient (where the resulting electroosmotic and shear flows are in opposite directions) are attracted to the wall at low electric field magnitude | E | , then assemble into concentrated bands that only exist within a few μm of the wall above a threshold value of | E | , | Ecr | . The ~ 6 μ m wide bands are aligned with the flow direction and are roughly periodic along the cross-stream direction. This talk focuses on quantitative characterization of these bands, for example how | Ecr | , the time required for bands to form after applying the electric field To, and the number of bands depend upon parameters such as particle volume fraction φ, shear rate γ˙ , | E | , and a. The dynamics of the particles within the bands are visualized by imaging a mixture of particles with different fluorescent labels. The visualizations show that the particles are in a liquid state within these bands, and suggest that the particles nearest the wall move in the direction of the electroosmotic flow, while those farther from the wall move in the direction of the shear flow. Supported by NSF.

Effects of Renal Denervation on Renal Artery Function in Humans: Preliminary Study

PubMed Central

Doltra, Adelina; Hartmann, Arthur; Stawowy, Philipp; Goubergrits, Leonid; Kuehne, Titus; Wellnhofer, Ernst; Gebker, Rolf; Schneeweis, Christopher; Schnackenburg, Bernhard; Esler, Murray; Fleck, Eckart; Kelle, Sebastian

2016-01-01

Aim To study the effects of RD on renal artery wall function non-invasively using magnetic resonance. Methods and Results 32 patients undergoing RD were included. A 3.0 Tesla magnetic resonance of the renal arteries was performed before RD and after 6-month. We quantified the vessel sharpness of both renal arteries using a quantitative analysis tool (Soap-Bubble®). In 17 patients we assessed the maximal and minimal cross-sectional area of both arteries, peak velocity, mean flow, and renal artery distensibility. In a subset of patients wall shear stress was assessed with computational flow dynamics. Neither renal artery sharpness nor renal artery distensibility differed significantly. A significant increase in minimal and maximal areas (by 25.3%, p = 0.008, and 24.6%, p = 0.007, respectively), peak velocity (by 16.9%, p = 0.021), and mean flow (by 22.4%, p = 0.007) was observed after RD. Wall shear stress significantly decreased (by 25%, p = 0.029). These effects were observed in blood pressure responders and non-responders. Conclusions RD is not associated with adverse effects at renal artery level, and leads to an increase in cross-sectional areas, velocity and flow and a decrease in wall shear stress. PMID:27003912

Shearing at the end of summer affects body temperature of free-living Angora goats ( Capra aegagrus) more than does shearing at the end of winter.

PubMed

Hetem, R S; de Witt, B A; Fick, L G; Fuller, A; Kerley, G I H; Maloney, S K; Meyer, L C R; Mitchell, D

2009-07-01

Angora goats are known to be vulnerable to cold stress, especially after shearing, but their thermoregulatory responses to shearing have not been measured. We recorded activity, and abdominal and subcutaneous temperatures, for 10 days pre-shearing and post-shearing, in 10 Angora goats inhabiting the succulent thicket of the Eastern Cape, South Africa, in both March (late summer) and September (late winter). Within each season, environmental conditions were similar pre-shearing and post-shearing, but September was an average 5°C colder than March. Shearing resulted in a decreased mean (P < 0.0001), minimum (P < 0.0001) and maximum daily abdominal temperature (P < 0.0001). Paradoxically, the decrease in daily mean (P = 0.03) and maximum (P = 0.01) abdominal temperatures, from pre-shearing to post-shearing, was greater in March than in September. Daily amplitude of body temperature rhythm (P < 0.0001) and the maximum rate of abdominal temperature rise (P < 0.0001) increased from pre-shearing to post-shearing, resulting in an earlier diurnal peak in abdominal temperature (P = 0.001) post-shearing. These changes in amplitude, rate of abdominal temperature rise and time of diurnal peak in abdominal temperature suggest that the goats' thermoregulatory system was more labile after shearing. Mean daily subcutaneous temperatures also decreased post-shearing (P < 0.0001), despite our index goat selecting more stable microclimates after shearing in March (P = 0.03). Following shearing, there was an increased difference between abdominal and subcutaneous temperatures (P < 0.0001) at night, suggesting that the goats used peripheral vasoconstriction to limit heat loss. In addition to these temperature changes, mean daily activity increased nearly two-fold after March shearing, but not September shearing. This increased activity after March shearing was likely the result of an increased foraging time, food intake and metabolic rate, as suggested by the increased water influx (P = 0.0008). Thus, Angora goats entered a heat conservation mode after shearing in both March and September. That the transition from the fleeced to the shorn state had greater thermoregulatory consequences in March than in September may provide a mechanistic explanation for Angora goats' vulnerability to cold in summer.

Experimental study on the seismic performance of new sandwich masonry walls

NASA Astrophysics Data System (ADS)

Xiao, Jianzhuang; Pu, Jie; Hu, Yongzhong

2013-03-01

Sandwich masonry walls are widely used as energy-saving panels since the interlayer between the outer leaves can act as an insulation layer. New types of sandwich walls are continually being introduced in research and applications, and due to their unique bond patterns, experimental studies have been performed to investigate their mechanical properties, especially with regard to their seismic performance. In this study, three new types of sandwich masonry wall have been designed, and cyclic lateral loading tests were carried out on five specimens. The results showed that the specimens failed mainly due to slippage along the bottom cracks or the development of diagonal cracks, and the failure patterns were considerably influenced by the aspect ratio. Analysis was undertaken on the seismic response of the new walls, which included ductility, stiffness degradation and energy dissipation capacity, and no obvious difference was observed between the seismic performance of the new walls and traditional walls. Comparisons were made between the experimental results and the calculated results of the shear capacity. It is concluded that the formulas in the two Chinese codes (GB 50011 and GB 50003) are suitable for the calculation of the shear capacity for the new types of walls, and the formula in GB 50011 tends to be more conservative.

Improving Nutrient Release of Wall-disruption Bee Pollen with a Combination of Ultrasonication and High Shear Technique.

PubMed

Wu, Wei; Wang, Kai; Qiao, Jiangtao; Dong, Jie; Li, Zhanping; Zhang, Hongcheng

2018-06-22

Bee pollen, collected by honey bees, contains a substantial amount of nutrients and has a high nutritive value. However, a high level of nutrients can be difficult to be digested and absorbed due to the complex wall of bee pollen. We observed that amino acids were mostly distributed inside cell wall of lotus bee pollen, rape bee pollen, apricot bee pollen, wuweizi bee pollen and camellia bee pollen, using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Thus, five species of bee pollen were wall-disrupted with a combination of ultrasonication and high shear technique (US-HS). After the treatment, bee pollen walls were entirely broken into fragments, and a high number of nutrients were released. The contents of amino acids, fatty acids, protein, crude fat, reducing sugar, β-carotene, calcium, iron, zinc, selenium obviously increased after wall-disruption. Overall, our study demonstrates that US-HS can disrupt bee pollen wall to release nutrients. Therefore, further studies are being conducted to compare the digestibility and absorptivity of pollen nutrients before and after wall-disruption. Additionally, TOF-SIMS seems to be a reliable mapping technique for determining the distribution of food ingredients. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Three-dimensional instability analysis of boundary layers perturbed by streamwise vortices

NASA Astrophysics Data System (ADS)

Martín, Juan A.; Paredes, Pedro

2017-12-01

A parametric study is presented for the incompressible, zero-pressure-gradient flat-plate boundary layer perturbed by streamwise vortices. The vortices are placed near the leading edge and model the vortices induced by miniature vortex generators (MVGs), which consist in a spanwise-periodic array of small winglet pairs. The introduction of MVGs has been experimentally proved to be a successful passive flow control strategy for delaying laminar-turbulent transition caused by Tollmien-Schlichting (TS) waves. The counter-rotating vortex pairs induce non-modal, transient growth that leads to a streaky boundary layer flow. The initial intensity of the vortices and their wall-normal distances to the plate wall are varied with the aim of finding the most effective location for streak generation and the effect on the instability characteristics of the perturbed flow. The study includes the solution of the three-dimensional, stationary, streaky boundary layer flows by using the boundary region equations, and the three-dimensional instability analysis of the resulting basic flows by using the plane-marching parabolized stability equations. Depending on the initial circulation and positioning of the vortices, planar TS waves are stabilized by the presence of the streaks, resulting in a reduction in the region of instability and shrink of the neutral stability curve. For a fixed maximum streak amplitude below the threshold for secondary instability (SI), the most effective wall-normal distance for the formation of the streaks is found to also offer the most stabilization of TS waves. By setting a maximum streak amplitude above the threshold for SI, sinuous shear layer modes become unstable, as well as another instability mode that is amplified in a narrow region near the vortex inlet position.

In-Plane Shear Testing of Medium and High Modulus Woven Graphite Fiber Reinforced/Polyimide Composites

NASA Technical Reports Server (NTRS)

Gentz, M.; Armentrout, D.; Rupnowski, P.; Kumosa, L.; Shin, E.; Sutter, J. K.; Kumosa, M.

2004-01-01

Iosipescu shear tests were performed at room temperature and at 316 C (600 F) o woven composites with either M40J or M60J graphite fibers and PMR-II-50 polyimide resin matrix. The composites were tested as supplied and after thermo-cycling, with the thermo-cycled composites being tested under dry and wet conditions. Acoustic emission (AE) was monitored during the room and high temperature Iosipescu experiments. The shear stresses at the maximum loads and the shear stresses at the significant onset of AE were determined for the composites as function of temperature and conditioning. The combined effects of thermo-cycling and moisture on the strength and stiffness properties of the composites were evaluated. It was determined that the room and high temperature shear stresses at the maximum loads were unaffected by conditioning. However, at room temperature the significant onset of AE was affected by conditioning; the thermal conditioned wet specimens showed the highest shear stress at the onset of AE followed by thermal-conditioned and then as received specimens. Also, at igh temperature the significant onset of AE occurred in some specimens after the maximum load due to the viscoelastoplastic nature of the matrix material.

Warm Core Structure of Hurricane Erin Diagnosed from High Altitude Dropsondes during CAMEX-4

NASA Technical Reports Server (NTRS)

Halverson, J. B.; Simpson, J.; Heymsfield, G.; Pierce, H.; Hock, T.; Ritchie, L.

2003-01-01

A combination multi-aircraft and several satellite sensors were used to examine the core of Hurricane Erin on September 10, 2001, as part of the CAMEX4 program. During the first set of aircraft passes, around 1700 UTC, Erin was still at its maximum intensity with a central pressure of 969 hpa and windspeed of 105 kts (54 m/s). The storm was moving slowly northwestward at 4 m/s, over an increasingly colder sea surface. Three instrumented aircraft, the NOAA P3 with radar, the NASA ER- 2 at 19 km, newly equipped with GPS dropwindsondes, and the NASA DC-8 with dropwindsondes flew in formation across the eye at about 1700 UTC and again 2.5 hrs later around 1930 UTC. The storm had weakened by 13 m/s between the first and second eye penetrations. The warm core had a maximum temperature anomaly of only 11 C, located at 500 hpa, much weaker and lower than active hurricanes. The core appeared to slant rearward above 400 hpa. Even on the first penetration, airborne radar showed that the eye wall cloud towers were dying. The tops fell short of reaching 15 km and a melting band was found throughout. The tropopause had a bulge to 15.8 km elevation (environment approx. 14.4 km) above the dying convection. A feature of Erin at this timt was a pronounced wave-number-one convective asymmetry with all convective activity being confined to the forward quadrants on the left side of the shear vector as calculated from analyses. This is similar to that predicted by the mesoscale numerical models, which also predict that such small amounts of shear would not affect the storm intensity. In Erin, it is remarkable that relatively small shear produced such a pronounced asymmetry in the convection. In addition, horizontal asymmetries in the low-level warm core were identified. Almost certainly, the colder ocean would kill the tall convective towers feeding the warm core, even if wind shear were absent.

Experimental and numerical investigation of the turbulent wake flow of a generic space launcher configuration

NASA Astrophysics Data System (ADS)

Statnikov, V.; Saile, D.; Meiß, J.-H.; Henckels, A.; Meinke, M.; Gülhan, A.; Schröder, W.

2015-06-01

The turbulent wake of a generic space launcher at cold hypersonic freestream conditions is investigated experimentally and numerically to gain detailed insight into the intricate base flow phenomena of space vehicles at upper stages of the flight trajectory. The experiments are done at Ma∞ = 6 and ReD = 1.7 · 106 m-1 by the German Aerospace Center (DLR) and the corresponding computations are performed by the Institute of Aerodynamics Aachen using a zonal Reynolds-averaged Navier-Stokes / Large-Eddy Simulation (RANS/LES) approach. Two different aft-body geometries consisting of a blunt base and an attached cylindrical nozzle dummy are considered. It is found that the wind tunnel model support attached to the upper side of the main body has a nonnegligible impact on the wake along the whole circumference, albeit on the opposite side, the effects are minimal compared to an axisymmetric configuration. In the blunt-base case, the turbulent supersonic boundary layer undergoes a strong aftexpansion on the model shoulder leading to the formation of a confined low-pressure (p/p∞ ≈ 0.2) recirculation region. Adding a nozzle dummy causes the shear layer to reattach on the its wall at x/D ˜ 0.6 and the base pressure level to increase (p/p∞ ≈ 0.25) compared to the blunt-base case. For both configurations, the pressure fluctuations on the base wall feature dominant frequencies at SrD ≈ 0.05 and SrD ≈ 0.2-0.27, but are of small amplitudes (prms/p∞ = 0.02-0.025) compared to the main body boundary layer. For the nozzle dummy configuration, when moving downstream along the nozzle extension, the wall pressure is increasingly influenced by the reattaching shear layer and the periodic low-frequency behavior becomes less pronounced. Directly behind the reattachment point, the wall pressure reaches maximum mean and root-mean-square (rms) values of about p/p∞ = 1 and p'rms/p∞ = 0.1 and features a broadband specrms trum without distinct frequencies determined by the incoming turbulent supersonic boundary layer.

Benchmark Wall Heat Flux Data for a GO2/GH2 Single Element Combustor

NASA Technical Reports Server (NTRS)

Marshall, William M.; Pal, Sibtosh; Woodward, Roger d.; Santoro, Robert J.

2005-01-01

Wall heat flux measurements in a 1.5 in. diameter circular cross-section rocket chamber for a uni-element shear coaxial injector element operating on gaseous oxygen (GOz)/gaseous hydrogen (GH,) propellants are presented. The wall heat flux measurements were made using arrays of Gardon type heat flux gauges and coaxial thermocouple instrumentation. Wall heat flux measurements were made for two cases. For the first case, GOZ/GHz oxidizer-rich (O/F=l65) and fuel-rich preburners (O/F=1.09) integrated with the main chamber were utilized to provide vitiated hot fuel and oxidizer to the study shear coaxial injector element. For the second case, the preburners were removed and ambient temperature gaseous oxygen/gaseous hydrogen propellants were supplied to the study injector. Experiments were conducted at four chamber pressures of 750, 600, 450 and 300psia for each case. The overall mixture ratio for the preburner case was 6.6, whereas for the ambient propellant case, the mixture ratio was 6.0. Total propellant flow was nominally 0.27-0.29 Ibm/s for the 750 psia case with flowrates scaled down linearly for lower chamber pressures. The axial heat flux profile results for both the preburner and ambient propellant cases show peak heat flux levels a t axial locations between 2.0 and 3.0 in. from the injector face. The maximum heat flux level was about two times greater for the preburner case. This is attributed to the higher injector fuel-to-oxidizer momentum flux ratio that promotes mixing and higher initial propellant temperature for the preburner case which results in a shorter reaction zone. The axial heat flux profiles were also scaled with respect to the chamber pressure to the power 0.8. The results at the four chamber pressures for both cases collapsed to a single profile indicating that at least to first approximation, the basic fluid dynamic structures in the flow field are pressure independent as long as the chamber/njector/nozzle geometry and injection velocities remain the same.

CFD: computational fluid dynamics or confounding factor dissemination? The role of hemodynamics in intracranial aneurysm rupture risk assessment.

PubMed

Xiang, J; Tutino, V M; Snyder, K V; Meng, H

2014-10-01

Image-based computational fluid dynamics holds a prominent position in the evaluation of intracranial aneurysms, especially as a promising tool to stratify rupture risk. Current computational fluid dynamics findings correlating both high and low wall shear stress with intracranial aneurysm growth and rupture puzzle researchers and clinicians alike. These conflicting findings may stem from inconsistent parameter definitions, small datasets, and intrinsic complexities in intracranial aneurysm growth and rupture. In Part 1 of this 2-part review, we proposed a unifying hypothesis: both high and low wall shear stress drive intracranial aneurysm growth and rupture through mural cell-mediated and inflammatory cell-mediated destructive remodeling pathways, respectively. In the present report, Part 2, we delineate different wall shear stress parameter definitions and survey recent computational fluid dynamics studies, in light of this mechanistic heterogeneity. In the future, we expect that larger datasets, better analyses, and increased understanding of hemodynamic-biologic mechanisms will lead to more accurate predictive models for intracranial aneurysm risk assessment from computational fluid dynamics. © 2014 by American Journal of Neuroradiology.

Modelling of single walled carbon nanotube cylindrical structures with finite element method simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Günay, E.

In this study, the modulus of elasticity and shear modulus values of single-walled carbon nanotubes SWCNTs were modelled by using both finite element method and the Matlab code. Initially, cylindrical armchair and zigzag single walled 3D space frames were demonstrated as carbon nanostructures. Thereafter, macro programs were written by the Matlab code producing the space truss for zigzag and armchair models. 3D space frames were introduced to the ANSYS software and then tension, compression and additionally torsion tests were performed on zigzag and armchair carbon nanotubes with BEAM4 element in obtaining the exact values of elastic and shear modulus values.more » In this study, two different boundary conditions were tested and especially used in torsion loading. The equivalent shear modulus data was found by averaging the corresponding values obtained from ten different nodal points on the nanotube path. Finally, in this study it was determined that the elastic constant values showed proportional changes by increasing the carbon nanotube diameters up to a certain level but beyond this level these values remained stable.« less

Substructure hybrid testing of reinforced concrete shear wall structure using a domain overlapping technique

NASA Astrophysics Data System (ADS)

Zhang, Yu; Pan, Peng; Gong, Runhua; Wang, Tao; Xue, Weichen

2017-10-01

An online hybrid test was carried out on a 40-story 120-m high concrete shear wall structure. The structure was divided into two substructures whereby a physical model of the bottom three stories was tested in the laboratory and the upper 37 stories were simulated numerically using ABAQUS. An overlapping domain method was employed for the bottom three stories to ensure the validity of the boundary conditions of the superstructure. Mixed control was adopted in the test. Displacement control was used to apply the horizontal displacement, while two controlled force actuators were applied to simulate the overturning moment, which is very large and cannot be ignored in the substructure hybrid test of high-rise buildings. A series of tests with earthquake sources of sequentially increasing intensities were carried out. The test results indicate that the proposed hybrid test method is a solution to reproduce the seismic response of high-rise concrete shear wall buildings. The seismic performance of the tested precast high-rise building satisfies the requirements of the Chinese seismic design code.

Behaviour of Plate Anchorage in Plate-Reinforced Composite Coupling Beams

PubMed Central

Lam, W. Y.; Li, Lingzhi; Su, R. K. L.; Pam, H. J.

2013-01-01

As a new alternative design, plate-reinforced composite (PRC) coupling beam achieves enhanced strength and ductility by embedding a vertical steel plate into a conventionally reinforced concrete (RC) coupling beam. Based on a nonlinear finite element model developed in the authors' previous study, a parametric study presented in this paper has been carried out to investigate the influence of several key parameters on the overall performance of PRC coupling beams. The effects of steel plate geometry, span-to-depth ratio of beams, and steel reinforcement ratios at beam spans and in wall regions are quantified. It is found that the anchorage length of the steel plate is primarily controlled by the span-to-depth ratio of the beam. Based on the numerical results, a design curve is proposed for determining the anchorage length of the steel plate. The load-carrying capacity of short PRC coupling beams with high steel ratio is found to be controlled by the steel ratio of wall piers. The maximum shear stress of PRC coupling beams should be limited to 15 MPa. PMID:24288465

Patient-Specific Simulations of Reactivity in Models of the Pulmonary Vasculature: A 3-D Numerical Study with Fluid-Structure Interaction

NASA Astrophysics Data System (ADS)

Hunter, Kendall; Zhang, Yanhang; Lanning, Craig

2005-11-01

Insight into the progression of pulmonary hypertension may be obtained from thorough study of vascular flow during reactivity testing, an invasive diagnostic procedure which can dramatically alter vascular hemodynamics. Diagnostic imaging methods, however, are limited in their ability to provide extensive data. Here we present detailed flow and wall deformation results from simulations of pulmonary arteries undergoing this procedure. Patient-specific 3-D geometric reconstructions of the first four branches of the pulmonary vasculature were obtained clinically and meshed for use with computational software. Transient simulations in normal and reactive states were obtained from four such models were completed with patient-specific velocity inlet conditions and flow impedance exit conditions. A microstructurally based orthotropic hyperelastic model that simulates pulmonary artery mechanics under normotensive and hypoxic hypertensive conditions treated wall constitutive changes due to pressure reactivity and arterial remodeling. Pressure gradients, velocity fields, arterial deformation, and complete topography of shear stress were obtained. These models provide richer detail of hemodynamics than can be obtained from current imaging techniques, and should allow maximum characterization of vascular function in the clinical situation.

Rheology of surface granular flows

NASA Astrophysics Data System (ADS)

Orpe, Ashish V.; Khakhar, D. V.

Surface granular flow, comprising granular material flowing on the surface of a heap of the same material, occurs in several industrial and natural systems. The rheology of such a flow was investigated by means of measurements of velocity and number-density profiles in a quasi-two-dimensional rotating cylinder, half-filled with a model granular material monosize spherical stainless-steel particles. The measurements were made at the centre of the cylinder, where the flow is fully developed, using streakline photography and image analysis. The stress profile was computed from the number-density profile using a force balance which takes into account wall friction. Mean-velocity and root-mean-square (r.m.s.)-velocity profiles are reported for different particle sizes and cylinder rotation speeds. The profiles for the mean velocity superimpose when distance is scaled by the particle diameter d and velocity by a characteristic shear rate dot{gamma}_C = [gsin(beta_m-beta_s)/dcosbeta_s](1/2) and the particle diameter, where beta_m is the maximum dynamic angle of repose and beta_s is the static angle of repose. The maximum dynamic angle of repose is found to vary with the local flow rate. The scaling is also found to work for the r.m.s. velocity profiles. The mean velocity is found to decay exponentially with depth in the bed, with decay length lambda=1.1d. The r.m.s. velocity shows similar behaviour but with lambda=1.7d. The r.m.s. velocity profile shows two regimes: near the free surface the r.m.s. velocity is nearly constant and below a transition point it decays linearly with depth. The shear rate, obtained by numerical differentiation of the velocity profile, is not constant anywhere in the layer and has a maximum which occurs at the same depth as the transition in the r.m.s. velocity profile. Above the transition point the velocity distributions are Gaussian and below the transition point the velocity distributions gradually approach a Poisson distribution. The shear stress increases roughly linearly with depth. The variation in the apparent viscosity eta with r.m.s. velocity u shows a relatively sharp transition at the shear-rate maximum, and in the region below this point the apparent viscosity eta˜ u(-1.5) . The measurements indicate that the flow comprises two layers: an upper low-viscosity layer with a nearly constant r.m.s. velocity and a lower layer of increasing viscosity with a decreasing r.m.s. velocity. The thickness of the upper layer depends on the local flow rate and is independent of particle diameter while the reverse is found to hold for the lower-layer thickness. The experimental data is compared with the predictions of three models for granular flow.

Failure mechanism of shear-wall dominant multi-story buildings

USGS Publications Warehouse

Yuksel, S.B.; Kalkan, E.

2008-01-01

The recent trend in the building industry of Turkey as well as in many European countries is towards utilizing the tunnel form (shear-wall dominant) construction system for development of multi-story residential units. The tunnel form buildings diverge from other conventional reinforced concrete (RC) buildings due to the lack of beams and columns in their structural integrity. The vertical load-carrying members of these buildings are the structural-walls only, and the floor system is a flat plate. Besides the constructive advantages, tunnel form buildings provide superior seismic performance compared to conventional RC frame and dual systems as observed during the recent devastating earthquakes in Turkey (1999 Mw 7.4 Kocaeli, Mw 7.2 Duzce, and 2004 Mw 6.5 Bingol). With its proven earthquake performance, the tunnel form system is becoming the primary construction technique in many seismically active regions. In this study, a series of nonlinear analyses were conducted using finite element (FE) models to augment our understanding on their failure mechanism under lateral forces. In order to represent the nonlinear behavior adequately, The FE models were verified with the results of experimental studies performed on three dimensional (3D) scaled tunnel form building specimens. The results of this study indicate that the structural walls of tunnel form buildings may exhibit brittle flexural failure under lateral loading, if they are not properly reinforced. The global tension/compression couple triggers this failure mechanism by creating pure axial tension in the outermost shear-walls.

Friction Angles of Open-Graded Aggregates from Large-Scale Direct Shear Testing : TechBrief

DOT National Transportation Integrated Search

2013-07-08

State and local transportation agencies frequently use opengraded aggregates for wall, roadway, and bridge construction. The primary advantages of using this type of material in wall and abutment applications are ease of constructability, lighter in-...

Turbulence Statistics in the Coastal Ocean Bottom Boundary Layer

NASA Astrophysics Data System (ADS)

Nayak, A. R.; Hackett, E. E.; Luznik, L.; Katz, J.; Osborn, T. R.

2010-12-01

A submersible particle image velocimetry (PIV) system was deployed off the coast of New Jersey, near the LEO-15 site, to characterize the flow and turbulence in the inner part of the continental shelf bottom boundary layer. The measurement domain extended from 5 mm at the bottom up to an elevation of 51 cm in different datasets. The flow comprised of a mean current and wave-induced flow with a period of 10 s. The ratio of wave velocity amplitude to mean current magnitude varied over the tidal cycle and with elevation, with a maximum of 2.35. Their relative orientation also varied. Large databases of time-resolved, high resolution, 2D velocity distributions enabled us to calculate the instantaneous spatial velocity gradients, and from them, the statistically converged vertical dissipation rate profiles. Reynolds Stresses were estimated using the Shaw & Trowbridge technique outside of the wave boundary layer (WBL), and directly, using the instantaneous spatial variations in velocity, near the wall. Results were utilized for calculating the shear production profiles. Hilbert Transforms were utilized for calculating the wave phase of each velocity distribution, and performing conditional sampling of data to determine variations in flow and turbulence parameters during a wave cycle. The mean velocity profiles indicated the presence of a wave boundary layer, followed by a transition region, and a log layer above it. The datasets extending to the wall show that there is no clear log layer within the WBL, but, as expected, profiles vary substantially with location relative to the ripples. Phase dependent variations in mean flow and dissipation rate occurred only in the WBL and transition region, but vanished at higher elevations. The dissipation rate typically peaked during acceleration phases of wave-induced motion, especially near the wall, but it sometimes peaked during wave-crest phases. Below the transition region, the dissipation rate increased rapidly as the wall was approached all the way to the ripple crest, presumably due to the increasing presence of eddies with characteristic size of 1-3 times the ripple height that fell in the dissipation range of the energy spectra. Shear production also peaked at the ripple crest, consistent with laboratory data for rough wall boundary layers. Acknowledgements : NSF

The Chunky Gal Mountain fault-detachment-normal fault providing evidence for Early-to-Middle Paleozoic extensional unroofing of the eastern Blue Ridge, or folded thrust

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hatcher, R.D. Jr.

1993-03-01

The Chunky Gal Mountain fault (CGMF), located in the western Blue Ridge of southern NC and northern GA, contains unequivocal evidence for hanging wall-down-to-the-west movement. The 50 m-thick fault zone here consists of a series of shear zones in the footwall in a mass of mylonitized garnet-rich biotite gneiss. The main contact with the hanging wall reveals both a contrast in rock type and truncation of fabrics. Above the fault are amphibolite, ultramafic rocks, and minor metasandstone and pelitic schist of the Buck Creek mafic-ultramafic complex, while the footwall contains complexly folded metasandstone, pelitic schist, and calcsilicate pods of themore » Coleman River Formation. In the present orientation, the mylonitic foliation in the footwall rocks of the GGMF is subvertical; foliation in the hanging wall is subhorizontal at road level. These rocks were metamorphosed to upper amphibolite facies assemblages, and, after emplacement of the CGMF, were cut by brittle faults and trondhjemite dikes that contain no obvious tectonic fabric. Movement on the CGMF occurred near the thermal peak because enough heat remained in the rocks after movement to statically anneal the mylonite microfabric, but mesoscopic rotated porphyroclasts, rotated (dragged) earlier foliation, and some S-C fabrics clearly indicate the shear sense and vergence of this structure. Shear zones related to the CGMF transposed earlier fabrics, although some relicts preserving earlier structures remain in the shear zones. These rotated but untransposed relicts of amphibolite and garnet-rich biotite gneiss mylonite may indicate locally higher strain rates in subsidiary shear zones. The thermal/mechanical properties of the CGMF make it difficult to connect to the Shope Fork or Soque River thrusts farther south and east. Thus the hanging-wall-down configuration provides an alternative hypothesis that the CGMF may be a detachment-normal fault related to Taconian extensional unroofing of the Appalachians.« less

Behavior of tunnel form buildings under quasi-static cyclic lateral loading

USGS Publications Warehouse

Yuksel, S.B.; Kalkan, E.

2007-01-01

In this paper, experimental investigations on the inelastic seismic behavior of tunnel form buildings (i.e., box-type or panel systems) are presented. Two four-story scaled building specimens were tested under quasi-static cyclic lateral loading in longitudinal and transverse directions. The experimental results and supplemental finite element simulations collectively indicate that lightly reinforced structural walls of tunnel form buildings may exhibit brittle flexural failure under seismic action. The global tension/compression couple triggers this failure mechanism by creating pure axial tension in outermost shear-walls. This type of failure takes place due to rupturing of longitudinal reinforcement without crushing of concrete, therefore is of particular interest in emphasizing the mode of failure that is not routinely considered during seismic design of shear-wall dominant structural systems.

Design Optimization of Hybrid FRP/RC Bridge

NASA Astrophysics Data System (ADS)

Papapetrou, Vasileios S.; Tamijani, Ali Y.; Brown, Jeff; Kim, Daewon

2018-04-01

The hybrid bridge consists of a Reinforced Concrete (RC) slab supported by U-shaped Fiber Reinforced Polymer (FRP) girders. Previous studies on similar hybrid bridges constructed in the United States and Europe seem to substantiate these hybrid designs for lightweight, high strength, and durable highway bridge construction. In the current study, computational and optimization analyses were carried out to investigate six composite material systems consisting of E-glass and carbon fibers. Optimization constraints are determined by stress, deflection and manufacturing requirements. Finite Element Analysis (FEA) and optimization software were utilized, and a framework was developed to run the complete analyses in an automated fashion. Prior to that, FEA validation of previous studies on similar U-shaped FRP girders that were constructed in Poland and Texas is presented. A finer optimization analysis is performed for the case of the Texas hybrid bridge. The optimization outcome of the hybrid FRP/RC bridge shows the appropriate composite material selection and cross-section geometry that satisfies all the applicable Limit States (LS) and, at the same time, results in the lightest design. Critical limit states show that shear stress criteria determine the optimum design for bridge spans less than 15.24 m and deflection criteria controls for longer spans. Increased side wall thickness can reduce maximum observed shear stresses, but leads to a high weight penalty. A taller cross-section and a thicker girder base can efficiently lower the observed deflections and normal stresses. Finally, substantial weight savings can be achieved by the optimization framework if base and side-wall thickness are treated as independent variables.

The relationship between the deep-level structure in crust and brewing of strong earthquakes in Xingtai area

NASA Astrophysics Data System (ADS)

Xiao, Lan-Xi; Zhu, Yuan-Qing; Zhang, Shao-Quan; Liu, Xu; Guo, Yu

1999-11-01

In this paper, crust medium is treated as Maxwell medium, and crust model includes hard inclusion, soft inclusion, deep-level fault. The stress concentration and its evolution with time are obtained by using three-dimensional finite element method and differential method. The conclusions are draw as follows: (1) The average stress concentration and maximum shear stress concentration caused by non-heterogeneous of crust are very high in hard inclusion and around the deep fault. With the time passing by, the concentration of average stress in the model gradually trends to uniform. At the same time, the concentration of maximum shear stress in hard inclusion increases gradually. This character is favorable to transfer shear strain energy from soft inclusion to hard inclusion. (2) When the upper mantle beneath the inclusion upheave at a certain velocity of 1 cm/a, the changes of average stress concentration with time become complex, and the boundary of the hard and soft inclusion become unconspicuous, but the maximum shear stress concentration increases much more in the hard inclusion with time at a higher velocity. This feature make for transformation of energy from the soft inclusion to the hard inclusion. (3) The changes of average stress concentration and maximum shear stress concentration with time around the deep-level fault result in further accumulation of maximum shear stress concentration and finally cause the deep-level fault instable and accelerated creep along fault direction. (4) The changes of vertical displacement on the surface of the model, which is caused by the accelerated creep of the deep-level fault, is similar to that of the observation data before Xingtai strong earthquake.

The numerical simulation study of the dynamic evolutionary processes in an earthquake cycle on the Longmen Shan Fault

NASA Astrophysics Data System (ADS)

Tao, Wei; Shen, Zheng-Kang; Zhang, Yong

2016-04-01

The Longmen Shan, located in the conjunction of the eastern margin the Tibet plateau and Sichuan basin, is a typical area for studying the deformation pattern of the Tibet plateau. Following the 2008 Mw 7.9 Wenchuan earthquake (WE) rupturing the Longmen Shan Fault (LSF), a great deal of observations and studies on geology, geophysics, and geodesy have been carried out for this region, with results published successively in recent years. Using the 2D viscoelastic finite element model, introducing the rate-state friction law to the fault, this thesis makes modeling of the earthquake recurrence process and the dynamic evolutionary processes in an earthquake cycle of 10 thousand years. By analyzing the displacement, velocity, stresses, strain energy and strain energy increment fields, this work obtains the following conclusions: (1) The maximum coseismic displacement on the fault is on the surface, and the damage on the hanging wall is much more serious than that on the foot wall of the fault. If the detachment layer is absent, the coseismic displacement would be smaller and the relative displacement between the hanging wall and foot wall would also be smaller. (2) In every stage of the earthquake cycle, the velocities (especially the vertical velocities) on the hanging wall of the fault are larger than that on the food wall, and the values and the distribution patterns of the velocity fields are similar. While in the locking stage prior to the earthquake, the velocities in crust and the relative velocities between hanging wall and foot wall decrease. For the model without the detachment layer, the velocities in crust in the post-seismic stage is much larger than those in other stages. (3) The maximum principle stress and the maximum shear stress concentrate around the joint of the fault and detachment layer, therefore the earthquake would nucleate and start here. (4) The strain density distribution patterns in stages of the earthquake cycle are similar. There are two concentration areas in the model, one is located in the mid and upper crust on the hanging wall where the strain energy could be released by permanent deformation like folding, and the other lies in the deep part of the fault where the strain energy could be released by earthquakes. (5) The whole earthquake dynamic process could be clearly reflected by the evolutions of the strain energy increments on the stages of the earthquake cycle. In the inter-seismic period, the strain energy accumulates relatively slowly; prior to the earthquake, the fault is locking and the strain energy accumulates fast, and some of the strain energy is released on the upper crust on the hanging wall of the fault. In coseismic stage, the strain energy is released fast along the fault. In the poseismic stage, the slow accumulation process of strain recovers rapidly as that in the inerseismic period in around one hundred years. The simulation study in this thesis would help better understand the earthquake dynamic process.

Shear Capacity of C-Shaped and L-Shaped Angle Shear Connectors

PubMed Central

Tahmasbi, Farzad; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N. H.; Tahir, M. M.

2016-01-01

This paper investigates the behaviour of C-shaped and L-shaped angle shear connectors embedded in solid concrete slabs. An effective finite element model is proposed to simulate the push out tests of these shear connectors that encompass nonlinear material behaviour, large displacement and damage plasticity. The finite element models are validated against test results. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength and connector dimensions. The finite element analyses also confirm the test results that increasing the length of shear connector increases their shear strength proportionately. It is observed that the maximum stress in L-shaped angle connectors takes place in the weld attachment to the beam, whereas in the C-shaped angle connectors, it is in the attached leg. The location of maximum concrete compressive damage is rendered in each case. Finally, a new equation for prediction of the shear capacity of C-shaped angle connectors is proposed. PMID:27478894

Shear Capacity of C-Shaped and L-Shaped Angle Shear Connectors.

PubMed

Tahmasbi, Farzad; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N H; Tahir, M M

2016-01-01

This paper investigates the behaviour of C-shaped and L-shaped angle shear connectors embedded in solid concrete slabs. An effective finite element model is proposed to simulate the push out tests of these shear connectors that encompass nonlinear material behaviour, large displacement and damage plasticity. The finite element models are validated against test results. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength and connector dimensions. The finite element analyses also confirm the test results that increasing the length of shear connector increases their shear strength proportionately. It is observed that the maximum stress in L-shaped angle connectors takes place in the weld attachment to the beam, whereas in the C-shaped angle connectors, it is in the attached leg. The location of maximum concrete compressive damage is rendered in each case. Finally, a new equation for prediction of the shear capacity of C-shaped angle connectors is proposed.

Measurement of surface shear stress vector beneath high-speed jet flow using liquid crystal coating

NASA Astrophysics Data System (ADS)

Wang, Cheng-Peng; Zhao, Ji-Song; Jiao, Yun; Cheng, Ke-Ming

2018-05-01

The shear-sensitive liquid crystal coating (SSLCC) technique is investigated in the high-speed jet flow of a micro-wind-tunnel. An approach to measure surface shear stress vector distribution using the SSLCC technique is established, where six synchronous cameras are used to record the coating color at different circumferential view angles. Spatial wall shear stress vector distributions on the test surface are obtained at different velocities. The results are encouraging and demonstrate the great potential of the SSLCC technique in high-speed wind-tunnel measurement.

Asymmetric bubble collapse and jetting in generalized Newtonian fluids

NASA Astrophysics Data System (ADS)

Shukla, Ratnesh K.; Freund, Jonathan B.

2017-11-01

The jetting dynamics of a gas bubble near a rigid wall in a non-Newtonian fluid are investigated using an axisymmetric simulation model. The bubble gas is assumed to be homogeneous, with density and pressure related through a polytropic equation of state. An Eulerian numerical description, based on a sharp interface capturing method for the shear-free bubble-liquid interface and an incompressible Navier-Stokes flow solver for generalized fluids, is developed specifically for this problem. Detailed simulations for a range of rheological parameters in the Carreau model show both the stabilizing and destabilizing non-Newtonian effects on the jet formation and impact. In general, for fixed driving pressure ratio, stand-off distance and reference zero-shear-rate viscosity, shear-thinning and shear-thickening promote and suppress jet formation and impact, respectively. For a sufficiently large high-shear-rate limit viscosity, the jet impact is completely suppressed. Thresholds are also determined for the Carreau power-index and material time constant. The dependence of these threshold rheological parameters on the non-dimensional driving pressure ratio and wall stand-off distance is similarly established. Implications for tissue injury in therapeutic ultrasound will be discussed.

Abdominal Aortic Hemodynamics in Intermittent Claudication Patients at Rest and During Dynamic Pedaling Exercise

PubMed Central

Cheng, Christopher P.; Taylor, Charles A.; Dalman, Ronald L.

2015-01-01

Introduction Lower extremity exercise has been shown to eliminate adverse hemodynamics conditions, such as low and oscillating blood flow and wall shear stress, in the abdominal aortas of healthy young and older adults. Methods We use cine phase-contrast magnetic resonance imaging and a custom MRI-compatible exercise cycle to quantify hemodynamic changes due to pedaling exercise in patients diagnosed with intermittent claudication. Results and Conclusions With only an average heart increase of 35±18% and exercise workload of 36±16 Watts, the patients experienced approximately 3- and 6-fold increases in blood flow, and 4- and 16-fold increases in wall shear stress at the supraceliac and infrarenal aortic locations, respectively. Also, all oscillations in flow and shear stress at rest were eliminated with exercise. Claudication patients experience 3 to 4-fold lower oscillations in flow and shear stress at rest as compared to healthy age-matched controls, likely due to reduced distal arterial compliance as a result of distal atherosclerosis. The magnitude of flow and shear oscillatory indices may be good indicators of distal arterial compliance and health, and may provide predictive power for the efficacy of focal interventions. PMID:26315797

Elastic turbulence in entangled semi-dilute DNA solutions measured with optical coherence tomography velocimetry.

PubMed

Malm, A V; Waigh, T A

2017-04-26

The flow instabilities of solutions of high molecular weight DNA in the entangled semi-dilute concentration regime were investigated using optical coherence tomography velocimetry, a technique that provides high spatial (probe volumes of 3.4 pL) and temporal resolution (sub μs) information on the flow behaviour of complex fluids in a rheometer. The velocity profiles of the opaque DNA solutions (high and low salt) were measured as a function of the distance across the gap of a parallel plate rheometer, and their evolution over time was measured. At lower DNA concentrations and low shear rates, the velocity fluctuations were well described by Gaussian functions and the velocity gradient was uniform across the rheometer gap, which is expected for Newtonian flows. As the DNA concentration and shear rate were increased there was a stable wall slip regime followed by an evolving wall slip regime, which is finally followed by the onset of elastic turbulence. Strain localization (shear banding) is observed on the boundaries of the flows at intermediate shear rates, but decreases in the high shear elastic turbulence regime, where bulk strain localization occurs. A dynamic phase diagram for non-linear flow was created to describe the different behaviours.

Mathematical Modeling of Intravascular Blood Coagulation under Wall Shear Stress

PubMed Central

Rukhlenko, Oleksii S.; Dudchenko, Olga A.; Zlobina, Ksenia E.; Guria, Georgy Th.

2015-01-01

Increased shear stress such as observed at local stenosis may cause drastic changes in the permeability of the vessel wall to procoagulants and thus initiate intravascular blood coagulation. In this paper we suggest a mathematical model to investigate how shear stress-induced permeability influences the thrombogenic potential of atherosclerotic plaques. Numerical analysis of the model reveals the existence of two hydrodynamic thresholds for activation of blood coagulation in the system and unveils typical scenarios of thrombus formation. The dependence of blood coagulation development on the intensity of blood flow, as well as on geometrical parameters of atherosclerotic plaque is described. Relevant parametric diagrams are drawn. The results suggest a previously unrecognized role of relatively small plaques (resulting in less than 50% of the lumen area reduction) in atherothrombosis and have important implications for the existing stenting guidelines. PMID:26222505

Assessment of fluctuating pressure gradient using acceleration spectra in near wall flows

NASA Astrophysics Data System (ADS)

Cadel, Daniel; Lowe, K. Todd

2015-11-01

Separation of contributions to the fluctuating acceleration from pressure gradient fluctuations and viscous shear fluctuations in the frequency domain is examined in a turbulent boundary layer. Past work leveraging turbulent accelerations for pressure gradient measurements has neglected the viscous shear term from the momentum equation--an invalid assumption in the case of near wall flows. The present study seeks to account for the influence of the viscous shear term and spectrally reject its contribution, which is thought to be concentrated at higher frequencies. Spectra of velocity and acceleration fluctuations in a flat plate, zero pressure gradient turbulent boundary layer at a momentum thickness Reynolds number of 7500 are measured using a spatially resolving three-component laser Doppler velocimeter. This canonical case data is applied for validation of the spectral approach for future application in more complex aerodynamic flows.

Hemodynamic analysis of intracranial aneurysms using phase-contrast magnetic resonance imaging and computational fluid dynamics

NASA Astrophysics Data System (ADS)

Zhao, Xuemei; Li, Rui; Chen, Yu; Sia, Sheau Fung; Li, Donghai; Zhang, Yu; Liu, Aihua

2017-04-01

Additional hemodynamic parameters are highly desirable in the clinical management of intracranial aneurysm rupture as static medical images cannot demonstrate the blood flow within aneurysms. There are two ways of obtaining the hemodynamic information—by phase-contrast magnetic resonance imaging (PCMRI) and computational fluid dynamics (CFD). In this paper, we compared PCMRI and CFD in the analysis of a stable patient's specific aneurysm. The results showed that PCMRI and CFD are in good agreement with each other. An additional CFD study of two stable and two ruptured aneurysms revealed that ruptured aneurysms have a higher statistical average blood velocity, wall shear stress, and oscillatory shear index (OSI) within the aneurysm sac compared to those of stable aneurysms. Furthermore, for ruptured aneurysms, the OSI divides the positive and negative wall shear stress divergence at the aneurysm sac.

Boundary-layer computational model for predicting the flow and heat transfer in sudden expansions

NASA Technical Reports Server (NTRS)

Lewis, J. P.; Pletcher, R. H.

1986-01-01

Fully developed turbulent and laminar flows through symmetric planar and axisymmetric expansions with heat transfer were modeled using a finite-difference discretization of the boundary-layer equations. By using the boundary-layer equations to model separated flow in place of the Navier-Stokes equations, computational effort was reduced permitting turbulence modelling studies to be economically carried out. For laminar flow, the reattachment length was well predicted for Reynolds numbers as low as 20 and the details of the trapped eddy were well predicted for Reynolds numbers above 200. For turbulent flows, the Boussinesq assumption was used to express the Reynolds stresses in terms of a turbulent viscosity. Near-wall algebraic turbulence models based on Prandtl's-mixing-length model and the maximum Reynolds shear stress were compared.

Fracture mechanics of shear crack propagation and dissection in the healthy bovine descending aortic media.

PubMed

Haslach, Henry W; Siddiqui, Ahmed; Weerasooriya, Amanda; Nguyen, Ryan; Roshgadol, Jacob; Monforte, Noel; McMahon, Eileen

2018-03-01

This experimental study adopts a fracture mechanics strategy to investigate the mechanical cause of aortic dissection. Inflation of excised healthy bovine aortic rings with a cut longitudinal notch that extends into the media from the intima suggests that an intimal tear may propagate a nearly circumferential-longitudinal rupture surface that is similar to the delamination that occurs in aortic dissection. Radial and 45°-from-radial cut notch orientations, as seen in the thickness surface, produce similar circumferential crack propagation morphologies. Partial cut notches, whose longitudinal length is half the width of the ring, measure the influence of longitudinal material on crack propagation. Such specimens also produce circumferential cracks from the notch root that are visible in the thickness circumferential-radial plane, and often propagate a secondary crack from the base of the notch, visible in the intimal circumferential-longitudinal plane. Inflation of rings with pairs of cut notches demonstrates that a second notch modifies the propagation created in a specimen with a single notch. The circumferential crack propagation is likely a consequence of the laminar medial structure. These fracture surfaces are probably due to non-uniform circumferential shear deformation in the heterogeneous media as the aortic wall expands. The qualitative deformation morphology around the root of the cut notch during inflation is evidence for such shear deformation. The shear apparently results from relative slip in the circumferential direction of collagen fibers. The slip may produce shear in the longitudinal-circumferential plane between medial layers or in the radial-circumferential plane within a medial lamina in an idealized model. Circumferential crack propagation in the media is then a shear mechanical process that might be facilitated by disease of the tissue. An intimal tear of an apparently healthy aortic wall near the aortic arch is life-threatening because it may lead to full rupture or to wall dissection in which delamination of the medial layer extends around most of the aortic circumference. The mechanical events underlying dissection are not definitively established. This experimental fracture mechanics study provides evidence that shear rupture is the main mechanical process underlying aortic dissection. The commonly performed tensile strength tests of aortic tissue are not clinically useful to predict or describe aortic dissection. One implication of the study is that shear tests might produce more fruitful simple assessments of the aortic wall strength. A clinical implication is that when presented with an intimal tear, those who guide care might recommend steps to reduce the shear load on the aorta. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Non-equilibrium phase behavior and friction of confined molecular films under shear: A non-equilibrium molecular dynamics study.

PubMed

Maćkowiak, Sz; Heyes, D M; Dini, D; Brańka, A C

2016-10-28

The phase behavior of a confined liquid at high pressure and shear rate, such as is found in elastohydrodynamic lubrication, can influence the traction characteristics in machine operation. Generic aspects of this behavior are investigated here using Non-equilibrium Molecular Dynamics (NEMD) simulations of confined Lennard-Jones (LJ) films under load with a recently proposed wall-driven shearing method without wall atom tethering [C. Gattinoni et al., Phys. Rev. E 90, 043302 (2014)]. The focus is on thick films in which the nonequilibrium phases formed in the confined region impact on the traction properties. The nonequilibrium phase and tribological diagrams are mapped out in detail as a function of load, wall sliding speed, and atomic scale surface roughness, which is shown can have a significant effect. The transition between these phases is typically not sharp as the external conditions are varied. The magnitude of the friction coefficient depends strongly on the nonequilibrium phase adopted by the confined region of molecules, and in general does not follow the classical friction relations between macroscopic bodies, e.g., the frictional force can decrease with increasing load in the Plug-Slip (PS) region of the phase diagram owing to structural changes induced in the confined film. The friction coefficient can be extremely low (∼0.01) in the PS region as a result of incommensurate alignment between a (100) face-centered cubic wall plane and reconstructed (111) layers of the confined region near the wall. It is possible to exploit hysteresis to retain low friction PS states well into the central localization high wall speed region of the phase diagram. Stick-slip behavior due to periodic in-plane melting of layers in the confined region and subsequent annealing is observed at low wall speeds and moderate external loads. At intermediate wall speeds and pressure values (at least) the friction coefficient decreases with increasing well depth of the LJ potential between the wall atoms, but increases when the attractive part of the potential between wall atoms and confined molecules is made larger.

Transitional Flow in an Arteriovenous Fistula: Effect of Wall Distensibility

NASA Astrophysics Data System (ADS)

McGah, Patrick; Leotta, Daniel; Beach, Kirk; Aliseda, Alberto

2012-11-01

Arteriovenous fistulae are created surgically to provide adequate access for dialysis in patients with end-stage renal disease. Transitional flow and the subsequent pressure and shear stress fluctuations are thought to be causative in the fistula failure. Since 50% of fistulae require surgical intervention before year one, understanding the altered hemodynamic stresses is an important step toward improving clinical outcomes. We perform numerical simulations of a patient-specific model of a functioning fistula reconstructed from 3D ultrasound scans. Rigid wall simulations and fluid-structure interaction simulations using an in-house finite element solver for the wall deformations were performed and compared. In both the rigid and distensible wall cases, transitional flow is computed in fistula as evidenced by aperiodic high frequency velocity and pressure fluctuations. The spectrum of the fluctuations is much more narrow-banded in the distensible case, however, suggesting a partial stabilizing effect by the vessel elasticity. As a result, the distensible wall simulations predict shear stresses that are systematically 10-30% lower than the rigid cases. We propose a possible mechanism for stabilization involving the phase lag in the fluid work needed to deform the vessel wall. Support from an NIDDK R21 - DK08-1823.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, Qi-lin, E-mail: xiongql@hust.edu.cn; Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment, Luoyu Road 1037, Wuhan 430074; Tian, Xiao Geng

The torsional mechanical properties of hexagonal single-walled boron nitride nanotubes (SWBNNTs), single-walled carbon nanotubes (SWCNTs), and their hybrid structures (SWBN-CNTs) are investigated using molecular dynamics (MD) simulation. Two approaches - force approach and energy approach, are adopted to calculate the shear moduli of SWBNNTs and SWCNTs, the discrepancy between two approaches is analyzed. The results show that the shear moduli of single-walled nanotubes (SWNTs), including SWBNNTs and SWCNTs are dependent on the diameter, especially for armchair SWNTs. The armchair SWNTs show the better ability of resistance the twisting comparable to the zigzag SWNTs. The effects of diameter and length onmore » the critical values of torque of SWNTs are obtained by comparing the torsional behaviors of SWNTs with different diameters and different lengths. It is observed that the MD results of the effect of diameter and length on the critical values of torque agrees well with the prediction of continuum shell model. The shear modulus of SWBN-CNT has a significant dependence on the percentages of SWCNT and the hybrid style has also an influence on shear modulus. The critical values of torque of SWBN-CNTs increase with the increase of the percentages of SWCNT. This phenomenon can be interpreted by the function relationship between the torque of different bonds (B-N-X, C-C-X, C-B-X, C-N-X) and the angles of bonds.« less

Experimental study on the deformation microstructures of lawsonite blueschist and implications for seismic anisotropy

NASA Astrophysics Data System (ADS)

Choi, S.; Jung, H.

2017-12-01

Various seismic anisotropy has been observed in the world, especially along subduction zones, and a part of the seismic anisotropy can be caused by the subducting slab, which is poorly understood. One of the main rocks at the top of the subducting slab in cold subduction zones is lawsonite blueschist, which has been rarely studied experimentally. Since lawsonite blueschist is composed of elastically anisotropic minerals such as glaucophane and lawsonite, development of the lattice preferred orientation (LPO) of these minerals can cause a large seismic anisotropy. Therefore, to understand deformation microstructures (i.e., LPOs) of lawsonite and glaucophane and the resultant seismic anisotropy, we conducted deformation experiments of lawsonite blueschist in simple shear using a modified Griggs apparatus. The experiments were performed under the pressures (P = 1 - 2 GPa), temperatures (T = 230 - 400 °), shear strain (γ = 1 - 4), and shear strain rates (10-6 - 10-4 s-1). LPOs of minerals were determined by SEM/EBSD technique. LPO of glaucophane after experiments at the shear strain (1 < γ ≤ 4.0) showed that the maxima of (110) poles and [100] axes were aligned subnormal to the shear plane and the maximum of [001] axes subparallel to the shear direction. LPO of lawsonite showed that at low strain (γ ≤ 1.4) the maximum of [010] axes were aligned sub-parallel to the shear direction, but at high strain (γ ≥ 2.1) the maximum of [100] axes were aligned sub-parallel to the direction with the [001] axes aligned subnormal to the shear plane. Using the LPO data, seismic properties of each minerals were calculated. Glaucophane showed a high P-wave anisotropy (7.7 - 16.9 %) and relatively low maximum S-wave anisotropy (4.4 - 9.2 %). In contrast, lawsonite showed much higher maximum S-wave anisotropy (8.3 - 20.7 %) than glaucophane, but showed a low P-wave anisotropy in the range of 4.7 - 10.3 %. Our results indicate that seismic anisotropy observed at the top of cold subducting slabs and at the slab-mantle interfaces can be attributed to the LPOs of lawsonite & glaucophane in the deformed blueschist facies rocks.

Why do we live for much less than 100 years? A fluid mechanics view and approach

NASA Astrophysics Data System (ADS)

Messaris, Gerasimos A. T.; Hadjinicolaou, Maria; Karahalios, George T.

2017-08-01

Blood flow in arteries induces shear stresses on the arterial walls. The present work is motivated by the implications of low shear stress on the human arterial system and its effect on the duration of the life of a subject. The low and/or bidirectional wall shear stress stiffens the arterial wall and in synergy with the fluctuating tissue stress due to the fluctuating blood pressure activates the mechanism of aging. If the shear stress were not low and/or bidirectional and if it did not contribute to local endothelium dysfunctions, the tissue stress alone would take more than 100 yr to cause a failure on the human arterial system. Applying the s-n diagram (tissue stress against the number of cycles to failure) to determine the fatigue life of the aorta, for example, we find that in the absence of other pathogenic factors, for a tissue stress 1.2 times bigger than the tissue stress of a non-stiff aorta, the potential 100 yr of life are reduced to nearly 80 yr. Calculation of the rate of variation of the tissue stress of a subject with time may lead to a possible prognosis about the evolution of wall stiffness and its impact on the arterial aging of this subject. Further patient-specific in vivo mechanistic studies complemented by molecular imaging are needed to contribute to the formation of a data base, from which improved models describing the evolution of the arterial stiffness can be developed. Accordingly, the degree of stiffness of the aorta compared with existing data from a corresponding data base may provide with information about the degree of the fatigue of the aortic wall and its possible future behavior and lead to a patient-adapted medical treatment as a means of a would-be preventive medication.

Molecular deformation mechanisms of the wood cell wall material.

PubMed

Jin, Kai; Qin, Zhao; Buehler, Markus J

2015-02-01

Wood is a biological material with outstanding mechanical properties resulting from its hierarchical structure across different scales. Although earlier work has shown that the cellular structure of wood is a key factor that renders it excellent mechanical properties at light weight, the mechanical properties of the wood cell wall material itself still needs to be understood comprehensively. The wood cell wall material features a fiber reinforced composite structure, where cellulose fibrils act as stiff fibers, and hemicellulose and lignin molecules act as soft matrix. The angle between the fiber direction and the loading direction has been found to be the key factor controlling the mechanical properties. However, how the interactions between theses constitutive molecules contribute to the overall properties is still unclear, although the shearing between fibers has been proposed as a primary deformation mechanism. Here we report a molecular model of the wood cell wall material with atomistic resolution, used to assess the mechanical behavior under shear loading in order to understand the deformation mechanisms at the molecular level. The model includes an explicit description of cellulose crystals, hemicellulose, as well as lignin molecules arranged in a layered nanocomposite. The results obtained using this model show that the wood cell wall material under shear loading deforms in an elastic and then plastic manner. The plastic regime can be divided into two parts according to the different deformation mechanisms: yielding of the matrix and sliding of matrix along the cellulose surface. Our molecular dynamics study provides insights of the mechanical behavior of wood cell wall material at the molecular level, and paves a way for the multi-scale understanding of the mechanical properties of wood. Copyright © 2014 Elsevier Ltd. All rights reserved.

On a turbulent wall model to predict hemolysis numerically in medical devices

NASA Astrophysics Data System (ADS)

Lee, Seunghun; Chang, Minwook; Kang, Seongwon; Hur, Nahmkeon; Kim, Wonjung

2017-11-01

Analyzing degradation of red blood cells is very important for medical devices with blood flows. The blood shear stress has been recognized as the most dominant factor for hemolysis in medical devices. Compared to laminar flows, turbulent flows have higher shear stress values in the regions near the wall. In case of predicting hemolysis numerically, this phenomenon can require a very fine mesh and large computational resources. In order to resolve this issue, the purpose of this study is to develop a turbulent wall model to predict the hemolysis more efficiently. In order to decrease the numerical error of hemolysis prediction in a coarse grid resolution, we divided the computational domain into two regions and applied different approaches to each region. In the near-wall region with a steep velocity gradient, an analytic approach using modeled velocity profile is applied to reduce a numerical error to allow a coarse grid resolution. We adopt the Van Driest law as a model for the mean velocity profile. In a region far from the wall, a regular numerical discretization is applied. The proposed turbulent wall model is evaluated for a few turbulent flows inside a cannula and centrifugal pumps. The results present that the proposed turbulent wall model for hemolysis improves the computational efficiency significantly for engineering applications. Corresponding author.

Earthquake Resilient Tall Reinforced Concrete Buildings at Near-Fault Sites Using Base Isolation and Rocking Core Walls

NASA Astrophysics Data System (ADS)

Calugaru, Vladimir

This dissertation pursues three main objectives: (1) to investigate the seismic response of tall reinforced concrete core wall buildings, designed following current building codes, subjected to pulse type near-fault ground motion, with special focus on the relation between the characteristics of the ground motion and the higher-modes of response; (2) to determine the characteristics of a base isolation system that results in nominally elastic response of the superstructure of a tall reinforced concrete core wall building at the maximum considered earthquake level of shaking; and (3) to demonstrate that the seismic performance, cost, and constructability of a base-isolated tall reinforced concrete core wall building can be significantly improved by incorporating a rocking core-wall in the design. First, this dissertation investigates the seismic response of tall cantilever wall buildings subjected to pulse type ground motion, with special focus on the relation between the characteristics of ground motion and the higher-modes of response. Buildings 10, 20, and 40 stories high were designed such that inelastic deformation was concentrated at a single flexural plastic hinge at their base. Using nonlinear response history analysis, the buildings were subjected to near-fault seismic ground motions as well as simple close-form pulses, which represented distinct pulses within the ground motions. Euler-Bernoulli beam models with lumped mass and lumped plasticity were used to model the buildings. Next, this dissertation investigates numerically the seismic response of six seismically base-isolated (BI) 20-story reinforced concrete buildings and compares their response to that of a fixed-base (FB) building with a similar structural system above ground. Located in Berkeley, California, 2 km from the Hayward fault, the buildings are designed with a core wall that provides most of the lateral force resistance above ground. For the BI buildings, the following are investigated: two isolation systems (both implemented below a three-story basement), isolation periods equal to 4, 5, and 6 s, and two levels of flexural strength of the wall. The first isolation system combines tension-resistant friction pendulum bearings and nonlinear fluid viscous dampers (NFVDs); the second combines low-friction tension-resistant cross-linear bearings, lead-rubber bearings, and NFVDs. Finally, this dissertation investigates the seismic response of four 20-story buildings hypothetically located in the San Francisco Bay Area, 0.5 km from the San Andreas fault. One of the four studied buildings is fixed-base (FB), two are base-isolated (BI), and one uses a combination of base isolation and a rocking core wall (BIRW). Above the ground level, a reinforced concrete core wall provides the majority of the lateral force resistance in all four buildings. The FB and BI buildings satisfy requirements of ASCE 7-10. The BI and BIRW buildings use the same isolation system, which combines tension-resistant friction pendulum bearings and nonlinear fluid viscous dampers. The rocking core-wall includes post-tensioning steel, buckling-restrained devices, and at its base is encased in a steel shell to maximize confinement of the concrete core. The total amount of longitudinal steel in the wall of the BIRW building is 0.71 to 0.87 times that used in the BI buildings. Response history two-dimensional analysis is performed, including the vertical components of excitation, for a set of ground motions scaled to the design earthquake and to the maximum considered earthquake (MCE). While the FB building at MCE level of shaking develops inelastic deformations and shear stresses in the wall that may correspond to irreparable damage, the BI and the BIRW buildings experience nominally elastic response of the wall, with floor accelerations and shear forces which are 0.36 to 0.55 times those experienced by the FB building. The response of the four buildings to two historical and two simulated near-fault ground motions is also studied, demonstrating that the BIRW building has the largest deformation capacity at the onset of structural damage. (Abstract shortened by UMI.).

Turbulent Boundary Layer Drag Reduction by Spanwise Wall Oscillation

NASA Astrophysics Data System (ADS)

Trujillo, S. M.; Bogard, D. G.; Ball, K. S.

1997-11-01

Changes in turbulence structure were investigated in a turbulent water boundary layer flow for which wall shear had been reduced 25 percent by spanwise wall oscillations. LDV and hot film measurements were made of streamwise and wall-normal velocities. For all wall oscillations examined, drag reduction was found to scale best with the peak velocity of the wall oscillation. Burst and sweep strength and duration were all reduced by the wall oscillation, with the greatest effects seen for the strongest events. The pdf of the velocity in the near-wall region showed greatly increased periods of low velocities, but little change was observed in the streamwise velocity autocorrelation.

The effect of crystal shape, size and bimodality on the maximum packing and the rheology of crystal bearing magma

NASA Astrophysics Data System (ADS)

Moitra, Pranabendu; Gonnermann, Helge

2014-05-01

Magma often contains crystals of various shapes and sizes. We present experimental results on the effect of the shape- and size-distribution of solid particles on the rheological properties of solid-liquid suspensions, which are hydrodynamically analogous to crystal-bearing magmas. The suspensions were comprised of either a single particle shape and size (unimodal) or a mixture of two different particle shapes and sizes (bimodal). For each type of suspension we characterized the dry maximum packing fraction of the particle mixture using the tap density method. We then systematically varied the total volume fraction of particles in the suspension, as well as the relative proportion of the two different particle types in the bimodal suspensions. For each of the resultant mixtures (suspensions) we performed controlled shear stress experiments using a rotational rheometer in parallel-plate geometry spanning 4 orders of magnitude in shear stress. The resultant data curves of shear stress as a function of shear rate were fitted using a Herschel-Bulkley rheological model. We find that the dry maximum packing decreases with increasing particle aspect ratio (ar) and decreasing particle size ratio (Λ). The highest dry maximum packing was obtained at 60-75% volume of larger particles for bimodal spherical particle mixture. Normalized consistency, Kr, defined as the ratio of the consistency of the suspension and the viscosity of the suspending liquid, was fitted using a Krieger-Dougherty model as a function of the total solid volume fraction (φ). The maximum packing fractions (φm) obtained from the shear experimental data fitting of the unimodal suspensions were similar in magnitude with the dry maximum packing fractions of the unimodal particles. Subsequently, we used the dry maximum packing fractions of the bimodal particle mixtures to fit Kr as a function of φ for the bimodal suspensions. We find that Kr increases rapidly for suspensions with larger ar and smaller Λ. We also find that both the apparent yield stress and the shear thinning behavior of the suspensions increase with increasing ar and become significant at φ/φm ≥ 0.4.

Shear conditions in clavulanic acid production by Streptomyces clavuligerus in stirred tank and airlift bioreactors.

PubMed

Cerri, M O; Badino, A C

2012-08-01

In biochemical processes involving filamentous microorganisms, the high shear rate may damage suspended cells leading to viability loss and cell disruption. In this work, the influence of the shear conditions in clavulanic acid (CA) production by Streptomyces clavuligerus was evaluated in a 4-dm(3) conventional stirred tank (STB) and in 6-dm(3) concentric-tube airlift (ALB) bioreactors. Batch cultivations were performed in a STB at 600 and 800 rpm and 0.5 vvm (cultivations B1 and B2) and in ALB at 3.0 and 4.1 vvm (cultivations A1 and A2) to define two initial oxygen transfer conditions in both bioreactors. The average shear rate ([Formula: see text]) of the cultivations was estimated using correlations of recent literature based on experimental data of rheological properties of the broth (consistency index, K, and flow index, n) and operating conditions, impeller speed (N) for STB and superficial gas velocity in the riser (UGR) for ALB. In the same oxygen transfer condition, the [Formula: see text] values for ALB were higher than those obtained in STB. The maximum [Formula: see text] presented a strong correlation with a maximum consistency index (K (max)) of the broth. Close values of maximum CA production were obtained in cultivations A1 and A2 (454 and 442 mg L(-1)) with similar maximum [Formula: see text] values of 4,247 and 4,225 s(-1). In cultivations B1 and B2, the maximum CA production of 269 and 402 mg L(-1) were reached with a maximum [Formula: see text] of 904 and 1,786 s(-1). The results show that high values of average shear rate increase the CA production regardless of the oxygen transfer condition and bioreactor model.

Influences of Shear History and Infilling on the Mechanical Characteristics and Acoustic Emissions of Joints

NASA Astrophysics Data System (ADS)

Meng, Fanzhen; Zhou, Hui; Wang, Zaiquan; Zhang, Liming; Kong, Liang; Li, Shaojun; Zhang, Chuanqing

2017-08-01

Filled joints, which are characterized by high deformability and low shear strength, are among the most critical discontinuities in rock mass and may be sheared repeatedly when subject to cyclic loading. Shear tests were carried out on tension splitting joints, with soil and granular cement mortar particles used as infillings, and the effects of the shear history on the mechanical behavior and acoustic emission (AE) of clean and filled joints were studied. The maximum strength in the subsequent shears was approximately 60% of the peak strength of the first shear for a clean joint, and the friction angle degraded from 63° to 45° after the first shear. The maximum shear strength of the filled joints was lower than 35% of the peak strength of the clean joint under the same normal stress. The change in the shear strength of filled joints with the number of shearing cycles was closely related to the transformation of the shear medium. Rolling friction occurred and the shear strength was low for the granular particle-filled joint, but the strength was elevated when the particles were crushed and sliding friction occurred. The AEs were significantly reduced during the second shear for the clean joint, and the peak AEs were mainly obtained at or near the turning point of the shear stress curve for the filled joint. The AEs were the highest for the cement particle-filled joint and lowest for the dry soil-filled joint; when subjected to repeated shears, the AEs were more complex because of the continuous changes to the shear medium. The evolution of the AEs with the shear displacement can accurately reflect the shear failure mechanism during a single shear process.

Hemodynamic effect of bypass geometry on intracranial aneurysm: A numerical investigation.

PubMed

Kurşun, Burak; Uğur, Levent; Keskin, Gökhan

2018-05-01

Hemodynamic analyzes are used in the clinical investigation and treatment of cardiovascular diseases. In the present study, the effect of bypass geometry on intracranial aneurysm hemodynamics was investigated numerically. Pressure, wall shear stress (WSS) and velocity distribution causing the aneurysm to grow and rupture were investigated and the best conditions were tried to be determined in case of bypassing between basilar (BA) and left/right posterior arteries (LPCA/RPCA) for different values of parameters. The finite volume method was used for numerical solutions and calculations were performed with the ANSYS-Fluent software. The SIMPLE algorithm was used to solve the discretized conservation equations. Second Order Upwind method was preferred for finding intermediate point values in the computational domain. As the blood flow velocity changes with time, the blood viscosity value also changes. For this reason, the Carreu model was used in determining the viscosity depending on the velocity. Numerical study results showed that when bypassed, pressure and wall shear stresses reduced in the range of 40-70% in the aneurysm. Numerical results obtained are presented in graphs including the variation of pressure, wall shear stress and velocity streamlines in the aneurysm. Considering the numerical results for all parameter values, it is seen that the most important factors affecting the pressure and WSS values in bypassing are the bypass position on the basilar artery (L b ) and the diameter of the bypass vessel (d). Pressure and wall shear stress reduced in the range of 40-70% in the aneurysm in the case of bypass for all parameters. This demonstrates that pressure and WSS values can be greatly reduced in aneurysm treatment by bypassing in cases where clipping or coil embolization methods can not be applied. Copyright © 2018 Elsevier B.V. All rights reserved.

Haemodynamical stress in mouse aortic arch with atherosclerotic plaques: Preliminary study of plaque progression

PubMed Central

Assemat, P.; Siu, K.K.; Armitage, J.A.; Hokke, S.N.; Dart, A.; Chin-Dusting, J.; Hourigan, K.

2014-01-01

Atherosclerotic plaques develop at particular sites in the arterial tree, and this regional localisation depends largely on haemodynamic parameters (such as wall shear stress; WSS) as described in the literature. Plaque rupture can result in heart attack or stroke and hence understanding the development and vulnerability of atherosclerotic plaques is critically important. The purpose of this study is to characterise the haemodynamics of blood flow in the mouse aortic arch using numerical modelling. The geometries are digitalised from synchrotron imaging and realistic pulsatile blood flow is considered under rigid wall assumptions. Two cases are considered; arteries with and without plaque. Mice that are fed under fat diet present plaques in the aortic arch whose size is dependent on the number of weeks under the diet. The plaque distribution in the region is however relatively constant through the different samples. This result underlines the influence of the geometry and consequently of the wall shear stresses for plaque formation with plaques growing in region of relative low shear stresses. A discussion of the flow field in real geometry in the presence and absence of plaques is conducted. The presence of plaques was shown to alter the blood flow and hence WSS distribution, with regions of localised high WSS, mainly on the wall of the brachiocephalic artery where luminal narrowing is most pronounced. In addition, arch plaques are shown to induce recirculation in the blood flow, a phenomenon with potential influence on the progression of the plaques. The oscillatory shear index and the relative residence time have been calculated on the geometry with plaques to show the presence of this recirculation in the arch, an approach that may be useful for future studies on plaque progression. PMID:25349678

Influence of vibration on structure rheological properties of a highly concentrated suspension

NASA Astrophysics Data System (ADS)

Ouriev Uriev, Boris N.; Uriev, Naum B.

2005-08-01

The influence of mechanical vibration on the flow properties of a highly concentrated multiphase food system is explored in this work. An experimental set-up was designed and adapted to a conventional rotational rheometer with precise rheological characterization capability. A number of calibration tests were performed prior to fundamental experiments with a highly concentrated chocolate suspension. Also, the prediction of wall slippage in shear flow under vibration was evaluated. Analysis of the boundary conditions shows that no side effects such as wall slippage or the Taylor effect were present during the shear experiment under vibration. It was found that superposition of mechanical vibration and shear flow radically decreases the shear viscosity. Comparison between reference shear viscosities at specified shear rates and those measured under vibration shows considerable differences in flow properties. Conversion of the behaviour of the concentrated suspension from strongly shear-thinning to Newtonian flow is reported. Also, the appearance of vibration-induced dilatancy as a new phenomenon is described. It is suggested to relate such phenomena to the non-equilibrium between structure formation and disintegration under vibration and hydrodynamic forces of shear flow. The influence of vibration on structure formation can be well observed during measurement of the yield value of the chocolate suspension under vibration. Comparison with reference data shows how sensitive the structure of the concentrated suspension is to vibration in general. The effects and observations revealed provide a solid basis for further fundamental investigations of structure formation regularities in the flow of any highly concentrated system. The results also show the technological potential for non-conventional treatment of concentrated, multiphase systems.

Shear-Induced Amyloid Formation in the Brain: I. Potential Vascular and Parenchymal Processes.

PubMed

Trumbore, Conrad N

2016-09-06

Shear distortion of amyloid-beta (Aβ) solutions accelerates amyloid cascade reactions that may yield different toxic oligomers than those formed in quiescent solutions. Recent experiments indicate that cerebrospinal fluid (CSF) and interstitial fluid (ISF) containing Aβ flow through narrow brain perivascular pathways and brain parenchyma. This paper suggests that such flow causes shear distortion of Aβ molecules involving conformation changes that may be one of the initiating events in the etiology of Alzheimer's disease. Aβ shearing can occur in or around brain arteries and arterioles and is suggested as the origin of cerebral amyloid angiopathy deposits in cerebrovascular walls. Comparatively low flow rates of ISF within the narrow extracellular spaces (ECS) of the brain parenchyma are suggested as a possible initiating factor in both the formation of neurotoxic Aβ42 oligomers and amyloid fibrils. Aβ42 in slow-flowing ISF can gain significant shear energy at or near the walls of tortuous brain ECS flow paths, promoting the formation of a shear-distorted, excited state hydrophobic Aβ42* conformation. This Aβ42* molecule could possibly be involved in one of two paths, one involving rapid adsorption to a brain membrane surface, ultimately forming neurotoxic oligomers on membranes, and the other ultimately forming plaque within the ECS flow pathways. Rising Aβ concentrations combined with shear at or near critical brain membranes are proposed as contributing factors to Alzheimer's disease neurotoxicity. These hypotheses may be applicable in other neurodegenerative diseases, including tauopathies and alpha-synucleinopathies, in which shear-distorted proteins also may form in the brain ECS.

49 CFR 173.302a - Additional requirements for shipment of nonliquefied (permanent) compressed gases in...

Code of Federal Regulations, 2011 CFR

2011-10-01

... elastic expansion was determined at the time of the last test or retest by the water jacket method. (3) Either the average wall stress or the maximum wall stress does not exceed the wall stress limitation shown in the following table: Type of steel Average wall stress limitation Maximum wall stress...

Stiffness Matrix of Thin-Walled Open Bar Subject to Bending, Bending Torsion and Shift of Cross Section Middle Surface

NASA Astrophysics Data System (ADS)

Panasenko, N. N.; Sinelschikov, A. V.

2017-11-01

One of the main stages in the analysis of complex 3D structures and engineering constructions made of thin-walled open bars using FEM is a stiffness matrix developing. Taking into account middle surface shear deformation caused by the work of tangential stresses in the formula to calculate a potential energy of thin-walled open bars, the authors obtain an important correction at calculation of the bar deformation and fundamental frequencies. The results of the analysis of the free end buckling of a cantilever H-bar under plane bending differ from exact solution by 0.53%. In the course of comparison of the obtained results with the cantilever bar buckling regardless the middle surface shear deformation, an increase made 16.6%. The stiffness matrix of a thin-walled open bar developed in the present work can be integrated into any software suite using FEM for the analysis of complex 3-D structures and engineering constructions with n-freedoms.

Simulation of blood flow in a small-diameter vascular graft model with a swirl (spiral) flow guider.

PubMed

Zhang, ZhiGuo; Fan, YuBo; Deng, XiaoYan; Wang, GuiXue; Zhang, He; Guidoin, Robert

2008-10-01

Small-diameter vascular grafts are in large demand for coronary and peripheral bypass procedures, but present products still fail in long-term clinical application. In the present communication, a new type of small-diameter graft with a swirl flow guider was proposed to improve graft patency rate. Flow pattern in the graft was simulated numerically and compared with that in a conventional graft. The numerical results revealed that the swirl flow guider could indeed make the blood flow rotate in the new graft. The swirling flow distal to the flow guider significantly altered the flow pattern in the new graft and the velocity profiles were re-distributed. Due to the swirling flow, the blood velocity near the vessel wall and wall shear rate were greatly enhanced. We believe that the increased blood velocity near the wall and the wall shear rate can impede the occurrence of acute thrombus formation and intimal hyperplasia, hence can improve the graft patency rate for long-term clinical use.

Damping of quasi-two-dimensional internal wave attractors by rigid-wall friction

NASA Astrophysics Data System (ADS)

Beckebanze, F.; Brouzet, C.; Sibgatullin, I. N.; Maas, L. R. M.

2018-04-01

The reflection of internal gravity waves at sloping boundaries leads to focusing or defocusing. In closed domains, focusing typically dominates and projects the wave energy onto 'wave attractors'. For small-amplitude internal waves, the projection of energy onto higher wave numbers by geometric focusing can be balanced by viscous dissipation at high wave numbers. Contrary to what was previously suggested, viscous dissipation in interior shear layers may not be sufficient to explain the experiments on wave attractors in the classical quasi-2D trapezoidal laboratory set-ups. Applying standard boundary layer theory, we provide an elaborate description of the viscous dissipation in the interior shear layer, as well as at the rigid boundaries. Our analysis shows that even if the thin lateral Stokes boundary layers consist of no more than 1% of the wall-to-wall distance, dissipation by lateral walls dominates at intermediate wave numbers. Our extended model for the spectrum of 3D wave attractors in equilibrium closes the gap between observations and theory by Hazewinkel et al. (2008).

Pros and cons of multistory RC tunnel-form (box-type) buildings

USGS Publications Warehouse

Kalkan, E.; Yuksel, S.B.

2008-01-01

Tunnel-form structural systems (i.e., box systems), having a load-carrying mechanism composed of reinforced concrete (RC) shear walls and slabs only, have been prevailingly utilized in the construction of multistory residential units. The superiority of tunnel-form buildings over their conventional counterparts stems from the enhanced earthquake resistance they provide, and the considerable speed and economy of their construction. During recent earthquakes in Turkey, they exhibited better seismic performance in contrast to the damaged condition of a number of RC frames and dual systems (i.e., RC frames with shear wall configurations). Thus the tunnel-form system has become a primary construction technique in many seismically active regions. In this paper, the strengths and weaknesses of tunnel-form buildings are addressed in terms of design considerations and construction applications. The impacts of shear wall reinforcement ratio and its detailing on system ductility, loadcarrying capacity and failure mechanism under seismic forces are evaluated at section and global system levels. Influences of tension/compression coupling and wall openings on the response are also discussed. Three-dimensional nonlinear finite element models, verified through comparisons with experimental results, were used for numerical assessments. Findings from this projection provide useful information on adequate vertical reinforcement ratio and boundary reinforcement to achieve enhanced performance of tunnel-form buildings under seismic actions. Copyright ?? 2007 John Wiley & Sons, Ltd.

Computational Analysis of Intra-Ventricular Flow Pattern Under Partial and Full Support of BJUT-II VAD.

PubMed

Zhang, Qi; Gao, Bin; Chang, Yu

2017-02-27

BACKGROUND Partial support, as a novel support mode, has been widely applied in clinical practice and widely studied. However, the precise mechanism of partial support of LVAD in the intra-ventricular flow pattern is unclear. MATERIAL AND METHODS In this study, a patient-specific left ventricular geometric model was reconstructed based on CT data. The intra-ventricular flow pattern under 3 simulated conditions - "heart failure", "partial support", and "full support" - were simulated by using fluid-structure interaction (FSI). The blood flow pattern, wall shear stress (WSS), time-average wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were calculated to evaluate the hemodynamic effects. RESULTS The results demonstrate that the intra-ventricular flow pattern is significantly changed by the support level of BJUT-II VAD. The intra-ventricular vortex was enhanced under partial support and was eliminated under full support, and the high OSI and RRT regions changed from the septum wall to the cardiac apex. CONCLUSIONS In brief, the support level of the BJUT-II VAD has significant effects on the intra-ventricular flow pattern. The partial support mode of BJUT-II VAD can enhance the intra-ventricular vortex, while the distribution of high OSI and RRT moved from the septum wall to the cardiac apex. Hence, the partial support mode of BJUT-II VAD can provide more benefit for intra-ventricular flow pattern.

Pressure measurements in a rapidly sheared turbulent wall layer

NASA Astrophysics Data System (ADS)

Diwan, Sourabh; Morrison, Jonathan

2014-11-01

The aim of the present work is to improve understanding of the role of pressure fluctuations in the generation of coherent structures in wall-bounded turbulent flows, with particular regard to the rapid and slow source terms. The work is in part motivated by the recent numerical simulations of Sharma et al. (Phy. Fluids, 23, 2011), which showed the importance of pressure fluctuations (and their spatial gradients) in the dynamics of large-scale turbulent motions. Our experimental design consists of first generating a shearless boundary layer in a wind tunnel by passing a grid-generated turbulent flow over a moving floor whose speed is matched to the freestream velocity, and then shearing it rapidly by passing it over a stationary floor further downstream. Close to the leading edge of the stationary floor, the resulting flow is expected to satisfy the approximations of the Rapid Distortion Theory and therefore would be an ideal candidate for studying linear processes in wall turbulence. We carry out pressure measurements on the wall as well as within the flow - the former using surface mounted pressure transducers and the latter using a static pressure probe similar in design to that used by Tsuji et al. (J. Fluid. Mech. 585, 2007). We also present a comparison between the rapidly sheared flow and a more conventional boundary layer subjected to a turbulent free stream. We acknowledge the financial support from EPSRC (Grant No. EP/I037938).

Modeling of flow-induced shear stress applied on 3D cellular scaffolds: Implications for vascular tissue engineering.

PubMed

Lesman, Ayelet; Blinder, Yaron; Levenberg, Shulamit

2010-02-15

Novel tissue-culture bioreactors employ flow-induced shear stress as a means of mechanical stimulation of cells. We developed a computational fluid dynamics model of the complex three-dimensional (3D) microstructure of a porous scaffold incubated in a direct perfusion bioreactor. Our model was designed to predict high shear-stress values within the physiological range of those naturally sensed by vascular cells (1-10 dyne/cm(2)), and will thereby provide suitable conditions for vascular tissue-engineering experiments. The model also accounts for cellular growth, which was designed as an added cell layer grown on all scaffold walls. Five model variants were designed, with geometric differences corresponding to cell-layer thicknesses of 0, 50, 75, 100, and 125 microm. Four inlet velocities (0.5, 1, 1.5, and 2 cm/s) were applied to each model. Wall shear-stress distribution and overall pressure drop calculations were then used to characterize the relation between flow rate, shear stress, cell-layer thickness, and pressure drop. The simulations showed that cellular growth within 3D scaffolds exposes cells to elevated shear stress, with considerably increasing average values in correlation to cell growth and inflow velocity. Our results provide in-depth analysis of the microdynamic environment of cells cultured within 3D environments, and thus provide advanced control over tissue development in vitro. 2009 Wiley Periodicals, Inc.

Pulsatile pressure driven rarefied gas flow in long rectangular ducts

NASA Astrophysics Data System (ADS)

Tsimpoukis, Alexandros; Valougeorgis, Dimitris

2018-04-01

The pulsatile pressure driven fully developed flow of a rarefied gas through an orthogonal duct is investigated, based on the time-dependent linear Bhatnagar, Gross, and Krook equation, by decomposing the flow into its steady and oscillatory parts. The investigation is focused on the oscillatory part, which is characterized by the gas rarefaction and oscillation parameters, the duct aspect ratio, and the accommodation coefficient. As the oscillation frequency is increased, the amplitude of all macroscopic quantities is decreased, while their phase angle lag is increased reaching the limiting value of π/2. As the gas becomes more rarefied, higher frequencies are needed to trigger this behavior. At small and moderate frequencies, there is a critical degree of gas rarefaction, where a maximum flow rate is obtained. As the duct aspect ratio is decreased and tends to zero, the flow rate and mean wall shear stress amplitudes are increased, while their phase angle lags are slightly affected. The accommodation coefficient has a significant effect on the amplitude and a very weak one on the phase angle of the macroscopic quantities. The computation of the inertia and viscous forces clarifies when the flow consists of only one oscillating viscous region or of two regions, namely, the inviscid piston flow in the core and the oscillating Stokes layer at the wall with the velocity overshooting. Finally, the time average oscillatory pumping power is increased as the oscillation frequency is reduced and its maximum value is one half of the corresponding steady one.

A three-dimensional spectral algorithm for simulations of transition and turbulence

NASA Technical Reports Server (NTRS)

Zang, T. A.; Hussaini, M. Y.

1985-01-01

A spectral algorithm for simulating three dimensional, incompressible, parallel shear flows is described. It applies to the channel, to the parallel boundary layer, and to other shear flows with one wall bounded and two periodic directions. Representative applications to the channel and to the heated boundary layer are presented.

Improvement of open and semi-open core wall system in tall buildings by closing of the core section in the last story

NASA Astrophysics Data System (ADS)

Kheyroddin, A.; Abdollahzadeh, D.; Mastali, M.

2014-09-01

Increasing number of tall buildings in urban population caused development of tall building structures. One of the main lateral load resistant systems is core wall system in high-rise buildings. Core wall system has two important behavioral aspects where the first aspect is related to reduce the lateral displacement by the core bending resistance and the second is governed by increasing of the torsional resistance and core warping of buildings. In this study, the effects of closed section core in the last story have been considered on the behavior of models. Regarding this, all analyses were performed by ETABS 9.2.v software (Wilson and Habibullah). Considering (a) drift and rotation of the core over height of buildings, (b) total and warping stress in the core body, (c) shear in beams due to warping stress, (d) effect of closing last story on period of models in various modes, (e) relative displacement between walls in the core system and (f) site effects in far and near field of fault by UBC97 spectra on base shear coefficient showed that the bimoment in open core is negative in the last quarter of building and it is similar to wall-frame structures. Furthermore, analytical results revealed that closed section core in the last story improves behavior of the last quarter of structure height, since closing of core section in the last story does not have significant effect on reducing base shear value in near and far field of active faults.

Coherent structures in wall-bounded turbulence

NASA Astrophysics Data System (ADS)

Jiménez, Javier

2018-05-01

This article discusses the description of wall-bounded turbulence as a deterministic high-dimensional dynamical system of interacting coherent structures, defined as eddies with enough internal dynamics to behave relatively autonomously from any remaining incoherent part of the flow. The guiding principle is that randomness is not a property, but a methodological choice of what to ignore in the flow, and that a complete understanding of turbulence, including the possibility of control, requires that it be kept to a minimum. After briefly reviewing the underlying low-order statistics of flows at moderate Reynolds numbers, the article examines what two-point statistics imply for the decomposition of the flow into individual eddies. Intense eddies are examined next, including their temporal evolution, and shown to satisfy many of the properties required for coherence. In particular, it is shown that coherent structures larger than the Corrsin scale are a natural consequence of the shear. In wall-bounded turbulence, they can be classified into coherent dispersive waves and transient bursts. The former are found in the viscous layer near the wall and as very-large structures spanning the boundary layer thickness. Although they are shear-driven, these waves have enough internal structure to maintain a uniform advection velocity. Conversely, bursts exist at all scales, are characteristic of the logarithmic layer, and interact almost linearly with the shear. While the waves require a wall to determine their length scale, the bursts are essentially independent from it. The article concludes with a brief review of our present theoretical understanding of turbulent structures, and with a list of open problems and future perspectives.

Shear-strain gradient induced polarization reversal in ferroelectric BaTiO3 thin films: A first-principles total-energy study

NASA Astrophysics Data System (ADS)

Li, Guannan; Huang, Xiaokun; Hu, Jingsan; Zhang, Weiyi

2017-04-01

Based on the first-principles total-energy calculation, we have studied the shear-strain gradient effect on the polarization reversal of ferroelectric BaTiO3 thin films. By calculating the energies of double-domain supercells for different electric polarization, shear-strain gradients, and domain-wall displacement, we extracted, in addition to the domain-wall energy, the polarization energy, elastic energy, and flexoelectric coefficient of a single domain. The constructed Landau-Devonshire phenomenological theory yields a critical shear-strain gradient of 9.091 ×107/m (or a curvature radius (R ) of 110 Å) for reversing the 180∘ domain at room temperature, which is on the same order of the experimentally estimated value of 3.333 ×107/m (R =300 Å ). In contrast to the commonly used linear response theory, the flexoelectric coefficient derived from fitting the total energy to a Landau-Devonshire energy functional does not depend on the specific pseudopotential. Thus, our method offers an alternative numerical approach to study the flexoelectric effect.

Linear and weakly nonlinear aspects of free shear layer instability, roll-up, subharmonic interaction and wall influence

NASA Technical Reports Server (NTRS)

Cain, A. B.; Thompson, M. W.

1986-01-01

The growth of the momentum thickness and the modal disturbance energies are examined to study the nature and onset of nonlinearity in a temporally growing free shear layer. A shooting technique is used to find solutions to the linearized eigenvalue problem, and pseudospectral weakly nonlinear simulations of this flow are obtained for comparison. The roll-up of a fundamental disturbance follows linear theory predictions even with a 20 percent disturbance amplitude. A weak nonlinear interaction of the disturbance creates a finite-amplitude mean shear stress which dominates the growth of the layer momentum thickness, and the disturbance growth rate changes until the fundamental disturbance dominates. The fundamental then becomes an energy source for the harmonic, resulting in an increase in the growth rate of the subharmonic over the linear prediction even when the fundamental has no energy to give. Also considered are phase relations and the wall influence.

Analysis of two-equation turbulence models for recirculating flows

NASA Technical Reports Server (NTRS)

Thangam, S.

1991-01-01

The two-equation kappa-epsilon model is used to analyze turbulent separated flow past a backward-facing step. It is shown that if the model constraints are modified to be consistent with the accepted energy decay rate for isotropic turbulence, the dominant features of the flow field, namely the size of the separation bubble and the streamwise component of the mean velocity, can be accurately predicted. In addition, except in the vicinity of the step, very good predictions for the turbulent shear stress, the wall pressure, and the wall shear stress are obtained. The model is also shown to provide good predictions for the turbulence intensity in the region downstream of the reattachment point. Estimated long time growth rates for the turbulent kinetic energy and dissipation rate of homogeneous shear flow are utilized to develop an optimal set of constants for the two equation kappa-epsilon model. The physical implications of the model performance are also discussed.

Plastic Faulting in Ice: Shear Localization under Elevated Pressure

NASA Astrophysics Data System (ADS)

Golding, N.; Durham, W. B.

2013-12-01

Ice exhibits, at least, two distinct kinds of shear faults when loaded triaxially under compression. Under moderate levels of confinement, brittle failure follows crack growth, crack coalescence and the development of a fault oriented about 30 degrees from the direction of maximum compression. The mechanism governing this mode of failure, termed frictional or Coulombic faulting, has previously been discussed for ice and rocks in connection with the comb-crack model. Under higher levels of confinement, where frictional sliding is suppressed by confining pressure, failure is characterized by sudden brittle-like loss in load bearing capacity and the development of a narrow shear band, comprised of recrystallized grains, oriented about 45 degrees from the direction of maximum compression, i.e. along the direction of maximum shear. This mode of failure, referred to here as plastic faulting, has previously been discussed for warm ice, T = 233 - 263 K, in connection with adiabatic shear heating and has been discussed for cold ice, T = 77 - 163 K, in connection with phase transformation. Here, new results are presented that examine the mechanical behavior and microstructural properties of plastic faulting in polycrystalline ice loaded at temperatures from T = 175 - 210 K and confining pressures up to P = 200 MPa. The results are reviewed in context of previous work and possible mechanisms to account for shear localization in ice under high pressure, including 1) adiabatic shear heating, 2) grain refinement and 3) phase transformation, are discussed. The present observations highlight the similarities in the behavior of plastic faulting under both warm and cold conditions and suggest adiabatic shear heating as a possible mechanism to account for shear instability and plastic faulting at temperatures ranging from T = 77 - 263 K.

Pressure fluctuations and time scales in turbulent channel flow

NASA Astrophysics Data System (ADS)

Septham, Kamthon; Morrison, Jonathan; Diwan, Sourabh

2015-11-01

Pressure fluctuations in turbulent channel flow subjected to globally stabilising linear feedback control are investigated at Reτ = 400 . The passivity-based control is adopted and explained by the conservative characteristics of the nonlinear terms contributing to the Reynolds-Orr equation (Sharma et al. Phys. Fluids 2011). The linear control operates via vU' ; the maximum forcing is located at y+ ~ 20 , corresponding to the location of the maximum in the mean-square pressure gradient. The responses of the rapid (linear) and slow (nonlinear) pressure fluctuations to the linear control are investigated using the Green's function representations. It demonstrates that the linear control operates via the linear source terms of the Poisson equation for pressure fluctuations. Landahl's timescales of the minimal flow unit (MFU) in turbulent channel flow are examined at y+ = 20 . It shows that the timescales of MFU agree well with the theoretical values proposed by Landahl (1993). Therefore, the effectiveness of the linear control to attenuate wall turbulence is explained by Landahl's theory for timescales, in that the control proceeds via the shear interaction timescale which is significantly shorter than both the nonlinear and viscous timescales.

Numerical Study of Controlling Jet Flow and Noise using Pores on Nozzle Inner Wall

NASA Astrophysics Data System (ADS)

Lin, Jian; Shi, Zhixiao; Lai, Huanxin

2018-04-01

In this paper, the feasibility of controlling the subsonic jet flow and its noise using pores of blind holes added on the nozzle inner wall is explored numerically. These pores are intended to introduce disturbances to the shear layer so as to change the flow mixing. This passive strategy has not been attempted so far. A convergent nozzle with a cylindrical extension is selected as the baseline case. Three nozzles with pores on the inner wall are set up. Validations of the numerical settings are carried out, then the compressible turbulent jets at the exit Mach number M j = 0.6 in the four nozzles are calculated by large eddy simulations (LES), while the radiated sounds are predicted by the FW-H acoustic analogy. The results show that the blind holes have produced some effects on weakening the turbulence intensity in the shear layer. Comparison reveals that both temporal and spatial correlations of the turbulent fluctuations in the modified cases are suppressed to some extent. Meanwhile, the porous nozzles are shown to suppress the pairing of vortices and enhance the flow mixing, and therefore, the development of shear layer and the fragmentation of large scale vortices are accelerated.

Heat transfer, velocity-temperature correlation, and turbulent shear stress from Navier-Stokes computations of shock wave/turbulent boundary layer interaction flows

NASA Technical Reports Server (NTRS)

Wang, C. R.; Hingst, W. R.; Porro, A. R.

1991-01-01

The properties of 2-D shock wave/turbulent boundary layer interaction flows were calculated by using a compressible turbulent Navier-Stokes numerical computational code. Interaction flows caused by oblique shock wave impingement on the turbulent boundary layer flow were considered. The oblique shock waves were induced with shock generators at angles of attack less than 10 degs in supersonic flows. The surface temperatures were kept at near-adiabatic (ratio of wall static temperature to free stream total temperature) and cold wall (ratio of wall static temperature to free stream total temperature) conditions. The computational results were studied for the surface heat transfer, velocity temperature correlation, and turbulent shear stress in the interaction flow fields. Comparisons of the computational results with existing measurements indicated that (1) the surface heat transfer rates and surface pressures could be correlated with Holden's relationship, (2) the mean flow streamwise velocity components and static temperatures could be correlated with Crocco's relationship if flow separation did not occur, and (3) the Baldwin-Lomax turbulence model should be modified for turbulent shear stress computations in the interaction flows.

Biofilms in 3D porous media: Delineating the influence of the pore network geometry, flow and mass transfer on biofilm development.

PubMed

Carrel, Maxence; Morales, Verónica L; Beltran, Mario A; Derlon, Nicolas; Kaufmann, Rolf; Morgenroth, Eberhard; Holzner, Markus

2018-05-01

This study investigates the functional correspondence between porescale hydrodynamics, mass transfer, pore structure and biofilm morphology during progressive biofilm colonization of a porous medium. Hydrodynamics and the structure of both the porous medium and the biofilm are experimentally measured with 3D particle tracking velocimetry and micro X-ray Computed Tomography, respectively. The analysis focuses on data obtained in a clean porous medium after 36 h of biofilm growth. Registration of the particle tracking and X-ray data sets allows to delineate the interplay between porous medium geometry, hydrodynamic and mass transfer processes on the morphology of the developing biofilm. A local analysis revealed wide distributions of wall shear stresses and concentration boundary layer thicknesses. The spatial distribution of the biofilm patches uncovered that the wall shear stresses controlled the biofilm development. Neither external nor internal mass transfer limitations were noticeable in the considered system, consistent with the excess supply of nutrient and electron acceptors. The wall shear stress remained constant in the vicinity of the biofilm but increased substantially elsewhere. Copyright © 2018 Elsevier Ltd. All rights reserved.

Computational Study of the Blood Flow in Three Types of 3D Hollow Fiber Membrane Bundles

PubMed Central

Zhang, Jiafeng; Chen, Xiaobing; Ding, Jun; Fraser, Katharine H.; Ertan Taskin, M.; Griffith, Bartley P.; Wu, Zhongjun J.

2013-01-01

The goal of this study is to develop a computational fluid dynamics (CFD) modeling approach to better estimate the blood flow dynamics in the bundles of the hollow fiber membrane based medical devices (i.e., blood oxygenators, artificial lungs, and hemodialyzers). Three representative types of arrays, square, diagonal, and random with the porosity value of 0.55, were studied. In addition, a 3D array with the same porosity was studied. The flow fields between the individual fibers in these arrays at selected Reynolds numbers (Re) were simulated with CFD modeling. Hemolysis is not significant in the fiber bundles but the platelet activation may be essential. For each type of array, the average wall shear stress is linearly proportional to the Re. For the same Re but different arrays, the average wall shear stress also exhibits a linear dependency on the pressure difference across arrays, while Darcy′s law prescribes a power-law relationship, therefore, underestimating the shear stress level. For the same Re, the average wall shear stress of the diagonal array is approximately 3.1, 1.8, and 2.0 times larger than that of the square, random, and 3D arrays, respectively. A coefficient C is suggested to correlate the CFD predicted data with the analytical solution, and C is 1.16, 1.51, and 2.05 for the square, random, and diagonal arrays in this paper, respectively. It is worth noting that C is strongly dependent on the array geometrical properties, whereas it is weakly dependent on the flow field. Additionally, the 3D fiber bundle simulation results show that the three-dimensional effect is not negligible. Specifically, velocity and shear stress distribution can vary significantly along the fiber axial direction. PMID:24141394

Stiffening of short small-size circular composite steel–concrete columns with shear connectors

PubMed Central

Younes, Sherif M.; Ramadan, Hazem M.; Mourad, Sherif A.

2015-01-01

An experimental program was conducted to investigate the effect of shear connectors’ distribution and method of load application on load–displacement relationship and behavior of thin-walled short concrete-filled steel tube (CFT) columns when subjected to axial load. The study focused on the compressive strength of the CFT columns and the efficiency of the shear stud in distribution of the load between the concrete core and steel tube. The study showed that the use of shear connectors enhanced slightly the axial capacity of CFT columns. It is also shown that shear connectors have a great effect on load distribution between the concrete and steel tubes. PMID:27222757

Wrinkling of reinforced plates subjected to shear stresses

NASA Technical Reports Server (NTRS)

Seydel, Edgar

1931-01-01

An analysis is made here of the problem of long plates with transverse stiffeners subject to shear. A typical example would be a long Wagner beam. The shear stress is calculated at which the web wrinkles and shear stress becomes a maximum. The equation is solved for both a condition of free support and rigidity of support on the edges.

Effect of non-Newtonian viscosity on the fluid-dynamic characteristics in stenotic vessels

NASA Astrophysics Data System (ADS)

Huh, Hyung Kyu; Ha, Hojin; Lee, Sang Joon

2015-08-01

Although blood is known to have shear-thinning and viscoelastic properties, the effects of such properties on the hemodynamic characteristics in various vascular environments are not fully understood yet. For a quantitative hemodynamic analysis, the refractive index of a transparent blood analogue needs to be matched with that of the flowing conduit in order to minimize the errors according to the distortion of the light. In this study, three refractive index-matched blood analogue fluids with different viscosities are prepared—one Newtonian and two non-Newtonian analogues—which correspond to healthy blood with 45 % hematocrit (i.e., normal non-Newtonian) and obese blood with higher viscosity (i.e., abnormal non-Newtonian). The effects of the non-Newtonian rheological properties of the blood analogues on the hemodynamic characteristics in the post-stenosis region of an axisymmetric stenosis model are experimentally investigated using particle image velocimetry velocity field measurement technique and pathline flow visualization. As a result, the centerline jet flow from the stenosis apex is suppressed by the shear-thinning feature of the blood analogues when the Reynolds number is smaller than 500. The lengths of the recirculation zone for abnormal and normal non-Newtonian blood analogues are 3.67 and 1.72 times shorter than that for the Newtonian analogue at Reynolds numbers smaller than 200. The Reynolds number of the transition from laminar to turbulent flow for all blood analogues increases as the shear-thinning feature increases, and the maximum wall shear stresses in non-Newtonian fluids are five times greater than those in Newtonian fluids. However, the shear-thinning effect on the hemodynamic characteristics is not significant at Reynolds numbers higher than 1000. The findings of this study on refractive index-matched non-Newtonian blood analogues can be utilized in other in vitro experiments, where non-Newtonian features dominantly affect the flow characteristics.

Changes in blood flow due to stented parent artery expansion in an intracranial aneurysm.

PubMed

Mori, Futoshi; Ohta, Makoto; Matsuzawa, Teruo

2015-01-01

Stent placement is thought to obstruct the inflow of blood to an aneurysm. However, we introduced parent artery expansion and demonstrated that this may reduce the blood flow by the stent. In our previous study using idealized shapes, the results showed that flow reduction was greater than 22.2%, even if the expansion rate was only 6%. Furthermore, the parent artery expansion is predominantly caused by the effect of flow reduction as compared to that of flow reduction due to the obstruction of flow under stent placement. However, a realistic shape is complex and the blood flow also becomes complex flow. It is not understood whether the results of flow in the idealized shape are reflective of flow from a realistic 3D model. Therefore, we examined the effect of parent artery expansion using a realistic model. The aim is to clarify the effects of parent artery expansion on inflow rate, wall shear stress, and oscillatory shear index. We used a patient-specific geometry of a human internal carotid artery with an aneurysm. The geometry of parent artery expansion due to oversized stent constructed based on the voronoi diagram. We performed calculations in the unsteady-state situations using constructed models. The complexity of the flow in the aneurysm decreases in case of expanded parent artery. The inflow rate decreases by 33.6% immediately after parent artery expansion alone without a stent. The effect of the parent artery expansion on flow reduction is larger than that of the obstruction flow by stent placement. In addition, wall shear stress and oscillatory shear index on the aneurysm wall decrease by change in blood flow due to the parent artery expansion. The effects of the parent artery expansion in a realistic aneurysm model with different stent lengths were evaluated on the basis of a numerical simulation. Although the flow was complex, the parent artery expansion with stent reduces the inflow to the aneurysm and wall shear stress and oscillatory shear index on the aneurysm. Therefore, we suggest that changes in the blood flow because of the parent artery expansion may be identified and, sometimes, is more effective than the obstruction flow due to the stent placement.

Mechanical Dissociation of Platelet Aggregates in Blood Stream

NASA Astrophysics Data System (ADS)

Hoore, Masoud; Fedosov, Dmitry A.; Gompper, Gerhard; Complex; Biological Fluids Group Team

2017-11-01

von Willebrand factor (VWF) and platelet aggregation is a key phenomenon in blood clotting. These aggregates form critically in high shear rates and dissolve reversibly in low shear rates. The emergence of a critical shear rate, beyond which aggregates form and below which they dissolve, has an interesting impact on aggregation in blood flow. As red blood cells (RBCs) migrate to the center of the vessel in blood flow, a RBC free layer (RBC-FL) is left close to the walls into which the platelets and VWFs are pushed back from the bulk flow. This margination process provides maximal VWF-platelet aggregation probability in the RBC-FL. Using mesoscale hydrodynamic simulations of aggregate dynamics in blood flow, it is shown that the aggregates form and grow in RBC-FL wherein shear rate is high for VWF stretching. By growing, the aggregates penetrate to the bulk flow and get under order of magnitude lower shear rates. Consequently, they dissolve and get back into the RBC-FL. This mechanical limitation for aggregates prohibits undesired thrombosis and vessel blockage by aggregates, while letting the VWFs and platelets to aggregate close to the walls where they are actually needed. The support by the DFG Research Unit FOR 1543 SHENC and CPU time Grant by the Julich Supercomputing Center are acknowledged.

Unsteady behavior of a reattaching shear layer

NASA Technical Reports Server (NTRS)

Driver, D. M.; Seegmiller, H. L.; Marvin, J.

1983-01-01

A detailed investigation of the unsteadiness in a reattaching, turbulent shear layer is reported. Laser-Doppler velocimeter measurements were conditionally sampled on the basis of instantaneous flow direction near reattachment. Conditions of abnormally short reattachment and abnormally long reattachment were considered. Ensemble-averaging of measurements made during these conditions was used to obtain mean velocities and Rreynolds stresses. In the mean flow, conditional streamlines show a global change in flow pattern which correlates with wall-flow direction. This motion can loosely be described as a 'flapping' of the shear layer. Tuft probes show that the flow direction reversals occur quite randomly and are shortlived. Streses shown also vary with the change in flow pattern. Yet, the global'flapping' motion does not appear to contribute significantly to the stress in the flow. A second type of unsteady motion was identified. Spectral analysis of both wall static pressure and streamwise velocity shows that most of the energy in the flow resides in frequencies that are significantly lower than that of the turbulence. The dominant frequency is at a Strouhal number equal to 0.2, which is the characteristic frequency of roll-up and pairing of vortical structure seen in free shear layers. It is conjectured that the 'flapping' is a disorder of the roll-up and pairing process occurring in the shear layer.

Concentration and shear rate dependence of solution viscosity for arabinoxylans from different sources

USDA-ARS?s Scientific Manuscript database

Arabinoxylans are cell wall polysaccharides abundant in plants. Alkaline extraction is commonly used to isolate arabinoxylans from cell wall rich materials, such as cereal brans, crop residues etc. While arabinoxylans from certain sources such as wheat endosperm, corn bran and rye bran have been wid...

Melt fracture revisited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenberg, J. M.

2003-07-16

In a previous paper the author and Demay advanced a model to explain the melt fracture instability observed when molten linear polymer melts are extruded in a capillary rheometer operating under the controlled condition that the inlet flow rate was held constant. The model postulated that the melts were a slightly compressible viscous fluid and allowed for slipping of the melt at the wall. The novel feature of that model was the use of an empirical switch law which governed the amount of wall slip. The model successfully accounted for the oscillatory behavior of the exit flow rate, typically referredmore » to as the melt fracture instability, but did not simultaneously yield the fine scale spatial oscillations in the melt typically referred to as shark skin. In this note a new model is advanced which simultaneously explains the melt fracture instability and shark skin phenomena. The model postulates that the polymer is a slightly compressible linearly viscous fluid but assumes no slip boundary conditions at the capillary wall. In simple shear the shear stress {tau}and strain rate d are assumed to be related by d = F{tau} where F ranges between F{sub 2} and F{sub 1} > F{sub 2}. A strain rate dependent yield function is introduced and this function governs whether F evolves towards F{sub 2} or F{sub 1}. This model accounts for the empirical observation that at high shears polymers align and slide more easily than at low shears and explains both the melt fracture and shark skin phenomena.« less

Analysis and measurement of the modulation transfer function of harmonic shear wave induced phase encoding imaging.

PubMed

McAleavey, Stephen A

2014-05-01

Shear wave induced phase encoding (SWIPE) imaging generates ultrasound backscatter images of tissue-like elastic materials by using traveling shear waves to encode the lateral position of the scatters in the phase of the received echo. In contrast to conventional ultrasound B-scan imaging, SWIPE offers the potential advantages of image formation without beam focusing or steering from a single transducer element, lateral resolution independent of aperture size, and the potential to achieve relatively high lateral resolution with low frequency ultrasound. Here a Fourier series description of the phase modulated echo signal is developed, demonstrating that echo harmonics at multiples of the shear wave frequency reveal target k-space data at identical multiples of the shear wavenumber. Modulation transfer functions of SWIPE imaging systems are calculated for maximum shear wave acceleration and maximum shear constraints, and compared with a conventionally focused aperture. The relative signal-to-noise ratio of the SWIPE method versus a conventionally focused aperture is found through these calculations. Reconstructions of wire targets in a gelatin phantom using 1 and 3.5 MHz ultrasound and a cylindrical shear wave source are presented, generated from the fundamental and second harmonic of the shear wave modulation frequency, demonstrating weak dependence of lateral resolution with ultrasound frequency.

Degradation of turbulent skin-friction drag reduction with superhydrophobic, liquid-infused and riblet surfaces with increasing Reynolds number

NASA Astrophysics Data System (ADS)

Akhavan, Rayhaneh; Rastegari, Amirreza

2017-11-01

It is shown that the magnitude of Drag Reduction (DR) with Super-Hydrophobic (SH), liquid-infused, or riblet surfaces can be parameterized in terms of the shift, ΔB , in the intercept of a log-law representation of the mean velocity profile and the friction coefficient of the base flow. Available DNS data shows ΔB to be Reynolds number independent and only a function of the geometrical parameters of the surface micro-texture in viscous wall units. This allows the DR results from DNS to be extrapolated to higher Reynolds numbers. It is shown that for a given geometry and size of the wall micro-texture in viscous wall units, the magnitude of DR degrades by factors of 2 - 3 as the friction Reynolds number of the base flow increases from Reτ0 200 of DNS to Reτ0 105 -106 of practical applications. Extrapolation of DNS results in turbulent channel flow at Reτ0 222 and 442 with SH longitudinal microgrooves of width 15 <=g+0 <= 60 and shear-free-fractions of 0.875 - 0.985 shows that the maximum DRs which can be sustained with SH longitudinal micro-grooves of size g+0 <= 20 - 30 in practical applications is limited to DRs of 25 - 35 % at Reτ0 105 and 20 - 25 % at Reτ0 106 .

An in silico framework to analyze the anisotropic shear wave mechanics in cardiac shear wave elastography

NASA Astrophysics Data System (ADS)

Caenen, Annette; Pernot, Mathieu; Peirlinck, Mathias; Mertens, Luc; Swillens, Abigail; Segers, Patrick

2018-04-01

Shear wave elastography (SWE) is a potential tool to non-invasively assess cardiac muscle stiffness. This study focused on the effect of the orthotropic material properties and mechanical loading on the performance of cardiac SWE, as it is known that these factors contribute to complex 3D anisotropic shear wave propagation. To investigate the specific impact of these complexities, we constructed a finite element model with an orthotropic material law subjected to different uniaxial stretches to simulate SWE in the stressed cardiac wall. Group and phase speed were analyzed in function of tissue thickness and virtual probe rotation angle. Tissue stretching increased the group and phase speed of the simulated shear wave, especially in the direction of the muscle fiber. As the model provided access to the true fiber orientation and material properties, we assessed the accuracy of two fiber orientation extraction methods based on SWE. We found a higher accuracy (but lower robustness) when extracting fiber orientations based on the location of maximal shear wave speed instead of the angle of the major axis of the ellipsoidal group speed surface. Both methods had a comparable performance for the center region of the cardiac wall, and performed less well towards the edges. Lastly, we also assessed the (theoretical) impact of pathology on shear wave physics and characterization in the model. It was found that SWE was able to detect changes in fiber orientation and material characteristics, potentially associated with cardiac pathologies such as myocardial fibrosis. Furthermore, the model showed clearly altered shear wave patterns for the fibrotic myocardium compared to the healthy myocardium, which forms an initial but promising outcome of this modeling study.

Impact of composite plates: Analysis of stresses and forces

NASA Technical Reports Server (NTRS)

Moon, F. C.; Kim, B. S.; Fang-Landau, S. R.

1976-01-01

The foreign object damage resistance of composite fan blades was studied. Edge impact stresses in an anisotropic plate were first calculated incorporating a constrained layer damping model. It is shown that a very thin damping layer can dramatically decrease the maximum normal impact stresses. A multilayer model of a composite plate is then presented which allows computation of the interlaminar normal and shear stresses. Results are presented for the stresses due to a line impact load normal to the plane of a composite plate. It is shown that significant interlaminar tensile stresses can develop during impact. A computer code was developed for this problem using the fast Fourier transform. A marker and cell computer code were also used to investigate the hydrodynamic impact of a fluid slug against a wall or turbine blade. Application of fluid modeling of bird impact is reviewed.

Effect of flow rate on growth and oxygen consumption of biofilm in gravity sewer.

PubMed

Xu, Jingwei; Li, Muzhi; He, Qiang; Sun, Xingfu; Zhou, Xiangren; Su, Zhenping; Ai, Hainan

2017-01-01

The function of sewer as reactors must rely on the biofilm in it. In this paper, the formation, structure, oxygen transfer, and activity of the biofilm under different hydraulic conditions were studied by the microelectrode technology, oxygen uptake rate (OUR) technology, and 454 high-throughput pyrosequencing technology. Results showed that when the wall-shear stresses were 1.12, 1.29, and 1.45 Pa, the porosity of the steady-state biofilm were 69.1, 64.4, and 55.1 %, respectively. The maximum values of OUR were 0.033, 0.027, and 0.022 mg/(L*s), respectively, and the COD removal efficiency in the sewers reached 40, 35, and 32 %, respectively. The research findings had an important significance on how to improve the treatment efficiency of the sewers. Fig. a Graphical Abstract.

Recent Turbulence Model Advances Applied to Multielement Airfoil Computations

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.; Gatski, Thomas B.

2000-01-01

A one-equation linear turbulence model and a two-equation nonlinear explicit algebraic stress model (EASM) are applied to the flow over a multielement airfoil. The effect of the K-epsilon and K-omega forms of the two-equation model are explored, and the K-epsilon form is shown to be deficient in the wall-bounded regions of adverse pressure gradient flows. A new K-omega form of EASM is introduced. Nonlinear terms present in EASM are shown to improve predictions of turbulent shear stress behind the trailing edge of the main element and near midflap. Curvature corrections are applied to both the one- and two-equation turbulence models and yield only relatively small local differences in the flap region, where the flow field undergoes the greatest curvature. Predictions of maximum lift are essentially unaffected by the turbulence model variations studied.

Effects of vessel compliance on flow pattern in porcine epicardial right coronary arterial tree.

PubMed

Huo, Yunlong; Choy, Jenny Susana; Svendsen, Mark; Sinha, Anjan Kumar; Kassab, Ghassan S

2009-03-26

The compliance of the vessel wall affects hemodynamic parameters which may alter the permeability of the vessel wall. Based on experimental measurements, the present study established a finite element (FE) model in the proximal elastic vessel segments of epicardial right coronary arterial (RCA) tree obtained from computed tomography. The motion of elastic vessel wall was measured by an impedance catheter and the inlet boundary condition was measured by an ultrasound flow probe. The Galerkin FE method was used to solve the Navier-Stokes and Continuity equations, where the convective term in the Navier-Stokes equation was changed in the arbitrary Lagrangian-Eulerian (ALE) framework to incorporate the motion due to vessel compliance. Various hemodynamic parameters (e.g., wall shear stress-WSS, WSS spatial gradient-WSSG, oscillatory shear index-OSI) were analyzed in the model. The motion due to vessel compliance affects the time-averaged WSSG more strongly than WSS at bifurcations. The decrease of WSSG at flow divider in elastic bifurcations, as compared to rigid bifurcations, implies that the vessel compliance decreases the permeability of vessel wall and may be atheroprotective. The model can be used to predict coronary flow pattern in subject-specific anatomy as determined by noninvasive imaging.

A Dissipative Connector for CLT Buildings: Concept, Design and Testing

PubMed Central

Scotta, Roberto; Marchi, Luca; Trutalli, Davide; Pozza, Luca

2016-01-01

This paper deals with the conception and characterization of an innovative connection for cross-laminated timber (CLT) panels. The connection is designed to provide an adequate level of dissipative capacity to CLT structures also when realized with large horizontal panels and therefore prone to fragile shear sliding failure. The connector, named X-bracket, has been theorized and designed by means of numerical parametric analyses. Furthermore, its cyclic behavior has been verified with experimental tests and compared to that of traditional connectors. Numerical simulations of cyclic tests of different CLT walls anchored to the foundation with X-brackets were also performed to assess their improved seismic performances. Finally, the analysis of the response of a 6 m × 3 m squat wall demonstrates that the developed connection provides good ductility and dissipation capacities also to shear walls realized with a single CLT panel. PMID:28773265

A Dissipative Connector for CLT Buildings: Concept, Design and Testing.

PubMed

Scotta, Roberto; Marchi, Luca; Trutalli, Davide; Pozza, Luca

2016-02-26

This paper deals with the conception and characterization of an innovative connection for cross-laminated timber (CLT) panels. The connection is designed to provide an adequate level of dissipative capacity to CLT structures also when realized with large horizontal panels and therefore prone to fragile shear sliding failure. The connector, named X-bracket, has been theorized and designed by means of numerical parametric analyses. Furthermore, its cyclic behavior has been verified with experimental tests and compared to that of traditional connectors. Numerical simulations of cyclic tests of different CLT walls anchored to the foundation with X-brackets were also performed to assess their improved seismic performances. Finally, the analysis of the response of a 6 m × 3 m squat wall demonstrates that the developed connection provides good ductility and dissipation capacities also to shear walls realized with a single CLT panel.

A Two-Axis Direct Fluid Shear Stress Sensor

NASA Technical Reports Server (NTRS)

Adcock, Edward E.; Scott, Michael A.; Bajikar, Sateesh S.

2010-01-01

This innovation is a miniature or micro sized semiconductor sensor design that provides two axis direct non-intrusive measurement of skin friction or wall shear stress in fluid flow. The sensor is fabricated by micro-electro-mechanical system (MEMS) technology, enabling small size and low cost reproductions. The sensors have been fabricated by utilizing MEMS fabrication processes to bond a sensing element wafer to a fluid coupling wafer. This layering technique provides for an out of plane dimension that is on the same order of length as the inplane dimensions. The sensor design has the following characteristics: a shear force collecting plate with dimensions that can be tailored to various application specific requirements such as spatial resolution, temporal resolution and shear force range and resolution. This plate is located coplanar to both the sensor body and flow boundary, and is connected to a dual axis gimbal structure by a connecting column or lever arm. The dual axis gimbal structure has torsional hinges with embedded piezoresistive torsional strain gauges which provide a voltage output that is correlated to the applied shear stress (and excitation current) on force collection plate that is located on the flow boundary surface (hence the transduction method). This combination of design elements create a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from the small shear stress on the flow boundary wall. This design as well as the use of back side electrical contacts establishes a non-intrusive method to quantitatively measure the shear force vector on aerodynamic bodies.

Flow-induced adhesion of shear-activated polymers to a substrate

NASA Astrophysics Data System (ADS)

Hoore, Masoud; Rack, Kathrin; Fedosov, Dmitry A.; Gompper, Gerhard

2018-02-01

Adhesion of polymers and proteins to substrates plays a crucial role in many technological applications and biological processes. A prominent example is the von Willebrand factor (VWF) protein, which is essential in blood clotting as it mediates adhesion of blood platelets to the site of injury at high shear rates. VWF is activated by flow and is able to bind efficiently to damaged vessel walls even under extreme flow-stress conditions; however, its adhesion is reversible when the flow strength is significantly reduced or the flow is ceased. Motivated by the properties and behavior of VWF in flow, we investigate adhesion of shear-activated polymers to a planar wall in flow and whether the adhesion is reversible under flow stasis. The main ingredients of the polymer model are cohesive inter-monomer interactions, a catch bond with the adhesive surface, and the shear activation/deactivation of polymer adhesion correlated with its stretching in flow. The cohesive interactions within the polymer maintain a globular conformation under low shear stresses and allow polymer stretching if a critical shear rate is exceeded, which is directly associated with its activation for adhesion. Our results show that polymer adhesion at high shear rates is significantly stabilized by catch bonds, while at the same time they also permit polymer dissociation from a surface at low or no flow stresses. In addition, the activation/deactivation mechanism for adhesion plays a crucial role in the reversibility of its adhesion. These observations help us better understand the adhesive behavior of VWF in flow and interpret its adhesion malfunctioning in VWF-related diseases.

Scan-rescan reproducibility of segmental aortic wall shear stress as assessed by phase-specific segmentation with 4D flow MRI in healthy volunteers.

PubMed

van der Palen, Roel L F; Roest, Arno A W; van den Boogaard, Pieter J; de Roos, Albert; Blom, Nico A; Westenberg, Jos J M

2018-05-26

The aim was to investigate scan-rescan reproducibility and observer variability of segmental aortic 3D systolic wall shear stress (WSS) by phase-specific segmentation with 4D flow MRI in healthy volunteers. Ten healthy volunteers (age 26.5 ± 2.6 years) underwent aortic 4D flow MRI twice. Maximum 3D systolic WSS (WSSmax) and mean 3D systolic WSS (WSSmean) for five thoracic aortic segments over five systolic cardiac phases by phase-specific segmentations were calculated. Scan-rescan analysis and observer reproducibility analysis were performed. Scan-rescan data showed overall good reproducibility for WSSmean (coefficient of variation, COV 10-15%) with moderate-to-strong intraclass correlation coefficient (ICC 0.63-0.89). The variability in WSSmax was high (COV 16-31%) with moderate-to-good ICC (0.55-0.79) for different aortic segments. Intra- and interobserver reproducibility was good-to-excellent for regional aortic WSSmax (ICC ≥ 0.78; COV ≤ 17%) and strong-to-excellent for WSSmean (ICC ≥ 0.86; COV ≤ 11%). In general, ascending aortic segments showed more WSSmax/WSSmean variability compared to aortic arch or descending aortic segments for scan-rescan, intraobserver and interobserver comparison. Scan-rescan reproducibility was good for WSSmean and moderate for WSSmax for all thoracic aortic segments over multiple systolic phases in healthy volunteers. Intra/interobserver reproducibility for segmental WSS assessment was good-to-excellent. Variability of WSSmax is higher and should be taken into account in case of individual follow-up or in comparative rest-stress studies to avoid misinterpretation.

Wall shear stress estimation in the aorta: Impact of wall motion, spatiotemporal resolution, and phase noise.

PubMed

Zimmermann, Judith; Demedts, Daniel; Mirzaee, Hanieh; Ewert, Peter; Stern, Heiko; Meierhofer, Christian; Menze, Bjoern; Hennemuth, Anja

2018-04-01

Wall shear stress (WSS) presents an important parameter for assessing blood flow characteristics and evaluating flow-mediated lesions in the aorta. To investigate the robustness of WSS and oscillatory shear index (OSI) estimation based on 4D flow MRI against vessel wall motion, spatiotemporal resolution, and velocity encoding (VENC). Simulated and prospective. Synthetic 4D flow MRI data of the aorta, simulated using the Lattice-Boltzmann method; in vivo 4D flow MRI data of the aorta from healthy volunteers (n = 11) and patients with congenital heart defects (n = 17). 1.5T; 4D flow MRI with PEAK-GRAPPA acceleration and prospective electrocardiogram triggering. Predicated upon 3D cubic B-splines interpolation of the image velocity field, WSS was estimated in mid-systole, early-diastole, and late-diastole and OSI was derived. We assessed the impact of spatiotemporal resolution and phase noise, and compared results based on tracked-using deformable registration-and static vessel wall location. Bland-Altman analysis to assess WSS/OSI differences; Hausdorff distance (HD) to assess wall motion; and Pearson's correlation coefficient (PCC) to assess correlation of HD with WSS. Synthetic data results show systematic over-/underestimation of WSS when different spatial resolution (mean ± 1.96 SD up to -0.24 ± 0.40 N/m 2 and 0.5 ± 1.38 N/m 2 for 8-fold and 27-fold voxel size, respectively) and VENC-depending phase noise (mean ± 1.96 SD up to 0.31 ± 0.12 N/m 2 and 0.94 ± 0.28 N/m 2 for 2-fold and 4-fold VENC increase, respectively) are given. Neglecting wall motion when defining the vessel wall perturbs WSS estimates to a considerable extent (1.96 SD up to 1.21 N/m 2 ) without systematic over-/underestimation (Bland-Altman mean range -0.06 to 0.05). In addition to sufficient spatial resolution and velocity to noise ratio, accurate tracking of the vessel wall is essential for reliable image-based WSS estimation and should not be neglected if wall motion is present. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Behaviour of partially composite precast concrete sandwich panels under flexural and axial loads

NASA Astrophysics Data System (ADS)

Tomlinson, Douglas George

Precast concrete sandwich panels are commonly used on building exteriors. They are typically composed of two concrete wythes that surround rigid insulation. They are advantageous as they provide both structural and thermal resistance. The structural response of sandwich panels is heavily influenced by shear connectors that link the wythes together. This thesis presents a study on partially composite non-prestressed precast concrete wall panels. Nine flexure tests were conducted on a wall design incorporating 'floating' concrete studs and Glass Fibre Reinforced Polymer (GFRP) connectors. The studs encapsulate and stiffen the connectors, reducing shear deformations. Ultimate loads increased from 58 to 80% that of a composite section as the connectors' reinforcement ratio increased from 2.6 to 9.8%. This design was optimized by reinforcing the studs and integrating them with the structural wythe; new connectors composed of angled steel or Basalt-FRP (BFRP) were used. The load-slip response of the new connector design was studied through 38 double shear push-through tests using various connector diameters and insertion angles. Larger connectors were stronger but more likely to pull out. Seven flexure tests were conducted on the new wall design reinforced with different combinations of steel and BFRP connectors and reinforcement. Composite action varied from 50 to 90% depending on connector and reinforcement material. Following this study, the axial-bending interaction curves were established for the new wall design using both BFRP and steel connectors and reinforcement. Eight panels were axially loaded to predesignated loads then loaded in flexure to failure. A technique is presented to experimentally determine the effective centroid of partially composite sections. Beyond the tension and compression-controlled failure regions of the interaction curve, a third region was observed in between, governed by connector failure. Theoretical models were developed for the bond-slip behaviour of the shear connection and to analyze the full panel's flexural and axial response to determine the longitudinal shear force transferred between wythes and account for partial composite behavior. The models were validated against experiments and used to conduct a parametric study. Among several interesting findings, the study demonstrated how composite action increases with the slenderness of axially loaded panels.

Effects of 8-week swimming training on carotid arterial stiffness and hemodynamics in young overweight adults.

PubMed

Yuan, Wen-Xue; Liu, Hai-Bin; Gao, Feng-Shan; Wang, Yan-Xia; Qin, Kai-Rong

2016-12-28

Exercise has been found to either reduce or increase arterial stiffness. Land-based exercise modalities have been documented as effective physical therapies to decrease arterial stiffness. However, these land-based exercise modalities may not be suitable for overweight individuals, in terms of risks of joint injury. The purpose of this study was to determine the effects of 8-week swimming training and 4-week detraining on carotid arterial stiffness and hemodynamics in young overweight adults. Twenty young male adults who were overweight were recruited and engaged in 8-week of swimming training and 4-week detraining. Five individuals withdrew due to lack of interest and failure to follow the training protocol. Body Fat Percentage (BFP) and carotid hemodynamic variables were measured on a resting day at the following intervals: baseline, 4 weeks, 8 weeks after swimming training and 4 weeks after detraining. A repeated analysis of variance (ANOVA) was used to assess the differences between baseline and each measurement. When significant differences were detected, Tukey's test for post hoc comparisons was used. Eight-week swimming training at moderate intensity decreased BFP, including the trunk and four extremities. Additionally, the BFP of the right and left lower extremities continued to decrease in these overweight adults 4 weeks after ceasing training. Carotid arterial stiffness decreased, while there were no significant changes in arterial diameters. Blood flow velocity, flow rate, maximal and mean wall shear stress increased, while systolic blood pressure and peripheral resistance decreased. No significant differences existed in minimal wall shear stress and oscillatory shear stress. Eight-week swimming training at moderate intensity exhibited beneficial effects on systolic blood pressure, arterial stiffness and blood supply to the brain in overweight adults. Moreover, maximal and mean wall shear stress increased after training. It is worth noting that these changes in hemodynamics did not last 4 weeks. Therefore, further studies are still warranted to clarify the underlying relationship between improvements in arterial stiffness and alterations in wall shear stress.

Buoyancy Driven Shear Flows of Bubble Suspensions

NASA Technical Reports Server (NTRS)

Koch, D. L.; Hill, R. J.; Chellppannair, T.; Zenit, R.; Zenit, R.; Spelt, P. D. M.

1999-01-01

In this work the gas volume fraction and the root-mean-squared fluid velocity are measured in buoyancy driven shear flows of bubble suspensions in a tall, inclined, rectangular channel. The experiments are performed under conditions where We << 1a nd Re >> 1, for which comparisons are made with kinetic theory and numerical simulations. Here Re = gamma(a(exp 2)/nu is the Reynolds number and We = rho(gamma(exp 2))a(exp 3)/sigma is the Weber number; gamma is the shear rate, a is the bubble radius, nu is the kinematic viscosity of the liquid, rho is the density of the liquid, and sigma is the surface tension of the gas/liquid interface. Kang et al. calculated the bubble phase pressure and velocity variance of sheared bubble suspensions under conditions where the bubbles are spherical and the liquid phase velocity field can be approximated using potential flow theory, i.e. We= 0 and Re >> 1. Such conditions can be achieved in an experiment using gas bubbles, with a radius of O(0.5mm), in water. The theory requires that there be no average relative motion of the gas and liquid phases, hence the motivation for an experimental program in microgravity. The necessity of performing preliminary, Earth based experiments, however, requires performing experiments where the gas phase rises in the liquid, which significantly complicates the comparison of experiments with theory. Rather than comparing experimental results with theory for a uniform, homogeneous shear flow, experiments can be compared directly with solutions of the averaged equations of motion for bubble suspensions. This requires accounting for the significant lift force acting on the gas phase when the bubbles rise parallel to the average velocity of the sheared suspension. Shear flows can be produced in which the bubble phase pressure gradient, arising from shear induced collisions amongst the bubbles, balances a body force (centrifugal or gravitational) on the gas phase. A steady, non-uniform gas volume fraction can be measured, from which the bubble phase pressure gradient can be obtained and compared to theory and numerical simulations. The presence of bounding walls further complicates the experiments, since the detailed interactions of the bubbles with bounding walls is not well understood, especially in the presence of gravity, where the momentum and energy exchange depends on the inclination of the wall.

Evaluation of bolted connections in wood-plastic composites

NASA Astrophysics Data System (ADS)

Arnandha, Yudhi; Satyarno, Iman; Awaludin, Ali; Irawati, Inggar Septia; Ihsan, Muhamad; Wijanarko, Felyx Biondy; William, Mahdinur, Fardhani, Arfiati

2017-03-01

Wood-plastic composite (WPC) is a relatively new material that consists of sawdust and plastic polymer using the extrusion process. Due to its attributes such as low water content, low maintenance, UV durability and being fungi and termite resistant. Nowadays, WPC has already been produced in Indonesia using sawdust from local wood such as Albizia (Paraserianthes falcataria) and Teak (Tectona grandis). Moreover preliminary studies about the physical and mechanical WPC board from Albizia sawdust and HDPE plastic have been carried out. Based on these studies, WPC has a high shear strength around 25-30 MPa higher than its original wood shear strength. This paper was a part of the research in evaluating WPC as potential sheathing in a shear wall system. Since still little is known about connection behavior in WPC using Indonesian local wood, this study evaluated the connection for both of these two types of wood-plastic composite. WPC board from Albizia sawdust will be projected as shear wall sheathing and WPC stud from Teak sawdust projected to be shear wall frame. For this study, the embedding strength for both WPC was determined according to ASTM D 5764 standard, using two types of bolts (stainless bolt and standard bolt) with several diameters as variation (6 mm, 8 mm, 10 and 12 mm). Hence, dowel-bearing test under fastened condition conducted accordance to ASTM D5652, hereby the yield strength then compared with the prediction yield strength from European Yield Model (EYM). According to both single and double shear connection, it can be concluded that yield strength from the EYM method tended to under-predict the 5% diameter offset yield than the actual yield strength from the test. The yield strength itself increase with the increase of bolt diameter. For single shear connection, the highest yield strength was 12 mm standard bolt around 9732 N, slightly higher than stainless bolt around 9393 N. Whereby for double shear connection, the highest yield strength was 12 mm standard bolt around 12009 N, slightly higher than stainless bolt around 12009 N. Using statistical approach ANOVA, the different type of bolt between stainless bolt and standard bolt gave an insignificant result. Both type of bolt can be used as structural connection, moreover it was recommended using a stainless bolt for outdoor purpose to reduce corrosion.

Shear thinning and shear thickening of a confined suspension of vesicles

NASA Astrophysics Data System (ADS)

Nait Ouhra, A.; Farutin, A.; Aouane, O.; Ez-Zahraouy, H.; Benyoussef, A.; Misbah, C.

2018-01-01

Widely regarded as an interesting model system for studying flow properties of blood, vesicles are closed membranes of phospholipids that mimic the cytoplasmic membranes of red blood cells. In this study we analyze the rheology of a suspension of vesicles in a confined geometry: the suspension, bound by two planar rigid walls on each side, is subject to a shear flow. Flow properties are then analyzed as a function of shear rate γ ˙, the concentration of the suspension ϕ , and the viscosity contrast λ =ηin/ηout , where ηin and ηout are the fluid viscosities of the inner and outer fluids, respectively. We find that the apparent (or effective viscosity) of the suspension exhibits both shear thinning (decreasing viscosity with shear rate) or shear thickening (increasing viscosity with shear rate) in the same concentration range. The shear thinning or thickening behaviors appear as subtle phenomena, dependant on viscosity contrast λ . We provide physical arguments on the origins of these behaviors.

Study on seismic performance of BFRP geogrid reinforced Tibetan rubble wall

NASA Astrophysics Data System (ADS)

Yang, Dan; Jia, Bin; Huang, Hui; Deng, Chuangli

2018-03-01

For the study of BFRP geogrid influence on Tibetan rubble wall seismic performance, in this paper, on the premise of not change the way of traditional masonry, laying and not join geogrid respectively on the the rubble wall, and carries on the cyclic loading experiment on them. The damage characteristics, crack width and seismic performance of the rubble walls with BFRP geogrid are studied. The experimental results show that the deformation of the rubble wall is mainly the shear deformation under the action of horizontal force, and the bearing capacity and energy dissipation capacity of the wall can be improved significantly after joining the geogrid.

Asymmetric deformation structure of lava spine in Unzen Volcano, Japan

NASA Astrophysics Data System (ADS)

Miwa, T.; Okumura, S.; Matsushima, T.; Shimizu, H.

2013-12-01

Lava spine is commonly generated by effusive eruption of crystal-rich, dacitic-andesitic magmas. Especially, deformation rock on surface of lava spine has been related with processes of magma ascent, outgassing, and generation of volcanic earthquake (e.g., Cashman et al. 2008). To reveal the relationships and generation process of the spine, it is needed to understand a spatial distribution of the deformation rock. Here we show the spatial distribution of the deformation rock of lava spine in the Unzen volcano, Japan, to discuss the generation process of the spine. The lava spine in Unzen volcano is elongated in the E-W direction, showing a crest like shape with 150 long, 40 m wide and 50 m high. The lava spine is divided into following four parts: 1) Massive dacite part: Dense dacite with 30 m of maximum thickness, showing slickenside on the southern face; 2) Sheared dacite part: Flow band developed dacite with 1.0 m of maximum thickness; 3) Tuffisite part: Network of red colored vein develops in dacite with 0.5 m of maximum thickness; 4) Breccia part: Dacitic breccia with 10 m of maximum thickness. The Breccia part dominates in the northern part of the spine, and flops over Massive dacite part accross the Sheared dacite and Tuffisite parts. The slickenside on southern face of massive dacite demonstrates contact of solids. The slickenside breaks both of phenocryst and groundmass, demonstrating that the slickenside is formed after significant crystallization at the shallow conduit or on the ground surface. The lineation of the slickenside shows E-W direction with almost horizontal rake angle, which is consistent with the movement of the spine to an east before emplacement. Development of sub-vertical striation due to extrusion was observed on northern face of the spine (Hayashi, 1994). Therefore, we suggest that the spine just at extrusion consisted of Massive dacite, Sheared dacite, Tuffisite, Breccia, and Striation parts in the northern half of the spine. Such a variation of rock type is analogous to tectonic fault zone, suggesting that brittle failure of rigid magma due to contact with the conduit wall. Also similar variation is observed in the spine of Mt. St. Helens (Kendrick et al., 2012), which implies the existence of fault zone and brittle failure of magma are common features in the lava spine. The lava spine in Unzen volcano exhibits asymmetric deformation structure about direction of north and south. There is positive correlation between width and length in tectonic fault (Wells and Coppersmith, 1994). Therefore, development of fault zone (Sheared dacite, Tuffisite, and Breccia parts) in northern half may indicate that brittle failure starts at the deeper conduit for the northern half than the southern half of the spine. The asymmetry of magma ascent process is possible to result in asymmetries of outgassing path and location of volcanic earthquake in the conduit.

Applications of a new wall function to turbulent flow computations

NASA Astrophysics Data System (ADS)

Chen, Y. S.

1986-01-01

A new wall function approach is developed based on a wall law suitable for incompressible turbulent boundary layers under strong adverse pressure gradients. This wall law was derived from a one-dimensional analysis of the turbulent kinetic energy equation with gradient diffusion concept employed in modeling the near-wall shear stress gradient. Numerical testing cases for the present wall functions include turbulent separating flows around an airfoil and turbulent recirculating flows in several confined regions. Improvements on the predictions using the present wall functions are illustrated. For cases of internal recirculating flows, one modification factor for improving the performance of the k-epsilon turbulence model in the flow recirculation regions is also included.

Intimal cushions and endothelial nuclear elongation around mouse aortic branches and their spatial correspondence with patterns of lipid deposition

PubMed Central

Bond, Andrew R.; Ni, Chih-Wen; Jo, Hanjoong

2010-01-01

Spatial variation in hemodynamic stresses acting on the arterial wall may explain the nonuniform distribution of atherosclerosis. In thoracic aortas of LDL receptor/apolipoprotein E double knockout mice, lesions develop preferentially around the entire circumference of intercostal branch ostia, regardless of age, with the highest prevalence occurring upstream. Additional chevron-shaped lesions occur further upstream of the ostia. This pattern differs from the age-related ones occurring in people and rabbits. In the present study, patterns of near-wall blood flow around intercostal ostia in wild-type mice were estimated from the morphology of endothelial nuclei, which were shown in vitro to elongate in response to elevated shear stress and to align with the flow, and wall structure was assessed from confocal and scanning electron microscopy. A triangular intimal cushion surrounded the upstream part of most ostia. Nuclear length-to-width ratios were lowest over this cushion and highest at the sides of branches, regardless of age. Nuclear orientations were consistent with flow diverging around the branch. The pattern of nuclear morphology differed from the age-related ones observed in rabbits. The intimal cushion and the distribution of shear stress inferred from these observations can partly account for the pattern of lesions observed in knockout mice. Nuclear elongation in nonbranch regions was approximately constant across animals of different size, demonstrating the existence of a mechanism by which endothelial cells compensate for the dependence of mean aortic wall shear stress on body mass. PMID:19933414

Blood Vessel Adaptation with Fluctuations in Capillary Flow Distribution

PubMed Central

Hu, Dan; Cai, David; Rangan, Aaditya V.

2012-01-01

Throughout the life of animals and human beings, blood vessel systems are continuously adapting their structures – the diameter of vessel lumina, the thickness of vessel walls, and the number of micro-vessels – to meet the changing metabolic demand of the tissue. The competition between an ever decreasing tendency of luminal diameters and an increasing stimulus from the wall shear stress plays a key role in the adaptation of luminal diameters. However, it has been shown in previous studies that the adaptation dynamics based only on these two effects is unstable. In this work, we propose a minimal adaptation model of vessel luminal diameters, in which we take into account the effects of metabolic flow regulation in addition to wall shear stresses and the decreasing tendency of luminal diameters. In particular, we study the role, in the adaptation process, of fluctuations in capillary flow distribution which is an important means of metabolic flow regulation. The fluctuation in the flow of a capillary group is idealized as a switch between two states, i.e., an open-state and a close-state. Using this model, we show that the adaptation of blood vessel system driven by wall shear stress can be efficiently stabilized when the open time ratio responds sensitively to capillary flows. As micro-vessel rarefaction is observed in our simulations with a uniformly decreased open time ratio of capillary flows, our results point to a possible origin of micro-vessel rarefaction, which is believed to induce hypertension. PMID:23029014

Two-axis direct fluid shear stress sensor

NASA Technical Reports Server (NTRS)

Bajikar, Sateesh (Inventor); Scott, Michael A. (Inventor); Adcock, Edward E. (Inventor)

2011-01-01

A micro sized multi-axis semiconductor skin friction/wall shear stress induced by fluid flow. The sensor design includes a shear/strain transduction gimble connected to a force collecting plate located at the flow boundary surface. The shear force collecting plate is interconnected by an arm to offset the tortional hinges from the fluid flow. The arm is connected to the shear force collecting plate through dual axis torsional hinges with piezoresistive torsional strain gauges. These gauges are disposed on the tortional hinges and provide a voltage output indicative of applied shear stress acting on the force collection plate proximate the flow boundary surface. Offsetting the torsional hinges creates a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from small shear stress, or small displacement of the collecting plate. The design also isolates the torsional sensors from exposure to the fluid flow.

The practicality of defensive ice walls: How would the great ice wall in Game of Thrones hold up?

NASA Astrophysics Data System (ADS)

Truffer, M.

2017-12-01

The Game of Thrones great ice wall is a colossal feature stretching several hundred miles and over 200 m high. Its purpose is to defend the realm from the wildlings. It is generally pictured as a near vertical wall. An ice wall of these proportions poses interesting challenges, mainly because ice acts as a non-linear shear-thinning fluid. A 200 m high vertical wall would create a large effective stress near its base of almost 1.8 MPa. Typical stresses responsible for ice flow in glaciers and ice sheets are more than a magnitude lower (0.1 MPa). Extrapolating a commonly used flow law for temperate ice to such high stresses would lead to strain rates at the bottom of the wall in excess of 1/day, meaning the wall would rapidly collapse and spread laterally under its own weight. To keep the wall stable, it would help to cool it significantly, as the flow of ice is also very temperature dependent. Cooling to a chilly -40 C would reduce strain rates by two orders of magnitude, but this still leads to significant slumping of the wall within just a few weeks. A time-dependent similarity solution for simplified ice flow equations that describe the evolving shape of the ice wall was provided by Halfar (1981), and demonstrates the rapid decay of the wall. A simple estimate can be derived by assuming that ice is a perfectly plastic fluid, able to maintain a basal shear stress of about 0.1 MPa. A stable ice wall would then spread laterally to about 4 km width. The resulting slope would only be steep at the very margin and the ice wall would loose much of its defensive capabilities. I conclude that the ice wall as proposed would not be a practicable defense under typical Earth conditions, and special magical powers would be necessary to maintain its shape, even for just a few days.

Effect of solid boundaries on a motile microorganism in a viscoelastic fluid

NASA Astrophysics Data System (ADS)

Karimi, Alireza; Li, Gaojin; Ardekani, Arezoo

2014-11-01

Microorganisms swimming in viscoelastic fluids are ubiquitous in nature; this includes biofilms grown on surfaces, Helicobacter pylori colonizing in the mucus layer covering the stomach and spermatozoa swimming through cervical mucus inside the mammalian female reproductive tract. Previous studies have focused on the locomotion of microorganisms in an unbounded viscoelastic fluid. However in many situations, microorganisms interact with solid boundaries and their hydrodynamic interaction is poorly understood. In this work, we numerically study the effect of solid boundaries on the swimming behavior of an archetypal low-Reynolds number swimmer, called ``squirmer,'' in a viscoelastic fluid. A Giesekus constitutive equation is used to model both viscoelasticity and shear-thinning behavior of the background fluid. We found that the time a neutral squirmer spends in the close proximity of the wall increases with polymer relaxation time and reaches a maximum at Weissenberg number of unity. A pusher is found to be trapped near the wall in a viscoelastic fluid, but the puller is less affected. This publication was made possible, in part, with support from NSF (Grant No. CBET-1150348-CAREER) and Indiana Clinical and Translational Sciences Institute Collaboration in Biomedical/Translational Research (Grant No. TR000006) from NIH.

Vortex dynamics of collapsing bubbles: Impact on the boundary layer measured by chronoamperometry.

PubMed

Reuter, Fabian; Cairós, Carlos; Mettin, Robert

2016-11-01

Cavitation bubbles collapsing in the vicinity to a solid substrate induce intense micro-convection at the solid. Here we study the transient near-wall flows generated by single collapsing bubbles by chronoamperometric measurements synchronously coupled with high-speed imaging. The individual bubbles are created at confined positions by a focused laser pulse. They reach a maximum expansion radius of approximately 425μm. Several stand-off distances to the flat solid boundary are investigated and all distances are chosen sufficiently large that no gas phase of the expanding and collapsing bubble touches the solid directly. With a microelectrode embedded into the substrate, the time-resolved perturbations in the liquid shear layer are probed by means of a chronoamperometric technique. The measurements of electric current are synchronized with high-speed imaging of the bubble dynamics. The perturbations of the near-wall layer are found to result mainly from ring vortices created by the jetting bubble. Other bubble induced flows, such as the jet and flows following the radial bubble oscillations are perceptible with this technique, but show a minor influence at the stand-off distances investigated. Copyright © 2016 Elsevier B.V. All rights reserved.

Oscillatory slip flow past a spherical inclusion embedded in a Brinkman medium

NASA Astrophysics Data System (ADS)

Palaniappan, D.

2016-11-01

Non-steady flow past an impermeable sphere embedded in a porous medium is investigated based on Brinkman model with Navier slip conditions. Exact analytic solution for the stream-function - involving modified Bessel function of the second kind - describing the slow oscillatory flow around a rigid spherical inclusion is obtained in the limit of low-Reynolds-number. The key parameters such as the frequency of oscillation λ, the permeability constant δ, and the slip coefficient ξ control the flow fields and physical quantities in the entire flow domain. Local streamlines for fixed times demonstrate the variations in flow patterns. Closed form expressions for the tangential velocity profile, wall shear stress, and the force acting on the sphere are computed and compared with the existing results. It is noted that the slip parameter in the range 0 <= ξ <= 0 . 5 has a significant effect in reducing the stress and force. The steady-state velocity overshoot behavior in the vicinity of the sphere is re-iterated. In the limit of large permeability, Darcy (potential) flow is recovered outside a boundary layer. The results are of some interest in predicting maximum wall stress and pressure drop associated with biological models in fibrous media.

Oscillatory flow past a slip cylindrical inclusion embedded in a Brinkman medium

NASA Astrophysics Data System (ADS)

Palaniappan, D.

2015-11-01

Transient flow past a circular cylinder embedded in a porous medium is studied based on Brinkman model with Navier slip conditions. Closed form analytic solution for the stream-function describing slow oscillatory flow around a solid cylindrical inclusion is obtained in the limit of low-Reynolds-number. The key parameters such as the frequency of oscillation λ, the permeability constant δ, and the slip coefficient ξ dictate the flow fields and physical quantities in the entire flow domain. Asymptotic steady-state analysis when δ --> 0 reveals the paradoxical behavior detected by Stokes. Local streamlines for small times demonstrate interesting flow patterns. Rapid transitions including flow separations and eddies are observed far away from the solid inclusion. Analytic expressions for the wall shear stress and the force acting on the cylinder are computed and compared with existing results. It is noted that the slip parameter in the range 0 <= ξ <= 0 . 5 has a significant effect in reducing the stress and force. In the limit of large permeability, Darcy (potential) flow is recovered outside a boundary layer. The results are of some interest in predicting maximum wall stress and pressure drop associated with biological models in fibrous media.

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Balasubramaniam, R.

1991-01-01

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Balasubramaniam, R.

1989-01-01

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Process analytical technology (PAT) approach to the formulation of thermosensitive protein-loaded pellets: Multi-point monitoring of temperature in a high-shear pelletization.

PubMed

Kristó, Katalin; Kovács, Orsolya; Kelemen, András; Lajkó, Ferenc; Klivényi, Gábor; Jancsik, Béla; Pintye-Hódi, Klára; Regdon, Géza

2016-12-01

In the literature there are some publications about the effect of impeller and chopper speeds on product parameters. However, there is no information about the effect of temperature. Therefore our main aim was the investigation of elevated temperature and temperature distribution during pelletization in a high shear granulator according to process analytical technology. During our experimental work, pellets containing pepsin were formulated with a high-shear granulator. A specially designed chamber (Opulus Ltd.) was used for pelletization. This chamber contained four PyroButton-TH® sensors built in the wall and three PyroDiff® sensors 1, 2 and 3cm from the wall. The sensors were located in three different heights. The impeller and chopper speeds were set on the basis of 3 2 factorial design. The temperature was measured continuously in 7 different points during pelletization and the results were compared with the temperature values measured by the thermal sensor of the high-shear granulator. The optimization parameters were enzyme activity, average size, breaking hardness, surface free energy and aspect ratio. One of the novelties was the application of the specially designed chamber (Opulus Ltd.) for monitoring the temperature continuously in 7 different points during high-shear granulation. The other novelty of this study was the evaluation of the effect of temperature on the properties of pellets containing protein during high-shear pelletization. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of sedimenting particles on the turbulence structure in a horizontal channel flow

NASA Astrophysics Data System (ADS)

Tay, Godwin F. K.; Kuhn, David C. S.; Tachie, Mark F.

2015-02-01

This work presents the results of experiments conducted in a horizontal channel to characterize low Reynolds number turbulent flows in the presence of small solid particles. The particle diameter relative to the integral length scale, dp/Λx, is approximately 0.02. Particles and fluid turbulence characteristics are measured for three average solid volume fractions of approximately ϕv = 2.0 × 10-4, 4.0 × 10-4, and 8.0 × 10-4 under conditions where the particle number density is evolving due to deposition. The results indicate that the mean slip between particles and the fluid is important only close to the wall. Away from the wall, the particles and unladen fluid mean velocities are similar. Differences between particles and the unladen fluid statistics are more pronounced in the wall-normal velocity fluctuations than the streamwise velocity fluctuations and Reynolds shear stress due to the stronger effect of the gravitational force in the wall-normal direction. The fluid turbulent intensities show no dependency on loading, but the peak Reynolds shear stress is significantly reduced. A quadrant decomposition of the Reynolds shear stress revealed a corresponding reduction in the ejections and sweeps for the laden flow in comparison with the unladen flow. Swirling strength and vorticity root-mean-square fluctuations decayed due to the damping effect of particles. The influence of particles on the turbulence structure was examined using two-point correlations of the velocity fluctuations and swirling strength, where it was demonstrated that the wall structures are attached eddies which are more extensive (much larger) in the particle-laden flow compared to the unladen flow.

Hot film wall shear instrumentation for compressible boundary layer transition research

NASA Technical Reports Server (NTRS)

Schneider, Steven P.

1992-01-01

Experimental and analytical studies of hot film wall shear instrumentation were performed. A new hot film anemometer was developed and tested. The anemometer performance was not quite as good as that of commercial anemometers, but the cost was much less and testing flexibility was improved. The main focus of the project was a parametric study of the effect of sensor size and substrate material on the performance of hot film surface sensors. Both electronic and shock-induced flow experiments were performed to determine the sensitivity and frequency response of the sensors. The results are presented in Michael Moen's M.S. thesis, which is appended. A condensed form of the results was also submitted for publication.

Numerical analysis of behaviour of cross laminated timber (CLT) in blast loading

NASA Astrophysics Data System (ADS)

Šliseris, J.; Gaile, L.; Pakrastiņš, L.

2017-10-01

A non-linear computation model for CLT wall element that includes explicit dynamics and composite damage constitutive model was developed. The numerical model was compared with classical beam theory and it turned out that shear wood layer has significant shear deformations that must be taken into account when designing CLT. It turned out that impulse duration time has a major effect on the strength of CLT. Special attention must be payed when designing CLT wall, window and door architectural system in order to guarantee the robustness of structure. The proposed numerical modelling framework can be used when designing CLT buildings that can be affected by blast loading, whilst structural robustness must be guaranteed.

Calculations of wall shear stress in harmonically oscillated turbulent pipe flow using a low-Reynolds-number {kappa}-{epsilon} model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ismael, J.O.; Cotton, M.A.

1996-03-01

The low-Reynolds-number {kappa}-{epsilon} turbulence model of Launder and Sharma is applied to the calculation of wall shear stress in spatially fully-developed turbulent pipe flow oscillated at small amplitudes. It is believed that the present study represents the first systematic evaluation of the turbulence closure under consideration over a wide range of frequency. Model results are well correlated in terms of the parameter {omega}{sup +} = {omega}{nu}/{bar U}{sub {tau}}{sup 2} at high frequencies, whereas at low frequencies there is an additional Reynolds number dependence. Comparison is made with the experimental data of Finnicum and Hanratty.

Research Advances on Fabricated Shear Wall System

NASA Astrophysics Data System (ADS)

Liu, Xudong; Wang, Donghui; Wang, Sheng; Zhai, Yu

2018-03-01

With the rapid development of the construction industry, building energy consumption has been increasing, has become a problem that can not be ignored. It is imperative to develop energy-saving buildings. A new type of prefabricated shear wall is assembled and partially assembled by prefabricated parts, and some concrete is spliced together. The new structure has good integrity, seismic resistance and excellent energy saving and environmental protection performance. It reduces building energy consumption to a great extent. Therefore, the design method, manufacturing process, site assembly process and key technical problems of the system are discussed. For the construction industry gradually entered the energy conservation, environmental protection, safety and durability of sustainable development laid the foundation.

Holt film wall shear instrumentation for boundary layer transition research

NASA Technical Reports Server (NTRS)

Schneider, Steven P.

1994-01-01

Measurements of the performance of hot-film wall-shear sensors were performed to aid development of improved sensors. The effect of film size and substrate properties on the sensor performance was quantified through parametric studies carried out both electronically and in a shock tube. The results show that sensor frequency response increases with decreasing sensor size, while at the same time sensitivity decreases. Substrate effects were also studied, through parametric variation of thermal conductivity and heat capacity. Early studies used complex dual-layer substrates, while later studies were designed for both single-layer and dual-layer substrates. Sensor failures and funding limitations have precluded completion of the substrate thermal-property tests.

Direct Numerical Simulation of Turbulent Couette-Poiseuille Flow With Zero Skin Friction

NASA Technical Reports Server (NTRS)

Coleman, Gary N.; Spalart, Philippe R.

2015-01-01

The near-wall scaling of mean velocity U(yw) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to the square root of yw in the region just above the wall at which the mean shear dU=dy = 0.

Turbulent boundary layers with secondary flow

NASA Technical Reports Server (NTRS)

Grushwitz, E.

1984-01-01

An experimental analysis of the boundary layer on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.

Fuel Injector With Shear Atomizer

NASA Technical Reports Server (NTRS)

Beal, George W.; Mills, Virgil L.; Smith, Durward B., II; Beacom, William F.

1995-01-01

Atomizer for injecting liquid fuel into combustion chamber uses impact and swirl to break incoming stream of fuel into small, more combustible droplets. Slanted holes direct flow of liquid fuel to stepped cylindrical wall. Impact on wall atomizes liquid. Air flowing past vanes entrains droplets of liquid in swirling flow. Fuel injected at pressure lower than customarily needed.

Vortex dynamics in ruptured and unruptured intracranial aneurysms

NASA Astrophysics Data System (ADS)

Trylesinski, Gabriel; Varble, Nicole; Xiang, Jianping; Meng, Hui

2013-11-01

Intracranial aneurysms (IAs) are potentially devastating pathological dilations of arterial walls that affect 2-5% of the population. In our previous CFD study of 119 IAs, we found that ruptured aneurysms were correlated with complex flow pattern and statistically predictable by low wall shear stress and high oscillatory shear index. To understand flow mechanisms that drive the pathophysiology of aneurysm wall leading to either stabilization or growth and rupture, we aim at exploring vortex dynamics of aneurysmal flow and provide insight into the correlation between the previous predictive morphological parameters and wall hemodynamic metrics. We adopt the Q-criterion definition of coherent structures (CS) and analyze the CS dynamics in aneurysmal flows for both ruptured and unruptured IA cases. For the first time, we draw relevant biological conclusions concerning aneurysm flow mechanisms and pathophysiological outcome. In pulsatile simulations, the coherent structures are analyzed in these 119 patient-specific geometries obtained using 3D angiograms. The images were reconstructed and CFD were performed. Upon conclusion of this work, better understanding of flow patterns of unstable aneurysms may lead to improved clinical outcome.

Characterization of Flow and Ohm's Law in the Rotating Wall Machine

NASA Astrophysics Data System (ADS)

Hannum, David; Brookhart, M.; Forest, C. B.; Kendrick, R.; Mengin, G.; Paz-Soldan, C.

2010-11-01

The rotating wall machine is a linear screw-pinch built to study the role of different electromagnetic boundary conditions on the Resistive Wall Mode (RWM). Its plasma is created by an array of electrostatic washer guns which can be biased to discharge up to 1 kA of current each. Individual flux ropes from the guns shear, merge, and expand into a 20 cm diameter, ˜1 m long plasma column. Langmuir (singletip) and tri-axial B-dot probes move throughout the column to measure radial and axial profiles of key plasma parameters. As the plasma current increases, more H2 fuel is ionized, raising ne to 5 x10^20 m-3 while Te stays at a constant 3 eV. The electron density expands to the wall while the current density (Jz) stays pinched to the central axis. E xB and diamagnetic drifts create radially and axially sheared plasma rotation. Plasma resistivity follows the Spitzer model in the core while exceeding it at the edge. These measurements improve the model used to predict the RWM growth rate.

Acoustic microstreaming due to an ultrasound contrast microbubble near a wall

NASA Astrophysics Data System (ADS)

Mobadersany, Nima; Sarkar, Kausik

2017-11-01

In an ultrasound field, in addition to the sinusoidal motion of fluid particles, particles experience a steady streaming velocity due to nonlinear second order effects. Here, we have simulated the microstreaming flow near a plane rigid wall caused by the pulsations of contrast microbubbles. Although these microbubbles were initially developed as a contrast enhancing agents for ultrasound imaging, they generate additional therapeutic effects that can be harnessed for targeted drug delivery or blood brain barrier (BBB) opening. The microbubbles have a gas core coated with a stabilizing layer of lipids or proteins. We use analytical models as well as boundary element (BEM) simulation to simulate the flow around these bubbles implementing interfacial rheology models for the coating. The microstreaming flow is characterized by two wall bounded vortices. The size of the vortices decreases with the decrease of the separation from the wall. The vortex-induced shear stress is simulated and analyzed as a function of excitation parameters and geometry. These microstreaming shear stress plays a critical role in increasing the membrane permeability facilitating drug delivery or rupturing biological tissues.

High-order numerical simulations of pulsatile flow in a curved artery model

NASA Astrophysics Data System (ADS)

Cox, Christopher; Liang, Chunlei; Plesniak, Michael W.

2016-11-01

Cardiovascular flows are pulsatile, incompressible and occur in complex geometries with compliant walls. Together, these factors can produce an environment that can affect the progression of cardiovascular disease by altering wall shear stresses. Unstructured high-order CFD methods are well suited for capturing unsteady vortex-dominated viscous flows, and these methods provide high accuracy for similar cost as low-order methods. We use an in-house three-dimensional flux reconstruction Navier-Stokes solver to simulate secondary flows and vortical structures within a rigid 180-degree curved artery model under pulsatile flow of a Newtonian blood-analog fluid. Our simulations use a physiological flowrate waveform taken from the carotid artery. We are particularly interested in the dynamics during the deceleration phase of the waveform, where we observe the deformed-Dean, Dean, Lyne and Wall vortices. Our numerical results reveal the complex nature of these vortices both in space and time and their effect on overall wall shear stress. Numerical results agree with and complement experimental results obtained in our laboratory using particle image velocimetry. Supported by the GW Center for Biomimetics and Bioinspired Engineering.

Basic Principles of Thin-Walled Open Bars Taking into Account Where Influence Shifts of Cross Sections are Concerned

NASA Astrophysics Data System (ADS)

Panasenko, N. N.; Sinelschikov, A. V.

2017-11-01

The finite element method is considered to be the most effective in relation to the calculation of strength and stability of buildings and engineering constructions. As a rule, for the modelling of supporting 3-D frameworks, finite elements with six degrees of freedom are used in each of the nodes. In practice, such supporting frameworks represent the thin-walled welded bars and hot-rolled bars of open and closed profiles in which cross-sectional deplanation must be taken into account. This idea was first introduced by L N Vorobjev and brought to one of the easiest variants of the thin-walled bar theory. The development of this approach is based on taking into account the middle surface shear deformation and adding the deformations of a thin-walled open bar to the formulas for potential and kinetic energy; these deformations depend on shearing stress and result in decreasing the frequency of the first tone of fluctuations to 13%. The authors of the article recommend taking into account this fact when calculating fail-proof dynamic systems.

Wall shear stress fixed points in cardiovascular fluid mechanics.

PubMed

Arzani, Amirhossein; Shadden, Shawn C

2018-05-17

Complex blood flow in large arteries creates rich wall shear stress (WSS) vectorial features. WSS acts as a link between blood flow dynamics and the biology of various cardiovascular diseases. WSS has been of great interest in a wide range of studies and has been the most popular measure to correlate blood flow to cardiovascular disease. Recent studies have emphasized different vectorial features of WSS. However, fixed points in the WSS vector field have not received much attention. A WSS fixed point is a point on the vessel wall where the WSS vector vanishes. In this article, WSS fixed points are classified and the aspects by which they could influence cardiovascular disease are reviewed. First, the connection between WSS fixed points and the flow topology away from the vessel wall is discussed. Second, the potential role of time-averaged WSS fixed points in biochemical mass transport is demonstrated using the recent concept of Lagrangian WSS structures. Finally, simple measures are proposed to quantify the exposure of the endothelial cells to WSS fixed points. Examples from various arterial flow applications are demonstrated. Copyright © 2018 Elsevier Ltd. All rights reserved.

Periodically sheared 2D Yukawa systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovács, Anikó Zsuzsa; Hartmann, Peter; Center for Astrophysics, Space Physics and Engineering Research

2015-10-15

We present non-equilibrium molecular dynamics simulation studies on the dynamic (complex) shear viscosity of a 2D Yukawa system. We have identified a non-monotonic frequency dependence of the viscosity at high frequencies and shear rates, an energy absorption maximum (local resonance) at the Einstein frequency of the system at medium shear rates, an enhanced collective wave activity, when the excitation is near the plateau frequency of the longitudinal wave dispersion, and the emergence of significant configurational anisotropy at small frequencies and high shear rates.

Structures Formed in Experimentally Sheared Artificial Fault Gouge: Precise Statistical Measurements

NASA Astrophysics Data System (ADS)

Dilov, T.; Yoshida, S.; Kato, A.; Nakatani, M.; Mochizuki, H.; Otsuki, K.

2004-12-01

The physical parameters governing earthquakes change with the ongoing formation and evolution of structures, formed in the course of a single or multiple earthquakes, within a particular fault zone or in a broad volume containing interacting tectonic faults. Our precise knowledge of these complex phenomena is still elusive. Especially, works considering geometrical evolution of shear structures under controlled conditions are rare. In order to gain some insights we accomplished a set of 12 laboratory experiments using a servo-controlled direct-shear apparatus, under room temperature and without controlling the air humidity. Two fault gouge layers (industrially produced quartz powder, average particle size of 5 μ m, and pre-shear thickness of 1.5, 2.0 and 3.0 mm,) were sandwiched between three granite blocks. The middle block was slid in order to create frictional structures within the simulated gouge. The total imposed shear strain varies between 0.14 and 11.80. The post-shear gouge layer thickness ranges from 0.99-2.11 mm. Each experiment was run under a constant normal stress (varying from 10-44 MPa through the experiments) and at a constant shear velocity (0.07, 0.7 and 7 μ m/s, through the experiments). Later, in cross-sections of solidified by epoxy glue gouge (parallel to the shear direction, normal to the gouge walls,) we quantified the numerous R-shears, according to their density distribution, fracture thickness (measured perpendicularly to the fracture walls), fracture angle and morphology, and fracture length. In gouge views parallel to the sliding blocks, we measured fracture length and along-strike R-shear morphology. Although the latter data are with lower quality, both observational sets provide precise statistical fracture data as well snapshots of evolving 3D structures. We observe shear localization with decreasing gouge layer thickness and with increasing normal stress. The average density of major fractures increases from 2.83 to 3.67 [fracture/cm] for decrease of the post-shear gouge layer thickness. This is at the expense of a considerable decrease of visible more diffusive minor fractures. On the other hand, the fractures formed at lower normal stress are more irregular and show average fracture density of 4.48 [fracture/cm]. The latter decreases down to 3.64 at higher normal stress, as the fracture morphology becomes more regular. The fracture density increases abruptly from zero, after a small total shear strain (0.15-0.50), and later the change is slower or none with the increase of the total shear strain; the fractures are already localized and they accommodate most of the brittle deformation. Also we observe weak polarity in fracture development in accordance to the sliding sense, especially in the subset of fractures starting from the gouge wall and dying out within the gouge layer. More such fractures are developed along the leading part of the sliding blocks. Our results throw new light over the formation and development of fault-related structures and their dependency on the earthquake-governing physical parameters.

Effects of transverse shear deformation on buckling of laminated cylinders as a function of thickness and ply orientation

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.

1987-01-01

Buckling loads of thick-walled, orthotropic, simply-supported right circular cylinders are predicted using a new higher-order transverse shear deformation theory. The higher-order theory shows that, by more accurately accounting for transverse shear deformation effects, the predicted buckling load may be reduced by as much as 80 percent compared to predictions based on conventional transverse shear deformation theory. A parametric study of the effect of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 0 deg plies are the most sensitive to transverse shear deformation effects. Interaction curves for buckling of cylinders with axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are much less sensitive to transverse shear deformation effects than those due to axial compressive loadings.

Development of a novel precision instrument for high-resolution simultaneous normal and shear force measurements between small planar samples

NASA Astrophysics Data System (ADS)

Lundstrom, Troy; Clark, William; Jalili, Nader

2017-05-01

In the design and development of end effector pads for silicon wafer handling robots, it is imperative that the static friction/adhesion force properties of the pads with respect to a variety of planar surfaces be characterized. In this work, the overall design, calibration, and data acquisition procedure of an instrument developed for performing these measurements on small (<10 mm × 10 mm) planar samples is presented. This device was used to perform adhesion/maximum shear force measurements on polydimethylsiloxane, a silicon wafer, and custom carbon nanotubes forest surfaces. The device was successfully able to measure an effective, mean profile adhesion force of 715 μN between a silicon wafer and a polydimethylsiloxane (2.768 × 10-6 m2) sample. In addition, a nonlinear maximum shear over normal force relationship was also measured between custom carbon nanotubes forest and the silicon wafer surfaces. The maximum shear over a normal force coefficient was found to decrease with increasing initial normal force. Currently, there are numerous devices for measuring normal/shear forces at the nano/micro- and macroscales; however, this device allows for the consistent measurement of these same types of forces on components with surface dimensions ranging from 0.1 mm to 10 mm.

45. WEST TO CIRCA 1900 SHEET METAL SHEAR, THE MACHINE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

45. WEST TO CIRCA 1900 SHEET METAL SHEAR, THE MACHINE USED TO CUT SHEET METAL USED IN WINDMILLS AND WATER TANKS. IN THE BACKGROUND IS THE INTERIOR WEST WALL OF THE FACTORY, ITS SHELVES BEARING WATER PUMPS, PARTS FOR PUMPS AND WATER SUPPLY EQUIPMENT, AND NEW OLD STOCK MERCHANDISE. - Kregel Windmill Company Factory, 1416 Central Avenue, Nebraska City, Otoe County, NE

A Novel Diagnostic Aid for Detection of Intra-Abdominal Adhesions to the Anterior Abdominal Wall Using Dynamic Magnetic Resonance Imaging.

PubMed

Randall, David; Fenner, John; Gillott, Richard; Ten Broek, Richard; Strik, Chema; Spencer, Paul; Bardhan, Karna Dev

2016-01-01

Introduction. Abdominal adhesions can cause serious morbidity and complicate subsequent operations. Their diagnosis is often one of exclusion due to a lack of a reliable, non-invasive diagnostic technique. Development and testing of a candidate technique are described below. Method. During respiration, smooth visceral sliding motion occurs between the abdominal contents and the walls of the abdominal cavity. We describe a technique involving image segmentation and registration to calculate shear as an analogue for visceral slide based on the tracking of structures throughout the respiratory cycle. The presence of an adhesion is attributed to a resistance to visceral slide resulting in a discernible reduction in shear. The abdominal movement due to respiration is captured in sagittal dynamic MR images. Results. Clinical images were selected for analysis, including a patient with a surgically confirmed adhesion. Discernible reduction in shear was observed at the location of the adhesion while a consistent, gradually changing shear was observed in the healthy volunteers. Conclusion. The technique and its validation show encouraging results for adhesion detection but a larger study is now required to confirm its potential.

A Novel Diagnostic Aid for Detection of Intra-Abdominal Adhesions to the Anterior Abdominal Wall Using Dynamic Magnetic Resonance Imaging

PubMed Central

Randall, David; Fenner, John; Gillott, Richard; ten Broek, Richard; Strik, Chema; Spencer, Paul; Bardhan, Karna Dev

2016-01-01

Introduction. Abdominal adhesions can cause serious morbidity and complicate subsequent operations. Their diagnosis is often one of exclusion due to a lack of a reliable, non-invasive diagnostic technique. Development and testing of a candidate technique are described below. Method. During respiration, smooth visceral sliding motion occurs between the abdominal contents and the walls of the abdominal cavity. We describe a technique involving image segmentation and registration to calculate shear as an analogue for visceral slide based on the tracking of structures throughout the respiratory cycle. The presence of an adhesion is attributed to a resistance to visceral slide resulting in a discernible reduction in shear. The abdominal movement due to respiration is captured in sagittal dynamic MR images. Results. Clinical images were selected for analysis, including a patient with a surgically confirmed adhesion. Discernible reduction in shear was observed at the location of the adhesion while a consistent, gradually changing shear was observed in the healthy volunteers. Conclusion. The technique and its validation show encouraging results for adhesion detection but a larger study is now required to confirm its potential. PMID:26880884

Composite Behavior of a Novel Insulated Concrete Sandwich Wall Panel Reinforced with GFRP Shear Grids: Effects of Insulation Types.

PubMed

Kim, JunHee; You, Young-Chan

2015-03-03

A full-scale experimental program was used in this study to investigate the structural behavior of novel insulated concrete sandwich wall panels (SWPs) reinforced with grid-type glass-fiber-reinforced polymer (GFRP) shear connectors. Two kinds of insulation-expanded polystyrene (EPS) and extruded polystyrene (XPS) with 100 mm thickness were incased between the two concrete wythes to meet the increasing demand for the insulation performance of building envelope. One to four GFRP shear grids were used to examine the degree of composite action of the two concrete wythes. Ten specimens of SWPs were tested under displacement control subjected to four-point concentrated loads. The test results showed that the SWPs reinforced with GFRP grids as shear connectors developed a high degree of composite action resulting in high flexural strength. The specimens with EPS foam exhibited an enhanced load-displacement behavior compared with the specimens with XPS because of the relatively stronger bond between insulation and concrete. In addition, the ultimate strength of the test results was compared to the analytical prediction with the mechanical properties of only GRFP grids. The specimens with EPS insulation presented higher strength-based composite action than the ones with XPS insulation.

A unified wall function for compressible turbulence modelling

NASA Astrophysics Data System (ADS)

Ong, K. C.; Chan, A.

2018-05-01

Turbulence modelling near the wall often requires a high mesh density clustered around the wall and the first cells adjacent to the wall to be placed in the viscous sublayer. As a result, the numerical stability is constrained by the smallest cell size and hence requires high computational overhead. In the present study, a unified wall function is developed which is valid for viscous sublayer, buffer sublayer and inertial sublayer, as well as including effects of compressibility, heat transfer and pressure gradient. The resulting wall function applies to compressible turbulence modelling for both isothermal and adiabatic wall boundary conditions with the non-zero pressure gradient. Two simple wall function algorithms are implemented for practical computation of isothermal and adiabatic wall boundary conditions. The numerical results show that the wall function evaluates the wall shear stress and turbulent quantities of wall adjacent cells at wide range of non-dimensional wall distance and alleviate the number and size of cells required.

Flow characteristics and scaling past highly porous wall-mounted fences

NASA Astrophysics Data System (ADS)

Rodríguez-López, Eduardo; Bruce, Paul J. K.; Buxton, Oliver R. H.

2017-07-01

An extensive characterization of the flow past wall-mounted highly porous fences based on single- and multi-scale geometries has been performed using hot-wire anemometry in a low-speed wind tunnel. Whilst drag properties (estimated from the time-averaged momentum equation) seem to be mostly dependent on the grids' blockage ratio; wakes of different size and orientation bars seem to generate distinct behaviours regarding turbulence properties. Far from the near-grid region, the flow is dominated by the presence of two well-differentiated layers: one close to the wall dominated by the near-wall behaviour and another one corresponding to the grid's wake and shear layer, originating from between this and the freestream. It is proposed that the effective thickness of the wall layer can be inferred from the wall-normal profile of root-mean-square streamwise velocity or, alternatively, from the wall-normal profile of streamwise velocity correlation. Using these definitions of wall-layer thickness enables us to collapse different trends of the turbulence behaviour inside this layer. In particular, the root-mean-square level of the wall shear stress fluctuations, longitudinal integral length scale, and spanwise turbulent structure is shown to display a satisfactory scaling with this thickness rather than with the whole thickness of the grid's wake. Moreover, it is shown that certain grids destroy the spanwise arrangement of large turbulence structures in the logarithmic region, which are then re-formed after a particular streamwise extent. It is finally shown that for fences subject to a boundary layer of thickness comparable to their height, the effective thickness of the wall layer scales with the incoming boundary layer thickness. Analogously, it is hypothesized that the growth rate of the internal layer is also partly dependent on the incoming boundary layer thickness.

Calculation of pressure drop in the developmental stages of the medaka fish heart and microvasculature

NASA Astrophysics Data System (ADS)

Chakraborty, Sreyashi; Vlachos, Pavlos

2016-11-01

Peristaltic contraction of the developing medaka fish heart produces temporally and spatially varying pressure drop across the atrioventricular (AV) canal. Blood flowing through the tail vessels experience a slug flow across the developmental stages. We have performed a series of live imaging experiments over 14 days post fertilization (dpf) of the medaka fish egg and cross-correlated the red blood cell (RBC) pattern intensities to obtain the two-dimensional velocity fields. Subsequently we have calculated the pressure field by integrating the pressure gradient in the momentum equation. Our calculations show that the pressure drop across the AV canal increases from 0.8mm Hg during 3dpf to 2.8 mm Hg during 14dpf. We have calculated the time-varying wall shear stress for the blood vessels by assuming a spatially constant velocity magnitude in each vessel. The calculated wall shear stress matches the wall shear stress sensed by human endothelial cells (10-12 dyne/sq. cm). The pressure drop per unit length of the vessel is obtained by doing a control volume analysis of flow in the caudal arteries and veins. The current results can be extended to investigate the effect of the fluid dynamic parameters on the vascular and cardiac morphogenesis.

GPU accelerated simulations of three-dimensional flow of power-law fluids in a driven cube

NASA Astrophysics Data System (ADS)

Jin, K.; Vanka, S. P.; Agarwal, R. K.; Thomas, B. G.

2017-01-01

Newtonian fluid flow in two- and three-dimensional cavities with a moving wall has been studied extensively in a number of previous works. However, relatively a fewer number of studies have considered the motion of non-Newtonian fluids such as shear thinning and shear thickening power law fluids. In this paper, we have simulated the three-dimensional, non-Newtonian flow of a power law fluid in a cubic cavity driven by shear from the top wall. We have used an in-house developed fractional step code, implemented on a Graphics Processor Unit. Three Reynolds numbers have been studied with power law index set to 0.5, 1.0 and 1.5. The flow patterns, viscosity distributions and velocity profiles are presented for Reynolds numbers of 100, 400 and 1000. All three Reynolds numbers are found to yield steady state flows. Tabulated values of velocity are given for the nine cases studied, including the Newtonian cases.

Composite Behavior of Insulated Concrete Sandwich Wall Panels Subjected to Wind Pressure and Suction.

PubMed

Choi, Insub; Kim, JunHee; Kim, Ho-Ryong

2015-03-19

A full-scale experimental test was conducted to analyze the composite behavior of insulated concrete sandwich wall panels (ICSWPs) subjected to wind pressure and suction. The experimental program was composed of three groups of ICSWP specimens, each with a different type of insulation and number of glass-fiber-reinforced polymer (GFRP) shear grids. The degree of composite action of each specimen was analyzed according to the load direction, type of the insulation, and number of GFRP shear grids by comparing the theoretical and experimental values. The failure modes of the ICSWPs were compared to investigate the effect of bonds according to the load direction and type of insulation. Bonds based on insulation absorptiveness were effective to result in the composite behavior of ICSWP under positive loading tests only, while bonds based on insulation surface roughness were effective under both positive and negative loading tests. Therefore, the composite behavior based on surface roughness can be applied to the calculation of the design strength of ICSWPs with continuous GFRP shear connectors.

The hemodynamics in intracranial aneurysm ruptured region with active contrast leakage during computed tomography angiography

NASA Astrophysics Data System (ADS)

Li, Ming-Lung; Wang, Yi-Chou; Liou, Tong-Miin; Lin, Chao-An

2014-10-01

Precise locations of rupture region under contrast agent leakage of five ruptured cerebral artery aneurysms during computed tomography angiography, which is to our knowledge for the first time, were successfully identified among 101 patients. These, together with numerical simulations based on the reconstructed aneurysmal models, were used to analyze hemodynamic parameters of aneurysms under different cardiac cyclic flow rates. For side wall type aneurysms, different inlet flow rates have mild influences on the shear stresses distributions. On the other hand, for branch type aneurysms, the predicted wall shear stress (WSS) correlates strongly with the increase of inlet vessel velocity. The mean and time averaged WSSes at rupture regions are found to be lower than those over the surface of the aneurysms. Also, the levels of the oscillatory shear index (OSI) are higher than the reported threshold value, supporting the assertion that high OSI correlates with rupture of the aneurysm. However, the present results also indicate that OSI level at the rupture region is relatively lower.

Computational Modeling of Blood Flow in the TrapEase Inferior Vena Cava Filter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singer, M A; Henshaw, W D; Wang, S L

To evaluate the flow hemodynamics of the TrapEase vena cava filter using three dimensional computational fluid dynamics, including simulated thrombi of multiple shapes, sizes, and trapping positions. The study was performed to identify potential areas of recirculation and stagnation and areas in which trapped thrombi may influence intrafilter thrombosis. Computer models of the TrapEase filter, thrombi (volumes ranging from 0.25mL to 2mL, 3 different shapes), and a 23mm diameter cava were constructed. The hemodynamics of steady-state flow at Reynolds number 600 was examined for the unoccluded and partially occluded filter. Axial velocity contours and wall shear stresses were computed. Flowmore » in the unoccluded TrapEase filter experienced minimal disruption, except near the superior and inferior tips where low velocity flow was observed. For spherical thrombi in the superior trapping position, stagnant and recirculating flow was observed downstream of the thrombus; the volume of stagnant flow and the peak wall shear stress increased monotonically with thrombus volume. For inferiorly trapped spherical thrombi, marked disruption to the flow was observed along the cava wall ipsilateral to the thrombus and in the interior of the filter. Spherically shaped thrombus produced a lower peak wall shear stress than conically shaped thrombus and a larger peak stress than ellipsoidal thrombus. We have designed and constructed a computer model of the flow hemodynamics of the TrapEase IVC filter with varying shapes, sizes, and positions of thrombi. The computer model offers several advantages over in vitro techniques including: improved resolution, ease of evaluating different thrombus sizes and shapes, and easy adaptation for new filter designs and flow parameters. Results from the model also support a previously reported finding from photochromic experiments that suggest the inferior trapping position of the TrapEase IVC filter leads to an intra-filter region of recirculating/stagnant flow with very low shear stress that may be thrombogenic.« less

Acoustic attenuation due to transformation twins in CaCl2: Analogue behaviour for stishovite

NASA Astrophysics Data System (ADS)

Zhang, Zhiying; Schranz, Wilfried; Carpenter, Michael A.

2012-09-01

CaCl2 undergoes a tetragonal (P42/mnm) to orthorhombic (Pnnm) transition as a function of temperature which is essentially the same as occurs in stishovite at high pressures. It can therefore be used as a convenient analogue material for experimental studies. In order to investigate variations in elastic properties associated with the transition and possible anelastic loss behaviour related to the mobility of ferroelastic twin walls in the orthorhombic phase, the transition in polycrystalline CaCl2 has been examined using resonant ultrasound spectroscopy (RUS) at high frequencies (0.1-1.5 MHz) in the temperature interval 7-626 K, and dynamic mechanical analysis (DMA) at low frequencies (0.1-50 Hz) in the temperature interval 378-771 K. RUS data show steep softening of the shear modulus as the transition temperature is approached from above and substantial acoustic dissipation in the stability field of the orthorhombic structure. DMA data show softening of the storage modulus, which continues through to a minimum ˜20 K below the transition point and is followed by stiffening with further lowering of temperature. There is no obvious acoustic dissipation associated with the transition, as measured by tan δ, however. The elastic softening and stiffening matches the pattern expected for a pseudoproper ferroelastic transition as predicted elsewhere. Acoustic loss behaviour at high frequencies fits with the pattern of behaviour expected for a twin wall loss mechanism but with relaxation times in the vicinity of ˜10-6 s. With such short relaxation times, the shear modulus of CaCl2 at frequencies corresponding to seismic frequencies would include relaxations of the twin walls and is therefore likely to be significantly lower than the intrinsic shear modulus. If these characteristics apply also to twin wall mobility in stishovite, the seismic signature of the orthorhombic phase should be an unusually soft shear modulus but with no increase in attenuation.

Bubble Motion through a Generalized Power-Law Fluid Flowing in a Vertical Tube

PubMed Central

Mukundakrishnan, Karthik; Eckmann, David M.; Ayyaswamy, P. S.

2009-01-01

Intravascular gas embolism may occur with decompression in space flight, as well as during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ, such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. To develop effective therapeutic strategies, there is a need for understanding the dynamics of bubble motion through blood and its interaction with the vessel wall through which it moves. Toward this goal, we numerically investigate the axisymmetric motion of a bubble moving through a vertical circular tube in a shear-thinning generalized power-law fluid, using a front-tracking method. The formulation is characterized by the inlet Reynolds number, capillary number, Weber number, and Froude number. The flow dynamics and the associated wall shear stresses are documented for a combination of two different inlet flow conditions (inlet Reynolds numbers) and three different effective bubble radii (ratio of the undeformed bubble radii to the tube radii). The results of the non-Newtonian model are then compared with that of the model assuming a Newtonian blood viscosity. Specifically, for an almost occluding bubble (effective bubble radius = 0.9), the wall shear stress and the bubble residence time are compared for both Newtonian and non-Newtonian cases. Results show that at low shear rates, for a given pressure gradient the residence time for a non-Newtonian flow is higher than that for a Newtonian flow. PMID:19426324

A computational study of the respiratory airflow characteristics in normal and obstructed human airways.

PubMed

Sul, Bora; Wallqvist, Anders; Morris, Michael J; Reifman, Jaques; Rakesh, Vineet

2014-09-01

Obstructive lung diseases in the lower airways are a leading health concern worldwide. To improve our understanding of the pathophysiology of lower airways, we studied airflow characteristics in the lung between the 8th and the 14th generations using a three-dimensional computational fluid dynamics model, where we compared normal and obstructed airways for a range of breathing conditions. We employed a novel technique based on computing the Pearson׳s correlation coefficient to quantitatively characterize the differences in airflow patterns between the normal and obstructed airways. We found that the airflow patterns demonstrated clear differences between normal and diseased conditions for high expiratory flow rates (>2300ml/s), but not for inspiratory flow rates. Moreover, airflow patterns subjected to filtering demonstrated higher sensitivity than airway resistance for differentiating normal and diseased conditions. Further, we showed that wall shear stresses were not only dependent on breathing rates, but also on the distribution of the obstructed sites in the lung: for the same degree of obstruction and breathing rate, we observed as much as two-fold differences in shear stresses. In contrast to previous studies that suggest increased wall shear stress due to obstructions as a possible damage mechanism for small airways, our model demonstrated that for flow rates corresponding to heavy activities, the wall shear stress in both normal and obstructed airways was <0.3Pa, which is within the physiological limit needed to promote respiratory defense mechanisms. In summary, our model enables the study of airflow characteristics that may be impractical to assess experimentally. Published by Elsevier Ltd.

Improved Bond Strength of Cyanoacrylate Adhesives Through Nanostructured Chromium Adhesion Layers

NASA Astrophysics Data System (ADS)

Gobble, Kyle; Stark, Amelia; Stagon, Stephen P.

2016-09-01

The performance of many consumer products suffers due to weak and inconsistent bonds formed to low surface energy polymer materials, such as polyolefin-based high-density polyethylene (HDPE), with adhesives, such as cyanoacrylate. In this letter, we present an industrially relevant means of increasing bond shear strength and consistency through vacuum metallization of chromium thin films and nanorods, using HDPE as a prototype material and cyanoacrylate as a prototype adhesive. For the as received HDPE surfaces, unmodified bond shear strength is shown to be only 0.20 MPa with a standard deviation of 14 %. When Cr metallization layers are added onto the HDPE at thicknesses of 50 nm or less, nanorod-structured coatings outperform continuous films and have a maximum bond shear strength of 0.96 MPa with a standard deviation of 7 %. When the metallization layer is greater than 50 nm thick, continuous films demonstrate greater performance than nanorod coatings and have a maximum shear strength of 1.03 MPa with a standard deviation of 6 %. Further, when the combination of surface roughening with P400 grit sandpaper and metallization is used, 100-nm-thick nanorod coatings show a tenfold increase in shear strength over the baseline, reaching a maximum of 2.03 MPa with a standard deviation of only 3 %. The substantial increase in shear strength through metallization, and the combination of roughening with metallization, may have wide-reaching implications in consumer products which utilize low surface energy plastics.

A Study of the Response of the Human Cadaver Head to Impact

PubMed Central

Hardy, Warren N.; Mason, Matthew J.; Foster, Craig D.; Shah, Chirag S.; Kopacz, James M.; Yang, King H.; King, Albert I.; Bishop, Jennifer; Bey, Michael; Anderst, William; Tashman, Scott

2008-01-01

High-speed biplane x-ray and neutral density targets were used to examine brain displacement and deformation during impact. Relative motion, maximum principal strain, maximum shear strain, and intracranial pressure were measured in thirty-five impacts using eight human cadaver head and neck specimens. The effect of a helmet was evaluated. During impact, local brain tissue tends to keep its position and shape with respect to the inertial frame, resulting in relative motion between the brain and skull and deformation of the brain. The local brain motions tend to follow looping patterns. Similar patterns are observed for impact in different planes, with some degree of posterior-anterior and right-left symmetry. Peak coup pressure and pressure rate increase with increasing linear acceleration, but coup pressure pulse duration decreases. Peak average maximum principal strain and maximum shear are on the order of 0.09 for CFC 60 Hz data for these tests. Peak average maximum principal strain and maximum shear increase with increasing linear acceleration, coup pressure, and coup pressure rate. Linear and angular acceleration of the head are reduced with use of a helmet, but strain increases. These results can be used for the validation of finite element models of the human head. PMID:18278591

Kinematics of syn- and post-exhumational shear zones at Lago di Cignana (Western Alps, Italy): constraints on the exhumation of Zermatt-Saas (ultra)high-pressure rocks and deformation along the Combin Fault and Dent Blanche Basal Thrust

NASA Astrophysics Data System (ADS)

Kirst, Frederik; Leiss, Bernd

2017-01-01

Kinematic analyses of shear zones at Lago di Cignana in the Italian Western Alps were used to constrain the structural evolution of units from the Piemont-Ligurian oceanic realm (Zermatt-Saas and Combin zones) and the Adriatic continental margin (Dent Blanche nappe) during Palaeogene syn- and post-exhumational deformation. Exhumation of Zermatt-Saas (U)HP rocks to approximately lower crustal levels at ca. 39 Ma occurred during normal-sense top-(S)E shearing under epidote-amphibolite-facies conditions. Juxtaposition with the overlying Combin zone along the Combin Fault at mid-crustal levels occurred during greenschist-facies normal-sense top-SE shearing at ca. 38 Ma. The scarcity of top-SE kinematic indicators in the hanging wall of the Combin Fault probably resulted from strain localization along the uppermost Zermatt-Saas zone and obliteration by subsequent deformation. A phase of dominant pure shear deformation around 35 Ma affected units in the direct footwall and hanging wall of the Combin Fault. It is interpreted to reflect NW-SE crustal elongation during updoming of the nappe stack as a result of underthrusting of European continental margin units and the onset of continental collision. This phase was partly accompanied and followed by ductile bulk top-NW shearing, especially at higher structural levels, which transitioned into semi-ductile to brittle normal-sense top-NW deformation due to Vanzone phase folding from ca. 32 Ma onwards. Our structural observations suggest that syn-exhumational deformation is partly preserved within units and shear zones exposed at Lago di Cignana but also that the Combin Fault and Dent Blanche Basal Thrust experienced significant post-exhumational deformation reworking and overprinting earlier structures.

The Role of Environmental Shear and Thermodynamic Conditions in Determining the Structure and Evolution of Mesoscale Convective Systems during TOGA COARE.

NASA Astrophysics Data System (ADS)

Lemone, Margaret A.; Zipser, Edward J.; Trier, Stanley B.

1998-12-01

A collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE). The soundings were constructed primarily from aircraft data below 5-6 km and primarily from radiosonde data at higher altitudes.The well-documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended. As noted by earlier investigators, nearly all convective bands occurring in environments with appreciable shear below a low-level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low-level shear at a speed close to the wind maximum; when there is appreciable shear at middle levels (800-400 mb), convective bands form parallel to the shear. With appreciable shear at both levels, the lower-level shear determines the orientation of the primary convective bands. If the midlevel shear is opposite the low-level shear, secondary bands parallel to the midlevel shear will extend rearward from the primary band in later stages of its evolution; if the midlevel shear is 90 degrees to the low-level shear, the primary band will retain its two-dimensional mesoscale structure. Convection has no obvious mesoscale organization on days with little shear or days with widespread convection.Environmental temperatures and humidities have no obvious effect on the mesoscale convective pattern, but they affect COARE convection in other ways. The high tops of COARE convection are related to high parcel equilibrium levels, which approach 100 mb in some cases. Convective available potential energies are larger than those in the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment (GATE) mainly because of the higher equilibrium levels. The buoyancy integrated over the lowest 500 mb is similar for the two experiments. Convective inihibitions are small, enabling convection to propagate with only weak forcing. Comparison of slow-moving shear-parallel bands in COARE and GATE suggests that lower relative humidities between the top of the mixed layer and 500 mb can shorten their lifetimes significantly.COARE mesoscale organization and evolution differs from what was observed in GATE. Less-organized convection is more common in COARE. Of the convective bands observed, a greater fraction in COARE are faster-moving, shear-perpendicular squall lines. GATE slow-moving lines tend to be longer lived than those for COARE. The differences are probably traceable to differences in environmental shear and relative humidity, respectively.

Self similarity of two point correlations in wall bounded turbulent flows

NASA Technical Reports Server (NTRS)

Hunt, J. C. R.; Moin, P.; Moser, R. D.; Spalart, P. R.

1987-01-01

The structure of turbulence at a height y from a wall is affected by the local mean shear at y, by the direct effect of the wall on the eddies, and by the action of other eddies close to or far from the wall. Some researchers believe that a single one of these mechanisms is dominant, while others believe that these effects have to be considered together. It is important to understand the relative importance of these effects in order to develop closure models, for example for the dissipation or for the Reynolds stress equation, and to understand the eddy structure of cross correlation functions and other measures. The specific objective was to examine the two point correlation, R sub vv, of the normal velocity component v near the wall in a turbulent channel flow and in a turbulent boundary layer. The preliminary results show that even in the inhomogeneous turbulent boundary layer, the two-point correlation function may have self similar forms. The results also show that the effects of shear and of blocking are equally important in the form of correlation functions for spacing normal to the wall. But for spanwise spacing, it was found that the eddy structure is quire different in these near flows. So any theory for turbulent structure must take both these effects into account.

Brownian dynamics of wall tethered polymers in shear flow

NASA Astrophysics Data System (ADS)

Lin, Tiras Y.; Saadat, Amir; Kushwaha, Amit; Shaqfeh, Eric S. G.

2017-11-01

The dynamics of a wall tethered polymer in shear flow is studied using Brownian dynamics. Simulations are performed with bead-spring chains, and the effect of hydrodynamic interactions (HI) is incorporated through Blake's tensor with a finite size bead correction. We characterize the configuration of the polymer as a function of the Weissenberg number by investigating the regions the polymer explores in both the flow-gradient and flow-vorticity planes. The fractional extension in the flow direction, the width in the vorticity direction, and the thickness in the gradient direction are reported as well, and these quantities are found to compare favorably with the experimental data of the literature. The cyclic motion of the polymer is demonstrated through analysis of the mean velocity field of the end bead. We characterize the collision process of each bead with the wall as a Poisson process and extract an average wall collision rate, which in general varies along the backbone of the chain. The inclusion of HI with the wall for a tethered polymer is found to reduce the average wall collision rate. We anticipate that results from this work will be directly applicable to, e.g., the design of polymer brushes or the use of DNA for making nanowires in molecular electronics. T.Y.L. is supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

Development of a rocking R/C shear wall system implementing repairable structural fuses

NASA Astrophysics Data System (ADS)

Parsafar, Saeed; Moghadam, Abdolreza S.

2017-09-01

In the last decades, the concept of earthquake resilient structural systems is becoming popular in which the rocking structure is considered as a viable option for buildings in regions of high seismicity. To this end, a novel wall-base connection based on the " repairable structure" approach is proposed and evaluated. The proposed system is made of several steel plates and high strength bolts act as a friction connection. To achieve the desired rocking motion in the proposed system, short-slotted holes are used in vertical directions for connecting the steel plates to the shear wall (SW). The experimental and numerical studies were performed using a series of displacement control quasi-static cyclic tests on a reference model and four different configurations of the proposed connection installed at the wall corners. The seismic response of the proposed system is compared to the conventional SW in terms of energy dissipation and damage accumulation. In terms of energy dissipation, the proposed system depicted better performance with 95% more energy dissipation capability compared to conventional SW. In terms of damage accumulation, the proposed SW system is nearly undamaged compared to the conventional wall system, which was severely damaged at the wall-base region. Overall, the introduced concept presents a feasible solution for R/C structures when a low-damage design is targeted, which can improve the seismic performance of the structural system significantly.

Chest wall mobility is related to respiratory muscle strength and lung volumes in healthy subjects.

PubMed

Lanza, Fernanda de Cordoba; de Camargo, Anderson Alves; Archija, Lilian Rocha Ferraz; Selman, Jessyca Pachi Rodrigues; Malaguti, Carla; Dal Corso, Simone

2013-12-01

Chest wall mobility is often measured in clinical practice, but the correlations between chest wall mobility and respiratory muscle strength and lung volumes are unknown. We investigate the associations between chest wall mobility, axillary and thoracic cirtometry values, respiratory muscle strength (maximum inspiratory pressure and maximum expiratory pressure), and lung volumes (expiratory reserve volume, FEV(1), inspiratory capacity, FEV(1)/FVC), and the determinants of chest mobility in healthy subjects. In 64 healthy subjects we measured inspiratory capacity, FVC, FEV(1), expiratory reserve volume, maximum inspiratory pressure, and maximum expiratory pressure, and chest wall mobility via axillary and thoracic cirtometry. We used linear regression to evaluate the influence of the measured variables on chest wall mobility. The subjects' mean ± SD values were: age 24 ± 3 years, axillary cirtometry 6.3 ± 2.0 cm, thoracic cirtometry 7.5 ± 2.3 cm; maximum inspiratory pressure 90.4 ± 10.6% of predicted, maximum expiratory pressure 92.8 ± 13.5% of predicted, inspiratory capacity 99.7 ± 8.6% of predicted, FVC 101.9 ± 10.6% of predicted, FEV(1) 98.2 ± 10.3% of predicted, expiratory reserve volume 90.9 ± 19.9% of predicted. There were significant correlations between axillary cirtometry and FVC (r = 0.32), FEV(1) (r = 0.30), maximum inspiratory pressure (r = 0.48), maximum expiratory pressure (r = 0.25), and inspiratory capacity (r = 0.24), and between thoracic cirtometry and FVC (r = 0.50), FEV(1) (r = 0.48), maximum inspiratory pressure (r = 0.46), maximum expiratory pressure (r = 0.37), inspiratory capacity (r = 0.39), and expiratory reserve volume (r = 0.47). In multiple regression analysis the variable that best explained the axillary cirtometry variation was maximum inspiratory pressure (R(2) 0.23), and for thoracic cirtometry it was FVC and maximum inspiratory pressure (R(2) 0.32). Chest mobility in healthy subjects is related to respiratory muscle strength and lung function; the higher the axillary cirtometry and thoracic cirtometry values, the greater the maximum inspiratory pressure, maximum expiratory pressure, and lung volumes in healthy subjects.

Design and Fabrication of Anatomical Bioreactor Systems Containing Alginate Scaffolds for Cartilage Tissue Engineering

PubMed Central

Gharravi, Anneh Mohammad; Orazizadeh, Mahmoud; Ansari-Asl, Karim; Banoni, Salem; Izadi, Sina; Hashemitabar, Mahmoud

2012-01-01

The aim of the present study was to develop a tissue-engineering approach through alginate gel molding to mimic cartilage tissue in a three-dimensional culture system. The perfusion biomimetic bioreactor was designed to mimic natural joint. The shear stresses exerting on the bioreactor chamber were calculated by Computational Fluid Dynamic (CFD). Several alginate/bovine chondrocyte constructs were prepared, and were cultured in the bioreactor. Histochemical and immunohistochemical staining methods for the presence of glycosaminoglycan(GAG), overall matrix production and type II collagen protein were performed, respectively. The dynamic mechanical device applied a linear mechanical displacement of 2 mm to 10 mm. The CFD modeling indicated peak velocity and maximum wall shear stress were 1.706×10−3 m/s and 0.02407 dyne/cm 2, respectively. Histochemical and immunohistochemical analysis revealed evidence of cartilage-like tissue with lacunas similar to those of natural cartilage and the production of sulfated GAG of matrix by the chondrons, metachromatic territorial matrix-surrounded cells and accumulation of type II collagen around the cells. The present study indicated that when chondrocytes were seeded in alginate hydrogel and cultured in biomimetic cell culture system, cells survived well and secreted newly synthesized matrix led to improvement of chondrogenesis. PMID:23408660

Formation and differentiation of three-dimensional rat marrow stromal cell culture on microcarriers in a rotating-wall vessel

NASA Technical Reports Server (NTRS)

Qiu, Q.; Ducheyne, P.; Gao, H.; Ayyaswamy, P.

1998-01-01

Using a high aspect ratio vessel (HARV), this study investigated the formation of 3-D rat marrow stromal cell culture on microcarriers and the expression of bone-related biochemical markers under conditions of simulated microgravity. In addition, it calculated the shear stresses imparted on the surface of microcarriers of different densities by the medium fluid in an HARV. Secondary rat marrow stromal cells were cultured on two types of microcarriers, Cytodex-3 beads and modified bioactive glass particles. Examination of cellular morphology by scanning electron microscopy revealed the presence of three-dimensional multicellular aggregates consisting of multiple cell-covered Cytodex-3 microcarriers bridged together. Mineralization was observed in the aggregates. Spherical cell-bead aggregates were observed in an HARV, while cell-bead assemblies were mostly loosely packed in a chain-like or branched structure in a cell bag. The expressions of alkaline phosphatase activity, collagen type I, and osteopontin were shown via the use of histochemical staining, immunolabeling, and confocal scanning electron microscopy. Using a numerical approach, it was found that at a given rotational speed and for a given culture medium, a larger density difference between the microcarrier and the culture medium (e.g., a modified bioactive glass particle) imparted a higher maximum shear stress on the microcarrier.

Turbulence production near walls: The role of flow structures with spanwise asymmetry

NASA Technical Reports Server (NTRS)

Alfredsson, P. Henrik; Johansson, Arne V.; Kim, John

1988-01-01

Space-time evolution of near wall flow structures is described by conditional sampling methods, in which conditional averages are formed at various stages of development of shear layer structures. The development of spanwise asymmetry of the structures was found to be important in the creation of the structures and for the process of turbulence production.

Similarity between turbulent kinetic energy and temperature spectra in the near-wall region

NASA Technical Reports Server (NTRS)

Antonia, R. A.; Kim, J.

1991-01-01

The similarity between turbulent kinetic energy and temperature spectra, previously confirmed using experimental data in various turbulent shear flows, is validated in the near-wall region using direct numerical simulation data in a fully developed turbulent channel flow. The dependence of this similarity on the molecular Prandtl number is also examined.

Generalized wall function and its application to compressible turbulent boundary layer over a flat plate

NASA Astrophysics Data System (ADS)

Liu, J.; Wu, S. P.

2017-04-01

Wall function boundary conditions including the effects of compressibility and heat transfer are improved for compressible turbulent boundary flows. Generalized wall function formulation at zero-pressure gradient is proposed based on coupled velocity and temperature profiles in the entire near-wall region. The parameters in the generalized wall function are well revised. The proposed boundary conditions are integrated into Navier-Stokes computational fluid dynamics code that includes the shear stress transport turbulence model. Numerical results are presented for a compressible boundary layer over a flat plate at zero-pressure gradient. Compared with experimental data, the computational results show that the generalized wall function reduces the first grid spacing in the directed normal to the wall and proves the feasibility and effectivity of the generalized wall function method.

Fluid-Structure Interaction Modeling of Intracranial Aneurysm Hemodynamics: Effects of Different Assumptions

NASA Astrophysics Data System (ADS)

Rajabzadeh Oghaz, Hamidreza; Damiano, Robert; Meng, Hui

2015-11-01

Intracranial aneurysms (IAs) are pathological outpouchings of cerebral vessels, the progression of which are mediated by complex interactions between the blood flow and vasculature. Image-based computational fluid dynamics (CFD) has been used for decades to investigate IA hemodynamics. However, the commonly adopted simplifying assumptions in CFD (e.g. rigid wall) compromise the simulation accuracy and mask the complex physics involved in IA progression and eventual rupture. Several groups have considered the wall compliance by using fluid-structure interaction (FSI) modeling. However, FSI simulation is highly sensitive to numerical assumptions (e.g. linear-elastic wall material, Newtonian fluid, initial vessel configuration, and constant pressure outlet), the effects of which are poorly understood. In this study, a comprehensive investigation of the sensitivity of FSI simulations in patient-specific IAs is investigated using a multi-stage approach with a varying level of complexity. We start with simulations incorporating several common simplifications: rigid wall, Newtonian fluid, and constant pressure at the outlets, and then we stepwise remove these simplifications until the most comprehensive FSI simulations. Hemodynamic parameters such as wall shear stress and oscillatory shear index are assessed and compared at each stage to better understand the sensitivity of in FSI simulations for IA to model assumptions. Supported by the National Institutes of Health (1R01 NS 091075-01).

Latest Developments on Obtaining Accurate Measurements with Pitot Tubes in ZPG Turbulent Boundary Layers

NASA Astrophysics Data System (ADS)

Nagib, Hassan; Vinuesa, Ricardo

2013-11-01

Ability of available Pitot tube corrections to provide accurate mean velocity profiles in ZPG boundary layers is re-examined following the recent work by Bailey et al. Measurements by Bailey et al., carried out with probes of diameters ranging from 0.2 to 1.89 mm, together with new data taken with larger diameters up to 12.82 mm, show deviations with respect to available high-quality datasets and hot-wire measurements in the same Reynolds number range. These deviations are significant in the buffer region around y+ = 30 - 40 , and lead to disagreement in the von Kármán coefficient κ extracted from profiles. New forms for shear, near-wall and turbulence corrections are proposed, highlighting the importance of the latest one. Improved agreement in mean velocity profiles is obtained with new forms, where shear and near-wall corrections contribute with around 85%, and remaining 15% of the total correction comes from turbulence correction. Finally, available algorithms to correct wall position in profile measurements of wall-bounded flows are tested, using as benchmark the corrected Pitot measurements with artificially simulated probe shifts and blockage effects. We develop a new scheme, κB - Musker, which is able to accurately locate wall position.