Flow Studies in Basilar Tip Aneurysm Models
NASA Astrophysics Data System (ADS)
Cole, Russell; Selby, Kathy; Saloner, David; Savas, Omer
2001-11-01
Particle image velocimetry and flow visualization are performed on two models of basilar tip bifurcation aneurysms. The models are intended to correspond to an aneurysm at two stages during its growth. The models are subject to steady flow conditions covering the physiological range of Reynold’s numbers while being subject to both symmetric and asymmetric outflow conditions. A brief investigation is also made using pulsatile input flow with a physiologically representative waveform. Experiment showed a general pattern of increasing unsteadiness in the aneurysm head with increasing Reynold’s number. Only for a case of a small-headed model and asymmetric outflow could a quasi-stable flow pattern be established. For the same model with symmetric outflow conditions, instability in the aneurysm head occurs at the low end of physiological Reynold’s numbers. A larger-headed aneurysm model displayed a similar onset of instability for both symmetric and asymmetric outflow conditions, with flow within the aneurysm head being less pronounced than the small-headed model.
Experimental flow studies in an elastic Y-model.
Mijovic, Budimir; Liepsch, Dieter
2003-01-01
To determine the causes and history of atherosclerosis it is necessary to understand the hemodynamic parameters of blood circulation. Hemodynamic parameters play an important role in the formation of atherosclerotic plaques, especially near bends and bifurcations where the flow separates from the wall. Here the flow is laminar and non-axial with eddies, secondary flow, flow separation and stagnation points. Stenoses are found predominantly in flow separation areas. Therefore, it is important to separately study the following flow parameters: steady and pulsatile flow, wall elasticity and non-Newtonian flow behavior of blood. A simplified silicon elastic y-model simulating the human carotid artery was used for the analysis of these parameters. This model can be used for numerical studies as well. Flow was visualized at steady flow using dyes and at pulsatile flow with a photoelastic apparatus and a birefringent solution. The local axial velocity at steady and pulsatile flow was determined with a one-component Laser-Doppler-Anemometer (LDA). Pulsatile flow was generated by a piston membrane pump. A glycerin-water solution was used to simulate the Newtonian flow behavior of blood. A DMSO-Separan water solution was used to simulate the non-Newtonian flow behavior. Pulsatile flow creates higher and lower shear rates so called oscillating shear rate compare to steady flow depending on the velocity amplitude. The non-Newtonian fluid showed a markedly different flow behavior than the Newtonian fluid especially in areas of flow separation. Shear gradients were calculated from these velocity measurements using a bicubic spline interpolation. Shear stresses were calculated from these velocity shear gradients and the viscosity of the non-Newtonian fluid at these shear gradients. At special areas, high shear stresses > 10 Pa were found. The elasticity of the model wall also influences the flow behavior. The measurements showed that the characteristics of pulsatile flow and the
A preliminary study to Assess Model Uncertainties in Fluid Flows
Marc Oliver Delchini; Jean C. Ragusa
2009-09-01
The goal of this study is to assess the impact of various flow models for a simplified primary coolant loop of a light water nuclear reactor. The various fluid flow models are based on the Euler equations with an additional friction term, gravity term, momentum source, and energy source. The geometric model is purposefully chosen simple and consists of a one-dimensional (1D) loop system in order to focus the study on the validity of various fluid flow approximations. The 1D loop system is represented by a rectangle; the fluid is heated up along one of the vertical legs and cooled down along the opposite leg. A pressurizer and a pump are included in the horizontal legs. The amount of energy transferred and removed from the system is equal in absolute value along the two vertical legs. The various fluid flow approximations are compressible vs. incompressible, and complete momentum equation vs. Darcy’s approximation. The ultimate goal is to compute the fluid flow models’ uncertainties and, if possible, to generate validity ranges for these models when applied to reactor analysis. We also limit this study to single phase flows with low-Mach numbers. As a result, sound waves carry a very small amount of energy in this particular case. A standard finite volume method is used for the spatial discretization of the system.
Study of flow through a bowl mill model
Murty, G.V.R.; Babu, U.S.
1998-07-01
Bowl Mills are used in Thermal Power plants for pulverizing the raw coal, while drying, to the required fineness and achieve the desired combustion efficiency in the boiler. The Indian coals contain high ash content (some times as high as 60%) and as such the primary air has to handle media of different density namely the coal and the quartz. In this context, the distribution of air in the mill plays a significant role in the lifting of particles from the mill. The wear on the rotating components is increased through repetitive grinding because of improper distribution of air within the mill. Reduction of wear and enhancement of life of mill internals including the rotating components is a continuing goal and few more studies have been carried out in this direction. One such study is the replacement of rotating vane wheel and deflector in the separator body with an air guide ring and air diversion plate. Model studies have been carried out by traversing a five hole prove at different locations within the mill to study the distribution of flow as a result of this modification. The variation of absolute velocity and the associated flow direction has been calculated to describe the flow structure within the mill. The results are presented in non dimensional form to draw suitable conclusions. The present study indicated the possibility of improvement in the distribution of flow within the mill with increased magnitude of velocity at different locations.
Physical Model Study: Rill Erosion Morphology and Flow Conditions
NASA Astrophysics Data System (ADS)
Strohmeier, S.; Klik, A.; Nouwakpo, S. K.
2012-04-01
Using common catchment size erosion model software either lack of knowledge or lack in process ability of watershed characteristics leads to increasing simplifications in model assumptions. Referring to open channel hydraulics, erosion model equations are prevalently based on stepwise uniform flow condition requirements. Approaching balance of gravitational and frictional resistance forces, channel roughness is fundamental model input. The fusion of simplified model assumptions and the use of lumped roughness determination cause ambivalence in model calibration. By means of a physical model experiment at the National Soil Erosion Laboratory (NSERL), West Lafayette, USA, channel roughness was itemized into skin friction and channel shape friction due to rill morphology. Particularly the Manning-Strickler equation was analyzed concerning the applicability of constant and holistic factors describing boundary friction impacts. The insufficiency in using the Manning-Strickler equation for non-uniform flow conditions is widely advised, whereas lack in predictability in rill erosion development inhibits proper model adoptions. The aim of the present study is to determine the impact of channel morphology on roughness assessment in rill erosion scale. Therefore a 1.9 meter long, 0.6 meter wide and 0.3 meter deep flume with an inclination of 10 % was filled with a loamy soil representing a section of a hill slope. The soil was prepared and saturated by simulated rainfall before each model run. A single erosion channel was enforced to develop by means of steady state runoff. Two different erosion channel types were initiated and observed: I.) a Straight Constrained Rill (SCR) shape by concentration of the runoff into a prepared straight initial rill and II.) a Free Developing Rill (FDR) by back-cut erosion through the plain soil body. Discharge of the outflow was measured in 5 minute interval and outflow sediment concentration was measured every minute. A top view stereo
Modeling study of terminal transients of blood flow
NASA Astrophysics Data System (ADS)
Stiukhina, Elena S.; Postnov, Dmitry E.
2016-04-01
In spite of growing body of experimental and theoretical results on blood flow (BF) patterns under the continuously sustained circulation, much less is known about BF dynamics under the exceptional, but still important cases of venous or arterial occlusion used in medical probes. Since these conditions finally lead to complete or nearly complete stop of red blood cells (RBC) motion, we term it as TTBF, being the Terminal Transients of Blood Flow. An extreme case of such transients is the ultimate extinction of BF after the stopping of heart contractions, during which it is governed by gravitation, some vascular-originated propulsion mechanisms, and, possibly, by RBC aggregation. Quite little is known about this process, while reports the detectable post-mortal motion of mice RBC during at least 2 hours. In our work we present the modeling study of TTBF patterns due to gravitational forces. We present the minimalistic model configuration of vasculature in order to simulate what happens immediately after the pumping of blood has been stopped. Our main findings are concerned to reversal of arterial BF, as well as to duration and non-monotonicity of transients.
NASA Technical Reports Server (NTRS)
Cappelli, Daniele; Mansour, Nagi N.
2012-01-01
Separation can be seen in most aerodynamic flows, but accurate prediction of separated flows is still a challenging problem for computational fluid dynamics (CFD) tools. The behavior of several Reynolds Averaged Navier-Stokes (RANS) models in predicting the separated ow over a wall-mounted hump is studied. The strengths and weaknesses of the most popular RANS models (Spalart-Allmaras, k-epsilon, k-omega, k-omega-SST) are evaluated using the open source software OpenFOAM. The hump ow modeled in this work has been documented in the 2004 CFD Validation Workshop on Synthetic Jets and Turbulent Separation Control. Only the baseline case is treated; the slot flow control cases are not considered in this paper. Particular attention is given to predicting the size of the recirculation bubble, the position of the reattachment point, and the velocity profiles downstream of the hump.
Comparative study of turbulence models in predicting hypersonic inlet flows
NASA Technical Reports Server (NTRS)
Kapoor, Kamlesh; Anderson, Bernhard H.; Shaw, Robert J.
1992-01-01
A numerical study was conducted to analyze the performance of different turbulence models when applied to the hypersonic NASA P8 inlet. Computational results from the PARC2D code, which solves the full two-dimensional Reynolds-averaged Navier-Stokes equation, were compared with experimental data. The zero-equation models considered for the study were the Baldwin-Lomax model, the Thomas model, and a combination of the Baldwin-Lomax and Thomas models; the two-equation models considered were the Chien model, the Speziale model (both low Reynolds number), and the Launder and Spalding model (high Reynolds number). The Thomas model performed best among the zero-equation models, and predicted good pressure distributions. The Chien and Speziale models compared wery well with the experimental data, and performed better than the Thomas model near the walls.
Comparative study of turbulence models in predicting hypersonic inlet flows
NASA Technical Reports Server (NTRS)
Kapoor, Kamlesh; Anderson, Bernhard H.; Shaw, Robert J.
1992-01-01
A numerical study was conducted to analyze the performance of different turbulence models when applied to the hypersonic NASA P8 inlet. Computational results from the PARC2D code, which solves the full two-dimensional Reynolds-averaged Navier-Stokes equation, were compared with experimental data. The zero-equation models considered for the study were the Baldwin-Lomax model, the Thomas model, and a combination of the Baldwin-Lomax and Thomas models; the two-equation models considered were the Chien model, the Speziale model (both low Reynolds number), and the Launder and Spalding model (high Reynolds number). The Thomas model performed best among the zero-equation models, and predicted good pressure distributions. The Chien and Speziale models compared very well with the experimental data, and performed better than the Thomas model near the walls.
NASA Astrophysics Data System (ADS)
Shokri, Ali; Bardsley, William Earl
2016-06-01
Hydrological and hydrogeological investigation of drained land is a complex and integrated procedure. The scale of drainage studies may vary from a high-resolution small scale project through to comprehensive catchment or regional scale investigations. This wide range of scales and integrated system behaviour poses a significant challenge for the development of suitable drainage models. Toward meeting these requirements, a fully distributed coupled surface-subsurface flow model titled DrainFlow has been developed and is described. DrainFlow includes both the diffusive wave equation for surface flow components (overland flow, open drain, tile drain) and Richard's equation for saturated/unsaturated zones. To overcome the non-linearity problem created from switching between wet and dry boundaries, a smooth transitioning technique is introduced to buffer the model at tile drains and at interfaces between surface and subsurface flow boundaries. This gives a continuous transition between Dirichlet and Neumann boundary conditions. DrainFlow is tested against five well-known integrated surface-subsurface flow benchmarks. DrainFlow as applied to some synthetic drainage study examples is quite flexible for changing all or part of the model dimensions as required by problem complexity, problem scale, and data availability. This flexibility enables DrainFlow to be modified to allow for changes in both scale and boundary conditions, as often encountered in real-world drainage studies. Compared to existing drainage models, DrainFlow has the advantage of estimating actual infiltration directly from the partial differential form of Richard's equation rather than through analytical or empirical infiltration approaches like the Green and Ampt equation.
NASA Technical Reports Server (NTRS)
Ghorashi, Bahman
1995-01-01
This report includes copies of relevant publications, including conference proceedings, resulting from studies funded by NAG3-1010. Topics include flow visualization, LDV (laser doppler velocimeter), straight and curved simulations, and kinetics modeling of nitrogen oxides, including a turbulent mixing model for O2 and a maximum mixedness model.
Experimental and modeling studies of two-phase flow in pipelines
Manabe, Ryo; Tochikawa, Tetsuro; Tsukuda, M.; Arihara, Norio
1997-11-01
The objectives of this study are to develop and evaluate a mechanistic model for gas/liquid two-phase flow in pipelines. A mechanistic model has been developed by combining currently available models and correlations. The approach of the modeling study was based on the work by Xiao et al. Modifications have been made on the annular flow model by implementing the currently developed film-thickness-distribution model. An experimental database has been developed for model evaluation. Seventy-five runs of steady-state air/water flow tests in horizontal and slightly inclined pipes were conducted using a large-scale experimental facility. The experimental program was set up in a wide range of experimental conditions to cover the intermittent, dispersed bubble, and annular flow patterns. An evaluation of the model was carried out for each flow pattern, namely, intermittent, dispersed bubble, and annular flow. The comparisons between the measured and calculated pressure drops show good agreement for each flow pattern. Also, overall evaluation revealed that the proposed model provided the best performance among the commonly used empirical correlations, such as Beggs and Brill, Mukherjee and Brill, and Dukler et al.
NASA Technical Reports Server (NTRS)
Bjarke, Lisa J.
1991-01-01
During flight testing of the AFTI/F111 aircraft, horizontal tail buffet was observed. Flutter analysis ruled out any aeroelastic instability, so a water-tunnel flow visualization study was conducted to investigate possible flow disturbances on the horizontal tail which might cause buffet. For this study, a 1/48-scale model was used. Four different wing cambers and one horizontal tail setting were tested between 0 and 20 deg angle of attack. These wing cambers corresponded to the following leading training edge deflections: 0/2, 10/10, 10/2, and 0/10. Flow visualization results in the form of still photographs are presented for each of the four wing cambers between 8 and 12 deg angle of attack. In general, the horizontal tail experiences flow disturbances which become more pronounced with angle of attack or wing trailing-edge deflection.
NASA Astrophysics Data System (ADS)
Freydier, Perrine; Chambon, Guillaume; Naaim, Mohamed
2016-04-01
Rheological studies concerning natural muddy debris flows have shown that these materials can be modelled as non-Newtonian viscoplastic fluids. These complex flows are generally represented using models based on a depth-integrated approach (Shallow Water) that take into account closure terms depending on the shape of the velocity profile. But to date, there is poor knowledge about the shape of velocity profiles and the position of the interface between sheared and unsheared regions (plug) in these flows, especially in the vicinity of the front. In this research, the internal dynamics of a free-surface viscoplastic flow down an inclined channel is investigated and compared to the predictions of a Shallow Water model based on the lubrication approximation. Experiments are conducted in an inclined channel whose bottom is constituted by an upward-moving conveyor belt with controlled velocity, which allows generating and observing gravity-driven stationary surges in the laboratory frame. Carbopol microgel has been used as a homogeneous and transparent viscoplastic fluid. High-resolution measurements of velocity field is performed through optical velocimetry techniques both in the uniform zone and within the front zone where flow thickness is variable and where recirculation takes place. Specific analyses have been developed to determine the position of the plug within the surge. Flow height is accessible through image processing and ultrasonic sensors. Sufficiently far from the front, experimental results are shown to be in good agreement with theoretical predictions regarding the velocity profiles and the flow height evolution. In the vicinity of the front, however, analysis of measured velocity profiles shows an evolution of the plug different from that predicted by lubrication approximation. Accordingly, the free surface shape also deviates from the predictions of the classical Shallow Water model. These results highlight the necessity to take into account higher
Turbulence model sensitivity and scour gap effect of unsteady flow around pipe: a CFD study.
Ali, Abbod; Sharma, R K; Ganesan, P; Akib, Shatirah
2014-01-01
A numerical investigation of incompressible and transient flow around circular pipe has been carried out at different five gap phases. Flow equations such as Navier-Stokes and continuity equations have been solved using finite volume method. Unsteady horizontal velocity and kinetic energy square root profiles are plotted using different turbulence models and their sensitivity is checked against published experimental results. Flow parameters such as horizontal velocity under pipe, pressure coefficient, wall shear stress, drag coefficient, and lift coefficient are studied and presented graphically to investigate the flow behavior around an immovable pipe and scoured bed.
Study of an engine flow diverter system for a large scale ejector powered aircraft model
NASA Technical Reports Server (NTRS)
Springer, R. J.; Langley, B.; Plant, T.; Hunter, L.; Brock, O.
1981-01-01
Requirements were established for a conceptual design study to analyze and design an engine flow diverter system and to include accommodations for an ejector system in an existing 3/4 scale fighter model equipped with YJ-79 engines. Model constraints were identified and cost-effective limited modification was proposed to accept the ejectors, ducting and flow diverter valves. Complete system performance was calculated and a versatile computer program capable of analyzing any ejector system was developed.
Parallelisation study of a three-dimensional environmental flow model
NASA Astrophysics Data System (ADS)
O'Donncha, Fearghal; Ragnoli, Emanuele; Suits, Frank
2014-03-01
There are many simulation codes in the geosciences that are serial and cannot take advantage of the parallel computational resources commonly available today. One model important for our work in coastal ocean current modelling is EFDC, a Fortran 77 code configured for optimal deployment on vector computers. In order to take advantage of our cache-based, blade computing system we restructured EFDC from serial to parallel, thereby allowing us to run existing models more quickly, and to simulate larger and more detailed models that were previously impractical. Since the source code for EFDC is extensive and involves detailed computation, it is important to do such a port in a manner that limits changes to the files, while achieving the desired speedup. We describe a parallelisation strategy involving surgical changes to the source files to minimise error-prone alteration of the underlying computations, while allowing load-balanced domain decomposition for efficient execution on a commodity cluster. The use of conjugate gradient posed particular challenges due to implicit non-local communication posing a hindrance to standard domain partitioning schemes; a number of techniques are discussed to address this in a feasible, computationally efficient manner. The parallel implementation demonstrates good scalability in combination with a novel domain partitioning scheme that specifically handles mixed water/land regions commonly found in coastal simulations. The approach presented here represents a practical methodology to rejuvenate legacy code on a commodity blade cluster with reasonable effort; our solution has direct application to other similar codes in the geosciences.
Jennings, M.E.; Land, L.F.
1977-01-01
Simulation studies were made of flow and sediment transport for the Atchafalaya River basin, Louisiana using a mathematical model calibrated and supplied by the Hydrologic Engineering Center and the New Orleans District, U.S. Army Corps of Engineers. The study results are based on three, 50-year computer simulations for the following alternatives: (1) no-action alternative, (2) channelization with a center-channel flow area of 80,000 sq ft, and (3) channelization with a center-channel flow area of 100,000 sq ft. Analyses of the simulated data base for depth-frequency, inundated-area, floodway cross-section and water-surface profile relationships were made for 10 flow rates. The analyses indicate a general trend of aggradation in the lower part of the floodway with a consequent trend toward increasing the inundated area, especially at higher flood flows. (Woodard-USGS)
Sott, Kristin; Gebäck, Tobias; Pihl, Maria; Lorén, Niklas; Hermansson, Anne-Marie; Heintz, Alexei; Rasmuson, Anders
2013-05-15
A methodology for studying flow in heterogeneous soft microstructures has been developed. The methodology includes: (1) model fractal or random heterogeneous microstructures fabricated in PDMS and characterised using CLSM; (2) μPIV measurements; (3) Lattice-Boltzmann simulations of flow. It has been found that the flow behaviour in these model materials is highly dependent on pore size as well as on the connectivity and occurrence of dead ends. The experimental flow results show good agreement with predictions from the Lattice-Boltzmann modelling. These simulations were performed in geometries constructed from 3D CLSM images of the actual PDMS structures. Given these results, mass transport behaviour may be predicted for even more complex structures, like gels or composite material in, e.g., food or biomaterials. This is a step in the direction towards predictive science with regards to tailoring soft biomaterials for specific mass transport properties.
Physics-driven CFD modeling of complex anatomical cardiovascular flows-a TCPC case study.
Pekkan, Kerem; de Zélicourt, Diane; Ge, Liang; Sotiropoulos, Fotis; Frakes, David; Fogel, Mark A; Yoganathan, Ajit P
2005-03-01
Recent developments in medical image acquisition combined with the latest advancements in numerical methods for solving the Navier-Stokes equations have created unprecedented opportunities for developing simple and reliable computational fluid dynamics (CFD) tools for meeting patient-specific surgical planning objectives. However, for CFD to reach its full potential and gain the trust and confidence of medical practitioners, physics-driven numerical modeling is required. This study reports on the experience gained from an ongoing integrated CFD modeling effort aimed at developing an advanced numerical simulation tool capable of accurately predicting flow characteristics in an anatomically correct total cavopulmonary connection (TCPC). An anatomical intra-atrial TCPC model is reconstructed from a stack of magnetic resonance (MR) images acquired in vivo. An exact replica of the computational geometry was built using transparent rapid prototyping. Following the same approach as in earlier studies on idealized models, flow structures, pressure drops, and energy losses were assessed both numerically and experimentally, then compared. Numerical studies were performed with both a first-order accurate commercial software and a recently developed, second-order accurate, in-house flow solver. The commercial CFD model could, with reasonable accuracy, capture global flow quantities of interest such as control volume power losses and pressure drops and time-averaged flow patterns. However, for steady inflow conditions, both flow visualization experiments and particle image velocimetry (PIV) measurements revealed unsteady, complex, and highly 3D flow structures, which could not be captured by this numerical model with the available computational resources and additional modeling efforts that are described. Preliminary time-accurate computations with the in-house flow solver were shown to capture for the first time these complex flow features and yielded solutions in good
Steady-state and dynamic models of unified power flow controller (UPFC) for power system studies
Nabavi-Niaki, A.; Iravani, M.R.
1996-11-01
This paper provides comprehensive development procedures and final forms of mathematical models of unified power flow controller (UPFC) for steady-state, transient stability and eigenvalue studies. Based on the developed models, the impacts of control strategy, parameters and location of UPFC on power system operating conditions are discussed. The accuracy of the developed models is verified through comparing the study results with those obtained from detailed time-domain simulation using the Electromagnetic Transients Program (EMTP).
The performance & flow visualization studies of three-dimensional (3-D) wind turbine blade models
NASA Astrophysics Data System (ADS)
Sutrisno, Prajitno, Purnomo, W., Setyawan B.
2016-06-01
Recently, studies on the design of 3-D wind turbine blades have a less attention even though 3-D blade products are widely sold. In contrary, advanced studies in 3-D helicopter blade tip have been studied rigorously. Studies in wind turbine blade modeling are mostly assumed that blade spanwise sections behave as independent two-dimensional airfoils, implying that there is no exchange of momentum in the spanwise direction. Moreover, flow visualization experiments are infrequently conducted. Therefore, a modeling study of wind turbine blade with visualization experiment is needed to be improved to obtain a better understanding. The purpose of this study is to investigate the performance of 3-D wind turbine blade models with backward-forward swept and verify the flow patterns using flow visualization. In this research, the blade models are constructed based on the twist and chord distributions following Schmitz's formula. Forward and backward swept are added to the rotating blades. Based on this, the additional swept would enhance or diminish outward flow disturbance or stall development propagation on the spanwise blade surfaces to give better blade design. Some combinations, i. e., b lades with backward swept, provide a better 3-D favorable rotational force of the rotor system. The performance of the 3-D wind turbine system model is measured by a torque meter, employing Prony's braking system. Furthermore, the 3-D flow patterns around the rotating blade models are investigated by applying "tuft-visualization technique", to study the appearance of laminar, separated, and boundary layer flow patterns surrounding the 3-dimentional blade system.
Modelling pulmonary blood flow.
Tawhai, Merryn H; Burrowes, Kelly S
2008-11-30
Computational model analysis has been used widely to understand and interpret complexity of interactions in the pulmonary system. Pulmonary blood transport is a multi-scale phenomenon that involves scale-dependent structure and function, therefore requiring different model assumptions for the microcirculation and the arterial or venous flows. The blood transport systems interact with the surrounding lung tissue, and are dependent on hydrostatic pressure gradients, control of vasoconstriction, and the topology and material composition of the vascular trees. This review focuses on computational models that have been developed to study the different mechanisms contributing to regional perfusion of the lung. Different models for the microcirculation and the pulmonary arteries are considered, including fractal approaches and anatomically-based methods. The studies that are reviewed illustrate the different complementary approaches that can be used to address the same physiological question of flow heterogeneity.
NASA Astrophysics Data System (ADS)
Kadian, Arun Kumar; Biswas, Pankaj
2015-10-01
Friction stir welding has been quite successful in joining aluminum alloy which has gained importance in almost all industrial sectors over the past two decades. It is a newer technique and therefore needs more attention in many sectors, flow of material being one among them. The material flow pattern actually helps in deciding the parameters required for particular tool geometry. The knowledge of material flow is very significant in removing defects from the weldment. In the work presented in this paper, the flow behavior of AA6061 under a threaded tool has been studied. The convective heat loss has been considered from all the surfaces, and a comparative study has been made with and without the use of temperature-dependent properties and their significance in the finite volume method model. The two types of models that have been implemented are turbulent and laminar models. Their thermal histories have been studied for all the cases. The material flow velocity has been analyzed to predict the flow of material. A swirl inside the weld material has been observed in all the simulations.
A low-order model for flow control studies in cylinder wakes
NASA Astrophysics Data System (ADS)
Balasubramanian, Ganapathi; Olinger, David J.; Demetriou, Michael
1998-11-01
Control of three-dimensional wake structures behind circular cylinders is investigated using a previously developed coupled map lattice. The map consists of circle map oscillators along the cylinder span coupled by a diffusion model. Our goal is to develop an efficient model for flow control studies in cylinder wakes. Complex vortex shedding patterns, such as vortex dislocations and frequency cells, are observed behind vibrating cables in uniform freestream flows and stationary cylinders in sheared flows. These structures are controlled by the addition of periodic control signals to the forcing term in the map. Discontinuous nonlinear control theory is used to derive the control laws. Parallel shedding is realized for the case of uniform flow and oblique shedding is achieved for sheared inflows. The effectiveness of the discontinuous nonlinear control theory is compared with the previous application of chaos control theory to the coupled map lattice.
Flow visualization studies of VTOL aircraft models during Hover in ground effect
NASA Technical Reports Server (NTRS)
Mourtos, Nikos J.; Couillaud, Stephane; Carter, Dale; Hange, Craig; Wardwell, Doug; Margason, Richard J.
1995-01-01
A flow visualization study of several configurations of a jet-powered vertical takeoff and landing (VTOL) aircraft model during hover in ground effect was conducted. A surface oil flow technique was used to observe the flow patterns on the lower surfaces of the model. There were significant configuration effects. Wing height with respect to fuselage, the presence of an engine inlet duct beside the fuselage, and nozzle pressure ratio are seen to have strong effects on the surface flow angles on the lower surface of the wing. This test was part of a program to improve the methods for predicting the hot gas ingestion (HGI) for jet-powered vertical/short takeoff and landing (V/STOL) aircraft. The tests were performed at the Jet Calibration and Hover Test (JCAHT) Facility at Ames Research Center.
Study of Gas Flow Characteristics in Tight Porous Media with a Microscale Lattice Boltzmann Model
NASA Astrophysics Data System (ADS)
Zhao, Jianlin; Yao, Jun; Zhang, Min; Zhang, Lei; Yang, Yongfei; Sun, Hai; An, Senyou; Li, Aifen
2016-09-01
To investigate the gas flow characteristics in tight porous media, a microscale lattice Boltzmann (LB) model with the regularization procedure is firstly adopted to simulate gas flow in three-dimensional (3D) digital rocks. A shale digital rock and a sandstone digital rock are reconstructed to study the effects of pressure, temperature and pore size on microscale gas flow. The simulation results show that because of the microscale effect in tight porous media, the apparent permeability is always higher than the intrinsic permeability, and with the decrease of pressure or pore size, or with the increase of temperature, the difference between apparent permeability and intrinsic permeability increases. In addition, the Knudsen numbers under different conditions are calculated and the results show that gas flow characteristics in the digital rocks under different Knudsen numbers are quite different. With the increase of Knudsen number, gas flow in the digital rocks becomes more uniform and the effect of heterogeneity of the porous media on gas flow decreases. Finally, two commonly used apparent permeability calculation models are evaluated by the simulation results and the Klinkenberg model shows better accuracy. In addition, a better proportionality factor in Klinkenberg model is proposed according to the simulation results.
Study of Gas Flow Characteristics in Tight Porous Media with a Microscale Lattice Boltzmann Model
Zhao, Jianlin; Yao, Jun; Zhang, Min; Zhang, Lei; Yang, Yongfei; Sun, Hai; An, Senyou; Li, Aifen
2016-01-01
To investigate the gas flow characteristics in tight porous media, a microscale lattice Boltzmann (LB) model with the regularization procedure is firstly adopted to simulate gas flow in three-dimensional (3D) digital rocks. A shale digital rock and a sandstone digital rock are reconstructed to study the effects of pressure, temperature and pore size on microscale gas flow. The simulation results show that because of the microscale effect in tight porous media, the apparent permeability is always higher than the intrinsic permeability, and with the decrease of pressure or pore size, or with the increase of temperature, the difference between apparent permeability and intrinsic permeability increases. In addition, the Knudsen numbers under different conditions are calculated and the results show that gas flow characteristics in the digital rocks under different Knudsen numbers are quite different. With the increase of Knudsen number, gas flow in the digital rocks becomes more uniform and the effect of heterogeneity of the porous media on gas flow decreases. Finally, two commonly used apparent permeability calculation models are evaluated by the simulation results and the Klinkenberg model shows better accuracy. In addition, a better proportionality factor in Klinkenberg model is proposed according to the simulation results. PMID:27587293
A one-dimensional mathematical model for studying the pulsatile flow in microvascular networks.
Pan, Qing; Wang, Ruofan; Reglin, Bettina; Cai, Guolong; Yan, Jing; Pries, Axel R; Ning, Gangmin
2014-01-01
Techniques that model microvascular hemodynamics have been developed for decades. While the physiological significance of pressure pulsatility is acknowledged, most of the microcirculatory models use steady flow approaches. To theoretically study the extent and transmission of pulsatility in microcirculation, dynamic models need to be developed. In this paper, we present a one-dimensional model to describe the dynamic behavior of microvascular blood flow. The model is applied to a microvascular network from a rat mesentery. Intravital microscopy was used to record the morphology and flow velocities in individual vessel segments, and boundaries are defined according to the experimental data. The system of governing equations constituting the model is solved numerically using the discontinuous Galerkin method. An implicit integration scheme is adopted to increase computing efficiency. The model allows the simulation of the dynamic properties of blood flow in microcirculatory networks, including the pressure pulsatility (quantified by a pulsatility index) and pulse wave velocity (PWV). From the main input arteriole to the main output venule, the pulsatility index decreases by 66.7%. PWV obtained along arterioles declines with decreasing diameters, with mean values of 77.16, 25.31, and 8.30 cm/s for diameters of 26.84, 17.46, and 13.33 μm, respectively. These results suggest that the 1D model developed is able to simulate the characteristics of pressure pulsatility and wave propagation in complex microvascular networks.
Model studies of blood flow in basilar artery with 3D laser Doppler anemometer
NASA Astrophysics Data System (ADS)
Frolov, S. V.; Sindeev, S. V.; Liepsch, D.; Balasso, A.; Proskurin, S. G.; Potlov, A. Y.
2015-03-01
It is proposed an integrated approach to the study of basilar artery blood flow using 3D laser Doppler anemometer for identifying the causes of the formation and development of cerebral aneurysms. Feature of the work is the combined usage of both mathematical modeling and experimental methods. Described the experimental setup and the method of measurement of basilar artery blood flow, carried out in an interdisciplinary laboratory of Hospital Rechts der Isar of Technical University of Munich. The experimental setup used to simulate the blood flow in the basilar artery and to measure blood flow characteristics using 3D laser Doppler anemometer (3D LDA). Described a method of numerical studies carried out in Tambov State Technical University and the Bakoulev Center for Cardiovascular Surgery. Proposed an approach for sharing experimental and numerical methods of research to identify the causes of the basilar artery aneurysms.
Application of a 2D air flow model to soil vapor extraction and bioventing case studies
Mohr, D.H.; Merz, P.H.
1995-05-01
Soil vapor extraction (SVE) is frequently the technology of choice to clean up hydrocarbon contamination in unsaturated soil. A two-dimensional air flow model provides a practical tool to evaluate pilot test data and estimate remediation rates for soil vapor extraction systems. The model predictions of soil vacuum versus distance are statistically compared to pilot test data for 65 SVE wells at 44 sites. For 17 of 21 sites where there was asphalt paving, the best agreement was obtained for boundary conditions with no barrier to air flow at the surface. The model predictions of air flow rates and stream lines around the well allow an estimate of the gasoline removal rates by both evaporation and bioremediation. The model can be used to quickly estimate the effective radius of influence, defined here as the maximum distance from the well where there is enough air flow to remove the contaminant present within the allowable time. The effective radius of influence is smaller than a radius of influence defined by soil vacuum only. For a case study, in situ bioremediation rates were estimated using the air flow model and compared to independent estimates based on changes in soil temperature. These estimate bioremediation rates for heavy fuel oil ranged from 2.5 to 11 mg oil degraded per kg soil per day, in agreement with values in the literature.
Numerical modelling study of gully recharge and debris flows in Haida Gwaii, British Columbia
NASA Astrophysics Data System (ADS)
Martin, Yvonne; Johnson, Edward; Chaikina, Olga
2015-04-01
In high mountains, debris flows are a major process responsible for transferring sediment to more downstream fluvial reaches. This sediment transfer begins on mountain hillslopes where various mass wasting processes move sediment from hillslopes to uppermost reaches of the channel system (these reaches are herein referred to as gullies and only experience water flow during high intensity precipitation events). Sediment recharge into gullies, which has received minimal attention in the scientific literature, refers to the transfer of sediment and other debris from surrounding hillslopes into gullies (Jakob and Oden, 2005). Debris flow occurrence and debris flow volumes depend on some precipitation threshold as well as volumes of material contained in the particular gully. For example, if one debris flow has removed all of the accumulated material from the gully, then any subsequent debris flow will be smaller if enough time has not yet passed for notable sediment recharge. Herein, we utilize the numerical model of landscape development, LandMod (Martin, 1998; Dadson and Church, 2005; Martin, 2007), to explore connections between hillslope processes, gully recharge rates, and transfer of sediment to downstream channel reaches in the Haida Gwaii, British Columbia. Hillslope processes in the model include shallow landsliding, bedrock failures and weathering. The updated debris flow algorithm is based on extensive field data available for debris flows in Haida Gwaii (e.g., Rood, 1984; Oden, 1994; Jakob and Oden, 2005), as well as theoretical considerations based on debris flow studies. The most significant model extension is the calculation of gully recharge rates; for each gully, the total accumulated sediment in gullies at each time step is determined using a power-law relation for area-normalized recharge rate versus elapsed time since the last debris flow. Thus, when the stochastic driver for debris flow occurrence triggers an event, the amount of stored material is
Winkel, Leah C; Hoogendoorn, Ayla; Xing, Ruoyu; Wentzel, Jolanda J; Van der Heiden, Kim
2015-07-01
Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed.
Studying Faculty Flows Using an Interactive Spreadsheet Model. AIR 1997 Annual Forum Paper.
ERIC Educational Resources Information Center
Kelly, Wayne
This paper describes a spreadsheet-based faculty flow model developed and implemented at the University of Calgary (Canada) to analyze faculty retirement, turnover, and salary issues. The study examined whether, given expected faculty turnover, the current salary increment system was sustainable in a stable or declining funding environment, and…
Cross-flow turbines: physical and numerical model studies towards improved array simulations
NASA Astrophysics Data System (ADS)
Wosnik, M.; Bachant, P.
2015-12-01
Cross-flow, or vertical-axis turbines, show potential in marine hydrokinetic (MHK) and wind energy applications. As turbine designs mature, the research focus is shifting from individual devices towards improving turbine array layouts for maximizing overall power output, i.e., minimizing wake interference for axial-flow turbines, or taking advantage of constructive wake interaction for cross-flow turbines. Numerical simulations are generally better suited to explore the turbine array design parameter space, as physical model studies of large arrays at large model scale would be expensive. However, since the computing power available today is not sufficient to conduct simulations of the flow in and around large arrays of turbines with fully resolved turbine geometries, the turbines' interaction with the energy resource needs to be parameterized, or modeled. Most models in use today, e.g. actuator disk, are not able to predict the unique wake structure generated by cross-flow turbines. Experiments were carried out using a high-resolution turbine test bed in a large cross-section tow tank, designed to achieve sufficiently high Reynolds numbers for the results to be Reynolds number independent with respect to turbine performance and wake statistics, such that they can be reliably extrapolated to full scale and used for model validation. To improve parameterization in array simulations, an actuator line model (ALM) was developed to provide a computationally feasible method for simulating full turbine arrays inside Navier--Stokes models. The ALM predicts turbine loading with the blade element method combined with sub-models for dynamic stall and flow curvature. The open-source software is written as an extension library for the OpenFOAM CFD package, which allows the ALM body force to be applied to their standard RANS and LES solvers. Turbine forcing is also applied to volume of fluid (VOF) models, e.g., for predicting free surface effects on submerged MHK devices. An
Richard Schultz
2011-09-01
The purpose of the fluid dynamics experiments in the MIR (Matched Index of-Refraction) flow system at Idaho National Laboratory (INL) is to develop benchmark databases for the assessment of Computational Fluid Dynamics (CFD) solutions of the momentum equations, scalar mixing, and turbulence models for the flow ratios between coolant channels and bypass gaps in the interstitial regions of typical prismatic standard fuel element (SFE) or upper reflector block geometries of typical Modular High-temperature Gas-cooled Reactors (MHTGR) in the limiting case of negligible buoyancy and constant fluid properties. The experiments use Particle Image Velocimetry (PIV) to measure the velocity fields that will populate the bypass flow study database.
Perrin, Christian L; Tardy, Philippe M J; Sorbie, Ken S; Crawshaw, John C
2006-03-15
The in situ rheology of polymeric solutions has been studied experimentally in etched silicon micromodels which are idealizations of porous media. The rectangular channels in these etched networks have dimensions typical of pore sizes in sandstone rocks. Pressure drop/flow rate relations have been measured for water and non-Newtonian hydrolyzed-polyacrylamide (HPAM) solutions in both individual straight rectangular capillaries and in networks of such capillaries. Results from these experiments have been analyzed using pore-scale network modeling incorporating the non-Newtonian fluid mechanics of a Carreau fluid. Quantitative agreement is seen between the experiments and the network calculations in the Newtonian and shear-thinning flow regions demonstrating that the 'shift factor,'alpha, can be calculated a priori. Shear-thickening behavior was observed at higher flow rates in the micromodel experiments as a result of elastic effects becoming important and this remains to be incorporated in the network model.
Numerical Study on a Detailed Air Flows in an Urban Area Using a CFD model
NASA Astrophysics Data System (ADS)
Kwon, A.
2014-12-01
In this study, detailed air flows in an urban area were analyzed using a computational fluid dynamics (CFD) model. For this model buildings used as the surface boundary in the model were constructed using Los Angeles Region Imagery Acquisition Consortium 2 Geographic Information System (LARIAC2 GIS) data. Three target areas centered at the cross roads of Broadway & 7th St., Olive & 12th St., and Wilshire blvd. & Carondelet, Los Angeles, California were considered. The size of each numerical domain is 400 m, 400 m, and 200 m in the x‒, y‒, and z‒directions, respectively. The grid sizes in the x‒, y‒, and z‒directions are 2 m, 2 m, and 2 m, respectively. Based on the inflow wind data provided by California Air Resources Board, detailed flow characteristics were investigated for each target area. Descending air flow were developed at the leeward area of tall building and ascending air current were occurred on the windward area of tall building. Vertically rotating vortices were formed in spaces between buildings, so-called, street canyons and horizontally rotating vortices appeared near cross roads. When flows came into narrow street canyon from wide street canyon, channeling effects appeared and flow speed increased for satisfying mass continuity.
Experimental study on unsteady open channel flow and bedload transport based on a physical model
NASA Astrophysics Data System (ADS)
Cao, W.
2015-12-01
Flow in a nature river are usually unsteady, while nearly all the theories about bedload transport are on the basis of steady, uniform flow, and also with supposed equilibrium state of sediment transport. This is may be one of the main reasons why the bedload transport formulas are notoriously poor accuracy to predict the bedload. The aim of this research is to shed light on the effect of unsteadiness on the bedload transport based on experimental studies. The novel of this study is that the experiments were not carried out in a conventional flume but in a physical model, which are more similar to the actual river. On the other hand, in our experiments, multiple consecutive flood wave were reproduced in the physical model, and all the flow and sediment parameters are based on a large number of data obtained from many of identical flood waves. This method allow us to get more data for one flood, efficiently avoids the uncertainty of bedload rate only for one single flood wave, due to the stochastic fluctuation of the bedload transport. Three different flood waves were selected in the experiments. During each run of experiment, the water level of five different positions along the model were measured by ultrasonic water level gauge, flow velocity at the middle of the channel were measured by two dimensional electromagnetic current meter. Moreover, the bedload transport rate was measured by a unique automatic trap collecting and weighing system at the end of the physical model. The results shows that the celerity of flood wave propagate varies for different flow conditions. The velocity distribution was approximately accord with log-law profile during the entire rising and falling limb of flood. The bedload transport rate show intensity fluctuation in all the experiments, moreover, for different flood waves, the moment when the shear stress reaches its maximum value is not the exact moment when the sediment transport rate reaches its maximum value, which indicates
Study of aerodynamic structure of flow in a model of vortex furnace using Stereo PIV method
NASA Astrophysics Data System (ADS)
Anufriev, I. S.; Kuibin, P. A.; Shadrin, E. Yu.; Sharaborin, D. K.; Sharypov, O. V.
2016-07-01
The aerodynamic structure of flow in a lab model of a perspective design of vortex furnace was studied. The chamber has a horizontal rotation axis, tangential inlet for fuel-air jets and vertical orientation of secondary injection nozzles. The Stereo PIV method was used for visualization of 3D velocity field for selected cross sections of the vortex combustion chamber. The experimental data along with "total pressure minimum" criterion were used for reconstruction of the vortex core of the flow. Results fit the available data from LDA and simulation.
NASA Astrophysics Data System (ADS)
Wosnik, M.; Bachant, P.
2014-12-01
Cross-flow turbines, often referred to as vertical-axis turbines, show potential for success in marine hydrokinetic (MHK) and wind energy applications, ranging from small- to utility-scale installations in tidal/ocean currents and offshore wind. As turbine designs mature, the research focus is shifting from individual devices to the optimization of turbine arrays. It would be expensive and time-consuming to conduct physical model studies of large arrays at large model scales (to achieve sufficiently high Reynolds numbers), and hence numerical techniques are generally better suited to explore the array design parameter space. However, since the computing power available today is not sufficient to conduct simulations of the flow in and around large arrays of turbines with fully resolved turbine geometries (e.g., grid resolution into the viscous sublayer on turbine blades), the turbines' interaction with the energy resource (water current or wind) needs to be parameterized, or modeled. Models used today--a common model is the actuator disk concept--are not able to predict the unique wake structure generated by cross-flow turbines. This wake structure has been shown to create "constructive" interference in some cases, improving turbine performance in array configurations, in contrast with axial-flow, or horizontal axis devices. Towards a more accurate parameterization of cross-flow turbines, an extensive experimental study was carried out using a high-resolution turbine test bed with wake measurement capability in a large cross-section tow tank. The experimental results were then "interpolated" using high-fidelity Navier--Stokes simulations, to gain insight into the turbine's near-wake. The study was designed to achieve sufficiently high Reynolds numbers for the results to be Reynolds number independent with respect to turbine performance and wake statistics, such that they can be reliably extrapolated to full scale and used for model validation. The end product of
Studying the flow dynamics of a karst aquifer system with an equivalent porous medium model.
Abusaada, Muath; Sauter, Martin
2013-01-01
The modeling of groundwater flow in karst aquifers is a challenge due to the extreme heterogeneity of its hydraulic parameters and the duality in their discharge behavior, that is, rapid response of highly conductive karst conduits and delayed drainage of the low-permeability fractured matrix after recharge events. There are a number of different modeling approaches for the simulation of the karst groundwater dynamics, applicable to different aquifer as well as modeling problem types, ranging from continuum models to double continuum models to discrete and hybrid models. This study presents the application of an equivalent porous model approach (EPM, single continuum model) to construct a steady-state numerical flow model for an important karst aquifer, that is, the Western Mountain Aquifer Basin (WMAB), shared by Israel and the West-Bank, using MODFLOW2000. The WMAB was used as a catchment since it is a well-constrained catchment with well-defined recharge and discharge components and therefore allows a control on the modeling approach, a very rare opportunity for karst aquifer modeling. The model demonstrates the applicability of equivalent porous medium models for the simulation of karst systems, despite their large contrast in hydraulic conductivities. As long as the simulated saturated volume is large enough to average out the local influence of karst conduits and as long as transport velocities are not an issue, EPM models excellently simulate the observed head distribution. The model serves as a starting basis that will be used as a reference for developing a long-term dynamic model for the WMAB, starting from the pre-development period (i.e., 1940s) up to date.
[Pulsatile flow model with elastic blood vessels for duplex ultrasound studies].
Petrick, J; Schlief, R; Zomack, M; Langholz, J; Urbank, A
1992-12-01
Using ultrasound duplex technique flow phenomena in patients' circulation can be examined. For the interpretation of these examinations it is necessary to have extensive knowledge on flow influencing parameters. This can be easily obtained from simplified flow models. This article describes the components of a flow model that allows examination of ultrasonic contrast media flowing through an artificial heart and vessel mimicking tubes. The artificial heart is the drive which pumps a water glycerol cellulose mixture through the circulation in a pulsatile manner. The shape of the ventricle, the compliance of the aorta, the viscosity of the flow medium and the wall elasticity of the examination vessel were taken into account. The attenuation caused by the surrounding tissue is simulated by a variable layer of castor oil. The flow model is suitable to produce flow profiles that are very similar to physiological profiles.
Modelling the effect of buried valleys on groundwater flow: case study in Ventspils vicinity, Latvia
NASA Astrophysics Data System (ADS)
Delina, Aija; Popovs, Konrads; Bikse, Janis; Retike, Inga; Babre, Alise; Kalvane, Gunta
2015-04-01
Buried subglacial valleys are widely distributed in glaciated regions and they can have great influence on groundwater flow and hence on groundwater resources. The aim of this study is to evaluate the effect of the buried valleys on groundwater flow in a confined aquifer (Middle Devonian Eifelian stage Arukila aquifer, D2ar) applying numerical modelling. The study area is located at vicinity of Ventspils Town, near wellfield Ogsils where number of the buried valleys with different depth and filling material are present. Area is located close to the Baltic Sea at Piejūra lowland Rinda plain and regional groundwater flow is towards sea. Territory is covered by thin layer of Quaternary sediments in thicknesses of 10 to 20 meters although Prequaternary sediments are exposed at some places. Buried valleys are characterized as narrow, elongated and deep formations that is be filled with various, mainly Pleistocene glacigene sediments - either till loam of different ages or sand and gravel or interbedding of both above mentioned. The filling material of the valleys influences groundwater flow in the confined aquifers which is intercepted by the valleys. It is supposed that glacial till loam filled valleys serves as a barrier to groundwater flow and as a recharge conduit when filled with sand and gravel deposits. Numerical model was built within MOSYS modelling system (Virbulis et al. 2012) using finite element method in order to investigate buried valley influence on groundwater flow in the study area. Several conceptual models were tested in numerical model depending on buried valley filling material: sand and gravel, till loam or mixture of them. Groundwater flow paths and travel times were studied. Results suggested that valley filled with glacial till is acting as barrier and it causes sharp drop of piezometric head and downward flow. Valley filled with sand and gravel have almost no effect on piezometric head distribution, however it this case buried valleys
NASA Technical Reports Server (NTRS)
Kavi, K. M.
1984-01-01
There have been a number of simulation packages developed for the purpose of designing, testing and validating computer systems, digital systems and software systems. Complex analytical tools based on Markov and semi-Markov processes have been designed to estimate the reliability and performance of simulated systems. Petri nets have received wide acceptance for modeling complex and highly parallel computers. In this research data flow models for computer systems are investigated. Data flow models can be used to simulate both software and hardware in a uniform manner. Data flow simulation techniques provide the computer systems designer with a CAD environment which enables highly parallel complex systems to be defined, evaluated at all levels and finally implemented in either hardware or software. Inherent in data flow concept is the hierarchical handling of complex systems. In this paper we will describe how data flow can be used to model computer system.
NASA Technical Reports Server (NTRS)
Sinha, Neeraj; Brinckman, Kevin; Jansen, Bernard; Seiner, John
2011-01-01
A method was developed of obtaining propulsive base flow data in both hot and cold jet environments, at Mach numbers and altitude of relevance to NASA launcher designs. The base flow data was used to perform computational fluid dynamics (CFD) turbulence model assessments of base flow predictive capabilities in order to provide increased confidence in base thermal and pressure load predictions obtained from computational modeling efforts. Predictive CFD analyses were used in the design of the experiments, available propulsive models were used to reduce program costs and increase success, and a wind tunnel facility was used. The data obtained allowed assessment of CFD/turbulence models in a complex flow environment, working within a building-block procedure to validation, where cold, non-reacting test data was first used for validation, followed by more complex reacting base flow validation.
Study of colloids transport during two-phase flow using a novel polydimethylsiloxane micro-model.
Zhang, Qiulan; Karadimitriou, N K; Hassanizadeh, S M; Kleingeld, P J; Imhof, A
2013-07-01
As a representation of a porous medium, a closed micro-fluidic device made of polydimethylsiloxane (PDMS), with uniform wettability and stable hydrophobic properties, was designed and fabricated. A flow network, with a mean pore size of 30 μm, was formed in a PDMS slab, covering an area of 1 mm × 10 mm. The PDMS slab was covered and bonded with a 120-μm-thick glass plate to seal the model. The glass plate was first spin-coated with a thin layer, roughly 10 μm, of PDMS. The micro-model was treated with silane in order to make it uniformly and stably hydrophobic. Fluorescent particles of 300 μm in diameter were used as colloids. It is known that more removal of colloids occurs under unsaturated conditions, compared to saturated flow in soil. At the same time, the change of saturation has been observed to cause remobilization of attached colloids. The mechanisms for these phenomena are not well understood. This is the first time that a closed micro-model, made of PDMS with uniform and stable wettability, has been used in combination with confocal microscopy to study colloid transport under transient two-phase flow conditions. With confocal microscopy, the movement of fluorescent particles and flow of two liquids within the pores can be studied. One can focus at different depths within the pores and thus determine where the particles exactly are. Thus, remobilization of attached colloids by moving fluid-fluid interfaces was visualized. In order to allow for the deposition and subsequent remobilization of colloids during two-phase flow, three micro-channels for the injection of liquids with and without colloids were constructed. An outlet channel was designed where effluent concentration breakthrough curves can be quantified by measuring the fluorescence intensity. A peak concentration also indicated in the breakthrough curve with the drainage event. The acquired images and breakthrough curve successfully confirmed the utility of the combination of such a PDMS
Hydrodynamic modelling and global datasets: Flow connectivity and SRTM data, a Bangkok case study.
NASA Astrophysics Data System (ADS)
Trigg, M. A.; Bates, P. B.; Michaelides, K.
2012-04-01
The rise in the global interconnected manufacturing supply chains requires an understanding and consistent quantification of flood risk at a global scale. Flood risk is often better quantified (or at least more precisely defined) in regions where there has been an investment in comprehensive topographical data collection such as LiDAR coupled with detailed hydrodynamic modelling. Yet in regions where these data and modelling are unavailable, the implications of flooding and the knock on effects for global industries can be dramatic, as evidenced by the recent floods in Bangkok, Thailand. There is a growing momentum in terms of global modelling initiatives to address this lack of a consistent understanding of flood risk and they will rely heavily on the application of available global datasets relevant to hydrodynamic modelling, such as Shuttle Radar Topography Mission (SRTM) data and its derivatives. These global datasets bring opportunities to apply consistent methodologies on an automated basis in all regions, while the use of coarser scale datasets also brings many challenges such as sub-grid process representation and downscaled hydrology data from global climate models. There are significant opportunities for hydrological science in helping define new, realistic and physically based methodologies that can be applied globally as well as the possibility of gaining new insights into flood risk through analysis of the many large datasets that will be derived from this work. We use Bangkok as a case study to explore some of the issues related to using these available global datasets for hydrodynamic modelling, with particular focus on using SRTM data to represent topography. Research has shown that flow connectivity on the floodplain is an important component in the dynamics of flood flows on to and off the floodplain, and indeed within different areas of the floodplain. A lack of representation of flow connectivity, often due to data resolution limitations, means
Centrifuge modeling of air sparging - a study of air flow through saturated porous media.
Marulanda, C; Culligan, P J; Germaine, J T
2000-02-25
The success of air sparging as a remedial technology for treatment of contaminated aquifers is well documented. However, there is no consensus, to date, on the mechanisms that control the flow of injected air through the saturated ground. Currently, only qualitative results from laboratory experiments are available to predict the zone of influence of a sparging well. Given that the patterns of air flow through the soil will ultimately determine the efficiency of an air sparging treatment, it is important to quantify how sparged air travels through a saturated porous medium. The main objective of this research is to develop a model that describes air transport through saturated porous media. This paper presents results from an ongoing study that employs centrifuge modeling to reproduce in situ air sparging conditions. Centrifuge testing is an experimental technique that allows reduced-scale duplication, in the laboratory, of the stresses and pressure distributions encountered in the field. In situ conditions are critical in the development of actual air flow patterns. Experiments are being conducted in a transparent porous medium consisting of crushed borosilicate glass submerged in fluids of matching indices of refraction. Air is observed as it flows through the porous medium at varying gravitational accelerations. Recorded images of experiments allow the determination of flow patterns, breakthrough velocities, and plume shapes as a function of g-level and injection pressure. Results show that air flow patterns vary from fingering, at low g-levels, to pulsing at higher accelerations. Grain and pore size distribution of the porous medium do not exclusively control air flow characteristics. Injector geometry has a definite effect on breakthrough velocities and air plume shapes. Experiments have been conducted to compare the velocity of air flow through the saturated porous medium to that of air in pure liquids. Results show that the velocity of air through the medium
A Comparative Study of Foreign Direct Investment Flow Using Diffusion Models
NASA Astrophysics Data System (ADS)
Li, Yiming; Chiang, Yi-Hui; Yu, Shao-Ming; Chiang, Su-Yun; Hung, C.-H.
2007-12-01
In this work, we apply an improvement dynamic model of the foreign direct investment (FDI) flow to analyze the evolution of FDI flow. In comparison with the fundamental growth model of FDI, the simulation result is further accurate if the asymmetric growth pattern and heterogeneity of the potential adopters are considered. According to the result, the internal influence dominates the growth of FDI flow from Taiwan to China during 2001-2006, taking the electronics industry for example.
Evolution of 3-D geologic framework modeling and its application to groundwater flow studies
Blome, Charles D.; Smith, David V.
2012-01-01
In this Fact Sheet, the authors discuss the evolution of project 3-D subsurface framework modeling, research in hydrostratigraphy and airborne geophysics, and methodologies used to link geologic and groundwater flow models.
Shen, Hua; Zhu, Yong; Qin, Kai-Rong
2016-12-01
The electrical conductivity of pulsatile blood flow in arteries is an important factor for the application of the electrical impedance measurement system in clinical settings. The electrical conductivity of pulsatile blood flow depends not only on blood-flow-induced red blood cell (RBC) orientation and deformation but also on artery wall motion. Numerous studies have investigated the conductivity of pulsatile blood based on a rigid tube model, in which the effects of wall motion on blood conductivity are not considered. In this study, integrating Ling and Atabek's local flow theory and Maxwell-Fricke theory, we develop an elastic tube model to explore the effects of wall motion as well as blood flow velocity on blood conductivity. The simulation results suggest that wall motion, rather than blood flow velocity, is the primary factor that affects the conductivity of flowing blood in arteries.
A benchmark study of numerical schemes for one-dimensional arterial blood flow modelling.
Boileau, Etienne; Nithiarasu, Perumal; Blanco, Pablo J; Müller, Lucas O; Fossan, Fredrik Eikeland; Hellevik, Leif Rune; Donders, Wouter P; Huberts, Wouter; Willemet, Marie; Alastruey, Jordi
2015-10-01
Haemodynamical simulations using one-dimensional (1D) computational models exhibit many of the features of the systemic circulation under normal and diseased conditions. Recent interest in verifying 1D numerical schemes has led to the development of alternative experimental setups and the use of three-dimensional numerical models to acquire data not easily measured in vivo. In most studies to date, only one particular 1D scheme is tested. In this paper, we present a systematic comparison of six commonly used numerical schemes for 1D blood flow modelling: discontinuous Galerkin, locally conservative Galerkin, Galerkin least-squares finite element method, finite volume method, finite difference MacCormack method and a simplified trapezium rule method. Comparisons are made in a series of six benchmark test cases with an increasing degree of complexity. The accuracy of the numerical schemes is assessed by comparison with theoretical results, three-dimensional numerical data in compatible domains with distensible walls or experimental data in a network of silicone tubes. Results show a good agreement among all numerical schemes and their ability to capture the main features of pressure, flow and area waveforms in large arteries. All the information used in this study, including the input data for all benchmark cases, experimental data where available and numerical solutions for each scheme, is made publicly available online, providing a comprehensive reference data set to support the development of 1D models and numerical schemes.
NASA Astrophysics Data System (ADS)
Jiménez, Juan; Smits, Alexander
2003-11-01
Experimental investigation over a DARPA SUBOFF submarine model (SUBOFF Model) was performed using flow visualization and Digital Particle Image Velocimetry (DPIV). The model has an axisymmetric body with sail and fins, and it was supported by a streamlined strut that was formed by the extension of the sail appendage. The range of flow conditions studied correspond to a Reynolds numbers based on model length, Re_L, of about 10^5. Velocity vector fields, turbulence intensities, vorticity fields, and flow visualization in the vicinity of the junction flows are presented. In the vicinity of the control surface and sail hull junctions, the presence of streamwise vortices in the form of horseshoe or necklace vortices locally dominates the flow. The effects of unsteady motions about an axis passing through the sail are also investigated to understand the evolution of the unsteady wake.
Flows In Model Human Femoral Arteries
NASA Technical Reports Server (NTRS)
Back, Lloyd H.; Kwack, Eug Y.; Crawford, Donald W.
1990-01-01
Flow is visualized with dye traces, and pressure measurements made. Report describes experimental study of flow in models of human femoral artery. Conducted to examine effect of slight curvature of artery on flow paths and distribution of pressure.
The role of diagenetic studies in flow-unit modeling: San Andres formation, Yoakum County, Texas
Henderson, S. )
1994-03-01
The Permian San Andres Formation represents one of the most prolific hydrocarbon-producing intervals of the Permian basin. Dolostone lithofacies intercalated with thin evaporites accommodate highly compartmentalized reservoirs resulting from complex depositional and diagenetic histories. This compartmentalization often facilitates the use of these reservoirs in flow-unit studies. Perhaps more important than the relationship of productive intervals to depositional facies is the degree to which diagenetic processes have influenced reservoir properties. Detailed petrographic evaluation of the reservoir in question, though often overlooked, should be an integral part of flow-unit studies. Once a diagenetic sequence is established, the information may be incorporated in to the facies model to better understand how to subdivide the reservoir. Such an investigation has been conducted on the San Andres Formation in Reeves field of southeastern Yoakum County, Texas. Here, multistage diagenetic overprints are superimposed on depositional facies that vary in degree of lateral extent, thereby complicating the geometries of individual productive zones within the reservoir. Analysis of the reservoir reveals that Reeves San Andres sediments were subjected to dominant diagenetic processes, including dolomitization and sulfate implacement, both of which are major factors in porosity preservation, and a variety of minor processes that have had little effect on reservoir quality. The recognition of diagenetic facies, and understanding of the processes that have created them, and identification of the implications of these processes on reservoir properties is a vital part of any flow-unit study.
NASA Astrophysics Data System (ADS)
Hao, Jiaao; Wang, Jingying; Lee, Chunhian
2016-09-01
Effects of two different 11-species chemical reaction models on hypersonic reentry flow simulations are numerically investigated. These two models were proposed by Gupta (1990) and Park (1990) [12,15], respectively. In this study, two typical configurations, the RAM-C II vehicle and FIRE II capsule, are selected as test cases, whose thermo-chemical nonequilibrium flowfields are computed by a multi-block finite volume code using a two-temperature model (a translational-rotational temperature and a vibrational-electron-electronic temperature). In the RAM-C II case, it is indicated that although electron number density distributions of the two reaction models appear in a similar trend, their values are distinctively different. Results of the Gupta's model show a better agreement with the electrostatic probe data, while those of the Park's model are more consistent with the reflectometers data. Both models give similar temperature distributions. In the FIRE II case, the two models yield significantly different distribution profiles of ions and electrons, whose differences could reach an order of magnitude. In addition, an abnormal nonequilibrium relaxation process in the shock layer is found in the FIRE II flowfield simulated by the Gupta's model, which proves to be a consequence of electron impact ionization reactions.
A modeling study of water flow in the vadose zone beneath the Radioactive Waste Management Complex
Baca, R.G.; Magnuson, S.O.; Nguyen, H.D.; Martian, P.
1992-01-01
A modeling study was conducted for the purpose of gaining insight into the nature of water flow in the vadose zone beneath the Radioactive Waste Management Complex (RWMC). The modeling study focused on three specific hydrologic aspects: (1) relationship between meteorologic conditions and net infiltration, (2) water movement associated with past flooding events, and (3) estimation of water travel-times through the vadose zone. This information is necessary for understanding how contaminants may be transported through the vadose zone. Evaluations of net infiltration at the RWMC were performed by modeling the processes of precipitation, evaporation, infiltration and soil-moisture redistribution. Water flow simulations were performed for two distinct time periods, namely 1955--1964 and 1984--1990. The patterns of infiltration were calculated for both the undisturbed (or natural sediments) and the pit/trench cover materials. Detailed simulations of the 1969 flooding of Pit 10 were performed to estimate the rate and extent of water movement through the vadose zone. Water travel-times through the vadose zone were estimated using a Monte Carlo simulation approach. The simulations accounted for variability of soil and rock hydraulic properties as well as variations in the infiltration rate.
Experimental and modeling studies of the micro-structures of opposed flow diffusion flames: Methane
Vincitore, A.M.; Senkan, S.M.; Marinov, N.; Pitz, W.J.; Westbrook, C.K.; Melius, C.F.
1996-01-15
The micro-structure of an atmospheric pressure, opposed flow, methane diffusion flame has been studied using heated micro-probe sampling and chemical kinetic modeling. Mole fraction profiles of major products as well as trace aromatic, substituted aromatic, and polycyclic aromatic hydrocarbons (PAH up to C{sub 16}H{sub 10}, e.g. pyrene) were quantified by direct gas chromatography/mass spectrometry (GC/MS) analysis of samples withdrawn from within the flame without any pre-concentration. Mole fractions range from 0.8 to 1.0 {times} 10{sup {minus}7}. The experimental measurements are compared to results from a newly-developed chemical kinetic model that includes chemistry for the production and consumption of aromatics and PAH species. The model predictions are in reasonable agreement with the experimental data for the major species profiles and for the peak concentrations of many of the trace aromatics and PAH species. 36 refs.
A Numerical Model Study of Nocturnal Drainage Flows with Strong Wind and Temperature Gradients.
NASA Astrophysics Data System (ADS)
Yamada, T.; Bunker, S.
1989-07-01
A second-moment turbulence-closure model described in Yamada and Bunker is used to simulate nocturnal drainage flows observed during the 1984 ASCOT field expedition in Brush Creek, Colorado. In order to simulate the observed strong wind directional shear and temperature gradients, two modifications are added to the model. The strong wind directional shear was maintained by introducing a `nudging' term in the equation of motion to guide the modeled winds in the layers above the ridge top toward the observed wind direction. The second modification was accomplished by reformulating the conservation equation for the potential temperature in such a way that only the deviation from the horizontally averaged value was prognostically computed.The vegetation distribution used in this study is undoubtedly crude. Nevertheless, the present simulation suggests that tall tree canopy can play an important role in producing inhomogeneous wind distribution, particularly in the levels below the canopy top.
Turbulence modeling for separated flow
NASA Technical Reports Server (NTRS)
Durbin, Paul A.
1994-01-01
Two projects are described in this report. The first involves assessing turbulence models in separated flow. The second addresses the anomalous behavior of certain turbulence models in stagnation point flow. The primary motivation for developing turbulent transport models is to provide tools for computing non-equilibrium, or complex, turbulent flows. Simple flows can be analyzed using data correlations or algebraic eddy viscosities, but in more complicated flows such as a massively separated boundary layer, a more elaborate level of modeling is required. It is widely believed that at least a two-equation transport model is required in such cases. The transport equations determine the evolution of suitable velocity and time-scales of the turbulence. The present study included assessment of second-moment closures in several separated flows, including sharp edge separation; smooth wall, pressure driven separation; and unsteady vortex shedding. Flows with mean swirl are of interest for their role in enhancing mixing both by turbulent and mean motion. The swirl can have a stabilizing effect on the turbulence. An axi-symmetric extension to the INS-2D computer program was written adding the capability of computing swirling flow. High swirl can produce vortex breakdown on the centerline of the jet and it occurs in various combustors.
NASA Astrophysics Data System (ADS)
Stella, J. C.; Battles, J. J.; McBride, J. R.; Orr, B. K.
2007-12-01
In the Central Valley of California, pioneer cottonwood and willow species dominate the near-river forests. Historically, seedling recruitment for these disturbance-adapted species coincided with spring floods. Changes in flow timing and magnitude due to river regulation have decreased the success of seedling cohorts and contributed to the decline of these riparian tree populations. In order to address gaps in our understanding of these species and potential restoration strategies, we field-calibrated a conceptual model of seedling recruitment for the dominant pioneer woody species, Populus fremontii, Salix gooddingii, and S. exigua. We conducted experiments to identify seedling desiccation thresholds and seed longevity, used field studies to measure seedling competition and seasonal seed release patterns, and modeled interannual differences in dispersal timing using a degree-day model. These studies were integrated into a recruitment model that generates annual estimates of seedling density and bank elevation based on inputs of seasonal river discharge, seed dispersal timing, and seedling mortality from desiccation. The model predictions successfully captured interannual and species-level patterns in recruitment observed independently throughout a 20-km reach of the lower Tuolumne River from 2002-04. The model correctly predicted that seedling densities were highest in 2004 and lowest in 2003, and that S. exigua recruitment would be less extensive than for the two tree species. This work shows promise as both a quantitative approach linking hydrology, climate and plant community dynamics, and as a process-based framework for guiding flow releases and other management actions to restore riparian tree population along Central Valley rivers.
A numerical study of the FENE-CR model applied to a jet flow problem
NASA Astrophysics Data System (ADS)
Paulo, G. S.; Oishi, C. M.; Tomé, M. F.
2013-10-01
The FENE-CR model is investigated through a numerical algorithm to simulate the time-dependent moving free surface flow produced by a jet impinging on a flat surface. The objective is to demonstrate that by increasing the extensibility parameter L, the numerical solutions converge to the solutions obtained with the Oldroyd-B model. The governing equations are solved by an established free surface flow solver based on the finite difference and marker-and-cell methods. Numerical predictions of the extensional viscosity obtained with several values of the parameter L are presented. The results show that if the extensibility parameter L is sufficiently large then the extensional viscosities obtained with the FENE-CR model approximate the corresponding Oldroyd-B viscosity. Moreover, the flow from a jet impinging on a flat surface is simulated with various values of the extensibility parameter L and the fluid flow visualizations display convergence to the Oldroyd-B jet flow results.
Systematic study of Reynolds stress closure models in the computations of plane channel flows
NASA Technical Reports Server (NTRS)
Demuren, A. O.; Sarkar, S.
1992-01-01
The roles of pressure-strain and turbulent diffusion models in the numerical calculation of turbulent plane channel flows with second-moment closure models are investigated. Three turbulent diffusion and five pressure-strain models are utilized in the computations. The main characteristics of the mean flow and the turbulent fields are compared against experimental data. All the features of the mean flow are correctly predicted by all but one of the Reynolds stress closure models. The Reynolds stress anisotropies in the log layer are predicted to varying degrees of accuracy (good to fair) by the models. None of the models could predict correctly the extent of relaxation towards isotropy in the wake region near the center of the channel. Results from the directional numerical simulation are used to further clarify this behavior of the models.
Bitzén, Ulrika; Niklason, Lisbet; Göransson, Ingegerd; Jonson, Björn
2010-11-01
Elastic pressure/volume (P(el) /V) and elastic pressure/resistance (P(el) /R) diagrams reflect parenchymal and bronchial properties, respectively. The objective was to develop a method for determination and mathematical characterization of P(el) /V and P(el) /R relationships, simultaneously studied at sinusoidal flow-modulated vital capacity expirations in a body plethysmograph. Analysis was carried out by iterative parameter estimation based on a composite mathematical model describing a three-segment P(el) /V curve and a hyperbolic P(el) /R curve. The hypothesis was tested that the sigmoid P(el) /V curve is non-symmetric. Thirty healthy subjects were studied. The hypothesis of a non-symmetric P(el) /V curve was verified. Its upper volume asymptote was nearly equal to total lung capacity (TLC), indicating lung stiffness increasing at high lung volume as the main factor limiting TLC at health. The asymptotic minimal resistance of the hyperbolic P(el) /R relationship reflected lung size. A detailed description of both P(el) /V and P(el) /R relationships was simultaneously derived from sinusoidal flow-modulated vital capacity expirations. The nature of the P(el) /V curve merits the use of a non-symmetric P(el) /V model.
NASA Astrophysics Data System (ADS)
Fix, Brandon R.; Popma, Christopher J.; Bulusu, Kartik V.; Plesniak, Michael W.
2013-11-01
Each year, hundreds of thousands of aortic and mitral heart valves are replaced with prosthetic valves. In efforts to develop a valve that does not require lifelong anticoagulation therapy, previous experimental research has been devoted to analyzing the hemodynamics of various heart valve designs, limited to the flow up to only 2 diameters downstream of the valve. Two-component, two-dimensional (2C-2D) particle image velocimetry (PIV) was used in this study to examine secondary flow velocity fields in a curved tube modeling an aorta at five locations (0-, 45-, 90-, 135-, 180-degrees). A bileaflet valve, opened to 30-, 45-, and 59-degrees, and one (no-valve) baseline condition were examined under three steady flow inflows (Re = 218, 429, 634). In particular, variations in the two-dimensional turbulent shear stresses at each cross sectional plane were analyzed. The results suggest that bileaflet valves in the aortic model produce significant turbulence and vorticity up to 5.5 downstream diameters, i.e. up to the 90-degrees location. Expanding this research towards aortic heart valve hemodynamics highlights a need for additional studies extending beyond the typical few diameters downstream to fully characterize valvular function. Supported by the NSF Grant No. CBET- 0828903 and GW Center for Biomimetics and Bioinspired Engineering.
Not Available
1981-10-01
(1) We recommend the establishment of an experimental test facility, appropriately instrumented, dedicated to research on theoretical modeling concepts. Validation of models for the various flow regimes, and establishment of the limitations or concepts used in the construction of models, are sorely needed areas of research. There exists no mechanism currently for funding of such research on a systematic basis. Such a facility would provide information fundamental to progress in the physics of turbulent multi-phase flow, which would also have impact on the understanding of coal utilization processes; (2) combustion research appears to have special institutional barriers to information exchange because it is an established, commercial ongoing effort, with heavy reliance on empirical data for proprietary configurations; (3) for both gasification and combustion reactors, current models appear to handle adequately some, perhaps even most, gross aspects of the reactors such as overall efficiency and major chemical output constituents. However, new and more stringent requirements concerning NOX, SOX and POX (small paticulate) production require greater understanding of process details and spatial inhomogenities, hence refinement of current models to include some greater detail is necessary; (4) further progress in the theory of single-phase turbulent flow would benefit our understanding of both combustors and gasifiers; and (5) another area in which theoretical development would be extremely useful is multi-phase flow.
Stochastic models for turbulent reacting flows
Kerstein, A.
1993-12-01
The goal of this program is to develop and apply stochastic models of various processes occurring within turbulent reacting flows in order to identify the fundamental mechanisms governing these flows, to support experimental studies of these flows, and to further the development of comprehensive turbulent reacting flow models.
A numerical study of the controlled flow tunnel for a high lift model
NASA Technical Reports Server (NTRS)
Parikh, P. C.
1984-01-01
A controlled flow tunnel employs active control of flow through the walls of the wind tunnel so that the model is in approximately free air conditions during the test. This improves the wind tunnel test environment, enhancing the validity of the experimentally obtained test data. This concept is applied to a three dimensional jet flapped wing with full span jet flap. It is shown that a special treatment is required for the high energy wake associated with this and other V/STOL models. An iterative numerical scheme is developed to describe the working of an actual controlled flow tunnel and comparisons are shown with other available results. It is shown that control need be exerted over only part of the tunnel walls to closely approximate free air flow conditions. It is concluded that such a tunnel is able to produce a nearly interference free test environment even with a high lift model in the tunnel.
Balaguru, Uma Maheswari; Sundaresan, Lakshmikirupa; Manivannan, Jeganathan; Majunathan, Reji; Mani, Krishnapriya; Swaminathan, Akila; Venkatesan, Saravanakumar; Kasiviswanathan, Dharanibalan; Chatterjee, Suvro
2016-01-01
Disturbed fluid flow or modulated shear stress is associated with vascular conditions such as atherosclerosis, thrombosis, and aneurysm. In vitro simulation of the fluid flow around the plaque micro-environment remains a challenging approach. Currently available models have limitations such as complications in protocols, high cost, incompetence of co-culture and not being suitable for massive expression studies. Hence, the present study aimed to develop a simple, versatile model based on Computational Fluid Dynamics (CFD) simulation. Current observations of CFD have shown the regions of modulated shear stress by the disturbed fluid flow. To execute and validate the model in real sense, cell morphology, cytoskeletal arrangement, cell death, reactive oxygen species (ROS) profile, nitric oxide production and disturbed flow markers under the above condition were assessed. Endothelium at disturbed flow region which had been exposed to low shear stress and swirling flow pattern showed morphological and expression similarities with the pathological disturbed flow environment reported previously. Altogether, the proposed model can serve as a platform to simulate the real time micro-environment of disturbed flow associated with eccentric plaque shapes and the possibilities of studying its downstream events. PMID:27255968
NASA Astrophysics Data System (ADS)
Balaguru, Uma Maheswari; Sundaresan, Lakshmikirupa; Manivannan, Jeganathan; Majunathan, Reji; Mani, Krishnapriya; Swaminathan, Akila; Venkatesan, Saravanakumar; Kasiviswanathan, Dharanibalan; Chatterjee, Suvro
2016-06-01
Disturbed fluid flow or modulated shear stress is associated with vascular conditions such as atherosclerosis, thrombosis, and aneurysm. In vitro simulation of the fluid flow around the plaque micro-environment remains a challenging approach. Currently available models have limitations such as complications in protocols, high cost, incompetence of co-culture and not being suitable for massive expression studies. Hence, the present study aimed to develop a simple, versatile model based on Computational Fluid Dynamics (CFD) simulation. Current observations of CFD have shown the regions of modulated shear stress by the disturbed fluid flow. To execute and validate the model in real sense, cell morphology, cytoskeletal arrangement, cell death, reactive oxygen species (ROS) profile, nitric oxide production and disturbed flow markers under the above condition were assessed. Endothelium at disturbed flow region which had been exposed to low shear stress and swirling flow pattern showed morphological and expression similarities with the pathological disturbed flow environment reported previously. Altogether, the proposed model can serve as a platform to simulate the real time micro-environment of disturbed flow associated with eccentric plaque shapes and the possibilities of studying its downstream events.
Unsaturated flow dynamics during irrigation with wastewater: field and modelling study
NASA Astrophysics Data System (ADS)
Martinez-Hernandez, V.; de Miguel, A.; Meffe, R.; Leal, M.; González-Naranjo, V.; de Bustamante, I.
2012-04-01
To deal with water scarcity combined with a growing water demand, the reuse of wastewater effluents of wastewater treatment plants (WWTP) for industrial and agricultural purposes is considered as a technically and economically feasible solution. In agriculture, irrigation with wastewater emerges as a sustainable practice that should be considered in such scenarios. Water infiltration, soil moisture storage and evapotranspiration occurring in the unsaturated zone are fundamental processes that play an important role in soil water balance. An accurate estimation of unsaturated flow dynamics (during and after irrigation) is essential to improve wastewater management (i.e. estimating groundwater recharge or maximizing irrigation efficiency) and to avoid possible soil and groundwater affections (i.e. predicting contaminant transport). The study site is located in the Experimental Plant of Carrión de los Céspedes (Seville, Spain). Here, treated wastewater is irrigated over the soil to enhance plants growth. To obtain physical characteristics of the soil (granulometry, bulk density and water retention curve), soil samples were collected at different depths. A drain gauge passive capillary lysimeter was installed to determine the volume of water draining from the vadose zone. Volumetric water content of the soil was monitored by measuring the dielectric constant using capacitance/frequency domain technology. Three soil moisture probes were located at different depths (20, 50 and 70 cm below the ground surface) to control the variation of the volumetric water content during infiltration. The main aim of this study is to understand water flow dynamics through the unsaturated zone during irrigation by using the finite element model Hydrus-1D. The experimental conditions were simulated by a 90 cm long, one dimensional solution domain. Specific climatic conditions, wastewater irrigation rates and physical properties of the soil were introduced in the model as input parameters
Turbulence modeling for hypersonic flows
NASA Technical Reports Server (NTRS)
Marvin, J. G.; Coakley, T. J.
1989-01-01
Turbulence modeling for high speed compressible flows is described and discussed. Starting with the compressible Navier-Stokes equations, methods of statistical averaging are described by means of which the Reynolds-averaged Navier-Stokes equations are developed. Unknown averages in these equations are approximated using various closure concepts. Zero-, one-, and two-equation eddy viscosity models, algebraic stress models and Reynolds stress transport models are discussed. Computations of supersonic and hypersonic flows obtained using several of the models are discussed and compared with experimental results. Specific examples include attached boundary layer flows, shock wave boundary layer interactions and compressible shear layers. From these examples, conclusions regarding the status of modeling and recommendations for future studies are discussed.
Numerical study on the pulsatile flow characteristics of proximal anastomotic models.
Chua, L P; Zhang, J-M; Yu, S C M; Ghista, D N; Tan, Y S
2005-09-01
Haemodynamics was widely believed to correlate with anastomosis restenosis. Utilizing the haemodynamic parameters as indicator functions, distal anastomosis was redesigned by some researchers so as to improve the long-term graft patency rate. However, there were few studies upon the proximal anastomosis. Therefore, in this study, flow characteristics and distributions of the haemodynamic parameters in proximal anastomosis under physiological flow condition have been investigated numerically for three different grafting angles: namely, 45 degrees forward facing, 45 degrees backward facing, and 90 degrees anastomotic joints. The simulation results showed a flow separation region along the graft inner wall immediately after the heel at peak flow phase and it decreased in size with the grafting angle shifting from 45 degrees forward facing to 45 degrees backward facing. At the same time, a pair of vortex was found in the cross-sectional planes of the 45 degrees backward facing and 90 degrees grafts. In addition, stagnation point was found along the graft outer wall with small shifting during the physiological cycle. High spatial and temporal wall shear stresses gradients (WSSG) were observed around the anastomotic joint. Low time-averaged wall shear stress (WSS) with elevated oscillation shear index (OSI) was found near the middle of anastomosis at the aorta wall and along the graft inner wall respectively, while high time-averaged WSS with low OSI was found at the heel, the toe, and the region downstream of the toe. These regions correlated to early lesion growth. Elevated time-averaged WSSG was found at the same region, where the elevated low-density lipoprotein (LDL) permeability was observed as reported in the literature. The existence of nearly fixed stagnating location, flow separation, vortex, high time-averaged WSS with low OSI, low time-averaged WSS with elevated OSI, and high time-averaged WSSG may lead to graft stenosis. Moreover, the simulation results
Fracture propagation and fluid flow in fractured reservoirs: field studies and numerical models
NASA Astrophysics Data System (ADS)
Brenner, S. L.
2005-05-01
In fractured reservoirs (e.g., for petroleum or geothermal water), fluid flow is largely controlled by the permeability of the fracture network. Together with shear fractures (faults), hydrofractures (extension fractures generated by internal fluid pressure, including mineral veins and joints) contribute considerably to the permeability in fractured reservoirs. The permeability of an individual fracture is proportional to the cube of its aperture. But for fluid flow to occur between two sites in a reservoir, there must be at least one interconnected cluster of fractures that links these sites, that is, the percolation threshold must be reached. Field observations show that in heterogeneous and anisotropic, e.g., layered, rocks many hydrofractures become arrested or offset at layer contacts (become stratabound) and do not form interconnected networks. Here I present results from field studies in layered sedimentary rocks from the Bristol Channel Basin, UK. The Lower Jurassic sections exposed near Kilve, Somerset Coast (Southwest England), and around Nash Point, Glamorgan Coast (South Wales) consist of limestone and shale layers dissected by normal faults (Kilve) or strike-slip faults (Nash Point). Whereas joints occur throughout the study areas, calcite veins occur almost exclusively in the cores and damage zones of the faults. These observations indicate that geothermal water was transported along the then-active faults into the host rocks. Furthermore, there is evidence that the veins were injected as hydrofractures from the fault planes into the limestone layers next to the faults. The most important factors that contribute to hydrofracture arrest or offset are discontinuities, stiffness (Young's modulus) changes between layers, and stress barriers - layers where the local stress field is unfavorable to the propagation of a hydrofracture. Using numerical models I explore the conditions for hydrofracture propagation and conclude that mechanical layering largely
NASA Technical Reports Server (NTRS)
Demuren, A. O.
1994-01-01
Various approaches to the modeling of jets in cross flow are reviewed. These are grouped into four classes, namely: empirical models, integral models, perturbation models, and numerical models. Empirical models depend largely on the correlation of experimental data and are mostly useful for first-order estimates of global properties such as jet trajectory and velocity and temperature decay rates. Integral models are based on some ordinary-differential form of the conservation laws, but require substantial empirical calibration. They allow more details of the flow field to be obtained; simpler versions have to assume similarity of velocity and temperature profiles, but more sophisticated ones can actually calculate these profiles. Perturbation models require little empirical input, but the need for small parameters to ensure convergent expansions limits their application to either the near-field or the far-field. Therefore, they are mostly useful for the study of flow physics. Numerical models are based on conservation laws in partial-differential form. They require little empirical input and have the widest range of applicability. They also require the most computational resources. Although many qualitative and quantitative features of jets in cross flow have been predicted with numerical models, many issues affecting accuracy such as grid resolution and turbulence model are not completely resolved.
Choi, Jiwoong; Xia, Guohua; Tawhai, Merryn H.; Hoffman, Eric A.; Lin, Ching-Long
2011-01-01
High frequency oscillatory ventilation (HFOV) is considered an efficient and safe respiratory technique to ventilate neonates and patients with acute respiratory distress syndrome. HFOV has very different characteristics from normal breathing physiology, with a much smaller tidal volume and a higher breathing frequency. In this work, the high frequency oscillatory flow is studied using a computational fluid dynamics (CFD) analysis in three different geometrical models with increasing complexity: a straight tube, a single-bifurcation tube model, and a computed-tomography (CT)-based human airway model of up to seven generations. We aim to understand the counter-flow phenomenon at flow reversal and its role in convective mixing in these models using sinusoidal waveforms of different frequencies and Reynolds numbers. Mixing is quantified by the stretch rate analysis. In the straight-tube model, coaxial counter flow with opposing fluid streams is formed around flow reversal, agreeing with an analytical Womersley solution. However, counter flow yields no net convective mixing at end cycle. In the single-bifurcation model, counter flow at high Re is intervened with secondary vortices in the parent (child) branch at end expiration (inspiration), resulting in an irreversible mixing process. For the CT-based airway model three cases are considered, consisting of the normal breathing case, the high-frequency-normal-Re case, and the HFOV case. The counter-flow structure is more evident in the high-frequency-normal-Re case than the HFOV case. The instantaneous and time-averaged stretch rates at the end of two breathing cycles and in the vicinity of flow reversal are computed. It is found that counter flow contributes about 20% to mixing in HFOV. PMID:20614248
Anh Bui; Nam Dinh; Brian Williams
2013-09-01
In addition to validation data plan, development of advanced techniques for calibration and validation of complex multiscale, multiphysics nuclear reactor simulation codes are a main objective of the CASL VUQ plan. Advanced modeling of LWR systems normally involves a range of physico-chemical models describing multiple interacting phenomena, such as thermal hydraulics, reactor physics, coolant chemistry, etc., which occur over a wide range of spatial and temporal scales. To a large extent, the accuracy of (and uncertainty in) overall model predictions is determined by the correctness of various sub-models, which are not conservation-laws based, but empirically derived from measurement data. Such sub-models normally require extensive calibration before the models can be applied to analysis of real reactor problems. This work demonstrates a case study of calibration of a common model of subcooled flow boiling, which is an important multiscale, multiphysics phenomenon in LWR thermal hydraulics. The calibration process is based on a new strategy of model-data integration, in which, all sub-models are simultaneously analyzed and calibrated using multiple sets of data of different types. Specifically, both data on large-scale distributions of void fraction and fluid temperature and data on small-scale physics of wall evaporation were simultaneously used in this work’s calibration. In a departure from traditional (or common-sense) practice of tuning/calibrating complex models, a modern calibration technique based on statistical modeling and Bayesian inference was employed, which allowed simultaneous calibration of multiple sub-models (and related parameters) using different datasets. Quality of data (relevancy, scalability, and uncertainty) could be taken into consideration in the calibration process. This work presents a step forward in the development and realization of the “CIPS Validation Data Plan” at the Consortium for Advanced Simulation of LWRs to enable
NASA Astrophysics Data System (ADS)
Juanes, R.; Jha, B.
2014-12-01
The coupling between subsurface flow and geomechanical deformation is critical in the assessment of the environmental impacts of groundwater use, underground liquid waste disposal, geologic storage of carbon dioxide, and exploitation of shale gas reserves. In particular, seismicity induced by fluid injection and withdrawal has emerged as a central element of the scientific discussion around subsurface technologies that tap into water and energy resources. Here we present a new computational approach to model coupled multiphase flow and geomechanics of faulted reservoirs. We represent faults as surfaces embedded in a three-dimensional medium by using zero-thickness interface elements to accurately model fault slip under dynamically evolving fluid pressure and fault strength. We incorporate the effect of fluid pressures from multiphase flow in the mechanical stability of faults and employ a rigorous formulation of nonlinear multiphase geomechanics that is capable of handling strong capillary effects. We develop a numerical simulation tool by coupling a multiphase flow simulator with a mechanics simulator, using the unconditionally stable fixed-stress scheme for the sequential solution of two-way coupling between flow and geomechanics. We validate our modeling approach using several synthetic, but realistic, test cases that illustrate the onset and evolution of earthquakes from fluid injection and withdrawal. We also present the application of the coupled flow-geomechanics simulation technology to the post mortem analysis of the Mw=5.1, May 2011 Lorca earthquake in south-east Spain, and assess the potential that the earthquake was induced by groundwater extraction.
Stoner, D. L.; Watson, S. M.; Stedtfeld, R. D.; Meakin, P.; Griffel, L. K.; Tyler, T. L.; Pegram, L. M.; Barnes, J. M.; Deason, V. A.
2005-01-01
Here we introduce the use of transparent experimental models fabricated by stereolithography for studying the impacts of biomass accumulation, minerals precipitation, and physical configuration of flow paths on liquid flow in fracture apertures. The internal configuration of the models ranged in complexity from simple geometric shapes to those that incorporate replicated surfaces of natural fractures and computationally derived fracture surfaces. High-resolution digital time-lapse imaging was employed to qualitatively observe the migration of colloidal and soluble dyes through the flow models. In this study, a Sphingomonas sp. and Sporosarcina (Bacillus) pasteurii influenced the fluid dynamics by physically altering flow paths. Microbial colonization and calcite deposition enhanced the stagnant regions adjacent to solid boundaries. Microbial growth and calcite precipitation occurred to a greater extent in areas behind the fabricated obstacles and less in high-velocity orifices. PMID:16332867
Experimental unsteady flow study in a patient-specific abdominal aortic aneurysm model
NASA Astrophysics Data System (ADS)
Stamatopoulos, Ch.; Mathioulakis, D. S.; Papaharilaou, Y.; Katsamouris, A.
2011-06-01
The velocity field in a patient-specific abdominal aneurysm model including the aorto-iliac bifurcation was measured by 2D PIV. Phase-averaged velocities obtained in 14 planes reveal details of the flow evolution during a cycle. The aneurysm expanding asymmetrically toward the anterior side of the aorta causes the generation of a vortex at its entrance, covering the entire aneurysm bulge progressively before flow peak. The fluid entering the aneurysm impinges on the left side of its distal end, following the axis of the upstream aorta segment, causing an increased flow rate in the left (compared to the right) common iliac artery. High shear stresses appear at the aneurysm inlet and outlet as well as along the posterior wall, varying proportionally to the flow rate. At the same regions, elevated flow disturbances are observed, being intensified at flow peak and during the deceleration phase. Low shear stresses are present in the recirculation region, being two orders of magnitude smaller than the previous ones. At flow peak and during the deceleration phase, a clockwise swirling motion (viewed from the inlet) is present in the aneurysm due to the out of plane curvature of the aorta.
Comparative study of hybrid RANS-LES models for separated flows
NASA Astrophysics Data System (ADS)
Kumar, G.; Lakshmanan, S. K.; Gopalan, H.; De, A.
2016-06-01
Hybrid RANS-LES models are proven to be capable of predicting massively separated flows with reasonable computation cost. In this paper, Spalart-Allmaras (S-A) based detached eddy simulation (DES) model and three SST based hybrid models with different RANS to LES switching criteriaare investigated. The flow over periodic hill at Re = 10,595 is chosen as the benchmark for comparing the performance of the different models due to the complex flow physics and reasonablecomputational cost. The model performances are evaluated based on their prediction capabilities of velocity and stress profiles, and separation and reattachment point. The simulated results are validatedagainst experimental and numerical results available in literature. The S-A DES model predicted separation bubble accurately at the top of the hill, as reported earlier in experiments and other numerical results. This model also correctly predicted velocity and stress profiles in recirculation region. However, the performance of this model was poor in the post reattachment region. On the other hand, the k-ω SST based hybrid models performed poorly in recirculation region, but it fairly predicted stress profiles in post reattachment region.
Mean surface temperature prediction models for broiler chickens—a study of sensible heat flow
NASA Astrophysics Data System (ADS)
Nascimento, Sheila Tavares; da Silva, Iran José Oliveira; Maia, Alex Sandro Campos; de Castro, Ariane Cristina; Vieira, Frederico Marcio Corrêa
2014-03-01
Body surface temperature can be used to evaluate thermal equilibrium in animals. The bodies of broiler chickens, like those of all birds, are partially covered by feathers. Thus, the heat flow at the boundary layer between broilers' bodies and the environment differs between feathered and featherless areas. The aim of this investigation was to use linear regression models incorporating environmental parameters and age to predict the surface temperatures of the feathered and featherless areas of broiler chickens. The trial was conducted in a climate chamber, and 576 broilers were distributed in two groups. In the first trial, 288 broilers were monitored after exposure to comfortable or stressful conditions during a 6-week rearing period. Another 288 broilers were measured under the same conditions to test the predictive power of the models. Sensible heat flow was calculated, and for the regions covered by feathers, sensible heat flow was predicted based on the estimated surface temperatures. The surface temperatures of the feathered and featherless areas can be predicted based on air, black globe or operative temperatures. According to the sensible heat flow model, the broilers' ability to maintain thermal equilibrium by convection and radiation decreased during the rearing period. Sensible heat flow estimated based on estimated surface temperatures can be used to predict animal responses to comfortable and stressful conditions.
Groundwater flow and mixing in a wetland-stream system: Field study and numerical modeling
NASA Astrophysics Data System (ADS)
Karan, Sachin; Engesgaard, Peter; Looms, Majken C.; Laier, Troels; Kazmierczak, Jolanta
2013-04-01
SummaryWe combined electrical resistivity tomography (ERT) on land and in a stream with zone-based hydraulic conductivities (from multi-level slug testing) to investigate the local geological heterogeneity of the deposits in a wetland-stream system. The detailed geology was incorporated into a numerical steady-state groundwater model that was calibrated against average head observations. The model results were tested against groundwater fluxes determined from streambed temperature measurements. Discharge varied up to one order of magnitude across the stream and the model was successful in capturing this variability. Water quality analyses from multi-level sampling underneath the streambed and in the wetland showed a stratification in groundwater composition with an aerobic shallow zone with oxygen and nitrate (top ˜3 m) overlying a reduced, anoxic zone. While NO3- concentrations up to 58 mg L-1 were found in the top of the aquifer and immediately underneath the streambed no NO3- was detected deeper within the aquifer. An inverse relationship between NO3- and SO42- suggests that pyrite oxidation takes place in the deeper parts of the aquifer. Simulated flow path lines showed very different origins for deeper groundwater samples. No nitrate reduction is believed to occur in the shallow zone, where oxygen is present, and the residence time is on the order of 1 year. Nitrate reduction can, however, occur in the deeper parts, which are oxygen-free, and where the residence time is on the order of 7 years. A simulation with a homogeneous model did not match the observations nearly as well as a heterogeneous model based on ERT and a spatially distributed hydraulic conductivity. Furthermore, the origin of the sampled groundwater could not have been predicted from groundwater hydraulic head and the groundwater chemistry alone. The presented approach of integrating such methods in groundwater-surface water exchange studies, proved efficient to obtain information of the
Comparison study of the reactive and predictive dynamic models for pedestrian flow
NASA Astrophysics Data System (ADS)
Jiang, Yan-Qun; Zhang, Wei; Zhou, Shu-Guang
2016-01-01
This paper formulates the reactive and predictive dynamic models for pedestrian flow and presents a comparison of the two models. The path-choice behavior of pedestrians in the reactive dynamic model is described that pedestrians tend to walk along a path with the lowest instantaneous cost. The desired walking direction of pedestrians in the predictive dynamic model is chosen to minimize the actual cost based on predictive traffic conditions. An algorithm used to solve the two models encompasses a cell-centered finite volume method for a hyperbolic system of conservation laws and a time-dependent Hamilton-Jacobi equation, a fast sweeping method for an Eikonal-type equation, and a self-adaptive method of successive averages for an arisen discrete fixed point problem. The two models and their algorithm are applied to investigate the spatio-temporal patterns of flux or density and path-choice behaviors of pedestrian flow marching in a facility scattered with an obstacle. Numerical results show that the two models are able to capture macroscopic features of pedestrian flow, traffic instability and other complex nonlinear phenomena in pedestrian traffic, such as the formation of stop-and-go waves and clogging at bottlenecks. Different path-choice strategies of pedestrians cause different spatial distributions of pedestrian density specially in the high-density regions (near the obstacle and exits).
Test Problems for Reactive Flow HE Model in the ALE3D Code and Limited Sensitivity Study
Gerassimenko, M.
2000-03-01
We document quick running test problems for a reactive flow model of HE initiation incorporated into ALE3D. A quarter percent change in projectile velocity changes the outcome from detonation to HE burn that dies down. We study the sensitivity of calculated HE behavior to several parameters of practical interest where modeling HE initiation with ALE3D.
Modeling studies for multiphase fluid and heat flow processes in nuclear waste isolation
Pruess, K.
1988-07-01
Multiphase fluid and heat flow plays an important role in many problems relating to the disposal of nuclear wastes in geologic media. Examples include boiling and condensation processes near heat-generating wastes, flow of water and formation gas in partially saturated formations, evolution of a free gas phase from waste package corrosion in initially water-saturated environments, and redistribution (dissolution, transport, and precipitation) of rock minerals in non-isothermal flow fields. Such processes may strongly impact upon waste package and repository design considerations and performance. This paper summarizes important physical phenomena occurring in multiphase and nonisothermal flows, as well as techniques for their mathematical modeling and numerical simulation. Illustrative applications are given for a number of specific fluid and heat flow problems, including: thermohydrologic conditions near heat-generating waste packages in the unsaturated zone; repository-wide convection effects in the unsaturated zone; effects of quartz dissolution and precipitation for disposal in the saturated zone; and gas pressurization and flow corrosion of low-level waste packages. 34 refs; 7 figs; 2 tabs.
Study of Critical Heat Flux Mechanism in Flow Boiling Using Bubble Crowding Model
NASA Astrophysics Data System (ADS)
Kinoshita, Hidetaka; Nariai, Hideki; Inasaka, Fujio
Critical heat flux (CHF) of Subcooled Flow Boiling with water in a tube was investigated from the viewpoint of mechanistic models. The Weisman-Pei bubble crowding model was selected to predict CHF in a short tube and in a tube with an internal twisted tape under nonuniform heating conditions, Based on the results of bubble behavior observation and preliminary analysis. The original Weisman-Pei model was modified in order to explain the physical phenomena of CHF. The modified model predicted well CHF in a smooth tube including the very short tube and the tube with an internal twisted tape under uniform and nonuniform heating conditions.
Nicole Lautze
2015-01-01
Groundwater flow model for the island of Oahu. Data is from the following sources: Rotzoll, K., A.I. El-Kadi. 2007. Numerical Ground-Water Flow Simulation for Red Hill Fuel Storage Facilities, NAVFAC Pacific, Oahu, Hawaii - Prepared TEC, Inc. Water Resources Research Center, University of Hawaii, Honolulu.; Whittier, R.B., K. Rotzoll, S. Dhal, A.I. El-Kadi, C. Ray, G. Chen, and D. Chang. 2004. Hawaii Source Water Assessment Program Report – Volume VII – Island of Oahu Source Water Assessment Program Report. Prepared for the Hawaii Department of Health, Safe Drinking Water Branch. University of Hawaii, Water Resources Research Center. Updated 2008.; and Whittier, R. and A.I. El-Kadi. 2009. Human and Environmental Risk Ranking of Onsite Sewage Disposal Systems – Final. Prepared by the University of Hawaii, Dept. of Geology and Geophysics for the State of Hawaii Dept. of Health, Safe Drinking Water Branch. December 2009.
Laminar flow studies of a low-temperature space radiator model using D-shaped tubes
NASA Technical Reports Server (NTRS)
Cintula, T. C.; Prok, G. M.; Johnston, D. B.
1972-01-01
Test results of a low-temperature space radiator model are presented. Radiator performance is evaluated with a low-thermal-conductivity fluid in laminar flow in D-shaped cross-section tubes. The test covered a Reynolds number range from 50 to 4500 and a fluid temperature range from 294 to 414 K (70 to 286 F). For low-temperature radiators, the fluid-to-surface temperature differential was predominately influenced by fluid temperature in laminar flow. Heat transfer and pressure drop for the radiator tube could be predicted within engineering accuracy from existing correlations.
A modelling study of the multiphase leakage flow from pressurised CO2 pipeline.
Zhou, Xuejin; Li, Kang; Tu, Ran; Yi, Jianxin; Xie, Qiyuan; Jiang, Xi
2016-04-05
The accidental leakage is one of the main risks during the pipeline transportation of high pressure CO2. The decompression process of high pressure CO2 involves complex phase transition and large variations of the pressure and temperature fields. A mathematical method based on the homogeneous equilibrium mixture assumption is presented for simulating the leakage flow through a nozzle in a pressurised CO2 pipeline. The decompression process is represented by two sub-models: the flow in the pipe is represented by the blowdown model, while the leakage flow through the nozzle is calculated with the capillary tube assumption. In the simulation, two kinds of real gas equations of state were employed in this model instead of the ideal gas equation of state. Moreover, results of the flow through the nozzle and measurement data obtained from laboratory experiments of pressurised CO2 pipeline leakage were compared for the purpose of validation. The thermodynamic processes of the fluid both in the pipeline and the nozzle were described and analysed.
Pulsatile Flow Studies in Atherosclerotic Carotid Bifurcations
NASA Astrophysics Data System (ADS)
Bale-Glickman, Jocelyn; Selby, Kathy; Saloner, David; Savas, Omer
2001-11-01
Particle image velocimetry and flow visualization techniques are used to study flows in models of atherosclerotic carotid bifurcations. The flow models exactly replicate the interior geometry of plaque excised from patients. The input flows are physiological wave forms derived from Doppler Ultrasound scans done on patients before surgery. The systolic and diastolic Reynolds numbers are 300 and 900. The complex internal geometry of the diseased artery combined with the pulsatile input flow results in exceedingly complex flow patterns. These flow patterns include internal jets, three-dimensional shear layers, stagnation lines, and multiple recirculation and separation regions. The physiological input flows are compared to flows when the wave form is sinusoidal.
MININR: a geochemical computer program for inclusion in water flow models - an application study
Felmy, A.R.; Reisenauer, A.E.; Zachara, J.M.; Gee, G.W.
1984-02-01
MININR is a reduced form of the computer program MINTEQ which calculates equilibrium precipitation/dissolution of solid phases, aqueous speciation, adsorption, and gas phase equilibrium. The user-oriented features in MINTEQ were removed to reduce the size and increase the computational speed. MININR closely resembles the MINEQL computer program developed by Westall (1976). The main differences between MININR and MINEQL involve modifications to accept an initial starting mass of solid and necessary changes for linking with a water flow model. MININR in combination with a simple water flow model which considers only dilution was applied to a laboratory column packed with retorted oil shale and percolated with distilled water. Experimental and preliminary model simulation results are presented for the constituents K/sup +/, Na/sup +/, SO/sub 4//sup 2 -/, Mg/sup 2 +/, Ca/sup 2 +/, CO/sub 3//sup 2 -/ and pH.
MULTI-LABORATORY STUDY OF FLOW-INDUCED HEMOLYSIS USING THE FDA BENCHMARK NOZZLE MODEL
Herbertson, Luke H.; Olia, Salim E.; Daly, Amanda; Noatch, Christopher P.; Smith, William A.; Kameneva, Marina V.; Malinauskas, Richard A.
2015-01-01
Multilaboratory in vitro blood damage testing was performed on a simple nozzle model to determine how different flow parameters and blood properties affect device-induced hemolysis and to generate data for comparison with computational fluid dynamics-based predictions of blood damage as part of an FDA initiative for assessing medical device safety. Three independent laboratories evaluated hemolysis as a function of nozzle entrance geometry, flow rate, and blood properties. Bovine blood anticoagulated with acid citrate dextrose solution (2–80 h post-draw) was recirculated through nozzle-containing and paired nozzle-free control loops for 2 h. Controlled parameters included hematocrit (36 ± 1.5%), temperature (25°C), blood volume, flow rate, and pressure. Three nozzle test conditions were evaluated (n = 26–36 trials each): (i) sudden contraction at the entrance with a blood flow rate of 5 L/min, (ii) gradual cone at the entrance with a 6-L/min blood flow rate, and (iii) sudden-contraction inlet at 6 L/min. The blood damage caused only by the nozzle model was calculated by subtracting the hemolysis generated by the paired control loop test. Despite high intralaboratory variability, significant differences among the three test conditions were observed, with the sharp nozzle entrance causing the most hemolysis. Modified index of hemolysis (MIHnozzle) values were 0.292 ± 0.249, 0.021 ± 0.128, and 1.239 ± 0.667 for conditions i–iii, respectively. Porcine blood generated hemolysis results similar to those obtained with bovine blood. Although the interlaboratory hemolysis results are only applicable for the specific blood parameters and nozzle model used here, these empirical data may help to advance computational fluid dynamics models for predicting blood damage. PMID:25180887
NASA Astrophysics Data System (ADS)
Wosnik, Martin; Bachant, Peter
2016-11-01
Cross-flow turbines show potential in marine hydrokinetic (MHK) applications. A research focus is on accurately predicting device performance and wake evolution to improve turbine array layouts for maximizing overall power output, i.e., minimizing wake interference, or taking advantage of constructive wake interaction. Experiments were carried with large laboratory-scale cross-flow turbines D O (1 m) using a turbine test bed in a large cross-section tow tank, designed to achieve sufficiently high Reynolds numbers for the results to be Reynolds number independent with respect to turbine performance and wake statistics, such that they can be reliably extrapolated to full scale and used for model validation. Several turbines of varying solidity were employed, including the UNH Reference Vertical Axis Turbine (RVAT) and a 1:6 scale model of the DOE-Sandia Reference Model 2 (RM2) turbine. To improve parameterization in array simulations, an actuator line model (ALM) was developed to provide a computationally feasible method for simulating full turbine arrays inside Navier-Stokes models. Results are presented for the simulation of performance and wake dynamics of cross-flow turbines and compared with experiments and body-fitted mesh, blade-resolving CFD. Supported by NSF-CBET Grant 1150797, Sandia National Laboratories.
On-line updating of a distributed flow routing model - River Vistula case study
NASA Astrophysics Data System (ADS)
Karamuz, Emilia; Romanowicz, Renata; Napiorkowski, Jaroslaw
2015-04-01
This paper presents an application of methods of on-line updating in the River Vistula flow forecasting system. All flow-routing codes make simplifying assumptions and consider only a reduced set of the processes known to occur during a flood. Hence, all models are subject to a degree of structural error that is typically compensated for by calibration of the friction parameters. Calibrated parameter values are not, therefore, physically realistic, as in estimating them we also make allowance for a number of distinctly non-physical effects, such as model structural error and any energy losses or flow processes which occur at sub-grid scales. Calibrated model parameters are therefore area-effective, scale-dependent values which are not drawn from the same underlying statistical distribution as the equivalent at-a-point parameter of the same name. The aim of this paper is the derivation of real-time updated, on-line flow forecasts at certain strategic locations along the river, over a specified time horizon into the future, based on information on the behaviour of the flood wave upstream and available on-line measurements at a site. Depending on the length of the river reach and the slope of the river bed, a realistic forecast lead time, obtained in this manner, may range from hours to days. The information upstream can include observations of river levels and/or rainfall measurements. The proposed forecasting system will integrate distributed modelling, acting as a spatial interpolator with lumped parameter Stochastic Transfer Function models. Daily stage data from gauging stations are typically available at sites 10-60 km apart and test only the average routing performance of hydraulic models and not their ability to produce spatial predictions. Application of a distributed flow routing model makes it possible to interpolate forecasts both in time and space. This work was partly supported by the project "Stochastic flood forecasting system (The River Vistula reach
Application of large-eddy simulation to the study of pulsatile flow in a modeled arterial stenosis.
Mittal, R; Simmons, S P; Udaykumar, H S
2001-08-01
The technique of large-eddy simulation (LES) has been applied to the study of pulsatile flow through a modeled arterial stenosis. A simple stenosis model has been used that consists of a one-sided 50 percent semicircular constriction in a planar channel. The inlet volume flux is varied sinusoidally in time in a manner similar to the laminar flow simulations of Tutty (1992). LES is used to compute flow at a peak Reynolds number of 2000 and a Strouhal number of 0.024. At this Reynolds number, the flow downstream of the stenosis transitions to turbulence and exhibits all the classic features of post-stenotic flow as described by Khalifa and Giddens (1981) and Lieber and Giddens (1990). These include the periodic shedding of shear layer vortices and transition to turbulence downstream of the stenosis. Computed frequency spectra indicate that the vortex shedding occurs at a distinct high frequency, and the potential implication of this for noninvasive diagnosis of arterial stenoses is discussed. A variety of statistics have been also extracted and a number of other physical features of the flow are described in order to demonstrate the usefulness of LES for the study of post-stenotic flows.
Oxidation flow reactors (OFRs): overview of recent field and modeling studies
NASA Astrophysics Data System (ADS)
Jimenez, Jose-Luis; Palm, Brett B.; Peng, Zhe; Hu, Weiwei; Ortega, Amber M.; Li, Rui; Campuzano-Jost, Pedro; Day, Douglas A.; Stark, Harald; Brune, William H.; de Gouw, Joost; Schroder, Jason
2016-04-01
Oxidation flow reactors (OFRs) are popular tools for studying SOA formation and aging in both laboratory and field experiments. In an OFR, the concentration of an oxidant (OH, O3, or NO3) can be increased, leading to hours-months of equivalent atmospheric oxidation during the several-minute OFR residence time. Using gas- and particle-phase measurements from several recent field campaigns, we demonstrate SOA formation after oxidation of ambient air in an OFR. Typically, more SOA formation is observed from nighttime air than daytime air. This indicates that the concentration of SOA-forming gases in ambient air is relatively higher at night. Measured ambient VOCs are not able to explain the magnitude of SOA formation in the OFR, suggesting that typically unmeasured S/IVOCs (possibly VOC oxidation products or direct emissions) play a substantial intermediary role in ambient SOA formation. We also present highlights from recent OFR oxidant chemistry modeling studies. HOx, Ox, and photolysis chemistry was modeled for two common OH production methods (utilizing 185+254 nm UV light, or 254 nm only). OH exposure (OHexp) can be estimated within a factor of ~2 using model-derived equations, and can be verified in situ using VOC decay measurements. OHexp is strongly dependent on external OH reactivity, which may cause significant OH suppression in some circumstances (e.g., lab/source studies with high precursor concentrations). UV light photolysis and reaction with oxygen atoms are typically not major reaction pathways. Modeling the fate of condensable low-volatility organic gases (LVOCs) formed in an OFR suggests that LVOC fate is dependent on particle condensational sink. E.g., for the range of particle condensational sink at a remote pine forest, anywhere from 20-80% of produced LVOCs were predicted to condense onto aerosols for an OHexp of ~1 day, with the remainder lost to OFR or sampling line walls. Similar to large chamber wall loss corrections, a correction is needed
Sikiö, Päivi; Jalali, Payman
2014-12-01
The hierarchical shell models of turbulence including a spatial dimension, namely, spatiotemporal tree models, reproduce the intermittent behavior of Navier-Stokes equations in both space and time dimensions corresponding to high Reynolds number turbulent flows. This model is used, for the first time in this paper, in a one-dimensional flow zone containing a dispersed-phase particle that can be used in the study of dispersed-phase flows. In this paper, a straightforward method has been used to introduce discrete phase into the spatiotemporal tree model that leads to an increased amount of turbulent energy dissipation rate in the vicinity of the discrete phase. The effects of particle insertion and particle size on the turbulent energy dissipation rate are demonstrated. Moreover, the space-scale behavior of the time-averaged turbulent energy dissipation rate in the presence of dispersed phase is demonstrated by means of continuous wavelet transform.
Modeling of transitional flows
NASA Technical Reports Server (NTRS)
Lund, Thomas S.
1988-01-01
An effort directed at developing improved transitional models was initiated. The focus of this work was concentrated on the critical assessment of a popular existing transitional model developed by McDonald and Fish in 1972. The objective of this effort was to identify the shortcomings of the McDonald-Fish model and to use the insights gained to suggest modifications or alterations of the basic model. In order to evaluate the transitional model, a compressible boundary layer code was required. Accordingly, a two-dimensional compressible boundary layer code was developed. The program was based on a three-point fully implicit finite difference algorithm where the equations were solved in an uncoupled manner with second order extrapolation used to evaluate the non-linear coefficients. Iteration was offered as an option if the extrapolation error could not be tolerated. The differencing scheme was arranged to be second order in both spatial directions on an arbitrarily stretched mesh. A variety of boundary condition options were implemented including specification of an external pressure gradient, specification of a wall temperature distribution, and specification of an external temperature distribution. Overall the results of the initial phase of this work indicate that the McDonald-Fish model does a poor job at predicting the details of the turbulent flow structure during the transition region.
NASA Astrophysics Data System (ADS)
Garcia, Florine; Folton, Nathalie; Oudin, Ludovic; Arnaud, Patrick
2015-04-01
Issues with water resource management result from both an increasing demand and climate changes. The situations of low-flows, droughts and more generally lack of water are critically scrutinized. In this context, there is a need for tools to assist water agencies in the prediction and management of reference low-flows at gauged and ungauged catchment locations. IRSTEA developed GR2M-LoiEau, a conceptual distributed rainfall-runoff model, which is combined with a regionalized model of snow storage and melt. GR2M-LoiEau relies on two parameters which are regionalized and mapped throughout France. This model allows to cartography annual and monthly reference low-flows. The input meteorological data come from the distributed mesoscale atmospheric analysis system SAFRAN, which provides daily solid and liquid precipitations and temperatures data from everywhere in the French territory. In order to fully exploit these daily meteorological data to estimate daily statistics on low flows, a new version of GR2M-LoiEau is being developed at a daily time step, yet keeping only a few regionalized parameters. The aim of this study is to design a comprehensive set of tests to allow comparing low-flows obtained with different regionalization methods used to estimate low-flow model parameters. The new version of GR2M-LoiEau being not yet operational, the tests are made with GR4J (Perrin, 2002), a conceptual rainfall-runoff model, which already provides daily estimations, but involves four parameters that cannot easily be regionalized. Many studies showed the good prediction performances of this model. This work includes two parts. On the one hand, good criteria must be identified to evaluate and compare model results, good predictions of the model being expected about low flows and reference low flows, but also annual means and high flows. On the other hand, two methods of regionalization will have to be compared to estimate model parameters. The first one is rough, all the
Experimental and modeling study of the flow over a skewed bump
NASA Astrophysics Data System (ADS)
Ching, David S.; Elkins, Christopher J.; Eaton, John K.
2016-11-01
Three-dimensional separated flows can be very sensitive to geometry and inlet conditions, such that a small change in the geometry or the upstream boundary layer could cause the flow structure to change drastically. This study examines the geometric sensitivity of a skewed bump with axis ratio 4/3 by changing the angle of the bump with respect to the flow. The three-dimensional, three-component mean velocity field was acquired using Magnetic Resonance Velocimetry (MRV) for several bump angles. The flow is dominated by large coherent vortices in the wake. For a symmetric case, two counter-rotating vortices exist in the wake, but when the bump is skewed relative to the oncoming flow one vortex structure is much stronger and overwhelms the other vortex. A comparison to RANS simulations found that the RANS simulations predict the velocity fields with reasonable accuracy within the separation bubble, but are very inaccurate downstream of reattachment. Using a time-resolved MRV sequence, the shedding frequency of the wake was determined for two bump angles. Hot-wire anemometry confirmed the shedding frequencies found from the MRV data and observed that the shedding frequency is sensitive to the bump angle at low bump angles, but is insensitive at high bump angles. Funding provided by the Office of Naval Research.
Flow stress and material model study at high strain rate and low temperature
NASA Astrophysics Data System (ADS)
Kandasamy, R.; Brar, N. S.
1994-07-01
The flow stress of M200 maraging steel, C1008 steel, and 6061-T6 aluminum at low temperatures to 123 K and at a strain rate of about 103 s-1 is measured using split Hopkinson bar (SHB). Liquid nitrogen is used to cool the specimen to the desired temperature. The flow stress of M200 increased to 1.93 GPa at 123 K, an increase of 22 percent compared to 1.58 GPa at room temperature. In the case of 6061-T6 aluminum the flow stress remains at about 390 MPa at temperatures in the range 293 to 123 K. For C1008 steel, the flow stress increased to 860 MPa at 123 K from its room temperature value of 610 MPa. The failure strain for C1008 steel at 123 K was 0.02, compared to 0.2 at room temperature, suggesting a ductile to brittle transition. The Johnson-Cook material model constant ``m'', which accounts for temperature effect, is 0.5 for C1008 at temperatures in the range 123 K to 950 K.
Y. Wu
2004-11-01
The purpose of this report is to document the unsaturated zone (UZ) flow models and submodels, as well as the flow fields that have been generated using the UZ flow model(s) of Yucca Mountain, Nevada. In this report, the term ''UZ model'' refers to the UZ flow model and the several submodels, which include tracer transport, temperature or ambient geothermal, pneumatic or gas flow, and geochemistry (chloride, calcite, and strontium) submodels. The term UZ flow model refers to the three-dimensional models used for calibration and simulation of UZ flow fields. This work was planned in the ''Technical Work Plan (TWP) for: Unsaturated Zone Flow Analysis and Model Report Integration'' (BSC 2004 [DIRS 169654], Section 1.2.7). The table of included Features, Events, and Processes (FEPs), Table 6.2-11, is different from the list of included FEPs assigned to this report in the ''Technical Work Plan for: Unsaturated Zone Flow Analysis and Model Report Integration'' (BSC 2004 [DIRS 169654], Table 2.1.5-1), as discussed in Section 6.2.6. The UZ model has revised, updated, and enhanced the previous UZ model (BSC 2001 [DIRS 158726]) by incorporating the repository design with new grids, recalibration of property sets, and more comprehensive validation effort. The flow fields describe fracture-fracture, matrix-matrix, and fracture-matrix liquid flow rates, and their spatial distributions as well as moisture conditions in the UZ system. These three-dimensional UZ flow fields are used directly by Total System Performance Assessment (TSPA). The model and submodels evaluate important hydrogeologic processes in the UZ as well as geochemistry and geothermal conditions. These provide the necessary framework to test hypotheses of flow and transport at different scales, and predict flow and transport behavior under a variety of climatic conditions. In addition, the limitations of the UZ model are discussed in Section 8.11.
A comparative study of turbulence models in predicting hypersonic inlet flows
NASA Technical Reports Server (NTRS)
Kapoor, Kamlesh
1993-01-01
A computational study has been conducted to evaluate the performance of various turbulence models. The NASA P8 inlet, which represents cruise condition of a typical hypersonic air-breathing vehicle, was selected as a test case for the study; the PARC2D code, which solves the full two dimensional Reynolds-averaged Navier-Stokes equations, was used. Results are presented for a total of six versions of zero- and two-equation turbulence models. Zero-equation models tested are the Baldwin-Lomax model, the Thomas model, and a combination of the two. Two-equation models tested are low-Reynolds number models (the Chien model and the Speziale model) and a high-Reynolds number model (the Launder and Spalding model).
As part of its continuing development and evaluation, the QUIC model (Quick Urban & Industrial Complex) was used to study flow and dispersion in complex terrain for two cases. First, for a small area of lower Manhattan near the World Trade Center site, comparisons were made bet...
As part of its continuing development and evaluation, the QUIC model (Quick Urban & Industrial Complex) was used to study flow and dispersion in complex terrain for two cases. First, for a small area of lower Manhattan near the World Trade Center site, comparisons were made bet...
MEMS based hair flow-sensors as model systems for acoustic perception studies
NASA Astrophysics Data System (ADS)
Krijnen, Gijs J. M.; Dijkstra, Marcel; van Baar, John J.; Shankar, Siripurapu S.; Kuipers, Winfred J.; de Boer, Rik J. H.; Altpeter, Dominique; Lammerink, Theo S. J.; Wiegerink, Remco
2006-02-01
Arrays of MEMS fabricated flow sensors inspired by the acoustic flow-sensitive hairs found on the cerci of crickets have been designed, fabricated and characterized. The hairs consist of up to 1 mm long SU-8 structures mounted on suspended membranes with normal translational and rotational degrees of freedom. Electrodes on the membrane and on the substrate form variable capacitors, allowing for capacitive read-out. Capacitance versus voltage, frequency dependence and directional sensitivity measurements have been successfully carried out on fabricated sensor arrays, showing the viability of the concept. The sensors form a model system allowing for investigations on sensory acoustics by their arrayed nature, their adaptivity via electrostatic interaction (frequency tuning and parametric amplification) and their susceptibility to noise (stochastic resonance).
MEMS based hair flow-sensors as model systems for acoustic perception studies.
Krijnen, Gijs J M; Dijkstra, Marcel; van Baar, John J; Shankar, Siripurapu S; Kuipers, Winfred J; de Boer, Rik J H; Altpeter, Dominique; Lammerink, Theo S J; Wiegerink, Remco
2006-02-28
Arrays of MEMS fabricated flow sensors inspired by the acoustic flow-sensitive hairs found on the cerci of crickets have been designed, fabricated and characterized. The hairs consist of up to 1 mm long SU-8 structures mounted on suspended membranes with normal translational and rotational degrees of freedom. Electrodes on the membrane and on the substrate form variable capacitors, allowing for capacitive read-out. Capacitance versus voltage, frequency dependence and directional sensitivity measurements have been successfully carried out on fabricated sensor arrays, showing the viability of the concept. The sensors form a model system allowing for investigations on sensory acoustics by their arrayed nature, their adaptivity via electrostatic interaction (frequency tuning and parametric amplification) and their susceptibility to noise (stochastic resonance).
Nicole Lautze
2015-01-01
Groundwater flow model for Kauai. Data is from the following sources: Whittier, R. and A.I. El-Kadi. 2014. Human and Environmental Risk Ranking of Onsite Sewage Disposal Systems For the Hawaiian Islands of Kauai, Molokai, Maui, and Hawaii – Final. Prepared by the University of Hawaii, Dept. of Geology and Geophysics for the State of Hawaii Dept. of Health, Safe Drinking Water Branch. September 2014.; and Whittier, R.B., K. Rotzoll, S. Dhal, A.I. El-Kadi, C. Ray, G. Chen, and D. Chang. 2004. Hawaii Source Water Assessment Program Report – Volume IV – Island of Kauai Source Water Assessment Program Report. Prepared for the Hawaii Department of Health, Safe Drinking Water Branch. University of Hawaii, Water Resources Research Center. Updated 2015.
Visualization study of flow in axial flow inducer.
NASA Technical Reports Server (NTRS)
Lakshminarayana, B.
1972-01-01
A visualization study of the flow through a three ft dia model of a four bladed inducer, which is operated in air at a flow coefficient of 0.065, is reported in this paper. The flow near the blade surfaces, inside the rotating passages, downstream and upstream of the inducer is visualized by means of smoke, tufts, ammonia filament, and lampblack techniques. Flow is found to be highly three dimensional, with appreciable radial velocity throughout the entire passage. The secondary flows observed near the hub and annulus walls agree with qualitative predictions obtained from the inviscid secondary flow theory.
Physical hydrodynamic propulsion model study on creeping viscous flow through a ciliated porous tube
NASA Astrophysics Data System (ADS)
Akbar, Noreen Sher; Butt, Adil Wahid; Tripathi, Dharmendra; Bég, O. Anwar
2017-03-01
The present investigation focusses on a mathematical study of creeping viscous flow induced by metachronal wave propagation in a horizontal ciliated tube containing porous media. Creeping flow limitations are imposed, i.e. inertial forces are small compared to viscous forces and therefore a very low Reynolds number (Re ≪ 1) is taken into account. The wavelength of metachronal wave is also considered to be very large for cilia movement. The physical problem is linearized and exact solutions are developed for the differential equation problem. Mathematica software is used to compute and illustrate numerical results. The influence of slip parameter and Darcy number on velocity profile, pressure gradient and trapping of bolus are discussed with the aid of graphs. It is found that with increasing magnitude of the slip parameter, the trapped bolus inside the streamlines increases in size. The study is relevant to biological propulsion of medical micromachines in drug delivery.
Turbulent flow structure response to a varying wall-roughness arrangement: a modelling study
NASA Astrophysics Data System (ADS)
Jakirlic, Suad; Krumbein, Benjamin; Fooroghi, Pourya; Magagnato, Franco; Frohnapfel, Bettina; Darmstadt Collaboration; Karlsruhe Collaboration
2016-11-01
Presently adopted approach to the modelling of rough surfaces relies on introducing an additional drag term in the appropriately 'filtered' Navier-Stokes equations, accounting for the form drag and blockage effects, the roughness elements exert on the flow. A non-dimensional drag function D(y) accounting for the shape of roughness elements is introduced. It is evaluated by applying a reference DNS of an open channel flow over a wall characterized by varying arrangement (aligned/staggered) of differently-shaped/sized roughness elements at a bulk Reynolds number Re =6500 by Fooroghi et al.. The prime objective of the present work is to assess the roughness model capability to predict mean velocities and turbulent intensities in conjunction with a recently formulated hybrid LES/RANS (Reynolds-Averaged Navier-Stokes) model, based on the Very Large Eddy Simulation (VLES) concept of Speziale. A seamless transition from RANS to LES is enabled depending on the ratio of the turbulent viscosities associated with the unresolved scales corresponding to the LES cut-off and those related to the turbulent properties of the VLES residual motion.
Snijder, Roland A; Konings, Maurits K; Lucas, Peter; Egberts, Toine C; Timmerman, Annemoon D
2015-08-01
Infusion therapy is medically and technically challenging and frequently associated with medical errors. When administering pharmaceuticals by means of infusion, dosing errors can occur due to flow rate variability. These dosing errors may lead to adverse effects. We aimed to systematically review the available biomedical literature for in vitro measurement and modeling studies that investigated the physical causes of flow rate variability. Special focus was given to syringe pump setups, which are typically used if very accurate drug delivery is required. We aimed to extract from literature the component with the highest mechanical compliance in syringe pump setups. We included 53 studies, six of which were theoretical models, two articles were earlier reviews of infusion literature, and 45 were in vitro measurement studies. Mechanical compliance, flow resistance, and dead volume of infusion systems were stated as the most important and frequently identified physical causes of flow rate variability. The syringe was indicated as the most important source of mechanical compliance in syringe pump setups (9.0×10-9 to 2.1×10-8 l/Pa). Mechanical compliance caused longer flow rate start-up times (from several minutes up to approximately 70 min) and delayed occlusion alarm times (up to 117 min).
Flow Environment Study Near the Empennage of a 15-Percent Scale Helicopter Model
NASA Technical Reports Server (NTRS)
Gorton, Susan Althoff; Berry, John D.; Hodges, W. Todd; Reis, Deane G.
2000-01-01
Development of advanced rotorcraft configurations has highlighted a need for high-quality experimental data to support the development of flexible and accurate analytical design tools. To provide this type of data, a test program was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to measure the flow near the empennage of a 15-percent scale powered helicopter model with an operating tail fan. Three-component velocity profiles were measured with laser velocimetry (LV) one chord forward of the horizontal tail for four advance ratios to evaluate the effect of the rotor wake impingement on the horizontal tail angle of attack. These velocity data indicate the horizontal tail can experience unsteady angle of attack variations of over 30 degrees due to the rotor wake influence. The horizontal tail is most affected by the rotor wake above advance ratios of 0.10. Velocity measurements of the flow on the inlet side of the tail fan were made for a low-speed flight condition using conventional LV techniques. The velocity data show an accelerated flow near the tail fan duct, and vorticity calculations track the passage of main rotor wake vortices through the measurement plane.
NASA Astrophysics Data System (ADS)
Shiau, C.; Lee, C.
2004-12-01
Taiwan is a narrow island. Due to the movement of the plate tectonics, the mountain ranges are almost in N - S direction. On the island, there are a lot of mountains, but few plains. Because of the rapid development on economies, the plains are nearly used-up. So people are trying to develop the mountainous land. However, when the typhoon, heavy rain, or earthquake occurred, there triggers the catastrophic events, such as the landslide and debris flow. Among these catastrophes, the debris flow is the most horrified and it happens frequently year after year. Thus, how to prevent the debris flow and pass this information to warn the local residents becomes an urgent matter. The most reliable method to identify the hazardous debris flow is to investigate in the field. Because the change of the factors, the debris flow may happen. So it will need a long-term monitoring system. The requirement of the manpower and financial resources will increase significantly. Although there are much studies on applying the GIS to the debris flow problem, but it¡¦s still difficult to become a practical tool due to the data gathering and law limitation. If a fast-accurate and self-recognized computer model is available, this will save the time and efforts. In this study of debris flow by using the neutral network and digital terrain model, we select the Chen-Yu-Lan River in Nantou (middle of Taiwan) as an area for study. The debris flow caused in 2001 right after the TORAJI typhoon. Using the GIS software, the MapInfo, which is much simple to get the numerical data from digital terrain model. We have firstly used the 15 factors to start the training. We obtain a successful ratio of about 88%. There are some areas can¡¦t be explained. We believed it is caused by the other factors of debris flow that weren't included. The geoscientific factors are important. However, because of the resolution of present-available geological data don't reach the standard of this study. Therefore, they
Agarwal, Sheetal; Swami, Bajrang L; Gupta, Akhilendra Bhushan
2009-01-01
The objective of this study is to develop an empirical noise prediction model for the evaluation of equivalent noise levels (Leq) under interrupted traffic flow conditions. A new factor tendency to blow horn (AH) was introduced in the conventional federal highway administrative noise prediction (FHWA) model and a comparative study was made between FHWA and modified FHWA models to evaluate the best suitability of the model. Monitoring and modeling of Leq were carried out at four selected intersections of Jaipur city. After comparison of the results, it was found that the modified FHWA model could be satisfactorily applied for Indian conditions as it gives acceptable results with a deviation of +/-3 dB (A). In addition, statistical analysis of the data comprising measured and estimated values shows a good agreement. Hence, the modified FHWA traffic noise prediction model can be applied to the cities having similar traffic conditions as in Jaipur city.
P. Dixon
2004-02-11
The purpose of this Model Report is to document the unsaturated zone (UZ) fluid flow and tracer transport models and submodels as well as the flow fields generated utilizing the UZ Flow and Transport Model of Yucca Mountain (UZ Model), Nevada. This work was planned in ''Technical Work Plan (TWP) for: Performance Assessment Unsaturated Zone'' (BSC 2002 [160819], Section 1.10, Work Package AUZM06). The UZ Model has revised, updated, and enhanced the previous UZ Flow Model REV 00 ICN 01 (BSC 2001 [158726]) by incorporation of the conceptual repository design with new grids, recalibration of property sets, and more comprehensive validation effort. The flow fields describe fracture-fracture, matrix-matrix, and fracture-matrix liquid flow rates and their spatial distributions as well as moisture conditions in the UZ system. These 3-D UZ flow fields are used directly by Performance Assessment (PA). The model and submodels evaluate important hydrogeologic processes in the UZ as well as geochemistry and geothermal conditions. These provide the necessary framework to test conceptual hypotheses of flow and transport at different scales and predict flow and transport behavior under a variety of climatic conditions. In addition, this Model Report supports several PA activities, including abstractions, particle-tracking transport simulations, and the UZ Radionuclide Transport Model.
Modeling studies of electrolyte flow and bubble behavior in advanced Hall cells
NASA Astrophysics Data System (ADS)
Shekhar, R.; Evans, J. W.
Much research was performed in recent years by corporations and university/government labs on materials for use in advanced Hall-Heroult cells. Attention has focussed on materials for use as wettable cathodes and inert anodes and much was achieved in terms of material development. Comparatively less attention was devoted to how these materials might be incorporated in new or existing cells, i.e., to how the cells should be designed and redesigned, to take full advantage of these materials. The effort, supported by the U.S. Department of Energy, to address this issue, is described. The primary objectives are cell design where electrolyte flow can be managed to promote both the removal of the anode gas bubbles and the convection of dissolved alumina in the inter-electrode region, under conditions where the anode-cathode distance is small. The principal experimental tool was a water model consisting of a large tank in which simulated anodes can be suspended in either the horizontal or vertical configurations. Gas generation was by forcing compressed air through porous graphite and the fine bubbles characteristic of inert anodes were produced by adding butanol to the water. Velocities were measured using a laser Doppler velocimeter. Velocity measurements with two different anode designs (one that is flat and the other that has grooves) are presented. The results show that the electrode configuration has a significant effect on the fluid flow pattern in the inter-electrode region. Furthermore, it is shown that rapid fluid flow is obtained when the cell is operated with a submerged anode.
NASA Technical Reports Server (NTRS)
Rumsey, Christopher L.; Greenblatt, David
2007-01-01
This is an expanded version of a limited-length paper that appeared at the 5th International Symposium on Turbulence and Shear Flow Phenomena by the same authors. A computational study was performed for steady and oscillatory flow control over a hump model with flow separation to assess how well the steady and unsteady Reynolds-averaged Navier-Stokes equations predict trends due to Reynolds number, control magnitude, and control frequency. As demonstrated in earlier studies, the hump model case is useful because it clearly demonstrates a failing in all known turbulence models: they under-predict the turbulent shear stress in the separated region and consequently reattachment occurs too far downstream. In spite of this known failing, three different turbulence models were employed to determine if trends can be captured even though absolute levels are not. Overall the three turbulence models showed very similar trends as experiment for steady suction, but only agreed qualitatively with some of the trends for oscillatory control.
NASA Astrophysics Data System (ADS)
Sjöberg, Ylva; Coon, Ethan; Sannel, A. Britta K.; Pannetier, Romain; Harp, Dylan; Frampton, Andrew; Painter, Scott L.; Lyon, Steve W.
2016-03-01
Modeling and observation of ground temperature dynamics are the main tools for understanding current permafrost thermal regimes and projecting future thaw. Until recently, most studies on permafrost have focused on vertical ground heat fluxes. Groundwater can transport heat in both lateral and vertical directions but its influence on ground temperatures at local scales in permafrost environments is not well understood. In this study we combine field observations from a subarctic fen in the sporadic permafrost zone with numerical simulations of coupled water and thermal fluxes. At the Tavvavuoma study site in northern Sweden, ground temperature profiles and groundwater levels were observed in boreholes. These observations were used to set up one- and two-dimensional simulations down to 2 m depth across a gradient of permafrost conditions within and surrounding the fen. Two-dimensional scenarios representing the fen under various hydraulic gradients were developed to quantify the influence of groundwater flow on ground temperature. Our observations suggest that lateral groundwater flow significantly affects ground temperatures. This is corroborated by modeling results that show seasonal ground ice melts 1 month earlier when a lateral groundwater flux is present. Further, although the thermal regime may be dominated by vertically conducted heat fluxes during most of the year, isolated high groundwater flow rate events such as the spring freshet are potentially important for ground temperatures. As sporadic permafrost environments often contain substantial portions of unfrozen ground with active groundwater flow paths, knowledge of this heat transport mechanism is important for understanding permafrost dynamics in these environments.
Manganin Gauge and Reactive Flow Modeling Study of the Shock Initiation of PBX 9501
Tarver, C M; Forbes, J W; Garcia, F; Urtiew, P A
2001-06-05
A series of 101mm diameter gas gun experiments was fired using manganin pressure gauges embedded in the HMX-based explosive PBX 9501 at initial temperatures of 20 C and 50 C. Flyer plate impact velocities were chosen to produce impact pressure levels in PBX 9501 at which the growth of explosive reaction preceding detonation was measured on most of the gauges and detonation pressure profiles were recorded on some of the gauges placed deepest into the explosive targets. All measured pressure histories for initial temperatures of 25 C and 50 C were essentially identical. Measured run distances to detonation at several input shock pressures agreed with previous results. An existing ignition and growth reactive flow computer model for shock initiation and detonation of PBX 9501, which was developed based on LANL embedded particle velocity gauge data, was tested on these pressure gauge results. The agreement was excellent, indicating that the embedded pressure and particle velocity gauge techniques yielded consistent results.
Modeling of Turbulent Swirling Flows
NASA Technical Reports Server (NTRS)
Shih, Tsan-Hsing; Zhu, Jiang; Liou, William; Chen, Kuo-Huey; Liu, Nan-Suey; Lumley, John L.
1997-01-01
Aircraft engine combustors generally involve turbulent swirling flows in order to enhance fuel-air mixing and flame stabilization. It has long been recognized that eddy viscosity turbulence models are unable to appropriately model swirling flows. Therefore, it has been suggested that, for the modeling of these flows, a second order closure scheme should be considered because of its ability in the modeling of rotational and curvature effects. However, this scheme will require solution of many complicated second moment transport equations (six Reynolds stresses plus other scalar fluxes and variances), which is a difficult task for any CFD implementations. Also, this scheme will require a large amount of computer resources for a general combustor swirling flow. This report is devoted to the development of a cubic Reynolds stress-strain model for turbulent swirling flows, and was inspired by the work of Launder's group at UMIST. Using this type of model, one only needs to solve two turbulence equations, one for the turbulent kinetic energy k and the other for the dissipation rate epsilon. The cubic model developed in this report is based on a general Reynolds stress-strain relationship. Two flows have been chosen for model evaluation. One is a fully developed rotating pipe flow, and the other is a more complex flow with swirl and recirculation.
Sjöberg, Ylva; Coon, Ethan; K. Sannel, A. Britta; Pannetier, Romain; Harp, Dylan; Frampton, Andrew; Painter, Scott L.; Lyon, Steve W.
2016-02-05
Modeling and observation of ground temperature dynamics are the main tools for understanding current permafrost thermal regimes and projecting future thaw. Until recently, most studies on permafrost have focused on vertical ground heat fluxes. Groundwater can transport heat in both lateral and vertical directions but its influence on ground temperatures at local scales in permafrost environments is not well understood. In this paper, we combine field observations from a subarctic fen in the sporadic permafrost zone with numerical simulations of coupled water and thermal fluxes. At the Tavvavuoma study site in northern Sweden, ground temperature profiles and groundwater levels were observed in boreholes. These observations were used to set up one- and two-dimensional simulations down to 2 m depth across a gradient of permafrost conditions within and surrounding the fen. Two-dimensional scenarios representing the fen under various hydraulic gradients were developed to quantify the influence of groundwater flow on ground temperature. Our observations suggest that lateral groundwater flow significantly affects ground temperatures. This is corroborated by modeling results that show seasonal ground ice melts 1 month earlier when a lateral groundwater flux is present. Further, although the thermal regime may be dominated by vertically conducted heat fluxes during most of the year, isolated high groundwater flow rate events such as the spring freshet are potentially important for ground temperatures. Finally, as sporadic permafrost environments often contain substantial portions of unfrozen ground with active groundwater flow paths, knowledge of this heat transport mechanism is important for understanding permafrost dynamics in these environments.
Experimental Study of a Reference Model Vertical-Axis Cross-Flow Turbine
Wosnik, Martin; Gunawan, Budi; Neary, Vincent S.
2016-01-01
The mechanical power, total rotor drag, and near-wake velocity of a 1:6 scale model (1.075 m diameter) of the US Department of Energy’s Reference Model vertical-axis cross-flow turbine were measured experimentally in a towing tank, to provide a comprehensive open dataset for validating numerical models. Performance was measured for a range of tip speed ratios and at multiple Reynolds numbers by varying the rotor’s angular velocity and tow carriage speed, respectively. A peak power coefficient CP = 0.37 and rotor drag coefficient CD = 0.84 were observed at a tip speed ratio λ0 = 3.1. A regime of weak linear Re-dependence of the power coefficient was observed above a turbine diameter Reynolds number ReD ≈ 106. The effects of support strut drag on turbine performance were investigated by covering the rotor’s NACA 0021 struts with cylinders. As expected, this modification drastically reduced the rotor power coefficient. Strut drag losses were also measured for the NACA 0021 and cylindrical configurations with the rotor blades removed. For λ = λ0, wake velocity was measured at 1 m (x/D = 0.93) downstream. Mean velocity, turbulence kinetic energy, and mean kinetic energy transport were compared with results from a high solidity turbine acquired with the same test apparatus. Like the high solidity case, mean vertical advection was calculated to be the largest contributor to near-wake recovery. However, overall, lower levels of streamwise wake recovery were calculated for the RM2 case—a consequence of both the relatively low solidity and tapered blades reducing blade tip vortex shedding—responsible for mean vertical advection—and lower levels of turbulence caused by higher operating tip speed ratio and therefore reduced dynamic stall. Datasets, code for processing and visualization, and a CAD model of the turbine have been made publicly available. PMID:27684076
Experimental Study of a Reference Model Vertical-Axis Cross-Flow Turbine.
Bachant, Peter; Wosnik, Martin; Gunawan, Budi; Neary, Vincent S
The mechanical power, total rotor drag, and near-wake velocity of a 1:6 scale model (1.075 m diameter) of the US Department of Energy's Reference Model vertical-axis cross-flow turbine were measured experimentally in a towing tank, to provide a comprehensive open dataset for validating numerical models. Performance was measured for a range of tip speed ratios and at multiple Reynolds numbers by varying the rotor's angular velocity and tow carriage speed, respectively. A peak power coefficient CP = 0.37 and rotor drag coefficient CD = 0.84 were observed at a tip speed ratio λ0 = 3.1. A regime of weak linear Re-dependence of the power coefficient was observed above a turbine diameter Reynolds number ReD ≈ 106. The effects of support strut drag on turbine performance were investigated by covering the rotor's NACA 0021 struts with cylinders. As expected, this modification drastically reduced the rotor power coefficient. Strut drag losses were also measured for the NACA 0021 and cylindrical configurations with the rotor blades removed. For λ = λ0, wake velocity was measured at 1 m (x/D = 0.93) downstream. Mean velocity, turbulence kinetic energy, and mean kinetic energy transport were compared with results from a high solidity turbine acquired with the same test apparatus. Like the high solidity case, mean vertical advection was calculated to be the largest contributor to near-wake recovery. However, overall, lower levels of streamwise wake recovery were calculated for the RM2 case-a consequence of both the relatively low solidity and tapered blades reducing blade tip vortex shedding-responsible for mean vertical advection-and lower levels of turbulence caused by higher operating tip speed ratio and therefore reduced dynamic stall. Datasets, code for processing and visualization, and a CAD model of the turbine have been made publicly available.
NASA Astrophysics Data System (ADS)
Seshadri, Kalyanasundaram; Frassoldati, Alessio; Cuoci, Alberto; Faravelli, Tiziano; Niemann, Ulrich; Weydert, Patrick; Ranzi, Eliseo
2011-08-01
Experimental and kinetic modeling studies are carried out to characterize premixed combustion of jet fuels, their surrogates, and reference components in laminar nonuniform flows. In previous studies, it was established that the Aachen surrogate made up of 80 % n-decane and 20 % trimethylbenzene by weight, and surrogate C made up of 57 % n-dodecane, 21 % methylcyclohexane and 22 % o-xylene by weight, reproduce key aspects of combustion of jet fuels in laminar nonpremixed flows. Here, these surrogates and a jet fuel are tested in premixed, nonuniform flows. The counterflow configuration is employed, and critical conditions of extinction are measured. In addition, the reference components tested are n-heptane, n-decane, n-dodecane, methylcyclohexane, trimethylbenzene, and o-xylene. Measured critical conditions of extinction of the Aachen surrogate and surrogate C are compared with those for the jet fuel. In general the alkanes n-heptane, n-decane, and n-dodecane, and methylcyclohexane are found to be more reactive than the aromatics o-xylene and trimethylbenzene. Flame structure and critical conditions of extinction are predicted for the reference components and the surrogates using a semi-detailed kinetic model. The predicted values are compared with experimental data. Sensitivity analysis shows that the lower reactivity of the aromatic species arises from the formation of resonantly stabilized radicals. These radicals are found to have a scavenging effect. The present study on premixed flows together with previous studies on nonpremixed flows show that the Aachen surrogate and surrogate C reproduce many aspects of premixed and nonpremixed combustion of jet fuels.
NASA Astrophysics Data System (ADS)
Zhou, J. X.; Shen, X.; Yin, Y. J.; Guo, Z.; Wang, H.
2015-06-01
In this paper, Gas-liquid two phase flow mathematic models of incompressible fluid were proposed to explore the feature of fluid under certain centrifugal force in vertical centrifugal casting (VCC). Modified projection-level-set method was introduced to solve the mathematic models. To validate the simulation results, two methods were used in this study. In the first method, the simulation result of basic VCC flow process was compared with its analytic solution. The relationship between the numerical solution and deterministic analytic solution was presented to verify the correctness of numerical algorithms. In the second method, systematic water simulation experiments were developed. In this initial experiment, special experimental vertical centrifugal device and casting shapes were designed to describe typical mold-filling processes in VCC. High speed camera system and data collection devices were used to capture flow shape during the mold-filling process. Moreover, fluid characteristic at different rotation speed (from 40rpm, 60rpmand 80rpm) was discussed to provide comparative resource for simulation results. As compared with the simulation results, the proposed mathematical models could be proven and the experimental design could help us advance the accuracy of simulation and further studies for VCC.
Fluid Transport in Porous Rocks. I. EPI Studies and a Stochastic Model of Flow
NASA Astrophysics Data System (ADS)
Mansfield, P.; Issa, B.
The velocity of water flowing through a Bentheimer sandstone core has been measured by NMR-imaging techniques. The localized pixel values of velocity indicate a random distribution centered around the mean value corresponding to Darcy's law. When the same flow state is repeated, the velocity map changes but the general characteristics of the velocity distribution remain unchanged. The random nature of the irreproducibility of the flow maps has led us to propose a stochastic theory of flow in porous rocks. The theory leads to a Gaussian velocity distribution which approximates well to the data. Also predicted is a linear relationship between flow variance and mean fluid flow through the rock, the Mansfield-Issa equation, originally proposed as an empirical relationship.
Manganin Gauge and Reactive Flow Modeling Study of the Shock Initiation of PBX 9501
NASA Astrophysics Data System (ADS)
Tarver, C. M.; Forbes, J. W.; Garcia, F.; Urtiew, P. A.
2002-07-01
A series of 101mm diameter gas gun experiments was fired using manganin pressure gauges embedded in the HMX-based explosive PBX 9501 at initial temperatures of 20degC and 50degC. Flyer plate impact velocities were chosen to produce impact pressure levels in PBX 9501 at which the growth of explosive reaction preceding detonation was measured on most of the gauges and detonation pressure profiles were recorded on some of the gauges placed deepest into the explosive targets. All measured pressure histories for initial temperatures of 25degC and 50degC were essentially identical. Measured run distances to detonation at three input shock pressures agreed with previous results. An existing Ignition and Growth reactive flow computer model for shock initiation and detonation of PBX 9501, which was developed based on LANL embedded particle velocity gauge data, was tested on these pressure gauge results. The agreement was excellent, indicating that the embedded pressure and particle velocity gauge techniques yielded consistent results.
NASA Astrophysics Data System (ADS)
Punjabi, Sangeeta B.; Sahasrabudhe, S. N.; Joshi, N. K.; Mangalvedekar, H. A.; Das, A. K.; Kothari, D. C.
2014-01-01
This paper provides 2D comparative study of results obtained using laminar and turbulent flow model for RF (radio frequency) Inductively Coupled Plasma (ICP) torch. The study was done for the RF-ICP torch operating at 50 kW DC power and 3 MHz frequency located at BARC. The numerical modeling for this RF-ICP torch is done using ANSYS software with the developed User Defined Function. A comparative study is done between laminar and turbulent flow model to investigate how temperature and flow fields change when using different operating conditions such as (a) swirl and no swirl velocity for sheath gas flow rate, (b) variation in sheath gas flow rate, and (c) variation in plasma gas flow rate. These studies will be useful for different material processing applications.
Modeling Size Polydisperse Granular Flows
NASA Astrophysics Data System (ADS)
Lueptow, Richard M.; Schlick, Conor P.; Isner, Austin B.; Umbanhowar, Paul B.; Ottino, Julio M.
2014-11-01
Modeling size segregation of granular materials has important applications in many industrial processes and geophysical phenomena. We have developed a continuum model for granular multi- and polydisperse size segregation based on flow kinematics, which we obtain from discrete element method (DEM) simulations. The segregation depends on dimensionless control parameters that are functions of flow rate, particle sizes, collisional diffusion coefficient, shear rate, and flowing layer depth. To test the theoretical approach, we model segregation in tri-disperse quasi-2D heap flow and log-normally distributed polydisperse quasi-2D chute flow. In both cases, the segregated particle size distributions match results from full-scale DEM simulations and experiments. While the theory was applied to size segregation in steady quasi-2D flows here, the approach can be readily generalized to include additional drivers of segregation such as density and shape as well as other geometries where the flow field can be characterized including rotating tumbler flow and three-dimensional bounded heap flow. Funded by The Dow Chemical Company and NSF Grant CMMI-1000469.
Pel, Johan J M; van Mastrigt, Ron
2007-01-01
A novel, non-invasive method to diagnose bladder outlet obstruction involves the recording of noise with a contact microphone pressed against the perineum (between anus and scrotum). This noise results from flow-generated vortices caused by prostatic obstruction. We developed a computational fluid dynamic (CFD) urethral model including urethral geometry to study the relation between generated noise and the degree of obstruction. This model comprised a bladder, bladder neck, prostate and urethra. Calculations were carried out at four bladder pressures, five degrees of obstruction and three obstruction shapes. For each of the sixty simulations, the velocity and pressure distributions along the urethra were calculated including wall shear stresses to localize flow transition from disturbed to normal. Negative pressures at the obstruction outlet induced recirculation of flow. The location of transition was independent of the applied bladder pressure, but it depended primarily on the degree and secondarily on the shape of the obstruction. Based on the presented results, we hypothesize that the location of the maximum amplitude of perineal noise mainly depends on the degree and shape of the prostatic obstruction. Our future aim is to test our hypothesis in male patients and to extend the presented model to 3D with a viscoelastic urethral wall to calculate the fluid-wall interaction.
HYDROGEN ELECTROLYZER FLOW DISTRIBUTOR MODEL
Shadday, M
2006-09-28
The hybrid sulfur process (HyS) hydrogen electrolyzer consists of a proton exchange membrane (PEM) sandwiched between two porous graphite layers. An aqueous solution of sulfuric acid with dissolved SO{sub 2} gas flows parallel to the PEM through the porous graphite layer on the anode side of the electrolyzer. A flow distributor, consisting of a number of parallel channels acting as headers, promotes uniform flow of the anolyte fluid through the porous graphite layer. A numerical model of the hydraulic behavior of the flow distributor is herein described. This model was developed to be a tool to aid the design of flow distributors. The primary design objective is to minimize spatial variations in the flow through the porous graphite layer. The hydraulic data from electrolyzer tests consists of overall flowrate and pressure drop. Internal pressure and flow distributions are not measured, but these details are provided by the model. The model has been benchmarked against data from tests of the current electrolyzer. The model reasonably predicts the viscosity effect of changing the fluid from water to an aqueous solution of 30 % sulfuric acid. The permeability of the graphite layer was the independent variable used to fit the model to the test data, and the required permeability for a good fit is within the range literature values for carbon paper. The model predicts that reducing the number of parallel channels by 50 % will substantially improve the uniformity of the flow in the porous graphite layer, while maintaining an acceptable pressure drop across the electrolyzer. When the size of the electrolyzer is doubled from 2.75 inches square to 5.5 inches square, the same number of channels as in the current design will be adequate, but it is advisable to increase the channel cross-sectional flow area. This is due to the increased length of the channels.
Groundwater flow and transport modeling
Konikow, L.F.; Mercer, J.W.
1988-01-01
Deterministic, distributed-parameter, numerical simulation models for analyzing groundwater flow and transport problems have come to be used almost routinely during the past decade. A review of the theoretical basis and practical use of groundwater flow and solute transport models is used to illustrate the state-of-the-art. Because of errors and uncertainty in defining model parameters, models must be calibrated to obtain a best estimate of the parameters. For flow modeling, data generally are sufficient to allow calibration. For solute-transport modeling, lack of data not only limits calibration, but also causes uncertainty in process description. Where data are available, model reliability should be assessed on the basis of sensitivity tests and measures of goodness-of-fit. Some of these concepts are demonstrated by using two case histories. ?? 1988.
Pulsatile Flow Studies in Atherosclerotic Carotid Bifurcation
NASA Astrophysics Data System (ADS)
Bale-Glickman, Jocelyn; Selby, Kathy; Saloner, David; Savas, Omer
2002-11-01
Particle image velocimetry and flow visualization techniques are used to study flow in models of atherosclerotic carotid bifurcations. The models exactly replicate the interior geometry of plaque excised from patients. The input flow is a physiological waveform derived from Doppler Ultrasound scans done on the patients before surgery. The systolic and diastolic Reynolds numbers are 200 and 900 respectively. The complex internal geometry of the diseased artery combined with the pulsatile input flows give exceedingly complex flow patterns. These flow patterns include internal jets, three-dimensional shear layers, stagnation lines, and multiple recirculation and separation regions. Ensemble averaged and instantaneous flow fields are compared. Wall shear stresses at the stenoses are estimated to be on the order of 10 PA. The physiological input flows are also compared to flows when the waveform is sinusoidal.
Traum, Jonathan A.; Phillips, Steven P.; Bennett, George Luther; Zamora, Celia; Metzger, Loren F.
2014-01-01
To better understand the potential effects of restoration flows on existing drainage problems, anticipated as a result of the San Joaquin River Restoration Program (SJRRP), the U.S. Geological Survey (USGS), in cooperation with the U.S. Bureau of Reclamation (Reclamation), developed a groundwater flow model (SJRRPGW) of the SJRRP study area that is within 5 miles of the San Joaquin River and adjacent bypass system from Friant Dam to the Merced River. The primary goal of the SJRRP is to reestablish the natural ecology of the river to a degree that restores salmon and other fish populations. Increased flows in the river, particularly during the spring salmon run, are a key component of the restoration effort. A potential consequence of these increased river flows is the exacerbation of existing irrigation drainage problems along a section of the river between Mendota and the confluence with the Merced River. Historically, this reach typically was underlain by a water table within 10 feet of the land surface, thus requiring careful irrigation management and (or) artificial drainage to maintain crop health. The SJRRPGW is designed to meet the short-term needs of the SJRRP; future versions of the model may incorporate potential enhancements, several of which are identified in this report. The SJRRPGW was constructed using the USGS groundwater flow model MODFLOW and was built on the framework of the USGS Central Valley Hydrologic Model (CVHM) within which the SJRRPGW model domain is embedded. The Farm Process (FMP2) was used to simulate the supply and demand components of irrigated agriculture. The Streamflow-Routing Package (SFR2) was used to simulate the streams and bypasses and their interaction with the aquifer system. The 1,300-square mile study area was subdivided into 0.25-mile by 0.25-mile cells. The sediment texture of the aquifer system, which was used to distribute hydraulic properties by model cell, was refined from that used in the CVHM to better represent
A numerical study of non-equilibrium flows with different vibrational relaxation models
NASA Astrophysics Data System (ADS)
Petrov, N. V.; Kirilovskiy, S. V.; Poplavskaya, T. V.; Shoev, G. V.
2016-07-01
Comparative analysis of a widely used Landau-Teller formula for small deviations from thermal equilibrium and its generalized form, derived from the kinetic theory of gaseous, for an arbitrary deviation from the thermal equilibrium is performed by numerical simulation. Thermally non-equilibrium flows of carbon dioxide near a sharp-edged plate, pure nitrogen flows between two symmetrically located wedges, and the N2/N mixture flow with vibrational relaxation and dissociation over a cone have been considered. A comparison has been performed with the available experimental data.
Kinetic model for dilute traffic flow
NASA Astrophysics Data System (ADS)
Balouchi, Ashkan; Browne, Dana A.
The flow of traffic represents a many-particle non-equilibrium problem with important practical consequences. Traffic behavior has been studied using a variety of approaches, including fluid dynamics models, Boltzmann equation, and recently cellular automata (CA). The CA model for traffic flow that Nagel and Schreckenberg (NS) introduced can successfully mimic many of the known features of the traffic flow. We show that in the dilute limit of the NS model, where vehicles exhibit free flow, cars show significant nearest neighbor correlation primarily via a short-range repulsion. introduce an approximate analytic model to describe this dilute limit. We show that the distribution of the distance between consecutive vehicles obeys a drift-diffusion equation. We compared this model with direct simulations. The steady state solution and relaxation of this model agrees well with direct simulations. We explore how this model breaks down as the transition to jams occurs.
Seshadri, K; Lu, T; Herbinet, O; Humer, S; Niemann, U; Pitz, W J; Law, C K
2008-01-09
Methyl decanoate is a large methyl ester that can be used as a surrogate for biodiesel. In this experimental and computational study, the combustion of methyl decanoate is investigated in nonpremixed, nonuniform flows. Experiments are performed employing the counterflow configuration with a fuel stream made up of vaporized methyl decanoate and nitrogen, and an oxidizer stream of air. The mass fraction of fuel in the fuel stream is measured as a function of the strain rate at extinction, and critical conditions of ignition are measured in terms of the temperature of the oxidizer stream as a function of the strain rate. It is not possible to use a fully detailed mechanism for methyl decanoate to simulate the counterflow flames because the number of species and reactions is too large to employ with current flame codes and computer resources. Therefore a skeletal mechanism was deduced from a detailed mechanism of 8555 elementary reactions and 3036 species using 'directed relation graph' method. This skeletal mechanism has only 713 elementary reactions and 125 species. Critical conditions of ignition were calculated using this skeletal mechanism and are found to agree well with experimental data. The predicted strain rate at extinction is found to be lower than the measurements. In general, the methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.
NASA Astrophysics Data System (ADS)
Shang, Xuekun; He, An; Wang, Yanli; Yang, Xiaoya; Zhang, Hailong; Wang, Xitao
2015-10-01
The present study focuses on comparison of accuracy of Johnson-Cook, modified Johnson-Cook, and modified Zerilli-Armstrong constitutive models to predict flow behavior of a nitrogen-alloyed ultralow carbon stainless steel at evaluated temperature. True strain-true stress data obtained from hot compression experiments performed with temperatures of 1223-1423 K and strain rates of 0.001-10 s-1 on a Gleeble-3500 thermal-simulator were employed to develop these three models. Furthermore, the ability of the three models to predict the outcomes was evaluated by comparing the correlation coefficient, absolute average related error, ability to track the experimental flow stress, numbers of material constants, and computational time required to develop models. The results show that the modified Johnson-Cook has a better description of the flow behaviors of the studied steel than the other two models. However, under certain conditions, the modified Zerilli-Armstrong model has accuracy comparable to the modified Johnson-Cook model.
Modelling Canopy Flows over Complex Terrain
NASA Astrophysics Data System (ADS)
Grant, Eleanor R.; Ross, Andrew N.; Gardiner, Barry A.
2016-12-01
Recent studies of flow over forested hills have been motivated by a number of important applications including understanding CO_2 and other gaseous fluxes over forests in complex terrain, predicting wind damage to trees, and modelling wind energy potential at forested sites. Current modelling studies have focussed almost exclusively on highly idealized, and usually fully forested, hills. Here, we present model results for a site on the Isle of Arran, Scotland with complex terrain and heterogeneous forest canopy. The model uses an explicit representation of the canopy and a 1.5-order turbulence closure for flow within and above the canopy. The validity of the closure scheme is assessed using turbulence data from a field experiment before comparing predictions of the full model with field observations. For near-neutral stability, the results compare well with the observations, showing that such a relatively simple canopy model can accurately reproduce the flow patterns observed over complex terrain and realistic, variable forest cover, while at the same time remaining computationally feasible for real case studies. The model allows closer examination of the flow separation observed over complex forested terrain. Comparisons with model simulations using a roughness length parametrization show significant differences, particularly with respect to flow separation, highlighting the need to explicitly model the forest canopy if detailed predictions of near-surface flow around forests are required.
Sjöberg, Ylva; Coon, Ethan; K. Sannel, A. Britta; ...
2016-02-05
Modeling and observation of ground temperature dynamics are the main tools for understanding current permafrost thermal regimes and projecting future thaw. Until recently, most studies on permafrost have focused on vertical ground heat fluxes. Groundwater can transport heat in both lateral and vertical directions but its influence on ground temperatures at local scales in permafrost environments is not well understood. In this paper, we combine field observations from a subarctic fen in the sporadic permafrost zone with numerical simulations of coupled water and thermal fluxes. At the Tavvavuoma study site in northern Sweden, ground temperature profiles and groundwater levels weremore » observed in boreholes. These observations were used to set up one- and two-dimensional simulations down to 2 m depth across a gradient of permafrost conditions within and surrounding the fen. Two-dimensional scenarios representing the fen under various hydraulic gradients were developed to quantify the influence of groundwater flow on ground temperature. Our observations suggest that lateral groundwater flow significantly affects ground temperatures. This is corroborated by modeling results that show seasonal ground ice melts 1 month earlier when a lateral groundwater flux is present. Further, although the thermal regime may be dominated by vertically conducted heat fluxes during most of the year, isolated high groundwater flow rate events such as the spring freshet are potentially important for ground temperatures. Finally, as sporadic permafrost environments often contain substantial portions of unfrozen ground with active groundwater flow paths, knowledge of this heat transport mechanism is important for understanding permafrost dynamics in these environments.« less
FlowSim/FlowRisk: A code system for studying risk associated with material process flows
Kaufman, A.M.
1993-10-01
The need to study and assess life-cycle risks of Pu release by nuclear warheads during peace time lead to the development of a code suite which could model day to day operations involving nuclear weapons and calculate the associated risk involved in these proceedings. The life-cycle study called LIONSHARE is described in Reference 1. The code that models the flow is called FlowSim. The code that evaluates the associated risk is called FlowRisk. We shall concentrate here on the methodology used by FlowSim in modeling material flows. FlowRisk, mainly a postprocessor of FlowSim runs, will be dealt with in less detail.
NASA Astrophysics Data System (ADS)
Hu, Litang; Jiao, Jiu Jimmy
2015-11-01
Traditional numerical models usually use extensive observed hydraulic-head data as calibration targets. However, this calibration process is not applicable in remote areas with limited or no monitoring data. This study presents an approach to calibrate a large-scale groundwater flow model using the monthly Gravity Recovery and Climate Experiment (GRACE) satellite data, which have been available globally on a spatial grid of 1° in the geographic coordinate system since 2002. A groundwater storage anomaly isolated from the terrestrial water storage (TWS) anomaly is converted into hydraulic head at the center of the grid, which is then used as observed data to calibrate a numerical model to estimate aquifer hydraulic conductivity. The aquifer system in the remote and hyperarid Qaidam Basin, China, is used as a case study to demonstrate the applicability of this approach. A groundwater model using FEFLOW is constructed for the Qaidam Basin and the GRACE-derived groundwater storage anomaly over the period 2003-2012 is included to calibrate the model, which is done using an automatic estimation method (PEST). The calibrated model is then run to output hydraulic heads at three sites where long-term hydraulic head data are available. The reasonably good fit between the calculated and observed hydraulic heads, together with the very similar groundwater storage anomalies from the numerical model and GRACE data, demonstrate that this approach is generally applicable in regions of groundwater data scarcity.
Evju, Øyvind; Valen-Sendstad, Kristian; Mardal, Kent-André
2013-11-15
Recent computational fluid dynamics (CFD) studies relate abnormal blood flow to rupture of cerebral aneurysms. However, it is still debated how to model blood flow with sufficient accuracy. Common assumptions made include Newtonian behaviour of blood, traction free outlet boundary conditions and inlet boundary conditions based on available literature. These assumptions are often required since the available patient specific data is usually restricted to the geometry of the aneurysm and the surrounding vasculature. However, the consequences of these assumptions have so far been inadequately addressed. This study investigates the effects of 4 different viscosity models, 2 different inflow conditions and 2 different outflow conditions in 12 middle cerebral artery aneurysms. The differences are quantified in terms of 3 different wall shear stress (WSS) metrics, involving maximal WSS, average WSS, and proportion of aneurysm sac area with low WSS. The results were compared with common geometrical metrics such as volume, aspect ratio, size ratio and parent vessel diameter and classifications in terms of sex and aneurysm type. The results demonstrate strong correlations between the different viscosity models and boundary conditions. The correlation between the different WSS metrics range from weak to medium. No strong correlations were found between the different WSS metrics and the geometrical metrics or classifications.
NASA Astrophysics Data System (ADS)
Huizer, Sebastian; Bierkens, Marc; Oude Essink, Gualbert
2015-04-01
The prospect of sea level rise and increase in extreme weather conditions has led to a new focus on coastal defense in the Netherlands. As an innovative solution for coastal erosion a mega-nourishment named the Sand Motor (or Sand Engine) has been constructed at the Dutch coast. This body of sand will be distributed slowly along the coastline by wind, waves and currents; keeping the coastal defense structures in place and creating a unique, dynamic environment with changing morphology over time. The large size and position of the Sand Motor might lead to a substantial increase of fresh ground water resources. This creates an opportunity to combine coastal protection with an increase of fresh water resources in coastal regions. With a three dimensional, density dependent, groundwater model the effects of changing morphology over time and the potential increase in fresh water availability have been studied. The preliminary model calculations show that in a period of 20 years volume of fresh water gradually increases to ca. 12 Mm3. In the nearby dune area 7-8 Mm3 is abstracted yearly, therefore the first results are promising in increasing fresh groundwater resources. More model calculations will be performed to investigate the sensitivity of the change in the fresh, brackish and salt water distribution.
Modeling Combustion in Supersonic Flows
NASA Technical Reports Server (NTRS)
Drummond, J. Philip; Danehy, Paul M.; Bivolaru, Daniel; Gaffney, Richard L.; Tedder, Sarah A.; Cutler, Andrew D.
2007-01-01
This paper discusses the progress of work to model high-speed supersonic reacting flow. The purpose of the work is to improve the state of the art of CFD capabilities for predicting the flow in high-speed propulsion systems, particularly combustor flow-paths. The program has several components including the development of advanced algorithms and models for simulating engine flowpaths as well as a fundamental experimental and diagnostic development effort to support the formulation and validation of the mathematical models. The paper will provide details of current work on experiments that will provide data for the modeling efforts along with with the associated nonintrusive diagnostics used to collect the data from the experimental flowfield. Simulation of a recent experiment to partially validate the accuracy of a combustion code is also described.
Preserving Flow Variability in Watershed Model Calibrations
Background/Question/Methods Although watershed modeling flow calibration techniques often emphasize a specific flow mode, ecological conditions that depend on flow-ecology relationships often emphasize a range of flow conditions. We used informal likelihood methods to investig...
PHYSICAL MODELING OF CONTRACTED FLOW.
Lee, Jonathan K.
1987-01-01
Experiments on steady flow over uniform grass roughness through centered single-opening contractions were conducted in the Flood Plain Simulation Facility at the U. S. Geological Survey's Gulf Coast Hydroscience Center near Bay St. Louis, Miss. The experimental series was designed to provide data for calibrating and verifying two-dimensional, vertically averaged surface-water flow models used to simulate flow through openings in highway embankments across inundated flood plains. Water-surface elevations, point velocities, and vertical velocity profiles were obtained at selected locations for design discharges ranging from 50 to 210 cfs. Examples of observed water-surface elevations and velocity magnitudes at basin cross-sections are presented.
NASA Astrophysics Data System (ADS)
Bahrin Jaafar, Kamal
2016-04-01
The phenomenon of debris flow occurs in Malaysia occasionally. The topography of Peningsular Malysia is characterized by the central mountain ranges running from south to north. Several parts of hilly areas with steep slopes, combined with high saturation of soil strata that deliberately increase the pore water pressure underneath the hill slope. As a tropical country Malaysia has very high intensity rainfall which is triggered the landslide. In the study area where the debris flow are bound to occur, there are a few factors that contribute to this phenomenon such as high rainfall intensity, very steep slope which an inclination more than 35 degree and sandy clay soil type which is easily change to liquidity soil. This paper will discuss the study of rainfall, mechanism, modeling and design of mitigation measure to avoid repeated failure in future in same area.
2010-01-01
Background Published studies of the past decades have established that mass transfer across the dialyzer membrane is governed by diffusion, convection and osmosis. While the former is independent of the pressure in the liquids, the latter two are pressure dependent and are enhanced when the pressure difference across the membrane is increased. The goal of the present study is to examine the impact of pulsatile flow on the transport phenomena across the membrane of a high-flux dialyzer in a wearable artificial kidney (WAK) with a novel single small battery-operated pulsatile pump that drives both the blood and dialysate in a counter-phased manner, maximizing the trans-membrane pressure. Methods Both in-vitro experimental and numerical tools are employed to compare the performance of the pulsatile WAK dialyzer with a traditional design of a single-channel roller blood pump together with a centrifugal pump that drives the dialysate flow. The numerical methods utilize the axisymmetric Navier-Stokes and mass transfer equations to model the flow in the fibers of the dialyzer. Results While diffusion is still the dominating transport regime, the WAK pump enhances substantially the trans-membrane pressure and thus increases mass convection that might be as high as 30% of the overall transfer. This increase is obtained due to the design of the pulsatile WAK pump that increases ultrafiltration by increasing the trans-membrane pressure. Conclusions The experimental and numerical results revealed that when pumping at similar flow rates, a small battery-operated pulsatile pump provides clearances of urea and creatinine similar as or better than a large heavy AC-powered roller pump. PMID:20497572
2011-07-31
18]) General Charles Campbell noted that , although…. “the Army has a system for organizing, staffing, equipping, training, deploying, sustaining...Harrell, Charles , Ghosh, Biman K., & Bowden Jr.,Royce O. 2004. Simulation Using ProModel. Second edition. McGraw Hill, New York. [22] Klimas, J...RUNS: A Senior Leader Reference Handbook. U.S. Army War College, Carlisle, PA. [24] McNeill , Dan K. 2005 (August). Army Force Generation
Wind Tunnel Model Design for Sonic Boom Studies of Nozzle Jet Flows with Shock Interactions
NASA Technical Reports Server (NTRS)
Cliff, Susan E.; Denison, Marie; Moini-Yekta, Shayan; Morr, Donald E.; Durston, Donald A.
2016-01-01
NASA and the U.S. aerospace industry are performing studies of supersonic aircraft concepts with low sonic boom pressure signatures. The computational analyses of modern aircraft designs have matured to the point where there is confidence in the prediction of the pressure signature from the front of the vehicle, but uncertainty remains in the aft signatures due to boundary layer and nozzle exhaust jet effects. Wind tunnel testing without inlet and nozzle exhaust jet effects at lower Reynolds numbers than in-flight make it difficult to accurately assess the computational solutions of flight vehicles. A wind tunnel test in the NASA Ames 9- by 7-Foot Supersonic Wind Tunnel is planned for February 2016 to address the nozzle jet effects on sonic boom. The experiment will provide pressure signatures of test articles that replicate waveforms from aircraft wings, tails, and aft fuselage (deck) components after passing through cold nozzle jet plumes. The data will provide a variety of nozzle plume and shock interactions for comparison with computational results. A large number of high-fidelity numerical simulations of a variety of shock generators were evaluated to define a reduced collection of suitable test models. The computational results of the candidate wind tunnel test models as they evolved are summarized, and pre-test computations of the final designs are provided.
Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Alsaedi, Ahmed
2017-01-01
Here two classes of viscoelastic fluids have been analyzed in the presence of Cattaneo-Christov double diffusion expressions of heat and mass transfer. A linearly stretched sheet has been used to create the flow. Thermal and concentration diffusions are characterized firstly by introducing Cattaneo-Christov fluxes. Novel features regarding Brownian motion and thermophoresis are retained. The conversion of nonlinear partial differential system to nonlinear ordinary differential system has been taken into place by using suitable transformations. The resulting nonlinear systems have been solved via convergent approach. Graphs have been sketched in order to investigate how the velocity, temperature and concentration profiles are affected by distinct physical flow parameters. Numerical values of skin friction coefficient and heat and mass transfer rates at the wall are also computed and discussed. Our observations demonstrate that the temperature and concentration fields are decreasing functions of thermal and concentration relaxation parameters. PMID:28046011
2012-06-01
both below and above ambient, were included. The resultant density ratios are presented in Table 2. Water was excluded from initial examination...because of the difficulty in achieving supercritical conditions of the water and freestream gas mixture. Table 2. Density Ratios for Sample Combinations...controlled with a cavitating venturi. The helium and argon mass flows were controlled by sonic venturis. The test chamber pressure was controlled by
Trapecar, Martin; Kelc, Robi; Gradisnik, Lidija; Vogrin, Matjaz; Rupnik, Marjan Slak
2014-12-01
Research on skeletal muscles suffers from a lack of appropriate human models to study muscle formation and regeneration on the regulatory level of single cells. This hampers both basic understanding and the development of new therapeutic approaches. The use of imaging multicolour flow cytometry and myogenic stem cells can help fill this void by allowing researchers to visualize and quantify the reaction of individual cultured cells to bioactives or other physiological impulses. As proof of concept, we subjected human CD56+ satellite cells to reference bioactives follistatin and Malva sylvestris extracts and then used imaging multicolor flow cytometry to visualize the stepwise activation of myogenic factors MyoD and myogenin in individual cells. This approach enabled us to evaluate the potency of these bioactives to stimulate muscle commitment. To validate this method, we used multi-photon confocal microscopy to confirm the potential of bioactives to stimulate muscle differentiation and expression of desmin. Imaging multicolor flow cytometry revealed statistically significant differences between treated and untreated groups of myogenic progenitors and we propose the utilization of this concept as an integral part of future muscle research strategies.
Mynard, Jonathan P; Smolich, Joseph J
2016-07-01
Coronary hemodynamics are known to be affected by intravascular and extravascular factors that vary regionally and transmurally between the perfusion territories of left and right coronary arteries. However, despite clinical evidence that left coronary arterial dominance portends greater cardiovascular risk, relatively little is known about the effects of left or right dominance on regional conduit arterial and microcirculatory blood flow patterns, particularly in the presence of systemic or pulmonary hypertension. We addressed this issue using a multiscale numerical model of the human coronary circulation situated in a closed-loop cardiovascular model. The coronary model represented left or right dominant anatomies and accounted for transmural and regional differences in vascular properties and extravascular compression. Regional coronary flow dynamics of the two anatomical variants were compared under normotensive conditions, raised systemic or pulmonary pressures with maintained flow demand, and after accounting for adaptations known to occur in acute and chronic hypertensive states. Key findings were that 1) right coronary arterial flow patterns were strongly influenced by dominance and systemic/pulmonary hypertension; 2) dominance had minor effects on left coronary arterial and all microvascular flow patterns (aside from mean circumflex flow); 3) although systemic hypertension favorably increased perfusion pressure, this benefit varied regionally and transmurally and was offset by increased left ventricular and septal flow demands; and 4) pulmonary hypertension had a substantial negative effect on right ventricular and septal flows, which was exacerbated by greater metabolic demands. These findings highlight the importance of interactions between coronary arterial dominance and hypertension in modulating coronary hemodynamics.
Turbulent motion of mass flows. Mathematical modeling
NASA Astrophysics Data System (ADS)
Eglit, Margarita; Yakubenko, Alexander; Yakubenko, Tatiana
2016-04-01
New mathematical models for unsteady turbulent mass flows, e.g., dense snow avalanches and landslides, are presented. Such models are important since most of large scale flows are turbulent. In addition to turbulence, the two other important points are taken into account: the entrainment of the underlying material by the flow and the nonlinear rheology of moving material. The majority of existing models are based on the depth-averaged equations and the turbulent character of the flow is accounted by inclusion of drag proportional to the velocity squared. In this paper full (not depth-averaged) equations are used. It is assumed that basal entrainment takes place if the bed friction equals the shear strength of the underlying layer (Issler D, M. Pastor Peréz. 2011). The turbulent characteristics of the flow are calculated using a three-parameter differential model (Lushchik et al., 1978). The rheological properties of moving material are modeled by one of the three types of equations: 1) Newtonian fluid with high viscosity, 2) power-law fluid and 3) Bingham fluid. Unsteady turbulent flows down long homogeneous slope are considered. The flow dynamical parameters and entrainment rate behavior in time as well as their dependence on properties of moving and underlying materials are studied numerically. REFERENCES M.E. Eglit and A.E. Yakubenko, 2014. Numerical modeling of slope flows entraining bottom material. Cold Reg. Sci. Technol., 108, 139-148 Margarita E. Eglit and Alexander E. Yakubenko, 2016. The effect of bed material entrainment and non-Newtonian rheology on dynamics of turbulent slope flows. Fluid Dynamics, 51(3) Issler D, M. Pastor Peréz. 2011. Interplay of entrainment and rheology in snow avalanches; a numerical study. Annals of Glaciology, 52(58), 143-147 Lushchik, V.G., Paveliev, A.A. , and Yakubenko, A.E., 1978. Three-parameter model of shear turbulence. Fluid Dynamics, 13, (3), 350-362
Mathematical Models of Continuous Flow Electrophoresis
NASA Technical Reports Server (NTRS)
Saville, D. A.; Snyder, R. S.
1985-01-01
Development of high resolution continuous flow electrophoresis devices ultimately requires comprehensive understanding of the ways various phenomena and processes facilitate or hinder separation. A comprehensive model of the actual three dimensional flow, temperature and electric fields was developed to provide guidance in the design of electrophoresis chambers for specific tasks and means of interpreting test data on a given chamber. Part of the process of model development includes experimental and theoretical studies of hydrodynamic stability. This is necessary to understand the origin of mixing flows observed with wide gap gravitational effects. To insure that the model accurately reflects the flow field and particle motion requires extensive experimental work. Another part of the investigation is concerned with the behavior of concentrated sample suspensions with regard to sample stream stability particle-particle interactions which might affect separation in an electric field, especially at high field strengths. Mathematical models will be developed and tested to establish the roles of the various interactions.
Debris Flow Distributed Propagation Model
NASA Astrophysics Data System (ADS)
Gregoretti, C.
The debris flow distributed propagation model is a DEM-based model. The fan is dis- cretized by square cells and each cell is assigned an altitude on the sea level. The cells of the catchment are distinguished in two categories: the source cells and the stripe cells. The source cells receive the input hydograph: the cells close to the torrent which are flooded by the debris flow overflowing the torrent embankment are source cells. The stripes cells are the cells flooded by debris flow coming from the surrounding cells. At the first time step only the source cells are flooded by debris flow coming from the torrent. At the second time step a certain number of cells are flooded by de- bris flow coming from the source cells. These cells constitute a stripe of cells and are assigned order two. At the third time step another group of cells are flooded by the debris flow coming from the cells whose order is two. These cells constitute another stripe and are assigned order three. The cell order of a stripe is the time step number corresponding to the transition from dry to flooded state. The mass transfer or mo- mentum exchange between cells is governed by two different mechanisms. The mass transfer is allowed only by a positive or equal to zero flow level difference between the drained cell and the receiving cell. The mass transfer is limited by a not negative final flow level difference between the drained cell and the receiving cells. This limitation excludes the case of possible oscillations in the mass transfer. Another limitation is that the mass drained by a cell should be less than the available mass in that cell. This last condition provides the respect of mass conservation. The first mechanism of mass transfer is the gravity. The mass in a cell is transferred to the neighbouring cells with lower altitude and flow level according to an uniform flow law: The second mecha- nism of mass transfer is the broad crested weir. The mass in a cell is transferred to the
NASA Astrophysics Data System (ADS)
Huizer, S.; Bierkens, M. F.; Oude Essink, G.
2014-12-01
In many coastal regions around the world climate change will lead to a sea level rise and an increase in extreme weather conditions. This prospect has resulted in a new focus on coastal protection in the Netherlands, resulting in the initiation of an innovative coastal defence project called the Sand Motor. In this project a large body of sand or so-called mega-nourishment has been constructed along the Dutch coast. This body of sand will be distributed slowly along the coastline by wind, waves and currents. Keeping the coastal defence structures in place and creating a unique, dynamic environment with changing morphology over time. Because of the large size of the body of sand (21.5 million m3) and the position at the coastline and near coastal dunes, the Sand Motor might cause a substantial increase of the fresh water availability by increasing the volume fresh water lens underneath the dunes. This creates an opportunity to combine coastal protection with an increase of fresh water resources in coastal regions. With a three dimensional, density dependent, groundwater model the effects of changing morphology over time and the potential increase in fresh water availability have been studied.
Numerical study of two classes of cellular automaton models for traffic flow on a two-lane roadway
NASA Astrophysics Data System (ADS)
Moussa, N.; Daoudia, A. K.
2003-02-01
In this paper, we present computer simulation results of traffic flow on a two-lane roadway with different types of vehicles, cars and trucks for example. We consider two classes of two-lane traffic cellular automaton models, namely the well known Nagel-Schreckenberg model and an extension of the Fukui-Ishibashi model. These two models, which differ in their acceleration limits, show an important differences in their fundamental diagrams, lane-changing and ping-pong behaviors. Moreover, we investigate the importance of braking noise and the proportion of trucks on the traffic flow of a two-lane roadway.
Jimenez, Jose-Luis
2016-02-01
This grant was originally funded for deployment of a suite of aerosol instrumentation by our group in collaboration with other research groups and DOE/ARM to the Ganges Valley in India (GVAX) to study aerosols sources and processing. Much of the first year of this grant was focused on preparations for GVAX. That campaign was cancelled due to political reasons and with the consultation with our program manager, the research of this grant was refocused to study the applications of oxidation flow reactors (OFRs) for investigating secondary organic aerosol (SOA) formation and organic aerosol (OA) processing in the field and laboratory through a series of laboratory and modeling studies. We developed a gas-phase photochemical model of an OFR which was used to 1) explore the sensitivities of key output variables (e.g., OH exposure, O_{3}, HO_{2}/OH) to controlling factors (e.g., water vapor, external reactivity, UV irradiation), 2) develop simplified OH exposure estimation equations, 3) investigate under what conditions non-OH chemistry may be important, and 4) help guide design of future experiments to avoid conditions with undesired chemistry for a wide range of conditions applicable to the ambient, laboratory, and source studies. Uncertainties in the model were quantified and modeled OH exposure was compared to tracer decay measurements of OH exposure in the lab and field. Laboratory studies using OFRs were conducted to explore aerosol yields and composition from anthropogenic and biogenic VOC as well as crude oil evaporates. Various aspects of the modeling and laboratory results and tools were applied to interpretation of ambient and source measurements using OFR. Additionally, novel measurement methods were used to study gas/particle partitioning. The research conducted was highly successful and details of the key results are summarized in this report through narrative text, figures, and a complete list of publications acknowledging this grant.
Modeling axisymmetric flow and transport
Langevin, C.D.
2008-01-01
Unmodified versions of common computer programs such as MODFLOW, MT3DMS, and SEAWAT that use Cartesian geometry can accurately simulate axially symmetric ground water flow and solute transport. Axisymmetric flow and transport are simulated by adjusting several input parameters to account for the increase in flow area with radial distance from the injection or extraction well. Logarithmic weighting of interblock transmissivity, a standard option in MODFLOW, can be used for axisymmetric models to represent the linear change in hydraulic conductance within a single finite-difference cell. Results from three test problems (ground water extraction, an aquifer push-pull test, and upconing of saline water into an extraction well) show good agreement with analytical solutions or with results from other numerical models designed specifically to simulate the axisymmetric geometry. Axisymmetric models are not commonly used but can offer an efficient alternative to full three-dimensional models, provided the assumption of axial symmetry can be justified. For the upconing problem, the axisymmetric model was more than 1000 times faster than an equivalent three-dimensional model. Computational gains with the axisymmetric models may be useful for quickly determining appropriate levels of grid resolution for three-dimensional models and for estimating aquifer parameters from field tests.
Modeling axisymmetric flow and transport.
Langevin, Christian D
2008-01-01
Unmodified versions of common computer programs such as MODFLOW, MT3DMS, and SEAWAT that use Cartesian geometry can accurately simulate axially symmetric ground water flow and solute transport. Axisymmetric flow and transport are simulated by adjusting several input parameters to account for the increase in flow area with radial distance from the injection or extraction well. Logarithmic weighting of interblock transmissivity, a standard option in MODFLOW, can be used for axisymmetric models to represent the linear change in hydraulic conductance within a single finite-difference cell. Results from three test problems (ground water extraction, an aquifer push-pull test, and upconing of saline water into an extraction well) show good agreement with analytical solutions or with results from other numerical models designed specifically to simulate the axisymmetric geometry. Axisymmetric models are not commonly used but can offer an efficient alternative to full three-dimensional models, provided the assumption of axial symmetry can be justified. For the upconing problem, the axisymmetric model was more than 1000 times faster than an equivalent three-dimensional model. Computational gains with the axisymmetric models may be useful for quickly determining appropriate levels of grid resolution for three-dimensional models and for estimating aquifer parameters from field tests.
Eve, David J; Musso, James; Park, Dong-Hyuk; Oliveira, Cathy; Pollock, Kenny; Hope, Andrew; Baradez, Marc-Olivier; Sinden, John D; Sanberg, Paul R
2009-05-30
Cerebral blood flow is impaired during middle cerebral artery occlusion in the rat model of stroke. However, the long term effects on cerebral blood flow following occlusion have received little attention. We examined cerebral blood flow in both sides at multiple time points following middle cerebral artery occlusion of the rat. The bilateral cerebral blood flow in young male Sprague Dawley rats was measured at the time of occlusion, as well as 4, 10 and 16 weeks after occlusion. Under the present experimental conditions, the difference between the left and right side's cerebral blood flow was observed to appear to switch in direction in a visual oscillatory fashion over time in the sham-treated group, whereas the occluded animals consistently showed left side dominance. One group of rats was intraparenchymally transplanted with a human neural stem cell line (CTX0E03 cells) known to have benefit in stroke models. Cerebral blood flow in the lesioned side of the cell-treated group was observed to be improved compared to the untreated rats and to demonstrate a similar oscillatory nature as that observed in sham-treated animals. These findings suggest that multiple bilateral monitoring of cerebral blood flow over time can show effects of stem cell transplantation efficiently as well as functional tests in an animal stroke model.
Modeling of thermotopographic flows in forested terrain
NASA Astrophysics Data System (ADS)
Froelich, Norma Jeanne
Thermotopographic flows are winds that develop from the interaction of local thermal gradients and sloping terrain. Strong heating or cooling of the air near the surface alters local temperature, density, and pressure gradients. During nighttime hours, the air near the surface cools more rapidly than that aloft due to radiative loss at the surface, and near-surface downslope winds may develop. During the day, surface heating by solar radiation may drive flow upslope. Recently, there has been an increased interest in thermotopographic flows in forested areas, largely because these flows may affect the accuracy of measurements of ecosystem-atmosphere exchange of carbon dioxide. In some forests, under some conditions, the diel pattern of thermotopographic flows differs from expected: at night, strong radiative cooling in the canopy layer may drive upslope sub-canopy flows, and daytime downslope flows may occur below the canopy due to heating of the canopy. There is still uncertainty as to whether thermotopographic flows will occur in a given forest, what diel pattern they will exhibit, what drivers (e.g., terrain or canopy characteristics, ambient winds) influence the flow, and what effects these flows have on measurements of forest-atmosphere exchange. As observational studies are limited, numerical modeling provides an attractive option for studying thermotopographic flows in forests. The aim of this research was to develop a numerical model which may be used to study thermotopographic flows in hilly forested terrain. The model is based on existing large-eddy simulation software (Advanced Regional Prediction System, ARPS) which is used to model flow in hilly terrain. Adaptations were made to the ARPS model to simulate the dynamic, radiative, and thermal influences of canopy elements (leaves, branches, and boles). Major contributions of this research are methodological advances and several outcomes from the results of the model application. Methodological
Shiba, Naoki; Nagano, Osamu; Hirayama, Takahiro; Ichiba, Shingo; Ujike, Yoshihito
2012-01-01
In adult high-frequency oscillatory ventilation (HFOV) with an R100 artificial ventilator, exhaled gas from patient's lung may warm the temperature probe and thereby disturb the humidification of base flow (BF) gas. We measured the humidity of BF gas during HFOV with frequencies of 6, 8 and 10 Hz, maximum stroke volumes (SV) of 285, 205, and 160 ml at the respective frequencies, and, BFs of 20, 30, 40 l/min using an original lung model. The R100 device was equipped with a heated humidifier, Hummax Ⅱ, consisting of a porous hollow fiber in circuit. A 50-cm length of circuit was added between temperature probe (located at 50 cm proximal from Y-piece) and the hollow fiber. The lung model was made of a plastic container and a circuit equipped with another Hummax Ⅱ. The lung model temperature was controlled at 37℃. The Hummax Ⅱ of the R100 was inactivated in study-1 and was set at 35℃ or 37℃ in study-2. The humidity was measured at the distal end of the added circuit in study-1 and at the proximal end in study-2. In study-1, humidity was detected at 6 Hz (SV 285 ml) and BF 20 l/min, indicating the direct reach of the exhaled gas from the lung model to the temperature probe. In study-2 the absolute humidity of the BF gas decreased by increasing SV and by increasing BF and it was low with setting of 35℃. In this study setting, increasing the SV induced significant reduction of humidification of the BF gas during HFOV with R100.
Benchmarking computational fluid dynamics models for lava flow simulation
NASA Astrophysics Data System (ADS)
Dietterich, Hannah; Lev, Einat; Chen, Jiangzhi
2016-04-01
Numerical simulations of lava flow emplacement are valuable for assessing lava flow hazards, forecasting active flows, interpreting past eruptions, and understanding the controls on lava flow behavior. Existing lava flow models vary in simplifying assumptions, physics, dimensionality, and the degree to which they have been validated against analytical solutions, experiments, and natural observations. In order to assess existing models and guide the development of new codes, we conduct a benchmarking study of computational fluid dynamics models for lava flow emplacement, including VolcFlow, OpenFOAM, FLOW-3D, and COMSOL. Using the new benchmark scenarios defined in Cordonnier et al. (Geol Soc SP, 2015) as a guide, we model viscous, cooling, and solidifying flows over horizontal and sloping surfaces, topographic obstacles, and digital elevation models of natural topography. We compare model results to analytical theory, analogue and molten basalt experiments, and measurements from natural lava flows. Overall, the models accurately simulate viscous flow with some variability in flow thickness where flows intersect obstacles. OpenFOAM, COMSOL, and FLOW-3D can each reproduce experimental measurements of cooling viscous flows, and FLOW-3D simulations with temperature-dependent rheology match results from molten basalt experiments. We can apply these models to reconstruct past lava flows in Hawai'i and Saudi Arabia using parameters assembled from morphology, textural analysis, and eruption observations as natural test cases. Our study highlights the strengths and weaknesses of each code, including accuracy and computational costs, and provides insights regarding code selection.
Modeling groundwater flow on MPPs
Ashby, S.F.; Falgout, R.D.; Smith, S.G.; Tompson, A.F.B.
1993-10-01
The numerical simulation of groundwater flow in three-dimensional heterogeneous porous media is examined. To enable detailed modeling of large contaminated sites, preconditioned iterative methods and massively parallel computing power are combined in a simulator called PARFLOW. After describing this portable and modular code, some numerical results are given, including one that demonstrates the code`s scalability.
ERIC Educational Resources Information Center
Stanford Univ., CA. School Mathematics Study Group.
This is the second unit of a 15-unit School Mathematics Study Group (SMSG) mathematics text for high school students. Topics presented in the first chapter (Informal Algorithms and Flow Charts) include: changing a flat tire; algorithms, flow charts, and computers; assignment and variables; input and output; using a variable as a counter; decisions…
Turbulence modeling for compressible flows
NASA Technical Reports Server (NTRS)
Marvin, J. G.
1977-01-01
Material prepared for a course on Applications and Fundamentals of Turbulence given at the University of Tennessee Space Institute, January 10 and 11, 1977, is presented. A complete concept of turbulence modeling is described, and examples of progess for its use in computational aerodynimics are given. Modeling concepts, experiments, and computations using the concepts are reviewed in a manner that provides an up-to-date statement on the status of this problem for compressible flows.
Study of the Standard k-ɛ Model for Tip Leakage Flow in an Axial Compressor Rotor
NASA Astrophysics Data System (ADS)
Gao, Yanfei; Liu, Yangwei; Zhong, Luyang; Hou, Jiexuan; Lu, Lipeng
2016-12-01
The standard k-ɛ model (SKE) and the Reynolds stress model (RSM) are employed to predict the tip leakage flow (TLF) in a low-speed large-scale axial compressor rotor. Then, a new research method is adopted to "freeze" the turbulent kinetic energy and dissipation rate of the flow field derived from the RSM, and obtain the turbulent viscosity using the Boussinesq hypothesis. The Reynolds stresses and mean flow field computed on the basis of the frozen viscosity are compared with the results of the SKE and the RSM. The flow field in the tip region based on the frozen viscosity is more similar to the results of the RSM than those of the SKE, although certain differences can be observed. This finding indicates that the non-equilibrium turbulence transport nature plays an important role in predicting the TLF, as well as the turbulence anisotropy.
Study of Multipiece, Flow-Through Wind Tunnel Models for HIRT
1975-11-01
used for model pa r t s is PH13 - 8 Mo in the H1000 condition. PH13 - 8 Mo H1000 and 18Ni-300 grade s ta in less steel are used for the support sy s...For example: PH13 - 8 Mo Steel Coefficient of Thermal Expansion 6061 Aluminum Coefficient of Thermal Expansion For a A T of 130°: Change in...ted f rom PH13 - 8 Mo H1000 s t a in less s tee l . d. The model sting is fabr ica ted from 18 Ni-300 grade s tee l . e. The exis t ing balance
NASA Astrophysics Data System (ADS)
Hsu, Shih-Meng; Ke, Chien-Chung; Lo, Hung-Chieh; Lin, Yen-Tsu; Huang, Chi-Chao
2016-04-01
On the basis of a relatively sparse data set, fractured aquifers are difficult to be characterized and modelled. The three-dimensional configuration of transmissive fractures and fracture zones is needed to be understood flow heterogeneity in the aquifer. Innovative technologies for the improved interpretation are necessary to facilitate the development of accurate predictive models of ground-water flow and solute transport or to precisely estimate groundwater potential. To this end, this paper presents a procedure for characterizing and modelling preferential flow path in the fractured rock aquifer carried out at Fractured Rock Hydrogeology Research Site in Shuangliou Forest Recreation Area, Pingtung County, Southern Taiwan. The Shuangliou well field is a 40 by 30-meter area consisting of 6 wells (one geological well, one pumping well and four hydrogeological testing wells). The bedrock at the site is mainly composed of slate and intercalated by meta-sandstone. The overburden consists of about 5.6 m of gravel deposits. Based on results of 100 m geological borehole with borehole televiewer logging, vertical flow logging and full-wave sonic logging, high transmissivity zones in the bedrock underlying the well field were identified. One of transmissivity zone (at the depths of 30~32 m) and its fracture orientation(N56/54) selected for devising a multiple well system with 4 boreholes (borehole depths :45m, 35m, 35m and 25m, respectively), which were utilized to perform cross-borehole flow velocity data under the ambient flow and pumped flow conditions to identify preferential flow paths. Results from the cross-borehole test show the preferential flow pathways are corresponding to the predicted ones. Subsequently, a 3-D discrete fracture network model based on outcrop data was generated by the FracMan code. A validation between observed and simulated data has proved that the present model can accurately predict the hydrogeological properties (e.g., number of fractures
SURFACE WATER FLOW IN LANDSCAPE MODELS: 1. EVERGLADES CASE STUDY. (R824766)
Many landscape models require extensive computational effort using a large array of grid cells that represent the landscape. The number of spatial cells may be in the thousands and millions, while the ecological component run in each of the cells to account for landscape dynamics...
TV News Flow Studies Revisited.
ERIC Educational Resources Information Center
Hjarvard, Stig
1995-01-01
Compares different theoretical approaches to the study of international news. Finds many comparative studies of the foreign news output of national broadcasters and few studies analyzing the actual flow of television news between actors at the wholesale level and the flow between wholesale and retail level. Suggests a better framework for the…
NASA Astrophysics Data System (ADS)
Castro, Marcelo A.; Peloc, Nora L.; Chien, Aichi; Goldberg, Ezequiel; Putman, Christopher M.; Cebral, Juan R.
2015-03-01
Cerebral aneurysms may rarely coexist with a proximal artery stenosis. In that small percent of patients, such coexistence poses a challenge for interventional neuroradiologists and neurosurgeons to make the best treatment decision. According to previous studies, the incidence of cerebral aneurysms in patients with internal carotid artery stenosis is no greater than five percent, where the aneurysm is usually incidentally detected, being about two percent for aneurysms and stenoses in the same cerebral circulation. Those cases pose a difficult management decision for the physician. Case reports showed patients who died due to aneurysm rupture months after endarterectomy but before aneurysm clipping, while others did not show any change in the aneurysm after plaque removal, having optimum outcome after aneurysm coiling. The aim of this study is to investigate the intra-aneurysmal hemodynamic changes before and after treatment of stenotic plaque. Virtually created moderate stenoses in vascular models of internal carotid artery aneurysm patients were considered in a number of cases reconstructed from three dimensional rotational angiography images. The strategy to create those plaques was based on parameters analyzed in a previous work where idealized models were considered, including relative distance and stenosis grade. Ipsilateral and contralateral plaques were modeled. Wall shear stress and velocity pattern were computed from finite element pulsatile blood flow simulations. The results may suggest that wall shear stress changes depend on relative angular position between the aneurysm and the plaque.
NASA Astrophysics Data System (ADS)
Abaimov, N. A.; Ryzhkov, A. F.
2015-11-01
Problems requiring solution in development of modern highly efficient gasification reactor of a promising high power integrated gasification combined-cycle plant are formulated. The task of creating and testing a numerical model of an entrained-flow reactor for thermochemical conversion of pulverized coal is solved. The basic method of investigation is computational fluid dynamics. The submodel of thermochemical processes, including a single-stage scheme of volatile substances outlet and three heterogeneous reactions of carbon residue conversion (complete carbon oxidation, Boudouard reaction and hydrogasification), is given. The mass loss rate is determined according to the basic assumptions of the diffusion-kinetic theory. The equations applied for calculation of the process of outlet of volatile substances and three stages of fuel gasifi-cation (diffusion of reagent gas toward the surface of the coal particle, heterogeneous reactions of gas with carbon on its surface, and homogeneous reactions beyond the particle surface) are presented. The universal combined submodel Eddy Dissipation/Finite Rate Chemistry with standard (built-in) constants is used for numerical estimates. Aerodynamic mechanisms of action on thermochemical processes of solid fuel gasification are studied, as exemplified by the design upgrade of a cyclone reactor of preliminary thermal fuel preparation. Volume concentrations of combustible gases and products of complete combustion in the syngas before and after primary air and pulverized coal flows' redistribution are given. Volume concentrations of CO in syngas at different positions of tangential secondary air inlet nozzle are compared.
Modified Numerical Simulation Model of Blood Flow in Bend
Liu, X; Zhou, X; Hao, X; Sang, X
2015-01-01
ABSTRACT The numerical simulation model of blood flow in bend is studied in this paper. The curvature modification is conducted for the blood flow model in bend to obtain the modified blood flow model in bend. The modified model is verified by U tube. By comparing the simulation results with the experimental results obtained by measuring the flow data in U tube, it was found that the modified blood flow model in bend can effectively improve the prediction accuracy of blood flow data affected by the curvature effect. PMID:27398727
Scaled Experimental Modeling of VHTR Plenum Flows
ICONE 15
2007-04-01
Abstract The Very High Temperature Reactor (VHTR) is the leading candidate for the Next Generation Nuclear Power (NGNP) Project in the U.S. which has the goal of demonstrating the production of emissions free electricity and hydrogen by 2015. Various scaled heated gas and water flow facilities were investigated for modeling VHTR upper and lower plenum flows during the decay heat portion of a pressurized conduction-cooldown scenario and for modeling thermal mixing and stratification (“thermal striping”) in the lower plenum during normal operation. It was concluded, based on phenomena scaling and instrumentation and other practical considerations, that a heated water flow scale model facility is preferable to a heated gas flow facility and to unheated facilities which use fluids with ranges of density to simulate the density effect of heating. For a heated water flow lower plenum model, both the Richardson numbers and Reynolds numbers may be approximately matched for conduction-cooldown natural circulation conditions. Thermal mixing during normal operation may be simulated but at lower, but still fully turbulent, Reynolds numbers than in the prototype. Natural circulation flows in the upper plenum may also be simulated in a separate heated water flow facility that uses the same plumbing as the lower plenum model. However, Reynolds number scaling distortions will occur at matching Richardson numbers due primarily to the necessity of using a reduced number of channels connected to the plenum than in the prototype (which has approximately 11,000 core channels connected to the upper plenum) in an otherwise geometrically scaled model. Experiments conducted in either or both facilities will meet the objectives of providing benchmark data for the validation of codes proposed for NGNP designs and safety studies, as well as providing a better understanding of the complex flow phenomena in the plenums.
An experimental study of Newtonian and non-Newtonian flow dynamics in an axial blood pump model.
Hu, Qi-Hui; Li, Jing-Yin; Zhang, Ming-Yuan; Zhu, Xian-Ran
2012-04-01
The head curves of a 1.5:1 new axial blood pump model were measured using five working fluids at five rotational speeds. The working fluids were water, a 39wt% aqueous glycerin solution (GS), and three aqueous xanthan gum solutions (XGSs) with different concentrations. The flow velocities and shear stresses in the mechanical clearance between the casing and rotor were investigated using a laser Doppler velocimeter and hot-film sensor. At every rotational speed, the experiment in which viscous GS was used in the pump model showed a head curve lower than that obtained using water, whereas the head obtained using viscoelastic XGS was higher than that generated using water. A maximum difference of 65.8% between the heads measured in the 0.06% XGS and GS experiments was detected. The higher head produced by the XGS may have originated from the drag-reduction effect of XGS viscoelasticity. The measurements showed that a reverse washout flow at a velocity of 0.05-0.11m/s occurs in the clearance. This reverse washout flow is crucial to preventing flow stagnation and accompanying thrombus formation. The wall shear stress and the Taylor number of the rotating Couette-like flow in the clearance both indicated that it is a turbulent flow.
Study on Effects of the Stochastic Delay Probability for 1d CA Model of Traffic Flow
NASA Astrophysics Data System (ADS)
Xue, Yu; Chen, Yan-Hong; Kong, Ling-Jiang
Considering the effects of different factors on the stochastic delay probability, the delay probability has been classified into three cases. The first case corresponding to the brake state has a large delay probability if the anticipant velocity is larger than the gap between the successive cars. The second one corresponding to the following-the-leader rule has intermediate delay probability if the anticipant velocity is equal to the gap. Finally, the third case is the acceleration, which has minimum delay probability. The fundamental diagram obtained by numerical simulation shows the different properties compared to that by the NaSch model, in which there exist two different regions, corresponding to the coexistence state, and jamming state respectively.
A wind tunnel study of air flow near model swine confinement buildings
Technology Transfer Automated Retrieval System (TEKTRAN)
One of the most significant and persistent environmental concerns regarding swine production is the transport of odor constituents, trace gases, and particulates from animal production and manure storage facilities. The objectives of this study were to determine how swine housing unit orientation af...
Izadmanesh, Y; Ghasemi, Jahan B
2016-08-05
Gradient flow injection technique-diode array spectrophotometry was applied for β-cyclodextrin (β-CD)-dye inclusion complex studies. A single injection of a small amount of mixed β-CD-dye solution (100μl) into the carrier solution of the dye and recording the spectra gave the titration data. The mole ratio data were calculated by calibrating the dispersion pattern using a calibrator dye (rose bengal). Model-based multivariate methods were used to analyze the spectral-mole ratio data and, as a result, estimate stability constants and concentration-spectral profiles. Reliability was tested by applying this method to study the β-CD host-guest complexes with several dyes as guest molecules. Singular value decomposition (SVD) was used to select the chemical model and reduce noise. Molecular modeling provided the ability to predict the guest conformation-orientation (posing) within the cavity of β-CD and the nature of the involved interactions. Among those dyes showing observable spectral variation, the stoichiometric ratio of β-CD: dye (and log Kf) of methyl orange, fluorescein, phenol red, 4-(2-pyridylazo) resorcinol (PAR), and crystal violet were calculated to be 1:1 (4.26±0.01), 1:1 (1.53±0.08), 1:1 (3.11±0.04), 1:1 (1.06±0.12), and 2:1 (5.27±0.03), respectively. Compared with the classical method of titration, this method is simple and fast and has the advantage of needing reduced human interference. Molecular modeling facilitates a better understanding of the type of interactions and conformation of guest molecules in the β-CD cavity. The details of the proposed method are discussed in this paper.
NASA Astrophysics Data System (ADS)
Izadmanesh, Y.; Ghasemi, Jahan B.
2016-08-01
Gradient flow injection technique-diode array spectrophotometry was applied for β-cyclodextrin (β-CD)-dye inclusion complex studies. A single injection of a small amount of mixed β-CD-dye solution (100 μl) into the carrier solution of the dye and recording the spectra gave the titration data. The mole ratio data were calculated by calibrating the dispersion pattern using a calibrator dye (rose bengal). Model-based multivariate methods were used to analyze the spectral-mole ratio data and, as a result, estimate stability constants and concentration-spectral profiles. Reliability was tested by applying this method to study the β-CD host-guest complexes with several dyes as guest molecules. Singular value decomposition (SVD) was used to select the chemical model and reduce noise. Molecular modeling provided the ability to predict the guest conformation-orientation (posing) within the cavity of β-CD and the nature of the involved interactions. Among those dyes showing observable spectral variation, the stoichiometric ratio of β-CD: dye (and log Kf) of methyl orange, fluorescein, phenol red, 4-(2-pyridylazo) resorcinol (PAR), and crystal violet were calculated to be 1:1 (4.26 ± 0.01), 1:1 (1.53 ± 0.08), 1:1 (3.11 ± 0.04), 1:1 (1.06 ± 0.12), and 2:1 (5.27 ± 0.03), respectively. Compared with the classical method of titration, this method is simple and fast and has the advantage of needing reduced human interference. Molecular modeling facilitates a better understanding of the type of interactions and conformation of guest molecules in the β-CD cavity. The details of the proposed method are discussed in this paper.
NASA Astrophysics Data System (ADS)
Matott, L. Shawn; Leung, Kenny; Sim, Junyoung
2011-11-01
One approach for utilizing geoscience models for management or policy analysis is via a simulation-based optimization framework—where an underlying model is linked with an optimization search algorithm. In this regard, MATLAB and Python are high-level programming languages that implement numerous optimization routines, including gradient-based, heuristic, and direct-search optimizers. The ever-expanding number of available algorithms makes it challenging for practitioners to identify optimizers that deliver good performance when applied to problems of interest. Thus, the primary contribution of this paper is to present a series of numerical experiments that investigated the performance of various MATLAB and Python optimizers. The experiments considered two simulation-based optimization case studies involving groundwater flow and contaminant transport. One case study examined the design of a pump-and-treat system for groundwater remediation, while the other considered least-squares calibration of a model of strontium (Sr) transport. Using these case studies, the performance of 12 different MATLAB and Python optimizers was compared. Overall, the Hooke-Jeeves direct search algorithm yielded the best performance in terms of identifying least-cost and best-fit solutions to the design and calibration problems, respectively. The IFFCO (implicit filtering for constrained optimization) direct search algorithm and the dynamically dimensioned search (DDS) heuristic algorithm also consistently yielded good performance and were up to 80% more efficient than Hooke-Jeeves when applied to the pump-and-treat problem. These results provide empirical evidence that, relative to gradient- and population-based alternatives, direct search algorithms and heuristic variants, such as DDS, are good choices for application to simulation-based optimization problems involving groundwater management.
A combined field and modeling study of groundwater flow in a tidal marsh
NASA Astrophysics Data System (ADS)
Xia, Y. Q.; Li, H. L.
2012-03-01
Bald mud beaches were found among the mangrove marshes in Dongzhaigang National Nature Reserve, Hainan, China. To investigate the possible reasons for this phenomenon, the intertidal zones of a mangrove transect and a bald beach transect with similar topography and tidal actions were selected for comparison study. Along both transects, observed water table variations were significant in the high and low intertidal zones and negligible in the middle intertidal zones. Despite the same tidal actions and above-mentioned similarities, observed groundwater salinity was significantly smaller along the mangrove transect (average 23.0 ppt) than along the bald beach transect (average 28.5 ppt). These observations invite one hypothesis: the hydraulic structure of tidal marsh and freshwater availability may be the main hydrogeological factors critical to mangrove development. Two-dimensional numerical simulations corroborated the speculation and gave results in line with the observed water table. The two transects investigated were found to have a mud-sand two-layered structure: a surface zone of low-permeability mud and an underlying high-permeability zone that outcrops at the high and low tide lines. The freshwater recharge from inland is considerable along the mangrove transect but negligible along the bald beach transect. The high-permeability zone may provide opportunity for the plants in the mangrove marsh to uptake freshwater and oxygen through their roots extending downward into the high-permeability zone, which may help limit the buildup of salt in the root zone caused by evapotranspiration and enhance salt removal, which may further increase the production of marsh grasses and influence their spatial distribution. The bald beach is most probably due to the lack of enough freshwater for generating a brackish beach soil condition essential to mangrove growth. It is also indicated that seawater infiltrated the high-permeability zone through its outcrop near the high
A combined field and modeling study of groundwater flow in a tidal marsh
NASA Astrophysics Data System (ADS)
Xia, Yuqiang; Li, Hailong
2011-05-01
Bald mud beaches were found among the mangrove marshes in Dongzhaigang National Nature Reserve, Hainan, China. To investigate the possible reasons for this phenomenon, the intertidal zones of a mangrove transect and a bald beach transect with similar topography and same tidal actions were selected for comparison study. Along both transects, observed water table variations were significant in the high and low intertidal zones and negligible in the middle intertidal zones. Field investigations and observations invite two speculations: (1) existence of a high-permeability zone on each transect which underlies the low-permeability surface mud sediments and outcrops in the high intertidal zone, and (2) considerable inland freshwater recharge along the mangrove transect but negligible freshwater recharge along the bald beach transect. Two-dimensional numerical simulations based on these speculations gave results in line with the observed water table. The bald beach is most probably due to the lack of enough freshwater for generating a brackish beach soil condition essential to mangrove growth. It is also indicated that seawater infiltrated the high-permeability zone through its outcrop near the high intertidal zone, and discharged from the tidal river bank in the vicinity of the low tide line, thereby forming a tide-induced seawater-groundwater circulation which may provide considerable contribution to the total submarine groundwater discharge.
Kollet, S J; Maxwell, R M
2005-04-08
Interactions between surface and ground water are a key component of the hydrologic budget on the watershed scale. Models that honor these interactions are commonly based on the conductance concept that presumes a distinct interface at the land surface, separating the surface from the subsurface domain. These types of models link the subsurface and surface domains via an exchange flux that depends upon the magnitude and direction of the hydraulic gradient across the interface and a proportionality constant (a measure of the hydraulic connectivity). Because experimental evidence of such a distinct interface is often lacking in field systems, there is a need for a more general coupled modeling approach. A more general coupled model is presented that incorporates a new two-dimensional overland flow simulator into the parallel three-dimensional variable saturated subsurface flow code ParFlow. In ParFlow, the overland flow simulator takes the form of an upper boundary condition and is, thus, fully integrated without relying on the conductance concept. Another important advantage of this approach is the efficient parallelism incorporated into ParFlow, which is efficiently exploited by the overland flow simulator. Several verification and simulation examples are presented that focus on the two main processes of runoff production: excess infiltration and saturation. The model is shown to reproduce an analytical solution for overland flow and compares favorably to other commonly used hydrologic models. The influence of heterogeneity of the shallow subsurface on overland flow is also examined. The results show the uncertainty in overland flow predictions due to subsurface heterogeneity and demonstrate the usefulness of our approach. Both the overland flow component and the coupled model are evaluated in a parallel scaling study and show to be efficient.
Turbulence models in pulsating flows
NASA Astrophysics Data System (ADS)
Scotti, Alberto; Piomelli, Ugo
2001-11-01
We compare the performance of four low-Reynolds-number models for the unsteady Reynolds-averaged Navier-Stokes equations applied to the flow in a channel driven by a pressure gradient oscillating around a non-zero mean. The models considered are the one-equation Spalart-Allmaras model, the k-\\varepsilon model with the wall functions of Lam and Bremhorst, the k-ω^2 model of Saffman and Wilcox, and the k-\\varepsilon-v^2 model of Durbin. The results are compared with experiments, direct simulations and large-eddy simulations. The models give similar and reasonably accurate results as far as predicting the velocity profile in the channel as a function of the phase, and reproduce the observed behavior during part of the cycle. However, large differences exist between the models themselves, as well as with respect to the LES, at the level of the Reynolds shear stress, turbulent kinetic energy and dissipation rate. The k-\\varepsilon-v^2 model is overall superior to the other models considered.
Greil, Oliver Kleinschmidt, Thomas; Weiss, Wolfgang; Wolf, Oliver; Heider, Peter; Schaffner, Silvio; Gianotti, Marc; Schmid, Thomas; Liepsch, Dieter; Berger, Hermann
2005-01-15
Purpose. To study the influence of a newly developed membrane stent design on flow patterns in a physiologic carotid artery model. Methods. Three different stents were positioned in silicone models of the carotid artery: a stainless steel stent (Wall-stent), a nitinol stent (SelfX), and a nitinol stent with a semipermeable membrane (MembraX). To increase the contact area of the membrane with the vessel wall, another MembranX model was modified at the outflow tract. The membrane consists of a biocompatible silicone-polyurethane copolymer (Elast-Eon) with a pore size of 100 {mu}m. All stents were deployed across the bifurcation and the external carotid artery origin. Flow velocity measurements were performed with laser Doppler anemometry (LDA), using pulsatile flow conditions (Re = 220; flow 0.39 l/min; flow rate ratio ICA:ECA = 70:30) in hemodynamically relevant cross-sections. The hemodynamic changes were analyzed by comparing velocity fluctuations of corresponding flow profiles. Results. The flow rate ratio ICA:ECA shifted significantly from 70/30 to 73.9/26.1 in the MembraX and remained nearly unchanged in the SelfX and Wallstent. There were no changes in the flow patterns at the inflow proximal to the stents. In the stent no relevant changes were found in the SelfX. In the Wallstent the separation zone shifted from the orifice of the ICA to the distal end of the stent. Four millimeters distal to the SelfX and the Wallstent the flow profile returned to normal. In the MembraX an increase in the central slipstreams was found with creation of a flow separation distal to the stent. With a modification of the membrane this flow separation vanished. In the ECA flow disturbances were seen at the inner wall distal to the stent struts in the SelfX and the Wallstent. With the MembraX a calming of flow could be observed in the ECA with a slight loss of flow volume. Conclusions. Stent placement across the carotid artery bifurcation induces alterations of the physiologic flow
A New Method of Studying the Flow of the Water Along the Bottom of a Model of a Flying-boat Hull
NASA Technical Reports Server (NTRS)
Ward, Kenneth E
1940-01-01
A new method of studying the flow of the water along the bottom of a model of a flying-boat hull is described. In this method, the model is fitted with a transparent bottom and is divided down the center line by a bulkhead. The flow is observed and photographed through one-half of the model by means of the diffused illumination from a battery of lamps contained in the other half of the model. Photographs of the flow, particularly of the changes that occur when the step ventilates, are shown. The results of the present investigation indicate that the method has considerable promise, chiefly in connection with motion-picture studies.
Lower Three Runs Instream Flow Study
del Carmen, B.R.; Paller, M.H.
1993-12-31
An Instream Flow Study was conducted to identify the minimum discharge from PAR Pond that will support a balanced biological fish community in Lower Three Runs. Hydraulic and habitat models of the Physical Habitat simulation System (PHABSIM), the major component of the US Fish and Wildlife Service`s Instream Flow Incremental Methodology (IFIM) were applied. Following calibration of the Water Surface Profile (WSP)Model for three study reaches, hydraulic data was input to the AVDEPTH habitat model to develop relationships between discharge and reaches, hydraulic data was input to the AVDEPTH habitat model to development relationship between discharge and available habitat.
NASA Astrophysics Data System (ADS)
Peng, Z.; Day, D. A.; Ortega, A. M.; Hu, W.; Palm, B. B.; Li, R.; De Gouw, J. A.; Brune, W. H.; Jimenez, J. L.
2014-12-01
Oxidation Flow Reactors (OFRs) using OH produced from low-pressure Hg lamps at 254 nm (OFR254) or both 185 and 254 nm (OFR185) are commonly used in atmospheric chemistry and other fields. OFR254 requires addition of externally formed O3 since OH is formed mainly from O3 photolysis, while OFR185 does not since OH can also be formed from H2O photolysis. In this study we use a plug-flow kinetic model to investigate OFR properties under a very wide range of conditions applicable to both field and laboratory studies. We show that radical chemistry in OFRs can be characterized as a function of 3 main parameters: UV light intensity, H2O concentration, and total external OH reactivity (e.g. from VOCs, NOx, and SO2). In OFR185, OH exposure is more sensitive to external OH reactivity than in OFR254, because injected O3 in OFR254 greatly promotes the recycling of HO2 to OH, making external perturbations to the radical chemistry less significant. The uncertainties of modeled OH, O3, and H2O2 due to uncertain kinetic parameters are within 40% in most cases. Sensitivity analysis shows that most of the uncertainty is contributed by photolysis and reactions involving OH and HO2, e.g. 2HO2→H2O2+O2 and OH+O3→HO2+O2. Reactants of atmospheric interest are dominantly consumed by OH, except some biogenics that can have substantial contributions from O3. Other highly reactive species (UV photons, O(1D), and O(3P)) only contribute for some species under conditions low H2O concentration and/or high external OH reactivity, which can be avoided by experimental planning. OFR185 and OFR254 are comparable in terms of non-OH oxidants' influence. In OFRs NO is fast oxidized. RO2 fate is similar to that in the atmosphere under low NO conditions. A comprehensive comparison of OFRs with typical environmental chamber studies with UV blacklights and with the atmosphere is also performed. OFRs' key advantages are their short experimental time scales, portability to field sites, and generally good
NASA Astrophysics Data System (ADS)
Mohammadi-Ghaleni, Mahdi; Asle Zaeem, Mohsen; Smith, Jeffrey D.; O'Malley, Ronald
2016-10-01
Melt flow patterns and turbulence inside a slide-gate throttled submerged entry nozzle (SEN) were studied using Detached-Eddy Simulation (DES) model, which is a combination of Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) models. The DES switching criterion between RANS and LES was investigated to closely reproduce the flow structures of low and high turbulence regions similar to RANS and LES simulations, respectively. The melt flow patterns inside the nozzle were determined by k- ɛ (a RANS model), LES, and DES turbulent models, and convergence studies were performed to ensure reliability of the results. Results showed that the DES model has significant advantages over the standard k- ɛ model in transient simulations and in regions containing flow separation from the nozzle surface. Moreover, due to applying a hybrid approach, DES uses a RANS model at wall boundaries which resolves the extremely fine mesh requirement of LES simulations, and therefore it is computationally more efficient. Investigation of particle distribution inside the nozzle and particle adhesion to the nozzle wall also reveals that the DES model simulations predict more particle-wall interactions compared to LES model.
NASA Astrophysics Data System (ADS)
Hoi, Yiemeng; Ionita, Ciprian N.; Tranquebar, Rekha V.; Hoffmann, Kenneth R.; Woodward, Scott H.; Taulbee, Dale B.; Meng, Hui; Rudin, Stephen
2006-03-01
An asymmetric stent with low porosity patch across the intracranial aneurysm neck and high porosity elsewhere is designed to modify the flow to result in thrombogenesis and occlusion of the aneurysm and yet to reduce the possibility of also occluding adjacent perforator vessels. The purposes of this study are to evaluate the flow field induced by an asymmetric stent using both numerical and digital subtraction angiography (DSA) methods and to quantify the flow dynamics of an asymmetric stent in an in vivo aneurysm model. We created a vein-pouch aneurysm model on the canine carotid artery. An asymmetric stent was implanted at the aneurysm, with 25% porosity across the aneurysm neck and 80% porosity elsewhere. The aneurysm geometry, before and after stent implantation, was acquired using cone beam CT and reconstructed for computational fluid dynamics (CFD) analysis. Both steady-state and pulsatile flow conditions using the measured waveforms from the aneurysm model were studied. To reduce computational costs, we modeled the asymmetric stent effect by specifying a pressure drop over the layer across the aneurysm orifice where the low porosity patch was located. From the CFD results, we found the asymmetric stent reduced the inflow into the aneurysm by 51%, and appeared to create a stasis-like environment which favors thrombus formation. The DSA sequences also showed substantial flow reduction into the aneurysm. Asymmetric stents may be a viable image guided intervention for treating intracranial aneurysms with desired flow modification features.
Preliminary Saturated-Zone Flow Model
1997-06-10
This milestone consists of an updated fully 3D model of ground-water flow within the saturated zone at Yucca Mountain, Nevada. All electronic files pertaining to this deliverable have been transferred via ftp transmission to Steve Bodnar (M and O) and the technical data base. The model was developed using a flow and transport simulator, FEHMN, developed at Los Alamos National Laboratory, and represents a collaborative effort between staff from the US Geological Survey and Los Alamos National Laboratory. The model contained in this deliverable is minimally calibrated and represents work in progress. The flow model developed for this milestone is designed to feed subsequent transport modeling studies at Los Alamos which also use the FEHMN software. In addition, a general-application parameter estimation routine, PEST, was used in conjunction with FEHMN to reduce the difference between observed and simulated values of hydraulic head through the adjustment of model variables. This deliverable in large part consists of the electronic files for Yucca Mountain Site saturated-zone flow model as it existed as of 6/6/97, including the executable version of FEHMN (accession no. MOL.19970610.0204) used to run the code on a Sun Ultrasparc I workstation. It is expected that users of the contents of this deliverable be knowledgeable about the oration of FEHMN.
NASA Astrophysics Data System (ADS)
Lu, Xiaofeng; Li, Yourong
2000-12-01
A cold model experimental study on the flowing characteristics of bed material between a fluidized bed ash cooler and a furnace of CFB boiler were discussed in this paper. The research results showed that flowing status of the bed material in a bubbling bed, which was run with a circulating fluidized bed together in parallel operation, was influenced by the pressure difference between the CFB and the bubbling bed, the switch status of unlocking air, and the structure of the exit of the bubbling bed. There was a circulating flow of bed material between CFB and bubbling bed.
VisFlow - Web-based Visualization Framework for Tabular Data with a Subset Flow Model.
Yu, Bowen; Silva, Claudio T
2017-01-01
Data flow systems allow the user to design a flow diagram that specifies the relations between system components which process, filter or visually present the data. Visualization systems may benefit from user-defined data flows as an analysis typically consists of rendering multiple plots on demand and performing different types of interactive queries across coordinated views. In this paper, we propose VisFlow, a web-based visualization framework for tabular data that employs a specific type of data flow model called the subset flow model. VisFlow focuses on interactive queries within the data flow, overcoming the limitation of interactivity from past computational data flow systems. In particular, VisFlow applies embedded visualizations and supports interactive selections, brushing and linking within a visualization-oriented data flow. The model requires all data transmitted by the flow to be a data item subset (i.e. groups of table rows) of some original input table, so that rendering properties can be assigned to the subset unambiguously for tracking and comparison. VisFlow features the analysis flexibility of a flow diagram, and at the same time reduces the diagram complexity and improves usability. We demonstrate the capability of VisFlow on two case studies with domain experts on real-world datasets showing that VisFlow is capable of accomplishing a considerable set of visualization and analysis tasks. The VisFlow system is available as open source on GitHub.
NASA Astrophysics Data System (ADS)
Li, Zhipeng; Xu, Xun; Xu, Shangzhi; Qian, Yeqing; Xu, Juan
2016-07-01
The car-following model is extended to take into account the characteristics of mixed traffic flow containing fast and slow vehicles. We conduct the linear stability analysis to the extended model with finding that the traffic flow can be stabilized with the increase of the percentage of the slow vehicle. It also can be concluded that the stabilization of the traffic flow closely depends on not only the average value of two maximum velocities characterizing two vehicle types, but also the standard deviation of the maximum velocities among all vehicles, when the percentage of the slow vehicles is the same as that of the fast ones. With increase of the average maximum velocity, the traffic flow becomes more and more unstable, while the increase of the standard deviation takes negative effect in stabilizing the traffic system. The direct numerical results are in good agreement with those of theoretical analysis. Moreover, the relation between the flux and the traffic density is investigated to simulate the effects of the percentage of slow vehicles on traffic flux in the whole density regions.
Mathematical Models Of Turbulence In Hypersonic Flow
NASA Technical Reports Server (NTRS)
Marvin, J. G.; Coakley, T. J.
1991-01-01
Report discusses mathematical models of turbulence used in numerical simulations of complicated viscous, hypersonic flows. Includes survey of essential features of models and their statuses in applications.
NASA Astrophysics Data System (ADS)
Strupczewski, Witold G.; Bogdanowich, Ewa; Debele, Sisay
2016-04-01
Under Polish climate conditions the series of Annual Maxima (AM) flows are usually a mixture of peak flows of thaw- and rainfall- originated floods. The northern, lowland regions are dominated by snowmelt floods whilst in mountainous regions the proportion of rainfall floods is predominant. In many stations the majority of AM can be of snowmelt origin, but the greatest peak flows come from rainfall floods or vice versa. In a warming climate, precipitation is less likely to occur as snowfall. A shift from a snow- towards a rain-dominated regime results in a decreasing trend in mean and standard deviations of winter peak flows whilst rainfall floods do not exhibit any trace of non-stationarity. That is why a simple form of trends (i.e. linear trends) are more difficult to identify in AM time-series than in Seasonal Maxima (SM), usually winter season time-series. Hence it is recommended to analyse trends in SM, where a trend in standard deviation strongly influences the time -dependent upper quantiles. The uncertainty associated with the extrapolation of the trend makes it necessary to apply a relationship for trend which has time derivative tending to zero, e.g. we can assume a new climate equilibrium epoch approaching, or a time horizon is limited by the validity of the trend model. For both winter and summer SM time series, at least three distributions functions with trend model in the location, scale and shape parameters are estimated by means of the GAMLSS package using the ML-techniques. The resulting trend estimates in mean and standard deviation are mutually compared to the observed trends. Then, using AIC measures as weights, a multi-model distribution is constructed for each of two seasons separately. Further, assuming a mutual independence of the seasonal maxima, an AM model with time-dependent parameters can be obtained. The use of a multi-model approach can alleviate the effects of different and often contradictory trends obtained by using and identifying
ERIC Educational Resources Information Center
Joo, Young Ju; Oh, Eunjung; Kim, Su Mi
2015-01-01
The purpose of this study is to examine the structural relationships among self-efficacy, intrinsic value, test anxiety, instructional design, flow, and achievement among students at a Korean online university. To address research questions, the researchers administered online surveys to 963 college students at an online university in Korea…
Slurry fired heater cold-flow modelling
Moujaes, S.F.
1983-07-01
This report summarizes the experimental and theoretical work leading to the scale-up of the SRC-I Demonstration Plant slurry fired heater. The scale-up involved a theoretical model using empirical relations in the derivation, and employed variables such as flow conditions, liquid viscosity, and slug frequency. Such variables have been shown to affect the heat transfer characteristics ofthe system. The model assumes that, if all other variables remain constant, the heat transfer coefficient can be scaled up proportional to D/sup -2/3/ (D = inside diameter of the fired heater tube). All flow conditions, liquid viscosities, and pipe inclinations relevant to the demonstration plant have indicated a slug flow regime in the slurry fired heater. The annular and stratified flow regimes should be avoided to minimize the potential for excessive pipe erosion and to decrease temperature gradients along the pipe cross section leading to coking and thermal stresses, respectively. Cold-flow studies in 3- and 6.75-in.-inside-diameter (ID) pipes were conducted to determine the effect of scale-up on flow regime, slug frequency, and slug dimensions. The developed model assumes that conduction heat transfer occurs through the liquid film surrounding the gas slug and laminar convective heat transfer to the liquid slug. A weighted average of these two heat transfer mechanisms gives a value for the average pipe heat transfer coefficient. The cold-flow work showed a decrease in the observed slug frequency between the 3- and 6.75-ID pipes. Data on the ratio of gas to liquid slug length in the 6.75-in. pipe are not yet complete, but are expected to yield generally lower values than those obtained in the 3-in. pipe; this will probably affect the scale-up to demonstration plant conditions. 5 references, 15 figures, 7 tables.
Turbulence and modeling in transonic flow
NASA Technical Reports Server (NTRS)
Rubesin, Morris W.; Viegas, John R.
1989-01-01
A review is made of the performance of a variety of turbulence models in the evaluation of a particular well documented transonic flow. This is done to supplement a previous attempt to calibrate and verify transonic airfoil codes by including many more turbulence models than used in the earlier work and applying the calculations to an experiment that did not suffer from uncertainties in angle of attack and was free of wind tunnel interference. It is found from this work, as well as in the earlier study, that the Johnson-King turbulence model is superior for transonic flows over simple aerodynamic surfaces, including moderate separation. It is also shown that some field equation models with wall function boundary conditions can be competitive with it.
NASA Astrophysics Data System (ADS)
Martin, Y. E.; Johnson, E. A.; Chaikina, O.
2014-12-01
Debris flows are a major process responsible for transferring sediment from high mountain locations to more downstream fluvial reaches. This sediment transfer begins on mountain hillslopes where various mass wasting processes move sediment from hillslopes to uppermost reaches of the channel system (these reaches are herein referred to as gullies and only experience water flow during high intensity precipitation events). Sediment recharge into gullies, which has received minimal attention in the scientific literature, refers to the transfer of sediment and other debris from surrounding hillslopes into gullies (Jakob and Oden, 2005). Debris flow occurrence and debris flow volumes depend on some precipitation threshold as well as volumes of material contained in the particular gully. For example, if one debris flow has removed all of the accumulated material from the gully, then any subsequent debris flow will be smaller if enough time has not yet passed for notable sediment recharge. Herein, we utilize the numerical model of landscape development, LandMod (Martin, 1998; Dadson and Church, 2005; Martin, 2007), to explore connections between hillslope processes, gully recharge rates, and transfer of sediment to downstream channel reaches in the Haida Gwaii, British Columbia. Hillslope processes in the model include shallow landsliding, bedrock failures and weathering. The updated debris flow algorithm is based on extensive field data available for debris flows in Haida Gwaii (e.g., Rood, 1984; Oden, 1994; Jakob and Oden, 2005), as well as theoretical considerations based on debris flow studies. The most significant model extension is the calculation of gully recharge rates; for each gully, the total accumulated sediment in gullies at each time step is determined using a power-law relation for area-normalized recharge rate versus elapsed time since the last debris flow. Thus, when the stochastic driver for debris flow occurrence triggers an event, the amount of stored
Comparing turbulence models for flow through a rigid glottal model.
Suh, Jungsoo; Frankel, Steven H
2008-03-01
Flow through a rigid model of the human vocal tract featuring a divergent glottis was numerically modeled using the Reynolds-averaged Navier-Stokes approach. A number of different turbulence models, available in a widely used commercial computational fluid dynamics code, were tested to determine their ability to capture various flow features recently observed in laboratory experiments and large eddy simulation studies. The study reveals that results from unsteady simulations employing the k-omega shear stress transport model were in much better agreement with previous measurements and predictions with regard to the ability to predict glottal jet skewing due to the Coanda effect and the intraglottal pressure distribution or related skin friction coefficient, than either steady or unsteady simulations using the Spalart-Allmaras model or any other two-equation turbulence model investigated in this study.
NASA Astrophysics Data System (ADS)
Kollet, Stefan J.; Maxwell, Reed M.
2006-07-01
propagation of uncertainty due to subsurface heterogeneity to the overland flow predictions and demonstrate the usefulness of our approach. Both the overland flow component and the coupled model are evaluated in a parallel scaling study and show to be efficient.
NASA Astrophysics Data System (ADS)
Peng, Z.; Day, D. A.; Ortega, A. M.; Palm, B. B.; Hu, W. W.; Stark, H.; Li, R.; Tsigaridis, K.; Brune, W. H.; Jimenez, J. L.
2015-09-01
Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to relative humidity (RH) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportional to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to VOC consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. Under "pathological OFR conditions" of low RH and/or high OHRext, the importance of non-OH reactants is enhanced because OH is suppressed. Some biogenics can have substantial destructions by O3, and photolysis at non-tropospheric wavelengths (185 and 254 nm) may also play a significant role in the degradation of some aromatics under pathological conditions. Working under low O2 with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in lab studies, and
Estimating Preferential Flow in Karstic Aquifers Using Statistical Mixed Models
Anaya, Angel A.; Padilla, Ingrid; Macchiavelli, Raul; Vesper, Dorothy J.; Meeker, John D.; Alshawabkeh, Akram N.
2013-01-01
Karst aquifers are highly productive groundwater systems often associated with conduit flow. These systems can be highly vulnerable to contamination, resulting in a high potential for contaminant exposure to humans and ecosystems. This work develops statistical models to spatially characterize flow and transport patterns in karstified limestone and determines the effect of aquifer flow rates on these patterns. A laboratory-scale Geo-HydroBed model is used to simulate flow and transport processes in a karstic limestone unit. The model consists of stainless-steel tanks containing a karstified limestone block collected from a karst aquifer formation in northern Puerto Rico. Experimental work involves making a series of flow and tracer injections, while monitoring hydraulic and tracer response spatially and temporally. Statistical mixed models are applied to hydraulic data to determine likely pathways of preferential flow in the limestone units. The models indicate a highly heterogeneous system with dominant, flow-dependent preferential flow regions. Results indicate that regions of preferential flow tend to expand at higher groundwater flow rates, suggesting a greater volume of the system being flushed by flowing water at higher rates. Spatial and temporal distribution of tracer concentrations indicates the presence of conduit-like and diffuse flow transport in the system, supporting the notion of both combined transport mechanisms in the limestone unit. The temporal response of tracer concentrations at different locations in the model coincide with, and confirms the preferential flow distribution generated with the statistical mixed models used in the study. PMID:23802921
NASA Astrophysics Data System (ADS)
Parsons, R. A.; Nimmo, F.; Hustoft, J. W.; Holtzman, B. K.; Kohlstedt, D. L.
2006-12-01
The flow of melt in partially-molten rocks has important implications for the geochemical and geophysical evolution of planetary bodies over a wide range of length scales. Surface tension is usually ignored in favor of differential stresses and buoyancy forces, but may still distribute melt over geologically interesting distances [1], particularly in small bodies such as asteroids. We have investigated experimentally the role of surface tension in the redistribution of melt. Shear deformation of synthetic mantle-type rocks composed of 76 vol% olivine, 20 vol% chromite, and 4 vol% mid-ocean ridge basalt (MORB) at upper mantle temperature and pressure conditions (1523 K, 300 MPa) produces anastomosing networks of melt-enriched (MORB) regions separated by melt-depleted lenses [2]. After the deformation phase of the experiment, each of three samples were statically annealed at 1523 K for 0, 10, or 100 hours to allow some MORB to redistribute back into the melt-depleted olivine plus chromite matrix via surface tension-driven capillary flow.". We modeled melt redistribution resulting from surface tension during the static anneal [3]. Using sample measurements of dihedral angle, and values for MORB and olivine viscosity from the literature (10 Pas [4] and 8x10^{12} Pas [5], [6], respectively), we are able to constrain the sample permeability by matching the model results to the experiments. Permeability is given by κ = d2φn/b. The model uses an exponential melt-dependent viscosity relation of the form ηo*10-α φ where ηo is the dry olivine viscosity, α = 25 [5], and φ is the melt fraction. We find that a permeability on the order of 10-18 m2, corresponding to n = 2 ± 0.2 and b = 7000 ± 2000, gives the best fit to the the experimental anneals. The relatively high value of b is probably due to clogging of melt paths by chromite grains (see Appendix A of Holtzmann et al.). [1] Stevenson D. J. (1986) GRL, 13, 1149-1152. [2] Holtzman B. K. et al. (2003) Science, 301
NASA Astrophysics Data System (ADS)
Ozer, C.; Yalciner, A. C.; Zaytsev, A.
2011-12-01
It has been clarified by 2004 Indian Ocean and 2001 Great East Japan tsunami events that the major reasons of impacts and damage of tsunamis depend on the flow parameters in nearshore and inundation zone. Hence the determination of impact level or tsunami drag force becomes essential. The square of Froude number (Fr2) which depends on the relation between current velocity and flow depth at any instant and any location is one of the effective parameters that represents the level of drag force exerted by the flow. Current velocity and flow depth change spatially and instantaneously in inundation zone. Therefore, maximum values of Fr2 occur in relation to the instantaneous values of current and flow depth. In this study, a series of fine grid simulations of tsunami inundation are performed using the numerical code NAMI DANCE which is modified in the frame of Joint Research Project MORAT between Russia and Turkey. A study domain having 1:20 beach slope is selected. At the coastal area, specially arranged rectangular coastal structures are located. The coastal area is selected as unprotected or protected by a seawall with different heights and/or a breakwater. The maximum values of Fr2 are computed at each grid node during the simulations of different incoming tsunami amplitudes. Furthermore the current velocities and flow depth at the time of maximum Fr2 are also computed. The spatial changes of these parameters along the lines perpendicular to the shore are plotted and the results are compared. A scale of Fr2 values for the assessment of the spatial change of damage level is developed. Damage level is also evaluated and discussed considering i) the presence of the coastal protection structures (i.e. tsunami walls etc.), ii) the presence of breakwaters, iii) the layout of the structures and roads, iv) type of the structures (R/C, timber, half-timbered, truss etc). The results are used to discuss the coastal damage by 2011 Japan tsunami event. In the case study, the
Mathematical Models Of Turbulence In Transonic Flow
NASA Technical Reports Server (NTRS)
Rubesin, Morris W.; Viegas, John R.
1989-01-01
Predictions of several models compared with measurements of well-documented flow. Report reviews performances of variety of mathematical models of turbulence in transonic flow. Predictions of models compared with measurements of flow in wind tunnel along outside of cylinder having axisymmetric bump of circular-arc cross section in meridional plane. Review part of continuing effort to calibrate and verify computer codes for prediction of transonic flows about airfoils. Johnson-and-King model proved superior in predicting transonic flow over bumpy cylinder.
Fractional-order variational optical flow model for motion estimation.
Chen, Dali; Sheng, Hu; Chen, YangQuan; Xue, Dingyü
2013-05-13
A new class of fractional-order variational optical flow models, which generalizes the differential of optical flow from integer order to fractional order, is proposed for motion estimation in this paper. The corresponding Euler-Lagrange equations are derived by solving a typical fractional variational problem, and the numerical implementation based on the Grünwald-Letnikov fractional derivative definition is proposed to solve these complicated fractional partial differential equations. Theoretical analysis reveals that the proposed fractional-order variational optical flow model is the generalization of the typical Horn and Schunck (first-order) variational optical flow model and the second-order variational optical flow model, which provides a new idea for us to study the optical flow model and has an important theoretical implication in optical flow model research. The experiments demonstrate the validity of the generalization of differential order.
East Maui Groundwater Flow Model
Nicole Lautze
2015-01-01
Groundwater flow model for East Maui. Data is from the following sources: Whittier, R. and A.I. El-Kadi. 2014. Human and Environmental Risk Ranking of Onsite Sewage Disposal Systems For the Hawaiian Islands of Kauai, Molokai, Maui, and Hawaii – Final. Prepared by the University of Hawaii, Dept. of Geology and Geophysics for the State of Hawaii Dept. of Health, Safe Drinking Water Branch. September 2014; and Whittier, R.B., K. Rotzoll, S. Dhal, A.I. El-Kadi, C. Ray, G. Chen, and D. Chang. 2004. Hawaii Source Water Assessment Program Report – Volume V – Island of Maui Source Water Assessment Program Report. Prepared for the Hawaii Department of Health, Safe Drinking Water Branch. University of Hawaii, Water Resources Research Center. Updated 2008.
Hawaii Island Groundwater Flow Model
Nicole Lautze
2015-01-01
Groundwater flow model for Hawaii Island. Data is from the following sources: Whittier, R.B., K. Rotzoll, S. Dhal, A.I. El-Kadi, C. Ray, G. Chen, and D. Chang. 2004. Hawaii Source Water Assessment Program Report – Volume II – Island of Hawaii Source Water Assessment Program Report. Prepared for the Hawaii Department of Health, Safe Drinking Water Branch. University of Hawaii, Water Resources Research Center. Updated 2008; and Whittier, R. and A.I. El-Kadi. 2014. Human and Environmental Risk Ranking of Onsite Sewage Disposal Systems For the Hawaiian Islands of Kauai, Molokai, Maui, and Hawaii – Final. Prepared by the University of Hawaii, Dept. of Geology and Geophysics for the State of Hawaii Dept. of Health, Safe Drinking Water Branch. September 2014.
West Maui Groundwater Flow Model
Nicole Lautze
2015-01-01
Groundwater flow model for West Maui. Data is from the following sources: Whittier, R. and A.I. El-Kadi. 2014. Human and Environmental Risk Ranking of Onsite Sewage Disposal Systems For the Hawaiian Islands of Kauai, Molokai, Maui, and Hawaii – Final. Prepared by the University of Hawaii, Dept. of Geology and Geophysics for the State of Hawaii Dept. of Health, Safe Drinking Water Branch. September 2014; and Whittier, R.B., K. Rotzoll, S. Dhal, A.I. El-Kadi, C. Ray, G. Chen, and D. Chang. 2004. Hawaii Source Water Assessment Program Report – Volume V – Island of Maui Source Water Assessment Program Report. Prepared for the Hawaii Department of Health, Safe Drinking Water Branch. University of Hawaii, Water Resources Research Center. Updated 2008.
In Vitro MRV-based Hemodynamic Study of Complex Helical Flow in a Patient-specific Jugular Model
NASA Astrophysics Data System (ADS)
Kefayati, Sarah; Acevedo-Bolton, Gabriel; Haraldsson, Henrik; Saloner, David
2014-11-01
Neurointerventional Radiologists are frequently requested to evaluate the venous side of the intracranial circulation for a variety of conditions including: Chronic Cerebrospinal Venous Insufficiency thought to play a role in the development of multiple sclerosis; sigmoid sinus diverticulum which has been linked to the presence of pulsatile tinnitus; and jugular vein distension which is related to cardiac dysfunction. Most approaches to evaluating these conditions rely on structural assessment or two dimensional flow analyses. This study was designed to investigate the highly complex jugular flow conditions using magnetic resonance velocimetry (MRV). A jugular phantom was fabricated based on the geometry of the dominant jugular in a tinnitus patient. Volumetric three-component time-resolved velocity fields were obtained using 4D PC-MRI -with the protocol enabling turbulence acquisition- and the patient-specific pulsatile waveform. Flow was highly complex exhibiting regions of jet, high swirling strength, and strong helical pattern with the core originating from the focal point of the jugular bulb. Specifically, flow was analyzed for helicity and the level of turbulence kinetic energy elevated in the core of helix and distally, in the post-narrowing region.
NASA Astrophysics Data System (ADS)
Salazar-Campoy, María M.; Morales, R. D.; Nájera-Bastida, A.; Cedillo-Hernández, Valentín; Delgado-Pureco, J. C.
2017-01-01
Momentum transfer of argon-steel flows in a slab mold were studied through an air-water physical model and particle image velocimetry measurements under the effects of nozzle design (nozzles with square ports S, square ports with bottom design U and circular ports C) and gas flow rate. The ratio of drag momentum of the gas phase over the liquid phase defines the conditions for coupled (existence of momentum transfer between the phases) and channeled flows (defined as those conditions where there is not further momentum transfer between both phases). When the ratio of superficial velocities of the gas phase over the liquid phase in the nozzle bore is less than 0.14, the flow pattern in the mold is dependent on the nozzle design and flow rate of gas (2 to 10 L/minute). Above this magnitude, the flow pattern becomes uncoupled and independent from the nozzle design and from the flow rate of gas. The ratios of drag velocities of the gas phase on the liquid phase and their superficial velocities in the nozzle bore are strongly dependent on the volume fraction of the gas phase. Nozzle U delivers the smallest sizes of bubbles and the smaller amount of bubble swarms per unit time impacting on the narrow face of the mold. It is, therefore, the most recommendable to cast ultra-low carbon steels. Practical implications derived from these results are written down in the text.
NASA Astrophysics Data System (ADS)
Salazar-Campoy, María M.; Morales, R. D.; Nájera-Bastida, A.; Cedillo-Hernández, Valentín; Delgado-Pureco, J. C.
2017-04-01
Momentum transfer of argon-steel flows in a slab mold were studied through an air-water physical model and particle image velocimetry measurements under the effects of nozzle design (nozzles with square ports S, square ports with bottom design U and circular ports C) and gas flow rate. The ratio of drag momentum of the gas phase over the liquid phase defines the conditions for coupled (existence of momentum transfer between the phases) and channeled flows (defined as those conditions where there is not further momentum transfer between both phases). When the ratio of superficial velocities of the gas phase over the liquid phase in the nozzle bore is less than 0.14, the flow pattern in the mold is dependent on the nozzle design and flow rate of gas (2 to 10 L/minute). Above this magnitude, the flow pattern becomes uncoupled and independent from the nozzle design and from the flow rate of gas. The ratios of drag velocities of the gas phase on the liquid phase and their superficial velocities in the nozzle bore are strongly dependent on the volume fraction of the gas phase. Nozzle U delivers the smallest sizes of bubbles and the smaller amount of bubble swarms per unit time impacting on the narrow face of the mold. It is, therefore, the most recommendable to cast ultra-low carbon steels. Practical implications derived from these results are written down in the text.
Estimation of instantaneous peak flow from simulated maximum daily flow using the HBV model
NASA Astrophysics Data System (ADS)
Ding, Jie; Haberlandt, Uwe
2014-05-01
Instantaneous peak flow (IPF) data are the foundation of the design of hydraulic structures and flood frequency analysis. However, the long discharge records published by hydrological agencies contain usually only average daily flows which are of little value for design in small catchments. In former research, statistical analysis using observed peak and daily flow data was carried out to explore the link between instantaneous peak flow (IPF) and maximum daily flow (MDF) where the multiple regression model is proved to have the best performance. The objective of this study is to further investigate the acceptability of the multiple regression model for post-processing simulated daily flows from hydrological modeling. The model based flood frequency analysis allows to consider change in the condition of the catchments and in climate for design. Here, the HBV model is calibrated on peak flow distributions and flow duration curves using two approaches. In a two -step approach the simulated MDF are corrected with a priory established regressions. In a one-step procedure the regression coefficients are calibrated together with the parameters of the model. For the analysis data from 18 mesoscale catchments in the Aller-Leine river basin in Northern Germany are used. The results show that: (1) the multiple regression model is capable to predict the peak flows with the simulated MDF data; (2) the calibrated hydrological model reproduces well the magnitude and frequency distribution of peak flows; (3) the one-step procedure outperforms the two-step procedure regarding the estimation of peak flows.
Numerical modeling of fluid flow with rafts: An application to lava flows
NASA Astrophysics Data System (ADS)
Tsepelev, Igor; Ismail-Zadeh, Alik; Melnik, Oleg; Korotkii, Alexander
2016-07-01
Although volcanic lava flows do not significantly affect the life of people, its hazard is not negligible as hot lava kills vegetation, destroys infrastructure, and may trigger a flood due to melting of snow/ice. The lava flow hazard can be reduced if the flow patterns are known, and the complexity of the flow with debris is analyzed to assist in disaster risk mitigation. In this paper we develop three-dimensional numerical models of a gravitational flow of multi-phase fluid with rafts (mimicking rigid lava-crust fragments) on a horizontal and topographic surfaces to explore the dynamics and the interaction of lava flows. We have obtained various flow patterns and spatial distribution of rafts depending on conditions at the surface of fluid spreading, obstacles on the way of a fluid flow, raft landing scenarios, and the size of rafts. Furthermore, we analyze two numerical models related to specific lava flows: (i) a model of fluid flow with rafts inside an inclined channel, and (ii) a model of fluid flow from a single vent on an artificial topography, when the fluid density, its viscosity, and the effusion rate vary with time. Although the studied models do not account for lava solidification, crust formation, and its rupture, the results of the modeling may be used for understanding of flows with breccias before a significant lava cooling.
NASA Technical Reports Server (NTRS)
Mudrick, S.
1985-01-01
The validity of quasi-geostrophic (QG) dynamics were tested on compared to primitive equation (PE) dynamics, for modeling the effect of cyclone waves on the larger scale flow. The formation of frontal cyclones and the dynamics of occluded frontogenesis were studied. Surface friction runs with the PE model and the wavelength of maximum instability is described. Also fine resolution PE simulation of a polar low is described.
A toy terrestrial carbon flow model
NASA Technical Reports Server (NTRS)
Parton, William J.; Running, Steven W.; Walker, Brian
1992-01-01
A generalized carbon flow model for the major terrestrial ecosystems of the world is reported. The model is a simplification of the Century model and the Forest-Biogeochemical model. Topics covered include plant production, decomposition and nutrient cycling, biomes, the utility of the carbon flow model for predicting carbon dynamics under global change, and possible applications to state-and-transition models and environmentally driven global vegetation models.
An improved turbulence model for rotating shear flows*
NASA Astrophysics Data System (ADS)
Nagano, Yasutaka; Hattori, Hirofumi
2002-01-01
In the present study, we construct a turbulence model based on a low-Reynolds-number non-linear k e model for turbulent flows in a rotating channel. Two-equation models, in particular the non-linear k e model, are very effective for solving various flow problems encountered in technological applications. In channel flows with rotation, however, the explicit effects of rotation only appear in the Reynolds stress components. The exact equations for k and e do not have any explicit terms concerned with the rotation effects. Moreover, the Coriolis force vanishes in the momentum equation for a fully developed channel flow with spanwise rotation. Consequently, in order to predict rotating channel flows, after proper revision the Reynolds stress equation model or the non-linear eddy viscosity model should be used. In this study, we improve the non-linear k e model so as to predict rotating channel flows. In the modelling, the wall-limiting behaviour of turbulence is also considered. First, we evaluated the non-linear k e model using the direct numerical simulation (DNS) database for a fully developed rotating turbulent channel flow. Next, we assessed the non-linear k e model at various rotation numbers. Finally, on the basis of these assessments, we reconstruct the non-linear k e model to calculate rotating shear flows, and the proposed model is tested on various rotation number channel flows. The agreement with DNS and experiment data is quite satisfactory.
Code validation study for base flows
NASA Astrophysics Data System (ADS)
Ascoli, Edward P.; Heiba, Adel H.; Lagnado, Ronald R.; Ungewitter, Ronald J.; Williams, Morgan
1993-07-01
New and old rocket launch concepts recommend the clustering of motors for improved lift capability. The flowfield of the base region of the rocket is very complex and can contain high temperature plume gases. These hot gases can cause catastrophic problems if not adequately designed for. To assess the base region characteristics, advanced computational fluid dynamics (CFD) is being used. As a precursor to these calculations the CFD code requires validation on base flows. The primary objective of this code validation study was to establish a high level of confidence in predicting base flows with the USA CFD code. USA has been extensively validated for fundamental flows and other applications. However, base heating flows have a number of unique characteristics so it was necessary to extend the existing validation for this class of problems. In preparation for the planned NLS 1.5 Stage base heating analysis, six case sets were studied to extend the USA code validation data base. This presentation gives a cursive review of three of these cases. The cases presented include a 2D axi-symmetric study, a 3D real nozzle study, and a 3D multi-species study. The results of all the studies show good general agreement with data with no adjustments to the base numerical algorithms or physical models in the code. The study proved the capability of the USA code for modeling base flows within the accuracy of available data.
Code Validation Study for Base Flows
NASA Technical Reports Server (NTRS)
Ascoli, Edward P.; Heiba, Adel H.; Lagnado, Ronald R.; Ungewitter, Ronald J.; Williams, Morgan
1993-01-01
New and old rocket launch concepts recommend the clustering of motors for improved lift capability. The flowfield of the base region of the rocket is very complex and can contain high temperature plume gases. These hot gases can cause catastrophic problems if not adequately designed for. To assess the base region characteristics, advanced computational fluid dynamics (CFD) is being used. As a precursor to these calculations the CFD code requires validation on base flows. The primary objective of this code validation study was to establish a high level of confidence in predicting base flows with the USA CFD code. USA has been extensively validated for fundamental flows and other applications. However, base heating flows have a number of unique characteristics so it was necessary to extend the existing validation for this class of problems. In preparation for the planned NLS 1.5 Stage base heating analysis, six case sets were studied to extend the USA code validation data base. This presentation gives a cursive review of three of these cases. The cases presented include a 2D axi-symmetric study, a 3D real nozzle study, and a 3D multi-species study. The results of all the studies show good general agreement with data with no adjustments to the base numerical algorithms or physical models in the code. The study proved the capability of the USA code for modeling base flows within the accuracy of available data.
Pedersen, Jenny M; Shim, Yoo-Sik; Hans, Vaibhav; Phillips, Martin B; Macdonald, Jeffrey M; Walker, Glenn; Andersen, Melvin E; Clewell, Harvey J; Yoon, Miyoung
2016-01-01
Accurate prediction of metabolism is a significant outstanding challenge in toxicology. The best predictions are based on experimental data from in vitro systems using primary hepatocytes. The predictivity of the primary hepatocyte-based culture systems, however, is still limited due to well-known phenotypic instability and rapid decline of metabolic competence within a few hours. Dynamic flow bioreactors for three-dimensional cell cultures are thought to be better at recapitulating tissue microenvironments and show potential to improve in vivo extrapolations of chemical or drug toxicity based on in vitro test results. These more physiologically relevant culture systems hold potential for extending metabolic competence of primary hepatocyte cultures as well. In this investigation, we used computational fluid dynamics to determine the optimal design of a flow-based hepatocyte culture system for evaluating chemical metabolism in vitro. The main design goals were (1) minimization of shear stress experienced by the cells to maximize viability, (2) rapid establishment of a uniform distribution of test compound in the chamber, and (3) delivery of sufficient oxygen to cells to support aerobic respiration. Two commercially available flow devices - RealBio(®) and QuasiVivo(®) (QV) - and a custom developed fluidized bed bioreactor were simulated, and turbulence, flow characteristics, test compound distribution, oxygen distribution, and cellular oxygen consumption were analyzed. Experimental results from the bioreactors were used to validate the simulation results. Our results indicate that maintaining adequate oxygen supply is the most important factor to the long-term viability of liver bioreactor cultures. Cell density and system flow patterns were the major determinants of local oxygen concentrations. The experimental results closely corresponded to the in silico predictions. Of the three bioreactors examined in this study, we were able to optimize the experimental
Pedersen, Jenny M.; Shim, Yoo-Sik; Hans, Vaibhav; Phillips, Martin B.; Macdonald, Jeffrey M.; Walker, Glenn; Andersen, Melvin E.; Clewell, Harvey J.; Yoon, Miyoung
2016-01-01
Accurate prediction of metabolism is a significant outstanding challenge in toxicology. The best predictions are based on experimental data from in vitro systems using primary hepatocytes. The predictivity of the primary hepatocyte-based culture systems, however, is still limited due to well-known phenotypic instability and rapid decline of metabolic competence within a few hours. Dynamic flow bioreactors for three-dimensional cell cultures are thought to be better at recapitulating tissue microenvironments and show potential to improve in vivo extrapolations of chemical or drug toxicity based on in vitro test results. These more physiologically relevant culture systems hold potential for extending metabolic competence of primary hepatocyte cultures as well. In this investigation, we used computational fluid dynamics to determine the optimal design of a flow-based hepatocyte culture system for evaluating chemical metabolism in vitro. The main design goals were (1) minimization of shear stress experienced by the cells to maximize viability, (2) rapid establishment of a uniform distribution of test compound in the chamber, and (3) delivery of sufficient oxygen to cells to support aerobic respiration. Two commercially available flow devices – RealBio® and QuasiVivo® (QV) – and a custom developed fluidized bed bioreactor were simulated, and turbulence, flow characteristics, test compound distribution, oxygen distribution, and cellular oxygen consumption were analyzed. Experimental results from the bioreactors were used to validate the simulation results. Our results indicate that maintaining adequate oxygen supply is the most important factor to the long-term viability of liver bioreactor cultures. Cell density and system flow patterns were the major determinants of local oxygen concentrations. The experimental results closely corresponded to the in silico predictions. Of the three bioreactors examined in this study, we were able to optimize the experimental
VISCOPLASTIC FLUID MODEL FOR DEBRIS FLOW ROUTING.
Chen, Cheng-lung
1986-01-01
This paper describes how a generalized viscoplastic fluid model, which was developed based on non-Newtonian fluid mechanics, can be successfully applied to routing a debris flow down a channel. The one-dimensional dynamic equations developed for unsteady clear-water flow can be used for debris flow routing if the flow parameters, such as the momentum (or energy) correction factor and the resistance coefficient, can be accurately evaluated. The writer's generalized viscoplastic fluid model can be used to express such flow parameters in terms of the rheological parameters for debris flow in wide channels. A preliminary analysis of the theoretical solutions reveals the importance of the flow behavior index and the so-called modified Froude number for uniformly progressive flow in snout profile modeling.
NASA Astrophysics Data System (ADS)
Li, Zhipeng; Zhong, Chenjie; Chen, Lizhu; Xu, Shangzhi; Qian, Yeqing
2016-09-01
In this paper, the original lattice hydrodynamic model of traffic flow is extended to take into account the traffic current cooperation among three consecutive sites. The basic idea of the new consideration is that the cooperative traffic current of the considered site is determined by the traffic currents of the site itself, the immediately preceding site and the immediately following one. The stability criterion of the extended model is obtained by applying the linear stability analysis. The result reveals the traffic current cooperation of the immediately preceding site is positive correlation with the stability of traffic system, while negative correlation is found between the traffic stability and the traffic current cooperation of the nearest follow site. To describe the phase transition, the modified KdV equation near the critical point is derived by using the reductive perturbation method, with obtaining the dependence of the propagation kink solution for traffic jams on the traffic current cooperation among three consecutive sites. The direct numerical are conducted to verify the results of theoretical analysis, and explore the effects of the traffic current cooperation on the traffic flux of the vehicle flow system.
Ahmad Khan, Junaid; Mustafa, M.; Hayat, T.; Alsaedi, A.
2015-01-01
This work deals with the flow and heat transfer in upper-convected Maxwell fluid above an exponentially stretching surface. Cattaneo-Christov heat flux model is employed for the formulation of the energy equation. This model can predict the effects of thermal relaxation time on the boundary layer. Similarity approach is utilized to normalize the governing boundary layer equations. Local similarity solutions are achieved by shooting approach together with fourth-fifth-order Runge-Kutta integration technique and Newton’s method. Our computations reveal that fluid temperature has inverse relationship with the thermal relaxation time. Further the fluid velocity is a decreasing function of the fluid relaxation time. A comparison of Fourier’s law and the Cattaneo-Christov’s law is also presented. Present attempt even in the case of Newtonian fluid is not yet available in the literature. PMID:26325426
Analytical study of Cattaneo-Christov heat flux model for a boundary layer flow of Oldroyd-B fluid
NASA Astrophysics Data System (ADS)
F, M. Abbasi; M, Mustafa; S, A. Shehzad; M, S. Alhuthali; T, Hayat
2016-01-01
We investigate the Cattaneo-Christov heat flux model for a two-dimensional laminar boundary layer flow of an incompressible Oldroyd-B fluid over a linearly stretching sheet. Mathematical formulation of the boundary layer problems is given. The nonlinear partial differential equations are converted into the ordinary differential equations using similarity transformations. The dimensionless velocity and temperature profiles are obtained through optimal homotopy analysis method (OHAM). The influences of the physical parameters on the velocity and the temperature are pointed out. The results show that the temperature and the thermal boundary layer thickness are smaller in the Cattaneo-Christov heat flux model than those in the Fourier’s law of heat conduction. Project supported by the Deanship of Scientific Research (DSR) King Abdulaziz University, Jeddah, Saudi Arabia (Grant No. 32-130-36-HiCi).
Ahmad Khan, Junaid; Mustafa, M; Hayat, T; Alsaedi, A
2015-01-01
This work deals with the flow and heat transfer in upper-convected Maxwell fluid above an exponentially stretching surface. Cattaneo-Christov heat flux model is employed for the formulation of the energy equation. This model can predict the effects of thermal relaxation time on the boundary layer. Similarity approach is utilized to normalize the governing boundary layer equations. Local similarity solutions are achieved by shooting approach together with fourth-fifth-order Runge-Kutta integration technique and Newton's method. Our computations reveal that fluid temperature has inverse relationship with the thermal relaxation time. Further the fluid velocity is a decreasing function of the fluid relaxation time. A comparison of Fourier's law and the Cattaneo-Christov's law is also presented. Present attempt even in the case of Newtonian fluid is not yet available in the literature.
NASA Astrophysics Data System (ADS)
Bromhal, G. S.; Wilson, T. H.; Wells, A.; Diehl, R.; Smith, D. H.
2003-12-01
Recently, a few thousand tons of CO2 were injected into the West Pearl Queen field, a depleted oil reservoir in southeastern New Mexico, for a pilot carbon sequestration project. Small amounts of 3 different perfluorocarbon tracers were injected with the CO2. Approximately 50 capillary absorption tube samplers (CATS) were located across the field within 2m of the grounds surface to detect the tracers in extremely small (~10-13L) quantities. After only several days, the CATS detected quantities of tracers at distances of up to 350m from the injection well. Greater amounts of tracers were detected in the different directions. The underground transport mechanism(s) are uncertain; however, appearance of tracer in the CATS after only a 6 day period suggests that CO2 movement may have occurred through near-surface processes. Subsequent tracer measurements made over 10 and 54 day time periods revealed continued tracer leakage. To try to understand the tracer information, we conducted lineament interpretations of the area using a black and white aerial photo taken in 1949, digital orthophotos, and Landsat TM imagery. Lineament interpretations revealed distinct northeast and northwest trending lineament sets. These directions coincided roughly with the direction of tracer-leakage into areas northwest and southwest of the injection well. The near-surface geology consists of a few-feet thick veneer of late Pleistocene and Holocene sand dunes covering the middle Pleistocene Mescalero caliche. A survey of the caliche was made using ground penetrating radar (GPR) to attempt to identify any preferential migration pathways. Modeling studies also were performed to identify the potential leakage pathways at the site. Because of the relatively fast appearance of tracers at large distances from the injection well, simple diffusion through the surface layers was ruled out. Wind patterns in the area have also made transport through the atmosphere and back into the ground highly unlikely
NASA Astrophysics Data System (ADS)
Peng, Zhe; Day, Douglas A.; Ortega, Amber M.; Palm, Brett B.; Hu, Weiwei; Stark, Harald; Li, Rui; Tsigaridis, Kostas; Brune, William H.; Jimenez, Jose L.
2016-04-01
Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define "riskier OFR conditions" as those with either low H2O (< 0.1 %) or high OHRext ( ≥ 100 s-1 in OFR185 and > 200 s-1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to
Peng, Zhe; Day, Douglas A.; Ortega, Amber M.; ...
2016-04-06
Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling.more » The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define “riskier OFR conditions” as those with either low H2O (< 0.1 %) or high OHRext ( ≥ 100 s−1 in OFR185 and > 200 s−1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have
NASA Astrophysics Data System (ADS)
Cuo, L.; Giambelluca, T. W.; Ziegler, A. D.; Nullet, M. A.
2003-12-01
The distributed-hydrology-soil-vegetation model (DHSVM) was applied in Pang Khum Experimental Watershed (PKEW), located near 19.05\\deg N, 98.65\\deg E in the mountainous region of northern Thailand, headwaters of the Chao Phraya River system. PKEW has a highly seasonal rainfall regime, with 90% of the annual 1200-1400 mm rainfall occurring during the southwest summer monsoon. The elevation of PKEW ranges from approximately 1100 to 1500 m. Total road area including road banks is about 1.2% of the basin area. About 57% of the road area occurs on slopes steeper than 10%. All roads are unpaved. Land cover in PKEW is affected by swidden agriculture. Six land cover and nine soil classes are identified in the basin. We have been working in the area since 1997 as part of the Thailand Roads Project (TRP). Within the basin, we are monitoring microclimate at two sites, soil moisture at four sites, and rainfall at five sites. Streamflow is measured at the outlet. Based on digital elevation data, DHSVM explicitly accounts for the spatial distribution of the stream and road networks, soil depth, soil and vegetation types. The model run period, including warm up, calibration and validation, is from August 1997 to January 2001. Field measurements provide forcing data, calibration data, and guidance in parameter selection. Model calibration and validation were done by aggregating simulated hourly soil moisture and stream flow into daily values and comparing them with aggregated daily measurements. For the calibration period, RMSEs of soil moisture and streamflow were lower than the observed variability as represented by the standard deviation, median absolute deviation, and (for stream flow) interquartile range. Model performance drops in validation period, but RMSEs remain near or lower than observed variability. We ran DHSVM with and without roads to examine their effects. Significant effects of roads were found despite the very low proportion of the watershed covered by roads
A superstatistical model of vehicular traffic flow
NASA Astrophysics Data System (ADS)
Kosun, Caglar; Ozdemir, Serhan
2016-02-01
In the analysis of vehicular traffic flow, a myriad of techniques have been implemented. In this study, superstatistics is used in modeling the traffic flow on a highway segment. Traffic variables such as vehicular speeds, volume, and headway were collected for three days. For the superstatistical approach, at least two distinct time scales must exist, so that a superposition of nonequilibrium systems assumption could hold. When the slow dynamics of the vehicle speeds exhibit a Gaussian distribution in between the fluctuations of the system at large, one speaks of a relaxation to a local equilibrium. These Gaussian distributions are found with corresponding standard deviations 1 /√{ β }. This translates into a series of fluctuating beta values, hence the statistics of statistics, superstatistics. The traffic flow model has generated an inverse temperature parameter (beta) distribution as well as the speed distribution. This beta distribution has shown that the fluctuations in beta are distributed with respect to a chi-square distribution. It must be mentioned that two distinct Tsallis q values are specified: one is time-dependent and the other is independent. A ramification of these q values is that the highway segment and the traffic flow generate separate characteristics. This highway segment in question is not only nonadditive in nature, but a nonequilibrium driven system, with frequent relaxations to a Gaussian.
Mutiscale Modeling of Segregation in Granular Flows
Sun, Jin
2007-01-01
Modeling and simulation of segregation phenomena in granular flows are investigated. Computational models at different scales ranging from particle level (microscale) to continuum level (macroscale) are employed in order to determine the important microscale physics relevant to macroscale modeling. The capability of a multi-fluid model to capture segregation caused by density difference is demonstrated by simulating grain-chaff biomass flows in a laboratory-scale air column and in a combine harvester. The multi-fluid model treats gas and solid phases as interpenetrating continua in an Eulerian frame. This model is further improved by incorporating particle rotation using kinetic theory for rapid granular flow of slightly frictional spheres. A simplified model is implemented without changing the current kinetic theory framework by introducing an effective coefficient of restitution to account for additional energy dissipation due to frictional collisions. The accuracy of predicting segregation rate in a gas-fluidized bed is improved by the implementation. This result indicates that particle rotation is important microscopic physics to be incorporated into the hydrodynamic model. Segregation of a large particle in a dense granular bed of small particles under vertical. vibration is studied using molecular dynamics simulations. Wall friction is identified as a necessary condition for the segregation. Large-scale force networks bearing larger-than-average forces are found with the presence of wall friction. The role of force networks in assisting rising of the large particle is analyzed. Single-point force distribution and two-point spatial force correlation are computed. The results show the heterogeneity of forces and a short-range correlation. The short correlation length implies that even dense granular flows may admit local constitutive relations. A modified minimum spanning tree (MST) algorithm is developed to asymptotically recover the force statistics in the
Modelling flow to leachate wells in landfills.
Al-Thani, A A; Beaven, R P; White, J K
2004-01-01
Vertical wells are frequently used as a means of controlling leachate levels in landfills. They are often the only available dewatering option for both old landfills without any basal leachate collection layer and for newer sites where the installed drainage infrastructure has failed. When the well is pumped, a seepage face develops at the entry into the well so that the drawdown in the surrounding waste will not be as great as might be expected. The numerical groundwater flow model MODFLOW-SURFACT, which contains the functionality to model seepage surfaces, has been used to investigate the transient dewatering of a landfill. The study concludes that the position of the seepage face and information about the characteristics of the induced seepage flow field are important and should not be neglected when designing wells in landfills.
Modelling flow to leachate wells in landfills
Al-Thani, A.A.; Beaven, R.P.; White, J.K
2004-07-01
Vertical wells are frequently used as a means of controlling leachate levels in landfills. They are often the only available dewatering option for both old landfills without any basal leachate collection layer and for newer sites where the installed drainage infrastructure has failed. When the well is pumped, a seepage face develops at the entry into the well so that the drawdown in the surrounding waste will not be as great as might be expected. The numerical groundwater flow model MODFLOW-SURFACT, which contains the functionality to model seepage surfaces, has been used to investigate the transient dewatering of a landfill. The study concludes that the position of the seepage face and information about the characteristics of the induced seepage flow field are important and should not be neglected when designing wells in landfills.
NASA Astrophysics Data System (ADS)
Liu, Yang-Wei; Liu, Bao-Jie; Lu, Li-Peng
2012-04-01
The average-passage equation system (APES) provides a rigorous mathematical framework for accounting for the unsteady blade row interaction through multistage compressors in steady state environment by introducing deterministic correlations (DC) that need to be modeled to close the equation system. The primary purpose of this study was to provide insight into the DC characteristics and the influence of DC on the time-averaged flow field of the APES. In Part 2 of this two-part paper, the influence of DC on the time-averaged flow field was systematically studied. Several time-averaging computations were conducted with various boundary conditions and DC for the downstream stator in a transonic compressor stage, by employing the CFD solver developed in Part 1 of this two-part paper. These results were compared with the time-averaged unsteady flow field and the steady one. The study indicated that the circumferential-averaged DC can take into account major part of the unsteady effects on spanwise redistribution of flow fields in compressors. Furthermore, it demonstrated that both deterministic stresses and deterministic enthalpy fluxes are necessary to reproduce the time-averaged flow field.
Feinstein, D.T.; Hunt, R.J.; Reeves, H.W.
2010-01-01
. Lastly, it describes several categories of limitations and discusses ways of extending the regional model to address issues at the local scale. Results of the simulations portray a regional groundwater-flow system that, over time, has largely maintained its natural predevelopment configuration but that locally has been strongly affected by well withdrawals. The quantity of rainfall in the Lake Michigan Basin and adjacent areas supports a dense surface-water network and recharge rates consistent with generally shallow water tables and predominantly shallow groundwater flow. At the regional scale, pumping has not caused major modifications of the shallow flow system, but it has resulted in decreases in base flow to streams and in direct discharge to Lake Michigan (about 2 percent of the groundwater discharged and about 0.5 cubic foot per second per mile of shoreline). On the other hand, well withdrawals have caused major reversals in regional flow patterns around pumping centers in deep, confined aquifers - most noticeably in the Cambrian-Ordovician aquifer system on the west side of Lake Michigan near the cities of Green Bay and Milwaukee in eastern Wisconsin, and around Chicago in northeastern Illinois, as well as in some shallow bedrock aquifers (for example, in the Marshall aquifer near Lansing, Mich.). The reversals in flow have been accompanied by large drawdowns with consequent local decrease in storage. On the west side of Lake Michigan, groundwater withdrawals have caused appreciable migration of the deep groundwater divides. Before the advent of pumping, the deep Lake Michigan groundwater-basin boundaries extended west of the Lake Michigan surface-water basin boundary, in some places by tens of miles. Over time, the pumping centers have replaced Lake Michigan as the regional sink for the deep flow system. The regional model is intended to support the framework pilot study of water availability and use for the Great Lakes Basin (Reeves, in press).
A study of thin liquid sheet flows
NASA Technical Reports Server (NTRS)
Chubb, Donald L.; Calfo, Frederick D.; Mcconley, Marc W.; Mcmaster, Matthew S.; Afjeh, Abdollah A.
1993-01-01
This study was a theoretical and experimental investigation of thin liquid sheet flows in vacuum. A sheet flow created by a narrow slit of width, W, coalesces to a point at a distance, L, as a result of surface tension forces acting at the sheet edges. As the flow coalesces, the fluid accumulates in the sheet edges. The observed triangular shape of the sheet agrees with the calculated triangular result. Experimental results for L/W as a function of Weber number, We, agree with the calculated result, L/W = the sq. root of 8We. The edge cross sectional shape is found to oscillate from elliptic to 'cigar' like to 'peanut' like and then back to elliptic in the flow direction. A theoretical one-dimensional model was developed that yielded only elliptic solutions for the edge cross section. At the points where the elliptic shapes occur, there is agreement between theory and experiment.
Roth, Christian J; Haeussner, Eva; Ruebelmann, Tanja; Koch, Franz V; Schmitz, Christoph; Frank, Hans-Georg; Wall, Wolfgang A
2017-01-19
Ischemic placental disease is a concept that links intrauterine growth retardation (IUGR) and preeclampsia (PE) back to insufficient remodeling of uterine spiral arteries. The rheological consequences of insufficient remodeling of uterine spiral arteries were hypothesized to mediate the considerably later manifestation of obstetric disease. However, the micro-rheology in the intervillous space (IVS) cannot be examined clinically and rheological animal models of the human IVS do not exist. Thus, an in silico approach was implemented to provide in vivo inaccessible data. The morphology of a spiral artery and the inflow region of the IVS were three-dimensionally reconstructed to provide a morphological stage for the simulations. Advanced high-end supercomputing resources were used to provide blood flow simulations at high spatial resolution. Our simulations revealed turbulent blood flow (high-velocity jets and vortices) combined with elevated blood pressure in the IVS and increased wall shear stress at the villous surface in conjunction with insufficient spiral artery remodeling only. Post-hoc histological analysis of uterine veins showed evidence of increased trophoblast shedding in an IUGR placenta. Our data support that rheological alteration in the IVS is a relevant mechanism linking ischemic placental disease to altered structural integrity and function of the placenta.
Thermomechanical Fractional Model of TEMHD Rotational Flow
Hamza, F.; Abd El-Latief, A.; Khatan, W.
2017-01-01
In this work, the fractional mathematical model of an unsteady rotational flow of Xanthan gum (XG) between two cylinders in the presence of a transverse magnetic field has been studied. This model consists of two fractional parameters α and β representing thermomechanical effects. The Laplace transform is used to obtain the numerical solutions. The fractional parameter influence has been discussed graphically for the functions field distribution (temperature, velocity, stress and electric current distributions). The relationship between the rotation of both cylinders and the fractional parameters has been discussed on the functions field distribution for small and large values of time. PMID:28045941
An electricity consumption model for electric vehicular flow
NASA Astrophysics Data System (ADS)
Xiao, Hong; Huang, Hai-Jun; Tang, Tie-Qiao
2016-09-01
In this paper, we apply the relationships between the macro and micro variables of traffic flow to develop an electricity consumption model for electric vehicular flow. We use the proposed model to study the quantitative relationships between the electricity consumption/total power and speed/density under uniform flow, and the electricity consumptions during the evolution processes of shock, rarefaction wave and small perturbation. The numerical results indicate that the proposed model can perfectly describe the electricity consumption for electric vehicular flow, which shows that the proposed model is reasonable.
Quasi-steady turbulence modeling of unsteady flows
NASA Technical Reports Server (NTRS)
Mankbadi, Reda R.; Mobark, Amin
1991-01-01
This article describes the results of numerical simulations of oscillating wall-bounded developing flows. The full phase-averaged Navier-Stokes equations are solved. The application of quasi-steady turbulence modeling to unsteady flows is demonstrated using an unsteady version of the k-epsilon model. The effects of unsteadiness on the mean flow and turbulence are studied. Critical evaluation of the applicability of the quasi-steady approach to turbulence modeling is presented. Suggestions are given for the future efforts in turbulence modeling of unsteady flows.
Performance of a 10-kJ SMES model cooled by liquid hydrogen thermo-siphon flow for ASPCS study
NASA Astrophysics Data System (ADS)
Makida, Y.; Shintomi, T.; Hamajima, T.; Ota, N.; Katsura, M.; Ando, K.; Takao, T.; Tsuda, M.; Miyagi, D.; Tsujigami, H.; Fujikawa, S.; Hirose, J.; Iwaki, K.; Komagome, T.
2015-12-01
We propose a new electrical power storage and stabilization system, called an Advanced Superconducting Power Conditioning System (ASPCS), which consists of superconducting magnetic energy storage (SMES) and hydrogen energy storage, converged on a liquid hydrogen station for fuel cell vehicles. A small 10- kJ SMES system, in which a BSCCO coil cooled by liquid hydrogen was installed, was developed to create an experimental model of an ASPCS. The SMES coil is conductively cooled by liquid hydrogen flow through a thermo-siphon line under a liquid hydrogen buffer tank. After fabrication of the system, cooldown tests were carried out using liquid hydrogen. The SMES coil was successfully charged up to a nominal current of 200 A. An eddy current loss, which was mainly induced in pure aluminum plates pasted onto each pancake coils for conduction cooling, was also measured.
Cozens-Roberts, C; Quinn, J A; Lauffenburger, D A
1990-01-01
Quantitative information regarding the kinetics of receptor-mediated cell adhesion to a ligand-coated surface are crucial for understanding the role of certain key parameters in many physiological and biotechnology-related processes. Here, we use the probabilistic attachment and detachment models developed in the preceding paper to interpret transient data from well-defined experiments. These data are obtained with a simple model cell system that consists of receptor-coated latex beads (prototype cells) and a Radial-Flow Detachment Assay (RFDA) using a ligand-coated glass disc. The receptors and ligands used in this work are complementary antibodies. The beads enable us to examine transient behavior with particles that possess fairly uniform properties that can be varied systematically, and the RFDA is designed for direct observation of adhesion to the ligand-coated glass surface over a range of shear stresses. Our experiments focus on the effects of surface shear stress, receptor density, and ligand density. These data provide a crucial test of the probabilistic framework. We show that these data can be explained with the probabilistic analyses, whereas they cannot be readily interpreted on the basis of a deterministic analysis. In addition, we examine transient data on cell adhesion reported from other assays, demonstrating the consistency of these data with the predictions of the probabilistic models. Images FIGURE 2 PMID:2174272
The influence of nonmonotonic synchronized flow branch in a cellular automaton traffic flow model
NASA Astrophysics Data System (ADS)
Jin, Cheng-Jie; Wang, Wei
2011-11-01
In this paper we study the congested patterns upstream of an isolated on-ramp in a cellular automaton traffic flow model, which is proposed in our previous paper [Cheng-Jie Jin, Wei Wang, Rui Jiang, Kun Gao, J. Stat. Mech (2010) P03018]. The simulation results under open boundary conditions are presented by spatiotemporal diagrams. Our diagram of congested patterns is quite similar to that of the cellular automaton models within Kerner’s three-phase traffic theory, while some differences in the “moving synchronized flow pattern” (MSP) should be noted. In our model the upstream front of MSP propagates not only upstream, but also downstream. The propagation direction depends on the flow rates and densities of free flow and synchronized flow. Besides, in our model the outflow of wide moving jams or bottlenecks could be free flow or synchronized flow, as reported in many empirical data. In the dissolving of congestions, the form of free flow may be hindered and stable synchronized flow may emerge. This phenomenon can help us understand more about the outflow. All the interesting characteristics of our model are due to the nonmonotonic structure of synchronized flow branch in the fundamental diagram, which has not been found in previous models.
Nuttall, H.E.; Travis, B.J.
1980-01-01
Field and modeling studies were performed to characterize two-phase flow within the natural cleat structure of an upper Cretaceous subbituminous coal seam. A two borehole pattern with open completion was used in a study of dewatering and tracer residence time distribution. Air was pumped into a five meter thick seam located about 170 meters below the surface. Krypton 85 was used as the airborne tracer. Air inflow and air and water production rates and tracer arrival times were monitored. The field tests were simulated with a two-phase, three component, porous flow code. Results showed that the air inflow and air and water outflow rates and breakthrough times could not be modeled assuming a uniform darcy-type permeability. The use of a pressure dependent permeability did provide, however, a much better match with the field data.
Modeling of Cavitating Flow through Waterjet Propulsors
2015-02-18
OCT-11 -31-DEC-14 To) 4. TITLE AND SUBTITLE Modeling of Cavitating Flow through Waterjet Propulsors 5a. CONTRACT NUMBER 5b. GRANT NUMBER N00014-12...239-18 Modeling of Cavitating Flow through Waterjet Propulsors Jules W. Lindau The Pennsylvania State University, Applied Research Laboratory, State...flow nature, waterjets are expected to maintain resistance to cavitation , are amenable to ad- vanced concepts such as thrust vectoring, should
Finite element modeling of nonisothermal polymer flows
NASA Technical Reports Server (NTRS)
Roylance, D.
1981-01-01
A finite element formulation designed to simulate polymer melt flows in which both conductive and convective heat transfer are important is described, and the numerical model is illustrated by means of computer experiments using extruder drag flow and entry flow as trial problems. Fluid incompressibility is enforced by a penalty treatment of the element pressures, and the thermal convective transport is modeled by conventional Galerkin and optimal upwind treatments.
Prodanov, L; Semeins, C M; van Loon, J J W A; te Riet, J; Jansen, J A; Klein-Nulend, J; Walboomers, X F
2013-05-01
Introducing nanoroughness on various biomaterials has been shown to profoundly effect cell-material interactions. Similarly, physical forces act on a diverse array of cells and tissues. Particularly in bone, the tissue experiences compressive or tensile forces resulting in fluid shear stress. The current study aimed to develop an experimental setup for bone cell behavior, combining a nanometrically grooved substrate (200 nm wide, 50 nm deep) mimicking the collagen fibrils of the extracellular matrix, with mechanical stimulation by pulsatile fluid flow (PFF). MC3T3-E1 osteoblast-like cells were assessed for morphology, expression of genes involved in cell attachment and osteoblastogenesis and nitric oxide (NO) release. The results showed that both nanotexture and PFF did affect cellular morphology. Cells aligned on nanotexture substrate in a direction parallel to the groove orientation. PFF at a magnitude of 0.7 Pa was sufficient to induce alignment of cells on a smooth surface in a direction perpendicular to the applied flow. When environmental cues texture and flow were interacting, PFF of 1.4 Pa applied parallel to the nanogrooves initiated significant cellular realignment. PFF increased NO synthesis 15-fold in cells attached to both smooth and nanotextured substrates. Increased collagen and alkaline phosphatase mRNA expression was observed on the nanotextured substrate, but not on the smooth substrate. Furthermore, vinculin and bone sialoprotein were up-regulated after 1 h of PFF stimulation. In conclusion, the data show that interstitial fluid forces and structural cues mimicking extracellular matrix contribute to the final bone cell morphology and behavior, which might have potential application in tissue engineering.
Average-passage flow model development
NASA Technical Reports Server (NTRS)
Adamczyk, John J.; Celestina, Mark L.; Beach, Tim A.; Kirtley, Kevin; Barnett, Mark
1989-01-01
A 3-D model was developed for simulating multistage turbomachinery flows using supercomputers. This average passage flow model described the time averaged flow field within a typical passage of a bladed wheel within a multistage configuration. To date, a number of inviscid simulations were executed to assess the resolution capabilities of the model. Recently, the viscous terms associated with the average passage model were incorporated into the inviscid computer code along with an algebraic turbulence model. A simulation of a stage-and-one-half, low speed turbine was executed. The results of this simulation, including a comparison with experimental data, is discussed.
NASA Astrophysics Data System (ADS)
Brown, Bruce P.
1995-05-01
Study of the motility of the gut and flow in the gut lumen is complex. We have used simple models of the colon to suggest that focal, segmental narrowing of the lumen of a large-bore tube produces an increase in distance traveled by solids and liquids compared to a tube of the same volume which has smooth cylindrical walls. This suggests that the colonic septae may promote efficient transit of solids and liquids even in an organ with large diameter.
Numerical study for Bödewadt flow of water based nanofluid over a deformable disk: Buongiorno model
NASA Astrophysics Data System (ADS)
Khan, J. A.; Mustafa, M.; Hayat, T.; Alzahrani, F.
2017-02-01
Here the well-known Bödewadt flow problem is extended to the case where nanofluid occupies the space above a stretchable disk. Both Brownian motion and thermophoresis effects are incorporated into the transport equations. Physically realistic condition accounting for zero normal flux of nanoparticles is invoked. Similar form of governing differential system is attained through conventional Von Kármán relations. An efficient Keller-box method with high accuracy is used to report numerical solutions of the problem. Our results show that hydrodynamic boundary layer becomes thinner when larger stretching rate is imposed. Negative value of axial velocity reveals downward flow which is the consequence of radial stretching. Velocity components have oscillatory decaying profiles when the radial stretching effect is absent. Larger thermophoretic force leads to thicker temperature and nanoparticle concentration profiles. Both two-and three-dimensional streamlines are plotted for a specified ratio of rotation to the stretching rate. Comparative study of present results with those of previous published results is also discussed in a special situation.
NASA Astrophysics Data System (ADS)
Scanlon, Bridget R.; Mace, Robert E.; Barrett, Michael E.; Smith, Brian
2003-05-01
Various approaches can be used to simulate groundwater flow in karst systems, including equivalent porous media distributed parameter, lumped parameter, and dual porosity approaches, as well as discrete fracture or conduit approaches. The purpose of this study was to evaluate two different equivalent porous media approaches: lumped and distributed parameter, for simulating regional groundwater flow in a karst aquifer and to evaluate the adequacy of these approaches. The models were applied to the Barton Springs Edwards aquifer, Texas. Unique aspects of this study include availability of detailed information on recharge from stream-loss studies and on synoptic water levels, long-term continuous water level monitoring in wells throughout the aquifer, and spring discharge data to compare with simulation results. The MODFLOW code was used for the distributed parameter model. Estimation of hydraulic conductivity distribution was optimized by using a combination of trial and error and automated inverse methods. The lumped parameter model consists of five cells representing each of the watersheds contributing recharge to the aquifer. Transient simulations were conducted using both distributed and lumped parameter models for a 10-yr period (1989-1998). Both distributed and lumped parameter models fairly accurately simulated the temporal variability in spring discharge; therefore, if the objective of the model is to simulate spring discharge, either distributed or lumped parameter approaches can be used. The distributed parameter model generally reproduced the potentiometric surface at different times. The impact of the amount of pumping on a regional scale on spring discharge can be evaluated using a lumped parameter model; however, more detailed evaluation of the effect of pumping on groundwater levels and spring discharge requires a distributed parameter modeling approach. Sensitivity analyses indicated that spring discharge was much more sensitive to variations in
A compressible Navier-Stokes code for turbulent flow modeling
NASA Technical Reports Server (NTRS)
Coakley, T. J.
1984-01-01
An implicit, finite volume code for solving two dimensional, compressible turbulent flows is described. Second order upwind differencing of the inviscid terms of the equations is used to enhance stability and accuracy. A diagonal form of the implicit algorithm is used to improve efficiency. Several zero and two equation turbulence models are incorporated to study their impact on overall flow modeling accuracy. Applications to external and internal flows are discussed.
Clark, Brian R.; Hart, Rheannon M.
2009-01-01
The Mississippi Embayment Regional Aquifer Study (MERAS) was conducted with support from the Groundwater Resources Program of the U.S. Geological Survey Office of Groundwater. This report documents the construction and calibration of a finite-difference groundwater model for use as a tool to quantify groundwater availability within the Mississippi embayment. To approximate the differential equation, the MERAS model was constructed with the U.S. Geological Survey's modular three-dimensional finite-difference code, MODFLOW-2005; the preconditioned conjugate gradient solver within MODFLOW-2005 was used for the numerical solution technique. The model area boundary is approximately 78,000 square miles and includes eight States with approximately 6,900 miles of simulated streams, 70,000 well locations, and 10 primary hydrogeologic units. The finite-difference grid consists of 414 rows, 397 columns, and 13 layers. Each model cell is 1 square mile with varying thickness by cell and by layer. The simulation period extends from January 1, 1870, to April 1, 2007, for a total of 137 years and 69 stress periods. The first stress period is simulated as steady state to represent predevelopment conditions. Areal recharge is applied throughout the MERAS model area using the MODFLOW-2005 Recharge Package. Irrigation, municipal, and industrial wells are simulated using the Multi-Node Well Package. There are 43 streams simulated by the MERAS model. Each stream or river in the model area was simulated using the Streamflow-Routing Package. The perimeter of the model area and the base of the flow system are represented as no-flow boundaries. The downgradient limit of each model layer is a no-flow boundary, which approximates the extent of water with less than 10,000 milligrams per liter of dissolved solids. The MERAS model was calibrated by making manual changes to parameter values and examining residuals for hydraulic heads and streamflow. Additional calibration was achieved through
Modeling multiphase flow using fluctuating hydrodynamics.
Chaudhri, Anuj; Bell, John B; Garcia, Alejandro L; Donev, Aleksandar
2014-09-01
Fluctuating hydrodynamics provides a model for fluids at mesoscopic scales where thermal fluctuations can have a significant impact on the behavior of the system. Here we investigate a model for fluctuating hydrodynamics of a single-component, multiphase flow in the neighborhood of the critical point. The system is modeled using a compressible flow formulation with a van der Waals equation of state, incorporating a Korteweg stress term to treat interfacial tension. We present a numerical algorithm for modeling this system based on an extension of algorithms developed for fluctuating hydrodynamics for ideal fluids. The scheme is validated by comparison of measured structure factors and capillary wave spectra with equilibrium theory. We also present several nonequilibrium examples to illustrate the capability of the algorithm to model multiphase fluid phenomena in a neighborhood of the critical point. These examples include a study of the impact of fluctuations on the spinodal decomposition following a rapid quench, as well as the piston effect in a cavity with supercooled walls. The conclusion in both cases is that thermal fluctuations affect the size and growth of the domains in off-critical quenches.
Approximate Model for Turbulent Stagnation Point Flow.
Dechant, Lawrence
2016-01-01
Here we derive an approximate turbulent self-similar model for a class of favorable pressure gradient wedge-like flows, focusing on the stagnation point limit. While the self-similar model provides a useful gross flow field estimate this approach must be combined with a near wall model is to determine skin friction and by Reynolds analogy the heat transfer coefficient. The combined approach is developed in detail for the stagnation point flow problem where turbulent skin friction and Nusselt number results are obtained. Comparison to the classical Van Driest (1958) result suggests overall reasonable agreement. Though the model is only valid near the stagnation region of cylinders and spheres it nonetheless provides a reasonable model for overall cylinder and sphere heat transfer. The enhancement effect of free stream turbulence upon the laminar flow is used to derive a similar expression which is valid for turbulent flow. Examination of free stream enhanced laminar flow suggests that the rather than enhancement of a laminar flow behavior free stream disturbance results in early transition to turbulent stagnation point behavior. Excellent agreement is shown between enhanced laminar flow and turbulent flow behavior for high levels, e.g. 5% of free stream turbulence. Finally the blunt body turbulent stagnation results are shown to provide realistic heat transfer results for turbulent jet impingement problems.
A turbulent two-phase flow model for nebula flows
NASA Technical Reports Server (NTRS)
Champney, Joelle M.; Cuzzi, Jeffrey N.
1990-01-01
A new and very efficient turbulent two-phase flow numericaly model is described to analyze the environment of a protoplanetary nebula at a stage prior to the formation of planets. Focus is on settling processes of dust particles in flattened gaseous nebulae. The model employs a perturbation technique to improve the accuracy of the numerical simulations of such flows where small variations of physical quantities occur over large distance ranges. The particles are allowed to be diffused by gas turbulence in addition to settling under gravity. Their diffusion coefficients is related to the gas turbulent viscosity by the non-dimensional Schmidt number. The gas turbulent viscosity is determined by the means of the eddy viscosity hypothesis that assumes the Reynolds stress tensor proportional to the mean strain rate tensor. Zero- and two-equation turbulence models are employed. Modeling assumptions are detailed and discussed. The numerical model is shown to reproduce an existing analytical solution for the settling process of particles in an inviscid nebula. Results of nebula flows are presented taking into account turbulence effects of nebula flows. Diffusion processes are found to control the settling of particles.
Enhancing debris flow modeling parameters integrating Bayesian networks
NASA Astrophysics Data System (ADS)
Graf, C.; Stoffel, M.; Grêt-Regamey, A.
2009-04-01
Applied debris-flow modeling requires suitably constraint input parameter sets. Depending on the used model, there is a series of parameters to define before running the model. Normally, the data base describing the event, the initiation conditions, the flow behavior, the deposition process and mainly the potential range of possible debris flow events in a certain torrent is limited. There are only some scarce places in the world, where we fortunately can find valuable data sets describing event history of debris flow channels delivering information on spatial and temporal distribution of former flow paths and deposition zones. Tree-ring records in combination with detailed geomorphic mapping for instance provide such data sets over a long time span. Considering the significant loss potential associated with debris-flow disasters, it is crucial that decisions made in regard to hazard mitigation are based on a consistent assessment of the risks. This in turn necessitates a proper assessment of the uncertainties involved in the modeling of the debris-flow frequencies and intensities, the possible run out extent, as well as the estimations of the damage potential. In this study, we link a Bayesian network to a Geographic Information System in order to assess debris-flow risk. We identify the major sources of uncertainty and show the potential of Bayesian inference techniques to improve the debris-flow model. We model the flow paths and deposition zones of a highly active debris-flow channel in the Swiss Alps using the numerical 2-D model RAMMS. Because uncertainties in run-out areas cause large changes in risk estimations, we use the data of flow path and deposition zone information of reconstructed debris-flow events derived from dendrogeomorphological analysis covering more than 400 years to update the input parameters of the RAMMS model. The probabilistic model, which consistently incorporates this available information, can serve as a basis for spatial risk
a Combustion Model for Incompressible Flows
NASA Astrophysics Data System (ADS)
Calzada, Maria Eugenia
We study the flow of a pre-mixed, reactive, incompressible, viscous fluid, using a combination of vortex methods and a flame propagation algorithm based on Huyghens' principle. The random vortex methods are lagrangian methods used to resolve the motion of incompressible fluids regulated by the Navier -Stokes equations. They are best suited for flows at high Reynolds numbers. Detailed description of the vortex blobs, and vortex sheets methods is given together with the presentation of a hybrid vortex method that relates the two. The combustion part of the problem is modeled by a variation of the SLIC (Simple Line Interface Calculation) algorithm, that involves the use of a flame dictionary which contains flame speeds and preheat thicknesses. The combined algorithms are tested on a cold flat late with different free stream velocities. The numerical results show the effects of cold boundaries, turbulence, and exothermicity on the burning process.
NASA Astrophysics Data System (ADS)
Le Coz, Mathieu; Bodin, Jacques; Renard, Philippe
2017-02-01
Limestone aquifers often exhibit complex groundwater flow behaviors resulting from depositional heterogeneities and post-lithification fracturing and karstification. In this study, multiple-point statistics (MPS) was applied to reproduce karst features and to improve groundwater flow modeling. For this purpose, MPS realizations were used in a numerical flow model to simulate the responses to pumping test experiments observed at the Hydrogeological Experimental Site of Poitiers, France. The main flow behaviors evident in the field data were simulated, particularly (i) the early-time inflection of the drawdown signal at certain observation wells and (ii) the convex behavior of the drawdown curves at intermediate times. In addition, it was shown that the spatial structure of the karst features at various scales is critical with regard to the propagation of the depletion wave induced by pumping. Indeed, (i) the spatial shape of the cone of depression is significantly affected by the karst proportion in the vicinity of the pumping well, and (ii) early-time inflection of the drawdown signal occurs only at observation wells crossing locally well-developed karst features.
Lattice Boltzmann model for traffic flow.
Meng, Jianping; Qian, Yuehong; Li, Xingli; Dai, Shiqiang
2008-03-01
Mesoscopic models for traffic flows are usually difficult to be employed because of the appearance of integro-differential terms in the models. In this work, a lattice Boltzmann model for traffic flow is introduced on the basis of the existing kinetics models by using the Bhatnagar-Gross-Krook-type approximation interaction term in the Boltzmann equation and discretizing it in time and phase space. The so-obtained model is simple while the relevant parameters are physically meaningful. Together with its discrete feature, the model can be easily used to investigate numerically the behavior of traffic flows. In consequence, the macroscopic dynamics of the model is derived using the Taylor and Chapman-Enskog expansions. For validating the model, numerical simulations are conducted under the periodic boundary conditions. It is found that the model could reasonably reproduce the fundamental diagram. Moreover, certain interesting physical phenomena can be captured by the model, such as the metastability and stop-and-go phenomena.
A turbulence model for pulsatile arterial flows.
Younis, B A; Berger, S A
2004-10-01
Difficulties in predicting the behavior of some high Reynolds number flows in the circulatory system stem in part from the severe requirements placed on the turbulence model chosen to close the time-averaged equations of fluid motion. In particular, the successful turbulence model is required to (a) correctly capture the "nonequilibrium" effects wrought by the interactions of the organized mean-flow unsteadiness with the random turbulence, (b) correctly reproduce the effects of the laminar-turbulent transitional behavior that occurs at various phases of the cardiac cycle, and (c) yield good predictions of the near-wall flow behavior in conditions where the universal logarithmic law of the wall is known to be not valid. These requirements are not immediately met by standard models of turbulence that have been developed largely with reference to data from steady, fully turbulent flows in approximate local equilibrium. The purpose of this paper is to report on the development of a turbulence model suited for use in arterial flows. The model is of the two-equation eddy-viscosity variety with dependent variables that are zero-valued at a solid wall and vary linearly with distance from it. The effects of transition are introduced by coupling this model to the local value of the intermittency and obtaining the latter from the solution of a modeled transport equation. Comparisons with measurements obtained in oscillatory transitional flows in circular tubes show that the model produces substantial improvements over existing closures. Further pulsatile-flow predictions, driven by a mean-flow wave form obtained in a diseased human carotid artery, indicate that the intermittency-modified model yields much reduced levels of wall shear stress compared to the original, unmodified model. This result, which is attributed to the rapid growth in the thickness of the viscous sublayer arising from the severe acceleration of systole, argues in favor of the use of the model for the
SRMAFTE facility checkout model flow field analysis
NASA Technical Reports Server (NTRS)
Dill, Richard A.; Whitesides, Harold R.
1992-01-01
The Solid Rocket Motor Air Flow Equipment (SRMAFTE) facility was constructed for the purpose of evaluating the internal propellant, insulation, and nozzle configurations of solid propellant rocket motor designs. This makes the characterization of the facility internal flow field very important in assuring that no facility induced flow field features exist which would corrupt the model related measurements. In order to verify the design and operation of the facility, a three-dimensional computational flow field analysis was performed on the facility checkout model setup. The checkout model measurement data, one-dimensional and three-dimensional estimates were compared, and the design and proper operation of the facility was verified. The proper operation of the metering nozzles, adapter chamber transition, model nozzle, and diffuser were verified. The one-dimensional and three-dimensional flow field estimates along with the available measurement data are compared.
Ma, Rui; Zheng, Chunmiao; Tonkin, Matthew J.; Zachara, John M.
2011-04-01
Correct interpretation of tracer test data is critical for understanding transport processes in the subsurface. This task can be greatly complicated by the presence of intraborehole flows in a highly dynamic flow environment. At a new tracer test site (Hanford IFRC) a dynamic flow field created by changes in the stage of the adjacent Columbia River, coupled with a heterogeneous hydraulic conductivity distribution, leads to considerable variations in vertical hydraulic gradients. These variations, in turn, create intraborehole flows in fully-screened (6.5 m) observation wells with frequently alternating upward and downward movement. This phenomenon, in conjunction with a highly permeable aquifer formation and small horizontal hydraulic gradients, makes modeling analysis and model calibration a formidable challenge. Groundwater head data alone were insufficient to define the flow model boundary conditions, and the movement of the tracer was highly sensitive to the dynamics of the flow field. This study shows that model calibration can be significantly improved by explicitly considering (a) dynamic flow model boundary conditions and (b) intraborehole flow. The findings from this study underscore the difficulties in interpreting tracer tests and understanding solute transport under highly dynamic flow conditions.
Ma, Rui; Zheng, Chunmiao; Tonkin, Matt; Zachara, John M
2011-04-01
Correct interpretation of tracer test data is critical for understanding transport processes in the subsurface. This task can be greatly complicated by the presence of intraborehole flows in a highly dynamic flow environment. At a new tracer test site (Hanford IFRC) a dynamic flow field created by changes in the stage of the adjacent Columbia River, coupled with a heterogeneous hydraulic conductivity distribution, leads to considerable variations in vertical hydraulic gradients. These variations, in turn, create intraborehole flows in fully-screened (6.5m) observation wells with frequently alternating upward and downward movement. This phenomenon, in conjunction with a highly permeable aquifer formation and small horizontal hydraulic gradients, makes modeling analysis and model calibration a formidable challenge. Groundwater head data alone were insufficient to define the flow model boundary conditions, and the movement of the tracer was highly sensitive to the dynamics of the flow field. This study shows that model calibration can be significantly improved by explicitly considering (a) dynamic flow model boundary conditions and (b) intraborehole flow. The findings from this study underscore the difficulties in interpreting tracer tests and understanding solute transport under highly dynamic flow conditions.
Regression modeling of ground-water flow
Cooley, R.L.; Naff, R.L.
1985-01-01
Nonlinear multiple regression methods are developed to model and analyze groundwater flow systems. Complete descriptions of regression methodology as applied to groundwater flow models allow scientists and engineers engaged in flow modeling to apply the methods to a wide range of problems. Organization of the text proceeds from an introduction that discusses the general topic of groundwater flow modeling, to a review of basic statistics necessary to properly apply regression techniques, and then to the main topic: exposition and use of linear and nonlinear regression to model groundwater flow. Statistical procedures are given to analyze and use the regression models. A number of exercises and answers are included to exercise the student on nearly all the methods that are presented for modeling and statistical analysis. Three computer programs implement the more complex methods. These three are a general two-dimensional, steady-state regression model for flow in an anisotropic, heterogeneous porous medium, a program to calculate a measure of model nonlinearity with respect to the regression parameters, and a program to analyze model errors in computed dependent variables such as hydraulic head. (USGS)
NASA Astrophysics Data System (ADS)
Iovine, G.; di Gregorio, S.; D'Ambrosio, D.; Lupiano, V.; Merenda, L.; Nardi, G.
On winter 1999, heavy rainfall severely stroke Campania region, triggering numerous debris flows on the slopes of the San Martino Valle Caudina-Cervinara area. Soil slips originated on the slopes, within the weathered volcaniclastic mantle of detrital cover overlying the carbonate skeleton of the massif. Debris slides soon turned into fast flow- ing mixtures of matrix and large blocks, downslope eroding the detrital mantle and increasing its original volume. At the base of the slopes, flows impacted on the urban areas, causing victims and severe destruction. Starting from a recent study on landslide risk conditions in Campania, carried out by the local Basin Authority, an evaluation of debris-flow susceptibility has been performed for n.8 selected areas ("red zones") of the above mentioned villages. According to that study, such red zones would be char- acterised by the highest risk levels (within the administrative boundaries of the same villages). Our susceptibility analysis has been performed by applying SCIDDICA-S3 - a Cellular Automata model, specifically developed, after the Sarno 1998 disaster, for simulating the spatial evolution of debris flows. Detailed topographic data and a map of the detrital coverage had to be given to the model, as input matrixes. A digi- tal "world" of hexagonal cells was adopted; type and amount of detrital mantle were collected through detailed field surveying. Real cases, selected among the landslides triggered on winter 1999, have been utilised for validating SCIDDICA and defining the best values for parameters: the validation has been carried out in a GIS environ- ment, by quantitatively comparing simulations with actual cases. Through geological evaluations, source locations of new phenomena have then been hypothesised within the red-zones. Initial volume for these new cases has been estimated by considering the actual statistics of the 1999 disaster. Finally, by merging the results of simulations, a deterministic
Dynamic modelling of packaging material flow systems.
Tsiliyannis, Christos A
2005-04-01
A dynamic model has been developed for reused and recycled packaging material flows. It allows a rigorous description of the flows and stocks during the transition to new targets imposed by legislation, product demand variations or even by variations in consumer discard behaviour. Given the annual reuse and recycle frequency and packaging lifetime, the model determines all packaging flows (e.g., consumption and reuse) and variables through which environmental policy is formulated, such as recycling, waste and reuse rates and it identifies the minimum number of variables to be surveyed for complete packaging flow monitoring. Simulation of the transition to the new flow conditions is given for flows of packaging materials in Greece, based on 1995--1998 field inventory and statistical data.
Punjabi, Sangeeta B.; Sahasrabudhe, S. N.; Das, A. K.; Joshi, N. K.; Mangalvedekar, H. A.; Kothari, D. C.
2014-01-15
This paper provides 2D comparative study of results obtained using laminar and turbulent flow model for RF (radio frequency) Inductively Coupled Plasma (ICP) torch. The study was done for the RF-ICP torch operating at 50 kW DC power and 3 MHz frequency located at BARC. The numerical modeling for this RF-ICP torch is done using ANSYS software with the developed User Defined Function. A comparative study is done between laminar and turbulent flow model to investigate how temperature and flow fields change when using different operating conditions such as (a) swirl and no swirl velocity for sheath gas flow rate, (b) variation in sheath gas flow rate, and (c) variation in plasma gas flow rate. These studies will be useful for different material processing applications.
Zero-range model of traffic flow.
Kaupuzs, J; Mahnke, R; Harris, R J
2005-11-01
A multicluster model of traffic flow is studied, in which the motion of cars is described by a stochastic master equation. Assuming that the escape rate from a cluster depends only on the cluster size, the dynamics of the model is directly mapped to the mathematically well-studied zero-range process. Knowledge of the asymptotic behavior of the transition rates for large clusters allows us to apply an established criterion for phase separation in one-dimensional driven systems. The distribution over cluster sizes in our zero-range model is given by a one-step master equation in one dimension. It provides an approximate mean-field dynamics, which, however, leads to the exact stationary state. Based on this equation, we have calculated the critical density at which phase separation takes place. We have shown that within a certain range of densities above the critical value a metastable homogeneous state exists before coarsening sets in. Within this approach we have estimated the critical cluster size and the mean nucleation time for a condensate in a large system. The metastablity in the zero-range process is reflected in a metastable branch of the fundamental flux-density diagram of traffic flow. Our work thus provides a possible analytical description of traffic jam formation as well as important insight into condensation in the zero-range process.
NASA Astrophysics Data System (ADS)
Bikshe, Janis; Babre, Alise; Delina, Aija; Popovs, Konrads
2014-05-01
Groundwater in karst environments tends to have difficulties to distinguish multiple flows if several sources of water are present. Skaistkalne vicinity faces with such situation where old groundwater, fresh groundwater and inflow from river Iecava occurs. Attempts were made to distinguish groundwater residence time of multiple components of water applying CFC and tritium dating techniques supplied by tracer test and numerical model of study area. Study area covers territory between two rivers Iecava and Memele with water level difference of 7 meters and horizontal distance of 2.2 kilometres between both. Study area consists of karst affected Devonian gypsum and carbonaceous rocks covered by Quaternary low to high permeable deposits. Confined groundwater at depth of 10-25 meters where analysed by CFC's and tritium. At this depth groundwater exhibits anoxic reducing environment that has caused degradation of CFC's at similar degree in all samples. Taking it into account, mean residence time based on CFC piston flow model is 22 - 42 years and 28 - 34 years based on binary mixing model. Tritium results show signs of incensement of groundwater residence time towards discharge area. CFC combined with tritium proved increased vertical velocity in middle part between the rivers likely caused by hydrogeological window in Quaternary deposits created by karst processes. Numerical model (Delina et al. 2012) was applied and calculations yielded groundwater flow velocity rate at 0.3 - 1 m/day in area between the rivers. Investigation of CFC data resulted in possible groundwater flow rate of at a minimum of 0.2 m/day although it's not applicable to all sampled wells due to specific hydrogeological conditions. Tracer test was made between the rivers in order to distinguish main water flow paths and flow velocity. Results showed that very high permeable conduits connect rivers and karst lakes with velocity rates of 800 - 1300 m/day. Complex investigation leads to conclude that
Study of argon-oxygen flowing afterglow
NASA Astrophysics Data System (ADS)
Mazánková, V.; Trunec, D.; Navrátil, Z.; Raud, J.; Krčma, F.
2016-06-01
The reaction kinetics in argon-oxygen flowing afterglow (post-discharge) was studied using NO titration and optical emission spectroscopy. The flowing DC post-discharge in argon-oxygen mixture was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 90 W. The O(3P) atom concentration was determined by NO titration at different places along the flow tube. The optical emission spectra were also measured along the flow tube. Argon spectral lines, oxygen lines at 777 nm and 844.6 nm and atmospheric A-band of {{\\text{O}}2} were identified in the spectra. Rotational temperature of {{\\text{O}}2} was determined from the oxygen atmospheric A-band and also the outer wall temperature of the flow tube was measured by a thermocouple and by an IR thermometer. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows the time dependencies of particle concentrations and of gas temperature to be calculated. The wall recombination probability for O(3P) atoms {γ\\text{O≤ft(\\text{P}\\right)}}=≤ft(1.63+/- 0.06\\right)× {{10}-3} and wall deactivation probability for {{\\text{O}}2} (b {{}1}Σ\\text{g}+ ) molecules {γ{{\\text{O}2}≤ft(\\text{b}\\right)}}=≤ft(1.7+/- 0.1\\right)× {{10}-3} were determined from the fit of model results to experimental data. Sensitivity analysis was applied for the analysis of kinetic model in order to reveal the most important reactions in the model. The calculated gas temperature increases in the afterglow and then decreases at later afterglow times after reaching the maximum. This behavior is in good agreement with the spatial rotational temperature dependence. A similar trend was also observed at outer wall temperature measurement.
Prospects of Elliptic Flow Studies at NICA/MPD
NASA Astrophysics Data System (ADS)
Geraksiev, Nikolay
2016-01-01
As a key observable, anisotropic flow presents a unique insight into heavy ion collision physics. The presented poster reveals the prospects of studying elliptic flow at the NICA/MPD facility through the UrQMD model. Here, results for the elliptic flow of simulated and reconstructed hadrons at the planned NICA energy range are presented.
Numerical modelling of the flow in the resin infusion process on the REV scale: A feasibility study
NASA Astrophysics Data System (ADS)
Jabbari, M.; Jambhekar, V. A.; Gersborg, A. R.; Spangenberg, J.; Hattel, J. H.; Helmig, R.
2016-06-01
The resin infusion process (RIP) has developed as a low cost method for manufacturing large fibre reinforced plastic parts. However, the process still presents some challenges to industry with regards to reliability and repeatability, resulting in expensive and inefficient trial and error development. In this paper, we show the implementation of 2D numerical models for the RIP using the open source simulator DuMuX. The idea of this study is to present a model which accounts for the interfacial forces coming from the capillary pressure on the so-called representative elementary volume (REV) scale. The model is described in detail and three different test cases — a constant and a tensorial permeability as well as a preform/Balsa domain — are investigated. The results show that the developed model is very applicable for the RIP for manufacturing of composite parts. The idea behind this study is to test the developed model for later use in a real application, in which the preform medium has numerous layers with different material properties.
Transition region modeling for compressible flow
NASA Technical Reports Server (NTRS)
Chang, C.-L.; Singer, B. A.; Dinavahi, S. P. G.; El-Hady, N. M.; Pruett, C. D.; Harris, J. E.; Streett, C. L.; Zang, T. A.; Wilcox, D. C.
1992-01-01
The ongoing effort at NASA Langley Research Center aimed at developing transitional zone models for Reynolds-averaged Navier-Stokes calculations is described. Results from three models that we have examined - two zero-equation models and a two-equation model of the k-omega type - are presented for high-speed flows. The use of analytical and computational tools to provide guidance and to provide the transitional flow-field data bases necessary to develop such models is discussed. Some results from validation of these tools are given; qualitative comparisons between modeled and theoretical/computational representations of the transitional zone are provided.
Analysis of Cortical Flow Models In Vivo
Benink, Hélène A.; Mandato, Craig A.; Bement, William M.
2000-01-01
Cortical flow, the directed movement of cortical F-actin and cortical organelles, is a basic cellular motility process. Microtubules are thought to somehow direct cortical flow, but whether they do so by stimulating or inhibiting contraction of the cortical actin cytoskeleton is the subject of debate. Treatment of Xenopus oocytes with phorbol 12-myristate 13-acetate (PMA) triggers cortical flow toward the animal pole of the oocyte; this flow is suppressed by microtubules. To determine how this suppression occurs and whether it can control the direction of cortical flow, oocytes were subjected to localized manipulation of either the contractile stimulus (PMA) or microtubules. Localized PMA application resulted in redirection of cortical flow toward the site of application, as judged by movement of cortical pigment granules, cortical F-actin, and cortical myosin-2A. Such redirected flow was accelerated by microtubule depolymerization, showing that the suppression of cortical flow by microtubules is independent of the direction of flow. Direct observation of cortical F-actin by time-lapse confocal analysis in combination with photobleaching showed that cortical flow is driven by contraction of the cortical F-actin network and that microtubules suppress this contraction. The oocyte germinal vesicle serves as a microtubule organizing center in Xenopus oocytes; experimental displacement of the germinal vesicle toward the animal pole resulted in localized flow away from the animal pole. The results show that 1) cortical flow is directed toward areas of localized contraction of the cortical F-actin cytoskeleton; 2) microtubules suppress cortical flow by inhibiting contraction of the cortical F-actin cytoskeleton; and 3) localized, microtubule-dependent suppression of actomyosin-based contraction can control the direction of cortical flow. We discuss these findings in light of current models of cortical flow. PMID:10930453
Modeling information flow in biological networks.
Kim, Yoo-Ah; Przytycki, Jozef H; Wuchty, Stefan; Przytycka, Teresa M
2011-06-01
Large-scale molecular interaction networks are being increasingly used to provide a system level view of cellular processes. Modeling communications between nodes in such huge networks as information flows is useful for dissecting dynamical dependences between individual network components. In the information flow model, individual nodes are assumed to communicate with each other by propagating the signals through intermediate nodes in the network. In this paper, we first provide an overview of the state of the art of research in the network analysis based on information flow models. In the second part, we describe our computational method underlying our recent work on discovering dysregulated pathways in glioma. Motivated by applications to inferring information flow from genotype to phenotype in a very large human interaction network, we generalized previous approaches to compute information flows for a large number of instances and also provided a formal proof for the method.
Modeling Rotating Turbulent Flows with the Body Force Potential Model.
NASA Astrophysics Data System (ADS)
Bhattacharya, Amitabh; Perot, Blair
2000-11-01
Like a Reynolds Stress Transport equation model, the turbulent potential model has an explicit Coriolis acceleration term that appears in the model that accounts for rotation effects. In this work the additional secondary effects that system rotation has on the dissipation rate, return-to-isotropy, and fast pressure strain terms are also included in the model. The resulting model is tested in the context of rotating isotropic turbulence, rotating homogeneous shear flow, rotating channel flow, and swirling pipe flow. Many of the model changes are applicable to Reynolds stress transport equation models. All model modifications are frame indifferent.
Zank, Ben; Bagstad, Kenneth J.; Voigt, Brian; Villa, Ferdinando
2016-01-01
Urban expansion and its associated landscape modifications are important drivers of changes in ecosystem service (ES). This study examined the effects of two alternative land use-change development scenarios in the Puget Sound region of Washington State on natural capital stocks and ES flows. Land-use change model outputs served as inputs to five ES models developed using the Artificial Intelligence for Ecosystem Services (ARIES) platform. While natural capital stocks declined under managed (1.3–5.8%) and unmanaged (2.8–11.8%) development scenarios, ES flows increased by 18.5–56% and 23.2–55.7%, respectively. Human development of natural landscapes reduced their capacity for service provision, while simultaneously adding beneficiaries, particularly along the urban fringe. Using global and local Moran’s I, we identified three distinct patterns of change in ES due to projected landuse change. For services with location-dependent beneficiaries – open space proximity, viewsheds, and flood regulation – urbanization led to increased clustering and hot-spot intensities. ES flows were greatest in the managed land-use change scenario for open space proximity and flood regulation, and in the unmanaged land-use change scenario for viewsheds—a consequence of the differing ES flow mechanisms underpinning these services. We observed a third pattern – general declines in service provision – for carbon storage and sediment retention, where beneficiaries in our analysis were not location dependent. Contrary to past authors’ finding of ES declines under urbanization, a more nuanced analysis that maps and quantifies ES provision, beneficiaries, and flows better identifies gains and losses for specific ES beneficiaries as urban areas expand.
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.
NASA Technical Reports Server (NTRS)
Ghee, Terence A.; Elliott, Joe W.
1992-01-01
An experimental investigation was conducted in the 14 by 22 ft subsonic tunnel at NASA Langley Research Center to quantify the rotor wake behind a scale model helicopter rotor in forward flight (mu = 0.15 and 0.23) at one thrust level (C sub T = 0.0064). The rotor system used in the present test consisted of a four-bladed, fully articulated hub and utilized blades of rectangular planform with a NACA-0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the flow in planes parallel and perpendicular to the freestream flow. Quantitative measurements of vortex location, vertical skew angle, and vortex particle void radius were obtained for vortices in the flow; convective velocities were obtained for blade tip vortices. Comparisons were made between the experimental results and the wake geometry generated by computational predictions. The results of these comparisons show that the interaction between wake vortex structures is an important consideration for correctly predicting the wake geometry.
Numerical Study of Tip Vortex Flows
NASA Technical Reports Server (NTRS)
Dacles-Mariani, Jennifer; Hafez, Mohamed
1998-01-01
This paper presents an overview and summary of the many different research work related to tip vortex flows and wake/trailing vortices as applied to practical engineering problems. As a literature survey paper, it outlines relevant analytical, theoretical, experimental and computational study found in literature. It also discusses in brief some of the fundamental aspects of the physics and its complexities. An appendix is also included. The topics included in this paper are: 1) Analytical Vortices; 2) Experimental Studies; 3) Computational Studies; 4) Wake Vortex Control and Management; 5) Wake Modeling; 6) High-Lift Systems; 7) Issues in Numerical Studies; 8) Instabilities; 9) Related Topics; 10) Visualization Tools for Vertical Flows; 11) Further Work Needed; 12) Acknowledgements; 13) References; and 14) Appendix.
Validation of numerical models for flow simulation in labyrinth seals
NASA Astrophysics Data System (ADS)
Frączek, D.; Wróblewski, W.
2016-10-01
CFD results were compared with the results of experiments for the flow through the labyrinth seal. RANS turbulence models (k-epsilon, k-omega, SST and SST-SAS) were selected for the study. Steady and transient results were analyzed. ANSYS CFX was used for numerical computation. The analysis included flow through sealing section with the honeycomb land. Leakage flows and velocity profiles in the seal were compared. In addition to the comparison of computational models, the divergence of modeling and experimental results has been determined. Tips for modeling these problems were formulated.
NASA Astrophysics Data System (ADS)
Ghasemizadeh, Reza; Yu, Xue; Butscher, Christoph; Padilla, Ingrid Y.; Alshawabkeh, Akram
2016-09-01
In northern Puerto Rico (USA), subsurface conduit networks with unknown characteristics, and surface features such as springs, rivers, lagoons and wetlands, drain the coastal karst aquifers. In this study, drain lines connecting sinkholes and springs are used to improve the developed regional model by simulating the drainage effects of conduit networks. Implemented in an equivalent porous media (EPM) approach, the model with drains is able to roughly reproduce the spring discharge hydrographs in response to rainfall. Hydraulic conductivities are found to be scale dependent and significantly increase with higher test radius, indicating scale dependency of the EPM approach. Similar to other karst regions in the world, hydraulic gradients are steeper where the transmissivity is lower approaching the coastline. This study enhances current understanding of the complex flow patterns in karst aquifers and suggests that using a drainage feature improves modeling results where available data on conduit characteristics are minimal.
Buitrago, Paula A.; Morrill, Mike; Lighty, JoAnn S.; Silcox, Geoffrey D.
2009-06-01
This report presents experimental and modeling mercury oxidation and adsorption data. Fixed-bed and single-particle models of mercury adsorption were developed. The experimental data were obtained with two reactors: a 300-W, methane-fired, tubular, quartz-lined reactor for studying homogeneous oxidation reactions and a fixed-bed reactor, also of quartz, for studying heterogeneous reactions. The latter was attached to the exit of the former to provide realistic combustion gases. The fixed-bed reactor contained one gram of coconut-shell carbon and remained at a temperature of 150°C. All methane, air, SO_{2}, and halogen species were introduced through the burner to produce a radical pool representative of real combustion systems. A Tekran 2537A Analyzer coupled with a wet conditioning system provided speciated mercury concentrations. At 150°C and in the absence of HCl or HBr, the mercury uptake was about 20%. The addition of 50 ppm HCl caused complete capture of all elemental and oxidized mercury species. In the absence of halogens, SO_{2} increased the mercury adsorption efficiency to up to 30 percent. The extent of adsorption decreased with increasing SO_{2} concentration when halogens were present. Increasing the HCl concentration to 100 ppm lessened the effect of SO_{2}. The fixed-bed model incorporates Langmuir adsorption kinetics and was developed to predict adsorption of elemental mercury and the effect of multiple flue gas components. This model neglects intraparticle diffusional resistances and is only applicable to pulverized carbon sorbents. It roughly describes experimental data from the literature. The current version includes the ability to account for competitive adsorption between mercury, SO_{2}, and NO_{2}. The single particle model simulates in-flight sorbent capture of elemental mercury. This model was developed to include Langmuir and Freundlich isotherms, rate equations, sorbent feed rate, and
CFD Modeling for Active Flow Control
NASA Technical Reports Server (NTRS)
Buning, Pieter G.
2001-01-01
This presentation describes current work under UEET Active Flow Control CFD Research Tool Development. The goal of this work is to develop computational tools for inlet active flow control design. This year s objectives were to perform CFD simulations of fully gridded vane vortex generators, micro-vortex genera- tors, and synthetic jets, and to compare flowfield results with wind tunnel tests of simple geometries with flow control devices. Comparisons are shown for a single micro-vortex generator on a flat plate, and for flow over an expansion ramp with sidewall effects. Vortex core location, pressure gradient and oil flow patterns are compared between experiment and computation. This work lays the groundwork for evaluating simplified modeling of arrays of devices, and provides the opportunity to test simple flow control device/sensor/ control loop interaction.
A percolation model of ecological flows
Gardner, R.H.; Turner, M.G.; Dale, V.H.; O'Neill, R.V.
1988-01-01
The boundary zone between adjacent communities has long been recognized as a functionally important component of ecosystems. The diversity and abundance of species, the flow and accumulation of material and energy, and the propagation of disturbances may all be affected by landscape boundaries. However, the spatial arrangement of different habitats and their boundaries has received little direct study. The difficulty in studying landscape boundaries has been due, in part, to the variety of responses of organisms to ecotones. Therefore, definitive tests of relationships between ecological processes and the pattern of landscape boundaries will be greatly assisted by developing a standard against which comparisons can be made. Neutral models can define this standard by producing the expected'' Poisson distribution have been well established, but a general approach for relating ecological processes and landscape patterns must still be defined. The purpose of this chapter is to illustrate how neutral models that are developed from percolation theory can be used to address the problem How do ecological system boundaries influence biotic diversity and the flow of energy, information and materials '' 26 refs., 4 figs., 1 tab.
Performance study of a data flow architecture
NASA Technical Reports Server (NTRS)
Adams, George
1985-01-01
Teams of scientists studied data flow concepts, static data flow machine architecture, and the VAL language. Each team mapped its application onto the machine and coded it in VAL. The principal findings of the study were: (1) Five of the seven applications used the full power of the target machine. The galactic simulation and multigrid fluid flow teams found that a significantly smaller version of the machine (16 processing elements) would suffice. (2) A number of machine design parameters including processing element (PE) function unit numbers, array memory size and bandwidth, and routing network capability were found to be crucial for optimal machine performance. (3) The study participants readily acquired VAL programming skills. (4) Participants learned that application-based performance evaluation is a sound method of evaluating new computer architectures, even those that are not fully specified. During the course of the study, participants developed models for using computers to solve numerical problems and for evaluating new architectures. These models form the bases for future evaluation studies.
Mathematical Modeling of Flow Through Vegetated Regions
2013-08-01
including stem population density and flow Reynolds number. These results are compared to well-respected experimental results. We model real- life beds of...We model real- life beds of Spartina alterniflora grass with represen- tative beds of flexible beams and perform similar comparisons. x 13 Table of...and pressure contours ( right ) for instanta- neous snapshots of flows of various Reynolds numbers in 2D porous media domain with circle diameter 0.25 m
Modeling Flow through a Lock Manifold Port
2013-01-01
computational model is to provide reliable loss coefficients. Energy losses for flow issuing from a port occur primarily in the submerged jet . The...computational flow model to determine the velocity and pressure distribution in a single-port manifold for a range of port-to-culvert discharge ...Engineers 2006). Navigation lock manifolds can be evaluated using analytical methods when the hydraulic characteristics associated with the manifold’s
General single phase wellbore flow model
Ouyang, Liang-Biao; Arbabi, S.; Aziz, K.
1997-02-05
A general wellbore flow model, which incorporates not only frictional, accelerational and gravitational pressure drops, but also the pressure drop caused by inflow, is presented in this report. The new wellbore model is readily applicable to any wellbore perforation patterns and well completions, and can be easily incorporated in reservoir simulators or analytical reservoir inflow models. Three dimensionless numbers, the accelerational to frictional pressure gradient ratio R{sub af}, the gravitational to frictional pressure gradient ratio R{sub gf}, and the inflow-directional to accelerational pressure gradient ratio R{sub da}, have been introduced to quantitatively describe the relative importance of different pressure gradient components. For fluid flow in a production well, it is expected that there may exist up to three different regions of the wellbore: the laminar flow region, the partially-developed turbulent flow region, and the fully-developed turbulent flow region. The laminar flow region is located near the well toe, the partially-turbulent flow region lies in the middle of the wellbore, while the fully-developed turbulent flow region is at the downstream end or the heel of the wellbore. Length of each region depends on fluid properties, wellbore geometry and flow rate. As the distance from the well toe increases, flow rate in the wellbore increases and the ratios R{sub af} and R{sub da} decrease. Consequently accelerational and inflow-directional pressure drops have the greatest impact in the toe region of the wellbore. Near the well heel the local wellbore flow rate becomes large and close to the total well production rate, here R{sub af} and R{sub da} are small, therefore, both the accelerational and inflow-directional pressure drops can be neglected.
Holistic Flow Model of Spiritual Wellness
ERIC Educational Resources Information Center
Purdy, Melanie; Dupey, Peggy
2005-01-01
The Holistic Flow Model of Spiritual Wellness is a conceptualization of spiritual health and well-being that has implications for clinical practice and research. The model is unique in its placement of the spirit at the center of Life and in its fluid vision of the spirit. The authors present the model after a discussion of spirituality and the…
A compendium of fracture flow models, 1994
Diodato, D.M.
1994-11-01
The report is designed to be used as a decision-making aid for individuals who need to simulate fluid flow in fractured porous media. Fracture flow codes of varying capability in the public and private domain were identified in a survey of government, academia, and industry. The selection and use of an appropriate code requires conceptualization of the geology, physics, and chemistry (for transport) of the fracture flow problem to be solved. Conceptual models that have been invoked to describe fluid flow in fractured porous media include explicit discrete fracture, dual continuum (porosity and/or permeability), discrete fracture network, multiple interacting continua, multipermeability/multiporosity, and single equivalent continuum. The explicit discrete-fracture model is a ``near-field`` representation, the single equivalent continuum model is a ``far-field`` representation, and the dual-continuum model is intermediate to those end members. Of these, the dual-continuum model is the most widely employed. The concept of multiple interacting continua has been applied in a limited number of examples. Multipermeability/multiporosity provides a unified conceptual model. The ability to accurately describe fracture flow phenomena will continue to improve as a result of advances in fracture flow research and computing technology. This improvement will result in enhanced capability to protect the public environment, safety, and health.
Modeling groundwater flow and quality
Konikow, Leonard F.; Glynn, Pierre D.; Selinus, Olle
2013-01-01
In most areas, rocks in the subsurface are saturated with water at relatively shallow depths. The top of the saturated zone—the water table—typically occurs anywhere from just below land surface to hundreds of feet below the land surface. Groundwater generally fills all pore spaces below the water table and is part of a continuous dynamic flow system, in which the fluid is moving at velocities ranging from feet per millennia to feet per day (Fig. 33.1). While the water is in close contact with the surfaces of various minerals in the rock material, geochemical interactions between the water and the rock can affect the chemical quality of the water, including pH, dissolved solids composition, and trace-elements content. Thus, flowing groundwater is a major mechanism for the transport of chemicals from buried rocks to the accessible environment, as well as a major pathway from rocks to human exposure and consumption. Because the mineral composition of rocks is highly variable, as is the solubility of various minerals, the human-health effects of groundwater consumption will be highly variable.
Modeling of Wall-Bounded Complex Flows and Free Shear Flows
NASA Technical Reports Server (NTRS)
Shih, Tsan-Hsing; Zhu, Jiang; Lumley, John L.
1994-01-01
Various wall-bounded flows with complex geometries and free shear flows have been studied with a newly developed realizable Reynolds stress algebraic equation model. The model development is based on the invariant theory in continuum mechanics. This theory enables us to formulate a general constitutive relation for the Reynolds stresses. Pope was the first to introduce this kind of constitutive relation to turbulence modeling. In our study, realizability is imposed on the truncated constitutive relation to determine the coefficients so that, unlike the standard k-E eddy viscosity model, the present model will not produce negative normal stresses in any situations of rapid distortion. The calculations based on the present model have shown an encouraging success in modeling complex turbulent flows.
Chakraborty, Chandrima; Chowdhury, Ranjana; Bhattacharya, Pinaki
2011-05-01
Bioremediation of lipid-rich model wastewater was investigated in a packed bed biofilm reactor (anaerobic filter). A detailed study was conducted about the influence of fatty acid concentration on biomethanation of the high-fat liquid effluent of edible oil refineries. The biochemical methane potential (BMP) of the liquid waste was reported and maximum cumulative methane production at the exit of the reactor is estimated to be 785 ml CH(4) (STP)/(gVSS added). The effects of hydraulic retention time (HRT), organic loading rate (OLR) and bed porosity on the cold gas efficiency or energy efficiency of the bioconversion process were also investigated. Results revealed that the maximum cold gas efficiency of the process is 42% when the total organic load is 2.1 g COD/l at HRT of 3.33 days. Classical substrate uninhibited Monod model is used to generate the differential system equations which can predict the reactor behavior satisfactorily.
Liu, Fen-Wu; Zhou, Li-Xiang; Zhou, Jun; Jiang, Feng
2011-10-01
A plug-flow bio-reactor of 700 L working volume for sludge bioleaching was used in this study. The reactor was operationally divided into six sections along the direction of the sludge movement. Ten duration of continuous operation of sludge bioleaching with Acidibacillus spp. and 1.2 m3 x h(-1) aeration amount was conducted. In this system, sludge retention time was 2.5 d, and the added amount of microbial nutritional substance was 4 g x L(-1). During sludge bioleaching, the dynamic changes of pH, dewaterability (specific resistance to filtration, SRF) of sewage sludge in different sections, the moisture content and moisture evaporation rate of dewatered bioleached sludge cake obtained by chamber filter press were investigated. The results showed that the SRF of sludge significantly decreased from initial 1.50 x 10(13) m x kg(-1) to the final 0.34 x 10(13) m x kg(-1). The wasted bioleached sludge was collected and dewatered by chamber filter press under the following pressures as 0.3 MPa for 4 h (2 h for feeding sludge, 2 h for holding pressure), 3 h (1.5 h for feeding sludge, 1.5 h for holding pressure), 2 h (1 h for feeding sludge, 1 h for holding pressure), and 1 h (0.5 h for feeding sludge, 0.5 h for holding pressure). Correspondingly, the moisture of dewatered sludge was reduced to 57.9%, 59.2%, 59.6%, and 63.4% of initial moisture, respectively. Moreover, the moisture content of bioleached sludge cake was reduced to about 45% and less than 10% if the cake was placed at 25 degrees C for 15 h and 96 h, respectively. Obviously, sludge bioleaching followed by sludge dewatering using chamber filter press is a promising attractive approach for sludge half-dryness treatment in engineering application.
Computational modeling of flow-altering surgeries in basilar aneurysms.
Rayz, V L; Abla, A; Boussel, L; Leach, J R; Acevedo-Bolton, G; Saloner, D; Lawton, M T
2015-05-01
In cases where surgeons consider different interventional options for flow alterations in the setting of pathological basilar artery hemodynamics, a virtual model demonstrating the flow fields resulting from each of these options can assist in making clinical decisions. In this study, image-based computational fluid dynamics (CFD) models were used to simulate the flow in four basilar artery aneurysms in order to evaluate postoperative hemodynamics that would result from flow-altering interventions. Patient-specific geometries were constructed using MR angiography and velocimetry data. CFD simulations carried out for the preoperative flow conditions were compared to in vivo phase-contrast MRI measurements (4D Flow MRI) acquired prior to the interventions. The models were then modified according to the procedures considered for each patient. Numerical simulations of the flow and virtual contrast transport were carried out in each case in order to assess postoperative flow fields and estimate the likelihood of intra-aneurysmal thrombus deposition following the procedures. Postoperative imaging data, when available, were used to validate computational predictions. In two cases, where the aneurysms involved vital pontine perforator arteries branching from the basilar artery, idealized geometries of these vessels were incorporated into the CFD models. The effect of interventions on the flow through the perforators was evaluated by simulating the transport of contrast in these vessels. The computational results were in close agreement with the MR imaging data. In some cases, CFD simulations could help determine which of the surgical options was likely to reduce the flow into the aneurysm while preserving the flow through the basilar trunk. The study demonstrated that image-based computational modeling can provide guidance to clinicians by indicating possible outcome complications and indicating expected success potential for ameliorating pathological aneurysmal flow
Modeling of karst aquifer genesis: Influence of exchange flow
NASA Astrophysics Data System (ADS)
Bauer, Sebastian; Liedl, Rudolf; Sauter, Martin
2003-10-01
This paper presents a numerical model study simulating the early karstification of a single conduit embedded in a fissured system. A hybrid continuum-discrete pipe flow model (CAVE) is used for the modeling. The effects of coupling of the two flow systems on type and duration of early karstification are studied for different boundary conditions. Assuming fixed head boundaries at both ends of the conduit, coupling of the two flow systems via exchange flow between the conduit and the fissured system leads to an enhanced evolution of the conduit. This effect is valid over a wide range of initial conduit diameters, and karstification is accelerated by a factor of about 100 as compared to the case of no exchange flow. Parameter studies reveal the influence of the exchange coefficient and of the hydraulic conductivity of the fissured system on the development time for the conduit. In a second scenario the upstream fixed head boundary is switched to a fixed flow boundary at a specified flow rate during the evolution, limiting the amount of water draining toward the evolving conduit. Depending on the flow rate specified, conduit evolution may be slowed down or greatly impaired if exchange flow is considered.
2008-04-22
deep depression to a plateau. The air flow in the channel is seeded with 1 Pm olive - oil droplets, a dual-cavity Nd:Yag laser is used for illumination...wall-normal plane over smooth, RF1 and RF2 surface conditions. All flows were seeded with nominally I pm olive oil droplets generated with a Laskin...Hama (1954) found that the roughness function is directly related to the local skin -friction coefficient, cf r/(1pU,2), over smooth and rough walls
A model for insect tracheolar flow
NASA Astrophysics Data System (ADS)
Staples, Anne; Chatterjee, Krishnashis
2015-11-01
Tracheoles are the terminal ends of the microscale tracheal channels present in most insect respiratory systems that transport air directly to the tissue. From a fluid dynamics perspective, tracheolar flow is notable because it lies at the intersection of several specialized fluid flow regimes. The flow through tracheoles is creeping, microscale gas flow in the rarefied regime. Here, we use lubrication theory to model the flow through a single microscale tracheole and take into account fluid-structure interactions through an imposed periodic wall deformation corresponding to the rhythmic abdominal compression found in insects, and rarefaction effects using slip boundary conditions. We compare the pressure, axial pressure gradient, and axial and radial velocities in the channel, and the volumetric flow rate through the channel for no-slip, low slip, and high slip conditions under two different channel deformation regimes. We find that the presence of slip tends to reduce the flow rate through the model tracheole and hypothesize that one of the mechanical functions of tracheoles is to act as a diffuser to decelerate the flow, enhance mixing, and increase the residency time of freshly oxygenated air at the surface of the tissue. This work was funded by the NSF under grant no. 1437387.
A Baroclinic Model of turbulent dusty flows
Kuhl, A.L.
1992-04-01
The problem considered here is the numerical simulation of the turbulent dusty flow induced by explosions over soil surfaces. Some of the unresolved issues are: (1) how much dust is scoured from such surfaces; (2) where does the dust go in the boundary layer; (3) what is the dusty boundary layer height versus time; (4) what are the dusty boundary layer profiles; (5) how much of the dust mass becomes entrained into the dust stem; and (6) where does the dust go in the buoyant cloud? The author proposes a Baroclinic Model for flows with large density variations that actually calculates the turbulent mixing and transport of dust on an adaptive grid. The model is based on the following idealizations: (1) a loose dust bed; (2) an instantaneous shock fluidization of the dust layer; (3) the dust and air are in local equilibrium (so air viscosity enforces the no-slip condition); (4) the dust-air mixture is treated as a continuum dense fluid with zero viscosity; and (5) the turbulent mixing is dominated by baroclinically-generated vorticity. These assumptions lead to an inviscid set of conservation laws for the mixture, which are solved by means of a high-order Godunov algorithm for gasdynamics. Adaptive Mesh Refinement (AMR) is used to capture the turbulent mixing processes on the grid. One of the unique characteristics of these flows is that mixing occurs because vorticity is produced by an inviscid, baroclinic mechanism. A number of examples are presented to illustrate these baroclinic effects including shock interactions with dense-gas layers and dust beds, and dusty wall jets of airblast precursors. The conclusion of these studies is that dusty boundary layers grow because of mass entrainment from the fluidized bed (and not because of viscous wall drag) as proven by the Mass Integral Equation.
Modeling flow and sedimention of slurries
NASA Astrophysics Data System (ADS)
Mondy, L.; Rao, R.; Altobelli, S.; Ingber, M.; Graham, A.
2002-12-01
Many natural processes involve flows of sediments at high particle concentrations. The equations describing such two-phase flows are highly nonlinear. We will give an overview of the performance of a continuum constitutive model of suspensions of particles in liquid for low Reynolds number flows. The diffusive flux model (Leighton and Acrivos, J. Fluid Mech., 1987, and Phillips et al., Phys. Fluids A, 1992) is implemented in a general purpose finite element computational program. This constitutive description couples a Newtonian stress/shear-rate relationship (where the local viscosity of the suspension is dependent on the local volume fraction of solids) with a shear-induced migration model of the suspended particles. The momentum transport, continuity, and diffusive flux equations are solved simultaneously. The formulation is fully three-dimensional and can be run on a parallel computer platform. Recent work introducing a flow-aligned tensor correction to this model has had success in representing the anisotropic force that is seen in curvilinear flows. Gravity effects are added in an approach similar to that of Zhang and Acrivos (Int. J. Multiphase Flow, 1994). The model results are compared with laboratory data obtained with Nuclear Magnetic Resonance (NMR) of evolving particle concentration profiles in complex flows, as well as in batch sedimentation. Interesting secondary flows appear both in the experiment and model. Overall, good agreement is found between the experiments and the simulations. This work was supported by the United States Department of Energy under Contract DE-AC04- 94AL85000. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy. The authors would like to acknowledge support for this work by the U.S. Department of Energy, Division of Engineering and Geosciences, Office of Basic Energy Sciences.
Modeling of Turbulent Free Shear Flows
NASA Technical Reports Server (NTRS)
Yoder, Dennis A.; DeBonis, James R.; Georgiadis, Nicolas J.
2013-01-01
The modeling of turbulent free shear flows is crucial to the simulation of many aerospace applications, yet often receives less attention than the modeling of wall boundary layers. Thus, while turbulence model development in general has proceeded very slowly in the past twenty years, progress for free shear flows has been even more so. This paper highlights some of the fundamental issues in modeling free shear flows for propulsion applications, presents a review of past modeling efforts, and identifies areas where further research is needed. Among the topics discussed are differences between planar and axisymmetric flows, development versus self-similar regions, the effect of compressibility and the evolution of compressibility corrections, the effect of temperature on jets, and the significance of turbulent Prandtl and Schmidt numbers for reacting shear flows. Large eddy simulation greatly reduces the amount of empiricism in the physical modeling, but is sensitive to a number of numerical issues. This paper includes an overview of the importance of numerical scheme, mesh resolution, boundary treatment, sub-grid modeling, and filtering in conducting a successful simulation.
International Trade Modelling Using Open Flow Networks: A Flow-Distance Based Analysis.
Shen, Bin; Zhang, Jiang; Li, Yixiao; Zheng, Qiuhua; Li, Xingsen
2015-01-01
This paper models and analyzes international trade flows using open flow networks (OFNs) with the approaches of flow distances, which provide a novel perspective and effective tools for the study of international trade. We discuss the establishment of OFNs of international trade from two coupled viewpoints: the viewpoint of trading commodity flow and that of money flow. Based on the novel model with flow distance approaches, meaningful insights are gained. First, by introducing the concepts of trade trophic levels and niches, countries' roles and positions in the global supply chains (or value-added chains) can be evaluated quantitatively. We find that the distributions of trading "trophic levels" have the similar clustering pattern for different types of commodities, and summarize some regularities between money flow and commodity flow viewpoints. Second, we find that active and competitive countries trade a wide spectrum of products, while inactive and underdeveloped countries trade a limited variety of products. Besides, some abnormal countries import many types of goods, which the vast majority of countries do not need to import. Third, harmonic node centrality is proposed and we find the phenomenon of centrality stratification. All the results illustrate the usefulness of the model of OFNs with its network approaches for investigating international trade flows.
International Trade Modelling Using Open Flow Networks: A Flow-Distance Based Analysis
Shen, Bin; Zhang, Jiang; Li, Yixiao; Zheng, Qiuhua; Li, Xingsen
2015-01-01
This paper models and analyzes international trade flows using open flow networks (OFNs) with the approaches of flow distances, which provide a novel perspective and effective tools for the study of international trade. We discuss the establishment of OFNs of international trade from two coupled viewpoints: the viewpoint of trading commodity flow and that of money flow. Based on the novel model with flow distance approaches, meaningful insights are gained. First, by introducing the concepts of trade trophic levels and niches, countries’ roles and positions in the global supply chains (or value-added chains) can be evaluated quantitatively. We find that the distributions of trading “trophic levels” have the similar clustering pattern for different types of commodities, and summarize some regularities between money flow and commodity flow viewpoints. Second, we find that active and competitive countries trade a wide spectrum of products, while inactive and underdeveloped countries trade a limited variety of products. Besides, some abnormal countries import many types of goods, which the vast majority of countries do not need to import. Third, harmonic node centrality is proposed and we find the phenomenon of centrality stratification. All the results illustrate the usefulness of the model of OFNs with its network approaches for investigating international trade flows. PMID:26569618
A study of grout flow pattern analysis
Lee, S. Y.; Hyun, S.
2013-01-10
A new disposal unit, designated as Salt Disposal Unit no. 6 (SDU6), is being designed for support of site accelerated closure goals and salt nuclear waste projections identified in the new Liquid Waste System plan. The unit is cylindrical disposal vault of 380 ft diameter and 43 ft in height, and it has about 30 million gallons of capacity. Primary objective was to develop the computational model and to perform the evaluations for the flow patterns of grout material in SDU6 as function of elevation of grout discharge port, and slurry rheology. A Bingham plastic model was basically used to represent the grout flow behavior. A two-phase modeling approach was taken to achieve the objective. This approach assumes that the air-grout interface determines the shape of the accumulation mound. The results of this study were used to develop the design guidelines for the discharge ports of the Saltstone feed materials in the SDU6 facility. The focusing areas of the modeling study are to estimate the domain size of the grout materials radially spread on the facility floor under the baseline modeling conditions, to perform the sensitivity analysis with respect to the baseline design and operating conditions such as elevation of discharge port, discharge pipe diameter, and grout properties, and to determine the changes in grout density as it is related to grout drop height. An axi-symmetric two-phase modeling method was used for computational efficiency. Based on the nominal design and operating conditions, a transient computational approach was taken to compute flow fields mainly driven by pumping inertia and natural gravity. Detailed solution methodology and analysis results are discussed here.
Discrete Element Modeling of Complex Granular Flows
NASA Astrophysics Data System (ADS)
Movshovitz, N.; Asphaug, E. I.
2010-12-01
Granular materials occur almost everywhere in nature, and are actively studied in many fields of research, from food industry to planetary science. One approach to the study of granular media, the continuum approach, attempts to find a constitutive law that determines the material's flow, or strain, under applied stress. The main difficulty with this approach is that granular systems exhibit different behavior under different conditions, behaving at times as an elastic solid (e.g. pile of sand), at times as a viscous fluid (e.g. when poured), or even as a gas (e.g. when shaken). Even if all these physics are accounted for, numerical implementation is made difficult by the wide and often discontinuous ranges in continuum density and sound speed. A different approach is Discrete Element Modeling (DEM). Here the goal is to directly model every grain in the system as a rigid body subject to various body and surface forces. The advantage of this method is that it treats all of the above regimes in the same way, and can easily deal with a system moving back and forth between regimes. But as a granular system typically contains a multitude of individual grains, the direct integration of the system can be very computationally expensive. For this reason most DEM codes are limited to spherical grains of uniform size. However, spherical grains often cannot replicate the behavior of real world granular systems. A simple pile of spherical grains, for example, relies on static friction alone to keep its shape, while in reality a pile of irregular grains can maintain a much steeper angle by interlocking force chains. In the present study we employ a commercial DEM, nVidia's PhysX Engine, originally designed for the game and animation industry, to simulate complex granular flows with irregular, non-spherical grains. This engine runs as a multi threaded process and can be GPU accelerated. We demonstrate the code's ability to physically model granular materials in the three regimes
How to Model Water Flow in Moulins?
NASA Astrophysics Data System (ADS)
Phillips, T. P.; Steffen, K.
2007-12-01
The development of large melt ponds on the Greenland Ice Sheet (GIS) and their drainage system indicate that moulins are a major contributor to the englacial water system. Here we review the current state of knowledge and the history of moulin research. In the late 19th century glaciologists led by Vallot climbed and studied the Grand Moulin on Mont Blanc. Despite being considered mystic due to their size and water drainage they have been studied by a few scientists such as Holmlund and Hooke (1980) or Puccini and Badino (1990). We develop a qualitative model of geometry as well as of the driving forces in the life cycle of moulins using data, photos, sketches, and climbing reports by ice speleologists and climbers. The GIS is temperate for the first 10 km at its margin and consists of cold ice further inland. The recent increase in melt water leads to an increase in basal water availability. The observed increase in ice velocity might be caused by the lubrication at the bed combined with a possible temperature rise in the cold part of the GIS. The raise of englacial water flow increases the volume of the conduits thus reducing the timing of water to reach the ice sheet bed. Our initial model starts with a narrow englacial non-arborescent channel network. We anticipate the development of the englacial hydrology system by using the 'Roethlisberger' conduit model. In addition we will show first model results on temperature fluctuations in the ice due to the hydrologic system.
NASA Astrophysics Data System (ADS)
Trambauer, P.; Nonner, J.; Heijkers, J.; Uhlenbrook, S.
2011-09-01
The groundwater flow models currently used in the western part of The Netherlands and in other similar peaty areas are thought to be a too simplified representation of the hydrological reality. One of the reasons is that, due to the schematization of the subsoil, its heterogeneity cannot be represented adequately. Moreover, the applicability of Darcy's law in these types of soils has been questioned, but this law forms the basis of most groundwater flow models. With the purpose of assessing the typical heterogeneity of the subsoil and to verify the applicability of Darcy's law, geo-hydrological fieldwork was completed at an experimental field within a research area in the western part of The Netherlands. The assessments were carried out for the so-called Complex Confining Layer (CCL), which is the Holocene peaty to clayey layer overlying Pleistocene sandy deposits. Borehole drilling through the CCL with a hand auger was completed and revealed the typical heterogeneous character of this layer, showing a dominance of muddy, humified peat which is alternated with fresher peat and clay. Slug tests were carried out to study the applicability of Darcy's law, given that previous studies suggested its non-validity for humified peat soils due to a variable horizontal hydraulic conductivity Kh with head differences. For higher humification degrees, the experiments indeed suggested a variable Kh, but this appeared to be the result of the inappropriate use of steady-state formulae for transient experiments in peaty environments. The muddy peat sampled has a rather plastic nature, and the high compressibility of this material leads to transient behavior. However, using transient formulae, the slug tests conducted for different initial groundwater heads showed that there was hardly any evidence of a variation of the hydraulic conductivity with the applied head differences. Therefore, Darcy's law can be used for typical peat soils present in The Netherlands. The heterogeneity of
Experimental Study of Flow in a Bifurcation
NASA Astrophysics Data System (ADS)
Fresconi, Frank; Prasad, Ajay
2003-11-01
An instability known as the Dean vortex occurs in curved pipes with a longitudinal pressure gradient. A similar effect is manifest in the flow in a converging or diverging bifurcation, such as those found in the human respiratory airways. The goal of this study is to characterize secondary flows in a bifurcation. Particle image velocimetry (PIV) and laser-induced fluorescence (LIF) experiments were performed in a clear, plastic model. Results show the strength and migration of secondary vortices. Primary velocity features are also presented along with dispersion patterns from dye visualization. Unsteadiness, associated with a hairpin vortex, was also found at higher Re. This work can be used to assess the dispersion of particles in the lung. Medical delivery systems and pollution effect studies would profit from such an understanding.
GENERALIZED VISCOPLASTIC MODELING OF DEBRIS FLOW.
Chen, Cheng-lung
1988-01-01
The earliest model developed by R. A. Bagnold was based on the concept of the 'dispersive' pressure generated by grain collisions. Some efforts have recently been made by theoreticians in non-Newtonian fluid mechanics to modify or improve Bagnold's concept or model. A viable rheological model should consist both of a rate-independent part and a rate-dependent part. A generalized viscoplastic fluid (GVF) model that has both parts as well as two major rheological properties (i. e. , the normal stress effect and soil yield criterion) is shown to be sufficiently accurate, yet practical for general use in debris-flow modeling. In fact, Bagnold's model is found to be only a particular case of the GVF model. analytical solutions for (steady) uniform debris flows in wide channels are obtained from the GVF model based on Bagnold's simplified assumption of constant grain concentration.
Modelling the emplacement of compound lava flows
NASA Astrophysics Data System (ADS)
Blake, S.; Bruno, B. C.
2000-12-01
The physical variables controlling crust-dominated lava flow have been investigated using laboratory experiments in which molten polyglycol wax was extruded from a point source on to a horizontal plane under cold water. The wax initially spread axisymmetrically and a crust of solid wax grew. Eventually wax broke out from the flow's periphery, sending out a flow lobe which in turn cooled and produced another breakout. The process repeated itself many times, building a 'compound lava'. The time for the first breakout to form correlates well with the theoretically predicted time ( tc) required for cooling to form a crust thick enough for its strength to limit the flow's spreading rate. This time is proportional to the product of effusion rate ( Q) and initial magma viscosity ( μ) and inversely proportional to the square of the crust strength at the flow front. The number of flow units and the apparent fractal dimension of the flow perimeter increase with time normalised by tc. Our model illuminates the physical basis for the observation by Walker [G.P.L. Walker, Bull. Volcanol. 35 (1972) 579-590] that compound lava flows form by slow effusion of low viscosity magma, whereas faster effusion and higher viscosity favour lavas with fewer flow units. Because compound flows require t≫ tc, and given that tc∝ Qμ and the relationship between volume and effusion rate is V= Qt, simple and compound lava flows are predicted to fall in separate fields on a graph of μ against V/ Q2, all else being equal. Compound flows plot at small values of μ and large values of V/ Q2, with the position of the simple/compound boundary defined by field data implying a crust strength of order 10 4 Pa for basaltic to intermediate lavas. Whether a flow remains as a simple flow or matures into a compound flow field depends on the combined effect of viscosity, eruption rate and eruption duration (and hence volume) and these parameters need to be taken in to account when using morphology to infer
NASA Technical Reports Server (NTRS)
Lorincz, D. J.
1980-01-01
The vortex flows generated at subsonic speed during the final portion of atmospheric reentry were defined using a 0.01 scale model of the orbiter in a diagnostic water tunnel. Flow visualization photographs were obtained over an angle-of-attack range to 40 deg and sideslip angles up to 10 deg. The vortex flow field development, vortex path, and vortex breakdown characteristics were determined as a function of angle-of-attack at zero sideslip. Vortex flows were found to develop on the highly swept glove, on the wing, and on the upper surface of the fuselage. No significant asymmetries were observed at zero sideslip in the water tunnel tests. The sensitivity of the upper surface vortex flow fields to variations in sideslip angle was also studied. The vortex formed on the glove remained very stable in position above the wing up through the 10 deg of sideslip tested. There was a change in the vortex lifts under sideslip due to effective change in leading-edge sweep angles. Asymmetric flow separation occurred on the upper surface of the fuselage at small sideslip angles. The influence of vortex flow fields in sideslip on the lateral/ directional characteristics of the orbiter is discussed.
Review and selection of unsaturated flow models
Reeves, M.; Baker, N.A.; Duguid, J.O.
1994-04-04
Since the 1960`s, ground-water flow models have been used for analysis of water resources problems. In the 1970`s, emphasis began to shift to analysis of waste management problems. This shift in emphasis was largely brought about by site selection activities for geologic repositories for disposal of high-level radioactive wastes. Model development during the 1970`s and well into the 1980`s focused primarily on saturated ground-water flow because geologic repositories in salt, basalt, granite, shale, and tuff were envisioned to be below the water table. Selection of the unsaturated zone at Yucca Mountain, Nevada, for potential disposal of waste began to shift model development toward unsaturated flow models. Under the US Department of Energy (DOE), the Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) has the responsibility to review, evaluate, and document existing computer models; to conduct performance assessments; and to develop performance assessment models, where necessary. This document describes the CRWMS M&O approach to model review and evaluation (Chapter 2), and the requirements for unsaturated flow models which are the bases for selection from among the current models (Chapter 3). Chapter 4 identifies existing models, and their characteristics. Through a detailed examination of characteristics, Chapter 5 presents the selection of models for testing. Chapter 6 discusses the testing and verification of selected models. Chapters 7 and 8 give conclusions and make recommendations, respectively. Chapter 9 records the major references for each of the models reviewed. Appendix A, a collection of technical reviews for each model, contains a more complete list of references. Finally, Appendix B characterizes the problems used for model testing.
Stochastic Modelling of Shallow Water Flows
NASA Astrophysics Data System (ADS)
Horritt, M. S.
2002-05-01
The application of computational fluid dynamics approaches to modelling shallow water flows in the environment is hindered by the uncertainty inherent to natural landforms, vegetation and processes. A stochastic approach to modelling is therefore required, but this has previously only been attempted through computationally intensive Monte Carlo methods. An efficient second order perturbation method is outlined in this presentation, whereby the governing equations are first discretised to form a non-linear system mapping model parameters to predictions. This system is then approximated using Taylor expansions to derive tractable expressions for the model prediction statistics. The approach is tested on a simple 1-D model of shallow water flow over uncertain topography, verified against ensembles of Monte Carlo simulations and approximate solutions derived by Fourier methods. Criteria for the applicability of increasing orders of Taylor expansions are derived as a function of flow depth and topographic variability. The results show that non-linear effects are important for even small topographic perturbations, and the second order perturbation method is required to derive model prediction statistics. This approximation holds well even as the flow depth tends towards the topographic roughness. The model predicted statistics are also well described by a Gaussian approximation, so only first and second moments need be calculated, even if these are significantly different to values predicted by a linear approximation. The implications for more sophisticated (2-D, advective etc.) models are discussed.
Mesoscopic Rhelogical Model for Polymeric Media Flows
NASA Astrophysics Data System (ADS)
Koshelev, K.; Kuznetcov, A.; Merzlikina, D.; Pyshnograi, G.; Pyshnograi, I.; Tolstykh, M. Y.
2017-01-01
The paper compares hydrodynamic properties of three-dimensional flows of polymer melts. A modified Vinogradov and Pokrovskii rheological model is used for the mathematical description of nonlinear viscoelastic fluid flows in a planeparallel channel with a sudden convergence. Discrete analogs for partial differential equations were obtained via the control volume method separating physical processes. The numerical implementation is carried out using the GPU-based parallel computing technology. Velocity and pressure fields have been calculated for two samples of polyethylene melts and the circulating flow at the entrance of the slit channel is noticeable. It is shown that the size of the vortex zone depends significantly on melt rheology.
NASA Astrophysics Data System (ADS)
Dang, Chao; Cui, Peng; Cheng, Zun-Lan
2009-06-01
Temporary dams can be formed by the sudden injection of debris flow into main streams by some favorable geomorphologic and hydraulic conditions, resulting in extensive inundations upstream and catastrophic floods downstream due to dam breaches and consequently dramatic changes of channels and valleys. Expeditious means of assessing dam-forming potential are necessary, particularly in geologically active regions. Complete blockages or dam formations are significantly related to the discharge ratio and velocity ratio between the tributary and the main stream, the bulk density of the debris flow, confluent angles and the degree of unevenness of grain sizes. In order to set up a critical index/ C for dam formation, 19 groups of flume tests were conducted. The results showed that there were three types of blockage in the intersections, and dam-forming processes were mainly controlled by the product of the dimensionless momentum ratio and the degree of unevenness of grain sizes in the debris flow. Complete blockages or dam formations occurred when C > 83.4, whereas semi-blockages were formed or no dams were formed when C < 71.5, which had been judged to be feasible by historical instances of dam formation in China. Dam failures commonly resulted from overtopping. No piping was observed in the course of dam failure, and the time elapsed between dams can be denoted by a linear relation with the momentum ratio.
Mathematical modeling of slope flows with entrainment as flows of non-Newtonian fluids
NASA Astrophysics Data System (ADS)
Zayko, Julia; Eglit, Margarita
2015-04-01
Non-Newtonian fluids in which the shear stresses are nonlinear functions of the shear strain rates are used to model slope flows such as snow avalanches, mudflows, debris flows. The entrainment of bottom material is included into the model basing on the assumption that in entraining flows the bed friction is equal to the shear stress of the bottom material (Issler et al, 2011). Unsteady motion down long homogeneous slopes with constant inclines is studied numerically for different flow rheologies and different slope angles. Variation of the velocity profile, increase of the flow depth and velocity due to entrainment as well as the value of the entrainment rate is calculated. Asymptotic formulae for the entrainment rate are derived for unsteady flows of different rheological properties. REFERENCES Chowdhury M., Testik F., 2011. Laboratory testing of mathematical models for high-concentration fluid mud turbidity currents. Ocean Engineering 38, 256-270. Eglit, M.E., Demidov, K.S., 2005. Mathematical modeling of snow entrainment in avalanche motion. Cold Reg. Sci. Technol. 43 (1-2), 10-23. Eglit M. E., Yakubenko A. E., 2012, Mathematical Modeling of slope flows entraining bottom material. Eglit M. E., Yakubenko A. E., 2014, Numerical modeling of slope flows entraining bottom material. Cold Reg. Sci. Technol. 108, 139-148. Issler D, M. Pastor Peréz. 2011. Interplay of entrainment and rheology in snow avalanches; a numerical study. Annals of Glaciology, 52(58), pp.143-147 Kern M. A., Tiefenbacher F., McElwaine J., N., 2004. The rheology of snow in large chute flows. Cold Regions Science and Technology, 39, 181 -192. Naaim, M., Faug, T., Naaim-Bouvet, F., 2003. Dry granular flow modelling including erosion and deposition. Surv. Geophys. 24, 569-585. Naaim, M., Naaim-Bouvet, F., Faug, T., Bouchet, A., 2004. Dense snow avalanche modeling: flow, erosion, deposition and obstacle effects. Cold Reg. Sci. Technol. 39, 193-204. Rougier, J & Kern, M 2010, 'Predicting snow
A model for transonic plasma flow
Guazzotto, Luca; Hameiri, Eliezer
2014-02-15
A linear, two-dimensional model of a transonic plasma flow in equilibrium is constructed and given an explicit solution in the form of a complex Laplace integral. The solution indicates that the transonic state can be solved as an elliptic boundary value problem, as is done in the numerical code FLOW [Guazzotto et al., Phys. Plasmas 11, 604 (2004)]. Moreover, the presence of a hyperbolic region does not necessarily imply the presence of a discontinuity or any other singularity of the solution.
Turbulence Modeling in Stratified Flows over Topography
2007-09-30
Details of the basic LES model can be found in Armenio and Sarkar [1]. To avoid the need to resolve the very small turbulent motions near the lower... Armenio and S. Sarkar. An investigation of stably stratified turbulent channel flow using large-eddy simulation. J. Fluid Mech., 459:1–42, 2002. [2...276, 1994. [12] J. Taylor, S. Sarkar, and V. Armenio . An investigation of stably stratified turbulent channel flow using large-eddy simulation. Phys
NASA Technical Reports Server (NTRS)
Baldwin, M. P.; Edmon, H. J., Jr.; Holton, J. R.
1984-01-01
Latitude-height cross sections of the Eliassen-Palm (ep) flux, its divergence, the residual mean meridional circulation as well as conventional eddy and mean flow fields are computed using both observational and general circulation model data.
Nonlocal modeling of granular flows down inclines.
Kamrin, Ken; Henann, David L
2015-01-07
Flows of granular media down a rough inclined plane demonstrate a number of nonlocal phenomena. We apply the recently proposed nonlocal granular fluidity model to this geometry and find that the model captures many of these effects. Utilizing the model's dynamical form, we obtain a formula for the critical stopping height of a layer of grains on an inclined surface. Using an existing parameter calibration for glass beads, the theoretical result compares quantitatively to existing experimental data for glass beads. This provides a stringent test of the model, whose previous validations focused on driven steady-flow problems. For layers thicker than the stopping height, the theoretical flow profiles display a thickness-dependent shape whose features are in agreement with previous discrete particle simulations. We also address the issue of the Froude number of the flows, which has been shown experimentally to collapse as a function of the ratio of layer thickness to stopping height. While the collapse is not obvious, two explanations emerge leading to a revisiting of the history of inertial rheology, which the nonlocal model references for its homogeneous flow response.
Analytic Model of Reactive Flow
Souers, P C; Vitello, P
2004-08-02
A simple analytic model allows prediction of rate constants and size effect behavior before a hydrocode run if size effect data exists. At infinite radius, it defines not only detonation velocity but also average detonation rate, pressure and energy. This allows the derivation of a generalized radius, which becomes larger as the explosive becomes more non-ideal. The model is applied to near-ideal PBX 9404, in-between ANFO and most non-ideal AN. The power of the pressure declines from 2.3, 1.5 to 0.8 across this set. The power of the burn fraction, F, is 0.8, 0 and 0, so that an F-term is important only for the ideal explosives. The size effect shapes change from concave-down to nearly straight to concave-up. Failure is associated with ideal explosives when the calculated detonation velocity turns in a double-valued way. The effect of the power of the pressure may be simulated by including a pressure cutoff in the detonation rate. The models allows comparison of a wide spectrum of explosives providing that a single detonation rate is feasible.
Analytic Model of Reactive Flow
Souers, P C; Vitello, P
2004-11-15
A simple analytic model allows prediction of rate constants and size effect behavior before a hydrocode run if size effect data exists. At infinite radius, it defines not only detonation velocity but also average detonation rate, pressure and energy. This allows the derivation of a generalized radius, which becomes larger as the explosive becomes more non-ideal. The model is applied to near-ideal PBX 9404, in-between ANFO and most non-ideal AN. The power of the pressure declines from 2.3, 1.5 to 0.8 across this set. The power of the burn fraction, F, is 0.8, 0 and 0, so that an F-term is important only for the ideal explosives. The size effect shapes change from concave-down to nearly straight to concave-up. Failure is associated with ideal explosives when the calculated detonation velocity turns in a double-valued way. The effect of the power of the pressure may be simulated by including a pressure cutoff in the detonation rate. The models allows comparison of a wide spectrum of explosives providing that a single detonation rate is feasible.
Unsteady flow through in-vitro models of the glottis
NASA Astrophysics Data System (ADS)
Hofmans, G. C. J.; Groot, G.; Ranucci, M.; Graziani, G.; Hirschberg, A.
2003-03-01
The unsteady two-dimensional flow through fixed rigid in vitro models of the glottis is studied in some detail to validate a more accurate model based on the prediction of boundary-layer separation. The study is restricted to the flow phenomena occurring within the glottis and does not include effects of vocal-fold movement on the flow. Pressure measurements have been carried out for a transient flow through a rigid scale model of the glottis. The rigid model with a fixed geometry driven by an unsteady pressure is used in order to achieve a high accuracy in the specification of the geometry of the glottis. The experimental study is focused on flow phenomena as they might occur in the glottis, such as the asymmetry of the flow due to the Coanda effect and the transition to turbulent flow. It was found that both effects need a relatively long time to establish themselves and are therefore unlikely to occur during the production of normal voiced speech when the glottis closes completely during part of the oscillation cycle. It is shown that when the flow is still laminar and symmetric the prediction of the boundary-layer model and the measurement of the pressure drop from the throat of the glottis to the exit of the glottis agree within 40%. Results of the boundary-layer model are compared with a two-dimensional vortex-blob method for viscous flow. The difference between the results of the simpiflied boundary-layer model and the experimental results is explained by an additional pressure difference between the separation point and the far field within the jet downstream of the separation point. The influence of the movement of the vocal folds on our conclusions is still unclear.
Unsteady flow through in-vitro models of the glottis.
Hofmans, G C J; Groot, G; Ranucci, M; Graziani, G; Hirschberg, A
2003-03-01
The unsteady two-dimensional flow through fixed rigid in vitro models of the glottis is studied in some detail to validate a more accurate model based on the prediction of boundary-layer separation. The study is restricted to the flow phenomena occurring within the glottis and does not include effects of vocal-fold movement on the flow. Pressure measurements have been carried out for a transient flow through a rigid scale model of the glottis. The rigid model with a fixed geometry driven by an unsteady pressure is used in order to achieve a high accuracy in the specification of the geometry of the glottis. The experimental study is focused on flow phenomena as they might occur in the glottis, such as the asymmetry of the flow due to the Coanda effect and the transition to turbulent flow. It was found that both effects need a relatively long time to establish themselves and are therefore unlikely to occur during the production of normal voiced speech when the glottis closes completely during part of the oscillation cycle. It is shown that when the flow is still laminar and symmetric the prediction of the boundary-layer model and the measurement of the pressure drop from the throat of the glottis to the exit of the glottis agree within 40%. Results of the boundary-layer model are compared with a two-dimensional vortex-blob method for viscous flow. The difference between the results of the simpiflied boundary-layer model and the experimental results is explained by an additional pressure difference between the separation point and the far field within the jet downstream of the separation point. The influence of the movement of the vocal folds on our conclusions is still unclear.
Filter-matrix lattice Boltzmann model for microchannel gas flows.
Zhuo, Congshan; Zhong, Chengwen
2013-11-01
The lattice Boltzmann method has been shown to be successful for microscale gas flows, and it has attracted significant research interest. In this paper, the recently proposed filter-matrix lattice Boltzmann (FMLB) model is first applied to study the microchannel gas flows, in which a Bosanquet-type effective viscosity is used to capture the flow behaviors in the transition regime. A kinetic boundary condition, the combined bounce-back and specular-reflection scheme with the second-order slip scheme, is also designed for the FMLB model. By analyzing a unidirectional flow, the slip velocity and the discrete effects related to the boundary condition are derived within the FMLB model, and a revised scheme is presented to overcome such effects, which have also been validated through numerical simulations. To gain an accurate simulation in a wide range of Knudsen numbers, covering the slip and the entire transition flow regimes, a set of slip coefficients with an introduced fitting function is adopted in the revised second-order slip boundary condition. The periodic and pressure-driven microchannel flows have been investigated by the present model in this study. The numerical results, including the velocity profile and the mass flow rate, as well as the nonlinear pressure distribution along the channel, agree fairly well with the solutions of the linearized Boltzmann equation, the direct simulation Monte Carlo results, the experimental data, and the previous results of the multiple effective relaxation lattice Boltzmann model. Also, the present results of the velocity profile and the mass flow rate show that the present model with the fitting function can yield improved predictions for the microchannel gas flow with higher Knudsen numbers in the transition flow regime.
NASA Technical Reports Server (NTRS)
Witte, Larry C.
1994-01-01
The development of instrumentation for the support of research in two-phase flow in simulated microgravity conditions was performed. The funds were expended in the development of a technique for characterizing the motion and size distribution of small liquid droplets dispersed in a flowing gas. Phenomena like this occur in both microgravity and normal earth gravity situations inside of conduits that are carrying liquid-vapor mixtures at high flow rates. Some effort to develop a conductance probe for the measurement of liquid film thickness was also expended.
Rarefied-flow Shuttle aerodynamics model
NASA Technical Reports Server (NTRS)
Blanchard, Robert C.; Larman, Kevin T.; Moats, Christina D.
1993-01-01
A rarefied-flow shuttle aerodynamic model spanning the hypersonic continuum to the free molecule-flow regime was formulated. The model development has evolved from the High Resolution Accelerometer Package (HiRAP) experiment conducted on the Orbiter since 1983. The complete model is described in detail. The model includes normal and axial hypersonic continuum coefficient equations as functions of angle-of-attack, body flap deflection, and elevon deflection. Normal and axial free molecule flow coefficient equations as a function of angle-of-attack are presented, along with flight derived rarefied-flow transition bridging formulae. Comparisons are made with data from the Operational Aerodynamic Design Data Book (OADDB), applicable wind-tunnel data, and recent flight data from STS-35 and STS-40. The flight-derived model aerodynamic force coefficient ratio is in good agreement with the wind-tunnel data and predicts the flight measured force coefficient ratios on STS-35 and STS-40. The model is not, however, in good agreement with the OADDB. But, the current OADDB does not predict the flight data force coefficient ratios of either STS-35 or STS-40 as accurately as the flight-derived model. Also, the OADDB differs with the wind-tunnel force coefficient ratio data.
Unsaturated Zone Flow Model Expert Elicitation Project
Coppersmith, K. J.
1997-05-30
This report presents results of the Unsaturated Zone Flow Model Expert Elicitation (UZFMEE) project at Yucca Mountain, Nevada. This project was sponsored by the US Department of Energy (DOE) and managed by Geomatrix Consultants, Inc. (Geomatrix), for TRW Environmental Safety Systems, Inc. The objective of this project was to identify and assess the uncertainties associated with certain key components of the unsaturated zone flow system at Yucca Mountain. This assessment reviewed the data inputs, modeling approaches, and results of the unsaturated zone flow model (termed the ''UZ site-scale model'') being developed by Lawrence Berkeley National Laboratory (LBNL) and the US Geological Survey (USGS). In addition to data input and modeling issues, the assessment focused on percolation flux (volumetric flow rate per unit cross-sectional area) at the potential repository horizon. An understanding of unsaturated zone processes is critical to evaluating the performance of the potential high-level nuclear waste repository at Yucca Mountain. A major goal of the project was to capture the uncertainties involved in assessing the unsaturated flow processes, including uncertainty in both the models used to represent physical controls on unsaturated zone flow and the parameter values used in the models. To ensure that the analysis included a wide range of perspectives, multiple individual judgments were elicited from members of an expert panel. The panel members, who were experts from within and outside the Yucca Mountain project, represented a range of experience and expertise. A deliberate process was followed in facilitating interactions among the experts, in training them to express their uncertainties, and in eliciting their interpretations. The resulting assessments and probability distributions, therefore, provide a reasonable aggregate representation of the knowledge and uncertainties about key issues regarding the unsaturated zone at the Yucca Mountain site.
Application of heat flow models to SOI current mirrors
NASA Astrophysics Data System (ADS)
Yu, Feixia; Cheng, Ming-C.
2004-11-01
An analytical heat flow model for SOI circuits is presented. The model is able to account for heat exchanges among devices and heat loss from the silicon film and interconnects to the substrate through the buried oxide. The developed model can accurately and efficiently predict the temperature distribution in the interconnect/poly-lines and SOI devices. The model is applied to SOI current mirrors to study heat flow in different layout designs. The results from the developed model are verified with those from Raphael, a 3D numerical simulator that can provide the detailed 3D temperature distribution in interconnect/poly-lines.
Evaluation of Two Lattice Boltzmann Models for Multiphase Flows
NASA Astrophysics Data System (ADS)
Hou, Shuling; Shan, Xiaowen; Zou, Qisu; Doolen, Gary D.; Soll, Wendy E.
1997-12-01
Two lattice Boltzmann models for multiphase flows, the immiscible fluid model proposed by Rothman and Keller (R-K) and the multicomponent nonideal gas lattice Boltzmann model by Shan and Chen (S-C), are studied numerically to compare their abilities to simulate the physics of multiphase flows. The test problem is the simulation of a static bubble. Isotropy, strength of surface tension, thickness of the interface, spurious currents, Laplace's law, and steadiness of the bubble are examined. The results show that the S-C model is a major improvement over the R-K model.
Saar, Martin O.; Seyfried, Jr., William E.; Longmire, Ellen K.
2016-06-24
A total of 12 publications and 23 abstracts were produced as a result of this study. In particular, the compilation of a thermodynamic database utilizing consistent, current thermodynamic data is a major step toward accurately modeling multi-phase fluid interactions with solids. Existing databases designed for aqueous fluids did not mesh well with existing solid phase databases. Addition of a second liquid phase (CO2) magnifies the inconsistencies between aqueous and solid thermodynamic databases. Overall, the combination of high temperature and pressure lab studies (task 1), using a purpose built apparatus, and solid characterization (task 2), using XRCT and more developed technologies, allowed observation of dissolution and precipitation processes under CO2 reservoir conditions. These observations were combined with results from PIV experiments on multi-phase fluids (task 3) in typical flow path geometries. The results of the tasks 1, 2, and 3 were compiled and integrated into numerical models utilizing Lattice-Boltzmann simulations (task 4) to realistically model the physical processes and were ultimately folded into TOUGH2 code for reservoir scale modeling (task 5). Compilation of the thermodynamic database assisted comparisons to PIV experiments (Task 3) and greatly improved Lattice Boltzmann (Task 4) and TOUGH2 simulations (Task 5). PIV (Task 3) and experimental apparatus (Task 1) have identified problem areas in TOUGHREACT code. Additional lab experiments and coding work has been integrated into an improved numerical modeling code.
NASA Astrophysics Data System (ADS)
Trambauer, P.; Nonner, J.; Heijkers, J.; Uhlenbrook, S.
2011-02-01
The groundwater flow models currently used in the western part of The Netherlands and in other similar peaty areas are thought to be a too simplified representation of the hydrological reality. One of the reasons is that due to the schematization of the subsoil, its heterogeneity cannot be represented adequately. Moreover, the applicability of Darcy's law in these types of soils has been questioned, but this law forms the basis of most groundwater flow models. With the purpose of assessing the typical heterogeneity of the subsoil and to verify the applicability of Darcy's law fieldwork was completed at a research site in the western part of The Netherlands. The assessments were carried for the so called Complex Confining Layer (CCL), which is the Holocene peaty to clayey layer overlying Pleistocene sandy deposits. Borehole drilling through the CCL with a hand auger was completed and revealed the typical heterogeneous character of this layer showing a dominance of muddy, humified peat which is alternated with fresher peat and clay. Slug tests were carried out to study the applicability of Darcy's law given that previous studies suggested the non validity for humified peat soils given by a variable hydraulic conductivity K with the hydraulic gradient. For higher humification degrees, the experiments indeed suggested a variable K, but this seems to be the result of the inappropriate use of steady-state formulae for transient experiments in peaty environments. The muddy peat sampled has a rather plastic nature, and the high compressibility of this material leads to transient behavior. However, using transient formulae, the slug tests conducted for different initial hydraulic heads showed that there was hardly any evidence of a variation of the hydraulic conductivity with the hydraulic gradient. Therefore, Darcy's law can be used for peat soils. The heterogeneity of the subsoil and the apparent applicability of Darcy's law were taking into account for the detailed
NASA Astrophysics Data System (ADS)
Wienhöfer, J.; Zehe, E.
2012-04-01
Rapid lateral flow processes via preferential flow paths are widely accepted to play a key role for rainfall-runoff response in temperate humid headwater catchments. A quantitative description of these processes, however, is still a major challenge in hydrological research, not least because detailed information about the architecture of subsurface flow paths are often impossible to obtain at a natural site without disturbing the system. Our study combines physically based modelling and field observations with the objective to better understand how flow network configurations influence the hydrological response of hillslopes. The system under investigation is a forested hillslope with a small perennial spring at the study area Heumöser, a headwater catchment of the Dornbirnerach in Vorarlberg, Austria. In-situ points measurements of field-saturated hydraulic conductivity and dye staining experiments at the plot scale revealed that shrinkage cracks and biogenic macropores function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of artificial tracers at the hillslope scale. For modelling of water and solute transport, we followed the approach of implementing preferential flow paths as spatially explicit structures of high hydraulic conductivity and low retention within the 2D process-based model CATFLOW. Many potential configurations of the flow path network were generated as realisations of a stochastic process informed by macropore characteristics derived from the plot scale observations. Together with different realisations of soil hydraulic parameters, this approach results in a Monte Carlo study. The model setups were used for short-term simulation of a sprinkling and tracer experiment, and the results were evaluated against measured discharges and tracer breakthrough curves. Although both criteria were taken for model evaluation, still several model setups
Flow-based model of computer hackers' motivation.
Voiskounsky, Alexander E; Smyslova, Olga V
2003-04-01
Hackers' psychology, widely discussed in the media, is almost entirely unexplored by psychologists. In this study, hackers' motivation is investigated, using the flow paradigm. Flow is likely to motivate hackers, according to views expressed by researchers and by hackers themselves. Taken as granted that hackers experience flow, it was hypothesized that flow increases with the increase of hackers' competence in IT use. Self-selected subjects were recruited on specialized web sources; 457 hackers filled out a web questionnaire. Competence in IT use, specific flow experience, and demographic data were questioned. An on-line research was administered within the Russian-speaking community (though one third of Ss are non-residents of Russian Federation); since hacking seems to be international, the belief is expressed that the results are universal. The hypothesis is not confirmed: flow motivation characterizes the least and the most competent hackers, and the members of an intermediate group, that is, averagely competent Ss report the "flow crisis"-no (or less) flow experience. Two differing strategies of task choice were self-reported by Ss: a step-by-step increase of the difficulty of choices leads to a match of challenges and skills (and to preserving the flow experience); putting choices irrespective of the likelihood of solution leads to a "flow crisis." The findings give productive hints on processes of hackers' motivational development. The flow-based model of computer hackers' motivation was developed. It combines both empirically confirmed and theoretically possible ways of hackers' "professional" growth.
RANS turbulence model form uncertainty quantification for wind engineering flows
NASA Astrophysics Data System (ADS)
Gorle, Catherine; Zeoli, Stephanie; Bricteux, Laurent
2016-11-01
Reynolds-averaged Navier-Stokes simulations with linear eddy-viscosity turbulence models are commonly used for modeling wind engineering flows, but the use of the results for critical design decisions is hindered by the limited capability of the models to correctly predict bluff body flows. A turbulence model form uncertainty quantification (UQ) method to define confidence intervals for the results could remove this limitation, and promising results were obtained in a previous study of the flow in downtown Oklahoma City. The objective of the present study is to further investigate the validity of these results by considering the simplified test case of the flow around a wall-mounted cube. DNS data is used to determine: 1. whether the marker, which identifies regions that deviate from parallel shear flow, is a good indicator for the regions where the turbulence model fails, and 2. which Reynolds stress perturbations, in terms of the tensor magnitude and the eigenvalues and eigenvectors of the normalized anisotropy tensor, can capture the uncertainty in the flow field. A comparison of confidence intervals obtained with the UQ method and the DNS solution indicates that the uncertainty in the velocity field can be captured correctly in a large portion of the flow field.
Flow interaction based propagation model and bursty influence behavior analysis of Internet flows
NASA Astrophysics Data System (ADS)
Wu, Xiao-Yu; Gu, Ren-Tao; Ji, Yue-Feng
2016-11-01
QoS (quality of service) fluctuations caused by Internet bursty flows influence the user experience in the Internet, such as the increment of packet loss and transmission time. In this paper, we establish a mathematical model to study the influence propagation behavior of the bursty flow, which is helpful for developing a deep understanding of the network dynamics in the Internet complex system. To intuitively reflect the propagation process, a data flow interaction network with a hierarchical structure is constructed, where the neighbor order is proposed to indicate the neighborhood relationship between the bursty flow and other flows. The influence spreads from the bursty flow to each order of neighbors through flow interactions. As the influence spreads, the bursty flow has negative effects on the odd order neighbors and positive effects on the even order neighbors. The influence intensity of bursty flow decreases sharply between two adjacent orders and the decreasing degree can reach up to dozens of times in the experimental simulation. Moreover, the influence intensity increases significantly when network congestion situation becomes serious, especially for the 1st order neighbors. Network structural factors are considered to make a further study. Simulation results show that the physical network scale expansion can reduce the influence intensity of bursty flow by decreasing the flow distribution density. Furthermore, with the same network scale, the influence intensity in WS small-world networks is 38.18% and 18.40% lower than that in ER random networks and BA scale-free networks, respectively, due to a lower interaction probability between flows. These results indicate that the macro-structural changes such as network scales and styles will affect the inner propagation behaviors of the bursty flow.
Kløve, Bjørn; Xu, Shulan; Lindahl, Anna; Wörman, Anders; Søvik, Anne-Kristine
2005-01-01
Hydraulics of subsurface flow filters (SSF) was studied by measurement of soil hydraulic conductivity (K) variation and performing tracer tests in two SSF filters consisting of 1-4 mm Ca rich sand (shell sand). Soil samples were carefully taken at several locations in Filter I. A tracer experiment was conducted in the undisturbed Filter II using KI. The measured K variability in Filer I was used to analyze the variations in tracer breakthrough. The spatially distribution of K was obtained by fitting a variogram to observed data and interpolation using Kriging. The tracer residence probability density function (PDF) was determined by modelling the tracer movement with a 3-D groundwater model. The observed and simulated tracer arrival was compared for cases with constant K, constant K and dispersion (D), and for spatially variable K and dispersion. The results show that groundwater models were well suited to simulate solute movement in the SSF system studied. An almost perfect fit to observed tracer PDF was obtained when variable K and dispersion was included in the model. This indicates that information on K variability and dispersion is important for studying solute movement in SSF constructed wetlands.
Low Mach Number Modeling of Stratified Flows
NASA Astrophysics Data System (ADS)
Almgren, A. S.; Bell, J. B.; Nonaka, A.; Zingale, M.
2015-06-01
Low Mach number equation sets approximate the equations of motion of a compressible fluid by filtering out the sound waves, which allows the system to evolve on the advective rather than the acoustic time scale. Depending on the degree of approximation, low Mach number models retain some sub set of possible compressible effects. In this paper we give an overview of low Mach number methods for modeling stratified flows arising in astrophysics and atmospheric science as well as low Mach number reacting flows. We discuss how elements from the different fields are combined to form MAESTRO, a code for modeling low Mach number stratified flows with general equations of state, reactions and time-varying stratification.
Development of a coupled wave-flow-vegetation interaction model
Beudin, Alexis; Kalra, Tarandeep; Ganju, Neil Kamal; Warner, John C.
2017-01-01
Emergent and submerged vegetation can significantly affect coastal hydrodynamics. However, most deterministic numerical models do not take into account their influence on currents, waves, and turbulence. In this paper, we describe the implementation of a wave-flow-vegetation module into a Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system that includes a flow model (ROMS) and a wave model (SWAN), and illustrate various interacting processes using an idealized shallow basin application. The flow model has been modified to include plant posture-dependent three-dimensional drag, in-canopy wave-induced streaming, and production of turbulent kinetic energy and enstrophy to parameterize vertical mixing. The coupling framework has been updated to exchange vegetation-related variables between the flow model and the wave model to account for wave energy dissipation due to vegetation. This study i) demonstrates the validity of the plant posture-dependent drag parameterization against field measurements, ii) shows that the model is capable of reproducing the mean and turbulent flow field in the presence of vegetation as compared to various laboratory experiments, iii) provides insight into the flow-vegetation interaction through an analysis of the terms in the momentum balance, iv) describes the influence of a submerged vegetation patch on tidal currents and waves separately and combined, and v) proposes future directions for research and development.
Development of a coupled wave-flow-vegetation interaction model
NASA Astrophysics Data System (ADS)
Beudin, Alexis; Kalra, Tarandeep S.; Ganju, Neil K.; Warner, John C.
2017-03-01
Emergent and submerged vegetation can significantly affect coastal hydrodynamics. However, most deterministic numerical models do not take into account their influence on currents, waves, and turbulence. In this paper, we describe the implementation of a wave-flow-vegetation module into a Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system that includes a flow model (ROMS) and a wave model (SWAN), and illustrate various interacting processes using an idealized shallow basin application. The flow model has been modified to include plant posture-dependent three-dimensional drag, in-canopy wave-induced streaming, and production of turbulent kinetic energy and enstrophy to parameterize vertical mixing. The coupling framework has been updated to exchange vegetation-related variables between the flow model and the wave model to account for wave energy dissipation due to vegetation. This study i) demonstrates the validity of the plant posture-dependent drag parameterization against field measurements, ii) shows that the model is capable of reproducing the mean and turbulent flow field in the presence of vegetation as compared to various laboratory experiments, iii) provides insight into the flow-vegetation interaction through an analysis of the terms in the momentum balance, iv) describes the influence of a submerged vegetation patch on tidal currents and waves separately and combined, and v) proposes future directions for research and development.
Modelling water flow under glaciers and ice sheets
Flowers, Gwenn E.
2015-01-01
Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development. PMID:27547082
Hassan, Yassin; Anand, Nk
2016-03-30
A 1/16th scaled VHTR experimental model was constructed and the preliminary test was performed in this study. To produce benchmark data for CFD validation in the future, the facility was first run at partial operation with five pipes being heated. PIV was performed to extract the vector velocity field for three adjacent naturally convective jets at statistically steady state. A small recirculation zone was found between the pipes, and the jets entered the merging zone at 3 cm from the pipe outlet but diverged as the flow approached the top of the test geometry. Turbulence analysis shows the turbulence intensity peaked at 41-45% as the jets mixed. A sensitivity analysis confirmed that 1000 frames were sufficient to measure statistically steady state. The results were then validated by extracting the flow rate from the PIV jet velocity profile, and comparing it with an analytic flow rate and ultrasonic flowmeter; all flow rates lie within the uncertainty of the other two methods for Tests 1 and 2. This test facility can be used for further analysis of naturally convective mixing, and eventually produce benchmark data for CFD validation for the VHTR during a PCC or DCC accident scenario. Next, a PTV study of 3000 images (1500 image pairs) were used to quantify the velocity field in the upper plenum. A sensitivity analysis confirmed that 1500 frames were sufficient to precisely estimate the flow. Subsequently, three (3, 9, and 15 cm) Y-lines from the pipe output were extracted to consider the output differences between 50 to 1500 frames. The average velocity field and standard deviation error that accrued in the three different tests were calculated to assess repeatability. The error was varied, from 1 to 14%, depending on Y-elevation. The error decreased as the flow moved farther from the output pipe. In addition, turbulent intensity was calculated and found to be high near the output. Reynolds stresses and turbulent intensity were used to validate the data by
Model flocks in a steady vortical flow
NASA Astrophysics Data System (ADS)
Baggaley, A. W.
2015-05-01
We modify the standard Vicsek model to clearly distinguish between intrinsic noise due to imperfect alignment between organisms and extrinsic noise due to fluid motion. We then consider the effect of a steady vortical flow, the Taylor-Green vortex, on the dynamics of the flock, for various flow speeds, with a fixed intrinsic particle speed. We pay particular attention to the morphology of the flow, and quantify its filamentarity. Strikingly, above a critical flow speed there is a pronounced increase in the filamentarity of the flock, when compared to the zero-flow case. This is due to the fact that particles appear confined to areas of low vorticity; a familiar phenomena, commonly seen in the clustering of inertial particles in vortical flows. Hence, the cooperative motion of the particles gives them an effective inertia, which is seen to have a profound effect on the morphology of the flock, in the presence of external fluid motion. Finally, we investigate the angle between the flow and the particles direction of movement and find it follows a power-law distribution.
A Substance Flow Model for Global Phosphorus
NASA Astrophysics Data System (ADS)
Vaccari, D. A.
2015-12-01
A system-based substance flow model (SFM) for phosphorus is developed based on the global phosphorus substance flow analysis (SFA) of Cordell et al (2009). The model is based strictly on mass balance considerations. It predicts the sensitivity of phosphorus consumption to various interventions intended to conserve reserves, as well as interactions among these efforts, allowing a comparison of their impacts on phosphorus demand. The interventions include control of phosphorus losses from soil erosion, food production and food waste, or phosphorus recycling such as from animal manure or human waste.
Path Flow Estimation Using Time Varying Coefficient State Space Model
NASA Astrophysics Data System (ADS)
Jou, Yow-Jen; Lan, Chien-Lun
2009-08-01
The dynamic path flow information is very crucial in the field of transportation operation and management, i.e., dynamic traffic assignment, scheduling plan, and signal timing. Time-dependent path information, which is important in many aspects, is nearly impossible to be obtained. Consequently, researchers have been seeking estimation methods for deriving valuable path flow information from less expensive traffic data, primarily link traffic counts of surveillance systems. This investigation considers a path flow estimation problem involving the time varying coefficient state space model, Gibbs sampler, and Kalman filter. Numerical examples with part of a real network of the Taipei Mass Rapid Transit with real O-D matrices is demonstrated to address the accuracy of proposed model. Results of this study show that this time-varying coefficient state space model is very effective in the estimation of path flow compared to time-invariant model.
A new dynamic model for heterogeneous traffic flow
NASA Astrophysics Data System (ADS)
Tang, T. Q.; Huang, H. J.; Zhao, S. G.; Shang, H. Y.
2009-06-01
Based on the property of heterogeneous traffic flow, we in this Letter present a new car-following model. Applying the relationship between the micro and macro variables, a new dynamic model for heterogeneous traffic flow is obtained. The fundamental diagram and the jam density of the heterogeneous traffic flow consisting of bus and car are studied under three different conditions: (1) without any restrictions, (2) under the action of the traffic control policy that restrains some private cars and (3) using bus to replace the private cars restrained by the traffic control policy. The numerical results show that our model can describe some qualitative properties of the heterogeneous traffic flow consisting of bus and car, which verifies that our model is reasonable.
Model Reduction for Flow Analysis and Control
NASA Astrophysics Data System (ADS)
Rowley, Clarence W.; Dawson, Scott T. M.
2017-01-01
Advances in experimental techniques and the ever-increasing fidelity of numerical simulations have led to an abundance of data describing fluid flows. This review discusses a range of techniques for analyzing such data, with the aim of extracting simplified models that capture the essential features of these flows, in order to gain insight into the flow physics, and potentially identify mechanisms for controlling these flows. We review well-developed techniques, such as proper orthogonal decomposition and Galerkin projection, and discuss more recent techniques developed for linear systems, such as balanced truncation and dynamic mode decomposition (DMD). We then discuss some of the methods available for nonlinear systems, with particular attention to the Koopman operator, an infinite-dimensional linear operator that completely characterizes the dynamics of a nonlinear system and provides an extension of DMD to nonlinear systems.
Modeling of the Bosphorus exchange flow dynamics
NASA Astrophysics Data System (ADS)
Sözer, Adil; Özsoy, Emin
2017-01-01
The fundamental hydrodynamic behavior of the Bosphorus Strait is investigated through a numerical modeling study using alternative configurations of idealized or realistic geometry. Strait geometry and basin stratification conditions allow for hydraulic controls and are ideally suited to support the maximal-exchange regime, which determines the rate of exchange of waters originating from the adjacent Black and Mediterranean Seas for a given net transport. Steady-state hydraulic controls are demonstrated by densimetric Froude number calculations under layered flow approximations when corrections are applied to account for high velocity shears typically observed in the Bosphorus. Analyses of the model results reveal many observed features of the strait, including critical transitions at hydraulic controls and dissipation by turbulence and hydraulic jumps. It is found that the solution depends on initialization, especially with respect to the basin initial conditions. Significant differences between the controlled maximal-exchange and drowned solutions suggest that a detailed modeling implementation involving coupling with adjacent basins needs to take full account of the Bosphorus Strait in terms of the physical processes to be resolved.
PWR internal flow modeling with fuel assemblies details
Popov, E.; Yan, J.; Karoutas, Z.; Gehin, J.; Brewster, R.; Baglietto, E.
2012-07-01
This study is an example of a massive parallel computing of the coolant flow in a nuclear reactor. It resolves the flow velocities in each assembly on pin level and predicts the flow distribution in complex geometries such as the lower and upper reactor plenums. The size of the developed model (1.035 billion cells) required the runs to be executed on the NCCS clusters (www.nccs.gov). STAR-CCM+ code (www.ed-adapco.com) was installed on two clusters: JAGUARXT5 and FROST, both of which were capable of executing this model. (authors)
The down-wind dispersal of pollen and the airborne spread of seed are affected by the size, shape and weight of the particles and by the strength, buoyancy and direction of surface winds. An atmospheric model (HYSPLIT model: www.arl.noaa.gov\\ready.html) was used to reconstruct w...
A compressible model of soap film flow
NASA Astrophysics Data System (ADS)
Fast, Petri
2004-11-01
We consider flowing soap films, and present a new theoretical model that resembles the compressible two dimensional Navier-Stokes equations. In experiments, the thickness of a gravity driven soap film can undergo significant variations. The thickness of the soap film plays the role of a density field in a 2D model: Hence significant thickness variations give rise to 2D compressibility effects that have been observed in experiments. We present a systematic derivation of a new compressible model of soap film flow using thin film asymptotics. We discuss the properties of the model, and present criteria for using the incompressible or compressible limiting equations. The properties of the model are illustrated with computational experiments.
Modeling Stromatolite Growth Under Oscillatory Flows
NASA Astrophysics Data System (ADS)
Patel, H. J.; Gong, J.; Tice, M. M.
2014-12-01
Stromatolite growth models based on diffusion limited aggregation (DLA) has been fairly successful at producing features commonly recognized in stromatolitic structures in the rock record. These models generally require slow mixing of solutes at time scales comparable to the growth of organisms and largely ignore fluid erosions. Recent research on microbial mats suggests that fluid flow might have a dominant control on the formation, deformation and erosion of surface microbial structures, raising the possibility that different styles of fluid flow may influence the morphology of stromatolites. Many stromatolites formed in relatively high energy, shallow water environments under oscillatory currents driven by wind-induced waves. In order to investigate the potential role of oscillatory flows in shaping stromatolites, we are constructing a numerical model of stromatolite growth parameterized by flume experiments with cyanobacterial biofilms. The model explicitly incorporates reaction-diffusion processes, surface deformation and erosion, biomass growth, sedimentation and mineral precipitation. A Lattice-Boltzmann numerical scheme was applied to the reaction-diffusion equations in order to boost computational efficiency. A basic finite element method was employed to compute surface deformation and erosion. Growth of biomass, sedimentation and carbonate precipitation was based on a modified discrete cellular automata scheme. This model will be used to test an alternative hypothesis for the formation of stromatolites in higher energy, shallow and oscillatory flow environments.
Stream flow and analysis study
Jackson, D.G.
1983-11-04
Lockwood Greene Engineers, Inc. (LGE) was retained by E.I. duPont de Nemours and Co., Inc., Savannah River Plant, Aiken, South Carolina, to conduct on-site flow measurements and sampling of tributaries and outfalls flowing into a portion of Tim`s Branch Creek. Water samples were analyzed for chemical characteristics. This report presents the results of the flow and analytical data collected during the 24 hour monitoring period, October 5 and 6, 1983. Tim`s Branch Creek is a tributary of the Upper Three Runs Creek which in turn is a tributary of the Savannah River. A map outlining the drainage area within the Savannah River Plant is included in this report.
A heat transfer model for slug flow boiling within microchannels
NASA Astrophysics Data System (ADS)
Magnini, Mirco; Thome, John
2016-11-01
We propose a novel physics-based model for the fluid mechanics and heat transfer associated with slug flow boiling in horizontal circular microchannels, to update the widely used three-zone model for the design of multi-microchannel evaporators. The flow is modelled as the cyclic passage of a liquid slug, an elongated bubble which traps a thin liquid film against the channel wall, and a dry vapor plug. The capillary flow theory, extended to incorporate evaporation effects, is applied to estimate the bubble velocity along the channel. A liquid film thickness prediction method considering bubble proximity effects, which may limit the radial extension of the film, is included. Theoretical heat transfer models accounting for the thermal inertia of the liquid film and for the recirculating flow within the liquid slug are utilized. The heat transfer model is compared to experimental data taken from three independent studies: 833 slug flow boiling data points covering R134a, R245fa and R236fa and channel diameters from 0.4 mm to 1 mm. The new model predicts more than 80% of the database to within +/- 30 % and it represents an important step toward a complete physics-based modelling of bubble dynamics and heat transfer within microchannels under evaporating flow conditions.
Stochastic modeling of a lava-flow aquifer system
Cronkite-Ratcliff, Collin; Phelps, Geoffrey A.
2014-01-01
This report describes preliminary three-dimensional geostatistical modeling of a lava-flow aquifer system using a multiple-point geostatistical model. The purpose of this study is to provide a proof-of-concept for this modeling approach. An example of the method is demonstrated using a subset of borehole geologic data and aquifer test data from a portion of the Calico Hills Formation, a lava-flow aquifer system that partially underlies Pahute Mesa, Nevada. Groundwater movement in this aquifer system is assumed to be controlled by the spatial distribution of two geologic units—rhyolite lava flows and zeolitized tuffs. The configuration of subsurface lava flows and tuffs is largely unknown because of limited data. The spatial configuration of the lava flows and tuffs is modeled by using a multiple-point geostatistical simulation algorithm that generates a large number of alternative realizations, each honoring the available geologic data and drawn from a geologic conceptual model of the lava-flow aquifer system as represented by a training image. In order to demonstrate how results from the geostatistical model could be analyzed in terms of available hydrologic data, a numerical simulation of part of an aquifer test was applied to the realizations of the geostatistical model.
Hybrid laminar flow control study
NASA Technical Reports Server (NTRS)
1982-01-01
Hybrid laminar flow control (HLFC) in which leading edge suction is used in conjunction with wing pressure distribution tailoring to postpone boundary layer transition and reduce friction drag was examined. Airfoil design characteristics required for laminar flow control (LFC) were determined. The aerodynamic design of the HLFC wing for a 178 passenger commercial turbofan transport was developed, and a drag was estimated. Systems changes required to install HLFC were defined, and weights and fuel economy were estimated. The potential for 9% fuel reduction for a 3926-km (2120-nmi) mission is identified.
On a Decomposition Model for Optical Flow
NASA Astrophysics Data System (ADS)
Abhau, Jochen; Belhachmi, Zakaria; Scherzer, Otmar
In this paper we present a variational method for determining cartoon and texture components of the optical flow of a noisy image sequence. The method is realized by reformulating the optical flow problem first as a variational denoising problem for multi-channel data and then by applying decomposition methods. Thanks to the general formulation, several norms can be used for the decomposition. We study a decomposition for the optical flow into bounded variation and oscillating component in greater detail. Numerical examples demonstrate the capabilities of the proposed approach.
Pan, Wenxiao; Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George E.
2011-05-27
In this work we compare the predictive capability of two mathematical models for red blood cells (RBCs) focusing on blood flow in capillaries and arterioles. Both RBC models as well as their corresponding blood flows are based on the dissipative particle dynamics (DPD) method, a coarse-grained molecular dynamics approach. The first model employs a multiscale description of the RBC (MS-RBC), with its membrane represented by hundreds or even thousands of DPD-particles connected by springs into a triangular network in combination with out-of-plane elastic bending resistance. Extra dissipation within the network accounts for membrane viscosity, while the characteristic biconcave RBC shape is achieved by imposition of constraints for constant membrane area and constant cell volume. The second model is based on a low-dimensional description (LD-RBC) constructed as a closed torus-like ring of only 10 large DPD colloidal particles. They are connected into a ring by worm-like chain (WLC) springs combined with bending resistance. The LD-RBC model can be fitted to represent the entire range of nonlinear elastic deformations as measured by optical-tweezers for healthy and for infected RBCs in malaria. MS-RBCs suspensions model the dynamics and rheology of blood flow accurately for any size vessel but this approach is computationally expensive above 100 microns. Surprisingly, the much more economical suspensions of LD-RBCs also capture the blood flow dynamics and rheology accurately except for vessels with sizes comparable to RBC diameter. In particular, the LD-RBC suspensions are shown to properly capture the experimental data for the apparent viscosity of blood and its cell-free layer (CFL) in tube flow. Taken together, these findings suggest a hierarchical approach in modeling blood flow in the arterial tree, whereby the MS-RBC model should be employed for capillaries and arterioles below 100 microns, the LD-RBC model for arterioles, and the continuum description for
Present-day heat flow model of Mars.
Parro, Laura M; Jiménez-Díaz, Alberto; Mansilla, Federico; Ruiz, Javier
2017-04-03
Until the acquisition of in-situ measurements, the study of the present-day heat flow of Mars must rely on indirect methods, mainly based on the relation between the thermal state of the lithosphere and its mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the radiogenic heat production of the crust and mantle, on scaling of heat flow variations arising from crustal thickness and topography variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model finds heat flows varying between 14 and 25 mW m(-2), with an average value of 19 mW m(-2). Similar results (although about ten percent higher) are obtained if we use heat flow based on the lithospheric strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and total heat loss through the surface), we estimate values close to 0.7-0.75, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with the low heat flow values deduced from lithosphere strength), unless heat-producing elements abundances for Mars are subchondritic.
Present-day heat flow model of Mars
Parro, Laura M.; Jiménez-Díaz, Alberto; Mansilla, Federico; Ruiz, Javier
2017-01-01
Until the acquisition of in-situ measurements, the study of the present-day heat flow of Mars must rely on indirect methods, mainly based on the relation between the thermal state of the lithosphere and its mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the radiogenic heat production of the crust and mantle, on scaling of heat flow variations arising from crustal thickness and topography variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model finds heat flows varying between 14 and 25 mW m−2, with an average value of 19 mW m−2. Similar results (although about ten percent higher) are obtained if we use heat flow based on the lithospheric strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and total heat loss through the surface), we estimate values close to 0.7–0.75, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with the low heat flow values deduced from lithosphere strength), unless heat-producing elements abundances for Mars are subchondritic. PMID:28367996
Improved modeling techniques for turbomachinery flow fields
Lakshminarayana, B.; Fagan, J.R. Jr.
1995-10-01
This program has the objective of developing an improved methodology for modeling turbomachinery flow fields, including the prediction of losses and efficiency. Specifically, the program addresses the treatment of the mixing stress tensor terms attributed to deterministic flow field mechanisms required in steady-state Computational Fluid Dynamic (CFD) models for turbo-machinery flow fields. These mixing stress tensors arise due to spatial and temporal fluctuations (in an absolute frame of reference) caused by rotor-stator interaction due to various blade rows and by blade-to-blade variation of flow properties. These tasks include the acquisition of previously unavailable experimental data in a high-speed turbomachinery environment, the use of advanced techniques to analyze the data, and the development of a methodology to treat the deterministic component of the mixing stress tensor. Penn State will lead the effort to make direct measurements of the momentum and thermal mixing stress tensors in high-speed multistage compressor flow field in the turbomachinery laboratory at Penn State. They will also process the data by both conventional and conditional spectrum analysis to derive momentum and thermal mixing stress tensors due to blade-to-blade periodic and aperiodic components, revolution periodic and aperiodic components arising from various blade rows and non-deterministic (which includes random components) correlations. The modeling results from this program will be publicly available and generally applicable to steady-state Navier-Stokes solvers used for turbomachinery component (compressor or turbine) flow field predictions. These models will lead to improved methodology, including loss and efficiency prediction, for the design of high-efficiency turbomachinery and drastically reduce the time required for the design and development cycle of turbomachinery.
The lagRST Model: A Turbulence Model for Non-Equilibrium Flows
NASA Technical Reports Server (NTRS)
Lillard, Randolph P.; Oliver, A. Brandon; Olsen, Michael E.; Blaisdell, Gregory A.; Lyrintzis, Anastasios S.
2011-01-01
This study presents a new class of turbulence model designed for wall bounded, high Reynolds number flows with separation. The model addresses deficiencies seen in the modeling of nonequilibrium turbulent flows. These flows generally have variable adverse pressure gradients which cause the turbulent quantities to react at a finite rate to changes in the mean flow quantities. This "lag" in the response of the turbulent quantities can t be modeled by most standard turbulence models, which are designed to model equilibrium turbulent boundary layers. The model presented uses a standard 2-equation model as the baseline for turbulent equilibrium calculations, but adds transport equations to account directly for non-equilibrium effects in the Reynolds Stress Tensor (RST) that are seen in large pressure gradients involving shock waves and separation. Comparisons are made to several standard turbulence modeling validation cases, including an incompressible boundary layer (both neutral and adverse pressure gradients), an incompressible mixing layer and a transonic bump flow. In addition, a hypersonic Shock Wave Turbulent Boundary Layer Interaction with separation is assessed along with a transonic capsule flow. Results show a substantial improvement over the baseline models for transonic separated flows. The results are mixed for the SWTBLI flows assessed. Separation predictions are not as good as the baseline models, but the over prediction of the peak heat flux downstream of the reattachment shock that plagues many models is reduced.
Mathematical Modeling of Electrochemical Flow Capacitors
Hoyt, NC; Wainright, JS; Savinell, RF
2015-01-13
Electrochemical flow capacitors (EFCs) for grid-scale energy storage are a new technology that is beginning to receive interest. Prediction of the expected performance of such systems is important as modeling can be a useful avenue in the search for design improvements. Models based off of circuit analogues exist to predict EFC performance, but these suffer from deficiencies (e.g. a multitude of fitting constants that are required and the ability to analyze only one spatial direction at a time). In this paper mathematical models based off of three-dimensional macroscopic balances (similar to models for porous electrodes) are reported. Unlike existing three-dimensional porous electrode-based approaches for modeling slurry electrodes, advection (i.e., transport associated with bulk fluid motion) of the overpotential is included in order to account for the surface charge at the interface between flowing particles and the electrolyte. Doing so leads to the presence of overpotential boundary layers that control the performance of EFCs. These models were used to predict the charging behavior of an EFC under both flowing and non-flowing conditions. Agreement with experimental data was good, including proper prediction of the steady-state current that is achieved during charging of a flowing EFC. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. All rights reserved.
Clark, Joseph B; Guan, Yulong; McCoach, Robert; Kunselman, Allen R; Myers, John L; Undar, Akif
2011-05-01
During extracorporeal life support with centrifugal blood pumps, retrograde pump flow may occur when the pump revolutions decrease below a critical value determined by the circuit resistance and the characteristics of the pump. We created a laboratory model to evaluate the occurrence of retrograde flow in each of three centrifugal blood pumps: the Rotaflow, the CentriMag, and the Bio-Medicus BP-50. At simulated patient pressures of 60, 80, and 100 mmHg, each pump was evaluated at speeds from 1000 to 2200 rpm and flow rates were measured. Retrograde flow occurred at low revolution speeds in all three centrifugal pumps. The Bio-Medicus pump was the least likely to demonstrate retrograde flow at low speeds, followed by the Rotaflow pump. The CentriMag pump showed the earliest transition to retrograde flow, as well as the highest degree of retrograde flow. At every pump speed evaluated, the Bio-Medicus pump delivered the highest antegrade flow and the CentriMag pump delivered the least.
Application of Wall-modeled LES to Turbulent Separated Flows
NASA Astrophysics Data System (ADS)
Iyer, Prahladh S.; Park, George I.; Malik, Mujeeb R.
2016-11-01
Resolved Large-Eddy Simulations (LES) and Direct Numerical Simulations (DNS) are unaffordable for very high Reynolds number (Re) wall-bounded flows. While the Reynolds Averaged Navier-Stokes (RANS) based methods predict high Re attached flows accurately with little cost, their fidelity is degraded significantly in flows involving separation. A popular compromise between cost and accuracy is to use a Wall-modeled LES (WMLES) approach. In WMLES, the outer portion of the boundary layer is resolved with LES while the inner portion is modeled. In order to assess the performance of the widely used wall-stress models in separated flows, we perform WMLES simulations using an unstructured, compressible finite volume LES solver. The equilibrium and non-equilibrium wall models that require the solution of the simplified/full RANS on a separate near-wall domain are employed. Two configurations are studied: the shock-induced separation in a transonic flow over an axisymmetric bump placed on a cylinder, and a low-Mach flow past a NACA 4412 airfoil at a near-stall condition. Detailed comparisons will be made with available experimental data to comment on the applicability of WMLES in predicting complex turbulent flows involving separation.
Fuzzy Temporal Logic Based Railway Passenger Flow Forecast Model
Dou, Fei; Jia, Limin; Wang, Li; Xu, Jie; Huang, Yakun
2014-01-01
Passenger flow forecast is of essential importance to the organization of railway transportation and is one of the most important basics for the decision-making on transportation pattern and train operation planning. Passenger flow of high-speed railway features the quasi-periodic variations in a short time and complex nonlinear fluctuation because of existence of many influencing factors. In this study, a fuzzy temporal logic based passenger flow forecast model (FTLPFFM) is presented based on fuzzy logic relationship recognition techniques that predicts the short-term passenger flow for high-speed railway, and the forecast accuracy is also significantly improved. An applied case that uses the real-world data illustrates the precision and accuracy of FTLPFFM. For this applied case, the proposed model performs better than the k-nearest neighbor (KNN) and autoregressive integrated moving average (ARIMA) models. PMID:25431586
Fuzzy temporal logic based railway passenger flow forecast model.
Dou, Fei; Jia, Limin; Wang, Li; Xu, Jie; Huang, Yakun
2014-01-01
Passenger flow forecast is of essential importance to the organization of railway transportation and is one of the most important basics for the decision-making on transportation pattern and train operation planning. Passenger flow of high-speed railway features the quasi-periodic variations in a short time and complex nonlinear fluctuation because of existence of many influencing factors. In this study, a fuzzy temporal logic based passenger flow forecast model (FTLPFFM) is presented based on fuzzy logic relationship recognition techniques that predicts the short-term passenger flow for high-speed railway, and the forecast accuracy is also significantly improved. An applied case that uses the real-world data illustrates the precision and accuracy of FTLPFFM. For this applied case, the proposed model performs better than the k-nearest neighbor (KNN) and autoregressive integrated moving average (ARIMA) models.
Carreau model for oscillatory blood flow in a tube
NASA Astrophysics Data System (ADS)
Tabakova, S.; Nikolova, E.; Radev, St.
2014-11-01
The analysis of the blood flow dynamics (hemodynamics) in tubes is crucial when investigating the rupture of different types of aneurysms. The blood viscosity nonlinear dependence on the flow shear rate creates complicated manifestations of the blood pulsations. Although a great number of studies exists, experimental and numerical, this phenomenon is still not very well understood. The aim of the present work is to propose a numerical model of the oscillatory blood flow in a tube on the basis of the Carreau model of the blood viscosity (nonlinear model with respect to the shear rate). The obtained results for the flow velocity and tangential stress on the tube wall are compared well with other authors' results.
Transition and Turbulence Modeling for Blunt-Body Wake Flows
NASA Technical Reports Server (NTRS)
Nance, Robert P.; Horvath, Thomas J.; Hassan, H. A.
1997-01-01
This study attempts t o improve the modeling and computational prediction of high- speed transitional wake flows. The recently developed kappa - zeta (Enstrophy) turbulence model is coupled with a newly developed transition prediction method and implemented in an implicit flow solver well-suited to hypersonic flows. In this model, transition onset is determined as part of the solution. Results obtained using the new model for a 70- deg blunted cone/sting geometry demonstrate better agreement with experimental heat- transfer measurements when compared to laminar calculations as well as solutions using the kappa - omega model. Results are also presented for the situation where transition onset is preselected. It is shown that, in this case, results are quite sensitive to location of the transition point.
NASA Astrophysics Data System (ADS)
Schneider, D.; Delgado Granados, H.; Huggel, C.; Kääb, A.
2008-06-01
Lahars frequently affect the slopes of ice-capped volcanoes. They can be triggered by volcano-ice interactions during eruptions but also by processes such as intense precipitation or by outbursts of glacial water bodies not directly related to eruptive activity. We use remote sensing, GIS and lahar models in combination with ground observations for an initial lahar hazard assessment on Iztaccíhuatl volcano (5230 m a.s.l.), considering also possible future developments of the glaciers on the volcano. Observations of the glacial extent are important for estimations of future hazard scenarios, especially in a rapidly changing tropical glacial environment. In this study, analysis of the glaciers on Iztaccíhuatl shows a dramatic retreat during the last 150 years: the glaciated area in 2007 corresponds to only 4% of the one in 1850 AD and the glaciers are expected to survive no later than the year 2020. Most of the glacial retreat is considered to be related to climate change but in-situ observations suggest also that geo- and hydrothermal heat flow at the summit-crater area can not be ruled out, as emphasized by fumarolic activity documented in a former study. However, development of crater lakes and englacial water reservoirs are supposed to be a more realistic scenario for lahar generation than sudden ice melting by rigorous volcano-ice interaction. Model calculations show that possible outburst floods have to be larger than ~5×105 m3 or to achieve an H/L ratio (Height/runout Length) of 0.2 and lower in order to reach the populated lower flanks. This threshold volume equals 2.4% melted ice of Iztaccíhuatl's total ice volume in 2007, assuming 40% water and 60% volumetric debris content of a potential lahar. The model sensitivity analysis reveals important effects of the generic type of the Digital Terrain Model (DTM) used on the results. As a consequence, the predicted affected areas can vary significantly. For such hazard zonation, we therefore suggest the use of
Flow stress model in metal cutting
NASA Technical Reports Server (NTRS)
Black, J. T.
1978-01-01
A model for the plastic deformation that occurs in metal cutting, based on dislocation mechanics, is presented. The model explains the fundamental deformation structure that develops during machining and is based on the well known Cottrell-Stokes Law, wherein the flow stress is partitioned into two parts; an athermal part which occurs in the shear fronts (or shear bands); and a thermal part which occurs in the lamella regions. The deformation envokes the presence of a cellular dislocation distribution which always exists in the material ahead of the shear process. This 'alien' dislocation distribution either exists in the metal prior to cutting or is produced by the compressive stress field which operates in front of the shear process. The magnitude of the flow stress and direction of the shear are shown to be correlated to the stacking fault energy of the metal being cut. The model is tested with respect to energy consumption rates and found to be consistent with observed values.
Continuum modeling of cooperative traffic flow dynamics
NASA Astrophysics Data System (ADS)
Ngoduy, D.; Hoogendoorn, S. P.; Liu, R.
2009-07-01
This paper presents a continuum approach to model the dynamics of cooperative traffic flow. The cooperation is defined in our model in a way that the equipped vehicle can issue and receive a warning massage when there is downstream congestion. Upon receiving the warning massage, the (up-stream) equipped vehicle will adapt the current desired speed to the speed at the congested area in order to avoid sharp deceleration when approaching the congestion. To model the dynamics of such cooperative systems, a multi-class gas-kinetic theory is extended to capture the adaptation of the desired speed of the equipped vehicle to the speed at the downstream congested traffic. Numerical simulations are carried out to show the influence of the penetration rate of the equipped vehicles on traffic flow stability and capacity in a freeway.
2007-12-01
pump inlet, on the priming of the waterjets. Visual observations as to the state of fluid flow through the waterjets indicated that the initial waterjet...Example model-scale rotor force variations due to yaw angle, port outboard rotor .......... 5 3. Model 5662-1 pump inlet diagram showing submergence...criteria definition .................. 6 4. Model-scale rotor RPM to attain primed waterjets at tested pump inlet submergences and m odel speeds
Experimental evaluations of the microchannel flow model
NASA Astrophysics Data System (ADS)
Parker, K. J.
2015-06-01
Recent advances have enabled a new wave of biomechanics measurements, and have renewed interest in selecting appropriate rheological models for soft tissues such as the liver, thyroid, and prostate. The microchannel flow model was recently introduced to describe the linear response of tissue to stimuli such as stress relaxation or shear wave propagation. This model postulates a power law relaxation spectrum that results from a branching distribution of vessels and channels in normal soft tissue such as liver. In this work, the derivation is extended to determine the explicit link between the distribution of vessels and the relaxation spectrum. In addition, liver tissue is modified by temperature or salinity, and the resulting changes in tissue responses (by factors of 1.5 or greater) are reasonably predicted from the microchannel flow model, simply by considering the changes in fluid flow through the modified samples. The 2 and 4 parameter versions of the model are considered, and it is shown that in some cases the maximum time constant (corresponding to the minimum vessel diameters), could be altered in a way that has major impact on the observed tissue response. This could explain why an inflamed region is palpated as a harder bump compared to surrounding normal tissue.
Experimental evaluations of the microchannel flow model.
Parker, K J
2015-06-07
Recent advances have enabled a new wave of biomechanics measurements, and have renewed interest in selecting appropriate rheological models for soft tissues such as the liver, thyroid, and prostate. The microchannel flow model was recently introduced to describe the linear response of tissue to stimuli such as stress relaxation or shear wave propagation. This model postulates a power law relaxation spectrum that results from a branching distribution of vessels and channels in normal soft tissue such as liver. In this work, the derivation is extended to determine the explicit link between the distribution of vessels and the relaxation spectrum. In addition, liver tissue is modified by temperature or salinity, and the resulting changes in tissue responses (by factors of 1.5 or greater) are reasonably predicted from the microchannel flow model, simply by considering the changes in fluid flow through the modified samples. The 2 and 4 parameter versions of the model are considered, and it is shown that in some cases the maximum time constant (corresponding to the minimum vessel diameters), could be altered in a way that has major impact on the observed tissue response. This could explain why an inflamed region is palpated as a harder bump compared to surrounding normal tissue.
Three-phase CFD analytical modeling of blood flow.
Jung, J.; Hassanein, A.; Mathematics and Computer Science
2008-01-01
The behavior of blood cells in disturbed flow regions of arteries has significant relevance for understanding atherogenesis. However, their distribution with red blood cells (RBCs) and leukocytes is not so well studied and understood. Our three-phase computational fluid dynamics approach including plasma, RBCs, and leukocytes was used to numerically simulate the local hemodynamics in such a flow regime. This model has tracked the wall shear stress (WSS), phase distributions, and flow patterns for each phase in a concentrated suspension shear flow of blood. Unlike other computational approaches, this approach does not require dispersion coefficients as an input. The non-Newtonian viscosity model was applied to a wide physiological range of hematocrits, including low shear rates. The migration and segregation of blood cells in disturbed flow regions were computed, and the results compared favorably with available experimental data. The predicted higher leukocyte concentration was correlated with relatively low WSS near the stenosis having a high WSS. This behavior was attributed to flow-dependent interactions of the leukocytes with RBCs in pulsatile flow. This three-phase hemodynamic analysis may have application to vulnerable plaque formation in arteries with in vivo complex flow conditions.
Experimental Study of Plasma Control of an Unstarting Supersonic Flow
NASA Astrophysics Data System (ADS)
Im, Seong-Kyun; Do, Hyungrok; Cappelli, Mark A.
2011-11-01
Experimental studies of the control of unstarting supersonic model inlet flows using Dielectric Barrier Discharges (DBD) is demonstrated at Mach 4.7 flow conditions and a static temperature of ~60K and static pressure of ~1kPa. Planar Laser Rayleigh Scattering (PLRS) is used to visualize important flow features, such as boundary layers and shockwaves. Supersonic flow unstart is initiated by injecting mass into model inlet flows of either laminar or tripped turbulent boundary layer flow conditions. DBD discharge actuation of the tripped turbulent flow delays the unstart process, shifting the unstart dynamics closer to what is seen for the laminar boundary layer case. In all studies, a single DBD actuator pair is used, oriented parallel to the freestream flow, generating spanwise disturbances. It is proposed that strong suction flow which brings high momentum freestream flow near exposed electrode can be a mechanism of this actuation. PLRS reveals that this actuation is spatially confined to the regions close to the actuator electrodes, greatly limiting their performance. This material is based upon work supported by the Department of Energy under Award Number(s)DE-FC52-08NA28614.
Symposium on unsaturated flow and transport modeling
Arnold, E.M.; Gee, G.W.; Nelson, R.W.
1982-09-01
This document records the proceedings of a symposium on flow and transport processes in partially saturated groundwater systems, conducted at the Battelle Seattle Research Center on March 22-24, 1982. The symposium was sponsored by the US Nuclear Regulatory Commission for the purpose of assessing the state-of-the-art of flow and transport modeling for use in licensing low-level nuclear waste repositories in partially saturated zones. The first day of the symposium centered around research in flow through partially saturated systems. Papers were presented with the opportunity for questions following each presentation. In addition, after all the talks, a formal panel discussion was held during which written questions were addressed to the panel of the days speakers. The second day of the Symposium was devoted to solute and contaminant transport in partially saturated media in an identical format. Individual papers are abstracted.
Dynamical Model of Flow in Martian Valleys
NASA Astrophysics Data System (ADS)
Czechowski, Leszek; Witek, Piotr; Misiura, Katarzyna
On the surface of Mars, under current conditions, liquid water could exist only occasionally in lowest regions of the planet. This water contains probably some components that decrease its freezing point and raised its boiling point. However billions years ago more dense atmosphere on the Mars allows for the presence of large volume of liquid water. There are a number of structures apparently resulting from flowing liquid water in the past. They are of two types: outflow channels and valley networks. We investigate here the possible flow in some chosen valley networks. The numerical model is used. We try to determine the basic properties of the flow, its erosion as well as the transport efficiencies of the material. The comparison with the terrestrial rivers indicates some important differences. Acknowledgments This work was partially supported by the National Science Centre (grant 2011/01/B/ST10/06653).
Modeling groundwater flow on massively parallel computers
Ashby, S.F.; Falgout, R.D.; Fogwell, T.W.; Tompson, A.F.B.
1994-12-31
The authors will explore the numerical simulation of groundwater flow in three-dimensional heterogeneous porous media. An interdisciplinary team of mathematicians, computer scientists, hydrologists, and environmental engineers is developing a sophisticated simulation code for use on workstation clusters and MPPs. To date, they have concentrated on modeling flow in the saturated zone (single phase), which requires the solution of a large linear system. they will discuss their implementation of preconditioned conjugate gradient solvers. The preconditioners under consideration include simple diagonal scaling, s-step Jacobi, adaptive Chebyshev polynomial preconditioning, and multigrid. They will present some preliminary numerical results, including simulations of groundwater flow at the LLNL site. They also will demonstrate the code`s scalability.
A study of vapor-liquid flow in porous media
Satik, Cengiz; Yortsos, Yanis C.
1994-01-20
We study the heat transfer-driven liquid-to-vapor phase change in single-component systems in porous media by using pore network models and flow visualization experiments. Experiments using glass micromodels were conducted. The flow visualization allowed us to define the rules for the numerical pore network model. A numerical pore network model is developed for vapor-liquid displacement where fluid flow, heat transfer and capillarity are included at the pore level. We examine the growth process at two different boundary conditions.
Coherent Structure-Reflective Turbulent Viscous Flow Modeling.
1987-09-07
REFLECTIVE TURBULENT VISCOUS FLOW MODELING PREPARED FOR: SELECTED Dr. James M. McMichael D Program Manager * Aerospace Sciences AFOSRINA or c...ceesM -=t ilb: t, j Dist ,,el- d I . ... " . . .. .a .1-I i1 - i | i Executive Summary The research reported upon here addresses several elements of the...here, an SBIR study of turbulence in hypersonic flow was initiated for AFOSR, the fruits of which now support an advanced R& D effort at Eglin AFB. 9 0
Modeling the interaction between flow and highly flexible aquatic vegetation
NASA Astrophysics Data System (ADS)
Dijkstra, J. T.; Uittenbogaard, R. E.
2010-12-01
Aquatic vegetation has an important role in estuaries and rivers by acting as bed stabilizer, filter, food source, and nursing area. However, macrophyte populations worldwide are under high anthropogenic pressure. Protection and restoration efforts will benefit from more insight into the interaction between vegetation, currents, waves, and sediment transport. Most aquatic plants are very flexible, implying that their shape and hence their drag and turbulence production depend on the flow conditions. We have developed a numerical simulation model that describes this dynamic interaction between very flexible vegetation and a time-varying flow, using the sea grass Zostera marina as an example. The model consists of two parts: an existing 1DV k-ɛ turbulence model simulating the flow combined with a new model simulating the bending of the plants, based on a force balance that takes account of both vegetation position and buoyancy. We validated this model using observations of positions of flexible plastic strips and of the forces they are subjected to, as well as hydrodynamic measurements. The model predicts important properties like the forces on plants, flow velocity profiles, and turbulence characteristics well. Although the validation data are limited, the results are sufficiently encouraging to consider our model to be of generic value in studying flow processes in fields of flexible vegetation.
1978-06-01
indicate the location of the pressure transducers (Reference 9) • • • • 31 2. The development of the flow at the vent hole. (a) t = 0, 52.9 [vis]; (b...x 10Ŗ [m]. Photographs courtesy of Dr. K. J. White, Propulsion Division, BRL 32 3. Comparison of calculated and experimentally observed pressure ...function of time in [s] 36 6- Vent hole temperature in degrees [K] as a function of time expressed in [s] 37 7. Vent hole pressure in units
Mathematical model of platelet deposition under flow conditions.
Affeld, K; Goubergrits, L; Kertzscher, U; Gadischke, J; Reininger, A
2004-08-01
Platelet deposition in resting blood is well researched and understood. However, the influence of hemodynamic parameters such as wall shear rate is less clear. Clinical experience and experiments show an interaction between flow and platelet deposition. But a complete understanding of the flow influence and hence a quantification has not yet been achieved. A well defined experiment of flow dependant platelet depositions is the stagnation point flow. This kind of flow is ubiquitous in the circulatory system, to be found in every bifurcation and recirculation region. These are the areas where thrombus formations are likely to occur if other conditions are also met. First, experiments were performed in a stagnation point flow chamber. A simplified blood model, platelet rich plasma, was used as a test fluid. With a microscope the platelet deposition was observed and recorded. Platelets deposit in a characteristic pattern showing the influence of the flow. An analysis of this pattern is the objective of this study and is achieved with the help of a numerical model, which is based on a convective diffusive transport. The model results in a platelet deposition pattern, which in its shape and temporal development is very similar to experimental results. Hence it is concluded that the assumed transport processes are causal for platelet depositions and thrombus formation.
Mehta, D.C.
1984-05-01
One of the major pieces of equipment in the SRC-I Demonstration Plant is the slurry fired heater. Because of the absence of any plant data at comparable combinations of operating severity, a cold-flow modelling experimental program was initiated at Creare, Inc. The first phase of the test program confirmed the fired heater design and established reliable boundaries of flow rates for proper operation of the fired heater. An experimental setup was designed and built at Creare to duplicate the piping arrangement and flow conditions of the fired heater. The pipe dimensions, flow rates, and fluid properties were selected to minimize areas of scale-up and extrapolation. This follow-up test program was developed to resolve concerns raised from the observations made in the first phase. Tests were conducted to establish the extent of mixing between the liquid carpet and the fast-moving liquid slugs above it. The other segment of the test program was designed to develop the flow regime and pressure drop data in the 1/sup 0/ downslope configuration. The results demonstrated a significant amount of mixing between the liquid carpet and the liquid slugs for water and the 400-cP fluid at the design flow conditions. The extent of mixing improved with increasing liquid and gas velocities and decreasing liquid viscosities. Adequate mixing was observed at liquid flow rates as low as 50% of the design flow conditions. Slug flow was observed at design conditions in the 1/sup 0/ downslope configuration. Although adequate mixing is expected in heater pipes, different techniques should be investigated to improve the extent of mixing, especially near the transition boundary. 4 references, 5 figures, 8 tables.
Rarefield-Flow Shuttle Aerodynamics Flight Model
NASA Technical Reports Server (NTRS)
Blanchard, Robert C.; Larman, Kevin T.; Moats, Christina D.
1994-01-01
A model of the Shuttle Orbiter rarefied-flow aerodynamic force coefficients has been derived from the ratio of flight acceleration measurements. The in-situ, low-frequency (less than 1Hz), low-level (approximately 1 x 10(exp -6) g) acceleration measurements are made during atmospheric re-entry. The experiment equipment designed and used for this task is the High Resolution Accelerometer Package (HiRAP), one of the sensor packages in the Orbiter Experiments Program. To date, 12 HiRAP re-entry mission data sets spanning a period of about 10 years have been processed. The HiRAP-derived aerodynamics model is described in detail. The model includes normal and axial hypersonic continuum coefficient equations as function of angle of attack, body-flap deflection, and elevon deflection. Normal and axial free molecule flow coefficient equations as a function of angle of attack are also presented, along with flight-derived rarefied-flow transition bridging formulae. Comparisons are made between the aerodynamics model, data from the latest Orbiter Operational Aerodynamic Design Data Book, applicable computer simulations, and wind-tunnel data.
The role of hand calculations in ground water flow modeling.
Haitjema, Henk
2006-01-01
Most ground water modeling courses focus on the use of computer models and pay little or no attention to traditional analytic solutions to ground water flow problems. This shift in education seems logical. Why waste time to learn about the method of images, or why study analytic solutions to one-dimensional or radial flow problems? Computer models solve much more realistic problems and offer sophisticated graphical output, such as contour plots of potentiometric levels and ground water path lines. However, analytic solutions to elementary ground water flow problems do have something to offer over computer models: insight. For instance, an analytic one-dimensional or radial flow solution, in terms of a mathematical expression, may reveal which parameters affect the success of calibrating a computer model and what to expect when changing parameter values. Similarly, solutions for periodic forcing of one-dimensional or radial flow systems have resulted in a simple decision criterion to assess whether or not transient flow modeling is needed. Basic water balance calculations may offer a useful check on computer-generated capture zones for wellhead protection or aquifer remediation. An easily calculated "characteristic leakage length" provides critical insight into surface water and ground water interactions and flow in multi-aquifer systems. The list goes on. Familiarity with elementary analytic solutions and the capability of performing some simple hand calculations can promote appropriate (computer) modeling techniques, avoids unnecessary complexity, improves reliability, and is likely to save time and money. Training in basic hand calculations should be an important part of the curriculum of ground water modeling courses.
Flow and transport simulation models for prediction of chlorine contact tank flow-through curves.
Wang, Hong; Shao, Xuejun; Falconer, Roger A
2003-01-01
Turbulent flow, solute transport, and chemical and biological decay are some of the basic processes encountered in water treatment plants. This paper presents recent developments in the numerical simulation of turbulent flow and disinfection processes in disinfection contact tanks. Simulation runs have been conducted for various tank design alternatives and in different grid resolutions. The accuracy of simulated contact tank flow and the disinfection process depends largely on calculations of the hydrodynamic and solute transport characteristics in the tanks. A key factor of this is the accuracy of advection and shear stress term computations, which can be affected by the use of different hydrodynamic submodels and numerical schemes. The performance of a simulation model relies to a great extent on the right combination of such submodels and numerical schemes. In this study, a number of simulation models were tested against realistic tank configurations and measurements to evaluate the various combinations of turbulence models and difference schemes by analyzing predicted flow and solute transport patterns, as well as the corresponding flow-through curves. Models for disinfection tank simulations are recommended based on comparisons of simulation results with measurements. These models may also be applied to other water treatment processes such as wastewater treatment.
Fan, Jinlong; Pan, Zhihua; Zhao, Ju; Zheng, Dawei; Tuo, Debao; Zhao, Peiyi
2004-04-01
The degradation of ecological environment in the agriculture-pasture ecotone in northern China has been paid more attentions. Based on our many years' research and under the guide of energy and material flow theory, this paper put forward an ecological management model, with a hill as the basic cell and according to the natural, social and economic characters of Houshan dryland farming area inside the north agriculture-pasture ecotone. The input and output of three models, i.e., the traditional along-slope-tillage model, the artificial grassland model and the ecological management model, were observed and recorded in detail in 1999. Energy and material flow analysis based on field test showed that compared with traditional model, ecological management model could increase solar use efficiency by 8.3%, energy output by 8.7%, energy conversion efficiency by 19.4%, N output by 26.5%, N conversion efficiency by 57.1%, P output by 12.1%, P conversion efficiency by 45.0%, and water use efficiency by 17.7%. Among the models, artificial grassland model had the lowest solar use efficiency, energy output and energy conversion efficiency; while the ecological management model had the most outputs and benefits, was the best model with high economic effect, and increased economic benefits by 16.1%, compared with the traditional model.
Analogue experiments as benchmarks for models of lava flow emplacement
NASA Astrophysics Data System (ADS)
Garel, F.; Kaminski, E. C.; Tait, S.; Limare, A.
2013-12-01
During an effusive volcanic eruption, the crisis management is mainly based on the prediction of lava flow advance and its velocity. The spreading of a lava flow, seen as a gravity current, depends on its "effective rheology" and on the effusion rate. Fast-computing models have arisen in the past decade in order to predict in near real time lava flow path and rate of advance. This type of model, crucial to mitigate volcanic hazards and organize potential evacuation, has been mainly compared a posteriori to real cases of emplaced lava flows. The input parameters of such simulations applied to natural eruptions, especially effusion rate and topography, are often not known precisely, and are difficult to evaluate after the eruption. It is therefore not straightforward to identify the causes of discrepancies between model outputs and observed lava emplacement, whereas the comparison of models with controlled laboratory experiments appears easier. The challenge for numerical simulations of lava flow emplacement is to model the simultaneous advance and thermal structure of viscous lava flows. To provide original constraints later to be used in benchmark numerical simulations, we have performed lab-scale experiments investigating the cooling of isoviscous gravity currents. The simplest experimental set-up is as follows: silicone oil, whose viscosity, around 5 Pa.s, varies less than a factor of 2 in the temperature range studied, is injected from a point source onto a horizontal plate and spreads axisymmetrically. The oil is injected hot, and progressively cools down to ambient temperature away from the source. Once the flow is developed, it presents a stationary radial thermal structure whose characteristics depend on the input flow rate. In addition to the experimental observations, we have developed in Garel et al., JGR, 2012 a theoretical model confirming the relationship between supply rate, flow advance and stationary surface thermal structure. We also provide
Gas flow modelling through clay and claystones
NASA Astrophysics Data System (ADS)
Alonso, E.
2012-12-01
Large scale gas flow experiments conducted in connection with nuclear waste disposal research have shown the dominant effect of "minor" details such as interfaces, contacts and layer boundaries. Even if the scale of the analysis is highly reduced, in search of homogeneous point-like conditions, a systematic development of preferential paths is very often reported. Small size samples become boundary value problems. Preferential paths, when their thickness is modified by the stress-strain response of the media, under the combined action of stress and fluid pressure changes, become highly conductive features for gas flow. The development of preferential paths for fluid flow has been approached in a simple manner by embedding a discontinuity feature into an otherwise continuous element which models clay or claystone matrix behavior. The joint is activated when tensile strains develop in the continuous element. Then, hydraulic properties (permeability, retention behavior) are modified by means of laws derived from the physics of flow in discontinuities. The outlined idea was incorporated into a full Thermo-Hydro-Mechanical finite element code (CODE_BRIGHT) which has a wide range of capabilities for the modeling of two-phase flow in elasto-viscoplastic porous materials. A particular aspect which required attention is the modeling of expansive and shrinkage behavior induced by suction changes. In this way, healing effects during re-saturation may be simulated. Two experimental programs on clay shale samples, performed under triaxial stress conditions will be discussed. In the first case samples of Opalinus shale were subjected to a series of gas pulse decay tests during the application of stress paths involving a particular sequence of confining stress and shearing up to failure. In the second experimental program, performed on a tertiary mudstone from the Norwegian shelf, attention was paid to the effect of bedding-induced anisotropy. Experimental results will be
NASA Astrophysics Data System (ADS)
Thieulot, C.; Braun, J.
2006-12-01
The Earth's lithosphere is a dynamic system where complex interplay between mechanical and thermal processes take place. With the advent of relatively cheap and efficient parallel computers, there has been a rise in the numerical approach to such a system. We have developed a new three-dimensional code 'DOUAR' which aims at expanding our understanding of the interplay between deep processes (convection, subduction, collision, ...) and surface processes (erosion, sedimentation, ...) that take place within the Earth's lithosphere. The Stokes and heat transport equations are discretised within the framework of the finite elements method, and solved for systems consisting of many layers of different materials with various physical properties. The adaptive grid is in our case a so-called octree: a space-filling set of cubes of different sizes which are in fact the elements on which calculations are performed. When an element is intersected by one or several interfaces, the respective volume of each material in the cube is assessed (divFEM technique) and used to perform the volume integration of the finite element equations. Once the set of coupled algebraic equations is obtained, we resort to a direct solver to obtain the solution. One of the most interesting features of our code resides in its ability to track and advect a free surface and/or interfaces. Furthermore, the total accumulated strain is computed by means of a dedicated cloud of Lagrangian points, and can be used, as well as temperature and pressure, in the implemented complex rheology models. These rheologies include linear and non-linear viscous behaviour, as well as von Mises and pressure- dependent plasticity (Mohr-Coulomb). The code has been developed to simulate tectonic events and predict a wide range of geological observations. It can thus be regarded as an integrator of field data and is used to test quantitatively tectonic scenarios suggested by the observations. Besides lithospheric problems, the
Renormalization flow of the hierarchical Anderson model at weak disorder
NASA Astrophysics Data System (ADS)
Metz, F. L.; Leuzzi, L.; Parisi, G.
2014-02-01
We study the flow of the renormalized model parameters obtained from a sequence of simple transformations of the 1D Anderson model with long-range hierarchical hopping. Combining numerical results with a perturbative approach for the flow equations, we identify three qualitatively different regimes at weak disorder. For a sufficiently fast decay of the hopping energy, the Cauchy distribution is the only stable fixed point of the flow equations, whereas for sufficiently slowly decaying hopping energy the renormalized parameters flow to a δ-peak fixed-point distribution. In an intermediate range of the hopping decay, both fixed-point distributions are stable and the stationary solution is determined by the initial configuration of the random parameters. We present results for the critical decay of the hopping energy separating the different regimes.
Wetting and free surface flow modeling for potting and encapsulation.
Brooks, Carlton, F.; Brooks, Michael J. (Los Alamos National Laboratory, Los Alamos, NM); Graham, Alan Lyman; Noble, David F. ); Notz, Patrick K.; Hopkins, Matthew Morgan; Castaneda, Jaime N.; Mahoney, Leo James; Baer, Thomas A.; Berchtold, Kathryn (Los Alamos National Laboratory, Los Alamos, NM); Adolf, Douglas Brian; Wilkes, Edward Dean; Rao, Rekha Ranjana; Givler, Richard C.; Sun, Amy Cha-Tien; Cote, Raymond O.; Mondy, Lisa Ann; Grillet, Anne Mary; Kraynik, Andrew Michael
2007-06-01
As part of an effort to reduce costs and improve quality control in encapsulation and potting processes the Technology Initiative Project ''Defect Free Manufacturing and Assembly'' has completed a computational modeling study of flows representative of those seen in these processes. Flow solutions are obtained using a coupled, finite-element-based, numerical method based on the GOMA/ARIA suite of Sandia flow solvers. The evolution of the free surface is solved with an advanced level set algorithm. This approach incorporates novel methods for representing surface tension and wetting forces that affect the evolution of the free surface. In addition, two commercially available codes, ProCAST and MOLDFLOW, are also used on geometries representing encapsulation processes at the Kansas City Plant. Visual observations of the flow in several geometries are recorded in the laboratory and compared to the models. Wetting properties for the materials in these experiments are measured using a unique flowthrough goniometer.
Modelling boundary layer flow over barnacle-fouled surfaces
NASA Astrophysics Data System (ADS)
Sadique, Jasim; Yang, Xiang; Meneveau, Charles; Mittal, Rajat
2014-11-01
Macro-biofouling is a critical concern for the marine industry. However, there is little data on flow and drag over such surfaces. Accurate modelling of such multi-scale flows remains a big challenge. Such simulations are vital in providing insights into the fundamental flow physics, and they can be used to estimate the timing, need and effectiveness of measures used to counteract bio-fouling. This talk focuses on the use of a sharp-interface immersed boundary method coupled with a wall model and large-eddy simulations to carry out accurate simulations of a turbulent boundary layer flow over macro-fouled surfaces. For the current study, high resolution scans of barnacles were used to create simple geometrical representations. Simulations were then carried out to test how well these simpler geometric models mimic the flow over actual barnacles. Simulations of array of modeled barnacles, with different barnacle densities have also been carried out and we present results on the effect distribution density on the flow physics and drag on the surfaces. This work is funded by ONR Grant N00014-12-1-0582.
Flow within Physical Models of the Vertebrate Embryonic Heart
NASA Astrophysics Data System (ADS)
Nguyen, Nhi; Santhanakrishnan, Arvind; Miller, Laura
2008-11-01
Vertebrate cardiogenesis is believed to be partially regulated by fluid forces imposed by blood flow in addition to myocardial activity and other epigenetic factors. Recent in vitro studies in embryonic cardiogenesis (see Hove et al., Nature, 2003) show that blood flowing through the embryonic heart tube creates shear forces necessary for the formation and development of the heart valves. It is suggested that these flow driven forces provide a biomechanical stimulus to the endothelial surface layer, which then feed into the biochemical regulatory networks that initiate heart looping and chamber ballooning. To understand the flow field within the embryonic heart, flow visualization experiments were performed on a series of physical models that represent the different morphological stages of early heart development. The chamber and valve depths of the models as well as the Reynolds numbers were varied in this study. Different compositions of solutions consisting of corn syrup and water were used as the fluid media to examine Reynolds numbers from 0.01 to 1000, corresponding to a scale of the early heart tube to the adult heart. The observed results showed that vortex formation within the chambers occurred for Reynolds numbers in the range of 1-10. This transition to vortical flow appears to be highly sensitive to the chamber and valve depths within the model.
Pulsatile flow in a compliant stenosed asymmetric model
NASA Astrophysics Data System (ADS)
Usmani, Abdullah Y.; Muralidhar, K.
2016-12-01
Time-varying velocity field in an asymmetric constricted tube is experimentally studied using a two-dimensional particle image velocimetry system. The geometry resembles a vascular disease which is characterized by arterial narrowing due to plaque deposition. The present study compares the nature of flow patterns in rigid and compliant asymmetric constricted tubes for a range of dimensionless parameters appearing in a human artery. A blood analogue fluid is employed along with a pump that mimics cardioflow conditions. The peak Reynolds number range is Re 300-800, while the Womersley number range considered in experiments is Wo 6-8. These values are based on the peak velocity in a straight rigid tube connected to the model, over a pulsation frequency range of 1.2-2.4 Hz. The medial-plane velocity distribution is used to investigate the nature of flow patterns. Temporal distribution of stream traces and hemodynamic factors including WSS, TAWSS and OSI at important phases of the pulsation cycle are discussed. The flow patterns obtained from PIV are compared to a limited extent against numerical simulation. Results show that the region downstream of the constriction is characterized by a high-velocity jet at the throat, while a recirculation zone, attached to the wall, evolves in time. Compliant models reveal large flow disturbances upstream during the retrograde flow. Wall shear stress values are lower in a compliant model as compared to the rigid. Cross-plane flow structures normal to the main flow direction are visible at select phases of the cycle. Positive values of largest Lyapunov exponent are realized for wall movement and are indicative of chaotic motion transferred from the flow to the wall. These exponents increase with Reynolds number as well as compliance. Period doubling is observed in wall displacement of highly compliant models, indicating possible triggering of hemodynamic events in a real artery that may cause fissure in the plaque deposits.
Incorporating immigrant flows into microsimulation models.
Duleep, Harriet Orcutt; Dowhan, Daniel J
2008-01-01
Building on the research on immigrant earnings reviewed in the first article of this series, "Research on Immigrant Earnings," the preceding article, "Adding Immigrants to Microsimulation Models," linked research results to various issues essential for incorporating immigrant earnings into microsimulation models. The discussions of that article were in terms of a closed system. That is, it examined a system in which immigrant earnings and emigration are forecast for a given population represented in the base sample in the microsimulation model. This article, the last in the series, addresses immigrant earnings projections for open systems--microsimulation models that include projections of future immigration. The article suggests a simple method to project future immigrants and their earnings. Including the future flow of immigrants in microsimulation models can dramatically affect the projected Social Security benefits of some groups.
Turbulence modelling of thermal plasma flows
NASA Astrophysics Data System (ADS)
Shigeta, Masaya
2016-12-01
This article presents a discussion of the ideas for modelling turbulent thermal plasma flows, reviewing the challenges, efforts, and state-of-the-art simulations. Demonstrative simulations are also performed to present the importance of numerical methods as well as physical models to express turbulent features. A large eddy simulation has been applied to turbulent thermal plasma flows to treat time-dependent and 3D motions of multi-scale eddies. Sub-grid scale models to be used should be able to express not only turbulent but also laminar states because both states co-exist in and around thermal plasmas which have large variations of density as well as transport properties under low Mach-number conditions. Suitable solution algorithms and differencing schemes must be chosen and combined appropriately to capture multi-scale eddies and steep gradients of temperature and chemical species, which are turbulent features of thermal plasma flows with locally variable Reynolds and Mach numbers. Several simulations using different methods under different conditions show commonly that high-temperature plasma regions exhibit less turbulent structures, with only large eddies, whereas low-temperature regions tend to be more turbulent, with numerous small eddies. These numerical results agree with both theoretical insight and photographs that show the characteristics of eddies. Results also show that a turbulence transition of a thermal plasma jet through a generation-breakup process of eddies in a torch is dominated by fluid dynamic instability after ejection rather than non-uniform or unsteady phenomena.
NASA Astrophysics Data System (ADS)
Zurek, Anna; Witczak, Stanislaw; Kania, Jaroslaw; Wachniew, Przemyslaw; Rozanski, Kazimierz; Dulinski, Marek; Jench, Olga
2013-04-01
Niepolomice Forest. There is a growing concern that continued exploitation of those wells may lead to lowering water table in the Niepolomice Forest area and, as a consequence, may trigger drastic changes in this unique ecosystem. A dedicated study was launched with the main aim to quantify the interaction between Niepolomice Forest, with the focus the Wielkie Bloto fen, and the underlying Bogucice Sands aquifer. The work was pursued along three major lines: (i) vertical profiling of the Wielkie Bloto fen aimed at characterizing chemical and isotope contrast in the shallow groundwater occupying the Quaternary cover in order to identify upward leakage of deeper groundwater in the investigated area, (ii) regular monitoring of flow rate, chemistry and environmental isotopes of the Dluga Woda stream draining the Wielkie Bloto fen, and (iii) 3D modeling of groundwater flow in the vicinity of the Wielkie Bloto fen focusing on quantifying the impact of the Wola Batorska well field on the regional groundwater flow patterns. The results of isotope and chemical analyses confirmed existence of upward seepage of groundwater from the Bogucice Sands aquifer in the area of Wielkie Bloto fen. Preliminary assessment of the water balance of Dluga Woda catchment indicates that the baseflow originating from groundwater seepage is equal approximately 16% of the annual precipitation. Results of 3D flow model applied to the study area indicate that prolonged operation of the well-field Wola Batorska at maximum capacity may lead to substantial lowering of water table in the Niepolomice Forest area and, as a consequence, endanger further existence of this unique GDTE. Acknowledgements. Partial financial support of this work through GENESIS project (http:/www.thegenesisproject.eu) funded by the European Commission 7FP contract 226536, and through statutory funds of the AGH University of Science and Technology (projects No.11.11.140.026 and 11.11.220.01) is kindly acknowledged.
Review and selection of unsaturated flow models
1993-09-10
Under the US Department of Energy (DOE), the Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) has the responsibility to review, evaluate, and document existing computer ground-water flow models; to conduct performance assessments; and to develop performance assessment models, where necessary. In the area of scientific modeling, the M&O CRWMS has the following responsibilities: To provide overall management and integration of modeling activities. To provide a framework for focusing modeling and model development. To identify areas that require increased or decreased emphasis. To ensure that the tools necessary to conduct performance assessment are available. These responsibilities are being initiated through a three-step process. It consists of a thorough review of existing models, testing of models which best fit the established requirements, and making recommendations for future development that should be conducted. Future model enhancement will then focus on the models selected during this activity. Furthermore, in order to manage future model development, particularly in those areas requiring substantial enhancement, the three-step process will be updated and reported periodically in the future.
Pan, Wenxiao; Fedosov, Dmitry A; Caswell, Bruce; Karniadakis, George Em
2011-09-01
We compare the predictive capability of two mathematical models for red blood cells (RBCs) focusing on blood flow in capillaries and arterioles. Both RBC models as well as their corresponding blood flows are based on the dissipative particle dynamics (DPD) method, a coarse-grained molecular dynamics approach. The first model employs a multiscale description of the RBC (MS-RBC), with its membrane represented by hundreds or even thousands of DPD-particles connected by springs into a triangular network in combination with out-of-plane elastic bending resistance. Extra dissipation within the network accounts for membrane viscosity, while the characteristic biconcave RBC shape is achieved by imposition of constraints for constant membrane area and constant cell volume. The second model is based on a low-dimensional description (LD-RBC) constructed as a closed torus-like ring of only 10 large DPD colloidal particles. They are connected into a ring by worm-like chain (WLC) springs combined with bending resistance. The LD-RBC model can be fitted to represent the entire range of nonlinear elastic deformations as measured by optical-tweezers for healthy and for infected RBCs in malaria. MS-RBCs suspensions model the dynamics and rheology of blood flow accurately for any vessel size but this approach is computationally expensive for vessel diameters above 100μm. Surprisingly, the much more economical suspensions of LD-RBCs also capture the blood flow dynamics and rheology accurately except for small-size vessels comparable to RBC diameter. In particular, the LD-RBC suspensions are shown to properly capture the experimental data for the apparent viscosity of blood and its cell-free layer (CFL) in tube flow. Taken together, these findings suggest a hierarchical approach in modeling blood flow in the arterial tree, whereby the MS-RBC model should be employed for capillaries and arterioles below 100μm, the LD-RBC model for arterioles, and the continuum description for arteries.
A new nonlinear Muskingum flood routing model incorporating lateral flow
NASA Astrophysics Data System (ADS)
Karahan, Halil; Gurarslan, Gurhan; Geem, Zong Woo
2015-06-01
A new nonlinear Muskingum flood routing model taking the contribution from lateral flow into consideration was developed in the present study. The cuckoo search algorithm, a quite novel and robust algorithm, was used in the calibration and verification of the model parameters. The success and the dependability of the proposed model were tested on five different sets of synthetic and real flood data. The optimal solutions for the test cases were determined by the currently proposed model rather than by different models taken from the literature, indicating that this model could be suitable for use in flood routing problems.
NASA Astrophysics Data System (ADS)
Oberleithner, Kilian; Rukes, Lothar; Paschereit, Oliver; Soria, Julio
2014-11-01
We report on a number of experimental and theoretical investigations of shear flow instabilities in jet flows. In these studies, linear stability analysis is employed to the time-averaged flow taken from experiments, contrasting the ``classic'' stability approach that is based on a stationary base flow. The eigenmodes of the time-averaged flow are considered as models for the nonlinearly saturated state of the instability waves. The accuracy of these models is validated through a detailed comparison with experiments. In this talk we outline the potential and limitation of these flow models for convectively and globally unstable jet flows. The first author was supported by a fellowship within the Postdoc-Program of the German Academic Exchange Service (DAAD). The support of the Australian Research Council (ARC) and the German Research Foundation (DFG) is greatfully acknowledged.
Smart licensing and environmental flows: Modeling framework and sensitivity testing
NASA Astrophysics Data System (ADS)
Wilby, R. L.; Fenn, C. R.; Wood, P. J.; Timlett, R.; Lequesne, T.
2011-12-01
Adapting to climate change is just one among many challenges facing river managers. The response will involve balancing the long-term water demands of society with the changing needs of the environment in sustainable and cost effective ways. This paper describes a modeling framework for evaluating the sensitivity of low river flows to different configurations of abstraction licensing under both historical climate variability and expected climate change. A rainfall-runoff model is used to quantify trade-offs among environmental flow (e-flow) requirements, potential surface and groundwater abstraction volumes, and the frequency of harmful low-flow conditions. Using the River Itchen in southern England as a case study it is shown that the abstraction volume is more sensitive to uncertainty in the regional climate change projection than to the e-flow target. It is also found that "smarter" licensing arrangements (involving a mix of hands off flows and "rising block" abstraction rules) could achieve e-flow targets more frequently than conventional seasonal abstraction limits, with only modest reductions in average annual yield, even under a hotter, drier climate change scenario.
Soltani, M; Chen, P
2013-01-01
Modeling of interstitial fluid flow involves processes such as fluid diffusion, convective transport in extracellular matrix, and extravasation from blood vessels. To date, majority of microvascular flow modeling has been done at different levels and scales mostly on simple tumor shapes with their capillaries. However, with our proposed numerical model, more complex and realistic tumor shapes and capillary networks can be studied. Both blood flow through a capillary network, which is induced by a solid tumor, and fluid flow in tumor's surrounding tissue are formulated. First, governing equations of angiogenesis are implemented to specify the different domains for the network and interstitium. Then, governing equations for flow modeling are introduced for different domains. The conservation laws for mass and momentum (including continuity equation, Darcy's law for tissue, and simplified Navier-Stokes equation for blood flow through capillaries) are used for simulating interstitial and intravascular flows and Starling's law is used for closing this system of equations and coupling the intravascular and extravascular flows. This is the first study of flow modeling in solid tumors to naturalistically couple intravascular and extravascular flow through a network. This network is generated by sprouting angiogenesis and consisting of one parent vessel connected to the network while taking into account the non-continuous behavior of blood, adaptability of capillary diameter to hemodynamics and metabolic stimuli, non-Newtonian blood flow, and phase separation of blood flow in capillary bifurcation. The incorporation of the outlined components beyond the previous models provides a more realistic prediction of interstitial fluid flow pattern in solid tumors and surrounding tissues. Results predict higher interstitial pressure, almost two times, for realistic model compared to the simplified model.
Soltani, M.; Chen, P.
2013-01-01
Modeling of interstitial fluid flow involves processes such as fluid diffusion, convective transport in extracellular matrix, and extravasation from blood vessels. To date, majority of microvascular flow modeling has been done at different levels and scales mostly on simple tumor shapes with their capillaries. However, with our proposed numerical model, more complex and realistic tumor shapes and capillary networks can be studied. Both blood flow through a capillary network, which is induced by a solid tumor, and fluid flow in tumor’s surrounding tissue are formulated. First, governing equations of angiogenesis are implemented to specify the different domains for the network and interstitium. Then, governing equations for flow modeling are introduced for different domains. The conservation laws for mass and momentum (including continuity equation, Darcy’s law for tissue, and simplified Navier–Stokes equation for blood flow through capillaries) are used for simulating interstitial and intravascular flows and Starling’s law is used for closing this system of equations and coupling the intravascular and extravascular flows. This is the first study of flow modeling in solid tumors to naturalistically couple intravascular and extravascular flow through a network. This network is generated by sprouting angiogenesis and consisting of one parent vessel connected to the network while taking into account the non-continuous behavior of blood, adaptability of capillary diameter to hemodynamics and metabolic stimuli, non-Newtonian blood flow, and phase separation of blood flow in capillary bifurcation. The incorporation of the outlined components beyond the previous models provides a more realistic prediction of interstitial fluid flow pattern in solid tumors and surrounding tissues. Results predict higher interstitial pressure, almost two times, for realistic model compared to the simplified model. PMID:23840579
Unified Model Deformation and Flow Transition Measurements
NASA Technical Reports Server (NTRS)
Burner, Alpheus W.; Liu, Tianshu; Garg, Sanjay; Bell, James H.; Morgan, Daniel G.
1999-01-01
The number of optical techniques that may potentially be used during a given wind tunnel test is continually growing. These include parameter sensitive paints that are sensitive to temperature or pressure, several different types of off-body and on-body flow visualization techniques, optical angle-of-attack (AoA), optical measurement of model deformation, optical techniques for determining density or velocity, and spectroscopic techniques for determining various flow field parameters. Often in the past the various optical techniques were developed independently of each other, with little or no consideration for other techniques that might also be used during a given test. Recently two optical techniques have been increasingly requested for production measurements in NASA wind tunnels. These are the video photogrammetric (or videogrammetric) technique for measuring model deformation known as the video model deformation (VMD) technique, and the parameter sensitive paints for making global pressure and temperature measurements. Considerations for, and initial attempts at, simultaneous measurements with the pressure sensitive paint (PSP) and the videogrammetric techniques have been implemented. Temperature sensitive paint (TSP) has been found to be useful for boundary-layer transition detection since turbulent boundary layers convect heat at higher rates than laminar boundary layers of comparable thickness. Transition is marked by a characteristic surface temperature change wherever there is a difference between model and flow temperatures. Recently, additional capabilities have been implemented in the target-tracking videogrammetric measurement system. These capabilities have permitted practical simultaneous measurements using parameter sensitive paint and video model deformation measurements that led to the first successful unified test with TSP for transition detection in a large production wind tunnel.
Mathematical models of continuous flow electrophoresis: Electrophoresis technology
NASA Technical Reports Server (NTRS)
Saville, Dudley A.
1986-01-01
Two aspects of continuous flow electrophoresis were studied: (1) the structure of the flow field in continuous flow devices; and (2) the electrokinetic properties of suspended particles relevant to electrophoretic separations. Mathematical models were developed to describe flow structure and stability, with particular emphasis on effects due to buoyancy. To describe the fractionation of an arbitrary particulate sample by continuous flow electrophoresis, a general mathematical model was constructed. In this model, chamber dimensions, field strength, buffer composition, and other design variables can be altered at will to study their effects on resolution and throughput. All these mathematical models were implemented on a digital computer and the codes are available for general use. Experimental and theoretical work with particulate samples probed how particle mobility is related to buffer composition. It was found that ions on the surface of small particles are mobile, contrary to the widely accepted view. This influences particle mobility and suspension conductivity. A novel technique was used to measure the mobility of particles in concentrated suspensions.
Drop Breakup in Fixed Bed Flows as Model Stochastic Flow Fields
NASA Technical Reports Server (NTRS)
Shaqfeh, Eric S. G.; Mosler, Alisa B.; Patel, Prateek
1999-01-01
We examine drop breakup in a class of stochastic flow fields as a model for the flow through fixed fiber beds and to elucidate the general mechanisms whereby drops breakup in disordered, Lagrangian unsteady flows. Our study consists of two parallel streams of investigation. First, large scale numerical simulations of drop breakup in a class of anisotropic Gaussian fields will be presented. These fields are generated spectrally and have been shown in a previous publication to be exact representations of the flow in a dilute disordered bed of fibers if close interactions between the fibers and the drops are dynamically unimportant. In these simulations the drop shape is represented by second and third order small deformation theories which have been shown to be excellent for the prediction of drop breakup in steady strong flows. We show via these simulations that the mechanisms of drop breakup in these flows are quite different than in steady flows. The predominant mechanism of breakup appears to be very short lived twist breakups. Moreover, the occurrence of breakup events is poorly predicted by either the strength of the local flow in which the drop finds itself at breakup, or the degree of deformation that the drop achieves prior to breakup. It is suggested that a correlation function of both is necessary to be predictive of breakup events. In the second part of our research experiments are presented where the drop deformation and breakup in PDMS/polyisobutylene emulsions is considered. We consider very dilute emulsions such that coalescence is unimportant. The flows considered are simple shear and the flow through fixed fiber beds. Turbidity, small angle light scattering, dichroism and microscopy are used to interrogate the drop deformation process in both flows. It is demonstrated that breakup at very low capillary numbers occurs in both flows but larger drop deformation occurs in the fixed bed flow. Moreover, it is witnessed that breakup in the bed occurs
A new approach to flow simulation using hybrid models
NASA Astrophysics Data System (ADS)
Solgi, Abazar; Zarei, Heidar; Nourani, Vahid; Bahmani, Ramin
2017-01-01
The necessity of flow prediction in rivers, for proper management of water resource, and the need for determining the inflow to the dam reservoir, designing efficient flood warning systems and so forth, have always led water researchers to think about models with high-speed response and low error. In the recent years, the development of Artificial Neural Networks and Wavelet theory and using the combination of models help researchers to estimate the river flow better and better. In this study, daily and monthly scales were used for simulating the flow of Gamasiyab River, Nahavand, Iran. The first simulation was done using two types of ANN and ANFIS models. Then, using wavelet theory and decomposing input signals of the used parameters, sub-signals were obtained and were fed into the ANN and ANFIS to obtain hybrid models of WANN and WANFIS. In this study, in addition to the parameters of precipitation and flow, parameters of temperature and evaporation were used to analyze their effects on the simulation. The results showed that using wavelet transform improved the performance of the models in both monthly and daily scale. However, it had a better effect on the monthly scale and the WANFIS was the best model.
The lag RST turbulence model applied to vortical flows
NASA Astrophysics Data System (ADS)
Churchfield, Matthew John
of misalignment between the principal axes of the Reynolds stress and the mean strain rate tensors increases (which also results in an increased misalignment between the contours of the Reynolds shear stress components and those of their corresponding strain rate components), and the peak magnitude of the Reynolds stresses is decreased. In these vortex flows, values of alpha0 that provide the correct amount of misalignment between the principal axes of the Reynolds stress and the mean strain rate tensors predict too small of peak values of Reynolds stresses. There is currently no way to independently control the misalignment and the Reynolds stress magnitudes. The lag RST model also does not properly predict the growth and decay rates of turbulence in the q-vortex, no matter which value of alpha0 is chosen. Although it has some flaws, its performance in predicting vortical flows is very good and could be a useful tool in the study of wingtip vortices. However, improvement of the model should be pursued. An outline for modifications that should be explored to improve the model's performance is included in this thesis. These modifications focus on replacing the model constant alpha 0 with a variable parameter and on the possibility of replacing the lag time scale, which is the specific dissipation rate of turbulent kinetic energy, o, with a more relevant time scale that incorporates the mean flow.
Measuring and Modeling Flow in Welded Fractured Tuffs
R. Salve; C. Doughty; J.S. Wang
2001-10-03
We have carried out a series of in situ liquid-release experiments in conjunction with a numerical modeling study to examine the effect of the rock matrix on liquid flow and transport occurring primarily through the fracture network. Field experiments were conducted in the highly fractured Topopah Spring welded tuff at a site accessed from the Exploratory Studies Facility (ESFS), an underground laboratory in the unsaturated zone at Yucca Mountain, Nevada. During the experiment, wetting-front movement, flow-field evolution, and drainage of fracture flow paths were evaluated. Modeling was used to aid in experimental design, predict experimental results, and study the physical processes accompanying liquid flow through unsaturated fractured welded tuff. Field experiments and modeling suggest that it may not be sufficient to conceptualize the fractured tuff as consisting of a single network of high-permeability fractures embedded in a low-permeability matrix. The need to include a secondary fracture network is demonstrated by comparison to the liquid flow observed in the field.
Modeling flow of mineralized carbon dioxide slurry
Penner, Larry R.; Dahlin, David C.; Gerdemann, Stephen J.; Saha, K.K.
2005-04-01
Direct mineral carbonation was investigated at Albany Research Center (US DOE) as a means to sequester carbon dioxide into stable mineral matrices. Although previous work focused on treating Mg-containing minerals in conventional autoclaves, recent work has been done using pipeline-reactor technology for the high-temperature, high-pressure (HTHP) reaction of the minerals in aqueous/CO2 media. Sequestration of CO2 using above-ground reactors may be uneconomical, but the technology may also be applicable in geological sequestration of CO2. Progress is described in using a prototype HTHP flow-loop reactor to model flow in the dynamic three-phase system to help determine the pumping-energy requirements to optimize reactivity.
A cellular automaton model for ship traffic flow in waterways
NASA Astrophysics Data System (ADS)
Qi, Le; Zheng, Zhongyi; Gang, Longhui
2017-04-01
With the development of marine traffic, waterways become congested and more complicated traffic phenomena in ship traffic flow are observed. It is important and necessary to build a ship traffic flow model based on cellular automata (CAs) to study the phenomena and improve marine transportation efficiency and safety. Spatial discretization rules for waterways and update rules for ship movement are two important issues that are very different from vehicle traffic. To solve these issues, a CA model for ship traffic flow, called a spatial-logical mapping (SLM) model, is presented. In this model, the spatial discretization rules are improved by adding a mapping rule. And the dynamic ship domain model is considered in the update rules to describe ships' interaction more exactly. Take the ship traffic flow in the Singapore Strait for example, some simulations were carried out and compared. The simulations show that the SLM model could avoid ship pseudo lane-change efficiently, which is caused by traditional spatial discretization rules. The ship velocity change in the SLM model is consistent with the measured data. At finally, from the fundamental diagram, the relationship between traffic ability and the lengths of ships is explored. The number of ships in the waterway declines when the proportion of large ships increases.
Modelling susceptibility of grassland soil to macropore flow
NASA Astrophysics Data System (ADS)
Alaoui, Abdallah
2015-06-01
Investigating preferential flow, including macropore flow, is crucial to predicting and preventing point sources of contamination in soil, for example in the vicinity of pumping wells. With a view to advancing groundwater protection, this study aimed (i) to quantify the strength of macropore flow in four representative natural grassland soils on the Swiss plateau, and (ii) to define the parameters that significantly control macropore flow in grassland soil. For each soil type we selected three measurement points on which three successive irrigation experiments were carried out, resulting in a total of 36 irrigations. The strength of macropore flow, parameterized as the cumulated water volume flowing from macropores at a depth of 1 m in response to an irrigation of 60 mm h-1 intensity and 1 h duration, was simulated using the dual-permeability MACRO model. The model calibration was based on the key soil parameters and fine measurements of water content at different depths. Modelling results indicate high performance of macropore flow in all investigated soil types except in gleysols. The volume of water that flowed from macropores and was hence expected to reach groundwater varied between 81% and 94% in brown soils, 59% and 67% in para-brown soils, 43% and 56% in acid brown soils, and 22% and 35% in gleysols. These results show that spreading pesticides and herbicides in pumping well protection zones poses a high risk of contamination and must be strictly prohibited. We also found that organic carbon content was not correlated with the strength of macropore flow, probably due to its very weak variation in our study, while saturated water content showed a negative correlation with macropore flow. The correlation between saturated hydraulic conductivity (Ks) and macropore flow was negative as well, but weak. Macropore flow appears to be controlled by the interaction between the bulk density of the uppermost topsoil layer (0-0.10 m) and the macroporosity of the soil
Modeling Suspersonic Flow in the High-Latitude Thermosphere
NASA Astrophysics Data System (ADS)
Demars, H. G.; Schunk, R. W.
2007-12-01
Supersonic flow has been observed in the high-latitude thermosphere via DE-2 satellite measurements. The supersonic flow events were observed to occur most frequently in the dawn sector at high magnetic latitudes and in the altitude range from about 300-600 km. To gain theoretical insight into these supersonic flow events, we used a high-resolution model of the global thermosphere to study the geophysical conditions that give rise to supersonic flow. In particular, we considered the dependence of the neutral wind on IMF orientation, magnetic activity level, convection pattern shape, solar activity level, season, and universal time. We also studied the extent to which narrow plasma convection channels can induce supersonic neutral winds. We found that the predominant factor controlling the thermospheric wind speed at high latitudes is the magnitude of the cross- polar-cap potential, indicating that interaction with the convecting ionosphere can drive the thermosphere to supersonic speeds. The region of supersonic flow predicted by the model corresponds closely to the region where supersonic flow events were most frequently observed by the DE satellite.
Modeling steam pressure under martian lava flows
Dundas, Colin M.; Keszthelyi, Laszlo P.
2013-01-01
Rootless cones on Mars are a valuable indicator of past interactions between lava and water. However, the details of the lava–water interactions are not fully understood, limiting the ability to use these features to infer new information about past water on Mars. We have developed a model for the pressurization of a dry layer of porous regolith by melting and boiling ground ice in the shallow subsurface. This model builds on previous models of lava cooling and melting of subsurface ice. We find that for reasonable regolith properties and ice depths of decimeters, explosive pressures can be reached. However, the energy stored within such lags is insufficient to excavate thick flows unless they draw steam from a broader region than the local eruption site. These results indicate that lag pressurization can drive rootless cone formation under favorable circumstances, but in other instances molten fuel–coolant interactions are probably required. We use the model results to consider a range of scenarios for rootless cone formation in Athabasca Valles. Pressure buildup by melting and boiling ice under a desiccated lag is possible in some locations, consistent with the expected distribution of ice implanted from atmospheric water vapor. However, it is uncertain whether such ice has existed in the vicinity of Athabasca Valles in recent history. Plausible alternative sources include surface snow or an aqueous flood shortly before the emplacement of the lava flow.
Model reduction and feedback control of transitional channel flow
NASA Astrophysics Data System (ADS)
Ilak, Milos
) compensators, which include a reduced-order estimator based on a small number of velocity measurements, are designed for these models and used for feedback control of the energy growth of a localized perturbation near the channel wall. The performance of both a localized body-force near the channel wall and wall blowing/suction as actuation mechanisms is first studied in linearized DNS. It is found that the linear compensators are successful in reducing the growth of the perturbation energy, and that the body force actuation results in a larger decrease of the perturbation energy growth than actuation using wall blowing/suction. We then proceed to show that these compensators are also able to prevent transition to turbulence for nonlinear simulations in some cases, despite performance limitations imposed by the spatial separation of the perturbation and the actuator. Finally, since it is found that a fundamentally nonlinear mechanism of transition is not captured by the linear models, it is of interest to study nonlinear models for flow control. As a first step towards investigating nonlinear balanced truncation models of channel flow, a method for empirical nonlinear balanced truncation proposed by Lall et al. (2002) is tested on a nonlinear 1-D model problem, the Complex Ginzburg-Landau (CGL) equation. The performance of the resulting models is compared to the performance of nonlinear models obtained by projection of the full equation onto modes computed via balanced truncation of the linear part of the CGL equation. It is found that the models obtained by the latter approach are not only able to capture the dynamics of the nonlinear CGL equation, but that they also outperform the models obtained using the empirical nonlinear balanced truncation method.
Model validation for karst flow using sandbox experiments
NASA Astrophysics Data System (ADS)
Ye, M.; Pacheco Castro, R. B.; Tao, X.; Zhao, J.
2015-12-01
The study of flow in karst is complex due of the high heterogeneity of the porous media. Several approaches have been proposed in the literature to study overcome the natural complexity of karst. Some of those methods are the single continuum, double continuum and the discrete network of conduits coupled with the single continuum. Several mathematical and computing models are available in the literature for each approach. In this study one computer model has been selected for each category to validate its usefulness to model flow in karst using a sandbox experiment. The models chosen are: Modflow 2005, Modflow CFPV1 and Modflow CFPV2. A sandbox experiment was implemented in such way that all the parameters required for each model can be measured. The sandbox experiment was repeated several times under different conditions. The model validation will be carried out by comparing the results of the model simulation and the real data. This model validation will allows ud to compare the accuracy of each model and the applicability in Karst. Also we will be able to evaluate if the results of the complex models improve a lot compared to the simple models specially because some models require complex parameters that are difficult to measure in the real world.
TANK MIXING STUDY WITH FLOW RECIRCULATION
Lee, S.
2014-06-25
The primary objective of this work is to quantify the mixing time when two miscible fluids are mixed by one recirculation pump and to evaluate adequacy of 2.5 hours of pump recirculation to be considered well mixed in SRS tanks, JT-71/72. The work scope described here consists of two modeling analyses. They are the steady state flow pattern analysis during pump recirculation operation of the tank liquid and transient species transport calculations based on the initial steady state flow patterns. The modeling calculations for the mixing time are performed by using the 99% homogeneity criterion for the entire domain of the tank contents.
NASA Astrophysics Data System (ADS)
Geistlinger, H. W.; Samani, S.
2010-12-01
The injection of gases into the subsurface has become an important research topic in groundwater remediation technology, e.g. air sparging, and in CCS-technology, e.g. CO2-sequestration into saline aquifers. In both cases risk assessment is based on 2-phase flow modeling assuming that the stochastic gas flow patterns can be described by the continuum approach. As Cinar et al. (2009) have stated: “The fundamental understanding of drainage, as it applies to CO2 sequestration process, is limited primarily by the lack of well characterized experiments that allow a detailed classification of the microscopic flow regimes”. In case of air sparging the two important flow regimes are capillary fingering and viscous fingering. Using pore scale network modeling Ewing and Berkowitz (1998) were able to describe the transition from capillary fingering (= incoherent channelized flow) to viscous fingering (= coherent channelized flow). In order to investigate the stability of buoyancy-driven gas flow and the transition between coherent channelized flow and incoherent channelized flow we conducted high-resolution optical bench scale experiments. Our main results, which are in strong contradiction to the commonly used continuum models (CM) are: (1) Capillary trapping can already occur during injection and at the front of the plume (Lazik and Geistlinger, 2008) (2) Gas clusters or bubbles can be mobile (incoherent gas flow) and immobile (capillary trapping), and (3) Incoherent gas flow can not be described by a generalized Darcy law (Geistlinger et al., 2006, 2009). Glass et al. (2000) conducted CO2-gas injection experiments. Based on their experimental results they also questioned the validity of CM to describe coherent and incoherent gas flow and the validity of homogeneous stability analysis to predict channel width, channel number and channel velocity in heterogeneous porous media. Despite these findings there is an ongoing controversial discussion in the literature about
In-line pressure-flow module for in vitro modelling of haemodynamics and biosensor validation
NASA Technical Reports Server (NTRS)
Koenig, S. C.; Schaub, J. D.; Ewert, D. L.; Swope, R. D.; Convertino, V. A. (Principal Investigator)
1997-01-01
An in-line pressure-flow module for in vitro modelling of haemodynamics and biosensor validation has been developed. Studies show that good accuracy can be achieved in the measurement of pressure and of flow, in steady and pulstile flow systems. The model can be used for development, testing and evaluation of cardiovascular-mechanical-electrical anlogue models, cardiovascular prosthetics (i.e. valves, vascular grafts) and pressure and flow biosensors.
HIGHER EDUCATION--A POPULATION FLOW FEEDBACK MODEL.
ERIC Educational Resources Information Center
REISMAN, ARNOLD
A MATHEMATICAL MODEL IS DEVELOPED TO STUDY THE PRODUCTION OF DOCTORAL, MASTER'S, AND BACHELOR'S DEGREES AND THEIR FEEDBACK INTO HIGHER EDUCATION. FEEDBACK IS DETERMINED BY A SET OF "BASIC BALANCE EQUATIONS" WHICH STATE THAT THE TOTAL RATE OF FLOW INTO A CATEGORY LESS THE RATE OF OUTFLOW IS EQUAL TO THE RATE OF ACCUMULATION OR GROWTH IN A GIVEN…
Modeling metal stocks and flows: a review of dynamic material flow analysis methods.
Müller, Esther; Hilty, Lorenz M; Widmer, Rolf; Schluep, Mathias; Faulstich, Martin
2014-02-18
Dynamic material flow analysis (MFA) is a frequently used method to assess past, present, and future stocks and flows of metals in the anthroposphere. Over the past fifteen years, dynamic MFA has contributed to increased knowledge about the quantities, qualities, and locations of metal-containing goods. This article presents a literature review of the methodologies applied in 60 dynamic MFAs of metals. The review is based on a standardized model description format, the ODD (overview, design concepts, details) protocol. We focus on giving a comprehensive overview of modeling approaches and structure them according to essential aspects, such as their treatment of material dissipation, spatial dimension of flows, or data uncertainty. The reviewed literature features similar basic modeling principles but very diverse extrapolation methods. Basic principles include the calculation of outflows of the in-use stock based on inflow or stock data and a lifetime distribution function. For extrapolating stocks and flows, authors apply constant, linear, exponential, and logistic models or approaches based on socioeconomic variables, such as regression models or the intensity-of-use hypothesis. The consideration and treatment of further aspects, such as dissipation, spatial distribution, and data uncertainty, vary significantly and highly depends on the objectives of each study.
Computational studies of flow through cross flow fans - effect of blade geometry
NASA Astrophysics Data System (ADS)
Govardhan, M.; Sampat, D. Lakshmana
2005-09-01
This present paper describes three dimensional computational analysis of complex internal flow in a cross flow fan. A commercial computational fluid dynamics (CFD) software code CFX was used for the computation. RNG k-ɛ two equation turbulence model was used to simulate the model with unstructured mesh. Sliding mesh interface was used at the interface between the rotating and stationary domains to capture the unsteady interactions. An accurate assessment of the present investigation is made by comparing various parameters with the available experimental data. Three impeller geometries with different blade angles and radius ratio are used in the present study. Maximum energy transfer through the impeller takes place in the region where the flow follows the blade curvature. Radial velocity is not uniform through blade channels. Some blades work in turbine mode at very low flow coefficients. Static pressure is always negative in and around the impeller region.
Observing and modeling Earths energy flows
Stevens B.; Schwartz S.
2012-05-11
This article reviews, from the authors perspective, progress in observing and modeling energy flows in Earth's climate system. Emphasis is placed on the state of understanding of Earth's energy flows and their susceptibility to perturbations, with particular emphasis on the roles of clouds and aerosols. More accurate measurements of the total solar irradiance and the rate of change of ocean enthalpy help constrain individual components of the energy budget at the top of the atmosphere to within {+-}2 W m{sup -2}. The measurements demonstrate that Earth reflects substantially less solar radiation and emits more terrestrial radiation than was believed even a decade ago. Active remote sensing is helping to constrain the surface energy budget, but new estimates of downwelling surface irradiance that benefit from such methods are proving difficult to reconcile with existing precipitation climatologies. Overall, the energy budget at the surface is much more uncertain than at the top of the atmosphere. A decade of high-precision measurements of the energy budget at the top of the atmosphere is providing new opportunities to track Earth's energy flows on timescales ranging from days to years, and at very high spatial resolution. The measurements show that the principal limitation in the estimate of secular trends now lies in the natural variability of the Earth system itself. The forcing-feedback-response framework, which has developed to understand how changes in Earth's energy flows affect surface temperature, is reviewed in light of recent work that shows fast responses (adjustments) of the system are central to the definition of the effective forcing that results from a change in atmospheric composition. In many cases, the adjustment, rather than the characterization of the compositional perturbation (associated, for instance, with changing greenhouse gas concentrations, or aerosol burdens), limits accurate determination of the radiative forcing. Changes in clouds
Observing and Modeling Earth's Energy Flows
NASA Astrophysics Data System (ADS)
Stevens, Bjorn; Schwartz, Stephen E.
2012-07-01
This article reviews, from the authors' perspective, progress in observing and modeling energy flows in Earth's climate system. Emphasis is placed on the state of understanding of Earth's energy flows and their susceptibility to perturbations, with particular emphasis on the roles of clouds and aerosols. More accurate measurements of the total solar irradiance and the rate of change of ocean enthalpy help constrain individual components of the energy budget at the top of the atmosphere to within ±2 W m-2. The measurements demonstrate that Earth reflects substantially less solar radiation and emits more terrestrial radiation than was believed even a decade ago. Active remote sensing is helping to constrain the surface energy budget, but new estimates of downwelling surface irradiance that benefit from such methods are proving difficult to reconcile with existing precipitation climatologies. Overall, the energy budget at the surface is much more uncertain than at the top of the atmosphere. A decade of high-precision measurements of the energy budget at the top of the atmosphere is providing new opportunities to track Earth's energy flows on timescales ranging from days to years, and at very high spatial resolution. The measurements show that the principal limitation in the estimate of secular trends now lies in the natural variability of the Earth system itself. The forcing-feedback-response framework, which has developed to understand how changes in Earth's energy flows affect surface temperature, is reviewed in light of recent work that shows fast responses (adjustments) of the system are central to the definition of the effective forcing that results from a change in atmospheric composition. In many cases, the adjustment, rather than the characterization of the compositional perturbation (associated, for instance, with changing greenhouse gas concentrations, or aerosol burdens), limits accurate determination of the radiative forcing. Changes in clouds contribute
Yakirevich, A; Pachepsky, Y A; Guber, A K; Gish, T J; Shelton, D R; Cho, K H
2013-05-15
Escherichia coli is the leading indicator of microbial contamination of natural waters, and so its in-stream fate and transport needs to be understood to eventually minimize surface water contamination by microorganisms. To better understand mechanisms of E. coli release and transport from soil sediment in a creek the artificial high-water flow events were created by releasing 60-80 m(3) of city water on a tarp-covered stream bank in four equal allotments in July 2008, 2009 and 2010. A conservative tracer difluorobenzoic acid (DFBA) was added to the released water in 2009 and 2010. Water flow rate, E. coli and DFBA concentrations as well as water turbidity were monitored with automated samplers at three in-stream weirs. A one-dimensional model was applied to simulate water flow, and E. coli and DFBA transport during these experiments. The Saint-Venant equations were used to calculate water depth and discharge while a stream solute transport model accounted for release of bacteria by shear stress from bottom sediments, advection-dispersion, and exchange with transient storage (TS). Reach-specific model parameters were estimated by evaluating observed time series of flow rates and concentrations of DFBA and E. coli at all three weir stations. Observed DFBA and E. coli breakthrough curves (BTC) exhibited long tails after the water pulse and tracer peaks had passed indicating that transient storage (TS) might be an important element of the in-stream transport process. Comparison of simulated and measured E. coli concentrations indicated that significant release of E. coli continued when water flow returned to the base level after the water pulse passed and bottom shear stress was small. The mechanism of bacteria continuing release from sediment could be the erosive boundary layer exchange enhanced by changes in biofilm properties by erosion and sloughing detachment.
Ida, Masato; Taniguchi, Nobuyuki
2003-09-01
This paper introduces a candidate for the origin of the numerical instabilities in large eddy simulation repeatedly observed in academic and practical industrial flow computations. Without resorting to any subgrid-scale modeling, but based on a simple assumption regarding the streamwise component of flow velocity, it is shown theoretically that in a channel-flow computation, the application of the Gaussian filtering to the incompressible Navier-Stokes equations yields a numerically unstable term, a cross-derivative term, which is similar to one appearing in the Gaussian filtered Vlasov equation derived by Klimas [J. Comput. Phys. 68, 202 (1987)] and also to one derived recently by Kobayashi and Shimomura [Phys. Fluids 15, L29 (2003)] from the tensor-diffusivity subgrid-scale term in a dynamic mixed model. The present result predicts that not only the numerical methods and the subgrid-scale models employed but also only the applied filtering process can be a seed of this numerical instability. An investigation concerning the relationship between the turbulent energy scattering and the unstable term shows that the instability of the term does not necessarily represent the backscatter of kinetic energy which has been considered a possible origin of numerical instabilities in large eddy simulation. The present findings raise the question whether a numerically stable subgrid-scale model can be ideally accurate.
Numerical modeling of an all vanadium redox flow battery.
Clausen, Jonathan R.; Brunini, Victor E.; Moffat, Harry K.; Martinez, Mario J.
2014-01-01
We develop a capability to simulate reduction-oxidation (redox) flow batteries in the Sierra Multi-Mechanics code base. Specifically, we focus on all-vanadium redox flow batteries; however, the capability is general in implementation and could be adopted to other chemistries. The electrochemical and porous flow models follow those developed in the recent publication by [28]. We review the model implemented in this work and its assumptions, and we show several verification cases including a binary electrolyte, and a battery half-cell. Then, we compare our model implementation with the experimental results shown in [28], with good agreement seen. Next, a sensitivity study is conducted for the major model parameters, which is beneficial in targeting specific features of the redox flow cell for improvement. Lastly, we simulate a three-dimensional version of the flow cell to determine the impact of plenum channels on the performance of the cell. Such channels are frequently seen in experimental designs where the current collector plates are borrowed from fuel cell designs. These designs use a serpentine channel etched into a solid collector plate.
DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS
X. Wang; X. Sun; H. Zhao
2011-09-01
In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in
Simultaneous 3D Strain and Flow Fields Measurement of a Model Artery under Unsteady Flows
NASA Astrophysics Data System (ADS)
Toloui, Mostafa; Sheng, Jian
2011-11-01
Fluid-Structure Interaction imposes challenges in both aero-elasticity and biomedical studies. A simultaneous solid deformation and fluid flow measurement technique based on digital in-line holographic particle tracking velocimetry (PTV) has been developed. It allows us to measure concurrently 3D strain field of a deforming structure and the unsteady flow near it. To facilitate the measurement, both wall and flow are seeded with tracer particles distinguished by size. The motion of these tracers provides the 3D deformation of the wall and the 3D velocity distribution of the flow separately. A fully index matched facility including transparent artery and NaI solution is constructed to enable observations near the wall or through the complex geometry. An arterial model with the inner diameter of 9.5 mm and the thickness of 0.9 mm is manufactured from the cross-linked transparent PDMS at the mixing ratio of 1:10 and doped with mono-dispersed 19 μm polystyrene particles. A cinematic holographic PTV system is used to trace the 3D particle motion in the model and flow simultaneously. Preliminary study is performed within a sample volume of 15 × 15 × 75 mm with the spatial resolution of 7.4 μm in lateral and 10 μm in depth. Uncertainty and accuracy analysis will be reported. NSF Grant No: CBET-0844647.
Data-Flow Based Model Analysis
NASA Technical Reports Server (NTRS)
Saad, Christian; Bauer, Bernhard
2010-01-01
The concept of (meta) modeling combines an intuitive way of formalizing the structure of an application domain with a high expressiveness that makes it suitable for a wide variety of use cases and has therefore become an integral part of many areas in computer science. While the definition of modeling languages through the use of meta models, e.g. in Unified Modeling Language (UML), is a well-understood process, their validation and the extraction of behavioral information is still a challenge. In this paper we present a novel approach for dynamic model analysis along with several fields of application. Examining the propagation of information along the edges and nodes of the model graph allows to extend and simplify the definition of semantic constraints in comparison to the capabilities offered by e.g. the Object Constraint Language. Performing a flow-based analysis also enables the simulation of dynamic behavior, thus providing an "abstract interpretation"-like analysis method for the modeling domain.
The Piece Wise Linear Reactive Flow Model
Vitello, P; Souers, P C
2005-08-18
For non-ideal explosives a wide range of behavior is observed in experiments dealing with differing sizes and geometries. A predictive detonation model must be able to reproduce many phenomena including such effects as: variations in the detonation velocity with the radial diameter of rate sticks; slowing of the detonation velocity around gentle corners; production of dead zones for abrupt corner turning; failure of small diameter rate sticks; and failure for rate sticks with sufficiently wide cracks. Most models have been developed to explain one effect at a time. Often, changes are made in the input parameters used to fit each succeeding case with the implication that this is sufficient for the model to be valid over differing regimes. We feel that it is important to develop a model that is able to fit experiments with one set of parameters. To address this we are creating a new generation of models that are able to produce better fitting to individual data sets than prior models and to simultaneous fit distinctly different regimes of experiments. Presented here are details of our new Piece Wise Linear reactive flow model applied to LX-17.
Grand valley irrigation return flow case study
Keys, J.W.
1981-06-01
Irrigation water supply is furnished annually to about 71,500 acres of land in the Grand Valley of western Colorado. Return flows from that irrigation contribute about 780,000 tpy of salt to the Colorado River, causing an increase of 77 mg/l in the salinity concentration at Imperial Dam. A case study of water quality in this region is focused on: water quality data for irrigation and return flows/ identification of regulations that affect irrigation and return flows/ and a proposed program for controlling salinity levels. (1 map, 9 references, 8 tables)
Theory and Low-Order Modeling of Unsteady Airfoil Flows
NASA Astrophysics Data System (ADS)
Ramesh, Kiran
Unsteady flow phenomena are prevalent in a wide range of problems in nature and engineering. These include, but are not limited to, aerodynamics of insect flight, dynamic stall in rotorcraft and wind turbines, leading-edge vortices in delta wings, micro-air vehicle (MAV) design, gust handling and flow control. The most significant characteristics of unsteady flows are rapid changes in the circulation of the airfoil, apparent-mass effects, flow separation and the leading-edge vortex (LEV) phenomenon. Although experimental techniques and computational fluid dynamics (CFD) methods have enabled the detailed study of unsteady flows and their underlying features, a reliable and inexpensive loworder method for fast prediction and for use in control and design is still required. In this research, a low-order methodology based on physical principles rather than empirical fitting is proposed. The objective of such an approach is to enable insights into unsteady phenomena while developing approaches to model them. The basis of the low-order model developed here is unsteady thin-airfoil theory. A time-stepping approach is used to solve for the vorticity on an airfoil camberline, allowing for large amplitudes and nonplanar wakes. On comparing lift coefficients from this method against data from CFD and experiments for some unsteady test cases, it is seen that the method predicts well so long as LEV formation does not occur and flow over the airfoil is attached. The formation of leading-edge vortices (LEVs) in unsteady flows is initiated by flow separation and the formation of a shear layer at the airfoil's leading edge. This phenomenon has been observed to have both detrimental (dynamic stall in helicopters) and beneficial (high-lift flight in insects) effects. To predict the formation of LEVs in unsteady flows, a Leading Edge Suction Parameter (LESP) is proposed. This parameter is calculated from inviscid theory and is a measure of the suction at the airfoil's leading edge. It
Modeling of heavy-gas effects on airfoil flows
NASA Technical Reports Server (NTRS)
Drela, Mark
1992-01-01
Thermodynamic models were constructed for a calorically imperfect gas and for a non-ideal gas. These were incorporated into a quasi one dimensional flow solver to develop an understanding of the differences in flow behavior between the new models and the perfect gas model. The models were also incorporated into a two dimensional flow solver to investigate their effects on transonic airfoil flows. Specifically, the calculations simulated airfoil testing in a proposed high Reynolds number heavy gas test facility. The results indicate that the non-idealities caused significant differences in the flow field, but that matching of an appropriate non-dimensional parameter led to flows similar to those in air.
The Piecewise Linear Reactive Flow Rate Model
Vitello, P; Souers, P C
2005-07-22
Conclusions are: (1) Early calibrations of the Piece Wise Linear reactive flow model have shown that it allows for very accurate agreement with data for a broad range of detonation wave strengths. (2) The ability to vary the rate at specific pressures has shown that corner turning involves competition between the strong wave that travels roughly in a straight line and growth at low pressure of a new wave that turns corners sharply. (3) The inclusion of a low pressure de-sensitization rate is essential to preserving the dead zone at large times as is observed.
Technology Transfer Automated Retrieval System (TEKTRAN)
Current physically based overland flow erosion models for rangeland application do not separate disturbed and undisturbed conditions in modeling concentrated flow erosion. In this study, concentrated flow simulations on disturbed and undisturbed rangelands were used to estimate the erodibility and t...
Complex groundwater flow systems as traveling agent models.
López Corona, Oliver; Padilla, Pablo; Escolero, Oscar; González, Tomas; Morales-Casique, Eric; Osorio-Olvera, Luis
2014-01-01
Analyzing field data from pumping tests, we show that as with many other natural phenomena, groundwater flow exhibits complex dynamics described by 1/f power spectrum. This result is theoretically studied within an agent perspective. Using a traveling agent model, we prove that this statistical behavior emerges when the medium is complex. Some heuristic reasoning is provided to justify both spatial and dynamic complexity, as the result of the superposition of an infinite number of stochastic processes. Even more, we show that this implies that non-Kolmogorovian probability is needed for its study, and provide a set of new partial differential equations for groundwater flow.
Complex groundwater flow systems as traveling agent models
Padilla, Pablo; Escolero, Oscar; González, Tomas; Morales-Casique, Eric; Osorio-Olvera, Luis
2014-01-01
Analyzing field data from pumping tests, we show that as with many other natural phenomena, groundwater flow exhibits complex dynamics described by 1/f power spectrum. This result is theoretically studied within an agent perspective. Using a traveling agent model, we prove that this statistical behavior emerges when the medium is complex. Some heuristic reasoning is provided to justify both spatial and dynamic complexity, as the result of the superposition of an infinite number of stochastic processes. Even more, we show that this implies that non-Kolmogorovian probability is needed for its study, and provide a set of new partial differential equations for groundwater flow. PMID:25337455
Conceptual and Numerical Models for UZ Flow and Transport
H. Liu
2000-03-03
The purpose of this Analysis/Model Report (AMR) is to document the conceptual and numerical models used for modeling of unsaturated zone (UZ) fluid (water and air) flow and solute transport processes. This is in accordance with ''AMR Development Plan for U0030 Conceptual and Numerical Models for Unsaturated Zone (UZ) Flow and Transport Processes, Rev 00''. The conceptual and numerical modeling approaches described in this AMR are used for models of UZ flow and transport in fractured, unsaturated rock under ambient and thermal conditions, which are documented in separate AMRs. This AMR supports the UZ Flow and Transport Process Model Report (PMR), the Near Field Environment PMR, and the following models: Calibrated Properties Model; UZ Flow Models and Submodels; Mountain-Scale Coupled Processes Model; Thermal-Hydrologic-Chemical (THC) Seepage Model; Drift Scale Test (DST) THC Model; Seepage Model for Performance Assessment (PA); and UZ Radionuclide Transport Models.
Computational Flow Modeling of Human Upper Airway Breathing
NASA Astrophysics Data System (ADS)
Mylavarapu, Goutham
Computational modeling of biological systems have gained a lot of interest in biomedical research, in the recent past. This thesis focuses on the application of computational simulations to study airflow dynamics in human upper respiratory tract. With advancements in medical imaging, patient specific geometries of anatomically accurate respiratory tracts can now be reconstructed from Magnetic Resonance Images (MRI) or Computed Tomography (CT) scans, with better and accurate details than traditional cadaver cast models. Computational studies using these individualized geometrical models have advantages of non-invasiveness, ease, minimum patient interaction, improved accuracy over experimental and clinical studies. Numerical simulations can provide detailed flow fields including velocities, flow rates, airway wall pressure, shear stresses, turbulence in an airway. Interpretation of these physical quantities will enable to develop efficient treatment procedures, medical devices, targeted drug delivery etc. The hypothesis for this research is that computational modeling can predict the outcomes of a surgical intervention or a treatment plan prior to its application and will guide the physician in providing better treatment to the patients. In the current work, three different computational approaches Computational Fluid Dynamics (CFD), Flow-Structure Interaction (FSI) and Particle Flow simulations were used to investigate flow in airway geometries. CFD approach assumes airway wall as rigid, and relatively easy to simulate, compared to the more challenging FSI approach, where interactions of airway wall deformations with flow are also accounted. The CFD methodology using different turbulence models is validated against experimental measurements in an airway phantom. Two case-studies using CFD, to quantify a pre and post-operative airway and another, to perform virtual surgery to determine the best possible surgery in a constricted airway is demonstrated. The unsteady
Uncertainty quantification in reacting flow modeling.
Le MaÒitre, Olivier P.; Reagan, Matthew T.; Knio, Omar M.; Ghanem, Roger Georges; Najm, Habib N.
2003-10-01
Uncertainty quantification (UQ) in the computational modeling of physical systems is important for scientific investigation, engineering design, and model validation. In this work we develop techniques for UQ based on spectral and pseudo-spectral polynomial chaos (PC) expansions, and we apply these constructions in computations of reacting flow. We develop and compare both intrusive and non-intrusive spectral PC techniques. In the intrusive construction, the deterministic model equations are reformulated using Galerkin projection into a set of equations for the time evolution of the field variable PC expansion mode strengths. The mode strengths relate specific parametric uncertainties to their effects on model outputs. The non-intrusive construction uses sampling of many realizations of the original deterministic model, and projects the resulting statistics onto the PC modes, arriving at the PC expansions of the model outputs. We investigate and discuss the strengths and weaknesses of each approach, and identify their utility under different conditions. We also outline areas where ongoing and future research are needed to address challenges with both approaches.
Evaluation of a watershed model for estimating daily flow using limited flow measurements
Technology Transfer Automated Retrieval System (TEKTRAN)
The Soil and Water Assessment Tool (SWAT) model was evaluated for estimation of continuous daily flow based on limited flow measurements in the Upper Oyster Creek (UOC) watershed. SWAT was calibrated against limited measured flow data and then validated. The Nash-Sutcliffe model Efficiency (NSE) and...
NASA Technical Reports Server (NTRS)
Cho, Y. I.; Crawford, D. W.; Back, L. H.; Back, M. R.
1987-01-01
A flow visualization study using selective dye injection and frame by frame analysis of a movie provided qualitative and quantitative data on the motion of marked fluid particles in a 60 degree artery branch model for simulation of physiological femoral artery flow. Physical flow features observed included jetting of the branch flow into the main lumen during the brief reverse flow period, flow separation along the main lumen wall during the near zero flow phase of diastole when the core flow was in the downstream direction, and inference of flow separation conditions along the wall opposite the branch later in systole at higher branch flow ratios. There were many similarities between dye particle motions in pulsatile flow and the comparative steady flow observations.
NASA Technical Reports Server (NTRS)
Lorincz, D. J.
1980-01-01
Water tunnel studies were performed to define the changes that occur in vortex flow fields above the wing due to spanwise blowing over the inboard and outboard wing panels and over the trailing-edge flaps. Flow visualization photographs were obtained for angles of attack up to 30 deg and sideslip angles up to 10 deg. The sensitivity of the vortex flows to changes in flap deflection angle, nozzle position, and jet momentum coefficient was determined. Deflection of the leading edge flap delayed flow separation and the formation of the wing vortex to higher angles of attack. Spanwise blowing delayed the breakdown of the wing vortex to farther outboard and to higher angles of attack. Spanwise blowing over the trailing edge flap entrained flow downward, producing a lift increase over a wide range of angles of attack. The sweep angle of the windward wing was effectively reduced in sideslip. This decreased the stability of the wing vortex, and it burst farther inboard. Reduced wing sweep required a higher blowing rate to maintain a stable vortex. A vortex could be stabilized on the outboard wing panel when an outboard blowing nozzle was used. Blowing from both an inboard and an outboard nozzle was found to have a favorable interaction.
Mathematical modelling of flow distribution in the human cardiovascular system
NASA Technical Reports Server (NTRS)
Sud, V. K.; Srinivasan, R. S.; Charles, J. B.; Bungo, M. W.
1992-01-01
The paper presents a detailed model of the entire human cardiovascular system which aims to study the changes in flow distribution caused by external stimuli, changes in internal parameters, or other factors. The arterial-venous network is represented by 325 interconnected elastic segments. The mathematical description of each segment is based on equations of hydrodynamics and those of stress/strain relationships in elastic materials. Appropriate input functions provide for the pumping of blood by the heart through the system. The analysis employs the finite-element technique which can accommodate any prescribed boundary conditions. Values of model parameters are from available data on physical and rheological properties of blood and blood vessels. As a representative example, simulation results on changes in flow distribution with changes in the elastic properties of blood vessels are discussed. They indicate that the errors in the calculated overall flow rates are not significant even in the extreme case of arteries and veins behaving as rigid tubes.
A model for multiphase flows through poroelastic media
Ahmadi, Goodarz; Mazaheri, Ali Reza; Smith, D.H
2003-01-01
A continuum model for multiphase fluid mixture flows through poroelastic media is presented. The basic conservation laws developed via a volume averaging technique are considered. Effects of phasic equilibrated forces are included in the model. Based on the thermodynamics of the multiphase mixture flows, appropriate constitutive equations are formulated. The entropy inequality is exploited, and the method of Lagrangian multiplier is used along with the phasic conservation laws to derive the constitutive equations for the phasic stress tensors, equilibrated stress vectors, and the interactions terms. The special cases of wave propagation in poroelastic media saturated with multiphase fluids, and multiphase flows through porous media, are studied. It is shown that the present theory leads to the extended Darcy’s law and contains, as a special case, Biot’s theory of saturated poroelastic media.
Optical instrumentation and study of gas-solid suspension flows
Ling, S.C.; Pao, H.P.
1990-09-01
A new technique and particle detecting system for the quantification of local fluid flow velocities, particle concentrations and size distributions in gas-solid suspension flows has been successfully developed and constructed. A new 2-inch diameter pneumatic-pipe test-loop facility for study of solids transport flows has been built and in operation. In order to check scaling law developed from the experimental results in the 2-inch pipe, a 4-inch pipe test-loop facility was also designed and constructed. In the past, the mechanics of suspended-solid flow have not been solved in a closed form due to the lack of a model for the turbulent field to pick up solid particles from the flow boundary. In this research project, we have identified the existence of micro-hairpin vortices as a major mechanism for the lifting of solid particles from the flow boundary. This permits one to formulate a realistic model. That is, the introduction of a particle source term in the governing transport equation for the suspended particles. The resultant solution predicts the correct critical flow conditions for the initial pickup of different sizes of solid particles and their subsequent concentrations in the flow field. 21 figs.
Study of the Transition Flow Regime using Monte Carlo Methods
NASA Technical Reports Server (NTRS)
Hassan, H. A.
1999-01-01
This NASA Cooperative Agreement presents a study of the Transition Flow Regime Using Monte Carlo Methods. The topics included in this final report are: 1) New Direct Simulation Monte Carlo (DSMC) procedures; 2) The DS3W and DS2A Programs; 3) Papers presented; 4) Miscellaneous Applications and Program Modifications; 5) Solution of Transitional Wake Flows at Mach 10; and 6) Turbulence Modeling of Shock-Dominated Fows with a k-Enstrophy Formulation.
Graphical models for optimal power flow
Dvijotham, Krishnamurthy; Chertkov, Michael; Van Hentenryck, Pascal; Vuffray, Marc; Misra, Sidhant
2016-09-13
Optimal power flow (OPF) is the central optimization problem in electric power grids. Although solved routinely in the course of power grid operations, it is known to be strongly NP-hard in general, and weakly NP-hard over tree networks. In this paper, we formulate the optimal power flow problem over tree networks as an inference problem over a tree-structured graphical model where the nodal variables are low-dimensional vectors. We adapt the standard dynamic programming algorithm for inference over a tree-structured graphical model to the OPF problem. Combining this with an interval discretization of the nodal variables, we develop an approximation algorithm for the OPF problem. Further, we use techniques from constraint programming (CP) to perform interval computations and adaptive bound propagation to obtain practically efficient algorithms. Compared to previous algorithms that solve OPF with optimality guarantees using convex relaxations, our approach is able to work for arbitrary tree-structured distribution networks and handle mixed-integer optimization problems. Further, it can be implemented in a distributed message-passing fashion that is scalable and is suitable for “smart grid” applications like control of distributed energy resources. In conclusion, numerical evaluations on several benchmark networks show that practical OPF problems can be solved effectively using this approach.
Graphical models for optimal power flow
Dvijotham, Krishnamurthy; Chertkov, Michael; Van Hentenryck, Pascal; ...
2016-09-13
Optimal power flow (OPF) is the central optimization problem in electric power grids. Although solved routinely in the course of power grid operations, it is known to be strongly NP-hard in general, and weakly NP-hard over tree networks. In this paper, we formulate the optimal power flow problem over tree networks as an inference problem over a tree-structured graphical model where the nodal variables are low-dimensional vectors. We adapt the standard dynamic programming algorithm for inference over a tree-structured graphical model to the OPF problem. Combining this with an interval discretization of the nodal variables, we develop an approximation algorithmmore » for the OPF problem. Further, we use techniques from constraint programming (CP) to perform interval computations and adaptive bound propagation to obtain practically efficient algorithms. Compared to previous algorithms that solve OPF with optimality guarantees using convex relaxations, our approach is able to work for arbitrary tree-structured distribution networks and handle mixed-integer optimization problems. Further, it can be implemented in a distributed message-passing fashion that is scalable and is suitable for “smart grid” applications like control of distributed energy resources. In conclusion, numerical evaluations on several benchmark networks show that practical OPF problems can be solved effectively using this approach.« less
Advanced Combustion Modeling for Complex Turbulent Flows
NASA Technical Reports Server (NTRS)
Ham, Frank Stanford
2005-01-01
The next generation of aircraft engines will need to pass stricter efficiency and emission tests. NASA's Ultra-Efficient Engine Technology (UEET) program has set an ambitious goal of 70% reduction of NO(x) emissions and a 15% increase in fuel efficiency of aircraft engines. We will demonstrate the state-of-the-art combustion tools developed a t Stanford's Center for Turbulence Research (CTR) as part of this program. In the last decade, CTR has spear-headed a multi-physics-based combustion modeling program. Key technologies have been transferred to the aerospace industry and are currently being used for engine simulations. In this demo, we will showcase the next-generation combustion modeling tools that integrate a very high level of detailed physics into advanced flow simulation codes. Combustor flows involve multi-phase physics with liquid fuel jet breakup, evaporation, and eventual combustion. Individual components of the simulation are verified against complex test cases and show excellent agreement with experimental data.
Free-surface turbulent flow and contaminants transport modeling
Wang, S.S.Y.
1994-12-31
The requirement of maintaining the environmental quality and ecological balance of the surface water systems at the acceptable level both now and in the future has accelerated the development and refinement of a cost-effective engineering analysis and design tool--Computational Modeling. This paper presents the progress of an on-going study to develop and refine computational models to simulate the free-surface turbulent flows and contaminants transport phenomena. New developments include: the efficient Element Method, which adopts the advantages of both Finite Element and Finite Difference; the most effective up-winding and/or characteristic-path integration; the prescribed solution forcing to conduct modeling verification studies of this correctness and capabilities in prediction of nonlinear effects; among others. The newly refined computational models have been applied to simulate unsteady, three-dimensional, turbulent, free-surface flows and pollutant transport in lakes, reservoirs, streams, rivers, estuaries, and coastal waters with natural (highly-irregular) geometric configurations. They have been verified in some cases to be able to predict basic physical characteristics of the free surface flows including boundary layer separations and re-attachments, wake flow and vortex shedding, corner separation and re-circulation, etc. They are also capable of simulating the transport of solute substances, solid particles and heat energy in these waters. Results can be displayed in stationary (snapshots) color graphics and in animation (motion pictures) recorded on video cassettes.
Electro-osmotic flow of a model electrolyte.
Zhu, Wei; Singer, Sherwin J; Zheng, Zhi; Conlisk, A T
2005-04-01
Electro-osmotic flow is studied by nonequilibrium molecular dynamics simulations in a model system chosen to elucidate various factors affecting the velocity profile and facilitate comparison with existing continuum theories. The model system consists of spherical ions and solvent, with stationary, uniformly charged walls that make a channel with a height of 20 particle diameters. We find that hydrodynamic theory adequately describes simple pressure-driven (Poiseuille) flow in this model. However, Poisson-Boltzmann theory fails to describe the ion distribution in important situations, and therefore continuum fluid dynamics based on the Poisson-Boltzmann ion distribution disagrees with simulation results in those situations. The failure of Poisson-Boltzmann theory is traced to the exclusion of ions near the channel walls resulting from reduced solvation of the ions in that region. When a corrected ion distribution is used as input for hydrodynamic theory, agreement with numerical simulations is restored. An analytic theory is presented that demonstrates that repulsion of the ions from the channel walls increases the flow rate, and attraction to the walls has the opposite effect. A recent numerical study of electro-osmotic flow is reanalyzed in the light of our findings, and the results conform well to our conclusions for the model system.
Chowdhury, Rubel Biswas; Moore, Graham A; Weatherley, Anthony J; Arora, Meenakshi
2016-12-01
Achieving sustainable management of phosphorus (P) is crucial for both global food security and global environmental protection. In order to formulate informed policy measures to overcome existing barriers of achieving sustainable P management, there is need for a sound understanding of the nature and magnitude of P flow through various systems at different geographical and temporal scales. So far, there is a limited understanding on the nature and magnitude of P flow over multiple years at the regional scale. In this study, we have developed a novel substance flow analysis (SFA) model in the MATLAB/Simulink® software platform that can be effectively utilized to analyse the nature and magnitude of multi-year P flow at the regional scale. The model is inclusive of all P flows and storage relating to all key systems, subsystems, processes or components, and the associated interactions of P flow required to represent a typical P flow system at the regional scale. In an annual time step, this model can analyse P flow and storage over as many as years required at a time, and therefore, can indicate the trends and changes in P flow and storage over many years, which is not offered by the existing regional scale SFA models of P. The model is flexible enough to allow any modification or the inclusion of any degree of complexity, and therefore, can be utilized for analysing P flow in any region around the world. The application of the model in the case of Gippsland region, Australia has revealed that the model generates essential information about the nature and magnitude of P flow at the regional scale which can be utilized for making improved management decisions towards attaining P sustainability. A systematic reliability check on the findings of model application also indicates that the model produces reliable results.
Comparative Study of Airfoil Flow Separation Criteria
NASA Astrophysics Data System (ADS)
Laws, Nick; Kahouli, Waad; Epps, Brenden
2015-11-01
Airfoil flow separation impacts a multitude of applications including turbomachinery, wind turbines, and bio-inspired micro-aerial vehicles. In order to achieve maximum performance, some devices operate near the edge of flow separation, and others use dynamic flow separation advantageously. Numerous criteria exist for predicting the onset of airfoil flow separation. This talk presents a comparative study of a number of such criteria, with emphasis paid to speed and accuracy of the calculations. We evaluate the criteria using a two-dimensional unsteady vortex lattice method, which allows for rapid analysis (on the order of seconds instead of days for a full Navier-Stokes solution) and design of optimal airfoil geometry and kinematics. Furthermore, dynamic analyses permit evaluation of dynamic stall conditions for enhanced lift via leading edge vortex shedding, commonly present in small flapping-wing flyers such as the bumblebee and hummingbird.
GENERAL: A modified weighted probabilistic cellular automaton traffic flow model
NASA Astrophysics Data System (ADS)
Zhuang, Qian; Jia, Bin; Li, Xin-Gang
2009-08-01
This paper modifies the weighted probabilistic cellular automaton model (Li X L, Kuang H, Song T, et al 2008 Chin. Phys. B 17 2366) which considered a diversity of traffic behaviors under real traffic situations induced by various driving characters and habits. In the new model, the effects of the velocity at the last time step and drivers' desire for acceleration are taken into account. The fundamental diagram, spatial-temporal diagram, and the time series of one-minute data are analyzed. The results show that this model reproduces synchronized flow. Finally, it simulates the on-ramp system with the proposed model. Some characteristics including the phase diagram are studied.
Modeling the flows of engineered nanomaterials during waste handling.
Mueller, Nicole C; Buha, Jelena; Wang, Jing; Ulrich, Andrea; Nowack, Bernd
2013-01-01
Little is known about the behavior of engineered nanomaterials (ENM) at the interface from the technosphere to the ecosphere. Previous modeling of ENM flows to the environment revealed that significant amounts of ENM enter the waste stream and therefore waste incineration plants and landfills. It is the aim of this study to model the flows of ENM during waste incineration and landfilling in greater depth by including a more detailed description of the different processes and considering ENM-specific transformation reactions. Four substances were modeled: nano-TiO2, nano-ZnO, nano-Ag and carbon nanotube (CNT). These ENM are representative for commonly used materials and products, illustrating a variety of ENM with different behavior. The modeling was performed for Switzerland where almost 100% of the municipal waste and sewage sludge are burned. The mass-based modeling showed that – despite several differences among the models for nano-TiO2, nano-ZnO and nano-Ag (e.g. partial dissolution of nano-ZnO in acid washing of exhaust air or fly ash) – the major ENM flows go from the waste incineration plant to the landfill as bottom ash. All other flows within the system boundary (e.g. with the fly ash) were predicted to be about one magnitude smaller than the bottom ash flow. A different ENM distribution was found for CNTs that are expected to burn to a large extent (94%) so that only insignificant amounts remain in the system. The results of the modeling show that waste incineration can have a strong influence on some ENM but that still the majority of the ENM-mass is expected to end up in landfills.
Flow behavior and applicability of models for different hemodynamic states.
Cymberknop, L; Pessana, F; Armentano, R; Legnani, W; Furfaro, A
2010-01-01
Arterial behavior analysis requires an accurate and dynamic knowledge of the stimuli and reactions involved. Belonging parameters quantification is performed by a data acquisition process and the application of existing models. However, it turns essentially to analyze the adjustment degree of the aforementioned models in terms of the arterial tree. Blood flow behavior as well as wall shear rate and the arterial compliance are anatomic location dependent. The main objective of the present work is to analyze the existing functional relationships between arterial wall and blood flow, in a particular place (brachial artery), in order to asses the specific model applicability, in cases such Poiseuille or Womersley models. In addition, due to the characteristic of the study, gender differential dynamic responses will be evaluated.
Concentrated Flow through a Riparian Buffer: A Case Study
NASA Astrophysics Data System (ADS)
Young, C. B.; Nogues, J. P.; Hutchinson, S. L.
2005-05-01
Riparian buffers are often used for in-situ treatment of agricultural runoff. Although the benefits of riparian buffers are well recongized, concentration of flow can restrict the efficiency of contaminant removal. This study evaluates flow concentration at a agricultural site near Manhattan, Kansas. Manual and automated GIS analyses of a high-resolution digital elevation model were used to determine the fraction of runoff contributing to each buffer segment. Subsequent simulation of the system in WEPP (Water Erosion and Prediction Project) demonstrates the extent to which flow concentration affects buffer efficiency. Recommendations are presented for the design of adaptive-width buffers.
Concentrated Flow through a Riparian Buffer: A Case Study
NASA Astrophysics Data System (ADS)
Young, C. B.; Nogues, J. P.; Hutchinson, S. L.
2004-05-01
Riparian buffers are often used for in-situ treatment of agricultural runoff. Although the benefits of riparian buffers are well recongized, concentration of flow can restrict the efficiency of contaminant removal. This study evaluates flow concentration at a agricultural site near Manhattan, Kansas. Manual and automated GIS analyses of a high-resolution digital elevation model were used to determine the fraction of runoff contributing to each buffer segment. Subsequent simulation of the system in WEPP (Water Erosion and Prediction Project) demonstrates the extend to which flow concentration affects buffer efficiency.
Reynolds stress modeling of separated turbulent flows over helicopters
NASA Astrophysics Data System (ADS)
Alpman, Emre
A numerical investigation of inviscid and viscous flows around three-dimensional complex bodies is made using unstructured meshes. Inviscid flow solutions around an RAH-66 Comanche helicopter fuselage are performed to analyze the aerodynamics of ducted tail rotors in low-power, near-edgewise flow conditions. A numerical solution of the Euler Equations is obtained for the flow over the Comanche fuselage with a uniform actuator disk and blade element models for the FANTAIL(TM); the main rotor is excluded in this study. The solutions are obtained by running the PUMA2 computational fluid dynamics code with an unstructured grid with 2.8 million tetrahedral cells. PUMA2 is an in-house computer code written in ANSI C++. Excellent correlation between the calculations and a variety of static test data are presented and discussed. The dynamic relationship between the antitorque thrust moment and applied collective pitch angle is studied by changing the pitch angle input by five degrees at a rate of 144 degrees per second. Dynamic fan thrust and moment response to applied collective pitch in hover and forward flight are presented and discussed. In order to remove the deficiency of the Euler equations in predicting separated flows, which is mostly the case in helicopter fuselage aerodynamics, a concurrent study is performed to simulate turbulent flows around three-dimensional bodies. Most of the turbulence models in the literature contain simplified assumptions which make them computationally cheap but of limited accuracy. Dramatic improvements in the computer processing speed and parallel processing made it possible to use more complete models, such as Reynolds Stress Models, for turbulent flow simulations around complex geometries, which is the focus of this work. The Reynolds Stress Model consists of coupling Reynolds transport equations with the Favre-Reynolds averaged Navier-Stokes equations, which results in a system of 12 coupled nonlinear partial differential equations
NASA Astrophysics Data System (ADS)
Aly, Emad H.; Sayed, Hamed M.
2017-01-01
In the current work, we investigated effects of the velocity slip for the flow and heat transfer of four nanofluids over a non-linear stretching sheet taking into account the thermal radiation and magnetic field in presence of the effective electrical conductivity. The governing partial differential equations were transformed into a set of nonlinear ordinary differential equation using similarity transformations before being solved numerically by the Chebyshev pseudospectral differentiation matrix (ChPDM). It was found that the investigated parameters affect remarkably on the nanofluid stream function for the whole investigated nanoparticles. In addition, velocity and skin friction profiles of the four investigated nanofluids decreases and increases, respectively, with the increase of the magnetic parameter, first-order and second-order velocity slips. Further, the flow velocity, surface shear stress and temperature are strongly influenced on applying the velocity slip model, where lower values of the second-order imply higher surface heat flux and thereby making the fluid warmer.