Effect of a 3D surface depression on boundary layer transition
NASA Astrophysics Data System (ADS)
Xu, Hui; Mughal, Shahid; Sherwin, Spencer J.
2015-11-01
The influence of a three-dimensional surface depression on the transitional boundary layer is investigated numerically. In the boundary layer transition, the primary mode is a Tollmien-Schlichting (TS) wave which is a viscous instability. These modes are receptive to surface roughness interacting with free stream disturbances and/or surface vibrations. In this paper, numerical calculations are carried out to investigate the effect of the depression on instability of the boundary layer. In order to implement linear analysis, two/three (2D/3D)-dimensional nonlinear Navier-Stokes equations are solved by spectral element method to generate base flows in a sufficient large domain. The linear analyses are done by the parabolic stability equations (PSE). Finally, a DNS calculation is done to simulate the boundary layer transition.
CFL3D Contribution to the AIAA Supersonic Shock Boundary Layer Interaction Workshop
NASA Technical Reports Server (NTRS)
Rumsey, Christopher L.
2010-01-01
This paper documents the CFL3D contribution to the AIAA Supersonic Shock Boundary Layer Interaction Workshop, held in Orlando, Florida in January 2010. CFL3D is a Reynolds-averaged Navier-Stokes code. Four shock boundary layer interaction cases are computed using a one-equation turbulence model widely used for other aerodynamic problems of interest. Two of the cases have experimental data available at the workshop, and two of the cases do not. The effect of grid, flux scheme, and thin-layer approximation are investigated. Comparisons are made to the available experimental data. All four cases exhibit strong three-dimensional behavior in and near the interaction regions, resulting from influences of the tunnel side-walls.
Vortex instabilities in 3D boundary layers: The relationship between Goertler and crossflow vortices
NASA Technical Reports Server (NTRS)
Bassom, Andrew; Hall, Philip
1990-01-01
The inviscid and viscous stability problems are addressed for a boundary layer which can support both Goertler and crossflow vortices. The change in structure of Goertler vortices is found when the parameter representing the degree of three-dimensionality of the basic boundary layer flow under consideration is increased. It is shown that crossflow vortices emerge naturally as this parameter is increased and ultimately become the only possible vortex instability of the flow. It is shown conclusively that at sufficiently large values of the crossflow there are no unstable Goertler vortices present in a boundary layer which, in the zero crossflow case, is centrifugally unstable. The results suggest that in many practical applications Goertler vortices cannot be a cause of transition because they are destroyed by the 3-D nature of the basic state. In swept wing flows the Goertler mechanism is probably not present for typical angles of sweep of about 20 degrees. Some discussion of the receptivity problem for vortex instabilities in weakly 3-D boundary layers is given; it is shown that inviscid modes have a coupling coefficient marginally smaller than those of the fastest growing viscous modes discussed recently by Denier, Hall, and Seddougui (1990). However the fact that the growth rates of the inviscid modes are the largest in most situations means that they are probably the most likely source of transition.
NASA Astrophysics Data System (ADS)
Späth, Florian; Behrendt, Andreas; Muppa, Shravan Kumar; Metzendorf, Simon; Riede, Andrea; Wulfmeyer, Volker
2016-04-01
High-resolution three-dimensional (3-D) water vapor data of the atmospheric boundary layer (ABL) are required to improve our understanding of land-atmosphere exchange processes. For this purpose, the scanning differential absorption lidar (DIAL) of the University of Hohenheim (UHOH) was developed as well as new analysis tools and visualization methods. The instrument determines 3-D fields of the atmospheric water vapor number density with a temporal resolution of a few seconds and a spatial resolution of up to a few tens of meters. We present three case studies from two field campaigns. In spring 2013, the UHOH DIAL was operated within the scope of the HD(CP)2 Observational Prototype Experiment (HOPE) in western Germany. HD(CP)2 stands for High Definition of Clouds and Precipitation for advancing Climate Prediction and is a German research initiative. Range-height indicator (RHI) scans of the UHOH DIAL show the water vapor heterogeneity within a range of a few kilometers up to an altitude of 2 km and its impact on the formation of clouds at the top of the ABL. The uncertainty of the measured data was assessed for the first time by extending a technique to scanning data, which was formerly applied to vertical time series. Typically, the accuracy of the DIAL measurements is between 0.5 and 0.8 g m-3 (or < 6 %) within the ABL even during daytime. This allows for performing a RHI scan from the surface to an elevation angle of 90° within 10 min. In summer 2014, the UHOH DIAL participated in the Surface Atmosphere Boundary Layer Exchange (SABLE) campaign in southwestern Germany. Conical volume scans were made which reveal multiple water vapor layers in three dimensions. Differences in their heights in different directions can be attributed to different surface elevation. With low-elevation scans in the surface layer, the humidity profiles and gradients can be related to different land cover such as maize, grassland, and forest as well as different surface layer
Skin-friction measurements in a 3-D, supersonic shock-wave/boundary-layer interaction
NASA Astrophysics Data System (ADS)
Wideman, Jeffrey Kenneth
An experimental study has been conducted in a three-dimensional, supersonic shockwave/boundary-layer interaction (3-D SW/BLI) with the intent of providing accurate experimental data for turbulence modeling and computational fluid dynamics (CFD) code validation. The experiment was performed in the High Reynolds Channel 1 (HRCI) wind tunnel at NASA Ames Research Center. The test was conducted at a Mach number of M(sub infinity) = 2.89 and at a Reynolds number of Re = 15 x 106/m. The model consisted of a sting-supported cylinder aligned with the tunnel axis and a 20 deg half-angle conical flare offset 1.27 cm from the cylinder centerline. The generated shock system was verified to be steady by schlieren visualization. The highlight of the study was the acquisition of 3-D skin-friction data by a laser interferometric skin friction (LISF) meter. Surface pressure measurements were obtained in 15 deg intervals around the cylinder and flare. Additional measurements included surface oil flow and laser light sheet illumination which were used to document the flow topology. Skin-friction measurements are proving to be a very challenging test of a CFD code predictive capability. However, at the present time there is a very limited amount of accurate skin-friction data in complex flows such as in 3-D SW/BLI. The LISF technique is advantageous as compared to other skin-friction measurement techniques for application in complex flows like the present since it is non-intrusive and is capable of performing measurements in flows with large shear and pressure gradients where the reliability of other techniques is questionable. Thus, the prevent skin-friction data will prove valuable to turbulence modeling and CFD code validation efforts.
Multigrid direct numerical simulation of the whole process of flow transition in 3-D boundary layers
NASA Technical Reports Server (NTRS)
Liu, Chaoqun; Liu, Zhining
1993-01-01
A new technology was developed in this study which provides a successful numerical simulation of the whole process of flow transition in 3-D boundary layers, including linear growth, secondary instability, breakdown, and transition at relatively low CPU cost. Most other spatial numerical simulations require high CPU cost and blow up at the stage of flow breakdown. A fourth-order finite difference scheme on stretched and staggered grids, a fully implicit time marching technique, a semi-coarsening multigrid based on the so-called approximate line-box relaxation, and a buffer domain for the outflow boundary conditions were all used for high-order accuracy, good stability, and fast convergence. A new fine-coarse-fine grid mapping technique was developed to keep the code running after the laminar flow breaks down. The computational results are in good agreement with linear stability theory, secondary instability theory, and some experiments. The cost for a typical case with 162 x 34 x 34 grid is around 2 CRAY-YMP CPU hours for 10 T-S periods.
NASA Technical Reports Server (NTRS)
Fleming, J. L.; Simpson, R. L.
1997-01-01
Laser Doppler velocimetry (LDV) measurements and hydrogen bubble flow visualization techniques were used to examine the near-wall flow structure of 2D and 3D turbulent boundary layers (TBLs) over a range of low Reynolds numbers. The goals of this research were (1) an increased understanding of the flow physics in the near wall region of turbulent boundary layers,(2) to observe and quantify differences between 2D and 3D TBL flow structures, and (3) to document Reynolds number effects for 3D TBLs. The LDV data have provided results detailing the turbulence structure of the 2D and 3D TBLs. These results include mean Reynolds stress distributions, flow skewing results, and U and V spectra. Effects of Reynolds number for the 3D flow were also examined. Comparison to results with the same 3D flow geometry but at a significantly higher Reynolds number provided unique insight into the structure of 3D TBLs. While the 3D mean and fluctuating velocities were found to be highly dependent on Reynolds number, a previously defined shear stress parameter was discovered to be invariant with Reynolds number. The hydrogen bubble technique was used as a flow visualization tool to examine the near-wall flow structure of 2D and 3D TBLs. Both the quantitative and qualitative results displayed larger turbulent fluctuations with more highly concentrated vorticity regions for the 2D flow.
Implementation of wall boundary conditions for transpiration in F3D thin-layer Navier-Stokes code
NASA Technical Reports Server (NTRS)
Kandula, M.; Martin, F. W., Jr.
1991-01-01
Numerical boundary conditions for mass injection/suction at the wall are incorporated in the thin-layer Navier-Stokes code, F3D. The accuracy of the boundary conditions and the code is assessed by a detailed comparison of the predictions of velocity distributions and skin-friction coefficients with exact similarity solutions for laminar flow over a flat plate with variable blowing/suction, and measurements for turbulent flow past a flat plate with uniform blowing. In laminar flow, F3D predictions for friction coefficient compare well with exact similarity solution with and without suction, but produces large errors at moderate-to-large values of blowing. A slight Mach number dependence of skin-friction coefficient due to blowing in turbulent flow is computed by F3D code. Predicted surface pressures for turbulent flow past an airfoil with mass injection are in qualitative agreement with measurements for a flat plate.
NASA Technical Reports Server (NTRS)
Boyle, R. J.; Haas, J. E.; Katsanis, T.
1984-01-01
A method for calculating turbine stage performance is described. The usefulness of the method is demonstrated by comparing measured and predicted efficiencies for nine different stages. Comparisons are made over a range of turbine pressure ratios and rotor speeds. A quasi-3D flow analysis is used to account for complex passage geometries. Boundary layer analyses are done to account for losses due to friction. Empirical loss models are used to account for incidence, secondary flow, disc windage, and clearance losses.
Turbulent boundary layer over 2D and 3D large-scale wavy walls
NASA Astrophysics Data System (ADS)
Chamorro, Leonardo P.; Hamed, Ali M.; Castillo, Luciano
2015-11-01
In this work, an experimental investigation of the developing and developed flow over two- and three-dimensional large-scale wavy walls was performed using high-resolution planar particle image velocimetry in a refractive-index-matching flume. The 2D wall is described by a sinusoidal wave in the streamwise direction with amplitude to wavelength ratio a/ λx = 0.05. The 3D wall is defined with an additional wave superimposed on the 2D wall in the spanwise direction with a/ λy = 0.1. The flow was characterized at Reynolds numbers of 4000 and 40000, based on the bulk velocity and the flume half height. Instantaneous velocity fields and time-averaged turbulence quantities reveal strong coupling between large-scale topography and the turbulence dynamics near the wall. Turbulence statistics show the presence of a well-structured shear layer that enhances the turbulence for the 2D wavy wall, whereas the 3D wall exhibits different flow dynamics and significantly lower turbulence levels, particularly for which shows about 30% reduction. The likelihood of recirculation bubbles, levels and spatial distribution of turbulence, and the rate of the turbulent kinetic energy production are shown to be severely affected when a single spanwise mode is superimposed on the 2D wall. POD analysis was also performed to further understand distinctive features of the flow structures due to surface topography.
A note on problems in 3D boundary layer computations in streamline coordinates
NASA Astrophysics Data System (ADS)
Scholtysik, M.; Bettelini, M.; Fanneløp, T. K.
1994-01-01
Turbulent boundary layers with convergent and divergent external streamlines over a flat plate in the neighbourhood of a plane of symmetry have been computed using a finite-difference method based on streamline coordinates. While the results for the divergent case are generally satisfactory, error growth has been observed for the convergent flowfield. This is most pronounced near the lateral boundary of the computational domain, but also occurs in the plane of symmetry. As an ad-hoc engineering solution, a modified and more restrictive definition of the domain of dependence is proposed, which eliminates the part of the computational domain where the largest error growth occurs. The observed tendency to instability in the convergent case is confirmed by a simplified stability analysis after von Neumann of the uncoupled governing equations.
Skin-Friction Measurements in a 3-D, Supersonic Shock-Wave/Boundary-Layer Interaction
NASA Technical Reports Server (NTRS)
Wideman, J. K.; Brown, J. L.; Miles, J. B.; Ozcan, O.
1994-01-01
The experimental documentation of a three-dimensional shock-wave/boundary-layer interaction in a nominal Mach 3 cylinder, aligned with the free-stream flow, and 20 deg. half-angle conical flare offset 1.27 cm from the cylinder centerline. Surface oil flow, laser light sheet illumination, and schlieren were used to document the flow topology. The data includes surface-pressure and skin-friction measurements. A laser interferometric skin friction data. Included in the skin-friction data are measurements within separated regions and three-dimensional measurements in highly-swept regions. The skin-friction data will be particularly valuable in turbulence modeling and computational fluid dynamics validation.
A fast and accurate method to predict 2D and 3D aerodynamic boundary layer flows
NASA Astrophysics Data System (ADS)
Bijleveld, H. A.; Veldman, A. E. P.
2014-12-01
A quasi-simultaneous interaction method is applied to predict 2D and 3D aerodynamic flows. This method is suitable for offshore wind turbine design software as it is a very accurate and computationally reasonably cheap method. This study shows the results for a NACA 0012 airfoil. The two applied solvers converge to the experimental values when the grid is refined. We also show that in separation the eigenvalues remain positive thus avoiding the Goldstein singularity at separation. In 3D we show a flow over a dent in which separation occurs. A rotating flat plat is used to show the applicability of the method for rotating flows. The shown capabilities of the method indicate that the quasi-simultaneous interaction method is suitable for design methods for offshore wind turbine blades.
Liu, C.; Liu, Z.
1994-12-31
A new multilevel technology was developed in this study which provides a successful numerical simulation for the whole process of flow transition in 3-D flat plate boundary layers, including linear growth, secondary instability, breakdown, and transition on a relatively coarse grid with low CPU cost. A fourth-order finite difference scheme on stretched and staggered grids, a fully implicit time-marching technique, a semi-coarsening multigrid based on the so-called approximate line-box relaxation, and a buffer domain for the outflow boundary conditions were all employed for high-order accuracy, good stability, and fast convergence. A new fine-coarse-fine grid mapping technique was developed to catch the large eddies and represent main roles of small eddies to keep the code running after the laminar flow breaks down. The computational results are in good agreement with linear stability theory, secondary instability theory, and some experiments. The computation also reproduced the K-type and C-type transition observed by laboratory experiments. The CPU cost for a typical case is around 2-9 CRAY-YMP hours.
NASA Astrophysics Data System (ADS)
Rottner, L.; Baehr, C.
2014-12-01
Turbulent phenomena in the atmospheric boundary layer (ABL) are characterized by small spatial and temporal scales which make them difficult to observe and to model.New remote sensing instruments, like Doppler Lidar, give access to fine and high-frequency observations of wind in the ABL. This study suggests to use a method of nonlinear estimation based on these observations to reconstruct 3D wind in a hemispheric volume, and to estimate atmospheric turbulent parameters. The wind observations are associated to particle systems which are driven by a local turbulence model. The particles have both fluid and stochastic properties. Therefore, spatial averages and covariances may be deduced from the particles. Among the innovative aspects, we point out the absence of the common hypothesis of stationary-ergodic turbulence and the non-use of particle model closure hypothesis. Every time observations are available, 3D wind is reconstructed and turbulent parameters such as turbulent kinectic energy, dissipation rate, and Turbulent Intensity (TI) are provided. This study presents some results obtained using real wind measurements provided by a five lines of sight Lidar. Compared with classical methods (e.g. eddy covariance) our technic renders equivalent long time results. Moreover it provides finer and real time turbulence estimations. To assess this new method, we suggest computing independently TI using different observation types. First anemometer data are used to have TI reference.Then raw and filtered Lidar observations have also been compared. The TI obtained from raw data is significantly higher than the reference one, whereas the TI estimated with the new algorithm has the same order.In this study we have presented a new class of algorithm to reconstruct local random media. It offers a new way to understand turbulence in the ABL, in both stable or convective conditions. Later, it could be used to refine turbulence parametrization in meteorological meso-scale models.
Assessment of a 3-D boundary layer code to predict heat transfer and flow losses in a turbine
NASA Technical Reports Server (NTRS)
Anderson, O. L.
1984-01-01
Zonal concepts are utilized to delineate regions of application of three-dimensional boundary layer (DBL) theory. The zonal approach requires three distinct analyses. A modified version of the 3-DBL code named TABLET is used to analyze the boundary layer flow. This modified code solves the finite difference form of the compressible 3-DBL equations in a nonorthogonal surface coordinate system which includes coriolis forces produced by coordinate rotation. These equations are solved using an efficient, implicit, fully coupled finite difference procedure. The nonorthogonal surface coordinate system is calculated using a general analysis based on the transfinite mapping of Gordon which is valid for any arbitrary surface. Experimental data is used to determine the boundary layer edge conditions. The boundary layer edge conditions are determined by integrating the boundary layer edge equations, which are the Euler equations at the edge of the boundary layer, using the known experimental wall pressure distribution. Starting solutions along the inflow boundaries are estimated by solving the appropriate limiting form of the 3-DBL equations.
Jeong, J.Y.; Ryou, H.S.
1997-03-01
Heat transfer characteristics and flow structure in turbulent flows through a flat plate three-dimensional turbulent boundary layer containing built-in vortex generators have been analyzed by means of the space marching Crank-Nicolson finite difference method. The method solves the slender flow approximation of the steady three-dimensional Navier-Stokes and energy equations. This study used the eddy diffusivity model and standard {kappa}-{epsilon} model to predict heat transfer and flow field in the turbulent flow with imbedded longitudinal vortex. The results show boundary layer distortion due to vortices, such as strong spanwise flow divergence and boundary layer thinning. The heat transfer and skin friction show relatively good results in comparison with experimental data. The vortex core moves slightly away from the wall and grows slowly; consequently, the vortex influences the flow over a very long distance downstream. The enhancement of the heat transfer in the vicinity of the wall is due to the increasing spanwise separation of the vortices as they develop in the streamwise direction.
NASA Astrophysics Data System (ADS)
Cai, D. S.; Lembege, B.; Esmaeili, A.; Nishikawa, K.
2013-12-01
Statistical experimental observations of the cusp boundaries from CLUSTER mission made by Lavraud et al. (2005) have clearly evidenced the presence of a transition layer inside the magnetosheath near the outer boundary of the cusp. This layer characterized by Log(MA)~ 1 allows a transition from super-Alfvenic to sub-Alfvenic bulk flow from the exterior to the interior side of the outer cusp and has been mainly observed experimentally under northward interplanetary magnetic field (IMF). The role of this layer is important in order to understand the flow variations (and later the entry and precipitation of particles) when penetrating the outer boundary of the cusp. In order to analyze this layer, a large 3D PIC simulation of the global solar wind-terrestrial magnetosphere interaction have been performed, and the attention has been focused on the cusp region and its nearby surrounding during IMF rotation from north to south. Present results retrieve quite well the presence of this layer within the meridian plane for exactly northward IMF, but its location differs in the sense that it is located slightly below the X reconnection region associated to the nearby magnetopause (above the outer boundary of the cusp). In order to clarify this question, an extensive study has been performed as follows: (i) a 3D mapping of this transition layer in order to analyze more precisely the thickness, the location and the spatial extension of this layer on the magnetosphere flanks for a fixed Northward IMF configuration; (ii) a parametric study in order to analyze the impact of the IMF rotation from north to south on the persistence and the main features of this transition layer. The locations of this transition layer slightly radially expand and shrink during the IMF rotation and the thickness of the layer increases during the rotation. We show how these transition layers render the flow from super to sub Alfvenic and allow the particles enter into the magnetic cusp region. Alfven
NASA Astrophysics Data System (ADS)
Romanova, M. M.; Ustyugova, G. V.; Koldoba, A. V.; Lovelace, R. V. E.
2012-03-01
We discuss results of global three-dimensional magnetohydrodynamic simulations of accretion on to a rotating magnetized star with a tilted dipole magnetic field, where the accretion is driven by the magnetorotational instability (MRI). The simulations show that MRI-driven turbulence develops in the disc, and angular momentum is transported outwards primarily due to the magnetic stress. The turbulent flow is strongly inhomogeneous and the densest matter is in azimuthally stretched turbulent cells. We investigate two regimes of accretion: a magnetospheric regime and a boundary layer (BL) regime. In the magnetospheric regime, the magnetic field of the star is dynamically important: the accretion disc is truncated by the star's magnetic field within a few stellar radii from the star's surface, and matter flows to the star in funnel streams. The funnel streams flow towards the south and north magnetic poles but are not equal due to the inhomogeneity of the flow. The hotspots on the stellar surface are not symmetric as well. In the BL regime, the magnetic field of the star is dynamically unimportant, and matter accretes on to the surface of the star through the BL. The magnetic field in the inner disc is strongly amplified by the shear of the accretion flow, and the matter and magnetic stresses become comparable. Accreting matter forms a belt-shaped hot region on the surface of the star. The belt has inhomogeneous density distribution which varies in time due to variable accretion rate. The peaks in the variability curve are associated with accretion of individual turbulent cells. They show 20-50 per cent density amplifications at periods of ˜5-10 dynamical time-scales at the surface of the star. Spiral waves in the disc are excited in both magnetospheric and BL regimes of accretion. Results of simulations can be applied to classical T Tauri stars, accreting brown dwarfs, millisecond pulsars, dwarf novae cataclysmic variables and other stars with magnetospheres smaller
NASA Technical Reports Server (NTRS)
Loitsianskii. L. G.
1956-01-01
The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.
NASA Technical Reports Server (NTRS)
Kapoor, Kamlesh; Anderson, Bernhard H.; Shaw, Robert J.
1994-01-01
A three-dimensional computational fluid dynamics code, RPLUS3D, which was developed for the reactive propulsive flows of ramjets and scramjets, was validated for glancing shock wave-boundary layer interactions. Both laminar and turbulent flows were studied. A supersonic flow over a wedge mounted on a flat plate was numerically simulated. For the laminar case, the static pressure distribution, velocity vectors, and particle traces on the flat plate were obtained. For turbulent flow, both the Baldwin-Lomax and Chien two-equation turbulent models were used. The static pressure distributions, pitot pressure, and yaw angle profiles were computed. In addition, the velocity vectors and particle traces on the flat plate were also obtained from the computed solution. Overall, the computed results for both laminar and turbulent cases compared very well with the experimentally obtained data.
NASA Technical Reports Server (NTRS)
Civinskas, K. C.; Povinelli, L. A.
1984-01-01
Application of a quasi-3D approach to the aerodynamic analysis of several radial turbine configurations is described. The objective was to improve the rotor aerodynamic characteristics by hub-shroud contouring. The approach relies on available 2D inviscid methods coupled with boundary layer analysis to calculate profile, mixing, and endwall losses. Windage, tip clearance, incidence, and secondary flow losses are estimated from correlations. To eliminate separation along the hub and blade suction surfaces of a baseline rotor, the analysis was also applied to three alternate hub-shroud geometries. Emphasis was on elimination an inducer velocity overshoot as well as increasing hub velocities. While separation was never eliminated, the extent of the separated area was progressively reduced. Results are presented in terms of mid-channel and blade surface velocities; kinetic energy loss coefficients; and efficiency. The calculation demonstrates a first step for a systematic approach to radial turbine design that can be used to identify and control aerodynamic characteristics that ultimately determine heat transfer and component life. Experimentation will be required to assess the extent to which flow and boundary layer behavior were predicted correctly.
NASA Technical Reports Server (NTRS)
Iyer, Venkit
1993-01-01
The theory, formulation, and solution of three-dimensional, compressible attached laminar flows, applied to swept wings in subsonic or supersonic flow are discussed. Several new features and modifications to an earlier general procedure described in NASA CR 4269, Jan. 1990 are incorporated. Details of interfacing the boundary-layer computation with solution of the inviscid Euler equations are discussed. A description of the computer program, complete with user's manual and example cases, is also included. Comparison of solutions with Navier-Stokes computations with or without boundary-layer suction is given. Output of solution profiles and derivatives required in boundary-layer stability analysis is provided.
Monolithic 3D CMOS Using Layered Semiconductors.
Sachid, Angada B; Tosun, Mahmut; Desai, Sujay B; Hsu, Ching-Yi; Lien, Der-Hsien; Madhvapathy, Surabhi R; Chen, Yu-Ze; Hettick, Mark; Kang, Jeong Seuk; Zeng, Yuping; He, Jr-Hau; Chang, Edward Yi; Chueh, Yu-Lun; Javey, Ali; Hu, Chenming
2016-04-01
Monolithic 3D integrated circuits using transition metal dichalcogenide materials and low-temperature processing are reported. A variety of digital and analog circuits are implemented on two sequentially integrated layers of devices. Inverter circuit operation at an ultralow supply voltage of 150 mV is achieved, paving the way to high-density, ultralow-voltage, and ultralow-power applications. PMID:26833783
3D geometry applied to atmospheric layers
NASA Astrophysics Data System (ADS)
Nadjib Kouahla, Mohamed; Moreels, Guy; Faivre, Michael
Epipolar geometry is an efficient method for generating 3D representations of objects. Here we present an original application of this method to the case of atmospheric layers. Two synchronized simultaneous images of the same scene are taken in two sites at a distance D. The 36*36 fields of view are oriented face to face along the same line of sight, but in opposite directions. The elevation angle of the optical axis above the horizon is 17. The observed objects are airglow emissions or cirrus clouds or aircraft trails. In the case of clouds, the shape of the objects is diffuse. To obtain a superposition of the common observed zone, it is necessary to calculate a normalized cross-correlation coefficient (NCC) to identify pairs of matching points in both images. The perspective effect in the rectangular images is inverted to produce a satellite-type view of the atmospheric layer as could be seen from an overlying satellite. We developed a triangulation algorithm to retrieve the 3D surface of the observed layer. The stereoscopic method was used to retrieve the wavy structure of the OH emissive layer at the altitude of 87 km. The distance between the observing sites was 600 km. Results obtained in Peru from the sites of Cerro Cosmos and Cerro Verde will be presented. We are currently extending the stereoscopic procedure to the study of troposphere cirruses, of natural origin or induced by aircraft engines. In this case, the distance between observation sites is D 60 km.
NASA Astrophysics Data System (ADS)
Zhang, Xu; Bao, Jian-Wen; Chen, Baode
2016-04-01
This presentation highlights a study in which a series of dry convective boundary layer (CBL) simulations are carried out using a generalized 3-dimensional (3-D) TKE-based parameterization scheme of sub-grid turbulent mixing in the Weather Research and Forecasting (WRF) model. The simulated characteristics of dry CBL are analyzed for the purpose of evaluating this scheme in comparison with a commonly-used scheme for sub-grid turbulent mixing in NWP models (i.e., the Mellor-Yamada 1.5-order TKE scheme). The same surface layer scheme is used in all the simulations so that only the sensitivity of the WRF model to different parameterizations of the sub-grid turbulent mixing above the surface layer is examined. The effect of horizontal grid resolution on the simulated CBL is also examined by running the model with grid sizes of 200, 400 m, 600 m, 1 km and 3 km. We will first compare the characteristics of the simulated CBL using the two schemes with the WRF LES dataset. We will then illustrate the importance of including the non-local component in the vertical buoyancy specification in the 3-D TKE-based scheme. Finally, comparing the results from the simulations against coarse-grained WRF LES dataset, we will show the feasibility and advantage of replacing conventional planetary boundary layer parameterization schemes with a scale-aware 3-D TKE-based scheme in the WRF model.
Lattice Boltzmann Method for 3-D Flows with Curved Boundary
NASA Technical Reports Server (NTRS)
Mei, Renwei; Shyy, Wei; Yu, Dazhi; Luo, Li-Shi
2002-01-01
In this work, we investigate two issues that are important to computational efficiency and reliability in fluid dynamics applications of the lattice, Boltzmann equation (LBE): (1) Computational stability and accuracy of different lattice Boltzmann models and (2) the treatment of the boundary conditions on curved solid boundaries and their 3-D implementations. Three athermal 3-D LBE models (D3QI5, D3Ql9, and D3Q27) are studied and compared in terms of efficiency, accuracy, and robustness. The boundary treatment recently developed by Filippova and Hanel and Met et al. in 2-D is extended to and implemented for 3-D. The convergence, stability, and computational efficiency of the 3-D LBE models with the boundary treatment for curved boundaries were tested in simulations of four 3-D flows: (1) Fully developed flows in a square duct, (2) flow in a 3-D lid-driven cavity, (3) fully developed flows in a circular pipe, and (4) a uniform flow over a sphere. We found that while the fifteen-velocity 3-D (D3Ql5) model is more prone to numerical instability and the D3Q27 is more computationally intensive, the 63Q19 model provides a balance between computational reliability and efficiency. Through numerical simulations, we demonstrated that the boundary treatment for 3-D arbitrary curved geometry has second-order accuracy and possesses satisfactory stability characteristics.
Turbulence and transport in a 3D magnetic boundary
NASA Astrophysics Data System (ADS)
Agostini, Matteo; Carraro, Lorella; Ciaccio, Giovanni; de Masi, Gianluca; Rea, Cristina; Scarin, Paolo; Spizzo, Gianluca; Spolaore, Monica; Vianello, Nicola
2014-10-01
In present fusion devices the interaction between 3D magnetic field, edge kinetic properties and turbulence is a crucial issue; not only in intrinsically 3D configurations such as the stellarators, but also in tokamaks, where magnetic perturbations are applied to control ELMs and plasma wall interaction. In the RFX-mod reversed field pinch the spontaneous development at high plasma current of a helical magnetic state displays strong analogies with the aforementioned configurations. At the edge the presence of a stochastic layer and magnetic islands with a well-defined helical symmetry leads to a helical pattern of flow, pressure gradients and turbulent fluctuations: larger fluctuations and shorter correlation lengths are observed near the X-point of the magnetic island, where also a flow slowing-down occurs. Aim of this work is to study the effect of edge turbulence on particle transport in a 3D magnetic boundary, characterizing the properties of the edge blobs along the helical deformation. The magnetic topology also modifies kinetic properties, with higher pressure gradients observed close to the O-point of the island. The measurement of the time evolution of pressure gradient and blob characteristics, can clarify the mutual relation between these two quantities.
NASA Astrophysics Data System (ADS)
Brüning, J.; Dobrokhotov, S. Yu.; Minenkov, D. S.
2011-12-01
The aim of this paper is to construct solutions of the Dirichlet problem for the 3D Laplace equation in a layer with highly oscillating boundary. The boundary simulates the surface of a nanotube array, and the solutions are applied to compute the cold field electron emission. We suggest a family of exact solutions that solve the problem for a boundary with appropriate geometry. These solutions, along with the Fowler-Nordheim formula, allow one to present explicit asymptotic formulas for the electric field and the emission current. In this part of the paper, we consider the main mathematical aspects, restricting ourselves to the analysis of properties of the potential created by a single tube and a regular array of tubes. In the next part, we shall consider some cases corresponding to nonregular arrays of tubes and concrete physical examples.
Dynamics of free subduction from 3-D boundary element modeling
NASA Astrophysics Data System (ADS)
Li, Zhong-Hai; Ribe, Neil M.
2012-06-01
In order better to understand the physical mechanisms underlying free subduction, we perform three-dimensional boundary-element numerical simulations of a dense fluid sheet with thickness h and viscosity η2 sinking in an `ambient mantle' with viscosity η1. The mantle layer is bounded above by a traction-free surface, and is either (1) infinitely deep or (2) underlain by a rigid boundary at a finite depth H + d, similar to the typical geometry used in laboratory experiments. Instantaneous solutions in configuration (1) show that the sheet's dimensionless `stiffness' S determines whether the slab's sinking speed is controlled by the viscosity of the ambient mantle (S < 1) or the viscosity of the sheet itself (S > 10). Time-dependent solutions with tracers in configuration (2) demonstrate a partial return flow around the leading edge of a retreating slab and return flow around its sides. The extra `edge drag' exerted by the flow around the sides causes transverse deformation of the slab, and makes the sinking speed of a 3-D slab up to 40% less than that of a 2-D slab. A systematic investigation of the slab's interaction with the bottom boundary as a function of η2/η1 and H/h delineates a rich regime diagram of different subduction modes (trench retreating, slab folding, trench advancing) and reveals a new `advancing-folding' mode in which slab folding is preceded by advancing trench motion. The solutions demonstrate that mode selection is controlled by the dip of the leading edge of the slab at the time when it first encounters the bottom boundary.
Boundary layer transition studies
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1995-01-01
A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated
Stability of compressible boundary layers
NASA Technical Reports Server (NTRS)
Nayfeh, Ali H.
1989-01-01
The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of disturbances in supersonic laminar boundary layers and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.
The Atmospheric Boundary Layer
ERIC Educational Resources Information Center
Tennekes, Hendrik
1974-01-01
Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)
Boundary layer simulator improvement
NASA Technical Reports Server (NTRS)
Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.
1989-01-01
Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.
The atmospheric boundary layer
Garratt, J.R.
1992-01-01
This book is aimed at researchers in the atmospheric and associated sciences who require a moderately advanced text on the Atmospheric Boundary Layer (ABL) in which the many links between turbulence, air-surface transfer, boundary-layer structure and dynamics, and numerical modeling are discussed and elaborated upon. Chapter 1 serves as an introduction, with Chapters 2 and 3 dealing with the development of mean and turbulence equations, and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modelling of the ABL is crucially dependent for its realism on the surface boundary conditions, and Chapters 4 and 5 deal with aerodynamic and energy considerations, with attention to both dry and wet land surfaces and the sea. The structure of the clear-sky, thermally stratified ABL is treated in Chapter 6, including the convective and stable cases over homogeneous land, the marine ABL and the internal boundary layer at the coastline. Chapter 7 then extends the discussion to the cloudy ABL. This is seen as particularly relevant since the extensive stratocumulus regions over the sub-tropical oceans and stratus regions over the Arctic are now identified as key players in the climate system. Finally, Chapters 8 and 9 bring much of the book's material together in a discussion of appropriate ABL and surface parameterization schemes for the general circulation models of the atmosphere that are being used for climate simulation.
Boundary layer simulator improvement
NASA Technical Reports Server (NTRS)
Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.
1984-01-01
High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.
NASA Astrophysics Data System (ADS)
Bell, R. E.; Morgan, J. V.; Warner, M.
2013-12-01
this basin in 1999 suitable for future 3D FWI. We build a 3D model of the sub-surface based on an existing velocity model that was used to migrate these data (Tsuji et al. 2000, JGR). We then add a low P-wave velocity layer along the décollement, which is supported by ODP core data but does not feature in the current seismic velocity model, to test if it could be recovered using 3D FWI. We use the same acquisition parameters as in the 1999 seismic survey (including a 6 km long streamer) to generate a fully-elastic synthetic seismic dataset, added noise and inverted the windowed transmitted arrivals only. We also ran a suite of resolution tests across the model. The results show that 3D FWI of conventionally collected 3D seismic data across the Muroto Basin would be capable of resolving variations in P-wave velocity along the décollement of the order of half the seismic wavelength at the plate boundary. This is a significant improvement on conventional travel-time tomography which resolves to the Fresnel width. In this presentation we will also postulate on the optimal 3D FWI experiment design for the next generation of 3D seismic surveys across subduction margins as a guide for those embarking on new data collection.
3D toroidal physics: Testing the boundaries of symmetry breakinga)
NASA Astrophysics Data System (ADS)
Spong, Donald A.
2015-05-01
Toroidal symmetry is an important concept for plasma confinement; it allows the existence of nested flux surface MHD equilibria and conserved invariants for particle motion. However, perfect symmetry is unachievable in realistic toroidal plasma devices. For example, tokamaks have toroidal ripple due to discrete field coils, optimized stellarators do not achieve exact quasi-symmetry, the plasma itself continually seeks lower energy states through helical 3D deformations, and reactors will likely have non-uniform distributions of ferritic steel near the plasma. Also, some level of designed-in 3D magnetic field structure is now anticipated for most concepts in order to provide the plasma control needed for a stable, steady-state fusion reactor. Such planned 3D field structures can take many forms, ranging from tokamaks with weak 3D edge localized mode suppression fields to stellarators with more dominant 3D field structures. This motivates the development of physics models that are applicable across the full range of 3D devices. Ultimately, the questions of how much symmetry breaking can be tolerated and how to optimize its design must be addressed for all fusion concepts. A closely coupled program of simulation, experimental validation, and design optimization is required to determine what forms and amplitudes of 3D shaping and symmetry breaking will be compatible with the requirements of future fusion reactors.
3D toroidal physics: Testing the boundaries of symmetry breaking
Spong, Donald A.
2015-05-15
Toroidal symmetry is an important concept for plasma confinement; it allows the existence of nested flux surface MHD equilibria and conserved invariants for particle motion. However, perfect symmetry is unachievable in realistic toroidal plasma devices. For example, tokamaks have toroidal ripple due to discrete field coils, optimized stellarators do not achieve exact quasi-symmetry, the plasma itself continually seeks lower energy states through helical 3D deformations, and reactors will likely have non-uniform distributions of ferritic steel near the plasma. Also, some level of designed-in 3D magnetic field structure is now anticipated for most concepts in order to provide the plasma control needed for a stable, steady-state fusion reactor. Such planned 3D field structures can take many forms, ranging from tokamaks with weak 3D edge localized mode suppression fields to stellarators with more dominant 3D field structures. This motivates the development of physics models that are applicable across the full range of 3D devices. Ultimately, the questions of how much symmetry breaking can be tolerated and how to optimize its design must be addressed for all fusion concepts. A closely coupled program of simulation, experimental validation, and design optimization is required to determine what forms and amplitudes of 3D shaping and symmetry breaking will be compatible with the requirements of future fusion reactors.
3D toroidal physics: testing the boundaries of symmetry breaking
NASA Astrophysics Data System (ADS)
Spong, Don
2014-10-01
Toroidal symmetry is an important concept for plasma confinement; it allows the existence of nested flux surface MHD equilibria and conserved invariants for particle motion. However, perfect symmetry is unachievable in realistic toroidal plasma devices. For example, tokamaks have toroidal ripple due to discrete field coils, optimized stellarators do not achieve exact quasi-symmetry, the plasma itself continually seeks lower energy states through helical 3D deformations, and reactors will likely have non-uniform distributions of ferritic steel near the plasma. Also, some level of designed-in 3D magnetic field structure is now anticipated for most concepts in order to lead to a stable, steady-state fusion reactor. Such planned 3D field structures can take many forms, ranging from tokamaks with weak 3D ELM-suppression fields to stellarators with more dominant 3D field structures. There is considerable interest in the development of unified physics models for the full range of 3D effects. Ultimately, the questions of how much symmetry breaking can be tolerated and how to optimize its design must be addressed for all fusion concepts. Fortunately, significant progress is underway in theory, computation and plasma diagnostics on many issues such as magnetic surface quality, plasma screening vs. amplification of 3D perturbations, 3D transport, influence on edge pedestal structures, MHD stability effects, modification of fast ion-driven instabilities, prediction of energetic particle heat loads on plasma-facing materials, effects of 3D fields on turbulence, and magnetic coil design. A closely coupled program of simulation, experimental validation, and design optimization is required to determine what forms and amplitudes of 3D shaping and symmetry breaking will be compatible with future fusion reactors. The development of models to address 3D physics and progress in these areas will be described. This work is supported both by the US Department of Energy under Contract DE
On the Implementation of 3D Galerkin Boundary Integral Equations
Nintcheu Fata, Sylvain; Gray, Leonard J
2010-01-01
In this article, a reverse contribution technique is proposed to accelerate the construction of the dense influence matrices associated with a Galerkin approximation of singular and hypersingular boundary integral equations of mixed-type in potential theory. In addition, a general-purpose sparse preconditioner for boundary element methods has also been developed to successfully deal with ill-conditioned linear systems arising from the discretization of mixed boundary-value problems on non-smooth surfaces. The proposed preconditioner, which originates from the precorrected-FFT method, is sparse, easy to generate and apply in a Krylov subspace iterative solution of discretized boundary integral equations. Moreover, an approximate inverse of the preconditioner is implicitly built by employing an incomplete LU factorization. Numerical experiments involving mixed boundary-value problems for the Laplace equation are included to illustrate the performance and validity of the proposed techniques.
NASA Astrophysics Data System (ADS)
Costigliola, V.
2010-09-01
It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate
Modeling the urban boundary layer
NASA Technical Reports Server (NTRS)
Bergstrom, R. W., Jr.
1976-01-01
A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.
Modeling the summertime Arctic cloudy boundary layer
Curry, J.A.; Pinto, J.O.; McInnes, K.L.
1996-04-01
Global climate models have particular difficulty in simulating the low-level clouds during the Arctic summer. Model problems are exacerbated in the polar regions by the complicated vertical structure of the Arctic boundary layer. The presence of multiple cloud layers, a humidity inversion above cloud top, and vertical fluxes in the cloud that are decoupled from the surface fluxes, identified in Curry et al. (1988), suggest that models containing sophisticated physical parameterizations would be required to accurately model this region. Accurate modeling of the vertical structure of multiple cloud layers in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the layered structure of the Arctic summertime boundary-layer clouds and in particular, the representation of the more complex boundary layer type consisting of a stable foggy surface layer surmounted by a cloud-topped mixed layer. A hierarchical modeling/diagnosis approach is used. A case study from the summertime Arctic Stratus Experiment is examined. A high-resolution, one-dimensional model of turbulence and radiation is tested against the observations and is then used in sensitivity studies to infer the optimal conditions for maintaining two separate layers in the Arctic summertime boundary layer. A three-dimensional mesoscale atmospheric model is then used to simulate the interaction of this cloud deck with the large-scale atmospheric dynamics. An assessment of the improvements needed to the parameterizations of the boundary layer, cloud microphysics, and radiation in the 3-D model is made.
Inflow/Outflow Boundary Conditions with Application to FUN3D
NASA Technical Reports Server (NTRS)
Carlson, Jan-Renee
2011-01-01
Several boundary conditions that allow subsonic and supersonic flow into and out of the computational domain are discussed. These boundary conditions are demonstrated in the FUN3D computational fluid dynamics (CFD) code which solves the three-dimensional Navier-Stokes equations on unstructured computational meshes. The boundary conditions are enforced through determination of the flux contribution at the boundary to the solution residual. The boundary conditions are implemented in an implicit form where the Jacobian contribution of the boundary condition is included and is exact. All of the flows are governed by the calorically perfect gas thermodynamic equations. Three problems are used to assess these boundary conditions. Solution residual convergence to machine zero precision occurred for all cases. The converged solution boundary state is compared with the requested boundary state for several levels of mesh densities. The boundary values converged to the requested boundary condition with approximately second-order accuracy for all of the cases.
DREAM-3D and the importance of model inputs and boundary conditions
NASA Astrophysics Data System (ADS)
Friedel, Reiner; Tu, Weichao; Cunningham, Gregory; Jorgensen, Anders; Chen, Yue
2015-04-01
Recent work on radiation belt 3D diffusion codes such as the Los Alamos "DREAM-3D" code have demonstrated the ability of such codes to reproduce realistic magnetospheric storm events in the relativistic electron dynamics - as long as sufficient "event-oriented" boundary conditions and code inputs such as wave powers, low energy boundary conditions, background plasma densities, and last closed drift shell (outer boundary) are available. In this talk we will argue that the main limiting factor in our modeling ability is no longer our inability to represent key physical processes that govern the dynamics of the radiation belts (radial, pitch angle and energy diffusion) but rather our limitations in specifying accurate boundary conditions and code inputs. We use here DREAM-3D runs to show the sensitivity of the modeled outcomes to these boundary conditions and inputs, and also discuss alternate "proxy" approaches to obtain the required inputs from other (ground-based) sources.
Boundary Layer Control on Airfoils.
ERIC Educational Resources Information Center
Gerhab, George; Eastlake, Charles
1991-01-01
A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)
Removing Boundary Layer by Suction
NASA Technical Reports Server (NTRS)
Ackeret, J
1927-01-01
Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl boundary-layer theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the boundary layer into the inside of a body through a slot or slots in its surface.
Layer-by-layer assembly of 3D tissue constructs with functionalized graphene
Shin, Su Ryon; Aghaei-Ghareh-Bolagh, Behnaz; Gao, Xiguang; Nikkhah, Mehdi; Jung, Sung Mi; Dolatshahi-Pirouz, Alireza; Kim, Sang Bok; Kim, Sun Min; Dokmeci, Mehmet R.; Tang, Xiaowu (Shirley); Khademhosseini, Ali
2014-01-01
Carbon-based nanomaterials have been considered as promising candidates to mimic certain structure and function of native extracellular matrix materials for tissue engineering. Significant progress has been made in fabricating carbon nanoparticle-incorporated cell culture substrates, but limited studies have been reported on the development of three-dimensional (3D) tissue constructs using these nanomaterials. Here, we present a novel approach to engineer 3D multi-layered constructs using layer-by-layer (LbL) assembly of cells separated with self-assembled graphene oxide (GO)-based thin films. The GO-based structures are shown to serve as cell adhesive sheets that effectively facilitate the formation of multi-layer cell constructs with interlayer connectivity. By controlling the amount of GO deposited in forming the thin films, the thickness of the multi-layer tissue constructs could be tuned with high cell viability. Specifically, this approach could be useful for creating dense and tightly connected cardiac tissues through the co-culture of cardiomyocytes and other cell types. In this work, we demonstrated the fabrication of stand-alone multi-layer cardiac tissues with strong spontaneous beating behavior and programmable pumping properties. Therefore, this LbL-based cell construct fabrication approach, utilizing GO thin films formed directly on cell surfaces, has great potential in engineering 3D tissue structures with improved organization, electrophysiological function, and mechanical integrity. PMID:25419209
Layer-by-layer assembly of 3D tissue constructs with functionalized graphene.
Shin, Su Ryon; Aghaei-Ghareh-Bolagh, Behnaz; Gao, Xiguang; Nikkhah, Mehdi; Jung, Sung Mi; Dolatshahi-Pirouz, Alireza; Kim, Sang Bok; Kim, Sun Min; Dokmeci, Mehmet R; Tang, Xiaowu Shirley; Khademhosseini, Ali
2014-10-22
Carbon-based nanomaterials have been considered as promising candidates to mimic certain structure and function of native extracellular matrix materials for tissue engineering. Significant progress has been made in fabricating carbon nanoparticle-incorporated cell culture substrates, but limited studies have been reported on the development of three-dimensional (3D) tissue constructs using these nanomaterials. Here, we present a novel approach to engineer 3D multi-layered constructs using layer-by-layer (LbL) assembly of cells separated with self-assembled graphene oxide (GO)-based thin films. The GO-based structures are shown to serve as cell adhesive sheets that effectively facilitate the formation of multi-layer cell constructs with interlayer connectivity. By controlling the amount of GO deposited in forming the thin films, the thickness of the multi-layer tissue constructs could be tuned with high cell viability. Specifically, this approach could be useful for creating dense and tightly connected cardiac tissues through the co-culture of cardiomyocytes and other cell types. In this work, we demonstrated the fabrication of stand-alone multi-layer cardiac tissues with strong spontaneous beating behavior and programmable pumping properties. Therefore, this LbL-based cell construct fabrication approach, utilizing GO thin films formed directly on cell surfaces, has great potential in engineering 3D tissue structures with improved organization, electrophysiological function, and mechanical integrity. PMID:25419209
Dislocation Content Measured Via 3D HR-EBSD Near a Grain Boundary in an AlCu Oligocrystal
NASA Technical Reports Server (NTRS)
Ruggles, Timothy; Hochhalter, Jacob; Homer, Eric
2016-01-01
Interactions between dislocations and grain boundaries are poorly understood and crucial to mesoscale plasticity modeling. Much of our understanding of dislocation-grain boundary interaction comes from atomistic simulations and TEM studies, both of which are extremely limited in scale. High angular resolution EBSD-based continuum dislocation microscopy provides a way of measuring dislocation activity at length scales and accuracies relevant to crystal plasticity, but it is limited as a two-dimensional technique, meaning the character of the grain boundary and the complete dislocation activity is difficult to recover. However, the commercialization of plasma FIB dual-beam microscopes have made 3D EBSD studies all the more feasible. The objective of this work is to apply high angular resolution cross correlation EBSD to a 3D EBSD data set collected by serial sectioning in a FIB to characterize dislocation interaction with a grain boundary. Three dimensional high angular resolution cross correlation EBSD analysis was applied to an AlCu oligocrystal to measure dislocation densities around a grain boundary. Distortion derivatives associated with the plasma FIB serial sectioning were higher than expected, possibly due to geometric uncertainty between layers. Future work will focus on mitigating the geometric uncertainty and examining more regions of interest along the grain boundary to glean information on dislocation-grain boundary interaction.
3D microband boundary alignments and transitions in a cold rolled commercial purity aluminum alloy
George, C.; Soe, B.; King, K.; Quadir, M.Z.; Ferry, M.; Bassman, L.
2013-05-15
In the study of microband formation during plastic deformation of face centered cubic metals and alloys, two theories have been proposed regarding the orientations of their boundaries: (i) they are aligned parallel to crystallographic planes associated with dislocation glide (i.e. (111) planes in FCC metals), or (ii) they are aligned in accordance with the macroscopic stress state generated during deformation. In this study, high resolution 3D electron backscatter diffraction (3D EBSD) was used to investigate the morphology and crystallographic nature of microband boundaries within a 19 × 9 × 8.6 μm volume of a deformed grain in commercial purity aluminum cold rolled to 22% reduction. It was found that microband boundaries correspond to both theories of orientation. Additionally, a single surface may contain both crystallographic and non-crystallographic alignments. Misorientations across boundaries in the regions of microband triple junctions have been identified for both boundary alignments. - Highlights: ► Reconstruction of a 3D volume of crystallographic orientations from EBSD data ► Subgrain features accurately reconstructed using specially designed strategies. ► Microband boundaries contain crystallographic and non-crystallographic alignments. ► Boundaries form by crystallographic process but rotate to non-crystallographic.
Physics of magnetospheric boundary layers
NASA Technical Reports Server (NTRS)
Cairns, Iver H.
1995-01-01
This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.
Unsteady turbulent boundary layer analysis
NASA Technical Reports Server (NTRS)
Singleton, R. E.; Nash, J. F.; Carl, L. W.; Patel, V. C.
1973-01-01
The governing equations for an unsteady turbulent boundary layer on a swept infinite cylinder, composed of a continuity equation, a pair of momentum equations and a pair of turbulent energy equations which include upstream history efforts, are solved numerically. An explicit finite difference analog to the partial differential equations is formulated and developed into a computer program. Calculations were made for a variety of unsteady flows in both two and three dimensions but primarily for two dimensional flow fields in order to first understand some of the fundamental physical aspects of unsteady turbulent boundary layers. Oscillating free stream flows without pressure gradient, oscillating retarded free stream flows and monotonically time-varying flows have all been studied for a wide frequency range. It was found that to the lowest frequency considered, the lower frequency bound being determined by economic considerations (machine time), there were significant unsteady effects on the turbulent boundary layer.
Boundary layer control for airships
NASA Technical Reports Server (NTRS)
Pake, F. A.; Pipitone, S. J.
1975-01-01
An investigation is summarized of the aerodynamic principle of boundary layer control for nonrigid LTA craft. The project included a wind tunnel test on a BLC body of revolution at zero angle of attack. Theoretical analysis is shown to be in excellent agreement with the test data. Methods are evolved for predicting the boundary layer development on a body of revolution and the suction pumping and propulsive power requirements. These methods are used to predict the performance characteristics of a full-scale airship. The analysis indicates that propulsive power reductions of 15 to 25 percent and endurance improvements of 20 to 40 percent may be realized in employing boundary-layer control to nonrigid airships.
Nonparallel stability of boundary layers
NASA Technical Reports Server (NTRS)
Nayfeh, Ali H.
1987-01-01
The asymptotic formulations of the nonparallel linear stability of incompressible growing boundary layers are critically reviewed. These formulations can be divided into two approaches. The first approach combines a numerical method with either the method of multiple scales, or the method of averaging, of the Wentzel-Kramers-Brillouin (WKB) approximation; all these methods yield the same result. The second approach combined a multi-structure theory with the method of multiple scales. The first approach yields results that are in excellent agreement with all available experimental data, including the growth rates as well as the neutral stability curve. The derivation of the linear stability of the incompressible growing boundary layers is explained.
BEST3D user's manual: Boundary Element Solution Technology, 3-Dimensional Version 3.0
NASA Technical Reports Server (NTRS)
1991-01-01
The theoretical basis and programming strategy utilized in the construction of the computer program BEST3D (boundary element solution technology - three dimensional) and detailed input instructions are provided for the use of the program. An extensive set of test cases and sample problems is included in the manual and is also available for distribution with the program. The BEST3D program was developed under the 3-D Inelastic Analysis Methods for Hot Section Components contract (NAS3-23697). The overall objective of this program was the development of new computer programs allowing more accurate and efficient three-dimensional thermal and stress analysis of hot section components, i.e., combustor liners, turbine blades, and turbine vanes. The BEST3D program allows both linear and nonlinear analysis of static and quasi-static elastic problems and transient dynamic analysis for elastic problems. Calculation of elastic natural frequencies and mode shapes is also provided.
Physics of magnetospheric boundary layers
NASA Technical Reports Server (NTRS)
Cairns, I. H.
1993-01-01
The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.
Turbulent boundary layers over nonstationary plane boundaries
NASA Technical Reports Server (NTRS)
Roper, A. T.
1976-01-01
Methods of predicting integral parameters and skin-friction coefficients of turbulent boundary layers developing over moving-ground-planes are evaluated using test information from three different wind tunnel facilities at the NASA Langley Research Center. These data include test information from the VSTOL tunnel which is presented for the first time. The three methods evaluated were: (1) relative integral parameter method, (2) relative power law method, and (3) modified law of the wall method. Methods (1) and (2) can be used to predict moving-ground-plane shape factors with an expected accuracy of + or - 10%. They may also be used to predict moving-ground-plane displacement and momentum thicknesses with lower expected accuracy. This decrease in accuracy can be traced to the failure of approximations upon which these methods are based to prove universal when compared with VSTOL tunnel test results.
Heat Transfer Boundary Conditions in the RELAP5-3D Code
Richard A. Riemke; Cliff B. Davis; Richard R. Schultz
2008-05-01
The heat transfer boundary conditions used in the RELAP5-3D computer program have evolved over the years. Currently, RELAP5-3D has the following options for the heat transfer boundary conditions: (a) heat transfer correlation package option, (b) non-convective option (from radiation/conduction enclosure model or symmetry/insulated conditions), and (c) other options (setting the surface temperature to a volume fraction averaged fluid temperature of the boundary volume, obtaining the surface temperature from a control variable, obtaining the surface temperature from a time-dependent general table, obtaining the heat flux from a time-dependent general table, or obtaining heat transfer coefficients from either a time- or temperature-dependent general table). These options will be discussed, including the more recent ones.
Boundary Layers, Transitions and Separation
NASA Technical Reports Server (NTRS)
2010-01-01
Effects of roughness in boundary layers have to be addressed. Until adverse pressure gradient effects are understood, roughness will not significantly drive design. Mechanisms responsible for separation not understood. Effects on Zero Pressure Gradient boundary layers (shear stress). Effects on separation in pressure gradient (prediction of separation). Effect on scalar transport (heat transfer) not understood. Model for skin friction needed in simulations - first grid point likely to be in buffer layer. Definition of roughness important for useful experiments. A lot of validation experiments will be needed. How to get to ks for roughness of engineering interest? - depends on wavelength height, etc. for engineering interest? Re-discovering the wheel should be avoided: existing knowledge (theoretical and experimental) should find its way into the engineering models. It is a task of the industry to filter out the existing information in the literature for results relevant to its application, being external or internal.
Kafieh, Raheleh; Rabbani, Hossein; Abramoff, Michael D.; Sonka, Milan
2013-01-01
Optical coherence tomography (OCT) is a powerful and noninvasive method for retinal imaging. In this paper, we introduce a fast segmentation method based on a new variant of spectral graph theory named diffusion maps. The research is performed on spectral domain (SD) OCT images depicting macular and optic nerve head appearance. The presented approach does not require edge-based image information in localizing most of boundaries and relies on regional image texture. Consequently, the proposed method demonstrates robustness in situations of low image contrast or poor layer-to-layer image gradients. Diffusion mapping applied to 2D and 3D OCT datasets is composed of two steps, one for partitioning the data into important and less important sections, and another one for localization of internal layers. In the first step, the pixels/voxels are grouped in rectangular/cubic sets to form a graph node. The weights of the graph are calculated based on geometric distances between pixels/voxels and differences of their mean intensity. The first diffusion map clusters the data into three parts, the second of which is the area of interest. The other two sections are eliminated from the remaining calculations. In the second step, the remaining area is subjected to another diffusion map assessment and the internal layers are localized based on their textural similarities. The proposed method was tested on 23 datasets from two patient groups (glaucoma and normals). The mean unsigned border positioning errors (mean ± SD) was 8.52 ± 3.13 and 7.56 ± 2.95 μm for the 2D and 3D methods, respectively. PMID:23837966
3D prostate boundary segmentation from ultrasound images using 2D active shape models.
Hodge, Adam C; Ladak, Hanif M
2006-01-01
Boundary outlining, or segmentation, of the prostate is an important task in diagnosis and treatment planning for prostate cancer. This paper describes an algorithm for semi-automatic, three-dimensional (3D) segmentation of the prostate boundary from ultrasound images based on two-dimensional (2D) active shape models (ASM) and rotation-based slicing. Evaluation of the algorithm used distance- and volume-based error metrics to compare algorithm generated boundary outlines to gold standard (manually generated) boundary outlines. The mean absolute distance between the algorithm and gold standard boundaries was 1.09+/-0.49 mm, the average percent absolute volume difference was 3.28+/-3.16%, and a 5x speed increase as compared manual planimetry was achieved. PMID:17946106
Pontoriero, Antonio; Iatì, Giuseppe; Marino, Daniele; La Torre, Domenico; Vinci, Sergio; Germanò, Antonino; Pergolizzi, Stefano; Tomasello, Francesco,
2016-01-01
Radiosurgery of arteriovenous malformations (AVMs) is a challenging procedure. Accuracy of target volume contouring is one major issue to achieve AVM obliteration while avoiding disastrous complications due to suboptimal treatment. We describe a technique to improve the understanding of the complex AVM angioarchitecture by 3D prototyping of individual lesions. Arteriovenous malformations of ten patients were prototyped by 3D printing using 3D rotational angiography (3DRA) as a template. A target volume was obtained using the 3DRA; a second volume was obtained, without awareness of the first volume, using 3DRA and the 3D-printed model. The two volumes were superimposed and the conjoint and disjoint volumes were measured. We also calculated the time needed to perform contouring and assessed the confidence of the surgeons in the definition of the target volumes using a six-point scale. The time required for the contouring of the target lesion was shorter when the surgeons used the 3D-printed model of the AVM (p=0.001). The average volume contoured without the 3D model was 5.6 ± 3 mL whereas it was 5.2 ± 2.9 mL with the 3D-printed model (p=0.003). The 3D prototypes proved to be spatially reliable. Surgeons were absolutely confident or very confident in all cases that the volume contoured using the 3D-printed model was plausible and corresponded to the real boundaries of the lesion. The total cost for each case was 50 euros whereas the cost of the 3D printer was 1600 euros. 3D prototyping of AVMs is a simple, affordable, and spatially reliable procedure that can be beneficial for radiosurgery treatment planning. According to our preliminary data, individual prototyping of the brain circulation provides an intuitive comprehension of the 3D anatomy of the lesion that can be rapidly and reliably translated into the target volume. PMID:27335707
Conti, Alfredo; Pontoriero, Antonio; Iatì, Giuseppe; Marino, Daniele; La Torre, Domenico; Vinci, Sergio; Germanò, Antonino; Pergolizzi, Stefano; Tomasello, Francesco
2016-01-01
Radiosurgery of arteriovenous malformations (AVMs) is a challenging procedure. Accuracy of target volume contouring is one major issue to achieve AVM obliteration while avoiding disastrous complications due to suboptimal treatment. We describe a technique to improve the understanding of the complex AVM angioarchitecture by 3D prototyping of individual lesions. Arteriovenous malformations of ten patients were prototyped by 3D printing using 3D rotational angiography (3DRA) as a template. A target volume was obtained using the 3DRA; a second volume was obtained, without awareness of the first volume, using 3DRA and the 3D-printed model. The two volumes were superimposed and the conjoint and disjoint volumes were measured. We also calculated the time needed to perform contouring and assessed the confidence of the surgeons in the definition of the target volumes using a six-point scale. The time required for the contouring of the target lesion was shorter when the surgeons used the 3D-printed model of the AVM (p=0.001). The average volume contoured without the 3D model was 5.6 ± 3 mL whereas it was 5.2 ± 2.9 mL with the 3D-printed model (p=0.003). The 3D prototypes proved to be spatially reliable. Surgeons were absolutely confident or very confident in all cases that the volume contoured using the 3D-printed model was plausible and corresponded to the real boundaries of the lesion. The total cost for each case was 50 euros whereas the cost of the 3D printer was 1600 euros. 3D prototyping of AVMs is a simple, affordable, and spatially reliable procedure that can be beneficial for radiosurgery treatment planning. According to our preliminary data, individual prototyping of the brain circulation provides an intuitive comprehension of the 3D anatomy of the lesion that can be rapidly and reliably translated into the target volume. PMID:27335707
Direct single-layered fabrication of 3D concavo convex patterns in nano-stereolithography
NASA Astrophysics Data System (ADS)
Lim, T. W.; Park, S. H.; Yang, D. Y.; Kong, H. J.; Lee, K. S.
2006-09-01
A nano-surfacing process (NSP) is proposed to directly fabricate three-dimensional (3D) concavo convex-shaped microstructures such as micro-lens arrays using two-photon polymerization (TPP), a promising technique for fabricating arbitrary 3D highly functional micro-devices. In TPP, commonly utilized methods for fabricating complex 3D microstructures to date are based on a layer-by-layer accumulating technique employing two-dimensional sliced data derived from 3D computer-aided design data. As such, this approach requires much time and effort for precise fabrication. In this work, a novel single-layer exposure method is proposed in order to improve the fabricating efficiency for 3D concavo convex-shaped microstructures. In the NSP, 3D microstructures are divided into 13 sub-regions horizontally with consideration of the heights. Those sub-regions are then expressed as 13 characteristic colors, after which a multi-voxel matrix (MVM) is composed with the characteristic colors. Voxels with various heights and diameters are generated to construct 3D structures using a MVM scanning method. Some 3D concavo convex-shaped microstructures were fabricated to estimate the usefulness of the NSP, and the results show that it readily enables the fabrication of single-layered 3D microstructures.
NASA Astrophysics Data System (ADS)
Meléndez, Adrià; Korenaga, Jun; Sallarès, Valentí; Miniussi, Alain; Ranero, César
2015-04-01
We present a new 3-D travel-time tomography code (TOMO3D) for the modelling of active-source seismic data that uses the arrival times of both refracted and reflected seismic phases to derive the propagation velocity distribution and the geometry of reflecting boundaries in the subsurface. The combination of refracted and reflected data provides a denser coverage of the study area. Moreover, because refractions only depend on the velocity parameters, they contribute to the mitigation of the negative effect of the ambiguity between layer thickness and propagation velocity that is intrinsic to the reflections that define these boundaries. This code is based on its renowned 2-D version TOMO2D from which it inherited the methods to solve the forward and inverse problems. The forward travel-time calculations are conducted using a hybrid ray-tracing technique combining the graph or shortest path method and the bending method. The LSQR algorithm is used to perform the iterative inversion of travel-time residuals to update the initial velocity and depth models. In order to cope with the increased computational demand due to the incorporation of the third dimension, the forward problem solver, which takes by far most of the run time (~90%), has been parallelised with a combination of MP and MPI standards. This parallelisation distributes the ray-tracing and travel-time calculations among the available computational resources, allowing the user to set the number of nodes, processors and cores to be used. The code's performance was evaluated with a complex synthetic case simulating a subduction zone. The objective is to retrieve the velocity distribution of both upper and lower plates and the geometry of the interplate and Moho boundaries. Our tomography method is designed to deal with a single reflector per inversion, and we show that a data-driven layer-stripping strategy allows to successfully recover several reflectors in successive inversions. This strategy consists in
Jupiter's deep magnetotail boundary layer
NASA Astrophysics Data System (ADS)
Nicolaou, G.; McComas, D. J.; Bagenal, F.; Elliott, H. A.; Ebert, R. W.
2015-06-01
In 2007 the New Horizons (NH) spacecraft flew by Jupiter for a gravity assist en route to Pluto. After closest approach on day of year (DOY) 58, 2007, NH followed a tailward trajectory that provided a unique opportunity to explore the deep jovian magnetotail and the surrounding magnetosheath. After DOY 132, 16 magnetopause crossings were observed between 1654 and 2429 Jupiter radii (Rj) along the dusk flank tailward of the planet. In some cases the crossings were identified as rapid transitions from the magnetotail to the magnetosheath and vice versa. In other cases a boundary layer was observed just inside the magnetopause. Solar Wind Around Pluto (SWAP) is an instrument on board NH that obtained spectra of low energy ions during the flyby period. We use a forward model including the SWAP instrument response to derive plasma parameters (density, temperature and velocity) which best reproduce the observations. We also vary the plasma parameters in our model in order to fit the observations more accurately on occasions where the measurements exhibit significant variability. We compare the properties of the plasma in the boundary layer with those of the magnetosheath plasma derived in our earlier work. We attempt to estimate the magnetic field in the boundary layer assuming pressure balance between it and the magnetosheath. Finally, we investigate several possible scenarios to assess if magnetopause movement and structure could cause the variations seen in the data.
OPTIMIZATION OF 3-D IMAGE-GUIDED NEAR INFRARED SPECTROSCOPY USING BOUNDARY ELEMENT METHOD
Srinivasan, Subhadra; Carpenter, Colin; Pogue, Brian W.; Paulsen, Keith D.
2010-01-01
Multimodality imaging systems combining optical techniques with MRI/CT provide high-resolution functional characterization of tissue by imaging molecular and vascular biomarkers. To optimize these hybrid systems for clinical use, faster and automatable algorithms are required for 3-D imaging. Towards this end, a boundary element model was used to incorporate tissue boundaries from MRI/CT into image formation process. This method uses surface rendering to describe light propagation in 3-D using diffusion equation. Parallel computing provided speedup of up to 54% in time of computation. Simulations showed that location of NIRS probe was crucial for quantitatively accurate estimation of tumor response. A change of up to 61% was seen between cycles 1 and 3 in monitoring tissue response to neoadjuvant chemotherapy. PMID:20523751
An accurate quadrature technique for the contact boundary in 3D finite element computations
NASA Astrophysics Data System (ADS)
Duong, Thang X.; Sauer, Roger A.
2015-01-01
This paper presents a new numerical integration technique for 3D contact finite element implementations, focusing on a remedy for the inaccurate integration due to discontinuities at the boundary of contact surfaces. The method is based on the adaptive refinement of the integration domain along the boundary of the contact surface, and is accordingly denoted RBQ for refined boundary quadrature. It can be used for common element types of any order, e.g. Lagrange, NURBS, or T-Spline elements. In terms of both computational speed and accuracy, RBQ exhibits great advantages over a naive increase of the number of quadrature points. Also, the RBQ method is shown to remain accurate for large deformations. Furthermore, since the sharp boundary of the contact surface is determined, it can be used for various purposes like the accurate post-processing of the contact pressure. Several examples are presented to illustrate the new technique.
OpenMP for 3D potential boundary value problems solved by PIES
NASA Astrophysics Data System (ADS)
KuŻelewski, Andrzej; Zieniuk, Eugeniusz
2016-06-01
The main purpose of this paper is examination of an application of modern parallel computing technique OpenMP to speed up the calculation in the numerical solution of parametric integral equations systems (PIES). The authors noticed, that solving more complex boundary problems by PIES sometimes requires large computing time. This paper presents the use of OpenMP and fast C++ linear algebra library Armadillo for boundary value problems modelled by 3D Laplace's equation and solved using PIES. The testing example shows that the use of mentioned technologies significantly increases speed of calculations in PIES.
Effect of sound on boundary layer stability
NASA Astrophysics Data System (ADS)
Saric, William S.; Spencer, Shelly Anne
1993-06-01
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S. (Principal Investigator); Spencer, Shelly Anne
1993-01-01
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-travelling, sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2(lambda)(sub TS)/pi, of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations and the Stokes wave subtracted) show the generation of 3-D-T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modelling are observed.
Effect of sound on boundary layer stability
NASA Technical Reports Server (NTRS)
Saric, William S.; Spencer, Shelly Anne
1993-01-01
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed.
Segmentation of 3D EBSD data for subgrain boundary identification and feature characterization.
Loeb, Andrew; Ferry, Michael; Bassman, Lori
2016-02-01
Subgrain structures formed during plastic deformation of metals can be observed by electron backscatter diffraction (EBSD) but are challenging to identify automatically. We have adapted a 2D image segmentation technique, fast multiscale clustering (FMC), to 3D EBSD data using a novel variance function to accommodate quaternion data. This adaptation, which has been incorporated into the free open source texture analysis software package MTEX, is capable of segmenting based on subtle and gradual variation as well as on sharp boundaries within the data. FMC has been further modified to group the resulting closed 3D segment boundaries into distinct coherent surfaces based on local normals of a triangulated surface. We demonstrate the excellent capabilities of this technique with application to 3D EBSD data sets generated from cold rolled aluminum containing well-defined microbands, cold rolled and partly recrystallized extra low carbon steel microstructure containing three magnitudes of boundary misorientations, and channel-die plane strain compressed Goss-oriented nickel crystal containing microbands with very subtle changes in orientation. PMID:26630071
Boundary layer receptivity and control
NASA Technical Reports Server (NTRS)
Hill, D. C.
1993-01-01
Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three
The entraining moist boundary layer
NASA Technical Reports Server (NTRS)
Randall, D. A.
1978-01-01
A unified theory of entrainment into the planetary boundary layer is presented. It is assumed that the rates of buoyant and shear production of turbulence kinetic energy can be determined in terms of the entrainment mass flux. An expression is derived from the conservation law for turbulence kinetic energy, which, with the introduction of an empirical parameter, can be used together with a second relation between turbulence kinetic energy and the turbulence velocity scale to obtain the mass entrainment flux. The theory provides descriptions of storage-limited entrainment, buoyancy-limited entrainment into a clear mixed layer, and shallowing. It has been incorporated into a simulation of Day 33 of the Wangara experiment using a simple mixed layer model.
Calculation of grain boundary normals directly from 3D microstructure images
Lieberman, E. J.; Rollett, A. D.; Lebensohn, R. A.; Kober, E. M.
2015-03-11
The determination of grain boundary normals is an integral part of the characterization of grain boundaries in polycrystalline materials. These normal vectors are difficult to quantify due to the discretized nature of available microstructure characterization techniques. The most common method to determine grain boundary normals is by generating a surface mesh from an image of the microstructure, but this process can be slow, and is subject to smoothing issues. A new technique is proposed, utilizing first order Cartesian moments of binary indicator functions, to determine grain boundary normals directly from a voxelized microstructure image. In order to validate the accuracy of this technique, the surface normals obtained by the proposed method are compared to those generated by a surface meshing algorithm. Specifically, the local divergence between the surface normals obtained by different variants of the proposed technique and those generated from a surface mesh of a synthetic microstructure constructed using a marching cubes algorithm followed by Laplacian smoothing is quantified. Next, surface normals obtained with the proposed method from a measured 3D microstructure image of a Ni polycrystal are used to generate grain boundary character distributions (GBCD) for Σ3 and Σ9 boundaries, and compared to the GBCD generated using a surface mesh obtained from the same image. Finally, the results show that the proposed technique is an efficient and accurate method to determine voxelized fields of grain boundary normals.
Calculation of grain boundary normals directly from 3D microstructure images
Lieberman, E. J.; Rollett, A. D.; Lebensohn, R. A.; Kober, E. M.
2015-03-11
The determination of grain boundary normals is an integral part of the characterization of grain boundaries in polycrystalline materials. These normal vectors are difficult to quantify due to the discretized nature of available microstructure characterization techniques. The most common method to determine grain boundary normals is by generating a surface mesh from an image of the microstructure, but this process can be slow, and is subject to smoothing issues. A new technique is proposed, utilizing first order Cartesian moments of binary indicator functions, to determine grain boundary normals directly from a voxelized microstructure image. In order to validate the accuracymore » of this technique, the surface normals obtained by the proposed method are compared to those generated by a surface meshing algorithm. Specifically, the local divergence between the surface normals obtained by different variants of the proposed technique and those generated from a surface mesh of a synthetic microstructure constructed using a marching cubes algorithm followed by Laplacian smoothing is quantified. Next, surface normals obtained with the proposed method from a measured 3D microstructure image of a Ni polycrystal are used to generate grain boundary character distributions (GBCD) for Σ3 and Σ9 boundaries, and compared to the GBCD generated using a surface mesh obtained from the same image. Finally, the results show that the proposed technique is an efficient and accurate method to determine voxelized fields of grain boundary normals.« less
Measurements of stress fields near a grain boundary: Exploring blocked arrays of dislocations in 3D
Guo, Y.; Collins, D. M.; Tarleton, E.; Hofmann, F.; Tischler, J.; Liu, W.; Xu, R.; Wilkinson, A. J.; Britton, T. B.
2015-06-24
The interaction between dislocation pile-ups and grain boundaries gives rise to heterogeneous stress distributions when a structural metal is subjected to mechanical loading. Such stress heterogeneity leads to preferential sites for damage nucleation and therefore is intrinsically linked to the strength and ductility of polycrystalline metals. To date the majority of conclusions have been drawn from 2D experimental investigations at the sample surface, allowing only incomplete observations. Our purpose here is to significantly advance the understanding of such problems by providing quantitative measurements of the effects of dislocation pile up and grain boundary interactions in 3D. This is accomplished throughmore » the application of differential aperture X-ray Laue micro-diffraction (DAXM) and high angular resolution electron backscatter diffraction (HR-EBSD) techniques. Our analysis demonstrates a similar strain characterization capability between DAXM and HR-EBSD and the variation of stress intensity in 3D reveals that different parts of the same grain boundary may have different strengths in resisting slip transfer, likely due to the local grain boundary curvature.« less
Measurements of stress fields near a grain boundary: Exploring blocked arrays of dislocations in 3D
Guo, Y.; Collins, D. M.; Tarleton, E.; Hofmann, F.; Tischler, J.; Liu, W.; Xu, R.; Wilkinson, A. J.; Britton, T. B.
2015-06-24
The interaction between dislocation pile-ups and grain boundaries gives rise to heterogeneous stress distributions when a structural metal is subjected to mechanical loading. Such stress heterogeneity leads to preferential sites for damage nucleation and therefore is intrinsically linked to the strength and ductility of polycrystalline metals. To date the majority of conclusions have been drawn from 2D experimental investigations at the sample surface, allowing only incomplete observations. Our purpose here is to significantly advance the understanding of such problems by providing quantitative measurements of the effects of dislocation pile up and grain boundary interactions in 3D. This is accomplished through the application of differential aperture X-ray Laue micro-diffraction (DAXM) and high angular resolution electron backscatter diffraction (HR-EBSD) techniques. Our analysis demonstrates a similar strain characterization capability between DAXM and HR-EBSD and the variation of stress intensity in 3D reveals that different parts of the same grain boundary may have different strengths in resisting slip transfer, likely due to the local grain boundary curvature.
Turbulent boundary layer of an airfoil
NASA Technical Reports Server (NTRS)
Fediaevsky, K
1937-01-01
A need has arisen for a new determination of the velocity profiles in the boundary layer. Assuming that the character of the velocity distribution depends to a large extent on the character of the shear distribution across the boundary layer, we shall consider the nature of the shear distribution for a boundary layer with a pressure gradient.
Instability of a Supersonic Boundary-Layer with Localized Roughness
NASA Technical Reports Server (NTRS)
Marxen, Olaf; Iaccarino, Gianluca; Shaqfeh, Eric S. G.
2010-01-01
A localized 3-D roughness causes boundary-layer separation and (weak) shocks. Most importantly, streamwise vortices occur which induce streamwise (low U, high T) streaks. Immersed boundary method (volume force) suitable to represent roughness element in DNS. Favorable comparison between bi-global stability theory and DNS for a "y-mode" Outlook: Understand the flow physics (investigate "z-modes" in DNS through sinuous spanwise forcing, study origin of the beat in DNS).
Song, Wei; Cho, Kyungeun; Um, Kyhyun; Won, Chee Sun; Sim, Sungdae
2012-01-01
Mobile robot operators must make rapid decisions based on information about the robot’s surrounding environment. This means that terrain modeling and photorealistic visualization are required for the remote operation of mobile robots. We have produced a voxel map and textured mesh from the 2D and 3D datasets collected by a robot’s array of sensors, but some upper parts of objects are beyond the sensors’ measurements and these parts are missing in the terrain reconstruction result. This result is an incomplete terrain model. To solve this problem, we present a new ground segmentation method to detect non-ground data in the reconstructed voxel map. Our method uses height histograms to estimate the ground height range, and a Gibbs-Markov random field model to refine the segmentation results. To reconstruct a complete terrain model of the 3D environment, we develop a 3D boundary estimation method for non-ground objects. We apply a boundary detection technique to the 2D image, before estimating and refining the actual height values of the non-ground vertices in the reconstructed textured mesh. Our proposed methods were tested in an outdoor environment in which trees and buildings were not completely sensed. Our results show that the time required for ground segmentation is faster than that for data sensing, which is necessary for a real-time approach. In addition, those parts of objects that were not sensed are accurately recovered to retrieve their real-world appearances. PMID:23235454
Song, Wei; Cho, Kyungeun; Um, Kyhyun; Won, Chee Sun; Sim, Sungdae
2012-01-01
Mobile robot operators must make rapid decisions based on information about the robot's surrounding environment. This means that terrain modeling and photorealistic visualization are required for the remote operation of mobile robots. We have produced a voxel map and textured mesh from the 2D and 3D datasets collected by a robot's array of sensors, but some upper parts of objects are beyond the sensors' measurements and these parts are missing in the terrain reconstruction result. This result is an incomplete terrain model. To solve this problem, we present a new ground segmentation method to detect non-ground data in the reconstructed voxel map. Our method uses height histograms to estimate the ground height range, and a Gibbs-Markov random field model to refine the segmentation results. To reconstruct a complete terrain model of the 3D environment, we develop a 3D boundary estimation method for non-ground objects. We apply a boundary detection technique to the 2D image, before estimating and refining the actual height values of the non-ground vertices in the reconstructed textured mesh. Our proposed methods were tested in an outdoor environment in which trees and buildings were not completely sensed. Our results show that the time required for ground segmentation is faster than that for data sensing, which is necessary for a real-time approach. In addition, those parts of objects that were not sensed are accurately recovered to retrieve their real-world appearances. PMID:23235454
NASA Astrophysics Data System (ADS)
Šedivý, Ondřej; Brereton, Tim; Westhoff, Daniel; Polívka, Leoš; Beneš, Viktor; Schmidt, Volker; Jäger, Aleš
2016-06-01
A compact and tractable representation of the grain structure of a material is an extremely valuable tool when carrying out an empirical analysis of the material's microstructure. Tessellations have proven to be very good choices for such representations. Most widely used tessellation models have convex cells with planar boundaries. Recently, however, a new tessellation model - called the generalised balanced power diagram (GBPD) - has been developed that is very flexible and can incorporate features such as curved boundaries and non-convexity of cells. In order to use a GBPD to describe the grain structure observed in empirical image data, the parameters of the model must be chosen appropriately. This typically involves solving a difficult optimisation problem. In this paper, we describe a method for fitting GBPDs to tomographic image data. This method uses simulated annealing to solve a suitably chosen optimisation problem. We then apply this method to both artificial data and experimental 3D electron backscatter diffraction (3D EBSD) data obtained in order to study the properties of fine-grained materials with superplastic behaviour. The 3D EBSD data required new alignment and segmentation procedures, which we also briefly describe. Our numerical experiments demonstrate the effectiveness of the simulated annealing approach (compared to heuristic fitting methods) and show that GBPDs are able to describe the structures of polycrystalline materials very well.
Modelling the transitional boundary layer
NASA Technical Reports Server (NTRS)
Narasimha, R.
1990-01-01
Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.
Boundary Layer Heights from CALIOP
NASA Astrophysics Data System (ADS)
Kuehn, R.; Ackerman, S. A.; Holz, R.; Roubert, L.
2012-12-01
This work is focused on the development of a planetary boundary layer (PBL) height retrieval algorithm for CALIOP and validation studies. Our current approach uses a wavelet covariance transform analysis technique to find the top of the boundary layer. We use the methodology similar to that found in Davis et. al. 2000, ours has been developed to work with the lower SNR data provided by CALIOP, and is intended to work autonomously. Concurrently developed with the CALIOP algorithm we will show results from a PBL height retrieval algorithm from profiles of potential temperature, these are derived from Aircraft Meteorological DAta Relay (AMDAR) observations. Results from 5 years of collocated AMDAR - CALIOP retrievals near O'Hare airport demonstrate good agreement between the CALIOP - AMDAR retrievals. In addition, because we are able to make daily retrievals from the AMDAR measurements, we are able to observe the seasonal and annual variation in the PBL height at airports that have sufficient instrumented-aircraft traffic. Also, a comparison has been done between the CALIOP retrievals and the NASA Langley airborne High Spectral Resolution Lidar (HSRL) PBL height retrievals acquired during the GoMACCS experiment. Results of this comparison, like the AMDAR comparison are favorable. Our current work also involves the analysis and verification of the CALIOP PBL height retrieval from the 6 year CALIOP global data set. Results from this analysis will also be presented.
Nonequilibrium chemistry boundary layer integral matrix procedure
NASA Technical Reports Server (NTRS)
Tong, H.; Buckingham, A. C.; Morse, H. L.
1973-01-01
The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.
Hirt, Luca; Ihle, Stephan; Pan, Zhijian; Dorwling-Carter, Livie; Reiser, Alain; Wheeler, Jeffrey M; Spolenak, Ralph; Vörös, János; Zambelli, Tomaso
2016-03-23
A novel 3D printing method for voxel-by-voxel metal printing is presented. Hollow atomic force microscopy (AFM) cantilevers are used to locally supply metal ions in an electrochemical cell, enabling a localized electroplating reaction. By exploiting the deflection feedback of these probes, electrochemical 3D metal printing is, for the first time, demonstrated in a layer-by-layer fashion, enabling the fabrication of arbitrary-shaped geometries. PMID:26783090
Reconstruction of 3d grain boundaries from rock thin sections, using polarised light
NASA Astrophysics Data System (ADS)
Markus Hammes, Daniel; Peternell, Mark
2016-04-01
Grain boundaries affect the physical and chemical properties of polycrystalline materials significantly by initiating reactions and collecting impurities (Birchenall, 1959), and play an essential role in recrystallization (Doherty et al. 1997). In particular, the shape and crystallographic orientation of grain boundaries reveal the deformation and annealing history of rocks (Kruhl and Peternell 2002, Kuntcheva et al. 2006). However, there is a lack of non-destructive and easy-to-use computer supported methods to determine grain boundary geometries in 3D. The only available instrument using optical light to measure grain boundary angles is still the polarising microscope with attached universal stage; operated manually and time-consuming in use. Here we present a new approach to determine 3d grain boundary orientations from 2D rock thin sections. The data is recorded by using an automatic fabric analyser microscope (Peternell et al., 2010). Due to its unique arrangement of 9 light directions the highest birefringence colour due to each light direction and crystal orientation (retardation) can be determined at each pixel in the field of view. Retardation profiles across grain boundaries enable the calculation of grain boundary angle and direction. The data for all positions separating the grains are combined and further processed. In combination with the lateral position of the grain boundary, acquired using the FAME software (Hammes and Peternell, in review), the data is used to reconstruct a 3d grain boundary model. The processing of data is almost fully automatic by using MATLAB®. Only minor manual input is required. The applicability was demonstrated on quartzite samples, but the method is not solely restricted on quartz grains and other birefringent polycrystalline materials could be used instead. References: Birchenall, C.E., 1959: Physical Metallurgy. McGraw-Hill, New York. Doherty, R.D., Hughes, D.A., Humphreys, F.J., Jonas, J.J., Juul Jensen, D., Kassner, M
Thermal analysis of 3D composites by a new fast multipole hybrid boundary node method
NASA Astrophysics Data System (ADS)
Miao, Yu; Wang, Qiao; Zhu, Hongping; Li, Yinping
2014-01-01
This paper applies the hybrid boundary node method (Hybrid BNM) for the thermal analysis of 3D composites. A new formulation is derived for the inclusion-based composites. In the new formulation, the unknowns of the interfaces are assembled only once in the final system equation, which can reduce nearly one half of degrees of freedom (DOFs) compared with the conventional multi-domain solver when there are lots of inclusions. A new version of the fast multipole method (FMM) is also coupled with the new formulation and the technique is applied to thermal analysis of composites with many inclusions. In the new fast multipole hybrid boundary node method (FM-HBNM), a diagonal form for translation operators is used and the method presented can be applied to the computation of more than 1,000,000 DOFs on a personal computer. Numerical examples are presented to analyze the thermal behavior of composites with many inclusions.
3D Multi-spectral Image-guided Near-infrared Spectroscopy using Boundary Element Method
Srinivasan, Subhadra; Pogue, Brian W.; Paulsen, Keith D.
2010-01-01
Image guided (IG) Near-Infrared spectroscopy (NIRS) has the ability to provide high-resolution metabolic and vascular characterization of tissue, with clinical applications in diagnosis of breast cancer. This method is specific to multimodality imaging where tissue boundaries obtained from alternate modalities such as MRI/CT, are used for NIRS recovery. IG-NIRS is severely limited in 3D by challenges such as volumetric meshing of arbitrary anatomical shapes and computational burden encountered by existing models which use finite element method (FEM). We present an efficient and feasible alternative to FEM using boundary element method (BEM). The main advantage is the use of surface discretization which is reliable and more easily generated than volume grids in 3D and enables automation for large number of clinical data-sets. The BEM has been implemented for the diffusion equation to model light propagation in tissue. Image reconstruction based on BEM has been tested in a multi-threading environment using four processors which provides 60% improvement in computational time compared to a single processor. Spectral priors have been implemented in this framework and applied to a three-region problem with mean error of 6% in recovery of NIRS parameters. PMID:21179380
Encapsulation layer design and scalability in encapsulated vertical 3D RRAM
NASA Astrophysics Data System (ADS)
Yu, Muxi; Fang, Yichen; Wang, Zongwei; Chen, Gong; Pan, Yue; Yang, Xue; Yin, Minghui; Yang, Yuchao; Li, Ming; Cai, Yimao; Huang, Ru
2016-05-01
Here we propose a novel encapsulated vertical 3D RRAM structure with each resistive switching cell encapsulated by dielectric layers, contributing to both the reliability improvement of individual cells and thermal disturbance reduction of adjacent cells due to the effective suppression of unwanted oxygen vacancy diffusion. In contrast to the traditional vertical 3D RRAM, encapsulated bar-electrodes are adopted in the proposed structure substituting the previous plane-electrodes, thus encapsulated resistive switching cells can be naturally formed by simply oxidizing the tip of the metal bar-electrodes. In this work, TaO x -based 3D RRAM devices with SiO2 and Si3N4 as encapsulation layers are demonstrated, both showing significant advantages over traditional unencapsulated vertical 3D RRAM. Furthermore, it was found thermal conductivity and oxygen blocking ability are two key parameters of the encapsulation layer design influencing the scalability of vertical 3D RRAM. Experimental and simulation data show that oxygen blocking ability is more critical for encapsulation layers in the relatively large scale, while thermal conductivity becomes dominant as the stacking layers scale to the sub-10 nm regime. Finally, based on the notable impacts of the encapsulation layer on 3D RRAM scaling, an encapsulation material with both excellent oxygen blocking ability and high thermal conductivity such as AlN is suggested to be highly desirable to maximize the advantages of the proposed encapsulated structure. The findings in this work could pave the way for reliable ultrahigh-density storage applications in the big data era.
Encapsulation layer design and scalability in encapsulated vertical 3D RRAM.
Yu, Muxi; Fang, Yichen; Wang, Zongwei; Chen, Gong; Pan, Yue; Yang, Xue; Yin, Minghui; Yang, Yuchao; Li, Ming; Cai, Yimao; Huang, Ru
2016-05-20
Here we propose a novel encapsulated vertical 3D RRAM structure with each resistive switching cell encapsulated by dielectric layers, contributing to both the reliability improvement of individual cells and thermal disturbance reduction of adjacent cells due to the effective suppression of unwanted oxygen vacancy diffusion. In contrast to the traditional vertical 3D RRAM, encapsulated bar-electrodes are adopted in the proposed structure substituting the previous plane-electrodes, thus encapsulated resistive switching cells can be naturally formed by simply oxidizing the tip of the metal bar-electrodes. In this work, TaO x -based 3D RRAM devices with SiO2 and Si3N4 as encapsulation layers are demonstrated, both showing significant advantages over traditional unencapsulated vertical 3D RRAM. Furthermore, it was found thermal conductivity and oxygen blocking ability are two key parameters of the encapsulation layer design influencing the scalability of vertical 3D RRAM. Experimental and simulation data show that oxygen blocking ability is more critical for encapsulation layers in the relatively large scale, while thermal conductivity becomes dominant as the stacking layers scale to the sub-10 nm regime. Finally, based on the notable impacts of the encapsulation layer on 3D RRAM scaling, an encapsulation material with both excellent oxygen blocking ability and high thermal conductivity such as AlN is suggested to be highly desirable to maximize the advantages of the proposed encapsulated structure. The findings in this work could pave the way for reliable ultrahigh-density storage applications in the big data era. PMID:27044065
Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height
NASA Astrophysics Data System (ADS)
Allaerts, Dries; Meyers, Johan
2015-11-01
In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer layer effects on wind-farm boundary layers. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.
NASA Astrophysics Data System (ADS)
Yu, H.-S.; Jackson, B. V.; Hick, P. P.; Buffington, A.; Odstrcil, D.; Wu, C.-C.; Davies, J. A.; Bisi, M. M.; Tokumaru, M.
2015-09-01
The University of California, San Diego, time-dependent analyses of the heliosphere provide three-dimensional (3D) reconstructions of solar wind velocities and densities from observations of interplanetary scintillation (IPS). Using data from the Solar-Terrestrial Environment Laboratory, Japan, these reconstructions provide a real-time prediction of the global solar-wind density and velocity throughout the whole heliosphere with a temporal cadence of about one day (ips.ucsd.edu). Updates to this modeling effort continue: in the present article, near-Sun results extracted from the time-dependent 3D reconstruction are used as inner boundary conditions to drive 3D-MHD models ( e.g. ENLIL and H3D-MHD). This allows us to explore the differences between the IPS kinematic-model data-fitting procedure and current 3D-MHD modeling techniques. The differences in these techniques provide interesting insights into the physical principles governing the expulsion of coronal mass ejections (CMEs). Here we detail for the first time several specific CMEs and an induced shock that occurred in September 2011 that demonstrate some of the issues resulting from these analyses.
Microgravity Effects on Plant Boundary Layers
NASA Technical Reports Server (NTRS)
Stutte, Gary; Monje, Oscar
2005-01-01
The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.
Goertler instability of compressible boundary layers
NASA Technical Reports Server (NTRS)
El-Hady, N. M.; Verma, A. K.
1984-01-01
The instability of the laminar compressible boundary-layer flows along concave surfaces is investigated. The linearized disturbance equations for the three-dimensional, counter-rotating, longitudinal-type vortices in two-dimensional boundary layers are presented in an orthogonal curvilinear system of coordinates. The basic approximation of the disturbance equations, which includes the effect of the growth of the boundary layer, is considered and solved numerically.
Turbulent boundary layers with secondary flow
NASA Technical Reports Server (NTRS)
Grushwitz, E.
1984-01-01
An experimental analysis of the boundary layer on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.
Three-dimensional boundary layers approaching separation
NASA Technical Reports Server (NTRS)
Williams, J. C., III
1976-01-01
The theory of semi-similar solutions of the laminar boundary layer equations is applied to several flows in which the boundary layer approaches a three-dimensional separation line. The solutions obtained are used to deduce the nature of three-dimensional separation. It is shown that in these cases separation is of the "ordinary" type. A solution is also presented for a case in which a vortex is embedded within the three-dimensional boundary layer.
Wang, Lisheng; Wang, Pai; Cheng, Liuhang; Ma, Yu; Wu, Shenzhi; Wang, Yu-Ping; Xu, Zongben
2014-11-01
In this paper we propose a novel and easy to use 3D reconstruction method. With the method, users only need to specify a small boundary surface patch in a 2D section image, and then an entire continuous implicit boundary surface (CIBS) can be automatically reconstructed from a 3D image. In the method, a hierarchical tracing strategy is used to grow the known boundary surface patch gradually in the 3D image. An adaptive detection technique is applied to detect boundary surface patches from different local regions. The technique is based on both context dependence and adaptive contrast detection as in the human vision system. A recognition technique is used to distinguish true boundary surface patches from the false ones in different cubes. By integrating these different approaches, a high-resolution CIBS model can be automatically reconstructed by adaptively expanding the small boundary surface patch in the 3D image. The effectiveness of our method is demonstrated by its applications to a variety of real 3D images, where the CIBS with complex shapes/branches and with varying gray values/gradient magnitudes can be well reconstructed. Our method is easy to use, which provides a valuable tool for 3D image visualization and analysis as needed in many applications. PMID:26355329
Interactions in boundary-layer transition
NASA Technical Reports Server (NTRS)
Smith, Frank T.
1989-01-01
Certain theoretical studies of boundary-layer transition are described, based on high Reynolds numbers and with attention drawn to the various nonlinear interactions and scales present. The article concentrates in particular on theories for which the mean-flow profile is completely altered from its original state. Two- and three-dimensional flow theory and conjectures on turbulent-boundary-layer structures are included. Specific recent findings noted, and in qualitative agreement with experiments, are: nonlinear finite-time break-ups in unsteady interactive boundary layers; strong vortex/wave interactions; and prediction of turbulent boundary-layer displacement- and stress sublayer-thicknesses.
Nonlinear breakdowns in boundary layer transition
NASA Technical Reports Server (NTRS)
Smith, Frank T.
1990-01-01
Theoretical studies of boundary-layer transition are described, based on high Reynolds numbers and with attention drawn to nonlinear interactions, breakdowns and scales. The article notes in particular truly nonlinear theories for which the mean-flow profile is completely altered from its original state. Two- and three-dimensional flow theory and conjectures on turbulent boundary-layer structures are included. Specific recent findings noted, and in qualitative agreement with experiments, are: nonlinear finite-time break-ups in unsteady interactive boundary layers; strong vortex/wave interactions; and prediction of turbulent boundary-layer displacement- and stress sublayer-thicknesses.
Development of perturbations in the boundary layer
NASA Technical Reports Server (NTRS)
Dovgal, A. V.; Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.; Maksimov, V. P.
1986-01-01
The transition of laminar flows into turbulent flows in a boundary layer is discussed. The individual aspects of the transition process, observed under controllable model conditions are examined. The aspect of this problem, namely the development or excitation of the natural oscillations in the boundary layer, the so-called Tollmin-Schlichting waves is covered. Three types of excitation of these waves are considered: (1) distributed generation throughout the boundary layer; (2) generation in the vicinity of the forward edge of a model, having either a sharp edge or an edge with a large radius or curvature, and (3) generation in a developed boundary layer by means of a focused effect.
Structure of the low latitude boundary layer
NASA Technical Reports Server (NTRS)
Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. O.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.
1980-01-01
Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more.
A 3D insight on the catalytic nanostructuration of few-layer graphene
Melinte, G.; Florea, I.; Moldovan, S.; Janowska, I.; Baaziz, W.; Arenal, R.; Wisnet, A.; Scheu, C.; Begin-Colin, S.; Begin, D.; Pham-Huu, C.; Ersen, O.
2014-01-01
The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting. PMID:24916201
Internal waves patterns in the wake of a 3D body towed in a two-layer fluid
NASA Astrophysics Data System (ADS)
Lacaze, Laurent; Mercier, Matthieu; Thual, Olivier; Paci, Alexandre
2014-11-01
Stratified flows over obstacles are important features in meteorology and oceanography. The characterization of these flows is crucial in order to propose models of geophysical processes such as mixing and ocean circulation or orographic drag in the atmosphere. For some specific stratification profiles, the energy of internal waves generated by the obstacle can be trapped at a given depth, at the base of the oceanic mixing layer or at the top of the atmospheric boundary layer for instance. This scenario can be modelled by a two-layer stratified fluid for which gravity waves spread at the interface between the two layers. The work presented here focuses on a two-layer flow over a 3D obstacle, or equivalently, an obstacle towed in a fluid at rest. Experiments performed both in the large-scale flume of CNRM-GAME Toulouse (METEO-FRANCE & CNRS) and in a smaller tank apparatus, are presented with a specific attention on the measurement of the 3D wave patterns. A non-hydrostatic linear analysis is used to describe the observed wave patterns. The experiments highlight the strong influence of the Froude number on the generated waves. More specifically, we investigate the nature of the wake angle obtained from the wave pattern, and discuss a transition from Kelvin to Mach angle.
Multimode observations and 3D magnetic control of the boundary of a tokamak plasma
NASA Astrophysics Data System (ADS)
Levesque, J. P.; Rath, N.; Shiraki, D.; Angelini, S.; Bialek, J.; Byrne, P. J.; DeBono, B. A.; Hughes, P. E.; Mauel, M. E.; Navratil, G. A.; Peng, Q.; Rhodes, D. J.; Stoafer, C. C.
2013-07-01
We present high-resolution detection and control of the 3D magnetic boundary in the High Beta Tokamak-Extended Pulse (HBT-EP) device. Measurements of non-axisymmetric radial and poloidal fields are made using 216 magnetic sensors positioned near the plasma surface. Control of 3D fields is accomplished using 40 independent saddle coils attached to the passive stabilizing wall. The control coils are energized with high-power solid-state amplifiers, and massively parallel, high-throughput feedback control experiments are performed using low-latency connections between PCI Express analogue input and output modules and a graphics processing unit. The time evolution of unstable and saturated wall-stabilized external kink modes are studied with and without applying magnetic perturbations using the control coils. The 3D dynamic structure of the magnetic field surrounding the plasma is determined through biorthogonal decomposition using the full set of magnetic sensors without the need to fit either a Fourier or a model-based basis. Naturally occurring external kinks are composed of multiple independent helical modes. Smooth transitions between dominant poloidal mode numbers are observed for simultaneous n = 1 and n = 2 modes as the edge safety factor changes. Relative amplitudes of coexistent m/n = 3/1 and 6/2 modes depend on the plasma's major radius and edge safety factor. When stationary 3/1 magnetic perturbations are applied, the resonant response can be linear, saturated, or disruptive, depending upon the perturbation amplitude and the edge safety factor; increased plasma-wall interactions from the perturbed plasma are proposed as a saturation mechanism. Initial feedback experiments have used 40 sensors and 40 control coils, producing mode amplification or suppression, and acceleration or deceleration depending on the feedback phase angle.
Boundary layers of the earth's outer magnetosphere
NASA Technical Reports Server (NTRS)
Eastman, T. E.; Frank, L. A.
1984-01-01
The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.
Understanding and Improving the Quality of Inter-Layer Interfaces in FDM 3-D Printing
NASA Astrophysics Data System (ADS)
Duranty, Edward; Spradlin, Brandon; Stark, Madeline; Dadmun, Mark
We have studied the effect of thermal history and material diffusion on inter-filament bonding in FDM 3D printed parts and developed methods to improve interlayer adhesion in 3D printed samples. The available thermal energy during the FDM print environment was determined quantitatively by tracking the temperature of the bottom most printed layer using a thermocouple attached to the print bed. The role of the thermal history of the filaments during the deposition process on the quality of inter-layer bonding in an FDM ABS part was monitored using a T-peel test and an innovative sample design. Additionally, the interfacial adhesion between 3D printed layers was improved by the addition of a chemical cross-linking agent 4,4 '-diaminodiphenylmethane (DADPM). These studies have increased our understanding of the importance of the complex thermal history of a filament in the 3D printing process and its impact on the interfaces that form during the fused deposition modeling print process. Furthermore, the chemical crosslinking process demonstrates a potential method to covalently link layers in FDM printed parts, improving the bulk strength of the part. The insight provided in this work may aid in the development of techniques that can produce FDM parts that could be used as replacement parts in structural applications, or as completely standalone products.
Finite Element Code For 3D-Hydraulic Fracture Propagation Equations (3-layer).
Energy Science and Technology Software Center (ESTSC)
1992-03-24
HYFRACP3D is a finite element program for simulation of a pseudo three-dimensional fracture geometries with a two-dimensional planar solution. The model predicts the height, width and winglength over time for a hydraulic fracture propagating in a three-layered system of rocks with variable rock mechanics properties.
Numerical simulation of transition control in boundary layers
NASA Astrophysics Data System (ADS)
Laurien, E.; Kleiser, L.
The transition process from laminar to turbulent boundary layers is simulated by numerical integration of the 3D incompressible Navier-Stokes equations. Spatially periodic wave disturbances in a parallel Blasius flow are assumed. A spectral method with real-space Chebyshev collocation in the normal direction is employed. Both the classical K-type and the subharmonic type of transition are investigated. Good agreement with measurements and flow visualizations of transition experiments is obtained. Control of transition by wave superposition is simulated using periodic wall suction/blowing. It is shown that 2D control works well at an early stage but fails after significant 3D disturbances have developed.
Abràmoff, Michael D.; Kardon, Randy; Russell, Stephen R.; Wu, Xiaodong; Sonka, Milan
2008-01-01
Current techniques for segmenting macular optical coherence tomography (OCT) images have been 2-D in nature. Furthermore, commercially available OCT systems have only focused on segmenting a single layer of the retina, even though each intraretinal layer may be affected differently by disease. We report an automated approach for segmenting (anisotropic) 3-D macular OCT scans into five layers. Each macular OCT dataset consisted of six linear radial scans centered at the fovea. The six surfaces defining the five layers were identified on each 3-D composite image by transforming the segmentation task into that of finding a minimum-cost closed set in a geometric graph constructed from edge/regional information and a priori determined surface smoothness and interaction constraints. The method was applied to the macular OCT scans of 12 patients (24 3-D composite image datasets) with unilateral anterior ischemic optic neuropathy (AION). Using the average of three experts’ tracings as a reference standard resulted in an overall mean unsigned border positioning error of 6.1 ± 2.9 µm, a result comparable to the interobserver variability (6.9 ± 3.3 µm). Our quantitative analysis of the automated segmentation results from AION subject data revealed that the inner retinal layer thickness for the affected eye was 24.1 µm (21%) smaller on average than for the unaffected eye (P < 0.001), supporting the need for segmenting the layers separately. PMID:18815101
Aerodynamic heating on 3-D bodies including the effects of entropy-layer swallowing
NASA Technical Reports Server (NTRS)
Dejarnette, F. R.; Hamilton, H. H.
1974-01-01
A relatively simple method was developed previously (authors, 1973) for calculating laminar, transitional, and turbulent heating rates on three-dimensional bodies in hypersonic flows. This method was shown to yield reasonably accurate results for laminar heating on blunted circular and elliptical cones and an earlier version of the space shuttle vehicle. As the boundary layer along the surface grows, more and more of the inviscid-flow mass is entrained into the boundary layer, and the streamlines which passed through the nearly normal portion of the bow shock wave are 'swallowed' by the boundary layer. This phenomenon is often referred to as entropy-layer or streamline swallowing, and it can have a significant effect on the calculated heating rates. An approximate, yet simple, method for including the effects of entropy-layer swallowing in the heating-rate calculations is given.
Quiescent H-Mode 3D MHD Free-Boundary Equilibrium
NASA Astrophysics Data System (ADS)
Cooper, W. Anthony; Graves, Jonathan P.; Duval, Basil P.; Porte, Laurie; Sauter, Olivier; Tran, Trach-Minh; Brunetti, Daniele; Pfefferle, David; Raghunathan, Madhusudan; Faustin, Jonathan M.; Patten, Hamish; Kleiner, Andreas; Reimerdes, Holger
2015-11-01
Free boundary magnetohydrodynamic equilibrium states with spontaneous three dimensional deformations of the plasma-vacuum interface are computed with the 3D VMEC solver [Hirshman et al., Comput. Phys. Commun. 43 (1986) 143]. The structures we have obtained have the appearance of saturated ideal external kink/peeling modes. Large edge pressure gradients yield toroidal mode number n = 1 corrugations when the edge bootstrap current is large and n = 4 distortions when this current is small. The deformations of the plasma boundary region induces a nonaxisymmetric Pfirsch-Schlüter current that drives a field-aligned current ribbon which is consistent with experimental observations reported. We claim that the equilibrium states we compute model the Edge Harmonic Oscillation [K.H. Burrell et al., Phys. Plasmas 22 (2005) 021805. W.M. Solomon et al., Phys. Rev. Lett. 113 (2014) 135001] observed on DIII-D and the Outer Mode [E.R. Solano et al., Phys. Rev. Lett. 104 (2014) 135001] found in JET during Quiescent H-mode operation. This work was supported in part by the Swiss National Science Foundation.
Cyclone separator having boundary layer turbulence control
Krishna, Coimbatore R.; Milau, Julius S.
1985-01-01
A cyclone separator including boundary layer turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the boundary layer of the vortical fluid flow through the separator.
Effect of density gradients in confined supersonic shear layers. Part 2: 3-D modes
NASA Technical Reports Server (NTRS)
Peroomian, Oshin; Kelly, R. E.
1994-01-01
The effect of basic flow density gradients on the supersonic wall modes were investigated in Part 1 of this analysis. In that investigation only the 2-D modes were studied. Tam and Hu investigated the 3-D modes in a confined vortex sheet and reported that the first 2-D Class A mode (A01) had the highest growth rate compared to all other 2-D and 3-D modes present in the vortex sheet for that particular set of flow patterns. They also showed that this result also held true for finite thickness shear layers with delta(sub w) less than 0.125. For free shear layers, Sandham and Reynolds showed that the 3-D K-H mode became the dominant mode for M(sub c) greater than 0.6. Jackson and Grosch investigated the effect of crossflow and obliqueness on the slow and fast odes present in a M(sub c) greater than 1 environment and showed that for certain combination of crossflow and wave angles the growth rates could be increased by up to a factor of 2 with respect to the 2-D case. The case studied here is a confined shear layer shown in Part 1. All solution procedures and basic low profiles are the same as in Part 1. The effect of density gradients on the 3-D modes present in the density ratios considered in Part 1 are investigated.
Boundary Layers of Air Adjacent to Cylinders
Nobel, Park S.
1974-01-01
Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for νwindd between 200 and 30,000 cm2/second (where νwind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855
Structure of relaminarizing turbulent boundary layers
NASA Astrophysics Data System (ADS)
Ramesh, O.; Patwardhan, Saurabh
2014-11-01
Relaminarization of a turbulent boundary layer in a strongly accelerated flow has received a great attention in recent times. It has been found that such relaminarization is a general and regularly occurring phenomenon in the leading-edge region of a swept wing of an airplane (van Dam et al., 1993). In this work, we investigate the effect of initial Reynolds number on the process of relaminarization in turbulent boundary layers. The experimental and numerical investigation of relaminarizing turbulent boundary layers undergoing same history reveals that the boundary layer with higher initial Reynolds number relaminarizes at a lower pressure gradient value compared to the one with lower Reynolds number. This effect can be explained on the inviscid theory proposed earlier in the literature. Further, various parameter criteria proposed to predict relaminarization, are assessed and the structure of relaminarizing boundary layers is investigated. A mechanism for stabilization of near-wall low speed streaks is proposed.
Lithographically-generated 3D lamella layers and their structural color
NASA Astrophysics Data System (ADS)
Zhang, Sichao; Chen, Yifang; Lu, Bingrui; Liu, Jianpeng; Shao, Jinhai; Xu, Chen
2016-04-01
Inspired by the structural color from the multilayer nanophotonic structures in Morpho butterfly wing scales, 3D lamellae layers in dielectric polymers (polymethyl methacrylate, PMMA) with n ~ 1.5 were designed and fabricated by standard top-down electron beam lithography with one-step exposure followed by an alternating development/dissolution process of PMMA/LOR (lift-off resist) multilayers. This work offers direct proof of the structural blue/green color via lithographically-replicated PMMA/air multilayers, analogous to those in real Morpho butterfly wings. The success of nanolithography in this work for the 3D lamellae structures in dielectric polymers not only enables us to gain deeper insight into the mysterious blue color of the Morpho butterfly wings, but also breaks through the bottleneck in technical development toward broad applications in gas/liquid sensors, 3D meta-materials, coloring media, and infrared imaging devices, etc.
Lithographically-generated 3D lamella layers and their structural color.
Zhang, Sichao; Chen, Yifang; Lu, Bingrui; Liu, Jianpeng; Shao, Jinhai; Xu, Chen
2016-04-28
Inspired by the structural color from the multilayer nanophotonic structures in Morpho butterfly wing scales, 3D lamellae layers in dielectric polymers (polymethyl methacrylate, PMMA) with n ∼ 1.5 were designed and fabricated by standard top-down electron beam lithography with one-step exposure followed by an alternating development/dissolution process of PMMA/LOR (lift-off resist) multilayers. This work offers direct proof of the structural blue/green color via lithographically-replicated PMMA/air multilayers, analogous to those in real Morpho butterfly wings. The success of nanolithography in this work for the 3D lamellae structures in dielectric polymers not only enables us to gain deeper insight into the mysterious blue color of the Morpho butterfly wings, but also breaks through the bottleneck in technical development toward broad applications in gas/liquid sensors, 3D meta-materials, coloring media, and infrared imaging devices, etc. PMID:27087577
LDV measurements of turbulent baroclinic boundary layers
Neuwald, P.; Reichenbach, H.; Kuhl, A.L.
1993-07-01
Described here are shock tube experiments of nonsteady, turbulent boundary layers with large density variations. A dense-gas layer was created by injecting Freon through the porous floor of the shock tube. As the shock front propagated along the layer, vorticity was created at the air-Freon interface by an inviscid, baroclinic mechanism. Shadow-schlieren photography was used to visualize the turbulent mixing in this baroclinic boundary layer. Laser-Doppler-Velocimetry (LDV) was used to measure the streamwise velocity histories at 14 heights. After transition, the boundary layer profiles may be approximated by a power-law function u {approximately} u{sup {alpha}} where {alpha} {approx_equal} 3/8. This value lies between the clean flat plate value ({alpha} = 1/7) and the dusty boundary layer value ({alpha} {approx_equal} 0.7), and is controlled by the gas density near the wall.
Borazjani, Iman; Ge, Liang; Sotiropoulos, Fotis
2008-08-10
The sharp-interface CURVIB approach of Ge and Sotiropoulos [L. Ge, F. Sotiropoulos, A Numerical Method for Solving the 3D Unsteady Incompressible Navier-Stokes Equations in Curvilinear Domains with Complex Immersed Boundaries, Journal of Computational Physics 225 (2007) 1782-1809] is extended to simulate fluid structure interaction (FSI) problems involving complex 3D rigid bodies undergoing large structural displacements. The FSI solver adopts the partitioned FSI solution approach and both loose and strong coupling strategies are implemented. The interfaces between immersed bodies and the fluid are discretized with a Lagrangian grid and tracked with an explicit front-tracking approach. An efficient ray-tracing algorithm is developed to quickly identify the relationship between the background grid and the moving bodies. Numerical experiments are carried out for two FSI problems: vortex induced vibration of elastically mounted cylinders and flow through a bileaflet mechanical heart valve at physiologic conditions. For both cases the computed results are in excellent agreement with benchmark simulations and experimental measurements. The numerical experiments suggest that both the properties of the structure (mass, geometry) and the local flow conditions can play an important role in determining the stability of the FSI algorithm. Under certain conditions unconditionally unstable iteration schemes result even when strong coupling FSI is employed. For such cases, however, combining the strong-coupling iteration with under-relaxation in conjunction with the Aitken's acceleration technique is shown to effectively resolve the stability problems. A theoretical analysis is presented to explain the findings of the numerical experiments. It is shown that the ratio of the added mass to the mass of the structure as well as the sign of the local time rate of change of the force or moment imparted on the structure by the fluid determine the stability and convergence of the FSI
Borazjani, Iman; Ge, Liang; Sotiropoulos, Fotis
2010-01-01
The sharp-interface CURVIB approach of Ge and Sotiropoulos [L. Ge, F. Sotiropoulos, A Numerical Method for Solving the 3D Unsteady Incompressible Navier-Stokes Equations in Curvilinear Domains with Complex Immersed Boundaries, Journal of Computational Physics 225 (2007) 1782–1809] is extended to simulate fluid structure interaction (FSI) problems involving complex 3D rigid bodies undergoing large structural displacements. The FSI solver adopts the partitioned FSI solution approach and both loose and strong coupling strategies are implemented. The interfaces between immersed bodies and the fluid are discretized with a Lagrangian grid and tracked with an explicit front-tracking approach. An efficient ray-tracing algorithm is developed to quickly identify the relationship between the background grid and the moving bodies. Numerical experiments are carried out for two FSI problems: vortex induced vibration of elastically mounted cylinders and flow through a bileaflet mechanical heart valve at physiologic conditions. For both cases the computed results are in excellent agreement with benchmark simulations and experimental measurements. The numerical experiments suggest that both the properties of the structure (mass, geometry) and the local flow conditions can play an important role in determining the stability of the FSI algorithm. Under certain conditions unconditionally unstable iteration schemes result even when strong coupling FSI is employed. For such cases, however, combining the strong-coupling iteration with under-relaxation in conjunction with the Aitken’s acceleration technique is shown to effectively resolve the stability problems. A theoretical analysis is presented to explain the findings of the numerical experiments. It is shown that the ratio of the added mass to the mass of the structure as well as the sign of the local time rate of change of the force or moment imparted on the structure by the fluid determine the stability and convergence of the
Proton exchange membrane micro fuel cells on 3D porous silicon gas diffusion layers
NASA Astrophysics Data System (ADS)
Kouassi, S.; Gautier, G.; Thery, J.; Desplobain, S.; Borella, M.; Ventura, L.; Laurent, J.-Y.
2012-10-01
Since the 90's, porous silicon has been studied and implemented in many devices, especially in MEMS technology. In this article, we present a new approach to build miniaturized proton exchange membrane micro-fuel cells using porous silicon as a hydrogen diffusion layer. In particular, we propose an innovative process to build micro fuel cells from a “corrugated iron like” 3D structured porous silicon substrates. This structure is able to increase up to 40% the cell area keeping a constant footprint on the silicon wafer. We propose here a process route to perform electrochemically 3D porous gas diffusion layers and to deposit fuel cell active layers on such substrates. The prototype peak power performance was measured to be 90 mW cm-2 in a “breathing configuration” at room temperature. These performances are less than expected if we compare with a reference 2D micro fuel cell. Actually, the active layer deposition processes are not fully optimized but this prototype demonstrates the feasibility of these 3D devices.
3D outflow jets originating from turbulence in the reconnection current layer
NASA Astrophysics Data System (ADS)
Fujimoto, Keizo
2016-07-01
Satellite observations in the Earth's magnetosphere and in solar flares have suggested that the reconnection outflow jets are fully three dimensional, consisting of a series of narrow channels. The jet structure is important in evaluating the energy and flux transport in the reconnection process. Previous theoretical models based on fluid simulations have relied on patchy reconnection where reconnection takes place predominantly in patchy portions of the current layer. The problem of the previous models is that the gross reconnection rate is much smaller than that in the 2D reconnection case. The present study shows a large-scale 3D PIC simulation revealing that the 3D outflow jets are generated through the 3D flux ropes formed in the turbulent electron current layer around the x-line. Reconnection proceeds almost uniformly along the x-line, so that the gross reconnection rate is comparable to that in the 2D reconnection case. The flux ropes and resultant outflow channels have a typical current-aligned scale provided by the wavelength of an electron shear mode that is much larger than the typical kinetic scales. It is found that the structure of the 3D outflow jets obtained in the simulation is consistent with the bursty bulk flow observed in the Earth's magnetotail.
A 5 MHz Cylindrical Dual-Layer Transducer Array for 3-D Transrectal Ultrasound Imaging
Chen, Yuling; Nguyen, Man; Yen, Jesse T.
2012-01-01
2-D transrectal ultrasound (TRUS) is being used in guiding prostate biopsies and treatments. In many cases, the TRUS probes are moved manually or mechanically to acquire volumetric information, making the imaging slow, user-dependent and unreliable. A real-time 3-D TRUS system could improve reliability and volume rates of imaging during these procedures. In this paper, we present a 5 MHz cylindrical dual-layer transducer array capable of real-time 3-D transrectal ultrasound without any mechanically moving parts. Compared to fully-sampled 2-D arrays, this design substantially reduces the channel count and fabrication complexity. This dual-layer transducer uses PZT elements for transmit and P[VDF-TrFE] copolymer elements for receive, respectively. The mechanical flexibility of both diced PZT and copolymer makes it practical for transrectal applications. Full synthetic aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics Data Acquisition System (VDAS). Offline 3-D beamforming was then performed to obtain volumes of two wire phantoms and a cyst phantom. Generalized coherence factor (GCF) was applied to improve the contrast of images. The measured −6 dB fractional bandwidth of the transducer was 62% with a center frequency of 5.66 MHz. The measured lateral beamwidths were 1.28 mm and 0.91 mm in transverse and longitudinal directions respectively, compared with a simulated beamwidth of 0.92 mm and 0.74 mm. PMID:22972914
Longitudinal vortices imbedded in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Mehta, R. D.; Shabaka, I. M. M.; Shibl, A.; Bradshaw, P.
1983-01-01
The attenuation of skew-induced longitudinal vortices by turbulent or viscous stresses is studied for the case of pure, artificially-generated longitudinal vortices entrained into initially two-dimensional boundary layers in nominally zero pressure gradients. Three types of vortex-boundary interactions are studied in detail: (1) an isolated vortex in a two-dimensional boundary layer; (2) a vortex pair in a turbulent boundary layer with the common flow between the vortices moving away from the surface; (3) a vortex pair in a boundary layer with the common flow moving towards the surface. Detailed mean flow and turbulence measurements are made, showing that the eddy viscosities defined for the different shear-stress components behave in different and complicated ways. Terms in the Reynolds stress transport equations, notably the triple products that effect turbulent diffusion of Reynolds stress, also fail to obey simple rules.
An Evaluation of Boundary Conditions for Modeling Urban Boundary Layers
Calhoun, R.J.; Chan, S.T.; Lee, R.L.
2000-05-18
Numerical modeling of the urban boundary layer is complicated by the need to describe airflow patterns outside of the computational domain. These patterns have an impact on how successfully the simulation is able to model the turbulence associated with the urban boundary layer. This talk presents experiments with the model boundary conditions for simulations that were done to support two Department of Energy observational programs involving the Salt Lake City basin. The Chemical/Biological Non-proliferation Program (CBNP) is concerned with the effects of buildings on influencing dispersion patterns in urban environments. The Vertical Transport and Mixing Program (VTMX) investigating mixing mechanisms in the stable boundary layer and how they are influenced by the channeling caused by drainage flows or by obstacles such as building complexes. Both of these programs are investigating the turbulent mixing caused by building complexes and other urban obstacles.
3D printing of layered brain-like structures using peptide modified gellan gum substrates.
Lozano, Rodrigo; Stevens, Leo; Thompson, Brianna C; Gilmore, Kerry J; Gorkin, Robert; Stewart, Elise M; in het Panhuis, Marc; Romero-Ortega, Mario; Wallace, Gordon G
2015-10-01
The brain is an enormously complex organ structured into various regions of layered tissue. Researchers have attempted to study the brain by modeling the architecture using two dimensional (2D) in vitro cell culturing methods. While those platforms attempt to mimic the in vivo environment, they do not truly resemble the three dimensional (3D) microstructure of neuronal tissues. Development of an accurate in vitro model of the brain remains a significant obstacle to our understanding of the functioning of the brain at the tissue or organ level. To address these obstacles, we demonstrate a new method to bioprint 3D brain-like structures consisting of discrete layers of primary neural cells encapsulated in hydrogels. Brain-like structures were constructed using a bio-ink consisting of a novel peptide-modified biopolymer, gellan gum-RGD (RGD-GG), combined with primary cortical neurons. The ink was optimized for a modified reactive printing process and developed for use in traditional cell culturing facilities without the need for extensive bioprinting equipment. Furthermore the peptide modification of the gellan gum hydrogel was found to have a profound positive effect on primary cell proliferation and network formation. The neural cell viability combined with the support of neural network formation demonstrated the cell supportive nature of the matrix. The facile ability to form discrete cell-containing layers validates the application of this novel printing technique to form complex, layered and viable 3D cell structures. These brain-like structures offer the opportunity to reproduce more accurate 3D in vitro microstructures with applications ranging from cell behavior studies to improving our understanding of brain injuries and neurodegenerative diseases. PMID:26231917
A Dual-Layer Transducer Array for 3-D Rectilinear Imaging
Yen, Jesse T.; Seo, Chi Hyung; Awad, Samer I.; Jeong, Jong S.
2010-01-01
2-D arrays for 3-D rectilinear imaging require very large element counts (16,000–65,000). The difficulties in fabricating and interconnecting 2-D arrays with a large number of elements (>5,000) have limited the development of suitable transducers for 3-D rectilinear imaging. In this paper, we propose an alternative solution to this problem by using a dual-layer transducer array design. This design consists of two perpendicular 1-D arrays for clinical 3-D imaging of targets near the transducer. These targets include the breast, carotid artery, and musculoskeletal system. This transducer design reduces the fabrication complexity and the channel count making 3-D rectilinear imaging more realizable. With this design, an effective N × N 2-D array can be developed using only N transmitters and N receivers. This benefit becomes very significant when N becomes greater than 128, for example. To demonstrate feasibility, we constructed a 4 × 4 cm prototype dual-layer array. The transmit array uses diced PZT-5H elements, and the receive array is a single sheet of undiced P[VDF-TrFE] copolymer. The receive elements are defined by the copper traces on the flexible interconnect circuit. The measured −6 dB fractional bandwidth was 80% with a center frequency of 4.8 MHz. At 5 MHz, the nearest neighbor crosstalk of the PZT array and PVDF array was −30.4 ± 3.1 dB and −28.8 ± 3.7 dB respectively. This dual-layer transducer was interfaced with an Ultrasonix Sonix RP system, and a synthetic aperture 3-D data set was acquired. We then performed off-line 3-D beamforming to obtain volumes of nylon wire targets. The theoretical lateral beamwidth was 0.52 mm compared to measured beamwidths of 0.65 mm and 0.67 mm in azimuth and elevation respectively. 3-D images of an 8 mm diameter anechoic cyst phantom were also acquired. PMID:19213647
Planetary Boundary Layer Simulation Using TASS
NASA Technical Reports Server (NTRS)
Schowalter, David G.; DeCroix, David S.; Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael
1996-01-01
Boundary conditions to an existing large-eddy simulation model have been changed in order to simulate turbulence in the atmospheric boundary layer. Several options are now available, including the use of a surface energy balance. In addition, we compare convective boundary layer simulations with the Wangara and Minnesota field experiments as well as with other model results. We find excellent agreement of modelled mean profiles of wind and temperature with observations and good agreement for velocity variances. Neutral boundary simulation results are compared with theory and with previously used models. Agreement with theory is reasonable, while agreement with previous models is excellent.
Boundary-layer linear stability theory
NASA Technical Reports Server (NTRS)
Mack, L. M.
1984-01-01
Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of boundary layer instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius boundary layer, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a boundary layer, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer
Boundary-layer linear stability theory
NASA Astrophysics Data System (ADS)
Mack, L. M.
1984-06-01
Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of boundary layer instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius boundary layer, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a boundary layer, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer
Calculation methods for compressible turbulent boundary layers
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.
1976-01-01
Calculation procedures for non-reacting compressible two- and three-dimensional turbulent boundary layers were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete boundary layer equations summarized. Alternative numerical solution procedures were examined, and both mean field and mean turbulence field closure models were considered. Physics and related calculation problems peculiar to compressible turbulent boundary layers are described. A catalog of available solution procedures of the finite difference, finite element, and method of weighted residuals genre is included. Influence of compressibility, low Reynolds number, wall blowing, and pressure gradient upon mean field closure constants are reported.
A new pillared-layer 3D coordination polymer involving in situ generated formate
NASA Astrophysics Data System (ADS)
Xia, Yu-Pei; Li, Yun-Wu; Li, Da-Cheng; Du, Yu-Chang; Yao, Qing-Xia; Dou, Jian-Min
2015-02-01
A new Cd-based coordination polymer, [Cd(cpt)(HCOO)]n (1), has been synthesized from 1-(4-carboxyphenyl)-1,2,4-triazole) ligand (Hcpt). The structure was characterized through X-ray crystallography, elemental analysis, and IR spectrum. Compound 1 presents a three-dimensional (3D) pillared-layer structure constructed by metal-formate layers and cpt- ligands. Moreover, the unusual formate anions are generated in situ from the decomposition of DMF precursors. The fluorescence property of 1 in solid state was also researched.
7.5 MHz dual-layer transducer array for 3-D rectilinear imaging.
Chen, Yuling; Nguyen, Man; Yen, Jesse T
2011-07-01
The difficulties associated with fabrication and interconnection have limited the development of 2-D ultrasound transducer arrays with a large number ofelements (>5000). In previous work, we described a 5 MHz center frequency PZT-P[VDF-TrFE] dual-layer transducer that used two perpendicular 1-D arrays for 3-D rectilinear imaging. This design substantially reduces the channel count as well as fabrication complexity, which makes 3-D imaging more realizable. Higher frequencies (>5 MHz) are more commonly used in clinical applications or imaging targets near transducers, such as the breast, carotid and musculoskeletal tissue. In this paper, we present a 7.5 MHz dual-layer transducer array for 3-D rectilinear imaging. A modified acoustic stack model was designed and fabricated. PZT elements were sub-diced to eliminate lateral coupling. This sub-dicing process made the PZT into a 2-2 composite material, which could help improve transducer sensitivity and bandwidth. Full synthetic-aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics data-acquisition system (VDAS). Offline 3-D beamforming was then performed to obtain volumes of a multiwire phantom and a cyst phantom. The generalized coherence factor (GCF) was applied to improve the contrast of cyst images. The measured -6 dB fractional bandwidth of the transducer was 71% with a center frequency of 7.5 MHz. The measured lateral beamwidths were 0.521 mm and 0.482 mm in azimuth and elevation, respectively, compared with a simulated beamwidth of 0.43 mm. PMID:21842584
A 7.5 MHz Dual-Layer Transducer Array for 3-D Rectilinear Imaging
Chen, Yuling; Nguyen, Man; Yen, Jesse T.
2011-01-01
The difficulties associated with fabrication and interconnection have limited the development of 2-D ultrasound transducer arrays with a large number of elements (>5000). In previous work, we described a 5 MHz center frequency PZT-P[VDF-TrFE] dual-layer transducer, which used 2 perpendicular 1-D arrays for 3-D rectilinear imaging. This design substantially reduces the channel count as well as fabrication complexity, which makes 3-D imaging more realizable. Higher frequencies (>5MHz) are more commonly used in clinical for imaging targets near transducers such as the breast, carotid, and musculoskeletal. In this paper, we present a 7.5 MHz dual-layer transducer array for 3-D rectilinear imaging. A modified acoustic stack model was designed and fabricated. PZT elements were sub-diced to eliminate lateral coupling. This sub-dicing process made the PZT into a 2–2 composite material, which could help improve transducer sensitivity and bandwidth. Full synthetic aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics data acquisition system (VDAS). Offline 3-D beamforming was then performed to obtain volumes of a multi-wire phantom and a cyst phantom. The generalized coherence factor (GCF) was applied to improve the contrast of cyst images. The measured −6 dB fractional bandwidth of the transducer was 71% with a center frequency of 7.5 MHz. The measured lateral beamwidths were 0.521 mm and 0.482 mm in azimuth and elevation respectively, compared with a simulated beamwidth of 0.43 mm. PMID:21842584
Grey zone simulations of the morning convective boundary layer development
NASA Astrophysics Data System (ADS)
Efstathiou, G. A.; Beare, R. J.; Osborne, S.; Lock, A. P.
2016-05-01
Numerical simulations of two cases of morning boundary layer development are conducted to investigate the impact of grid resolution on mean profiles and turbulent kinetic energy (TKE) partitioning from the large eddy simulation (LES) to the mesoscale limit. Idealized LES, using the 3-D Smagorinsky scheme, is shown to be capable of reproducing the boundary layer evolution when compared against measurements. However, increasing grid spacing results in the damping of resolved TKE and the production of superadiabatic temperature profiles in the boundary layer. Turbulence initiation is significantly delayed, exhibiting an abrupt onset at intermediate resolutions. Two approaches, the bounding of vertical diffusion coefficient and the blending of the 3-D Smagorinsky with a nonlocal 1D scheme, are used to model subgrid diffusion at grey zone resolutions. Simulations are compared against the coarse-grained fields from the validated LES results for each case. Both methods exhibit particular strengths and weaknesses, indicating the compromise that needs to be made currently in high-resolution numerical weather prediction. The blending scheme is able to reproduce the adiabatic profiles although turbulence is underestimated in favor of the parametrized heat flux, and the spin-up of TKE remains delayed. In contrast, the bounding approach gives an evolution of TKE that follows the coarse-grained LES very well, relying on the resolved motions for the nonlocal heat flux. However, bounding gives unrealistic static instability in the early morning temperature profiles (similar to the 3-D Smagorinsky scheme) because model dynamics are unable to resolve TKE when the boundary layer is too shallow compared to the grid spacing.
Godfrey, A.W.; Holm, E.A.; Hughes, D.A.; Miodownik, M.
1998-12-23
The fundamental difficulties incorporating experimentally obtained-boundary disorientation distributions (BMD) into 3D microstructural models are discussed. An algorithm is described which overcomes these difficulties. The boundary misorientations are treated as a statistical ensemble which is evolved toward the desired BMD using a Monte Carlo method. The application of this algorithm to a number complex arbitrary BMDs shows that the approach is effective for both conserved and non-conserved textures. The algorithm is successfully used to create the BMDs observed in deformation microstructure containing both incidental dislocation boundaries (IDBs) and geometrically necessary boundaries (GNBs).
Polymer-Based Mesh as Supports for Multi-layered 3D Cell Culture and Assays
Simon, Karen A.; Park, Kyeng Min; Mosadegh, Bobak; Subramaniam, Anand Bala; Mazzeo, Aaron; Ngo, Phil M.; Whitesides, George M.
2013-01-01
Three-dimensional (3D) culture systems can mimic certain aspects of the cellular microenvironment found in vivo, but generation, analysis and imaging of current model systems for 3D cellular constructs and tissues remain challenging. This work demonstrates a 3D culture system – Cells-in-Gels-in-Mesh (CiGiM) – that uses stacked sheets of polymer-based mesh to support cells embedded in gels to form tissue-like constructs; the stacked sheets can be disassembled by peeling the sheets apart to analyze cultured cells—layer-by-layer—within the construct. The mesh sheets leave openings large enough for light to pass through with minimal scattering, and thus allowing multiple options for analysis—(i) using straightforward analysis by optical light microscopy, (ii) by high-resolution analysis with fluorescence microscopy, or (iii) with a fluorescence gel scanner. The sheets can be patterned into separate zones with paraffin film-based decals, in order to conduct multiple experiments in parallel; the paraffin-based decal films also block lateral diffusion of oxygen effectively. CiGiM simplifies the generation and analysis of 3D culture without compromising throughput, and quality of the data collected: it is especially useful in experiments that require control of oxygen levels, and isolation of adjacent wells in a multi-zone format. PMID:24095253
Boundary layer flow visualization for flight testing
NASA Technical Reports Server (NTRS)
Obara, Clifford J.
1986-01-01
Flow visualization is used extensively in flight testing to determine aerodynamic characteristics such as surface flow direction and boundary layer state. Several visualization techniques are available to the aerodynamicist. Two of the most popular are oil flows and sublimating chemicals. Oil is used to visualize boundary layer transition, shock wave location, regions of separated flow, and surface flow direction. Boundary layer transition can also be visualized with sublimating chemicals. A summary of these two techniques is discussed, and the use of sublimating chemicals is examined in some detail. The different modes of boundary layer transition are characterized by different patterns in the sublimating chemical coating. The discussion includes interpretation of these chemical patterns and the temperature and velocity operating limitations of the chemical substances. Information for selection of appropriate chemicals for a desired set of flight conditions is provided.
Dynamic Acoustic Detection of Boundary Layer transition
NASA Technical Reports Server (NTRS)
Grohs, Jonathan R.
1995-01-01
The wind tunnel investigation into the acoustic nature of boundary layer transition using miniature microphones. This research is the groundwork for entry into the National Transonic Facility (NTF) at the NASA Langley Research Center (LaRC). Due to the extreme environmental conditions of NTF testing, low temperatures and high pressures, traditional boundary layer detection methods are not available. The emphasis of this project and further studies is acoustical sampling of a typical boundary layer and environmental durability of the miniature microphones. The research was conducted with the 14 by 22 Foot Subsonic Tunnel, concurrent with another wind tunnel test. Using the resources of LaRC, a full inquiry into the feasibility of using Knowles Electronics, Inc. EM-3086 microphones to detect the surface boundary layer, under differing conditions, was completed. This report shall discuss the difficulties encountered, product performance and observations, and future research adaptability of this method.
Boundary-layer control for drag reduction
NASA Technical Reports Server (NTRS)
Harvey, William D.
1988-01-01
Although the number of possible applications of boundary-layer control is large, a discussion is given only of those that have received the most attention recently at NASA Langley Research Center to improve airfoil drag characteristics. This research concerns stabilizing the laminar boundary layer through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (laminar flow control, LFC) either through discrete slots or a perforated surface. At low Reynolds numbers, a combination of shaping and forced transition has been used to achieve the desired run of laminar flow and control of laminar separation. In the design of both natural laminar flow and laminar flow control airfoils and wings, boundary layer stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.
NASA Astrophysics Data System (ADS)
Honda, M.; Satake, S.; Suzuki, Y.; Yoshida, M.; Hayashi, N.; Kamiya, K.; Matsuyama, A.; Shinohara, K.; Matsunaga, G.; Nakata, M.; Ide, S.; Urano, H.
2015-07-01
The integrated simulation framework for toroidal momentum transport is developed, which self-consistently calculates the neoclassical toroidal viscosity (NTV), the radial electric field {{E}r} and the resultant toroidal rotation {{V}φ} together with the scrape-off-layer (SOL) physics-based boundary model. The coupling of three codes, the 1.5D transport code TOPICS, the three-dimensional (3D) equilibrium code VMEC and the 3D δ f drift-kinetic equation solver FORTEC-3D, makes it possible to calculate the NTV due to the non-axisymmetric perturbed magnetic field caused by toroidal field coils. Analyses reveal that the NTV significantly influences {{V}φ} in JT-60U and {{E}r} holds the key to determine the NTV profile. The sensitivity of the {{V}φ} profile to the boundary rotation necessitates a boundary condition modelling for toroidal momentum. Owing to the high-resolution measurement system in JT-60U, the {{E}r} gradient is found to be virtually zero at the separatrix regardless of toroidal rotation velocities. Focusing on {{E}r} , the boundary model of toroidal momentum is developed in conjunction with the SOL/divertor plasma code D5PM. This modelling realizes self-consistent predictive simulations for operation scenario development in ITER.
Boundary-layer stability and airfoil design
NASA Technical Reports Server (NTRS)
Viken, Jeffrey K.
1986-01-01
Several different natural laminar flow (NLF) airfoils have been analyzed for stability of the laminar boundary layer using linear stability codes. The NLF airfoils analyzed come from three different design conditions: incompressible; compressible with no sweep; and compressible with sweep. Some of the design problems are discussed, concentrating on those problems associated with keeping the boundary layer laminar. Also, there is a discussion on how a linear stability analysis was effectively used to improve the design for some of the airfoils.
3D Printing of Human Tissue Mimics via Layer-by-Layer Assembly of Polymer/Hydrogel Biopapers
NASA Astrophysics Data System (ADS)
Ringeisen, Bradley
2015-03-01
The foundations of tissue engineering were built on two fundamental areas of research: cells and scaffolds. Multipotent cells and their derivatives are traditionally randomly seeded into sophisticated polymer or hydrogel scaffolds, ultimately with the goal of forming a tissue-like material through cell differentiation and cell-material interactions. One problem with this approach is that no matter how complex or biomimetic the scaffold is, the cells are still homogeneously distributed throughout this three dimensional (3D) material. Natural tissue is inherently heterogeneous on both a microscopic and macroscopic level. It also contains different types of cells in close proximity, extracellular matrix, voids, and a complex vascularized network. Recently developed 3D cell and organ printers may be able to enhance traditional tissue engineering experiments by building scaffolds layer-by-layer that are crafted to mimic the microscopic and macroscopic structure of natural tissue or organs. Over the past decade, my laboratory has developed a capillary-free, live cell printer termed biological laser printing, or BioLP. We find that printed cells do not express heat shock protein and retain >99% viability. Printed cells also incur no DNA strand fracture and preserve their ability to differentiate. Recent work has used a layer-by-layer approach, stacking sheets of hybrid polymer/hydrogel biopapers in conjunction with live cell printing to create 3D tissue structures. Our specific work is now focused on the blood-brain-barrier and air-lung interface and will be described during the presentation.
NASA Astrophysics Data System (ADS)
Wang, Jianwei; Zhang, Yong
2016-04-01
When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side.
Wang, Jianwei; Zhang, Yong
2016-01-01
When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side. PMID:27090430
Wang, Jianwei; Zhang, Yong
2016-01-01
When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III-V, and II-VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain-low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side. PMID:27090430
NASA Astrophysics Data System (ADS)
Li, Xiaomin; Zai, Jiantao; Liu, Yuanyuan; He, Xiaobo; Xiang, Shijie; Ma, Zifeng; Qian, Xuefeng
2016-09-01
LDHs in atomic thickness (mono-/bi-layers) usually exhibit novel physicochemical properties, especially in surface-dependent energy storage and catalysis areas. However, the thickness of the commonly reported 2D LDHs is in nanoscale and the bottom-up synthesis of atomically thin LDHs is rarely reported. Herein, high-quality atomically thin layered NiFe-LDHs assembled 3D microspheres were synthesized via a rational designed reaction system, where the formation of atomically thin building blocks was controlled by the synergetic effects of released carbonate anions and butanol. Furthermore, the complexant and solvents played important effects on the process of coprecipitation and the assembling of LDHs. Due to the nature of atomically thin LDHs nanosheets and unique 3D hierarchical structures, the obtained microspheres exhibited excellent electrocatalytic oxygen evolution reaction (OER) activity in alkaline medium with an onset overpotential (0.435 V, which is lower than that of common LDHs) and good durability. The as-prepared 3D NiFe-LDHs microspheres were also firstly used as supercapacitor materials and displayed a high specific capacitance of 1061 F g-1 at the current density of 1 A g-1.
3D Simulation of the Entire Process of Earthquake Generation at Subduction-Zone Plate Boundaries
NASA Astrophysics Data System (ADS)
Matsu'Ura, M.; Hashimoto, C.; Fukuyama, E.
2003-12-01
In general, the entire process of earthquake generation consists of tectonic loading due to relative plate motion, quasi-static rupture nucleation, dynamic rupture propagation and stop, and restoration of fault strength. This process can be completely described by a coupled nonlinear system, which consists of an elastic/viscoelastic slip-response function that relates fault slip to shear stress change and a fault constitutive law that prescribes change in shear strength with fault slip and contact time. The shear stress and the shear strength are related with each other through boundary conditions on the fault. The driving force of this system is observed relative plate motion. The system to describe the earthquake generation cycle is conceptually quite simple. The complexity in practical modelling mainly comes from complexity in structure of the real earth. As a product of Crustal Activity Modelling Program (CAMP), which is one of the three main programs composing the Solid Earth Simulator project (1998-2003) promoted by MEXT, we have completed a physics-based predictive simulation model for the entire process of earthquake generation cycles in and around Japan, where the four plates of Pacific, North American, Philippine Sea and Eurasian are interacting with each other in a very complicated way. The total simulation system consists of a crust-mantle structure model, a tectonic loading model and a dynamic rupture model. First, we constructed a realistic 3D standard model of plate interfaces in and around Japan by applying an inversion technique to ISC hypocenter distribution data, and computed viscoelastic slip-response functions for this structure model. Second, we introduced the slip- and time-dependent fault constitutive law with an inherent strength-restoration mechanism as a basic equation governing the entire process of earthquake generation. Third, combining all these elements, we developed a simulation model for quasi-static stress accumulation due to
NASA Astrophysics Data System (ADS)
Guerfi, Y.; Doucet, J. B.; Larrieu, G.
2015-10-01
Three-dimensional (3D) nanostructures are emerging as promising building blocks for a large spectrum of applications. One critical issue in integration regards mastering the thin, flat, and chemically stable insulating layer that must be implemented on the nanostructure network in order to build striking nano-architectures. In this letter, we report an innovative method for nanoscale planarization on 3D nanostructures by using hydrogen silesquioxane as a spin-on-glass (SOG) dielectric material. To decouple the thickness of the final layer from the height of the nanostructure, we propose to embed the nanowire network in the insulator layer by exploiting the planarizing properties of the SOG approach. To achieve the desired dielectric thickness, the structure is chemically etched back with a highly diluted solution to control the etch rate precisely. The roughness of the top surface was less than 2 nm. There were no surface defects and the planarity was excellent, even in the vicinity of the nanowires. This newly developed process was used to realize a multilevel stack architecture with sub-deca-nanometer-range layer thickness.
NASA Astrophysics Data System (ADS)
Conti, Caroline; Nunes, Paulo; Ducla Soares, Luís.
2013-09-01
Holoscopic imaging, also known as integral imaging, has been recently attracting the attention of the research community, as a promising glassless 3D technology due to its ability to create a more realistic depth illusion than the current stereoscopic or multiview solutions. However, in order to gradually introduce this technology into the consumer market and to efficiently deliver 3D holoscopic content to end-users, backward compatibility with legacy displays is essential. Consequently, to enable 3D holoscopic content to be delivered and presented on legacy displays, a display scalable 3D holoscopic coding approach is required. Hence, this paper presents a display scalable architecture for 3D holoscopic video coding with a three-layer approach, where each layer represents a different level of display scalability: Layer 0 - a single 2D view; Layer 1 - 3D stereo or multiview; and Layer 2 - the full 3D holoscopic content. In this context, a prediction method is proposed, which combines inter-layer prediction, aiming to exploit the existing redundancy between the multiview and the 3D holoscopic layers, with self-similarity compensated prediction (previously proposed by the authors for non-scalable 3D holoscopic video coding), aiming to exploit the spatial redundancy inherent to the 3D holoscopic enhancement layer. Experimental results show that the proposed combined prediction can improve significantly the rate-distortion performance of scalable 3D holoscopic video coding with respect to the authors' previously proposed solutions, where only inter-layer or only self-similarity prediction is used.
Free-Boundary 3D Equilibria and Resistive Wall Instabilities with Extended-MHD
NASA Astrophysics Data System (ADS)
Ferraro, N. M.
2015-11-01
The interaction of the plasma with external currents, either imposed or induced, is a critical element of a wide range of important tokamak phenomena, including resistive wall mode (RWM) stability and feedback control, island penetration and locking, and disruptions. A model of these currents may be included within the domain of extended-MHD codes in a way that preserves the self-consistency, scalability, and implicitness of their numerical methods. Such a model of the resistive wall and non-axisymmetric coils is demonstrated using the M3D-C1 code for a variety of applications, including RWMs, perturbed non-axisymmetric equilibria, and a vertical displacement event (VDE) disruption. The calculated free-boundary equilibria, which include Spitzer resistivity, rotation, and two-fluid effects, are compared to external magnetic and internal thermal measurements for several DIII-D discharges. In calculations of the perturbed equilibria in ELM suppressed discharges, the tearing response at the top of the pedestal is found to correlate with the onset of ELM suppression. Nonlinear VDE calculations, initialized using a vertically unstable DIII-D equilibrium, resolve in both space and time the currents induced in the wall and on the plasma surface, and also the currents flowing between the plasma and the wall. The relative magnitude of these contributions and the total impulse to the wall depend on the resistive wall time, although the maximum axisymmetric force on the wall over the course of the VDE is found to be essentially independent of the wall conductivity. This research was supported by US DOE contracts DE-FG02-95ER54309, DE-FC02-04ER54698 and DE-AC52-07NA27344.
Dependence of Boundary Layer Mixing On Lateral Boundary Conditions
NASA Astrophysics Data System (ADS)
Straub, D.
Ocean circulation models often show strong mixing in association with lateral bound- ary layers. Such mixing is generally considered to be artifactual rather than real. Fur- thermore, the severity of the problem is boundary condition dependent. For example, an inconsistency between geostrophy and insulating boundary conditions on tempera- ture and salinity cause many modelers to opt for the no slip, rather than slip boundary condtion on the tangential component of momentum. As modellers increasingly move into the eddy revealing regime, biharmonic, rather than harmonic dissipative operators are likely to become more common. Biharmonic operators, however, require specifi- cation of additional boundary conditions. For example, there are several `natural ex- tensions' to each of the slip and no slip conditions. Here, these various possiblities are considered in the context of a simple model. Particular attention is payed to how mixing (and the associated overturning cell) is affected by the choice of boundary condition.
Clusters, molecular layers, and 3D crystals of water on Ni(111)
Thürmer, Konrad; Nie, Shu; Bartelt, Norman C.; Feibelman, Peter J.
2014-11-14
We examined the growth and stability of ice layers on Ni(111) up to ∼7 molecular layers (ML) thick using scanning tunneling microscopy. At low coverage, films were comprised of ∼1 nm wide two-dimensional (2D) clusters. Only above ∼0.5 ML did patches of continuous 2D layers emerge, coexisting with the clusters until the first ML was complete. The structure of the continuous layer is clearly different from that of the 2D clusters. Subsequently, a second molecular layer grew on top of the first. 3D crystallites started to form only after this 2nd ML was complete. 2D clusters re-appeared when thicker films were partially evaporated, implying that these clusters represent the equilibrium configuration at low coverage. Binding energies and image simulations computed with density functional theory suggest that the 2D clusters are partially dissociated and surrounded by H adatoms. The complete 2D layer contains only intact water molecules because of the lack of favorable binding sites for H atoms. We propose molecular structures for the 2D layer that are composed of the same pentagon-heptagon binding motif and water density observed on Pt(111). The similarity of the water structures on Pt and Ni suggests a general prescription for generating low-energy configurations on close-packed metal substrates.
NASA Technical Reports Server (NTRS)
Omori, S.; Krebsbach, A.; Gross, K. W.
1972-01-01
Modifications of the turbulent boundary layer (TBL) computer program refer to a more accurate representation of boundary layer edge conditions, internal calculation of the Prandtl number, a changed friction coefficient relationship, and computation of the performance degradation. Important input parameters of the modified TBL program such as wall temperature distribution, Prandtl number, Stanton number, and velocity profile exponent were changed and the individual effects on significant boundary layer parameters, heat transfer, and performance degradation are described.
Multi-layer 3D imaging using a few viewpoint images and depth map
NASA Astrophysics Data System (ADS)
Suginohara, Hidetsugu; Sakamoto, Hirotaka; Yamanaka, Satoshi; Suyama, Shiro; Yamamoto, Hirotsugu
2015-03-01
In this paper, we propose a new method that makes multi-layer images from a few viewpoint images to display a 3D image by the autostereoscopic display that has multiple display screens in the depth direction. We iterate simple "Shift and Subtraction" processes to make each layer image alternately. The image made in accordance with depth map like a volume slicing by gradations is used as the initial solution of iteration process. Through the experiments using the prototype stacked two LCDs, we confirmed that it was enough to make multi-layer images from three viewpoint images to display a 3D image. Limiting the number of viewpoint images, the viewing area that allows stereoscopic view becomes narrow. To broaden the viewing area, we track the head motion of the viewer and update screen images in real time so that the viewer can maintain correct stereoscopic view within +/- 20 degrees area. In addition, we render pseudo multiple viewpoint images using depth map, then we can generate motion parallax at the same time.
NASA Astrophysics Data System (ADS)
Wang, Xinlong; Qin, Chao; Wang, Enbo; Xu, Lin
2005-02-01
A novel metal-organic coordination polymer, [Cd(HPT) 2(4,4'-bpy)] n (PT=phthalate), has been hydrothermally synthesized and characterized by elemental analysis, IR, TG and single crystal X-ray diffraction. Colorless crystals crystallized in the tetragonal system, space group I4 122, a=8.294(5), b=8.294(5), c=33.7535(17) Å, V=2321.8(18) Å 3, Z=4 and R=0.0207. The structure of the compound exhibiting a homochiral 3D covalent framework based on achiral bridging ligands has been constructed by an alternating assembly of vertical chiral layers consisting of homochiral helices.
Lear jet boundary layer/shear layer laser propagation experiments
NASA Technical Reports Server (NTRS)
Gilbert, K.
1980-01-01
Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.
Stereoscopic PIV measurement of boundary layer affected by DBD actuator
NASA Astrophysics Data System (ADS)
Procházka, Pavel; Uruba, Václav
2016-03-01
The effect of ionic wind generated by plasma actuator on developed boundary layer inside a narrow channel was investigated recently. Since the main investigated plane was parallel to the channel axis, the description of flow field was not evaluated credibly. This paper is dealing with cross-section planes downstream the actuator measured via 3D time-resolved PIV. The actuator position is in spanwise or in streamwise orientation so that ionic wind is blown in the same direction as the main flow or in opposite direction or perpendicularly. The interaction between boundary layer and ionic wind is evaluated for three different velocities of main flow and several parameters of plasma actuation (steady and unsteady regime, frequency etc.). Statistical properties of the flow are shown as well as dynamical behaviour of arising longitudinal vortices are discussed via phase-locked measurement and decomposition method.
Excitation of Crossflow Instabilities in a Swept Wing Boundary Layer
NASA Technical Reports Server (NTRS)
Carpenter, Mark H.; Choudhari, Meelan; Li, Fei; Streett, Craig L.; Chang, Chau-Lyan
2010-01-01
The problem of crossflow receptivity is considered in the context of a canonical 3D boundary layer (viz., the swept Hiemenz boundary layer) and a swept airfoil used recently in the SWIFT flight experiment performed at Texas A&M University. First, Hiemenz flow is used to analyze localized receptivity due to a spanwise periodic array of small amplitude roughness elements, with the goal of quantifying the effects of array size and location. Excitation of crossflow modes via nonlocalized but deterministic distribution of surface nonuniformity is also considered and contrasted with roughness induced acoustic excitation of Tollmien-Schlichting waves. Finally, roughness measurements on the SWIFT model are used to model the effects of random, spatially distributed roughness of sufficiently small amplitude with the eventual goal of enabling predictions of initial crossflow disturbance amplitudes as functions of surface roughness parameters.
High enthalpy hypersonic boundary layer flow
NASA Technical Reports Server (NTRS)
Yanow, G.
1972-01-01
A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
2008-01-01
An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.
Boundary Layer Cloudiness Parameterizations Using ARM Observations
Bruce Albrecht
2004-09-15
This study used DOE ARM data and facilities to: (1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, (2) develop a scientific basis for understanding the processes responsible for the formation of boundary layer clouds using ARM observations in conjunction with simple parametric models and LES, and (3) evaluate cumulus cloud characteristics retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of boundary layer clouds and precipitation to: (1) develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer cloud studies, (2) evaluate the capability and limitations of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low- signal-to-noise conditions associated with weak no n-precipitating clouds, (3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of boundary layer clouds, and (4) retrieve updraft and downdraft structures under precipitating conditions.
The Kinematics of Turbulent Boundary Layer Structure
NASA Technical Reports Server (NTRS)
Robinson, Stephen Kern
1991-01-01
The long history of research into the internal structure of turbulent boundary layers has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of boundary layer structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.
Self-aligned metallization on organic semiconductor through 3D dual-layer thermal nanoimprint
NASA Astrophysics Data System (ADS)
Jung, Y.; Cheng, X.
2014-09-01
High-resolution patterning of metal structures on organic semiconductors is important to the realization of high-performance organic transistors for organic integrated circuit applications. The traditional shadow mask technique has a limited resolution, precluding sub-micron metal structures on organic semiconductors. Thus organic transistors cannot benefit from scaling into the deep sub-micron region to improve their dc and ac performances. In this work, we report an efficient multiple-level metallization on poly (3-hexylthiophene) (P3HT) with a deep sub-micron lateral gap. By using a 3D nanoimprint mold in a dual-layer thermal nanoimprint process, we achieved self-aligned two-level metallization on P3HT. The 3D dual-layer thermal nanoimprint enables the first metal patterns to have suspending side-wings that can clearly define a distance from the second metal patterns. Isotropic and anisotropic side-wing structures can be fabricated through two different schemes. The process based on isotropic side-wings achieves a lateral-gap in the order of 100 nm (scheme 1). A gap of 60 nm can be achieved from the process with anisotropic side-wings (scheme 2). Because of the capability of nanoscale metal patterning on organic semiconductors with high overlay accuracy, this self-aligned metallization technique can be utilized to fabricate high-performance organic metal semiconductor field-effect transistor.
Microporous polymeric 3D scaffolds templated by the layer-by-layer self-assembly.
Paulraj, Thomas; Feoktistova, Natalia; Velk, Natalia; Uhlig, Katja; Duschl, Claus; Volodkin, Dmitry
2014-08-01
Polymeric scaffolds serve as valuable supports for biological cells since they offer essential features for guiding cellular organization and tissue development. The main challenges for scaffold fabrication are i) to tune an internal structure and ii) to load bio-molecules such as growth factors and control their local concentration and distribution. Here, a new approach for the design of hollow polymeric scaffolds using porous CaCO3 particles (cores) as templates is presented. The cores packed into a microfluidic channel are coated with polymers employing the layer-by-layer (LbL) technique. Subsequent core elimination at mild conditions results in formation of the scaffold composed of interconnected hollow polymer microspheres. The size of the cores determines the feature dimensions and, as a consequence, governs cellular adhesion: for 3T3 fibroblasts an optimal microsphere size is 12 μm. By making use of the carrier properties of the porous CaCO3 cores, the microspheres are loaded with BSA as a model protein. The scaffolds developed here may also be well suited for the localized release of bio-molecules using external triggers such as IR-light. PMID:25042776
NASA Astrophysics Data System (ADS)
Bayona, V.; Flyer, N.; Lucas, G. M.; Baumgaertner, A. J. G.
2015-04-01
A numerical model based on Radial Basis Function-generated Finite Differences (RBF-FD) is developed for simulating the Global Electric Circuit (GEC) within the Earth's atmosphere, represented by a 3-D variable coefficient linear elliptic PDE in a spherically-shaped volume with the lower boundary being the Earth's topography and the upper boundary a sphere at 60 km. To our knowledge, this is (1) the first numerical model of the GEC to combine the Earth's topography with directly approximating the differential operators in 3-D space, and related to this (2) the first RBF-FD method to use irregular 3-D stencils for discretization to handle the topography. It benefits from the mesh-free nature of RBF-FD, which is especially suitable for modeling high-dimensional problems with irregular boundaries. The RBF-FD elliptic solver proposed here makes no limiting assumptions on the spatial variability of the coefficients in the PDE (i.e. the conductivity profile), the right hand side forcing term of the PDE (i.e. distribution of current sources) or the geometry of the lower boundary.
Numerical simulation of supersonic boundary layer transition
NASA Technical Reports Server (NTRS)
Guo, Y.; Adams, N. A.; Sandham, N. D.; Kleiser, L.
1994-01-01
The present contribution reviews some of the recent progress obtained at our group in the direct numerical simulation (DNS) of compressible boundary layer transition. Elements of the different simulation approaches and numerical techniques employed are surveyed. Temporal and spatial simulations, as well as comparisons with results obtained from Parabolized Stability Equations, are discussed. DNS results are given for flat plate boundary layers in the Mach number range 1.6 to 4.5. A temporal DNS at Mach 4.5 has been continued through breakdown all the way to the turbulent stage. In addition results obtained with a recently developed extended temporal DNS approach are presented, which takes into account some nonparallel effects of a growing boundary layer. Results from this approach are quite close to those of spatial DNS, while preserving the efficiency of the temporal DNS.
NASA Technical Reports Server (NTRS)
Mack, L. M.
1967-01-01
The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.
Aerosol buffering of marine boundary layer cloudiness
NASA Astrophysics Data System (ADS)
Kazil, J.; Feingold, G.; Wang, H.
2010-12-01
The role of aerosol particles in maintaining a cloudy boundary layer in the remote marine environment is explored. It has previously been shown that precipitation can result in the transition from a closed- to open-cellular state but that the boundary layer cannot maintain this open-cell state without a resupply of particles. Potential sources include wind-driven production of sea salt particles from the ocean, nucleation from the gas phase, and entrainment from the free troposphere. Here we investigate with model simulations how the interplay of cloud properties, aerosol production, and boundary layer dynamics results in aerosol sources acting as a buffer against processes that destabilize cloudiness and the dynamic state of the marine boundary layer. For example, at nighttime, cloud liquid water increases in the absence of solar heating, resulting in increased precipitation, stronger cloud top cooling, accelerated boundary layer turbulence, and faster surface wind speeds. Faster surface wind speeds drive an enhanced flux of sea salt aerosol, at a time when aerosol particles are scavenged more readily by enhanced precipitation. In contrast, absorption of solar radiation during daytime reduces cloud water, decelerates boundary layer turbulence, reduces surface wind speeds, and therefore slows surface emissions. This is compensated by nucleation of small aerosol particles from the gas phase in response to the nigh complete removal of cloud condensation nuclei in precipitating open cell walls. These newly formed particles need to grow to larger sizes before they can serve as cloud condensation nuclei (CCN), but will likely contribute to the CCN population during the nighttime and, together with ocean emissions, buffer the system against precipitation removal.
Stability of an oscillating boundary layer
NASA Technical Reports Server (NTRS)
Levchenko, V. Y.; Solovyev, A. S.
1985-01-01
Levchenko and Solov'ev (1972, 1974) have developed a stability theory for space periodic flows, assuming that the Floquet theory is applicable to partial differential equations. In the present paper, this approach is extended to unsteady periodic flows. A complete unsteady formulation of the stability problem is obtained, and the stability characteristics over an oscillating period are determined from the solution of the problem. Calculations carried out for an oscillating incompressible boundary layer on a plate showed that the boundary layer flow may be regarded as a locally parallel flow.
Stability of an oscillating boundary layer
NASA Astrophysics Data System (ADS)
Levchenko, V. Y.; Solovyev, A. S.
1985-03-01
Levchenko and Solov'ev (1972, 1974) have developed a stability theory for space periodic flows, assuming that the Floquet theory is applicable to partial differential equations. In the present paper, this approach is extended to unsteady periodic flows. A complete unsteady formulation of the stability problem is obtained, and the stability characteristics over an oscillating period are determined from the solution of the problem. Calculations carried out for an oscillating incompressible boundary layer on a plate showed that the boundary layer flow may be regarded as a locally parallel flow.
Boundary-Layer Code For Supersonic Combustion
NASA Technical Reports Server (NTRS)
Pinckney, S. Z.; Walton, J. T.
1994-01-01
HUD is integral computer code based on Spaulding-Chi method for predicting development of boundary layers in laminar, transitional, and turbulent regions of flows on two-dimensional or axisymmetric bodies. Approximates nonequilibrium velocity profiles as well as local surface friction in presence of pressure gradient. Predicts transfer of heat in turbulent boundary layer in presence of high axial presure gradient. Provides for pressure gradients both normal and lateral to surfaces. Also used to estimate requirements for cooling scramjet engines. Because of this capability, HUD program incorporated into several scramjet-cycle-performance-analysis codes, including SCRAM (ARC-12338) and SRGULL (LEW-15093). Written in FORTRAN 77.
Hairpin vortices in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Eitel-Amor, G.; Örlü, R.; Schlatter, P.; Flores, O.
2015-02-01
The present work presents a number of parallel and spatially developing simulations of boundary layers to address the question of whether hairpin vortices are a dominant feature of near-wall turbulence, and which role they play during transition. In the first part, the parent-offspring regeneration mechanism is investigated in parallel (temporal) simulations of a single hairpin vortex introduced in a mean shear flow corresponding to either turbulent channels or boundary layers (Reτ ≲ 590). The effect of a turbulent background superimposed on the mean flow is considered by using an eddy viscosity computed from resolved simulations. Tracking the vortical structure downstream, it is found that secondary hairpins are only created shortly after initialization, with all rotational structures decaying for later times. For hairpins in a clean (laminar) environment, the decay is relatively slow, while hairpins in weak turbulent environments (10% of νt) dissipate after a couple of eddy turnover times. In the second part, the role of hairpin vortices in laminar-turbulent transition is studied using simulations of spatial boundary layers tripped by hairpin vortices. These vortices are generated by means of specific volumetric forces representing an ejection event, creating a synthetic turbulent boundary layer initially dominated by hairpin-like vortices. These hairpins are advected towards the wake region of the boundary layer, while a sinusoidal instability of the streaks near the wall results in rapid development of a turbulent boundary layer. For Reθ > 400, the boundary layer is fully developed, with no evidence of hairpin vortices reaching into the wall region. The results from both the parallel and spatial simulations strongly suggest that the regeneration process is rather short-lived and may not sustain once a turbulent background is developed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former direct numerical
Boundary layer halogens in coastal Antarctica.
Saiz-Lopez, Alfonso; Mahajan, Anoop S; Salmon, Rhian A; Bauguitte, Stephane J-B; Jones, Anna E; Roscoe, Howard K; Plane, John M C
2007-07-20
Halogens influence the oxidizing capacity of Earth's troposphere, and iodine oxides form ultrafine aerosols, which may have an impact on climate. We report year-round measurements of boundary layer iodine oxide and bromine oxide at the near-coastal site of Halley Station, Antarctica. Surprisingly, both species are present throughout the sunlit period and exhibit similar seasonal cycles and concentrations. The springtime peak of iodine oxide (20 parts per trillion) is the highest concentration recorded anywhere in the atmosphere. These levels of halogens cause substantial ozone depletion, as well as the rapid oxidation of dimethyl sulfide and mercury in the Antarctic boundary layer. PMID:17641195
Physical properties and microstructures of nanocrystals reinforced ice laser 3D print layer
NASA Astrophysics Data System (ADS)
Li, Jia-Ning; Liu, Ke-Gao; Gong, Shui-Li; Zhang, Yuan-Bin; Liu, Peng
2015-02-01
Rapid prototyping based on laser alloying by the pre-placed mixed powders has been used to produce the nanocrystals reinforced three-dimensional layer in this study. Such a layer was fabricated on a TC17 titanium alloy by laser rapid prototyping (LRP) of the Co-Sb-TiB2 mixed powders in ice. Scanning electron microscope (SEM) and high resolution transmission electron microscopy (HRTEM) test results indicated that the ice addition was able to decrease the maximum temperature of molten pool during the LRP process, favoring the formation of nanocrystals; growth of such nanocrystals was retarded by the surrounded amorphous in a certain extent, favoring the formations of ultrafine nanoparticles (UN), and the twin crystals and the high-angle grain boundaries were also observed; differential thermal analysis (DTA) test was used to explain the physical properties and formation mechanism of amorphous-nanocrystals, and also the relationship between the amorphous and nanocrystalline phases in such a LRP layer.
Boundary-layer theory for blast waves
NASA Technical Reports Server (NTRS)
Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.
1975-01-01
It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.
Lee, Yejin; Hong, Kyunghi; Hong, Sung-Ae
2007-05-01
Garment fit and resultant air volume is a crucial factor in thermal insulation, and yet, it has been difficult to quantify the air volume of clothing microclimate and relate it to the thermal insulation value just using the information on the size of clothing pattern without actual 3D volume measurement in wear condition. As earlier methods for the computation of air volume in clothing microclimate, vacuum over suit and circumference model have been used. However, these methods have inevitable disadvantages in terms of cost or accuracy due to the limitations of measurement equipment. In this paper, the phase-shifting moiré topography was introduced as one of the 3D scanning tools to measure the air volume of clothing microclimate quantitatively. The purpose of this research is to adopt a non-contact image scanning technology, phase-shifting moiré topography, to ascertain relationship between air volume and insulation value of layered clothing systems in wear situations where the 2D fabric creates new conditions in 3D spaces. The insulation of vests over shirts as a layered clothing system was measured with a thermal manikin in the environmental condition of 20 degrees C, 65% RH and air velocity of 0.79 m/s. As the pattern size increased, the insulation of the clothing system was increased. But beyond a certain limit, the insulation started to decrease due to convection and ventilation, which is more apparent when only the vest was worn over the torso of manikin. The relationship between clothing air volume and insulation was difficult to predict with a single vest due to the extreme openings which induced active ventilation. But when the vest was worn over the shirt, the effects of thickness of the fabrics on insulation were less pronounced compared with that of air volume. In conclusion, phase-shifting moiré topography was one of the efficient and accurate ways of quantifying air volume and its distribution across the clothing microclimate. It is also noted
Calculation methods for compressible turbulent boundary layers, 1976
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.
1977-01-01
Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.
Advanced quadratures and periodic boundary conditions in parallel 3D S{sub n} transport
Manalo, K.; Yi, C.; Huang, M.; Sjoden, G.
2013-07-01
Significant updates in numerical quadratures have warranted investigation with 3D Sn discrete ordinates transport. We show new applications of quadrature departing from level symmetric (S{sub 2}o). investigating 3 recently developed quadratures: Even-Odd (EO), Linear-Discontinuous Finite Element - Surface Area (LDFE-SA), and the non-symmetric Icosahedral Quadrature (IC). We discuss implementation changes to 3D Sn codes (applied to Hybrid MOC-Sn TITAN and 3D parallel PENTRAN) that can be performed to accommodate Icosahedral Quadrature, as this quadrature is not 90-degree rotation invariant. In particular, as demonstrated using PENTRAN, the properties of Icosahedral Quadrature are suitable for trivial application using periodic BCs versus that of reflective BCs. In addition to implementing periodic BCs for 3D Sn PENTRAN, we implemented a technique termed 'angular re-sweep' which properly conditions periodic BCs for outer eigenvalue iterative loop convergence. As demonstrated by two simple transport problems (3-group fixed source and 3-group reflected/periodic eigenvalue pin cell), we remark that all of the quadratures we investigated are generally superior to level symmetric quadrature, with Icosahedral Quadrature performing the most efficiently for problems tested. (authors)
Hodge, Adam C; Fenster, Aaron; Downey, Dónal B; Ladak, Hanif M
2006-12-01
Boundary outlining, or segmentation, of the prostate is an important task in diagnosis and treatment planning for prostate cancer. This paper describes an algorithm based on two-dimensional (2D) active shape models (ASM) for semi-automatic segmentation of the prostate boundary from ultrasound images. Optimisation of the 2D ASM for prostatic ultrasound was done first by examining ASM construction and image search parameters. Extension of the algorithm to three-dimensional (3D) segmentation was then done using rotational-based slicing. Evaluation of the 3D segmentation algorithm used distance- and volume-based error metrics to compare algorithm generated boundary outlines to gold standard (manually generated) boundary outlines. Minimum description length landmark placement for ASM construction, and specific values for constraints and image search were found to be optimal. Evaluation of the algorithm versus gold standard boundaries found an average mean absolute distance of 1.09+/-0.49 mm, an average percent absolute volume difference of 3.28+/-3.16%, and a 5x speed increase versus manual segmentation. PMID:16930764
Three-dimensional boundary layer flow with streamwise adverse pressure gradient
NASA Technical Reports Server (NTRS)
Driver, David M.; Johnston, James P.
1989-01-01
The present study examines the effects of a strong adverse pressure gradient on a 3D turbulent boundary layer in an axisymmetric spinning cylinder geometry. Velocity measurements made with a three-component laser Doppler velocimeter include all three mean flow components, all six Reynolds stress components, and all ten triple-product correlations. Total Reynolds shear stress diminishes as the flow becomes 3D. Lower levels of shear stress were found to persist under adverse pressure gradient conditions. This low stress level was observed to roughly correlate with the magnitude of the crossflow. Variations in the pressure gradient do not alter this correlation. It is inferred that a 3D boundary layer is more prone to separate than a 2D boundary layer.
2016-01-01
Objective. Our objective is to develop a computerized scheme for liver tumor segmentation in MR images. Materials and Methods. Our proposed scheme consists of four main stages. Firstly, the region of interest (ROI) image which contains the liver tumor region in the T1-weighted MR image series was extracted by using seed points. The noise in this ROI image was reduced and the boundaries were enhanced. A 3D fast marching algorithm was applied to generate the initial labeled regions which are considered as teacher regions. A single hidden layer feedforward neural network (SLFN), which was trained by a noniterative algorithm, was employed to classify the unlabeled voxels. Finally, the postprocessing stage was applied to extract and refine the liver tumor boundaries. The liver tumors determined by our scheme were compared with those manually traced by a radiologist, used as the “ground truth.” Results. The study was evaluated on two datasets of 25 tumors from 16 patients. The proposed scheme obtained the mean volumetric overlap error of 27.43% and the mean percentage volume error of 15.73%. The mean of the average surface distance, the root mean square surface distance, and the maximal surface distance were 0.58 mm, 1.20 mm, and 6.29 mm, respectively. PMID:27597960
Le, Trong-Ngoc; Bao, Pham The; Huynh, Hieu Trung
2016-01-01
Objective. Our objective is to develop a computerized scheme for liver tumor segmentation in MR images. Materials and Methods. Our proposed scheme consists of four main stages. Firstly, the region of interest (ROI) image which contains the liver tumor region in the T1-weighted MR image series was extracted by using seed points. The noise in this ROI image was reduced and the boundaries were enhanced. A 3D fast marching algorithm was applied to generate the initial labeled regions which are considered as teacher regions. A single hidden layer feedforward neural network (SLFN), which was trained by a noniterative algorithm, was employed to classify the unlabeled voxels. Finally, the postprocessing stage was applied to extract and refine the liver tumor boundaries. The liver tumors determined by our scheme were compared with those manually traced by a radiologist, used as the "ground truth." Results. The study was evaluated on two datasets of 25 tumors from 16 patients. The proposed scheme obtained the mean volumetric overlap error of 27.43% and the mean percentage volume error of 15.73%. The mean of the average surface distance, the root mean square surface distance, and the maximal surface distance were 0.58 mm, 1.20 mm, and 6.29 mm, respectively. PMID:27597960
Nonlinear Transient Growth and Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Paredes, Pedro; Choudhari, Meelan M.; Li, Fei
2016-01-01
Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the boundary layer flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed boundary layer without any streaks.
Flow unsteadiness effects on boundary layers
NASA Technical Reports Server (NTRS)
Murthy, Sreedhara V.
1989-01-01
The development of boundary layers at high subsonic speeds in the presence of either mass flux fluctuations or acoustic disturbances (the two most important parameters in the unsteadiness environment affecting the aerodynamics of a flight vehicle) was investigated. A high quality database for generating detailed information concerning free-stream flow unsteadiness effects on boundary layer growth and transition in high subsonic and transonic speeds is described. The database will be generated with a two-pronged approach: (1) from a detailed review of existing literature on research and wind tunnel calibration database, and (2) from detailed tests in the Boundary Layer Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). Special instrumentation, including hot wire anemometry, the buried wire gage technique, and laser velocimetry were used to obtain skin friction and turbulent shear stress data along the entire boundary layer for various free stream noise levels, turbulence content, and pressure gradients. This database will be useful for improving the correction methodology of applying wind tunnel test data to flight predictions and will be helpful for making improvements in turbulence modeling laws.
Boundary Layer Transition on X-43A
NASA Technical Reports Server (NTRS)
Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert
2008-01-01
The successful Mach 7 and 10 flights of the first fully integrated scramjet propulsion systems by the Hyper-X (X-43A) program have provided the means with which to verify the original design methodologies and assumptions. As part of Hyper-X s propulsion-airframe integration, the forebody was designed to include a spanwise array of vortex generators to promote boundary layer transition ahead of the engine. Turbulence at the inlet is thought to provide the most reliable engine design and allows direct scaling of flight results to groundbased data. Pre-flight estimations of boundary layer transition, for both Mach 7 and 10 flight conditions, suggested that forebody boundary layer trips were required to ensure fully turbulent conditions upstream of the inlet. This paper presents the results of an analysis of the thermocouple measurements used to infer the dynamics of the transition process during the trajectories for both flights, on both the lower surface (to assess trip performance) and the upper surface (to assess natural transition). The approach used in the analysis of the thermocouple data is outlined, along with a discussion of the calculated local flow properties that correspond to the transition events as identified in the flight data. The present analysis has confirmed that the boundary layer trips performed as expected for both flights, providing turbulent flow ahead of the inlet during critical portions of the trajectory, while the upper surface was laminar as predicted by the pre-flight analysis.
Orbiter Boundary Layer Transition Prediction Tool Enhancements
NASA Technical Reports Server (NTRS)
Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.
2010-01-01
Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The boundary layer transition criteria utilized within the tool were updated based on new local boundary layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.
Planetary Boundary Layer from AERI and MPL
Sawyer, Virginia
2014-02-13
The distribution and transport of aerosol emitted to the lower troposphere is governed by the height of the planetary boundary layer (PBL), which limits the dilution of pollutants and influences boundary-layer convection. Because radiative heating and cooling of the surface strongly affect the PBL top height, it follows diurnal and seasonal cycles and may vary by hundreds of meters over a 24-hour period. The cap the PBL imposes on low-level aerosol transport makes aerosol concentration an effective proxy for PBL height: the top of the PBL is marked by a rapid transition from polluted, well-mixed boundary-layer air to the cleaner, more stratified free troposphere. Micropulse lidar (MPL) can provide much higher temporal resolution than radiosonde and better vertical resolution than infrared spectrometer (AERI), but PBL heights from all three instruments at the ARM SGP site are compared to one another for validation. If there is agreement among them, the higher-resolution remote sensing-derived PBL heights can accurately fill in the gaps left by the low frequency of radiosonde launches, and thus improve model parameterizations and our understanding of boundary-layer processes.
Astrophysical Boundary Layers: A New Picture
NASA Astrophysics Data System (ADS)
Belyaev, Mikhail; Rafikov, Roman R.; Mclellan Stone, James
2016-04-01
Accretion is a ubiquitous process in astrophysics. In cases when the magnetic field is not too strong and a disk is formed, accretion can proceed through the mid plane all the way to the surface of the central compact object. Unless that compact object is a black hole, a boundary layer will be formed where the accretion disk touches its surfaces. The boundary layer is both dynamically and observationally significant as up to half of the accretion energy is dissipated there.Using a combination of analytical theory and computer simulations we show that angular momentum transport and accretion in the boundary layer is mediated by waves. This breaks with the standard astrophysical paradigm of an anomalous turbulent viscosity that drives accretion. However, wave-mediated angular momentum transport is a natural consequence of "sonic instability." The sonic instability, which we describe analytically and observe in our simulations, is a close cousin of the Papaloizou-Pringle instability. However, it is very vigorous in the boundary layer due to the immense radial velocity shear present at the equator.Our results are applicable to accreting neutron stars, white dwarfs, protostars, and protoplanets.
Boundary layer control device for duct silencers
NASA Technical Reports Server (NTRS)
Schmitz, Fredric H. (Inventor); Soderman, Paul T. (Inventor)
1993-01-01
A boundary layer control device includes a porous cover plate, an acoustic absorber disposed under the porous cover plate, and a porous flow resistive membrane interposed between the porous cover plate and the acoustic absorber. The porous flow resistive membrane has a flow resistance low enough to permit sound to enter the acoustic absorber and high enough to damp unsteady flow oscillations.
Tang, Yanwei; Zhao, Yan; Wang, Hongxia; Gao, Yuan; Liu, Xin; Wang, Xungai; Lin, Tong
2012-08-01
Bonded fibrous matrices have shown great potential in tissue engineering because of their unique 3D structures and pore characteristics. For some applications, bacterial infections must be taken into account, and antibacterial function is highly desired. In this study, an antibacterial polymer, polyhexamethylene biguanide (PHMB), was applied onto the fiber surface of a bonded poly(ε-caprolactone) (PCL) fibrous matrix with the objective to achieve both strong antibacterial effect and good cell compatibility. The coatings were prepared by using an electrostatic layer-by-layer (LbL) assembly technique, which allowed the control of PHMB loading and coating uniformity on the fiber surface. The PHMB coating provided antibacterial activities, but had no toxicity on mammalian cells. This bonded PCL fibrous matrix with electrostatically self-assembled PHMB may provide a new antiinfective tissue scaffold for various biomedical applications. PMID:22581705
INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT
Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...
Application of Arnoldi method to boundary layer instability
NASA Astrophysics Data System (ADS)
Zhang, Yong-Ming; Luo, Ji-Sheng
2015-12-01
The Arnoldi method is applied to boundary layer instability, and a finite difference method is employed to avoid the limit of the finite element method. This modus operandi is verified by three comparison cases, i.e., comparison with linear stability theory (LST) for two-dimensional (2D) disturbance on one-dimensional (1D) basic flow, comparison with LST for three-dimensional (3D) disturbance on 1D basic flow, and comparison with Floquet theory for 3D disturbance on 2D basic flow. Then it is applied to secondary instability analysis on the streaky boundary layer under spanwise-localized free-stream turbulence (FST). Three unstable modes are found, i.e., an inner mode at a high-speed center streak, a sinuous type outer mode at a low-speed center streak, and a sinuous type outer mode at low-speed side streaks. All these modes are much more unstable than Tollmien-Schlichting (TS) waves, implying the dominant contribution of secondary instability in bypass transition. The modes at strong center streak are more unstable than those at weak side streaks, so the center streak is ‘dangerous’ in secondary instability. Project supported by the National Natural Science Foundation of China (Grant Nos. 11202147, 11332007, 11172203, and 91216111) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120032120007).
3D Dynamics of Freshwater Lenses in the Near-Surface Layer of the Tropical Ocean
NASA Astrophysics Data System (ADS)
Soloviev, Alexander; Dean, Cayla
2015-04-01
Convective rains in the Intertropical Convergence Zone (ITCZ) produce lenses of freshened water on the ocean surface. These lenses are localized in space and typically involve both salinity and temperature anomalies. Due to significant density anomalies, strong pressure gradients develop, which result in lateral spreading of freshwater lenses in a form resembling gravity currents. Gravity currents inherently involve three-dimensional dynamics. As a type of organized structure, gravity currents in the upper layer of the ocean may also interact with, and be shaped by, the ambient oceanic environment and atmospheric conditions. Among the important factors are the background stratification, wind stress, wind/wave mixing and spatially coherent organized motions in the near-surface layer of the ocean. Under certain conditions, a resonant interaction between a propagating freshwater lens and internal waves in the underlying pycnocline (e.g., barrier layer) may develop, whereas interaction with wind stress may produce an asymmetry in the freshwater lens and associated mixing. These two types of interactions working in concert may explain the series of sharp frontal interfaces, which have been observed in association with freshwater lenses during TOGA COARE. In this work, we have conducted a series of numerical experiments using computational fluid dynamics tools. These numerical simulations were designed to elucidate the relationship between vertical mixing and horizontal advection of salinity under various environmental conditions and potential impact on the Aquarius and SMOS satellite image formation. Available near-surface data from field experiments served as a guidance for numerical simulations. The results of this study indicate that 3D dynamics of freshwater lenses are essential within a certain range of wind/wave conditions and the freshwater influx in the surface layer of the ocean.
Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers
NASA Technical Reports Server (NTRS)
Popham, Robert; Narayan, Ramesh
1995-01-01
We develop numerical models of accretions disks in cataclysmic variables (CVs), including and emphasizing the boundary layer region where the accretion disk meets the accreting white dwarf. We confine ourselves to solutions where the boundary layer region is vertically optically thick, and find that these solutions share several common features. The angular and radial velocities of the accreting material drop rapidly in a dynamical boundary layer, which has a radial width approximately 1%-3% of the white dwarf radius. The energy dissipated in this region diffuses through the inner part of the disk and is radiated from the disk surface in a thermal boundary layer, which has a radial width comparable to the disk thickness, approximately 5%-15% of the white dwarf radius. We examine the dependence of the boundary layer structure on the mass accretion rate, the white dwarf mass and rotation rate, and the viscosity parameter alpha. We delineate the boundary between optically thick and optically thin boundary layer solutions as a function of these parameters and suggest that by means of a careful comparison with observations it may be possible to estimate alpha in CVs. We derive an expression for the total boundary layer luminosities as a function of the parameters and show that it agrees well with the luminosites of our numerical solutions. Finally, we calcuate simple blackbody continuum spectra of the boundary layer and disk emission for our solutions and compare these to soft X-ray, EUV, and He II emission-line observations of CVs. We show that, through such comparisons, it may be possible to determine the rotation rates of the accreting stars in CVs, and perhaps also the white dwarf masses and the accretion rates. The spectra are quite insensitive to alpha, so the uncertainty in this parameter does not affect such comparisons.
Manipulation of Turbulent Boundary Layers Using Synthetic Jets
NASA Astrophysics Data System (ADS)
Berger, Zachary; Gomit, Guillaume; Lavoie, Philippe; Ganapathisubramani, Bharath
2015-11-01
This work focuses on the application of active flow control, in the form of synthetic jet actuators, of turbulent boundary layers. An array of 2 synthetic jets are oriented in the spanwise direction and located approximately 2.7 meters downstream from the leading edge of a flat plate. Actuation is applied perpendicular to the surface of the flat plate with varying blowing ratios and reduced frequencies (open-loop). Two-component large window particle image velocimetry (PIV) was performed at the University of Southampton, in the streamwise-wall-normal plane. Complementary stereo PIV measurements were performed at the University of Toronto Institute for Aerospace Studies (UTIAS), in the spanwise-wall-normal plane. The freestream Reynolds number is 3x104, based on the boundary layer thickness. The skin friction Reynolds number is 1,200 based on the skin friction velocity. The experiments at Southampton allow for the observation of the control effects as the flow propagates downstream. The experiments at UTIAS allow for the observation of the streamwise vorticity induced from the actuation. Overall the two experiments provide a 3D representation of the flow field with respect to actuation effects. The current work focuses on the comparison of the two experiments, as well as the effects of varying blowing ratios and reduced frequencies on the turbulent boundary layer. Funded Supported by Airbus.
NASA Astrophysics Data System (ADS)
Pohl, M.; Bulatov, D.
2015-03-01
We describe a work flow to border building faces which aims to obtain a detailed and closed building model. Initially, we use the estimated roof planes and the rasterized binary mask of the corresponding inlier set to generate bordering polygons. To close the gaps between the initial boundary polygons and between the polygons and the building ground outline, we introduce an algorithm to align boundaries which successfully works in 2.5D and 3D. To enhance the accuracy of the boundary alignment, we use additional reliable model entities such as cut lines and step lines between the initial estimated roof planes. All gaps that cannot be avoided by this procedure are afterwards covered by a method searching for uncovered details.
Full Waveform 3D Synthetic Seismic Algorithm for 1D Layered Anelastic Models
NASA Astrophysics Data System (ADS)
Schwaiger, H. F.; Aldridge, D. F.; Haney, M. M.
2007-12-01
Numerical calculation of synthetic seismograms for 1D layered earth models remains a significant aspect of amplitude-offset investigations, surface wave studies, microseismic event location approaches, and reflection interpretation or inversion processes. Compared to 3D finite-difference algorithms, memory demand and execution time are greatly reduced, enabling rapid generation of seismic data within workstation or laptop computational environments. We have developed a frequency-wavenumber forward modeling algorithm adapted to realistic 1D geologic media, for the purpose of calculating seismograms accurately and efficiently. The earth model consists of N layers bounded by two halfspaces. Each layer/halfspace is a homogeneous and isotropic anelastic (attenuative and dispersive) solid, characterized by a rectangular relaxation spectrum of absorption mechanisms. Compressional and shear phase speeds and quality factors are specified at a particular reference frequency. Solution methodology involves 3D Fourier transforming the three coupled, second- order, integro-differential equations for particle displacements to the frequency-horizontal wavenumber domain. An analytic solution of the resulting ordinary differential system is obtained. Imposition of welded interface conditions (continuity of displacement and stress) at all interfaces, as well as radiation conditions in the two halfspaces, yields a system of 6(N+1) linear algebraic equations for the coefficients in the ODE solution. An optimized inverse 2D Fourier transform to the space domain gives the seismic wavefield on a horizontal plane. Finally, three-component seismograms are obtained by accumulating frequency spectra at designated receiver positions on this plane, followed by a 1D inverse FFT from angular frequency ω to time. Stress-free conditions may be applied at the top or bottom interfaces, and seismic waves are initiated by force or moment density sources. Examples reveal that including attenuation
Bursting frequency prediction in turbulent boundary layers
LIOU,WILLIAM W.; FANG,YICHUNG
2000-02-01
The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted using global numerical solution of the Orr-Sommerfeld and the vertical vorticity equations of hydrodynamic stability problems. The structures were modeled as wavelike disturbances associated with the turbulent mean flow. The global method developed here involves the use of second and fourth order accurate finite difference formula for the differential equations as well as the boundary conditions. An automated prediction tool, BURFIT, was developed. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data.
Particulate plumes in boundary layers with obstacles
NASA Astrophysics Data System (ADS)
Petrosyan, Arakel; Karelsky, Kirill
2013-04-01
This presentation is aimed at creating and realization of new physical model of impurity transfer (solid particles and heavy gases) in areas with non-flat and/or nonstationary boundaries. The main idea of suggested method is to use non-viscous equations for solid particles transport modeling in the vicinity of complex boundary. In viscous atmosphere with as small as one likes coefficient of molecular viscosity, the non-slip boundary condition on solid surface must be observed. This postulates the reduction of velocity to zero at a solid surface. It is unconditionally in this case Prandtle hypothesis must be observed: for rather wide range of conditions in the surface neighboring layers energy dissipation of atmosphere flows is comparable by magnitude with manifestation of inertia forces. That is why according to Prandtle hypothesis in atmosphere movement characterizing by a high Reynolds number the boundary layer is forming near a planet surface, within which the required transition from zero velocities at the surface to magnitudes at the external boundary of the layer that are quite close to ones in ideal atmosphere flow. In that layer fast velocity gradients cause viscous effects to be comparable in magnitude with inertia forces influence. For conditions considered essential changes of hydrodynamic fields near solid boundary caused not only by non-slip condition but also by a various relief of surface: mountains, street canyons, individual buildings. Transport of solid particles, their ascent and precipitation also result in dramatic changes of meteorological fields. As dynamic processes of solid particles transfer accompanying the flow past of complex relief surface by wind flows is of our main interest we are to use equations of non-viscous hydrodynamic. We should put up with on the one hand idea of big wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations.We deal with describing big field
Hairpin vortices in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Eitel-Amor, G.; Flores, O.; Schlatter, P.
2014-04-01
The present work addresses the question whether hairpin vortices are a dominant feature of near-wall turbulence and which role they play during transition. First, the parent-offspring mechanism is investigated in temporal simulations of a single hairpin vortex introduced in a mean shear flow corresponding to turbulent channels and boundary layers up to Reτ = 590. Using an eddy viscosity computed from resolved simulations, the effect of a turbulent background is also considered. Tracking the vortical structure downstream, it is found that secondary hairpins are created shortly after initialization. Thereafter, all rotational structures decay, whereas this effect is enforced in the presence of an eddy viscosity. In a second approach, a laminar boundary layer is tripped to transition by insertion of a regular pattern of hairpins by means of defined volumetric forces representing an ejection event. The idea is to create a synthetic turbulent boundary layer dominated by hairpin-like vortices. The flow for Reτ < 250 is analysed with respect to the lifetime of individual hairpin-like vortices. Both the temporal and spatial simulations demonstrate that the regeneration process is rather short-lived and may not sustain once a turbulent background has formed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former DNS studies is an outer layer phenomenon not being connected to the onset of near-wall turbulence.
Edery, Ariel; Graham, Noah; MacDonald, Ilana
2009-06-15
Under dimensional reduction, a system in D spacetime dimensions will not necessarily yield its D-1-dimensional analog version. Among other things, this result will depend on the boundary conditions and the dimension D of the system. We investigate this question for scalar and Abelian gauge fields under boundary conditions that obey the symmetries of the action. We apply our findings to the Casimir piston, an ideal system for detecting boundary effects. Our investigation is not limited to extra dimensions and we show that the original piston scenario proposed in 2004, a toy model involving a scalar field in 3D (2+1) dimensions, can be obtained via dimensional reduction from a more realistic 4D electromagnetic (EM) system. We show that for perfect conductor conditions, a D-dimensional EM field reduces to a D-1 scalar field and not its lower-dimensional version. For Dirichlet boundary conditions, no theory is recovered under dimensional reduction and the Casimir pressure goes to zero in any dimension. This ''zero Dirichlet'' result is useful for understanding the EM case. We then identify two special systems where the lower-dimensional version is recovered in any dimension: systems with perfect magnetic conductor (PMC) and Neumann boundary conditions. We show that these two boundary conditions can be obtained from a variational procedure in which the action vanishes outside the bounded region. The fields are free to vary on the surface and have zero modes, which survive after dimensional reduction.
Ou, Jao J.; Ong, Rowena E.; Miga, Michael I.
2013-01-01
Modality-independent elastography (MIE) is a method of elastography that reconstructs the elastic properties of tissue using images acquired under different loading conditions and a biomechanical model. Boundary conditions are a critical input to the algorithm and are often determined by time-consuming point correspondence methods requiring manual user input. This study presents a novel method of automatically generating boundary conditions by nonrigidly registering two image sets with a demons diffusion-based registration algorithm. The use of this method was successfully performed in silico using magnetic resonance and X-ray-computed tomography image data with known boundary conditions. These preliminary results produced boundary conditions with an accuracy of up to 80% compared to the known conditions. Demons-based boundary conditions were utilized within a 3-D MIE reconstruction to determine an elasticity contrast ratio between tumor and normal tissue. Two phantom experiments were then conducted to further test the accuracy of the demons boundary conditions and the MIE reconstruction arising from the use of these conditions. Preliminary results show a reasonable characterization of the material properties on this first attempt and a significant improvement in the automation level and viability of the method. PMID:21690002
NASA Astrophysics Data System (ADS)
Li, Jing; Zeng, Zhaofa; Huang, Ling; Liu, Fengshan
2012-12-01
When applying the finite difference time domain (FDTD) method in Ground Penetrating Radar (GPR) simulation, the absorbing boundary conditions (ABC) are used to mitigate undesired reflection that can arise at the model's truncation boundaries. The classical PML boundary can make spurious reflection for the waves, such as reaching to the PML interface with near-grazing angles, low frequency waves or evanescent waves. The non-split complex frequency shifted PML which base on recursive integration (CFS-RIPML) has a good absorption effect for these interference waves. Meanwhile, the recursive integration, which does not need split field component, can overcome the shortcoming of CFS technique that needs more intermediate variable and large memory. In addition, the high-order FDTD can improve calculation accuracy and reduce the error caused by numerical dispersion effectively. In this paper, we derive the 3D high-order FDTD method with CFS-RIPML boundary and apply it in GPR simulation. The results show that the CFS-RIPML has significantly better absorption effect and lower reflections error than UPML and PML boundary. Compared with the two-order, the high-order FDTD can improve calculation accuracy effectively with the same grid size. Combination with CFS-RIPML boundary and high-order FDTD can improve the reliability and calculation accuracy of GPR and other geophysics numerical simulation.
Toward parameterization of the stable boundary layer
NASA Technical Reports Server (NTRS)
Wetzel, P. J.
1982-01-01
Wangara data is used to examine the depth of the nocturnal boundary layer (NBL) and the height to which surface-linked turbulence extends. It is noted that a linearity of virtual temperature profiles has been found to extend up to a significant portion of the NBL, and then diverge where the wind shear rides over the surface-induced turbulence. A series of Richardson numbers are examined for varying degrees of turbulence and the significant cooling region is observed to have greater depth than the depth of the linear relationship layer. A three-layer parameterization of the thermodynamic structure of the NBL is developed so that a system of five equations must be solved when the wind velocity profile and the temperature at the surface are known. A correlation between the bulk Richardson number and the depth of the linear layer was found to be 0.89.
Borazjani, Iman; Ge, Liang; Le, Trung; Sotiropoulos, Fotis
2013-01-01
We develop an overset-curvilinear immersed boundary (overset-CURVIB) method in a general non-inertial frame of reference to simulate a wide range of challenging biological flow problems. The method incorporates overset-curvilinear grids to efficiently handle multi-connected geometries and increase the resolution locally near immersed boundaries. Complex bodies undergoing arbitrarily large deformations may be embedded within the overset-curvilinear background grid and treated as sharp interfaces using the curvilinear immersed boundary (CURVIB) method (Ge and Sotiropoulos, Journal of Computational Physics, 2007). The incompressible flow equations are formulated in a general non-inertial frame of reference to enhance the overall versatility and efficiency of the numerical approach. Efficient search algorithms to identify areas requiring blanking, donor cells, and interpolation coefficients for constructing the boundary conditions at grid interfaces of the overset grid are developed and implemented using efficient parallel computing communication strategies to transfer information among sub-domains. The governing equations are discretized using a second-order accurate finite-volume approach and integrated in time via an efficient fractional-step method. Various strategies for ensuring globally conservative interpolation at grid interfaces suitable for incompressible flow fractional step methods are implemented and evaluated. The method is verified and validated against experimental data, and its capabilities are demonstrated by simulating the flow past multiple aquatic swimmers and the systolic flow in an anatomic left ventricle with a mechanical heart valve implanted in the aortic position. PMID:23833331
Boundary Layer Theory. Part 1; Laminar Flows
NASA Technical Reports Server (NTRS)
Schlichting, H.
1949-01-01
The purpose of this presentation is to give you a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. As you know, a great many considerations of aerodynamics are based on the so-called ideal fluid, that is, the frictionless incompressible fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid (potential theory) has been made possible.
Numerical simulation of boundary-layer transition
NASA Technical Reports Server (NTRS)
Spalart, P. R.
1984-01-01
The transition to turbulence in boundary layers was investigated by direct numerical solution of the nonlinear, three-dimensional, incompressible Navier-Stokes equations in the half-infinite domain over a flat plate. Periodicity was imposed in the streamwise and spanwise directions. A body force was applied to approximate the effect of a nonparallel mean flow. The numerical method was spectra, based on Fourier series and Jacobi polynomials, and used divergence-free basis functions. Extremely rapid convergence was obtained when solving the linear Orr-Sommerfeld equation. The early nonlinear and three-dimensional stages of transition, in a boundary layer disturbed by a vibrating ribbon, were successfully simulated. Excellent qualitative agreement was observed with either experiments or weakly nonlinear theories. In particular, the breakdown pattern was staggered or nonstaggered depending on the disturbance amplitude.
Turbulent shear stresses in compressible boundary layers
NASA Technical Reports Server (NTRS)
Laderman, A. J.; Demetriades, A.
1979-01-01
Hot-wire anemometer measurements of turbulent shear stresses in a Mach 3 compressible boundary layer were performed in order to investigate the effects of heat transfer on turbulence. Measurements were obtained by an x-probe in a flat plate, zero pressure gradient, two dimensional boundary layer in a wind tunnel with wall to freestream temperature ratios of 0.94 and 0.71. The measured shear stress distributions are found to be in good agreement with previous results, supporting the contention that the shear stress distribution is essentially independent of Mach number and heat transfer for Mach numbers from incompressible to hypersonic and wall to freestream temperature ratios of 0.4 to 1.0. It is also found that corrections for frequency response limitations of the electronic equipment are necessary to determine the correct shear stress distribution, particularly at the walls.
Boundary layer transition detection by luminescence imaging
NASA Technical Reports Server (NTRS)
Mclachlan, B. G.; Bell, J. H.; Gallery, J.; Gouterman, M.; Callis, J.
1993-01-01
In recent experiments we have demonstrated the feasibility of a new approach to boundary layer transition detection. This new approach employs the temperature dependence of certain photoluminescent materials in the form of a surface coating or 'paint' to detect the change in heat transfer characteristics that accompany boundary layer transition. The feasibility experiments were conducted for low subsonic to transonic Mach numbers on two-dimensional airfoil and flat plate configurations. Paint derived transition locations were determined and compared to those obtained from Preston pressure probe measurements. Artificial heating of the models was used to obtain transition temperature signatures suitable for the instrumentation available to us. Initial estimates show, however, that passive kinetic heating at high Mach numbers is a promising alternative.
Burst vortex/boundary layer interaction
NASA Technical Reports Server (NTRS)
Bradshaw, P.; Naaseri, M.
1988-01-01
Several configurations of delta wing vortex generator and boundary layer test plate were tested, and two final ones selected. Sample measurements and flow visualizations in the candidate configurations, together with more detailed measurements in one of the two final arrangements, which were selected so that a pure vortex bursts repeatably and then interacts, in as simple fashion as possible, with a simple turbulent boundary layer, are included. It is concluded that different intensities of bursting or breakdown, like different strengths of shock wave or hydraulic jump, can be produced by minor changes of configuration. The weaker breakdowns do not produce flow reversal. The initial measurements were done with a fairly weak, but repeatable, breakdown. Basic measurements on the second final arrangement, with a stronger breakdown, are in progress.
BOREAS AFM-6 Boundary Layer Height Data
NASA Technical Reports Server (NTRS)
Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)
2000-01-01
The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides boundary layer height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The boundary layer height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).
Van, Anh T; Aksoy, Murat; Holdsworth, Samantha J; Kopeinigg, Daniel; Vos, Sjoerd B; Bammer, Roland
2014-01-01
Purpose To propose a method for mitigating slab boundary artifacts in 3D multislab diffusion imaging with no or minimal increases in scan time. Methods The multislab acquisition was treated as parallel imaging acquisition where the slab profiles acted as the traditional receiver sensitivity profiles. All the slabs were then reconstructed simultaneously along the slab direction using Cartesian-based sensitivity encoding (SENSE) reconstruction. The slab profile estimation was performed using either a Bloch simulation or a calibration scan. Results Both phantom and in vivo results showed negligible slab boundary artifacts after reconstruction using the proposed method. The performance of the proposed method is comparable to the state-of-the-art slab combination method without the scan time penalty that depends on the number of acquired volumes. The obtained g-factor map of the SENSE reconstruction problem showed a maximum g-factor of 1.7 in the region of interest. Conclusion We proposed a novel method for mitigating slab boundary artifacts in 3D diffusion imaging by treating the multislab acquisition as a parallel imaging acquisition and reconstructing all slabs simultaneously using Cartesian SENSE. Unlike existing methods, the scan time increase, if any, does not scale with the number of image volumes acquired. PMID:24691843
Shock-boundary-layer interaction in flight
NASA Technical Reports Server (NTRS)
Bertelrud, Arild
1989-01-01
A brief survey is given on the study of transonic shock/boundary layer effects in flight. Then the possibility of alleviating the adverse shock effects through passive shock control is discussed. A Swedish flight experiment on a swept wing attack aircraft is used to demonstrate how it is possible to reduce the extent of separated flow and increase the drag-rise Mach number significantly using a moderate amount of perforation of the surface.
The boundary layer on compressor cascade blades
NASA Technical Reports Server (NTRS)
Deutsch, S.
1981-01-01
Some redesign of the cascade facility was necessary in order to incoporate the requirements of the LDA system into the design. Of particular importance was the intended use of a combination of suction upstream of the blade pack with diverging pack walls, as opposed to blade pack suction alone, for spanwise dimensionality control. An ARL blade was used to redo some tests using this arrangement. Preliminary testing and boundary layer measurements began on the double circular arc blades.
Clidar Mountain Boundary Layer Case Studies
NASA Astrophysics Data System (ADS)
Sharma, Nimmi C. P.; Barnes, John E.
2016-06-01
A CCD Camera Lidar system called the CLidar system images a vertically pointing laser from the side with a spatially separated CCD camera and wide angle optics. The system has been used to investigate case studies of aerosols in mountain boundary layers in in the times following sunset. The aerosols detected by the system demonstrate the wide variation of near ground aerosol structure and capabilities of the CLidar system.
Boundary Layer Control for Hypersonic Airbreathing Vehicles
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Nowak, Robert J.; Horvath, Thomas J.
2004-01-01
Active and passive methods for tripping hypersonic boundary layers have been examined in NASA Langley Research Center wind tunnels using a Hyper-X model. This investigation assessed several concepts for forcing transition, including passive discrete roughness elements and active mass addition (or blowing), in the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air Tunnels. Heat transfer distributions obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the Hyper-X nominal Mach 7 flight test-point of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For passive roughness, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The passive roughness study resulted in a swept ramp configuration, scaled to be roughly 0.6 of the calculated boundary layer thickness, being selected for the Mach 7 flight vehicle. For the active blowing study, the manifold pressure was systematically varied (while monitoring the mass flow) for each configuration to determine the jet penetration height, with schlieren, and transition movement, with the phosphor system, for comparison to the passive results. All the blowing concepts tested, which included various rows of sonic orifices (holes), two- and three-dimensional slots, and random porosity, provided transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model surface static pressure, which is adequate to ensure sonic jets. The present results indicate that the jet penetration height for blowing was roughly half the height required with passive roughness elements for an equivalent amount of transition movement.
NASA Astrophysics Data System (ADS)
Maerten, F.; Maerten, L.; Pollard, D. D.
2014-11-01
Most analytical solutions to engineering or geological problems are limited to simple geometries. For example, analytical solutions have been found to solve for stresses around a circular hole in a plate. To solve more complex problems, mathematicians and engineers have developed powerful computer-aided numerical methods, which can be categorized into two main types: differential methods and integral methods. The finite element method (FEM) is a differential method that was developed in the 1950s and is one of the most commonly used numerical methods today. Since its development, other differential methods, including the boundary element method (BEM), have been developed to solve different types of problems. The purpose of this paper is to describe iBem3D, formally called Poly3D, a C++ and modular 3D boundary element computer program based on the theory of angular dislocations for modeling three-dimensional (3D) discontinuities in an elastic, heterogeneous, isotropic whole- or half-space. After 20 years and more than 150 scientific publications, we present in detail the formulation behind this method, its enhancements over the years as well as some important applications in several domains of the geosciences. The main advantage of using this formulation, for describing geological objects such as faults, resides in the possibility of modeling complex geometries without gaps and overlaps between adjacent triangular dislocation elements, which is a significant shortcoming for models using rectangular dislocation elements. Reliability, speed, simplicity, and accuracy are enhanced in the latest version of the computer code. Industrial applications include subseismic fault modeling, fractured reservoir modeling, interpretation and validation of fault connectivity and reservoir compartmentalization, depleted area and fault reactivation, and pressurized wellbore stability. Academic applications include earthquake and volcano monitoring, hazard mitigation, and slope
Pressure gradient influence in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Reuther, Nico; Kaehler, Christian J.
2015-11-01
Understanding wall-bounded turbulence is still an ongoing process. Although remarkable progress has been made in the last decades, many challenges still remain. Mean flow statistics are well understood in case of zero pressure gradient flows. However, almost all turbulent boundary layers in technical applications, such as aircrafts, are subjected to a streamwise pressure gradient. When subjecting turbulent boundary layers to adverse pressure gradients, significant changes in the statistical behavior of the near-wall flow have been observed in experimental studies conducted however the details dynamics and characteristics of these flows has not been fully resolved. The sensitivity to Reynolds number and the dependency on several parameters, including the dependence on the pressure gradient parameter, is still under debate and very little information exists about statistically averaged quantities such as the mean velocity profile or Reynolds stresses. In order to improve the understanding of wall-bounded turbulence, this work experimentally investigates turbulent boundary layer subjected to favorable and adverse pressure gradients by means of Particle Image Velocimetry over a wide range of Reynolds numbers, 4200
Shock-wave boundary layer interactions
NASA Technical Reports Server (NTRS)
Delery, J.; Marvin, J. G.; Reshotko, E.
1986-01-01
Presented is a comprehensive, up-to-date review of the shock-wave boundary-layer interaction problem. A detailed physical description of the phenomena for transonic and supersonic speed regimes is given based on experimental observations, correlations, and theoretical concepts. Approaches for solving the problem are then reviewed in depth. Specifically, these include: global methods developed to predict sudden changes in boundary-layer properties; integral or finite-difference methods developed to predict the continuous evolution of a boundary-layer encountering a pressure field induced by a shock wave; coupling methods to predict entire flow fields; analytical methods such as multi-deck techniques; and finite-difference methods for solving the time-dependent Reynolds-averaged Navier-Stokes equations used to predict the development of entire flow fields. Examples are presented to illustrate the status of the various methods and some discussion is devoted to delineating their advantages and shortcomings. Reference citations for the wide variety of subject material are provided for readers interested in further study.
Coupled wake boundary layer model of windfarms
NASA Astrophysics Data System (ADS)
Stevens, Richard; Gayme, Dennice; Meneveau, Charles
2014-11-01
We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.
NASA Astrophysics Data System (ADS)
Ge, Liang; Sotiropoulos, Fotis
2007-08-01
A novel numerical method is developed that integrates boundary-conforming grids with a sharp interface, immersed boundary methodology. The method is intended for simulating internal flows containing complex, moving immersed boundaries such as those encountered in several cardiovascular applications. The background domain (e.g. the empty aorta) is discretized efficiently with a curvilinear boundary-fitted mesh while the complex moving immersed boundary (say a prosthetic heart valve) is treated with the sharp-interface, hybrid Cartesian/immersed-boundary approach of Gilmanov and Sotiropoulos [A. Gilmanov, F. Sotiropoulos, A hybrid cartesian/immersed boundary method for simulating flows with 3d, geometrically complex, moving bodies, Journal of Computational Physics 207 (2005) 457-492.]. To facilitate the implementation of this novel modeling paradigm in complex flow simulations, an accurate and efficient numerical method is developed for solving the unsteady, incompressible Navier-Stokes equations in generalized curvilinear coordinates. The method employs a novel, fully-curvilinear staggered grid discretization approach, which does not require either the explicit evaluation of the Christoffel symbols or the discretization of all three momentum equations at cell interfaces as done in previous formulations. The equations are integrated in time using an efficient, second-order accurate fractional step methodology coupled with a Jacobian-free, Newton-Krylov solver for the momentum equations and a GMRES solver enhanced with multigrid as preconditioner for the Poisson equation. Several numerical experiments are carried out on fine computational meshes to demonstrate the accuracy and efficiency of the proposed method for standard benchmark problems as well as for unsteady, pulsatile flow through a curved, pipe bend. To demonstrate the ability of the method to simulate flows with complex, moving immersed boundaries we apply it to calculate pulsatile, physiological flow
Implicit Approaches for Moving Boundaries in a 3-D Cartesian Method
NASA Technical Reports Server (NTRS)
Murman, Scott M.; Aftosmis, Michael J.; Berger, Marsha J.; Kwak, Dochan
2003-01-01
This work considers numerical simulation of three-dimensional flows with time-evolving boundaries. Such problems pose a variety of challenges for numerical schemes, and have received a substantial amount of attention in the recent literature. Since such simulations are unsteady, time-accurate solution of the governing equations is required. In special cases, the body motion can be treated by a uniform rigid motion of the computational domain. For the more general situation of relative-body motion, however, this simplification is unavailable and the simulations require a mechanism for ensuring that the mesh evolves with the moving boundaries. This involves a "remeshing" of the computational domain (either localized or global) at each physical timestep, and places a premium on both the speed and robustness of the remeshing algorithms. This work presents a method which includes unsteady flow simulation, rigid domain motion, and relative body motion using a time-evolving Cartesian grid system in three dimensions.
Data-driven inversion of 3D GPR data for layered media
NASA Astrophysics Data System (ADS)
Slob, E. C.
2013-12-01
The number of GPR applications is large and still increasing. In several applications fixed-offset measurements can be sufficient and many dedicated imaging and inversion methods have been developed. Because there is insufficient amounts of data, these are necessarily model-driven schemes. For problems where quantitative information is needed, usually it is better to record multi-offset and possibly multicomponent data. Even for this data inversion is usually model-driven. This means the inverse problem is formulated as an iterative forward modeling problem and is solved by minimizing the amplitude difference between modeled and measured data. The model is modified such that data computed from the model fits the measured data. The information in the measured data itself is not used, except as a measure of the model data fit. For multi-offset multicomponent data a data-driven scheme is here developed to perform full waveform inversion of 3D ground-penetrating radar reflection data acquired on the surface of a layered medium. For data-driven models to work well, the data has to be properly sampled. The advantage is that no model information is necessary to carry out the inversion. The inversion is carried out in three steps. First the data is decomposed into up- and downgoing wave modes. In a layered earth the two modes are separable and are treated separately. This step provides the reflection response of the layered medium. For 3D waves in a layered medium this requires knowledge of the horizontal electric and magnetic field components. If the data is properly sampled the solution is unique. The second step consists of wave field synthesis, where the reflection response is used to construct a focusing wave field that can focus in a virtual receiver position at any depth level. At this stage of the process the depth level is only known in terms of one-way travel time. This is the intercept time in the slowness domain obtained directly from the data. A virtual
High-resolution imaging and inversion of 3D GPR data for layered media
NASA Astrophysics Data System (ADS)
Slob, Evert
2013-04-01
Ground penetrating radar is increasingly being used to provide quantitative information of layered structures. For application in civil engineering these can be roads, highway pavements, airport runways, bridges, tunnels, or buildings. Monitoring is important for the management and safety of these structures. Standard imaging uses a modeled wavefield extrapolator to image the data and the quality of the image depends heavily on the quality of the modeled extrapolator. Usually, data inversion is implemented by minimizing a cost function involving the measured data and the modeled data. The model is modified such that data computed from the model fits to the measured data. The data itself is not used, except as a measure of the model data fit. A recently developed alternative method is to use results from inverse scattering theory to first construct an image while all multiple reflections are simultaneously eliminated from the data. This image can be constructed from surface reflection data if the data allows separating the subsurface reflection response from the down going emitted field. For 3D waves in a layered medium this requires knowledge of all horizontal electric and magnetic field components. If the data is properly sampled the solution is unique. In layered media the plane wave decomposition allows computing the image for each angle of incidence separately as a function of image time that is equal to the one-way intercept time. Once the image is constructed for all available angles of incidence a simple matrix inversion leads to the desired electric permittivity and magnetic permeability values in each layer. Finally these values provide interval velocities that can be used to convert image time to depth and the inverse problem is solved. The theory requires infinite bandwidth frequency domain data, which is equivalent to measuring the true impulse response. This is not possible in practice and numerical results show that data with finite bandwidths can be
Unsteadiness of Shock Wave / Boundary Layer Interactions
NASA Astrophysics Data System (ADS)
Clemens, Noel
2009-11-01
Shock wave / boundary layer interactions are an important feature of high-speed flows that occur in a wide range of practical configurations including aircraft control surfaces, inlets, missile base flows, nozzles, and rotating machinery. These interactions are often associated with severe boundary layer separation, which is highly unsteady, and exhibits high fluctuating pressure and heat loads. The unsteady motions are characterized by a wide range of frequencies, including low-frequency motions that are about two orders of magnitude lower than those that characterize the upstream boundary layer. It is these low-frequency motions that are of most interest because they have been the most difficult to explain and model. Despite significant work over the past few decades, the source of the low-frequency motions remains a topic of intense debate. Owing to a flurry of activity over the past decade on this single topic we are close to developing a comprehensive understanding of the low-frequency unsteadiness. For example, recent work in our laboratory and others suggests that the driving mechanism is related to low-frequency fluctuations in the upstream boundary layer. However, several recent studies suggest the dominant mechanism is an intrinsic instability of the separated flow. Here we attempt to reconcile these views by arguing that the low-frequency unsteadiness is driven by both upstream and downstream processes, but the relative importance of each mechanism depends on the strength (or length-scale) of separation. In cases where the separation bubble is relatively small, then the flow is intermittently separated, and there exists a strong correlation between upstream velocity fluctuations and the separation bubble dynamics. It appears that superstructures in the upstream boundary layer can play an important role in driving the unsteadiness for this case. It is not clear, however, if the upstream fluctuations directly move the separation point or indirectly couple
The role of nonlinear critical layers in boundary layer transition
NASA Technical Reports Server (NTRS)
Goldstein, M.E.
1995-01-01
Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.
Scaling the heterogeneously heated convective boundary layer
NASA Astrophysics Data System (ADS)
Van Heerwaarden, C.; Mellado, J.; De Lozar, A.
2013-12-01
We have studied the heterogeneously heated convective boundary layer (CBL) by means of large-eddy simulations (LES) and direct numerical simulations (DNS). What makes our study different from previous studies on this subject are our very long simulations in which the system travels through multiple states and that from there we have derived scaling laws. In our setup, a stratified atmosphere is heated from below by square patches with a high surface buoyancy flux, surrounded by regions with no or little flux. By letting a boundary layer grow in time we let the system evolve from the so-called meso-scale to the micro-scale regime. In the former the heterogeneity is large and strong circulations can develop, while in the latter the heterogeneity is small and does no longer influence the boundary layer structure. Within each simulation we can now observe the formation of a peak in kinetic energy, which represents the 'optimal' heterogeneity size in the meso-scale, and the subsequent decay of the peak and the development towards the transition to the micro-scale. We have created a non-dimensional parameter space that describes all properties of this system. By studying the previously described evolution for different combinations of parameters, we have derived three important conclusions. First, there exists a horizontal length scale of the heterogeneity (L) that is a function of the boundary layer height (h) and the Richardson (Ri) number of the inversion at the top of the boundary layer. This relationship has the form L = h Ri^(3/8). Second, this horizontal length scale L allows for expressing the time evolution, and thus the state of the system, as a ratio of this length scale and the distance between two patches Xp. This ratio thus describes to which extent the circulation fills up the space that exists between two patch centers. The timings of the transition from the meso- to the micro-scale collapse under this scaling for all simulations sharing the same flux
Pushing the Limits: 3D Layer-by-Layer-Assembled Composites for Cathodes with 160 C Discharge Rates.
Mo, Runwei; Tung, Siu On; Lei, Zhengyu; Zhao, Guangyu; Sun, Kening; Kotov, Nicholas A
2015-05-26
Deficiencies of cathode materials severely limit cycling performance and discharge rates of Li batteries. The key problem is that cathode materials must combine multiple properties: high lithium ion intercalation capacity, electrical/ionic conductivity, porosity, and mechanical toughness. Some materials revealed promising characteristics in a subset of these properties, but attaining the entire set of often contrarian characteristics requires new methods of materials engineering. In this paper, we report high surface area 3D composite from reduced graphene oxide loaded with LiFePO4 (LFP) nanoparticles made by layer-by-layer assembly (LBL). High electrical conductivity of the LBL composite is combined with high ionic conductivity, toughness, and low impedance. As a result of such materials properties, reversible lithium storage capacity and Coulombic efficiency were as high as 148 mA h g(-1) and 99%, respectively, after 100 cycles at 1 C. Moreover, these composites enabled unusually high reversible charge-discharge rates up to 160 C with a storage capacity of 56 mA h g(-1), exceeding those of known LFP-based cathodes, some of them by several times while retaining high content of active cathode material. The study demonstrates that LBL-assembled composites enable resolution of difficult materials engineering tasks. PMID:25910177
A Laplacian Equation Method for Numerical Generation of Boundary-Fitted 3D Orthogonal Grids
NASA Astrophysics Data System (ADS)
Theodoropoulos, T.; Bergeles, G. C.
1989-06-01
A sethod for generating boundary fitted orthogonal curvilinear grids in 3-dimensional space is described. The mapping between the curvilinear coordinates and the Cartesian coordinates is provided by a set of Laplace equations which, expressed in curvilinear coordinates, involve the components of the metric tensor and are therefore non-linear and coupled. An iterative algorithm is described, which achieves a numerical solution. Grids appropriate for the calculation of flow fields over complex topography or in complex flow passages as those found in turbomachinery, and for other engineering applications can be constructed using the proposed method. Various examples are presented and plotted in perspective, and data for the assessment of the properties of the resulting meshes is provided.
NASA Astrophysics Data System (ADS)
Krizsky, V.
2003-04-01
The problems of definition inclusion's boundaries in part-homogeneous media are actual in ore-mineral and oil-gas exploring geophysics. Interpolating spline-function S(t) , which approximate guide-line of cylindrical inclusion or generatrix-line of surface S of rotation body Ω_0 , which located in medium Ω_k of horizontally-stratified half-space, is obtained as normal quasi-solution in the W_2^1 [a,b] . Spline S(t) minimize the A.N. Tichonov functional F^α (S(t)) = left\\| {u(S(t),P,A) - u^e(P,A)} right\\|L_2 (E × E) + α left\\| {S(t)} right\\|W_2^1 [a,b], where u^e (P,A) - experimental potential data on area E × E ( P,A in E ), P - pointed receiver and A - pointed source of direct current, α- regularization parameter, u(S(t),P,A) - solution of direct problem about potential field of pointed source A in horizontally-stratified medium. The solution of direct problem can be defined by combine methods of integral transforms and integral equations. The problem of the determination parametric-given boundary is reduced to the problem of the determination limited component of finite dimensional vector. Extremum of functional F^α (S(t)) is obtained by variation type algorithm based on the Hook-Jeves method, which is conformed for searching the badly ravine functions minimum. Designed software programs have allowed us to conduct the computer experiment.
Acoustic radar investigations of boundary layer phenomena
NASA Technical Reports Server (NTRS)
Marks, J. R.
1974-01-01
A comparison is made between acoustic radar echoes and conventional meteorological data obtained from the WKY tower, for the purpose of better understanding the relationships between acoustic radar echoes and boundary layer processes. Two thunderstorm outflow cases are presented and compared to both acoustic radar data and Charba's gust front model. The acoustic radar echoes reveal the boundary between warm and cold air and other areas of mixing and strong thermal gradient quite well. The thunderstorm outflow of 27 June 1972 is found to compare with in most respects to Charba's gust front model. The major difference is the complete separation of the head from the main body of cold air, probably caused by erosion of the area behind the head by mixing with the ambient air. Two cases of nocturnal inversions caused by advection of warmer air aloft are presented. It is found that areas of turbulent mixing or strong thermal gradient can be identified quite easily in the acoustic radar record.
Three-dimensional shock-wave/boundary-layer interactions with bleed through a circular hole
NASA Technical Reports Server (NTRS)
Rimlinger, M. J.; Shih, T. I.-P.; Chyu, W. J.
1992-01-01
Computations were performed to study three-dimensional (3-D), shock-wave/boundary-layer interactions on a flat plate in which fluid in the boundary layer was bled through a circular hole into a plenum to control shock-wave induced separation. Results are presented which show the details of the 3-D flowfield about the bleed hole and how bleed-hole placement relative to shock-wave impingement affect upstream, spanwise, and downstream influence lengths. This study revealed an underlying mechanisms by which bleed holes can affect shock-wave/boundary-layer interactions. This investigation is based on the ensemble-averaged, "full-compressible" Navier-Stokes equations closed by the Baldwin-Lomax turbulence model. Solutions to these equations were obtained by an implicit finite-volume method based on the partially-split, two-factored algorithm of Steger.
NASA Astrophysics Data System (ADS)
Maljers, Denise; den Dulk, Maryke; ten Veen, Johan; Hummelman, Jan; Gunnink, Jan; van Gessel, Serge
2016-04-01
The Geological Survey of the Netherlands (GSN) develops and maintains subsurface models with regional to national coverage. These models are paramount for petroleum exploration in conventional reservoirs, for understanding the distribution of unconventional reservoirs, for mapping geothermal aquifers, for the potential to store carbon, or for groundwater- or aggregate resources. Depending on the application domain these models differ in depth range, scale, data used, modelling software and modelling technique. Depth uncertainty information is available for the Geological Survey's 3D raster layer models DGM Deep and DGM Shallow. These models cover different depth intervals and are constructed using different data types and different modelling software. Quantifying the uncertainty of geological models that are constructed using multiple data types as well as geological expert-knowledge is not straightforward. Examples of geological expert-knowledge are trend surfaces displaying the regional thickness trends of basin fills or steering points that are used to guide the pinching out of geological formations or the modelling of the complex stratal geometries associated with saltdomes and saltridges. This added a-priori knowledge, combined with the assumptions underlying kriging (normality and second-order stationarity), makes the kriging standard error an incorrect measure of uncertainty for our geological models. Therefore the methods described below were developed. For the DGM Deep model a workflow has been developed to assess uncertainty by combining precision (giving information on the reproducibility of the model results) and accuracy (reflecting the proximity of estimates to the true value). This was achieved by centering the resulting standard deviations around well-tied depths surfaces. The standard deviations are subsequently modified by three other possible error sources: data error, structural complexity and velocity model error. The uncertainty workflow
Multigrid methods for flow transition in three-dimensional boundary layers with surface roughness
NASA Technical Reports Server (NTRS)
Liu, Chaoqun; Liu, Zhining; Mccormick, Steve
1993-01-01
The efficient multilevel adaptive method has been successfully applied to perform direct numerical simulations (DNS) of flow transition in 3-D channels and 3-D boundary layers with 2-D and 3-D isolated and distributed roughness in a curvilinear coordinate system. A fourth-order finite difference technique on stretched and staggered grids, a fully-implicit time marching scheme, a semi-coarsening multigrid method associated with line distributive relaxation scheme, and an improved outflow boundary-condition treatment, which needs only a very short buffer domain to damp all order-one wave reflections, are developed. These approaches make the multigrid DNS code very accurate and efficient. This allows us not only to be able to do spatial DNS for the 3-D channel and flat plate at low computational costs, but also to do spatial DNS for transition in the 3-D boundary layer with 3-D single and multiple roughness elements, which would have extremely high computational costs with conventional methods. Numerical results show good agreement with the linear stability theory, the secondary instability theory, and a number of laboratory experiments. The contribution of isolated and distributed roughness to transition is analyzed.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
2006-01-01
This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCP(sub avg)) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.
Boundary-Layer-Ingesting Inlet Flow Control
NASA Technical Reports Server (NTRS)
Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.
2006-01-01
This paper gives an overview of a research study conducted in support of the small-scale demonstration of an active flow control system for a boundary-layer-ingesting (BLI) inlet. The effectiveness of active flow control in reducing engine inlet circumferential distortion was assessed using a 2.5% scale model of a 35% boundary-layer-ingesting flush-mounted, offset, diffusing inlet. This experiment was conducted in the NASA Langley 0.3-meter Transonic Cryogenic Tunnel at flight Mach numbers with a model inlet specifically designed for this type of testing. High mass flow actuators controlled the flow through distributed control jets providing the active flow control. A vortex generator point design configuration was also tested for comparison purposes and to provide a means to examine a hybrid vortex generator and control jets configuration. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion and pressure recovery were determined by 40 total pressure measurements on 8 rake arms each separated by 45 degrees and were located at the aerodynamic interface plane. The test matrix was limited to a maximum free-stream Mach number of 0.85 with scaled mass flows through the inlet for that condition. The data show that the flow control jets alone can reduce circumferential distortion (DPCPavg) from 0.055 to about 0.015 using about 2.5% of inlet mass flow. The vortex generators also reduced the circumferential distortion from 0.055 to 0.010 near the inlet mass flow design point. Lower inlet mass flow settings with the vortex generator configuration produced higher distortion levels that were reduced to acceptable levels using a hybrid vortex generator/control jets configuration that required less than 1% of the inlet mass flow.
Electrical conduction mechanisms in PbSe and PbS nano crystals 3D matrix layer
NASA Astrophysics Data System (ADS)
Arbell, Matan; Hechster, Elad; Sarusi, Gabby
2016-02-01
A simulation study and measurements of the electrical conductance in a PbSe and PbS spherical Nano-crystal 3D matrix layer was carried out focusing on its dependences of Nano-crystal size distribution and size gradient along the layer thickness (z-direction). The study suggests a new concept of conductance enhancement by utilizing a size gradient along the layer thickness from mono-layer to the next mono-layer of the Nano-crystals, in order to create a gradient of the energy levels and thus improve directional conductance in this direction. A Monte Carlo simulation of the charge carriers path along the layer thickness of the Nano-crystals 3D matrix using the Miller-Abrahams hopping model was performed. We then compared the conductance characteristics of the gradual size 3D matrix layer to a constant-sized 3D matrix layer that was used as a reference in the simulation. The numerical calculations provided us with insights into the actual conductance mechanism of the PbSe and PbS Nano-crystals 3D matrix and explained the discrepancies in actual conductance and the variability in measured mobilities published in the literature. It is found that the mobility and thus conductance are dependent on a critical electrical field generated between two adjacent nano-crystals. Our model explains the conductance dependents on the: Cathode-Anode distance, the distance between the adjacent nano-crystals in the 3D matrix layer and the size distribution along the current direction. Part of the model (current-voltage dependence) was validated using a current-voltage measurements taken on a constant size normal distribution nano-crystals PbS layer (330nm thick) compared with the predicted I-V curves. It is shown that under a threshold bias, the current is very low, while after above a threshold bias the conductance is significantly increased due to increase of hopping probability. Once reaching the maximum probability the current tend to level-off reaching the maximal conductance
Boundary-layer Transition at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Low, George M
1956-01-01
Recent results of the effects of Mach number, stream turbulence, leading-edge geometry, leading-edge sweep, surface temperature, surface finish, pressure gradient, and angle of attack on boundary-layer transition are summarized. Factors that delay transition are nose blunting, surface cooling, and favorable pressure gradient. Leading-edge sweep and excessive surface roughness tend to promote early transition. The effects of leading-edge blunting on two-dimensional surfaces and surface cooling can be predicted adequately by existing theories, at least in the moderate Mach number range.
Coherent motions in the turbulent boundary layer
NASA Technical Reports Server (NTRS)
Robinson, Stephen K.
1991-01-01
The role of coherent structures in the production and dissipation of turbulence in a boundary layer is characterized, summarizing the results of recent investigations. Coherent motion is defined as a three-dimensional region of flow where at least one fundamental variable exhibits significant correlation with itself or with another variable over a space or time range significantly larger than the smallest local scales of the flow. Sections are then devoted to flow-visualization experiments, statistical analyses, numerical simulation techniques, the history of coherent-structure studies, vortices and vortical structures, conceptual models, and predictive models. Diagrams and graphs are provided.
The minisodar and planetary boundary layer studies
Coulter, R.L.
1996-06-01
The minisodar, in addition to being smaller than conventional sodar, operates at higher frequencies, obtains usable signal returns closer to the surface, and can use smaller range gates. Because the max range is generally limited to the lower 200 m above the surface, the minisodar is not able to interrogate the entire daytime atmospheric Planetary Boundary Layer (PBL); however it can be a very useful tool for understanding the PBL. In concert with other instruments, the minisodar can add significant new insights to our understanding of the PBL. This paper gives examples of past and potential uses of minisodars in such situations.
NASA Astrophysics Data System (ADS)
Calvisi, Michael; Manmi, Kawa; Wang, Qianxi
2014-11-01
Ultrasound contrast agents (UCAs) are microbubbles stabilized with a shell typically of lipid, polymer, or protein and are emerging as a unique tool for noninvasive therapies ranging from gene delivery to tumor ablation. The nonspherical dynamics of contrast agents are thought to play an important role in both diagnostic and therapeutic applications, for example, causing the emission of subharmonic frequency components and enhancing the uptake of therapeutic agents across cell membranes and tissue interfaces. A three-dimensional model for nonspherical contrast agent dynamics based on the boundary integral method is presented. The effects of the encapsulating shell are approximated by adapting Hoff's model for thin-shell, spherical contrast agents to the nonspherical case. A high-quality mesh of the bubble surface is maintained by implementing a hybrid approach of the Lagrangian method and elastic mesh technique. Numerical analyses for the dynamics of UCAs in an infinite liquid and near a rigid wall are performed in parameter regimes of clinical relevance. The results show that the presence of a coating significantly reduces the oscillation amplitude and period, increases the ultrasound pressure amplitude required to incite jetting, and reduces the jet width and velocity.
The Rufous Hummingbird in hovering flight -- full-body 3D immersed boundary simulation
NASA Astrophysics Data System (ADS)
Ferreira de Sousa, Paulo; Luo, Haoxiang; Bocanegra Evans, Humberto
2009-11-01
Hummingbirds are an interesting case study for the development of micro-air vehicles since they combine the high flight stability of insects with the low metabolic power per unit of body mass of bats, during hovering flight. In this study, simulations of a full-body hummingbird in hovering flight were performed at a Reynolds number around 3600. The simulations employ a versatile sharp-interface immersed boundary method recently enhanced at our lab that can treat thin membranes and solid bodies alike. Implemented on a Cartesian mesh, the numerical method allows us to capture the vortex dynamics of the wake accurately and efficiently. The whole-body simulation will allow us to clearly identify the three general patterns of flow velocity around the body of the hummingbird referred in Altshuler et al. (Exp Fluids 46 (5), 2009). One focus of the current study is to understand the interaction between the wakes of the two wings at the end of the upstroke, and how the tail actively defects the flow to contribute to pitch stability. Another focus of the study will be to identify the pair of unconnected loops underneath each wing.
Bae, Sung-Kuk; Choi, Beomjoon; Chung, Haseung; Shin, Seungwon; Song, Hee-eun; Seo, Jung Hwan
2016-01-01
This article presents a novel technique to estimate the mechanical properties of the aluminum composite layer on silicon solar cells by using a hybrid 3-dimensional laser scanning force measurement (3-D LSFM) system. The 3-D LSFM system measures the material properties of sub-layers constituting a solar cell. This measurement is critical for realizing high-efficient ultra-thin solar cells. The screen-printed aluminum layer, which significantly affects the bowing phenomenon, is separated from the complete solar cell by removing the silicon (Si) layer with deep reactive ion etching. An elastic modulus of ~15.1 GPa and a yield strength of ~35.0 MPa for the aluminum (Al) composite layer were obtained by the 3-D LSFM system. In experiments performed for 6-inch Si solar cells, the bowing distances decreased from 12.02 to 1.18 mm while the Si layer thicknesses increased from 90 to 190 μm. These results are in excellent agreement with the theoretical predictions for ultra-thin Si thickness (90 μm) based on the obtained Al composite layer properties. PMID:26948248
NASA Astrophysics Data System (ADS)
Bae, Sung-Kuk; Choi, Beomjoon; Chung, Haseung; Shin, Seungwon; Song, Hee-Eun; Seo, Jung Hwan
2016-03-01
This article presents a novel technique to estimate the mechanical properties of the aluminum composite layer on silicon solar cells by using a hybrid 3-dimensional laser scanning force measurement (3-D LSFM) system. The 3-D LSFM system measures the material properties of sub-layers constituting a solar cell. This measurement is critical for realizing high-efficient ultra-thin solar cells. The screen-printed aluminum layer, which significantly affects the bowing phenomenon, is separated from the complete solar cell by removing the silicon (Si) layer with deep reactive ion etching. An elastic modulus of ~15.1 GPa and a yield strength of ~35.0 MPa for the aluminum (Al) composite layer were obtained by the 3-D LSFM system. In experiments performed for 6-inch Si solar cells, the bowing distances decreased from 12.02 to 1.18 mm while the Si layer thicknesses increased from 90 to 190 μm. These results are in excellent agreement with the theoretical predictions for ultra-thin Si thickness (90 μm) based on the obtained Al composite layer properties.