2D and 3D Numerical Simulations of Flux Cancellation
NASA Technical Reports Server (NTRS)
Karpen, Judith T.; DeVore, C.; Antiochos, S. K.; Linton, M. G.
2009-01-01
Cancellation of magnetic flux in the solar photosphere and chromosphere has been linked observationally and theoretically to a broad range of solar activity, from filament channel formation to CME initiation. Because this phenomenon is typically measured at only a single layer in the atmosphere, in the radial (line of sight) component of the magnetic field, the actual processes behind this observational signature are ambiguous. It is clear that reconnection is involved in some way, but the location of the reconnection sites and associated connectivity changes remain uncertain in most cases. We are using numerical modeling to demystify flux cancellation, beginning with the simplest possible configuration: a subphotospheric Lundquist flux tube surrounded by a potential field, immersed in a gravitationally stratified atmosphere, spanning many orders of magnitude in plasma beta. In this system, cancellation is driven slowly by a 2-cell circulation pattern imposed in the convection zone, such that the tops of the cells are located around the beta=1 level (i.e., the photosphere) and the flows converge and form a downdraft at the polarity inversion line; note however that no flow is imposed along the neutral line. We will present the results of 2D and 3D MHD-AMR simulations of flux cancellation, in which the flux at the photosphere begins in either an unsheared or sheared state. In all cases, a low-lying flux rope is formed by reconnection at the polarity inversion line within a few thousand seconds. The flux rope remains stable and does not rise, however, in contrast to models which do not include the presence of significant mass loading.
Numerical simulation of rock cutting using 2D AUTODYN
NASA Astrophysics Data System (ADS)
Woldemichael, D. E.; Rani, A. M. Abdul; Lemma, T. A.; Altaf, K.
2015-12-01
In a drilling process for oil and gas exploration, understanding of the interaction between the cutting tool and the rock is important for optimization of the drilling process using polycrystalline diamond compact (PDC) cutters. In this study the finite element method in ANSYS AUTODYN-2D is used to simulate the dynamics of cutter rock interaction, rock failure, and fragmentation. A two-dimensional single PDC cutter and rock model were used to simulate the orthogonal cutting process and to investigate the effect of different parameters such as depth of cut, and back rake angle on two types of rocks (sandstone and limestone). In the simulation, the cutting tool was dragged against stationary rock at predetermined linear velocity and the depth of cut (1,2, and 3 mm) and the back rake angles(-10°, 0°, and +10°) were varied. The simulation result shows that the +10° back rake angle results in higher rate of penetration (ROP). Increasing depth of cut leads to higher ROP at the cost of higher cutting force.
Numerical simulation of 2D buoyant jets in ice-covered and temperature-stratified water
NASA Astrophysics Data System (ADS)
Gu, Ruochuan
A two-dimensional (2D) unsteady simulation model is applied to the problem of a submerged warm water discharge into a stratified lake or reservoir with an ice cover. Numerical simulations and analyses are conducted to gain insight into large-scale convective recirculation and flow processes in a cold waterbody induced by a buoyant jet. Jet behaviors under various discharge temperatures are captured by directly modeling flow and thermal fields. Flow structures and processes are described by the simulated spatial and temporal distributions of velocity and temperature in various regions: deflection, recirculation, attachment, and impingement. Some peculiar hydrothermal and dynamic features, e.g. reversal of buoyancy due to the dilution of a warm jet by entraining cold ambient water, are identified and examined. Simulation results show that buoyancy is the most important factor controlling jet behavior and mixing processes. The inflow boundary is treated as a liquid wall from which the jet is offset. Similarity and difference in effects of boundaries perpendicular and parallel to flow, and of buoyancy on jet attachment and impingement, are discussed. Symmetric flow configuration is used to de-emphasize the Coanda effect caused by offset.
A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds
Li, Tingwen; Zhang, Yongmin
2013-10-11
Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.
Direct numerical simulation of a 2D-stented aortic heart valve at physiological flow rates.
Dimakopoulos, Y; Bogaerds, A C B; Anderson, P D; Hulsen, M A; Baaijens, F P T
2012-01-01
We study the nonlinear interaction of an aortic heart valve, composed of hyperelastic corrugated leaflets of finite density attached to a stented vessel under physiological flow conditions. In our numerical simulations, we use a 2D idealised representation of this arrangement. Blood flow is caused by a time-varying pressure gradient that mimics that of the aortic valve and corresponds to a peak Reynolds number equal to 4050. Here, we fully account for the shear-thinning behaviour of the blood and large deformations and contact between the leaflets by solving the momentum and mass balances for blood and leaflets. The mixed finite element/Galerkin method along with linear discontinuous Lagrange multipliers for coupling the fluid and elastic domains is adopted. Moreover, a series of challenging numerical issues such as the finite length of the computational domain and the conditions that should be imposed on its inflow/outflow boundaries, the accurate time integration of the parabolic and hyperbolic momentum equations, the contact between the leaflets and the non-conforming mesh refinement in part of the domain are successfully resolved. Calculations for the velocity and the shear stress fields of the blood reveal that boundary layers appear on both sides of a leaflet. The one along the ventricular side transfers blood with high momentum from the core region of the vessel to the annulus or the sinusoidal expansion, causing the continuous development of flow instabilities. At peak systole, vortices are convected in the flow direction along the annulus of the vessel, whereas during the closure stage of the valve, an extremely large vortex develops in each half of the flow domain.
2-D MHD numerical simulations of EML plasma armatures with ablation
NASA Astrophysics Data System (ADS)
Boynton, G. C.; Huerta, M. A.; Thio, Y. C.
1993-01-01
We use a 2-D) resistive MHD code to simulate an EML plasma armature. The energy equation includes Ohmic heating, radiation heat transport and the ideal gas equation of state, allowing for variable ionization using the Saha equations. We calculate rail ablation taking into account the flow of heat into the interior of the rails. Our simulations show the development of internal convective flows and secondary arcs. We use an explicit Flux Corrected Transport algorithm to advance all quantities in time.
NASA Astrophysics Data System (ADS)
Wang, X.; Cai, M.
2016-11-01
A nonlinear velocity model that considers the influence of confinement and rock mass failure on wave velocity is developed. A numerical method, which couples FLAC and SPECFEM2D, is developed for ground motion modeling near excavation boundaries in underground mines. The motivation of developing the FLAC/SPECFEM2D coupled approach is to take merits of each code, such as the stress analysis capability in FLAC and the powerful wave propagation analysis capability in SPECFEM2D. Because stress redistribution and failure of the rock mass around an excavation are considered, realistic non-uniform velocity fields for the SPECFEM2D model can be obtained, and this is a notable feature of this study. Very large differences in wavefields and ground motion are observed between the results from the non-uniform and the uniform velocity models. If the non-uniform velocity model is used, the ground motion around a stope can be amplified up to five times larger than that given by the design scaling law. If a uniform velocity model is used, the amplification factor is only about three. Using the FLAC/SPECFEM2D coupled modeling approach, accurate velocity models can be constructed and this in turn will assist in predicting ground motions accurately around underground excavations.
Numerical Simulation of Slinger Combustor Using 2-D Axisymmetric Computational Model
NASA Astrophysics Data System (ADS)
Lee, Semin; Park, Soo Hyung; Lee, Donghun
2010-06-01
Small-size turbojet engines have difficulties in maintaining the chemical reaction due to the limitation of chamber size. The combustion chamber is generally designed to improve the reaction efficiency by the generation of vortices in the chamber and to enhance air-fuel mixing characteristics. In the initial stage of designing the combustor, analysis of the 3-D full configuration is not practical due to the huge time consuming computation and grid generation followed by modifications of the geometry. In the present paper, an axisymmetric model maintaining geometric similarity and flow characteristic of 3-D configuration is developed. Based on numerical results from the full 3-D configuration, model reduction is achieved toward 2-D axisymmetric configuration. In the modeling process, the area and location of each hole in 3-D full configuration are considered reasonably and replaced to the 2-D axisymmetric model. By using the 2-D axisymmetric model, the factor that can affect the performance is investigated with the assumption that the flow is non-reacting and turbulent. Numerical results from the present model show a good agreement with numerical results from 3-D full configuration model such as existence of vortex pair in forward region and total pressure loss. By simplifying the complex 3-D model, computing time can be remarkably reduced and it makes easy to find effects of geometry modification.
2D Numerical simulations of intraoceanic subduction: the case study of the Ligurian Alps.
NASA Astrophysics Data System (ADS)
Malatesta, Cristina; Gerya, Taras; Federico, Laura; Scambelluri, Marco; Crispini, Laura; Capponi, Giovanni
2010-05-01
Intraoceanic subduction is an important part of the present and past subduction systems, and some features of such process are not yet fully understood. We therefore studied intraoceanic subduction zones with the help of 2D numerical models, analyzing the parameters influencing their evolution in time and space. We applied the finite differences method on a rectangular grid, to calculate properties such as pressure, temperatures and velocities inside the models solving a set of equations. The latter comprise the Stokes equation of motion, the continuity equation and the heat transport equation. Temperature and velocities are computed on the nodes of the grid whereas pressures are calculated for the geometrical centers of the cells. We defined material properties such as density or viscosity on marker points, initially positioned on a regular rectangular grid. The markers and therefore the material properties are moved through the mesh according to the velocity field using the forth order Runge-Kutta method (Gerya et al. 2002). Subduction is forced to begin at a weak zone in the lithospheric mantle within an oceanic basin of prescribed width. The effect of different arrangements of rock bodies inside the subducting lithosphere on the evolution of the process was carefully analyzed. In particular we reproduced two distinct structures of the oceanic lithosphere: i) the layered oceanic crust made up of a stratified succession typical of fast-spreading ridges and ii) the oceanic lithosphere typical of slow and ultra-slow spreading centers, where an incomplete sequence is observable. The latter structure lacks a sheeted dike complex, has a low volume of gabbros and basalts and gabbros form discrete intrusions in variably serpentinized peridotites (Lagabrielle et al., 1997; Mével, 2003). Such an "heterogeneous" structure is characteristic of the Alpine and Appennine ophiolites that characterized the Mesozoic Ligurian Tethys located between Europe and Adria. The depth of
NASA Astrophysics Data System (ADS)
Schaerlaekens, J.; Mallants, D.; Imûnek, J.; van Genuchten, M. Th.; Feyen, J.
1999-12-01
Microbiological degradation of perchloroethylene (PCE) under anaerobic conditions follows a series of chain reactions, in which, sequentially, trichloroethylene (TCE), cis-dichloroethylene (c-DCE), vinylchloride (VC) and ethene are generated. First-order degradation rate constants, partitioning coefficients and mass exchange rates for PCE, TCE, c-DCE and VC were compiled from the literature. The parameters were used in a case study of pump-and-treat remediation of a PCE-contaminated site near Tilburg, The Netherlands. Transport, non-equilibrium sorption and biodegradation chain processes at the site were simulated using the CHAIN_2D code without further calibration. The modelled PCE compared reasonably well with observed PCE concentrations in the pumped water. We also performed a scenario analysis by applying several increased reductive dechlorination rates, reflecting different degradation conditions (e.g. addition of yeast extract and citrate). The scenario analysis predicted considerably higher concentrations of the degradation products as a result of enhanced reductive dechlorination of PCE. The predicted levels of the very toxic compound VC were now an order of magnitude above the maximum permissible concentration levels.
Numerical Simulations of High-Frequency Respiratory Flows in 2D and 3D Lung Bifurcation Models
NASA Astrophysics Data System (ADS)
Chen, Zixi; Parameswaran, Shamini; Hu, Yingying; He, Zhaoming; Raj, Rishi; Parameswaran, Siva
2014-07-01
To better understand the human pulmonary system and optimize the high-frequency oscillatory ventilation (HFOV) design, numerical simulations were conducted under normal breathing frequency and HFOV condition using a CFD code Ansys Fluent and its user-defined C programs. 2D and 3D double bifurcating lung models were created, and the geometry corresponds to fifth to seventh generations of airways with the dimensions based on the Weibel's pulmonary model. Computations were carried out for different Reynolds numbers (Re = 400 and 1000) and Womersley numbers (α = 4 and 16) to study the air flow fields, gas transportation, and wall shear stresses in the lung airways. Flow structure was compared with experimental results. Both 2D and 3D numerical models successfully reproduced many results observed in the experiment. The oxygen concentration distribution in the lung model was investigated to analyze the influence of flow oscillation on gas transport inside the lung model.
The 1963 Vajont landslide (Italy) simulated through a numerical 2D code
NASA Astrophysics Data System (ADS)
Zaniboni, Filippo; Ausilia Paparo, Maria; Elsen, Katharina; Tinti, Stefano
2013-04-01
On October 9th, 1963, a huge mass of about 260 million m3 collapsed along Mt. Toc flank into the artificial lake called Vajont and generated a gigantic wave that invested the town of Longarone (North-East Italy, about 100 km north of Venice), provoking about 2000 casualties. The event started a public debate on the responsibilities for the disaster, and also raised crucial issues for the scientific and engineering community, regarding reservoir flank instability and safety of the hydroelectric plant. The peculiar features of the event were immediately evident. The clay layers remained uncovered in the upper part of the detachment niche, supporting the hypothesis of a well-defined pre-existing sliding surface, that could explain the high falling velocity (around 20 m/s as a maximum) and the compactness of the deposit layers that were found to sit almost unperturbed on the bottom of the valley. The numerical study presented here contributes to the understanding of dynamics of the Vajont landslide. It is found that the accurate knowledge of the pre- and post-slide morphology provides tight constraints on the parameters of the numerical model, that are tuned to fit the observed deposit. Numerical simulations are carried out by means of the in-house built code UBO-BLOCK2. The initial sliding body is divided into a mesh of interacting volume-conserving blocks, whose motion is computed numerically. The friction coefficient at the base of the landslide is determined through a best fit search by maximizing the degree of overlapping between the calculated and observed deposits. Our best solution is also able to account for the observed slight easterly rotation of the mass, the different behaviors of the eastern and western part of the sliding surface and the retrogressive motion of the slide that after climbing up the opposite flank of the valley reverted velocity to settle down on the bottom of the valley.
NASA Technical Reports Server (NTRS)
Kapoor, Kamlesh; Anderson, Bernhard H.; Shaw, Robert J.
1994-01-01
A two-dimensional computational code, PRLUS2D, which was developed for the reactive propulsive flows of ramjets and scramjets, was validated for two-dimensional shock-wave/turbulent-boundary-layer interactions. The problem of compression corners at supersonic speeds was solved using the RPLUS2D code. To validate the RPLUS2D code for hypersonic speeds, it was applied to a realistic hypersonic inlet geometry. Both the Baldwin-Lomax and the Chien two-equation turbulence models were used. Computational results showed that the RPLUS2D code compared very well with experimentally obtained data for supersonic compression corner flows, except in the case of large separated flows resulting from the interactions between the shock wave and turbulent boundary layer. The computational results compared well with the experiment results in a hypersonic NASA P8 inlet case, with the Chien two-equation turbulence model performing better than the Baldwin-Lomax model.
NASA Astrophysics Data System (ADS)
Krause, M.; Camenzind, M.
2001-12-01
In the present paper, we examine the convergence behavior and inter-code reliability of astrophysical jet simulations in axial symmetry. We consider both pure hydrodynamic jets and jets with a dynamically significant magnetic field. The setups were chosen to match the setups of two other publications, and recomputed with the MHD code NIRVANA. We show that NIRVANA and the two other codes give comparable, but not identical results. We explain the differences by the different application of artificial viscosity in the three codes and numerical details, which can be summarized in a resolution effect, in the case without magnetic field: NIRVANA turns out to be a fair code of medium efficiency. It needs approximately twice the resolution as the code by Lind (Lind et al. 1989) and half the resolution as the code by Kössl (Kössl & Müller 1988). We find that some global properties of a hydrodynamical jet simulation, like e.g. the bow shock velocity, converge at 100 points per beam radius (ppb) with NIRVANA. The situation is quite different after switching on the toroidal magnetic field: in this case, global properties converge even at 10 ppb. In both cases, details of the inner jet structure and especially the terminal shock region are still insufficiently resolved, even at our highest resolution of 70 ppb in the magnetized case and 400 ppb for the pure hydrodynamic jet. The magnetized jet even suffers from a fatal retreat of the Mach disk towards the inflow boundary, which indicates that this simulation does not converge, in the end. This is also in definite disagreement with earlier simulations, and challenges further studies of the problem with other codes. In the case of our highest resolution simulation, we can report two new features: first, small scale Kelvin-Helmholtz instabilities are excited at the contact discontinuity next to the jet head. This slows down the development of the long wavelength Kelvin-Helmholtz instability and its turbulent cascade to smaller
A Parallel 2D Numerical Simulation of Tumor Cells Necrosis by Local Hyperthermia
NASA Astrophysics Data System (ADS)
Reis, R. F.; Loureiro, F. S.; Lobosco, M.
2014-03-01
Hyperthermia has been widely used in cancer treatment to destroy tumors. The main idea of the hyperthermia is to heat a specific region like a tumor so that above a threshold temperature the tumor cells are destroyed. This can be accomplished by many heat supply techniques and the use of magnetic nanoparticles that generate heat when an alternating magnetic field is applied has emerged as a promise technique. In the present paper, the Pennes bioheat transfer equation is adopted to model the thermal tumor ablation in the context of magnetic nanoparticles. Numerical simulations are carried out considering different injection sites for the nanoparticles in an attempt to achieve better hyperthermia conditions. Explicit finite difference method is employed to solve the equations. However, a large amount of computation is required for this purpose. Therefore, this work also presents an initial attempt to improve performance using OpenMP, a parallel programming API. Experimental results were quite encouraging: speedups around 35 were obtained on a 64-core machine.
NASA Astrophysics Data System (ADS)
Smirnov, E. M.; Smirnovsky, A. A.; Schur, N. A.; Zaitsev, D. K.; Smirnov, P. E.
2016-09-01
The contribution covers results of numerical study of air flow and heat transfer past a backward-facing step at the Reynolds number of 28,000. The numerical simulation was carried out under conditions of the experiments of Vogel&Eaton (1985), where nominally 2D fluid dynamics and heat transfer in a channel with expansion ratio of 1.25 was investigated. Two approaches were used for turbulence modelling. First, the Menter SST turbulence model was used to perform refined 2D and 3D RANS steady-state computations. The 3D analysis was undertaken to evaluate effects of boundary layers developing on the sidewalls of the experimental channel. Then, 3D time-dependent computations were carried out using the vortex-resolving IDDES method and applying the spanwise-periodicity conditions. Comparative computations were performed using an in-house finite-volume code SINF/Flag-S and the ANSYS Fluent. The codes produced practically identical RANS solutions, showing in particular a difference of 4% in the central-line peak Stanton number calculated in 2D and 3D cases. The IDDES results obtained with two codes are in a satisfactory agreement. Comparing with the experimental data, the IDDES produces the best agreement for the wall friction, whereas the RANS solutions show superiority in predictions of the local Stanton number distribution.
NASA Astrophysics Data System (ADS)
Zhao, J. W.; Ding, G. H.; Yin, W. Y.; Yang, X. J.; Shi, W. C.; Zhang, X. L.
The objective of this study is to investigate the effect of hemodynamic parameters on the formation, growth and rupture of an aneurysm. Our simulation of the elastic and rigid aneurysm is based on a DSA or other clinic image. The simulatied results are that there are great differences in the distribution of velocity magnitude at some sections which are predicted by the two models. For the elastic wall model, the distribution of velocity magnitude of one outlet is obviously off-center, which influences the distribution of wall shear stress (WSS) and exchange of substance through the vessel wall. The currents of the distributions of WSS along the wall of aneurysm for the two models are similar. But there are obvious differences between the two models in the values especially at the neck of aneurysm. This study demonstrates obviously that the elastic wall model suits the simulation for growth and rupture of an aneurysm better.
NASA Astrophysics Data System (ADS)
Gramusset, Anneli; Herrera, Paulo; Parada, Miguel Angel
2014-05-01
A thorough understanding of the thermal processes that occur in aquifers is essential to assess local and regional low enthalpy geothermal resources. The relationship between heat convection and heat conduction has been widely studied in basins around the world at a regional scale. However, few studies have focused on smaller, shallower basins containing free aquifers hosted in unconsolidated fluvial-alluvial sediments, like Santiago Basin. We use numerical modeling to simulate the fluid dynamics of the Santiago basin groundwater system under different thermal conditions. Despite the current computational advances, modeling such a complex system with a full 3D approach is still numerically time demanding and unstable. Besides, the basin has irregular geometry and variable hydraulic and thermal features. Thus, we performed a 2D model comprising a thin water saturated slice of sediments beneath the central part of the city, where the basin morphology is well constrained. We simulate coupled groundwater and heat flow throughout this vertical slice and we compare results for different scenarios that comprise different hydraulic, thermal and geometric parameters. Results obtained with certain hydraulic conductivities show that instabilities appear giving rise to free thermal convection in the deepest parts of the basin. If the system is split into several hydrogeological units, the onset of these instabilities is inhibited. Consequently, we suggest that the stratigraphic complexities of a fluvial-alluvial deposit should be considered to better understanding the thermal-driven groundwater fluid dynamics.
NASA Astrophysics Data System (ADS)
Hallo, L.; Olazabal-Loumé, M.; Maire, P. H.; Breil, J.; Morse, R.-L.; Schurtz, G.
2006-06-01
This paper deals with ablation front instabilities simulations in the context of direct drive ICF. A simplified DT target, representative of realistic target on LIL is considered. We describe here two numerical approaches: the linear perturbation method using the perturbation codes Perle (planar) and Pansy (spherical) and the direct simulation method using our Bi-dimensional hydrodynamic code Chic. Numerical solutions are shown to converge, in good agreement with analytical models.
NASA Technical Reports Server (NTRS)
Scalapino, D. J.; Sugar, R. L.; White, S. R.; Bickers, N. E.; Scalettar, R. T.
1989-01-01
Numerical simulations on the half-filled three-dimensional Hubbard model clearly show the onset of Neel order. Simulations of the two-dimensional electron-phonon Holstein model show the competition between the formation of a Peierls-CDW state and a superconducting state. However, the behavior of the partly filled two-dimensional Hubbard model is more difficult to determine. At half-filling, the antiferromagnetic correlations grow as T is reduced. Doping away from half-filling suppresses these correlations, and it is found that there is a weak attractive pairing interaction in the d-wave channel. However, the strength of the pair field susceptibility is weak at the temperatures and lattice sizes that have been simulated, and the nature of the low-temperature state of the nearly half-filled Hubbard model remains open.
Numerical Evaluation of 2D Ground States
NASA Astrophysics Data System (ADS)
Kolkovska, Natalia
2016-02-01
A ground state is defined as the positive radial solution of the multidimensional nonlinear problem
Realistic and efficient 2D crack simulation
NASA Astrophysics Data System (ADS)
Yadegar, Jacob; Liu, Xiaoqing; Singh, Abhishek
2010-04-01
Although numerical algorithms for 2D crack simulation have been studied in Modeling and Simulation (M&S) and computer graphics for decades, realism and computational efficiency are still major challenges. In this paper, we introduce a high-fidelity, scalable, adaptive and efficient/runtime 2D crack/fracture simulation system by applying the mathematically elegant Peano-Cesaro triangular meshing/remeshing technique to model the generation of shards/fragments. The recursive fractal sweep associated with the Peano-Cesaro triangulation provides efficient local multi-resolution refinement to any level-of-detail. The generated binary decomposition tree also provides efficient neighbor retrieval mechanism used for mesh element splitting and merging with minimal memory requirements essential for realistic 2D fragment formation. Upon load impact/contact/penetration, a number of factors including impact angle, impact energy, and material properties are all taken into account to produce the criteria of crack initialization, propagation, and termination leading to realistic fractal-like rubble/fragments formation. The aforementioned parameters are used as variables of probabilistic models of cracks/shards formation, making the proposed solution highly adaptive by allowing machine learning mechanisms learn the optimal values for the variables/parameters based on prior benchmark data generated by off-line physics based simulation solutions that produce accurate fractures/shards though at highly non-real time paste. Crack/fracture simulation has been conducted on various load impacts with different initial locations at various impulse scales. The simulation results demonstrate that the proposed system has the capability to realistically and efficiently simulate 2D crack phenomena (such as window shattering and shards generation) with diverse potentials in military and civil M&S applications such as training and mission planning.
NASA Astrophysics Data System (ADS)
Farsi, Mohammad; Ghadimi, Parviz
2014-09-01
Main aim of this paper is to find the best combination of numerical schemes for 2-D SPH simulation of wedge water entry. Diffusion term is considered as laminar, turbulent, and artificial viscosity. Density filter that seriously affects the pressure distribution is investigated by adopting no filter, first order filter, and second order filter. Validation of the results indicates that turbulent model and first order density filter can lead to more reasonable solutions. This simulation was then conducted for wedge water entry with wide range of deadrise angles including 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees and 81 degrees, with extreme deadrise angles of 10 degrees, 60 degrees and 81 degrees being considered. Comparison of SPH results with BEM solutions has displayed favorable agreement. In two particular cases where experimental data are available, the SPH results are shown to be closer to the experiments than BEM solution. While, accuracy of the obtained results for moderate deadrise angles is desirable, numerical findings for very small or very large deadrise angles are also very reasonable
NASA Astrophysics Data System (ADS)
Ghizzo, A.; Bertrand, P.; Lebas, J.; Shoucri, M.; Johnston, T.; Fijalkow, E.; Feix, M. R.
1992-10-01
The present 1 1/2D relativistic Euler-Vlasov code has been used to check the validity of a hydrodynamic description used in a 1D version of the Vlasov code. By these means, detailed numerical results can be compared; good agreement furnishes full support for the 1D electromagnetic Vlasov code, which runs faster than the 1 1/2D code. The results obtained assume a nonrelativistic v(y) velocity.
NASA Astrophysics Data System (ADS)
López-Venegas, Alberto M.; Horrillo, Juan; Pampell-Manis, Alyssa; Huérfano, Victor; Mercado, Aurelio
2015-06-01
The most recent tsunami observed along the coast of the island of Puerto Rico occurred on October 11, 1918, after a magnitude 7.2 earthquake in the Mona Passage. The earthquake was responsible for initiating a tsunami that mostly affected the northwestern coast of the island. Runup values from a post-tsunami survey indicated the waves reached up to 6 m. A controversy regarding the source of the tsunami has resulted in several numerical simulations involving either fault rupture or a submarine landslide as the most probable cause of the tsunami. Here we follow up on previous simulations of the tsunami from a submarine landslide source off the western coast of Puerto Rico as initiated by the earthquake. Improvements on our previous study include: (1) higher-resolution bathymetry; (2) a 3D-2D coupled numerical model specifically developed for the tsunami; (3) use of the non-hydrostatic numerical model NEOWAVE (non-hydrostatic evolution of ocean WAVE) featuring two-way nesting capabilities; and (4) comprehensive energy analysis to determine the time of full tsunami wave development. The three-dimensional Navier-Stokes model tsunami solution using the Navier-Stokes algorithm with multiple interfaces for two fluids (water and landslide) was used to determine the initial wave characteristic generated by the submarine landslide. Use of NEOWAVE enabled us to solve for coastal inundation, wave propagation, and detailed runup. Our results were in agreement with previous work in which a submarine landslide is favored as the most probable source of the tsunami, and improvement in the resolution of the bathymetry yielded inundation of the coastal areas that compare well with values from a post-tsunami survey. Our unique energy analysis indicates that most of the wave energy is isolated in the wave generation region, particularly at depths near the landslide, and once the initial wave propagates from the generation region its energy begins to stabilize.
NASA Astrophysics Data System (ADS)
Constantinescu, R.; Thouret, J. C.; Sandri, L.; Irimus, I. A.; Stefanescu, R.
2012-04-01
Pyroclastic density currents, which include pyroclastic surges and pyroclastic flows (PFs), are among the most dangerous volcanic phenomena. We present a probabilistic hazard assessment of the PFs generated from eruptive column collapse at El Misti volcano (5822 m) in South Peru. The high relief of the cone, the location of the city of Arequipa (~1,000,000 people) on two large volcanoclastic fans and the H (3.5 km)/L (17 km) ratio (0.2) between the summit and the city center, make PFs a direct threat. We consider three eruption scenario sizes: small Vulcanian/Phreatomagmatic (VEI 2), medium Sub-Plinian (VEI 3-4), and large Plinian (VEI 4+). We use the Event-Tree approach in a Bayesian scheme with BET_VH (Bayesian Event Tree for Volcanic Hazard) software. Quantitative data that stem from numerical simulations from TITAN2D (termed prior models) and from stratigraphic record (termed past data) are input to BET_VH, which enables us to compute the probabilities (in a 1-year time window) of (i) having an eruption (ii) in a selected location/vent (iii) of a specific size, (iv) and that this eruption will produce PFs (v) that will reach a location of interest around El Misti. TITAN2D simulation runs, expressed as color-coded thicknesses of PDC deposits, fit well the extent of past PFs deposits, including thick confined deposits (0.5-7 m) in the Rio Chili canyon and its tributary ravines (Quebradas San Lazaro, Huarangal and Agua Salada).The unconfined, thinner (≤10cm) deposits, as displayed by simulation runs on the interfluves, is attributed to ash-cloud surges. Such thin, fine ash deposits have not been emphasized in geological maps either because they have been removed away or remain yet unrecognized. The simulated Vulcanian flows, restricted to the upper part of the cone, become confined (0.1-1m thick) in the ravines which converge towards each of the three Quebradas. The simulated Subplinian PF deposits reach 0.1 to 1 m thick in the Quebradas and 1-4 m WNW of El
NASA Astrophysics Data System (ADS)
Tirupathi, S.; Schiemenz, A. R.; Liang, Y.; Parmentier, E.; Hesthaven, J.
2013-12-01
The style and mode of melt migration in the mantle are important to the interpretation of basalts erupted on the surface. Both grain-scale diffuse porous flow and channelized melt migration have been proposed. To better understand the mechanisms and consequences of melt migration in a heterogeneous mantle, we have undertaken a numerical study of reactive dissolution in an upwelling and viscously deformable mantle where solubility of pyroxene increases upwards. Our setup is similar to that described in [1], except we use a larger domain size in 2D and 3D and a new numerical method. To enable efficient simulations in 3D through parallel computing, we developed a high-order accurate numerical method for the magma dynamics problem using discontinuous Galerkin methods and constructed the problem using the numerical library deal.II [2]. Linear stability analyses of the reactive dissolution problem reveal three dynamically distinct regimes [3] and the simulations reported in this study were run in the stable regime and the unstable wave regime where small perturbations in porosity grows periodically. The wave regime is more relevant to melt migration beneath the mid-ocean ridges but computationally more challenging. Extending the 2D simulations in the stable regime in [1] to 3D using various combinations of sustained perturbations in porosity at the base of the upwelling column (which may result from a viened mantle), we show the geometry and distribution of dunite channel and high-porosity melt channels are highly correlated with inflow perturbation through superposition. Strong nonlinear interactions among compaction, dissolution, and upwelling give rise to porosity waves and high-porosity melt channels in the wave regime. These compaction-dissolution waves have well organized but time-dependent structures in the lower part of the simulation domain. High-porosity melt channels nucleate along nodal lines of the porosity waves, growing downwards. The wavelength scales
NASA Astrophysics Data System (ADS)
Zhao, Yi; Fu, Ceji
2016-10-01
Tailoring the spectrum of thermal emission from the emitter is important for improving the performance of a thermophotovoltaic (TPV) system. In this work, a two-dimensional (2D) layered grating structure made of SiO2 and tungsten (W), which can realize wavelength-selective control of thermal emission, was proposed for a potential emitter in TPV applications. Numerical simulations of the spectral emissivity of the structure from the ultraviolet (UV) to the mid-infrared region reveals that the spectral-normal emissivity of the structure is enhanced to above 0.95 in the wavelength region from 0.55 μm to 1.9 μm for both TE and TM waves, but drops sharply at wavelength larger than 2 μm. Physical mechanisms responsible for the wavelength-selective emissivity were elucidated as due to resonance of magnetic polaritons (MPs) in the SiO2 spacer and in the grooves of the tungsten grating, Wood's anomaly (WA), excitation of surface plasmon polaritons (SPPs) and wave interference. Furthermore, the structure was found to exhibit quasi-diffuse and polarization-insensitive features of thermal emission, suggesting that the proposed structure can serve as the emitter in the design of high performance TPV systems.
Simulation of Yeast Cooperation in 2D.
Wang, M; Huang, Y; Wu, Z
2016-03-01
Evolution of cooperation has been an active research area in evolutionary biology in decades. An important type of cooperation is developed from group selection, when individuals form spatial groups to prevent them from foreign invasions. In this paper, we study the evolution of cooperation in a mixed population of cooperating and cheating yeast strains in 2D with the interactions among the yeast cells restricted to their small neighborhoods. We conduct a computer simulation based on a game theoretic model and show that cooperation is increased when the interactions are spatially restricted, whether the game is of a prisoner's dilemma, snow drifting, or mutual benefit type. We study the evolution of homogeneous groups of cooperators or cheaters and describe the conditions for them to sustain or expand in an opponent population. We show that under certain spatial restrictions, cooperator groups are able to sustain and expand as group sizes become large, while cheater groups fail to expand and keep them from collapse.
NASA Astrophysics Data System (ADS)
Castro, Maria Clara; Patriarche, Delphine; Goblet, Patrick
2005-09-01
Because helium and heat production results from a common source, a continental 4He crustal flux of 4.65 * 10 - 14 mol m - 2 s - 1 has been estimated based on heat flow considerations. In addition, because the observed mantle He / heat flux ratio at the proximity of mid-ocean ridges (6.6 * 10 - 14 mol J - 1 ) is significantly lower than the radiogenic production ratio (1.5 * 10 - 12 mol J - 1 ), the presence of a terrestrial helium-heat imbalance was suggested. The latter could be explained by the presence of a layered mantle in which removal of He is impeded from the lower mantle [R.K. O'Nions, E.R. Oxburgh, Heat and helium in the Earth, Nature 306 (1983) 429-431; E.R. Oxburgh, R.K. O'Nions, Helium loss, tectonics, and the terrestrial heat budget, Science 237 (1987) 1583-1588]. van Keken et al. [P.E. van Keken, C.J. Ballentine, D. Porcelli, A dynamical investigation of the heat and helium imbalance, Earth Planet, Sci. Lett. 188 (2001) 421-434] have recently claimed that the helium-heat imbalance remains a robust observation. Such conclusions, however, were reached under the assumption that a steady-state regime was in place for both tracers and that their transport properties are similar at least in the upper portion of the crust. Here, through 2-D simulations of groundwater flow, heat transfer and 4He transport carried out simultaneously in the Carrizo aquifer and surrounding formations in southwest Texas, we assess the legitimacy of earlier assumptions. Specifically, we show that the driving transport mechanisms for He and heat are of a fundamentally different nature for a high range of permeabilities ( k ≤ 10 - 16 m 2) found in metamorphic and volcanic rocks at all depths in the crust. The assumption that transport properties for these two tracers are similar in the crust is thus unsound. We also show that total 4He / heat flux ratios lower than radiogenic production ratios do not reflect a He deficit in the crust or mantle original reservoir. Instead, they
NASA Technical Reports Server (NTRS)
Mikellides, Ioannis G.; Katz, Ira; Goebel, Dan M.; Jameson, Kristina K.
2006-01-01
Numerical simulations with the time-dependent Orificed Cathode (OrCa2D-II) computer code show that classical enhancements of the plasma resistivity can not account for the elevated electron temperatures and steep plasma potential gradients measured in the plume of a 25-27.5 A discharge hollow cathode. The cathode, which employs a 0.11-in diameter orifice, was operated at 5.5 sccm without an applied magnetic field using two different anode geometries. It is found that anomalous resistivity based on electron-driven instabilities improves the comparison between theory and experiment. It is also estimated that other effects such as the Hall-effect from the self-induced magnetic field, not presently included in OrCa2D-II, may contribute to the constriction of the current density streamlines thus explaining the higher plasma densities observed along the centerline.
Numerical 2D-modeling of multiroll leveling
NASA Astrophysics Data System (ADS)
Mathieu, N.; Potier-Ferry, M.; Zahrouni, H.
2016-10-01
Multiroll leveling is a forming process used in the metals industries (aluminum, steel, …) in order to correct flatness defects and minimize residual stresses in strips thanks to alternating bending. This work proposes a Finite Element 2D model to simulate the metal sheet conveying through the machine. Obtained results (plastic strain and residual stress distributions through thickness) are analysed. Strip deformation, after elastic springback and potential buckling, is also predicted (residual curvatures).
2D Numerical MHD Models of Solar Explosive Events
NASA Astrophysics Data System (ADS)
Roussev, I.
2001-10-01
Observations of the Sun reveal a great variety of dynamic phenomena interpretable as a manifestation of magnetic reconnection. These range from small-scale 'Explosive events' seen in the 'quiet' Sun, through violent flares observed in active regions. The high degree of complexity of the magnetic field inferred from observations may locally produce a fruitful environment for the process of magnetic reconnection to take place. Explosive events are associated with regions undergoing magnetic flux cancellation. This thesis presents a 2-dimensional (2D) numerical study devoted to explore the idea that the salient spectral signatures seen in explosive events are most probably caused by bi-directional outflow jets as a results of an ongoing magnetic reconnection. In order to provide qualitative results needed for the better physical interpretation of solar explosive events, several models intended to represent a 'quiet' Sun transition of solar explosive events, several models intended to represent a 'quiet' Sun transition region undergoing magnetic reconnection are examined, in both unstratified and gravitationally stratified atmospheres. The magnetic reconnection is initiated in an ad hoc manner, and the dynamic evolution is followed by numerically solving the equations of 2D dissipative magnetohydrodynamics (MHD), including the effects of field-aligned thermal conduction, radiative losses, volumetric heating, and anomalous resistivity.
Improvement of a 2D numerical model of lava flows
NASA Astrophysics Data System (ADS)
Ishimine, Y.
2013-12-01
I propose an improved procedure that reduces an improper dependence of lava flow directions on the orientation of Digital Elevation Model (DEM) in two-dimensional simulations based on Ishihara et al. (in Lava Flows and Domes, Fink, JH eds., 1990). The numerical model for lava flow simulations proposed by Ishihara et al. (1990) is based on two-dimensional shallow water model combined with a constitutive equation for a Bingham fluid. It is simple but useful because it properly reproduces distributions of actual lava flows. Thus, it has been regarded as one of pioneer work of numerical simulations of lava flows and it is still now widely used in practical hazard prediction map for civil defense officials in Japan. However, the model include an improper dependence of lava flow directions on the orientation of DEM because the model separately assigns the condition for the lava flow to stop due to yield stress for each of two orthogonal axes of rectangular calculating grid based on DEM. This procedure brings a diamond-shaped distribution as shown in Fig. 1 when calculating a lava flow supplied from a point source on a virtual flat plane although the distribution should be circle-shaped. To improve the drawback, I proposed a modified procedure that uses the absolute value of yield stress derived from both components of two orthogonal directions of the slope steepness to assign the condition for lava flows to stop. This brings a better result as shown in Fig. 2. Fig. 1. (a) Contour plots calculated with the original model of Ishihara et al. (1990). (b) Contour plots calculated with a proposed model.
Representativeness of 2D models to simulate 3D unstable variable density flow in porous media
NASA Astrophysics Data System (ADS)
Knorr, Bastian; Xie, Yueqing; Stumpp, Christine; Maloszewski, Piotr; Simmons, Craig T.
2016-11-01
Variable density flow in porous media has been studied primarily using numerical models because it is a semi-chaotic and transient process. Most of these studies have been 2D, owing to the computational restrictions on 3D simulations, and the ability to observe variable density flow in 2D experimentation. However, it is recognised that variable density flow is a three-dimensional process. A 3D system may cause weaker variable density flow than a 2D system due to stronger dispersion, but may also result in bigger fingers and hence stronger variable density flow because of more space for fingers to coalesce. This study aimed to determine the representativeness of 2D modelling to simulate 3D variable density flow. 3D homogeneous sand column experiments were conducted at three different water flow velocities with three different bromide tracer solutions mixed with methanol resulting in different density ratios. Both 2D axisymmetric and 3D numerical simulations were performed to reproduce experimental data. Experimental results showed that the magnitude of variable density flow increases with decreasing flow rates and decreasing density ratios. The shapes of the observed breakthrough curves differed significantly from those produced by 2D axisymmetric and 3D simulations. Compared to 2D simulations, the onset of instabilities was delayed but the growth was more pronounced in 3D simulations. Despite this difference, both 2D axisymmetric and 3D models successfully simulated mass recovery with high efficiency (between 77% and 99%). This study indicates that 2D simulations are sufficient to understand integrated features of variable density flow in homogeneous sand column experiments.
Numerical modelling of spallation in 2D hydrodynamics codes
NASA Astrophysics Data System (ADS)
Maw, J. R.; Giles, A. R.
1996-05-01
A model for spallation based on the void growth model of Johnson has been implemented in 2D Lagrangian and Eulerian hydrocodes. The model has been extended to treat complete separation of material when voids coalesce and to describe the effects of elevated temperatures and melting. The capabilities of the model are illustrated by comparison with data from explosively generated spall experiments. Particular emphasis is placed on the prediction of multiple spall effects in weak, low melting point, materials such as lead. The correlation between the model predictions and observations on the strain rate dependence of spall strength is discussed.
2-D Clinostat for Simulated Microgravity Experiments with Arabidopsis Seedlings
NASA Astrophysics Data System (ADS)
Wang, Hui; Li, Xugang; Krause, Lars; Görög, Mark; Schüler, Oliver; Hauslage, Jens; Hemmersbach, Ruth; Kircher, Stefan; Lasok, Hanna; Haser, Thomas; Rapp, Katja; Schmidt, Jürgen; Yu, Xin; Pasternak, Taras; Aubry-Hivet, Dorothée; Tietz, Olaf; Dovzhenko, Alexander; Palme, Klaus; Ditengou, Franck Anicet
2016-04-01
Ground-based simulators of microgravity such as fast rotating 2-D clinostats are valuable tools to study gravity related processes. We describe here a versatile g-value-adjustable 2-D clinostat that is suitable for plant analysis. To avoid seedling adaptation to 1 g after clinorotation, we designed chambers that allow rapid fixation. A detailed protocol for fixation, RNA isolation and the analysis of selected genes is described. Using this clinostat we show that mRNA levels of LONG HYPOCOTYL 5 (HY5), MIZU-KUSSEI 1 (MIZ1) and microRNA MIR163 are down-regulated in 5-day-old Arabidopsis thaliana roots after 3 min and 6 min of clinorotation using a maximal reduced g-force of 0.02 g, hence demonstrating that this 2-D clinostat enables the characterization of early transcriptomic events during root response to microgravity. We further show that this 2-D clinostat is able to compensate the action of gravitational force as both gravitropic-dependent statolith sedimentation and subsequent auxin redistribution (monitoring D R5 r e v :: G F P reporter) are abolished when plants are clinorotated. Our results demonstrate that 2-D clinostats equipped with interchangeable growth chambers and tunable rotation velocity are suitable for studying how plants perceive and respond to simulated microgravity.
Resistivity inversion in 2-D anisotropic media: numerical experiments
NASA Astrophysics Data System (ADS)
Wiese, Timothy; Greenhalgh, Stewart; Zhou, Bing; Greenhalgh, Mark; Marescot, Laurent
2015-04-01
Many rocks and layered/fractured sequences have a clearly expressed electrical anisotropy although it is rare in practice to incorporate anisotropy into resistivity inversion. In this contribution, we present a series of 2.5-D synthetic inversion experiments for various electrode configurations and 2-D anisotropic models. We examine and compare the image reconstructions obtained using the correct anisotropic inversion code with those obtained using the false but widely used isotropic assumption. Superior reconstruction in terms of reduced data misfit, true anomaly shape and position, and anisotropic background parameters were obtained when the correct anisotropic assumption was employed for medium to high coefficients of anisotropy. However, for low coefficient values the isotropic assumption produced better-quality results. When an erroneous isotropic inversion is performed on medium to high level anisotropic data, the images are dominated by patterns of banded artefacts and high data misfits. Various pole-pole, pole-dipole and dipole-dipole data sets were investigated and evaluated for the accuracy of the inversion result. The eigenvalue spectra of the pseudo-Hessian matrix and the formal resolution matrix were also computed to determine the information content and goodness of the results. We also present a data selection strategy based on high sensitivity measurements which drastically reduces the number of data to be inverted but still produces comparable results to that of the comprehensive data set. Inversion was carried out using transversely isotropic model parameters described in two different co-ordinate frames for the conductivity tensor, namely Cartesian versus natural or eigenframe. The Cartesian frame provided a more stable inversion product. This can be simply explained from inspection of the eigenspectra of the pseudo-Hessian matrix for the two model descriptions.
Reactor2D: A tool for simulation of shock deformation
NASA Astrophysics Data System (ADS)
Kraus, Eugeny I.; Shabalin, Ivan I.
2016-10-01
The basic steps for creating a numerical tool to simulate the deformation and failure processes of complex technical objects (CTO) are presented. Calculations of shock loading of CTO both at low and high speeds, showing the efficiency of the numerical tools created are carried out.
Rocket engine numerical simulation
NASA Technical Reports Server (NTRS)
Davidian, Ken
1993-01-01
The topics are presented in view graph form and include the following: a definition of the rocket engine numerical simulator (RENS); objectives; justification; approach; potential applications; potential users; RENS work flowchart; RENS prototype; and conclusions.
Rocket engine numerical simulator
NASA Technical Reports Server (NTRS)
Davidian, Ken
1993-01-01
The topics are presented in viewgraph form and include the following: a rocket engine numerical simulator (RENS) definition; objectives; justification; approach; potential applications; potential users; RENS work flowchart; RENS prototype; and conclusion.
Numerical and experimental study of gas flows in 2D and 3D microchannels
NASA Astrophysics Data System (ADS)
Guo, Xiaohui; Huang, Chihyung; Alexeenko, Alina; Sullivan, John
2008-02-01
In the experiments conducted at Purdue, the air flow in rectangular cross-section microchannels was investigated using pressure sensitive paint. The high resolution pressure measurements were obtained for inlet-to-outlet pressure ratios from 1.76 to 20 with the outlet Knudsen numbers in the range from 0.003 to 0.4 based on the hydraulic diameter of 151.7 µm and the length-to-height ratio of about 50. In the slip flow regime, the air flow was simulated by the 2D and 3D Navier-Stokes equations with no-slip and slip boundary conditions. For various pressure ratios, the entrance flow development, compressibility and rarefaction effects were observed in both experiments and numerical simulations. It was found that the accurate modeling of gas flows in finite-length channels requires the inlet and outlet reservoirs to be included in computations. Effects of entrance geometry on the friction factor were studied for 3D cases. In both experiments and numerical modeling, significant pressure drop was found starting at the inlet chamber. The numerical modeling also predicted an apparent temperature drop at the channel exit.
2D-3D hybrid stabilized finite element method for tsunami runup simulations
NASA Astrophysics Data System (ADS)
Takase, S.; Moriguchi, S.; Terada, K.; Kato, J.; Kyoya, T.; Kashiyama, K.; Kotani, T.
2016-09-01
This paper presents a two-dimensional (2D)-three-dimensional (3D) hybrid stabilized finite element method that enables us to predict a propagation process of tsunami generated in a hypocentral region, which ranges from offshore propagation to runup to urban areas, with high accuracy and relatively low computational costs. To be more specific, the 2D shallow water equation is employed to simulate the propagation of offshore waves, while the 3D Navier-Stokes equation is employed for the runup in urban areas. The stabilized finite element method is utilized for numerical simulations for both of the 2D and 3D domains that are independently discretized with unstructured meshes. The multi-point constraint and transmission methods are applied to satisfy the continuity of flow velocities and pressures at the interface between the resulting 2D and 3D meshes, since neither their spatial dimensions nor node arrangements are consistent. Numerical examples are presented to demonstrate the performance of the proposed hybrid method to simulate tsunami behavior, including offshore propagation and runup to urban areas, with substantially lower computation costs in comparison with full 3D computations.
Numerical Instability in a 2D Gyrokinetic Code Caused by Divergent E × B Flow
NASA Astrophysics Data System (ADS)
Byers, J. A.; Dimits, A. M.; Matsuda, Y.; Langdon, A. B.
1994-12-01
In this paper, a numerical instability first observed in a 2D electrostatic gyrokinetic code is described. The instability should also be present in some form in many versons of particle-in-cell simulation codes that employ guiding center drifts. A perturbation analysis of the instability is given and its results agree quantitatively with the observations from the gyrokinetic code in all respects. The basic mechanism is a false divergence of the E × B flow caused by the interpolation between the grid and the particles as coupled with the specific numerical method for calculating E - ∇φ. Stability or instability depends in detail on the specific choice of particle interpolation method and field method. One common interpolation method, subtracted dipole, is stable. Other commonly used interpolation methods, linear and quadratic, are unstable when combined with a finite difference for the electric field. Linear and quadratic interpolation can be rendered stable if combined with another method for the electric field, the analytic differential of the interpolated potential.
Long ranged interactions in computer simulations and for quasi-2D systems
NASA Astrophysics Data System (ADS)
Mazars, Martial
2011-03-01
Taking correctly into account long ranged interactions in molecular simulations of molecular models based on classical atomistic representations are essential to obtain reliable results on model systems and in simulations of biological systems. A lot of numerical methods have been developed to this end; the most important of them are reviewed in this paper. Particular attention is paid to the analytical relations between the methods, this allows comparisons on efficiency and accuracy between them and also to proceed to precise implementations of these techniques. While most of the methods have been developed for Coulomb interactions, we give also some analytical details to apply these methods to screened Coulomb (Yukawa interactions), inverse power law and dipolar interactions. Particular types of systems, the quasi-2D systems, are also considered in this paper. Quasi-2D systems represent a large class of physical systems where the spatial extension in one direction of the space is very small by comparison to the other two. These representations are very useful to describe the properties of interfaces, surfaces, fluids confined in slab geometry, etc. In computer simulations, these systems are studied with partial periodic boundary conditions: periodic boundary conditions are taken in directions where spatial extensions are large and some other boundary conditions are taken in directions with smaller extensions. In this review, we describe also the numerical methods developed to handle long ranged interactions in numerical simulations of quasi-2D systems. The properties of quasi-2D systems depend strongly on interactions between components; more specifically electrostatic and magnetic interactions and interactions with external fields are of particular interest in these systems.
Numerical Propulsion System Simulation
NASA Technical Reports Server (NTRS)
Naiman, Cynthia
2006-01-01
The NASA Glenn Research Center, in partnership with the aerospace industry, other government agencies, and academia, is leading the effort to develop an advanced multidisciplinary analysis environment for aerospace propulsion systems called the Numerical Propulsion System Simulation (NPSS). NPSS is a framework for performing analysis of complex systems. The initial development of NPSS focused on the analysis and design of airbreathing aircraft engines, but the resulting NPSS framework may be applied to any system, for example: aerospace, rockets, hypersonics, power and propulsion, fuel cells, ground based power, and even human system modeling. NPSS provides increased flexibility for the user, which reduces the total development time and cost. It is currently being extended to support the NASA Aeronautics Research Mission Directorate Fundamental Aeronautics Program and the Advanced Virtual Engine Test Cell (AVETeC). NPSS focuses on the integration of multiple disciplines such as aerodynamics, structure, and heat transfer with numerical zooming on component codes. Zooming is the coupling of analyses at various levels of detail. NPSS development includes capabilities to facilitate collaborative engineering. The NPSS will provide improved tools to develop custom components and to use capability for zooming to higher fidelity codes, coupling to multidiscipline codes, transmitting secure data, and distributing simulations across different platforms. These powerful capabilities extend NPSS from a zero-dimensional simulation tool to a multi-fidelity, multidiscipline system-level simulation tool for the full development life cycle.
Modelling 2001 lahars at Popocatépetl volcano using FLO2D numerical code
NASA Astrophysics Data System (ADS)
Caballero, L.; Capra, L.
2013-12-01
Popocatépetl volcano is located on the central part of the Transmexican Volcanic Belt. It is one of the most active volcanoes in Mexico and endanger more than 25 million people that lives in its surroundings. In the last months, the renewal of its volcanic activity put into alert scientific community. One of the possible scenarios is the 2001 explosive activity, which was characterized by a 8 km eruptive column and the subsequent formation of pumice flows up to 4 km from the crater. Lahars were generated few hours after, remobilizing the new deposits towards NE flank of the volcano, along Huiloac Gorge, almost reaching Santiago Xalitzintla town (Capra et al., 2004). The occurrence of a similar scenario makes very important to reproduce this event to delimitate accurately lahar hazard zones. In this work, 2001 lahar deposit is modeled using FLO2D numerical code. Geophone data is used to reconstruct initial hydrograph and sediment concentration. Sensitivity study of most important parameters used by this code like Manning, and α and β coefficients was conducted in order to achieve a good simulation. Results obtained were compared with field data and demonstrated a good agreement in thickness and flow distribution. A comparison with previously published data with laharZ program (Muñoz-Salinas, 2009) is also made. Additionally, lahars with fluctuating sediment concentrations but with similar volume are simulated to observe the influence of the rheological behavior on lahar distribution.
Penetration of tungsten-alloy rods into composite ceramic targets: Experiments and 2-D simulations
NASA Astrophysics Data System (ADS)
Rosenberg, Z.; Dekel, E.; Hohler, V.; Stilp, A. J.; Weber, K.
1998-07-01
A series of terminal ballistics experiments, with scaled tungsten-alloy penetrators, was performed on composite targets consisting of ceramic tiles glued to thick steel backing plates. Tiles of silicon-carbide, aluminum nitride, titanium-dibroide and boron-carbide were 20-80 mm thick, and impact velocity was 1.7 km/s. 2-D numerical simulations, using the PISCES code, were performed in order to simulate these shots. It is shown that a simplified version of the Johnson-Holmquist failure model can account for the penetration depths of the rods but is not enough to capture the effect of lateral release waves on these penetrations.
PFC2D simulation of thermally induced cracks in concrete specimens
NASA Astrophysics Data System (ADS)
Liu, Xinghong; Chang, Xiaolin; Zhou, Wei; Li, Shuirong
2013-06-01
The appearance of cracks exposed to severe environmental conditions can be critical for concrete structures. The research is to validate Particle Flow Code(PFC2D) method in the context of concrete thermally-induced cracking simulations. First, concrete was discreted as meso-level units of aggregate, cement mortar and the interfaces between them. Parallel bonded-particle model in PFC2D was adapted to describe the constitutive relation of the cementing material. Then, the concrete mechanics meso-parameters were obtained through several groups of biaxial tests, in order to make the numerical results comply with the law of the indoor test. The concrete thermal meso-parameters were determined by compared with the parameters in the empirical formula through the simulations imposing a constant heat flow to the left margin of concrete specimens. At last, a case of 1000mm×500mm concrete specimen model was analyzed. It simulated the formation and development process of the thermally-induced cracks under the cold waves of different durations and temperature decline. Good agreements in fracture morphology and process were observed between the simulations, previous studies and laboratory data. The temperature decline limits during cold waves were obtained when its tensile strength was given as 3MPa. And it showed the feasibility of using PFC2D to simulate concrete thermally-induced cracking.
Confidence in Numerical Simulations
Hemez, Francois M.
2015-02-23
This PowerPoint presentation offers a high-level discussion of uncertainty, confidence and credibility in scientific Modeling and Simulation (M&S). It begins by briefly evoking M&S trends in computational physics and engineering. The first thrust of the discussion is to emphasize that the role of M&S in decision-making is either to support reasoning by similarity or to “forecast,” that is, make predictions about the future or extrapolate to settings or environments that cannot be tested experimentally. The second thrust is to explain that M&S-aided decision-making is an exercise in uncertainty management. The three broad classes of uncertainty in computational physics and engineering are variability and randomness, numerical uncertainty and model-form uncertainty. The last part of the discussion addresses how scientists “think.” This thought process parallels the scientific method where by a hypothesis is formulated, often accompanied by simplifying assumptions, then, physical experiments and numerical simulations are performed to confirm or reject the hypothesis. “Confidence” derives, not just from the levels of training and experience of analysts, but also from the rigor with which these assessments are performed, documented and peer-reviewed.
A 2D strain estimator with numerical optimization method for soft-tissue elastography.
Liu, Ke; Zhang, Pengfei; Shao, Jinhua; Zhu, Xinjian; Zhang, Yun; Bai, Jing
2009-12-01
Elastography is a bioelasticity-based imaging modality which has been proved to be a potential evaluation tool to detect the tissue abnormalities. Conventional method for elastography is to estimate the displacement based on cross-correlation technique firstly, then strain profile is calculated as the gradient of the displacement. The main problem of this method arises from the fact that the cross-correlation between pre- and post-compression signals will be decreased because of the signal's compression-to-deformation. It may constrain the estimation of the displacement. Numerical optimization, as an efficient tool to estimate the non-rigid deformation in image registration, has its potential to achieve the elastogram. This paper incorporates the idea of image registration into elastography and proposes a radio frequency (RF) signal registration strain estimator based on the minimization of a cost function using numerical optimization method with Powell algorithm (NOMPA). To evaluate the proposed scheme, the simulation data with a hard inclusion embedded in the homogeneous background is produced for analysis. NOMPA can obtain the displacement profiles and strain profiles simultaneously. When compared with the cross-correlation based method, NOMPA presents better signal-to-noise ratio (SNR, 32.6+/-1.5 dB vs. 23.8+/-1.1 dB) and contrast-to-noise ratio (CNR, 28.8+/-1.8 dB vs. 21.7+/-0.9 dB) in axial normal strain estimation. The in vitro experiment of porcine liver with ethanol-induced lesion is also studied. The statistic results of SNR and CNR indicate that strain profiles by NOMPA performs better anti-noise and target detectability than that by cross-correlation based method. Though NOMPA carry a heavier computational burden than cross-correlation based method, it may be an useful method to obtain 2D strains in elastography.
A 2D simulation model for urban flood management
NASA Astrophysics Data System (ADS)
Price, Roland; van der Wielen, Jonathan; Velickov, Slavco; Galvao, Diogo
2014-05-01
The European Floods Directive, which came into force on 26 November 2007, requires member states to assess all their water courses and coast lines for risk of flooding, to map flood extents and assets and humans at risk, and to take adequate and coordinated measures to reduce the flood risk in consultation with the public. Flood Risk Management Plans are to be in place by 2015. There are a number of reasons for the promotion of this Directive, not least because there has been much urban and other infrastructural development in flood plains, which puts many at risk of flooding along with vital societal assets. In addition there is growing awareness that the changing climate appears to be inducing more frequent extremes of rainfall with a consequent increases in the frequency of flooding. Thirdly, the growing urban populations in Europe, and especially in the developing countries, means that more people are being put at risk from a greater frequency of urban flooding in particular. There are urgent needs therefore to assess flood risk accurately and consistently, to reduce this risk where it is important to do so or where the benefit is greater than the damage cost, to improve flood forecasting and warning, to provide where necessary (and possible) flood insurance cover, and to involve all stakeholders in decision making affecting flood protection and flood risk management plans. Key data for assessing risk are water levels achieved or forecasted during a flood. Such levels should of course be monitored, but they also need to be predicted, whether for design or simulation. A 2D simulation model (PriceXD) solving the shallow water wave equations is presented specifically for determining flood risk, assessing flood defense schemes and generating flood forecasts and warnings. The simulation model is required to have a number of important properties: -Solve the full shallow water wave equations using a range of possible solutions; -Automatically adjust the time step and
A hybrid experimental-numerical technique for determining 3D velocity fields from planar 2D PIV data
NASA Astrophysics Data System (ADS)
Eden, A.; Sigurdson, M.; Mezić, I.; Meinhart, C. D.
2016-09-01
Knowledge of 3D, three component velocity fields is central to the understanding and development of effective microfluidic devices for lab-on-chip mixing applications. In this paper we present a hybrid experimental-numerical method for the generation of 3D flow information from 2D particle image velocimetry (PIV) experimental data and finite element simulations of an alternating current electrothermal (ACET) micromixer. A numerical least-squares optimization algorithm is applied to a theory-based 3D multiphysics simulation in conjunction with 2D PIV data to generate an improved estimation of the steady state velocity field. This 3D velocity field can be used to assess mixing phenomena more accurately than would be possible through simulation alone. Our technique can also be used to estimate uncertain quantities in experimental situations by fitting the gathered field data to a simulated physical model. The optimization algorithm reduced the root-mean-squared difference between the experimental and simulated velocity fields in the target region by more than a factor of 4, resulting in an average error less than 12% of the average velocity magnitude.
Well-posedness and generalized plane waves simulations of a 2D mode conversion model
Imbert-Gérard, Lise-Marie
2015-12-15
Certain types of electro-magnetic waves propagating in a plasma can undergo a mode conversion process. In magnetic confinement fusion, this phenomenon is very useful to heat the plasma, since it permits to transfer the heat at or near the plasma center. This work focuses on a mathematical model of wave propagation around the mode conversion region, from both theoretical and numerical points of view. It aims at developing, for a well-posed equation, specific basis functions to study a wave mode conversion process. These basis functions, called generalized plane waves, are intrinsically based on variable coefficients. As such, they are particularly adapted to the mode conversion problem. The design of generalized plane waves for the proposed model is described in detail. Their implementation within a discontinuous Galerkin method then provides numerical simulations of the process. These first 2D simulations for this model agree with qualitative aspects studied in previous works.
Numerical studies of the melting transition in 2D Yukawa systems
Hartmann, P.; Donko, Z.; Kalman, G. J.
2008-09-07
We present the latest results of our systematic studies of the solid--liquid phase transition in 2D classical many-particle systems interacting with the Yukawa potential. Our previous work is extended by applying the molecular dynamic simulations to systems with up to 1.6 million particles in the computational box (for {kappa} = 2 case). Equilibrium simulations are performed for different coupling parameters in the vicinity of the expected melting transition ({gamma}{sub m}{sup {kappa}}{sup ={sup 2}}{approx_equal}415) and a wide range of observables are averaged over uncorrelated samples of the micro-canonical ensemble generated by the simulations.
NASA Astrophysics Data System (ADS)
Yu, Ting; Chaix, Jean-François; Komatitsch, Dimitri; Garnier, Vincent; Audibert, Lorenzo; Henault, Jean-Marie
2017-02-01
Multiple scattering is important when ultrasounds propagate in a heterogeneous medium such as concrete, the scatterer size of which is in the order of the wavelength. The aim of this work is to build a 2D numerical model of ultrasonic wave propagation integrating the multiple scattering phenomena in SPECFEM software. The coherent field of multiple scattering could be obtained by averaging numerical wave fields, and it is used to determine the effective phase velocity and attenuation corresponding to an equivalent homogeneous medium. After the creation of numerical model under several assumptions, its validation is completed in a case of scattering by one cylinder through the comparison with analytical solution. Two cases of multiple scattering by a set of cylinders at different concentrations are simulated to perform a parametric study (of frequency, scatterer concentration, scatterer size). The effective properties are compared with the predictions of Waterman-Truell model as well, to verify its validity.
Numerical Simulation of Confined Multiple Transverse Jets
2012-06-25
equations. The solutions of three commercial RANS solvers, Fluent, STAR - CCM +, and CFD++, are compared to experimental data and large-eddy simulation...Objective: o Validate commercial CFD codes—Fluent, CFD++, and Star - ccm ++ against experimental data and an LES results o Provide numerical data for...Pairs Diluent Flow X = 2d: X = 5d: X = 10d: Fluent STAR - CCM + CFD++ Axial locations (d = inj. dia.) Experiment LES (ONERA) Distribution A: Approved
Numerical solution of 2D-vector tomography problem using the method of approximate inverse
NASA Astrophysics Data System (ADS)
Svetov, Ivan; Maltseva, Svetlana; Polyakova, Anna
2016-08-01
We propose a numerical solution of reconstruction problem of a two-dimensional vector field in a unit disk from the known values of the longitudinal and transverse ray transforms. The algorithm is based on the method of approximate inverse. Numerical simulations confirm that the proposed method yields good results of reconstruction of vector fields.
Brief Communication: 2-D numerical modeling of the transformation mechanism of a braided channel
NASA Astrophysics Data System (ADS)
Xiao, Y.; Yang, S. F.; Shao, X.; Chen, W. X.; Xu, X. M.
2014-05-01
This paper investigates the controls on the transformation mechanism among different channel patterns. A 2-D depth-averaged numerical model is applied to produce the evolution of channel patterns with complex interactions among water flow, sediment transport, and bank erosion. Changes of the variables as discharge, sediment supply, and vegetation are considered in the numerical experiments, leading to the transformation from a braided pattern into a meandering one. What controls the transformation is discussed with the numerical results: vegetation helps stabilize the cut bank and bar surface, but is not a key in the transition; a decrease in discharge and sediment supply could lead a braided pattern to a meandering one. The conclusion is in agreement with various previous field work, confirming the two dimensional model's potential in predicting the transition between different rivers and improving understanding of patterning processes.
Towards more realistic 2D & 3D numerical models of Earth's mantle
NASA Astrophysics Data System (ADS)
Ghias, Sanaz
2011-12-01
There are a number of simplifying assumptions in modeling Earth's deep interior. These are mostly simplifying assumptions that make the mathematics simpler either for less complicated modeling or for numerical efficiency purposes. The aim of this study is to investigate the effects of some of these simplifying assumptions on 2D and 3D mantle convection models. In particular, the cases with variable coefficients of thermal expansion, alpha, and the inclusion of mineral phase transitions and viscosity stratification have been studied. The coefficient of thermal expansion is temperature- and depth-dependent in Earth. But for simplicity, it has been considered as constant in most mantle convection models and only depth-dependent in others. 2D mantle convection models (2D Cartesian and 2D cylindrical) have been created based on an existing model from Jarvis [1992] to investigate the effects of temperature- and depth-dependent alpha on mantle convection compared with the simplified cases. Also an existing version of a 3D parallel mantle convection model, MC3D, from Lowman et al. [2001] have been modified to include the temperature- and depth-dependent alpha. In the 3D study it has also been investigated that how the effects of temperature- and depth-dependent alpha vary with or without lithospheric plates. There are at least two mineral phase transitions in Earth. There is an exothermic phase boundary at 410km below the surface and an endothermic phase boundary at 660km below the surface. For simplicity, most mantle convection models do not consider any of the phase boundaries. Some consider only the endothermic phase boundary. A 2D cylindrical model from Shahnas and Jarvas [2005] has been employed to investigate the effects of considering both phase boundaries compared to models with either no, or one, phase boundary. Different viscosity stratifications have been used in addition to the phase boundaries.
Numerical simulation of dusty plasmas
Winske, D.
1995-09-01
The numerical simulation of physical processes in dusty plasmas is reviewed, with emphasis on recent results and unresolved issues. Three areas of research are discussed: grain charging, weak dust-plasma interactions, and strong dust-plasma interactions. For each area, we review the basic concepts that are tested by simulations, present some appropriate examples, and examine numerical issues associated with extending present work.
Pool Formation in Boulder-Bed Streams: Implications From 1-D and 2-D Numerical Modeling
NASA Astrophysics Data System (ADS)
Harrison, L. R.; Keller, E. A.
2003-12-01
In mountain rivers of Southern California, boulder-large roughness elements strongly influence flow hydraulics and pool formation and maintenance. In these systems, boulders appear to control the stream morphology by converging flow and producing deep pools during channel forming discharges. Our research goal is to develop quantitative relationships between boulder roughness elements, temporal patterns of scour and fill, and geomorphic processes that are important in producing pool habitat. The longitudinal distribution of shear stress, unit stream power and velocity were estimated along a 48 m reach on Rattlesnake Creek, using the HEC-RAS v 3.0 and River 2-D numerical models. The reach has an average slope of 0.02 and consists of a pool-riffle sequence with a large boulder constriction directly above the pool. Model runs were performed for a range of stream discharges to test if scour and fill thresholds for pool and riffle environments could be identified. Results from the HEC-RAS simulations identified that thresholds in shear stress, unit stream power and mean velocity occur above a discharge of 5.0 cms. Results from the one-dimensional analysis suggest that the reversal in competency is likely due to changes in cross-sectional width at varying flows. River 2-D predictions indicated that strong transverse velocity gradients were present through the pool at higher modeled discharges. At a flow of 0.5 cms (roughly 1/10th bankfull discharge), velocities are estimated at 0.6 m/s and 1.3 m/s for the pool and riffle, respectively. During discharges of 5.15 cms (approximate bankfull discharge), the maximum velocity in the pool center increased to nearly 3.0 m/s, while the maximum velocity over the riffle is estimated at approximately 2.5 cms. These results are consistent with those predicted by HEC-RAS, though the reversal appears to be limited to a narrow jet that occurs through the pool head and pool center. Model predictions suggest that the velocity reversal is
Romero, V.J.; Ingber, M.S.
1995-07-01
A numerical model for simulating the transient nonlinear behavior of 2-D viscous sloshing flows in rectangular containers subjected to arbitrary horizontal accelerations is presented. The potential-flow formulation uses Rayleigh damping to approximate the effects of viscosity, and Lagrangian node movement is used to accommodate violent sloshing motions. A boundary element approach is used to efficiently handle the time-changing fluid geometry. Additionally, a corrected equation is presented for the constraint condition relating normal and tangential derivatives of the velocity potential where the fluid free surface meets the rigid container wall. The numerical model appears to be more accurate than previous sloshing models, as determined by comparison against exact analytic solutions and results of previously published models.
Ion acoustic wave collapse via two-ion wave decay: 2D Vlasov simulation and theory
NASA Astrophysics Data System (ADS)
Chapman, Thomas; Berger, Richard; Banks, Jeffrey; Brunner, Stephan
2015-11-01
The decay of ion acoustic waves (IAWs) via two-ion wave decay may transfer energy from the electric field of the IAWs to the particles, resulting in a significant heating of resonant particles. This process has previously been shown in numerical simulations to decrease the plasma reflectivity due to stimulated Brillouin scattering. Two-ion wave decay is a fundamental property of ion acoustic waves that occurs over most if not all of the parameter space of relevance to inertial confinement fusion experiments, and can lead to a sudden collapse of IAWs. The treatment of all species kinetically, and in particular the electrons, is required to describe the decay process correctly. We present fully kinetic 2D+2V Vlasov simulations of IAWs undergoing decay to a highly nonlinear turbulent state using the code LOKI. The scaling of the decay rate with characteristic plasma parameters and wave amplitude is shown. A new theory describing two-ion wave decay in 2D, that incorporates key kinetic properties of the electrons, is presented and used to explain quantitatively for the first time the observed decay of IAWs. Work performed under auspices of U.S. DoE by LLNL, Contract DE-AC52-07NA2734. Funded by LDRD 15-ERD-038 and supported by LLNL Grand Challenge allocation.
GMC COLLISIONS AS TRIGGERS OF STAR FORMATION. I. PARAMETER SPACE EXPLORATION WITH 2D SIMULATIONS
Wu, Benjamin; Loo, Sven Van; Tan, Jonathan C.; Bruderer, Simon
2015-09-20
We utilize magnetohydrodynamic (MHD) simulations to develop a numerical model for giant molecular cloud (GMC)–GMC collisions between nearly magnetically critical clouds. The goal is to determine if, and under what circumstances, cloud collisions can cause pre-existing magnetically subcritical clumps to become supercritical and undergo gravitational collapse. We first develop and implement new photodissociation region based heating and cooling functions that span the atomic to molecular transition, creating a multiphase ISM and allowing modeling of non-equilibrium temperature structures. Then in 2D and with ideal MHD, we explore a wide parameter space of magnetic field strength, magnetic field geometry, collision velocity, and impact parameter and compare isolated versus colliding clouds. We find factors of ∼2–3 increase in mean clump density from typical collisions, with strong dependence on collision velocity and magnetic field strength, but ultimately limited by flux-freezing in 2D geometries. For geometries enabling flow along magnetic field lines, greater degrees of collapse are seen. We discuss observational diagnostics of cloud collisions, focussing on {sup 13}CO(J = 2–1), {sup 13}CO(J = 3–2), and {sup 12}CO(J = 8–7) integrated intensity maps and spectra, which we synthesize from our simulation outputs. We find that the ratio of J = 8–7 to lower-J emission is a powerful diagnostic probe of GMC collisions.
Reynolds-Averaged Navier-Stokes Simulation of a 2D Circulation Control Wind Tunnel Experiment
NASA Technical Reports Server (NTRS)
Allan, Brian G.; Jones, Greg; Lin, John C.
2011-01-01
Numerical simulations are performed using a Reynolds-averaged Navier-Stokes (RANS) flow solver for a circulation control airfoil. 2D and 3D simulation results are compared to a circulation control wind tunnel test conducted at the NASA Langley Basic Aerodynamics Research Tunnel (BART). The RANS simulations are compared to a low blowing case with a jet momentum coefficient, C(sub u), of 0:047 and a higher blowing case of 0.115. Three dimensional simulations of the model and tunnel walls show wall effects on the lift and airfoil surface pressures. These wall effects include a 4% decrease of the midspan sectional lift for the C(sub u) 0.115 blowing condition. Simulations comparing the performance of the Spalart Allmaras (SA) and Shear Stress Transport (SST) turbulence models are also made, showing the SST model compares best to the experimental data. A Rotational/Curvature Correction (RCC) to the turbulence model is also evaluated demonstrating an improvement in the CFD predictions.
NASA Astrophysics Data System (ADS)
Li, Jinghe; Song, Linping; Liu, Qing Huo
2016-02-01
A simultaneous multiple frequency contrast source inversion (CSI) method is applied to reconstructing hydrocarbon reservoir targets in a complex multilayered medium in two dimensions. It simulates the effects of a salt dome sedimentary formation in the context of reservoir monitoring. In this method, the stabilized biconjugate-gradient fast Fourier transform (BCGS-FFT) algorithm is applied as a fast solver for the 2D volume integral equation for the forward computation. The inversion technique with CSI combines the efficient FFT algorithm to speed up the matrix-vector multiplication and the stable convergence of the simultaneous multiple frequency CSI in the iteration process. As a result, this method is capable of making quantitative conductivity image reconstruction effectively for large-scale electromagnetic oil exploration problems, including the vertical electromagnetic profiling (VEP) survey investigated here. A number of numerical examples have been demonstrated to validate the effectiveness and capacity of the simultaneous multiple frequency CSI method for a limited array view in VEP.
1D and 2D simulations of seismic wave propagation in fractured media
NASA Astrophysics Data System (ADS)
Möller, Thomas; Friederich, Wolfgang
2016-04-01
Fractures and cracks have a significant influence on the propagation of seismic waves. Their presence causes reflections and scattering and makes the medium effectively anisotropic. We present a numerical approach to simulation of seismic waves in fractured media that does not require direct modelling of the fracture itself, but uses the concept of linear slip interfaces developed by Schoenberg (1980). This condition states that at an interface between two imperfectly bonded elastic media, stress is continuous across the interface while displacement is discontinuous. It is assumed that the jump of displacement is proportional to stress which implies a jump in particle velocity at the interface. We use this condition as a boundary condition to the elastic wave equation and solve this equation in the framework of a Nodal Discontinuous Galerkin scheme using a velocity-stress formulation. We use meshes with tetrahedral elements to discretise the medium. Each individual element face may be declared as a slip interface. Numerical fluxes have been derived by solving the 1D Riemann problem for slip interfaces with elastic and viscoelastic rheology. Viscoelasticity is realised either by a Kelvin-Voigt body or a Standard Linear Solid. These fluxes are not limited to 1D and can - with little modification - be used for simulations in higher dimensions as well. The Nodal Discontinuous Galerkin code "neXd" developed by Lambrecht (2013) is used as a basis for the numerical implementation of this concept. We present examples of simulations in 1D and 2D that illustrate the influence of fractures on the seismic wavefield. We demonstrate the accuracy of the simulation through comparison to an analytical solution in 1D.
Simulation of subgrid orographic precipitation with an embedded 2-D cloud-resolving model
NASA Astrophysics Data System (ADS)
Jung, Joon-Hee; Arakawa, Akio
2016-03-01
By explicitly resolving cloud-scale processes with embedded two-dimensional (2-D) cloud-resolving models (CRMs), superparameterized global atmospheric models have successfully simulated various atmospheric events over a wide range of time scales. Up to now, however, such models have not included the effects of topography on the CRM grid scale. We have used both 3-D and 2-D CRMs to simulate the effects of topography with prescribed "large-scale" winds. The 3-D CRM is used as a benchmark. The results show that the mean precipitation can be simulated reasonably well by using a 2-D representation of topography as long as the statistics of the topography such as the mean and standard deviation are closely represented. It is also shown that the use of a set of two perpendicular 2-D grids can significantly reduce the error due to a 2-D representation of topography.
Hall-Effect Thruster Simulations with 2-D Electron Transport and Hydrodynamic Ions
NASA Technical Reports Server (NTRS)
Mikellides, Ioannis G.; Katz, Ira; Hofer, Richard H.; Goebel, Dan M.
2009-01-01
A computational approach that has been used extensively in the last two decades for Hall thruster simulations is to solve a diffusion equation and energy conservation law for the electrons in a direction that is perpendicular to the magnetic field, and use discrete-particle methods for the heavy species. This "hybrid" approach has allowed for the capture of bulk plasma phenomena inside these thrusters within reasonable computational times. Regions of the thruster with complex magnetic field arrangements (such as those near eroded walls and magnets) and/or reduced Hall parameter (such as those near the anode and the cathode plume) challenge the validity of the quasi-one-dimensional assumption for the electrons. This paper reports on the development of a computer code that solves numerically the 2-D axisymmetric vector form of Ohm's law, with no assumptions regarding the rate of electron transport in the parallel and perpendicular directions. The numerical challenges related to the large disparity of the transport coefficients in the two directions are met by solving the equations in a computational mesh that is aligned with the magnetic field. The fully-2D approach allows for a large physical domain that extends more than five times the thruster channel length in the axial direction, and encompasses the cathode boundary. Ions are treated as an isothermal, cold (relative to the electrons) fluid, accounting for charge-exchange and multiple-ionization collisions in the momentum equations. A first series of simulations of two Hall thrusters, namely the BPT-4000 and a 6-kW laboratory thruster, quantifies the significance of ion diffusion in the anode region and the importance of the extended physical domain on studies related to the impact of the transport coefficients on the electron flow field.
NASA Technical Reports Server (NTRS)
Shie, Chung-Lin; Tao, Wei-Kuo; Simpson, Joanne
2003-01-01
The 1999 Kwajalein Atoll field experiment (KWAJEX), one of several major TRMM (Tropical Rainfall Measuring Mission) field experiments, has successfully obtained a wealth of information and observation data on tropical convective systems over the western Central Pacific region. In this paper, clouds and convective systems that developed during three active periods (Aug 7-12, Aug 17-21, and Aug 29-Sep 13) around Kwajalein Atoll site are simulated using both 2D and 3D Goddard Cumulus Ensemble (GCE) models. Based on numerical results, the clouds and cloud systems are generally unorganized and short lived. These features are validated by radar observations that support the model results. Both the 2D and 3D simulated rainfall amounts and their stratiform contribution as well as the heat, water vapor, and moist static energy budgets are examined for the three convective episodes. Rainfall amounts are quantitatively similar between the two simulations, but the stratiform contribution is considerably larger in the 2D simulation. Regardless of dimension, fo all three cases, the large-scale forcing and net condensation are the two major physical processes that account for the evolution of the budgets with surface latent heat flux and net radiation solar and long-wave radiation)being secondary processes. Quantitative budget differences between 2D and 3D as well as between various episodes will be detailed.Morover, simulated radar signatures and Q1/Q2 fields from the three simulations are compared to each other and with radar and sounding observations.
Numerical Simulation of Nix's Rotation
This is a numerical simulation of the orientation of Nix as seen from the center of the Pluto system. It has been sped up so that one orbit of Nix around Pluto takes 2 seconds instead of 25 days. L...
On numerical solving a rigid inclusions problem in 2D elasticity
NASA Astrophysics Data System (ADS)
Rudoy, Evgeny
2017-02-01
A 2D elastic problem for a body containing a set of bulk and thin rigid inclusions of arbitrary shapes is considered. It is assumed that rigid inclusions are bonded into elastic matrix. To state the equilibrium problem, a variational approach is used. The problem is formulated as a problem of minimization of the energy functional over the set of admissible displacements. Moreover, it is equivalent to a variational equality which holds for test functions belonging to the subspace of functions with the prescribed rigid displacement structure on the inclusions. We propose a novel algorithm of solving the equilibrium problem. The algorithm is based on reducing the original problem to a system of the Dirichlet and Neumann problems. A numerical examination is carried out to demonstrate the efficiency of the proposed technique.
Numerical simulation of Bootstrap Current
Wu, Yanlin; White, R.B.
1993-05-01
The neoclassical theory of Bootstrap Current in toroidal systems is calculated in magnetic flux coordinates and confirmed by numerical simulation. The effects of magnetic ripple, loop voltage, and magnetic and electrostatic perturbations on bootstrap current for the cases of zero and finite plasma pressure are studied. The numerical results are in reasonable agreement with analytical estimates.
Extended MHD simulations of Rayleigh-Taylor instability with real frequency in a 2D slab
NASA Astrophysics Data System (ADS)
Goto, Ryosuke; Miura, Hideaki; Ito, Atsushi; Sato, Masahiko; Hatori, Tomoharu
2014-10-01
Small scale effects such as the Finite Larmor Radius (FLR) effect and the Hall term can change the linear and non-linear growth of the high wave number unstable modes of the pressure driven instability considerably. Here we consider a simple Rayleigh-Taylor (R-T) instability in a 2D slab, and study the effect of the Hall term and the FLR effect to the R-T instability by means of numerical simulations of the Braginskii-type extended MHD equations. As we have reported earlier, the linear growth rates of the high wave number modes are highly reduced when the Hall term and the FLR effect are added simultaneously. However, there appears little real frequency in the previous work. Since the diamagnetic drift associated with the real frequency is considered to affect the growth of the linear and nonlinear evolutions, we provide a new equilibrium in which appearance of the real frequency is expected and carry out numerical simulations. Influences of the real frequency on the growth rates as well as on the nonlinear mixing width for some combinations of the Hall and the FLR parameters are going to be presented.
Fanchi, J.R.
1985-04-01
Under the sponsorship of the US Department of Energy, a publicly available chemical simulator has been evaluated and substantially enhanced to serve as a useful tool for projecting polymer or chemical flood performance. The program, CHEM2D, is a two-dimensional, three-phase, nine-component finite-difference numerical simulator. It can model primary depletion, waterfloods, polymer floods, and micellar/polymer floods using heterogeneous linear, areal, or cross-sectional reservoir descriptions. The user may specify well performance as either pressure or rate constrained. Both a constant time step size and a variable time step size based on extrapolation of concentration changes are available as options. A solution technique which is implicit in pressure and explicit in saturations and concentrations is used. The major physical mechanisms that are modeled include adsorption, capillary trapping, cation exchange, dilution, dispersion, interfacial tension, binary or ternary phase behavior, non-Newtonian polymer rheology, and two-phase or three-phase relative permeability. Typical components include water, oil, surfactant, polymer, and three ions (chloride, calcium, and sodium). Components may partition amongst the aqueous, oleic, and microemulsion phases. Volume I of this report provides a discussion of the formulation and algorithms used within CHEM2D. Included in Volume I are a number of validation and illustrative examples, as well as the FORTRAN code. The CHEM2D user's manual, Volume II, contains both the input data sets for the examples presented in Volume I and an example output. All appendices and a phase behavior calculation program are collected in Volume III. 20 references.
NASA Astrophysics Data System (ADS)
Chen, Xihui; Sun, Zhigang; Sun, Jianfen; Song, Yingdong
2017-02-01
In this paper, a numerical model which incorporates the oxidation damage model and the finite element model of 2D plain woven composites is presented for simulation of the oxidation behaviors of 2D plain woven C/SiC composite under preloading oxidation atmosphere. The equal proportional reduction method is firstly proposed to calculate the residual moduli and strength of unidirectional C/SiC composite. The multi-scale method is developed to simulate the residual elastic moduli and strength of 2D plain woven C/SiC composite. The multi-scale method is able to accurately predict the residual elastic modulus and strength of the composite. Besides, the simulated residual elastic moduli and strength of 2D plain woven C/SiC composites under preloading oxidation atmosphere show good agreements with experimental results. Furthermore, the preload, oxidation time, temperature and fiber volume fractions of the composite are investigated to show their influences upon the residual elastic modulus and strength of 2D plain woven C/SiC composites.
NASA Astrophysics Data System (ADS)
Liu, Zhen; Qu, Hengliang; Shi, Hongda; Hu, Gexing; Hyun, Beom-Soo
2016-12-01
Tidal current energy is renewable and sustainable, which is a promising alternative energy resource for the future electricity supply. The straight-bladed vertical-axis turbine is regarded as a useful tool to capture the tidal current energy especially under low-speed conditions. A 2D unsteady numerical model based on Ansys-Fluent 12.0 is established to conduct the numerical simulation, which is validated by the corresponding experimental data. For the unsteady calculations, the SST model, 2×105 and 0.01 s are selected as the proper turbulence model, mesh number, and time step, respectively. Detailed contours of the velocity distributions around the rotor blade foils have been provided for a flow field analysis. The tip speed ratio (TSR) determines the azimuth angle of the appearance of the torque peak, which occurs once for a blade in a single revolution. It is also found that simply increasing the incident flow velocity could not improve the turbine performance accordingly. The peaks of the averaged power and torque coefficients appear at TSRs of 2.1 and 1.8, respectively. Furthermore, several shapes of the duct augmentation are proposed to improve the turbine performance by contracting the flow path gradually from the open mouth of the duct to the rotor. The duct augmentation can significantly enhance the power and torque output. Furthermore, the elliptic shape enables the best performance of the turbine. The numerical results prove the capability of the present 2D model for the unsteady hydrodynamics and an operating performance analysis of the vertical tidal stream turbine.
Requirements definition by numerical simulation
NASA Astrophysics Data System (ADS)
Hickman, James J.; Kostas, Chris; Tsang, Kang T.
1994-10-01
We are investigating the issues involved in requirements definition for narcotics interdiction: how much of a particular signature is possible, how does this amount change for different conditions, and what is the temporal relationship in various scenarios. Our approach has been to simulate numerically the conditions that arise during vapor or particulate transport. The advantages of this approach are that (1) a broad range of scenarios can be rapidly and inexpensively analyzed by simulation, and (2) simulations can display quantities that are difficult or impossible to measure. The drawback of this approach is that simulations cannot include all of the phenomena present in a real measurement, and therefore the fidelity of the simulation results is always an issue. To address this limitation, we will ultimately combine the results of numerical simulations with measurements of physical parameters for inclusion in the simulation. In this paper, we discuss these issues and how they apply to the current problems in narcotics interdictions, especially cargo containers. We also show the results of 1D and 3D numerical simulations, and compare these results with analytical solutions. The results indicate that this approach is viable. We also present data from 3D simulations of vapor transport in a loaded cargo container and some of the issues present in this ongoing work.
NASA Astrophysics Data System (ADS)
Simmons, Daniel; Cools, Kristof; Sewell, Phillip
2016-11-01
Time domain electromagnetic simulation tools have the ability to model transient, wide-band applications, and non-linear problems. The Boundary Element Method (BEM) and the Transmission Line Modeling (TLM) method are both well established numerical techniques for simulating time-varying electromagnetic fields. The former surface based method can accurately describe outwardly radiating fields from piecewise uniform objects and efficiently deals with large domains filled with homogeneous media. The latter volume based method can describe inhomogeneous and non-linear media and has been proven to be unconditionally stable. Furthermore, the Unstructured TLM (UTLM) enables modelling of geometrically complex objects by using triangular meshes which removes staircasing and unnecessary extensions of the simulation domain. The hybridization of BEM and UTLM which is described in this paper is named the Boundary Element Unstructured Transmission-line (BEUT) method. It incorporates the advantages of both methods. The theory and derivation of the 2D BEUT method is described in this paper, along with any relevant implementation details. The method is corroborated by studying its correctness and efficiency compared to the traditional UTLM method when applied to complex problems such as the transmission through a system of Luneburg lenses and the modelling of antenna radomes for use in wireless communications.
NASA Astrophysics Data System (ADS)
Rubino, J. Germán.; Caspari, Eva; Müller, Tobias M.; Milani, Marco; Barbosa, Nicolás. D.; Holliger, Klaus
2016-09-01
The presence of stiffness contrasts at scales larger than the typical pore sizes but smaller than the predominant seismic wavelengths can produce seismic attenuation and velocity dispersion in fluid-saturated porous rocks. This energy dissipation mechanism is caused by wave-induced fluid pressure diffusion among the different components of the probed geological formations. In many cases, heterogeneities have elongated shapes and preferential orientations, which implies that the overall response of the medium is anisotropic. In this work, we propose a numerical upscaling procedure that permits to quantify seismic attenuation and phase velocity considering fluid pressure diffusion effects as well as generic anisotropy at the sample's scale. The methodology is based on a set of three relaxation tests performed on a 2-D synthetic rock sample representative of the medium of interest. It provides a complex-valued frequency-dependent equivalent stiffness matrix through a least squares procedure. We also derive an approach for computing various poroelastic fields associated with the considered sample in response to the propagation of a seismic wave with arbitrary incidence angle. Using this approach, we provide an energy-based estimation of seismic attenuation. A comprehensive numerical analysis indicates that the methodology is suitable for handling complex media and different levels of overall anisotropy. Comparisons with the energy-based estimations demonstrate that the dynamic-equivalent viscoelastic medium assumption made by the numerical upscaling procedure is reasonable even in the presence of high levels of overall anisotropy. This work also highlights the usefulness of poroelastic fields for the physical interpretation of seismic wave phenomena in strongly heterogeneous and complex media.
2-D simulation of a waveguide free electron laser having a helical undulator
Kim, S.K.; Lee, B.C.; Jeong, Y.U.
1995-12-31
We have developed a 2-D simulation code for the calculation of output power from an FEL oscillator having a helical undulator and a cylindrical waveguide. In the simulation, the current and the energy of the electron beam is 2 A and 400 keV, respectively. The parameters of the permanent-magnet helical undulator are : period = 32 mm, number of periods = 20, magnetic field = 1.3 kG. The gain per pass is 10 and the output power is calculated to be higher than 10 kW The results of the 2-D simulation are compared with those of 1-D simulation.
Numerical simulation of gravel packing
Winterfeld, P.H.; Schroeder, D.E. Jr. )
1992-08-01
To obtain maximum productivity from unconsolidated formations where sand control is required, it is important to understand the mechanics of gravel packing. This paper describes a finite-element, numerical simulator that can predict gravel placement in the perforations and annulus of a wellbore. The equations for the simulator include mass and momentum conservation. Wellbore geometry, physical properties, and fluid and gravel-pack properties are simulator input. Experiments in a 100-ft full-scale wellbore model for three gravel-packing configurations have been successfully simulated. These configurations are a circulating pack with a washpipe, a squeeze pack, and a circulating/squeeze pack with a washpipe and a lower telltale screen. The low cost, speed, and extrapolation capabilities of the numerical simulator will greatly enhance our ability to predict gravel placement in a wellbore.
Numerical simulation of Ulysses nutation
NASA Technical Reports Server (NTRS)
Marirrodriga, C. Garcia; Zeischka, J.; Boslooper, E. C.
1993-01-01
A numerical simulation has been performed on the in-orbit instability of the Ulysses Spacecraft. The thermal excitation from the solar flux, the flexible axial boom and its deployment mechanism have been modeled and analyzed. The simulation shows that the nutation build-up has been originated by the solar input on the axial boom coupled with the system nutation frequency of the spacecraft. The results agree with the observed behavior.
Numerical simulation of dynamic fracture and failure in solids
Chen, E.P.
1994-05-01
Numerical simulation of dynamic fracture and failure processes in solid continua using Lagrangian finite element techniques is the subject of discussion in this investigation. The specific configurations in this study include penetration of steel projectiles into aluminum blocks and concrete slabs. The failure mode in the aluminum block is excessive deformation while the concrete slab fails by hole growth, spallation, and scabbing. The transient dynamic finite element code LS-DYNA2D was used for the numerical analysis. The erosion capability in LS-DYNA2D was exercised to carry out the fracture and failure simulations. Calculated results were compared to the experimental data. Good correlations were obtained.
Numerical modeling of 2-D granular step collapse on erodible and nonerodible surface
NASA Astrophysics Data System (ADS)
Crosta, G. B.; Imposimato, S.; Roddeman, D.
2009-09-01
The study of the collapse of a granular step is of great interest for understanding transient dense granular flow conditions and for modeling geophysical flows in granular materials. We present the results of a series of finite elements simulations considering variable column aspect ratios and properties for an elastoplastic material with a Mohr-Coulomb yield rule and nonassociate flow rule. The adopted approach does not suffer limitations of typical shallow water equation methods, being able to consider strong vertical motion components. Transition from initial instability to complete flow development is simulated for columns with different aspect ratios (a ≤ 20). Simulation results are compared to original tests and available well-documented experimental data, in terms of flow development, duration, profile geometry, velocity distribution, erosion and deposition, and evolution of the interface between static and moving material. Tests involving a thick erodible layer have been performed and numerical simulation results are compared also with a real case study. Numerical results support both those of qualitative and theoretical models and the proposed general scaling laws and clarify the dependence on frictional properties. Power laws describe the normalized runout versus aspect ratio (a > 4) relationship with constants of proportionality dependent on internal friction angle and exponents ranging between 0.68 and 0.77, in good agreement with experimental results. Total duration and evolution in three successive phases agree with observations. Time for the flow front to cease motion with respect to aspect ratio is best represented by the 3.68a 0.448 relationships for a 30° internal friction angle material.
Simulation and calculation of particle trapping using a quasistatic 2D simulation code
NASA Astrophysics Data System (ADS)
Morshed, Sepehr; Antonsen, Thomas; Huang, Chengkun; Mori, Warren
2008-11-01
In LWFA schemes the laser pulse must propagate several centimeters and maintain its coherence over this distance, which corresponds to many Rayleigh lengths. These Wakefields and their effect on the laser can be simulated in quasistatic approximation [1, 2]. In this approximation the assumption is that the driver (laser) does not change shape during the time it takes for it to pass by a plasma particle. As a result the particles that are trapped and moving with near-luminal velocity can not be treated with this approximation. Here we have modified the 2D code WAKE with an alternate algorithm so that when a plasma particle gains sufficient energy from wakefields it is promoted to beam particle status which later on may become trapped in the wakefields of laser. Similar implementations have been made in the 3D code QUICKPIC [2]. We also have done comparison between WAKE and results from 200 TW laser simulations using OSIRIS [3]. These changes in WAKE will give users a tool that can be used on a desk top machine to simulate GeV acceleration.[0pt] [1] P. Mora and T. M. Antonsen Jr., Phys Plasma 4, 217 (1997)[0pt] [2] C. Huang et al. Comp Phys. 217 (2006)[0pt] [3] W. Lu et al. PRST, Accelerators and Beams 10, 061301 (2007)
Numerical and experimental studies of the elastic enhancement factor of 2D open systems
NASA Astrophysics Data System (ADS)
Sirko, Leszek; Białous, Małgorzata; Yunko, Vitalii; Bauch, Szymon; Ławniczak, Michał
We present the results of numerical and experimental studies of the elastic enhancement factor W for microwave rough and rectangular cavities simulating two-dimensional chaotic and partially chaotic quantum billiards in the presence of moderate absorption strength. We show that for the frequency range ν = 15 . 0 - 18 . 5 GHz, in which the coupling between antennas and the system is strong enough, the values of W for the microwave rough cavity lie below the predictions of random matrix theory and on average they are above the theoretical results of V. Sokolov and O. Zhirov, Phys. Rev. E, 91, 052917 (2015). We also show that the enhancement factor W of a microwave rectangular cavity coupled to the external channels via microwave antennas, simulating a partially chaotic quantum billiard, calculated by applying the Potter-Rosenzweig model with κ = 2 . 8 +/- 0 . 5 is close to the experimental one. Our numerical and experimental results suggest that the enhancement factor can be used as a measure of internal chaos which can be especially useful for systems with significant openness or absorption. This work was partially supported by the Ministry of Science and Higher Education Grants N N202 130239 and UMO-2013/09/D/ST2/03727.
On craton thinning/destruction: Insight from 2D thermal-mechanical numerical modeling
NASA Astrophysics Data System (ADS)
Liao, J.
2014-12-01
Although most cratons maintain stable, some exceptions are present, such as the North China craton, North Atlantic craton, and Wyoming craton, which have experienced dramatic lithospheric deformation/thinning. Mechanisms triggering cratonic thinning remains enigmatic [Lee et al., 2011]. Using a 2D thermo-mechanical coupled numerical model [Gerya and Yuen, 2007], we investigate two possible mechanisms: (1) stratification of cratonic lithospheric mantle, and (2) rheological weakening due to hydration.Lithospheric mantle stratification is a common feature in cratonic areas which has been demonstrated by geophysical and geochemical studies [Thybo and Perchuc, 1997; Griffin et al., 2004; Romanowicz, 2009; Rychert and Shearer, 2009; Yuan and Romanowicz, 2010]. The influence of lithospheric mantle stratification during craton evolution remains poorly understood. A rheologically weak layer representing hydrated and/or metasomatized composition is implemented in the lithospheric mantle. Our results show that the weak mantle layer changes the dynamics of lithospheric extension by enhancing the deformation of the overlying mantle and crust and inhibiting deformation of the underlying mantle [Liao et al., 2013; Liao and Gerya, 2014]. Modeling results are compared with North China and North Atlantic cratons. Our work indicates that although the presence of a weak layer may not be sufficient to initiate craton deformation, it enhances deformation by lowering the required extensional plate boundary force. Rheological weakening due to hydration is a possible mechanism triggering/enhancing craton deformation, especially for cratons jaxtaposing with a subduction, since water can release from a subducting slab. We investigate the influence of wet mantle flow laws [Hirth and Kohlstedt, 2003], in which a water parameter (i.e. constant water content) is involved. Our results show that wet dislocation alone does not accelerate cratonic deformation significantly. However, if wet diffusion
Absorption and scattering 2-D volcano images from numerically calculated space-weighting functions
NASA Astrophysics Data System (ADS)
Del Pezzo, Edoardo; Ibañez, Jesus; Prudencio, Janire; Bianco, Francesca; De Siena, Luca
2016-08-01
Short-period small magnitude seismograms mainly comprise scattered waves in the form of coda waves (the tail part of the seismogram, starting after S waves and ending when the noise prevails), spanning more than 70 per cent of the whole seismogram duration. Corresponding coda envelopes provide important information about the earth inhomogeneity, which can be stochastically modeled in terms of distribution of scatterers in a random medium. In suitable experimental conditions (i.e. high earth heterogeneity), either the two parameters describing heterogeneity (scattering coefficient), intrinsic energy dissipation (coefficient of intrinsic attenuation) or a combination of them (extinction length and seismic albedo) can be used to image Earth structures. Once a set of such parameter couples has been measured in a given area and for a number of sources and receivers, imaging their space distribution with standard methods is straightforward. However, as for finite-frequency and full-waveform tomography, the essential problem for a correct imaging is the determination of the weighting function describing the spatial sensitivity of observable data to scattering and absorption anomalies. Due to the nature of coda waves, the measured parameter couple can be seen as a weighted space average of the real parameters characterizing the rock volumes illuminated by the scattered waves. This paper uses the Monte Carlo numerical solution of the Energy Transport Equation to find approximate but realistic 2-D space-weighting functions for coda waves. Separate images for scattering and absorption based on these sensitivity functions are then compared with those obtained with commonly used sensitivity functions in an application to data from an active seismic experiment carried out at Deception Island (Antarctica). Results show that these novel functions are based on a reliable and physically grounded method to image magnitude and shape of scattering and absorption anomalies. Their
2D PIC simulations of a curved supercritical shock: dynamics of the whistler precursor
NASA Astrophysics Data System (ADS)
Stienlet, J.; Lembege, B.; Savoini, P.
2009-12-01
directions of the shock normal and compared with previous modes (Gary et Mellott, 1985). These results will be discussed and compared with previous 1D and 2D simulations of planar shocks. References: Gary S. P. and M.M.Mellott, Whistler Damping at oblique propagation: Laminar Shock Precursors, J. Geophys .Res., 1985. Liewer J., K. Decyk, J.M. Dawson and B. Lembege, Numerical Studies of Electron Dynamics in Oblique Quasi-Perpendicular Collisionless Shock Waves, J. Geophys.Res. ,96, 9455, 1991. Krauss-Varban D., F. Pantellini et D. Burgess, Electron dynamics and whistler waves at quasi-perpendicular shocks , G. Res. Lett., 22, 16, 2091, 1995 Krasnoselskikh V. , B. Lembège, P. Savoini and V.V. Lobzin, Nonstationarity of strong Collisionless quasiperpendicular shocks: theory and full particle simulations, Phys. Plasma, 9, 4, 1192, 2002.
A 2D spring model for the simulation of ultrasonic wave propagation in nonlinear hysteretic media.
Delsanto, P P; Gliozzi, A S; Hirsekorn, M; Nobili, M
2006-07-01
A two-dimensional (2D) approach to the simulation of ultrasonic wave propagation in nonclassical nonlinear (NCNL) media is presented. The approach represents the extension to 2D of a previously proposed one dimensional (1D) Spring Model, with the inclusion of a PM space treatment of the intersticial regions between grains. The extension to 2D is of great practical relevance for its potential applications in the field of quantitative nondestructive evaluation and material characterization, but it is also useful, from a theoretical point of view, to gain a better insight of the interaction mechanisms involved. The model is tested by means of virtual 2D experiments. The expected NCNL behaviors are qualitatively well reproduced.
NASA Astrophysics Data System (ADS)
Darvini, G.; Salandin, P.
2009-12-01
To analyze the impact of the hydraulic conductivity K spatial variability in a real field case (as an example to delimitate a well catchment), numerical simulations can be reasonably developed in a two-dimensional vertical average context. Nevertheless the plume evolution is a consequence of a more complex three-dimensional heterogeneous structure whose vertical variability dominates the dispersion phenomena at local scale. In larger domains, the effect of the vertical heterogeneity combines itself with that one due to the horizontal variability of K, and only when the plume has travelled a large number of (horizontal) integral scales, its evolution can be analyzed in a regional context, under the hypothesis that the transmissivity spatial distribution prevails. Until this limit is reached, the vertical and horizontal variability of K are combined to give a fully 3-D dispersion process. In all these situations, to successfully accomplish the 3-D heterogeneous structure of the aquifer in 2-D simulations, more than the planimetric depth-averaged variability of K must be accounted for. To define the uncertainty related to the use of different planimetric schematizations of the real hydraulic conductivity spatial distribution, we present here the results of some numerical experiments that compare the 3-D plume evolution with 2-D simulations developed by tacking into account different hydraulic conductivity distribution schematization, by considering a hierarchical architecture of media also. This description of a sedimentary formation combined with the finite size of the plume requires theoretical and numerical tools able to take into account the flow field inhomogeneity and the ergodicity lack that characterize the transport phenomena. Following this way it will be possible to quantify / reduce the uncertainty related to a 2-D schematization in a large number of real cases where the domain spans between the local and the regional scale and whose dimension may lead to
The simulation of 3D microcalcification clusters in 2D digital mammography and breast tomosynthesis
Shaheen, Eman; Van Ongeval, Chantal; Zanca, Federica; Cockmartin, Lesley; Marshall, Nicholas; Jacobs, Jurgen; Young, Kenneth C.; Dance, David R.; Bosmans, Hilde
2011-12-15
Purpose: This work proposes a new method of building 3D models of microcalcification clusters and describes the validation of their realistic appearance when simulated into 2D digital mammograms and into breast tomosynthesis images. Methods: A micro-CT unit was used to scan 23 breast biopsy specimens of microcalcification clusters with malignant and benign characteristics and their 3D reconstructed datasets were segmented to obtain 3D models of microcalcification clusters. These models were then adjusted for the x-ray spectrum used and for the system resolution and simulated into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. Six radiologists were asked to distinguish between 40 real and 40 simulated clusters of microcalcifications in two separate studies on 2D mammography and tomosynthesis datasets. Receiver operating characteristic (ROC) analysis was used to test the ability of each observer to distinguish between simulated and real microcalcification clusters. The kappa statistic was applied to assess how often the individual simulated and real microcalcification clusters had received similar scores (''agreement'') on their realistic appearance in both modalities. This analysis was performed for all readers and for the real and the simulated group of microcalcification clusters separately. ''Poor'' agreement would reflect radiologists' confusion between simulated and real clusters, i.e., lesions not systematically evaluated in both modalities as either simulated or real, and would therefore be interpreted as a success of the present models. Results: The area under the ROC curve, averaged over the observers, was 0.55 (95% confidence interval [0.44, 0.66]) for the 2D study, and 0.46 (95% confidence interval [0.29, 0.64]) for the tomosynthesis study, indicating no statistically significant difference between real and simulated
Numerical Simulation of Black Holes
NASA Astrophysics Data System (ADS)
Teukolsky, Saul
2003-04-01
Einstein's equations of general relativity are prime candidates for numerical solution on supercomputers. There is some urgency in being able to carry out such simulations: Large-scale gravitational wave detectors are now coming on line, and the most important expected signals cannot be predicted except numerically. Problems involving black holes are perhaps the most interesting, yet also particularly challenging computationally. One difficulty is that inside a black hole there is a physical singularity that cannot be part of the computational domain. A second difficulty is the disparity in length scales between the size of the black hole and the wavelength of the gravitational radiation emitted. A third difficulty is that all existing methods of evolving black holes in three spatial dimensions are plagued by instabilities that prohibit long-term evolution. I will describe the ideas that are being introduced in numerical relativity to deal with these problems, and discuss the results of recent calculations of black hole collisions.
Numerical Simulation of Protoplanetary Vortices
2003-12-01
UNCLASSIFIED Center for Turbulence Research 81 Annual Research Briefs 2003 Numerical simulation of protoplanetary vortices By H. Lin, J.A. Barranco t AND P.S...planetesimals and planets. In earlier works ( Barranco & Marcus 2000; Barranco et al. 2000; Lin et al. 2000) we have briefly described the possible physical...transport. In particular, Barranco et al. (2000) provided a general mathe- matical framework that is suitable for the asymptotic regime of the disk
NASA Astrophysics Data System (ADS)
Fan, Cui-Ying; Zhao, Ming-Hao; Zhou, You-He
2009-09-01
The polarization saturation (PS) model [Gao, H., Barnett, D.M., 1996. An invariance property of local energy release rates in a strip saturation model of piezoelectric fracture. Int. J. Fract. 79, R25-R29; Gao, H., Zhang, T.Y., Tong, P., 1997. Local and global energy release rates for an electrically yielded crack in a piezoelectric ceramic. J. Mech. Phys. Solids 45, 491-510], and the dielectric breakdown (DB) model [Zhang, T.Y., Zhao, M.H., Cao, C.F., 2005. The strip dielectric breakdown model. Int. J. Fract. 132, 311-327] explain very well some experimental observations of fracture of piezoelectric ceramics. In this paper, the nonlinear hybrid extended displacement discontinuity-fundamental solution method (NLHEDD-FSM) is presented for numerical analysis of both the PS and DB models of two-dimensional (2D) finite piezoelectric media under impermeable and semi-permeable electric boundary conditions. In this NLHEDD-FSM, the solution is expressed approximately by a linear combination of fundamental solutions of the governing equations, which includes the extended point force fundamental solutions with sources placed at chosen points outside the domain of the problem under consideration, and the extended Crouch fundamental solutions with extended displacement discontinuities placed on the crack and the electric yielding zone. The coefficients of the fundamental solutions are determined by letting the approximated solution satisfy certain conditions on the boundary of the domain, on the crack face and the electric yielding zone. The zero electric displacement intensity factor in the PS model or the zero electric field strength intensity factor in the DB model at the outer tips of the electric yielding zone is used as a supplementary condition to determine the size of the electric yielding zone. Iteration approaches are adopted in the NLHEDD-FSM. The electric yielding zone is determined, and the extended intensity factors and the local J-integral are calculated for
2D Mesoscale Simulations of Quasielastic Reloading and Unloading in Shock Compressed Aluminum
NASA Astrophysics Data System (ADS)
Dwivedi, S. K.
2007-06-01
2D mesoscale simulations of planar shock compression, followed by either reloading or unloading, are presented that predict quasi-elastic (QE) response observed experimentally in shocked polycrystalline aluminum. The representative volume element (RVE) of the plate impact experiments included a realistic representation of a grain ensemble with apparent heterogeneities in the polycrystalline sample. Simulations were carried out using a 2D updated Lagrangian finite element code ISP-TROTP incorporating elastic-plastic deformation in grain interior and contact/cohesive methodology to analyze finite strength grain boundaries. Local heterogeneous response was quantified by calculating appropriate material variables along in-situ Lagrangian tracer lines and comparing the temporal variation of their mean values with results from 2D continuum simulations. Simulations were carried out by varying a large number of individual heterogeneities to predict QE response on reloading and unloading from shock state. The heterogeneities important for simulating the QE response identified from these simulations were: hardened grain boundaries, hard inclusions, and micro-porosity. It is shown that the shock-deformed state of polycrystalline aluminum in the presence of these effects is strongly heterogeneous with considerable variations in lateral stresses. This distributed stress state unloads the shear stress from flow stress causing QE response on reloading as well as unloading. The simulated velocity profiles and calculated shear strength and shear stresses for a representative reloading and unloading experimental configuration were found to agree well with the reported experimental data. Work supported by DOE.
NASA Astrophysics Data System (ADS)
Sirait, S. H.; Edison, R. E.; Baidillah, M. R.; Taruno, W. P.; Haryanto, F.
2016-08-01
The aim of this study is to simulate the potential distribution of 2D brain geometry based on two electrodes ECVT. ECVT (electrical capacitance tomography) is a tomography modality which produces dielectric distribution image of a subject from several capacitance electrodes measurements. This study begins by producing the geometry of 2D brain based on MRI image and then setting the boundary conditions on the boundaries of the geometry. The values of boundary conditions follow the potential values used in two electrodes brain ECVT, and for this reason the first boundary is set to 20 volt and 2.5 MHz signal and another boundary is set to ground. Poisson equation is implemented as the governing equation in the 2D brain geometry and finite element method is used to solve the equation. Simulated Hodgkin-Huxley action potential is applied as disturbance potential in the geometry. We divide this study into two which comprises simulation without disturbance potential and simulation with disturbance potential. From this study, each of time dependent potential distributions from non-disturbance and disturbance potential of the 2D brain geometry has been generated.
Numerical Propulsion System Simulation Architecture
NASA Technical Reports Server (NTRS)
Naiman, Cynthia G.
2004-01-01
The Numerical Propulsion System Simulation (NPSS) is a framework for performing analysis of complex systems. Because the NPSS was developed using the object-oriented paradigm, the resulting architecture is an extensible and flexible framework that is currently being used by a diverse set of participants in government, academia, and the aerospace industry. NPSS is being used by over 15 different institutions to support rockets, hypersonics, power and propulsion, fuel cells, ground based power, and aerospace. Full system-level simulations as well as subsystems may be modeled using NPSS. The NPSS architecture enables the coupling of analyses at various levels of detail, which is called numerical zooming. The middleware used to enable zooming and distributed simulations is the Common Object Request Broker Architecture (CORBA). The NPSS Developer's Kit offers tools for the developer to generate CORBA-based components and wrap codes. The Developer's Kit enables distributed multi-fidelity and multi-discipline simulations, preserves proprietary and legacy codes, and facilitates addition of customized codes. The platforms supported are PC, Linux, HP, Sun, and SGI.
Transverse instability of electron plasma waves study via direct 2 +2D Vlasov simulations
NASA Astrophysics Data System (ADS)
Silantyev, Denis; Lushnikov, Pavel; Rose, Harvey
2016-10-01
Transverse instability can be viewed as initial stage of electron plasma waves (EPWs) filamentation. We performed direct 2 +2D Vlasov-Poisson simulations of collisionless plasma to systematically study the growth rates of oblique modes of finite-amplitude EPW depending on its amplitude, wavenumber, angle of the oblique mode wavevector relative to the EPW's wavevector and the configuration of the trapped electrons in the EPW. Simulation results are compared to the predictions of theoretical models.
Numerical investigation of 3D effects on a 2D-dominated shocked mixing layer
NASA Astrophysics Data System (ADS)
Reese, Daniel; Weber, Christopher
2016-11-01
A nominally two-dimensional interface, unstable to the Rayleigh-Taylor or Richtmyer-Meshkov instability, will become three-dimensional at high Reynolds numbers due to the growth of background noise and 3D effects like vortex stretching. This three-dimensionality changes macroscopic features, such as the perturbation growth rate and mixing, as it enhances turbulent dissipation. In this study, a 2D perturbation with small-scale, 3D fluctuations is modeled using the hydrodynamics code Miranda. A Mach 1.95 shockwave accelerates a helium-over-SF6 interface, similar to the experiments of Motl et al. ["Experimental validation of a Richtmyer-Meshkov scaling law over large density ratio and shock strength ranges," Phys. Fluids 21(12), 126102 (2009)], to explore the regime where a 2D dominated flow will experience 3D effects. We report on the structure, growth, and mixing of the post-shocked interface in 2D and 3D.
The simulation of 3D mass models in 2D digital mammography and breast tomosynthesis
Shaheen, Eman De Keyzer, Frederik; Bosmans, Hilde; Ongeval, Chantal Van; Dance, David R.; Young, Kenneth C.
2014-08-15
Purpose: This work proposes a new method of building 3D breast mass models with different morphological shapes and describes the validation of the realism of their appearance after simulation into 2D digital mammograms and breast tomosynthesis images. Methods: Twenty-five contrast enhanced MRI breast lesions were collected and each mass was manually segmented in the three orthogonal views: sagittal, coronal, and transversal. The segmented models were combined, resampled to have isotropic voxel sizes, triangularly meshed, and scaled to different sizes. These masses were referred to as nonspiculated masses and were then used as nuclei onto which spicules were grown with an iterative branching algorithm forming a total of 30 spiculated masses. These 55 mass models were projected into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. The realism of the appearance of these mass models was assessed by five radiologists via receiver operating characteristic (ROC) analysis when compared to 54 real masses. All lesions were also given a breast imaging reporting and data system (BIRADS) score. The data sets of 2D mammography and tomosynthesis were read separately. The Kendall's coefficient of concordance was used for the interrater observer agreement assessment for the BIRADS scores per modality. Further paired analysis, using the Wilcoxon signed rank test, of the BIRADS assessment between 2D and tomosynthesis was separately performed for the real masses and for the simulated masses. Results: The area under the ROC curves, averaged over all observers, was 0.54 (95% confidence interval [0.50, 0.66]) for the 2D study, and 0.67 (95% confidence interval [0.55, 0.79]) for the tomosynthesis study. According to the BIRADS scores, the nonspiculated and the spiculated masses varied in their degrees of malignancy from normal (BIRADS 1) to highly
Applicability extent of 2-D heat equation for numerical analysis of a multiphysics problem
NASA Astrophysics Data System (ADS)
Khawaja, H.
2017-01-01
This work focuses on thermal problems, solvable using the heat equation. The fundamental question being answered here is: what are the limits of the dimensions that will allow a 3-D thermal problem to be accurately modelled using a 2-D Heat Equation? The presented work solves 2-D and 3-D heat equations using the Finite Difference Method, also known as the Forward-Time Central-Space (FTCS) method, in MATLAB®. For this study, a cuboidal shape domain with a square cross-section is assumed. The boundary conditions are set such that there is a constant temperature at its center and outside its boundaries. The 2-D and 3-D heat equations are solved in a time dimension to develop a steady state temperature profile. The method is tested for its stability using the Courant-Friedrichs-Lewy (CFL) criteria. The results are compared by varying the thickness of the 3-D domain. The maximum error is calculated, and recommendations are given on the applicability of the 2-D heat equation.
2D transient granular flows over obstacles: experimental and numerical work
NASA Astrophysics Data System (ADS)
Juez, Carmelo; Caviedes-Voullième, Daniel; Murillo, Javier; García-Navarro, Pilar
2016-04-01
the material is traditionally oriented in a predominant longitudinal direction and the layer of the mass is thin in comparison to the scale of interest, the depth-averaged procedure can be performed in the mass and momentum equations. Regarding the friction theory embedded in the landslide motion, a Coulomb-like basal friction law can be assumed as a first attempt of reproducing the phenomena. On the other hand, the presence of obstacles, involves the study of the development of schock waves imposing the simulation of the granular behavior by means of a schock-tracking numerical scheme. The numerical scheme employed, is based on an approximate solvers based on Roe approaches, devoting especial attention to the frictional source terms. This work was partially funded by the ITN-Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7-PEOPLE-2013-ITN under REA grant agreement n_607394-SEDITRANS. The granular experiments were funded by DGA, Diputación General de Aragón, España.
FRANC2D: A two-dimensional crack propagation simulator. Version 2.7: User's guide
NASA Technical Reports Server (NTRS)
Wawrzynek, Paul; Ingraffea, Anthony
1994-01-01
FRANC 2D (FRacture ANalysis Code, 2 Dimensions) is a menu driven, interactive finite element computer code that performs fracture mechanics analyses of 2-D structures. The code has an automatic mesh generator for triangular and quadrilateral elements. FRANC2D calculates the stress intensity factor using linear elastic fracture mechanics and evaluates crack extension using several methods that may be selected by the user. The code features a mesh refinement and adaptive mesh generation capability that is automatically developed according to the predicted crack extension direction and length. The code also has unique features that permit the analysis of layered structure with load transfer through simulated mechanical fasteners or bonded joints. The code was written for UNIX workstations with X-windows graphics and may be executed on the following computers: DEC DecStation 3000 and 5000 series, IBM RS/6000 series, Hewlitt-Packard 9000/700 series, SUN Sparc stations, and most Silicon Graphics models.
Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model
Balakrishnan, Minimol; Chakravarthy, V. Srinivasa; Guhathakurta, Soma
2015-01-01
Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias. PMID:26733873
Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model.
Balakrishnan, Minimol; Chakravarthy, V Srinivasa; Guhathakurta, Soma
2015-01-01
Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias.
Numerical Simulations of Disk-Planet Interactions
NASA Astrophysics Data System (ADS)
D'Angelo, Gennaro
2003-06-01
The aim of this thesis is the study the dynamical interactions occurring between a forming planet and its surrounding protostellar environment. This task is accomplished by means of both 2D and 3D numerical simulations. The first part of this work concerned global simulations in 3D. These were intended to investigate large-scale effects caused by a Jupiter-size body still in the process of accreting matter from its surroundings. Simulations show that, despite a density gap forms along the orbital path, Jupiter-mass protoplanets still accrete at a rate on the order of 0.01 Earth's masses per year when they are embedded in a minimum-mass Solar nebula. In the same conditions, the migration time scale due to gravitational torques by the disk is around 100000 years. The second part of the work was dedicated to perform 2D calculations, by employing a nested-grid technique. This method allows to carry out global simulations of planets orbiting in disks and, at the same time, to resolve in great detail the dynamics of the flow inside the Roche lobe of both massive and low-mass planets. Regardless of the planet mass, the high resolution supplied by the nested-grid technique permits an evaluation of the torques, resulting from short and very short range gravitational interactions, more reliable than the one previously estimated with the aid of numerical methods. Likewise, the mass flow onto the planet is computed in a more accurate fashion. Resulting migration time scales are in the range from 20000 years, for intermediate-mass planets, to 1000000 years, for very low-mass as well as high-mass planets. Circumplanetary disks form inside of the Roche lobe of Jupiter-size secondaries. In order to evaluate the consequences of the flat geometry on the local flow structure around planets, 3D nested-grid simulations were carried out to investigate a range of planetary masses spanning from 1.5 Earth's masses to one Jupiter's mass. Outcomes show that migration rates are relatively
NASA Technical Reports Server (NTRS)
Tang, H. T.; Hofmann, R.; Yee, G.; Vaughan, D. K.
1980-01-01
Transient, nonlinear soil-structure interaction simulations of an Electric Power Research Institute, SIMQUAKE experiment were performed using the large strain, time domain STEALTH 2D code and a cyclic, kinematically hardening cap soil model. Results from the STEALTH simulations were compared to identical simulations performed with the TRANAL code and indicate relatively good agreement between all the STEALTH and TRANAL calculations. The differences that are seen can probably be attributed to: (1) large (STEALTH) vs. small (TRANAL) strain formulation and/or (2) grid discretization differences.
NASA Astrophysics Data System (ADS)
Michelson, Sara; Bao, Jian-Wen; Grell, Evelyn
2016-04-01
In this study, numerical model simulations of an idealized 2-D squall line are investigated using microphysics budget analysis. Four commonly-used microphysics schemes of various complexity are used in the simulations. Diagnoses of the source and sink terms of the hydrometeor budget equations reveal that the differences related to the assumptions of hydrometeor size-distributions between the schemes lead to the differences in the simulations due to the net effect of various microphysical processes on the interaction between latent heating/evaporative cooling and flow dynamics as the squall line develops. Results from this study also highlight the possibility that the advantage of double-moment formulations can be overshadowed by the uncertainties in the spectral definition of individual hydrometeor categories and spectrum-dependent microphysical processes.
Numerical model of water flow and solute accumulation in vertisols using HYDRUS 2D/3D code
NASA Astrophysics Data System (ADS)
Weiss, Tomáš; Dahan, Ofer; Turkeltub, Tuvia
2015-04-01
Keywords: dessication-crack-induced-salinization, preferential flow, conceptual model, numerical model, vadose zone, vertisols, soil water retention function, HYDRUS 2D/3D Vertisols cover a hydrologically very significant area of semi-arid regions often through which water infiltrates to groundwater aquifers. Understanding of water flow and solute accumulation is thus very relevant to agricultural activity and water resources management. Previous works suggest a conceptual model of dessication-crack-induced-salinization where salinization of sediment in the deep section of the vadose zone (up to 4 m) is induced by subsurface evaporation due to convective air flow in the dessication cracks. It suggests that the salinization is induced by the hydraulic gradient between the dry sediment in the vicinity of cracks (low potential) and the relatively wet sediment further from the main cracks (high potential). This paper presents a modified previously suggested conceptual model and a numerical model. The model uses a simple uniform flow approach but unconventionally prescribes the boundary conditions and the hydraulic parameters of soil. The numerical model is bound to one location close to a dairy farm waste lagoon, but the application of the suggested conceptual model could be possibly extended to all semi-arid regions with vertisols. Simulations were conducted using several modeling approaches with an ultimate goal of fitting the simulation results to the controlling variables measured in the field: temporal variation in water content across thick layer of unsaturated clay sediment (>10 m), sediment salinity and salinity the water draining down the vadose zone to the water table. The development of the model was engineered in several steps; all computed as forward solutions by try-and-error approach. The model suggests very deep instant infiltration of fresh water up to 12 m, which is also supported by the field data. The paper suggests prescribing a special atmospheric
Momentum Transport: 2D and 3D Cloud Resolving Model Simulations
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo
2001-01-01
The major objective of this study is to investigate the momentum budgets associated with several convective systems that developed during the TOGA COARE IOP (west Pacific warm pool region) and GATE (east Atlantic region). The tool for this study is the improved Goddard Cumulas Ensemble (GCE) model which includes a 3-class ice-phase microphysical scheme, explicit cloud radiative interactive processes and air-sea interactive surface processes. The model domain contains 256 x 256 grid points (with 2 km resolution) in the horizontal and 38 grid points (to a depth of 22 km) in the vertical. The 2D domain has 1024 grid points. The simulations were performed over a 7-day time period (December 19-26, 1992, for TOGA COARE and September 1-7, 1994 for GATE). Cyclic literal boundary conditions are required for this type of long-term integration. Two well organized squall systems (TOGA, COARE February 22, 1993, and GATE September 12, 1994) were also simulated using the 3D GCE model. Only 9 h simulations were required to cover the life time of the squall systems. the lateral boundary conditions were open for these two squall systems simulations. the following will be examined: (1) the momentum budgets in the convective and stratiform regions, (2) the relationship between momentum transport and cloud organization (i.e., well organized squall lines versus less organized convective), (3) the differences and similarities in momentum transport between 2D and 3D simulated convective systems, and (4) the differences and similarities in momentum budgets between cloud systems simulated with open and cyclic lateral boundary conditions. Preliminary results indicate that there are only small differences between 2D and 3D simulated momentum budgets. Major differences occur, however, between momentum budgets associated with squall systems simulated using different lateral boundary conditions.
3D Numerical simulations of oblique subduction
NASA Astrophysics Data System (ADS)
Malatesta, C.; Gerya, T.; Scambelluri, M.; Crispini, L.; Federico, L.; Capponi, G.
2012-04-01
In the past 2D numerical studies (e.g. Gerya et al., 2002; Gorczyk et al., 2007; Malatesta et al., 2012) provided evidence that during intraoceanic subduction a serpentinite channel forms above the downgoing plate. This channel forms as a result of hydration of the mantle wedge by uprising slab-fluids. Rocks buried at high depths are finally exhumed within this buoyant low-viscosity medium. Convergence rate in these 2D models was described by a trench-normal component of velocity. Several present and past subduction zones worldwide are however driven by oblique convergence between the plates, where trench-normal motion of the subducting slab is coupled with trench-parallel displacement of the plates. Can the exhumation mechanism and the exhumation rates of high-pressure rocks be affected by the shear component of subduction? And how uprise of these rocks can vary along the plate margin? We tried to address these questions performing 3D numerical models that simulate an intraoceanic oblique subduction. The models are based on thermo-mechanical equations that are solved with finite differences method and marker-in-cell techniques combined with multigrid approach (Gerya, 2010). In most of the models a narrow oceanic basin (500 km-wide) surrounded by continental margins is depicted. The basin is floored by either layered or heterogeneous oceanic lithosphere with gabbro as discrete bodies in serpentinized peridotite and a basaltic layer on the top. A weak zone in the mantle is prescribed to control the location of subduction initiation and therefore the plate margins geometry. Finally, addition of a third dimension in the simulations allowed us to test the role of different plate margin geometries on oblique subduction dynamics. In particular in each model we modified the dip angle of the weak zone and its "lateral" geometry (e.g. continuous, segmented). We consider "continuous" weak zones either parallel or increasingly moving away from the continental margins
NASA Astrophysics Data System (ADS)
Szerszeń, Krzysztof; Zieniuk, Eugeniusz
2016-06-01
The paper presents a strategy for numerical solving of parametric integral equation system (PIES) for 2D potential problems without explicit calculation of singular integrals. The values of these integrals will be expressed indirectly in terms of easy to compute non-singular integrals. The effectiveness of the proposed strategy is investigated with the example of potential problem modeled by the Laplace equation. The strategy simplifies the structure of the program with good the accuracy of the obtained solutions.
Modeling and 2-D discrete simulation of dislocation dynamics for plastic deformation of metal
NASA Astrophysics Data System (ADS)
Liu, Juan; Cui, Zhenshan; Ou, Hengan; Ruan, Liqun
2013-05-01
Two methods are employed in this paper to investigate the dislocation evolution during plastic deformation of metal. One method is dislocation dynamic simulation of two-dimensional discrete dislocation dynamics (2D-DDD), and the other is dislocation dynamics modeling by means of nonlinear analysis. As screw dislocation is prone to disappear by cross-slip, only edge dislocation is taken into account in simulation. First, an approach of 2D-DDD is used to graphically simulate and exhibit the collective motion of a large number of discrete dislocations. In the beginning, initial grains are generated in the simulation cells according to the mechanism of grain growth and the initial dislocation is randomly distributed in grains and relaxed under the internal stress. During the simulation process, the externally imposed stress, the long range stress contribution of all dislocations and the short range stress caused by the grain boundaries are calculated. Under the action of these forces, dislocations begin to glide, climb, multiply, annihilate and react with each other. Besides, thermal activation process is included. Through the simulation, the distribution of dislocation and the stress-strain curves can be obtained. On the other hand, based on the classic dislocation theory, the variation of the dislocation density with time is described by nonlinear differential equations. Finite difference method (FDM) is used to solve the built differential equations. The dislocation evolution at a constant strain rate is taken as an example to verify the rationality of the model.
Numerical simulation of aneurysm hemodynamics
NASA Astrophysics Data System (ADS)
MacVicar, Stephen; Huynh, Sophia; Rossmann, Jenn
2003-11-01
Rupture of intracranial aneurysms is the leading cause of spontaneous subarachnoid hemorrhage, with high rates of morbidity and mortality. Numerical simulations of flow in a variety of two-dimensional and three-dimensional saccular aneurysm geometries were performed to evaluate possible sites and mechanisms for aneurysm growth and rupture. The governing equations were solved in their finite volume formulation for both steady and pulsatile flows. Recirculation zones and secondary flows were observed in aneurysms and arteries. Regions of elevated and oscillating shear stress were observed, often at the aneurysm's distal shoulder. The influence of several geometric factors, including vessel curvature, branching angle, and aneurysm shape, on flow patterns and fluid mechanical forces was studied, with the goal of assessing the risks posed by given aneurysm geometry.
2-D and 3-D PIC simulations of a SLAC Klystrino
NASA Astrophysics Data System (ADS)
Spencer, Thomas; Luginsland, John; Hackett, Kirk; Haworth, Michael; Song, Liqun; Scheitrum, Glenn
2000-10-01
The Air Force Research Laboratory is collaborating with the Stanford Linear Accelerator Center in performing 3-D PIC simulations using ARGUS and ICEPIC on a klystrino with the following parameters: voltage of 110 kV, current of 2.4 A, frequency of 94 GHz, peak magnetic field of 4 kG. Results wll be presented and will be compared to 2-D MAGIC simulations, as well as to experimental test data. This work is supported in part by the Air Force Office of Scientific Research.
An interactive 2-D power-line modeling and simulation tool
NASA Astrophysics Data System (ADS)
Hull, David; Adelman, Ross
2012-06-01
The U.S. Army Research Laboratory's Power-Line unmanned aerial vehicle (UAV) Modeling and Simulation (ARL-PLUMS) is a tool for estimating and analyzing quasi-static electric and magnetic fields due to power lines. This tool consists of an interactive 2-D graphical user interface (GUI) and a compute engine that can be used to calculate and visualize the E-Field and H-Field due to as many as seven conductors (two 3-phase circuits and a ground wire). ARL-PLUMS allows the user to set the geometry of the lines and the load conditions on those lines, and then calculate Ey, Ez, Hy, or Hz along a linear path or cutting plane, or in the form of a movie. The path can be along the ground or in the air to simulate the fields that might be observed, for example, by a robotic vehicle or a UAV. ARL-PLUMS makes several simplifying assumptions in order to allow simulations to be completed on a laptop PC interactively. In most cases, the results are excellent, providing a "90% solution" in just a few minutes of total modeling and simulation time. This paper describes the physics used by ARL-PLUMS, including the simplifying assumptions and the 2-D Method of Moments solver. Examples of electric and magnetic fields for different wire configurations, including typical 3-phase distribution and transmissions lines, are provided. Comparisons to similar results using a full 3-D model are also shown, and a discussion of errors that may be expected from the 2-D simulations is provided.
An efficient numerical model for hydrodynamic parameterization in 2D fractured dual-porosity media
NASA Astrophysics Data System (ADS)
Fahs, Hassane; Hayek, Mohamed; Fahs, Marwan; Younes, Anis
2014-01-01
This paper presents a robust and efficient numerical model for the parameterization of the hydrodynamic in fractured porous media. The developed model is based upon the refinement indicators algorithm for adaptive multi-scale parameterization. For each level of refinement, the Levenberg-Marquardt method is used to minimize the difference between the measured and predicted data that are obtained by solving the direct problem with the mixed finite element method. Sensitivities of state variables with respect to the parameters are calculated by the sensitivity method. The adjoint-state method is used to calculate the local gradients of the objective function necessary for the computation of the refinement indicators. Validity and efficiency of the proposed model are demonstrated by means of several numerical experiments. The developed numerical model provides encouraging results, even for noisy data and/or with a reduced number of measured heads.
Simulating reionization in numerical cosmology
NASA Astrophysics Data System (ADS)
Sokasian, Aaron
2003-11-01
The incorporation of radiative transfer effects into cosmological hydrodynamical simulations is essential for understanding how the intergalactic medium (IGM) makes the transition from a neutral medium to one that is almost fully ionized. I present an approximate numerical method designed to study in a statistical sense how a cosmological density field is ionized by various sets of sources. The method requires relatively few time steps and can be employed with simulations of high resolution. First, I explore the reionization history of Helium II by z < 6 quasars. Comparisons between HeII opacities measured observationally and inferred from our analysis reveal that the uncertainties in the empirical luminosity function provide enough leeway to provide a satisfactory match. A property common to all the calculations is that the epoch of Helium II reionization must have occurred between 3≲
Quantum simulation of 2D topological physics in a 1D array of optical cavities.
Luo, Xi-Wang; Zhou, Xingxiang; Li, Chuan-Feng; Xu, Jin-Shi; Guo, Guang-Can; Zhou, Zheng-Wei
2015-07-06
Orbital angular momentum of light is a fundamental optical degree of freedom characterized by unlimited number of available angular momentum states. Although this unique property has proved invaluable in diverse recent studies ranging from optical communication to quantum information, it has not been considered useful or even relevant for simulating nontrivial physics problems such as topological phenomena. Contrary to this misconception, we demonstrate the incredible value of orbital angular momentum of light for quantum simulation by showing theoretically how it allows to study a variety of important 2D topological physics in a 1D array of optical cavities. This application for orbital angular momentum of light not only reduces required physical resources but also increases feasible scale of simulation, and thus makes it possible to investigate important topics such as edge-state transport and topological phase transition in a small simulator ready for immediate experimental exploration.
A faster method for 3D/2D medical image registration—a simulation study
NASA Astrophysics Data System (ADS)
Birkfellner, Wolfgang; Wirth, Joachim; Burgstaller, Wolfgang; Baumann, Bernard; Staedele, Harald; Hammer, Beat; Claudius Gellrich, Niels; Jacob, Augustinus Ludwig; Regazzoni, Pietro; Messmer, Peter
2003-08-01
3D/2D patient-to-computed-tomography (CT) registration is a method to determine a transformation that maps two coordinate systems by comparing a projection image rendered from CT to a real projection image. Iterative variation of the CT's position between rendering steps finally leads to exact registration. Applications include exact patient positioning in radiation therapy, calibration of surgical robots, and pose estimation in computer-aided surgery. One of the problems associated with 3D/2D registration is the fact that finding a registration includes solving a minimization problem in six degrees of freedom (dof) in motion. This results in considerable time requirements since for each iteration step at least one volume rendering has to be computed. We show that by choosing an appropriate world coordinate system and by applying a 2D/2D registration method in each iteration step, the number of iterations can be grossly reduced from n6 to n5. Here, n is the number of discrete variations around a given coordinate. Depending on the configuration of the optimization algorithm, this reduces the total number of iterations necessary to at least 1/3 of it's original value. The method was implemented and extensively tested on simulated x-ray images of a tibia, a pelvis and a skull base. When using one projective image and a discrete full parameter space search for solving the optimization problem, average accuracy was found to be 1.0 +/- 0.6(°) and 4.1 +/- 1.9 (mm) for a registration in six parameters, and 1.0 +/- 0.7(°) and 4.2 +/- 1.6 (mm) when using the 5 + 1 dof method described in this paper. Time requirements were reduced by a factor 3.1. We conclude that this hardware-independent optimization of 3D/2D registration is a step towards increasing the acceptance of this promising method for a wide number of clinical applications.
A faster method for 3D/2D medical image registration--a simulation study.
Birkfellner, Wolfgang; Wirth, Joachim; Burgstaller, Wolfgang; Baumann, Bernard; Staedele, Harald; Hammer, Beat; Gellrich, Niels Claudius; Jacob, Augustinus Ludwig; Regazzoni, Pietro; Messmer, Peter
2003-08-21
3D/2D patient-to-computed-tomography (CT) registration is a method to determine a transformation that maps two coordinate systems by comparing a projection image rendered from CT to a real projection image. Iterative variation of the CT's position between rendering steps finally leads to exact registration. Applications include exact patient positioning in radiation therapy, calibration of surgical robots, and pose estimation in computer-aided surgery. One of the problems associated with 3D/2D registration is the fact that finding a registration includes solving a minimization problem in six degrees of freedom (dof) in motion. This results in considerable time requirements since for each iteration step at least one volume rendering has to be computed. We show that by choosing an appropriate world coordinate system and by applying a 2D/2D registration method in each iteration step, the number of iterations can be grossly reduced from n6 to n5. Here, n is the number of discrete variations around a given coordinate. Depending on the configuration of the optimization algorithm, this reduces the total number of iterations necessary to at least 1/3 of it's original value. The method was implemented and extensively tested on simulated x-ray images of a tibia, a pelvis and a skull base. When using one projective image and a discrete full parameter space search for solving the optimization problem, average accuracy was found to be 1.0 +/- 0.6(degrees) and 4.1 +/- 1.9 (mm) for a registration in six parameters, and 1.0 +/- 0.7(degrees) and 4.2 +/- 1.6 (mm) when using the 5 + 1 dof method described in this paper. Time requirements were reduced by a factor 3.1. We conclude that this hardware-independent optimization of 3D/2D registration is a step towards increasing the acceptance of this promising method for a wide number of clinical applications.
Spatially Resolved Synthetic Spectra from 2D Simulations of Stainless Steel Wire Array Implosions
Clark, R. W.; Giuliani, J. L.; Thornhill, J. W.; Chong, Y. K.; Dasgupta, A.; Davis, J.
2009-01-21
A 2D radiation MHD model has been developed to investigate stainless steel wire array implosion experiments on the Z and refurbished Z machines. This model incorporates within the Mach2 MHD code a self-consistent calculation of the non-LTE kinetics and ray trace based radiation transport. Such a method is necessary in order to account for opacity effects in conjunction with ionization kinetics of K-shell emitting plasmas. Here the model is used to investigate multi-dimensional effects of stainless steel wire implosions. In particular, we are developing techniques to produce non-LTE, axially and/or radially resolved synthetic spectra based upon snapshots of our 2D simulations. Comparisons between experimental spectra and these synthetic spectra will allow us to better determine the state of the experimental pinches.
Matrone, G; Quaglia, F; Magenes, G
2010-01-01
Modern ultrasound imaging instrumentation for clinical applications allows real-time volumetric scanning of the patients' body. 4D imaging has been made possible thanks to the development of new echographic probes which consist in 2D phased arrays of piezoelectric transducers. In these new devices it is the system electronics which properly drives the matrix elements and focuses the beam in order to obtain a sequence of volumetric images. This paper introduces an ultrasound field simulator based on the Spatial Impulse Response method which is being properly developed to analyze the characteristics of the ultrasound field generated by a 2D phased array of transducers. Thanks to its high configurability by the user, it will represent a very useful tool for electronics designers in developing 4D ultrasound imaging systems components.
Application of 2-D simulations to hollow z-pinch implosions
Peterson, D.L.; Bowers, R.L.; Brownell, J.H.
1997-12-01
The application of simulations of z-pinch implosions should have at least two goals: first, to properly model the most important physical processes occurring in the pinch allowing for a better understanding of the experiments and second, provide a design capability for future experiments. Beginning with experiments fielded at Los Alamos on the Pegasus 1 and Pegasus 2 capacitor banks, the authors have developed a methodology for simulating hollow z-pinches in two dimensions which has reproduced important features of the measured experimental current drive, spectrum, radiation pulse shape, peak power and total radiated energy. This methodology employs essentially one free parameter, the initial level of the random density perturbations imposed at the beginning of the 2-D simulation, but in general no adjustments to other parameters are required. Currently the authors are applying this capability to the analysis of recent Saturn and PBFA-Z experiments. The code results provide insight into the nature of the pinch plasma prior to arrival on-axis, during thermalization and development after peak pinch time. Among other things, the simulation results provide an explanation for the production of larger amounts of radiated energy than would be expected from a simple slug-model kinetic energy analysis and the appearance of multiple peaks in the radiation power. The 2-D modeling has also been applied to the analysis of Saturn dynamic hohlraum experiments and is being used in the design of this and other Z-Pinch applications on PBFA-Z.
2D PIC simulations of a curved supercritical shock: dynamics of the whistler precursor
NASA Astrophysics Data System (ADS)
Stienlet, Joël.; Savoini, Philippe; Lembege, Bertrand
2010-05-01
The whistler precursor emitted from the curved terrestrial shock front plays an important role in pre-decelerating and heating the incoming solar wind. Most previous works have mainly analyzed the features of the whistler precursor emission for a 1D planar shock where it is forced to propagate along the shock normal (Liewer and al, 1991) or to propagate obliquely with respect to a fixed shock normal direction in 2D planar shock simulation (Krauss-Varban et al., 1995). In the present case, the dynamics of the precursor is analyzed with the help of a 2D full particle simulation for a continuously curved shock within the angular range 90o ≥ ?Bn ≥ 45o where ?Bn is the angle between the shock normal and the upstream magnetostatic field. Both electrons and ions dynamics are described by a self consistent approach. Our results show that (i) the whistler precursor extends far from the shock front mainly along the magnetostatic field (projected on the simulation plane) and not along the shock normal; (ii) the width of these curved wave fronts (precursor) strongly decreases when moving far from the shock front; (iii) at the shock front, the precursor is emitted within an angular range much larger than that predicted by linear theory; (iv) the damping rate of the whistler precursor is analyzed for different directions of the shock normal. Wave particle energy transfer is analysed, and these results will be discussed and compared with previous 1D and 2D simulations of planar shocks; (v) the whistler precursor is not monochromatic, and interferences between modes are evidenced by beats and wave-packets in front of the shock. The impact of this effect on damping rate measurements will be discussed.
NASA Astrophysics Data System (ADS)
Cepeda, Jose; Luna, Byron Quan; Nadim, Farrokh
2013-04-01
An essential component of a quantitative landslide hazard assessment is establishing the extent of the endangered area. This task requires accurate prediction of the run-out behaviour of a landslide, which includes the estimation of the run-out distance, run-out width, velocities, pressures, and depth of the moving mass and the final configuration of the deposits. One approach to run-out modelling is to reproduce accurately the dynamics of the propagation processes. A number of dynamic numerical models are able to compute the movement of the flow over irregular topographic terrains (3-D) controlled by a complex interaction between mechanical properties that may vary in space and time. Given the number of unknown parameters and the fact that most of the rheological parameters cannot be measured in the laboratory or field, the parametrization of run-out models is very difficult in practice. For this reason, the application of run-out models is mostly used for back-analysis of past events and very few studies have attempted to achieve forward predictions. Consequently all models are based on simplified descriptions that attempt to reproduce the general features of the failed mass motion through the use of parameters (mostly controlling shear stresses at the base of the moving mass) which account for aspects not explicitly described or oversimplified. The uncertainties involved in the run-out process have to be approached in a stochastic manner. It is of significant importance to develop methods for quantifying and properly handling the uncertainties in dynamic run-out models, in order to allow a more comprehensive approach to quantitative risk assessment. A method was developed to compute the variation in run-out intensities by using a dynamic run-out model (MassMov2D) and a probabilistic framework based on a Monte Carlo simulation in order to analyze the effect of the uncertainty of input parameters. The probability density functions of the rheological parameters
A Beam-Fourier Technique for the Numerical Investigation of 2D Nonlinear Convective Flows
NASA Astrophysics Data System (ADS)
Papanicolaou, N. C.
2011-11-01
In the current work, we develop a numerical method suitable for treating the problem of nonlinear two-dimensional flows in rectangular domains. For the spatial approximation we employ the Fourier-Galerkin approach. More specifically, our basis functions are products of trigonometric and Beam functions. This choice means that the solutions automatically satisfy the boundary and periodic conditions in the x and y directions respectively. The accuracy of the method is assessed by applying it to model problems which admit exact analytical solutions. The numerical and analytic solutions are found to be in good agreement. The convergence rate of the spectral coefficients is found to be fifth-order algebraic in the x-direction and y-direction, confirming the efficiency and speed of our technique.
A numerical study of 2D detonation waves with adaptive finite volume methods on unstructured grids
NASA Astrophysics Data System (ADS)
Hu, Guanghui
2017-02-01
In this paper, a framework of adaptive finite volume solutions for the reactive Euler equations on unstructured grids is proposed. The main ingredients of the algorithm include a second order total variation diminishing Runge-Kutta method for temporal discretization, and the finite volume method with piecewise linear solution reconstruction of the conservative variables for the spatial discretization in which the least square method is employed for the reconstruction, and weighted essentially nonoscillatory strategy is used to restrain the potential numerical oscillation. To resolve the high demanding on the computational resources due to the stiffness of the system caused by the reaction term and the shock structure in the solutions, the h-adaptive method is introduced. OpenMP parallelization of the algorithm is also adopted to further improve the efficiency of the implementation. Several one and two dimensional benchmark tests on the ZND model are studied in detail, and numerical results successfully show the effectiveness of the proposed method.
Ion cyclotron emission calculations using a 2D full wave numerical code
NASA Astrophysics Data System (ADS)
Batchelor, D. B.; Jaeger, E. F.; Colestock, P. L.
1987-09-01
Measurement of radiation in the HF band due to cyclotron emission by energetic ions produced by fusion reactions or neutral beam injection promises to be a useful diagnostic on large devices which are entering the reactor regime of operation. A number of complications make the modelling and interpretation of such measurements difficult using conventional geometrical optics methods. In particular the long wavelength and lack of high directivity of antennas in this frequency regime make observation of a single path across the plasma into a viewing dump impractical. Pickup antennas effectively see the whole plasma and wall reflection effects are important. We have modified our 2D full wave ICRH code2 to calculate wave fields due to a distribution of energetic ions in tokamak geometry. The radiation is modeled as due to an ensemble of localized source currents distributed in space. The spatial structure of the coherent wave field is then calculated including cyclotron harmonic damping as compared to the usual procedure of incoherently summing powers of individual radiators. This method has the advantage that phase information from localized radiating currents is globally retained so the directivity of the pickup antennas is correctly represented. Also standing waves and wall reflections are automatically included.
Numerical Simulation of Protoplanetary Vortices
NASA Technical Reports Server (NTRS)
Lin, H.; Barranco, J. A.; Marcus, P. S.
2003-01-01
The fluid dynamics within a protoplanetary disk has been attracting the attention of many researchers for a few decades. Previous works include, to list only a few among many others, the well-known prescription of Shakura & Sunyaev, the convective and instability study of Stone & Balbus and Hawley et al., the Rossby wave approach of Lovelace et al., as well as a recent work by Klahr & Bodenheimer, which attempted to identify turbulent flow within the disk. The disk is commonly understood to be a thin gas disk rotating around a central star with differential rotation (the Keplerian velocity), and the central quest remains as how the flow behavior deviates (albeit by a small amount) from a strong balance established between gravitational and centrifugal forces, transfers mass and momentum inward, and eventually forms planetesimals and planets. In earlier works we have briefly described the possible physical processes involved in the disk; we have proposed the existence of long-lasting, coherent vortices as an efficient agent for mass and momentum transport. In particular, Barranco et al. provided a general mathematical framework that is suitable for the asymptotic regime of the disk; Barranco & Marcus (2000) addressed a proposed vortex-dust interaction mechanism which might lead to planetesimal formation; and Lin et al. (2002), as inspired by general geophysical vortex dynamics, proposed basic mechanisms by which vortices can transport mass and angular momentum. The current work follows up on our previous effort. We shall focus on the detailed numerical implementation of our problem. We have developed a parallel, pseudo-spectral code to simulate the full three-dimensional vortex dynamics in a stably-stratified, differentially rotating frame, which represents the environment of the disk. Our simulation is validated with full diagnostics and comparisons, and we present our results on a family of three-dimensional, coherent equilibrium vortices.
Numerical Simulations of Thermobaric Explosions
Kuhl, A L; Bell, J B; Beckner, V E; Khasainov, B
2007-05-04
A Model of the energy evolution in thermobaric explosions is presented. It is based on the two-phase formulation: conservation laws for the gas and particle phases along with inter-phase interaction terms. It incorporates a Combustion Model based on the mass conservation laws for fuel, air and products; source/sink terms are treated in the fast-chemistry limit appropriate for such gas dynamic fields. The Model takes into account both the afterburning of the detonation products of the booster with air, and the combustion of the fuel (Al or TNT detonation products) with air. Numerical simulations were performed for 1.5-g thermobaric explosions in five different chambers (volumes ranging from 6.6 to 40 liters and length-to-diameter ratios from 1 to 12.5). Computed pressure waveforms were very similar to measured waveforms in all cases - thereby proving that the Model correctly predicts the energy evolution in such explosions. The computed global fuel consumption {mu}(t) behaved as an exponential life function. Its derivative {dot {mu}}(t) represents the global rate of fuel consumption. It depends on the rate of turbulent mixing which controls the rate of energy release in thermobaric explosions.
Fast Acceleration of 2D Wave Propagation Simulations Using Modern Computational Accelerators
Wang, Wei; Xu, Lifan; Cavazos, John; Huang, Howie H.; Kay, Matthew
2014-01-01
Recent developments in modern computational accelerators like Graphics Processing Units (GPUs) and coprocessors provide great opportunities for making scientific applications run faster than ever before. However, efficient parallelization of scientific code using new programming tools like CUDA requires a high level of expertise that is not available to many scientists. This, plus the fact that parallelized code is usually not portable to different architectures, creates major challenges for exploiting the full capabilities of modern computational accelerators. In this work, we sought to overcome these challenges by studying how to achieve both automated parallelization using OpenACC and enhanced portability using OpenCL. We applied our parallelization schemes using GPUs as well as Intel Many Integrated Core (MIC) coprocessor to reduce the run time of wave propagation simulations. We used a well-established 2D cardiac action potential model as a specific case-study. To the best of our knowledge, we are the first to study auto-parallelization of 2D cardiac wave propagation simulations using OpenACC. Our results identify several approaches that provide substantial speedups. The OpenACC-generated GPU code achieved more than speedup above the sequential implementation and required the addition of only a few OpenACC pragmas to the code. An OpenCL implementation provided speedups on GPUs of at least faster than the sequential implementation and faster than a parallelized OpenMP implementation. An implementation of OpenMP on Intel MIC coprocessor provided speedups of with only a few code changes to the sequential implementation. We highlight that OpenACC provides an automatic, efficient, and portable approach to achieve parallelization of 2D cardiac wave simulations on GPUs. Our approach of using OpenACC, OpenCL, and OpenMP to parallelize this particular model on modern computational accelerators should be applicable to other computational models of wave propagation in
High-resolution 2D3V simulations of forced hybrid-kinetic turbulence
NASA Astrophysics Data System (ADS)
Cerri, Silvio Sergio; Califano, Francesco; Rincon, Francois; Told, Daniel; Jenko, Frank; Pegoraro, Francesco
2016-10-01
The understanding of the kinetic processes at play in plasma turbulence is a frontier problem in plasma physics and among the topics currently of most interest in space plasma research. Here we investigate the properties of turbulence from the end of the magnetohydrodynamic (MHD) cascade to scales well below the ion gyroradius (i.e., the so-called ``dissipation'' or ``dispersion'' range) by means of unprecedented high-resolution simulations of forced hybrid-kinetic turbulence in a 2D3V phase-space (two real-space and three velocity-space dimensions). Different values of the plasma beta parameter typical of the solar wind (SW) are investigated. Several aspects of turbulence at small-scales emerging from the simulations are presented and discussed. Even within the limitations of the hybrid approach in 2D3V, a reasonable agreement with SW observations and with theory is found. Finally, we identify possible implications and questions related to SW turbulence which arise from this study. This research has been funded by European Union's Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement No.277870 and by Euratom research and training programme 2014-2018. Simulations were performed on Fermi (CINECA, IT) and Hydra (MPCDF, DE).
NASA Astrophysics Data System (ADS)
Mendoza-Torres, F.; Diaz-Viera, M. A.
2015-12-01
In many natural fractured porous media, such as aquifers, soils, oil and geothermal reservoirs, fractures play a crucial role in their flow and transport properties. An approach that has recently gained popularity for modeling fracture systems is the Discrete Fracture Network (DFN) model. This approach consists in applying a stochastic boolean simulation method, also known as object simulation method, where fractures are represented as simplified geometric objects (line segments in 2D and polygons in 3D). One of the shortcomings of this approach is that it usually does not consider the dependency relationships that may exist between the geometric properties of fractures (direction, length, aperture, etc), that is, each property is simulated independently. In this work a method for modeling such dependencies by copula theory is introduced. In particular, a nonparametric model using Bernstein copulas for direction-length fracture dependency in 2D is presented. The application of this method is illustrated in a case study for a fractured rock sample from a carbonate reservoir outcrop.
Tuning and simulating a 193-nm resist for 2D applications
NASA Astrophysics Data System (ADS)
Howard, William B.; Wiaux, Vincent; Ercken, Monique; Bui, Bang; Byers, Jeff D.; Pochkowski, Mike
2002-07-01
For some applications, the usefulness of lithography simulation results depends strongly on the matching between experimental conditions and the simulation input parameters. If this matching is optimized and other sources of error are minimized, then the lithography model can be used to explain printed wafer experimental results. Further, simulation can be useful in predicting the results or in choosing the correct set of experiments. In this paper, PROLITH and ProDATA AutoTune were used to systematically vary simulation input parameters to match measured results on printed wafers used in a 193 nm process. The validity of the simulation parameters was then checked using 3D simulation compared to 2D top-down SEM images. The quality of matching was evaluated using the 1D metrics of average gate CD and Line End Shortening (LES). To ensure the most accurate simulation, a new approach was taken to create a compound mask from GDSII contextual information surrounding an accurate SEM image of the reticle region of interest. Corrections were made to account for all metrology offsets.
2-D/3-D ECE imaging data for validation of turbulence simulations
NASA Astrophysics Data System (ADS)
Choi, Minjun; Lee, Jaehyun; Yun, Gunsu; Lee, Woochang; Park, Hyeon K.; Park, Young-Seok; Sabbagh, Steve A.; Wang, Weixing; Luhmann, Neville C., Jr.
2015-11-01
The 2-D/3-D KSTAR ECEI diagnostic can provide a local 2-D/3-D measurement of ECE intensity. Application of spectral analysis techniques to the ECEI data allows local estimation of frequency spectra S (f) , wavenumber spectra S (k) , wavernumber and frequency spectra S (k , f) , and bispectra b (f1 ,f2) of ECE intensity over the 2-D/3-D space, which can be used to validate turbulence simulations. However, the minimum detectable fluctuation amplitude and the maximum detectable wavenumber are limited by the temporal and spatial resolutions of the diagnostic system, respectively. Also, the finite measurement area of the diagnostic channel could introduce uncertainty in the spectra estimation. The limitations and accuracy of the ECEI estimated spectra have been tested by a synthetic ECEI diagnostic with the model and/or fluctuations calculated by GTS. Supported by the NRF of Korea under Contract No. NRF-2014M1A7A1A03029881 and NRF-2014M1A7A1A03029865 and by U.S. DOE grant DE-FG02-99ER54524.
2012-11-08
Comparison between adaptive and uniform discontinuous Galerkin simulations in dry 2D bubble experiments Andreas Müllera,∗, Jörn Behrensb, Francis X...joern.behrens@zmaw.de (Jörn Behrens), fxgirald@nps.edu ( Francis X. Giraldo), vwirth@uni-mainz.de (Volkmar Wirth) Accepted by Journal of Computational...Mon. Weather Rev. 120 (1992) 1675–1706. [3] D. P. Bacon , N. N. Ahmad, Z. Boybeyi, T. J. Dunn, M. S. Hall, P. C. S. Lee, R. A. Sarma, M. D. Turner, K. T
Simulations of two-particle interactions with 2D quantum walks in time
Schreiber, A.; Laiho, K.; Silberhorn, C.; Rohde, P. P.; Štefaňak, M.; Potoček, V.; Hamilton, C.; Jex, I.
2014-12-04
We present the experimental implementation of a quantum walk on a two-dimensional lattice and show how to employ the optical system to simulate the quantum propagation of two interacting particles. Our quantum walk in time transfers the spatial spread of a quantum walk into the time domain, which guarantees a high stability and scalability of the setup. We present with our device quantum walks over 12 steps on a 2D lattice. By changing the properties of the driving quantum coin, we investigate different kinds of two-particle interactions and reveal their impact on the occurring quantum propagation.
Solution of the field equations for 2-D electromagnetic direct implicit plasma simulation
NASA Astrophysics Data System (ADS)
Hewett, D. W.; Langdon, A. B.
1985-01-01
A direct implicit particle-in-cell (PIC) simulation model with full electromagnetic (EM) effects has been implemented in 2-D Cartesian geometry. The model, implemented with the D1 time differencing scheme, was first implemented in a 1-D electrostatic (ES) version to gain some experience with spatial differencing in forms suitable for extension to the full EM field in two dimensions. The implicit EM field solve is considerably different from the implicit ES code. The EM field calculation requires an inductive part as well as the electrostatic and the B field must be self-consistently advanced.
A numerical method for computing unsteady 2-D boundary layer flows
NASA Technical Reports Server (NTRS)
Krainer, Andreas
1988-01-01
A numerical method for computing unsteady two-dimensional boundary layers in incompressible laminar and turbulent flows is described and applied to a single airfoil changing its incidence angle in time. The solution procedure adopts a first order panel method with a simple wake model to solve for the inviscid part of the flow, and an implicit finite difference method for the viscous part of the flow. Both procedures integrate in time in a step-by-step fashion, in the course of which each step involves the solution of the elliptic Laplace equation and the solution of the parabolic boundary layer equations. The Reynolds shear stress term of the boundary layer equations is modeled by an algebraic eddy viscosity closure. The location of transition is predicted by an empirical data correlation originating from Michel. Since transition and turbulence modeling are key factors in the prediction of viscous flows, their accuracy will be of dominant influence to the overall results.
Elastic properties of large tow 2-D braided composites by numerical and analytical methods
Nguyen, T D; Zywicz, E
1998-09-01
The homogenized extensional and flexural properties of a large tow, two- dimensional, braided carbon-fiber composite lamina were evaluated using analytical and numerical methods. The plane-stress composite lamina was assumed to be periodic in its plane and was modeled with a single representative volume element. The homogenized elastic properties were analytically estimated using beam-theory concepts and upper and lower bound techniques as well as using three-dimensional finite element analyses. The homogenized extensional and bending lamina properties are, in general, distinct properties and are not simply related to each other as in monolithic beams and plates or in composites with very fine and highly periodic microstructures. The importance and cause of distinct homogenized extensional and flexural elastic properties is briefly discussed.
Numerical simulation of interplanetary dynamics
NASA Astrophysics Data System (ADS)
Wu, Chin-Chun
This dissertation discusses investigations into the physics of the propagation of solar generated disturbances in the interplanetary medium. The motivation to initiate this study was two-fold: (1) understanding the fundamental physics of the nonlinear interactions of solar generated MHD shocks and non-homogeneous interplanetary medium, and (2) understanding the physics of solar generated disturbance effects on the Earth's environment, (i.e. the solar connection to the geomagnetic storm). In order to achieve these goals, the authors employed two numerical models to encompass these studies. In the first part, a one-dimensional MHD code with adaptive grids is used to study the evolution of interplanetary slow shocks (ISS), the interaction of a forward slow shock with a reverse slow shock, and the interaction of a fast shock with a slow shock. Results show that the slow shocks can be generated by a decreasing density, velocity or temperature perturbation or by a pressure pulse by following a forward fast shock and that slow shocks can propagate over 1 AU; results also show that the ISS never evolves into fast shocks. Interestingly, it is also found that an ISS could be 'eaten up' by an interplanetary fast shock (IFS) catching up from behind. This could be a reason that the slow shock has been difficult to observe near 1 AU. In addition, a forward slow shock could be dissipated by following a strong forward fast shock (Mach number greater than 1.7). In the second part, a fully three-dimensional (3D), time-dependent, MHD interplanetary global model (3D IGM) is used to study the relationship between different forms of solar activity and transient variations of the north-south component, Bx, of the interplanetary magnetic field, IMF, at 1 AU. One form of solar activity, the flare, is simulated by using a pressure pulse at different locations near the solar surface and observing the simulated IMF evolution of Btheta (= -Bx) at 1 AU. Results show that, for a given pressure
Numerical Simulations of Granular Processes
NASA Astrophysics Data System (ADS)
Richardson, Derek C.; Michel, Patrick; Schwartz, Stephen R.; Ballouz, Ronald-Louis; Yu, Yang; Matsumura, Soko
2014-11-01
Spacecraft images and indirect observations including thermal inertia measurements indicate most small bodies have surface regolith. Evidence of granular flow is also apparent in the images. This material motion occurs in very low gravity, therefore in a completely different gravitational environment than on the Earth. Understanding and modeling these motions can aid in the interpretation of imaged surface features that may exhibit signatures of constituent material properties. Also, upcoming sample-return missions to small bodies, and possible future manned missions, will involve interaction with the surface regolith, so it is important to develop tools to predict the surface response. We have added new capabilities to the parallelized N-body gravity tree code pkdgrav [1,2] that permit the simulation of granular dynamics, including multi-contact physics and friction forces, using the soft-sphere discrete-element method [3]. The numerical approach has been validated through comparison with laboratory experiments (e.g., [3,4]). Ongoing and recently completed projects include: impacts into granular materials using different projectile shapes [5]; possible tidal resurfacing of asteroid Apophis during its 2029 encounter [6]; the Brazil-nut effect in low gravity [7]; and avalanche modeling.Acknowledgements: DCR acknowledges NASA (grants NNX08AM39G, NNX10AQ01G, NNX12AG29G) and NSF (AST1009579). PM acknowledges the French agency CNES. SRS works on the NEOShield Project funded under the European Commission’s FP7 program agreement No. 282703. SM acknowledges support from the Center for Theory and Computation at U Maryland and the Dundee Fellowship at U Dundee. Most simulations were performed using the YORP cluster in the Dept. of Astronomy at U Maryland and on the Deepthought High-Performance Computing Cluster at U Maryland.References: [1] Richardson, D.C. et al. 2000, Icarus 143, 45; [2] Stadel, J. 2001, Ph.D. Thesis, U Washington; [3] Schwartz, S.R. et al. 2012, Gran
Numerical simulations of drainage flows on Mars
NASA Technical Reports Server (NTRS)
Parish, Thomas R.; Howard, Alan D.
1992-01-01
Data collected by Viking Landers have shown that the meteorology of the near surface Martian environment is analogous to desertlike terrestrial conditions. Geological evidence such as dunes and frost streaks indicate that the surface wind is a potentially important factor in scouring of the martian landscape. In particular, the north polar basin shows erosional features that suggest katabatic wind convergence into broad valleys near the margin of the polar cap. The pattern of katabatic wind drainage off the north polar cap is similar to that observed on Earth over Antarctica or Greenland. The sensitivity is explored of Martian drainage flows to variations in terrain slope and diurnal heating using a numerical modeling approach. The model used is a 2-D sigma coordinate primitive equation system that has been used for simulations of Antarctic drainage flows. Prognostic equations include the flux forms of the horizontal scalar momentum equations, temperature, and continuity. Parameterization of both longwave (terrestrial) and shortwave (solar) radiation is included. Turbulent transfer of heat and momentum in the Martian atmosphere remains uncertain since relevant measurements are essentially nonexistent.
Superclusters of galaxies from the 2dF redshift survey. 2. Comparison with simulations
Einasto, Jaan; Einasto, M.; Saar, E.; Tago, E.; Liivamagi, L.J.; Joeveer, M.J; Suhhonenko, I.; Hutsi, G.; Jaaniste, J.; Heinamaki, P.; Muller, V.; Knebe, A.; Tucker, D.; /Fermilab
2006-04-01
We investigate properties of superclusters of galaxies found on the basis of the 2dF Galaxy Redshift Survey, and compare them with properties of superclusters from the Millennium Simulation.We study the dependence of various characteristics of superclusters on their distance from the observer, on their total luminosity, and on their multiplicity. The multiplicity is defined by the number of Density Field (DF) clusters in superclusters. Using the multiplicity we divide superclusters into four richness classes: poor, medium, rich and extremely rich.We show that superclusters are asymmetrical and have multi-branching filamentary structure, with the degree of asymmetry and filamentarity being higher for the more luminous and richer superclusters. The comparison of real superclusters with Millennium superclusters shows that most properties of simulated superclusters agree very well with real data, the main differences being in the luminosity and multiplicity distributions.
NASA Astrophysics Data System (ADS)
Bezzeccheri, E.; Colasanti, S.; Falco, A.; Liguori, R.; Rubino, A.; Lugli, P.
2016-05-01
Vertical Organic Transistors and Phototransistors have been proven to be promising technologies due to the advantages of reduced channel length and larger sensitive area with respect to planar devices. Nevertheless, a real improvement of their performance is subordinate to the quantitative description of their operation mechanisms. In this work, we present a comparative study on the modeling of vertical and planar Organic Phototransistor (OPT) structures. Computer-based simulations of the devices have been carried out with Synopsys Sentaurus TCAD in a 2D Drift-Diffusion framework. The photoactive semiconductor material has been modeled using the virtual semiconductor approach as the archetypal P3HT:PC61BM bulk heterojunction. It has been found that both simulated devices have comparable electrical and optical characteristics, accordingly to recent experimental reports on the subject.
Numerical studies of gravity destabilized percolation in 2D porous media
NASA Astrophysics Data System (ADS)
Bo, Z.; Loggia, D.; Xiaorong, L.; Vasseur, G.; Ping, H.
2006-04-01
Two dimensional simulations of percolation are realized on square networks of pore throats with a random capillary pressure distribution. We analyse the influence of a destabilizing gravity field (g) and of the standard deviation of the distribution of the capillary pressure thresholds (Wt). The fragmentation process is not taken into account in this study. For an increase of g or/and when Wt decreases, two transitions are analyzed with three different regimes displacement patterns: Invasion percolation, invasion percolation in a gradient, and invasion in a pure gradient. The transitions are controlled both by the ratio g/Wt and by the sample size (L). A scaling law between the saturation at the percolation threshold and g/Wt allows delineating the three regimes in agreement with theoretical argument of the percolation in a gradient.
Mixed-RKDG Finite Element Methods for the 2-D Hydrodynamic Model for Semiconductor Device Simulation
Chen, Zhangxin; Cockburn, Bernardo; Jerome, Joseph W.; ...
1995-01-01
In this paper we introduce a new method for numerically solving the equations of the hydrodynamic model for semiconductor devices in two space dimensions. The method combines a standard mixed finite element method, used to obtain directly an approximation to the electric field, with the so-called Runge-Kutta Discontinuous Galerkin (RKDG) method, originally devised for numerically solving multi-dimensional hyperbolic systems of conservation laws, which is applied here to the convective part of the equations. Numerical simulations showing the performance of the new method are displayed, and the results compared with those obtained by using Essentially Nonoscillatory (ENO) finite difference schemes. Frommore » the perspective of device modeling, these methods are robust, since they are capable of encompassing broad parameter ranges, including those for which shock formation is possible. The simulations presented here are for Gallium Arsenide at room temperature, but we have tested them much more generally with considerable success.« less
Resolution requirements for numerical simulations of transition
NASA Technical Reports Server (NTRS)
Zang, Thomas A.; Krist, Steven E.; Hussaini, M. Yousuff
1989-01-01
The resolution requirements for direct numerical simulations of transition to turbulence are investigated. A reliable resolution criterion is determined from the results of several detailed simulations of channel and boundary-layer transition.
Highly-resolved 2D HYDRA simulations of Double-Shell Ignition Designs
Milovich, J L; Amendt, P; Hamza, A; Marinak, M; Robey, H
2006-06-30
Double-shell (DS) targets (Amendt, P. A. et al., 2002) offer a complementary approach to the cryogenic baseline design (Lindl, J. et al., 2004) for achieving ignition on the National Ignition Facility (NIF). Among the expected benefits are the ease of room temperature preparation and fielding, the potential for lower laser backscatter and the reduced need for careful shock timing. These benefits are offset, however, by demanding fabrication tolerances, e.g., shell concentricity and shell surface smoothness. In particular, the latter is of paramount importance since DS targets are susceptible to the growth of interface perturbations from impulsive and time-dependent accelerations. Previous work (Milovich, J. L. et al., 2004) has indicated that the growth of perturbations on the outer surface of the inner shell is potentially disruptive. To control this instability new designs have been proposed requiring bimetallic inner shells and material-matching mid-Z nanoporous foam. The challenges in manufacturing such exotic foams have led to a further evaluation of the densities and pore sizes needed to reduce the seeding of perturbations on the outer surface of the inner shell, thereby guiding the ongoing material science research efforts. Highly-resolved 2D simulations of porous foams have been performed to establish an upper limit on the allowable pore sizes for instability growth. Simulations indicate that foams with higher densities than previously thought are now possible. Moreover, while at the present time we are only able to simulate foams with average pore sizes larger than 1 micron (due to computational limitations), we can conclude that these pore sizes are potentially problematic. Furthermore, the effect of low-order hohlraum radiation asymmetries on the growth of intrinsic surface perturbations is also addressed. Highly-resolved 2D simulations indicate that the transverse flows that are set up by these low-order mode features (which can excite Kelvin
Spot size variation FCS in simulations of the 2D Ising model.
Burns, Margaret C; Nouri, Mariam; Veatch, Sarah L
2016-06-02
Spot variation fluorescence correlation spectroscopy (svFCS) was developed to study the movement and organization of single molecules in plasma membranes. This experimental technique varies the size of an illumination area while measuring correlations in time using standard fluorescence correlation methods. Frequently, this data is interpreted using the assumption that correlation measurements reflect the dynamics of single molecule motions, and not motions of the average composition. Here, we explore how svFCS measurements report on the dynamics of components diffusing within simulations of a 2D Ising model with a conserved order parameter. Simulated correlation functions report on both the fast dynamics of single component mobility and the slower dynamics of the average composition. Over a range of simulation conditions, a conventional svFCS analysis suggests the presence of anomalous diffusion even though single molecule motions are nearly Brownian in these simulations. This misinterpretation is most significant when the surface density of the fluorescent label is elevated, therefore we suggest future measurements be made over a range of tracer densities. Some simulation conditions reproduce qualitative features of published svFCS experimental data. Overall, this work emphasizes the need to probe membranes using multiple complimentary experimental methodologies in order to draw conclusions regarding the nature of spatial and dynamical heterogeneity in these systems.
Numerical solution of 2D wet steam flow with non-equilibrium condensation and real thermodynamics
Hric, V.; Halama, J.
2015-03-10
An approach to modeling of wet steam flow with non-equilibrium condensation phenomenon is presented. The first part of our flow model is homogeneous Euler system of transport equations for mass, momentum and total energy of wet steam (mixture). The additional second part describes liquid phase via non-homogeneous system of transport equations for moments of droplets number distribution function and relies on corrected classical nucleation theory. Moment equations are closed by linearization of droplet growth rate model. All necessary relations for thermodynamic properties of steam are provided by IAPWS set of equations. However, properties of condensate are simply modeled by liquid saturation data. Two real equations of state are implemented. Recently developed CFD formulation for entropy (does not require iteration process) and so-called IAPWS special gas equation for Helmholtz energy (one iteration loop is necessary). Flow model is validated on converging-diverging supersonic nozzle with Barschdorff geometry. Simulations were performed by in-house CFD code based on finite volume method and stiff character of equations was solved by symmetrical time operator splitting. Achieved results satisfactorily agreed with experimental data.
Tropical Oceanic Precipitation Processes over Warm Pool: 2D and 3D Cloud Resolving Model Simulations
NASA Technical Reports Server (NTRS)
Tao, W.- K.; Johnson, D.
1998-01-01
Rainfall is a key link in the hydrologic cycle as well as the primary heat source for the atmosphere, The vertical distribution of convective latent-heat release modulates the large-scale circulations of the tropics, Furthermore, changes in the moisture distribution at middle and upper levels of the troposphere can affect cloud distributions and cloud liquid water and ice contents. How the incoming solar and outgoing longwave radiation respond to these changes in clouds is a major factor in assessing climate change. Present large-scale weather and climate models simulate cloud processes only crudely, reducing confidence in their predictions on both global and regional scales. One of the most promising methods to test physical parameterizations used in General Circulation Models (GCMS) and climate models is to use field observations together with Cloud Resolving Models (CRMs). The CRMs use more sophisticated and physically realistic parameterizations of cloud microphysical processes, and allow for their complex interactions with solar and infrared radiative transfer processes. The CRMs can reasonably well resolve the evolution, structure, and life cycles of individual clouds and cloud systems, The major objective of this paper is to investigate the latent heating, moisture and momenti,im budgets associated with several convective systems developed during the TOGA COARE IFA - westerly wind burst event (late December, 1992). The tool for this study is the Goddard Cumulus Ensemble (CCE) model which includes a 3-class ice-phase microphysical scheme, The model domain contains 256 x 256 grid points (using 2 km resolution) in the horizontal and 38 grid points (to a depth of 22 km depth) in the vertical, The 2D domain has 1024 grid points. The simulations are performed over a 7 day time period. We will examine (1) the precipitation processes (i.e., condensation/evaporation) and their interaction with warm pool; (2) the heating and moisture budgets in the convective and
Numerical simulation package for speckle metrology
NASA Astrophysics Data System (ADS)
Kornis, Janos; Bokor, Nandor; Nemeth, Attila
1998-09-01
A computer program package for numerical simulation of speckle phenomena has been developed. It is suitable for simulating both objective and subjective speckle effects in various optical setups. Several simulation results are presented in this paper. The simulations was made in UNIX and Windows NT environment.
FireStem2D--a two-dimensional heat transfer model for simulating tree stem injury in fires.
Chatziefstratiou, Efthalia K; Bohrer, Gil; Bova, Anthony S; Subramanian, Ravishankar; Frasson, Renato P M; Scherzer, Amy; Butler, Bret W; Dickinson, Matthew B
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes.
FireStem2D – A Two-Dimensional Heat Transfer Model for Simulating Tree Stem Injury in Fires
Chatziefstratiou, Efthalia K.; Bohrer, Gil; Bova, Anthony S.; Subramanian, Ravishankar; Frasson, Renato P. M.; Scherzer, Amy; Butler, Bret W.; Dickinson, Matthew B.
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes. PMID:23894599
Rise characteristics of gas bubbles in a 2D rectangular column: VOF simulations vs experiments
Krishna, R.; Baten, J.M. van
1999-10-01
About five centuries ago, Leonardo da Vinci described the sinuous motion of gas bubbles rising in water. The authors have attempted to simulate the rise trajectories of bubbles of 4, 5, 7, 8, 9, 12, and 20 mm in diameter rising in a 2D rectangular column filled with water. The simulations were carried out using the volume-of-fluid (VOF) technique developed by Hirt and Nichols (J. Computational Physics, 39, 201--225 (1981)). To solve the Navier-Stokes equations of motion the authors used a commercial solver, CFX 4.1c of AEA Technology, UK. They developed their own bubble-tracking algorithm to capture sinuous bubble motions. The 4 and 5 mm bubbles show large lateral motions observed by Da Vinci. The 7, 8 and 9 mm bubble behave like jellyfish. The 12 mm bubble flaps its wings like a bird. The extent of lateral motion of the bubbles decreases with increasing bubble size. Bubbles larger than 20 mm in size assume a spherical cap form and simulations of the rise characteristics match experiments exactly. VOF simulations are powerful tools for a priori determination of the morphology and rise characteristics of bubbles rising in a liquid. Bubble-bubble interactions are also properly modeled by the VOF technique.
SIMULATIONS OF 2D AND 3D THERMOCAPILLARY FLOWS BY A LEAST-SQUARES FINITE ELEMENT METHOD. (R825200)
Numerical results for time-dependent 2D and 3D thermocapillary flows are presented in this work. The numerical algorithm is based on the Crank-Nicolson scheme for time integration, Newton's method for linearization, and a least-squares finite element method, together with a matri...
Atomistic simulations of J-integral in 2D graphene nanosystems.
Jin, Y; Yuan, F G
2005-12-01
The J-integral is investigated in discrete atomic systems using molecular mechanics simulations. A method of calculating J-integral in specified atomic domains is developed. Two cases, a semiinfinite crack in an infinite domain under the remote K-field deformation and a finite crack length in a finite geometry under the tensile and shear deformation prescribed on the boundary, are studied in the two-dimensional graphene sheets and the values of J-integral are obtained under small-strain deformation. The comparison with energy release rates in Mode I and Mode II based on continuum theory of linear elastic fracture mechanics show good agreements. Meanwhile, the nonlinear strain and stress relation of a 2D graphene sheet is evaluated and is fitted with a power law curve. With necessary modifications on the Tersoff-Brenner potential, the critical values of J-integral of 2D graphene systems, which denoted as Jc, are eventually obtained. The results are then compared with those from the relevant references.
Rocket Engine Numerical Simulator (RENS)
NASA Technical Reports Server (NTRS)
Davidian, Kenneth O.
1997-01-01
Work is being done at three universities to help today's NASA engineers use the knowledge and experience of their Apolloera predecessors in designing liquid rocket engines. Ground-breaking work is being done in important subject areas to create a prototype of the most important functions for the Rocket Engine Numerical Simulator (RENS). The goal of RENS is to develop an interactive, realtime application that engineers can utilize for comprehensive preliminary propulsion system design functions. RENS will employ computer science and artificial intelligence research in knowledge acquisition, computer code parallelization and objectification, expert system architecture design, and object-oriented programming. In 1995, a 3year grant from the NASA Lewis Research Center was awarded to Dr. Douglas Moreman and Dr. John Dyer of Southern University at Baton Rouge, Louisiana, to begin acquiring knowledge in liquid rocket propulsion systems. Resources of the University of West Florida in Pensacola were enlisted to begin the process of enlisting knowledge from senior NASA engineers who are recognized experts in liquid rocket engine propulsion systems. Dr. John Coffey of the University of West Florida is utilizing his expertise in interviewing and concept mapping techniques to encode, classify, and integrate information obtained through personal interviews. The expertise extracted from the NASA engineers has been put into concept maps with supporting textual, audio, graphic, and video material. A fundamental concept map was delivered by the end of the first year of work and the development of maps containing increasing amounts of information is continuing. Find out more information about this work at the Southern University/University of West Florida. In 1996, the Southern University/University of West Florida team conducted a 4day group interview with a panel of five experts to discuss failures of the RL10 rocket engine in conjunction with the Centaur launch vehicle. The
Simulating ultrasound fields for 2D phased-array probes design optimization.
Matrone, Giulia; Quaglia, Fabio; Magenes, Giovanni
2011-01-01
Nowadays, ultrasound diagnostic imaging is one of the non-invasive techniques mostly used in the clinical practice. Recent advances in this field have brought to the development of small and portable systems. New bidimensional probes consisting of 2D phased arrays, allow to obtain real-time 3D representations of moving organs and blood vessels anatomy. Being the complexity of such 4D ultrasound imaging systems significantly increased, new challenges concerning electronics integration arise for designers. In this paper a software simulator is described, which has been developed in order to model ultrasound wave generation, pressure field distribution and echoes reception, with the aim to become a useful tool for optimizing the probe design. The paper mainly focuses on linear ultrasound field modeling; preliminary results on non-linear interactions with contrast agents are also here introduced.
Catalog of velocity distributions around a reconnection site in 2D PIC simulations
NASA Astrophysics Data System (ADS)
Lechner, Lukas; Bourdin, Philippe-A.; Nakamura, Takuma K. M.; Nakamura, Rumi; Narita, Yasuhito
2016-04-01
The velocity distribution of electrons and ions are known to be a marker for regions where magnetic reconnection develops. Past theoretical and computational works demonstrated that non-gyrotropic and anisotropic distributions depending on particle meandering motions and accelerations are seen around the reconnection point. The Magnetospheric Multiscale (MMS) mission is expected to resolve such kinetic scale reconnection regions. We present a catalog of velocity distribution functions that can give hints on the location within the current sheet relative to the reconnection point, which is sometimes unclear from pure spacecraft observations. We use 2D PIC simulations of anti-parallel magnetic reconnection to obtain velocity distributions at different locations, like in the center of the reconnection site, the ion and electron diffusion regions, or the reconnection inflow and outflow regions. With sufficiently large number of particles we resolve the distribution functions also in rather small regions. Such catalog may be compared with future MMS observations of the Earth's magnetotail.
Simulation of abrasive flow machining process for 2D and 3D mixture models
NASA Astrophysics Data System (ADS)
Dash, Rupalika; Maity, Kalipada
2015-12-01
Improvement of surface finish and material removal has been quite a challenge in a finishing operation such as abrasive flow machining (AFM). Factors that affect the surface finish and material removal are media viscosity, extrusion pressure, piston velocity, and particle size in abrasive flow machining process. Performing experiments for all the parameters and accurately obtaining an optimized parameter in a short time are difficult to accomplish because the operation requires a precise finish. Computational fluid dynamics (CFD) simulation was employed to accurately determine optimum parameters. In the current work, a 2D model was designed, and the flow analysis, force calculation, and material removal prediction were performed and compared with the available experimental data. Another 3D model for a swaging die finishing using AFM was simulated at different viscosities of the media to study the effects on the controlling parameters. A CFD simulation was performed by using commercially available ANSYS FLUENT. Two phases were considered for the flow analysis, and multiphase mixture model was taken into account. The fluid was considered to be a
What Can We Learn about Magnetotail Reconnection from 2D PIC Harris-Sheet Simulations?
NASA Astrophysics Data System (ADS)
Goldman, M. V.; Newman, D. L.; Lapenta, G.
2016-03-01
The Magnetosphere Multiscale Mission (MMS) will provide the first opportunity to probe electron-scale physics during magnetic reconnection in Earth's magnetopause and magnetotail. This article will address only tail reconnection—as a non-steady-state process in which the first reconnected field lines advance away from the x-point in flux pile-up fronts directed Earthward and anti-Earthward. An up-to-date microscopic physical picture of electron and ion-scale collisionless tail reconnection processes is presented based on 2-D Particle-In-Cell (PIC) simulations initiated from a Harris current sheet and on Cluster and Themis measurements of tail reconnection. The successes and limitations of simulations when compared to measured reconnection are addressed in detail. The main focus is on particle and field diffusion region signatures in the tail reconnection geometry. The interpretation of these signatures is vital to enable spacecraft to identify physically significant reconnection events, to trigger meaningful data transfer from MMS to Earth and to construct a useful overall physical picture of tail reconnection. New simulation results and theoretical interpretations are presented for energy transport of particles and fields, for the size and shape of electron and ion diffusion regions, for processes occurring near the fronts and for the j × B (Hall) electric field.
Numerical simulation and experimental progress on plasma window
NASA Astrophysics Data System (ADS)
Wang, S. Z.; Zhu, K.; Huang, S.; Lu, Y. R.; Shi, B. L.
2016-11-01
In this paper, a numerical 2D FLUENT-based magneto-hydrodynamic simulation on 3mm plasma window using argon, taken as a windowless vacuum device, was developed. The gas inlet, arc creation and developing and plasma expansion segments are all contained in this model. In the axis-symmetry cathode structure, a set of parameters including pressure, temperature, velocity and current distribution were obtained and discussed. The fluid dynamics of plasma in cavities with different shapes was researched. Corresponding experiments was carried out and the result agrees well to the numerical simulation. The validity of sealing ability of plasma window has been verified. Relevant further research upon deuteron gas as neutron production target is to be continued, considering larger diameter plasma window experimentally and numerically.
Advancing Nucleosynthesis in Core-Collapse Supernovae Models Using 2D CHIMERA Simulations
NASA Astrophysics Data System (ADS)
Harris, J. A.; Hix, W. R.; Chertkow, M. A.; Bruenn, S. W.; Lentz, E. J.; Messer, O. B.; Mezzacappa, A.; Blondin, J. M.; Marronetti, P.; Yakunin, K.
2014-01-01
The deaths of massive stars as core-collapse supernovae (CCSN) serve as a crucial link in understanding galactic chemical evolution since the birth of the universe via the Big Bang. We investigate CCSN in polar axisymmetric simulations using the multidimensional radiation hydrodynamics code CHIMERA. Computational costs have traditionally constrained the evolution of the nuclear composition in CCSN models to, at best, a 14-species α-network. However, the limited capacity of the α-network to accurately evolve detailed composition, the neutronization and the nuclear energy generation rate has fettered the ability of prior CCSN simulations to accurately reproduce the chemical abundances and energy distributions as known from observations. These deficits can be partially ameliorated by "post-processing" with a more realistic network. Lagrangian tracer particles placed throughout the star record the temporal evolution of the initial simulation and enable the extension of the nuclear network evolution by incorporating larger systems in post-processing nucleosynthesis calculations. We present post-processing results of the four ab initio axisymmetric CCSN 2D models of Bruenn et al. (2013) evolved with the smaller α-network, and initiated from stellar metallicity, non-rotating progenitors of mass 12, 15, 20, and 25 M⊙ from Woosley & Heger (2007). As a test of the limitations of post-processing, we provide preliminary results from an ongoing simulation of the 15 M⊙ model evolved with a realistic 150 species nuclear reaction network in situ. With more accurate energy generation rates and an improved determination of the thermodynamic trajectories of the tracer particles, we can better unravel the complicated multidimensional "mass-cut" in CCSN simulations and probe for less energetically significant nuclear processes like the νp-process and the r-process, which require still larger networks.
Transport simulations of the C-2 and C-2U Field Reversed Configurations with the Q2D code
NASA Astrophysics Data System (ADS)
Onofri, Marco; Dettrick, Sean; Barnes, Daniel; Tajima, Toshiki; TAE Team
2016-10-01
The Q2D code is a 2D MHD code, which includes a neutral fluid and separate ion and electron temperatures, coupled with a 3D Monte Carlo code, which is used to calculate source terms due to neutral beams. Q2D has been benchmarked against the 1D transport code Q1D and is used to simulate the evolution of the C-2 and C-2U field reversed configuration experiments [1]. Q2D simulations start from an initial equilibrium and transport coefficients are chosen to match C-2 experimental data. C-2U is an upgrade of C-2, with more beam power and angled beam injection, which demonstrates plasma sustainment for 5 + ms. The simulations use the same transport coefficients for C-2 and C-2U, showing the formation of a steady state in C-2U, sustained by fast ion pressure and current drive.
Numerical Simulation of Turbulent Fluid Flows
NASA Technical Reports Server (NTRS)
Leonard, A.
1983-01-01
Numerical simulation of turbulent flows is discussed. Computational requirements for the direct simulaton of turbulence, simulation of arbitrary homogeneous flows, an expansion technique for wall bounded flows with application to pipe flow, and possibilities of flow representations or modeling techniques that allow the simulation of high Reynolds number flows with a relatively small number of dependent variables are included.
Numerical simulation of premixed H2-air cellular tubular flames
NASA Astrophysics Data System (ADS)
Hall, Carl Alan; Wendell Pitz, Robert
2016-03-01
The detailed flame structure of laminar premixed cellular flames in the tubular domain is simulated in 2D using a fully-implicit primitive variable finite difference formulation that includes multicomponent transport and detailed chemical kinetics. Numerical results for H2/air flames are presented and compared against spatially resolved experimental measurements of temperature and chemical species including atomic H and OH. The experimental results compare well for flame structure and cell number, despite the numerical model under-predicting the peak temperature by 200 K. Numerical experiments were performed to assess the ability for cellular tubular flames to impact experimental and numerical investigations of practical flames. The cellular flame structure is found to provide a highly sensitive geometry that is useful for validating diffusive transport modelling approximations. This capability is exemplified through the development of a simple and accurate approximation for thermal diffusion (i.e. the Soret effect) that is suitable for practical combustion codes.
Numerical simulation of heat exchanger
Sha, W.T.
1985-01-01
Accurate and detailed knowledge of the fluid flow field and thermal distribution inside a heat exchanger becomes invaluable as a large, efficient, and reliable unit is sought. This information is needed to provide proper evaluation of the thermal and structural performance characteristics of a heat exchanger. It is to be noted that an analytical prediction method, when properly validated, will greatly reduce the need for model testing, facilitate interpolating and extrapolating test data, aid in optimizing heat-exchanger design and performance, and provide scaling capability. Thus tremendous savings of cost and time are realized. With the advent of large digital computers and advances in the development of computational fluid mechanics, it has become possible to predict analytically, through numerical solution, the conservation equations of mass, momentum, and energy for both the shellside and tubeside fluids. The numerical modeling technique will be a valuable, cost-effective design tool for development of advanced heat exchangers.
Numerical simulation of conservation laws
NASA Technical Reports Server (NTRS)
Chang, Sin-Chung; To, Wai-Ming
1992-01-01
A new numerical framework for solving conservation laws is being developed. This new approach differs substantially from the well established methods, i.e., finite difference, finite volume, finite element and spectral methods, in both concept and methodology. The key features of the current scheme include: (1) direct discretization of the integral forms of conservation laws, (2) treating space and time on the same footing, (3) flux conservation in space and time, and (4) unified treatment of the convection and diffusion fluxes. The model equation considered in the initial study is the standard one dimensional unsteady constant-coefficient convection-diffusion equation. In a stability study, it is shown that the principal and spurious amplification factors of the current scheme, respectively, are structurally similar to those of the leapfrog/DuFort-Frankel scheme. As a result, the current scheme has no numerical diffusion in the special case of pure convection and is unconditionally stable in the special case of pure diffusion. Assuming smooth initial data, it will be shown theoretically and numerically that, by using an easily determined optimal time step, the accuracy of the current scheme may reach a level which is several orders of magnitude higher than that of the MacCormack scheme, with virtually identical operation count.
Self-Consistent, 2D Magneto-Hydrodynamic Simulations of Magnetically Driven Flyer Plates
NASA Astrophysics Data System (ADS)
Lemke, Raymond W.
2002-11-01
The intense magnetic field generated in the 20 MA Z-machine is used to accelerate flyer plates to high velocity for equation of state experiments. A peak magnetic drive pressure on the order of 2 Mbar can be generated, which accelerates an approximately 0.2 g aluminum disc to 21 km/s [1]. We have used 2D magneto-hydrodynamic (MHD) simulation to investigate the physics of accelerating flyer plates using multi-megabar magnetic drive pressures. A typical shock physics load is formed by a rectangular slab cathode enclosed by a hollow rectangular duct (the anode). The anode and cathode are connected (shorted) at one end. The electrodes are highly compressible at multi-megabar pressures. Electrode deformation that occurs during the rise time of the current pulse causes significant inductance increase, which reduces the peak current (drive pressure) relative to a static geometry. This important dynamic effect is modeled self-consistently by driving the MHD simulation with a circuit model of Z. Comparison of simulation results with highly accurate velocity interferometry measurements shows that the drive pressure waveform is affected by current losses and short circuiting in the machine, in conjunction with time varying load inductance. The understanding gained from these comparisons has allowed us to optimize shock physics loads using simulation. In this way a load was designed to produce a flyer velocity of 28 km/s, which was achieved experimentally on Z. We have identified paths to producing a flyer velocity of 40 km/s and peak isentropic pressure of 10 Mbar on the refurbished Z-machine [2]. Details of the modeling, the physics and comparisons with experiment are presented. [1] M. D. Knudson et al., Phys. Rev. Letters 87 (22), 22550-1 (2002). [2] R. W. Lemke et al., to be published in Proc. of the Int. Conf. on High Power Particle Beams and Dense Z-Pinches, Albuquerque, NM, June 23-28, 2002.
Simulation and analysis of solute transport in 2D fracture/pipe networks: the SOLFRAC program.
Bodin, Jacques; Porel, Gilles; Delay, Fred; Ubertosi, Fabrice; Bernard, Stéphane; de Dreuzy, Jean-Raynald
2007-01-05
The Time Domain Random Walk (TDRW) method has been recently developed by Delay and Bodin [Delay, F. and Bodin, J., 2001. Time domain random walk method to simulate transport by advection-dispersion and matrix diffusion in fracture networks. Geophys. Res. Lett., 28(21): 4051-4054.] and Bodin et al. [Bodin, J., Porel, G. and Delay, F., 2003c. Simulation of solute transport in discrete fracture networks using the time domain random walk method. Earth Planet. Sci. Lett., 6566: 1-8.] for simulating solute transport in discrete fracture networks. It is assumed that the fracture network can reasonably be represented by a network of interconnected one-dimensional pipes (i.e. flow channels). Processes accounted for are: (1) advection and hydrodynamic dispersion in the channels, (2) matrix diffusion, (3) diffusion into stagnant zones within the fracture planes, (4) sorption reactions onto the fracture walls and in the matrix, (5) linear decay, and (6) mass sharing at fracture intersections. The TDRW method is handy and very efficient in terms of computation costs since it allows for the one-step calculation of the particle residence time in each bond of the network. This method has been programmed in C++, and efforts have been made to develop an efficient and user-friendly software, called SOLFRAC. This program is freely downloadable at the URL (labo.univ-poitiers.fr/hydrasa/intranet/telechargement.htm). It calculates solute transport into 2D pipe networks, while considering different types of injections and different concepts of local dispersion within each flow channel. Post-simulation analyses are also available, such as the mean velocity or the macroscopic dispersion at the scale of the entire network. The program may be used to evaluate how a given transport mechanism influences the macroscopic transport behaviour of fracture networks. It may also be used, as is the case, e.g., with analytical solutions, to interpret laboratory or field tracer test experiments performed
Kolkoori, S R; Rahman, M-U; Chinta, P K; Ktreutzbruck, M; Rethmeier, M; Prager, J
2013-02-01
Ultrasound propagation in inhomogeneous anisotropic materials is difficult to examine because of the directional dependency of elastic properties. Simulation tools play an important role in developing advanced reliable ultrasonic non destructive testing techniques for the inspection of anisotropic materials particularly austenitic cladded materials, austenitic welds and dissimilar welds. In this contribution we present an adapted 2D ray tracing model for evaluating ultrasonic wave fields quantitatively in inhomogeneous anisotropic materials. Inhomogeneity in the anisotropic material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The presented algorithm evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase relations as well as transmission coefficients. The ray tracing model is able to calculate the ultrasonic wave fields generated by a point source as well as a finite dimension transducer. The ray tracing model results are validated quantitatively with the results obtained from 2D Elastodynamic Finite Integration Technique (EFIT) on several configurations generally occurring in the ultrasonic non destructive testing of anisotropic materials. Finally, the quantitative comparison of ray tracing model results with experiments on 32mm thick austenitic weld material and 62mm thick austenitic cladded material is discussed.
2D Kinetic Particle in Cell Simulations of a Shear-Flow Stabilized Z-Pinch
NASA Astrophysics Data System (ADS)
Tummel, Kurt; Higginson, Drew; Schmidt, Andrea; Link, Anthony; McLean, Harry; Shumlak, Uri; Nelson, Brian; Golingo, Raymond; Claveau, Elliot; Lawrence Livermore National Lab Team; University of Washington Team
2016-10-01
The Z-pinch is a relatively simple and attractive potential fusion reactor design, but attempts to develop such a reactor have consistently struggled to overcome Z-pinch instabilities. The ``sausage'' and ``kink'' modes are among the most robust and prevalent Z-pinch instabilities, but theory and simulations suggest that axial flow-shear, dvz / dr ≠ 0 , can suppress these modes. Experiments have confirmed that Z-pinch plasmas with embedded axial flow-shear display a significantly enhanced resilience to the sausage and kink modes at a demonstration current of 50kAmps. A new experiment is under way to test the concept at higher current, and efforts to model these plasmas are being expanded. The performance and stability of these devices will depend on features like the plasma viscosity, anomalous resistivity, and finite Larmor radius effects, which are most accurately characterized in kinetic models. To predict these features, kinetic simulations using the particle in cell code LSP are now in development, and initial benchmarking and 2D stability analyses of the sausage mode are presented here. These results represent the first kinetic modeling of the flow-shear stabilized Z-pinch. This work is funded by the USDOE/ARPAe Alpha Program. Prepared by LLNL under Contract DE-AC52-07NA27344.
2D IR spectra of cyanide in water investigated by molecular dynamics simulations
Lee, Myung Won; Carr, Joshua K.; Göllner, Michael; Hamm, Peter; Meuwly, Markus
2013-01-01
Using classical molecular dynamics simulations, the 2D infrared (IR) spectroscopy of CN− solvated in D2O is investigated. Depending on the force field parametrizations, most of which are based on multipolar interactions for the CN− molecule, the frequency-frequency correlation function and observables computed from it differ. Most notably, models based on multipoles for CN− and TIP3P for water yield quantitatively correct results when compared with experiments. Furthermore, the recent finding that T 1 times are sensitive to the van der Waals ranges on the CN− is confirmed in the present study. For the linear IR spectrum, the best model reproduces the full widths at half maximum almost quantitatively (13.0 cm−1 vs. 14.9 cm−1) if the rotational contribution to the linewidth is included. Without the rotational contribution, the lines are too narrow by about a factor of two, which agrees with Raman and IR experiments. The computed and experimental tilt angles (or nodal slopes) α as a function of the 2D IR waiting time compare favorably with the measured ones and the frequency fluctuation correlation function is invariably found to contain three time scales: a sub-ps, 1 ps, and one on the 10-ps time scale. These time scales are discussed in terms of the structural dynamics of the surrounding solvent and it is found that the longest time scale (≈10 ps) most likely corresponds to solvent exchange between the first and second solvation shell, in agreement with interpretations from nuclear magnetic resonance measurements.
2D properties of core turbulence on DIII-D and comparison to gyrokinetic simulations
Shafer, Morgan W; Fonck, R. J.; McKee, G. R.; Holland, Chris; White, A. E.; Schlossberg, D J
2012-01-01
Quantitative 2D characteristics of localized density fluctuations are presented over the range of 0.3 < r/a < 0.9 in L-mode plasmas on DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)]. Broadband density fluctuations increase in amplitude from (n) over tilde/n < 0.5% in the deep core to (n) over tilde/n similar to 2.5% near the outer region. The observed Doppler-shift due to the E x B velocity matches well with the measured turbulence group and phase velocities (in toroidally rotating neutral beam heated plasmas). Turbulence decorrelation rates are found to be similar to 200 kHz at the edge and to decrease toward the core (0.45 < r/a < 0.9) where they approach the E x B shearing rate (similar to 50 kHz). Radial and poloidal correlation lengths are found to scale with the ion gyroradius and exhibit an asymmetric poloidally elongated eddy structure. The ensemble-averaged turbulent eddy structure changes its tilt with respect to the radial-poloidal coordinates in the core, consistent with an E x B shear mechanism. The 2D spatial correlation and wavenumber spectra [S(k(r); k(theta))] are presented and compared to nonlinear flux-tube GYRO simulations at two radii, r/a = 0.5 and r/a = 0.75, showing reasonable overall agreement, but the GYRO spectrum exhibits a peak at finite kr for r/a = 0.75 that is not observed experimentally; E x B shear may cause this discrepancy. (C) 2012 American Institute of Physics.
NASA Astrophysics Data System (ADS)
Bateman, A.; Medina, V.; Hürlimann, M.
2009-04-01
Debris flows are present in every country where a combination of high mountains and flash floods exists. In the northern part of the Iberian Peninsula, at the Pyrenees, sporadic debris events occur. We selected two different events. The first one was triggered at La Guingueta by the big exceptional flood event that produced many debris flows in 1982 which were spread all over the Catalonian Pyrenees. The second, more local event occurred in 2000 at the mountain Montserrat at the Pre-litoral mountain chain. We present here some results of the FLATModel, entirely developed at the Research Group in Sediment Transport of the Hydraulic, Marine and Environmental Engineering Department (GITS-UPC). The 2D FLATModel is a Finite Volume method that uses the Godunov scheme. Some numerical arranges have been made to analyze the entrainment process during the events, the Stop & Go phenomena and the final deposit of the material. The material rheology implemented is the Voellmy approach, because it acts very well evaluating the frictional and turbulent behavior. The FLATModel uses a GIS environment that facilitates the data analysis as the comparison between field and numerical data. The two events present two different characteristics, one is practically a one dimensional problem of 1400 m in length and the other has a more two dimensional behavior that forms a big fan.
NASA Astrophysics Data System (ADS)
Jung, J.; Arakawa, A.
2015-12-01
Through explicitly resolved cloud-scale processes by embedded 2-D cloud-resolving models (CRMs), the Multiscale Modeling Framework (MMF) known as the superparameterization has been reasonably successful to simulate various atmospheric events over a wide range of time scales. One thing to be justified is, however, if the influence of complex 3-D topography can be adequately represented by the embedded 2-D CRMs. In this study, simulations are performed in the presence of a variety of topography with embedded 3-D and 2-D CRMs in a single-column inactive GCM. Through the comparison between these simulations, it is demonstrated that the 2-D representation of topography is able to simulate the statistics of precipitation due to 3-D topography reasonably well as long as the topographic characteristics, such as the mean and standard deviation, are closely recognized. It is also shown that the use of two perpendicular sets of 2-D representations tends to reduce the error due to a 2-D representation.
Numerical tools for atomistic simulations.
Fang, H.; Gullett, Philip Michael; Slepoy, Alexander; Horstemeyer, Mark F.; Baskes, Michael I.; Wagner, Gregory John; Li, Mo
2004-01-01
The final report for a Laboratory Directed Research and Development project entitled 'Parallel Atomistic Computing for Failure Analysis of Micromachines' is presented. In this project, atomistic algorithms for parallel computers were developed to assist in quantification of microstructure-property relations related to weapon micro-components. With these and other serial computing tools, we are performing atomistic simulations of various sizes, geometries, materials, and boundary conditions. These tools provide the capability to handle the different size-scale effects required to predict failure. Nonlocal continuum models have been proposed to address this problem; however, they are phenomenological in nature and are difficult to validate for micro-scale components. Our goal is to separately quantify damage nucleation, growth, and coalescence mechanisms to provide a basis for macro-scale continuum models that will be used for micromachine design. Because micro-component experiments are difficult, a systematic computational study that employs Monte Carlo methods, molecular statics, and molecular dynamics (EAM and MEAM) simulations to compute continuum quantities will provide mechanism-property relations associated with the following parameters: specimen size, number of grains, crystal orientation, strain rates, temperature, defect nearest neighbor distance, void/crack size, chemical state, and stress state. This study will quantify sizescale effects from nanometers to microns in terms of damage progression and thus potentially allow for optimized micro-machine designs that are more reliable and have higher fidelity in terms of strength. In order to accomplish this task, several atomistic methods needed to be developed and evaluated to cover the range of defects, strain rates, temperatures, and sizes that a material may see in micro-machines. Therefore we are providing a complete set of tools for large scale atomistic simulations that include pre-processing of
NASA Astrophysics Data System (ADS)
Humair, F.; Matasci, B.; Carrea, D.; Pedrazzini, A.; Loye, A.; Pedrozzi, G.; Nicolet, P.; Jaboyedoff, M.
2012-04-01
account the results of the experimental testing are performed and compared with the a-priori simulations. 3D simulations were performed using a software that takes into account the effect of the forest cover in the blocky trajectory (RockyFor 3D) and an other that neglects this aspect (Rotomap; geo&soft international). 2D simulation (RocFall; Rocscience) profiles were located in the blocks paths deduced from 3D simulations. The preliminary results show that: (1) high speed movies are promising and allow us to track the blocks using video software, (2) the a-priori simulations tend to overestimate the runout distance which is certainly due to an underestimation of the obstacles as well as the breaking of the failing rocks which is not taken into account in the models, (3) the trajectories deduced from both a-priori simulation and real size experiment highlights the major influence of the channelized slope morphology on rock paths as it tends to follow the flow direction. This indicates that the 2D simulation have to be performed along the line of flow direction.
Efficient simulation of 2+2-D multi-species plasmas waves using an Eulerian Vlasov code
NASA Astrophysics Data System (ADS)
Banks, Jeffrey; Berger, Richard; Chapman, Thomas; Hittinger, Jeffrey; Bruner, Stephan
2013-10-01
We discuss multi-species aspects of the Eulerian-based kinetic code LOKI that evolves the Vlasov-Poisson system in 2+2-dimensional phase space (Banks et al., Phys. Plasmas 18, 052102 (2011)). In order to control the inherent cost associated with phase-space simulation, our approach uses a minimally diffuse, fourth-order-accurate finite-volume discretization (Banks and Hittinger, IEEE T. Plasma Sci. 39, 2198-2207). The scheme is discretely conservative and controls unphysical oscillations. The details of the numerical scheme will be presented, and the implementation on modern highly concurrent parallel computers will be discussed. We will present results of 2D simulations of propagating ion acoustic waves (IAWs) created using an external driving potential. The evolution of the plasma wave field and associated self-consistent distribution of trapped electrons and ions is studied after the external drive is turned off. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the Laboratory Research and Development Program at LLNL under project tracking code 12-ERD-061.
Numerical Simulations of Thermographic Responses in Composites
NASA Technical Reports Server (NTRS)
Winfree, William P.; Cramer, K. Elliot; Zalameda, Joseph N.; Howell, Patricia A.
2015-01-01
Numerical simulations of thermographic responses in composite materials have been a useful for evaluating and optimizing thermographic analysis techniques. Numerical solutions are particularly beneficial for thermographic techniques, since the fabrication of specimens with realistic flaws is difficult. Simulations are presented with different ply layups that incorporated the anisotropic thermal properties that exist in each ply. The results are compared to analytical series solutions and thermal measurements on composites with flat bottom holes and delaminations.
Numerical simulations of pendant droplets
NASA Astrophysics Data System (ADS)
Pena, Carlos; Kahouadji, Lyes; Matar, Omar; Chergui, Jalel; Juric, Damir; Shin, Seungwon
2015-11-01
We simulate the evolution of a three-dimensional pendant droplet through pinch-off using a new parallel two-phase flow solver called BLUE. The parallelization of the code is based on the technique of algebraic domain decomposition where the velocity field is solved by a parallel GMRes method for the viscous terms and the pressure by a parallel multigrid/GMRes method. Communication is handled by MPI message passing procedures. The method for the treatment of the fluid interfaces uses a hybrid Front Tracking/Level Set technique which defines the interface both by a discontinuous density field as well as by a local triangular Lagrangian mesh. This structure allows the interface to undergo large deformations including the rupture and coalescence of fluid interfaces. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Fediai, Artem; Ryndyk, Dmitry A; Cuniberti, Gianaurelio
2016-10-05
Up to now, the electrical properties of the contacts between 3D metals and 2D materials have never been computed at a fully ab initio level due to the huge number of atomic orbitals involved in a current path from an electrode to a pristine 2D material. As a result, there are still numerous open questions and controversial theories on the electrical properties of systems with 3D/2D interfaces-for example, the current path and the contact length scalability. Our work provides a first-principles solution to this long-standing problem with the use of the modular approach, a method which rigorously combines a Green function formalism with the density functional theory (DFT) for this particular contact type. The modular approach is a general approach valid for any 3D/2D contact. As an example, we apply it to the most investigated among 3D/2D contacts-metal/graphene contacts-and show its abilities and consistency by comparison with existing experimental data. As it is applicable to any 3D/2D interface, the modular approach allows the engineering of 3D/2D contacts with the pre-defined electrical properties.
NASA Astrophysics Data System (ADS)
Machado, Christiano B.; Pereira, Wagner C. A.; Padilla, Frédéric; Laugier, Pascal
2012-05-01
Ultrasound axial transmission (UAT) has been proposed to the diagnosis and follow-up of fracture healing. Some researchers have already pointed out the influence of fracture length, geometry and callus composition on the ultrasound time-of-flight and attenuation, with experimental and simulation studies. The aim of this work was to develop a pilot study on the effect of bone fracture unevenness on UAT measurements. Two-dimensional (2D) numerical simulations of ultrasound wave propagation were run using a custom-made finite-difference time domain code (SimSonic2D). Numerical models were composed of two 4-mm thick bone plates, with fracture lengths varying from 0 to 4 mm. For each case, an upward (UWun) and downward (DWun) unevenness of 0.5, 1.0 and 1.5 mm was implemented in the second plate. The 1-MHz emitter and receptor transducers were placed at 40 mm from each other, 20 mm apart from the center fracture. Two configurations were considered: 1.5 mm above the plates (for the 0-mm unevenness case) and transducers in contact with bone plate. For each situation, the time-of-flight of the first arriving signal (TOFFAS) and the FAS energy amplitude loss measured by the sound pressure level (SPLFAS) were computed. Results showed that there was a linear increase in TOFFAS with increasing fracture length, and a decrease of SPLFAS with the presence of a discontinuity. TOFFAS values were decreased with UWun (-0.87 μs for UWun = 1.5 mm), and increased with DWun (+0.99 μs for DWun = 1.5 mm). The SPLFAS increased with both UWun (+3.54 dB for UWun = 1.5 mm) and DWun (+8.15 dB for DWun = 1.5 mm). Both parameters showed the same variability. When transducers were put in contact with bone surface, fracture unevenness had no influence on TOF and SPL estimates. Previous works have already demonstrated that a fracture of 3 mm can increase TOFFAS in an order of 1 μs. Considering these preliminary results, it can be concluded that, although the variable fracture unevenness (until 1
Simulation of bootstrap current in 2D and 3D ideal magnetic fields in tokamaks
NASA Astrophysics Data System (ADS)
Raghunathan, M.; Graves, J. P.; Cooper, W. A.; Pedro, M.; Sauter, O.
2016-09-01
We aim to simulate the bootstrap current for a MAST-like spherical tokamak using two approaches for magnetic equilibria including externally caused 3D effects such as resonant magnetic perturbations (RMPs), the effect of toroidal ripple, and intrinsic 3D effects such as non-resonant internal kink modes. The first approach relies on known neoclassical coefficients in ideal MHD equilibria, using the Sauter (Sauter et al 1999 Phys. Plasmas 6 2834) expression valid for all collisionalities in axisymmetry, and the second approach being the quasi-analytic Shaing-Callen (Shaing and Callen 1983 Phys. Fluids 26 3315) model in the collisionless regime for 3D. Using the ideal free-boundary magnetohydrodynamic code VMEC, we compute the flux-surface averaged bootstrap current density, with the Sauter and Shaing-Callen expressions for 2D and 3D ideal MHD equilibria including an edge pressure barrier with the application of resonant magnetic perturbations, and equilibria possessing a saturated non-resonant 1/1 internal kink mode with a weak internal pressure barrier. We compare the applicability of the self-consistent iterative model on the 3D applications and discuss the limitations and advantages of each bootstrap current model for each type of equilibrium.
A hierarchical lattice spring model to simulate the mechanics of 2-D materials-based composites
NASA Astrophysics Data System (ADS)
Brely, Lucas; Bosia, Federico; Pugno, Nicola
2015-07-01
In the field of engineering materials, strength and toughness are typically two mutually exclusive properties. Structural biological materials such as bone, tendon or dentin have resolved this conflict and show unprecedented damage tolerance, toughness and strength levels. The common feature of these materials is their hierarchical heterogeneous structure, which contributes to increased energy dissipation before failure occurring at different scale levels. These structural properties are the key to exceptional bioinspired material mechanical properties, in particular for nanocomposites. Here, we develop a numerical model in order to simulate the mechanisms involved in damage progression and energy dissipation at different size scales in nano- and macro-composites, which depend both on the heterogeneity of the material and on the type of hierarchical structure. Both these aspects have been incorporated into a 2-dimensional model based on a Lattice Spring Model, accounting for geometrical nonlinearities and including statistically-based fracture phenomena. The model has been validated by comparing numerical results to continuum and fracture mechanics results as well as finite elements simulations, and then employed to study how structural aspects impact on hierarchical composite material properties. Results obtained with the numerical code highlight the dependence of stress distributions on matrix properties and reinforcement dispersion, geometry and properties, and how failure of sacrificial elements is directly involved in the damage tolerance of the material. Thanks to the rapidly developing field of nanocomposite manufacture, it is already possible to artificially create materials with multi-scale hierarchical reinforcements. The developed code could be a valuable support in the design and optimization of these advanced materials, drawing inspiration and going beyond biological materials with exceptional mechanical properties.
Numerical Simulation of Nanostructure Growth
NASA Technical Reports Server (NTRS)
Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.
2004-01-01
Nanoscale structures, such as nanowires and carbon nanotubes (CNTs), are often grown in gaseous or plasma environments. Successful growth of these structures is defined by achieving a specified crystallinity or chirality, size or diameter, alignment, etc., which in turn depend on gas mixture ratios. pressure, flow rate, substrate temperature, and other operating conditions. To date, there has not been a rigorous growth model that addresses the specific concerns of crystalline nanowire growth, while demonstrating the correct trends of the processing conditions on growth rates. Most crystal growth models are based on the Burton, Cabrera, and Frank (BCF) method, where adatoms are incorporated into a growing crystal at surface steps or spirals. When the supersaturation of the vapor is high, islands nucleate to form steps, and these steps subsequently spread (grow). The overall bulk growth rate is determined by solving for the evolving motion of the steps. Our approach is to use a phase field model to simulate the growth of finite sized nanowire crystals, linking the free energy equation with the diffusion equation of the adatoms. The phase field method solves for an order parameter that defines the evolving steps in a concentration field. This eliminates the need for explicit front tracking/location, or complicated shadowing routines, both of which can be computationally expensive, particularly in higher dimensions. We will present results demonstrating the effect of process conditions, such as substrate temperature, vapor supersaturation, etc. on the evolving morphologies and overall growth rates of the nanostructures.
NUMERICAL SIMULATIONS OF SPICULE ACCELERATION
Guerreiro, N.; Carlsson, M.; Hansteen, V. E-mail: mats.carlsson@astro.uio.no
2013-04-01
Observations in the H{alpha} line of hydrogen and the H and K lines of singly ionized calcium on the solar limb reveal the existence of structures with jet-like behavior, usually designated as spicules. The driving mechanism for such structures remains poorly understood. Sterling et al. shed some light on the problem mimicking reconnection events in the chromosphere with a one-dimensional code by injecting energy with different spatial and temporal distributions and tracing the thermodynamic evolution of the upper chromospheric plasma. They found three different classes of jets resulting from these injections. We follow their approach but improve the physical description by including non-LTE cooling in strong spectral lines and non-equilibrium hydrogen ionization. Increased cooling and conversion of injected energy into hydrogen ionization energy instead of thermal energy both lead to weaker jets and smaller final extent of the spicules compared with Sterling et al. In our simulations we find different behavior depending on the timescale for hydrogen ionization/recombination. Radiation-driven ionization fronts also form.
Numerical simulation of gravitational lenses
NASA Astrophysics Data System (ADS)
Cherniak, Yakov
Gravitational lens is a massive body or system of bodies with gravitational field that bends directions of light rays propagating nearby. This may cause an observer to see multiple images of a light source, e.g. a star, if there is a gravitational lens between the star and the observer. Light rays that form each individual image may have different distances to travel, which creates time delays between them. In complex gravitational fields generated by the system of stars, analytical calculation of trajectories and light intensities is virtually impossible. Gravitational lens of two massive bodies, one behind another, are able to create four images of a light source. Furthermore, the interaction between the four light beams can form a complicated interference pattern. This article provides a brief theory of light behavior in a gravitational field and describes the algorithm for constructing the trajectories of light rays in a gravitational field, calculating wave fronts and interference pattern of light. If you set gravitational field by any number of transparent and non- transparent objects (stars) and set emitters of radio wave beams, it is possible to calculate the interference pattern in any region of space. The proposed method of calculation can be applied even in the case of the lack of continuity between the position of the emitting stars and position of the resulting image. In this paper we propose methods of optimization, as well as solutions for some problems arising in modeling of gravitational lenses. The simulation of light rays in the sun's gravitational field is taken as an example. Also caustic is constructed for objects with uniform mass distribution.
Boundary acquisition for setup of numerical simulation
Diegert, C.
1997-12-31
The author presents a work flow diagram that includes a path that begins with taking experimental measurements, and ends with obtaining insight from results produced by numerical simulation. Two examples illustrate this path: (1) Three-dimensional imaging measurement at micron scale, using X-ray tomography, provides information on the boundaries of irregularly-shaped alumina oxide particles held in an epoxy matrix. A subsequent numerical simulation predicts the electrical field concentrations that would occur in the observed particle configurations. (2) Three-dimensional imaging measurement at meter scale, again using X-ray tomography, provides information on the boundaries fossilized bone fragments in a Parasaurolophus crest recently discovered in New Mexico. A subsequent numerical simulation predicts acoustic response of the elaborate internal structure of nasal passageways defined by the fossil record. The author must both add value, and must change the format of the three-dimensional imaging measurements before the define the geometric boundary initial conditions for the automatic mesh generation, and subsequent numerical simulation. The author applies a variety of filters and statistical classification algorithms to estimate the extents of the structures relevant to the subsequent numerical simulation, and capture these extents as faceted geometries. The author will describe the particular combination of manual and automatic methods used in the above two examples.
NASA Technical Reports Server (NTRS)
Li, Xiaofan; Sui, C.-H.; Lau, K.-M.
1999-01-01
The phase relation between the perturbation kinetic energy (K') associated with the tropical convection and the horizontal-mean moist available potential energy (bar-P) associated with environmental conditions is investigated by an energetics analysis of a numerical experiment. This experiment is performed using a 2-D cloud resolving model forced by the TOGA-COARE derived vertical velocity. The imposed upward motion leads to a decrease of bar-P directly through the associated vertical advective cooling, and to an increase of K' directly through cloud related processes, feeding the convection. The maximum K' and its maximum growth rate lags and leads, respectively, the maximum imposed large-scale upward motion by about 1-2 hours, indicating that convection is phase locked with large-scale forcing. The dominant life cycle of the simulated convection is about 9 hours, whereas the time scales of the imposed large-scale forcing are longer than the diurnal cycle. In the convective events, maximum growth of K' leads maximum decay of the perturbation moist available potential energy (P') by about 3 hours through vertical heat transport by perturbation circulation, and perturbation cloud heating. Maximum decay of P' leads maximum decay of bar-P by about one hour through the perturbation radiative, processes, the horizontal-mean cloud heating, and the large-scale vertical advective cooling. Therefore, maximum gain of K' occurs about 4-5 hours before maximum decay of bar-P.
Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT
Collins, Benjamin; Stimpson, Shane; Kelley, Blake W.; ...
2016-08-25
We derived a consistent “2D/1D” neutron transport method from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. Our paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. We also performed several applications on both leadership-class and industry-classmore » computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.« less
Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT
NASA Astrophysics Data System (ADS)
Collins, Benjamin; Stimpson, Shane; Kelley, Blake W.; Young, Mitchell T. H.; Kochunas, Brendan; Graham, Aaron; Larsen, Edward W.; Downar, Thomas; Godfrey, Andrew
2016-12-01
A consistent "2D/1D" neutron transport method is derived from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. This paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. Several applications have been performed on both leadership-class and industry-class computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.
Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT
Collins, Benjamin; Stimpson, Shane; Kelley, Blake W.; Young, Mitchell T. H.; Kochunas, Brendan; Graham, Aaron; Larsen, Edward W.; Downar, Thomas; Godfrey, Andrew
2016-08-25
We derived a consistent “2D/1D” neutron transport method from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. Our paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. We also performed several applications on both leadership-class and industry-class computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.
Study of Cardiac Defibrillation Through Numerical Simulations
NASA Astrophysics Data System (ADS)
Bragard, J.; Marin, S.; Cherry, E. M.; Fenton, F. H.
Three-dimensional numerical simulations of the defibrillation problem are presented. In particular, in this study we use the rabbit ventricular geometry as a realistic model system for evaluating the efficacy of defibrillatory shocks. Statistical data obtained from the simulations were analyzed in term of a dose-response curve. Good quantitative agreement between our numerical results and clinically relevant values is obtained. An electric field strength of about 6.6 V/cm indicates a fifty percent probability of successful defibrillation for a 12-ms monophasic shock. Our validated model will be useful for optimizing defibrillation protocols.
Numerical simulations of cryogenic cavitating flows
NASA Astrophysics Data System (ADS)
Kim, Hyunji; Kim, Hyeongjun; Min, Daeho; Kim, Chongam
2015-12-01
The present study deals with a numerical method for cryogenic cavitating flows. Recently, we have developed an accurate and efficient baseline numerical scheme for all-speed water-gas two-phase flows. By extending such progress, we modify the numerical dissipations to be properly scaled so that it does not show any deficiencies in low Mach number regions. For dealing with cryogenic two-phase flows, previous EOS-dependent shock discontinuity sensing term is replaced with a newly designed EOS-free one. To validate the proposed numerical method, cryogenic cavitating flows around hydrofoil are computed and the pressure and temperature depression effect in cryogenic cavitation are demonstrated. Compared with Hord's experimental data, computed results are turned out to be satisfactory. Afterwards, numerical simulations of flow around KARI turbopump inducer in liquid rocket are carried out under various flow conditions with water and cryogenic fluids, and the difference in inducer flow physics depending on the working fluids are examined.
Direct Numerical Simulations of Plunging Airfoils
2010-01-07
Schmidt and E Turkel, Numerical Solutions of the Euler Equations by Finite Volume Methods Using Runge-Kutta Time-Stepping Schemes, AIAA paper 81-1259...Ω ( p ∂vj ∂xj − σij ∂v i ∂xj ) dV (4) Definition 1 A numerical scheme to solve the viscous Navier-Stokes equations is said to be Kinetic Energy...Direct Numerical Simulations of Plunging Airfoils Yves Allaneau∗ and Antony Jameson† Stanford University, Stanford, California, 94305, USA This paper
Numerically simulating the sandwich plate system structures
NASA Astrophysics Data System (ADS)
Feng, Guo-Qing; Li, Gang; Liu, Zhi-Hui; Niu, Huai-Lei; Li, Chen-Feng
2010-09-01
Sandwich plate systems (SPS) are advanced materials that have begun to receive extensive attention in naval architecture and ocean engineering. At present, according to the rules of classification societies, a mixture of shell and solid elements are required to simulate an SPS. Based on the principle of stiffness decomposition, a new numerical simulation method for shell elements was proposed. In accordance with the principle of stiffness decomposition, the total stiffness can be decomposed into the bending stiffness and shear stiffness. Displacement and stress response related to bending stiffness was calculated with the laminated shell element. Displacement and stress response due to shear was calculated by use of a computational code write by FORTRAN language. Then the total displacement and stress response for the SPS was obtained by adding together these two parts of total displacement and stress. Finally, a rectangular SPS plate and a double-bottom structure were used for a simulation. The results show that the deflection simulated by the elements proposed in the paper is larger than the same simulated by solid elements and the analytical solution according to Hoff theory and approximate to the same simulated by the mixture of shell-solid elements, and the stress simulated by the elements proposed in the paper is approximate to the other simulating methods. So compared with calculations based on a mixture of shell and solid elements, the numerical simulation method given in the paper is more efficient and easier to do.
Reliability of Complex Nonlinear Numerical Simulations
NASA Technical Reports Server (NTRS)
Yee, H. C.
2004-01-01
This work describes some of the procedure to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations. Examples relevant to turbulent flow computations are included.
NASA Astrophysics Data System (ADS)
Chevalier, Laure; Collombet, Marielle; Pinel, Virginie
2017-03-01
Understanding magma degassing evolution during an eruption is essential to improving forecasting of effusive/explosive regime transitions at andesitic volcanoes. Lava domes frequently form during effusive phases, inducing a pressure increase both within the conduit and within the surrounding rocks. To quantify the influence of dome height on magma flow and degassing, we couple magma and gas flow in a 2D numerical model. The deformation induced by magma flow evolution is also quantified. From realistic initial magma flow conditions in effusive regime (Collombet, 2009), we apply increasing pressure at the conduit top as the dome grows. Since volatile solubility increases with pressure, dome growth is then associated with an increase in magma dissolved water content at a given depth, which corresponds with a decrease in magma porosity and permeability. Magma flow evolution is associated with ground deflation of a few μrad in the near field. However this signal is not detectable as it is hidden by dome subsidence (a few mrad). A Darcy flow model is used to study the impact of pressure and permeability conditions on gas flow in the conduit and surrounding rock. We show that dome permeability has almost no influence on magma degassing. However, increasing pressure in the surrounding rock, due to dome loading, as well as decreasing magma permeability in the conduit limit permeable gas loss at the conduit walls, thus causing gas pressurization in the upper conduit by a few tens of MPa. Decreasing magma permeability and increasing gas pressure increase the likelihood of magma explosivity and hazard in the case of a rapid decompression due to dome collapse.
SmaggIce 2D Version 1.8: Software Toolkit Developed for Aerodynamic Simulation Over Iced Airfoils
NASA Technical Reports Server (NTRS)
Choo, Yung K.; Vickerman, Mary B.
2005-01-01
SmaggIce 2D version 1.8 is a software toolkit developed at the NASA Glenn Research Center that consists of tools for modeling the geometry of and generating the grids for clean and iced airfoils. Plans call for the completed SmaggIce 2D version 2.0 to streamline the entire aerodynamic simulation process--the characterization and modeling of ice shapes, grid generation, and flow simulation--and to be closely coupled with the public-domain application flow solver, WIND. Grid generated using version 1.8, however, can be used by other flow solvers. SmaggIce 2D will help researchers and engineers study the effects of ice accretion on airfoil performance, which is difficult to do with existing software tools because of complex ice shapes. Using SmaggIce 2D, when fully developed, to simulate flow over an iced airfoil will help to reduce the cost of performing flight and wind-tunnel tests for certifying aircraft in natural and simulated icing conditions.
Numerical Simulation of Heliospheric Transients Approaching Geospace
2009-12-01
12/15/08 – 12/14/09 Numerical Simulation of Heliospheric Transients Approaching Geospace Report by Dusan Odstrcil, University of Colorado...simulations of heliospheric transients approaching geospace . The project was supervised by Dr. Dusan Odstrcil at the University of Colorado (CU...plays a key role in the prediction accuracy of heliospheric transients approaching geospace . This report presents main results achieved within the
Numerical propulsion system simulation: An interdisciplinary approach
NASA Technical Reports Server (NTRS)
Nichols, Lester D.; Chamis, Christos C.
1991-01-01
The tremendous progress being made in computational engineering and the rapid growth in computing power that is resulting from parallel processing now make it feasible to consider the use of computer simulations to gain insights into the complex interactions in aerospace propulsion systems and to evaluate new concepts early in the design process before a commitment to hardware is made. Described here is a NASA initiative to develop a Numerical Propulsion System Simulation (NPSS) capability.
Numerical propulsion system simulation - An interdisciplinary approach
NASA Technical Reports Server (NTRS)
Nichols, Lester D.; Chamis, Christos C.
1991-01-01
The tremendous progress being made in computational engineering and the rapid growth in computing power that is resulting from parallel processing now make it feasible to consider the use of computer simulations to gain insights into the complex interactions in aerospace propulsion systems and to evaluate new concepts early in the design process before a commitment to hardware is made. Described here is a NASA initiative to develop a Numerical Propulsion System Simulation (NPSS) capability.
Direct Numerical Simulation of Multiphase Flows with Unstable Interfaces
NASA Astrophysics Data System (ADS)
Schillaci, Eugenio; Lehmkuhl, Oriol; Antepara, Oscar; Oliva, Assensi
2016-09-01
This paper presents a numerical model that intends to simulate efficiently the surface instability that arise in multiphase flows, typically liquid-gas, both for laminar or turbulent regimes. The model is developed on the in-house computing platform TermoFluids, and operates the finite-volume, direct numerical simulation (DNS) of multiphase flows by means of a conservative level-set method for the interface-capturing. The mesh size is optimized by means of an adaptive mesh refinement (AMR) strategy, that allows the dynamic re-concentration of the mesh in the vicinity of the interfaces between fluids, in order to correctly represent the diverse structures (as ligaments and droplets) that may rise from unstable phenomena. In addition, special attention is given to the discretization of the various terms of the momentum equations, to ensure stability of the flow and correct representation of turbulent vortices. As shown, the method is capable of truthfully simulate the interface phenomena as the Kelvin-Helmholtz instability and the Plateau-Rayleigh instability, both in the case of 2-D and 3-D configurations. Therefore it is suitable for the simulation of complex phenomena such as simulation of air-blast atomization, with several important application in the field of automotive and aerospace engines. A prove is given by our preliminary study of the 3-D coaxial liquid-gas jet.
IRIS Spectrum Line Plot - Numeric Simulation
This video is similar to the IRIS Spectrum Line Plot video at http://www.youtube.com/watch?v=E4V_vF3qMSI, but now as derived from a numerical simulation of the Sun by the University of Oslo. Credit...
Gilbert, Robert P; Guyenne, Philippe; Li, Jing
2014-02-01
In this paper, we compare ultrasound interrogations of actual CT-scanned images of trabecular bone with artificial randomly constructed bone. Even though it is known that actual bone does not have randomly distributed trabeculae, we find that the ultrasound attenuations are close enough to cast doubt on any microstructural information, such as trabeculae width and distance between trabeculae, being gleaned from such experiments. More precisely, we perform numerical simulations of ultrasound interrogation on cancellous bone to investigate the phenomenon of ultrasound attenuation as a function of excitation frequency and bone porosity. The theoretical model is based on acoustic propagation equations for a composite fluid-solid material and is solved by a staggered-grid finite-difference scheme in the time domain. Numerical experiments are performed on two-dimensional bone samples reconstructed from CT-scanned images of real human calcaneus and from random distributions of fluid-solid particles generated via the turning bands method. A detailed comparison is performed on various parameters such as the attenuation rate and speed of sound through the bone samples as well as the normalized broadband ultrasound attenuation coefficient. Comparing results from these two types of bone samples allows us to assess the role of bone microstructure in ultrasound attenuation. It is found that the random model provides suitable bone samples for ultrasound interrogation in the transverse direction of the trabecular network.
Simulation study of 2D spectrum of molecular aggregates coupled to correlated vibrations
NASA Astrophysics Data System (ADS)
Abramavicius, Darius; Butkus, Vytautas; Valkunas, Leonas; Mukamel, Shaul
2011-03-01
Oscillatory dynamics of two-dimensional (2D) spectra of photosynthetic pigment-protein complexes raise the questions of how to disentangle various origins of these oscillations, which may include quantum beats, quantum transport, or molecular vibrations. We study the effects of correlated overdamped fluctuations and under-damped vibrations on the 2D spectra of Fenna-Matthews-Olson (FMO) aggregate, which has well-resolved exciton resonances, and a circular porphyrin aggregate (P6), whose absorption shows vibrational progression. We use a generic exciton Hamiltonian coupled to a bath, characterized by a spectral density. Fluctuations have smooth, while vibtations have δ -type spectral densities. We show how various scenarios of correlated molecular fluctuations lead to some highly oscillatory crosspeaks. Molecular vibrations cause progression of diagonal peaks in the 2D spectrum and make their corresponding cross-peaks highly oscillatory. We, thus, demonstrate that bath fluctuations and molecular vibrations of realistic molecular aggregates are highly entangled in 2D spectroscopy. DA acknowledges grant VP1-3.1-SMM-07-V, SM - the grants CHE0745892 (NSF), DRPA BAA-10-40 QUBE.
Numerical Simulation of a Convective Turbulence Encounter
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.
2002-01-01
A numerical simulation of a convective turbulence event is investigated and compared with observational data. The numerical results show severe turbulence of similar scale and intensity to that encountered during the test flight. This turbulence is associated with buoyant plumes that penetrate the upper-level thunderstorm outflow. The simulated radar reflectivity compares well with that obtained from the aircraft's onboard radar. Resolved scales of motion as small as 50 m are needed in order to accurately diagnose aircraft normal load accelerations. Given this requirement, realistic turbulence fields may be created by merging subgrid-scales of turbulence to a convective-cloud simulation. A hazard algorithm for use with model data sets is demonstrated. The algorithm diagnoses the RMS normal loads from second moments of the vertical velocity field and is independent of aircraft motion.
A New Cell-Centered Implicit Numerical Scheme for Ions in the 2-D Axisymmetric Code Hall2de
NASA Technical Reports Server (NTRS)
Lopez Ortega, Alejandro; Mikellides, Ioannis G.
2014-01-01
We present a new algorithm in the Hall2De code to simulate the ion hydrodynamics in the acceleration channel and near plume regions of Hall-effect thrusters. This implementation constitutes an upgrade of the capabilities built in the Hall2De code. The equations of mass conservation and momentum for unmagnetized ions are solved using a conservative, finite-volume, cell-centered scheme on a magnetic-field-aligned grid. Major computational savings are achieved by making use of an implicit predictor/multi-corrector algorithm for time evolution. Inaccuracies in the prediction of the motion of low-energy ions in the near plume in hydrodynamics approaches are addressed by implementing a multi-fluid algorithm that tracks ions of different energies separately. A wide range of comparisons with measurements are performed to validate the new ion algorithms. Several numerical experiments with the location and value of the anomalous collision frequency are also presented. Differences in the plasma properties in the near-plume between the single fluid and multi-fluid approaches are discussed. We complete our validation by comparing predicted erosion rates at the channel walls of the thruster with measurements. Erosion rates predicted by the plasma properties obtained from simulations replicate accurately measured rates of erosion within the uncertainty range of the sputtering models employed.
Numerical Simulation of Conductivity Gradient-Induced Electrokinetic Flow Instabilities
NASA Astrophysics Data System (ADS)
Bradford, Stephen; Meinhart, Carl
2006-03-01
This research is focused on the electrokinetic flow instabilities observed in long, thin microchannels with conductivity gradients orthogonal to the streamwise direction and applied potential. This situation often occurs in field amplified sample stacking (FASS) and isoelectric focusing, where control of the instabilities is imperative. Alternatively, the inherently chaotic flow patterns can be leveraged to fabricate an efficient micromixer under specific conditions. These instabilities arise from fluid body forces generated by the action of applied electric fields on electrolyte concentration-based conductivity gradients. A model is developed to describe the phenomena in general and applied specifically to thin microchannels with the conductivity gradient perpendicular to the applied field (both DC and AC). A higher-order, depth averaged correlation is proposed to account for the out of plane effects. Numerical simulations performed using COMSOL 3.2 are compared to 2-D and 3-D simulations as well as experimental data for multiple geometries with good agreement.
Linking Paleomagnetic Observations to Numerical Dynamo Simulations
NASA Astrophysics Data System (ADS)
Constable, C.
2006-05-01
Over the past decade a number of numerical dynamo simulations have successfully mimicked properties considered important for the geomagnetic field. These include predominantly dipolar surface field structures and the ability to reverse polarity, along with some sensitivities to the presence and size of a conductive inner core and to spatial variations in core-mantle boundary conditions. The surface manifestations of geomagnetic excursions and reversals in these models are spatially and temporally variable as in paleomagnetic data. Detailed comparisons with paleosecular variation models lead to less satisfying comparisons in many cases. A huge advantage in studying the geodynamo from a numerical perspective is the detailed knowledge available about physical processes going on throughout the simulated core, instead of non-unique interpretations of inexact and incomplete actual surface observations. The well-known disadvantage to such simulations is that the parameter regime in which they operate is still far from that of Earth (resulting in viscous boundary layers that are too thick) despite concerted efforts to approach the appropriate numerical regime. The importance of these limitations in reproducing Earth-like geomagnetic field variations remains in doubt, but an optimistic view is that although the dynamics at short time scales may not be realistic, one can hope for viable comparisons on sufficiently long time scales, with the definition of sufficiently long dependent on the parameter regime. Both paleomagnetic and numerical studies appear to support the idea that the same kind of processes contribute to very long term secular variations, geomagnetic excursions, and reversals. This work attempts to link the statistical descriptions of long term paleomagnetic observations with physical descriptions from numerical simulations, and identify conditions associated with geomagnetic reversals and excursions.
NASA Technical Reports Server (NTRS)
Proffitt, M. H.; Solomon, S.; Loewenstein, M.
1992-01-01
A linear reference relationship between O3 and N2O has been used to estimate polar winter O3 loss from aircraft data taken in the lower stratosphere. Here, this relationship is evaluated at high latitudes by comparing it with a 2D model simulation and with NIMBUS 7 satellite measurements. Although comparisons with satellite measurements are limited to January through May, the model simulations are compared during other seasons. The model simulations and the satellite data are found to be consistent with the winter O3 loss analysis. It is shown that such analyses are likely to be inappropriate during other seasons.
Numerical Simulation of Aircraft Trailing Vortices
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Switzer, George F.
2000-01-01
The increase in air traffic is currently outpacing the development of new airport runways. This is leading to greater air traffic congestion, resulting in costly delays and cancellations. The National Aeronautics and Space Administration (NASA) under its Terminal Area Productivity (TAP) program is investigating new technologies that will allow increased airport capacity while maintaining the present standards for safety. As an element of this program, the Aircraft Vortex Spacing System (AVOSS) is being demonstrated in July 2000, at Dallas Ft-Worth Airport. This system allows reduced aircraft separations, thus increasing the arrival and departure rates, while insuring that wake vortices from a leading aircraft do not endanger trailing aircraft. The system uses predictions or wake vortex position and strength based on input from the current weather state. This prediction is accomplished by a semi-empirical model developed from theory, field observations, and relationships derived from numerical wake vortex simulations. Numerical experiments with a Large Eddy Simulation (LES) model are being conducted in order to provide guidance for the enhancement of these prediction algorithms. The LES Simulations of wake vortices are carried out with NASA's Terminal Area Simulation System (TASS). Previous wake vortex investigations with TASS are described. The primary objective of these numerical studies has been to quantify vortex transport and decay in relation to atmospheric variables. This paper summarizes many of the previous investigations with the TASS model and presents some new results regarding the onset of wake vortex decay.
Mach number validation of a new zonal CFD method (ZAP2D) for airfoil simulations
NASA Technical Reports Server (NTRS)
Strash, Daniel J.; Summa, Michael; Yoo, Sungyul
1991-01-01
A closed-loop overlapped velocity coupling procedure has been utilized to combine a two-dimensional potential-flow panel code and a Navier-Stokes code. The fully coupled two-zone code (ZAP2D) has been used to compute the flow past a NACA 0012 airfoil at Mach numbers ranging from 0.3 to 0.84 near the two-dimensional airfoil C(lmax) point for a Reynolds number of 3 million. For these cases, the grid domain size can be reduced to 3 chord lengths with less than 3-percent loss in accuracy for freestream Mach numbers through 0.8. Earlier validation work with ZAP2D has demonstrated a reduction in the required Navier-Stokes computation time by a factor of 4 for subsonic Mach numbers. For this more challenging condition of high lift and Mach number, the saving in CPU time is reduced to a factor of 2.
EDGE2D Simulations of JET{sup 13}C Migration Experiments
J.D. Strachan; J.P. Coad; G. Corrigan; G.F. Matthews; J. Spence
2004-06-16
Material migration has received renewed interest due to tritium retention associated with carbon transport to remote vessel locations. Those results influence the desirability of carbon usage on ITER. Subsequently, additional experiments have been performed, including tracer experiments attempting to identify material migration from specific locations. In this paper, EDGE2D models a well-diagnosed JET{sup 13}C tracer migration experiment. The role of SOL flows upon the migration patterns is identified.
Simulation of multi-steps thermal transition in 2D spin-crossover nanoparticles
NASA Astrophysics Data System (ADS)
Jureschi, Catalin-Maricel; Pottier, Benjamin-Louis; Linares, Jorge; Richard Dahoo, Pierre; Alayli, Yasser; Rotaru, Aurelian
2016-04-01
We have used an Ising like model to study the thermal behavior of a 2D spin crossover (SCO) system embedded in a matrix. The interaction parameter between edge SCO molecules and its local environment was included in the standard Ising like model as an additional term. The influence of the system's size and the ratio between the number of edge molecules and the other molecules were also discussed.
Numerical simulation of centrifugal casting of pipes
NASA Astrophysics Data System (ADS)
Kaschnitz, E.
2012-07-01
A numerical simulation model for the horizontal centrifugal pipe casting process was developed with the commercial simulation package Flow3D. It considers - additionally to mass, energy and momentum conservation equations and free surface tracking - the fast radial and slower horizontal movement of the mold. The iron inflow is not steady state but time dependent. Of special importance is the friction between the liquid and the mold in connection with the viscosity and turbulence of the iron. Experiments with the mold at controlled revolution speeds were carried out using a high-speed camera. From these experiments friction coefficients for the description of the interaction between mold and melt were obtained. With the simulation model, the influence of typical process parameters (e.g. melts inflow, mold movement, melt temperature, cooling media) on the wall thickness of the pipes can be studied. The comparison to results of pipes from production shows a good agreement between simulation and reality.
Numerical Simulation of a Tornado Generating Supercell
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Ahmad, Nashat N.; LimonDuparcmeur, Fanny M.
2012-01-01
The development of tornadoes from a tornado generating supercell is investigated with a large eddy simulation weather model. Numerical simulations are initialized with a sounding representing the environment of a tornado producing supercell that affected North Carolina and Virginia during the Spring of 2011. The structure of the simulated storm was very similar to that of a classic supercell, and compared favorably to the storm that affected the vicinity of Raleigh, North Carolina. The presence of mid-level moisture was found to be important in determining whether a supercell would generate tornadoes. The simulations generated multiple tornadoes, including cyclonic-anticyclonic pairs. The structure and the evolution of these tornadoes are examined during their lifecycle.
Issues in Numerical Simulation of Fire Suppression
Tieszen, S.R.; Lopez, A.R.
1999-04-12
This paper outlines general physical and computational issues associated with performing numerical simulation of fire suppression. Fire suppression encompasses a broad range of chemistry and physics over a large range of time and length scales. The authors discuss the dominant physical/chemical processes important to fire suppression that must be captured by a fire suppression model to be of engineering usefulness. First-principles solutions are not possible due to computational limitations, even with the new generation of tera-flop computers. A basic strategy combining computational fluid dynamics (CFD) simulation techniques with sub-grid model approximations for processes that have length scales unresolvable by gridding is presented.
Numerical Simulation in a Supercirtical CFB Boiler
NASA Astrophysics Data System (ADS)
Zhang, Yanjun; Gaol, Xiang; Luo, Zhongyang; Jiang, Xiaoguo
The dimension of the hot circulation loop of the supercritical CFB boiler is large, and there are many unknowns and challenges that should be identified and resolved during the development. In order to realize a reasonable and reliable design of the hot circulation loop, numerical simulation of gas-solid flow in a supercritical CFB boiler was conducted by using FLUENT software. The working condition of hot circulation loop flow field, gas-solid flow affected by three unsymmetrical cyclones, air distribution and pressure drop in furnace were analyzed. The simulation results showed that the general arrangement of the 600MWe supercritical CFB boiler is reasonable.
Numerical simulations of catastrophic disruption: Recent results
NASA Technical Reports Server (NTRS)
Benz, W.; Asphaug, E.; Ryan, E. V.
1994-01-01
Numerical simulations have been used to study high velocity two-body impacts. In this paper, a two-dimensional Largrangian finite difference hydro-code and a three-dimensional smooth particle hydro-code (SPH) are described and initial results reported. These codes can be, and have been, used to make specific predictions about particular objects in our solar system. But more significantly, they allow us to explore a broad range of collisional events. Certain parameters (size, time) can be studied only over a very restricted range within the laboratory; other parameters (initial spin, low gravity, exotic structure or composition) are difficult to study at all experimentally. The outcomes of numerical simulations lead to a more general and accurate understanding of impacts in their many forms.
Magnetohydrodynamic Numerical Simulations of Magnetic Reconnection in Interstellar Medium
NASA Astrophysics Data System (ADS)
Tanuma, Syuniti
2000-03-01
In this thesis, we perform two-dimensional (2D) resistive magnetohydrodynamic (MHD) numerical simulations of the magnetic reconnection in interstellar medium. Part I is introduction. The motivation of the study is to investigate the origin of hot gas in interstellar medium. A scenario for generating X-ray gas in Galaxy is proposed, and examined by performing 2D MHD simulations with simple assumptions (Part II). The magnetic reconnection triggered by a supernova (Part III) and Parker instability (Part IV) are studied in detail, by performing 2D MHD simulations. Furthermore, the magnetic reconnection is also studied by performing three-dimensional (3D) MHD numerical simulation in (Part V). % Finally, we discuss and summarize the thesis (Parts VI and VII). Part I First, we review observation of Galactic Ridge X-ray Emission (GRXE) and its problems. Second, we describe observation of interstellar magnetic field briefly. Third, we review magnetic reconnection, theoretical models, numerical simulations, observations and experiments, and tearing instability. Forth, Parker instability (undular mode of magnetobuoyancy instability) is mentioned. Finally, we show the purpose of this thesis. Part II We present a scenario for the origin of the hot plasma in Galaxy as a model of strong X-ray emission [sim 3-10 keV; LX(2-10 keV) sim 1038 erg s-1], called GRXE, which has been observed near to the galactic plane. GRXE is thermal emission from a hot component (sim 7 keV) and a cool component (sim 0.8 keV). Observations suggest that the hot component is diffuse, and that it is not escaping away freely. Both what heats the hot component and what confines it in Galactic ridge still remain puzzling, while the cool component is believed to be created by supernovae. We propose a new scenario: the hot component is heated by magnetic reconnection, and confined by a helical magnetic field produced by magnetic reconnection. We solved 2D MHD equations numerically to study how magnetic
Numerical simulation and nasal air-conditioning
Keck, Tilman; Lindemann, Jörg
2011-01-01
Heating and humidification of the respiratory air are the main functions of the nasal airways in addition to cleansing and olfaction. Optimal nasal air conditioning is mandatory for an ideal pulmonary gas exchange in order to avoid desiccation and adhesion of the alveolar capillary bed. The complex three-dimensional anatomical structure of the nose makes it impossible to perform detailed in vivo studies on intranasal heating and humidification within the entire nasal airways applying various technical set-ups. The main problem of in vivo temperature and humidity measurements is a poor spatial and time resolution. Therefore, in vivo measurements are feasible only to a restricted extent, solely providing single temperature values as the complete nose is not entirely accessible. Therefore, data on the overall performance of the nose are only based on one single measurement within each nasal segment. In vivo measurements within the entire nose are not feasible. These serious technical issues concerning in vivo measurements led to a large number of numerical simulation projects in the last few years providing novel information about the complex functions of the nasal airways. In general, numerical simulations merely calculate predictions in a computational model, e.g. a realistic nose model, depending on the setting of the boundary conditions. Therefore, numerical simulations achieve only approximations of a possible real situation. The aim of this review is the synopsis of the technical expertise on the field of in vivo nasal air conditioning, the novel information of numerical simulations and the current state of knowledge on the influence of nasal and sinus surgery on nasal air conditioning. PMID:22073112
Numerical simulation of swept-wing flows
NASA Technical Reports Server (NTRS)
Reed, Helen L.
1991-01-01
The transition process characteristics of flows over swept wings were computationally modelled. The crossflow instability and crossflow/T-S wave interaction are analyzed through the numerical solution of the full three dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. The leading-edge region of a swept wing is considered in a three-dimensional spatial simulation with random disturbances as the initial conditions.
Numerical simulation of magma energy extraction
Hickox, C.E.
1991-01-01
The Magma Energy Program is a speculative endeavor regarding practical utility of electrical power production from the thermal energy which reside in magma. The systematic investigation has identified an number of research areas which have application to the utilization of magma energy and to the field of geothermal energy. Eight topics were identified which involve thermal processes and which are areas for the application of the techniques of numerical simulation. These areas are: (1) two-phase flow of the working fluid in the wellbore, (2) thermodynamic cycles for the production of electrical power, (3) optimization of the entire system, (4) solidification and fracturing of the magma caused by the energy extraction process, (5) heat transfer and fluid flow within an open, direct-contact, heat-exchanger, (6) thermal convection in the overlying geothermal region, (7) thermal convection within the magma body, and (8) induced natural convection near the thermal energy extraction device. Modeling issues have been identified which will require systematic investigation in order to develop the most appropriate strategies for numerical simulation. It appears that numerical simulations will be of ever increasing importance to the study of geothermal processes as the size and complexity of the systems of interest increase. It is anticipated that, in the future, greater emphasis will be placed on the numerical simulation of large-scale, three-dimensional, transient, mixed convection in viscous flows and porous media. Increased computational capabilities, e.g.; massively parallel computers, will allow for the detailed study of specific processes in fractured media, non-Darcy effects in porous media, and non-Newtonian effects. 23 refs., 13 figs., 1 tab.
On numerical simulation of viscous flows
NASA Astrophysics Data System (ADS)
Ghia, K. N.; Ghia, U.
Numerical simulation methods for viscous incompressible laminar flows are reviewed, with a focus on finite-difference schemes. The approaches to high/moderate-Reynolds-number flows (strong-viscous-interaction model or single sets of equations) and the factors affecting the versatility, reliability, and accuracy of the analysis algorithms are considered; approximate-factorization implicit solution techniques for low-Reynolds-number flows are discussed; and the procedures used in a number of specific problems are indicated.
Numerical Simulation of Thin Film Breakup on Nonwettable Surfaces
NASA Astrophysics Data System (ADS)
Suzzi, N.; Croce, G.
2017-01-01
When a continuous film flows on a nonwettable substrate surface, it may break up, with the consequent formation of a dry-patch. The actual shape of the resulting water layer is of great interest in several engineering applications, from in-flight icing simulation to finned dehumidifier behavior modeling. Here, a 2D numerical solver for the prediction of film flow behavior is presented. The effect of the contact line is introduced via the disjoining pressure terms, and both gravity and shear are included in the formulation. The code is validated with literature experimental data for the case of a stationary dry-patch on an inclined plane. Detailed numerical results are compared with literature simplified model prediction. Numerical simulation are then performed in order to predict the threshold value of the film thickness allowing for film breakup and to analyze the dependence of the dynamic contact angle on film velocity and position along the contact line. Those informations will be useful in order to efficiently predict more complex configuration involving multiple breakups on arbitrarily curved substrate surfaces (as those involved in in-flight icing phenomena on aircraft).
Sidler, Rolf; Carcione, José M.; Holliger, Klaus
2013-02-15
We present a novel numerical approach for the comprehensive, flexible, and accurate simulation of poro-elastic wave propagation in 2D polar coordinates. An important application of this method and its extensions will be the modeling of complex seismic wave phenomena in fluid-filled boreholes, which represents a major, and as of yet largely unresolved, computational problem in exploration geophysics. In view of this, we consider a numerical mesh, which can be arbitrarily heterogeneous, consisting of two or more concentric rings representing the fluid in the center and the surrounding porous medium. The spatial discretization is based on a Chebyshev expansion in the radial direction and a Fourier expansion in the azimuthal direction and a Runge–Kutta integration scheme for the time evolution. A domain decomposition method is used to match the fluid–solid boundary conditions based on the method of characteristics. This multi-domain approach allows for significant reductions of the number of grid points in the azimuthal direction for the inner grid domain and thus for corresponding increases of the time step and enhancements of computational efficiency. The viability and accuracy of the proposed method has been rigorously tested and verified through comparisons with analytical solutions as well as with the results obtained with a corresponding, previously published, and independently benchmarked solution for 2D Cartesian coordinates. Finally, the proposed numerical solution also satisfies the reciprocity theorem, which indicates that the inherent singularity associated with the origin of the polar coordinate system is adequately handled.
Direct Numerical Simulation of Combustion Using Principal Component Analysis
NASA Astrophysics Data System (ADS)
Owoyele, Opeoluwa; Echekki, Tarek
2016-11-01
We investigate the potential of accelerating chemistry integration during the direct numerical simulation (DNS) of complex fuels based on the transport equations of representative scalars that span the desired composition space using principal component analysis (PCA). The transported principal components (PCs) offer significant potential to reduce the computational cost of DNS through a reduction in the number of transported scalars, as well as the spatial and temporal resolution requirements. The strategy is demonstrated using DNS of a premixed methane-air flame in a 2D vortical flow and is extended to the 3D geometry to further demonstrate the computational efficiency of PC transport. The PCs are derived from a priori PCA of a subset of the full thermo-chemical scalars' vector. The PCs' chemical source terms and transport properties are constructed and tabulated in terms of the PCs using artificial neural networks (ANN). Comparison of DNS based on a full thermo-chemical state and DNS based on PC transport based on 6 PCs shows excellent agreement even for species that are not included in the PCA reduction. The transported PCs reproduce some of the salient features of strongly curved and strongly strained flames. The 2D DNS results also show a significant reduction of two orders of magnitude in the computational cost of the simulations, which enables an extension of the PCA approach to 3D DNS under similar computational requirements. This work was supported by the National Science Foundation Grant DMS-1217200.
2001 Numerical Propulsion System Simulation Review
NASA Technical Reports Server (NTRS)
Lytle, John; Follen, Gregory; Naiman, Cynthia; Veres, Joseph; Owen, Karl; Lopez, Isaac
2002-01-01
The technologies necessary to enable detailed numerical simulations of complete propulsion systems are being developed at the NASA Glenn Research Center in cooperation with industry, academia and other government agencies. Large scale, detailed simulations will be of great value to the nation because they eliminate some of the costly testing required to develop and certify advanced propulsion systems. In addition, time and cost savings will be achieved by enabling design details to be evaluated early in the development process before a commitment is made to a specific design. This concept is called the Numerical Propulsion System Simulation (NPSS). NPSS consists of three main elements: (1) engineering models that enable multidisciplinary analysis of large subsystems and systems at various levels of detail, (2) a simulation environment that maximizes designer productivity, and (3) a cost-effective, high-performance computing platform. A fundamental requirement of the concept is that the simulations must be capable of overnight execution on easily accessible computing platforms. This will greatly facilitate the use of large-scale simulations in a design environment. This paper describes the current status of the NPSS with specific emphasis on the progress made over the past year on air breathing propulsion applications. Major accomplishments include the first formal release of the NPSS object-oriented architecture (NPSS Version 1) and the demonstration of a one order of magnitude reduction in computing cost-to-performance ratio using a cluster of personal computers. The paper also describes the future NPSS milestones, which include the simulation of space transportation propulsion systems in response to increased emphasis on safe, low cost access to space within NASA's Aerospace Technology Enterprise. In addition, the paper contains a summary of the feedback received from industry partners on the fiscal year 2000 effort and the actions taken over the past year to
2000 Numerical Propulsion System Simulation Review
NASA Technical Reports Server (NTRS)
Lytle, John; Follen, Greg; Naiman, Cynthia; Veres, Joseph; Owen, Karl; Lopez, Isaac
2001-01-01
The technologies necessary to enable detailed numerical simulations of complete propulsion systems are being developed at the NASA Glenn Research Center in cooperation with industry, academia, and other government agencies. Large scale, detailed simulations will be of great value to the nation because they eliminate some of the costly testing required to develop and certify advanced propulsion systems. In addition, time and cost savings will be achieved by enabling design details to be evaluated early in the development process before a commitment is made to a specific design. This concept is called the Numerical Propulsion System Simulation (NPSS). NPSS consists of three main elements: (1) engineering models that enable multidisciplinary analysis of large subsystems and systems at various levels of detail, (2) a simulation environment that maximizes designer productivity, and (3) a cost-effective. high-performance computing platform. A fundamental requirement of the concept is that the simulations must be capable of overnight execution on easily accessible computing platforms. This will greatly facilitate the use of large-scale simulations in a design environment. This paper describes the current status of the NPSS with specific emphasis on the progress made over the past year on air breathing propulsion applications. Major accomplishments include the first formal release of the NPSS object-oriented architecture (NPSS Version 1) and the demonstration of a one order of magnitude reduction in computing cost-to-performance ratio using a cluster of personal computers. The paper also describes the future NPSS milestones, which include the simulation of space transportation propulsion systems in response to increased emphasis on safe, low cost access to space within NASA'S Aerospace Technology Enterprise. In addition, the paper contains a summary of the feedback received from industry partners on the fiscal year 1999 effort and the actions taken over the past year to
Sengupta, Neelanjana; Maekawa, Hiroaki; Zhuang, Wei; Toniolo, Claudio; Mukamel, Shaul; Tobias, Douglas J.; Ge, Nien-Hui
2010-01-01
We have investigated the sensitivity of two-dimensional infrared (2D IR) spectroscopy to peptide helicity with an experimental and theoretical study of Z-[L-(αMe)Val]8-OtBu in CDCl3. 2D IR experiments were carried out in the amide-I region under the parallel and the double-crossed polarization configurations. In the latter polarization configuration, the 2D spectra taken with the rephasing and nonrephasing pulse sequences exhibit a doublet feature and a single peak, respectively. These cross-peak patterns are highly sensitive to the underlying peptide structure. Spectral calculations were performed on the basis of a vibrational exciton model, with the local mode frequencies and couplings calculated from snapshots of molecular dynamics (MD) simulation trajectories using six different models for the Hamiltonian. Conformationally variant segments of the MD trajectory, while reproducing the main features of the experimental spectra, are characterized by extraneous features, suggesting that the structural ensembles sampled by the simulation are too broad. By imposing periodic restraints on the peptide dihedral angles with the crystal structure as a reference, much better agreement between the measured and the calculated spectra was achieved. The result indicates that the structure of Z-[L-(αMe)Val]8-OtBu in CDCl3 is a fully developed 310-helix with only a small fraction of α-helical or nonhelical conformations in the middle of the peptide. Of the four different combinations of pulse sequences and polarization configurations, the nonrephasing double-crossed polarization 2D IR spectrum exhibits the highest sensitivity in detecting conformational variation. Of the six local mode frequency models tested, the electrostatic maps of Mukamel and Cho perform the best. Our results show that the high sensitivity of 2D IR spectroscopy can provide a useful basis for developing methods to improve the sampling accuracy of force fields and for characterizing the relative merits of
Direct Numerical Simulation of the Leidenfrost Effect
NASA Astrophysics Data System (ADS)
Tanguy, Sebastien; Rueda Villegas, Lucia; Fluid Mechanics Institute of Toulouse Team
2015-11-01
The development of numerical methods for the direct numerical simulation of two-phase flows with phase changes, is the main topic of this study. We propose a novel numerical method which allows dealing with both evaporation and boiling at the interface between a liquid and a gas. For instance it can occur for a Leidenfrost droplet; a water drop levitating above a hot plate which temperature is much higher than the boiling temperature. In this case, boiling occurs in the film of saturated vapor which is entrapped between the bottom of the drop and the plate, whereas the top of the water droplet evaporates in contact of ambient air. Thus, boiling and evaporation can occur simultaneously on different regions of the same liquid interface or occur successively at different times of the history of an evaporating droplet. Usual numerical methods are not able to perform computations in these transient regimes, therefore, we propose in this paper a novel numerical method to achieve this challenging task. Finally, we present several accurate validations against experimental results on Leidenfrost Droplets to strengthen the relevance of this new method.
Prediction of cavitating flow noise by direct numerical simulation
NASA Astrophysics Data System (ADS)
Seo, Jung H.; Moon, Young J.; Shin, Byeong Rog
2008-06-01
In this study, a direct numerical simulation procedure for the cavitating flow noise is presented. The compressible Navier-Stokes equations are written for the two-phase fluid, employing a density-based homogeneous equilibrium model with a linearly-combined equation of state. To resolve the linear and non-linear waves in the cavitating flow, a sixth-order compact central scheme is utilized with the selective spatial filtering technique. The present cavitation model and numerical methods are validated for two benchmark problems: linear wave convection and acoustic saturation in a bubbly flow. The cavitating flow noise is then computed for a 2D circular cylinder flow at Reynolds number based on a cylinder diameter, 200 and cavitation numbers, σ=0.7-2. It is observed that, at cavitation numbers σ=1 and 0.7, the cavitating flow and noise characteristics are significantly changed by the shock waves due to the coherent collapse of the cloud cavitation in the wake. To verify the present direct simulation and further analyze the sources of cavitation noise, an acoustic analogy based on a classical theory of Fitzpatrik and Strasberg is derived. The far-field noise predicted by direct simulation is well compared with that of acoustic analogy, and it also confirms the f-2 decaying rate in the spectrum, as predicted by the model of Fitzpatrik and Strasberg with the Rayleigh-Plesset equation.
Karavitis, G.A.
1984-01-01
The SIMSYS2D two-dimensional water-quality simulation system is a large-scale digital modeling software system used to simulate flow and transport of solutes in freshwater and estuarine environments. Due to the size, processing requirements, and complexity of the system, there is a need to easily move the system and its associated files between computer sites when required. A series of job control language (JCL) procedures was written to allow transferability between IBM and IBM-compatible computers. (USGS)
NASA Astrophysics Data System (ADS)
Beaudoin, Anthony; de Dreuzy, Jean-Raynald; Erhel, Jocelyne
2010-12-01
We investigate the influences of pore-scale dispersion and of larger-scale permeability heterogeneities on the macrodispersion without the molecular diffusion. Permeability follows a lognormal exponentially correlated distribution characterized by its correlation length λ and its lognormal variance σ2. Macrodispersion is evaluated numerically by using parallel simulations on grids of characteristic size ranging from 200λ to 1600λ. We note αL and αT the pore-scale longitudinal and transversal dispersivities. For αL/λ < 10-2 and αT/λ < 10-3, the influence of pore-scale dispersion on the macrodispersion is smaller than 5% of the macrodispersion due only to permeability heterogeneities. Larger dispersivities (αL/λ ≥ 10-2 or αT/λ ≥ 10-3) induce larger effects than those obtained by the semianalytical expression of Salandin and Fiorotto (1998) for σ2 > 1. The effects of local dispersion on the longitudinal macrodispersion remain limited to 25% at most of the macrodispersion due only to permeability heterogeneities. For σ2 > 1, isotropic local dispersion induces a reduction of the longitudinal macrodispersion, whereas anisotropic local dispersion lets it increase. The longitudinal and transverse local dispersions induce opposite effects on the longitudinal macrodispersion, which are respectively an increase and a reduction. The transverse macrodispersion null without local dispersion or molecular diffusion becomes strictly positive with local dispersion. Because of the velocity field heterogeneities, it is amplified by a factor of 2 to 50 from the grid scale to the macro scale. The transverse dispersion is triggered by both longitudinal and transverse local dispersions. A reduction of a factor of 2 of the transverse local dispersion at fixed longitudinal local dispersion yields only a reduction of a factor of 4 at most of the transverse macrodispersion for σ2 ≥ 2.25.
Lin, Shangchao; Shih, Chih-Jen; Sresht, Vishnu; Govind Rajan, Ananth; Strano, Michael S; Blankschtein, Daniel
2016-08-03
The colloidal dispersion stability of 1D and 2D materials in the liquid phase is critical for scalable nano-manufacturing, chemical modification, composites production, and deployment as conductive inks or nanofluids. Here, we review recent computational and theoretical studies carried out by our group to model the dispersion stability of 1D and 2D materials, including single-walled carbon nanotubes, graphene, and graphene oxide in aqueous surfactant solutions or organic solvents. All-atomistic (AA) molecular dynamics (MD) simulations can probe the molecular level details of the adsorption morphology of surfactants and solvents around these materials, as well as quantify the interaction energy between the nanomaterials mediated by surfactants or solvents. Utilizing concepts from reaction kinetics and diffusion, one can directly predict the rate constants for the aggregation kinetics and dispersion life times using MD outputs. Furthermore, the use of coarse-grained (CG) MD simulations allows quantitative prediction of surfactant adsorption isotherms. Combined with the Poisson-Boltzmann equation, the Langmuir isotherm, and the DLVO theory, one can directly use CGMD outputs to: (i) predict electrostatic potentials around the nanomaterial, (ii) correlate surfactant surface coverages with surfactant concentrations in the bulk dispersion medium, and (iii) determine energy barriers against coagulation. Finally, we discuss challenges associated with studying emerging 2D materials, such as, hexagonal boron nitride (h-BN), phosphorene, and transition metal dichalcogenides (TMDCs), including molybdenum disulfide (MoS2). An outlook is provided to address these challenges with plans to develop force-field parameters for MD simulations to enable predictive modeling of emerging 2D materials in the liquid phase.
Numerical recipes for mold filling simulation
Kothe, D.; Juric, D.; Lam, K.; Lally, B.
1998-07-01
Has the ability to simulate the filling of a mold progressed to a point where an appropriate numerical recipe achieves the desired results? If results are defined to be topological robustness, computational efficiency, quantitative accuracy, and predictability, all within a computational domain that faithfully represents complex three-dimensional foundry molds, then the answer unfortunately remains no. Significant interfacial flow algorithm developments have occurred over the last decade, however, that could bring this answer closer to maybe. These developments have been both evolutionary and revolutionary, will continue to transpire for the near future. Might they become useful numerical recipes for mold filling simulations? Quite possibly. Recent progress in algorithms for interface kinematics and dynamics, linear solution methods, computer science issues such as parallelization and object-oriented programming, high resolution Navier-Stokes (NS) solution methods, and unstructured mesh techniques, must all be pursued as possible paths toward higher fidelity mold filling simulations. A detailed exposition of these algorithmic developments is beyond the scope of this paper, hence the authors choose to focus here exclusively on algorithms for interface kinematics. These interface tracking algorithms are designed to model the movement of interfaces relative to a reference frame such as a fixed mesh. Current interface tracking algorithm choices are numerous, so is any one best suited for mold filling simulation? Although a clear winner is not (yet) apparent, pros and cons are given in the following brief, critical review. Highlighted are those outstanding interface tracking algorithm issues the authors feel can hamper the reliable modeling of today`s foundry mold filling processes.
Simulation of Ultra-Small MOSFETs Using a 2-D Quantum-Corrected Drift-Diffusion Model
NASA Technical Reports Server (NTRS)
Biegal, Bryan A.; Rafferty, Connor S.; Yu, Zhiping; Ancona, Mario G.; Dutton, Robert W.; Saini, Subhash (Technical Monitor)
1998-01-01
The continued down-scaling of electronic devices, in particular the commercially dominant MOSFET, will force a fundamental change in the process of new electronics technology development in the next five to ten years. The cost of developing new technology generations is soaring along with the price of new fabrication facilities, even as competitive pressure intensifies to bring this new technology to market faster than ever before. To reduce cost and time to market, device simulation must become a more fundamental, indeed dominant, part of the technology development cycle. In order to produce these benefits, simulation accuracy must improve markedly. At the same time, device physics will become more complex, with the rapid increase in various small-geometry and quantum effects. This work describes both an approach to device simulator development and a physical model which advance the effort to meet the tremendous electronic device simulation challenge described above. The device simulation approach is to specify the physical model at a high level to a general-purpose (but highly efficient) partial differential equation solver (in this case PROPHET, developed by Lucent Technologies), which then simulates the model in 1-D, 2-D, or 3-D for a specified device and test regime. This approach allows for the rapid investigation of a wide range of device models and effects, which is certainly essential for device simulation to catch up with, and then stay ahead of, electronic device technology of the present and future. The physical device model used in this work is the density-gradient (DG) quantum correction to the drift-diffusion model [Ancona, Phys. Rev. B 35(5), 7959 (1987)]. This model adds tunneling and quantum smoothing of carrier density profiles to the drift-diffusion model. We used the DG model in 1-D and 2-D (for the first time) to simulate both bipolar and unipolar devices. Simulations of heavily-doped, short-base diodes indicated that the DG quantum
HEAT.PRO - THERMAL IMBALANCE FORCE SIMULATION AND ANALYSIS USING PDE2D
NASA Technical Reports Server (NTRS)
Vigue, Y.
1994-01-01
HEAT.PRO calculates the thermal imbalance force resulting from satellite surface heating. The heated body of a satellite re-radiates energy at a rate that is proportional to its temperature, losing the energy in the form of photons. By conservation of momentum, this momentum flux out of the body creates a reaction force against the radiation surface, and the net thermal force can be observed as a small perturbation that affects long term orbital behavior of the satellite. HEAT.PRO calculates this thermal imbalance force and then determines its effects on satellite orbits, especially where the Earth's shadowing of an orbiting satellite causes periodic changes in the spacecraft's thermal environment. HEAT.PRO implements a finite element method routine called PDE2D which incorporates material properties to determine the solar panel surface temperatures. The nodal temperatures are computed at specified time steps and are used to determine the magnitude and direction of the thermal force on the spacecraft. These calculations are based on the solar panel orientation and satellite's position with respect to the earth and sun. It is necessary to have accurate, current knowledge of surface emissivity, thermal conductivity, heat capacity, and material density. These parameters, which may change due to degradation of materials in the environment of space, influence the nodal temperatures that are computed and thus the thermal force calculations. HEAT.PRO was written in FORTRAN 77 for Cray series computers running UNICOS. The source code contains directives for and is used as input to the required partial differential equation solver, PDE2D. HEAT.PRO is available on a 9-track 1600 BPI magnetic tape in UNIX tar format (standard distribution medium) or a .25 inch streaming magnetic tape cartridge in UNIX tar format. An electronic copy of the documentation in Macintosh Microsoft Word format is included on the distribution tape. HEAT.PRO was developed in 1991. Cray and UNICOS are
Numerical Simulation of Fluid Mud Gravity Currents
NASA Astrophysics Data System (ADS)
Yilmaz, N. A.; Testik, F. Y.
2011-12-01
Fluid mud bottom gravity currents are simulated numerically using a commercial computational fluid dynamics software, ANSYS-Fluent. In this study, Eulerian-Eulerian multi-fluid method is selected since this method treats all phases in a multiphase system as interpenetrated continua. There are three different phases in the computational model constructed for this study: water, fluid mud, and air. Water and fluid mud are defined as two miscible fluids and the mass and momentum transfers between these two phases are taken into account. Fluid mud, which is a dense suspension of clay particles and water, is defined as a single-phase non-Newtonian fluid via user-defined-functions. These functions define the physical characteristics (density, viscosity, etc.) of the fluid mud and these characteristics vary with changing suspension concentration due to mass transfer between the fluid mud and the water phase. Results of this two-dimensional numerical model are verified with data obtained from experiments conducted in a laboratory flume with a lock-release set-up. Numerical simulations are currently being conducted to elucidate turbulent entrainment of ambient water into fluid mud gravity currents. This study is motivated by coastal dredge disposal operations.
A Numerical Simulation of the Density Oscilator
NASA Astrophysics Data System (ADS)
Hernandez Zapata, Sergio; Lopez Sanchez, Erick Javier; Ruiz Chavarria, Gerardo
2016-11-01
In this work we carry out a numerical simulation for the dynamics that originates when a fluid (salty water) is located on top of another less dense fluid (pure water) in the presence of gravity. This is an unstable situation that leads to the development of intercalating lines of descending salty water and ascending pure water. Another situation is studied where the fluids are in two containers joined by a small hole. In this case a time pattern of alternating flows develops leading to an oscillator. The study of the velocity field around the hole shows than in a certain interval of time it develops intercalating lines like in the former situation. An interesting result is the fact that when a given fluid is flowing in one direction a vorticity pattern develops in the other fluid. The Navier-Stokes, continuity and salt diffusion equations, are solved numerically in cylindrical coordinates, using a finite difference scheme in the axial and radial directions and a Fourier spectral method for the angular coordinate. On the other hand, the second order Adams-Bashfort method is used for the time evolution. The results are compared to a numerical simulation of a pedestrian oscillator we developed based on the Hebling and Molnar social force model. The authors want to acknowledge support by DGAPA-UNAM (Project PAPIIT IN-115315 "Ondas y estructuras coherentes en dinámica de fluidos".
NASA Astrophysics Data System (ADS)
Sengupta, M.; Ganesh, R.
2017-03-01
In this paper, we have investigated, through simulation, the process of destabilization of a cylindrically confined electron cloud due to the presence of a single species of neutral atoms, Ar in the background of the trap at a pressure relevant to experiments. The destabilization occurs because of a gradual accumulation of Ar+ in the cloud by the electron-impact ionization of the background neutrals. The trapped ions gradually collectively form a sizeable ion cloud which engages in a rotational two-stream instability (the ion resonance instability) with the electron cloud. The instability excites a growing fundamental diocotron mode on both components of the mixed non-neutral cloud. With the help of a set of numerical diagnostics, we have investigated the nonlinear evolution of the excited fundamental mode under the combined influence of two ongoing processes viz, (i) the changing electron and ion populations caused by electron impact ionization of the background Ar, and also by the radial loss of both charged species to the grounded trap wall at later stages and (ii) the elastic scattering of electrons and ions that make non-ionizing collisions with the background neutrals. The 2D collisionless dynamics of the instability has been simulated using a 2D Particle-in-Cell code operating on a Cartesian grid laid out on the cylindrical trap's cross-section, and the 3D ionizing and non-ionizing collisions between charged particles and background neutrals have been simulated using the technique of Monte-Carlo-Collisions.
2D Quantum Simulation of MOSFET Using the Non Equilibrium Green's Function Method
NASA Technical Reports Server (NTRS)
Svizhenko, Alexel; Anantram, M. P.; Govindan, T. R.; Yan, Jerry (Technical Monitor)
2000-01-01
The objectives this viewgraph presentation summarizes include: (1) the development of a quantum mechanical simulator for ultra short channel MOSFET simulation, including theory, physical approximations, and computer code; (2) explore physics that is not accessible by semiclassical methods; (3) benchmarking of semiclassical and classical methods; and (4) study other two-dimensional devices and molecular structure, from discretized Hamiltonian to tight-binding Hamiltonian.
A numerical simulation of photothermal response in laser medicine
NASA Astrophysics Data System (ADS)
Li, Xiaoxia; Fan, Shifu; Zhao, Youquan; Xiao, Songshan
2004-03-01
In this paper, we reported a numerical solution of laser induced thermal effect in the bio-tissue. The model of photothermal effect and classical Pennes bio-heat transfer equation were introduced. Finite element method (FEM), which was realized by Matlab software, was used to calculate the temperature distribution. He-Ne laser (633 nm) was used to simulate the physical therapy in in vivo skin tissue. Under the cylinder coordinates, the three-dimension (3-D) geometry of tissue was reduced to two-dimension (2-D) computation. The results contained the radial, axial and temperature 3-D color plot. Combining the time animation display was possible. By changing the laser and tissue parameters we can get different results. This will be the initial and indispensable work of the non-destructive evaluation of the laser induced injury.
Implementation, study and calibration of a modified ASM2d for the simulation of SBR processes.
Marsili Libelli, S; Ratini, P; Spagni, A; Bortone, G
2001-01-01
An enhanced process model for SBRs has been developed. Though the basic mechanism largely draws on the Activated Sludge Model n. 2d, its new features are the splitting of the nitrification stage in a two-step process, according to the well known Nitrosomonas-Nitrobacter oxidation sequence, and an improved XPAO dynamics, involved in the anaerobic/aerobic phosphorus removal process. The model was implemented through the DLL technique allowing complied C++ modules to be linked to an ordinary Simulink block diagram. The static sensitivity study revealed that if the parameter vector is partitioned into subsets of biologically related parameters and calibrated separately, the calibration procedure does not present particularly difficult aspects. Trajectory sensitivity showed also to which extent data collection could be optimised in order to improve calibration accuracy. The study of the shape of the error functional generated by parameters couples allows a much more effective calibration strategy.
NASA Astrophysics Data System (ADS)
Hidrovo, Carlos; Salamat, Yasamin
2016-11-01
Capacitive Deionization (CDI) is a relatively new electrically based desalination method that uses porous media to adsorb ions in solution from water, with the potential to recover part of the energy used during the desalination process. Previous studies have investigated the physics underlying the electro-adsorption process in the electrical double layers in the CDI porous electrodes. In order to improve CDI performance in terms of minimum average concentration, total amount of water treated, and duration of the desalination process, herein we propose and evaluate different CDI architectures. Two previously validated 2D and 1D models are used alongside each other to study different CDI system configurations based on various convective-diffusive layer regimes. Moreover, the effects of micro pore and macro pore capacities on the total number of ions adsorbed in the porous media is investigated. This will open new opportunities for further researches toward engineered CDI units for better desalination.
Direct numerical simulation of hot jets
NASA Technical Reports Server (NTRS)
Jacob, Marc C.
1993-01-01
The ultimate motivation of this work is to investigate the stability of two dimensional heated jets and its implications for aerodynamic sound generation from data obtained with direct numerical simulations (DNS). As pointed out in our last report, these flows undergo two types of instabilities, convective or absolute, depending on their temperature. We also described the limits of earlier experimental and theoretical studies and explained why a numerical investigation could give us new insight into the physics of these instabilities. The aeroacoustical interest of these flows was also underlined. In order to reach this goal, we first need to succeed in the DNS of heated jets. Our past efforts have been focused on this issue which encountered several difficulties. Our numerical difficulties are directly related to the physical problem we want to investigate since these absolutely or almost absolutely unstable flows are by definition very sensitive to the smallest disturbances and are very likely to reach nonlinear saturation through a numerical feedback mechanism. As a result, it is very difficult to compute a steady laminar solution using a spatial DNS. A steady state was reached only for strongly co-flowed jets, but these flows are almost equivalent to two independent mixing layers. Thus they are far from absolute instability and have much lower growth rates.
Numerical simulation of real-world flows
NASA Astrophysics Data System (ADS)
Hayase, Toshiyuki
2015-10-01
Obtaining real flow information is important in various fields, but is a difficult issue because measurement data are usually limited in time and space, and computational results usually do not represent the exact state of real flows. Problems inherent in the realization of numerical simulation of real-world flows include the difficulty in representing exact initial and boundary conditions and the difficulty in representing unstable flow characteristics. This article reviews studies dealing with these problems. First, an overview of basic flow measurement methodologies and measurement data interpolation/approximation techniques is presented. Then, studies on methods of integrating numerical simulation and measurement, namely, four-dimensional variational data assimilation (4D-Var), Kalman filters (KFs), state observers, etc are discussed. The first problem is properly solved by these integration methodologies. The second problem can be partially solved with 4D-Var in which only initial and boundary conditions are control parameters. If an appropriate control parameter capable of modifying the dynamical structure of the model is included in the formulation of 4D-Var, unstable modes are properly suppressed and the second problem is solved. The state observer and KFs also solve the second problem by modifying mathematical models to stabilize the unstable modes of the original dynamical system by applying feedback signals. These integration methodologies are now applied in simulation of real-world flows in a wide variety of research fields. Examples are presented for basic fluid dynamics and applications in meteorology, aerospace, medicine, etc.
NASA Technical Reports Server (NTRS)
Morrison, Joseph H.
1998-01-01
This report details calculations for the McDonnell-Douglas 30P/30N and the NHLP-2D three-element highlift configurations. Calculations were performed with the Reynolds averaged Navier-Stokes code ISAAC to study the effects of various numerical issues on high lift predictions. These issues include the effect of numerical accuracy on the advection terms of the turbulence equations, Navier-Stokes versus the thin-layer Navier-Stokes approximation, an alternative formulation of the production term, and the performance of several turbulence models. The effect of the transition location on the NHLP-2D flow solution was investigated. Two empirical transition models were used to estimate the transition location.
Numerical simulation of platelet margination in microcirculation
NASA Astrophysics Data System (ADS)
Zhao, Hong; Shaqfeh, Eric
2009-11-01
The adhesion of platelets to vascular walls is the first step in clotting. This process critically depends on the preferential concentration of platelets near walls. The presence of red blood cells, which are the predominant blood constituents, is known to affect the steady state platelet concentration and the dynamic platelet margination, but the underlying mechanism is not well understood to-day. We use a direct numerical simulation to study the platelet margination process, with particular emphasis on the Stokesian hydrodynamic interactions among red cells, platelets, and vessel walls. Well-known mechanical models are used for the shearing and bending stiffness of red cell membranes, and the stiffer platelets are modeled as rigid discoids. A boundary integral formulation is used to solve the flow field, where the numerical solution procedure is accelerated by a parallel O(N N) smooth particle-mesh Ewald method. The effects of red cell hematocrit and deformability will be discussed.
Direct numerical simulation of chemically reacting turbulence
NASA Astrophysics Data System (ADS)
Miyauchi, Toshio; Tanahashi, Mamoru
In this paper, we present two results of direct numerical simulation of chemically reacting flows. One is direct numerical simulation of chemically reacting two-dimensional mixing layer and the other is direct numerical simulation of chemically reacting compressible isotropic turbulence. As for the mixing layer, a low Mach number approximation was used to take into account the variable density effects on the flow fields and to clarify the effects of heat release and density difference of a mean flow. In the case of density difference, expansion and baroclinic torque has a negative contribution to the local vorticity transport in the high density side and a positive contribution in the low density side which results in an asymmetric vortical structure structure. Thes density difference suppresses the growth of mixing layer and causes the overshoot of mean velocity only in the high density side which coincides with an experimental result. Coupling effects of heat release and desnity difference are also investigated. As for the homogeneous turbulence, fully compressible Navier-Stokes equations are solved to clarify the interaction between turbulence and chemical reaction in turbulent diffusion flame. The chemical reaction is suppressed by the increase of heat release because of the decrease of density and local Reynolds number. However, the decay of enstrophy with heat release is slower than that without heat release because of strong baroclinic torque which is generated near the reaction zone. Also, large amount of heat release causes increase in turbulent energy through the pressure dilatation term. The pressure dilatation term shows the periodic fluctuation which has an acoustic time scale. The fluctuation is enhanced by the heat release and travels in the turbulent field as pressure and dilatation waves.
Tracer dispersion simulation in low wind speed conditions with a new 2D Langevin equation system
NASA Astrophysics Data System (ADS)
Anfossi, D.; Alessandrini, S.; Trini Castelli, S.; Ferrero, E.; Oettl, D.; Degrazia, G.
The simulation of atmospheric dispersion in low wind speed conditions (LW) is still recognised as a challenge for modellers. Recently, a new system of two coupled Langevin equations that explicitly accounts for meandering has been proposed. It is based on the study of turbulence and dispersion properties in LW. The new system was implemented in the Lagrangian stochastic particle models LAMBDA and GRAL. In this paper we present simulations with this new approach applying it to the tracer experiments carried out in LW by Idaho National Engineering Laboratory (INEL, USA) in 1974 and by the Graz University of Technology and CNR-Torino near Graz in 2003. To assess the improvement obtained with the present model with respect to previous models not taking into account the meandering effect, the simulations for the INEL experiments were also performed with the old version of LAMBDA. The results of the comparisons clearly indicate that the new approach improves the simulation results.
Lindenschmidt, Karl-Erich; Huang, Shaochun; Baborowski, Martina
2008-07-01
In flood modeling, many one-dimensional (1D) hydrodynamic and water quality models are too restricted in capturing the spatial differentiation of processes within a polder or system of polders and two-dimensional (2D) models are too demanding in data requirements and computational resources, especially if Monte-Carlo techniques are to be used for model uncertainty analyses. The first goal of this paper is to show the successful development of a quasi-2D modeling approach which still calculates the dynamic wave in 1D but the discretisation of the computational units is in 2D, allowing a better spatial representation of the flow and substance transport processes in the polders without a large additional expenditure on data pre-processing and simulation processing. The models DYNHYD (1D hydrodynamics) and TOXI (sediment and micro-pollutant transport) were used as a basis for the hydrodynamic and water quality simulations. An extreme flood event on the Elbe River, Germany, with a proposed polder system variant was used as a test case. The results show a plausible differentiation of suspended sediment and zinc concentrations within the polders both spatially and temporally. This fulfills the second goal of this research. The third goal of this work is to provide an example methodology of carrying out an environmental risk assessment in inundated areas by flood waters, as required by the European Union floods directive. The deposition of zinc in polders was used for this example, due to its high contamination potential in the Elbe River. The extended quasi-2D modeling system incorporates a Monte-Carlo uncertainty analysis to assess the environmental impact of heavy metal deposition in the polders during extreme flooding. The environmental risk computed gives a 48% chance of exceeding the inspection value of 500 mg zinc/kg sediment for a flood such as the August 2002 event.
Numerical Flow Simulation for Complete Vehicle Configurations
1993-09-01
TITLE AND SUBTITLE 5. •uNOING NUMBERS Numerical Field Simulation around complete configuration F49620-90-C- 6. AUTHOR(S) 0027PO006 Bharat K. Soni...2_3 d 71 7. PERFORMING ORGANIZATION NAME(S) AND ADORESS(ES) 8. PERFORMING CRGANIZATION NSF/Engineering Research Center f•r . 5 j 5 ( F i REPORT NUMBER P...AVAILABLE. THE COPY FURNISHED TO DTIC CONTAINED A SIGNIFICANT NUMBER OF PAGES WHICH DO NOT REPRODUCE LEGIBLY. TABLE OF CONTENTS A bstract
Numerical aspects of compressible turbulence simulations
NASA Astrophysics Data System (ADS)
Honein, Albert Edward
Nonlinear instabilities present a long standing hurdle for compact, high order, non dissipative, finite difference computation of compressible turbulence. The spectral-like accuracy of these schemes, while attractive, results in significant aliasing errors that corrupt the solution. As a result, successful simulations have been limited to moderate Reynolds numbers ( Re) and low-order or upwind schemes with inherent numerical dissipation. However, resorting to dissipative schemes in discretizing the nonlinear terms was shown to have a detrimental effect on turbulence. A recent LES approach is to abandon the subgrid model altogether and rely on the scheme dissipation to mimic the effect of small scales. A dissipative monotone integrated LES (MILES) algorithm based on a multidimensional flux-corrected transport (FCT) algorithm has been developed and tested for decaying compressible isotropic turbulence. Agreement with the benchmark experiments of Comte-Bellot and Corrsin is very sensitive to the parameters involved in the FCT algorithm, while the evolution of thermodynamic fluctuations do not compare well with direct numerical simulations. An under-resolved simulation of inviscid, compressible, isotropic turbulence at low Mach number is chosen as a severe benchmark to investigate the nonlinear stability properties of nondissipative schemes. The behavior of this benchmark is predicted by performing a fully de-aliased spectral simulation on a 32 3 grid with turbulent Mach number of Mto = 0.07. The kinetic energy and thermodynamic fluctuations are found to decay for finite Re, and remain constant at infinite Re for a long time before the occurrence of numerical shocks. Extending the proof of Kraichnan (Journal of the Acoustical Society of America, 27(3), 1955), this inviscid statistical equilibrium is demonstrated to be a consequence of the discrete equivalent of the Liouville theorem of classical statistical mechanics. Several existing non-dissipative methods are
Numerical simulation for fan broadband noise prediction
NASA Astrophysics Data System (ADS)
Hase, Takaaki; Yamasaki, Nobuhiko; Ooishi, Tsutomu
2011-03-01
In order to elucidate the broadband noise of fan, the numerical simulation of fan operating at two different rotational speeds is carried out using the three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The computed results are compared to experiment to estimate its accuracy and are found to show good agreement with experiment. A method is proposed to evaluate the turbulent kinetic energy in the framework of the Spalart-Allmaras one equation turbulence model. From the calculation results, the turbulent kinetic energy is visualized as the turbulence of the flow which leads to generate the broadband noise, and its noise sources are identified.
Numerical simulations of vibrating sessile drop
NASA Astrophysics Data System (ADS)
Kahouadji, Lyes; Chergui, Jalel; Juric, Damir; Shin, Seungwon; Craster, Richard; Matar, Omar
2016-11-01
A vibrated drop constitutes a very rich physical system, blending both interfacial and volume phenomena. A remarkable experimental study was performed by M. Costalonga highlighting sessile drop motion subject to horizontal, vertical and oblique vibration. Several intriguing phenomena are observed such as drop walking and rapid droplet ejection. We perform three-dimensional direct numerical simulations of vibrating sessile drops where the phenomena described above are computed using the massively parallel multiphase code BLUE. EPSRC UK Programme Grant MEMPHIS (EP/K003976/1).
Direct numerical simulation of turbulent mixing.
Statsenko, V P; Yanilkin, Yu V; Zhmaylo, V A
2013-11-28
The results of three-dimensional numerical simulations of turbulent flows obtained by various authors are reviewed. The paper considers the turbulent mixing (TM) process caused by the development of the main types of instabilities: those due to gravitation (with either a fixed or an alternating-sign acceleration), shift and shock waves. The problem of a buoyant jet is described as an example of the mixed-type problem. Comparison is made with experimental data on the TM zone width, profiles of density, velocity and turbulent energy and degree of homogeneity.
Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores
Burris, Paul C.; Laage, Damien; Thompson, Ward H.
2016-05-20
Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this Paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D_{2}O is considered. An empirical mapping approach is used to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. Lastly, the simulated spectra indicate that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra.
Burris, Paul C; Laage, Damien; Thompson, Ward H
2016-05-21
Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D2O is considered. An empirical mapping approach is used to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. The simulated spectra indicates that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra.
Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores
Burris, Paul C.; Laage, Damien; Thompson, Ward H.
2016-05-20
Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this Paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D2O is considered. An empirical mapping approach is usedmore » to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. Lastly, the simulated spectra indicate that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra.« less
Kamiya, Tetsu; Toyama, Yoshio; Michiwaki, Yukihiro; Kikuchi, Takahiro
2013-01-01
The aim of the present study was to evaluate the possibility of numerical simulation of the swallowing process using a moving particle simulation (MPS) method, which defined the food bolus as a number of particles in a fluid, a solid, and an elastic body. In order to verify the accuracy of the simulation results, a simple water bolus falling model was solved using the three-dimensional (3D) MPS method. We also examined the simplified swallowing simulation using a two-dimensional (2D) MPS method to confirm the interactions between the liquid, solid, elastic bolus, and organ structure. In a comparison of the 3D MPS simulation and experiments, the falling time of the water bolus and the configuration of the interface between the liquid and air corresponded exactly to the experimental measurements and the visualization images. The results showed that the accuracy of the 3D MPS simulation was qualitatively high for the simple falling model. Based on the results of the simplified swallowing simulation using the 2D MPS method, each bolus, defined as a liquid, solid, and elastic body, exhibited different behavior when the organs were transformed forcedly. This confirmed that the MPS method could be used for coupled simulations of the fluid, the solid, the elastic body, and the organ structures. The results suggested that the MPS method could be used to develop a numerical simulator of the swallowing process.
A Novel Numerical Algorithm of Numerov Type for 2D Quasi-linear Elliptic Boundary Value Problems
NASA Astrophysics Data System (ADS)
Mohanty, R. K.; Kumar, Ravindra
2014-11-01
In this article, using three function evaluations, we discuss a nine-point compact scheme of O(Δ y2 + Δ x4) based on Numerov-type discretization for the solution of 2D quasi-linear elliptic equations with given Dirichlet boundary conditions, where Δy > 0 and Δx > 0 are grid sizes in y- and x-directions, respectively. Iterative methods for diffusion-convection equation are discussed in detail. We use block iterative methods to solve the system of algebraic linear and nonlinear difference equations. Comparative results of some physical problems are given to illustrate the usefulness of the proposed method.
Numerical simulation of large fabric filter
NASA Astrophysics Data System (ADS)
Sedláček, Jan; Kovařík, Petr
2012-04-01
Fabric filters are used in the wide range of industrial technologies for cleaning of incoming or exhaust gases. To achieve maximal efficiency of the discrete phase separation and long lifetime of the filter hoses, it is necessary to ensure uniform load on filter surface and to avoid impacts of heavy particles with high velocities to the filter hoses. The paper deals with numerical simulation of two phase flow field in a large fabric filter. The filter is composed of six chambers with approx. 1600 filter hoses in total. The model was simplified to one half of the filter, the filter hoses walls were substituted by porous zones. The model settings were based on experimental data, especially on the filter pressure drop. Unsteady simulations with different turbulence models were done. Flow field together with particles trajectories were analyzed. The results were compared with experimental observations.
Numerical simulation of space UV spectrographs
NASA Astrophysics Data System (ADS)
Yushkin, Maksim; Fatkhullin, Timur; Panchuk, Vladimir; Sachkov, Mikhail; Kanev, Evgeny
2016-07-01
Based on the ray tracing method, we developed algorithms for constructing numerical model of spectroscopic instrumentation. The Software is realized in C ++ using nVidia CUDA technology. The software package consists of three separate modules: the ray tracing module, a module for calculating energy efficiency and module of CCD image simulation. The main objective of this work was to obtain images of the spectra for the cross-dispersed spectrographs as well as segmented aperture Long Slit Spectrograph. The software can be potentially used by WSO-UV project. To test our algorithms and the software package we have performed simulations of the ground cross-dispersed Nasmyth Echelle Spectrometer (NES) installed on the platform of the Nasmyth focus of the Russian 6-meter BTA telescope. The comparison of model images of stellar spectra with observations on this device confirms that the software works well. The high degree of agreement between the theoretical and real spectra is shown.
NASA Astrophysics Data System (ADS)
Lee, Khil-Ha; Kim, Sung-Wook; Kim, Sang-Hyun
2014-05-01
model, called FLO-2D runs to simulate channel routing downstream to give the maximum water level. Once probable inundation areas are identified by the huge volume of water in the caldera lake, the unique geography, and the limited control capability, a potential hazard assessment can be represented. The study will contribute to build a geohazard map for the decision-makers and practitioners. Keywords: Volcanic flood, Caldera lake, Hazard assessment, Magma effusion Acknowledgement This research was supported by a grant [NEMA-BAEKDUSAN-2012-1-2] from the Volcanic Disaster Preparedness Research Center sponsored by National Emergency Management Agency of Korea.
3D EFT imaging with planar electrode array: Numerical simulation
NASA Astrophysics Data System (ADS)
Tuykin, T.; Korjenevsky, A.
2010-04-01
Electric field tomography (EFT) is the new modality of the quasistatic electromagnetic sounding of conductive media recently investigated theoretically and realized experimentally. The demonstrated results pertain to 2D imaging with circular or linear arrays of electrodes (and the linear array provides quite poor quality of imaging). In many applications 3D imaging is essential or can increase value of the investigation significantly. In this report we present the first results of numerical simulation of the EFT imaging system with planar array of electrodes which allows 3D visualization of the subsurface conductivity distribution. The geometry of the system is similar to the geometry of our EIT breast imaging system providing 3D conductivity imaging in form of cross-sections set with different depth from the surface. The EFT principle of operation and reconstruction approach differs from the EIT system significantly. So the results of numerical simulation are important to estimate if comparable quality of imaging is possible with the new contactless method. The EFT forward problem is solved using finite difference time domain (FDTD) method for the 8×8 square electrodes array. The calculated results of measurements are used then to reconstruct conductivity distributions by the filtered backprojections along electric field lines. The reconstructed images of the simple test objects are presented.
Direct Numerical Simulations of Transient Dispersion
NASA Astrophysics Data System (ADS)
Porter, M.; Valdes-Parada, F.; Wood, B.
2008-12-01
Transient dispersion is important in many engineering applications, including transport in porous media. A common theoretical approach involves upscaling the micro-scale mass balance equations for convection- diffusion to macro-scale equations that contain effective medium quantities. However, there are a number of assumptions implicit in the various upscaling methods. For example, results obtained from volume averaging are often dependent on a given set of length and time scale constraints. Additionally, a number of the classical models for dispersion do not fully capture the early-time dispersive behavior of the solute for a general set of initial conditions. In this work, we present direct numerical simulations of micro-scale transient mass balance equations for convection-diffusion in both capillary tubes and porous media. Special attention is paid to analysis of the influence of a new time- decaying coefficient that filters the effects of the initial conditions. The direct numerical simulations were compared to results obtained from solving the closure problem associated with volume averaging. These comparisons provide a quantitative measure of the significance of (1) the assumptions implicit in the volume averaging method and (2) the importance of the early-time dispersive behavior of the solute due to various initial conditions.
Numerical Simulations of 1990 Saturn's Giant Storm
NASA Astrophysics Data System (ADS)
Garcia-Melendo, E.; Sanchez-Lavega, A.
2015-12-01
We present here a study of the Saturn's 1990 equatorial major storm based on numerical simulations. Six planetary scale storms, nicknamed as Great White Spots (GWS) have been observed since the nineteenth century, three of them at the equatorial region in 1876 (~ +8º), 1933 (~ +2º), and 1990 (+12º), on the broad prograde equatorial jet where equatorial dynamics dominated producing a storm nucleus, with rapid expansion to the east and west to become a planetary-scale disturbance (Sánchez-Lavega, CHAOS 4, 341-353, 1994). We have detailed information, ground-based CCD imaging and Hubble Space Telescope (HST) data, for the 1990 event. Numerical experiments on the 1990 storm indicate that the onset of the storm can only be reproduced if the Voyager era background zonal flow is used, which suggests that it dominated the circulation dynamics at the storm's outbreak region at that time. We review the possible impact of the 1990 storm on the equatorial jet, storm dynamics, and how it relates to the observed storm morphology and zonal wind measurements derived from HST observations (Barnet et al., Icarus 100, 499-511, 1992). Observations also describe the formation of equatorial planetary waves and instabilities during the disturbance. We discuss the impact of major energy and mass injection by a planetary-scale convective event on the equatorial dynamics following our simulation results.
Direct numerical simulation of incompressible axisymmetric flows
NASA Technical Reports Server (NTRS)
Loulou, Patrick
1994-01-01
In the present work, we propose to conduct direct numerical simulations (DNS) of incompressible turbulent axisymmetric jets and wakes. The objectives of the study are to understand the fundamental behavior of axisymmetric jets and wakes, which are perhaps the most technologically relevant free shear flows (e.g. combuster injectors, propulsion jet). Among the data to be generated are various statistical quantities of importance in turbulence modeling, like the mean velocity, turbulent stresses, and all the terms in the Reynolds-stress balance equations. In addition, we will be interested in the evolution of large-scale structures that are common in free shear flow. The axisymmetric jet or wake is also a good problem in which to try the newly developed b-spline numerical method. Using b-splines as interpolating functions in the non-periodic direction offers many advantages. B-splines have local support, which leads to sparse matrices that can be efficiently stored and solved. Also, they offer spectral-like accuracy that are C(exp O-1) continuous, where O is the order of the spline used; this means that derivatives of the velocity such as the vorticity are smoothly and accurately represented. For purposes of validation against existing results, the present code will also be able to simulate internal flows (ones that require a no-slip boundary condition). Implementation of no-slip boundary condition is trivial in the context of the b-splines.
The 2-D simulations of the NRL (Naval Research Laboratory) laser experiment
NASA Astrophysics Data System (ADS)
Lyon, J. G.
1985-05-01
Two-dimensional gas-dynamic simulations of the NRL laser experiment have been performed to study the formation of aneurysms in the blast wave and to study the formation of structure internal to the blast front itself. In one set of simulations the debris shell was perturbed sinusoidally in mass and position and also perturbed to mimic the action of a slow jet of material leaving the target at slower speeds than the bulk of the debris. In all cases the blast wave remained stable to any aneurysm-like instability. Internal structure, however, was quite easily produced and grew as a function of time. In the other set of simulations the effect of a pre-heated channel upon the propagation of the blast wave was examined. Bulges in the blast wave shock front were produced in these simulations that could be the beginning of the aneurysm phenomenon, but the preheated channel by itself appears to be insufficient to produce the observed aneurysm.
Numerical simulation of tides in Ontario Lacus
NASA Astrophysics Data System (ADS)
Vincent, David; Karatekin, Ozgür
2015-04-01
Hydrocarbons liquid filled lakes has been recently detected on Titan's surface. Most of these lakes are located in the northern latitudes but there is a substantial lake in the southern latitudes: Ontario Lacus. This lake gets our attention because of possible shoreline changes suggested by Cassini flybys over Ontario Lacus between September 2005 (T7) et January 2010 (T65). The shoreline changes could be due to evaporation-precipitation processes but could also be a consequence of tides. Previous studies showed that the maximal tidal amplitudes of Ontario Lacus would be about 0.2m (for an uniform bathymetry of 20m). In this study we simulate tidal amplitude and currents with SLIM (Second-generation Louvain-la-Neuve Ice-ocean Model, http://sites.uclouvain.be/slim/ ) which resolves 2D shallow water equation on an unstructured mesh. Unstructured mesh prevents problems like mesh discontinuities at poles and allows higher accuracy at some place like coast or straits without drastically increasing computing costs. The tide generating force modeled in this work is the gradient of tidal potential due to titan's obliquity and titan's orbital eccentricity around Saturn (other contribution such as sun tide generating force are unheeded). The uncertain input parameters such as the wind direction and amplitude, bottom friction and thermo-physical properties of hydrocarbons liquids are varied within their expected ranges. SAR data analysis can result in different bathymetry according to the method. We proceed simulations for different bathymetries: tidal amplitudes doesn't change but this is not the case for tidal currents. Using a recent bathymetry deduced from most recent RADAR/SAR observations and a finer mesh, the peak-to peak tidal amplitudes are calculated to be up to 0.6 m. which is more than a factor two larger than the previous results. The maximal offshore tidal currents magnitude is about 0.06 m/s.
NASA Technical Reports Server (NTRS)
Vashi, Bharat I.
1992-01-01
The first Tethered-Satellite-System (TSS-1), scheduled for a flight in late 1992, is expected to provide relevant information related to the concept of generating an emf in a 20-km-long (or longer) conducting wire. This paper presents numerical simulations of the electrodynamic interactions between the TSS system and space plasma, using a 2D and 3D models of the system. The 2D case code simulates the motion of a long cylinder past a plasma, which is composed of electrons and H(+) ions. The system is solved by allowing the plasma to flow past the cylinder with an imposed magnetic field. The more complex 3D case is considered to study the dynamics in great detail. Results of 2D simulation show that the interaction of a satellite with plasma flowing perpendicularly to the magnetic field results in an enhancement in the current collection.
NASA Astrophysics Data System (ADS)
Sellmeier, B.; Thuro, K.
2012-04-01
In between the last years rock falls seem to occur more often in high mountainous regions. Linked with the climate change problem, this topic is mentioned in the media more and more frequently. As a consequence, especially in populated alpine regions in Europe, public authorities have to act more and more towards prevention of rock fall events. Important questions in that context are how events can be predicted more precisely in the future and how mitigation methods can be improved in endangered areas. On that purpose, a research project has been established giving an input in different ways by means of a project site which is situated along the federal road B 305 between Unterjettenberg and Schwarzbachwacht near Berchtesgaden in the Bavarian Alps, Germany. In that context the uncertainties concerning field work in difficult terrain are considered with regard to the subsequent simulations. It is often the case that not every part of the rock fall site can be examined in the same way. A further origin of uncertainty is the variation of the initial parameters in between a certain period of time. For example the variation of forest stands parameters because of windbreakage or avalanches. Consequently the factors of uncertainty and their possible consequences for the simulations will be analyzed. As further aspects of the project it is intended to compare the possibilities and limitations of 2D and 3D rock fall simulations concerning the runout zones. In particular the application ranges of both methods will be analyzed using the 2 dimensional simulation codes Rockfall (Dr. Spang) and Rofmod 2D (Geotest) in comparison with the 3 dimensional simulation code Rofmod 3D (Geotest). In this contribution the results of the field work, the analyses of the uncertainties concerning the initial parameters of rockfall simulations will be presented. (SELLMEIER & THURO 2011)
NASA Astrophysics Data System (ADS)
Caballero, L.; Capra, L.
2014-07-01
Lahar modelling represents an excellent tool to design hazard maps. It allows the definition of potential inundation zones for different lahar magnitude scenarios and sediment concentrations. Here we present the results obtained for the 2001 syneruptive lahar at Popocatépetl volcano, based on simulations performed with FLO2D software. An accurate delineation of this event is needed since it is one of the possible scenarios considered during a volcanic crisis. One of the main issues for lahar simulation using FLO2D is the calibration of the input hydrograph and rheologic flow properties. Here we verified that geophone data can be properly calibrated by means of peak discharge calculations obtained by superelevation method. Simulation results clearly show the influence of concentration and rheologic properties on lahar depth and distribution. Modifying rheologic properties during lahar simulation strongly affect lahar distribution. More viscous lahars have a more restricted aerial distribution, thicker depths, and resulting velocities are noticeable smaller. FLO2D proved to be a very successful tool to delimitate lahar inundation zones as well as to generate different lahar scenarios not only related to lahar volume or magnitude but also to take into account different sediment concentrations and rheologies widely documented to influence lahar prone areas.
Kasinathan, N.; Rajakumar, A.; Vaidyanathan, G.; Chetal, S.C.
1995-09-01
Post shutdown decay heat removal is an important safety requirement in any nuclear system. In order to improve the reliability of this function, Liquid metal (sodium) cooled fast breeder reactors (LMFBR) are equipped with redundant hot pool dipped immersion coolers connected to natural draught air cooled heat exchangers through intermediate sodium circuits. During decay heat removal, flow through the core, immersion cooler primary side and in the intermediate sodium circuits are also through natural convection. In order to establish the viability and validate computer codes used in making predictions, a 1:20 scale experimental model called RAMONA with water as coolant has been built and experimental simulation of decay heat removal situation has been performed at KfK Karlsruhe. Results of two such experiments have been compiled and published as benchmarks. This paper brings out the results of the numerical simulation of one of the benchmark case through a 1D/2D coupled code system, DHDYN-1D/THYC-2D and the salient features of the comparisons. Brief description of the formulations of the codes are also included.
2D and 3D numerical simulations of morphodynamics structures in a large-amplitude meanders
Technology Transfer Automated Retrieval System (TEKTRAN)
In the pioneering study of the Ishikari River, Japan, Kinoshita (Kinoshita 1957, 1961) described two types of meandering channels: (1) channel with two bars per meander wavelength (one bar per bend), and (2) channel with three or more bars per meander wavelength (multiple bars per bend). Based on th...
``SAFFMAN-TAYLOR'' Finger in 2d Parallel Viscous: BGK Lattice Gas Simulations
NASA Astrophysics Data System (ADS)
Salin, Dominique; Rakotomalala, Nicole; Watzky, Philippe
1996-11-01
We study the displacement of miscible fluids between two parallel plates for different values of the Peclet number Pe and of the viscosity ratio M. The full Navier-Stokes problem is addressed. We use the BGK lattice gas method, which is well suited for miscible fluids and allows to introduce molecular diffusion at the microscopic scale of the lattice. This numerical experiment leads to a symmetric concentration profile about the middle of the gap between the plates. At Pe numbers of the order of 1, mixing involves diffusion and advection in the flow direction. At large Pe, the fluids do not mix and an interface between them can be defined. Moreover, above M ~ 10, the interface becomes a well defined finger, the reduced width of which tends to λ_∞=0.56 at large values of M. Assuming that miscible fluids at high Pe numbers are similar to immiscible fluids at high capillary numbers, we find the analytical shape of the finger, using an extrapolation of the Reinelt-Saffman calculations for a Stokes immiscible flow. Surprisingly, the result is that our finger can be deduced from the celebrated Saffman-Taylor' s one, obtained in a potential flow, by a streching in the flow direction by a numerical factor of 2.125.
Direct numerical simulation of turbulent reacting flows
Chen, J.H.
1993-12-01
The development of turbulent combustion models that reflect some of the most important characteristics of turbulent reacting flows requires knowledge about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between the turbulence and the chemistry is so strong in certain regimes that is is very difficult to isolate the role played by one individual phenomenon. Direct numerical simulation (DNS) is an extremely useful tool to study in detail the turbulence-chemistry interactions in certain well defined regimes. Globally, non-premixed flames are controlled by two limiting cases: the fast chemistry limit, where the turbulent fluctuations. In between these two limits, finite-rate chemical effects are important and the turbulence interacts strongly with the chemical processes. This regime is important because industrial burners operate in regimes in which, locally the flame undergoes extinction, or is at least in some nonequilibrium condition. Furthermore, these nonequilibrium conditions strongly influence the production of pollutants. To quantify the finite-rate chemistry effect, direct numerical simulations are performed to study the interaction between an initially laminar non-premixed flame and a three-dimensional field of homogeneous isotropic decaying turbulence. Emphasis is placed on the dynamics of extinction and on transient effects on the fine scale mixing process. Differential molecular diffusion among species is also examined with this approach, both for nonreacting and reacting situations. To address the problem of large-scale mixing and to examine the effects of mean shear, efforts are underway to perform large eddy simulations of round three-dimensional jets.
Generalized source method in curvilinear coordinates for 2D grating diffraction simulation
NASA Astrophysics Data System (ADS)
Shcherbakov, Alexey A.; Tishchenko, Alexandre V.
2017-01-01
The article presents a curvilinear coordinate Fourier space integral method for linear optical rigorous grating diffraction simulation in 3D (crossed grating diffraction). The presented formulation extends our previous work on a related method for 1D periodic grating diffraction. Following this previous work we exploit a concept of the generalized metric sources to efficiently solve the Maxwell's equations. The article provides a general description of the method together with a detailed formulation and analysis of sinusoidal corrugation crossed grating diffraction.
Zhou, Y. L.; Wang, Z. H.; Xu, X. Q.; Li, H. D.; Feng, H.; Sun, W. G.
2015-01-09
Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Furthermore, two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density, heat and momentum transport equations along with neutral density, and momentum transport equations. In transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. Moreover, it is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.
Zhou, Y. L.; Wang, Z. H.; Xu, X. Q.; Li, H. D.; Feng, H.; Sun, W. G.
2015-01-15
Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density, heat and momentum transport equations along with neutral density, and momentum transport equations. Transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. It is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.
Zhou, Y. L.; Wang, Z. H.; Xu, X. Q.; ...
2015-01-09
Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Furthermore, two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density,more » heat and momentum transport equations along with neutral density, and momentum transport equations. In transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. Moreover, it is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP.« less
Development of a 2-D large-scale micellar/polymer simulator
Wang, B.
1982-01-01
A large-scale, two-dimensional, multicomponent, multiphase, compositional simulator for micellar/polymer flooding has been developed and applied. It can be used to calculate the areal sweep with any well pattern and any irregular reservoir boundary. This model involves both streamline and finite-difference techniques. Time invariant streamlines without transverse dispersion are assumed. The change in the flow rates into each streamline is accounted for as a function of mobility ratio. The sensitivity of the oil recovery for micellar/polymer flood to several reservoir and process variables was investigated. The reservoir variables included the well spacing, pattern type, pattern orientation in an anisotropic reservoir, and degree of confinement. The process variables included the salinity gradient, surfactant content of the slug, slug and polymer bank sizes, mobility ratio of polymer drive to oil bank, and polymer shear thinning effect. In order to demonstrate that this model is capable of handling large field problems, a large-scale simulation of the north lease of the El Dorado micellar/polymer pilot test was made. The simulated final oil recovery and the production histories of each producer are illustrated.
Numerical Simulations of High Enthalpy Pulse Facilities
NASA Technical Reports Server (NTRS)
Wilson, Gregory J.; Edwards, Thomas A. (Technical Monitor)
1995-01-01
Axisymmetric flows within shock tubes and expansion tubes are simulated including the effects of finite rate chemistry and both laminar and turbulent boundary layers. The simulations demonstrate the usefulness of computational fluid dynamics for characterizing the flows in high enthalpy pulse facilities. The modeling and numerical requirements necessary to simulate these flows accurately are also discussed. Although there is a large body of analysis which explains and quantifies the boundary layer growth between the shock and the interface in a shock tube, there is a need for more detailed solutions. Phenomena such as thermochemical nonequilibrium. or turbulent transition behind the shock are excluded in the assumptions of Mirels' analysis. Additionally there is inadequate capability to predict the influence of the boundary layer on the expanded gas behind the interface. Quantifying the gas in this region is particularly important in expansion tubes because it is the location of the test gas. Unsteady simulations of the viscous flow in shock tubes are computationally expensive because they must follow features such as a shock wave over the length of the facility and simultaneously resolve the small length scales within the boundary layer. As a result, efficient numerical algorithms are required. The numerical approach of the present work is to solve the axisymmetric gas dynamic equations using an finite-volume formulation where the inviscid fluxes are computed with a upwind TVD scheme. Multiple species equations are included in the formulation so that finite-rate chemistry can be modeled. The simulations cluster grid points at the shock and interface and translate this clustered grid with these features to minimize numerical errors. The solutions are advanced at a CFL number of less than one based on the inviscid gas dynamics. To avoid limitations on the time step due to the viscous terms, these terms are treated implicitly. This requires a block tri
The Numerical Propulsion System Simulation: An Overview
NASA Technical Reports Server (NTRS)
Lytle, John K.
2000-01-01
Advances in computational technology and in physics-based modeling are making large-scale, detailed simulations of complex systems possible within the design environment. For example, the integration of computing, communications, and aerodynamics has reduced the time required to analyze major propulsion system components from days and weeks to minutes and hours. This breakthrough has enabled the detailed simulation of major propulsion system components to become a routine part of designing systems, providing the designer with critical information about the components early in the design process. This paper describes the development of the numerical propulsion system simulation (NPSS), a modular and extensible framework for the integration of multicomponent and multidisciplinary analysis tools using geographically distributed resources such as computing platforms, data bases, and people. The analysis is currently focused on large-scale modeling of complete aircraft engines. This will provide the product developer with a "virtual wind tunnel" that will reduce the number of hardware builds and tests required during the development of advanced aerospace propulsion systems.
Direct numerical simulation of human phonation
NASA Astrophysics Data System (ADS)
Saurabh, Shakti; Bodony, Daniel
2016-11-01
A direct numerical simulation study of the generation and propagation of the human voice in a full-body domain is conducted. A fully compressible fluid flow model, anatomically representative vocal tract geometry, finite deformation model for vocal fold (VF) motion and a fully coupled fluid-structure interaction model are employed. The dynamics of the multi-layered VF tissue with varying stiffness are solved using a quadratic finite element code. The fluid-solid domains are coupled through a boundary-fitted interface and utilize a Poisson equation-based mesh deformation method. A new inflow boundary condition, based upon a quasi-1D formulation with constant sub-glottal volume velocity, linked to the VF movement, has been adopted. Simulations for both child and adult phonation were performed. Acoustic characteristics obtained from these simulation are consistent with expected values. A sensitivity analysis based on VF stiffness variation is undertaken and sound pressure level/fundamental frequency trends are established. An evaluation of the data against the commonly-used quasi-1D equations suggest that the latter are not sufficient to model phonation. Phonation threshold pressures are measured for several VF stiffness variations and comparisons to clinical data are carried out. Supported by the National Science Foundation (CAREER Award Number 1150439).
Numerical simulation of pump-intake vortices
NASA Astrophysics Data System (ADS)
Rudolf, Pavel; Klas, Roman
2015-05-01
Pump pre-swirl or uneven flow distribution in front of the pump can induce pump-intake vortices. These phenomena result in blockage of the impeller suction space, deterioration of efficiency, drop of head curve and earlier onset of cavitation. Real problematic case, where head curve drop was documented, is simulated using commercial CFD software. Computational simulation was carried out for three flow rates, which correspond to three operating regimes of the vertical pump. The domain consists of the pump sump, pump itself excluding the impeller and the delivery pipe. One-phase approach is applied, because the vortex cores were not filled with air during observation of the real pump operation. Numerical simulation identified two surface vortices and one bottom vortex. Their position and strength depend on the pump flow rate. Paper presents detail analysis of the flow field on the pump intake, discusses influence of the vortices on pump operation and suggests possible actions that should be taken to suppress the intake vortices.
Numerical simulation of premixed turbulent methane combustion
Bell, John B.; Day, Marcus S.; Grcar, Joseph F.
2001-12-14
In this paper we study the behavior of a premixed turbulent methane flame in three dimensions using numerical simulation. The simulations are performed using an adaptive time-dependent low Mach number combustion algorithm based on a second-order projection formulation that conserves both species mass and total enthalpy. The species and enthalpy equations are treated using an operator-split approach that incorporates stiff integration techniques for modeling detailed chemical kinetics. The methodology also incorporates a mixture model for differential diffusion. For the simulations presented here, methane chemistry and transport are modeled using the DRM-19 (19-species, 84-reaction) mechanism derived from the GRIMech-1.2 mechanism along with its associated thermodynamics and transport databases. We consider a lean flame with equivalence ratio 0.8 for two different levels of turbulent intensity. For each case we examine the basic structure of the flame including turbulent flame speed and flame surface area. The results indicate that flame wrinkling is the dominant factor leading to the increased turbulent flame speed. Joint probability distributions are computed to establish a correlation between heat release and curvature. We also investigate the effect of turbulent flame interaction on the flame chemistry. We identify specific flame intermediates that are sensitive to turbulence and explore various correlations between these species and local flame curvature. We identify different mechanisms by which turbulence modulates the chemistry of the flame.
Numerical simulations of the NREL S826 airfoil
NASA Astrophysics Data System (ADS)
Sagmo, KF; Bartl, J.; Sætran, L.
2016-09-01
2D and 3D steady state simulations were done using the commercial CFD package Star-CCM+ with three different RANS turbulence models. Lift and drag coefficients were simulated at different angles of attack for the NREL S826 airfoil at a Reynolds number of 100 000, and compared to experimental data obtained at NTNU and at DTU. The Spalart-Allmaras and the Realizable k-epsilon turbulence models reproduced experimental results for lift well in the 2D simulations. The 3D simulations with the Realizable two-layer k-epsilon model predicted essentially the same lift coefficients as the 2D Spalart-Allmaras simulations. A comparison between 2D and 3D simulations with the Realizable k-epsilon model showed a significantly lower prediction in drag by the 2D simulations. From the conducted 3D simulations surface pressure predictions along the wing span were presented, along with volumetric renderings of vorticity. Both showed a high degree of span wise flow variation when going into the stall region, and predicted a flow field resembling that of stall cells for angles of attack above peak lift.
A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging.
Gallio, Elena; Rampado, Osvaldo; Gianaria, Elena; Bianchi, Silvio Diego; Ropolo, Roberto
2015-01-01
Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies.
A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging
Gallio, Elena; Rampado, Osvaldo; Gianaria, Elena; Bianchi, Silvio Diego; Ropolo, Roberto
2015-01-01
Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies. PMID:26545097
2D fluid simulations of discharges at atmospheric pressure in reactive gas mixtures
NASA Astrophysics Data System (ADS)
Bourdon, Anne
2015-09-01
Since a few years, low-temperature atmospheric pressure discharges have received a considerable interest as they efficiently produce many reactive chemical species at a low energy cost. This potential is of great interest for a wide range of applications as plasma assisted combustion or biomedical applications. Then, in current simulations of atmospheric pressure discharges, there is the need to take into account detailed kinetic schemes. It is interesting to note that in some conditions, the kinetics of the discharge may play a role on the discharge dynamics itself. To illustrate this, we consider the case of the propagation of He-N2 discharges in long capillary tubes, studied for the development of medical devices for endoscopic applications. Simulation results put forward that the discharge dynamics and structure depend on the amount of N2 in the He-N2 mixture. In particular, as the amount of N2 admixture increases, the discharge propagation velocity in the tube increases, reaches a maximum for about 0 . 1 % of N2 and then decreases, in agreement with experiments. For applications as plasma assisted combustion with nanosecond repetitively pulsed discharges, there is the need to handle the very different timescales of the nanosecond discharge with the much longer (micro to millisecond) timescales of combustion processes. This is challenging from a computational point of view. It is also important to better understand the coupling of the plasma induced chemistry and the gas heating. To illustrate this, we present the simulation of the flame ignition in lean mixtures by a nanosecond pulsed discharge between two point electrodes. In particular, among the different discharge regimes of nanosecond repetitively pulsed discharges, a ``spark'' regime has been put forward in the experiments, with an ultra-fast local heating of the gas. For other discharge regimes, the gas heating is much weaker. We have simulated the nanosecond spark regime and have observed shock waves
Dunbar, Josef A; Arthur, Evan J; White, Aaron M; Kubarych, Kevin J
2015-05-21
Using a derivative of the vitamin biotin labeled with a transition-metal carbonyl vibrational probe in a series of aqueous N,N-dimethylformamide (DMF) solutions, we observe a striking slowdown in spectral diffusion dynamics with decreased DMF concentration. Equilibrium solvation dynamics, measured with the rapidly acquired spectral diffusion (RASD) technique, a variant of heterodyne-detected photon-echo peak shift experiments, range from 1 ps in neat DMF to ∼3 ps in 0.07 mole fraction DMF/water solution. Molecular dynamics simulations of the biotin-metal carbonyl solute in explicit aqueous DMF solutions show marked preferential solvation by DMF, which becomes more pronounced at lower DMF concentrations. The simulations and the experimental data are consistent with an interpretation where the slowdown in spectral diffusion is due to solvent exchange involving distinct cosolvent species. A simple two-component model reproduces the observed spectral dynamics as well as the DMF concentration dependence, enabling the extraction of the solvent exchange time scale of 8 ps. This time scale corresponds to the diffusive motion of a few Å, consistent with a solvent-exchange mechanism. Unlike most previous studies of solvation dynamics in binary mixtures of polar solvents, our work highlights the ability of vibrational probes to sense solvent exchange as a new, slow component in the spectral diffusion dynamics.
Real-time 2D floating-point fast Fourier transforms for seeker simulation
NASA Astrophysics Data System (ADS)
Chamberlain, Richard; Lord, Eric; Shand, David J.
2002-07-01
The floating point Fast Fourier Transform (FFT) is one of the most useful basic functions available to the image and signal processing engineer allowing many complex and detailed special functions to be implemented more simply in the frequency domain. In the Hardware-in-the-Loop field an image transformed using FFT would allow the designer to think about accurate frequency based simulation of seeker lens effects, motion blur, detector transfer functions and much more. Unfortunately, the transform requires many hundreds of thousands or millions of floating point operations on a single modest sized image making it impractical for realtime Hardware-in-the-Loop systems. .until now. This paper outlines the development, by Nallatech, of an FPGA based IEEE floating point core. It traces the subsequent use of this core to develop a full 256 X 256 FFT and filter process implemented on COTS hardware at frame rates up to 150Hz. This transform can be demonstrated to model optical transfer functions at a far greater accuracy than the current spatial models. Other applications and extensions of this technique will be discussed such as filtering for image tracking algorithms and in the simulation of radar processing in the frequency domain.
Simulation of 2D Kinetic Effects in Plasmas using the Grid Based Continuum Code LOKI
NASA Astrophysics Data System (ADS)
Banks, Jeffrey; Berger, Richard; Chapman, Tom; Brunner, Stephan
2016-10-01
Kinetic simulation of multi-dimensional plasma waves through direct discretization of the Vlasov equation is a useful tool to study many physical interactions and is particularly attractive for situations where minimal fluctuation levels are desired, for instance, when measuring growth rates of plasma wave instabilities. However, direct discretization of phase space can be computationally expensive, and as a result there are few examples of published results using Vlasov codes in more than a single configuration space dimension. In an effort to fill this gap we have developed the Eulerian-based kinetic code LOKI that evolves the Vlasov-Poisson system in 2+2-dimensional phase space. The code is designed to reduce the cost of phase-space computation by using fully 4th order accurate conservative finite differencing, while retaining excellent parallel scalability that efficiently uses large scale computing resources. In this poster I will discuss the algorithms used in the code as well as some aspects of their parallel implementation using MPI. I will also overview simulation results of basic plasma wave instabilities relevant to laser plasma interaction, which have been obtained using the code.
Evans, T.E.; Leonard, A.W.; West, W.P.; Finkenthal, D.F.; Fenstermacher, M.E.; Porter, G.D.
1998-08-01
Experimentally measured carbon line emissions and total radiated power distributions from the DIII-D divertor and Scrape-Off Layer (SOL) are compared to those calculated with the Monte Carlo Impurity (MCI) model. A UEDGE background plasma is used in MCI with the Roth and Garcia-Rosales (RG-R) chemical sputtering model and/or one of six physical sputtering models. While results from these simulations do not reproduce all of the features seen in the experimentally measured radiation patterns, the total radiated power calculated in MCI is in relatively good agreement with that measured by the DIII-D bolometric system when the Smith78 physical sputtering model is coupled to RG-R chemical sputtering in an unaltered UEDGE plasma. Alternatively, MCI simulations done with UEDGE background ion temperatures along the divertor target plates adjusted to better match those measured in the experiment resulted in three physical sputtering models which when coupled to the RG-R model gave a total radiated power that was within 10% of measured value.
Numerical Simulation of DC Coronal Heating
NASA Astrophysics Data System (ADS)
Dahlburg, Russell B.; Einaudi, G.; Taylor, Brian D.; Ugarte-Urra, Ignacio; Warren, Harry; Rappazzo, A. F.; Velli, Marco
2016-05-01
Recent research on observational signatures of turbulent heating of a coronal loop will be discussed. The evolution of the loop is is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. HYPERION calculates the full energy cycle involving footpoint convection, magnetic reconnection, nonlinear thermal conduction and optically thin radiation. The footpoints of the loop magnetic field are convected by random photospheric motions. As a consequence the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is non-uniformly distributed so that only a fraction of thecoronal mass and volume gets heated at any time. Temperature and density are highly structured at scales which, in the solar corona, remain observationally unresolved: the plasma of the simulated loop is multi thermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. Typical simulated coronal loops are 50000 km length and have axial magnetic field intensities ranging from 0.01 to 0.04 Tesla. To connect these simulations to observations the computed number densities and temperatures are used to synthesize the intensities expected in emission lines typically observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. These intensities are then employed to compute differential emission measure distributions, which are found to be very similar to those derived from observations of solar active regions.
Numerical simulations of black-hole spacetimes
NASA Astrophysics Data System (ADS)
Chu, Tony
This thesis covers various aspects of the numerical simulation of black-hole spacetimes according to Einstein's general theory of relativity, using the Spectral Einstein Code developed by the Caltech-Cornell-CITA collaboration. The first topic is improvement of binary-black-hole initial data. One such issue is the construction of binary-black-hole initial data with nearly extremal spins that remain nearly constant during the initial relaxation in an evolution. Another concern is the inclusion of physically realistic tidal deformations of the black holes to reduce the high-frequency components of the spurious gravitational radiation content, and represents a first step in incorporating post-Newtonian results in constraint-satisfying initial data. The next topic is the evolution of black-hole binaries and the gravitational waves they emit. The first spectral simulation of two inspiralling black holes through merger and ringdown is presented, in which the black holes are nonspinning and have equal masses. This work is extended to perform the first spectral simulations of two inspiralling black holes with moderate spins and equal masses, including the merger and ringdown. Two configurations are considered, in which both spins are either anti-aligned or aligned with the orbital angular momentum. Highly accurate gravitational waveforms are computed for all these cases, and are used to calibrate waveforms in the effective-one-body model. The final topic is the behavior of quasilocal black-hole horizons in highly dynamical situations. Simulations of a rotating black hole that is distort ed by a pulse of ingoing gravitational radiation are performed. Multiple marginally outer trapped surfaces are seen to appear and annihilate with each other during the evolution, and the world tubes th ey trace out are all dynamical horizons. The dynamical horizon and angular momentum flux laws are evaluated in this context, and the dynamical horizons are contrasted with the event horizon
NASA Astrophysics Data System (ADS)
Pérez-Corona, M.; García, J. A.; Taller, G.; Polgár, D.; Bustos, E.; Plank, Z.
2016-02-01
The purpose of geophysical electrical surveys is to determine the subsurface resistivity distribution by making measurements on the ground surface. From these measurements, the true resistivity of the subsurface can be estimated. The ground resistivity is related to various geological parameters, such as the mineral and fluid content, porosity and degree of water saturation in the rock. Electrical resistivity surveys have been used for many decades in hydrogeological, mining and geotechnical investigations. More recently, they have been used for environmental surveys. To obtain a more accurate subsurface model than is possible with a simple 1-D model, a more complex model must be used. In a 2-D model, the resistivity values are allowed to vary in one horizontal direction (usually referred to as the x direction) but are assumed to be constant in the other horizontal (the y) direction. A more realistic model would be a fully 3-D model where the resistivity values are allowed to change in all three directions. In this research, a simulation of the cone penetration test and 2D imaging resistivity are used as tools to simulate the distribution of hydrocarbons in soil.
History of the numerical aerodynamic simulation program
NASA Technical Reports Server (NTRS)
Peterson, Victor L.; Ballhaus, William F., Jr.
1987-01-01
The Numerical Aerodynamic Simulation (NAS) program has reached a milestone with the completion of the initial operating configuration of the NAS Processing System Network. This achievement is the first major milestone in the continuing effort to provide a state-of-the-art supercomputer facility for the national aerospace community and to serve as a pathfinder for the development and use of future supercomputer systems. The underlying factors that motivated the initiation of the program are first identified and then discussed. These include the emergence and evolution of computational aerodynamics as a powerful new capability in aerodynamics research and development, the computer power required for advances in the discipline, the complementary nature of computation and wind tunnel testing, and the need for the government to play a pathfinding role in the development and use of large-scale scientific computing systems. Finally, the history of the NAS program is traced from its inception in 1975 to the present time.
Direct numerical simulations of vortex ring collisions
NASA Astrophysics Data System (ADS)
Ostilla Monico, Rodolfo; Pumir, Alain; Brenner, Michael
2016-11-01
We numerically simulate the ring vortex collision experiment of Lim and Nickels in an attempt to understand the rapid formation of very fine scale turbulence (or 'smoke') from relatively smooth initial conditions. Reynolds numbers of up to Re = Γ / ν = 7500 , where Γ is the vortex ring circulation and ν the kinematic viscosity of the fluid are reached, which coincide with the highest Reynolds number case of the experiments. Different perturbations to the ring vortex are added, and their effect on the generation and amplification of turbulence is quantified. The underlying dynamics of the vortex core is analyzed, and compared to the dynamics arising from a simple Biot-Savart filament model for the core.
Numerical simulation of excited jet mixing layers
NASA Astrophysics Data System (ADS)
Scott, J. N.; Hankey, W. L.
1987-01-01
A numerical simulation of unsteady flow in jet mixing layers, both with and without external excitation, has been performed by solving the time-dependent compressible Navier-Stokes equations. Computations were performed on a CRAY X-MP computer using MacCormick's explicit finite difference algorithm. Different excitation methods were investigated and were shown to be very effective in controlling the well organized periodic production, shedding and pairing of large scale vortex structures. It is found that pressure excitation was generally more effective than temperature excitation, and that grid refinement results in substantial improvement in the resolution of unsteady features. The location and orientation, in addition to the frequency, of the excitation source are shown to have a significant influence on the production and interaction of large scale vortex structures in the jet mixing layer.
Numerical simulation of transonic flows in diffusers
NASA Technical Reports Server (NTRS)
Liou, M.-S.; Coakley, T. J.; Bergmann, M. Y.
1981-01-01
Numerical simulations were made of two-dimensional transonic flows in diffusers, including flow separation induced by a shock or adverse pressure gradient. The mass-averaged, time-dependent, compressible Navier-Stokes equations, simplified by the thin-layer approximation, were solved using MacCormack's hybrid method. The eddy-viscosity formulation was described by the Wilcox-Rubesin's two-equation, k-omega model. Detailed comparison of the computed results with measurements showed good agreement in all cases, including one with massive separation induced by a strong shock. The computation correctly predicted the details of a distinct lambda shock pattern, closely duplicating the configuration observed experimentally in spark-schlieren photographs.
Numerical aerodynamic simulation facility feasibility study
NASA Technical Reports Server (NTRS)
1979-01-01
There were three major issues examined in the feasibility study. First, the ability of the proposed system architecture to support the anticipated workload was evaluated. Second, the throughput of the computational engine (the flow model processor) was studied using real application programs. Third, the availability reliability, and maintainability of the system were modeled. The evaluations were based on the baseline systems. The results show that the implementation of the Numerical Aerodynamic Simulation Facility, in the form considered, would indeed be a feasible project with an acceptable level of risk. The technology required (both hardware and software) either already exists or, in the case of a few parts, is expected to be announced this year. Facets of the work described include the hardware configuration, software, user language, and fault tolerance.
Numerical Simulations of Acoustically Driven, Burning Droplets
NASA Technical Reports Server (NTRS)
Kim, H.-C.; Karagozian, A. R.; Smith, O. I.; Urban, Dave (Technical Monitor)
1999-01-01
This computational study focuses on understanding and quantifying the effects of external acoustical perturbations on droplet combustion. A one-dimensional, axisymmetric representation of the essential diffusion and reaction processes occurring in the vicinity of the droplet stagnation point is used here in order to isolate the effects of the imposed acoustic disturbance. The simulation is performed using a third order accurate, essentially non-oscillatory (ENO) numerical scheme with a full methanol-air reaction mechanism. Consistent with recent microgravity and normal gravity combustion experiments, focus is placed on conditions where the droplet is situated at a velocity antinode in order for the droplet to experience the greatest effects of fluid mechanical straining of flame structures. The effects of imposed sound pressure level and frequency are explored here, and conditions leading to maximum burning rates are identified.
Efficient simulation of pitch angle collisions in a 2+2-D Eulerian Vlasov code
NASA Astrophysics Data System (ADS)
Banks, Jeff; Berger, R.; Brunner, S.; Tran, T.
2014-10-01
Here we discuss pitch angle scattering collisions in the context of the Eulerian-based kinetic code LOKI that evolves the Vlasov-Poisson system in 2+2-dimensional phase space. The collision operator is discretized using 4th order accurate conservative finite-differencing. The treatment of the Vlasov operator in phase-space uses an approach based on a minimally diffuse, fourth-order-accurate discretization (Banks and Hittinger, IEEE T. Plasma Sci. 39, 2198). The overall scheme is therefore discretely conservative and controls unphysical oscillations. Some details of the numerical scheme will be presented, and the implementation on modern highly concurrent parallel computers will be discussed. We will present results of collisional effects on linear and non-linear Landau damping of electron plasma waves (EPWs). In addition we will present initial results showing the effect of collisions on the evolution of EPWs in two space dimensions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the LDRD program at LLNL under project tracking code 12-ERD-061.
Simulation of a pulsatile non-Newtonian flow past a stenosed 2D artery with atherosclerosis.
Tian, Fang-Bao; Zhu, Luoding; Fok, Pak-Wing; Lu, Xi-Yun
2013-09-01
Atherosclerotic plaque can cause severe stenosis in the artery lumen. Blood flow through a substantially narrowed artery may have different flow characteristics and produce different forces acting on the plaque surface and artery wall. The disturbed flow and force fields in the lumen may have serious implications on vascular endothelial cells, smooth muscle cells, and circulating blood cells. In this work a simplified model is used to simulate a pulsatile non-Newtonian blood flow past a stenosed artery caused by atherosclerotic plaques of different severity. The focus is on a systematic parameter study of the effects of plaque size/geometry, flow Reynolds number, shear-rate dependent viscosity and flow pulsatility on the fluid wall shear stress and its gradient, fluid wall normal stress, and flow shear rate. The computational results obtained from this idealized model may shed light on the flow and force characteristics of more realistic blood flow through an atherosclerotic vessel.
Simulating HFIR Core Thermal Hydraulics Using 3D-2D Model Coupling
Travis, Adam R; Freels, James D; Ekici, Kivanc
2013-01-01
A model utilizing interdimensional variable coupling is presented for simulating the thermal hydraulic interactions of the High Flux Isotope Reactor (HFIR) core at Oak Ridge National Laboratory (ORNL). The model s domain consists of a single, explicitly represented three-dimensional fuel plate and a simplified two-dimensional coolant channel slice. In simplifying the coolant channel, and thus the number of mesh points in which the Navier-Stokes equations must be solved, the computational cost and solution time are both greatly reduced. In order for the reduced-dimension coolant channel to interact with the explicitly represented fuel plate, however, interdimensional variable coupling must be enacted along all shared boundaries. The primary focus of this paper is in detailing the collection, storage, passage, and application of variables across this interdimensional interface. Comparisons are made showing the general speed-up associated with this simplified coupled model.
Gomez, Juan F.; Cardona, Karen; Martinez, Laura; Saiz, Javier; Trenor, Beatriz
2014-01-01
Background Heart failure is operationally defined as the inability of the heart to maintain blood flow to meet the needs of the body and it is the final common pathway of various cardiac pathologies. Electrophysiological remodeling, intercellular uncoupling and a pro-fibrotic response have been identified as major arrhythmogenic factors in heart failure. Objective In this study we investigate vulnerability to reentry under heart failure conditions by incorporating established electrophysiological and anatomical remodeling using computer simulations. Methods The electrical activity of human transmural ventricular tissue (5 cm×5 cm) was simulated using the human ventricular action potential model Grandi et al. under control and heart failure conditions. The MacCannell et al. model was used to model fibroblast electrical activity, and their electrotonic interactions with myocytes. Selected degrees of diffuse fibrosis and variations in intercellular coupling were considered and the vulnerable window (VW) for reentry was evaluated following cross-field stimulation. Results No reentry was observed in normal conditions or in the presence of HF ionic remodeling. However, defined amount of fibrosis and/or cellular uncoupling were sufficient to elicit reentrant activity. Under conditions where reentry was generated, HF electrophysiological remodeling did not alter the width of the VW. However, intermediate fibrosis and cellular uncoupling significantly widened the VW. In addition, biphasic behavior was observed, as very high fibrotic content or very low tissue conductivity hampered the development of reentry. Detailed phase analysis of reentry dynamics revealed an increase of phase singularities with progressive fibrotic components. Conclusion Structural remodeling is a key factor in the genesis of vulnerability to reentry. A range of intermediate levels of fibrosis and intercellular uncoupling can combine to favor reentrant activity. PMID:25054335
Direct Numerical Simulation of Automobile Cavity Tones
NASA Technical Reports Server (NTRS)
Kurbatskii, Konstantin; Tam, Christopher K. W.
2000-01-01
The Navier Stokes equation is solved computationally by the Dispersion-Relation-Preserving (DRP) scheme for the flow and acoustic fields associated with a laminar boundary layer flow over an automobile door cavity. In this work, the flow Reynolds number is restricted to R(sub delta*) < 3400; the range of Reynolds number for which laminar flow may be maintained. This investigation focuses on two aspects of the problem, namely, the effect of boundary layer thickness on the cavity tone frequency and intensity and the effect of the size of the computation domain on the accuracy of the numerical simulation. It is found that the tone frequency decreases with an increase in boundary layer thickness. When the boundary layer is thicker than a certain critical value, depending on the flow speed, no tone is emitted by the cavity. Computationally, solutions of aeroacoustics problems are known to be sensitive to the size of the computation domain. Numerical experiments indicate that the use of a small domain could result in normal mode type acoustic oscillations in the entire computation domain leading to an increase in tone frequency and intensity. When the computation domain is expanded so that the boundaries are at least one wavelength away from the noise source, the computed tone frequency and intensity are found to be computation domain size independent.
Numerical simulation of turbulent slurry flows
NASA Astrophysics Data System (ADS)
Haghgoo, Mohammad Reza; Spiteri, Reymond J.; Bergstrom, Donlad J.
2016-11-01
Slurry flows, i.e., the flow of an agglomeration of liquid and particles, are widely employed in many industrial applications, such as hydro-transport systems, pharmaceutical batch crystallizers, and wastewater disposal. Although there are numerous studies available in the literature on turbulent gas-particle flows, the hydrodynamics of turbulent liquid-particle flows has received much less attention. In particular, the fluid-phase turbulence modulation due to the particle fluctuating motion is not yet well understood and remains challenging to model. This study reports the results of a numerical simulation of a vertically oriented slurry pipe flow using a two-fluid model based on the kinetic theory of granular flows. The particle stress model also includes the effects of frictional contact. Different turbulence modulation models are considered, and their capability to capture the characteristic features of the turbulent flow is assessed. The model predictions are validated against published experimental data and demonstrate the significant effect of the particles on the fluid-phase turbulence.
Numerical relativity simulations of binary neutron stars
NASA Astrophysics Data System (ADS)
Thierfelder, Marcus; Bernuzzi, Sebastiano; Brügmann, Bernd
2011-08-01
We present a new numerical relativity code designed for simulations of compact binaries involving matter. The code is an upgrade of the BAM code to include general relativistic hydrodynamics and implements state-of-the-art high-resolution-shock-capturing schemes on a hierarchy of mesh refined Cartesian grids with moving boxes. We test and validate the code in a series of standard experiments involving single neutron star spacetimes. We present test evolutions of quasiequilibrium equal-mass irrotational binary neutron star configurations in quasicircular orbits which describe the late inspiral to merger phases. Neutron star matter is modeled as a zero-temperature fluid; thermal effects can be included by means of a simple ideal gas prescription. We analyze the impact that the use of different values of damping parameter in the Gamma-driver shift condition has on the dynamics of the system. The use of different reconstruction schemes and their impact in the post-merger dynamics is investigated. We compute and characterize the gravitational radiation emitted by the system. Self-convergence of the waves is tested, and we consistently estimate error bars on the numerically generated waveforms in the inspiral phase.
The Beam Break-Up Numerical Simulator
Travish, G.A.
1989-11-01
Beam Break-Up (BBU) is a severe constraint in accelerator design, limiting beam current and quality. The control of BBU has become the focus of much research in the design of the next generation collider, recirculating and linear induction accelerators and advanced accelerators. Determining the effect on BBU of modifications to cavities, the focusing elements or the beam is frequently beyond the ability of current analytic models. A computer code was written to address this problem. The Beam Break-Up Numerical Simulator (BBUNS) was designed to numerically solve for beam break-up (BBU) due to an arbitrary transverse wakefield. BBUNS was developed to be as user friendly as possible on the Cray computer series. The user is able to control all aspects of input and output by using a single command file. In addition, the wakefield is specified by the user and read in as a table. The program can model energy variations along and within the beam, focusing magnetic field profiles can be specified, and the graphical output can be tailored. In this note we discuss BBUNS, its structure and application. Included are detailed instructions, examples and a sample session of BBUNS. This program is available for distribution. 50 refs., 18 figs., 5 tabs.
NASA Astrophysics Data System (ADS)
Wendling, A.; Daniel, J. L.; Hivet, G.; Vidal-Sallé, E.; Boisse, P.
2015-12-01
Numerical simulation is a powerful tool to predict the mechanical behavior and the feasibility of composite parts. Among the available numerical approaches, as far as woven reinforced composites are concerned, 3D finite element simulation at the mesoscopic scale leads to a good compromise between realism and complexity. At this scale, the fibrous reinforcement is modeled by an interlacement of yarns assumed to be homogeneous that have to be accurately represented. Among the numerous issues induced by these simulations, the first one consists in providing a representative meshed geometrical model of the unit cell at the mesoscopic scale. The second one consists in enabling a fast data input in the finite element software (contacts definition, boundary conditions, elements reorientation, etc.) so as to obtain results within reasonable time. Based on parameterized 3D CAD modeling tool of unit-cells of dry fabrics already developed, this paper presents an efficient strategy which permits an automated meshing of the models with 3D hexahedral elements and to accelerate of several orders of magnitude the simulation data input. Finally, the overall modeling strategy is illustrated by examples of finite element simulation of the mechanical behavior of fabrics.
NASA Astrophysics Data System (ADS)
Lardeau, Sylvain; Ferrari, Simone; Rossi, Lionel
2008-12-01
Three-dimensional (3D) direct numerical simulations of a flow driven by multiscale electromagnetic forcing are performed in order to reproduce with maximum accuracy the quasi-two-dimensional (2D) flow generated by the same multiscale forcing in the laboratory. The method presented is based on a 3D description of the flow and the electromagnetic forcing. Very good agreements between our simulations and the experiments are found both on velocity and acceleration field, this last comparison being, to our knowledge, done for the first time. Such agreement requires that both experiments and simulations are carefully performed and, more importantly, that the underlying simplification to model the experiments and the multiscale electromagnetic forcing do not introduce significant errors. The results presented in this paper differ significantly from previous 2D direct numerical simulation in which a classical linear Rayleigh friction modeling term was used to mimic the effect of the wall-normal friction. Indeed, purely 2D simulations are found to underestimate the Reynolds number and, due to the dominance of nonhomogeneous bottom friction, lead to the wrong physical mechanism. For the range of conditions presented in this paper, the Reynolds number, defined by the ratio between acceleration and viscous terms, remains the order of unity, and the Hartmann number, defined by the ratio between electromagnetic force terms and viscous terms, is about 2. The main conclusion is that 3D simulations are required to model the (3D) electromagnetic forces and the wall-normal shear. Indeed, even if the flow is quasi-2D in terms of energy, a full 3D approach is required to simulate these shallow layer flows driven by multiscale electromagnetic forcing. In the range of forcing intensity investigated in this paper, these multiscale flows remain quasi-2D, with negligible energy in the wall-normal velocity component. It is also shown that the driving terms are the electromagnetic forcing and
Numerical Simulations of Particle Deposition in Metal Foam Heat Exchangers
NASA Astrophysics Data System (ADS)
Sauret, Emilie; Saha, Suvash C.; Gu, Yuantong
2013-01-01
Australia is a high-potential country for geothermal power with reserves currently estimated in the tens of millions of petajoules, enough to power the nation for at least 1000 years at current usage. However, these resources are mainly located in isolated arid regions where water is scarce. Therefore, wet cooling systems for geothermal plants in Australia are the least attractive solution and thus air-cooled heat exchangers are preferred. In order to increase the efficiency of such heat exchangers, metal foams have been used. One issue raised by this solution is the fouling caused by dust deposition. In this case, the heat transfer characteristics of the metal foam heat exchanger can dramatically deteriorate. Exploring the particle deposition property in the metal foam exchanger becomes crucial. This paper is a numerical investigation aimed to address this issue. Two-dimensional (2D) numerical simulations of a standard one-row tube bundle wrapped with metal foam in cross-flow are performed and highlight preferential particle deposition areas.
Tropical Oceanic Precipitation Processes Over Warm Pool: 2D and 3D Cloud Resolving Model Simulations
NASA Technical Reports Server (NTRS)
Tao, W.-K.; Johnson, D.; Simpson, J.; Einaudi, Franco (Technical Monitor)
2001-01-01
Rainfall is a key link in the hydrologic cycle as well as the primary heat source for the atmosphere. The vertical distribution of convective latent-heat release modulates the large-scale circulations of the topics. Furthermore, changes in the moisture distribution at middle and upper levels of the troposphere can affect cloud distributions and cloud liquid water and ice contents. How the incoming solar and outgoing longwave radiation respond to these changes in clouds is a major factor in assessing climate change. Present large-scale weather and climate model simulate processes only crudely, reducing confidence in their predictions on both global and regional scales. One of the most promising methods to test physical parameterizations used in General Circulation Models (GCMs) and climate models is to use field observations together with Cloud Resolving Models (CRMs). The CRMs use more sophisticated and physically realistic parameterizations of cloud microphysical processes, and allow for their complex interactions with solar and infrared radiative transfer processes. The CRMs can reasonably well resolve the evolution, structure, and life cycles of individual clouds and clouds systems. The major objective of this paper is to investigate the latent heating, moisture and momentum budgets associated with several convective systems developed during the TOGA COARE IFA - westerly wind burst event (late December, 1992). The tool for this study is the Goddard Cumulus Ensemble (GCE) model which includes a 3-class ice-phase microphysics scheme.
NASA Technical Reports Server (NTRS)
Zimmerman, Michael I.; Farrell, W. M.; Snubbs, T. J.; Halekas, J. S.
2011-01-01
Anticipating the plasma and electrical environments in permanently shadowed regions (PSRs) of the moon is critical in understanding local processes of space weathering, surface charging, surface chemistry, volatile production and trapping, exo-ion sputtering, and charged dust transport. In the present study, we have employed the open-source XOOPIC code [I] to investigate the effects of solar wind conditions and plasma-surface interactions on the electrical environment in PSRs through fully two-dimensional pattic1e-in-cell simulations. By direct analogy with current understanding of the global lunar wake (e.g., references) deep, near-terminator, shadowed craters are expected to produce plasma "mini-wakes" just leeward of the crater wall. The present results (e.g., Figure I) are in agreement with previous claims that hot electrons rush into the crater void ahead of the heavier ions, fanning a negative cloud of charge. Charge separation along the initial plasma-vacuum interface gives rise to an ambipolar electric field that subsequently accelerates ions into the void. However, the situation is complicated by the presence of the dynamic lunar surface, which develops an electric potential in response to local plasma currents (e.g., Figure Ia). In some regimes, wake structure is clearly affected by the presence of the charged crater floor as it seeks to achieve current balance (i.e. zero net current to the surface).
Study of liquid water by computer simulations. I. Static properties of a 2D model
NASA Astrophysics Data System (ADS)
Okazaki, Keiji; Nosé, Shuichi; Kataoka, Yosuke; Yamamoto, Tsunenobu
1981-12-01
A computer-simulation study of a water-like system is carried out by making use of a two-dimensional version of the Ben-Naim and Stillinger potential. The pair potential is set up such that at 0 K it yields a square net structure at low pressures and an interpretation of two square nets at high pressures. The liquid state is surveyed over a wide range of temperature and pressure. Various kinds of molecular distribution functions are derived to see how the hydrogen-bond network structure depends on temperature and density. The pressure and thermal equations of state are ''experimentally'' determined by a least square fitting to the pressures and energies calculated for about 200 different state points. The well-known anomalous behavior of liquid water is reproduced at least in a semiquantitative way. The singular properties of supercooled water also are reproduced and their origin is ascribed to the thermodynamical instability. New anomalies are predicted at high temperatures and pressures.
Numerical simulation of solar coronal magnetic fields
NASA Technical Reports Server (NTRS)
Dahlburg, Russell B.; Antiochos, Spiro K.; Zang, T. A.
1990-01-01
Many aspects of solar activity are believed to be due to the stressing of the coronal magnetic field by footpoint motions at the photosphere. The results are presented of a fully spectral numerical simulation which is the first 3-D time dependent simulation of footpoint stressing in a geometry appropriate for the corona. An arcade is considered that is initially current-free and impose a smooth footpoint motion that produces a twist in the field of approx 2 pi. The footprints were fixed and the evolution was followed until the field relaxes to another current-free state. No evidence was seen for any instability, either ideal or resistive and no evidence for current sheet formation. The most striking feature of the evolution is that in response to photospheric motions, the field expands rapidly upward to minimize the stress. The expansion has two important effects. First, it suppresses the development of dips in the field that could support dense, cool material. For the motions assumed, the magnetic field does not develop a geometry suitable for prominence formation. Second, the expansion inhibits ideal instabilities such as kinking. The results indicate that simple stearing of a single arcade is unlikely to lead to solar activity such as flares or prominences. Effects are discussed that might possibly lead to such activity.
Hybrid Numerical Simulations Of Planetesimal Accretion
NASA Astrophysics Data System (ADS)
Marzari, Francesco; Weidenschilling, S. J.
2006-09-01
The multi-zone simulation code modelling the accretion of planetesimals into planets (Spaute et al. 1991, Icarus 92, 147; Weidenschilling et al. 1997, ICARUS 128, 429) includes a statistical continuum of small bodies in logarithmic mass bins, while large bodies are discrete objects with individual masses and orbits. Formerly, gravitational interactions between large planetary embryos were treated by statistical scattering. The code has now been updated to properly handle the orbits of protoplanets in a deterministic way. The trajectories of the larger bodies are numerically computed with the symplectic integrator SyYMBA. The additional forces acting on the protoplanets due to collisions with smaller planetesimals and their gravitational perturbations, including dynamical friction, as well as gas drag and tidal interaction with the solar nebula, are incorporated in the N-body algorithm by applying a further step in the leap-frog structure of the SyMBA integrator. The changes in the orbital elements of the large bodies, computed in the stochastic part of the code with a Monte Carlo approach, are applied for half a timestep before and after the N-body Hamiltonian propagation as suggested in Lee & Peale (ApJ 567, 596, 2002). With this code we intend to study the effect of dynamical friction on terrestrial planet formation and the accretion of planetary cores in the outer solar system. We will present preliminary results of simulations performed with the updated code.
Collisionless microinstabilities in stellarators. II. Numerical simulations
NASA Astrophysics Data System (ADS)
Proll, J. H. E.; Xanthopoulos, P.; Helander, P.
2013-12-01
Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here, the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes, and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations.
Numerical simulation of tulip flame dynamics
Cloutman, L.D.
1991-11-30
A finite difference reactive flow hydrodynamics program based on the full Navier-Stokes equations was used to simulate the combustion process in a homogeneous-charge, constant-volume combustion bomb in which an oddly shaped flame, known as a ``tulip flame`` in the literature, occurred. The ``tulip flame`` was readily reproduced in the numerical simulations, producing good agreement with the experimental flame shapes and positions at various times. The calculations provide sufficient detail about the dynamics of the experiment to provide some insight into the physical mechanisms responsible for the peculiar flame shape. Several factors seem to contribute to the tulip formation. The most important process is the baroclinic production of vorticity by the flame front, and this rate of production appears to be dramatically increased by the nonaxial flow generated when the initial semicircular flame front burns out along the sides of the chamber. The vorticity produces a pair of vortices behind the flame that advects the flame into the tulip shape. Boundary layer effects contribute to the details of the flame shape next to the walls of the chamber, but are otherwise not important. 24 refs.
Numerical simulation of tulip flame dynamics
Cloutman, L.D.
1991-11-30
A finite difference reactive flow hydrodynamics program based on the full Navier-Stokes equations was used to simulate the combustion process in a homogeneous-charge, constant-volume combustion bomb in which an oddly shaped flame, known as a tulip flame'' in the literature, occurred. The tulip flame'' was readily reproduced in the numerical simulations, producing good agreement with the experimental flame shapes and positions at various times. The calculations provide sufficient detail about the dynamics of the experiment to provide some insight into the physical mechanisms responsible for the peculiar flame shape. Several factors seem to contribute to the tulip formation. The most important process is the baroclinic production of vorticity by the flame front, and this rate of production appears to be dramatically increased by the nonaxial flow generated when the initial semicircular flame front burns out along the sides of the chamber. The vorticity produces a pair of vortices behind the flame that advects the flame into the tulip shape. Boundary layer effects contribute to the details of the flame shape next to the walls of the chamber, but are otherwise not important. 24 refs.
Numerical simulation of premixed turbulent methane combustion
Day, Marc S.; Bell, John B.; Almgren, Ann S.; Beckner, Vincent E.; Lijewski, Michael J.; Cheng, Robert; Shepherd, Ian; Johnson, Matthew
2003-06-14
With adaptive-grid computational methodologies and judicious use of compressible and low Mach number combustion models, we are carrying out three-dimensional, time-dependent direct numerical simulations of a laboratory-scale turbulent premixed methane burner. In the laboratory experiment, turbulence is generated by a grid located in the throat of a 50mm diameter circular nozzle; swirl is be introduced by four tangential air jets spaced uniformly around the circumference of the nozzle just above the turbulence grid. A premixed methane flame is stabilized above the nozzle in the central core region where a velocity deficit is induced7the swirling flow. The time-dependent flow field inside the nozzle, from the turbulence grid and the high-speed jets, to the nozzle exit plane is simulated using an adaptive-grid embedded-boundary compressible Navier-Stokes solver. The compressible calculation then provides time-dependent boundary conditions for an adaptive low Mach number model of the swirl-stabilized premixed flame. The low Mach model incorporates detailed chemical kinetics and species transport using 20 species and 84 reactions. Laboratory diagnostics available for comparisons include characterizations of the flow field just down stream of the nozzle exit plane, and flame surface statistics, such as mean location, wrinkling and crossing frequencies.
Numerical simulations of capillary barrier field tests
Morris, C.E.; Stormont, J.C.
1997-12-31
Numerical simulations of two capillary barrier systems tested in the field were conducted to determine if an unsaturated flow model could accurately represent the observed results. The field data was collected from two 7-m long, 1.2-m thick capillary barriers built on a 10% grade that were being tested to investigate their ability to laterally divert water downslope. One system had a homogeneous fine layer, while the fine soil of the second barrier was layered to increase its ability to laterally divert infiltrating moisture. The barriers were subjected first to constant infiltration while minimizing evaporative losses and then were exposed to ambient conditions. The continuous infiltration period of the field tests for the two barrier systems was modelled to determine the ability of an existing code to accurately represent capillary barrier behavior embodied in these two designs. Differences between the field test and the model data were found, but in general the simulations appeared to adequately reproduce the response of the test systems. Accounting for moisture retention hysteresis in the layered system will potentially lead to more accurate modelling results and is likely to be important when developing reasonable predictions of capillary barrier behavior.
NASA Astrophysics Data System (ADS)
LeVeque, R. J.; Motley, M. R.
2015-12-01
A series of tsunami wave basin experiments of flow through a scale model of Seaside, Oregon have been used as validation data for a 2015 benchmarking workshop hosted by the National Tsunami Mitigation Program, which focused on better understanding the ability of tsunami models to predict flow velocities and inundation depths following a coastal inundation event. As researchers begin to assess the safety of coastal infrastructures, proper assessment of tsunami-induced forces on coastal structures is critical. Hydrodynamic forces on these structures are fundamentally proportional to the local momentum flux of the fluid, and experimental data included momentum flux measurements at many instrumented gauge locations. The GeoClaw tsunami model, which solves the two-dimensional shallow water equations, was compared against other codes during the benchmarking workshop, and more recently a three-dimensional computational fluid dynamics model using the open-source OpenFOAM software has been developed and results from this model are being compared with both the experimental data and the 2D GeoClaw results. In addition, the 3D model allows for computation of fluid forces on the faces of structures, permitting an investigation of the common use of momentum flux as a proxy for these forces. This work aims to assess the potential to apply these momentum flux predictions locally within the model to determine tsunami-induced forces on critical structures. Difficulties in working with these data sets and cross-model comparisons will be discussed. Ultimately, application of the more computationally efficient GeoClaw model, informed by the 3D OpenFOAM models, to predict forces on structures at the community scale can be expected to improve the safety and resilience of coastal communities.
Numerical investigation of the flat band Bloch modes in a 2D photonic crystal with Dirac cones.
Zhang, Peng; Fietz, Chris; Tassin, Philippe; Koschny, Thomas; Soukoulis, Costas M
2015-04-20
A numerical method combining complex-k band calculations and absorbing boundary conditions for Bloch waves is presented. We use this method to study photonic crystals with Dirac cones. We demonstrate that the photonic crystal behaves as a zero-index medium when excited at normal incidence, but that the zero-index behavior is lost at oblique incidence due to excitation of modes on the flat band. We also investigate the formation of monomodal and multimodal cavity resonances inside the photonic crystals, and the physical origins of their different line-shape features.
Origin of energetic ions observed in the terrestrial ion foreshock : 2D full-particle simulations
NASA Astrophysics Data System (ADS)
Savoini, Philippe; Lembege, bertrand
2016-04-01
Collisionless shocks are well-known structures in astrophysical environments which dissipate bulk flow kinetic energy and accelerate large fraction of particle. Spacecrafts have firmly established the existence of the so-called terrestrial foreshock region magnetically connected to the shock and filled by two distinct populations in the quasi-perpendicular shock region (i.e. for 45r{ } ≤ quad θ Bn quad ≤ 90r{ }, where θ Bn is the angle between the shock normal and the upstream magnetic field) : (i) the field-aligned ion beams or `` FAB '' characterized by a gyrotropic distributionsout{,} and (ii) the gyro-phase bunched ions or `` GPB '' characterized by a NON gyrotropic distribution. The present work is based on the use of two dimensional PIC simulation of a curved shock and associated foreshock region where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described by a self consistent approach. Our previous analysis (Savoini et Lembège, 2015) has evidenced that these two types of backstreaming populations can originate from the shock front itself without invoking any local diffusion by ion beam instabilities. Present results are focussed on individual ion trajectories and evidence that "FAB" population is injected into the foreshock mainly along the shock front whereas the "GPB" population penetrates more deeply the shock front. Such differences explain why the "FAB" population loses their gyro-phase coherency and become gyrotropic which is not the case for the "GPB". The impact of these different injection features on the energy gain for each ion population will be presented in détails. Savoini, P. and B. Lembège (2015), `` Production of nongyrotropic and gyrotropic backstreaming ion distributions in the quasi-perpendicular ion foreshock région '', J. Geophys. Res., 120, pp 7154-7171, doi = 10.1002/2015JA021018.
NASA Astrophysics Data System (ADS)
El Kadi Abderrezzak, Kamal; Die Moran, Andrés; Tassi, Pablo; Ata, Riadh; Hervouet, Jean-Michel
2016-07-01
Bank erosion can be an important form of morphological adjustment in rivers. With the advances made in computational techniques, two-dimensional (2D) depth-averaged numerical models have become valuable tools for resolving many engineering problems dealing with sediment transport. The objective of this research work is to present a simple, new, bank-erosion operator that is integrated into a 2D Saint-Venant-Exner morphodynamic model. The numerical code is based on an unstructured grid of triangular elements and finite-element algorithms. The slope of each element in the grid is compared to the angle of repose of the bank material. Elements for which the slope is too steep are tilted to bring them to the angle of repose along a horizontal axis defined such that the volume loss above the axis is equal to the volume gain below, thus ensuring mass balance. The model performance is assessed using data from laboratory flume experiments and a scale model of the Old Rhine. For the flume experiment case with uniform bank material, relevant results are obtained for bank geometry changes. For the more challenging case (i.e. scale model of the Old Rhine with non-uniform bank material), the numerical model is capable of reproducing the main features of the bank failure, induced by the newly designed groynes, as well as the transport of the mobilized sediment material downstream. Some deviations between the computed results and measured data are, however, observed. They are ascribed to the effects of three-dimensional (3D) flow structures, pore pressure and cohesion, which are not considered in the present 2D model.
A numerical simulation of the Catalina Eddy
Ueyoshi, Kyozo; Roads, J.O.; Alpert, J.
1991-12-31
A shallow cyclonic eddy termed the Catalina Eddy has occasionally been observed during summer in the bight of southern California. The Catalina Eddy occurs within {approximately}100 km from the coastal mountains with a depth typically extending up to the marine inversion level of several hundred meters above sea level and a diameter on the order of 100--200 km. The Catalina Eddy is produced by the interaction between the synoptic-scale northerly flow and the formidable topography along the southern California coast. A favorable synoptic situation that enhances the increased low-level climatological northerly flow along the central California coastline is the presence of the prominent east-west pressure gradient between the subtropical East Pacific high and the inland thermal low over California. Increased northerlies impinging on the San Rafael mountains north of Santa Barbara result in enhanced mesoscale lee troughing in the bight and establishment of a narrow ridge alongshore, leading to establishment of cyclonic vorticity in the bight. This paper describes numerical simulations and predictions of a Catalina Eddy event with a high-resolution multi-level limited area model. The model is initialized and forced at the lateral boundaries by the National Meteorological Center`s (NMC) 2.5{degree} {times} 2.5{degree} global objective analysis and also by NMC`s medium range forecast model (MRF) 1--10 day forecasts. In the authors previous effort to simulate mesoscale disturbances such as the Catalina Eddy the integrations were performed up to 1 model-day utilizing the NMC analysis as fixed lateral boundary conditions. In this paper they describe the results of continuous 5- to 7-day simulations of the Catalina Eddy event of 26--30 June 1988 by utilizing time-dependent lateral boundary conditions obtained from NMC`s global objective analysis as well as NMC`s MRF forecasts.
NASA Astrophysics Data System (ADS)
Dages, Cecile; Samouelian, Anatja; Lanoix, Marthe; Dollinger, Jeanne; Chakkour, Sara; Chovelon, Gabrielle; Trabelsi, Khouloud; Voltz, Marc
2015-04-01
Ditches are involved in the transfer of pesticide to surface and groundwaters (e.g. Louchart et al., 2001). Soil horizons underlying ditch beds may present specific soil characteristics compared to neighbouring field soils due to erosion/deposition processes, to the specific biological activities (rooting dynamic and animal habitat) in the ditches (e.g. Vaughan et al., 2008) and to management practices (burning, dredging, mowing,...). Moreover, in contrast to percolation processes in field soils that can be assumed to be mainly 1D vertical, those occurring in the ditch beds are by essence 2D or even 3D. Nevertheless, due to a lake of knowledge, these specific aspects of transfer within ditch beds are generally omitted for hydrological simulation at the catchment scale (Mottes et al., 2014). Accordingly, the aims of this study were i) to characterize subsurface solute transfer through ditch beds and ii) to determine equivalent hydraulic parameters of the ditch beds for use in catchment scale hydrological simulations. A complementary aim was to evaluate the error in predictions performed when percolation in ditches is assumed to be similar to that in the neighbouring field soil. First, bromide transfer experiments were performed on undisturbed soil column (15 cm long with a 15 cm inner-diameter), horizontally and vertically sampled within each soil horizon underlying a ditch bed and within the neighboring field. Columns were sampled at the Roujan catchment (Hérault, France), which belongs to the long term Mediterranean hydrological observatory OMERE (Voltz and Albergel, 2002). Second, for each column, a set of parameters was determined by inverse optimization with mobile-immobile or dual permeability models, with CXTFIT (Toride et al., 1999) or with HYDRUS (Simunek et al., 1998). Third, infiltration and percolation in the ditch was simulated by a 2D flow domain approach considering the 2D variation in hydraulic properties of the cross section of a ditch bed. Last
NASA Technical Reports Server (NTRS)
Mcmurtry, Patrick A.; Givi, Peyman
1992-01-01
An account is given of the implementation of the spectral-element technique for simulating a chemically reacting, spatially developing turbulent mixing layer. Attention is given to experimental and numerical studies that have investigated the development, evolution, and mixing characteristics of shear flows. A mathematical formulation is presented of the physical configuration of the spatially developing reacting mixing layer, in conjunction with a detailed representation of the spectral-element method's application to the numerical simulation of mixing layers. Results from 2D and 3D calculations of chemically reacting mixing layers are given.
NASA Astrophysics Data System (ADS)
Campforts, Benjamin; Vanacker, Veerle; Vanderborght, Jan; Baken, Stijn; Smolders, Erik; Govers, Gerard
2016-04-01
Meteoric 10Be allows for the quantification of vertical and lateral soil fluxes over long time scales (103-105 yr). However, the mobility of meteoric 10Be in the soil system makes a translation of meteoric 10Be inventories into erosion and deposition rates complex. Here, we present a spatially explicit 2D model simulating the behaviour of meteoric 10Be on a hillslope. The model consists of two parts. The first component deals with advective and diffusive mobility of meteoric 10Be within the soil profile, and the second component describes lateral soil and meteoric 10Be fluxes over the hillslope. Soil depth is calculated dynamically, accounting for soil production through weathering as well as downslope fluxes of soil due to creep, water and tillage erosion. Synthetic model simulations show that meteoric 10Be inventories can be related to erosion and deposition across a wide range of geomorphological and pedological settings. Our results also show that meteoric 10Be can be used as a tracer to detect human impact on soil fluxes for soils with a high affinity for meteoric 10Be. However, the quantification of vertical mobility is essential for a correct interpretation of the observed variations in meteoric 10Be profiles and inventories. Application of the Be2D model to natural conditions using data sets from the Southern Piedmont (Bacon et al., 2012) and Appalachian Mountains (Jungers et al., 2009; West et al., 2013) allows to reliably constrain parameter values. Good agreement between simulated and observed meteoric 10Be concentrations and inventories is obtained with realistic parameter values. Furthermore, our results provide detailed insights into the processes redistributing meteoric 10Be at the soil-hillslope scale.
3D Numerical Simulations of the Breakout Model
NASA Astrophysics Data System (ADS)
Choe, G. S.; Cheng, C. Z.; Lee, J.; Lynch, B. J.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.
2005-05-01
We present the continuing progress of the numerical simulations of the breakout model for coronal mass ejection initiation. To validate the 3D spherical ARMS code we have run the 2.5D breakout problem and compare the eruption to the published 2D results. The ARMS 2.5D CME also forms a large magnetic island ahead of the erupting plasmoid due to the code's excellent maintenance of equatorial symmetry. Progress on the fully 3D breakout problem is also discussed. To build up enough magnetic free energy for an eruption the active region field must be strong with a steep gradient near the polarity inversion line and the shear must be highly concentrated there. This requires adaptive griding techniques. In the current simulation, the active region to background field ratio is 20-to-1 and the neutral line is long compared to the active region width. We present the evolution of this topology under Br-conserving shearing flow and discuss implications for a 3D eruption. This work is supported by NASA and ONR. BJL is supported by NASA GSRP grant NGT5-50453.
Numerical Simulation of the Detonation Propagation in Silicon Carbide Shell
NASA Astrophysics Data System (ADS)
Balagansky, Igor; Terechov, Anton
2013-06-01
Last years it was experimentally shown that in condensed high explosive charges (HE) placed in silicon carbide shell with sound velocity greater than the detonation velocity in HE, there may be observed interesting phenomena. Depending on the conditions, as an increase or decrease of the detonation velocity and pressure on the detonation front can be observed. There is also the distortion of the detonation front until the formation of a concave front. For a detailed explanation of the physical nature of the phenomenon we have provided numerical simulation of detonation wave propagation in Composition B HE charge, which was placed in silicon carbide shell. Modeling was performed with Ansys Autodyn in 2D-axis symmetry posting on an Eulerian mesh. Special attention was paid to selection of the parameters values in Lee-Tarver kinetic equation for HE and choice of constants to describe behavior of the ceramics. For comparison, also we have carried out the modeling of propagation of detonation in a completely similar assembly with brass shell. The simulation results agree well with the experimental data. In particular, in silicon carbide shell distortion of the detonation front was observed. A characteristic feature of the process is the pressure waves propagating in the direction of the axis of symmetry on the back surface of the detonation front.
Numerical simulations of groundwater flow at New Jersey Shallow Shelf
NASA Astrophysics Data System (ADS)
Fehr, Annick; Patterson, Fabian; Lofi, Johanna; Reiche, Sönke
2016-04-01
During IODP Expedition 313, three boreholes were drilled in the so-called New Jersey transect. Hydrochemical studies revealed the groundwater situation as more complex than expected, characterized by several sharp boundaries between fresh and saline groundwater. Two conflicting hypotheses regarding the nature of these freshwater reservoirs are currently debated. One hypothesis is that these reservoirs are connected with onshore aquifers and continuously recharged by seaward-flowing groundwater. The second hypothesis is that fresh groundwater was emplaced during the last glacial period. In addition to the petrophysical properties measured during IODP 313 expedition, Nuclear Magnetic Resonance (NMR) measurements were performed on samples from boreholes M0027, M0028 and M0029 in order to deduce porosities and permeabilities. These results are compared with data from alternative laboratory measurements and with petrophysical properties inferred from downhole logging data. We incorporate these results into a 2D numerical model that reflects the shelf architecture as known from drillings and seismic data to perform submarine groundwater flow simulations. In order to account for uncertainties related to the spatial distribution of physical properties, such as porosity and permeability, systematic variation of input parameters was performed during simulation runs. The target is to test the two conflicting hypotheses of fresh groundwater emplacements offshore New Jersey and to improve the understanding of fluid flow processes at marine passive margins.
Possible tsunami transmission across the Strait of Gibraltar: numerical simulations
NASA Astrophysics Data System (ADS)
Carbone, V.; Servidio, S.; Vecchio, A.; Anzidei, M.; Guerra, I.
2012-12-01
The possibility that a tsunami, generated as a consequence of the large earthquake in the Atlantic or Pacific ocean, could be recorded by the tide gauge stations located in the Mediterranean has been numerically investigated. In particular, direct numerical simulations of the nonlinear Shallow Water Equations (SWE) have been performed in order to simulate the transmission of large scale waves trough the Strait of Gibraltar. The SWE have wide applications in ocean and hydraulic engineering: tidal flows in estuary and coastal water regions, bore wave propagation, hydraulic jump, open channel flows, and so on. Among all these examples, the application of SWE to tsunamies is indeed one of the most successful. A numerical scheme, based on a Godunov-type method for solving the SWE with source term, has been proposed in Ref. [1]. In contrast to conventional data reconstruction methods based on conservative variables, the water surface level is chosen as the basis for data reconstruction. This provides accurate values of the conservative variables at cell interfaces so that the fluxes can be accurately calculated with a Riemann solver. The surface gradient method can be incorporated into any Godunov-type method which requires data reconstruction. Here, the MUSCL-Hancock finite-volume method has been combined with a body-fitted cut cell mesh [2], which can efficiently treat irregular boundaries while retaining the simplicity of a Cartesian grid implementation. Preliminary results show that incident waves, coming from the free ocean, can enter the Mediterraneum sea, passing trough the Strait. The incoming wave, altough is strongly reduced in intensity, fragmentate because of the bed profile and the interaction with the coasts, producing low ang high frequency disturbances. In agreement with observations (See Ref. [3]), these numerical simulations suggest that large tsunamis can pass through Gibraltar, initiating anomalous fluctuations in the Mediterraneum. [1] J. G. Zhou, D
Numerical simulations of interacting disk galaxies
NASA Technical Reports Server (NTRS)
Noguchi, Masafumi
1990-01-01
Galaxy-galaxy interactions have long attracted many extragalactic astronomers in various aspects. A number of computer simulations performed in the 1970s have successfully reproduced the peculiar morphologies observed in interacting disk galaxies and clarified that tidal deformation explains most of the observed global peculiarities. However, most of these simulations have used test particles in modelling the disk component. Tidal response of a self-gravitating disk remains to be further clarified. Another topic which is intensely discussed at present is the relation between galaxy-galaxy interactions and activity. Many observations suggest that interactions trigger strong starbursts and possibly active galactic nuclei (AGN). However, the detailed mechanism of triggering is not yet clear. It is vital here to understand the dynamics of interstellar gas. In order to understand various phenomena related to galaxy-galaxy interactions (mainly for disk galaxies), the author performed a series of numerical simulations on close galaxy encounters which includes both interstellar gas and self-gravitating disk components. In these simulations, the galaxy model to be perturbed (target galaxy) consists of a halo and a disk. The halo was treated as a rigid spherical gravitational field which is assumed to remain fixed during the interaction. The disk is composed of stars and gas. The stellar disk was constructed by 20000 collisionless particles of the same mass. Those particles move in the halo gravitational field, interacting with each other and with the perturber. Therefore, the self-graviy of the disk is properly taken into account. Stellar particles were initially given circular velocities with small random motions required to stabilize the disk against local axisymmetric disturbances. The gravitational field of the stellar disk was calculated by the particle-mesh scheme (e.g. Hockney and Eastwood 1981). The gaseous component was modelled by the cloud-particle scheme (e
Bolmatov, Dima; Zhernenkov, Mikhail; Zav’yalov, Dmitry; ...
2016-08-19
Here in this work we report on terahertz phononic excitations in 2D gold nanoparticle arrays in a water matrix through a series of large-scale molecular dynamics simulations. For the first time, we observe acoustic Dirac-like crossings in H (H2O) atomic (molecular) networks which emerge due to an intraband phononic scattering. These crossings are the phononic fingerprints of ice-like arrangements of H (H2O) atomic (molecular) networks at nanometer scale. We reveal how phononic excitations in metallic nanoparticles and the water matrix reciprocally impact on one another providing the mechanism for the THz phononics manipulation via structural engineering. In addition, we showmore » that by tuning the arrangement of 2D gold nanoparticle assemblies the Au phononic polarizations experience sub-terahertz hybridization (Kohn anomaly) due to surface electron-phonon relaxation processes. This opens the way for the sound control and manipulation in soft matter metamaterials at nanoscale.« less
Bolmatov, Dima; Zhernenkov, Mikhail; Zav’yalov, Dmitry; Cai, Yong Q.; Cunsolo, Alessandro
2016-08-19
Here in this work we report on terahertz phononic excitations in 2D gold nanoparticle arrays in a water matrix through a series of large-scale molecular dynamics simulations. For the first time, we observe acoustic Dirac-like crossings in H (H_{2}O) atomic (molecular) networks which emerge due to an intraband phononic scattering. These crossings are the phononic fingerprints of ice-like arrangements of H (H_{2}O) atomic (molecular) networks at nanometer scale. We reveal how phononic excitations in metallic nanoparticles and the water matrix reciprocally impact on one another providing the mechanism for the THz phononics manipulation via structural engineering. In addition, we show that by tuning the arrangement of 2D gold nanoparticle assemblies the Au phononic polarizations experience sub-terahertz hybridization (Kohn anomaly) due to surface electron-phonon relaxation processes. This opens the way for the sound control and manipulation in soft matter metamaterials at nanoscale.
Numerical simulation of "an American haboob"
NASA Astrophysics Data System (ADS)
Vukovic, A.; Vujadinovic, M.; Pejanovic, G.; Andric, J.; Kumjian, M. R.; Djurdjevic, V.; Dacic, M.; Prasad, A. K.; El-Askary, H. M.; Paris, B. C.; Petkovic, S.; Nickovic, S.; Sprigg, W. A.
2014-04-01
A dust storm of fearful proportions hit Phoenix in the early evening hours of 5 July 2011. This storm, an American haboob, was predicted hours in advance because numerical, land-atmosphere modeling, computing power and remote sensing of dust events have improved greatly over the past decade. High-resolution numerical models are required for accurate simulation of the small scales of the haboob process, with high velocity surface winds produced by strong convection and severe downbursts. Dust productive areas in this region consist mainly of agricultural fields, with soil surfaces disturbed by plowing and tracks of land in the high Sonoran Desert laid barren by ongoing draught. Model simulation of the 5 July 2011 dust storm uses the coupled atmospheric-dust model NMME-DREAM (Non-hydrostatic Mesoscale Model on E grid, Janjic et al., 2001; Dust REgional Atmospheric Model, Nickovic et al., 2001; Pérez et al., 2006) with 4 km horizontal resolution. A mask of the potentially dust productive regions is obtained from the land cover and the normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The scope of this paper is validation of the dust model performance, and not use of the model as a tool to investigate mechanisms related to the storm. Results demonstrate the potential technical capacity and availability of the relevant data to build an operational system for dust storm forecasting as a part of a warning system. Model results are compared with radar and other satellite-based images and surface meteorological and PM10 observations. The atmospheric model successfully hindcasted the position of the front in space and time, with about 1 h late arrival in Phoenix. The dust model predicted the rapid uptake of dust and high values of dust concentration in the ensuing storm. South of Phoenix, over the closest source regions (~25 km), the model PM10 surface dust concentration reached ~2500 μg m-3, but
Numerical simulation of "An American Haboob"
NASA Astrophysics Data System (ADS)
Vukovic, A.; Vujadinovic, M.; Pejanovic, G.; Andric, J.; Kumjian, M. R.; Djurdjevic, V.; Dacic, M.; Prasad, A. K.; El-Askary, H. M.; Paris, B. C.; Petkovic, S.; Nickovic, S.; Sprigg, W. A.
2013-10-01
A dust storm of fearful proportions hit Phoenix in the early evening hours of 5 July 2011. This storm, an American haboob, was predicted hours in advance because numerical, land-atmosphere modeling, computing power and remote sensing of dust events have improved greatly over the past decade. High resolution numerical models are required for accurate simulation of the small-scales of the haboob process, with high velocity surface winds produced by strong convection and severe downbursts. Dust productive areas in this region consist mainly of agricultural fields, with soil surfaces disturbed by plowing and tracks of land in the high Sonoran desert laid barren by ongoing draught. Model simulation of the 5 July 2011 dust storm uses the coupled atmospheric-dust model NMME-DREAM with 3.5 km horizontal resolution. A mask of the potentially dust productive regions is obtained from the land cover and the Normalized Difference Vegetation Index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). Model results are compared with radar and other satellite-based images and surface meteorological and PM10 observations. The atmospheric model successfully hindcasted the position of the front in space and time, with about 1 h late arrival in Phoenix. The dust model predicted the rapid uptake of dust and high values of dust concentration in the ensuing storm. South of Phoenix, over the closest source regions (~ 25 km), the model PM10 surface dust concentration reached ~ 2500 μg m-3, but underestimated the values measured by the PM10stations within the city. Model results are also validated by the MODIS aerosol optical depth (AOD), employing deep blue (DB) algorithms for aerosol loadings. Model validation included Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), equipped with the lidar instrument, to disclose the vertical structure of dust aerosols as well as aerosol subtypes. Promising results encourage further research and
Rossi, Michael R; Rabin, Yoed
2007-08-07
As a part of an ongoing effort to develop computerized planning tools for cryosurgery, an experimental study has been conducted to verify a recently developed numerical technique for bioheat transfer simulations. Experiments were performed on gelatin solution as a phantom material, using proprietary liquid-nitrogen cryoprobes. Urethral warming was simulated with the application of a cryoheater, which is a proprietary temperature-controlled electrical heater. The experimental design was aimed at creating a 2D heat transfer problem. Analysis of experimental results was based on reconstruction of the frozen region from video recordings, using a region-growing segmentation algorithm. Results of this study show an average disagreement of 2.9% in the size of the frozen region, between experimental data and numerical simulation of the same experiment, which validates both the recently developed algorithm for numerical simulations and the newly developed algorithm for segmentation from video recordings.
Rossi, Michael R.; Rabin, Yoed
2007-01-01
As a part of an ongoing effort to develop computerized planning tools for cryosurgery, an experimental study has been conducted to verify a recently developed numerical technique for bioheat transfer simulations. Experiments were performed on gelatin solution as a phantom material, using proprietary liquid-nitrogen cryoprobes. Urethral warming was simulated with the application of a cryoheater, which is a proprietary temperature-controlled electrical heater. The experimental design was aimed at creating a 2D heat-transfer problem. Analysis of experimental results was based on reconstruction of the frozen region from video recordings, using a region-growing segmentation algorithm. Results of this study show an average disagreement of 2.9% in the size of the frozen region, between experimental data and numerical simulation of the same experiment, which validates both the recently developed algorithm for numerical simulations and the newly developed algorithm for segmentation from video recordings. PMID:17634650
Analysis of Highly-Resolved Simulations of 2-D Humps Toward Improvement of Second-Moment Closures
NASA Technical Reports Server (NTRS)
Jeyapaul, Elbert; Rumsey Christopher
2013-01-01
Fully resolved simulation data of flow separation over 2-D humps has been used to analyze the modeling terms in second-moment closures of the Reynolds-averaged Navier- Stokes equations. Existing models for the pressure-strain and dissipation terms have been analyzed using a priori calculations. All pressure-strain models are incorrect in the high-strain region near separation, although a better match is observed downstream, well into the separated-flow region. Near-wall inhomogeneity causes pressure-strain models to predict incorrect signs for the normal components close to the wall. In a posteriori computations, full Reynolds stress and explicit algebraic Reynolds stress models predict the separation point with varying degrees of success. However, as with one- and two-equation models, the separation bubble size is invariably over-predicted.
Direct Numerical Simulation of Cell Printing
NASA Astrophysics Data System (ADS)
Qiao, Rui; He, Ping
2010-11-01
Structural cell printing, i.e., printing three dimensional (3D) structures of cells held in a tissue matrix, is gaining significant attention in the biomedical community. The key idea is to use desktop printer or similar devices to print cells into 3D patterns with a resolution comparable to the size of mammalian cells, similar to that in living organs. Achieving such a resolution in vitro can lead to breakthroughs in areas such as organ transplantation and understanding of cell-cell interactions in truly 3D spaces. Although the feasibility of cell printing has been demonstrated in the recent years, the printing resolution and cell viability remain to be improved. In this work, we investigate one of the unit operations in cell printing, namely, the impact of a cell-laden droplet into a pool of highly viscous liquids using direct numerical simulations. The dynamics of droplet impact (e.g., crater formation and droplet spreading and penetration) and the evolution of cell shape and internal stress are quantified in details.
The numerical simulation of subsonic flutter
NASA Technical Reports Server (NTRS)
Strganac, Thomas W.; Mitchum, Maria V.; Mook, Dean T.
1987-01-01
The present paper describes a numerical simulation of unsteady, subsonic aeroelastic responses. The technique accounts for aerodynamic nonlinearities associated with angles of attack, vortex-dominated flow, static deformations, and unsteady behavior. The fluid and the wing together are treated as a single dynamic system, and the equations of motion for the structure and flowfield are integrated simultaneously and interactively in the time domain. The method employs an iterative scheme based on a predictor-corrector technique. The aerodynamic loads are computed by the general unsteady vortex-lattice method and are determined simultaneously with the motion of the wing. Two models are used to demonstrate the technique: a rigid wing on an elastic support experiencing plunge and pitch about the elastic axis, and a continuous wing rigidly supported at the root chord experiencing spanwise bending and twisting. The time domain solution coupled with the unsteady vortex-lattice method provides the capability of graphically depicting wing and wake motion. Several graphs that illustrate the time domain behavior of the wing and wake are presented.
Cloud interactions and merging - Numerical simulations
NASA Technical Reports Server (NTRS)
Tao, W.-K.; Simpson, J.
1984-01-01
A total of 48 numerical experiments have been performed to study cloud interactions adn merging by means of a two-dimensional multi-cell model. Two soundings of deep convection during GATE and two different magnitudes of large-scale lifting have been used as the initial conditions and as the main forcing on the model. Over two hundred groups of cloud systems with a life history of over sixty minutes have been generated under the influence of different combinations of the stratification and large-scale lifting. The results demonstrate the increase in convective activity and in amount of precipitation with increased intensity of large-scale lifting. The results also show increased occurrence of cloud merger with increased intensity of large-scale lifting. The most unfavorable environmental conditions for cloud merging are (1) less unstable stratification of the atmosphere and (2) weaker large-scale lifting. A total of fourteen cloud systems qualify as mergers. Two selected cases will be described dynamically and thermodynamically in this paper. Although these cloud mergers have been simulated under the influence of different synoptic-scale conditions, the major physical mechanism related to the cloud merging process is the same as that proposed by Simpson. Cumulus downdrafts and associated cold outflows play a dominant role in the merging process in all cases studied.
Numerical simulation of condensation on structured surfaces.
Fu, Xiaowu; Yao, Zhaohui; Hao, Pengfei
2014-11-25
Condensation of liquid droplets on solid surfaces happens widely in nature and industrial processes. This phase-change phenomenon has great effect on the performance of some microfluidic devices. On the basis of micro- and nanotechnology, superhydrophobic structured surfaces can be well-fabricated. In this work, the nucleating and growth of droplets on different structured surfaces are investigated numerically. The dynamic behavior of droplets during the condensation is simulated by the multiphase lattice Boltzmann method (LBM), which has the ability to incorporate the microscopic interactions, including fluid-fluid interaction and fluid-surface interaction. The results by the LBM show that, besides the chemical properties of surfaces, the topography of structures on solid surfaces influences the condensation process. For superhydrophobic surfaces, the spacing and height of microridges have significant influence on the nucleation sites. This mechanism provides an effective way for prevention of wetting on surfaces in engineering applications. Moreover, it suggests a way to prevent ice formation on surfaces caused by the condensation of subcooled water. For hydrophilic surfaces, however, microstructures may be submerged by the liquid films adhering to the surfaces. In this case, microstructures will fail to control the condensation process. Our research provides an optimized way for designing surfaces for condensation in engineering systems.
NASA Astrophysics Data System (ADS)
Klochko, Andrei V.; Starikovskaia, Svetlana M.; Xiong, Zhongmin; Kushner, Mark J.
2014-09-01
Nanosecond electrical discharges in the form of ionization waves are of interest for rapidly ionizing and exciting complex gas mixtures to initiate chemical reactions. Operating with a small discharge tube diameter can significantly increase the specific energy deposition and so enable optimization of the initiation process. Analysis of the uniformity of energy release in small diameter capillary tubes will aid in this optimization. In this paper, results for the experimentally derived characteristics of nanosecond capillary discharges in air at moderate pressure are presented and compared with results from a two-dimensional model. The quartz capillary tube, having inner and outer diameters of 1.5 and 3.4 mm, is about 80 mm long and filled with synthetic dry air at 27 mbar. The capillary tube with two electrodes at the ends is inserted into a break of the central wire of a long coaxial cable. A metal screen around the tube is connected to the cable ground shield. The discharge is driven by a 19 kV 35 ns voltage pulse applied to the powered electrode. The experimental measurements are conducted primarily by using a calibrated capacitive probe and back current shunts. The numerical modelling focuses on the fast ionization wave (FIW) and the plasma properties in the immediate afterglow after the conductive plasma channel has been established between the two electrodes. The FIW produces a highly focused region of electric field on the tube axis that sustains the ionization wave that eventually bridges the electrode gap. Results from the model predict FIW propagation speed and current rise time that agree with the experiment.
Numerical Simulations of Merging Clusters of Galaxies
NASA Astrophysics Data System (ADS)
Roettiger, Kurt; Loken, Chris; Burns, Jack O.
1997-04-01
We present results from three-dimensional numerical simulations of head-on mergers between two clusters of galaxies using a hybrid hydro/N-body code. In these simulations, the gaseous intracluster medium (ICM) is evolved as a massless fluid within a changing gravitational potential defined by the collisionless dark matter component. The ICM is represented by the equations of hydrodynamics which are solved by an Eulerian, finite-difference method. The cluster dark matter component is represented by the N-body particle distribution. A series of simulations have been conducted in which we have systematically varied the cluster-subcluster mass ratio between 8:1 and 1:1. We find that cluster-subcluster mergers result in an elongation of both the cluster dark matter and gas distributions. The dark matter distribution is elongated parallel to the merger axis and accompanied by anisotropy in the dark matter velocity dispersion. Both the elongation and corresponding velocity anisotropy are sustained for more than 5 Gyr after the merger. The elongation of the gas distribution is also generally along the merger axis, although shocks and adiabatic compressions produce elongations perpendicular to the merger axis at various times during the merger. We also find a significant offset between dark matter and gas centroids in the period following core passage. The gasdynamics is also severely affected by the cluster-subcluster merger. In these simulations, the subcluster enters the primary at supersonic speeds initiating bulk flows that can exceed 2000 km s-1. The width of the bulk flows are seen to range between several hundred kiloparsecs to nearly 1 Mpc. We believe the bulk flows can produce the bending of wide-angle tailed (WAT) radio sources. The most significant gasdynamics is seen to subside on timescales of 2 Gyr, although still significant dynamics is seen even after 5 Gyr. The merger-induced gasdynamics may also play a role in the formation of radio halo sources, and
NASA Astrophysics Data System (ADS)
Schiettekatte, François; Chicoine, Martin
2016-03-01
Corteo is a program that implements Monte Carlo (MC) method to simulate ion beam analysis (IBA) spectra of several techniques by following the ions trajectory until a sufficiently large fraction of them reach the detector to generate a spectrum. Hence, it fully accounts for effects such as multiple scattering (MS). Here, a version of Corteo is presented where the target can be a 2D or 3D image. This image can be derived from micrographs where the different compounds are identified, therefore bringing extra information into the solution of an IBA spectrum, and potentially significantly constraining the solution. The image intrinsically includes many details such as the actual surface or interfacial roughness, or actual nanostructures shape and distribution. This can for example lead to the unambiguous identification of structures stoichiometry in a layer, or at least to better constraints on their composition. Because MC computes in details the trajectory of the ions, it simulates accurately many of its aspects such as ions coming back into the target after leaving it (re-entry), as well as going through a variety of nanostructures shapes and orientations. We show how, for example, as the ions angle of incidence becomes shallower than the inclination distribution of a rough surface, this process tends to make the effective roughness smaller in a comparable 1D simulation (i.e. narrower thickness distribution in a comparable slab simulation). Also, in ordered nanostructures, target re-entry can lead to replications of a peak in a spectrum. In addition, bitmap description of the target can be used to simulate depth profiles such as those resulting from ion implantation, diffusion, and intermixing. Other improvements to Corteo include the possibility to interpolate the cross-section in angle-energy tables, and the generation of energy-depth maps.
NASA Astrophysics Data System (ADS)
Awad, Esam; Toorman, Erik; Lacor, Chris
2009-06-01
In this study, the performance of the horizontal large eddy simulation module, developed at the University of Leuven (HLES-KULeuven module) is assessed. A comparison between different subgrid scale models has been carried out. The study is concerned with the non-rotating and unstratified flows. The results of the simulation for an oscillatory backward facing (BFS) flow are presented in case of an expanding flume based on a one-length scale approach and a two-length scale approach. Three subgrid scale (SGS) models have been tested: Smagorinsky SGS model (Smagorinsky, J., (1963). General circulation experiments with the primitive equations, I. the basic experiments. Monthly Weather Review, 91(3), 99-164), Uittenbogaard SGS model (Uittenbogaard, R.E., and van Vossen, B., (2004). Subgrid-scale model for quasi-2D turbulence in shallow water. Shallow Flows. Jirka and Uijttewaal (Eds.), Taylor & Francis Group, London, ISBN 90 5809 700 5) and a proposed two-length scale approach. The first two models are considered to be a one-length scale models. A simulation without a subgrid scale model for the horizontal mixing has also been conducted. In all simulations, a quadratic friction model parameterizes the dissipation produced by the 3D-subdepth scale turbulence. The two-length scale concept uses a newly mixing length formulation for the quasi-2D turbulence and doesn't depend on the filter width in contrast to the one-length scale approach, in which the mixing length is function of the filter width. The outputs of the HLES-KULeuven module have been compared with the experimental data taken from Stelling, G.S., and Wang, L.X., (1984). Experiments and computations on separating flow in an expanding flume. Dept. Civil Engineering, Delft University of Technology, Report 2-84.). The two-length scale approach has been validated with experimental data from SERC Flood Channel Facility at HR Wallingford. In general, there is a qualitative agreement with the experimental data. It has
Numerical Simulation of the Hemming Process in the case of Al Alloys
Thuillier, S.; Le Maout, N.; Manach, P.Y.
2005-08-05
This work deals with the 2D numerical simulation of a hemming process. It consists of tree steps: bending, pre-hemming and final hemming; springback occurs in-between each forming operations. This study investigates the influence of the constitutive law on force-displacement curves as well as on the geometry of the hemmed. Three hardening laws are considered, i.e isotropic, kinematic and mixed hardening, and two yield criteria, i.e. Von Mises and Hill'48.
Numerical Simulation of Complex Turbomachinery Flows
NASA Technical Reports Server (NTRS)
Chernobrovkin, A. A.; Lakshiminarayana, B.
1999-01-01
An unsteady, multiblock, Reynolds Averaged Navier Stokes solver based on Runge-Kutta scheme and Pseudo-time step for turbo-machinery applications was developed. The code was validated and assessed against analytical and experimental data. It was used to study a variety of physical mechanisms of unsteady, three-dimensional, turbulent, transitional, and cooling flows in compressors and turbines. Flow over a cylinder has been used to study effects of numerical aspects on accuracy of prediction of wake decay and transition, and to modify K-epsilon models. The following simulations have been performed: (a) Unsteady flow in a compressor cascade: Three low Reynolds number turbulence models have been assessed and data compared with Euler/boundary layer predictions. Major flow features associated with wake induced transition were predicted and studied; (b) Nozzle wake-rotor interaction in a turbine: Results compared to LDV data in design and off-design conditions, and cause and effect of unsteady flow in turbine rotors were analyzed; (c) Flow in the low-pressure turbine: Assessed capability of the code to predict transitional, attached and separated flows at a wide range of low Reynolds numbers and inlet freestream turbulence intensity. Several turbulence and transition models have been employed and comparisons made to experiments; (d) leading edge film cooling at compound angle: Comparisons were made with experiments, and the flow physics of the associated vortical structures were studied; and (e) Tip leakage flow in a turbine. The physics of the secondary flow in a rotor was studied and sources of loss identified.
NASA Astrophysics Data System (ADS)
Deca, Jan; Lapenta, Giovanni; Lembège, Bertrand; Divin, Andrey; Markidis, Stefano; Amaya, Jorge
2013-04-01
We present the first 2D/3D fully kinetic Particle-in-Cell simulations of the solar wind interaction with lunar crustal magnetic anomalies. The simulations are performed using the implicit electromagnetic Particle-in-Cell code iPIC3D [Markidis, Lapenta & Rizwan-uddin, 2010]. Multiscale physics is resolved for all plasma components (heavy ions, protons and electrons) in the code, recently updated with a set of open boundary conditions designed for solar wind-body interactions. We use a dipole to model the crustal anomaly. The dipole center is located outside the computational domain and the boundary representing the lunar surface is modeled as a particle-absorbing plane. Photo-emission from the lunar surface is at this point not included, but will be in future work. We study the behaviour of the dipole model with variable surface magnetic field strength under changing solar wind conditions and confirm that lunar crustal magnetic fields may indeed be strong enough to stand off the solar wind and form a mini-magnetosphere, as suggested by MHD simulations [Harnett & Winglee, 2000, 2002, 2003] and spacecraft observations [Kurata et al., 2005; Halekas et al., 2008; Wieser et al., 2010]. 3D-PIC simulations reveal to be very helpful to analyze the diversion/braking of the particle flux and the characteristics of the resulting particles accumulation. The particle flux to the surface is significantly reduced at the magnetic anomaly, surrounded by a region of enhanced density due to the magnetic mirror effect. Finally we will present preliminary results on the interaction of the solar wind with weaker magnetic anomalies in which highly non-adiabatic interactions are expected.
NASA Astrophysics Data System (ADS)
Simão Ferreira, C. J.; Bijl, H.; van Bussel, G.; van Kuik, G.
2007-07-01
The implementation of wind energy conversion systems in the built environment renewed the interest and the research on Vertical Axis Wind Turbines (VAWT), which in this application present several advantages over Horizontal Axis Wind Turbines (HAWT). The VAWT has an inherent unsteady aerodynamic behavior due to the variation of angle of attack with the angle of rotation, perceived velocity and consequentially Reynolds number. The phenomenon of dynamic stall is then an intrinsic effect of the operation of a Vertical Axis Wind Turbine at low tip speed ratios, having a significant impact in both loads and power. The complexity of the unsteady aerodynamics of the VAWT makes it extremely attractive to be analyzed using Computational Fluid Dynamics (CFD) models, where an approximation of the continuity and momentum equations of the Navier-Stokes equations set is solved. The complexity of the problem and the need for new design approaches for VAWT for the built environment has driven the authors of this work to focus the research of CFD modeling of VAWT on: •comparing the results between commonly used turbulence models: URANS (Spalart-Allmaras and k-epsilon) and large eddy models (Large Eddy Simulation and Detached Eddy Simulation) •verifying the sensitivity of the model to its grid refinement (space and time), •evaluating the suitability of using Particle Image Velocimetry (PIV) experimental data for model validation. The 2D model created represents the middle section of a single bladed VAWT with infinite aspect ratio. The model simulates the experimental work of flow field measurement using Particle Image Velocimetry by Simão Ferreira et al for a single bladed VAWT. The results show the suitability of the PIV data for the validation of the model, the need for accurate simulation of the large eddies and the sensitivity of the model to grid refinement.
Geometry and Grid Modeling for Numerical Simulation
2005-06-01
three dimensional spatial region (a mesh) is a prerequisite of most computer aided engineering ( CAE ) software, including computational structural...Parasolid Parasolid [13] is a commercial solid-modeling kernel. It serves as the basis for Unigraphics and several other CAD/CAM/ CAE packages. It is...As mentioned earlier, 1D and 2D arrays of standard data types are the most complex data type permitted. This method has the advantage of
Simulations of P-SV wave scattering due to cracks by the 2-D finite difference method
NASA Astrophysics Data System (ADS)
Suzuki, Yuji; Shiina, Takahiro; Kawahara, Jun; Okamoto, Taro; Miyashita, Kaoru
2013-12-01
We simulate P-SV wave scattering by 2-D parallel cracks using the finite difference method (FDM). Here, special emphasis is put on simplicity; we apply a standard FDM (second-order velocity-stress scheme with a staggered grid) to media including traction-free, infinitesimally thin cracks, which are expressed in a simple manner. As an accuracy test of the present method, we calculate the displacement discontinuity along an isolated crack caused by harmonic waves using the method, which is compared with the corresponding results based on a reliable boundary integral equation method. The test resultantly indicates that the present method yields sufficient accuracy. As an application of this method, we also simulate wave propagation in media with randomly distributed cracks. We experimentally determine the attenuation and velocity dispersion induced by scattering from the synthetic seismograms, using a waveform averaging technique. It is shown that the results are well explained by a theory based on the Foldy approximation, if the crack density is sufficiently low. The theory appears valid with a crack density up to at least 0.1 for SV wave incidence, whereas the validity limit appears lower for P wave incidence.
2D simulation of active species and ozone production in a multi-tip DC air corona discharge
NASA Astrophysics Data System (ADS)
Meziane, M.; Eichwald, O.; Sarrette, J. P.; Ducasse, O.; Yousfi, M.
2011-11-01
The present paper shows for the first time in the literature a complete 2D simulation of the ozone production in a DC positive multi-tip to plane corona discharge reactor crossed by a dry air flow at atmospheric pressure. The simulation is undertaken until 1 ms and involves tens of successive discharge and post-discharge phases. The air flow is stressed by several monofilament corona discharges generated by a maximum of four anodic tips distributed along the reactor. The nonstationary hydrodynamics model for reactive gas mixture is solved using the commercial FLUENT software. During each discharge phase, thermal and vibrational energies as well as densities of radical and metastable excited species are locally injected as source terms in the gas medium surrounding each tip. The chosen chemical model involves 10 neutral species reacting following 24 reactions. The obtained results allow us to follow the cartography of the temperature and the ozone production inside the corona reactor as a function of the number of high voltage anodic tips.
Numerical simulation of burst defects in cold extrusion process
NASA Astrophysics Data System (ADS)
Labergère, C.; Lestriez, P.; Saanouni, K.
2007-05-01
The formation of the central bursts in axisymmetric cold extrusion is numerically simulated by using 2D finite element analysis (FEA) accounting for the mixed isotropic and kinematic hardening together with the ductile damage effect. The coupling between the ductile damage and the elastoplastic constitutive equations is formulated in the framework of the thermodynamics of irreversible processes together with the Continuum Damage Mechanics (CDM) theory. An isotropic ductile damage model is fully coupled with elastoplastic constitutive equations including non linear isotropic and kinematic hardening. A modified ductile damage criterion based on linear combination of the stress tensor invariants is used in order to predict the occurrence of micro-crack initiation as a discontinuous central bursts along the bar axis. The implicit integration scheme of the fully coupled constitutive equations and the Dynamic Explicit resolution scheme to solve the associated initial and boundary value problem are outlined. Application is made to the prediction of the chevron shaped cracks in cold extrusion of a round bar. The effect of various process parameters, as the diameter reduction ratio, the die semi-angle, the friction coefficient and the material ductility, on the central bursts occurrence are discussed.
NUMERICAL NOISE PM SIMULATION IN CMAQ
We have found that numerical noise in the latest release of CMAQ using the yamo advection scheme when compiled on Linux cluster with pgf90 (5.0 or 6.0). We recommend to use -C option to eliminate the numerical noise.
NASA Astrophysics Data System (ADS)
Boukenkoul, M. A.; Li, F. C.; Aounallah, M.
2017-03-01
The present study aims to investigate numerically the flow control possibility using a synthetic jet actuation over a bi-dimensional NACA0015 airfoil manoeuvring at a highly turbulent flow (8.9e105 Reynolds to chord number). The 2-D flow behaviour was computed using the ANSYS Fluent commercial code. The so-called Reynolds Averaged Navier-Stocks (RANS) approach has been tested for one (Spalat-Allmaras S-A) and two (K-ε) transport equations for the turbulence modelling. Both present a weakness to predict the stall angle effectively. The S-A lift coefficient slope seems to be the closest to the experimental data. The synthetic jet control exhibits an extraordinary lift coefficient enhancement at high Angles Of Attack (AOA) but seems to be less obvious at low AOA, where the flow is still attached. A synthetic jet of a Strouhal (St = 2) and momentum (Cμ of 0.56%), delays the stall onset from 15 to 19deg with enhancing the lift coefficient by 40%. The actual work has been enriched by studying the effect of the jet’s frequency and momentum on the lift temporal signal. Also, the interaction between the mean flow and the synthetic jet structures topology was undertaken.
Numerical simulation of seasonal groundwater pumping
NASA Astrophysics Data System (ADS)
Filimonova, Elena; Baldenkov, Mikhail
2015-04-01
Increasing scarcity and contamination of water recourses require innovative water management strategies such as combined water system. The combined water system is a complex technology comprising two separate wells, major catchment-zone well and compensation pumping well, located inside a single stream basin. The major well is supplied by the well's catchment zone or surface flow, thus depleting the stream flow. The pumping rate of a major well is determined by the difference between the current stream flow and the minimum permissible stream flow. The deficiency of the stream flow in dry seasons can be compensated for by the short-term pumping of groundwater. The compensation pumping rate is determined by the difference between water demand and the permissible water withdrawal of the major well. The source for the compensation well is the aquifer storage. The estimation of streamflow depletion caused by compensation pumping is major question to evaluate the efficiency of the combined water system. Short-term groundwater pumping can use aquifer storage instead of catchment-zone water until the drawdown reaches the edge of the stream. Traditionally pumping simulation calculates in two-step procedure. Natural conditions, an aquifer system is in an approximate dynamic equilibrium, describe by steady-state model. A steady-state solution provides an initial heads, a set of flows through boundaries, and used as initial state for transient solutions, when pumping is imposed on an aquifer system. The transient solutions provide the total change in flows through the boundaries. A difference between the transient and steady-state solutions estimates the capture and the streamflow depletion. Numerical modeling of cyclical compensation pumping has special features: the periodic solution, the seasonal changes through the boundaries and the importance even small drawdown of stream level. When seasonality is a modeling feature, traditional approach leads to mistaken values of
NASA Astrophysics Data System (ADS)
Llanes, F.; dela Resma, M.; Ferrer, P.; Realino, V.; Aquino, D. T.; Eco, R. C.; Lagmay, A.
2013-12-01
From November 14 to December 3, 2004, Luzon Island was ravaged by 4 successive typhoons: Typhoon Mufia, Tropical Storm Merbok, Tropical Depression Winnie, and Super Typhoon Nanmadol. Tropical Depression Winnie was the most destructive of the four when it triggered landslides on November 29 that devastated the municipalities of Infanta, General Nakar, and Real in Quezon Province, southeast Luzon. Winnie formed east of Central Luzon on November 27 before it moved west-northwestward over southeastern Luzon on November 29. A total of 1,068 lives were lost and more than USD 170 million worth of damages to crops and infrastructure were incurred from the landslides triggered by Typhoon Winnie on November 29 and the flooding caused by the 4 typhoons. FLO-2D, a flood routing software for generating flood and debris flow hazard maps, was utilized to simulate the debris flows that could potentially affect the study area. Based from the rainfall intensity-duration-frequency analysis, the cumulative rainfall from typhoon Winnie on November 29 which was approximately 342 mm over a 9-hour period was classified within a 100-year return period. The Infanta station of the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) was no longer able to measure the amount of rainfall after this period because the rain gauge in that station was washed away by floods. Rainfall data with a 100-year return period was simulated over the watersheds delineated from a SAR-derived digital elevation model. The resulting debris flow hazard map was compared with results from field investigation and previous studies made on the landslide event. The simulation identified 22 barangays (villages) with a total of 45,155 people at risk of turbulent flow and flooding.
Diameter Effect In Initiating Explosives, Numerical Simulations
Lefrancois, A.; Benterou, J.; Roeske, F.; Roos, E.
2006-02-10
The ability to safely machine small pieces of HE with the femtosecond laser allows diameter effect experiments to be performed in initiating explosives in order to study the failure diameter, the reduction of the detonation velocity and curvature versus the diameter. The reduced diameter configuration needs to be optimized, so that the detonation products of the first cylinder will not affect the measurement of the detonation velocity of the second cylinder with a streak camera. Different 2D axi-symmetrical configurations have been calculated to identify the best solution using the Ignition and Growth reactive flow model for LX16 Pellet with Ls-Dyna.
Development of Pelton turbine using numerical simulation
NASA Astrophysics Data System (ADS)
Patel, K.; Patel, B.; Yadav, M.; Foggia, T.
2010-08-01
This paper describes recent research and development activities in the field of Pelton turbine design. Flow inside Pelton turbine is most complex due to multiphase (mixture of air and water) and free surface in nature. Numerical calculation is useful to understand flow physics as well as effect of geometry on flow. The optimized design is obtained using in-house special optimization loop. Either single phase or two phase unsteady numerical calculation could be performed. Numerical results are used to visualize the flow pattern in the water passage and to predict performance of Pelton turbine at full load as well as at part load. Model tests are conducted to determine performance of turbine and it shows good agreement with numerically predicted performance.
Reconnection and small-scale fields in 2D-3V hybrid-kinetic driven turbulence simulations
NASA Astrophysics Data System (ADS)
Cerri, S. S.; Califano, F.
2017-02-01
The understanding of the fundamental properties of turbulence in collisionless plasmas, such as the solar wind, is a frontier problem in plasma physics. In particular, the occurrence of magnetic reconnection in turbulent plasmas and its interplay with a fully-developed turbulent state is still a matter of great debate. Here we investigate the properties of small-scale electromagnetic fluctuations and the role of fast magnetic reconnection in the development of a quasi-steady turbulent state by means of 2D-3V high-resolution Vlasov–Maxwell simulations. At the largest scales turbulence is fed by external random forcing. We show that large-scale turbulent motions establish a -5/3 spectrum at {k}\\perp {d}i< 1 and, at the same time, feed the formation of current sheets where magnetic reconnection occurs. As a result coherent magnetic structures are generated which, together with the rise of the associated small-scale non-ideal electric field, mediate the transition between the inertial and the subproton-scale spectrum. A mechanism that boosts the magnetic reconnection process is identified, making the generation of coherent structures rapid enough to be competitive with wave mode interactions and leading to the formation of a fully-developed turbulent spectrum across the so-called ion break.
NASA Astrophysics Data System (ADS)
Williams, Westin B.; Michaels, Thomas E.; Michaels, Jennifer E.
2017-02-01
Reliable detection of damage in composites is critically important for failure prevention in the aerospace industry since these materials are more frequently being used in high stress applications. Structural health monitoring (SHM) via guided wave sensors mounted on or embedded within a composite structure can help detect and localize damage in real-time while potentially reducing overall maintenance costs. One approach to guided wave SHM is sparse array imaging via the minimum variance algorithm, and it has been shown in prior work that incorporating expected scattering from defects of interest can improve the quality of damage localization and characterization. For this study, simulated damage in the form of attached magnets was used for estimating scattering from recorded wavefield data. Data were recorded on a circle centered at the damage location from multiple incident directions before and after the magnets were attached. Baseline subtraction is used to estimate scattering patterns for each incident direction, and these patterns are combined and interpolated to form a full 2-D scattering matrix. This matrix is then incorporated into the minimum variance imaging algorithm, and the efficacy of this scattering estimation methodology is evaluated by comparing the resulting sparse array images to those generated using simpler scattering assumptions.
Lee, K. H.; Lee, L. C.; Omura, Y.
2011-09-15
We carried out a series of 2D simulations to study the beam instability and cyclotron maser instability (CMI) with the initial condition that a population of tenuous energetic electrons with a ring-beam distribution is present in a magnetized background plasma. In this paper, weakly relativistic cases are discussed with the ring-beam kinetic energy ranging from 25 to 100 keV. The beam component leads to the two-stream or beam instability at an earlier stage, and the beam mode is coupled with Langmuir or whistler mode, leading to excitation of beam-Langmuir or beam-whistler waves. When the beam velocity is large with a strong beam instability, the initial ring-beam distribution is diffused in the parallel direction rapidly. The diffused distribution may still support CMI to amplify the X1 mode (the fundamental X mode). On the contrary, when the beam velocity is small and the beam instability is weak, CMI can amplify the Z1 (the fundamental Z mode) effectively while the O1 (the fundamental O mode) and X2 (the second harmonic X mode) modes are very weak and the X1 mode is not excited. In this report, different cases with various parameters are presented and discussed for a comprehensive understanding of ring-beam instabilities.
Numerical Simulation Of Cutting Of Gear Teeth
NASA Technical Reports Server (NTRS)
Oswald, Fred B.; Huston, Ronald L.; Mavriplis, Dimitrios
1994-01-01
Shapes of gear teeth produced by gear cutters of specified shape simulated computationally, according to approach based on principles of differential geometry. Results of computer simulation displayed as computer graphics and/or used in analyses of design, manufacturing, and performance of gears. Applicable to both standard and non-standard gear-tooth forms. Accelerates and facilitates analysis of alternative designs of gears and cutters. Simulation extended to study generation of surfaces other than gears. Applied to cams, bearings, and surfaces of arbitrary rolling elements as well as to gears. Possible to develop analogous procedures for simulating manufacture of skin surfaces like automobile fenders, airfoils, and ship hulls.
The Analysis, Numerical Simulation, and Diagnosis of Extratropical Weather Systems
1999-09-30
respectively, and iv ) the numerical simulation and observational validation of high-spatial resolution (~10 km) numerical predictions. APPROACH My approach...satellite and targeted dropwindsonde observations; in collaboration with Xiaolie Zou (Fla. State Univ.), Chris Velden (Univ. Wisc ./CIMMS), and Arlin...Univ. Wisc .), and Arlin Krueger (NASA/GSFC). Analysis and numerical simulation of the fine-scale structure of upper-level jet streams from high- spatial
TITAN2D simulations of pyroclastic flows at Cerro Machín Volcano, Colombia: Hazard implications
NASA Astrophysics Data System (ADS)
Murcia, H. F.; Sheridan, M. F.; Macías, J. L.; Cortés, G. P.
2010-03-01
Cerro Machín is a dacitic tuff ring located in the central part of the Colombian Andes. It lies at the southern end of the Cerro Bravo-Cerro Machín volcanic belt. This volcano has experienced at least six major explosive eruptions during the last 5000 years. These eruptions have generated pyroclastic flows associated with Plinian activity that have traveled up to 8 km from the crater, and pyroclastic flows associated with Vulcanian activity with shorter runouts of 5 km from the source. Today, some 21,000 people live within a 8 km radius of Cerro Machín. The volcano is active with fumaroles and has shown increasing seismic activity since 2004, and therefore represents a potentially increasing threat to the local population. To evaluate the possible effects of future eruptions that may generate pyroclastic density currents controlled by granular flow dynamics we performed flow simulations with the TITAN2D code. These simulations were run in all directions around the volcano, using the input parameters of the largest eruption reported. The results show that an eruption of 0.3 km 3 of pyroclastic flows from a collapsing Plinian column would travel up to 9 km from the vent, emplacing a deposit thicker than 60 m within the Toche River valley. Deposits >45 m thick can be expected in the valleys of San Juan, Santa Marta, and Azufral creeks, while 30 m thick deposits could accumulate within the drainages of the Tochecito, Bermellón, and Coello Rivers. A minimum area of 56 km 2 could be affected directly by this kind of eruption. In comparison, Vulcanian column-collapse pyroclastic flows of 0.1 km 3 would travel up to 6 km from the vent depositing >45 m thick debris inside the Toche River valley and more than 30 m inside the valleys of San Juan, Santa Marta, and Azufral creeks. The minimum area that could be affected directly by this kind of eruption is 33 km 2. The distribution and thickness of the deposits obtained by these simulations are consistent with the hazard
Numerical Simulation of Two Phase Flows
NASA Technical Reports Server (NTRS)
Liou, Meng-Sing
2001-01-01
Two phase flows can be found in broad situations in nature, biology, and industry devices and can involve diverse and complex mechanisms. While the physical models may be specific for certain situations, the mathematical formulation and numerical treatment for solving the governing equations can be general. Hence, we will require information concerning each individual phase as needed in a single phase. but also the interactions between them. These interaction terms, however, pose additional numerical challenges because they are beyond the basis that we use to construct modern numerical schemes, namely the hyperbolicity of equations. Moreover, due to disparate differences in time scales, fluid compressibility and nonlinearity become acute, further complicating the numerical procedures. In this paper, we will show the ideas and procedure how the AUSM-family schemes are extended for solving two phase flows problems. Specifically, both phases are assumed in thermodynamic equilibrium, namely, the time scales involved in phase interactions are extremely short in comparison with those in fluid speeds and pressure fluctuations. Details of the numerical formulation and issues involved are discussed and the effectiveness of the method are demonstrated for several industrial examples.
Numerical simulation of turbulent combustion: Scientific challenges
NASA Astrophysics Data System (ADS)
Ren, ZhuYin; Lu, Zhen; Hou, LingYun; Lu, LiuYan
2014-08-01
Predictive simulation of engine combustion is key to understanding the underlying complicated physicochemical processes, improving engine performance, and reducing pollutant emissions. Critical issues as turbulence modeling, turbulence-chemistry interaction, and accommodation of detailed chemical kinetics in complex flows remain challenging and essential for high-fidelity combustion simulation. This paper reviews the current status of the state-of-the-art large eddy simulation (LES)/prob-ability density function (PDF)/detailed chemistry approach that can address the three challenging modelling issues. PDF as a subgrid model for LES is formulated and the hybrid mesh-particle method for LES/PDF simulations is described. Then the development need in micro-mixing models for the PDF simulations of turbulent premixed combustion is identified. Finally the different acceleration methods for detailed chemistry are reviewed and a combined strategy is proposed for further development.
Schaffranek, Raymond W.
2004-01-01
A numerical model for simulation of surface-water integrated flow and transport in two (horizontal-space) dimensions is documented. The model solves vertically integrated forms of the equations of mass and momentum conservation and solute transport equations for heat, salt, and constituent fluxes. An equation of state for salt balance directly couples solution of the hydrodynamic and transport equations to account for the horizontal density gradient effects of salt concentrations on flow. The model can be used to simulate the hydrodynamics, transport, and water quality of well-mixed bodies of water, such as estuaries, coastal seas, harbors, lakes, rivers, and inland waterways. The finite-difference model can be applied to geographical areas bounded by any combination of closed land or open water boundaries. The simulation program accounts for sources of internal discharges (such as tributary rivers or hydraulic outfalls), tidal flats, islands, dams, and movable flow barriers or sluices. Water-quality computations can treat reactive and (or) conservative constituents simultaneously. Input requirements include bathymetric and topographic data defining land-surface elevations, time-varying water level or flow conditions at open boundaries, and hydraulic coefficients. Optional input includes the geometry of hydraulic barriers and constituent concentrations at open boundaries. Time-dependent water level, flow, and constituent-concentration data are required for model calibration and verification. Model output consists of printed reports and digital files of numerical results in forms suitable for postprocessing by graphical software programs and (or) scientific visualization packages. The model is compatible with most mainframe, workstation, mini- and micro-computer operating systems and FORTRAN compilers. This report defines the mathematical formulation and computational features of the model, explains the solution technique and related model constraints, describes the
NASA Astrophysics Data System (ADS)
Xiaobo, Shen; Jinhua, Sun
The CFD simulation study was carried out on the spontaneous ignition of high pressure leaking hydrogen from some terminal units. An integrated 2D axisymmetric PDF numerical model was established. The results show that, the strong and weak discontinuous surfaces accompanied by combustion phenomenon are formed leading the local temperature and density rising up sharply. Near the outer-edge of the tube mouth, the vortexes are prone to take shape, which contribute to the mixing of hydrogen and air resulting in intenser and longer time combustion. But the combustion is not sustainable and will die out finally. The simulation catches the detailed jet structure including mach disk and barrel shock.
NASA Astrophysics Data System (ADS)
Morgan, J. P.; de Monserrat, A.; Hall, R.; Taramon, J. M.; Perez-Gussinye, M.
2015-12-01
This work focuses on improving current 2D numerical approaches to modeling the boundary conditions associated with computing accurate deformation and melting associated with continental rifting. Recent models primarily use far-field boundary conditions that have been used for decades with little assessment of their effects on asthenospheric flow beneath the rifting region. All are clearly extremely oversimplified — Huismans and Buiter assume there is no vertical flow into the rifting region, with the asthenosphere flowing uniformly into the rifting region from the sides beneath lithosphere moving in the opposing direction, Armitage et al. and van Wijk use divergent velocities on the upper boundary to impose break-up within a Cartesian box, while other studies generally assume there is uniform horizontal flow away from the center of rifting, with uniform vertical flow replenishing the material pulled out of the sides of the computational region. All are likely to significantly shape the pattern of asthenospheric flow beneath the stretching lithosphere that is associated with pressure-release melting and rift volcanism. Thus while ALL may lead to similar predictions of the effects of crustal stretching and thinning, NONE may lead to accurate determination of the the asthenospheric flow and melting associated with lithospheric stretching and breakup. Here we discuss a suite of numerical experiments that compare these choices to likely more realistic boundary condition choices like the analytical solution for flow associated with two diverging plates stretching over a finite-width region, and a high-resolution 2-D region embedded within a cylindrical annulus 'whole mantle cross-section' at 5% extra numerical problem size. Our initial results imply that the choice of far-field boundary conditions does indeed significantly influence predicted melting distributions and melt volumes associated with continental breakup. For calculations including asthenospheric melting
Roux, Emmanuel; Ramalli, Alessandro; Tortoli, Piero; Cachard, Christian; Robini, Marc; Liebgott, Herve
2016-08-24
Full matrix arrays are excellent tools for 3D ultrasound imaging, but the required number of active elements is too high to be individually controlled by an equal number of scanner channels. The number of active elements is significantly reduced by the sparse array techniques, but the position of the remaining elements must be carefully optimized. This issue is here faced by introducing novel energy functions in the simulated annealing algorithm. At each iteration step of the optimization process, one element is freely translated and the associated radiated pattern is simulated. To control the pressure field behavior at multiple depths, three energy functions inspired by the pressure field radiated by a Blackman-tapered spiral array are introduced. Such energy functions aim at limiting the main lobe width while lowering the side lobe and grating lobe levels at multiple depths. Numerical optimization results illustrate the influence of the number of iterations, pressure measurement points and depths as well as the influence of the energy function definition on the optimized layout. It is also shown that performance close to- or even better than the one provided by a spiral array, here assumed as reference, may be obtained. The finite-time convergence properties of simulated annealing allow the duration of the optimization process to be set in advance.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
In this study, we examine the sensitivity of long lived tracers to changes in the base transport components in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric mean age, and increased the rate of removal of material from the stratosphere. Increasing the stratospheric K(sub yy) increased the mean age due to the greater recycling of air parcels through the middle atmosphere, via the residual circulation, before returning to the troposphere. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and produces significantly younger ages throughout the stratosphere. Simulations with very small tropical stratospheric K(sub yy) decreased the globally averaged age of air by as much as 25% in the middle and upper stratosphere, and resulted in substantially weaker vertical age gradients above 20 km in the extratropics. We found only very small stratospheric tracer sensitivity to the magnitude of the horizontal mixing across the tropopause, and to the strength of the mesospheric gravity wave drag and diffusion used in the model. We also investigated the transport influence on chemically active tracers and found a strong age-tracer correlation, both in concentration and calculated lifetimes. The base model transport gives the most favorable overall comparison with a variety of inert tracer observations, and provides a significant improvement over our previous 1995 model transport. Moderate changes to the base transport were found to provide modest agreement with some of the measurements. Transport scenarios with residence times ranging from moderately shorter to slightly longer relative to the base case simulated N2O lifetimes
NASA Astrophysics Data System (ADS)
Sato, Haruo; Fehler, Michael C.
2016-10-01
The envelope broadening and the peak delay of the S-wavelet of a small earthquake with increasing travel distance are results of scattering by random velocity inhomogeneities in the earth medium. As a simple mathematical model, Sato proposed a new stochastic synthesis of the scalar wavelet envelope in 3-D von Kármán type random media when the centre wavenumber of the wavelet is in the power-law spectral range of the random velocity fluctuation. The essential idea is to split the random medium spectrum into two components using the centre wavenumber as a reference: the long-scale (low-wavenumber spectral) component produces the peak delay and the envelope broadening by multiple scattering around the forward direction; the short-scale (high-wavenumber spectral) component attenuates wave amplitude by wide angle scattering. The former is calculated by the Markov approximation based on the parabolic approximation and the latter is calculated by the Born approximation. Here, we extend the theory for the envelope synthesis of a wavelet in 2-D random media, which makes it easy to compare with finite difference (FD) simulation results. The synthetic wavelet envelope is analytically written by using the random medium parameters in the angular frequency domain. For the case that the power spectral density function of the random velocity fluctuation has a steep roll-off at large wavenumbers, the envelope broadening is small and frequency independent, and scattering attenuation is weak. For the case of a small roll-off, however, the envelope broadening is large and increases with frequency, and the scattering attenuation is strong and increases with frequency. As a preliminary study, we compare synthetic wavelet envelopes with the average of FD simulation wavelet envelopes in 50 synthesized random media, which are characterized by the RMS fractional velocity fluctuation ε = 0.05, correlation scale a = 5 km and the background wave velocity V0 = 4 km s-1. We use the radiation
NASA Astrophysics Data System (ADS)
Dekker, T.; de Zwart, S. T.; Willemsen, O. H.; Hiddink, M. G. H.; IJzerman, W. L.
2006-02-01
A prerequisite for a wide market acceptance of 3D displays is the ability to switch between 3D and full resolution 2D. In this paper we present a robust and cost effective concept for an auto-stereoscopic switchable 2D/3D display. The display is based on an LCD panel, equipped with switchable LC-filled lenticular lenses. We will discuss 3D image quality, with the focus on display uniformity. We show that slanting the lenticulars in combination with a good lens design can minimize non-uniformities in our 20" 2D/3D monitors. Furthermore, we introduce fractional viewing systems as a very robust concept to further improve uniformity in the case slanting the lenticulars and optimizing the lens design are not sufficient. We will discuss measurements and numerical simulations of the key optical characteristics of this display. Finally, we discuss 2D image quality, the switching characteristics and the residual lens effect.
Numerical simulation of in situ bioremediation
Travis, B.J.
1998-12-31
Models that couple subsurface flow and transport with microbial processes are an important tool for assessing the effectiveness of bioremediation in field applications. A numerical algorithm is described that differs from previous in situ bioremediation models in that it includes: both vadose and groundwater zones, unsteady air and water flow, limited nutrients and airborne nutrients, toxicity, cometabolic kinetics, kinetic sorption, subgridscale averaging, pore clogging and protozoan grazing.
Numerical Simulation of Chemically Reacting Flows
2015-09-03
interest to the Air Force. 15. SUBJECT TERMS Numerical methods, Diffusion Flames, Adaptive Gridding, Velocity-Vorticity, Compact Methods 16...robust unst tions, and s ’ unstructur acobian, as g in 2012, th ploy a full convergenc ory-efficien potentially grid adapts , he computat...the multiple-scale discretizations are precomputed (each time the grid adapts ) to save CPU time later during residual formation, and that additional
Numerical characteristics of quantum computer simulation
NASA Astrophysics Data System (ADS)
Chernyavskiy, A.; Khamitov, K.; Teplov, A.; Voevodin, V.; Voevodin, Vl.
2016-12-01
The simulation of quantum circuits is significantly important for the implementation of quantum information technologies. The main difficulty of such modeling is the exponential growth of dimensionality, thus the usage of modern high-performance parallel computations is relevant. As it is well known, arbitrary quantum computation in circuit model can be done by only single- and two-qubit gates, and we analyze the computational structure and properties of the simulation of such gates. We investigate the fact that the unique properties of quantum nature lead to the computational properties of the considered algorithms: the quantum parallelism make the simulation of quantum gates highly parallel, and on the other hand, quantum entanglement leads to the problem of computational locality during simulation. We use the methodology of the AlgoWiki project (algowiki-project.org) to analyze the algorithm. This methodology consists of theoretical (sequential and parallel complexity, macro structure, and visual informational graph) and experimental (locality and memory access, scalability and more specific dynamic characteristics) parts. Experimental part was made by using the petascale Lomonosov supercomputer (Moscow State University, Russia). We show that the simulation of quantum gates is a good base for the research and testing of the development methods for data intense parallel software, and considered methodology of the analysis can be successfully used for the improvement of the algorithms in quantum information science.
Numerical simulation of hemorrhage in human injury
NASA Astrophysics Data System (ADS)
Chong, Kwitae; Jiang, Chenfanfu; Santhanam, Anand; Benharash, Peyman; Teran, Joseph; Eldredge, Jeff
2015-11-01
Smoothed Particle Hydrodynamics (SPH) is adapted to simulate hemorrhage in the injured human body. As a Lagrangian fluid simulation, SPH uses fluid particles as computational elements and thus mass conservation is trivially satisfied. In order to ensure anatomical fidelity, a three-dimensional reconstruction of a portion of the human body -here, demonstrated on the lower leg- is sampled as skin, bone and internal tissue particles from the CT scan image of an actual patient. The injured geometry is then generated by simulation of ballistic projectiles passing through the anatomical model with the Material Point Method (MPM) and injured vessel segments are identified. From each such injured segment, SPH is used to simulate bleeding, with inflow boundary condition obtained from a coupled 1-d vascular tree model. Blood particles interact with impermeable bone and skin particles through the Navier-Stokes equations and with permeable internal tissue particles through the Brinkman equations. The SPH results are rendered in post-processing for improved visual fidelity. The overall simulation strategy is demonstrated on several injury scenarios in the lower leg.
Numerical simulation of magmatic hydrothermal systems
Ingebritsen, S.E.; Geiger, S.; Hurwitz, S.; Driesner, T.
2010-01-01
The dynamic behavior of magmatic hydrothermal systems entails coupled and nonlinear multiphase flow, heat and solute transport, and deformation in highly heterogeneous media. Thus, quantitative analysis of these systems depends mainly on numerical solution of coupled partial differential equations and complementary equations of state (EOS). The past 2 decades have seen steady growth of computational power and the development of numerical models that have eliminated or minimized the need for various simplifying assumptions. Considerable heuristic insight has been gained from process-oriented numerical modeling. Recent modeling efforts employing relatively complete EOS and accurate transport calculations have revealed dynamic behavior that was damped by linearized, less accurate models, including fluid property control of hydrothermal plume temperatures and three-dimensional geometries. Other recent modeling results have further elucidated the controlling role of permeability structure and revealed the potential for significant hydrothermally driven deformation. Key areas for future reSearch include incorporation of accurate EOS for the complete H2O-NaCl-CO2 system, more realistic treatment of material heterogeneity in space and time, realistic description of large-scale relative permeability behavior, and intercode benchmarking comparisons. Copyright 2010 by the American Geophysical Union.
A numerical simulation of auroral ionospheric electrodynamics
NASA Technical Reports Server (NTRS)
Mallinckrodt, A. J.
1985-01-01
A computer simulation of auroral ionospheric electrodynamics in the altitude range 80 to 250 km has been developed. The routine will either simulate typical electron precipitation profiles or accept observed data. Using a model background ionosphere, ion production rates are calculated from which equilibrium electron densities and the Hall and Pedersen conductivities may be determined. With the specification of suitable boundary conditions, the entire three-dimensional current system and electric field may be calculated within the simulation region. The results of the application of the routine to a typical inverted-V precipitation profile are demonstrated. The routine is used to explore the observed anticorrelation between electric field magnitude and peak energy in the precipitating electron spectrum of an auroral arc.
20 and 3D Numerical Simulations of Flux Cancellation
NASA Technical Reports Server (NTRS)
Karpen, Judith T.; DeVore, C.; Antiochos, S. K.; Linton, M. G.
2009-01-01
Cancellation of magnetic flux in the solar photosphere and chromosphere has been linked observationally and theoretically to a broad range of solar activity, from filament channel formation to CME initiation. Because this phenomenon is typically measured at only a single layer in the atmosphere, in the radial (line of sight) component of the magnetic field, the actual processes behind this observational signature are ambiguous. It is clear that reconnection is involved in some way, but the location of the reconnection sites and associated connectivity changes remain uncertain in most cases. We are using numerical modeling to demystify flux cancellation, beginning with the simplest possible configuration: a subphotospheric Lundquist flux tube surrounded by a potential field, immersed in a gravitationally stratified atmosphere, spanning many orders of magnitude in plasma beta. In this system, cancellation is driven slowly by a 2-cell circulation pattern imposed in the convection zone, such that the tops of the cells are located around the beta= 1 level (Le., the photosphere) and the flows converge and form a downdraft at the polarity inversion line; note however that no flow is imposed along the neutral line. We will present the results of 2D and 3D MHD-AMR simulations of flux cancellation, in which the flux at the photosphere begins in either an unsheared or sheared state. In all cases, a lOW-lying flux rope is formed by reconnection at the polarity inversion line within a few thousand seconds. The flux rope remains stable and does not rise, however, in contrast to models which do not include the presence of significant mass loading.
Numerical simulations of superluminous supernovae of type IIn
NASA Astrophysics Data System (ADS)
Dessart, Luc; Audit, Edouard; Hillier, D. John
2015-06-01
We present numerical simulations that include 1D Eulerian multigroup radiation-hydrodynamics, 1D non-local thermodynamic equilibrium (non-LTE) radiative transfer, and 2D polarized radiative transfer for superluminous interacting supernovae (SNe). Our reference model is a ˜10 M⊙ inner shell with 1051 erg ramming into an ˜3 M⊙ cold outer shell (the circumstellar medium, or CSM) that extends from 1015 to 2 × 1016 cm and moves at 100 km s-1. We discuss the light-curve evolution, which cannot be captured adequately with a grey approach. In this type of interactions, the shock-crossing time through the optically thick CSM is much longer than the photon diffusion time. Radiation is thus continuously leaking from the shock through the CSM. This configuration is distinct from the shell-shocked model. Our spectra redden with time, with a peak distribution in the near-UV during the first month gradually shifting to the optical range over the following year. Initially, Balmer lines exhibit a narrow line core and the broad line wings that are characteristic of electron scattering in the SNe IIn atmospheres (CSM). At later times, they also exhibit a broad blue-shifted component which arises from the cold dense shell. Our model results are broadly consistent with the bolometric light curve and spectral evolution observed for SN 2010jl. Invoking a prolate pole-to-equator density ratio in the CSM, we can also reproduce the ˜2 per cent continuum polarization, and line depolarization, observed in SN 2010jl. By varying the inner shell kinetic energy and the mass and extent of the outer shell, a large range of peak luminosities and durations, broadly compatible with superluminous SNe IIn like 2010jl or 2006gy, can be produced.
A Computing Cluster for Numerical Simulation
2006-10-23
34Contact and Friction for Cloth Animation", SIGGRAPH 2002, ACM TOG 21, 594-603 (2002). "* [BHTF] Bao, Z., Hong, J.-M., Teran , J. and Fedkiw, R...Simulation of Large Bodies of Water by Coupling Two and Three Dimensional Techniques", SIGGRAPH 2006, ACM TOG 25, 805-811 (2006). "* [ITF] Irving, G., Teran ...O’Brien (2006) "* [TSBNLF] Teran , J., Sifakis, E., Blemker, S., Ng Thow Hing, V., Lau, C. and Fedkiw, R., "Creating and Simulating Skeletal Muscle from the
NASA Astrophysics Data System (ADS)
Lembege, B.; Savoini, P.; Stienlet, J.
2013-05-01
Two distinct ion populations backstreaming into the solar wind have been clearly evidenced by various space missions within the quasi-perpendicular region of the ion foreshock located upstream of the Earth's Bow shock (i.e. for 45° ≤ Theta_Bn ≤ 90°, where Theta_Bn is the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned ion beams (« FAB ») characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions («GPB »), characterized by a NON gyrotropic distribution. The origin of these backstreaming ions has not been clearly identified and is presently analyzed with the help of 2D PIC simulation of a curved shock, where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described within a self consistent approach. Present simulations evidence that these two populations can be effectively created directly by the shock front without invoking microinstabilities. The analysis of both individual and statistical ion trajectories evidences that: (i) two new parameters, namely the interaction time DT_inter and distance of penetration L_depth into the shock wave, play a key role and allow to discriminate these two populations. "GPB" population is characterized by a very short interaction time (DT_inter = 1 to 2 Tci) in comparison to the "FAB" population (DT_inter = 2 Tci to 10 Tci) which moves back and forth between the upstream edge of the shock front and the overshoot, where tci is the upstream ion gyroperiod. (ii) the importance of the injection angle (i.e. the angle between the normal of the shock front and the gyration velocity when ions reach the shock) to understand how the reflection process takes place. (iii) "FAB" population drifts along the curved shock front scanning a large Theta_Bn range from 90°. (iv) "GPB" population is embedded within the "FAB" population near the shock front which explains the difficulty to identify such a population in the experimental
Numerical simulation of cross field amplifiers
Eppley, K.
1990-01-01
Cross field amplifiers (CFA) have been used in many applications where high power, high frequency microwaves are needed. Although these tubes have been manufactured for decades, theoretical analysis of their properties is not as highly developed as for other microwave devices such as klystrons. One feature distinguishing cross field amplifiers is that the operating current is produced by secondary emission from a cold cathode. This removes the need for a heater and enables the device to act as a switch tube, drawing no power until the rf drive is applied. However, this method of generating the current does complicate the simulation. We are developing a simulation model of cross field amplifiers using the PIC code CONDOR. We simulate an interaction region, one traveling wavelength long, with periodic boundary conditions. An electric field with the appropriate phase velocity is imposed on the upper boundary of the problem. Evaluation of the integral of E{center dot}J gives the power interchanged between the wave and the beam. Given the impedance of the structure, we then calculate the change in the traveling wave field. Thus we simulate the growth of the wave through the device. The main advance of our model over previous CFA simulations is the realistic tracking of absorption and secondary emission. The code uses experimental curves to calculate secondary production as a function of absorbed energy, with a theoretical expression for the angular dependence. We have used this code to model the 100 MW X-band CFA under construction at SLAC, as designed by Joseph Feinstein and Terry Lee. We are examining several questions of practical interest, such as the power and spectrum of absorbed electrons, the minimum traveling wave field needed to initiate spoke formation, and the variation of output power with dc voltage, anode-cathode gap, and magnetic field. 5 refs., 8 figs.
Brush seal numerical simulation: Concepts and advances
NASA Technical Reports Server (NTRS)
Braun, M. J.; Kudriavtsev, V. V.
1994-01-01
The development of the brush seal is considered to be most promising among the advanced type seals that are presently in use in the high speed turbomachinery. The brush is usually mounted on the stationary portions of the engine and has direct contact with the rotating element, in the process of limiting the 'unwanted' leakage flows between stages, or various engine cavities. This type of sealing technology is providing high (in comparison with conventional seals) pressure drops due mainly to the high packing density (around 100 bristles/sq mm), and brush compliance with the rotor motions. In the design of modern aerospace turbomachinery leakage flows between the stages must be minimal, thus contributing to the higher efficiency of the engine. Use of the brush seal instead of the labyrinth seal reduces the leakage flow by one order of magnitude. Brush seals also have been found to enhance dynamic performance, cost less, and are lighter than labyrinth seals. Even though industrial brush seals have been successfully developed through extensive experimentation, there is no comprehensive numerical methodology for the design or prediction of their performance. The existing analytical/numerical approaches are based on bulk flow models and do not allow the investigation of the effects of brush morphology (bristle arrangement), or brushes arrangement (number of brushes, spacing between them), on the pressure drops and flow leakage. An increase in the brush seal efficiency is clearly a complex problem that is closely related to the brush geometry and arrangement, and can be solved most likely only by means of a numerically distributed model.
Roux, Emmanuel; Ramalli, Alessandro; Tortoli, Piero; Cachard, Christian; Robini, Marc C; Liebgott, Herve
2016-12-01
Full matrix arrays are excellent tools for 3-D ultrasound imaging, but the required number of active elements is too high to be individually controlled by an equal number of scanner channels. The number of active elements is significantly reduced by the sparse array techniques, but the position of the remaining elements must be carefully optimized. This issue is faced here by introducing novel energy functions in the simulated annealing (SA) algorithm. At each iteration step of the optimization process, one element is freely translated and the associated radiated pattern is simulated. To control the pressure field behavior at multiple depths, three energy functions inspired by the pressure field radiated by a Blackman-tapered spiral array are introduced. Such energy functions aim at limiting the main lobe width while lowering the side lobe and grating lobe levels at multiple depths. Numerical optimization results illustrate the influence of the number of iterations, pressure measurement points, and depths, as well as the influence of the energy function definition on the optimized layout. It is also shown that performance close to or even better than the one provided by a spiral array, here assumed as reference, may be obtained. The finite-time convergence properties of SA allow the duration of the optimization process to be set in advance.
High order hybrid numerical simulations of two dimensional detonation waves
NASA Technical Reports Server (NTRS)
Cai, Wei
1993-01-01
In order to study multi-dimensional unstable detonation waves, a high order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves was developed. The numerical algorithm uses a multi-domain approach so different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A yields B. Several cases of unstable two dimensional detonation waves are simulated and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity in order to obtain the correct cellular patterns.
Numerical simulation of vortex-wedge interaction
NASA Astrophysics Data System (ADS)
Park, Jin-Ho; Lee, Duck-Joo
1994-06-01
Interactions between vortical flows and a solid surface cause one of the primary sources of noise and unsteady loading. The mechanism of the interaction is studied numerically for a single Rankine vortex impinging upon a wedge. An Euler-Lagrangian method is employed to calculate the unsteady, viscous, incompressible flows in two dimensions. A random vortex method is used to describe the vorticity dominant field. A fast vortex method is used to reduce the computational time in the calculation of the convection velocity of each vortex particle. A Schwarz-Christoffel transformation is used to map the numerical domain onto the physical domain. Vortex partical plots, velocity vectors, and streamlines are presented at selected times for both inviscid and viscous interactions. It is observed that the incident rankine vortex distorts and is split by the wedge as it nears and passes the wedge, and the vortices generated from the leading edge toward the underside of the wedge form into a single vortex. The vorticity orientation of the shed vortex is opposite to that of the incident vortex. It is found that the convection velocity of the shed vortex is changed wheen it comes off the leading edge of the wedge, and the strength of the shed vortex varies with the time during the vortex-wedge interaction. This strength variation is presumed to influence the shed vortex convection velocity. The overall features for the interaction agree well with the experimental results of Ziada and Rockwell.
Representation of wells in numerical reservoir simulation
Ding, Y.; Renard, G.; Weill, L.
1995-12-31
In reservoir simulation, linear approximations are generally used for well modeling. However, this type of approximations can be inaccurate for fluid flow calculation in the vicinity of wells leading to incorrect well performance predictions. To overcome such problems, a new well representation has been proposed that uses a ``logarithmic`` type of approximation for vertical wells. In this paper, it is shown how the new well model can be easily implemented in existing simulator through the conventional PI. The relationship between wellbore pressure, wellblock pressure and flow rate is discussed in more detail, especially for the definition of wellblock pressure. Extension of the new approach to off-center wells and to flexible grids are both presented. Through this extension, the equivalence of various gridding techniques for the well model is emphasized. The key element is the accurate calculation of flow components in the vicinity of wells.
Studying Spacecraft Charging via Numerical Simulations
NASA Astrophysics Data System (ADS)
Delzanno, G. L.; Moulton, D.; Meierbachtol, C.; Svyatskiy, D.; Vernon, L.
2015-12-01
The electrical charging of spacecraft due to bombarding charged particles can affect their performance and operation. We study this charging using CPIC; a particle-in-cell code specifically designed for studying plasma-material interactions [1]. CPIC is based on multi-block curvilinear meshes, resulting in near-optimal computational performance while maintaining geometric accuracy. Relevant plasma parameters are imported from the SHIELDS framework (currently under development at LANL), which simulates geomagnetic storms and substorms in the Earth's magnetosphere. Simulated spacecraft charging results of representative Van Allen Probe geometries using these plasma parameters will be presented, along with an overview of the code. [1] G.L. Delzanno, E. Camporeale, J.D. Moulton, J.E. Borovsky, E.A. MacDonald, and M.F. Thomsen, "CPIC: A Curvilinear Particle-In-Cell Code for Plasma-Material Interaction Studies," IEEE Trans. Plas. Sci., 41 (12), 3577 (2013).
Numerical Simulation of Ion Thruster Optics
NASA Technical Reports Server (NTRS)
Rawlin, Vincent K. (Technical Monitor); Farnell, Cody C.; Williams, John D.; Wilbur, Paul J.
2003-01-01
A three-dimensional simulation code (ffx) designed to analyze ion thruster optics is described. It is an extension of an earlier code and includes special features like the ability to model a wide range of grid geometries, cusp details, and mis-aligned aperture pairs to name a few. However, the principle reason for advancing the code was in the study of ion optics erosion. Ground based testing of ion thruster optics, essential to the understanding of the processes of grid erosion, can be time consuming and costly. Simulation codes that can accurately predict grid lifetimes and the physical mechanisms of grid erosion can be of great utility in the development of future ion thruster optics designed for more ambitious applications. Results of simulations are presented that describe wear profiles for several standard and nonstandard aperture geometries, such as those grid sets with square- or slotted-hole layout patterns. The goal of this paper will be to introduce the methods employed in the ffx code and to briefly demonstrate their use.
NASA Astrophysics Data System (ADS)
Kaus, B. J.
2007-12-01
The processes that generate stress in the lithosphere are incompletely understood. Whereas it is obvious that lithospheric deformation (and topography) is ultimately caused by cooling of the Earth from the time of formation, it is less clear how lithospheric deformation is coupled to mantle flow and how this affect stresses. Part of this is due to the somewhat complicated rheology of the lithosphere, which varies from brittle (elastoplastic) to ductile (viscous). In addition, vertical layering of the lithosphere may give rise to instabilities which affect its dynamics and stress evolution in a non-trivial manner. Obtaining a better insight in these processes thus requires numerical tools that can model the mantle-lithosphere system in a self-consistent manner (i.e. in a single computational domain) including topographic effects (i.e. free surface) and viscoelastoplastic rheologies. I have recently developed 2-D and 3-D numerical tools that incorporate the above mentioned features. Here I focus on a number of case studies to illustrate how differences in rheology and boundary conditions alter the dynamics and in particular the stress evolution of the lithosphere. Instabilities such as bending or buckling of compressed lithosphere reduce the average stress ('structural weakening"). Viscoelasticity results in time- dependencies, which are particularly pronounced in highly viscous parts of the lithosphere (e.g. the mantle lithosphere). Strong parts of the lithospere thus don't necessarily have large differential stresses (and earthquakes). The Christmas-tree approximation should therefore be used with care to infer stress levels in the lithosphere. Finally I will illustrate differences in stresses between "kinematically-driven" and "internally-driven" lithospheric- scale deformation models.
NASA Astrophysics Data System (ADS)
Liu, Yun; Wang, Xu-Ben; Wang, Yun
2013-06-01
To effectively minimize the electromagnetic field response in the total field solution, we propose a numerical modeling method for the two-dimensional (2D) timedomain transient electromagnetic secondary field of the line source based on the DuFort-Frankel finite-difference method. In the proposed method, we included the treatment of the earth-air boundary conductivity, calculated the normalized partial derivative of the induced electromotive force (Emf), and determined the forward time step. By extending upward the earth-air interface to the air grid nodes and the zero-value boundary conditions, not only we have a method that is more efficient but also simpler than the total field solution. We computed and analyzed the homogeneous half-space model and the flat layered model with high precision—the maximum relative error is less than 0.01% between our method and the analytical method—and the solution speed is roughly three times faster than the total-field solution. Lastly, we used the model of a thin body embedded in a homogeneous half-space at different delay times to depict the downward and upward spreading characteristics of the induced eddy current, and the physical interaction processes between the electromagnetic field and the underground low-resistivity body.
NASA Astrophysics Data System (ADS)
Zhou, Huai-Chun; Ai, Yu-Hua
2006-09-01
Both light and heat are produced during a chemical reaction in a combustion process, but traditionally all the energy released is taken as to be transformed into the internal energy of the combustion medium. So the temperature of the medium increases, and then the thermal radiation emitted from it increases too. Chemiluminescence is generated during a chemical reaction and independent of the temperature, and has been used widely for combustion diagnostics. It was assumed in this paper that the total energy released in a combustion reaction is divided into two parts, one part is a self-absorbed heat, and the other is a directly emitted heat. The former is absorbed immediately by the products, becomes the internal energy and then increases the temperature of the products as treated in the traditional way. The latter is emitted directly as radiation into the combustion domain and should be included in the radiation transfer equation (RTE) as a part of radiation source. For a simple, 2-D, gray, emitting absorbing, rectangular system, the numerical study showed that the temperatures in reaction zones depended on the fraction of the directly emitted energy, and the smaller the gas absorption coefficient was, the more strong the dependence appeared. Because the effect of the fraction of the directly emitted heat on the temperature distribution in the reacting zones for gas combustion is significant, it is required to conduct experimental measurements to determine the fraction of self-absorbed heat for different combustion processes.
Classical MHD shocks: theory and numerical simulation
Pogorelov, Nikolai V.
2005-08-01
Recent results are surveyed in the investigation of the behavior of shocks in ideal magnetohydrodynamics (MHD) and corresponding structures in dissipative/resistive plasma flows. In contrast to evolutionary shocks, a solution of the problem of the nonevolutionary shock interaction with small perturbations is either nonunique or does not exist. The peculiarity of non-ideal MHD is in that some nonevolutionary shocks have dissipative structures. Since this structure is always non-plane, it can reveal itself in problems where transverse perturbations do not exist due to symmetries restrictions. We discuss the numerical behavior of nonevolutionary shocks and argue that they necessarily disappear once the problem is solved in a genuinely three-dimensional statement.
Vector Potential Generation for Numerical Relativity Simulations
NASA Astrophysics Data System (ADS)
Silberman, Zachary; Faber, Joshua; Adams, Thomas; Etienne, Zachariah; Ruchlin, Ian
2017-01-01
Many different numerical codes are employed in studies of highly relativistic magnetized accretion flows around black holes. Based on the formalisms each uses, some codes evolve the magnetic field vector B, while others evolve the magnetic vector potential A, the two being related by the curl: B=curl(A). Here, we discuss how to generate vector potentials corresponding to specified magnetic fields on staggered grids, a surprisingly difficult task on finite cubic domains. The code we have developed solves this problem in two ways: a brute-force method, whose scaling is nearly linear in the number of grid cells, and a direct linear algebra approach. We discuss the success both algorithms have in generating smooth vector potential configurations and how both may be extended to more complicated cases involving multiple mesh-refinement levels. NSF ACI-1550436
Numerical simulation of electrophoresis separation processes
NASA Technical Reports Server (NTRS)
Ganjoo, D. K.; Tezduyar, T. E.
1986-01-01
A new Petrov-Galerkin finite element formulation has been proposed for transient convection-diffusion problems. Most Petrov-Galerkin formulations take into account the spatial discretization, and the weighting functions so developed give satisfactory solutions for steady state problems. Though these schemes can be used for transient problems, there is scope for improvement. The schemes proposed here, which consider temporal as well as spatial discretization, provide improved solutions. Electrophoresis, which involves the motion of charged entities under the influence of an applied electric field, is governed by equations similiar to those encountered in fluid flow problems, i.e., transient convection-diffusion equations. Test problems are solved in electrophoresis and fluid flow. The results obtained are satisfactory. It is also expected that these schemes, suitably adapted, will improve the numerical solutions of the compressible Euler and the Navier-Stokes equations.
Numerical simulation of ac plasma arc thermodynamics
NASA Astrophysics Data System (ADS)
Wu, Han-Ming; Carey, G. F.; Oakes, M. E.
1994-05-01
A mathematical model and approximate analysis for the energy distribution of an ac plasma arc with a moving boundary is developed. A simplified electrical conductivity function is assumed so that the dynamic behavior of the arc may be determined, independent of the gas type. The model leads to a reduced set of non-linear partial differential equations which governs the quasi-steady ac arc. This system is solved numerically and it is found that convection plays an important role, not only in the temperature distribution, but also in arc disruptions. Moreover, disruptions are found to be influenced by convection only for a limited frequency range. The results of the present studies are applicable to the frequnecy range of 10-10(exp 2) Hz which includes most industry ac arc frequencies.
Numerical Simulation of AC Plasma Arc Thermodynamics
NASA Astrophysics Data System (ADS)
Wu, Han-Ming; Carey, G. F.; Oakes, M. E.
1994-05-01
A mathematical model and approximate analysis for the energy distribution of an ac plasma arc with a moving boundary is developed. A simplified electrical conductivity function is assumed so that the dynamic behavior of the arc may be determined, independent of the gas type. The model leads to a reduced set of non-linear partial differential equations which governs the quasi-steady ac arc. This system is solved numerically and it is found that convection plays an important role, not only in the temperature distribution, but also in arc disruptions. Moreover, disruptions are found to be influenced by convection only for a limited frequency range. The results of the present studies are applicable to the frequency range of 10-102 Hz which includes most industry ac arc frequencies.
Numerical Simulation of Transition in Hypersonic Boundary Layers
2011-02-01
T∗∞=103.6K, flat plate. . . . . . . . . 139 6.1 Boundary layer edge Reynolds number as a function of downstream posi- tion for the computed baseflow...200 7.1 Computational domain used for Temporal Direct Numerical Simulations. 205 7.2 Comparison of base flow profiles at downstream location...the computational methods used for all direct numerical simulations (DNS) discussed in this report are presented. The results for a flat plate (Chapter
Floret Test, Numerical Simulations of the Dent, Comparison with Experiments
Lefrancois, A.; Cutting, J.; Gagliardi, F.; Tarver, C.; Tran, T.
2006-02-14
The Floret test has been developed as a screening test to study the performance of a small amount of HE. Numerical simulations have been performed recently using CTH. The objective of this study is to perform numerical simulations in order to better understand the shock waves interactions, involved in the dent formation. Different 3D wedge configurations have been tested using the Ignition and Growth reactive flow model for the HE receptor with Ls-Dyna.
Numerical simulation of turbulent flows around airfoil and wing
NASA Technical Reports Server (NTRS)
Marx, Yves P.
1990-01-01
During the last years the simulation of compressible viscous flows has received much attention. While the numerical methods were improved drastically, a satisfactory modeling of the Reynolds stresses is still missing. In this paper, after a short description of the numerical procedure used for solving the Reynolds equations, experiments with a promising simple turbulence model are discussed.
The numerical simulation of multistage turbomachinery flows
NASA Technical Reports Server (NTRS)
Adamczyk, J. J.; Beach, T. A.; Celestina, M. L.; Mulac, R. A.; To, W. M.
1990-01-01
The need to account for momentum and energy transport by the unsteady deterministic flow field in modeling the time-averaged flow state within a blade row passage embedded in a multistage compressor is assessed. It was found that, within the endwall regions, large-scale three-dimensional unsteady structures existed which caused significant transport of momentum and energy across the time-averaged stream surface of a stator flow field. These experiments confirmed that the tranport process is dominated by turbulent diffusion in the midspan region. A model was then proposed for simulating this transport process, and a limited study was undertaken to assess its validity.
NASA Astrophysics Data System (ADS)
Fuchsluger, Martin; Götzl, Gregor
2014-05-01
In general most aquifers have a much larger lateral extent than vertical. This fact leads to the application of the Dupuit-Forchheimer assumptions to many groundwater problems, whereas a two dimensional simulation is considered sufficient. By coupling transient fluid flow modeling with heat transport the 2D aquifer approximation is in many cases insufficient as it does not consider effects of the subjacent and overlying aquitards on heat propagation as well as the impact of surface climatic effects on shallow aquifers. A shallow Holocene aquifer in Vienna served as a case study to compare different modeling approaches in two and three dimensions in order to predict the performance and impact of a thermal aquifer utilization for heating (1.3 GWh) and cooling (1.4 GWh) of a communal building. With the assumption of a 6 doublets well field, the comparison was realized in three steps: At first a two dimensional model for unconfined flow was set up, assuming a varying hydraulic conductivity as well as a varying top and bottom elevation of the aquifer (gross - thickness). The model area was chosen along constant hydraulic head at steady state conditions. A second model was made by mapping solely the aquifer in three dimensions using the same subdomain and boundary conditions as defined in step one. The third model consists of a complete three dimensional geological build-up including the aquifer as well as the overlying and subjacent layers and additionally an annually variable climatic boundary condition at the surface. The latter was calibrated with measured water temperature at a nearby water gauge. For all three models the same annual operating mode of the 6 hydraulic doublets was assumed. Furthermore a limited maximal groundwater temperature at a range between 8 and 18 °C as well as a constrained well flow rate has been given. Finally a descriptive comparison of the three models concerning the extracted thermal power, drawdown, temperature distribution and Darcy
Numerical simulation of the SOFIA flowfield
NASA Technical Reports Server (NTRS)
Klotz, Stephen P.
1994-01-01
This report provides a concise summary of the contribution of computational fluid dynamics (CFD) to the SOFIA (Stratospheric Observatory for Infrared Astronomy) project at NASA Ames and presents results obtained from closed- and open-cavity SOFIA simulations. The aircraft platform is a Boeing 747SP and these are the first SOFIA simulations run with the aircraft empennage included in the geometry database. In the open-cavity run the telescope is mounted behind the wings. Results suggest that the cavity markedly influences the mean pressure distribution on empennage surfaces and that 110-140 decibel (db) sound pressure levels are typical in the cavity and on the horizontal and vertical stabilizers. A strong source of sound was found to exist on the rim of the open telescope cavity. The presence of this source suggests that additional design work needs to be performed in order to minimize the sound emanating from that location. A fluid dynamic analysis of the engine plumes is also contained in this report. The analysis was part of an effort to quantify the degradation of telescope performance resulting from the proximity of the port engine exhaust plumes to the open telescope bay.
Numerical simulation of the SOFIA flow field
NASA Technical Reports Server (NTRS)
Klotz, Stephen P.
1995-01-01
This report provides a concise summary of the contribution of computational fluid dynamics (CFD) to the SOFIA (Stratospheric Observatory for Infrared Astronomy) project at NASA Ames and presents results obtained from closed- and open-cavity SOFIA simulations. The aircraft platform is a Boeing 747SP and these are the first SOFIA simulations run with the aircraft empennage included in the geometry database. In the open-cavity runs the telescope is mounted behind the wings. Results suggest that the cavity markedly influences the mean pressure distribution on empennage surfaces and that 110-140 decibel (db) sound pressure levels are typical in the cavity and on the horizontal and vertical stabilizers. A strong source of sound was found to exist on the rim of the open telescope cavity. The presence of this source suggests that additional design work needs to be performed in order to minimize the sound emanating from that location. A fluid dynamic analysis of the engine plumes is also contained in this report. The analysis was part of an effort to quantify the degradation of telescope performance resulting from the proximity of the port engine exhaust plumes to the open telescope bay.
Numerical and laboratory simulations of auroral acceleration
Gunell, H.; De Keyser, J.; Mann, I.
2013-10-15
The existence of parallel electric fields is an essential ingredient of auroral physics, leading to the acceleration of particles that give rise to the auroral displays. An auroral flux tube is modelled using electrostatic Vlasov simulations, and the results are compared to simulations of a proposed laboratory device that is meant for studies of the plasma physical processes that occur on auroral field lines. The hot magnetospheric plasma is represented by a gas discharge plasma source in the laboratory device, and the cold plasma mimicking the ionospheric plasma is generated by a Q-machine source. In both systems, double layers form with plasma density gradients concentrated on their high potential sides. The systems differ regarding the properties of ion acoustic waves that are heavily damped in the magnetosphere, where the ion population is hot, but weakly damped in the laboratory, where the discharge ions are cold. Ion waves are excited by the ion beam that is created by acceleration in the double layer in both systems. The efficiency of this beam-plasma interaction depends on the acceleration voltage. For voltages where the interaction is less efficient, the laboratory experiment is more space-like.
Numerical Simulations of the Mechanics of Vitrectomy
NASA Astrophysics Data System (ADS)
Young, Ethan; Eldredge, Jeff; Hubschman, Jean-Pierre
2015-11-01
Vitreous is the clear, gel-like substance that fills the cavity between the lens and retina in the eye. Treating certain eye abnormalities requires removing this substance using a minimally-invasive device called a vitreous cutter. Understanding the behavior of this viscoelastic biofluid during surgeries is essential to improving the effectiveness of the procedure. In this study, three-dimensional computational models of vitreous cutters are investigated using an immersed boundary method paired with a viscoelastic constitutive model. The solver uses a fractional-step method to satisfy continuity and traction boundary conditions to simulate the applied suction. The current work extends previous efforts to accurately model the rheological parameters measured by Sharif-Kashani et al. using the Giesekus constitutive equation [Retina, 2013]. The simulations were used to quantify both the average and time-varying flow rate through the device. Values for flow rate are compared with experimental results from Hubschman et al. [Retina, 2009]. Flow features associated with the cutting dynamics are of particular interest, as is the geometry of the cutter itself. These operational and design changes are a target for improving cutter efficacy while minimizing potential tissue damage.
NASA Astrophysics Data System (ADS)
Savoini, P.; Lembege, B.; Stienlet, J.
2012-04-01
The foreshock region is located upstream of the terrestrial bow shock and is characterized by energetic backstreaming particles (electrons and ions) issued from the shock and by an important wave activity as observed by many space missions. In order to analyse the foreshock region, a curved shock is simulated with the help of a 2 - D full particle (PIC) code, where full curvature and time of flight effects, and where both electrons and ions dynamics are fully described by a self consistent approach. The analysis is presently restricted to the quasi-perpendicular angular range defined by 45°≤ θBn ≤ 90°, where θBn is the angle between the shock normal and the upstream magnetostatic field, and we focus only on the ion foreshock. In a good agreement with experimental data, present preliminary results evidence two distinct ion populations collimated along the interplanetary magnetic field (IMF): (i) the Field-Aligned Beam population (hereafter named "FAB") and (ii) the gyro-phase bunch population (hereafter named "GPB") which differ from each other by their gyrotropic or non-gyrotropic behavior, respectively. Additionally, the "FAB" population is observed at the edge of the ion foreshock and near the curved shock front, while the "'GPB" population is observed deeper in the foreshock and further from the shock front. The analysis shows that no pitch angle scattering mechanism needs to be invoked to account for the generation of the "GPB", but rather additional criteria are necessary namely: the interaction time Δtint of backstreaming ions with the shock front and their downstream penetration depth. These criteria allow to evidence that (i) the "FAB" population corresponds to particles which move back and forth between the upstream edge of the front and the overshoot, and are characterized by a quite large Δtint (covering several local gyro-periods, 4 ≤ τci ≤ 12). In contrast, (ii) the "GPB" ions have suffered a very short interaction time (i.e. Δtint < 1
Allain, Ariane; Chauvot de Beauchêne, Isaure; Langenfeld, Florent; Guarracino, Yann; Laine, Elodie; Tchertanov, Luba
2014-01-01
Allostery is a universal phenomenon that couples the information induced by a local perturbation (effector) in a protein to spatially distant regulated sites. Such an event can be described in terms of a large scale transmission of information (communication) through a dynamic coupling between structurally rigid (minimally frustrated) and plastic (locally frustrated) clusters of residues. To elaborate a rational description of allosteric coupling, we propose an original approach - MOdular NETwork Analysis (MONETA) - based on the analysis of inter-residue dynamical correlations to localize the propagation of both structural and dynamical effects of a perturbation throughout a protein structure. MONETA uses inter-residue cross-correlations and commute times computed from molecular dynamics simulations and a topological description of a protein to build a modular network representation composed of clusters of residues (dynamic segments) linked together by chains of residues (communication pathways). MONETA provides a brand new direct and simple visualization of protein allosteric communication. A GEPHI module implemented in the MONETA package allows the generation of 2D graphs of the communication network. An interactive PyMOL plugin permits drawing of the communication pathways between chosen protein fragments or residues on a 3D representation. MONETA is a powerful tool for on-the-fly display of communication networks in proteins. We applied MONETA for the analysis of communication pathways (i) between the main regulatory fragments of receptors tyrosine kinases (RTKs), KIT and CSF-1R, in the native and mutated states and (ii) in proteins STAT5 (STAT5a and STAT5b) in the phosphorylated and the unphosphorylated forms. The description of the physical support for allosteric coupling by MONETA allowed a comparison of the mechanisms of (a) constitutive activation induced by equivalent mutations in two RTKs and (b) allosteric regulation in the activated and non
NASA Astrophysics Data System (ADS)
De Wilde, Juray; Lorant, Christophe; Descamps, Pierre
2017-04-01
In atmospheric-pressure plasma reactors, the flow dynamics can be complex, determine the reactor performance and complicate scale-up. Coupling computational fluid dynamics to the calculation of the electric field and plasma chemistry is challenging because of the numerical stiffness introduced by the difference in time scale of the different phenomena involved. Focusing on low-temperature, atmospheric-pressure pure nitrogen plasma, a model and model reduction based solution strategy to deal with the numerical stiffness are presented and evaluated. The influence of the electric field on the flow dynamics and species concentration fields is first qualitatively studied by means of 2D simulations of a sharp-end plate-to-plane configuration. Next, a specific reactor prototype for low-temperature, atmospheric-pressure plasma-enhanced chemical vapor deposition for in-line surface treatments is simulated to illustrate the importance of accounting for the detailed flow dynamics.
Numerical Simulations of a Flux Rope Ejection
NASA Astrophysics Data System (ADS)
Pagano, P.; Mackay, D. H.; Poedts, S.
2015-03-01
Coronal mass ejections (CMEs) are the most violent phenomena observed on the Sun. One of the most successful models to explain CMEs is the flux rope ejection model, where a magnetic flux rope is expelled from the solar corona after a long phase along which the flux rope stays in equilibrium while magnetic energy is being accumulated. However, still many questions are outstanding on the detailed mechanism of the ejection and observations continuously provide new data to interpret and put in the context. Currently, extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) are providing new insights into the early phase of CME evolution. In particular, observations show the ejection of magnetic flux ropes from the solar corona and how they evolve into CMEs. However, these observations are difficult to interpret in terms of basic physical mechanisms and quantities, thus, we need to compare equivalent quantities to test and improve our models. In our work, we intend to bridge the gap between models and observations with our model of flux rope ejection where we consistently describe the full life span of a flux rope from its formation to ejection. This is done by coupling the global non-linear force-free model (GNLFFF) built to describe the slow low- β formation phase, with a full MHD simulation run with the software MPI-AMRVAC, suitable to describe the fast MHD evolution of the flux rope ejection that happens in a heterogeneous β regime. We also explore the parameter space to identify the conditions upon which the ejection is favoured (gravity stratification and magnetic field intensity) and we produce synthesised AIA observations (171 Å and 211 Å). To carry this out, we run 3D MHD simulation in spherical coordinates where we include the role of thermal conduction and radiative losses, both of which are important for determining the temperature distribution of the solar corona during a CME. Our model of
Numerical Simulation of Supersonic Gap Flow
Jing, Xu; Haiming, Huang; Guo, Huang; Song, Mo
2015-01-01
Various gaps in the surface of the supersonic aircraft have a significant effect on airflows. In order to predict the effects of attack angle, Mach number and width-to-depth ratio of gap on the local aerodynamic heating environment of supersonic flow, two-dimensional compressible Navier-Stokes equations are solved by the finite volume method, where convective flux of space term adopts the Roe format, and discretization of time term is achieved by 5-step Runge-Kutta algorithm. The numerical results reveal that the heat flux ratio is U-shaped distribution on the gap wall and maximum at the windward corner of the gap. The heat flux ratio decreases as the gap depth and Mach number increase, however, it increases as the attack angle increases. In addition, it is important to find that chamfer in the windward corner can effectively reduce gap effect coefficient. The study will be helpful for the design of the thermal protection system in reentry vehicles. PMID:25635395
NASA Technical Reports Server (NTRS)
Gnoffo, Peter A.; Berry, Scott A.; VanNorman, John W.
2011-01-01
This paper is one of a series of five papers in a special session organized by the NASA Fundamental Aeronautics Program that addresses uncertainty assessments for CFD simulations in hypersonic flow. Simulations of a shock emanating from a compression corner and interacting with a fully developed turbulent boundary layer are evaluated herein. Mission relevant conditions at Mach 7 and Mach 14 are defined for a pre-compression ramp of a scramjet powered vehicle. Three compression angles are defined, the smallest to avoid separation losses and the largest to force a separated flow engaging more complicated flow physics. The Baldwin-Lomax and the Cebeci-Smith algebraic models, the one-equation Spalart-Allmaras model with the Catrix-Aupoix compressibility modification and two-equation models including Menter SST, Wilcox k-omega 98, and Wilcox k-omega 06 turbulence models are evaluated. Each model is fully defined herein to preclude any ambiguity regarding model implementation. Comparisons are made to existing experimental data and Van Driest theory to provide preliminary assessment of model form uncertainty. A set of coarse grained uncertainty metrics are defined to capture essential differences among turbulence models. Except for the inability of algebraic models to converge for some separated flows there is no clearly superior model as judged by these metrics. A preliminary metric for the numerical component of uncertainty in shock-turbulent-boundary-layer interactions at compression corners sufficiently steep to cause separation is defined as 55%. This value is a median of differences with experimental data averaged for peak pressure and heating and for extent of separation captured in new, grid-converged solutions presented here. This value is consistent with existing results in a literature review of hypersonic shock-turbulent-boundary-layer interactions by Roy and Blottner and with more recent computations of MacLean.
Numerical simulation of synthesis gas incineration
NASA Astrophysics Data System (ADS)
Kazakov, A. V.; Khaustov, S. A.; Tabakaev, R. B.; Belousova, Y. A.
2016-04-01
The authors have analysed the expediency of the suggested low-grade fuels application method. Thermal processing of solid raw materials in the gaseous fuel, called synthesis gas, is investigated. The technical challenges concerning the applicability of the existing gas equipment developed and extensively tested exclusively for natural gas were considered. For this purpose computer simulation of three-dimensional syngas-incinerating flame dynamics was performed by means of the ANSYS Multiphysics engineering software. The subjects of studying were: a three-dimensional aerodynamic flame structure, heat-release and temperature fields, a set of combustion properties: a flare range and the concentration distribution of burnout reagents. The obtained results were presented in the form of a time-averaged pathlines with color indexing. The obtained results can be used for qualitative and quantitative evaluation of complex multicomponent gas incineration singularities.
Numerical simulation of the world ocean circulation
NASA Technical Reports Server (NTRS)
Takano, K.; Mintz, Y.; Han, Y. J.
1973-01-01
A multi-level model, based on the primitive equations, is developed for simulating the temperature and velocity fields produced in the world ocean by differential heating and surface wind stress. The model ocean has constant depth, free slip at the lower boundary, and neglects momentum advection; so that there is no energy exchange between the barotropic and baroclinic components of the motion, although the former influences the latter through temperature advection. The ocean model was designed to be coupled to the UCLA atmospheric general circulation model, for the study of the dynamics of climate and climate changes. But here, the model is tested by prescribing the observed seasonally varying surface wind stress and the incident solar radiation, the surface air temperature and humidity, cloudiness and the surface wind speed, which, together with the predicted ocean surface temperature, determine the surface flux of radiant energy, sensible heat and latent heat.
Numerical aerodynamic simulation facility. Preliminary study extension
NASA Technical Reports Server (NTRS)
1978-01-01
The production of an optimized design of key elements of the candidate facility was the primary objective of this report. This was accomplished by effort in the following tasks: (1) to further develop, optimize and describe the function description of the custom hardware; (2) to delineate trade off areas between performance, reliability, availability, serviceability, and programmability; (3) to develop metrics and models for validation of the candidate systems performance; (4) to conduct a functional simulation of the system design; (5) to perform a reliability analysis of the system design; and (6) to develop the software specifications to include a user level high level programming language, a correspondence between the programming language and instruction set and outline the operation system requirements.
Numerical simulation of electrospray in the cone-jet mode.
Herrada, M A; López-Herrera, J M; Gañán-Calvo, A M; Vega, E J; Montanero, J M; Popinet, S
2012-08-01
We present a robust and computationally efficient numerical scheme for simulating steady electrohydrodynamic atomization processes (electrospray). The main simplification assumed in this scheme is that all the free electrical charges are distributed over the interface. A comparison of the results with those calculated with a volume-of-fluid method showed that the numerical scheme presented here accurately describes the flow pattern within the entire liquid domain. Experiments were performed to partially validate the numerical predictions. The simulations reproduced accurately the experimental shape of the liquid cone jet, providing correct values of the emitted electric current even for configurations very close to the cone-jet stability limit.
Numerical simulation of Glacial Isostatic Adjustment
NASA Astrophysics Data System (ADS)
Miglio, E.
2015-12-01
In the Earth's crust, stress can be subdivided into tectonic background stress, overburden pressure, and pore-fluid pressure. The superposition of the first two and the variation of the third part are key factors in controlling movement along faults. Furthermore, stresses due to sedimentation and erosion contribute to the total stress field. In deglaciated regions, an additional stress must be considered: the rebound stress, which is related to rebounding of the crust and mantle after deglaciation. During the growth of a continental ice sheet, the lithosphere under the iceload is deformed and the removal of the ice load during deglaciation initiates a rebound process. The uplift is well known in formerly glaciated areas, e.g.North America and Scandinavia, and in currently deglaciating areas, e.g.Alaska, Antarctica, and Greenland. The whole process of subsiding and uplifting during the growth and melting of an iceload and all related phenomena is known as glacial isostatic adjustment. During the process of glaciation, the surface of the lithosphere is depressed underneath the ice load and compressional flexural stresses are induced in the upper lithosphere, whereas the bottom of the lithosphere experiences extensional flexural stresses; an additional vertical stress due to the ice load is present and it decreases to zero during deglaciation. During rebound, flexural stresses relax slowly. These stresses are able to change the original stress directions and regime.In this work we aim to study the effect of the GIA process in the context of petroleum engineering. The main aspect we will focus on is the mathematical and numerical modeling of the GIA including thermal effects. We plan also to include a preliminary study of the effect of the glacial erosion. All these phenomena are of paramount importance in petroleum engineering: for example some reservoir have been depleted due to tilting caused by both GIA, erosion and thermal effects.
Numerical simulation of baroclinic Jovian vortices
NASA Technical Reports Server (NTRS)
Achterberg, Richard K.; Ingersoll, Andrew P.
1994-01-01
We examine the evolution of baroclinic vortices in a time-dependent, nonlinear numerical model of a Jovian atmosphere. The model uses a normal-mode expansion in the vertical, using the barotropic and first two baroclinic modes. Results for the stability of baroclinic vortices on an f plane in the absence of a mean zonal flow are similar to results of Earth vortex models, although the presence of a fluid interior on the Jovian planets shifts the stability boundaries to smaller length scales. The presence of a barotropic mean zonal flow in the interior stabilizes vortices against instability and significantly modifies the finite amplitude form of baroclinic instabilities. The effect of a zonal flow on a form of barotropic instability produces periodic oscillations in the latitude and longitude of the vortex as observed at the level of the cloud tops. This instability may explain some, but not all, observations of longitudinal oscillations of vortices on the outer planets. Oscillations in aspect ratio and orientation of stable vortices in a zonal shear flow are observed in this baroclinic model, as in simpler two-dimensional models. Such oscillations are also observed in the atmospheres of Jupiter and Neptune. The meridional propagation and decay of vortices on a beta plane is inhibited by the presence of a mean zonal flow. The direction of propagation of a vortex relative to the mean zonal flow depends upon the sign of the meridional potential vorticity gradient; combined with observations of vortex drift rates, this may provide a constraint on model assumption for the flow in the deep interior of the Jovian planets.
NASA Astrophysics Data System (ADS)
Juez, C.; Caviedes-Voullième, D.; Murillo, J.; García-Navarro, P.
2014-12-01
Dense granular flows are present in geophysics and in several industrial processes, which has lead to an increasing interest for the knowledge and understanding of the physics which govern their propagation. For this reason, a wide range of laboratory experiments on gravity-driven flows have been carried out during the last two decades. The present work is focused on geomorphological processes and, following previous work, a series of laboratory studies which constitute a further step in mimicking natural phenomena are described and simulated. Three situations are considered with some common properties: a two-dimensional configuration, variable slope of the topography and the presence of obstacles. The setup and measurement technique employed during the development of these experiments are deeply explained in the companion work. The first experiment is based on a single obstacle, the second one is performed against multiple obstacles and the third one studies the influence of a dike on which overtopping occurs. Due to the impact of the flow against the obstacles, fast moving shocks appear, and a variety of secondary waves emerge. In order to delve into the physics of these types of phenomena, a shock-capturing numerical scheme is used to simulate the cases. The suitability of the mathematical models employed in this work has been previously validated. Comparisons between computed and experimental data are presented for the three cases. The computed results show that the numerical tool is able to predict faithfully the overall behavior of this type of complex dense granular flow.
Numerical Simulations of Asymmetric Mixing in Planar Shear Flows.
2014-09-26
unsteady shear flows with periodic boundary conditions (Riley & Metcalfe 1980), or in previous simulations of the splitter-plate geometry using either...Soloukhin, AIMA. Riley, 3.3. & Metcalfe , R.W. 1980, Direct Numerical simulation or a Perturbed, Turbulent Mixing Layer, AIAA paper 80-02741, Pasadena
NASA Astrophysics Data System (ADS)
Saanouni, Kkemais; Labergère, Carl; Issa, Mazen; Rassineux, Alain
2010-06-01
This work proposes a complete adaptive numerical methodology which uses `advanced' elastoplastic constitutive equations coupling: thermal effects, large elasto-viscoplasticity with mixed non linear hardening, ductile damage and contact with friction, for 2D machining simulation. Fully coupled (strong coupling) thermo-elasto-visco-plastic-damage constitutive equations based on the state variables under large plastic deformation developed for metal forming simulation are presented. The relevant numerical aspects concerning the local integration scheme as well as the global resolution strategy and the adaptive remeshing facility are briefly discussed. Applications are made to the orthogonal metal cutting by chip formation and segmentation under high velocity. The interactions between hardening, plasticity, ductile damage and thermal effects and their effects on the adiabatic shear band formation including the formation of cracks are investigated.
NASA Astrophysics Data System (ADS)
Sengupta, M.; Ganesh, R.
2016-10-01
This paper is a simulation based investigation of the effect of elastic collisions and effectively elastic-like excitation collisions between electrons and background neutrals on the dynamics of a cylindrically trapped electron cloud that also has an ion contaminant mixed in it. A cross section of the trapped non neutral cloud composed of electrons mixed uniformly with a fractional population of ions is loaded on a 2D PIC grid with the plasma in a state of unstable equilibrium due to differential rotation between the electron and the ion component. The electrons are also loaded with an axial velocity component, vz, that mimics their bouncing motion between the electrostatic end plugs of a Penning-Malmberg trap. This vz loading facilitates 3D elastic and excitation collisions of the electrons with background neutrals under a MCC scheme. In the present set of numerical experiments, the electrons do not ionize the neutrals. This helps in separating out only the effect of non-ionizing collisions of electrons on the dynamics of the cloud. Simulations reveal that these non-ionizing collisions indirectly influence the ensuing collisionless ion resonance instability of the contaminated electron cloud by a feedback process. The collisional relaxation reduces the average density of the electron cloud and thereby increases the fractional density of the ions mixed in it. The dynamically changing electron density and fractional density of ions feed back on the ongoing ion-resonance (two-stream) instability between the two components of the nonneutral cloud and produce deviations in the paths of progression of the instability that are uncorrelated at different background gas pressures. Effects of the collisions on the instability are evident from alteration in the growth rate and energetics of the instability caused by the presence of background neutrals as compared to a vacuum background. Further in order to understand if the non-ionizing collisions can independently be a cause
Numerical simulation of aluminum extrusion processes
NASA Astrophysics Data System (ADS)
Hughes, T. J.; Muller, A.
1995-04-01
This presentation describes a research program directed towards the development of automated design procedures for aluminum extrusion technology. The objective is to eliminate costly trial and error by being able to simultaneously design the product, die, billet, and process (e.g.. extrusion temperatures and speeds, uniformizing metal flow, etc.), within constraints of feasibility, and satisfying objectives including, but not limited to, optimizing shape, surface finish, and properties of the product, processing costs, time to market, and full utilization of capabilities. The approach is based on the development of efficient and effective analysis of the whole processing system employing newly developed finite element solution technologies for complex, multi region, multiphysical behavior. Generalizations of these methodologies to include Arbitrary Lagrangian-Eulerian (ALE) mesh descriptions for nonlinear, elastic viscoplastic mechanical constitution equations will allow the faithful modeling of the metal flow within the die system and the accurate attainment of final shape upon exit. Automatic meshing and adaptive remeshing will insure efficient and accurate simulation of the entire forming process. New element technologies facilitating the use of general meshing procedures for difficult metal-forming processes involving a variety of kinematical constraints, such as incompressibility, contact, etc., are utilized. Feature based design methodologies, parametric modeling, and knowledge-based engineering techniques will constitute the fundamental methodologies for representing designs, managing the hierarchy of analysis models, performing model reduction and feature removal, and effectively utilizing design knowledge.
Numerical simulation of the edge tone phenomenon
NASA Technical Reports Server (NTRS)
Dougherty, N. S.; Liu, B. L.; Ofarrell, J. M.
1994-01-01
Time accurate Navier-Stokes computations were performed to study a class 2 (acoustic) whistle, the edge tone, and to gain knowledge of the vortex-acoustic coupling mechanisms driving production of these tones. Results were obtained by solving the full Navier-Stokes equations for laminar compressible air flow of a two dimensional jet issuing from a slit interacting with a wedge. Cases considered were determined by varying the distance from the slit to the wedge. Flow speed was kept constant at 1,750 cm/s as was the slit thickness of 0.1 cm, corresponding to conditions in the experiments of Brown. The analytical computations revealed edge tones to be present in four harmonic stages of jet flow instability over the wedge as the jet length was varied from 0.3 to 1.6 cm. Excellent agreement was obtained in all four edge tone stage cases between the present computational results and the experimentally obtained frequencies and flow visualization results of Brown. Specific edge tone generation phenomena and further confirmation of certain theories and empirical formulas concerning these phenomena were brought to light in this analytical simulation of edge tones.
Numerical simulation of photoexcited polaron states in water
Zemlyanaya, E. V. Volokhova, A. V.; Amirkhanov, I. V.; Puzynin, I. V.; Puzynina, T. P.; Rikhvitskiy, V. S.; Lakhno, V. D.; Atanasova, P. Kh.
2015-10-28
We consider the dynamic polaron model of the hydrated electron state on the basis of a system of three nonlinear partial differential equations with appropriate initial and boundary conditions. A parallel numerical algorithm for the numerical solution of this system has been developed. Its effectiveness has been tested on a few multi-processor systems. A numerical simulation of the polaron states formation in water under the action of the ultraviolet range laser irradiation has been performed. The numerical results are shown to be in a reasonable agreement with experimental data and theoretical predictions.
Feasibility study for a numerical aerodynamic simulation facility. Volume 1
NASA Technical Reports Server (NTRS)
Lincoln, N. R.; Bergman, R. O.; Bonstrom, D. B.; Brinkman, T. W.; Chiu, S. H. J.; Green, S. S.; Hansen, S. D.; Klein, D. L.; Krohn, H. E.; Prow, R. P.
1979-01-01
A Numerical Aerodynamic Simulation Facility (NASF) was designed for the simulation of fluid flow around three-dimensional bodies, both in wind tunnel environments and in free space. The application of numerical simulation to this field of endeavor promised to yield economies in aerodynamic and aircraft body designs. A model for a NASF/FMP (Flow Model Processor) ensemble using a possible approach to meeting NASF goals is presented. The computer hardware and software are presented, along with the entire design and performance analysis and evaluation.
Three-Dimensional Numerical Simulation to Mud Turbine for LWD
NASA Astrophysics Data System (ADS)
Yao, Xiaojiang; Dong, Jingxin; Shang, Jie; Zhang, Guanqi
Hydraulic performance analysis was discussed for a type of turbine on generator used for LWD. The simulation models were built by CFD analysis software FINE/Turbo, and full three-dimensional numerical simulation was carried out for impeller group. The hydraulic parameter such as power, speed and pressure drop, were calculated in two kinds of medium water and mud. Experiment was built in water environment. The error of numerical simulation was less than 6%, verified by experiment. Based on this rationalization proposals would be given to choice appropriate impellers, and the rationalization of methods would be explored.
Numerical simulation of evolutionary erodible bedforms using the particle finite element method
NASA Astrophysics Data System (ADS)
Bravo, Rafael; Becker, Pablo; Ortiz, Pablo
2016-07-01
This paper presents a numerical strategy for the simulation of flows with evolutionary erodible boundaries. The fluid equations are fully resolved in 3D, while the sediment transport is modelled using the Exner equation and solved with an explicit Lagrangian procedure based on a fixed 2D mesh. Flow and sediment are coupled in geometry by deforming the fluid mesh in the vertical direction and in velocities with the experimental sediment flux computed using the Meyer Peter Müller model. A comparison with real experiments on channels is performed, giving good agreement.
NASA Astrophysics Data System (ADS)
Mitsui, Y.; Hirahara, K.
2006-12-01
There have been a lot of studies that simulate large earthquakes occurring quasi-periodically at a subduction zone, based on the laboratory-derived rate-and-state friction law [eg. Kato and Hirasawa (1997), Hirose and Hirahara (2002)]. All of them assume that pore fluid pressure in the fault zone is constant. However, in the fault zone, pore fluid pressure changes suddenly, due to coseismic pore dilatation [Marone (1990)] and thermal pressurization [Mase and Smith (1987)]. If pore fluid pressure drops and effective normal stress rises, fault slip is decelerated. Inversely, if pore fluid pressure rises and effective normal stress drops, fault slip is accelerated. The effect of pore fluid may cause slow slip events and low-frequency tremor [Kodaira et al. (2004), Shelly et al. (2006)]. For a simple spring model, how pore dilatation affects slip instability was investigated [Segall and Rice (1995), Sleep (1995)]. When the rate of the slip becomes high, pore dilatation occurs and pore pressure drops, and the rate of the slip is restrained. Then the inflow of pore fluid recovers the pore pressure. We execute 2D earthquake cycle simulations at a subduction zone, taking into account such changes of pore fluid pressure following Segall and Rice (1995), in addition to the numerical scheme in Kato and Hirasawa (1997). We do not adopt hydrostatic pore pressure but excess pore pressure for initial condition, because upflow of dehydrated water seems to exist at a subduction zone. In our model, pore fluid is confined to the fault damage zone and flows along the plate interface. The smaller the flow rate is, the later pore pressure recovers. Since effective normal stress keeps larger, the fault slip is decelerated and stress drop becomes smaller. Therefore the smaller flow rate along the fault zone leads to the shorter earthquake recurrence time. Thus, not only the frictional parameters and the subduction rate but also the fault zone permeability affects the recurrence time of
Numerical simulation of porosity-free titanium dental castings.
Wu, M; Augthun, M; Schädlich-Stubenrauch, J; Sahm, P R; Spiekermann, H
1999-08-01
The objective of this research was to analyse, predict and control the porosity in titanium dental castings by the use of numerical simulation. A commercial software package (MAGMASOFT) was used. In the first part of the study, a model casting (two simplified tooth crowns connected by a connector bar) was simulated to analyse shrinkage porosity. Secondly, gas pores were numerically examined by means of a ball specimen with a "snake" sprue. The numerical simulation results were compared with the experimental casting results, which were made on a centrifugal casting machine. The predicted shrinkage levels coincided well with the experimentally determined levels. Based on the above numerical analyses, an optimised running and gating system design for the crown model was proposed. The numerical filling and solidification results of the ball specimen showed that this simulation model could be helpful for the explanation of the experimentally indicated gas pores. It was concluded that shrinkage porosity in titanium dental casting was predictable, and it could be minimised by improving the running and gating system design. Entrapped gas pores can be explained from the simulation results of the mould filling and solidification.
NASA Astrophysics Data System (ADS)
Zhang, Ning
This thesis presents the parasitic extraction and magnetic analysis for transformers, inductors, and IGBT bridge busbars with Maxwell 2D and Maxwell 3D simulation. In the first chapter, the magnetic field of a transformer in Maxwell 2D is analyzed. The parasitic capacitance between each winding of the transformer are extracted by Maxwell 2D. According to the actual dimensions, the parasitic capacitances are calculated. The results are verified by comparing with the measurement results from 4395A impedance analyzer. In the second chapter, two CM inductors are simulated in Maxwell 3D. One is the conventional winding inductor, the other one is the proposed one. The magnetic field distributions of different winding directions are analyzed. The analysis is verified by the simulation result. The last chapter introduces a technique to analyze, extract, and measure the parasitic inductance of planar busbars. With this technique, the relationship between self-inductance and mutual-inductance is analyzed. Secondly, a total inductance is calculated based on the developed technique. Thirdly, the current paths and the inductance on a planar busbar are investigated with DC-link capacitors. Furthermore, the analysis of the inductance is addressed. Ansys Q3D simulation and analysis are presented. Finally, the experimental verification is shown by the S-parameter measurement.
NASA Astrophysics Data System (ADS)
Chen, T.; Wang, P.; Fehler, M.; Zhang, Y.; Burns, D.
2009-12-01
Localizing subsurface fractures and estimating their mechanical parameters and geometric properties are very important in oil and gas industry as well as geothermal energy research. It is essential to quantitatively understand how the elastic wave propagation is affected by these fractures. In this paper, an analytical expression for the scattered P- and SV waves from a 2D fracture is formulated based on a normal mode method, where the 2D fracture is modeled by a low-aspect ratio elliptical cylinder. The scatter function of this 2D fracture are expressed in terms of the incident angle, the orientation and aspect ratio of the fracture as well as the elastic impedance contrast between the surrounding medium and the inhomogeneity inside the fracture. Results from this analytical solution match well with those from a finite-difference approach. Solutions of this analytical model at two limiting cases (a circular cylinder with aspect ratio equal to one and a strip with aspect ratio equal to zero) are also compared to analytical solutions directly derived for the circular cylinder and strip by other studies.
Numerical Simulation of SNCR Technology with Simplified Chemical Kinetics Model
NASA Astrophysics Data System (ADS)
Blejchař, T.; Dolníčková, D.
2013-04-01
The paper deals with numerical simulation of SNCR method. For numerical modelling was used CFD code Ansys/CFX. SNCR method was described by dominant chemical reaction, which were look up NIST Chemical database. The reactions including reduction of NOx and concentration change of pollutants, like N2O and CO in flue gas too. Proposed chemical kinetics and CFD model was applied to two boilers. Both simulations were compared with experimental measurements. First simulation was used to validation of chemical mechanism. Second simulation was based on first simulation and it was used to verification of compiled SNCR chemical mechanism. Next the new variant of the reagent penetration lance was proposed and compared with the original variants.
Numerical simulation of wave propagation in cancellous bone.
Padilla, F; Bossy, E; Haiat, G; Jenson, F; Laugier, P
2006-12-22
Numerical simulation of wave propagation is performed through 31 3D volumes of trabecular bone. These volumes were reconstructed from high synchrotron microtomography experiments and are used as the input geometry in a simulation software developed in our laboratory. The simulation algorithm accounts for propagation into both the saturating fluid and bone but absorption is not taken into account. We show that 3D simulation predicts phenomena observed experimentally in trabecular bones : linear frequency dependence of attenuation, increase of attenuation and speed of sound with the bone volume fraction, negative phase velocity dispersion in most of the specimens, propagation of fast and slow wave depending on the orientation of the trabecular network compared to the direction of propagation of the ultrasound. Moreover, the predicted attenuation is in very close agreement with the experimental one measured on the same specimens. Coupling numerical simulation with real bone architecture therefore provides a powerful tool to investigate the physics of ultrasound propagation in trabecular structures.
NASA Astrophysics Data System (ADS)
Elleuch, Amal; Sahraoui, Melik; Boussetta, Ahlem; Halouani, Kamel; Li, Yongdan
2014-02-01
A two-dimensional modeling of a lab-scale planar Direct Carbon Fuel Cell (DCFC) of 20 mm in diameter is developed by taking into account of the electrochemical mechanisms and mass and heat transfer phenomena in all regions of the cell simultaneously. The electrodes and the electrolyte of the DCFC are both considered as distinct regions with different local properties such as permeability, conductivity and diffusivity. An improved packed bed anodic structure with a finite thickness is also adopted. General boundary conditions are implemented by taking into consideration the species concentrations at the DCFC inlet such as oxygen concentration which is a very important parameter to determine the cell efficiency. The effects of the main operating parameters such as temperature, inlet gas flow velocity and porosity of the electrolyte matrix on the DCFC efficiency are investigated. A sensitivity analysis based on numerical simulations of the effects of cathode kinetic parameters and the anode specific surface area is also performed. Good agreement is obtained between numerical results and experimental data with an absolute average deviation of about 9%.
Yan, Chang; Yuan, Rongfeng; Pfalzgraff, William C.; Nishida, Jun; Wang, Lu; Markland, Thomas E.; Fayer, Michael D.
2016-01-01
Functionalized self-assembled monolayers (SAMs) are the focus of ongoing investigations because they can be chemically tuned to control their structure and dynamics for a wide variety of applications, including electrochemistry, catalysis, and as models of biological interfaces. Here we combine reflection 2D infrared vibrational echo spectroscopy (R-2D IR) and molecular dynamics simulations to determine the relationship between the structures of functionalized alkanethiol SAMs on gold surfaces and their underlying molecular motions on timescales of tens to hundreds of picoseconds. We find that at higher head group density, the monolayers have more disorder in the alkyl chain packing and faster dynamics. The dynamics of alkanethiol SAMs on gold are much slower than the dynamics of alkylsiloxane SAMs on silica. Using the simulations, we assess how the different molecular motions of the alkyl chain monolayers give rise to the dynamics observed in the experiments. PMID:27044113
Compressible Turbulent Flow Numerical Simulations of Tip Vortex Cavitation
NASA Astrophysics Data System (ADS)
Khatami, F.; van der Weide, E.; Hoeijmakers, H.
2015-12-01
For an elliptic Arndt's hydrofoil numerical simulations of vortex cavitation are presented. An equilibrium cavitation model is employed. This single-fluid model assumes local thermodynamic and mechanical equilibrium in the mixture region of the flow, is employed. Furthermore, for characterizing the thermodynamic state of the system, precomputed multiphase thermodynamic tables containing data for the appropriate equations of state for each of the phases are used and a fast, accurate, and efficient look-up approach is employed for interpolating the data. The numerical simulations are carried out using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations for compressible flow. The URANS equations of motion are discretized using an finite volume method for unstructured grids. The numerical simulations clearly show the formation of the tip vortex cavitation in the flow about the elliptic hydrofoil.
Numerical Simulation of Turbulent Flames using Vortex Methods.
1987-10-05
layer," Phys. Fluids , 30, pp. 706-721, 1987. (11) Ghoniem, A.F., and Knio, O.M., "Numerical Simulation of Flame Propagation in Constant Volume Chambers...1985. 4. "Numerical solution of a confined shear layer using vortex methods," The International Symposium on Computational Fluid Dynamics, Tokyo...Symposium on Computational Fluid Dynamics, Tokyo, Japan, September 1985. 8. "Application of Computational Methods in Turbulent Reacting Flow
Study on the numerical schemes for hypersonic flow simulation
NASA Astrophysics Data System (ADS)
Nagdewe, S. P.; Shevare, G. R.; Kim, Heuy-Dong
2009-10-01
Hypersonic flow is full of complex physical and chemical processes, hence its investigation needs careful analysis of existing schemes and choosing a suitable scheme or designing a brand new scheme. The present study deals with two numerical schemes Harten, Lax, and van Leer with Contact (HLLC) and advection upstream splitting method (AUSM) to effectively simulate hypersonic flow fields, and accurately predict shock waves with minimal diffusion. In present computations, hypersonic flows have been modeled as a system of hyperbolic equations with one additional equation for non-equilibrium energy and relaxing source terms. Real gas effects, which appear typically in hypersonic flows, have been simulated through energy relaxation method. HLLC and AUSM methods are modified to incorporate the conservation laws for non-equilibrium energy. Numerical implementation have shown that non-equilibrium energy convect with mass, and hence has no bearing on the basic numerical scheme. The numerical simulation carried out shows good comparison with experimental data available in literature. Both numerical schemes have shown identical results at equilibrium. Present study has demonstrated that real gas effects in hypersonic flows can be modeled through energy relaxation method along with either AUSM or HLLC numerical scheme.
Preface to advances in numerical simulation of plasmas
NASA Astrophysics Data System (ADS)
Parker, Scott E.; Chacon, Luis
2016-10-01
This Journal of Computational Physics Special Issue, titled "Advances in Numerical Simulation of Plasmas," presents a snapshot of the international state of the art in the field of computational plasma physics. The articles herein are a subset of the topics presented as invited talks at the 24th International Conference on the Numerical Simulation of Plasmas (ICNSP), August 12-14, 2015 in Golden, Colorado. The choice of papers was highly selective. The ICNSP is held every other year and is the premier scientific meeting in the field of computational plasma physics.
Numerical simulation of tornado wind loading on structures
NASA Technical Reports Server (NTRS)
Maiden, D. E.
1976-01-01
A numerical simulation of a tornado interacting with a building was undertaken in order to compare the pressures due to a rotational unsteady wind with that due to steady straight winds used in design of nuclear facilities. The numerical simulations were performed on a two-dimensional compressible hydrodynamics code. Calculated pressure profiles for a typical building were then subjected to a tornado wind field and the results were compared with current quasisteady design calculations. The analysis indicates that current design practices are conservative.
Numerical simulation of wall-bounded turbulent shear flows
NASA Technical Reports Server (NTRS)
Moin, P.
1982-01-01
Developments in three dimensional, time dependent numerical simulation of turbulent flows bounded by a wall are reviewed. Both direct and large eddy simulation techniques are considered within the same computational framework. The computational spatial grid requirements as dictated by the known structure of turbulent boundary layers are presented. The numerical methods currently in use are reviewed and some of the features of these algorithms, including spatial differencing and accuracy, time advancement, and data management are discussed. A selection of the results of the recent calculations of turbulent channel flow, including the effects of system rotation and transpiration on the flow are included. Previously announced in STAR as N82-28577
Numerical simulation of wall-bounded turbulent shear flows
NASA Technical Reports Server (NTRS)
Moin, P.
1982-01-01
Developments in three dimensional, time dependent numerical simulation of turbulent flows bounded by a wall are reviewed. Both direct and large eddy simulation techniques are considered within the same computational framework. The computational spatial grid requirements as dictated by the known structure of turbulent boundary layers are presented. The numerical methods currently in use are reviewed and some of the features of these algorithms, including spatial differencing and accuracy, time advancement, and data management are discussed. A selection of the results of the recent calculations of turbulent channel flow, including the effects of system rotation and transpiration on the flow are included.
Numerical simulation of transition in wall-bounded shear flows
NASA Technical Reports Server (NTRS)
Kleiser, Leonhard; Zang, Thomas A.
1991-01-01
The current status of numerical simulation techniques for the transition to turbulence in incompressible channel and boundary-layer flows is surveyed, and typical results are presented graphically. The focus is on direct numerical simulations based on the full nonlinear time-dependent Navier-Stokes equations without empirical closure assumptions for prescribed initial and boundary conditions. Topics addressed include the vibrating ribbon problem, space and time discretization, initial and boundary conditions, alternative methods based on the triple-deck approximation, two-dimensional channel and boundary-layer flows, three-dimensional boundary layers, wave packets and turbulent spots, compressible flows, transition control, and transition modeling.
Leblanc, M D; Whitehead, J P; Plumer, M L
2013-05-15
A combination of Metropolis and modified Wolff cluster algorithms is used to examine the impact of uniaxial single-ion anisotropy on the phase transition to ferromagnetic order of Heisenberg macrospins on a 2D square lattice. This forms the basis of a model for granular perpendicular recording media where macrospins represent the magnetic moment of grains. The focus of this work is on the interplay between anisotropy D, intragrain exchange J' and intergrain exchange J on the ordering temperature T(C) and extends our previous reported analysis of the granular Ising model. The role of intragrain degrees of freedom in heat assisted magnetic recording is discussed.
NASA Astrophysics Data System (ADS)
Leblanc, M. D.; Whitehead, J. P.; Plumer, M. L.
2013-05-01
A combination of Metropolis and modified Wolff cluster algorithms is used to examine the impact of uniaxial single-ion anisotropy on the phase transition to ferromagnetic order of Heisenberg macrospins on a 2D square lattice. This forms the basis of a model for granular perpendicular recording media where macrospins represent the magnetic moment of grains. The focus of this work is on the interplay between anisotropy D, intragrain exchange J‧ and intergrain exchange J on the ordering temperature TC and extends our previous reported analysis of the granular Ising model. The role of intragrain degrees of freedom in heat assisted magnetic recording is discussed.
Building Blocks for Reliable Complex Nonlinear Numerical Simulations. Chapter 2
NASA Technical Reports Server (NTRS)
Yee, H. C.; Mansour, Nagi N. (Technical Monitor)
2001-01-01
This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations. Examples relevant to turbulent flow computations are included.
Building Blocks for Reliable Complex Nonlinear Numerical Simulations
NASA Technical Reports Server (NTRS)
Yee, H. C.
2005-01-01
This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations.
Building Blocks for Reliable Complex Nonlinear Numerical Simulations
NASA Technical Reports Server (NTRS)
Yee, H. C.; Mansour, Nagi N. (Technical Monitor)
2002-01-01
This talk describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations. Examples relevant to turbulent flow computations are included.
Numerical simulation of double-diffusive finger convection
Hughes, J.D.; Sanford, W.E.; Vacher, H.L.
2005-01-01
A hybrid finite element, integrated finite difference numerical model is developed for the simulation of double-diffusive and multicomponent flow in two and three dimensions. The model is based on a multidimensional, density-dependent, saturated-unsaturated transport model (SUTRA), which uses one governing equation for fluid flow and another for solute transport. The solute-transport equation is applied sequentially to each simulated species. Density coupling of the flow and solute-transport equations is accounted for and handled using a sequential implicit Picard iterative scheme. High-resolution data from a double-diffusive Hele-Shaw experiment, initially in a density-stable configuration, is used to verify the numerical model. The temporal and spatial evolution of simulated double-diffusive convection is in good agreement with experimental results. Numerical results are very sensitive to discretization and correspond closest to experimental results when element sizes adequately define the spatial resolution of observed fingering. Numerical results also indicate that differences in the molecular diffusivity of sodium chloride and the dye used to visualize experimental sodium chloride concentrations are significant and cause inaccurate mapping of sodium chloride concentrations by the dye, especially at late times. As a result of reduced diffusion, simulated dye fingers are better defined than simulated sodium chloride fingers and exhibit more vertical mass transfer. Copyright 2005 by the American Geophysical Union.
Processing biobased polymers using plasticizers: Numerical simulations versus experiments
NASA Astrophysics Data System (ADS)
Desplentere, Frederik; Cardon, Ludwig; Six, Wim; Erkoç, Mustafa
2016-03-01
In polymer processing, the use of biobased products shows lots of possibilities. Considering biobased materials, biodegradability is in most cases the most important issue. Next to this, bio based materials aimed at durable applications, are gaining interest. Within this research, the influence of plasticizers on the processing of the bio based material is investigated. This work is done for an extrusion grade of PLA, Natureworks PLA 2003D. Extrusion through a slit die equipped with pressure sensors is used to compare the experimental pressure values to numerical simulation results. Additional experimental data (temperature and pressure data along the extrusion screw and die are recorded) is generated on a dr. Collin Lab extruder producing a 25mm diameter tube. All these experimental data is used to indicate the appropriate functioning of the numerical simulation tool Virtual Extrusion Laboratory 6.7 for the simulation of both the industrial available extrusion grade PLA and the compound in which 15% of plasticizer is added. Adding the applied plasticizer, resulted in a 40% lower pressure drop over the extrusion die. The combination of different experiments allowed to fit the numerical simulation results closely to the experimental values. Based on this experience, it is shown that numerical simulations also can be used for modified bio based materials if appropriate material and process data are taken into account.
Simulation of intra-aneurysmal blood flow by different numerical methods.
Weichert, Frank; Walczak, Lars; Fisseler, Denis; Opfermann, Tobias; Razzaq, Mudassar; Münster, Raphael; Turek, Stefan; Grunwald, Iris; Roth, Christian; Veith, Christian; Wagner, Mathias
2013-01-01
The occlusional performance of sole endoluminal stenting of intracranial aneurysms is controversially discussed in the literature. Simulation of blood flow has been studied to shed light on possible causal attributions. The outcome, however, largely depends on the numerical method and various free parameters. The present study is therefore conducted to find ways to define parameters and efficiently explore the huge parameter space with finite element methods (FEMs) and lattice Boltzmann methods (LBMs). The goal is to identify both the impact of different parameters on the results of computational fluid dynamics (CFD) and their advantages and disadvantages. CFD is applied to assess flow and aneurysmal vorticity in 2D and 3D models. To assess and compare initial simulation results, simplified 2D and 3D models based on key features of real geometries and medical expert knowledge were used. A result obtained from this analysis indicates that a combined use of the different numerical methods, LBM for fast exploration and FEM for a more in-depth look, may result in a better understanding of blood flow and may also lead to more accurate information about factors that influence conditions for stenting of intracranial aneurysms.
Numerical Simulations of the Digital Microfluidic Manipulation of Single Microparticles.
Lan, Chuanjin; Pal, Souvik; Li, Zhen; Ma, Yanbao
2015-09-08
Single-cell analysis techniques have been developed as a valuable bioanalytical tool for elucidating cellular heterogeneity at genomic, proteomic, and cellular levels. Cell manipulation is an indispensable process for single-cell analysis. Digital microfluidics (DMF) is an important platform for conducting cell manipulation and single-cell analysis in a high-throughput fashion. However, the manipulation of single cells in DMF has not been quantitatively studied so far. In this article, we investigate the interaction of a single microparticle with a liquid droplet on a flat substrate using numerical simulations. The droplet is driven by capillary force generated from the wettability gradient of the substrate. Considering the Brownian motion of microparticles, we utilize many-body dissipative particle dynamics (MDPD), an off-lattice mesoscopic simulation technique, in this numerical study. The manipulation processes (including pickup, transport, and drop-off) of a single microparticle with a liquid droplet are simulated. Parametric studies are conducted to investigate the effects on the manipulation processes from the droplet size, wettability gradient, wetting properties of the microparticle, and particle-substrate friction coefficients. The numerical results show that the pickup, transport, and drop-off processes can be precisely controlled by these parameters. On the basis of the numerical results, a trap-free delivery of a hydrophobic microparticle to a destination on the substrate is demonstrated in the numerical simulations. The numerical results not only provide a fundamental understanding of interactions among the microparticle, the droplet, and the substrate but also demonstrate a new technique for the trap-free immobilization of single hydrophobic microparticles in the DMF design. Finally, our numerical method also provides a powerful design and optimization tool for the manipulation of microparticles in DMF systems.
GPU Accelerated Numerical Simulation of Viscous Flow Down a Slope
NASA Astrophysics Data System (ADS)
Gygax, Remo; Räss, Ludovic; Omlin, Samuel; Podladchikov, Yuri; Jaboyedoff, Michel
2014-05-01
Numerical simulations are an effective tool in natural risk analysis. They are useful to determine the propagation and the runout distance of gravity driven movements such as debris flows or landslides. To evaluate these processes an approach on analogue laboratory experiments and a GPU accelerated numerical simulation of the flow of a viscous liquid down an inclined slope is considered. The physical processes underlying large gravity driven flows share certain aspects with the propagation of debris mass in a rockslide and the spreading of water waves. Several studies have shown that the numerical implementation of the physical processes of viscous flow produce a good fit with the observation of experiments in laboratory in both a quantitative and a qualitative way. When considering a process that is this far explored we can concentrate on its numerical transcription and the application of the code in a GPU accelerated environment to obtain a 3D simulation. The objective of providing a numerical solution in high resolution by NVIDIA-CUDA GPU parallel processing is to increase the speed of the simulation and the accuracy on the prediction. The main goal is to write an easily adaptable and as short as possible code on the widely used platform MATLAB, which will be translated to C-CUDA to achieve higher resolution and processing speed while running on a NVIDIA graphics card cluster. The numerical model, based on the finite difference scheme, is compared to analogue laboratory experiments. This way our numerical model parameters are adjusted to reproduce the effective movements observed by high-speed camera acquisitions during the laboratory experiments.
Direct numerical simulation of compressible free shear flows
NASA Technical Reports Server (NTRS)
Lele, Sanjiva K.
1989-01-01
Direct numerical simulations of compressible free shear layers in open domains are conducted. Compact finite-difference schemes of spectral-like accuracy are used for the simulations. Both temporally-growing and spatially-growing mixing layers are studied. The effect of intrinsic compressibility on the evolution of vortices is studied. The use of convective Mach number is validated. Details of vortex roll up and pairing are studied. Acoustic radiation from vortex roll up, pairing and shape oscillations is studied and quantified.
NASA Astrophysics Data System (ADS)
Ito, Y.; Noborio, K.
2015-12-01
In Japan, soil disinfection with hot water has been popular since the use of methyl bromide was restricted in 2005. Decreasing the amount of hot water applied may make farmers reduce the operation cost. To determine the appropriate amount of hot water needed for soil disinfection, HYDRUS-2D was evaluated. A field experiment was conducted and soil water content and soil temperature were measured at 5, 10, 20, 40, 60, 80 and 100 cm deep when 95oC hot water was applied. Irrigation tubing equipped with drippers every 30 cm were laid at the soil surface, z=0 cm. An irrigation rate for each dripper was 0.83 cm min-1 between t=0 and 120 min, and thereafter it was zero. Temperature of irrigation water was 95oC. Total simulation time with HYDRUS-2D was 720 min for a homogeneous soil. A simulating domain was selected as x=60 cm and z=100 cm. A potential evaporation rate was assumed to be 0 cm min-1 because the soil surface was covered with a plastic sheet. The boundary condition at the bottom was free drainage and those of both sides were no-flux conditions. Hydraulic properties and bulk densities measured at each depth were used for simulation. It was assumed that there was no organic matter contained. Soil thermal properties were adopted from previous study and HYDRUS 2D. Simulated temperatures at 5, 10, 20 and 40 cm deep agreed well with those measured although simulated temperatures at 60, 80, and 100 cm deep were overly estimated. Estimates of volumetric water content at 5 cm deep agreed well with measured values. Simulated values at 10 to 100 cm deep were overly estimated by 0.1 to 0.3 (m3 m-3). The deeper the soil became, the more the simulated wetting front lagged behind the measured one. It was speculated that water viscosity estimated smaller at high temperature might attributed to the slower advances of wetting front simulated with HYDRUS 2-D.
Numerical simulation of piezoelectric effect of bone under ultrasound irradiation
NASA Astrophysics Data System (ADS)
Hosokawa, Atsushi
2015-07-01
The piezoelectric effect of bone under ultrasound irradiation was numerically simulated using an elastic finite-difference time-domain method with piezoelectric constitutive equations (PE-FDTD method). First, to demonstrate the validity of the PE-FDTD method, the ultrasound propagation in piezoelectric ceramics was simulated and then compared with the experimental results. The simulated and experimental waveforms propagating through the ceramics were in good agreement. Next, the piezoelectric effect of human cortical bone on the ultrasound propagation was investigated by PE-FDTD simulation. The simulated result showed that the difference between the waveforms propagating through the bone without and with piezoelectricity was negligible. Finally, the spatial distributions of the electric fields in a human femur induced by ultrasound irradiation were simulated. The electric fields were changed by a bone fracture, which depended on piezoelectric anisotropy. In conclusion, the PE-FDTD method is considered to be useful for investigating the piezoelectric effect of bone.
NASA Astrophysics Data System (ADS)
Kim, Kyeong-Hyeon; Kim, Dong-Su; Kim, Tae-Ho; Kang, Seong-Hee; Cho, Min-Seok; Suh, Tae Suk
2015-11-01
The phantom-alignment error is one of the factors affecting delivery quality assurance (QA) accuracy in intensity-modulated radiation therapy (IMRT). Accordingly, a possibility of inadequate use of spatial information in gamma evaluation may exist for patient-specific IMRT QA. The influence of the phantom-alignment error on gamma evaluation can be demonstrated experimentally by using the gamma passing rate and the gamma value. However, such experimental methods have a limitation regarding the intrinsic verification of the influence of the phantom set-up error because experimentally measuring the phantom-alignment error accurately is impossible. To overcome this limitation, we aimed to verify the effect of the phantom set-up error within the gamma evaluation formula by using a Monte Carlo simulation. Artificial phantom set-up errors were simulated, and the concept of the true point (TP) was used to represent the actual coordinates of the measurement point for the mathematical modeling of these effects on the gamma. Using dose distributions acquired from the Monte Carlo simulation, performed gamma evaluations in 2D and 3D. The results of the gamma evaluations and the dose difference at the TP were classified to verify the degrees of dose reflection at the TP. The 2D and the 3D gamma errors were defined by comparing gamma values between the case of the imposed phantom set-up error and the TP in order to investigate the effect of the set-up error on the gamma value. According to the results for gamma errors, the 3D gamma evaluation reflected the dose at the TP better than the 2D one. Moreover, the gamma passing rates were higher for 3D than for 2D, as is widely known. Thus, the 3D gamma evaluation can increase the precision of patient-specific IMRT QA by applying stringent acceptance criteria and setting a reasonable action level for the 3D gamma passing rate.
Can numerical simulations accurately predict hydrodynamic instabilities in liquid films?
NASA Astrophysics Data System (ADS)
Denner, Fabian; Charogiannis, Alexandros; Pradas, Marc; van Wachem, Berend G. M.; Markides, Christos N.; Kalliadasis, Serafim
2014-11-01
Understanding the dynamics of hydrodynamic instabilities in liquid film flows is an active field of research in fluid dynamics and non-linear science in general. Numerical simulations offer a powerful tool to study hydrodynamic instabilities in film flows and can provide deep insights into the underlying physical phenomena. However, the direct comparison of numerical results and experimental results is often hampered by several reasons. For instance, in numerical simulations the interface representation is problematic and the governing equations and boundary conditions may be oversimplified, whereas in experiments it is often difficult to extract accurate information on the fluid and its behavior, e.g. determine the fluid properties when the liquid contains particles for PIV measurements. In this contribution we present the latest results of our on-going, extensive study on hydrodynamic instabilities in liquid film flows, which includes direct numerical simulations, low-dimensional modelling as well as experiments. The major focus is on wave regimes, wave height and wave celerity as a function of Reynolds number and forcing frequency of a falling liquid film. Specific attention is paid to the differences in numerical and experimental results and the reasons for these differences. The authors are grateful to the EPSRC for their financial support (Grant EP/K008595/1).
NASA Astrophysics Data System (ADS)
Janković, I.; Fiori, A.; Dagan, G.
2003-09-01
results are in the comparison of the macrodispersivities, computed with the aid of the Lagrangian velocity covariances, as functions of travel time. For the longitudinal macrodispersivity, the SC approximation yields results close to the numerical ones in 2-D for n = 0.4 but underestimates them for n = 0.9. The asymptotic, large travel time values of macrodispersivities in the SC and FO approximations are close for low to moderate σY2, as shown and explained in part 1. However, while the slow tendency to Fickian behavior is well reproduced by SC, it is much quicker in the FO approximation. In 3-D the SC approximation is closer to numerical one for the highest n = 0.7 and the different σY2 = 2, 4, 8, and the comparison improves if molecular diffusion is taken into account. Transverse macrodispersivity for small travel times is underestimated by SC in 2-D and is closer to numerical results in 3-D, whereas FO overestimates them. Transverse macrodispersivity asymptotically tends to zero in 2-D for large travel times. In 3-D the numerical simulations lead to a small but persistent transverse macrodispersivity for large travel times, whereas it tends to zero in the approximate solutions. The results suggest that the self-consistent semianalytical approximation provides a valuable tool to model transport in highly heterogeneous isotropic formations of a 3-D structure in terms of trajectories statistical moments. It captures effects like slow transition to Fickian behavior and to Gaussian trajectory distribution, which are neglected by the first-order approximation.
Numerical approaches for multidimensional simulations of stellar explosions
NASA Astrophysics Data System (ADS)
Chen, Ke-Jung; Heger, Alexander; Almgren, Ann S.
2013-11-01
We introduce numerical algorithms for initializing multidimensional simulations of stellar explosions with 1D stellar evolution models. The initial mapping from 1D profiles onto multidimensional grids can generate severe numerical artifacts, one of the most severe of which is the violation of conservation laws for physical quantities. We introduce a numerical scheme for mapping 1D spherically-symmetric data onto multidimensional meshes so that these physical quantities are conserved. We verify our scheme by porting a realistic 1D Lagrangian stellar profile to the new multidimensional Eulerian hydro code CASTRO. Our results show that all important features in the profiles are reproduced on the new grid and that conservation laws are enforced at all resolutions after mapping. We also introduce a numerical scheme for initializing multidimensional supernova simulations with realistic perturbations predicted by 1D stellar evolution models. Instead of seeding 3D stellar profiles with random perturbations, we imprint them with velocity perturbations that reproduce the Kolmogorov energy spectrum expected for highly turbulent convective regions in stars. Our models return Kolmogorov energy spectra and vortex structures like those in turbulent flows before the modes become nonlinear. Finally, we describe approaches to determining the resolution for simulations required to capture fluid