NASA Technical Reports Server (NTRS)
VanZante, Dale E.; Strazisar, Anthony J.; Wood, Jerry R,; Hathaway, Michael D.; Okiishi, Theodore H.
2000-01-01
The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. While numerical simulations of these flows are quite sophisticated. they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip clearance flow details (e.g. trajectory and radial extent) with corresponding data obtained from a numerical simulation. Recommendations for achieving accurate numerical simulation of tip clearance flows are presented based on this comparison. Laser Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor was simulated using a Navier-Stokes turbomachinery solver that incorporates an advanced k-epsilon turbulence model derived for flows that are not in local equilibrium. Comparison between measured and simulated results indicates that simulation accuracy is primarily dependent upon the ability of the numerical code to resolve important details of a wall-bounded shear layer formed by the relative motion between the over-tip leakage flow and the shroud wall. A simple method is presented for determining the strength of this shear layer.
Recommendations for accurate numerical blood flow simulations of stented intracranial aneurysms.
Janiga, Gábor; Berg, Philipp; Beuing, Oliver; Neugebauer, Mathias; Gasteiger, Rocco; Preim, Bernhard; Rose, Georg; Skalej, Martin; Thévenin, Dominique
2013-06-01
The number of scientific publications dealing with stented intracranial aneurysms is rapidly increasing. Powerful computational facilities are now available; an accurate computational modeling of hemodynamics in patient-specific configurations is, however, still being sought. Furthermore, there is still no general agreement on the quantities that should be computed and on the most adequate analysis for intervention support. In this article, the accurate representation of patient geometry is first discussed, involving successive improvements. Concerning the second step, the mesh required for the numerical simulation is especially challenging when deploying a stent with very fine wire structures. Third, the description of the fluid properties is a major challenge. Finally, a founded quantitative analysis of the simulation results is obviously needed to support interventional decisions. In the present work, an attempt has been made to review the most important steps for a high-quality computational fluid dynamics computation of virtually stented intracranial aneurysms. In consequence, this leads to concrete recommendations, whereby the obtained results are not discussed for their medical relevance but for the evaluation of their quality. This investigation might hopefully be helpful for further studies considering stent deployment in patient-specific geometries, in particular regarding the generation of the most appropriate computational model. PMID:23729530
Numerical Simulation of the 2004 Indian Ocean Tsunami: Accurate Flooding and drying in Banda Aceh
NASA Astrophysics Data System (ADS)
Cui, Haiyang; Pietrzak, Julie; Stelling, Guus; Androsov, Alexey; Harig, Sven
2010-05-01
The Indian Ocean Tsunami on December 26, 2004 caused one of the largest tsunamis in recent times and led to widespread devastation and loss of life. One of the worst hit regions was Banda Aceh, which is the capital of the Aceh province, located in the northern part of Sumatra, 150km from the source of the earthquake. A German-Indonesian Tsunami Early Warning System (GITEWS) (www.gitews.de) is currently under active development. The work presented here is carried out within the GITEWS framework. One of the aims of this project is the development of accurate models with which to simulate the propagation, flooding and drying, and run-up of a tsunami. In this context, TsunAWI has been developed by the Alfred Wegener Institute; it is an explicit, () finite element model. However, the accurate numerical simulation of flooding and drying requires the conservation of mass and momentum. This is not possible in the current version of TsunAWi. The P1NC - P1element guarantees mass conservation in a global sense, yet as we show here it is important to guarantee mass conservation at the local level, that is within each individual cell. Here an unstructured grid, finite volume ocean model is presented. It is derived from the P1NC - P1 element, and is shown to be mass and momentum conserving. Then a number of simulations are presented, including dam break problems flooding over both a wet and a dry bed. Excellent agreement is found. Then we present simulations for Banda Aceh, and compare the results to on-site survey data, as well as to results from the original TsunAWI code.
Meek, Garrett A; Levine, Benjamin G
2014-07-01
Spikes in the time-derivative coupling (TDC) near surface crossings make the accurate integration of the time-dependent Schrödinger equation in nonadiabatic molecular dynamics simulations a challenge. To address this issue, we present an approximation to the TDC based on a norm-preserving interpolation (NPI) of the adiabatic electronic wave functions within each time step. We apply NPI and two other schemes for computing the TDC in numerical simulations of the Landau-Zener model, comparing the simulated transfer probabilities to the exact solution. Though NPI does not require the analytical calculation of nonadiabatic coupling matrix elements, it consistently yields unsigned population transfer probability errors of ∼0.001, whereas analytical calculation of the TDC yields errors of 0.0-1.0 depending on the time step, the offset of the maximum in the TDC from the beginning of the time step, and the coupling strength. The approximation of Hammes-Schiffer and Tully yields errors intermediate between NPI and the analytical scheme. PMID:26279558
NASA Astrophysics Data System (ADS)
Wosnik, M.; Bachant, P.
2014-12-01
Cross-flow turbines, often referred to as vertical-axis turbines, show potential for success in marine hydrokinetic (MHK) and wind energy applications, ranging from small- to utility-scale installations in tidal/ocean currents and offshore wind. As turbine designs mature, the research focus is shifting from individual devices to the optimization of turbine arrays. It would be expensive and time-consuming to conduct physical model studies of large arrays at large model scales (to achieve sufficiently high Reynolds numbers), and hence numerical techniques are generally better suited to explore the array design parameter space. However, since the computing power available today is not sufficient to conduct simulations of the flow in and around large arrays of turbines with fully resolved turbine geometries (e.g., grid resolution into the viscous sublayer on turbine blades), the turbines' interaction with the energy resource (water current or wind) needs to be parameterized, or modeled. Models used today--a common model is the actuator disk concept--are not able to predict the unique wake structure generated by cross-flow turbines. This wake structure has been shown to create "constructive" interference in some cases, improving turbine performance in array configurations, in contrast with axial-flow, or horizontal axis devices. Towards a more accurate parameterization of cross-flow turbines, an extensive experimental study was carried out using a high-resolution turbine test bed with wake measurement capability in a large cross-section tow tank. The experimental results were then "interpolated" using high-fidelity Navier--Stokes simulations, to gain insight into the turbine's near-wake. The study was designed to achieve sufficiently high Reynolds numbers for the results to be Reynolds number independent with respect to turbine performance and wake statistics, such that they can be reliably extrapolated to full scale and used for model validation. The end product of
A time-accurate adaptive grid method and the numerical simulation of a shock-vortex interaction
NASA Technical Reports Server (NTRS)
Bockelie, Michael J.; Eiseman, Peter R.
1990-01-01
A time accurate, general purpose, adaptive grid method is developed that is suitable for multidimensional steady and unsteady numerical simulations. The grid point movement is performed in a manner that generates smooth grids which resolve the severe solution gradients and the sharp transitions in the solution gradients. The temporal coupling of the adaptive grid and the PDE solver is performed with a grid prediction correction method that is simple to implement and ensures the time accuracy of the grid. Time accurate solutions of the 2-D Euler equations for an unsteady shock vortex interaction demonstrate the ability of the adaptive method to accurately adapt the grid to multiple solution features.
NASA Technical Reports Server (NTRS)
Przekwas, A. J.; Athavale, M. M.; Hendricks, R. C.; Steinetz, B. M.
2006-01-01
Detailed information of the flow-fields in the secondary flowpaths and their interaction with the primary flows in gas turbine engines is necessary for successful designs with optimized secondary flow streams. Present work is focused on the development of a simulation methodology for coupled time-accurate solutions of the two flowpaths. The secondary flowstream is treated using SCISEAL, an unstructured adaptive Cartesian grid code developed for secondary flows and seals, while the mainpath flow is solved using TURBO, a density based code with capability of resolving rotor-stator interaction in multi-stage machines. An interface is being tested that links the two codes at the rim seal to allow data exchange between the two codes for parallel, coupled execution. A description of the coupling methodology and the current status of the interface development is presented. Representative steady-state solutions of the secondary flow in the UTRC HP Rig disc cavity are also presented.
AN ACCURATE AND EFFICIENT ALGORITHM FOR NUMERICAL SIMULATION OF CONDUCTION-TYPE PROBLEMS. (R824801)
A modification of the finite analytic numerical method for conduction-type (diffusion) problems is presented. The finite analytic discretization scheme is derived by means of the Fourier series expansion for the most general case of nonuniform grid and variabl...
Differential-equation-based representation of truncation errors for accurate numerical simulation
NASA Astrophysics Data System (ADS)
MacKinnon, Robert J.; Johnson, Richard W.
1991-09-01
High-order compact finite difference schemes for 2D convection-diffusion-type differential equations with constant and variable convection coefficients are derived. The governing equations are employed to represent leading truncation terms, including cross-derivatives, making the overall O(h super 4) schemes conform to a 3 x 3 stencil. It is shown that the two-dimensional constant coefficient scheme collapses to the optimal scheme for the one-dimensional case wherein the finite difference equation yields nodally exact results. The two-dimensional schemes are tested against standard model problems, including a Navier-Stokes application. Results show that the two schemes are generally more accurate, on comparable grids, than O(h super 2) centered differencing and commonly used O(h) and O(h super 3) upwinding schemes.
Pre-Stall Behavior of a Transonic Axial Compressor Stage via Time-Accurate Numerical Simulation
NASA Technical Reports Server (NTRS)
Chen, Jen-Ping; Hathaway, Michael D.; Herrick, Gregory P.
2008-01-01
CFD calculations using high-performance parallel computing were conducted to simulate the pre-stall flow of a transonic compressor stage, NASA compressor Stage 35. The simulations were run with a full-annulus grid that models the 3D, viscous, unsteady blade row interaction without the need for an artificial inlet distortion to induce stall. The simulation demonstrates the development of the rotating stall from the growth of instabilities. Pressure-rise performance and pressure traces are compared with published experimental data before the study of flow evolution prior to the rotating stall. Spatial FFT analysis of the flow indicates a rotating long-length disturbance of one rotor circumference, which is followed by a spike-type breakdown. The analysis also links the long-length wave disturbance with the initiation of the spike inception. The spike instabilities occur when the trajectory of the tip clearance flow becomes perpendicular to the axial direction. When approaching stall, the passage shock changes from a single oblique shock to a dual-shock, which distorts the perpendicular trajectory of the tip clearance vortex but shows no evidence of flow separation that may contribute to stall.
NASA Astrophysics Data System (ADS)
Moore, Christopher; Hopkins, Matthew; Moore, Stan; Boerner, Jeremiah; Cartwright, Keith
2015-09-01
Simulation of breakdown is important for understanding and designing a variety of applications such as mitigating undesirable discharge events. Such simulations need to be accurate through early time arc initiation to late time stable arc behavior. Here we examine constraints on the timestep and mesh size required for arc simulations using the particle-in-cell (PIC) method with direct simulation Monte Carlo (DMSC) collisions. Accurate simulation of electron avalanche across a fixed voltage drop and constant neutral density (reduced field of 1000 Td) was found to require a timestep ~ 1/100 of the mean time between collisions and a mesh size ~ 1/25 the mean free path. These constraints are much smaller than the typical PIC-DSMC requirements for timestep and mesh size. Both constraints are related to the fact that charged particles are accelerated by the external field. Thus gradients in the electron energy distribution function can exist at scales smaller than the mean free path and these must be resolved by the mesh size for accurate collision rates. Additionally, the timestep must be small enough that the particle energy change due to the fields be small in order to capture gradients in the cross sections versus energy. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
NASA Astrophysics Data System (ADS)
Zhang, Na; Yao, Jun; Huang, Zhaoqin; Wang, Yueying
2013-06-01
Numerical simulation in naturally fractured media is challenging because of the coexistence of porous media and fractures on multiple scales that need to be coupled. We present a new approach to reservoir simulation that gives accurate resolution of both large-scale and fine-scale flow patterns. Multiscale methods are suitable for this type of modeling, because it enables capturing the large scale behavior of the solution without solving all the small features. Dual-porosity models in view of their strength and simplicity can be mainly used for sugar-cube representation of fractured media. In such a representation, the transfer function between the fracture and the matrix block can be readily calculated for water-wet media. For a mixed-wet system, the evaluation of the transfer function becomes complicated due to the effect of gravity. In this work, we use a multiscale finite element method (MsFEM) for two-phase flow in fractured media using the discrete-fracture model. By combining MsFEM with the discrete-fracture model, we aim towards a numerical scheme that facilitates fractured reservoir simulation without upscaling. MsFEM uses a standard Darcy model to approximate the pressure and saturation on a coarse grid, whereas fine scale effects are captured through basis functions constructed by solving local flow problems using the discrete-fracture model. The accuracy and the robustness of MsFEM are shown through several examples. In the first example, we consider several small fractures in a matrix and then compare the results solved by the finite element method. Then, we use the MsFEM in more complex models. The results indicate that the MsFEM is a promising path toward direct simulation of highly resolution geomodels.
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
Accurate numerical solutions of conservative nonlinear oscillators
NASA Astrophysics Data System (ADS)
Khan, Najeeb Alam; Nasir Uddin, Khan; Nadeem Alam, Khan
2014-12-01
The objective of this paper is to present an investigation to analyze the vibration of a conservative nonlinear oscillator in the form u" + lambda u + u^(2n-1) + (1 + epsilon^2 u^(4m))^(1/2) = 0 for any arbitrary power of n and m. This method converts the differential equation to sets of algebraic equations and solve numerically. We have presented for three different cases: a higher order Duffing equation, an equation with irrational restoring force and a plasma physics equation. It is also found that the method is valid for any arbitrary order of n and m. Comparisons have been made with the results found in the literature the method gives accurate results.
Numerical Aerodynamic Simulation
NASA Technical Reports Server (NTRS)
1989-01-01
An overview of historical and current numerical aerodynamic simulation (NAS) is given. The capabilities and goals of the Numerical Aerodynamic Simulation Facility are outlined. Emphasis is given to numerical flow visualization and its applications to structural analysis of aircraft and spacecraft bodies. The uses of NAS in computational chemistry, engine design, and galactic evolution are mentioned.
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.
NASA Astrophysics Data System (ADS)
Ahmed, Mahmoud; Eslamian, Morteza
2015-07-01
Laminar natural convection in differentially heated ( β = 0°, where β is the inclination angle), inclined ( β = 30° and 60°), and bottom-heated ( β = 90°) square enclosures filled with a nanofluid is investigated, using a two-phase lattice Boltzmann simulation approach. The effects of the inclination angle on Nu number and convection heat transfer coefficient are studied. The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation. The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors. Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect. Here we show that thermophoresis has a considerable effect on heat transfer augmentation in laminar natural convection. Our non-homogenous modeling approach shows that heat transfer in nanofluids is a function of the inclination angle and Ra number. It also reveals some details of flow behavior which cannot be captured by single-phase models. The minimum heat transfer rate is associated with β = 90° (bottom-heated) and the maximum heat transfer rate occurs in an inclination angle which varies with the Ra number.
Ahmed, Mahmoud; Eslamian, Morteza
2015-12-01
Laminar natural convection in differentially heated (β = 0°, where β is the inclination angle), inclined (β = 30° and 60°), and bottom-heated (β = 90°) square enclosures filled with a nanofluid is investigated, using a two-phase lattice Boltzmann simulation approach. The effects of the inclination angle on Nu number and convection heat transfer coefficient are studied. The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation. The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors. Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect. Here we show that thermophoresis has a considerable effect on heat transfer augmentation in laminar natural convection. Our non-homogenous modeling approach shows that heat transfer in nanofluids is a function of the inclination angle and Ra number. It also reveals some details of flow behavior which cannot be captured by single-phase models. The minimum heat transfer rate is associated with β = 90° (bottom-heated) and the maximum heat transfer rate occurs in an inclination angle which varies with the Ra number. PMID:26183389
Numerical simulations in combustion
NASA Technical Reports Server (NTRS)
Chung, T. J.
1989-01-01
This paper reviews numerical simulations in reacting flows in general and combustion phenomena in particular. It is shown that use of implicit schemes and/or adaptive mesh strategies can improve convergence, stability, and accuracy of the solution. Difficulties increase as turbulence and multidimensions are considered, particularly when finite-rate chemistry governs the given combustion problem. Particular attention is given to the areas of solid-propellant combustion dynamics, turbulent diffusion flames, and spray droplet vaporization.
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.
Numerical Aerodynamic Simulation (NAS)
NASA Technical Reports Server (NTRS)
Peterson, V. L.; Ballhaus, W. F., Jr.; Bailey, F. R.
1983-01-01
The history of the Numerical Aerodynamic Simulation Program, which is designed to provide a leading-edge capability to computational aerodynamicists, is traced back to its origin in 1975. Factors motivating its development and examples of solutions to successively refined forms of the governing equations are presented. The NAS Processing System Network and each of its eight subsystems are described in terms of function and initial performance goals. A proposed usage allocation policy is discussed and some initial problems being readied for solution on the NAS system are identified.
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.
NASA Technical Reports Server (NTRS)
Graves, R. A., Jr.
1975-01-01
The previously obtained second-order-accurate partial implicitization numerical technique used in the solution of fluid dynamic problems was modified with little complication to achieve fourth-order accuracy. The Von Neumann stability analysis demonstrated the unconditional linear stability of the technique. The order of the truncation error was deduced from the Taylor series expansions of the linearized difference equations and was verified by numerical solutions to Burger's equation. For comparison, results were also obtained for Burger's equation using a second-order-accurate partial-implicitization scheme, as well as the fourth-order scheme of Kreiss.
Coincidental match of numerical simulation and physics
NASA Astrophysics Data System (ADS)
Pierre, B.; Gudmundsson, J. S.
2010-08-01
Consequences of rapid pressure transients in pipelines range from increased fatigue to leakages and to complete ruptures of pipeline. Therefore, accurate predictions of rapid pressure transients in pipelines using numerical simulations are critical. State of the art modelling of pressure transient in general, and water hammer in particular include unsteady friction in addition to the steady frictional pressure drop, and numerical simulations rely on the method of characteristics. Comparison of rapid pressure transient calculations by the method of characteristics and a selected high resolution finite volume method highlights issues related to modelling of pressure waves and illustrates that matches between numerical simulations and physics are purely coincidental.
A numerical method for cardiac mechanoelectric simulations.
Pathmanathan, Pras; Whiteley, Jonathan P
2009-05-01
Much effort has been devoted to developing numerical techniques for solving the equations that describe cardiac electrophysiology, namely the monodomain equations and bidomain equations. Only a limited selection of publications, however, address the development of numerical techniques for mechanoelectric simulations where cardiac electrophysiology is coupled with deformation of cardiac tissue. One problem commonly encountered in mechanoelectric simulations is instability of the coupled numerical scheme. In this study, we develop a stable numerical scheme for mechanoelectric simulations. A number of convergence tests are carried out using this stable technique for simulations where deformations are of the magnitude typically observed in a beating heart. These convergence tests demonstrate that accurate computation of tissue deformation requires a nodal spacing of around 1 mm in the mesh used to calculate tissue deformation. This is a much finer computational grid than has previously been acknowledged, and has implications for the computational efficiency of the resulting numerical scheme. PMID:19263223
Numerical simulations of Lake Vostok
NASA Astrophysics Data System (ADS)
Curchitser, E.; Tremblay, B.
2003-04-01
Numerical simulations of Lake Vostok We present a systematic approach towards a realistic hydrodynamic model of lake Vostok. The lake is characterized by the unusual combination of size (permitting significant geostrophic motion) and an overlying ice sheet several kilometers thick. A priori estimates of the circulation in the deep lake predict a mostly geostrophic circulation driven by horizontal temperature gradients produced by the pressure-dependent freezing point at the base of the (non-uniform) ice sheet. Further preliminary (remote) research has revealed the steep topography and the elliptical geometry of the lake. A three dimensional, primitive equation, free surface, model is used as a starting point for the Lake configuration. We show how the surface pressure gradient forces are modified to permit a simulation that includes the hydrostatic effects of the overlying ice sheet. A thermodynamic ice model is coupled with the circulation component to simulate the ice accretion/melting at the base of the ice sheet. A stretching of the terrain following vertical coordinate is used to resolve the boundary layer in the ice/water interface. Furthermore, the terrain-following coordinate evolves in time, and is used to track the evolution of the ice sheet due to ice accretion/melting. Both idealized and realistic ice sheet bottom topographies (from remote radar data) are used to drive the simulations. Steady state and time evolving simulations (i.e., constant and evolving ice sheet geometry) will be descirbed, as well as a comparison to an idealized box model (Tremblay, Clarke, and Hohman). The coastline and lake bathymetry used in the simulation are derived from radar data and are accurately represented in our model.
Time accurate simulations of compressible shear flows
NASA Technical Reports Server (NTRS)
Givi, Peyman; Steinberger, Craig J.; Vidoni, Thomas J.; Madnia, Cyrus K.
1993-01-01
The objectives of this research are to employ direct numerical simulation (DNS) to study the phenomenon of mixing (or lack thereof) in compressible free shear flows and to suggest new means of enhancing mixing in such flows. The shear flow configurations under investigation are those of parallel mixing layers and planar jets under both non-reacting and reacting nonpremixed conditions. During the three-years of this research program, several important issues regarding mixing and chemical reactions in compressible shear flows were investigated.
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.
Accurate complex scaling of three dimensional numerical potentials
Cerioni, Alessandro; Genovese, Luigi; Duchemin, Ivan; Deutsch, Thierry
2013-05-28
The complex scaling method, which consists in continuing spatial coordinates into the complex plane, is a well-established method that allows to compute resonant eigenfunctions of the time-independent Schroedinger operator. Whenever it is desirable to apply the complex scaling to investigate resonances in physical systems defined on numerical discrete grids, the most direct approach relies on the application of a similarity transformation to the original, unscaled Hamiltonian. We show that such an approach can be conveniently implemented in the Daubechies wavelet basis set, featuring a very promising level of generality, high accuracy, and no need for artificial convergence parameters. Complex scaling of three dimensional numerical potentials can be efficiently and accurately performed. By carrying out an illustrative resonant state computation in the case of a one-dimensional model potential, we then show that our wavelet-based approach may disclose new exciting opportunities in the field of computational non-Hermitian quantum mechanics.
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...
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.
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.
Numerical Simulations of Ion Cloud Dynamics
NASA Astrophysics Data System (ADS)
Sillitoe, Nicolas; Hilico, Laurent
We explain how to perform accurate numerical simulations of ion cloud dynamics by discussing the relevant orders of magnitude of the characteristic times and frequencies involved in the problem and the computer requirement with respect to the ion cloud size. We then discuss integration algorithms and Coulomb force parallelization. We finally explain how to take into account collisions, cooling laser interaction and chemical reactions in a Monte Carlo approach and discuss how to use random number generators to that end.
Numerical simulations of hot spots
NASA Astrophysics Data System (ADS)
Norman, Michael L.
Numerical simulations of hot spots and their associated jets are examined with emphasis on their dynamical variability. Attention is given to two-dimensional simulations, which incorporate dynamically passive and important magnetic fields in the ideal MHD limit. Distributions of total and polarized radio brightness have been derived for comparison with observations. The move toward three-dimensional simulations is documented, and hydrodynamical models for multiple hot spots are discussed. It is suggested that useful insights can be obtained from two-dimensional slab jet simulation, which relax the axisymmetric constraints while allowing high numerical resolution. In particular the dentist-drill model of Scheuer (1982) for working-surface variability is substantiated, and it is shown to result from self-excited jet instabilities near the working surface.
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.
Accurate Langevin approaches to simulate Markovian channel dynamics
NASA Astrophysics Data System (ADS)
Huang, Yandong; Rüdiger, Sten; Shuai, Jianwei
2015-12-01
The stochasticity of ion-channels dynamic is significant for physiological processes on neuronal cell membranes. Microscopic simulations of the ion-channel gating with Markov chains can be considered to be an accurate standard. However, such Markovian simulations are computationally demanding for membrane areas of physiologically relevant sizes, which makes the noise-approximating or Langevin equation methods advantageous in many cases. In this review, we discuss the Langevin-like approaches, including the channel-based and simplified subunit-based stochastic differential equations proposed by Fox and Lu, and the effective Langevin approaches in which colored noise is added to deterministic differential equations. In the framework of Fox and Lu’s classical models, several variants of numerical algorithms, which have been recently developed to improve accuracy as well as efficiency, are also discussed. Through the comparison of different simulation algorithms of ion-channel noise with the standard Markovian simulation, we aim to reveal the extent to which the existing Langevin-like methods approximate results using Markovian methods. Open questions for future studies are also discussed.
Numerical simulation of electrochemical desalination.
Hlushkou, D; Knust, K N; Crooks, R M; Tallarek, U
2016-05-18
We present an effective numerical approach to simulate electrochemically mediated desalination of seawater. This new membraneless, energy efficient desalination method relies on the oxidation of chloride ions, which generates an ion depletion zone and local electric field gradient near the junction of a microchannel branch to redirect sea salt into the brine stream, consequently producing desalted water. The proposed numerical model is based on resolution of the 3D coupled Navier-Stokes, Nernst-Planck, and Poisson equations at non-uniform spatial grids. The model is implemented as a parallel code and can be employed to simulate mass-charge transport coupled with surface or volume reactions in 3D systems showing an arbitrarily complex geometrical configuration. PMID:27089841
Numerical simulation of electrochemical desalination
NASA Astrophysics Data System (ADS)
Hlushkou, D.; Knust, K. N.; Crooks, R. M.; Tallarek, U.
2016-05-01
We present an effective numerical approach to simulate electrochemically mediated desalination of seawater. This new membraneless, energy efficient desalination method relies on the oxidation of chloride ions, which generates an ion depletion zone and local electric field gradient near the junction of a microchannel branch to redirect sea salt into the brine stream, consequently producing desalted water. The proposed numerical model is based on resolution of the 3D coupled Navier–Stokes, Nernst–Planck, and Poisson equations at non-uniform spatial grids. The model is implemented as a parallel code and can be employed to simulate mass–charge transport coupled with surface or volume reactions in 3D systems showing an arbitrarily complex geometrical configuration.
Relativistic positioning systems: Numerical simulations
NASA Astrophysics Data System (ADS)
Puchades Colmenero, Neus
The position of users located on the Earth's surface or near it may be found with the classic positioning systems (CPS). Certain information broadcast by satellites of global navigation systems, as GPS and GALILEO, may be used for positioning. The CPS are based on the Newtonian formalism, although relativistic post-Newtonian corrections are done when they are necessary. This thesis contributes to the development of a different positioning approach, which is fully relativistic from the beginning. In the relativistic positioning systems (RPS), the space-time position of any user (ship, spacecraft, and so on) can be calculated with the help of four satellites, which broadcast their proper times by means of codified electromagnetic signals. In this thesis, we have simulated satellite 4-tuples of the GPS and GALILEO constellations. If a user receives the signals from four satellites simultaneously, the emission proper times read -after decoding- are the user "emission coordinates". In order to find the user "positioning coordinates", in an appropriate almost inertial reference system, there are two possibilities: (a) the explicit relation between positioning and emission coordinates (broadcast by the satellites) is analytically found or (b) numerical codes are designed to calculate the positioning coordinates from the emission ones. Method (a) is only viable in simple ideal cases, whereas (b) allows us to consider realistic situations. In this thesis, we have designed numerical codes with the essential aim of studying two appropriate RPS, which may be generalized. Sometimes, there are two real users placed in different positions, which receive the same proper times from the same satellites; then, we say that there is bifurcation, and additional data are needed to choose the real user position. In this thesis, bifurcation is studied in detail. We have analyzed in depth two RPS models; in both, it is considered that the satellites move in the Schwarzschild's space
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.
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.
Accurate simulation of optical properties in dyes.
Jacquemin, Denis; Perpète, Eric A; Ciofini, Ilaria; Adamo, Carlo
2009-02-17
Since Antiquity, humans have produced and commercialized dyes. To this day, extraction of natural dyes often requires lengthy and costly procedures. In the 19th century, global markets and new industrial products drove a significant effort to synthesize artificial dyes, characterized by low production costs, huge quantities, and new optical properties (colors). Dyes that encompass classes of molecules absorbing in the UV-visible part of the electromagnetic spectrum now have a wider range of applications, including coloring (textiles, food, paintings), energy production (photovoltaic cells, OLEDs), or pharmaceuticals (diagnostics, drugs). Parallel to the growth in dye applications, researchers have increased their efforts to design and synthesize new dyes to customize absorption and emission properties. In particular, dyes containing one or more metallic centers allow for the construction of fairly sophisticated systems capable of selectively reacting to light of a given wavelength and behaving as molecular devices (photochemical molecular devices, PMDs).Theoretical tools able to predict and interpret the excited-state properties of organic and inorganic dyes allow for an efficient screening of photochemical centers. In this Account, we report recent developments defining a quantitative ab initio protocol (based on time-dependent density functional theory) for modeling dye spectral properties. In particular, we discuss the importance of several parameters, such as the methods used for electronic structure calculations, solvent effects, and statistical treatments. In addition, we illustrate the performance of such simulation tools through case studies. We also comment on current weak points of these methods and ways to improve them. PMID:19113946
Progress in fast, accurate multi-scale climate simulations
Collins, W. D.; Johansen, H.; Evans, K. J.; Woodward, C. S.; Caldwell, P. M.
2015-06-01
We present a survey of physical and computational techniques that have the potential to contribute to the next generation of high-fidelity, multi-scale climate simulations. Examples of the climate science problems that can be investigated with more depth with these computational improvements include the capture of remote forcings of localized hydrological extreme events, an accurate representation of cloud features over a range of spatial and temporal scales, and parallel, large ensembles of simulations to more effectively explore model sensitivities and uncertainties. Numerical techniques, such as adaptive mesh refinement, implicit time integration, and separate treatment of fast physical time scales are enablingmore » improved accuracy and fidelity in simulation of dynamics and allowing more complete representations of climate features at the global scale. At the same time, partnerships with computer science teams have focused on taking advantage of evolving computer architectures such as many-core processors and GPUs. As a result, approaches which were previously considered prohibitively costly have become both more efficient and scalable. In combination, progress in these three critical areas is poised to transform climate modeling in the coming decades.« less
Progress in fast, accurate multi-scale climate simulations
Collins, W. D.; Johansen, H.; Evans, K. J.; Woodward, C. S.; Caldwell, P. M.
2015-06-01
We present a survey of physical and computational techniques that have the potential to contribute to the next generation of high-fidelity, multi-scale climate simulations. Examples of the climate science problems that can be investigated with more depth with these computational improvements include the capture of remote forcings of localized hydrological extreme events, an accurate representation of cloud features over a range of spatial and temporal scales, and parallel, large ensembles of simulations to more effectively explore model sensitivities and uncertainties. Numerical techniques, such as adaptive mesh refinement, implicit time integration, and separate treatment of fast physical time scales are enabling improved accuracy and fidelity in simulation of dynamics and allowing more complete representations of climate features at the global scale. At the same time, partnerships with computer science teams have focused on taking advantage of evolving computer architectures such as many-core processors and GPUs. As a result, approaches which were previously considered prohibitively costly have become both more efficient and scalable. In combination, progress in these three critical areas is poised to transform climate modeling in the coming decades.
Progress in Fast, Accurate Multi-scale Climate Simulations
Collins, William D; Johansen, Hans; Evans, Katherine J; Woodward, Carol S.; Caldwell, Peter
2015-01-01
We present a survey of physical and computational techniques that have the potential to con- tribute to the next generation of high-fidelity, multi-scale climate simulations. Examples of the climate science problems that can be investigated with more depth include the capture of remote forcings of localized hydrological extreme events, an accurate representation of cloud features over a range of spatial and temporal scales, and parallel, large ensembles of simulations to more effectively explore model sensitivities and uncertainties. Numerical techniques, such as adaptive mesh refinement, implicit time integration, and separate treatment of fast physical time scales are enabling improved accuracy and fidelity in simulation of dynamics and allow more complete representations of climate features at the global scale. At the same time, part- nerships with computer science teams have focused on taking advantage of evolving computer architectures, such as many-core processors and GPUs, so that these approaches which were previously considered prohibitively costly have become both more efficient and scalable. In combination, progress in these three critical areas is poised to transform climate modeling in the coming decades.
Anisotropic Turbulence Modeling for Accurate Rod Bundle Simulations
Baglietto, Emilio
2006-07-01
An improved anisotropic eddy viscosity model has been developed for accurate predictions of the thermal hydraulic performances of nuclear reactor fuel assemblies. The proposed model adopts a non-linear formulation of the stress-strain relationship in order to include the reproduction of the anisotropic phenomena, and in combination with an optimized low-Reynolds-number formulation based on Direct Numerical Simulation (DNS) to produce correct damping of the turbulent viscosity in the near wall region. This work underlines the importance of accurate anisotropic modeling to faithfully reproduce the scale of the turbulence driven secondary flows inside the bundle subchannels, by comparison with various isothermal and heated experimental cases. The very low scale secondary motion is responsible for the increased turbulence transport which produces a noticeable homogenization of the velocity distribution and consequently of the circumferential cladding temperature distribution, which is of main interest in bundle design. Various fully developed bare bundles test cases are shown for different geometrical and flow conditions, where the proposed model shows clearly improved predictions, in close agreement with experimental findings, for regular as well as distorted geometries. Finally the applicability of the model for practical bundle calculations is evaluated through its application in the high-Reynolds form on coarse grids, with excellent results. (author)
Fast and Accurate Learning When Making Discrete Numerical Estimates.
Sanborn, Adam N; Beierholm, Ulrik R
2016-04-01
Many everyday estimation tasks have an inherently discrete nature, whether the task is counting objects (e.g., a number of paint buckets) or estimating discretized continuous variables (e.g., the number of paint buckets needed to paint a room). While Bayesian inference is often used for modeling estimates made along continuous scales, discrete numerical estimates have not received as much attention, despite their common everyday occurrence. Using two tasks, a numerosity task and an area estimation task, we invoke Bayesian decision theory to characterize how people learn discrete numerical distributions and make numerical estimates. Across three experiments with novel stimulus distributions we found that participants fell between two common decision functions for converting their uncertain representation into a response: drawing a sample from their posterior distribution and taking the maximum of their posterior distribution. While this was consistent with the decision function found in previous work using continuous estimation tasks, surprisingly the prior distributions learned by participants in our experiments were much more adaptive: When making continuous estimates, participants have required thousands of trials to learn bimodal priors, but in our tasks participants learned discrete bimodal and even discrete quadrimodal priors within a few hundred trials. This makes discrete numerical estimation tasks good testbeds for investigating how people learn and make estimates. PMID:27070155
Fast and Accurate Learning When Making Discrete Numerical Estimates
Sanborn, Adam N.; Beierholm, Ulrik R.
2016-01-01
Many everyday estimation tasks have an inherently discrete nature, whether the task is counting objects (e.g., a number of paint buckets) or estimating discretized continuous variables (e.g., the number of paint buckets needed to paint a room). While Bayesian inference is often used for modeling estimates made along continuous scales, discrete numerical estimates have not received as much attention, despite their common everyday occurrence. Using two tasks, a numerosity task and an area estimation task, we invoke Bayesian decision theory to characterize how people learn discrete numerical distributions and make numerical estimates. Across three experiments with novel stimulus distributions we found that participants fell between two common decision functions for converting their uncertain representation into a response: drawing a sample from their posterior distribution and taking the maximum of their posterior distribution. While this was consistent with the decision function found in previous work using continuous estimation tasks, surprisingly the prior distributions learned by participants in our experiments were much more adaptive: When making continuous estimates, participants have required thousands of trials to learn bimodal priors, but in our tasks participants learned discrete bimodal and even discrete quadrimodal priors within a few hundred trials. This makes discrete numerical estimation tasks good testbeds for investigating how people learn and make estimates. PMID:27070155
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.
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. PMID:23005852
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.
The development of accurate and efficient methods of numerical quadrature
NASA Technical Reports Server (NTRS)
Feagin, T.
1973-01-01
Some new methods for performing numerical quadrature of an integrable function over a finite interval are described. Each method provides a sequence of approximations of increasing order to the value of the integral. Each approximation makes use of all previously computed values of the integrand. The points at which new values of the integrand are computed are selected in such a way that the order of the approximation is maximized. The methods are compared with the quadrature methods of Clenshaw and Curtis, Gauss, Patterson, and Romberg using several examples.
Accurate numerical solution of compressible, linear stability equations
NASA Technical Reports Server (NTRS)
Malik, M. R.; Chuang, S.; Hussaini, M. Y.
1982-01-01
The present investigation is concerned with a fourth order accurate finite difference method and its application to the study of the temporal and spatial stability of the three-dimensional compressible boundary layer flow on a swept wing. This method belongs to the class of compact two-point difference schemes discussed by White (1974) and Keller (1974). The method was apparently first used for solving the two-dimensional boundary layer equations. Attention is given to the governing equations, the solution technique, and the search for eigenvalues. A general purpose subroutine is employed for solving a block tridiagonal system of equations. The computer time can be reduced significantly by exploiting the special structure of two matrices.
NASA Astrophysics Data System (ADS)
Blackman, Jonathan; Field, Scott E.; Galley, Chad R.; Szilágyi, Béla; Scheel, Mark A.; Tiglio, Manuel; Hemberger, Daniel A.
2015-09-01
Simulating a binary black hole coalescence by solving Einstein's equations is computationally expensive, requiring days to months of supercomputing time. Using reduced order modeling techniques, we construct an accurate surrogate model, which is evaluated in a millisecond to a second, for numerical relativity (NR) waveforms from nonspinning binary black hole coalescences with mass ratios in [1, 10] and durations corresponding to about 15 orbits before merger. We assess the model's uncertainty and show that our modeling strategy predicts NR waveforms not used for the surrogate's training with errors nearly as small as the numerical error of the NR code. Our model includes all spherical-harmonic -2Yℓm waveform modes resolved by the NR code up to ℓ=8 . We compare our surrogate model to effective one body waveforms from 50 M⊙ to 300 M⊙ for advanced LIGO detectors and find that the surrogate is always more faithful (by at least an order of magnitude in most cases).
Direct numerical simulation of the Leidenfrost Effect
NASA Astrophysics Data System (ADS)
Rueda Villegas, Lucia; Tanguy, Sébastien
2012-11-01
We present direct numerical simulations of the impact of a single droplet on a heated flat surface in the Leidenfrost regime. To that end, we solve the Navier-Stokes equations, the energy equation, and the species mass fraction equation. The Level Set method is used to track the liquid-gas interface motion and the Ghost Fluid Method is implemented to treat the jump conditions. To get rid of the temporal stability condition due to viscosity, an implicit temporal discretization is used. Some specific numerical methods have been developed to deal with droplet vaporization interface jump conditions. Since the vapor layer is very thin compared to the droplet size, a non-uniform structured grid strongly refined near the wall is used to capture the droplet bounce. We present numerical simulations that enable us to study accurately the bouncing dynamics by analyzing the momentum balance during the droplet bounce. Moreover, we determine from such computation the ratio of the droplet heat transfer flux by comparing the energy used for the phase change (latent heat) to the energy used for droplet heating (specific heat). We then compare the shape of the droplet during the impact with some experimental results.
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≲
Linking scales through numerical simulations
NASA Astrophysics Data System (ADS)
Lunati, I.
2012-12-01
Field-scale models of flow through porous media rely on a continuum description, which disregard pore-scale details and focus on macroscopic effects. As it is always the case, this choice is quite effective in reducing the number of model parameters, but this comes at expenses of an inherent loss of information and generality. Models based on Darcy's law, for instance, require spatial and temporal scale separation (locality and equilibrium). Although these conditions are generally met for single-phase flow, multiphase flow is far more complex: the interaction between nonlinearity of the interface behavior and the pore structure (disorder) creates a variety of flow regimes for which scale separation does not hold. In recent years, the increased computational power has led to a revival of pore-scale modeling in order to overcome this issue and describe the flow at the scale in which it physically occurs. If appropriate techniques are chosen, it is possible to use numerical simulations to complement experimental observations and advance our understanding of multiphase flow. By means of examples, we discuss the role played by these models in contributing to solve open problems and in devising alternatives to the standard description of flow through porous media.
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.
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.
Material Models for Accurate Simulation of Sheet Metal Forming and Springback
NASA Astrophysics Data System (ADS)
Yoshida, Fusahito
2010-06-01
For anisotropic sheet metals, modeling of anisotropy and the Bauschinger effect is discussed in the framework of Yoshida-Uemori kinematic hardening model incorporating with anisotropic yield functions. The performances of the models in predicting yield loci, cyclic stress-strain responses on several types of steel and aluminum sheets are demonstrated by comparing the numerical simulation results with the corresponding experimental observations. From some examples of FE simulation of sheet metal forming and springback, it is concluded that modeling of both the anisotropy and the Bauschinger effect is essential for the accurate numerical simulation.
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 multifluid flows
NASA Astrophysics Data System (ADS)
Unverdi, Salih Ozen
1990-01-01
A method for full numerical simulations of unsteady, incompressible Navier-Stokes equations for multi-fluid systems is developed. Moving interfaces between dissimilar fluids are explicitly tracked and fluid properties are constructed on a stationary grid using the position of the interfaces. While the interfaces are explicitly tracked, they are not kept completely sharp but are given a finite thickness of the order of the mesh size to provide stability and smoothness. This thickness remains constant for all time but decreases with finer resolution of the stationary grid. A unique feature of the method is that the tracked interfaces carry the jump in properties across the interface and that, at each time step, the property fields are reconstructed by solving a Poisson equation. The advantage of this approach is that interfaces can interact in a natural way, since the gradients add or cancel as the grid distribution is constructed from the information carried by the tracked front. The emphasis is on the shape regimes of bubbles and bubble-bubble interactions in a stationary fluid. The circular, elliptical and skirted shape regimes and wake structures of two-dimensional bubbles are studied. Three-dimensional evolution of the interaction of two bubbles in a stationary fluid is investigated. Interaction of bubbles in a periodic array is also studied and it is found that a pair of bubbles in a free rise can interact in the absence of a toroidal wake below the upper bubble and that the interaction time is smaller as the viscosity of the outer fluid decreases. It is shown that the kinetic energy of the flow field decreases during this interaction. Sensitivity of the bubble interaction process to fluid properties is shown by different trajectories followed by bubbles in fluids of different viscosity. The Rayleigh-Taylor instability is also studied.
Exploring accurate Poisson–Boltzmann methods for biomolecular simulations
Wang, Changhao; Wang, Jun; Cai, Qin; Li, Zhilin; Zhao, Hong-Kai; Luo, Ray
2013-01-01
Accurate and efficient treatment of electrostatics is a crucial step in computational analyses of biomolecular structures and dynamics. In this study, we have explored a second-order finite-difference numerical method to solve the widely used Poisson–Boltzmann equation for electrostatic analyses of realistic bio-molecules. The so-called immersed interface method was first validated and found to be consistent with the classical weighted harmonic averaging method for a diversified set of test biomolecules. The numerical accuracy and convergence behaviors of the new method were next analyzed in its computation of numerical reaction field grid potentials, energies, and atomic solvation forces. Overall similar convergence behaviors were observed as those by the classical method. Interestingly, the new method was found to deliver more accurate and better-converged grid potentials than the classical method on or nearby the molecular surface, though the numerical advantage of the new method is reduced when grid potentials are extrapolated to the molecular surface. Our exploratory study indicates the need for further improving interpolation/extrapolation schemes in addition to the developments of higher-order numerical methods that have attracted most attention in the field. PMID:24443709
Earthquake Rupture Dynamics using Adaptive Mesh Refinement and High-Order Accurate Numerical Methods
NASA Astrophysics Data System (ADS)
Kozdon, J. E.; Wilcox, L.
2013-12-01
Our goal is to develop scalable and adaptive (spatial and temporal) numerical methods for coupled, multiphysics problems using high-order accurate numerical methods. To do so, we are developing an opensource, parallel library known as bfam (available at http://bfam.in). The first application to be developed on top of bfam is an earthquake rupture dynamics solver using high-order discontinuous Galerkin methods and summation-by-parts finite difference methods. In earthquake rupture dynamics, wave propagation in the Earth's crust is coupled to frictional sliding on fault interfaces. This coupling is two-way, required the simultaneous simulation of both processes. The use of laboratory-measured friction parameters requires near-fault resolution that is 4-5 orders of magnitude higher than that needed to resolve the frequencies of interest in the volume. This, along with earlier simulations using a low-order, finite volume based adaptive mesh refinement framework, suggest that adaptive mesh refinement is ideally suited for this problem. The use of high-order methods is motivated by the high level of resolution required off the fault in earlier the low-order finite volume simulations; we believe this need for resolution is a result of the excessive numerical dissipation of low-order methods. In bfam spatial adaptivity is handled using the p4est library and temporal adaptivity will be accomplished through local time stepping. In this presentation we will present the guiding principles behind the library as well as verification of code against the Southern California Earthquake Center dynamic rupture code validation test problems.
Takahashi, F; Endo, A
2007-01-01
A system utilising radiation transport codes has been developed to derive accurate dose distributions in a human body for radiological accidents. A suitable model is quite essential for a numerical analysis. Therefore, two tools were developed to setup a 'problem-dependent' input file, defining a radiation source and an exposed person to simulate the radiation transport in an accident with the Monte Carlo calculation codes-MCNP and MCNPX. Necessary resources are defined by a dialogue method with a generally used personal computer for both the tools. The tools prepare human body and source models described in the input file format of the employed Monte Carlo codes. The tools were validated for dose assessment in comparison with a past criticality accident and a hypothesized exposure. PMID:17510203
Numeric simulation of plant signaling networks.
Genoud, T; Trevino Santa Cruz, M B; Métraux, J P
2001-08-01
Plants have evolved an intricate signaling apparatus that integrates relevant information and allows an optimal response to environmental conditions. For instance, the coordination of defense responses against pathogens involves sophisticated molecular detection and communication systems. Multiple protection strategies may be deployed differentially by the plant according to the nature of the invading organism. These responses are also influenced by the environment, metabolism, and developmental stage of the plant. Though the cellular signaling processes traditionally have been described as linear sequences of events, it is now evident that they may be represented more accurately as network-like structures. The emerging paradigm can be represented readily with the use of Boolean language. This digital (numeric) formalism allows an accurate qualitative description of the signal transduction processes, and a dynamic representation through computer simulation. Moreover, it provides the required power to process the increasing amount of information emerging from the fields of genomics and proteomics, and from the use of new technologies such as microarray analysis. In this review, we have used the Boolean language to represent and analyze part of the signaling network of disease resistance in Arabidopsis. PMID:11500542
Numeric Simulation of Plant Signaling Networks1
Genoud, Thierry; Trevino Santa Cruz, Marcela B.; Métraux, Jean-Pierre
2001-01-01
Plants have evolved an intricate signaling apparatus that integrates relevant information and allows an optimal response to environmental conditions. For instance, the coordination of defense responses against pathogens involves sophisticated molecular detection and communication systems. Multiple protection strategies may be deployed differentially by the plant according to the nature of the invading organism. These responses are also influenced by the environment, metabolism, and developmental stage of the plant. Though the cellular signaling processes traditionally have been described as linear sequences of events, it is now evident that they may be represented more accurately as network-like structures. The emerging paradigm can be represented readily with the use of Boolean language. This digital (numeric) formalism allows an accurate qualitative description of the signal transduction processes, and a dynamic representation through computer simulation. Moreover, it provides the required power to process the increasing amount of information emerging from the fields of genomics and proteomics, and from the use of new technologies such as microarray analysis. In this review, we have used the Boolean language to represent and analyze part of the signaling network of disease resistance in Arabidopsis. PMID:11500542
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
Numerical wind speed simulation model
Ramsdell, J.V.; Athey, G.F.; Ballinger, M.Y.
1981-09-01
A relatively simple stochastic model for simulating wind speed time series that can be used as an alternative to time series from representative locations is described in this report. The model incorporates systematic seasonal variation of the mean wind, its standard deviation, and the correlation speeds. It also incorporates systematic diurnal variation of the mean speed and standard deviation. To demonstrate the model capabilities, simulations were made using model parameters derived from data collected at the Hanford Meteorology Station, and results of analysis of simulated and actual data were compared.
NUMERICAL SIMULATION OF LARYNGEAL FLOW
In this study, we have investigated laryngeal air flows by numerically solving the corresponding Navier-Stokes equations expressed in a two-dimensional cylindrical coordinate system. The glottal aperture, defined by the geometry of the vocal folds was allowed to change with the v...
Blackman, Jonathan; Field, Scott E; Galley, Chad R; Szilágyi, Béla; Scheel, Mark A; Tiglio, Manuel; Hemberger, Daniel A
2015-09-18
Simulating a binary black hole coalescence by solving Einstein's equations is computationally expensive, requiring days to months of supercomputing time. Using reduced order modeling techniques, we construct an accurate surrogate model, which is evaluated in a millisecond to a second, for numerical relativity (NR) waveforms from nonspinning binary black hole coalescences with mass ratios in [1, 10] and durations corresponding to about 15 orbits before merger. We assess the model's uncertainty and show that our modeling strategy predicts NR waveforms not used for the surrogate's training with errors nearly as small as the numerical error of the NR code. Our model includes all spherical-harmonic _{-2}Y_{ℓm} waveform modes resolved by the NR code up to ℓ=8. We compare our surrogate model to effective one body waveforms from 50M_{⊙} to 300M_{⊙} for advanced LIGO detectors and find that the surrogate is always more faithful (by at least an order of magnitude in most cases). PMID:26430979
Numerical simulation of small perturbation transonic flows
NASA Technical Reports Server (NTRS)
Seebass, A. R.; Yu, N. J.
1976-01-01
The results of a systematic study of small perturbation transonic flows are presented. Both the flow over thin airfoils and the flow over wedges were investigated. Various numerical schemes were employed in the study. The prime goal of the research was to determine the efficiency of various numerical procedures by accurately evaluating the wave drag, both by computing the pressure integral around the body and by integrating the momentum loss across the shock. Numerical errors involved in the computations that affect the accuracy of drag evaluations were analyzed. The factors that effect numerical stability and the rate of convergence of the iterative schemes were also systematically studied.
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.
NUMERICAL SIMULATIONS OF CHROMOSPHERIC MICROFLARES
Jiang, R. L.; Fang, C.; Chen, P. F.
2010-02-20
With gravity, ionization, and radiation being considered, we perform 2.5 dimensional (2.5D) compressible resistive magnetohydrodynamic (MHD) simulations of chromospheric magnetic reconnection using the CIP-MOCCT scheme. The temperature distribution of the quiet-Sun atmospheric model VALC and the helium abundance (10%) are adopted. Our 2.5D MHD simulation reproduces qualitatively the temperature enhancement observed in chromospheric microflares. The temperature enhancement DELTAT is demonstrated to be sensitive to the background magnetic field, whereas the total evolution time DELTAt is sensitive to the magnitude of the anomalous resistivity. Moreover, we found a scaling law, which is described as DELTAT/DELTAt {approx} n{sub H} {sup -1.5} B {sup 2.1}eta{sub 0} {sup 0.88}. Our results also indicate that the velocity of the upward jet is much greater than that of the downward jet, and the X-point may move up or down.
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
Numerical simulation of jet noise
NASA Astrophysics Data System (ADS)
Paliath, Umesh
In the present work, computational aeroacoustics and parallel computers are used to conduct a study of flow-induced noise from different jet nozzle geometries. The nozzle is included as part of the computational domain. This is important to predict jet noise from nozzles associated with military aircraft engines. The Detached Eddy Simulation (DES) approach is used to simulate both the jet nozzle internal and external flows as well as the jet plume. This methodology allows the turbulence model to transition from an unsteady Reynolds Averaged Navier-Stokes (URANS) method for attached boundary layers to a Large Eddy Simulation (LES) in separated regions. Thus, it is ideally suited to jet flow simulations where the nozzle is included. Both cylindrical polar and Cartesian coordinate systems are used. A spectral method is used to avoid the centerline singularity when using the cylindrical coordinate system. The one equation Spalart-Allmaras turbulence model, in DES mode, is used to describe the evolution of the turbulent eddy viscosity. An explicit 4th order Runge-Kutta time marching scheme is used. For spatial discritization the Dispersion Relation Preserving scheme(DRP) is used. The farfield sound is evaluated using the Ffowcs Williams-Hawkings permeable surface wave extrapolation method. This permits the noise to be predicted at large distances from the jet based on fluctuations in the jets near field. The present work includes a study of the effect of different nozzle geometries such as axisymmetric/non-axisymmetric and planar/non-planar exits on the far field noise predictions. Also the effect of operating conditions such as a heated/unheated jet, the effect of forward flight, a jet flow at an angle of attack, and the effect of a supersonic exit Mach number, are included in the study.
Numerical simulation of transitional flow
NASA Technical Reports Server (NTRS)
Biringen, Sedat
1986-01-01
The applicability of active control of transition by periodic suction-blowing is investigated via direct simulations of the Navier-Stokes equations. The time-evolution of finite-amplitude disturbances in plane channel flow is compared in detail with and without control. The analysis indicates that, for relatively small three-dimensional amplitudes, a two-dimensional control effectively reduces disturbance growth rates even for linearly unstable Reynolds numbers. After the flow goes through secondary instability, three-dimensional control seems necessary to stabilize the flow. An investigation of the temperature field suggests that passive temperature contamination is operative to reflect the flow dynamics during transition.
Numerical simulation of ball-racket impact
NASA Astrophysics Data System (ADS)
Yu, Yingpang
The collision of a ball with a tennis racket is usually modeled in terms of rigid body dynamics or an elastic system involving only a few springs. In this paper, we study the impact between a tennis ball and racket, by modeling the tennis ball in two different yaws. One method models the tennis ball as a Hertz elastic body and the other one models the ball by a more accurate finite element analysis. In the first model, we assume that the elastic properties of the ball obeys Hertz's law. In the finite element model, we consider the tennis ball as a shell witch is a elastic system constructed out of many isotropic small linear flat, elements, witch have both elastic and damping properties. The damping in each way is approximated as viscous term. In both methods, we study the static condition of deformation against a rigid surface before applying these models to dynamical processes. We compare these two methods and eventually determine how the racket parameters effect the performance of the racket, using numerical simulations. Comparison with experiment are show to confirm the general conclusion of the model.
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 Falling Sphere Viscometry Experiments.
NASA Astrophysics Data System (ADS)
O Dwyer, L.; Kellogg, L. H.; Lesher, C. E.
2007-12-01
The falling sphere technique based on Stokes' law is widely used to determine the viscosities of geologically relevant melts at high pressures. Stokes' law is valid when a rigid sphere falls slowly and steadily through a stationary and infinite Newtonian medium of uniform properties. High-pressure falling sphere experiments however, usually involve dropping a dense, refractory sphere through a liquid contained by a cylindrical capsule of finite size. The sphere velocity is influenced by the walls (Faxen correction) and ends of the capsule, and possible convective motion of the fluid. Efforts are made to minimize thermal gradients in laboratory experiments, but small temperature differences within the capsule can lead to convection complicating interpretation. We utilize GALE (Moresi et al., 2003;), a finite element particle-in-cell code, to examine these factors in numerical models of conditions similar to those of high-pressure experiments. Our modeling considers a three- dimensional box or cylinder containing a cluster of particles that represent the dense sphere in laboratory experiments surrounded by low viscosity particles representing the melt. GALE includes buoyancy forces, heat flow, and viscosity variations so our model can be used to assess the effects of the capsule's walls and ends, and the consequences of thermal gradients on the sphere's velocity and trajectory. Comparisons between our numerical simulations and real-time falling sphere experiments involving lower viscosity molten komatiite are made to assess the validity of Stokes' law with the standard Faxen correction included, and formulations considering end effects. The modeling also permits an evaluation of the uncertainties in recovering accurate liquid viscosities from Stokes' law when a dense sphere falls through a convecting low viscosity melt. It also allows us to assess acceleration to a terminal velocity that can provide constraints on melt viscosity in experiments in which the terminal
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
Numerical simulations of the reditron
NASA Astrophysics Data System (ADS)
Kwan, Thomas J. T.; Davis, Harold A.
1988-04-01
The reflected-electrons discrimination microwave generator (reditron) is a high-power, narrow-band, and single-mode microwave generation that makes exclusive use of the oscillatory character of the virtual-cathode of a relativistic electron beam. The complex, nonlinear character of the virtual-cathode device necessitates particle-in-cell plasma simulation techniques. Investigations indicate two sources of the radiation: (1) the trapped electrons reflexing between the real and virtual cathodes, and (2) the oscillation of the virtual cathode. In the conventional design, the two mechanisms coexist and interfere with each other destructively, causing degradation of the efficiency of microwave generation. The authors have investigated a configuration with a slotted, thick anode and an external magnetic field, which effectively eliminates the reflexing electrons. Two-dimensional particle-in-cell simulations showed that such a configuration exploits the oscillation of the virtual cathode exclusively, and it generates single-mode, narrowbandwidth, and high-power microwave radiation with a potential efficiency over 10 percent. It was found that further optimization could be achieved by the use of a density (current) modulated electron beam at appropriate frequencies.
Numerical simulations of disordered superconductors
Bedell, K.S.; Gubernatis, J.E.; Scalettar, R.T.; Zimanyi, G.T.
1997-12-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The authors carried out Monte Carlo studies of the critical behavior of superfluid {sup 4}He in aerogel. They found the superfluid density exponent increases in the presence of fractal disorder with a value roughly consistent with experimental results. They also addressed the localization of flux lines caused by splayed columnar pins. Using a Sine-Gordon-type of renormalization group study they obtained an analytic form for the critical temperature. They also determined the critical temperature from I-V characteristics obtained from a molecular dynamics simulation. The combined studies enabled one to construct the phase diagram as a function of interaction strength, temperature, and disorder. They also employed the recently developed mapping between boson world-lines and the flux motion to use quantum Monte Carlo simulations to analyze localization in the presence of disorder. From measurements of the transverse flux line wandering, they determined the critical ratio of columnar to point disorder strength needed to localize the bosons.
Numerical simulations of protostellar jets
NASA Astrophysics Data System (ADS)
Suttner, Gerhard; Smith, Michael D.; Yorke, Harold W.; Zinnecker, Hans
Molecular jets announce the successful birth of a protostar. We develop here a model for the jets and their environments, adapting a multi-dimensional hydrocode to follow the molecular-atomic transitions of hydrogen. We examine powerful outflows into dense gas. The cocoon which forms around a jet is a very low density cavity of atomic gas. These atoms originate from strong shocks which dissociate the molecules. The rest of the molecules are either within the jet or swept up into very thin layers. Pulsed jets produce wider cavities and molecular layers which can grow onto resolvable jet knots. Three-dimensional simulations produce shocked molecular knots, distorted and multiple bow shocks and arclike structures. Spectroscopic and excitation properties of the hydrogen molecules are calculated. In the infrared, strong emission is seen from shocks within the jet (when pulsed) as well as from discrete regions along the cavity walls. Excitation, as measured by line ratios, is not generally constant. Broad double-peaked, shifted emission lines are predicted. The jet model for protostellar outflows is confronted with the constraints imposed by CO spectroscopic observations. From the three dimensional simulations we calculate line profiles and construct position-velocity diagrams for the (low-J) CO transitions. We find (1) the profiles imply power law variation of integrated brightness with velocity over a wide range of velocities, (2) the velocity field resembles a `Hubble Law' and (3) a hollow-shell structure at low velocities becomes an elongated lobe at high velocities. Deviations from the simple power law dependence of integrated brightness versus velocity occur at high velocities in our simulations. The curve first dips to a shallow minimum and then rises rapidly and peaks sharply. Reanalysis of the NGC 2264G and Cepheus E data confirm these predictions. We identify these two features with a jet-ambient shear layer and the jet itself. A deeper analysis reveals that
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.
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.
Accurate direct Eulerian simulation of dynamic elastic-plastic flow
Kamm, James R; Walter, John W
2009-01-01
The simulation of dynamic, large strain deformation is an important, difficult, and unsolved computational challenge. Existing Eulerian schemes for dynamic material response are plagued by unresolved issues. We present a new scheme for the first-order system of elasto-plasticity equations in the Eulerian frame. This system has an intrinsic constraint on the inverse deformation gradient. Standard Godunov schemes do not satisfy this constraint. The method of Flux Distributions (FD) was devised to discretely enforce such constraints for numerical schemes with cell-centered variables. We describe a Flux Distribution approach that enforces the inverse deformation gradient constraint. As this approach is new and novel, we do not yet have numerical results to validate our claims. This paper is the first installment of our program to develop this new method.
D-BRAIN: Anatomically Accurate Simulated Diffusion MRI Brain Data.
Perrone, Daniele; Jeurissen, Ben; Aelterman, Jan; Roine, Timo; Sijbers, Jan; Pizurica, Aleksandra; Leemans, Alexander; Philips, Wilfried
2016-01-01
Diffusion Weighted (DW) MRI allows for the non-invasive study of water diffusion inside living tissues. As such, it is useful for the investigation of human brain white matter (WM) connectivity in vivo through fiber tractography (FT) algorithms. Many DW-MRI tailored restoration techniques and FT algorithms have been developed. However, it is not clear how accurately these methods reproduce the WM bundle characteristics in real-world conditions, such as in the presence of noise, partial volume effect, and a limited spatial and angular resolution. The difficulty lies in the lack of a realistic brain phantom on the one hand, and a sufficiently accurate way of modeling the acquisition-related degradation on the other. This paper proposes a software phantom that approximates a human brain to a high degree of realism and that can incorporate complex brain-like structural features. We refer to it as a Diffusion BRAIN (D-BRAIN) phantom. Also, we propose an accurate model of a (DW) MRI acquisition protocol to allow for validation of methods in realistic conditions with data imperfections. The phantom model simulates anatomical and diffusion properties for multiple brain tissue components, and can serve as a ground-truth to evaluate FT algorithms, among others. The simulation of the acquisition process allows one to include noise, partial volume effects, and limited spatial and angular resolution in the images. In this way, the effect of image artifacts on, for instance, fiber tractography can be investigated with great detail. The proposed framework enables reliable and quantitative evaluation of DW-MR image processing and FT algorithms at the level of large-scale WM structures. The effect of noise levels and other data characteristics on cortico-cortical connectivity and tractography-based grey matter parcellation can be investigated as well. PMID:26930054
D-BRAIN: Anatomically Accurate Simulated Diffusion MRI Brain Data
Perrone, Daniele; Jeurissen, Ben; Aelterman, Jan; Roine, Timo; Sijbers, Jan; Pizurica, Aleksandra; Leemans, Alexander; Philips, Wilfried
2016-01-01
Diffusion Weighted (DW) MRI allows for the non-invasive study of water diffusion inside living tissues. As such, it is useful for the investigation of human brain white matter (WM) connectivity in vivo through fiber tractography (FT) algorithms. Many DW-MRI tailored restoration techniques and FT algorithms have been developed. However, it is not clear how accurately these methods reproduce the WM bundle characteristics in real-world conditions, such as in the presence of noise, partial volume effect, and a limited spatial and angular resolution. The difficulty lies in the lack of a realistic brain phantom on the one hand, and a sufficiently accurate way of modeling the acquisition-related degradation on the other. This paper proposes a software phantom that approximates a human brain to a high degree of realism and that can incorporate complex brain-like structural features. We refer to it as a Diffusion BRAIN (D-BRAIN) phantom. Also, we propose an accurate model of a (DW) MRI acquisition protocol to allow for validation of methods in realistic conditions with data imperfections. The phantom model simulates anatomical and diffusion properties for multiple brain tissue components, and can serve as a ground-truth to evaluate FT algorithms, among others. The simulation of the acquisition process allows one to include noise, partial volume effects, and limited spatial and angular resolution in the images. In this way, the effect of image artifacts on, for instance, fiber tractography can be investigated with great detail. The proposed framework enables reliable and quantitative evaluation of DW-MR image processing and FT algorithms at the level of large-scale WM structures. The effect of noise levels and other data characteristics on cortico-cortical connectivity and tractography-based grey matter parcellation can be investigated as well. PMID:26930054
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
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.
How Accurate Are Transition States from Simulations of Enzymatic Reactions?
2015-01-01
The rate expression of traditional transition state theory (TST) assumes no recrossing of the transition state (TS) and thermal quasi-equilibrium between the ground state and the TS. Currently, it is not well understood to what extent these assumptions influence the nature of the activated complex obtained in traditional TST-based simulations of processes in the condensed phase in general and in enzymes in particular. Here we scrutinize these assumptions by characterizing the TSs for hydride transfer catalyzed by the enzyme Escherichia coli dihydrofolate reductase obtained using various simulation approaches. Specifically, we compare the TSs obtained with common TST-based methods and a dynamics-based method. Using a recently developed accurate hybrid quantum mechanics/molecular mechanics potential, we find that the TST-based and dynamics-based methods give considerably different TS ensembles. This discrepancy, which could be due equilibrium solvation effects and the nature of the reaction coordinate employed and its motion, raises major questions about how to interpret the TSs determined by common simulation methods. We conclude that further investigation is needed to characterize the impact of various TST assumptions on the TS phase-space ensemble and on the reaction kinetics. PMID:24860275
Numerical Simulation Of Buckling In Waffle Plants
NASA Technical Reports Server (NTRS)
Yin, Dah N.; Tran, Vu M.
1990-01-01
Accurate results obtained when fillet radii considered. Two reports describe numerical and experimental study of application of PASCO and WAFFLE computer programs to analysis of buckling in integrally machined, biaxially stiffened panel. PASCO (Panal Analysis and Sizing Code) is finite-element stress-and-strain code written for analysis and sizing of uniaxially stiffened panels. WAFFLE program provides comprehensive stress analysis of waffle panel, used to determine bending moments at interfaces.
Numerical Resolution of Seismic Wavefield Simulations in Southern California
NASA Astrophysics Data System (ADS)
Tape, C.; Casarotti, E.
2014-12-01
Seismic wavefield simulations can provide accurate solutions to the wave equation, even for three-dimensional seismic velocity models with topography, basin structures, anisotropy, attenuation, and other complexities. But how accurate are these numerical solutions? In many cases the effect of numerical dispersion on the synthetic seismograms looks quite similar to the effects of structural complexities. Therefore it is important to know the numerical resolution of the synthetic seismograms, that is, the minimum period that provides a quantifiably numerically accurate solution to the wave equation. Numerical resolution can be discussed in terms of a combined mesh and velocity model, or in terms of an individual source-station path within the same mesh and velocity model. Here we discuss two approaches for quantifying the numerical resolution. In the first approach we estimate the minimum resolvable period of each element within the finite element mesh. This calculation, performed within SPECFEM3D, requires no wavefield simulations and is based only on the size of each element and the minimum velocity within each element. The calculation produces a volumetric field that shows the estimated minimum resolvable period within each element of the (generally unstructured) mesh. In the second approach we choose a set of earthquakes to be used within a tomographic inversion. For each earthquake we compute one simulation using a fine discretization of gridpoints on the finite-element mesh and another simulation using a coarse discretization. We filter both sets of seismograms over a range of periods and then quantify the waveform differences. The minimum resolvable period (or numerical resolution) is identified by the minimum period for which the synthetic seismogram from the coarse-mesh and fine-mesh simulations is quantifiably the same. This calculation provides a path-specific minimum resolvable period that can be used to guide the choice of measurement filtering for a
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.
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.
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.
Symphony: a framework for accurate and holistic WSN simulation.
Riliskis, Laurynas; Osipov, Evgeny
2015-01-01
Research on wireless sensor networks has progressed rapidly over the last decade, and these technologies have been widely adopted for both industrial and domestic uses. Several operating systems have been developed, along with a multitude of network protocols for all layers of the communication stack. Industrial Wireless Sensor Network (WSN) systems must satisfy strict criteria and are typically more complex and larger in scale than domestic systems. Together with the non-deterministic behavior of network hardware in real settings, this greatly complicates the debugging and testing of WSN functionality. To facilitate the testing, validation, and debugging of large-scale WSN systems, we have developed a simulation framework that accurately reproduces the processes that occur inside real equipment, including both hardware- and software-induced delays. The core of the framework consists of a virtualized operating system and an emulated hardware platform that is integrated with the general purpose network simulator ns-3. Our framework enables the user to adjust the real code base as would be done in real deployments and also to test the boundary effects of different hardware components on the performance of distributed applications and protocols. Additionally we have developed a clock emulator with several different skew models and a component that handles sensory data feeds. The new framework should substantially shorten WSN application development cycles. PMID:25723144
Symphony: A Framework for Accurate and Holistic WSN Simulation
Riliskis, Laurynas; Osipov, Evgeny
2015-01-01
Research on wireless sensor networks has progressed rapidly over the last decade, and these technologies have been widely adopted for both industrial and domestic uses. Several operating systems have been developed, along with a multitude of network protocols for all layers of the communication stack. Industrial Wireless Sensor Network (WSN) systems must satisfy strict criteria and are typically more complex and larger in scale than domestic systems. Together with the non-deterministic behavior of network hardware in real settings, this greatly complicates the debugging and testing of WSN functionality. To facilitate the testing, validation, and debugging of large-scale WSN systems, we have developed a simulation framework that accurately reproduces the processes that occur inside real equipment, including both hardware- and software-induced delays. The core of the framework consists of a virtualized operating system and an emulated hardware platform that is integrated with the general purpose network simulator ns-3. Our framework enables the user to adjust the real code base as would be done in real deployments and also to test the boundary effects of different hardware components on the performance of distributed applications and protocols. Additionally we have developed a clock emulator with several different skew models and a component that handles sensory data feeds. The new framework should substantially shorten WSN application development cycles. PMID:25723144
Numerical simulation of the flow field around a complete aircraft
NASA Technical Reports Server (NTRS)
Shang, J. S.; Scherr, S. J.
1986-01-01
The present effort represents a first attempt of numerical simulation of the flow field around a complete aircraft-like, lifting configuration utilizing the Reynolds averaged Navier-Stokes equations. The numerical solution generated for the experimental aircraft concept X24C-10D at a Mach number of 5.95 not only exhibited accurate prediction of detailed flow properties but also of the integrated aerodynamic coefficients. In addition, the present analysis demonstrated that a page structure of data collected into cyclic blocks is an efficient and viable means for processing the Navier-Stokes equations on the CRAY XMP-22 computer with external memory device.
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.
Liquid propellant rocket engine combustion simulation with a time-accurate CFD method
NASA Technical Reports Server (NTRS)
Chen, Y. S.; Shang, H. M.; Liaw, Paul; Hutt, J.
1993-01-01
Time-accurate computational fluid dynamics (CFD) algorithms are among the basic requirements as an engineering or research tool for realistic simulations of transient combustion phenomena, such as combustion instability, transient start-up, etc., inside the rocket engine combustion chamber. A time-accurate pressure based method is employed in the FDNS code for combustion model development. This is in connection with other program development activities such as spray combustion model development and efficient finite-rate chemistry solution method implementation. In the present study, a second-order time-accurate time-marching scheme is employed. For better spatial resolutions near discontinuities (e.g., shocks, contact discontinuities), a 3rd-order accurate TVD scheme for modeling the convection terms is implemented in the FDNS code. Necessary modification to the predictor/multi-corrector solution algorithm in order to maintain time-accurate wave propagation is also investigated. Benchmark 1-D and multidimensional test cases, which include the classical shock tube wave propagation problems, resonant pipe test case, unsteady flow development of a blast tube test case, and H2/O2 rocket engine chamber combustion start-up transient simulation, etc., are investigated to validate and demonstrate the accuracy and robustness of the present numerical scheme and solution algorithm.
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.
A numerical simulation of galaxy subcluster mergers
NASA Technical Reports Server (NTRS)
Roettiger, Kurt; Burns, Jack O.; Loken, Chris
1993-01-01
We present preliminary results of a 3-D numerical simulation of two merging subclusters of galaxies. By self-consistently modelling the intracluster gas and dark matter dynamics, we hope to gain insight as to how the dynamics of both relate to such observables as the cluster x-ray emission, radio source morphology, and velocity dispersions.
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...
Simple Numerical Simulation of Strain Measurement
NASA Technical Reports Server (NTRS)
Tai, H.
2002-01-01
By adopting the basic principle of the reflection (and transmission) of a plane polarized electromagnetic wave incident normal to a stack of films of alternating refractive index, a simple numerical code was written to simulate the maximum reflectivity (transmittivity) of a fiber optic Bragg grating corresponding to various non-uniform strain conditions including photo-elastic effect in certain cases.
Numerical simulation of plasma opening switches
Mason, R.J.; Jones, M.E.; Bergman, C.D.
1989-01-01
Plasma Opening Switches have been examined numerically with the aid of the ANTHEM plasma simulation model. A generic bi-cylindrical switch is studied. The switching of generator pulses ranging from 50 ns to 1 ..mu..sec is reviewed, for a variety of plasma fill lengths and densities, and for a range of resistive loads. 7 refs., 9 figs.
Accurate Critical Stress Intensity Factor Griffith Crack Theory Measurements by Numerical Techniques
Petersen, Richard C.
2014-01-01
Critical stress intensity factor (KIc) has been an approximation for fracture toughness using only load-cell measurements. However, artificial man-made cracks several orders of magnitude longer and wider than natural flaws have required a correction factor term (Y) that can be up to about 3 times the recorded experimental value [1-3]. In fact, over 30 years ago a National Academy of Sciences advisory board stated that empirical KIc testing was of serious concern and further requested that an accurate bulk fracture toughness method be found [4]. Now that fracture toughness can be calculated accurately by numerical integration from the load/deflection curve as resilience, work of fracture (WOF) and strain energy release (SIc) [5, 6], KIc appears to be unnecessary. However, the large body of previous KIc experimental test results found in the literature offer the opportunity for continued meta analysis with other more practical and accurate fracture toughness results using energy methods and numerical integration. Therefore, KIc is derived from the classical Griffith Crack Theory [6] to include SIc as a more accurate term for strain energy release rate (𝒢Ic), along with crack surface energy (γ), crack length (a), modulus (E), applied stress (σ), Y, crack-tip plastic zone defect region (rp) and yield strength (σys) that can all be determined from load and deflection data. Polymer matrix discontinuous quartz fiber-reinforced composites to accentuate toughness differences were prepared for flexural mechanical testing comprising of 3 mm fibers at different volume percentages from 0-54.0 vol% and at 28.2 vol% with different fiber lengths from 0.0-6.0 mm. Results provided a new correction factor and regression analyses between several numerical integration fracture toughness test methods to support KIc results. Further, bulk KIc accurate experimental values are compared with empirical test results found in literature. Also, several fracture toughness mechanisms
Numerical simulation of supersonic boundary layer transition
NASA Technical Reports Server (NTRS)
Guo, Y.; Adams, N. A.; Sandham, N. D.; Kleiser, L.
1994-01-01
The present contribution reviews some of the recent progress obtained at our group in the direct numerical simulation (DNS) of compressible boundary layer transition. Elements of the different simulation approaches and numerical techniques employed are surveyed. Temporal and spatial simulations, as well as comparisons with results obtained from Parabolized Stability Equations, are discussed. DNS results are given for flat plate boundary layers in the Mach number range 1.6 to 4.5. A temporal DNS at Mach 4.5 has been continued through breakdown all the way to the turbulent stage. In addition results obtained with a recently developed extended temporal DNS approach are presented, which takes into account some nonparallel effects of a growing boundary layer. Results from this approach are quite close to those of spatial DNS, while preserving the efficiency of the temporal DNS.
Numerical simulation of tip clearance effects in turbomachinery
Basson, A.; Lakshminarayana, B.
1995-07-01
The numerical formulation developed here includes an efficient grid generation scheme, particularly suited to computational grids for the analysis of turbulent turbomachinery flows and tip clearance flows, and a semi-implicit, pressure-based computational fluid dynamics scheme that directly includes artificial dissipation,a nd is applicable to both viscous and inviscid flows. The value of this artificial dissipation is optimized to achieve accuracy and convergency in the solution. The numerical model is used to investigate the structure of tip clearance flows in a turbine nozzle. The structure of leakage flow is captured accurately, including blade-to-blade variation of all three velocity components, pitch and yaw angles, losses and blade static pressures in the tip clearance region. The simulation also includes evaluation of such quantities the spanwise extent affected by the leakage flow. It is demonstrated, through optimization of grid size and artificial dissipation, that the tip clearance flow field can be captured accurately.
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.
Time-Accurate Simulations and Acoustic Analysis of Slat Free-Shear-Layer. Part 2
NASA Technical Reports Server (NTRS)
Khorrami, Mehdi R.; Singer, Bart A.; Lockard, David P.
2002-01-01
Unsteady computational simulations of a multi-element, high-lift configuration are performed. Emphasis is placed on accurate spatiotemporal resolution of the free shear layer in the slat-cove region. The excessive dissipative effects of the turbulence model, so prevalent in previous simulations, are circumvented by switching off the turbulence-production term in the slat cove region. The justifications and physical arguments for taking such a step are explained in detail. The removal of this excess damping allows the shear layer to amplify large-scale structures, to achieve a proper non-linear saturation state, and to permit vortex merging. The large-scale disturbances are self-excited, and unlike our prior fully turbulent simulations, no external forcing of the shear layer is required. To obtain the farfield acoustics, the Ffowcs Williams and Hawkings equation is evaluated numerically using the simulated time-accurate flow data. The present comparison between the computed and measured farfield acoustic spectra shows much better agreement for the amplitude and frequency content than past calculations. The effect of the angle-of-attack on the slat's flow features radiated acoustic field are also simulated presented.
Direct numerical simulation of a recorder.
Giordano, N
2013-02-01
The aeroacoustics of a recorder are studied using a direct numerical simulation based on the Navier-Stokes equations in two dimensions. Spatial maps for the air pressure and velocity give a detailed picture of vortex shedding near the labium. Changes in the spectrum as a result of variations in the blowing speed are also investigated. The results are in good semi-quantitative agreement with general results for these phenomena from experiments. PMID:23363126
Numerical simulation of droplet impact on interfaces
NASA Astrophysics Data System (ADS)
Kahouadji, Lyes; Che, Zhizhao; Matar, Omar; Shin, Seungwon; Chergui, Jalel; Juric, Damir
2015-11-01
Simulations of three-dimensional droplet impact on interfaces are carried out using BLUE, a massively-parallel code based on a hybrid Front-Tracking/Level-Set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. High resolution numerical results show fine details and features of droplet ejection, crown formation and rim instability observed under similar experimental conditions. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
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 simulations of hyperfine transitions of antihydrogen
NASA Astrophysics Data System (ADS)
Kolbinger, B.; Capon, A.; Diermaier, M.; Lehner, S.; Malbrunot, C.; Massiczek, O.; Sauerzopf, C.; Simon, M. C.; Widmann, E.
2015-08-01
One of the ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration's goals is the measurement of the ground state hyperfine transition frequency in antihydrogen, the antimatter counterpart of one of the best known systems in physics. This high precision experiment yields a sensitive test of the fundamental symmetry of CPT. Numerical simulations of hyperfine transitions of antihydrogen atoms have been performed providing information on the required antihydrogen events and the achievable precision.
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.
Numerical Simulations of Boundary-Driven Dynamos
NASA Astrophysics Data System (ADS)
White, K.; Brummell, N.; Glatzmaier, G. A.
2012-12-01
An important topic of physics research is how magnetic fields are generated and maintained in the many astrophysical bodies where they are ubiquitously observed. Of particular interest, are reversals of magnetic fields of planets and stars, especially those of the Earth and the Sun. In an attempt to provide intuition on this problem, numerous physical dynamo experiments have been performed in different configurations. Recently, a tremendous breakthrough was made in the Von Karman sodium (VKS) experiments in France when the most realistic laboratory fluid dynamo to date was produced by driving an unconstrained flow in a cylinder of liquid sodium (Monchaux et al, 2007, PRL). One of the curiosities of the VKS experiment however is the effect of the composition of the impellers that drive the flow. Steel blades failed to produce a dynamo, but soft iron impellers, which have much higher magnetic permeability, succeeded. The role of the magnetic properties of the boundaries in boundary-driven dynamos is therefore clearly of interest. Kinematic and laminar numerical dynamo simulations (Giesecke et al, 2010, PRL & Gissinger et al, 2008 EPL) have shed some light but turbulent, nonlinear simulations are necessary. Roberts, Glatzmaier & Clune 2010 created a simplified model of the VKS setup by using three-dimensional numerical simulations in a spherical geometry with differential zonal motions of the boundary replacing the driving impellers of the VKS experiment. We have extended these numerical simulations further towards a more complete understanding of such boundary-forced dynamos. In particular, we have examined the effect of the magnetic boundary conditions - changes in the wall thickness, the magnetic permeability, and the electrical conductivity - on the mechanisms responsible for dynamo generation. Enhanced permeability, conductivity and wall thickness all help dynamo action to different degrees. We are further extending our investigations to asymmetric forcing to
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
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
Numerical simulations and modeling of turbulent combustion
NASA Astrophysics Data System (ADS)
Cuenot, B.
Turbulent combustion is the basic physical phenomenon responsible for efficient energy release by any internal combustion engine. However it is accompanied by other undesirable phenomena such as noise, pollutant species emission or damaging instabilities that may even lead to the system desctruction. It is then crucial to control this phenomenon, to understand all its mecanisms and to master it in industrial systems. For long time turbulent combustion has been explored only through theory and experiment. But the rapid increase of computers power during the last years has allowed an important development of numerical simulation, that has become today an essential tool for research and technical design. Direct numerical simulation has then allowed to rapidly progress in the knowledge of turbulent flame structures, leading to new modelisations for steady averaged simulations. Recently large eddy simulation has made a new step forward by refining the description of complex and unsteady flames. The main problem that arises when performing numerical simulation of turbulent combustion is linked to the description of the flame front. Being very thin, it can not however be reduced to a simple interface as it is the location of intense chemical transformation and of strong variations of thermodynamical quantities. Capturing the internal structure of a zone with a thickness of the order of 0.1 mm in a computation with a mesh step 10 times larger being impossible, it is necessary to model the turbulent flame. Models depend on the chemical structure of the flame, on the ambiant turbulence, on the combustion regime (flamelets, distributed combustion, etc.) and on the reactants injection mode (premixed or not). One finds then a large class of models, from the most simple algebraic model with a one-step chemical kinetics, to the most complex model involving probablity density functions, cross-correlations and multiple-step or fully complex chemical kinetics.
Seth A Veitzer
2008-10-21
Effects of stray electrons are a main factor limiting performance of many accelerators. Because heavy-ion fusion (HIF) accelerators will operate in regimes of higher current and with walls much closer to the beam than accelerators operating today, stray electrons might have a large, detrimental effect on the performance of an HIF accelerator. A primary source of stray electrons is electrons generated when halo ions strike the beam pipe walls. There is some research on these types of secondary electrons for the HIF community to draw upon, but this work is missing one crucial ingredient: the effect of grazing incidence. The overall goal of this project was to develop the numerical tools necessary to accurately model the effect of grazing incidence on the behavior of halo ions in a HIF accelerator, and further, to provide accurate models of heavy ion stopping powers with applications to ICF, WDM, and HEDP experiments.
Numerical simulation of freeway traffic flow
Liu, G.; Lyrintzis, A.S.; Michalopoulos, P.G.
1997-11-01
A new high-order continuum model is presented in this paper. This high-order model exhibits smooth solutions rather than discontinuities, is able to describe the amplification of small disturbances on heavy traffic, and allows fluctuations of speed around the equilibrium values. Furthermore, unlike some earlier high-order models, it does not result in negative speeds at the tail of congested regions and disturbance propagation speeds greater than the flow speed. The model takes into account the relaxation time as a function of density and, in the equilibrium limit, it is consistent with the simple continuum model. A Riemann-problem-based numerical method is proposed for the solution of the new high-order model. Modeling of interrupted flow behavior such as merging, diverging, and weaving is also investigated. Based on the new high order model, the proposed numerical method and the modeling of interrupted flow, a versatile code is developed for the numerical simulation of freeway traffic flow that includes several freeway geometries. The authors compare the high-order model with the simple continuum model and the proposed numerical method with the Lax method based on 30-s and 5-min field data. The model is tested in interrupted flow situations (e.g., pipeline, merging, diverging, and weaving areas). A comparison of numerical results with limited field data shows that the high-order model performs better than the simple continuum model and describes better than a previously proposed method.
Numerical Simulation of a Seaway with Breaking
NASA Astrophysics Data System (ADS)
Dommermuth, Douglas; O'Shea, Thomas; Brucker, Kyle; Wyatt, Donald
2012-11-01
The focus of this presentation is to describe the recent efforts to simulate a fully non-linear seaway with breaking by using a high-order spectral (HOS) solution of the free-surface boundary value problem to drive a three-dimensional Volume of Fluid (VOF) solution. Historically, the two main types of simulations to simulate free-surface flows are the boundary integral equations method (BIEM) and high-order spectral (HOS) methods. BIEM calculations fail at the point at which the surface impacts upon itself, if not sooner, and HOS methods can only simulate a single valued free-surface. Both also employ a single-phase approximation in which the effects of the air on the water are neglected. Due to these limitations they are unable to simulate breaking waves and air entrainment. The Volume of Fluid (VOF) method on the other hand is suitable for modeling breaking waves and air entrainment. However it is computationally intractable to generate a realistic non-linear sea-state. Here, we use the HOS solution to quickly drive, or nudge, the VOF solution into a non-linear state. The computational strategies, mathematical formulation, and numerical implementation will be discussed. The results of the VOF simulation of a seaway with breaking will also be presented, and compared to the single phase, single valued HOS results.
Numerical simulations of localized high field 1H MR spectroscopy
Kaiser, Lana G.; Young, Karl; Matson, Gerald B.
2008-01-01
The limited bandwidths of volume selective RF pulses in localized in vivo MRS experiments introduce spatial artifacts that complicate spectral quantification of J-coupled metabolites. These effects are commonly referred to as a spatial interference or “4 compartment” artifacts and are more pronounced at higher field strengths. The main focus of this study is to develop a generalized approach to numerical simulations that combines full density matrix calculations with 3D localization to investigate the spatial artifacts and to provide accurate prior knowledge for spectral fitting. Full density matrix calculations with 3D localization using experimental pulses were carried out for PRESS (TE=20, 70 ms), STEAM (TE=20, 70 ms) and LASER (TE=70 ms) pulse sequences and compared to non-localized simulations and to phantom solution data at 4 Tesla. Additional simulations at 1.5 and 7 Tesla were carried out for STEAM and PRESS (TE=20 ms). Four brain metabolites that represented a range from weak to strong J-coupling networks were included in the simulations (lactate, N-acetylaspartate, glutamate and myo-inositol). For longer TE, full 3D localization was necessary to achieve agreement between the simulations and phantom solution spectra for the majority of cases in all pulse sequence simulations. For short echo time (TE=20 ms), ideal pulses without localizing gradients gave results that were in agreement with phantom results at 4 T for STEAM, but not for PRESS (TE=20). Numerical simulations that incorporate volume localization using experimental RF pulses are shown to be a powerful tool for generation of accurate metabolic basis sets for spectral fitting and for optimization of experimental parameters. PMID:18789736
Efficient and accurate numerical methods for the Klein-Gordon-Schroedinger equations
Bao, Weizhu . E-mail: bao@math.nus.edu.sg; Yang, Li . E-mail: yangli@nus.edu.sg
2007-08-10
In this paper, we present efficient, unconditionally stable and accurate numerical methods for approximations of the Klein-Gordon-Schroedinger (KGS) equations with/without damping terms. The key features of our methods are based on: (i) the application of a time-splitting spectral discretization for a Schroedinger-type equation in KGS (ii) the utilization of Fourier pseudospectral discretization for spatial derivatives in the Klein-Gordon equation in KGS (iii) the adoption of solving the ordinary differential equations (ODEs) in phase space analytically under appropriate chosen transmission conditions between different time intervals or applying Crank-Nicolson/leap-frog for linear/nonlinear terms for time derivatives. The numerical methods are either explicit or implicit but can be solved explicitly, unconditionally stable, and of spectral accuracy in space and second-order accuracy in time. Moreover, they are time reversible and time transverse invariant when there is no damping terms in KGS, conserve (or keep the same decay rate of) the wave energy as that in KGS without (or with a linear) damping term, keep the same dynamics of the mean value of the meson field, and give exact results for the plane-wave solution. Extensive numerical tests are presented to confirm the above properties of our numerical methods for KGS. Finally, the methods are applied to study solitary-wave collisions in one dimension (1D), as well as dynamics of a 2D problem in KGS.
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.
Dynamic stiffness removal for direct numerical simulations
Lu, Tianfeng; Law, Chung K.; Yoo, Chun Sang; Chen, Jacqueline H.
2009-08-15
A systematic approach was developed to derive non-stiff reduced mechanisms for direct numerical simulations (DNS) with explicit integration solvers. The stiffness reduction was achieved through on-the-fly elimination of short time-scales induced by two features of fast chemical reactivity, namely quasi-steady-state (QSS) species and partial-equilibrium (PE) reactions. The sparse algebraic equations resulting from QSS and PE approximations were utilized such that the efficiency of the dynamic stiffness reduction is high compared with general methods of time-scale reduction based on Jacobian decomposition. Using the dimension reduction strategies developed in our previous work, a reduced mechanism with 52 species was first derived from a detailed mechanism with 561 species. The reduced mechanism was validated for ignition and extinction applications over the parameter range of equivalence ratio between 0.5 and 1.5, pressure between 10 and 50 atm, and initial temperature between 700 and 1600 K for ignition, and worst-case errors of approximately 30% were observed. The reduced mechanism with dynamic stiffness removal was then applied in homogeneous and 1-D ignition applications, as well as a 2-D direct numerical simulation of ignition with temperature inhomogeneities at constant volume with integration time-steps of 5-10 ns. The integration was numerically stable and good accuracy was achieved. (author)
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.
Numerical Simulations of Radar Acoustic Scattering
NASA Astrophysics Data System (ADS)
Boluriaan, Said; Morris, Philip J.
1998-11-01
Wake vortices are produced by the lifting surfaces of all aircraft. The vortex created by a large aircraft can have a catastrophic effect on a small plane following closely behind. A vortex detection system would not only increase airport productivity by allowing adaptive spacing, but would also increase the safety of all aircraft operating around the airport by alerting controllers to hazardous conditions that might exist near the runways. In the present research, one and two-dimensional models have been considered for the study of wake vortex detection using a Radar Acoustic Sounding System (RASS). The permittivity perturbation caused by the vortex is modeled as a traveling wave with a Gaussian envelope and a variable propagation speed. The model equations are solved numerically. The one-dimensional model is also solved analytically. The main problem with a time domain simulation is the number of samples required to resolve the Doppler shift. Even for a 1D model with a typical scatterer size, the CPU time required to run the code is far beyond the currently available computer resources. One way to make the time domain simulation feasible is to recast the governing differential equation in order to remove the carrier frequency and solve only for the frequency shift in the scattered wave. The numerical stability characteristics of the resulting equation with complex coefficients are discussed. In order to validate the numerical scheme, the code is run for a fictitious speed of light.
Numerical Simulation of Low-Density Shock-Wave Interactions
NASA Technical Reports Server (NTRS)
Glass, Christopher E.
1999-01-01
Computational Fluid Dynamics (CFD) numerical simulations of low-density shock-wave interactions for an incident shock impinging on a cylinder have been performed. Flow-field density gradient and surface pressure and heating define the type of interference pattern and corresponding perturbations. The maximum pressure and heat transfer level and location for various interaction types (i.e., shock-wave incidence with respect to the cylinder) are presented. A time-accurate solution of the Type IV interference is employed to demonstrate the establishment and the steadiness of the low-density flow interaction.
Numerical Simulation of a High Mach Number Jet Flow
NASA Technical Reports Server (NTRS)
Hayder, M. Ehtesham; Turkel, Eli; Mankbadi, Reda R.
1993-01-01
The recent efforts to develop accurate numerical schemes for transition and turbulent flows are motivated, among other factors, by the need for accurate prediction of flow noise. The success of developing high speed civil transport plane (HSCT) is contingent upon our understanding and suppression of the jet exhaust noise. The radiated sound can be directly obtained by solving the full (time-dependent) compressible Navier-Stokes equations. However, this requires computational storage that is beyond currently available machines. This difficulty can be overcome by limiting the solution domain to the near field where the jet is nonlinear and then use acoustic analogy (e.g., Lighthill) to relate the far-field noise to the near-field sources. The later requires obtaining the time-dependent flow field. The other difficulty in aeroacoustics computations is that at high Reynolds numbers the turbulent flow has a large range of scales. Direct numerical simulations (DNS) cannot obtain all the scales of motion at high Reynolds number of technological interest. However, it is believed that the large scale structure is more efficient than the small-scale structure in radiating noise. Thus, one can model the small scales and calculate the acoustically active scales. The large scale structure in the noise-producing initial region of the jet can be viewed as a wavelike nature, the net radiated sound is the net cancellation after integration over space. As such, aeroacoustics computations are highly sensitive to errors in computing the sound sources. It is therefore essential to use a high-order numerical scheme to predict the flow field. The present paper presents the first step in a ongoing effort to predict jet noise. The emphasis here is in accurate prediction of the unsteady flow field. We solve the full time-dependent Navier-Stokes equations by a high order finite difference method. Time accurate spatial simulations of both plane and axisymmetric jet are presented. Jet Mach
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.
Numerical reproducibility for implicit Monte Carlo simulations
Cleveland, M.; Brunner, T.; Gentile, N.
2013-07-01
We describe and compare different approaches for achieving numerical reproducibility in photon Monte Carlo simulations. Reproducibility is desirable for code verification, testing, and debugging. Parallelism creates a unique problem for achieving reproducibility in Monte Carlo simulations because it changes the order in which values are summed. This is a numerical problem because double precision arithmetic is not associative. In [1], a way of eliminating this roundoff error using integer tallies was described. This approach successfully achieves reproducibility at the cost of lost accuracy by rounding double precision numbers to fewer significant digits. This integer approach, and other extended reproducibility techniques, are described and compared in this work. Increased precision alone is not enough to ensure reproducibility of photon Monte Carlo simulations. A non-arbitrary precision approaches required a varying degree of rounding to achieve reproducibility. For the problems investigated in this work double precision global accuracy was achievable by using 100 bits of precision or greater on all unordered sums which where subsequently rounded to double precision at the end of every time-step. (authors)
Direct Numerical Simulation of Cosmological Reionization
NASA Astrophysics Data System (ADS)
So, Geoffrey C.
We examine the epoch of hydrogen reionization using a new numerical method that allows us to self-consistently couple all the relevant physical processes (gas dynamics, dark matter dynamics, self-gravity, star formation/feedback, radiative transfer, ionization, recombination, heating and cooling) and evolve the system of coupled equations on the same high resolution mesh. We refer to this approach as direct numerical simulation, in contrast to existing approaches which decouple and coarse-grain the radiative transfer and ionization balance calculations relative to the underlying dynamical calculation. Our method is scalable with respect to the number of radiation sources, size of the mesh, and the number of computer processors employed, and is described in Chapter 2 of this thesis. This scalability permits us to simulate cosmological reionization in large cosmological volumes (~100 Mpc) while directly modeling the sources and sinks of ionizing radiation, including radiative feedback effects such as photoevaporation of gas from halos, Jeans smoothing of the IGM, and enhanced recombination due to small scale clumping. With our fiducial simulation, we find that roughly 2 ionizing photons per baryon is needed to highly ionize the intergalactic medium. The complicated events during reionization that lead to this number can be generally described as inside-out, but in reality the narrative depends on the level of ionization of the gas one defines as ionized. We have updated the formula observers often use for estimating the ionized volume filling fraction formula with a delta b and trec,eff to get from O(10%) to O(1%) consistency with our simulation results. This improvement comes from not using the traditional clumping factor, but instead, considering the history and local effects which were neglected in formulating the original expression. And finally, we have a new upper limit for the escape fraction of ~0.6 from our simulation, which takes into account the photons in
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.
Numerical simulation of boundary-layer transition
NASA Technical Reports Server (NTRS)
Spalart, P. R.
1984-01-01
The transition to turbulence in boundary layers was investigated by direct numerical solution of the nonlinear, three-dimensional, incompressible Navier-Stokes equations in the half-infinite domain over a flat plate. Periodicity was imposed in the streamwise and spanwise directions. A body force was applied to approximate the effect of a nonparallel mean flow. The numerical method was spectra, based on Fourier series and Jacobi polynomials, and used divergence-free basis functions. Extremely rapid convergence was obtained when solving the linear Orr-Sommerfeld equation. The early nonlinear and three-dimensional stages of transition, in a boundary layer disturbed by a vibrating ribbon, were successfully simulated. Excellent qualitative agreement was observed with either experiments or weakly nonlinear theories. In particular, the breakdown pattern was staggered or nonstaggered depending on the disturbance amplitude.
Numerical simulations of internal wave generation by convection in water.
Lecoanet, Daniel; Le Bars, Michael; Burns, Keaton J; Vasil, Geoffrey M; Brown, Benjamin P; Quataert, Eliot; Oishi, Jeffrey S
2015-06-01
Water's density maximum at 4°C makes it well suited to study internal gravity wave excitation by convection: an increasing temperature profile is unstable to convection below 4°C, but stably stratified above 4°C. We present numerical simulations of a waterlike fluid near its density maximum in a two-dimensional domain. We successfully model the damping of waves in the simulations using linear theory, provided we do not take the weak damping limit typically used in the literature. To isolate the physical mechanism exciting internal waves, we use the spectral code dedalus to run several simplified model simulations of our more detailed simulation. We use data from the full simulation as source terms in two simplified models of internal-wave excitation by convection: bulk excitation by convective Reynolds stresses, and interface forcing via the mechanical oscillator effect. We find excellent agreement between the waves generated in the full simulation and the simplified simulation implementing the bulk excitation mechanism. The interface forcing simulations overexcite high-frequency waves because they assume the excitation is by the "impulsive" penetration of plumes, which spreads energy to high frequencies. However, we find that the real excitation is instead by the "sweeping" motion of plumes parallel to the interface. Our results imply that the bulk excitation mechanism is a very accurate heuristic for internal-wave generation by convection. PMID:26172801
Application of the G-JF discrete-time thermostat for fast and accurate molecular simulations
NASA Astrophysics Data System (ADS)
Grønbech-Jensen, Niels; Hayre, Natha Robert; Farago, Oded
2014-02-01
A new Langevin-Verlet thermostat that preserves the fluctuation-dissipation relationship for discrete time steps is applied to molecular modeling and tested against several popular suites (AMBER, GROMACS, LAMMPS) using a small molecule as an example that can be easily simulated by all three packages. Contrary to existing methods, the new thermostat exhibits no detectable changes in the sampling statistics as the time step is varied in the entire numerical stability range. The simple form of the method, which we express in the three common forms (Velocity-Explicit, Störmer-Verlet, and Leap-Frog), allows for easy implementation within existing molecular simulation packages to achieve faster and more accurate results with no cost in either computing time or programming complexity.
Numerical simulation of swept-wing flows
NASA Technical Reports Server (NTRS)
Reed, Helen L.
1991-01-01
Efforts of the last six months to computationally model the transition process characteristics of flow over swept wings are described. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full 3D Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiment. The leading edge region of a swept wing is considered in a 3D spatial simulation with random disturbances as the initial conditions.
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. PMID:24146009
Numerical simulation of coupler cavities for linacs
Ng, C.K.; Derutyer, H.; Ko, K.
1993-04-01
We present numerical procedures involved in the evaluation of the performance of coupler cavities for linacs. The MAFIA code is used to simulate an X-Band accelerator section in the time domain. The input/output coupler cavities for the structure arc of the symmetrical double-input design. We calculate the transmission properties of the coupler and compare the results with measurements. We compare the performance of the symmetrical double-input design with that of the conventional single-input type by evaluating the field amplitude and phase asymmetries. We also evaluate the peak field gradient in the computer.
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.
The numerical simulation of accelerator components
Herrmannsfeldt, W.B.; Hanerfeld, H.
1987-05-01
The techniques of the numerical simulation of plasmas can be readily applied to problems in accelerator physics. Because the problems usually involve a single component ''plasma,'' and times that are at most, a few plasma oscillation periods, it is frequently possible to make very good simulations with relatively modest computation resources. We will discuss the methods and illustrate them with several examples. One of the more powerful techniques of understanding the motion of charged particles is to view computer-generated motion pictures. We will show several little movie strips to illustrate the discussions. The examples will be drawn from the application areas of Heavy Ion Fusion, electron-positron linear colliders and injectors for free-electron lasers. 13 refs., 10 figs., 2 tabs.
Numerical Simulations of Double White Dwarf Mergers
NASA Astrophysics Data System (ADS)
Motl, Patrick M.; Clayton, G.; Tohline, J. E.; Even, W.; Fryer, C.; Diehl, S.; Geballe, T.; Herwig, F.
2010-03-01
We will present evolutions of white dwarf binaries from two independent codes (one SPH and one Eulerian). We attempt to match the initial data for semi-detached synchronously rotating binaries between these two fluid representations. Our set of simulations includes various initial mass ratios and we assume one of two different equations of state (polytropic or ideal gas) to span the parameter space between the two possible extreme cases of rapid, catastrophic merger through to long-lived, steady mass transfer. In this presentation, we will primarily highlight the level of agreement between the two codes and how the results vary with increasing numerical resolution. We will also discuss future work incorporating nuclear reactions into our simulations and the possible connections of double white dwarf mergers to astrophysical sources.
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.
Method for numerical simulations of metastable states
Heller, U.M.; Seiberg, N.
1983-06-15
We present a numerical simulation of metastable states near a first-order phase transition in the example of a U(1) lattice gauge theory with a generalized action. In order to make measurements in these states possible their decay has to be prevented. We achieve this by using a microcanonical simulation for a finite system. We then obtain the coupling constant (inverse temperature) as a function of the action density. It turns out to be nonmonotonic and hence not uniquely invertible. From it we derive the effective potential for the action density. This effective potential is not always convex, a property that seems to be in contradiction with the standard lore about its convexity. This apparent ''paradox'' is resolved in a discussion about different definitions of the effective potential.
Numerical simulation of flow through biofluid devices
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Kwak, Dochan; Kiris, Cetin; Chang, I-Dee
1990-01-01
The results of a numerical simulation of flow through an artificial heart and through an artificial tilting-disk heart valve are presented. The simulation involves solving the incompressible Navier-Stokes equations; the solution process is described. The details and difficulties of modeling these particular geometries are discussed. The artificial heart geometry uses a single moving grid, and the valve computation uses an overlaid-grid approach with one moving grid and one stationary grid. The equations must be solved iteratively for each discrete time step of the computations, requiring a significant amount of computing time. It is particularly difficult to analyze and present the fluid physics represented by these calculations because of the time-varying nature of the flow, and because the flows are internal. Three-dimensional graphics and scientific visualization techniques have become instrumental in solving these problems.
Danshita, Ippei; Polkovnikov, Anatoli
2010-09-01
We study the quantum dynamics of supercurrents of one-dimensional Bose gases in a ring optical lattice to verify instanton methods applied to coherent macroscopic quantum tunneling (MQT). We directly simulate the real-time quantum dynamics of supercurrents, where a coherent oscillation between two macroscopically distinct current states occurs due to MQT. The tunneling rate extracted from the coherent oscillation is compared with that given by the instanton method. We find that the instanton method is quantitatively accurate when the effective Planck's constant is sufficiently small. We also find phase slips associated with the oscillations.
Numerical Simulation of Taylor Cone-Jet
NASA Astrophysics Data System (ADS)
Toledo, Ronne
The Taylor cone-jet is a particular type of electrohydrodynamic phenomenon where electrostatic stresses and surface tension effects shape the interface of the jet in a peculiar conical shape. A thin jet is issued from the cone apex that further breaks up into a fine aerosol. Due to its monodispersive properties, this fine aerosol has found a number of applications, ranging from mass spectrometry, colloidal space propulsion, combustion, nano-fabrication, coating/painting, and many others. In this study, a general non-dimensional analysis is performed to derive the governing equations and boundary conditions. In accordance with the observations of Gamero-Castano (2010), noting that droplet electric potential is insensitive to the flow rate conditions, a particular set of characteristic parameters is proposed, based on the terminal jet diameter. In order to solve the non-dimensional set of governing equations and boundary conditions, a numerical method combining the Boundary Element Method and the Finite Volume Method is developed. Results of electric current have shown good agreement with numerical and experimental data available in the literature. The main feature of the algorithm developed is related to the decoupling of the electrostatic from the hydrodynamic problem, allowing us to accurately prescribe the far field electric potential boundary conditions away from the hydrodynamic computational domain used to solve the hydrodynamics of the transition region near the cone apex.
Numerical Simulations of the Wake of Kauai
NASA Astrophysics Data System (ADS)
Lane, Todd P.; Sharman, Robert D.; Frehlich, Rod G.; Brown, John M.
2006-09-01
This study uses a series of numerical simulations to examine the structure of the wake of the Hawaiian island of Kauai. The primary focus is on the conditions on 26 June 2003, which was the day of the demise of the Helios aircraft within Kauai’s wake. The simulations show that, in an east-northeasterly trade wind flow, Kauai produces a well-defined wake that can extend 40 km downstream of the island. The wake is bounded to the north and south by regions of strong vertical and horizontal shear—that is, shear lines. These shear lines mark the edge of the wake in the horizontal plane and are aligned approximately parallel to the upstream flow direction at each respective height. The highest-resolution simulations show that these shear lines can become unstable and break down through Kelvin Helmholtz instability. The breakdown generates turbulent eddies that are advected both downstream and into the recirculating wake flow. Turbulence statistics are estimated from the simulation using a technique that analyzes model-derived structure functions. A number of sensitivity studies are also completed to determine the influence of the upstream conditions on the structure of the wake. These simulations show that directional shear controls the tilt of the wake in the north south plane with height. These simulations also show that at lower incident wind speeds the wake has a qualitatively similar structure but is less turbulent. At higher wind speeds, the flow regime changes, strong gravity waves are generated, and the wake is poorly defined. These results are consistent with previous idealized studies of stratified flow over isolated obstacles.
Transient productivity index for numerical well test simulations
Blanc, G.; Ding, D.Y.; Ene, A.
1997-08-01
The most difficult aspect of numerical simulation of well tests is the treatment of the Bottom Hole Flowing (BHF) Pressure. In full field simulations, this pressure is derived from the Well-block Pressure (WBP) using a numerical productivity index which accounts for the grid size and permeability, and for the well completion. This productivity index is calculated assuming a pseudo-steady state flow regime in the vicinity of the well and is therefore constant during the well production period. Such a pseudo-steady state assumption is no longer valid for the early time of a well test simulation as long as the pressure perturbation has not reached several grid-blocks around the well. This paper offers two different solutions to this problem: (1) The first one is based on the derivation of a Numerical Transient Productivity Index (NTPI) to be applied to Cartesian grids; (2) The second one is based on the use of a Corrected Transmissibility and Accumulation Term (CTAT) in the flow equation. The representation of the pressure behavior given by both solutions is far more accurate than the conventional one as shown by several validation examples which are presented in the following pages.
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.
Visualization techniques in plasma numerical simulations
NASA Astrophysics Data System (ADS)
Kulhánek, P.; Smetana, M.
2004-03-01
Numerical simulations of plasma processes usually yield a huge amount of raw numerical data. Information about electric and magnetic fields and particle positions and velocities can be typically obtained. There are two major ways of elaborating these data. First of them is called plasma diagnostics. We can calculate average values, variances, correlations of variables, etc. These results may be directly comparable with experiments and serve as the typical quantitative output of plasma simulations. The second possibility is the plasma visualization. The results are qualitative only, but serve as vivid display of phenomena in the plasma followed-up. An experience with visualizing electric and magnetic fields via Line Integral Convolution method is described in the first part of the paper. The LIC method serves for visualization of vector fields in two dimensional section of the three dimensional plasma. The field values can be known only in grid points of three-dimensional grid. The second part of the paper is devoted to the visualization techniques of the charged particle motion. The colour tint can be used for particle’s temperature representation. The motion can be visualized by a trace fading away with the distance from the particle. In this manner the impressive animations of the particle motion can be achieved.
Numerical simulations of rotating axisymmetric sunspots
NASA Astrophysics Data System (ADS)
Botha, G. J. J.; Busse, F. H.; Hurlburt, N. E.; Rucklidge, A. M.
2008-07-01
A numerical model of axisymmetric convection in the presence of a vertical magnetic flux bundle and rotation about the axis is presented. The model contains a compressible plasma described by the non-linear MHD equations, with density and temperature gradients simulating the upper layer of the Sun's convection zone. The solutions exhibit a central magnetic flux tube in a cylindrical numerical domain, with convection cells forming collar flows around the tube. When the numerical domain is rotated with a constant angular velocity, the plasma forms a Rankine vortex, with the plasma rotating as a rigid body where the magnetic field is strong, as in the flux tube, while experiencing sheared azimuthal flow in the surrounding convection cells, forming a free vortex. As a result, the azimuthal velocity component has its maximum value close to the outer edge of the flux tube. The azimuthal flow inside the magnetic flux tube and the vortex flow is prograde relative to the rotating cylindrical reference frame. A retrograde flow appears at the outer wall. The most significant convection cell outside the flux tube is the location for the maximum value of the azimuthal magnetic field component. The azimuthal flow and magnetic structure are not generated spontaneously, but decay exponentially in the absence of any imposed rotation of the cylindrical domain.
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 Technical Reports Server (NTRS)
Venkatachari, Balaji Shankar; Streett, Craig L.; Chang, Chau-Lyan; Friedlander, David J.; Wang, Xiao-Yen; Chang, Sin-Chung
2016-01-01
Despite decades of development of unstructured mesh methods, high-fidelity time-accurate simulations are still predominantly carried out on structured, or unstructured hexahedral meshes by using high-order finite-difference, weighted essentially non-oscillatory (WENO), or hybrid schemes formed by their combinations. In this work, the space-time conservation element solution element (CESE) method is used to simulate several flow problems including supersonic jet/shock interaction and its impact on launch vehicle acoustics, and direct numerical simulations of turbulent flows using tetrahedral meshes. This paper provides a status report for the continuing development of the space-time conservation element solution element (CESE) numerical and software framework under the Revolutionary Computational Aerosciences (RCA) project. Solution accuracy and large-scale parallel performance of the numerical framework is assessed with the goal of providing a viable paradigm for future high-fidelity flow physics simulations.
Numerical Simulation of nZVI at the Field Scale
NASA Astrophysics Data System (ADS)
Chowdhury, A. I.; Krol, M.; Sleep, B. E.; O'Carroll, D. M.
2014-12-01
Nano-scale zero valent iron (nZVI) has been used at a number of contaminated sites over the last decade. At most of these sites, significant decreases in contaminant concentrations have resulted from the application of nZVI. However, limited work has been completed investigating nZVI mobility at the field-scale. In this study a three dimensional, three phase, finite difference numerical simulator (CompSim) was used to simulate nZVI and polymer transport in a variably saturated site. The model was able to accurately predict the field observed head data without parameter fitting. In addition, the numerical simulator estimated the amount of nZVI delivered to the saturated and unsaturated zones as well as the phase of nZVI (i.e., attached or aqueous phase). The simulation results showed that the injected slurry migrated radially outward from the injection well, and therefore nZVI transport was governed by injection velocity as well as viscosity of the injected solution. A suite of sensitivity analyses was performed to investigate the impact of different injection scenarios (e.g. different volume and injection rate) on nZVI migration. Simulation results showed that injection of a higher volume of nZVI delivered more iron particles at a given distance; however, not necessarily to a greater distance proportionate to the increase in volume. This study suggests that on-site synthesized nZVI particles are mobile in the subsurface and the numerical simulator can be a valuable tool for optimum design of nZVI applications.
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.
A novel numerical technique to obtain an accurate solution to the Thomas-Fermi equation
NASA Astrophysics Data System (ADS)
Parand, Kourosh; Yousefi, Hossein; Delkhosh, Mehdi; Ghaderi, Amin
2016-07-01
In this paper, a new algorithm based on the fractional order of rational Euler functions (FRE) is introduced to study the Thomas-Fermi (TF) model which is a nonlinear singular ordinary differential equation on a semi-infinite interval. This problem, using the quasilinearization method (QLM), converts to the sequence of linear ordinary differential equations to obtain the solution. For the first time, the rational Euler (RE) and the FRE have been made based on Euler polynomials. In addition, the equation will be solved on a semi-infinite domain without truncating it to a finite domain by taking FRE as basic functions for the collocation method. This method reduces the solution of this problem to the solution of a system of algebraic equations. We demonstrated that the new proposed algorithm is efficient for obtaining the value of y'(0) , y(x) and y'(x) . Comparison with some numerical and analytical solutions shows that the present solution is highly accurate.
Numerical Simulation of Tangling in Jet Engine Turbines
NASA Astrophysics Data System (ADS)
Cendón, David A.; Erice, Borja; Gálvez, Francisco; Sánchez-Gálvez, Vicente
2012-12-01
The numerical analysis of certain safety related problems presents serious difficulties, since the large number of components present leads to huge finite element models that can only be solved by using large and expensive computers or by making rough approaches to the problem. Tangling, or clashing, in the turbine of a jet engine airplane is an example of such problems. This is caused by the crash and friction between rotor and stator blades in the turbine after an eventual shaft failure. When facing the study of an event through numerical modelling, the accurate simulation of this problem would require the engineer to model all the rotor and stator blades existing in the turbine stage, using a small element size in all pieces. Given that the number of stator and rotor blades is usually around 200, such simulations would require millions of elements. This work presents a new numerical methodology, specifically developed for the accurate modelling of the tangling problem that, depending on the turbine configuration, is able to reduce the number of nodes up to an order of magnitude without losing accuracy. The methodology, which benefits from the cyclic configuration of turbines, is successfully applied to the numerical analysis of a hypothetical tangling event in a turbine, providing valuable data such as the rotating velocity decrease of the turbine, the braking torque and the damage suffered by the blades. The methodology is somewhat general and can be applied to any problem in which damage caused by the interaction between a rotating and static piece is to be analysed.
Massively Parallel Processing for Fast and Accurate Stamping Simulations
NASA Astrophysics Data System (ADS)
Gress, Jeffrey J.; Xu, Siguang; Joshi, Ramesh; Wang, Chuan-tao; Paul, Sabu
2005-08-01
The competitive automotive market drives automotive manufacturers to speed up the vehicle development cycles and reduce the lead-time. Fast tooling development is one of the key areas to support fast and short vehicle development programs (VDP). In the past ten years, the stamping simulation has become the most effective validation tool in predicting and resolving all potential formability and quality problems before the dies are physically made. The stamping simulation and formability analysis has become an critical business segment in GM math-based die engineering process. As the simulation becomes as one of the major production tools in engineering factory, the simulation speed and accuracy are the two of the most important measures for stamping simulation technology. The speed and time-in-system of forming analysis becomes an even more critical to support the fast VDP and tooling readiness. Since 1997, General Motors Die Center has been working jointly with our software vendor to develop and implement a parallel version of simulation software for mass production analysis applications. By 2001, this technology was matured in the form of distributed memory processing (DMP) of draw die simulations in a networked distributed memory computing environment. In 2004, this technology was refined to massively parallel processing (MPP) and extended to line die forming analysis (draw, trim, flange, and associated spring-back) running on a dedicated computing environment. The evolution of this technology and the insight gained through the implementation of DM0P/MPP technology as well as performance benchmarks are discussed in this publication.
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.
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.
The FLUKA Code: An Accurate Simulation Tool for Particle Therapy
Battistoni, Giuseppe; Bauer, Julia; Boehlen, Till T.; Cerutti, Francesco; Chin, Mary P. W.; Dos Santos Augusto, Ricardo; Ferrari, Alfredo; Ortega, Pablo G.; Kozłowska, Wioletta; Magro, Giuseppe; Mairani, Andrea; Parodi, Katia; Sala, Paola R.; Schoofs, Philippe; Tessonnier, Thomas; Vlachoudis, Vasilis
2016-01-01
Monte Carlo (MC) codes are increasingly spreading in the hadrontherapy community due to their detailed description of radiation transport and interaction with matter. The suitability of a MC code for application to hadrontherapy demands accurate and reliable physical models capable of handling all components of the expected radiation field. This becomes extremely important for correctly performing not only physical but also biologically based dose calculations, especially in cases where ions heavier than protons are involved. In addition, accurate prediction of emerging secondary radiation is of utmost importance in innovative areas of research aiming at in vivo treatment verification. This contribution will address the recent developments of the FLUKA MC code and its practical applications in this field. Refinements of the FLUKA nuclear models in the therapeutic energy interval lead to an improved description of the mixed radiation field as shown in the presented benchmarks against experimental data with both 4He and 12C ion beams. Accurate description of ionization energy losses and of particle scattering and interactions lead to the excellent agreement of calculated depth–dose profiles with those measured at leading European hadron therapy centers, both with proton and ion beams. In order to support the application of FLUKA in hospital-based environments, Flair, the FLUKA graphical interface, has been enhanced with the capability of translating CT DICOM images into voxel-based computational phantoms in a fast and well-structured way. The interface is capable of importing also radiotherapy treatment data described in DICOM RT standard. In addition, the interface is equipped with an intuitive PET scanner geometry generator and automatic recording of coincidence events. Clinically, similar cases will be presented both in terms of absorbed dose and biological dose calculations describing the various available features. PMID:27242956
The FLUKA Code: An Accurate Simulation Tool for Particle Therapy.
Battistoni, Giuseppe; Bauer, Julia; Boehlen, Till T; Cerutti, Francesco; Chin, Mary P W; Dos Santos Augusto, Ricardo; Ferrari, Alfredo; Ortega, Pablo G; Kozłowska, Wioletta; Magro, Giuseppe; Mairani, Andrea; Parodi, Katia; Sala, Paola R; Schoofs, Philippe; Tessonnier, Thomas; Vlachoudis, Vasilis
2016-01-01
Monte Carlo (MC) codes are increasingly spreading in the hadrontherapy community due to their detailed description of radiation transport and interaction with matter. The suitability of a MC code for application to hadrontherapy demands accurate and reliable physical models capable of handling all components of the expected radiation field. This becomes extremely important for correctly performing not only physical but also biologically based dose calculations, especially in cases where ions heavier than protons are involved. In addition, accurate prediction of emerging secondary radiation is of utmost importance in innovative areas of research aiming at in vivo treatment verification. This contribution will address the recent developments of the FLUKA MC code and its practical applications in this field. Refinements of the FLUKA nuclear models in the therapeutic energy interval lead to an improved description of the mixed radiation field as shown in the presented benchmarks against experimental data with both (4)He and (12)C ion beams. Accurate description of ionization energy losses and of particle scattering and interactions lead to the excellent agreement of calculated depth-dose profiles with those measured at leading European hadron therapy centers, both with proton and ion beams. In order to support the application of FLUKA in hospital-based environments, Flair, the FLUKA graphical interface, has been enhanced with the capability of translating CT DICOM images into voxel-based computational phantoms in a fast and well-structured way. The interface is capable of importing also radiotherapy treatment data described in DICOM RT standard. In addition, the interface is equipped with an intuitive PET scanner geometry generator and automatic recording of coincidence events. Clinically, similar cases will be presented both in terms of absorbed dose and biological dose calculations describing the various available features. PMID:27242956
PolyPole-1: An accurate numerical algorithm for intra-granular fission gas release
NASA Astrophysics Data System (ADS)
Pizzocri, D.; Rabiti, C.; Luzzi, L.; Barani, T.; Van Uffelen, P.; Pastore, G.
2016-09-01
The transport of fission gas from within the fuel grains to the grain boundaries (intra-granular fission gas release) is a fundamental controlling mechanism of fission gas release and gaseous swelling in nuclear fuel. Hence, accurate numerical solution of the corresponding mathematical problem needs to be included in fission gas behaviour models used in fuel performance codes. Under the assumption of equilibrium between trapping and resolution, the process can be described mathematically by a single diffusion equation for the gas atom concentration in a grain. In this paper, we propose a new numerical algorithm (PolyPole-1) to efficiently solve the fission gas diffusion equation in time-varying conditions. The PolyPole-1 algorithm is based on the analytic modal solution of the diffusion equation for constant conditions, combined with polynomial corrective terms that embody the information on the deviation from constant conditions. The new algorithm is verified by comparing the results to a finite difference solution over a large number of randomly generated operation histories. Furthermore, comparison to state-of-the-art algorithms used in fuel performance codes demonstrates that the accuracy of PolyPole-1 is superior to other algorithms, with similar computational effort. Finally, the concept of PolyPole-1 may be extended to the solution of the general problem of intra-granular fission gas diffusion during non-equilibrium trapping and resolution, which will be the subject of future work.
Numerical simulations of ultrasimple ultrashortlaser-pulse measurement.
Liu, Xuan; Trebino, Rick; Smith, Arlee V
2007-04-16
We numerically simulate the performance of the ultrasimple frequency-resolved-optical-gating (FROG) technique, GRENOUILLE, for measuring ultrashort laser pulses. While simple in practice, GRENOUILLE has many theoretical subtleties because it involves the second-harmonic generation of relatively tightly focused and broadband pulses. In addition, these processes occur in a thick crystal, in which the phase-matching bandwidth is deliberately made narrow compared to the pulse bandwidth. In these simulations, we include all sum-frequency-generation processes, both collinear and noncollinear. We also include dispersion using the Sellmeier equation for the crystal BBO. Working in the frequency domain, we compute the GRENOUILLE trace for practical-and impractical- examples and show that accurate measurements are easily obtained for properly designed devices. PMID:19532705
NASA Astrophysics Data System (ADS)
Garrison, Stephen L.
2005-07-01
The combination of molecular simulations and potentials obtained from quantum chemistry is shown to be able to provide reasonably accurate thermodynamic property predictions. Gibbs ensemble Monte Carlo simulations are used to understand the effects of small perturbations to various regions of the model Lennard-Jones 12-6 potential. However, when the phase behavior and second virial coefficient are scaled by the critical properties calculated for each potential, the results obey a corresponding states relation suggesting a non-uniqueness problem for interaction potentials fit to experimental phase behavior. Several variations of a procedure collectively referred to as quantum mechanical Hybrid Methods for Interaction Energies (HM-IE) are developed and used to accurately estimate interaction energies from CCSD(T) calculations with a large basis set in a computationally efficient manner for the neon-neon, acetylene-acetylene, and nitrogen-benzene systems. Using these results and methods, an ab initio, pairwise-additive, site-site potential for acetylene is determined and then improved using results from molecular simulations using this initial potential. The initial simulation results also indicate that a limited range of energies important for accurate phase behavior predictions. Second virial coefficients calculated from the improved potential indicate that one set of experimental data in the literature is likely erroneous. This prescription is then applied to methanethiol. Difficulties in modeling the effects of the lone pair electrons suggest that charges on the lone pair sites negatively impact the ability of the intermolecular potential to describe certain orientations, but that the lone pair sites may be necessary to reasonably duplicate the interaction energies for several orientations. Two possible methods for incorporating the effects of three-body interactions into simulations within the pairwise-additivity formulation are also developed. A low density
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.
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
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 Simulation of Coherent Error Correction
NASA Astrophysics Data System (ADS)
Crow, Daniel; Joynt, Robert; Saffman, Mark
A major goal in quantum computation is the implementation of error correction to produce a logical qubit with an error rate lower than that of the underlying physical qubits. Recent experimental progress demonstrates physical qubits can achieve error rates sufficiently low for error correction, particularly for codes with relatively high thresholds such as the surface code and color code. Motivated by experimental capabilities of neutral atom systems, we use numerical simulation to investigate whether coherent error correction can be effectively used with the 7-qubit color code. The results indicate that coherent error correction does not work at the 10-qubit level in neutral atom array quantum computers. By adding more qubits there is a possibility of making the encoding circuits fault-tolerant which could improve performance.
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.
Numerical simulation of three dimensional transonic flows
NASA Technical Reports Server (NTRS)
Sahu, Jubaraj; Steger, Joseph L.
1987-01-01
The three-dimensional flow over a projectile has been computed using an implicit, approximately factored, partially flux-split algorithm. A simple composite grid scheme has been developed in which a single grid is partitioned into a series of smaller grids for applications which require an external large memory device such as the SSD of the CRAY X-MP/48, or multitasking. The accuracy and stability of the composite grid scheme has been tested by numerically simulating the flow over an ellipsoid at angle of attack and comparing the solution with a single grid solution. The flowfield over a projectile at M = 0.96 and 4 deg angle-of-attack has been computed using a fine grid, and compared with experiment.
Polarimetric bio-aerosol detection: numerical simulation
NASA Astrophysics Data System (ADS)
Snow, J. William; Bicknell, W. Ed; Burke, Hsiao-hua K.
2005-11-01
This paper examines the use of bi-static lidar to remotely detect the release of aerosolized biological agent. The detection scheme exploits bio-aerosol induced changes in the Stokes parameters of scattered radiation in comparison to scattered radiation from ambient background aerosols alone. A polarization distance metric is introduced to discriminate between changes caused by the two types of aerosols. Scattering code computations are the information source. Three application scenarios are considered: outdoor arena, indoor auditorium, and building heating-ventilation-air-conditioning (HVAC) system. Numerical simulations are employed to determine sensitivity of detection to laser wavelength and to particle physical properties. Results of the study are described and details are given for the specific example of a 1.50 μm lidar system operating outdoors over a 1000-m range.
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.
Computing abstraction hierarchies by numerical simulation
Bundy, A.; Giunchiglia, F.; Sebastiani, R.; Walsh, T.
1996-12-31
We present a novel method for building ABSTRIPS-style abstraction hierarchies in planning. The aim of this method is to minimize the amount of backtracking between abstraction levels. Previous approaches have determined the criticality of operator preconditions by reasoning about plans directly. Here, we adopt a simpler and faster approach where we use numerical simulation of the planning process. We demonstrate the theoretical advantages of our approach by identifying some simple properties lacking in previous approaches but possessed by our method. We demonstrate the empirical advantages of our approach by a set of four benchmark experiments using the ABTWEAK system. We compare the quality of the abstraction hierarchies generated with those built by the ALPINE and HIGHPOINT algorithms.
Developing accurate simulations for high-speed fiber links
NASA Astrophysics Data System (ADS)
Searcy, Steven; Stark, Andrew; Hsueh, Yu-Ting; Detwiler, Thomas; Tibuleac, Sorin; Chang, GK; Ralph, Stephen E.
2011-01-01
Reliable simulations of high-speed fiber optic links are necessary to understand, design, and deploy fiber networks. Laboratory experiments cannot explore all possible component variations and fiber environments that are found in today's deployed systems. Simulations typically depict relative penalties compared to a reference link. However, absolute performance metrics are required to assess actual deployment configurations. Here we detail the efforts within the Georgia Tech 100G Consortium towards achieving high absolute accuracy between simulation and experimental performance with a goal of +/-0.25 dB for back-to-back configuration, and +/-0.5 dB for transmission over multiple spans with different dispersion maps. We measure all possible component parameters including fiber length, loss, and dispersion for use in simulation. We also validate experimental methods of performance evaluation including OSNR assessment and DSP-based demodulation. We investigate a wide range of parameters including modulator chirp, polarization state, polarization dependent loss, transmit spectrum, laser linewidth, and fiber nonlinearity. We evaluate 56 Gb/s (single-polarization) and 112 Gb/s (dual-polarization) DQPSK and coherent QPSK within a 50 GHz DWDM environment with 10 Gb/s OOK adjacent channels for worst-case XPM effects. We demonstrate good simulation accuracy within linear and some nonlinear regimes for a wide range of OSNR in both back-to-back configuration and up to eight spans, over a range of launch powers. This allows us to explore a wide range of environments not available in the lab, including different fiber types, ROADM passbands, and levels of crosstalk. Continued exploration is required to validate robustness over various demodulation algorithms.
Numerical relativistic hydrodynamic simulations of neutron stars
NASA Astrophysics Data System (ADS)
Haywood, Joe R.
Developments in numerical relativistic hydrodynamics over the past thirty years, along with the advent of high speed computers, have made problems needing general relativity and relativistic hydrodynamics tractable. One such problem is the relativistic evolution of neutron stars, either in a head on collision or in binary orbit. Also of current interest is the detection of gravitational radiation from binary neutron stars, black-hole neutron star binaries, binary black holes, etc. Such systems expected to emit gravitational radiation with amplitude large enough to be detected on Earth by such groups as LIGO and VIRGO. Unfortunately, the expected signal strength is below the current noise level. However, signal processing techniques have been developed which should eventually find a signal, if a good theoretical template can be found. In the cases above it is not possible to obtain an analytic solution to the Einstein equations and a numerical approximation is therefore most necessary. In this thesis the Einstein equations are written using the formalism of Arnowitt, Desser and Misner and a conformally flat metric is assumed. Numerical simulations of colliding neutron stars, having either a realistic or Gamma = 2 polytropic equation of state (EOS), are presented which confirm the rise in central density seen by [51, 89] for the softer EOS. For the binary calculation, the results of Wilson et al. [89] are confirmed, which show that the neutron stars can collapse to black holes before colliding when the EOS is realistic and we also confirm results of Miller [56] and others that there is essentially no compression, the central density does not increase, when the stiffer equation of state is used. Finally, a template for the gravitational radiation emitted from the binary is calculated and we show that the frequency of the emitted gravitational waves changes more slowly for the [89] EOS, which may result in a stronger signal in the 50-100 Hz band of LIGO.
Numerical simulation of detonation failure in nitromethane
Kipp, M.E.; Nunziato, J.W.
1981-01-01
Detonation failure in the homogeneous liquid explosive nitromethane has been observed experimentally in a wide variety of confining geometries. However, numerical simulation of these failure situations with a wave propagation code has been essentially non-existent due to the large differences between the critical diameter and the length of the reaction zone - characteristic dimensions which differ by about two orders of magnitude. This inability to spatially resolve both the reaction zone and geometries of significant size has led us to propose a new numerical technique, based on the stability criterion for rate-type material models, in which only temporal resolution of the reaction zone is required. Using an improved model for nitromethane, we have carried out a series of two-dimensional calculations which illustrate the utility of the present approach in predicting a wide range of experimental observations. Of particular computational significance is the removal of the difficulty requiring spatial resolution of the reaction zone, so that problems of practical size can be analyzed with existing computer capabilities.
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.
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.
Numerical simulation of turbulent gas flames in tubes.
Salzano, E; Marra, F S; Russo, G; Lee, J H S
2002-12-01
Computational fluid dynamics (CFD) is an emerging technique to predict possible consequences of gas explosion and it is often considered a powerful and accurate tool to obtain detailed results. However, systematic analyses of the reliability of this approach to real-scale industrial configurations are still needed. Furthermore, few experimental data are available for comparison and validation. In this work, a set of well documented experimental data related to the flame acceleration obtained within obstacle-filled tubes filled with flammable gas-air mixtures, has been simulated. In these experiments, terminal steady flame speeds corresponding to different propagation regimes were observed, thus, allowing a clear and prompt characterisation of the numerical results with respect to numerical parameters, as grid definition, geometrical parameters, as blockage ratio and to mixture parameters, as mixture reactivity. The CFD code AutoReagas was used for the simulations. Numerical predictions were compared with available experimental data and some insights into the code accuracy were determined. Computational results are satisfactory for the relatively slower turbulent deflagration regimes and became fair when choking regime is observed, whereas transition to quasi-detonation or Chapman-Jogouet (CJ) were never predicted. PMID:12423940
Accurate, practical simulation of satellite infrared radiometer spectral data
Sullivan, T.J.
1982-09-01
This study's purpose is to determine whether a relatively simple random band model formulation of atmospheric radiation transfer in the infrared region can provide valid simulations of narrow interval satellite-borne infrared sounder system data. Detailed ozonesondes provide the pertinent atmospheric information and sets of calibrated satellite measurements provide the validation. High resolution line-by-line model calculations are included to complete the evaluation.
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 simulations of phase change in microgravity
Juric, D.; Tryggvason, G.
1996-12-31
Direct numerical simulations of liquid-solid and liquid-vapor phase change are conducted under microgravity conditions. The time-dependent governing equations are solved using a two-dimensional finite-difference/front-tracking method. Large interface deformations, topology change, latent heat, surface tension and unequal material properties between the phases are included in the simulations. Results are presented for two specific problems: directional solidification of a dilute binary alloy and the rapid evaporation of a superheated liquid (vapor explosion). For the directional solidification problem, solution of the fully coupled solute and energy equations reveals the evolution of morphologically complex structures such as tip splitting, coarsening and droplet detachment from deep intercellular grooves. A variety of important solute segregation patterns such as necking, coring and banding are also observed. The boiling problem couples the phase change with fluid flow. This requires the solution of the Navier-Stokes and energy equations with interphase mass transfer. The energetic growth of instabilities on planar and circular interfaces during the unstable explosive evaporation of a superheated liquid in microgravity is demonstrated.
Numerical simulation of `DMSP` dosimeter response
Jordan, T.M. ||
1993-12-31
Four Defense Meteorological Satellite Program (DMSP) dosimeters were modeled for numerical simulation of radiation response. The modeling included the hemispherical aluminum dome, the solid state detector, and the tungsten base plate. Orbits were generated for 840 km and 98 degrees inclination and used with 1965 and 1985 magnetic field models and the AP8 and AE8 data sets to obtain solar minimum and solar maximum integral fluences for protons and electrons. Adjoint Monte Carlo methods were then used to simulate the transport of these environments in the geometric models of the dosimeters. Volume average dose calculations were used to calculate the response of the LOLET (less than 1 MeV deposited per particle) channels to electrons and secondary bremsstrahlung. Monte Carlo methods were used, in conjunction with a pulse height analysis, to obtain the proton response of the LOLET and HILET (1 to 10 MeV deposited per particle) channels. The HILET and LOLET responses obtained from these calculations are in good agreement with DMSP measurements for 1984-85.
Numerical simulation of turbulence over tensegrity fabric
NASA Astrophysics Data System (ADS)
Luo, Haoxiang; Bewley, Thomas
2003-11-01
In this research we aim to reduce turbulent skin friction by designing and optimizing tensegrity fabrics. Such fabrics form a new class of compliant surfaces consisting of a weave of both members under tension and members under compression. Boundary conditions on the flow are handled with a time-dependent coordinate transformation. We first note that, when designing the numerical algorithm for approximating the Navier-Stokes equation in the flow domain (with moving boundaries), special care (intrinsic differentiation of a contravariant vector) is needed to handle the temporal differentiation of the momentum term when using a contravariant formulation. A Cartesian-based formulation may also be used, and has proven to be more tractable in the 3D setting. The spectral DNS flow code is coupled with a tensegrity simulation code to compute the flow/structure interaction; recent simulation results will be presented. A complex-step derivative (CSD) technique may then be used to optimize the response characteristics of the tensegrity structure in order to minimize the drag at the flow/structure interface; this strategy will also be discussed.
Numerical simulation of LIGO input optics
NASA Astrophysics Data System (ADS)
None, Shivanand; Jamal, Nafis; Yoshida, Sanichiro
2005-11-01
Numerical analysis has been carried out to understand the performance of the Input Optics used in the first generation of LIGO (Laser Interferometer Gravitational-wave Observatory) detector. The input optics is a subsystem consisting of a mode cleaner and mode-matching telescope, where all the optics are suspended and installed in vacuum. Using the end-to-end package (LIGO programming language), computer codes have been made to simulate the input optics. Giving realistic seismic noise to the suspension point of the optics and using the length sensing/alignment sensing control for the mode cleaner, the performance of the input optics has been simulated under various scenarios such as with an order of magnitude higher seismic noise than the normal level, and with/without the alignment sensing control feedback from the arm cavity to the mode-matching telescope. The results are assessed in terms of the beam pointing fluctuation of the laser beam going into the arm cavities, and its influence on the optical coupling to the arm cavities and the noise level at the gravitational wave port signal.
Entropy Splitting for High Order Numerical Simulation of Compressible Turbulence
NASA Technical Reports Server (NTRS)
Sandham, N. D.; Yee, H. C.; Kwak, Dochan (Technical Monitor)
2000-01-01
A stable high order numerical scheme for direct numerical simulation (DNS) of shock-free compressible turbulence is presented. The method is applicable to general geometries. It contains no upwinding, artificial dissipation, or filtering. Instead the method relies on the stabilizing mechanisms of an appropriate conditioning of the governing equations and the use of compatible spatial difference operators for the interior points (interior scheme) as well as the boundary points (boundary scheme). An entropy splitting approach splits the inviscid flux derivatives into conservative and non-conservative portions. The spatial difference operators satisfy a summation by parts condition leading to a stable scheme (combined interior and boundary schemes) for the initial boundary value problem using a generalized energy estimate. A Laplacian formulation of the viscous and heat conduction terms on the right hand side of the Navier-Stokes equations is used to ensure that any tendency to odd-even decoupling associated with central schemes can be countered by the fluid viscosity. A special formulation of the continuity equation is used, based on similar arguments. The resulting methods are able to minimize spurious high frequency oscillation producing nonlinear instability associated with pure central schemes, especially for long time integration simulation such as DNS. For validation purposes, the methods are tested in a DNS of compressible turbulent plane channel flow at a friction Mach number of 0.1 where a very accurate turbulence data base exists. It is demonstrated that the methods are robust in terms of grid resolution, and in good agreement with incompressible channel data, as expected at this Mach number. Accurate turbulence statistics can be obtained with moderate grid sizes. Stability limits on the range of the splitting parameter are determined from numerical tests.
Efficient numerical simulation of heat storage in subsurface georeservoirs
NASA Astrophysics Data System (ADS)
Boockmeyer, A.; Bauer, S.
2015-12-01
The transition of the German energy market towards renewable energy sources, e.g. wind or solar power, requires energy storage technologies to compensate for their fluctuating production. Large amounts of energy could be stored in georeservoirs such as porous formations in the subsurface. One possibility here is to store heat with high temperatures of up to 90°C through borehole heat exchangers (BHEs) since more than 80 % of the total energy consumption in German households are used for heating and hot water supply. Within the ANGUS+ project potential environmental impacts of such heat storages are assessed and quantified. Numerical simulations are performed to predict storage capacities, storage cycle times, and induced effects. For simulation of these highly dynamic storage sites, detailed high-resolution models are required. We set up a model that accounts for all components of the BHE and verified it using experimental data. The model ensures accurate simulation results but also leads to large numerical meshes and thus high simulation times. In this work, we therefore present a numerical model for each type of BHE (single U, double U and coaxial) that reduces the number of elements and the simulation time significantly for use in larger scale simulations. The numerical model includes all BHE components and represents the temporal and spatial temperature distribution with an accuracy of less than 2% deviation from the fully discretized model. By changing the BHE geometry and using equivalent parameters, the simulation time is reduced by a factor of ~10 for single U-tube BHEs, ~20 for double U-tube BHEs and ~150 for coaxial BHEs. Results of a sensitivity study that quantify the effects of different design and storage formation parameters on temperature distribution and storage efficiency for heat storage using multiple BHEs are then shown. It is found that storage efficiency strongly depends on the number of BHEs composing the storage site, their distance and
Numerical simulation of pressure pulsations in Francis turbines
NASA Astrophysics Data System (ADS)
Magnoli, M. V.; Schilling, R.
2012-11-01
In the last decades, hydraulic turbines have experienced the increase of their power density and the extension of their operating range, leading the fluid and mechanical dynamic effects to become significantly more pronounced. The understanding of the transient fluid flow and of the associated unsteady effects is essential for the reduction of the pressure pulsation level and improvement of the machine dynamic behaviour. In this study, the instationary fluid flow through the complete turbine was numerically calculated for an existing Francis machine with high specific speed. The hybrid turbulence models DES (detached eddy simulation) and SAS (scale adaptive simulation) allowed the accurate simulation of complex dynamic flow effects, such as the rotor-stator-interaction and the draft tube instabilities. Different operating conditions, as full load, part load, higher part load and deep part load, were successfully simulated and showed very tight agreement with the experimental results from the model tests. The transient pressure field history, obtained from the CFD (computational fluid dynamics) simulation and stored for each time step, was used as input for the full instationary FEA (finite element analysis) of turbine components. The assessment of the machine dynamic motion also offered the possibility to contribute to the understanding of the pressure pulsation effects and to further increase the turbine stability. This research project was developed at the Institute of Fluid Mechanics of the TU München.
Stochastic algorithms for the analysis of numerical flame simulations
Bell, John B.; Day, Marcus S.; Grcar, Joseph F.; Lijewski, Michael J.
2004-04-26
Recent progress in simulation methodologies and high-performance parallel computers have made it is possible to perform detailed simulations of multidimensional reacting flow phenomena using comprehensive kinetics mechanisms. As simulations become larger and more complex, it becomes increasingly difficult to extract useful information from the numerical solution, particularly regarding the interactions of the chemical reaction and diffusion processes. In this paper we present a new diagnostic tool for analysis of numerical simulations of reacting flow. Our approach is based on recasting an Eulerian flow solution in a Lagrangian frame. Unlike a conventional Lagrangian view point that follows the evolution of a volume of the fluid, we instead follow specific chemical elements, e.g., carbon, nitrogen, etc., as they move through the system . From this perspective an ''atom'' is part of some molecule of a species that is transported through the domain by advection and diffusion. Reactions cause the atom to shift from one chemical host species to another and the subsequent transport of the atom is given by the movement of the new species. We represent these processes using a stochastic particle formulation that treats advection deterministically and models diffusion and chemistry as stochastic processes. In this paper, we discuss the numerical issues in detail and demonstrate that an ensemble of stochastic trajectories can accurately capture key features of the continuum solution. The capabilities of this diagnostic are then demonstrated by applications to study the modulation of carbon chemistry during a vortex-flame interaction, and the role of cyano chemistry in rm NO{sub x} production for a steady diffusion flame.
Accurately simulating anisotropic thermal conduction on a moving mesh
NASA Astrophysics Data System (ADS)
Kannan, Rahul; Springel, Volker; Pakmor, Rüdiger; Marinacci, Federico; Vogelsberger, Mark
2016-05-01
We present a novel implementation of an extremum preserving anisotropic diffusion solver for thermal conduction on the unstructured moving Voronoi mesh of the AREPO code. The method relies on splitting the one-sided facet fluxes into normal and oblique components, with the oblique fluxes being limited such that the total flux is both locally conservative and extremum preserving. The approach makes use of harmonic averaging points and a simple, robust interpolation scheme that works well for strong heterogeneous and anisotropic diffusion problems. Moreover, the required discretization stencil is small. Efficient fully implicit and semi-implicit time integration schemes are also implemented. We perform several numerical tests that evaluate the stability and accuracy of the scheme, including applications such as point explosions with heat conduction and calculations of convective instabilities in conducting plasmas. The new implementation is suitable for studying important astrophysical phenomena, such as the conductive heat transport in galaxy clusters, the evolution of supernova remnants, or the distribution of heat from black hole-driven jets into the intracluster medium.
Accurate simulation of terahertz transmission through doped silicon junctions
NASA Astrophysics Data System (ADS)
Jen, Chih-Yu; Richter, Christiaan
2015-03-01
In the previous work we presented results demonstrating the ability of transmission mode terahertz time domain spectroscopy (THz-TDS) to detect doping profile differences and deviations in silicon. This capability is potentially useful for quality control in the semiconductor and photovoltaic industry. We shared subsequent experimental results revealing that terahertz interactions with both electrons and holes are strong enough to recognize both n- and p-type doping profile changes. We also displayed that the relatively long wavelength (~ 1 mm) of THz radiation allows this approach to be compatible with surface treatments like for instance the texturing (scattering layer) typically used in the solar industry. In this work we continuously demonstrate the accuracy with which current terahertz optical models can simulate the power spectrum of terahertz radiation transmitted through junctions with known doping profiles (as determined with SIMS). We conclude that current optical models predict the terahertz transmission and absorption in silicon junctions well.
Accurate Position Sensing of Defocused Beams Using Simulated Beam Templates
Awwal, A; Candy, J; Haynam, C; Widmayer, C; Bliss, E; Burkhart, S
2004-09-29
In position detection using matched filtering one is faced with the challenge of determining the best position in the presence of distortions such as defocus and diffraction noise. This work evaluates the performance of simulated defocused images as the template against the real defocused beam. It was found that an amplitude modulated phase-only filter is better equipped to deal with real defocused images that suffer from diffraction noise effects resulting in a textured spot intensity pattern. It is shown that the there is a tradeoff of performance dependent upon the type and size of the defocused image. A novel automated system was developed that can automatically select the right template type and size. Results of this automation for real defocused images are presented.
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.
Orbital Advection by Interpolation: A Fast and Accurate Numerical Scheme for Super-Fast MHD Flows
Johnson, B M; Guan, X; Gammie, F
2008-04-11
In numerical models of thin astrophysical disks that use an Eulerian scheme, gas orbits supersonically through a fixed grid. As a result the timestep is sharply limited by the Courant condition. Also, because the mean flow speed with respect to the grid varies with position, the truncation error varies systematically with position. For hydrodynamic (unmagnetized) disks an algorithm called FARGO has been developed that advects the gas along its mean orbit using a separate interpolation substep. This relaxes the constraint imposed by the Courant condition, which now depends only on the peculiar velocity of the gas, and results in a truncation error that is more nearly independent of position. This paper describes a FARGO-like algorithm suitable for evolving magnetized disks. Our method is second order accurate on a smooth flow and preserves {del} {center_dot} B = 0 to machine precision. The main restriction is that B must be discretized on a staggered mesh. We give a detailed description of an implementation of the code and demonstrate that it produces the expected results on linear and nonlinear problems. We also point out how the scheme might be generalized to make the integration of other supersonic/super-fast flows more efficient. Although our scheme reduces the variation of truncation error with position, it does not eliminate it. We show that the residual position dependence leads to characteristic radial variations in the density over long integrations.
Linaro, Daniele; Storace, Marco; Giugliano, Michele
2011-01-01
Stochastic channel gating is the major source of intrinsic neuronal noise whose functional consequences at the microcircuit- and network-levels have been only partly explored. A systematic study of this channel noise in large ensembles of biophysically detailed model neurons calls for the availability of fast numerical methods. In fact, exact techniques employ the microscopic simulation of the random opening and closing of individual ion channels, usually based on Markov models, whose computational loads are prohibitive for next generation massive computer models of the brain. In this work, we operatively define a procedure for translating any Markov model describing voltage- or ligand-gated membrane ion-conductances into an effective stochastic version, whose computer simulation is efficient, without compromising accuracy. Our approximation is based on an improved Langevin-like approach, which employs stochastic differential equations and no Montecarlo methods. As opposed to an earlier proposal recently debated in the literature, our approximation reproduces accurately the statistical properties of the exact microscopic simulations, under a variety of conditions, from spontaneous to evoked response features. In addition, our method is not restricted to the Hodgkin-Huxley sodium and potassium currents and is general for a variety of voltage- and ligand-gated ion currents. As a by-product, the analysis of the properties emerging in exact Markov schemes by standard probability calculus enables us for the first time to analytically identify the sources of inaccuracy of the previous proposal, while providing solid ground for its modification and improvement we present here. PMID:21423712
Numerical simulation of magma chamber dynamics.
NASA Astrophysics Data System (ADS)
Longo, Antonella; Papale, Paolo; Montagna, Chiara Paola; Vassalli, Melissa; Giudice, Salvatore; Cassioli, Andrea
2010-05-01
Magma chambers are characterized by periodic arrivals of deep magma batches that give origin to complex patterns of magma convection and mixing, and modify the distribution of physical quantities inside the chamber. We simulate the transient, 2D, multi-component homogeneous dynamics in geometrically complex dyke+chamber systems, by means of GALES, a finite element parallel C++ code solving mass, momentum and energy equations for multi-component homogeneous gas-liquid (± crystals) mixtures in compressible-to-incompressible flow conditions. Code validation analysis includes several cases from the classical engineering literature, corresponding to a variety of subsonic to supersonic gas-liquid flow regimes (see http://www.pi.ingv.it/~longo/gales/gales.html). The model allows specification of the composition of the different magmas in the domain, in terms of ten major oxides plus the two volatile species H2O and CO2. Gas-liquid thermodynamics are modeled by using the compositional dependent, non-ideal model in Papale et al. (Chem.. Geol., 2006). Magma properties are defined in terms of local pressure, temperature, and composition including volatiles. Several applications are performed within domains characterized by the presence of one or more magma chambers and one or more dykes, with different geometries and characteristic size from hundreds of m to several km. In most simulations an initial compositional interface is placed at the top of a feeding dyke, or at larger depth, with the deeper magma having a lower density as a consequence of larger volatile content. The numerical results show complex patterns of magma refilling in the chamber, with alternating phases of magma ingression and magma sinking from the chamber into the feeding dyke. Intense mixing takes place in feeding dykes, so that the new magma entering the chamber is always a mixture of the deep and the initially resident magma. Buoyant plume rise occurs through the formation of complex convective
Numerical Simulations of Saturn's Polar Cyclones
NASA Astrophysics Data System (ADS)
Brueshaber, Shawn R.; Sayanagi, Kunio M.
2014-11-01
Shawn R. Brueshaber, Department of Mechanical Engineering, Western Michigan UniversityKunio M. Sayanagi, Atmospheric and Planetary Sciences, Hampton UniversityCassini mission to Saturn has revealed evidences of a warm core cyclone centered on each of the poles of the planet. The morphology of the clouds in these cyclones resembles that of a terrestrial hurricane. The formation and maintenance mechanisms of these large polar cyclones are yet to be explained. Scott (2011, Astrophys. Geophys. Fluid Dyn) proposed that cyclonic vortices beta-drifting poleward can result in a polar cyclone, and demonstrated that beta-drifting cyclonic vortices can indeed cause accumulation of cyclonic vorticity at the pole using a 1-layer quasi-geostrophic model.The objectives of our project is to test Scott's hypothesis using a 1.5-layer shallow-water model and many-layer primitive equations model. We use the Explicit Planetary Isentropic Coordinate (EPIC) model (Dowling et al. 1998, 2004, Icarus) to perform direct numerical simulations of Saturn's polar atmosphere. To date, our project has focused on modifying the model to construct a polar rectangular model grid in order to avoid the problem of polar singularity associated with the conventional latitude-longitude grids employed in many general circulation models. We present our preliminary simulations, which show beta-drifting cyclones cause a poleward flux of cyclonic vorticity, which is consistent with Scott's results.Our study is partially supported by NASA Outer Planets Research Grant NNX12AR38G and NSF Astronomy and Astrophysics Grant 1212216 to KMS.
Toward the Accurate Simulation of Two-Dimensional Electronic Spectra
NASA Astrophysics Data System (ADS)
Giussani, Angelo; Nenov, Artur; Segarra-Martí, Javier; Jaiswal, Vishal K.; Rivalta, Ivan; Dumont, Elise; Mukamel, Shaul; Garavelli, Marco
2015-06-01
Two-dimensional pump-probe electronic spectroscopy is a powerful technique able to provide both high spectral and temporal resolution, allowing the analysis of ultrafast complex reactions occurring via complementary pathways by the identification of decay-specific fingerprints. [1-2] The understanding of the origin of the experimentally recorded signals in a two-dimensional electronic spectrum requires the characterization of the electronic states involved in the electronic transitions photoinduced by the pump/probe pulses in the experiment. Such a goal constitutes a considerable computational challenge, since up to 100 states need to be described, for which state-of-the-art methods as RASSCF and RASPT2 have to be wisely employed. [3] With the present contribution, the main features and potentialities of two-dimensional electronic spectroscopy are presented, together with the machinery in continuous development in our groups in order to compute two-dimensional electronic spectra. The results obtained using different level of theory and simulations are shown, bringing as examples the computed two-dimensional electronic spectra for some specific cases studied. [2-4] [1] Rivalta I, Nenov A, Cerullo G, Mukamel S, Garavelli M, Int. J. Quantum Chem., 2014, 114, 85 [2] Nenov A, Segarra-Martí J, Giussani A, Conti I, Rivalta I, Dumont E, Jaiswal V K, Altavilla S, Mukamel S, Garavelli M, Faraday Discuss. 2015, DOI: 10.1039/C4FD00175C [3] Nenov A, Giussani A, Segarra-Martí J, Jaiswal V K, Rivalta I, Cerullo G, Mukamel S, Garavelli M, J. Chem. Phys. submitted [4] Nenov A, Giussani A, Fingerhut B P, Rivalta I, Dumont E, Mukamel S, Garavelli M, Phys. Chem. Chem. Phys. Submitted [5] Krebs N, Pugliesi I, Hauer J, Riedle E, New J. Phys., 2013,15, 08501
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 Modified Newtonian Dynamics
NASA Astrophysics Data System (ADS)
Candlish, G. N.; Smith, R.; Fellhauer, M.
2016-05-01
The ΛCDM standard cosmological model is strongly supported by multiple lines of evidence, particularly from observations at large scales such as the CMB and large scale structure. There are some indications, however, of problems at smaller scales. An alternative to the CDM approach is to modify the gravitational force, as exemplified by the MOdified Newtonian Dynamics (MOND) idea. While evidence suggests MOND cannot account for dynamics at all scales without dark matter, it has been successful at galactic scales. Due to the complexity of the theory, however, most tests of MOND have extended no further than using a simple scaling relation to determine rotation curves or velocity dispersions. Therefore, to test the concept more thoroughly we require numerical simulations. We discuss the development and testing of a new N-body solver, using two distinct formulations of MOND, that is incorporated into the RAMSES code. The theory of MOND as a modification of Newtonian gravity is briefly summarised. We then show how it is implemented in the code, providing an example of an idealised test case and future applications.
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 simulations of drainage flows on Mars
NASA Astrophysics Data System (ADS)
Parish, Thomas R.; Howard, Alan D.
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.
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.
Direct numerical simulations of aeolian sand ripples
Durán, Orencio; Claudin, Philippe; Andreotti, Bruno
2014-01-01
Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873
Direct numerical simulations of aeolian sand ripples.
Durán, Orencio; Claudin, Philippe; Andreotti, Bruno
2014-11-01
Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873
Direct numerical simulation of active fiber composite
NASA Astrophysics Data System (ADS)
Kim, Seung J.; Hwang, Joon S.; Paik, Seung H.
2003-08-01
Active Fiber Composites (AFC) possess desirable characteristics for smart structure applications. One major advantage of AFC is the ability to create anisotropic laminate layers useful in applications requiring off-axis or twisting motions. AFC is naturally composed of two different constituents: piezoelectric fiber and matrix. Therefore, homogenization method, which is utilized in the analysis of laminated composite material, has been used to characterize the material properties. Using this approach, the global behaviors of the structures are predicted in an averaged sense. However, this approach has intrinsic limitations in describing the local behaviors in the level of the constituents. Actually, the failure analysis of AFC requires the knowledge of the local behaviors. Therefore, microscopic approach is necessary to predict the behaviors of AFC. In this work, a microscopic approach for the analysis of AFC was performed. Piezoelectric fiber and matrix were modeled separately and finite element method using three-dimensional solid elements was utilized. Because fine mesh is essential, high performance computing technology was applied to the solution of the immense degree-of-freedom problem. This approach is called Direct Numerical Simulation (DNS) of structure. Through the DNS of AFC, local stress distribution around the interface of fiber and matrix was analyzed.
Numerical simulation of noninvasive blood pressure measurement.
Hayashi, Satoru; Hayase, Toshiyuki; Shirai, Atsushi; Maruyama, Masaru
2006-10-01
In this paper, a simulation model based on the partially pressurized collapsible tube model for reproducing noninvasive blood pressure measurement is presented. The model consists of a collapsible tube, which models the pressurized part of the artery, rigid pipes connected to the collapsible tube, which model proximal and distal region far from the pressurized part, and the Windkessel model, which represents the capacitance and the resistance of the distal part of the circulation. The blood flow is simplified to a one-dimensional system. Collapse and expansion of the tube is represented by the change in the cross-sectional area of the tube considering the force balance acting on the tube membrane in the direction normal to the tube axis. They are solved using the Runge-Kutta method. This simple model can easily reproduce the oscillation of inner fluid and corresponding tube collapse typical for the Korotkoff sounds generated by the cuff pressure. The numerical result is compared with the experiment and shows good agreement. PMID:16995754
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.
Advanced in turbulence physics and modeling by direct numerical simulations
NASA Technical Reports Server (NTRS)
Reynolds, W. C.
1987-01-01
The advent of direct numerical simulations of turbulence has opened avenues for research on turbulence physics and turbulence modeling. Direct numerical simulation provides values for anything that the scientist or modeler would like to know about the flow. An overview of some recent advances in the physical understanding of turbulence and in turbulence modeling obtained through such simulations is presented.
Unfitted Two-Phase Flow Simulations in Pore-Geometries with Accurate
NASA Astrophysics Data System (ADS)
Heimann, Felix; Engwer, Christian; Ippisch, Olaf; Bastian, Peter
2013-04-01
The development of better macro scale models for multi-phase flow in porous media is still impeded by the lack of suitable methods for the simulation of such flow regimes on the pore scale. The highly complicated geometry of natural porous media imposes requirements with regard to stability and computational efficiency which current numerical methods fail to meet. Therefore, current simulation environments are still unable to provide a thorough understanding of porous media in multi-phase regimes and still fail to reproduce well known effects like hysteresis or the more peculiar dynamics of the capillary fringe with satisfying accuracy. Although flow simulations in pore geometries were initially the domain of Lattice-Boltzmann and other particle methods, the development of Galerkin methods for such applications is important as they complement the range of feasible flow and parameter regimes. In the recent past, it has been shown that unfitted Galerkin methods can be applied efficiently to topologically demanding geometries. However, in the context of two-phase flows, the interface of the two immiscible fluids effectively separates the domain in two sub-domains. The exact representation of such setups with multiple independent and time depending geometries exceeds the functionality of common unfitted methods. We present a new approach to pore scale simulations with an unfitted discontinuous Galerkin (UDG) method. Utilizing a recursive sub-triangulation algorithm, we extent the UDG method to setups with multiple independent geometries. This approach allows an accurate representation of the moving contact line and the interface conditions, i.e. the pressure jump across the interface. Example simulations in two and three dimensions illustrate and verify the stability and accuracy of this approach.
Determination of damping properties in laminated composites via numerical simulation
Surana, K.S.; Ahmadi, A.R.
1997-07-01
This paper presents a numerical simulation procedure based on finite element method which could be utilized for establishing the damping characteristic of laminated composite material. Viscoelastic fluids such as upper convected Maxwell fluid and White Metzner fluids are used as sample problems to illustrate the procedure and its usefulness. For many viscoelastic materials, the damping characteristics are incorporated through what is known as loss factor while simulating dynamic response of structures containing such materials. The loss factor is directly related to the dissipative mechanism in the equations describing the behavior can be accurately obtained. In this paper the authors utilize p-version Least Squares Finite Element Method (LSFEM) to numerically solve the equations and then calculate loss factor in the post processing phase of the computations. The governing differential equations and the constitutive laws describing the material behavior are recast into a system of first order differential equations using auxiliary variables (often the stresses). Both the dependent and the auxiliary variables are interpolated over an element using unequal order C{sup 0} interpolations (element approximation). When the element approximation is substituted into the first order differential equations the authors obtain element error or residual equations. In LSFEM they minimize the integrated sum of squares of these errors over the whole discretization. They utilize Newton`s method with line search to obtain a solution iteratively.
Numerical Simulation of Spray Atomization in Supersonic Flows
NASA Astrophysics Data System (ADS)
Wang, Jiangfeng; Liu, Chen; Wu, Yizhao
With the rapid development of the air-breathing hypersonic vehicle design, an accurate description of the combustion properties becomes more and more important, where one of the key techniques is the procedure of the liquid fuel mixing, atomizing and burning coupled with the supersonic crossflow in the combustion chamber. The movement and distribution of the liquid fuel droplets in the combustion chamber will influence greatly the combustion properties, as well as the propulsion performance of the ramjet/scramjet engine. In this paper, numerical simulation methods on unstructured hybrid meshes were carried out for liquid spray atomization in supersonic crossflows. The Kelvin-Helmholtz/Rayleigh-Taylor hybrid model was used to simulate the breakup process of the liquid spray in a supersonic crossflow with Mach number 1.94. Various spray properties, including spray penetration height, droplet size distribution, were quantitatively compared with experimental results. In addition, numerical results of the complex shock wave structure induced by the presence of liquid spray were illustrated and discussed.
TOPLHA: an accurate and efficient numerical tool for analysis and design of LH antennas
NASA Astrophysics Data System (ADS)
Milanesio, D.; Lancellotti, V.; Meneghini, O.; Maggiora, R.; Vecchi, G.; Bilato, R.
2007-09-01
Auxiliary ICRF heating systems in tokamaks often involve large complex antennas, made up of several conducting straps hosted in distinct cavities that open towards the plasma. The same holds especially true in the LH regime, wherein the antennas are comprised of arrays of many phased waveguides. Upon observing that the various cavities or waveguides couple to each other only through the EM fields existing over the plasma-facing apertures, we self-consistently formulated the EM problem by a convenient set of multiple coupled integral equations. Subsequent application of the Method of Moments yields a highly sparse algebraic system; therefore formal inversion of the system matrix happens to be not so memory demanding, despite the number of unknowns may be quite large (typically 105 or so). The overall strategy has been implemented in an enhanced version of TOPICA (Torino Polytechnic Ion Cyclotron Antenna) and in a newly developed code named TOPLHA (Torino Polytechnic Lower Hybrid Antenna). Both are simulation and prediction tools for plasma facing antennas that incorporate commercial-grade 3D graphic interfaces along with an accurate description of the plasma. In this work we present the new proposed formulation along with examples of application to real life large LH antenna systems.
Direct numerical simulation of turbulent aerosol coagulation
NASA Astrophysics Data System (ADS)
Reade, Walter Caswell
There are numerous systems-including both industrial applications and natural occurring phenomena-in which the collision/coagulation rates of aerosols are of significant interest. Two examples are the production of fine powders (such as titanium dioxide) and the formation of rain drops in the atmosphere. During the last decade, it has become apparent that dense aerosol particles behave much differently in a turbulent fluid than has been previously assumed. Particles with a response time on the order of the small-scale fluid time scale tend to collect in regions of low vorticity. The result is a particle concentration field that can be highly non-uniform. Sundaram and Collins (1997) recently demonstrated the effect that turbulence can have on the particle collision rate of a monodisperse system. The collision rates of finite-inertia particles can be as much as two orders of magnitude greater than particles that precisely follow the fluid streamlines. Sundaram and Collins derived a general collision expression that explicitly accounted for the two phenomena that affect the collision rate-changes in the particle concentration field and changes in the particle relative velocities. The result of Sundaram and Collins has generated further interest in the turbulent-aerosol problem. This thesis shows that, in addition to changing the rate that an aerosol size distribution might form, turbulence has the potential of dramatically changing the shape of the distribution. This result is demonstrated using direct numerical simulation of a turbulent-aerosol system over a wide range of particle parameters, and a moderate range of turbulence levels. Results show that particles with a small (but finite) initial inertia have the greatest potential of forming broad size distributions. The shape of the resulting size distribution is also affected by the initial size of the particles. Observations are explained using the statistics identified by Sundaram and Collins (1997). A major
Numerical simulation of subcooled flow boiling
NASA Astrophysics Data System (ADS)
Park, Won Cheol
Sub-cooled flow boiling in a U-bend has been examined using numerical methods. An Eulerian/Eulerian mathematical description was used with a multiphase computational algorithm to predict several types of flows and to examine sub-cooled flow boiling. As a prelude to the study of sub-cooled boiling and two-phase flows, single-phase laminar and turbulent flows in a U-bend were investigated. Air-water bubbly up flow in a vertical straight duct followed by a U-bend with heat transfer was analyzed. In such a flow, as the flow develops through the U-bend the bubbles move from center and outer wall toward inner wall. After half way through the U-bend, the fluids do not have sufficient time for complete reorganization in the presence of centrifugal forces and the pressure gradients. After the U-bend, the bubbles finally reach the original distribution in about forty diameters. The heat transfer in the U-bend was also calculated and as expected heat transfer rate on the outer wall is higher than on the inner wall. For air-water bubbly two-phase flow, Nusselt numbers in the U-bend can be as high as 400 percent of the value in the straight duct on one of the walls. The method of partitioned wall heat flux was used to study sub-cooled flow boiling. For sub-cooled flow boiling in a U-bend, axial and lateral velocity distributions as well as quality and void fraction variations were analyzed. Computed axial and lateral variations of void fraction compare favorably with existing experimental data. As expected, the pressure drop for bubbly flow through the U-bend is larger than for single-phase flow by as much as fifty percent. Computed pressure drop for flow with phase change falls between the predictions of two different correlations in the literature, and thus seems reasonable. Predictions of heat transfer and void fraction under sub-cooled flow boiling using two-fluid models need better quantitative knowledge related to the mechanisms associated with bubble growth and
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.
Numerical simulation of 3D breaking waves
NASA Astrophysics Data System (ADS)
Fraunie, Philippe; Golay, Frederic
2015-04-01
Numerical methods dealing with two phase flows basically can be classified in two ways : the "interface tracking" methods when the two phases are resolved separately including boundary conditions fixed at the interface and the "interface capturing" methods when a single flow is considered with variable density. Physical and numerical properties of the two approaches are discussed, based on some numerical experiments performed concerning 3D breaking waves. Acknowledgements : This research was supported by the Modtercom program of Region PACA.
Numerical simulation of a 100-ton ANFO detonation
NASA Astrophysics Data System (ADS)
Weber, P. W.; Millage, K. K.; Crepeau, J. E.; Happ, H. J.; Gitterman, Y.; Needham, C. E.
2015-03-01
This work describes the results from a US government-owned hydrocode (SHAMRC, Second-Order Hydrodynamic Automatic Mesh Refinement Code) that simulated an explosive detonation experiment with 100,000 kg of Ammonium Nitrate-Fuel Oil (ANFO) and 2,080 kg of Composition B (CompB). The explosive surface charge was nearly hemispherical and detonated in desert terrain. Two-dimensional axisymmetric (2D) and three-dimensional (3D) simulations were conducted, with the 3D model providing a more accurate representation of the experimental setup geometry. Both 2D and 3D simulations yielded overpressure and impulse waveforms that agreed qualitatively with experiment, including the capture of the secondary shock observed in the experiment. The 2D simulation predicted the primary shock arrival time correctly but secondary shock arrival time was early. The 2D-predicted impulse waveforms agreed very well with the experiment, especially at later calculation times, and prediction of the early part of the impulse waveform (associated with the initial peak) was better quantitatively for 2D compared to 3D. The 3D simulation also predicted the primary shock arrival time correctly, and secondary shock arrival times in 3D were closer to the experiment than in the 2D results. The 3D-predicted impulse waveform had better quantitative agreement than 2D for the later part of the impulse waveform. The results of this numerical study show that SHAMRC may be used reliably to predict phenomena associated with the 100-ton detonation. The ultimate fidelity of the simulations was limited by both computer time and memory. The results obtained provide good accuracy and indicate that the code is well suited to predicting the outcomes of explosive detonations.
Direct Numerical Simulation of Soot Particle Dynamics using DQMOM
NASA Astrophysics Data System (ADS)
Blanquart, Guillaume; Pitsch, Heinz; Fox, Rodney
2006-11-01
The understanding of soot particle dynamics in combustion systems is a key issue in the development of low emission engines. Of particular importance are the processes shaping the soot particle size distribution function (PSDF). However, it is not always necessary to represent exactly the full distribution but rather some of its moments. The Direct Quadrature Method of Moments (DQMOM) allows for a very accurate prediction of the moments of the soot PSDF without the cost of expensive methods like Direct Simulation Monte-Carlo (DSMC). This method has been validated for laminar premixed and diffusion flames with detailed chemistry and is now implemented in a semi-implicit low Mach number Navier-Stokes solver. A Direct Numerical Simulation (DNS) of an ethylene jet diffusion flame is performed to study the dynamics of soot particles in a turbulent environment. Soot particles are formed in very rich regions of the flames and are then transported to lean regions where they get oxidized. The time evolution of the soot PSDF will be analyzed and compared to similar distributions from laminar simulations.
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.
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)
Shukla, Ratnesh K.
2014-11-01
Single fluid schemes that rely on an interface function for phase identification in multicomponent compressible flows are widely used to study hydrodynamic flow phenomena in several diverse applications. Simulations based on standard numerical implementation of these schemes suffer from an artificial increase in the width of the interface function owing to the numerical dissipation introduced by an upwind discretization of the governing equations. In addition, monotonicity requirements which ensure that the sharp interface function remains bounded at all times necessitate use of low-order accurate discretization strategies. This results in a significant reduction in accuracy along with a loss of intricate flow features. In this paper we develop a nonlinear transformation based interface capturing method which achieves superior accuracy without compromising the simplicity, computational efficiency and robustness of the original flow solver. A nonlinear map from the signed distance function to the sigmoid type interface function is used to effectively couple a standard single fluid shock and interface capturing scheme with a high-order accurate constrained level set reinitialization method in a way that allows for oscillation-free transport of the sharp material interface. Imposition of a maximum principle, which ensures that the multidimensional preconditioned interface capturing method does not produce new maxima or minima even in the extreme events of interface merger or breakup, allows for an explicit determination of the interface thickness in terms of the grid spacing. A narrow band method is formulated in order to localize computations pertinent to the preconditioned interface capturing method. Numerical tests in one dimension reveal a significant improvement in accuracy and convergence; in stark contrast to the conventional scheme, the proposed method retains its accuracy and convergence characteristics in a shifted reference frame. Results from the test
Advanced material modelling in numerical simulation of primary acetabular press-fit cup stability.
Souffrant, R; Zietz, C; Fritsche, A; Kluess, D; Mittelmeier, W; Bader, R
2012-01-01
Primary stability of artificial acetabular cups, used for total hip arthroplasty, is required for the subsequent osteointegration and good long-term clinical results of the implant. Although closed-cell polymer foams represent an adequate bone substitute in experimental studies investigating primary stability, correct numerical modelling of this material depends on the parameter selection. Material parameters necessary for crushable foam plasticity behaviour were originated from numerical simulations matched with experimental tests of the polymethacrylimide raw material. Experimental primary stability tests of acetabular press-fit cups consisting of static shell assembly with consecutively pull-out and lever-out testing were subsequently simulated using finite element analysis. Identified and optimised parameters allowed the accurate numerical reproduction of the raw material tests. Correlation between experimental tests and the numerical simulation of primary implant stability depended on the value of interference fit. However, the validated material model provides the opportunity for subsequent parametric numerical studies. PMID:22817471
Numerical Simulation of Rocket Exhaust Interaction with Lunar Soil
NASA Technical Reports Server (NTRS)
Liever, Peter; Tosh, Abhijit; Curtis, Jennifer
2012-01-01
This technology development originated from the need to assess the debris threat resulting from soil material erosion induced by landing spacecraft rocket plume impingement on extraterrestrial planetary surfaces. The impact of soil debris was observed to be highly detrimental during NASA s Apollo lunar missions and will pose a threat for any future landings on the Moon, Mars, and other exploration targets. The innovation developed under this program provides a simulation tool that combines modeling of the diverse disciplines of rocket plume impingement gas dynamics, granular soil material liberation, and soil debris particle kinetics into one unified simulation system. The Unified Flow Solver (UFS) developed by CFDRC enabled the efficient, seamless simulation of mixed continuum and rarefied rocket plume flow utilizing a novel direct numerical simulation technique of the Boltzmann gas dynamics equation. The characteristics of the soil granular material response and modeling of the erosion and liberation processes were enabled through novel first principle-based granular mechanics models developed by the University of Florida specifically for the highly irregularly shaped and cohesive lunar regolith material. These tools were integrated into a unique simulation system that accounts for all relevant physics aspects: (1) Modeling of spacecraft rocket plume impingement flow under lunar vacuum environment resulting in a mixed continuum and rarefied flow; (2) Modeling of lunar soil characteristics to capture soil-specific effects of particle size and shape composition, soil layer cohesion and granular flow physics; and (3) Accurate tracking of soil-borne debris particles beginning with aerodynamically driven motion inside the plume to purely ballistic motion in lunar far field conditions. In the earlier project phase of this innovation, the capabilities of the UFS for mixed continuum and rarefied flow situations were validated and demonstrated for lunar lander rocket
Numerical simulation of a cross flow Marine Hydrokinetic turbine.
NASA Astrophysics Data System (ADS)
Hall, Taylor; Aliseda, Alberto
2011-11-01
In the search for alternative sources of energy, the kinetic energy of water currents in oceans, rivers and estuaries is being explored as predictable and environmentally benign. We are investigating the flow past a cross flow turbine in which a helical blade under hydrodynamic forces turns around a shaft perpendicular to the free stream. This type of turbine, while very different from the classical horizontal axis turbine commonly used in the wind energy field, presents advantages for stacking in very narrow constricted channels where the water currents are consistently high and therefore turbine installation may be economically feasible. We use a model of a helical four-bladed turbine in cross flow to investigate the efficiency of the energy capture and the dynamics of the turbulent wake. Scale model experiments in a flume are used to validate the numerical results on a stationary configuration as an initial step towards creating an accurate numerical model of the turbine. The simulation of the rotating turbine provides a full perspective on the effect of angular position on flow detachment and vortex shedding from the blade, as well as on the fluctuations of the shaft torque produced (a problematic feature of this type of turbine). The results are analyzed in terms of hydrodynamic optimization of the blade and its structural loading. Supported by DOE through the Northwest National Marine Renewable Energy Center.
Numerical simulation of the 1988 midwestern drought
Chern, Jiun-Dar; Sun, Wen-Yih
1997-11-01
In this study, the Purdue Regional Model (PRM) is utilized to simulate the monthly evolution of the weather patterns during the summer of 1988. The primary goal of this study is to develop and validate the PRM. The PRM, a regional climate model, is a hydrostatic primitive-equation model that uses the Arakawa C staggered grid in the horizontal and a terrain-following vertical coordinate. The model was used to simulate the 1988 drought for one month with lateral boundary conditions. The simulation reproduced the driest events in the Midwest; however, the simulated precipitation along the Gulf coast and Florida was underestimated. This suggests that the 60 km model resolution used in the simulation was not high enough to simulate the convective precipitation associated with the sea breeze circulations. 10 refs., 5 figs.
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.
Direct numerical simulation of transition and turbulence in a spatially evolving boundary layer
NASA Technical Reports Server (NTRS)
Rai, Man M.; Moin, Parviz
1991-01-01
A high-order-accurate finite-difference approach to direct simulations of transition and turbulence in compressible flows is described. Attention is given to the high-free-stream disturbance case in which transition to turbulence occurs close to the leading edge. In effect, computation requirements are reduced. A method for numerically generating free-stream disturbances is presented.
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.
Direct numerical simulations of collision efficiency of cohesive sediments
NASA Astrophysics Data System (ADS)
Zhang, Jin-Feng; Maa, Jerome P.-Y.; Zhang, Qing-He; Shen, Xiao-Teng
2016-09-01
A clear understanding of the collision efficiency of cohesive sediment particles is critical for more accurate simulation of the flocculation processes. It is difficult, if not impossible, to carry out laboratory experiments to determine the collision efficiency for small particles. Direct Numerical Simulation (DNS) is a relatively feasible approach to describe the motion of spherical particles under gravity in calm water, and thus, to study the collision efficiency of these particles. In this study, the Lattice Boltzmann (LB) method is used to calculate the relative trajectories of two approaching particles with different ratios of sizes and densities. Results show that the inter-molecular forces (i.e., van der Waals attractive force, electrostatic repulsive/attractive force, and displacement force), which are usually neglected in previous studies, would affect the trajectories, and thus, lead to an overestimation of the collision efficiency. It is found that to increase the particle size ratio from 0.1 to 0.8 only slightly increases the collision efficiency, since the force caused by fluid-solid interaction between these two particles is reduced. To increase the submerged particle density ratio from 1 to 22, however, would significantly decrease the collision efficiency. Earlier analytical formulations of collision efficiency, which only consider the effects of particle size ratio, have significantly overestimated the collision efficiency (change from 0.01 to 0.6) when the particle size ratio is around 0.5.
How to obtain accurate resist simulations in very low-k1 era?
NASA Astrophysics Data System (ADS)
Chiou, Tsann-Bim; Park, Chan-Ha; Choi, Jae-Seung; Min, Young-Hong; Hansen, Steve; Tseng, Shih-En; Chen, Alek C.; Yim, Donggyu
2006-03-01
A procedure for calibrating a resist model iteratively adjusts appropriate parameters until the simulations of the model match the experimental data. The tunable parameters may include the shape of the illuminator, the geometry and transmittance/phase of the mask, light source and scanner-related parameters that affect imaging quality, resist process control and most importantly the physical/chemical factors in the resist model. The resist model can be accurately calibrated by measuring critical dimensions (CD) of a focus-exposure matrix (FEM) and the technique has been demonstrated to be very successful in predicting lithographic performance. However, resist model calibration is more challenging in the low k1 (<0.3) regime because numerous uncertainties, such as mask and resist CD metrology errors, are becoming too large to be ignored. This study demonstrates a resist model calibration procedure for a 0.29 k1 process using a 6% halftone mask containing 2D brickwall patterns. The influence of different scanning electron microscopes (SEM) and their wafer metrology signal analysis algorithms on the accuracy of the resist model is evaluated. As an example of the metrology issue of the resist pattern, the treatment of a sidewall angle is demonstrated for the resist line ends where the contrast is relatively low. Additionally, the mask optical proximity correction (OPC) and corner rounding are considered in the calibration procedure that is based on captured SEM images. Accordingly, the average root-mean-square (RMS) error, which is the difference between simulated and experimental CDs, can be improved by considering the metrological issues. Moreover, a weighting method and a measured CD tolerance are proposed to handle the different CD variations of the various edge points of the wafer resist pattern. After the weighting method is implemented and the CD selection criteria applied, the RMS error can be further suppressed. Therefore, the resist CD and process window can
Direct numerical simulation of supersonic turbulent boundary layers
NASA Astrophysics Data System (ADS)
Guarini, Stephen
The objectives of this research were to develop a method by which the spatially developing compressible turbulent boundary layer could be simulated using a temporally developing numerical simulation and to study the physics of the compressible turbulent boundary layer. We take advantage of the technique developed by Spalart (1987, 1988) for the incompressible case. In this technique, it is recognized that the boundary layer exhibits slow growth in the streamwise direction, so the turbulence can be treated as approximately homogeneous in this direction. The slow growth is accounted for with a coordinate transformation and a multiple scale analysis. The result is a modified system of equations (Navier-Stokes plus some extra terms, which we call "slow growth terms") that are homogeneous in both the streamwise and spanwise directions and represent the state of the boundary layer at a given streamwise location (or, equivalently, a given thickness). The compressible Navier-Stokes equations are solved using a mixed Fourier and B-spline "spectral" method. The dependent variables are expanded in terms of a Fourier representation in the horizontal directions and a B-spline representation in the wall-normal direction. In the wall-normal direction non-reflecting boundary conditions are used at the freestream boundary, and zero-heat-flux no-slip boundary conditions are used at the wall. This combination of splines and Fourier methods produces a very accurate numerical method. Mixed implicit/explicit time discretization is used. Results are presented for a case with a Mach number of 2.5, and a Reynolds number, based on momentum integral thickness and wall viscosity, of Rsb{thetasp'} = 840. The results show that the van Driest transformed velocity satisfies the incompressible scalings and a narrow logarithmic region is obtained. The results for the turbulence intensities compare well with the incompressible simulations of Spalart. Pressure fluctuations are found to be higher than
Chen, Chun-Chi; Chen, Chao-Lieh; Lin, You-Ting
2016-01-01
This study proposes a new behavioral simulator that uses SIMULINK for all-digital CMOS time-domain smart temperature sensors (TDSTSs) for performing rapid and accurate simulations. Inverter-based TDSTSs offer the benefits of low cost and simple structure for temperature-to-digital conversion and have been developed. Typically, electronic design automation tools, such as HSPICE, are used to simulate TDSTSs for performance evaluations. However, such tools require extremely long simulation time and complex procedures to analyze the results and generate figures. In this paper, we organize simple but accurate equations into a temperature-dependent model (TDM) by which the TDSTSs evaluate temperature behavior. Furthermore, temperature-sensing models of a single CMOS NOT gate were devised using HSPICE simulations. Using the TDM and these temperature-sensing models, a novel simulator in SIMULINK environment was developed to substantially accelerate the simulation and simplify the evaluation procedures. Experiments demonstrated that the simulation results of the proposed simulator have favorable agreement with those obtained from HSPICE simulations, showing that the proposed simulator functions successfully. This is the first behavioral simulator addressing the rapid simulation of TDSTSs. PMID:27509507
Polarization transmission at RHIC, numerical simulations
Meot F.; Bai, M.; Liu, C.; Minty, M.; Ranjbar, V.
2012-05-20
Typical tracking simulations regarding the transmission of the polarization in the proton-proton collider RHIC are discussed. They participate in general studies aimed at understanding and improving polarization performances during polarized proton-proton runs.
Numerical error in groundwater flow and solute transport simulation
NASA Astrophysics Data System (ADS)
Woods, Juliette A.; Teubner, Michael D.; Simmons, Craig T.; Narayan, Kumar A.
2003-06-01
Models of groundwater flow and solute transport may be affected by numerical error, leading to quantitative and qualitative changes in behavior. In this paper we compare and combine three methods of assessing the extent of numerical error: grid refinement, mathematical analysis, and benchmark test problems. In particular, we assess the popular solute transport code SUTRA [Voss, 1984] as being a typical finite element code. Our numerical analysis suggests that SUTRA incorporates a numerical dispersion error and that its mass-lumped numerical scheme increases the numerical error. This is confirmed using a Gaussian test problem. A modified SUTRA code, in which the numerical dispersion is calculated and subtracted, produces better results. The much more challenging Elder problem [Elder, 1967; Voss and Souza, 1987] is then considered. Calculation of its numerical dispersion coefficients and numerical stability show that the Elder problem is prone to error. We confirm that Elder problem results are extremely sensitive to the simulation method used.
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 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 simulations in the development of propellant management devices
NASA Astrophysics Data System (ADS)
Gaulke, Diana; Winkelmann, Yvonne; Dreyer, Michael
Propellant management devices (PMDs) are used for positioning the propellant at the propel-lant port. It is important to provide propellant without gas bubbles. Gas bubbles can inflict cavitation and may lead to system failures in the worst case. Therefore, the reliable operation of such devices must be guaranteed. Testing these complex systems is a very intricate process. Furthermore, in most cases only tests with downscaled geometries are possible. Numerical sim-ulations are used here as an aid to optimize the tests and to predict certain results. Based on these simulations, parameters can be determined in advance and parts of the equipment can be adjusted in order to minimize the number of experiments. In return, the simulations are validated regarding the test results. Furthermore, if the accuracy of the numerical prediction is verified, then numerical simulations can be used for validating the scaling of the experiments. This presentation demonstrates some selected numerical simulations for the development of PMDs at ZARM.
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.
Numerical simulations of plasma double layers
NASA Technical Reports Server (NTRS)
Goertz, C. K.; Borovsky, J. E.
1983-01-01
The results of analytical studies of quasi-static electric fields along geomagnetic field lines are discussed. The calculations were targeted at the structure, generation mechanisms and stability parameters. The field consists of two oppositely charged layers, either weakly or strongly charged, with an electric field between. Existence conditions are defined for the double layer field and balancing requirements are explored. Details of the simulation techniques, i.e., particle in cell and Vlasov simulations, for studying the double layer are outlined, noting that both periodic and quasi-periodic simulations are used. Solutions to Poisson's equation for fixed and floating point boundary conditions are generated. Finally, attention is also given to oblique and two-dimensional magnetic double layers.
Cobb, J.W.
1995-02-01
There is an increasing need for more accurate numerical methods for large-scale nonlinear magneto-fluid turbulence calculations. These methods should not only increase the current state of the art in terms of accuracy, but should also continue to optimize other desired properties such as simplicity, minimized computation, minimized memory requirements, and robust stability. This includes the ability to stably solve stiff problems with long time-steps. This work discusses a general methodology for deriving higher-order numerical methods. It also discusses how the selection of various choices can affect the desired properties. The explicit discussion focuses on third-order Runge-Kutta methods, including general solutions and five examples. The study investigates the linear numerical analysis of these methods, including their accuracy, general stability, and stiff stability. Additional appendices discuss linear multistep methods, discuss directions for further work, and exhibit numerical analysis results for some other commonly used lower-order methods.
Numerical simulation of interacting vortex tubes
Pumir, A.; Kerr, R.M.
1987-04-20
The structure of the cores of interacting vortex tubes in three-dimensional incompressible hydrodynamics has been simulated by a pseudospectral method. A fast reconnection is observed for Reynolds numbers of order 1 000. At higher Reynolds numbers, the core tends to flatten, suggesting the formation of vortex ribbons.
Scaling of turbulence and turbulent mixing using Terascale numerical simulations
NASA Astrophysics Data System (ADS)
Donzis, Diego A.
Fundamental aspects of turbulence and turbulent mixing are investigated using direct numerical simulations (DNS) of stationary isotropic turbulence, with Taylor-scale Reynolds numbers (Rlambda) ranging from 8 to 650 and Schmidt numbers (Sc) from 1/8 to 1024. The primary emphasis is on important scaling issues that arise in the study of intermittency, mixing and turbulence under solid-body rotation. Simulations up to 20483 in size have been performed using large resource allocations on Terascale computers at leading supercomputing centers. Substantial efforts in algorithmic development have also been undertaken and resulted in a new code based on a two-dimensional domain decomposition which allows the use of very large number of processors. Benchmark tests indicate very good parallel performance for resolutions up to 40963 on up to 32768 processors, which is highly promising for future simulations at higher resolutions and processor counts eventually to approach Petascale levels. Investigation of intermittency through the statistics of dissipation and enstrophy in a series of simulations at the same Reynolds number but different resolution indicate that accurate results in high-order moments require a higher degree of fine-scale resolution than commonly practiced. However, statistics up to fourth order are satisfactory if the grid spacing is not larger than Komogorov scale, without the requirement of a clear analytic range for corresponding structure functions as suggested by recent theories. Results from highly resolved simulations provide support for a modified resolution criterion derived in this work for structure functions of different orders and as a function of Rlambda. At the highest Reynolds number in our simulations (400 and 650) dissipation and enstrophy exhibit extreme fluctuations of O(1000) the mean which have not been studied in the literature before. The far tails of the probability density functions of dissipation and enstrophy appear to coincide
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.
Brush seal numerical simulation: Concepts and advances
NASA Astrophysics Data System (ADS)
Braun, M. J.; Kudriavtsev, V. V.
1994-07-01
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.
Numerical simulations at CEBAF using PARMELA
NASA Astrophysics Data System (ADS)
Liu, H.
1993-12-01
PARMELA has been used at CEBAF for numerical modeling of the nuclear physics injector chopping system, a possible FEL laser gun injector, and the rf steering and focusing effects of the standard CEBAF SRF cavities. These applications call for the code to input field data consistently from SUPERFISH, POISSON, and MAFIA, to properly treat a focusing solenoidal lens having an actual field profile either individually or together with its adjacent rf cavity, to deal with the space charge forces, to model the longitudinal phase space matching required for bunching electrons using a phase-compressor chicane, etc. In this paper, we describe in detail these issues of general interest.
Numerical simulation of oil pool boundary evolution
NASA Astrophysics Data System (ADS)
Khudobina, Yulia; Bubenchikov, Aleksey; Bubenchikov, Mikhail; Matvienko, Oleg; Libin, Eduard
2016-01-01
The study of spatial distribution of hydrocarbon resources and forecasting their geographical location is of great importance for the most complete recovery of hydrocarbons from deposits. The present study gives new mathematical results in the theory of stratified fluid flow in a porous medium. This paper analyzes the evolution of oil pool boundary basing on vortex numerical model for movement of the boundary separating fluids of different densities. It presents the investigation of how the location of light fluid regarding the heavier fluid influences on the changes in the boundary between two media in case of various shifting of the well.
Numerical simulation scattered imaging in deep mines
NASA Astrophysics Data System (ADS)
Hu, Ming-Shun; Pan, Dong-Ming; Li, Juan-Juan
2010-09-01
Conventional seismic exploration, mostly based on reflection theory, hardly has accurate imaging results for disaster geologic bodies which have small scale, steep dip, or complex structure. In this paper, we design two typical geologic models for analyzing the characteristics of scattered waves in mines for forward modeling by finite difference and apply the equivalent offset migration (EOM) and EOM-based interference stack migration methods to mine prospecting. We focus on the analysis of scatted imaging’s technological superiority to reflection imaging. Research shows: 1) scattered imaging can improve fold and make the best of weak scattered information, so it shows better results than post-stack migration imaging and 2) it can utilize the diffraction stack migration method-based ray path theory for mine seismic advanced prediction, so it provides an new efficient imaging method for improving resolution of mine seismic exploration.
Numerical simulation of the 1993 midwestern flood
NASA Astrophysics Data System (ADS)
Bosilovich, Michael Gerard
During the summer of 1993, persistent and heavy precipitation caused a long-lived catastrophic flood in the midwestern United States. In this paper, Midwest hydrology, atmospheric circulation of the 1993 summer, and feedback between the surface and precipitating systems were investigated using the Purdue Regional Model (PRM). Observational analyses of the monthly mean circulation have identified several differences between June and July 1993 that should be considered when studying the interaction of the surface and precipitation systems. The PRM is utilized to simulate the weather during each thirty day period. The PRM is verified against European Centre for Medium Range Weather Forecasts (ECMWF) monthly mean observational analyses. Key features, such as the upper level jet stream and trough, moisture transport and heavy precipitation are reproduced by the PRM. Furthermore, the model is able to simulate the different daily precipitation patterns observed during each month. Some model biases are identified and discussed. The verisimilitude between the model and observed circulations allows for sensitivity experiments to investigate the interaction between the surface and precipitation systems. In general, the results indicated that the June (transient cyclone period) simulations were not as sensitive to the surface anomalies as the July (stationary convective period) simulations. While a large-scale dry soil anomaly slightly decreased the moist convective instability of the planetary boundary layer (PBL), a large scale surface pressure perturbation occurred and weakened the low level jet and moisture transport from the Gulf of Mexico. Both wet and dry soil moisture anomalies, imposed across the southern Great Plains, caused a reduction in the low level jet and Midwestern precipitation. Differential heating at the surface in the control simulations associated with the gradient of soil moisture in the southern Great Plains enhanced the mean southerly wind in the PBL
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 simulations of bent, disrupted radio jets
NASA Technical Reports Server (NTRS)
Loken, Chris; Burns, Jack O.
1993-01-01
We present preliminary results from three-dimensional hydrodynamical simulations designed to investigate the physics of jet bending and disruption. The specific scenario considered here involves a mildly supersonic jet crossing a contact discontinuity at the interface between the interstellar medium (ISM) and the intercluster medium (ICM) and then encountering a cross-wind in the ICM. The resultant morphologies show many of the features observed in radio sources including jet flaring, bending, and extended tails.
Numerical Simulations of Plasma Jets for PLX
NASA Astrophysics Data System (ADS)
Wu, L.; Messer, S.; Case, A.; Phillips, M.; Witherspoon, F. D.; Welch, D.; Thoma, C.; Bogatu, I. N.; Galkin, S.; Thompson, J. R.; Kim, J. S.; Macfarlane, J.; Golovkin, I.
2011-10-01
Two and three-dimensional simulations are performed using the hybrid particle-in-cell code LSP to study liner formation for the Plasma Liner Experiment (PLX). These include studies of plasma transport within small parallel-plate MiniRailguns, issues related to detachment of the jet from the nozzle, and the subsequent propagation of single jets in Cartesian coordinates. Merging of plasma jets is studied mainly in cylindrical coordinates at present. Varied number of railguns (or jets) are used in this study with initial velocity of 50-100 km/s, initial argon number density of 1016 cm-3 to 1017 cm-3, and initial temperature of ~3 eV. The effects on liner formation from jet initial profiles (density, velocity and temperature distribution) are studied to explore behavior. Simulation results are presented and compared with experimental data from merging jet experiments currently being conducted at HyperV using 1cm bore MiniRailguns. The LSP code is used to perform the simulations using improved fluid algorithms and equation-of-state models from Voss and atomic data from Prism.
Numerical Simulations of Europa Hydrothermal Plumes
NASA Astrophysics Data System (ADS)
Goodman, J. C.; Lenferink, E.
2009-12-01
The liquid water interiors of Europa and other icy moons of the outer solar system are likely to be driven by geothermal heating from the sea floor, leading to the development of buoyant hydrothermal plumes. These plumes potentially control icy surface geomorphology, and are of interest to astrobiologists. We have performed a series of simulations of these plumes using the MITGCM. We assume in this experiment that Europa's ocean is deep (of order 100 km) and unstratified, and that plume buoyancy is controlled by temperature, not composition. A series of experiments was performed to explore a limited region of parameter space, with ocean depth H ranging from 50 to 100 km deep, source heat flux Q between 1 and 10 GW, and values of the Coriolis parameter f between 30% and 90% of the Europa average value. As predicted by earlier work, the plumes in our simulations form narrow cylindrical chimneys (a few km across) under the influence of the Coriolis effect. These plumes broaden over time until they become baroclinically unstable, breaking up into cone-shaped eddies when they become 20-35 km in diameter; the shed eddies are of a similar size. Large-scale currents in the region of the plume range between 1.5 and 5 cm/s; temperature anomalies in the plume far from the seafloor are tiny, varying between 30 and 160 microkelvin. Variations in plume size, shape, speed, and temperature are in excellent agreement with previous laboratory tank experiments, and in rough agreement with theoretical predictions. Plume dynamics and geometry are controlled by a "natural Rossby number" which depends strongly on depth H and Coriolis parameter f, but only weakly on source heat flux Q. However, some specific theoretical predictions are not borne out by these simulations. The time elapsed between startup of the source and the beginning of eddy-shedding is much less variable than predicted; also, the plume temperature varies with ocean depth H when our theory says it should not. Both of
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.
Dynamics of a compound vesicle: numerical simulations
NASA Astrophysics Data System (ADS)
Veerapaneni, Shravan; Young, Yuan-Nan; Vlahovska, Petia; Blawzdziewicz, Jerzy
2010-11-01
Vesicles (self-enclosing lipid membranes) in simple linear flows are known to exhibit rich dynamics such as tank-treading, tumbling, trembling (swinging), and vacillating breathing. Recently, vesicles have been used as a multi-functional platform for drug-delivery. In this work, the dynamics of simplified models for such compound vesicles is investigated numerically using a state-of-the-art boundary-integral code that has been validated with high accuracy and efficiency. Results show that for a vesicle enclosing a rigid particle in a simple shear flow, transition from tank-treading to tumbling is possible even in the absence of viscosity mismatch in the interior and exterior fluids. We will discuss the shape transformations, multiple particle interactions and the flow properties. Comparison with results from analytical modeling gives insights to the underlying physics for such novel dynamics.
Scramjet Propulsive Flowpath Design and Numerical Simulation
NASA Astrophysics Data System (ADS)
Li, Jian-ping; Song, Wen-yan; Liu, Xin
2014-06-01
The integrated propulsive flowpath of scramjet configuration was preliminarily designed and analyzed in this paper. The flow-fields characteristics and performance of the designed two-dimensional integrated propulsive flowpath were numerically calculated under various equivalent fuel-air ratio conditions, using computational fluid dynamics methods. The calculation results were then compared with the experimental data on some typical conditions, and the flow-field and performance of the integrated scramjet flowpath with different equivalent fuel-air ratios were analyzed and discussed in detail. The investigation results from these efforts showed that: (1) the inlet function was beyond disturbances by combustion induced shock wave and pressure fluctuations under the equivalent fuel-air ratio condition of 1.0, which well satisfied the design requirements; (2) with the increasing equivalent fuel-air ratio, the combustion intensity in the combustor was significantly enhanced, resulting in an increasing net-thrust of the propulsive flowpath.
Numerical simulation of an axial blood pump.
Chua, Leok Poh; Su, Boyang; Lim, Tau Meng; Zhou, Tongming
2007-07-01
The axial blood pump with a magnetically suspended impeller is superior to other artificial blood pumps because of its small size. In this article, the distributions of velocity, path line, pressure, and shear stress in the straightener, the rotor, and the diffuser of the axial blood pump, as well as the gap zone were obtained using the commercial software, Fluent (version 6.2). The main focus was on the flow field of the blood pump. The numerical results showed that the axial blood pump could produce 5.14 L/min of blood at 100 mm Hg through the outlet when rotating at 11,000 rpm. However, there was a leakage flow of 1.06 L/min in the gap between the rotor cylinder and the pump housing, and thus the overall flow rate the impeller could generate was 6.2 L/min. The numerical results showed that 75% of the scalar shear stresses (SSs) were less than 250 Pa, and 10% were higher than 500 Pa within the whole pump. The high SS region appeared around the blade tip where a large variation of velocity direction and magnitude was found, which might be due to the steep angle variation at the blade tip. Because the exposure time of the blood cell at the high SS region within the pump was relatively short, it might not cause serious damage to the blood cells, but the improvement of blade profile should be considered in the future design of the axial pump. PMID:17584481
NASA Technical Reports Server (NTRS)
Ellison, Donald; Conway, Bruce; Englander, Jacob
2015-01-01
A significant body of work exists showing that providing a nonlinear programming (NLP) solver with expressions for the problem constraint gradient substantially increases the speed of program execution and can also improve the robustness of convergence, especially for local optimizers. Calculation of these derivatives is often accomplished through the computation of spacecraft's state transition matrix (STM). If the two-body gravitational model is employed as is often done in the context of preliminary design, closed form expressions for these derivatives may be provided. If a high fidelity dynamics model, that might include perturbing forces such as the gravitational effect from multiple third bodies and solar radiation pressure is used then these STM's must be computed numerically. We present a method for the power hardward model and a full ephemeris model. An adaptive-step embedded eight order Dormand-Prince numerical integrator is discussed and a method for the computation of the time of flight derivatives in this framework is presented. The use of these numerically calculated derivatieves offer a substantial improvement over finite differencing in the context of a global optimizer. Specifically the inclusion of these STM's into the low thrust missiondesign tool chain in use at NASA Goddard Spaceflight Center allows for an increased preliminary mission design cadence.
Numerical simulation of optically trapped particles
NASA Astrophysics Data System (ADS)
Volpe, Giorgio; Volpe, Giovanni
2014-07-01
Some randomness is present in most phenomena, ranging from biomolecules and nanodevices to financial markets and human organizations. However, it is not easy to gain an intuitive understanding of such stochastic phenomena, because their modeling requires advanced mathematical tools, such as sigma algebras, the Itô formula and martingales. Here, we discuss a simple finite difference algorithm that can be used to gain understanding of such complex physical phenomena. In particular, we simulate the motion of an optically trapped particle that is typically used as a model system in statistical physics and has a wide range of applications in physics and biophysics, for example, to measure nanoscopic forces and torques.
Numerical simulations of two-dimensional QED
Carson, S.R.; Kenway, R.D.
1986-02-01
We describe the computer simulation of two-dimensional QED on a 64 x 64 Euclidean space-time lattice using the Susskind lattice fermion action. Theorder parameter for chiral symmetry breaking and the low-lying meson masses are calculated for both the model with two continuum flavours, which arises naturally in this formulation, and the model with one continuum falvour obtained by including a nonsymmetric mass term and setting one fermion mass equal to the cut-off. Results are compared with those obtined using the quenched approximation, and with analytic predictions.
Three-Dimensional Numerical Simulation of Airflow in Nasopharynx.
NASA Astrophysics Data System (ADS)
Shome, Biswadip; Wang, Lian-Ping; Santare, Michael H.; Szeri, Andras Z.; Prasad, Ajay K.; Roberts, David
1996-11-01
A three-dimensional numerical simulation of airflow in nasopharynx (from the soft palate to the epiglottis) was conducted, using anatomically accurate model and finite element method, to study the influence of flow characteristics on obstructive sleep apnea (OSA). The results showed that the pressure drop in the nasopharynx is in the range 200-500 Pa. Ten different nasopharynx geometries resulting from three OSA treatment therapies (CPAP, mandibular repositioning devices, and surgery) were compared. The results confirmed that the airflow in the nasopharynx lies in the transitional flow regime and thus, a subtle change in the morphology caused by these treatment therapies has a large effect on the airflow. The onset of turbulence can cause as much as 40% of increase in pressure drop. For the transitional flow regime, the k-ɛ turbulence model was found to be the most appropriate model, when compared to the mixing length and the k-ω model, as it correctly reproduces the limiting laminar behavior. In addition, the pressure drop increased approximately as the square of the volumetric flow rate. Supported by NIH.
Direct numerical simulation of evaporation-induced particle motion
NASA Astrophysics Data System (ADS)
Hwang, Hochan; Son, Gihun
2015-11-01
A sharp-interface level-set (LS) method is presented for direct numerical simulation (DNS) of evaporation-induced particle motion. The liquid surface is tracked by the LS function, which is defined as a signed distance from the liquid-gas interface. The conservation equations of mass, momentum, energy for the liquid and gas phases and vapor mass fraction for the gas phase are solved accurately imposing the coupled temperature and vapor fraction conditions at the evaporating liquid-gas interface. A dynamic contact angle model is also incorporated into the LS method to account for the change between advancing and receding contact angles at the liquid-gas-solid contact line. The solid surface is tracked by another LS function, which is defined as a signed distance from the fluid-solid interface. The conservation equations for multiphase flows are extended to treat the solid particle as a high-viscosity non-evaporating fluid phase. The velocity inside the solid domain is modified to enforce the rigid body motion using the translational velocity and angular velocity of the particle centroid. The DNS results demonstrate the particle accumulation near the evaporating interface and the contact line pinning and stick-slip motion near the evaporating contact line.
Direct numerical simulation of vector-controlled free jets
NASA Astrophysics Data System (ADS)
Tsujimoto, K.; Ao, K.; Shakouchi, T.; Ando, T.
2011-12-01
We conduct DNS (direct numerical simulation) of vector controlled free jets. The inflow velocity of jet is periodically oscillated perpendicular to the jet axis. In order to realize the high accurate computation, a discretization in space is performed with hybrid scheme in which Fourier spectral and 6th order compact scheme are adopted. From visualized instantaneous vortex structures, it is found that the flow pattern considerably changes according to the oscillating frequency, i.e., according to the increasing the frequency, wave, bifurcating and flapping modes appear in turn. In order to quantify mixing efficiency under the vector control, as the mixing measure, statistical entropy is investigated. Compared to the uncontrolled jet, the mixing efficiency is improved in order of wavy, flapping and bifurcating modes. Thus the vector control can be expected for the improvement of mixing efficiency. Further to make clear the reason for the mixing enhancement, Snapshot POD and DMD method are applied. The primary flow structures under the vector control are demonstrated.
Numerical study of error propagation in Monte Carlo depletion simulations
Wyant, T.; Petrovic, B.
2012-07-01
Improving computer technology and the desire to more accurately model the heterogeneity of the nuclear reactor environment have made the use of Monte Carlo depletion codes more attractive in recent years, and feasible (if not practical) even for 3-D depletion simulation. However, in this case statistical uncertainty is combined with error propagating through the calculation from previous steps. In an effort to understand this error propagation, a numerical study was undertaken to model and track individual fuel pins in four 17 x 17 PWR fuel assemblies. By changing the code's initial random number seed, the data produced by a series of 19 replica runs was used to investigate the true and apparent variance in k{sub eff}, pin powers, and number densities of several isotopes. While this study does not intend to develop a predictive model for error propagation, it is hoped that its results can help to identify some common regularities in the behavior of uncertainty in several key parameters. (authors)
Numerical simulation of supersonic and hypersonic inlet flow fields
NASA Technical Reports Server (NTRS)
Mcrae, D. Scott; Kontinos, Dean A.
1995-01-01
This report summarizes the research performed by North Carolina State University and NASA Ames Research Center under Cooperative Agreement NCA2-719, 'Numerical Simulation of Supersonic and Hypersonic Inlet Flow Fields". Four distinct rotated upwind schemes were developed and investigated to determine accuracy and practicality. The scheme found to have the best combination of attributes, including reduction to grid alignment with no rotation, was the cell centered non-orthogonal (CCNO) scheme. In 2D, the CCNO scheme improved rotation when flux interpolation was extended to second order. In 3D, improvements were less dramatic in all cases, with second order flux interpolation showing the least improvement over grid aligned upwinding. The reduction in improvement is attributed to uncertainty in determining optimum rotation angle and difficulty in performing accurate and efficient interpolation of the angle in 3D. The CCNO rotational technique will prove very useful for increasing accuracy when second order interpolation is not appropriate and will materially improve inlet flow solutions.
Direct numerical simulation of flow past superhydrophobic surfaces
NASA Astrophysics Data System (ADS)
Luchini, Paolo; Bottaro, Alessandro
2014-11-01
Superhydrophobic surfaces trap a discontinuous air layer through their texture which, in addition to changing the apparent contact angle of water drops, also changes the friction coefficient of a continuous water flow. Locally this effect can be represented through a slip coefficient (e.g. Lauga & Stone, J. Fluid Mech. 489, 55, 2003), or equivalently through an effective displacement of the wall by a distance (different for each different velocity component) comparable to the spacing of the texture. For this reason they are being considered for drag reduction in turbulent flow, more sensitive to this displacement than laminar flow for its intrisic small features. Since the upper limit on texture size imposed by the destruction of the surface-tension-bound air layer eventually constrains the reduction available, to quantify the effect accurately is essential. In its simplest representation, the superhydrophobic surface may be assumed to be flat and composed of alternating patches of no-slip and free-slip wall. Here direct numerical simulations will be presented of turbulent flow past such a surface, and their results compared with those produced by the corresponding effective wall displacement.
Numerical simulation of high speed incremental forming of aluminum alloy
NASA Astrophysics Data System (ADS)
Giuseppina, Ambrogio; Teresa, Citrea; Luigino, Filice; Francesco, Gagliardi
2013-12-01
In this study, an innovative process is analyzed with the aim to satisfy the industrial requirements, such as process flexibility, differentiation and customizing of products, cost reduction, minimization of execution time, sustainable production, etc. The attention is focused on incremental forming process, nowadays used in different fields such as: rapid prototyping, medical sector, architectural industry, aerospace and marine, in the production of molds and dies. Incremental forming consists in deforming only a small region of the workspace through a punch driven by a NC machine. SPIF is the considered variant of the process, in which the punch gives local deformation without dies and molds; consequently, the final product geometry can be changed by the control of an actuator without requiring a set of different tools. The drawback of this process is its slowness. The aim of this study is to assess the IF feasibility at high speeds. An experimental campaign will be performed by a CNC lathe with high speed to test process feasibility and the influence on materials formability mainly on aluminum alloys. The first results show how the material presents the same performance than in conventional speed IF and, in some cases, better material behavior due to the temperature field. An accurate numerical simulation has been performed to investigate the material behavior during the high speed process substantially confirming experimental evidence.
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 Physical and Chemical Processes in Fluidized Bed
NASA Astrophysics Data System (ADS)
Baturin, D. A.; Gil, A. V.
2015-10-01
The paper presents a numerical simulation of the furnace with a circulating fluidized bed. Numerical study carried out for the bottom of the combustion chamber with the varying heights of volume filling. The results contours of particulate matter concentration and of velocities, as well as a graphical representation of changes in the concentration of particles on the bed height are shown. Simulation performed in Eulerian - Eulerian representation on a 2D model.
NUMERICAL METHODS FOR THE SIMULATION OF HIGH INTENSITY HADRON SYNCHROTRONS.
LUCCIO, A.; D'IMPERIO, N.; MALITSKY, N.
2005-09-12
Numerical algorithms for PIC simulation of beam dynamics in a high intensity synchrotron on a parallel computer are presented. We introduce numerical solvers of the Laplace-Poisson equation in the presence of walls, and algorithms to compute tunes and twiss functions in the presence of space charge forces. The working code for the simulation here presented is SIMBAD, that can be run as stand alone or as part of the UAL (Unified Accelerator Libraries) package.
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.
Numerical simulation of electromagnetic turbulence in tokamaks
Waltz, R.E.
1985-02-01
Nonlinear two- and three-fluid equations are written for the time evolution of the perturbed electrostatic potential, densities, vector potential, and parallel ion motion of collisional and trapped electron plasmas in tokamak geometry. The nonlinear terms arise from the E x B/sub 0/ convection (d/dt = partial/partialt+v/sub E/ x del/sub perpendicular/) and magnetic flutter (del-tilde/sub parallel/ = del/sub parallel/+(B/sub perpendicular//B/sub 0/) x del/sub perpendicular/). Simplified two-dimensional (k/sub perpendicular/) mode coupling simulations with a fixed average parallel wavenumber (k/sub parallel/ = 1/Rq) and curvature drift (..omega../sub g/ = (L/sub n//R)..omega../sub asterisk/ ) characteristic of outward ballooning are performed. Homogeneous stationary turbulent states of the dissipative drift and interchange modes from 0< or =..beta..<..beta../sub crit/ for both the collisional and trapped electron plasmas are obtained. Transport coefficients associated with E x B and magnetic motions are calculated. The problem of simulating plasmas with high viscous Reynolds number is treated with an absorbing mantle at the largest wavenumbers.
Numerical Simulations of the Mechanics of Vitrectomy
NASA Astrophysics Data System (ADS)
Young, Ethan; Eldredge, Jeff D.; Hubschman, Jean-Pierre
2014-11-01
Filling the cavity between the lens and retina in the eye is a clear, gel-like substance known as vitreous humor. The treatment of certain eye abnormalities necessitates the removal of this substance, in a surgical procedure called a vitrectomy, using a device called a vitreous cutter. Understanding the behavior of this viscoelastic biofluid during operations is essential to improving the effectiveness of the procedure. In this work, a three-dimensional computational model of a vitreous cutter is investigated using an immersed boundary method and a viscoelastic constitutive model. The solver uses a fractional-step method to satisfy continuity and traction boundary conditions to simulate the applied suction. The Giesekus constitutive equation is used to model the vitreous, as it captures both elastic and shear-thinning effects. Rheological parameters were obtained from the work of Sharif-Kashani et al. [Retina, 2013]. These simulations were used to quantify both the average and time-varying flow rate through the device during different stages in the cutting cycle. Characteristics of the flow field illustrate how surgical variables like cutting speed, duty cycle, and aspiration pressure affect overall flow rate and suggest targets for improving cutter efficacy.
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 moon-ringlet interaction
NASA Astrophysics Data System (ADS)
Hanninen, J.
1993-05-01
Nonaxisymmetric ring features excited by perturbations of shepherd satellites are studied in terms of direct particle simulations using Aarseth's N-body integrator combined with the calculation of particle-particle impacts. Interaction parameters typical to Saturn's F-ring are investigated. The generation of clumps by external satellites is verified, but the interparticle collisions tend to smooth sharp features. Using F-ring parameters the clumps are observed to cover the total azimuthal length, but it is not clear whether these azimuthally overlapping clumps would be detectable in the actual F-ring. Gravitational scattering by ring particles increases the velocity dispersion, smearing regular azimuthal features at least in the rings of low optical depths. Considerable accretion is observed to occur, particles sticking pairwise to each other, even if the tendency of the particles to accrete is artificially reduced in the simulations. A new explanation for the braided appearance of the F-ring is proposed, based on the interaction between the shepherding satellites and the ring containing embedded moonlets. In our model the braiding is a dynamic phenomenon: the braids are destroyed and recreated in a cyclical manner.
Numerical simulation of fractional Cable equation of spiny neuronal dendrites.
Sweilam, N H; Khader, M M; Adel, M
2014-03-01
In this article, numerical study for the fractional Cable equation which is fundamental equations for modeling neuronal dynamics is introduced by using weighted average of finite difference methods. The stability analysis of the proposed methods is given by a recently proposed procedure similar to the standard John von Neumann stability analysis. A simple and an accurate stability criterion valid for different discretization schemes of the fractional derivative and arbitrary weight factor is introduced and checked numerically. Numerical results, figures, and comparisons have been presented to confirm the theoretical results and efficiency of the proposed method. PMID:25685492
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
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
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 a porous honeycomb burner
Hackert, C.L.; Elizey, J.L.; Ezekoye, O.A.
1997-07-01
A two-dimensional simulation of a honeycomb burner using single step global chemistry is used to investigate the importance of thermal properties and boundary conditions to inert porous burners. Comparisons to available experimental results are made where possible, and a parametric study of the effects of burner properties on the flame is performed. The burner solid emissivity is found to be relatively unimportant to the achievable burning rate and radiant output fraction, so long as it is above a certain minimum value (about 0.3). In contrast, increases in solid conductivity always lead to marked increases in burning rate. The flame is shown to exhibit significant curvature on both a pore scale and burner scale.
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 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.
Numerical simulations of shoaling internal solitary waves of elevation
NASA Astrophysics Data System (ADS)
Xu, Chengzhu; Subich, Christopher; Stastna, Marek
2016-07-01
We present high-resolution, two- and three-dimensional direct numerical simulations of large amplitude internal solitary waves of elevation on the laboratory scale, shoaling onto and over a small-amplitude shelf. The three-dimensional, mapped coordinate, spectral collocation method used for the simulations allows for accurate modelling of both the shoaling waves and the bottom boundary layer. The shoaling of the waves is characterized by the formation of a quasi-trapped core which undergoes a spatially growing stratified shear instability at its edge and a lobe-cleft instability in its nose. Both of these instabilities develop and three-dimensionalize concurrently, leading to strong bottom shear stress. We explore significant regions of Schmidt and Reynolds number space and demonstrate that the formation of shear instabilities during shoaling is robust and should be readily observable in a number of standard laboratory setups. In the experiments with a corrugated bottom boundary, boundary layer separation is found inside each of the corrugations during shoaling. This more complex boundary layer phenomenology precludes the formation of the lobe-cleft instability almost completely and hence provides a different mechanism for fluid and material exchange across the bottom boundary layer. Our analyses suggest that all of these wave-induced instabilities can lead to enhanced turbulence in the water column and increased shear stress on the bottom boundary. Through the generation and evolution of these instabilities, the shoaling of internal solitary waves of elevation is likely to provide systematic mechanisms for material mixing, cross-boundary layer transport, and sediment resuspension.
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 Astrophysics Data System (ADS)
Achterberg, R. K.; Ingersoll, A. P.
1994-02-01
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.
Towards more accurate numerical modeling of impedance based high frequency harmonic vibration
NASA Astrophysics Data System (ADS)
Lim, Yee Yan; Kiong Soh, Chee
2014-03-01
The application of smart materials in various fields of engineering has recently become increasingly popular. For instance, the high frequency based electromechanical impedance (EMI) technique employing smart piezoelectric materials is found to be versatile in structural health monitoring (SHM). Thus far, considerable efforts have been made to study and improve the technique. Various theoretical models of the EMI technique have been proposed in an attempt to better understand its behavior. So far, the three-dimensional (3D) coupled field finite element (FE) model has proved to be the most accurate. However, large discrepancies between the results of the FE model and experimental tests, especially in terms of the slope and magnitude of the admittance signatures, continue to exist and are yet to be resolved. This paper presents a series of parametric studies using the 3D coupled field finite element method (FEM) on all properties of materials involved in the lead zirconate titanate (PZT) structure interaction of the EMI technique, to investigate their effect on the admittance signatures acquired. FE model updating is then performed by adjusting the parameters to match the experimental results. One of the main reasons for the lower accuracy, especially in terms of magnitude and slope, of previous FE models is the difficulty in determining the damping related coefficients and the stiffness of the bonding layer. In this study, using the hysteretic damping model in place of Rayleigh damping, which is used by most researchers in this field, and updated bonding stiffness, an improved and more accurate FE model is achieved. The results of this paper are expected to be useful for future study of the subject area in terms of research and application, such as modeling, design and optimization.
Numerical Simulations of Hot Vertical Displacement Events
NASA Astrophysics Data System (ADS)
Bunkers, K. J.; Sovinec, C. R.
2015-11-01
Loss of vertical positioning control in tokamaks leads to instability where hot confined plasma rests against the chamber wall. Resistive-MHD modeling with the NIMROD code is applied to model these events. After divertor-coil current is perturbed, resistive diffusion through the non-ideal wall sets the timescale as the simulated tokamak evolves from a diverted equilibrium to a limited configuration. Results show that plasma outflow along opening magnetic surfaces, just outside the confinement zone, approaches the local ion-acoustic speed. The projection of the plasma flow velocity into the surface-normal direction (n . V) near the surface exceeds the local E × B drift speed; near surfaces n × E is approximately the same as n ×Ewall in the nearly steady conditions. The safety factor of flux surfaces that remain intact is approximately constant over the evolution time, which is much shorter than the plasma resistive diffusion time. Assessment of external-kink stability and initial findings from 3D nonlinear computations are presented. This effort is supported by the U.S. Dept. of Energy, award numbers DE-FG02-06ER54850 and DE-FC02-08ER54975.
Numerical simulation of reversing buoyancy gravity currents
NASA Astrophysics Data System (ADS)
Radhakrishnan, Senthil; Lenk, Erik; Boekels, Michael; Meiburg, Eckart
2012-11-01
Sediment laden fluid propagates as an underflow when its bulk density is higher than the density of the ambient fluid. If the density of the interstitial fluid in gravity current is smaller than the density of the ambient fluid, the gravity current can become positively buoyant after sufficient particles have settled. The current then lifts off from the bottom surface and travels as a surface gravity current over the heavier ambient fluid. These types of currents, where the buoyancy reverses its direction, have been observed when sediment laden fresh water enters the sea or during volcanic eruption that creates a pyroclastic flow. We use a lock-exchange configuration with mono-disperse and bi-disperse particles to study the lofting characteristics of reversing buoyancy currents. This talk will focus on results obtained from Large-eddy Simulation of high Reynolds number currents. In particular, the deposit profiles show a sharp decay at the lift-off point unlike a ground hugging turbidity current whose deposit profile has a slow monotonic decay from the lock region.
Numerical simulation of photoexcited polaron states in water
NASA Astrophysics Data System (ADS)
Zemlyanaya, E. V.; Volokhova, A. V.; Lakhno, V. D.; Amirkhanov, I. V.; Puzynin, I. V.; Puzynina, T. P.; Rikhvitskiy, V. S.; Atanasova, P. Kh.
2015-10-01
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.
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.
TOPICA: an accurate and efficient numerical tool for analysis and design of ICRF antennas
NASA Astrophysics Data System (ADS)
Lancellotti, V.; Milanesio, D.; Maggiora, R.; Vecchi, G.; Kyrytsya, V.
2006-07-01
The demand for a predictive tool to help in designing ion-cyclotron radio frequency (ICRF) antenna systems for today's fusion experiments has driven the development of codes such as ICANT, RANT3D, and the early development of TOPICA (TOrino Polytechnic Ion Cyclotron Antenna) code. This paper describes the substantive evolution of TOPICA formulation and implementation that presently allow it to handle the actual geometry of ICRF antennas (with curved, solid straps, a general-shape housing, Faraday screen, etc) as well as an accurate plasma description, accounting for density and temperature profiles and finite Larmor radius effects. The antenna is assumed to be housed in a recess-like enclosure. Both goals have been attained by formally separating the problem into two parts: the vacuum region around the antenna and the plasma region inside the toroidal chamber. Field continuity and boundary conditions allow formulating of a set of two coupled integral equations for the unknown equivalent (current) sources; then the equations are reduced to a linear system by a method of moments solution scheme employing 2D finite elements defined over a 3D non-planar surface triangular-cell mesh. In the vacuum region calculations are done in the spatial (configuration) domain, whereas in the plasma region a spectral (wavenumber) representation of fields and currents is adopted, thus permitting a description of the plasma by a surface impedance matrix. Owing to this approach, any plasma model can be used in principle, and at present the FELICE code has been employed. The natural outcomes of TOPICA are the induced currents on the conductors (antenna, housing, etc) and the electric field in front of the plasma, whence the antenna circuit parameters (impedance/scattering matrices), the radiated power and the fields (at locations other than the chamber aperture) are then obtained. An accurate model of the feeding coaxial lines is also included. The theoretical model and its TOPICA
NASA Technical Reports Server (NTRS)
Alter, Stephen J.; Brauckmann, Gregory J.; Kleb, Bil; Streett, Craig L; Glass, Christopher E.; Schuster, David M.
2015-01-01
Using the Fully Unstructured Three-Dimensional (FUN3D) computational fluid dynamics code, an unsteady, time-accurate flow field about a Space Launch System configuration was simulated at a transonic wind tunnel condition (Mach = 0.9). Delayed detached eddy simulation combined with Reynolds Averaged Naiver-Stokes and a Spallart-Almaras turbulence model were employed for the simulation. Second order accurate time evolution scheme was used to simulate the flow field, with a minimum of 0.2 seconds of simulated time to as much as 1.4 seconds. Data was collected at 480 pressure taps at locations, 139 of which matched a 3% wind tunnel model, tested in the Transonic Dynamic Tunnel (TDT) facility at NASA Langley Research Center. Comparisons between computation and experiment showed agreement within 5% in terms of location for peak RMS levels, and 20% for frequency and magnitude of power spectral densities. Grid resolution and time step sensitivity studies were performed to identify methods for improved accuracy comparisons to wind tunnel data. With limited computational resources, accurate trends for reduced vibratory loads on the vehicle were observed. Exploratory methods such as determining minimized computed errors based on CFL number and sub-iterations, as well as evaluating frequency content of the unsteady pressures and evaluation of oscillatory shock structures were used in this study to enhance computational efficiency and solution accuracy. These techniques enabled development of a set of best practices, for the evaluation of future flight vehicle designs in terms of vibratory loads.
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.
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.
Numerical simulations of aerodynamic contribution of flows about a space-plane-type configuration
NASA Technical Reports Server (NTRS)
Matsushima, Kisa; Takanashi, Susume; Fujii, Kozo; Obayashi, Shigeru
1987-01-01
The slightly supersonic viscous flow about the space-plane under development at the National Aerospace Laboratory (NAL) in Japan was simulated numerically using the LU-ADI algorithm. The wind-tunnel testing for the same plane also was conducted with the computations in parallel. The main purpose of the simulation is to capture the phenomena which have a great deal of influence to the aerodynamic force and efficiency but is difficult to capture by experiments. It includes more accurate representation of vortical flows with high angles of attack of an aircraft. The space-plane shape geometry simulated is the simplified model of the real space-plane, which is a combination of a flat and slender body and a double-delta type wing. The comparison between experimental results and numerical ones will be done in the near future. It could be said that numerical results show the qualitatively reliable phenomena.
TOPLHA: an accurate and efficient numerical tool for analysis and design of LH antennas
NASA Astrophysics Data System (ADS)
Milanesio, D.; Meneghini, O.; Maggiora, R.; Guadamuz, S.; Hillairet, J.; Lancellotti, V.; Vecchi, G.
2012-01-01
This paper presents a self-consistent, integral-equation approach for the analysis of plasma-facing lower hybrid (LH) launchers; the geometry of the waveguide grill structure can be completely arbitrary, including the non-planar mouth of the grill. This work is based on the theoretical approach and code implementation of the TOPICA code, of which it shares the modular structure and constitutes the extension into the LH range. Code results are validated against the literature results and simulations from similar codes.
Kottmann, Jakob S; Höfener, Sebastian; Bischoff, Florian A
2015-12-21
In the present work, we report an efficient implementation of configuration interaction singles (CIS) excitation energies and oscillator strengths using the multi-resolution analysis (MRA) framework to address the basis-set convergence of excited state computations. In MRA (ground-state) orbitals, excited states are constructed adaptively guaranteeing an overall precision. Thus not only valence but also, in particular, low-lying Rydberg states can be computed with consistent quality at the basis set limit a priori, or without special treatments, which is demonstrated using a small test set of organic molecules, basis sets, and states. We find that the new implementation of MRA-CIS excitation energy calculations is competitive with conventional LCAO calculations when the basis-set limit of medium-sized molecules is sought, which requires large, diffuse basis sets. This becomes particularly important if accurate calculations of molecular electronic absorption spectra with respect to basis-set incompleteness are required, in which both valence as well as Rydberg excitations can contribute to the molecule's UV/VIS fingerprint. PMID:25913482
Numerical simulation of turbulent flow in a cyclonic separator
NASA Astrophysics Data System (ADS)
Bogdanov, Dmitry; Poniaev, Sergey
2014-12-01
Numerical simulation of a turbulent flow of air with dispersed particles through a cyclonic separator is presented. Because of a high streamline curvature in the separator it is difficult to simulate the flow by using the conventional turbulent models. In this work the curvature correction term was included into the k - ω - SST turbulence model implemented in the OpenFOAM® software. Experimental data and results of numerical simulation by the commercial ANSYS Fluent® solver for a turbulent flow in a U-duct were used to validate the model. The numerical simulation of the flow in the cyclonic separator demonstrates that the implemented turbulence model successfully predicts the cyclonic separator efficiency.
The use of experimental bending tests to more accurate numerical description of TBC damage process
NASA Astrophysics Data System (ADS)
Sadowski, T.; Golewski, P.
2016-04-01
Thermal barrier coatings (TBCs) have been extensively used in aircraft engines to protect critical engine parts such as blades and combustion chambers, which are exposed to high temperatures and corrosive environment. The blades of turbine engines are additionally exposed to high mechanical loads. These loads are created by the high rotational speed of the rotor (30 000 rot/min), causing the tensile and bending stresses. Therefore, experimental testing of coated samples is necessary in order to determine strength properties of TBCs. Beam samples with dimensions 50×10×2 mm were used in those studies. The TBC system consisted of 150 μm thick bond coat (NiCoCrAlY) and 300 μm thick top coat (YSZ) made by APS (air plasma spray) process. Samples were tested by three-point bending test with various loads. After bending tests, the samples were subjected to microscopic observation to determine the quantity of cracks and their depth. The above mentioned results were used to build numerical model and calibrate material data in Abaqus program. Brittle cracking damage model was applied for the TBC layer, which allows to remove elements after reaching criterion. Surface based cohesive behavior was used to model the delamination which may occur at the boundary between bond coat and top coat.
Direct Numerical Simulation of a Coolant Jet in a Periodic Crossflow
NASA Technical Reports Server (NTRS)
Sharma, Chirdeep; Acharya, Sumanta
1998-01-01
A Direct Numerical Simulation of a coolant jet injected normally into a periodic crossflow is presented. The physical situation simulated represents a periodic module in a coolant hole array with a heated crossflow. A collocated finite difference scheme is used which is fifth-order accurate spatially and second-order accurate temporally. The scheme is based on a fractional step approach and requires the solution of a pressure-Poisson equation. The simulations are obtained for a blowing ratio of 0.25 and a channel Reynolds number of 5600. The simulations reveal the dynamics of several large scale structures including the Counter-rotating Vortex Pair (CVP), the horse-shoe vortex, the shear layer vortex, the wall vortex and the wake vortex. The origins and the interactions of these vortical structures are identified and explored. Also presented are the turbulence statistics and how they relate to the flow structures.
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. PMID:10467947
NASA Astrophysics Data System (ADS)
Dinpajooh, Mohammadhasan; Bai, Peng; Allan, Douglas A.; Siepmann, J. Ilja
2015-09-01
Since the seminal paper by Panagiotopoulos [Mol. Phys. 61, 813 (1997)], the Gibbs ensemble Monte Carlo (GEMC) method has been the most popular particle-based simulation approach for the computation of vapor-liquid phase equilibria. However, the validity of GEMC simulations in the near-critical region has been questioned because rigorous finite-size scaling approaches cannot be applied to simulations with fluctuating volume. Valleau [Mol. Simul. 29, 627 (2003)] has argued that GEMC simulations would lead to a spurious overestimation of the critical temperature. More recently, Patel et al. [J. Chem. Phys. 134, 024101 (2011)] opined that the use of analytical tail corrections would be problematic in the near-critical region. To address these issues, we perform extensive GEMC simulations for Lennard-Jones particles in the near-critical region varying the system size, the overall system density, and the cutoff distance. For a system with N = 5500 particles, potential truncation at 8σ and analytical tail corrections, an extrapolation of GEMC simulation data at temperatures in the range from 1.27 to 1.305 yields Tc = 1.3128 ± 0.0016, ρc = 0.316 ± 0.004, and pc = 0.1274 ± 0.0013 in excellent agreement with the thermodynamic limit determined by Potoff and Panagiotopoulos [J. Chem. Phys. 109, 10914 (1998)] using grand canonical Monte Carlo simulations and finite-size scaling. Critical properties estimated using GEMC simulations with different overall system densities (0.296 ≤ ρt ≤ 0.336) agree to within the statistical uncertainties. For simulations with tail corrections, data obtained using rcut = 3.5σ yield Tc and pc that are higher by 0.2% and 1.4% than simulations with rcut = 5 and 8σ but still with overlapping 95% confidence intervals. In contrast, GEMC simulations with a truncated and shifted potential show that rcut = 8σ is insufficient to obtain accurate results. Additional GEMC simulations for hard-core square-well particles with various ranges of the
Dinpajooh, Mohammadhasan; Bai, Peng; Allan, Douglas A.; Siepmann, J. Ilja
2015-09-21
Since the seminal paper by Panagiotopoulos [Mol. Phys. 61, 813 (1997)], the Gibbs ensemble Monte Carlo (GEMC) method has been the most popular particle-based simulation approach for the computation of vapor–liquid phase equilibria. However, the validity of GEMC simulations in the near-critical region has been questioned because rigorous finite-size scaling approaches cannot be applied to simulations with fluctuating volume. Valleau [Mol. Simul. 29, 627 (2003)] has argued that GEMC simulations would lead to a spurious overestimation of the critical temperature. More recently, Patel et al. [J. Chem. Phys. 134, 024101 (2011)] opined that the use of analytical tail corrections would be problematic in the near-critical region. To address these issues, we perform extensive GEMC simulations for Lennard-Jones particles in the near-critical region varying the system size, the overall system density, and the cutoff distance. For a system with N = 5500 particles, potential truncation at 8σ and analytical tail corrections, an extrapolation of GEMC simulation data at temperatures in the range from 1.27 to 1.305 yields T{sub c} = 1.3128 ± 0.0016, ρ{sub c} = 0.316 ± 0.004, and p{sub c} = 0.1274 ± 0.0013 in excellent agreement with the thermodynamic limit determined by Potoff and Panagiotopoulos [J. Chem. Phys. 109, 10914 (1998)] using grand canonical Monte Carlo simulations and finite-size scaling. Critical properties estimated using GEMC simulations with different overall system densities (0.296 ≤ ρ{sub t} ≤ 0.336) agree to within the statistical uncertainties. For simulations with tail corrections, data obtained using r{sub cut} = 3.5σ yield T{sub c} and p{sub c} that are higher by 0.2% and 1.4% than simulations with r{sub cut} = 5 and 8σ but still with overlapping 95% confidence intervals. In contrast, GEMC simulations with a truncated and shifted potential show that r{sub cut} = 8σ is insufficient to obtain accurate results. Additional GEMC simulations for hard
Numerical Simulations of Two Wildfire Events Using a Combined Modeling System (HIGRAD/BEHAVE)
Reisner, J.; Bossert, J.; Winterkamp, J.
1997-12-31
The ability to accurately forecast the spread of a wildfire would significantly reduce human suffering and loss of life, the destruction of property, and expenditures for assessment and recovery. To help achieve this goal we have developed a model which accurately simulates the interactions between winds and the heat source associated with a wildfire. We have termed our new model HIGRAD or High resolution model for strong GRA-Dient applications. HIGRAD employs a sophisticated numerical technique to prevent numerical Oscillations from occurring in the vicinity of the lire. Of importance for fire modeling, HIGRAD uses a numerical technique which allows for the use of a compressible equation set, but without the time-step restrictions associated with the propagation of sound-waves.
Numerical simulations of plasma brush behavior in hybrid armatures
NASA Astrophysics Data System (ADS)
Hawke, R. S.; Pincosy, P. A.
1993-01-01
Hybrid armatures used to accelerate projectiles in railguns are often the consequence of using a solid armature or in some cases the preferred armature type. Although hybrid armatures are often used, their design has been empirical and their performance sporadic. As a first step towards understanding hybrid design and performance, we have begun a combined numerical simulation and experimental verification effort. This paper will describe numerical simulations performed with a quasi 1-D MHD code (CONFUSE) which has been applied to simulate the behavior of plasma brushes used in hybrid armatures. The simulations have provided estimates of the plasma brush length, resistive voltage drop and temperatures corresponding to a range of; 1) brush gap size, 2) fuse thickness, and 3) magnetic pressure. The results of these simulations is presented and discussed.
Molina, John J; Yamamoto, Ryoichi
2013-12-21
An improved formulation of the "Smoothed Profile" method is introduced to perform direct numerical simulations of arbitrary rigid body dispersions in a Newtonian host solvent. Previous implementations of the method were restricted to spherical particles, severely limiting the types of systems that could be studied. The validity of the method is carefully examined by computing the friction/mobility tensors for a wide variety of geometries and comparing them to reference values obtained from accurate solutions to the Stokes-Equation. PMID:24359350
Numerical simulation of human orientation perception during lunar landing
NASA Astrophysics Data System (ADS)
Clark, Torin K.; Young, Laurence R.; Stimpson, Alexander J.; Duda, Kevin R.; Oman, Charles M.
2011-09-01
In lunar landing it is necessary to select a suitable landing point and then control a stable descent to the surface. In manned landings, astronauts will play a critical role in monitoring systems and adjusting the descent trajectory through either supervisory control and landing point designations, or by direct manual control. For the astronauts to ensure vehicle performance and safety, they will have to accurately perceive vehicle orientation. A numerical model for human spatial orientation perception was simulated using input motions from lunar landing trajectories to predict the potential for misperceptions. Three representative trajectories were studied: an automated trajectory, a landing point designation trajectory, and a challenging manual control trajectory. These trajectories were studied under three cases with different cues activated in the model to study the importance of vestibular cues, visual cues, and the effect of the descent engine thruster creating dust blowback. The model predicts that spatial misperceptions are likely to occur as a result of the lunar landing motions, particularly with limited or incomplete visual cues. The powered descent acceleration profile creates a somatogravic illusion causing the astronauts to falsely perceive themselves and the vehicle as upright, even when the vehicle has a large pitch or roll angle. When visual pathways were activated within the model these illusions were mostly suppressed. Dust blowback, obscuring the visual scene out the window, was also found to create disorientation. These orientation illusions are likely to interfere with the astronauts' ability to effectively control the vehicle, potentially degrading performance and safety. Therefore suitable countermeasures, including disorientation training and advanced displays, are recommended.
CgWind: A high-order accurate simulation tool for wind turbines and wind farms
Chand, K K; Henshaw, W D; Lundquist, K A; Singer, M A
2010-02-22
CgWind is a high-fidelity large eddy simulation (LES) tool designed to meet the modeling needs of wind turbine and wind park engineers. This tool combines several advanced computational technologies in order to model accurately the complex and dynamic nature of wind energy applications. The composite grid approach provides high-quality structured grids for the efficient implementation of high-order accurate discretizations of the incompressible Navier-Stokes equations. Composite grids also provide a natural mechanism for modeling bodies in relative motion and complex geometry. Advanced algorithms such as matrix-free multigrid, compact discretizations and approximate factorization will allow CgWind to perform highly resolved calculations efficiently on a wide class of computing resources. Also in development are nonlinear LES subgrid-scale models required to simulate the many interacting scales present in large wind turbine applications. This paper outlines our approach, the current status of CgWind and future development plans.
Improving light propagation Monte Carlo simulations with accurate 3D modeling of skin tissue
Paquit, Vincent C; Price, Jeffery R; Meriaudeau, Fabrice; Tobin Jr, Kenneth William
2008-01-01
In this paper, we present a 3D light propagation model to simulate multispectral reflectance images of large skin surface areas. In particular, we aim to simulate more accurately the effects of various physiological properties of the skin in the case of subcutaneous vein imaging compared to existing models. Our method combines a Monte Carlo light propagation model, a realistic three-dimensional model of the skin using parametric surfaces and a vision system for data acquisition. We describe our model in detail, present results from the Monte Carlo modeling and compare our results with those obtained with a well established Monte Carlo model and with real skin reflectance images.
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 three-dimensional self-gravitating flow
NASA Technical Reports Server (NTRS)
Shebalin, John V.
1993-01-01
The three-dimensional flow of a self-gravitating fluid is numerically simulated using a Fourier pseudospectral method with a logarithmic variable formulation. Two cases with zero total angular momentum are studied in detail, a 323 simulation (Run B). Other than the grid size, the primary difference between the two cases are that Run A modeled atomic hydrogen and had considerably more compressible motion initially than Run B, which modeled molecular hydrogen. The numerical results indicate that gravitational collapse can proceed in a variety of ways. In the Run A, collapse led to an elongated tube-like structure, while in the Run B, collapse led to a flatter, disklike structure.
Direct numerical simulation of wall turbulent flows with microbubbles
NASA Astrophysics Data System (ADS)
Kanai, Akihiro; Miyata, Hideaki
2001-03-01
The marker-density-function (MDF) method has been developed to conduct direct numerical simulation (DNS) for bubbly flows. The method is applied to turbulent bubbly channel flows to elucidate the interaction between bubbles and wall turbulence. The simulation is designed to clarify the structure of the turbulent boundary layer containing microbubbles and the mechanism of frictional drag reduction. It is deduced from the numerical tests that the interaction between bubbles and wall turbulence depends on the Weber and Froude numbers. The reduction of the frictional resistance on the wall is attained and its mechanism is explained from the modulation of the three-dimensional structure of the turbulent flow. Copyright
Numerical simulations of the QUELL experiment in SULTAN
Marinucci, C.
1995-03-01
The QUench Experiment on Long Length (QUELL) in the SULTAN Facility is planned to investigate the quench propagation and detection of a conductor with ITER relevant geometry and scaled performance. The objective of this study is to show the ability of QUELL to provide quench conditions relevant for ITER and to simulate the system performance, dealing in particular with the design aspects of the power supply, cryogenic system and heaters. The numerical analysis was performed with GANDALF - a 1-D code to analyze Dual Channel Cable-in-Conduit Conductors. A numerical convergence test and a comparison with another code and with analytical results have confirmed the validity of the simulations.
Numerical Simulation of Incompressible Flows with Moving Interfaces
NASA Astrophysics Data System (ADS)
Medale, Marc; Jaeger, Marc
1997-03-01
A numerical model has been developed for the 2D simulation of free surface flows or, more generally speaking, moving interface ones. The bulk fluids on both sides of the interface are taken into account in simulating the incompressible laminar flow state. In the case of heat transfer the whole system, i.e. walls as well as possible obstacles, is considered. This model is based on finite element analysis with an Eulerian approach and an unstructured fixed mesh. A special technique to localize the interface allows its temporal evolution through this mesh. Several numerical examples are presented to demonstrate the capabilities of the model.
Numerical simulation of surface waves instability on a homogeneous grid
NASA Astrophysics Data System (ADS)
Korotkevich, Alexander O.; Dyachenko, Alexander I.; Zakharov, Vladimir E.
2016-05-01
We performed full-scale numerical simulation of instability of weakly nonlinear waves on the surface of deep fluid. We show that the instability development leads to chaotization and formation of wave turbulence. Instability of both propagating and standing waves was studied. We separately studied pure capillary wave, that was unstable due to three-wave interactions and pure gravity waves, that were unstable due to four-wave interactions. The theoretical description of instabilities in all cases is included in the article. The numerical algorithm used in these and many other previous simulations performed by the authors is described in detail.
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.
Rheometry and numerical simulations of antennas onboard the Resonance spacecraft
NASA Astrophysics Data System (ADS)
Sampl, M.; Macher, W.; Gruber, Ch.; Oswald, Th.; Rucker, H. O.
2009-04-01
We report on the calibration effort for the monopole antennas onboard the Resonance spacecraft which will be launched in the middle of the next decade. The Resonance mission is dedicated to the study of the wave-particle interactions and plasma dynamics in the inner magnetosphere and the auroral region. It is intended to fly four spacecrafts on specific trajectories, so that on parts of the orbits the four spacecraft fly along the same field line (precisely speaking in the same flux tube) of the geomagnetic field. Time and space correlated measurements are planned which will reveal new insights into processes propagating along the field lines and phenomena which span large parts of the flux tubes. The calibration is performed for four boom antennas and four cylindrical sensors at the boom tips. These antennas are devised for the measurement of electric fields and plasma parameters. We apply two methods for the antenna analysis: First, electrolytic tank measurements (rheometry), which is a method to determine the effective length vectors of electrically short antennas (in this context up to about 1MHz); second, numerical computer simulations which enable us to study also the transition to higher frequencies. The accuracy of the applied methods is about 1 degree for directions of effective axes and some percent for effective lengths and capacitances. With both methods we determined the following antenna parameters which are most relevant in the present context: The effective length vectors (comprising effective axes and effective lengths), and the antenna capacitance matrix. For that purpose the whole antenna-spacecraft system is treated as an 8-port antenna. For the first time this kind of analysis is performed for a spaceborne antenna system consisting of boom monopoles and cylindrical tip antennas. The results show that the effective antenna lengths do not coincide with the physical ones but are tilted away from the solar panels by several degrees. The numerical
Vortical flow aerodynamics - Physical aspects and numerical simulation
NASA Technical Reports Server (NTRS)
Newsome, Richard W.; Kandil, Osama A.
1987-01-01
Progress in the numerical simulation of vortical flow due to three-dimensional flow separation about flight vehicles at high angles of attack and quasi-steady flight conditions is surveyed. Primary emphasis is placed on Euler and Reynolds-averaged Navier-Stokes methods where the vortices are 'captured' as a solution to the governing equations. A discussion of the relevant flow physics provides a perspective from which to assess numerical solutions. Current numerical prediction capabilities and their evolutionary development are surveyed. Future trends and challenges are identified and discussed.
Bangalore, Sai Santosh; Wang, Jelai; Allison, David B.
2009-01-01
In the fields of genomics and high dimensional biology (HDB), massive multiple testing prompts the use of extremely small significance levels. Because tail areas of statistical distributions are needed for hypothesis testing, the accuracy of these areas is important to confidently make scientific judgments. Previous work on accuracy was primarily focused on evaluating professionally written statistical software, like SAS, on the Statistical Reference Datasets (StRD) provided by National Institute of Standards and Technology (NIST) and on the accuracy of tail areas in statistical distributions. The goal of this paper is to provide guidance to investigators, who are developing their own custom scientific software built upon numerical libraries written by others. In specific, we evaluate the accuracy of small tail areas from cumulative distribution functions (CDF) of the Chi-square and t-distribution by comparing several open-source, free, or commercially licensed numerical libraries in Java, C, and R to widely accepted standards of comparison like ELV and DCDFLIB. In our evaluation, the C libraries and R functions are consistently accurate up to six significant digits. Amongst the evaluated Java libraries, Colt is most accurate. These languages and libraries are popular choices among programmers developing scientific software, so the results herein can be useful to programmers in choosing libraries for CDF accuracy. PMID:20161126
Numerical simulations of time-resolved quantum electronics
NASA Astrophysics Data System (ADS)
Gaury, Benoit; Weston, Joseph; Santin, Matthieu; Houzet, Manuel; Groth, Christoph; Waintal, Xavier
2014-01-01
Numerical simulation has become a major tool in quantum electronics both for fundamental and applied purposes. While for a long time those simulations focused on stationary properties (e.g. DC currents), the recent experimental trend toward GHz frequencies and beyond has triggered a new interest for handling time-dependent perturbations. As the experimental frequencies get higher, it becomes possible to conceive experiments which are both time-resolved and fast enough to probe the internal quantum dynamics of the system. This paper discusses the technical aspects-mathematical and numerical-associated with the numerical simulations of such a setup in the time domain (i.e. beyond the single-frequency AC limit). After a short review of the state of the art, we develop a theoretical framework for the calculation of time-resolved observables in a general multiterminal system subject to an arbitrary time-dependent perturbation (oscillating electrostatic gates, voltage pulses, time-varying magnetic fields, etc.) The approach is mathematically equivalent to (i) the time-dependent scattering formalism, (ii) the time-resolved non-equilibrium Green’s function (NEGF) formalism and (iii) the partition-free approach. The central object of our theory is a wave function that obeys a simple Schrödinger equation with an additional source term that accounts for the electrons injected from the electrodes. The time-resolved observables (current, density, etc.) and the (inelastic) scattering matrix are simply expressed in terms of this wave function. We use our approach to develop a numerical technique for simulating time-resolved quantum transport. We find that the use of this wave function is advantageous for numerical simulations resulting in a speed up of many orders of magnitude with respect to the direct integration of NEGF equations. Our technique allows one to simulate realistic situations beyond simple models, a subject that was until now beyond the simulation capabilities
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.
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.
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.
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.
Numerical Simulations of the Digital Microfluidic Manipulation of Single Microparticles.
Lan, Chuanjin; Pal, Souvik; Li, Zhen; Ma, Yanbao
2015-09-01
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. PMID:26241832
Numerical simulation of deformation and figure quality of precise mirror
NASA Astrophysics Data System (ADS)
Vit, Tomáš; Melich, Radek; Sandri, Paolo
2015-01-01
The presented paper shows results and a comparison of FEM numerical simulations and optical tests of the assembly of a precise Zerodur mirror with a mounting structure for space applications. It also shows how the curing of adhesive film can impact the optical surface, especially as regards deformations. Finally, the paper shows the results of the figure quality analysis, which are based on data from FEM simulation of optical surface deformations.
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 Technical Reports Server (NTRS)
Cohen, Charles
1998-01-01
A method is developed which uses numerical tracers to make accurate diagnoses of entraimnent and detrainment rates and of the properties of the entrained and detrained air in numerically simulated clouds. The numerical advection scheme is modified to make it nondispersive, as required by the use of the tracers. Tests of the new method are made, and an appropriate definition of clouds is selected. Distributions of mixing fractions in the model consistently show maximums at the end points, for nearly undilute environmental air or nearly undilute cloud air, with a uniform distribution between. The cumulonimbus clouds simulated here entrain air that had been substantially changed by the clouds, and detrained air that is not necessarily representative of the cloud air at the same level.
Springback Simulation: Impact of Some Advanced Constitutive Models and Numerical Parameters
NASA Astrophysics Data System (ADS)
Haddag, Badis; Balan, Tudor; Abed-Meraim, Farid
2005-08-01
The impact of material models on the numerical simulation of springback is investigated. The study is focused on the strain-path sensitivity of two hardening models. While both models predict the Bauschinger effect, their response in the transient zone after a strain-path change is fairly different. Their respective predictions are compared in terms of sequential test response and of strip-drawing springback. For this purpose, an accurate and general time integration algorithm has been developed and implemented in the Abaqus code. The impact of several numerical parameters is also studied in order to assess the overall accuracy of the finite element prediction. For some test geometries, both material and numerical parameters are shown to clearly influence the springback behavior at a large extent. Moreover, a general trend cannot always be extracted, thus justifying the need for the finite element simulation of the stamping process.
High-Resolution Tsunami Inundation Simulations Based on Accurate Estimations of Coastal Waveforms
NASA Astrophysics Data System (ADS)
Oishi, Y.; Imamura, F.; Sugawara, D.; Furumura, T.
2015-12-01
We evaluate the accuracy of high-resolution tsunami inundation simulations in detail using the actual observational data of the 2011 Tohoku-Oki earthquake (Mw9.0) and investigate the methodologies to improve the simulation accuracy.Due to the recent development of parallel computing technologies, high-resolution tsunami inundation simulations are conducted more commonly than before. To evaluate how accurately these simulations can reproduce inundation processes, we test several types of simulation configurations on a parallel computer, where we can utilize the observational data (e.g., offshore and coastal waveforms and inundation properties) that are recorded during the Tohoku-Oki earthquake.Before discussing the accuracy of inundation processes on land, the incident waves at coastal sites must be accurately estimated. However, for megathrust earthquakes, it is difficult to find the tsunami source that can provide accurate estimations of tsunami waveforms at every coastal site because of the complex spatiotemporal distribution of the source and the limitation of observation. To overcome this issue, we employ a site-specific source inversion approach that increases the estimation accuracy within a specific coastal site by applying appropriate weighting to the observational data in the inversion process.We applied our source inversion technique to the Tohoku tsunami and conducted inundation simulations using 5-m resolution digital elevation model data (DEM) for the coastal area around Miyako Bay and Sendai Bay. The estimated waveforms at the coastal wave gauges of these bays successfully agree with the observed waveforms. However, the simulations overestimate the inundation extent indicating the necessity to improve the inundation model. We find that the value of Manning's roughness coefficient should be modified from the often-used value of n = 0.025 to n = 0.033 to obtain proper results at both cities.In this presentation, the simulation results with several
Numerical simulations and modeling for stochastic biological systems with jumps
NASA Astrophysics Data System (ADS)
Zou, Xiaoling; Wang, Ke
2014-05-01
This paper gives a numerical method to simulate sample paths for stochastic differential equations (SDEs) driven by Poisson random measures. It provides us a new approach to simulate systems with jumps from a different angle. The driving Poisson random measures are assumed to be generated by stationary Poisson point processes instead of Lévy processes. Methods provided in this paper can be used to simulate SDEs with Lévy noise approximately. The simulation is divided into two parts: the part of jumping integration is based on definition without approximation while the continuous part is based on some classical approaches. Biological explanations for stochastic integrations with jumps are motivated by several numerical simulations. How to model biological systems with jumps is showed in this paper. Moreover, method of choosing integrands and stationary Poisson point processes in jumping integrations for biological models are obtained. In addition, results are illustrated through some examples and numerical simulations. For some examples, earthquake is chose as a jumping source which causes jumps on the size of biological population.
Numerical Simulation of Flow-Induced Structure in Complex Fluids
NASA Astrophysics Data System (ADS)
Yamamoto, Takehiro
2007-04-01
It is important to investigate the flow-induced structure for the analysis of the mechanism of flow behavior of complex fluids. The present paper includes two topics in which the flow-induced structure is numerically investigated. The first topic treats the suspensions of disc-like particles under simple shear flows. Disc-like particles were modeled by oblate spheroid particles, and the Brownian dynamics simulation was performed for suspensions of the particles interacting via the Gay-Berne potential. This simulation confirmed that this model system was applicable to the analysis of flow of suspension of disc-like particles. The second one is the numerical simulation of the deformation behavior of a droplet in shear flows. The present simulation is the first step for the numerical simulation of the flow-induced structure in emulsions. This simulation can demonstrate the deformation behavior of droplet observed in experiments and predict effects of non-Newtonian property of fluids on the droplet deformation.
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.
Study on Applicability of Numerical Simulation to Evaluation of Gas Entrainment From Free Surface
Kei Ito; Takaaki Sakai; Hiroyuki Ohshima
2006-07-01
An onset condition of gas entrainment (GE) due to free surface vortex has been studied to establish a design of fast breeder reactor with higher coolant velocity than conventional designs, because the GE might cause the reactor operation instability and therefore should be avoided. The onset condition of the GE has been investigated experimentally and theoretically, however, dependency of the vortex type GE on local geometry configuration of each experimental system and local velocity distribution has prevented researchers from formulating the universal onset condition of the vortex type GE. A real scale test is considered as an accurate method to evaluate the occurrence of the vortex type GE, but the real scale test is generally expensive and not useful in the design study of large and complicated FBR systems, because frequent displacement of inner equipments accompanied by the design change is difficult in the real scale test. Numerical simulation seems to be promising method as an alternative to the real scale test. In this research, to evaluate the applicability of the numerical simulation to the design work, numerical simulations were conducted on the basic experimental system of the vortex type GE. This basic experiment consisted of rectangular flow channel and two important equipments for vortex type GE in the channel, i.e. vortex generation and suction equipments. Generated vortex grew rapidly interacting with the suction flow and the grown vortex formed a free surface dent (gas core). When the tip of the gas core or the bubbles detached from the tip of the gas core reached the suction mouth, the gas was entrained to the suction tube. The results of numerical simulation under the experimental conditions were compared to the experiment in terms of velocity distributions and free surface shape. As a result, the numerical simulation showed qualitatively good agreement with experimental data. The numerical simulation results were similar to the experimental
NASA Astrophysics Data System (ADS)
Stecca, Guglielmo; Siviglia, Annunziato; Blom, Astrid
2016-07-01
We present an accurate numerical approximation to the Saint-Venant-Hirano model for mixed-sediment morphodynamics in one space dimension. Our solution procedure originates from the fully-unsteady matrix-vector formulation developed in [54]. The principal part of the problem is solved by an explicit Finite Volume upwind method of the path-conservative type, by which all the variables are updated simultaneously in a coupled fashion. The solution to the principal part is embedded into a splitting procedure for the treatment of frictional source terms. The numerical scheme is extended to second-order accuracy and includes a bookkeeping procedure for handling the evolution of size stratification in the substrate. We develop a concept of balancedness for the vertical mass flux between the substrate and active layer under bed degradation, which prevents the occurrence of non-physical oscillations in the grainsize distribution of the substrate. We suitably modify the numerical scheme to respect this principle. We finally verify the accuracy in our solution to the equations, and its ability to reproduce one-dimensional morphodynamics due to streamwise and vertical sorting, using three test cases. In detail, (i) we empirically assess the balancedness of vertical mass fluxes under degradation; (ii) we study the convergence to the analytical linearised solution for the propagation of infinitesimal-amplitude waves [54], which is here employed for the first time to assess a mixed-sediment model; (iii) we reproduce Ribberink's E8-E9 flume experiment [46].
NASA Astrophysics Data System (ADS)
Jiang, Shidong; Luo, Li-Shi
2016-07-01
The integral equation for the flow velocity u (x ; k) in the steady Couette flow derived from the linearized Bhatnagar-Gross-Krook-Welander kinetic equation is studied in detail both theoretically and numerically in a wide range of the Knudsen number k between 0.003 and 100.0. First, it is shown that the integral equation is a Fredholm equation of the second kind in which the norm of the compact integral operator is less than 1 on Lp for any 1 ≤ p ≤ ∞ and thus there exists a unique solution to the integral equation via the Neumann series. Second, it is shown that the solution is logarithmically singular at the endpoints. More precisely, if x = 0 is an endpoint, then the solution can be expanded as a double power series of the form ∑n=0∞∑m=0∞cn,mxn(xln x) m about x = 0 on a small interval x ∈ (0 , a) for some a > 0. And third, a high-order adaptive numerical algorithm is designed to compute the solution numerically to high precision. The solutions for the flow velocity u (x ; k), the stress Pxy (k), and the half-channel mass flow rate Q (k) are obtained in a wide range of the Knudsen number 0.003 ≤ k ≤ 100.0; and these solutions are accurate for at least twelve significant digits or better, thus they can be used as benchmark solutions.
NASA Astrophysics Data System (ADS)
Heidari, M.; Cortes-Huerto, R.; Donadio, D.; Potestio, R.
2016-07-01
In adaptive resolution simulations the same system is concurrently modeled with different resolution in different subdomains of the simulation box, thereby enabling an accurate description in a small but relevant region, while the rest is treated with a computationally parsimonious model. In this framework, electrostatic interaction, whose accurate treatment is a crucial aspect in the realistic modeling of soft matter and biological systems, represents a particularly acute problem due to the intrinsic long-range nature of Coulomb potential. In the present work we propose and validate the usage of a short-range modification of Coulomb potential, the Damped shifted force (DSF) model, in the context of the Hamiltonian adaptive resolution simulation (H-AdResS) scheme. This approach, which is here validated on bulk water, ensures a reliable reproduction of the structural and dynamical properties of the liquid, and enables a seamless embedding in the H-AdResS framework. The resulting dual-resolution setup is implemented in the LAMMPS simulation package, and its customized version employed in the present work is made publicly available.
NUMERICAL SIMULATION OF THREE-DIMENSIONAL TUFT CORONA AND ELECTROHYDRODYNAMICS
The numerical simulation of three-dimensional tuft corona and electrohydrodynamics (EHD) is discussed. The importance of high-voltage and low-current operation in the wire-duct precipitator has focused attention on collecting high-resistivity dust. The local current density of in...
Numerical aerodynamic simulation facility preliminary study: Executive study
NASA Technical Reports Server (NTRS)
1977-01-01
A computing system was designed with the capability of providing an effective throughput of one billion floating point operations per second for three dimensional Navier-Stokes codes. The methodology used in defining the baseline design, and the major elements of the numerical aerodynamic simulation facility are described.
Numerical Simulation of the Perrin-Like Experiments
ERIC Educational Resources Information Center
Mazur, Zygmunt; Grech, Dariusz
2008-01-01
A simple model of the random Brownian walk of a spherical mesoscopic particle in viscous liquids is proposed. The model can be solved analytically and simulated numerically. The analytic solution gives the known Einstein-Smoluchowski diffusion law r[superscript 2] = 2Dt, where the diffusion constant D is expressed by the mass and geometry of a…
Numerical Simulation and Cold Modeling experiments on Centrifugal Casting
NASA Astrophysics Data System (ADS)
Keerthiprasad, Kestur Sadashivaiah; Murali, Mysore Seetharam; Mukunda, Pudukottah Gopaliengar; Majumdar, Sekhar
2011-02-01
In a centrifugal casting process, the fluid flow eventually determines the quality and characteristics of the final product. It is difficult to study the fluid behavior here because of the opaque nature of melt and mold. In the current investigation, numerical simulations of the flow field and visualization experiments on cold models have been carried out for a centrifugal casting system using horizontal molds and fluids of different viscosities to study the effect of different process variables on the flow pattern. The effects of the thickness of the cylindrical fluid annulus formed inside the mold and the effects of fluid viscosity, diameter, and rotational speed of the mold on the hollow fluid cylinder formation process have been investigated. The numerical simulation results are compared with corresponding data obtained from the cold modeling experiments. The influence of rotational speed in a real-life centrifugal casting system has also been studied using an aluminum-silicon alloy. Cylinders of different thicknesses are cast at different rotational speeds, and the flow patterns observed visually in the actual castings are found to be similar to those recorded in the corresponding cold modeling experiments. Reasonable agreement is observed between the results of numerical simulation and the results of cold modeling experiments with different fluids. The visualization study on the hollow cylinders produced in an actual centrifugal casting process also confirm the conclusions arrived at from the cold modeling experiments and numerical simulation in a qualitative sense.
A review of numerical simulation of hydrothermal systems.
Mercer, J.W.; Faust, C.R.
1979-01-01
Many advances in simulating single and two-phase fluid flow and heat transport in porous media have recently been made in conjunction with geothermal energy research. These numerical models reproduce system thermal and pressure behaviour and can be used for other heat-transport problems, such as high-level radioactive waste disposal and heat-storage projects. -Authors
NUMERICAL SIMULATION OF NATURAL GAS-SWIRL BURNER
Ala Qubbaj
2005-03-01
A numerical simulation of a turbulent natural gas jet diffusion flame at a Reynolds number of 9000 in a swirling air stream is presented. The numerical computations were carried out using the commercially available software package CFDRC. The instantaneous chemistry model was used as the reaction model. The thermal, composition, flow (velocity), as well as stream function fields for both the baseline and air-swirling flames were numerically simulated in the near-burner region, where most of the mixing and reactions occur. The results were useful to interpret the effects of swirl in enhancing the mixing rates in the combustion zone as well as in stabilizing the flame. The results showed the generation of two recirculating regimes induced by the swirling air stream, which account for such effects. The present investigation will be used as a benchmark study of swirl flow combustion analysis as a step in developing an enhanced swirl-cascade burner technology.
Time Accurate CFD Simulations of the Orion Launch Abort Vehicle in the Transonic Regime
NASA Technical Reports Server (NTRS)
Ruf, Joseph; Rojahn, Josh
2011-01-01
Significant asymmetries in the fluid dynamics were calculated for some cases in the CFD simulations of the Orion Launch Abort Vehicle through its abort trajectories. The CFD simulations were performed steady state with symmetric boundary conditions and geometries. The trajectory points at issue were in the transonic regime, at 0 and 5 angles of attack with the Abort Motors with and without the Attitude Control Motors (ACM) firing. In some of the cases the asymmetric fluid dynamics resulted in aerodynamic side forces that were large enough that would overcome the control authority of the ACMs. MSFC s Fluid Dynamics Group supported the investigation into the cause of the flow asymmetries with time accurate CFD simulations, utilizing a hybrid RANS-LES turbulence model. The results show that the flow over the vehicle and the subsequent interaction with the AB and ACM motor plumes were unsteady. The resulting instantaneous aerodynamic forces were oscillatory with fairly large magnitudes. Time averaged aerodynamic forces were essentially symmetric.
Numerical Simulation of the Flow in Vascular Grafts for Surgical Applications
NASA Astrophysics Data System (ADS)
McGah, Patrick; Aliseda, Alberto
2009-11-01
Numerical simulation of the human blood vessels, is becoming an important tool in surgical planning and research. Accurate vascular simulations might grant physicians the predictive capability to perform pre-surgical planning. We focus our attention on the implantation of vascular grafts. The high rate of failure of this common vascular interaction is intimately related to the fluid mechanics in the affected region and the subsequent wall tissue remodeling. Here, we will present our current work in developing a methodology for the numerical simulation of vascular grafts which incorporates physiologically realistic geometries and flow boundary conditions. In particular, we seek to correlate the wall shear stress and its spatial (WSSG) and temporal (OSI) variability to wall remodeling as observed in patient specific longitudinal studies. The pulsatility (Remean= 800 , Repeak= 2000, Wo = 2) of the flow gives rise to additional fluid dynamics phenomena such as instability, flow separation, transition, and unsteadiness. Our goal is to describe and evaluate their effect on the wall physiology.
Calculation of pressure statistics in turbulent free shear flows by direct numerical simulation
NASA Technical Reports Server (NTRS)
Metcalfe, R. W.; Riley, J. J.
1982-01-01
Accurate numerical simulations of turbulent free shear flows were performed in order to study the behavior of certain critical turbulence quantities which have been difficult to measure in the laboratory. The three-dimensional time-dependent nonlinear Navier-Stokes equations are solved by the direct numerical simulation technique without turbulence modeling or ad hoc closure assumptions. The pressure interaction terms were factored into diffusion and return-to-isotropy components according to two models. Simulations of the evolution of a turbulent wake with and without swirl present were performed at sufficiently high Reynolds numbers to insure that the flows were strongly nonlinear and turbulent, but low enough so that all scales of motion containing significant energy are adequately resolved. It is noted that the presence of swirl tends to enhance the amplitude of the rms pressure levels.
NASA Astrophysics Data System (ADS)
Hu, P.; Shi, D. Y.; Ying, L.; Shen, G. Z.; Chang, Y.; Liu, W. Q.
2013-05-01
Thermal-mechanical-transformation coupled theoretical model for hot stamping and rheological behavior of high strength steel at elevated temperatures were obtained through non-isothermal and isothermal tensile tests respectively in this work. The static explicit finite element equations for hot stamping were proposed based on thermal-mechanical-transformation coupled constitutive laws and nonlinear, large deformation analysis. According to these equations, the hot stamping module of KMAS (King Mesh Analysis System) was developed for the numerical simulation of sheet metal forming at elevated temperatures. Afterwards, the hot stamping simulation of a typical B-pillar conducted by the KMAS software was compared to the experiment. The comparison consists of the following sides: temperature distribution, thickness distribution and martensite fraction. The good agreement between numerical simulation and the experiment confirms that the multi-field coupled constitutive laws and the KMAS software can predict hot stamping process accurately.
NASA Astrophysics Data System (ADS)
Zhou, Lian; Li, Xu; Zhu, Shanan; He, Bin
2011-04-01
Magnetoacoustic tomography with magnetic induction (MAT-MI) was recently introduced as a noninvasive electrical conductivity imaging approach with high spatial resolution close to ultrasound imaging. In this study, we test the feasibility of the MAT-MI method for breast tumor imaging using numerical modeling and computer simulation. Using the finite element method, we have built three-dimensional numerical breast models with varieties of embedded tumors for this simulation study. In order to obtain an accurate and stable forward solution that does not have numerical errors caused by singular MAT-MI acoustic sources at conductivity boundaries, we first derive an integral forward method for calculating MAT-MI acoustic sources over the entire imaging volume. An inverse algorithm for reconstructing the MAT-MI acoustic source is also derived with spherical measurement aperture, which simulates a practical setup for breast imaging. With the numerical breast models, we have conducted computer simulations under different imaging parameter setups and all the results suggest that breast tumors that have large conductivity in contrast to the surrounding tissue as reported in the literature may be readily detected in the reconstructed MAT-MI images. In addition, our simulations also suggest that the sensitivity of imaging breast tumors using the presented MAT-MI setup depends more on the tumor location and the conductivity contrast between the tumor and its surrounding tissue than on the tumor size.
Numerical simulation studies of unsteady low Reynolds number separated flows
NASA Astrophysics Data System (ADS)
Tatineni, Mahidhar
Numerical simulations were used to study unsteady low-Reynolds-number separated flows. The studies were focused on the instability of the separation bubbles, the associated vortex shedding, and the response to imposed disturbances. The simulations were performed for separation bubbles in both low Mach number compressible and incompressible flow regimes. The compressible study consisted of unsteady simulations of flows over the Eppler 387 airfoil and the APEX airfoil. For a sufficiently high Reynolds number the simulations showed that the flow over the airfoils is inherently unsteady, with associated vortex shedding. A Fourier analysis of the unsteady flowfield revealed the presence of a dominant frequency in the flow. The dominant frequency from the numerical solution was found to agree with the most unstable frequency calculated using linear stability theory. The vortex shedding was shown to be caused by the growth of the disturbance waves corresponding to the dominant mode calculated from the linear stability analysis. In order to study the separation bubble and the vortex shedding in detail, a simpler two-dimensional (2-D) and three-dimensional (3-D) incompressible flow over a flat plate was considered. The onset of self excited vortex shedding, and the response of the separation bubble to 2-D and 3-D disturbances was studied in detail through numerical simulations. The incompressible Navier-Stokes equations were solved using a fifth order finite difference scheme for spatial discretization and a fourth order Runge-Kutta scheme for time advancement. A new high-order nonuniform grid finite difference scheme was also developed for the simulations. The incompressible simulation results showed that it was possible to induce vortex shedding by imposing disturbances upstream of the separation bubble. For a sufficiently large freestream velocity gradient the separation bubble was globally unstable, leading to a growth in the size of the separation bubble and the
Numerical relativity simulations in the era of the Einstein Telescope
NASA Astrophysics Data System (ADS)
Hannam, Mark; Hawke, Ian
2011-02-01
Numerical-relativity (NR) simulations of compact binaries are expected to be an invaluable tool in gravitational-wave astronomy. The sensitivity of future detectors such as the Einstein Telescope (ET) will place much higher demands on NR simulations than first- and second-generation ground-based detectors. We discuss the issues facing compact-object simulations over the next decade, with an emphasis on estimating where the accuracy and parameter space coverage will be sufficient for ET and where significant work is needed.
Accurate and efficient halo-based galaxy clustering modelling with simulations
NASA Astrophysics Data System (ADS)
Zheng, Zheng; Guo, Hong
2016-06-01
Small- and intermediate-scale galaxy clustering can be used to establish the galaxy-halo connection to study galaxy formation and evolution and to tighten constraints on cosmological parameters. With the increasing precision of galaxy clustering measurements from ongoing and forthcoming large galaxy surveys, accurate models are required to interpret the data and extract relevant information. We introduce a method based on high-resolution N-body simulations to accurately and efficiently model the galaxy two-point correlation functions (2PCFs) in projected and redshift spaces. The basic idea is to tabulate all information of haloes in the simulations necessary for computing the galaxy 2PCFs within the framework of halo occupation distribution or conditional luminosity function. It is equivalent to populating galaxies to dark matter haloes and using the mock 2PCF measurements as the model predictions. Besides the accurate 2PCF calculations, the method is also fast and therefore enables an efficient exploration of the parameter space. As an example of the method, we decompose the redshift-space galaxy 2PCF into different components based on the type of galaxy pairs and show the redshift-space distortion effect in each component. The generalizations and limitations of the method are discussed.
Numerical simulation of the laminar diffusion flame in a simplified burner. Revision 1
Cloutman, L.D.
1996-02-01
The laminar ethylene-air diffusion flame in a simple laboratory burner was simulated with the COYOTE reactive flow program. This program predicts the flow field, transport, and chemistry for the purposes of code validation and providing physical understanding of the processes occurring in the flame. The authors show the results of numerical experiments to test the importance of several physical phenomena, including gravity, radiation, and differential diffusion. The computational results compare favorably with the experimental measurements, and all three phenomena are important to accurate simulations.
Numerical simulation of the vortical flow over a round-edged double-delta wing
NASA Technical Reports Server (NTRS)
Hsu, C.-H.; Liu, C. H.
1988-01-01
Simulations of three-dimensional vortical flows over a thin double-delta wing with an aspect ratio of 2.05 have been performed. Steady-state solutions to the unsteady incompressible Navier-Stokes equations are obtained using a new implicit upwind-relaxation finite-difference scheme. The method is second-order accurate spatially and naturally dissipative. Numerical results indicate that key features of both vortical interaction and vortex breakdown are successfully simulated. The computed lift coefficients and lateral trajectories of the vortical cores are in good agreement with the experimental data.
Collapse of a Liquid Column: Numerical Simulation and Experimental Validation
NASA Astrophysics Data System (ADS)
Cruchaga, Marcela A.; Celentano, Diego J.; Tezduyar, Tayfun E.
2007-03-01
This paper is focused on the numerical and experimental analyses of the collapse of a liquid column. The measurements of the interface position in a set of experiments carried out with shampoo and water for two different initial column aspect ratios are presented together with the corresponding numerical predictions. The experimental procedure was found to provide acceptable recurrence in the observation of the interface evolution. Basic models describing some of the relevant physical aspects, e.g. wall friction and turbulence, are included in the simulations. Numerical experiments are conducted to evaluate the influence of the parameters involved in the modeling by comparing the results with the data from the measurements. The numerical predictions reasonably describe the physical trends.
Wijma, Hein J; Marrink, Siewert J; Janssen, Dick B
2014-07-28
Computational approaches could decrease the need for the laborious high-throughput experimental screening that is often required to improve enzymes by mutagenesis. Here, we report that using multiple short molecular dynamics (MD) simulations makes it possible to accurately model enantioselectivity for large numbers of enzyme-substrate combinations at low computational costs. We chose four different haloalkane dehalogenases as model systems because of the availability of a large set of experimental data on the enantioselective conversion of 45 different substrates. To model the enantioselectivity, we quantified the frequency of occurrence of catalytically productive conformations (near attack conformations) for pairs of enantiomers during MD simulations. We found that the angle of nucleophilic attack that leads to carbon-halogen bond cleavage was a critical variable that limited the occurrence of productive conformations; enantiomers for which this angle reached values close to 180° were preferentially converted. A cluster of 20-40 very short (10 ps) MD simulations allowed adequate conformational sampling and resulted in much better agreement to experimental enantioselectivities than single long MD simulations (22 ns), while the computational costs were 50-100 fold lower. With single long MD simulations, the dynamics of enzyme-substrate complexes remained confined to a conformational subspace that rarely changed significantly, whereas with multiple short MD simulations a larger diversity of conformations of enzyme-substrate complexes was observed. PMID:24916632
Margot Gerritsen
2008-10-31
Gas-injection processes are widely and increasingly used for enhanced oil recovery (EOR). In the United States, for example, EOR production by gas injection accounts for approximately 45% of total EOR production and has tripled since 1986. The understanding of the multiphase, multicomponent flow taking place in any displacement process is essential for successful design of gas-injection projects. Due to complex reservoir geometry, reservoir fluid properties and phase behavior, the design of accurate and efficient numerical simulations for the multiphase, multicomponent flow governing these processes is nontrivial. In this work, we developed, implemented and tested a streamline based solver for gas injection processes that is computationally very attractive: as compared to traditional Eulerian solvers in use by industry it computes solutions with a computational speed orders of magnitude higher and a comparable accuracy provided that cross-flow effects do not dominate. We contributed to the development of compositional streamline solvers in three significant ways: improvement of the overall framework allowing improved streamline coverage and partial streamline tracing, amongst others; parallelization of the streamline code, which significantly improves wall clock time; and development of new compositional solvers that can be implemented along streamlines as well as in existing Eulerian codes used by industry. We designed several novel ideas in the streamline framework. First, we developed an adaptive streamline coverage algorithm. Adding streamlines locally can reduce computational costs by concentrating computational efforts where needed, and reduce mapping errors. Adapting streamline coverage effectively controls mass balance errors that mostly result from the mapping from streamlines to pressure grid. We also introduced the concept of partial streamlines: streamlines that do not necessarily start and/or end at wells. This allows more efficient coverage and avoids
Design and numerical simulation of an optofluidic pressure sensor.
Ebnali-Heidari, Majid; Mansouri, Morteza; Mokhtarian, Saeed; Moravvej-Farshi, Mohammed Kazem
2012-06-01
We present a numerical design procedure for an all-optical compact sensor by means of integrating the optofluidic switch polymer interferometers to measure the microfluidic air pressure and flow rate. The design is based on a flexible air gap optical cavity that can generate an interference pattern when illuminated by a monochromatic light. The optical interference pattern directly depends on the pressure. In our numerical simulations, we take the effects of fluid flow rate, solid deformation, and the light interference into account. We use the beam propagation method for simulating the optics and the finite element method for simulating the mechanics. The significance of the proposed sensor lies with its low power consumption, compactness, low cost, and short length. This sensor can operate under pressure range of 0-60±6% Pa at a constant temperature of 20 °C. PMID:22695574
The Role of Numerical Simulation in Advancing Plasma Propulsion
NASA Astrophysics Data System (ADS)
Turchi, P. J.; Mikellides, P. G.; Mikellides, I. G.
1999-11-01
Plasma thrusters often involve a complex set of interactions among several distinct physical processes. While each process can yield to separate mathematical representation, their combination generally requires numerical simulation. We have extended and used the MACH2 code successfully to simulate both self-field and applied-field magnetoplasmadynamic thrusters and, more recently, ablation-fed pulsed plasma microthrusters. MACH2 provides a framework in which to compute 2-1/2 dimensional, unsteady, MHD flows in two-temperature LTE. It couples to several options for electrical circuitry and allows access to both analytic formulas and tabular values for material properties and transport coefficients, including phenomenological models for anomalous transport. Even with all these capabilities, however, successful modeling demands comparison with experiment and with analytic solutions in idealized limits, and careful combination of MACH2 results with separate physical reasoning. Although well understood elsewhere in plasma physics, the strengths and limitations of numerical simulation for plasma propulsion needs further discussion.
Numerical simulation of three-dimensional self-gravitating flow
NASA Technical Reports Server (NTRS)
Shebalin, J. V.
1994-01-01
The three-dimensional flow of a self-gravitating fluid is numerically simulated using a Fourier pseudospectral method with a logarithmic variable formulation. Two cases with zero total angular momentum are studied in detail, a 32(exp 3) simulation (Run A) and a 64(exp 3) simulation (Run B). Other than the grid size, the primary differences between the two cases are that Run A modeled atomic hydrogen and had considerably more compressible motion initially than Run B, which modeled molecular hydrogen. ('Compressible motion' is that part of the velocity which has zero curl, but non-zero divergence). The numerical results indicate that gravitational collapse can proceed in a variety of ways. In Run A, collapse led to an elongated tube-like structure, while in Run B, collapse led to a flatter, disk-like structure.
Configuration Management File Manager Developed for Numerical Propulsion System Simulation
NASA Technical Reports Server (NTRS)
Follen, Gregory J.
1997-01-01
One of the objectives of the High Performance Computing and Communication Project's (HPCCP) Numerical Propulsion System Simulation (NPSS) is to provide a common and consistent way to manage applications, data, and engine simulations. The NPSS Configuration Management (CM) File Manager integrated with the Common Desktop Environment (CDE) window management system provides a common look and feel for the configuration management of data, applications, and engine simulations for U.S. engine companies. In addition, CM File Manager provides tools to manage a simulation. Features include managing input files, output files, textual notes, and any other material normally associated with simulation. The CM File Manager includes a generic configuration management Application Program Interface (API) that can be adapted for the configuration management repositories of any U.S. engine company.
Numerical simulation of unsteady flows generated by dissociating nitrogen diffusion
NASA Technical Reports Server (NTRS)
Marraffa, Lionel; Dulikravich, George S.; Deiwert, George S.
1989-01-01
An explicit time accurate predictor-corrector scheme, similar to MacCormack's, has been used to simulate unsteady nonequilibrium laminar chemically-reacting diffusion-reaction generated flows. A zonal approach, along with nonstructured boundaries, allows computation of internal and external flow with the same computer code. Results for equilibrium flows generated by dissociating, vibrationally relaxing nitrogen in a rectangular chamber are presented. The unsteady flows were generated strictly by the chemical reactions and concentration gradients.
Towards direct numerical simulation of pressure swirl injectors with realistic geometries
NASA Astrophysics Data System (ADS)
Czajkowski, Mark; Desjardins, Olivier
2011-11-01
Atomization of hydrocarbon fuels is of critical importance to the transportation sector, in particular for aircraft gas turbine engines. In this work, simulations of a Delevan pressure swirl injector with realistic geometry was investigated. Results were compared with simulations performed by Fuster et al. (Int J Multiphase Flow, 2009) of a swirl jet at lower density ratios. The pressure swirl injector is used for many applications and is a component within air-blast injectors commonly found in gas turbines and aeroengines. Direct numerical simulation of the pressure swirl injection process has the potential to provide much-needed information about the complex physics of atomization in swirling flows, but has yet to be used due to the interaction of a complex turbulent multiphase flow with complicated injector geometries. A variety of novel numerical methods are used to facilitate the numerical simulations including a conservative implementation of immersed boundaries used to represent the injector geometry, an accurate interface transport scheme with mass conservation properties based on a discontinuous Galerkin discretization of the conservative level set method, and a novel discretization of the Navier-Stokes convective term allowing for robust simulations at high density ratios. Simulations were conducted by combining the methods with a fully parallelized computational code called NGA.
Numerical simulation of shock interaction with above-ground structures
NASA Astrophysics Data System (ADS)
Baum, Joseph D.; Lohner, Rainald
1994-05-01
This final report for DNA contract DNA 001-89-C-0098 for the time period May 15, 1989 to Dec 31, 1992 describes the results of several of the computations conducted under this research effort. The numerical simulations conducted simulated shock wave diffraction phenomenon about complex-geometry two-dimensional and three-dimensional structures. Since a significant part of this effort was composed of parametric studies that have been delivered to the sponsors, the Defense Nuclear Agency and the Air Force Ballistic Missile Organization (BMO), and conducted under the now defunct Rail Garrison project, we included in this report a detailed description of the results of the major computations, and a brief summary of all the repetitive computations. The final report is divided into three sections. Chapter 1 describes in detail the two-dimensional numerical methodology and typical two-dimensional computation, i.e., the application of the numerical methodology to the simulation of shock interaction with a typical 2-D train (a 2-D cut at the center of a 3-D train). Chapter 2 describes the numerical development of a passive shock reflector, a major effort undertaken in this project. The objective of this effort was to design a passive device that, while allowing the ventilation of the enclosure under steady conditions, will prevent blast waves impinging on the wall from entering the enclosure when the structure is impacted by a shock.
Development of modified cable models to simulate accurate neuronal active behaviors
2014-01-01
In large network and single three-dimensional (3-D) neuron simulations, high computing speed dictates using reduced cable models to simulate neuronal firing behaviors. However, these models are unwarranted under active conditions and lack accurate representation of dendritic active conductances that greatly shape neuronal firing. Here, realistic 3-D (R3D) models (which contain full anatomical details of dendrites) of spinal motoneurons were systematically compared with their reduced single unbranched cable (SUC, which reduces the dendrites to a single electrically equivalent cable) counterpart under passive and active conditions. The SUC models matched the R3D model's passive properties but failed to match key active properties, especially active behaviors originating from dendrites. For instance, persistent inward currents (PIC) hysteresis, frequency-current (FI) relationship secondary range slope, firing hysteresis, plateau potential partial deactivation, staircase currents, synaptic current transfer ratio, and regional FI relationships were not accurately reproduced by the SUC models. The dendritic morphology oversimplification and lack of dendritic active conductances spatial segregation in the SUC models caused significant underestimation of those behaviors. Next, SUC models were modified by adding key branching features in an attempt to restore their active behaviors. The addition of primary dendritic branching only partially restored some active behaviors, whereas the addition of secondary dendritic branching restored most behaviors. Importantly, the proposed modified models successfully replicated the active properties without sacrificing model simplicity, making them attractive candidates for running R3D single neuron and network simulations with accurate firing behaviors. The present results indicate that using reduced models to examine PIC behaviors in spinal motoneurons is unwarranted. PMID:25277743
Direct Simulations of Transition and Turbulence Using High-Order Accurate Finite-Difference Schemes
NASA Technical Reports Server (NTRS)
Rai, Man Mohan
1997-01-01
In recent years the techniques of computational fluid dynamics (CFD) have been used to compute flows associated with geometrically complex configurations. However, success in terms of accuracy and reliability has been limited to cases where the effects of turbulence and transition could be modeled in a straightforward manner. Even in simple flows, the accurate computation of skin friction and heat transfer using existing turbulence models has proved to be a difficult task, one that has required extensive fine-tuning of the turbulence models used. In more complex flows (for example, in turbomachinery flows in which vortices and wakes impinge on airfoil surfaces causing periodic transitions from laminar to turbulent flow) the development of a model that accounts for all scales of turbulence and predicts the onset of transition may prove to be impractical. Fortunately, current trends in computing suggest that it may be possible to perform direct simulations of turbulence and transition at moderate Reynolds numbers in some complex cases in the near future. This seminar will focus on direct simulations of transition and turbulence using high-order accurate finite-difference methods. The advantage of the finite-difference approach over spectral methods is that complex geometries can be treated in a straightforward manner. Additionally, finite-difference techniques are the prevailing methods in existing application codes. In this seminar high-order-accurate finite-difference methods for the compressible and incompressible formulations of the unsteady Navier-Stokes equations and their applications to direct simulations of turbulence and transition will be presented.
Enabling R&D for accurate simulation of non-ideal explosives.
Aidun, John Bahram; Thompson, Aidan Patrick; Schmitt, Robert Gerard
2010-09-01
We implemented two numerical simulation capabilities essential to reliably predicting the effect of non-ideal explosives (NXs). To begin to be able to treat the multiple, competing, multi-step reaction paths and slower kinetics of NXs, Sandia's CTH shock physics code was extended to include the TIGER thermochemical equilibrium solver as an in-line routine. To facilitate efficient exploration of reaction pathways that need to be identified for the CTH simulations, we implemented in Sandia's LAMMPS molecular dynamics code the MSST method, which is a reactive molecular dynamics technique for simulating steady shock wave response. Our preliminary demonstrations of these two capabilities serve several purposes: (i) they demonstrate proof-of-principle for our approach; (ii) they provide illustration of the applicability of the new functionality; and (iii) they begin to characterize the use of the new functionality and identify where improvements will be needed for the ultimate capability to meet national security needs. Next steps are discussed.
Numerical validation of MR-measurement-integrated simulation of blood flow in a cerebral aneurysm.
Funamoto, Kenichi; Suzuki, Yoshitsugu; Hayase, Toshiyuki; Kosugi, Takashi; Isoda, Haruo
2009-06-01
This study proposes magnetic resonance (MR)-measurement-integrated (MR-MI) simulation, in which the difference between the computed velocity field and the phase-contrast MRI measurement data is fed back to the numerical simulation. The computational accuracy and the fundamental characteristics, such as steady characteristics and transient characteristics, of the MR-MI simulation were investigated by a numerical experiment. We dealt with reproduction of three-dimensional steady and unsteady blood flow fields in a realistic cerebral aneurysm developed at a bifurcation. The MR-MI simulation reduced the error derived from the incorrect boundary conditions in the blood flow in the cerebral aneurysm. For the reproduction of steady and unsteady standard solutions, the error of velocity decreased to 13% and to 22% in one cardiac cycle, respectively, compared with the ordinary simulation without feedback. Moreover, the application of feedback shortened the computational convergence, and thus the convergent solution and periodic solution were obtained within less computational time in the MR-MI simulation than that in the ordinary simulation. The dividing flow ratio toward the two outlets after bifurcation was well estimated owing to the improvement of computational accuracy. Furthermore, the MR-MI simulation yielded wall shear stress distribution on the cerebral aneurysm of the standard solution accurately and in detail. PMID:19350390
Numerical Propulsion System Simulation (NPSS) 1999 Industry Review
NASA Technical Reports Server (NTRS)
Lytle, John; Follen, Greg; Naiman, Cynthia; Evans, Austin
2000-01-01
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. In addition, the paper contains a summary of the feedback received from industry partners in the development effort and the actions taken over the past year to respond to that feedback. The NPSS development was supported in FY99 by the High Performance Computing and Communications Program.
Thermal numerical simulator for laboratory evaluation of steamflood oil recovery
Sarathi, P.
1991-04-01
A thermal numerical simulator running on an IBM AT compatible personal computer is described. The simulator was designed to assist laboratory design and evaluation of steamflood oil recovery. An overview of the historical evolution of numerical thermal simulation, NIPER's approach to solving these problems with a desk top computer, the derivation of equations and a description of approaches used to solve these equations, and verification of the simulator using published data sets and sensitivity analysis are presented. The developed model is a three-phase, two-dimensional multicomponent simulator capable of being run in one or two dimensions. Mass transfer among the phases and components is dictated by pressure- and temperature-dependent vapor-liquid equilibria. Gravity and capillary pressure phenomena were included. Energy is transferred by conduction, convection, vaporization and condensation. The model employs a block centered grid system with a five-point discretization scheme. Both areal and vertical cross-sectional simulations are possible. A sequential solution technique is employed to solve the finite difference equations. The study clearly indicated the importance of heat loss, injected steam quality, and injection rate to the process. Dependence of overall recovery on oil volatility and viscosity is emphasized. The process is very sensitive to relative permeability values. Time-step sensitivity runs indicted that the current version is time-step sensitive and exhibits conditional stability. 75 refs., 19 figs., 19 tabs.
Numerical simulation of landfill aeration using computational fluid dynamics.
Fytanidis, Dimitrios K; Voudrias, Evangelos A
2014-04-01
The present study is an application of Computational Fluid Dynamics (CFD) to the numerical simulation of landfill aeration systems. Specifically, the CFD algorithms provided by the commercial solver ANSYS Fluent 14.0, combined with an in-house source code developed to modify the main solver, were used. The unsaturated multiphase flow of air and liquid phases and the biochemical processes for aerobic biodegradation of the organic fraction of municipal solid waste were simulated taking into consideration their temporal and spatial evolution, as well as complex effects, such as oxygen mass transfer across phases, unsaturated flow effects (capillary suction and unsaturated hydraulic conductivity), temperature variations due to biochemical processes and environmental correction factors for the applied kinetics (Monod and 1st order kinetics). The developed model results were compared with literature experimental data. Also, pilot scale simulations and sensitivity analysis were implemented. Moreover, simulation results of a hypothetical single aeration well were shown, while its zone of influence was estimated using both the pressure and oxygen distribution. Finally, a case study was simulated for a hypothetical landfill aeration system. Both a static (steadily positive or negative relative pressure with time) and a hybrid (following a square wave pattern of positive and negative values of relative pressure with time) scenarios for the aeration wells were examined. The results showed that the present model is capable of simulating landfill aeration and the obtained results were in good agreement with corresponding previous experimental and numerical investigations. PMID:24525420
Non-robust numerical simulations of analogue extension experiments
NASA Astrophysics Data System (ADS)
Naliboff, John; Buiter, Susanne
2016-04-01
Numerical and analogue models of lithospheric deformation provide significant insight into the tectonic processes that lead to specific structural and geophysical observations. As these two types of models contain distinct assumptions and tradeoffs, investigations drawing conclusions from both can reveal robust links between first-order processes and observations. Recent studies have focused on detailed comparisons between numerical and analogue experiments in both compressional and extensional tectonics, sometimes involving multiple lithospheric deformation codes and analogue setups. While such comparisons often show good agreement on first-order deformation styles, results frequently diverge on second-order structures, such as shear zone dip angles or spacing, and in certain cases even on first-order structures. Here, we present finite-element experiments that are designed to directly reproduce analogue "sandbox" extension experiments at the cm-scale. We use material properties and boundary conditions that are directly taken from analogue experiments and use a Drucker-Prager failure model to simulate shear zone formation in sand. We find that our numerical experiments are highly sensitive to numerous numerical parameters. For example, changes to the numerical resolution, velocity convergence parameters and elemental viscosity averaging commonly produce significant changes in first- and second-order structures accommodating deformation. The sensitivity of the numerical simulations to small parameter changes likely reflects a number of factors, including, but not limited to, high angles of internal friction assigned to sand, complex, unknown interactions between the brittle sand (used as an upper crust equivalent) and viscous silicone (lower crust), highly non-linear strain weakening processes and poor constraints on the cohesion of sand. Our numerical-analogue comparison is hampered by (a) an incomplete knowledge of the fine details of sand failure and sand
NASA Astrophysics Data System (ADS)
Rensonnet, Gaëtan; Jacobs, Damien; Macq, Benoît.; Taquet, Maxime
2016-03-01
Diffusion-weighted magnetic resonance imaging (DW-MRI) is a powerful tool to probe the diffusion of water through tissues. Through the application of magnetic gradients of appropriate direction, intensity and duration constituting the acquisition parameters, information can be retrieved about the underlying microstructural organization of the brain. In this context, an important and open question is to determine an optimal sequence of such acquisition parameters for a specific purpose. The use of simulated DW-MRI data for a given microstructural configuration provides a convenient and efficient way to address this problem. We first present a novel hybrid method for the synthetic simulation of DW-MRI signals that combines analytic expressions in simple geometries such as spheres and cylinders and Monte Carlo (MC) simulations elsewhere. Our hybrid method remains valid for any acquisition parameters and provides identical levels of accuracy with a computational time that is 90% shorter than that required by MC simulations for commonly-encountered microstructural configurations. We apply our novel simulation technique to estimate the radius of axons under various noise levels with different acquisition protocols commonly used in the literature. The results of our comparison suggest that protocols favoring a large number of gradient intensities such as a Cube and Sphere (CUSP) imaging provide more accurate radius estimation than conventional single-shell HARDI acquisitions for an identical acquisition time.
A fast and accurate simulator for the design of birdcage coils in MRI.
Giovannetti, Giulio; Landini, Luigi; Santarelli, Maria Filomena; Positano, Vincenzo
2002-11-01
The birdcage coils are extensively used in MRI systems since they introduce a high signal to noise ratio and a high radiofrequency magnetic field homogeneity that guarantee a large field of view. The present article describes the implementation of a birdcage coil simulator, operating in high-pass and low-pass modes, using magnetostatic analysis of the coil. Respect to other simulators described in literature, our simulator allows to obtain in short time not only the dominant frequency mode, but also the complete resonant frequency spectrum and the relevant magnetic field pattern with high accuracy. Our simulator accounts for all the inductances including the mutual inductances between conductors. Moreover, the inductance calculation includes an accurately birdcage geometry description and the effect of a radiofrequency shield. The knowledge of all the resonance modes introduced by a birdcage coil is twofold useful during birdcage coil design: --higher order modes should be pushed far from the fundamental one, --for particular applications, it is necessary to localize other resonant modes (as the Helmholtz mode) jointly to the dominant mode. The knowledge of the magnetic field pattern allows to a priori verify the field homogeneity created inside the coil, when varying the coil dimension and mainly the number of the coil legs. The coil is analyzed using equivalent circuit method. Finally, the simulator is validated by implementing a low-pass birdcage coil and comparing our data with the literature. PMID:12413563
Simulation for the expansion of the wildfire with numerical weather simulation MM5
NASA Astrophysics Data System (ADS)
Kimura, K.; Honma, T.
2008-12-01
1. Background Frequent occurrence of wildfires all over the world is considered as one of major resources of greenhouse gases. For example, a lot of wildfires in Alaska occur in summer. Now, the satellites of NOAA and Terra/Aqua are watching the earth and the wildfire are detected. Of course, to detection wildfire is very important, but the influence on inhabitants is more important. Our purpose is to make the numerical simulation of the wildfire spread in the small area with numerical weather simulation MM5. We think this will be useful to help fire fighting and global environment such as the replace of CO2. 2. Numerical Wildfire Spread Simulation There are many type of the numerical simulation of wildfire spread. In our simulation, the wildfire velocity is based on the Rhothermel equation and other parts are made of the cell automata. The area of the wildfire is the uniform vegetation consisted of the boreal forest (Picea mariana). The main factor of the expansion speed is wind velocity and speed. The continuous change of the weather is simulated with regional meteorological simulation MM5. The real spread of the Boundary Fire are observed by Alaska Fire Service. In this study, we validate the simulation result with the AFS data. 3. The Simulation Results We are constructing the simulation with Boundary Fire in 2004 in central Alaska. MM5 is very useful to reconstruct or forecast the distribution of local weather. We show the examples of the results in the poster. 4. Conclusion We constructed the numerical simulation model of wildfire spread with numerical weather simulation MM5. The result of simulation is being verified by the observed data by AFS .
Graphics interfaces and numerical simulations: Mexican Virtual Solar Observatory
NASA Astrophysics Data System (ADS)
Hernández, L.; González, A.; Salas, G.; Santillán, A.
2007-08-01
Preliminary results associated to the computational development and creation of the Mexican Virtual Solar Observatory (MVSO) are presented. Basically, the MVSO prototype consists of two parts: the first, related to observations that have been made during the past ten years at the Solar Observation Station (EOS) and at the Carl Sagan Observatory (OCS) of the Universidad de Sonora in Mexico. The second part is associated to the creation and manipulation of a database produced by numerical simulations related to solar phenomena, we are using the MHD ZEUS-3D code. The development of this prototype was made using mysql, apache, java and VSO 1.2. based GNU and `open source philosophy'. A graphic user interface (GUI) was created in order to make web-based, remote numerical simulations. For this purpose, Mono was used, because it is provides the necessary software to develop and run .NET client and server applications on Linux. Although this project is still under development, we hope to have access, by means of this portal, to other virtual solar observatories and to be able to count on a database created through numerical simulations or, given the case, perform simulations associated to solar phenomena.
Fish Pectoral Fin Hydrodynamics; Part II: Numerical Simulations and Analysis
NASA Astrophysics Data System (ADS)
Dong, H.; Madden, P. G.
2005-11-01
High-fidelity numerical simulations are being used to examine the key hydrodynamic features and thrust performance of the pectoral fin of a bluegill sunfish which is moving at a constant forward velocity. The numerical modeling approach employs a parallelized immersed boundary solver which can perform direct (DNS) or large-eddy simulation (LES) of flow past highly deformable bodies such as fish pectoral fins. The three-dimensional, time-dependent fin kinematics is obtained via a stereo-videographic technique and experiments also provide PIV data which is used to validate the numerical simulations. The primary objectives of the CFD effort are to quantify the thrust performance of the bluegill sunfish pectoral fin as well as to establish the mechanisms responsible for thrust production. Simulations show that the pectoral fin produces a relatively large amount of thrust at all phases in the fin motion while limiting the magnitude of the transverse forces. The motion of the fin produces a distinct system of connected vortices which are examined in detail in order to gain insight into the thrust producing mechanisms.
NASA Astrophysics Data System (ADS)
Nallatamby, Jean-Christophe; Abdelhadi, Khaled; Jacquet, Jean-Claude; Prigent, Michel; Floriot, Didier; Delage, Sylvain; Obregon, Juan
2013-03-01
Commercially available simulators present considerable advantages in performing accurate DC, AC and transient simulations of semiconductor devices, including many fundamental and parasitic effects which are not generally taken into account in house-made simulators. Nevertheless, while the TCAD simulators of the public domain we have tested give accurate results for the simulation of diffusion noise, none of the tested simulators perform trap-assisted GR noise accurately. In order to overcome the aforementioned problem we propose a robust solution to accurately simulate GR noise due to traps. It is based on numerical processing of the output data of one of the simulators available in the public-domain, namely SENTAURUS (from Synopsys). We have linked together, through a dedicated Data Access Component (DAC), the deterministic output data available from SENTAURUS and a powerful, customizable post-processing tool developed on the mathematical SCILAB software package. Thus, robust simulations of GR noise in semiconductor devices can be performed by using GR Langevin sources associated to the scalar Green functions responses of the device. Our method takes advantage of the accuracy of the deterministic simulations of electronic devices obtained with SENTAURUS. A Comparison between 2-D simulations and measurements of low frequency noise on InGaP-GaAs heterojunctions, at low as well as high injection levels, demonstrates the validity of the proposed simulation tool.
Numerical simulations of the thermoacoustic computed tomography breast imaging system
NASA Astrophysics Data System (ADS)
Kiser, William Lester, Jr.
A thermoacoustic wave is produced when an object absorbs energy and experiences a subsequent thermal expansion. We have developed a Thermoacoustic Computed Tomography (TACT) breast imaging system to exploit the thermoacoustic phenomena as a method of soft tissue imaging. By exposing the breast to short pulses of 434 MHz microwaves, ultrasonic pulses are generated and detected with a hemispherical transducer array submersed in a water bath. Filtering and back projecting the transducer signals generates a 3-D image that maps the localized microwave absorption properties of the breast. In an effort to understand the factors limiting image quality, the TACT system was numerically simulated. The simulations were used to generate the transducer signals that would be collected by the TACT system during a scan of an object. These simulated data streams were then fed into the system image reconstruction software to provide images of simulated phantoms. The effects of transducer diameter, transducer response, transducer array geometry and stimulating pulse width on the spatial and contrast resolution of the system were quantified using the simulations. The spatial resolution was highly dependent upon location in the imaging volume. This was due to the off axis response of transducers of finite aperture. Simulated data were compared with experimental data, obtained by imaging a parallel-piped resolution phantom, to verify the accuracy of the simulation code. A contrast-detail phantom was numerically simulated to determine the ability of the system to image spheres of diameters <1 cm with absorption values on the order of physiologic saline, when located in a background of noise. The results of the contrast-detail analysis were dependent on the location of the spheres in the imaging volume and the diameter of the simulated transducers. This work sets the foundation for the initial image quality studies of the TACT system. Improvements to the current imaging system, based on
Direct numerical simulation of inertial flows in porous media
NASA Astrophysics Data System (ADS)
Apte, S.; Finn, J.; Wood, B. D.
2010-12-01
At modest flow rates (10 ≤ Re ≤ 300) through porous media and packed beds, fluid inertia can result in complex steady and unsteady recirculation regions, dependent on the local pore geometry. Body fitted CFD is a broadly used design and analysis tool for flows in porous media and packed bed type reactors. Unfortunately, the inherent complexities of porous media make unstructured mesh generation a difficult and time consuming step in the simulation process. To accurately capture the inertial dynamics using high-fidelity direct simulations, body fitted meshes must be high quality and sufficiently refined. We present methods to parameterize and simplify mesh generation for packed beds, with an eye toward obtaining efficient mesh independence for Reynolds numbers in the inertial and unsteady regimes. The crux of mesh generation for packed beds is dealing with sphere-sphere or sphere-wall contact points, where a geometric singularity exists. To handle the sphere-sphere and sphere-wall contact points, we use a fillet bridge model, in which every pair of contacting entities are bridged by a fillet, eliminating a small fluid region near the contact point. This results in a continuous surface mesh which does not require resizing of the spheres and can accommodate prism cells for improved boundary layer resolution. A second order accurate, parallel, incompressible flow solver [Moin and Apte, AIAA J. 2006] is used to simulate flow through three different sphere packings: a periodic simple cubic packing, a wall bounded hexagonal close packing, and a randomly packed tube. Mesh independence is assessed using several measures including Ergun pressure drop coefficients, viscous and pressure components of drag force, kinetic energy, kinetic energy dissipation and interstitial velocity profiles. The results of these test cases are used to determine the feasibility of accurate and very large scale simulations of flow through a randomly packed bed of 103 pores. Preliminary results
NASA Technical Reports Server (NTRS)
Tamma, Kumar K.; Namburu, Raju R.
1989-01-01
Numerical simulations are presented for hyperbolic heat-conduction problems that involve non-Fourier effects, using explicit, Lax-Wendroff/Taylor-Galerkin FEM formulations as the principal computational tool. Also employed are smoothing techniques which stabilize the numerical noise and accurately predict the propagating thermal disturbances. The accurate capture of propagating thermal disturbances at characteristic time-step values is achieved; numerical test cases are presented which validate the proposed hyperbolic heat-conduction problem concepts.
Simulation of guided wave propagation near numerical Brillouin zones
NASA Astrophysics Data System (ADS)
Kijanka, Piotr; Staszewski, Wieslaw J.; Packo, Pawel
2016-04-01
Attractive properties of guided waves provides very unique potential for characterization of incipient damage, particularly in plate-like structures. Among other properties, guided waves can propagate over long distances and can be used to monitor hidden structural features and components. On the other hand, guided propagation brings substantial challenges for data analysis. Signal processing techniques are frequently supported by numerical simulations in order to facilitate problem solution. When employing numerical models additional sources of errors are introduced. These can play significant role for design and development of a wave-based monitoring strategy. Hence, the paper presents an investigation of numerical models for guided waves generation, propagation and sensing. Numerical dispersion analysis, for guided waves in plates, based on the LISA approach is presented and discussed in the paper. Both dispersion and modal amplitudes characteristics are analysed. It is shown that wave propagation in a numerical model resembles propagation in a periodic medium. Consequently, Lamb wave propagation close to numerical Brillouin zone is investigated and characterized.
Karatay, Elif; Druzgalski, Clara L; Mani, Ali
2015-05-15
Many microfluidic and electrochemical applications involve chaotic transport phenomena that arise due to instabilities stemming from coupling of hydrodynamics with ion transport and electrostatic forces. Recent investigations have revealed the contribution of a wide range of spatio-temporal scales in such electro-chaotic systems similar to those observed in turbulent flows. Given that these scales can span several orders of magnitude, significant numerical resolution is needed for accurate prediction of these phenomena. The objective of this work is to assess accuracy and efficiency of commercial software for prediction of such phenomena. We have considered the electroconvective flow induced by concentration polarization near an ion selective surface as a model problem representing chaotic elecrokinetic phenomena. We present detailed comparison of the performance of a general-purpose commercial computational fluid dynamics (CFD) and transport solver against a custom-built direct numerical simulation code that has been tailored to the specific physics of unsteady electrokinetic flows. We present detailed statistics including velocity and ion concentration spectra over a wide range of frequencies as well as time-averaged statistics and computational time required for each simulation. Our results indicate that while accuracy can be guaranteed with proper mesh resolution and avoiding numerical dissipation, commercial solvers are generally at least an order of magnitude slower than custom-built direct numerical simulation codes. PMID:25660706
Maudlin, P.J.; Stout, M.G.
1996-09-01
Strength and fracture constitutive relationships containing strain rate dependence and thermal softening are important for accurate simulation of metal cutting. The mechanical behavior of a hardened 4340 steel was characterized using the von Mises yield function, the Mechanical Threshold Stress model and the Johnson- Cook fracture model. This constitutive description was implemented into the explicit Lagrangian FEM continuum-mechanics code EPIC, and orthogonal plane-strain metal cutting calculations were performed. Heat conduction and friction at the toolwork-piece interface were included in the simulations. These transient calculations were advanced in time until steady state machining behavior (force) was realized. Experimental cutting force data (cutting and thrust forces) were measured for a planning operation and compared to the calculations. 13 refs., 6 figs.
Numerical Simulation of Screech Tones from Supersonic Jets: Physics and Prediction
NASA Technical Reports Server (NTRS)
Tam, Christopher K. W.; Zaman, Khairul Q. (Technical Monitor)
2002-01-01
The objectives of this project are to: (1) perform a numerical simulation of the jet screech phenomenon; and (2) use the data of the simulations to obtain a better understanding of the physics of jet screech. The original grant period was for three years. This was extended at no cost for an extra year to allow the principal investigator time to publish the results. We would like to report that our research work and results (supported by this grant) have fulfilled both objectives of the grant. The following is a summary of the important accomplishments: (1) We have now demonstrated that it is possible to perform accurate numerical simulations of the jet screech phenomenon. Both the axisymmetric case and the fully three-dimensional case were carried out successfully. It is worthwhile to note that this is the first time the screech tone phenomenon has been successfully simulated numerically; (2) All four screech modes were reproduced in the simulation. The computed screech frequencies and intensities were in good agreement with the NASA Langley Research Center data; (3) The staging phenomenon was reproduced in the simulation; (4) The effects of nozzle lip thickness and jet temperature were studied. Simulated tone frequencies at various nozzle lip thickness and jet temperature were found to agree well with experiments; (5) The simulated data were used to explain, for the first time, why there are two axisymmetric screech modes and two helical/flapping screech modes; (6) The simulated data were used to show that when two tones are observed, they co-exist rather than switching from one mode to the other, back and forth, as some previous investigators have suggested; and (7) Some resources of the grant were used to support the development of new computational aeroacoustics (CAA) methodology. (Our screech tone simulations have benefited because of the availability of these improved methods.)
Nielsen, Jens; D’Avezac, Mayeul; Hetherington, James; Stamatakis, Michail
2013-12-14
Ab initio kinetic Monte Carlo (KMC) simulations have been successfully applied for over two decades to elucidate the underlying physico-chemical phenomena on the surfaces of heterogeneous catalysts. These simulations necessitate detailed knowledge of the kinetics of elementary reactions constituting the reaction mechanism, and the energetics of the species participating in the chemistry. The information about the energetics is encoded in the formation energies of gas and surface-bound species, and the lateral interactions between adsorbates on the catalytic surface, which can be modeled at different levels of detail. The majority of previous works accounted for only pairwise-additive first nearest-neighbor interactions. More recently, cluster-expansion Hamiltonians incorporating long-range interactions and many-body terms have been used for detailed estimations of catalytic rate [C. Wu, D. J. Schmidt, C. Wolverton, and W. F. Schneider, J. Catal. 286, 88 (2012)]. In view of the increasing interest in accurate predictions of catalytic performance, there is a need for general-purpose KMC approaches incorporating detailed cluster expansion models for the adlayer energetics. We have addressed this need by building on the previously introduced graph-theoretical KMC framework, and we have developed Zacros, a FORTRAN2003 KMC package for simulating catalytic chemistries. To tackle the high computational cost in the presence of long-range interactions we introduce parallelization with OpenMP. We further benchmark our framework by simulating a KMC analogue of the NO oxidation system established by Schneider and co-workers [J. Catal. 286, 88 (2012)]. We show that taking into account only first nearest-neighbor interactions may lead to large errors in the prediction of the catalytic rate, whereas for accurate estimates thereof, one needs to include long-range terms in the cluster expansion.
Numerical simulation of H2/air detonation using unstructured mesh
NASA Astrophysics Data System (ADS)
Togashi, Fumiya; Löhner, Rainald; Tsuboi, Nobuyuki
2009-06-01
To explore the capability of unstructured mesh to simulate detonation wave propagation phenomena, numerical simulation of H2/air detonation using unstructured mesh was conducted. The unstructured mesh has several adv- antages such as easy mesh adaptation and flexibility to the complicated configurations. To examine the resolution dependency of the unstructured mesh, several simulations varying the mesh size were conducted and compared with a computed result using a structured mesh. The results show that the unstructured mesh solution captures the detailed structure of detonation wave, as well as the structured mesh solution. To capture the detailed detonation cell structure, the unstructured mesh simulations required at least twice, ideally 5times the resolution of structured mesh solution.
Numerical simulation of cavitating turbulent flow through a Francis turbine
NASA Astrophysics Data System (ADS)
Zhang, L.; Liu, J. T.; Wu, Y. L.; Liu, S. H.
2012-11-01
The unsteady cavitating turbulent flow in a Francis turbine is simulated based on governing equations of the mixture model for cavity-liquid two-phase flows with the RNG k-epsilon turbulence model in the present paper. An improved mass transfer expression in the mixture model is obtained based on evaporation and condensation mechanics with considering the effects of the non-dissolved gas, the turbulence, the tension of interface at cavity and the effect of phase change rate and so on. The governing equations of the mixture model for the unsteady cavitating-liquid flow is solved by a direct coupling method numerically with the finite volume method (FVM) using the unstructured tetrahedron grid and the structured hexahedral grid system. This direct coupling simulation was successfully applied to simulate the cavitating two-phase turbulent flow through a Francis turbine. The simulated external results agreed well with the experimental results.
Characterizing Electron Temperature Gradient Turbulence Via Numerical Simulation
Nevins, W M; Candy, J; Cowley, S; Dannert, T; Dimits, A; Dorland, W; Estrada-Mila, C; Hammett, G W; Jenko, F; Pueschel, M J; Shumaker, D E
2006-05-22
Numerical simulations of electron temperature gradient (ETG) turbulence are presented which characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasmaoperating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation techniques and convergence by benchmarking simulations of ETG turbulence from four microturbulence codes, demonstrating agreement on the electron heat flux, correlation functions, fluctuation intensity, and rms flow shear at fixed simulation cross section and resolution in the plane perpendicular to the magnetic field. Excellent convergence of both continuum and particle-in-cell codes with time step and velocity-space resolution is demonstrated, while numerical issues relating to perpendicular (to the magnetic field) simulation dimensions and resolution are discussed. A parameter scan in the magnetic shear, s, demonstrates that the adiabatic ion model is valid at small values of s (s < 0.4 for the parameters used in this scan) but breaks down at higher magnetic shear. A proper treatment employing gyrokinetic ions reveals a steady increase in the electron heat transport with increasing magnetic shear, reaching electron heat transport rates consistent with analyses of experimental tokamak discharges.
Numerical Simulation of Cast Distortion in Gas Turbine Engine Components
NASA Astrophysics Data System (ADS)
Inozemtsev, A. A.; Dubrovskaya, A. S.; Dongauser, K. A.; Trufanov, N. A.
2015-06-01
In this paper the process of multiple airfoilvanes manufacturing through investment casting is considered. The mathematical model of the full contact problem is built to determine stress strain state in a cast during the process of solidification. Studies are carried out in viscoelastoplastic statement. Numerical simulation of the explored process is implemented with ProCASTsoftware package. The results of simulation are compared with the real production process. By means of computer analysis the optimization of technical process parameters is done in order to eliminate the defect of cast walls thickness variation.
Direct numerical simulations of electrophoresis of charged colloids.
Kim, Kang; Nakayama, Yasuya; Yamamoto, Ryoichi
2006-05-26
We propose a numerical method to simulate electrohydrodynamic phenomena in charged colloidal dispersions. This method enables us to compute the time evolutions of colloidal particles, ions, and host fluids simultaneously by solving Newton, advection-diffusion, and Navier-Stokes equations so that the electrohydrodynamic couplings can be fully taken into account. The electrophoretic mobilities of charged spherical particles are calculated in several situations. The comparisons with approximation theories show quantitative agreements for dilute dispersions without any empirical parameters; however, our simulation predicts notable deviations in the case of dense dispersions. PMID:16803214
Numerical simulation of transition control in boundary layers
NASA Astrophysics Data System (ADS)
Laurien, E.; Kleiser, L.
The transition process from laminar to turbulent boundary layers is simulated by numerical integration of the 3D incompressible Navier-Stokes equations. Spatially periodic wave disturbances in a parallel Blasius flow are assumed. A spectral method with real-space Chebyshev collocation in the normal direction is employed. Both the classical K-type and the subharmonic type of transition are investigated. Good agreement with measurements and flow visualizations of transition experiments is obtained. Control of transition by wave superposition is simulated using periodic wall suction/blowing. It is shown that 2D control works well at an early stage but fails after significant 3D disturbances have developed.
Numerical Simulation of a Spatially Evolving Supersonic Turbulent Boundary Layer
NASA Technical Reports Server (NTRS)
Gatski, T. B.; Erlebacher, G.
2002-01-01
The results from direct numerical simulations of a spatially evolving, supersonic, flat-plate turbulent boundary-layer flow, with free-stream Mach number of 2.25 are presented. The simulated flow field extends from a transition region, initiated by wall suction and blowing near the inflow boundary, into the fully turbulent regime. Distributions of mean and turbulent flow quantities are obtained and an analysis of these quantities is performed at a downstream station corresponding to Re(sub x)= 5.548 x10(exp 6) based on distance from the leading edge.
Numerical simulation of the shock compaction of copper powder
Benson, D.J. ); Nellis, W.J. )
1994-07-10
The shock compaction of an aggregate of randomly distributed copper particles with a nonuniform size distribution is simulated using an Eulerian hydrocode. A shock Hugoniot for a copper powder is calculated from a series of shock compaction simulations and compared to experimental results. The powder particles are modeled as rods in two dimensions. The particle size distribution is generated from a representative powder size distribution via a simple Monte-Carlo method and is initially numerically packed to a dense powder compact using the pseudo-gravity method. [copyright] 1994 American Institute of Physics
Numerical simulation of the circulation of the atmosphere of Titan
NASA Technical Reports Server (NTRS)
Hourdin, F.; Levan, P.; Talagrand, O.; Courtin, Regis; Gautier, Daniel; Mckay, Christopher P.
1992-01-01
A three dimensional General Circulation Model (GCM) of Titan's atmosphere is described. Initial results obtained with an economical two dimensional (2D) axisymmetric version of the model presented a strong superrotation in the upper stratosphere. Because of this result, a more general numerical study of superrotation was started with a somewhat different version of the GCM. It appears that for a slowly rotating planet which strongly absorbs solar radiation, circulation is dominated by global equator to pole Hadley circulation and strong superrotation. The theoretical study of this superrotation is discussed. It is also shown that 2D simulations systemically lead to instabilities which make 2D models poorly adapted to numerical simulation of Titan's (or Venus) atmosphere.
Numerical simulation of three-dimensional tuft corona and electrohydrodynamics
Yamamoto, T.; Sparks, L.E.
1986-01-01
The numerical simulation of three-dimensional tuft corona and electrohydrodynamics (EHD) is discussed. The importance of high-voltage and low-current operation in the wire-duct precipitator has focused attention on collecting high-resistivity dust. The local current density of individual tufts is considerably higher even at a low average current level and, therefore, could contribute to both the formation of back corona in the collected-dust layer and the generation of the secondary flow. Numerical simulation for three-dimensional tuft corona is successfully solved. The electrical characteristics of tuft corona are investigated, and the structure and role of the three-dimensional secondary flow and EHD in relation to transport of the fine particles are described.
Development of a numerical simulation model of the cardiovascular system.
Geertsema, A A; Rakhorst, G; Mihaylov, D; Blanksma, P K; Verkerke, G J
1997-12-01
A numerical simulation model of the cardiovascular system has been developed. It consists of a model of the left atrium, the left ventricle, the coronary vascular system, the aorta, the arterial system, and the venous system. The input of the complete model is the elastance (pressure/volume ratio) developed by the left ventricle. The shape of this elastance is constant in different circumstances. Left ventricular (LV) myocardial oxygen consumption and the amount of oxygen offered to the left ventricle can be calculated with the model. The model has been validated using data from a patient suffering from coronary artery disease. The measured clinical hemodynamical waveforms could be fitted to those generated by the model. With the numerical simulation model, it is possible to predict the functioning of the left ventricle under different circumstances. This makes it possible to study in vitro various pathological clinical situations. PMID:9423983
Numerical simulation of the nonlinear optical response of bacteriorhodopsin
NASA Astrophysics Data System (ADS)
Kowalski, Gregory J.
1996-10-01
The numerical simulation of the nonlinear optical behavior of bacteriorhodopsin in a solution of water is described. Relationships for the intensity dependent absorption coefficient and index of refraction are developed and used in the numerical simulation of bacteriorhodopsin as an optical limiter and as defocussing element for laser pulses in the picosecond regime. The algorithm is a transient finite volume method that is coupled with a 'ray model' of the radiation which simultaneously solves the heat transfer and Maxwell's equations. The nonlinear behavior of the material is included in this analysis using a modified Euler predictor-corrector integration technique. Calculated power limiting and z-scan curves are in qualitative agreement with experiments. These results indicate that the code can be used to investigate and optimize optical systems which use the nonlinear behavior of bacteriorhodopsin.
Numerical aerodynamic simulation program long haul communications prototype
NASA Technical Reports Server (NTRS)
Cmaylo, Bohden K.; Foo, Lee
1987-01-01
This document is a report of the Numerical Aerodynamic Simulation (NAS) Long Haul Communications Prototype (LHCP). It describes the accomplishments of the LHCP group, presents the results from all LHCP experiments and testing activities, makes recommendations for present and future LHCP activities, and evaluates the remote workstation accesses from Langley Research Center, Lewis Research Center, and Colorado State University to Ames Research Center. The report is the final effort of the Long Haul (Wideband) Communications Prototype Plan (PT-1133-02-N00), 3 October 1985, which defined the requirements for the development, test, and operation of the LHCP network and was the plan used to evaluate the remote user bandwidth requirements for the Numerical Aerodynamic Simulation Processing System Network.
Simulating Prosthetic Heart Valve Hemodynamics: Numerical Model Development
NASA Astrophysics Data System (ADS)
Ge, Liang
2005-11-01
Since the first successful implantation of a prosthetic heart valve four decades ago, over 50 different designs have been developed including both mechanical and bio-prosthetic valves. Valve implants, however, are associated with increased risk of blood clotting, a trend which is believed to be linked to the complex hemodynamics induced by the prosthesis. To understand prosthetic valve hemodynamics under physiological conditions, we develop a numerical method capable of simulating flows in realistic prosthetic heart valves in anatomical geometries. The method employs a newly developed hybrid numerical technique that integrates the chimera overset grid approach with a Cartesian, sharp-interface immersed boundary methodology. The capabilities of the method are demonstrated by applying it to simulate pulsatile flow in both bileaflet and tri-leaflet valves moving with prescribed leaflet kinematics.
Numerical simulation of asymmetric particle precipitation by pitch angle diffusion
NASA Astrophysics Data System (ADS)
Thorne, Richard M.; Abel, Robert W.; Summers, Danny
1996-11-01
A numerical simulation code is developed to evaluate the loss rate of particles trapped in a mirror magnetic field geometry with asymmetric loss cones. The one-dimensional model can accommodate particle diffusion at any prescribed rate and loss cones of any prescribed sizes, and it incorporates the important effect of atmospheric backscattering. Numerical solutions for the loss cone particle distribution function calculated for the case of equal loss cones provide an acceptable simulation of the well-known modified Bessel function solution. The code provides the first quantitative solutions for any specified rate of pitch angle scattering for the general case of arbitrary asymmetry in loss cone size. In the case of weak or moderate diffusion the ratio of particle precipitation fluxes into the two loss cones can provide a sensitive measurement of the rate of particle scattering, but to utilize this important diagnostic property, one must also have information on the fraction of particles that are backscattered from the atmosphere.
Numerical Relativity Simulations for Black Hole Merger Astrophysics
NASA Technical Reports Server (NTRS)
Baker, John G.
2010-01-01
Massive black hole mergers are perhaps the most energetic astronomical events, establishing their importance as gravitational wave sources for LISA, and also possibly leading to observable influences on their local environments. Advances in numerical relativity over the last five years have fueled the development of a rich physical understanding of general relativity's predictions for these events. Z will overview the understanding of these event emerging from numerical simulation studies. These simulations elucidate the pre-merger dynamics of the black hole binaries, the consequent gravitational waveform signatures ' and the resulting state, including its kick velocity, for the final black hole produced by the merger. Scenarios are now being considered for observing each of these aspects of the merger, involving both gravitational-wave and electromagnetic astronomy.
De Vos, Maarten; De Lathauwer, Lieven; Vanrumste, Bart; Van Huffel, Sabine; Van Paesschen, W.
2007-01-01
Long-term electroencephalographic (EEG) recordings are important in the presurgical evaluation of refractory partial epilepsy for the delineation of the ictal onset zones. In this paper, we introduce a new concept for an automatic, fast, and objective localisation of the ictal onset zone in ictal EEG recordings. Canonical decomposition of ictal EEG decomposes the EEG in atoms. One or more atoms are related to the seizure activity. A single dipole was then fitted to model the potential distribution of each epileptic atom. In this study, we performed a simulation study in order to estimate the dipole localisation error. Ictal dipole localisation was very accurate, even at low signal-to-noise ratios, was not affected by seizure activity frequency or frequency changes, and was minimally affected by the waveform and depth of the ictal onset zone location. Ictal dipole localisation error using 21 electrodes was around 10.0 mm and improved more than tenfold in the range of 0.5–1.0 mm using 148 channels. In conclusion, our simulation study of canonical decomposition of ictal scalp EEG allowed a robust and accurate localisation of the ictal onset zone. PMID:18301715
NASA Technical Reports Server (NTRS)
Chaky, R. C.; Enoch, J.; Nonnast, J. H.
1982-01-01
A numerical simulation has been made of the 'pinhole effect' which produces the characteristic 'S-shaped' current-voltage curve. A disk-shaped conducting probe immersed in a plasma is modeled using a particle-in-cell (PIC) code. A probe partially covered by a very thin insulating layer is considered, as well as a probe mounted on an insulating disk. The simulation uses a cylindrical particle mover and allows for a variable number of particles in the system. The simulation space grid uses three different mesh sizes, the coarsest being away from the probe and the finest near the probe, in order to accurately calculate the trajectories of the simulation particles contributing the current to the probe and to the surface charge density on the dielectric. The calculation of the electrostatic potential is done self-consistently using successive over-relaxation (SOR). Backscattering and secondary electron emission are included for the case of positive probe voltage.
Numerical Simulations of the Geodynamo and Scaling Laws
NASA Astrophysics Data System (ADS)
Oruba, L.; Dormy, E.
2013-12-01
State of the art numerical models of the Geodynamo are still performed in a parameter regime extremely remote from the values relevant to the physics of the Earth core. In order to establish a connection between dynamo modeling and the geophysical motivation, it is necessary to use scaling laws. Such laws establish the dependency of essential quantities (such as the magnetic field strength) on measured or controlled quantities. They allow for a direct confrontation of advanced models with geophysical constraints. We will present a detailed analysis of scaling laws based on a wide database of 185 direct numerical simulations (courtesy of U. Christensen) and test various existing scaling laws. Our main concern is to stress the risks of a direct numerical fit free from physical insight. We show that different a priori hypothesis can yield contradictory dependences, in particular concerning the dependence of the magnetic field strength on the rotation rate as well as on the viscosity.
Numerical simulation of shock wave diffraction by TVD schemes
NASA Technical Reports Server (NTRS)
Young, Victor Y. C.; Yee, H. C.
1987-01-01
An upwind total variation diminishing (TVD) scheme and a predictor-corrector symmetric TVD scheme were used to numerically simulate the blast wave diffraction on a stationary object. The objective is to help design an optimum configuration so that lateral motion is minimized and at the same time vortex shedding and flow separation are reduced during a blast wave encounter. Results are presented for a generic configuration for both a coarse grid and a fine grid to illustrate the global and local diffraction flow fields. Numerical experiments for the shock wave reflection on a wedge are also included to validate the current approach. Numerical study indicated that these TVD schemes are more stable and produced higher shock resolution than classical shock capturing methods such as the explicit MacCormack scheme.
Numerical simulation for the high performance industrial reheating furnace design
Murakami, Hideki; Saito, Toshiaki; Hayashi, Junnichi; Hida, Atsushi
1999-07-01
The high performance industrial furnace, providing significant energy savings, low pollutant emission and high control ability on heating, has been developing. For designing the process, numerical simulations of a slab reheating furnace, with the advanced combustion system adopting highly preheated air have been performed, using a three-dimensional unsteady mathematical model. An essential feature of the model is the incorporation of the three-dimensional turbulent model (LES) and the Radiative Energy Absorption Distribution (READ) method. Numerical results has been verified with experimental results, velocity data of a water-model and heat flux data of a large unit furnace. The results have been, also, visualized by the thermal particle method. The numerical results lead to the conclusion that the regenerative burner system developed has the large advantage of heating slabs uniformly in a wide reheating furnace, and suggest possibility of a compact reheating furnace.
Numerical model for learning concepts of streamflow simulation
DeLong, L.L.
1993-01-01
Numerical models are useful for demonstrating principles of open-channel flow. Such models can allow experimentation with cause-and-effect relations, testing concepts of physics and numerical techniques. Four PT is a numerical model written primarily as a teaching supplement for a course in one-dimensional stream-flow modeling. Four PT options particularly useful in training include selection of governing equations, boundary-value perturbation, and user-programmable constraint equations. The model can simulate non-trivial concepts such as flow in complex interconnected channel networks, meandering channels with variable effective flow lengths, hydraulic structures defined by unique three-parameter relations, and density-driven flow.The model is coded in FORTRAN 77, and data encapsulation is used extensively to simplify maintenance and modification and to enhance the use of Four PT modules by other programs and programmers.
Numerical simulation and optimization of NO emissions in a precalciner
Lai Huang; Jidong Lu; Zhijuan Hu; Shijie Wang
2006-02-01
For cement plants, great attention is being given to the emission of the pollutant gases, especially NO. Because of the increasingly stringent emission constraints at cement plants, it is becoming more important to predict emissions accurately and then decrease the release quantity. The precalciner is an important apparatus in the cement production process, in that it can reduce not only the heat loading of the rotary kiln but also the NO emission, because of its relative low operating temperature. In this paper, the NO release was simulated based on the full-scale modeling for the precalciner and the model results were compared with measurements to validate the simulation models. The optimum cases of air staging and fuel staging were analyzed by executing a simulation technique on the restructuring precalciner with no effect on the operation process, and the conclusion is that the fuel staging case is the optimum method economically. 14 refs., 6 figs., 7 tabs.
NASA Technical Reports Server (NTRS)
Alter, Stephen J.; Brauckmann, Gregory J.; Kleb, William L.; Glass, Christopher E.; Streett, Craig L.; Schuster, David M.
2015-01-01
A transonic flow field about a Space Launch System (SLS) configuration was simulated with the Fully Unstructured Three-Dimensional (FUN3D) computational fluid dynamics (CFD) code at wind tunnel conditions. Unsteady, time-accurate computations were performed using second-order Delayed Detached Eddy Simulation (DDES) for up to 1.5 physical seconds. The surface pressure time history was collected at 619 locations, 169 of which matched locations on a 2.5 percent wind tunnel model that was tested in the 11 ft. x 11 ft. test section of the NASA Ames Research Center's Unitary Plan Wind Tunnel. Comparisons between computation and experiment showed that the peak surface pressure RMS level occurs behind the forward attach hardware, and good agreement for frequency and power was obtained in this region. Computational domain, grid resolution, and time step sensitivity studies were performed. These included an investigation of pseudo-time sub-iteration convergence. Using these sensitivity studies and experimental data comparisons, a set of best practices to date have been established for FUN3D simulations for SLS launch vehicle analysis. To the author's knowledge, this is the first time DDES has been used in a systematic approach and establish simulation time needed, to analyze unsteady pressure loads on a space launch vehicle such as the NASA SLS.
Numerical Simulations of the Metallicity Distribution in Dwarf Spheroidal Galaxies
Ripamonti, Emanuele; Tolstoy, E.; Helmi, A.; Battaglia, G.; Abel, T.; /KIPAC, Menlo Park
2006-12-12
Recent observations show that the number of stars with very low metallicities in the dwarf spheroidal satellites of the Milky Way is low, despite the low average metallicities of stars in these systems. We undertake numerical simulations of star formation and metal enrichment of dwarf galaxies in order to verify whether this result can be reproduced with ''standard'' assumptions. The answer is likely to be negative, unless some selection bias against very low metallicity stars is present in the observations.
Numerical simulation of flow in the wet scrubber for desulfurization
NASA Astrophysics Data System (ADS)
Novosád, Jan; Vít, Tomáš
2015-05-01
This article deals with numerical simulation of flow and chemical reactions in absorber for desulfurization of flue-gas. The objective of the work is the investigation of effect of different nozzles types and their placement in spray layers. These nozzles distribute lime suspension into flue gas stream. The research includes two types of nozzles and four different arrangements of nozzles and spray layers. Conclusion describes the effect of nozzle types and their arrangements on the suspension concentration in absorber.
Numerical simulation of melting ice around a floating by microwaves
NASA Astrophysics Data System (ADS)
Lakzian, Esmail; Parsian, Armin; Lakzian, Kazem
2016-03-01
In this paper a new method in using microwaves is provided for melting the ice around a floating equipment in a freezing condition in cold regions. The numerical simulation's results for validation are compared with the simple model's experimental data. Using microwave in melting the ice around a floating equipment is caused by lack of the mechanical wear, low energy dissipation factor and acceptable defrosting process speed in small lakes.
EXTENDED SCALING LAWS IN NUMERICAL SIMULATIONS OF MAGNETOHYDRODYNAMIC TURBULENCE
Mason, Joanne; Cattaneo, Fausto; Perez, Jean Carlos; Boldyrev, Stanislav E-mail: cattaneo@flash.uchicago.edu E-mail: boldyrev@wisc.edu
2011-07-10
Magnetized turbulence is ubiquitous in astrophysical systems, where it notoriously spans a broad range of spatial scales. Phenomenological theories of MHD turbulence describe the self-similar dynamics of turbulent fluctuations in the inertial range of scales. Numerical simulations serve to guide and test these theories. However, the computational power that is currently available restricts the simulations to Reynolds numbers that are significantly smaller than those in astrophysical settings. In order to increase computational efficiency and, therefore, probe a larger range of scales, one often takes into account the fundamental anisotropy of field-guided MHD turbulence, with gradients being much slower in the field-parallel direction. The simulations are then optimized by employing the reduced MHD equations and relaxing the field-parallel numerical resolution. In this work we explore a different possibility. We propose that there exist certain quantities that are remarkably stable with respect to the Reynolds number. As an illustration, we study the alignment angle between the magnetic and velocity fluctuations in MHD turbulence, measured as the ratio of two specially constructed structure functions. We find that the scaling of this ratio can be extended surprisingly well into the regime of relatively low Reynolds number. However, the extended scaling easily becomes spoiled when the dissipation range in the simulations is underresolved. Thus, taking the numerical optimization methods too far can lead to spurious numerical effects and erroneous representation of the physics of MHD turbulence, which in turn can affect our ability to identify correctly the physical mechanisms that are operating in astrophysical systems.
Boltzmann Fluctuations in Numerical Simulations of Nonequilibrium Lattice Threshold Systems
Rundle, J.B.; Klein, W.; Gross, S.; Turcotte, D.L.
1995-08-21
Nonequilibrium threshold systems such as slider blocks are now used to model a variety of dynamical systems, including earthquake faults, driven neural networks, and sliding charge density waves. We show that for general mean field models driven at low rates fluctuations in the internal energy field are characterized by Boltzmann statistics. Numerical simulations confirm this prediction. Our results indicate that mean field models can be effectively treated as equilibrium systems.
Numerical simulations of the decay of primordial magnetic turbulence
Kahniashvili, Tina; Brandenburg, Axel; Tevzadze, Alexander G.; Ratra, Bharat
2010-06-15
We perform direct numerical simulations of forced and freely decaying 3D magnetohydrodynamic turbulence in order to model magnetic field evolution during cosmological phase transitions in the early Universe. Our approach assumes the existence of a magnetic field generated either by a process during inflation or shortly thereafter, or by bubble collisions during a phase transition. We show that the final configuration of the magnetic field depends on the initial conditions, while the velocity field is nearly independent of initial conditions.
Zhao, A P; Cvetkovic, S R
1994-08-20
An efficient, accurate, and automated vectorial finite-element software package (named WAVEGIDE), which is implemented within a PDE/Protran problem-solving environment, has been extended to general multilayer anisotropic waveguides. With our system, through an interactive question-and-answer session, the problem can be simply defined with high-level PDE/Protran commands. The problem can then be solved easily and quickly by the main processor within this intelligent environment. In particular, in our system the eigenvalue of waveguide problems may be either a propagation constant (β) or an operated light frequency (F). Furthermore, the cutoff frequencies of propagation modes in waveguides can be calculated. As an application of this approach, numerical results for both scalar and hybrid modes in multilayer anisotropic waveguides are presented and are also compared with results obtained with the domain-integral method. These results clearly illustrate the unique flexibility, accuracy, and the ease of use f the WAVEGIDE program. PMID:20935964
Development of a carburizing and quenching simulation tool: numerical simulations of rings and gears
Anderson, C.; Godlman, P.; Rangaswamy, P.
1996-10-01
The ability to accurately calculate temperatures, stresses and metallurgical transformations in a single calculation or in a sequence of calculations is the key to prediction of distortion, residual stress and phase distribution in quench hardened automotive parts. Successful predictions in turn rely on the adequacy of the input data to the calculational procedure. These data include mechanical and thermal properties of the alloy phases over the range of temperature and strain rates experienced during the heat treat process, the mathematical description of the transformation kinetics, and the accuracy of the heat transfer boundary conditions. In this presentation we describe a calculational procedure using the ABAQUS{sup (1)} finite element code that simulates a carburizing and quench heat treat cycle for automotive gears. The calculational procedure features a numerically efficient 2-phase constitutive model, developed as part of the NCMS-Heat Treatment Distortion Prediction program, to represent transformational plasticity effects for the austenite/martensite Deformation together with refined finite element meshes to capture the steep gradients in stress and composition near the gear surfaces. The calculational procedure is illustrated on carburizing and quenching of a thick ring and comparison of model predictions for distortion, phase distribution, and residual stress with experimental measurements are discussed. Included in this model study is an investigation of the sensitivity of the predictions to mesh refinement.
NASA Astrophysics Data System (ADS)
Reckinger, Scott J.; Livescu, Daniel; Vasilyev, Oleg V.
2016-05-01
An investigation of compressible Rayleigh-Taylor instability (RTI) using Direct Numerical Simulations (DNS) requires efficient numerical methods, advanced boundary conditions, and consistent initialization in order to capture the wide range of scales and vortex dynamics present in the system, while reducing the computational impact associated with acoustic wave generation and the subsequent interaction with the flow. An advanced computational framework is presented that handles the challenges introduced by considering the compressive nature of RTI systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification dependent vorticity production. The foundation of the numerical methodology described here is the wavelet-based grid adaptivity of the Parallel Adaptive Wavelet Collocation Method (PAWCM) that maintains symmetry in single-mode RTI systems to extreme late-times. PAWCM is combined with a consistent initialization, which reduces the generation of acoustic disturbances, and effective boundary treatments, which prevent acoustic reflections. A dynamic time integration scheme that can handle highly nonlinear and potentially stiff systems, such as compressible RTI, completes the computational framework. The numerical methodology is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.
Numerical Simulation of Microbiological Growth in the Capillary Fringe
NASA Astrophysics Data System (ADS)
Hron, P.; Jost, D.; Engwer, C.; Ippisch, O.; Bastian, P.
2012-04-01
The capillary fringe (CF) is a highly dynamic zone in a porous media at the interface between water-saturated aquifer and vadose zone, where steep biogeochemical gradients and thus high bioactivities are expected. In recent years, considerable effort has been undertaken to deepen the understanding of the physical (flow, diffusion, dispersion), geochemical (dissolution, precipitation) and biological (metabolism, excretion, biofilm formation) processes in the CF. We developed a numerical simulator for multiphase multicomponent flow in porous media which is able to consider simultaneously multiphase flow, component transport, phase exchange, geochemical reactions and microbiological processes. A splitting approach for phase transport, component transport and reaction/phase exchanges allows the usage of higher-order discretizations for the component transport. This reduces numerical dispersion significantly, which is especially important in the simulation of reactive flow. In a flow-through laboratory experiment performed at the Karlsruhe Institute of Technology, Germany, within the project "Dynamic Capillary Fringes - A Multidisciplinary Approach", the oxygen phase transfer, the growth and the transport of a bacteria (green fluorescent Escherichia coli) were investigated. The results of numerical simulations of the E. coli growth in the CF with a high nutrient supply under steady-state and transient flow conditions are compared to the experimental data.
The numerical simulation based on CFD of hydraulic turbine pump
NASA Astrophysics Data System (ADS)
Duan, X. H.; Kong, F. Y.; Liu, Y. Y.; Zhao, R. J.; Hu, Q. L.
2016-05-01
As the functions of hydraulic turbine pump including self-adjusting and compensation with each other, it is far-reaching to analyze its internal flow by the numerical simulation based on CFD, mainly including the pressure field and the velocity field in hydraulic turbine and pump.The three-dimensional models of hydraulic turbine pump are made by Pro/Engineer software;the internal flow fields in hydraulic turbine and pump are simulated numerically by CFX ANSYS software. According to the results of the numerical simulation in design condition, the pressure field and the velocity field in hydraulic turbine and pump are analyzed respectively .The findings show that the static pressure decreases systematically and the pressure gradient is obvious in flow area of hydraulic turbine; the static pressure increases gradually in pump. The flow trace is regular in suction chamber and flume without spiral trace. However, there are irregular traces in the turbine runner channels which contrary to that in flow area of impeller. Most of traces in the flow area of draft tube are spiral.
Numerical Homogenization of Jointed Rock Masses Using Wave Propagation Simulation
NASA Astrophysics Data System (ADS)
Gasmi, Hatem; Hamdi, Essaïeb; Bouden Romdhane, Nejla
2014-07-01
Homogenization in fractured rock analyses is essentially based on the calculation of equivalent elastic parameters. In this paper, a new numerical homogenization method that was programmed by means of a MATLAB code, called HLA-Dissim, is presented. The developed approach simulates a discontinuity network of real rock masses based on the International Society of Rock Mechanics (ISRM) scanline field mapping methodology. Then, it evaluates a series of classic joint parameters to characterize density (RQD, specific length of discontinuities). A pulse wave, characterized by its amplitude, central frequency, and duration, is propagated from a source point to a receiver point of the simulated jointed rock mass using a complex recursive method for evaluating the transmission and reflection coefficient for each simulated discontinuity. The seismic parameters, such as delay, velocity, and attenuation, are then calculated. Finally, the equivalent medium model parameters of the rock mass are computed numerically while taking into account the natural discontinuity distribution. This methodology was applied to 17 bench fronts from six aggregate quarries located in Tunisia, Spain, Austria, and Sweden. It allowed characterizing the rock mass discontinuity network, the resulting seismic performance, and the equivalent medium stiffness. The relationship between the equivalent Young's modulus and rock discontinuity parameters was also analyzed. For these different bench fronts, the proposed numerical approach was also compared to several empirical formulas, based on RQD and fracture density values, published in previous research studies, showing its usefulness and efficiency in estimating rapidly the Young's modulus of equivalent medium for wave propagation analysis.
A new class of accurate, mesh-free hydrodynamic simulation methods
NASA Astrophysics Data System (ADS)
Hopkins, Philip F.
2015-06-01
We present two new Lagrangian methods for hydrodynamics, in a systematic comparison with moving-mesh, smoothed particle hydrodynamics (SPH), and stationary (non-moving) grid methods. The new methods are designed to simultaneously capture advantages of both SPH and grid-based/adaptive mesh refinement (AMR) schemes. They are based on a kernel discretization of the volume coupled to a high-order matrix gradient estimator and a Riemann solver acting over the volume `overlap'. We implement and test a parallel, second-order version of the method with self-gravity and cosmological integration, in the code GIZMO:1 this maintains exact mass, energy and momentum conservation; exhibits superior angular momentum conservation compared to all other methods we study; does not require `artificial diffusion' terms; and allows the fluid elements to move with the flow, so resolution is automatically adaptive. We consider a large suite of test problems, and find that on all problems the new methods appear competitive with moving-mesh schemes, with some advantages (particularly in angular momentum conservation), at the cost of enhanced noise. The new methods have many advantages versus SPH: proper convergence, good capturing of fluid-mixing instabilities, dramatically reduced `particle noise' and numerical viscosity, more accurate sub-sonic flow evolution, and sharp shock-capturing. Advantages versus non-moving meshes include: automatic adaptivity, dramatically reduced advection errors and numerical overmixing, velocity-independent errors, accurate coupling to gravity, good angular momentum conservation and elimination of `grid alignment' effects. We can, for example, follow hundreds of orbits of gaseous discs, while AMR and SPH methods break down in a few orbits. However, fixed meshes minimize `grid noise'. These differences are important for a range of astrophysical problems.
Draxl, C.; Churchfield, M.; Mirocha, J.; Lee, S.; Lundquist, J.; Michalakes, J.; Moriarty, P.; Purkayastha, A.; Sprague, M.; Vanderwende, B.
2014-06-01
Wind plant aerodynamics are influenced by a combination of microscale and mesoscale phenomena. Incorporating mesoscale atmospheric forcing (e.g., diurnal cycles and frontal passages) into wind plant simulations can lead to a more accurate representation of microscale flows, aerodynamics, and wind turbine/plant performance. Our goal is to couple a numerical weather prediction model that can represent mesoscale flow [specifically the Weather Research and Forecasting model] with a microscale LES model (OpenFOAM) that can predict microscale turbulence and wake losses.
SIVEH: numerical computing simulation of wireless energy-harvesting sensor nodes.
Sanchez, Antonio; Blanc, Sara; Climent, Salvador; Yuste, Pedro; Ors, Rafael
2013-01-01
The paper presents a numerical energy harvesting model for sensor nodes, SIVEH (Simulator I-V for EH), based on I-V hardware tracking. I-V tracking is demonstrated to be more accurate than traditional energy modeling techniques when some of the components present different power dissipation at either different operating voltages or drawn currents. SIVEH numerical computing allows fast simulation of long periods of time-days, weeks, months or years-using real solar radiation curves. Moreover, SIVEH modeling has been enhanced with sleep time rate dynamic adjustment, while seeking energy-neutral operation. This paper presents the model description, a functional verification and a critical comparison with the classic energy approach. PMID:24008287
Numerical Simulations of Single Flow Element in a Nuclear Thermal Thrust Chamber
NASA Technical Reports Server (NTRS)
Cheng, Gary; Ito, Yasushi; Ross, Doug; Chen, Yen-Sen; Wang, Ten-See
2007-01-01
The objective of this effort is to develop an efficient and accurate computational methodology to predict both detailed and global thermo-fluid environments of a single now element in a hypothetical solid-core nuclear thermal thrust chamber assembly, Several numerical and multi-physics thermo-fluid models, such as chemical reactions, turbulence, conjugate heat transfer, porosity, and power generation, were incorporated into an unstructured-grid, pressure-based computational fluid dynamics solver. The numerical simulations of a single now element provide a detailed thermo-fluid environment for thermal stress estimation and insight for possible occurrence of mid-section corrosion. In addition, detailed conjugate heat transfer simulations were employed to develop the porosity models for efficient pressure drop and thermal load calculations.
High-order accurate multi-phase simulations: building blocks and whats tricky about them
NASA Astrophysics Data System (ADS)
Kummer, Florian
2015-11-01
We are going to present a high-order numerical method for multi-phase flow problems, which employs a sharp interface representation by a level-set and an extended discontinuous Galerkin (XDG) discretization for the flow properties. The shape of the XDG basis functions is dynamically adapted to the position of the fluid interface, so that the spatial approximation space can represent jumps in pressure and kinks in velocity accurately. By this approach, the `hp-convergence' property of the classical discontinuous Galerkin (DG) method can be preserved for the low-regularity, discontinuous solutions, such as those appearing in multi-phase flows. Within the past years, several building blocks of such a method were presented: this includes numerical integration on cut-cells, the spatial discretization by the XDG method, precise evaluation of curvature and level-set algorithms tailored to the special requirements of XDG-methods. The presentation covers a short review on these building-block and their integration into a full multi-phase solver. A special emphasis is put on the discussion of the several pitfalls one may expire in the formulation of such a solver. German Research Foundation.
Restoration of cloud contaminated ocean color images using numerical simulation
NASA Astrophysics Data System (ADS)
Yang, Xuefei; Mao, Zhihua; Chen, Jianyu; Huang, Haiqing
2015-10-01
It is very hard to access cloud-free remote sensing data, especially for the ocean color images. A cloud removal approach from ocean color satellite images based on numerical modeling is introduced. The approach removes cloud-contaminated portions and then reconstructs the missing data utilizing model simulated values. The basic idea is to create the relationship between cloud-free patches and cloud-contaminated patches under the assumption that both of them are influenced by the same marine hydrodynamic conditions. Firstly, we find cloud-free GOCI (the Geostationary Ocean Color Imager) retrieved suspended sediment concentrations (SSC) in the East China Sea before and after the time of cloudy images, which are set as initial field and validation data for numerical model, respectively. Secondly, a sediment transport model based on COHERENS, a coupled hydrodynamic-ecological ocean model for regional and shelf seas, is configured. The comparison between simulated results and validation images show that the sediment transport model can be used to simulate actual sediment distribution and transport in the East China Sea. Then, the simulated SSCs corresponding to the cloudy portions are used to remove the cloud and replace the missing values. Finally, the accuracy assessments of the results are carried out by visual and statistical analysis. The experimental results demonstrate that the proposed method can effectively remove cloud from GOCI images and reconstruct the missing data, which is a new way to enhance the effectiveness and availability of ocean color data, and is of great practical significance.
Towards an Automated Full-Turbofan Engine Numerical Simulation
NASA Technical Reports Server (NTRS)
Reed, John A.; Turner, Mark G.; Norris, Andrew; Veres, Joseph P.
2003-01-01
The objective of this study was to demonstrate the high-fidelity numerical simulation of a modern high-bypass turbofan engine. The simulation utilizes the Numerical Propulsion System Simulation (NPSS) thermodynamic cycle modeling system coupled to a high-fidelity full-engine model represented by a set of coupled three-dimensional computational fluid dynamic (CFD) component models. Boundary conditions from the balanced, steady-state cycle model are used to define component boundary conditions in the full-engine model. Operating characteristics of the three-dimensional component models are integrated into the cycle model via partial performance maps generated automatically from the CFD flow solutions using one-dimensional meanline turbomachinery programs. This paper reports on the progress made towards the full-engine simulation of the GE90-94B engine, highlighting the generation of the high-pressure compressor partial performance map. The ongoing work will provide a system to evaluate the steady and unsteady aerodynamic and mechanical interactions between engine components at design and off-design operating conditions.
Direct numerical simulation of nonpremixed flame-wall interactions
Wang, Yi; Trouve, Arnaud
2006-02-01
The objective of the present study is to use detailed numerical modeling to obtain basic information on the interaction of nonpremixed flames with cold wall surfaces. The questions of turbulent fuel-air-temperature mixing, flame extinction, and wall-surface heat transfer are studied using direct numerical simulation (DNS). The DNS configuration corresponds to an ethylene-air diffusion flame stabilized in the near-wall region of a chemically inert solid surface. Simulations are performed with adiabatic or isothermal wall boundary conditions and with different turbulence intensities. The simulations feature flame extinction events resulting from excessive wall cooling and convective heat transfer rates up to 90 kW/m{sup 2}. The structure of the simulated wall flames is studied in terms of a classical mass-mixing variable, the fuel-air based mixture fraction, and a less familiar heat loss variable, the excess enthalpy variable, introduced to provide a measure of nonadiabatic behavior due to wall cooling. In addition to the flame structure, extinction events are also studied in detail and a modified flame extinction criterion that combines the concepts of mixture fraction and excess enthalpy is proposed and then tested against the DNS data. (author)
Numerical Simulation of Ferrofluid Flow for Subsurface Environmental Engineering Applications
Oldenburg, Curtis M.; Borglin, Sharon E.; Moridis, George J.
1997-05-05
Ferrofluids are suspensions of magnetic particles of diameter approximately 10 nm stabilized by surfactants in carrier liquids. The large magnetic susceptibility of ferrofluids allows the mobilization of ferrofluid through permeable rock and soil by the application of strong external magnetic fields. We have developed simulation capabilities for both miscible and immiscible conceptualizations of ferrofluid flow through porous media in response to magnetic forces arising from the magnetic field of a rectangular permanent magnet. The flow of ferrofluid is caused by the magnetization of the particles and their attraction toward a magnet, regardless of the orientation of the magnet. The steps involved in calculating the flow of ferrofluid are (1) calculation of the external magnetic field, (2) calculation of the gradient of the external magnetic field, (3) calculation of the magnetization of the ferrofluid, and (4) assembly of the magnetic body force term and addition of this term to the standard pressure gradient and gravity force terms. We compare numerical simulations to laboratory measurements of the magnetic field, fluid pressures, and the two-dimensional flow of ferrofluid to demonstrate the applicability of the methods coded in the numerical simulators. We present an example of the use of the simulator for a field-scale application of ferrofluids for barrier verification.
Numerical simulation of supersonic wake flow with parallel computers
Wong, C.C.; Soetrisno, M.
1995-07-01
Simulating a supersonic wake flow field behind a conical body is a computing intensive task. It requires a large number of computational cells to capture the dominant flow physics and a robust numerical algorithm to obtain a reliable solution. High performance parallel computers with unique distributed processing and data storage capability can provide this need. They have larger computational memory and faster computing time than conventional vector computers. We apply the PINCA Navier-Stokes code to simulate a wind-tunnel supersonic wake experiment on Intel Gamma, Intel Paragon, and IBM SP2 parallel computers. These simulations are performed to study the mean flow in the near wake region of a sharp, 7-degree half-angle, adiabatic cone at Mach number 4.3 and freestream Reynolds number of 40,600. Overall the numerical solutions capture the general features of the hypersonic laminar wake flow and compare favorably with the wind tunnel data. With a refined and clustering grid distribution in the recirculation zone, the calculated location of the rear stagnation point is consistent with the 2D axisymmetric and 3D experiments. In this study, we also demonstrate the importance of having a large local memory capacity within a computer node and the effective utilization of the number of computer nodes to achieve good parallel performance when simulating a complex, large-scale wake flow problem.
Numerical Simulation of Delamination Growth in Composite Materials
NASA Technical Reports Server (NTRS)
Camanho, P. P.; Davila, C. G.; Ambur, D. R.
2001-01-01
The use of decohesion elements for the simulation of delamination in composite materials is reviewed. The test methods available to measure the interfacial fracture toughness used in the formulation of decohesion elements are described initially. After a brief presentation of the virtual crack closure technique, the technique most widely used to simulate delamination growth, the formulation of interfacial decohesion elements is described. Problems related with decohesion element constitutive equations, mixed-mode crack growth, element numerical integration and solution procedures are discussed. Based on these investigations, it is concluded that the use of interfacial decohesion elements is a promising technique that avoids the need for a pre-existing crack and pre-defined crack paths, and that these elements can be used to simulate both delamination onset and growth.
Numerical simulation of hydrogen plasma in MPCVD reactor
NASA Astrophysics Data System (ADS)
Huang, Di
A numerical study was conducted to build a model able to estimate the plasma properties under different working conditions for pure hydrogen plasma in a MPCVD reactor. A plasma model based on standing wave assumption and a linear estimation of ne and coupled the EM simulation, heat transfer simulation and UDF calculations of plasma properties was built in COMSOL Muitiphysics and tested with six different working conditions. The reliability of COMSOL EM solver was tested through comparing the simulation results with a benchmark EM solver, ANSYS HFSS. The validities of two assumptions made about the electrical field, standing wave assumption and sinusoidal oscillation field assumption, were tested by a PDE solver in COMSOL for utilizing the drift-diffusion model of ne.
Numerical simulation of radiative heat loss in an experimental burner
Cloutman, L.D.; Brookshaw, L.
1993-09-01
We describe the numerical algorithm used in the COYOTE two-dimensional, transient, Eulerian hydrodynamics program to allow for radiative heat losses in simulations of reactive flows. The model is intended primarily for simulations of industrial burners, but it is not confined to that application. It assumes that the fluid is optically thin and that photons created by the fluid immediately escape to free space or to the surrounding walls, depending upon the application. The use of the model is illustrated by simulations of a laboratory-scale experimental burner. We find that the radiative heat losses reduce the local temperature of the combustion products by a modest amount, typically on the order of 50 K. However, they have a significant impact on NO{sub x} production.
Numerical simulation of plasma processes driven by transverse ion heating
NASA Technical Reports Server (NTRS)
Singh, Nagendra; Chan, C. B.
1993-01-01
The plasma processes driven by transverse ion heating in a diverging flux tube are investigated with numerical simulation. The heating is found to drive a host of plasma processes, in addition to the well-known phenomenon of ion conics. The downward electric field near the reverse shock generates a doublestreaming situation consisting of two upflowing ion populations with different average flow velocities. The electric field in the reverse shock region is modulated by the ion-ion instability driven by the multistreaming ions. The oscillating fields in this region have the possibility of heating electrons. These results from the simulations are compared with results from a previous study based on a hydrodynamical model. Effects of spatial resolutions provided by simulations on the evolution of the plasma are discussed.
Numerical simulation of experiments in the Giant Planet Facility
NASA Technical Reports Server (NTRS)
Green, M. J.; Davy, W. C.
1979-01-01
Utilizing a series of existing computer codes, ablation experiments in the Giant Planet Facility are numerically simulated. Of primary importance is the simulation of the low Mach number shock layer that envelops the test model. The RASLE shock-layer code, used in the Jupiter entry probe heat-shield design, is adapted to the experimental conditions. RASLE predictions for radiative and convective heat fluxes are in good agreement with calorimeter measurements. In simulating carbonaceous ablation experiments, the RASLE code is coupled directly with the CMA material response code. For the graphite models, predicted and measured recessions agree very well. Predicted recession for the carbon phenolic models is 50% higher than that measured. This is the first time codes used for the Jupiter probe design have been compared with experiments.
Numerical simulations of Kadomtsev-Petviashvili soliton interactions
NASA Astrophysics Data System (ADS)
Infeld, E.; Senatorski, A.; Skorupski, A. A.
1995-04-01
The Kadomtsev-Petviashvili equation generalizes that of Korteweg and de Vries to two space dimensions and arises in various weakly dispersive media. Two very different species of soliton solutions are known for one variant, KPI. The first species to be discovered are line solitons, the second are two dimensional lumps. This paper describes numerical simulations, consistent with all constraints of the equation, in which very distorted line solitons break up into smaller line solitons and arrays of lumps. The arrays can interact with one another. In some cases, aspects of the results of the simulations can be understood in the light of specially constructed exact solutions. Simulations in which initial conditions fail to satisfy the constraints of the equation are also described.
Numerical simulation of a compressible homogeneous, turbulent shear flow
NASA Astrophysics Data System (ADS)
Feiereisen, W. J.; Reynolds, W. C.; Ferziger, J. H.
1981-03-01
A direct, low Reynolds number, numerical simulation was performed on a homogeneous turbulent shear flow. The full compressible Navier-Stokes equations were used in a simulation on the ILLIAC IV computer with a 64,000 mesh. The flow fields generated by the code are used as an experimental data base, to examine the behavior of the Reynols stresses in this simple, compressible flow. The variation of the structure of the stresses and their dynamic equations as the character of the flow changed is emphasized. The structure of the tress tensor is more heavily dependent on the shear number and less on the fluctuating Mach number. The pressure-strain correlation tensor in the dynamic uations is directly calculated in this simulation. These correlations are decomposed into several parts, as contrasted with the traditional incompressible decomposition into two parts. The performance of existing models for the conventional terms is examined, and a model is proposed for the 'mean fluctuating' part.
Numerical Simulation of Liquid Nitrogen Chilldown of a Vertical Tube
NASA Technical Reports Server (NTRS)
Darr, Samuel; Hu, Hong; Schaeffer, Reid; Chung, Jacob; Hartwig, Jason; Majumdar, Alok
2015-01-01
This paper presents the results of a one-dimensional numerical simulation of the transient chilldown of a vertical stainless steel tube with liquid nitrogen. The direction of flow is downward (with gravity) through the tube. Heat transfer correlations for film, transition, and nucleate boiling, as well as critical heat flux, rewetting temperature, and the temperature at the onset of nucleate boiling were used to model the convection to the tube wall. Chilldown curves from the simulations were compared with data from 55 recent liquid nitrogen chilldown experiments. With these new correlations the simulation is able to predict the time to rewetting temperature and time to onset of nucleate boiling to within 25% for mass fluxes ranging from 61.2 to 1150 kg/(sq m s), inlet pressures from 175 to 817 kPa, and subcooled inlet temperatures from 0 to 14 K below the saturation temperature.
Numerical simulation and modeling of combustion in scramjets
NASA Astrophysics Data System (ADS)
Clark, Ryan James
In the last fifteen years the development of a viable scramjet has quickly approached the following long term goals: responsive sub-orbital space access; long-range, prompt global strike; and high-speed transportation. Nonetheless, there are significant challenges that need to be resolved. These challenges include high skin friction drag and high heat transfer rates, inherent to vehicles in sustained, hypersonic flight. Another challenge is sustaining combustion. Numerical simulation and modeling was performed to provide insight into reducing skin friction drag and sustaining combustion. Numerical simulation was used to investigate boundary layer combustion, which has been shown to reduce skin friction drag. The objective of the numerical simulations was to quantify the effect of fuel injection parameters on boundary layer combustion and ultimately on the change in the skin friction coefficient and heat transfer rate. A qualitative analysis of the results suggest that the reduction in the skin friction coefficient depends on multiple parameters and potentially an interaction between parameters. Sustained combustion can be achieved through a stabilized detonation wave. Additionally, stabilizing a detonation wave will yield rapid combustion. This will allow for a shorter and lighter-weight engine system, resulting in less required combustor cooling. A stabilized detonation wave was numerically modeled for various inlet and geometric cases. The effect of fuel concentration, inlet Mach number, and geometric configuration on the stability of a detonation wave was quantified. Correlations were established between fuel concentration, inlet speed, geometric configuration and parameters characterizing the detonation wave. A linear relationship was quantified between the fuel concentration and the parameters characterizing the detonation wave.
Assessing the numerical dissipation rate and viscosity in CFD simulations of fluid flows
NASA Astrophysics Data System (ADS)
Schranner, F. S.; Domaradzki, J. A.; Hickel, S.; Adams, N. A.
2014-11-01
We describe a method for quantifying the effective numerical dissipation rate and the effective numerical viscosity in Computational Fluid Dynamics simulations. Differently from the previous approach that was formulated in spectral space, the proposed method is developed in a physical-space representation and allows for determining numerical dissipation rates and viscosities locally, i.e., at the individual cell level or for arbitrary subdomains of the computational domain. The method is self-contained using only results produced by the Navier-Stokes solver being investigated. Since no extraneous information is required, the method is suitable for a straightforward quantification of the numerical dissipation as a post-processing step. We demonstrate the method's capabilities on the example of implicit large-eddy simulations of three-dimensional Taylor-Green vortex flows that exhibit laminar, transitional, and turbulent flow behavior at different stages of time evolution. For validation, we compare the numerical dissipation rate obtained using this method with exact reference data obtained with an accurate, spectral-space approach. Supported by Deutsche Forschungsgemeinschaft and Alexander von Humboldt Foundation.
Numerical Simulation of the Behavior of Falling Films on Horizontal Plain Tubes
NASA Astrophysics Data System (ADS)
Lei, X. L.; Li, H. X.
2010-03-01
In this paper, a numerical simulation is performed in order to reveal the evaporation heating transfer mechanism of the falling-film of water on the outer wall of horizontal tubes, and the influence of gas-water-solid contact angles on the film distribution on the tube is mainly addressed. The simulation is performed by solving the motion equation of the fluid on fixed three-dimensional (3D) grid systems, and the so-called volume of fluid (VOF) method is employed to handle the movement of interface between the liquid and the vapor phase. The numerical results are compared with that of a simplified model and also with the experimental recordings obtained in visualization experiments conducted with tubes made of different materials, and it is shown that the numerical results are in very good agreement with the experimental observation of the falling films, indicating that the numerical methods applied in the present study is correct and accurate. Based on the numerical results, effects of the contact angle, the flow rate, the tube diameter and the liquid feeder height on the falling film behavior are discussed. Generally, the film width increases along with the increase of flow rate or the liquid feeder height, while variation of the film thickness exhibits different features at different conditions, and the contact angle is one of the major factors governing the behavior of the falling films.
Lee, M.W.; Meuwly, M.
2013-01-01
The evaluation of hydration free energies is a sensitive test to assess force fields used in atomistic simulations. We showed recently that the vibrational relaxation times, 1D- and 2D-infrared spectroscopies for CN(-) in water can be quantitatively described from molecular dynamics (MD) simulations with multipolar force fields and slightly enlarged van der Waals radii for the C- and N-atoms. To validate such an approach, the present work investigates the solvation free energy of cyanide in water using MD simulations with accurate multipolar electrostatics. It is found that larger van der Waals radii are indeed necessary to obtain results close to the experimental values when a multipolar force field is used. For CN(-), the van der Waals ranges refined in our previous work yield hydration free energy between -72.0 and -77.2 kcal mol(-1), which is in excellent agreement with the experimental data. In addition to the cyanide ion, we also study the hydroxide ion to show that the method used here is readily applicable to similar systems. Hydration free energies are found to sensitively depend on the intermolecular interactions, while bonded interactions are less important, as expected. We also investigate in the present work the possibility of applying the multipolar force field in scoring trajectories generated using computationally inexpensive methods, which should be useful in broader parametrization studies with reduced computational resources, as scoring is much faster than the generation of the trajectories.
Lee, Myung Won; Meuwly, Markus
2013-12-14
The evaluation of hydration free energies is a sensitive test to assess force fields used in atomistic simulations. We showed recently that the vibrational relaxation times, 1D- and 2D-infrared spectroscopies for CN(-) in water can be quantitatively described from molecular dynamics (MD) simulations with multipolar force fields and slightly enlarged van der Waals radii for the C- and N-atoms. To validate such an approach, the present work investigates the solvation free energy of cyanide in water using MD simulations with accurate multipolar electrostatics. It is found that larger van der Waals radii are indeed necessary to obtain results close to the experimental values when a multipolar force field is used. For CN(-), the van der Waals ranges refined in our previous work yield hydration free energy between -72.0 and -77.2 kcal mol(-1), which is in excellent agreement with the experimental data. In addition to the cyanide ion, we also study the hydroxide ion to show that the method used here is readily applicable to similar systems. Hydration free energies are found to sensitively depend on the intermolecular interactions, while bonded interactions are less important, as expected. We also investigate in the present work the possibility of applying the multipolar force field in scoring trajectories generated using computationally inexpensive methods, which should be useful in broader parametrization studies with reduced computational resources, as scoring is much faster than the generation of the trajectories. PMID:24170171
Time Accurate CFD Simulations of the Orion Launch Abort Vehicle in the Transonic Regime
NASA Technical Reports Server (NTRS)
Rojahn, Josh; Ruf, Joe
2011-01-01
Significant asymmetries in the fluid dynamics were calculated for some cases in the CFD simulations of the Orion Launch Abort Vehicle through its abort trajectories. The CFD simulations were performed steady state and in three dimensions with symmetric geometries, no freestream sideslip angle, and motors firing. The trajectory points at issue were in the transonic regime, at 0 and +/- 5 angles of attack with the Abort Motors with and without the Attitude Control Motors (ACM) firing. In some of the cases the asymmetric fluid dynamics resulted in aerodynamic side forces that were large enough that would overcome the control authority of the ACMs. MSFC's Fluid Dynamics Group supported the investigation into the cause of the flow asymmetries with time accurate CFD simulations, utilizing a hybrid RANS-LES turbulence model. The results show that the flow over the vehicle and the subsequent interaction with the AB and ACM motor plumes were unsteady. The resulting instantaneous aerodynamic forces were oscillatory with fairly large magnitudes. Time averaged aerodynamic forces were essentially symmetric.
Direct numerical simulation of sharkskin denticles in turbulent channel flow
NASA Astrophysics Data System (ADS)
Boomsma, A.; Sotiropoulos, F.
2016-03-01
The hydrodynamic function of sharkskin has been under investigation for the past 30 years. Current literature conflicts on whether sharkskin is able to reduce skin friction similar to riblets. To contribute insights toward reconciling these conflicting views, direct numerical simulations are carried out to obtain detailed flow fields around realistic denticles. A sharp interface immersed boundary method is employed to simulate two arrangements of actual sharkskin denticles (from Isurus oxyrinchus) in a turbulent boundary layer at Reτ ≈ 180. For comparison, turbulent flow over drag-reducing scalloped riblets is also simulated with similar flow conditions and with the same numerical method. Although the denticles resemble riblets, both sharkskin arrangements increase total drag by 44%-50%, while the riblets reduce drag by 5%. Analysis of the simulated flow fields shows that the turbulent flow around denticles is highly three-dimensional and separated, with 25% of the total drag being form drag. The complex three-dimensional shape of the denticles gives rise to a mean flow dominated by strong secondary flows in sharp contrast with the mean flow generated by riblets, which is largely two-dimensional. The so resulting three-dimensionality of sharkskin flows leads to an increase in the magnitude of the turbulent statistics near the denticles, which further contributes to increasing the total drag. The simulations also show that, at least for the simulated arrangements, sharkskin, in sharp contrast with drag-reducing riblets, is unable to isolate high shear stress near denticle ridges causing a significant portion of the denticle surface to be exposed to high mean shear.
Numerical Model Simulation of Atmosphere above A.C. Airport
NASA Astrophysics Data System (ADS)
Lutes, Tiffany; Trout, Joseph
2014-03-01
In this research project, the Weather Research & Forecasting (WRF) model from the National Center for Atmospheric Research (NCAR) is used to investigate past and present weather conditions. The Atlantic City Airport area in southern New Jersey is the area of interest. Long-term hourly data is analyzed and model simulations are created. By inputting high resolution surface data, a more accurate picture of the effects of different weather conditions will be portrayed. Currently, the impact of gridded model runs is being tested, and the impact of surface characteristics is being investigated.
High order numerical simulations of the Richtmyer- Meshkov instability in a relativistic fluid
NASA Astrophysics Data System (ADS)
Zanotti, O.; Dumbser, M.
2015-07-01
We study the Richtmyer-Meshkov (RM) instability of a relativistic perfect fluid by means of high order numerical simulations with adaptive mesh refinement (AMR). The numerical scheme combines a finite volume reconstruction in space, a local space-time discontinuous Galerkin predictor method, a high order one-step time update scheme, and a "cell-by-cell" space-time AMR strategy with time-accurate local time stepping. In this way, third order accurate (both in space and in time) numerical simulations of the RM instability are performed, spanning a wide parameter space. We present results both for the case in which a light fluid penetrates into a higher density one (Atwood number A > 0) and for the case in which a heavy fluid penetrates into a lower density one (Atwood number A < 0). We find that for large Lorentz factors γs of the incident shock wave, the relativistic RM instability is substantially weakened and ultimately suppressed. More specifically, the growth rate of the RM instability in the linear phase has a local maximum which occurs at a critical value of γs ≈ [1.2, 2]. Moreover, we have also revealed a genuinely relativistic effect, absent in Newtonian hydrodynamics, which arises in three dimensional configurations with a non-zero velocity component tangent to the incident shock front. In particular, in A > 0 models, the tangential velocity has a net magnification effect, while in A < 0 models, the tangential velocity has a net suppression effect.
Numerical simulation of airflow in the human nose.
Weinhold, Ivo; Mlynski, Gunter
2004-09-01
Unobstructed air passageways as well as sufficient contact of the air stream with the mucous membrane are essential for the correct function of the nose. For that, local flow phenomena, which often cannot be captured by standard diagnostic methods, are important. We developed and validated a method for the numerical simulation of the nasal airflow. Two anatomically correct, transparent resin models of human nasal cavities, manufactured by a special casting technology, and the nasal cavities of two patients were reconstructed as Computer Aided Design models based on computed tomography (CT) scans. One of the nasal models and one clinical case represented a normal nasal anatomy, while the others were examples of pathological alterations. The velocity and pressure fields in these reconstructed cavities were calculated for the entire range of physiological nasal inspiration using commercially available computational fluid dynamics software. To validate the results rhinoresistometric data were measured and characteristic streamlines were videotaped for the resin models. The numerical results were in good agreement with the experimental data for the investigated cases. An example of a complex clinical case demonstrates the potential benefit of the developed simulation method for rhinosurgical planning. The results support the assumption that even under the specific conditions of the clinical practice the application of numerical simulation of nasal airflow phenomena may become realistic in the near future. However, important technical issues such as a completely automated reconstruction of the nasal cavity still need to be resolved before such simulations are efficient and cost effective enough to become a standard tool for the rhinologist. PMID:14652769
Numerical simulations of waves in a magnetically structured atmosphere
NASA Astrophysics Data System (ADS)
Espinola, Thomas Peter
A physical model for simulating waves in a stellar atmosphere was developed from a combination of basic fluid mechanics, plasma physics, and electrodynamics. The model was three dimensional and included the effects of gravity, magnetic fields, and viscosity. An algorithm was developed to numerically implement this model. The resulting program used an explicit time integration scheme based on Runge-Kutta and a combination of finite difference and spectral methods to evaluate the spatial derivatives. A number of numerical boundary conditions were developed—the most successful used a modified Sommerfeld radiation condition. The program was written and coded in Fortran on a Vax computer. Additional routines were written to evaluate the required fast fourier transforms and to graph and display the data. The program was tested on a large number of one and two dimensional problems for which the solutions were known. These problems included acoustic waves, Alfvén waves, magnetoacoustic waves, shocks, rarefactions, and contact discontinuities. The numerical results agreed with the analytic solutions of the physical problems to within the precision requested of the simulation. The program proved to be stable and robust for all the problems attempted. This program was then used to simulate three problems for which analytic solutions are not known. All three simulations concerned the propagation of waves in magnetically structured atmospheres and may be applied to outstanding problems in solar physics. First, the interactions of non-linear waves and a flux slab were studied. From the result it is apparent that sources of shocks and rarefactions, such as the solar convection zone, do not concentrate the magnetic field in flux sheaths. Next I used the program to simulate the interaction of non-linear waves with a flux tube. The results suggest that the magnetic fields in flux tubes are also not concentrated by pairs of passing shocks and rarefactions; however, a complete
Field Study and Numerical Simulation of Sub Slab Ventilation Systems
Bonnefous, Y.C.; Gadgil, A.J.; Fisk, W.J.; Prill, R.J.; Nematollahi, A.R.
1992-05-01
The effectiveness of the technique of subslab ventilation (SSV) for limiting radon entry into basements was investigated through complementary experimentation and numerical modeling. Subslab pressure fields resulting from SSV were measured in six well-characterized basements, each with a different combination of soil and aggregate permeability. The relationship between air velocity and pressure gradient was measured in the laboratory for the three types of aggregate installed beneath the basement slabs. A new numerical model of SSV was developed and verified with the field data. This model simulates non-Darcy flow in the aggregate. We demonstrate that non-Darcy effects significantly impact SSV performance. Field data and numerical simulations indicate that increasing the aggregate permeability within the investigated range of 2 x 10{sup -8} m{sup 2} to 3 x 10{sup -7} m{sup 2} substantially improves the extension of the subslab pressure field due to SSV operation. Sealing of cracks in the slab and excavation of a small pit where the SSV pipe penetrates the slab also dramatically improve this pressure field extension. Our findings are consistent with the results of prior field studies; however, the studies reported here have improved our understanding of factors affecting SSV performance. The dependence of SSV performance on the relevant parameters are currently under investigation with the model.
Towards direct numerical simulation of freely swimming fish.
NASA Astrophysics Data System (ADS)
Curet, Oscar; Patankar, Neelesh; Maciver, Malcolm
2006-11-01
Swimming mechanisms employed by fish are currently inspiring unique underwater vehicles and robotic devices as well as basic science research into the neural control of movement. Key engineering issues include propulsion efficiency, precise motion control and maneuverability. A numerical scheme that simulates the motion of freely swimming fish will be a valuable design and research tool. We are working towards this goal. In particular we are interested in simulating the motion of a gymnotiform fish that swims by producing undulations of a ventral ribbon fin while keeping its body rigid. We model the fish as a rigid body with an attached undulating membrane. In our numerical scheme the key idea is to assume that the entire fluid-fish domain is a fluid. Then we impose two constraints: the first requires that the fluid in the region occupied by the fish body moves rigidly (a fictitious domain approach), and the second requires that the fluid at the location of the fin has the traveling wave velocity of the fin (an immersed boundary approach). Given the traveling wave form of the fin, the objective is for the numerical scheme to give the swimming velocity of the fish by solving the coupled fluid-fish problem. We will present results for the forces generated by a fin attached to a fixed body and preliminary results for freely swimming fish.
Numerical Simulation of Interplanetary Coronal Mass Ejections and STEREO Observations
NASA Astrophysics Data System (ADS)
Odstrcil, D.
2009-05-01
Since numerical simulation of solar eruptions is still in research phase various empirically-based techniques have been developed for predicting arrivals of coronal mass ejections (CMEs) at the Earth. These techniques take advantage of remote observations of CMEs in coronagraphs, fit their geometric and kinematic properties, and apply kinematic or numerical model to predict heliospheric propagation and evolution. Due to limited remote and in-situ observations, simple geometric structures have been assumed so far and the validation of such predictions has been limited. We use the 3-D numerical heliospheric code ENLIL to simulate propagation of well-observed interplanetary CMEs in 2007 and 2008. This heliospheric code uses the MAS or WSA coronal model for computing the structured background solar wind and the so-called CME cone model for specification of the geometric and kinematic parameters of the hydrodynamic transient disturbances. We use the ACE, MESSENGER, and STEREO in-situ observations to constrain the model predictions. We found that "traditional" approaches based on simple cone models over-predicts disturbances at those spacecraft. New geometric models of CMEs are clearly needed and we have incorporated rope-like hydrodynamic structure. We present result achieved by launching the cone-like and rope-like structures and compare the heliospheric predictions with the multi-spacecraft in-situ observations.
Cartesian Off-Body Grid Adaption for Viscous Time- Accurate Flow Simulation
NASA Technical Reports Server (NTRS)
Buning, Pieter G.; Pulliam, Thomas H.
2011-01-01
An improved solution adaption capability has been implemented in the OVERFLOW overset grid CFD code. Building on the Cartesian off-body approach inherent in OVERFLOW and the original adaptive refinement method developed by Meakin, the new scheme provides for automated creation of multiple levels of finer Cartesian grids. Refinement can be based on the undivided second-difference of the flow solution variables, or on a specific flow quantity such as vorticity. Coupled with load-balancing and an inmemory solution interpolation procedure, the adaption process provides very good performance for time-accurate simulations on parallel compute platforms. A method of using refined, thin body-fitted grids combined with adaption in the off-body grids is presented, which maximizes the part of the domain subject to adaption. Two- and three-dimensional examples are used to illustrate the effectiveness and performance of the adaption scheme.
Pacheco, P; Miller, P; Kim, J; Leese, T; Zabiyaka, Y
2003-05-07
Object-oriented NeuroSys (ooNeuroSys) is a collection of programs for simulating very large networks of biologically accurate neurons on distributed memory parallel computers. It includes two principle programs: ooNeuroSys, a parallel program for solving the large systems of ordinary differential equations arising from the interconnected neurons, and Neurondiz, a parallel program for visualizing the results of ooNeuroSys. Both programs are designed to be run on clusters and use the MPI library to obtain parallelism. ooNeuroSys also includes an easy-to-use Python interface. This interface allows neuroscientists to quickly develop and test complex neuron models. Both ooNeuroSys and Neurondiz have a design that allows for both high performance and relative ease of maintenance.
Numerical simulation of high speed chemically reacting flows
NASA Astrophysics Data System (ADS)
Schuricht, Scott Richard
A single step second-order accurate flux-difference-splitting method has been developed for solving unsteady quasi-one-dimensional and two-dimensional flows of multispecies fluids with finite rate chemistry. A systematic method for incorporating the source term effects into the wave strength parameters of Roe's linearized approximate Riemann solver is presented that is consistent with characteristic theory. The point implicit technique is utilized to achieve second-order time accuracy of the local area source term The stiffness associated with the chemical reactions is removed by implicitly integrating the kinetics system using the LSODE package. From the implicit integration, values of the species production rates are developed and incorporated into the flux-difference-splitting framework using a source term projection and splitting technique that preserves the upwind nature of source terms. Numerous validation studies are presented to illustrate the capability of the numerical method. Shock tube and converging-diverging nozzle cases show the method is second order accurate in space and time for one-dimensional flows. A supersonic source flow case and a subsonic sink flow case show the method is second order spatially accurate for two-dimensional flows. Static combustion and steady supersonic combustion cases illustrate the ability of the method to accurately capture the ignition delay for hydrogen-air mixtures. Demonstration studies are presented to illustrate the capabilities of the method. One-dimensional flow in a shock tube predicts species dissociation behind the main shock wave. One-dimension flow in supersonic nozzles predicts the well-known chemical freezing effect in an expanding flow. Two-dimensional cases consisted of a model of a scramjet combustor and a rocket motor nozzle. A parametric study was performed on a model of a scramjet combustor. The parameters studied were; wall angle, inlet Mach number, inlet temperature, and inlet equivalence ratio
The Impact of TRMM Data on Mesoscale Numerical Simulation of Super Typhoon Paka
NASA Technical Reports Server (NTRS)
Pu, Zhao-Xia; Tao, Wei-Kuo; Jia, Yi-Qin; Simpson, Joanne; Braun, Scott A.; Halverson, Jeffrey; Hou, Arthur; Olson, William; Starr, David OC. (Technical Monitor)
2001-01-01
Accurate measurement of the spatial and temporal variations of tropical rainfall around the globe had remained as a critical problem in meteorology until the recent launch of the Tropical Rainfall Measuring Mission (TRMM). TRMM offers a unique opportunity to improve understanding of tropical meteorology and also offers a great opportunity to evaluate the impact of rainfall data on tropical weather forecasts. This study assesses the impact of TRMM Microwave Imager (TMI) derived surface rainfall data on the numerical simulation of Super Typhoon Paka (1997).
Numerical Simulation of Seimic Behavior of Pipeline in Liquefiable Soil
NASA Astrophysics Data System (ADS)
Zou, Degao; Kong, Xianjing; Xu, Bin
This study focused on the behavior of a burial pipe with special reference to its stability against floatation subject to soil liquefaction. The excess pore water pressure response behaviors of soil foundations, and the effectiveness of different types of drainage or reinforcement measures were investigated using Finite Element Method (FEM). FEM numerical model is a coupled stress-flow finite element procedure, based on u-p formulation of dynamic Biot's equations (Zienkiewicz, 1982). The hyperbolic stress and strain relationship was used in the numerical model, which takes into account the stiffness and strength degradation. Pore pressure generation due to earthquake loading was calculated via the pore pressure model (Seed et al, 1979). Performance of the numerical models was studied by simulating a series of shake table tests. Excess pore pressures predicted by numerical models were compared with the pore pressure transducer records during experiments. Also, the effectiveness of different drainage measures against uplifting of pipelines was compared. It was demonstrated that the models were able to provide results in agreement with experiments.
Time-Accurate Computational Fluid Dynamics Simulation of a Pair of Moving Solid Rocket Boosters
NASA Technical Reports Server (NTRS)
Strutzenberg, Louise L.; Williams, Brandon R.
2011-01-01
Since the Columbia accident, the threat to the Shuttle launch vehicle from debris during the liftoff timeframe has been assessed by the Liftoff Debris Team at NASA/MSFC. In addition to engineering methods of analysis, CFD-generated flow fields during the liftoff timeframe have been used in conjunction with 3-DOF debris transport methods to predict the motion of liftoff debris. Early models made use of a quasi-steady flow field approximation with the vehicle positioned at a fixed location relative to the ground; however, a moving overset mesh capability has recently been developed for the Loci/CHEM CFD software which enables higher-fidelity simulation of the Shuttle transient plume startup and liftoff environment. The present work details the simulation of the launch pad and mobile launch platform (MLP) with truncated solid rocket boosters (SRBs) moving in a prescribed liftoff trajectory derived from Shuttle flight measurements. Using Loci/CHEM, time-accurate RANS and hybrid RANS/LES simulations were performed for the timeframe T0+0 to T0+3.5 seconds, which consists of SRB startup to a vehicle altitude of approximately 90 feet above the MLP. Analysis of the transient flowfield focuses on the evolution of the SRB plumes in the MLP plume holes and the flame trench, impingement on the flame deflector, and especially impingment on the MLP deck resulting in upward flow which is a transport mechanism for debris. The results show excellent qualitative agreement with the visual record from past Shuttle flights, and comparisons to pressure measurements in the flame trench and on the MLP provide confidence in these simulation capabilities.
Achieving accurate simulations of urban impacts on ozone at high resolution
NASA Astrophysics Data System (ADS)
Li, J.; Georgescu, M.; Hyde, P.; Mahalov, A.; Moustaoui, M.
2014-11-01
The effects of urbanization on ozone levels have been widely investigated over cities primarily located in temperate and/or humid regions. In this study, nested WRF-Chem simulations with a finest grid resolution of 1 km are conducted to investigate ozone concentrations [O3] due to urbanization within cities in arid/semi-arid environments. First, a method based on a shape preserving Monotonic Cubic Interpolation (MCI) is developed and used to downscale anthropogenic emissions from the 4 km resolution 2005 National Emissions Inventory (NEI05) to the finest model resolution of 1 km. Using the rapidly expanding Phoenix metropolitan region as the area of focus, we demonstrate the proposed MCI method achieves ozone simulation results with appreciably improved correspondence to observations relative to the default interpolation method of the WRF-Chem system. Next, two additional sets of experiments are conducted, with the recommended MCI approach, to examine impacts of urbanization on ozone production: (1) the urban land cover is included (i.e., urbanization experiments) and, (2) the urban land cover is replaced with the region’s native shrubland. Impacts due to the presence of the built environment on [O3] are highly heterogeneous across the metropolitan area. Increased near surface [O3] due to urbanization of 10-20 ppb is predominantly a nighttime phenomenon while simulated impacts during daytime are negligible. Urbanization narrows the daily [O3] range (by virtue of increasing nighttime minima), an impact largely due to the region’s urban heat island. Our results demonstrate the importance of the MCI method for accurate representation of the diurnal profile of ozone, and highlight its utility for high-resolution air quality simulations for urban areas.
Numerical simulation of scramjet combustion in a shock tunnel
NASA Astrophysics Data System (ADS)
Star, Jason B.
Three-dimensional computational simulations of reactive flowfields within a hydrogen-fueled scramjet-like geometry experimentally tested in a free piston shock tunnel are presented. The experimental configuration (Odam and Paull, AIAA Paper 2003-5244) involves injection of hydrogen fuel into the scramjet inlet, followed by mixing, shock-induced ignition, and combustion. The predictions for both fuel-off and fuel-on conditions were observed to be sensitive to the choice of the wall temperature boundary conditions. The best comparison with experimental data were achieved through the implementation of an approach that involves a simplified conjugate heat transfer model that couples the heat conduction through the wall with the heat conduction of the fluid within the boundary layer. This approach is able to predict thermal loads on the walls of the scramjet model due to shock wave interactions and due to heat release. As such, it is able to more accurately represent the physical temperature response of the engine model. Also shown to produce very good agreement with the statistically-steady experimental data was the isothermal ghost-cell boundary condition, which is based on a simplification of the time-dependent conjugate heat transfer boundary condition. This simplified boundary condition assumes a linear temperature distribution within the wall based on the effective depth that an applied heat load would penetrate, thus, it also allows the actual wall temperature to vary in response to the applied heat load. Results for fuel-off simulations showed that the solution generated by a steady-state simulation implementing the isothermal ghost-cell wall boundary condition was very comparable with the statistically-steady solution obtained from a fully transient simulation with coupled heat conduction within the walls. When integrated in a fully time-accurate manner, the fuel-on simulations showed a striking sensitivity to the modeled rate of air ingestion into the engine
Numerical simulation of multi-layered textile composite reinforcement forming
NASA Astrophysics Data System (ADS)
Wang, P.; Hamila, N.; Boisse, P.
2011-05-01
One important perspective in aeronautics is to produce large, thick or/and complex structural composite parts. The forming stage presents an important role during the whole manufacturing process, especially for LCM processes (Liquid Composites Moulding) or CFRTP (Continuous Fibre Reinforcements and Thermoplastic resin). Numerical simulations corresponding to multi-layered composite forming allow the prediction for a successful process to produce the thick parts, and importantly, the positions of the fibres after forming to be known. This paper details a set of simulation examples carried out by using a semi-discrete shell finite element made up of unit woven cells. The internal virtual work is applied on all woven cells of the element taking into account tensions, in-plane shear and bending effects. As one key problem, the contact behaviours of tool/ply and ply/ply are described in the numerical model. The simulation results not only improve our understanding of the multi-layered composite forming process but also point out the importance of the fibre orientation and inter-ply friction during formability.
Numerical simulation of the non-Newtonian mixing layer
NASA Technical Reports Server (NTRS)
Azaiez, Jalel; Homsy, G. M.
1993-01-01
This work is a continuing effort to advance our understanding of the effects of polymer additives on the structures of the mixing layer. In anticipation of full nonlinear simulations of the non-Newtonian mixing layer, we examined in a first stage the linear stability of the non-Newtonian mixing layer. The results of this study show that, for a fluid described by the Oldroyd-B model, viscoelasticity reduces the instability of the inviscid mixing layer in a special limit where the ratio (We/Re) is of order 1 where We is the Weissenberg number, a measure of the elasticity of the flow, and Re is the Reynolds number. In the present study, we pursue this project with numerical simulations of the non-Newtonian mixing layer. Our primary objective is to determine the effects of viscoelasticity on the roll-up structure. We also examine the origin of the numerical instabilities usually encountered in the simulations of non-Newtonian fluids.
Numerical simulation of multi-layered textile composite reinforcement forming
Wang, P.; Hamila, N.; Boisse, P.
2011-05-04
One important perspective in aeronautics is to produce large, thick or/and complex structural composite parts. The forming stage presents an important role during the whole manufacturing process, especially for LCM processes (Liquid Composites Moulding) or CFRTP (Continuous Fibre Reinforcements and Thermoplastic resin). Numerical simulations corresponding to multi-layered composite forming allow the prediction for a successful process to produce the thick parts, and importantly, the positions of the fibres after forming to be known. This paper details a set of simulation examples carried out by using a semi-discrete shell finite element made up of unit woven cells. The internal virtual work is applied on all woven cells of the element taking into account tensions, in-plane shear and bending effects. As one key problem, the contact behaviours of tool/ply and ply/ply are described in the numerical model. The simulation results not only improve our understanding of the multi-layered composite forming process but also point out the importance of the fibre orientation and inter-ply friction during formability.
Wind Tunnel to Flight: Numerical Simulations of Hypersonic Propulsion Systems
NASA Astrophysics Data System (ADS)
Iaccarino, Gianluca
2009-11-01
Uncertainties in the flight conditions and limitations of ground based facilities create inherent difficulties in assessing the performance of hypersonic propulsion systems. We use numerical simulations to investigate the correlation of wind-tunnel measurements (Steelant et al., 2006) and flight data (Hass et al., 2005) for the HyShot vehicle; the objective is to identify potential engine unstart events occurring under different combustion regimes. As a first step we perform simulations corresponding to both reacting and non-reacting conditions in the ground-based facility to validate the numerical tools. Next, we focus on reproducing the flight conditions; a fundamental difficulty is the lack of precise information about the vehicle trajectory. A Bayesian inversion strategy is used to infer the altitude, angle of attack and Mach number from the noisy pressure measurements collected during the flight. The estimated conditions, together with the scatter due to the measurement uncertainty, are then used to study the flow and thermal fields in the combustor. The details of the methods used to characterize the uncertainty in the flow simulations and to perform the Bayesian inversion will also be discussed.
An Object Model for a Rocket Engine Numerical Simulator
NASA Technical Reports Server (NTRS)
Mitra, D.; Bhalla, P. N.; Pratap, V.; Reddy, P.
1998-01-01
Rocket Engine Numerical Simulator (RENS) is a packet of software which numerically simulates the behavior of a rocket engine. Different parameters of the components of an engine is the input to these programs. Depending on these given parameters the programs output the behaviors of those components. These behavioral values are then used to guide the design of or to diagnose a model of a rocket engine "built" by a composition of these programs simulating different components of the engine system. In order to use this software package effectively one needs to have a flexible model of a rocket engine. These programs simulating different components then should be plugged into this modular representation. Our project is to develop an object based model of such an engine system. We are following an iterative and incremental approach in developing the model, as is the standard practice in the area of object oriented design and analysis of softwares. This process involves three stages: object modeling to represent the components and sub-components of a rocket engine, dynamic modeling to capture the temporal and behavioral aspects of the system, and functional modeling to represent the transformational aspects. This article reports on the first phase of our activity under a grant (RENS) from the NASA Lewis Research center. We have utilized Rambaugh's object modeling technique and the tool UML for this purpose. The classes of a rocket engine propulsion system are developed and some of them are presented in this report. The next step, developing a dynamic model for RENS, is also touched upon here. In this paper we will also discuss the advantages of using object-based modeling for developing this type of an integrated simulator over other tools like an expert systems shell or a procedural language, e.g., FORTRAN. Attempts have been made in the past to use such techniques.
Using Numerical Modeling to Simulate Space Capsule Ground Landings
NASA Technical Reports Server (NTRS)
Heymsfield, Ernie; Fasanella, Edwin L.
2009-01-01
Experimental work is being conducted at the National Aeronautics and Space Administration s (NASA) Langley Research Center (LaRC) to investigate ground landing capabilities of the Orion crew exploration vehicle (CEV). The Orion capsule is NASA s replacement for the Space Shuttle. The Orion capsule will service the International Space Station and be used for future space missions to the Moon and to Mars. To evaluate the feasibility of Orion ground landings, a series of capsule impact tests are being performed at the NASA Langley Landing and Impact Research Facility (LandIR). The experimental results derived at LandIR provide means to validate and calibrate nonlinear dynamic finite element models, which are also being developed during this study. Because of the high cost and time involvement intrinsic to full-scale testing, numerical simulations are favored over experimental work. Subsequent to a numerical model validated by actual test responses, impact simulations will be conducted to study multiple impact scenarios not practical to test. Twenty-one swing tests using the LandIR gantry were conducted during the June 07 through October 07 time period to evaluate the Orion s impact response. Results for two capsule initial pitch angles, 0deg and -15deg , along with their computer simulations using LS-DYNA are presented in this article. A soil-vehicle friction coefficient of 0.45 was determined by comparing the test stopping distance with computer simulations. In addition, soil modeling accuracy is presented by comparing vertical penetrometer impact tests with computer simulations for the soil model used during the swing tests.
Chen, Zikuan; Calhoun, Vince
2013-01-01
The magnetic field resulting from material magnetization in magnetic resonance imaging (MRI) has an object orientation effect, which produces an orientation dependence for acquired T2* images. On one hand, the orientation effect can be exploited for object anisotropy investigation (via multi-angle imaging); on the other hand, it is desirable to remove the orientation dependence using magnetic susceptibility reconstruction. In this report, we design a stick-star digital phantom to simulate multiple orientations of a stick-like object and use it to conduct various numerical simulations. Our simulations show that the object orientation effect is not propagated to the reconstructed magnetic susceptibility distribution. This suggests that accurate susceptibility reconstruction methods should be largely orientation independent. PMID:25114542
INEX (integrated numerical experiment) simulations of the Boeing FEL system
Tokar, R.L.; Young, L.M.; Lumpkin, A.H.; McVey, B.D.; Thode, L.E.; Bender, S.C.; Chan, K.C.D. ); Yeremian, A.D.; Dowell, D.H.; Lowrey, A.R. )
1989-01-01
The INEX (integrated numerical experiment) numerical model is applied to the 0.6 {mu}m FEL oscillator at Boeing Aerospace and Electronics Company in Seattle, WA. This system consists of a 110 MeV L-band rf linac, a beam transport line from the accelerator to the entrance of the wiggler, the 5.0 meter THUNDER variable taper wiggler, and a near concentric two mirror optical oscillator. Many aspects of the model for the electron beam accelerator and transport line agree with experimental measurements. Predictions for lasing performance are compared with data obtained in May and June 1989 using a mild tapered wiggler. We obtain good agreement with the achieved extraction efficiency, while 1D pulse simulations reproduce the observed sideband instability. 15 refs., 11 figs.
Incompressible and anelastic flow simulations on numerically generated grids
NASA Technical Reports Server (NTRS)
Sharman, R. D.; Keller, T. L.; Wurtele, M. G.
1988-01-01
In the numerical simulation of incompressible and anelastic flows, it is necessary to solve an elliptic equation at each time step. When the boundaries of such flows are nonrectangular, it may be advantageous to solve the equations on a new, numerically generated coordinate grid, in which the property of orthogonality has been preserved. Flow equations in general curvilinear coordinates maintaining the conservative form are given for both anelastic models using the momentum equations, and for incompressible models, using the vorticity equation. The general problem of grid-generation in two dimensions is presented, and a quasi-conformal transformation technique is discussed in detail. Some examples of grids generated by this technique are exhibited. Three examples of the flow of a stratified fluid over obstacles are presented, in which the grid-generation permits some new results to be obtained.
Numerical simulations of electrostatically driven jets from nonviscous droplets.
Garzon, M; Gray, L J; Sethian, J A
2014-03-01
The evolution of a perfectly conducting and nonviscous fluid, under the action of an electric field (uniform at infinity), is studied numerically. Level set techniques are employed to develop an Eulerian potential flow model that can follow the drop evolution past breakup, while the free surface fluid velocity and the electric field force are obtained via axisymmetric boundary integral calculations. Numerical results are presented for neutral and charged droplets and for free charged droplets. In all cases, the evolution droplet aspect ratio, progeny droplet size, Taylor cone angles, jet shapes, and self-similar scaling exponents are reported. In particular, for free charged water droplets, the bursting frequency and other jetting characteristics have been carefully analyzed. Wherever possible, these results are compared with previously reported experiments and simulations. PMID:24730941
A Numerical simulation of transition in plane channel flow
NASA Astrophysics Data System (ADS)
Goglia, G.; Biringen, S.
1982-08-01
A numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 7500 is described. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two and three dimensional finite amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 by 33 by 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and which are characteristic of various stages of transition that lead to final breakdown. Details of the resulting flow field after breakdown indicate the evolution of streak-like formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), implementation of subgrid-scale terms are necessary to obtain proper turbulent statistics.
A numerical simulation of transition in plane channel flow
NASA Astrophysics Data System (ADS)
Biringen, S.
1983-01-01
This paper involves a numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 7500. Three-dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time-evolution of two- and three-dimensional finite-amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 x 33 x 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and which are characteristic of various stages of transition that lead to final breakdown. Details of the resulting flow field after breakdown indicate the evolution of streak-like formations found in turbulent flows. Although the flow field does approach a steady-state (turbulent channel flow), implementation of subgrid-scale terms are necesary to obtain proper turbulent statistics.
Mechanical characterisation of Dacron graft: Experiments and numerical simulation.
Bustos, Claudio A; García-Herrera, Claudio M; Celentano, Diego J
2016-01-01
Experimental and numerical analyses focused on the mechanical characterisation of a woven Dacron vascular graft are presented. To that end, uniaxial tensile tests under different orientations have been performed to study the anisotropic behaviour of the material. These tests have been used to adjust the parameters of a hyperelastic anisotropic constitutive model which is applied to predict through numerical simulation the mechanical response of this material in the ring tensile test. The obtained results show that the model used is capable of representing adequately the nonlinear elastic region and, in particular, it captures the progressive increase of the rigidity and the anisotropy due to the stretching of the Dacron. The importance of this research lies in the possibility of predicting the graft׳s mechanical response under generalized loading such as those that occur under physiological conditions after surgical procedures. PMID:26627367
A Numerical simulation of transition in plane channel flow
NASA Technical Reports Server (NTRS)
Goglia, G.; Biringen, S.
1982-01-01
A numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 7500 is described. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two and three dimensional finite amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 by 33 by 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and which are characteristic of various stages of transition that lead to final breakdown. Details of the resulting flow field after breakdown indicate the evolution of streak-like formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), implementation of subgrid-scale terms are necessary to obtain proper turbulent statistics.
Numerical simulations of drop impact on superhydrophobic structured surfaces
NASA Astrophysics Data System (ADS)
Guzzetti, Davide; Larentis, Stefano; Pugno, Nicola
2011-11-01
During the last decade drop impact dynamics on superhydrophobic surfaces has been intensively investigated because of the incredible properties of water repellency exhibited by this kind of surfaces, mostly inspired by biological examples such as Lotus leave. Thanks to the recent progress in micro-fabrication technology is possible to tailor surfaces wettability defining specific pillar-like structured surfaces. In this work, the behavior of impinging drops on these pillar-like surfaces is simulated, characterizing temporal evolution of droplets contact radius and drop maximal deformation dependence on Weber number. Numerical simulations results are compared with theoretical and experimental results guaranteeing simulation reliability. Fingering patterns obtained from drop impact has been studied obtaining a correlation between number of fingers and Weber number. Drop fragmentation pattern obtained from simulations supports the proposed correlation. Different drop impact outcomes (e.g. rebound, fragmentation) on structured superhydrophobic surfaces are simulated, focusing on the influence of micro-structured surface geometrical pattern. This investigation is relevant in order to define design rules for possible reliable non wettable surfaces. Financial support by Alta Scuola Politecnica.
Numerical Simulation of Cellular Blood Flow through a Rigid Artery
NASA Astrophysics Data System (ADS)
Reasor, Daniel; Clausen, Jonathan; Aidun, Cyrus
2009-11-01
In blood flow, red blood cells (RBCs), the most numerous constituent of blood, influence continuum-level measures by altering the suspension at microscopic scales. The presence of RBCs alters the stress and diffusion individual cells experience, which can influence cardiovascular diseases by affecting other cells present in blood like platelets and white blood cells. Simulations of blood at a cellular level provide a tool that allows exploration of both the rheology and the stress and diffusion of individual suspended cells. In this work, a hybrid lattice-Boltzmann/finite element method is used to simulate suspension flows characteristic of blood with deformable RBCs at realistic hematocrit values. We have shown the ability to simulate thousands deformable suspensions capturing non-Newtonian flow characteristics such as shear thinning, and the results agree well with experimental observations. Simulations through rigid arteries have been deformed with as many as 2500 RBCs. This work outlines results obtained for pressure-gradient driven blood flow through a rigid artery with 20%, 30%, 40%, and 50% hematocrit values. Results include the effect these deformable RBCs have on mean velocity, flow rate, radial variation of RBC concentration, and the effective viscosity for simulations at moderate to low cell capillary numbers, Ca <=0.08.
Numerical simulation and wave extraction of binary black hole system
NASA Astrophysics Data System (ADS)
Imbiriba, Breno Cesar De Oliveira
In the first part of this work, we apply finite difference methods, specially mesh refinement techniques, in order to numerically evolve a single black hole, which is represented by the puncture initial data. We use standard second order finite differences, and the second order Iterated Crank-Nicholson integrator. We observe that, in order to obtain a second order accurate evolution we must impose second order accurate interface conditions at the refinement boundaries. We test our evolution with both the geodesic and the 1+log slicing conditions, and observe the expected results. We conclude that our mesh refinement technique generates convergent evolutions, and the puncture method behaves very well with it. The second part of this work deals with a modification of the hybrid "Lazarus" method for wave extraction. This method is divided in three parts: an early evolution, a set of transformations to produce perturbations over a Kerr background from the numerical data, and Teukolsky evolution. By using our evolution code (with mesh refinement) and gauges (1+log, gamma-driver, shifting-shift), we deviate from the original Lazarus approach. We used an independent implementation of the Lazarus transformations, validating the original results, and of the Teukolsky equation. We obtained results similar to the original Lazarus, both on the waveforms as well as on the negative results at later times. For instance, strong pulses that contaminate some gauge transformations, which may be explained in part by the propagating gauge modes of the 1+log slicing. Increasing the accuracy of the initial black hole evolution we seem to obtain better final results for the Kerr test case. Because of the gauge problems, we develop an approximated embedding method which approximates location of the numerical slice into the Kerr spacetime. This method is much less sensitive to the gauge perturbations. Given the difficulties of the Lazarus procedure, we decide to use the Lazarus method as a
NASA Astrophysics Data System (ADS)
Martin-Short, R.; Edmiston, J. K.
2015-12-01
Typical hydraulic fracturing operations involve the use of a large quantity of water, which can be problematic for several reasons including possible formation (permeability) damage, disposal of waste water, and the use of precious local water resource. An alternate reservoir permeability enhancing technology not requiring water is cryogenic fracturing. This method induces controlled fracturing of rock formations by thermal shock and has potentially important applications in the geothermal and hydrocarbon industries. In this process, cryogenic fluid—such as liquid nitrogen—is injected into the subsurface, causing fracturing due to thermal gradients. These fractures may improve the formation permeability relative to that achievable by hydraulic fracturing alone. We conducted combined laboratory visualization and numerical simulations studies of thermal-shock-induced fracture initiation and propagation resulting from liquid nitrogen injection in rock and analog materials. The experiment used transparent soda-lime glass cubes to facilitate real-time visualization of fracture growth and the fracture network geometry. In this contribution, we report the effect of overall temperature difference between cryogenic fluid and solid material on the produced fracture network, by pre-heating the glass cubes to several temperatures and injecting liquid nitrogen. Temperatures are monitored at several points by thermocouple and the fracture evolution is captured visually by camera. The experiment was modeled using a customized, thermoelastic, fracture-capable numerical simulation code based on peridynamics. The performance of the numerical code was validated by the results of the laboratory experiments, and then the code was used to study the different factors affecting a cryogenic fracturing operation, including the evolution of residual stresses and constitutive relationships for material failure. In complex rock such as shale, understanding the process of cryogenic
Numerical simulation of a liquid propellant rocket motor
NASA Astrophysics Data System (ADS)
Salvador, Nicolas M. C.; Morales, Marcelo M.; Migueis, Carlos E. S. S.; Bastos-Netto, Demétrio
2001-03-01
This work presents a numerical simulation of the flow field in a liquid propellant rocket engine chamber and exit nozzle using techniques to allow the results to be taken as starting points for designing those propulsive systems. This was done using a Finite Volume method simulating the different flow regimes which usually take place in those systems. As the flow field has regions ranging from the low subsonic to the supersonic regimes, the numerical code used, initially developed for compressible flows only, was modified to work proficiently in the whole velocity range. It is well known that codes have been developed in CFD, for either compressible or incompressible flows, the joint treatment of both together being complex even today, given the small number of references available in this area. Here an existing code for compressible flow was used and primitive variables, the pressure, the Cartesian components of the velocity and the temperature instead of the conserved variables were introduced in the Euler and Navier-Stokes equations. This was done to permit the treatment at any Mach number. Unstructured meshes with adaptive refinements were employed here. The convective terms were treated with upwind first and second order methods. The numerical stability was kept with artificial dissipation and in the spatial coverage one used a five stage Runge-Kutta scheme for the Fluid Mechanics and the VODE (Value of Ordinary Differential Equations) scheme along with the Chemkin II in the chemical reacting solution. During the development of this code simulating the flow in a rocket engine, comparison tests were made with several different types of internal and external flows, at different velocities, seeking to establish the confidence level of the techniques being used. These comparisons were done with existing theoretical results and with other codes already validated and well accepted by the CFD community.