Toward Scientific Numerical Modeling
NASA Technical Reports Server (NTRS)
Kleb, Bil
2007-01-01
Ultimately, scientific numerical models need quantified output uncertainties so that modeling can evolve to better match reality. Documenting model input uncertainties and verifying that numerical models are translated into code correctly, however, are necessary first steps toward that goal. Without known input parameter uncertainties, model sensitivities are all one can determine, and without code verification, output uncertainties are simply not reliable. To address these two shortcomings, two proposals are offered: (1) an unobtrusive mechanism to document input parameter uncertainties in situ and (2) an adaptation of the Scientific Method to numerical model development and deployment. Because these two steps require changes in the computational simulation community to bear fruit, they are presented in terms of the Beckhard-Harris-Gleicher change model.
Numerical Modeling of Airblast.
1987-06-01
REPORT SAIC 87/1701 June 1987 Dr.. Submitted to: cp Dr. Jay Boris Laboratory for Computational Physics Accet F4,r Naval Research Laboratory I...boundary layer physical assumptions provides an unsteady prediction of the mass flux emerging from the ground. This model was first proposed by Mirels...the physics modeled will be explained. High explosive dust cloud simulation provides a research path when combined with numerical calculations can lead
Numerical Modeling Experiments
1974-09-01
presence of clouds is associated with the occurvence of condensation in the atmospheric models. Cloudiness 3t a particulat grid point is introduced -4...when saturation is predicted as a result of either large-scale moisture flux convergence or vertical convective adjustment. In most models such clouds ... cloud top, cloud thickness, and liquid-water content. In some general circulation models the local fractional convective cloud amountv tre taken
Numerical modeling of preburner flowfield
NASA Astrophysics Data System (ADS)
Chow, A. S.; Mo, J. D.; Jin, K. R.
1993-06-01
This work is intended to numerically predict the flowfields inside the preburner of the Space Shuttle Main Engine. The computer code (FDNS) based on pressure correction method is modified and adapted with an elliptic grid generator. The original configuration of the preburner in conjunction with downstream gas turbines has been simplified geometrically and numerically modeled at its full power in this work. The computational results are presented and qualitatively discussed with test data collected in NASA/MSFC.
Moore's Law and Numerical Modeling
NASA Astrophysics Data System (ADS)
Voller, V. R.; Porté-Agel, F.
2002-07-01
An estimate of the rate of increase in numerical simulation grid sizes with time is obtained by counting the grids (measured in terms of number of node points) reported in the nine volumes of an established proceedings on the numerical modeling of solidification phenomena dating back to 1980. It is shown that the largest grids used in a given year increase at a rate consistent with the well-known Moore's law on computing power, i.e., the number of nodes in the grids double every 18 months. From this observation, approximate bounds on the available grid size in a current year are established. This approximation is used to provide projections as to when, assuming Moore's law continues to hold, direct simulations of physical phenomena, which resolve to the smallest scale present, will be achievable.
Numerical Model for Hydrovolcanic Explosions.
NASA Astrophysics Data System (ADS)
Mader, Charles; Gittings, Michael
2007-03-01
A hydrovolcanic explosion is generated by the interaction of hot magma with ground water. It is called Surtseyan after the 1963 explosive eruption off Iceland. The water flashes to steam and expands explosively. Liquid water becomes water gas at constant volume and generates pressures of about 3GPa. The Krakatoa hydrovolcanic explosion was modeled using the full Navier-Stokes AMR Eulerian compressible hydrodynamic code called SAGE [1] which includes the high pressure physics of explosions. The water in the hydrovolcanic explosion was described as liquid water heated by magma to 1100 K. The high temperature water is treated as an explosive with the hot liquid water going to water gas. The BKW [2] steady state detonation state has a peak pressure of 8.9 GPa, a propagation velocity of 5900 meters/sec and the water is compressed to 1.33 g/cc. [1] Numerical Modeling of Water Waves, Second Edition, Charles L. Mader, CRC Press 2004. [2] Numerical Modeling of Explosions and Propellants, Charles L. Mader, CRC Press 1998.
Numerical models of complex diapirs
NASA Astrophysics Data System (ADS)
Podladchikov, Yu.; Talbot, C.; Poliakov, A. N. B.
1993-12-01
Numerically modelled diapirs that rise into overburdens with viscous rheology produce a large variety of shapes. This work uses the finite-element method to study the development of diapirs that rise towards a surface on which a diapir-induced topography creeps flat or disperses ("erodes") at different rates. Slow erosion leads to diapirs with "mushroom" shapes, moderate erosion rate to "wine glass" diapirs and fast erosion to "beer glass"- and "column"-shaped diapirs. The introduction of a low-viscosity layer at the top of the overburden causes diapirs to develop into structures resembling a "Napoleon hat". These spread lateral sheets.
Numerical methods used in fusion science numerical modeling
NASA Astrophysics Data System (ADS)
Yagi, M.
2015-04-01
The dynamics of burning plasma is very complicated physics, which is dominated by multi-scale and multi-physics phenomena. To understand such phenomena, numerical simulations are indispensable. Fundamentals of numerical methods used in fusion science numerical modeling are briefly discussed in this paper. In addition, the parallelization technique such as open multi processing (OpenMP) and message passing interface (MPI) parallel programing are introduced and the loop-level parallelization is shown as an example.
Numerical Modeling of Nanoelectronic Devices
NASA Technical Reports Server (NTRS)
Klimeck, Gerhard; Oyafuso, Fabiano; Bowen, R. Chris; Boykin, Timothy
2003-01-01
Nanoelectronic Modeling 3-D (NEMO 3-D) is a computer program for numerical modeling of the electronic structure properties of a semiconductor device that is embodied in a crystal containing as many as 16 million atoms in an arbitrary configuration and that has overall dimensions of the order of tens of nanometers. The underlying mathematical model represents the quantummechanical behavior of the device resolved to the atomistic level of granularity. The system of electrons in the device is represented by a sparse Hamiltonian matrix that contains hundreds of millions of terms. NEMO 3-D solves the matrix equation on a Beowulf-class cluster computer, by use of a parallel-processing matrix vector multiplication algorithm coupled to a Lanczos and/or Rayleigh-Ritz algorithm that solves for eigenvalues. In a recent update of NEMO 3-D, a new strain treatment, parameterized for bulk material properties of GaAs and InAs, was developed for two tight-binding submodels. The utility of the NEMO 3-D was demonstrated in an atomistic analysis of the effects of disorder in alloys and, in particular, in bulk In(x)Ga(l-x)As and in In0.6Ga0.4As quantum dots.
Equivalent beam modeling using numerical reduction techniques
NASA Technical Reports Server (NTRS)
Chapman, J. M.; Shaw, F. H.
1987-01-01
Numerical procedures that can accomplish model reductions for space trusses were developed. Three techniques are presented that can be implemented using current capabilities within NASTRAN. The proposed techniques accomplish their model reductions numerically through use of NASTRAN structural analyses and as such are termed numerical in contrast to the previously developed analytical techniques. Numerical procedures are developed that permit reductions of large truss models containing full modeling detail of the truss and its joints. Three techniques are presented that accomplish these model reductions with various levels of structural accuracy. These numerical techniques are designated as equivalent beam, truss element reduction, and post-assembly reduction methods. These techniques are discussed in detail.
Numerical Modelling of Electrical Discharges
NASA Astrophysics Data System (ADS)
Durán-Olivencia, F. J.; Pontiga, F.; Castellanos, A.
2014-03-01
The problem of the propagation of an electrical discharge between a spherical electrode and a plane has been solved by means of finite element methods (FEM) using a fluid approximation and assuming weak ionization and local equilibrium with the electric field. The numerical simulation of this type of problems presents the usual difficulties of convection-diffusion-reaction problems, in addition to those associated with the nonlinearities of the charged species velocities, the formation of steep gradients of the electric field and particle densities, and the coexistence of very different temporal scales. The effect of using different temporal discretizations for the numerical integration of the corresponding system of partial differential equations will be here investigated. In particular, the so-called θ-methods will be used, which allows to implement implicit, semi-explicit and fully explicit schemes in a simple way.
Numerical approaches to combustion modeling
Oran, E.S.; Boris, J.P. )
1991-01-01
This book presents a series of topics ranging from microscopic combustion physics to several aspects of macroscopic reactive-flow modeling. As the reader progresses into the book, the successive chapters generally include a wider range of physical and chemical processes in the mathematical model. Including more processes, however, usually means that they will be represented phenomenologically at a cruder level. In practice the detailed microscopic models and simulations are often used to develop and calibrate the phenomenologies used in the macroscopic models. The book first describes computations of the most microscopic chemical processes, then considers laminar flames and detonation modeling, and ends with computations of complex, multiphase combustion systems.
Numerical tsunami modeling and the bottom relief
NASA Astrophysics Data System (ADS)
Kulikov, E. A.; Gusiakov, V. K.; Ivanova, A. A.; Baranov, B. V.
2016-11-01
The effect of the quality of bathymetric data on the accuracy of tsunami-wave field calculation is considered. A review of the history of the numerical tsunami modeling development is presented. Particular emphasis is made on the World Ocean bottom models. It is shown that the modern digital bathymetry maps, for example, GEBCO, do not adequately simulate the sea bottom in numerical models of wave propagation, leading to considerable errors in estimating the maximum tsunami run-ups on the coast.
Survey of numerical electrostimulation models.
Reilly, J Patrick
2016-06-21
This paper evaluates results of a survey of electrostimulation models of myelinated nerve. Participants were asked to determine thresholds of excitation for 18 cases involving different characteristics of the neuron, the stimulation waveform, and the electrode arrangement. Responses were received from 7 investigators using 10 models. Excitation thresholds differed significantly among these models. For example, with a 2 ms monophasic stimulus pulse and an electrode/fiber distance of 1 cm, thresholds from the least to greatest value differed by a factor of 8.3; with a 5 μs pulse, thresholds differed by the factor 3.8. Significant differences in reported simulations point to the need for experimental validation. Additional efforts are needed to develop computational models for unmyelinated C-fibers, A-delta fibers, CNS neurons, and CNS Synapses.
Survey of numerical electrostimulation models
NASA Astrophysics Data System (ADS)
Reilly, J. Patrick
2016-06-01
This paper evaluates results of a survey of electrostimulation models of myelinated nerve. Participants were asked to determine thresholds of excitation for 18 cases involving different characteristics of the neuron, the stimulation waveform, and the electrode arrangement. Responses were received from 7 investigators using 10 models. Excitation thresholds differed significantly among these models. For example, with a 2 ms monophasic stimulus pulse and an electrode/fiber distance of 1 cm, thresholds from the least to greatest value differed by a factor of 8.3; with a 5 μs pulse, thresholds differed by the factor 3.8. Significant differences in reported simulations point to the need for experimental validation. Additional efforts are needed to develop computational models for unmyelinated C-fibers, A-delta fibers, CNS neurons, and CNS Synapses.
Numerical modeling of enclosure convection
NASA Technical Reports Server (NTRS)
Duh, J. C.
1989-01-01
A numerical study on the steady and unsteady natural convection in two-dimensional rectangular enclosures has been performed by a time-accurate ADI finite difference scheme. The study covered a range of Rayleigh numbers between 1000 and 10 to the 7th, aspect ratios between 0.2 and 10.0, and tilt angles between -90 (heating from bottom) and +90 deg (heating from top). Various Prandtl numbers have been studied, but only the results of water (Pr = 7.0) are reported here due to space limitations. The physics revealed, however, includes the convection phenomena and the Rayleigh-Benard stability, as well as the combined mechanism of these two. The onset of secondary cells is determined by using a velocity map, which is simpler and cleaner, instead of a streamline plot. The critical Ra number for the occurrence of these secondary cells is shown to be lower than can be detected by experimental studies. On the Rayleigh-Benard stability part, a second transition from stable single-cell convection to periodic multicellular convection is disclosed.
Numerical noise in ocean and estuarine models
Walters, R.; Carey, G.F.
1984-01-01
Approximate methods for solving the shallow water equations may lead to solutions exhibiting large fictitious, numerically-induced oscillations. The analysis of the discrete dispersion relation and modal solutions of small wavelengths provides a powerful technique for assessing the sensitivity of alternative numerical schemes to irregular data which may lead to such oscillatory numerical noise. For those schemes where phase speed vanishes at a finite wavenumber or there are multiple roots for wavenumber, oscillation modes can exist which are uncoupled from the dynamics of the problem. The discrete modal analysis approach is used here to identify two classes of spurious oscillation modes associated respectively with the two different asymptotic limits corresponding to estuarine and large scale ocean models. The analysis provides further insight into recent numerical results for models which include large spatial scales and Coriolis acceleration. ?? 1984.
Numerical Modeling of Ablation Heat Transfer
NASA Technical Reports Server (NTRS)
Ewing, Mark E.; Laker, Travis S.; Walker, David T.
2013-01-01
A unique numerical method has been developed for solving one-dimensional ablation heat transfer problems. This paper provides a comprehensive description of the method, along with detailed derivations of the governing equations. This methodology supports solutions for traditional ablation modeling including such effects as heat transfer, material decomposition, pyrolysis gas permeation and heat exchange, and thermochemical surface erosion. The numerical scheme utilizes a control-volume approach with a variable grid to account for surface movement. This method directly supports implementation of nontraditional models such as material swelling and mechanical erosion, extending capabilities for modeling complex ablation phenomena. Verifications of the numerical implementation are provided using analytical solutions, code comparisons, and the method of manufactured solutions. These verifications are used to demonstrate solution accuracy and proper error convergence rates. A simple demonstration of a mechanical erosion (spallation) model is also provided to illustrate the unique capabilities of the method.
Numerical FEM modeling in dental implantology
NASA Astrophysics Data System (ADS)
Roateşi, Iulia; Roateşi, Simona
2016-06-01
This paper is devoted to a numerical approach of the stress and displacement calculation of a system made up of dental implant, ceramic crown and surrounding bone. This is the simulation of a clinical situation involving both biological - the bone tissue, and non-biological - the implant and the crown, materials. On the other hand this problem deals with quite fine technical structure details - the threads, tapers, etc with a great impact in masticatory force transmission. Modeling the contact between the implant and the bone tissue is important to a proper bone-implant interface model and implant design. The authors proposed a three-dimensional numerical model to assess the biomechanical behaviour of this complex structure in order to evaluate its stability by determining the risk zones. A comparison between this numerical analysis and clinical cases is performed and a good agreement is obtained.
Reduced-order modelling numerical homogenization.
Abdulle, A; Bai, Y
2014-08-06
A general framework to combine numerical homogenization and reduced-order modelling techniques for partial differential equations (PDEs) with multiple scales is described. Numerical homogenization methods are usually efficient to approximate the effective solution of PDEs with multiple scales. However, classical numerical homogenization techniques require the numerical solution of a large number of so-called microproblems to approximate the effective data at selected grid points of the computational domain. Such computations become particularly expensive for high-dimensional, time-dependent or nonlinear problems. In this paper, we explain how numerical homogenization method can benefit from reduced-order modelling techniques that allow one to identify offline and online computational procedures. The effective data are only computed accurately at a carefully selected number of grid points (offline stage) appropriately 'interpolated' in the online stage resulting in an online cost comparable to that of a single-scale solver. The methodology is presented for a class of PDEs with multiple scales, including elliptic, parabolic, wave and nonlinear problems. Numerical examples, including wave propagation in inhomogeneous media and solute transport in unsaturated porous media, illustrate the proposed method.
Numerical modeling techniques for flood analysis
NASA Astrophysics Data System (ADS)
Anees, Mohd Talha; Abdullah, K.; Nawawi, M. N. M.; Ab Rahman, Nik Norulaini Nik; Piah, Abd. Rahni Mt.; Zakaria, Nor Azazi; Syakir, M. I.; Mohd. Omar, A. K.
2016-12-01
Topographic and climatic changes are the main causes of abrupt flooding in tropical areas. It is the need to find out exact causes and effects of these changes. Numerical modeling techniques plays a vital role for such studies due to their use of hydrological parameters which are strongly linked with topographic changes. In this review, some of the widely used models utilizing hydrological and river modeling parameters and their estimation in data sparse region are discussed. Shortcomings of 1D and 2D numerical models and the possible improvements over these models through 3D modeling are also discussed. It is found that the HEC-RAS and FLO 2D model are best in terms of economical and accurate flood analysis for river and floodplain modeling respectively. Limitations of FLO 2D in floodplain modeling mainly such as floodplain elevation differences and its vertical roughness in grids were found which can be improve through 3D model. Therefore, 3D model was found to be more suitable than 1D and 2D models in terms of vertical accuracy in grid cells. It was also found that 3D models for open channel flows already developed recently but not for floodplain. Hence, it was suggested that a 3D model for floodplain should be developed by considering all hydrological and high resolution topographic parameter's models, discussed in this review, to enhance the findings of causes and effects of flooding.
Benchmarking numerical models of brittle thrust wedges
NASA Astrophysics Data System (ADS)
Buiter, Susanne J. H.; Schreurs, Guido; Albertz, Markus; Gerya, Taras V.; Kaus, Boris; Landry, Walter; le Pourhiet, Laetitia; Mishin, Yury; Egholm, David L.; Cooke, Michele; Maillot, Bertrand; Thieulot, Cedric; Crook, Tony; May, Dave; Souloumiac, Pauline; Beaumont, Christopher
2016-11-01
We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedge test, showing negligible internal deformation and maintaining the initial surface slope upon horizontal translation over a frictional interface. Eight codes participated in the unstable wedge test that examines the evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. The critical taper is recovered, but the models show two deformation modes characterised by either mainly forward dipping thrusts or a series of thrust pop-ups. We speculate that the two modes are caused by differences in effective basal boundary friction related to different algorithms for modelling boundary friction. The third experiment examines stacking of forward thrusts that are translated upward along a backward thrust. The results of the seven codes that run this experiment show variability in deformation style, number of thrusts, thrust dip angles and surface slope. Overall, our experiments show that numerical models run with different numerical techniques can successfully simulate laboratory brittle thrust wedge models at the cm-scale. In more detail, however, we find that it is challenging to reproduce sandbox-type setups numerically, because of frictional boundary conditions and velocity discontinuities. We recommend that future numerical-analogue comparisons use simple boundary conditions and that the numerical Earth Science community defines a plasticity test to resolve the variability in model shear zones.
Numerical modeling of the solar wind turbulence
Kryukov, I.A.; Pogorelov, N.V.; Zank, G.P.; ...
2012-05-21
Here we describe an extension of the Multi-Scale Fluid-Kinetic Simulation Suite (MSFLUKSS) by adding a solar wind turbulence model and a fluid treatment of pickup ions. Numerical results are presented of the time-dependent solar wind modeling with the boundary conditions provided by the OMNI data. The distributions of plasma properties and interplanetary magnetic field are compared with the Voyager 2 observations in the distant solar wind.
Numerical modeling tools for chemical vapor deposition
NASA Technical Reports Server (NTRS)
Jasinski, Thomas J.; Childs, Edward P.
1992-01-01
Development of general numerical simulation tools for chemical vapor deposition (CVD) was the objective of this study. Physical models of important CVD phenomena were developed and implemented into the commercial computational fluid dynamics software FLUENT. The resulting software can address general geometries as well as the most important phenomena occurring with CVD reactors: fluid flow patterns, temperature and chemical species distribution, gas phase and surface deposition. The physical models are documented which are available and examples are provided of CVD simulation capabilities.
Numerical modeling of nonintrusive inspection systems
Hall, J.; Morgan, J.; Sale, K.
1992-12-01
A wide variety of nonintrusive inspection systems have been proposed in the past several years for the detection of hidden contraband in airline luggage and shipping containers. The majority of these proposed techniques depend on the interaction of radiation with matter to produce a signature specific to the contraband of interest, whether drugs or explosives. In the authors` role as diagnostic specialists in the Underground Test Program over the past forty years, L-Division of the Lawrence Livermore National Laboratory has developed a technique expertise in the combined numerical and experimental modeling of these types of system. Based on their experience, they are convinced that detailed numerical modeling provides a much more accurate estimate of the actual performance of complex experiments than simple analytical modeling. Furthermore, the construction of detailed numerical prototypes allows experimenters to explore the entire region of parameter space available to them before committing their ideas to hardware. This sort of systematic analysis has often led to improved experimental designs and reductions in fielding costs. L-Division has developed an extensive suite of computer codes to model proposed experiments and possible background interactions. These codes allow one to simulate complex radiation sources, model 3-dimensional system geometries with {open_quotes}real world{close_quotes} complexity, specify detailed elemental distributions, and predict the response of almost any type of detector. In this work several examples are presented illustrating the use of these codes in modeling experimental systems at LLNL and their potential usefulness in evaluating nonintrusive inspection systems is discussed.
Quantifying Numerical Model Accuracy and Variability
NASA Astrophysics Data System (ADS)
Montoya, L. H.; Lynett, P. J.
2015-12-01
The 2011 Tohoku tsunami event has changed the logic on how to evaluate tsunami hazard on coastal communities. Numerical models are a key component for methodologies used to estimate tsunami risk. Model predictions are essential for the development of Tsunami Hazard Assessments (THA). By better understanding model bias and uncertainties and if possible minimizing them, a more accurate and reliable THA will result. In this study we compare runup height, inundation lines and flow velocity field measurements between GeoClaw and the Method Of Splitting Tsunami (MOST) predictions in the Sendai plain. Runup elevation and average inundation distance was in general overpredicted by the models. However, both models agree relatively well with each other when predicting maximum sea surface elevation and maximum flow velocities. Furthermore, to explore the variability and uncertainties in numerical models, MOST is used to compare predictions from 4 different grid resolutions (30m, 20m, 15m and 12m). Our work shows that predictions of particular products (runup and inundation lines) do not require the use of high resolution (less than 30m) Digital Elevation Maps (DEMs). When predicting runup heights and inundation lines, numerical convergence was achieved using the 30m resolution grid. On the contrary, poor convergence was found in the flow velocity predictions, particularly the 1 meter depth maximum flow velocities. Also, runup height measurements and elevations from the DEM were used to estimate model bias. The results provided in this presentation will help understand the uncertainties in model predictions and locate possible sources of errors within a model.
Numerical Modelling Of Pumpkin Balloon Instability
NASA Astrophysics Data System (ADS)
Wakefield, D.
Tensys have been involved in the numerical formfinding and load analysis of architectural stressed membrane structures for 15 years. They have recently broadened this range of activities into the `lighter than air' field with significant involvement in aerostat and heavy-lift hybrid airship design. Since early 2004 they have been investigating pumpkin balloon instability on behalf of the NASA ULDB programme. These studies are undertaken using inTENS, an in-house finite element program suite based upon the Dynamic Relaxation solution method and developed especially for the non-linear analysis and patterning of membrane structures. The paper describes the current state of an investigation that started with a numerical simulation of the lobed cylinder problem first studied by Calladine. The influence of material properties and local geometric deformation on stability is demonstrated. A number of models of complete pumpkin balloons have then been established, including a 64-gore balloon with geometry based upon Julian Nott's Endeavour. This latter clefted dramatically upon initial inflation, a phenomenon that has been reproduced in the numerical model. Ongoing investigations include the introduction of membrane contact modelling into inTENS and correlation studies with the series of large-scale ULDB models currently in preparation.
Lattice Boltzmann model for numerical relativity
NASA Astrophysics Data System (ADS)
Ilseven, E.; Mendoza, M.
2016-02-01
In the Z4 formulation, Einstein equations are written as a set of flux conservative first-order hyperbolic equations that resemble fluid dynamics equations. Based on this formulation, we construct a lattice Boltzmann model for numerical relativity and validate it with well-established tests, also known as "apples with apples." Furthermore, we find that by increasing the relaxation time, we gain stability at the cost of losing accuracy, and by decreasing the lattice spacings while keeping a constant numerical diffusivity, the accuracy and stability of our simulations improve. Finally, in order to show the potential of our approach, a linear scaling law for parallelization with respect to number of CPU cores is demonstrated. Our model represents the first step in using lattice kinetic theory to solve gravitational problems.
A Numerical Model for Atomtronic Circuit Analysis
Chow, Weng W.; Straatsma, Cameron J. E.; Anderson, Dana Z.
2015-07-16
A model for studying atomtronic devices and circuits based on finite-temperature Bose-condensed gases is presented. The approach involves numerically solving equations of motion for atomic populations and coherences, derived using the Bose-Hubbard Hamiltonian and the Heisenberg picture. The resulting cluster expansion is truncated at a level giving balance between physics rigor and numerical demand mitigation. This approach allows parametric studies involving time scales that cover both the rapid population dynamics relevant to nonequilibrium state evolution, as well as the much longer time durations typical for reaching steady-state device operation. This model is demonstrated by studying the evolution of a Bose-condensed gas in the presence of atom injection and extraction in a double-well potential. In this configuration phase locking between condensates in each well of the potential is readily observed, and its influence on the evolution of the system is studied.
Lattice Boltzmann model for numerical relativity.
Ilseven, E; Mendoza, M
2016-02-01
In the Z4 formulation, Einstein equations are written as a set of flux conservative first-order hyperbolic equations that resemble fluid dynamics equations. Based on this formulation, we construct a lattice Boltzmann model for numerical relativity and validate it with well-established tests, also known as "apples with apples." Furthermore, we find that by increasing the relaxation time, we gain stability at the cost of losing accuracy, and by decreasing the lattice spacings while keeping a constant numerical diffusivity, the accuracy and stability of our simulations improve. Finally, in order to show the potential of our approach, a linear scaling law for parallelization with respect to number of CPU cores is demonstrated. Our model represents the first step in using lattice kinetic theory to solve gravitational problems.
Infrared radiation parameterizations in numerical climate models
NASA Technical Reports Server (NTRS)
Chou, Ming-Dah; Kratz, David P.; Ridgway, William
1991-01-01
This study presents various approaches to parameterizing the broadband transmission functions for utilization in numerical climate models. One-parameter scaling is applied to approximate a nonhomogeneous path with an equivalent homogeneous path, and the diffuse transmittances are either interpolated from precomputed tables or fit by analytical functions. Two-parameter scaling is applied to parameterizing the carbon dioxide and ozone transmission functions in both the lower and middle atmosphere. Parameterizations are given for the nitrous oxide and methane diffuse transmission functions.
Numerical modeling of the acoustic guitar
NASA Astrophysics Data System (ADS)
Chaigne, Antoine; Derveaux, Grégoire; Joly, Patrick; Bécache, Eliane
2003-10-01
An interactive DVD has been created, based on a numerical model of the acoustic guitar. In a first chapter, the retained physical model is described and illustrated, from the pluck to the 3D radiation field. The second chapter is devoted to the presentation of the numerical tools used for solving the equations of the model. Numerical simulations of plate vibrations and radiated sound pressure are shown in the third chapter. A number of simulated sounds are presented and analyzed in the fourth chapter. In addition, the DVD includes a discussion between a guitar maker, an acoustician, a guitar player and a mathematician. This discussion is entitled ``towards a common language.'' Its aim is to show the interest of simulations with respect to complementary professional approaches of the instrument. This DVD received the Henri Poincaré Prize from the 8th Research Film Festival of Nancy (June 2003), sponsored by the CNRS, in the category ``Documents for the scientific community and illustrations of the research for teaching purpose.''
Avoiding numerical pitfalls in social force models
NASA Astrophysics Data System (ADS)
Köster, Gerta; Treml, Franz; Gödel, Marion
2013-06-01
The social force model of Helbing and Molnár is one of the best known approaches to simulate pedestrian motion, a collective phenomenon with nonlinear dynamics. It is based on the idea that the Newtonian laws of motion mostly carry over to pedestrian motion so that human trajectories can be computed by solving a set of ordinary differential equations for velocity and acceleration. The beauty and simplicity of this ansatz are strong reasons for its wide spread. However, the numerical implementation is not without pitfalls. Oscillations, collisions, and instabilities occur even for very small step sizes. Classic solution ideas from molecular dynamics do not apply to the problem because the system is not Hamiltonian despite its source of inspiration. Looking at the model through the eyes of a mathematician, however, we realize that the right hand side of the differential equation is nondifferentiable and even discontinuous at critical locations. This produces undesirable behavior in the exact solution and, at best, severe loss of accuracy in efficient numerical schemes even in short range simulations. We suggest a very simple mollified version of the social force model that conserves the desired dynamic properties of the original many-body system but elegantly and cost efficiently resolves several of the issues concerning stability and numerical resolution.
Advanced Numerical Model for Irradiated Concrete
Giorla, Alain B.
2015-03-01
In this report, we establish a numerical model for concrete exposed to irradiation to address these three critical points. The model accounts for creep in the cement paste and its coupling with damage, temperature and relative humidity. The shift in failure mode with the loading rate is also properly represented. The numerical model for creep has been validated and calibrated against different experiments in the literature [Wittmann, 1970, Le Roy, 1995]. Results from a simplified model are shown to showcase the ability of numerical homogenization to simulate irradiation effects in concrete. In future works, the complete model will be applied to the analysis of the irradiation experiments of Elleuch et al. [1972] and Kelly et al. [1969]. This requires a careful examination of the experimental environmental conditions as in both cases certain critical information are missing, including the relative humidity history. A sensitivity analysis will be conducted to provide lower and upper bounds of the concrete expansion under irradiation, and check if the scatter in the simulated results matches the one found in experiments. The numerical and experimental results will be compared in terms of expansion and loss of mechanical stiffness and strength. Both effects should be captured accordingly by the model to validate it. Once the model has been validated on these two experiments, it can be applied to simulate concrete from nuclear power plants. To do so, the materials used in these concrete must be as well characterized as possible. The main parameters required are the mechanical properties of each constituent in the concrete (aggregates, cement paste), namely the elastic modulus, the creep properties, the tensile and compressive strength, the thermal expansion coefficient, and the drying shrinkage. These can be either measured experimentally, estimated from the initial composition in the case of cement paste, or back-calculated from mechanical tests on concrete. If some
a Numerical Model for Subsonic Acoustic Choking.
NASA Astrophysics Data System (ADS)
Walkington, Noel John
In aircraft turbofan inlets, fan generated noise is observed experimentally to be significantly attenuated at high subsonic inlet Mach numbers. This phenomenon cannot be predicted by linear acoustic theory. In order to study the physical process by which this may occur, a numerical algorithm has been developed to solve a related nonlinear problem in one dimensional gas dynamics. The nonlinear solution admits the possibility of wave steepening and shock waves. Approximate solutions are obtained using several finite difference schemes. The boundary conditions required to model an acoustic source and an anechoic termination are developed. The numerical solutions agree closely with those obtained using the method of matched asymptotic expansions. Solutions involving shock waves exhibit a large reduction in the ratio of transmitted to incident power. This offers an explanation for acoustic choking. The results indicate that more power is dissipated as the Mach number, sound amplitude and frequency are increased. These observations are in agreement with those observed experimentally.
Constraining Numerical Geodynamo Modeling with Surface Observations
NASA Technical Reports Server (NTRS)
Kuang, Weijia; Tangborn, Andrew
2006-01-01
Numerical dynamo solutions have traditionally been generated entirely by a set of self-consistent differential equations that govern the spatial-temporal variation of the magnetic field, velocity field and other fields related to dynamo processes. In particular, those solutions are obtained with parameters very different from those appropriate for the Earth s core. Geophysical application of the numerical results therefore depends on correct understanding of the differences (errors) between the model outputs and the true states (truth) in the outer core. Part of the truth can be observed at the surface in the form of poloidal magnetic field. To understand these differences, or errors, we generate new initial model state (analysis) by assimilating sequentially the model outputs with the surface geomagnetic observations using an optimal interpolation scheme. The time evolution of the core state is then controlled by our MoSST core dynamics model. The final outputs (forecasts) are then compared with the surface observations as a means to test the success of the assimilation. We use the surface geomagnetic data back to year 1900 for our studies, with 5-year forecast and 20-year analysis periods. We intend to use the result; to understand time variation of the errors with the assimilation sequences, and the impact of the assimilation on other unobservable quantities, such as the toroidal field and the fluid velocity in the core.
Testing Numerical Dynamo Models Against Experimental Results
NASA Astrophysics Data System (ADS)
Gissinger, C. J.; Fauve, S.; Dormy, E.
2007-12-01
Significant progress has been achieved over the past few years in describing the geomagnetic field using computer models for dynamo action. Such models are so far limited to parameter regimes which are very remote from actual values relevant to the Earth core or any liquid metal (the magnetic Prandtl number is always over estimated by a factor at least 104). While existing models successfully reproduce many of the magnetic observations, it is difficult to assert their validity. The recent success of an experimental homogeneous unconstrained dynamo (VKS) provides a new way to investigate dynamo action in turbulent conducting flows, but it also offers a chance to test the validity of exisiting numerical models. We use a code originaly written for the Geodynamo (Parody) and apply it to the experimental configuration. The direct comparison of simulations and experiments is of great interest to test the predictive value of numerical simulations for dynamo action. These turbulent simulations allow us to approach issues which are very relevant for geophysical dynamos, especially the competition between different magnetic modes and the dynamics of reversals.
A numerical method to model excitable cells.
Joyner, R W; Westerfield, M; Moore, J W; Stockbridge, N
1978-01-01
We have extended a fast, stable, and accurate method for the numerical solution of cable equations to include changes in geometry and membrane properties in order to model a single excitable cell realistically. In addition, by including the provision that the radius may be a function of distance along an axis, we have achieved a general and powerful method for simulating a cell with any number of branched processes, any or all of which may be nonuniform in diameter, and with no restriction on the branching pattern. PMID:656539
Objective calibration of numerical weather prediction models
NASA Astrophysics Data System (ADS)
Voudouri, A.; Khain, P.; Carmona, I.; Bellprat, O.; Grazzini, F.; Avgoustoglou, E.; Bettems, J. M.; Kaufmann, P.
2017-07-01
Numerical weather prediction (NWP) and climate models use parameterization schemes for physical processes, which often include free or poorly confined parameters. Model developers normally calibrate the values of these parameters subjectively to improve the agreement of forecasts with available observations, a procedure referred as expert tuning. A practicable objective multi-variate calibration method build on a quadratic meta-model (MM), that has been applied for a regional climate model (RCM) has shown to be at least as good as expert tuning. Based on these results, an approach to implement the methodology to an NWP model is presented in this study. Challenges in transferring the methodology from RCM to NWP are not only restricted to the use of higher resolution and different time scales. The sensitivity of the NWP model quality with respect to the model parameter space has to be clarified, as well as optimize the overall procedure, in terms of required amount of computing resources for the calibration of an NWP model. Three free model parameters affecting mainly turbulence parameterization schemes were originally selected with respect to their influence on the variables associated to daily forecasts such as daily minimum and maximum 2 m temperature as well as 24 h accumulated precipitation. Preliminary results indicate that it is both affordable in terms of computer resources and meaningful in terms of improved forecast quality. In addition, the proposed methodology has the advantage of being a replicable procedure that can be applied when an updated model version is launched and/or customize the same model implementation over different climatological areas.
Convecting reference frames and invariant numerical models
NASA Astrophysics Data System (ADS)
Bihlo, Alexander; Nave, Jean-Christophe
2014-09-01
In the recent paper by Bernardini et al. [1] the discrepancy in the performance of finite difference and spectral models for simulations of flows with a preferential direction of propagation was studied. In a simplified investigation carried out using the viscous Burgers equation the authors attributed the poorer numerical results of finite difference models to a violation of Galilean invariance in the discretization and propose to carry out the computations in a reference frame moving with the bulk velocity of the flow. Here we further discuss this problem and relate it to known results on invariant discretization schemes. Non-invariant and invariant finite difference discretizations of Burgers equation are proposed and compared with the discretization using the remedy proposed by Bernardini et al.
NUMERICAL MODELING OF CATHODE CONTACT MATERIAL DENSIFICATION
Koeppel, Brian J.; Liu, Wenning N.; Stephens, Elizabeth V.; Khaleel, Mohammad A.
2011-11-01
Numerical modeling was used to simulate the constrained sintering process of the cathode contact layer during assembly of solid oxide fuel cells (SOFCs). A finite element model based on the continuum theory for sintering of porous bodies was developed and used to investigate candidate low-temperature cathode contact materials. Constitutive parameters for various contact materials under investigation were estimated from dilatometry screening tests, and the influence of processing time, processing temperature, initial grain size, and applied compressive stress on the free sintering response was predicted for selected candidate materials. The densification behavior and generated stresses within a 5-cell planar SOFC stack during sintering, high temperature operation, and room temperature shutdown were predicted. Insufficient constrained densification was observed in the stack at the proposed heat treatment, but beneficial effects of reduced grain size, compressive stack preload, and reduced thermal expansion coefficient on the contact layer densification and stresses were observed.
Adaptive Numerical Algorithms in Space Weather Modeling
NASA Technical Reports Server (NTRS)
Toth, Gabor; vanderHolst, Bart; Sokolov, Igor V.; DeZeeuw, Darren; Gombosi, Tamas I.; Fang, Fang; Manchester, Ward B.; Meng, Xing; Nakib, Dalal; Powell, Kenneth G.; Stout, Quentin F.; Glocer, Alex; Ma, Ying-Juan; Opher, Merav
2010-01-01
Space weather describes the various processes in the Sun-Earth system that present danger to human health and technology. The goal of space weather forecasting is to provide an opportunity to mitigate these negative effects. Physics-based space weather modeling is characterized by disparate temporal and spatial scales as well as by different physics in different domains. A multi-physics system can be modeled by a software framework comprising of several components. Each component corresponds to a physics domain, and each component is represented by one or more numerical models. The publicly available Space Weather Modeling Framework (SWMF) can execute and couple together several components distributed over a parallel machine in a flexible and efficient manner. The framework also allows resolving disparate spatial and temporal scales with independent spatial and temporal discretizations in the various models. Several of the computationally most expensive domains of the framework are modeled by the Block-Adaptive Tree Solar wind Roe Upwind Scheme (BATS-R-US) code that can solve various forms of the magnetohydrodynamics (MHD) equations, including Hall, semi-relativistic, multi-species and multi-fluid MHD, anisotropic pressure, radiative transport and heat conduction. Modeling disparate scales within BATS-R-US is achieved by a block-adaptive mesh both in Cartesian and generalized coordinates. Most recently we have created a new core for BATS-R-US: the Block-Adaptive Tree Library (BATL) that provides a general toolkit for creating, load balancing and message passing in a 1, 2 or 3 dimensional block-adaptive grid. We describe the algorithms of BATL and demonstrate its efficiency and scaling properties for various problems. BATS-R-US uses several time-integration schemes to address multiple time-scales: explicit time stepping with fixed or local time steps, partially steady-state evolution, point-implicit, semi-implicit, explicit/implicit, and fully implicit numerical
Adaptive numerical algorithms in space weather modeling
NASA Astrophysics Data System (ADS)
Tóth, Gábor; van der Holst, Bart; Sokolov, Igor V.; De Zeeuw, Darren L.; Gombosi, Tamas I.; Fang, Fang; Manchester, Ward B.; Meng, Xing; Najib, Dalal; Powell, Kenneth G.; Stout, Quentin F.; Glocer, Alex; Ma, Ying-Juan; Opher, Merav
2012-02-01
Space weather describes the various processes in the Sun-Earth system that present danger to human health and technology. The goal of space weather forecasting is to provide an opportunity to mitigate these negative effects. Physics-based space weather modeling is characterized by disparate temporal and spatial scales as well as by different relevant physics in different domains. A multi-physics system can be modeled by a software framework comprising several components. Each component corresponds to a physics domain, and each component is represented by one or more numerical models. The publicly available Space Weather Modeling Framework (SWMF) can execute and couple together several components distributed over a parallel machine in a flexible and efficient manner. The framework also allows resolving disparate spatial and temporal scales with independent spatial and temporal discretizations in the various models. Several of the computationally most expensive domains of the framework are modeled by the Block-Adaptive Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code that can solve various forms of the magnetohydrodynamic (MHD) equations, including Hall, semi-relativistic, multi-species and multi-fluid MHD, anisotropic pressure, radiative transport and heat conduction. Modeling disparate scales within BATS-R-US is achieved by a block-adaptive mesh both in Cartesian and generalized coordinates. Most recently we have created a new core for BATS-R-US: the Block-Adaptive Tree Library (BATL) that provides a general toolkit for creating, load balancing and message passing in a 1, 2 or 3 dimensional block-adaptive grid. We describe the algorithms of BATL and demonstrate its efficiency and scaling properties for various problems. BATS-R-US uses several time-integration schemes to address multiple time-scales: explicit time stepping with fixed or local time steps, partially steady-state evolution, point-implicit, semi-implicit, explicit/implicit, and fully implicit
Global Tectonics of Enceladus: Numerical Model
NASA Astrophysics Data System (ADS)
Czechowski, Leszek
2016-10-01
Introduction: Enceladus, a satellite of Saturn, is the smallest celestial body in the Solar System where volcanic and tectonic activities are observed. Every second, the mass of 200 kg is ejected into space from the South Polar Terrain (SPT) - [1]. The loss of matter from the body's interior should lead to global compression of the crust. Typical effects of compression are: thrust faults, folding and subduction. However, such forms are not dominant on Enceladus. We propose here special tectonic process that could explain this paradox. Our hypotheses states that the mass loss from SPT is the main driving mechanism of the following tectonic processes: subsidence of SPT, flow in the mantle and motion of adjacent tectonic plates. The hypotheses is presented in [2], [3] and[4].We suggest that the loss of the volatiles results in a void, an instability, and motion of solid matter to fill the void. The motion is presented at the Fig.1 and includes:Subsidence of the 'lithosphere' of SPT.Flow of the matter in the mantle.Motion of plates adjacent to SPT towards the active regionMethods and results: The numerical model of processes presented is developed. It is based on the equations of continuous media..If emerging void is being filled by the subsidence of SPT only, then the velocity of subsidence is 0.05 mmyr-1. However, numerical calculations indicate that all three types of motion are usually important. The role of a given motion depends on the viscosity distribution. Generally, for most of the models the subsidence is 0.02 mmyr-1, but mantle flow and plates' motion also play a role in filling the void. The preliminary results of the numerical model indicate also that the velocity of adjacent plates could be 0.02 mmyr-1 for the Newtonian rheology.Note that in our model the reduction of the crust area is not a result of compression but it is a result of the plate sinking. Therefore the compressional surface features do not have to be dominant. The SPT does not have to be
Numerical modeling of volcanic arc development
NASA Astrophysics Data System (ADS)
Gerya, T.; Gorczyk, W.; Nikolaeva, K.
2007-05-01
We have created a new coupled geochemical-petrological-thermomechanical numerical model of subduction associated with volcanic arc development. The model includes spontaneous slab bending, subducted crust dehydration, aqueous fluid transport, mantle wedge melting and melt extraction resulting in crustal growth. Two major volcanic arc settings are modeled so far: active continental margins, and intraoceanic subduction. In case of Pacific-type continental margin two fundamentally different regimes of melt productivity are observed in numerical experiments which are in line with natural observations: (1) During continuous convergence with coupled plates highest amounts of melts are formed immediately after the initiation of subduction and then decrease rapidly with time due to the steepening of the slab inclination angle precluding formation of partially molten mantle wedge plumes; (2) During subduction associated with slab delamination and trench retreat resulting in the formation of a pronounced back arc basin with a spreading center in the middle melt production increases with time due to shallowing/stabilization of slab inclination associated with upward asthenospheric mantle flow toward the extension region facilitating propagation of hydrous partially molten plumes from the slab. In case of spontaneous nucleation of retreating oceanic subduction two scenarios of tecono-magmatic evolution are distinguished: (1) decay and, ultimately, the cessation of subduction and related magmatic activity, (2) increase in subduction rate (to up to ~12 cm/yr) and stabilization of subduction and magmatic arc growth. In the first case the duration of subduction correlates positively with the intensity of melt extraction: the period of continued subduction increases from 15,4 Myrs to 47,6 Myrs with the increase of melt extraction threshold from 1% to 9%. In scenario (1) the magmatic arc crust includes large amounts of rocks formed by melting of subducted crust atop the thermally
Anisotropic halo model: implementation and numerical results
NASA Astrophysics Data System (ADS)
Sgró, Mario A.; Paz, Dante J.; Merchán, Manuel
2013-07-01
In the present work, we extend the classic halo model for the large-scale matter distribution including a triaxial model for the halo profiles and their alignments. In particular, we derive general expressions for the halo-matter cross-correlation function. In addition, by numerical integration, we obtain instances of the cross-correlation function depending on the directions given by halo shape axes. These functions are called anisotropic cross-correlations. With the aim of comparing our theoretical results with the simulations, we compute averaged anisotropic correlations in cones with their symmetry axis along each shape direction of the centre halo. From these comparisons we characterize and quantify the alignment of dark matter haloes on the Λcold dark matter context by means of the presented anisotropic halo model. Since our model requires multidimensional integral computation we implement a Monte Carlo method on GPU hardware which allows us to increase the precision of the results and it improves the performance of the computation.
Oblique Impact and Its Ejecta: Numerical Modeling
NASA Astrophysics Data System (ADS)
Artemieva, N.; Pierazzo, E.
2003-01-01
It is well known that impact events strike planetary surfaces at an angle from the surface. Assuming an isotropic flux of projectiles, probability theory indicates that the most likely angle of impact is 45 regardless of the body's gravitational field. While crater rims appear circular down to low impact angles, the distribution of ejecta around the crater is sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts. A fair amount of numerical modeling of vertical impacts has been carried out from the early 60-s to the present time and references herein]. In vertical impacts, the axial symmetry of the process allows the simplification of the model to two dimensions (2D). Oblique impact modeling requires 3D hydro-codes and, hence, much more powerful computers. The first documented detailed oblique impact studies were carried out at Sandia National Labs' supercomputers less than 10 years ago to describe the 1994 collision of comet SL9 with Jupiter. Since then, substantial progress in computer science has made 3D modeling a reachable objective for the scientific community.
Numerical Modeling of Ocular Dysfunction in Space
NASA Technical Reports Server (NTRS)
Nelson, Emily S.; Mulugeta, Lealem; Vera, J.; Myers, J. G.; Raykin, J.; Feola, A. J.; Gleason, R.; Samuels, B.; Ethier, C. R.
2014-01-01
Upon introduction to microgravity, the near-loss of hydrostatic pressure causes a marked cephalic (headward) shift of fluid in an astronaut's body. The fluid shift, along with other factors of spaceflight, induces a cascade of interdependent physiological responses which occur at varying time scales. Long-duration missions carry an increased risk for the development of the Visual Impairment and Intracranial Pressure (VIIP) syndrome, a spectrum of ophthalmic changes including posterior globe flattening, choroidal folds, distension of the optic nerve sheath, kinking of the optic nerve and potentially permanent degradation of visual function. In the cases of VIIP found to date, the initial onset of symptoms occurred after several weeks to several months of spaceflight, by which time the gross bodily fluid distribution is well established. We are developing a suite of numerical models to simulate the effects of fluid shift on the cardiovascular, central nervous and ocular systems. These models calculate the modified mean volumes, flow rates and pressures that are characteristic of the altered quasi-homeostatic state in microgravity, including intracranial and intraocular pressures. The results of the lumped models provide initial and boundary data to a 3D finite element biomechanics simulation of the globe, optic nerve head and retrobulbar subarachnoid space. The integrated set of models will be used to investigate the evolution of the biomechanical stress state in the ocular tissues due to long-term exposure to microgravity.
Numerical Modeling of Glaciers in Martian Paleoclimates
NASA Technical Reports Server (NTRS)
Colaprete, A.; Haberle, R. M.; Montmessin, F.; Scheaffer, J.
2004-01-01
Numerous geologic features suggest the presence of ice flow on the surface of mars. These features include lobate debris aprons, concentric crater fill, and lineated valley fill. The lateral extent of these features can range from 100 meters to over 20 km. Previous work has demonstrated that these features could not have formed in current Martian conditions. It has long been speculated that changes in Mars orbital properties, namely its obliquity, eccentricity, and argument of perihelion, can result in dramatic changes to climate. Recent climate model studies have shown that at periods of increased obliquity north polar water ice is mobilized southward and deposited at low ad mid latitudes. Mid latitude accumulation of ice would provide the necessary conditions for rock glaciers to form. A time-marching, finite element glacier model is used to demonstrate the ability of ice and ice-rock mixtures to flow under Martian paleoclimate conditions. Input to this model is constrained by the NASA Ames Mars General Circulation Model (MGCM).
Numerical modeling of a vortex stabilized arcjet
NASA Astrophysics Data System (ADS)
Pawlas, Gary Edward
Arcjet thrusters are being actively considered for use in Earth orbit maneuvering applications. Satellite station-keeping is an example of a maneuvering application requiring the low thrust, high specific impulse of an arcjet. Experimental studies are currently the chief means of determining an optimal thruster configuration. Earlier numerical studies have failed to include all of the effects found in typical arcjets including complex geometries, viscosity and swirling flow. Arcjet geometries are large area ratio converging-diverging nozzles with centerbodies in the subsonic portion of the nozzle. The nozzle walls serve as the anode while the centerbody functions as the cathode. Viscous effects are important because the Reynolds number, based on the throat radius, is typically less than 1,000. Experimental studies have shown a swirl or circumferential velocity component stabilizes a constricted arc. The equations are described which governs the flow through a constricted arcjet thruster. An assumption that the flowfield is in local thermodynamic equilibrium leads to a single fluid plasma temperature model. An order of magnitude analysis reveals the governing fluid mechanics equations are uncoupled from the electromagnetic field equations. A numerical method is developed to solve the governing fluid mechanics equations, the Thin Layer Navier-Stokes equations. A coordinate transformation is used in deriving the governing equations to simplify the application of boundary conditions in complex geometries. An axisymmetric formulation is employed to include the swirl velocity component as well as the axial and redial velocity components. The numerical method is an implicit finite-volume technique and allows for large time steps to reach a converged steady-state solution. The inviscid fluxes are flux-split and Gauss-Seidel line relaxation is used to accelerate convergence. 'Converging diverging' nozzles with exit-to-throat area ratios up to 100:1 and annual nozzles were
Modeling Biodegradation and Reactive Transport: Analytical and Numerical Models
Sun, Y; Glascoe, L
2005-06-09
The computational modeling of the biodegradation of contaminated groundwater systems accounting for biochemical reactions coupled to contaminant transport is a valuable tool for both the field engineer/planner with limited computational resources and the expert computational researcher less constrained by time and computer power. There exists several analytical and numerical computer models that have been and are being developed to cover the practical needs put forth by users to fulfill this spectrum of computational demands. Generally, analytical models provide rapid and convenient screening tools running on very limited computational power, while numerical models can provide more detailed information with consequent requirements of greater computational time and effort. While these analytical and numerical computer models can provide accurate and adequate information to produce defensible remediation strategies, decisions based on inadequate modeling output or on over-analysis can have costly and risky consequences. In this chapter we consider both analytical and numerical modeling approaches to biodegradation and reactive transport. Both approaches are discussed and analyzed in terms of achieving bioremediation goals, recognizing that there is always a tradeoff between computational cost and the resolution of simulated systems.
Transient Numerical Modeling of Catalytic Channels
NASA Technical Reports Server (NTRS)
Struk, Peter M.; Dietrich, Daniel L.; Miller, Fletcher J.; T'ien, James S.
2007-01-01
This paper presents a transient model of catalytic combustion suitable for isolated channels and monolith reactors. The model is a lumped two-phase (gas and solid) model where the gas phase is quasi-steady relative to the transient solid. Axial diffusion is neglected in the gas phase; lateral diffusion, however, is accounted for using transfer coefficients. The solid phase includes axial heat conduction and external heat loss due to convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations while the solid phase reduces, after discretization, into a system of stiff ordinary differential-algebraic equations. The time evolution of the system came from alternating integrations of the quasi-steady gas and transient solid. This work outlines the numerical model and presents some sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, and external heat-loss (if applicable). The model is compared to two experiments using CO fuel: (1) steady-state conversion through an isothermal platinum (Pt) tube and (2) transient propagation of a catalytic reaction inside a small Pt tube. The model requires internal mass-transfer resistance to match the experiments at lower residence times. Under mass-transport limited conditions, the model reasonably predicted exit conversion using global mass-transfer coefficients. Near light-off, the model results did not match the experiment precisely even after adjustment of mass-transfer coefficients. Agreement improved for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increased compared to O2. The CO / O2 surface mechanism came from a sub-set of reactions in a popular CH4 / O2 mechanism. For the second case, predictions improved for lean conditions with increased external heat loss or adjustment of the kinetics as in the
Numerical Modeling of Supra-Arcade Downflows
NASA Astrophysics Data System (ADS)
Huang, Y. M.; Bhattacharjee, A.; Guo, L.; Innes, D.
2015-12-01
Abstract Supra-arcade downflows (SADs) are elongated features usually observed above post-eruption flare arcades, with low emission, low density, and high temperature. Although SADs have been observed and studied extensively, their physical interpretation and mechanism remain not well understood and controversial. In our recent numerical and observational studies, we suggest that SADs may be due to Rayleigh-Taylor type instabilities occurring at the front of reconnection outflow jets as they encounter the underlying arcades (Innes et al. Astrophys. J. 796, 27; Guo et al. Astrophys. J. Lett., 796, L29). In this work, we further improve our three-dimensional magnetohydrodynamic model of SADs by incorporating viscous and resistive heating, anisotropic heat conduction, as well as line-tied lower boundary conditions. Synthetic SDO AIA emission measure profiles are calculated from simulation data and compared with observations.
Numerical linearized MHD model of flapping oscillations
NASA Astrophysics Data System (ADS)
Korovinskiy, D. B.; Ivanov, I. B.; Semenov, V. S.; Erkaev, N. V.; Kiehas, S. A.
2016-06-01
Kink-like magnetotail flapping oscillations in a Harris-like current sheet with earthward growing normal magnetic field component Bz are studied by means of time-dependent 2D linearized MHD numerical simulations. The dispersion relation and two-dimensional eigenfunctions are obtained. The results are compared with analytical estimates of the double-gradient model, which are found to be reliable for configurations with small Bz up to values ˜ 0.05 of the lobe magnetic field. Coupled with previous results, present simulations confirm that the earthward/tailward growth direction of the Bz component acts as a switch between stable/unstable regimes of the flapping mode, while the mode dispersion curve is the same in both cases. It is confirmed that flapping oscillations may be triggered by a simple Gaussian initial perturbation of the Vz velocity.
Numerical modelling of ion transport in flames
NASA Astrophysics Data System (ADS)
Han, Jie; Belhi, Memdouh; Bisetti, Fabrizio; Mani Sarathy, S.
2015-11-01
This paper presents a modelling framework to compute the diffusivity and mobility of ions in flames. The (n, 6, 4) interaction potential is adopted to model collisions between neutral and charged species. All required parameters in the potential are related to the polarizability of the species pair via semi-empirical formulas, which are derived using the most recently published data or best estimates. The resulting framework permits computation of the transport coefficients of any ion found in a hydrocarbon flame. The accuracy of the proposed method is evaluated by comparing its predictions with experimental data on the mobility of selected ions in single-component neutral gases. Based on this analysis, the value of a model constant available in the literature is modified in order to improve the model's predictions. The newly determined ion transport coefficients are used as part of a previously developed numerical approach to compute the distribution of charged species in a freely propagating premixed lean CH4/O2 flame. Since a significant scatter of polarizability data exists in the literature, the effects of changes in polarizability on ion transport properties and the spatial distribution of ions in flames are explored. Our analysis shows that changes in polarizability propagate with decreasing effect from binary transport coefficients to species number densities. We conclude that the chosen polarizability value has a limited effect on the ion distribution in freely propagating flames. We expect that the modelling framework proposed here will benefit future efforts in modelling the effect of external voltages on flames. Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/13647830.2015.1090018.
Foehn wind detection using numerical modelling
NASA Astrophysics Data System (ADS)
Irimescu, A.; Caian, M.
2010-09-01
In Romania, foehn is a short-lived atmospheric phenomenon, of a low to average intensity, not always highlighted by weather station observations. When such situations occur additional data are resorted to, rendering a continuous, aggregate image, in comparison to the punctual information yielded by weather stations. This paper aims to describe how foehn is detected in northern Oltenia (the Inner Carpathian-Balkan Curvature), using numerical modelling. Results generated by the RegCM3 Regional Climatic Model thus represent an undisputed tool, their most important advantage being the 10-km spatial resolution. The presence of foehn in northern Oltenia and its climatic peculiarities have been disclosed through the analysis in time and space of the meteorological elements specific to the phenomenon (air temperature, wind speed and direction etc) over a 40-year interval (1961-2000). The paper presents a new methodology that can be used to estimate the probability of production and the foehn characteristics (intensity, duration etc.). Interpretation of the RegCM3 model results has led to the statistical analysis of foehn occurrences within the studied area during the cold season (December, January and February). The resulted climatology, with fine resolution, can be used in foehn forecast of predictability.
Numerical Modeling of Suspension HVOF Spray
NASA Astrophysics Data System (ADS)
Jadidi, M.; Moghtadernejad, S.; Dolatabadi, A.
2016-02-01
A three-dimensional two-way coupled Eulerian-Lagrangian scheme is used to simulate suspension high-velocity oxy-fuel spraying process. The mass, momentum, energy, and species equations are solved together with the realizable k-ɛ turbulence model to simulate the gas phase. Suspension is assumed to be a mixture of solid particles [mullite powder (3Al2O3·2SiO2)], ethanol, and ethylene glycol. The process involves premixed combustion of oxygen-propylene, and non-premixed combustion of oxygen-ethanol and oxygen-ethylene glycol. One-step global reaction is used for each mentioned reaction together with eddy dissipation model to compute the reaction rate. To simulate the droplet breakup, Taylor Analogy Breakup model is applied. After the completion of droplet breakup, and solvent evaporation/combustion, the solid suspended particles are tracked through the domain to determine the characteristics of the coating particles. Numerical simulations are validated against the experimental results in the literature for the same operating conditions. Seven or possibly eight shock diamonds are captured outside the nozzle. In addition, a good agreement between the predicted particle temperature, velocity, and diameter, and the experiment is obtained. It is shown that as the standoff distance increases, the particle temperature and velocity reduce. Furthermore, a correlation is proposed to determine the spray cross-sectional diameter and estimate the particle trajectories as a function of standoff distance.
Impact of numerical models on fragmentation processes
NASA Astrophysics Data System (ADS)
Renouf, Mathieu; Gezahengn, Belien; Abbas, Micheline; Bourgeois, Florent
2013-06-01
Simulated fragmentation process in granular assemblies is a challenging problem which date back the beginning of the 90'. If first approaches have focus on the fragmentation on a single particle, with the development of robust, fast numerical method is is possible today to simulated such process in a large collection of particles. But the question of the fragmentation problem is still open: should the fragmentation be done dynamically (one particle becoming two fragments) and according which criterion or should the fragment paths be defined initially and which is the impact of the discretization and the model of fragments? The present contribution proposes to investigate the second aspect i.e. the impact of fragment modeling on the fragmentation processes. First to perform such an analysis, the geometry of fragments (disks/sphere or polygon/polyhedra), their behavior (rigid/deformable) and the law governing their interactions are investigated. Then such model will be used in a grinding application where the evolution of fragments and impact on the behavior of the whole packing are investigate.
Numerical modeling of polar mesocyclones generation mechanisms
NASA Astrophysics Data System (ADS)
Sergeev, Dennis; Stepanenko, Victor
2013-04-01
parameters, lateral boundary conditions are varied in the typically observed range. The approach is fully nonlinear: we use a three-dimensional non-hydrostatic mesoscale model NH3D_MPI [1] coupled with one-dimensional water body model LAKE. A key method used in the present study is the analysis of eddy kinetic and available potential energy budgets. References 1. Mikushin, D.N., and Stepanenko, V.M., The implementation of regional atmospheric model numerical algorithms for CBEA-based clusters. Lecture Notes in Computer Science, Parallel Processing and Applied Mathematics, 2010, vol. 6067, p. 525-534. 2. Rasmussen, E., and Turner, J. (eds), Polar Lows: Mesoscale Weather Systems in the Polar Regions. Cambridge: Cambridge University Press, 2003, 612 pp. 3. Yanase, W., and Niino, H., Dependence of Polar Low Development on Baroclinicity and Physical Processes: An Idealized High-Resolution Experiment, J. Atmos. Sci., 2006, vol. 64, p. 3044-3067.
Numerical Models of Ophiolite Genesis and Obduction
NASA Astrophysics Data System (ADS)
Guilmette, C.; Beaumont, C.; Jamieson, R.
2013-12-01
Ophiolites are relics of oceanic lithosphere tectonically emplaced in continental settings. They are diagnostic features of continental suture zones, where they mark past plate boundaries. Even after having been studied for more than 40 years, the mechanisms involved in the genesis and subsequent obduction of ophiolites over continental margins are still debated. We present the results of 2D thermal-mechanical numerical models that successfully reproduce characteristics of natural examples like the Semail, Bay of Islands, Yarlung-Zangbo, and Coast Range ophiolites. The numerical models are upper mantle scale and use pressure-, temperature- and strain-dependent viscous-plastic rheologies. Both divergent and convergent velocity boundary conditions are used and tectonic boundary forces are monitored. The models start with the rifting of a stable continent, followed by development of an ocean ridge and accretion of oceanic lithosphere at a total rate of 3 cm/y. Once a specified ocean size/age is achieved, the velocity boundary conditions are reversed leading to convergence and the spontaneous inception of a suduction zone at the mid-ocean ridge. We present results for models including different ages of oceans (40 to 90 Ma) and different convergence velocities (5 to 15 cm/y). The interaction between the lower plate passive margin and the oceanic upper plate results in 5 different tectonic styles. These differ mainly by the presence or absence of oceanic spreading in the upper plate (back-arc basin), leading to supra-subduction zone ophiolites vs. MORB-type, and by the behaviour of the oceanic slab, e.g., slab rollback vs. breakoff. The evolution of effective slab pull is interpreted to be the major control on the resulting tectonic style. Low effective slab pull models (young oceans and fast convergence rates) fail to obduct an ophiolite. Strong effective slab pull models (old oceans and lower convergence rates) result in subduction zone retreat and spontaneous oceanic
Numerical modeling of a vortex stabilized arcjet
NASA Astrophysics Data System (ADS)
Pawlas, Gary E.
1992-11-01
Arcjet thrusters are being actively considered for use in Earth orbit maneuvering applications. Experimental studies are currently the chief means of determining an optimal thruster configuration. Earlier numerical studies have failed to include all of the effects found in typical arcjets including complex geometries, viscosity, and swirling flow. Arcjet geometries are large area ratio converging nozzles with centerbodies in the subsonic portion of the nozzle. The nozzle walls serve as the anode while the centerbody functions as the cathode. Viscous effects are important because the Reynolds number, based on the throat radius, is typically less than 1,000. Experimental studies have shown that a swirl or circumferential velocity component stabilizes a constricted arc. This dissertation describes the equations governing flow through a constricted arcjet thruster. An assumption that the flowfield is in local thermodynamic equilibrium leads to a single fluid plasma temperature model. An order of magnitude analysis reveals the governing fluid mechanics equations are uncoupled from the electromagnetic field equations. A numerical method is developed to solve the governing fluid mechanics equations, the Thin Layer Navier-Stokes equations. A coordinate transformation is employed in deriving the governing equations to simplify the application of boundary conditions in complex geometries. An axisymmetric formulation is employed to include the swirl velocity component as well as the axial and radial velocity components. The numerical method is an implicit finite-volume technique and allows for large time steps to reach a converged steady-state solution. The inviscid fluxes are flux-split, and Gauss-Seidel line relaxation is used to accelerate convergence. Converging-diverging nozzles with exit-to-throat area ratios up to 100:1 and annular nozzles were examined. Quantities examined included Mach number and static wall pressure distributions, and oblique shock structures. As
Numerical Modeling of a Magnetic Nozzle
NASA Astrophysics Data System (ADS)
Tushentsov, Mikhail; Breizman, Boris; Arefiev, Alexey
2007-11-01
We present computational study of a magnetic nozzle, which is a component of the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) plasma-based propulsion system for a space vehicle. The magnetic nozzle transforms ion gyromotion into directed axial motion, adiabatically accelerating the plasma, and enabling plasma detachment from the spaceship via self-consistent magnetic field modification. VASIMR employs ion cyclotron resonance heating to deposit rf-power directly to the plasma ions created by the low energy plasma source. We have developed a numerical code to model the axisymmetric nozzle within the framework of collisionless MHD with an azimuthal ion velocity spread. The code implements a reduced model that consists of truncated steady-state equations for the velocity space moments of the ion distribution function and takes advantage of the plasma flow paraxiality. This makes it possible to study the conversion of the ion gyro-energy at the nozzle entrance into the energy of the directed flow at the exhaust. The magnetic field in the vacuum, which is not assumed to be paraxial, is calculated using a given magnetic coil configuration in the presence of plasma. From the computed steady-state flow configuration, the code evaluates magnetic nozzle efficiency, defined as the ratio of the axial momentum flux in the outgoing flow to the axial momentum flux in the incoming flow.
Frustration in model glass systems: Numerical investigations
NASA Astrophysics Data System (ADS)
Jullien, Rémi; Jund, Philippe; Caprion, Didier; Sadoc, Jean-François
1999-11-01
Numerical Voronoï tessellation is used to investigate the mechanisms of frustration in some model glass systems. First, random packings of 8192 hard spheres of increasing volume fraction c are built using an efficient computer algorithm. Their Voronoï statistics evolves with c as if the system would like to reach a pure icosahedral order when extrapolating the volume fraction above the Bernal limit cb≃0.645. Second, super-cooled liquid and glass samples of 1000 atoms are generated at different temperatures T after a quench from the liquid state, using classical micro-canonical molecular dynamics with a simple soft-sphere potential. When decreasing T, the ideal icosahedral order appears again as an extrapolated situation which cannot be realized due to geometrical frustration. Third, a model silica glass of 648 atoms is studied using the potential of van Beest, Kramer and van Santen and a quite similar quenching procedure is performed. As in the soft-sphere case the structural freezing following upon the glass transition is noticeable in all the geometrical characteristics of the Voronoï cells and again a possible interpretation in terms of geometrical frustration is proposed.
Numerical modeling of atoll island hydrogeology.
Bailey, R T; Jenson, J W; Olsen, A E
2009-01-01
We implemented Ayers and Vachers' (1986) inclusive conceptual model for atoll island aquifers in a comprehensive numerical modeling study to evaluate the response of the fresh water lens to selected controlling climatic and geologic variables. Climatic factors include both constant and time-varying recharge rates, with particular attention paid to the effects of El Niño and the associated drought it brings to the western Pacific. Geologic factors include island width; hydraulic conductivity of the uppermost Holocene-age aquifer, which contains the fresh water lens; the depth to the contact with the underlying, and much more conductive, Pleistocene karst aquifer, which transmits tidal signals to the base of the lens; and the presence or absence of a semiconfining reef flat plate on the ocean side. Sensitivity analyses of steady-steady simulations show that lens thickness is most strongly sensitive to the depth to the Holocene-Pleistocene contact and to the hydraulic conductivity of the Holocene aquifer, respectively. Comparisons between modeling results and published observations of atoll island lens thicknesses suggest a hydraulic conductivity of approximately 50 m/d for leeward islands and approximately 400 m/d for windward islands. Results of transient simulations show that lens thickness fluctuations during average seasonal conditions and El Niño events are quite sensitive to island width, recharge rate, and hydraulic conductivity of the Holocene aquifer. In general, the depletion of the lens during drought conditions is most drastic for small, windward islands. Simulation results suggest that recovery from a 6-month drought requires about 1.5 years.
Numerical model of circumpolar Antarctic ice shelves
Johnson, R.C.
1985-01-01
Extensive floating ice shelves in the Antarctic have been proposed to explain the discrepancies between Pleistocene high sea levels shown by dated coral reefs and coeval low sea levels inferred from glacial ice volumes calculated from oxygen isotope ratios in deep sea cores. A numerical model using the floating shelf creep analysis of Weertman (1957) has provided a plausible basis for the acceptance of such shelves. Shelf outer limits were set at 55/sup 0/S in East Antarctica and 58/sup 0/S in West Antarctica, based in part on diatom-deficient deep sea sediments deposited prior to the Holocene. Precipitation varied from 10 gm cm/sup -2/yr/sup -1/ at 75/sup 0/S to 80 gm cm/sup -2/yr/sup -1/ at 55/sup 0/S. Mean air temperatures varied from -35/sup 0/C at the 75/sup 0/S coast to -17/sup 0/C at the outer limits. Isotope ratios were those of present Antarctic precipitation at corresponding model shelf temperatures. In the calculation, a steady state is assumed. Integration begins at the coast with summation over successive years as creep and continental ice discharge move the integration element to the outer limits. The oceanic oxygen isotope ratio change required by the discrepancies in the record is 0.40 to 0.50 ppmil. Using the flow law constant of 4.2 and a creep activation energy of 134 kjoules mol/sup -1/, the resulting change is 0.44 ppmil. Difference results reflect the uncertainties associated with the critical creep constants used in the modeling. Nevertheless, the results suggest that a quantity of Antarctic shelf ice comparable to ice volumes in major Northern glacial areas existed at times during the Pleistocene.
Numerical modeling of confined liquid crystal systems
NASA Astrophysics Data System (ADS)
Mkaddem, Sami
There has been much research interest in fine structures and defects of equilibrium configurations of nematic liquid crystal droplets subject to strong homeotropic anchoring and modeled by Landau-de Gennes free-energy functionals. In particular, two configurations are the center of attention. The first one is the radial hedgehog, which has an isotropic core and a spherically symmetric structure. The second one is the ring disclination, which has a ring disclination of strength 1/2 and a cylindrically symmetric structure. In this dissertation, we undertake a detailed numerical study of the two described equilibrium configurations using the imposed symmetries to simplify the problem and utilizing a high order finite element discretization to solve it. In addition to the radial hedgehog and the ring disclination, we found a new, metastable configuration, which also is axially symmetric and consists of two isotropic points along its symmetry axis narrowly separated by a line disclination. We generate phase and bifurcation diagrams of the equilibrium configurations. We also investigate the qualitative behavior and the stability of the radial hedgehog. Using a perturbation against the radial hedgehog, we show that such configurations must become unstable at sufficiently low temperatures or in sufficiently large droplets.
Numerical models for high beta magnetohydrodynamic flow
Brackbill, J.U.
1987-01-01
The fundamentals of numerical magnetohydrodynamics for highly conducting, high-beta plasmas are outlined. The discussions emphasize the physical properties of the flow, and how elementary concepts in numerical analysis can be applied to the construction of finite difference approximations that capture these features. The linear and nonlinear stability of explicit and implicit differencing in time is examined, the origin and effect of numerical diffusion in the calculation of convective transport is described, and a technique for maintaining solenoidality in the magnetic field is developed. Many of the points are illustrated by numerical examples. The techniques described are applicable to the time-dependent, high-beta flows normally encountered in magnetically confined plasmas, plasma switches, and space and astrophysical plasmas. 40 refs.
Validation of Numerical Shallow Water Models for Tidal Lagoons
Eliason, D.; Bourgeois, A.
1999-11-01
An analytical solution is presented for the case of a stratified, tidally forced lagoon. This solution, especially its energetics, is useful for the validation of numerical shallow water models under stratified, tidally forced conditions. The utility of the analytical solution for validation is demonstrated for a simple finite difference numerical model. A comparison is presented of the energetics of the numerical and analytical solutions in terms of the convergence of model results to the analytical solution with increasing spatial and temporal resolution.
Simplified method for numerical modeling of fiber lasers.
Shtyrina, O V; Yarutkina, I A; Fedoruk, M P
2014-12-29
A simplified numerical approach to modeling of dissipative dispersion-managed fiber lasers is examined. We present a new numerical iteration algorithm for finding the periodic solutions of the system of nonlinear ordinary differential equations describing the intra-cavity dynamics of the dissipative soliton characteristics in dispersion-managed fiber lasers. We demonstrate that results obtained using simplified model are in good agreement with full numerical modeling based on the corresponding partial differential equations.
Multiscale numerical modeling of the spherically symmetric cryosurgery problem
NASA Astrophysics Data System (ADS)
Kudryashov, N. A.; Shilnikov, K. E.
2017-01-01
The work is concerned with the numerical studying of the cryogenic biotissue destruction by a spherically symmetric tip. The multiscale bioheat transfer model is used for the describing of the biological solutions crystallization features. An explicit finite volume based approximation is applied for the numerical modeling of the processes taking place during the cryosurgery. The phase averaging method is applied as an computationally economic approach for the numerical modeling of the problem under study.
Technology Transfer Automated Retrieval System (TEKTRAN)
When Lagrangian stochastic models for turbulent dispersion are applied to complex flows, some type of ad hoc intervention is almost always necessary to eliminate unphysical behavior in the numerical solution. This paper discusses numerical considerations when solving the Langevin-based particle velo...
Conceptual and Numerical Models for UZ Flow and Transport
H. Liu
2000-03-03
The purpose of this Analysis/Model Report (AMR) is to document the conceptual and numerical models used for modeling of unsaturated zone (UZ) fluid (water and air) flow and solute transport processes. This is in accordance with ''AMR Development Plan for U0030 Conceptual and Numerical Models for Unsaturated Zone (UZ) Flow and Transport Processes, Rev 00''. The conceptual and numerical modeling approaches described in this AMR are used for models of UZ flow and transport in fractured, unsaturated rock under ambient and thermal conditions, which are documented in separate AMRs. This AMR supports the UZ Flow and Transport Process Model Report (PMR), the Near Field Environment PMR, and the following models: Calibrated Properties Model; UZ Flow Models and Submodels; Mountain-Scale Coupled Processes Model; Thermal-Hydrologic-Chemical (THC) Seepage Model; Drift Scale Test (DST) THC Model; Seepage Model for Performance Assessment (PA); and UZ Radionuclide Transport Models.
NUMERICAL MODELING OF FINE SEDIMENT PHYSICAL PROCESSES.
Schoellhamer, David H.
1985-01-01
Fine sediment in channels, rivers, estuaries, and coastal waters undergo several physical processes including flocculation, floc disruption, deposition, bed consolidation, and resuspension. This paper presents a conceptual model and reviews mathematical models of these physical processes. Several general fine sediment models that simulate some of these processes are reviewed. These general models do not directly simulate flocculation and floc disruption, but the conceptual model and existing functions are shown to adequately model these two processes for one set of laboratory data.
Numerical Modeling in Geodynamics: Success, Failure and Perspective
NASA Astrophysics Data System (ADS)
Ismail-Zadeh, A.
2005-12-01
A real success in numerical modeling of dynamics of the Earth can be achieved only by multidisciplinary research teams of experts in geodynamics, applied and pure mathematics, and computer science. The success in numerical modeling is based on the following basic, but simple, rules. (i) People need simplicity most, but they understand intricacies best (B. Pasternak, writer). Start from a simple numerical model, which describes basic physical laws by a set of mathematical equations, and move then to a complex model. Never start from a complex model, because you cannot understand the contribution of each term of the equations to the modeled geophysical phenomenon. (ii) Study the numerical methods behind your computer code. Otherwise it becomes difficult to distinguish true and erroneous solutions to the geodynamic problem, especially when your problem is complex enough. (iii) Test your model versus analytical and asymptotic solutions, simple 2D and 3D model examples. Develop benchmark analysis of different numerical codes and compare numerical results with laboratory experiments. Remember that the numerical tool you employ is not perfect, and there are small bugs in every computer code. Therefore the testing is the most important part of your numerical modeling. (iv) Prove (if possible) or learn relevant statements concerning the existence, uniqueness and stability of the solution to the mathematical and discrete problems. Otherwise you can solve an improperly-posed problem, and the results of the modeling will be far from the true solution of your model problem. (v) Try to analyze numerical models of a geological phenomenon using as less as possible tuning model variables. Already two tuning variables give enough possibilities to constrain your model well enough with respect to observations. The data fitting sometimes is quite attractive and can take you far from a principal aim of your numerical modeling: to understand geophysical phenomena. (vi) If the number of
Numerical bifurcation analysis of immunological models with time delays
NASA Astrophysics Data System (ADS)
Luzyanina, Tatyana; Roose, Dirk; Bocharov, Gennady
2005-12-01
In recent years, a large number of mathematical models that are described by delay differential equations (DDEs) have appeared in the life sciences. To analyze the models' dynamics, numerical methods are necessary, since analytical studies can only give limited results. In turn, the availability of efficient numerical methods and software packages encourages the use of time delays in mathematical modelling, which may lead to more realistic models. We outline recently developed numerical methods for bifurcation analysis of DDEs and illustrate the use of these methods in the analysis of a mathematical model of human hepatitis B virus infection.
Experimental & Numerical Modeling of Non-combusting Model Firebrands' Transport
NASA Astrophysics Data System (ADS)
Tohidi, Ali; Kaye, Nigel
2016-11-01
Fire spotting is one of the major mechanisms of wildfire spread. Three phases of this phenomenon are firebrand formation and break-off from burning vegetation, lofting and downwind transport of firebrands through the velocity field of the wildfire, and spot fire ignition upon landing. The lofting and downwind transport phase is modeled by conducting large-scale wind tunnel experiments. Non-combusting rod-like model firebrands with different aspect ratios are released within the velocity field of a jet in a boundary layer cross-flow that approximates the wildfire velocity field. Characteristics of the firebrand dispersion are quantified by capturing the full trajectory of the model firebrands using the developed image processing algorithm. The results show that the lofting height has a direct impact on the maximum travel distance of the model firebrands. Also, the experimental results are utilized for validation of a highly scalable coupled stochastic & parametric firebrand flight model that, couples the LES-resolved velocity field of a jet-in-nonuniform-cross-flow (JINCF) with a 3D fully deterministic 6-degrees-of-freedom debris transport model. The validation results show that the developed numerical model is capable of estimating average statistics of the firebrands' flight. Authors would like to thank support of the National Science Foundation under Grant No. 1200560. Also, the presenter (Ali Tohid) would like to thank Dr. Michael Gollner from the University of Maryland College Park for the conference participation support.
Recent developments in three-dimensional numerical estuarine models
Cheng, Ralph T.; Smith, Peter E.; Casulli, Vincenzo
1993-01-01
For a fixed cost, computing power increases 5 to 10 times every five years. The readily available computing resources have inspired new modal formulations and innovative model applications. Significant progress has been advanced in three-dimensional numerical estuarine modeling within the past three or four years. This paper attempts to review and summarize properties of new 3-D estuarine hydrodynamic models. The emphasis of the review is placed on the formulation, numerical methods. The emphasis of the review is placed on the formulation, numerical methods, spatial and temporal resolution, computational efficiency, and turbulence closure of new models. Recent research has provided guidelines for the proper use of 3-D models involving in the σ-transformation. Other models resort to a fixed level discretization in the vertical. The semi-implicit treatment in time-stepping models appears to have gained momentum. Future research in three-dimensional numerical modeling remains to be on computational efficiency and turbulent closure.
Software Simplifies the Sharing of Numerical Models
NASA Technical Reports Server (NTRS)
2014-01-01
To ease the sharing of climate models with university students, Goddard Space Flight Center awarded SBIR funding to Reston, Virginia-based Parabon Computation Inc., a company that specializes in cloud computing. The firm developed a software program capable of running climate models over the Internet, and also created an online environment for people to collaborate on developing such models.
Numerical MHD codes for modeling astrophysical flows
NASA Astrophysics Data System (ADS)
Koldoba, A. V.; Ustyugova, G. V.; Lii, P. S.; Comins, M. L.; Dyda, S.; Romanova, M. M.; Lovelace, R. V. E.
2016-05-01
We describe a Godunov-type magnetohydrodynamic (MHD) code based on the Miyoshi and Kusano (2005) solver which can be used to solve various astrophysical hydrodynamic and MHD problems. The energy equation is in the form of entropy conservation. The code has been implemented on several different coordinate systems: 2.5D axisymmetric cylindrical coordinates, 2D Cartesian coordinates, 2D plane polar coordinates, and fully 3D cylindrical coordinates. Viscosity and diffusivity are implemented in the code to control the accretion rate in the disk and the rate of penetration of the disk matter through the magnetic field lines. The code has been utilized for the numerical investigations of a number of different astrophysical problems, several examples of which are shown.
Numerical Modeling of the Nearshore Region.
1982-06-01
THEORETICAL FRAMEWORK FOR THE MODELS The basis for anv fluid dynamic model rests on the principle of conservation of mass, conservation of momentum...which he chose to be Vgh, the speed of a wave in shallow water where h is the local water depth. Therefore, E can be written asx C = Nx g- where N is a...leading to the principle theoretical difference between the models as well as explaining the distinction expressed by their names. The mathematical
On numerical modeling of one-dimensional geothermal histories
Haugerud, R.A.
1989-01-01
Numerical models of one-dimensional geothermal histories are one way of understanding the relations between tectonics and transient thermal structure in the crust. Such models can be powerful tools for interpreting geochronologic and thermobarometric data. A flexible program to calculate these models on a microcomputer is available and examples of its use are presented. Potential problems with this approach include the simplifying assumptions that are made, limitations of the numerical techniques, and the neglect of convective heat transfer. ?? 1989.
a Numerical Study on Predator Prey Model
NASA Astrophysics Data System (ADS)
Laham, Mohamed Faris; Krishnarajah, Isthrinayagy; Jumaat, Abdul Kadir
Stochastic spatial models are becoming a popular tool for understand the ecological and evolution of ecosystem problems. We consider the predator prey interactions in term of stochastic representation of this Lotka-Volterra model and explore the use of stochastic processes to extinction behavior of the interacting populations. Here, we present simulation of stochastic processes of continuous time Lotka-Volterra model. Euler method has been used to solve the predator prey system. The trajectory spiral graph has been plotted based on obtained solution to show the population cycle of predator as a function of time.
Evaluation of wave runup predictions from numerical and parametric models
Stockdon, Hilary F.; Thompson, David M.; Plant, Nathaniel G.; Long, Joseph W.
2014-01-01
Wave runup during storms is a primary driver of coastal evolution, including shoreline and dune erosion and barrier island overwash. Runup and its components, setup and swash, can be predicted from a parameterized model that was developed by comparing runup observations to offshore wave height, wave period, and local beach slope. Because observations during extreme storms are often unavailable, a numerical model is used to simulate the storm-driven runup to compare to the parameterized model and then develop an approach to improve the accuracy of the parameterization. Numerically simulated and parameterized runup were compared to observations to evaluate model accuracies. The analysis demonstrated that setup was accurately predicted by both the parameterized model and numerical simulations. Infragravity swash heights were most accurately predicted by the parameterized model. The numerical model suffered from bias and gain errors that depended on whether a one-dimensional or two-dimensional spatial domain was used. Nonetheless, all of the predictions were significantly correlated to the observations, implying that the systematic errors can be corrected. The numerical simulations did not resolve the incident-band swash motions, as expected, and the parameterized model performed best at predicting incident-band swash heights. An assimilated prediction using a weighted average of the parameterized model and the numerical simulations resulted in a reduction in prediction error variance. Finally, the numerical simulations were extended to include storm conditions that have not been previously observed. These results indicated that the parameterized predictions of setup may need modification for extreme conditions; numerical simulations can be used to extend the validity of the parameterized predictions of infragravity swash; and numerical simulations systematically underpredict incident swash, which is relatively unimportant under extreme conditions.
Numerical Calculation of Model Rocket Trajectories.
ERIC Educational Resources Information Center
Keeports, David
1990-01-01
Discussed is the use of model rocketry to teach the principles of Newtonian mechanics. Included are forces involved; calculations for vertical launches; two-dimensional trajectories; and variations in mass, drag, and launch angle. (CW)
Modelling asteroid brightness variations. I - Numerical methods
NASA Technical Reports Server (NTRS)
Karttunen, H.
1989-01-01
A method for generating lightcurves of asteroid models is presented. The effects of the shape of the asteroid and the scattering law of a surface element are distinctly separable, being described by chosen functions that can easily be changed. The shape is specified by means of two functions that yield the length of the radius vector and the normal vector of the surface at a given point. The general shape must be convex, but spherical concavities producing macroscopic shadowing can also be modeled.
A hybrid (numerical-physical) model of the left ventricle.
Ferrari, G; Kozarski, M; De Lazzari, C; Clemente, F; Merolli, M; Tosti, G; Guaragno, M; Mimmo, R; Ambrosi, D; Glapinski, J
2001-07-01
Hydraulic models of the circulation are used to test mechanical devices and for training and research purposes; when compared to numerical models, however, they are not flexible enough and rather expensive. The solution proposed here is to merge the characteristics and the flexibility of numerical models with the functions of physical models. The result is a hybrid model with numerical and physical sections connected by an electro-hydraulic interface - which is to some extent the main problem since the numerical model can be easily changed or modified. The concept of hybrid model is applied to the representation of ventricular function by a variable elastance numerical model. This prototype is an open loop circuit and the physical section is built out of a reservoir (atrium) and a modified windkessel (arterial tree). The corresponding equations are solved numerically using the variables (atrial and arterial pressures) coming from the physical circuit. Ventricular output flow is the computed variable and is sent to a servo amplifier connected to a DC motor-gear pump system. The gear pump, behaving roughly as a flow source, is the interface to the physical circuit. Results obtained under different hemodynamic conditions demonstrate the behaviour of the ventricular model on the pressure-volume plane and the time course of output flow and arterial pressure.
Mathematical and Numerical Modeling of Turbulent Flows.
Vedovoto, João M; Serfaty, Ricardo; Da Silveira Neto, Aristeu
2015-01-01
The present work is devoted to the development and implementation of a computational framework to perform numerical simulations of low Mach number turbulent flows over complex geometries. The algorithm under consideration is based on a classical predictor-corrector time integration scheme that employs a projection method for the momentum equations. The domain decomposition strategy is adopted for distributed computing, displaying very satisfactory levels of speed-up and efficiency. The Immersed Boundary Methodology is used to characterize the presence of a complex geometry. Such method demands two separate grids: An Eulerian, where the transport equations are solved with a Finite Volume, second order discretization and a Lagrangian domain, represented by a non-structured shell grid representing the immersed geometry. The in-house code developed was fully verified by the Method of Manufactured Solutions, in both Eulerian and Lagrangian domains. The capabilities of the resulting computational framework are illustrated on four distinct cases: a turbulent jet, the Poiseuille flow, as a matter of validation of the implemented Immersed Boundary methodology, the flow over a sphere covering a wide range of Reynolds numbers, and finally, with the intention of demonstrating the applicability of Large Eddy Simulations - LES - in an industrial problem, the turbulent flow inside an industrial fan.
NASA Astrophysics Data System (ADS)
Bailey, Brian N.
2017-01-01
When Lagrangian stochastic models for turbulent dispersion are applied to complex atmospheric flows, some type of ad hoc intervention is almost always necessary to eliminate unphysical behaviour in the numerical solution. Here we discuss numerical strategies for solving the non-linear Langevin-based particle velocity evolution equation that eliminate such unphysical behaviour in both Reynolds-averaged and large-eddy simulation applications. Extremely large or `rogue' particle velocities are caused when the numerical integration scheme becomes unstable. Such instabilities can be eliminated by using a sufficiently small integration timestep, or in cases where the required timestep is unrealistically small, an unconditionally stable implicit integration scheme can be used. When the generalized anisotropic turbulence model is used, it is critical that the input velocity covariance tensor be realizable, otherwise unphysical behaviour can become problematic regardless of the integration scheme or size of the timestep. A method is presented to ensure realizability, and thus eliminate such behaviour. It was also found that the numerical accuracy of the integration scheme determined the degree to which the second law of thermodynamics or `well-mixed condition' was satisfied. Perhaps more importantly, it also determined the degree to which modelled Eulerian particle velocity statistics matched the specified Eulerian distributions (which is the ultimate goal of the numerical solution). It is recommended that future models be verified by not only checking the well-mixed condition, but perhaps more importantly by checking that computed Eulerian statistics match the Eulerian statistics specified as inputs.
Mathematical and Numerical Analyses of Peridynamics for Multiscale Materials Modeling
Gunzburger, Max
2015-02-17
We have treated the modeling, analysis, numerical analysis, and algorithmic development for nonlocal models of diffusion and mechanics. Variational formulations were developed and finite element methods were developed based on those formulations for both steady state and time dependent problems. Obstacle problems and optimization problems for the nonlocal models were also treated and connections made with fractional derivative models.
Numerical Modeling of Ophthalmic Response to Space
NASA Technical Reports Server (NTRS)
Nelson, E. S.; Myers, J. G.; Mulugeta, L.; Vera, J.; Raykin, J.; Feola, A.; Gleason, R.; Samuels, B.; Ethier, C. R.
2015-01-01
To investigate ophthalmic changes in spaceflight, we would like to predict the impact of blood dysregulation and elevated intracranial pressure (ICP) on Intraocular Pressure (IOP). Unlike other physiological systems, there are very few lumped parameter models of the eye. The eye model described here is novel in its inclusion of the human choroid and retrobulbar subarachnoid space (rSAS), which are key elements in investigating the impact of increased ICP and ocular blood volume. Some ingenuity was required in modeling the blood and rSAS compartments due to the lack of quantitative data on essential hydrodynamic quantities, such as net choroidal volume and blood flowrate, inlet and exit pressures, and material properties, such as compliances between compartments.
Gulf of Mexico numerical model. Project summary
Blumberg, A. F.; Mellor, G. L.; Herring, H. J.
1981-02-01
An efficient three-dimensional, time dependent prognostic model of the Gulf of Mexico has been developed. The model is driven by winds and surface heat flux derived from climatological, atmospheric surface data, the result of an intensive data analysis study. Mean velocity, temperature, salinity, turbulence kinetic energy and turbulence macroscale are the prognostic variables. Lateral boundary conditions for temperature and salinity and geostrophically derived velocity at the Straits of Yucatan and Florida are obtained from climatological ocean data. An analytical second moment turbulence closure scheme embedded within the model provides realistic surface mixed layer dynamics. Free surface elevation distributions are calculated with an algorithm which calculates the external (tidal) mode separately from the internal mode. The external mode, an essentially two-dimensional calculation, requires a short integrating timestep whereas the more costly, three-dimensional, internal mode can be executed with a long step. The result is a fully three-dimensional code which includes a free surface at no sacrifice in computer cost compared to rigid lid models.
A numerical model for ground temperature determination
NASA Astrophysics Data System (ADS)
Jaszczur, M.; Polepszyc, I.; Biernacka, B.; Sapińska-Śliwa, A.
2016-09-01
The ground surface temperature and the temperature with respect to depth are one of the most important issues for geotechnical and environmental applications as well as for plants and other living organisms. In geothermal systems, temperature is directly related to the energy resources in the ground and it influences the efficiency of the ground source system. The ground temperature depends on a very large number of parameters, but it often needs to be evaluated with good accuracy. In the present work, models for the prediction of the ground temperature with a focus on the surface temperature at which all or selected important ground and environmental phenomena are taken into account have been analysed. It has been found that the simplest models and the most complex model may result in a similar temperature variation, yet at a very low depth and for specific cases only. A detailed analysis shows that taking into account different types of pavement or a greater depth requires more complex and advanced models.
Numerical modelling of instantaneous plate tectonics
NASA Technical Reports Server (NTRS)
Minster, J. B.; Haines, E.; Jordan, T. H.; Molnar, P.
1974-01-01
Assuming lithospheric plates to be rigid, 68 spreading rates, 62 fracture zones trends, and 106 earthquake slip vectors are systematically inverted to obtain a self-consistent model of instantaneous relative motions for eleven major plates. The inverse problem is linearized and solved iteratively by a maximum-likelihood procedure. Because the uncertainties in the data are small, Gaussian statistics are shown to be adequate. The use of a linear theory permits (1) the calculation of the uncertainties in the various angular velocity vectors caused by uncertainties in the data, and (2) quantitative examination of the distribution of information within the data set. The existence of a self-consistent model satisfying all the data is strong justification of the rigid plate assumption. Slow movement between North and South America is shown to be resolvable.
Geometry and Grid Modeling for Numerical Simulation
2005-06-01
three dimensional spatial region (a mesh) is a prerequisite of most computer aided engineering ( CAE ) software, including computational structural...Parasolid Parasolid [13] is a commercial solid-modeling kernel. It serves as the basis for Unigraphics and several other CAD/CAM/ CAE packages. It is...As mentioned earlier, 1D and 2D arrays of standard data types are the most complex data type permitted. This method has the advantage of
Rio Hondo Sediment Assessment Analysis Using SAM. Numerical Model Investigation
1991-05-01
MISCELLANEOUS PAPER HL-91-1 M ~ RIO HONDO SEDIMENT ASSESSMENT ANALYSIS USING SAM Numerical Model Investigation AD-A238 572Ii 1 11byIll lil Nolan K...FUNDING NUMBERS Rio Hondo Sediment Assessment Analysis Using SAM; Numerical Model Investigation 6. AUTHOR(S) Nolan K. Raphelt Michael J. Trawle William A... Rio Hondo through Roswell, NM, was conducted. The investigation represented a sediment assessment level study conducted to test for potential
Numerical Modelling of Embankment on Soft Clay
NASA Astrophysics Data System (ADS)
Nujid, M. M.; Taha, M. R.
2016-07-01
This paper aims to predict deformation of embankment on soft clay of Muar. The prediction performance focusing on displacement at critical fill height of 5.5 m. The study was based on reported result in 1992. With the aid of computer intelligence, the advanced constitutive soil models could be adopted to analyze the soft clay behavior. The COMSOL Multiphysics (v4.4) has been used to simulate the problem with coupled physics available in the software. The vertical displacements are in good agreement close to published result.
Numerical modeling with application to tracking marine debris.
Potemra, James T
2012-01-01
This paper describes different numerical models of ocean circulation the output of which can be applied to study patterns and pathways of drifting marine debris. The paper focuses on model output that is readily available rather than on numerical models that could be configured and run locally. These include operational models from the US Navy (the Navy Layered Ocean Model (NLOM), Coastal Ocean Model (NCOM), and Hybrid Coordinate Ocean Model (HYCOM)), data assimilating reanalysis models (the Simple Ocean Data Assimilation (SODA), the Global Ocean Data Assimilation Experiment (GODAE) models), and the European Center for Medium-Range Weather Forecasts (ECMWF) ocean reanalysis (Ocean Reanalysis System, ECMWF/ORA-S3). The paper describes the underlying physics in each model system, limitations, and where to obtain the model output.
Terrane accretion: Insights from numerical modelling
NASA Astrophysics Data System (ADS)
Vogt, Katharina; Gerya, Taras
2016-04-01
The oceanic crust is not homogenous, but contains significantly thicker crust than norm, i.e. extinct arcs, spreading ridges, detached continental fragments, volcanic piles or oceanic swells. These (crustal) fragments may collide with continental crust and form accretionary complexes, contributing to its growth. We analyse this process using a thermo-mechanical computer model (i2vis) of an ocean-continent subduction zone. In this model the oceanic plate can bend spontaneously under the control of visco-plastic rheologies. It moreover incorporates effects such as mineralogical phase changes, fluid release and consumption, partial melting and melt extraction. Based on our 2-D experiments we suggest that the lithospheric buoyancy of the downgoing slab and the rheological strength of crustal material may result in a variety of accretionary processes. In addition to terrane subduction, we are able to identify three distinct modes of terrane accretion: frontal accretion, basal accretion and underplating plateaus. We show that crustal fragments may dock onto continental crust and cease subduction, be scrapped off the downgoing plate, or subduct to greater depth prior to slab break off and subsequent exhumation. Direct consequences of these processes include slab break off, subduction zone transference, structural reworking, formation of high-pressure terranes, partial melting and crustal growth.
Numerical analysis and modeling of atmospheric phenomena
NASA Technical Reports Server (NTRS)
Stone, Peter H.
1994-01-01
For the past 22 years Grant NGR 22-009-727 has been supporting research in the Center for Meteorology and Physical Oceanography (and its predecessors) in a wide variety of diagnostic and modeling studies of atmospheric and ocean phenomena. Professor Jule Charney was the initial Principal Investigator. Professor Peter Stone joined him as co-Principal Investigator in 1975 and became the sole Principal Investigator in 1981. During its lifetime the Grant has supported in whole or in part 11 Master's theses, 14 Ph.D. theses, and 45 papers published in refereed scientific journals. All of these theses and papers (with bibliographic references) are listed below. All but one of the theses were used to fulfill the requirements for MIT (Massachusetts Institute of Technology) degrees and are available from the MIT libraries. The one exception is F. Chen's Ph.D. thesis which was for a Harvard degree and is available from the Harvard libraries. In addition to the work described in the citations listed below, the Grant has supported Research Assistant Amy Solomon during the past two years to carry out a study of how baroclinic adjustment is affected by vertical resolution, vertical temperature structure, and dissipation. Ms. Solomon plans to use this project for her Ph.D. thesis. Support for this project will continue under NASA Grant NAG 5-2490, 'The Factors Controlling Poleward Heat Transport in Climate Models.'
Multidimensional numerical modeling of heat exchangers
NASA Astrophysics Data System (ADS)
Sha, W. T.; Yang, C. I.; Kao, T. T.; Cho, S. M.
A comprehensive, multidimensional, thermal-hydraulic model is developed for the analysis of shell-and-tube heat exchangers for liquid-metal services. For the shellside fluid, the conservation equations of mass, momentum, and energy for continuum fluids are modified using the concept of porosity, surface permeability and distributed resistance to account for the blockage effects due to the presence of heat-transfer tubes, flow baffles/shrouds, the support plates, etc. On the tubeside, the heat-transfer tubes are connected in parallel between the inlet and outlet plenums, and tubeside flow distribution is calculated based on the plenum-to-plenum pressure difference being equal for all tubes. It is assumed that the fluid remains single-phase on the shell side and may undergo phase-change on the tube side, thereby simulating the conditions of Liquid Metal Fast Breeder Reactor (LMFBR) intermediate heat exchangers (IHX) and steam generators (SG).
Experimental, Numerical and Observational Models in Geodynamics
NASA Astrophysics Data System (ADS)
Lithgow-Bertelloni, Carolina
2015-04-01
Geodynamics, the study of the forces that drives all Earth's processes is a rich field that deeply connects all aspects of geological and geophysical studies, from surface observations of the sedimentary record to knowledge of deep Earth structure from mineral physics and seismology. In the context of the solid Earth geodynamics primarily focuses on lithosphere and mantle dynamics, while core dynamics is the purview of geomagnetism. I will focus this talk on the former, its historical context and future developments. We have known the equations of motion and mechanics for ~200 years, but only relatively recently can they be solved with enough accuracy and resolution to do geology. We have made great strides since Arthur Holmes conceptual models of mantle flow, thanks to computational and experimental advances. We can know model plate boundaries globally with resolutions in the order of a few kms and image temperature and velocity simultaneously in the laboratory in 3D and non-intrusively. We have also learned a great deal about the physics of the Earth, from composition to rheology. New theories on plate boundary rheology are paving the way for self-consistent generation of plates from mantle flow. New computational methods allow for adaptive meshing, fabric development and history, so we can study deformation and compare directly to geological observations in mountain ranges and continental rifts. We can use ever more sophisticated images of mantle structure from seismic and other geophysical data to probe the relationship between melting, flow and dynamical processes. We can reconstruct landscapes and relief, plate motions and sedimentation and ask how much the mantle has contributed to drainage reversal, sedimentation and climate change. The future of the field is ever brighter.
Seismoelectric numerical modeling on a grid
Haines, S.S.; Pride, S.R.
2006-01-01
Our finite-difference algorithm provides a new method for simulating how seismic waves in arbitrarily heterogeneous porous media generate electric fields through an electrokinetic mechanism called seismoelectric coupling. As the first step in our simulations, we calculate relative pore-fluid/grain-matrix displacement by using existing poroelastic theory. We then calculate the electric current resulting from the grain/fluid displacement by using seismoelectric coupling theory. This electrofiltration current acts as a source term in Poisson's equation, which then allows us to calculate the electric potential distribution. We can safely neglect induction effects in our simulations because the model area is within the electrostatic near field for the depth of investigation (tens to hundreds of meters) and the frequency ranges (10 Hz to 1 kHz) of interest for shallow seismoelectric surveys.We can independently calculate the electric-potential distribution for each time step in the poroelastic simulation without loss of accuracy because electro-osmotic feedback (fluid flow that is perturbed by generated electric fields) is at least 105 times smaller than flow that is driven by fluid-pressure gradients and matrix acceleration, and is therefore negligible. Our simulations demonstrate that, distinct from seismic reflections, the seismoelectric interface response from a thin layer (at least as thin as one-twentieth of the seismic wavelength) is considerably stronger than the response from a single interface. We find that the interface response amplitude decreases as the lateral extent of a layer decreases below the width of the first Fresnel zone. We conclude, on the basis of our modeling results and of field results published elsewhere, that downhole and/or crosswell survey geometries and time-lapse applications are particularly well suited to the seismoelectric method. ?? 2006 Society of Exploration Geophysicists.
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.
Quantitative analysis of numerical solvers for oscillatory biomolecular system models
Quo, Chang F; Wang, May D
2008-01-01
Background This article provides guidelines for selecting optimal numerical solvers for biomolecular system models. Because various parameters of the same system could have drastically different ranges from 10-15 to 1010, the ODEs can be stiff and ill-conditioned, resulting in non-unique, non-existing, or non-reproducible modeling solutions. Previous studies have not examined in depth how to best select numerical solvers for biomolecular system models, which makes it difficult to experimentally validate the modeling results. To address this problem, we have chosen one of the well-known stiff initial value problems with limit cycle behavior as a test-bed system model. Solving this model, we have illustrated that different answers may result from different numerical solvers. We use MATLAB numerical solvers because they are optimized and widely used by the modeling community. We have also conducted a systematic study of numerical solver performances by using qualitative and quantitative measures such as convergence, accuracy, and computational cost (i.e. in terms of function evaluation, partial derivative, LU decomposition, and "take-off" points). The results show that the modeling solutions can be drastically different using different numerical solvers. Thus, it is important to intelligently select numerical solvers when solving biomolecular system models. Results The classic Belousov-Zhabotinskii (BZ) reaction is described by the Oregonator model and is used as a case study. We report two guidelines in selecting optimal numerical solver(s) for stiff, complex oscillatory systems: (i) for problems with unknown parameters, ode45 is the optimal choice regardless of the relative error tolerance; (ii) for known stiff problems, both ode113 and ode15s are good choices under strict relative tolerance conditions. Conclusions For any given biomolecular model, by building a library of numerical solvers with quantitative performance assessment metric, we show that it is possible
Experimentation and numerical modeling of forging induced bending (FIB) process
NASA Astrophysics Data System (ADS)
Naseem, S.; van den Boogaard, A. H.
2016-10-01
Accurate prediction of the final shape using numerical modeling has been a top priority in the field of sheet and bulk forming. Better shape prediction is the result of a better estimation of the physical stress and strain state. For experimental and numerical investigations of such estimations, simple benchmark processes are used. In this paper a benchmark process involving forging (flattening) of sheet metal between punch and die with negative clearance is proposed. The introduced material flow results in bending. Easy measurability of the angle of this bend makes this process suitable for validation purpose. Physical experiments are performed to characterize this bending angle due to flattening. Furthermore a numerical model is developed to capture this phenomenon. The main focus of this paper is the validation of the numerical model in terms of accurate prediction of the physical results.
Squeal noise in simple numerical brake models
NASA Astrophysics Data System (ADS)
Oberst, S.; Lai, J. C. S.
2015-09-01
Since the early 1920s, automotive disc brake squeal has caused warranty issues and customer dissatisfaction. Despite a good deal of progress achieved, predicting brake squeal propensity is as difficult as ever as not all mechanisms and interactions are known owing to their highly fugitive complex nature. In recent years, research has been focused on the prediction of unstable vibration modes by the complex eigenvalue analysis (CEA) for the mode-coupling type of instability. There has been very limited consideration given to the calculation of the acoustic radiation properties due to friction contact between a pad and a rotor. Recent analyses using a forced response analysis with harmonic contact pressure excitation indicates negative dissipated energy at some pad eigenfrequencies predicted to be stable by the CEA. A transient nonlinear time domain analysis with no external excitation indicates that squeal could develop at these eigenfrequencies. Here, the acoustic radiation characteristics of those pad modes are determined by analysing the acoustic power levels and radiation efficiencies of simplified brake models in the form of a pad rubbing on a plate or on a disc using the acoustic boundary element method based on velocities extracted from the forced response analysis. Results show that unstable pad modes trigger unstable disc vibrations resulting in instantaneous mode squeal similar to those observed experimentally. Changes in the radiation efficiency with pressure variations are smaller than those with friction coefficient variations and are caused by the phase difference of the velocities out-of-plane vibration between the pad and the disc.
Numerical simulations of a reduced model for blood coagulation
NASA Astrophysics Data System (ADS)
Pavlova, Jevgenija; Fasano, Antonio; Sequeira, Adélia
2016-04-01
In this work, the three-dimensional numerical resolution of a complex mathematical model for the blood coagulation process is presented. The model was illustrated in Fasano et al. (Clin Hemorheol Microcirc 51:1-14, 2012), Pavlova et al. (Theor Biol 380:367-379, 2015). It incorporates the action of the biochemical and cellular components of blood as well as the effects of the flow. The model is characterized by a reduction in the biochemical network and considers the impact of the blood slip at the vessel wall. Numerical results showing the capacity of the model to predict different perturbations in the hemostatic system are discussed.
Quantitative comparisons of numerical models of brittle wedge dynamics
NASA Astrophysics Data System (ADS)
Buiter, Susanne
2010-05-01
Numerical and laboratory models are often used to investigate the evolution of deformation processes at various scales in crust and lithosphere. In both approaches, the freedom in choice of simulation method, materials and their properties, and deformation laws could affect model outcomes. To assess the role of modelling method and to quantify the variability among models, we have performed a comparison of laboratory and numerical experiments. Here, we present results of 11 numerical codes, which use finite element, finite difference and distinct element techniques. We present three experiments that describe shortening of a sand-like, brittle wedge. The material properties of the numerical ‘sand', the model set-up and the boundary conditions are strictly prescribed and follow the analogue setup as closely as possible. Our first experiment translates a non-accreting wedge with a stable surface slope of 20 degrees. In agreement with critical wedge theory, all models maintain the same surface slope and do not deform. This experiment serves as a reference that allows for testing against analytical solutions for taper angle, root-mean-square velocity and gravitational rate of work. The next two experiments investigate an unstable wedge in a sandbox-like setup, which deforms by inward translation of a mobile wall. The models accommodate shortening by formation of forward and backward shear zones. We compare surface slope, rate of dissipation of energy, root-mean-square velocity, and the location, dip angle and spacing of shear zones. We show that we successfully simulate sandbox-style brittle behaviour using different numerical modelling techniques and that we obtain the same styles of deformation behaviour in numerical and laboratory experiments at similar levels of variability. The GeoMod2008 Numerical Team: Markus Albertz, Michelle Cooke, Tony Crook, David Egholm, Susan Ellis, Taras Gerya, Luke Hodkinson, Boris Kaus, Walter Landry, Bertrand Maillot, Yury Mishin
Sheet Hydroforming Process Numerical Model Improvement Through Experimental Results Analysis
NASA Astrophysics Data System (ADS)
Gabriele, Papadia; Antonio, Del Prete; Alfredo, Anglani
2010-06-01
The increasing application of numerical simulation in metal forming field has helped engineers to solve problems one after another to manufacture a qualified formed product reducing the required time [1]. Accurate simulation results are fundamental for the tooling and the product designs. The wide application of numerical simulation is encouraging the development of highly accurate simulation procedures to meet industrial requirements. Many factors can influence the final simulation results and many studies have been carried out about materials [2], yield criteria [3] and plastic deformation [4,5], process parameters [6] and their optimization. In order to develop a reliable hydromechanical deep drawing (HDD) numerical model the authors have been worked out specific activities based on the evaluation of the effective stiffness of the blankholder structure [7]. In this paper after an appropriate tuning phase of the blankholder force distribution, the experimental activity has been taken into account to improve the accuracy of the numerical model. In the first phase, the effective capability of the blankholder structure to transfer the applied load given by hydraulic actuators to the blank has been explored. This phase ended with the definition of an appropriate subdivision of the blankholder active surface in order to take into account the effective pressure map obtained for the given loads configuration. In the second phase the numerical results obtained with the developed subdivision have been compared with the experimental data of the studied model. The numerical model has been then improved, finding the best solution for the blankholder force distribution.
Numerical modelling of river morphodynamics: Latest developments and remaining challenges
NASA Astrophysics Data System (ADS)
Siviglia, Annunziato; Crosato, Alessandra
2016-07-01
Numerical morphodynamic models provide scientific frameworks for advancing our understanding of river systems. The research on involved topics is an important and socially relevant undertaking regarding our environment. Nowadays numerical models are used for different purposes, from answering questions about basic morphodynamic research to managing complex river engineering problems. Due to increasing computer power and the development of advanced numerical techniques, morphodynamic models are now more and more used to predict the bed patterns evolution to a broad spectrum of spatial and temporal scales. The development and the success of application of such models are based upon a wide range of disciplines from applied mathematics for the numerical solution of the equations to geomorphology for the physical interpretation of the results. In this light we organized this special issue (SI) soliciting multidisciplinary contributions which encompass any aspect needed for the development and applications of such models. Most of the papers in the SI stem from contributions to session HS9.5/GM7.11 on numerical modelling and experiments in river morphodynamics at the European Geosciences Union (EGU) General Assembly held in Vienna, April 27th to May 2nd 2014.
Considering digits in a current model of numerical development
Roesch, Stephanie; Moeller, Korbinian
2015-01-01
Numerical cognition has long been considered the perfect example of abstract information processing. Nevertheless, there is accumulating evidence in recent years suggesting that the representation of number magnitude may not be entirely abstract but may present a specific case of embodied cognition rooted in the sensory and bodily experiences of early finger counting and calculating. However, so far none of the existing models of numerical development considers the influence of finger-based representations. Therefore, we make first suggestions on (i) how finger-based representations may be integrated into a current model of numerical development; and (ii) how they might corroborate the acquisition of basic numerical competencies at different development levels. PMID:25628559
Numerical Modeling of Shatter Cones Development in Impact Craters
NASA Astrophysics Data System (ADS)
Baratoux, D.; Melosh, H. J.
2003-03-01
We present a new model for the formation of shatter cones in impact craters. Our model has been tested by means of numerical simulations. Our results are consistent with the observations of shatter cones in natural impact craters and explosions experiments.
Hydroforming Of Patchwork Blanks — Numerical Modeling And Experimental Validation
NASA Astrophysics Data System (ADS)
Lamprecht, Klaus; Merklein, Marion; Geiger, Manfred
2005-08-01
In comparison to the commonly applied technology of tailored blanks the concept of patchwork blanks offers a number of additional advantages. Potential application areas for patchwork blanks in automotive industry are e.g. local reinforcements of automotive closures, structural reinforcements of rails and pillars as well as shock towers. But even if there is a significant application potential for patchwork blanks in automobile production, industrial realization of this innovative technique is decelerated due to a lack of knowledge regarding the forming behavior and the numerical modeling of patchwork blanks. Especially for the numerical simulation of hydroforming processes, where one part of the forming tool is replaced by a fluid under pressure, advanced modeling techniques are required to ensure an accurate prediction of the blanks' forming behavior. The objective of this contribution is to provide an appropriate model for the numerical simulation of patchwork blanks' forming processes. Therefore, different finite element modeling techniques for patchwork blanks are presented. In addition to basic shell element models a combined finite element model consisting of shell and solid elements is defined. Special emphasis is placed on the modeling of the weld seam. For this purpose the local mechanical properties of the weld metal, which have been determined by means of Martens-hardness measurements and uniaxial tensile tests, are integrated in the finite element models. The results obtained from the numerical simulations are compared to experimental data from a hydraulic bulge test. In this context the focus is laid on laser- and spot-welded patchwork blanks.
Numerical Models of Broad Bandwidth Nanosecond Optical Parametric Oscillators
Bowers, M.S.; Gehr, R.J.; Smith, A.V.
1998-10-14
We describe results from three new methods of numerically modeling broad-bandwidth, nanosecond OPO's in the plane-wave approximate ion. They account for differences in group velocities among the three mixing waves, and also include a qutt~ttun noise model.
Numerical Modelling of Wave Interaction with Porous Structures
NASA Astrophysics Data System (ADS)
Gao, F.; M., D.; M., D.; G., C.
This paper presents a numerical model for simulating wave interaction with porous structures. By using the free surface-capturing approach together with a novel Cartesian cut cell treatment, the Finite Volume Model calculates the two phase flows out side of porous structure based on the Navier-Stokes equations, while the flow in the porous structure is described by Navier-Stokes type model equations. The free surface of water is treated as a contact discontinuity in the density field which is captured automatically as part of the numerical solution by using a time-accurate artificial compressibility method and high resolution Godunov-type scheme. The numerical model is first calibrated by simple test for a steady flow passing through a porous block. Reasonably good agreements with other numerical results are obtained. After that, the numerical model is used to simulate the breaking wave overtopping a caisson breakwater, protected by a layer of armor units. The results show that the porous armor layer is effective in reducing the overtopping rate as well as in protecting the stability of the caisson breakwater.
Rapid installation of numerical models in multiple parent codes
Brannon, R.M.; Wong, M.K.
1996-10-01
A set of``model interface guidelines``, called MIG, is offered as a means to more rapidly install numerical models (such as stress-strain laws) into any parent code (hydrocode, finite element code, etc.) without having to modify the model subroutines. The model developer (who creates the model package in compliance with the guidelines) specifies the model`s input and storage requirements in a standardized way. For portability, database management (such as saving user inputs and field variables) is handled by the parent code. To date, NUG has proved viable in beta installations of several diverse models in vectorized and parallel codes written in different computer languages. A NUG-compliant model can be installed in different codes without modifying the model`s subroutines. By maintaining one model for many codes, MIG facilitates code-to-code comparisons and reduces duplication of effort potentially reducing the cost of installing and sharing models.
Ensemble-type numerical uncertainty information from single model integrations
Rauser, Florian Marotzke, Jochem; Korn, Peter
2015-07-01
We suggest an algorithm that quantifies the discretization error of time-dependent physical quantities of interest (goals) for numerical models of geophysical fluid dynamics. The goal discretization error is estimated using a sum of weighted local discretization errors. The key feature of our algorithm is that these local discretization errors are interpreted as realizations of a random process. The random process is determined by the model and the flow state. From a class of local error random processes we select a suitable specific random process by integrating the model over a short time interval at different resolutions. The weights of the influences of the local discretization errors on the goal are modeled as goal sensitivities, which are calculated via automatic differentiation. The integration of the weighted realizations of local error random processes yields a posterior ensemble of goal approximations from a single run of the numerical model. From the posterior ensemble we derive the uncertainty information of the goal discretization error. This algorithm bypasses the requirement of detailed knowledge about the models discretization to generate numerical error estimates. The algorithm is evaluated for the spherical shallow-water equations. For two standard test cases we successfully estimate the error of regional potential energy, track its evolution, and compare it to standard ensemble techniques. The posterior ensemble shares linear-error-growth properties with ensembles of multiple model integrations when comparably perturbed. The posterior ensemble numerical error estimates are of comparable size as those of a stochastic physics ensemble.
A general numerical model for wave rotor analysis
NASA Technical Reports Server (NTRS)
Paxson, Daniel W.
1992-01-01
Wave rotors represent one of the promising technologies for achieving very high core temperatures and pressures in future gas turbine engines. Their operation depends upon unsteady gas dynamics and as such, their analysis is quite difficult. This report describes a numerical model which has been developed to perform such an analysis. Following a brief introduction, a summary of the wave rotor concept is given. The governing equations are then presented, along with a summary of the assumptions used to obtain them. Next, the numerical integration technique is described. This is an explicit finite volume technique based on the method of Roe. The discussion then focuses on the implementation of appropriate boundary conditions. Following this, some results are presented which first compare the numerical approximation to the governing differential equations and then compare the overall model to an actual wave rotor experiment. Finally, some concluding remarks are presented concerning the limitations of the simplifying assumptions and areas where the model may be improved.
A general numerical model for wave rotor analysis
NASA Astrophysics Data System (ADS)
Paxson, Daniel W.
1992-07-01
Wave rotors represent one of the promising technologies for achieving very high core temperatures and pressures in future gas turbine engines. Their operation depends upon unsteady gas dynamics and as such, their analysis is quite difficult. This report describes a numerical model which has been developed to perform such an analysis. Following a brief introduction, a summary of the wave rotor concept is given. The governing equations are then presented, along with a summary of the assumptions used to obtain them. Next, the numerical integration technique is described. This is an explicit finite volume technique based on the method of Roe. The discussion then focuses on the implementation of appropriate boundary conditions. Following this, some results are presented which first compare the numerical approximation to the governing differential equations and then compare the overall model to an actual wave rotor experiment. Finally, some concluding remarks are presented concerning the limitations of the simplifying assumptions and areas where the model may be improved.
Numerical Modeling of Compressible Flow and Its Control
2014-03-01
numerical methods are described here. 2.1.1 Plasma Modeling A reduced plasma kinetic model (23 species and 50 processes ) was developed by...carrying out a sensitivity analysis of a zero-dimensional plasma computation with an extended chemical kinetic model (46 species and 395 processes ). The...interpolation scheme with the following form: 2 8 15 45 (3) Here is the scalar (dot) product of the gradient of in Cell i and the vector
Numerical modeling of runback water on ice protected aircraft surfaces
NASA Technical Reports Server (NTRS)
Al-Khalil, Kamel M.; Keith, Theo G., Jr.; Dewitt, Kenneth J.
1992-01-01
A numerical simulation for 'running wet' aircraft anti-icing systems is developed. The model includes breakup of the water film, which exists in regions of direct impingement, into individual rivulets. The wetness factor distribution resulting from the film breakup and the rivulet configuration on the surface are predicted in the numerical solution procedure. The solid wall is modeled as a multilayer structure and the anti-icing system used is of the thermal type utilizing hot air and/or electrical heating elements embedded with the layers. Details of the calculation procedure and the methods used are presented.
Numerical hysteresis model for intermittent studies in unsaturated soils
NASA Astrophysics Data System (ADS)
Banerjee, M.
1986-07-01
In the present study, the use of one of the recent dependent domain models of capillary hysteresis in the numerical analysis of intermittent infiltration and redistribution of water in two types of soils (a sand and Rubicon Sandy Loam) has been shown. The numerical results for both the soils have been presented in terms of pressure head depth, moisture content depth and the pressure head-moisture content relationships. The capillary hysteresis model has been found to be very useful for the prediction of both wetting and drying scanning curves of various orders.
A numerical model and spreadsheet interface for pumping test analysis.
Johnson, G S; Cosgrove, D M; Frederick, D B
2001-01-01
Curve-matching techniques have been the standard method of aquifer test analysis for several decades. A variety of techniques provide the capability of evaluating test data from confined, unconfined, leaky aquitard, and other conditions. Each technique, however, is accompanied by a set of assumptions, and evaluation of a combination of conditions can be complicated or impossible due to intractable mathematics or nonuniqueness of the solution. Numerical modeling of pumping tests provides two major advantages: (1) the user can choose which properties to calibrate and what assumptions to make; and (2) in the calibration process the user is gaining insights into the conceptual model of the flow system and uncertainties in the analysis. Routine numerical modeling of pumping tests is now practical due to computer hardware and software advances of the last decade. The RADFLOW model and spreadsheet interface presented in this paper is an easy-to-use numerical model for estimation of aquifer properties from pumping test data. Layered conceptual models and their properties are evaluated in a trial-and-error estimation procedure. The RADFLOW model can treat most combinations of confined, unconfined, leaky aquitard, partial penetration, and borehole storage conditions. RADFLOW is especially useful in stratified aquifer systems with no identifiable lateral boundaries. It has been verified to several analytical solutions and has been applied in the Snake River Plain Aquifer to develop and test conceptual models and provide estimates of aquifer properties. Because the model assumes axially symmetrical flow, it is limited to representing multiple aquifer layers that are laterally continuous.
Feedbacks Between Numerical and Analytical Models in Hydrogeology
NASA Astrophysics Data System (ADS)
Zlotnik, V. A.; Cardenas, M. B.; Toundykov, D.; Cohn, S.
2012-12-01
Hydrogeology is a relatively young discipline which combines elements of Earth science and engineering. Mature fundamental disciplines (e.g., physics, chemistry, fluid mechanics) have centuries-long history of mathematical modeling even prior to discovery of Darcy's law. Thus, in hydrogeology, relatively few classic analytical models (such those by Theis, Polubarinova-Kochina, Philip, Toth, Henry, Dagan, Neuman) were developed by the early 1970's. The advent of computers and practical demands refocused mathematical models towards numerical techniques. With more diverse but less mathematically-oriented training, most hydrogeologists shifted from analytical methods to use of standardized computational software. Spatial variability in internal properties and external boundary conditions and geometry, and the added complexity of chemical and biological processes will remain major challenges for analytical modeling. Possibly, analytical techniques will play a subordinate role to numerical approaches in many applications. On the other hand, the rise of analytical element modeling of groundwater flow is a strong alternative to numerical models when data demand and computational efficiency is considered. The hallmark of analytical models - transparency and accuracy - will remain indispensable for scientific exploration of complex phenomena and for benchmarking numerical models. Therefore, there will always be feedbacks and complementarities between numerical and analytical techniques, as well as a certain ideological schism among various views to modeling. We illustrate the idea of feedbacks by reviewing evolution of Joszef Toth's analytical model of gravity driven flow systems. Toth's (1963) approach was to reduce the flow domain to a rectangle which allowed for closed-form solution of the governing equations. Succeeding numerical finite-element models by Freeze and Witherspoon (1966-1968) explored the effects of geometry and heterogeneity on regional groundwater flow
Numerical model of Fanuc AM100iB robot
NASA Astrophysics Data System (ADS)
Cholewa, A.; Świder, J.; Zbilski, A.
2016-08-01
The article presents a numerical model of Fanuc AM 100iB robot, prepared in the form of a block diagram in Simulink software, using the SimMechanics toolbox. The main task of the numerical model of Fanuc AM 100iB robot is to calculate the value of torques putting a load on motor shafts, and to calculate the values of kinematic parameters of the robot's arms in real time and in interactive mode. The values and format of torques putting a load on subsequent joints, and then on the motor shafts, resulted from the effect of the simultaneous action of all torques and the delay, resulting from the implementation of numerical calculations in real time. The numerical model developed is a result of design focused on recreating the effects of simultaneous action of all these factors, which are present in the actual drives and affect the consumption of electricity. A very important criterion, taken into account when designing the model, was also its computational efficiency. In addition, the model was used to visualise the work of the tested machine in three-dimensional space.
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.
Numerical Model Studies of the Martian Mesoscale Circulations
NASA Technical Reports Server (NTRS)
Segal, Moti; Arritt, Raymond W.
1997-01-01
The study objectives were to evaluate by numerical modeling various possible mesoscale circulation on Mars and related atmospheric boundary layer processes. The study was in collaboration with J. Tillman of the University of Washington (who supported the study observationally). Interaction has been made with J. Prusa of Iowa State University in numerical modeling investigation of dynamical effects of topographically-influenced flow. Modeling simulations included evaluations of surface physical characteristics on: (i) the Martian atmospheric boundary layer and (ii) their impact on thermally and dynamically forced mesoscale flows. Special model evaluations were made in support of selection of the Pathfinder landing sites. J. Tillman's finding of VL-2 inter-annual temperature difference was followed by model simulations attempting to point out the forcing for this feature. Publication of the results in the reviewed literature in pending upon completion of the manuscripts in preparation as indicated later.
Numerical characterization and modeling of adiabatic slot film cooling
NASA Astrophysics Data System (ADS)
Voegele, Andrew
Film cooling is a technique used to protect critical surfaces in combustors, thrust chambers, turbines and nozzles from hot, chemically reacting gases. Accurately predicting the film's performance is especially challenging in the vicinity of the wall and the film injection plane due to the complex interactions of two highly turbulent, shearing, boundary layer flows. Properly characterizing the streams at the inlet of a numerical simulation and the choice of turbulence model are crucial to accurately predicting the decay of the film. To address these issues, this study employs a RANS solver that is used to model a film cooled wall. Menter's baseline model, and shear-stress transport model and the Spalart-Allmaras model are employed to determine the effect on film cooling predictions. Several methods for prescribing the inlet planes are explored. These numerical studies are compared with experimental data obtained in a UMD film cooling wind tunnel.
Numerical modeling of consolidation processes in hydraulically deposited soils
NASA Astrophysics Data System (ADS)
Brink, Nicholas Robert
Hydraulically deposited soils are encountered in many common engineering applications including mine tailing and geotextile tube fills, though the consolidation process for such soils is highly nonlinear and requires the use of advanced numerical techniques to provide accurate predictions. Several commercially available finite element codes poses the ability to model soil consolidation, and it was the goal of this research to assess the ability of two of these codes, ABAQUS and PLAXIS, to model the large-strain, two-dimensional consolidation processes which occur in hydraulically deposited soils. A series of one- and two-dimensionally drained rectangular models were first created to assess the limitations of ABAQUS and PLAXIS when modeling consolidation of highly compressible soils. Then, geotextile tube and TSF models were created to represent actual scenarios which might be encountered in engineering practice. Several limitations were discovered, including the existence of a minimum preconsolidation stress below which numerical solutions become unstable.
Development, validation and application of numerical space environment models
NASA Astrophysics Data System (ADS)
Honkonen, Ilja
2013-10-01
Currently the majority of space-based assets are located inside the Earth's magnetosphere where they must endure the effects of the near-Earth space environment, i.e. space weather, which is driven by the supersonic flow of plasma from the Sun. Space weather refers to the day-to-day changes in the temperature, magnetic field and other parameters of the near-Earth space, similarly to ordinary weather which refers to changes in the atmosphere above ground level. Space weather can also cause adverse effects on the ground, for example, by inducing large direct currents in power transmission systems. The performance of computers has been growing exponentially for many decades and as a result the importance of numerical modeling in science has also increased rapidly. Numerical modeling is especially important in space plasma physics because there are no in-situ observations of space plasmas outside of the heliosphere and it is not feasible to study all aspects of space plasmas in a terrestrial laboratory. With the increasing number of computational cores in supercomputers, the parallel performance of numerical models on distributed memory hardware is also becoming crucial. This thesis consists of an introduction, four peer reviewed articles and describes the process of developing numerical space environment/weather models and the use of such models to study the near-Earth space. A complete model development chain is presented starting from initial planning and design to distributed memory parallelization and optimization, and finally testing, verification and validation of numerical models. A grid library that provides good parallel scalability on distributed memory hardware and several novel features, the distributed cartesian cell-refinable grid (DCCRG), is designed and developed. DCCRG is presently used in two numerical space weather models being developed at the Finnish Meteorological Institute. The first global magnetospheric test particle simulation based on the
NASA Astrophysics Data System (ADS)
Graham, Jason; Meneveau, Charles
2012-12-01
Simulating turbulent flows over objects characterized by hierarchies of length-scales poses special challenges associated with the cost of resolving small-scale elements. If these are treated as subgrid-scale elements, their effects on the resolved scales must be captured realistically. Most importantly, the associated drag forces must be parameterized. Prior work [S. Chester, C. Meneveau, and M. B. Parlange, "Modeling turbulent flow over fractal trees with renormalized numerical simulation," J. Comput. Phys. 225, 427-448 (2007), 10.1016/j.jcp.2006.12.009] proposed a technique called renormalized numerical simulation (RNS), which is applicable to objects that display scale-invariant geometric (fractal) properties. The idea of RNS is similar to that of the dynamic model used in large eddy simulation to determine model parameters for the subgrid-stress tensor model in the bulk of the flow. In RNS, drag forces from the resolved elements that are obtained during the simulation are re-scaled appropriately by determining drag coefficients that are then applied to specify the drag forces associated with the subgrid-scale elements. The technique has already been applied to model turbulent flow over a canopy of fractal trees [S. Chester, C. Meneveau, and M. B. Parlange, "Modeling turbulent flow over fractal trees with renormalized numerical simulation," J. Comput. Phys. 225, 427-448 (2007), 10.1016/j.jcp.2006.12.009], using a particular set of assumptions in evaluating the drag coefficient. In the current work we introduce a generalized framework for describing and implementing the RNS methodology. Furthermore, we describe various other possible practical implementations of RNS that differ on important, technical aspects related to (1) time averaging, (2) spatial localization, and (3) numerical representation of the drag forces. As part of this study, several RNS formulations are presented and compared. The various models are first implemented and compared in simulations of
Oscillation characteristics of endodontic files: numerical model and its validation.
Verhaagen, Bram; Lea, Simon C; de Bruin, Gerrit J; van der Sluis, Luc W M; Walmsley, A Damien; Versluis, Michel
2012-11-01
During a root canal treatment, an antimicrobial fluid is injected into the root canal to eradicate all bacteria from the root canal system. Agitation of the fluid using an ultrasonically vibrating miniature file results in a significant improvement in the cleaning efficacy over conventional syringe irrigation. Numerical analysis of the oscillation characteristics of the file, modeled as a tapered, driven rod, shows a sinusoidal wave pattern with an increase in amplitude and decrease in wavelength toward the free end of the file. Measurements of the file oscillation with a scanning laser vibrometer show good agreement with the numerical simulation. The numerical model of endodontic file oscillation has the potential for predicting the oscillation pattern and fracture likeliness of various file types and the acoustic streaming they induce during passive ultrasonic irrigation.
Physical and numerical modeling of Joule-heated melters
NASA Astrophysics Data System (ADS)
Eyler, L. L.; Skarda, R. J.; Crowder, R. S., III; Trent, D. S.; Reid, C. R.; Lessor, D. L.
1985-10-01
The Joule-heated ceramic-lined melter is an integral part of the high level waste immobilization process under development by the US Department of Energy. Scaleup and design of this waste glass melting furnace requires an understanding of the relationships between melting cavity design parameters and the furnace performance characteristics such as mixing, heat transfer, and electrical requirements. Developing empirical models of these relationships through actual melter testing with numerous designs would be a very costly and time consuming task. Additionally, the Pacific Northwest Laboratory (PNL) has been developing numerical models that simulate a Joule-heated melter for analyzing melter performance. This report documents the method used and results of this modeling effort. Numerical modeling results are compared with the more conventional, physical modeling results to validate the approach. Also included are the results of numerically simulating an operating research melter at PNL. Physical Joule-heated melters modeling results used for qualiying the simulation capabilities of the melter code included: (1) a melter with a single pair of electrodes and (2) a melter with a dual pair (two pairs) of electrodes. The physical model of the melter having two electrode pairs utilized a configuration with primary and secondary electrodes. The principal melter parameters (the ratio of power applied to each electrode pair, modeling fluid depth, electrode spacing) were varied in nine tests of the physical model during FY85. Code predictions were made for five of these tests. Voltage drops, temperature field data, and electric field data varied in their agreement with the physical modeling results, but in general were judged acceptable.
Physical and numerical modeling of Joule-heated melters
Eyler, L.L.; Skarda, R.J.; Crowder, R.S. III; Trent, D.S.; Reid, C.R.; Lessor, D.L.
1985-10-01
The Joule-heated ceramic-lined melter is an integral part of the high level waste immobilization process under development by the US Department of Energy. Scaleup and design of this waste glass melting furnace requires an understanding of the relationships between melting cavity design parameters and the furnace performance characteristics such as mixing, heat transfer, and electrical requirements. Developing empirical models of these relationships through actual melter testing with numerous designs would be a very costly and time consuming task. Additionally, the Pacific Northwest Laboratory (PNL) has been developing numerical models that simulate a Joule-heated melter for analyzing melter performance. This report documents the method used and results of this modeling effort. Numerical modeling results are compared with the more conventional, physical modeling results to validate the approach. Also included are the results of numerically simulating an operating research melter at PNL. Physical Joule-heated melters modeling results used for qualiying the simulation capabilities of the melter code included: (1) a melter with a single pair of electrodes and (2) a melter with a dual pair (two pairs) of electrodes. The physical model of the melter having two electrode pairs utilized a configuration with primary and secondary electrodes. The principal melter parameters (the ratio of power applied to each electrode pair, modeling fluid depth, electrode spacing) were varied in nine tests of the physical model during FY85. Code predictions were made for five of these tests. Voltage drops, temperature field data, and electric field data varied in their agreement with the physical modeling results, but in general were judged acceptable. 14 refs., 79 figs., 17 tabs.
An improved numerical model for wave rotor design and analysis
NASA Technical Reports Server (NTRS)
Paxson, Daniel E.; Wilson, Jack
1993-01-01
A numerical model has been developed which can predict both the unsteady flows within a wave rotor and the steady averaged flows in the ports. The model is based on the assumptions of one-dimensional, unsteady, and perfect gas flow. Besides the dominant wave behavior, it is also capable of predicting the effects of finite tube opening time, leakage from the tube ends, and viscosity. The relative simplicity of the model makes it useful for design, optimization, and analysis of wave rotor cycles for any application. This paper discusses some details of the model and presents comparisons between the model and two laboratory wave rotor experiments.
An improved numerical model for wave rotor design and analysis
NASA Technical Reports Server (NTRS)
Paxson, Daniel E.; Wilson, Jack
1992-01-01
A numerical model has been developed which can predict both the unsteady flows within a wave rotor and the steady averaged flows in the ports. The model is based on the assumptions of one-dimensional, unsteady, and perfect gas flow. Besides the dominant wave behavior, it is also capable of predicting the effects of finite tube opening time, leakage from the tube ends, and viscosity. The relative simplicity of the model makes it useful for design, optimization, and analysis of wave rotor cycles for any application. This paper discusses some details of the model and presents comparisons between the model and two laboratory wave rotor experiments.
Modified Numerical Simulation Model of Blood Flow in Bend
Liu, X; Zhou, X; Hao, X; Sang, X
2015-01-01
ABSTRACT The numerical simulation model of blood flow in bend is studied in this paper. The curvature modification is conducted for the blood flow model in bend to obtain the modified blood flow model in bend. The modified model is verified by U tube. By comparing the simulation results with the experimental results obtained by measuring the flow data in U tube, it was found that the modified blood flow model in bend can effectively improve the prediction accuracy of blood flow data affected by the curvature effect. PMID:27398727
Development of numerical Grids for UZ Flow and Transport Modeling
P. Dobson
2004-08-31
This report describes the methods used to develop numerical grids of the unsaturated hydrogeologic system beneath Yucca Mountain, Nevada. Numerical grid generation is an integral part of the development of the unsaturated zone (UZ) flow and transport model, a complex, three-dimensional (3-D) model of Yucca Mountain. This revision contains changes made to improve the clarity of the description of grid generation. The numerical grids, developed using current geologic, hydrogeologic, and mineralogic data, provide the necessary framework to: (1) develop calibrated hydrogeologic property sets and flow fields, (2) test conceptual hypotheses of flow and transport, and (3) predict flow and transport behavior under a variety of climatic and thermal-loading conditions. The technical scope, content, and management for the current revision of this report are described in the planning document ''Technical Work Plan for: Unsaturated Zone Flow Analysis and Model Report Integration'' (BSC 2004 [DIRS 169654], Section 2). Grids generated and documented in this report supersede those documented in Revision 00 of this report, ''Development of Numerical Grids for UZ Flow and Transport Modeling'' (BSC 2001 [DIRS 159356]). The grids presented in this report are the same as those developed in Revision 01 (BSC 2003 [DIRS 160109]); however, the documentation of the development of the grids in Revision 02 has been updated to address technical inconsistencies and achieve greater transparency, readability, and traceability. The constraints, assumptions, and limitations associated with this report are discussed in the appropriate sections that follow.
An Approach to Query Cost Modelling in Numeric Databases.
ERIC Educational Resources Information Center
Jarvelin, Kalervo
1989-01-01
Examines factors that determine user charges based on query processing costs in numeric databases, and analyzes the problem of estimating such charges in advance. An approach to query cost estimation is presented which is based on the relational data model and the query optimization, cardinality estimation, and file design techniques developed in…
Numerical Modeling of Drying Residual RP-1 in Rocket Engines
NASA Technical Reports Server (NTRS)
Majumdar, Alok; Polsgrove, Robert; Tiller, Bruce; Rodriquez, Pete (Technical Monitor)
2000-01-01
When a Rocket Engine shuts down under a fuel rich environment, a significant amount of unburned RP-1 is trapped In the engine. It is necessary to clean the residual RP-1 prior to subsequent firing to avoid any explosion due to detonation. The conventional method is to dry RP-1 with inert gas such as Nitrogen or Helium. It is difficult to estimate the drying time unless the engine is adequately equipped with instruments to measure the trace of RP-1 during the drying process. Such instrumentation in flight hardware is often impractical and costly. On the other hand numerical modeling of the drying process can provide a good insight for a satisfactory operation of the process. A numerical model can provide answer to questions such as a) how long it takes to dry, b) which fluid is a better dryer for RP-1, c) how to reduce drying time etc. The purpose of the present paper is to describe a numerical model of drying RP-1 trapped in a cavity with flowing nitrogen or helium. The numerical model assumes one dimensional flow of drying fluid in contact with liquid pool of RP-1. An evaporative mass transfer takes place across the contact surface.
A SPATIO-TEMPORAL DOWNSCALER FOR OUTPUT FROM NUMERICAL MODELS
Often, in environmental data collection, data arise from two sources: numerical models and monitoring networks. The first source provides predictions at the level of grid cells, while the second source gives measurements at points. The first is characterized by full spatial cove...
Modeling collisional processes in plasmas using discontinuous numerical methods
NASA Astrophysics Data System (ADS)
Miller, Sean
Fluid-based plasma models are typically applied to parameter regimes where a local thermal equilibrium is assumed. The applicability of this regime is valid for many plasmas, however, it is limited to plasma dynamics dominated by collisional effects. This study attempts to extend the validity of the collisional fluid regime using an anisotropic 13-moment fluid model derived from the Pearson type-IV probability distribution. The model explicitly evolves the heat flux hyperbolically alongside the density, momentum, and energy in order to capture dynamics usually restricted to costly kinetic models. Each particle species is modeled individually and collectively coupled through electromagnetic and collision operators. To remove electromagnetic divergence errors inherent to numerical representations of Maxwell's equations, both hyperbolic and parabolic cleaning methods are presented. The plasma models are implemented using high-order finite volume and discontinuous Galerkin numerical methods designed for unstructured meshes. The unstructured code framework, numerical methods, and plasma models were developed in the University of Washington's WARPXM code for use on heterogeneous accelerated clusters.
A numerical framework for modelling floating wind turbines
NASA Astrophysics Data System (ADS)
Vire, Axelle; Xiang, Jiansheng; Piggott, Matthew; Latham, John-Paul; Pain, Christopher
2012-11-01
This work couples a fluid/ocean- and a solid- dynamics model in order to numerically study fluid-structure interactions. The fully non-linear Navier-Stokes and solid-dynamics equations are solved on two distinct finite-element and unstructured grids. The interplay between fluid and solid is represented through a penalty force in the momentum balances of each material. The present algorithm is novel in that it spatially conserves the discrete penalty force, when exchanging it between both models, independently of the mesh resolution and of the shape-function orders in each model. This numerical framework targets the modelling of offshore floating wind turbines. Results will be shown for the flow past a moving pile and an actuator-disk representation of a turbine. This research is supported by the European Union Seventh Framework Programme (grant agreement PIEF-GA-2010-272437).
Numerical integration of population models satisfying conservation laws: NSFD methods.
Mickens, Ronald E
2007-10-01
Population models arising in ecology, epidemiology and mathematical biology may involve a conservation law, i.e. the total population is constant. In addition to these cases, other situations may occur for which the total population, asymptotically in time, approach a constant value. Since it is rarely the situation that the equations of motion can be analytically solved to obtain exact solutions, it follows that numerical techniques are needed to provide solutions. However, numerical procedures are only valid if they can reproduce fundamental properties of the differential equations modeling the phenomena of interest. We show that for population models, involving a dynamical conservation law the use of nonstandard finite difference (NSFD) methods allows the construction of discretization schemes such that they are dynamically consistent (DC) with the original differential equations. The paper will briefly discuss the NSFD methodology, the concept of DC, and illustrate their application to specific problems for population models.
Assessing Accuracy of Waveform Models against Numerical Relativity Waveforms
NASA Astrophysics Data System (ADS)
Pürrer, Michael; LVC Collaboration
2016-03-01
We compare currently available phenomenological and effective-one-body inspiral-merger-ringdown models for gravitational waves (GW) emitted from coalescing black hole binaries against a set of numerical relativity waveforms from the SXS collaboration. Simplifications are used in the construction of some waveform models, such as restriction to spins aligned with the orbital angular momentum, no inclusion of higher harmonics in the GW radiation, no modeling of eccentricity and the use of effective parameters to describe spin precession. In contrast, NR waveforms provide us with a high fidelity representation of the ``true'' waveform modulo small numerical errors. To focus on systematics we inject NR waveforms into zero noise for early advanced LIGO detector sensitivity at a moderately optimistic signal-to-noise ratio. We discuss where in the parameter space the above modeling assumptions lead to noticeable biases in recovered parameters.
Validation Testing and Numerical Modeling of Advanced Armor Materials
2012-11-01
constitutive material strength response with an appropriate yield surface model. The research is sub-divided into three areas: engineering design...and specimen preparation for Taylor impact testing, analytical solution for the dynamic yield strength of the materials used, and numerical modeling...aluminum alloy only. We perform a detailed analysis of the deformed specimen shapes to determine the dynamic yield strength . Additionally, hydrocode
Numerical modeling and simulation of flow through porous fabric surface
NASA Astrophysics Data System (ADS)
Gao, Zheng; Li, Xiaolin
We designed a numerical scheme to model the permeability of the fabric surface in an incompressible fluid by coupling the projection method with the Ghost Fluid Method in the front tracking framework. The pressure jump condition is obtained by adding a source term to the Poisson's equation in the projection step without modifications on its coefficients. The numerical results suggest that this approach has the ability to reproduce the relationship between pressure drop and relative velocity observed in the experiments. We use this algorithm to study the effects of porosity on the drag force and stability of parachutes during its inflation and deceleration.
Validation of numerical models for flow simulation in labyrinth seals
NASA Astrophysics Data System (ADS)
Frączek, D.; Wróblewski, W.
2016-10-01
CFD results were compared with the results of experiments for the flow through the labyrinth seal. RANS turbulence models (k-epsilon, k-omega, SST and SST-SAS) were selected for the study. Steady and transient results were analyzed. ANSYS CFX was used for numerical computation. The analysis included flow through sealing section with the honeycomb land. Leakage flows and velocity profiles in the seal were compared. In addition to the comparison of computational models, the divergence of modeling and experimental results has been determined. Tips for modeling these problems were formulated.
Numerical model for the uptake of groundwater contaminants by phreatophytes
Widdowson, M.A.; El-Sayed, A.; Landmeyer, J.E.
2008-01-01
Conventional solute transport models do not adequately account for the effects of phreatophytic plant systems on contaminant concentrations in shallow groundwater systems. A numerical model was developed and tested to simulate threedimensional reactive solute transport in a heterogeneous porous medium. Advective-dispersive transport is coupled to biodegradation, sorption, and plantbased attenuation processes including plant uptake and sorption by plant roots. The latter effects are a function of the physical-chemical properties of the individual solutes and plant species. Models for plant uptake were tested and evaluated using the experimental data collected at a field site comprised of hybrid poplar trees. A non-linear equilibrium isotherm model best represented site conditions.
Analysis and modeling of subgrid scalar mixing using numerical data
NASA Technical Reports Server (NTRS)
Girimaji, Sharath S.; Zhou, YE
1995-01-01
Direct numerical simulations (DNS) of passive scalar mixing in isotropic turbulence is used to study, analyze and, subsequently, model the role of small (subgrid) scales in the mixing process. In particular, we attempt to model the dissipation of the large scale (supergrid) scalar fluctuations caused by the subgrid scales by decomposing it into two parts: (1) the effect due to the interaction among the subgrid scales; and (2) the effect due to interaction between the supergrid and the subgrid scales. Model comparisons with DNS data show good agreement. This model is expected to be useful in the large eddy simulations of scalar mixing and reaction.
A numerical cloud model for the support of laboratory experimentation
NASA Technical Reports Server (NTRS)
Hagen, D. E.
1979-01-01
A numerical cloud model is presented which can describe the evolution of a cloud starting from moist aerosol-laden air through the diffusional growth regime. The model is designed for the direct support of cloud chamber laboratory experimentation, i.e., experiment preparation, real-time control and data analysis. In the model the thermodynamics is uncoupled from the droplet growth processes. Analytic solutions for the cloud droplet growth equations are developed which can be applied in most laboratory situations. The model is applied to a variety of representative experiments.
The numerical scheme development of a simplified frozen soil model
NASA Astrophysics Data System (ADS)
Li, Qian; Sun, Shufen; Dai, Qiudan
2009-09-01
In almost all frozen soil models used currently, three variables of temperature, ice content and moisture content are used as prognostic variables and the rate term, accounting for the contribution of the phase change between water and ice, is shown explicitly in both the energy and mass balance equations. The models must be solved by a numerical method with an iterative process, and the rate term of the phase change needs to be pre-estimated at the beginning in each iteration step. Since the rate term of the phase change in the energy equation is closely related to the release or absorption of the great amount of fusion heat, a small error in the rate term estimation will introduce greater error in the energy balance, which will amplify the error in the temperature calculation and in turn, cause problems for the numerical solution convergence. In this work, in order to first reduce the trouble, the methodology of the variable transformation is applied to a simplified frozen soil model used currently, which leads to new frozen soil scheme used in this work. In the new scheme, the enthalpy and the total water equivalent are used as predictive variables in the governing equations to replace temperature, volumetric soil moisture and ice content used in many current models. By doing so, the rate terms of the phase change are not shown explicitly in both the mass and energy equations and its pre-estimation is avoided. Secondly, in order to solve this new scheme more functionally, the development of the numerical scheme to the new scheme is described and a numerical algorithm appropriate to the numerical scheme is developed. In order to evaluate the new scheme of the frozen soil model and its relevant algorithm, a series of model evaluations are conducted by comparing numerical results from the new model scheme with three observational data sets. The comparisons show that the results from the model are in good agreement with these data sets in both the change trend of
Modeling supersonic combustion using a fully-implicit numerical method
NASA Technical Reports Server (NTRS)
Maccormack, Robert W.; Wilson, Gregory J.
1990-01-01
A fully-implicit finite-volume algorithm for two-dimensional axisymmetric flows has been coupled to a detailed hydrogen-air reaction mechanism (13 species and 33 reactions) so that supersonic combustion phenomena may be investigated. Numerical computations are compared with ballistic-range shadowgraphs of Lehr (1972) that exhibit two discontinuities caused by a blunt body as it passes through a premixed stoichiometric hydrogen-air mixture. The suitability of the numerical procedure for simulating these double-front flows is shown. The requirements for the physical formulation and the numerical modeling of these flowfields are discussed. Finally, the sensitivity of these external flowfields to changes in certain key reaction rate constants is examined.
An application of fast algorithms to numerical electromagnetic modeling
Bezvoda, V.; Segeth, K.
1987-03-01
Numerical electromagnetic modeling by the finite-difference or finite-element methods leads to a large sparse system of linear algebraic equations. Fast direct methods, requiring an order of at most q log q arithmetic operations to solve a system of q equations, cannot easily be applied to such a system. This paper describes the iterative application of a fast method, namely cyclic reduction, to the numerical solution of the Helmholtz equation with a piecewise constant imaginary coefficient of the absolute term in a plane domain. By means of numerical tests the advantages and limitations of the method compared with classical direct methods are discussed. The iterative application of the cyclic reduction method is very efficient if one can exploit a known solution of a similar (e.g., simpler) problem as the initial approximation. This makes cyclic reduction a powerful tool in solving the inverse problem by trial-and-error.
GPU accelerated numerical simulations of viscoelastic phase separation model.
Yang, Keda; Su, Jiaye; Guo, Hongxia
2012-07-05
We introduce a complete implementation of viscoelastic model for numerical simulations of the phase separation kinetics in dynamic asymmetry systems such as polymer blends and polymer solutions on a graphics processing unit (GPU) by CUDA language and discuss algorithms and optimizations in details. From studies of a polymer solution, we show that the GPU-based implementation can predict correctly the accepted results and provide about 190 times speedup over a single central processing unit (CPU). Further accuracy analysis demonstrates that both the single and the double precision calculations on the GPU are sufficient to produce high-quality results in numerical simulations of viscoelastic model. Therefore, the GPU-based viscoelastic model is very promising for studying many phase separation processes of experimental and theoretical interests that often take place on the large length and time scales and are not easily addressed by a conventional implementation running on a single CPU.
Numerical Modeling of Plasmas in which Nanoparticles Nucleate and Grow
NASA Astrophysics Data System (ADS)
Agarwal, Pulkit
Dusty plasmas refer to a broad category of plasmas. Plasmas such as argon-silane plasmas in which particles nucleate and grow are widely used in semiconductor processing and nanoparticle manufacturing. In such dusty plasmas, the plasma and the dust particles are strongly coupled to each other. This means that the presence of dust particles significantly affects the plasma properties and vice versa. Therefore such plasmas are highly complex and they involve several interesting phenomena like nucleation, growth, coagulation, charging and transport. Dusty plasma afterglow is equally complex and important. Especially, residual charge on dust particles carries special significance in several industrial and laboratory situations and it has not been well understood. A 1D numerical model was developed of a low-pressure capacitively-coupled plasma in which nanoparticles nucleate and grow. Polydispersity of particle size distributions can be important in such plasmas. Sectional method, which is well known in aerosol literature, was used to model the evolving particle size and charge distribution. The numerical model is transient and one-dimensional and self consistently accounts for nucleation, growth, coagulation, charging and transport of dust particles and their effect on plasma properties. Nucleation and surface growth rates were treated as input parameters. Results were presented in terms of particle size and charge distribution with an emphasis on importance of polydispersity in particle growth and dynamics. Results of numerical model were compared with experimental measurements of light scattering and light emission from plasma. Reasonable qualitative agreement was found with some discrepancies. Pulsed dusty plasma can be important for controlling particle production and/or unwanted particle deposition. In this case, it is important to understand the behavior of the particle cloud during the afterglow following plasma turn-off. Numerical model was modified to self
FEM numerical model analysis of magnetic nanoparticle tumor heating experiments.
Pearce, John A; Petyk, Alicia A; Hoopes, P Jack
2014-01-01
Iron oxide nanoparticles are currently under investigation as heating agents for hyperthermic treatment of tumors. Major determinants of effective heating include the biodistribution of magnetic materials, the minimum iron oxide loading required to achieve adequate heating, and practically achievable magnetic field strengths. These are inter-related criteria that ultimately determine the practicability of this approach to tumor treatment. Currently, we lack fundamental engineering design criteria that can be used in treatment planning and assessment. Coupling numerical models to experimental studies illuminate the underlying physical processes and can separate physical processes to determine their relative importance. Further, adding thermal damage and cell death process to the models provides valuable perspective on the likelihood of successful treatment. FEM numerical models were applied to increase the understanding of a carefully calibrated series of experiments in mouse mammary carcinoma. The numerical models results indicate that tumor loadings equivalent to approximately 1 mg of Fe3O4 per gram of tumor tissue are required to achieve adequate heating in magnetic field strengths of 34 kA/m (rms) at 160 kHz. Further, the models indicate that direct intratumoral injection of the nanoparticles results in between 1 and 20% uptake in the tissues.
Biomechanical behaviour of ankle ligaments: constitutive formulation and numerical modelling.
Forestiero, A; Carniel, E L; Natali, A N
2014-01-01
This study was aimed at the definition of a constitutive formulation of ankle ligaments and of a procedure for the constitutive parameters evaluation, for the biomechanical analysis by means of numerical models. To interpret the typical features of ligaments mechanical response, as anisotropic configuration, geometric non-linearity, non-linear elasticity and time-dependent behaviour, a specific fibre-reinforced visco-hyperelastic model is provided. The identification of constitutive parameters is performed by a stochastic-deterministic procedure that minimises the discrepancy between experimental and computational results. A preliminary evaluation of parameters is performed by analytical models in order to define reference values. Afterwards, solid models are developed to consider the complex histo-morphometric configuration of samples as a basis for the definition of numerical models. The results obtained are adopted for upgrading parameter values by comparison with specific mechanical tests. Assuming the new parameters set, the final numerical results are compared with the overall set of experimental data, to assess the reliability and efficacy of the analysis developed for the interpretation of the mechanical response of ankle ligaments.
Modern Perspectives on Numerical Modeling of Cardiac Pacemaker Cell
Maltsev, Victor A.; Yaniv, Yael; Maltsev, Anna V.; Stern, Michael D.; Lakatta, Edward G.
2015-01-01
Cardiac pacemaking is a complex phenomenon that is still not completely understood. Together with experimental studies, numerical modeling has been traditionally used to acquire mechanistic insights in this research area. This review summarizes the present state of numerical modeling of the cardiac pacemaker, including approaches to resolve present paradoxes and controversies. Specifically we discuss the requirement for realistic modeling to consider symmetrical importance of both intracellular and cell membrane processes (within a recent “coupled-clock” theory). Promising future developments of the complex pacemaker system models include the introduction of local calcium control, mitochondria function, and biochemical regulation of protein phosphorylation and cAMP production. Modern numerical and theoretical methods such as multi-parameter sensitivity analyses within extended populations of models and bifurcation analyses are also important for the definition of the most realistic parameters that describe a robust, yet simultaneously flexible operation of the coupled-clock pacemaker cell system. The systems approach to exploring cardiac pacemaker function will guide development of new therapies, such as biological pacemakers for treating insufficient cardiac pacemaker function that becomes especially prevalent with advancing age. PMID:24748434
Numerical modelling of the shoulder for clinical applications.
Favre, Philippe; Snedeker, Jess G; Gerber, Christian
2009-05-28
Research activity involving numerical models of the shoulder is dramatically increasing, driven by growing rates of injury and the need to better understand shoulder joint pathologies to develop therapeutic strategies. Based on the type of clinical question they can address, existing models can be broadly categorized into three groups: (i) rigid body models that can simulate kinematics, collisions between entities or wrapping of the muscles over the bones, and which have been used to investigate joint kinematics and ergonomics, and are often coupled with (ii) muscle force estimation techniques, consisting mainly of optimization methods and electromyography-driven models, to simulate muscular action and joint reaction forces to address issues in joint stability, muscular rehabilitation or muscle transfer, and (iii) deformable models that account for stress-strain distributions in the component structures to study articular degeneration, implant failure or muscle/tendon/bone integrity. The state of the art in numerical modelling of the shoulder is reviewed, and the advantages, limitations and potential clinical applications of these modelling approaches are critically discussed. This review concentrates primarily on muscle force estimation modelling, with emphasis on a novel muscle recruitment paradigm, compared with traditionally applied optimization methods. Finally, the necessary benchmarks for validating shoulder models, the emerging technologies that will enable further advances and the future challenges in the field are described.
Applications of Numerical Models for Rough Surface Scattering
NASA Astrophysics Data System (ADS)
Johnson, Joel Tidmore
This thesis provides new computational models for electromagnetic surface scattering which allow large one and two dimensional problems to be considered through the use of efficient numerical algorithms and parallel computing techniques. This is in contrast with previous numerical studies that have been limited to relatively small surfaces rough in one dimension only. The new numerically exact models are applied to several problems of current interest, and allow studies of phenomena not predicted by any available analytical theories. In addition, comparisons are made with predictions of standard analytical models to obtain an assessment of their performance. A one dimensional model for VHF propagation is the first numerical model considered. Comparisons with measurement data show the model to produce accurate results, and conclusively demonstrate the importance of terrain measurements in propagation predictions. Comparisons with approximate models allow their appropriate regions of validity to be determined. Polarimetric thermal emission from two dimensional periodic surfaces is studied using an extended boundary condition (EBC) numerical solution. The model is applied to generate the only numerically exact results for two dimensional surface polarimetric thermal emission currently available, and demonstrates that properties of U _{B}, the third Stokes emission parameter, remain similar to those observed previously for one dimensional periodic surfaces. The response of U_{B} to level of medium anisotropy is also investigated. A Monte Carlo study of backscattering enhancement from two dimensional perfectly conducting random rough surfaces follows, using a recently developed more efficient version of the method of moments which allows the large two dimensional surfaces investigated to be treated. Comparisons with bistatic scattering data from machine fabricated random surfaces taken at the University of Washington illustrate the first such validation of a two
Ultrasonic and numerical modeling of reflections from simulated fractured reservoirs
Stephen, T.; Zhu, Xiang,
1997-10-01
In order to develop modeling techniques for the characterization of fracture properties in tight gas sands from surface seismic reflection data we examine seismic waves scattered from anisotropic heterogeneity with laboratory data and numerical modeling. Laboratory models representing features of a fractured reservoir were constructed using Phenolite embedded in a Lucite background, and seismic surveys were gathered over these models. In parallel with laboratory measurement, finite-difference modeling of reflections from a fractured medium were carried out. Fracture zone properties were calculated using an effective medium theory, the variation of fracture density produced a heterogeneous medium. The heterogeneity was modeled with a stochastic process, characterized by a probability density function and an auto-correlation function. Results from both modeling efforts show that prestacked AVO data can contain important information describing reservoir heterogeneity.
Handling geophysical flows: Numerical modelling using Graphical Processing Units
NASA Astrophysics Data System (ADS)
Garcia-Navarro, Pilar; Lacasta, Asier; Juez, Carmelo; Morales-Hernandez, Mario
2016-04-01
Computational tools may help engineers in the assessment of sediment transport during the decision-making processes. The main requirements are that the numerical results have to be accurate and simulation models must be fast. The present work is based on the 2D shallow water equations in combination with the 2D Exner equation [1]. The resulting numerical model accuracy was already discussed in previous work. Regarding the speed of the computation, the Exner equation slows down the already costly 2D shallow water model as the number of variables to solve is increased and the numerical stability is more restrictive. On the other hand, the movement of poorly sorted material over steep areas constitutes a hazardous environmental problem. Computational tools help in the predictions of such landslides [2]. In order to overcome this problem, this work proposes the use of Graphical Processing Units (GPUs) for decreasing significantly the simulation time [3, 4]. The numerical scheme implemented in GPU is based on a finite volume scheme. The mathematical model and the numerical implementation are compared against experimental and field data. In addition, the computational times obtained with the Graphical Hardware technology are compared against Single-Core (sequential) and Multi-Core (parallel) CPU implementations. References [Juez et al.(2014)] Juez, C., Murillo, J., & Garca-Navarro, P. (2014) A 2D weakly-coupled and efficient numerical model for transient shallow flow and movable bed. Advances in Water Resources. 71 93-109. [Juez et al.(2013)] Juez, C., Murillo, J., & Garca-Navarro, P. (2013) . 2D simulation of granular flow over irregular steep slopes using global and local coordinates. Journal of Computational Physics. 225 166-204. [Lacasta et al.(2014)] Lacasta, A., Morales-Hernndez, M., Murillo, J., & Garca-Navarro, P. (2014) An optimized GPU implementation of a 2D free surface simulation model on unstructured meshes Advances in Engineering Software. 78 1-15. [Lacasta
Numerical modeling of shallow magma intrusions with finite element method
NASA Astrophysics Data System (ADS)
Chen, Tielin; Cheng, Shaozhen; Fang, Qian; Zhou, Cheng
2017-03-01
A numerical approach for simulation of magma intrusion process, considering the couplings of the stress distribution, the viscous fluid flow of magma, and the fracturing of host rock, has been developed to investigate the mechanisms of fracture initiation and propagation in host rock during magma intrusion without pre-placing a set of fractures. The study focused on the dike intrusions filled with injected viscous magma in shallow sediments. A series of numerical modellings were carried out to simulate the process of magma intrusion in host rocks, with particular attention on the magma propagation processes and the formation of intrusion shapes. The model materials were Mohr-Coulomb materials with tension failure and shear failure. The scenarios of both stochastically heterogeneous host rocks and layered host rocks were analyzed. The injected magma formed intrusions shapes of (a) dyke, (b) sill, (c) cup-shaped intrusion, (d) saucer-shaped intrusion. The numerical results were in agreement with the experimental and field observed results, which confirmed the adequacy and the power of the numerical approach.
Mathematical and Numerical Techniques in Energy and Environmental Modeling
NASA Astrophysics Data System (ADS)
Chen, Z.; Ewing, R. E.
Mathematical models have been widely used to predict, understand, and optimize many complex physical processes, from semiconductor or pharmaceutical design to large-scale applications such as global weather models to astrophysics. In particular, simulation of environmental effects of air pollution is extensive. Here we address the need for using similar models to understand the fate and transport of groundwater contaminants and to design in situ remediation strategies. Three basic problem areas need to be addressed in the modeling and simulation of the flow of groundwater contamination. First, one obtains an effective model to describe the complex fluid/fluid and fluid/rock interactions that control the transport of contaminants in groundwater. This includes the problem of obtaining accurate reservoir descriptions at various length scales and modeling the effects of this heterogeneity in the reservoir simulators. Next, one develops accurate discretization techniques that retain the important physical properties of the continuous models. Finally, one develops efficient numerical solution algorithms that utilize the potential of the emerging computing architectures. We will discuss recent advances and describe the contribution of each of the papers in this book in these three areas. Keywords: reservoir simulation, mathematical models, partial differential equations, numerical algorithms
Numerical solutions of the three-dimensional magnetohydrodynamic alpha model.
Mininni, Pablo D; Montgomery, David C; Pouquet, Annick
2005-04-01
We present direct numerical simulations and alpha -model simulations of four familiar three-dimensional magnetohydrodynamic (MHD) turbulence effects: selective decay, dynamic alignment, inverse cascade of magnetic helicity, and the helical dynamo effect. The MHD alpha model is shown to capture the long-wavelength spectra in all these problems, allowing for a significant reduction of computer time and memory at the same kinetic and magnetic Reynolds numbers. In the helical dynamo, not only does the alpha model correctly reproduce the growth rate of magnetic energy during the kinematic regime, it also captures the nonlinear saturation level and the late generation of a large scale magnetic field by the helical turbulence.
Numerical modeling of electron-beam welding of dissimilar metals
NASA Astrophysics Data System (ADS)
Krektuleva, R. A.; Cherepanov, O. I.; Cherepanov, R. O.
2016-11-01
This paper is devoted to numerical modeling of heat transfer processes and estimation of thermal stresses in weld seams created by electron beam welding of heterogeneous metals. The mathematical model is based on a system of equations that includes the Lagrange's variational equation of theory of plasticity and variational equation of M. Biot's principle to simulate the heat transfer processes. The two-dimensional problems (plane strain and plane stress) are considered for estimation of thermal stresses in welds considering differences of mechanical properties of welded materials. The model is developed for simulation of temperature fields and stresses during electron beam welding.
Numerical modeling of microwave switchers with subpicosecond time delay
NASA Astrophysics Data System (ADS)
Konoplev, B.; Ryndin, E.
2016-12-01
In this article the layout and structure of the microwave switcher based on the managed electron density maximum rearrangement in multi-contacts functionally integrated active region are considered. The basis of the microwave switcher is a normally opened high electron mobility transistor structure (HEMT) with multiple Schottky gates and the corresponding number of switching ohmic contacts. In this research two-dimensional finite-difference physical and topological model of the considered microwave switchers is proposed. The distinctive features of the proposed model are combination of two different sets of variables and explicit first-order upwind discretization scheme for the normalized continuity equation. The obtained results of numerical modeling are discussed.
Numerical model of solar dynamic radiator for parametric analysis
NASA Technical Reports Server (NTRS)
Rhatigan, Jennifer L.
1989-01-01
Growth power requirements for Space Station Freedom will be met through addition of 25 kW solar dynamic (SD) power modules. Extensive thermal and power cycle modeling capabilities have been developed which are powerful tools in Station design and analysis, but which prove cumbersome and costly for simple component preliminary design studies. In order to aid in refining the SD radiator to the mature design stage, a simple and flexible numerical model was developed. The model simulates heat transfer and fluid flow performance of the radiator and calculates area mass and impact survivability for many combinations of flow tube and panel configurations, fluid and material properties, and environmental and cycle variations.
Preliminary numerical analysis of improved gas chromatograph model
NASA Technical Reports Server (NTRS)
Woodrow, P. T.
1973-01-01
A mathematical model for the gas chromatograph was developed which incorporates the heretofore neglected transport mechanisms of intraparticle diffusion and rates of adsorption. Because a closed-form analytical solution to the model does not appear realizable, techniques for the numerical solution of the model equations are being investigated. Criteria were developed for using a finite terminal boundary condition in place of an infinite boundary condition used in analytical solution techniques. The class of weighted residual methods known as orthogonal collocation is presently being investigated and appears promising.
Numerical Modeling of Fracture Propagation in Naturally Fractured Formations
NASA Astrophysics Data System (ADS)
Wang, W.; Prodanovic, M.; Olson, J. E.; Schultz, R.
2015-12-01
Hydraulic fracturing consists of injecting fluid at high pressure and high flowrate to the wellbore for the purpose of enhancing production by generating a complex fracture network. Both tensile failure and shear failure occur during the hydraulic fracturing treatment. The shear event can be caused by slip on existing weak planes such as faults or natural fractures. From core observation, partially cemented and fully cemented opening mode natural fractures, often with considerable thickness are widely present. Hydraulic fractures can propagate either within the natural fracture (tensile failure) or along the interface between the natural fracture and the rock matrix (tensile/shear failure), depending on the relative strength of cement and rock matrix materials, the bonding strength of interface, as well as the presence of any heterogeneities. In this study, we evaluate the fracture propagation both experimentally and numerically. We embed one or multiple inclusions of different mechanical properties within synthetic hydrostone samples in order to mimic cemented natural fractures and rock. A semi-circular bending test is performed for each set of properties. A finite element model built with ABAQUS is used to mimic the semi-circular bending test and study the fracture propagation path, as well as the matrix-inclusion bonding interface status. Mechanical properties required for the numerical model are measured experimentally. The results indicate that the match between experiment and modeling fracture path are extremely sensitive to the chosen interface (bonding) model and related parameters. The semi-circular bending test is dry and easily conducted, providing a good platform for validating numerical approaches. A validated numerical model will enable us to add pressurized fluid within the crack and simulate hydraulic fracture-natural fracture interaction in the reservoir conditions, ultimately providing insights into the extent of the fracture network.
Busted Butte: Achieving the Objectives and Numerical Modeling Results
W.E. Soll; M. Kearney; P. Stauffer; P. Tseng; H.J. Turin; Z. Lu
2002-10-07
The Unsaturated Zone Transport Test (UZTT) at Busted Butte is a mesoscale field/laboratory/modeling investigation designed to address uncertainties associated with flow and transport in the UZ site-process models for Yucca Mountain. The UZTT test facility is located approximately 8 km southeast of the potential Yucca Mountain repository area. The UZTT was designed in two phases, to address five specific objectives in the UZ: the effect of heterogeneities, flow and transport (F&T) behavior at permeability contrast boundaries, migration of colloids , transport models of sorbing tracers, and scaling issues in moving from laboratory scale to field scale. Phase 1A was designed to assess the influence of permeability contrast boundaries in the hydrologic Calico Hills. Visualization of fluorescein movement , mineback rock analyses, and comparison with numerical models demonstrated that F&T are capillary dominated with permeability contrast boundaries distorting the capillary flow. Phase 1B was designed to assess the influence of fractures on F&T and colloid movement. The injector in Phase 1B was located at a fracture, while the collector, 30 cm below, was placed at what was assumed to be the same fracture. Numerical simulations of nonreactive (Br) and reactive (Li) tracers show the experimental data are best explained by a combination of molecular diffusion and advective flux. For Phase 2, a numerical model with homogeneous unit descriptions was able to qualitatively capture the general characteristics of the system. Numerical simulations and field observations revealed a capillary dominated flow field. Although the tracers showed heterogeneity in the test block, simulation using heterogeneous fields did not significantly improve the data fit over homogeneous field simulations. In terms of scaling, simulations of field tracer data indicate a hydraulic conductivity two orders of magnitude higher than measured in the laboratory. Simulations of Li, a weakly sorbing tracer
Temperature sensitivity of a numerical pollen forecast model
NASA Astrophysics Data System (ADS)
Scheifinger, Helfried; Meran, Ingrid; Szabo, Barbara; Gallaun, Heinz; Natali, Stefano; Mantovani, Simone
2016-04-01
Allergic rhinitis has become a global health problem especially affecting children and adolescence. Timely and reliable warning before an increase of the atmospheric pollen concentration means a substantial support for physicians and allergy suffers. Recently developed numerical pollen forecast models have become means to support the pollen forecast service, which however still require refinement. One of the problem areas concerns the correct timing of the beginning and end of the flowering period of the species under consideration, which is identical with the period of possible pollen emission. Both are governed essentially by the temperature accumulated before the entry of flowering and during flowering. Phenological models are sensitive to a bias of the temperature. A mean bias of -1°C of the input temperature can shift the entry date of a phenological phase for about a week into the future. A bias of such an order of magnitude is still possible in case of numerical weather forecast models. If the assimilation of additional temperature information (e.g. ground measurements as well as satellite-retrieved air / surface temperature fields) is able to reduce such systematic temperature deviations, the precision of the timing of phenological entry dates might be enhanced. With a number of sensitivity experiments the effect of a possible temperature bias on the modelled phenology and the pollen concentration in the atmosphere is determined. The actual bias of the ECMWF IFS 2 m temperature will also be calculated and its effect on the numerical pollen forecast procedure presented.
Comparison between analytical and numerical solution of mathematical drying model
NASA Astrophysics Data System (ADS)
Shahari, N.; Rasmani, K.; Jamil, N.
2016-02-01
Drying is often related to the food industry as a process of shifting heat and mass inside food, which helps in preserving food. Previous research using a mass transfer equation showed that the results were mostly concerned with the comparison between the simulation model and the experimental data. In this paper, the finite difference method was used to solve a mass equation during drying using different kinds of boundary condition, which are equilibrium and convective boundary conditions. The results of these two models provide a comparison between the analytical and the numerical solution. The result shows a close match between the two solution curves. It is concluded that the two proposed models produce an accurate solution to describe the moisture distribution content during the drying process. This analysis indicates that we have confidence in the behaviour of moisture in the numerical simulation. This result demonstrated that a combined analytical and numerical approach prove that the system is behaving physically. Based on this assumption, the model of mass transfer was extended to include the temperature transfer, and the result shows a similar trend to those presented in the simpler case.
Performance benchmarks for a next generation numerical dynamo model
NASA Astrophysics Data System (ADS)
Matsui, Hiroaki; Heien, Eric; Aubert, Julien; Aurnou, Jonathan M.; Avery, Margaret; Brown, Ben; Buffett, Bruce A.; Busse, Friedrich; Christensen, Ulrich R.; Davies, Christopher J.; Featherstone, Nicholas; Gastine, Thomas; Glatzmaier, Gary A.; Gubbins, David; Guermond, Jean-Luc; Hayashi, Yoshi-Yuki; Hollerbach, Rainer; Hwang, Lorraine J.; Jackson, Andrew; Jones, Chris A.; Jiang, Weiyuan; Kellogg, Louise H.; Kuang, Weijia; Landeau, Maylis; Marti, Philippe; Olson, Peter; Ribeiro, Adolfo; Sasaki, Youhei; Schaeffer, Nathanaël.; Simitev, Radostin D.; Sheyko, Andrey; Silva, Luis; Stanley, Sabine; Takahashi, Futoshi; Takehiro, Shin-ichi; Wicht, Johannes; Willis, Ashley P.
2016-05-01
Numerical simulations of the geodynamo have successfully represented many observable characteristics of the geomagnetic field, yielding insight into the fundamental processes that generate magnetic fields in the Earth's core. Because of limited spatial resolution, however, the diffusivities in numerical dynamo models are much larger than those in the Earth's core, and consequently, questions remain about how realistic these models are. The typical strategy used to address this issue has been to continue to increase the resolution of these quasi-laminar models with increasing computational resources, thus pushing them toward more realistic parameter regimes. We assess which methods are most promising for the next generation of supercomputers, which will offer access to O(106) processor cores for large problems. Here we report performance and accuracy benchmarks from 15 dynamo codes that employ a range of numerical and parallelization methods. Computational performance is assessed on the basis of weak and strong scaling behavior up to 16,384 processor cores. Extrapolations of our weak-scaling results indicate that dynamo codes that employ two-dimensional or three-dimensional domain decompositions can perform efficiently on up to ˜106 processor cores, paving the way for more realistic simulations in the next model generation.
Quantitative comparisons of numerical models of brittle deformation
NASA Astrophysics Data System (ADS)
Buiter, S.
2009-04-01
Numerical modelling of brittle deformation in the uppermost crust can be challenging owing to the requirement of an accurate pressure calculation, the ability to achieve post-yield deformation and localisation, and the choice of rheology (plasticity law). One way to approach these issues is to conduct model comparisons that can evaluate the effects of different implementations of brittle behaviour in crustal deformation models. We present a comparison of three brittle shortening experiments for fourteen different numerical codes, which use finite element, finite difference, boundary element and distinct element techniques. Our aim is to constrain and quantify the variability among models in order to improve our understanding of causes leading to differences between model results. Our first experiment of translation of a stable sand-like wedge serves as a reference that allows for testing against analytical solutions (e.g., taper angle, root-mean-square velocity and gravitational rate of work). The next two experiments investigate an unstable wedge in a sandbox-like setup which deforms by inward translation of a mobile wall. All models accommodate shortening by in-sequence formation of forward shear zones. We analyse the location, dip angle and spacing of thrusts in detail as previous comparisons have shown that these can be highly variable in numerical and analogue models of crustal shortening and extension. We find that an accurate implementation of boundary friction is important for our models. Our results are encouraging in the overall agreement in their dynamic evolution, but show at the same time the effort that is needed to understand shear zone evolution. GeoMod2008 Team: Markus Albertz, Michele Cooke, Susan Ellis, Taras Gerya, Luke Hodkinson, Kristin Hughes, Katrin Huhn, Boris Kaus, Walter Landry, Bertrand Maillot, Christophe Pascal, Anton Popov, Guido Schreurs, Christopher Beaumont, Tony Crook, Mario Del Castello and Yves Leroy
Reevaluating the two-representation model of numerical magnitude processing.
Jiang, Ting; Zhang, Wenfeng; Wen, Wen; Zhu, Haiting; Du, Han; Zhu, Xiangru; Gao, Xuefei; Zhang, Hongchuan; Dong, Qi; Chen, Chuansheng
2016-01-01
One debate in mathematical cognition centers on the single-representation model versus the two-representation model. Using an improved number Stroop paradigm (i.e., systematically manipulating physical size distance), in the present study we tested the predictions of the two models for number magnitude processing. The results supported the single-representation model and, more importantly, explained how a design problem (failure to manipulate physical size distance) and an analytical problem (failure to consider the interaction between congruity and task-irrelevant numerical distance) might have contributed to the evidence used to support the two-representation model. This study, therefore, can help settle the debate between the single-representation and two-representation models.
Mathematical analysis and numerical simulation of a model of morphogenesis.
Muñoz, Ana I; Tello, José Ignacio
2011-10-01
We consider a simple mathematical model of distribution of morphogens (signaling molecules responsible for the differentiation of cells and the creation of tissue patterns). The mathematical model is a particular case of the model proposed by Lander, Nie and Wan in 2006 and similar to the model presented in Lander, Nie, Vargas and Wan 2005. The model consists of a system of three equations: a PDE of parabolic type with dynamical boundary conditions modelling the distribution of free morphogens and two ODEs describing the evolution of bound and free receptors. Three biological processes are taken into account: diffusion, degradation and reversible binding. We study the stationary solutions and the evolution problem. Numerical simulations show the behavior of the solution depending on the values of the parameters.
Numerical Modeling of Table-Top X-Ray Lasers
Shlyaptsev, V N; Dunn, J; Moon, S; Osterheld, A L; Rocca, J J; Detering, F; Rozmus, W; Matte, J P; Fiedorowicz, H; Bartnik, A; Kanouff, M
2002-04-29
In this work we report numerical modeling results of laser-generated transient inversion and capillary discharge X-ray lasers. We have found the importance of plasma kinetics approaches in transient X-ray lasers physics by expanding the physical model beyond hydrodynamics approximation. Using Particle and Fokker-Planck codes the clear evidence of the Langdon effect was inferred from the recent experimental data obtained with the Ni-like Pd X-ray laser. In the search for more efficient X-ray lasers we looked closely at alternative target designs utilizing low density targets. In conjunction with recent experiments at LLNL the numerical investigations of gas puff targets has been performed.
On numerical considerations for modeling reactive astrophysical shocks
Papatheodore, Thomas L.; Messer, O. E. Bronson E-mail: bronson@ornl.gov
2014-02-10
Simulating detonations in astrophysical environments is often complicated by numerical approximations to shock structure. A common prescription to ensure correct detonation speeds and associated quantities is to prohibit burning inside the numerically broadened shock. We have performed a series of simulations to verify the efficacy of this approximation and to understand how resolution and dimensionality might affect its use. Our results show that in one dimension, prohibiting burning in the shock is important wherever the carbon burning length is not resolved, in keeping with the results of Fryxell et al. In two dimensions, we find that the prohibition of shock burning effectively inhibits the development of cellular structure for all but the most highly resolved cases. We discuss the possible impacts this outcome may have on sub-grid models and detonation propagation in models of Type Ia supernovae, including potential impacts on observables.
A Numerical Model of Viscoelastic Flow in Microchannels
Trebotich, D; Colella, P; Miller, G; Liepmann, D
2002-11-14
The authors present a numerical method to model non-Newtonian, viscoelastic flow at the microscale. The equations of motion are the incompressible Navier-Stokes equations coupled with the Oldroyd-B constitutive equation. This constitutive equation is chosen to model a Boger fluid which is representative of complex biological solutions exhibiting elastic behavior due to macromolecules in the solution (e.g., DNA solution). The numerical approach is a projection method to impose the incompressibility constraint and a Lax-Wendroff method to predict velocities and stresses while recovering both viscous and elastic limits. The method is second-order accurate in space and time, free-stream preserving, has a time step constraint determined by the advective CFL condition, and requires the solution of only well-behaved linear systems amenable to the use of fast iterative methods. They demonstrate the method for viscoelastic incompressible flow in simple microchannels (2D) and microducts (3D).
Wake redirection: comparison of analytical, numerical and experimental models
NASA Astrophysics Data System (ADS)
Wang, Jiangang; Bottasso, Carlo L.; Campagnolo, Filippo
2016-09-01
This paper focuses on wake redirection techniques for wind farm control. Two control strategies are investigated: yaw misalignment and cyclic pitch control. First, analytical formulas are derived for both techniques, with the goal of providing a simple physical interpretation of the behavior of the two methods. Next, more realistic results are obtained by numerical simulations performed with CFD and by experiments conducted with scaled wind turbine models operating in a boundary layer wind tunnel. Comparing the analytical, numerical and experimental models allows for a cross-validation of the results and a better understanding of the two wake redirection techniques. Results indicate that yaw misalignment is more effective than cyclic pitch control in displacing the wake laterally, although the latter may have positive effects on wake recovery.
Optimum employment of satellite indirect soundings as numerical model input
NASA Technical Reports Server (NTRS)
Horn, L. H.; Derber, J. C.; Koehler, T. L.; Schmidt, B. D.
1981-01-01
The characteristics of satellite-derived temperature soundings that would significantly affect their use as input for numerical weather prediction models were examined. Independent evaluations of satellite soundings were emphasized to better define error characteristics. Results of a Nimbus-6 sounding study reveal an underestimation of the strength of synoptic scale troughs and ridges, and associated gradients in isobaric height and temperature fields. The most significant errors occurred near the Earth's surface and the tropopause. Soundings from the TIROS-N and NOAA-6 satellites were also evaluated. Results again showed an underestimation of upper level trough amplitudes leading to weaker thermal gradient depictions in satellite-only fields. These errors show a definite correlation to the synoptic flow patterns. In a satellite-only analysis used to initialize a numerical model forecast, it was found that these synoptically correlated errors were retained in the forecast sequence.
Numerical Simulation of SNCR Technology with Simplified Chemical Kinetics Model
NASA Astrophysics Data System (ADS)
Blejchař, T.; Dolníčková, D.
2013-04-01
The paper deals with numerical simulation of SNCR method. For numerical modelling was used CFD code Ansys/CFX. SNCR method was described by dominant chemical reaction, which were look up NIST Chemical database. The reactions including reduction of NOx and concentration change of pollutants, like N2O and CO in flue gas too. Proposed chemical kinetics and CFD model was applied to two boilers. Both simulations were compared with experimental measurements. First simulation was used to validation of chemical mechanism. Second simulation was based on first simulation and it was used to verification of compiled SNCR chemical mechanism. Next the new variant of the reagent penetration lance was proposed and compared with the original variants.
SToRM: A numerical model for environmental surface flows
Simoes, Francisco J.
2009-01-01
SToRM (System for Transport and River Modeling) is a numerical model developed to simulate free surface flows in complex environmental domains. It is based on the depth-averaged St. Venant equations, which are discretized using unstructured upwind finite volume methods, and contains both steady and unsteady solution techniques. This article provides a brief description of the numerical approach selected to discretize the governing equations in space and time, including important aspects of solving natural environmental flows, such as the wetting and drying algorithm. The presentation is illustrated with several application examples, covering both laboratory and natural river flow cases, which show the model’s ability to solve complex flow phenomena.
Numerical Modeling of ISS Thruster Plume Induced Contamination Environment
2007-11-02
Numerical Method- ology The flow conditions and geometry considered in this work correspond to the bipropellant NTO/ UDMH 130 N thruster. A conical...the expansion angle of the diverging section is 20 deg. The propellant is UDMH /NTO, and the stagnation temperature and pressure are 2,900 K and 3.85...atm, respectively. Ten species mixture was used to model UDMH /NTO combustion products. The equilibrium combustion products composition for assumed
Numerical modeling of turbulent supersonic reacting coaxial jets
NASA Technical Reports Server (NTRS)
Eklund, Dean R.; Hassan, H. A.; Drummond, J. Philip
1989-01-01
The paper considers the mixing and subsequent combustion within turbulent reacting shear layers. A computer program was developed to solve the axisymmetric Reynolds averaged Navier-Stokes equations. The numerical method integrates the Reynolds averaged Navier-Stokes equations using a finite volume approach while advancing the solution forward in time using a Runge-Kutta scheme. Three separate flowfields are investigated and it is found that no single turbulence model considered could accurately predict the degree of mixing for all three cases.
Numerical modeling of injection experiments at The Geysers
Pruess, Karsten; Enedy, Steve
1993-01-28
Data from injection experiments in the southeast Geysers are presented that show strong interference (both negative and positive) with a neighboring production well. Conceptual and numerical models are developed that explain the negative interference (decline of production rate) in terms of heat transfer limitations and water-vapor relative permeability effects. Recovery and overrecovery following injection shut-in are attributed to boiling of injected fluid, with heat of vaporization provided by the reservoir rocks.
Numerical modeling of injection experiments at The Geysers
Pruess, K.; Enedy, S.
1993-01-01
Data from injection experiments in the southeast Geysers are presented that show strong interference (both negative and positive) with a neighboring production well. Conceptual and numerical models are developed that explain the negative interference (decline of production rate) in terms of heat transfer limitations and water-vapor relative permeability effects. Recovery and over-recovery following injection shut-in are attributed to boiling of injected fluid, with heat of vaporization provided by the reservoir rocks.
Numerical modeling of two-dimensional confined flows
NASA Technical Reports Server (NTRS)
Greywall, M. S.
1979-01-01
A numerical model of two-dimensional confined flows is presented. The flow in the duct is partitioned into finite streams. The difference equations are then obtained by applying conservation principles directly to the individual streams. A listing of a computer code based on this approach in FORTRAN 4 language is presented. The code computes two dimensional compressible turbulent flows in ducts when the duct area along the flow is specified and the pressure gradient is unknown.
Fast Numerically Based Modeling for Ground Penetrating Radar
NASA Astrophysics Data System (ADS)
Sassen, D. S.; Everett, M. E.
2007-05-01
There is a need for computationally fast GPR numerical modeling. This includes circumstances where real time performance is needed, for example discrimination of landmines or UXO's, and in circumstances that require a high number of successive forward problems, for example inversion or imaging. Traditional numerical techniques such as finite difference or finite element are too slow for these applications, but they provide results from general scenarios such as scattering from very complicated shapes with high contrast. Neural networks may fit in the niche between analytical techniques and traditional numerical techniques. Our concept is training a neural network to associate the model inputs of electromagnetic properties of the background and targets, and the size and shape of the targets, with the output generated by a 3-D finite difference model. Successive examples from various electromagnetic properties and targets are displayed to the neural network, until the neural network has adapted itself though optimization. The trained neural network is now used as the forward model by displaying new input parameters and the neural network then generates the appropriate output. The results from the neural network are then compared to results from finite difference models to see how well the neural networks is performing and at what point it breaks down. Areas of poor fit can be addressed through further training. The neural network GPR model can be adapted by displaying additional finite difference results to the neural network, and can also be adapted to a specific field area by actual field data examples. Because of this adaptation ability the neural network GPR model can be optimized for specific environments and applications.
Numerical modeling of bubble dynamics in viscoelastic media with relaxation.
Warnez, M T; Johnsen, E
2015-06-01
Cavitation occurs in a variety of non-Newtonian fluids and viscoelastic materials. The large-amplitude volumetric oscillations of cavitation bubbles give rise to high temperatures and pressures at collapse, as well as induce large and rapid deformation of the surroundings. In this work, we develop a comprehensive numerical framework for spherical bubble dynamics in isotropic media obeying a wide range of viscoelastic constitutive relationships. Our numerical approach solves the compressible Keller-Miksis equation with full thermal effects (inside and outside the bubble) when coupled to a highly generalized constitutive relationship (which allows Newtonian, Kelvin-Voigt, Zener, linear Maxwell, upper-convected Maxwell, Jeffreys, Oldroyd-B, Giesekus, and Phan-Thien-Tanner models). For the latter two models, partial differential equations (PDEs) must be solved in the surrounding medium; for the remaining models, we show that the PDEs can be reduced to ordinary differential equations. To solve the general constitutive PDEs, we present a Chebyshev spectral collocation method, which is robust even for violent collapse. Combining this numerical approach with theoretical analysis, we simulate bubble dynamics in various viscoelastic media to determine the impact of relaxation time, a constitutive parameter, on the associated physics. Relaxation time is found to increase bubble growth and permit rebounds driven purely by residual stresses in the surroundings. Different regimes of oscillations occur depending on the relaxation time.
Numerical Modeling of Inclusion Behavior in Liquid Metal Processing
NASA Astrophysics Data System (ADS)
Bellot, Jean-Pierre; Descotes, Vincent; Jardy, Alain
2013-09-01
Thermomechanical performance of metallic alloys is directly related to the metal cleanliness that has always been a challenge for metallurgists. During liquid metal processing, particles can grow or decrease in size either by mass transfer with the liquid phase or by agglomeration/fragmentation mechanisms. As a function of numerical density of inclusions and of the hydrodynamics of the reactor, different numerical modeling approaches are proposed; in the case of an isolated particle, the Lagrangian technique coupled with a dissolution model is applied, whereas in the opposite case of large inclusion phase concentration, the population balance equation must be solved. Three examples of numerical modeling studies achieved at Institut Jean Lamour are discussed. They illustrate the application of the Lagrangian technique (for isolated exogenous inclusion in titanium bath) and the Eulerian technique without or with the aggregation process: for precipitation and growing of inclusions at the solidification front of a Maraging steel, and for endogenous inclusions in the molten steel bath of a gas-stirred ladle, respectively.
Optimization methods and silicon solar cell numerical models
NASA Technical Reports Server (NTRS)
Girardini, K.; Jacobsen, S. E.
1986-01-01
An optimization algorithm for use with numerical silicon solar cell models was developed. By coupling an optimization algorithm with a solar cell model, it is possible to simultaneously vary design variables such as impurity concentrations, front junction depth, back junction depth, and cell thickness to maximize the predicted cell efficiency. An optimization algorithm was developed and interfaced with the Solar Cell Analysis Program in 1 Dimension (SCAP1D). SCAP1D uses finite difference methods to solve the differential equations which, along with several relations from the physics of semiconductors, describe mathematically the performance of a solar cell. A major obstacle is that the numerical methods used in SCAP1D require a significant amount of computer time, and during an optimization the model is called iteratively until the design variables converge to the values associated with the maximum efficiency. This problem was alleviated by designing an optimization code specifically for use with numerically intensive simulations, to reduce the number of times the efficiency has to be calculated to achieve convergence to the optimal solution.
Numerical modeling of bubble dynamics in viscoelastic media with relaxation
Warnez, M. T.; Johnsen, E.
2015-01-01
Cavitation occurs in a variety of non-Newtonian fluids and viscoelastic materials. The large-amplitude volumetric oscillations of cavitation bubbles give rise to high temperatures and pressures at collapse, as well as induce large and rapid deformation of the surroundings. In this work, we develop a comprehensive numerical framework for spherical bubble dynamics in isotropic media obeying a wide range of viscoelastic constitutive relationships. Our numerical approach solves the compressible Keller–Miksis equation with full thermal effects (inside and outside the bubble) when coupled to a highly generalized constitutive relationship (which allows Newtonian, Kelvin–Voigt, Zener, linear Maxwell, upper-convected Maxwell, Jeffreys, Oldroyd-B, Giesekus, and Phan-Thien-Tanner models). For the latter two models, partial differential equations (PDEs) must be solved in the surrounding medium; for the remaining models, we show that the PDEs can be reduced to ordinary differential equations. To solve the general constitutive PDEs, we present a Chebyshev spectral collocation method, which is robust even for violent collapse. Combining this numerical approach with theoretical analysis, we simulate bubble dynamics in various viscoelastic media to determine the impact of relaxation time, a constitutive parameter, on the associated physics. Relaxation time is found to increase bubble growth and permit rebounds driven purely by residual stresses in the surroundings. Different regimes of oscillations occur depending on the relaxation time. PMID:26130967
Numerical solution of High-kappa model of superconductivity
Karamikhova, R.
1996-12-31
We present formulation and finite element approximations of High-kappa model of superconductivity which is valid in the high {kappa}, high magnetic field setting and accounts for applied magnetic field and current. Major part of this work deals with steady-state and dynamic computational experiments which illustrate our theoretical results numerically. In our experiments we use Galerkin discretization in space along with Backward-Euler and Crank-Nicolson schemes in time. We show that for moderate values of {kappa}, steady states of the model system, computed using the High-kappa model, are virtually identical with results computed using the full Ginzburg-Landau (G-L) equations. We illustrate numerically optimal rates of convergence in space and time for the L{sup 2} and H{sup 1} norms of the error in the High-kappa solution. Finally, our numerical approximations demonstrate some well-known experimentally observed properties of high-temperature superconductors, such as appearance of vortices, effects of increasing the applied magnetic field and the sample size, and the effect of applied constant current.
Numerical modeling of bubble dynamics in viscoelastic media with relaxation
NASA Astrophysics Data System (ADS)
Warnez, M. T.; Johnsen, E.
2015-06-01
Cavitation occurs in a variety of non-Newtonian fluids and viscoelastic materials. The large-amplitude volumetric oscillations of cavitation bubbles give rise to high temperatures and pressures at collapse, as well as induce large and rapid deformation of the surroundings. In this work, we develop a comprehensive numerical framework for spherical bubble dynamics in isotropic media obeying a wide range of viscoelastic constitutive relationships. Our numerical approach solves the compressible Keller-Miksis equation with full thermal effects (inside and outside the bubble) when coupled to a highly generalized constitutive relationship (which allows Newtonian, Kelvin-Voigt, Zener, linear Maxwell, upper-convected Maxwell, Jeffreys, Oldroyd-B, Giesekus, and Phan-Thien-Tanner models). For the latter two models, partial differential equations (PDEs) must be solved in the surrounding medium; for the remaining models, we show that the PDEs can be reduced to ordinary differential equations. To solve the general constitutive PDEs, we present a Chebyshev spectral collocation method, which is robust even for violent collapse. Combining this numerical approach with theoretical analysis, we simulate bubble dynamics in various viscoelastic media to determine the impact of relaxation time, a constitutive parameter, on the associated physics. Relaxation time is found to increase bubble growth and permit rebounds driven purely by residual stresses in the surroundings. Different regimes of oscillations occur depending on the relaxation time.
ASSIMILATION OF DOPPLER RADAR DATA INTO NUMERICAL WEATHER MODELS
Chiswell, S.; Buckley, R.
2009-01-15
During the year 2008, the United States National Weather Service (NWS) completed an eight fold increase in sampling capability for weather radars to 250 m resolution. This increase is expected to improve warning lead times by detecting small scale features sooner with increased reliability; however, current NWS operational model domains utilize grid spacing an order of magnitude larger than the radar data resolution, and therefore the added resolution of radar data is not fully exploited. The assimilation of radar reflectivity and velocity data into high resolution numerical weather model forecasts where grid spacing is comparable to the radar data resolution was investigated under a Laboratory Directed Research and Development (LDRD) 'quick hit' grant to determine the impact of improved data resolution on model predictions with specific initial proof of concept application to daily Savannah River Site operations and emergency response. Development of software to process NWS radar reflectivity and radial velocity data was undertaken for assimilation of observations into numerical models. Data values within the radar data volume undergo automated quality control (QC) analysis routines developed in support of this project to eliminate empty/missing data points, decrease anomalous propagation values, and determine error thresholds by utilizing the calculated variances among data values. The Weather Research and Forecasting model (WRF) three dimensional variational data assimilation package (WRF-3DVAR) was used to incorporate the QC'ed radar data into input and boundary conditions. The lack of observational data in the vicinity of SRS available to NWS operational models signifies an important data void where radar observations can provide significant input. These observations greatly enhance the knowledge of storm structures and the environmental conditions which influence their development. As the increase in computational power and availability has made higher
The CMEE Library for Numerical Modeling of Electron Effects
NASA Astrophysics Data System (ADS)
Stoltz, Peter; Cohen, Ron; Molvik, Art; Furman, Miguel; Vay, Jean-Luc; Adelmann, Andreas
2003-10-01
The CMEE (Computational Modules for Electron Effects) library is a collection of computer routines for numerical modeling of electron effects in accelerator and plasma physics codes. The goal of this library is to make these numerical models available to any code in need of electron effects modeling, including high-power microwave codes, fusion wall interaction codes, laser-plasma codes, proton accelerator codes, and HIF codes. CMEE includes routines to model secondary electrons, neutral gas desorption and ionization. The secondary electron routines are based on routines from the POSINST code. The neutral gas desorption routines are based on a thermal binding model similar to the model in ,e.g., the LSP code. The ionization routines are based on the IONPACK library from Tech-X. This poster discusses the latest state of these routines, specifically implementation in the WARP code and comparisons to data from the High Current Experiment (HCX). In particular, recent comparisons between the CMEE routines and neutral gas desorption measurements from HCX are presented.
Numerical modelling of the memory effect in wet scrubbers.
Löthgren, Carl-Johan; Andersson, Sven
2008-08-01
Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) can be absorbed in and desorbed from polypropylene (PP) tower packings in wet scrubbers utilized in waste incineration lines. This behaviour, also known as the memory effect, has been modelled using a gas phase-PP surface equilibrium and a numerical solid phase diffusion model describing the transport of PCDD/Fs inside the PP. The diffusivities and gas-PP partition coefficients of TCDD/F to HxCDD/Fs in PP have been estimated using the numerical model. Two incineration lines were modelled. In the first line, the absorption and desorption in PP test rods was followed before and after installation of a fabric filter that was placed before a wet scrubber. In the second incineration line, the accumulation of PCDD/Fs in a wet scrubber during start up periods and the subsequent decline during the following three months was modelled and compared to continuous two-week gas measurements after the scrubber. The obtained diffusivities in PP range from 10(-13) m(2)/s for TCDD to 10(-16) m(2)/s for HxCDD. Lower chlorinated homologues with a distinctive change in concentrations during the desorption period (e.g. TCDF) are easier to model, and show the best agreement between the two incineration lines.
Mathematical and Numerical Analyses of Peridynamics for Multiscale Materials Modeling
Du, Qiang
2014-11-12
The rational design of materials, the development of accurate and efficient material simulation algorithms, and the determination of the response of materials to environments and loads occurring in practice all require an understanding of mechanics at disparate spatial and temporal scales. The project addresses mathematical and numerical analyses for material problems for which relevant scales range from those usually treated by molecular dynamics all the way up to those most often treated by classical elasticity. The prevalent approach towards developing a multiscale material model couples two or more well known models, e.g., molecular dynamics and classical elasticity, each of which is useful at a different scale, creating a multiscale multi-model. However, the challenges behind such a coupling are formidable and largely arise because the atomistic and continuum models employ nonlocal and local models of force, respectively. The project focuses on a multiscale analysis of the peridynamics materials model. Peridynamics can be used as a transition between molecular dynamics and classical elasticity so that the difficulties encountered when directly coupling those two models are mitigated. In addition, in some situations, peridynamics can be used all by itself as a material model that accurately and efficiently captures the behavior of materials over a wide range of spatial and temporal scales. Peridynamics is well suited to these purposes because it employs a nonlocal model of force, analogous to that of molecular dynamics; furthermore, at sufficiently large length scales and assuming smooth deformation, peridynamics can be approximated by classical elasticity. The project will extend the emerging mathematical and numerical analysis of peridynamics. One goal is to develop a peridynamics-enabled multiscale multi-model that potentially provides a new and more extensive mathematical basis for coupling classical elasticity and molecular dynamics, thus enabling next
A preliminary numerical model of the Geminid meteoroid stream
NASA Astrophysics Data System (ADS)
Ryabova, G. O.
2016-02-01
A pilot numerical model of the Geminid meteoroid stream is presented. This model implies cometary origin of the stream. Ejection of relatively small amount of particles (90 000 test meteoroids with masses 0.02, 0.003 and 0.0003 g) from the asteroid (3200) Phaethon (the parent body) was simulated, and their evolution was followed till the present time. The particles close to the Earth orbit were considered as the `shower'. It was found that the width of the model shower is at least twice less comparatively the real shower. The maximum activity of the model shower is dislocated and occurs about one day late. The most probable reason for both discrepancies is the drastic transformation of the parent body orbit during rapid release of the volatiles in the process of the stream initial formation. The dispersion of the model stream was evaluated in terms of the Southworth-Hawkins D-criterion.
Numerical treatment of a geometrically nonlinear planar Cosserat shell model
NASA Astrophysics Data System (ADS)
Sander, Oliver; Neff, Patrizio; Bîrsan, Mircea
2016-05-01
We present a new way to discretize a geometrically nonlinear elastic planar Cosserat shell. The kinematical model is similar to the general six-parameter resultant shell model with drilling rotations. The discretization uses geodesic finite elements (GFEs), which leads to an objective discrete model which naturally allows arbitrarily large rotations. GFEs of any approximation order can be constructed. The resulting algebraic problem is a minimization problem posed on a nonlinear finite-dimensional Riemannian manifold. We solve this problem using a Riemannian trust-region method, which is a generalization of Newton's method that converges globally without intermediate loading steps. We present the continuous model and the discretization, discuss the properties of the discrete model, and show several numerical examples, including wrinkling of thin elastic sheets in shear.
Numerical modeling of anisotropic fiber bundle behavior in oxygenators.
Bhavsar, Sonya S; Schmitz-Rode, Thomas; Steinseifer, Ulrich
2011-11-01
Prediction of flow patterns through oxygenator fiber bundles can allow shape optimization so that efficient gas exchange occurs with minimal thrombus formation and hemolysis. Computational fluid dynamics (CFD) simulations can be used to predict three-dimensional flow velocities and flow distribution from spatially dependent variables and they allow estimations of erythrocyte residence time within the fiber bundle. This study builds upon previous work to develop an accurate numerical model for oxygenators, which would allow for accelerated iterations in oxygenator shape and diffuser plate design optimization. Hollow fiber flow channels were developed to permit experimental calculation of fluid permeability in two directions: main flow along the hollow fiber and perpendicular to the hollow fibers. Commercial software was used to develop three-dimensional CFD models of the experimental flow channels and an anisotropic porous media model for oxygenators from these experimental results. The oxygenator model was used to predict pressure loss throughout the device, visualize blood distribution within the fiber bundle, and estimate erythrocyte residence time within the bundle. Experimental flow channels measurements produced a streamwise permeability of 1.143e(-8) m(2) and transverse permeability of 2.385e(-9) m(2) . These permeabilities, coupled with previous work with volume porosity, were used to develop the numerical model of anisotropic behavior through porous fiber bundles, which indicated a more uniform flow field throughout the oxygenator. Incorporation of known anisotropic fiber bundle behavior in previous numerical models more accurately represents fluid behavior through an oxygenator fiber bundle. CFD coupled with experimental validation can produce a powerful tool for oxygenator design and development.
Dynamical modeling of elliptical galaxies. II. numerical prolate models
Lake, G.
1981-01-01
The analytical solutions of Paper I are generalized using the self-consistent field method. These prolate models are constructed using only two integrals of motion, the energy (E) and the angular momentum about the axis of symmetry, (L/sub z/). They are the first models with flattening greater than E4 which possess elliptical isophotes and realistic density profiles. The singularity in the surface brightness which characterized the models of Paper I has been removed by smoothing the extreme suppression of L/sub z/. The new models (like those of Paper I) still show a sharp rise in the velocity dispersion at the center. This feature is due to the strongly anisotropic velocity dispersions, rather than the existence of a supermassive object.
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.
Numerical Schemes for a Model for Nonlinear Dispersive Waves.
1983-11-01
2604 November 1983 ABSTRACT A description is given of a number of numerical schemes to solve an evolution equation Athat arises when modelling the...travel at constant speed and whose shape is independent of time. One of the models, the Korteweg -de Vries equation , has been studied extensively, both...inital-value problem for the Korteweg -de Vries equation y~~~-2u 0(I) ut + ux + Buu x +fYu inO, Department of Mathematics, University of Chicago, Chicago
Numerical simulation model for vertical flow in geothermal wells
Tachimori, M.
1982-01-01
A numerical simulation model for vertical flow in geothermal wells is presented. The model consists of equations for the conservation of mass, momentum, and energy, for thermodynamic state of water, for friction losses, for slip velocity relations, and of the criteria for various flow regimes. A new set of correlations and criteria is presented for two-phase flow to improve the accuracy of predictions; bubbly flow - Griffith and Wallis correlation, slug flow - Nicklin et al. one, annular-mist flow - Inoue and Aoki and modified by the author. The simulation method was verified by data from actual wells.
Thermoinertial bouncing of a relativistic collapsing sphere: A numerical model
Herrera, L.; Di Prisco, A.; Barreto, W.
2006-01-15
We present a numerical model of a collapsing radiating sphere, whose boundary surface undergoes bouncing due to a decreasing of its inertial mass density (and, as expected from the equivalence principle, also of the 'gravitational' force term) produced by the 'inertial' term of the transport equation. This model exhibits for the first time the consequences of such an effect, and shows that under physically reasonable conditions this decreasing of the gravitational term in the dynamic equation may be large enough as to revert the collapse and produce a bouncing of the boundary surface of the sphere.
Numerical modeling of a cryogenic fluid within a fuel tank
NASA Technical Reports Server (NTRS)
Greer, Donald S.
1994-01-01
The computational method developed to study the cryogenic fluid characteristics inside a fuel tank in a hypersonic aircraft is presented. The model simulates a rapid draining of the tank by modeling the ullage vapor and the cryogenic liquid with a moving interface. A mathematical transformation was developed and applied to the Navier-Stokes equations to account for the moving interface. The formulation of the numerical method is a transient hybrid explicit-implicit technique where the pressure term in the momentum equations is approximated to first order in time by combining the continuity equation with an ideal equation of state.
Standards and Guidelines for Numerical Models for Tsunami Hazard Mitigation
NASA Astrophysics Data System (ADS)
Titov, V.; Gonzalez, F.; Kanoglu, U.; Yalciner, A.; Synolakis, C. E.
2006-12-01
An increased number of nations around the workd need to develop tsunami mitigation plans which invariably involve inundation maps for warning guidance and evacuation planning. There is the risk that inundation maps may be produced with older or untested methodology, as there are currently no standards for modeling tools. In the aftermath of the 2004 megatsunami, some models were used to model inundation for Cascadia events with results much larger than sediment records and existing state-of-the-art studies suggest leading to confusion among emergency management. Incorrectly assessing tsunami impact is hazardous, as recent events in 2006 in Tonga, Kythira, Greece and Central Java have suggested (Synolakis and Bernard, 2006). To calculate tsunami currents, forces and runup on coastal structures, and inundation of coastlines one must calculate the evolution of the tsunami wave from the deep ocean to its target site, numerically. No matter what the numerical model, validation (the process of ensuring that the model solves the parent equations of motion accurately) and verification (the process of ensuring that the model used represents geophysical reality appropriately) both are an essential. Validation ensures that the model performs well in a wide range of circumstances and is accomplished through comparison with analytical solutions. Verification ensures that the computational code performs well over a range of geophysical problems. A few analytic solutions have been validated themselves with laboratory data. Even fewer existing numerical models have been both validated with the analytical solutions and verified with both laboratory measurements and field measurements, thus establishing a gold standard for numerical codes for inundation mapping. While there is in principle no absolute certainty that a numerical code that has performed well in all the benchmark tests will also produce correct inundation predictions with any given source motions, validated codes
Numerical Modeling of Propellant Boiloff in Cryogenic Storage Tank
NASA Technical Reports Server (NTRS)
Majumdar, A. K.; Steadman, T. E.; Maroney, J. L.
2007-01-01
This Technical Memorandum (TM) describes the thermal modeling effort undertaken at Marshall Space Flight Center to support the Cryogenic Test Laboratory at Kennedy Space Center (KSC) for a study of insulation materials for cryogenic tanks in order to reduce propellant boiloff during long-term storage. The Generalized Fluid System Simulation program has been used to model boiloff in 1,000-L demonstration tanks built for testing the thermal performance of glass bubbles and perlite insulation. Numerical predictions of boiloff rate and ullage temperature have been compared with the measured data from the testing of demonstration tanks. A satisfactory comparison between measured and predicted data has been observed for both liquid nitrogen and hydrogen tests. Based on the experience gained with the modeling of the demonstration tanks, a numerical model of the liquid hydrogen storage tank at launch complex 39 at KSC was built. The predicted boiloff rate of hydrogen has been found to be in good agreement with observed field data. This TM describes three different models that have been developed during this period of study (March 2005 to June 2006), comparisons with test data, and results of parametric studies.
Influence of clearance model on numerical simulation of centrifugal pump
NASA Astrophysics Data System (ADS)
Wang, Z.; Gao, B.; Yang, L.; Du, W. Q.
2016-05-01
Computing models are always simplified to save the computing resources and time. Particularly, the clearance that between impeller and pump casing is always ignored. But the completer model is, the more precise result of numerical simulation is in theory. This paper study the influence of clearance model on numerical simulation of centrifugal pump. We present such influence via comparing performance, flow characteristic and pressure pulsation of two cases that the one of two cases is the model pump with clearance and the other is not. And the results show that the head decreases and power increases so that efficiency decreases after computing with front and back cavities. Then no-leakage model would improve absolute velocity magnitude in order to reach the rated flow rate. Finally, more disturbance induced by front cavity flow and wear-ring flow would change the pressure pulsation of impeller and volute. The performance of clearance flow is important for the whole pump in performance, flow characteristic, pressure pulsation and other respects.
Benchmark problems for numerical implementations of phase field models
Jokisaari, A. M.; Voorhees, P. W.; Guyer, J. E.; Warren, J.; Heinonen, O. G.
2016-10-01
Here, we present the first set of benchmark problems for phase field models that are being developed by the Center for Hierarchical Materials Design (CHiMaD) and the National Institute of Standards and Technology (NIST). While many scientific research areas use a limited set of well-established software, the growing phase field community continues to develop a wide variety of codes and lacks benchmark problems to consistently evaluate the numerical performance of new implementations. Phase field modeling has become significantly more popular as computational power has increased and is now becoming mainstream, driving the need for benchmark problems to validate and verify new implementations. We follow the example set by the micromagnetics community to develop an evolving set of benchmark problems that test the usability, computational resources, numerical capabilities and physical scope of phase field simulation codes. In this paper, we propose two benchmark problems that cover the physics of solute diffusion and growth and coarsening of a second phase via a simple spinodal decomposition model and a more complex Ostwald ripening model. We demonstrate the utility of benchmark problems by comparing the results of simulations performed with two different adaptive time stepping techniques, and we discuss the needs of future benchmark problems. The development of benchmark problems will enable the results of quantitative phase field models to be confidently incorporated into integrated computational materials science and engineering (ICME), an important goal of the Materials Genome Initiative.
How to produce flat slabs: insights from numeric modeling
NASA Astrophysics Data System (ADS)
Constantin Manea, Vlad; Perez-Gussinye, Marta; Manea, Marina
2010-05-01
Flat slab subduction occurs at ~10% of the active convergent margins and it is assumed that subduction of oceanic aseismic ridges or seamount chains is the main mechanism to produce very low angle subduction slabs. However, recent numeric and analog modeling showed that ridges alone of moderate dimensions subducted perpendicular to the trench are not sufficient to produce flat-slab geometries. Therefore an alternative mechanism able to produce flat-slabs is required. In this paper we present dynamic numeric modeling results of subduction in the vicinity of thick continental lithosphere, as a craton for example. We tailored our modeling setup for the Chilean margins at ~31° and our models are integrated back in time 30 Myr. Modeling results show that a craton thickness of 200 km or more when approaching the trench is capable of blocking the asthenospheric flow in the mantle wedge and increasing considerably the suction force. We were able to produce a flat slab that fits well the flat slab geometry in Chile (based on seismicity) and stress distribution. We conclude that thick cratons located in the vicinity of subduction zones, are capable to produce very low angle slabs, and probable a combination of buoyant ridge subduction with a neighbor thick craton represent a better mechanism to produce flat slabs.
Constitutive Modeling and Numerical Simulation of Frp Confined Concrete Specimens
NASA Astrophysics Data System (ADS)
Smitha, Gopinath; Ramachandramurthy, Avadhanam; Nagesh, Ranganatha Iyer; Shahulhameed, Eduvammal Kunhimoideen
2014-09-01
Fiber-reinforced polymer (FRP) composites are generally used for the seismic retrofit of concrete members to enhance their strength and ductility. In the present work, the confining effect of Carbon Fiber-Reinforced Polymer (CFRP) composite layers has been investigated by numerical simulation. The numerical simulation has been carried out using nonlinear finite element analysis (FEA) to predict the response behaviour of CFRP-wrapped concrete cylinders. The nonlinear behaviour of concrete in compression and the linear elastic behaviour of CFRP has been modeled using an appropriate constitutive relationship. A cohesive model has been developed for modeling the interface between the concrete and CFRP. The interaction and damage failure criteria between the concrete to the cohesive element and the cohesive element to the CFRP has also been accounted for in the modeling. The response behaviour of the wrapped concrete specimen has been compared with the proposed interface model and with a perfectly bonded condition. The results obtained from the present study showed good agreement with the experimental load-displacement response and the failure pattern in the literature. Further, a sensitivity analysis has been carried out to study the effect of the number of layers of CFRP on the concrete specimens. It has been observed that wrapping with two layers was found to be the optimum, beyond which the response becomes flexible but with a higher load-carrying capacity
Benchmark problems for numerical implementations of phase field models
Jokisaari, A. M.; Voorhees, P. W.; Guyer, J. E.; ...
2016-10-01
Here, we present the first set of benchmark problems for phase field models that are being developed by the Center for Hierarchical Materials Design (CHiMaD) and the National Institute of Standards and Technology (NIST). While many scientific research areas use a limited set of well-established software, the growing phase field community continues to develop a wide variety of codes and lacks benchmark problems to consistently evaluate the numerical performance of new implementations. Phase field modeling has become significantly more popular as computational power has increased and is now becoming mainstream, driving the need for benchmark problems to validate and verifymore » new implementations. We follow the example set by the micromagnetics community to develop an evolving set of benchmark problems that test the usability, computational resources, numerical capabilities and physical scope of phase field simulation codes. In this paper, we propose two benchmark problems that cover the physics of solute diffusion and growth and coarsening of a second phase via a simple spinodal decomposition model and a more complex Ostwald ripening model. We demonstrate the utility of benchmark problems by comparing the results of simulations performed with two different adaptive time stepping techniques, and we discuss the needs of future benchmark problems. The development of benchmark problems will enable the results of quantitative phase field models to be confidently incorporated into integrated computational materials science and engineering (ICME), an important goal of the Materials Genome Initiative.« less
Numerical modelling of the 28 October 2011 Haida Gwaii tsunami
NASA Astrophysics Data System (ADS)
Fine, I.; Cherniawsky, J. Y.; Thomson, R.
2013-12-01
On October 28, 2012, a strong (Mw=7.7) earthquake occurred offshore of Moresby Island, Haida Gwaii (formerly the Queen Charlotte Islands). The earthquake generated a trans-Pacific tsunami observed from New Zealand to Alaska. We used an updated finite-fault model of the earthquake of Hayes (2013) to estimate the tsunami source. The location of this source was subsequently adjusted using tsunami waveforms recorded by bottom pressure recorders at NOAA DART stations and on the NEPTUNE Canada cabled observatory. The adjusted source was then used in a high-resolution model of tsunami wave propagation towards the bays and inlets of Moresby Island. According to the model, tsunami run-up in some bays would have been higher than 7 m. Subsequent post-surveys at several Moresby Island sites were undertaken in mid-November of 2012 and in June 2013, directed in part by the numerical model results. These surveys showed clear evidence of recent tsunami run-up of more than 8 m above the tide at specific coastal embayments, in good agreement with the numerical model results.
Antarctic glacial history from numerical models and continental margin sediments
Barker, P.F.; Barrett, P.J.; Cooper, A. K.; Huybrechts, P.
1999-01-01
The climate record of glacially transported sediments in prograded wedges around the Antarctic outer continental shelf, and their derivatives in continental rise drifts, may be combined to produce an Antarctic ice sheet history, using numerical models of ice sheet response to temperature and sea-level change. Examination of published models suggests several preliminary conclusions about ice sheet history. The ice sheet's present high sensitivity to sea-level change at short (orbital) periods was developed gradually as its size increased, replacing a declining sensitivity to temperature. Models suggest that the ice sheet grew abruptly to 40% (or possibly more) of its present size at the Eocene-Oligocene boundary, mainly as a result of its own temperature sensitivity. A large but more gradual middle Miocene change was externally driven, probably by development of the Antarctic Circumpolar Current (ACC) and Polar Front, provided that a few million years' delay can be explained. The Oligocene ice sheet varied considerably in size and areal extent, but the late Miocene ice sheet was more stable, though significantly warmer than today's. This difference probably relates to the confining effect of the Antarctic continental margin. Present-day numerical models of ice sheet development are sufficient to guide current sampling plans, but sea-ice formation, polar wander, basal topography and ice streaming can be identified as factors meriting additional modelling effort in the future.
A dynamic spar numerical model for passive shape change
NASA Astrophysics Data System (ADS)
Calogero, J. P.; Frecker, M. I.; Hasnain, Z.; Hubbard, J. E., Jr.
2016-10-01
A three-dimensional constraint-driven dynamic rigid-link numerical model of a flapping wing structure with compliant joints (CJs) called the dynamic spar numerical model is introduced and implemented. CJs are modeled as spherical joints with distributed mass and spring-dampers with coupled nonlinear spring and damping coefficients, which models compliant mechanisms spatially distributed in the structure while greatly reducing computation time compared to a finite element model. The constraints are established, followed by the formulation of a state model used in conjunction with a forward time integrator, an experiment to verify a rigid-link assumption and determine a flapping angle function, and finally several example runs. Modeling the CJs as coupled bi-linear springs shows the wing is able to flex more during upstroke than downstroke. Coupling the spring stiffnesses allows an angular deformation about one axis to induce an angular deformation about another axis, where the magnitude is proportional to the coupling term. Modeling both the leading edge and diagonal spars shows that the diagonal spar changes the kinematics of the leading edge spar verses only considering the leading edge spar, causing much larger axial rotations in the leading edge spar. The kinematics are very sensitive to CJ location, where moving the CJ toward the wing root causes a stronger response, and adding multiple CJs on the leading edge spar with a CJ on the diagonal spar allows the wing to deform with larger magnitude in all directions. This model lays a framework for a tool which can be used to understand flapping wing flight.
Starting laminar plumes: Comparison of laboratory and numerical modeling
NASA Astrophysics Data System (ADS)
Vatteville, Judith; van Keken, Peter E.; Limare, Angela; Davaille, Anne
2009-12-01
A detailed comparison of starting laminar plumes in viscous fluids is provided using the complementary approaches of laboratory modeling and numerical simulation. In the laboratory experiments the plumes are started in a nearly isoviscous silicone oil with heat supplied through a fixed circular source. The temperature field is measured by differential interferometry and thermochromic liquid crystals. The velocity field is determined by particle image velocimetry. Numerical simulations of the laboratory experiments are performed using a finite element method that employs the measured properties of the physical oil and the heating history. No further adjustments are made to match the laboratory results. For fluids at two different viscosities and for variable power supplied to the plume there is excellent agreement in the temporal evolution and fine spatial detail of the plume. Minor differences remain, particulary in the transient stage of the plume in the low-viscosity fluid, but the differences are within the experimental uncertainties. In contrast, the assumption of constant viscosity in the numerical models leads to differences that are larger than the experimental uncertainties, demonstrating that these near-isoviscous fluids should not be considered to have constant viscosity.
Global Numerical Modeling of the Muon Collider Target
NASA Astrophysics Data System (ADS)
Roman, Samulyak; Glimm, James
2000-11-01
The problem of free surface instabilities is the major concern in the study of the Muon Collider target. The target is in the form of a mercury jet interacting with high energy proton beams in the presence of a strong magnetic field. Strong pressure waves caused by the target - proton beam interaction lead to strong disturbances of the jet surface and to the jet breakup into droplets. The global numerical simulation of the Muon Collider target was done by using FronTier, a compressible fluid dynamics code. FronTier is capable to work with free surfaces and, in particular, to model the propagation of free jets. The code is based on the method of front tracking, a numerical technique for solving systems of conservation laws in which the evolution of discontinuities is determined through the solution of the associated Riemann problem. To model the behavior of the real material (mercury) under the influence of proton beams a SESAME type tabulated equation of state for mercury was created in a wide temperature - density domain which includes the fluid state of mercury, the vapor state and the state above the critical point. The numerical simulation of the target evolution driven by strong pressure waves is important for the optimal target design.
A simplified model for TIG-dressing numerical simulation
NASA Astrophysics Data System (ADS)
Ferro, P.; Berto, F.; James, M. N.
2017-04-01
Irrespective of the mechanical properties of the alloy to be welded, the fatigue strength of welded joints is primarily controlled by the stress concentration associated with the weld toe or weld root. In order to reduce the effects of such notch defects in welds, which are influenced by tensile properties of the alloy, post-weld improvement techniques have been developed. The two most commonly used techniques are weld toe grinding and TIG dressing, which are intended to both remove toe defects such as non-metallic intrusions and to re-profile the weld toe region to give a lower stress concentration. In the case of TIG dressing the weld toe is re-melted to provide a smoother transition between the plate and the weld crown and to beneficially modify the residual stress redistribution. Assessing the changes to weld stress state arising from TIG-dressing is most easily accomplished through a complex numerical simulation that requires coupled thermo-fluid dynamics and solid mechanics. However, this can be expensive in terms of computational cost and time needed to reach a solution. The present paper therefore proposes a simplified numerical model that overcomes such drawbacks and which simulates the remelted toe region by means of the activation and deactivation of elements in the numerical model.
On Numerical Considerations for Modeling Reactive Astrophysical Shocks
Papatheodore, Thomas L; Messer, Bronson
2014-01-01
Simulating detonations in astrophysical environments is often complicated by numerical approximations to shock structure. A common prescription to ensure correct detonation speeds (and associated quantities) is to prohibit burning inside the numerically broadened shock (Fryxell et al. 1989). We have performed a series of simulations to verify the efficacy of this approximation and to understand how resolution and dimensionality might affect its use. Our results show that, in one dimension, prohibiting burning in the shock is important wherever the carbon burning length is not resolved, in keeping with the results of Fryxell et al. (1989). In two dimensions, we find that the prohibition of shock burning effectively inhibits the development of cellular structure for all but the most highly-resolved cases. We discuss the possible impacts this outcome may have on sub-grid models and detonation propagation in Type Ia supernovae.
Numerical modelling of multimode fibre-optic communication lines
Sidelnikov, O S; Fedoruk, M P; Sygletos, S; Ferreira, F
2016-01-31
The results of numerical modelling of nonlinear propagation of an optical signal in multimode fibres with a small differential group delay are presented. It is found that the dependence of the error vector magnitude (EVM) on the differential group delay can be reduced by increasing the number of ADC samples per symbol in the numerical implementation of the differential group delay compensation algorithm in the receiver. The possibility of using multimode fibres with a small differential group delay for data transmission in modern digital communication systems is demonstrated. It is shown that with increasing number of modes the strong coupling regime provides a lower EVM level than the weak coupling one. (fibre-optic communication lines)
Numerical Modeling of Electroacoustic Logging Including Joule Heating
NASA Astrophysics Data System (ADS)
Plyushchenkov, Boris D.; Nikitin, Anatoly A.; Turchaninov, Victor I.
It is well known that electromagnetic field excites acoustic wave in a porous elastic medium saturated with fluid electrolyte due to electrokinetic conversion effect. Pride's equations describing this process are written in isothermal approximation. Update of these equations, which allows to take influence of Joule heating on acoustic waves propagation into account, is proposed here. This update includes terms describing the initiation of additional acoustic waves excited by thermoelastic stresses and the heat conduction equation with right side defined by Joule heating. Results of numerical modeling of several problems of propagation of acoustic waves excited by an electric field source with and without consideration of Joule heating effect in their statements are presented. From these results, it follows that influence of Joule heating should be taken into account at the numerical simulation of electroacoustic logging and at the interpretation of its log data.
Newest insights from MHD numerical modeling of Pulsar Wind Nebulae
NASA Astrophysics Data System (ADS)
Olmi, B.; Del Zanna, L.; Amato, E.; Bucciantini, N.; Bandiera, R.
2016-06-01
Numerical MHD models are considered very successful in accounting for many of the observed properties of Pulsar Wind Nebulae (PWNe), especially those concerning the high energy emission morphology and the inner nebula dynamics. Although PWNe are known to be among the most powerful accelerators in nature, producing particles up to PeV energies, the mechanisms responsible of such an efficient acceleration are still a deep mystery. Indeed, these processes take place in one of the most hostile environment for particle acceleration: the relativistic and highly magnetized termination shock of the pulsar wind. The newest results from numerical simulations of the Crab Nebula, the PWN prototype, will be presented, with special attention to the problem of particle acceleration. In particular it will be shown how a multi-wavelengths analysis of the wisps properties can be used to constrain the particle acceleration mechanisms working at the Crab's termination shock, by identifying the particle acceleration site at the shock front.
Numerical modeling of spray combustion with an advanced VOF method
NASA Technical Reports Server (NTRS)
Chen, Yen-Sen; Shang, Huan-Min; Shih, Ming-Hsin; Liaw, Paul
1995-01-01
This paper summarizes the technical development and validation of a multiphase computational fluid dynamics (CFD) numerical method using the volume-of-fluid (VOF) model and a Lagrangian tracking model which can be employed to analyze general multiphase flow problems with free surface mechanism. The gas-liquid interface mass, momentum and energy conservation relationships are modeled by continuum surface mechanisms. A new solution method is developed such that the present VOF model can be applied for all-speed flow regimes. The objectives of the present study are to develop and verify the fractional volume-of-fluid cell partitioning approach into a predictor-corrector algorithm and to demonstrate the effectiveness of the present approach by simulating benchmark problems including laminar impinging jets, shear coaxial jet atomization and shear coaxial spray combustion flows.
Numerical and experimental verification of physical blast thermodynamic model
NASA Astrophysics Data System (ADS)
Chorowski, Maciej; Iluk, Artur; Grabowski, Maciej; Jędrusyna, Artur
2015-12-01
Helium inventory in big cryogenic systems may be of the order of hundred tons. During the warm up of the machine the helium has to be stored in warm pressurized tanks. A potential rupture of the tank may create a danger to adjacent objects. In order to formulate recommendations concerning storage of compressed gases in close vicinity of nuclear installations, a thermodynamic model of physical blast has been formulated. The model has been experimentally verified in a laboratory scale test rig. To simulate rupture of compressed gas storage tanks, plastic tanks have been used. Scaling of the results to real cases like ITER compressed gas inventory requires good understanding of potential rupture of high volume gas storage tanks. Numerical model of tanks rupture have been elaborated and verified against experimental results. The model allows scaling of thermodynamic simplified description to real gas storage installations.
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.
Parallelism and optimization of numerical ocean forecasting model
NASA Astrophysics Data System (ADS)
Xu, Jianliang; Pang, Renbo; Teng, Junhua; Liang, Hongtao; Yang, Dandan
2016-10-01
According to the characteristics of Chinese marginal seas, the Marginal Sea Model of China (MSMC) has been developed independently in China. Because the model requires long simulation time, as a routine forecasting model, the parallelism of MSMC becomes necessary to be introduced to improve the performance of it. However, some methods used in MSMC, such as Successive Over Relaxation (SOR) algorithm, are not suitable for parallelism. In this paper, methods are developedto solve the parallel problem of the SOR algorithm following the steps as below. First, based on a 3D computing grid system, an automatic data partition method is implemented to dynamically divide the computing grid according to computing resources. Next, based on the characteristics of the numerical forecasting model, a parallel method is designed to solve the parallel problem of the SOR algorithm. Lastly, a communication optimization method is provided to avoid the cost of communication. In the communication optimization method, the non-blocking communication of Message Passing Interface (MPI) is used to implement the parallelism of MSMC with complex physical equations, and the process of communication is overlapped with the computations for improving the performance of parallel MSMC. The experiments show that the parallel MSMC runs 97.2 times faster than the serial MSMC, and root mean square error between the parallel MSMC and the serial MSMC is less than 0.01 for a 30-day simulation (172800 time steps), which meets the requirements of timeliness and accuracy for numerical ocean forecasting products.
Numerical model of solar dynamic radiator for parametric analysis
NASA Technical Reports Server (NTRS)
Rhatigan, Jennifer L.
1989-01-01
Growth power requirements for Space Station Freedom will be met through addition of 25 kW solar dynamic (SD) power modules. The SD module rejects waste heat from the power conversion cycle to space through a pumped-loop, multi-panel, deployable radiator. The baseline radiator configuration was defined during the Space Station conceptual design phase and is a function of the state point and heat rejection requirements of the power conversion unit. Requirements determined by the overall station design such as mass, system redundancy, micrometeoroid and space debris impact survivability, launch packaging, costs, and thermal and structural interaction with other station components have also been design drivers for the radiator configuration. Extensive thermal and power cycle modeling capabilities have been developed which are powerful tools in Station design and analysis, but which prove cumbersome and costly for simple component preliminary design studies. In order to aid in refining the SD radiator to the mature design stage, a simple and flexible numerical model was developed. The model simulates heat transfer and fluid flow performance of the radiator and calculates area mass and impact survivability for many combinations of flow tube and panel configurations, fluid and material properties, and environmental and cycle variations. A brief description and discussion of the numerical model, it's capabilities and limitations, and results of the parametric studies performed is presented.
Multiphase, multicomponent numerical model of bioventing with nonequilibrium mass exchange
Lang, J.R.; Rathfelder, K.M.; Abriola, L.M.
1995-12-31
A numerical model is presented that has been specifically designed to simulate the combined processes of soil vapor extraction and enhanced bioremediation known as bioventing. In this model, equations describing multiphase flow, multicomponent advective diffusive transport, and biodegradation are coupled. An entrapped organic residual, mobile gas and aqueous phases, and a reactive biophase are modeled. Components include n organic contaminants, oxygen, nitrogen, and water. Rate-limited mass exchange between the phases is simulated using linear driving force expressions. These expressions model volatilization and dissolution of the entrapped organic residual, rate-limited transport between the gas and aqueous phases, and rate-limited transport to the biophase. Monod-type kinetic expressions are employed to describe biophase utilization of substrates, the electron acceptor, and a limiting nutrient, as well as the growth of the microbial population. The coupled nonlinear governing equations are solved using a set iterative finite element method. Numerical simulations are presented for one-dimensional bench-scale column studies. These simulations illustrate the potential importance of biological degradation in the remediation of systems that are subject to mass transfer limitations.
A numerical investigation of a simplified human birth model
NASA Astrophysics Data System (ADS)
Pealatere, Roseanna; Baumer, Alexa; Fauci, Lisa; Leftwich, Megan C.
2015-11-01
This work uses simplified models and numerical computations to explore the effects of both the fetal velocity and the viscosity of the surrounding fluid on the forces associated with human birth. The numerical results are compared with the results of an experimental model representing the fetus moving through the birth canal using a rigid cylinder (fetus) that moves at a constant velocity through the center of a passive elastic tube (birth canal). The entire system is immersed in highly viscous fluid. Due to low Reynolds' number, the Stokes equations can be used to describe the relationship between velocity and forces in the system. The mathematical model uses the method of regularized Stokeslets to estimate the pulling force necessary to move the rigid inner cylinder at a constant velocity. The elastic tube through which the rigid cylinder passes is constructed by a discrete network of Hookean springs, with macroscopic elasticity matched to the tube used in the physical experiment. More complex geometries as well as peristaltic activation of the elastic tube can be added to the model to provide more insight into the relationship between force and velocity during human birth.
Numerical model for thermal parameters in optical materials
NASA Astrophysics Data System (ADS)
Sato, Yoichi; Taira, Takunori
2016-04-01
Thermal parameters of optical materials, such as thermal conductivity, thermal expansion, temperature coefficient of refractive index play a decisive role for the thermal design inside laser cavities. Therefore, numerical value of them with temperature dependence is quite important in order to develop the high intense laser oscillator in which optical materials generate excessive heat across mode volumes both of lasing output and optical pumping. We already proposed a novel model of thermal conductivity in various optical materials. Thermal conductivity is a product of isovolumic specific heat and thermal diffusivity, and independent modeling of these two figures should be required from the viewpoint of a clarification of physical meaning. Our numerical model for thermal conductivity requires one material parameter for specific heat and two parameters for thermal diffusivity in the calculation of each optical material. In this work we report thermal conductivities of various optical materials as Y3Al5O12 (YAG), YVO4 (YVO), GdVO4 (GVO), stoichiometric and congruent LiTaO3, synthetic quartz, YAG ceramics and Y2O3 ceramics. The dependence on Nd3+-doping in laser gain media in YAG, YVO and GVO is also studied. This dependence can be described by only additional three parameters. Temperature dependence of thermal expansion and temperature coefficient of refractive index for YAG, YVO, and GVO: these are also included in this work for convenience. We think our numerical model is quite useful for not only thermal analysis in laser cavities or optical waveguides but also the evaluation of physical properties in various transparent materials.
Improvement of a 2D numerical model of lava flows
NASA Astrophysics Data System (ADS)
Ishimine, Y.
2013-12-01
I propose an improved procedure that reduces an improper dependence of lava flow directions on the orientation of Digital Elevation Model (DEM) in two-dimensional simulations based on Ishihara et al. (in Lava Flows and Domes, Fink, JH eds., 1990). The numerical model for lava flow simulations proposed by Ishihara et al. (1990) is based on two-dimensional shallow water model combined with a constitutive equation for a Bingham fluid. It is simple but useful because it properly reproduces distributions of actual lava flows. Thus, it has been regarded as one of pioneer work of numerical simulations of lava flows and it is still now widely used in practical hazard prediction map for civil defense officials in Japan. However, the model include an improper dependence of lava flow directions on the orientation of DEM because the model separately assigns the condition for the lava flow to stop due to yield stress for each of two orthogonal axes of rectangular calculating grid based on DEM. This procedure brings a diamond-shaped distribution as shown in Fig. 1 when calculating a lava flow supplied from a point source on a virtual flat plane although the distribution should be circle-shaped. To improve the drawback, I proposed a modified procedure that uses the absolute value of yield stress derived from both components of two orthogonal directions of the slope steepness to assign the condition for lava flows to stop. This brings a better result as shown in Fig. 2. Fig. 1. (a) Contour plots calculated with the original model of Ishihara et al. (1990). (b) Contour plots calculated with a proposed model.
Numerical modeling of LCD electro-optical performance
NASA Astrophysics Data System (ADS)
Woehler, Henning; Becker, Michael E.
2002-06-01
Realization of complex high information density LCDs and systematic optimization of their electro-optical and ergonomic performance would not be possible in the required time-frame without reliable numerical modeling of the electro-optical performance of such display devices. In this paper we outline the history of numerical LDC modeling starting with Berreman and van Doorn, finally arriving at modern state-of-the-art LCD-modeling in two and three dimensions. Numerical modeling of LCDs is carried out in two steps: first, the effect of the electrical field on the orientation of the liquid crystalline alignment has to be evaluated before the corresponding optical properties can be computed. Starting from LC-elasticity theory we present suitable numerical methods for computing various states of LC-deformation (stable, metastable, bistable, etc.) in one- dimensional problems Light propagation in layered anisotropic absorbing media is evaluated with methods that are based on Maxwell's equations (Berreman 4 X 4-matrix approach). This approach can be simplified to yield methods with reduced computing time and sufficient accuracy for many problems (e.g. extended Jones 2 X 2-matrix formalism). A finite element method with automatic mesh generation and refinement for computing accurate solutions in two- dimensional problems is presented and its application illustrated with examples (e.g. IPS-effect, VAN-cells, etc.). In two- and three-dimensional problems, i.e. in cells with lateral dimensions comparable to the cell thickness, a variety of different director configurations are possible for a given geometry and electrical driving and addressing, making the modeling more complicated. Moreover, local defects can occur, which should also be considered in the simulation. Suitable approaches for the director field calculation, i.e. the vector and the tensor approach, are discussed. The complexity of the problem increases considerably when a third dimension is added, e.g. the
Numerical and Analytic Studies of Random-Walk Models.
NASA Astrophysics Data System (ADS)
Li, Bin
We begin by recapitulating the universality approach to problems associated with critical systems, and discussing the role that random-walk models play in the study of phase transitions and critical phenomena. As our first numerical simulation project, we perform high-precision Monte Carlo calculations for the exponents of the intersection probability of pairs and triplets of ordinary random walks in 2 dimensions, in order to test the conformal-invariance theory predictions. Our numerical results strongly support the theory. Our second numerical project aims to test the hyperscaling relation dnu = 2 Delta_4-gamma for self-avoiding walks in 2 and 3 dimensions. We apply the pivot method to generate pairs of self-avoiding walks, and then for each pair, using the Karp-Luby algorithm, perform an inner -loop Monte Carlo calculation of the number of different translates of one walk that makes at least one intersection with the other. Applying a least-squares fit to estimate the exponents, we have obtained strong numerical evidence that the hyperscaling relation is true in 3 dimensions. Our great amount of data for walks of unprecedented length(up to 80000 steps), yield a updated value for the end-to-end distance and radius of gyration exponent nu = 0.588 +/- 0.001 (95% confidence limit), which comes out in good agreement with the renormalization -group prediction. In an analytic study of random-walk models, we introduce multi-colored random-walk models and generalize the Symanzik and B.F.S. random-walk representations to the multi-colored case. We prove that the zero-component lambdavarphi^2psi^2 theory can be represented by a two-color mutually -repelling random-walk model, and it becomes the mutually -avoiding walk model in the limit lambda to infty. However, our main concern and major break-through lies in the study of the two-point correlation function for the lambda varphi^2psi^2 theory with N > 0 components. By representing it as a two-color random-walk expansion
Numerical modeling of laser isochoric heating of hot dense matter
NASA Astrophysics Data System (ADS)
Sentoku, Yasuhiko
2005-10-01
Ultra-intense short-pulse lasers are important tools for creating short-lived high energy plasmas, however to date, it has not been possible to create several hundred eV solid density matter because of the rapid transport of the laser-generated hot electrons throughout the target volume. We proposed a new way to isochorically heat matter at solid density to extreme temperatures by magnetic confinement of laser- generated hot electrons for several picoseconds by application of a multi-MG external field. In advance of an experiment at the Nevada Terawatt Facility (NTF), using a 100 TW- class laser, which will be synchronized to a 1MA Z-pinch machine, we have performed theoretical studies using a collisional particle-in-cell codes PICLS, which is optimized for a study of isochoric heating of solid density plasmas. One of the critical issues of the PIC simulation of the the laser isochoric heating is significant numerical heating, which makes difficult to simulate 100 eV solid density plasmas over picoseconds by PIC. In this talk, we introduce a couple of numerical techniques to extend the grid size with suppressing the numerical heating and also the full relativistic collision model to simulate the isochoric heating by ultra-intense lasers. This work was supported by DOE/NNSA-UNR grant DE-FC52-01NV14050.
Numerical Analysis of Electromagnetic Fields in Multiscale Model
NASA Astrophysics Data System (ADS)
Ma, Ji; Fang, Guang-You; Ji, Yi-Cai
2015-04-01
Modeling technique for electromagnetic fields excited by antennas is an important topic in computational electromagnetics, which is concerned with the numerical solution of Maxwell's equations. In this paper, a novel hybrid technique that combines method of moments (MoM) with finite-difference time-domain (FDTD) method is presented to handle the problem. This approach employed Huygen's principle to realize the hybridization of the two classical numerical algorithms. For wideband electromagnetic data, the interpolation scheme is used in the MoM based on the dyadic Green's function. On the other hand, with the help of equivalence principle, the scattered electric and magnetic fields on the Huygen's surface calculated by MoM are taken as the sources for FDTD. Therefore, the electromagnetic fields in the environment can be obtained by employing finite-difference time-domain method. Finally, numerical results show the validity of the proposed technique by analyzing two canonical samples. Supported in part by China Postdoctoral Science Foundation under Grant No. 201M550839, and in part by the Key Research Program of the Chinese Academy of Sciences under Grant No. KGZD-EW-603
Numerical modelling and image reconstruction in diffuse optical tomography
Dehghani, Hamid; Srinivasan, Subhadra; Pogue, Brian W.; Gibson, Adam
2009-01-01
The development of diffuse optical tomography as a functional imaging modality has relied largely on the use of model-based image reconstruction. The recovery of optical parameters from boundary measurements of light propagation within tissue is inherently a difficult one, because the problem is nonlinear, ill-posed and ill-conditioned. Additionally, although the measured near-infrared signals of light transmission through tissue provide high imaging contrast, the reconstructed images suffer from poor spatial resolution due to the diffuse propagation of light in biological tissue. The application of model-based image reconstruction is reviewed in this paper, together with a numerical modelling approach to light propagation in tissue as well as generalized image reconstruction using boundary data. A comprehensive review and details of the basis for using spatial and structural prior information are also discussed, whereby the use of spectral and dual-modality systems can improve contrast and spatial resolution. PMID:19581256
Numerical modeling of shear band formation in PBX-9501
Dey, T.N.; Kamm, J.R.
1998-12-31
Adiabatic shear bands in explosives may be a source of ignition and lead to detonation. Three possible mechanisms leading to shear banding are (1) thermal softening, (2) mechanical softening due to microcracking, and (3) quasi-granular constitutive response. The latter two mechanisms can lead to shear band formation in PBXs at nominal strains much smaller than those required for the thermal softening mechanism. The authors study formation of shear bands with models including the latter two mechanisms under unconfined compression. Statistical variation of numerical results is similar to that observed in some experiments. However, the commonly used methods of calibrating constitutive models can be misleading because of effects due to shear band formation. One model currently being used for studies of shear band formation and ignition in PBX 9501 was calibrated in this way and may need re-examination.
Numerical model for electrical explosion of copper wires in water
NASA Astrophysics Data System (ADS)
Chung, Kyoung-Jae; Lee, Kern; Hwang, Y. S.; Kim, Deok-Kyu
2016-11-01
This paper presents a simple but quite accurate numerical model for analyzing electrical explosion of copper wires in water. The numerical model solves a circuit equation coupled with one-dimensional magneto-hydrodynamic (MHD) equations with the help of appropriate wide-range equation of state (EOS) and electrical conductivity for copper. The MHD equations are formulated in a Lagrangian form to identify the interface between the wire and surrounding water clearly. A quotidian EOS (QEOS) that is known as the simplest form of EOS is utilized to build wide-range EOS for copper. In the QEOS, we consider the liquid-vapor phase transition, which is critical in analyzing the wire explosion system. For the electrical conductivity of copper, a semi-empirical set of equations covering from solid state to partially ionized plasma state are employed. Experimental validation has been performed with copper wires of various diameters, which are exploded by a microsecond timescale pulsed capacitive discharge. The simulation results show excellent agreements with the experimental results in terms of temporal motions of a plasma channel boundary and a shock front as well as current and voltage waveforms. It is found that the wire explodes (vaporizes) along the liquid branch of a binodal curve irrespective of wire dimension and operating voltage. After the explosion, the wire becomes a plasma state right away or after the current pause (dwell), depending on the operating conditions. It is worth noting that such a peculiar characteristic of wire explosion, i.e., current pause and restrike, is well simulated with the present numerical model. In particular, it is shown that the wire cools down along the vapor branch of the binodal curve during the current dwell, due to a significant difference of thermodynamic characteristics across the binodal curve. The influence of radiation for studying nonideal plasmas with a wire explosion technique and a physical process for shock wave formation
Aerospace laser sensing of cloudiness: numerical statistical modeling
NASA Astrophysics Data System (ADS)
Kargin, A. B.; Kargin, B. A.; Lavrov, M. V.
2013-08-01
In the numerical modeling of laser radiation transfer in optically dense cloudy media it is necessary to take into account multiple scattering effects, which alter the spatiotemporal structure of light pulses. The Monte Carlo method makes it possible to achieve the most complete account of these effects in the solution of direct problems of laser sensing of scattering media. This work considers two problems. The first is connected with construction of an adequate optical model of crystalline clouds which takes account their optical anisotropy. The second touches on questions of Monte Carlo modeling of laser radiation transfer in optically anisotropic media. A number of results of numerical experiments are presented which establish a quantitative connection between some cloud parameters and the magnitude and shape of the time convolution of a non-stationary laser return signal reflected by a single-layer continuous crystalline or liquid-droplet cloud and by two-level continuous cloudiness, when the crystalline cloud is located above the liquid-droplet cloud.
Numerical modeling of flexible insect wings using volume penalization
NASA Astrophysics Data System (ADS)
Engels, Thomas; Kolomenskiy, Dmitry; Schneider, Kai; Sesterhenn, Joern
2012-11-01
We consider the effects of chordwise flexibility on the aerodynamic performance of insect flapping wings. We developed a numerical method for modeling viscous fluid flows past moving deformable foils. It extends on the previously reported model for flows past moving rigid wings (J Comput Phys 228, 2009). The two-dimensional Navier-Stokes equations are solved using a Fourier pseudo-spectral method with the no-slip boundary conditions imposed by the volume penalization method. The deformable wing section is modeled using a non-linear beam equation. We performed numerical simulations of heaving flexible plates. The results showed that the optimal stroke frequency, which maximizes the mean thrust, is lower than the resonant frequency, in agreement with the experiments by Ramananarivo et al. (PNAS 108(15), 2011). The oscillatory part of the force only increases in amplitude when the frequency increases, and at the optimal frequency it is about 3 times larger than the mean force. We also study aerodynamic interactions between two heaving flexible foils. This flow configuration corresponds to the wings of dragonflies. We explore the effects of the phase difference and spacing between the fore- and hind-wing.
A Computational Model for the Numerical Simulation of FSW Processes
NASA Astrophysics Data System (ADS)
Agelet de Saracibar, C.; Chiumenti, M.; Santiago, D.; Cervera, M.; Dialami, N.; Lombera, G.
2010-06-01
In this paper a computational model for the numerical simulation of Friction Stir Welding (FSW) processes is presented. FSW is a new method of welding in solid state in which a shouldered tool with a profile probe is rotated and slowly plunged into the joint line between two pieces of sheet or plate material which are butted together. Once the probe has been completely inserted, it is moved with a small tilt angle in the welding direction. Here a quasi-static, thermal transient, mixed multiscale stabilized Eulerian formulation is used. Norton-Hoff and Sheppard-Wright rigid thermo-viscoplastic material models have been considered. A staggered solution algorithm is defined such that for any time step, the mechanical problem is solved at constant temperature and then the thermal problem is solved keeping constant the mechanical variables. A pressure multiscale stabilized mixed linear velocity/linear pressure finite element interpolation formulation is used to solve the mechanical problem and a convection multiscale stabilized linear temperature interpolation formulation is used to solve the thermal problem. The model has been implemented into the in-house developed FE code COMET. Results obtained in the simulation of FSW process are compared to other numerical results or experimental results, when available.
Collision and Break-off : Numerical models and surface observables
NASA Astrophysics Data System (ADS)
Bottrill, Andrew; van Hunen, Jeroen; Allen, Mark
2013-04-01
The process of continental collision and slab break-off has been explored by many authors using a number of different numerical models and approaches (Andrews and Billen, 2009; Gerya et al., 2004; van Hunen and Allen, 2011). One of the challenges of using numerical models to explore collision and break-off is relating model predictions to real observables from current collision zones. Part of the reason for this is that collision zones by their nature destroy a lot of potentially useful surface evidence of deep dynamics. One observable that offers the possibility for recording mantle dynamics at collision zones is topography. Here we present topography predictions from numerical models and show how these can be related to actual topography changes recoded in the sedimentary record. Both 2D and 3D numerical simulation of the closure of a small oceanic basin are presented (Bottrill et al., 2012; van Hunen and Allen, 2011). Topography is calculated from the normal stress at the surface applied to an elastic beam, to give a more realist prediction of topography by accounting for the expected elasticity of the lithosphere. Predicted model topography showed a number of interesting features on the overriding plate. The first is the formation of a basin post collision at around 300km from the suture. Our models also showed uplift postdating collision between the suture and this basin, caused by subduction of buoyant material. Once break-off has occurred we found that this uplift moved further into the overriding plate due to redistribution of stresses from the subducted plate. With our 3D numerical models we simulate a collision that propagates laterally along a subduction system. These models show that a basin forms, similar to that found in our 2D models, which propagates along the system at the same rate as collision. The apparent link between collision and basin formation leads to the investigation into the stress state in the overriding lithosphere. Preliminary
A numerical investigation of a simplified human birth model
NASA Astrophysics Data System (ADS)
Gossmann, Roseanna; Baumer, Alexa; Fauci, Lisa; Leftwich, Megan C.
2016-11-01
This work uses a simplified model to explore the forces experienced by the fetus during human birth. Numerical results are compared with the results of a physical model representing the fetus moving through the birth canal using a rigid cylinder (fetus) that moves at a constant velocity through the center of a passive elastic tube (birth canal). The entire system is immersed in a highly viscous fluid. Numerical simulations are run at low and zero Reynolds numbers. In each case, the pulling force necessary to move the rigid inner cylinder at a constant velocity through the tube is measured. The discrete elastic tube through which the rigid cylinder passes has macroscopic elasticity matched to the tube used in the physical experiment. The buckling behavior of the elastic tube is explored by varying velocity, length, and diameter of the rigid cylinder, and length of the elastic tube. More complex geometries as well as peristaltic activation of the elastic tube can be added to the model to provide more insight into the relationship between force and velocity during human birth.
An operational phenological model for numerical pollen prediction
NASA Astrophysics Data System (ADS)
Scheifinger, Helfried
2010-05-01
The general prevalence of seasonal allergic rhinitis is estimated to be about 15% in Europe, and still increasing. Pre-emptive measures require both the reliable assessment of production and release of various pollen species and the forecasting of their atmospheric dispersion. For this purpose numerical pollen prediction schemes are being developed by a number of European weather services in order to supplement and improve the qualitative pollen prediction systems by state of the art instruments. Pollen emission is spatially and temporally highly variable throughout the vegetation period and not directly observed, which precludes a straightforward application of dispersion models to simulate pollen transport. Even the beginning and end of flowering, which indicates the time period of potential pollen emission, is not (yet) available in real time. One way to create a proxy for the beginning, the course and the end of the pollen emission is its simulation as function of real time temperature observations. In this work the European phenological data set of the COST725 initiative forms the basis of modelling the beginning of flowering of 15 species, some of which emit allergic pollen. In order to keep the problem as simple as possible for the sake of spatial interpolation, a 3 parameter temperature sum model was implemented in a real time operational procedure, which calculates the spatial distribution of the entry dates for the current day and 24, 48 and 72 hours in advance. As stand alone phenological model and combined with back trajectories it is thought to support the qualitative pollen prediction scheme at the Austrian national weather service. Apart from that it is planned to incorporate it in a numerical pollen dispersion model. More details, open questions and first results of the operation phenological model will be discussed and presented.
Predictability and numerical modelling of the North Atlantic Oscillation
NASA Astrophysics Data System (ADS)
Bojariu, Roxana; Gimeno, Luis
2003-10-01
The North Atlantic Oscillation (NAO) is the dominant pattern of atmospheric circulation variability in the extratropical Northern Hemisphere and it is a major controlling factor in basic meteorological variables such as surface wind, temperature and precipitation which have large socioeconomic impacts on energy, agriculture, industry, traffic and human health throughout the whole of Europe and eastern North America. Because of this dominant impact on the weather and climate of the wealthiest areas of the planet, there is a growing interest in quantifying the possible limits of predictability of the phenomenon and the ability of the climate numerical models of simulating it. This paper reviews recent work on predictability and methods of numerical modelling of the North Atlantic Oscillation used to simulate the phenomenon. Atmospheric models with no orography or land-sea contrasts are able to capture the main feature of the NAO; however, to capture any interannual or interdecadal variability of the NAO, atmospheric general circulation models (AGCM) with seasonally varying sea surface temperature (SSTs) forcing are required. Still, no model reproduces the recent observed upward trend in the NAO index, suggesting that either the models are deficient or external forcing such as man-made effects are responsible for this feature. Predictive patterns have been identified in the Atlantic SSTs preceding specific phases of the NAO by up to 6 months, in the atmospheric temperatures anomalies in the previous November, in the Eurasian snow cover and in the sea-ice extent over Arctic. The use of simulations based on ensemble prediction to estimate potential predictability shows the possibility of capturing the upward trend of the NAO and suggests that multiannual to multidecadal variations in the NAO are more predictable than interannual fluctuations.
Analytical and numerical modeling of surface morphologies in thin films
Genin, F.Y.
1995-05-01
Experimental studies have show that strains due to thermal expansion mismatch between a film and its substrate can produce very large stresses in the film that can lead to the formation of holes and hillocks. Based on a phenomenological description of the evolution of a solid surface under both capillary and stress driving forces and for surface and grain boundary self-diffusion, this article provides analytical and numerical solutions for surface profiles of model geometries in polycrystalline thin films. Results can explain a variety of surface morphologies commonly observed experimentally and are discussed to give some practical insights on how to control the growth of holes and hillocks in thin films.
Thrombosis modeling in intracranial aneurysms: a lattice Boltzmann numerical algorithm
NASA Astrophysics Data System (ADS)
Ouared, R.; Chopard, B.; Stahl, B.; Rüfenacht, D. A.; Yilmaz, H.; Courbebaisse, G.
2008-07-01
The lattice Boltzmann numerical method is applied to model blood flow (plasma and platelets) and clotting in intracranial aneurysms at a mesoscopic level. The dynamics of blood clotting (thrombosis) is governed by mechanical variations of shear stress near wall that influence platelets-wall interactions. Thrombosis starts and grows below a shear rate threshold, and stops above it. Within this assumption, it is possible to account qualitatively well for partial, full or no occlusion of the aneurysm, and to explain why spontaneous thrombosis is more likely to occur in giant aneurysms than in small or medium sized aneurysms.
An explicit mixed numerical method for mesoscale model
NASA Technical Reports Server (NTRS)
Hsu, H.-M.
1981-01-01
A mixed numerical method has been developed for mesoscale models. The technique consists of a forward difference scheme for time tendency terms, an upstream scheme for advective terms, and a central scheme for the other terms in a physical system. It is shown that the mixed method is conditionally stable and highly accurate for approximating the system of either shallow-water equations in one dimension or primitive equations in three dimensions. Since the technique is explicit and two time level, it conserves computer and programming resources.
Numerical Modeling of Pulse Detonation Rocket Engine Gasdynamics and Performance
NASA Technical Reports Server (NTRS)
Morris, C. I.
2003-01-01
Pulse detonation engines (PDB) have generated considerable research interest in recent years as a chemical propulsion system potentially offering improved performance and reduced complexity compared to conventional gas turbines and rocket engines. The detonative mode of combustion employed by these devices offers a theoretical thermodynamic advantage over the constant-pressure deflagrative combustion mode used in conventional engines. However, the unsteady blowdown process intrinsic to all pulse detonation devices has made realistic estimates of the actual propulsive performance of PDES problematic. The recent review article by Kailasanath highlights some of the progress that has been made in comparing the available experimental measurements with analytical and numerical models.
Magnetohydrodynamic (MHD) modelling of solar active phenomena via numerical methods
NASA Technical Reports Server (NTRS)
Wu, S. T.
1988-01-01
Numerical ideal MHD models for the study of solar active phenomena are summarized. Particular attention is given to the following physical phenomena: (1) local heating of a coronal loop in an isothermal and stratified atmosphere, and (2) the coronal dynamic responses due to magnetic field movement. The results suggest that local heating of a magnetic loop will lead to the enhancement of the density of the neighboring loops through MHD wave compression. It is noted that field lines can be pinched off and may form a self-contained magnetized plasma blob that may move outward into interplanetary space.
Numerical modeling of dish-Stirling reflux solar receivers
Hogan, R.E.
1990-01-01
Using reflux solar receivers to collect solar energy for dish-Stirling electric power generation systems is currently being investigated by several organizations, including Sandia National Laboratories, Albuquerque, New Mexico. In support of this program, Sandia has developed two numerical models describing the energy transfer within and thermal performance of pool-boiler and heat-pipe receivers. Both models are applicable to axisymmetric geometries and they both consider the radiative and convective energy transfer within the receiver cavity, the conductive and convective energy transfer within the receiver cavity, the conductive and convective energy transfer from the receiver housing, and the energy transfer to the receiver working fluid. In these models, the radiative transfer within the receiver is analyzed using a two-band (solar and infrared) net-radiation formulation for enclosure radiation. Empirical convective correlations describe the convective heat transfer from the cavity to the surroundings. The primary difference between the models is the level of detail in modeling the heat conduction through the receiver walls. The more detailed model uses a two-dimensional finite control volume method, whereas the simpler model uses a one-dimensional thermal resistance approach. 20 refs., 7 figs., 2 tabs.
Cloud-Scale Numerical Modeling of the Arctic Boundary Layer
NASA Technical Reports Server (NTRS)
Kruegen, Steven K.; Delnore, Victor E. (Technical Monitor)
2002-01-01
The research objective of this NASA grant-funded project was to determine in detail how large-scale processes. in combination with cloud-scale radiative, microphysical, and dynamical processes, govern the formation and multi-layered structure of Arctic stratus clouds. This information will be useful for developing and improving 1D (one dimensional) boundary layer models for the Arctic. Also, to quantitatively determine the effects of leads on the large-scale budgets of sensible heat, water vapor, and condensate in a variety of Arctic winter conditions. This information will be used to identify the most important lead-flux processes that require parameterization in climate models. Our approach was to use a high-resolution numerical model, the 2D (two dimensional) University of Utah Cloud Resolving Model (UU CRM), and its 1D version, the University of Utah Turbulence Closure Model (UU TCM), a boundary layer model based on third-moment turbulence closure, as well as a large-eddy simulation (LES) model originally developed by C.H. Moeng.
Sound Transmission Validation and Sensitivity Studies in Numerical Models.
Oberrecht, Steve P; Krysl, Petr; Cranford, Ted W
2016-01-01
In 1974, Norris and Harvey published an experimental study of sound transmission into the head of the bottlenose dolphin. We used this rare source of data to validate our Vibroacoustic Toolkit, an array of numerical modeling simulation tools. Norris and Harvey provided measurements of received sound pressure in various locations within the dolphin's head from a sound source that was moved around the outside of the head. Our toolkit was used to predict the curves of pressure with the best-guess input data (material properties, transducer and hydrophone locations, and geometry of the animal's head). In addition, we performed a series of sensitivity analyses (SAs). SA is concerned with understanding how input changes to the model influence the outputs. SA can enhance understanding of a complex model by finding and analyzing unexpected model behavior, discriminating which inputs have a dominant effect on particular outputs, exploring how inputs combine to affect outputs, and gaining insight as to what additional information improves the model's ability to predict. Even when a computational model does not adequately reproduce the behavior of a physical system, its sensitivities may be useful for developing inferences about key features of the physical system. Our findings may become a valuable source of information for modeling the interactions between sound and anatomy.
A Numerical Modeling Approach to Cometary Nucleus Surface Roughness Determination
NASA Astrophysics Data System (ADS)
Höfner, S.; Vincent, J.-B.; Sierks, H.; Blum, J.
2013-09-01
Activity of cometary nuclei is closely linked with thermophysical processes. Main catalyst to activity is the diurnal temperature wave induced by solar heating. Highly resolved comet nucleus geometric models are used to model temperatures with flat surfacial facets taken from shape modeling approaches [1, 3]. Recent analyses of Groussin et al. [4] and Davidsson et al. [2] compared thermal inertia and surface temperatures of Tempel 1 and Hartley 2 synthetic models to those derived from spectral images. They outlined that applying beaming factors and radiative self-heating is not sufficient to understand the thermal behaviour of the nucleus surface. Regions with large incidence angles (e.g. at the morning terminator) distinctively deviate from predicted temperatures. One of the main contributions to this deviation is the effect of surface roughness with scals that are considerably smaller than the model facets. Combined with a relatively low thermal inertia, temperatures cover a wide range of values even at closest neighbourhood to each other. The radiative measurement for a distant observer unveils a smearing effect that indicates higher temperatures compared to average. The authors follow two numerical approaches to model small-scale surface roughness: (A) by using randomly generated fractal surfaces and (B) by downscaling groups of facets originating from larger shape models of Tempel 1. We apply a model that accounts for both radiative heat exchange for all facets and shadowing effects due to incoming solar radiation. These values are calculated in a thermal model. The revealed temperatures are analyzed with respect to average large-scale surface temperatures. Hence, they are compared to deviating temperatures that are measured by a distant observer that is unable to resolve sub-structure surface patterns. A parametric study varying thermal inertia and the degree of surface roughness then outlines a bandwidth of feasible surface structures and relates them to
Analysis of single ring infiltrometer test by direct numerical modeling
NASA Astrophysics Data System (ADS)
Réfloch, Aurore; Oxarango, Laurent; Rossier, Yvan; Gaudet, Jean Paul
2016-04-01
The well field of the Lyon metropolitan area provides drinking water to approximately 1,300,000 inhabitants. It is equipped with 12 infiltration basins. These basins have two main goals: sustaining the water table in times of peak demand for water, and preventing a possible contamination from the Rhône river by inverting groundwater flow direction. The water infiltration under the basins is thus crucial for the overall hydrogeologic behavior of the site. In order to characterize this phenomenon, a set of infiltrometer tests were performed to estimate the soil hydraulic properties. The soil is a coarse alluvial deposits. In order to deal with its sparse granulometric curve, a large single ring infiltrometer (1 meter in diameter) was used. A constant hydraulic head (=0.07 m) was imposed during the test. Two kinds of data are recorded: the amount of water infiltrated over time and the extension of the moisture stain around the ring. The main hydraulic properties are estimated using Richard's equation in a 2D axi-symmetric configuration. Simulations are performed using a finite element commercial software package (Comsol Multiphysics 5.1). According to simplified numerical models, an average homogeneous saturated permeability of the alluvial deposits is estimated at 5.0 10-6 m.s-1. However, such a simple model is not able to represent accurately the moisture stain at the soil surface. More complex models introduce anisotropy of permeability in the alluvium layer, with mono or bi-layer domain. In these cases, experimental and modeling results are consistent, both for the amount of water infiltrated over time and the extension of the moisture stain around the ring. The hydraulic anisotropy in the soil could be due to the stratified nature of alluvial deposits and to soil compaction during the construction of infiltration basins. Keywords: Single ring infiltrometer test, artificial aquifer recharge, numerical modeling.
Numerical modeling for an electric-field hyperthermia applicator
NASA Technical Reports Server (NTRS)
Wu, Te-Kao; Chou, C. K.; Chan, K. W.; Mcdougall, J.
1993-01-01
Hyperthermia, in conjunction with radiation and chemotherapy for treatment of cancers, is an area of current concern. Experiments have shown that hyperthermia can increase the potency of many chemotherapy drugs and the effectiveness of radiation for treating cancer. A combination of whole body or regional hyperthermia with chemotherapy or radiation should improve treatment results. Conventional methods for inducing whole body hyperthermia, such as exposing a patient in a radiant cabinet or under a hot water blanket, conduct heat very slowly from the skin to the body core. Thus a more efficient system, such as the three-plate electric-field hyperthermia applicator (EHA), is developed. This three-plate EHA has one top plate over and two lower plates beneath the patient. It is driven at 27.12 MHz with 500 Watts through a matching circuit. Using this applicator, a 50 kg pig was successfully heated to 42 C within 45 minutes. However, phantom and animal studies have indicated non-uniform heating near the side of the body. In addition, changes in the size and distance between the electrode plates can affect the heating (or electromagnetic field) pattern. Therefore, numerical models using the method of moments (MOM) or the finite difference time domain (FDTD) technique are developed to optimize the heating pattern of this EHA before it is used for human trials. The accuracy of the numerical modeling has been achieved by the good agreement between the MOM and FDTD results for the three-plate EHA without a biological body. The versatile FDTD technique is then applied to optimize the EHA design with a human body. Both the numerical and measured data in phantom blocks will be presented. The results of this study will be used to design an optimized system for whole body or regional hyperthermia.
A numerical oil spill model based on a hybrid method.
Guo, W J; Wang, Y X
2009-05-01
The purpose of this paper is the development of a hybrid particle tracking/Eulerian-Lagrangian approach for the simulation of spilled oil in coastal areas. Oil discharge from the source is modeled by the release of particles. When the oil slick thickness or the oil concentration reaches a critical value, particles are mapped on slick thickness or node concentrations, and the calculations proceed in the Eulerian-Lagrangian mode. To acquire accurate environment information, the model is coupled with the 3-D free-surface hydrodynamics model (POM) and the third-generation wave model (SWAN). By simulating the oil processes of spreading, advection, turbulent diffusion, evaporation, emulsification, dissolution and shoreline deposition, it has the ability to predict the horizontal movement of surface oil slick, the vertical distribution of oil particles, the concentration in the water column and the mass balance of spilled oil. An accidental oil release near Dalian coastal waters is simulated to validate the developed model. Compared with the satellite images of oil slicks on the surface, the numerical results indicate that the model has a reasonable accuracy.
On the impact of buttressing on numerical ice sheet models.
NASA Astrophysics Data System (ADS)
Cornford, Stephen; Martin, Daniel; Lee, Victoria; Payne, Antony; Ng, Esmond
2016-04-01
Idealized problems with little or no lateral variation are frequently used to study numerical ice sheet models that are then applied to realistic problems that have substantial lateral stresses. Given that the strong lateral variation can, for example, result in a stable grounding line on retrograde slope - an impossible result otherwise - it seems unwise to assume that any conclusion drawn from an unbuttressed flow-line geometry can be extrapolated to the general case. We will present results from two problems which do involve significant lateral stresses, the idealized MISMIP+ tests and 1000-year simulations of the entire Antarctic ice sheet, both resolved to sub-kilometre spatial resolution with the BISICLES ice sheet model. We will consider some numerical issues - for example, whether sub-grid friction schemes are as useful as they appear to be in flow-line problems. We will also consider the impact of the Coulomb limited basal traction law proposed by Tsai (2015), which results in flow-line marine ice streams that are more sensitive to climate perturbations than with the usual Weertman law: to what extent does that hold true in buttressed ice streams?
Optimization methods and silicon solar cell numerical models
NASA Technical Reports Server (NTRS)
Girardini, K.
1986-01-01
The goal of this project is the development of an optimization algorithm for use with a solar cell model. It is possible to simultaneously vary design variables such as impurity concentrations, front junction depth, back junctions depth, and cell thickness to maximize the predicted cell efficiency. An optimization algorithm has been developed and interfaced with the Solar Cell Analysis Program in 1 Dimension (SCAPID). SCAPID uses finite difference methods to solve the differential equations which, along with several relations from the physics of semiconductors, describe mathematically the operation of a solar cell. A major obstacle is that the numerical methods used in SCAPID require a significant amount of computer time, and during an optimization the model is called iteratively until the design variables converge to the value associated with the maximum efficiency. This problem has been alleviated by designing an optimization code specifically for use with numerically intensive simulations, to reduce the number of times the efficiency has to be calculated to achieve convergence to the optimal solution. Adapting SCAPID so that it could be called iteratively by the optimization code provided another means of reducing the cpu time required to complete an optimization. Instead of calculating the entire I-V curve, as is usually done in SCAPID, only the efficiency is calculated (maximum power voltage and current) and the solution from previous calculations is used to initiate the next solution.
Numerical modeling of compensation mechanisms for peripheral arterial stenoses.
Drzisga, D; Köppl, T; Pohl, U; Helmig, R; Wohlmuth, B
2016-03-01
The goal of this paper is to develop a numerical model for physiological mechanisms that help to compensate reduced blood flow caused by a peripheral arterial stenosis. Thereby we restrict ourselves to the following compensation mechanisms: Metabolic regulation and arteriogenesis, i.e., growth of pre-existing collateral arteries. Our model is based on dimensionally reduced differential equations to simulate large time periods with low computational cost. As a test scenario, we consider a stenosis located in the right posterior tibial artery of a human. We study its impact on blood supply for different narrowing degrees by the help of numerical simulations. Moreover, the efficiency of the above compensation mechanisms is examined. Our results reveal that even a complete occlusion of this artery exhibiting a cross-section area of 0.442cm(2) can be compensated at rest, if metabolic regulation is combined with collateral arteries whose total cross-section area accounts for 8.14% of the occluded artery.
Attenuation of numerical artefacts in the modelling of fluid interfaces
NASA Astrophysics Data System (ADS)
Evrard, Fabien; van Wachem, Berend G. M.; Denner, Fabian
2015-11-01
Numerical artefacts in the modelling of fluid interfaces, such as parasitic currents or spurious capillary waves, present a considerable problem in two-phase flow modelling. Parasitic currents result from an imperfect evaluation of the interface curvature and can severely affect the flow, whereas spatially underresolved (spurious) capillary waves impose strict limits on the time-step and, hence, dictate the required computational resources for surface-tension-dominated flows. By applying an additional shear stress term at the fluid interface, thereby dissipating the surface energy associated with small wavelengths, we have been able to considerably reduce the adverse impact of parasitic currents and mitigate the time-step limit imposed by capillary waves. However, a careful choice of the applied interface viscosity is crucial, since an excess of additional dissipation compromises the accuracy of the solution. We present the derivation of the additional interfacial shear stress term, explain the underlying physical mechanism and discuss the impact on parasitic currents and interface instabilities based on a variety of numerical experiments. We acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) through Grant No. EP/M021556/1 and from PETROBRAS.
2D Numerical MHD Models of Solar Explosive Events
NASA Astrophysics Data System (ADS)
Roussev, I.
2001-10-01
Observations of the Sun reveal a great variety of dynamic phenomena interpretable as a manifestation of magnetic reconnection. These range from small-scale 'Explosive events' seen in the 'quiet' Sun, through violent flares observed in active regions. The high degree of complexity of the magnetic field inferred from observations may locally produce a fruitful environment for the process of magnetic reconnection to take place. Explosive events are associated with regions undergoing magnetic flux cancellation. This thesis presents a 2-dimensional (2D) numerical study devoted to explore the idea that the salient spectral signatures seen in explosive events are most probably caused by bi-directional outflow jets as a results of an ongoing magnetic reconnection. In order to provide qualitative results needed for the better physical interpretation of solar explosive events, several models intended to represent a 'quiet' Sun transition of solar explosive events, several models intended to represent a 'quiet' Sun transition region undergoing magnetic reconnection are examined, in both unstratified and gravitationally stratified atmospheres. The magnetic reconnection is initiated in an ad hoc manner, and the dynamic evolution is followed by numerically solving the equations of 2D dissipative magnetohydrodynamics (MHD), including the effects of field-aligned thermal conduction, radiative losses, volumetric heating, and anomalous resistivity.
Pulse shape control in a dual cavity laser: numerical modeling
NASA Astrophysics Data System (ADS)
Yashkir, Yuri
2006-04-01
We present a numerical model of the laser system for generating a special shape of the pulse: a steep peak at the beginning followed by a long pulse tail. Laser pulses of this nature are required for various applications (laser material processing, optical breakdown spectroscopy, etc.). The laser system consists of two "overlapped" cavities with different round-trip times. The laser crystal, the Q-switching element, the back mirror, and the output coupler are shared. A shorter pulse is generated in a short cavity. A small fraction of this pulse is injected into the long cavity as a seed. It triggers generation of the longer pulse. The output emission from this hybrid laser produces a required pulse shape. Parameters of the laser pulse (ratios of durations and energies of short- and long- pulse components) can be controlled through cavity length and the output coupler reflection. Modelling of the laser system is based on a set of coupled rate equations for dynamic variables of the system: the inverse population in an active laser media and photon densities in coupled cavities. Numerical experiments were provided with typical parameters of a Nd:YAG laser to study the system behaviour for different combinations of parameters.
Parameterization of mires in a numerical weather prediction model
NASA Astrophysics Data System (ADS)
Yurova, Alla; Tolstykh, Mikhail; Nilsson, Mats; Sirin, Andrey
2014-11-01
Mires (peat-accumulating wetlands) occupy 8.1% of Russian territory and are especially numerous in the western Siberian Lowlands, where they can significantly modify atmospheric heat and water balances. They also influence air temperatures and humidity in the boundary layers closest to the earth's surface. The purpose of our study was to incorporate the influence of mires into the SL-AV numerical weather prediction model, which is used operationally in the Hydrometeorological Center of Russia. This was done by adjusting the multilayer soil component (by modifying the peat thermal conductivity in the heat diffusion equation and reformulating the lower boundary condition for Richard's equation), and reformulating both the evapotranspiration and runoff from mires. When evaporation from mires was incorporated into the SL-AV model, the latent heat flux in the areas dominated by mires increased strongly, resulting in surface cooling and hence reductions in the sensible heat flux and outgoing terrestrial long-wave radiation. Presented results show that including mires significantly decreased the bias and RMSE of predictions of temperature and relative humidity 2 m above the ground for lead times of 12, 36, and 60 h from 00 h Coordinated Universal Time (evening conditions), but did not eliminate the bias in forecasts for lead times of 24, 48, and 72 h (morning conditions) in Siberia. Different parameterizations of mire evapotranspiration are also compared.
Laboratory and Numerical Modeling of Smoke Characteristics for Superfog Formation
NASA Astrophysics Data System (ADS)
Bartolome, C.; Lu, V.; Tsui, K.; Princevac, M.; Venkatram, A.; Mahalingam, S.; Achtemeier, G.; Weise, D.
2011-12-01
Land management techniques in wildland areas include prescribed fires to promote biodiversity and reduce risk of severe wildfires across the United States. Several fatal car pileups have been associated with smoke-related visibility reduction from prescribed burns. Such events have occurred in year 2000 on the interstate highways I-10 and I-95, 2001 on the I-4, 2006 on the I-95, and 2008 on the I-4 causing numerous fatalities, injuries, and damage to property. In some of the cases visibility reduction caused by smoke and fog combinations traveling over roadways have been reported to be less than 3 meters, defined as superfog. Our research focuses on delineating the conditions that lead to formation of the rare phenomena of superfog and creating a tool to enable land managers to effectively plan prescribed burns and prevent tragic events. It is hypothesized that the water vapor from combustion, live fuels, soil moisture, and ambient air condense onto the cloud condensation nuclei (CCN) particles emitted from low intensity smoldering fires. Physical and numerical modeling has been used to investigate these interactions. A physical model in the laboratory has been developed to characterize the properties of smoke resulting from smoldering pine needle litters at the PSW Forest Service in Riverside, CA. Temporal measurements of temperature, relative humidity, sensible heat flux, radiation heat flux, convective heat flux, particulate matter concentrations and visibilities have been measured for specific cases. The size distribution and number concentrations of the fog droplets formed inside the chamber by mixing cool dry and moist warm air masses to produce near superfog visibilities were measured by a Phase Doppler Particle Analyzer. Thermodynamic modeling of smoke and ambient air was conducted to estimate liquid water contents (LWC) available to condense into droplets and form significant reductions in visibility. The results show that LWC of less than 2 g m-3 can be
Fifty years of numerical modeling of baroclinic ocean
NASA Astrophysics Data System (ADS)
Sarkisyan, A. S.
2012-02-01
This paper presents a brief critical analysis of the main historical stages of numerical modeling for the last fifty years. It was a half a century ago that the numerical simulation of an actual baroclinic ocean was initiated by the author and his students [1, 2]. In meteorology, studies on the numerical modeling of a baroclinic atmosphere existed much earlier [21, 22]. Despite this, a similar move in oceanography was met with strong resistance. At that time, there were many studies on the calculation of the total mass transport. The founders of this field, V.B. Shtokman, H. Sverdrup, and W. Munk, were mistaken in believing that they addressed baroclinic models of the ocean. The author preferred works by V. Ekman [12] and I. Sandström and B. Helland-Hansen [19]. A generalization of recent studies made it possible to come to some conclusions on the need to use the level of the free oceanic surface as a basis rather than the function of total mass transport, on the role of the baroclinic β effect (BARBE), on the joint effect of baroclinicity and bottom relief (JEBAR), etc. The author conditionally divides these fifty years into the following three stages. (1) The first stage was 1961-1969, when the author and his students performed almost exclusively diagnostic and adaptation calculations of climatic characteristics. (2) The second stage began with papers by K. Bryan [23] and his students. This is an important and promising stage involving mainly prognostic studies and four-dimensional analysis. The major advances in modeling at this stage (the Gulf Stream separation point [61], the Kuroshio seasonal evolution [63], the formation of the cold intermediate layer in the Black Sea [80], the subsurface countercurrent in the Caspian Sea [25], the realistic four-dimensional analysis of the Kara Sea [60], etc.) were due to high-resolution and/or data assimilation with an adequate period of integration. (3) The third stage began with the activities of international
Numerical Modeling and Optimization of Warm-water Heat Sinks
NASA Astrophysics Data System (ADS)
Hadad, Yaser; Chiarot, Paul
2015-11-01
For cooling in large data-centers and supercomputers, water is increasingly replacing air as the working fluid in heat sinks. Utilizing water provides unique capabilities; for example: higher heat capacity, Prandtl number, and convection heat transfer coefficient. The use of warm, rather than chilled, water has the potential to provide increased energy efficiency. The geometric and operating parameters of the heat sink govern its performance. Numerical modeling is used to examine the influence of geometry and operating conditions on key metrics such as thermal and flow resistance. This model also facilitates studies on cooling of electronic chip hot spots and failure scenarios. We report on the optimal parameters for a warm-water heat sink to achieve maximum cooling performance.
A mathematical model and numerical method for thermoelectric DNA sequencing
NASA Astrophysics Data System (ADS)
Shi, Liwei; Guilbeau, Eric J.; Nestorova, Gergana; Dai, Weizhong
2014-05-01
Single nucleotide polymorphisms (SNPs) are single base pair variations within the genome that are important indicators of genetic predisposition towards specific diseases. This study explores the feasibility of SNP detection using a thermoelectric sequencing method that measures the heat released when DNA polymerase inserts a deoxyribonucleoside triphosphate into a DNA strand. We propose a three-dimensional mathematical model that governs the DNA sequencing device with a reaction zone that contains DNA template/primer complex immobilized to the surface of the lower channel wall. The model is then solved numerically. Concentrations of reactants and the temperature distribution are obtained. Results indicate that when the nucleoside is complementary to the next base in the DNA template, polymerization occurs lengthening the complementary polymer and releasing thermal energy with a measurable temperature change, implying that the thermoelectric conceptual device for sequencing DNA may be feasible for identifying specific genes in individuals.
Three-Dimensional Numerical Modeling of Magnetohydrodynamic Augmented Propulsion Experiment
NASA Technical Reports Server (NTRS)
Turner, M. W.; Hawk, C. W.; Litchford, R. J.
2009-01-01
Over the past several years, NASA Marshall Space Flight Center has engaged in the design and development of an experimental research facility to investigate the use of diagonalized crossed-field magnetohydrodynamic (MHD) accelerators as a possible thrust augmentation device for thermal propulsion systems. In support of this effort, a three-dimensional numerical MHD model has been developed for the purpose of analyzing and optimizing accelerator performance and to aid in understanding critical underlying physical processes and nonideal effects. This Technical Memorandum fully summarizes model development efforts and presents the results of pretest performance optimization analyses. These results indicate that the MHD accelerator should utilize a 45deg diagonalization angle with the applied current evenly distributed over the first five inlet electrode pairs. When powered at 100 A, this configuration is expected to yield a 50% global efficiency with an 80% increase in axial velocity and a 50% increase in centerline total pressure.
Progress report on LBL's numerical modeling studies on Cerro Prieto
Halfman-Dooley, S.E.; Lippman, M.J.; Bodvarsson, G.S.
1989-04-01
An exploitation model of the Cerro Prieto geothermal system is needed to assess the energy capacity of the field, estimate its productive lifetime and develop an optimal reservoir management plan. The model must consider the natural state (i.e., pre-exploitation) conditions of the system and be able to predict changes in the reservoir thermodynamic conditions (and fluid chemistry) in response to fluid production (and injection). This paper discusses the results of a three-dimensional numerical simulation of the natural state conditions of the Cerro Prieto field and compares computed and observed pressure and temperature/enthalpy changes for the 1973--1987 production period. 16 refs., 24 figs., 2 tabs.
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.
Numerical modeling of frontal and basal accretion at collisional margins
NASA Astrophysics Data System (ADS)
Selzer, Cornelia; Buiter, Susanne J. H.; Pfiffner, O. Adrian
2008-06-01
We investigate the deformation of orogenic wedges that form in the early stages of continent-continent collisions using a two-dimensional numerical model limited to the upper lithosphere. Our models show that deformation at the plate margins is influenced by rheology, surface processes, and the balance between inward mass flux and outward subduction flux, as controlled by the subduction load (which represents the effects of slab pull and resistive forces) and flexural downbending. We find three characteristic deformation modes: (1) near-pure subduction with little or no accretion; (2) frontal accretion with development of an accretionary wedge built up by offscraping of the sediment layer at shallow depth; and (3) independent frontal and basal accretion where a retrothrust allows stacking of basement nappes at crustal to mantle depths. Near-pure subduction is enabled for "ordinary-rheology" materials, characterized by brittle and viscous material behavior (approximating a "Christmas tree-type" depth profile), and almost zero friction along the subduction shear zone. Frontal accretion occurs when slightly increased friction along the subduction shear zone allows offscraping of the sediment layer from the subducting plate. Independent frontal and basal accretion develops in strong-rheology models with an almost fully brittle material behavior. Major surface erosion or a reduction of the subduction load promote the development of large basement nappes. Frontal accretion is favored by major sedimentation during convergence, a large backstop, and in the case of a lateral transition from a "strong-rheology" to an "ordinary-rheology" subducting plate. Our numerical models develop first-order characteristics as observed in natural orogenic wedges, for example upper crustal nappe stacks, frontal and basal accretion, or extension in the core of an orogen. Frontal and basal accretion are interdependent, and tend to stabilize the subduction system.
A numerical model for dynamic wave rotor analysis
NASA Technical Reports Server (NTRS)
Paxson, D. E.
1995-01-01
A numerical model has been developed which can predict the dynamic (and steady state) performance of a wave rotor, given the geometry and time dependent boundary conditions. The one-dimensional, perfect gas, CFD based code tracks the gasdynamics in each of the wave rotor passages as they rotate past the various ducts. The model can operate both on and off-design, allowing dynamic behavior to be studied throughout the operating range of the wave rotor. The model accounts for several major loss mechanisms including finite passage opening time, fluid friction, heat transfer to and from the passage walls, and leakage to and from the passage ends. In addition, it can calculate the amount of work transferred to and from the fluid when the flow in the ducts is not aligned with the passages such as occurs in off-design operation. Since it is one-dimensional, the model runs reasonably fast on a typical workstation. This paper will describe the model and present the results of some transient calculations for a conceptual four port wave rotor designed as a topping cycle for a small gas turbine engine.
Numerical Modeling of Shatter Cones Development in Impact Craters
NASA Technical Reports Server (NTRS)
Baratoux, D.; Melosh, H. J.
2003-01-01
Shatter cones are the characteristic forms of rock fractures in impact structures. They have been used for decades as unequivocal fingerprints of meteoritic impacts on Earth. The abundant data about shapes, apical angles, sizes and distributions of shatter cones for many terrestrial impact structures should provide insights for the determination of impact conditions and characteristics of shock waves produced by high-velocity projectiles in geologic media. However, previously proposed models for the formation of shatter cones do not agree with observations. For example, the widely accepted Johnson-Talbot mechanism requires that the longitudinal stress drops to zero between the arrival of the elastic precursor and the main plastic wave. Unfortunately, observations do not support such a drop. A model has been also proposed to explain the striated features on the surface of shatter cones but can not invoked for their conical shape. The mechanism by which shatter cones form thus remains enigmatic to date. In this paper we present a new model for the formation of shatter cones. Our model has been tested by means of numerical simulations using the hydrocodes SALE 2D enhanced with the Grady-Kipp-Melosh fragmentation model.
Numerical modelling of blue mussel (Mytilus edulis) bacterial contamination
NASA Astrophysics Data System (ADS)
Dabrowski, Tomasz; Doré, William J.; Lyons, Kieran; Nolan, Glenn D.
2014-05-01
Bivalve shellfish such as oysters and mussels can concentrate human pathogens when grown in areas impacted by municipal wastewater. Under EU regulation this risk to consumers is controlled by determining the sanitary quality of bivalve shellfish production areas based on the concentration of Escherichia coli present in shellfish flesh. The authors present a modelling approach to simulate an uptake of E. coli from seawater and subsequent depuration by Mytilus edulis. The model that dynamically predicts E. coli concentration in the mussel tissue is embedded within a 3-D numerical modelling system comprising hydrodynamic, biogeochemical, shellfish ecophysiological and the newly proposed microbial modules. The microbial module has two state variables, namely, the concentrations of E. coli in water and in the mussel tissue. Novel formulations to calculate the filtration rates by mussels and the resulting uptake of bacteria are proposed; these rates are updated at every computational time step. Concentrations of E. coli in seawater are also updated accordingly taking into account the amounts ingested by mussels. The model has been applied to Bantry Bay in the south-west of Ireland. The results indicate that the model is capable of reproducing the official classification of shellfish waters in the bay based on monthly sampling at several stations. The predicted filtration rates and ratios of E. coli in water and mussels also compare well with the literature. The model thus forms a tool that may be used to assist in the classification of shellfish waters at much greater spatial and temporal detail than that offered by a field monitoring programme. Moreover, it can also aid in designing an efficient monitoring programme. The model can also be utilised to determine the contribution of individual point sources of pollution on the microbial loading in mussels and, when incorporated into an operational framework, it can provide a short-term forecasting of microbial
Numerical modeling of an estuary: A comprehensive skill assessment
Warner, J.C.; Geyer, W.R.; Lerczak, J.A.
2005-01-01
Numerical simulations of the Hudson River estuary using a terrain-following, three-dimensional model (Regional Ocean Modeling System (ROMS)) are compared with an extensive set of time series and spatially resolved measurements over a 43 day period with large variations in tidal forcing and river discharge. The model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure, including tidal, spring neap, and river discharge-induced variability. Large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model. The observed structure and variations of the longitudinal salinity gradient are also well reproduced. The most notable discrepancy between the model and the data is in the vertical salinity structure. While the surface-to-bottom salinity difference is well reproduced, the stratification in the model tends to extend all the way to the water surface, whereas the observations indicate a distinct pycnocline and a surface mixed layer. Because the southern boundary coindition is located near the mouth the estuary, the salinity within the domain is particularly sensitive to the specification of salinity at the boundary. A boundary condition for the horizontal salinity gradient, based on the local value of salinity, is developed to incorporate physical processes beyond the open boundary not resolved by the model. Model results are sensitive to the specification of the bottom roughness length and vertical stability functions, insofar as they influence the intensity of vertical mixing. The results only varied slightly between different turbulence closure methods of k-??, k-??, and k-kl. Copyright 2005 by the American Geophysical Union.
Numerical Modeling for Yield Pillar Design: A Case Study
NASA Astrophysics Data System (ADS)
Li, Wenfeng; Bai, Jianbiao; Peng, Syd; Wang, Xiangyu; Xu, Ying
2015-01-01
Two single-entry gateroad systems employing a yield pillar for bump control in a Chinese coal mine were introduced. The overburden depth of the longwall panels was approximately 390 m. When the width/height (W/H) ratio of the yield pillar was 2.67, coal bumps in the tailgate occurred in front of the longwall retreating face. However, in another panel, the coal bump was eliminated because the W/H ratio was reduced to 1.67. Under this condition, instrumentation results indicated that the roof-to-floor and rib-to-rib convergences reached 1,050 and 790 mm, respectively, during longwall retreat. The numerical model was used to back-analyze the two cases of yield pillar application in the hope to find the principle for yield pillar design. In order to improve the reliability of the numerical model, the strain-hardening gob and strain-softening pillar materials were meticulously calibrated, and the coal/rock interface strength was determined by laboratory direct shear tests. The results of the validated model indicate that if the W/H ratio of the yield pillar equals 1.67, the peak vertical stress in the panel rib (37.7 MPa) is much larger than that in the yield pillar (21.1 MPa); however, the peak vertical stress in the panel rib (30.87 MPa) is smaller than that in the yield pillar (36 MPa) when the W/H ratio of yield pillar is 2.67. These findings may be helpful to the design of yield pillars for bump control.
3-D numerical modeling of plume-induced subduction initiation
NASA Astrophysics Data System (ADS)
Baes, Marzieh; Gerya, taras; Sobolev, Stephan
2016-04-01
Investigation of mechanisms involved in formation of a new subduction zone can help us to better understand plate tectonics. Despite numerous previous studies, it is still unclear how and where an old oceanic plate starts to subduct beneath the other plate. One of the proposed scenarios for nucleation of subduction is plume-induced subduction initiation, which was investigated in detail, using 2-D models, by Ueda et al. (2008). Recently. Gerya et al. (2015), using 3D numerical models, proposed that plume-lithosphere interaction in the Archean led to the subduction initiation and onset of plate tectonic. In this study, we aim to pursue work of Ueda et al. (2008) by incorporation of 3-D thermo-mechanical models to investigate conditions leading to oceanic subduction initiation as a result of thermal-chemical mantle plume-lithosphere interaction in the modern earth. Results of our experiments show four different deformation regimes in response to plume-lithosphere interaction, that are a) self-sustaining subduction initiation where subduction becomes self-sustained, b) freezing subduction initiation where subduction stops at shallow depths, c) slab break-off where subducting circular slab breaks off soon after formation and d) plume underplating where plume does not pass through the lithosphere but spreads beneath it (failed subduction initiation). These different regimes depend on several parameters such as plume's size, composition and temperature, lithospheric brittle/plastic strength, age of the oceanic lithosphere and presence/absence of lithospheric heterogeneities. Results show that subduction initiates and becomes self-sustained when lithosphere is older than 10 Myr and non-dimensional ratio of the plume buoyancy force and lithospheric strength above the plume is higher than 2.
Rivers on Titan - numerical modelling of sedimentary structures
NASA Astrophysics Data System (ADS)
Misiura, Katarzyna; Czechowski, Leszek
2016-07-01
On Titan surface we can expect a few different geomorphological forms, e.g. fluvial valley and river channels. In our research we use numerical model of the river to determine the limits of different fluvial parameters that play important roles in evolution of the rivers on Titan and on Earth. We have found that transport of sediments as suspended load is the main way of transport for Titan [1]. We also determined the range of the river's parameters for which braided river is developed rather than meandering river. Similar, parallel simulations for rivers deltas are presented in [2]. Introduction Titan is a very special body in the Solar System. It is the only moon that has dense atmosphere and flowing liquid on its surface. The Cassini-Huygens mission has found on Titan meandering rivers, and indicated processes of erosion, transport of solid material and its sedimentation. This work is aimed to investigate the similarity and differences between these processes on Titan and the Earth. Numerical model The dynamical analysis of the considered rivers is performed using the package CCHE modified for the specific conditions on Titan. The package is based on the Navier-Stokes equations for depth-integrated two dimensional, turbulent flow and three dimensional convection-diffusion equation of sediment transport. For more information about equations see [1]. Parameters of the model We considered our model for a few different parameters of liquid and material transported by a river. For Titan we consider liquid corresponding to a Titan's rain (75% methane, 25% nitrogen), for Earth, of course, the water. Material transported in rivers on Titan is water ice, for Earth - quartz. Other parameters of our model are: inflow discharge, outflow level, grain size of sediments etc. For every calculation performed for Titan's river similar calculations are performed for terrestrial ones. Results and Conclusions The results of our simulation show the differences in behaviour of the
A numerical strategy for modelling rotating stall in core compressors
NASA Astrophysics Data System (ADS)
Vahdati, M.
2007-03-01
The paper will focus on one specific core-compressor instability, rotating stall, because of the pressing industrial need to improve current design methods. The determination of the blade response during rotating stall is a difficult problem for which there is no reliable procedure. During rotating stall, the blades encounter the stall cells and the excitation depends on the number, size, exact shape and rotational speed of these cells. The long-term aim is to minimize the forced response due to rotating stall excitation by avoiding potential matches between the vibration modes and the rotating stall pattern characteristics. Accurate numerical simulations of core-compressor rotating stall phenomena require the modelling of a large number of bladerows using grids containing several tens of millions of points. The time-accurate unsteady-flow computations may need to be run for several engine revolutions for rotating stall to get initiated and many more before it is fully developed. The difficulty in rotating stall initiation arises from a lack of representation of the triggering disturbances which are inherently present in aeroengines. Since the numerical model represents a symmetric assembly, the only random mechanism for rotating stall initiation is provided by numerical round-off errors. In this work, rotating stall is initiated by introducing a small amount of geometric mistuning to the rotor blades. Another major obstacle in modelling flows near stall is the specification of appropriate upstream and downstream boundary conditions. Obtaining reliable boundary conditions for such flows can be very difficult. In the present study, the low-pressure compression (LPC) domain is placed upstream of the core compressor. With such an approach, only far field atmospheric boundary conditions are specified which are obtained from aircraft speed and altitude. A chocked variable-area nozzle, placed after the last compressor bladerow in the model, is used to impose boundary
Comparison of Laboratory Experimental Data to XBeach Numerical Model Output
NASA Astrophysics Data System (ADS)
Demirci, Ebru; Baykal, Cuneyt; Guler, Isikhan; Sogut, Erdinc
2016-04-01
Coastal zones are living and constantly changing environments where both the natural events and the human-interaction results come into picture regarding to the shoreline behavior. Both the nature of the coastal zone and the human activities shape together the resultants of the interaction with oceans and coasts. Natural extreme events may result in the need of human interference, such as building coastal structures in order to prevent from disasters or any man-made structure throughout a coastline may affect the hydrodynamics and morphology in the nearshore. In order to understand and cope with this cycle of cause and effect relationship, the numerical models developed. XBeach is an open-source, 2DH, depth average numerical model including the hydrodynamic processes of short wave transformation (refraction, shoaling and breaking), long wave (infragravity wave) transformation (generation, propagation and dissipation), wave-induced setup and unsteady currents, as well as overwash and inundation and morphodynamic processes of bed load and suspended sediment transport, dune face avalanching, bed update and breaching (Roelvink et al., 2010). Together with XBeach numerical model, it is possible to both verify and visualize the resultant external effects to the initial shorelines in coastal zones. Recently, Baykal et al. (2015) modelled the long term morphology changes with XBeach near Kızılırmak river mouth consisting of one I-shaped and one Y-shaped groins. In order to investigate the nature of the shoreline and near shore hydrodynamic conditions and morphology, the five laboratory experiments are conducted in the Largescale Sediment Transport Facility at the U.S. Army Engineer Research and Development Center in order to be used to improve longshore sand transport relationships under the combined influence of waves and currents and the enhancement of predictive numerical models of beach morphology evolution. The first series of the experiments were aimed at
Numerical modeling of infrasound propagation at very long distance
NASA Astrophysics Data System (ADS)
Piserchia, Pierre-Franck; Roche, Roger
2004-05-01
Compliance with the CTBT in the atmosphere will be monitored by a world-wide network of infrasound stations consisting of 60 stations equipped with microbarographs in order to measure small changes in the air pressure in the frequency range 0.02 to 4 Hz. They are characterized by a good sensitivity, and by a large dynamic. By the application of array techniques, it is possible to determine the direction of pressure pulses caused by small explosions in the atmosphere, as well as shock waves caused by supersonic aircraft or meteorites. To take into account the nonlinear phenomena at the source and during the propagation, we are developing a numerical approach to solve the Euler nonlinear equation. In a first step, in the linear domain, this method is compared with two other numerical modeling approaches based on the ray tracing technique and the parabolic approach. In our test case, the source is on the ground and generates a 1-Pa pressure pulse centered at the frequency of 0.1 Hz. We considered an infrasound propagation over a distance of 500 km and an atmosphere height of 200 km. In a further step, the source level will be increased to study nonlinear phenomena.
Numerical modeling of colloid facilitated virus transport in porus media
NASA Astrophysics Data System (ADS)
Katzourakis, Vasileios E.; Chrysikopoulos, Constantinos V.
2013-04-01
A conceptual mathematical model was developed to describethe simultaneous transport (cotransport) of viruses and colloids in three-dimensional, water saturated, homogeneous porous media with uniform flow. The model accounts for the migration of individual virus and colloid particles as well as viruses attached onto colloids. Viruses can be suspended in the aqueous phase, attached onto suspended colloids and the solid matrix, and attached onto colloids previously attached on the solid matrix. Colloids can be suspended in the aqueous phase or attached on the solid matrix. Viruses in all four phases (suspended in the aqueous phase, attached onto suspended colloid particles, attached onto the solid matrix, and attached onto colloids previously attached on the solid matrix) may undergo inactivation with different inactivation coefficients. The governing coupled partial differential equations were solved numerically by employing finite difference methods, which were implemented explicitly or implicitly so that both stability and accuracy factors were satisfied. Furthermore, available experimental data were used to test the newly developed cotransport model. The model was shown to simulate quite accurately the available experimental data.
Numerical modelling of propagation of landslides using SPH
NASA Astrophysics Data System (ADS)
Montull, Carlos; Pastor, Manuel; Springman, Sarah
2015-04-01
Landslides cause severe economic damage and a large number of casualties every year around the world. Engineers and geologists need to understand and predict their properties, such as velocity, depth and run out distance. In addition to experience gained on similar cases, predictions require the application of mathematical, constitutive/rheological and numerical models. Different models are currently used to simulate long run-out landslides in order to elaborate hazard maps. Among the available alternatives, depth integrated models present a reasonable compromise between computational cost and accuracy. The purpose of this paper is to apply the SPH depth integrated model, together with suitable rheological laws, to analize fast landslides. We will present the results obtained with the code Geoflow_SPH to three selected cases: (i) The Frank avalanche, (ii) the Cougar Hill flowslide and (iii) the Sham Tseng debris flow. The results of the simulations include estimations of fundamental aspects of the problem, such as the path followed by the sliding mass, the shape of the run-out area, the maximum run-out, the depth of the final deposit, the pore pressure evolution and the speed evolution of the landslide.
Numerical Modeling of Flow through Phloem Considering Active Loading
NASA Astrophysics Data System (ADS)
Liu, Jin; Sze, Tsun-Kay Jackie; Dutta, Prashanta
2013-11-01
Transport through phloem is of significant interest in engineering applications including self-powered microfluidic pumps. We present a phloem model, combining protein level mechanics with cellular level fluid transport. Fluid flow and sucrose transport through a petiole sieve tube are simulated using the Nernst-Planck, Navier-Stokes, and continuity equations. Governing equations are solved using the finite volume method with dynamically calculated boundary conditions. Sieve tube cell structure consisting of sieve plates is included in a two dimensional model by computational cell blocking. Sucrose transport is incorporated as a boundary condition through a six-state model, bringing in active loading mechanisms with consideration of physical plant properties. The effects of reaction rates and leaf sucrose concentration are investigated to understand the transport mechanism in petiole sieve tubes. Numerical results show that increasing forward reactions of the proton sucrose transporter significantly promotes the pumping ability. A lower leaf sieve sucrose concentration results in a lower wall inflow velocity, but yields a higher inflow of water due to the active loading mechanism. The overall effect is higher outflow velocity for lower leaf sieve sucrose concentration because the increase in inflow velocity outweighs wall velocity. This new phloem model provides new insights on mechanisms potentially useful for fluidic pumping in self-powered microfluidic pumps. This work is supported in part by the National Science Fundation grant CBET-1250107.
Numerical Modeling of the Evolving Stable Boundary Layer
NASA Astrophysics Data System (ADS)
Sorbjan, Z.
2013-12-01
A single-column model of the evolving stable boundary layer is tested for the consistency of turbulence parameterization, self-similar properties of the flow, and effects of ambient forcing. The turbulence closure of the model is based on the K-theory approach, with stability functions based on empirical data, and a semi-empirical form of the mixing length. The model has one internal, governing stability parameter, the Richardson number Ri, which dynamically adjusts to the boundary conditions and to external forcing. Model results, expressed in terms of local similarity scales, are universal functions of the Richardson number, i.e. they are satisfied in the entire stable boundary layer, for all instants of time, and all kinds of external forcing. Based on similarity expression, a realizability condition is derived for the minimum turbulent heat flux in the stable boundary layer. Numerical experiments show that the development of 'horse-shoe' shaped, 'fixed-elevation' wind hodographs in the interior of the stable boundary layer are solely caused by effects imposed by surface thermal forcing, and are not related to the inertial oscillation mechanism.
A Numerical Model for the Microcirculation in Skeletal Muscle Fascia
NASA Astrophysics Data System (ADS)
Jacobitz, Frank G.; Schmid-Schönbein, Geert W.
2002-11-01
A numerical model for blood flow in a microvascular network has been developed. The model uses the complete network topology of rat spinotrapezius muscle fascia that was reconstructed from microscopic images. The fascia's network is composed of a feeding arterial network, a collecting venous network, and bundles of capillaries. The flow in the network's vessels is characterized by low Reynolds and Womersley numbers. The model consideres that the microvessels are distensible by pressure and that the arterioles are actively contractile. The blood has non-Newtonian apparent viscosity and blood cells are distributed at bifurcations according to the flow rates into the side branches. These properties have previously been determined experimentally. The method of indefinite admittances is used to compute the flow in the network. The apparent viscosity is computed from local values of hematocrit, shear, and vessel diameter. The model provides detailed information about the flow in all of the network's vessels. Statistical properties of the network, such as the overall flowrate through the network or distributions of pressure, shear stress, and hematocrit in the network are determined. Results for the flow in arterial, venous, and capillary vessels are compared.
A numerical-physical planetary boundary layer model
NASA Astrophysics Data System (ADS)
Padro, Jacob
1983-07-01
A numerical-physical model for the planetary boundary layer has been formulated for the purpose of predicting the winds, temperatures and humidities in the lowest 1600 m of the atmosphere. An application of the model to the synoptic situation of 30 August, 1972, demonstrates its ability to produce useful forecasts for a period of 24 h. Results are illustrated in terms of horizontal maps and time-height sections of winds and temperatures. The model is divided in the vertical direction into three layers that are governed, respectively, by different physical formulations. At the lowest level, which is the surface of the earth, forecasts of temperature and humidity are computed from empirical relations. In the first layer, the surface layer, application is made of the similarity theories of Monin-Obukhov, Monin-Kazanski and Businger’s form of the universal functions. The second layer, the Ekman layer, is 1550 m deep and is governed by diagnostic momentum and time-dependent thermodynamic and humidity equations. External input to the model are large-scale pressure gradients and middle-level cloudiness. Cressman’s objective analysis procedure is applied to conventional surface and upper air data over a horizontal region of about 2500 km by 2500 km, centered about Lake Ontario. With a grid distance of 127 km and a time interval of 30 min, the computer time required on Control Data Cyber 76 for a 24 h forecast for the case study is less than two minutes.
Numerical modeling of rapidly varying flows using HEC-RAS and WSPG models.
Rao, Prasada; Hromadka, Theodore V
2016-01-01
The performance of two popular hydraulic models (HEC-RAS and WSPG) for modeling hydraulic jump in an open channel is investigated. The numerical solutions are compared with a new experimental data set obtained for varying channel bottom slopes and flow rates. Both the models satisfactorily predict the flow depths and location of the jump. The end results indicate that the numerical models output is sensitive to the value of chosen roughness coefficient. For this application, WSPG model is easier to implement with few input variables.
Numerical modeling of the SNS H- ion source
NASA Astrophysics Data System (ADS)
Veitzer, Seth A.; Beckwith, Kristian R. C.; Kundrapu, Madhusudhan; Stoltz, Peter H.
2015-04-01
Ion source rf antennas that produce H- ions can fail when plasma heating causes ablation of the insulating coating due to small structural defects such as cracks. Reducing antenna failures that reduce the operating capabilities of the Spallation Neutron Source (SNS) accelerator is one of the top priorities of the SNS H- Source Program at ORNL. Numerical modeling of ion sources can provide techniques for optimizing design in order to reduce antenna failures. There are a number of difficulties in developing accurate models of rf inductive plasmas. First, a large range of spatial and temporal scales must be resolved in order to accurately capture the physics of plasma motion, including the Debye length, rf frequencies on the order of tens of MHz, simulation time scales of many hundreds of rf periods, large device sizes on tens of cm, and ion motions that are thousands of times slower than electrons. This results in large simulation domains with many computational cells for solving plasma and electromagnetic equations, short time steps, and long-duration simulations. In order to reduce the computational requirements, one can develop implicit models for both fields and particle motions (e.g. divergence-preserving ADI methods), various electrostatic models, or magnetohydrodynamic models. We have performed simulations using all three of these methods and have found that fluid models have the greatest potential for giving accurate solutions while still being fast enough to perform long timescale simulations in a reasonable amount of time. We have implemented a number of fluid models with electromagnetics using the simulation tool USim and applied them to modeling the SNS H- ion source. We found that a reduced, single-fluid MHD model with an imposed magnetic field due to the rf antenna current and the confining multi-cusp field generated increased bulk plasma velocities of > 200 m/s in the region of the antenna where ablation is often observed in the SNS source. We report
Modeling Collisional Cascades in Debris Disks: The Numerical Method
NASA Astrophysics Data System (ADS)
Gáspár, András; Psaltis, Dimitrios; Özel, Feryal; Rieke, George H.; Cooney, Alan
2012-04-01
We develop a new numerical algorithm to model collisional cascades in debris disks. Because of the large dynamical range in particle masses, we solve the integro-differential equations describing erosive and catastrophic collisions in a particle-in-a-box approach, while treating the orbital dynamics of the particles in an approximate fashion. We employ a new scheme for describing erosive (cratering) collisions that yields a continuous set of outcomes as a function of colliding masses. We demonstrate the stability and convergence characteristics of our algorithm and compare it with other treatments. We show that incorporating the effects of erosive collisions results in a decay of the particle distribution that is significantly faster than with purely catastrophic collisions.
Numerical model study of radio frequency vessel sealing thermodynamics
NASA Astrophysics Data System (ADS)
Pearce, John
2015-03-01
Several clinically successful clinical radio frequency vessel-sealing devices are currently available. The dominant thermodynamic principles at work involve tissue water vaporization processes. It is necessary to thermally denature vessel collagen, elastin and their adherent proteins to achieve a successful fusion. Collagens denature at middle temperatures, between about 60 and 90 C depending on heating time and rate. Elastin, and its adherent proteins, are more thermally robust, and require temperatures in excess of the boiling point of water at atmospheric pressure to thermally fuse. Rapid boiling at low apposition pressures leads to steam vacuole formation, brittle tissue remnants and frequently to substantial disruption in the vessel wall, particularly in high elastin-content arteries. High apposition pressures substantially increase the equilibrium boiling point of tissue water and are necessary to ensure a high probability of a successful seal. The FDM numerical models illustrate the beneficial effects of high apposition pressures.
MODELING COLLISIONAL CASCADES IN DEBRIS DISKS: THE NUMERICAL METHOD
Gaspar, Andras; Psaltis, Dimitrios; Oezel, Feryal; Rieke, George H.; Cooney, Alan E-mail: dpsaltis@as.arizona.edu E-mail: grieke@as.arizona.edu
2012-04-10
We develop a new numerical algorithm to model collisional cascades in debris disks. Because of the large dynamical range in particle masses, we solve the integro-differential equations describing erosive and catastrophic collisions in a particle-in-a-box approach, while treating the orbital dynamics of the particles in an approximate fashion. We employ a new scheme for describing erosive (cratering) collisions that yields a continuous set of outcomes as a function of colliding masses. We demonstrate the stability and convergence characteristics of our algorithm and compare it with other treatments. We show that incorporating the effects of erosive collisions results in a decay of the particle distribution that is significantly faster than with purely catastrophic collisions.
Numerical model of long-lived Jovian vortices
NASA Technical Reports Server (NTRS)
Ingersoll, A. P.; Cuong, P. G.
1981-01-01
The extension of the measured zonal velocity profile into the adiabatic interior of Jupiter, while eddies and large oval structures are confined to a shallow stably-stratified upper layer, are assumed in a nonlinear numerical model of long-lived Jovian vortices. In agreement of the observed flows of Jupiter, each vortex is stationary with respect to the shear flow at a critical latitude that is close to the latitude of the vortex center. The solutions obtained are strongly nonlinear, in contrast to the solitary wave solutions that are the weakly nonlinear extensions of ultralong linear waves. The merging of two stable vortices upon collision, rather than the non-interaction predicted by solitary wave theory, is in keeping with Jovian vortex observations. It is suggested that long-lived vortices maintain themselves against dissipation by absorbing smaller vortices produced by convection.
Numerical modeling of perovskite solar cells with a planar structure
NASA Astrophysics Data System (ADS)
Malyukov, S. P.; Sayenko, A. V.; Ivanova, A. V.
2016-10-01
The paper is devoted to the research and development of high-efficiency solar cells with a planar perovskite n-i-p structure. A numerical model of this solar cell in the drift- diffusion approximation based on Poisson equation and continuity equations provided to determine their photoelectric characteristics and design optimization. The author considers the spectral photogeneration, bulk and surface recombination, transport charge carriers in perovskite and their collection by the electron and hole transport layers. As a result of the simulation, it was obtained efficiency dependence on perovskite absorber material thickness and lifetime (diffusion length) of the charge carriers. It is found that in addition to absorption coefficient optimal perovskite thickness is determined largely by the charge carrier diffusion length, and it has the upper limit in thickness of 500-600 nm.
Modeling extracellular electrical stimulation: II. Computational validation and numerical results.
Tahayori, Bahman; Meffin, Hamish; Dokos, Socrates; Burkitt, Anthony N; Grayden, David B
2012-12-01
The validity of approximate equations describing the membrane potential under extracellular electrical stimulation (Meffin et al 2012 J. Neural Eng. 9 065005) is investigated through finite element analysis in this paper. To this end, the finite element method is used to simulate a cylindrical neurite under extracellular stimulation. Laplace's equations with appropriate boundary conditions are solved numerically in three dimensions and the results are compared to the approximate analytic solutions. Simulation results are in agreement with the approximate analytic expressions for longitudinal and transverse modes of stimulation. The range of validity of the equations describing the membrane potential for different values of stimulation and neurite parameters are presented as well. The results indicate that the analytic approach can be used to model extracellular electrical stimulation for realistic physiological parameters with a high level of accuracy.
Numerical Modeling of Impact Initiation of High Explosives
Wu, C J; Piggott, T; Yoh, J; Reaugh, J
2006-05-31
We performed continuum mechanics simulations to examine the behavior of energetic materials in Ballistic Chamber Impact (BIC) experiments, using an Arbitrary Lagrangian-Eulerian code (ALE3D). Our simulations revealed that interface friction plays an important role in inducing the formation of shear bands, which result in 'hot spots' for ignition. The temperature localization during BIC impact was found to be significant in materials with high yield strength. In those materials, there are multiple locations inside shear bands can achieve temperatures exceeding the threshold temperature for reaction. In addition, we investigated the relevant parameters influencing the pressure profile of a BIC test by numerical analysis from a simple phenomenological model. To our surprise, we found that the peaks of BIC pressure profiles not only can be a result of multi-center chemical reactions, but can also arise from factors associated apparatus configuration.
Numerical modeling of radionuclide migration through a borehole disposal site.
Yeboah, Serwaa; Akiti, Thomas T; Fletcher, John J
2014-01-01
The migration of radionuclides from a borehole repository located about 20 km from the Akwapim fault line which lies in an area of high seismicity was analyzed for some selected radionuclides. In the event of a seismic activity, fractures and faults could be rejuvenated or initiated resulting in container failure leading to the release of radionuclides. A numerical model was solved using a two-dimensional finite element code (Comsol Multiphysics) by taking into account the effect of heterogeneities. Results showed that, the fractured medium created preferential pathways indicating that, fault zones generated potential paths for released radionuclides from a radioactive waste repository. The results obtained showed that variations in hydraulic conductivity as a result of the heterogeneity considered within the domain significantly affected the direction of flow.
Numerical simulations for a variable order fractional Schnakenberg model
NASA Astrophysics Data System (ADS)
Hammouch, Z.; Mekkaoui, T.; Belgacem, F. B. M.
2014-12-01
This paper is concerned with the numerical solutions of a variable-order space-time fractional reaction-diffusion model. The space-time fractional derivative is considered in the sense of Riesz-Feller, the system is defined by replacing the second order space derivatives with the variable Riesz-Feller derivatives. The problem is solved by an explicit finite difference method. Finally, simulation results to this problem are presented and discussed. In the original article PDF file, as supplied to AIP Publishing, the name and affiliation of author F. B. M. Belgacem was missing due to a Latex compiling error. This article was updated on 29 January 2015 to correct that error.
Numerical Investigation of a Model Scramjet Combustor Using DDES
NASA Astrophysics Data System (ADS)
Shin, Junsu; Sung, Hong-Gye
2017-04-01
Non-reactive flows moving through a model scramjet were investigated using a delayed detached eddy simulation (DDES), which is a hybrid scheme combining Reynolds averaged Navier-Stokes scheme and a large eddy simulation. The three dimensional Navier-Stokes equations were solved numerically on a structural grid using finite volume methods. An in-house was developed. This code used a monotonic upstream-centered scheme for conservation laws (MUSCL) with an advection upstream splitting method by pressure weight function (AUSMPW+) for space. In addition, a 4th order Runge-Kutta scheme was used with preconditioning for time integration. The geometries and boundary conditions of a scramjet combustor operated by DLR, a German aerospace center, were considered. The profiles of the lower wall pressure and axial velocity obtained from a time-averaged solution were compared with experimental results. Also, the mixing efficiency and total pressure recovery factor were provided in order to inspect the performance of the combustor.
Constraining Slab Breakoff Induced Magmatism through Numerical Modelling
NASA Astrophysics Data System (ADS)
Freeburn, R.; Van Hunen, J.; Maunder, B. L.; Magni, V.; Bouilhol, P.
2015-12-01
Post-collisional magmatism is markedly different in nature and composition than pre-collisional magmas. This is widely interpreted to mark a change in the thermal structure of the system due to the loss of the oceanic slab (slab breakoff), allowing a different source to melt. Early modelling studies suggest that when breakoff takes place at depths shallower than the overriding lithosphere, magmatism occurs through both the decompression of upwelling asthenopshere into the slab window and the thermal perturbation of the overriding lithosphere (Davies & von Blanckenburg, 1995; van de Zedde & Wortel, 2001). Interpretations of geochemical data which invoke slab breakoff as a means of generating magmatism mostly assume these shallow depths. However more recent modelling results suggest that slab breakoff is likely to occur deeper (e.g. Andrews & Billen, 2009; Duretz et al., 2011; van Hunen & Allen, 2011). Here we test the extent to which slab breakoff is a viable mechanism for generating melting in post-collisional settings. Using 2-D numerical models we conduct a parametric study, producing models displaying a range of dynamics with breakoff depths ranging from 150 - 300 km. Key models are further analysed to assess the extent of melting. We consider the mantle wedge above the slab to be hydrated, and compute the melt fraction by using a simple parameterised solidus. Our models show that breakoff at shallow depths can generate a short-lived (< 3 Myr) pulse of mantle melting, through the hydration of hotter, undepleted asthenosphere flowing in from behind the detached slab. However, our results do not display the widespread, prolonged style of magmatism, observed in many post-collisional areas, suggesting that this magmatism may be generated via alternative mechanisms. This further implies that using magmatic observations to constrain slab breakoff is not straightforward.
Numerical modeling, calibration, and validation of an ultrasonic separator.
Cappon, Hans; Keesman, Karel J
2013-03-01
Our overall goal is to apply acoustic separation technology for the recovery of valuable particulate matter from wastewater in industry. Such large-scale separator systems require detailed design and evaluation to optimize the system performance at the earliest stage possible. Numerical models can facilitate and accelerate the design of this application; therefore, a finite element (FE) model of an ultrasonic particle separator is a prerequisite. In our application, the particle separator consists of a glass resonator chamber with a piezoelectric transducer attached to the glass by means of epoxy adhesive. Separation occurs most efficiently when the system is operated at its main eigenfrequency. The goal of the paper is to calibrate and validate a model of a demonstrator ultrasonic separator, preserving known physical parameters and estimating the remaining unknown or less-certain parameters to allow extrapolation of the model beyond the measured system. A two-step approach was applied to obtain a validated model of the separator. The first step involved the calibration of the piezoelectric transducer. The second step, the subject of this paper, involves the calibration and validation of the entire separator using nonlinear optimization techniques. The results show that the approach lead to a fully calibrated 2-D model of the empty separator, which was validated with experiments on a filled separator chamber. The large sensitivity of the separator to small variations indicated that such a system should either be made and operated within tight specifications to obtain the required performance or the operation of the system should be adaptable to cope with a slightly off-spec system, requiring a feedback controller.
Three dimensional numerical modeling of land subsidence in Shanghai
NASA Astrophysics Data System (ADS)
Ye, S.; Luo, Y.; Wu, J.; Teatini, P.; Wang, H.; Jiao, X.
2015-11-01
Shanghai city has been suffering land subsidence caused by overly exploitation of ground water since 1921, which is a serious problem for this coastal city with altitude of 2.2-4.8 m above mean sea level. The largest cumulative land subsidence amounted to 2.6 m in the downtown area. Measures to decrease the ground water exploitation, change the pumping aquifers, and increase aquifer artificial recharge have been used to mitigate land subsidence since 1961. It is necessary to develop a proper numerical model to simulate and predict land subsidence. In this study, a decoupled three-dimensional (3-D) finite element land subsidence model including a 3-D ground water flow model and a 3-D geo-mechanical model was developed to simulate the 3-D deformation of the aquifer systems in the center area of Shanghai. The area of downtown Shanghai is 660 km2, with 10 million inhabitants, dense high buildings, and 11 metro lines. The simulation spans the period from 1979 to 1995. Two different assumptions have been tested on the side boundary, i.e., precluding the three components of the displacement, or assuming a free-displacement condition. The distribution of calculated land subsidence and horizontal displacements in different aquifers was analyzed. The computed vertical displacement fitted well with the available observations. It has been verified that the two different assumptions on the lateral boundaries in the geo-mechanical model caused different results just limited on nodes close to boundary. The developed 3-D land subsidence model is reasonable and can be used to simulate and predict 3-D movement of aquifer systems in the center area of Shanghai, which could provide scientific support to local government in controlling land subsidence and differential movements of the land surface.
Numerical modeling of Atlantic hurricanes moving into the middle latitudes
NASA Astrophysics Data System (ADS)
Fogarty, Christopher T.
Hurricanes that form over the Atlantic Ocean very frequently migrate into the middle latitudes where they encounter very different oceanic and atmospheric conditions than in the tropics. Cool sea surface temperatures (SSTs) cause these storms to weaken and become thermodynamically decoupled from the ocean, while baroclinic atmospheric environments often cause them to transform into extratropical storms---a process known as extratropical transition (ET). The changing structure of these storms in the middle latitudes presents many unique forecasting challenges related to the increasing asymmetry in moisture and wind fields, and their potentially destructive nature. An examination of three such events over Eastern Canada---using a combination of observations and a numerical model---forms the foundation of this work, with an emphasis on applying the research to weather forecasting. The case studies include Hurricane Michael (2000), Hurricane Karen (2001) and Hurricane Juan (2003). Hurricane Michael intensified in a strongly-baroclinc environment and evolved into an intense extratropical storm over Newfoundland. Karen also underwent ET, but weakened quickly during its approach to Nova Scotia, while Hurricane Juan struck the province as a category-two hurricane, experiencing only marginal weakening over anomalously warm SSTs. In essence, these cases represent a cross section of the behavior of many tropical cyclones in this part of the world. Hindcast simulations are conducted for each event using the Canadian Mesoscale Compressible Community (MC2) model with a synthetic, observationally-consistent hurricane vortex used in the model's initial conditions. Sensitivity experiments are run for each case by modifying initial specifications of the vortex, model physics parameterizations, and surface boundary conditions like SST. In the case of Hurricane Juan, it is determined that the anomalously-warm SSTs played a significant role in the landfall intensity, while Hurricane
On the time to steady state: insights from numerical modeling
NASA Astrophysics Data System (ADS)
Goren, L.; Willett, S.; McCoy, S. W.; Perron, J.
2013-12-01
How fast do fluvial landscapes approach steady state after an application of tectonic or climatic perturbation? While theory and some numerical models predict that the celerity of the advective wave (knickpoint) controls the response time for perturbations, experiments and other landscape evolution models demonstrate that the time to steady state is much longer than the theoretically predicted response time. We posit that the longevity of transient features and the time to steady state are controlled by the stability of the topology and geometry of channel networks. Evolution of a channel network occurs by a combination of discrete capture events and continuous migration of water divides, processes, which are difficult to represent accurately in landscape evolution models. We therefore address the question of the time to steady state using the DAC landscape evolution model that solves accurately for the location of water divides, using a combination of analytical solution for hillslopes and low-order channels together with a numerical solution for higher order channels. DAC also includes an explicit capture criterion. We have tested fundamental predictions from DAC and show that modeled networks reproduce natural network characteristics such as the Hack's exponent and coefficient and the fractal dimension. We define two steady-state criteria: a topographic steady state, defined by global, pointwise steady elevation, and a topological steady state defined as the state in which no further reorganization of the drainage network takes place. Analyzing block uplift simulations, we find that the time to achieve either topographic or topological steady state exceeds by an order of magnitude the theoretical response time of the fluvial network. The longevity of the transient state is the result of the area feedback, by which, migration of a divide changes the local contributing area. This change propagates downstream as a slope adjustment, forcing further divide migrations
A General Framework for Multiphysics Modeling Based on Numerical Averaging
NASA Astrophysics Data System (ADS)
Lunati, I.; Tomin, P.
2014-12-01
In the last years, multiphysics (hybrid) modeling has attracted increasing attention as a tool to bridge the gap between pore-scale processes and a continuum description at the meter-scale (laboratory scale). This approach is particularly appealing for complex nonlinear processes, such as multiphase flow, reactive transport, density-driven instabilities, and geomechanical coupling. We present a general framework that can be applied to all these classes of problems. The method is based on ideas from the Multiscale Finite-Volume method (MsFV), which has been originally developed for Darcy-scale application. Recently, we have reformulated MsFV starting with a local-global splitting, which allows us to retain the original degree of coupling for the local problems and to use spatiotemporal adaptive strategies. The new framework is based on the simple idea that different characteristic temporal scales are inherited from different spatial scales, and the global and the local problems are solved with different temporal resolutions. The global (coarse-scale) problem is constructed based on a numerical volume-averaging paradigm and a continuum (Darcy-scale) description is obtained by introducing additional simplifications (e.g., by assuming that pressure is the only independent variable at the coarse scale, we recover an extended Darcy's law). We demonstrate that it is possible to adaptively and dynamically couple the Darcy-scale and the pore-scale descriptions of multiphase flow in a single conceptual and computational framework. Pore-scale problems are solved only in the active front region where fluid distribution changes with time. In the rest of the domain, only a coarse description is employed. This framework can be applied to other important problems such as reactive transport and crack propagation. As it is based on a numerical upscaling paradigm, our method can be used to explore the limits of validity of macroscopic models and to illuminate the meaning of
In Marriage of Model and Numerics, Glimpses of the Future
NASA Astrophysics Data System (ADS)
Nejadmalayeri, Alireza; Vasilyev, Oleg V.; Vezolainen, Alexei
2012-11-01
A newly defined concept of m-refinement (model-refinement), which provides two-way coupling of physical models and numerical methods, is employed to study the Reynolds scaling of SCALES with constant levels of fidelity. Within the context of wavelet-based methods, this new hybrid methodology provides a hierarchical space/time dynamically adaptive automatic smooth transition from resolving the Kolmogorov length-scale (WDNS) to decomposing deterministic-coherent/stochastic-incoherent modes (CVS) to capturing more/less energetic structures (SCALES). This variable fidelity turbulence modeling approach utilizes a unified single solver framework by means of a Lagrangian spatially varying thresholding technique. The fundamental findings of this computational complexity study are summarized as follows: 1) SCALES can achieve the objective of ``controlling the captured flow-physics as desired'' by profoundly small number of spatial modes; 2) Reynolds scaling of constant-dissipation SCALES is the same regardless of fidelity of the simulations; 3) the number of energy containing structures at a fixed level of resolved turbulent kinetic energy scales linearly with Re; and 4) the fractal dimension of coherent energy containing structures is close to unity. This work was supported by NSF under grant No. CBET-0756046.
Numerical Modeling of High-Temperature Corrosion Processes
NASA Technical Reports Server (NTRS)
Nesbitt, James A.
1995-01-01
Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.
A Comprehensive Numerical Model for Simulating Fluid Transport in Nanopores.
Zhang, Yuan; Yu, Wei; Sepehrnoori, Kamy; Di, Yuan
2017-01-16
Since a large amount of nanopores exist in tight oil reservoirs, fluid transport in nanopores is complex due to large capillary pressure. Recent studies only focus on the effect of nanopore confinement on single-well performance with simple planar fractures in tight oil reservoirs. Its impacts on multi-well performance with complex fracture geometries have not been reported. In this study, a numerical model was developed to investigate the effect of confined phase behavior on cumulative oil and gas production of four horizontal wells with different fracture geometries. Its pore sizes were divided into five regions based on nanopore size distribution. Then, fluid properties were evaluated under different levels of capillary pressure using Peng-Robinson equation of state. Afterwards, an efficient approach of Embedded Discrete Fracture Model (EDFM) was applied to explicitly model hydraulic and natural fractures in the reservoirs. Finally, three fracture geometries, i.e. non-planar hydraulic fractures, non-planar hydraulic fractures with one set natural fractures, and non-planar hydraulic fractures with two sets natural fractures, are evaluated. The multi-well performance with confined phase behavior is analyzed with permeabilities of 0.01 md and 0.1 md. This work improves the analysis of capillarity effect on multi-well performance with complex fracture geometries in tight oil reservoirs.
Numerical modeling of higher order magnetic moments in UXO discrimination
Sanchez, V.; Yaoguo, L.; Nabighian, M.N.; Wright, D.L.
2008-01-01
The surface magnetic anomaly observed in unexploded ordnance (UXO) clearance is mainly dipolar, and consequently, the dipole is the only magnetic moment regularly recovered in UXO discrimination. The dipole moment contains information about the intensity of magnetization but lacks information about the shape of the target. In contrast, higher order moments, such as quadrupole and octupole, encode asymmetry properties of the magnetization distribution within the buried targets. In order to improve our understanding of magnetization distribution within UXO and non-UXO objects and to show its potential utility in UXO clearance, we present a numerical modeling study of UXO and related metallic objects. The tool for the modeling is a nonlinear integral equation describing magnetization within isolated compact objects of high susceptibility. A solution for magnetization distribution then allows us to compute the magnetic multipole moments of the object, analyze their relationships, and provide a depiction of the anomaly produced by different moments within the object. Our modeling results show the presence of significant higher order moments for more asymmetric objects, and the fields of these higher order moments are well above the noise level of magnetic gradient data. The contribution from higher order moments may provide a practical tool for improved UXO discrimination. ?? 2008 IEEE.
Numerical modelling methods for predicting antenna performance on aircraft
NASA Astrophysics Data System (ADS)
Kubina, S. J.
1983-09-01
Typical case studies that involve the application of Moment Methods to the prediction of the radiation characteristics of antennas in the HF frequency band are examined. The examples consist of the analysis of a shorted transmission line HF antenna on a CHSS-2/Sea King helicopter, wire antennas on the CP-140/Aurora patrol aircraft and a long dipole antenna on the Space Shuttle Orbiter spacecraft. In each of these cases the guidelines for antenna modeling by the use of the program called the Numerical Electromagnetic Code are progressively applied and results are compared to measurements made by the use of scale-model techniques. In complex examples of this type comparisons based on individual radiation patterns are insufficient for the validation of computer models. A volumetric method of radiation pattern comparison is used based on criteria that result from pattern integration and that are related to communication system performance. This is supplemented by hidden-surface displays of an entire set of conical radiation patterns resulting from measurements and computations. Antenna coupling considerations are discussed for the case of the dual HF installation on the CP-140/Aurora aircraft.
A Comprehensive Numerical Model for Simulating Fluid Transport in Nanopores
Zhang, Yuan; Yu, Wei; Sepehrnoori, Kamy; Di, Yuan
2017-01-01
Since a large amount of nanopores exist in tight oil reservoirs, fluid transport in nanopores is complex due to large capillary pressure. Recent studies only focus on the effect of nanopore confinement on single-well performance with simple planar fractures in tight oil reservoirs. Its impacts on multi-well performance with complex fracture geometries have not been reported. In this study, a numerical model was developed to investigate the effect of confined phase behavior on cumulative oil and gas production of four horizontal wells with different fracture geometries. Its pore sizes were divided into five regions based on nanopore size distribution. Then, fluid properties were evaluated under different levels of capillary pressure using Peng-Robinson equation of state. Afterwards, an efficient approach of Embedded Discrete Fracture Model (EDFM) was applied to explicitly model hydraulic and natural fractures in the reservoirs. Finally, three fracture geometries, i.e. non-planar hydraulic fractures, non-planar hydraulic fractures with one set natural fractures, and non-planar hydraulic fractures with two sets natural fractures, are evaluated. The multi-well performance with confined phase behavior is analyzed with permeabilities of 0.01 md and 0.1 md. This work improves the analysis of capillarity effect on multi-well performance with complex fracture geometries in tight oil reservoirs. PMID:28091599
A Comprehensive Numerical Model for Simulating Fluid Transport in Nanopores
NASA Astrophysics Data System (ADS)
Zhang, Yuan; Yu, Wei; Sepehrnoori, Kamy; di, Yuan
2017-01-01
Since a large amount of nanopores exist in tight oil reservoirs, fluid transport in nanopores is complex due to large capillary pressure. Recent studies only focus on the effect of nanopore confinement on single-well performance with simple planar fractures in tight oil reservoirs. Its impacts on multi-well performance with complex fracture geometries have not been reported. In this study, a numerical model was developed to investigate the effect of confined phase behavior on cumulative oil and gas production of four horizontal wells with different fracture geometries. Its pore sizes were divided into five regions based on nanopore size distribution. Then, fluid properties were evaluated under different levels of capillary pressure using Peng-Robinson equation of state. Afterwards, an efficient approach of Embedded Discrete Fracture Model (EDFM) was applied to explicitly model hydraulic and natural fractures in the reservoirs. Finally, three fracture geometries, i.e. non-planar hydraulic fractures, non-planar hydraulic fractures with one set natural fractures, and non-planar hydraulic fractures with two sets natural fractures, are evaluated. The multi-well performance with confined phase behavior is analyzed with permeabilities of 0.01 md and 0.1 md. This work improves the analysis of capillarity effect on multi-well performance with complex fracture geometries in tight oil reservoirs.
Numerical modeling of high-temperature corrosion processes
Nesbitt, J.A.
1995-08-01
Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element may form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.
Numerical modeling of magnetic moments for UXO applications
Sanchez, V.; Li, Y.; Nabighian, M.; Wright, D.
2006-01-01
The surface magnetic anomaly observed in UXO clearance is mainly dipolar and, consequently, the dipole is the only magnetic moment regularly recovered in UXO applications. The dipole moment contains information about intensity of magnetization but lacks information about shape. In contrast, higher-order moments, such as quadrupole and octupole, encode asymmetry properties of the magnetization distribution within the buried targets. In order to improve our understanding of magnetization distribution within UXO and non-UXO objects and its potential utility in UXO clearance, we present a 3D numerical modeling study for highly susceptible metallic objects. The basis for the modeling is the solution of a nonlinear integral equation describing magnetization within isolated objects. A solution for magnetization distribution then allows us to compute magnetic moments of the object, analyze their relationships, and provide a depiction of the surface anomaly produced by different moments within the object. Our modeling results show significant high-order moments for more asymmetric objects situated at depths typical of UXO burial, and suggest that the increased relative contribution to magnetic gradient data from these higher-order moments may provide a practical tool for improved UXO discrimination.
Numerical study of similarity in prototype and model pumped turbines
NASA Astrophysics Data System (ADS)
Li, Z. J.; Wang, Z. W.; Bi, H. L.
2014-03-01
Similarity study of prototype and model pumped turbines are performed by numerical simulation and the partial discharge case is analysed in detail. It is found out that in the RSI (rotor-stator interaction) region where the flow is convectively accelerated with minor flow separation, a high level of similarity in flow patterns and pressure fluctuation appear with relative pressure fluctuation amplitude of model turbine slightly higher than that of prototype turbine. As for the condition in the runner where the flow is convectively accelerated with severe separation, similarity fades substantially due to different topology of flow separation and vortex formation brought by distinctive Reynolds numbers of the two turbines. In the draft tube where the flow is diffusively decelerated, similarity becomes debilitated owing to different vortex rope formation impacted by Reynolds number. It is noted that the pressure fluctuation amplitude and characteristic frequency of model turbine are larger than those of prototype turbine. The differences in pressure fluctuation characteristics are discussed theoretically through dimensionless Navier-Stokes equation. The above conclusions are all made based on simulation without regard to the penstock response and resonance.
Numerical Simulations of Separated Flows Using Wall-Modeled LES
NASA Astrophysics Data System (ADS)
Vane, Zachary; Ortega, Jason; Salari, Kambiz
2014-11-01
Calculations using an unstructured, wall-modeled large eddy simulation (WMLES) solver are performed for several high Reynolds number test cases of interest. While the equilibrium formulation of this wall-model (Bodart, Larsson & Moin, AIAA 2013-2724) has proven to be accurate for steady, attached boundary layers, its application to non-equilibrium or highly three-dimensional problems has yet to be fully explored. A series of turbulent flows that exhibit boundary layer separation due to the geometries involved in each test case are considered. First, spanwise-periodic simulations for the flow over periodic hills are performed at multiple Reynolds numbers. Next, calculations involving separation caused by three-dimensional bodies are used to generate more complex flow fields and to evaluate the accuracy of the WMLES in the separated wake region downstream. The performance of the WMLES is quantified through comparisons with existing numerical and experimental data sets. The effects of grid resolution and variations in several wall-model parameters are also investigated to determine their influence on the overall calculation.
Two-Dimensional Numerical Modeling of Anthropogenic Beach Berm Erosion
NASA Astrophysics Data System (ADS)
Shakeri Majd, M.; Schubert, J.; Gallien, T.; Sanders, B. F.
2014-12-01
Anthropogenic beach berms (sometimes called artificial berms or artificial dunes) temporarily enhance the ability of beaches to withstand overtopping and thus guard against coastal flooding. However, the combination of a rising tide, storm surge, and/or waves may erode anthropogenic berms in a matter of hours or less and cause flooding [1]. Accurate forecasts of coastal flooding therefore demand the ability to predict where and when berms fail and the volume of water that overtops into defended coastal lowlands. Here, a two-dimensional numerical model of swash zone waves and erosion is examined as a tool for predicting the erosion of anthropogenic beach berms. The 2D model is known as a Debris Flow Model (DFM) because it tightly couples flow and sediment transport within an approximate Riemann solver and is able to resolve shocks in fluid/sediment interface [2]. The DFM also includes a two dimensional avalanching scheme to account for gravity-driven slumping of steep slopes. The performance of the DFM is examined with field-scale anthropogenic berm erosion data collected at Newport Beach, California. Results show that the DFM can be applied in the swash zone to resolve wave-by-wave flow and sediment transport. Results also show that it is possible to calibrate the model for a particular event, and then predict erosion for another event, but predictions are sensitive to model parameters, such as erosion and avalanching. References: [1] Jochen E. Schubert, Timu W. Gallien, Morteza Shakeri Majd, and Brett F. Sanders. Terrestrial laser scanning of anthropogenic beach berm erosion and overtopping. Journal of Coastal Research In-Press, 2014. [2] Morteza Shakeri Majd and Brett F. Sanders. The LHLLC scheme for Two-Layer and Two-Phase transcritical flows over a mobile bed with avalanching, wetting and drying. Advances in Water Resources, 64, 16-31, 2014.
Experimental validation of a numerical model for subway induced vibrations
NASA Astrophysics Data System (ADS)
Gupta, S.; Degrande, G.; Lombaert, G.
2009-04-01
This paper presents the experimental validation of a coupled periodic finite element-boundary element model for the prediction of subway induced vibrations. The model fully accounts for the dynamic interaction between the train, the track, the tunnel and the soil. The periodicity or invariance of the tunnel and the soil in the longitudinal direction is exploited using the Floquet transformation, which allows for an efficient formulation in the frequency-wavenumber domain. A general analytical formulation is used to compute the response of three-dimensional invariant or periodic media that are excited by moving loads. The numerical model is validated by means of several experiments that have been performed at a site in Regent's Park on the Bakerloo line of London Underground. Vibration measurements have been performed on the axle boxes of the train, on the rail, the tunnel invert and the tunnel wall, and in the free field, both at the surface and at a depth of 15 m. Prior to these vibration measurements, the dynamic soil characteristics and the track characteristics have been determined. The Bakerloo line tunnel of London Underground has been modelled using the coupled periodic finite element-boundary element approach and free field vibrations due to the passage of a train at different speeds have been predicted and compared to the measurements. The correspondence between the predicted and measured response in the tunnel is reasonably good, although some differences are observed in the free field. The discrepancies are explained on the basis of various uncertainties involved in the problem. The variation in the response with train speed is similar for the measurements as well as the predictions. This study demonstrates the applicability of the coupled periodic finite element-boundary element model to make realistic predictions of the vibrations from underground railways.
Comparing Numerical Spall Simulations with a Nonlinear Spall Formation Model
NASA Astrophysics Data System (ADS)
Ong, L.; Melosh, H. J.
2012-12-01
Spallation accelerates lightly shocked ejecta fragments to speeds that can exceed the escape velocity of the parent body. We present high-resolution simulations of nonlinear shock interactions in the near surface. Initial results show the acceleration of near-surface material to velocities up to 1.8 times greater than the peak particle velocity in the detached shock, while experiencing little to no shock pressure. These simulations suggest a possible nonlinear spallation mechanism to produce the high-velocity, low show pressure meteorites from other planets. Here we pre-sent the numerical simulations that test the production of spall through nonlinear shock interactions in the near sur-face, and compare the results with a model proposed by Kamegai (1986 Lawrence Livermore National Laboratory Report). We simulate near-surface shock interactions using the SALES_2 hydrocode and the Murnaghan equation of state. We model the shock interactions in two geometries: rectangular and spherical. In the rectangular case, we model a planar shock approaching the surface at a constant angle phi. In the spherical case, the shock originates at a point below the surface of the domain and radiates spherically from that point. The angle of the shock front with the surface is dependent on the radial distance of the surface point from the shock origin. We model the target as a solid with a nonlinear Murnaghan equation of state. This idealized equation of state supports nonlinear shocks but is tem-perature independent. We track the maximum pressure and maximum velocity attained in every cell in our simula-tions and compare them to the Hugoniot equations that describe the material conditions in front of and behind the shock. Our simulations demonstrate that nonlinear shock interactions in the near surface produce lightly shocked high-velocity material for both planar and cylindrical shocks. The spall is the result of the free surface boundary condi-tion, which forces a pressure gradient
Sheet Hydroforming Pre-bulging Numerical Model Improvement
NASA Astrophysics Data System (ADS)
Gabriele, Papadia; Antonio, Del Prete; Alfredo, Anglani
2010-06-01
Sheet hydroforming has gained increasing interest during the last years, especially as application in the manufacturing of some components for automotive, aerospace, and electrical appliances[1,2]. Many parameters influence the process of sheet hydroforming, one of them is the pre-bulging[3]. Different studies have been also done to determine the optimal forming parameters through FEA[4,5]. In the case of sheet hydromechanical forming process the blank is first placed on the lower die (a fluid chamber combined with draw ring) and then, after sealing the blank between blank holder and draw ring, punch progresses to deform the blank[6]. Pressure of the fluid chamber is also increased simultaneously with the punch progression[7]. In this paper, the pre-bulging effect on active hydromechanical deep drawing process has been investigated experimentally and numerically. Pre-bulging includes two parameters: pre-bulging height and pre-bulging pressure, which influence the forming process significantly[3]. Numerical simulations and experimental tests were carried out for a given shape to investigate the pre-bulging effect on the maximum hydroforming depth. During this activity, the authors have verified that the low numerical—experimental accuracy detected it was caused also by the simulation of the pre-bulging phase. The authors have analyzed the problem to define a correct procedure to simulate the pre-bulging phase. From this point of view, nine different levels of pre-bulging (taking into account the level equal to zero also) have been tested to experimentally calculate the Thickness Percentage Reduction (TPR) at the maximum pre-bulging height. For each level, the experiment has been conducted two times for a total number of eighteen experiments. The experimental TPR values have been compared with the numerical ones reaching a good accuracy only in the case of pre-bulging height greater than forty millimeters. The experimental activity has given a valid contribution to
Dispersion of conservative properties for SGD effects by numerical modeling
NASA Astrophysics Data System (ADS)
Gallegos, G.; Marino-Tapia, I.; Enriquez, C.
2013-05-01
The submarine groundwater discharges around de coasts of theYucatán Peninsula are very common because of its karstic nature. These discharges of fresh water into the sea can change the thermohaline conditions of the region. There are several studies that demonstrate that point submarine groundwater discharges can change the superficial temperature and haline conditions near the point-SGD. Furthermore, there is evidence that considerable concentrations of nutrients are transported to the sea via SGDs. In order to quantify the area of influence of a point-SGD and the ability of the coastal system to dissipate the ground water, this study presents a numerical simulation of a point-SGD on the north coast of Yucatán, Dzilam Bravo. Teh flow recorded for this SGD is ~1m^3/s and it is located 200m offshore in waters of less than 2m detph.. The numerical simulation was carried out in the model DELFT-3D which has been calibrated with water level and hydrodynamics data for the region with a grid of 486 x 243 nodes that cover an area of 6 km alongshore by 2 km crosshore with a resolution of 14 m. Three ideal numerical scenarios were simulated: only wind forcing, only tidal forcing and wind-tide forcing. The real cases are for two different wind conditions, the first is a southeast wind, and the second is a breeze with an easterly component; the dominant winds in the region are easterly. Seasonal variation was also simulated; the two conditions that exist in the region are the rainy and dry seasons. The extreme events of ENSO and northerly storms locally known as "nortes" were also simulated. The results of the ideal set of scenarios shows wind as the principal forcing for dispersion and it governs the direction of the salinity gradient. The seasonal variations show that the area of influence in terms of salinity is also a function of the contrast between fresh and sea water, and finally the set of extreme condition simulations shows, in case of the northerly storms, that the
Kramers problem: numerical Wiener-Hopf-like model characteristics.
Ezin, A N; Samgin, A L
2010-11-01
Since the Kramers problem cannot be, in general, solved in terms of elementary functions, various numerical techniques or approximate methods must be employed. We present a study of characteristics for a particle in a damped well, which can be considered as a discretized version of the Melnikov [Phys. Rev. E 48, 3271 (1993)] turnover theory. The main goal is to justify the direct computational scheme to the basic Wiener-Hopf model. In contrast to the Melnikov approach, which implements factorization through a Cauchy-theorem-based formulation, we employ the Wiener-Levy theorem to reduce the Kramers problem to a Wiener-Hopf sum equation written in terms of Toeplitz matrices. This latter can provide a stringent test for the reliability of analytic approximations for energy distribution functions occurring in the Kramers problems at arbitrary damping. For certain conditions, the simulated characteristics are compared well with those determined using the conventional Fourier-integral formulas, but sometimes may differ slightly depending on the value of a dissipation parameter. Another important feature is that, with our method, we can avoid some complications inherent to the Melnikov method. The calculational technique reported in the present paper may gain particular importance in situations where the energy losses of the particle to the bath are a complex-shaped function of the particle energy and analytic solutions of desired accuracy are not at hand. In order to appreciate more readily the significance and scope of the present numerical approach, we also discuss concrete aspects relating to the field of superionic conductors.
Numerical Modeling of Tube Forming by HPTR Cold Pilgering Process
NASA Astrophysics Data System (ADS)
Sornin, D.; Pachón-Rodríguez, E. A.; Vanegas-Márquez, E.; Mocellin, K.; Logé, R.
2016-09-01
For new fast-neutron sodium-cooled Generation IV nuclear reactors, the candidate cladding materials for the very strong burn-up are ferritic and martensitic oxide dispersion strengthened grades. Classically, the cladding tube is cold formed by a sequence of cold pilger milling passes with intermediate heat treatments. This process acts upon the geometry and the microstructure of the tubes. Consequently, crystallographic texture, grain sizes and morphologies, and tube integrity are highly dependent on the pilgering parameters. In order to optimize the resulting mechanical properties of cold-rolled cladding tubes, it is essential to have a thorough understanding of the pilgering process. Finite Element Method (FEM) models are used for the numerical predictions of this task; however, the accuracy of the numerical predictions depends not only on the type of constitutive laws but also on the quality of the material parameters identification. Therefore, a Chaboche-type law which parameters have been identified on experimental observation of the mechanical behavior of the material is used here. As a complete three-dimensional FEM mechanical analysis of the high-precision tube rolling (HPTR) cold pilgering of tubes could be very expensive, only the evolution of geometry and deformation is addressed in this work. The computed geometry is compared to the experimental one. It is shown that the evolution of the geometry and deformation is not homogeneous over the circumference. Moreover, it is exposed that the strain is nonhomogeneous in the radial, tangential, and axial directions. Finally, it is seen that the dominant deformation mode of a material point evolves during HPTR cold pilgering forming.
Numerical and physical modelling of bubbly flow phenomena
Sangani, A.S.
1992-02-01
The objective of the proposed research is to develop a theoretical framework for analyzing various two-phase flows, with special emphasis on the flows, with special emphasis on the flows of gas- liquid dispersions. The macroscopic behavior of these flows depends on the details of the microstructure of the dispersion, and these details, in turn, depend on the nature of the flow. Given the very diverse nature of the flows and their complex dependence on the microstructure of the dispersion, it is unlikely that a single set of equations, similar to the Navier-Stokes equations for homogeneous fluids, will apply to all the different situations. What is possible, however, is to develop general methodologies that can be used to examine specific situations and a general understanding about different kinds of macroscopic flows. The aim of the proposed research is to develop efficient numerical techniques for carrying out dynamic simulations of flows of dispersions and to apply them to a carefully selected problems whose solutions would reveal important qualitative as well as quantitative insights into the complex interdependence of the microstructure and macroscopic properties of the flows. These numerical techniques are to be supplemented with the techniques of ensemble averaging and statistical physics to obtain results that could be used in modelling more complicated flows through a set of relatively simple equations. Two classes of macroscopic flows were analyzed in detail during the current funding period. The first is the oscillatory flows, as in the case of acoustic or pressure wave propagation through bubbly liquids, and the second is convective flows as in bubbles rising through a liquid. 20 refs.
Numerical and physical modelling of bubbly flow phenomena. Progress report
Sangani, A.S.
1992-02-01
The objective of the proposed research is to develop a theoretical framework for analyzing various two-phase flows, with special emphasis on the flows, with special emphasis on the flows of gas- liquid dispersions. The macroscopic behavior of these flows depends on the details of the microstructure of the dispersion, and these details, in turn, depend on the nature of the flow. Given the very diverse nature of the flows and their complex dependence on the microstructure of the dispersion, it is unlikely that a single set of equations, similar to the Navier-Stokes equations for homogeneous fluids, will apply to all the different situations. What is possible, however, is to develop general methodologies that can be used to examine specific situations and a general understanding about different kinds of macroscopic flows. The aim of the proposed research is to develop efficient numerical techniques for carrying out dynamic simulations of flows of dispersions and to apply them to a carefully selected problems whose solutions would reveal important qualitative as well as quantitative insights into the complex interdependence of the microstructure and macroscopic properties of the flows. These numerical techniques are to be supplemented with the techniques of ensemble averaging and statistical physics to obtain results that could be used in modelling more complicated flows through a set of relatively simple equations. Two classes of macroscopic flows were analyzed in detail during the current funding period. The first is the oscillatory flows, as in the case of acoustic or pressure wave propagation through bubbly liquids, and the second is convective flows as in bubbles rising through a liquid. 20 refs.
FEM numerical model study of heating in magnetic nanoparticles
Pearce, John A.; Cook, Jason R.; Hoopes, P. Jack; Giustini, Andrew
2013-01-01
Electromagnetic heating of nanoparticles is complicated by the extremely short thermal relaxation time constants and difficulty of coupling sufficient power into the particles to achieve desired temperatures. Magnetic field heating by the hysteresis loop mechanism at frequencies between about 100 and 300 kHz has proven to be an effective mechanism in magnetic nanoparticles. Experiments at 2.45 GHz show that Fe3O4 magnetite nanoparticle dispersions in the range of 1012 to 1013 NP/mL also heat substantially at this frequency. An FEM numerical model study was undertaken to estimate the order of magnitude of volume power density, Qgen (W m−3) required to achieve significant heating in evenly dispersed and aggregated clusters of nanoparticles. The FEM models were computed using Comsol Multiphysics; consequently the models were confined to continuum formulations and did not include film nano-dimension heat transfer effects at the nanoparticle surface. As an example, the models indicate that for a single 36 nm diameter particle at an equivalent dispersion of 1013 NP/mL located within one control volume (1.0 × 10−19 m3) of a capillary vessel a power density in the neighborhood of 1017 (W m−3) is required to achieve a steady state particle temperature of 52 °C — the total power coupled to the particle is 2.44 μW. As a uniformly distributed particle cluster moves farther from the capillary the required power density decreases markedly. Finally, the tendency for particles in vivo to cluster together at separation distances much less than those of the uniform distribution further reduces the required power density. PMID:24386534
FEM numerical model study of heating in magnetic nanoparticles
NASA Astrophysics Data System (ADS)
Pearce, John A.; Cook, Jason R.; Hoopes, P. Jack; Giustini, Andrew
2011-03-01
Electromagnetic heating of nanoparticles is complicated by the extremely short thermal relaxation time constants and difficulty of coupling sufficient power into the particles to achieve desired temperatures. Magnetic field heating by the hysteresis loop mechanism at frequencies between about 100 and 300 kHz has proven to be an effective mechanism in magnetic nanoparticles. Experiments at 2.45 GHz show that Fe3O4 magnetite nanoparticle dispersions in the range of 1012 to 1013 NP/mL also heat substantially at this frequency. An FEM numerical model study was undertaken to estimate the order of magnitude of volume power density, Qgen (W m-3) required to achieve significant heating in evenly dispersed and aggregated clusters of nanoparticles. The FEM models were computed using Comsol Multiphysics; consequently the models were confined to continuum formulations and did not include film nano-dimension heat transfer effects at the nanoparticle surface. As an example, the models indicate that for a single 36 nm diameter particle at an equivalent dispersion of 1013 NP/mL located within one control volume (1.0 x 10-19 m3) of a capillary vessel a power density in the neighborhood of 1017 (W m-3) is required to achieve a steady state particle temperature of 52°C - the total power coupled to the particle is 2.44 μW. As a uniformly distributed particle cluster moves farther from the capillary the required power density decreases markedly. Finally, the tendency for particles in vivo to cluster together at separation distances much less than those of the uniform distribution further reduces the required power density.
Numerical modeling of the interstellar medium in galactic disks
NASA Technical Reports Server (NTRS)
Rosen, A.; Bregman, J. N.; Norman, Michael L.
1993-01-01
We have been developing detailed hydrodynamic models of the global interstellar medium in the hope of understanding the mass and volume occupied by various phases, as well as their structure and kinematics. In our model, the gas is modeled by one fluid while representative Pop 1 stars are modeled by a second fluid. The two fluids are coupled in that the gas forms into stars at a rate given by a Schmidt law while stellar mass loss returns matter into the gas phase (on a time scale of 100 Myr). Also, the stars heat the gas through stellar winds and the gas cools through optically thin radiation. The time behavior of these two fluids is studied in two spatial dimensions with the Eulerian finite difference numerical hydrodynamic code Zen. The two spatial dimensions are along the plane of a disk (x, total length of 2 kpc) and perpendicular to the disk (z, total height of +/- 15 kpc) and a galactic gravitational field in the z direction, typical of that at the solar circle, is imposed upon the simulation; self-gravity and rotation are absent. For the boundary conditions, outflow is permitted at the top and bottom of the grid (z = +/- 15 kpc) while periodic boundary conditions are imposed upon left and right sides of the grid. As initial conditions, we assumed a gaseous distribution like that seen for the H1 by earlier researchers, although the results are insensitive to the initial conditions. We have run simulations in which the heating due to stars, parameterized as a stellar wind velocity, a, is varied from low (a = 150 km/s), to intermediate (a = 300 km/s), to high (a = 600 km/s). Since the intermediate case is roughly equivalent to the Galactic energy injection rate from supernovae, this summary will concentrate on results from this simulation.
Thinning factor distributions viewed through numerical models of continental extension
NASA Astrophysics Data System (ADS)
Svartman Dias, Anna Eliza; Hayman, Nicholas W.; Lavier, Luc L.
2016-12-01
A long-standing question surrounding rifted margins concerns how the observed fault-restored extension in the upper crust is usually less than that calculated from subsidence models or from crustal thickness estimates, the so-called "extension discrepancy." Here we revisit this issue drawing on recently completed numerical results. We extract thinning profiles from four end-member geodynamic model rifts with varying width and asymmetry and propose tectonic models that best explain those results. We then relate the spatial and temporal evolution of upper to lower crustal thinning, or crustal depth-dependent thinning (DDT), and crustal thinning to mantle thinning, or lithospheric DDT, which are difficult to achieve in natural systems due to the lack of observations that constrain thinning at different stages between prerift extension and lithospheric breakup. Our results support the hypothesis that crustal DDT cannot be the main cause of the extension discrepancy, which may be overestimated because of the difficulty in recognizing distributed deformation, and polyphase and detachment faulting in seismic data. More importantly, the results support that lithospheric DDT is likely to dominate at specific stages of rift evolution because crustal and mantle thinning distributions are not always spatially coincident and at times are not even balanced by an equal magnitude of thinning in two dimensions. Moreover, either pure or simple shear models can apply at various points of time and space depending on the type of rift. Both DDT and pure/simple shear variations across space and time can result in observed complex fault geometries, uplift/subsidence, and thermal histories.
Numerical modeling of fluid migration in subduction zones
NASA Astrophysics Data System (ADS)
Walter, M. J.; Quinteros, J.; Sobolev, S. V.
2015-12-01
It is well known that fluids play a crucial role in subduction evolution. For example, mechanical weakening along tectonic interfaces, due to high fluid pressure, may enable oceanic subduction. Hence, the fluid content seems to be a critical parameter for subduction initiation. Studies have also shown a correlation between the location of slab dehydration and intermediate seismic activity. Furthermore, expelled fluids from the subduction slab affect the melting temperature, consequently, contributing to partial melting in the wedge above the down-going plate and extensive volcanism. In summary, fluids have a great impact on tectonic processes and therefore should be incorporated into geodynamic numerical models. Here we use existing approaches to couple and solve fluid flow equations in the SLIM-3D thermo-mechanical code. SLIM-3D is a three-dimensional thermo-mechanical code capable of simulating lithospheric deformation with elasto-visco-plastic rheology. It has been successfully applied to model geodynamic processes at different tectonic settings, including subduction zones. However, although SLIM-3D already includes many features, fluid migration has not been incorporated into the model yet. To this end, we coupled solid and fluid flow assuming that fluids flow through a porous and deformable solid. Thereby, we introduce a two-phase flow into the model, in which the Stokes flow is coupled with the Darcy law for fluid flow. Ultimately, the evolution of porosity is governed by a compaction pressure and the advection of the porous solid. We show the details of our implementation of the fluid flow into the existing thermo-mechanical finite element code and present first results of benchmarks and experiments. We are especially interested in the coupling of subduction processes and the evolution of the magmatic arc. Thereby, we focus on the key factors controlling magma emplacement and its influence on subduction processes.
Numerical Modeling of Conjugate Heat Transfer in Fluid Network
NASA Technical Reports Server (NTRS)
Majumdar, Alok
2004-01-01
Fluid network modeling with conjugate heat transfer has many applications in Aerospace engineering. In modeling unsteady flow with heat transfer, it is important to know the variation of wall temperature in time and space to calculate heat transfer between solid to fluid. Since wall temperature is a function of flow, a coupled analysis of temperature of solid and fluid is necessary. In cryogenic applications, modeling of conjugate heat transfer is of great importance to correctly predict boil-off rate in propellant tanks and chill down of transfer lines. In TFAWS 2003, the present author delivered a paper to describe a general-purpose computer program, GFSSP (Generalized Fluid System Simulation Program). GFSSP calculates flow distribution in complex flow circuit for compressible/incompressible, with or without heat transfer or phase change in all real fluids or mixtures. The flow circuit constitutes of fluid nodes and branches. The mass, energy and specie conservation equations are solved at the nodes where as momentum conservation equations are solved at the branches. The proposed paper describes the extension of GFSSP to model conjugate heat transfer. The network also includes solid nodes and conductors in addition to fluid nodes and branches. The energy conservation equations for solid nodes solves to determine the temperatures of the solid nodes simultaneously with all conservation equations governing fluid flow. The numerical scheme accounts for conduction, convection and radiation heat transfer. The paper will also describe the applications of the code to predict chill down of cryogenic transfer line and boil-off rate of cryogenic propellant storage tank.
Numerical modeling transport phenomena in proton exchange membrane fuel cells
NASA Astrophysics Data System (ADS)
Suh, DongMyung
To study the coupled phenomena occurring in proton exchange membrane fuel cells, a two-phase, one-dimensional, non-isothermal model is developed in the chapter 1. The model includes water phase change, proton transport in the membrane and electro-osmotic effect. The thinnest, but most complex layer in the membrane electrode assembly, catalyst layer, is considered an interfacial boundary between the gas diffusion layer and the membrane. Mass and heat transfer and electro-chemical reaction through the catalyst layer are formulated into equations, which are applied to boundary conditions for the gas diffusion layer and the membrane. Detail accounts of the boundary equations and the numerical solving procedure used in this work are given. The polarization curve is calculated at different oxygen pressures and compared with the experimental results. When the operating condition is changed along the polarization curve, the change of physicochemical variables in the membrane electrode assembly is studied. In particular, the over-potential diagram presents the usage of the electrochemical energy at each layer of the membrane electrode assembly. Humidity in supplying gases is one of the most important factors to consider for improving the performance of PEMFE. Both high and low humidity conditions can result in a deteriorating cell performance. The effect of humidity on the cell performance is studied in the chapter 2. First, a numerical model based on computational fluid dynamics is developed. Second, the cell performances are simulated, when the relative humidity is changed from 0% to 100% in the anode and the cathode channel. The simulation results show how humidity in the reactant gases affects the water content distribution in the membrane, the over-potential at the catalyst layers and eventually the cell performance. In particular, the rapid enhancement in the cell performance caused by self-hydrating membrane is captured by the simulation. Fully humidifying either H2
Physical and numerical modeling of seawater intrusion in coastal aquifers
NASA Astrophysics Data System (ADS)
Crestani, Elena; Camporese, Matteo; Salandin, Paolo
2016-04-01
Seawater intrusion in coastal aquifers is a worldwide problem caused, among others factors, by aquifer overexploitation, rising sea levels, and climate changes. To limit the deterioration of both surface water and groundwater quality caused by saline intrusion, in recent years many research studies have been developed to identify possible countermeasures, mainly consisting of underground barriers. In this context, physical models are fundamental to study the saltwater intrusion, since they provide benchmarks for numerical model calibrations and for the evaluation of the effectiveness of general solutions to contain the salt wedge. This work presents a laboratory experiment where seawater intrusion was reproduced in a specifically designed sand-box. The physical model, built at the University of Padova, represents the terminal part of a coastal aquifer and consists of a flume 500 cm long, 30 cm wide and 60 cm high, filled for an height of 49 cm with glass beads characterized by a d50 of 0.6 mm and a uniformity coefficient d60/d10 ≈ 1.5. The resulting porous media is homogeneous, with porosity of about 0.37 and hydraulic conductivity of about 1.3×10-3 m/s. Upstream from the sand-box, a tank filled by freshwater provides the recharge to the aquifer. The downstream tank simulates the sea and red food dye is added to the saltwater to easily visualize the salt wedge. The volume of the downstream tank is about five times the upstream one, and, due to the small filtration discharge, salt concentration variations (i.e., water density variations) due to the incoming freshwater flow are negligible. The hydraulic gradient during the tests is constant, due to the fixed water level in the two tanks. Water levels and discharged flow rate are continuously monitored. The experiment presented here had a duration of 36 h. For the first 24 h, the saltwater wedge was let to evolve until quasi stationary condition was obtained. In the last 12 h, water withdrawal was carried out at a
Numerical Modeling of Mixing and Venting from Explosions in Bunkers
NASA Astrophysics Data System (ADS)
Liu, Benjamin
2005-07-01
2D and 3D numerical simulations were performed to study the dynamic interaction of explosion products in a concrete bunker with ambient air, stored chemical or biological warfare (CBW) agent simulant, and the surrounding walls and structure. The simulations were carried out with GEODYN, a multi-material, Godunov-based Eulerian code, that employs adaptive mesh refinement and runs efficiently on massively parallel computer platforms. Tabular equations of state were used for all materials with the exception of any high explosives employed, which were characterized with conventional JWL models. An appropriate constitutive model was used to describe the concrete. Interfaces between materials were either tracked with a volume-of-fluid method that used high-order reconstruction to specify the interface location and orientation, or a capturing approach was employed with the assumption of local thermal and mechanical equilibrium. A major focus of the study was to estimate the extent of agent heating that could be obtained prior to venting of the bunker and resultant agent dispersal. Parameters investigated included the bunker construction, agent layout, energy density in the bunker and the yield-to-agent mass ratio. Turbulent mixing was found to be the dominant heat transfer mechanism for heating the agent.
The numerical modelling of a driven nonlinear oscillator
Shew, C.
1995-11-01
The torsional oscillator in the Earth Sciences Division was developed at Lawrence Livermore National Laboratory and is the only one of its kind. It was developed to study the way rocks damp vibrations. Small rock samples are tested to determine the seismic properties of rocks, but unlike other traditional methods that propagate high frequency waves through small samples, this machine forces the sample to vibrate at low frequencies, which better models real-life properties of large masses. In this particular case, the rock sample is tested with a small crack in its middle. This forces the rock to twist against itself, causing a {open_quotes}stick-slip{close_quotes} friction, known as stiction. A numerical model that simulates the forced torsional osillations of the machine is currently being developed. The computer simulation implements the graphical language LabVIEW, and is looking at the nonlinear spring effects, the frictional forces, and the changes in amplitude and frequency of the forced vibration. Using LabVIEW allows for quick prototyping and greatly reduces the {open_quotes}time to product{close_quotes} factor. LabVIEW`s graphical environment allows scientists and engineers to use familiar terminology and icons (e.g. knobs, switches, graphs, etc.). Unlike other programming systems that use text-based languages, such as C and Basic, LabVIEW uses a graphical programming language to create programs in block diagram form.
Numerically modelling the large scale coronal magnetic field
NASA Astrophysics Data System (ADS)
Panja, Mayukh; Nandi, Dibyendu
2016-07-01
The solar corona spews out vast amounts of magnetized plasma into the heliosphere which has a direct impact on the Earth's magnetosphere. Thus it is important that we develop an understanding of the dynamics of the solar corona. With our present technology it has not been possible to generate 3D magnetic maps of the solar corona; this warrants the use of numerical simulations to study the coronal magnetic field. A very popular method of doing this, is to extrapolate the photospheric magnetic field using NLFF or PFSS codes. However the extrapolations at different time intervals are completely independent of each other and do not capture the temporal evolution of magnetic fields. On the other hand full MHD simulations of the global coronal field, apart from being computationally very expensive would be physically less transparent, owing to the large number of free parameters that are typically used in such codes. This brings us to the Magneto-frictional model which is relatively simpler and computationally more economic. We have developed a Magnetofrictional Model, in 3D spherical polar co-ordinates to study the large scale global coronal field. Here we present studies of changing connectivities between active regions, in response to photospheric motions.
A numerical model of localized convection cells of Euglena suspensions
NASA Astrophysics Data System (ADS)
Iima, Makoto; Shoji, Erika; Yamaguchi, Takayuki
2014-11-01
Suspension of Euglena gracilis shows localized convection cells when it is illuminated form below with strong light intensity. Experiments in an annular container shows that there are two elementary localized structures. One consists of a pair of convection cells and a single region where number density of Euglena is high. The other consists a localized traveling wave. Based on the measurements of the flux of number density, we propose a model of bioconvection incorporating lateral phototaxis effect proportional to the light intensity gradient. Using pseudo spectral method, we performed numerical simulation of this model. We succeed in reproducing one of the localized structures, a convection pair with single region of high number density. Also, when the aspect ratio is large, there are a parameter region where the localized structure and conductive state are both stable, which is suggested by experiments. Spatial distribution of the number density implies that the accumulation of microorganism due to the convective flow causes such bistability. CREST(PJ74100011) and KAKENHI(26400396).
InSAR and Numeric Modeling for Land Subsidence
NASA Astrophysics Data System (ADS)
Wulamu, A.; Grzovic, M.
2015-12-01
Monitoring land subsidence due to coal mining is a function of several controlling factors, including: depth of the mine, stratigraphy, presence or absence of faults, thickness of mineral seam, mining method used, and hydrogeological conditions. Numerical modeling, e.g., finite element modeling (FEM), provides a comprehensive tool to simulate three-dimensional deformation at specific locations. The basis of the FEM is the representation of a body or a structure by an assemblage of subdivisions called finite elements, which requires the availability of site specific environmental and physical characteristics. The lack of availability of the necessary data leads to large uncertainties in subsidence estimates. With the use of InSAR, many of the needed controlling parameters for improving mine subsidence rate estimates can be identified. Coupling InSAR with FEM can further improve subsidence rate estimates through additional analysis yielding information on the relative importance of various controlling parameters contributing to the mine subsidence, the key mechanisms of failure associated with these parameters, and the surface expressions of these processes. In this contribution, we show that utilizing InSAR and FEM leads to an overall enhanced understanding of mine behavior, including the physical mechanisms that lead to mine subsidence through understanding the rheological behavior of the material over the mine in response to wide range of physical and environmental conditions.
Hydrological regime of the Black Sea waters: numerical modeling
NASA Astrophysics Data System (ADS)
Gippius, F. N.; Arkhipkin, V. S.
2012-04-01
The aim of the present work was to study the hydrological regime of the Black Sea basing on climatic temperature and salinity data massives and using numerical modeling techniques. The climatic temperature and salinity data massives used in this research are based on measurements performed between 1956 and 1995. Measurements from each month of the year were averaged during this period and the averaged values were interpolated to a grid of 12' x 16' cells. To optimize the calculations monthly data were replaced by three-month running average at depths more than 400 m and by yearly averaged data at depths more than 1000 m. In order to improve the quality of the data a search for water density inversion was performed at every grid node. The model used in this research is a mode split sigma-coordinate numerical ocean model developed at the University of Bergen. It is also known as the Bergen Ocean Model (BOM). Monthly 3-D fields of temperature, salinity and current velocity were received as a result of modeling. In order to visualize this data maps of temperature and salinity distribution at different depths and sections were created. Quite good accordance of modeling results with the present knowledge on the hydrological regime and termohaline structure of the Black Sea was found. The surface temperature values are higher in the southeastern part of the sea in all seasons. It is particulary evident in February, when the waters in the shallow northwestern region become extremely cold - down to 0 °C - due to strong heat exchange with the atmosphere and considerable river discharge. At the same time the surface water close to the Georgian coast is relatively warm, its temperature may rise up to 10 °C. The vertical distribution of water temperature is unique in the Black Sea due to the presence of the well-known cold intermediate layer, which exists from summer to autumn, and a gradual temperature growth from the depth of approximately 200 m and till the bottom. The
Numerical Models for Sound Propagation in Long Spaces
NASA Astrophysics Data System (ADS)
Lai, Chenly Yuen Cheung
Both reverberation time and steady-state sound field are the key elements for assessing the acoustic condition in an enclosed space. They affect the noise propagation, speech intelligibility, clarity index, and definition. Since the sound field in a long space is non diffuse, classical room acoustics theory does not apply in this situation. The ray tracing technique and the image source methods are two common models to fathom both reverberation time and steady-state sound field in long enclosures nowadays. Although both models can give an accurate estimate of reverberation times and steady-state sound field directly or indirectly, they often involve time-consuming calculations. In order to simplify the acoustic consideration, a theoretical formulation has been developed for predicting both steady-state sound fields and reverberation times in street canyons. The prediction model is further developed to predict the steady-state sound field in a long enclosure. Apart from the straight long enclosure, there are other variations such as a cross junction, a long enclosure with a T-intersection, an U-turn long enclosure. In the present study, an theoretical and experimental investigations were conducted to develop formulae for predicting reverberation times and steady-state sound fields in a junction of a street canyon and in a long enclosure with T-intersection. The theoretical models are validated by comparing the numerical predictions with published experimental results. The theoretical results are also compared with precise indoor measurements and large-scale outdoor experimental results. In all of previous acoustical studies related to long enclosure, most of the studies are focused on the monopole sound source. Besides non-directional noise source, many noise sources in long enclosure are dipole like, such as train noise and fan noise. In order to study the characteristics of directional noise sources, a review of available dipole source was conducted. A dipole was
3D numerical modeling of India-Asia-like collision
NASA Astrophysics Data System (ADS)
-Erika Püsök, Adina; Kaus, Boris; Popov, Anton
2013-04-01
above a strong mantle lithosphere - the jelly sandwich model (Burov and Watts, 2006). 3D models are thus needed to investigate these hypotheses. However, fully 3D models of the dynamics of continent collision zones have only been developed very recently, and presently most research groups have relied on certain explicit assumptions for their codes. Here, we employ the parallel 3D code LaMEM (Lithosphere and Mantle Evolution Model), with a finite difference staggered grid solver, which is capable of simulating lithospheric deformation while simultaneously taking mantle flow and a free surface into account. We here report on first lithospheric and upper-mantle scale simulations in which the Indian lithosphere is indented into Asia. Acknowledgements. Funding was provided by the European Research Council under the European Community's Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830. Numerical computations have been performed on JUQUEEN of the Jülich high-performance computing center. • Beaumont, C., Jamieson, R.A., Nguyen, M.H., Medvedev, S.E., 2004. Crustal channel flows: 1. Numerical models with applications to the tectonics of the Himalayan-Tibetan orogeny. J. Geophys. Res. 109, B06406. • Burov, E. & Watts, W.S., 2006. The long-term strength of continental lithosphere: "jelly sandwich" or "crème brûlée"?. GSA Today, 16, doi: 10.1130/1052-5173(2006)1016<1134:TLTSOC>1132.1130.CO;1132. • England P., Houseman, G., 1986. Finite strain calculations of continental deformation. 2. Comparison with the India-Asia collision zone. J. Geophys. Res.- Solid Earth and Planets 91 (B3), 3664-3676. • Jackson, J., 2002. Strength of the continental lithosphere: time to abandon the jelly sandwich?. GSA Today, September, 4-10. • Lechmann, S.M., May, D.A., Kaus, B.J.P., Schmalholz, S.M., 2011. Comparing thin-sheet models with 3D multilayer models for continental collision. Geophy. Int. J. doi: 10.1111/j.1365-246X.2011.05164.x • Royden, L.H., Burchfiel, B
Numerical Modeling of Continental Subduction In Apennines Style Context
NASA Astrophysics Data System (ADS)
Toussaint, G.; Burov, E.; Jolivet, L.
We performed numerical experiments of early stages of continental subduction and slab detachment at the mantle scale, using a 2D thermo-mechanical model which ac- counts for brittle-elasto-ductile behaviour, phase changes and surface processes. Our goal is to study the influence of various parameters on subduction-related orogens (for instance the Apennines) such as density contrasts, convergence rate, thermal state, eclogitisation and intensity of surface processes. The model reproduces the subduction cycle from early stages to penetration of the slab to the 660 km boundary. Depending of the parameters' combination, the evolution of the initiated slab varies from rapid detachment, stagnation of the subduction to stable, oceanic type subduction. An im- portant feature of our experiments is the almost systematic occurrence of underplating of the lower plate crust beneath the upper plate, leading to formation of double-Moho like structures. It appears that the subducted upper crust and sediments may play a role of lubrification layer, like the low friction coefficients used in some previous models, The results show that the main controlling parameter of slab evolution is the density contrast between the slab, subducted crust, and surrounding asthenosphere : for in- stance, when the contrast between the slab and the asthenosphere is larger than 0.02, the sinking rate of the slab is high, and slab detachment can occur within the first mil- lion years after onset of subduction. For smaller contrasts, stable subduction occurs only in case of full crustal metamorphism. The rate of convergence appears to be a second-order parameter, a high rate being able to prevent detachment. The intensity of surface processes predominantly controls the surface topography, and also seems to be able to influence deep processes such as the sinking rate. Thus, the same topography can be maintained for completely different subduction scenarios.
Numerical modelling of granular flows: a reality check
NASA Astrophysics Data System (ADS)
Windows-Yule, C. R. K.; Tunuguntla, D. R.; Parker, D. J.
2016-07-01
Discrete particle simulations provide a powerful tool for the advancement of our understanding of granular media, and the development and refinement of the multitudinous techniques used to handle and process these ubiquitous materials. However, in order to ensure that this tool can be successfully utilised in a meaningful and reliable manner, it is of paramount importance that we fully understand the degree to which numerical models can be trusted to accurately and quantitatively recreate and predict the behaviours of the real-world systems they are designed to emulate. Due to the complexity and diverse variety of physical states and dynamical behaviours exhibited by granular media, a simulation algorithm capable of closely reproducing the behaviours of a given system may be entirely unsuitable for other systems with different physical properties, or even similar systems exposed to differing control parameters. In this paper, we focus on two widely used forms of granular flow, for which discrete particle simulations are shown to provide a full, quantitative replication of the behaviours of real industrial and experimental systems. We identify also situations for which quantitative agreement may fail are identified, but important general, qualitative trends are still recreated, as well as cases for which computational models are entirely unsuitable. By assembling this information into a single document, we hope not only to provide researchers with a useful point of reference when designing and executing future studies, but also to equip those involved in the design of simulation algorithms with a clear picture of the current strengths and shortcomings of contemporary models, and hence an improved knowledge of the most valuable areas on which to focus their work.
Galaxy formation in LCDM: numerical models for CANDELS project
NASA Astrophysics Data System (ADS)
Klypin, Anatoly
2011-10-01
We propose to create a large library of high-resolution cosmological simulations of galaxies forming in the standard LCDM cosmology with the goal to provide theoretical support for the interpretation of HST observations, especially in connection with the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey {CANDELS}, focused on galaxies at z=2-8. The simulations will provide a statistical sample of galaxies in different environments and with different degrees of interaction. Our hydrodynamic plus N-body code ART models numerous physical processes including molecular cooling, radiation pressure due to young stars, feedback due to SNII and SNI, metal enrichment, and fueling of and feedback from AGN. We plan to produce hundreds of simulations of Milky- Way-size galaxies run to redshift different z's with hundreds of additional dwarf and satellites galaxies in surrounding regions. The simulations have extremely high resolution of 20-50 parsec - the best currently available. Using radiative-transfer code SUNRISE we will produce many observable properties of the simulated galaxies, including images in many wavebands including the effects of stellar evolution and dust, SEDs out to the far-IR, star-formation histories, and kinematics. For years, understanding galaxy formation suffered from two big obstacles: lack of data on the underlying "stellar scaffolding" of galaxies beyond z 1 and lack of realistic codes to model early stages of galaxy formation. The WFC3-IR camera is solving the first problem, and now is the right moment to invest in the first extensive realistic suite of hydrodynamic models, without which the precious new data cannot be properly used.
Numerical Modeling of the 2014 Oso, Washington, Landslide.
NASA Astrophysics Data System (ADS)
George, D. L.; Iverson, R. M.
2014-12-01
Numerical simulations of alternative scenarios that could have transpired during the Oso, Washington, landslide of 22 March 2014 provide insight into factors responsible for the landslide's devastating high-speed runout.We performed these simulations using D-Claw, a numerical model we recently developed to simulate landslide and debris-flow motion from initiation to deposition. D-Claw solves a hyperbolic system of five partial differential equations that describe simultaneous evolution of the thickness,solid volume fraction, basal pore-fluid pressure, and two components of momentum of the moving mass. D-Claw embodies the concept ofstate-dependent dilatancy, which causes the solid volume fraction m to evolve toward a value that is equilibrated to the ambient stress state andshear rate. As the value of m evolves, basal pore-fluid pressure coevolves,and thereby causes an evolution in frictional resistance to motion. Our Oso simulations considered alternative scenarios in which values of all model parameters except the initial solid volume fraction m0 were held constant.These values were: basal friction angle = 36°; static critical-state solidvolume fraction = 0.64; initial sediment permeability = 10-8 m2; pore-fluid density = 1100 kg/m3; sediment grain density = 2700 kg/m3; pore-fluid viscosity = 0.005 Pa-s; and dimensionless sediment compressibility coefficient = 0.03. Simulations performed using these values and m0 = 0.62 produced widespread landslide liquefaction, runaway acceleration, andlandslide runout distances, patterns and speeds similar to those observed or inferred for the devastating Oso event. Alternative simulations that usedm0 = 0.64 produced a much slower landslide that did not liquefy and that traveled only about 100 m before stopping. This relatively benign behavioris similar to that of several landslides at the Oso site prior to 2014. Our findings illustrate a behavioral bifurcation that is highly sensitive to the initial solid volume fraction
Numerical modelling of the 1979 Nice landslide-generated tsunami
NASA Astrophysics Data System (ADS)
Donnadieu, Claire; Hebert, Hélène; Silva Jacinto, Ricardo; Meyniel, Pauline
2010-05-01
On the 16th October 1979, a part of the building site of the Nice airport extension intended to become the new Nice harbour collapsed into the Mediterranean Sea during landfilling operations. This submarine slide of initial volume of 10 millions of m3, located near the seashore, generated a turbidity current that propagated along the Var canyon. A few minutes after the landslide, a small tsunami was observed by several witnesses 60 km along the coast, called "Baie des Anges". The most destructive effect occurred near the city of Antibes, 10 km away from the source, which was inundated and where one person died. In the framework of the RATCOM (Réseau d'Alertes aux Tsunamis et COtiers en Méditerranée) project, this event is numerically simulated with the goal of establishing the appropriate monitoring network which could have detected this event by means of gauges located offshore. Two additional scenarios of hypothetical sources recently identified by IFREMER in the same area are also computed : a small volume of 0.6 millions of m3, close to the 1979 breakdown area, and a larger one of 7 millions of m3, located easterly. A very accurate bathymetric map of the area provided by IFREMER and completed by SHOM data near the coast is used. The dynamics of the slide and the water waves generated are both computed in the shallow water approximation, considering the interaction between the mass of sediments constituting the slide and the water. The landslide is modelled as a Newtonian homogeneous viscous flow sliding under gravity along the bathymetry and the tsunami model is initialized by taking into account the bottom deformation induced by the slide. Incorporation of water in the mass of sediments at the interface between landslide and water can be considered. The equations are solved by a finite difference method based on shock capturing. Numerical results of tsunami waves amplitudes generated by the landslide during the propagation and along the coast are compared
The interacting gaps model: reconciling theoretical and numerical approaches to limit-order models
NASA Astrophysics Data System (ADS)
Muchnik, Lev; Slanina, Frantisek; Solomon, Sorin
2003-12-01
We consider the emergence of power-law tails in the returns distribution of limit-order driven markets. We explain a previously observed clash between the theoretical and numerical studies of such models. We introduce a solvable model that interpolates between the previous studies and agrees with each of them in the relevant limit.
NASA Astrophysics Data System (ADS)
Kavetski, D.; Clark, M. P.; Fenicia, F.
2011-12-01
Hydrologists often face sources of uncertainty that dwarf those normally encountered in many engineering and scientific disciplines. Especially when representing large scale integrated systems, internal heterogeneities such as stream networks, preferential flowpaths, vegetation, etc, are necessarily represented with a considerable degree of lumping. The inputs to these models are themselves often the products of sparse observational networks. Given the simplifications inherent in environmental models, especially lumped conceptual models, does it really matter how they are implemented? At the same time, given the complexities usually found in the response surfaces of hydrological models, increasingly sophisticated analysis methodologies are being proposed for sensitivity analysis, parameter calibration and uncertainty assessment. Quite remarkably, rather than being caused by the model structure/equations themselves, in many cases model analysis complexities are consequences of seemingly trivial aspects of the model implementation - often, literally, whether the start-of-step or end-of-step fluxes are used! The extent of problems can be staggering, including (i) degraded performance of parameter optimization and uncertainty analysis algorithms, (ii) erroneous and/or misleading conclusions of sensitivity analysis, parameter inference and model interpretations and, finally, (iii) poor reliability of a calibrated model in predictive applications. While the often nontrivial behavior of numerical approximations has long been recognized in applied mathematics and in physically-oriented fields of environmental sciences, it remains a problematic issue in many environmental modeling applications. Perhaps detailed attention to numerics is only warranted for complicated engineering models? Would not numerical errors be an insignificant component of total uncertainty when typical data and model approximations are present? Is this really a serious issue beyond some rare isolated
Numerical Modelling of the Expansion Phase of Vapor Explosions
NASA Astrophysics Data System (ADS)
Hwang, Moonkyu
When a cold liquid is brought into contact with a molten material with a temperature significantly higher than the liquid boiling point, an explosive interaction, involving sudden fragmentation of some of the molten material and rapid evaporation of the liquid, takes place. This phenomenon is referred to as a "vapor explosion" or "steam explosion". In the event of a core meltdown accident in a light water reactor, the molten fuel can interact with cooling water inside or outside the reactor vessel and cause a vapor explosion. The mechanical energy released during such an explosion can result in structural damage, and ultimately may lead to the release of radioactive material into the environment. Vapor explosions are extremely fast transients, involving a flow field consisting of at least three distinct phases, accompanied by thermal non-equilibrium and strong interfacial transfer processes. The objective of this research was to mechanistically model the expansion phase of a vapor explosion. A transient three-dimensional, three -fluid thermal hydraulic model was developed. Coolant liquid plus fragmented fuel particles, coolant vapor plus noncondensables and unfragmented fuel constitute the three fluids. Hydrodynamic and thermal interactions between the three phases were mechanistically treated, using flow regime-dependent models. The models were incorporated into a computer code, in which the conservation equations are cast in finite-difference form and are numerically solved using the point-relaxation method. The code was utilized in parametric and sensitivity calculations aimed at assessing the significance of interfacial transfer processes, and the effect of the premixture initial conditions on the phenomenology of the expansion phase of steam explosions. The initial conditions for the expansion phase were estimated by assuming that the propagation phase was a constant volume heat exchange process. Parametric results indicate that thermal and mechanical
Integrating Numerical Computation into the Modeling Instruction Curriculum
ERIC Educational Resources Information Center
Caballero, Marcos D.; Burk, John B.; Aiken, John M.; Thoms, Brian D.; Douglas, Scott S.; Scanlon, Erin M.; Schatz, Michael F.
2014-01-01
Numerical computation (the use of a computer to solve, simulate, or visualize a physical problem) has fundamentally changed the way scientific research is done. Systems that are too difficult to solve in closed form are probed using computation. Experiments that are impossible to perform in the laboratory are studied numerically. Consequently, in…
Forecasting natural aquifer discharge using a numerical model and convolution.
Boggs, Kevin G; Johnson, Gary S; Van Kirk, Rob; Fairley, Jerry P
2014-01-01
If the nature of groundwater sources and sinks can be determined or predicted, the data can be used to forecast natural aquifer discharge. We present a procedure to forecast the relative contribution of individual aquifer sources and sinks to natural aquifer discharge. Using these individual aquifer recharge components, along with observed aquifer heads for each January, we generate a 1-year, monthly spring discharge forecast for the upcoming year with an existing numerical model and convolution. The results indicate that a forecast of natural aquifer discharge can be developed using only the dominant aquifer recharge sources combined with the effects of aquifer heads (initial conditions) at the time the forecast is generated. We also estimate how our forecast will perform in the future using a jackknife procedure, which indicates that the future performance of the forecast is good (Nash-Sutcliffe efficiency of 0.81). We develop a forecast and demonstrate important features of the procedure by presenting an application to the Eastern Snake Plain Aquifer in southern Idaho.
Morphology and dynamics of star dunes from numerical modelling
NASA Astrophysics Data System (ADS)
Zhang, Deguo; Narteau, Clément; Rozier, Olivier; Courrech Du Pont, Sylvain
2012-07-01
Star dunes are giant, pyramid-shaped dunes composed of interlaced arms. These arms are marked by sinuous crests and slip faces of various directions. Their radial symmetry and scale suggest that the star dunes form as a result of complex interactions between a multidirectional wind regime and topography. However, despite their ubiquity in modern sand seas, comparatively little is known about their formation and evolution. Here we present a discrete numerical model of star-dune behaviour based on the feedback mechanisms between wind flow and bedform dynamics. Our simulations indicate that the morphology of star dunes results from the combination of individual longitudinal dunes. We find that the arms of the star dunes propagate only under favourable wind regimes. In contrast to dunes that form from an erodible bed, the crests of the propagating arms are oriented such that sand flux is maximized in the direction of arm growth. Our analysis of the simulated three-dimensional structures suggests that the morphodynamics of the arms are controlled by the frequency of wind reorientation, with a high frequency of reorientation leading to smaller arm dimension and high rates of growth. We suggest that arm propagation is an important process of mass exchange in dune fields.
3D Numerical Simulations of the Breakout Model
NASA Astrophysics Data System (ADS)
Choe, G. S.; Cheng, C. Z.; Lee, J.; Lynch, B. J.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.
2005-05-01
We present the continuing progress of the numerical simulations of the breakout model for coronal mass ejection initiation. To validate the 3D spherical ARMS code we have run the 2.5D breakout problem and compare the eruption to the published 2D results. The ARMS 2.5D CME also forms a large magnetic island ahead of the erupting plasmoid due to the code's excellent maintenance of equatorial symmetry. Progress on the fully 3D breakout problem is also discussed. To build up enough magnetic free energy for an eruption the active region field must be strong with a steep gradient near the polarity inversion line and the shear must be highly concentrated there. This requires adaptive griding techniques. In the current simulation, the active region to background field ratio is 20-to-1 and the neutral line is long compared to the active region width. We present the evolution of this topology under Br-conserving shearing flow and discuss implications for a 3D eruption. This work is supported by NASA and ONR. BJL is supported by NASA GSRP grant NGT5-50453.
Fast and stable numerical method for neuronal modelling
NASA Astrophysics Data System (ADS)
Hashemi, Soheil; Abdolali, Ali
2016-11-01
Excitable cell modelling is of a prime interest in predicting and targeting neural activity. Two main limits in solving related equations are speed and stability of numerical method. Since there is a tradeoff between accuracy and speed, most previously presented methods for solving partial differential equations (PDE) are focused on one side. More speed means more accurate simulations and therefore better device designing. By considering the variables in finite differenced equation in proper time and calculating the unknowns in the specific sequence, a fast, stable and accurate method is introduced in this paper for solving neural partial differential equations. Propagation of action potential in giant axon is studied by proposed method and traditional methods. Speed, consistency and stability of the methods are compared and discussed. The proposed method is as fast as forward methods and as stable as backward methods. Forward methods are known as fastest methods and backward methods are stable in any circumstances. Complex structures can be simulated by proposed method due to speed and stability of the method.
Numerical modeling of high temperature fracture of metallic composites
NASA Astrophysics Data System (ADS)
Cendales, E. D.; García, A.
2016-02-01
Mechanical properties of materials are strongly affected by increasing temperature, showing behaviors that could cause failure as creep. This article provides a brief theoretical description about fracture of materials, deepening on creep and intergranular creep. Some parameters as creep strain, strain rate, time to failure and displacement of the crack tip of a metallic glass selected at high temperature were studied. This paper shows a computer numerical model that permits establish mechanical behavior of a metal composite material Zr52.5Cu18Ni14.5Al10Ti5, bulk metallic glass. In the presence of cracking when the material is subjected to temperatures exceeding 30% of the melt temperature of material. The results obtained by computer simulation show correlation with the results about the behavior of the material viewed through the creep test. From the results we conclude that the mechanical properties of the material generally do not undergo major changes at high temperatures. However, at temperatures greater than 650C, the effect of the application of stress during creep entails failures in this kind of material.
Numerical Modelling of the Deep Impact Mission Experiment
NASA Technical Reports Server (NTRS)
Wuennemann, K.; Collins, G. S.; Melosh, H. J.
2005-01-01
NASA s Deep Impact Mission (launched January 2005) will provide, for the first time ever, insights into the interior of a comet (Tempel 1) by shooting a approx.370 kg projectile onto the surface of a comets nucleus. Although it is usually assumed that comets consist of a very porous mixture of water ice and rock, little is known about the internal structure and in particular the constitutive material properties of a comet. It is therefore difficult to predict the dimensions of the excavated crater. Estimates of the crater size are based on laboratory experiments of impacts into various target compositions of different densities and porosities using appropriate scaling laws; they range between 10 s of meters up to 250 m in diameter [1]. The size of the crater depends mainly on the physical process(es) that govern formation: Smaller sizes are expected if (1) strength, rather than gravity, limits crater growth; and, perhaps even more crucially, if (2) internal energy losses by pore-space collapse reduce the coupling efficiency (compaction craters). To investigate the effect of pore space collapse and strength of the target we conducted a suite of numerical experiments and implemented a novel approach for modeling porosity and the compaction of pores in hydrocode calculations.
Biomechanics of Growing Trees: Mathematical Model, Numerical Resolution and Perspectives
NASA Astrophysics Data System (ADS)
Fourcaud, Thierry; Guillon, Thomas; Dumont, Yves
2011-09-01
The growth of trees is characterized by the elongation and thickening of its axes. New cells are formed at the periphery of the existing body, the properties of the older inner material being unchanged. The calculation of the progressive deflection of a growing stem is not a classical problem in mechanics for three main reasons: 1- the hypothesis of mass conservation is not valid; 2- the new material added at the periphery of the existing and deformed structure does not participate retroactively to the total equilibrium and tends to "fix" the actual shape; 3- an initial reference configuration corresponding to the unloaded structure cannot be classically defined to formulate the equilibrium equations. This paper proposes a theoretical framework that allows bypassing these difficulties. Equations adapted from the beam theory and considering the strong dependencies between space and time are given. A numerical scheme based on the finite element method is proposed to solve these equations. The model opens new research perspectives both in mathematics and plant biology.
Representing Cloud Processing of Aerosol in Numerical Models
Mechem, D.B.; Kogan, Y.L.
2005-03-18
The satellite imagery in Figure 1 provides dramatic examples of how aerosol influences the cloud field. Aerosol from ship exhaust can serve as nucleation centers in otherwise cloud-free regions, forming ship tracks (top image), or can enhance the reflectance/albedo in already cloudy regions. This image is a demonstration of the first indirect effect, in which changes in aerosol modulate cloud droplet radius and concentration, which influences albedo. It is thought that, through the effects it has on precipitation (drizzle), aerosol can also affect the structure and persistence of planetary boundary layer (PBL) clouds. Regions of cellular convection, or open pockets of cloudiness (bottom image) are thought to be remnants of strongly drizzling PBL clouds. Pockets of Open Cloudiness (POCs) (Stevens et al. 2005) or Albrecht's ''rifts'' are low cloud fraction regions characterized by anomalously low aerosol concentrations, implying they result from precipitation. These features may in fact be a demonstration of the second indirect effect. To accurately represent these clouds in numerical models, we have to treat the coupled cloud-aerosol system. We present the following series of mesoscale and large eddy simulation (LES) experiments to evaluate the important aspects of treating the coupled cloud-aerosol problem. 1. Drizzling and nondrizzling simulations demonstrate the effect of drizzle on a mesoscale forecast off the California coast. 2. LES experiments with explicit (bin) microphysics gauge the relative importance of the shape of the aerosol spectrum on the 3D dynamics and cloud structure. 3. Idealized mesoscale model simulations evaluate the relative roles of various processes, sources, and sinks.
Numerical modeling of perched water under Yucca Mountain, Nevada
Hinds, J.J.; Ge, S.; Fridrich, C.J.
1999-01-01
The presence of perched water near the potential high-level nuclear waste repository area at Yucca Mountain, Nevada, has important implications for waste isolation. Perched water occurs because of sharp contrasts in rock properties, in particular between the strongly fractured repository host rock (the Topopah Spring welded tuff) and the immediately underlying vitrophyric (glassy) subunit, in which fractures are sealed by clays that were formed by alteration of the volcanic glass. The vitrophyre acts as a vertical barrier to unsaturated flow throughout much of the potential repository area. Geochemical analyses (Yang et al. 1996) indicate that perched water is relatively young, perhaps younger than 10,000 years. Given the low permeability of the rock matrix, fractures and perhaps fault zones must play a crucial role in unsaturated flow. The geologic setting of the major perched water bodies under Yucca Mountain suggests that faults commonly form barriers to lateral flow at the level of the repository horizon, but may also form important pathways for vertical infiltration from the repository horizon down to the water table. Using the numerical code UNSAT2, two factors believed to influence the perched water system at Yucca Mountain, climate and fault-zone permeability, are explored. The two-dimensional model predicts that the volume of water held within the perched water system may greatly increase under wetter climatic conditions, and that perched water bodies may drain to the water table along fault zones. Modeling results also show fault flow to be significantly attenuated in the Paintbrush Tuff non-welded hydrogeologic unit.
Laser Applications for Nanotechnology : Insights From Numerical Modeling
NASA Astrophysics Data System (ADS)
Itina, T. E.; Shcheblanov, N.; Colombier, J.-Ph.; Stoian, R.; Audouard, E.; Derrien, Th. Y.; Torres, R.; Hermann, J.; Povarnitsyn, M. E.; Khishchenko, K. V.
2010-10-01
Laser-produced nanoparticles have found many applications in bio-photonics, medicine and in the development of photovolvatic cells. Many experiments have been performed demonstrating the formation of these particles from solid targets in vacuum, in the presence of a gas or a liquid. However, it is still difficult to predict the size distribution of these particles. Therefore, we have performed an extensive numerical modeling of the involved physical processes. The developed models allow us to compare the relative contribution of several processes involved in the cluster production by laser ablation: (i) direct cluster ejection from a target under rapid laser interaction, (ii) condensation/evaporation; (iii) fragmentation/aggregation processes during cluster diffusion; and (iv) diffusion and coalescence if nanoparticles are deposited on a substrate. The calculation results of both hydrodynamic and molecular dynamics simulations demonstrate that an exposure of a target to a short or ultra-short laser pulse leads to an explosive target decomposition and to the ejection of nanoparticles. These cluster precursors are formed during rapid target expansion through both thermal and mechanical processes. Collisions with background species affect the cluster size distribution. The influences of the parameters, such as initial cluster temperature and size, background temperature and density, on the cluster evolution are analyzed. Laser-induced phase explosion process affects the formation of small surface structures, obtained with small number of shots. However, the non-resonant "conical" surface structures with the mean size as large as several micrometers are formed due to the presence of harder less absorbing centers. These obtained results can be used to explain many recent experimental observations.
Numeric Modeling of Valley Networks and Drainage Systems on Mars
NASA Astrophysics Data System (ADS)
Vidal, A.
2006-12-01
Valley networks observed on Mars are often invoked to support the historical presence of water on the surface of Mars. There is a need for quantification of these networks and the drainage processes associated with them. Numerical modeling of these streams and drainage basins within a GIS environment allows for rapid assessment of hydrologic surface processes. In this study, several areas of valley networks which had been previously mapped visually using Viking, MOC, and MOLA datasets were re-examined using numeric processes and tools available in ArcGIS. Specifically, stream length and drainage density were quantified using the MOLA gridded DEM and ArcGIS tools. This process is significantly faster than the visual identification and delineation techniques used in the past. The project sought to test whether or not computer-assisted techniques were comparable in accuracy and precision to previous studies using visual techniques. To do this, two quadrangles previously visually mapped by Carr (1995) and Hynek and Phillips (2003) were analyzed. Total valley network length at the first site was found to be 18,300 km, compared to previous estimates of 1,308 km (Carr) and 11,100 km (Hynek and Phillips). Drainage density was calculated to be 0.0605/km, compared to previous estimates of 0.0076/km (Carr) and 0.065/km (Hynek and Phillips). The highest stream order found was 5th, compared to 3rd (Carr) and 6th (Hynek and Phillips). In the second quadrangle, total valley network length was measured at 4,010 km, compared to 453 km and 3,496 km. The drainage density was calculated to be 0.068/km, compared to 0.011/km and 0.082/km. The highest stream order found was 4th, compared to 2nd and 5th. Results were very similar to those using visual interpretation of MOC shaded relief by Hynek and Phillips. A difference in stream order, however, suggests that the computer-aided technique may not connect systems that visually have been connected. Still, automated results offer an
European Air Quality and Climate Change: a numerical modeling study
NASA Astrophysics Data System (ADS)
Lacressonniere, G.
2011-12-01
In the context of climate change, the evolution of air quality in Europe is a challenging scientific question, despite the political measures taken to limit and reduce anthropogenic emissions. Heat waves, changes in transport pathways or synoptic patterns, increase of emissions in other areas in the world, or for instance possible increase of biogenic emissions or changes in deposition and land use may affect adversely future Air Quality levels in Europe. In the context of a project co-funded by the French environment agency ADEME, a numerical modeling study has begun relying on the tools used by Météo-France for its contribution to the 5th IPCC assessment report, to GMES atmospheric services (MACC FP7 project) and to the French national operational Air Quality platform Prév'Air (http://www.prevair.org). In particular, the MOCAGE 3-D chemical transport model (CTM) is used with a configuration comprising a global (2°) and a European domain (0.2°), allowing representation of both long-range transport of pollutants and European Air Quality at relevant resolutions and with a two-ways coupling. MOCAGE includes 47 layers from the surface to 5hPa. The first step of this project was to assess the impact of meteorological forcings, either analyses ("best" meteorology available for the recent past) or climate runs for the current atmosphere, on air quality hindcasts with MOCAGE over Europe. For these climate runs, we rely on Météo-France Earth-System model CNRM-CM, and particularly the ARPEGE-climate general circulation model for the atmosphere. By studying several key variables for Air Quality (surface and low troposphere concentrations of ozone, nitrogen oxides, volatile organic compounds, radicals, PM,...), we investigated the indicators that are robust, through averages over several years, (monthly averages, frequency of exceedances, AOTs, ...) for a given climate when using climatological forcings instead of analyses, which constitutes the reference. Both
Numerical Results of 3-D Modeling of Moon Accumulation
NASA Astrophysics Data System (ADS)
Khachay, Yurie; Anfilogov, Vsevolod; Antipin, Alexandr
2014-05-01
For the last time for the model of the Moon usually had been used the model of mega impact in which the forming of the Earth and its sputnik had been the consequence of the Earth's collision with the body of Mercurial mass. But all dynamical models of the Earth's accumulation and the estimations after the Pb-Pb system, lead to the conclusion that the duration of the planet accumulation was about 1 milliard years. But isotopic results after the W-Hf system testify about a very early (5-10) million years, dividing of the geochemical reservoirs of the core and mantle. In [1,2] it is shown, that the account of energy dissipating by the decay of short living radioactive elements and first of all Al26,it is sufficient for heating even small bodies with dimensions about (50-100) km up to the iron melting temperature and can be realized a principal new differentiation mechanism. The inner parts of the melted preplanets can join and they are mainly of iron content, but the cold silicate fragments return to the supply zone and additionally change the content of Moon forming to silicates. Only after the increasing of the gravitational radius of the Earth, the growing area of the future Earth's core can save also the silicate envelope fragments [3]. For understanding the further system Earth-Moon evolution it is significant to trace the origin and evolution of heterogeneities, which occur on its accumulation stage.In that paper we are modeling the changing of temperature,pressure,velocity of matter flowing in a block of 3d spherical body with a growing radius. The boundary problem is solved by the finite-difference method for the system of equations, which include equations which describe the process of accumulation, the Safronov equation, the equation of impulse balance, equation Navier-Stocks, equation for above litho static pressure and heat conductivity in velocity-pressure variables using the Businesque approach.The numerical algorithm of the problem solution in velocity
Numerical modeling of fluid migration in subduction zones
NASA Astrophysics Data System (ADS)
Walter, Marius J.; Quinteros, Javier; Sobolev, Stephan V.
2015-04-01
It is well known that fluids play a crucial role in subduction evolution. For example, excess mechanical weakening along tectonic interfaces, due to excess fluid pressure, may enable oceanic subduction. Hence, the fluid content seems to be a critical parameter for subduction initiation. Studies have also shown a correlation between the location of slab dehydration and intermediate seismic activity. Furthermore, expelled fluids from the subduction slab affect the melting temperature, consequently, contributing to partial melting in the wedge above the downgoing plate, and resulting in chemical changes in earth interior and extensive volcanism. In summary, fluids have a great impact on tectonic processes and therefore should be incorporated into geodynamic numerical models. Here we use existing approaches to couple and solve fluid flow equations in the SLIM-3D thermo-mechanical code. SLIM-3D is a three-dimensional thermo-mechanical code capable of simulating lithospheric deformation with elasto-visco-plastic rheology. It incorporates an arbitrary Lagrangian Eulerian formulation, free surface, and changes in density and viscosity, due to endothermic and exothermic phase transitions. It has been successfully applied to model geodynamic processes at different tectonic settings, including subduction zones. However, although SLIM-3D already includes many features, fluid migration has not been incorporated into the model yet. To this end, we coupled solid and fluid flow assuming that fluids flow through a porous and deformable solid. Thereby, we introduce a two-phase flow into the model, in which the Stokes flow is coupled with the Darcy law for fluid flow. This system of equations becomes, however, nonlinear, because the rheology and permeability are depended on the porosity (fluid fraction of the matrix). Ultimately, the evolution of porosity is governed by the compaction pressure and the advection of the porous solid. We show the details of our implementation of the
Numerical modeling of Thermal Response Tests in Energy Piles
NASA Astrophysics Data System (ADS)
Franco, A.; Toledo, M.; Moffat, R.; Herrera, P. A.
2013-05-01
conductivity of the soil is the most determinant parameter that affects the estimated thermal conductivity. For example, we observed differences of up to 50% from the expected value at the end of 100 hours of simulation for values of thermal conductivity of the soil in the range of 1 to 6 W/mK. Additionally, we observed that the results of the synthetic TRT depend upon several other parameters such as the boundary conditions used to model the interaction of the top face of the pile with the surrounding media. For example, Simulations with a constant temperature boundary condition tended to overestimate the total thermal conductivity of the whole system. This analysis demonstrates that numerical modeling is a useful tool to model energy pile systems and to interpret and design tests to evaluate their performance. Furthermore, it also reveals that the results of thermal response tests interpreted with analytical models must be evaluated with care for the assessment of the potential of low enthalpy systems, because their results depend upon a variety of factors which are neglected in the analytical models.
The Coastal Modeling System: A System of Numerical Models and Support Programs
1991-12-01
via the Coastal Modeling System ( CMS ). The CMS is a software package aimed at organizing CERC’s larger numerical models and their supporting software...reduced because of user familiarity with the system structure. COMPONENTS: The CMS is a supercomputer-based system of models and supporting software...elevations from tidal constituent input. Generally, CMS users are not required to learn the JCL of the host computer system . Most of the job’control commands
Numerical Weather Prediction Over Caucasus Region With Nested Grid Models
NASA Astrophysics Data System (ADS)
Davitashvili, Dr.; Kutaladze, Dr.; Kvatadze, Dr.
2010-09-01
territory of Georgia. Both use the default 31 vertical levels. We have studied the effect of thermal and advective-dynamic factors of atmosphere on the changes of the West Georgian climate. We have shown that non-proportional warming of the Black Sea and Colkhi lowland provokes the intensive strengthening of circulation. Some results of calculations of the interaction of airflow with complex orography of Caucasus with horizontal grid-point resolutions of 15 and 5 km are presented. Also with the purpose of study behavior of nested grid method above complex terrain we have elaborated in sigma coordinate system short term prediction regional numerical model for Caucasus region. The results of computation carried out with one directional, two directional and new combined methods are given.
Numerical modeling of cyclic strengthening and weaking of material
NASA Astrophysics Data System (ADS)
Dudda, Waldemar
2007-04-01
The study concerns analytical and numerical tools for description of strengthening and weakening effects of materials put under influence of cyclic mechanical loads. The paper presents formulas describing the change in material mechanical properties such as the yield point and strain hardening modulus depending on the number of load cycles and stress ratio. Numerical simulations for cases based on experimental studies presented in the existing literature were conducted. The results of numerical calculations and their comparison with the experimental data are presented in the form of stress-strain hysteresis loop graphs.
Numerical Modeling of Flat Slab Formation in Central Chile
NASA Astrophysics Data System (ADS)
Manea, M.; Perez-Gussinye, M.; Manea, V.; Fernandez, M.
2009-12-01
Subduction of oceanic plates beneath large continental masses is a rare process and at present it occurs only along western South America and Central Mexico. Likewise, flat subduction, understood here as where the slab enters at a normal angle and reverses its curvature to flatten at ~70-120 km depth, only occurs at present beneath South America. In general, the angle at which subduction occurs in the depth range of ~100 to ~200 km reflects the balance between negative buoyancy of the slab, elastic resistance of the slab to change the angle of subduction, and non-hydrostatic pressure forces induced by subduction-driven flow within the asthenosphere. The latter force, known as suction force, acts to prevent the slab from sinking into the mantle, and its magnitude increases with increasing subduction velocity, narrowness and viscosity decrease of the mantle wedge [Manea and Gurnis, 2007]. Recent observations show that the upper plate structure varies along the Andean margin, indicating that it is thicker and stronger above flat subduction zones and suggesting a correlation between upper plate structure and subduction angle [Pérez-Gussinyé et al., 2008; Booker et al., 2004]. In this study we use numerical models to explore the extent to which upper plate structure, through its influence on asthenospheric wedge shape and viscosity, can affect the angle of subduction. We test for which upper plate thickness and asthenospheric viscosity repeated cycles of steep and flat subduction are reproduced and compare our results to estimations of lithospheric thickness and the duration of flat and steep subduction cycles hypothesized along the Andean margin. Our models are constrained by realistic plate velocities in hot spot reference frame for both Nazca and South American plates [Muller et al., 2008], the Miocene-Present shortening for the Andes [Schelart et al., 2007] and realistic Nazca plate age distribution [Sdrolias and Muller, 2006]. Using the finite element package
Numerical treatment of a mathematical model arising from a model of neuronal variability
NASA Astrophysics Data System (ADS)
Kadalbajoo, M. K.; Sharma, K. K.
2005-07-01
In this paper, we describe a numerical approach based on finite difference method to solve a mathematical model arising from a model of neuronal variability. The mathematical modelling of the determination of the expected time for generation of action potentials in nerve cells by random synaptic inputs in dendrites includes a general boundary-value problem for singularly perturbed differential-difference equation with small shifts. In the numerical treatment for such type of boundary-value problems, first we use Taylor approximation to tackle the terms containing small shifts which converts it to a boundary-value problem for singularly perturbed differential equation. A rigorous analysis is carried out to obtain priori estimates on the solution of the problem and its derivatives up to third order. Then a parameter uniform difference scheme is constructed to solve the boundary-value problem so obtained. A parameter uniform error estimate for the numerical scheme so constructed is established. Though the convergence of the difference scheme is almost linear but its beauty is that it converges independently of the singular perturbation parameter, i.e., the numerical scheme converges for each value of the singular perturbation parameter (however small it may be but remains positive). Several test examples are solved to demonstrate the efficiency of the numerical scheme presented in the paper and to show the effect of the small shift on the solution behavior.
Numerical modeling of active separation control by synthetic jets
NASA Astrophysics Data System (ADS)
Aram, Shawn
Zero-Net Mass-Flux (ZNMF) actuators or synthetic jet actuators are versatile micro scale devices with numerous applications in the field of fluid mechanics. The primary focus of the current work is to use time-accurate simulations to study the interaction of these jets with cross flows and to optimize their performance for the control of boundary layer separation. This study consists of four parts. In the first part, a class of phenomenology-based models is proposed to reproduce the flow associated with synthetic jets in grazing flows and simplify the task of ZNMF-based flow control simulations. The proposed models have a non-uniform jet velocity profile with only two spatial degrees of freedom and a uniform slip velocity on the slot-flow boundary. A comparison of key integral quantities associated with the momentum, energy and vorticity fluxes shows that the models with a non-uniform jet velocity during the expulsion phase and uniform jet velocity during the ingestion phase can predict these quantities with good accuracy, whereas a simple plug flow model with a zero slip and uniform jet velocity under-predicts these three quantities during the expulsion phase. Based on our initial analysis, three of the simplest models are selected for further study, including an assessment of their performance for a canonical separated flow at different forcing frequencies. A key finding is that a simple plug-flow type model can predict incorrect trends for separation reduction with the jet frequency. A preliminary attempt is also made to provide empirical closure to these models. The effect of synthetic jets orientation on its interaction with a zero pressure gradient laminar boundary layer is explored in the second part. A rectangular slot is chosen in this study and streamwise and spanwise orientations of this slot are examined. The orientation of the slot is found to have a significant impact on its interaction with the boundary layer. The dominant feature in the streamwise
Numerical model of sonic boom in 3D kinematic turbulence
NASA Astrophysics Data System (ADS)
Coulouvrat, François; Luquet, David; Marchiano, Régis
2015-10-01
Sonic boom is one of the key issues to be considered in the development of future supersonic or hypersonic civil aircraft concepts. The classical sonic boom, typical for Concorde with an N-wave shape and a ground amplitude of the order of 100 Pa, prevents overland flight. Future concepts target carefully shaped sonic booms with low amplitude weak shocks. However, sonic boom when perceived at the ground level is influenced not only by the aircraft characteristics, but also by atmospheric propagation. In particular, the effect of atmospheric turbulence on sonic boom propagation near the ground is not well characterized. Flight tests performed as early as the 1960s demonstrated that classical sonic booms are sensitive to atmospheric turbulence. However, this sensitivity remains only partially understood. This is related to the fact that i) turbulence is a random process that requires a statistical approach, ii) standard methods used to predict sonic booms, mainly geometrical acoustics based on ray tracing, are inadequate within the turbulent planetary boundary layer. Moreover, the ray theory fails to predict the acoustical field in many areas of interest, such as caustics or shadow zones. These zones are of major interest for sonic boom acceptability (highest levels, lateral extent of zone of impact). These limitations outline the need for a numerical approach that is sufficiently efficient to perform a large number of realizations for a statistical approach, but that goes beyond the limitations of ray theory. With this in view, a 3D one-way numerical method solving a nonlinear scalar wave equation established for heterogeneous, moving and absorbing atmosphere, is used to assess the effects of a 3D kinematic turbulence on sonic boom in various configurations. First, a plane N-wave is propagated in the free field through random realizations of kinematic fluctuations. Then the case of a more realistic Atmospheric Boundary Layer (ABL) is investigated, with a mean
Numerical models of Oort Cloud formation and comet delivery
NASA Astrophysics Data System (ADS)
Kaib, Nathan A.
I use a newly designed numerical algorithm to simulate the dynamics of the Oort Cloud. The processes I model are the formation of the cloud, the current delivery of comets to the planetary region, and long-period comet production during comet showers. Concerning the cloud's formation, I find that the Sun's birth environment dramatically affects the structure of the inner Oort Cloud as well as the amount of material trapped in this region. In addition, the structure of this reservoir is also sensitive to the Sun's orbital history in the Milky Way. This raises the possibility that constraining our inner Oort Cloud's properties can constrain the Sun's dynamical history. In this regard, I use my simulations of comet delivery to better understand what the population of comets passing through the planetary region can tell us about the inner Oort Cloud. I find that the inner Oort Cloud (rather than the scattered disk) dominates the production of planet-crossing TNOs with perihelia beyond 15 AU and semimajor axes greater than a few hundred AU. My results indicate that two objects representing this population (2000 00 67 and 2006 SQ 372 ) have already been detected, and the detection of many analogous objects can constrain the inner Oort Cloud. In addition, these simulations of comet delivery also demonstrate that, contrary to previous understanding, the inner Oort Cloud is a significant and perhaps the dominant source of known long-period comets. This result can be used to place the first observationally motivated upper limit on the inner Oort Cloud's population. Finally, with this maximum population value, I use my comet shower simulations to show that comet showers are unlikely to be responsible for more than one minor extinction event since the Cambrian Explosion.
NASA Astrophysics Data System (ADS)
Turco, Emilio; dell'Isola, Francesco; Cazzani, Antonio; Rizzi, Nicola Luigi
2016-08-01
Hencky (Über die angenäherte Lösung von Stabilitätsproblemen im Raum mittels der elastischen Gelenkkette. Ph.D. thesis, Engelmann, 1921) proposed a discrete model for elasticae by introducing rigid bars and rotational springs. Hencky (Proc R Soc Lond A Math Phys Eng Sci 472(2185), 2016) approach has been introduced to heuristically motivate the need of second gradient continua. Here, we present a novel numerical code implementing directly the discrete Hencky-type model which is robust enough to solve the problem of the determination of equilibrium configurations in the large deformation and displacement regimes. We apply this model to study some potentially applicable problems, and we compare its performances with those of the second gradient continuum model. The numerical evidence presented supports the conjecture that Hencky-type converges to second gradient model.
NASA Astrophysics Data System (ADS)
Rivière, Agnès.; Goncalves, Julio; Jost, Anne; Font, Marianne
2010-05-01
Development and degradation of permafrost directly affect numerous hydrogeological processes such as thermal regime, exchange between river and groundwater, groundwater flows patterns and groundwater recharge (Michel, 1994). Groundwater in permafrost area is subdivided into two zones: suprapermafrost and subpermafrost which are separated by permafrost. As a result of the volumetric expansion of water upon freezing and assuming ice lenses and frost heave do not form freezing in a saturated aquifer, the progressive formation of permafrost leads to the pressurization of the subpermafrost groundwater (Wang, 2006). Therefore disappearance or aggradation of permafrost modifies the confined or unconfined state of subpermafrost groundwater. Our study focuses on modifications of pore water pressure of subpermafrost groundwater which could appear during thawing and freezing of soil. Numerical simulation allows elucidation of some of these processes. Our numerical model accounts for phase changes for coupled heat transport and variably saturated flow involving cycles of freezing and thawing. The flow model is a combination of a one-dimensional channel flow model which uses Manning-Strickler equation and a two-dimensional vertically groundwater flow model using Richards equation. Numerical simulation of heat transport consisted in a two dimensional model accounting for the effects of latent heat of phase change of water associated with melting/freezing cycles which incorporated the advection-diffusion equation describing heat-transfer in porous media. The change of hydraulic conductivity and thermal conductivity are considered by our numerical model. The model was evaluated by comparing predictions with data from laboratory freezing experiments. Experimental design was undertaken at the Laboratory M2C (Univesité de Caen-Basse Normandie, CNRS, France). The device consisted of a Plexiglas box insulated on all sides except on the top. Precipitation and ambient temperature are
Numerical modeling of lightning, blue jets, and gigantic jets
NASA Astrophysics Data System (ADS)
Riousset, Jeremy A.
Blue jets and gigantic jets are transient luminous events in the middle atmosphere that form when conventional lightning leaders escape upward from thundercloud tops and propagate toward the lower ionosphere. These events are believed to be initiated by `classic' parent lightning discharges, when they escape upward from cloud tops. The present study builds upon a previously introduced lightning model that combines the hypotheses of equipotentiality and overall charge neutrality of the lightning channel with the fractal approach allowing to describe the stochasticity and branching of the discharge. The modeling indicates that blue jets occur as a result of electrical breakdown between the upper storm charge and screening charge attracted to the cloud top; they are predicted to occur 5--10 s or less after a cloud-to-ground or intracloud discharge produces a sudden charge imbalance in the storm. A new observation is also presented of an upward discharge that supports this basic mechanism. Gigantic jets are indicated to begin as a normal intracloud discharge between dominant midlevel charge and a screening-depleted upper level charge that continues to propagate out the top of the storm. Observational support for this mechanism comes from similarity with `bolt-from-the-blue' discharges and from data on the polarity of gigantic jets. Upward discharges are analogous to cloud-to-ground lightning and their explanation provides a unifying view of how lightning escapes from a thundercloud. A two-dimensional axisymmetric model of charge relaxation in the conducting atmosphere is developed. It is used in conjunction with the lightning model to demonstrate how realistic cloud electrodynamics leads to the development of blue and gigantic jets. This model accounts for the time-dependent conduction currents and screening charges formed under the influence of the thundercloud charge sources. Particular attention is given to numerical modeling of the screening charges near the cloud
3 Lectures: "Lagrangian Models", "Numerical Transport Schemes", and "Chemical and Transport Models"
NASA Technical Reports Server (NTRS)
Douglass, A.
2005-01-01
The topics for the three lectures for the Canadian Summer School are Lagrangian Models, numerical transport schemes, and chemical and transport models. In the first lecture I will explain the basic components of the Lagrangian model (a trajectory code and a photochemical code), the difficulties in using such a model (initialization) and show some applications in interpretation of aircraft and satellite data. If time permits I will show some results concerning inverse modeling which is being used to evaluate sources of tropospheric pollutants. In the second lecture I will discuss one of the core components of any grid point model, the numerical transport scheme. I will explain the basics of shock capturing schemes, and performance criteria. I will include an example of the importance of horizontal resolution to polar processes. We have learned from NASA's global modeling initiative that horizontal resolution matters for predictions of the future evolution of the ozone hole. The numerical scheme will be evaluated using performance metrics based on satellite observations of long-lived tracers. The final lecture will discuss the evolution of chemical transport models over the last decade. Some of the problems with assimilated winds will be demonstrated, using satellite data to evaluate the simulations.
Modelling surface water flood risk using coupled numerical and physical modelling techniques
NASA Astrophysics Data System (ADS)
Green, D. L.; Pattison, I.; Yu, D.
2015-12-01
Surface water (pluvial) flooding occurs due to intense precipitation events where rainfall cannot infiltrate into the sub-surface or drain via storm water systems. The perceived risk appears to have increased in recent years with pluvial flood events seeming more severe and frequent within the UK. Surface water flood risk currently accounts for one third of all UK flood risk, with approximately two million people living in urban areas being at risk of a 1 in 200 year flood event. Surface water flooding research often focuses upon using 1D, 2D or 1D-2D coupled numerical modelling techniques to understand the extent, depth and severity of actual or hypothetical flood scenarios. Although much research has been conducted using numerical modelling, field data available for model calibration and validation is limited due to the complexities associated with data collection in surface water flood conditions. Ultimately, the data which numerical models are based upon is often erroneous and inconclusive. Physical models offer an alternative and innovative environment to collect data within. A controlled, closed system allows independent variables to be altered individually to investigate cause and effect relationships. Despite this, physical modelling approaches are seldom used in surface water flooding research. Scaled laboratory experiments using a 9m2, two-tiered physical model consisting of: (i) a mist nozzle type rainfall simulator able to simulate a range of rainfall intensities similar to those observed within the United Kingdom, and; (ii) a fully interchangeable, scaled plot surface have been conducted to investigate and quantify the influence of factors such as slope, impermeability, building density/configuration and storm dynamics on overland flow and rainfall-runoff patterns within a range of terrestrial surface conditions. Results obtained within the physical modelling environment will be compared with numerical modelling results using FloodMap (Yu & Lane, 2006
Numerical Results of Earth's Core Accumulation 3-D Modelling
NASA Astrophysics Data System (ADS)
Khachay, Yurie; Anfilogov, Vsevolod
2013-04-01
For a long time as a most convenient had been the model of mega impact in which the early forming of the Earth's core and mantle had been the consequence of formed protoplanet collision with the body of Mercurial mass. But all dynamical models of the Earth's accumulation and the estimations after the Pb-Pb system, lead to the conclusion that the duration of the planet accumulation was about 1 milliard years. But isotopic results after the W-Hf system testify about a very early (5-10) million years, dividing of the geochemical reservoirs of the core and mantle. In [1,3] it is shown, that the account of energy dissipating by the decay of short living radioactive elements and first of all Al,it is sufficient for heating even small bodies with dimensions about (50-100) km up to the iron melting temperature and can be realized a principal new differentiation mechanism. The inner parts of the melted preplanets can join and they are mainly of iron content, but the cold silicate fragments return to the supply zone. Only after the increasing of the gravitational radius, the growing area of the future core can save also the silicate envelope fragments. All existing dynamical accumulation models are constructed by using a spherical-symmetrical model. Hence for understanding the further planet evolution it is significant to trace the origin and evolution of heterogeneities, which occur on the planet accumulation stage. In that paper we are modeling distributions of temperature, pressure, velocity of matter flowing in a block of 3D- spherical body with a growing radius. The boundary problem is solved by the finite-difference method for the system of equations, which include equations which describe the process of accumulation, the Safronov equation, the equation of impulse balance, equation Navier-Stocks, equation for above litho static pressure and heat conductivity in velocity-pressure variables using the Businesque approach. The numerical algorithm of the problem solution in
Potential and limits of numerical modelling for supporting the development of HTS devices
NASA Astrophysics Data System (ADS)
Sirois, Frédéric; Grilli, Francesco
2015-04-01
In this paper, we present a general review of the status of numerical modelling applied to the design of high temperature superconductor devices. The importance of this tool is emphasized at the beginning of the paper, followed by formal definitions of the notions of models, numerical methods and numerical models. The state-of-the-art models are listed, and the main limitations of existing numerical models are reported. Those limitations are shown to concern two aspects: on the one hand, the numerical performance (i.e. speed) of the methods themselves is not good enough yet; on the other hand, the availability of model file templates, material data and benchmark problems is clearly insufficient. Paths for improving those elements are indicated in the paper. Besides the technical aspects of the research to be further pursued, for instance in adaptive numerical methods, most recommendations command for an increased collective effort for sharing files, data, codes and their documentation.
Numerical forecasting of radiation fog. Part I: Numerical model and sensitivity tests
Bergot, T.; Guedalia, D. )
1994-06-01
To improve the forecast of dense radiative fogs, a method has been developed using a one-dimensional model of the nocturnal boundary layer forced by the mesoscale fields provided by a 3D limited-area operational model. The 1D model involves a treatment of soil-atmosphere exchanges and a parameterization of turbulence in stable layers in order to correctly simulate the nocturnal atmospheric cooling. Various sensitivity tests have been carried out to evaluate the influence of the main input parameters of the model (geostrophic wind, horizontal advections, cloud cover, soil moisture, etc.) on the predicted fog characteristics. The principal result concerns the difficulty of obtaining accurate forecasts in the case of fog appearing in the middle or at the end of the night, when the local atmospheric cooling is weak. 33 refs., 13 figs.
Numerical models of a far turbulent wake of an elongated body of revolution
NASA Astrophysics Data System (ADS)
Demenkov, A. G.; Druzhinin, O. A.; Chernykh, G. G.
2016-11-01
The work presents a comparison of numerical models of a far turbulent wake of a towed elongated body of revolution in a homogeneous fluid: model based on the direct numerical simulation, and two semi-empirical models involving the equation of the turbulence energy balance. Computational results demonstrate the self-similarity of the decay and agree with known experimental data.
Numerical Modeling of Cometary Meteoroid Streams Encountering Mars and Venus
NASA Technical Reports Server (NTRS)
Christou, A. A.; Vaubaillon, J.
2011-01-01
We have simulated numerically the existence of meteoroid streams that encounter the orbits of Mars and Venus, potentially producing meteor showers at those planets. We find that 17 known comets can produce such showers, the intensity of which can be determined through observations. Six of these streams contain dense dust trails capable of producing meteor outbursts.
Numerical Cognition: On the Convergence of Componential and Psychometric Models.
ERIC Educational Resources Information Center
Geary, David C.; Widaman, Keith F.
1992-01-01
The relationship between elementary operations underlying processing of numerical information and performance on psychometrically derived ability measures requiring processing of numbers but defining separate ability factors was studied for 102 Air Force recruits (54 males and 48 females). Patterns of convergent and discriminate relationships for…
Analysis and Modeling of Buoyancy Generated Turbulence using Numerical Data.
1997-09-01
Rayleigh- Bernard convection offers a unique flow situation in which buoyancy-generated turbulence can be studied in isolation, free of the...using direct numerical simulation (DNS) data of Rayleigh- Bernard convection. In particular, we examine the pressure-strain and pressure temperature
Numerical Modelling by FLAC on Coal Fires in North China
NASA Astrophysics Data System (ADS)
Gusat, D.; Drebenstedt, C.
2009-04-01
Coal fires occur in many countries all over the world (e.g. Australia, China, India, Indonesia, USA and Russia) in underground and on surface. In China the most coal fires occur especially in the North. Economical and environmental damages are the negative effects of the coal fires: coal fires induce open fractures and fissures within the seam and neighbouring rocks. So that these are the predominant pathways for oxygen flow and exhaust gases from a coal fire. All over northern China there are a large number of coal fires, which cause and estimated yearly coal loss of between 100 and 200 million tons ([1], [2], [3]). Spontaneous combustion is a very complicated process and is influenced by number of factors. The process is an exothermic reaction in which the heat generated is dissipated by conduction to the surrounding environment, by radiation, by convection to the ventilation flow, and in some cases by evaporation of moisture from the coal [4]. The coal fires are very serious in China, and the dangerous extent of spontaneous combustion is bad which occupies about 72.9% in mining coal seams. During coal mining in China, the coal fires of spontaneous combustion are quite severity. The dangerous of coal spontaneous combustion has been in 56% of state major coalmines [5]. The 2D and 3D-simulation models describing coal fire damages are strong tools to predict fractures and fissures, to estimate the risk of coal fire propagation into neighbouring seams, to test and evaluate coal fire fighting and prevention methods. The numerical simulations of the rock mechanical model were made with the software for geomechanical and geotechnical calculations, the programs FLAC and FLAC3D [6]. To fight again the coal fires, exist several fire fighting techniques. Water, slurries or liquefied nitrogen can be injected to cool down the coal or cut of air supply with the backfill and thereby extinct the fire. Air supply also can be cut of by covering the coal by soil or sealing of the
NASA Astrophysics Data System (ADS)
Kiełczewski, K.; Tuliszka-Sznitko, E.; Bontoux, P.
2014-08-01
In the paper the authors present the results obtained during a numerical investigation (Direct Numerical Simulation/Spectral Vanishing Viscosity method - DNS/SVV) of a flow with heat transfer in rotating cavities (i.e. the flow between two concentric disks and two concentric cylinders). These model flows are useful from numerical and experimental point of view among others because of the simplicity of their geometry. Simultaneously, the flows in rotating cavities appear in numerous industrial installations and machines in the field of mechanics and chemistry, e.g., in ventilation installations, desalination tanks and waste water tanks, in cooling system, in gas turbines and axial compressors. In the paper attention is focused on the laminar-turbulent region in the configuration of the large aspect ratio i.e. Taylor-Couette flow (a Batchelor flow case of small aspect ratio Γ = 0.04 is also presented for comparison). The main purpose of computations is to investigate the influence of different parameters (the aspect ratio, the end-wall boundary conditions and temperature gradient) on the flow structure and flow characteristics. For the non-isothermal flow cases the Nusselt number distributions along cylinders are presented and are correlated with the flow structures. The λ2 method has been used for visualization.
Fractional calculus in hydrologic modeling: A numerical perspective.
Benson, David A; Meerschaert, Mark M; Revielle, Jordan
2013-01-01
Fractional derivatives can be viewed either as handy extensions of classical calculus or, more deeply, as mathematical operators defined by natural phenomena. This follows the view that the diffusion equation is defined as the governing equation of a Brownian motion. In this paper, we emphasize that fractional derivatives come from the governing equations of stable Lévy motion, and that fractional integration is the corresponding inverse operator. Fractional integration, and its multi-dimensional extensions derived in this way, are intimately tied to fractional Brownian (and Lévy) motions and noises. By following these general principles, we discuss the Eulerian and Lagrangian numerical solutions to fractional partial differential equations, and Eulerian methods for stochastic integrals. These numerical approximations illuminate the essential nature of the fractional calculus.
Fractional Calculus in Hydrologic Modeling: A Numerical Perspective
David A. Benson; Mark M. Meerschaert; Jordan Revielle
2012-01-01
Fractional derivatives can be viewed either as a handy extension of classical calculus or, more deeply, as mathematical operators defined by natural phenomena. This follows the view that the diffusion equation is defined as the governing equation of a Brownian motion. In this paper, we emphasize that fractional derivatives come from the governing equations of stable Levy motion, and that fractional integration is the corresponding inverse operator. Fractional integration, and its multi-dimensional extensions derived in this way, are intimately tied to fractional Brownian (and Levy) motions and noises. By following these general principles, we discuss the Eulerian and Lagrangian numerical solutions to fractional partial differential equations, and Eulerian methods for stochastic integrals. These numerical approximations illuminate the essential nature of the fractional calculus.
Numerical Modeling of Flow Distribution in Micro-Fluidics Systems
NASA Technical Reports Server (NTRS)
Majumdar, Alok; Cole, Helen; Chen, C. P.
2005-01-01
This paper describes an application of a general purpose computer program, GFSSP (Generalized Fluid System Simulation Program) for calculating flow distribution in a network of micro-channels. GFSSP employs a finite volume formulation of mass and momentum conservation equations in a network consisting of nodes and branches. Mass conservation equation is solved for pressures at the nodes while the momentum conservation equation is solved at the branches to calculate flowrate. The system of equations describing the fluid network is solved by a numerical method that is a combination of the Newton-Raphson and successive substitution methods. The numerical results have been compared with test data and detailed CFD (computational Fluid Dynamics) calculations. The agreement between test data and predictions is satisfactory. The discrepancies between the predictions and test data can be attributed to the frictional correlation which does not include the effect of surface tension or electro-kinetic effect.
Mathematical modeling and numerical computation of narrow escape problems
NASA Astrophysics Data System (ADS)
Cheviakov, Alexei F.; Reimer, Ashton S.; Ward, Michael J.
2012-02-01
The narrow escape problem refers to the problem of calculating the mean first passage time (MFPT) needed for an average Brownian particle to leave a domain with an insulating boundary containing N small well-separated absorbing windows, or traps. This mean first passage time satisfies the Poisson partial differential equation subject to a mixed Dirichlet-Neumann boundary condition on the domain boundary, with the Dirichlet condition corresponding to absorbing traps. In the limit of small total trap size, a common asymptotic theory is presented to calculate the MFPT in two-dimensional domains and in the unit sphere. The asymptotic MFPT formulas depend on mutual trap locations, allowing for global optimization of trap locations. Although the asymptotic theory for the MFPT was developed in the limit of asymptotically small trap radii, and under the assumption that the traps are well-separated, a comprehensive study involving comparison with full numerical simulations shows that the full numerical and asymptotic results for the MFPT are within 1% accuracy even when total trap size is only moderately small, and for traps that may be rather close together. This close agreement between asymptotic and numerical results at finite, and not necessarily asymptotically small, values of the trap size clearly illustrates one of the key side benefits of a theory based on a systematic asymptotic analysis. In addition, for the unit sphere, numerical results are given for the optimal configuration of a collection of traps on the surface of a sphere that minimizes the average MFPT. The case of N identical traps and a pattern of traps with two different sizes are considered. The effect of trap fragmentation on the average MFPT is also discussed.
Numerical modeling of a large deformation thermoforming process
Schrank, M.G.
1988-04-01
A numerical solution, using finite element methods, is presented for the simulation of a blow-molding process used to form a thermoplastic polymer (polyethylene terephthalate). The constitutive relationship employed in the analysis is a modification of the creep power law, allowing both strain hardening and strain rate hardening of the material. Analytical results compare well with experimental data for both rate of deformation during the forming process and strain distribution in the final formed configuration. 15 figs.
Numerical Facility: Convergence of Cognitive and Factor Analytic Models
1989-09-30
ability measures spanning Numerical Facility, Perceptual Speed, General Reasoning, and Memory Span factors . The 400 cognitive arithmetic problems...variable showed a direct relation to the General Reasoning and Memory Span factors . The discriminant validity of these results was demonstrated by no...Facility, Perceptual Speed, General Reasoning, and Memory Span factors . Both of the general reasoning measures require knowledge of and/or execution of
Numerical and measured data from the 3D salt canopy physical modeling project
Bradley, C.; House, L.; Fehler, M.; Pearson, J.; TenCate, J.; Wiley, R.
1997-11-01
The evolution of salt structures in the Gulf of Mexico have been shown to provide a mechanism for the trapping of significant hydrocarbon reserves. Most of these structures have complex geometries relative to the surrounding sedimentary layers. This aspect in addition to high velocities within the salt tend to scatter and defocus seismic energy and make imaging of subsalt lithology extremely difficult. An ongoing program the SEG/EAEG modeling project (Aminzadeh et al. 1994a: Aminzadeh et al. 1994b: Aminzadeh et al. 1995), and a follow-up project funded as part of the Advanced Computational Technology Initiative (ACTI) (House et al. 1996) have sought to investigate problems with imaging beneath complex salt structures using numerical modeling and more recently, construction of a physical model patterned after the numerical subsalt model (Wiley and McKnight. 1996). To date, no direct comparison of the numerical and physical aspects of these models has been attempted. We present the results of forward modeling a numerical realization of the 3D salt canopy physical model with the French Petroleum Institute (IFP) acoustic finite difference algorithm used in the numerical subsalt tests. We compare the results from the physical salt canopy model, the acoustic modeling of the physical/numerical model and the original numerical SEG/EAEG Salt Model. We will be testing the sensitivity of migration to the presence of converted shear waves and acquisition geometry.
The GISS model of the global atmosphere. [Goddard Institute for Space Studies numerical model
NASA Technical Reports Server (NTRS)
Somerville, R. C. J.; Stone, P. H.; Halem, M.; Hansen, J. E.; Hogan, J. S.; Druyan, L. M.; Quirk, W. J.; Russell, G.; Lacis, A. A.; Tenenbaum, J.
1974-01-01
A description and numerical results are presented for a global atmospheric circulation model developed at the Goddard Institute for Space Studies (GISS). The model version described is a 9-level primitive-equation model in sigma coordinates. It includes a realistic distribution of continents, oceans and topography. Detailed calculations of energy transfer by solar and terrestrial radiation make use of cloud and water vapor fields calculated by the model. The model hydrologic cycle includes two precipitation mechanisms: large-scale supersaturation and a parameterization of subgrid-scale cumulus convection. Results are presented both from a comparison of the 13th to the 43rd days (January) of one integration with climatological statistics, and from five short-range forecasting experiments. In the extended integration, the near-equilibrium January-mean model atmosphere exhibits an energy cycle in good agreement with observational estimates, together with generally realistic zonal mean fields of winds, temperature, humidity, transports, diabatic heating, evaporation, precipitation, and cloud cover.
THE EMERGENCE OF NUMERICAL AIR QUALITY FORECASTING MODELS AND THEIR APPLICATION
In recent years the U.S. and other nations have begun programs for short-term local through regional air quality forecasting based upon numerical three-dimensional air quality grid models. These numerical air quality forecast (NAQF) models and systems have been developed and test...
NASA Technical Reports Server (NTRS)
Beers, B. L.; Pine, V. W.; Hwang, H. C.; Bloomberg, H. W.; Lin, D. L.; Schmidt, M. J.; Strickland, D. J.
1979-01-01
The model consists of four phases: single electron dynamics, single electron avalanche, negative streamer development, and tree formation. Numerical algorithms and computer code implementations are presented for the first three phases. An approach to developing a code description of fourth phase is discussed. Numerical results are presented for a crude material model of Teflon.
THE EMERGENCE OF NUMERICAL AIR QUALITY FORCASTING MODELS AND THEIR APPLICATIONS
In recent years the U.S. and other nations have begun programs for short-term local through regional air quality forecasting based upon numerical three-dimensional air quality grid models. These numerical air quality forecast (NAQF) models and systems have been developed and test...
A participatory modelling approach to developing a numerical sediment dynamics model
NASA Astrophysics Data System (ADS)
Jones, Nicholas; McEwen, Lindsey; Parker, Chris; Staddon, Chad
2016-04-01
Fluvial geomorphology is recognised as an important consideration in policy and legislation in the management of river catchments. Despite this recognition, limited knowledge exchange occurs between scientific researchers and river management practitioners. An example of this can be found within the limited uptake of numerical models of sediment dynamics by river management practitioners in the United Kingdom. The uptake of these models amongst the applied community is important as they have the potential to articulate how, at the catchment-scale, the impacts of management strategies of land-use change affect sediment dynamics and resulting channel quality. This paper describes and evaluates a new approach which involves river management stakeholders in an iterative and reflexive participatory modelling process. The aim of this approach was to create an environment for knowledge exchange between the stakeholders and the research team in the process of co-constructing a model. This process adopted a multiple case study approach, involving four groups of river catchment stakeholders in the United Kingdom. These stakeholder groups were involved in several stages of the participatory modelling process including: requirements analysis, model design, model development, and model evaluation. Stakeholders have provided input into a number of aspects of the modelling process, such as: data requirements, user interface, modelled processes, model assumptions, model applications, and model outputs. This paper will reflect on this process, in particular: the innovative methods used, data generated, and lessons learnt.
Numerical Solutions for a Model of Tissue Invasion and Migration of Tumour Cells
Kolev, M.; Zubik-Kowal, B.
2011-01-01
The goal of this paper is to construct a new algorithm for the numerical simulations of the evolution of tumour invasion and metastasis. By means of mathematical model equations and their numerical solutions we investigate how cancer cells can produce and secrete matrix degradative enzymes, degrade extracellular matrix, and invade due to diffusion and haptotactic migration. For the numerical simulations of the interactions between the tumour cells and the surrounding tissue, we apply numerical approximations, which are spectrally accurate and based on small amounts of grid-points. Our numerical experiments illustrate the metastatic ability of tumour cells. PMID:21331265
NASA Astrophysics Data System (ADS)
Pilz, Tobias; Francke, Till; Bronstert, Axel
2016-04-01
Until today a large number of competing computer models has been developed to understand hydrological processes and to simulate and predict streamflow dynamics of rivers. This is primarily the result of a lack of a unified theory in catchment hydrology due to insufficient process understanding and uncertainties related to model development and application. Therefore, the goal of this study is to analyze the uncertainty structure of a process-based hydrological catchment model employing a multiple hypotheses approach. The study focuses on three major problems that have received only little attention in previous investigations. First, to estimate the impact of model structural uncertainty by employing several alternative representations for each simulated process. Second, explore the influence of landscape discretization and parameterization from multiple datasets and user decisions. Third, employ several numerical solvers for the integration of the governing ordinary differential equations to study the effect on simulation results. The generated ensemble of model hypotheses is then analyzed and the three sources of uncertainty compared against each other. To ensure consistency and comparability all model structures and numerical solvers are implemented within a single simulation environment. First results suggest that the selection of a sophisticated numerical solver for the differential equations positively affects simulation outcomes. However, already some simple and easy to implement explicit methods perform surprisingly well and need less computational efforts than more advanced but time consuming implicit techniques. There is general evidence that ambiguous and subjective user decisions form a major source of uncertainty and can greatly influence model development and application at all stages.
Numerical models of jet disruption in cluster cooling flows
NASA Technical Reports Server (NTRS)
Loken, Chris; Burns, Jack O.; Roettiger, Kurt; Norman, Mike
1993-01-01
We present a coherent picture for the formation of the observed diverse radio morphological structures in dominant cluster galaxies based on the jet Mach number. Realistic, supersonic, steady-state cooling flow atmospheres are evolved numerically and then used as the ambient medium through which jets of various properties are propagated. Low Mach number jets effectively stagnate due to the ram pressure of the cooling flow atmosphere while medium Mach number jets become unstable and disrupt in the cooling flow to form amorphous structures. High Mach number jets manage to avoid disruption and are able to propagate through the cooling flow.
Implementation of a numerical holding furnace model in foundry and construction of a reduced model
NASA Astrophysics Data System (ADS)
Loussouarn, Thomas; Maillet, Denis; Remy, Benjamin; Dan, Diane
2016-09-01
Vacuum holding induction furnaces are used for the manufacturing of turbine blades by loss wax foundry process. The control of solidification parameters is a key factor for the manufacturing of these parts in according to geometrical and structural expectations. The definition of a reduced heat transfer model with experimental identification through an estimation of its parameters is required here. In a further stage this model will be used to characterize heat exchanges using internal sensors through inverse techniques to optimize the furnace command and the optimization of its design. Here, an axisymmetric furnace and its load have been numerically modelled using FlexPDE, a finite elements code. A detailed model allows the calculation of the internal induction heat source as well as transient radiative transfer inside the furnace. A reduced lumped body model has been defined to represent the numerical furnace. The model reduction and the estimation of the parameters of the lumped body have been made using a Levenberg-Marquardt least squares minimization algorithm with Matlab, using two synthetic temperature signals with a further validation test.
NASA Technical Reports Server (NTRS)
Cushman, Paula P.
1993-01-01
Research will be undertaken in this contract in the area of Modeling Resource and Facilities Enhancement to include computer, technical and educational support to NASA investigators to facilitate model implementation, execution and analysis of output; to provide facilities linking USRA and the NASA/EADS Computer System as well as resident work stations in ESAD; and to provide a centralized location for documentation, archival and dissemination of modeling information pertaining to NASA's program. Additional research will be undertaken in the area of Numerical Model Scale Interaction/Convective Parameterization Studies to include implementation of the comparison of cloud and rain systems and convective-scale processes between the model simulations and what was observed; and to incorporate the findings of these and related research findings in at least two refereed journal articles.
Survey of three-dimensional numerical estuarine models
Cheng, Ralph T.; Smith, Peter E.
1989-01-01
This paper surveys the existing 3-D estuarine hydrodynamic and solute transport models by a review of the commonly used assumptions and approximations, and by an examination of the methods of solution. The model formulations, methods of solution, and known applications are surveyed and summarized in tables. In conclusion, the authors present their modeling philosophy and suggest future research needs.
How to Overcome Numerical Challenges to Modeling Stirling Engines
NASA Technical Reports Server (NTRS)
Dyson, Rodger W.; Wilson, Scott D.; Tew, Roy C.
2004-01-01
Nuclear thermal to electric power conversion carries the promise of longer duration missions and higher scientific data transmission rates back to Earth for a range of missions, including both Mars rovers and deep space missions. A free-piston Stirling convertor is a candidate technology that is considered an efficient and reliable power conversion device for such purposes. While already very efficient, it is believed that better Stirling engines can be developed if the losses inherent in current designs could be better understood. However, they are difficult to instrument and so efforts are underway to simulate a complete Stirling engine numerically. This has only recently been attempted and a review of the methods leading up to and including such computational analysis is presented. And finally it is proposed that the quality and depth of Stirling loss understanding may be improved by utilizing the higher fidelity and efficiency of recently developed numerical methods. One such method, the Ultra HI-FI technique is presented in detail.
Numerical modeling of turbulent flow in a channel
NASA Technical Reports Server (NTRS)
Dai, Y. W.; Ghoniem, A. F.; Sherman, F. S.; Oppenheim, A. K.
1983-01-01
Two-dimensional incompressible turbulent flow in a channel with a backward-facing step was studied numerically by Chorin's Random Vortex Method (RVM), an algorithm capable of tracing the action of elementary turbulent eddies and their cumulative effects without imposing any restrictions upon their motions. The step occurs in one side of a channel with otherwise flat, parallel walls; its height equals 1/3, 1/4 or 1/5 the width of the channel downstream. The main objective was to investigate the behavior of the large-scale turbulent eddies in a flow and the flow characteristics in the separated shear layer, the reattached zone, and the rebuilding boundary layer after reattachment. The unsteady vorticity field and the distribution of time-averaged turbulent statistics were obtained. The effects of expansion step height and initial boundary layer state were also studied. Comparisons were made with the available experimental results. The agreement is satisfactory in the velocity profiles and in the reattachment length, and fairly good in the turbulence profiles. Also a mechanism of the development of the reattaching turbulent flow was suggested by the numerical results.
Numerical modeling of incline plate LiBr absorber
NASA Astrophysics Data System (ADS)
Karami, Shahram; Farhanieh, Bijan
2011-03-01
Among major components of LiBr-H2O absorption chillers is the absorber, which has a direct effect on the chillier size and whose characteristics have significant effects on the overall efficiency of absorption machines. In this article, heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water-cooled incline plate absorber in the Reynolds number range of 5 < Re < 150 is performed numerically. The boundary layer assumptions are used for the mass, momentum and energy transport equations and the fully implicit finite difference method is employed to solve the governing equations. Dependence of lithium bromide aqueous properties to the temperature and concentration is employed as well as dependence of film thickness to vapor absorption. An analysis for linear distribution of wall temperature condition carries out to investigate the reliability of the present numerical method through comparing with previous investigation. The effect of plate angle on heat and mass transfer parameters is investigated and the results show that absorption mass flux and heat and mass transfer coefficient increase as the angle of the plate increase. The main parameters of absorber design, namely Nusselt and Sherwood numbers, are correlated as a function of Reynolds Number and the plate angle.
Nonlinear ultrasonic propagation in bubbly liquids: a numerical model.
Vanhille, Christian; Campos-Pozuelo, Cleofé
2008-05-01
In this paper, we investigate the problem of ultrasonic propagation in liquids with bubbles. A new numerical algorithm is constructed to solve the acoustic field-bubbles vibration coupled system. For this purpose, a second-order equation written in a volume formulation is considered for bubbles vibration and coupled with the linear nondissipative wave equation, i.e., attenuation and nonlinear effects are supposed to occur exclusively because of the presence of bubbles. Nonlinear characteristics of the phenomenon are particularly analyzed and illustrated. Plane harmonic waves are first considered in a mixture of air bubbles in water, and conclusions about changes in the wave speed, attenuation, harmonic distortion, effective nonlinearity parameter and nonlinear effects with distance are given. In particular, a law relating the second-harmonic progression with the density of bubbles is found. The propagation of plane pulses is also analyzed to give results on nonlinear attenuation, changes of frequency, and self-demodulation. The influence of the resonance frequency of bubbles on the nonlinear field is then determined. Differences and similarities with nonlinear acoustics in homogeneous fluid are shown and commented. The possibilities and limits of an equivalent nonlinear fluid are then discussed. The propagation of a high-frequency pulsed signal in a bubbly liquid used in a biological application is also the subject of numerical experiments, for frequencies near and beyond the resonance frequency of the bubbles.
Interrogation of numerical simulation for modeling of flow induced microstructure
Joseph, D.D.
1994-12-31
This paper summarizes recent efforts using direct numerical simulations to determine microstructural properties of fluidized suspensions of a few particles. The authors have been studying the motions of a few particles in a viscous fluid by direct numerical simulation at moderate values of the Reynolds number in the 100`s. From these simulations, they find the mechanisms which give rise to lateral migration of particles and turn the broad side of long bodies perpendicular to the stream. They find that a viscous ``stagnation`` point is a point on the body where the shear stress vanishes and the pressure is nearly a maximum. They show how the migration is controlled by stagnation and separation points and go further than before in the discussion of Segre-Silberberg effects of cross-streamline migration in two dimensions. They have analyzed the lift off and steady flight of solid capsules in Poiseuille flows. They do a three-dimensional simulation of steady flow at slow speeds and show that the extensional stresses in a viscoelastic flow change the sign of the normal stress which would exist at points of stagnation in a Newtonian fluid, causing the long side of the body to line up with the stream.
Numerical modeling of oxygen exclusion experiments of anaerobic bioventing
NASA Astrophysics Data System (ADS)
Mihopoulos, Philip G.; Suidan, Makram T.; Sayles, Gregory D.; Kaskassian, Sebastien
2002-10-01
A numerical and experimental study of transport phenomena underlying anaerobic bioventing (ABV) is presented. Understanding oxygen exclusion patterns in vadose zone environments is important in designing an ABV process for bioremediation of soil contaminated with chlorinated solvents. In particular, the establishment of an anaerobic zone of influence by nitrogen injection in the vadose zone is investigated. Oxygen exclusion experiments are performed in a pilot scale flow cell (2×1.1×0.1 m) using different venting flows and two different outflow boundary conditions (open and partially covered). Injection gas velocities are varied from 0.25×10 -3 to 1.0×10 -3 cm/s and are correlated with the ABV radius of influence. Numerical simulations are used to predict the collected experimental data. In general, reasonable agreement is found between observed and predicted oxygen concentrations. Use of impervious covers can significantly reduce the volume of forcing gas used, where an increase in oxygen exclusion efficiency is consistent with a decrease in the outflow area above the injection well.
Numerical modeling of oxygen exclusion experiments of anaerobic bioventing.
Mihopoulos, Philip G; Suidan, Makram T; Sayles, Gregory D; Kaskassian, Sebastien
2002-10-01
A numerical and experimental study of transport phenomena underlying anaerobic bioventing (ABV) is presented. Understanding oxygen exclusion patterns in vadose zone environments is important in designing an ABV process for bioremediation of soil contaminated with chlorinated solvents. In particular, the establishment of an anaerobic zone of influence by nitrogen injection in the vadose zone is investigated. Oxygen exclusion experiments are performed in a pilot scale flow cell (2 x 1.1 x 0.1 m) using different venting flows and two different outflow boundary conditions (open and partially covered). Injection gas velocities are varied from 0.25 x 10(-3) to 1.0 x 10(-3) cm/s and are correlated with the ABV radius of influence. Numerical simulations are used to predict the collected experimental data. In general, reasonable agreement is found between observed and predicted oxygen concentrations. Use of impervious covers can significantly reduce the volume of forcing gas used, where an increase in oxygen exclusion efficiency is consistent with a decrease in the outflow area above the injection well.
Numerical modelling of spallation in 2D hydrodynamics codes
NASA Astrophysics Data System (ADS)
Maw, J. R.; Giles, A. R.
1996-05-01
A model for spallation based on the void growth model of Johnson has been implemented in 2D Lagrangian and Eulerian hydrocodes. The model has been extended to treat complete separation of material when voids coalesce and to describe the effects of elevated temperatures and melting. The capabilities of the model are illustrated by comparison with data from explosively generated spall experiments. Particular emphasis is placed on the prediction of multiple spall effects in weak, low melting point, materials such as lead. The correlation between the model predictions and observations on the strain rate dependence of spall strength is discussed.
Numerical Analysis of Modeling Based on Improved Elman Neural Network
Jie, Shao
2014-01-01
A modeling based on the improved Elman neural network (IENN) is proposed to analyze the nonlinear circuits with the memory effect. The hidden layer neurons are activated by a group of Chebyshev orthogonal basis functions instead of sigmoid functions in this model. The error curves of the sum of squared error (SSE) varying with the number of hidden neurons and the iteration step are studied to determine the number of the hidden layer neurons. Simulation results of the half-bridge class-D power amplifier (CDPA) with two-tone signal and broadband signals as input have shown that the proposed behavioral modeling can reconstruct the system of CDPAs accurately and depict the memory effect of CDPAs well. Compared with Volterra-Laguerre (VL) model, Chebyshev neural network (CNN) model, and basic Elman neural network (BENN) model, the proposed model has better performance. PMID:25054172
Verification of a numerical ocean model of the Arabian Sea
NASA Astrophysics Data System (ADS)
Simmons, Ray C.; Luther, Mark E.; O'Brien, James J.; Legler, David M.
1988-12-01
A case study evaluating the predictive capability of an upper layer circulation model of the northwest Indian Ocean is presented. The model is a nonlinear, reduced gravity model incorporating realistic boundary geometry and is forced by observed winds. Model results for the fall of 1985 are compared with and evaluated against U.S. Navy bathythermograph and NOAA satellite data collected during August-November 1985. An assessment is made of the model's ability to simulate correctly the circulation structure. Ship wind observations are converted to wind stress for model forcing by a procedure developed by Legler and Navon (1988). The model is only moderately successful in reproducing the structure of the large, rather homogeneous pool of water located off the Arabian Peninsula in September. However, the model behaves remarkably well in the dynamically active region around Socotra. Major fronts and eddies frequently observed in the region during the transition period between the southwest and the northeast monsoon appear in the 1985 model results and compare well, both temporally and spatially, with the observational data. Thus given accurate wind information, the model appears highly effective in dynamically active regions and demonstrates potential as a useful prognostic tool for evaluation of the Arabian Sea when real time winds become available.
Improved numerical modeling of morphodynamics of rivers with steep banks
NASA Astrophysics Data System (ADS)
Langendoen, Eddy J.; Mendoza, Alejandro; Abad, Jorge D.; Tassi, Pablo; Wang, Dongchen; Ata, Riadh; El kadi Abderrezzak, Kamal; Hervouet, Jean-Michel
2016-07-01
The flow and sediment transport processes near steep streambanks, which are commonly found in meandering, braided, and anastomosing stream systems, exhibit complex patterns that produce intricate interactions between bed and bank morphologic adjustment. Increasingly, multi-dimensional computer models of riverine morphodynamics are used to aid in the study of these processes. A number of depth-averaged two-dimensional models are available to simulate morphologic adjustment of both bed and banks. Unfortunately, these models use overly simplified conceptual models of riverbank erosion, are limited by inflexible structured mesh systems, or are unable to accurately account for the flow and sediment transport adjacent to streambanks of arbitrary geometry. A new, nonlinear model is introduced that resolves these limitations. The model combines the river morphodynamics computer models TELEMAC-2D and SISYPHE of the open source TELEMAC-MASCARET suite of solvers with the bank erosion modules of the CONCEPTS channel evolution computer model. The performance of the new model is evaluated for meander-planform initiation and development. The most important findings are: (1) the model is able to simulate a much greater variety and complexity in meander wavelengths; (2) simulated meander development agrees closely with the unified bar-bend theory of Tubino and Seminara (1990); and (3) the rate of meander planform adjustment is greatly reduced if the wavelength of alternate bars is similar to that of meanders.
Ultrasonic-assisted manufacturing processes: variational model and numerical simulations.
Siddiq, Amir; El Sayed, Tamer
2012-04-01
We present a computational study of ultrasonic assisted manufacturing processes including sheet metal forming, upsetting, and wire drawing. A fully variational porous plasticity model is modified to include ultrasonic softening effects and then utilized to account for instantaneous softening when ultrasonic energy is applied during deformation. Material model parameters are identified via inverse modeling, i.e. by using experimental data. The versatility and predictive ability of the model are demonstrated and the effect of ultrasonic intensity on the manufacturing process at hand is investigated and compared qualitatively with experimental results reported in the literature.
Numerical and Qualitative Contrasts of Two Statistical Models ...
Two statistical approaches, weighted regression on time, discharge, and season and generalized additive models, have recently been used to evaluate water quality trends in estuaries. Both models have been used in similar contexts despite differences in statistical foundations and products. This study provided an empirical and qualitative comparison of both models using 29 years of data for two discrete time series of chlorophyll-a (chl-a) in the Patuxent River estuary. Empirical descriptions of each model were based on predictive performance against the observed data, ability to reproduce flow-normalized trends with simulated data, and comparisons of performance with validation datasets. Between-model differences were apparent but minor and both models had comparable abilities to remove flow effects from simulated time series. Both models similarly predicted observations for missing data with different characteristics. Trends from each model revealed distinct mainstem influences of the Chesapeake Bay with both models predicting a roughly 65% increase in chl-a over time in the lower estuary, whereas flow-normalized predictions for the upper estuary showed a more dynamic pattern, with a nearly 100% increase in chl-a in the last 10 years. Qualitative comparisons highlighted important differences in the statistical structure, available products, and characteristics of the data and desired analysis. This manuscript describes a quantitative comparison of two recently-
Pohlmann, Karl; Ye, Ming; Pohll, Greg; Chapman, Jenny
2007-01-19
Numerical groundwater models are based on conceptualizations of hydrogeologic systems that are by necessity developed from limited information and therefore are simplifications of real conditions. Each aspect (e.g. recharge, hydrostratigraphy, boundary conditions) of the groundwater model is often based on a single conceptual model that is considered to be the best representation given the available data. However, the very nature of their construction means that each conceptual model is inherently uncertain and the available information may be insufficient to refute plausible alternatives, thereby raising the possibility that the flow model is underestimating overall uncertainty. In this study we use the Death Valley Regional Flow System model developed by the U.S. Geological Survey as a framework to predict regional groundwater flow southward into Yucca Flat on the Nevada Test Site. An important aspect of our work is to evaluate the uncertainty associated with multiple conceptual models of groundwater recharge and subsurface hydrostratigraphy and quantify the impacts of this uncertainty on model predictions. In our study, conceptual model uncertainty arises from two sources: (1) alternative interpretations of the hydrostratigraphy in the northern portion of Yucca Flat where, owing to sparse data, the hydrogeologic system can be conceptualized in different ways, and (2) uncertainty in groundwater recharge in the region as evidenced by the existence of several independent approaches for estimating this aspect of the hydrologic system. The composite prediction of groundwater flow is derived from the regional model that formally incorporates the uncertainty in these alternative input models using the maximum likelihood Bayesian model averaging method. An assessment of the joint predictive uncertainty of the input conceptual models is also produced. During this process, predictions of the alternative models are weighted by model probability, which is the degree of
Mathematical model and its fast numerical method for the tumor growth.
Lee, Hyun Geun; Kim, Yangjin; Kim, Junseok
2015-12-01
In this paper, we reformulate the diffuse interface model of the tumor growth (S.M. Wise et al., Three-dimensional multispecies nonlinear tumor growth-I: model and numerical method, J. Theor. Biol. 253 (2008) 524--543). In the new proposed model, we use the conservative second-order Allen--Cahn equation with a space--time dependent Lagrange multiplier instead of using the fourth-order Cahn--Hilliard equation in the original model. To numerically solve the new model, we apply a recently developed hybrid numerical method. We perform various numerical experiments. The computational results demonstrate that the new model is not only fast but also has a good feature such as distributing excess mass from the inside of tumor to its boundary regions.
Numerical Modeling of Two-Dimensional Width-Averaged Flows using Boundary-Fitted Coordinate Systems.
1985-08-01
A This report should be cited as follows: Thompson , J . F ., and Bernard, R. S. 1985. "Numerical Modeling of Two...Part 1. Theory," Journal of Fluid Mechanics, Vol 65, No. 657. 8. Thompson , J . F ., ed. 1982a. Numerical Grid Generation, Proceed- ings of a Symposium on...a’ . . . . . . . . , ,- . . . . ... . . ... . • . .r, . . . 12. Thompson , J . F ., and Bernard, R. S. 1985. "WESSEL: Code for f Numerical Simulation of
Numerical modeling of the flow in a cryogenic fuel tank
NASA Astrophysics Data System (ADS)
Greer, Donald Steven
Developing reusable flight weight cryogenic fuel tanks is one of the technological challenges in designing advanced hypersonic aircraft and the next generation of spacecraft. As an aid in the design of these aircraft, a computational fluid dynamics (CFD) model has been developed specifically for the analysis of flow in a cryogenic fuel tank. The model simulates the transient, two dimensional draining of a fuel tank cross section. The interface between the ullage gas and liquid fuel is modeled as a free surface to enable the calculation of slosh wave dynamics. The drain rate of the liquid fuel is specified as a boundary condition to the model. The ullage gas enters the model to replace the volume of drained liquid. The rate of ullage gas entering the model is calculated from boundary conditions of constant pressure and temperature for the ullage gas. The model employs the full set of Navier-Stokes equations with the exception that viscous dissipation is neglected in the energy equation. The method of solution is an explicit finite difference technique in two dimensional generalized coordinates approximated to second order accuracy in both space and time. The stiffness due to the low Mach number is handled by the method of artificial compressibility. Model comparisons are made to experimental data for free convection to a vertical plate and to free convection inside a horizontal cylinder. Slosh wave dynamics are compared to potential flow calculations for waves inside a square tank. Sample calculations are also performed on a rectangular tank and an eight sided polygon tank to demonstrate the capability of the model.
2011-07-28
nonequilibrium. For example, the plasma transport may transition between rarefied and continuum flow , requiring appropriate models for each case through...AFRL-AFOSR-UK-TR-2011-0023 Advanced Physical Models and Numerical Methods for High Enthalpy and Plasma Flows Applied to Hypersonics...2010 4. TITLE AND SUBTITLE Advanced Physical Models and Numerical Methods for High Enthalpy and Plasma Flows Applied to Hypersonics 5a
Numerical modeling of geothermal systems with applications to Krafla, Iceland and Olkaria, Kenya
Bodvarsson, G.S.
1987-08-01
The use of numerical models for the evaluation of the generating potential of high temperature geothermal fields has increased rapidly in recent years. In the present paper a unified numerical approach to the modeling of geothermal systems is discussed and the results of recent modeling of the Krafla geothermal field in Iceland and the Olkaria, Kenya, are described. Emphasis is placed on describing the methodology using examples from the two geothermal fields.
Improved numerical solutions for chaotic-cancer-model
NASA Astrophysics Data System (ADS)
Yasir, Muhammad; Ahmad, Salman; Ahmed, Faizan; Aqeel, Muhammad; Akbar, Muhammad Zubair
2017-01-01
In biological sciences, dynamical system of cancer model is well known due to its sensitivity and chaoticity. Present work provides detailed computational study of cancer model by counterbalancing its sensitive dependency on initial conditions and parameter values. Cancer chaotic model is discretized into a system of nonlinear equations that are solved using the well-known Successive-Over-Relaxation (SOR) method with a proven convergence. This technique enables to solve large systems and provides more accurate approximation which is illustrated through tables, time history maps and phase portraits with detailed analysis.
Numerically Solvable Model for Resonant Collisions of Electronswith Diatomic Molecules
Houfek, Karel; Rescigno, T.N.; McCurdy, C.W.
2006-01-27
We describe a simple model for electron-molecule collisions that has one nuclear and one electronic degree of freedom and that can be solved to arbitrarily high precision, without making the Born-Oppenheimer approximation, by employing a combination of the exterior complex scaling method and a finite-element implementation of the discrete variable representation. We compare exact cross sections for vibrational excitation and dissociative attachment with results obtained using the local complex potential approximation as commonly applied in the ''boomerang'' model, and suggest how this two-dimensional model can be used to test the underpinnings of contemporary nonlocal approximations to resonant collisions.
Evaluation of kinetic uncertainty in numerical models of petroleum generation
Peters, K.E.; Walters, C.C.; Mankiewicz, P.J.
2006-01-01
Oil-prone marine petroleum source rocks contain type I or type II kerogen having Rock-Eval pyrolysis hydrogen indices greater than 600 or 300-600 mg hydrocarbon/g total organic carbon (HI, mg HC/g TOC), respectively. Samples from 29 marine source rocks worldwide that contain mainly type II kerogen (HI = 230-786 mg HC/g TOC) were subjected to open-system programmed pyrolysis to determine the activation energy distributions for petroleum generation. Assuming a burial heating rate of 1??C/m.y. for each measured activation energy distribution, the calculated average temperature for 50% fractional conversion of the kerogen in the samples to petroleum is approximately 136 ?? 7??C, but the range spans about 30??C (???121-151??C). Fifty-two outcrop samples of thermally immature Jurassic Oxford Clay Formation were collected from five locations in the United Kingdom to determine the variations of kinetic response for one source rock unit. The samples contain mainly type I or type II kerogens (HI = 230-774 mg HC/g TOC). At a heating rate of 1??C/m.y., the calculated temperatures for 50% fractional conversion of the Oxford Clay kerogens to petroleum differ by as much as 23??C (127-150??C). The data indicate that kerogen type, as defined by hydrogen index, is not systematically linked to kinetic response, and that default kinetics for the thermal decomposition of type I or type II kerogen can introduce unacceptable errors into numerical simulations. Furthermore, custom kinetics based on one or a few samples may be inadequate to account for variations in organofacies within a source rock. We propose three methods to evaluate the uncertainty contributed by kerogen kinetics to numerical simulations: (1) use the average kinetic distribution for multiple samples of source rock and the standard deviation for each activation energy in that distribution; (2) use source rock kinetics determined at several locations to describe different parts of the study area; and (3) use a weighted
Numerical Modelling of Drawbeads for Forming of Aluminium Alloys
NASA Astrophysics Data System (ADS)
Joshi, Y.; Christiansen, P.; Masters, I.; Bay, N.; Dashwood, R.
2016-08-01
The drawbeads in stamping tools are usually designed based on experience from the forming of steel. However, aluminium alloys display different forming behaviour to steels, which is not reflected in the drawbead design for tools used for stamping aluminium. This paper presents experimental results from different semi-circular drawbead geometries commonly encountered in automotive dies and compares them to those obtained from Stoughton's analytical drawbead model and the 2D plane strain drawbead model set up using LS-DYNA. The study was conducted on lubricated NG5754 strips. The results presented are in terms of drawbead restraining force versus strip displacement, as a function of drawbead depth. The FE drawbead model agrees well with the experiments whereas the analytical model overpredicted the drawbead forces.
Comparison of Numerical Models for Computing Underwater Light Fields
1994-04-01
L is an analytic process, and thus there are body. Depth integration of the Riccati equations (by no Monte Carlo fluctuations in the computed radi - a...1)gj(T) C. Model MCI [ Monte Carlo (Gordon)] i=m This model simulates radiative transfer in both the ( M - i)! ocean and the atmosphere, as coupled...Kattawar and C. Adams, " Radiative transfer in spherical (1974). shell atmospheres. II. asymmetric phase functions ," Icarus 38. R. Stavn and A
Numerical modeling of hydrofracturing in a multilayer coal seam
Nasedkina, A.A.; Trufanov, V.N.
2006-01-15
The mathematical model of the process for hydrodynamic fracturing in a multilayer coal seam is proposed. The model is based on the equation of continuity and Darcy's law. The filtration-temperature analogy allows solving the obtained non-linear, non-stationary problem in an axisymmetric statement for the pressure function as the heat-conductivity problem, by the finite-element method. The calculation results yield estimation of the radius of degassing borehole influence zone.
Numerical considerations in the development and implementation of constitutive models
NASA Technical Reports Server (NTRS)
Haisler, W. E.; Imbrie, P. K.
1985-01-01
Several unified constitutive models were tested in uniaxial form by specifying input strain histories and comparing output stress histories. The purpose of the tests was to evaluate several time integration methods with regard to accuracy, stability, and computational economy. The sensitivity of the models to slight changes in input constants was also investigated. Results are presented for In100 at 1350 F and Hastelloy-X at 1800 F.
Coastal Modeling System: Mathematical Formulations and Numerical Methods
2014-03-01
number [rad/m]. The wave radiation stresses and their gradients are computed within the wave model and interpolated in space and time in the flow...operator. The equation is solved given any number of user-specified initial salinity values at locations within the model domain, using the initial...load correction factors based on the logarithmic velocity profile and (a) exponential and (b) Rouse suspended sediment profile. The Rouse number is
Implementation of the Automated Numerical Model Performance Metrics System
2011-09-26
gradient ( BLG ) are computed forming additional sets of matches, all of which can be statistically analysed. More RP33 parameters are being considered for...terminology for the type of model, the domain over which the model ran, a 10-digit date- time group and, if applicable, the one TAU. The date-time group ...extensions are used in this software package. The root part of the name is a 10-digit date-time group with the same layout as described above
Numerical Model Sensitivity to Heterogeneous Satellite Derived Vegetation Roughness
NASA Technical Reports Server (NTRS)
Jasinski, Michael; Eastman, Joseph; Borak, Jordan
2011-01-01
The sensitivity of a mesoscale weather prediction model to a 1 km satellite-based vegetation roughness initialization is investigated for a domain within the south central United States. Three different roughness databases are employed: i) a control or standard lookup table roughness that is a function only of land cover type, ii) a spatially heterogeneous roughness database, specific to the domain, that was previously derived using a physically based procedure and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery, and iii) a MODIS climatologic roughness database that like (i) is a function only of land cover type, but possesses domain specific mean values from (ii). The model used is the Weather Research and Forecast Model (WRF) coupled to the Community Land Model within the Land Information System (LIS). For each simulation, a statistical comparison is made between modeled results and ground observations within a domain including Oklahoma, Eastern Arkansas, and Northwest Louisiana during a 4-day period within IHOP 2002. Sensitivity analysis compares the impact the three roughness initializations on time-series temperature, precipitation probability of detection (POD), average wind speed, boundary layer height, and turbulent kinetic energy (TKE). Overall, the results indicate that, for the current investigation, replacement of the standard look-up table values with the satellite-derived values statistically improves model performance for most observed variables. Such natural roughness heterogeneity enhances the surface wind speed, PBL height and TKE production up to 10 percent, with a lesser effect over grassland, and greater effect over mixed land cover domains.
Investigation of some numerical issues in a chemistry-transport model: Gas-phase simulations
NASA Astrophysics Data System (ADS)
Mallet, Vivien; Pourchet, AdéLaïDe; QuéLo, Denis; Sportisse, Bruno
2007-08-01
Many numerical strategies have been specifically developed for chemistry-transport models. Since no exact solutions are available for 3-D real problems, there are only few insights to choose between alternative numerical schemes and approximations, or to estimate the performance discrepancy between two approaches. However it is possible to assess the importance of numerical approximations through the comparison of different strategies. We estimated the impact of several numerical schemes for advection, diffusion and stiff chemistry. We also addressed operator splitting with different methods and operator orders. The study is performed with a gas-phase Eulerian model from the modeling platform Polyphemus. It is applied to ozone forecasts mainly over Europe, with focus on a few key species: ozone, nitric oxide, nitrogen dioxide, sulfur dioxide and hydroxy radical. The outcome is a ranking of the most sensitive numerical choices. It stresses the prominent impact of the advection scheme and of the splitting time step.
Numerical Modeling of Liquid-Vapor Phase Change
NASA Technical Reports Server (NTRS)
Esmaeeli, Asghar; Arpaci, Vedat S.
2001-01-01
We implemented a two- and three-dimensional finite difference/front tracking technique to solve liquid-vapor phase change problems. The mathematical and the numerical features of the method were explained in great detail in our previous reports, Briefly, we used a single formula representation which incorporated jump conditions into the governing equations. The interfacial terms were distributed as singular terms using delta functions so that the governing equations would be the same as conventional conservation equations away from the interface and in the vicinity of the interface they would provide correct jump conditions. We used a fixed staggered grid to discretize these equations and an unstructured grid to explicitly track the front. While in two dimensions the front was simply a connection of small line segments, in three dimensions it was represented by a connection of small triangular elements. The equations were written in conservative forms and during the course of computations we used regriding to control the size of the elements of the unstructured grid. Moreover, we implemented a coalescence in two dimensions which allowed the merging of different fronts or two segments of the same front when they were sufficiently close. We used our code to study thermocapillary migration of bubbles, burst of bubbles at a free surface, buoyancy-driven interactions of bubbles, evaporation of drops, rapid evaporation of an interface, planar solidification of an undercooled melt, dendritic solidification, and a host of other problems cited in the reference.
Numerical modelling of longitudinal vibrations of a sucker rod string
NASA Astrophysics Data System (ADS)
Shardakov, I. N.; Wasserman, I. N.
2010-03-01
A new technique for analyzing the dynamic behavior of a sucker rod string used in the oil well industry is presented. The main difficulty in the numerical calculation of the examined structure is a multivalued velocity—force relation determined by Coulomb's friction and by loads generated during operation of pump valves. Both the monotonic and nonmonotonic velocity—force relations are considered. A quasi-variational inequality formulation of the problem is proposed. The solution of the inequality amounts to finding the minimum of a convex nonsmooth functional at each time step by means of the Newmark difference time scheme, successive iterations and finite element discretization. The problem of functional minimization is reduced to construction of a sequence of smooth nonlinear programming problems by introducing the auxiliary variables and applying the augmented Lagrangian method. The proposed approach is used to study the longitudinal vibrations of sucker rod strings under near-real conditions. In such systems the most commonly occurring vibration modes are the stick-slip vibrations and the vibrations with natural force excited twice a cycle. The nonmonotonic character of the friction law leads to intensification of these vibrations. In the case of nonmonotonic friction law the stick-slip vibrations can occur even under the action of constant external forces.
Numerical and physical modelling of bubbly flow phenomena
Sangani, A.S.
1991-01-01
The objective of this study is to develop theoretical tools -- analytical as well as numerical -- for understanding how the flows of bubbly liquids are affected by its microstructure, i.e., the detailed spatial, size, and velocity distribution of bubbles, and how the microstructure, in turn, is affected by the flow. This report describes the progress made to date on the several problems that are being studied. The first problem is concerned with the molecular-dynamics type simulations of monodispersed bubbly liquids under equilibrium and homogeneous conditions and their application to slightly inhomogeneous flows. The Reynolds number is large and the Weber and Froud numbers are small in these simulations. The second problem is concerned with the simulations of flows of bubbly liquids undergoing small amplitude oscillatory motion. Both the cases of bubbles with rigid (due to impurities) and stress-free interfaces are examined. The results are related to the added mass, Basset, and viscous drag coefficients. The third problem is concerned with the acoustic wave propagation in bubbly liquids at frequencies above natural frequency of the bubbles. The second problem is completed as of this writing. Work on the other two problems is currently in progress. A summary of the work to be carried out during the period 1/91 to 6/92 is given in the last section. 4 figs.
Numerical modeling of high power breakdown in metamaterials
NASA Astrophysics Data System (ADS)
Kourtzanidis, Konstantinos; Pederson, Dylan; Raja, Laxminarayan
2016-09-01
Metamaterials consist of sub-wavelength structural inclusions layered in a periodic fashion, which provide an effective response to electromagnetic (EM) radiation. The electric or magnetic responses of these materials are based on the resonant nature of their constitutive micro-structures. Under high power EM radiation, these resonances can result in the production of high amplitude currents and field amplification. Depending on the background gas and supporting pressure, breakdown can occur. The formation of plasma can strongly modify the EM response of the metamaterial and thus a detailed study on the breakdown threshold, plasma localization and EM response modification is necessary. Here, we present three-dimensional numerical simulations of high power - high frequency air breakdown in metamaterials. We use a self-consistent fluid description of the plasma formation and dynamics coupled with Maxwell's equations via the electron momentum equation. We study two typical (for metamaterials) micro-structures: The Split Ring Resonator and the Cut Wire pairs. Breakdown threshold is identified for both configurations. Calculations of transmittance and retrieval of the metamaterials' effective parameters help us quantify the effect of plasma formation on the EM response of these metamaterials.
Numerical model of porewater fluxes in a hypothetical mud island
Langevin, C.D.; Vacher, H.L.; Stewart, M.T. . Geology Dept.)
1994-03-01
The barely emergent circular islands of Florida Bay consist of a low-permeability aragonite mud overlying a high-permeability limestone that is hydraulically connected with the bay. An ephemeral pond, which forms when tides are above a low-lying berm that surrounds the island, increases in density because of intense evaporation. As a result, porewater in the island can be expected to flow downward through the sediments in response to a topographic drive, which results from the elevated level of the pond, and a variable-density drive due to the higher densities of the pond water. Porewater fluxes for an infinite-strip version of a Florida Bay mud island re obtained by numerical simulation using MODFLOW and MOCDENSE. Eight variables describe porewater flow through such an island: porewater flux (Q), cross-sectional width (w), pond length ([ell]), island length (L), depth to limestone (b), hydraulic conductivity of the mud and limestone layers (K[sub 1] and K[sub 2], respectively), and total head drive. These eight variables are reduced to five dimensionless variables; dimensionless flux (Q/K[sub 1]wL), hydraulic conductivity ratio (K[sub 2]/K[sub 1]), dimensionless head drive (T[sub D]/b), relative pond size ([ell]/L), and aspect ratio (L/b; which is held constant in this study with a value of 56). The results of the dimensionless relationships can be used to assess the porewater flux in islands resembling those of Florida Bay.
Numerical modeling of the wind flow over a transverse dune.
Araújo, Ascânio D; Parteli, Eric J R; Pöschel, Thorsten; Andrade, José S; Herrmann, Hans J
2013-10-04
Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee - the separation bubble - displays a surprisingly strong dependence on the wind shear velocity, u: it is nearly independent of u for shear velocities within the range between 0.2 m/s and 0.8 m/s but increases linearly with u for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if u is larger than approximately 0.39 m/s, whereas a larger value of u (about 0.49 m/s) is required to initiate this reverse transport.
Numerical modeling of the wind flow over a transverse dune
Araújo, Ascânio D.; Parteli, Eric J. R.; Pöschel, Thorsten; Andrade, José S.; Herrmann, Hans J.
2013-01-01
Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee — the separation bubble — displays a surprisingly strong dependence on the wind shear velocity, u*: it is nearly independent of u* for shear velocities within the range between 0.2 m/s and 0.8 m/s but increases linearly with u* for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if u* is larger than approximately 0.39 m/s, whereas a larger value of u* (about 0.49 m/s) is required to initiate this reverse transport. PMID:24091456
Numerical modelling of crural fascia mechanical interaction with muscular compartments.
Pavan, Piero G; Pachera, Paola; Natali, Arturo N
2015-05-01
The interaction of the crural fascia with muscular compartments and surrounding tissues can be at the origin of different pathologies, such as compartment syndrome. This pathology consists in the onset of excessive intracompartmental pressure, which can have serious consequences for the patient, compromising blood circulation. The investigation of compartment syndrome etiology also takes into account the alteration of crural fascia mechanical properties as a cause of the syndrome, where the fascial stiffening would result in the rise of intracompartmental pressure. This work presents a computational approach toward evaluating some biomechanical aspects of the problem, within the context of a more global viewpoint. Finite element analyses of the interaction phenomena of the crural fascia with adjacent regions are reported here. This study includes the effects of a fascial stiffness increase along the proximal-distal direction and their possible clinical implications. Furthermore, the relationship between different pre-strain levels of the crural fascia in the proximal-distal direction and the rise of internal pressure in muscular compartments are considered. The numerical analyses can clarify which aspects could be directly implied in the rise of compartment syndrome, leading to greater insight into muscle-fascia mechanical phenomena, as well as promoting experimental investigation and clinical analysis of the syndrome.
Numerical Modeling of the South Pole-Aitkin Impact
NASA Technical Reports Server (NTRS)
Collins, G. S.; Melosh, H. J.
2004-01-01
The South Pole-Aitkin (SPA) basin, on the far side of the Moon, is the largest and oldest impact structure still preserved in the solar system. The crater is about 2500 km in diameter and formed in the Pre-Nectarian era of lunar history, over 4 Gyr ago. At this time, the thermal state of the Moon was much hotter than it is today. Accretional energy from the rapidly forming Moon melted the outermost few hundred kilometers of the Moon. As this magma ocean differentiated and cooled a 60 100-km thick low-density crust formed at the surface; below this the residual melt, with a higher density, cooled to form the lunar mantle. The giant SPA impact event punctured the Moon some time during the cooling of the magma ocean and thus provides a unique window for studying the lunar interior and the early formative processes of the Moon. The impact excavated otherwise inaccessible samples of the deep crust and (possibly) upper mantle, which has inspired proposed sample return missions. Furthermore, the thermal and rheologic state of the early Moon played a role in shaping the final structure of the basin. To aid in site selection for future sample return missions to the SPA basin, and to investigate the effect of thermal state on final crater structure, we performed some numerical simulations of the SPA impact event.
A benchmark study of numerical schemes for one-dimensional arterial blood flow modelling.
Boileau, Etienne; Nithiarasu, Perumal; Blanco, Pablo J; Müller, Lucas O; Fossan, Fredrik Eikeland; Hellevik, Leif Rune; Donders, Wouter P; Huberts, Wouter; Willemet, Marie; Alastruey, Jordi
2015-10-01
Haemodynamical simulations using one-dimensional (1D) computational models exhibit many of the features of the systemic circulation under normal and diseased conditions. Recent interest in verifying 1D numerical schemes has led to the development of alternative experimental setups and the use of three-dimensional numerical models to acquire data not easily measured in vivo. In most studies to date, only one particular 1D scheme is tested. In this paper, we present a systematic comparison of six commonly used numerical schemes for 1D blood flow modelling: discontinuous Galerkin, locally conservative Galerkin, Galerkin least-squares finite element method, finite volume method, finite difference MacCormack method and a simplified trapezium rule method. Comparisons are made in a series of six benchmark test cases with an increasing degree of complexity. The accuracy of the numerical schemes is assessed by comparison with theoretical results, three-dimensional numerical data in compatible domains with distensible walls or experimental data in a network of silicone tubes. Results show a good agreement among all numerical schemes and their ability to capture the main features of pressure, flow and area waveforms in large arteries. All the information used in this study, including the input data for all benchmark cases, experimental data where available and numerical solutions for each scheme, is made publicly available online, providing a comprehensive reference data set to support the development of 1D models and numerical schemes.
Current status of one- and two-dimensional numerical models: Successes and limitations
NASA Technical Reports Server (NTRS)
Schwartz, R. J.; Gray, J. L.; Lundstrom, M. S.
1985-01-01
The capabilities of one and two-dimensional numerical solar cell modeling programs (SCAP1D and SCAP2D) are described. The occasions when a two-dimensional model is required are discussed. The application of the models to design, analysis, and prediction are presented along with a discussion of problem areas for solar cell modeling.
IMPROVED NUMERICAL METHODS FOR MODELING RIVER-AQUIFER INTERACTION.
Tidwell, Vincent Carroll; Sue Tillery; Phillip King
2008-09-01
A new option for Local Time-Stepping (LTS) was developed to use in conjunction with the multiple-refined-area grid capability of the U.S. Geological Survey's (USGS) groundwater modeling program, MODFLOW-LGR (MF-LGR). The LTS option allows each local, refined-area grid to simulate multiple stress periods within each stress period of a coarser, regional grid. This option is an alternative to the current method of MF-LGR whereby the refined grids are required to have the same stress period and time-step structure as the coarse grid. The MF-LGR method for simulating multiple-refined grids essentially defines each grid as a complete model, then for each coarse grid time-step, iteratively runs each model until the head and flux changes at the interfacing boundaries of the models are less than some specified tolerances. Use of the LTS option is illustrated in two hypothetical test cases consisting of a dual well pumping system and a hydraulically connected stream-aquifer system, and one field application. Each of the hypothetical test cases was simulated with multiple scenarios including an LTS scenario, which combined a monthly stress period for a coarse grid model with a daily stress period for a refined grid model. The other scenarios simulated various combinations of grid spacing and temporal refinement using standard MODFLOW model constructs. The field application simulated an irrigated corridor along the Lower Rio Grande River in New Mexico, with refinement of a small agricultural area in the irrigated corridor.The results from the LTS scenarios for the hypothetical test cases closely replicated the results from the true scenarios in the refined areas of interest. The head errors of the LTS scenarios were much smaller than from the other scenarios in relation to the true solution, and the run times for the LTS models were three to six times faster than the true models for the dual well and stream-aquifer test cases, respectively. The results of the field application
Numerical simulations of Hurricane Bertha using a mesoscale atmospheric model
Buckley, R.L.
1996-08-01
The Regional Atmospheric Model System (RAMS) has been used to simulate Hurricane Bertha as it moved toward and onto shore during the period July 10--12, 1996. Using large-scale atmospheric data from 00 UTC, 11 July (Wednesday evening) to initialize the model, a 36-hour simulation was created for a domain centered over the Atlantic Ocean east of the Florida coast near Jacksonville. The simulated onshore impact time of the hurricane was much earlier than observed (due to the use of results from the large-scale model, which predicted early arrival). However, the movement of the hurricane center (eye) as it approached the North Carolina/South Carolina coast as simulated in RAMS was quite good. Observations revealed a northerly storm track off the South Carolina coast as it moved toward land. As it approached landfall, Hurricane Bertha turned to the north-northeast, roughly paralleling the North Carolina coast before moving inland near Wilmington. Large-scale model forecasts were unable to detect this change in advance and predicted landfall near Myrtle Beach, South Carolina; RAMS, however, correctly predicted the parallel coastal movement. For future hurricane activity in the southeast, RAMS is being configured to run in an operational model using input from the large-scale pressure data in hopes of providing more information on predicted hurricane movement and landfall location.
NASA Astrophysics Data System (ADS)
Napier, W. J.; Ensberg, J. J.; Seinfeld, J. H.
2014-10-01
The new generation of secondary organic aerosol (SOA) models that represent gas- and particle-phase chemistry and thermodynamic partitioning using discrete two-dimensional grids (e.g. SOM, 2D-VBS) cannot be efficiently implemented into three-dimensional atmospheric chemical transport models (CTMs) due to the large number of bins (tracers) required. In this study, we introduce a novel mathematical framework, termed the Oxidation State/Volatility Moment Method, that is designed to address these computational burdens so as to allow the new generation of SOA models to be implemented into CTMs. This is accomplished by mapping the two-dimensional grids onto probability distributions that conserve carbon and oxygen mass. Assessment of the Moment Method strengths (speed, carbon and oxygen conservation) and weaknesses (numerical drift) provide valuable insight that can guide future development of SOA modules for atmospheric CTMs.
Remote sensing applied to numerical modelling. [water resources pollution
NASA Technical Reports Server (NTRS)
Sengupta, S.; Lee, S. S.; Veziroglu, T. N.; Bland, R.
1975-01-01
Progress and remaining difficulties in the construction of predictive mathematical models of large bodies of water as ecosystems are reviewed. Surface temperature is at present the only variable than can be measured accurately and reliably by remote sensing techniques, but satellite infrared data are of sufficient resolution for macro-scale modeling of oceans and large lakes, and airborne radiometers are useful in meso-scale analysis (of lakes, bays, and thermal plumes). Finite-element and finite-difference techniques applied to the solution of relevant coupled time-dependent nonlinear partial differential equations are compared, and the specific problem of the Biscayne Bay and environs ecosystem is tackled in a finite-differences treatment using the rigid-lid model and a rigid-line grid system.
Numerical modeling of cavitational resonant oscillations of a liquid
NASA Astrophysics Data System (ADS)
Iakovtsov, A. V.
Using the method of differential approximation, the dispersion characteristics of the Lax-Wendroff (LW) schemes and LW schemes with correction of Boris-Book flows are analyzed. It is shown that the combined Lax-Wendroff-Boris-Books scheme is capable of suppressing variance errors. Several fluid models are analyzed. Using three models of the combined scheme, the induced oscillations of a water column are calculated, and it is shown that the amplitude-frequency characteristics of oscillations calculated using a model of a liquid with bubbles are in good agreement with experimental data. Special attention is given to estimating boundary conditions and to determinations of the behavior of an oscillation process with increasing excitation frequencies.
Numerical simulation of turbomachinery flows with advanced turbulence models
NASA Technical Reports Server (NTRS)
Lakshminarayana, B.; Kunz, R.; Luo, J.; Fan, S.
1992-01-01
A three dimensional full Navier-Stokes (FNS) code is used to simulate complex turbomachinery flows. The code incorporates an explicit multistep scheme and solves a conservative form of the density averaged continuity, momentum, and energy equations. A compressible low Reynolds number form of the k-epsilon turbulence model, and a q-omega model and an algebraic Reynolds stress model have been incorporated in a fully coupled manner to approximate Reynolds stresses. The code is used to predict the viscous flow field in a backswept transonic centrifugal compressor for which laser two focus data is available. The code is also used to simulate the tip clearance flow in a cascade. The code has been extended to include unsteady Euler solutions for predicting the unsteady flow through a cascade due to incoming wakes, simulating rotor-stator interactions.
Numerical Investigation of Grain Coarsening and Coalescence Model
NASA Astrophysics Data System (ADS)
Muradova, Aliki D.; Hristopulos, Dionisios T.
2015-01-01
A kinetic nonlinear model of mass transfer, grain coarsening and coalescence with potential applications in sintering processes is studied. The model involves nonlinear differential equations that determine the transport of mass between grains. The rate of mass transfer is controlled by the activation energy (an Arrhenius factor) leading to a nonlinear model of mass transfer and grain coarsening. The resulting dynamical system of coupled nonlinear differential equations with random initial conditions (i.e., initial grain mass configuration) is solved by means of the Runge-Kutta method. An analysis of the fixed points of the two-grain system is carried out, and the solution of the multi-grain system is studied. We incorporate coalescence of smaller grains with larger neighbors using a cellular automaton step in the evolution of the system.
Numerical modelling of floating debris in the world's oceans.
Lebreton, L C-M; Greer, S D; Borrero, J C
2012-03-01
A global ocean circulation model is coupled to a Lagrangian particle tracking model to simulate 30 years of input, transport and accumulation of floating debris in the world ocean. Using both terrestrial and maritime inputs, the modelling results clearly show the formation of five accumulation zones in the subtropical latitudes of the major ocean basins. The relative size and concentration of each clearly illustrate the dominance of the accumulation zones in the northern hemisphere, while smaller seas surrounded by densely populated areas are also shown to have a high concentration of floating debris. We also determine the relative contribution of different source regions to the total amount of material in a particular accumulation zone. This study provides a framework for describing the transport, distribution and accumulation of floating marine debris and can be continuously updated and adapted to assess scenarios reflecting changes in the production and disposal of plastic worldwide.
Development, testing, and numerical modeling of a foam sandwich biocomposite
NASA Astrophysics Data System (ADS)
Chachra, Ricky
This study develops a novel sandwich composite material using plant based materials for potential use in nonstructural building applications. The face sheets comprise woven hemp fabric and a sap based epoxy, while the core comprises castor oil based foam with waste rice hulls as reinforcement. Mechanical properties of the individual materials are tested in uniaxial compression and tension for the foam and hemp, respectively. The sandwich composite is tested in 3 point bending. Flexural results are compared to a finite element model developed in the commercial software Abaqus, and the validated model is then used to investigate alternate sandwich geometries. Sandwich model responses are compared to existing standards for nonstructural building panels, showing that the novel material is roughly half the strength of equally thick drywall. When space limitations are not an issue, a double thickness sandwich biocomposite is found to be a structurally acceptable replacement for standard gypsum drywall.
Numerical Modeling of Natural and Enhanced Denitrification Processes in Aquifers
NASA Astrophysics Data System (ADS)
Kinzelbach, Wolfgang; SchäFer, Wolfgang; Herzer, JöRg
1991-06-01
Nitrate modeling in the groundwater environment must incorporate microbial denitrification as the major process of nitrate elimination. A multispecies transport model is presented which describes the interaction of oxygen, nitrate, organic carbon, and bacteria. Three phases (mobile pore water, biophase, and aquifer material) are taken into account. The model is applied to a natural aquifer situation as well as to an in situ remediation case where nitrate is employed as an oxidant. In the natural aquifer it is shown that the release of organic carbon from the matrix is the controlling factor for denitrification. In the remediation case, on the other hand, the data suggest that diffusion limitation of the nutrient supply to the biophase controls bacterial growth.
Numerical modeling of solar irradiance on earth's surface
NASA Astrophysics Data System (ADS)
Mera, E.; Gutierez, L.; Da Silva, L.; Miranda, E.
2016-05-01
Modeling studies and estimation of solar radiation in base area, touch from the problems of estimating equation of time, distance equation solar space, solar declination, calculation of surface irradiance, considering that there are a lot of studies you reported the inability of these theoretical equations to be accurate estimates of radiation, many authors have proceeded to make corrections through calibrations with Pyranometers field (solarimeters) or the use of satellites, this being very poor technique last because there a differentiation between radiation and radiant kinetic effects. Because of the above and considering that there is a weather station properly calibrated ground in the Susques Salar in the Jujuy Province, Republic of Argentina, proceeded to make the following modeling of the variable in question, it proceeded to perform the following process: 1. Theoretical Modeling, 2. graphic study of the theoretical and actual data, 3. Adjust primary calibration data through data segmentation on an hourly basis, through horizontal and adding asymptotic constant, 4. Analysis of scatter plot and contrast series. Based on the above steps, the modeling data obtained: Step One: Theoretical data were generated, Step Two: The theoretical data moved 5 hours, Step Three: an asymptote of all negative emissivity values applied, Solve Excel algorithm was applied to least squares minimization between actual and modeled values, obtaining new values of asymptotes with the corresponding theoretical reformulation of data. Add a constant value by month, over time range set (4:00 pm to 6:00 pm). Step Four: The modeling equation coefficients had monthly correlation between actual and theoretical data ranging from 0.7 to 0.9.
Effect of numerical diffusion on the water mass transformation in eddy-resolving models
NASA Astrophysics Data System (ADS)
Urakawa, L. Shogo; Hasumi, Hiroyasu
2014-02-01
This study investigates the effect of numerical diffusion associated with advection schemes on water mass transformation in an eddy-resolving model. The effect of numerical diffusion is evaluated as a residual between the total water mass transformation and the explicit water mass transformation: the former is calculated as the sum of meridional streamfunction and the temporal change rate of an isopycnal surface depth, and the latter is directly calculated with the use of the tendency equation of density. This method is used for investigating a dependency of numerical diffusion on explicit diffusivity. It is found that idealized channel experiments are categorized into three regimes according to a magnitude of explicit diffusivity: numerical diffusion, transitional, and explicit diffusion regimes. The numerical diffusion regime is defined as the regime where explicit diffusion changes do not significantly impact the solution. The magnitude of numerical diffusion is independent of the explicit diffusivity there. In the transitional regime, explicit (numerical) diffusion works more (less) with higher explicit diffusivity. Explicit and numerical diffusions are comparably important there. The explicit diffusion becomes significantly large and the numerical diffusion is almost negligible in the explicit diffusion regime. The total diffusion effect on water mass transformation there is considerably larger than those in the two other regimes. Two experiments are conducted with a Southern Ocean model under a realistic configuration. These belong to the numerical diffusion and transitional regimes. The model becomes a little too diffusive in the latter experiment. This result and results of channel experiments indicate that it is not an adequate option for a realistic Southern Ocean simulation that we adopt a diffusion coefficient in the explicit diffusion regime in order to reduce levels of numerical diffusion. It indicates that numerical diffusion is inevitable for eddy
Numerical modelling of MHD waves in the solar chromosphere.
Carlsson, Mats; Bogdan, Thomas J
2006-02-15
Acoustic waves are generated by the convective motions in the solar convection zone. When propagating upwards into the chromosphere they reach the height where the sound speed equals the Alfvén speed and they undergo mode conversion, refraction and reflection. We use numerical simulations to study these processes in realistic configurations where the wavelength of the waves is similar to the length scales of the magnetic field. Even though this regime is outside the validity of previous analytic studies or studies using ray-tracing theory, we show that some of their basic results remain valid: the critical quantity for mode conversion is the angle between the magnetic field and the k-vector: the attack angle. At angles smaller than 30 degrees much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In three-dimensions, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low-mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves. The oscillatory power is suppressed in magnetic field concentrations and enhanced in ring-formed patterns around them. The complex interference patterns caused by mode-conversion, refraction and reflection, even with simple incident waves and in simple magnetic field geometries, make direct inversion of observables exceedingly difficult. In a dynamic chromosphere it is doubtful if the determination of mean quantities is even meaningful.
Numerical model of induction heating of steel-tube ends
Garbulsky, G.D.; Marino, P.; Pignotti, A.
1997-01-01
A two-dimensional model of induction heating of steel-tube ends, that takes into account magnetic induction saturation and temperature dependence of material properties, is developed as an aid to process design and optimization. The model is solved by the finite difference method, and is validated by comparison with thermocouple measurements at an industrial facility at which three tubes are heated concurrently prior to an upsetting process. An example of the dependence of the final temperature distribution on geometrical parameters is discussed in detail.
Validation of engineering dynamic inflow models by experimental and numerical approaches
NASA Astrophysics Data System (ADS)
Yu, W.; Hong, V. W.; Ferreira, C.; van Kuik, G. A. M.
2016-09-01
The state of the art engineering dynamic inflow models of Pitt-Peters, Øye and ECN have been used to correct Blade Element Momentum theory for unsteady load prediction of a wind turbine for two decades. However, their accuracy is unknown. This paper is to benchmark the performance of these engineering models by experimental and numerical methods. The experimental load and flow measurements of an unsteady actuator disc were performed in the Open Jet Facility at Delft University of Technology. The unsteady load was generated by a ramp-type variation of porosity of the disc. A Reynolds Averaged Navier-Stokes (RANS) model, a Free Wake Vortex Ring (FWVR) model and a Vortex Tube Model (VTM) simulate the same transient load changes. The velocity field obtained from the experimental and numerical methods are compared with the engineering dynamic inflow models. Velocity comparison aft the disc between the experimental and numerical methods shows the numerical models of RANS and FWVR model are capable to predict the velocity transient behaviour during transient disc loading. Velocity comparison at the disc between the engineering models and the numerical methods further shows that the engineering models predict much faster velocity decay, which implies the need for more advanced or better tuned dynamic inflow models.
PHYSICAL AND NUMERICAL MODELING OF ASD EXHAUST DISPERSION AROUND HOUSES
The report discusses the use of a wind tunnel to physically model the dispersion of exhaust plumes from active soil depressurization (ASD) radon mitigation systems in houses. he testing studied the effects of exhaust location (grade level vs. above the eave), as house height, roo...
A numerical model to simulate foams during devolatilization of polymers
NASA Astrophysics Data System (ADS)
Khan, Irfan; Dixit, Ravindra
2014-11-01
Customers often demand that the polymers sold in the market have low levels of volatile organic compounds (VOC). Some of the processes for making polymers involve the removal of volatiles to the levels of parts per million (devolatilization). During this step the volatiles are phase separated out of the polymer through a combination of heating and applying lower pressure, creating foam with the pure polymer in liquid phase and the volatiles in the gas phase. The efficiency of the devolatilization process depends on predicting the onset of solvent phase change in the polymer and volatiles mixture accurately based on the processing conditions. However due to the complex relationship between the polymer properties and the processing conditions this is not trivial. In this work, a bubble scale model is coupled with a bulk scale transport model to simulate the processing conditions of polymer devolatilization. The bubble scale model simulates the nucleation and bubble growth based on the classical nucleation theory and the popular ``influence volume approach.'' As such it provides the information of bubble size distribution and number density inside the polymer at any given time and position. This information is used to predict the bulk properties of the polymer and its behavior under the applied processing conditions. Initial results of this modeling approach will be presented.
Numerical simulations of altocumulus with a cloud resolving model
Liu, S.; Krueger, S.K.
1996-04-01
Altocumulus and altostratus clouds together cover approximately 22% of the earth`s surface. They play an important role in the earth`s energy budget through their effect on solar and infrared radiation. However, there has been little altocumulus cloud investigation by either modelers or observational programs. Starr and Cox (SC) (1985a,b) simulated an altostratus case as part of the same study in which they modeled a thin layer of cirrus. Although this calculation was originally described as representing altostratus, it probably better represents altocumulus stratiformis. In this paper, we simulate altocumulus cloud with a cloud resolving model (CRM). We simply describe the CRM first. We calculate the same middle-level cloud case as SC to compare our results with theirs. We will look at the role of cloud-scale processes in response to large-scale forcing. We will also discuss radiative effects by simulating diurnal and nocturnal cases. Finally, we discuss the utility of a 1D model by comparing 1D simulations and 2D simulations.
A Model for Minimizing Numeric Function Generator Complexity and Delay
2007-12-01
model_Linear_NonUniform_Basic with the size of the number system (n) and the number of segments ( mins ). The author’s MATLAB m-file segments.m returns the...Navigator ............................................................20 2. MATLAB ...103 APPENDIX A. MATLAB SOURCE CODE............................................................105 A.1
Comprehensive Numerical Modeling of the Blast Furnace Ironmaking Process
NASA Astrophysics Data System (ADS)
Zhou, Chenn; Tang, Guangwu; Wang, Jichao; Fu, Dong; Okosun, Tyamo; Silaen, Armin; Wu, Bin
2016-05-01
Blast furnaces are counter-current chemical reactors, widely utilized in the ironmaking industry. Hot reduction gases injected from lower regions of the furnace ascend, reacting with the descending burden. Through this reaction process, iron ore is reduced into liquid iron that is tapped from the furnace hearth. Due to the extremely harsh environment inside the blast furnace, it is difficult to measure or observe internal phenomena during operation. Through the collaboration between steel companies and the Center for Innovation through Visualization and Simulation, multiple computational fluid dynamics (CFD) models have been developed to simulate the complex multiphase reacting flow in the three regions of the furnace, the shaft, the raceway, and the hearth. The models have been used effectively to troubleshoot and optimize blast furnace operations. In addition, the CFD models have been integrated with virtual reality. An interactive virtual blast furnace has been developed for training purpose. This paper summarizes the developments and applications of blast furnace CFD models and the virtual blast furnace.
Numerical modeling of overland flow due to rainfall-runoff
Technology Transfer Automated Retrieval System (TEKTRAN)
Runoff is a basic hydrologic process that can be influenced by management activities in agricultural watersheds. Better description of runoff patterns through modeling will help to understand and predict watershed sediment transport and water quality. Normally, runoff is studied with kinematic wave ...
The role of global cloud climatologies in validating numerical models
NASA Technical Reports Server (NTRS)
HARSHVARDHAN
1993-01-01
The purpose of this work is to estimate sampling errors of area-time averaged rain rate due to temporal samplings by satellites. In particular, the sampling errors of the proposed low inclination orbit satellite of the Tropical Rainfall Measuring Mission (TRMM) (35 deg inclination and 350 km altitude), one of the sun synchronous polar orbiting satellites of NOAA series (98.89 deg inclination and 833 km altitude), and two simultaneous sun synchronous polar orbiting satellites--assumed to carry a perfect passive microwave sensor for direct rainfall measurements--will be estimated. This estimate is done by performing a study of the satellite orbits and the autocovariance function of the area-averaged rain rate time series. A model based on an exponential fit of the autocovariance function is used for actual calculations. Varying visiting intervals and total coverage of averaging area on each visit by the satellites are taken into account in the model. The data are generated by a General Circulation Model (GCM). The model has a diurnal cycle and parameterized convective processes. A special run of the GCM was made at NASA/GSFC in which the rainfall and precipitable water fields were retained globally for every hour of the run for the whole year.
Numerical modeling of an all vanadium redox flow battery.
Clausen, Jonathan R.; Brunini, Victor E.; Moffat, Harry K.; Martinez, Mario J.
2014-01-01
We develop a capability to simulate reduction-oxidation (redox) flow batteries in the Sierra Multi-Mechanics code base. Specifically, we focus on all-vanadium redox flow batteries; however, the capability is general in implementation and could be adopted to other chemistries. The electrochemical and porous flow models follow those developed in the recent publication by [28]. We review the model implemented in this work and its assumptions, and we show several verification cases including a binary electrolyte, and a battery half-cell. Then, we compare our model implementation with the experimental results shown in [28], with good agreement seen. Next, a sensitivity study is conducted for the major model parameters, which is beneficial in targeting specific features of the redox flow cell for improvement. Lastly, we simulate a three-dimensional version of the flow cell to determine the impact of plenum channels on the performance of the cell. Such channels are frequently seen in experimental designs where the current collector plates are borrowed from fuel cell designs. These designs use a serpentine channel etched into a solid collector plate.
Insights into Coignimbrite Plume Dynamics from Numerical Models
NASA Astrophysics Data System (ADS)
Engwell, S. L.; De'Michieli Vitturi, M.; Barsotti, S.; Eychenne, J.; Esposti Ongaro, T.; Neri, A.
2014-12-01
Great advances have been made in recent years to better understand and model the processes that occur in Plinian plumes. However, comparatively little work has been conducted on modeling coignimbrite plumes, which form as fine-grained material is lofted from the top of pyroclastic density currents, rising into the atmosphere due to buoyancy. This fundamental difference in source condition (gas thrust vs. buoyancy) means that the parameters used to describe Plinian plumes, for example initial source radius, upwards velocity, temperature, gas mass fraction and grain-size distribution are not appropriate for modeling coignimbrite events. In this study, the ash flow model of Bursik and Woods (1996) is coupled with a plume model (Bursik 2001, Barsotti et al. 2008) to investigate the controls on coignimbrite plume formation, and once formed, the height and dynamics of the plume. Sensitivity analysis was conducted using DAKOTA software and results show that source temperature and gas mass fraction play a key role in controlling when 'lift-off' occurs. Once formed, maximum plume height is controlled by the source radius, the temperature at 'liftoff' and the entrainment assumption. Finally, we use the May 18th 1980 Mount St. Helens co-blast eruption to test the application of an ash dispersion model, specifically VOLCALPUFF (Barsotti et al., 2008), to the coignimbrite problem, with the specific aim of distinguishing differences in application for coignimbrite and Plinian events. The results highlight the importance of coignimbrite events when considering ash fall hazard and a requirement to treat such events separately to Plinian events. Andrews, B.J. and Manga, M.. JVGR , 225-226, 30-44, 2012 Barsotti, S, Neri, A, and Scire, JS. The vol-calpuff model for atmospheric ash dispersal: 1. Approach and physical formulation. JGR, 113(B03208), 2008 Bursik, M. Effect of wind on the rise height of volcanic plumes. GRL, 28(18), 3621-3624, 2001. Bursik, M and Woods, A. W. The dynamics
Rajaraman, Prathish K; Manteuffel, T A; Belohlavek, M; Heys, Jeffrey J
2017-01-01
A new approach has been developed for combining and enhancing the results from an existing computational fluid dynamics model with experimental data using the weighted least-squares finite element method (WLSFEM). Development of the approach was motivated by the existence of both limited experimental blood velocity in the left ventricle and inexact numerical models of the same flow. Limitations of the experimental data include measurement noise and having data only along a two-dimensional plane. Most numerical modeling approaches do not provide the flexibility to assimilate noisy experimental data. We previously developed an approach that could assimilate experimental data into the process of numerically solving the Navier-Stokes equations, but the approach was limited because it required the use of specific finite element methods for solving all model equations and did not support alternative numerical approximation methods. The new approach presented here allows virtually any numerical method to be used for approximately solving the Navier-Stokes equations, and then the WLSFEM is used to combine the experimental data with the numerical solution of the model equations in a final step. The approach dynamically adjusts the influence of the experimental data on the numerical solution so that more accurate data are more closely matched by the final solution and less accurate data are not closely matched. The new approach is demonstrated on different test problems and provides significantly reduced computational costs compared with many previous methods for data assimilation. Copyright © 2016 John Wiley & Sons, Ltd.
Numerical modeling of lightning initiation and stepped leader propagation
NASA Astrophysics Data System (ADS)
Karunarathne, Sumedhe
Initial breakdown pulses (IBPs) observed at the beginning of cloud-to-ground (CG) lightning flashes and stepped leaders that followed IBPs were modeled using multi-sensor electric field change (E-change) measurements. This study uses data collected with a network of ten E-change sensors located at Kennedy Space Center. Locations (x,y,z,t) of IBPs were found using a time-of-arrival technique called PBFA. Location errors were determined from Monte Carlo simulations and were usually less than 100 m for horizontal coordinates and several hundreds of meters for altitude. Comparison of PBFA source locations to locations from a VHF lightning mapping system shows that PBFA locates most of the `classic' IBPs while the VHF system locates only a few percent of them. As the flash develops during the IB stage, PBFA and the VHF system obtain similar locations when they detect the same IBPs. PBFA also can reliably locate the IBPs of intra-cloud flashes and return stroke (RS) locations. PBFA locations were used as constraints to model six 'classic' IBPs using three modified transmission line (MTL) models (MTLL--linearly decaying current, MTLE---exponentially decaying current, MTLEI---exponentially increasing current) from the literature and a new model, MTLK, with the current following the Kumaraswami distribution. All four models did a good job of modeling all six IBPs; the MTLE model was most often the best fit. It is important to note that for a given pulse, there is good agreement between the different models on a number of parameters: current risetime, current falltime, two current shape factors, current propagation speed, and the IBP charge moment change. Ranges and mean values of physical quantities found are: current risetime [4.8--25, (13+/-6)] microseconds, current falltime [15--37, (25+/-6)] microseconds, current speed [0.78--1.8, (1.3+/-0.3)]x10 8 m/s (excluding one extreme case of MTLEI), channel length [0.20--1.6, (0.6+/-0.3)] km, charge moment [0.015--0.30, (0
Numerical modelling of cryogenic propellant behavior in low-G
NASA Technical Reports Server (NTRS)
Hochstein, John I.
1987-01-01
A partial survey is presented of recent research, sponsored by the NASA Lewis Research Center, into the computational modelling of cryogenic propellant behavior in a low gravity environment. This presentation is intended to provide insight into some of the specific problems being studied and into how these studies are part of an integrated plan to develop predictive capabilities. A brief description of the computational models developed to analyze jet induced mixing in cryogenic propellant tankage is presented along with representative results. Similar information is presented for a recent examination of on-orbit self-pressurization. A study of propellant reorientation has recently been initiated and preliminary results are included. The presentation concludes with a list of ongoing efforts and projected goals.
Numerical Modelling of Soil Arching in a Shallow Backfill Layer
NASA Astrophysics Data System (ADS)
Szajna, Waldemar St.
2015-03-01
The paper presents the application of the finite element method into the modelling of soil arching. The phenomenon plays fundamental role in soil-shell flexible structures behaviour. To evaluate the influence of arching on a pressure reduction, a plain strain trapdoor under a shallow layer of backfill was simulated. The Coulomb-Mohr plasticity condition and the nonassociated flow rule were used for the soil model. The research examines the impact of the internal friction angle and the influence of the backfill layer thickness on the value of soil arching. The carried out analyses indicate that the reduction of pressures acting on a structure depends on the value of the internal friction angle, which confirms the earlier research. For a shallow backfill layer however, the reduction is only a local phenomenon and can influence only a part of the structure.
Parameterization of bulk condensation in numerical cloud models
NASA Technical Reports Server (NTRS)
Kogan, Yefim L.; Martin, William J.
1994-01-01
The accuracy of the moist saturation adjustment scheme has been evaluated using a three-dimensional explicit microphysical cloud model. It was found that the error in saturation adjustment depends strongly on the Cloud Condensation Nucleii (CCN) concentration in the ambient atmosphere. The scheme provides rather accurate results in the case where a sufficiently large number of CCN (on the order of several hundred per cubic centimeter) is available. However, under conditions typical of marine stratocumulus cloud layers with low CCN concentration, the error in the amounts of condensed water vapor and released latent heat may be as large as 40%-50%. A revision of the saturation adjustment scheme is devised that employs the CCN concentration, dynamical supersaturation, and cloud water content as additional variables in the calculation of the condensation rate. The revised condensation model reduced the error in maximum updraft and cloud water content in the climatically significant case of marine stratocumulus cloud layers by an order of magnitude.
Numerical Modeling Studies of Wake Vortices: Real Case Simulations
NASA Technical Reports Server (NTRS)
Shen, Shao-Hua; Ding, Feng; Han, Jongil; Lin, Yuh-Lang; Arya, S. Pal; Proctor, Fred H.
1999-01-01
A three-dimensional large-eddy simulation model, TASS, is used to simulate the behavior of aircraft wake vortices in a real atmosphere. The purpose for this study is to validate the use of TASS for simulating the decay and transport of wake vortices. Three simulations are performed and the results are compared with the observed data from the 1994-1995 Memphis field experiments. The selected cases have an atmospheric environment of weak turbulence and stable stratification. The model simulations are initialized with appropriate meteorological conditions and a post roll-up vortex system. The behavior of wake vortices as they descend within the atmospheric boundary layer and interact with the ground is discussed.
Joint physical and numerical modeling of water distribution networks.
Zimmerman, Adam; O'Hern, Timothy John; Orear, Leslie Jr.; Kajder, Karen C.; Webb, Stephen Walter; Cappelle, Malynda A.; Khalsa, Siri Sahib; Wright, Jerome L.; Sun, Amy Cha-Tien; Chwirka, J. Benjamin; Hartenberger, Joel David; McKenna, Sean Andrew; van Bloemen Waanders, Bart Gustaaf; McGrath, Lucas K.; Ho, Clifford Kuofei
2009-01-01
This report summarizes the experimental and modeling effort undertaken to understand solute mixing in a water distribution network conducted during the last year of a 3-year project. The experimental effort involves measurement of extent of mixing within different configurations of pipe networks, measurement of dynamic mixing in a single mixing tank, and measurement of dynamic solute mixing in a combined network-tank configuration. High resolution analysis of turbulence mixing is carried out via high speed photography as well as 3D finite-volume based Large Eddy Simulation turbulence models. Macroscopic mixing rules based on flow momentum balance are also explored, and in some cases, implemented in EPANET. A new version EPANET code was developed to yield better mixing predictions. The impact of a storage tank on pipe mixing in a combined pipe-tank network during diurnal fill-and-drain cycles is assessed. Preliminary comparison between dynamic pilot data and EPANET-BAM is also reported.
Numerical Modeling of Narrow Band Soft X-ray Sources
1988-05-01
at discrete time steps. A post-processor code models the transport of radiation through the plasma. The time scale of atomic processes is very short...compared to the time step of the hydrocode. We can therefore take the view that the atomic processes are essentially instantaneous, or, to put it...another way, that the atomic quantities are essentially in steady state. In this view, as every now hydrocode time step is taken, ionization and excitation
Numerical modeling of natural and ventilated cavitating flows
NASA Astrophysics Data System (ADS)
Qin, Qiao
Cavitation is a phenomenon that frequently occurs in fluid-handling machinery, ranging from all types of pumps, turbines, and propellers to various piping systems and hydraulic structures. Cavitation research has been pursued for over a century and an enormous quantity of literature on cavitation has been generated. Cavitation modeling is challenging and is still in the development stage due to its inherent complexity of the physics involved. There are basically three objectives in this thesis work. First, an existing virtual single-phase natural cavitation model is used to extensively explore the unsteadiness of sheet/cloud cavitation on two hydrofoils (NACA 0015 and CAV2003). Five discrete vortex shedding mechanisms are identified in this research. Second, this existing virtual single-phase natural cavitation model is further modified to take into account the effect of incondensable gas that comes out of solution due to the cavitation evaporation process. This was motivated by the observation that the computed mean velocity distribution in the wake of a cavitating hydrofoil, without the effect of incondensable gas, agrees well with experimental data close to the trailing edge but deviates systematically further downstream. This revision shows a significant improvement on the computed mean velocity distribution in the wake compared to that without the incondensable gas effect and the results are in agreement with those from experiments. These are two new findings that are absent in literature. Third, a two-phase, fully compressible flow model based on Large Eddy Simulation (LES) for ventilated cavitating flows is developed and is successfully implemented in the simulation of an axisymmetric underwater body.
Numerical Modelling of Vegetation Flow Interaction: the Wienfluss Test Case
NASA Astrophysics Data System (ADS)
Wilson, C.; Yagci, O.; Rauch, H.; Stoesser, T.
2003-04-01
We apply a three-dimensional computational fluid dynamics code based on a finite-volume discretisation to a 170m test reach of the a river in Vienna. One of the primary aims of this paper is to test various methods for representing the flow resistance of natural vegetation. The two approaches considered vary in complexity and could be practically implemented and applied within 2D and 3D flood modelling tools. The first approach uses empirical relationships derived from the laboratory data and modifies the existing friction term in the momentum equations. While the second approach introduces a drag related sink term in addition to the bed friction term. The roughness closure models considered do not modify the turbulence model (in this case the k-e model) and hence do not require re-calibration for each application. The test reach is straight and comprises an asymmetrical compound channel that is vegetated on the floodplain by willows and unvegetated within the main channel. The development of the willows has been monitored over a four year period and plant parameters which characterise the dimensions of individual trees and their distribution have been quantified. Further, streamwise velocity data of high-spatial resolution has been collected at one cross-section for a series of flood events. The performance of each approach is quantified in terms of its ability to reproduce the streamwise velocity distribution in a partially vegetated channel. Different parameter tests are conducted to allow the sensitivity of the computed velocities against mesh resolution, and other important plant properties to be examined. For both flow resistance approaches, reasonable agreement is found between the measured and computed floodplain velocities.
Numerical 2D-modeling of multiroll leveling
NASA Astrophysics Data System (ADS)
Mathieu, N.; Potier-Ferry, M.; Zahrouni, H.
2016-10-01
Multiroll leveling is a forming process used in the metals industries (aluminum, steel, …) in order to correct flatness defects and minimize residual stresses in strips thanks to alternating bending. This work proposes a Finite Element 2D model to simulate the metal sheet conveying through the machine. Obtained results (plastic strain and residual stress distributions through thickness) are analysed. Strip deformation, after elastic springback and potential buckling, is also predicted (residual curvatures).
Numerical Modelling of Circulation and Exchange through Singapore Straits
NASA Astrophysics Data System (ADS)
Liu, G.; Xu, M.; Chua, V. P.
2014-12-01
The circulation in the Singapore coastal region is complicated and influenced by the combination of tidal forcing of the surrounding seas, complex bathymetry, irregular coastlines, and seasonal monsoon and local winds. An unstructured-grid SUNTANS (Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator) model is employed to perform three-dimensional simulations of flow in Singapore coastal waters. The unstructured-grid has an average resolution of 50 - 100 m around Singapore and in areas close to the shoreline, while a coarse grid resolution is employed in the open waters. The model is tidally forced at the three open boundaries, located to the west, south and east of Singapore, using the 8 main tidal constituents as derived from the OSU Tidal Prediction Software (OTPS). A detailed calibration is performed, and the model-predicted water levels and currents compare well with observed data throughout the model domain. We examine the individual and combined effects of tidal and wind forcing by performing simulations with (1) tides only, (2) winds only and (3) both tides and wind. The exchange through Singapore Strait is investigated by computing volume fluxes and transport pathways at four transects, namely the Malacca Strait, Java Sea, South China Sea and Singapore transects. The transport pathways are computed by releasing particles on each side of the transects, and identifying the spatial distribution of the particles over one tidal cycle. Our results show that tidal forcing is predominant in Singapore Strait, and wind forcing is an important mechanism during the monsoon season. The residual effects, attributed to nonlinear interactions between tidal and wind forcing, is dominant during the inter-monsoon season.
Numerical Modeling of ETS in the Cascadia Region - An Application of Nankai Model -
NASA Astrophysics Data System (ADS)
Matsuzawa, T.; Shibazaki, B.
2015-12-01
Episodic tremor and slip (ETS) is found in various subduction zones. We have modeled slip of subducting plate interface including the ETS region in Shikoku, and successfully reproduced the characteristics of the segments and recurrences of ETS (Matsuzawa et al., 2013). However, it is important to examine whether our model can explain the characteristics of ETS in the other region. We have tentatively applied our model to the ETS in Cascadia. In our numerical model, a rate- and state- dependent friction law (RS-law) with a cutoff velocity is adopted, as in our previous studies. Low effective normal stress and a low cutoff velocity are assumed at the depth where ETS occur. Negative and positive (a-b) value in the RS-law is assumed within and outside of the ETS region, respectively. In this study, the ETS region is based on the actual distribution of tremor which is located by the monitoring system of Wech (2010). We assume that frictional parameters have similar depth-dependence to our previous study (Matsuzawa et al., 2013). Subducting plate interface is modeled by 203,064 triangular elements, based on the configuration in McCrory et al. (2004). In our numerical result, SSEs recur at the intervals of about 1 year. In addition, SSEs are relatively active between the south of Vancouver Island and the Olympic Peninsula. These characteristics are similar to observations (e.g. Brudzinski and Allen, 2007). Minor ETS activities at the down-dip portion occur between the major ETS activities both in the up-dip and down-dip portion. This feature is similar to the actual ETS in Cascadia (Wech and Creager, 2011). In addition, long-term SSEs recur between the ETS region and shallow locked region where large earthquakes are expected. These long-term SSEs are frequently found around the region with curved plate interface, and may be characterized by the configuration of the plate as in Shikoku (Matsuzawa et al., 2013).
Cloud-Scale Numerical Modeling of the Arctic Boundary Layer
NASA Technical Reports Server (NTRS)
Krueger, Steven K.
1998-01-01
The interactions between sea ice, open ocean, atmospheric radiation, and clouds over the Arctic Ocean exert a strong influence on global climate. Uncertainties in the formulation of interactive air-sea-ice processes in global climate models (GCMs) result in large differences between the Arctic, and global, climates simulated by different models. Arctic stratus clouds are not well-simulated by GCMs, yet exert a strong influence on the surface energy budget of the Arctic. Leads (channels of open water in sea ice) have significant impacts on the large-scale budgets during the Arctic winter, when they contribute about 50 percent of the surface fluxes over the Arctic Ocean, but cover only 1 to 2 percent of its area. Convective plumes generated by wide leads may penetrate the surface inversion and produce condensate that spreads up to 250 km downwind of the lead, and may significantly affect the longwave radiative fluxes at the surface and thereby the sea ice thickness. The effects of leads and boundary layer clouds must be accurately represented in climate models to allow possible feedbacks between them and the sea ice thickness. The FIRE III Arctic boundary layer clouds field program, in conjunction with the SHEBA ice camp and the ARM North Slope of Alaska and Adjacent Arctic Ocean site, will offer an unprecedented opportunity to greatly improve our ability to parameterize the important effects of leads and boundary layer clouds in GCMs.
Numerical Modeling of Pulse Detonation Rocket Engine Gasdynamics And Performance
NASA Technical Reports Server (NTRS)
Morris, Christopher I.
2004-01-01
Pulse detonation rocket engines (PDREs) offer potential performance improvements over conventional designs, but represent a challenging modeling task. A quasi-1-D, finite-rate chemistry computational fluid dynamics model for PDREs is described and implemented. Four different PDRE geometries are evaluated in this work: a baseline detonation tube, a detonation tube with a straight extension, and a detonation tube with two types of converging-diverging (C-D) nozzles. The effect of extension length and C-D nozzle area ratio on the single-shot gasdynamics and performance of a PDRE is studied over a wide range of blowdown pressure ratios (1-1000). The results indicate that a C-D nozzle is generally more effective than a straight extension in improving PDRE performance, particularly at higher pressure ratios. Additionally, the results show that the blowdown process of the C-D nozzle systems could be beneficially cut off well before the pressure at the end-wall reaches the ambient value. The performance results are also compared to a steady-state rocket system using similar modeling assumptions.
Numerical experiments with model monophyletic and paraphyletic taxa
NASA Technical Reports Server (NTRS)
Sepkoski, J. J. Jr; Kendrick, D. C.; Sepkoski JJ, J. r. (Principal Investigator)
1993-01-01
The problem of how accurately paraphyletic taxa versus monophyletic (i.e., holophyletic) groups (clades) capture underlying species patterns of diversity and extinction is explored with Monte Carlo simulations. Phylogenies are modeled as stochastic trees. Paraphyletic taxa are defined in an arbitrary manner by randomly choosing progenitors and clustering all descendants not belonging to other taxa. These taxa are then examined to determine which are clades, and the remaining paraphyletic groups are dissected to discover monophyletic subgroups. Comparisons of diversity patterns and extinction rates between modeled taxa and lineages indicate that paraphyletic groups can adequately capture lineage information under a variety of conditions of diversification and mass extinction. This suggests that these groups constitute more than mere "taxonomic noise" in this context. But, strictly monophyletic groups perform somewhat better, especially with regard to mass extinctions. However, when low levels of paleontologic sampling are simulated, the veracity of clades deteriorates, especially with respect to diversity, and modeled paraphyletic taxa often capture more information about underlying lineages. Thus, for studies of diversity and taxic evolution in the fossil record, traditional paleontologic genera and families need not be rejected in favor of cladistically-defined taxa.
Efficient numerical modeling of the cornea, and applications
NASA Astrophysics Data System (ADS)
Gonzalez, L.; Navarro, Rafael M.; Hdez-Matamoros, J. L.
2004-10-01
Corneal topography has shown to be an essential tool in the ophthalmology clinic both in diagnosis and custom treatments (refractive surgery, keratoplastia), having also a strong potential in optometry. The post processing and analysis of corneal elevation, or local curvature data, is a necessary step to refine the data and also to extract relevant information for the clinician. In this context a parametric cornea model is proposed consisting of a surface described mathematically by two terms: one general ellipsoid corresponding to a regular base surface, expressed by a general quadric term located at an arbitrary position and free orientation in 3D space and a second term, described by a Zernike polynomial expansion, which accounts for irregularities and departures from the basic geometry. The model has been validated obtaining better adjustment of experimental data than other previous models. Among other potential applications, here we present the determination of the optical axis of the cornea by transforming the general quadric to its canonical form. This has permitted us to perform 3D registration of corneal topographical maps to improve the signal-to-noise ratio. Other basic and clinical applications are also explored.
Numerical Modeling of Methanogenesis at Walker Ridge, Gulf of Mexico
NASA Astrophysics Data System (ADS)
Glosser, D.; Cook, A.; Malinverno, A.; Daigle, H.
2014-12-01
Methane migration is a crucial link between locations of methane generation and natural gas hydrate reservoirs, yet migration mechanisms are poorly understood in the natural environment. In this study, we evaluate constraints on methanogenesis and methane diffusion through the development