Numerical study of the effect of water addition on gas explosion.
Liang, Yuntao; Zeng, Wen
2010-02-15
Through amending the SENKIN code of CHEMKIN III chemical kinetics package, a computational model of gas explosion in a constant volume bomb was built, and the detailed reaction mechanism (GRI-Mech 3.0) was adopted. The mole fraction profiles of reactants, some selected free radicals and catastrophic gases in the process of gas explosion were analyzed by this model. Furthermore, through the sensitivity analysis of the reaction mechanism of gas explosion, the dominant reactions that affect gas explosion and the formation of catastrophic gases were found out. At the same time, the inhibition mechanisms of water on gas explosion and the formation of catastrophic gases were analyzed. The results show that the induced explosion time is prolonged, and the mole fractions of reactant species such as CH(4), O(2) and catastrophic gases such as CO, CO(2) and NO are decreased as water is added to the mixed gas. With the water fraction in the mixed gas increasing, the sensitivities of the dominant reactions contributing to CH(4), CO(2) are decreased and the sensitivity coefficients of CH(4), CO and NO mole fractions are also decreased. The inhibition of gas explosion with water addition can be ascribed to the significant decrease of H, O and OH in the process of gas explosion due to the water presence. PMID:19811873
Guo, Hongsheng; Liu, Fengshan; Smallwood, Gregory J.; Guelder, OEmer L.
2006-04-15
The influence of hydrogen addition to the fuel of an atmosphere pressure coflow laminar ethylene-air diffusion flame on soot formation was studied by numerical simulation. A detailed gas-phase reaction mechanism, which includes aromatic chemistry up to four rings, and complex thermal and transport properties were used. The fully coupled elliptic governing equations were solved. The interactions between soot and gas-phase chemistry were taken into account. Radiation heat transfer from CO{sub 2}, CO, H{sub 2}O, and soot was calculated using the discrete-ordinates method coupled to a statistical narrow-band-correlated K-based wide-band model. The predicted results were compared with the available experimental data and analyzed. It is indicated that the addition of hydrogen to the fuel in an ethylene-air diffusion flame suppresses soot formation through the effects of dilution and chemistry. This result is in agreement with available experiments. The simulations further suggest that the chemically inhibiting effect of hydrogen addition on soot formation is due to the decrease of hydrogen atom concentration in soot surface growth regions and higher concentration of molecular hydrogen in the lower flame region. (author)
NASA Astrophysics Data System (ADS)
Jiang, C. X.; Cheng, J. P.; Li, F. C.
2015-01-01
This paper attempts to introduce a numerical simulation procedure to simulate water-entry problems influenced by turbulent drag-reducing additives in a viscous incompressible medium. Firstly we performed a numerical investigation on water-entry supercavities in water and turbulent drag-reducing solution at the impact velocity of 28.4 m/s to confirm the accuracy of the numerical method. Based on the verification, projectile entering water and turbulent drag-reducing solution at relatively high velocity of 142.7 m/s (phase transition is considered) is simulated. The cross viscosity equation was adopted to represent the shear-thinning characteristic of aqueous solution of drag-reducing additives. The configuration and dynamic characteristics of water entry supercavity, flow resistance were discussed respectively. It was obtained that the numerical simulation results are in consistence with experimental data. Numerical results show that the supercavity length in drag-reducing solution is larger than one in water and the velocity attenuates faster at high velocity than at low velocity; the influence of drag-reducing solution is more obvious at high impact velocity. Turbulent drag-reducing additives have the great potential for enhancement of supercavity.
Van den Schoor, F; Norman, F; Vandebroek, L; Verplaetsen, F; Berghmans, J
2009-05-30
In this study the auto-ignition limit of ammonia/methane/air mixtures is calculated based upon a perfectly stirred reactor model with convective heat transfer. The results of four different reaction mechanisms are compared with existing experimental data at an initial temperature of 723 K with ammonia concentrations of 0-20 mol.% and methane concentrations of 2.5-10 mol.%. It is found that the calculation of the auto-ignition limit pressure at constant temperature leads to larger relative deviations between calculated and experimental results than the calculation of the auto-ignition temperature at constant pressure. In addition to the calculations, a reaction path analysis is performed to explain the observed lowering of the auto-ignition limit of methane/air mixtures by ammonia addition. It is found that this decrease is caused by the formation of NO and NO(2), which enhance the oxidation of methane at low temperatures. PMID:18926632
Addition polyimide end cap study
NASA Technical Reports Server (NTRS)
St.clair, T. L.
1980-01-01
The characterization of addition polyimides with various end caps for adhesive applications at 120-250 C environments is discussed. Oligometric polyimides were prepared from 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 3,3'-methylenedianiline which were end-capped with functionally reactive moities which cause crosslinking when the oligomers are heated to 200-400 C. The syntheses of the oligomers are outlined. The thermolysis of the oligomers was studied by differential scanning calorimetry and the resulting polymers were characterized by differential thermal analysis and adhesive performance. The adhesive data include lap shear strengths on titanium 6-4 adherends both before and after aging for 1000 hours at 121 C and/or 232 C.
Numerical study of rock blasting
NASA Astrophysics Data System (ADS)
Stefanov, Yu. P.; Bakeev, R. A.; Yudin, A. S.; Kuznetsova, N. S.
2015-10-01
The paper presents numerical simulation results on fracture of a concrete block due to dynamic explosive loads applied to the walls of a blast hole. Considered in the study is the influence of the pulse shape and rock properties on the pattern of irreversible deformation and cracking. It is found that a fractured zone bounded by a plastically deformed contour always arises around the explosion site. Comparison of elastoplastic deformation and fracture induced in the concrete block by explosion pulses of different durations and amplitudes shows that shorter pulses with higher amplitudes and steeper rise times provide a higher blasting efficiency.
Numerical studies of frontal dynamics
NASA Technical Reports Server (NTRS)
Keyser, Daniel
1986-01-01
Efforts concentrated on the development of a two dimensional primitive equation (PE) model of frontogenesis that simultaneously incorporates the frontagenetical mechanisms of confluence and horizontal shear. Applying this model to study the effects of upper level frontogenesis, it appeared to be dominated by tilting effects associated with cross front variation of vertical motion, in which subsidence is maximized within and to the warm side of the frontal zone. Results suggest that aspects characteristic of three-dimensional baroclinic waves may be abstracted to a significant extent in a two dimensional framework. They also show that upper-level frontogenesis and tropopause folding can occur in the absence of three-dimensional curvature effects, commonly believed to be necessary for realistic upper-level frontogenesis. An implication of the dominant tilting effects is that they may have to be adequately resolved by numerical weather prediction models, thus requiring better horizontal and vertical resolution.
Numerical Studies of Topological phases
NASA Astrophysics Data System (ADS)
Geraedts, Scott
The topological phases of matter have been a major part of condensed matter physics research since the discovery of the quantum Hall effect in the 1980s. Recently, much of this research has focused on the study of systems of free fermions, such as the integer quantum Hall effect, quantum spin Hall effect, and topological insulator. Though these free fermion systems can play host to a variety of interesting phenomena, the physics of interacting topological phases is even richer. Unfortunately, there is a shortage of theoretical tools that can be used to approach interacting problems. In this thesis I will discuss progress in using two different numerical techniques to study topological phases. Recently much research in topological phases has focused on phases made up of bosons. Unlike fermions, free bosons form a condensate and so interactions are vital if the bosons are to realize a topological phase. Since these phases are difficult to study, much of our understanding comes from exactly solvable models, such as Kitaev's toric code, as well as Levin-Wen and Walker-Wang models. We may want to study systems for which such exactly solvable models are not available. In this thesis I present a series of models which are not solvable exactly, but which can be studied in sign-free Monte Carlo simulations. The models work by binding charges to point topological defects. They can be used to realize bosonic interacting versions of the quantum Hall effect in 2D and topological insulator in 3D. Effective field theories of ''integer'' (non-fractionalized) versions of these phases were available in the literature, but our models also allow for the construction of fractional phases. We can measure a number of properties of the bulk and surface of these phases. Few interacting topological phases have been realized experimentally, but there is one very important exception: the fractional quantum Hall effect (FQHE). Though the fractional quantum Hall effect we discovered over 30
Tsai, Pei-I; Hsu, Ching-Chi; Chen, San-Yuan; Wu, Tsung-Han; Huang, Chih-Chieh
2016-09-01
Traditional solid cages have been widely used in posterior lumbar interbody fusion (PLIF) surgery. However, solid cages significantly affect the loading mechanism of the human spine due to their extremely high structural stiffness. Previous studies proposed and investigated porous additive manufactured (AM) cages; however, their biomechanical performances were analyzed using oversimplified bone-implant numerical models. Thus, the aim of this study was to investigate the outer shape and inner porous structure of the AM cages. The outer shape of the AM cages was discovered using a simulation-based genetic algorithm; their inner porous structure was subsequently analyzed parametrically using T10-S1 multilevel spine models. Finally, six types of the AM cages, which were manufactured using selective laser melting, were tested to validate the numerical outcomes. The subsidence resistance of the optimum design was superior to the conventional cage designs. A porous AM cage with a pillar diameter of 0.4mm, a pillar angle of 40°, and a porosity of between 69% and 80% revealed better biomechanical performances. Both the numerical and experimental outcomes can help surgeons to understand the biomechanics of PLIF surgery combined with the use of AM cages. PMID:27392226
Gyrotactic trapping: A numerical study
NASA Astrophysics Data System (ADS)
Ghorai, S.
2016-04-01
Gyrotactic trapping is a mechanism proposed by Durham et al. ["Disruption of vertical motility by shear triggers formation of thin Phytoplankton layers," Science 323, 1067-1070 (2009)] to explain the formation of thin phytoplankton layer just below the ocean surface. This mechanism is examined numerically using a rational model based on the generalized Taylor dispersion theory. The crucial role of sedimentation speed in the thin layer formation is demonstrated. The effects of variation in different parameters on the thin layer formation are also investigated.
Numerical Simulation of High Drag Reduction in a Turbulent Channel Flow with Polymer Additives
NASA Technical Reports Server (NTRS)
Dubief, Yves
2003-01-01
The addition of small amounts of long chain polymer molecules to wall-bounded flows can lead to dramatic drag reduction. Although this phenomenon has been known for about fifty years, the action of the polymers and its effect on turbulent structures are still unclear. Detailed experiments have characterized two distinct regimes (Warholic et al. 1999), which are referred to as low drag reduction (LDR) and high drag reduction (HDR). The first regime exhibits similar statistical trends as Newtonian flow: the log-law region of the mean velocity profile remains parallel to that of the Newtonian ow but its lower bound moves away from the wall and the upward shift of the log-region is a function of drag reduction, DR. Although streamwise fluctuations are increased and transverse ones are reduced, the shape of the rms velocity profiles is not qualitatively modified. At higher drag reductions, of the order of 40-50%, the ow enters the HDR regime for which the slope of the log-law is dramatically augmented and the Reynolds shear stress is small (Warholic et al. 1999; Ptasinski et al. 2001). The drag reduction is eventually bounded by a maximum drag reduction (MDR) (Virk & Mickley 1970) which is a function of the Reynolds number. While several experiments report mean velocity profiles very close to the empirical profile of Virk & Mickley (1970) for MDR conditions, the observations regarding the structure of turbulence can differ significantly. For instance, Warholic et al. (1999) measured a near-zero Reynolds shear stress, whereas a recent experiment (Ptasinski et al. 2001) shows evidence of non-negligible Reynolds stress in their MDR flow. To the knowledge of the authors, only the LDR regime has been documented in numerical simulations (Sureshkumar et al. 1997; Dimitropoulos et al. 1998; Min et al. 2001; Dubief & Lele 2001; Sibilla & Baron 2002). This paper discusses the simulation of polymer drag reduced channel ow at HDR using the FENE-P (Finite Elastic non
Numerical Studies of Collisionless Current Layers
NASA Technical Reports Server (NTRS)
Quest, Kevin B.
1993-01-01
The purpose of this proposal was to investigate collisionless current layers using a variety of analytic and numerical tools. The first year of the contract was dedicated to analytical studies, to the porting and adaption of codes being used in this study, and to the numerical simulation of collisionless current layers. The second year entailed the development of multi-dimensional hybrid algorithms as well as the re-examination of the problem of integro-differential equations that occur in the linear stage of plasma instabilities.
NASA Technical Reports Server (NTRS)
Smalheer, C. V.
1973-01-01
The chemistry of lubricant additives is discussed to show what the additives are chemically and what functions they perform in the lubrication of various kinds of equipment. Current theories regarding the mode of action of lubricant additives are presented. The additive groups discussed include the following: (1) detergents and dispersants, (2) corrosion inhibitors, (3) antioxidants, (4) viscosity index improvers, (5) pour point depressants, and (6) antifouling agents.
A Numerical Study of Boson Star Binaries
NASA Astrophysics Data System (ADS)
Mundim, Bruno C.
2010-02-01
This thesis describes a numerical study of binary boson stars within the context of an approximation to general relativity. The approximation we adopt places certain restrictions on the dynamical variables of general relativity (conformal flatness of the 3-metric), and on the time-slicing of the spacetime (maximal slicing). The resulting modeling problem requires the solution of a coupled nonlinear system of 4 hyperbolic, and 5 elliptic partial differential equations (PDEs) in three space dimensions and time. We approximately solve this system as an initial-boundary value problem, using finite difference techniques and well known, computationally efficient numerical algorithms such as the multigrid method in the case of the elliptic equations. Careful attention is paid to the issue of code validation, and a key part of the thesis is the demonstration that, as the basic scale of finite difference discretization is reduced, our numerical code generates results that converge to a solution of the continuum system of PDEs as desired. The thesis concludes with a discussion of results from some initial explorations of the orbital dynamics of boson star binaries. In particular, we describe calculations in which motion of such a binary is followed for more than two orbital periods, which is a significant advance over previous studies. We also present results from computations in which the boson stars merge, and where there is evidence for black hole formation.
Numerical and Experimental Study of Levee Breach
NASA Astrophysics Data System (ADS)
Elalfy, E. Y.; LaRocque, L.; Riahi-Nezhad, C. K.; Chaudhry, H.
2014-12-01
Levees are constructed along rivers and channels for flood protection. Failure of these levees can cause loss of life and property damage. A better understanding of the flow field from a levee breach allows the decision maker to assess risks and to prepare emergency plans. For this purpose, a two-dimensional numerical model is developed to simulate the levee breach. The model solves the shallow-water equations using the MacCormack explicit, finite- difference two-step, predictor-corrector scheme. The scheme is second-order accurate in time and space. The artificial viscosity technique is used to smooth the high-frequency oscillations in the computed results. The numerical results compare satisfactorily with the experimental results. A parametric study is carried-out to investigate the effect of main channel width, breach width on the computed flow field.
Numerical study of flow turning phenomenon
NASA Astrophysics Data System (ADS)
Baum, J. D.; Levine, J. N.
1986-01-01
A research project is currently being conducted that is to provide an understanding of the physical mechanisms by which energy is exchanged between the mean and acoustic flowfields in resonant combustion chambers, giving particular attention to solid rocket motors. The present paper is concerned with progress which has been made toward the understanding of the 'flow turning' phenomenon. This term is used to describe the loss of acoustic energy by the acoustic field in the combustor resulting from the inflow of combustion products through the lateral boundary of a combustion chamber containing longitudinal acoustic waves. Attention is given to the modeling of flow turning, acoustic refraction, the numerical solution, numerical results, acoustic wave propagation with no mean flow, and a flow turning study. The discussed research verifies the existence of the flow turning loss phenomenon.
A Numerical Study of Feathering Instability
NASA Astrophysics Data System (ADS)
Lee, Wing-Kit; Wang, Hsiang-Hsu
2016-06-01
The stability of a spiral shock of self-gravitating, magnetized interstellar medium is studied by performing two-dimensional numerical simulations of a local patch of tight-winding spiral arm. As previously suggested by the linear studies, two types of instabilities are identified, namely, wiggle instability and feathering instability. The former instability occurs in the hydrodynamics limit and results in short wavelength perturbations. On the other hand, the feathering instability requires both self-gravitating and magnetic fields and results in wider structures.
Experimental and Numerical Studies of Oceanic Overflow
NASA Astrophysics Data System (ADS)
Gibson, Thomas; Hohman, Fred; Morrison, Theresa; Reckinger, Shanon; Reckinger, Scott
2014-11-01
Oceanic overflows occur when dense water flows down a continental slope into less dense ambient water. The resulting density driven plumes occur naturally in various regions of the global ocean and affect the large-scale circulation. General circulation models currently rely on parameterizations for representing dense overflows due to resolution restrictions. The work presented here involves a direct qualitative and quantitative comparison between physical laboratory experiments and lab-scale numerical simulations. Laboratory experiments are conducted using a rotating square tank customized for idealized overflow and a high-resolution camera mounted on the table in the rotating reference frame for data collection. Corresponding numerical simulations are performed using the MIT general circulation model (MITgcm) run in the non-hydrostatic configuration. Resolution and numerical parameter studies are presented to ensure accuracy of the simulation. Laboratory and computational experiments are compared across a wide range of physical parameters, including Coriolis parameter, inflow density anomaly, and dense inflow volumetric flow rate. The results are analyzed using various calculated metrics, such as the plume velocity. Funding for this project is provided by the National Science Foundation.
Study on the numerical schemes for hypersonic flow simulation
NASA Astrophysics Data System (ADS)
Nagdewe, S. P.; Shevare, G. R.; Kim, Heuy-Dong
2009-10-01
Hypersonic flow is full of complex physical and chemical processes, hence its investigation needs careful analysis of existing schemes and choosing a suitable scheme or designing a brand new scheme. The present study deals with two numerical schemes Harten, Lax, and van Leer with Contact (HLLC) and advection upstream splitting method (AUSM) to effectively simulate hypersonic flow fields, and accurately predict shock waves with minimal diffusion. In present computations, hypersonic flows have been modeled as a system of hyperbolic equations with one additional equation for non-equilibrium energy and relaxing source terms. Real gas effects, which appear typically in hypersonic flows, have been simulated through energy relaxation method. HLLC and AUSM methods are modified to incorporate the conservation laws for non-equilibrium energy. Numerical implementation have shown that non-equilibrium energy convect with mass, and hence has no bearing on the basic numerical scheme. The numerical simulation carried out shows good comparison with experimental data available in literature. Both numerical schemes have shown identical results at equilibrium. Present study has demonstrated that real gas effects in hypersonic flows can be modeled through energy relaxation method along with either AUSM or HLLC numerical scheme.
Numerical Study of Tip Vortex Flows
NASA Technical Reports Server (NTRS)
Dacles-Mariani, Jennifer; Hafez, Mohamed
1998-01-01
This paper presents an overview and summary of the many different research work related to tip vortex flows and wake/trailing vortices as applied to practical engineering problems. As a literature survey paper, it outlines relevant analytical, theoretical, experimental and computational study found in literature. It also discusses in brief some of the fundamental aspects of the physics and its complexities. An appendix is also included. The topics included in this paper are: 1) Analytical Vortices; 2) Experimental Studies; 3) Computational Studies; 4) Wake Vortex Control and Management; 5) Wake Modeling; 6) High-Lift Systems; 7) Issues in Numerical Studies; 8) Instabilities; 9) Related Topics; 10) Visualization Tools for Vertical Flows; 11) Further Work Needed; 12) Acknowledgements; 13) References; and 14) Appendix.
Additional EIPC Study Analysis. Final Report
Hadley, Stanton W; Gotham, Douglas J.; Luciani, Ralph L.
2014-12-01
Between 2010 and 2012 the Eastern Interconnection Planning Collaborative (EIPC) conducted a major long-term resource and transmission study of the Eastern Interconnection (EI). With guidance from a Stakeholder Steering Committee (SSC) that included representatives from the Eastern Interconnection States Planning Council (EISPC) among others, the project was conducted in two phases. Phase 1 involved a long-term capacity expansion analysis that involved creation of eight major futures plus 72 sensitivities. Three scenarios were selected for more extensive transmission- focused evaluation in Phase 2. Five power flow analyses, nine production cost model runs (including six sensitivities), and three capital cost estimations were developed during this second phase. The results from Phase 1 and 2 provided a wealth of data that could be examined further to address energy-related questions. A list of 14 topics was developed for further analysis. This paper brings together the earlier interim reports of the first 13 topics plus one additional topic into a single final report.
Numerical Studies of Doped Iron Pnictides
NASA Astrophysics Data System (ADS)
Bishop, Christopher; Liang, Shuhua; Moreo, Adriana; Dagotto, Elbio
The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic disorder strength and dilution via numerical studies of a three-orbital spin-fermion model with lattice degrees of freedom. Doping introduces disorder but in theoretical studies the effect of the randomly located dopants is difficult to address. Numerically the effects of electronic doping, regulated by a chemical potential, and impurity disorder at randomly selected sites can be independently controlled. It was found that the reduction with doping of the Neel and the structural transition temperatures, and the stabilization of a nematic state, is mainly controlled by the magnetic dilution due to the disorder. Fermi surface changes due to doping affect only slightly both critical temperatures. Our findings are compatible with neutron scattering and STM results, unveiling a patchy network of locally magnetically ordered anisotropic clusters, despite the isotropic disorder. The fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 pnictides. National Science Foundation Grant No. DMR-1404375.
A Numerical Climate Observing Network Design Study
NASA Technical Reports Server (NTRS)
Stammer, Detlef
2003-01-01
This project was concerned with three related questions of an optimal design of a climate observing system: 1. The spatial sampling characteristics required from an ARGO system. 2. The degree to which surface observations from ARGO can be used to calibrate and test satellite remote sensing observations of sea surface salinity (SSS) as it is anticipated now. 3. The more general design of an climate observing system as it is required in the near future for CLIVAR in the Atlantic. An important question in implementing an observing system is that of the sampling density required to observe climate-related variations in the ocean. For that purpose this project was concerned with the sampling requirements for the ARGO float system, but investigated also other elements of a climate observing system. As part of this project we studied the horizontal and vertical sampling characteristics of a global ARGO system which is required to make it fully complementary to altimeter data with the goal to capture climate related variations on large spatial scales (less thanAttachment: 1000 km). We addressed this question in the framework of a numerical model study in the North Atlantic with an 1/6 horizontal resolution. The advantage of a numerical design study is the knowledge of the full model state. Sampled by a synthetic float array, model results will therefore allow to test and improve existing deployment strategies with the goal to make the system as optimal and cost-efficient as possible. Attachment: "Optimal observations for variational data assimilation".
Numerical study of a magnesium hydride tank
NASA Astrophysics Data System (ADS)
Delhomme, Baptiste; de Rango, Patricia; Marty, Philippe
2012-11-01
Hydrogen storage in metal hydride tanks (MHT) is a very promising solution. Several experimental tanks, studied by different teams, have already proved the feasibility and the interesting performances of this solution. However, in much cases, an optimization of tank geometry is still needed in order to perform fast hydrogen loading. The development of efficient numerical tools is a key issue for MHT design and optimization. We propose a simple model representing a metal hydride tank exchanging its heat of reaction with a thermal fluid flow. In this model, the radial and axial discretisations have been decoupled by using Matlab® one-dimensional tools. Calculations are compared to experimental results obtained in a previous study. A good agreement is found for the loading case. The discharging case shows some discrepancies, which are discussed in this paper.
Numerical aerodynamic simulation facility feasibility study
NASA Technical Reports Server (NTRS)
1979-01-01
There were three major issues examined in the feasibility study. First, the ability of the proposed system architecture to support the anticipated workload was evaluated. Second, the throughput of the computational engine (the flow model processor) was studied using real application programs. Third, the availability reliability, and maintainability of the system were modeled. The evaluations were based on the baseline systems. The results show that the implementation of the Numerical Aerodynamic Simulation Facility, in the form considered, would indeed be a feasible project with an acceptable level of risk. The technology required (both hardware and software) either already exists or, in the case of a few parts, is expected to be announced this year. Facets of the work described include the hardware configuration, software, user language, and fault tolerance.
A numerical study of thin flame representations
Rotman, D.A.; Pindera, M.Z.
1989-08-11
In studies of reacting flows, the flame may be viewed as a moving discontinuity endowed with certain properties; notably, it acts as a source of velocity and vorticity. Asymptotic analysis shows this to be justified provided that the flame curvature is small compared to the flame thickness. Such an approach is useful when one is interested in the hydrodynamic effects of the flame on the surrounding flowfield. In numerical models of this kind it is customary to treat the discontinuity as a collection of discrete velocity blobs. In this study, we show that the velocities associated with such a representation can be very non-smooth, particularly very near to the flame surface. As an alternative, we propose the use of a finite line source as the basic flame element. Comparisons of the two flame representations are made for several simple test cases as well as for a flame propagating through an enclosure forming the tulip shape. The results show that the use of line sources eliminates spurious fluctuations in nearfield velocities thus allowing for a more accurate calculation of flame propagation and flame-flowfield interactions. 7 refs., 15 figs.
Structure Property Studies for Additively Manufactured Parts
Milenski, Helen M; Schmalzer, Andrew Michael; Kelly, Daniel
2015-08-17
Since the invention of modern Additive Manufacturing (AM) processes engineers and designers have worked hard to capitalize on the unique building capabilities that AM allows. By being able to customize the interior fill of parts it is now possible to design components with a controlled density and customized internal structure. The creation of new polymers and polymer composites allow for even greater control over the mechanical properties of AM parts. One of the key reasons to explore AM, is to bring about a new paradigm in part design, where materials can be strategically optimized in a way that conventional subtractive methods cannot achieve. The two processes investigated in my research were the Fused Deposition Modeling (FDM) process and the Direct Ink Write (DIW) process. The objectives of the research were to determine the impact of in-fill density and morphology on the mechanical properties of FDM parts, and to determine if DIW printed samples could be produced where the filament diameter was varied while the overall density remained constant.
Numerical studies of solar chromospheric jets
NASA Astrophysics Data System (ADS)
Iijima, Haruhisa
2016-03-01
The solar chromospheric jet is one of the most characteristic structures near the solar surface. The quantitative understanding of chromospheric jets is of substantial importance for not only the partially ionized phenomena in the chromosphere but also the energy input and dissipation processes in the corona. In this dissertation, the formation and dynamics of chromospheric jets are investigated using the radiation magnetohydrodynamic simulations. We newly develop a numerical code for the radiation magnetohydrodynamic simulations of the comprehensive modeling of solar atmosphere. Because the solar chromosphere is highly nonlinear, magnetic pressure dominated, and turbulent, a robust and high-resolution numerical scheme is required. In Chapter 2, we propose a new algorithm for the simulation of magnetohydrodynamics. Through the test problems and accuracy analyses, the proposed scheme is proved to satisfy the requirements. In Chapter 3, the effect of the non-local radiation energy transport, Spitzer-type thermal conduction, latent heat of partial ionization and molecule formation, and gravity are implemented to the magnetohydrodynamic code. The numerical schemes for the radiation transport and thermal conduction is carefully chosen in a view of the efficiency and compatibility with the parallel computation. Based on the developed radiation magnetohydrodynamic code, the formation and dynamics of chromospheric jets are investigated. In Chapter 4, we investigate the dependence of chromospheric jets on the coronal temperature in the two-dimensional simulations. Various scale of chromospheric jets with the parabolic trajectory are found with the maximum height of 2–8 Mm, lifetime of 2–7 min, maximum upward velocity of 10– 50 km/s, and deceleration of 100–350 m/s2. We find that chromospheric jets are more elongated under the cool corona and shorter under the hot corona. We also find that the pressure gradient force caused by the periodic shock waves accelerates
The double pendulum: a numerical study
NASA Astrophysics Data System (ADS)
Calvão, A. M.; Penna, T. J. P.
2015-07-01
Analysis and characterization of dynamical systems is a common task in computational physics. It frequently demands new algorithms for finding solutions and new techniques for analysing the results. Here we review some of these algorithms and techniques in the study of the double pendulum, which, despite being a very simple mechanical system, can display complex behaviour. Even though it has been studied before (Yu and Bi 1998 J. Sound Vib. 217 691736; Stachowiak and Okada 2006 Chaos, Solitons & Fractals 29 417422; Rafat, Wheatland and Bedding 2009 Am. J. Phys. 77 216-23; Levien and Tan 1993 Am. J. Phys. 61 103844), here we present a deeper discussion of the several methods and algorithms that are used in typical studies of dynamical systems. In addition, we present new results obtained through techniques commonly used in the analysis of complex systems.
Supersymmetric Q-balls: A numerical study
Campanelli, L.; Ruggieri, M.
2008-02-15
We study numerically a class of nontopological solitons, the Q-balls, arising in a supersymmetric extension of the standard model with low-energy, gauge-mediated symmetry breaking. Taking into account the exact form of the supersymmetric potential giving rise to Q-balls, we find that there is a lower limit on the value of the charge Q in order to make them classically stable: Q > or approx. 5x10{sup 2}Q{sub cr}, where Q{sub cr} is constant depending on the parameters defining the potential and can be in the range 1 < or approx. Q{sub cr} < or approx. 10{sup 8} {sup divide} {sup 16}. If Q is the baryon number, stability with respect to the decay into protons requires Q > or approx. 10{sup 17}Q{sub cr}, while if the gravitino mass is greater then m{sub 3/2} > or approx. 61 MeV, no stable gauge-mediation supersymmetric Q-balls exist. Finally, we find that energy and radius of Q-balls can be parametrized as E{approx}{xi}{sub E}Q{sup 3/4} and R{approx}{xi}{sub R}Q{sup 1/4}, where {xi}{sub E} and {xi}{sub R} are slowly varying functions of the charge.
Numerical Study of a Convective Turbulence Encounter
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.
2002-01-01
A numerical simulation of a convective turbulence event is investigated and compared with observational data. The specific case was encountered during one of NASA's flight tests and was characterized by severe turbulence. The event was associated with overshooting convective turrets that contained low to moderate radar reflectivity. Model comparisons with observations are quite favorable. Turbulence hazard metrics are proposed and applied to the numerical data set. Issues such as adequate grid size are examined.
Influence of Ar addition on ozone generation in a non-thermal plasma—a numerical investigation
NASA Astrophysics Data System (ADS)
Chen, Hsin Liang; Lee, How Ming; Chen, Shiaw Huei; Wei, Ta Chin; Been Chang, Moo
2010-10-01
A numerical model based on a dielectric barrier discharge is developed in this study to investigate the influence of Ar addition on ozone generation. The simulation results show good agreement with the experimental data, confirming the validity of the numerical model. The mechanisms regarding how the Ar addition affects ozone generation are investigated with the assistance of a numerical simulation by probing into the following two questions, (1) why the ozone concentration just slightly decreases in the low specific input energy (SIE, the ratio of discharge power to gas flow rate) region even if the inlet O2 concentration is substantially decreased and (2) why the variation of the increased rate of ozone concentration with SIE (i.e. the variation in the slope of ozone concentration versus SIE) is more significant for an O2/Ar mixture plasma. As SIE is relatively low, ozone decomposition through electron-impact and radical attack reactions is less significant because of low ozone concentration and gas temperature. Therefore, the ozone concentration depends mainly on the amount of oxygen atoms generated. The simulation results indicate that the amount of oxygen atoms generated per electronvolt for Ar concentrations of 0%, 10%, 30%, 50% and 80% are 0.178, 0.174, 0.169, 0.165 and 0.166, respectively, explaining why the ozone concentration does not decrease linearly with the inlet O2 concentration in the low SIE region. On the other hand, the simulation results show that increasing Ar concentration would lead to a lower reduced field and a higher gas temperature. The former would lead to an increase in the rate constant of e + O3 → e + O + O2 while the latter would result in a decrease in the rate constant of O + O2 + M → O3 + M and an increase in that of O3 + O → 2O2. The changes in the rate constants of these reactions would have a negative effect on ozone generation, which is the rationale for the second question.
Numerical study of a microscopic artificial swimmer
NASA Astrophysics Data System (ADS)
Gauger, Erik; Stark, Holger
2006-08-01
We present a detailed numerical study of a microscopic artificial swimmer realized recently by Dreyfus in experiments [Dreyfus , Nature 437, 862 (2005)]. It consists of an elastic filament composed of superparamagnetic particles that are linked together by DNA strands. Attached to a load particle, the resulting swimmer is actuated by an oscillating external magnetic field so that it performs a nonreciprocal motion in order to move forward. We model the superparamagnetic filament by a bead-spring configuration that resists bending like a rigid rod and whose beads experience friction with the surrounding fluid and hydrodynamic interactions with each other. We show that, aside from finite-size effects, its dynamics is governed by the dimensionless sperm number, the magnitude of the magnetic field, and the angular amplitude of the field’s oscillating direction. Then we study the mean velocity and the efficiency of the swimmer as a function of these parameters and the size of the load particle. In particular, we clarify that the real velocity of the swimmer is influenced by two main factors, namely the shape of the beating filament (determined by the sperm number and the magnetic-field strength) and the oscillation frequency. Furthermore, the load size influences the performance of the swimmer and has to be chosen as a compromise between the largest swimming velocity and the best efficiency. Finally, we demonstrate that the direction of the swimming velocity changes in a symmetry-breaking transition when the angular amplitude of the field’s oscillating direction is increased, in agreement with experiments.
Numerical studies of solar chromospheric jets
NASA Astrophysics Data System (ADS)
Iijima, Haruhisa
2016-03-01
The solar chromospheric jet is one of the most characteristic structures near the solar surface. The quantitative understanding of chromospheric jets is of substantial importance for not only the partially ionized phenomena in the chromosphere but also the energy input and dissipation processes in the corona. In this dissertation, the formation and dynamics of chromospheric jets are investigated using the radiation magnetohydrodynamic simulations. We newly develop a numerical code for the radiation magnetohydrodynamic simulations of the comprehensive modeling of solar atmosphere. Because the solar chromosphere is highly nonlinear, magnetic pressure dominated, and turbulent, a robust and high-resolution numerical scheme is required. In Chapter 2, we propose a new algorithm for the simulation of magnetohydrodynamics. Through the test problems and accuracy analyses, the proposed scheme is proved to satisfy the requirements. In Chapter 3, the effect of the non-local radiation energy transport, Spitzer-type thermal conduction, latent heat of partial ionization and molecule formation, and gravity are implemented to the magnetohydrodynamic code. The numerical schemes for the radiation transport and thermal conduction is carefully chosen in a view of the efficiency and compatibility with the parallel computation. Based on the developed radiation magnetohydrodynamic code, the formation and dynamics of chromospheric jets are investigated. In Chapter 4, we investigate the dependence of chromospheric jets on the coronal temperature in the two-dimensional simulations. Various scale of chromospheric jets with the parabolic trajectory are found with the maximum height of 2-8 Mm, lifetime of 2-7 min, maximum upward velocity of 10-50 km/s, and deceleration of 100-350 m/s2. We find that chromospheric jets are more elongated under the cool corona and shorter under the hot corona. We also find that the pressure gradient force caused by the periodic shock waves accelerates some of the
Mathematical modeling of electrocardiograms: a numerical study.
Boulakia, Muriel; Cazeau, Serge; Fernández, Miguel A; Gerbeau, Jean-Frédéric; Zemzemi, Nejib
2010-03-01
This paper deals with the numerical simulation of electrocardiograms (ECG). Our aim is to devise a mathematical model, based on partial differential equations, which is able to provide realistic 12-lead ECGs. The main ingredients of this model are classical: the bidomain equations coupled to a phenomenological ionic model in the heart, and a generalized Laplace equation in the torso. The obtention of realistic ECGs relies on other important features--including heart-torso transmission conditions, anisotropy, cell heterogeneity and His bundle modeling--that are discussed in detail. The numerical implementation is based on state-of-the-art numerical methods: domain decomposition techniques and second order semi-implicit time marching schemes, offering a good compromise between accuracy, stability and efficiency. The numerical ECGs obtained with this approach show correct amplitudes, shapes and polarities, in all the 12 standard leads. The relevance of every modeling choice is carefully discussed and the numerical ECG sensitivity to the model parameters investigated. PMID:20033779
Numerical studies of supersonic/hypersonic combustion
Yoon, W.S.; Chung, T.J. )
1992-01-01
This paper is concerned with the development of direct numerical simulations of turbulence interacting with shock waves and chemical reactions using unstructured adaptive finite element h-p methods. Reliable methods for resolving the complicated time and length scales involved in turbulence interacting with shock waves and chemical reactions are not yet available. Direct numerical simulations are here developed via Taylor-Galerkin finite element implicit scheme, with mesh refinements and spectral orders optimized such that errors are reduced where gradients of variables are large. 31 refs.
Hurtado, Pablo I; Garrido, Pedro L
2010-04-01
Most systems, when pushed out of equilibrium, respond by building up currents of locally conserved observables. Understanding how microscopic dynamics determines the averages and fluctuations of these currents is one of the main open problems in nonequilibrium statistical physics. The additivity principle is a theoretical proposal that allows to compute the current distribution in many one-dimensional nonequilibrium systems. Using simulations, we validate this conjecture in a simple and general model of energy transport, both in the presence of a temperature gradient and in canonical equilibrium. In particular, we show that the current distribution displays a Gaussian regime for small current fluctuations, as prescribed by the central limit theorem, and non-Gaussian (exponential) tails for large current deviations, obeying in all cases the Gallavotti-Cohen fluctuation theorem. In order to facilitate a given current fluctuation, the system adopts a well-defined temperature profile different from that of the steady state and in accordance with the additivity hypothesis predictions. System statistics during a large current fluctuation is independent of the sign of the current, which implies that the optimal profile (as well as higher-order profiles and spatial correlations) are invariant upon current inversion. We also demonstrate that finite-time joint fluctuations of the current and the profile are well described by the additivity functional. These results suggest the additivity hypothesis as a general and powerful tool to compute current distributions in many nonequilibrium systems. PMID:20481672
Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S
2016-03-01
In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1-0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. PMID:26706539
Numerical study of mixing in hypervelocity flows
Krishnamurthy, R.; Woods, D.M.; Chandra, S.
1996-12-31
Results are reported from an analysis of data obtained with a combustor model tested in the new pulse facility at California Institute of Technology. Data analysis was performed using the numerical code GASP. Comparisons were drawn between the predictions of the algebraic Baldwin-Lomax and the two equation k-{epsilon} turbulence models. It is concluded that the use of the simpler Baldwin-Lomax model is sufficient as it saves computational resources and yields adequate predictions, for the conditions considered here.
A numerical study of confined turbulent jets
NASA Technical Reports Server (NTRS)
Zhu, J.; Shih, T.-H.
1993-01-01
A numerical investigation is reported of turbulent incompressible jets confined in two ducts, one cylindrical and the other conical with a 5 degree divergence. In each case, three Craya-Curtet numbers are considered which correspond, respectively, to flow situations with no moderate and strong recirculation. Turbulence closure is achieved by using the k-epsilon model and a recently proposed realizable Reynolds stress algebraic equation model that relates the Reynolds stresses explicitly to the quadratic terms of the mean velocity gradients and ensures the positiveness of each component of the turbulent kinetic energy. Calculations are carried out with a finite-volume procedure using boundary-fitted curvilinear coordinates. A second-order accurate, bounded convection scheme and sufficiently fine grids are used to prevent the solutions from being contaminated by numerical diffusion. The calculated results are compared extensively with the available experimental data. It is shown that the numerical methods presented are capable of capturing the essential flow features observed in the experiments and that the realizable Reynolds stress algebraic equation model performs much better than the k-epsilon model for this class of flows of great practical importance.
Numerical study of insect free hovering flight
NASA Astrophysics Data System (ADS)
Wu, Di; Yeo, Khoon Seng; Lim, Tee Tai; Fluid lab, Mechanical Engineering, National University of Singapore Team
2012-11-01
In this paper we present the computational fluid dynamics study of three-dimensional flow field around a free hovering fruit fly integrated with unsteady FSI analysis and the adaptive flight control system for the first time. The FSI model being specified for fruitfly hovering is achieved by coupling a structural problem based on Newton's second law with a rigorous CFD solver concerning generalized finite difference method. In contrast to the previous hovering flight research, the wing motion employed here is not acquired from experimental data but governed by our proposed control systems. Two types of hovering control strategies i.e. stroke plane adjustment mode and paddling mode are explored, capable of generating the fixed body position and orientation characteristic of hovering flight. Hovering flight associated with multiple wing kinematics and body orientations are shown as well, indicating the means by which fruitfly actually maintains hovering may have considerable freedom and therefore might be influenced by many other factors beyond the physical and aerodynamic requirements. Additionally, both the near- and far-field flow and vortex structure agree well with the results from other researchers, demonstrating the reliability of our current model.
Numerical study of combustion processes in afterburners
NASA Technical Reports Server (NTRS)
Zhou, Xiaoqing; Zhang, Xiaochun
1986-01-01
Mathematical models and numerical methods are presented for computer modeling of aeroengine afterburners. A computer code GEMCHIP is described briefly. The algorithms SIMPLER, for gas flow predictions, and DROPLET, for droplet flow calculations, are incorporated in this code. The block correction technique is adopted to facilitate convergence. The method of handling irregular shapes of combustors and flameholders is described. The predicted results for a low-bypass-ratio turbofan afterburner in the cases of gaseous combustion and multiphase spray combustion are provided and analyzed, and engineering guides for afterburner optimization are presented.
Numerical Study of Orbits around Europa
NASA Astrophysics Data System (ADS)
Mourao, Decio; Carvalho, Jean Paulo; Vilhena de Moraes, Rodolpho; Cardoso dos Santos, Josué; Campos de Carvalho Costa, Luis Fernando
NASA's Galileo spacecraft probe recently discovered what appears to be a body of liquid water locked inside the icy shell of Jupiter’s moon Europa. The improved likelihood of life on Europa motivated new mission proposals. In this work we used numerical simulations to compare several possible orbits of satellites near the surface of Europa. We spread a set of particles around the satellite with different initially conditions, from 50 to 500km altitude and inclinations higher than 35 degrees, and we monitored the evolution of the test particles during the numerical integrations. We consider the effect of the oblateness of Europa by considering the C22,J2 and J4 parameters and Jupiter gravitational perturbation. These perturbations were first accounted for separately in order to better understand the importance of each effect, and then considered jointly. All particles collide with the Europa surface in a few days. The oblateness of Jupiter alone causes particles with high inclination to collide with the surface of Europa, while the oblateness of Europa affects low orbits decreasing the lifetime of most of the particles. We identified a stable region of orbits with initial altitudes around 300 km of altitude and 90 degrees of inclination. Particles in this region survived more than 200 days. In most of the simulations pericenter initial values near 90 or 270 degrees favor a higher lifetime for the particles, even when considering Europa oblateness.
Numerical Studies of Impurities in Fusion Plasmas
DOE R&D Accomplishments Database
Hulse, R. A.
1982-09-01
The coupled partial differential equations used to describe the behavior of impurity ions in magnetically confined controlled fusion plasmas require numerical solution for cases of practical interest. Computer codes developed for impurity modeling at the Princeton Plasma Physics Laboratory are used as examples of the types of codes employed for this purpose. These codes solve for the impurity ionization state densities and associated radiation rates using atomic physics appropriate for these low-density, high-temperature plasmas. The simpler codes solve local equations in zero spatial dimensions while more complex cases require codes which explicitly include transport of the impurity ions simultaneously with the atomic processes of ionization and recombination. Typical applications are discussed and computational results are presented for selected cases of interest.
Reconstruction of Fractional Quantum Hall Edges: Numerical Studies
NASA Astrophysics Data System (ADS)
Wan, Xin; Yang, Kun; Rezayi, E. H.
2003-03-01
The interplay of electron-electron interaction and confining potential can lead to the reconstruction of fractional quantum Hall edges (Xin Wan, Kun Yang, and E. H. Rezayi, Phys. Rev. Lett. 88, 056802 (2002).). We have performed exact diagonalization studies on microscopic models of fractional quantum Hall liquids, in finite size systems with disc geometry, and found numerical evidence that suggests edge reconstruction occurs under rather general conditions. Due to edge reconstruction, additional nonchiral edge modes can arise for both incompressible and compressible states. We have studied the electron dipole spectral function that is directly related to the microwave conductivity measurement of a two-dimensional electron gas with an array of antidots (P. D. Ye et al., Phys. Rev. B 65, 121305 (2002).). Our results are consistent with the enhanced microwave conductivity observed in experiments at low temperatures, and its suppression at higher temperatures. We also discuss the effects of the edge reconstruction on the fractional quantum Hall edge tunneling experiments.
Numerical Studies of Boundary-Layer Receptivity
NASA Technical Reports Server (NTRS)
Reed, Helen L.
1995-01-01
Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments.
Externally fed star formation: a numerical study
NASA Astrophysics Data System (ADS)
Mohammadpour, Motahareh; Stahler, Steven W.
2013-08-01
We investigate, through a series of numerical calculations, the evolution of dense cores that are accreting external gas up to and beyond the point of star formation. Our model clouds are spherical, unmagnetized configurations with fixed outer boundaries, across which gas enters subsonically. When we start with any near-equilibrium state, we find that the cloud's internal velocity also remains subsonic for an extended period, in agreement with observations. However, the velocity becomes supersonic shortly before the star forms. Consequently, the accretion rate building up the protostar is much greater than the benchmark value c_s^3/G, where cs is the sound speed in the dense core. This accretion spike would generate a higher luminosity than those seen in even the most embedded young stars. Moreover, we find that the region of supersonic infall surrounding the protostar races out to engulf much of the cloud, again in violation of the observations, which show infall to be spatially confined. Similar problematic results have been obtained by all other hydrodynamic simulations to date, regardless of the specific infall geometry or boundary conditions adopted. Low-mass star formation is evidently a quasi-static process, in which cloud gas moves inward subsonically until the birth of the star itself. We speculate that magnetic tension in the cloud's deep interior helps restrain the infall prior to this event.
Numerical study of homogeneous nanodroplet growth.
Quang, Tran Si Bui; Leong, Fong Yew; Mirsaidov, Utkur M
2015-01-15
We investigate the axisymmetric homogeneous growth of 10-100 nm water nanodroplets on a substrate surface. The main mechanism of droplet growth is attributed to the accumulation of laterally diffusing water monomers, formed by the absorption of water vapour in the environment onto the substrate. Under assumptions of quasi-steady thermodynamic equilibrium, the nanodroplet evolves according to the augmented Young-Laplace equation. Using continuum theory, we model the dynamics of nanodroplet growth including the coupled effects of disjoining pressure, contact angle and monomer diffusion. Our numerical results show that the initial droplet growth is dominated by monomer diffusion, and the steady late growth rate of droplet radius follows a power law of 1/3, which is unaffected by the substrate disjoining pressure. Instead, the disjoining pressure modifies the growth rate of the droplet height, which then follows a power law of 1/4. We demonstrate how spatial depletion of monomers could lead to a growth arrest of the nanodroplet, as observed experimentally. This work has further implications on the growth kinetics, transport and phase transition of liquids at the nanoscale. PMID:25454424
Numerical studies of 2-dimensional flows
NASA Technical Reports Server (NTRS)
Moretti, G.
1985-01-01
A formulation of the lambda scheme for the analysis of two dimensional inviscid, compressible, unsteady transonic flows is presented. The scheme uses generalized Riemann variables to determine the appropriate two point, one sided finite difference approximation for each derivative in the unsteady Euler equations. These finite differences are applied at the predictor and corrector levels with shock updating at each level. The weaker oblique shocks are captured, but strong near normal shocks are fitted into the flow using the Rankine-Hugoniot relations. This code is demonstrated with a numerical example of a duct flow problem with developing normal and oblique shock waves. The technique is implemented in a code which has been made efficient by streamlining to a minimal number of operations and by eliminating branch statements. The scheme is shown to provide an accurate analysis of the flow, including formation, motions, and interactions of shocks; the results obtained on a relatively coarse mesh are comparable to those obtained by other methods on much finer meshes.
Additional Treatments Offer Little Benefit for Pancreatic Cancer: Study
... 158633.html Additional Treatments Offer Little Benefit for Pancreatic Cancer: Study Neither extra chemotherapy drug nor add-on ... 2016 (HealthDay News) -- Additional treatments for locally advanced pancreatic cancer don't appear to boost survival, a new ...
Numerical study of fluid motion in bioreactor with two mixers
NASA Astrophysics Data System (ADS)
Zheleva, I.; Lecheva, A.
2015-10-01
Numerical study of hydrodynamic laminar behavior of a viscous fluid in bioreactor with multiple mixers is provided in the present paper. The reactor is equipped with two disk impellers. The fluid motion is studied in stream function-vorticity formulation. The calculations are made by a computer program, written in MATLAB. The fluid structure is described and numerical results are graphically presented and commented.
Numerical study of fluid motion in bioreactor with two mixers
Zheleva, I.; Lecheva, A.
2015-10-28
Numerical study of hydrodynamic laminar behavior of a viscous fluid in bioreactor with multiple mixers is provided in the present paper. The reactor is equipped with two disk impellers. The fluid motion is studied in stream function-vorticity formulation. The calculations are made by a computer program, written in MATLAB. The fluid structure is described and numerical results are graphically presented and commented.
Numerical study of nonlinear streaming inside a standing wave resonator
NASA Astrophysics Data System (ADS)
Daru, V.; Carlès, D. Baltean; Weisman, C.
2012-09-01
The acoustic streaming associated to standing waves in a cylindrical resonator is studied for increasing nonlinear Reynolds numbers by numerically solving the compressible Navier-Stokes equations, using a high resolution finite difference scheme. The resonator is excited by shaking it along the axis at imposed frequency, corresponding to the fundamental resonance frequency of the waveguide. For sufficiently large acoustic velocities, shocks are visible. The mean field is computed by time-averaging over the main acoustic period. When the nonlinear Reynolds number increases, the center of the outer streaming cells are pushed toward the acoustic velocity nodes and two additional vortices per quarter-wavelength are generated on the axis, near the velocity antinodes. This result differs from linear models and is in agreement with several recent experimental measurement performed in the nonlinear regime. The mean temperature field evolution within the resonator is also investigated.
ERIC Educational Resources Information Center
Iler, H. Darrell; Brown, Amber; Landis, Amanda; Schimke, Greg; Peters, George
2014-01-01
A numerical analysis of the free radical addition polymerization system is described that provides those teaching polymer, physical, or advanced organic chemistry courses the opportunity to introduce students to numerical methods in the context of a simple but mathematically stiff chemical kinetic system. Numerical analysis can lead students to an…
A Study of Additional Costs of Second Language Instruction.
ERIC Educational Resources Information Center
McEwen, Nelly
A study was conducted whose primary aim was to identify and explain additional costs incurred by Alberta, Canada school jurisdictions providing second language instruction in 1980. Additional costs were defined as those which would not have been incurred had the second language program not been in existence. Three types of additional costs were…
A Numerical Study of Nonlinear Wave Interactions
NASA Astrophysics Data System (ADS)
de Bakker, A.; Tissier, M.; Ruessink, G.
2014-12-01
Nonlinear triad interactions redistribute energy among a wave field, which transforms the shape of the incident short waves (f = 0.05 - 2 Hz) and generates energy at infragravity frequencies (f = 0.005-0.05 Hz). Recently, it has been suggested that infragravity energy may dissipate by energy transfers from infragravity frequencies to either the (former) short-wave spectral peak, or through infragravity-infragravity self-interactions that cause the infragravity waves to steepen and to eventually break. To investigate these infragravity dissipation mechanisms, we use the non-hydrostatic SWASH model. In this study, we first validate the model with the high-resolution GLOBEX laboratory data set and then explore the dependence of the energy transfers, with a focus on infragravity frequencies, on beach slope. Consistent with previous studies we find that SWASH is able to reproduce the transformation and corresponding nonlinear energy transfers of shoreward propagating waves to great detail. Bispectral analysis is used to study the coupling between wave frequencies; nonlinear energy transfers are then quantified using the Boussinesq coupling coefficient. To obtain more detailed insight we divide the nonlinear interactions in four categories based on triads including 1) infragravity frequencies only, 2) two infragravity frequencies and one short-wave frequency, 3) one infragravity frequency and two short-wave frequencies and 4) short-wave frequencies only. Preliminary results suggest that interactions are rather weak on gently beach slopes (1:80) and, in the innermost part of the surf zone, are dominated by infragravity-infragravity interactions. On steeper slopes (1:20), interactions are stronger, but entirely dominated by those involving short-wave frequencies only. The dependence of the transfers on offshore wave conditions and beach shape will be explored too. Funded by NWO.
A Numerical Study of Superconducting Cavity Components
B.C. Yunn; J.J. Bisognano
1990-09-10
Computer programs which solve Maxwell's equations in three dimensions are becoming an invaluable tool in the design of RF structures for particle accelerators. In particular, the lack of cylindrical symmetry of superconducting cavities with waveguide couplers demands a 3-D analysis for a reasonable description of a number of important phenomena. A set of codes, collectively known as MAFIA, developed by Weiland and his collaborators, has been used at CEBAF to study its five-cell superconducting accelerating cavities. The magnitude of RF crosstalk between cavities is found to depend critically on the breaking of cylindrical symmetry by the fundamental power couplers. A model of the higher order mode coupler exhibits an unexpected mode which is in good agreement with measurement.
A numerical study of aircraft empennage buffet
NASA Astrophysics Data System (ADS)
Findlay, David Bruce
1999-10-01
A method to predict tightly-coupled dynamic aeroelastic vertical tail buffet was presented. Analysis of high angle of attack vertical tail buffet was performed. A Navier-Stokes fluid dynamics method was coupled with a modal structural dynamics method. The approach was to improve upon existing methods to evaluate complex geometric arrangements with general multi-zone interfacing. The method was demonstrated through a step- wise approach beginning with a simple configuration and building up to a complete aircraft at high angle of attack with flexible tail surfaces. Results compared well with in-flight and Full-scale wind tunnel measured trends and frequency content. Comparisons with measured absolute values of buffet loads showed the computations to be under-predicting the test data. This was primarily attributed to insufficient grid resolution, in particular in the vicinity of the main vortex flow. The demanding computational requirements of full-configuration tail buffet prediction limited the fidelity. The primary contribution of the present study was the extension and demonstration of a tightly-coupled aeroelastic computational fluid dynamics/structural dynamics based analysis method for analysis of aircraft empennage buffet. The focus was on improving the development process associated with characterizing empennage buffet loads and the resulting structural response. The intent was to establish a computationally based alternative approach to the experimentally based process currently employed. The computational method was employed to provide far greater insight into the flow physics phenomena associated with specific configurations and conditions of interest.
Numerical Study of Explosive Dispersal of Particles
NASA Astrophysics Data System (ADS)
Rollin, Bertrand; Annamalai, Subramanian; Neal, Christopher; Jackson, Thomas; Balachandar, S.
2014-11-01
Recent experiments have shown that when a layer of solid particles is explosively dispersed, a multiphase instability front occurs, which leads to the formation of aerodynamically stable jet-like particle structures. We aim at replicating these experimental observations using highly resolved large-scale simulations, to improve our understanding of particulate front instabilities and jetting phenomenon. We consider a cylindrical core of high pressure and density gas generated from energetic material. Throughout the length of the cylinder, an annular region of micron-sized inert spherical particles surrounds the charge. The particles are treated as point particles, the gas is treated as a continuum, and a rigorous two-way coupled compressible multiphase formulation is used. The jets are believed to have their origin during the early phase of rapid acceleration of the bed of particles. Therefore, this work focuses on capturing the early-time behavior and growth of the instabilities caused by the presence of particles. The accuracy of our predictive simulations will be studied by comparing the shock radius, particle front location, and other relevant metrics against the data extracted from experimental results. This work is supported by the U.S. DoE, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science Academic Alliance Program, under Contract No. DE-NA0002378.
Numerical Studies of Properties of Confined Helium
NASA Technical Reports Server (NTRS)
Manousakis, Efstratios
2003-01-01
We carry out state of the art simulations of properties of confined liquid helium near the superfluid transition to a degree of accuracy which allows to make predictions for the outcome of fundamental physics experiments in microgravity. First we report our results for the finite-size scaling behavior of heat capacity of superfluids for cubic and parallel-plate geometry. This allows us to study the crossover from zero and two dimensions to three dimensions. Our calculated scaling functions are in good agreement with recently measured specific heat scaling functions for the above mentioned geometries. We also present our results of a quantum simulation of submonolayer of molecular hydrogen deposited on an ideal graphite substrate using path-integral quantum Monte Carlo simulation. We find that the monolayer phase diagram is rich and very similar to that of helium monolayer. We are able to uncover the main features of the complex monolayer phase diagram, such as the commensurate solid phases and the commensurate to incommensurate transition, in agreement with the experiments and to find some features which are missing from the experimental analysis.
NASA Technical Reports Server (NTRS)
Kwon, J. H.
1977-01-01
Numerical solution of two dimensional, time dependent, compressible viscous Navier-Stokes equations about arbitrary bodies was treated using density gradients as additional dependent variables. Thus, six dependent variables were computed with the SOR iteration method. Besides formulation for pressure gradient terms, a formulation for computing the body density was presented. To approximate the governing equations, an implicit finite difference method was employed. In computing the solution for the flow about a circular cylinder, a problem arose near the wall at both stagnation points. Thus, computations with various conditions were tried to examine the problem. Also, computations with and without formulations are compared. The flow variables were computed on 37 by 40 field first, then on an 81 by 40 field.
A numerical comparison of discrete Kalman filtering algorithms: An orbit determination case study
NASA Technical Reports Server (NTRS)
Thornton, C. L.; Bierman, G. J.
1976-01-01
The numerical stability and accuracy of various Kalman filter algorithms are thoroughly studied. Numerical results and conclusions are based on a realistic planetary approach orbit determination study. The case study results of this report highlight the numerical instability of the conventional and stabilized Kalman algorithms. Numerical errors associated with these algorithms can be so large as to obscure important mismodeling effects and thus give misleading estimates of filter accuracy. The positive result of this study is that the Bierman-Thornton U-D covariance factorization algorithm is computationally efficient, with CPU costs that differ negligibly from the conventional Kalman costs. In addition, accuracy of the U-D filter using single-precision arithmetic consistently matches the double-precision reference results. Numerical stability of the U-D filter is further demonstrated by its insensitivity of variations in the a priori statistics.
Numerical study of free surface flow around large obstacles
NASA Astrophysics Data System (ADS)
Zhang, Yanming
In this thesis a numerical model was developed to study three-dimensional turbulent flows around large obstacles in an open channel. With this numerical model, a series of numerical tests was carried out, and the properties of turbulent flows around a single obstacle or a cluster of obstacles were investigated. The origin of this study was to study the flow properties around fish habitat structures. Actually, the numerical model can be applied to the study of general turbulent flows under free surfaces. In the numerical model the three-dimensional Reynolds-averaged Navier-Stokes equations in conjunction with k-epsilon turbulence model were solved in a free surface fitted coordinate system. First, different forms of governing equations for turbulent flow were investigated, and a concise form of fully transformed governing equations in a general curvilinear coordinate system was derived. In the numerical solution the FAVOR (Fractional Area/Volume Obstacle Representation) technique was extended into the free surface fitted coordinate system. With this feature the problem of complex turbulent flow with a free surface and general shaped obstacles could be solved efficiently. To locate the free surface, a method based on integrating the momentum equation in the vertical direction was developed. After study and tests of several popular difference schemes, a QUICK scheme with UMIST limiter was adopted in this numerical model. Several test cases were presented to demonstrate the present numerical model. The first test case was to simulate a submerged hydraulic jump. The calculated velocity, free surface profile and turbulence properties of the flow showed a close match with the experimental data. The second test was a submerged hydraulic jump with a baffle sill. The comparison between numerical and experimental data indicated that the current numerical model could catch the general flow structures of the submerged hydraulic jumps. The last two test cases were flows around a
A numerical study of three-dimensional vortex breakdown
NASA Technical Reports Server (NTRS)
Spall, Robert E.; Ash, Robert L.
1987-01-01
A numerical simulation of bubble-type vortex breakdown using a unique discrete form of the full 3-D, unsteady incompressible Navier-Stokes equations was performed. The Navier-Stokes equations were written in a vorticity-velocity form and the physical problem was not restricted to axisymmetric flow. The problem was parametized on a Rossby- Reynolds-number basis. Utilization of this parameter duo was shown to dictate the form of the free-field boundary condition specification and allowed control of axial breakdown location within the computational domain. The structure of the breakdown bubble was studied through time evolution plots of planar projected velocity vectors as well as through plots of particle traces and vortex lines. These results compared favorably with previous experimental studies. In addition, profiles of all three velocity components are presented at various axial stations and a Fourier analysis was performed to identify the dominant circumferential modes. The dynamics of the breakdown process were studied through plots of axial variation of rate of change of integrated total energy and rate of change of integrated enstrophy, as well as through contour plots of velocity, vorticity and pressure.
Numerical study of dynamical mass generation in QED3
NASA Astrophysics Data System (ADS)
Bashir, A.; Huet, A.; Raya, A.
2006-05-01
We carry out a numerical study of dynamical generation of fermion masses by solving the Schwinger-Dyson equation for the fermion propagator in three-dimensional quenched Quantum Electrodynamics (QED3) in various gauges. We employ an ansatz for the three-point vertex which satisfies the Ward-Green-Takahashi identity, namely, the Ball-Chiu Vertex. We discuss the advantages of our numerical method over some earlier ones.
Numerical Study of a Hydrodynamic Instability Driven by Evaporation
NASA Astrophysics Data System (ADS)
Hernandez-Zapata, Sergio; Romo-Cruz, Julio Cesar Ruben; Lopez-Sanchez, Erick Javier; Ruiz-Chavarria, Gerardo
2013-11-01
The study of hydrodynamic instabilities in liquid layers produced by evaporation has several applications on industry and technology. In this work we study numerically the conditions under which a liquid layer becomes unstable when evaporation in the vapor-liquid interphase is present. The evaporation process follows the Hertz-Knudsen law (the evaporation rate is proportional to the difference between the saturated vapor pressure at the liquid layer temperature and the vapor partial pressure in the environment). Additionally to the usual boundary conditions on solid walls (for example, the non-slip condition for the velocity), we analyze the boundary conditions in the vapor-liquid interphase where the momentum and energy balances have to be taken into account and where the evaporation plays a crucial role. To solve this problem the linear theory of stability is used; that is, a small perturbation around the basic solution is applied (flow at rest and a temperature stationary field). The equations are solved using the Chebyshev pseudo-spectral method. The results are compared with the more usual Rayleigh-Bénard and Marangoni mechanisms as well as with some experiments carried out by our team. Authors acknowledge DGAPA-UNAM by support under project IN116312, ``Vorticidad y Ondas no lineales en fluidos.''
Experimental and numerical study on condensation in transonic steam flow
NASA Astrophysics Data System (ADS)
Majkut, Mirosław; Dykas, Sławomir; Strozik, Michał; Smołka, Krystian
2015-09-01
The present paper describes an experimental and numerical study of steam condensing flow in a linear cascade of turbine stator blades. The experimental research was performed on the facility of a small scale steam power plant located at Silesian University of Technology in Gliwice, Poland. The test rig of the facility allows us to perform the tests of steam transonic flows for the conditions corresponding to these which prevail in the low-pressure (LP) condensing steam turbine stages. The experimental data of steam condensing flow through the blade-to- blade stator channel were compared with numerical results obtained using the in-house CFD numerical code TraCoFlow. Obtained results confirmed a good quality of the performed experiment and numerical calculations.
Black shale weathering: An integrated field and numerical modeling study
NASA Astrophysics Data System (ADS)
Bolton, E. W.; Wildman, R. A., Jr.; Berner, R. A.; Eckert, J. O., Jr.; Petsch, S. T.; Mok, U.; Evans, B.
2003-04-01
We present an integrated study of black shale weathering in a near surface environment. Implications of this study contribute to our understanding of organic matter oxidation in uplifted sediments, along with erosion and reburial of ancient unoxidized organic matter, as major controls on atmospheric oxygen levels over geologic time. The field study used to launch the modeling effort is based on core samples from central-eastern Kentucky near Clay City (Late Devonian New Albany/Ohio Shale), where the strata are essentially horizontal. Samples from various depth intervals (up to 12 m depth) were analyzed for texture (SEM images), porosity fraction (0.02 to 0.1), and horizontal and vertical permeability (water and air permeabilities differ due to the fine-grained nature of the sediments, but are on the order of 0.01 to 1. millidarcies, respectively). Chemical analyses were also performed for per cent C, N, S, and basic mineralogy was determined (clays, quartz, pyrite, in addition to organic matter). The samples contained from 2 to 15 per cent ancient (non-modern soil) organic matter. These results were used in the creation of a numerical model for kinetically controlled oxidation of the organic matter within the shale (based on kinetics from Chang and Berner, 1999). The one-dimensional model includes erosion, oxygen diffusion in the partially saturated vadose zone as well as water percolation and solute transport. This study extends the studies of Petsch (2000) and the weathering component of Lasaga and Ohmoto (2002) to include more reactions (e.g., pyrite oxidation to sulfuric acid and weathering of silicates due to low pH) and to resolve the near-surface boundary layer. The model provides a convenient means of exploring the influence of variable rates of erosion, oxygen level, rainfall, as well as physical and chemical characteristics of the shale on organic matter oxidation.
Numerical study of subcritical flow with fluid injection
NASA Technical Reports Server (NTRS)
Balasubramanian, R.
1990-01-01
It is suggested that the study of synthetic flows, where controlled experiments can be performed, is useful in understanding turbulent flow structures. The early states of formation of hairpin structures in shear flows and the subsequent evolution of these structures is studied in shear flows and the subsequent evolution of these structures is studied through numerical simulations, by developing full-time dependent three-dimensional flow solution of an initially laminar (subcritical) flow in which injection of fluid through a narrow streamwise slot from the bottom wall of a plate is carried out. Details of the numerical approach and significance of the present findings are reported in this work.
Coupled laboratory and numerical studies of impacts into planetary regolith
NASA Astrophysics Data System (ADS)
Dove, A.; Li, Y.; Curtis, J.; Colwell, J. E.
2014-12-01
We present the initial results from coupled experimental and numerical study of the response of particles to low-velocity impacts. In this study, laboratory experiments are used to validate and tune a new DEM capable of handling complex particle shapes for simulation of the behavior of planetary regolith. These studies have fundamental applications to granular material science, as well as broader applications to the response to low-energy impacts of surface layers on other planetary bodies, including planetesimals, asteroids, small moons, and planetary ring particles. Knowledge of the velocities and mass distributions of dust knocked off of planetary surfaces is necessary to understand the evolution of the upper layers of the soil, the plasma environment, and to develop mitigation strategies for transported dust. In addition, the fine particles in the regolith pose an engineering and safety hazard for equipment, experiments, and astronauts working in severe environments. Our laboratory experiments consist of impacting a spherical impactor into a bed of particles and tracking the subsequent mass loss and trajectories of the ejected particles. We begin with spherical particles and then we will expand to elongated rods, flake-like particles, and well-characterized aggregates. Complementary discrete element method (DEM) simulations are validated by these experimental studies; in the DEM simulations, the non-spherical nature of these particles will be described using a glued-sphere approach. An initial comparison between the particle ejection velocities observed in the experiments and simulations for spherical particles is shown in the figure. Discrepancies at low velocities are due to the fact that the trajectories of particles with such low ejection speeds are not observable in this setup. The simulations will then be used to gain physical insight and to evaluate a broader range of scenarios than can be easily explored experimentally, such as conditions similar to
Experimental and Numerical Study of Free-Field Blast Mitigation
NASA Astrophysics Data System (ADS)
Allen, R. M.; Kirkpatrick, D. J.; Longbottom, A. W.; Milne, A. M.; Bourne, N. K.
2004-07-01
The development of a fundamental understanding of the mechanisms governing the attenuation of explosives effects by a surrounding mitigant material or system would benefit many civilian and military applications. Current approaches rely almost exclusively on empirical data, few if any truly predictive models exist. Dstl has recently pursued an experimental programme investigating the mitigation of effects from detonating explosives in support of general requirements to attenuate blast and fragmentation. The physical properties of a range of mitigant materials have been studied at a more fundamental level, both experimentally and numerically. A preliminary numerical parameter study has been undertaken by FGE using two-phase numerical simulations to complement the experimental studies. Initial work used idealised equations of state for generic mitigants but more recently material characterisation experiments have been undertaken at RMCS. Results confirm that porosity and particle density are dominant factors affecting the efficiency of the mitigant in reducing free-field blast.
A Numerical Study of Hypersonic Forebody/Inlet Integration Problem
NASA Technical Reports Server (NTRS)
Kumar, Ajay
1991-01-01
A numerical study of hypersonic forebody/inlet integration problem is presented in the form of the view-graphs. The following topics are covered: physical/chemical modeling; solution procedure; flow conditions; mass flow rate at inlet face; heating and skin friction loads; 3-D forebogy/inlet integration model; and sensitivity studies.
Numerical studies of laminar and turbulent drag reduction
NASA Technical Reports Server (NTRS)
Balasubramanian, R.; Orszag, S. A.
1981-01-01
Two-dimensional incompressible flow over wavy surfaces is studied numerically by spectral methods. Turbulence effects are modeled. Results for symmetric and asymmetric wave forms are presented. Effect of propagating surface waves on drag reduction is studied. Comparisons between computer simulations and experimental results are made.
Numerical Study of Magnetic Damping During Unidirectional Solidification
NASA Technical Reports Server (NTRS)
Li, Ben Q.
1997-01-01
A fully 3-D numerical model is developed to represent magnetic damping of complex fluid flow, heat transfer and electromagnetic field distributions in a melt cavity. The model is developed based on our in-house finite element code for the fluid flow, heat transfer and electromagnetic field calculations. The computer code has been tested against benchmark test problems that are solved by other commercial codes as well as analytical solutions whenever available. The numerical model is tested against numerical and experimental results for water reported in literature. With the model so tested, various numerical simulations are carried out for the Sn-35.5% Pb melt convection and temperature distribution in a cylindrical cavity with and without the presence of a transverse magnetic field. Numerical results show that magnetic damping can be effectively applied to reduce turbulence and flow levels in the melt undergoing solidification and over a certain threshold value a higher magnetic field resulted in a higher velocity reduction. It is found also that for a fully 3-D representation of the magnetic damping effects, the electric field induced in the melt by the applied DC magnetic field does not vanish, as some researchers suggested, and must be included even for molten metal and semiconductors. Also, for the study of the melt flow instability, a long enough time has to be applied to ensure the final fluid flow recirculation pattern. Moreover, our numerical results suggested that there seems to exist a threshold value of applied magnetic field, above which magnetic damping becomes possible and below which the convection in the melt is actually enhanced. Because of the limited financial resource allocated for the project, we are unable to carry out extensive study on this effect, which should warrant further theoretical and experimental study. In that endeavor, the developed numerical model should be very useful; and the model should serve as a useful tool for exploring
Numerical aerodynamic simulation facility preliminary study: Executive study
NASA Technical Reports Server (NTRS)
1977-01-01
A computing system was designed with the capability of providing an effective throughput of one billion floating point operations per second for three dimensional Navier-Stokes codes. The methodology used in defining the baseline design, and the major elements of the numerical aerodynamic simulation facility are described.
Dynamical Approach Study of Spurious Numerics in Nonlinear Computations
NASA Technical Reports Server (NTRS)
Yee, H. C.; Mansour, Nagi (Technical Monitor)
2002-01-01
The last two decades have been an era when computation is ahead of analysis and when very large scale practical computations are increasingly used in poorly understood multiscale complex nonlinear physical problems and non-traditional fields. Ensuring a higher level of confidence in the predictability and reliability (PAR) of these numerical simulations could play a major role in furthering the design, understanding, affordability and safety of our next generation air and space transportation systems, and systems for planetary and atmospheric sciences, and in understanding the evolution and origin of life. The need to guarantee PAR becomes acute when computations offer the ONLY way of solving these types of data limited problems. Employing theory from nonlinear dynamical systems, some building blocks to ensure a higher level of confidence in PAR of numerical simulations have been revealed by the author and world expert collaborators in relevant fields. Five building blocks with supporting numerical examples were discussed. The next step is to utilize knowledge gained by including nonlinear dynamics, bifurcation and chaos theories as an integral part of the numerical process. The third step is to design integrated criteria for reliable and accurate algorithms that cater to the different multiscale nonlinear physics. This includes but is not limited to the construction of appropriate adaptive spatial and temporal discretizations that are suitable for the underlying governing equations. In addition, a multiresolution wavelets approach for adaptive numerical dissipation/filter controls for high speed turbulence, acoustics and combustion simulations will be sought. These steps are corner stones for guarding against spurious numerical solutions that are solutions of the discretized counterparts but are not solutions of the underlying governing equations.
Numerical study of the simplest string bit model
NASA Astrophysics Data System (ADS)
Chen, Gaoli; Sun, Songge
2016-05-01
String bit models provide a possible method to formulate a string as a discrete chain of pointlike string bits. When the bit number M is large, a chain behaves as a continuous string. We study the simplest case that has only one bosonic bit and one fermionic bit. The creation and annihilation operators are adjoint representations of the U (N ) color group. We show that the supersymmetry reduces the parameter number of a Hamiltonian from 7 to 3 and, at N =∞ , ensures a continuous energy spectrum, which implies the emergence of one spatial dimension. The Hamiltonian H0 is constructed so that in the large N limit it produces a world sheet spectrum with one Grassmann world sheet field. We concentrate on the numerical study of the model in finite N . For the Hamiltonian H0, we find that the would-be ground energy states disappear at N =(M -1 ) /2 for odd M ≤11 . Such a simple pattern is spoiled if H has an additional term ξ Δ H which does not affect the result of N =∞ . The disappearance point moves to higher (lower) N when ξ increases (decreases). Particularly, the ±(H0-Δ H ) cases suggest a possibility that the ground state could survive at large M and M ≫N . Our study reveals that the model has stringy behavior: when N is fixed and large enough, the ground energy decreases linearly with respect to M , and the excitation energy is roughly of order M-1. We also verify that a stable system of Hamiltonian ±H0+ξ Δ H requires ξ ≥∓1 .
Numerical study of damage growth in particulate composites
Kwon, Y.W.; Liu, C.T.
1999-10-01
A numerical study was conducted to simulate and predict damage initiation and growth around the crack tip in particulate composite specimens made of hard particles embedded in a soft rubber-like matrix material. Therefore, damage evolution in the matrix material around crack tips was investigated. The progressive damage was modeled using a micro/macro-approach which combined two levels of analyses like the micro-level and the macro-level analyses. Damage description was undertaken at the microlevel using a simplified three-dimensional unit-cell model and an isotropic continuum damage theory. The numerical study examined both thin and thick specimens with a short or long edge crack to understand the effects of specimen thickness and crack size on the damage initiation, growth, and saturation. Numerical results were compared with experimental data.
Numerical study of axisymmetric collapses of submarine granular > columns
NASA Astrophysics Data System (ADS)
Monsorno, Davide; Varsakelis, Christos
2014-11-01
In this talk, we report on the results of a numerical study of the axisymmetric collapse of subaqueous granular columns. Our study is based on a 2-pressure, 2-velocity continuum flow model for fluid-saturated granular materials. This model is integrated via a multi-phase projection method that incorporates a regularization method for the treatment of material interfaces. In our simulations, a dense column of a granular material immersed in water is placed on a horizontal plane and is allowed to collapse and spread due to its weight. Emphasis is placed on the run-out distance and the termination height and their correlation with the aspect ratio, the volume fraction and the diameter of the grains. Comparisons against experimental measurements and previous numerical predictions are also performed. Finally, in order to examine and quantify the role of the interstitial fluid, we compare our numerical predictions against experimental results from column collapses of dry granular materials.
An Ensemble Numerical Modeling Study of Atlantic Basin Hurricane Intensification
NASA Astrophysics Data System (ADS)
Brown, Bonnie R.
Rapid intensification of tropical cyclones is an active area of research in the atmospheric sciences due to the difficulty of forecasting cyclone intensity and the unclear mechanism by which a hurricane my undergo explosive deepening. Ensemble numerical modeling studies of six tropical cyclones from 2009, 2010 and 2011 which underwent periods of strong intensification are conducted here. The goal is to identify common storm structures in intensifying hurricanes while filling a gap in the current research between case studies of rapid intensification and climatological/statistical type studies of hurricane intensification rates by using a compositing method. A 96-member ensemble is run for a 24 hour forecast using the Weather Research and Forecasting (WRF) model for hurricanes Bill (2009), Earl (2010), Igor (2010), Julia (2010), Katia (2011), and Ophelia (2011). Ensemble sensitivity analysis is used to investigate which patterns in the analysis have a strong influence on the forecast intensity and then a novel sensitivity compositing is used to identify common patterns which affect the forecast intensity. It is found that these hurricanes are all predicted to respond to an increased primary and secondary circulation, an increased warm core, a raised tropopause and moistening of rain bands with an increased forecast intensity. Perturbed initial conditions show a linear model response for small perturbations but also signs of non-linearity at large perturbations, indicating that these sensitivity patterns are robust for limited additional strengthening of the hurricane. When perturbations are partitioned into dry and moist variables, it is seen that most of the model response is achieved by the dry dynamics. Further investigation is conducted into the rapid intensification of Earl (2010) and Igor (2010) but creating ensemble forecasts with additional, high-resolution nested domains which allow explicit convection. When the ensemble sensitivity analysis is repeated
NUMERICAL STUDY OF THE VISHNIAC INSTABILITY IN SUPERNOVA REMNANTS
Michaut, C.; Cavet, C.; Bouquet, S. E.; Roy, F.; Nguyen, H. C.
2012-11-10
The Vishniac instability is thought to explain the complex structure of radiative supernova remnants in their Pressure-Driven Thin Shell (PDTS) phase after a blast wave (BW) has propagated from a central explosion. In this paper, the propagation of the BW and the evolution of the PDTS stage are studied numerically with the two-dimensional (2D) code HYDRO-MUSCL for a finite-thickness shell expanding in the interstellar medium (ISM). Special attention is paid to the adiabatic index, {gamma}, and three distinct values are taken for the cavity ({gamma}{sub 1}), the shell ({gamma}{sub 2}), and the ISM ({gamma}{sub 3}) with the condition {gamma}{sub 2} < {gamma}{sub 1}, {gamma}{sub 3}. This low value of {gamma}{sub 2} accounts for the high density in the shell achieved by a strong radiative cooling. Once the spherical background flow is obtained, the evolution of a 2D-axisymmetric perturbation is computed from the linear to the nonlinear regime. The overstable mechanism, previously demonstrated theoretically by E. T. Vishniac in 1983, is recovered numerically in the linear stage and is expected to produce and enhance anisotropies and clumps on the shock front, leading to the disruption of the shell in the nonlinear phase. The period of the increasing oscillations and the growth rate of the instability are derived from several points of view (the position of the perturbed shock front, mass fluxes along the shell, and density maps), and the most unstable mode differing from the value given by Vishniac is computed. In addition, the influence of several parameters (the Mach number, amplitude and wavelength of the perturbation, and adiabatic index) is examined and for wavelengths that are large enough compared to the shell thickness, the same conclusion arises: in the late stage of the evolution of the radiative supernova remnant, the instability is dampened and the angular initial deformation of the shock front is smoothed while the mass density becomes uniform with the
A Numerical/Experimental Study of Nitinol Actuator Springs
NASA Astrophysics Data System (ADS)
Auricchio, Ferdinando; Scalet, Giulia; Urbano, Marco
2014-07-01
This study deals with the numerical modeling, simulation and experimental analysis of shape-memory alloy (SMA) helicoidal springs. An experimental campaign is conducted on both SMA straight wires and helicoidal springs that experienced the same annealing process. Then, we use such experimental results to investigate three phenomenological constitutive models able to represent SMA macroscopic behavior. In particular, after the identification of all the material parameters from experimental results on SMA wires, we inspect the thermo-mechanical behavior of SMA helicoidal springs by comparing numerical predictions to experimental data. Finally, we discuss models capabilities and some aspects characterizing SMA material behavior.
Numerical study of the small scale structures in Boussinesq convection
NASA Technical Reports Server (NTRS)
Weinan, E.; Shu, Chi-Wang
1992-01-01
Two-dimensional Boussinesq convection is studied numerically using two different methods: a filtered pseudospectral method and a high order accurate Essentially Nonoscillatory (ENO) scheme. The issue whether finite time singularity occurs for initially smooth flows is investigated. The numerical results suggest that the collapse of the bubble cap is unlikely to occur in resolved calculations. The strain rate corresponding to the intensification of the density gradient across the front saturates at the bubble cap. We also found that the cascade of energy to small scales is dominated by the formulation of thin and sharp fronts across which density jumps.
Experimental and numerical study of pulsating transversal jets
NASA Astrophysics Data System (ADS)
Goldfeld, M. A.; Fedorova, N. N.; Fedorchenko, I. A.; Pozdnyakov, G. A.; Timofeev, K. Yu.; Zhakharova, Yu. V.
2015-06-01
Paper presents results of joint experimental and numerical investigation of pulsating jet penetration into still air and supersonic flow. Goal of the study is to investigate two-dimensional (2D) Hartmann generator (HG) properties and clear up its possibilities in providing better mixing between air and secondary (injected) gases.
Numerical study of the Kerr solution in rotating coordinates
NASA Astrophysics Data System (ADS)
Bai, S.; Izquierdo, G.; Klein, C.
2016-06-01
The Kerr solution in coordinates corotating with the horizon is studied as a testbed for a spacetime with a helical Killing vector in the Ernst picture. The solution is numerically constructed by solving the Ernst equation with a spectral method and a Newton iteration. We discuss convergence of the iteration for several initial iterates and different values of the Kerr parameters.
Numerical studies of gravity effects in two-phase reservoirs
Bodvarsson, G.S.; Cox, B.L.
1986-06-01
Numerical studies are performed to investigate the effects of localized feed zones on the pressure transients in two-phase reservoirs. It is shown that gravity effects can significantly affect the pressure transients, because of the large difference in the density of liquid water and vapor. Pressure transients for shallow and deep feed zones and the resulting fluid flow patterns are discussed.
Numerical study of porosity in titanium dental castings.
Wu, M; Sahm, P R; Augthun, M; Spiekermann, H; Schädlich-Stubenrauch, J
1999-09-01
A commercial software package, MAGMASOFT (MAGMA Giessereitechnologie GmbH, Aachen, Germany), was used to study shrinkage and gas porosity in titanium dental castings. A geometrical model for two simplified tooth crowns connected by a connector bar was created. Both mold filling and solidification of this casting model were numerically simulated. Shrinkage porosity was quantitatively predicted by means of a built-in feeding criterion. The risk of gas pore formation was investigated using the numerical filling and solidification results. The results of the numerical simulations were compared with experiments, which were carried out on a centrifugal casting machine with an investment block mold. The block mold was made of SiO2 based slurry with a 1 mm thick Zr2 face coat to reduce metal-mold reactions. Both melting and casting were carried out under protective argon (40 kPa). The finished castings were sectioned and the shrinkage porosity determined. The experimentally determined shrinkage porosity coincided with the predicted numerical simulation results. No apparent gas porosity was found in these model castings. Several running and gating systems for the above model casting were numerically simulated. An optimized running and gating system design was then experimentally cast, which resulted in porosity-free castings. PMID:15348102
Stability of vegetated slopes in unsaturated conditions: a numerical study
NASA Astrophysics Data System (ADS)
Battista Chirico, Giovanni; Borga, Marco; Tarolli, Paolo; Rigon, Riccardo; Preti, Federico
2014-05-01
Extreme rainfall events can trigger shallow landslides with failure planes located in soils far from saturated conditions. The stability of shallow soils on very steep slopes under unsaturated conditions can be highly influenced by the vegetation, according to both geo-mechanical and soil-hydrological factors, particularly in regions characterized by a strong climatic seasonality. The root structure of the vegetation reinforces the shallow soils, by providing additional apparent cohesion to the soil. The root water uptake enhances the stability by increasing the frequency of high suction pressure heads in the soil layers explored by the roots. In water controlled eco-systems, such as Mediterranean areas, these two factors are mutually related. Plants develop their root structure in order to optimize the uptake of the water available in the soil, since water availability is limited during the growing season. In this study we present the results of some numerical experiments with the aim to assess the relative importance of these two factors. We simulated the soil water dynamics within homogeneous loamy-sand soils, assuming climatic conditions and root structures typically observed in a deciduous forest of central and southern Italy. An infinite slope stability model is employed for assessing the temporal evolution of the contribute of the soil suction regime to the slope stability, as compared with the contribute of the soil root reinforcement. The results suggest that, during the wet season, the effect of the soil suction state on slope stability is much smaller than that attributable to the mechanical reinforcement provided by the root structure, at least within soil depths explored by the plant roots. Instead, during the growing and dry summer seasons, the soil suction state is far more relevant than the mechanical reinforcement. Thus, accounting for the antecedent soil suction state can be relevant for an appropriate prediction of shallow landslide hazards in
A Numerical Study of Micrometeoroids Entering Titan's Atmosphere
NASA Technical Reports Server (NTRS)
Templeton, M.; Kress, M. E.
2011-01-01
A study using numerical integration techniques has been performed to analyze the temperature profiles of micrometeors entering the atmosphere of Saturn s moon Titan. Due to Titan's low gravity and dense atmosphere, arriving meteoroids experience a significant cushioning effect compared to those entering the Earth's atmosphere. Temperature profiles are presented as a function of time and altitude for a number of different meteoroid sizes and entry velocities, at an entry angle of 45. Titan's micrometeoroids require several minutes to reach peak heating (ranging from 200 to 1200 K), which occurs at an altitude of about 600 km. Gentle heating may allow for gradual evaporation of volatile components over a wide range of altitudes. Computer simulations have been performed using the Cassini/Huygens atmospheric data for Titan. Keywords micrometeoroid Titan atmosphere 1 Introduction On Earth, incoming micrometeoroids (100 m diameter) are slowed by collisions with air molecules in a relatively compact atmosphere, resulting in extremely rapid deceleration and a short heating pulse, often accompanied by brilliant meteor displays. On Titan, lower gravity leads to an atmospheric scale height that is much larger than on Earth. Thus, deceleration of meteors is less rapid and these particles undergo more gradual heating. This study uses techniques similar to those used for Earth meteoroid studies [1], exchanging Earth s planetary characteristics (e.g., mass and atmospheric profile) for those of Titan. Cassini/Huygens atmospheric data for Titan were obtained from the NASA Planetary Atmospheres Data Node [4]. The objectives of this study were 1) to model atmospheric heating of meteoroids for a range of micrometeor entry velocities for Titan, 2) to determine peak heating temperatures and rates for micrometeoroids entering Titan s atmosphere, and 3) to create a general simulation environment that can be extended to incorporate additional parameters and variables, including different
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 studies of HF Doppler variations caused by ionospheric disturbances
NASA Astrophysics Data System (ADS)
Takefu, M.; Hiroshige, N.
HF Doppler variations caused by ionospheric disturbances are studied using an ionosphere model containing sinusoidal traveling electron density fluctuations. The present study uses a more realistic ionosphere model and a more accurate numerical method than previous works using corrugated specular reflector models. The study gives a clue to estimate the TID-associated fluctuations of ionospheric electron density by means of HF Doppler measurements. It is shown that some kinds of characteristic HF Doppler traces result depending on the wavelength of the disturbance and its traveling direction. Numerical results suggest that more or less 5 percent of the background electron density can explain most of the quasi-periodic variations on the observed HF Doppler records.
Electrostatic Levitation for Studies of Additive Manufactured Materials
NASA Technical Reports Server (NTRS)
SanSoucie, Michael P.; Rogers, Jan R.; Tramel, Terri
2014-01-01
The electrostatic levitation (ESL) laboratory at NASA's Marshall Space Flight Center is a unique facility for investigators studying high temperature materials. The laboratory boasts two levitators in which samples can be levitated, heated, melted, undercooled, and resolidified. Electrostatic levitation minimizes gravitational effects and allows materials to be studied without contact with a container or instrumentation. The lab also has a high temperature emissivity measurement system, which provides normal spectral and normal total emissivity measurements at use temperature. The ESL lab has been instrumental in many pioneering materials investigations of thermophysical properties, e.g., creep measurements, solidification, triggered nucleation, and emissivity at high temperatures. Research in the ESL lab has already led to the development of advanced high temperature materials for aerospace applications, coatings for rocket nozzles, improved medical and industrial optics, metallic glasses, ablatives for reentry vehicles, and materials with memory. Modeling of additive manufacturing materials processing is necessary for the study of their resulting materials properties. In addition, the modeling of the selective laser melting processes and its materials property predictions are also underway. Unfortunately, there is very little data for the properties of these materials, especially of the materials in the liquid state. Some method to measure thermophysical properties of additive manufacturing materials is necessary. The ESL lab is ideal for these studies. The lab can provide surface tension and viscosity of molten materials, density measurements, emissivity measurements, and even creep strength measurements. The ESL lab can also determine melting temperature, surface temperatures, and phase transition temperatures of additive manufactured materials. This presentation will provide background on the ESL lab and its capabilities, provide an approach to using the ESL
Analytical and Numerical Studies of Coherent Field Configurations
NASA Astrophysics Data System (ADS)
Muller, Hans-Reinhard
Motivated by the goal of investigating the dynamics of the electroweak phase transition in the early Universe, a study of dynamical aspects of nonlinear field-theoretical systems is performed. Symmetric and asymmetric double-well potentials in the φ4 theory are used as a model for these systems. In the first part, it is shown that in this model, a class of localized, time-dependent, spherically-symmetric objects dubbed oscillons exists. The most distinctive feature of these objects is that they are extremely long-lived. The properties of oscillons are studied by numerical and analytical means. In the second part of the study, the matching between (1+1)-dimensional nonlinear field theories coupled to an external stochastic environment and their lattice simulations is investigated. In particular, a method is developed to obtain numerical results which are lattice-spacing independent, and to extract the correct effective potential which emerges from the simulations. As an application, the thermal production of kinks is studied, obtaining the lattice-spacing independent number density of kinks and the effective barrier for kink production, i.e., the effective kink mass. Within its range of validity, the approach can be used to match numerical simulations to continuum studies of the emergence of coherent field structures in cosmology and condensed matter physics.
Experimental, theoretical, and numerical studies of small scale combustion
NASA Astrophysics Data System (ADS)
Xu, Bo
Recently, the demand increased for the development of microdevices such as microsatellites, microaerial vehicles, micro reactors, and micro power generators. To meet those demands the biggest challenge is obtaining stable and complete combustion at relatively small scale. To gain a fundamental understanding of small scale combustion in this thesis, thermal and kinetic coupling between the gas phase and the structure at meso and micro scales were theoretically, experimentally, and numerically studied; new stabilization and instability phenomena were identified; and new theories for the dynamic mechanisms of small scale combustion were developed. The reduction of thermal inertia at small scale significantly reduces the response time of the wall and leads to a strong flame-wall coupling and extension of burning limits. Mesoscale flame propagation and extinction in small quartz tubes were theoretically, experimentally and numerically studied. It was found that wall-flame interaction in mesoscale combustion led to two different flame regimes, a heat-loss dominant fast flame regime and a wall-flame coupling slow flame regime. The nonlinear transition between the two flame regimes was strongly dependent on the channel width and flow velocity. It is concluded that the existence of multiple flame regimes is an inherent phenomenon in mesoscale combustion. In addition, all practical combustors have variable channel width in the direction of flame propagation. Quasi-steady and unsteady propagations of methane and propane-air premixed flames in a mesoscale divergent channel were investigated experimentally and theoretically. The emphasis was the impact of variable cross-section area and the flame-wall coupling on the flame transition between different regimes and the onset of flame instability. For the first time, spinning flames were experimentally observed for both lean and rich methane and propane-air mixtures in a broad range of equivalence ratios. An effective Lewis number
Numerical study on 3D composite morphing actuators
NASA Astrophysics Data System (ADS)
Oishi, Kazuma; Saito, Makoto; Anandan, Nishita; Kadooka, Kevin; Taya, Minoru
2015-04-01
There are a number of actuators using the deformation of electroactive polymer (EAP), where fewer papers seem to have focused on the performance of 3D morphing actuators based on the analytical approach, due mainly to their complexity. The present paper introduces a numerical analysis approach on the large scale deformation and motion of a 3D half dome shaped actuator composed of thin soft membrane (passive material) and EAP strip actuators (EAP active coupon with electrodes on both surfaces), where the locations of the active EAP strips is a key parameter. Simulia/Abaqus Static and Implicit analysis code, whose main feature is the high precision contact analysis capability among structures, are used focusing on the whole process of the membrane to touch and wrap around the object. The unidirectional properties of the EAP coupon actuator are used as input data set for the material properties for the simulation and the verification of our numerical model, where the verification is made as compared to the existing 2D solution. The numerical results can demonstrate the whole deformation process of the membrane to wrap around not only smooth shaped objects like a sphere or an egg, but also irregularly shaped objects. A parametric study reveals the proper placement of the EAP coupon actuators, with the modification of the dome shape to induce the relevant large scale deformation. The numerical simulation for the 3D soft actuators shown in this paper could be applied to a wider range of soft 3D morphing actuators.
Numerical Study on Cryogenic Coflowing Jets under Transcritical Conditions
NASA Astrophysics Data System (ADS)
Tani, Hiroumi; Teramoto, Susumu; Okamoto, Koji; Yamanishi, Nobuhiro
2012-11-01
A numerical and experimental study is presented on cryogenic coflowing jets under transcritical conditions for a better understanding of the propellant mixing in supercritical-pressure rocket engines. The major concerns are dominant flow structures in the mixing of cryogenic coflowing jets under transcritical conditions. Experimentally, in advance of detailed numerical simulations, cryogenic nitrogen/gaseous nitrogen coaxial jets were visualized by the backlighting photography technique. It was observed that a dense nitrogen core has a shear-layer instability near the injector exit and eventually breaks up into large lumps which dissolve and fade away downstream. In numerical simulations, LES technique was employed for more detailed discussion on the flow structures. LES of a cryogenic nitrogen/gaseous nitrogen coflowing plane jet was conducted with the same density and velocity ratios of inner/outer jets as the experiments. As observed in the experiments, the shear-layer instability in the inner mixing layers is predominant near the injector exit. After roll-up and paring, the shear-layer instability waves become large-scale vortices. They cause coherent vortex structures which become dominant in the downstream and break the dense core into lumps. Strouhal numbers of the shear-layer instability and the dense lump shedding in the numerical simulations were comparable to those measured in the experiments, respectively.
On the Numerical Study of Heavy Rainfall in Taiwan
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo; Chen, Ching-Sen; Chen, Yi-Leng; Jou, Ben Jong-Dao; Lin, Pay-Liam; Starr, David OC. (Technical Monitor)
2001-01-01
Heavy rainfall events are frequently observed over the western side of the CMR (central mountain range), which runs through Taiwan in a north-south orientation, in a southwesterly flow regime and over the northeastern side of the CMR in a northeasterly flow regime. Previous studies have revealed the mechanisms by which the heavy rainfall events are formed. Some of them have examined characteristics of the heavy rainfall via numerical simulations. In this paper, some of the previous numerical studies on heavy rainfall events around Taiwan during the Mei-Yu season (May and June), summer (non-typhoon cases) and autumn will be reviewed. Associated mechanisms proposed from observational studies will be reviewed first, and then characteristics of numerically simulated heavy rainfall events will be presented. The formation mechanisms of heavy rainfall from simulated results and from observational analysis are then compared and discussed. Based on these previous modeling studies, we will also discuss what are the major observations and modeling processes which will be needed for understanding the heavy precipitation in the future.
Numerical Studies of a Fluidic Diverter for Flow Control
NASA Technical Reports Server (NTRS)
Gokoglu, Suleyman A.; Kuczmarski, Maria A.; Culley, Dennis E.; Raghu, Surya
2009-01-01
The internal flow structure in a specific fluidic diverter is studied over a range from low subsonic to sonic inlet conditions by a time-dependent numerical analysis. The understanding will aid in the development of fluidic diverters with minimum pressure losses and advanced designs of flow control actuators. The velocity, temperature and pressure fields are calculated for subsonic conditions and the self-induced oscillatory behavior of the flow is successfully predicted. The results of our numerical studies have excellent agreement with our experimental measurements of oscillation frequencies. The acoustic speed in the gaseous medium is determined to be a key factor for up to sonic conditions in governing the mechanism of initiating the oscillations as well as determining its frequency. The feasibility of employing plasma actuation with a minimal perturbation level is demonstrated in steady-state calculations to also produce oscillation frequencies of our own choosing instead of being dependent on the fixed-geometry fluidic device.
Numerical study of fractional nonlinear Schrödinger equations
Klein, Christian; Sparber, Christof; Markowich, Peter
2014-01-01
Using a Fourier spectral method, we provide a detailed numerical investigation of dispersive Schrödinger-type equations involving a fractional Laplacian in an one-dimensional case. By an appropriate choice of the dispersive exponent, both mass and energy sub- and supercritical regimes can be identified. This allows us to study the possibility of finite time blow-up versus global existence, the nature of the blow-up, the stability and instability of nonlinear ground states and the long-time dynamics of solutions. The latter is also studied in a semiclassical setting. Moreover, we numerically construct ground state solutions of the fractional nonlinear Schrödinger equation. PMID:25484604
Numerical study of unsteady processes in a Faraday MHD generator
NASA Astrophysics Data System (ADS)
Vinogradova, G. N.; Panchenko, V. P.
1981-07-01
A numerical study is presented on the unsteady processes occurring in a Faraday MHD generator with a high power-conversion efficiency. A supersonic MHD generator operating with an equilibrium plasma and designed to convert energy in a system using a thermonuclear reactor is considered, and the steady operating modes are established for cases when an ohmic load is connected, disconnected, or reduced. A magnetic field is assumed to be generated by a suitable profiling of the external magnetic field, and the working medium is modeled by an ideal gas. Partial differential equations are solved numerically by using a central difference predictor-corrector scheme. The study can be applied to problems (e.g., transient times, nominal parameter maximal values and rates of change, methods of regulating the generator and switching it on and off) arising during the design of MHD generators.
Attosecond lighthouses in gases: A theoretical and numerical study
NASA Astrophysics Data System (ADS)
Auguste, T.; Gobert, O.; Ruchon, T.; Quéré, F.
2016-03-01
We present an extensive theoretical and numerical study of the attosecond lighthouse effect in gases. We study how this scheme impacts the spatiotemporal structure of the driving laser field all along the generation medium, and show that this can modify the phase matching relation governing high-harmonic generation (HHG) in gases. We then present a set of numerical simulations performed to test the robustness of the effect against variations of HHG parameters, and to identify possible solutions for relaxing the constraint on the driving laser pulse duration. We thus demonstrate that the lighthouse effect can actually be achieved with laser pulses consisting of up to ˜8 optical periods available from current lasers without postcompression, for instance by using an appropriate combination of 800 - and 1600 -nm wavelength fields.
Numerical study of fractional nonlinear Schrödinger equations.
Klein, Christian; Sparber, Christof; Markowich, Peter
2014-12-01
Using a Fourier spectral method, we provide a detailed numerical investigation of dispersive Schrödinger-type equations involving a fractional Laplacian in an one-dimensional case. By an appropriate choice of the dispersive exponent, both mass and energy sub- and supercritical regimes can be identified. This allows us to study the possibility of finite time blow-up versus global existence, the nature of the blow-up, the stability and instability of nonlinear ground states and the long-time dynamics of solutions. The latter is also studied in a semiclassical setting. Moreover, we numerically construct ground state solutions of the fractional nonlinear Schrödinger equation. PMID:25484604
BIG FROG WILDERNESS STUDY AREA AND ADDITIONS, TENNESSEE AND GEORGIA.
Slack, John F.; Gazdik, Gertrude C.
1984-01-01
A mineral-resource survey was made of the Big Frog Wilderness Study Area and additions, Tennessee-Georgia. Geochemical sampling found traces of gold, zinc, copper, and arsenic in rocks, stream sediments, and panned concentrates, but not in sufficient quantities to indicate the presence of deposits of these metals. The results of the survey indicate that there is little promise for the occurrence of metallic mineral deposits within the study area. The only apparent resources are nonmetallic commodities including rock suitable for construction materials, and small amounts of sand and gravel; however, these commodities are found in abundance outside the study area. A potential may exist for oil and natural gas at great depths, but this cannot be evaluated by the present study.
Numerical study of multicomponent droplet vaporization at near critical conditions
NASA Technical Reports Server (NTRS)
Hsieh, Kwang-Chung; Shuen, Jian-Shun; Yang, Vigor
1988-01-01
A comprehensive numerical analysis of multicomponent droplet vaporization at near critical conditions has been carried out. The model is based on the full time-dependent conservation equations and accommodates various important high-pressure phenomena. As an example, the case involving a two-component (n-pentane and n-octane) fuel droplet in nitrogen gas is studied. The influences of transient effects, surface regression, ambient gas solubility, and phase-equilibrium relations on vaporization mechanisms are examined in detail.
A numerical study of the Nordic Sea circulation and outflows
NASA Astrophysics Data System (ADS)
Yang, J.; Pratt, L. J.
2010-12-01
The Nordic Seas outflow over the Greenland-Iceland-Scotland Ridge is investigated by using a two-layer numerical model with both idealized and realistic topography. The study focuses on physical processes and topographic effects that influence the pathways of the Nordic Seas source water that feeds the overflow through the Denmark Strait and Faroe Bank Channel. The potential vorticity balance and integral constraints will be used to explain the sensitivity of the overflows to the upstream (Nordic Seas) circulation and forcing.
Recommended Protocol for Round Robin Studies in Additive Manufacturing
Moylan, Shawn; Brown, Christopher U.; Slotwinski, John
2016-01-01
One way to improve confidence and encourage proliferation of additive manufacturing (AM) technologies and parts is by generating more high quality data describing the performance of AM processes and parts. Many in the AM community see round robin studies as a way to generate large data sets while distributing the cost among the participants, thereby reducing the cost to individual users. The National Institute of Standards and Technology (NIST) has conducted and participated in several of these AM round robin studies. While the results of these studies are interesting and informative, many of the lessons learned in conducting these studies concern the logistics and methods of the study and unique issues presented by AM. Existing standards for conducting interlaboratory studies of measurement methods, along with NIST’s experience, form the basis for recommended protocols for conducting AM round robin studies. The role of round robin studies in AM qualification, some of the limitations of round robin studies, and the potential benefit of less formal collaborative experiments where multiple factors, AM machine being only one, are varied simultaneously are also discussed. PMID:27274602
Experimental and numerical study on fragmentation of steel projectiles
NASA Astrophysics Data System (ADS)
Råkvaag, K. G.; Børvik, T.; Hopperstad, O. S.; Westermann, I.
2012-08-01
A previous experimental study on penetration and perforation of circular Weldox 460E target plates with varying thicknesses struck by blunt-nose projectiles revealed that fragmentation of the projectile occurred if the target thickness or impact velocity exceeded a certain value. Thus, numerical simulations that do not account for fragmentation during impact can underestimate the perforation resistance of protective structures. Previous numerical studies have focused primarily on the target plate behaviour. This study considers the behaviour of the projectile and its possible fragmentation during impact. Hardened steel projectiles were launched at varying velocities in a series of Taylor tests. The impact events were captured using a high-speed camera. Fractography of the fragmented projectiles showed that there are several fracture mechanisms present during the fragmentation process. Tensile tests of the projectile material revealed that the hardened material has considerable variations in yield stress and fracture stress and strain. In the finite element model, the stress-strain behaviour from tensile tests was used to model the projectile material with solid elements and the modified Johnson-Cook constitutive relation. Numerical simulations incorporating the variations in material properties are capable of reproducing the experimental fracture patterns, albeit the predicted fragmentation velocities are too low.
Genotoxicity studies of the food additive ester gum.
Mukherjee, A; Agarwal, K; Chakrabarti, J
1992-07-01
Ester gum (EG) is used in citrus oil-based beverage flavourings as a weighting or colouring agent. In the present study, concentrations of 50, 100 and 150 mg/kg body weight were administered orally to male Swiss albino mice, and sister chromatid exchange and chromosomal aberration were used as the cytogenetic endpoints to determine the genotoxic and clastogenic potential of the food additive. Although EG was weakly clastogenic and could induce a marginal increase in sister chromatid exchange frequencies, it was not a potential health hazard at the doses tested. PMID:1521837
Numerical simulation studies of unsteady low Reynolds number separated flows
NASA Astrophysics Data System (ADS)
Tatineni, Mahidhar
Numerical simulations were used to study unsteady low-Reynolds-number separated flows. The studies were focused on the instability of the separation bubbles, the associated vortex shedding, and the response to imposed disturbances. The simulations were performed for separation bubbles in both low Mach number compressible and incompressible flow regimes. The compressible study consisted of unsteady simulations of flows over the Eppler 387 airfoil and the APEX airfoil. For a sufficiently high Reynolds number the simulations showed that the flow over the airfoils is inherently unsteady, with associated vortex shedding. A Fourier analysis of the unsteady flowfield revealed the presence of a dominant frequency in the flow. The dominant frequency from the numerical solution was found to agree with the most unstable frequency calculated using linear stability theory. The vortex shedding was shown to be caused by the growth of the disturbance waves corresponding to the dominant mode calculated from the linear stability analysis. In order to study the separation bubble and the vortex shedding in detail, a simpler two-dimensional (2-D) and three-dimensional (3-D) incompressible flow over a flat plate was considered. The onset of self excited vortex shedding, and the response of the separation bubble to 2-D and 3-D disturbances was studied in detail through numerical simulations. The incompressible Navier-Stokes equations were solved using a fifth order finite difference scheme for spatial discretization and a fourth order Runge-Kutta scheme for time advancement. A new high-order nonuniform grid finite difference scheme was also developed for the simulations. The incompressible simulation results showed that it was possible to induce vortex shedding by imposing disturbances upstream of the separation bubble. For a sufficiently large freestream velocity gradient the separation bubble was globally unstable, leading to a growth in the size of the separation bubble and the
Field Study and Numerical Simulation of Sub Slab Ventilation Systems
Bonnefous, Y.C.; Gadgil, A.J.; Fisk, W.J.; Prill, R.J.; Nematollahi, A.R.
1992-05-01
The effectiveness of the technique of subslab ventilation (SSV) for limiting radon entry into basements was investigated through complementary experimentation and numerical modeling. Subslab pressure fields resulting from SSV were measured in six well-characterized basements, each with a different combination of soil and aggregate permeability. The relationship between air velocity and pressure gradient was measured in the laboratory for the three types of aggregate installed beneath the basement slabs. A new numerical model of SSV was developed and verified with the field data. This model simulates non-Darcy flow in the aggregate. We demonstrate that non-Darcy effects significantly impact SSV performance. Field data and numerical simulations indicate that increasing the aggregate permeability within the investigated range of 2 x 10{sup -8} m{sup 2} to 3 x 10{sup -7} m{sup 2} substantially improves the extension of the subslab pressure field due to SSV operation. Sealing of cracks in the slab and excavation of a small pit where the SSV pipe penetrates the slab also dramatically improve this pressure field extension. Our findings are consistent with the results of prior field studies; however, the studies reported here have improved our understanding of factors affecting SSV performance. The dependence of SSV performance on the relevant parameters are currently under investigation with the model.
Numerical study of cluster formation in binary charged colloids
NASA Astrophysics Data System (ADS)
Okuzono, Tohru; Odai, Kana; Masuda, Tatsuhiro; Toyotama, Akiko; Yamanaka, Junpei
2016-07-01
Cluster formation of oppositely charged colloidal particles is studied numerically. A simple Brownian dynamics method with a screened-Coulomb (Yukawa) potential is employed for numerical simulations. An equilibrium phase which consists of clusters and unassociated particles is obtained. It is shown that the equilibrium association number of clusters and their shapes are determined by charge numbers and charge ratio of the binary particles. The phase diagram of cluster formation for various charge numbers and their ratios is obtained. A simple relation between the association number and the charge ratio is found. It is demonstrated that in the case of high charge ratio the cluster takes a multilayer structure which is highly symmetric. It is also pointed out that the cluster-particle interaction changes dynamically in the cluster formation process, which is involved in the selection of final cluster structure.
Numerical and experimental study of rotating jet flows
NASA Astrophysics Data System (ADS)
Shin, Seungwon; Che, Zhizhao; Kahouadji, Lyes; Matar, Omar; Chergui, Jalel; Juric, Damir
2015-11-01
Rotating jets are investigated through experimental measurements and numerical simulations. The experiments are performed on a rotating jet rig and the effects of a range of parameters controlling the liquid jet are investigated, e.g. jet flow rate, rotation speed, jet diameter, etc. Different regimes of the jet morphology are identified, and the dependence on several dimensionless numbers is studied, e.g. Reynolds number, Weber number, etc. The breakup process of droplets is visualized through high speed imaging. Full three-dimensional direct numerical simulations are performed using BLUE, a massively parallel two-phase flow code. The novel interface algorithms in BLUE track the gas-liquid interface through a wide dynamic range including ligament formation, break up and rupture. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Numerical Relativity as a tool for studying the Early Universe
NASA Astrophysics Data System (ADS)
Garrison, David
2013-04-01
Numerical simulations are becoming a more effective tool for conducting detailed investigations into the evolution of our universe. In this presentation, I show how the framework of numerical relativity can be used for studying cosmological models. We are working to develop a large-scale simulation of the dynamical processes in the early universe. These take into account interactions of dark matter, scalar perturbations, gravitational waves, magnetic fields and a turbulent plasma. The code described in this report is a GRMHD code based on the Cactus framework and is structured to utilize one of several different differencing methods chosen at run-time. It is being developed and tested on the Texas Learning and Computation Center's Xanadu cluster.
Numerical study on tsunami hazard mitigation using a submerged breakwater.
Ha, Taemin; Yoo, Jeseon; Han, Sejong; Cho, Yong-Sik
2014-01-01
Most coastal structures have been built in surf zones to protect coastal areas. In general, the transformation of waves in the surf zone is quite complicated and numerous hazards to coastal communities may be associated with such phenomena. Therefore, the behavior of waves in the surf zone should be carefully analyzed and predicted. Furthermore, an accurate analysis of deformed waves around coastal structures is directly related to the construction of economically sound and safe coastal structures because wave height plays an important role in determining the weight and shape of a levee body or armoring material. In this study, a numerical model using a large eddy simulation is employed to predict the runup heights of nonlinear waves that passed a submerged structure in the surf zone. Reduced runup heights are also predicted, and their characteristics in terms of wave reflection, transmission, and dissipation coefficients are investigated. PMID:25215334
Numerical study of cluster formation in binary charged colloids.
Okuzono, Tohru; Odai, Kana; Masuda, Tatsuhiro; Toyotama, Akiko; Yamanaka, Junpei
2016-07-01
Cluster formation of oppositely charged colloidal particles is studied numerically. A simple Brownian dynamics method with a screened-Coulomb (Yukawa) potential is employed for numerical simulations. An equilibrium phase which consists of clusters and unassociated particles is obtained. It is shown that the equilibrium association number of clusters and their shapes are determined by charge numbers and charge ratio of the binary particles. The phase diagram of cluster formation for various charge numbers and their ratios is obtained. A simple relation between the association number and the charge ratio is found. It is demonstrated that in the case of high charge ratio the cluster takes a multilayer structure which is highly symmetric. It is also pointed out that the cluster-particle interaction changes dynamically in the cluster formation process, which is involved in the selection of final cluster structure. PMID:27575181
Numerical study of librationally driven Flow in planetary interiors
NASA Astrophysics Data System (ADS)
Laguerre, Raphael; Karatekin, Ozgur; Noir, Jérôme
2010-05-01
Forced librations are observed for many planetary bodies. In the case of interior fluid layers, i.e. liquid cores or subsurface oceans, the resulting librational response could be different compared to that of a solid body. The coupling between the fluid layer and mantle depends strongly on the interior properties of the planet. Here we study numerically the properties of a librationally driven flow by taking into account both longitudinal and latitudinal forcing. The numerical method is based on an finite element approximation in meridian planes and a Fourier decomposition of the variables in the azimuthal direction (SFEMANS, Spectral Finite Element for Maxwell and Navier Stokes ). This allows us to specify the direction of rotation vector arbitrarily. In the case of longitudinal forcing we compare our solutions to the experimental results of Noir et al. 2009 obtained for cores with spherical shape. For latitudinal librations, we consider also the influence of ellipticity.
An analytical and numerical study of axisymmetric flow around spheroids
NASA Astrophysics Data System (ADS)
Chang, Chien-Cheng; Liou, Biing-Horng; Chern, Ruey-Ling
1992-01-01
Axisymmetric viscous flow around ellipsoids of circular section is examined in detail using a matched asymptotic analysis and a deterministic hybrid vortex method. The hybrid vortex method solves the viscous vorticity equation by combining a finite-difference method for diffusion and a vortex-in-cell method for convection and stretching. The numerical study was carried out for an ellipsoid of axis ratio 2:1 and the limiting case of a sphere at Reynolds numbers between 100 and 3000. Particular attention is given to evaluation of the drag coefficient using three different approaches. Numerical and asymptotic results at small times are found to be in good agreement. Separation angles, wake lengths, and stationary drag coefficients for the sphere are also in good agreement with previous results obtained by a finite-difference method and with the standard drag curve.
Numerical Study on Tsunami Hazard Mitigation Using a Submerged Breakwater
Yoo, Jeseon; Han, Sejong; Cho, Yong-Sik
2014-01-01
Most coastal structures have been built in surf zones to protect coastal areas. In general, the transformation of waves in the surf zone is quite complicated and numerous hazards to coastal communities may be associated with such phenomena. Therefore, the behavior of waves in the surf zone should be carefully analyzed and predicted. Furthermore, an accurate analysis of deformed waves around coastal structures is directly related to the construction of economically sound and safe coastal structures because wave height plays an important role in determining the weight and shape of a levee body or armoring material. In this study, a numerical model using a large eddy simulation is employed to predict the runup heights of nonlinear waves that passed a submerged structure in the surf zone. Reduced runup heights are also predicted, and their characteristics in terms of wave reflection, transmission, and dissipation coefficients are investigated. PMID:25215334
Making intelligent systems team players: Additional case studies
NASA Technical Reports Server (NTRS)
Malin, Jane T.; Schreckenghost, Debra L.; Rhoads, Ron W.
1993-01-01
Observations from a case study of intelligent systems are reported as part of a multi-year interdisciplinary effort to provide guidance and assistance for designers of intelligent systems and their user interfaces. A series of studies were conducted to investigate issues in designing intelligent fault management systems in aerospace applications for effective human-computer interaction. The results of the initial study are documented in two NASA technical memoranda: TM 104738 Making Intelligent Systems Team Players: Case Studies and Design Issues, Volumes 1 and 2; and TM 104751, Making Intelligent Systems Team Players: Overview for Designers. The objective of this additional study was to broaden the investigation of human-computer interaction design issues beyond the focus on monitoring and fault detection in the initial study. The results of this second study are documented which is intended as a supplement to the original design guidance documents. These results should be of interest to designers of intelligent systems for use in real-time operations, and to researchers in the areas of human-computer interaction and artificial intelligence.
Feasibility study for a numerical aerodynamic simulation facility: Summary
NASA Technical Reports Server (NTRS)
Lincoln, N. R.
1979-01-01
The Ames Research Center of NASA is engaged in the development and investigation of numerical methods and computer technologies to be employed in conjunction with physical experiments, particularly utilizing wind tunnels in the furtherance of the field of aircraft and aerodynamic body design. Several studies, aimed primarily at the areas of development and production of extremely high-speed computing facilities, were conducted. The studies focused on evaluating the aspects of feasibility, reliability, costs, and practicability of designing, constructing, and bringing into effect production of a special-purpose system. An executive summary of the activities for this project is presented in this volume.
Numerical studies of transverse curvature effects on transonic flow stability
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
Numerical study of transient flow phenomena in shock tunnels
NASA Technical Reports Server (NTRS)
Tokarcik-Polsky, Susan; Cambier, Jean-Luc
1994-01-01
Computational fluid dynamics (CFD) was used to study some transient flow features that can occur during the startup process of a shoch tunnel. The investigation concentrated on two areas: (1) the flow near the endwall of the driven tube during shock reflection and (2) the transient flow in the nozzle. The driven tube calculations were inviscid and focused on the study of a vortex system that was seen to form at the driven tube's axis of symmetry. The nozzle flow calculations examined viscous and inviscid effects during nozzle startup. The CFD solutions of the nozzle flows were compared with experimental data to demonstrate the effectiveness of the numerical analysis.
RAMSEYS DRAFT WILDERNESS STUDY AREA AND ADDITION, VIRGINIA.
Lesure, Frank G.; Mory, Peter C.
1984-01-01
Mineral-resource surveys of the Ramseys Draft Wilderness Study Area and adjoining roadless area addition in George Washington National Forest in the western valley and ridge province, Augusta and Highland Counties, Virginia, were done. The surveys outlined three small areas containing anomalous amounts of copper, lead, and zinc related to stratabound red-bed copper mineralization, but these occurrences are not large and are not considered as having mineral-resource potential. The area contains abundant sandstone suitable for construction materials and shale suitable for making brick, tile, and other low-grade ceramic products, but these commodities occur in abundance outside the wilderness study area. Structural conditions are probably favorable for the accumulation of natural gas, but exploratory drilling has not been done sufficiently near the area to evaluate the gas potential.
Numerical study of forced convective heat transfer around airships
NASA Astrophysics Data System (ADS)
Dai, Qiumin; Fang, Xiande
2016-02-01
Forced convective heat transfer is an important factor that affects the thermal characteristics of airships. In this paper, the steady state forced convective heat transfer around an ellipsoid is numerically investigated. The numerical simulation is carried out by commercial computational fluid dynamic (CFD) software over the extended Re range from 20 to 108 and the aspect ratio from 2 to 4. Based on the regression and optimization with software, a new piecewise correlation of the Nusselt number at constant wall temperature for ellipsoid is proposed, which is suitable for applications to airships and other ellipse shaped bodies such as elliptical balloons. The thermal characteristics of a stratospheric airship in midsummer located in the north hemisphere are numerical studied. The helium temperature predicated using the new correlation is compared to those predicted by correlations applicable for spheres and flat plates. The results show that the helium temperature obtained using the new correlation at noon is about 5.4 K lower than that using the correlation of spheres and about 2.1 K higher than that of flat plates.
Hydraulic fracturing: insights from field, lab, and numerical studies
NASA Astrophysics Data System (ADS)
Walsh, S. D.; Johnson, S.; Fu, P.; Settgast, R. R.
2011-12-01
Hydraulic fracturing has become an increasingly important technique in stimulating reservoirs for gas, oil, and geothermal energy production. In use commercially since the 1950's, the technique has been widely lauded, when combined with other techniques, for enabling the development of shale gas resources in the United States, providing a valuable and extensive source of domestic energy. However, the technique has also drawn a degree of notoriety from high-profile incidents involving contamination of drinking water associated with gas extraction operations in the Marcellus shale region. This work highlights some of the insights on the behavior of subsurface hydraulic fracturing operations that have been derived from field and laboratory observations as well as from numerical simulations. The sensitivity of fracture extent and orientation to parameters such as matrix material heterogeneity, presence and distribution of discontinuities, and stress orientation is of particular interest, and we discuss this in the context of knowledge derived from both observation and simulation. The limitations of these studies will also be addressed in terms of resolution, uncertainty, and assumptions as well as the balance of fidelity to cost, both in computation time (for numerical studies) and equipment / operation cost (for observational studies). We also identify a number of current knowledge gaps and propose alternatives for addressing those gaps. We especially focus on the role of numerical studies for elucidating key concepts and system sensitivities. The problem is inherently multi-scale in both space and time as well as highly coupled hydromechanically, and, in several applications, thermally as well. We will summarize the developments to date in analyzing these systems and present an approach for advancing the capabilities of our models in the short- to long-term and how these advances can help provide solutions to reduce risk and improve efficiency of hydraulic fracturing
Numerical study of the Azov Sea level seiche oscillations
NASA Astrophysics Data System (ADS)
Matishov, G. G.; Inzhebeikin, Yu. I.
2009-08-01
Seiche oscillations of the Azov Sea level are studied on the basis of the developed two-dimensional numerical hydrodynamic model grounded on the shallow water theory and recent data on the morphometric characteristics of the Sea of Azov. Frequency and spatial characteristics of the first five modes corresponding to seiche oscillations of the Azov Sea level are computed. It is shown that the frequency and spatial characteristics of the first five modes obtained for the Sea of Azov level changes correspond to seiche oscillations. The calculated parameters are compared with the field observations, which show their realistic character.
The shape of a growing crystal: a numerical study
NASA Astrophysics Data System (ADS)
Rakin, V. I.
1995-10-01
A numerical model of the "crystal-solution" system based on experimental data on K-alum sulphate was proposed. The development of the crystal shape under different physical and chemical growth conditions was studied. A correlation between crystal shape and supersaturation during crystal growth was not observed. We introduced the idea of a "steady shape" of the crystal. The correlation between the shape and the growth conditions was measured. A parameter indicating the dynamic equilibrium of the growth system was introduced. The crystal growth process can be optimised using the proposed model.
A numerical and experimental study of confined swirling jets
NASA Technical Reports Server (NTRS)
Nikjooy, M.; Mongia, H. C.; Samuelsen, G. S.; Mcdonell, V. G.
1989-01-01
A numerical and experimental study of a confined strong swirling flow is presented. Detailed velocity measurements are made using a two-component laser Doppler velocimeter (LDV) technique. Computations are performed using a differential second-moment (DSM) closure. The effect of inlet dissipation rate on calculated mean and turbulence fields is investigated. Various model constants are employed in the pressure-strain model to demonstrate their influences on the predicted results. Finally, comparison of the DSM calculations with the algebraic second-monent (ASM) closure results shows that the DSM is better suited for complex swirling flow analysis.
Numerical study of Q-ball formation in gravity mediation
Hiramatsu, Takashi; Kawasaki, Masahiro; Takahashi, Fuminobu E-mail: kawasaki@icrr.u-tokyo.ac.jp
2010-06-01
We study Q-ball formation in the expanding universe on 1D, 2D and 3D lattice simulations. We obtain detailed Q-ball charge distributions, and find that the distribution is peaked at Q{sup 3D}{sub peak} ≅ 1.9 × 10{sup −2}(|Φ{sub in}|/m){sup 2}, which is greater than the existing result by about 60%. Based on the numerical simulations, we discuss how the Q-ball formation proceeds. Also we make a comment on possible deviation of the charge distributions from what was conjectured in the past.
Dispersion of helically corrugated waveguides: analytical, numerical, and experimental study.
Burt, G; Samsonov, S V; Ronald, K; Denisov, G G; Young, A R; Bratman, V L; Phelps, A D R; Cross, A W; Konoplev, I V; He, W; Thomson, J; Whyte, C G
2004-10-01
Helically corrugated waveguides have recently been studied for use in various applications such as interaction regions in gyrotron traveling-wave tubes and gyrotron backward-wave oscillators and as a dispersive medium for passive microwave pulse compression. The paper presents a summary of various methods that can be used for analysis of the wave dispersion of such waveguides. The results obtained from an analytical approach, simulations with the three-dimensional numerical code MAGIC, and cold microwave measurements are analyzed and compared. PMID:15600525
Numerical Study of Low Emission Gas Turbine Combustor Concepts
NASA Technical Reports Server (NTRS)
Yang, Song-Lin
2002-01-01
To further reduce pollutant emissions, such as CO, NO(x), UHCs, etc., in the next few decades, innovative concepts of gas turbine combustors must be developed. Several concepts, such as the LIPP (Lean- Premixed- Prevaporized), RQL (Rich-Burn Quick-Quench Lean-Burn), and LDI (Lean-Direct-Injection), have been under study for many years. To fully realize the potential of these concepts, several improvements, such as inlet geometry, air swirler, aerothermochemistry control, fuel preparation, fuel injection and injector design, etc., must be made, which can be studied through the experimental method and/or the numerical technique. The purpose of this proposal is to use the CFD technique to study, and hence, to guide the design process for low emission gas turbine combustors. A total of 13 technical papers have been (or will be) published.
Analytical and Numerical Studies of Several Fluid Mechanical Problems
NASA Astrophysics Data System (ADS)
Kong, D. L.
2014-03-01
In this thesis, three parts, each with several chapters, are respectively devoted to hydrostatic, viscous, and inertial fluids theories and applications. Involved topics include planetary, biological fluid systems, and high performance computing technology. In the hydrostatics part, the classical Maclaurin spheroids theory is generalized, for the first time, to a more realistic multi-layer model, establishing geometries of both the outer surface and the interfaces. For one of its astrophysical applications, the theory explicitly predicts physical shapes of surface and core-mantle-boundary for layered terrestrial planets, which enables the studies of some gravity problems, and the direct numerical simulations of dynamo flows in rotating planetary cores. As another application of the figure theory, the zonal flow in the deep atmosphere of Jupiter is investigated for a better understanding of the Jovian gravity field. An upper bound of gravity field distortions, especially in higher-order zonal gravitational coefficients, induced by deep zonal winds is estimated firstly. The oblate spheroidal shape of an undistorted Jupiter resulting from its fast solid body rotation is fully taken into account, which marks the most significant improvement from previous approximation based Jovian wind theories. High viscosity flows, for example Stokes flows, occur in a lot of processes involving low-speed motions in fluids. Microorganism swimming is such a typical case. A fully three dimensional analytic solution of incompressible Stokes equation is derived in the exterior domain of an arbitrarily translating and rotating prolate spheroid, which models a large family of microorganisms such as cocci bacteria. The solution is then applied to the magnetotactic bacteria swimming problem, and good consistency has been found between theoretical predictions and laboratory observations of the moving patterns of such bacteria under magnetic fields. In the analysis of dynamics of planetary
Numerical Study of Pyrolysis of Biomass in Fluidized Beds
NASA Technical Reports Server (NTRS)
Bellan, Josette; Lathouwers, Danny
2003-01-01
A report presents a numerical-simulation study of pyrolysis of biomass in fluidized-bed reactors, performed by use of the mathematical model described in Model of Fluidized Bed Containing Reacting Solids and Gases (NPO-30163), which appears elsewhere in this issue of NASA Tech Briefs. The purpose of the study was to investigate the effect of various operating conditions on the efficiency of production of condensable tar from biomass. The numerical results indicate that for a fixed particle size, the fluidizing-gas temperature is the foremost parameter that affects the tar yield. For the range of fluidizing-gas temperatures investigated, and under the assumption that the pyrolysis rate exceeds the feed rate, the optimum steady-state tar collection was found to occur at 750 K. In cases in which the assumption was not valid, the optimum temperature for tar collection was found to be only slightly higher. Scaling up of the reactor was found to exert a small negative effect on tar collection at the optimal operating temperature. It is also found that slightly better scaling is obtained by use of shallower fluidized beds with greater fluidization velocities.
Mechanical stability of propped hydraulic fractures: A numerical study
Asgian, M.I.; Cundall, P.A.; Brady, B.H.
1995-03-01
Proppant is sometimes produced along with hydrocarbons in hydraulically fractured petroleum wells. Sometimes 10% to 20% of the proppant is backproduced, which can lead to damaged equipment and downtime. Furthermore, proppant flowback can lead to a substantial loss of fracture conductivity. A numerical study was conducted to help understand what conditions are likely to lead to proppant flowback. In the simulations, the mechanical interaction of a larger number (several thousand) individual proppant grains was modeled with a distinct-element-type code. The numerical simulations show that hydraulic fractures propped with cohesionless, unbonded proppant fail under closure stress at a critical ratio of mean grain diameter to fracture width. This is consistent with published laboratory studies. The simulations identify the mechanism (arch failure) that triggers the mechanical instability and also show that the primary way that drawdowns (less than {approx} 75 psi/ft) affect proppant flowback is to transport loose proppant grains in front of the stable arch to the wellbore. Drawdowns > 75 psi/ft are sufficient to destabilize the arch and to cause progressive failure of the propped fractures.
Numerical Study of Rotating Turbulence with External Forcing
NASA Technical Reports Server (NTRS)
Yeung, P. K.; Zhou, Ye
1998-01-01
Direct numerical simulation at 256(exp 3) resolution have been carried out to study the response of isotropic turbulence to the concurrent effects of solid-body rotation and numerical forcing at the large scales. Because energy transfer to the smaller scales is weakened by rotation, energy input from forcing gradually builds up at the large scales, causing the overall kinetic energy to increase. At intermediate wavenumbers the energy spectrum undergoes a transition from a limited k(exp -5/3) inertial range to k(exp -2) scaling recently predicted in the literature. Although the Reynolds stress tensor remains approximately isotropic and three-components, evidence for anisotropy and quasi- two-dimensionality in length scales and spectra in different velocity components and directions is strong. The small scales are found to deviate from local isotropy, primarily as a result of anisotropic transfer to the high wavenumbers. To understand the spectral dynamics of this flow we study the detailed behavior of nonlinear triadic interactions in wavenumber space. Spectral transfer in the velocity component parallel to the axis of rotation is qualitatively similar to that in non-rotating turbulence; however the perpendicular component is characterized by a greatly suppressed energy cascade at high wavenumber and a local reverse transfer at the largest scales. The broader implications of this work are briefly addressed.
Experimental and numerical study of open-air active cooling
NASA Astrophysics Data System (ADS)
Al-Fifi, Salman Amsari
The topic of my thesis is Experimental and Numerical Study of Open Air Active Cooling. The present research is intended to investigate experimentally and Numerically the effectiveness of cooling large open areas like stadiums, shopping malls, national gardens, amusement parks, zoos, transportation facilities and government facilities or even in buildings outdoor gardens and patios. Our cooling systems are simple cooling fans with different diameters and a mist system. This type of cooling systems has been chosen among the others to guarantee less energy consumption, which will make it the most favorable and applicable for cooling such places mentioned above. In the experiments, the main focus is to study the temperature domain as a function of different fan diameters aerodynamically similar in different heights till we come up with an empirical relationship that can determine the temperature domain for different fan diameters and for different heights of these fans. The experimental part has two stages. The first stage is devoted to investigate the maximum range of airspeed and profile for three different fan diameters and for different heights without mist, while the second stage is devoted to investigate the maximum range of temperature and profile for the three different diameter fans and for different heights with mist. The computational study is devoted to built an experimentally verified mathematical model to be used in the design and optimization of water mist cooling systems, and to compare the mathematical results to the experimental results and to get an insight of how to apply such evaporative mist cooling for different places for different conditions. In this study, numerical solution is presented based on experimental conditions, such dry bulb temperature, wet bulb temperature, relative humidity, operating pressure and fan airspeed. In the computational study, all experimental conditions are kept the same for the three fans except the fan airspeed
Experimental Study of Additives on Viscosity biodiesel at Low Temperature
NASA Astrophysics Data System (ADS)
Fajar, Berkah; Sukarno
2015-09-01
An experimental investigation was performed to find out the viscosity of additive and biodiesel fuel mixture in the temperature range from 283 K to 318 K. Solutions to reduce the viscosity of biodiesel is to add the biodiesel with some additive. The viscosity was measured using a Brookfield Rheometer DV-II. The additives were the generic additive (Diethyl Ether/DDE) and the commercial additive Viscoplex 10-330 CFI. Each biodiesel blends had a concentration of the mixture: 0.0; 0.25; 0.5; 0.75; 1.0; and 1.25% vol. Temperature of biodiesel was controlled from 40°C to 0°C. The viscosity of biodiesel and additive mixture at a constant temperature can be approximated by a polynomial equation and at a constant concentration by exponential equation. The optimum mixture is at 0.75% for diethyl ether and 0.5% for viscoplex.
Numerical Study of EUV Wave Phenomenon on 2009 February 13
NASA Astrophysics Data System (ADS)
Zhang, Lei; Zheng, Hui-Nan; Liao, Chi-Jian
2014-01-01
Combining the observations of STEREO satellites with the method of three-dimensional magnetohydrodynamic (MHD) numerical simulation, adopt- ing the magnetic field data of the Wilcox Solar Observatory (WSO) and the model of potential field source surface to build up the initial magnetic field in solar corona, and adding a time-varying disturbance of pressure to the active re- gion on the solar surface, the study on the event of coronal mass ejection (CME) and extreme-ultraviolet (EUV) wave happened at 05:35 UT of 2009 February 13 has been performed. It is judged from the images of COR1/STEREO-A that the front speed of this CME is about 350 km·s-1, and the angular width is about 60∘. By analyzing the running difference images of EUVI/STEREO-B at 195 ˚A, it is found that the bright toroidal wavefront is spreading toward all directions around the active region, and behind the bright toroidal wavefront is a coronal dimming area. The positions of the wavefront in four directions are taken to perform linear fittings, it is known that the EUV wave speed is 247 km·s-1, and the EUV wave speed obtained from the numerical simulation is 245 km·s-1. After the IDL visualization program has been carried out for the calculated result, the structures of the bright loop and dimming area can be seen clearly. The numerical simulation is consistent with the satellite observation, which shows that the observed EUV wave may belong to the fast magnetosonic wave.
A numerical study of fundamental shock noise mechanisms
NASA Astrophysics Data System (ADS)
Meadows, Kristine R.
1995-05-01
The results of this thesis demonstrate that direct numerical simulation can predict sound generation in unsteady aerodynamic flows containing shock waves. Shock waves can be significant sources of sound in high speed jet flows, on helicopter blades, and in supersonic combustion inlets. Direct computation of sound permits the prediction of noise levels in the preliminary design stage and can be used as a tool to focus experimental studies, thereby reducing cost and increasing the probability of a successfully quiet product in less time. This thesis reveals and investigates two mechanisms fundamental to sound generation by shocked flows: shock motion and shock deformation. Shock motion is modeled by the interaction of a sound wave with a shock. During the interaction, the shock wave begins to move and the sound pressure is amplified as the wave passes through the shock. The numerical approach presented in this thesis is validated by the comparison of results obtained in a quasi-one dimensional simulation with linear theory. Analysis of the perturbation energy demonstrated for the first time that acoustic energy is generated by the interaction. Shock deformation is investigated by the numerical simulation of a ring vortex interacting with a shock. This interaction models the passage of turbulent structures through the shock wave. The simulation demonstrates that both acoustic waves and contact surfaces are generated downstream during the interaction. Analysis demonstrates that the acoustic wave spreads cylindrically, that the sound intensity is highly directional, and that the sound pressure level increases significantly with increasing shock strength. The effect of shock strength on sound pressure level is consistent with experimental observations of shock noise, indicating that the interaction of a ring vortex with a shock wave correctly models a dominant mechanism of shock noise generation.
NASA Technical Reports Server (NTRS)
Hsieh, Kwang-Chung
1992-01-01
The steady three-dimensional thermocapillary motion with a deformable free surface is studied numerically in both normal and zero gravity environments. Flow configurations consist of a square cavity heated from the side. In the analysis, the free surface is allowed to deform and the grid distribution is adapted to the surface deformation. The divergence-free condition is satisfied by using a dual time-stepping approach in the numerical scheme. Convective flux derivatives are evaluated using a third-order accurate upwind-biased flux-split differencing technique. The numerical solutions at the midplane of the square cavity are compared with the results from two-dimensional calculations. In addition, numerial results for cases under zero and normal gravity conditions are compared. Significantly different flow structures and surface deformation have been observed. The comparison of calculated results will be compared with experimental data in the updated version of this paper.
Numerical aerodynamic simulation facility feasibility study, executive summary
NASA Technical Reports Server (NTRS)
1979-01-01
There were three major issues examined in the feasibility study. First, the ability of the proposed system architecture to support the anticipated workload was evaluated. Second, the throughput of the computational engine (the flow model processor) was studied using real application programs. Third, the availability, reliability, and maintainability of the system were modeled. The evaluations were based on the baseline systems. The results show that the implementation of the Numerical Aerodynamic Simulation Facility, in the form considered, would indeed be a feasible project with an acceptable level of risk. The technology required (both hardware and software) either already exists or, in the case of a few parts, is expected to be announced this year.
Numerical study of rowing hydrofoil performance at low Reynolds numbers
NASA Astrophysics Data System (ADS)
Chung, M.-H.
2008-04-01
In this paper, the hydrodynamic performance of a 2-D flat-plate hydrofoil in rowing motion is numerically studied by a Cartesian grid method with the cut-cell approach. Adaptive mesh refinement is used to save on the number of mesh cells without harming spatial resolution in critical regions. The rowing kinematics of the hydrofoil is the same for all simulations in this work. The design parameters studied are the reduced frequency of the rowing motion, the heave amplitude, and the time lags of the feathered-to-broadside rotation and the broadside-to-feathered rotation. Results show that larger thrust and efficiency can be attained if the feathered-to-broadside rotation is started right after the beginning of the power stroke and the broadside-to-feathered rotation is finished right before the end of the power stroke. Finally, both the thrust and the efficiency increase with Reynolds number.
Impacts on foam stabilised composite structures: Experimental and numerical study
NASA Astrophysics Data System (ADS)
Rivallant, S.; Ferrero, J. F.; Barrau, J. J.
2003-09-01
A dropweight tester is used to make low velocity tests on specific sandwich type structures. Sandwich are made of glass-epoxy skin and polyurethane foam core. The skins can be straight or little curved, and impact direction is the global skin direction. The aim of these tests is to study the initiation of rupture in such structures: local buckling of skin and foam core rupture. Experimental results are given. They show the evolution of buckling critical stress in the skin when impact velocity increases. The rupture mode in curved skin specimen is also studied: rupture is no more provoked by buckling. A numerical analysis is proposed to model the behaviour of the structure and the rupture initiation. Finally, a method is developed, in order to predict the propagation of skin debonding during impact: an element layer under the skin is damaged with a specific law to simulate debonding.
Additive Manufacturing in Production: A Study Case Applying Technical Requirements
NASA Astrophysics Data System (ADS)
Ituarte, Iñigo Flores; Coatanea, Eric; Salmi, Mika; Tuomi, Jukka; Partanen, Jouni
Additive manufacturing (AM) is expanding the manufacturing capabilities. However, quality of AM produced parts is dependent on a number of machine, geometry and process parameters. The variability of these parameters affects the manufacturing drastically and therefore standardized processes and harmonized methodologies need to be developed to characterize the technology for end use applications and enable the technology for manufacturing. This research proposes a composite methodology integrating Taguchi Design of Experiments, multi-objective optimization and statistical process control, to optimize the manufacturing process and fulfil multiple requirements imposed to an arbitrary geometry. The proposed methodology aims to characterize AM technology depending upon manufacturing process variables as well as to perform a comparative assessment of three AM technologies (Selective Laser Sintering, Laser Stereolithography and Polyjet). Results indicate that only one machine, laser-based Stereolithography, was feasible to fulfil simultaneously macro and micro level geometrical requirements but mechanical properties were not at required level. Future research will study a single AM system at the time to characterize AM machine technical capabilities and stimulate pre-normative initiatives of the technology for end use applications.
Numerical study of a high-speed miniature centrifugal compressor
NASA Astrophysics Data System (ADS)
Li, Xiaoyi
A miniature centrifugal compressor is a key component of reverse Brayton cycle cryogenic cooling system. The system is commonly used to generate a low cryogenic temperature environment for electronics to increase their efficiency, or generate, store and transport cryogenic liquids, such as liquid hydrogen and oxygen, where space limit is also an issue. Because of space limitation, the compressor is composed of a radial IGV, a radial impeller and an axial-direction diffuser (which reduces the radial size because of smaller diameter). As a result of reduction in size, rotating speed of the impeller is as high as 313,000 rpm, and Helium is used as the working fluid, in order to obtain the required static pressure ratio/rise. Two main characteristics of the compressor---miniature and high-speed, make it distinct from conventional compressors. Higher compressor efficiency is required to obtain a higher COP (coefficient of performance) system. Even though miniature centrifugal compressors start to draw researchers' attention in recent years, understanding of the performance and loss mechanism is still lacking. Since current experimental techniques are not advanced enough to capture details of flow at miniature scale, numerical methods dominate miniature turbomachinery study. This work numerically studied a high speed miniature centrifugal compressor with commercial CFD code. The overall performance of the compressor was predicted with consideration of interaction between blade rows by using sliding mesh model. The law of similarity of turbomachinery was validated for small scale machines. It was found that the specific ratio effect needs to be considered when similarity law is applied. But Reynolds number effect can be neglected. The loss mechanism of each component was analyzed. Loss due to turning bend was significant in each component. Tip leakage loss of small scale turbomachines has more impact on the impeller performance than that of large scale ones. Because the
Numerical study of delta wing leading edge blowing
NASA Technical Reports Server (NTRS)
Yeh, David; Tavella, Domingo; Roberts, Leonard
1988-01-01
Spanwise and tangential leading edge blowing as a means of controlling the position and strength of the leading edge vortices are studied by numerical solution of the three-dimensional Navier-Stokes equations. The leading edge jet is simulated by defining a permeable boundary, corresponding to the jet slot, where suitable boundary conditions are implemented. Numerical results are shown to compare favorably with experimental measurements. It is found that the use of spanwise leading edge blowing at moderate angle of attack magnifies the size and strength of the leading edge vortices, and moves the vortex cores outboard and upward. The increase in lift primarily comes from the greater nonlinear vortex lift. However, spanwise blowing causes earlier vortex breakdown, thus decreasing the stall angle. The effects of tangential blowing at low to moderate angles of attack tend to reduce the pressure peaks associated with leading edge vortices and to increase the suction peak around the leading edge, so that the integrated value of the surface pressure remains about the same. Tangential leading edge blowing in post-stall conditions is shown to re-establish vortical flow and delay vortex bursting, thus increasing C sub L sub max and stall angle.
Numerical Study of Unsteady Flow in Centrifugal Cold Compressor
NASA Astrophysics Data System (ADS)
Zhang, Ning; Zhang, Peng; Wu, Jihao; Li, Qing
In helium refrigeration system, high-speed centrifugal cold compressor is utilized to pumped gaseous helium from saturated liquid helium tank at low temperature and low pressure for producing superfluid helium or sub-cooled helium. Stall and surge are common unsteady flow phenomena in centrifugal cold compressors which severely limit operation range and impact efficiency reliability. In order to obtain the installed range of cold compressor, unsteady flow in the case of low mass flow or high pressure ratio is investigated by the CFD. From the results of the numerical analysis, it can be deduced that the pressure ratio increases with the decrease in reduced mass flow. With the decrease of the reduced mass flow, backflow and vortex are intensified near the shroud of impeller. The unsteady flow will not only increase the flow loss, but also damage the compressor. It provided a numerical foundation of analyzing the effect of unsteady flow field and reducing the flow loss, and it is helpful for the further study and able to instruct the designing.
Numerical Study on Mixed-mode Fracture in Reinforced Concrete
NASA Astrophysics Data System (ADS)
Yu, Rena C.; Saucedo, Luis; Ruiz, Gonzalo
2010-05-01
The object of this work is to model the propagation of fracture in mixed-mode in lightly reinforced concrete beams. When a notched beam does not have enough shear reinforcement, fracture can initiate and propagate unstably and lead to failure through diagonal tension. In order to study this phenomenon numerically, a model capable of dealing with both static and dynamic crack propagation as well as the natural transition of those two regimes is necessary. We adopt a cohesive model for concrete fracture and an interface model for the deterioration between concrete and steel re-bar, both combined with an insertion algorithm. The static process is solved by dynamic relaxation (DR) method together with a modified technique [1] to enhance convergence rate. The same DR method is used to detect a dynamic process and switch to a dynamic calculation. The numerically obtained load-displacement curves, load-CMOD curves and crack patterns fit reasonably well with their experimental counterparts, having in mind that we fed the calculations only with parameters measured experimentally.
Numerical study of Taylor bubbles with adaptive unstructured meshes
NASA Astrophysics Data System (ADS)
Xie, Zhihua; Pavlidis, Dimitrios; Percival, James; Pain, Chris; Matar, Omar; Hasan, Abbas; Azzopardi, Barry
2014-11-01
The Taylor bubble is a single long bubble which nearly fills the entire cross section of a liquid-filled circular tube. This type of bubble flow regime often occurs in gas-liquid slug flows in many industrial applications, including oil-and-gas production, chemical and nuclear reactors, and heat exchangers. The objective of this study is to investigate the fluid dynamics of Taylor bubbles rising in a vertical pipe filled with oils of extremely high viscosity (mimicking the ``heavy oils'' found in the oil-and-gas industry). A modelling and simulation framework is presented here which can modify and adapt anisotropic unstructured meshes to better represent the underlying physics of bubble rise and reduce the computational effort without sacrificing accuracy. The numerical framework consists of a mixed control-volume and finite-element formulation, a ``volume of fluid''-type method for the interface capturing based on a compressive control volume advection method, and a force-balanced algorithm for the surface tension implementation. Numerical examples of some benchmark tests and the dynamics of Taylor bubbles are presented to show the capability of this method. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Experimental and numerical FSI study of compliant hydrofoils
NASA Astrophysics Data System (ADS)
Augier, B.; Yan, J.; Korobenko, A.; Czarnowski, J.; Ketterman, G.; Bazilevs, Y.
2015-06-01
A propulsion system based on tandem hydrofoils is studied experimentally and numerically. An experimental measurement system is developed to extract hydrodynamic loads on the foils and capture their twisting deformation during operation. The measured data allowed us to assess the efficiency of the propulsion system as a function of travel speed and stroke frequency. The numerical simulation of the propulsion system is also presented and involves 3D, full-scale fluid-structure interaction (FSI) computation of a single (forward) foil. The foil is modeled as a combination of the isogeometric rotation-free Kirchhoff-Love shell and bending-stabilized cable, while the hydrodynamics makes use of the finite-element-based arbitrary Lagrangian-Eulerian variational multiscale formulation. The large added mass is handled through a quasi-direct FSI coupling technique. The measurement data collected is used in the validation of the FSI simulation, and excellent agreement is achieved between the predicted and measured hydrodynamic loads and foil twisting motion.
Numerical Study of a Four-Roll Coating System
NASA Astrophysics Data System (ADS)
Tsuda, Takeaki
The characteristics of a four-roll coating system were numerically investigated and compared with experimental data to validate the theoretical models used in this study. In the theoretical models, a film splitting model using a power-law-type equation, a roll-gap model based on elastohydrodynamics, and a flow model from a rotating-cylinder system were applied. The parametric computations for each operational condition revealed the steady and dynamic behaviors of a coating film and liquid films on the coating rolls. The results of the frequency response to the speed disturbances of the coating rolls indicated that the sensitivity of the lowest coating roll to the disturbance was half that of the others; this implies that the requirement for the accuracy of a driving system of the coating roll is not as severe as compared with others. The experimental data and the numerical results at steady state agreed well. Therefore, the theoretical models used in this research were found to be appropriate.
Numerical study of sink-flow boundary layers
NASA Technical Reports Server (NTRS)
Spalart, Philippe R.
1986-01-01
Direct numerical simulations of sink-flow boundary layers, with acceleration parameters K between 1.5 x 10 to the -6th and 3.0 x 10 to the -6th, are presented. The three-dimensional, time-dependent Navier-Stokes equations are solved numerically, using a spectral method, with about one million degrees of freedom. The flow is assumed to be statistically steady, and self-similar. A multiple-scale approximation and periodic conditions are applied to the fluctuations. The turbulence is studied using instantaneous and statistical results. Good agreement with the experiments of Jones and Launder (1972) is observed. The two effects of the favorable pressure gradient are to extend the logarithmic layer, and to alter the energy balance of the turbulence near the edge of the boundary layer. At low Reynolds number the logarithmic layer is shortened and slightly displaced, but wall-layer streaks are present even at the lowest values of R(theta) for which turbulence can be sustained. Large quiescent patches appear in the flow. Relaminarization occurs at K = 3.0 x 10 to the -6th, corresponding to a Reynolds number R(theta) of about 330.
MAGNETIZATION DEGREE OF GAMMA-RAY BURST FIREBALLS: NUMERICAL STUDY
Harrison, Richard; Kobayashi, Shiho
2013-08-01
The relative strength between forward and reverse shock emission in early gamma-ray burst (GRB) afterglow reflects that of magnetic energy densities in the two shock regions. We numerically show that with the current standard treatment, the fireball magnetization is underestimated by up to two orders of magnitude. This discrepancy is especially large in the sub-relativistic reverse shock regime (i.e., the thin shell and intermediate regime), where most optical flashes were detected. We provide new analytic estimates of the reverse shock emission based on a better shock approximation, which well describe numerical results in the intermediate regime. We show that the reverse shock temperature at the onset of afterglow is constant, ( {Gamma}-bar{sub d}-1){approx}8 Multiplication-Sign 10{sup -2}, when the dimensionless parameter {xi}{sub 0} is more than several. Our approach is applied to case studies of GRB 990123 and 090102, and we find that magnetic fields in the fireballs are even stronger than previously believed. However, these events are still likely to be due to a baryonic jet with {sigma} {approx} 10{sup -3} for GRB 990123 and {approx}3 Multiplication-Sign 10{sup -4} to 3 for GRB 090102.
Experimental and numerical study of tornado-like vortex formation
NASA Astrophysics Data System (ADS)
Kotelnikova, M. S.; Verbitskaya, Z. V.; Nikulin, V. V.
2012-04-01
Swirling flows of fluids in vortex chambers have been extensively studied because they are widely used in various technical devices [A. K. Gupta, D. G. Lilley, and N. Syred, Swirl Flows (Abacus Press, 1984)]. However, most of these investigations have been devoted to the swirling flows in steady-state regimes, while basic questions concerning the formation of tornado-like vortices remain unanswered. The determination of the laws of vortex formation is also of considerable practical significance, since swirling flows can be used, for example, for the rapid removal of atmospheric contaminations. The laws of tornado-like vortex formation in a closed chamber have been experimentally and numerically studied as dependent on the air volume flow rate and swirl intensity. A physical interpretation of the obtained empirical relationships is proposed. It is established that a flow regime can exist in which the impurity mass transfer along the vortex core is accompanied by mass exchange between the core and surrounding atmosphere. This exchange has the form of spiral formations ejected regularly out of the vortex core. This process takes place under stationary conditions at the chamber input and output, which implies an autooscillatory character of the flow in the system studied. Also it is shown that the time of tornado-like vortex formation weakly depends on the airflow swirl parameter and approximately inversely proportional to the airflow rate. In the case when the vertical and horizontal chamber dimensions are close, this time is approximately equal to the characteristic time of air renewal in the chamber. The established laws and numerical models can be used for evaluating the time of formation of the vortex flows of this type and for the development of theoretical models of the formation of tornado-like vortices.
Numerical Study of Stratified Charge Combustion in Wave Rotors
NASA Technical Reports Server (NTRS)
Nalim, M. Razi
1997-01-01
A wave rotor may be used as a pressure-gain combustor effecting non-steady flow, and intermittent, confined combustion to enhance gas turbine engine performance. It will be more compact and probably lighter than an equivalent pressure-exchange wave rotor, yet will have similar thermodynamic and mechanical characteristics. Because the allowable turbine blade temperature limits overall fuel/air ratio to sub-flammable values, premixed stratification techniques are necessary to burn hydrocarbon fuels in small engines with compressor discharge temperature well below autoignition conditions. One-dimensional, unsteady numerical simulations of stratified-charge combustion are performed using an eddy-diffusivity turbulence model and a simple reaction model incorporating a flammability limit temperature. For good combustion efficiency, a stratification strategy is developed which concentrates fuel at the leading and trailing edges of the inlet port. Rotor and exhaust temperature profiles and performance predictions are presented at three representative operating conditions of the engine: full design load, 40% load, and idle. The results indicate that peak local gas temperatures will result in excessive temperatures within the rotor housing unless additional cooling methods are used. The rotor itself will have acceptable temperatures, but the pattern factor presented to the turbine may be of concern, depending on exhaust duct design and duct-rotor interaction.
Oki, Delwyn S.
1998-01-01
-calculated freshwater-saltwater interface location for the future recharge and pumping conditions. Model results indicate that an additional 10 million gallons per day (beyond the 1995-allocated rates) of freshwater can potentially be developed from northern Oahu. Various distributions of pumping can be used to obtain the additional 10 million gallons per day of water. The quality of the water pumped will be dependent on site-specific factors and cannot be predicted on the basis of model results. If the additional 10 million gallons per day pumpage is restricted to the Kawailoa and Waialua areas, model results indicate that a regional drawdown (relative to the water-level distribution associated with the 1995-allocated pumping rates) of less than 0.6 foot can be maintained in these two areas. The additional pumping, however, would cause salinity increases in water pumped by existing deep wells. In addition, increases in salinity may occur at other wells in areas where the model indicates no significant problem with upconing.
Numerical Study of Classical Spins on Soccer Ball Lattice
NASA Astrophysics Data System (ADS)
Nakamura, Yasunobu
2008-07-01
We study a classical Ising spin system on a soccer ball lattice. The magnetic easy axis of the system is adopted parallel to the radial direction. We apply a magnetic field to this system in several directions. Ferromagnetic and antiferromagnetic nearest-neighbor interaction cases are considered. In the case of the antiferromagnetic interaction, a frustration effect is observed because of a pentagonal interaction loop. We carry out a numerical calculation for the system to obtain the ground states for various magnetic fields. A Monte Carlo simulation is also performed to compute thermodynamic quantities at finite temperatures. The obtained magnetization process has many magnetic phases reflecting the frustration effect. The thermodynamic quantities are characteristic because the Zeeman energy for each spin is different due to the geometrical property of the soccer ball.
Study cosmic ray modulation near the heliopause: A numerical approach
NASA Astrophysics Data System (ADS)
Luo, X.; Zhang, M.; Potgieter, M. S.; Feng, X.; Pogorelov, N. V.
2016-03-01
By incorporating the MagnetoHydroDynamic (MHD) global heliospheric data into the Parker's cosmic-rays (CRs) transport equation, we constructed a hybrid galactic cosmic ray transport model to study the galactic cosmic-rays (GCR) behaviour near the heliopause(HP). Based on this hybrid model, we found that: (1)By increasing the ratio of the parallel diffusion coefficient to the perpendicular diffusion coefficient in the outer heliosheath (the region near HP and beyond), the simulated radial flux gradient near the HP increases as well. As this ratio multiplying factor reaches 1010, the flux experiences a sudden jump near the HP, similar to what Voyager 1 had observed in 2012. (2)After increasing the ratio of the diffusion coefficients beyond the HP, more pseudo- particles in our numerical approach which have been traced from the upwind nose region exit in the downwind tail region. It is thus possible that they diffuse more directly from the tail region to the nose region.
Theoretical and numerical studies of nonlinear shell equations
NASA Astrophysics Data System (ADS)
Hermann, M.; Kaiser, D.; Schröder, M.
1999-07-01
We study the solution field M of a parameter dependent nonlinear two-point boundary value problem presented by Troger and Steindl [H. Troger, A. Steindl, Nonlinear Stability and Bifurcation Theory, Springer, Wien, New York, 1991]. This problem models the buckling of a thin-walled spherical shell under a uniform external static pressure. The boundary value problem is formulated as an abstract operator equation T( x, λ)=0 in appropriate Banach spaces. By exploiting the equivariance of T, we obtain detailed informations about the structure of M. These theoretical results are used to compute efficiently interesting parts of M with numerical standard techniques. Bifurcation diagrams, a stability diagram and pictures of deformed shells are presented.
Numerical study of metal oxide heterojunction solar cells
NASA Astrophysics Data System (ADS)
Zhu, L.; Shao, G.; Luo, J. K.
2011-08-01
Metal oxide (MO) semiconductors have great potential for photovoltaic (PV) application owing to some optimal bandgaps and a variety of possible combinations of the materials. The progress is limited due to lack of high-quality materials, reliable process and theoretical study and models which can guide the development. This paper reports on the numerical modelling of MO semiconductor PV cells. The effects of the bandgap structure, material, doping concentration and layer thickness on the proposed oxide solar cells have been investigated. It was found that, in an ideal case of no defects and no interface states, wide-gap MO, CuO and Cu2O can form a heterostructure n+/p/p+ cell with efficiency up to 28.6%, demonstrating great potential for development.
Infrared spectroscopy of molecules with nanorod arrays: a numerical study.
Tardieu, Clément; Vincent, Grégory; Haïdar, Riad; Collin, Stéphane
2016-04-15
Nanorod arrays with diameters much smaller than the wavelength exhibit sharp resonances with strong electric-field enhancement and angular dependence. They are investigated for enhanced infrared spectroscopy of molecular bonds. The molecule 3-cyanopropyldimethylchlorosilane (CS) is taken as a reference, and its complex permittivity is determined experimentally in the 3-5 μm wavelength range. When grafted on silicon nitride nanorods, we show numerically that its weak absorption bands due to chemical bond vibrations can be enhanced by several orders of magnitude compared with unstructured thin film. We propose a figure of merit (FoM) to assess the performance of this spectroscopic scheme, and we study the impact of the nanorod cross section on the FoM. PMID:27082334
Numerical study of metal oxide Schottky type solar cells
NASA Astrophysics Data System (ADS)
Zhu, L.; Shao, G.; Luo, J. K.
2012-07-01
Metal oxide (MO) semiconductors hold the promise for the development of high efficiency solar cells with low cost. Currently heterostructure type MO solar cells have been theoretically and experimentally studied, demonstrated their potential for applications. This paper highlights a numerical investigation on Schottky type MO solar cells using CuO as the absorption layer. It is shown that the doping concentration, absorption layer thickness, barrier height and back surface field have significant effects on the performance of the devices. Under the optimal structure and doping, the Schottky barrier solar cells, if can be fabricated with suitable techniques, can have a conversion efficiency up to 18.5%, comparable to MO heterojunction solar cells, but at a much simpler structure and lower cost. Some guidelines about the materials selection and structure design for MO Schottky barrier solar cells are summarized.
Numerical study of carbon nanotubes under circularly polarized irradiation
NASA Astrophysics Data System (ADS)
Liu, Feng; Nakajima, Yudai; Wakabayashi, Katsunori
2016-08-01
We numerically study the energy band structures and the corresponding wavefunctions of carbon nanotubes under circularly polarized irradiation perpendicular to the tube axis on the basis of the Floquet–Bloch theory. We focus on two typical irradiation frequencies, ħΩ ≪ γ and ħΩ ∼ γ, where γ ≈ 3 eV is the hopping energy of graphene. Circularly polarized irradiation is found to open gaps for metallic zigzag nanotubes near the Fermi energy and shift the degenerate points of armchair nanotubes in the energy spectra away from the K and K‧ points. Furthermore, high-frequency irradiation localizes the wavefunctions on either side of the nanotubes; in particular, the localized wavefunctions have different valley indices on each side of the nanotubes.
Dynamics of a cylinder plunging into liquid: a numerical study
NASA Astrophysics Data System (ADS)
Ding, Hang
2012-11-01
The impact of a cylinder on a liquid surface and subsequent events are investigated numerically. The flows are resolved by solving the Navier-Stokes equations and the Cahn-Hilliard equation. Moving contact lines are modeled by a diffuse interface model (Seppecher 1996; Jaqcmin 2000), and contact-angle hysteresis is included (Ding&Spelt 2008). The method is validated by comparison to the experiments by Aristoff and Bush (2009). Our studies focus on the dynamics of the waves induced by the impact and the cavity collapse behind the cylinder. A variety of parameters affect the flow behaviors such as wettability, impact speed, viscosity etc. Their effects on the transition of the flow phenomena are investigated through parametric simulations over relevant ranges of Weber and Reynolds numbers and contact angles. This work is supposed by the 100 Talents Program of the Chinese Academy of Sciences and the National Natural Science Foundation of China (Grant No. 11172294).
Numerical study of a disordered model for DNA denaturation transition.
Coluzzi, Barbara
2006-01-01
We numerically study a disordered version of the model for DNA denaturation transition consisting of two interacting self-avoiding walks in three dimensions, which undergoes a first order transition in the homogeneous case. The two possible values epsilonAT and epsilonGC of the interactions between base pairs are taken as quenched random variables distributed with equal probability along the chain. We measure quantities averaged over disorder such as the energy density, the specific heat, and the probability distribution of the loop lengths. When applying the scaling laws used in the homogeneous case we find that the transition seems to be smoother in the presence of disorder, in agreement with general theoretical arguments, although we cannot rule out the possibility of a first order transition. PMID:16486189
Numerical Study on Microwave Scattering by Various Plasma Objects
NASA Astrophysics Data System (ADS)
Wang, Guibin; Zhang, Lin; He, Feng; Ouyang, Jiting
2016-08-01
The scattering features of microwave (MW) by planar plasma layer, plasma column and plasma-column array under different parameters have been numerically studied by the finite-difference time-domain (FDTD) method. The effects of the plasma frequency and electron collision rate on MW's reflectance, transmittance and absorptance are examined. The results show that for the planar plasma layer, the electron collision plays an important role in MW absorption and the reduction of wave reflection. In the plasma column condition, strong scattering occurs in certain directions. The scattering pattern depends on the plasma frequency, electron collision rate and column radius. A collisional, non-planar shaped plasma object like the plasma-column array can reduce significantly the wave reflection comparing with the planar plasma layer.
Infrasonic interferometry of stratospherically refracted microbaroms--a numerical study.
Fricke, Julius T; El Allouche, Nihed; Simons, Dick G; Ruigrok, Elmer N; Wapenaar, Kees; Evers, Läslo G
2013-10-01
The atmospheric wind and temperature can be estimated through the traveltimes of infrasound between pairs of receivers. The traveltimes can be obtained by infrasonic interferometry. In this study, the theory of infrasonic interferometry is verified and applied to modeled stratospherically refracted waves. Synthetic barograms are generated using a raytracing model and taking into account atmospheric attenuation, geometrical spreading, and phase shifts due to caustics. Two types of source wavelets are implemented for the experiments: blast waves and microbaroms. In both numerical experiments, the traveltimes between the receivers are accurately retrieved by applying interferometry to the synthetic barograms. It is shown that microbaroms can be used in practice to obtain the traveltimes of infrasound through the stratosphere, which forms the basis for retrieving the wind and temperature profiles. PMID:24116404
A 3D numerical study of antimicrobial persistence in heterogeneous multi-species biofilms.
Zhao, Jia; Shen, Ya; Haapasalo, Markus; Wang, Zhejun; Wang, Qi
2016-03-01
We develop a 3D hydrodynamic model to investigate the mechanism of antimicrobial persistence in a multi-species oral biofilm and its recovery after being treated by bisbiguanide chlorhexidine gluconate (CHX). In addition to the hydrodynamic transport in the spatially heterogeneous biofilm, the model also includes mechanisms of solvent-biomass interaction, bacterial phenotype conversion, and bacteria-drug interaction. A numerical solver for the model is developed using a second order numerical scheme in 3D space and time and implemented on GPUs for high-performance computing. The model is calibrated against a set of experimental data obtained using confocal laser scan microscopy (CLSM) on multi-species oral biofilms, where a quantitative agreement is reached. Our numerical results reveal that quorum sensing molecules and growth factors in this model are instrumental in biofilm formation and recovery after the antimicrobial treatment. In particular, we show that (i) young biofilms are more susceptible to the antimicrobial treatment than the mature ones, (ii) this phenomenon is strongly correlated with volume fractions of the persister and EPS in the biofilm being treated. This suggests that antimicrobial treatment should be best administered to biofilms earlier before they mature to produce a thick protective EPS layer. In addition, the numerical study also indicates that an antimicrobial effect can be achieved should a proper mechanism be devised to minimize the conversion of susceptible bacteria to persisters during and even after the treatment. PMID:26739374
Addition of molecular methods to mutation studies with Drosophila melanogaster
Lee, W.R. )
1989-01-01
For 80 years, Drosophila melanogaster has been used as a major tool in analyzing Mendelian genetics. By using chromosome inversions that suppress crossing over, geneticists have developed a large number of stocks for mutation analysis. These stocks permit numerous tests for specific locus mutations, lethals at multiple loci on any chromosome, chromosome exchanges, insertions, and deletions. The entire genome can be manipulated for a degree of genetic control not found in other germ-line systems. Recombinant DNA techniques now permit analysis of mutations to the nucleotide level. By combining classical genetic analysis with recombinant DNA techniques, it is possible to analyze mutations that range from chromosome aberrations and multilocus deficiencies to single nucleotide transitions.
Health studies indicate MTBE is safe gasoline additive
Anderson, E.V.
1993-09-01
Implementation of the oxygenated fuels program by EPA in 39 metropolitan areas, including Fairbanks and Anchorage, Alaska, in the winter of 1992, encountered some unexpected difficulties. Complaints of headaches, dizziness, nausea, and irritated eyes started in Fairbanks, jumped to Anchorage, and popped up in various locations in the lower 48 states. The suspected culprit behind these complaints was the main additive for oxygenation of gasoline is methyl tert-butyl ether (MTBE). A test program, hastily organized in response to these complaints, has indicated that MTBE is a safe gasoline additive. However, official certification of the safety of MTBE is still awaited.
Magnetoroton modes of the ultraquantum crystal: Numerical study
NASA Astrophysics Data System (ADS)
Lederer, Pascal; Chaves, C. M.
1998-08-01
The field-induced spin-density-wave phases observed in quasi-one-dimensional conductors of the Bechgaard salts family under magnetic field exhibit both spin-density-wave order and a quantized Hall effect, which may exhibit sign reversals. The original nature of the condensed phases is evidenced by the collective mode spectrum. Besides the Goldstone modes, a quasiperiodic structure of magnetoroton modes, predicted to exist for a monotonic sequence of Hall quantum numbers, is confirmed, and a second mode is shown to exist within the single-particle gap. We present numerical estimates of the magnetoroton mode energies in a generic case of the monotonic sequence. The mass anisotropy of the collective mode is calculated. We show how differently the magnetoroton spectrum evolves with magnetic field at low and high fields. The collective mode spectrum should have specific features, in the sign-reversed ``Ribault Phase,'' as compared to modes of the majority sign phases. We investigate numerically the collective mode in the Ribault phase, and find in this latter case a previously unnoticed field-independent low-energy magnetoroton mode at an intermediate wave vector. The occurrence of the Ribault phase depends sensitively on the electron-electron interactions. A byproduct of our study deals with the metal-ultraquantum-crystal instability line: we find, in a monotonic sequence, a reentrant behavior of the metallic phase, at a given temperature, as a function of field, which has been observed experimentally. This behavior is also sensitive to the strength of electron-electron interactions.
A numerical study of droplet trapping in microfluidic devices
NASA Astrophysics Data System (ADS)
Nagel, Mathias; Brun, P.-T.; Gallaire, François
2014-03-01
Microfluidic channels are powerful means of control of minute volumes such as droplets. These droplets are usually conveyed at will in an externally imposed flow which follows the geometry of the micro-channel. It has recently been pointed out by Dangla et al. ["Trapping microfluidic drops in wells of surface energy," Phys. Rev. Lett. 107(12), 124501 (2011)] that the motion of transported droplets may also be stopped in the flow, when they are anchored to grooves which are etched in the channels top wall. This feature of the channel geometry explores a direction that is usually uniform in microfluidics. Herein, this anchoring effect exploiting the three spatial directions is studied combining a depth averaged fluid description and a geometrical model that accounts for the shape of the droplet in the anchor. First, the presented method is shown to enable the capture and release droplets in numerical simulations. Second, this tool is used in a numerical investigation of the physical mechanisms at play in the capture of the droplet: a localized reduced Laplace pressure jump is found on its interface when the droplet penetrates the groove. This modified boundary condition helps the droplet cope with the linear pressure drop in the surrounding fluid. Held on the anchor the droplet deforms and stretches in the flow. The combination of these ingredients leads to recover the scaling law for the critical capillary number at which the droplets exit the anchors C a^{star} ∝ h2/R2 where h is the channel height and R the droplet undeformed radius.
A numerical study of the upwelling circulation off Central Chile
NASA Astrophysics Data System (ADS)
Mesias, Jorge M.
The summer upwelling circulation off Central Chile between 34°--40°S is studied using the Princeton Ocean Circulation numerical model, implemented with realistic atmospheric forcings and bottom topography. The simulations are made for summers of years 1992, 1993, and 1994. Sea surface temperature (SST) from the model results and satellite sensors (derived from NASA/NOAA Pathfinder Project datasets) are compared to determine regions where the numerical simulations more realistically represent the oceanic fields. The summer local winds are predominantly equatorward and fluctuate affected by the seasonal displacement of the Subtropical Anticyclone of the Southeast Pacific. The model ocean circulation shows the presence of a surface coastal equatorward jet flowing over a poleward undercurrent that spreads over the continental shelf and slope break. These currents resemble those historically observed off Central Chile, following a classical Ekman-geostrophy dynamics. The oceanic variability is strongly related to the variability of the local wind forcing, bottom relief, and coastline geometry. Strong wind fluctuations induce the formation of cyclonic/anticyclonic mesoscale eddies, favored by the separation of the equatorward jet from the coast, downstream of a prominent mid-domain cape. The flow variability between regions depends on the spatial variability of the wind forcing. The wind relaxation is larger in the southern regions, where the upwelling tends to disappear. In the northern areas, the separation of the jet and the formation of eddies induce a strong cross-shelf transport activity. Comparisons among SST fields for all years indicate that the model and satellite fields vary in similar patterns, especially in the northern coastal areas, and suggest that oceanic fields are largely affected by changes in local winds during El Nino events. During El Nino periods, the upwelling activity weakens due to a rapid decrease of the equatorward winds, and the passage of
Observational and numerical studies of extreme frontal scale contraction
NASA Technical Reports Server (NTRS)
Koch, Steven E.
1995-01-01
The general objective of this effort is to increase understanding of how frontal scale contraction processes may create and sustain intense mesoscale precipitation along intensifying cold fronts. The five-part project (an expansion of the originally proposed two-part project) employed conventional meteorological data, special mesoscale data, remote sensing measurements, and various numerical models. First an idealized hydrostatic modeling study of the scale contraction effects of differential cloud cover on low-level frontal structure and dynamics was completed and published in a peer-reviewed journal. The second objective was to complete and publish the results from a three dimensional numerical model simulation of a cold front in which differential sensible heating related to cloud coverage patterns was apparently crucial in the formation of a severe frontal squall line. The third objective was to use a nonhydrostatic model to examine the nonlinear interactions between the transverse circulation arising from inhomogeneous cloud cover, the adiabatic frontal circulation related to semi-geostrophic forcing, and diabatic effects related to precipitation processes, in the development of a density current-like microstructure at the leading edge of cold fronts. Although the development of a frontal model that could be used to initialize such a primitive equation model was begun, we decided to focus our efforts instead on a project that could be successfully completed in this short time, due to the lack of prospects for continued NASA funding beyond this first year (our proposal was not accepted for future funding). Thus, a fourth task was added, which was to use the nonhydrostatic model to test tentative hypotheses developed from the most detailed observations ever obtained on a density current (primarily sodar and wind profiler data). These simulations were successfully completed, the findings were reported at a scientific conference, and the results have recently been
A numerical study of laminar flames propagating in stratified mixtures
NASA Astrophysics Data System (ADS)
Zhang, Jiacheng
Numerical simulations are carried out to study the structure and speed of laminar flames propagating in compositionally and thermally stratified fuel-air mixtures. The study is motivated by the need to understand the physics of flame propagation in stratified-charge engines and model it. The specific question of interest in this work is: how does the structure and speed of the flame in the stratified mixture differ from that of the flame in a corresponding homogeneous mixture at the same equivalence ratio, temperature, and pressure? The studies are carried out in hydrogen-air, methane-air, and n-heptane-air mixtures. A 30-species 184-step skeletal mechanism is employed for methane oxidation, a 9-species 21-step mechanism for hydrogen oxidation, and a 37-species 56-step skeletal mechanism for n-heptane oxidation. Flame speed and structure are compared with corresponding values for homogeneous mixtures. For compositionally stratified mixtures, as shown in prior experimental work, the numerical results suggest that when the flame propagates from a richer mixture to a leaner mixture, the flame speed is faster than the corresponding speed in the homogeneous mixture. This is caused by enhanced diffusion of heat and species from the richer mixture to the leaner mixture. In fact, the effects become more pronounced in leaner mixtures. Not surprisingly, the stratification gradient influences the results with shallower gradients showing less effect. The controlling role that diffusion plays is further assessed and confirmed by studying the effect of a unity Lewis number assumption in the hydrogen/air mixtures. Furthermore, the effect of stratification becomes less important when using methane or n-heptane as fuel. The laminar flame speed in a thermally stratified mixture is similar to the laminar flame speed in homogeneous mixture at corresponding unburned temperature. Theoretical analysis is performed and the ratio of extra thermal diffusion rate to flame heat release rate
Numerical renormalization group study of a dissipative quantum dot
NASA Astrophysics Data System (ADS)
Glossop, M. T.; Ingersent, K.
2007-03-01
We study the quantum phase transition (QPT) induced by dissipation in a quantum dot device at the degeneracy point. We employ a Bose-Fermi numerical renormalization group approach [1] to study the simplest case of a spinless resonant-level model that couples the charge density on the dot to a dissipative bosonic bath with density of states B(φ)ŝ. In anticipation of future experiments [2] and to assess further the validity of theoretical techniques in this rapidly developing area, we take the conduction-electron leads to have a pseudogap density of states: ρ(φ) |φ|^r, as considered in a very recent perturbative renormalization group study [3]. We establish the conditions on r and s such that a QPT arises with increasing dissipation strength --- from a delocalized phase, where resonant tunneling leads to large charge fluctuations on the dot, to a localized phase where such fluctuations are frozen. We present results for the single-particle spectrum and the response of the system to a local electric field, extracting critical exponents that depend in general on r and s and obey hyperscaling relations. We make full comparison with results of [3] where appropriate. Supported by NSF Grant DMR-0312939. [1] M. T. Glossop and K. Ingersent, PRL 95, 067202 (2005); PRB (2006). [2] L. G. G. V. Dias da Silva, N. P. Sandler, K. Ingersent, and S. E. Ulloa, PRL 97, 096603 (2006). [3] C.-H. Chung, M. Kir'can, L. Fritz, and M. Vojta (2006).
Experimental and numerical study of high intensity argon cluster beams
Korobeishchikov, N. G.; Kalyada, V. V.; Shmakov, A. A.; Zarvin, A. E.; Skovorodko, P. A.
2014-12-09
Experimental and numerical investigations of expansion of argon with homogeneous condensation in supersonic conical nozzle and in free jet behind it were carried out. Optimal parameters (stagnation pressure, nozzle-skimmer distance) for the formation of cluster beam with maximum intensity were determined. Two available models for nonequilibrium nucleation were tested. The numerical results are in satisfactory agreement with the measured data.
Interphase anisotropy effects on lamellar eutectics: a numerical study.
Ghosh, Supriyo; Choudhury, Abhik; Plapp, Mathis; Bottin-Rousseau, Sabine; Faivre, Gabriel; Akamatsu, Silvère
2015-02-01
In directional solidification of binary eutectics, it is often observed that two-phase lamellar growth patterns grow tilted with respect to the direction z of the imposed temperature gradient. This crystallographic effect depends on the orientation of the two crystal phases α and β with respect to z. Recently, an approximate theory was formulated that predicts the lamellar tilt angle as a function of the anisotropy of the free energy of the solid(α)-solid(β) interphase boundary. We use two different numerical methods-phase field (PF) and dynamic boundary integral (BI)-to simulate the growth of steady periodic patterns in two dimensions as a function of the angle θ(R) between z and a reference crystallographic axis for a fixed relative orientation of α and β crystals, that is, for a given anisotropy function (Wulff plot) of the interphase boundary. For Wulff plots without unstable interphase-boundary orientations, the two simulation methods are in excellent agreement with each other and confirm the general validity of the previously proposed theory. In addition, a crystallographic "locking" of the lamellae onto a facet plane is well reproduced in the simulations. When unstable orientations are present in the Wulff plot, it is expected that two distinct values of the tilt angle can appear for the same crystal orientation over a finite θ(R) range. This bistable behavior, which has been observed experimentally, is well reproduced by BI simulations but not by the PF model. Possible reasons for this discrepancy are discussed. PMID:25768518
Numerical study of surface water waves generated by mass movement
NASA Astrophysics Data System (ADS)
Ghozlani, Belgacem; Hafsia, Zouhaier; Maalel, Khlifa
2013-10-01
In this paper waves generated by two-dimensional mass movement are simulated using a numerical model based on the full hydrodynamic coupling between rigid-body motion and ambient fluid flow. This approach has the capability to represent the dynamics of the moving rigid body, which avoids the need to prescribe the body velocity based on the data measurements. This model is implemented in the CFX code and uses the Reynolds average Navier-Stokes equations solver coupled to the recently developed immersed solid technique. The latter technique allows us to follow implicitly the motion of the solid block based on the rigid body solver. The volume-of-fluid method is used to track the free surface locations. The accuracy of the present model is firstly examined against the simple physical case of a freely falling rigid body into water reproducing Scott Russell's solitary waves. More complex and realistic simulations of aerial and submarine mass-movement, simulated by a rigid wedge sliding into water along a 45° slope, are then performed. Simulated results of the aerial mass movement show the complex flow patterns in terms of the velocity fields and free surface profiles. Results are in good agreement with the available experimental data. In addition, the physical processes associated with the generation of water wave by two-dimensional submarine mass-movement are explored. The effects of the initial submergence and specific gravity on the slide mass kinematics and maximum wave amplitude are investigated. The terminal velocity and initial acceleration of the slide mass are well predicted when compared to experimental results. It is found that the initial submergence did not have a significant effect on the initial acceleration of the slide block centre of mass. However, it depends nonlinearly\\vadjust{\
Grain size assisted formation of pseudotachylites: A numerical study
NASA Astrophysics Data System (ADS)
Thielmann, Marcel; Rozel, Antoine; Kaus, Boris; Ricard, Yanick
2014-05-01
The processes resulting in the formation of lithospheric-scale shear zones are still poorly understood. Among others, shear heating and grain size reduction have been proposed to be viable weakening mechanisms to localize deformation and form lithospheric-scale shear zones. The interplay between both mechanisms is particularly interesting, as both compete for a part of the deformational work. High temperatures favor grain growth, therefore one would expect larger grain sizes in shear zones that have been formed by shear heating. However, larger temperatures increase strain rates, thus also the amount of deformational work, which in turn would favor grain size reduction. Here we investigate the interplay between both mechanisms using numerical models of a viscoelastic slab deforming in simple shear, employing a viscous rheology composed of dislocation and diffusion creep. Grain size evolution is governed by a recently developed physics-based evolution law. We develop scaling laws for the peak stress and the dominating deformation mechanisms depending on various material parameters and boundary conditions. We find that grain size reduction alone does not localize deformation in simple shear. In conjunction with shear heating however, a localized shear zone is formed due to thermal runaway. During this process, grain size is significantly reduced. Depending on grain growth parameters, a mylonitic shear zone is formed in which deformation is permanently localized and which deforms in diffusion creep. Additionally, the stress required to initiate thermal runaway is reduced compare to cases with shear heating alone, thus facilitating the formation of a narrow localized shear zone in the ductile regime. These results have several implications ranging and from simultaneous pseudotachylite and mylonite formation at depths below the seismogenic depth to subduction initiation.
Numerical Study on the 1682 Tainan Historic Tsunami Event
NASA Astrophysics Data System (ADS)
Tsai, Y.; Wu, T.; Lee, C.; KO, L.; Chuang, M.
2013-12-01
We intend to reconstruct the tsunami source of the 1682/1782 tsunami event in Tainan, Taiwan, based on the numerical method. According to Soloviev and Go (1974), a strong earthquake shook the Tainan and caused severe damage, followed by tsunami waves. Almost the whole island was flooded by tsunami for over 120 km. More than 40,000 inhabitants were killed. Forts Zealand and Pigchingi were washed away. 1682/1782 event was the highest death toll in the Pacific Ocean regarded by Bryant (2001). However, the year is ambiguous in 1682 or 1782, and death toll is doubtful. We tend to believe that this event was happened in 1682 based on the evolution of the harbor name. If the 1682 tsunami event does exist, the hazard mitigation plan has to be modified, and restoring the 1682 event becomes important. In this study, we adopted the tsunami reverse tracking method (TRTM) to examine the possible tsunami sources. A series of numerical simulations were carried out by using COMCOT (Cornell Multi-grid Coupled Tsunami model), and nested grid with 30 m resolution was applied to the study area. According to the result of TRTM, the 1682 tsunami is most likely sourcing from the north segment of Manila Trench. From scenario study, we concluded that the 1682 event was triggered by an Mw >= 8.8 earthquake in north segment of Manila Trench, and 4 m wave height was observed in Tainan and its inundation range is agreeable with historical records. If this scenario occurred again, sever damage and death toll will be seen many high population cities, such as Tainan city, Kaohsiung city and Kenting, where No. 3 nuclear power plant is located. Detailed results will be presented in the full paper. Figure 1. Map of Tsunami Reverse Tracking Method (TRTM) in Tainan. Black arrow indicates direction of possible tsunami direction. The color bar denotes the magnitude of the maximum moment flux. Figure 2. Scenario result of Mw 8.8 in northern segment of Manila Trench. (Left: Initial free surface elevation
Systematic analytical and numerical studies of highly correlated electron systems
NASA Astrophysics Data System (ADS)
Tsai, Shan-Wen
Strong electron correlations in condensed matter systems give rise to a wide range of striking physical properties, producing phenomena as varied as high temperature superconductivity, metal-insulator transitions and the integer and fractional quantum Hall effects. Quantum critical systems also exhibit strong correlations between a large number of degrees of freedom. In this thesis we study these complicated systems using a combination of analytical and numerical approaches. We perform systematic investigations, which adds to the robustness of our results. We develop a new method, based on the density-matrix renormalization-group (DMRG) algorithm combined with finite-size scaling analysis, to study critical behavior in quantum spin chains and extract critical exponents. Accurate results are obtained for spin-1/2 antiferromagnetic chains and the spin-1 chain at the critical point separating the Haldane and the dimerized phases. Disorder in a system can change its properties drastically. Plateau transitions in the integer quantum Hall effect provide the clearest example of quantum critical behavior in a disordered system. We provide analytical proof that the Chalker-Coddington model, which is used to describe the plateau transitions, is quantum critical. Starting from a field theory based on this model, equivalent to a non-Hermitian supersymmetric spin chain, we prove quantum criticality by a Lieb-Schultz-Mattis type theorem. This approach was motivated by numerical results obtained using the DMRG/finite-size scaling method. Our generalized LSM theorem also applies to the spin quantum Hall effect, which can appear in disordered d-wave superconductors with broken time-reversal symmetry. The last part of the thesis is a renormalization-group study of two dimensional interacting electron systems. We obtain results relevant to high-temperature superconductors and also to the family of kappa - (BEDT - TTF)2X organic superconductors. At half filling, the fully nested
Numerical study of error propagation in Monte Carlo depletion simulations
Wyant, T.; Petrovic, B.
2012-07-01
Improving computer technology and the desire to more accurately model the heterogeneity of the nuclear reactor environment have made the use of Monte Carlo depletion codes more attractive in recent years, and feasible (if not practical) even for 3-D depletion simulation. However, in this case statistical uncertainty is combined with error propagating through the calculation from previous steps. In an effort to understand this error propagation, a numerical study was undertaken to model and track individual fuel pins in four 17 x 17 PWR fuel assemblies. By changing the code's initial random number seed, the data produced by a series of 19 replica runs was used to investigate the true and apparent variance in k{sub eff}, pin powers, and number densities of several isotopes. While this study does not intend to develop a predictive model for error propagation, it is hoped that its results can help to identify some common regularities in the behavior of uncertainty in several key parameters. (authors)
Numerical study on dielectrophoretic chaining of two ellipsoidal particles.
House, Dustin L; Luo, Haoxiang; Chang, Siyuan
2012-05-15
Electric field-induced assembly of biological and synthetic particles has proven useful in two- and three-dimensional fabrication of composite materials, microwires, photonic crystals, artificial tissues, and more. Biological particles are typically irregularly shaped, and using non-spherical synthetic particles has the ability to expand current applications. However, there is much to be understood about the dielectrophoretic (DEP) interaction that takes place between particles of general shape. In this work, we numerically study the DEP interaction between two prolate spheroid particles suspended in an unbounded fluid. The boundary-element method (BEM) is applied to solve the coupled electric field, Stokes flow, and particle motion, and the DEP forces are obtained by integrating the Maxwell stress tensor over the particle surfaces. Effects of the initial configuration and aspect ratio are investigated. Results show that the particles go through a self-rotation process, that is, electro-orientation, while translating slowly to form a chain pair. The final formation resembles the chaining pattern observed previously in experiments using densely distributed ellipsoidal particles. Thus, the transient behavior and particle-particle interaction exhibited in the current study could be used as the fundamental mechanism to explain the phenomenon in the experiment. PMID:22340950
Naghieh, S; Karamooz Ravari, M R; Badrossamay, M; Foroozmehr, E; Kadkhodaei, M
2016-06-01
In recent years, thanks to additive manufacturing technology, researchers have gone towards the optimization of bone scaffolds for the bone reconstruction. Bone scaffolds should have appropriate biological as well as mechanical properties in order to play a decisive role in bone healing. Since the fabrication of scaffolds is time consuming and expensive, numerical methods are often utilized to simulate their mechanical properties in order to find a nearly optimum one. Finite element analysis is one of the most common numerical methods that is used in this regard. In this paper, a parametric finite element model is developed to assess the effects of layers penetration׳s effect on inter-layer adhesion, which is reflected on the mechanical properties of bone scaffolds. To be able to validate this model, some compression test specimens as well as bone scaffolds are fabricated with biocompatible and biodegradable poly lactic acid using fused deposition modeling. All these specimens are tested in compression and their elastic modulus is obtained. Using the material parameters of the compression test specimens, the finite element analysis of the bone scaffold is performed. The obtained elastic modulus is compared with experiment indicating a good agreement. Accordingly, the proposed finite element model is able to predict the mechanical behavior of fabricated bone scaffolds accurately. In addition, the effect of post-heating of bone scaffolds on their elastic modulus is investigated. The results demonstrate that the numerically predicted elastic modulus of scaffold is closer to experimental outcomes in comparison with as-built samples. PMID:26874065
Numerical Studies of Magnetohydrodynamic Activity Resulting from Inductive Transients Final Report
Sovinec, Carl R.
2005-08-29
This report describes results from numerical studies of transients in magnetically confined plasmas. The work has been performed by University of Wisconsin graduate students James Reynolds and Giovanni Cone and by the Principal Investigator through support from contract DE-FG02-02ER54687, a Junior Faculty in Plasma Science award from the DOE Office of Science. Results from the computations have added significantly to our knowledge of magnetized plasma relaxation in the reversed-field pinch (RFP) and spheromak. In particular, they have distinguished relaxation activity expected in sustained configurations from transient effects that can persist over a significant fraction of the plasma discharge. We have also developed the numerical capability for studying electrostatic current injection in the spherical torus (ST). These configurations are being investigated as plasma confinement schemes in the international effort to achieve controlled thermonuclear fusion for environmentally benign energy production. Our numerical computations have been performed with the NIMROD code (http://nimrodteam.org) using local computing resources and massively parallel computing hardware at the National Energy Research Scientific Computing Center. Direct comparisons of simulation results for the spheromak with laboratory measurements verify the effectiveness of our numerical approach. The comparisons have been published in refereed journal articles by this group and by collaborators at Lawrence Livermore National Laboratory (see Section 4). In addition to the technical products, this grant has supported the graduate education of the two participating students for three years.
Numerical study of a delta planform with multiple jets in ground effect
NASA Technical Reports Server (NTRS)
Chawla, K.; Van Dalsem, W. R.; Rao, K. V.
1989-01-01
The flow past a 60-deg delta wing equipped with two thrust-reverser jets near the inboard trailing edge has been analyzed by numerical solution of the 3D thin-layer Navier-Stokes equations. An implicit, partially flux-split, approximately-factored Navier-Stokes solver coupled with a multiple grid embedding scheme has been adapted to this problem. Studies of the impact of numerical parameters (e.g., grid refinement and dissipation levels), and flow-field parameters such as the height of the delta wing above the ground plane and the jet size on the solution, were performed. Results of these numerical studies indicate some challenges in the accurate resolution of complex 3D free shear layers and jets. Nevertheless, flow features such as jet deformation and ground vortex formation observed in experimental flow visualizations are captured. Further, comparisons with experimental data confirm the ability to simulate the loss of wing-borne lift, commonly referred to 'suckdown, as the delta planform flies at slow speeds in close proximity to the ground. Detailed analysis of the numerical results has also given additional insight into the structure of the ground vortex and the mechanisms of lift loss.
Méndez-Méndez, J V; Alonso-Rasgado, M T; Faria, E Correia; Flores-Johnson, E A; Snook, R D
2014-11-01
When atomic force microscopy (AFM) is employed for in vivo study of immersed biological samples, the fluid medium presents additional complexities, not least of which is the hydrodynamic drag force due to viscous friction of the cantilever with the liquid. This force should be considered when interpreting experimental results and any calculated material properties. In this paper, a numerical model is presented to study the influence of the drag force on experimental data obtained from AFM measurements using computational fluid dynamics (CFD) simulation. The model provides quantification of the drag force in AFM measurements of soft specimens in fluids. The numerical predictions were compared with experimental data obtained using AFM with a V-shaped cantilever fitted with a pyramidal tip. Tip velocities ranging from 1.05 to 105 μm/s were employed in water, polyethylene glycol and glycerol with the platform approaching from a distance of 6000 nm. The model was also compared with an existing analytical model. Good agreement was observed between numerical results, experiments and analytical predictions. Accurate predictions were obtained without the need for extrapolation of experimental data. In addition, the model can be employed over the range of tip geometries and velocities typically utilized in AFM measurements. PMID:25080275
A Numerical Study on Possible Driving Mechanisms of Core Convection
NASA Astrophysics Data System (ADS)
Breuer, M.; Harder, H.; Hansen, U.
2005-12-01
We present a numerical study on core convection based on a model of a rotating spherical shell where different driving mechanisms are investigated. Two different sources are potentially available to act as driving forces. The first is based on the super adiabatic temperature gradient in the outer core. The second is of chemical nature and is derived from light elements which emerge at the boundary between the inner and the outer core as a result of the freezing process of the outer core. So far it is uncertain if the convective flow in the outer core is dominated by thermal or by chemical buoyancy. Dynamically, both components differ mainly in terms of their diffusional time scales, whereas the chemical component diffuses much faster than the thermal one. To investigate the influence of the driving mechanisms on the convective flow pattern we considered different scenarios including the two extreme cases of purely thermal and purely chemical driven convection and the more likely situation of a joint action of both sources. We focused on the question how the driving mechanisms affects the differential rotation and the spatial distribution of helicity which are particularly important for the dynamo process.
Numerical Study of Surface Connectivity in the Eastern Mexican Pacific
NASA Astrophysics Data System (ADS)
Inda Diaz, H. A.; Pares-Sierra, A.
2014-12-01
East boundary ecosystems are the most productive regions in the world and they sustain a large percentage of world fisheries. Understand and describe the connectivity and exchange between different regions of the ocean is very important for larvae dispersion study and other tracers like pollutants. In this work we use an offline numerical model to simulate Lagrangian particle trajectories in the Eastern Mexican Pacific (between 120-94 W and 12-34 N). Particles are advected whit velocity fields generated with the model ROMS (Regional Ocean Modeling System) in the period 1980-2006. We define connectivity indexes in order to classify different zones by their capacity of exporting, receiving and retaining particles. We aim to identify the most transited pathways, quantify connectivity between different regions of EMP through connectivity matrix and describe their seasonal variability. It has been identified zones of high isolation and retention (Vizcaino Bay, Northern of Gulf of California), high retention and importation (between Ensenada and Point Conception) and high exportation and importation (Cabo Corrientes). Connectivity has clear equatoward preference in the California Peninsula region dominated by the influence of California Current with an increase in winter and spring, and also equatoward in the south region of Mexico (from Cabo Corrientes to Tehuantepec Gulf), dominated by the anticyclonic circulation of Tehuantepec Dome. It is observed a complete disconnection between the Baja California Peninsula and Cabo Corrientes zone and further south. Results suggest that the scales of connectivity does not significantly change for simulations over 3 months.
Numerical study on inter-tidal transports in coastal seas
NASA Astrophysics Data System (ADS)
Mao, Xinyan; Jiang, Wensheng; Zhang, Ping; Feng, Shizuo
2016-06-01
Inter-tidal (subtidal) transport processes in coastal sea depend on the residual motion, turbulent dispersion and relevant sources/sinks. In Feng et al. (2008), an updated Lagrangian inter-tidal transport equation, as well as new concept of Lagrangian inter-tidal concentration (LIC), has been proposed for a general nonlinear shallow water system. In the present study, the LIC is numerically applied for the first time to passive tracers in idealized settings and salinity in the Bohai Sea, China. Circulation and tracer motion in the three idealized model seas with different topography or coastline, termed as `flat-bottom', `stairs' and `cape' case, respectively, are simulated. The dependence of the LIC on initial tidal phase suggests that the nonlinearities in the stairs and cape cases are stronger than that in the flat-bottom case. Therefore, the `flat-bottom' case still meets the convectively weakly nonlinear condition. For the Bohai Sea, the simulation results show that most parts of it still meet the weakly nonlinear condition. However, the dependence of the LIS (Lagrangian inter-tidal salinity) on initial tidal phase is significant around the southern headland of the Liaodong Peninsula and near the mouth of the Yellow River. The nonlinearity in the former region is mainly related to the complicated coastlines, and that in the latter region is due to the presence of the estuarine salinity front.
Experimental and numerical studies on standing surface acoustic wave microfluidics.
Mao, Zhangming; Xie, Yuliang; Guo, Feng; Ren, Liqiang; Huang, Po-Hsun; Chen, Yuchao; Rufo, Joseph; Costanzo, Francesco; Huang, Tony Jun
2016-02-01
Standing surface acoustic waves (SSAW) are commonly used in microfluidics to manipulate cells and other micro/nano particles. However, except for a simple one-dimensional (1D) harmonic standing waves (HSW) model, a practical model that can predict particle behaviour in SSAW microfluidics is still lacking. Herein, we established a two-dimensional (2D) SSAW microfluidic model based on the basic theory in acoustophoresis and our previous modelling strategy to predict the acoustophoresis of microparticles in SSAW microfluidics. This 2D SSAW microfluidic model considers the effects of boundary vibrations, channel materials, and channel dimensions on the acoustic propagation; as an experimental validation, the acoustophoresis of microparticles under continuous flow through narrow channels made of PDMS and silicon was studied. The experimentally observed motion of the microparticles matched well with the numerical predictions, while the 1D HSW model failed to predict many of the experimental observations. Particularly, the 1D HSW model cannot account for particle aggregation on the sidewall in PDMS channels, which is well explained by our 2D SSAW microfluidic model. Our model can be used for device design and optimization in SSAW microfluidics. PMID:26698361
Numerical study of chemically reacting flows using an LU scheme
NASA Technical Reports Server (NTRS)
Shuen, Jian Shun; Yoon, Seokkwan
1988-01-01
A new computational fluid dynamic code has been developed for the study of mixing and chemical reactions in the flow fields of ramjets and scramjets. The code employs an implicit finite volume, lower-upper symmetric successive overrelaxation scheme for solving the complete two-dimensional Navier-Stokes equations and species transport equations in a fully-coupled and very efficient manner. The combustion processes are modeled by an 8-species, 14-step finite rate chemistry model whereas turbulence is simulated by a Baldwin-Lomax algebraic model. The validity of the code is demonstrated by comparing the numerical calculations with both experimental data and previous calculations of a cold flow helium injection into a straight channel and premixed hydrogen-air reacting flows in a ramped duct. The code is then used to calculate the mixing and chemical reactions of a hydrogen jet transversely injected into a supersonic airstream. Results are presented describing the flow field, the recirculation regions in front and behind the injector, and the chemical reactions.
Drag Reduction by Riblets & Sharkskin Denticles: A Numerical Study
NASA Astrophysics Data System (ADS)
Boomsma, Aaron
Riblet films are a passive method of turbulent boundary layer control that can reduce viscous drag. They have been studied with great detail for over 30 years. Although common riblet applications include flows with Adverse Pressure Gradients (APG), nearly all research thus far has been performed in channel flows. Recent research has provided motivation to study riblets in more complicated turbulent flows with claims that riblet drag reduction can double in mild APG common to airfoils at moderate angles of attack. Therefore, in this study, we compare drag reduction by scalloped riblet films between riblets in a zero pressure gradient and those in a mild APG using high-resolution large eddy simulations. In order to gain a fundamental understanding of the relationship between drag reduction and pressure gradient, we simulated several different riblet sizes that encompassed a broad range of s + (riblet width in wall units), similarly to many experimental studies. We found that there was only a slight improvement in drag reduction for riblets in the mild APG. We also observed that peak values of streamwise turbulence intensity, turbulent kinetic energy, and streamwise vorticity scale with riblet width. Primary Reynolds shear stresses and turbulence kinetic energy production however scale with the ability of the riblet to reduce skin-friction. Another turbulent roughness of similar shape and size to riblets is sharkskin. The hydrodynamic function of sharkskin has been under investigation for the past 30 years. Current literature conflicts on whether sharkskin is able to reduce skin friction similarly to riblets. To contribute insights toward reconciling these conflicting views, Direct Numerical Simulations (DNS) are carried out to obtain detailed flow fields around realistic denticles. A sharp interface immersed boundary method is employed to simulate two arrangements of actual sharkskin denticles (from Isurus oxyrinchus) in a turbulent boundary layer at Retau ≈ 180
Reigosa-Crespo, Vivian; González-Alemañy, Eduardo; León, Teresa; Torres, Rosario; Mosquera, Raysil; Valdés-Sosa, Mitchell
2013-01-01
The first aim of the present study was to investigate whether numerical effects (Numerical Distance Effect, Counting Effect and Subitizing Effect) are domain-specific predictors of mathematics development at the end of elementary school by exploring whether they explain additional variance of later mathematics fluency after controlling for the effects of general cognitive skills, focused on nonnumerical aspects. The second aim was to address the same issues but applied to achievement in mathematics curriculum that requires solutions to fluency in calculation. These analyses assess whether the relationship found for fluency are generalized to mathematics content beyond fluency in calculation. As a third aim, the domain specificity of the numerical effects was examined by analyzing whether they contribute to the development of reading skills, such as decoding fluency and reading comprehension, after controlling for general cognitive skills and phonological processing. Basic numerical capacities were evaluated in children of 3rd and 4th grades (n=49). Mathematics and reading achievements were assessed in these children one year later. Results showed that the size of the Subitizing Effect was a significant domain-specific predictor of fluency in calculation and also in curricular mathematics achievement, but not in reading skills, assessed at the end of elementary school. Furthermore, the size of the Counting Effect also predicted fluency in calculation, although this association only approached significance. These findings contrast with proposals that the core numerical competencies measured by enumeration will bear little relationship to mathematics achievement. We conclude that basic numerical capacities constitute domain-specific predictors and that they are not exclusively “start-up” tools for the acquisition of Mathematics; but they continue modulating this learning at the end of elementary school. PMID:24255710
Reigosa-Crespo, Vivian; González-Alemañy, Eduardo; León, Teresa; Torres, Rosario; Mosquera, Raysil; Valdés-Sosa, Mitchell
2013-01-01
The first aim of the present study was to investigate whether numerical effects (Numerical Distance Effect, Counting Effect and Subitizing Effect) are domain-specific predictors of mathematics development at the end of elementary school by exploring whether they explain additional variance of later mathematics fluency after controlling for the effects of general cognitive skills, focused on nonnumerical aspects. The second aim was to address the same issues but applied to achievement in mathematics curriculum that requires solutions to fluency in calculation. These analyses assess whether the relationship found for fluency are generalized to mathematics content beyond fluency in calculation. As a third aim, the domain specificity of the numerical effects was examined by analyzing whether they contribute to the development of reading skills, such as decoding fluency and reading comprehension, after controlling for general cognitive skills and phonological processing. Basic numerical capacities were evaluated in children of 3(rd) and 4(th) grades (n=49). Mathematics and reading achievements were assessed in these children one year later. Results showed that the size of the Subitizing Effect was a significant domain-specific predictor of fluency in calculation and also in curricular mathematics achievement, but not in reading skills, assessed at the end of elementary school. Furthermore, the size of the Counting Effect also predicted fluency in calculation, although this association only approached significance. These findings contrast with proposals that the core numerical competencies measured by enumeration will bear little relationship to mathematics achievement. We conclude that basic numerical capacities constitute domain-specific predictors and that they are not exclusively "start-up" tools for the acquisition of Mathematics; but they continue modulating this learning at the end of elementary school. PMID:24255710
Raghavan, Narendran; Dehoff, Ryan; Pannala, Sreekanth; Simunovic, Srdjan; Kirka, Michael; Turner, John; Carlson, Neil; Babu, Sudarsanam S.
2016-04-26
The fabrication of 3-D parts from CAD models by additive manufacturing (AM) is a disruptive technology that is transforming the metal manufacturing industry. The correlation between solidification microstructure and mechanical properties has been well understood in the casting and welding processes over the years. This paper focuses on extending these principles to additive manufacturing to understand the transient phenomena of repeated melting and solidification during electron beam powder melting process to achieve site-specific microstructure control within a fabricated component. In this paper, we have developed a novel melt scan strategy for electron beam melting of nickel-base superalloy (Inconel 718) andmore » also analyzed 3-D heat transfer conditions using a parallel numerical solidification code (Truchas) developed at Los Alamos National Laboratory. The spatial and temporal variations of temperature gradient (G) and growth velocity (R) at the liquid-solid interface of the melt pool were calculated as a function of electron beam parameters. By manipulating the relative number of voxels that lie in the columnar or equiaxed region, the crystallographic texture of the components can be controlled to an extent. The analysis of the parameters provided optimum processing conditions that will result in columnar to equiaxed transition (CET) during the solidification. Furthermore, the results from the numerical simulations were validated by experimental processing and characterization thereby proving the potential of additive manufacturing process to achieve site-specific crystallographic texture control within a fabricated component.« less
Drainage flows: A mountain-plains interface numerical case study
Poulos, G.S.; Bossert, J.E.
1992-01-01
In January/February, 1991 an intensive set of measurements was taken around Rocky Flats near Denver, CO, USA under the auspices of the Atmospheric Studies in Complex Terrain (ASCOT) program. This region of the country is known as the Front Range, and is characterized by a transition from the relatively flat terrain of the Great Plains to the highly varied terrain of the Rocky Mountains. The mountains are oriented north-south and rise from 1800m above mean sea level (MSL) to 3600m MSL at the Continental Divide. Numerous east-west oriented valleys begin in the mountains and end at the plains interface. This terrain makes the Front Range a challenging region to model. One of the more important flows created by this severe terrain are the highly-varying drainage flows found during stagnant, wintertime conditions. These flows can interact with larger-scale mountain and synoptic winds. One goal of the ASCOT 1991 program was to gain insight into multi-scale meteorological interaction by observing wintertime drainage conditions at the mountain-valley-plains interface. ASCOT data included surface and upper air measurements on approximately a 50km{sup 2} scale. Simultaneously, an SF{sub 6} tracer release study was being conducted around Rocky Flats, a nuclear materials production facility. Detailed surface concentration measurements were completed for the SF{sub 6} plume. This combination of meteorological and tracer concentration data provided a unique data set for comparisons of mesoscale and dispersion modeling results with observations and for evaluating our capability to predict pollutant transport. Our approach is to use the Regional Atmospheric Modeling System (RAMS) mesoscale model to simulate atmospheric conditions and the Lagrangian Particle Dispersion Model (LPDM) to model the dispersion of the SF{sub 6}.
Drainage flows: A mountain-plains interface numerical case study
Poulos, G.S.; Bossert, J.E.
1992-09-01
In January/February, 1991 an intensive set of measurements was taken around Rocky Flats near Denver, CO, USA under the auspices of the Atmospheric Studies in Complex Terrain (ASCOT) program. This region of the country is known as the Front Range, and is characterized by a transition from the relatively flat terrain of the Great Plains to the highly varied terrain of the Rocky Mountains. The mountains are oriented north-south and rise from 1800m above mean sea level (MSL) to 3600m MSL at the Continental Divide. Numerous east-west oriented valleys begin in the mountains and end at the plains interface. This terrain makes the Front Range a challenging region to model. One of the more important flows created by this severe terrain are the highly-varying drainage flows found during stagnant, wintertime conditions. These flows can interact with larger-scale mountain and synoptic winds. One goal of the ASCOT 1991 program was to gain insight into multi-scale meteorological interaction by observing wintertime drainage conditions at the mountain-valley-plains interface. ASCOT data included surface and upper air measurements on approximately a 50km{sup 2} scale. Simultaneously, an SF{sub 6} tracer release study was being conducted around Rocky Flats, a nuclear materials production facility. Detailed surface concentration measurements were completed for the SF{sub 6} plume. This combination of meteorological and tracer concentration data provided a unique data set for comparisons of mesoscale and dispersion modeling results with observations and for evaluating our capability to predict pollutant transport. Our approach is to use the Regional Atmospheric Modeling System (RAMS) mesoscale model to simulate atmospheric conditions and the Lagrangian Particle Dispersion Model (LPDM) to model the dispersion of the SF{sub 6}.
Numerical Simulation Study of the Sanchiao Fault Earthquake Scenarios
NASA Astrophysics Data System (ADS)
Wang, Yi-Min; Lee, Shiann-Jong
2015-04-01
Sanchiao fault is a western boundary fault of the Taipei basin located in northern Taiwan, close to the densely populated Taipei metropolitan area. Recent study indicated that there is about 40 km of the fault trace extended to the marine area offshore northern Taiwan. Combining the marine and terrestrial parts, the total fault length of Sanchiao fault could be nearly 70 kilometers which implies that this fault has potential to produce a big earthquake. In this study, we analyze several Sanchiao fault earthquake scenarios based on the recipe for predicting strong ground motion. The characterized source parameters include fault length, rupture area, seismic moment, asperity, and slip pattern on the fault plane. According to the assumption of the characterized source model, Sanchiao fault has been inferred to have the potential to produce an earthquake with moment magnitude (Mw) larger than 7.0. Three-dimensional seismic simulation results based upon spectral-element method (SEM) indicate that peak ground acceleration (PGA) is significantly stronger along the fault trace. The basin effect also plays an important role when wave propagates in the Taipei basin which cause seismic wave amplified and prolong the shaking for a very long time. Among all rupture scenarios, the rupture propagated from north to south is the most serious one. Owing to the rupture directivity as well as the basin effects, large PGA (>1g) was observed in the Taipei basin, especially in the northwest side. The results of these scenario earthquake simulations will provide important physically-based numerical data for earthquake mitigation and seismic hazard assessment.
Additional Treatments Offer Little Benefit for Pancreatic Cancer: Study
... of gastroenterology-pancreatology at Beaujon Hospital, in Clichy, France. The study was funded by the pharmaceutical company ... D., department of gastroenterology-pancreatology, Beaujon Hospital, Clichy, France; Deborah Schrag, M.D., M.P.H., chief ...
NMR relaxometry study of plaster mortar with polymer additives
Jumate, E.; Manea, D.; Moldovan, D.; Fechete, R.
2013-11-13
The cement mixed with water forms a plastic paste or slurry which stiffness in time and finally hardens into a resistant stone. The addition of sand aggregates, polymers (Walocel) and/or calcium carbonate will modify dramatically the final mortar mechanic and thermal properties. The hydration processes can be observed using the 1D NMR measurements of transverse T{sub 2} relaxation times distributions analysed by a Laplace inversion algorithm. These distributions were obtained for mortar pasta measured at 2 hours after preparation then at 3, 7 and 28 days after preparation. Multiple components are identified in the T{sub 2} distributions. These can be associated with the proton bounded chemical or physical to the mortar minerals characterized by a short T{sub 2} relaxation time and to water protons in pores with three different pore sizes as observed from SEM images. The evaporation process is faster in the first hours after preparation, while the mortar hydration (bonding of water molecules to mortar minerals) can be still observed after days or months from preparation. Finally, the mechanic resistance was correlated with the transverse T{sub 2} relaxation rates corresponding to the bound water.
Numerical Study of Solar Storms From the Sun to Earth
NASA Astrophysics Data System (ADS)
Feng, Xueshang
2015-08-01
As solar storms are sweeping the Earth, adverse changes occur in geospace environment. It is of both scientific significance to understand the dynamic process during solar storm’s propagation in interplanetary space and realistic value to conduct physics-based numerical researches on the three-dimensional process of solar storms in interplanetary space with the aid of powerful computing capacity to predict the arrival times, intensities, and probable geoeffectiveness of solar storms at the Earth. Numerical modeling community has a common goal to develop an end-to-end physics-based modeling system for forecasting the Sun-Earth relationship. It is hoped that the models’ prediction capabilities may be improved by incorporating the observational findings and constraints into physics-based models, combining the observations, empirical models and MHD simulations in organic ways.In this talk, we birefly review the current status of the existing three-dimensional numerical physics-based coronal and interplanetary models and their recent research results, particularly our recent progress in using solar observations to produce realistic magnetic configurations of CMEs as they leave the Sun, and coupling data-driven simulations of CMEs to heliospheric simulations that then propagate the CME configuration to 1AU, and outlook the important numerical issues and their possible solutions in numerical space weather modeling from the Sun to Earth for future research.
Numerical study of pseudoscalar inflation with an axion-gauge field coupling
NASA Astrophysics Data System (ADS)
Cheng, Shu-Lin; Lee, Wolung; Ng, Kin-Wang
2016-03-01
A numerical study of a pseudoscalar inflation having an axion-photon-like coupling is performed by solving numerically the coupled differential equations of motion for inflaton and photon mode functions from the onset of inflation to the end of reheating. The backreaction due to particle production is also included self-consistently. We find that this particular inflation model realizes the idea of a warm inflation in which a steady thermal bath is established by the particle production. In most cases, this thermal bath exceeds the amount of radiation released in the reheating process. In the strong coupling regime, the transition from the inflationary to the radiation-dominated phase does not involve either a preheating nor reheating process. In addition, energy density peaks produced near the end of inflation may lead to the formation of primordial black holes.
FEM numerical model study of heating in magnetic nanoparticles.
Pearce, John A; Cook, Jason R; Hoopes, P Jack; Giustini, Andrew
2011-02-22
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 10(12) to 10(13) 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 10(13) NP/mL located within one control volume (1.0 × 10(-19) m(3)) of a capillary vessel a power density in the neighborhood of 10(17) (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 study of a Taylor bubble rising in stagnant liquids.
Kang, Chang-Wei; Quan, Shaoping; Lou, Jing
2010-06-01
The dynamics of a Taylor bubble rising in stagnant liquids is numerically investigated using a front tracking coupled with finite difference method. Parametric studies on the dynamics of the rising Taylor bubble including the final shape, the Reynolds number (Re(T)), the Weber number (We(T)), the Froude number (Fr), the thin liquid film thickness (w/D), and the wake length (l(w)/D) are carried out. The effects of density ratio (η), viscosity ratio (λ), Eötvös number (Eo), and Archimedes number (Ar) are examined. The simulations demonstrate that the density ratio and the viscosity ratio under consideration have minimal effect on the dynamics of the Taylor bubble. Eötvös number and Archimedes number influence the elongation of the tail and the wake structures, where higher Eo and Ar result in longer wake. To explain the sudden extension of the tail, a Weber number (We(l)) based on local curvature and velocity is evaluated and a critical We(l) is detected around unity. The onset of flow separation at the wake occurs in between Ar=2×10(3) and Ar=1×10(4), which corresponds to Re(T) between 13.39 and 32.55. Archimedes number also drastically affects the final shape of Taylor bubble, the terminal velocity, the thickness of thin liquid film, as well as the wall shear stress. It is found that w/D=0.32 Ar(-0.1). PMID:20866523
Direct numerical simulation studies of Lagrangian intermittency in turbulence
NASA Astrophysics Data System (ADS)
Sawford, Brian L.; Yeung, P. K.
2015-06-01
Lag-averaged Lagrangian statistics from direct numerical simulations over a range of Reynolds numbers are analyzed to test the predictions of the Lagrangian Refined Similarity Hypothesis (LRSH). The analysis uses the Lagrangian integral time scale to scale the lag since it is the natural time scale to reveal trends and scaling with Reynolds number. Both the velocity difference and the dissipation rate probability density functions (PDFs) collapse across inertial sub-range and diffusive scales for approximately the same values of the scaled lag, and in the zero lag limit are independent of the lag and depend only on the Reynolds number. These findings are consistent with the LRSH. The velocity difference PDFs are characterized by stretched exponential tails, while the dissipation rate PDFs for small lags have a log normal core with power law tails at both large and small values of the dissipation rate. The velocity structure functions show inertial sub-range similarity scaling with Reynolds number which extends to smaller scales with increasing Reynolds number. Estimates of the scaling exponents obtained are consistent with those from previous studies. They tend to saturate at a value of about two for high order moments. Non-dimensional acceleration moments show a striking power law dependence on Reynolds number from which novel estimates of the scaling exponents have been determined. Similarity scaling is much more elusive to demonstrate in the dissipation rate moments. The data are consistent with, but do not confirm, the Oboukhov relationship connecting velocity structure functions and dissipation rate moments on inertial sub-range scales.
Numerical study of a confined slot impinging jet with nanofluids
2011-01-01
Background Heat transfer enhancement technology concerns with the aim of developing more efficient systems to satisfy the increasing demands of many applications in the fields of automotive, aerospace, electronic and process industry. A solution for obtaining efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the possibility of increasing the thermal performances of the working fluids can be taken into account, and the introduction of nanoparticles in a base fluid can be considered. Results In this article, a numerical investigation on confined impinging slot jet working with a mixture of water and Al2O3 nanoparticles is described. The flow is turbulent and a constant temperature is applied on the impinging. A single-phase model approach has been adopted. Different geometric ratios, particle volume concentrations and Reynolds number have been considered to study the behavior of the system in terms of average and local Nusselt number, convective heat transfer coefficient and required pumping power profiles, temperature fields and stream function contours. Conclusions The dimensionless stream function contours show that the intensity and size of the vortex structures depend on the confining effects, given by H/W ratio, Reynolds number and particle concentrations. Furthermore, for increasing concentrations, nanofluids realize increasing fluid bulk temperature, as a result of the elevated thermal conductivity of mixtures. The local Nusselt number profiles show the highest values at the stagnation point, and the lowest at the end of the heated plate. The average Nusselt number increases for increasing particle concentrations and Reynolds numbers; moreover, the highest values are observed for H/W = 10, and a maximum increase of 18% is detected at a concentration equal to 6%. The required pumping power as well as Reynolds number increases and particle concentrations grow, which is almost 4.8 times greater than the
Coordinated Optimization of Visual Cortical Maps (II) Numerical Studies
Reichl, Lars; Heide, Dominik; Löwel, Siegrid; Crowley, Justin C.; Kaschube, Matthias; Wolf, Fred
2012-01-01
In the juvenile brain, the synaptic architecture of the visual cortex remains in a state of flux for months after the natural onset of vision and the initial emergence of feature selectivity in visual cortical neurons. It is an attractive hypothesis that visual cortical architecture is shaped during this extended period of juvenile plasticity by the coordinated optimization of multiple visual cortical maps such as orientation preference (OP), ocular dominance (OD), spatial frequency, or direction preference. In part (I) of this study we introduced a class of analytically tractable coordinated optimization models and solved representative examples, in which a spatially complex organization of the OP map is induced by interactions between the maps. We found that these solutions near symmetry breaking threshold predict a highly ordered map layout. Here we examine the time course of the convergence towards attractor states and optima of these models. In particular, we determine the timescales on which map optimization takes place and how these timescales can be compared to those of visual cortical development and plasticity. We also assess whether our models exhibit biologically more realistic, spatially irregular solutions at a finite distance from threshold, when the spatial periodicities of the two maps are detuned and when considering more than 2 feature dimensions. We show that, although maps typically undergo substantial rearrangement, no other solutions than pinwheel crystals and stripes dominate in the emerging layouts. Pinwheel crystallization takes place on a rather short timescale and can also occur for detuned wavelengths of different maps. Our numerical results thus support the view that neither minimal energy states nor intermediate transient states of our coordinated optimization models successfully explain the architecture of the visual cortex. We discuss several alternative scenarios that may improve the agreement between model solutions and biological
Convective instability in sedimentation: 3-D numerical study
NASA Astrophysics Data System (ADS)
Yu, Xiao; Hsu, Tian-Jian; Balachandar, S.
2014-11-01
To provide a probable explanation on the field observed rapid sedimentation process near river mouths, we investigate the convective sedimentation in stably stratified saltwater using 3-D numerical simulations. Guided by the linear stability analysis, this study focuses on the nonlinear interactions of several mechanisms, which lead to various sediment finger patterns, and the effective settling velocity for sediment ranging from clay (single-particle settling velocity V0 = 0.0036 and 0.0144 mm/s, or particle diameter d = 2 and 4 μm) to silt (V0 = 0.36 mm/s, or d = 20 μm). For very fine sediment with V0 = 0.0036 mm/s, the convective instability is dominated by double diffusion, characterized by millimeter-scale fingers. Gravitational settling slightly increases the growth rate; however, it has notable effect on the downward development of vertical mixing shortly after the sediment interface migrates below the salt interface. For sediment with V0 = 0.0144 mm/s, Rayleigh-Taylor instabilities become dominant before double-diffusive modes grow sufficiently large. Centimeter-scale and highly asymmetric sediment fingers are obtained due to nonlinear interactions between different modes. For sediment with V0 = 0.36 mm/s, Rayleigh-Taylor mechanism dominates and the resulting centimeter-scale sediment fingers show a plume-like structure. The flow pattern is similar to that without ambient salt stratification. Rapid sedimentation with effective settling velocity on the order of 1 cm/s is likely driven by convective sedimentation for sediment with V0 greater than 0.1 mm/s at concentration greater than 10-20 g/L.
Numerical Study for Baroclinic Tides Modified By an Oblique Current
NASA Astrophysics Data System (ADS)
Wang, C. A.; Jan, S.
2014-12-01
Previous investigations suggest that when the internal waves throughout a northwest - southeast background flow, its amplitudes, propagation path, phase speed might be changed. The process occurring when internal tides meet a background geostrophic current at an angle rather than perpendicular to the current in a zonal channel is investigated using a numerical model with simplified forcing, topography and hydrographic setting. We compared numerical results of two different background conditions: (1) no background flow and (2) oblique background flow. Results indicate that the westward baroclinic energy flux tends to increase when internal tides pass through the background geostrophic flow. Different oblique angles of the background flow also cause different responses on the propagation of internal tides. The energy exchange between the internal tides and background flow is analyzed using an energy balance equation as well as the numerical results.
Numerical bifurcation study of electrohydrodynamic convection in nematic liquid crystals.
Tavener, S J; Mullin, T; Blake, G I; Cliffe, K A
2001-01-01
We present the results of a numerical investigation of the Ericksen-Leslie equations for the problem of electrohydrodynamic convection in a nematic liquid crystal. The combination of a finite element approach and numerical bifurcation techniques allows us to provide details of the basic flow and include the physically relevant effect of nonslip side walls. We are also able to include material properties as parameters and this permits us to draw comparisons with available experimental data. We then compare and contrast the bifurcation structure with that of Rayleigh-Bénard and Taylor-Couette flows and explore the role of symmetries by including a fringing electric field. PMID:11304279
A numerical study of drop-on-demand ink jets
NASA Technical Reports Server (NTRS)
Fromm, J.
1982-01-01
Ongoing work related to development and utilization of a numerical model for treating the fluid dynamics of ink jets is discussed. The model embodies the complete nonlinear, time dependent, axi-symmetric equations in finite difference form. The jet nozzle geometry with no-slip boundary conditions and the existence of a contact circle are included. The contact circle is allowed some freedom of movement, but wetting of exterior surfaces is not addressed. The principal objective in current numerical experiments is to determine what pressure history, in conjunction with surface forces, will lead to clean drop formation.
Feasibility study for a numerical aerodynamic simulation facility. Volume 1
NASA Technical Reports Server (NTRS)
Lincoln, N. R.; Bergman, R. O.; Bonstrom, D. B.; Brinkman, T. W.; Chiu, S. H. J.; Green, S. S.; Hansen, S. D.; Klein, D. L.; Krohn, H. E.; Prow, R. P.
1979-01-01
A Numerical Aerodynamic Simulation Facility (NASF) was designed for the simulation of fluid flow around three-dimensional bodies, both in wind tunnel environments and in free space. The application of numerical simulation to this field of endeavor promised to yield economies in aerodynamic and aircraft body designs. A model for a NASF/FMP (Flow Model Processor) ensemble using a possible approach to meeting NASF goals is presented. The computer hardware and software are presented, along with the entire design and performance analysis and evaluation.
Numerical studies of third-harmonic generation in laser filament in air perturbed by plasma spot
Feng Liubin; Lu Xin; Liu Xiaolong; Li Yutong; Chen Liming; Ma Jinglong; Dong Quanli; Wang Weimin; Xi Tingting; Sheng Zhengming; Zhang Jie; He Duanwei
2012-07-15
Third-harmonic emission from laser filament intercepted by plasma spot is studied by numerical simulations. Significant enhancement of the third-harmonic generation is obtained due to the disturbance of the additional plasma. The contribution of the pure plasma effect and the possible plasma-enhanced third-order susceptibility on the third-harmonic generation enhancement are compared. It is shown that the plasma induced cancellation of destructive interference [Y. Liu et al., Opt. Commun. 284, 4706 (2011)] of two-colored filament is the dominant mechanism of the enhancement of third-harmonic generation.
BEM-based numerical study of three-dimensional compressible bubble dynamics in stokes flow
NASA Astrophysics Data System (ADS)
Abramova, O. A.; Akhatov, I. Sh.; Gumerov, N. A.; Itkulova, Yu. A.
2014-09-01
The dynamics of compressible gas bubbles in a viscous shear flow and an acoustic field at low Reynolds numbers is studied. The numerical approach is based on the boundary element method (BEM), which is effective as applied to the three-dimensional simulation of bubble deformation. However, the application of the conventional BEM to compressible bubble dynamics faces difficulties caused by the degeneration of the resulting algebraic system. Additional relations based on the Lorentz reciprocity principle are used to cope with this problem. Test computations of the dynamics of a single bubble and bubble clusters in acoustic fields and shear flows are presented.
Numerical study of 1-D, 3-vector component, thermally-conductive MHD solar wind
NASA Technical Reports Server (NTRS)
Han, S.; Wu, S. T.; Dryer, M.
1993-01-01
In the present study, transient, 1-dimensional, 3-vector component MHD equations are used to simulate steady and unsteady, thermally conductive MHD solar wind expansions between the solar surface and 1 AU (astronomical unit). A variant of SIMPLE numerical method was used to integrate the equations. Steady state solar wind properties exhibit qualitatively similar behavior with the known Weber-Davies Solutions. Generation of Alfven shock, in addition to the slow and fast MHD shocks, was attempted by the boundary perturbations at the solar surface. Property changes through the disturbance were positively correlated with the fast and slow MHD shocks. Alfven shock was, however, not present in the present simulations.
Additional EIPC Study Analysis: Interim Report on High Priority Topics
Hadley, Stanton W
2013-11-01
Between 2010 and 2012 the Eastern Interconnection Planning Collaborative (EIPC) conducted a major long-term resource and transmission study of the Eastern Interconnection (EI). With guidance from a Stakeholder Steering Committee (SSC) that included representatives from the Eastern Interconnection States Planning Council (EISPC) among others, the project was conducted in two phases. Phase 1 involved a long-term capacity expansion analysis that involved creation of eight major futures plus 72 sensitivities. Three scenarios were selected for more extensive transmission- focused evaluation in Phase 2. Five power flow analyses, nine production cost model runs (including six sensitivities), and three capital cost estimations were developed during this second phase. The results from Phase 1 and 2 provided a wealth of data that could be examined further to address energy-related questions. A list of 13 topics was developed for further analysis; this paper discusses the first five.
Numerical Study of a Bosonic Topological Insulator in three dimensions
NASA Astrophysics Data System (ADS)
Geraedts, Scott; Motrunich, Olexei
2014-03-01
We construct a model which realizes a (3+1)-dimensional symmetry-protected topological phase of bosons with U(1) charge conservation and time reversal symmetry, envisioned by A. Vishwanath and T. Senthil [PRX 4 011016]. Our model works by introducing an additional O(3) degree of freedom, and binding its hedgehogs to a species of charged bosons; the continuous symmetry is thus enlarged to SO(3) × U(1) . We study the model using Monte Carlo and determine its bulk phase diagram; the phase where the bound states of hedgehogs and charges condense is the topological phase. We also study surface phase diagram on a (2+1)-dimensional boundary between the topological and trivial insulators. The theory for the surface is the same as for a (2+1)D hedgehog-suppressed non-linear sigma model, which confirms the proposed so-called NCCP1 field theory. We apply a Zeeman field to the surface, which breaks time reversal on the surface only, and observe a surface Hall conductivity which is half of a quantized value allowed for bosons in strictly (2+1)D, thus establishing topological nature of the (3+1)D bulk phase. Support from NSF Grant DMR-1206096; Caltech Institute of Quantum Imformation and Matter, and an NSERC PGS fellowship.
Numerical Study of Interaction of a Vortical Density Inhomogeneity with Shock and Expansion Waves
NASA Technical Reports Server (NTRS)
Povitsky, A.; Ofengeim, D.
1998-01-01
We studied the interaction of a vortical density inhomogeneity (VDI) with shock and expansion waves. We call the VDI the region of concentrated vorticity (vortex) with a density different from that of ambiance. Non-parallel directions of the density gradient normal to the VDI surface and the pressure gradient across a shock wave results in an additional vorticity. The roll-up of the initial round VDI towards a non-symmetrical shape is studied numerically. Numerical modeling of this interaction is performed by a 2-D Euler code. The use of an adaptive unstructured numerical grid makes it possible to obtain high accuracy and capture regions of induced vorticity with a moderate overall number of mesh points. For the validation of the code, the computational results are compared with available experimental results and good agreement is obtained. The interaction of the VDI with a propagating shock wave is studied for a range of initial and induced circulations and obtained flow patterns are presented. The splitting of the VDI develops into the formation of a non-symmetrical vortex pair and not in a set of vortices. A method for the analytical computation of an overall induced circulation Gamma(sub 1) as a result of the interaction of a moving VDI with a number of waves is proposed. Simplified, approximated, expressions for Gamma(sub 1) are derived and their accuracy is discussed. The splitting of the VDI passing through the Prandtl-Meyer expansion wave is studied numerically. The obtained VDI patterns are compared to those for the interaction of the VDI with a propagating shock wave for the same values of initial and induced circulations. These patterns have similar shapes for corresponding time moments.
Huang, Jian; Du, Feng-lei; Yao, Yuan; Wan, Qun; Wang, Xiao-Song; Chen, Fei-Yan
2015-08-01
Distance effect has been regarded as the best established marker of basic numerical magnitude processes and is related to individual mathematical abilities. A larger behavioral distance effect is suggested to be concomitant with lower mathematical achievement in children. However, the relationship between distance effect and superior mathematical abilities is unclear. One could get superior mathematical abilities by acquiring the skill of abacus-based mental calculation (AMC), which can be used to solve calculation problems with exceptional speed and high accuracy. In the current study, we explore the relationship between distance effect and superior mathematical abilities by examining whether and how the AMC training modifies numerical magnitude processing. Thus, mathematical competencies were tested in 18 abacus-trained children (who accepted the AMC training) and 18 non-trained children. Electroencephalography (EEG) waveforms were recorded when these children executed numerical comparison tasks in both Arabic digit and dot array forms. We found that: (a) the abacus-trained group had superior mathematical abilities than their peers; (b) distance effects were found both in behavioral results and on EEG waveforms; (c) the distance effect size of the average amplitude on the late negative-going component was different between groups in the digit task, with a larger effect size for abacus-trained children; (d) both the behavioral and EEG distance effects were modulated by the notation. These results revealed that the neural substrates of magnitude processing were modified by AMC training, and suggested that the mechanism of the representation of numerical magnitude for children with superior mathematical abilities was different from their peers. In addition, the results provide evidence for a view of non-abstract numerical representation. PMID:26238541
Huang, Jian; Du, Feng-lei; Yao, Yuan; Wan, Qun; Wang, Xiao-song; Chen, Fei-yan
2015-01-01
Distance effect has been regarded as the best established marker of basic numerical magnitude processes and is related to individual mathematical abilities. A larger behavioral distance effect is suggested to be concomitant with lower mathematical achievement in children. However, the relationship between distance effect and superior mathematical abilities is unclear. One could get superior mathematical abilities by acquiring the skill of abacus-based mental calculation (AMC), which can be used to solve calculation problems with exceptional speed and high accuracy. In the current study, we explore the relationship between distance effect and superior mathematical abilities by examining whether and how the AMC training modifies numerical magnitude processing. Thus, mathematical competencies were tested in 18 abacus-trained children (who accepted the AMC training) and 18 non-trained children. Electroencephalography (EEG) waveforms were recorded when these children executed numerical comparison tasks in both Arabic digit and dot array forms. We found that: (a) the abacus-trained group had superior mathematical abilities than their peers; (b) distance effects were found both in behavioral results and on EEG waveforms; (c) the distance effect size of the average amplitude on the late negative-going component was different between groups in the digit task, with a larger effect size for abacus-trained children; (d) both the behavioral and EEG distance effects were modulated by the notation. These results revealed that the neural substrates of magnitude processing were modified by AMC training, and suggested that the mechanism of the representation of numerical magnitude for children with superior mathematical abilities was different from their peers. In addition, the results provide evidence for a view of non-abstract numerical representation. PMID:26238541
A numerical study of scaling issues for trench power MOSFETs
NASA Astrophysics Data System (ADS)
Roig, J.; Cortés, I.; Jiménez, D.; Flores, D.; Iñiguez, B.; Hidalgo, S.; Rebollo, J.
2005-06-01
The effect of the scaling down on the electrical performance of trench power MOSFET structures is investigated in this work by means of numerical simulation tools. Layout dimensions of trench power MOSFETs have been continuously reduced in order to decrease the specific on-resistance, maintaining equal vertical dimensions. Nowadays, the last scaling efforts provide trench width and distance between two consecutive trenches in the submicron range. The resultant short distance between gates is expected to induce significant modifications in the device electrical performances, since the fully depletion condition will be feasible in the body region. Hence, the influence of the fully depleted body on the on-state resistance, threshold voltage, breakdown voltage, parasitic bipolar transistor and internal capacitances are features of particular interest. Furthermore, device reliability aspects, such as hot-carrier and self-heating effects, are evaluated by numerical simulation in trench power MOSFETs for the first time.
Numerical studies of motion and decay of vortex filaments
NASA Technical Reports Server (NTRS)
Liu, C. H.; Tavantzis, J.; Ting, L.
1986-01-01
A computational code is developed for the integro-differential equations governing the motion of the centerlines of vortex filaments submerged in a background potential flow. These equations, which are derived from the method of matched asymptotic analysis, include the effect of decaying large-magnitude circumferential and axial velocity components in the vortical cores. Numerical examples are presented to assess the effect of large axial velocity and of nonsimilar initial profiles in vortical cores. The initial configurations of the filaments are chosen so as to fulfill the basic assumption of asymptotic analysis, which is the effective vortical core size is much smaller than all other length scales in the flowfield, e.g., the radius of curvature and interfilament distance. The computations are continued until the basic assumption is no longer valid, that is, when the merging or intersection of filaments have begun. Various types of local or global merging or intersection of filaments are classified and demonstrated by numerical examples.
Lift augmentation via spanwise tip blowing - A numerical study
NASA Technical Reports Server (NTRS)
Childs, R. E.
1986-01-01
Numerical simulations of a low aspect ratio wing with and without a spanwise directed jet issuing from the wing tip have been performed. The results show that the tip vortex is displaced outward and upward by the blowing. This gives rise to a local lift augmentation mechanism, vortex lift caused by the vortex core being above the wing, and a global mechanism, the reduction of induced velocities due to greater apparent spin.
Numerical study on thermodynamic characteristics of rotational supercavitating evaporator
NASA Astrophysics Data System (ADS)
Li, Q.; Zheng, Z. Y.; Li, F. C.; Kulagin, V. A.
2016-05-01
Rotational Supercavitating Evaporator (RSCE) has been proposed as a new technology for seawater desalination. However, thermodynamic characteristics of rotational supercavitation are still vacant. In this paper, numerical simulations are conducted on the supercavitating flows around a 3D rotating blade of RSCE with different rotational speeds and extraction pressures. Energy effect is taken into consideration in the simulation and thermodynamic characteristics of rotational supercavitation are obtained. Rotational supercavitation has a larger convective heat transfer coefficient than the boiling on a heated wall.
Computed microtomography and numerical study of porous rock samples
NASA Astrophysics Data System (ADS)
Bielecki, J.; Jarzyna, J.; Bożek, S.; Lekki, J.; Stachura, Z.; Kwiatek, W. M.
2013-12-01
Measurement of physical properties of porous geological materials is a crucial issue in oil and gas recovery industry. A conventional experimental way to obtain information on porosity, pore size distribution, specific surface area and permeability are the intrusion porosimetry and permeameter measurement. However, in this approach Washburn's equation is usually used, thus approximation of cylindrical pore shapes is made. However, in recent times the computed microtomography (CMT) technique is more widely used in geoscience (Appoloni et al., 2007). We have already reported preliminary results of investigation of elemental content, microporosity, and specific surface area of porous rocks by means of the CMT technique based on a laboratory source (Bielecki et al., 2012). In this paper, results of complex study of porous rock samples with the use of X-ray CMT (laboratory-source-based facility and synchrotron radiation source) combined with permeability tensor computation by means of the Lattice Boltzmann Method (LBM) are presented. Moreover, the proton induced X-ray emission (PIXE) method was additionally used for elemental content determination of pores-filling substance.
Numerical study on dry deposition processes in canopy layer
NASA Astrophysics Data System (ADS)
Lei, Xiaoen; Chang, Julius S.
1992-12-01
A coupling model between the canopy layer(CL) and atmospheric boundary layer (ABL) for the study of dry deposition velocity is developed. The model consists of six parts: chemical species conservation equation including absorptive factor; the species uptake action including detailed vertical variation of absorptive element in CL; momentum exchange in CL which is represented by a first-order closure momentum equation with an additional larger-scale diffusive term; momentum exchange in ABL which is described by a complete set of the ABL turbulent statistic parameters; absorptivity (or solubility or reflection) at the surface including effects of the physical and chemical characters of the species, land type, seasonal and diurnal variations of the meteorological variables; and deposition velocity derived by distributions of the species with height in CL. Variational rules of the concentration and deposition velocity with both height and time are simulated with the model for both corn and forest canopies. Results predicted with the bulk deposition velocity derived in the paper consist well with experimental data.
Numerical studies of a plasma diode with external forcing
Rekaa, V. L.; Pecseli, H. L.; Trulsen, J. K.
2012-08-15
With reference to laboratory Q-machine studies we analyze the dynamics of a plasma diode under external forcing. Assuming a strong axial magnetic field, the problem is analyzed in one spatial dimension by a particle-in-cell code. The cathode is assumed to be operated in electron rich conditions, supplying an abundance of electrons. We compare different forcing schemes with the results obtained by solving the van der Pol equation. In one method of forcing we apply an oscillation in addition to the DC end plate bias and consider both amplitude and frequency variations. An alternative method of perturbation consists of modelling an absorbing grid at some internal position. Also in this case we can have a constant frequency with varying amplitude or alternatively an oscillation with chirped frequency but constant amplitude. We find that the overall features of the forced van der Pol equation are recovered, but the details in the plasma response need more attention to the harmonic responses, requiring extensions of the model equation. The analysis is extended by introducing collisional effects, where we emphasize charge exchange collisions of ions, since these processes usually have the largest cross sections and give significant modifications of the diode performance. In particular we find a reduction in oscillator frequency, although a linear scaling of the oscillation time with the system length remains also in this case.
Experimental and Numerical Study of Ammonium Perchlorate Counterflow Diffusion Flames
NASA Technical Reports Server (NTRS)
Smooke, M. D.; Yetter, R. A.; Parr, T. P.; Hanson-Parr, D. M.; Tanoff, M. A.
1999-01-01
Many solid rocket propellants are based on a composite mixture of ammonium perchlorate (AP) oxidizer and polymeric binder fuels. In these propellants, complex three-dimensional diffusion flame structures between the AP and binder decomposition products, dependent upon the length scales of the heterogeneous mixture, drive the combustion via heat transfer back to the surface. Changing the AP crystal size changes the burn rate of such propellants. Large AP crystals are governed by the cooler AP self-deflagration flame and burn slowly, while small AP crystals are governed more by the hot diffusion flame with the binder and burn faster. This allows control of composite propellant ballistic properties via particle size variation. Previous measurements on these diffusion flames in the planar two-dimensional sandwich configuration yielded insight into controlling flame structure, but there are several drawbacks that make comparison with modeling difficult. First, the flames are two-dimensional and this makes modeling much more complex computationally than with one-dimensional problems, such as RDX self- and laser-supported deflagration. In addition, little is known about the nature, concentration, and evolution rates of the gaseous chemical species produced by the various binders as they decompose. This makes comparison with models quite difficult. Alternatively, counterflow flames provide an excellent geometric configuration within which AP/binder diffusion flames can be studied both experimentally and computationally.
Numerical studies of a plasma diode with external forcing
NASA Astrophysics Data System (ADS)
Rekaa, V. L.; Pécseli, H. L.; Trulsen, J. K.
2012-08-01
With reference to laboratory Q-machine studies we analyze the dynamics of a plasma diode under external forcing. Assuming a strong axial magnetic field, the problem is analyzed in one spatial dimension by a particle-in-cell code. The cathode is assumed to be operated in electron rich conditions, supplying an abundance of electrons. We compare different forcing schemes with the results obtained by solving the van der Pol equation. In one method of forcing we apply an oscillation in addition to the DC end plate bias and consider both amplitude and frequency variations. An alternative method of perturbation consists of modelling an absorbing grid at some internal position. Also in this case we can have a constant frequency with varying amplitude or alternatively an oscillation with chirped frequency but constant amplitude. We find that the overall features of the forced van der Pol equation are recovered, but the details in the plasma response need more attention to the harmonic responses, requiring extensions of the model equation. The analysis is extended by introducing collisional effects, where we emphasize charge exchange collisions of ions, since these processes usually have the largest cross sections and give significant modifications of the diode performance. In particular we find a reduction in oscillator frequency, although a linear scaling of the oscillation time with the system length remains also in this case.
A numerical study of electromagnetic scattering from ocean like surfaces
NASA Technical Reports Server (NTRS)
Lentz, R. R.
1972-01-01
The integral equations describing electromagnetic scattering from one dimensional conducting surfaces are formulated and numerical results are presented. The results are compared with those obtained using approximate methods such as physical optics, geometrical optics, and perturbation theory. The integral equation solutions show that the surface radius of curvature must be greater than 2.5 wavelengths for either the physical optics or geometric optics to give satisfactory results. It has also been shown that perturbation theory agrees with the exact fields as long as the root mean square surface roughness is less than one-tenth of a wavelength.
Numerical aerodynamic simulation facility preliminary study, volume 1
NASA Technical Reports Server (NTRS)
1977-01-01
A technology forecast was established for the 1980-1985 time frame and the appropriateness of various logic and memory technologies for the design of the numerical aerodynamic simulation facility was assessed. Flow models and their characteristics were analyzed and matched against candidate processor architecture. Metrics were established for the total facility, and housing and support requirements of the facility were identified. An overview of the system is presented, with emphasis on the hardware of the Navier-Stokes solver, which is the key element of the system. Software elements of the system are also discussed.
Numerical study of flow around NACA0015 in ground effect
NASA Astrophysics Data System (ADS)
Malti, Khadidja; Hebow, Hanaa; Imine, Bachir
2016-03-01
The aim of this work is to present a numerical simulation of flow around a wing profile NACA0015 under the ground effect. CFD software has been used to determine the aerodynamic performance for different angles of incidence. The flow is considered two-dimensional and the adopted meshing considered the effects of the boundary layer. The Spalart-Almaras turbulence model was adopted for the investigation of complex flow around the profile. The results obtained by CFD were compared to those obtained by the literature.
Numerical study of a scramjet engine flow field
NASA Technical Reports Server (NTRS)
Drummond, J. P.; Weidner, E. H.
1981-01-01
A computer program has been developed to analyze the turbulent reacting flow field in a two-dimensional scramjet engine configuration. The program numerically solves the full two-dimensional Navier-Stokes and species equations in the engine inlet and combustor, allowing consideration of flow separation and possible inlet-combustor interactions. The current work represents an intermediate step towards development of a three-dimensional program to analyze actual scramjet engine flow fields. Results from the current program are presented that predict the flow field for two inlet-combustor configurations, and comparisons of the program with experiment are given to allow assessment of the modeling that is employed.
Numerical studies of ablation and ionization of railgun materials
Schnurr, N.M.; Kerrisk, J.F.
1985-01-01
The intense radiation from the arc in a railgun may cause vaporization and partial ionization of rail and insulator material. The mass of material added to the arc can have a significant adverse effect on projectile velocity. A numerical model has been developed to predict the change in mass of the arc as a function of several parameters. That model has been incorporated in the Los Alamos Railgun Estimator (LARGE) code and simulations have been run to assess the accuracy of the model. Analytical predictions were found to be in good agreement with experimental data for railgun tests run at Los Alamos. Ablation appears to have a significant effect on railgun performance.
Numerical studies of the radiant flash pyrolysis of cellulose
Kothari, V.; Antal, M.J. Jr.
1983-01-01
When biomass particles are heated very rapidly (temperatures greater than 1000 degrees/s) in an oxygen free environment, they undergo pyrolysis with the formation of little or no char. If concentrated solar energy is used to rapidly heat the particles their temperature may exceed that of the surrounding gaseous environment by several hundred degrees Celsius when pyrolysis occurs. This two temperature effect gives rise to the formation of high yields of syrups from the pyrolyzing biomass. Numerical exploration of the combined effects of heat and mass transfer on the radiative flash pyrolysis phenonmena are described in this paper. 12 references.
Numerical Study on Coalescence of Pre-Existing Flaw Pairs in Rock-Like Material
NASA Astrophysics Data System (ADS)
Li, Huan-Qiang; Wong, Louis Ngai Yuen
2014-11-01
The present numerical study, which is an extension of our previous numerical analysis on cracking processes of a single pre-existing flaw, focuses on the coalescence of two pre-existing parallel open flaws in rock subjected to a uniaxial compressive loading. To facilitate a systematic investigation, the arrangements of the flaw pair are classified into 11 categories. Simulations engaging AUTODYN are conducted on each category. The numerical results are compared with some published physical experimental test results. Eleven typical coalescence patterns are obtained, which are in good agreement with the experimental results, which include two coalescence patterns obtained in flaw pair arrangements (II) and (VIII″) not being reported in previous studies. The information gathered in the simulations helps identify the type (tensile/shear) of each crack segment involved in the coalescence. Most of the coalescence cracks initiate at or around the flaw tips, except those in flaw pair arrangements (II) and (IX') with a very short ligament length, in which the coalescence cracks initiate on the flaw surfaces away from the flaw tip regions. Based on the numerical simulation results, the properties of the 11 coalescence patterns are obtained. Except those in flaw pair arrangements (II) and (IX'), the other coalescence patterns can be interpreted with respect to the basic crack types—tensile wing crack, horsetail crack and anti-wing crack. In addition, based on the type of crack segments involved in coalescence, namely tensile and shear, the coalescence can be classified into T mode (tensile mode), S mode (shear mode) and TS mode (mixed tensile-shear mode).
Numerical study on the power extraction performance of a flapping foil with a flexible tail
NASA Astrophysics Data System (ADS)
Wu, J.; Shu, C.; Zhao, N.; Tian, F.-B.
2015-01-01
The numerical study on the power extraction performance of a flapping foil with a flexible tail is performed in this work. A NACA0015 airfoil is arranged in a two-dimensional laminar flow and imposed with a synchronous harmonic plunge and pitch rotary motion. A flat plate that is attached to the trailing edge of the foil is utilized to model a tail, and so they are viewed as a whole for the purpose of power extraction. In addition, the tail either is rigid or can deform due to the exerted hydrodynamic forces. To implement numerical simulations, an immersed boundary-lattice Boltzmann method is employed. At a Reynolds number of 1100 and the position of the pitching axis at third chord, the influences of the mass and flexibility of the tail as well as the frequency of motion on the power extraction are systematically examined. It is found that compared to the foil with a rigid tail, the efficiency of power extraction for the foil with a deformable tail can be improved. Based on the numerical analysis, it is indicated that the enhanced plunging component of the power extraction, which is caused by the increased lift force, directly contributes to the efficiency improvement. Since a flexible tail with medium and high masses is not beneficial to the efficiency improvement, a flexible tail with low mass together with high flexibility is recommended in the flapping foil based power extraction system.
Numerical study of the anode boundary layer in atmospheric pressure arc discharges
NASA Astrophysics Data System (ADS)
Semenov, I. L.; Krivtsun, I. V.; Reisgen, U.
2016-03-01
The anode boundary layer in atmospheric pressure arc discharges is studied numerically on the basis of the hydrodynamic (diffusion) equations for plasma components. The governing equations are formulated in a unified manner without the assumptions of thermal equilibrium, ionization equilibrium or quasi-neutrality. For comparison, a quasi-neutral model of the anode layer is also considered. The numerical computations are performed for an argon arc at typical values of the current density in anode layers (500-2000 A cm-2). The results of numerical modelling show that the common collisionless model of the sheath fails to describe the sheath region for the problem under consideration. For this reason, a detailed analysis of the anode sheath is performed using the results of unified modelling. In addition, the distributions of plasma parameters in the anode layer are analysed and the basic characteristics of the layer (anode voltage drop, sheath voltage drop, anode layer thickness, sheath thickness, heat flux to the anode) are calculated. Our results are found to be in good agreement with the existing theoretical predictions and experimental data. The dependence of the anode layer characteristics on the current density is also discussed.
Numerical study of the impact response of woodpecker's head
NASA Astrophysics Data System (ADS)
Zhu, Zhao Dan; Ma, Guo Jun; Wu, Cheng Wei; Chen, Zhen
2012-12-01
Woodpecker can beat trees 20-25 times per second and lasts for several seconds, with a 1200 g deceleration, but it appears that they never get brain concussion. How does the stress wave propagate from the beak tip to brain and how does a woodpecker protect itself from brain damage? In this paper, we establish a finite element model of typical woodpecker head based on its X-ray tomography images and conduct the numerical analysis of the impact response of the woodpecker's head by using a viscoelasticity material model. Especially, the woodpecker head response to an impact speed of 7 m/s is investigated to explore the stress concentration zone and how the stress wave propagates in its head. The numerical results show that the stress wave in the head propagates from the upper beak to back skull and is reduced by the specific structure of hyoid and viscoelasticity of biomaterials. The maximum stresses in skull and brain are both below the safe level. The stress in skull almost disappears before the next impact. The stress in brain lasts for a little longer but shows smaller value with little variation. The stress is impossible to accumulate in the limited pecking time, so the brain damage can be avoided.
Numerical and Experimental Studies on Impact Loaded Concrete Structures
Saarenheimo, Arja; Hakola, Ilkka; Karna, Tuomo; Hyvarinen, Juhani
2006-07-01
An experimental set-up has been constructed for medium scale impact tests. The main objective of this effort is to provide data for the calibration and verification of numerical models of a loading scenario where an aircraft impacts against a nuclear power plant. One goal is to develop and take in use numerical methods for predicting response of reinforced concrete structures to impacts of deformable projectiles that may contain combustible liquid ('fuel'). Loading, structural behaviour, like collapsing mechanism and the damage grade, will be predicted by simple analytical methods and using non-linear FE-method. In the so-called Riera method the behavior of the missile material is assumed to be rigid plastic or rigid visco-plastic. Using elastic plastic and elastic visco-plastic material models calculations are carried out by ABAQUS/Explicit finite element code, assuming axisymmetric deformation mode for the missile. With both methods, typically, the impact force time history, the velocity of the missile rear end and the missile shortening during the impact were recorded for comparisons. (authors)
Numerical Studies of Magnetization Reversal in Thin Annular Nanorings
NASA Astrophysics Data System (ADS)
Chaves-O'Flynn, Gabriel; Kent, Andrew; Stein, Daniel; Bedau, Daniel
2009-03-01
The rate of thermally activated magnetization reversal in thin ferromagnetic nanorings has been found analytically in a 1D model in which the demagnetization energy is approximated by a local surface term [1]. Numerical micromagnetic calculations confirm all aspects of the analytic model for narrow thin rings, such as permalloy rings of 200 nm mean radius, 40 nm width and 2 nm thickness [2]. However, the model breaks down in for extremely wide rings, when the ring width approaches its mean diameter. Here we present numerical micromagnetic results for the transition states between the clockwise and counterclockwise state in this limit. We describe how the two transition configurations of narrow rings cease to be saddles of the energy functional. Also, a new low energy metastable state is found to exist for a narrow range of fields. We discuss the results of applying the String Method [3] to determine the transition states and energy barriers between the lowest magnetization configurations of rings. [1] K. Martens, D.L. Stein, and A.D. Kent, PRB 73, 054413 (2006) [2] G. D. Chaves-O'Flynn, D.L. Stein, and A.D. Kent, arXiv:0811.0440 (2008) [3] W. E, W. Ren, E. Vanden-Eijnden, J. Chem. Phys 126, 164103 (2007)
A water soluble additive to suppress respirable dust from concrete-cutting chainsaws: a case study.
Summers, Michael P; Parmigiani, John P
2015-01-01
Respirable dust is of particular concern in the construction industry because it contains crystalline silica. Respirable forms of silica are a severe health threat because they heighten the risk of numerous respirable diseases. Concrete cutting, a common work practice in the construction industry, is a major contributor to dust generation. No studies have been found that focus on the dust suppression of concrete-cutting chainsaws, presumably because, during normal operation water is supplied continuously and copiously to the dust generation points. However, there is a desire to better understand dust creation at low water flow rates. In this case study, a water-soluble surfactant additive was used in the chainsaw's water supply. Cutting was performed on a free-standing concrete wall in a covered outdoor lab with a hand-held, gas-powered, concrete-cutting chainsaw. Air was sampled at the operator's lapel, and around the concrete wall to simulate nearby personnel. Two additive concentrations were tested (2.0% and 0.2%), across a range of fluid flow rates (0.38-3.8 Lpm [0.1-1.0 gpm] at 0.38 Lpm [0.1 gpm] increments). Results indicate that when a lower concentration of additive is used exposure levels increase. However, all exposure levels, once adjusted for 3 hours of continuous cutting in an 8-hour work shift, are below the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 5 mg/m(3). Estimates were made using trend lines to predict the fluid flow rates that would cause respirable dust exposure to exceed both the OSHA PEL and the American Conference of Governmental Industrial Hygienists (ACGIH®) threshold limit value (TLV). PMID:25714034
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.
Poroelastic toughening in polymer gels: A theoretical and numerical study
NASA Astrophysics Data System (ADS)
Noselli, Giovanni; Lucantonio, Alessandro; McMeeking, Robert M.; DeSimone, Antonio
2016-09-01
We explore the Mode I fracture toughness of a polymer gel containing a semi-infinite, growing crack. First, an expression is derived for the energy release rate within the linearized, small-strain setting. This expression reveals a crack tip velocity-independent toughening that stems from the poroelastic nature of polymer gels. Then, we establish a poroelastic cohesive zone model that allows us to describe the micromechanics of fracture in gels by identifying the role of solvent pressure in promoting poroelastic toughening. We evaluate the enhancement in the effective fracture toughness through asymptotic analysis. We confirm our theoretical findings by means of numerical simulations concerning the case of a steadily propagating crack. In broad terms, our results explain the role of poroelasticity and of the processes occurring in the fracturing region in promoting toughening of polymer gels.
Numerical Study of Unsteady Supercavitation Perturbed by a Pressure Wave
NASA Astrophysics Data System (ADS)
Zheng, J. G.; Khoo, B. C.
2016-06-01
The unsteady features of supercavitation disturbed by an introduced pressure wave are investigated numerically using a one-fluid cavitation model. The supercavitating flow is assumed to be the homogeneous mixture of liquid and vapour which are locally under both kinetic and thermodynamic equilibrium. The compressibility effects of liquid water are taken into account to model the propagation of pressure wave through flow and its interaction with supercavitation bubble. The interaction between supercavity enveloping an underwater flat-nose cylinder and pressure wave is simulated and the resulting unsteady behavior of supercavitation is illustrated. It is observed that the supercavity will become unstable under the impact of the pressure wave and may collapse locally, which depends on the strength of perturbation. The huge pressure surge accompanying the collapse of supercavitation may cause the material erosion, noise, vibration and efficiency loss of operating underwater devices.
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.
Statistical properties of a cloud ensemble - A numerical study
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo; Simpson, Joanne; Soong, Su-Tzai
1987-01-01
The statistical properties of cloud ensembles under a specified large-scale environment, such as mass flux by cloud drafts and vertical velocity as well as the condensation and evaporation associated with these cloud drafts, are examined using a three-dimensional numerical cloud ensemble model described by Soong and Ogura (1980) and Tao and Soong (1986). The cloud drafts are classified as active and inactive, and separate contributions to cloud statistics in areas of different cloud activity are then evaluated. The model results compare well with results obtained from aircraft measurements of a well-organized ITCZ rainband that occurred on August 12, 1974, during the Global Atmospheric Research Program's Atlantic Tropical Experiment.