Hydrodynamic Program Research Articles

Solving the radiation diffusion and energy balance equations using pseudo-transient continuation

We develop a scheme for the system coupling the radiation diffusion and matter energy balance equations. The method is based on fully implicit, first-order, backward Euler differencing; Picard–Newton iterations solve the nonlinear system. We show that iterating on the radiation energy density and the emission source is more robust. Since the Picard–Newton scheme may not converge for all initial conditions and time steps, pseudo-transient continuation ( Ψtc) is introduced. The combined Ψtc–Picard–Newton scheme is analyzed. We derive conditions on the Ψtc parameter that guarantee physically meaningful iterates, e.g., positive energies. Successive Ψtc iterates are bounded and the radiation energy density and emission source tend to equilibrate. The scheme is incorporated into a multiply dimensioned, massively parallel, Eulerian, radiation–hydrodynamic computer program with automatic mesh refinement (AMR). Three examples are presented that exemplify the scheme's performance. (1) The Pomraning test problem that models radiation flow into cold matter. (2) A similar, but more realistic problem simulating the propagation of an ionization front into tenuous hydrogen gas with a Saha model for the equation-of-state. (3) A 2D axisymmetric ( R, Z) simulation with real materials featuring jetting, radiatively driven, interacting shocks.

Numerical Simulations of the Effect of Conical Dimension on the Hydrodynamic Behaviour in Spouted Beds

AbstractThe flow behaviours of gas‐solids were predicted by means of a hydrodynamic model of dense gas‐solid flow in spouted beds. Constitutive equations describing the particulate solids pressure and viscosity were implemented into a hydrodynamic simulation computer program. The effect of operating conditions (inclined angle and gas spouting velocity) on particle velocity and concentration in the spout, annulus and fountain regions were numerical studied. Both vertical and horizontal particle velocities increased with increasing spouting gas velocity. The diameter of the spout increases with decreasing the inclination angle. As the inclination angle is set greater than 60°, the spout cross‐section starts becoming bottlenecked, limiting the upwards flow of solids.

Numerical Simulations of Hydrodynamic Behaviour in Spouted Beds

A hydrodynamic model of dense gas-solid flow was developed to predict the flow behaviour in spouted beds. Constitutive equations describing the particulate solids pressure, viscosity and elasticity moduli were implemented into a hydrodynamic simulation computer program. The resulting hydrodynamic simulations agree well with experimental measurements of time-averaged particle-and-gas velocity profiles, as well as with experimental solids concentration distributions obtained from three different articles issued from the fluidization literature.

Investigation of the ocean acoustic signatures from strong explosions at a long distance in the ocean sound channel by computer simulation

The identification and location of ocean acoustic signatures are the principal objectives of a program to discourage clandestine testing of nuclear explosives. Difficulties arise primarily from variations in the water column. In turn, these variations affect acoustic propagation in the SOFAR channel. In this study, the path effects on the signals generated by strong explosions (1 and 10 kn) are investigated. The goal is to make a quantitative correlation between the initial source description and the final acoustical signatures received at a great distance under various conditions. The study is performed entirely by computer simulations applying two computer programs in succession. First, the explosions are simulated by a 2-D hydrodynamic computer program, CALE, which was originally developed to calculate astrophysical problems. The computed signals have reached more than 700 m deep approaching the SOFAR channel. At this point, the CALE output is linked to a hydro-acoustic computer program, the NPE code, by which wave propagation in the SOFAR channel is modeled. The NPE code was developed at the Naval Research Laboratory to study ocean acoustics. [Work supported by the U. S. Department of Energy under Contract No. W-7405-ENG-48.]

Bubble Expension and Collapse Near a Rigid Wall

A series of experiments was performed that covered the entire range of expansion and collapse of an underwater bubble in the vicinity of a rigid wall. These experiments have been successfully simulated using a new arbitrary Lagrangian Eulerian hydrodynamic computer program which can run numerical simulations of practical bubble problems in 10 to 20 minutes of CPU time on a CRAY-YMP at an overall rate of 80 MFLOPS.

Circumstellar ring formation in rapidly rotating protostars

view Abstract Citations (65) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Circumstellar Ring Formation in Rapidly Rotating Protostars Williams, Harold A. ; Tohline, Joel E. Abstract A three-dimensional hydrodynamic computer program is used to study rapidly rotating, self-gravitating polytropes with polytropic indices n = 0.8 and n = 1.8. The initial ratio of the rotational to gravitational potential energy is βi = 0.310 in both models. Both models, initially axisymmetric, are dynamically unstable toward the development of a nonaxisymmetric, two-armed spiral structure. Here the models are shown as they evolve to extremely nonlinear amplitudes: the end result in both cases is a type of fission. The models shed a fraction of their mass and angular momentum, producing a ring which surrounds a more centrally condensed object with βd= 0.27. The central object is a triaxial figure that is rotating about its shortest axis. The low-mass, roughly axisymmetric ring probably is capable of condensing into planets. Publication: The Astrophysical Journal Pub Date: November 1988 DOI: 10.1086/166849 Bibcode: 1988ApJ...334..449W Keywords: Protostars; Star Formation; Stellar Envelopes; Stellar Rotation; Angular Momentum; Computerized Simulation; Hydrodynamics; Molecular Clouds; Potential Energy; Astrophysics; HYDRODYNAMICS; PLANETS: GENERAL; STARS: CIRCUMSTELLAR SHELLS; STARS: ROTATION full text sources ADS |

Linear and nonlinear dynamic instability of rotating polytropes

A three-dimensional hydrodynamic computer program is used to study the growth of nonaxisymmetric structures in rapidly rotating, self-gravitating polytropes. Models with polytropic index n = 0.8, 1.0, 1.3, 1.5, and 1.8 are studied. The initially axisymmetric equilibria are constructed by the Ostriker-Mark self-consistent-field method. The nonaxisymmetric pattern that develops out of low-amplitude random noise is a two-armed spiral with a well-defined pattern speed and growth rate which closely match properties of the toroidal mode predicted from the linear, second-order tensor-virial equation. A Fourier analysis of each polytrope's azimuthal density distribution shows that, even in the linear amplitude regime, higher-order angular patterns also develop exponentially in time. The higher-order patterns ultimately move in synchronization with the broad two-armed spiral, creating a narrow two-armed spiral. As the polytropic index is decreased, a more open and centrally more barlike pattern develops.

The linear and nonlinear dynamic stability of rotating N = 3/2 polytropes

A three-dimensional hydrodynamic computer program has been used to study the growth of nonaxisymmetric structure in rapidly rotating, n = 3/2 polytropes whose initial axisymmetric equilibria were constructed with the Ostriker-Mark, self-consistent field method. Differentially rotating models were studied, whose initial ratios t of rotational to gravitational potential energy were t = 0.28, 0.30, 0.33, and 0.35. An open, two-armed, trailing spiral pattern, rather than a coherent bar mode, has been found to grow dynamically in all models with t at least 0.30. The results of the investigation support the reliability of both the tensor virial equation (TVE) analysis of such systems and the computer simulation itself. The 3D code can be used with confidence to study the dynamical growth of nonaxisymmetric structure into the nonlinear amplitude regime.

Analysis and Modeling of Large-Scale Steam Explosion Experiments

This paper describes current analysis and modeling results of large-scale steam explosion experiments. For the large-scale experiments, a transient one-dimensional explosion model was developed that can qualitatively predict the trends in the experimental data. The model employs a description of vapor film collapse and subsequent fuel fragmentation by thermal and mechanical means. In addition, a simple empirical explosion model was developed and incorporated into a two-dimensional hydrodynamic computer program. This combination can be used to investigate the two-dimensional characteristics of the propagation and expansion phases for large-scale explosions.

LOCA hydroloads calculations with multidimensional nonlinear fluid-structure interaction

A methodology for realistically analyzing three-dimensional fluid-structure interaction effects and the resulting hydrodynamic loads during the subcooled portion of a hypothetical loss of coolant accident (LOCA) in a pressurized water reactor (PWR) is discussed. The methodology uses a hydrodynamic computer program, STEALTH 3D, coupled with a structural response program, WHAMSE 3D, to calculate the dynamic interaction of fluid and structure during a reactor vessel blowdown. This coupled program is user oriented and highly versatile in modeling the various components in complex reactor systems. Assessment of the methodology is provided by STEALTH/WHAMSE 3D calculations of blowdown tests in the German Battelle-Frankfurt RS-16B facility (Test DWR5) and the HDR facility (Test V31.1). The calculations are described and the results compared with experimental data. Agreement between the calculational results and experimental data is extremely good.

Prediction of crack motion from detonation in brittle materials

A numerical model was formulated to predict propagation of a crack that is initiated and driven by an explosive. The model joins an energy release rate vs crack velocity fracture criteria with a two-dimensional finite difference computer program. The energy release rate for the material being fractured is computed with the J-Integral method. Crack velocity is determined from the energy release rate vs crack velocity curve of the fracturing material. Both the fracture criteria and the J-Integral computation were coded and adapted for use with an elastic-plastic hydrodynamic Lagrangian computer program. The accuracy of the code was verified by comparison of computed results with those obtained either theoretically or experimentally for three problems. In the first problem the stress intensity factor for a static edge crack in an infinite strip subjected to a uniform tensile stress perpendicular to the crack was calculated. The value computed with the model agreed to within 2% of the exact value. The second problem involved the computation of the stress intensity factor for a constant velocity central crack in a thick (plane strain) infinite plate. The computer generated values were found to converge to the theoretical ones as the finite difference mesh size was decreased. The final validation of the computer code model utilized results from dynamic photoelastic experiments involving an explosively loaded grooved borehole in a large plate. Comparison of crack length vs time data computed by the code with the experimental values showed good agreement.

Hydrodynamic calculations of surface response in the presence of laser-supported detonation waves

Numerical calculations of the formation, propagation, and effect on surface response of laser-supported detonation waves have been performed with a cylindrically symmetric two-dimensional Eulerian hydrodynamic computer program. These calculations demonstrate the validity and limits of applicability of blast wave models which have been used to describe such phenomena in the past and are consistent with a large body of experimental data. It is concluded that all these data may be understood within the framework of the model presented.

Sensitivity of Laser Absorption Wave Formation to Nonequilibrium and Transport Phenomena

Experiments have shown that laser absorption waves (LAW's) may be ignited in air from aerosols or solid surfaces at laser intensities below the clean air breakdown threshold. We present detailed numerical calculations of the formation and structure of such LA W's made with a two-temperature, Laprangian hydrodynamic computer program containing a fully coupled nonequilibrium breakdown chemistry, electron diffusion, and radiation transport. The detailed LAW structure is then interpreted to delineate the roles of the nonequilibrium, radiative, and transport processes in various regimes.