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A survey of numerical methods for shock physics applications

Description: Hydrocodes or more accurately, shock physics analysis packages, have been widely used in the US Department of Energy (DOE) laboratories and elsewhere around the world for over 30 years. Initial applications included weapons effects studies where the pressure levels were high enough to disregard the material strength, hence the term hydrocode. Over the last 30 years, Sandia has worked extensively to develop and apply advanced hydrocodes to armor/anti-armor interactions, warhead design, high explosive initiation, and nuclear weapon safety issues. The needs of the DOE have changed over the last 30 years, especially over the last decade. A much stronger emphasis is currently placed on the details of material deformation and high explosive initiation phenomena. The hydrocodes of 30 years ago have now evolved into sophisticated analysis tools that can replace testing in some situations and complement it in all situations. A brief history of the development of hydrocodes in the US will be given. The author also discusses and compares the four principal methods in use today for the solution of the conservation equations of mass, momentum, and energy for shock physics applications. The techniques discussed are the Eulerian methods currently employed by the Sandia multi-dimensional shock physics analysis package known as CTH; the element based Lagrangian method currently used by codes like DYNA; the element free Lagrangian method (also known as smooth particle hydrodynamics) used by codes like the Los Alamos code SPHINX; and the Arbitrary Lagrangian Eulerian methods used by codes like the Lawrence Livermore code CALE or the Sandia code ALEGRA.
Date: October 1, 1997
Creator: Hertel, E.S. Jr.
Partner: UNT Libraries Government Documents Department

Systems engineering programs for geologic nuclear waste disposal

Description: The design sequence and system programs presented begin with general approximate solutions that permit inexpensive analysis of a multitude of possible wastes, disposal media, and disposal process properties and configurations. It then continues through progressively more precise solutions as parts of the design become fixed, and ends with repository and waste form optimization studies. The programs cover both solid and gaseous waste forms. The analytical development, a program listing, a users guide, and examples are presented for each program. Sensitivity studies showing the effects of disposal media and waste form thermophysical properties and repository layouts are presented as examples.
Date: June 1, 1980
Creator: Klett, R. D.; Hertel, E. S., Jr. & Ellis, M. A.
Partner: UNT Libraries Government Documents Department

Comparison of analytic Whipple bumper shield ballistic limits with CTH simulations

Description: A series of CTH simulations were conducted to assess the feasibility of using the hydrodynamic code for debris cloud formation and to predict any damage due to the subsequent loading on rear structures. Six axisymmetric and one 3-dimensional simulations were conducted for spherical projectiles impacting Whipple bumper shields. The projectile diameters were chosen to correlate with two well known analytic expressions for the ballistic limit of a Whipple bumper shield. It has been demonstrated that CTH can be used to simulate the debris cloud formation, the propagation of the debris across a void region, and the secondary impact of the debris against a structure. In addition, the results from the CTH simulations were compared to the analytic estimates of the ballistic limit. At impact velocities of 10 km/s or less, the CTH predicted ballistic limit lays between the two analytic estimates. However, for impact velocities greater than 10 km/s, CTH simulations predicted a ballistic limit larger than both analytical estimates. The differences at high velocities are not well understood. Structural failure at late times due to the time integrated loading of a very diffuse debris cloud has not been considered in the CTH model. In addition, the analytic predictions are extrapolated from relatively low velocity data and the extrapolation technique may not be valid. The discrepancy between the two techniques should be investigated further.
Date: May 1, 1993
Creator: Hertel, E.S. Jr.
Partner: UNT Libraries Government Documents Department

Areal power density: A preliminary examination of underground heat transfer in a potential Yucca Mountain repository and recommendations for thermal design approaches; Yucca Mountain Site Characterization Project

Description: The design of the potential Yucca Mountain repository is subject to many thermal goals related to the compliance of the site with federal regulations. This report summarizes a series of sensitivity studies that determined the expected temperatures near the potential repository. These sensitivity studies were used to establish an efficient loading scheme for the spent fuel canisters and a maximum areal power density based strictly on thermal goals. Given the current knowledge of the site, a design-basis areal power density of 80 kW/acre can be justified based on thermal goals only. Further analyses to investigate the impacts of this design-basis APD on mechanical and operational aspects of the potential repository must be undertaken before a final decision is made.
Date: November 1, 1991
Creator: Hertel, E.S. Jr. & Ryder, E.E.
Partner: UNT Libraries Government Documents Department

Multi-processing CTH: Porting legacy FORTRAN code to MP hardware

Description: CTH is a family of codes developed at Sandia National Laboratories for use in modeling complex multi-dimensional, multi-material problems that are characterized by large deformations and/or strong shocks. A two-step, second-order accurate Eulerian solution algorithm is used to solve the mass, momentum, and energy conservation equations. CTH has historically been run on systems where the data are directly accessible to the cpu, such as workstations and vector supercomputers. Multiple cpus can be used if all data are accessible to all cpus. This is accomplished by placing compiler directives or subroutine calls within the source code. The CTH team has implemented this scheme for Cray shared memory machines under the Unicos operating system. This technique is effective, but difficult to port to other (similar) shared memory architectures because each vendor has a different format of directives or subroutine calls. A different model of high performance computing is one where many (> 1,000) cpus work on a portion of the entire problem and communicate by passing messages that contain boundary data. Most, if not all, codes that run effectively on parallel hardware were written with a parallel computing paradigm in mind. Modifying an existing code written for serial nodes poses a significantly different set of challenges that will be discussed. CTH, a legacy FORTRAN code, has been modified to allow for solutions on distributed memory parallel computers such as the IBM SP2, the Intel Paragon, Cray T3D, or a network of workstations. The message passing version of CTH will be discussed and example calculations will be presented along with performance data. Current timing studies indicate that CTH is 2--3 times faster than equivalent C++ code written specifically for parallel hardware. CTH on the Intel Paragon exhibits linear speed up with problems that are scaled (constant problem size per node) for the number ...
Date: December 31, 1996
Creator: Bell, R.L.; Elrick, M.G. & Hertel, E.S. Jr.
Partner: UNT Libraries Government Documents Department

The impact of tungsten long rod penetrators into water filled targets

Description: Twelve experiments were conducted to determine the effect of water filled targets on the penetration of tungsten long rods in terms of their residual mass and integrity. CTH hydrocode calculations were performed for each of the experiments to ensure that the erosion and breakup of the tungsten projectiles could be accurately reproduced. The CTH hydrocode predictions correlation well with the experimental results in most cases. Only 8% of the variance is unexplained. The slip interface between the rod and water was approximated in one of two ways: (1) using the CTH BLINT option in 2-D or (2) using a standard Eulerian mixed cells treatment. Results indicate that a 3-D BLINT algorithm is critical to predicting rod residual lengths. The authors were unable to reproduce rod fracture that occurred in every experiment where the water column exceeded 25 cm in length. The authors feel that this is due to a change in rod material properties during penetration, and continue to investigate the issue.
Date: February 1, 1998
Creator: Wilson, L.T.; Dickinson, D.L. & Hertel, E.S. Jr.
Partner: UNT Libraries Government Documents Department

Simulation of armor penetration by tungsten rods: ALEGRA validation report

Description: Results from simulations of the impact and penetration of tungsten alloy rods into thick rolled armor plates are presented. The calculations were performed with the CTH and ALEGRA computer codes using the DOE massively parallel TFLOPS computer co-developed by Sandia National Laboratory and Intel Corporation. Comparisons with experimental results are presented. Agreement of the two codes with each other and with the empirical results for penetration channel depth and radius is very close. Other shock physics and penetration features are also compared to simulation results.
Date: November 1, 1997
Creator: Carroll, D.E.; Hertel, E.S. Jr. & Trucano, T.G.
Partner: UNT Libraries Government Documents Department

Projectile shape influence on ballistic limit curves as determined by computational simulation

Description: A requirement for an effective debris shield is that it must protect a spacecraft from impacts by irregularly shaped particles. A series of numerical simulations has been performed using the multi-dimensional shock physics code CTH to numerically determine the ballistic limit curve for a Whipple bumper shield. Two different projectile shapes are considered for the numerical simulations, flat plates of varying diameters with a constant thickness and spheres of varying diameters. The critical diameter of ballistic limit was determined over a velocity range from 4 km/s to 15 km/s. We have found both experimentally and numerically that the particle shape has a significant effect on the debris cloud distribution, ballistic limit curve, and penetration capability.
Date: September 1, 1995
Creator: Hertel, E.S. Jr. & Chhabildas, L.C.
Partner: UNT Libraries Government Documents Department

A domain decomposition scheme for Eulerian shock physics codes

Description: A new algorithm which allows for complex domain decomposition in Eulerian codes was developed at Sandia National Laboratories. This new feature allows a user to customize the zoning for each portion of a calculation and to refine volumes of the computational space of particular interest This option is available in one, two, and three dimensions. The new technique will be described in detail and several examples of the effectiveness of this technique will also be discussed.
Date: August 1, 1994
Creator: Bell, R. L. & Hertel, E. S. Jr.
Partner: UNT Libraries Government Documents Department

High strain rate properties and constitutive modeling of glass

Description: This paper presents experimental data and computational modeling for a well-defined glass material. The experimental data cover a wide range of strains, strain rates, and pressures that are obtained from quasi-static compression and tension tests, split Hopkinson pressure bar compression tests, explosively driven flyer plate impact tests, and depth of penetration ballistic tests. The test data are used to obtain constitutive model constants for the improved Johnson-Holmquist (JH-2) brittle material model. The model and constants are then used to perform computations of the various tests.
Date: March 1, 1995
Creator: Holmquist, T.J.; Johnson, G.R.; Lopatin, C.M.; Grady, D.E. & Hertel, E.S. Jr.
Partner: UNT Libraries Government Documents Department

Simulation of orbital debris impacts on bumper shields

Description: A series of numerical simulations have been performed using CTH to predict secondary debris formation and rear structure damage for typical bumper shields under a variety of impact geometries The simulations span a range of velocities from {approximately}3 to 12 km/s and are compared to the experiment data for the lower velocities (3 to 7 km/s). For one velocity ({approximately}7 km/s), CTH was used to demonstrate the effects of bumper thickness on secondary debris formation and rear structure damage. CTH was also used to stimulate a 12 km/s impact of a sphere on a simple Whipple bumper shield and this result will be compared to analytic damage predictions at that velocity. It has been found that CTH accurately predicts secondary debris propagation and rear damage for velocities throughout the experimentally accessible range. The CTH damage predictions at 12 km/s result in a higher ballistic limit than would be predicted from the analytic techniques.
Date: December 31, 1992
Creator: Hertel, E. S. Jr.
Partner: UNT Libraries Government Documents Department

Recent progress in ALEGRA development and application to ballistic impacts

Description: ALEGRA is a multi-material, arbitrary-Lagrangian-Eulerian (ALE) code for solid dynamics being developed by the Computational Physics Research and Development Department at Sandia National Laboratories. It combines the features of modem Eulerian shock codes, such as CTH, with modem Lagrangian structural analysis codes. With the ALE algorithm , the mesh can be stationary (Eulerian) with the material flowing through the mesh, the mesh ran move with the material (Lagrangian) so there is no flow between elements, or the mesh motion can be entirely independent of the material motion (Arbitrary). All three mesh types can coexist in the same problem and any mesh may change its type during the calculation. In this paper we summarize several key capabilities that have recently been added to the code or are currently being implemented. As a demonstration of the capabilities of ALEGRA, we have applied it to the experimental data taken by Silsby.
Date: December 1, 1996
Creator: Summers, R.M.; Peery, J.S.; Wong, M.W.; Hertel, E.S. Jr.; Trucano, T.G. & Chhabildas, L.C.
Partner: UNT Libraries Government Documents Department