Initial Volume Fraction Geometry question
Thiagarajan Ganesh
James Kennedy
Dear Thiagarajan,
Some notes of possible interest.
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1\ The best model for this problem would be 2D Axisymmetric ALE and likely a multistage solution using ALE Mapping 2D-to-2D.
2\ A fine mesh is needed in the explosive zone, 6.45mm dia, where a minimum of 10 cells across the RADIUS is recommended, e.g. 0.3725mm cells, then radial meshing can use geometric progression of element sizes.
3\ The Eulerian mesh in the axial direction, needs to extend both above (especially) and below the rock domain. This because the explosive top needs to vent into air/vacuum. Radially, the Eulerian mesh needs to extend well into the rock cylinder – how far depends on the deformation of the inner radius of the rock.
4\ I suggest modeling All the materials, except the rock, as ALE and coupling the rock to the outer ALE materials (void and copper – more?) using CLIS.
5\ The large Eulerian grid can be filled using *INITIAL_VOLUME_FRACTION_GEOMETRY
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Some additional (details) references related to above comments.
1\ 2D-to-3D ALE mapping
A 2D Multi-Material Arbitrary Lagrange Euler (MM-ALE) code was implemented in LS-DYNA. Like the 3D MM-ALE, already available, each 2D computational cycle is divided into two steps. First a multi-material version of the two-dimensional shell formulations solves the physical problem on quadrangle meshes during the Lagrangian step. The 2D shell formulations are plane strain and are-weighted axisymmetric. An advection cycle adapted to the 2D shell approaches follows to control the mesh motion. 2D ALE data of the last cycle can be mapped on 3D ALE mesh:
Aquelet, N., and Souli, M., "2D to 3D ALE Mapping", 10th International LS-DYNA Users Conference, Dearborn, Michigan, June, 2008.
http://www.dynalook.com/international-conf-2008/FluidStructure-3.pdf
Pure MMALE was tested on impacts and explosives studies from defense and spatial fields. A high velocity impact, a long rod penetration, and explosively formed projectile, a shaped charge jet and an air blast were modeled using 2D axisymmetric models and compared with experimental data:
Van Dorsselaer, N., and Lapoujade, V., "A Contribution to New ALE 2D Method Validation", 11th International LS-DYNA Users Conference, Dearborn, Michigan, June, 2010.
http://www.dynalook.com/international-conf-2010/Simulation-2-5.pdf
A new 2D ALE method with an associated Mapping became available with LS-DYNA v971 r4. Mapping enables the decomposition of a calculation in several steps; at the end of a 2D ALE calculation, data from the last cycle can be mapped into another 2D or 3D mesh. Several finite element studies of Air Blast were modeled to evaluate efficiency and potential of this LS-DYNA feature:
Lapoujade, V., Van Dorsselaer, N., Kevorkian, S., and Cheval, K., "A Study of Mapping Technique for Air Blast Modeling", 11th International LS-DYNA User's Conference, Dearborn, Michigan, June, 2010.
http://www.dynalook.com/international-conf-2010/BlastImpact-1-3.pdf
IA numerical simulation was conducted to model explosive detonation and blast wave propagation in the open air field. The mesh size and boundary conditions as well as size of air domain were the sensitive variables which may significantly affect the predicted pressure wave magnitude and rising time in blast simulations. The current approach focused on determining the optimal key parameters to predict the blast wave accurately. A 2D to 3D mapping was performed to save computational time:
Kalra, A., Zhu, F., Yang, K.H., and King, A.I., "Key parameters in Blast Modeling Using 2D to 3D ALE Mapping Technique", 13th International LS-DYNA Users Conference, Dearborn, Michigan, June, 2014.
When simulating structures subjected to the effects of blast loading, one might resort to three different methods of simulation. These methods are the empirical blast method, also known as *LOAD_BLAST_ENHANCED (LBE), the Arbitrary Lagrangian Eulerian (ALE) method, and a coupling method that allows the application of empirical blast loads (LBE) on air domain simulated with the ALE formulation. Furthermore, for the ALE method, both a mapping technique, that allows the mapping of data from 2D ALE simulations to 2D and 3D ALE meshes, and a complete 3D ALE simulation could be performed. In order to verify and compare the efficiency and accuracy of these air blast methods, an air blast loading on a reinforced concrete slab was modelled. Additionally, mesh convergence studies of 2D and 3D ALE simulations were performed:
Rebelo, H.B., and Cismasiu, C., "A Comparison between Three Air Blast Simulation Techniques in LS-DYNA", 11th European LS-DYNA Users Conference, Salzburg, Austria, May, 2017.
For further ALE help in 2D regarding the details, Nicolas Aquelet has generously shared the following.
Here are a few input decks and power point presentations, plus the KEYWORD description entries. The first input deck (slam.tar.gz) is an example of coupling. It is a wedge of beams entering water at a constant velocity.
input decks:
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/slam.tar.gz
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/explo.tar.gz
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/airblastreflection.tar.gz
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/underwaterexplo.bounmapping.tar.gz
power points (the 2008 LS-DYNA Conference presentation plus a set of class type like notes that are similar to the Conference presentation):
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/dyna08.zip
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/class09.zip
KEYWORD descriptions (most of the mapping applications only require the first 2 entries):
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/SECTION_ALE2D.doc
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/INITIAL_ALE_MAPPING.doc
ftp://ftp.lstc.com/outgoing/aquelet/ale2d/BOUNDARY_ALE_MAPPING.doc
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5\ INITIAL_VOLUME_FRACTION_GEOMETRY
The space debris is modeled as a simple sphere while the structure is modeled as a rectangular plate. The *INITIAL_VOLUME_FRACTION_GEOMETRY feature initially presents the background to be an ALE mesh; creates and specifies location, shape, and velocity of the simple sphere and rectangular plate in the background mesh; and relates each component to an *ALE_MULTI-MATERIAL_GROUP for tracking the interface.
*INITIAL_VOLUME_FRACTION_GEOMETRY
$# background ALE mesh - FMSID = 1 and background AMMGID - BAMMG=1
$# fmsid fmitdyp bammg trace
1 1 1 3
$# sphere container - CNTTYP = 6
$# cnttyp fillopt fammg vx vy vz
6 0 3 0.000 0.664000 0.000
$# x0 y0 z0 r0
0.000 3.300000 0.000 0.476500
$# rectangular box container - CNTTYP = 5
$# cnttyp fillopt fammg vx vy vz
5 0 2 0.000 0.000 0.000
$# x0 y0 z0 x1 y1 z1
2.500000 4.022500 0.000 0.000 3.800000 0.000
Aquelet, N., Seddon, C., Souli, M., and Moatamedi, M., "Initialisation of Volume Fraction in Fluid/Structure Interaction Problem", International Journal of Crash-worthiness, Vol. 10, Issue 3, pp. 237-247, March, 2005.
http://www.tandfonline.com/doi/abs/10.1533/ijcr.2005.0341
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Sincerely,
James M. Kennedy
KBS2 Inc.
October 31, 2024
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