Input Files
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Introduction
The aim of this example is to introduce /INIVOL for initial volume fractions of different materials in multi-material ALE elements, /SURF/PLANE for infinite plane, and fluid structure interaction (FSI) with a Lagrange container.
Options and Keywords Used
Keyword documentation may be found in the reference guide available from
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Solid element (/BRICK)
Material law (/MAT/LAW51 (MULTIMAT) and /ALE/MAT)
ALE grid velocity (/ALE/GRID/DONEA)
MUSCL scheme for ALE LAW51 (/ALE/MUSCL)
Property (/PROP/TYPE14 (SOLID))
Load (/INIVEL)
Define initial volume (/INIVOL)
Infinite surface plane (/SURF/PLANE)
Fluid structure contact (/INTER/TYPE18)
Model Description
A hex mesh is created that fully encloses the structural container. The mesh size of the hex mesh should be ½ the size of the structural mesh. Ideally the hex mesh should also be ¼ of the structural mesh size in the direction of impact. To simplify this example, the hex mesh in this model does not adhere to the ¼ mesh size guideline.
A container partially filled with water is simulated being dropped from a height of 1 meter. The container is partially filled with water with the remainder filled with air.
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Boundary Conditions
Each outer side of the hex mesh is constrained to prevent displacement in the direction normal to the side. For example, the top and bottom of the hex mesh is constrained in the z translation DOF (Figure 2). The same is done for the other four sides. The velocity at impact of a drop from 1 meter would be 4429 mm/s. Since the simulation is started right before impact, an initial velocity of 4429 mm/s is applied to the container and the fluid hex mesh (Figure 2).
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Water is defined with the following characteristics:
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Coupled Euler_Lagrange (CEL) Interface
To define the contact between the fluid and the structure a visco-elastic penalty formulation /INTER/TYPE18 interface is defined as:
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Gap is the Interface gap. The recommended value is 1.5 times fluid element size along the normal direction to contact.
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Where:
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For this example:
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Simulation Iterations and Modeling
Fill Container with /INIVOL.
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You can contour the model and use section cut to see inside, or use iso-surface, as shown in Figure 4.
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/ALE/MUSCL - Anti-diffusive Technique
/ALE/MUSCL allowing for a better localization of the interface between fluids, and much less numerical diffusion. In this example, use default for Beta.
/ALE/GRID/DONEA - ALE Grid Velocity
This activates the J. Donea Grid Formulation, where the velocity of a given grid node depends on velocity and displacements of neighboring grid nodes.
Engine Control
It is recommended to use time step scale factor 0.5 for ALE in /DT/BRICK in order to keep computation stable, and use fac=1.0 in /UPWM/SUPG. This option provides better velocity field in Cartesian grids when ALE material velocity is not normal to brick faces.
Results
To see the movement of the water in the container, and iso-surface plot of results type "density” can be done. If the simple averaging method is used in HyperView, the results will look smoother.
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