INIVOL and Fluid Structure Interaction (Drop Container)

Input Files

Model Files (1.6 MB)

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

OpenRadioss User Documentation

• Solid element (/BRICK)

• Material law /MAT/LAW51 (MULTIMAT)

• Material law /MAT/LAW6

• Property (/PROP/TYPE14 (SOLID)) with ALE property formulation ‘Iale = 1’

• Load (/INIVEL)

• Define initial volume (/INIVOL)

• Infinite surface plane (/SURF/PLANE)

• Fluid structure contact (/INTER/TYPE18)

Model Description

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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Figure 1. Problem 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.

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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Figure 2. Boundary Condition of Container in z-direction

Units: mm, s, Mg, N, MPa

In one /MAT/LAW51 card, three different phases can be defined. The two phases are: Air and Water

Air is defined with the following characteristics using sub-material /MAT/LAW6:

Water is defined with the following characteristics using sub-material /MAT/LAW6:

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:

• Main is the Lagrange structure

• Secondary is the ALE fluid nodes

Gap is the Interface gap. The recommended value is 1.5 times fluid element size along the normal direction to contact.

Where:

For this example:

Simulation Iterations and Modeling

Fill Container with /INIVOL.

With /INIVOL, the water line can be defined in this part.

part_ID = Part ID of ALE hex mesh

surf_IDn = 3-nodes or 4-nodes surfaces only or /SURF/PLANE

ALE_PHASE = Phase of the multi-material ALE material

FILL_OPT = 0 or 1

=0: filling the side which along normal direction

=1: filling the side which against normal direction

ICUMU = if remove the previous material and then fill new material or mixed.

FILL_RATIO = ratio of filling material

/INIVOL uses successive filling actions of the initial background multi-material ALE mesh, to get the final configuration of the initial volume fractions (three containers and three ALE phases). Initially the volume is filled by the first material defined in the /MAT/LAW51 field. In this case, the first material is air, so the entire hex mesh is first filled with air. Next, a surface is defined from the container part ID.

Since the surface normal of container part point outside, use FILL_OPT = 1 to fill the water (phase 3) inside the container (filling the side which against surface normal direction).

Now, ALE mesh is filled with ALE material 1 (air) from /MAT/LAW51 on the outside of the container and material 3 (water) inside the container. Lastly, define a surface plane, /SURF/PLANE to define the fill height. The normal of this plane points upward, use FILL_OPT = 0 to fill the air (phase 2) above the plane (filling the side along normal direction).

To check the initial fill, the following animation or h3d options can be used in the Engine file.

• /ANIM/ELEM/DENSITY

• /ANIM/ELEM/VFRAC

or

• /H3D/ELEM/DENS

• /H3D/ELEM/VFRAC

You can contour the model and use section cut to see inside, or use iso-surface, as shown in Figure 5.

Engine Control

It is recommended to use time step scale factor 0.5 for ALE in /DT/BRICK in order to keep computation stable.

Results

To see the movement of the water in the container, an iso-surface plot of results type "density” can be done. If the simple averaging method is used in HyperView, the results will look smoother.

Also notice that water is starting to splash up the sides of the container at the end of the simulation.