RD-E: 5000 INIVOL and Fluid Structure Interaction (Drop Container)

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.

Figure 1. Problem Description

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).

Figure 2. Boundary Condition of Container in z-direction

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

EoS_Options_input (IDEAL_GAS)

Value

Reference density

1.22e-12

Initial density

1.22e-12

Heat Capacity Ration (Gamma)

1.4

Initial Pressure (P0)

0.1

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

EoS_Options_Input (LINEAR)

Value

Initial density

1e-9

Initial Pressure (P0)

0.1013

Bulk Modulus (B)

2089.0

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

The contact stiffness is calculated as:(1) $$Stfval=\frac{\rho \cdot v^2\cdot S_{el}}{Gap}$$

Where,

$\rho$

The (highest) fluid density

$\upsilon$

Velocity.

• For incompressible models (ditching, sloshing, and so on), use the velocity of the event.
• For compressible but not supersonic, use the speed of the sound in the material.
• Compressible and transonic (Mach 0.8 to 1.0), replace the term $${\nu }^2$$ with $$v\cdot c$$
  Where,

  $\upsilon$

  Speed of the sound in the material

  $$c$$

  Speed of sound in air

• Compressible and supersonic, use the velocity of the event
• For an explosion, use the Chapman Jouguet velocity

$$S_{el}$$

Surface area of the Lagrangian elements

$$Gap$$

Interface gap, as defined above

For this example:(2) $$Gap=1.5fluid\begin{array}{c}\end{array}element\begin{array}{c}\end{array}size=1.5\times 2.5=3.75[\mathrm{mm}]$$ (3) $$Stfval=\frac{\rho \cdot v^2\cdot S_{el}}{Gap}=\frac{1\times {10}^{-9}\times {4429}^2\times \left(5\times 5\right)}{3.75}=0.131$$

/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.

/SURF/PART/998
Vessel_Surf_Part
      85

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).

/INIVOL/86/10003507
INIVOL                 
#  Surf_ID ALE_PHASE  FILL_OPT     ICUMU          FILL_RATIO
       998         2         1         0                 0.0

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).

#  Surf_ID ALE_PHASE  FILL_OPT     ICUMU          FILL_RATIO
      9999         1         0         0                 0.0

Figure 4.

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

• /H3D/ELEM/DENS
• /H3DE/ELEM/VFRAC

Water is starting to splash up the sides of the container at the end of the simulation.

Figure 6.