Overview

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Aim of the Problem

The fluid flow is studied during the fuel tank overturning. This example uses the ALE (Arbitrary Lagrangian Eulerian) formulation and the hydrodynamic bi-material law (/MAT/LAW37) to simulate interaction between water and air. The tank container is presumed without deformation and it will not be modeled.

Physical Problem Description

A rectangular tank is partially filled with water, the remainder being supplemented by air. The tank turns once around itself on the Y-axis. The overturning is achieved by defining a gravity field in the X direction, which is parallel to the liquid gas interface. All gravity is applied in other directions. The initial distribution pressure is already known and supposed homogeneous. The tank dimensions are 460 mm x 300 mm x 10 mm.

Fig 7: Problem description.

The example deals with two loading cases: an instantaneous rotation of the fuel tank by 90 degrees (gravity function 1) and a progressive rotation (gravity function 2).

The main material properties for the ALE bi-phase air-water are:

Analysis, Assumptions and Modeling Description

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Modeling Methodology

The bi-material air-water is described in the hydrodynamic material law (/MAT/LAW37). See previous section for information about this law, including full input data.

This loading case does not require a tank container mesh and the model, air and water are only comprised of the brick element using an ALE formulation.

Fig 8: Air and water mesh (ALE bricks).

Using the ALE formulation, brick mesh is only deformed by the tank deformation, the water flowing through the mesh. The Lagrangian shell nodes still coincide with the material points, while the elements are deformed with the material: this is the Lagrangian mesh. For the ALE mesh, nodes on boundaries are fixed to remain on the border, while the interior nodes are moved.

RADIOSS Options Used

Regarding the ALE boundary conditions (/ALE/BCS), constraints are applied on:

All nodes inside the border have grid and material velocities fixed in the Z direction; the nodes on the left and right sides have a material velocity fixed in the X and Z directions, while the nodes on the high and low sides have a material velocity fixed in the Y and Z directions. The grid velocity is fully fixed on the border, just as the material velocity is fixed on the corners.

A function defines gravity acceleration in the X direction compared with time in order to simulate the rotation effect. Gravity is activated by /GRAV. Two cases are studied depending on the acceleration function selected:

 

Gravity is considered for all nodes.

Simulation Results and Conclusions

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Conclusion

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This example studied hydrodynamic bi-material using Law 37 in RADIOSS, using ALE and Eulerian formulations. The application of boundary conditions in ALE formations and handling the fluid-structure interaction were discussed. Furthermore, the results obtained correctly represent the physical problem.