Learning Forum

[Abhemanyu Palaniswamy Chandrasekaran]

Hello,

I am setting up a FSI problem in LS-DYNA using the S-ALE structured mesh. I want to prefill the structured mesh with a fluid and then apply a rigid body force on a submerged structure. I dont want the submerged lagrangian structure to move out of the fluid mesh, so I use the *STRUCTURED_MESH_MOTION keycard and allow the S-ALE mesh to follow the lagrangian structure.

I would like to know if this mesh motion also imparts velocity and acceleration to the fluid filled inside at the start of simulation. If I want the mesh to move along with the lagrangian structure, but also keep the fluid domain(in which the lagrangian rigid body is submerged) fixed in space, what is the correct way to model it?

[Ian Do]

Hello Abhemanyu,

[Q1] I would like to know if this mesh motion also imparts velocity and acceleration to the fluid filled inside at the start of simulation

[A1] For ALE, the (a) mesh is a computational domain through which many ALE (b) mats can flow. The mesh defines the logical locations of the elms. Only the mat is subjected to F=m*a. So, NO, mesh motion is only logical movement of the nodal locations. It does not affect the ALE mats, nor does it inpose any forces on the ALE mats.

Sound to me like you already are doing the right thing:

• define the LAG part with motion
• define the FSI with the ALE multi-mat group (AMMG)
• move the LAG part
• let the ALE mesh move with the LAG part

The LAG part motion will impose force on the ALE mats via FSI mechanism. The mesh motion is only there to make sure that there is computational domain to receive the ALE mats as they flow.

Hope this is clear enough.

Ian Do, PhD

[Abhemanyu Palaniswamy Chandrasekaran]

Thank you Ian.