P-FSI with VWT

Snow85_20719

Hello,

Currently I am doing P-FSI with VWT 2017.2. For this purpose I have looked at the instructions on this topic by Ratzel and Nainani. I have two questions regarding the generation of stiffness information about eigenmodes.

1. Is it pointless to carry out the eigenvalue analysis for a single component without spatial fixation (with the consequence that one would have six rigid body modes)? Or can VWT via AccuSolve handle it?

2. Suppose I have an assembly that is made up of several components. Only one component from this assembly is to be exposed to a flow in the VWT. However, in order to map the correct deformation of this component due to the flow, one would have to know the stiffness information of the whole assembly (the components are mechanically coupled in the assembly).

Is it possible to generate the eigenmodes for the whole assembly and assign them to the one component (via OP2 in OptiStruct) that is considered in the VWT so that this one component combines the stiffness information of all components?

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ydigit

1. For PFSI you need input in OP2 format (from OptiStruct) with fixed nodes at one end.

2. Not an optiStruct Expert, but you should be able to specify in OP2 output that you want only modes for one component in that file.

acupro

1. AcuSolve itself also has a rigid body motion type - this really wouldn't be a candidate for P-FSI, where it's more targeted to deforming bodies. The rigid body motion in AcuSolve has the six possible degrees of freedom (3 translation, 3 rotation) plus linear and rotational damping, stiffness, initial displacement/rotation, initial velocity/angular velocity, external forces/moments, etc - a pretty complete rigid body motion calculator, where the fluid forces yield appropriate motion. What is the scenario/case you're trying to simulate?

2. If the base of that single fluid-exposed component also moves due to motions of other components for other reasons (like a rigid body motion), P-FSI is probably not the way to go. One would typically assume the base of the fluid-exposed component is fixed, with the modal analysis performed only for that component. You'll probably need to use DC-FSI for a more complex scenario

Snow85_20818

Hello,

First of all thanks for your answers and sorry for the late reply.

1. This question has no application purpose. It was only theoretical.

2. For reflection the assembly consists of three parts. One at the top, one in the middle and one at the bottom. They are all connected by connector elemens, bars or rigids. The part at the bottom is grounded/fixed (i.e. no rigid body moves). Only the part at the top shall exposed to a flow.
The deformation of the top part due to flow depends of course also on the two lower parts. So the eigenvalue anaylsis is done for the assembly.
Maybe, as @ydigit said, it is possible to modify the op2-file to gain the proper deformation behavior via eigen modes of the top part when it is exposed to flow.
But it probably makes no physical sense.