Mapping forces defined at coarse mesh to fine structural mesh

[hnng]

Hi,

I am trying to setup an analysis where the velocities have been recorded in a fluid medium at particular locations. Now I have to use Morison equation to calculate the force at those particular locations.

The structure under analysis is to be applied with forces generated by the Morison equation. As mentioned earlier these records are available at few locations or in other words these forces are available over a coarse mesh. The flexible structure is discretized using a much finer mesh. When the structure vibrates the forces have to be mapped appropriately to the structure's node location at the current time step.

Is there a feature in ANSYS which can help me achieve this. I know there are mesh mapping algorithm when present in ANSYS when a Fluid Structure Interaction problem is solved. But in my case the fluid side has already been replaced with velocity or forces.

I appreciate you help.

HN

 

[hnng]

Please let me know if I am thinking in the right direction. I can define the locations at which velocity was recorded as keypoints. Provide I can calculate appropriate forces at these points using Morison equation, I can easily transfer these loads to structural node locations.

Force Calculation:
The place I am getting stuck now is calculation of force using Morison equation (

http://en.wikipedia.org/wiki/Morison_equation).

This equation depends on the relative velocity between fluid and structure. So in my analysis I have to first calculate the structural velocity at keypoints and then use Morison's formula to get the force at keypoints. I will appreciate if anyone can comment if I am thinking in the right direction.

HN

 

[flash3780]

The CBDOF command is used for mapping displacements from a course model onto a submodel. Is that what you're trying to do?

//signed//
Christopher K. Hubley
Mechanical Engineer
Sunpower Incorporated
Athens, Ohio

 

[hnng]

Hi flash3780, thanks for your reply. Yes this is the direction I am looking for. However if I understood the CBDOF command properly. It interpolates the output of the ANSYS analysis and and provides solution at specified node location.

In my case I have not started the analysis yet. I have fluid velocity records at some locations (may not coincide with any node on the structure). Now I want to calculate force using Morison equation (

http://tiny.cc/l6zxi)

that uses relative velocity between fluid and structural velocity.

My first question is:
How do I define such kind of non-linear forcing function (

http://tiny.cc/l6zxi)?

My second question is:
Does CBDOF will map my input velocities at some arbitrary locations to node locations?


I apologize if I was not clear before.

HN

 

[flash3780]

HN,
The CBDOF command merely maps displacement results onto the cut boundaries of your submodel. Other boundary conditions (temperatures, velocities, etc.) will have to be carefully applied to both models in an identical fashion (if they are, in fact, important in the sub-model).

I don't have experience with the Morrison equation, but it looks like you're doing a harmonic response analysis first, and then mapping the results onto a smaller submodel (in an area of interest), is that correct? It's hard for me to make suggestions about how to apply the actual loads without seeing a picture or two.

I believe that you'll want to solve your larger dynamic model, and then map the cut-boundary displacement results at the phase angle you're interested in onto the (static?) submodel.

If temperatures are important, you'll also want to interpolate your thermal results onto the submodel with the BFINT command and perform a steady-state conduction run before running solving the structural submodel.

//signed//
Christopher K. Hubley
Mechanical Engineer
Sunpower Incorporated
Athens, Ohio