# Dynamically adding shapes to existing geometry during fluid-structure interaction?

Member

Hello!

This might be an unusual question; I haven't found anything like this in the ANSYS archives, so bear with me,

I'm on ANSYS 2020R1, student edition.

Let's say I have a block suspended upright in a static pool of liquid, and I want to see how the fluid moves starting from rest as I move my block straight up and out of the pool.

Let's pretend my block has a 10x10 mm square at its bottom face, and starts fully submerged. But, let's say my block is changing shape as I move! Now, let's pretend that at the bottom of the submerged face of the block, a 1 mm diameter mini cylinder is tacked onto the end of my original block, and a new 1 mm diameter mini cylinder continues to be tacked onto the end at some periodic time interval.

I can imagine the UDF's required to make the block move, and I might have to use VOF methods for the fluid motion (which I'm still looking into), but I haven't figured out a way to 'add new shapes to existing geometry' with ANSYS. Any ideas from the more knowledgeable crowd?

Thank you!

edited May 27

As far as I understand, you should be able to estimate the deformation (if any) and modify the shape of your block based on these deformations using the FSI analysis. However, you cannot dynamically change the shape from a rectangular block to a circular cylinder in the middle of a simulation. You might have to start with a new geometry from scratch.

Is there a reason why you are asking this question? Is this part of your physics where the solid structure changes shape in the middle of your simulation? Please elaborate and we might be able to find you an alternate approach (perhaps).

Thanks.

Karthik

• Member
edited May 28

Hi Karthik,

I acknowledge that this is an unusual question, but I promise that shape-changing is a relevant effect to my problem.

However, a point of clarification - the shape of the block does not spontaneously change from rectangular to cylindrical, but rather you can imagine that new cylindrical geometries are being added to the face of the existing geometry.

The context: I am attempting to simulate a type of 3D printing called photopolymerization printing, where light is used to convert liquid prepolymer into solid polymer.

Imagine I have a build platform moving through a volume of liquid, while simultaneously new geometry is being formed on top of that platform as it moves through the liquid. I am interested in investigating how the flow of liquid changes around this build platform as it effectively 'changes shape' with the addition of these new geometries.

I hope that clarifies the situation; please let me know if this is possible at all, or if I will have to turn to other FEA methods.

Thank you!

• Forum Coordinator
edited May 29

Thanks for the additional details. This type of analysis can be done entirely in Fluent. I would recommend starting with a single fluid and then adding VOF once the single fluid is running. The growing cylinder can be modelled by defining the deformation with a UDF and using Dynamic Meshing to smooth and remesh the mesh to accommodate the new shape. If you didn't want to use a UDF, you could define the deformation in Ansys Mechanical, then use a 1way transfer with System Coupling to send the deformation from Mechanical to Fluent.

Steve