## Fluids

#### Multi-strip numerical modelling of a riser

• dan_123
Subscriber

Hi,

I am trying to simulate the response of a long vertical tube subjected to a uniform flow using multi-strip modelling. Basically, my idea is to perform multiple 2D analysis (strips) along the span of the tube. Each strip will give me a local force on the cylinder which, added together, will give the total force and, solving the equation of motion, the complete response of the riser can be estimated. An example of this method can be found here, for example:

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1628976

or here:

https://www.tandfonline.com/doi/full/10.1080/17445302.2018.1438067

Currently, I can do a 2D vortex-induced vibration modelling of a rigid cylinder subjected to a uniform flow using Fluent and a UDF I wrote. The problem I have is how to implement the multi-strip method in ANSYS. My idea is to model the 3D structure and somehow connect the multiple 2D flow models (strips) along the span of the cylinder. Can anyone give me some guidelines as to how to model this?

Thank you.

Daniel

• Rob
Ansys Employee

Not an easy problem, and the model can get very complicated very quickly.

You currently have a 2d force on a section. In a Mechanical model of the whole riser what happens if you apply that force over the whole length of the unit (I assume you've fixed one/both ends or have some motion limit on the bridge)?

• pengxu
Subscriber

Dear all,

I also want to run this multi-strip modeling using 2-D CFD  on planes spaced evenly along the riser structure. My question is how to implement this method in ANSYS?

I found a brief introduction to it using ANSYS on page 25:

https://support.ansys.com/staticassets/ANSYS%20UK/staticassets/04.%20Offshore%20Marine%20Viscous%20CFD%20Phil%20Stopford.pdf

Are there any detailed guidelines or manuals on it?

Thank you.

Pengxu

• Rob
Ansys Employee

There won't be any additional documentation, and I suspect it's a case of running many CFD models and then transferring whatever data is needed (force I suspect) back to the relevant positions of the riser.