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Hello, the developers.
During the postprocessing in paraview, we can directly get the WSS ,average WSS, OSI. now i want to get the WSS spatial gradient, .the question is when i define it in the 3D simulation, which direction i should follow? how to define it,thanks so much for your help.

Hi Jianfei,

Thank you for your question! Since WSS is a vector quantity, taking the derivative will create a 3x3 matrix. This can be done with the "Gradients" filter in Paraview (click FIlters and Search by Name). The components of this matrix will be the (x,y,z) derivatives of the (x,y,z) components of the WSS. You can then compute invariants of this matrix to get scalar indices for the wss gradient. Another option is to first compute the magnitude of the wall shear stress (using the Calculator filter in Paraview). This will create a scalar field which represents the magnitude of the WSS. You can then take the gradient of this scalar field to get a vector (x,y,z) representing the spatial gradient of the magnitude of WSS. You can then take the magnitude of this vector to get a scalar index for the intensity for which the WSS magnitude is changing with space.

Whichever option you choose from above, we recommend using the .vtp version of the result (NOT the .vtu). Since the WSS is only defined on the walls, you want to PolyData .vtp version of the results, which only computes results on the exterior surface of your model. Using the volumetric .vtu version (which assigns 0 WSS on all interior nodes) will mess up the gradient computation.

Hope that help! Let us know if you have anymore questions.