## LS Dyna

#### viscous drag force into shear stress value

• Robert Owsiński
Subscriber

Hello!

I conducted aortic valve simulation (with similar settings to those available on the page https://www.dynaexamples.com/icfd/advanced-examples/heartvalve). I would like to get information about scalar shear stresses for the fluid domain (every element in the numerical mesh). I have not found such functionality in the program directly. One of the ideas that came to my mind was exporting viscous drag force using ICFD_DATABASE_DRAG_VOL:

To convert viscous drag force into shear stress value, I would also need information about the surface on which the indicated forces work. However, this may be problematic because of the remeshing.

Honestly, I have the impression that the whole process would be simpler if I used the following equations:

In this case, what is the possibility of obtaining velocity components/shear components (all unknows in above equations) for each time step?

2. The next task I have to face with is to get information about the time of the shear stress acting to the mesh elements. A tool similar to Particle Tracking/Particle Injection in Ansys Fluent would be perfect. I am not very familiar with the time integration formula used in the ICFD solver, so  that's why I have no idea how to get such information. Maybe the integration of the flow analysis  (ICFD) and discrete elements (DEM) would be a solution?

• Jim Day
Ansys Employee
Sorry for the long delay. I sought advice from the LS-DYNA ICFD development team. Their response was, "I believe that the best way to post-process these values is using Paraview. To output results in Paraview format for ICFD take a look at the *ICFD_CONTROL_OUTPUT keyword and set OUTL=7. Then in Paraview you could compute shear stresses using the following Pipeline to compute the derivative of the velocity field (which you will have to multiply by the viscosity using the calculator tool or the python calculator): (image) Once you compute the shear stresses you can inject particles into the fluid domain using the ParticleTracer filter. The shear stress can be mapped to the particles. I am not exactly sure what your goal is in item 2 but I believe that you want to integrate the shear stress values in time along a path. This should be possible in Paraview but I have not done it myself. I hope that this helps."
• Jim Day
Ansys Employee

Here's the image to accompany the previous reply.

• Laura Pałys
Subscriber

I can't open the picture above. Thank you for your answer. EnSight also has the ability to load d3plot files from LS-Dyna. With the calculator you can evaluate shear stress like in Parview. If I have any problems with obtaining these results, I will reply under this post.

• Jim Day
Ansys Employee

Here's the image that was previously unreadable.