Discrepancy in Expected Deformation Results with Given Units

[antonagafonov]

Hello,

I'm encountering an issue with the units in my simulation and could use some assistance in pinpointing the problem. My 3D mesh is scaled in meters, and based on this, I'm using Newtons (N) for forces and Pascals (Pa) for the Young's modulus. The simulation aims to replicate deformation forces on human soft tissue, specifically in the arm region. The expected Young's modulus range for this tissue is between 0.1 to 1 GPa.

However, to achieve deformations within a realistic range (approximately 0.5-3 mm), I find myself having to set the Young's modulus $E$ to an unusually low value of 2 $Pa$, while the total force is set to 1000 $N$. These values seem inconsistent with standard expectations.

Could there be an error in my understanding of the units or in the simulation setup? Any insights or suggestions would be greatly appreciated.

Thank you.

[zfergus]

How are you applying the forces? Are they Neumann boundary conditions? If so, the units of NBCs are not force but force over area (i.e., pressure).

[antonagafonov]

Hi @zfergus ,
Thanks for your reply.
As I see here, it is Force over Face in [N], which is Force in [N] and not Pressure in [Pa].
https://polyfem.github.io/tutorials/ipc_quick_start_guide/ipc_quick_start_guide/?h=neuman#neumann
Also, if I apply pressure over a triangle surface, should it be a scalar?
I am confused...
Can you please explain?
Appreciate your help,
Thanks