Question to the file "iner3d.f"

[sicheng6699]

Hello dear FEAP Admin,

I have a question on the damping effect for nonlinear dynamic problems (finite deformation).

As the user Manuel said, the damping is not jet implemented for finite deformation, but only for small deformation.
And the file "inmate.f" tells that the material parameter d(77) is for the mass proportional factor for damping, through "DAMP RAYL a0 a1" in the material input part.
Finally in the file "iner3d.f" d(77) is used somehow. This file is called in the file "fld3d1.f" which is instead for finite deformation.

Does it work somehow as consistent damping? If yes, is it also possible to include d(78) for the stiffness part?

Thank you very much for your kind reply!

Best
sicheng6699

[Prof. R.L. Taylor]

The damping is not implemented in any of the finite deformation solid elements.  While the d(77) does appear in the inter3d.f file, it does not appear in any of the residuals, thus, it would not converge properly to a damped solution.  The inertia computations were moved from solid elements when triangles and tetrahedra were added since the inertia requires higher order quadrature than what can be done for the residual/stiffness terms.  In the process the d(77) was included, however, this is still useful only for linear elements.

[sicheng6699]

Thank your Prof. Taylor,

Now it is clear to me that this kind of combination is not recommended.
As you said, I noticed also that if the terms "FINITE" and "DAMP" were used at the same time, the convergence was extremely slow.
The reason why I want to risk and try is that without any damping,  the nonlinear dynamic problem will never converge, in my opinion due to the approximation in Newmark method, specifically speaking in my case after around 200-300 steps.

My further question is whether there is a way to include the consistent damping matrix? like the results from "OUTP, DAMP" command?
What I know is that, the stiffness matrix and the residual force have to be modified. It will take me several days to verified it, but the main problem is that I am not very sure to modify the original code. Can you give me any advise regarding the damping terms, like the mentioned consistent one?

Thank you again for your time.
sicheng6699