I have just a general question how people approach the problem of spurious oscillations generated in dynamic analysis when using nonlinear soil constitutive models.
I understand sometimes numerical damping can be introduced into the original Newmark integration scheme. However, it seems that this is not always effective.
I also see that sometimes scientific papers simply do not show accelerations, and focus more on the primary unknowns, i.e. displacements.
The other option would be to introduce Rayleigh damping. Has anyone done it? How easy it is to be done for the models in umat format?
Thank you in advance for the tips and possibly discussion.
Rayleigh damping is used when the problem consists of very small plastic behavior in the low strain region. To implement this is through the momentum equilibrium equation instead of the constitutive models see Bandara, 2015.
I do not know if it is possible through the umat because the spurious oscillations are a problem associated with the numerical method, not with the constitutive model.
Thank you for your reply.
You are correct about the use of Rayleigh damping in the small strain region where the soil constitutive models often predict elastic behavior only.
I do not fully agree with the last statement. At least some of the soil constitutive models give oscillations (high frequency content) in the accelerations, and these oscillations remain insensitive to changes in the numerical method (i.e. insensitive to the introduced numerical damping in the Newmark method or HHT method in Abaqus).
Regarding the implementation of Rayleigh damping, could you be more specific about the reference Bandara, 2015? I mean, the title of the article, journal, etc. Unfortunately, I did not find it from the provided data. Thanks in advance for more details.