How can I create an absorbing boundary condition for waves in soil with dashpots and springs?
I have created springs and dashpots at the bottom of my soil model, but the analysis aborts because the elements distorted excessively. I don't know what I am doing wrong, so can anybody help me?
I am very thankful for every answer.
Absorbing bc: (a) lumped damping (dashpots) / with material damping (Rayleigh, structural, viscous.).
please go through http://www.simulia.com/forms/world/pdf2006/Nielsen.pdf
http://www.agu.org/WPS/ChineseJGeo/47/47.01/articles/xf.pdf
http://gji.oxfordjournals.org/content/154/1/146.full.pdf
https://www.researchgate.net/post/How_can_i_define_Absorbing_boundary_in_ABAQUS_EXPLICIT
Abdelmonaam Sassi,
I work with Abaqus CAE and I used a linear elastic soil with E=72MPa, rho=1800 kg/m3 and poisson's ratio=0.25. At the top of my soil I applied a dynamic load and I am using Abaqus explicit. For the dashpot coefficient I used c=rho*wavespeed*A=3600 and for the spring stiffness I used the E-Modul.
Thank you for your help
For absorbing boundaries in elastic wave propagation dash-pots seems OK. However the value of 3600 seems not right. What is the area covered by dash-pots? Did you consider Speed of the wave in 2D.
Apart from the above check the following
a). Reducing the Time step
b). refining the element size
c) . Boundaries should be sufficiently away from the loading region
d). If damping applied better start from zero damping and start increase to observe how it effect the solution.
Ravi shankar Badry,
I considered the wavespeed, for shear waves it is 115,5 m/s and for the compression waves it is 200 m/s. The dashpots should cover a soil layer with the height of 10m and with the same material constants as the soil above.
Thank you for the helpful hints, I will try that.
Mi Mss Delia,
As you said, that's the correct form of apply the viscous normal and shear traction of the dashpots. As for the springs, it depens on how your sortware resolve the equation of motion. For example, i work with FLAC and it applys an unbalanced force that is expressed in function of the material density, wave velocity in media, grid point veloctiy in the grid (or mesh), area of infuence and a force that comes from the elements in the free fiel boundary.
For your best understandings, you can check the basic article that is:
Lysmer, J., and R. L. Kuhlemeyer. “Finite Dynamic Model for Infinite Media,” J. Eng. Mech.,95(EM4), 859-877 (1969).
And Maybe the Dynamic Manual of FLAC3D, it has very good and clear concepts. If can't find it contact me.
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