Hello,
Here I have a question:
I performed a static calculation in Abaqus/Implicit and then I imported the results to Abaqus/Explicit to do geo-balance and continue for a dynamic calculation. I buried an anchor in the ground and applied acceleration at the bottom of the soil to simulate an earthquake. When I observed the acceleration history at a point on my anchor, I noticed that there is a very large acceleration (around 200-500 m/sec^2) at time t=0 seconds, and the acceleration throughout the earthquake simulation seems highly unrealistic. I'm pretty sure my units are in meters. Furthermore,I monitor the soil acceleration history near the anchor, I find that the soil's acceleration is normal.
I can't understand this phenomenon. Could anyone gives me an explanation?
Thank you very much.
Best regards,
Yang Cheng-Hua, the large acceleration at t=0 seconds is likely due to the initial displacements that were imported from the static analysis. When you perform a dynamic analysis, the solver needs to calculate the initial velocity and acceleration of the system. These initial values are calculated from the equilibrium equation of motion, which is:
Mu + Cu + Ku = P(t)
where:
- M is the mass matrix
- C is the damping matrix
- K is the stiffness matrix
P(t) is the applied load. At t=0, the damping matrix is zero, so the equation becomes:
Mu + Ku = P(t)
If the initial displacements are nonzero, then the mass matrix will be nonzero, and the system will have an initial acceleration. This is the reason why you are seeing a large acceleration at t=0 seconds.
To avoid this problem, you can try the following:
- Set the initial displacements to zero in the static analysis.
- Use a different method to transfer the results from the static analysis to the dynamic analysis. For example, you could use the restart file instead of the .odb file.
- Use a different boundary condition in the dynamic analysis to prevent the anchor from moving at t=0 seconds. For example, you could use a fixed boundary condition or a spring boundary condition.
I hope it helps !
- Badges
- Science topic