Duration of parallel analysis increases for more CPUs

[rafetsisman]

Hi,

I have an OpenSees model for a soil deposit including a tunnel in 2D. I used pressure independent material for soil and linear elastic material for frame elements. The model has approximately 10000 nodes which corresponds to 20000 DOFs. I added the following lines to my tcl file to create an appropriate analysis object.

constraints Transformation
test NormDispIncr 5e-5 1000 1
algorithm KrylovNewton
numberer RCM
system Mumps
integrator Newmark 0.5 0.25
analysis Transient
analyze $motionSteps $motionDT

The model is solved with OpenSeesSP tool by using 6, 8, 12 and 24 CPUs on a workstation with 24 CPUs (48 cores) and 64 GB RAM. Duration of the analyses are 9, 9, 10 and 13 mins respectively.

What can be wrong with model? What is the reason for analysis duration increase? Why more CPUs in parallel analysis do not decrease the analysis duration?

Thanks