convergence analysis using Cosmos
convergence analysis using Cosmos
(OP)
Hi, My company uses Cosmos for sructural analysis and I was hoping someone with some experience can help me assess the convergence.
I am using the adaptive analysis option, p-element. I find that typically after running an analysis it reaches it's stopping criteria and when I check the adaptive convergence plot I have 2 loops with a large change in degrees of freedom and sometimes a large change in max stress, sometimes nearly zero. The nearly zero change probably indicates that the max stress is pretty stable relative to the number of degrees of freedom, but sometimes there is a large change. When this occurs what I would really like is for Cosmos to run at least a third loop so I can see if the stress is linearlly going up toward infinity or if it begins to level off.
I guess the best way to ask my question is, how do I force Cosmos to use enough loops for me to determine the convergence?
Alternitivley, how can I use p-elements and specify the order so I might perform this convergence analysis myself without resorting to h-elements in the area of interest (and using a ton of them).
Thanks
I am using the adaptive analysis option, p-element. I find that typically after running an analysis it reaches it's stopping criteria and when I check the adaptive convergence plot I have 2 loops with a large change in degrees of freedom and sometimes a large change in max stress, sometimes nearly zero. The nearly zero change probably indicates that the max stress is pretty stable relative to the number of degrees of freedom, but sometimes there is a large change. When this occurs what I would really like is for Cosmos to run at least a third loop so I can see if the stress is linearlly going up toward infinity or if it begins to level off.
I guess the best way to ask my question is, how do I force Cosmos to use enough loops for me to determine the convergence?
Alternitivley, how can I use p-elements and specify the order so I might perform this convergence analysis myself without resorting to h-elements in the area of interest (and using a ton of them).
Thanks





RE: convergence analysis using Cosmos
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
"Node news is good news."
RE: convergence analysis using Cosmos
Like kellnerp said if the stress continues to increase infinitely then you have a singularity, so make sure to measure away from any intensification factors because you don't want to plot the peak stress.
This is the problem with the adaptive methods, they are not recommended on geometry that is prone to singularities, since COSMOS will continue to refine the mesh in areas where it is not important.
RE: convergence analysis using Cosmos
I didn't realize you could get a separation of the bending and membrane stress. Is this an option in the plot settings somewhere?
RE: convergence analysis using Cosmos
Otherwise, you will have to probe the nodes across the thickness and probe the average stress on a face away from the discontinuity and then linearize the stress, to calculate the bending and peak stresses. See ASME VIII Div.2 section 5 (I think) or Google stress linearization.
I don't think you can increase the order without using adaptive.
RE: convergence analysis using Cosmos
"If you are using solids ....... it will output, membrane, bending ......"
How does Cosmos do this? How is it possible?
Just curious!
www.Roshaz.com
RE: convergence analysis using Cosmos
Cosmos/M
CosmosWorks
Simulation
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
"Node news is good news."
RE: convergence analysis using Cosmos
I'm not a huge fan of it, I liked ANSYS Workbench better, I could scope the results away from singularities and then use the adaptive mesh refinement to get pretty decent results.
RE: convergence analysis using Cosmos
Ansys and SW Simulation both have almost identical tools for linearizing the stress across the thickness.