# Mesh changing resulted in stress change

• amirrezaaj
In summary, the stress in the section increased when the mesh size was changed. There may be a stress concentration in the area, and it may be necessary to locally refine the mesh to see the real stress.
amirrezaaj
HI
I have a problem in ansys that made me confused...I have modeled a conceret dam and meshed it with solid 45 elements...after that I have assigned the available surface pressure on the dam to the model...in another modeling, I changed the mesh size only and analyzed the the model with the same loading conditions...but the results have been changed? why the results are depended to the mesh size in this situation? is there any relation with surface pressure loading and mesh number...?! what should i do...? with kind regards...

Rajan Kumar
That is normal for a finite element model. Changing the mesh density can help you figure out if you have any singularities. As you increase the mesh density the result should change less and less each time as it converges on a solution. If the results never stop increasing or decreasing, then there is a singularity at one of the nodes and the solution is divergent. There should be plenty of papers on the web over "convergence analysis."

Thanks for your regards dear friend...But there is a point that the mesh change that I mentioned, affects the results considerabley...for example when the number of the elements in the model increase about 2 times in the dam ansys model,the stresses in the model increases about 4 times... Also, when some elements in the model refined in mesh size in one location, the results increase 2 time...I don't understand why this happen in my model since the loading condition is the same in both models...this amount of incease in the stress s value is not logical...

It's probably a stress singularity as it get worse with mesh refinement, or a stress concentration near a boundary condition that is breaking the model. So it may or may not be important.

Take a convergence plot at several nominal locations away from boundaries, see how those results are affected.

Thanks a lot chris...
I had a section in my model that was wncountered with stress concentration and i excactly want to control and read the stress in this section...this section has a low thickness and is connected to another part that is considered as a constrain for the mentioned section...i check this section and see that changing element size in this section resulted in stress increase...now how can remove the effect of stress concentration in this section chirs...? is there any special method or trick in ansys to reduce the effect of stress concentration...?? thank u some much for your kind regards...

amirrezaaj said:
I had a section in my model that was wncountered with stress concentration and i excactly want to control and read the stress in this section
...
is there any special method or trick in ansys to reduce the effect of stress concentration...??

Since you want to know the stress at the concentration, you can't use any tricks to get rid of it. You have to locally refine the mesh until the stress stops increasing much.

However if you have a singularity, that's not physical and you must get rid of it to see the real stress. For re-entrant corners, use their actual radius, don't make them sharp. Also watch out for other discontinuities like the edges of fixed faces - these may need to be radiussed too.

Be aware that singularities aren't a fault in FEA, they're the software trying to model something that cannot exist in the real world. If you approach it in the real world, the stress really will approach infinite, just like the model says.

Thank u so much for your kind regards...

## What is meant by "mesh changing resulted in stress change"?

Mesh changing refers to altering the structure of a finite element mesh, which is a discretized representation of a continuous object. Stress change refers to the change in internal forces and deformations within the object due to the mesh alteration. Therefore, "mesh changing resulted in stress change" refers to the impact of modifying the mesh on the stress distribution and behavior of the object.

## Why is mesh changing important in scientific simulations?

Mesh changing is crucial in scientific simulations because it allows for a more accurate representation of complex geometries and behaviors. By refining or coarsening the mesh in specific regions, researchers can capture finer details or reduce computational cost without sacrificing accuracy. Mesh changing is also necessary for adaptive simulations, where the mesh is updated in response to changing conditions.

## What are some common methods for changing the mesh in simulations?

There are various techniques for mesh changing, such as local refinement, global refinement, coarsening, and adaptive methods. Local refinement involves adding more elements in a specific region, while global refinement increases the overall mesh resolution. Coarsening, on the other hand, reduces the number of elements in the mesh. Adaptive methods combine these techniques and dynamically update the mesh based on certain criteria.

## What are the potential challenges or limitations of mesh changing?

One challenge of mesh changing is ensuring the mesh quality remains high after modification. Poorly designed mesh changes can lead to distorted elements, incorrect results, and numerical instability. Additionally, mesh changing can significantly increase computational time and resources, particularly in large-scale simulations. It also requires expertise and careful consideration to determine the appropriate mesh changes for a specific problem.

## How can one evaluate the effectiveness of mesh changing in a simulation?

The effectiveness of mesh changing can be evaluated by comparing the results with a reference solution or experimental data. One can also perform mesh convergence studies, where the mesh is successively refined, and the results are compared to assess the accuracy and convergence rate. Additionally, examining the mesh quality and ensuring it meets certain criteria can also indicate the effectiveness of the mesh changes.

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