Post Processing Countour Key Issue 1

[sdanderson]

I have been having issues with my Post Processing in Femap 10.2.1. In the attachment that I have added I show a screen shot of a problem I am currently working. The contour key to the right shows that my max stress (max principal) is 8828 psi. But in my Select PostProcessing Data menu shows that the maximum stress is 7477.209 psi, and in the bottom left of the imagae it shows that the contour represents Solid Max Principal. The load that is being applied in the center of the lug is a surface pressure load that is in a custom Cylindrical Coordinate System. I have a feeling there is a transformation issue, but I have tried to switch my results to different coordinate systems and nothing seems to work. I am fresh out of ideas on how to get my Contour Key to reflect my actual results but I have no clue. Would love some help on this.

 

[BlasMolero]

Hello!,
The value you see in the POSTPROCESSING DATA is the stress in the CENTER of the element, but the plot stress you get in the screen is an averaged NODAL stress value, then depending pf the options choosed in the contour options like USE CONRNER DATA, or DATA CONVERSION = AVERAGE, etc..

If you want to plot ELEMENTAL STRESS results, simply use CONTOUR TYPE = ELEMENTAL, set USE CORNER DATA=OFF, and ELEMENT CONTOUR DISCONTITUITY=NO AVERAGING, and you are done!.

Best regards,
Blas.



~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[sdanderson]

Thanks Blas. In the "Select PostProcessing Data" menu when it shows "Type" next to the "Contour" menu, do you know how to change the "Type" from "Element" to "Node" for the "Maximum" and "Minimum"?

 

[BlasMolero]

Hello!,
When dealing with elemental results, it dosn´t matter you choose minimum, maximum or average in DATA CONVERSION, the result is the same, is in the CENTER OF ELEMENT, remember. Only if you choose to plot NODAL STRESS RESULTS, then results will change.

If Average is on, FEMAP will take an average of the surrounding values to obtain a result, whereas Max or Min Value will just use the max or min value, respectively, of the pertinent surrounding locations. The Min Value option should only be used when performing contours for vectors where the minimum values are actually the worst case, such as safety factor or large compressive stresses.

The easiest way to understand the data conversion process is through an example. If an interior node of a continu­ous mesh (no geometric or material breaks and averaging is on) is attached to four elements, there will be four val­ues associated with it for a given stress vector (either corner data or if Use Corner Data is off elemental centroidal data). If these values are 100, 200, 300 and 400, an Average conversion would result in 250 at that node, a Max con­version with 400, and a Min conversion of 100. This procedure would be used at all nodal locations to get the basis of the plot, and then FEMAP would produce the corresponding colors between locations. Thus, the data conversion can significantly affect the results if there is a large gradient across adjacent elements.

Hint:
You can use the difference in Max, Min and average results to make a quick estimate of the fidelity of the model. If there is a large difference between these two contours, especially at locations that do not have sharp corners or breaks in the model, your FEA model may require a finer mesh.

If elemental contours are on, FEMAP only averages results at the specific node if there are no discontinuities according to the Elemental Contour Discontinuities settings. FEMAP produces results at each node and element centroid, and then uses this information to generate the display.

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/