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In this article, we are going to be taking a look at a Simulation Results plot that helps to determine if you have sufficiently refined the mesh in critical areas of your model. The plot is called the Energy Norm Error and it is a type of Stress plot. The Energy Norm Error plot tells you how much error there is in the stress and strain values in individual mesh elements. To reduce error you can refine the mesh, but as always, you will want to save the most extreme mesh refinement for areas of interest, such as high-stress spots.
So, how is the Energy Norm Error calculated? To understand this we first must know the difference between Elemental and Nodal values. When you create a Stress plot you either display it with Elemental or Nodal stress values, this not only affects the way the results are graphically displayed, but also the actual result values that are shown as well. Each mesh element is made up of nodes where the edges of the element meet and Gauss points that are located inside the mesh elements.
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The Gauss points are where the actual calculations for displacement, and therefore stress and strain, take place. The standard display for many Results plots is to use Nodal values. These values are determined by averaging the Gauss points found near each node, these are taken from multiple mesh elements. This means that the Nodal values act as local area averages and produce that characteristic color blend in the Results Plot.
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When Elemental values are used, each mesh element is treated individually and only the Gauss points within that individual element are averaged, you can think of this as an internal average.
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In any discretized FEA study there will be a discrepancy between the Nodal and Elemental values. In theory though, as the sizes of the mesh elements are reduced the closer the Nodes and the Gauss points physically are to each other and closer the calculated Elemental and Nodal values will be. To bring this back to a general rule for FEA—the smaller the mesh elements, the more accurate the results and the more time it takes to calculate.
So, what does this all mean to you? The Energy Norm Error plot shows you the percent error between the Elemental and Nodal values and thus points to locations where mesh refinement should be considered. Couple this with your standard Stress plot (and also the new Stress Hotspot Diagnostics tool available starting in SOLIDWORKS 2017) to inspect locations of interest (critical design areas) and/or areas with the highest stress. With these considerations, you will be able to make informed decisions on where to refine mesh to help achieve accurate results while minimizing the calculation time. The Energy Norm Error plot can be found under the Components drop down in the Stress Plot PropertyManager.
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Here is the link to the SOLIDWORKS help file: http://help.solidworks.com/2017/english/solidworks/cworks/c_node_values_versus_element_values.htm
For more information, check out our YouTube channel, get a SOLIDWORKS Simulation quote or contact us at Hawk Ridge Systems today. Thanks for reading!