Nastran In-CAD: Understanding Data Conversion, Data Type, and Contour Type

Transcription

1 Nastran In-CAD: Understanding,, and Issue When creating a contour plot of a result, what is meant by " ", " ", and " "? The options in the drop-downs are as follows: 1. : "Average", "Maximum", or "Minimum" 2. : "Corner" or "Centroidal" 3. : "Nodal", "Elemental" with averaging ("No Averaging" unchecked), or "Elemental" without averaging ("No Averaging" checked) Understanding.docx rev 1 page 1 of 5

2 Cause Some types of results have multiple results calculated at the same node. How the multiple calculated results are displayed is controlled by the three selections. Solution : When a result has values at the nodes and centroid, the data type lets you select which result to use for the contour plot. If the result only exists at one location, both options behave the same. "Corner" = use the calculated results from the nodes. "Centroidal" = use the calculated results from the centroid of the s. : When multiple calculated results are available, the lets you choose how to combine the result to use in the display. If there is only one result, all options behave the same. "Average" = use the average of all results from the location. "Maximum" = use the largest of all results from the location. "Minimum" = use the smallest of all results from the location. : Now that the result values are selected, you can choose where to display them on the model. The contour plot then smooths the colors between the values shown at the chosen location. "Nodal" = display the result value at the nodes. In most cases, you want to display the nodal results (the corners) at the nodes. "Elemental" and "No Averaging" is checked = display the result value over the entire. "Elemental" and "No Averaging" is unchecked. This option gives the same result as Nodal. Background: Some types of results have a single value at a node. Displacement results are an example. All s connected to the node have the same amount of displacement. Some types of results have multiple values at a node. Stress results are an example. The displacement of the creates a different at each node on the. Because each displaces differently, the calculated in the at a common node can be different in each. Nastran also calculates a result at the centroid of the. If you could view the results without any manipulation (that is, look at the "raw" results or "unsmoothed" results), they would look like the following image. In this image, the s are separated to help visualize that the results at a common node are different, and the at the centroid is underlined. Understanding.docx rev 1 page 2 of 5

3 The difference in the result at a node from one to the next changes as follows: o When in the same part, the should change very little when the mesh is sufficiently fine. If the changes by a large magnitude, the mesh size needs to be smaller. o When in different parts, the can change. The above example shows a step-change in the due to the change in thickness of the shell s. When viewing the contour or probing on the results, the value displayed is controlled by the options chosen for the " ", " ", and " ". Examples: Using the raw es from the figure above, some common settings and example results are as follows: Average at a node, smoothed across part boundaries The raw nodal es from all s in all parts attached to the node are averaged to create one value. The average value is shown at the node. No Averaging Average Corner Nodal at A = ( )/ at B = ( )/4 Raw at centroid The raw from the center of the is displayed over the entire. No Averaging Average Centroidal Elemental Checked not Understanding.docx rev 1 page 3 of 5

4 All combinations of,, and No Averaging Description Average Corner Nodal - Raw nodal from all s across all parts attached to node are averaged as one Average Corner Elemental Unchecked Average Corner Elemental Checked not Where displayed At node at A = ( )/ at B = ( )/4 Raw nodal from all nodes on are averaged Average Centroidal Nodal - Raw centroid from all s attached to node are averaged, each part treated Average Centroidal Elemental Unchecked Average Centroidal Elemental Checked not at C = ( )/4 At node at A, part 1 = ( )/ at A, part 2 = ( )/ at B = ( )/4 Maximum Corner Nodal - Maximum of raw all s across all parts attached to node Maximum Corner Elemental Unchecked Maximum Corner Elemental Checked not At node at A = max of (31.571, 7.835, 9.157, ) at B = max of (8.574, 7.207, 7.309, 7.183) Maximum of raw all nodes on Maximum Centroidal Nodal - Maximum raw centroid from all s attached to node, each part treated Maximum Centroidal Elemental Unchecked Maximum Centroidal Elemental Checked not at C At node at A, part 1 = max of (31.110, ) at A, part 2 = max of (7.647, 8.112) at B = max of (7.647, 7.357, 6.998, 8.112) Element Understanding.docx rev 1 page 4 of 5

5 No Averaging Description Minimum Corner Nodal - Minimum of raw all s across all parts attached to node Minimum Corner Elemental Unchecked Minimum Corner Elemental Checked not Where displayed At node at A= min of (31.571, 7.835, 9.157, ) at B = min of (8.574, 7.207, 7.309, 7.183) Minimum of raw all nodes on Minimum Centroidal Nodal - Minimum raw centroid from all s attached to node, each part treated Minimum Centroidal Elemental Unchecked Minimum Centroidal Elemental Checked not at C At node at A, part 1 = min of (31.110, ) at A, part 2 = min of (7.647, 8.112) at B= min of (7.647, 7.357, 6.998, 8.112) Element See Also Depending on the result (displacement,, safety factor, etc.), some combinations of the options from the three drop-downs produce the same result. Which combinations provide different results and which provide the same result can be difficult to know. It is not possible to display the raw values from the nodes. It is not possible to display the average nodal without averaging across the part. This can be critical where the has a step-change due to differences in each part. Safety factor is not correctly reconciled in Autodesk Nastran In-CAD Understanding.docx rev 1 page 5 of 5