Enveloping in GSA

Most results produced by GSA can be enveloped. A result envelope is the worst (maximum and minimum) results encountered in a series of analysis or combination cases. Result envelopes are produced for enveloping combination cases.

Envelopes may be specified in the Combination Cases table. The syntax of the combination case description allows the use of various keywords for describing enveloping combination cases. Typically an enveloping case will include the keyword “or”, though other syntax is available that is interpreted as such. An enveloping case represents a number of permutations of simple cases; during the enveloping process GSA compares the results for each of these simple cases to arrive at an envelope.

Envelopes described in the Combination Cases table are extracted from the permutations that the case describes at the time of requesting output. This can be a time consuming operation especially when the enveloping combination case identifies large numbers of permutations. (See below.) Alternatively Analysis Envelopes may be calculated as a batch operation to store the envelope results for subsequent, immediate display.

In Output Views the output for an enveloping case reports the maximum and minimum values, each coupled with the permutation number of the permutation that produced that value. The permutation numbers are listed against the interpreted simple cases in the Combination Case and Envelope Details output. Output of envelopes may be either for all components listed or for a defined “subject component” reported alongside coexistent values for other components.

Output of a particular permutation of an enveloping case may be requested.

Note: Where different components being enveloped in a table are related (and a component has a direction as well as magnitude which can vary between cases – e.g. resolved forces and displacements, 2D element derived stresses) the relationship between the components will not be satisfied where the values come from different permutations.

In Graphic Views enveloping is offered as follows.

• The maximum and minimum deformed shape is drawn.
• The maximum and minimum diagram is drawn and there is an option to annotate just the maximum or minimum or both.
• Either the maximum, minimum, absolute or signed absolute value is contoured.

Note: If a diagram of 2D element derived stresses is requested, what will be plotted is the most positive Max and Min stresses at the most positive Angle, and the most negative Max and Min stresses at the most negative Angle. If the Angle is from a different permutation to the Max and Min stresses this is not an accurate representation of the state of stress.

An enveloping case yields maximum and minimum values, as discussed above. The syntax of the combination case description also allows operators to be applied to enveloping cases to yield just the maximum, just the minimum, the absolute or the signed absolute values. These operators are useful for both specifying the required output and minimising the processing involved in calculating large enveloping cases. Examples of their use are given in the Syntax of combination case descriptions section.