After the geometry and material of a structure are defined, loads and boundary conditions need to be applied. These differ depending on the desired solution sequence.
OptiStruct allows single-point constraint (SPC, SPC1), multi-point constraint (MPC), and fictitious support (SUPORT, SUPORT1) boundary conditions to be applied at nodal locations on the structure. For a complete list of applicable boundary conditions in OptiStruct, see the Constraints section on the List of Bulk Data Entries (by function). An example of a single-point constraint definition is included below:
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Example: Single-point constraint - Set ID 2 - Grid ID 101 - degrees-of-freedom 1, 2 and 3 are fixed. |
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SPC |
2 |
101 |
123 |
0.0 |
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Static loads can be applied in the form of point forces (FORCE, FORCE1), gravity loads (GRAV), moments (MOMENT, MOMENT1), pressures (PLOAD, PLOAD1, PLOAD2, PLOAD4), rotational forces (RFORCE), enforced displacements (SPCD), and temperature gradients (TEMP, TEMPD). For a complete list of applicable static forces in OptiStruct, see the Static Loads section on the List of Bulk Data Entries (by function). Below is an example of a point force definition:
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Example: Point force - Set ID 3 - Grid ID 102 - force magnitude = 1000.0, force direction = 1-direction relative to basic coordinate system (x-direction). |
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FORCE |
3 |
102 |
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1.0 |
1000.0 |
0.0 |
0.0 |
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For normal modes analysis, a number of frequencies or a frequency range is required. For linear buckling analysis, a number of eigenvalues or an eigenvalue range is required. Both requirements are met through the use of the real eigenvalue extraction (EIGRL) card. One difference in the use of this card for the different solution sequences is that for normal modes analysis, the range provided on this card is a range of frequencies; whereas for linear buckling analysis, it is a range of eigenvalues. Below is an example of a real eigenvalue extraction card:
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Example: Real eigenvalue extraction - Set ID 4 - requests first 20 eigenvalues and corresponding modes within the range of 1.0 to 40.0 (remember range is different depending on solution sequence used). |
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EIGRL |
4 |
1.0 |
40.0 |
20 |
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Loading for frequency and transient response analysis is applied through frequency response and transient dynamic load cards (RLOAD1, RLOAD2, TLOAD1, TLOAD2). A number of other cards are referenced by these cards, descriptions of which are available in the Frequency Response Loads and Transient Loads sections of the List of Bulk Data Entries (by function) page. Below is an example of a frequency response dynamic load card:
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Example: Frequency response dynamic load - Set ID 5 - A is provided by DAREA card with ID 3 - C(f) is provided by TABLED# card with ID 1. |
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RLOAD1 |
5 |
3 |
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1 |
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