TR.30.1 Cut-Off Frequency, Mode Shapes, or Time
These commands are used in conjunction with dynamic analysis. They may be used to specify the highest frequency or the number of mode shapes that need to be considered.
General Format
CUT (OFF) { FREQUENCY f1 | MODE SHAPE i1 ( SHIFT MODE i2 ) (FREQ f2 ) | TIME t1 }
Where:
| Parameter | Description |
|---|---|
| FREQUENCY f1 | Highest frequency (cycle/sec) to be considered for dynamic analysis. |
| MODE SHAPE i1 | Number of mode shapes to be considered for dynamic analysis. If the cut off frequency command is not provided, the cut off frequency will default to 108 cps. If the cut off mode shape command is not provided, the first six modes will be calculated. These commands should be provided prior to the loading specifications. |
| SHIFT MODE i2 | Number of eigen vectors per shift. This input may be used only when the solver fails to extract i1 number of modes due to insufficient memory. |
| FREQUENCY f2 | Frequency (in Hz) to be used as initial shift in Arnoldi/Lanczos method (i.e., it is not applicable to the basic solver). This is an optional input. If provided, the solver looks for eigenvalues close to the shift. The eigen values found may not necessarily be the smallest eigenvalues (i.e., closest to zero). If a full scale eigen solution is required, this value should not be defined. The engine default value in 0.0 (zero) |
| TIME t1 | Ending time for a time history analysis. If zero (default), the time history will end when the last forcing function ends. |
A maximum of i1 mode shapes will be computed regard-less of f1. If during convergence testing, the 0 through f1 frequencies are converged, then the modal calculation will be completed before i1 mode shapes are calculated.