Eigenfrequencies
Use Eigenfrequencies to calculate natural frequencies and mode shapes of the structure.
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No. of shapes – numeric field for how many eigenmodes the solver should calculate.
Second field (which is greyed out) shows how many shapes was required to reach 90% of horizontal effective mass, if that option was enabled in previous analysis. Otherwise it shows number of calculated shapes.
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Try to reach 90% of horizontal effective mass – when enabled, the solver continues calculating shapes until at least 90% of the effective mass is reached in the horizontal directions
- Max no. of iteration – maximum number of iterations allowed when trying to reach 90%
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Max no. of Sturm check steps (checking missing eigenvalues) – number of additional Sturm sequence checks to detect missing eigenvalues
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Mode shape normalization – choose how the mode shapes are normalised
- Mass matrix – normalises with respect to the mass matrix
- Unit – normalises to unit modal displacement
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Consider masses in the following global directions – enable or disable mass participation in the X, Y, and Z global directions
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Top of substructure – elevation below which masses are ignored. Masses or mass-converted loads on this level and below are not considered in eigenfrequency calculation