PARAM, CHKM0

Bulk Data Entry OptiStruct calculates the ratio of ${m}_{0}}{{m}_{0}^{\mathrm{log}}}$ and prints a WARNING if the frequency interval may not be fine enough for accurate Fatigue Damage calculation.

Parameter Values Description
CHKM0 <YES, NO>
YES
OptiStruct calculates the ratio of ${m}_{0}}{{m}_{0}^{\mathrm{log}}}$ . 1
NO (Default)
OptiStruct does not calculate the ratio of ${m}_{0}}{{m}_{0}^{\mathrm{log}}}$ . 2
Note: WARNING #4403 is not issued even if the frequency interval is not fine enough.
Where,
${m}_{0}$
0th moment (area under the PSD curve) is calculated using linear interpolation of stress PSD.
${m}_{0}^{\mathrm{log}}$
0th moment is calculated using logarithmic interpolation of stress PSD with the frequency interval of min (1Hz, minimum frequency interval of FRF analysis results).

1. If ${m}_{0}}{{m}_{0}^{\mathrm{log}}}<0.95$ , a WARNING message is issued indicating that the frequency interval does not seem fine enough for calculation of accurate moments. This implies that the frequency interval may not be fine enough for accurate Fatigue Damage calculation. A way to improve this is to increase number of frequencies defined on the FREQi entries appropriately.
2. If the frequency interval is fine enough, you can expect ${m}_{0}$ and ${m}_{0}^{\mathrm{log}}$ to be close to each other. If ${m}_{0}^{\mathrm{log}}$ is greater than or equal to 95% of ${m}_{0}$ , the ${m}_{0}$ value can become stable with regard to number of frequencies. If the ${m}_{0}$ value is stable, the subsequent Fatigue Damage values are also stable.