This method is defined in the USNRC Regulatory Guide 1.92. The ten percent method is like the grouping method. It assumes that modes are completely correlated with any modes with similar closely spaced frequencies and are completely uncorrelated with those modes with widely different frequencies. The grouping method assumes that modes are only correlated with those that fall within the group (within a 10% band). This method assumes that modes are correlated with those that fall within 10% of the subject model, effectively creating a 20% band (10% up and approximately 10% down). The total system response is calculated as
Where:
Ri, Rj = the peak value of the response of the element due to the ith and jth mode, respectively, where mode i and j are any frequencies within 10% of the each other,
The 10% value controlling the definition of closely spaced frequencies can be changed
by using the Closely Spaced Mode Criteria/Time History Time Step (ms) parameter.