NRLSUM
NRLSUM, SIGNIF
, Label
, LabelCSM
, ForceType
Specifies the Naval Research Laboratory (NRL) sum mode
combination method.
SIGNIF
Combine only those modes whose significance level exceeds the
SIGNIF
threshold. For single-point, multi-point, or DDAM response spectrum (Spectype
= SPRS, MPRS, or DDAM on SPOPT), the significance level of a mode is defined as the mode coefficient divided by the maximum mode coefficient of all modes. Any mode whose significance level is less thanSIGNIF
is considered insignificant and is not contributed to the mode combinations. The higher theSIGNIF
threshold, the fewer the number of modes combined.SIGNIF
defaults to 0.001. IfSIGNIF
is specified as 0.0, it is taken as 0.0. (This mode combination method is not valid for SPOPT,PSD.)Label
Label identifying the combined mode solution output.
DISP
—
Displacement solution (default). Displacements, stresses, forces, etc., are available.
VELO
—
Velocity solution. Velocities, "stress velocities," "force velocities," etc., are available.
ACEL
—
Acceleration solution. Accelerations, "stress accelerations," "force accelerations," etc., are available.
LabelCSM
Label identifying the CSM (Closely Spaced Modes) method.
CSM
—
Use the CSM method.
Blank
—
Do not use the CSM method (default).
ForceType
Label identifying the forces to be combined:
STATIC
—
Combine the modal static forces (default).
TOTAL
—
Combine the modal static plus inertial forces.
Notes
This command is also valid in PREP7. This mode combination method is usually used for SPOPT,DDAM.
This CSM method is only applicable in a DDAM analysis
(SPOPT,DDAM
). Element
results calculation based on modal element results (Elcalc
on
SPOPT) is not supported and is automatically reset for this method.
The CSM method combines two closely spaced modes into one mode when their frequencies
are within 10 percent of the common mean frequency and their responses are opposite in sign. The
contribution of these closely spaced modes is then included in the NRL sum as a single effective
mode. Refer to Closely Spaced Modes (CSM) Method in the Theory Reference for
more information.