I've been running a random vibration model where I have Random Vibration/Properties/Frequency Options set to Upper bound frequency. But now when I run the model, the random vibration status window indicates that there is a predefined(?) number of natural frequencies = 120. Initially I had run the model with the option of Number of Frequencies = 120, but that box is now grayed out, since I've chosen the Upper bound frequency option.
Under global damping, options is set to Modal damping with the first mode = 0 and the last mode = 120. I've had this setting all along, so I don't understand how the model is now indicating a predefined number of natural frequencies? I don't think I've changed anything that would cause the software not to calculate the number of natural frequencies instead of setting the number equal to 120.
Hi Dave: Can you check the option in frequency setup for the Linear Dynamic Study Properties? I'm assuming the upper bound value is controlled by the number of frequencies initially specified in the frequency extraction portion of linear dynamics module.