Base Excitation

Transient/Frequency Response
  1. Two types of base excitations are possible. The excitation can be specified in terms of displacements or accelerations. Both are applied in the global X, Y or Z coordinate frames only.
  2. You can select the excitation type (displacement or acceleration), time function, scaling amplitude and direction.
  3. In addition, displacement-based excitations can be applied to individual supports which can be important for long ground-based structures like pipe systems, bridges, and transportation systems.
Random Response
  1. The excitation can be specified in terms of accelerations. They are applied in the global X, Y or Z coordinate frames only.
  2. You can select the excitation type (acceleration), frequency/PSD function, scaling amplitude and direction.
  3. The Power Spectral Density (PSD) of the response, S x o ( f ) MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4uamaaBa aaleaacaWG4bGaam4BaaqabaGccaGGOaGaamOzaiaacMcaaaa@3B36@ , is related to the power spectral density of the source, S a ( f ) MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4uamaaBa aaleaacaWGHbaabeaakiaacIcacaWGMbGaaiykaaaa@3A2B@ , by:(1)
    S x o ( f ) = ( H x a ( f ) S 2 a ( f ) MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4uamaaBa aaleaacaWG4bGaam4BaaqabaGccaGGOaGaamOzaiaacMcacqGH9aqp daabdaqaaiaacIcacaWGibWaaSbaaSqaaiaadIhacaWGHbaabeaaki aacIcacaWGMbGaaiykaaGaay5bSlaawIa7amaaCeaaleqabaGaaGOm aaaakiaadofadaWgaaWcbaGaamyyaaqabaGccaGGOaGaamOzaiaacM caaaa@4A60@
    Where, H x a ( f ) MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamisamaaBa aaleaacaWG4bGaamyyaaqabaGccaGGOaGaamOzaiaacMcaaaa@3B1D@ is the frequency response function.

    Let us take an example of base excitation as an input to a random response analysis.

    The base excitation with amplitude is used to define the input for frequency response analysis, so the units of the acceleration excitation type would be any of the below highlighted units
    • m/sec2
    • mm/sec2
    • cm/sec2
    • G
    • in/sec2
    Units for PSD function depend on the boundary condition. In this example, as base excitation is given as acceleration, the unit for PSD is (mm/s2)2/Hz.


    Figure 1.
    Note: Only immovable and general constraints can be used as the source location. Hinges, springs and sliders are not supported at this time.