See the adjacent Software Information
links for general details regarding LUSAS software products and
Interactive Modal Dynamics
In all LUSAS
products, modal dynamics problems can be solved using Interactive
Modal Dynamics (IMD) techniques. An additional LUSAS Dynamics
option caters for more advanced dynamics analysis. An IMDPlus
option caters for multiple event simulation.
With IMD, an eigen
solution is computed using either Subspace, Lanczos or Guyan reduction
eigenvalue extraction procedures. The resulting eigenvectors are then
read into the LUSAS Modeller where the loading function is defined and
the dynamic response calculated. Since the solution is only computed
either for a given part of the structure across a specified time or
frequency range, or for the whole structure at a specified sampling
time or frequency a solution is obtained very rapidly.
Results can be displayed using the
extensive graph plotting facilities or using the standard contour,
vector or peak value features. Since both the damping (structural or
viscous) and ‘time-step’ are specified within IMD there is no need
to carry out a series of computationally expensive transient dynamics
analyses to assess the effect of these parameters on the structural
response. IMD thus offers large savings in design and analysis time
and greatly reduces the computational resources required for linear
transient dynamic analysis.
Typical uses of IMD include forced
response when a dynamic analysis is being used to investigate the
effects of structural resonance and spectral response where a dynamic
analysis is being carried out to investigate the effects of ground
motion on the structural behaviour. For spectral response problems the
support excitation is defined using a spectral curve and the modal
results may be combined using either the SRSS or CQC combination.
Using IMD the response to random
vibration problems is computed using power spectral density (PSD)
techniques which compute the response of a structure from the PSD
input. Typically this may be used to compute the behaviour of a
structure due to wind loading or the behaviour of a component mounted
on an randomly vibrating platform such as an engine.
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