Software Option for Plus versions
Straightforward modal dynamics problems
can be solved using Interactive
Modal Dynamics (IMD) techniques which are provided in all
products. A software option, IMDPlus Analysis,
allows
multiple loading events with more advanced loading conditions such as
moving load, moving mass or moving sprung mass, or seismic response
modelling to be solved.
The LUSAS Dynamics Option contains the
facilities required to solve a wider range of dynamic problems in both
the time and frequency domains.
- By combining the LUSAS Dynamic and
LUSAS Nonlinear
options both high and low velocity nonlinear impact problems can be
solved using either implicit or explicit solution techniques, or creep
can be modelled.
- By
combining the LUSAS Dynamic and LUSAS Thermal
options time-domain
analyses such as Transient Field can be carried out.
Note that the Dynamic Analysis option
includes the IMDPlus
Analysis option for all new sales from Version 18 onwards.
Contact sales@lusas.com for more
details.
Dynamic
analysis option capabilities:
Transient Dynamic analysis is usually
carried out to provide the solution to nonlinear dynamics problems
when material nonlinearity, geometric nonlinear effects or changes in
boundary conditions occur due to dynamic events. When carrying out a
transient dynamic analysis both distributed and discrete damping may
be specified. Damping is defined by specifying mass and stiffness
Rayleigh damping constants. By combining the LUSAS Dynamic and LUSAS Nonlinear
options both high and low velocity nonlinear dynamic problems can be
solved using either implicit or explicit solution techniques. Note
that the dynamic analysis option must be combined with the nonlinear
analysis option in order for creep to be investigated.
Implicit
Transient Dynamics
Implicit dynamic analysis is used to
solve "low velocity" problems where low frequency effects
dominate the response. Typical applications include sesmic analysis or
plant and structures (including soil structure interaction), low
velocity impact and analysis of deformable blast panels. LUSAS has a
highly accurate state-of-the-art facility based on the second order
Hilber-Hughes-Taylor algorithm. This algorithm is self-starting
(meaning no preliminary static solution is required) and allows
variable time steps to be used. It is unconditionally stable for
linear problems enabling large time steps to be taken without loss in
stability. An automatic time step computation is available if
required. The implicit dynamics option is available for all implicit
element types with either consistent or lumped mass idealisation and
may also be combined with the other analysis options.
For large dynamic problems
superelements may be used to reduce the size of the model while
accurately including the boundaries effects. This is achieved by
including generalised internal modes within the superelement matrices.
This technique can be used for both linear and nonlinear dynamic
analyses.
Explicit
Transient Dynamics
For high velocity dynamic problems
where shock waves dominate the time step has to be very small. In
these situations, explicit dynamic analysis is the most appropriate
and efficient solution technique. The explicit dynamics algorithm
within LUSAS has been vectorised to enable rapid solutions to be
obtained. Dedicated, optimised, single Gauss point explicit dynamics
elements are provided with hourglass control to avoid mechanisms.
Furthermore, Eulerian geometric nonlinearity is automatically invoked
in these elements to effectively handle the large strains which often
occur in such analyses. To optimise the procedure required still
further, automatic time stepping is provided to ensure that an
accurate and efficient solution is obtained.
Nonlinear
Boundary Conditions
In both implicit and explicit analysis
a slideline facility allows contact between discrete bodies to be
modelled in two and three dimensions even when the meshes across
adjacent contacting surfaces are incompatible. A nodal monitoring
procedure within the algorithm enables contact and rebound to be
handled automatically avoiding the need to manually define contact
joint elements between contacting nodes. A tied slideline option also
exists which can be used to eliminate the need to define a transition
mesh region between areas of the model with different degrees of mesh
refinement. Friction is modelled using a Coulomb friction model which
may be included in the contact algorithm.
The LUSAS restart facility provides a
high level of control over successive increments of a nonlinear or
dynamic analysis. With the restart facility all analysis data can be
optionally saved between successive increments. This has an important
benefit for extremely large problems where disk space may be a
critical factor. Analyses which have been interrupted or terminated
before completion may be restarted from the last converged solution.
In addition to the standard loading
available in LUSAS, tabular input of displacement, velocity and
acceleration time histories provide efficient control over the
application of loading and is especially suited to seismic studies.
Variations of loading with time may also be defined using the
comprehensive load curve facility. This enables multiple load
variations to be defined and assigned to different loading actions as
required.
In addition to the powerful contouring,
graphing and plotting features in LUSAS Graphics, a large number of
specific dynamics results processing features are available including:
- Generation of time histories over
multiple results files of any node or Gauss point result value
- Animation of load cases over
multiple time steps and over multiple results files.
- Selective results history to speed
post processing and reduce data storage requirements
- Links to LMS Software for validation
and updating of modal models
Find out more
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