Keyword type: step
This procedure is used to perform a coupled thermomechanical analysis. A thermomechanical analysis is a nonlinear calculation in which the displacements and temperatures are simultaneously solved. In this way the reciprocal action of the temperature on the displacements and the displacements on the temperature can be taken into account. At the present state, the influence of the temperature on the displacements is calculated through the thermal expansion, the effect of the displacements on the temperature is limited to radiation effects. In addition, the influence of the network fluid pressure on the deformation of a structure and the influence of the structural deformation on the network fluid mass flow can be considered. Other heating effects, e.g. due to plasticity, or not yet taken into account. This card is also correct for CFD-calculations with heat transfer.
There are five optional parameters: SOLVER, DIRECT, ALPHA, STEADY STATE and DELTMX.
SOLVER determines the package used to solve the ensuing system of equations. The following solvers can be selected:
Default is the first solver which has been installed of the following list: SGI, PARDISO, SPOOLES and TAUCS. If none is installed, the default is the iterative solver, which comes with the CalculiX package.
The SGI solver is the fastest, but is is proprietary: if you own SGI
hardware you might have gotten the scientific software package as well, which
contains the SGI sparse system solver. SPOOLES is also very fast, but has no
out-of-core capability: the size of systems you can solve is limited by your
RAM memory. With 2GB of RAM you can solve up to 250,000 equations. TAUCS is
also good, but my experience is limited to the decomposition, which
only applies to positive definite systems. It has an out-of-core capability
and also offers a
decomposition, however, I was not able to run either of
them so far. Next comes the iterative solver. If SOLVER=ITERATIVE SCALING is
selected, the pre-conditioning is limited to a scaling of the diagonal terms,
SOLVER=ITERATIVE CHOLESKY triggers Incomplete Cholesky
pre-conditioning. Cholesky pre-conditioning leads to a better convergence and
maybe to shorter execution times, however, it requires additional storage
roughly corresponding to the non-zeros in the matrix. If you are short of
memory, diagonal scaling might be your last resort. The iterative methods
perform well for truly three-dimensional structures. For instance,
calculations for a hemisphere were about nine times faster with the ITERATIVE
SCALING solver, and three times faster with the ITERATIVE CHOLESKY solver than
with SPOOLES. For two-dimensional structures such as plates or shells, the
performance might break down drastically and convergence often requires the
use of Cholesky pre-conditioning. SPOOLES (and any of the other direct solvers)
performs well in most situations with emphasis on slender structures but
requires much more storage than the iterative solver. PARDISO is the Intel proprietary solver.
The parameter DIRECT indicates that automatic incrementation should be switched off. The increments will have the fixed length specified by the user on the second line.
The parameter ALPHA takes an argument between -1/3 and 0. It controls the dissipation of the high frequency response: lower numbers lead to increased numerical damping ([50]). The default value is -0.05.
The parameter STEADY STATE indicates that only the steady state should be calculated. If this parameter is absent, the calculation is assumed to be time dependent and a transient analysis is performed. For a transient analysis the specific heat of the materials involved must be provided. In a steady state analysis any loading is applied using linear ramping, in a transient analysis step loading is applied.
The parameter DELTMX can be used to limit the temperature change in two
subsequent increments. If the temperature change exceeds DELTMX the increment
is restarted with a size equal to times DELTMX divided by the
temperature change. The default for
is 0.85, however, it can be changed
by the *CONTROLS keyword. DELTMX is only active in
transient calculations. Default value is
.
First line:
Example:
*COUPLED TEMPERATURE-DISPLACEMENT .1,1.
defines a thermomechanical step and selects the SPOOLES solver as linear equation solver in the step (default). The second line indicates that the initial time increment is .1 and the total step time is 1.
Example files: thermomech.