Ingenieurgesellschaft für
technische Software

Temperature Fields

  • The temperature field may be steady-state or transient.
  • Nonlinear material data for conductivity and heat capacity may be specified by tabular input.
  • Temperature and space-dependent convectivity coefficients may be specified in a very general way by functions.
Elements: PERMAS-HT provides a complete set of convectivity elements to model surface convection. In addition, they allow for the determination of the surface area of a set of elements in order to get the drained or injected heat through the related surface. Moreover, an optional film thickness may be specified for the convectivity elements, which allows to model the heat capacity of boundary layers in transient analysis.

All finite elements applicable in static analysis may be used in heat transfer analysis. For shell elements a temperature gradient between top and bottom surface is allowed.

Analyses: Coupled analysis of thermo-mechanical problems is fully automatic, i.e. the resulting temperature field is directly used to derive the related displacements, strains and stresses. The material data for the static analysis (elasticity and thermal expansion data) may be temperature-dependent.

In addition, using PERMAS-CCL convective boundary conditions can be imported from a CFD analysis or fully coupled analyses can be performed, respectively.

A transient analysis may be continued by reference to the results of the previous run. Among others, during the simulation of complete cycles of thermal loads this feature easily allows for sudden changes of the surrounding conditions.

A modal analysis allows for the computation of eigenvalues and eigenmodes for heat transfer problems.

Loads and boundary conditions:
  • Stationary 'loads' may be defined as point heat fluxes or distributed heat fluxes along lines, on surfaces and in volumes.
  • Transient 'loads' are built conveniently by combination of a stationary 'load pattern' with time-dependent functions.
  • Additional boundary conditions are prescribed temperatures and a surrounding temperature for convectivity elements.
Results: Primary results of a heat transfer analysis are the temperature field and the heat fluxes. In addition, the following derived results are available:

  • the gradient of the temperature field,
  • the heat flux through any internal face
  • arbitrarily composed element sets allow for the output of the heat flux through a part of the surface in absolute or area specific values.

In addition, for transient analyses primary and derived results may be issued for any point in order to generate xy-plots.

Transient temperature analysis.

Radiation with heat exchange

Heat transfer by radiation is increasingly important with higher temperatures and for parts with cavities and self-shadowing effects like brakes, combustion engines, and cooling elements. This allows heat transfer analyses with convection and radiation coupled with heat conduction.

The assumptions for this function are heat exchange between surfaces (no radiation from within bodies), radiation of grey bodies (radiation not dependent on wave length), and diffuse emission (radiation not dependent on radiating direction).

The calculation of radiation has the following characteristics:

  • The radiation is integrated in the heat transfer analysis process.
  • The convection elements are extended to model also radiating surfaces, i.e. all surface elements where radiation has to be taken into account have to be modeled with convection elements.
  • There is a direct integration of the view factors over the surface elements instead of averaged view factors.
  • In order to accelerate the calculation of viewing factors with a very high number of surface elements an automatic (selective) coarsening procedure is provided to reduce the number of surface elements.
  • The computational efficiency is obtained by using parallelization.
  • The coupled solution of the nonlinear heat transfer equation with radiation boundary conditions is performed in a few iteration steps either for steady-state or transient calculations.

Cavity radiation.