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Thermal Solver
Contains thermal solver related guides, such as the TMG reference manual, thermal API guide, and error message list.
Thermal solver theory
Describes the theory and methods of the thermal solver.
Radiation exchange
Thermal radiation is a heat transfer due to electromagnetic radiation emitted by the surface of bodies due to their temperature.
Radiation patches
The radiation patches are used to accelerate the solution of radiative heat transfer when using the Oppenheim method. This approach is not supported by the Gebhardt method.

Thermal Solver
Contains thermal solver related guides, such as the TMG reference manual, thermal API guide, and error message list.
- Thermal solver guides
  Maya HTT's thermal solver is included in Simcenter 3D and in Simcenter Femap. This page contains links to thermal solver guides, which help you understand how the thermal solver works.
- Thermal solver reference
  Describes the format and contents of the thermal solver's input and output files
- Thermal solver theory
  Describes the theory and methods of the thermal solver.
  - Introduction
    This guide provides the theory and methods used by the thermal solver, including methods to calculate conduction, convection, and radiation, as well as modeling specific topics using the thermal solver.
  - Elements in the thermal solver
    The thermal solver uses elements to calculate conductive, convective, and radiative conductances, as well as hydraulic resistances.
  - Supported element types for radiation
    Radiating elements may be defined with 1 to 4 corner nodes. The elements may be linear or parabolic.
  - Conduction methods
    To model heat conduction, the thermal solver can use two finite volume methods, center of element method or element's center of gravity method, or the finite element method.
  - Convective heat transfer methods
    The thermal solver computes convection conductances for various geometrical configurations using correlations that depend on specified characteristic lengths, convective surfaces, and type of convection.
  - Radiation exchange
    Thermal radiation is a heat transfer due to electromagnetic radiation emitted by the surface of bodies due to their temperature.
    - Basic view factor concepts
    - View factor calculation using deterministic without ray-tracing
    - View factor calculation using deterministic ray-tracing
    - View factor calculation using the hemicube method
      The thermal solver uses the hemicube method to compute diffuse blackbody view factors.
    - View factor calculation using the Monte Carlo method
      The thermal solver uses the CPU-based Monte Carlo algorithm for calculating view factors in radiation modeling using ray-tracing technique when modeling advanced optical properties.
    - Radiative conductance calculation methods
      Radiative conductance quantifies the rate at which thermal radiation is exchanged between surfaces. The thermal solver supports several computational methods, each with distinct advantages and limitations depending on the complexity of the geometry, material properties, and computational resources available.
    - GPU-based radiation calculation methods
      GPU-based calculation methods for radiation exchange use the graphics processing unit (GPU) to perform accelerated radiation computation.
    - Radiation patches
      The radiation patches are used to accelerate the solution of radiative heat transfer when using the Oppenheim method. This approach is not supported by the Gebhardt method.
    - Comparison of radiation calculation methods
      This tables compares different radiation computation methods used for computing radiation exchange in thermal simulations.
    - Radiation enclosures
      The thermal solver separates elements into enclosures. An enclosure is defined to be a set of elements that view each other and only each other.
    - Diffuse reflectivity calculation
      This section describes the calculation of diffuse reflectivity for materials with angle-dependent specular reflectivity or transmissivity.
    - Effective property calculation
      For each element, the thermal solver calculates the effective properties from the surface properties and self-view factors.
    - Heat flux calculation in radiative heat transfer
      The thermal solver computes the incident, reflected, absorbed, and transmitted energy fluxes for radiative heat transfer analysis.
    - Plane stress view factor calculation when modeling with axisymmetric or 3D elements
      This section explains how the thermal solver computes the view factor for axisymmetric or mixed 2D axi-3D models with plane stress elements for radiation requests.
  - Solar heating
  - Steady state analysis
    In a steady state analysis, the thermal solver solves the temperatures of non-sink elements iteratively using the following algorithm.
  - Transient analysis
    Transient analysis is performed using the following algorithm.
  - Hydraulic network analysis
    When the hydraulic pressure-flow network is present in the model, the thermal solver solves it at each iteration or time step using the following algorithm.
  - Miscellaneous topics
  - Thermal solver theory bibliography
    The following bibliography lists all sources used to explain how the thermal solver works.
- Thermal solver API
  Allows you to create or add functionality to enhance the thermal solver capabilities.
- Thermal solver error message list
  Lists solver messages that the thermal solver generates to communicate issues with the model or the solve.

Radiation patches

The radiation patches are used to accelerate the solution of radiative heat transfer when using the Oppenheim method. This approach is not supported by the Gebhardt method.

The Oppenheim method is used to model radiative heat transfer by tracking the radiosity of each surface element. This is achieved through the automatic creation of non-geometric Oppenheim elements, which are incorporated into the thermal solution matrix.

The governing equation for radiative exchange in an enclosure using this method is:

Where:

ε_k is the emissivity of surface element k
T_k is the temperature of surface element k
T_o,k is the radiosity temperature of element k
F_kj is the view factor from element k to element j

The concept of coarse radiation patches is introduced to improve computational efficiency. In this approach, the Oppenheim elements of several adjacent surface elements are merged into a single patch.

On the left, many brown and green bars —representing elements and imaginary Oppenheim elements respectively— are connected by dotted lines. On the right, the green bars are grouped with fewer, simpler dotted connections.

However, this process can introduce false conduction paths—unintended thermal connections that do not physically exist. When multiple elements are patched together, especially across misaligned surfaces, the solver may incorrectly assume thermal connectivity between elements. To correct this, negative conductance terms are introduced between patched elements. These terms eliminate the artificial thermal pathways created by the patching process.

The solver scans the finite element mesh and automatically groups elements into patches based on the following criteria:

Elements must share at least one common node to be included in the same patch.
Patches cannot span across physical barriers, such as fences in the mesh.
All elements within a patch must have identical radiative characteristics, for example, emissivity, reflectivity.
The angle between the normals of adjacent elements must not exceed a specified limit, which is by default is 15°.

You can refine the automatic patching process as follows:

Define specific groups of elements to be patched together.
Specify groups of elements that should not be patched together.
Restrict patching to within defined groups.
Set allowable element size for patching.