Radiation modeling methods and optical properties
This lesson explains the two Radiation simulation object types and how each defines radiative enclosures and affects radiation calculation efficiency.
This lesson may include hands-on exercises. Review the Discussion section for background information or click the button to proceed to the practical section.
Discussion
Accurate radiation modeling requires both appropriate optical properties and reliable numerical methods for calculating radiative exchange.
- Thermo-optical properties
- Thermo-optical properties define how a surface emits, absorbs, reflects, and transmits radiation. These properties can be defined as gray, where values are independent of wavelength, or non-gray, where properties vary with wavelength, direction, or angle of incidence.
Simcenter 3D supports advanced thermo-optical modeling, including temperature-dependent emissivity, wavelength-dependent properties, and multiple optical property states. These capabilities are essential when modeling applications such as solar heating, multilayer insulation, or materials with strong spectral variation.
- Radiation modeling
- There are two types of Radiation simulation objects,
which define how radiative enclosures are treated.
Use All Radiation to automatically detect enclosures based on element sides with defined thermo-optical properties. This option is suitable for models that form a single, complete enclosure and do not require explicit modeling of radiation leaving the enclosure.
Use Enclosure Radiation to explicitly define physical enclosures. This approach improves efficiency by reducing the size of the radiation matrix.
- Radiation methods
- Several numerical methods are available to calculate view factors and radiative exchange, including:
- Hemicube Rendering to calculate view factors using the workstations' graphics card.
- Deterministic to calculate view factors by iteratively selecting element pairs.
- Monte Carlo that is a ray-casting or ray-tracing method used in many applications including the calculation of view factors.
- GPU Computed View Factors to compute the radiative view factors. The thermal solver initially computes the black body view factors assuming the body is perfectly black. Then, it adjusts them to account for the actual surface properties, resulting in gray body view factors.
- GPU Computed Ray Tracing to perform ray tracing on the GPU to compute radiative conductances directly.
Each method provides a different balance between accuracy and computational cost. To better understand how to select a radiation computation method, use the following table, which shows a comparison of the computational methods.
Comparison parameters Hemicube Rendering Deterministic Monte Carlo GPU Computed View Factors GPU Computed Ray Tracing Computation device CPU CPU CPU GPU GPU Supported thermo-optical properties Diffuse properties Diffuse, specular, and transmissive properties All Diffuse properties, ignores transmissivity and specular properties Diffuse, specular, and transmissive properties Performance Fast Good Competitive with Hemicube for planar surfaces
Slow for diffuse properties and large models Competitive for specular and transmissive properties
Very fast Much faster than the Monte Carlo or deterministic methods, but slower than the GPU computed view factors method View factor results Yes Yes Only when specified Yes No Computation of radiative heat loads No Only used to compute geometric view factors for diffuse reflections
Yes Diffuse reflections calculated using geometric view factors
Yes Direct computation
No Yes Direct computation
Advantages Fast for large diffuse problems Computes shadowed view factors quickly and accurately
High accuracy for complex radiation Handles specular effects
Handles partial illumination of individual elements accurately Handles complex models of diffuse reflection and transmission, through definition of BRDFs and scattering in participating media
Extremely fast Handles partial illumination of individual elements accurately
Very fast Models complex physical effects of real surfaces including reflection, transmission, absorption, solar and IR properties
Accounts for specular and transparent effects
Disadvantages Assumes uniform illumination per element; less accurate for complex shading Computationally expensive, slower on large models Inefficient for large models, requires significant computational resources Cannot model real surfaces effects Computationally more expensive than GPU computed view factors - Radiative heating
- Radiative heating models the conversion of incoming solar or infrared radiation into thermal heat loads on model surfaces. In this process, defined heat sources emit radiation, while surrounding surfaces interact with that radiation through absorption, reflection, and transmission.
Radiative heating is defined using the Radiative Heating simulation object. This object allows you to specify radiative heat sources, identify illuminated entities, and control the magnitude, type, and direction of the emitted radiation. Both collimated and diffuse radiation sources can be defined, depending on the physical characteristics of the heat source.
The thermal solver calculates the direct incident flux by computing radiative view factors between emitting sources and illuminated surfaces. Ray tracing is automatically used to model specular reflections and transmissions of the incident radiation. Deterministic and Monte Carlo methods control how rays are traced and how reflected energy is distributed.
Radiative heating capabilities enable accurate modeling of complex illumination scenarios, including reflected radiation, directional heat sources, and interactions with advanced thermo-optical properties.
Hands-on material
To gain experience with the topics discussed here, complete the following:
