Radiation Shield, Upside (Surface-to-Surface Radiation Interface)
This node defines the shield type and radiative properties on the upside of the Radiation Shield (Surface-to-Surface Radiation Interface) parent node. Depending on the shield type, this feature computes the innermost temperature of the shield and the heat flux between the boundary and the shield if the shield consists of only one layer, as well as the outermost temperature of the shield and the heat flux across the shield if it consists of multiple layers. These temperatures are calculated in order to reach the equilibrium between the heat flux between the upside of the boundary and the shield and all heat fluxes involved on the outermost side of the shield. The heat fluxes involved inside the shield are assumed to be all radiative.
This condition can only be applied on boundaries that radiate on the upside. See Diffuse Surface (Surface-to-Surface Radiation Interface) to define the radiation direction.
In order to calculate the heat flux between the boundary and the shield, the emissivity on the upside of the boundary under the radiation shield is required. This emissivity is defined by the Diffuse Surface (Surface-to-Surface Radiation Interface) or Opaque Surface (Surface-to-Surface Radiation Interface) node with which the radiation shield is used. When combined with a Opaque Surface feature, its Directional emissivity function is not considered and thus must be set to Zero.
Fractional Emissive Power
These settings are the same as for the Diffuse Surface (Surface-to-Surface Radiation Interface) node.
Initial values
Depending on the Shield type set in the Shield Settings section of this node, further settings display underneath.
When the Shield type is set to Single-layer insulation, the Shield initial temperature can be defined From boundary or User defined.
When the Shield type is set to Multilayer insulation, the Shield initial temperature, outermost side and the Shield initial temperature, innermost side can also be defined From boundary or User defined.
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When From boundary is selected, the corresponding initial temperature is set to the initial temperature of the boundary, defined by the Initial Values (Surface-to-Surface Radiation Interface) node.
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When User defined is selected, enter a value or expression to define the corresponding initial temperature.
Shield Settings
The upside direction is shown on the geometry in the Graphics window. Hide the symbols with the Show Upside Direction button () (selected by default).
Select the Shield type from the list:
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For Multilayer insulation (default), the shield consists of at least two layers, with N layers in between. Set the Number of inner layers to specify N.
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For Single-layer insulation, the shield consists of only one layer.
Layer Radiative Properties
This section defines the emissivity of the layers, as well as the specular reflectivity of the outermost side of the shield when the Surface-to-surface radiation method is set to Ray shooting in the Surface-to-Surface Radiation interface settings.
Depending on the Shield type and the Wavelength dependence of radiative properties set in the Radiation Settings section of the interface, further settings display underneath.
If Wavelength dependence of radiative properties is Constant:
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By default, the Emissivity εsh (dimensionless) and Specular reflectivity, outermost side ρs,sh use values From material. Make sure that a material is defined at the boundary level (by default materials are defined at the domain level). The Specular reflectivity, outermost side can only be set when the Surface-to-surface radiation method is set to Ray shooting in the Surface-to-Surface Radiation interface settings.
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For User defined, set a value or expression.
If Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands:
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By default, the Emissivity εsh (dimensionless) and Specular reflectivity, outermost side ρs,sh use values From material.
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When Emissivity is set to User defined, enter a value or expression for the Emissivity εsh. The wavelength can be accessed through the rad.lambda variable. Any expression set for the emissivity is then averaged on each spectral band to obtain a piecewise constant emissivity. If the average value of the emissivity on each band is known, you can instead use the User-defined for each band option to avoid the evaluation of the average.
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When Specular reflectivity, outermost side is set to User defined, enter a value or expression for the Specular reflectivity, outermost side ρs,sh. The wavelength can be accessed through the rad.lambda variable. Any expression set for the emissivity is then averaged on each spectral band to obtain a piecewise constant emissivity. If the average value of the emissivity on each band is known, you can instead use the User-defined for each band option to avoid the evaluation of the average.
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When Emissivity is set to User-defined for each band, enter a value for the Emissivity for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.
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When Specular reflectivity, outermost side is set to User-defined for each band, enter a value for the Specular reflectivity, outermost side for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.
Select the Define emissivity on each layer side checkbox to set specific values on each layer side. When the Shield type is set to Single-layer insulation, select the Shield boundary material, outermost side and the Shield boundary material, innermost side to have different emissivities on each side of the shield. In addition, when the Shield type is set to Multilayer insulation, select the Shield boundary material, inner sides to specify the emissivity on all inner sides, including those of the innermost and outermost layers. The boundary material specified is used only when Emissivity, outermost side or Emissivity, innermost side or Emissivity, inner sides are From material.
Inconsistent Stabilization
This section is available by clicking the Show More Options button () and selecting Stabilization in the Show More Options dialog.
The Thermal mass option (selected by default) adds an extra time-derivative term to the shield temperature variables, representing a thermal mass. Increasing the Tuning parameter δ amplifies the effect of the thermal mass. As a rule of thumb, the tuning parameter should be large enough to ensure convergence, while remaining as small as possible as it reduces the accuracy of the original problem. For steady-state problems, this option has no effect.
To define temperature dependencies for the user inputs, use the rad.Tshieldu if the Shield type is set to Single-layer insulation, and rad.Tshield_ou or rad.Tshield_iu if the Shield type is set to Multilayer insulation to refer to the outermost or innermost temperature of the shield respectively.