External Radiation Source

Use this node in 2D and 3D components to define an external radiation source as a point or directional radiation source with view factors calculation. Only the external view factors (Fext) are recomputed when the radiation source moves, not the complete view factors. When specular radiation is involved (with or ), the cost of computation of these external view factors can be important. Each node contributes to the incident radiative heat flux on all spectral bands, GBi on all the boundaries where a , or boundary condition is active. The source contribution, GextDir, i, is equal to the product of the view factor of the source by the source radiosity. For radiation sources located on a point, GextDir, i=Fext, i Ps, i. For directional radiative source, GextDir, i = Fext, i q0, s.

Only direct irradiation from the source is accounted for. Diffuse irradiation inclusion is controlled through the check box in section of Diffuse Surface (Surface-to-Surface Radiation Interface) and Diffuse Mirror (Surface-to-Surface Radiation Interface) features.

	The external radiation sources are ignored on the boundaries when neither Diffuse Surface, Diffuse Mirror, Opaque Surface nor Semitransparent Surface is active.

Select a : (default) or . In 3D, is also available.

For define the xs. The source radiates uniformly in all directions.

	xs should not belong to any surface where a Diffuse Surface, Diffuse Mirror, Opaque Surface or Semitransparent Surface boundary condition is active.

For define the is.

	Solar position is available for 3D components. When this option is selected, use it to estimate the external radiative heat source due to the direct striking of the Sun rays. North, west, and the up directions correspond to the x, y, and z directions, respectively. Azimuth angle is measured from true north, hence x direction corresponds to true north as well.

Depending on the presence of an node under and on the type of selected in this node, further parameters should be set for the definition of the location on earth.

If the type of is or in the node under , it is available in the list of the node. When selected from this list, the location is set to the selected in the node under . Click to select the check box to add one hour to the default setting for the station selected.

Else, when is in the node under , is the only option in the list of the node, and the following parameters should be set.

Select an option from the list: (default) or .

For select a predefined city and country combination from the list. Click to select the check box to add one hour to the default setting for the city selected. For example, if is selected and the default standard time zone is UTC–5 hours, when the check box is selected, the daylight saving time is used instead (UTC–4 hours).

If is selected, or your city is not listed in the table, define the following parameters:

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, a decimal value, positive in the northern hemisphere (the default is Greenwich UK latitude, 51.477). Enter a value without a unit to avoid double conversion. This is because the latitude value is expected to represent degrees but the model’s unit for angles may be different (for example, the SI unit for the angle is radians).

•

, a decimal value, positive at the east of the Prime Meridian (the default is Greenwich UK longitude, −0.0005). Enter a value without a unit to avoid double conversion. This is because the latitude value is expected to represent degrees but the model’s unit for angles may be different (for example, the SI unit for the angle is radians).

•

, the number of hours to add to UTC to get local time (the default is Greenwich UK time zone, 0). For example in the time zone is UTC–5 hours (standard time zone) or UTC–4 hours (with daylight saving time).

For either selection ( or ), in the table enter the:

•

, the default is 01. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent days but the model’s unit for time may be different (for example, the SI unit for time is seconds).

•

, the default is 6 (June). Enter a value without a unit to avoid double conversion. This is because the value is expected to represent months but the model’s unit for time may be different (for example, the SI unit for time is seconds).

•

, the default is 2012. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent years but the model’s unit for time may be different (for example, the SI unit for time is seconds). The solar position is accurate for a date between 2000 and 2199.

For either selection ( or ), in the table enter the:

•

, the default is 12. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent hours but the model’s unit for time may be different (for example, the SI unit for time is seconds).

•

, the default is 0. Enter a value without a unit to avoid double conversion. This is because the value is expected to represent minutes but the model’s unit for time may be different (for example, the SI unit for time is seconds).

For temporal studies, these inputs define the start time of the simulation. By default, the check box is selected, and the time is then automatically updated with the time from the solver. Clear this check box to manually set the time update.

For either selection of type in an node under , define the field Is as the incident radiative intensity coming directly from the sun. Is represents the heat flux received from the sun by a surface perpendicular to the sun rays. When surfaces are not perpendicular to the sun rays the heat flux received from the sun depends on the incident angle.

For , enter a value or expression for the Is. Else, select a defined in an node under .

If is or , the solar irradiance is divided among all spectral bands Bi as qs, i = q0,sFEPi(Tsun) where FEPi(Tsun) is the fractional blackbody emissive power over Bi interval at Tsun = 5780 K.

This section is available when is set either to or .

If is , enter a value or expression to define the Ps.

If is or , set the to , , or .

When is set to , enter a value or expression for the Ps,λ. The wavelength may be accessed through the rad.lambda variable. This distribution is integrated on each spectral band to obtain the source heat rate Ps,i for each spectral band.

When is set to , enter a value for the Ts and the Ps, to define the source power on the spectral band Bi as Ps, i = FEPi(Ts)Ps where FEPi(Ts) is the fractional blackbody emissive power over Bi interval at Ts.

When is set to , enter a value for the Ps,i for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.

If is , enter a value or expression to define the q0,s. Alternatively, select a defined in an node under .

If is or , set the to , , or .

When is set to , enter a value or expression for the q0,s,λ. The wavelength may be accessed through the rad.lambda variable. This distribution is integrated on each spectral band to obtain the source heat flux q0,s,i for each spectral band.

When is set to , enter a value for the Ts and the q0,s, to define the source heat flux on the spectral band Bi as qs, i = FEPi(Ts)q0,s where FEPi(Ts) is the fractional blackbody emissive power over Bi interval at Ts.

When is set to , enter a value for the q0,s,i for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.