COMSOL Multiphysics™

elirradiation
Purpose
elirradiation
Define irradiation variables for radiative heat transfer.
Syntax
Description
el.elem = 'elirradiation'
el.g{ig} = geomnum
el.method = 'area' | 'hemicube'
el.iorder = order
el.resolution = res
el.cache = 'on' | 'off'
el.geomdim{ig}{edim}.ind{eldomgrp} = domainlist
el.geomdim{ig}{edim}.name{eldomgrp} = Gname
el.geomdim{ig}{edim}.ambname{eldomgrp} = Fname
el.geomdim{ig}{edim}.expr{eldomgrp} = Jexpr
el.geomdim{ig}{edim}.opexpr{eldomgrp} = opacity
el.geomdim{ig}{edim}.cavity{eldomgrp} = cavitylist
The elirradiation element defines one variable Gname representing the local
irradiation from other surfaces and one Fname, known as ambient view factor,
representing the fraction of the field of view not covered by other surfaces. The
variable names can differ between domain groups.
The irradiation at each point depends on the radiosity at all other visible surface
points. An expression for the radiosity is provided in the expr field. For interior
boundaries, it has to be made clear in which direction the radiation goes. The
opacity expression is evaluated on adjacent subdomains, and is expected to be
non-zero on exactly one.
To avoid unnecessary visibility checks, the surfaces can be manually assigned to one
or more cavities, each of which exchanges radiation only with other surfaces in the
same cavity. For each domain group, specify to which cavities the group belongs.
There are currently two view factor evaluation methods which can be selected using
the method field. The 'area' method implies direct area integration using a simple
quadrature rule of order order and no visibility checks. Different convex cavities
can be held apart using the cavity field. The 'hemicube' method, and its
generalizations to lower dimensions, uses techniques borrowed from computer
graphics to handle surfaces obstructing each other. Essentially, images of resolution
res-by-res are generated from each evaluation point in 3D.
Due to the rather complex evaluation, it is usually beneficial to store the view factors
between calls. This can, however, generate a lot of data, which can potentially be a
limiting factor preventing a solution on a given system. Therefore, the cache field
can be set to 'off', but this increases run times considerably.
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