SURF251 Element Description

SURF251 is used for radiation surface loads and can be used only with the radiosity solver method. It can be overlaid onto a face of any 2-D thermal solid element that supports temperature DOF. This element is applicable to 2-D thermal analyses (planar or axisymmetric). Various other loads and surface effects may exist simultaneously (e.g., SURF151 and SURF153 and SURF251 may be applied on the same solid element faces to support convection heat flux and radiation heat flux loads).

This element can be created only by the RSURF command. The underlying solid surface must also have the RDSF flag.

Figure 251.1:  SURF251 Geometry

SURF251 Input Data

The geometry, node locations, and the coordinate system for this element are shown in Figure 251.1: SURF251 Geometry. The element is defined by two nodes, regardless of the underlying solid element.

You would typically generate SURF251 elements via the RSURF command, creating elements which are coincident with the solid element surface. However, if you are using decimation (RDEC), then the surface elements created will not coincide with the underlying solid element topology. See Figure 251.2: SURF251 Elements Without Coincident Nodes. Symmetrical SURF251 elements (produced when using the symmetry options [RSYMM]) can have no underlying solid elements. The RSURF command always produces extra nodes to define the SURF251 topology as shown in Figure 251.2: SURF251 Elements Without Coincident Nodes, regardless if RDEC is used.

Figure 251.2:  SURF251 Elements Without Coincident Nodes

You cannot apply any loads on this element. During solution, the element extracts the temperature of the solid element and computes the radiation heat flux, which is transferred back as a surface load to the solid element.

The next table summarizes the element input. Element Input gives a general description of element input.

SURF251 Output Data

Table 251.1: SURF251 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in Table 151.3: SURF151 Item and Sequence Numbers:

The net radiation heat flux is the sum of the directly emitted radiation flux [εσT⁴] plus the reflected radiation flux [(1–ε)q_i] minus the incoming radiation [q_i], as shown in Figure 251.3: Net Radiation Heat Flux.

Figure 251.3:  Net Radiation Heat Flux

SURF251 Assumptions and Restrictions

SURF251 Product Restrictions

There are no product-specific restrictions for this element.