SFA
SFA, Area, LKEY, Lab, VALUE, VALUE2
Specifies surface loads on the selected areas.
AreaArea to which surface load applies. If ALL, apply load to all selected areas (ASEL). If
Area= P, graphical picking is enabled and all remaining command fields are ignored (valid only in the GUI). A component may be substituted forArea.LKEYLoad key associated with surface load (defaults to 1). Load keys (1,2,3, etc.) are listed under "Surface Loads" in the input data table for each element type in the Element Reference.
LKEYis ignored if the area is the face of a volume region meshed with volume elements.LabValid surface load label. Load labels are listed under "Surface Loads" in the input table for each area type in the Element Reference.
Discipline Body Load Label Label Description Structural PRES pressure Thermal CONV[1] convection HFLUX[1] heat flux RDSF surface-to-surface radiation Acoustic fluid FSI[2] fluid-structure interaction flag IMPD impedance boundary flag SHLD surface normal velocity or acceleration MXWF Maxwell surface flag or equivalent source surface FREE free surface flag INF exterior Robin radiation boundary flag PORT Port number ATTN Absorption coefficient BLI Viscous-thermal boundary layer surface flag Magnetic MXWF Maxwell force flag Electric CHRGS surface charge density MXWF Maxwell force flag Infinite element INF Exterior surface flag for INFIN110 and INFIN111 Field-surface interface FSIN field-surface interface number VALUESurface load value or table name reference for specifying tabular boundary conditions.
If
Lab= CONV:VALUEis typically the film coefficient andVALUE2(below) is typically the bulk temperature. IfLab= CONV andVALUE= -N, the film coefficient may be a function of temperature and is determined from the HF property table for materialN(MP). (See the SCOPT command for a way to override this option and use -Nas the film coefficient.) The temperature used to evaluate the film coefficient is usually the average between the bulk and wall temperatures, but may be user-defined for some elements.If KBC,0 has been issued for ramped loads, it affects only VALUE2, the bulk temperature, and the film coefficient specification is unaffected.If
Lab= PORT,VALUEis a port number representing a waveguide exterior port. The port number must be an integer between 1 and 50. For acoustic 2×2 transfer admittance matrix, the port number can be any positive integer. The smaller port number corresponds to the port 1 of the 2×2 transfer admittance matrix and the greater port number corresponds to the port 2. If one port of the transfer admittance matrix is connecting to the acoustic-structural interaction interface, the port number corresponds to the port 2 of the transfer admittance matrix. A pair of ports of the 2×2 transfer admittance matrix must be defined in the same element.If
Lab= SHLD,VALUEis the surface normal velocity in harmonic analysis and the surface normal acceleration in transient analysis for acoustics.If
Lab= IMPD,VALUEis resistance in (N)(s)/m3 ifVALUE> 0 and is conductance in mho ifVALUE< 0 for acoustics. In acoustic transient analyses,VALUE2is not used.If
Lab= RDSF,VALUEis the emissivity value; the following conditions apply: IfVALUEis between 0 and 1, apply a single value to the surface. IfVALUE= -N, the emissivity may be a function of the temperature, and is determined from the EMISS property table for materialN(MP). The materialNdoes not need to correlate with the underlying solid thermal elements.If
Lab= FSIN in a unidirectional Mechanical APDL to CFX analysis,VALUEis not used.If
Lab= ATTN,VALUEis the absorption coefficient of the surface.VALUE2Second surface load value (if any).
VALUE2is typically the bulk temperature for thermal analyses.If KBC,0 has been issued for ramped loads, the bulk temperature is ramped from the value defined by TUNIF to the value specified by VALUE2for the first loadstep. If tabular boundary conditions are defined, the KBC command is ignored and tabular values are used.For acoustic analyses, VALUE2 is not used. If
Lab= SHLD,VALUE2is the phase angle of the normal surface velocity (defaults to zero) for harmonic response analyses whileVALUE2is not used for transient analyses in acoustics.If
Lab= IMPD,VALUE2is reactance in (N)(s)/m3 ifVALUE> 0 and is the product of susceptance and angular frequency ifVALUE< 0 for acoustics.If
Lab= RDSF,VALUE2is the enclosure number. Radiation will occur between surfaces flagged with the same enclosure numbers. If the enclosure is open, radiation will also occur to ambient. IfVALUE2is negative, radiation direction is reversed and will occur inside the element for the flagged radiation surfaces.If
Lab= FSIN in a unidirectional Mechanical APDL to CFX analysis,VALUE2is the surface interface number (not available from within the GUI).
Notes
Surface loads may be transferred from areas to elements with the SFTRAN or SBCTRAN commands. See the SFGRAD command for an alternate tapered load capability.
Tabular boundary conditions — Tabular boundary conditions (VALUE = %tabname% and/or VALUE2 = %tabname%) are available for the following surface load labels
(Lab) only: PRES (real and/or imaginary components), CONV
(film coefficient and/or bulk temperature) or HFLUX. Use the *DIM command
to define a table.
In a mode-superposition harmonic or transient analysis, you must apply the load in the modal portion of the analysis. Mechanical APDL calculates a load vector and writes it to the MODE file, which you can apply via the LVSCALE command.
This command is also valid in PREP7.