Directional Flux applies to 2D or 3D Target, but does not apply to Nodal and 1D targets. Normal surface directions are uniquely and simply determined for 2D & 3D types. Directional flux may be applied to 2D edges. Edges are considered a long and narrow surface by referencing the thickness of 2D property. The surface normal vector is parallel with the surface and vertical with the edge. The Vector Pointing to Source direction is from the surface to the source. If the angle between the surface normal and the source vector is less than 90 degrees, a heat source is created. If the angle exceeds 90 degrees, no heat source is created. The effective heat applied to an element is the product of incident heat times absorptivity, element surface area, dot product between the vectors (if the dot product is positive, zero if it is negative).

Absorptivity can refer to a temperature function (tabular input), heat flux can refer to a time function or a temperature function (also tabular input). Please note: absorptivity and heat flux here will be merged into one variable during translation. Because of this, only one function can be specified for the entire load. Two different temperature functions, or a combination of temperature and time functions is not supported.

Directional flux has three variables that can reference spatial fields: Absorptivity, Heat Flux and Vector Pointing to Source. They can reference 3 spatial fields at the same time. Please note: Vector Pointing to Source can reference one vector spatial field, not 3 scalar spatial fields for the 3 directions. The Thermostat option may NOT be combined with the Directional Flux load.