# Coordinate System#

Coordinate System = {char_string}


## Description / Usage#

This card is required for each material section in the Problem Description File. It is used to specify formulation of the equations to be solved. Valid options for {char_string} are as follows:

 CARTESIAN For a two (x-y) or three (x-y-z) dimensional Cartesian formulation. CYLINDRICAL For an axisymmetric (z-r) or three-dimensional cylindrical (z-r-$$\theta$$) formulation; the three-dimensional option has not been tested. SPHERICAL For a spherical (r-$$\theta$$-$$\phi$$) formulation. SWIRLING For a two-dimensional formulation (z-r-$$\theta$$) with a swirling velocity component that is independent of azimuthal coordinate. PROJECTED_CARTESIAN For use in the analysis of the three-dimensional stability of a two-dimensional flow field. The formulation (x-yz) has a z-velocity component that is independent of the z-direction.

## Examples#

The following is a sample card that sets the coordinate system to Cartesian:

Coordinate System = CARTESIAN


## Technical Discussion#

Note the coordinate ordering for the CYLINDRICAL and SWIRLING options where the z-direction is first followed by the r-component (which in lay terms means the modeled region/part will appear to be ”lying down.”) If the SWIRLING option is activated, Goma expects a third momentum equation for the $$\theta$$-direction, i.e. EQ = momentum3, as explained in the equation section. The third component is basically the azimuthal $$\theta$$-velocity component, and the appropriate boundary conditions must be applied, e.g., on the w-component as described in the Category 4 boundary conditions for Fluid Momentum Equations.

No References.