This routine models the aerodynamic forces and moments which act on a vehicle. Aerodynamics modeling provides the sensitivities of a particular vehicle to wind gusts. This program requires wind tunnel aerodynamic coefficient data for the vehicle being modeled and they must be taken according to SAE J1594 conventions for Vehicle Aerodynamics Terminology.

The user is provided an option of using two wind force points of application or only one. This option depends on the source and type of wind tunnel data. Europe tends to require two points where data in the U.S. is typically resolves to a single point. To apply aerodynamic forces at two positions on the body, the GFORCE statement described below must be duplicated at both points.

A wind velocity and angle SPLINES allow the modeler to simulate wind fans, chaotic wind forces and so on. The wind properties can be dependent on distance (useful for wind fan modeling) or on time (which allows to user to more easily investigate vehicle sensitivity versus speed). The wind velocity and angle are with respect to ground. The routine calculates relative wind speed and direction based on vehicle velocity and yaw angle.

The aerodynamic GFORCE statement takes the following form:

GFORCE/id, I=imrkr, JFLOAT=jmrkr, RM=bm_sae ,
,FUN = USER ( 1102,tarea,twb,rho,dscale,dragid,sforid,liftid,rollid, pitid,yawid,itype,windv,winda,imark)

where:

The force application MARKER, "imark", must be in vehicle SAE orientation. The origin of this MARKER must coincide with the location at which the coefficients were measured (or be placed at the location to which the coefficients were resolved).

As a general note, the force consistency factor is test section area of the vehicle and the moment consistency factor is the test area * wheelbase. These factors must be properly passed to accurately represent the forces and moments.

The following is an example of the aerodynamics GFORCE in a vehicle model: