OBJECTIVE DATA DRIVEN AERODYNAMIC FORCES - MOTORSPORTS APPLICATIONS
This routine models the aerodynamic forces and moments which act on a vehicle. This program requires wind tunnel or track tested aerodynamic downforce and drag data for the vehicle being modeled. This information is typically in a 3-D force format with each downforce and dragforce a function of the front and rear ride height. It is important that wind tunnel or track tested data is referenced to the appropriate points in the Adams model. These points are defined in the body subsystem file and can be placed where actual ride height measurements are taken.
The front and rear downforces application points are defaulted to the centerline of front/rear axle locations at ground height. The dragforce is applied to the vehicle cg location.
There are four forces that represent the aerodynamic forces on the body: Front Downforce, Rear Downforce, Drag Force and the Drag Restoring Moment. Since the aerodynamic pitch moment caused by the drag force is directly represented by the front and rear downforce value from the tunnel or track, a restoring moment is required to elimate the duplication of the pitch forces.
The aerodynamic drag and lift of the tire/wheel assembly can also be modeled and are funtions of vehicle speed.
The aerodynamic SFORCE statement takes the following form:
SFORCE/id, TRANS, ACTION, I=imrkr, J=jmrkr
,FUN = USER (1104,aeroid,shiftid,setupid,clipid,velconv,forconv,disconv)
where:
aeroid | = | id of aeroforce; 1 = Front Downforce, 2 = Rear Downforce, 3 = Dragforce |
shiftid | = | ARRAY id of aeroforce shift and scale |
setupid | = | ARRAY id of aerodynamic reference values |
clipid | = | ARRAY id of aerodynamic extrapolation limits |
velconv | = | aerodynamic velocity conversion (mph to mm/s) |
forconv | = | aerodynamic force conversion (lbf to N) |
disconv | = | ride height conversion (in to mm) |
Three ARRAYS are used to define the aerodynamic setup and additional parameters
ARRAY/shiftid, NUM=(currho, fdfscale, fdfshift, rdfscale, rdfshift, dfscale, dfshift)
where: currho = density of air in simulation
fdfscale = front downforce scale factor
fdfshift = front downforce shift factor
rdfscale = rear downforce scale factor
rdfshift = rear downforce shift factor
dfscale = downforce scale factor
dfshift = downforce shift factor
ARRAY/setupid, NUM=(refrho, refvel, fdfid, rdfid, dfid, frhmkr, rrhmkr, gndmkr, cgmkr)
where:
refrho = density of air during wind-tunnel or track test
refvel = airspeed during wind-tunnel or track test
fdfid = SPLINE id of front aerodynamic downforce spline
rdfid = SPLINE id of rear aerodynamic downforce spline
dfid = SPLINE id of aerodynamic dragforce spline
frhmkr = front ride height reference marker
drrhmkr = rear ride height reference marker
fgndmkr = ground reference marker
dcgmkr = body cg reference marker
ARRAY/clipid, NUM=(frhmin, frhmax, rrhmin, rrhmax)
where:
frhmin = front ride height minimum extrapolation limit
frhmax = front ride height maximum extrapolation limit
rrhmin = rear ride height minimum extrapolation limit
rrhmax = rear ride height maximum extrapolation limit
The following is an example of the front downforce SPLINE where the first row (X) is the matrix of front ride height values. The additional rows of Y represent the rear heights and the associated front downforce value at the corresponding front and rear ride height value.
! FRONT DOWN FORCE (LBS @ VEHICLE VELOCITY = 200 MPH)
! X = front ride height (inches)
! Y = rear ride height (inches)
!SPLINE/11,
,X=0.25,0.5,0.75,1,1.25,1.5,2
,Y= 0.25,2064,1937,1795,1622,1410,1198,913
,Y= 0.50,2124,1963,1836,1658,1460,1250,960
,Y= 0.75,2151,2009,1877,1697,1510,1316,1015
,Y= 1.00,2200,2056,1918,1735,1697,1348,1051
,Y= 1.50,2287,2126,2000,1845,1644,1441,1140
,Y= 2.00,2372,2187,2053,1920,1737,1552,1203
,Y= 2.50,2437,2238,2120,2000,1813,1626,1280
,Y= 3.00,2497,2296,2185,2049,1868,1687,1339
, LINEAR_EXTRAPOLATE