Inertia loading: 1G GRAV load (down)
Description: Used to define gravity vectors to determine gravity loading for the structural model.
$2345678$2345678$2345678$2345678$2345678$2345678$2345678$2345678 $1111111$0222222$3333333$4444444$5555555$6666666$7777777$8888888 $GRAV SID CID G N1 N2 N3 GRAV 200 0 386.4 0.0 0.0 -1.0
SID = load id.
CID = coordinate system id. A CID=0 references the basic coordinate system. If CID=-1, the gravity vector components are in the local displacement coordinate system of the grid points.
G = gravity vector scale factor.
N1, N2, N3 = gravity vector components measured in coordinate system defined by CID.
Nastran does allow a global change in Mass units with the parameter WTMASS. This is typically used when using English units so the user can enter concentrated masses, densities, etc with weight units since this is easier to think in terms of weight than actual English mass units. NASTRAN will then multiple the assembled structural mass matrix by the value on the PARAM WTMASS card hence converting the weight to mass. The relationship of mass to weight is: weight= mass*gravity. So to convert weight to mass is 1/gravity. Applicable WTMASS values would be:
PARAM, WTMASS, value
1/32.2[ft/s^2]=0.031056
1/386.4[in/s^2]=0.002588
This parameter is used when material density is input in weight instead of mass units.
rho_m = (1/g)*rho_w
rho_m = mass or mass density
rho_w = weight or weight density
Recent Comments