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How to use 'Gravity card'

User: "allen_21155"
Altair Community Member
Updated by allen_21155

I have confused the definition of "gravity vector scale factor"(G) which is a parameter in the GRAV card. It's that mean the gravitational acceleration in kg/s^2 or the weight in Newton?  Here is a Screenshotimage. Does anyone have an idea? 

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    User: "Adriano_Koga"
    Altair Employee
    Updated by Adriano_Koga

    gravity is just gravity acceleration (m/s2 or mm/s2 or whatever units you're using).

     

    This is a vector, so it has the magnitude and its components (X, Y and Z multipliers) defining its direction.

     

    So, if G = 9810mm/s2, and you want to make it work in -Z direction, your vector will be N1=0, N2=0 and N3=-1.0

    if you want to apply a 4G load in Y+ direction, G=9180mm/s2 and N1=0, N2=4.0 and N3=0.

     

    User: "Vladimir_Gantovnik"
    Altair Community Member
    Updated by Vladimir_Gantovnik

    gravity is just gravity acceleration (m/s2 or mm/s2 or whatever units you're using).

     

    This is a vector, so it has the magnitude and its components (X, Y and Z multipliers) defining its direction.

     

    So, if G = 9810mm/s2, and you want to make it work in -Z direction, your vector will be N1=0, N2=0 and N3=-1.0

    if you want to apply a 4G load in Y+ direction, G=9180mm/s2 and N1=0, N2=4.0 and N3=0.

     

    Adriano, so if the model is in inches (US system), G=386.0885 in/s^2, then for 75G in x+ direction I should use this card:

    GRAV     3       1      386.0885   75.       0.      0.  

    Is it correct?

    p.s. For US units (if the density is in lb/in^3) we also add (Nastran type parameter):

    PARAM, WTMASS, 0.00259

    Thank you!

    Vladimir