Learning Forum

[DavideGiuliano]

Good morning,

I bumped into the Explicit dynamics guide and I was wondering if somebody could explain to me a bit more in detail what P_shift represents in the ideal gas EOS (see figure attached):

[Ram Gopisetti]

the pshift has to be defined by the user, but you may leave it blank given that if the material undergoing compression in isothermal environemnts. one way is to to calibrate Pshift based on an test case untill residual velocities are minimised.
Cheers, Ram

[Chris Quan]

P_shift is a parameter defined by the user. Its default value is zero.
Specific Internal Energy e is a parameter in Ideal Gas EOS that requires input and cannot be zero.
When ideal gas EOS is used to model ambient air and P_shift is equal to zero, the initial pressure of the gas will not be zero. It is equal to one atmospheric pressure, due to non-zero Specific Internal Energy. This can result in the small unwanted velocities in both gas and its surrounding materials.
When ideal gas EOS is used to model ambient air and P_shift is equal to the initial pressure, for example the atmospheric pressure. The ambient air will have zero initial pressure, which won't have any unwanted initial velocity in the gas and its surrounding materials.
If ideal gas EOS is used to model explosions or blast loadings with P_shift is equal to one atmospheric pressure, the pressure you got from the equation in the explosion region will be over-pressure. More information about over-pressure can be found in Overpressure - Wikipedia

[DavideGiuliano]

Thank you very much!
Davide