visoelastic parameter in Abaqus

Hi,

I am trying to input the parameters for a viscoelastic material. I have the complex shear modulus [GS(ω) and GL(ω)] of the material within a certain frequency range. How do I derive the I(g*), R(g*) and G∞ that are required for Abaqus to work?

From the Abaqus manual:

R(g*) = GL(ω)/(ωG∞)

I(g*) =  [G∞ - GS(ω)]/(ωG∞)

However, the question is G∞ is a another unknown, how do I derive it?

Thanks a lot!

Bo