visoelastic parameter in Abaqus

Hi,

I am trying to input the parameters for a viscoelastic material. I have the complex shear modulus [G_S(ω) and G_L(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*) = G_L(ω)/(ωG_∞)

I(g*) =  [G_∞ - G_S(ω)]/(ωG_∞)

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

Thanks a lot!

Bo