Question in modeling pounding

[Muneebalam]

Hello.

I am new to OpenSees. I want to model pounding between 2 adjacent 2D frames during earthquake. I want to use the impact material which can be found on this page https://opensees.berkeley.edu/wiki/inde ... t_Material . This material is an approximated model of the hertz contact model with damping as mentioned on this page.

I am facing one issue in using this model. In the description of this page, there can be found a formula for the energy dissipation during impact.

E = kh * δm^(n+1) * (1-e^2) / (N+1)

Here E is the energy dissipated, kh is the impact stiffness parameter of the hertz model, n is the exponent in the hertz power rule ( typically taken as 3/2), e is the coefficient of restitution, δm is the maximum penetration during the pounding event .

However there is no explanation of what capital "N" means here in this formula. Can anyone please help me and explain what is this capital "N" here and how I can get its value?