Exact Phase-Space Analytical Solution for the Power-Law Damped Contact Oscillator

Abstract: We present an exact phase-space analytical treatment of the power-law damped contact oscillator governed by $m\ddotδ + α\sqrt{mk_H}\,δ^{(p-1)/2}\dotδ + k_Hδ^p = 0$, valid for all force-law exponents $p \geq 1$ and all initial impact velocities $v_0$. The central result is the transformation $δ= Ax^{2/(p+1)}$, where $A = [(p+1)/2]^{1/(p+1)}$, which maps the nonlinear phase-space equation $v\,dv/dδ+ \dots = 0$ exactly onto a linear spring-dashpot (LSD) system with effective damping ratio $α\text{eff} = \fracα{\sqrt{2(p+1)}}$. The phase portrait $v(δ)$, coefficient of restitution $e$, and maximum penetration $δ\text{max}$ follow in closed form. The physical time-domain solution $(δ(t), v(t))$ is obtained parametrically via a single quadrature, which evaluates analytically for $p=1$ and at negligible numerical cost for all other $p$. We prove that $e$ is exactly independent of $v_0$ for all $p \geq 1$ and derive the universal calibration formula: $α= \sqrt{2(p+1)}\cdot\frac{-\ln e}{\sqrt{π^2 + \ln^2 e}}$. This generalises the known results for $p=1$ (linear spring-dashpot) and $p=3/2$ (Hertz contact, Antypov and Elliott, 2011) to the entire power-law family. A closed-form estimate for the critical timestep of explicit time integration is also derived, exhibiting universal scaling with impact velocity and force-law exponent.