  We present a new method for incorporating nonthermal pressure from bulk
motions of gas into an analytic model of the intracluster medium in clusters of
galaxies, which is based on a polytropic equation of state and hydrostatic
equilibrium inside gravitational potential wells drawn from cosmological dark
matter simulations. The pressure is allowed to have thermal and nonthermal
components with different radial distributions; the overall level of nonthermal
support is based on the dynamical state of the halo, such that it is lower in
more relaxed clusters. This level is normalized by comparison to pressure
profiles derived from X-ray observations, and to a high resolution
hydrodynamical simulation. The nonthermal pressure fraction measured at r_500
is typically in the range 10-20%, increasing with cluster mass and with
redshift. The resulting model cluster properties are in accord with
Sunyaev-Zel'dovich (SZ) effect observations of clusters. Inclusion of
nonthermal pressure reduces the expected angular power spectrum of SZ
fluctuations in the microwave sky by 24%.
