The thermal circuit method is used to model the heat transfer in the ring land and skirt region with the following
assumptions: the effect of piston motion on the heat transfer is neglected, the rings do not twist, the rings and skirt are
fully engulfed in oil and there is no cavitation, and also the conductive heat transfer in the oil film is neglected.
Symmetric constraints are imposed in axi symmetric axis. That is, all of the displacements on the axi symmetrical axis
are set to zero in the radial direction. The symmetric thermal boundary condition is also applied to the radial direction
on the symmetry axis. Local average heat transfer coefficient and gas temperature boundary conditions are applied for
the piston top. The piston surface is heated at the outlet of the swirl chamber and cooled through contact with cooler
components of the combustion chamber. In the analyses, the Hohenberg equation is used to predict instantaneous heat
transfer coefficients,