  We have performed numerical simulations of weakly and strongly magnetized
relativistic jets embedded in a weakly and strongly magnetized stationary or
mildly relativistic (0.5c) sheath using the RAISHIN code. In the numerical
simulations a jet with Lorentz factor \gamma=2.5 is precessed to break the
initial equilibrium configuration. Results of the numerical simulations are
compared to theoretical predictions from a normal mode analysis of the
linearized RMHD equations describing a uniform axially magnetized cylindrical
relativistic jet embedded in a uniform axially magnetized moving sheath. The
prediction of increased stability of a weakly-magnetized system with mildly
relativistic sheath flow to Kelvin-Helmholtz instabilities and the
stabilization of a strongly-magnetized system with mildly relativistic sheath
flow is confirmed by the numerical simulations.
