Chris Quan
Ansys Employee

Regarding to "But during rotation, the nozzle experiences enormous stresses and is greatly deformed. Why? It does not contact with anything", were you using Program Controlled for the Precision under Analysis Settings?

If yes, can you change it to Double so double precision is used, rather than single precision (default). 

For typical mechanical simulations, velocity is usually low. Thus the change of all variables (displacement, stress, strain) at each time step is very small. Use of double precision can prevent any possible round-off error from floating point calculations.