problem with oscillating cylinder

ammi

problem with oscillating cylinder I'm trying to simulate piston oscillating in in cylinder(a compressor). I've met with some problems which i hope someone can help... my problem 2d axisymetric dynamic one. these are the steps i took: 1. Read in the mesh 2. Prepare the udf file given as #include "udf.h"DEFINE_CG_MOTION(vel_comp,dt,vel,omega,time ,dtime){real freq = 34.0;real w = 2.0 * M_PI * freq;real Xcomp = 0.004511;NV_S(vel, = ,0.0);NV_S(omega, = ,0.0);vel[0] = w * Xcomp * cos (w * time)} 3. Compile the source file , its ok. 4. gone to dynamic mesh - zones. Choose the remeshing and smoothing option I've selected piston with rigid body motion with the udf profile just compiled. Cylinder and axis as deforming one. Setted the value as in poppet valve example 5 )in BC condition where to set the velocity of wall (a udf function). ?????? Is it require. ? i am getting negative volume problem. how to solve ? from mesh motion review i got it is not remeshing plz reply ammi