Piston movement-User function
 

I tried using user defined function to provide translational motion of the piston using time-displacement steps. But i couldnt solve it. Kndly help me solve this simple case.

This is very simple to do. Define a CEL expression for piston location versus time, set the domain to moving mesh and define the piston face to have displacement of your CEL function.

thats wat i did sir, but the plot says some error in defining the expression. kindly help me..

Posting what the error message says might make it easier for us......

While you are at it, also post an image of what you are modelling, an image of your mesh and your CCL.