{"id":28632,"date":"2018-01-30T11:38:24","date_gmt":"2018-01-30T11:38:24","guid":{"rendered":"\/forum\/forums\/topic\/udf-for-equation-of-motion\/"},"modified":"2018-01-30T11:38:24","modified_gmt":"2018-01-30T11:38:24","slug":"udf-for-equation-of-motion","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/udf-for-equation-of-motion\/","title":{"rendered":"UDF for equation of motion"},"content":{"rendered":"

I have a 2D dynamic mesh case of a piston-cylinder arrangement as attached. I can create a udf to move the piston under certain velocity and the simulation proceeds with no problems. <\/span>

What I need<\/strong> <\/em><\/span>is to set the dynamic mesh zones according to a udf expressing the equation of motion<\/strong> of the piston which is :<\/span>

a = (F + p1*A1 – p2*A2) \/ m  or if represented with velocity <\/strong><\/em> <\/span>dv = <\/span>(F + p1*A1 – p2*A2)<\/span> * dt \/ m<\/span>

where: a .. acceleration, F .. External force, p1,p2 .. pressures on upper and lower piston boundaries respectively, A1,A2 .. areas at same locations and m .. mass of the piston.<\/span><\/p>\n

<\/p>\n

I have got through a similar udf in the udf manual for equation of motion in x-dir, but I do not understand how the pressure forces are computed. So, I want to know how the pressure on both sides is represented in the udf in my case<\/strong>.<\/p>\n

<\/p>\n

 <\/p>\n

<\/p>\n

This udf link is<\/strong>: https:\/\/www.cfd-online.com\/Forums\/fluent\/87021-code-dynamic-meshing-udf.html <\/p>\n

<\/p>\n


Can you help me on this udf ?<\/span><\/strong><\/p>\n","protected":false},"template":"","class_list":["post-28632","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t