Dear all, I am interested about studying the rotational cylinder in free flow (for incompressible flow). Looking around the Nektar's manual I realized that there is an option which, I think, allows to compute it, the MovingBody along with the Mapping (10.6.3 - 10.6.5) from Nektar++'s manual v4.4.0. I am using the example: the CylFlow_Mov_mapping as a reference one. However, I can not completely understand how it works. (I took the example from the 4.3.5 version) First of all, that example is for a rotational cylinder or is it for a cylinder moving up and down on a periodic motion? Tanking into account the first option, The mapping function computes the new coordinates for the specified boundary, However, I do not understand why the function is specified in that way: <FUNCTION NAME="Mapping"> <E VAR="x" VALUE="x" /> <E VAR="y" VALUE="y+A*cos(omega*t)" /> </FUNCTION> The value of the parameter A is not the radius of the cylinder, so it is not deifying a rotation over its center. Also, the new /x/ coordinate is the same as before, so the cylinder just moved upwards or downwards. Secondly, what is the MappingVel functions used for? I think it is used for specify the velocity on the new coordinates. However, the way it is defined, I think, it does not define a new velocity coordinates. What I am misleading? A part from that, I would also compute the aerodynamic forces on the moving surface, so I inserted the following: <FORCE TYPE="MovingBody"> <PARAM NAME="OutputFile">DragLift.frc</PARAM> <PARAM NAME="OutputFrequency">10</PARAM> <PARAM NAME="Boundary"> B[0] </PARAM> </FORCE> and also: <MAPPING TYPE="Translation"> <COORDS>MovingBody</COORDS> <VEL>MappingVel</VEL> </MAPPING> However, the file DragLift.frc is not generated. Hope I have well explained and clarified all my inquiries. Thank you very much, Guillermo Suarez.