HI Zhicheng, I am forwarding your request to Yan Bao who is probably the most experienced in this setup. Not sure if Yan is using the Nektar++ users list however. I would be inclined to use the SpectralVanishingViscosity with DGKernel and Dealisasing if you get any flow instability issues. Cheers, Spencer PS Mohsen might be able to help too. On 25 Feb 2020, at 15:05, Wang, Zhicheng <zhicheng_wang@brown.edu<mailto:zhicheng_wang@brown.edu>> wrote: This email from zhicheng_wang@brown.edu<mailto:zhicheng_wang@brown.edu> originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list<https://spam.ic.ac.uk/SpamConsole/Senders.aspx> to disable email stamping for this address. Hi nektar++ users, I wonder if there is anyone could check my simulation parameters for the simulation of 2D vortex induced vibration (VIV) of flow past a cylinder that is allowed to move in crossflow direction ? Here the cylinder is rigidly mounted with a natural frequency f=0.17, mass per unit length =2.0, Re=100. For this particular case, the vibration amplitude is expected to be around 0.5D, but the simulation gave me 0.05D. So I think I must have made some mistakes somewhere in the parameter file. The parameter file I used is posted below. ****************************************************************** <EXPANSIONS> <E COMPOSITE="C[0]" BASISTYPE="Modified_A, Modified_A" NUMMODES="3,3" POINTSTYPE="GaussLobattoLegendre, GaussLobattoLegendre" NUMPOINTS="5,5" FIELDS="u,v,w,p" /> </EXPANSIONS> <CONDITIONS> <SOLVERINFO> <I PROPERTY="SolverType" VALUE="VCSMapping" /> <I PROPERTY="EQTYPE" VALUE="UnsteadyNavierStokes" /> <I PROPERTY="AdvectionForm" VALUE="Convective" /> <I PROPERTY="Projection" VALUE="Galerkin" /> <I PROPERTY="HOMOGENEOUS" VALUE="1D"/> <I PROPERTY="USEFFT" VALUE="FFTW" /> <I PROPERTY="TimeIntegrationMethod" VALUE="IMEXOrder2" /> <I PROPERTY="GlobalSysSoln" VALUE="IterativeStaticCond" /> <I PROPERTY="Preconditioner" VALUE="Block"/> <I PROPERTY="VibrationType" VALUE="Constrained"/> <I PROPERTY="SupportType" VALUE="Free-Free"/> <I PROPERTY="FictitiousMassMethod" VALUE="True"/> </SOLVERINFO> <PARAMETERS> <P> TimeStep = 0.005 </P> <P> FinalTime = 1000 </P> <P> NumSteps = FinalTime/TimeStep </P> <P> IO_CheckSteps = 2000 </P> <P> IO_InfoSteps = 25 </P> <P> IO_CFLSteps = 25 </P> <P> Re = 100 </P> <P> Kinvis = 1/Re </P> <P> HomModesZ = 2 </P> <P> LZ = 0.01 </P> <P> FreqY = 0.17 </P> <P> OmegaY = 2.0*PI*FreqY </P> <P> StructStiff = 0.0 </P> <P> StructRho = 2.0 </P> <P> CableTension = OmegaY*OmegaY*StructRho </P> <P> BendingStiff = 0.0 </P> <P> FictDamp = 1.0 </P> <P> FictMass = 1.5 </P> </PARAMETERS> <VARIABLES> <V ID="0"> u </V> <V ID="1"> v </V> <V ID="2"> w </V> <V ID="3"> p </V> </VARIABLES> <BOUNDARYREGIONS> <B ID="0"> C[5] </B> <!-- Wall --> <B ID="1"> C[3] </B> <!-- y_min --> <B ID="2"> C[4] </B> <!-- y_max --> <B ID="3"> C[2] </B> <!-- Outlet --> <B ID="4"> C[1] </B> <!-- Inflow --> </BOUNDARYREGIONS> <BOUNDARYCONDITIONS> <REGION REF="0"> <D VAR="u" USERDEFINEDTYPE="MovingBody" VALUE="0" /> <D VAR="v" USERDEFINEDTYPE="MovingBody" VALUE="0" /> <D VAR="w" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" /> </REGION> <REGION REF="1"> <P VAR="u" VALUE="[2]" /> <P VAR="v" VALUE="[2]" /> <P VAR="w" VALUE="[2]" /> <P VAR="p" VALUE="[2]" /> </REGION> <REGION REF="2"> <P VAR="u" VALUE="[1]" /> <P VAR="v" VALUE="[1]" /> <P VAR="w" VALUE="[1]" /> <P VAR="p" VALUE="[1]" /> </REGION> <REGION REF="3"> <N VAR="u" VALUE="0" /> <N VAR="v" VALUE="0" /> <N VAR="w" VALUE="0" /> <D VAR="p" VALUE="0" /> </REGION> <REGION REF="4"> <D VAR="u" VALUE="1" /> <D VAR="v" VALUE="0" /> <D VAR="w" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" /> </REGION> </BOUNDARYCONDITIONS> <FUNCTION NAME="InitialConditions"> <E VAR="u" VALUE="0" /> <E VAR="v" VALUE="0" /> <E VAR="w" VALUE="0" /> <E VAR="p" VALUE="0" /> </FUNCTION> <FUNCTION NAME="displacements"> <E VAR="x" VALUE="0.0" /> <E VAR="y" VALUE="A*cos(omega*t)*cos(2*PI*z/LZ)" /> </FUNCTION> <FUNCTION NAME="velocities"> <E VAR="x" VALUE="0.0" /> <E VAR="y" VALUE="-1.0*omega*A*sin(omega*t)*cos(2*PI*z/LZ)" /> </FUNCTION> <FUNCTION NAME="Mapping"> <E VAR="x" VALUE="x" /> <E VAR="y" VALUE="y+A*cos(omega*t)*cos(2*PI*z/LZ)" /> </FUNCTION> <FUNCTION NAME="MappingVel"> <E VAR="vx" VALUE="0.0" /> <E VAR="vy" VALUE="-1.0*omega*A*sin(omega*t)*cos(2*PI*z/LZ)" /> </FUNCTION> <FUNCTION NAME="accelerations"> <E VAR="x" VALUE="0.0" /> <E VAR="y" VALUE="-1.0*omega*omega*A*cos(omega*t)*cos(2*PI*z/LZ)" /> </FUNCTION> </CONDITIONS> <MAPPING TYPE="XYofZ"> <COORDS>Mapping</COORDS> <VEL>MappingVel</VEL> <TIMEDEPENDENT>True</TIMEDEPENDENT> </MAPPING> <FORCING> <FORCE TYPE="MovingBody"> <DISPLACEMENTS> displacements </DISPLACEMENTS> <VELOCITIES> velocities </VELOCITIES> <ACCELERATIONS> accelerations </ACCELERATIONS> <PARAM NAME="OutputFile">TensionedCable</PARAM> <PARAM NAME="OutputFrequency">25</PARAM> <PARAM NAME="Boundary"> B[0] </PARAM> </FORCE> </FORCING> **************************************************************************************** Best Wishes, Zhicheng Wang _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk<mailto:Nektar-users@imperial.ac.uk> https://mailman.ic.ac.uk/mailman/listinfo/nektar-users Spencer Sherwin FREng, FRAeS Head of Aerodynamics Section, Director of Research Computing Service, Professor of Computational Fluid Mechanics, Department of Aeronautics, s.sherwin@imperial.ac.uk<mailto:s.sherwin@imperial.ac.uk> South Kensington Campus, Phone: +44 (0)20 7594 5052 Imperial College London, Fax: +44 (0)20 7594 1974 London, SW7 2AZ, UK http://www.imperial.ac.uk/people/s.sherwin/