HI Mahdi, Not sure what to suggest here since the list you provided is what I would normally suggest. Obviously by increasing the frequency you have increased the velocity so possibly there is something going wrong with the mesh movement when the velocity is so high. Possibly the explicit mapping terms in this case are just getting to big to be handled explicitly. For a problem with just a prescribed vertical translation like this it is possible to simulate the flow in the reference frame of the cylinder by just imposing the motion on the outer velocity boundary conditions. Have you tried that approach rather than moving the body? Cheers, Spencer. 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/ On 6 Jun 2020, at 00:58, Mahdi Erfanian Nakhchi <mahdi.nakhchi@northumbria.ac.uk<mailto:mahdi.nakhchi@northumbria.ac.uk>> wrote: This email from mahdi.nakhchi@northumbria.ac.uk<mailto:mahdi.nakhchi@northumbria.ac.uk> 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 help me to converge my 2D simulations over a moving cylinder with high frequency. I've been stuck with this problem for two months. Actually the case is exactly the same as CylFlow_Mov_mapping.xml case (attached here). I have only increased the vibration frequency (f) to 200 and reduced the amplitude (A) to 0.01. But it is not working at all. I have tried every possible option such as: 1. Using SpectralVanishingViscosity (DGKernel), DEALIASING, SPECTRALHPDEALIASING: Not helpful. I have tried all of the SVV options, but non of them helped me to converge the results. 2. Performing simulations at very low Re numbers and low P orders and then shifting to higher orders : Not helpful. It diverges even at Re=200 and P=4. 3. Using too small time steps (1e-7 or 1e-8): Not helpful. It diverges anyway. 4. Using low frequencies, such as f=2, 3 etc and then shifting gradually to higher frequencies: Not working. It diverges even at f=30 or lower values. 5. Usign HOutflow boundary conditions at the outflow: Not helpful in this study. I would be grateful if someone has experience to resolve the divergence issue of this problem. (The initial conditions are set as default values in the code below.) ****************************** <EXPANSIONS> <E COMPOSITE="C[73]" NUMMODES="5" TYPE="MODIFIED" FIELDS="u,v,p" /> </EXPANSIONS> <CONDITIONS> <SOLVERINFO> <I PROPERTY="EQTYPE" VALUE="UnsteadyNavierStokes" /> <I PROPERTY="SolverType" VALUE="VCSMapping" /> <I PROPERTY="EvolutionOperator" VALUE="Nonlinear" /> <I PROPERTY="Projection" VALUE="Galerkin" /> <I PROPERTY="TimeIntegrationMethod" VALUE="IMEXOrder1" /> <I PROPERTY="SpectralVanishingViscosity" VALUE="DGKernel" /> <I PROPERTY="DEALIASING" VALUE="True"/> <I PROPERTY="SPECTRALHPDEALIASING" VALUE="True" /> </SOLVERINFO> <PARAMETERS> <P> TimeStep = 1e-7 </P> <P> NumSteps = 100000000 </P> <P> IO_CheckSteps = 500 </P> <P> IO_InfoSteps = 100 </P> <P> IO_CFLSteps = 100 </P> <P> Re = 200 </P> <P> Kinvis = 1/Re </P> <P> f = 200 </P> <P> A = 0.01 </P> <P> omega = 2*PI*f </P> </PARAMETERS> <VARIABLES> <V ID="0"> u </V> <V ID="1"> v </V> <V ID="2"> p </V> </VARIABLES> <BOUNDARYREGIONS> <B ID="0"> C[74] </B> <!-- Wall --> <B ID="1"> C[76] </B> <!-- Far Field --> <B ID="2"> C[77] </B> <!-- Outflow --> <B ID="3"> C[75] </B> <!-- Inflow --> </BOUNDARYREGIONS> <BOUNDARYCONDITIONS> <REGION REF="0"> <D VAR="u" USERDEFINEDTYPE="MovingBody" VALUE="0" /> <D VAR="v" USERDEFINEDTYPE="MovingBody" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" /> </REGION> <REGION REF="1"> <D VAR="u" VALUE="1" /> <D VAR="v" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" /> </REGION> <REGION REF="2"> <N VAR="u" VALUE="0" /> <N VAR="v" VALUE="0" /> <D VAR="p" VALUE="0" /> </REGION> <REGION REF="3"> <D VAR="u" VALUE="1" /> <D VAR="v" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" /> </REGION> </BOUNDARYCONDITIONS> <FUNCTION NAME="Mapping"> <E VAR="x" VALUE="x" /> <E VAR="y" VALUE="y+A*cos(omega*t)" /> </FUNCTION> <FUNCTION NAME="MappingVel"> <E VAR="vx" VALUE="0.0" /> <E VAR="vy" VALUE="-1.0*omega*A*sin(omega*t)" /> </FUNCTION> <FUNCTION NAME="InitialConditions"> <E VAR="u" VALUE="1.0" /> <E VAR="v" VALUE="0.1" /> <E VAR="p" VALUE="0.0"/> </FUNCTION> </CONDITIONS> <MAPPING TYPE="Translation"> <COORDS>Mapping</COORDS> <VEL>MappingVel</VEL> <TIMEDEPENDENT>True</TIMEDEPENDENT> </MAPPING> ************************************ Many thanks Mahdi This message is intended solely for the addressee and may contain confidential and/or legally privileged information. 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