[Nektar-users] VIV flow past a cylinder

25 Feb 2020


      *******************
This email 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] VIV flow past a cylinder

Wang, Zhicheng