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Hi,
Could some please give me some hints as how to output time series data (for
example, pressure evolution at some given point) using Nektar++?
Thanks
Chengeng
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Hello everyone,
I get the following error in the first iteration (or sometimes after some
iterations):
CG iterations made = 5001 using tolerance of 1e-09 (error = -nan, rhs_mag =
13729.7)
Fatal : Level 0 assertion violation
Exceeded maximum number of iterations
My question is a bit general: What are the possible causes of this error?
What I understand is that the solvers are unable to converge to a solution
(in finite iterations). The mesh is okay. I sometimes solve it by tweaking
the initial conditions or increasing/decreasing the time step. But, this is
a bit heuristic. As long-time users/developers, do you know other roots of
this error? Does this type of error indicate to you a certain kind of
problem?
For example, if the solver diverges quickly or doesn't even complete one
iteration I usually suspect the mesh (provided all the other schemes are
set reasonably). However, I am able to get results with a very similar mesh
and meshing technique, so I think it is okay in this case.
Happy holidays,
Best regards,
Ilteber
--
İlteber R. Özdemir
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Hi,
I tried to run Sod problem using Nektar. The solver information is as
follows,
<SOLVERINFO>
<I PROPERTY="EQType" VALUE="EulerCFE"
/>
<I PROPERTY="Projection" VALUE="DisContinuous"
/>
<I PROPERTY="AdvectionType" VALUE="WeakDG"
/>
<I PROPERTY="TimeIntegrationMethod" VALUE="ForwardEuler"
/>
<I PROPERTY="UpwindType" VALUE="HLLC"
/>
<I PROPERTY="LocalTimeStep" VALUE="True"
/>
<I PROPERTY="ShockCaptureType" VALUE="NonSmooth"
/>
</SOLVERINFO>
The information of expansion is
<E COMPOSITE="C[1]" NUMMODES="3" FIELDS="rho,rhou,rhov,E" TYPE="MODIFIED" />
The mesh is generated by Gmsh. For simplicity, I use qausi-structured mesh
with dx=0.0047 and dy=0.0036. According to my knowledge of numerical
scheme, CFL is usually between 0.1 and 0.5. However, I found out that CFL
must be 0.01 to ensure stable simulation. Why is CFL so small in Nektar?
Chengeng
Excellent.
With regards
Abhishek
On Mon, 21 Nov 2022 at 4:58 pm, <nandan.sarkar(a)iitkgp.ac.in> wrote:
> Dear Sir,
>
>
>
> Thanks for the correction. The code is working now.
>
>
>
> Regards
>
> Nandan Sarkar
>
>
>
> *From:* Abhishek Kumar <abhishek.kir(a)gmail.com>
> *Sent:* Monday, November 21, 2022 1:16 AM
> *To:* nandan.sarkar(a)iitkgp.ac.in
> *Cc:* nektar-users(a)imperial.ac.uk
> *Subject:* Re: [Nektar-users] Floquet stability analysis
>
>
>
> Dear Nandan,
>
>
>
> I can see that there is an issue with your expansion definition. You are
> missing the field "w". The correct expansion is as follows:
>
>
>
> *<EXPANSIONS>*
>
> *<E *COMPOSITE*=*"C[0]" NUMMODES*=*"7" TYPE*=*"GLL_LAGRANGE_SEM"
> FIELDS*=*"u,v,w,p"* />*
>
> *</EXPANSIONS>*
>
>
>
> Also, remember to put "period" in the parameters. I have attached the XML
> file, which I used to reproduce Barkley and Henderson, JFM, 1996.
>
>
>
> With regards
>
> Abhishek
>
>
>
>
> ---------------------------------------------------------------------------------------
>
> Abhishek Kumar
>
> Assistant Professor (Research)
>
> Centre for Fluid and Complex Systems
>
> Coventry University, Coventry CV15FB
>
> Web: https://sites.google.com/view/abhishekkir
>
>
> ---------------------------------------------------------------------------------------
>
>
>
>
>
> On Fri, Nov 18, 2022 at 9:55 AM <nandan.sarkar(a)iitkgp.ac.in> wrote:
>
> This email from nandan.sarkar(a)iitkgp.ac.in 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.
>
>
>
> Dear all,
>
>
>
> I am trying to perform a Floquet stability analysis using Nektar++ but
> facing some errors. I have generated a two-dimensional periodic base flow
> of flow past a cylinder, at slices, and using the same in an XML file for
> stability analysis. Below are the output and some relevant sections of the
> XML file. It would be of great help to fix the issue or point to some
> already set-up example cases for the Floquet stability analysis.
>
>
>
> #IncNavierStokesSolver Cylinder_Floquet.xml
>
> read base flow file Cylinder-Base_0.chk
>
> read base flow file Cylinder-Base_1.chk
>
> read base flow file Cylinder-Base_2.chk
>
> read base flow file Cylinder-Base_3.chk
>
> read base flow file Cylinder-Base_4.chk
>
> read base flow file Cylinder-Base_5.chk
>
> read base flow file Cylinder-Base_6.chk
>
> read base flow file Cylinder-Base_7.chk
>
> read base flow file Cylinder-Base_8.chk
>
> read base flow file Cylinder-Base_9.chk
>
> baseflow info : interpolation order 0, period 0.00111111, periodicity yes
>
> baseflow info : files from 0 to 9 (skip 1) with 10 time intervals
>
> Fatal : Level 0 assertion violation
>
> Expect to have three velocity fields with homogenous expansion
>
>
>
> XML file snippet:
>
> <SOLVERINFO>
>
> <I PROPERTY="SOLVERTYPE"
> VALUE="VelocityCorrectionScheme"/>
>
> <I PROPERTY="EQTYPE"
> VALUE="UnsteadyNavierStokes" />
>
> <I PROPERTY="EvolutionOperator"
> VALUE="Direct" />
>
> <I PROPERTY="Projection"
> VALUE="Galerkin" />
>
> <I PROPERTY="TimeIntegrationMethod"
> VALUE="IMEXOrder2" />
>
> <I PROPERTY="ModeType"
> VALUE="HalfMode" />
>
> <I PROPERTY="Driver"
> VALUE="ModifiedArnoldi" />
>
> <I PROPERTY="Homogeneous"
> VALUE="1D" />
>
> </SOLVERINFO>
>
> <PARAMETERS>
>
> <P> TimeStep = 0.001 </P>
>
> <P> NumSteps = 1000 </P>
>
> <P> IO_CheckSteps = 100 </P>
>
> <P> IO_InfoSteps = 100 </P>
>
> <P> Re = 188 </P>
>
> <P> Kinvis = 1./Re </P>
>
> <P> kdim = 4 </P>
>
> <P> nvec = 2 </P>
>
> <P> evtol = 1e-6 </P>
>
> <P> N_slices = 10 </P>
>
> <P> LZ = 2.4166 </P>
>
> </PARAMETERS>
>
> <EXPANSIONS>
>
> <E COMPOSITE="C[0]" NUMMODES="7" FIELDS="u,v,p"
> TYPE="GLL_LAGRANGE" />
>
> </EXPANSIONS>
>
>
>
> Thank you in advance.
>
>
>
> Regards,
>
> Nandan Sarkar
>
> PhD candidate
>
> Dept. of Mechanical Engineering
>
> Indian Institute of Technology Kharagpur
>
> India 721302
>
> _______________________________________________
> Nektar-users mailing list
> Nektar-users(a)imperial.ac.uk
> https://mailman.ic.ac.uk/mailman/listinfo/nektar-users
>
>
>
>
> --
>
>
>
--
Sent from IPhone
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Dear all,
I am trying to perform a Floquet stability analysis using Nektar++ but
facing some errors. I have generated a two-dimensional periodic base flow of
flow past a cylinder, at slices, and using the same in an XML file for
stability analysis. Below are the output and some relevant sections of the
XML file. It would be of great help to fix the issue or point to some
already set-up example cases for the Floquet stability analysis.
#IncNavierStokesSolver Cylinder_Floquet.xml
read base flow file Cylinder-Base_0.chk
read base flow file Cylinder-Base_1.chk
read base flow file Cylinder-Base_2.chk
read base flow file Cylinder-Base_3.chk
read base flow file Cylinder-Base_4.chk
read base flow file Cylinder-Base_5.chk
read base flow file Cylinder-Base_6.chk
read base flow file Cylinder-Base_7.chk
read base flow file Cylinder-Base_8.chk
read base flow file Cylinder-Base_9.chk
baseflow info : interpolation order 0, period 0.00111111, periodicity yes
baseflow info : files from 0 to 9 (skip 1) with 10 time intervals
Fatal : Level 0 assertion violation
Expect to have three velocity fields with homogenous expansion
XML file snippet:
<SOLVERINFO>
<I PROPERTY="SOLVERTYPE"
VALUE="VelocityCorrectionScheme"/>
<I PROPERTY="EQTYPE"
VALUE="UnsteadyNavierStokes" />
<I PROPERTY="EvolutionOperator" VALUE="Direct"
/>
<I PROPERTY="Projection"
VALUE="Galerkin" />
<I PROPERTY="TimeIntegrationMethod" VALUE="IMEXOrder2"
/>
<I PROPERTY="ModeType"
VALUE="HalfMode" />
<I PROPERTY="Driver"
VALUE="ModifiedArnoldi" />
<I PROPERTY="Homogeneous" VALUE="1D"
/>
</SOLVERINFO>
<PARAMETERS>
<P> TimeStep = 0.001 </P>
<P> NumSteps = 1000 </P>
<P> IO_CheckSteps = 100 </P>
<P> IO_InfoSteps = 100 </P>
<P> Re = 188 </P>
<P> Kinvis = 1./Re </P>
<P> kdim = 4 </P>
<P> nvec = 2 </P>
<P> evtol = 1e-6 </P>
<P> N_slices = 10 </P>
<P> LZ = 2.4166 </P>
</PARAMETERS>
<EXPANSIONS>
<E COMPOSITE="C[0]" NUMMODES="7" FIELDS="u,v,p" TYPE="GLL_LAGRANGE"
/>
</EXPANSIONS>
Thank you in advance.
Regards,
Nandan Sarkar
PhD candidate
Dept. of Mechanical Engineering
Indian Institute of Technology Kharagpur
India 721302
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*******************
Hi all teachers,
I am a Ph.D. student. Recently, I went through a tutorial where finite-strip theory was used to model the VIV of flexible cables. I have a question: can I achieve a wind profile along the z-direction by changing the inflow conditions?
for example,
<REGIONREF="3">
<DVAR="u"VALUE="0.5*z"/><!-- Inflow -->
<DVAR="v"VALUE="0"/>
<DVAR="w"VALUE="0"/>
<NVAR="p"USERDEFINEDTYPE="H"VALUE="0"/
Regards
| |
郭艳娇
|
|
fancyjiao(a)126.com
|
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Dear all;
When solving a problem in parallel with a restart file( e.g. restart.rst) as an initial condition I will encounter an error.
I am using compressed binary output to solve the problem in parallel. I think this is because the .xml file depends on the number of cores converted to a smaller domain for each processor. However, the restart file contains field data for the entire domain.
How can I restart a solver in parallel?
Any comments would be appreciated.
Best regards,
Mohammad
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Dear Nektar users,
I am running some 3D incompressible simulations. The problem I faced is that the software gives me identical CFL numbers for all time steps. Also, the simulation results do not change with time, which is not correct. The flow is turbulent and the Reynolds number is 10000.
Steps: 20 Time: 2e-06 CPU Time: 8.2572s
CFL: 0.338963 (in elmt 105130)
Steps: 30 Time: 3e-06 CPU Time: 7.98256s
CFL: 0.338963 (in elmt 105130)
Steps: 40 Time: 4e-06 CPU Time: 7.94238s
CFL: 0.338963 (in elmt 105130)
Steps: 50 Time: 5e-06 CPU Time: 7.99028s
CFL: 0.338963 (in elmt 105130)
Steps: 60 Time: 6e-06 CPU Time: 8.02182s
CFL: 0.338963 (in elmt 105130)
Steps: 70 Time: 7e-06 CPU Time: 8.03556s
Have you ever faced this issue? and any solutions for that? Many thanks.
Best regards
Mahdi
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*******************
Hi all,
Has anyone been successful in using Nektar++ format for direct
visualization with Visit? I managed to compile visit with Nektar++
support but I am unable to read in data that use Homogeneous expansion.
The reader issues an error and in the command line from which I invoke
Visit I see what seems like a Nektar++ message stating "HomModesZ/npz
should be an even integer." like if I would be using the parallel strip
version.
So, does anyone knows if the implementation that Visit uses is capable
of Homogeneous1D?
Cheers,
Stan
--
Pozdrawiam,
dr inż. Stanisław Gepner,
*Wydział Mechaniczny Energetyki i Lotnictwa*
Nowowiejska 21/25 Str.
00-665 Warszawa, Polska
tel. +48 (22) 234 51 70
<http://www.pw.edu.pl/>
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Hi,
I am trying to convert a simple mesh made in Gmsh (cyl.msh) to Nektar++
usable format (.xml). I can view the mesh in Gmsh. NekMesh gives the
following error when I try to convert:
NekMesh -v cyl.msh out.xml
[InputGmsh] Reading Gmsh file: 'cyl.msh'
[InputGmsh] Finished reading mesh.
[InputGmsh] - Element dimension : 0
[InputGmsh] - Space dimension : 2
[InputGmsh] - No. of nodes : 0
[InputGmsh] - No. of 0D elements : 0
[InputGmsh] - No. of boundary elements : 0
[InputGmsh] - Elapsed time: 0.0542657s.
[OutputNekpp] Writing Nektar++ file 'out.xml'
Fatal : Level 0 assertion violation
Unable to read composite index range:
terminate called after throwing an instance of 'Nektar::ErrorUtil::NekError'
what(): Level 0 assertion violation
Unable to read composite index range:
Aborted
Can you help me with this problem?
With kind regards,
Ilteber
--
İlteber R. Özdemir