June 2025 - Nektar-users - imperial.ac.uk

Questions on implicit integration and file coupling in AcousticSolver (v5.2.0)
by dxz324＠student.bham.ac.uk 29 Jun '25

29 Jun '25

******************* 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. ******************* Dear Nektar++ developers, I am a researcher at the University of Birmingham using AcousticSolver v5.2.0 on ARCHER2 to solve the acoustic perturbation equations. My work involves sparse source data for a mixing layer, and with only explicit schemes (for example RK4), I must use very small "TimeStep" to maintain stability(The smallest element size of the grid cannot be modified, as it is already the largest option for identify source). I have two questions: 1. Implicit integrator support Currently AcousticSolver does not include any implicit time�\integration methods. Could you provide a test or development version that includes an implicit scheme such as backward Euler or Crank�\Nicolson? If no such version exists, could you advise how I might modify the solver code to add an implicit integrator? 2. Errors when inputting files As shown in my code(figure below), I input the source data using the "COUPLING" element with TYPE="File" and provide a series of .pts files named in floating point format (%14.8E). I also set TIMEDEPENDENT="1" so that they are read in time order. Since the time interval between these files is much larger than my solver TimeStep, when I tried to adjust ReceiveSteps to read a new file every n steps, the solver still tried to load the file at each dt(TimeStep) and failed when the file at the interpolation time did not exist. Is there a way to instruct AcousticSolver to read coupling files strictly according to the ReceiveSteps schedule��i.e. to load only when a new file index is due��without triggering ��file not found�� errors at intermediate time steps? Any guidance or pointers to relevant code sections or example configurations would be greatly appreciated. Thank you very much for your time and assistance. Best regards, Dao University of Birmingham [cid:511f73a2-b6b1-4275-bc1a-e1a0ac686633]

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Promote your Nektar++-related publications on the website!
by Chris Cantwell 28 Jun '25

28 Jun '25

Dear all, As announced by Dave at the recent Nektar++ Workshop, we have a publications page on the website which strives to list the many publications which have contributed to, or made use of, Nektar++ from across the community: https://www.nektar.info/community/publications/ *If you have such a paper, we encourage you to add it to this page!* As well as giving a little extra promotion for your publication, it also helps us to demonstrate to potential funders the impact of the software, which can support further development. We have recently sought to make it easier for people to contribute their publications, by generating the webpage dynamically from BibTeX files stored in a GitLab repository. You can therefore contribute to the list as follows: 1. Fork the https://gitlab.nektar.info/nektar/nektar-publications repository into your own namespace on GitLab. 2. Clone the repository and create a new branch. 3. Update the BibTeX files accordingly to add your publication(s), tagging them with a 'group' attribute as 'core','app' or 'thesis'. 4. Commit and push your changes to GitLab. 5. Create a merge request from the branch in your fork, to 'master' in the main nektar-publications repository. Some automated checks will be performed to ensure the BibTeX is valid. Once these pass, we will then merge the MR and it will appear on the webpage. For further details on the process, please see: https://gitlab.nektar.info/nektar/nektar-publications/-/blob/master/README.… Finally, thanks to Dave for getting all of the GitLab CI and webpage-generation magic to work! Kind regards, Chris -- Chris Cantwell Reader in Computational Engineering Director of Postgraduate Studies (PhD) Department of Aeronautics Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0)20 759 45050 Email:c.cantwell@imperial.ac.uk www.imperial.ac.uk/people/c.cantwell

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2D linear stability analysis
by Ben 26 Jun '25

26 Jun '25

******************* 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. ******************* Dear all, I am studying 2D linear stability analysis. I have browsed through the emails of the nektar community and learned a lot about solving settings, but there are still some questions that I cannot understand. Everyone can offer their opinions. 1. Is the combination of fine mesh and low order unfolding more effective? Is it better for the order of pressure 'p' to be 1 order lower than the velocity 'u, v'? 2. When using Arpack for serial computing, will setting kdim to a larger value result in faster solving speed, such as 64 and 128? Because I encountered incorrect eigenvalues in my calculations, such as an unstable flow with a growth rate less than 0. Do I need to set the nvc to a large value? 3. The post mentioned that using smooth initial conditions can avoid calculating eigenvalues as 1. How should I set it up? Can you provide a specific example? 4. How should base flow be calculated? Should I average the extraction time of DNS results or use the SFD method? How to set the parameters in the adaptive SFD method to ensure both solution convergence and fast computation speed? The direct.xml and SFD.xml files are attached.Thank you for your suggestions. Qiancheng

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Filter_Integral_for 3DH1D_segmentation fault
by Wang Boning 24 Jun '25

24 Jun '25

******************* 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. ******************* Dear Nektar++ team, I hope this email finds you well! I'm a student from TUM in Munich, Germany. And I am currently running a 3DH1D simulation using the IncSolver module in Nektar++ version 5.8.0. I encountered an issue when trying to use the Integral filter. The simulation terminates with an error message (included at the end of this email). Moreover, when I comment out the <FILTER TYPE="Integral"> block, the simulation runs normally. I found an early issue, 4yr ago, on GitLab (#227), which reveals that the Integral filter should be supported in homogenous simulations. I also tried using same modals for all composites/variables, still same error message. My question is, dose ' integral' support 3DH1D since composites are 2D(Quadrilateral), which is not mentioned specifically in the doc? And if yes, what can I do to fix my issue for 3DH1D simulation? I really tested a lot before I send this email. Your sincerely, Boning P.S. Partial set-up are listed here, and full session.xml, mesh.xml and log (verbose) file are attached. <EXPANSIONS> <E COMPOSITE="C[1,2,3,5]" NUMMODES="6" TYPE="MODIFIED" FIELDS="u,v,w,p" /> <E COMPOSITE="C[4,6]" NUMMODES="8" TYPE="MODIFIED" FIELDS="u,v,w" /> <E COMPOSITE="C[4,6]" NUMMODES="7" TYPE="MODIFIEDQUADPLUS1" FIELDS="p" /> </EXPANSIONS> <FILTER TYPE="Integral"> <PARAM NAME="OutputFile">Integral</PARAM> <PARAM NAME="OutputFrequency">5</PARAM> <PARAM NAME="OutputPrecision"> 12 </PARAM> <PARAM NAME="Composites">C[4,5], C[4,6], C[1-4]</PARAM> </FILTER> [hyd39:90887] *** Process received signal *** [hyd39:90887] Signal: Segmentation fault (11) [hyd39:90887] Signal code: Address not mapped (1) [hyd39:90887] Failing at address: 0xb0 [hyd39:90887] [ 0] /lib64/libc.so.6(+0x57900)[0x7fb616e57900] [hyd39:90887] [ 1] /opt/nektar++/5.8.0/lib64/libSolverUtils.so.5.8.0(_ZN6Nektar11SolverUtils14FilterIntegral12v_InitialiseERKNS_5ArrayINS_4OneDEKSt10shared_ptrINS_12MultiRegions7ExpListEEEERKd+0x23b)[0x7fb61ce9f2cb] [hyd39:90887] [ 2] /opt/nektar++/5.8.0/lib64/libSolverUtils.so.5.8.0(_ZN6Nektar11SolverUtils14UnsteadySystem9v_DoSolveEv+0x360)[0x7fb61cee3240] [hyd39:90887] [ 3] /opt/nektar++/5.8.0/lib64/libSolverUtils.so.5.8.0(_ZN6Nektar11SolverUtils14DriverStandard9v_ExecuteERSo+0x30a)[0x7fb61ce2ceba] [hyd39:90887] [ 4] IncNavierStokesSolver[0x44928a] [hyd39:90887] [ 5] /lib64/libc.so.6(+0x40e6c)[0x7fb616e40e6c] [hyd39:90887] [ 6] /lib64/libc.so.6(__libc_start_main+0x87)[0x7fb616e40f35] [hyd39:90887] [ 7] IncNavierStokesSolver[0x4782f1] [hyd39:90887] *** End of error message ***

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JFM Paper on Instability Suppression Published
by Abhishek Kumar 23 Jun '25

23 Jun '25

******************* 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. ******************* Dear all, I hope you're all doing well. I’m pleased to share that our paper, *“Suppressing instabilities in mixed baroclinic flow using an actuation based on receptivity,”* has now been published in the *Journal of Fluid Mechanics*: https://doi.org/10.1017/jfm.2025.10241 The study presents a receptivity-based strategy to suppress instabilities in a mixed convective flow, with actuation designed from adjoint eigenmodes. The work builds on our previous stability analysis and was carried out entirely within the Nektar++ framework. Some of the earlier results were presented at a previous Nektar++ meeting. I’ve attached the published version in case it’s of interest. Unfortunately, I won’t be able to attend this year’s Nektar++ meeting due to personal circumstances. I wish you all a successful and enjoyable meeting! Best regards, Abhishek

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Nektar++ 5.8.0 Released.
by Chris Cantwell 16 Jun '25

16 Jun '25

Dear all, We are pleased to announce the release of Nektar++ v5.8.0. As always, if you encounter any problems please feel free to contact us on the mailing list nektar-users(a)imperial.ac.uk. You can also report bugs and issues on our issue tracker (https://gitlab.nektar.info/nektar/nektar/-/issues) This release includes a range of new features and improvements over the 5.7.0 release: **Library** - Use GLL quadrature points on Tri Dirichlet BCs with CG (!1895) - Add FieldConvert module to perform local stability analysis for compressible flows (!1319) - Remove get() accessor from Array data structure (!1937) - Fix issue with `StdTetExp::v_LocCollapsedToLocCoord` (!1946) - Fix issue with `NodalTriExp::v_GetTracePhysVals` (!1951) - Remove deprecated version of v_SetCoeffsToOrientation functions (!1954) - Fix issue with Dirichlet BCs when using variable P (!1972) - Patch for implicit-function error in scotch-6.0.4 (!1938) - Tidy virtual inheritance in NodalTriExp (!1979) - Fix partial overload virtual function in AssemblyMap, StdRegions, and LocalRegions (!1978) - Fix partial overload virtual function v_PhysEvaluate (!1980) - Matrix free ops shape cleanup (!1735) - Fix NodalTri processing and static condensation matrix release (!1989) - Fix third-party Scotch patch (!1998) - Fixed Modified Arnoldi driver to remove discontinuities from random vectors (!2002) - Addedd support for backing up filters output when the file name have already existis (!2006) - Partially revert Geometry::v_ContainsPoint (!2007) - Make the CWIPI third-party patch work with IntelLLVM (!2053) - Use C++17 value template for traits (!2081) - Add H1-norm to Error filter (!1834) - Delete redundant lines in the Navier-Stokes diffusion functions (!2058) - Various tidy-up for solvers (!2056) - Add Compilation option for boost filesystem (!2092) - Update minimum Cmake version to 3.10 (!2096) - Deprecated FR method (!2102) - Remove some boost include in favor of C++17 build-in features (!2097) - Various tidy-up in SolverUtils (!2100) - Use forward declaration in header files for GlobalMapping (!2099) - Remove dummy `APESolver` executable. (!2119) - Tidy use of boost_lexical_cast (!2109) - Tidy-up SpatialDomains (!2120) - Remove NekInt, NekInt32, NekInt64, NekUInt, NekUInt32, NekUInt64 typedef (! 2123) - Fix CMake warnings related to modern policy changes (!2129) - Add support for unsigned int in SessionReader parameters (!2127) - Put in check for variable p diagonal preconditioner (2132) **CI** - Fix CubeAllElements performance test tolerance (!1943) - Remove `allow_failure` from compiler warnings and formatting (!1958, !1966) - remove CI image tag when dockerhub deploy completes (!1960) - Use recursive strategy for submodule (!1997) - cleanup CI environment images after packaging (!1991) - Update Fedora test environments to Fedora 40 (!1993) - Fix broken Fedora packaging library dependency (!2160) **NekMesh** - Add high-order pyramid and prism support from gmsh (!1956) - Industrial Pipeline Mesh Curving and CAD-Mesh link Reconstruction for all type of elements (!2057) **Python** - Transition bindings to use pybind11 (!1950) **Documentation** - Updated the User-guide with additional inofrmation for outflow BC, addressing the issue #103 (!1990) **PulseWaveSolver** - Added ability to output history points (and other filters) (!2000) **Miscellaneous** - Deprecate use of TimeIntegrationMethod in SolverInfo (!2059) Kind regards, Chris -- Chris Cantwell Reader in Computational Engineering Director of Postgraduate Studies (PhD) Department of Aeronautics Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0)20 759 45050 Email: c.cantwell(a)imperial.ac.uk www.imperial.ac.uk/people/c.cantwell

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Planar Jet Flow with Predefined Velocity Distribution
by Diksan Muhammad 04 Jun '25

04 Jun '25

******************* 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, I am new to Nektar++. I want to simulate planar jet flow with predefined velocity distribution, based on a csv file. Any recommendation from which tutorial should I start and which tutorial does provide an example of employing arbitrary distribution for a boundary condition? Best Regards, Diksan M

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build issues with versions 5.6.0 and 5.7.0
by Aidan Forknall 04 Jun '25

04 Jun '25

******************* 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 I am having issues compiling fresh installs of nektar v5.6.0 and v5.7.0 onto a linux workstation. The tar.gz files are downloaded from nektar src. Once extracted I follow the user guide instructions to create a build directory and pull up the ccmake gui (versions of ccmake and cmake on the PC are 4.0.2 stored in /snap/bin/cmake). Only the IncNavirStokesSolver is on, with USE_MPI switched on with thirdparty builds of GSMPI and SCOTCH. When configuring a cmake warning appears regarding policy CMP0177, and when running 'make install' the following error is displayed: ~~~~ CMake Error at CMakeLists.txt:1 (CMAKE_MINIMUM_REQUIRED): Compatibility with CMake < 3.5 has been removed from CMake. Update the VERSION argument <min> value. Or, use the <min>...<max> syntax to tell CMake that the project requires at least <min> but has been updated to work with policies introduced by <max> or earlier. Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway. -- Configuring incomplete, errors occurred! make[2]: *** [CMakeFiles/gsmpi-1.2.1_2.dir/build.make:92: ThirdParty/stamp/gsmpi-1.2.1_2-configure] Error 1 make[1]: *** [CMakeFiles/Makefile2:1405: CMakeFiles/gsmpi-1.2.1_2.dir/all] Error 2 make: *** [Makefile:146: all] Error 2 ~~~~ I assume it is an error with gsmpi, however when trying to configure with MPI on without building thirdparty GSMPI, the configuring crashes stating it must be built. Any advice is most welcome. Kind regards, Aidan -------------------------------------------------------------------------------------------------- Aidan Forknall Research Associate - Computational Fluid Dynamics of Spray Combustion Rolls-Royce UTC in Combustion System Aerothermal Processes Department of Aeronautical and Automotive Engineering Loughborough University LE11 3TU, UK --------------------------------------------------------------------------------------------------

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No such module: NekFFTW
by ztdepyahoo 04 Jun '25

04 Jun '25

******************* 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. ******************* I use IncNavierStokesSolver to solve the channel flow. but it feedback me with "No such module: NekFFTW" I have compiled nektar with fftw support. why did i get this error. | | ztdepyahoo | | ztdepyahoo(a)163.com |

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