What is new?

• FP32 solver mode
• DPCPP backend to support Intel GPUs
• Interpolation based recycling + support of arbitrary fields
• Ascent in situ visualisation plugin
• iofld class reading/writing field files including ADIOS2 support
• Addtional output options (element filter and interpolation on uniform grid / different polynomial-order)
• Multi session nek-nek including multi-rate time stepping
• Typed device memory and pool allocation
• CHT nek-nek support
• nrsqsub nek-nek handling
• Improved JIT compilation performance
• HIP support for SEMFEM
• Aero forces
• SEM ops
• Mesh surface ops
• Gradient jump penalty method and improved avm reguarlization
• Linear implicit velocity source term
• T-mesh support for all scalars
• Robin boundary conditions
• RANS ktau variants SST, DDES, IDDES
• Various bug fixes

Good to know

• GPU aware MPI is disabled by default (to enable set env-var NEKRS_GPU_MPI=1) which may cause a performance regression
• [reproducibility] variable time step controller restricts dt to 5 significant digits
• nrsman <par, env> can be used to display man pages
• AmgX support was removed (replaced by HYPRE)
• Field file extension starts with 0-index
• nrsqsub scripts are moved to HPCsupport
• First time step may take longer due to initialization overhead

Breaking Changes

This list provides an overview of the most significant changes in this release, although it may not encompass all modifications. We recognize that several of these updates directly affect the user experience. These adjustments were essential to enhance the stability of the user interface in future iterations. We apologize for any inconvenience this may cause.

• run build.sh instead of nrsconfig to build the code
• host mirrored variables like nrs->U, cds->S, mesh->x have been removed
• send signal (defined in env-var NEKRS_SIGNUM_UPD) to process trigger file nekrs.upd
• use auto foo = platform->deviceMemoryPool.reserve<T>(nWords) instead of platform->o_mempool.slice[0-15]
• change count argument of occa::memory::slice, occa::memory::copyFrom, occa::memory::copyTo to number of words instead of bytes
• use nekrs_registerPtr instead of common blocks NRSSCPTR / SCNRS in usr file and access them using nek::ptr in udf (see examples)
• use par section [GEOM] for geometry solver instead of [MESH]
• usr scalars = FOO1, FOO2, ... in [GENERAL] to define additional scalar transport equations
• use mesh = fluid+solid for T-mesh (conjugate heat transfer) for a scalar e.g. temperature
• use iofld class () instead of writeFld
• use planarCopy class instead of velRecycling
• ::postProcessing functions are now members of nrs_t (except planarAvg)
• use boundary functions like udfDirichlet for all fields
• par key GENERAL::checkpointInterval <= 0 will turn off checkpoints

Interface Changes

• define time as double (instead of defloat) in all UDF functions
• nrs_t is no longer passed from UDF functions (nrs object is now globally accessible within udf if the Navier Stokes solver is enabled)
• nrs_t is no longer passed from <plugin>::setup
• udf::properties = std::function<void(nrs_t *, dfloat, occa::memory, occa::memory, occa::memory, occa::memory)> -> nrs_t::userProperties = std::function<void(double)>
• udf::uEqnSource = std::function<void(nrs_t *, dfloat, occa::memory, occa::memory)> -> nrs_t::userSource = std::function<void(double)> (same hook for all fields)
• udf::udfconv = std::function<int(nrs_t *, int)> -> nrs_t::userConvergenceCheck = std::function<bool(int)>
• udf::udfdif = std::function<void(nrs_t *, dfloat, occa::memory)> -> nrs_t::userDivergence = std::function<void(double)>
• tavg::setup(nrs_t*) -> tavg::setup(dlong fieldOffset, const fields& fields)
• postProcessing::planarAvg(nrs_t*, const std::string&, int, int, int, int, occa::memory) -> mesh_t::planarAvg(const std::string&, int, int, int, int, dlong, occa::memory o_avg)
• pointInterpolation_t::setPoints(int, dfloat*, dfloat*, dfloat*) -> pointInterpolation_t::setPoints(const std::vector<dfloat>&, const std::vector<dfloat>&, const std::vector<dfloat>&)

Name Changes

• boundary type names: codedFixed -> udf, value -> Dirichlet, Gradient -> Neumann
• some member names of bcData changed (see include/app/nrs/bdry/bcData.h)
• velocityDirichletConditions -> udfDirichlet (same for all fields)
• velocityNeumannConditions -> udfNeumann (same for all fields)
• nrs->o_usrwrk-> platform->app->bc->o_usrwrk
• nrs->_mesh -> nrs->meshT
• nek::ocopyToNek -> nrs->copyToNek
• nek::ocopyFromNek -> nrs->copyFromNek
• nrs->o_FU -> nrs->fluid->o_explicitTerms()
• cds -> scalar
• cds->o_FS -> scalar->o_explicitTerms(std::string)
• cds->o_rho -> scalar->o_transportCoeff(std::string)
• cds->o_diff -> scalar->o_diffusionCoeff(std::string)
• cds->o_diff -> scalar->o_diffusionCoeff(std::string)
• cds->mesh[...] -> scalar->mesh(...)
• occaKernel -> deviceKernel
• occaProperties > deviceKernelProperties
• occa::memory -> deviceMemory
• nrs->isOutputStep -> nrs->checkpointStep
• subCyclingSteps -> advectionSubCyclingSteps in par
• par section VELOCITY -> FLUID VELOCITY
• par section PRESSURE -> FLUID PRESSURE
• par section TEMPERATURE -> SCALAR TEMPERATURE
• par section SCALAR01 -> SCALAR FOO
• par SCALAR key diffusivity -> diffusionCoeff
• par SCALARkey density -> transportCoeff
• comm.mpiRank -> comm.mpiRank()
• comm.mpiComm -> comm.mpiComm()

Known Bugs / Restrictions

• Code is not fully optimized on CPUs and AMD MI300 GPUs
• planar avg in 1D is limited to 256 gridpoints per direction locally (per MPI Rank)
• SEMFEM preconditioner not available when using DPCPP
• 507
• 485
• 258

Thanks to our Contributors

@yslan, @kris-rowe, @tcew, @MalachiTimothyPhillips, @thilinarmtb, @nandu90

We are grateful to all who added new features, filed issues or helped resolve them,
asked and answered questions, and were part of inspiring discussions.

What is new?

• Lagrangian phase model (one-way coupling)
• Overset grids (neknek)
• Particle tracking
• Single source udf+oudf
• Device support BoomerAMG
• Improved runtime statistics
• 4th-kind Chebyshev smoothers
• Configureable time averaging
• Extrapolation initialGuess method
• Scaleable JIT compilation
• Real gas support for lowMach
• More examples
• Various bug fixes

Good to know

• [udf] Changes in include files do not trigger a rebuild automatically
• [udf] Plugins kernels will be loaded automatically (call in UDF_LoadKernels no longer required)

Breaking Changes

• [nrsconfig] Ensure env-vars CC, CXX and FC point to the correct MPI compiler wrappers (see README.md for an example)
• [udf] Plugin header files need to be included explicitly
• [udf] Rename bc->wrk => bc->usrwrk
• [udf] Update to new API of lowMach plugin (see lowMach example)
• Time step was added to nekRS::outfld(..., int step, ...)
• [par] Use pMGSchedule instead of pMultigridCoarsening (see help for more details)
• [par] Rename writeControl value runTime => simulationTime
• [par] Remove multigrid qualifier coarse
• [par] Remove SEMFEM solver specification from key preconditioner, use semfemSolver instead
• [par] Replace stressFormulation = true by equation = navierStokes+variableViscosity
• [par] Replace bcType fixedValue by codedFixedValue
• [par] Replace elasticity by pcg+block for mesh solver
• Use occa::memory mesh_t objects for vgeo, cubvgeo, ggeom, sgeom, LMM, invLMM (no longer mirrored on host)
• All boundaryIDs need to be assigned in boundaryTypeMap (use none for an internal boundary)

Known Bugs / Restrictions

• Code is not fully optimized on CPUs in general and Intel GPUs
• 485
• 729
• 258

Thanks to our Contributors

@neil-lindquist, @kris-rowe, @pwang234, @nandu90, @yhaomin2007

We are grateful to all who added new features, filed issues or helped resolve them,
asked and answered questions, and were part of inspiring discussions.

What is new?

• Multi-session (uncoupled) support
• Support unaligned symmetry boundary condition
• Support (unaligned) traction boundary condition
• Better performance on AMD MI-GPUs
• FLOP counters
• Various bug fixes

Good to know

• OpenCL support is now disabled by default

Breaking Changes

• [udf] Rename udfBuildKernel => oudfBuildKernel
• [par] Separate details of coarse grid discretization from coarse grid solver
  e.g., coarseSolver = SEMFEM+AmgX is replaced by
  coarseSolver = AmgX and coarseGridDiscretization = SEMFEM
• [par] Remove preconditioner=semg and preconditioner=semg_amg
• [udf] Rename plug-in name avg => tavg
• [udf] Rename udf.converged => udf.timeStepConverged
• [nrsconfig] Rename env-var AMGX_ENABLE => ENABLE_AMGX

Known Bugs / Restrictions

• Mesh solver does not support CHT and unaligned sym/shl BCs
• 729
• 300
• 258

Thanks to our Contributors

@tcew, @kris-rowe, @aprilnovak

We are grateful to all who added new features, filed issues or helped resolve them,
asked and answered questions, and were part of inspiring discussions.

A special shout out to Tim Warburton at VT for tuning some critical kernels.