February 2016 - Nektar-users

Nektar++ 4.2.0 and Nektar++ 3.2.0 compatibility issues
by Amitvikram Dutta 02 Feb '16

02 Feb '16

Hi, I've been using Nektar++ for DNS studies of Laminar Separation Bubbles over airfoils. So far I've been running Nektar++4.2.0 on my personal workstation. However, now that I am dealing with meshes containing more than 200k elements, I'll start submitting jobs to a cluster. The cluster however has Nektar++3.2.0 installed. Might there be any compatibility issues for the cases that I have been running so far? I have been using the IncNavierStokesSolver with Galerkin projection and a time-integration method of IMEXOrder2. Sincerely, *Amitvikram Dutta* *MASc Candidate* *Graduate Research Assistant * *Okanagan CFD Laboratory* *University of British Columbia | Okanagan Campus*

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basis functions for Discontinuous Galerkin
by Manh Nguyen 01 Feb '16

01 Feb '16

Dear all, I am a new Nektar++ user. I want to use the Advection-Diffusion-Reaction Solver where Discontinuous Galerkin method is chosen (property "Projection" has the value "Discontinuous") to solve 2D Unsteady Advection equations over a mesh comprised of both triangles and quads. I have two questions. Q1) When TYPE = "MODIFIED" (in the "EXPANSIONS" node in a xml file), what are the basis functions over a triangle, over a quad used? The user guide v4.2.0, Section 3.2 addresses this part only generally. Q2) The approximate solution is a linear combination of basis functions. How can one export the coefficients of the linear combination to an output file? I opened a file *.fld, those coefficients seem to be written inside the node <"ELEMENTS FIELDS="u"...> but the output coefficients are in some kind of encrypted format. Are there any documents that I can find answers to the two questions? Of course, I appreciate very much if someone can answer those questions via this mailing list. Thank you very much in advance, Manh Nguyen Department of Computer & Information Science & Engineering, University of Florida

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ExpList::SmoothField produces artifacts
by Kilian Lackhove 01 Feb '16

01 Feb '16

Dear all, I want to create a C0-continuous field from interpolated input data. The input field is obtained from a FVM code and was filtered with a gaussian in space and interpolated to the quadrature points. I store the field in a ContField2D m_bf = Array<OneD, MultiRegions::ExpListSharedPtr>(m_spacedim + 2); m_bf[i] = MemoryManager<MultiRegions::ContField2D>::AllocateSharedPtr(m_session, m_graph); copy the interpolated data into its m_phys array Vmath::Vcopy(nq, filteredField[i], 1, m_bf[i]->UpdatePhys(), 1); and then try to smooth the field. Until now, i just did: m_bf[i]->IProductWRTBase(m_bf[i]->GetPhys(), m_bf[i]->UpdateCoeffs()); m_bf[i]->MultiplyByElmtInvMass(m_bf[i]->GetCoeffs(), m_bf[i]->UpdateCoeffs()); m_bf[i]->BwdTrans(m_bf[i]->GetCoeffs(), m_bf[i]->UpdatePhys()); which yields the field depicted in DG.png. However, this does not ensure C0- continuity, so i tried to call ExpList::SmoothField afterward: m_bf[i]->SmoothField(m_bf[i]->UpdatePhys()); However, this produces a distorted field as shown in smoothed.png. I am using a 6th order modified expansion basis: <E COMPOSITE="C[10]" NUMMODES="6" FIELDS="p,u,v,w" TYPE="MODIFIED"/> and the mesh is depicted in smoothed_mesh.png. What is the cause of this problem and what can i do do fix it? Cheers, Kilian -- Kilian Lackhove, M.Sc. Fachgebiet für Energie- und Kraftwerkstechnik L1|08 114 Technische Universität Darmstadt Jovanka-Bontschits-Straße 2 D-64287 Darmstadt Germany Tel.: +49 6151 16 - 28915 Fax: +49 6151 16 - 6555 e-mail: lackhove(a)ekt.tu-darmstadt.de

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