Hello Jean, Thanks for your reply.
In my case, since I am physically moving the mesh ( as I was discussing here <https://groups.google.com/forum/#!topic/dealii/8I21UqIWAmU>), even after calling fe_values.reinit(cell), I am getting the gradients on the geometry before mesh movement which should not be the case. Also, note that once I move the mesh, this happens only if I use the same fe_values object. But if I create a new FEValues object (lets call it fe_values_new), then if I use fe_values_new.get_function_gradients(), I get the gradients on the updated geometry. Code given below for reference. Code 1: (Does not work) // Everything is in one big function FEValues<dim> fe_values (fe, quadrature_formula, update_values <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa4057ca2f127aa619c65886a9d3ad4aea> | update_gradients <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52facbcc430975fa6af05f75ca786dc6fe20> | update_quadrature_points <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fad5c9ff886b9615349a5d04a6c782df4a> | update_JxW_values <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa714204722e9eeb43aadbd0d5ddc48c85> ); // do some stuff // move mesh like step 17, adding displacements to cell->vertex(i) fe_values.reinit(cell); fe_values.get_function_gradients(); Code 2:(It works) // Everything is in one big function FEValues<dim> fe_values = new FEValues<dim>(fe, quadrature_formula, update_values <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa4057ca2f127aa619c65886a9d3ad4aea> | update_gradients <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52facbcc430975fa6af05f75ca786dc6fe20> | update_quadrature_points <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fad5c9ff886b9615349a5d04a6c782df4a> | update_JxW_values <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa714204722e9eeb43aadbd0d5ddc48c85> ); // do some stuff // move mesh like step 17, adding displacements to cell->vertex(i) delete fe_values; fe_values = new FEValues<dim> (fe, quadrature_formula, update_values <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa4057ca2f127aa619c65886a9d3ad4aea> | update_gradients <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52facbcc430975fa6af05f75ca786dc6fe20> | update_quadrature_points <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fad5c9ff886b9615349a5d04a6c782df4a> | update_JxW_values <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa714204722e9eeb43aadbd0d5ddc48c85> ); fe_values.reinit(cell); fe_values.get_function_gradients(); Does that mean the instant FEValues object is created, it takes that as a reference configuration and do all the gradients on this reference configuration ? I also read the posts related to this issue here <https://groups.google.com/forum/#!searchin/dealii/mesh$20fevalues/dealii/KvqA-fQAYgM/yQdzNZsRSOUJ> and here <https://groups.google.com/forum/#!searchin/dealii/mesh$20fevalues/dealii/B2v7qSLrnck/0e44LC4bCQAJ> . On Tuesday, May 31, 2016 at 1:41:10 AM UTC-4, Jean-Paul Pelteret wrote: > > If you physically move the mesh vertices, like you were discussing here > <https://groups.google.com/forum/#!topic/dealii/8I21UqIWAmU>, then when > you call fe_values.reinit(cell), the mapping between the current cell > geometry (as defined by the triangulation) and isoparametric cell are > accounted for and used when computing gradient quantities. > > For example, compare the update_quadrature_point_history functions in > step-18 > <https://dealii.org/8.4.0/doxygen/deal.II/step_18.html#TopLevelupdate_quadrature_point_history> > > and step-44 > <https://dealii.org/8.4.0/doxygen/deal.II/step_44.html#Solidupdate_qph_incremental>. > > In step-44 the mesh is not physically moved, so "get_function_gradients" > applied to the total displacement vector will return elements of > \frac{\partial \mathbf{u}}{\partial \mathbf{X}} (i.e. the material > gradient), while in step-18 the mesh is moved and "get_function_gradients" > returns elements of \frac{\partial \mathbf{u}}{\partial \mathbf{x}} (i.e. > the spatial gradient). However, you will note that in step-18, only the > incremental displacement gradient is computed as the stresses are > systematically incremented using this result. > > On Tuesday, May 31, 2016 at 2:54:32 AM UTC+2, RAJAT ARORA wrote: >> >> Hello all, >> >> I have a question about FEValues<dim> object that we use in the >> computation of element stiffness and other places. >> >> >> If I declare fe_values object and get then move the mesh and then try to >> call fe_values.get_function_gradients() >> will this give me gradients on the deformed mesh or the mesh that was >> chosen to begin with ? (Code structure below) >> >> >> FEValues<dim> fe_values (fe, quadrature_formula, >> update_values >> <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa4057ca2f127aa619c65886a9d3ad4aea> >> >> | update_gradients >> <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52facbcc430975fa6af05f75ca786dc6fe20> >> >> | >> update_quadrature_points >> <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fad5c9ff886b9615349a5d04a6c782df4a> >> >> | update_JxW_values >> <https://dealii.org/8.4.1/doxygen/deal.II/group__feaccess.html#ggaa94b67d2fdcc390690c523f28019e52fa714204722e9eeb43aadbd0d5ddc48c85> >> ); >> >> // do some stuff >> >> // move mesh like step 17, adding displacements to cell->vertex(i) >> >> fe_values.get_function_gradients(); >> >> >> >> >> >> If it gives gradients on the initial mesh, then how does it know those >> coordinates once you change the coordinates of the >> vertices of the triangulation ? >> >> >> > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. 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