Use Tensors in solid-poro elements

[amgebauer]

With this PR, I try to use a few more Tensors in the solid-poro framework. I could not transfer all Voigt-notations, but at least a few. This will simplify things if we want to use the elements in 2D.

I also changed many methods to return the linearization w.r.t. det F instead of the displacements. This allows us to reuse assembly methods that we have implemented for the solids (and extract a pure pressure term assembly which might be useful in a broader context.)

[Copilot]

Pull request overview

This PR expands tensor-based formulations in the solid-poro element implementations (reducing Voigt usage) and refactors several pressure-related linearizations to be expressed w.r.t. the determinant of the deformation gradient (J=\det F), enabling reuse of solid assembly utilities and facilitating future 2D support.

Changes:

• Switch multiple solid-poro calculations (velocity/pressure-based) from Voigt/matrix plumbing to tensor types + Voigt “views” where needed.
• Refactor pressure/stress internal force and stiffness contributions to use PK2 tensors and a new pressure-only stiffness assembly helper.
• Update solid element geometric stiffness assembly API/call sites to pass PK2 explicitly (stress.pk2_) and adjust unit tests/benchmarks accordingly.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
unittests/solid_3D_ele/4C_solid_3D_ele_calc_lib_test.cpp	Updates unit test call to geometric stiffness to pass PK2 tensor.
tests/benchmark_tests/solid_3D_ele/4C_solid_3D_ele_calc_lib_benchmark.cpp	Updates benchmark call to geometric stiffness to pass PK2 tensor.
src/solid_poro_3D_ele/4C_solid_poro_3D_ele_calc_pressure_velocity_based.cpp	Converts several operations to tensor-based forms; refactors pressure-force/stiffness assembly paths.
src/solid_poro_3D_ele/4C_solid_poro_3D_ele_calc_pressure_based.cpp	Refactors porosity/solid-pressure linearization to be w.r.t. (J); uses tensor-based pressure force/stiffness assembly.
src/solid_poro_3D_ele/4C_solid_poro_3D_ele_calc_lib.hpp	Broad tensorization (stress, gradients, Cauchy–Green); refactors porosity linearizations to scalar d/d(J).
src/solid_3D_ele/4C_solid_3D_ele_calc_mulf_fbar.hpp	Updates geometric stiffness call to pass PK2 tensor explicitly.
src/solid_3D_ele/4C_solid_3D_ele_calc_mulf.hpp	Updates geometric stiffness call to pass PK2 tensor explicitly.
src/solid_3D_ele/4C_solid_3D_ele_calc_lib.hpp	Adds add_pressure_stiffness_matrix and changes geometric stiffness API to accept PK2 tensor.
src/solid_3D_ele/4C_solid_3D_ele_calc_fbar.hpp	Updates geometric stiffness call to pass PK2 tensor explicitly.
src/solid_3D_ele/4C_solid_3D_ele_calc_eas.hpp	Updates geometric stiffness call to pass PK2 tensor explicitly.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.