Implement a function in the Node class that computes the change in momentum of all the properties in the nodal properties pool, and call this function from the MPMExplicit by iterating over all nodes. The following describe the rationale behind the compute_multimaterial_change_in_momentum() function:

Iterate over all the material ids stored in the node -- stored in std::set material_ids_.
Compute the change in momentum for each material and for this node as: delta_momentum = velocity_ * mass - momentum, where mass and momentum are values obtained from the existing property pool for the given material id and node id, and velocity_ is the velocity of the node in question.

After proper implementation, call this function while iterating over nodes at every computational step in the MPMExplicit class.

    if (interface_)
      mesh_->iterate_over_nodes(std::bind(
          &mpm::NodeBase<Tdim>::compute_multimaterial_change_in_momentum,
          std::placeholders::_1));

This function is only called after the velocities at the nodes are computed but before velocity constraints are applied. Additionally, the computation must only be done if interface_ == true.

This PR is related to the RFC #636 . The calculation of the change in momentum for each node and different material is expected with this PR. This property is essential for the contact algorithm since it represents one of the verifications of the contact between two adjacent materials while also being the main property used to change the momentum accordingly if contact is identified.

Codecov Report

Merging #648 into develop will increase coverage by 0.00%. The diff coverage is 98.41%.

@@           Coverage Diff            @@
##           develop     #648   +/-   ##
========================================
  Coverage    96.56%   96.56%           
========================================
  Files          122      122           
  Lines        25200    25247   +47     
========================================
+ Hits         24332    24378   +46     
- Misses         868      869    +1

Impacted Files	Coverage Δ
include/node.h	`100.00% <ø> (ø)`
include/node_base.h	`100.00% <ø> (ø)`
include/solvers/mpm_explicit.tcc	`64.00% <50.00%> (-0.19%)`	:arrow_down:
include/mesh.tcc	`83.99% <100.00%> (+0.04%)`	:arrow_up:
include/node.tcc	`95.32% <100.00%> (+0.19%)`	:arrow_up:
tests/interface_test.cc	`100.00% <100.00%> (ø)`

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cb-geo / mpm

Feature/contact/compute momenta change #648

Codecov Report