Constraint and vessel API names¶

Use names that identify the operation rather than the generic word “coupling”. A multiplier constraint, a prescribed wall pressure, vessel postprocessing, and exchange with an external flow solver are separate operations.

Operation	Normal API	Compatibility name
Map multiplier coefficients to bulk loads	`ElasticityProblem::multiplier_load_matrix()`	Public `coupling_matrix` storage
Assemble that matrix from a reduced space	`ReducedCoupling::assemble_multiplier_load_matrix()`	`assemble_coupling_matrix()` overloads
Inspect the reduced Poisson load matrix	`ReducedPoisson::assembled_multiplier_load_matrix()`	`assembled_coupling()`
Inspect its global Frobenius norm	`multiplier_load_matrix_frobenius_norm()`	`coupling_matrix_frobenius_norm()`
Solve elasticity and recover vessel wall pressure/radius	`VesselElasticityProblem` in `<immersx/physics/vessel_elasticity.h>`	`CoupledElasticityProblem` and its header
Select prescribed vessel pressure rather than a displacement constraint	`uses_prescribed_vessel_pressure()` / `set_prescribed_vessel_pressure(bool)`	Public `pressure_coupling` storage
Select that mode in a parameter file	`Prescribed vessel pressure`	`Pressure coupling`

Multiplier constraints¶

The multiplier load matrix has bulk rows and multiplier columns. It is the transpose of the discrete constraint operator: if the constraint is B u = g, the bulk reaction is B^T lambda. Transverse reduction is already part of this operator. It is not a time exchange interface with a flow solver.

The old Elasticity matrix member remains the storage returned by the new accessor. Both names observe identical entries. The old assembly overloads forward to the new overloads, including the affine background correction to the reduced right hand side. No transpose, normalization or numerical operation changes when using the new names.

Vessel elasticity and wall pressure¶

VesselElasticityProblem<dim, spacedim> is the same C++ type as CoupledElasticityProblem<dim, spacedim>. Existing specializations, derived classes, constructors and binary instantiations therefore retain their type identity. Use the vessel name for the tissue problem even when no external flow solver is present. The coupled_elasticity executable remains an external staggered coupling application; its exchanged pressure is named vessel_wall_pressure in the implementation.

The tissue problem recovers normal wall stress from its multiplier field. pressure_at_immersed_surface and pressure_at_immersed_surface_by_inclusion name the vessel and inclusion data; they do not imply that an external solver owns the pressure.

Prescribed pressure mode¶

Use parameters.set_prescribed_vessel_pressure(true) or:

subsection Immersed Problem
  set Prescribed vessel pressure = true
end

This mode projects the supplied vessel pressure and applies its transpose load to the displacement equation. With the mode disabled, the static path solves the multiplier saddle-point system instead. The mode does not select an external solver or turn data exchange on or off. Existing restrictions on quasistatic and dynamic point formulations remain unchanged.

Pressure coupling is a ParameterHandler alias for the same entry. It accepts existing files without a deprecation warning. If a file deliberately sets both spellings, the last assignment wins, as for repeated assignments to one entry. The C++ compatibility member and both accessors also share the same boolean; there is no second value to synchronize.

Modern Constraint, Interaction, ReducedCoupling, and application names that describe an actual pairing of physical systems retain their meanings. This migration does not replace the mathematical concept of coupling or introduce another application hierarchy.