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Draft. This manual is new and still growing. If something here does not match what you see in the software, the software is right — tell us and we will fix the page.

Coupling

Where it is

Setup tree: Coupling

Controls

EXCHANGE

Physics

  • Control: choice (ComboRow)

FLUID PROPERTIES

The flow study is incompressible

  • Control: on/off (ToggleRow)

An incompressible solver works in kinematic pressure and carries no density or heat capacity of its own, so they have to be stated here. A compressible one has a thermophysical model and the adapter reads them from it.

Fluid density

  • Control: value (ValueField)
  • Unit: kg/m³
  • Value modes: none (plain entry)
  • Shown when: CouplingState.incompressibleFlow

Water is about 1000, seawater 1025, air 1.2. The same number the one-way flow load asks for, and for the same reason: it is the factor between p/rho and a pressure.

Specific heat

  • Control: value (ValueField)
  • Unit: J/(kg·K)
  • Value modes: none (plain entry)
  • Shown when: CouplingState.incompressibleFlow && !root.fsi

Cp. Water is about 4180, air 1005.

Prandtl number

  • Control: value (ValueField)
  • Value modes: none (plain entry)
  • Shown when: CouplingState.incompressibleFlow && !root.fsi

How the adapter turns the turbulent diffusivity into a wall conductivity. Water is about 7 at room temperature, air 0.71.

PARTICIPANTS

Flow study

  • Control: choice (ComboRow)
  • Options: ``

Its patch

  • Control: choice (ComboRow)
  • Shown when: CouplingState.fluidSimulation !== ""

Solid study

  • Control: choice (ComboRow)
  • Options: ``

Its face group

  • Control: value (ValueField)
  • Value modes: none (plain entry)
  • Shown when: CouplingState.solidSimulation !== ""

The in-app guidance depends on the case:

  • That study already names: …
  • The named face on the solid mesh that touches the flow. The run lists every group the mesh has if this one is not on it.

MORE PARTICIPANTS

+ Add a participant

  • Control: action (ToolButton2)

COUPLING SCHEME

Scheme

  • Control: choice (ComboRow)

Time window

  • Control: value (ValueField)
  • Unit: s
  • Value modes: none (plain entry)

The interval the two solvers agree on, not either one's own time step. Each may sub-step inside it.

Windows

  • Control: value (ValueField)
  • Value modes: none (plain entry)

How many windows to run. Zero means use the finish time instead.

Finish time

  • Control: value (ValueField)
  • Unit: s
  • Value modes: none (plain entry)

An alternative end for the run. Zero means use the window count. One of the two has to be set, or the run has no end at all.

Max iterations

  • Control: value (ValueField)
  • Value modes: none (plain entry)
  • Shown when: root.implicit

Per window. Reaching this without converging does not stop the run — preCICE moves on, and the window is simply not converged.

Convergence

  • Control: value (ValueField)
  • Value modes: none (plain entry)
  • Shown when: root.implicit

Relative change in the exchanged data below which the window is settled. 1e-3 is the usual starting point for FSI.

Acceleration

  • Control: choice (ComboRow)
  • Shown when: root.implicit

Initial relaxation

  • Control: value (ValueField)
  • Value modes: none (plain entry)
  • Shown when: root.implicit && CouplingState.acceleration !== "None"

How much of the first iteration's change to take. Between 0 and 1.

Windows reused

  • Control: value (ValueField)
  • Value modes: none (plain entry)
  • Shown when: root.implicit && CouplingState.acceleration === "Quasi-Newton (IQN-ILS)"

How many past windows the quasi-Newton history keeps. More is usually faster and can become ill-conditioned.

INTERFACE MAPPING

Mapping

  • Control: choice (ComboRow)

Support radius

  • Control: value (ValueField)
  • Unit: m
  • Value modes: none (plain entry)
  • Shown when: CouplingState.mapping === "Radial basis functions"

A length, so there is no sensible default: about the size of the interface, or a few times the mesh spacing on it. Too small is nearest-neighbour at RBF prices; too large is slow and then ill-conditioned.

Dimensions

  • Control: value (ValueField)
  • Value modes: none (plain entry)

2 or 3. Stated rather than derived, because the coupling is written before either mesh necessarily exists.

OUTPUT

Export the interface

  • Control: on/off (ToggleRow)

Writes what preCICE actually carried across, per window, into precice-exports. When a coupling is wrong both solvers' own results look plausible and this is the only place it shows.

Timing breakdown

  • Control: on/off (ToggleRow)

preCICE's own profile of where the time went — mapping, communication, or waiting for the other participant.

GENERATED CONFIGURATION

Hide

Label changes with the case; the source gives these forms: Hide, Show.

  • Control: action (ToolButton2)

Conditional and repeated groups

repeated once for every entry in CouplingState.extraLinks

Remove

  • Control: action (ToolButton2)

Exchange

  • Control: choice (ComboRow)

Solid study

  • Control: choice (ComboRow)
  • Options: ``

Its face group

  • Control: value (ValueField)
  • Value modes: none (plain entry)

The named face on this solid's mesh that touches the flow - its own interface, not the first link's.

Fluid patch

  • Control: choice (ComboRow)

Problems reported against this step

The application checks these before a run and reports them in the Problems tab against this step.

Severity Message
error

… marks a value the application computes at run time, so the source carries no fixed text for it.