# Coupling applications

## Introduction

Usually, the term of coupling is used when we want to study, for a given device, several physical phenomena: electrical, magnetic, thermal, mechanical…

Each phenomenon is described by equations (Maxwell's equations, Fourier's equation, circuit equation, mechanical equation…). Thus, the coupling requires the solving of a complex system of equations.

## Strong/weak coupling

• strong coupling : when is carried out a simultaneously solving of two systems of equations

(example: for circuit coupling, the equations of magnetic field and the circuit equations are solved simultaneously).

• weak coupling: when the two systems of equations are separately solved, so that impose the transfer of the results between the two systems (example: for kinematic coupling the equations of the magnetic field and the mechanical equations are solved successively for each time step).

## … in Flux

The coupling proposed in Flux for the applications called “ … coupled with Transient Thermal application ” is a weak coupling: the thermal and electromagnetic processes are solved separately. The two systems of equations are coupled by means of some terms:

• The temperature (resulting from thermal resolution) is a quantity which is involved in the system of electromagnetic equations by means of the material physical properties: magnetic permeability, electric resistivity, permittivity…
• The power losses (resulting from the electromagnetic solving) is the term corresponding to the heating source of the system of thermal equations.

## Principle of coupling: details

The principle of coupling for the Steady State AC Magnetic (SM) coupled with Transient Thermal (TT) application is detailed in chapter Steady State AC Magnetic coupled with Transient Thermal application: principles