Elmer: open-source multiphysics for EM, thermal and acoustics

Elmer is an open-source multiphysics finite element package developed by CSC — IT Center for Science in Finland, in development since 1995 and open source since 2005. The solver is GPL; the libraries are LGPL.

It is unusual among open-source simulation tools in being genuinely multi-domain rather than a specialist code with extras bolted on. Electromagnetics, heat transfer, elasticity, acoustics and fluid flow are all first-class modules within one solver, and — the part that matters — coupled-field problems are solved inside the code rather than by shuttling files between separate programs.

Elmer is the mature open-source answer for low-frequency electromagnetics, which is a genuinely under-served area — there is no OpenFOAM-equivalent with an obvious claim to the space.

• Magnetostatics — field, flux density, force and torque from permanent magnets and coils, including where the iron saturates.
• Eddy currents — induced circulating currents, the losses they cause, magnetic braking and shielding.
• Induction and Joule heating — with the thermal coupling handled internally, which is exactly the case where an external coupling layer is most painful.
• Motors and transformers — torque against rotor position, back-EMF, cogging, core and copper loss.
• Electrostatics and current conduction — capacitance, field strength for breakdown assessment, and resistive heating in conductors.

It handles nonlinear magnetic materials, which is not optional: iron saturates, and efficient machines operate exactly in the regime where permeability collapses. A linear assumption there is comfortable and usually optimistic.

Heat transfer. Conduction with convection and radiation boundaries, steady and transient — the solid-side thermal analysis that most electromagnetic loss calculations feed into.

Acoustics. Helmholtz problems for duct and cavity modes, and vibro-acoustics where a vibrating structure radiates sound — using its own elasticity solver for the structural half. See acoustic simulation.

Elasticity. Linear and nonlinear structural mechanics, primarily as the structural side of a coupled problem rather than as a replacement for a dedicated structural code.

That breadth is the strategic point: one integration covers electromagnetics, thermal and acoustics at once, which is why a single solver can carry several module families.

An Elmer case is driven by a solver input file — a .sif — which is a readable, structured text file: a set of Simulation, Body, Material, Boundary Condition and Solver blocks. It is more approachable than many solver inputs, and it is still a text file you must write correctly, with the parameter names and units the solver expects.

Meshing is separate. Elmer works from a mesh produced elsewhere and prepared with ElmerGrid, which converts and partitions it for parallel runs. As with structural analysis, the finite element mesh path — Netgen, SMESH or equivalent — is a real prerequisite rather than a detail, and it is a different kind of mesh from the hex-dominant one CFD wants.

There is an official GUI, ElmerGUI, which lowers the entry barrier considerably compared with hand-writing a .sif. It is closer to a solver front end than to an integrated workbench: geometry preparation, meshing, physics setup, running and post-processing still tend to involve several tools.

Elmer is installed and running today, behind the thermal and electromagnetics modules. For how the backends fit together, see the open-source stack.