EM
The *EM keyword cards provide input for a new electromagnetism module for solving 3D
eddycurrent, inductive heating or resistive heating problems, coupled with mechanical
and thermal solvers. Typical applications include magnetic metal forming and welding. A
boundary element method in the air is coupled to finite elements in the conductor in order
to avoid meshing the air.
This LSDYNA simulation shows a simple Electromagnetic forming example using the EM solver. A R,L,C circuit is defined in the coil which produces induced currents in the workpiece. This in turn generates Lorentz forces which cause the plate to move. Local heating is also produced and handled by the thermal solver. An EM EOS couples back the temperature to the Electromagnetic solver by making the electromagnetic conductivity temperature dependent. The FEM and BEM matrices are recalculated every 20 timesteps in order to save calculation times. Coupling between EM and the thermal and mechanical solvers is automatic (no extra keyword mandatory).

This LSDYNA simulation shows a simple Tube expansion example using the EM solver. A current is imposed in the coil which produces induced currents in the workpiece. This in turn generates Lorentz forces which cause the tube to expand. This problem is of medium size so running with 4 or more CPUs is recommended.

This LSDYNA simulation shows a simple inductive heating problem. A micro EM timestep is calculated using the circuit's current period divided by a factor NUMLS. Over a whole period, the full Eddy current problem is solved. An average Joule heating is calculated which is then given to the thermal solver over all the subsequent periods until reaching a time defined by a EM macro timestep. At that point, the matrices are recomputed and the whole procedure is repeated. If the conductor do not move and have a constant conductivity, then the EM macro timestep can be as long as the run. An optional 'switch.k' file can be included which turn the EM solver on and off based on a specific node temperature.

This LSDYNA simulation shows a simple resistive heating problem. The EM resistive heating solver considers the rise time of the current to be slow or non existent (DC current). As such, no inductive and diffusive effects appear which allows the solver to remove the BEM system. The EM solve is consequently very fast and a very high EM timestep can be used. In the current example, no heat convection or radiation is taken into account for simplification purposes.

A railgun consists of two parallel metal rails connected to an electric power supply. The projectile completes the circuit. The current flowing through the rails and projectile generates a magnetic field which in turn generates a Lorentz force propelling the projectile out of the barrel at a very high speed. This problem serves as an example to illustrate the EM contact. Current is allowed to flow through conductors by 'stitching the BEM meshes of the various parts together. As such, it is highly recommended to recompute the BEM matrix often to ensure stability.

The R9 version introduced many new advanced capabilities to the axisymmetric solver. For example, it is now possible to simulate pancake or helicoid type of coils by connecting the different turns using EM_CIRCUIT_CONNECT therefore expanding the range of applicable EM forming or bending problems that can be solved using the axisymmetric solver. Run times are tremendously reduced which allows the set up of advanced optimization studies in combination with LSOpt.

A module that allows the simulation of batteries under normal use (charge and discharge) as well as during internal and external short circuits is under development within the EM solver of LSDYNA. It simulates the migration of ions from the anode to the cathode by the introduction of the socalled Randle circuit models. In case of an internal short circuit, the local Randle circuit can be replaced by a resistance and the corresponding Joule heating can be added to the thermal solver allowing for a local current flow and a local heating. The battery pins can be connected to various types of isopotentials simulating the different conditions of use of a battery. The current example features a simple charge/discharge of a battery. A Development version is needed to run this problem. Please contact your local distributor for further information.
