Velocity (Lorentz Term)
The Velocity (Lorentz term) node adds velocity v. The external current is equal to σv × B.
This node is available in 2D and 2D axisymmetry space dimensions of the Magnetic Fields, Magnetic and Electric Fields, and Rotating Machinery, Magnetic interfaces. In 2D and 2D axisymmetry, it is available when only solving for the out-of-plane component of the magnetic vector potential. The node is also available in 3D Magnetic and Electric Fields interface when solving for both the electric potential and the magnetic vector potential.
 
Correct use of the velocity feature requires deep physical insight. In situations when the moving domain is of bounded extent in the direction of the motion, material properties vary in this direction, or the domains contains magnetic sources that also move, the Lorentz term must not be used.
There are several library examples demonstrating the correct usage:
•
Magnet Falling Through Copper Tube: Application Library path ACDC_Module/Devices,_Transducers_and_Actuators/falling_magnet
•
Magnetic Brake: Application Library path ACDC_Module/Devices,_Transducers_and_Actuators/magnetic_brake
•
Homopolar Generator: Application Library path ACDC_Module/Devices,_Motors_and_Generators/homopolar_generator
An operational definition of when it can be used is that the moving domain should only contain an induced magnetic source (magnetization plus eddy currents) that has to be stationary with respect to the motion. Thus, it cannot be used for modeling projectiles of finite length or projectiles containing magnets. It can be used to model conductive, homogeneous spinning disks (magnetic brakes); magnets over a moving infinite homogeneous plane (maglev trains); and flow of homogeneous conducting fluid past a magnet (liquid metal pumps or Hall generators/thrusters, for example).
If you are not sure how to proceed, contact the COMSOL Support Center: www.comsol.com/support.
Velocity (Lorentz Term)
User defined is selected by default. Enter the components for the Velocity vector v (SI unit: m/s) or, if present, select any velocity field defined in the model. For example, using the velocity field is useful when coupling to the velocity field of a fluid for a magnetohydrodynamic model.