when the velocity or velocity-potential has to be calculated at all control points in a bounded lattice, a multi-threading operation is started: for each control point in the targeting lattice, all rings from all bounded lattices and associated wakes are run over in an isolated thread. this multi-threading system allows running several vortex rings simultaneously, what considerably reduces the calculation time in multiple-cores machines. the reduction of time is proportional to the number of processors in the machine.