Conclusion
Hydrodynamic Transmissions

The energy delivered by a thermal engine (with the exception of the steam engine!) – most often a diesel engine and very rarely a gas turbine – cannot be used directly to drive the wheels of a rail vehicle, and a transmission system is needed to adapt it to traction requirements.

By taking up the basic principles of hydrodynamics, such as Euler's theorem, this article explicitly shows the inherent natural characteristics of hydrodynamic converters, couplers and retarders, starting from an ideal, non-viscous fluid. This approximation provides a simpler approach that is sufficient for the railway user, without having to resort to the Navier-Stokes equations that describe the motion of "Newtonian" fluids.

Depending on the power/speed characteristics of diesel engines, and the different applications for different types of vehicle (railcars,...