Thermo-hydraulic components, such as turbo machines, generators, electric motors, pumps, etc., transfer mechanical power by means of a shaft and/or gearbox. Flownex takes into account mechanical interaction between these thermo-hydraulic components which allows simulation and prediction of torque balancing, power losses, power and speed matching and shaft inertia due to the mechanical couplings.

Some examples where calculation of effects due to mechanical couplings are required

• Transfer of mechanical power between rotating equipment.
• Steady-state and transient power matching between mechanical components.
• Inertia caused by shaft rotation during plant start-up and shutdown.
• Excessive speed prediction and management on shafts during generator trip.
• Facilitating speed ratios between coupled components on a gearbox.
• Matching power and speed of components connected on a single shaft.

Mechanical couplings available:

Shaft

The Flownex shaft element serves as a connecting element to facilitate mechanical interaction, i.e. the transfer of mechanical power, between rotating equipment.

Gearbox

The Gearbox element allows the modelling of speed ratios between turbo machines, generators, electric motors, pumps, etc, when coupled to  each other through a gearbox.

Mechanical Coupling Effects & Calculations:

Torque Balancing & Power Matching

Torque balancing and power matching is an optimisation routine by Flownex to ensure that power provided to the shaft is equal to the power absorbed by other components on the shaft during steady state conditions.

The routine can be implemented for both steady state and transient scenarios. During dynamic simulation any excess power on the shaft will cause the shaft to accelerate taking excess power and the shaft, gearbox and machine inertias into account.

There are various methods to match the power, these options include:

Inertia

Inertia is the resistance of any physical object to a change in its state of motion, therefore for mechanical couplings it is the resistance seen during rotational acceleration or deceleration of the shaft, gearbox or the turbines, generators, pumps, etc. connected to it.

A typical example of this is when a turbine and compressor is connected by means of a mechanical shaft to a generator and the power load trips, causing the shaft to speed up (accelerate), because of the loss of power absorbed by the generator (Excess power on the shaft).

Power Losses

Power losses are the calculation of the power lost in the mechanical couplings or machines connected due to inefficiencies (shaft and gearbox efficiency, switching efficiency and generating efficiency) and also power used for example by the auxiliaries and house loads such as lighting.