Latest Developments in Voith Schneider Propulsion Systems

The 18th International Tug & Salvage Convention Technical Workshop Day 2 Organised by The ABR Company Limited Paper No. 6 Latest Developments in Voith Schneider Propulsion Systems Dr Jens-Erk Bartels & Dr Dirk Jürgens, Voith Turbo, Germany SYNOPSIS: The vertical axis cycloidal or Voith Schneider® Propeller (VSP) has by no means reached the limit of its development. The first new six-bladed VSP units with enhanced hydrodynamics and improved construction have been introduced into the workboat market and have met all expectations. With modern design tools like the latest computational fluid dynamic methods (CFD), the hydrodynamic is continuously improved. New blade profiles with higher efficiency have been developed. The new VSP generation with higher maximum input powers is under progress. For the re-design of each component, an industry leading structural analysis FEM program is used. This provides the power of linear and non-linear structural capabilities to deliver reliable structural simulation results. New construction principles for key components as blades and main bearings have been developed. Additionally to the propeller, the hull design of ships with VSP is subject of continuous research and improvement. A new guard and nozzle plate has been developed for Voith Water Tractors. The new Voith Turbo Fin® (VTF) offers to modern and compact harbour class water tractors outstanding dynamic shiphandling capabilities in the performance range of today’s enhanced Escort Voith Water Tractors in operation at the major terminals worldwide. A further good example of enhanced cycloidal propulsion is the Voith Cycloidal® Rudder (VCR). This modified VSP with only two blades, is the latest propulsion and manoeuvring device acting in the , passive mode at high speeds like a conventional rudder and in the active mode at slow speeds like a normal VSP with the proven high degree of manoeuvrability. 1. HYDRODYNAMIC PRINCIPLE OF CYCLOIDAL The consideration of each blade during the revolution PROPULSION provides the simplest explanation of the generated Voith Schneider® Propellers (VSP) are mainly used where hydrodynamic forces. By superimposing the rotary movement high demands are made for the safety and manoeuvrability of of the rotor casing on a straight-line perpendicular to the ships. The idea of this unique propulsion and manoeuvring rotational axis (to represent the movement of the vessel), system was born by the Austrian engineer Ernst Schneider in each blade of the VSP follows a cycloid (Fig. 1). To generate 1926 [1]. thrust the blade profile has to be turned against the blade path by the angle ?. Thereby the hydrodynamic lift will be On a VSP the blades protrude below the ship’s hull and , generated at right angles to the resultant velocity rotate uniformly on a rotor casing around the vertical axis. (perpendicular to the cycloidal path). The magnitude of the lift The blade’s oscillating movement determines the magnitude depends on the angle of attack ? and the inflow velocity. The of thrust by variation of the amplitude (pitch) as well as the lift varies during the blade’s revolution. Integration of the phase correlation (pitch direction) determines the thrust components of the lift forces generated over the entire direction between 0 and 360 degrees. The VSP is a flexible circumference acting in the direction of motion result in the controllable pitch propeller allowing a steeples variable thrust thrust. Due to the rotational symmetry, identical thrust can be adjustment according to the Cartesian X – Y co-ordinate generated in all directions. system. Therefore, an identical thrust can be generated in any direction stepless, extremely fast and very precise. Unlike screw propellers, the speed through the water over the whole VSP blade is constant. The non-stationary flow conditions over the blade length allow much higher angles of attack. Furthermore the VSP is a “twin” or “contra-rotating” propeller as each blade is used twice – once in the fore and secondly in the aft semicircle of the blade orbit – during each revolution. The VSP rectangular propeller swept area is about twice as large as the screw propeller area at specified design conditions resulting in considerably less specific propeller loads. The hydrodynamic principle of the blade action is produced mechanically by the crank type kinematics inside the VSP . The lower spherical bush of the central control rod, which can be displaced eccentrically, directly supports the links of each blade actuating system (Fig. 2). Fig 1 Cycloidal path of VSP blade 1 Fig 4 Voith circulation model tank test facility dimensional non-stationary flow around the VSP [2]. The flow field is divided into about 1.5 million small volume elements. For each volume, the physical constraints including viscosity are estimated. For Comet, the SPMD (Single Program Multiple Data) model is adopted. In this approach, each processor runs an identical program but only solves for its own set of data. To solve the global problem, the computational domain needs to be distributed over all the processors via domain decomposition. Space and time parallelisation are implemented in Comet using PVM (Parallel Virtual Machine) Fig 2 VSP crank type kinematics and MPI (Message Passing Interface) message passing libraries [2]. Two hydraulic servomotors arranged at 90 degrees to each other actuate the control rod, whereby the speed servomotor The permanent verification and calibration of CFD results controls the longitudinal thrust (ahead and astern) and the with model tank test data and full-scale measurements will be steering servomotor controls the transverse thrust (port and essential. So far, the results of the numerical calculations, starboard). model scale experiments, as well as sea trial measurements, correspond promisingly well. The global hydrodynamic propeller loads calculated by CFD methods are input data for a complex FEM analysis by ANSYS for the structural design of each propeller component. Dynamic loads are estimated for a simplified three-dimensional cinematic VSP model. An accurate mathematical model for the critical components is built up by the 3-D CAD program IDEAS. Cut-boundary techniques are used for regions of special interest. Nonlinearities, such as contact surfaces, are solved by applying the load gradually. 3.