Podded Propulsor Research Articles

Experimental study on a model azimuthing podded propulsor in ice

The objective of this study was to investigate the performance of a model azimuthing podded propulsor in ice-covered water. Model tests were carried out with two different depths of cut into the ice (15 and 35 mm), two different ice conditions (presawn and pack ice conditions), and four different azimuthing angles. The depth of cut is the maximum penetration depth of the propeller blade into the ice block. The 0.3-m-diameter model propeller was operated in a continuous ice milling condition. Ice loads were measured by several sensors which were installed in various positions on the model. Six one-axis pancake-style load cells on the top of the model measured the global loads and two six-component dynamometers were installed on the shaft to measure the shaft loads. One six-component dynamometer was attached to the one of the propeller blades inside the hub to measure the blade loads. The pod unit and propeller performance in ice are presented. Ice-related loads, which were obtained when the blade was inside the ice block, are introduced and discussed. During the propeller–ice interaction, a blade can experience the path generated by the previous blade, which is called the shadowing effect. The effects of shadowing, depth of cut, azimuthing angle, and advance coefficient on propulsor performance are presented and discussed.

Podded propulsors: some results of recent research and full scale experience

Following the introduction of podded propulsors into the marine industry the market demanded a rapid increase in size of the units from a few megawatts to where they are now in excess of 20MW. Such an increase led Lloyd’s Register to undertake a major research programme into the loadings experienced by these propulsors and the way in which they are reacted by the individual components. In addition much emphasis was given to the practical problems of achieving the design intent both at the time of building and subsequently through life. The results of this work were used to update the Rules, originally published in July 2003, and in developing a system of survey procedures which embraced the practical problems of initial manufacture and assembly as well as drydocking maintenance activities. This paper, in conjunction with two further papers published elsewhere on the hydrodynamics of podded propulsors and another on the philosophy of developing Rule formulations for ships driven by podded, summarises much of this work.

Experimental investigation into the impact of slipstream wash of a podded propulsor on the marine environment

The paper presents the results of an experimental investigation into the velocity field of a podded propulsor carried out by laser Doppler anemometry and the use of this information for assessing the potential impact of a podded propulsor slipstream, in terms of wash velocity, on the marine environment. The investigation was carried out in the Emerson cavitation tunnel of Newcastle University with the roll-on roll-off passenger ship or ferry (ROPAX) hull model as part of the project entitled ‘optimal design and implementation of azimuthing pods for the safe and efficient propulsion of ships’ sponsored by the EU Fifth Framework Programme initiative. Comprehensive velocity field measurements were made in open water, behind the simulated wake of the ROPAX hull and in the bollard pull condition. The mean velocity distributions in the axial and radial directions were calculated from the measured velocity fields to evaluate the potential impact of the slipstream wash of a podded propulsor on the environment. For comparison purposes, some results from similar measurements made with a conventional shafted propeller are also included. The experimental results have revealed that the most significant impact of the propeller slipstream wash on the environment could occur when a ship departs from a port.

Manoeuvring forces on azimuthing podded propulsor model

Manoeuvring forces on azimuthing podded propulsor model This paper presents the preliminary part of comprehensive manoeuvring open-water tests of a gas carrier model. The paper focuses on open water experiments with an azimuthing podded propulsor. The test program was carried out in the cavitation tunnel and the large towing tank of Ship Hydromechanics Division, Ship Design and Research Centre, Gdańsk. The pod was tested as a pushing unit with a 161.3 mm diameter propeller. Steering forces were measured in the range of advance coefficient from 0.0 to 0.8 combined with the range of deflection angles from -45° up to +45°. Measurements on the pod without propeller were also performed. The experiment results are presented in the form of non-dimensional coefficients in function of advance coefficient and deflection angle. Analysis of the experimental results and the conclusions are presented.

Ice Loads Acting on a Model Podded Propeller Blade (OMAE2005-67416)

Abstract With the increase in popularity of podded propulsors and arctic navigation, understanding the interaction between a podded propulsor and ice has become more important. Propeller-ice interaction itself is a complicated process with a high level of uncertainty resulting from the uncertainties associated with the properties of the ice and with the propeller-ice interaction conditions. Model tests provide relatively well-controlled ice properties and interaction conditions to reduce the uncertainties. In order to improve the understanding of this interaction and to develop numerical models of it, a model podded propulsor was used in “Puller” mode, and ice loads were measured on its instrumented blade and propeller shaft. The results of the experiments conducted to simulate the interactions (milling) of the instrumented blade with ice in different operating conditions are reported in this paper. Loads measured during the milling consist of ice milling loads, “inseparable” hydrodynamic loads, and “separable” hydrodynamic loads. The sample results presented here include ice milling and inseparable hydrodynamic loads for various advance coefficients and depths of cut (amount of blade penetration into ice). Some results are compared with existing ice load models.

Numerical Study of Hub Taper Angle on Podded Propeller Performance

Presently, the majority of podded propulsion systems are of the pulling type, because this type provides better hydrodynamic efficiency than the pushing type. There are several possible explanations for the better overall performance of a puller-type podded propulsor. One is related to the difference in hub taper angle. Puller and pusher propellers have opposite hub taper angles, hence different hub and blade root shape. These differences cause changes in the flow condition and possibly influence the overall performance. The current study focuses on the variation in performance of pusher and puller propellers with the same design of blade sections, but different hub taper angles. A hyperboloidal low-order source-doublet steady/unsteady time domain panel method code, PROPELLA, was modified and used to evaluate effects of hub taper angle on the open water propulsive performance of some fixed-pitch screw propellers used in podded propulsion systems. Major findings include good agreement between predictions using the modified code and measurements, significant effects of hub taper angle on propulsive performance of tapered hub propellers, and noticeable effects of hub taper angle on sectional pressure distributions of tapered hub propeller blades.

Operability of fast podded RoPax vessels in rough seas

Methods are described for the evaluation of the seakeeping performance of a fast RoPax vessel driven by podded propulsors in the North Sea environment. The evaluation procedure is based on the responses of the vessel in regular waves, the wave conditions encountered, and the limiting values associated with the vessel's mission. The seakeeping performance is represented by the average attainable speed (AAS), which is defined as the ratio of the average speed of the vessel on a specified route to the calm water speed. Both the natural (due to the added wave resistance) and the voluntary (due to the excessive ship responses) speed losses are taken into account. The annual average speed of the fast RoPax design in the North Sea is evaluated and compared with that of a similar size conventional RoPax vessel. The results indicate that, despite its 20 per cent smaller displacement, the fast RoPax design, in general, has better seakeeping performance characteristics than that of the conventional design. The effect of podded propulsors on the average annual speed is also investigated and it is found that the presence of podded propulsors can have favourable effects on the seakeeping performance characteristics, particularly on the vertical plane responses.

Numerical Analysis of the Steering Capability of a Podded Drive

Numerical results of the different components of a commercial podded propulsor in oblique flow were obtained by different calculation methods. Steering forces and moments were calculated with an unsteady Reynolds-averaged Navier-Stokes solver and correlated to those of a conventional rudder. Traditional formulae are applied for both (propulsor and conventional rudder) and different methods to determine an equivalent rudder stock diameter with respect to SOLAS requirements are discussed.

Scale Model Testing of a Commercial Rim-Driven Propulsor Pod

Podded propulsion is gaining more widespread use in the marine industry and is prevalent in newer cruise ships in particular. This propulsion system can provide many advantages to the ship owner that include increased propulsion efficiency, arrangement flexibility, payload, and harbor maneuverability. A new, unique podded propulsor concept is being developed that allows optimization of each element of the system. The concept comprises a ducted, multiple-blade row propulsor with a permanent magnet, radial field motor rotor mounted on the tips of the propulsor rotor blades, and the motor stator mounted within the duct of the propulsor. This concept, designated a commercial rim-driven propulsor pod (CRDP), when compared to a conventional hub-driven pod (HDP), offers improved performance in a number of areas, including equal or improved efficiency, cavitation, and hull unsteady pressures. The combination of these CRDP performance parameters allows the ship designer much greater flexibility to provide improved ship performance as compared to that of an HDP. A CRDP is being developed to power a panamax-size cruise vessel. The paper addresses the hydrodynamic performance of that CRDP design demonstrated at 1/25th scale as tested at the Hamburg Ship Model Basin, Hamburg Germany (HSVA).

Modular Gas Turbine Propulsors: A Viable Alternative for Today’s Merchant Fleet

Gas turbines offer the commercial shipping industry the best power to volume ratio available for a propulsion package. When coupled with a podded propulsor, gas turbines can be placed in a module anywhere on the vessel, allowing optimal use of vessel space for cargo. As the shipping market continues to evolve, modular gas turbines seem to be the logical choice for future vessels. The object of this paper is to demonstrate the substantial increase in profits associated with a modular gas turbine propulsion package.

Integrated System Analysis and Design of Podded Ship Propulsors

AlliedSignal has studied podded propulsion for surface combatants for the US Navy under a contract sponsored by DARPA. The integrated system analysis included mathematical models for the main components of a podded propulsor. The models addressed both performance and cost. Components modeled included the propulsor itself (single propeller, ducted propeller, etc.), bearings, coupling, gearbox, motor, and azimuthing system. Simplified, approximate methods, especially for propulsor sizing and performance, were used. Other information in the literature and product data from leading vendors was used to size the components and to estimate their efficiencies. In other sections of the model, life-cycle fuel costs and costs of reliability were computed. The model was used to size and estimate the total costs for different configurations for four surface ships. A conceptual design for each vessel was selected, and three-dimensional CAD renderings of four pods were prepared. Sensitivity studies were run to show the effects of variations in fuel cost and in the relative efficiencies of propulsor types. Subsequent to the naval program data on a typical cruise ship were obtained and the spreadsheet model was applied to that platform.

Hydro dynamic Evaluation of Hull Forms with Podded Propulsors

ABSTRACTA computational capability has been developed to predict and visualize the flow about podded propulsors appended to the 154‐foot transom stern research vessel, R/V Athena. The computer generation of a complex geometric model for the hull and appendages is an important part of this new capability. The flow field is computed using a free surface potential flow method. The steady flow induced by the propulsor is simulated by an idealized propeller model (actuator disk). The upstream effects of an actuator disk are examined and results are compared to the case without an actuator disk. Computed results for the inflow to the propeller disk are presented as velocity vector plots and contour plots. Harmonic analyses are performed on the computed velocity components.The numerical results can be used in conjunction with experiments performed at DTRC to aid in the design of podded propulsors. These flow studies are used to examine the proper alignment of the pod/strut system with the aim of obtaining the optimal flow into the propeller. The combined numerical and experimental approach is shown to be an efficient way to evaluate complex hull forms with podded propulsors. This powerful design approach can be used for future Navy ship designs.

<i>Propella</i>: A numerical tool to investigate various aspects of podded propulsors

This paper describes the numerical aspects of a research program on podded propulsors, which is being undertaken jointly by the Ocean Engineering Research Centre at Memorial University of Newfoundland, the National Research Council's Institute for Ocean Technology, Oceanic Consulting Corporation, and Thordon Bearings Ltd. The numerical tool is an in-house panel method code, PROPELLA. The code is a low order source-doublet, steady/unsteady time domain panel method code having capabilities to predict hydrodynamic performance of screw propellers with various configurations. Under the research program, the code was extended and used to model the propellers, pod-strut combinations and strut-wake impingement model. Amongst the hydrodynamic issues that have been addressed through numerical predictions were questions regarding the effects of hub taper angle (propeller only case and pod-strut-propeller case), pod-strut configuration (push and pull), geometric variations, azimuthing conditions and pod-strut interactions (wake impingement effect) on podded propeller performance. Predictions were made both in pusher and puller configurations for the pods and reasonable agreement was achieved between the predictions and measurements. The code is being modified to study the podded propulsors' performance at static and dynamic azimuthing conditions. The code is also capable of performing simulations with propellers and bodies like ship hull, underwater vehicles with fins.DOI: http://dx.doi.org/10.3329/jname.v4i2.990Â Journal of Naval Architecture and Marine Engineering Vol.4(2) 2007 p.73-86