Pod Propulsion System Research Articles

Dynamic and quantitative risk assessment of Cruise ship pod propulsion system failure: An integrated Type-2 Fuzzy-Bayesian approach

Azipod propulsion has revolutionized the future of ship propulsion and maneuvering operations with over 20 years of experience, eventually improving ship safety, reliability, energy efficiency, and overall vessel performance. However, it consists of technically complex machinery systems; its breakdown can result in many potential failures with severe repercussions. In this work, an accident-based dynamic risk assessment study of the Cruise ship pod propulsion system has been carried out. It is based on the real-ship accident of the Norwegian Star, which resulted in the loss of ship propulsion. When historical accident statistics are limited, traditional methods fail to address the uncertainty, dynamic environment, and quantitative risk assessment problems. The goals include avoiding worst-case scenarios by illustrating the progression of dynamic change in risk and establishing the Bayesian network framework for dealing with uncertainty more effectively. Interval type-2 Fuzzy expert system is integrated with the dynamic Bayesian network and bow-tie model for quantitative risk assessment, which laid the groundwork for the subsequent hazard identification and quantitative risk assessment. This accident network summarizes how pod machinery operational failures can cause accidents. The estimated sensitive machinery nodes such as Main motor failure, propulsion system, and power system failure are the leading causes of pod propulsion system failures on board cruise vessels. Risk analysts and decision-makers in the marine and offshore engineering industry can use the suggested model as a decision support tool to considerably reduce and eliminate potential failures, improving the ship's safety and system reliability.

Novel Multi-Physics Computational Simulation of a 10 kW Permanent Magnet Motor for Podded Propulsion

This paper presents a 10 kW, 12-slot 10-pole surface-mounted permanent magnet synchronous motor (SPMSM) design with fractional-slot concentrated winding for a podded propulsion system. Its load is a propeller that is proportional to the square of the rotational speed and the fifth power of the propeller diameter. Taking this into account, three SPMSMs with rated rotational speeds of 600, 1200, and 1800 rpm with the same rated output power of 10 kW were analyzed. These were designed under the same conditions (i.e., torque per rotor volume, air-gap length, current density, power factor, fill-factor, and supply voltage). Based on the SPMSMs designed by electromagnetic analysis, the housing of a podded propulsor for each SPMSM was modeled for mechanical analysis, including such parameters as forced vibration, radiated noise, and modal acoustics analysis in air and water. From the modal acoustics analysis, it is confirmed that the natural frequencies of a structure in water are lower than those in air because of the added mass effect of water.

Comparison of self-propulsion performance between vessels with single-screw propulsion and hybrid contra-rotating podded propulsion

The present work compares the self-propulsion performance between vessels with single-screw propulsion and hybrid contra-rotating podded propulsion. The viscous flow fields of 4000 TEU container vessels with single-screw, single-rudder propulsion and hybrid contra-rotating propeller (CRP) podded propulsion systems were solved numerically by the Reynolds-averaged Navier–Stokes equations (RANS), the shear stress transport (SST) k−ω turbulence model, and the sliding mesh method. Numerical uncertainty analysis of the resistance and self-propulsion factor were employed according to ITTC Quality Manual 7.5-03-01-01. Self-propulsion factor, viscous flow field, and pressure distribution at the stern of the vessels were analyzed in detail. Numerical results suggested that the vessel with the hybrid CRP podded propulsion showed a 17.59% larger effective wake fraction, a 40.2% smaller thrust deduction fraction, a 15.1% higher hull efficiency, and a 4.12% higher overall propulsive efficiency compared with the single-screw vessel. In addition, the vessel with the hybrid CRP podded propulsion showed a basically symmetric, smaller velocity gradient and more uniform flow field at the stern, resulting in a much smaller propeller-induced fluctuating pressure on the hull, compared with the single-screw vessel. In conclusion, the hybrid CRP podded propulsion system exhibited high efficiency and low vibration levels.

Numerical investigation of the unsteady flow of a hybrid CRP pod propulsion system at behind-hull condition

Flows induced by hybrid CRP pod propulsion systems (CRP-POD) are fundamentally characterized by unsteadiness. This work presents a numerical study on the unsteady flow of a CRP-POD at behind-hull condition based on CFD (Computational Fluid Dynamics). Unsteady RANS method is adopted, coupled with SST k-ω turbulence model and sliding mesh method. The propeller thrusts and torques obtained by CFD is validated by model tests and acceptable agreements are obtained. The time histories of shingle-blade loads and pressures near the hull surface are recorded for the analysis of unsteady flow features. The cases of forward propeller alone and aft propeller alone are also computed to distinguish the hull-propeller interaction and propeller-propeller interaction. The results show the blade loads of both forward and aft propellers strongly fluctuate with phase angles. For the forward propeller, the blade load fluctuation is mainly governed by the hull-propeller interaction, while the aft blade load is remarkably affected by the propeller-propeller interaction in terms of the load average and fluctuation pattern. The fields of pressure, vorticity and velocity are also analyzed to reveal the unsteady flow features.

A numerical study on the interaction between forward and aft propellers of hybrid CRP pod propulsion systems

This paper presents a numerical study on the interaction between the forward and aft propellers of hybrid CRP pod propulsion systems (CRP-POD) in open water with a focus on both global quantities, that is, thrust and torque, and flow details, such as vortical structure, slipstream evolution, and lateral load on the pod unit. Improved delayed detached eddy simulation (IDDES) method is adopted and combined with the γ−Reθ transition model. The open-water characteristics of CRP-POD obtained by CFD are in satisfactory agreement with model test data. Two sets of CRP-PODs with different propeller geometries are considered. It is found independently of propeller geometry that (i) in terms of thrust and torque, the forward propeller is slightly affected by the aft propeller, while it has a large effect on the aft propeller; (ii) the wake of the forward propeller is accelerated in the axial direction and weakened in the tangential direction by the aft propeller; and (iii) the time-averaged lateral force on the pod unit is reduced remarkably by the propeller-propeller interaction. However, the vortex interaction between the forward and aft propellers depends significantly on the propeller geometry. In the case when the tip vortices shed by the forward and aft propellers can directly collide with each other, the vortical structure in the wake becomes unstable and rapidly breaks down.

A Generic Multi-Criteria Design Approach Toward High Power Density and Fault-Tolerant Low-Speed PMSM for Pod Applications

Pod propulsion systems are widely used, since they exhibit high efficiency and reliability, especially when they are combined with permanent magnet synchronous motors (PMSMs). Except from high efficiency, high power density and increased fault-tolerance capability are also the main requirements for a motor in order to be used in such an application. Generally, PMSMs present high power density in high-speed operation. However, in low-speed applications, the achievement of increased power density is not an easy task. Moreover, PMSMs with surface-mounted magnets are characterized by low winding self-inductance which limits the fault-tolerance capability. Thus, this paper presents an effective generic multicriteria PMSM design approach and proposes a global selection strategy for both the slots/poles combination and the motor’s airgap diameter to axial length ratio aiming to enhance the two aforementioned characteristics. At the same time, numerous practical and physical constraints have been thoroughly described and taken into account in the proposed process. These constraints are not adequately presented in the relative literature. The derived topologies are validated through finite element method analysis and several important quantities are calculated and used as comparison metrics. Finally, useful conclusions are extracted that could be of great help for designers and manufacturers of pod propulsion systems.

Numerical and experimental studies on the effect of axial spacing on hydrodynamic performance of the hybrid CRP pod propulsion system

The hydrodynamic performance of a hybrid CRP pod propulsion system was studied by RANS method with SST k - ω turbulence model and sliding mesh. The effect of axial spacing on the hydrodynamic performance of the hybrid CRP pod propulsion system was investigated numerically and experimentally. It shows that RANS with the sliding mesh method and SST k - ω turbulence model predicts accurately the hydrodynamic performance of the hybrid CRP pod propulsion system. The axial spacing has little influence on the hydrodynamic performance of the forward propeller, but great influence on that of the pod unit. Thrust coefficient of the pod unit declines with the increase of the axial spacing, but the trend becomes weaker, and the decreasing amplitude at the lower advance coefficient is larger than that at the higher advance coefficient. The thrust coefficient and open water efficiency of the hybrid CRP pod propulsion system decrease with the increase of the axial spacing, while the torque coefficient keeps almost constant. On this basis, the design principle of axial spacing of the hybrid CRP pod propulsion system was proposed.

Numerical investigation of the scale effect of hydrodynamic performance of the hybrid CRP pod propulsion system

The scale effect of hydrodynamic performance of the hybrid CRP pod propulsion system was investigated numerically using the RANS method combined with SST k−ω turbulence model and moving mesh method. The pod resistance influence factor was introduced to represent the effect of wake field of CRP on the pod resistance. Results showed the pod resistance influence factor to be a function of the Reynolds number and revolution ratio. Representative function expression can be obtained by regression analysis using multiplication of multinomial polynomials and linear function. The standard ITTC 1978 extrapolation procedure can be utilized to predict hydrodynamic performance of forward propeller because of the slightness of the influence of the pod unit on the forward propeller. The thrust and torque coefficient influence factors of aft propeller were introduced, and they were found to represent the effect of wake field of forward propeller and blockage effect of the pod on the hydrodynamic performance of aft propeller. It shows that thrust and torque coefficient influence factors are independent of the Reynolds number and have a linear relationship with the revolution ratio. On this basis, a method of estimating the hydrodynamic performance was proposed for full scale propulsion system.

Improved Vector Control for Marine Podded Propulsion Control System Based on Wavelet Analysis

ABSTRACT Yao, W.; Zhang, J.; Liu, Y.; Zhou, M.; Sun, M., and Zhang G., 2015. Improved vector control for marine podded propulsion control system based on wavelet analysis. In this paper, the rotor speed and the position of the marine SSP propulsion motor were estimated for building sensorless vector control system with speed and current double closed loops, based on a wavelet square-root unscented Kalman filter (Wavelet-SRUKF) algorithm. The observed data were pretreated by wavelet analysis and the high frequency noise was filtered, thus offering further smooth observed data for the UKF (Unscented Kalman Filter). This Wavelet-SRUKF algorithm can not only filter the spike point but also showed a better dynamic tracing property of the marine SSP podded propulsion system. Simulation results showed that the improved UKF algorithm was more accurate and demonstrated a higher rate of convergence compared with UKF speed controller.

SSP Podded Propulsion Motor Control Based on SR-CDKF

In this paper,the rotor speed and the position of the SSP propulsion motor are estimated for building sensorless vector control system with speed and current double closed loops based on square root center difference Kalman filter (SR-CDKF) algorithm. This method makes use of the QR decomposition linear algebra techniques and so on, and it updates the matrix square-root of the state covariance by the Cholesky factor updating. This method can not only get the more steady results but also improve the estimation accuracy of the SSP podded propulsion system. Simulation result shows that the improved CDKF algorithm is not only more accurate but also has higher rate of convergence compared with CDKF speed controller.

Z-Manoeuvring of a Liquified Natural Gas Carrier with Podded Propulsion System

The application of pod propulsion has become an important concern in designing a new LNG carrier due to the high maneuverability characteristic. However, podded propulsion LNG carrier is a new concept which is still in the evaluation stage. Practically, the maneuverability of podded propulsion LNG carrier is an uncertainty. Hence, it is essential to assess the ship’s maneuvering characteristics. Z-Manoeuvre assessment is one of the recommended tests for maneuverability prediction. This paper discusses on Z-Manoeuvre characteristic of the podded propulsion LNG carrier. A mathematical model for podded propulsion LNG carrier was presented and a simulation program was developed for the Z-Manoeuvre assessment. Finally, simulations were carried out on both conventional propulsion and podded propulsion LNG carriers. The simulation results show that podded propulsion LNG carrier has a better Z-Manoeuvre characteristic.

크루즈선의 횡동요 제어시스템에 미치는 포드 각속도의 영향

Recently, the application and installation of the pod propeller to the cruise ship is dramatically increased. It is because pod propulsion system allows a lot of flexibility in design of the internal arrangement of a ship. To reflect this trend, many researches have conducted to use the pod propeller for the roll stabilization of a ship. In the paper, a roll stabilization controller is designed by using fins and pod propellers as the control actuators for cruise ships. Two kinds of control algorithms are adopted for the roll control system; LQR (Linear Quadratic Regulator) algorithm and frequency-weighted LQR algorithm. Through the numerical simulation, the effect of the turning rate of the pod propeller on the roll control system is analyzed. Analysis of the simulation results indicated that the turning rate of the pod propellers is one of the important parameters which give the significant effects on the roll stabilization.

Recent Research on Podded Propulsor and Analysis of Key Technologies for Naval Vessels

Podded propulsor has been adapted for both commercial and naval vessels because of its unique features and excellent performance.Researches of pod propulsion system have been made by many naval sectors worldwide.This paper starts with an elaboration of the podded propulsor in terms of principle,structure,flaws and merits,and summarizes a range of typical products and the characteristics of the podded propulsor,with particular atte ntion to the analysis of recent researches and developments both domestic and abroad.Key technologies for naval application are then discussed,an overview of technical developments trends and future challenges is prese nted.

タンデム型（ハイブリッド型）電気推進船

The Super Eco-Ship Project was conducted by the National Maritime Research Institute of Japan (NMRI) as a national project from April, 2001, under the Ministry of Land, Infrastructure and Transport. It aims at achieving the ship with environment friendliness and economical benefit. The Super Eco-Ship has high propulsion efficiency by contra-rotating propeller (CRP) effect. The high propulsive efficiency due to the combination with the optimum hull design and podded propulsion system enables the reduction of CO2 compared with the conventional ship. In addition, the podded propulsion system enables drastically superior manoeuvrability and flexible control system in ship operation as well as high propulsive efficiency. NMRI developed, cooperated with ship owner Ube Shipping & Logistics, LTD., the modified buttock flow hull form equipped with one podded propulsion system close behind the conventional propulsion system for Cement Tanker “KOZAN MARU”. This paper introduced history on Research & Development of The Super Eco-Ship Project and described the Hybrid type’s Electric Podded Propulsion Cement Tanker.

Numerical investigations of the engine cooling system in a small power vessel pod propulsion system

Numerical investigations of the engine cooling system in a small power vessel pod propulsion system The development of electronics and electrotechnology enabled to put electric motors of the alternating current in the pod and to use them for the main drive of ships. A lot of heat which must be picked up from the system is a problem which is turning up at applying the system of this type. Many big ships lately contended with these problems. Building the small propeller for the boat powered with solar power we decided to check the influence of the chilling middle on the temperature of the work of an engine. In the article we are presenting a built propeller and a way, into which an issue of the exchange of the heat was analysed using the Fluent software.

Quantitative reliability and availability analysis for design evaluation of generic pod propulsion systems

Application of pod propulsion on a variety of vessels such as cruise ships, ropax, and tanker vessels has increased significantly over the last two decades owing to the benefits offered by pods. Despite the clear benefits, operators are still reluctant to have this innovation on board because of unknown overall reliability. Many of the published research efforts in the area of pod propulsion have been concentrated on hydrodynamics and manoeuvring aspects with little in the area of quantitative pod reliability assessment. In this paper, the applicability and appropriateness of various quantitative fault tree solution techniques (exact and approximate) for the reliability assessment of a generic pod propulsion system are investigated. Also, the paper demonstrates that the proposed quantitative reliability assessment methodology can be used to make design changes by identifying critical components in system functionality and modifying the system with improvements, where needed.

Keeping a World-Wide Watch on Propulsion Pod Performance

Queen Mary 2 is the largest, longest, tallest, widest and most expensive passenger vessel ever built, she also has the biggest and most powerful pod propulsion system to date, with each pod constantly monitored by a condition-monitoring system that includes remote monitoring by satellite.

POD 추진기선의 조종성능 추정 연구

To improve ship`s maneuverability and carry out special goal POD propulsion system was equipped as propulsion and maneuvering system. To predict the maneuverability of a ship with POD propulsion system HPMM tests and POD open water test are carried out. In this paper modular model with 4 degree of freedom of a ship with twin POD propulsion system is presented. To use modular model the forces of POD propulsion system are measured separately from the hull forces. The measured forces and moments are analyzed by using modular model and whole ship model The simulation results of modular model are compared with those of whole ship model. From the present study it is Possible to analyze HPMM tests of a ship with twin POD propulsion system by modular model.

Reliability and Availability of Pod Propulsion Systems

AbstractThe application of pod propulsion in a number of vessel types has been increasing steadily over the last two decades. This increase is attributed to the great advantages being offered by pod propulsion systems such as high manoeuvring capability, low noise and vibration, low fuel consumption, etc. Despite these advantages, operators are cautious due to the encountered teething problems, especially in the very competitive passenger ship market, where reliability and the maintainability of the service are crucial. This paper presents a reliability assessment methodology and its application to a combined four‐pod propulsion system on a vessel equipped with two fixed‐ and two rotating‐pod units. The assessment methodology made use of Failure Mode and Effect Analysis, Fault Tree Analysis (FTA) and Markov Analysis complementarily. In the FTA, minimal cut set, reliability importance measure and availability analyses were also considered. From the quantitative reliability assessment, the calculated reliabilities of each fixed‐ and rotating‐pod unit, their components' reliabilities as well as the reliability of the combined four‐pod propulsion system showed good agreement with the acceptable reliability criteria suggested by the pod manufacturers/operators based on the service experience. Copyright © 2006 John Wiley & Sons, Ltd.

Hydrodynamic Development of Azimuthing Podded Propulsion System

Hydrodynamic Development of Azimuthing Podded Propulsion System