Behavior Of Propulsion Systems Research Articles

A comprehensive propulsion system analysis: an integrated approach utilising engine simulation and free-running model experiments

Regulations concerning the environmental impact and energy efficiency of ships are becoming increasingly stringent. To meet these demanding criteria, new technologies are actively being developed to achieve emission reductions while maintaining efficient fuel energy conversion into propulsion power. However, the propulsion system behaviour in a dynamic environment of the actual sea is highly nonlinear and complex, and a profound understanding of the mutual interactions is still lacking. This paper proposes an integrated approach for comprehensive propulsion system analysis. The key feature of this technique is the utilisation of an intelligent propeller drive controlled by a marine diesel engine simulator (MDES) to drive the free-running model of a ship, providing real-like behaviour of the engine model in real-time in response to actual measured values. The core of the MDES consists of a continuous cycle-mean value dynamic engine model supplemented with a detailed combustion cycle evaluation. The developed fast calculation algorithm of crank-angle resolved thermodynamic equations of the gas state in the engine cylinder enables the complete engine model to be integrated into the real-time environment of a physical model ship. Thus, the propulsion system's performance can be analysed under conditions that closely mimic those of the actual sea environment.

Experimental and Numerical Investigation of Propeller Propulsion System Behavior Considering the Ground Effect

Experimental and Numerical Investigation of Propeller Propulsion System Behavior Considering the Ground Effect

Simulation Modeling of a Ship Propulsion System in Waves for Control Purposes

The article deals with a simulation approach to the representation of the ship motions in waves, interacting with the propulsion system behavior (diesel engine and propeller). The final goal is the development of a simulator, as complete as possible, that allows the analysis of the main engine thermodynamics in different sea conditions, also in the unfavorable event of dynamic instability of the hull, and the correct management of the other propulsion components. This latter aspect is particularly interesting in some of the last new energy solutions for decarbonization of ships, concerning, for example, auxiliary electric motors, powered by batteries, to support the traditional diesel-mechanical propulsion (especially in heavy weather conditions). From this point of view, a proper analysis of the engine dynamic performance, affected by particular sea states, is fundamental for a smart management and control of shaft generators/auxiliary electric motors, batteries, etc. To this end, the work presents and highlights the main features of a ship simulator, suitable for the study of the new propulsion solutions that are emerging in maritime transport. Some representative results will point out the complex non-linear behavior of the propulsion plant in waves. Moreover, a parametric roll scenario will be investigated, in order to highlight the capability of the conceived simulator in modeling the effects of the dynamic instability of the hull on the propulsion plant.

Numerical investigation of interaction between propulsion system behaviour and manoeuvrability of a large containership

In actual operation process of a ship, the engine-propeller-hull is an integrated system with internal coupling effects, and thus there is a close interaction between the diesel engine propulsion system operation conditions and the ship manoeuvring motions. The propulsion system can experience large power fluctuation during manoeuvring, with considerable torque increase with regard to the stabilized value in straight course. However, the diesel engine propulsion system behaviour and ship manoeuvrability are usually studied separately as they are considered to belong to different disciplines. Thus, it is difficult to reflect the actual operating characteristics of the propulsion system and ship manoeuvring motion under coupled conditions in actual operation. To investigate the interaction between the propulsion system behaviour and the manoeuvrability of a large containership, this paper proposed a multi-disciplinary ship mobility model capable of coupling the marine diesel engine model and the ship manoeuvring model. In the engine model, the mean value modelling approach was adopted to simulate the two-stroke marine diesel engine considering the fact that it can capture the performance of the engine sub-systems including scavenging receiver, exhaust gas receiver, turbocharger, etc. In the manoeuvring model, the MMG-based method was used to simulate the ship manoeuvring motion with three degrees-of-freedom. The engine model and manoeuvring model were coupled through the propeller model that transferring propeller speed and torque between the two models. The coupled model was validated against the engine shop test data and the sea trial results. By applying this coupled model, a series of simulations of turning circle manoeuvres under various scenarios were performed. The simulation results presented the dynamic response of engine internal sub-systems during turning circle manoeuvring, explained the effect of the torque limiter on engine performance and ship manoeuvring motion, and analyse the influence of different propulsion system control strategies on the ship turning circle manoeuvrability. Although the presented case study has been validated on a specific ship, most of the discussed models have a general application.

Composite methodology to prevent ship propeller erosion

The jet flow generated by manoeuvring ships nearby vertical structures is known to erode the seabed sediment but is still difficult to predict the effects of a particular ship operating in a harbour basin. This paper presents a methodology to quantify the scouring action generated by ship's propellers combining field and real data with a manoeuvre numerical simulator testing some of the most commonly used formulas for maximum scouring depth prediction. From the real manoeuvres, analysed through Automatic Identification System (AIS) data, the manoeuvre patterns are identified to be later reproduced at the simulator, thus obtaining the propulsion system behaviour to apply the formulae and to estimate the maximum erosion depth expected in a harbour basin. The obtained results are validated with field data from bathymetries and Acoustic Doppler Velocimeter (ADV). Results show the arrival and departure manoeuvre sections where the vessel is potentially harmful. The different formulae applied yielded results in accordance with the provided bathymetry of the study area in terms of maximum erosion depth. Also, the areas of maximum expected seabed velocity are coincident with the areas where the maximum scour is observed in the bathymetry.

Linearisation of a ship propulsion system model

The understanding, modelling and analysis of the behaviour of a non-linear ship propulsion plant are of great importance for conceptual system design, component selection, selection of control strategy and for propulsion control system tuning. Conceptual propulsion system design activities, such as deciding the combinator curve, require a relatively simple steady state simulation model, while propulsion controller design and tuning requires a non-linear time domain simulation model which captures the intricacies of the propulsion plant. In this paper a linearised model of the uncontrolled ship propulsion system is derived which can be used for analysis of propulsion system behaviour in waves and for initial controller design and tuning. Furthermore a thorough analysis is made of the conditions under which local instability of the system can occur. In a follow up paper the linearised model is extended and verified by means of comparison with a non-linear model. There it is furthermore used to investigate the effect of engine governor settings on a propulsion plant when sailing in waves at different encounter frequencies. The authors believe that, due to its transparency and clear link to well known parameters and variables, the linearised core propulsion system model as derived in this paper should appeal to marine system engineers, control engineers and hydrodynamicists alike. The linearised model should however not be seen as the replacement for a non-linear model, but rather as an additional tool that can be used.

Development of a combined mean value–zero dimensional model and application for a large marine four-stroke Diesel engine simulation

In this article, a combined mean value–zero dimensional model is developed using a modular approach in the computational environment of Matlab/Simulink. According to that, only the closed cycle of one engine cylinder is modelled by following the zero-dimensional approach, whereas the cylinder open cycle as well as the other engine components are modelled according to the mean value concept. The proposed model combines the advantages of the mean value and zero-dimensional models allowing for the calculation of engine performance parameters including the in-cylinder ones in relatively short execution time and therefore, it can be used in cases where the mean value model exceeds its limitations. A large marine four-stroke Diesel engine steady state operation at constant speed was simulated and the results were validated against the engine shop trials data. The model provided results comparable to the respective ones obtained by using a mean value model. Then, a number of simulation runs were performed, so that the mapping of the brake specific fuel consumption for the whole operating envelope was derived. In addition, runs with varying turbocharger turbine geometric area were carried out and the influence of variable turbine geometry on the engine performance was evaluated. Finally, the developed model was used to investigated the propulsion system behaviour of a handymax size product carrier for constant and variable engine speed operation. The results are presented and discussed enlightening the most efficient strategies for the ship operation and quantifying the expected fuel savings.

A computational study on the performance and emission parameters mapping of a ship propulsion system

In this article, the mapping of the performance and emission parameters of a merchant vessel propulsion system over the ship operating envelope was carried out by using a model capable of representing the ship propulsion system behaviour. The model was developed based on a modular approach and was implemented in the MATLAB/Simulink environment. The various parts of the propulsion engine as well as the shafting system, the propeller and ship hull were represented by separate submodels having the appropriate interface for exchanging the required variables to each other. The output of the model includes the performance and emission parameters of the engine as well as the operating parameters of the propeller and ship. Initially, the propulsion engine operation under steady-state conditions was simulated and the predicted engine performance parameters results were validated. Then, simulations of the ship propulsion system operating points at various resistance curves were performed. Based on the derived results, the mapping of the ship propulsion system performance and emission parameters was presented and their variation throughout the ship operating envelope was discussed. Finally, an example of using the derived results in order to minimise the fuel consumption and CO2 emissions for a typical ship route is presented and discussed.

Speed loss of a vessel sailing in oblique waves

In order to demonstrate the effect of oblique waves on ocean-going vessel behavior in realistic sea states, this paper addresses an effective and useful tool to predict the ship's motion and propulsion system behavior with sufficient accuracy, considering the wave conditions on the operating route. Seakeeping model test was carried out with a freely running model in oblique waves in the ocean basin at the Marine Technology Centre, Trondheim, Norway. A time domain numerical simulation study was performed, and the results of the simulation are compared with the model test data.Due to the length limitation of the ocean basin, converged speed in waves cannot be achieved in all runs. A correction method is proposed in this paper to determine the converged speed from non-converged runs. The correction method is based on the condition that the converged speed in waves is dependent on the balance between resistance and propulsion force.

Speed loss due to seakeeping and maneuvering in zigzag motion

Ships are prone to experience a slight zigzag motion due to the interaction between steering, waves and other external disturbances. The zigzag motion will induce an added resistance and hence speed loss. This paper aims at addressing an effective tool to predict a ship's zigzag motion and azimuth propulsion system behavior in calm water and different sea conditions, and the resulting speed loss. Both model tests and numerical simulations have been carried out. Model tests with a freely running model were done in MARINTEK, Trondheim, Norway. The propulsion system was composed of two azipull thrusters, with autopilot control system to keep the power constant during the test process. Model speeds and the propulsion system behavior were recorded as time series when the models were freely running in calm water and regular head sea waves. Numerical simulations with simplified modular maneuvering model were conducted to verify the model test data. Good agreement between simulations and experimental results was found. The results also showed that when wave added resistance reach its peak value, the vessel has the most severe speed loss.

Experimental and Numerical Study of Stem Shape Influence on Speed Loss in Waves

This paper addresses prediction of ship motion and propulsion system behaviour to demonstrate the effect of waves in real sea states. For a 8000 t deadweight tanker, three different stem shapes are studied experimentally and numerically. Numerical simulations of speed loss were performed in time and frequency domain, generally agreeing well with experimental results. While a conventional bow with bulb and flare gave least calm water resistance, a bow without bulb and flare gave least total resistance in severe wave conditions.

Control of propeller cavitation in operational conditions

Off-design conditions can have a severe impact on ship propulsion system behaviour. Resistance increase, for instance, leads to higher engine loading, and can also easily lead to a decrease of cavitation inception speed with respect to calm water conditions. Wakefield variations due to ship motions, waves and manoeuvres also have an effect on engine loading and on propeller cavitation. This paper discusses the model-based development of a propulsion control system aiming at increased cavitation free time in operational conditions, while preventing engine overloading and keeping manoeuvring characteristics acceptable. The developed propulsion control system was tested extensively in a simulation environment before full-scale trials took place in February 2008, onboard a Royal Netherlands Navy frigate. Results in terms of full-scale propulsion system behaviour are presented, including photos showing the propeller cavitation behaviour in operational conditions.

Analysis of ship propulsion system behaviour and the impact on fuel consumption

From fuel to ship moving, the overall energy conversion efficiency consists of three parts: the engine efficiency, the transmission efficiency and the propulsive efficiency. In off-design conditions, there are three factors, namely the engine speed, the propeller pitch ratio and the rudder activity, and an additional disturbance, ship loading factor that can impact the behaviour of ship propulsion system and influence the overall energy conversion efficiency. In this study, by means of computer simulation, four elementary types of off-design conditions, each of which is relevant to one of the impact factors, and entire voyage simulations which combines the off-design and design operation conditions, are investigated to reveal the behaviour of the ship propulsion system. The results demonstrate that, in terms of fuel consumption, the power specific fuel consumption is mainly determined by engine efficiency while ship speed plays the most important role in calculation of ton-mile specific fuel consumption. On the voyage basis, high percentage of manoeuvering stage and intensive rudder activity result in large ton-mile specific fuel consumption, while low cruising speed could improve the fuel economy on ton-mile basis.