Douwe Stapersma

Systematic modelling, verification, calibration and validation of a ship propulsion simulation model

The need for ship propulsion simulation models is widely acknowledged. However, a ship propulsion simulation model can only rightfully be used after its validity has been assessed. The importance of high quality validation increases when the simulation model is intended to be used to design working equipment. This paper proposes a systematic approach towards the modelling, verification, calibration and validation of a ship propulsion simulation model. Both the validity of static operating points and of the dynamic system behaviour are quantified, enabling objective quality assessment. The model that is validated here has successfully been used to develop and test a propulsion control system, aiming at increased cavitation free time in operational conditions. This is the topic of a further paper.

Matching propulsion engine with propulsor

The basic matching problem of a propulsion engine to the propulsor is discussed and the influences which should be taken into account. The concepts of sea margin, engine margin and light running margin are handled and an indication of their values is given. The methods of calculation to evaluate design and off design conditions are discussed.

A study of the validity of a complex simulation model

In this paper the uncertainty in relation with the validity of a complex simulation model (a ship mobility model) is assessed. First, the theory of uncertainty analysis of simulation models is presented with attention for the process of verification, matching and validation. Second, uncertainty analysis is performed on the ship mobility model and its validity is evaluated. Finally, it is argued why the uncertainty and validity assessment is useful for every complex model. The article is based on part of the PhD-thesis by the main author.1

Efficient uncertainty analysis of a complex multidisciplinary simulation model

The merit of a simulation model can only be assessed if the uncertainty in the simulation output is quantified. Knowledge on the uncertainty of simulation results helps the engineer/designer to decide whether the simulation model is suited for the goal that is pursued. Uncertainty analysis of complex multidisciplinary models is a laborious task. Du and Chen1 presented a method to increase the efficiency of the time consuming uncertainty analysis procedure. In this paper their uncertainty analysis method is applied to the Ship Mobility Model and compared with another uncertainty analysis method as applied by Schulten.7 The end results in terms of output uncertainty are comparable and small differences are explained. In terms of efficiency the Du and Chen method is found to be four times faster than the other method.

Evaluation of losses in maritime gearboxes

Gearboxes are a necessary part of almost any propulsion train and their percentual losses are usually assumed to be small and constant. However, in low-load and part-load conditions, gearbox losses may be significant. With the current trend of slow steaming, the performance of gearboxes is once again in focus. In order to estimate the performance of maritime gearboxes, an evaluation of losses was done using a thermal network. The analysis was done for a standard double-input single-output maritime gearbox and over the entire range of torque and revolutions per minute. Results indicate that the transmission losses are not negligible in low-load condition; in fact they may as high as 10% of delivered power. Further results show that the maximum temperature in the teeth contact can reach 70 °C but this might be an overestimate. Finally, using the investigated thermal network models, a simplified model of transmission losses is proposed together with the fit coefficients for the torque and revolutions per minute.

Cylinder Process Simulation with Heat Release Analysis in Diesel Engine

The use of thermodynamic models for the simulation of the cylinder process from analyzing heat release has been a common practice as a way to predict the performance of internal combustion engines. However, it is of importance to apply a suitable heat release model, as well as the gas properties, fuel properties, heat loss models, etc. In this paper, in order to distinguish two stages of combustion process, a double Vibe model is used to determine the heat release rate and a systematic investigation of the influence of several parameters in it to the pressure and temperature in cylinder is carried out. In addition, the Woschni heat transfer coefficient model is used to determine the heat loss to the cylinder wall during combustion. The gas properties, such as gas constant, specific heat and lower heat value are acquired by determining the components of air, stoichiometric gas and fuel, and using the mass fraction of air in the working gas as parameter. The reliability of the model has been verified by using a 4-stroke diesel engine MAN 4L20/27 to simulate in MATLAB/SIMULINK and the result of the simulation model is coincident with the actual operating condition of this engine.

Adjustable bolted propellers: mitigating uncertainty

One of the activities during the design of a ship propulsion system is the matching of the ship, propeller, gearbox and driving machine. The theory behind this matching process is well defined and documented. An important choice in the process is the range of operating conditions for which the system is to be designed. Good practise is to design with some margin for seastate, fouling and displacement growth. This margin is traditionally taken into account for by the empirical factor called Service Margin. Besides the operational factors that are included in the Service Margin, there are many design uncertainties involved in the matching process that are normally not taken into account. This paper shows that these uncertainties can result in a significant uncertainty of the operating points of the propulsion plant, which can easily lead to overloading of the driving machine or to early onset of cavitation. As a possible mitigation of this uncertainty, the benefits of an adjustable bolted propeller (ABP) are analysed. As will be shown, an ABP can be used to compensate for uncertainty during the design process, as well as for increase of ship resistance during the ship’s life.

Simulation of the Influence of Ship Voyage Profiles on Air Emissions

Simulation methodology is used to assess fuel related pollutants, CO2 and SO2 , based on several reference ship voyages. Firstly, the definition of ton-mile specific emission factor is introduced. This emission factor is related to a wide range of factors extending from fuel parameters and engine operational condition to ship design and ship activity. In this case study, a simulation model is built that applies to both transient and stationary conditions. By running this model, ton-mile specific emission factors of CO2 and SO2 , for both the full voyage and a single part of the voyage are achieved. The influences on exhaust emissions of ship speed fluctuation and in port operation strategy are considered, as well as the influence of loading fraction. After a series of simulations it is demonstrated that, a larger speed fluctuation and more intense variation of ship operational activities during maneuvering in port would cause higher emissions and the assumption of full load will underestimate the ton-mile specific emissions.Copyright