Multi-objective Optimisation of Marine Propellers

AbstractReal world problems have usually multiple objectives. These objective functions are of- ten in conflict, making them highly challenging in terms of determining optimal solutions and analysing solutions obtained. In this work Multi-objective Particle Swarm Optimisation (MOPSO) is employed to optimise the shape of marine propellers for the first time. The two objectives identified are maximising efficiency and minimising cavitation. Several experiments are undertaken to observe and analyse the impacts of structural parameters (shape and number of blades) and operating conditions (RPM) on both objective. The paper also investigates the negative effects of uncertainties in parameters and operating conditions on efficiency and cavitation. Firstly, the results showed that MOPSO is able to find a very accurate and uniformly distributed approximation of the true Pareto optimal front. The analysis of the results also shows that a propeller with 5 or 6 blades operating between 180 and 190 RPM results in the best trade-offs for efficiency and cavitation. Secondly, the simulation results show the significant negative impacts of uncertainties on both objectives

An integrated methodology for the design of Ro-Ro passenger ships

The present paper provides a brief introduction to the holistic approach to ship design, defines the generic ship design optimization problem and demonstrates its solution by use of advanced optimization techniques

Marine propeller optimisation tools for scenario-based design

The marine propulsion system is one of the most important components of a ship in order to cover the demanding operating needs of propulsion nowadays and to increase performance in a wide range of operating conditions. Marine propellers are designed with the purpose of matching the hull and machinery system, create the required thrust for the entire operational profile, and fulfil the techno-economical requirements that depend on the decision-making of several stakeholders. The final product must represent a unique propeller, designed for a specific vessel, and is a trade-off between all requirements. In an industrial framework, the marine propeller design process should therefore be straightforward and well-developed. The limited time under which the design process must be performed, plays a decisive role in the methods utilised to carry it out, as for example in the selection of the analysis tools, which must be fast and they usually involve semi-empirical evaluations. Since blade design is a multi-objective and multidisciplinary problem, automated optimisation has been used with the aim to search good solutions in the design space efficiently. However, automated optimisation has failed to be used in industrial applications due to obtaining solutions with high performance but with infeasible geometries, and as a method it proved to be inferior to the manual design process, something that shows the importance of the designer\u27s expertise. The main research question of this thesis is therefore related to incorporating optimisation in a systematic way in order to improve the propeller design process and assist the blade designers to obtain feasible and high-performing propellers in strict time constraints. A methodology is proposed that combines interactive optimisation with machine learning and in parallel new objectives are implemented for more complex scenarios. The designer is enabled to manually evaluate cavitation nuisance during the optimisation and guide the algorithm towards areas of the design space with satisfactory cavitation characteristics. Several scenario-based situations have been investigated by using the proposed methodology, that involve different propeller types, design and off-design conditions, several objectives and constraints, cavitation nuisance on the suction and the pressure side of the blade, and applications within conventional and wind propulsion. The results have shown that by involving the blade designer\u27s expertise in the design and optimisation process systematically, competitive propeller designs with feasible geometries can be obtained efficiently

Marine propeller optimisation through user interaction and machine learning for advanced blade design scenarios

The complexity of the marine propeller design process is well recognised and is related to contradicting requirements of the stakeholders, complex physical phenomena, and fast analysis tools, where the latter are preferred due to the strict time limitations under which the entire process is carried out. With all this in mind, an optimisation methodology has been proposed and presented earlier that combines user interactivity with machine learning and proved to be useful for a simple blade design scenario. More specifically, the blade designer manually evaluates the cavitation of the designs during the optimisation and this information is systematically returned into the optimisation algorithm, a process called interactive optimisation. As part of the optimisation, a machine learning pipeline has been implemented in this study, which is used for cavitation evaluation prediction in order to solve the user fatigue problem that is connected to interactive optimisation processes. The proposed methodology is investigated for two case studies of advanced design scenarios, relevant for a real commercial situation, that regard controllable-pitch propellers for ROPAX vessels, and the aim is to obtain a set of optimal, competent blade designs. Both cases represent scenarios with several design variables, objectives and constraints and with conditions that have either suction side or pressure side cavitation. The results show that the proposed methodology can be used as a support tool for the blade designers to, under strict time constraints, find a suitable set of propeller designs, some of which can be considered equal or even superior to the delivered design

Interactive Optimisation in Marine Propeller Design

Marine propeller design is a complex engineering problem that depends on the collaboration of several scientific disciplines. During the design process, the blade designers need to consider contradicting requirements and come up with one optimal propeller design as a solution to the specific problem. This solution is usually the trade-o between the stakeholders\u27 requirements and the objectives and constraints of the problem.The significant amount of design variables related to blade design problems requires a systematic search in a large design space. Automated optimisation has been utilised for a number of blade design applications, as it has the advantage of creating a large set of design alternatives in a short period of time. However, automated optimisation has failed to be used in industrial applications, due to its complex set-up and the fact that in more complex scenarios the majority of the non-dominated design alternatives are infeasible. This necessitates a way of enabling the blade designers to interact with the algorithm during the optimisation process.The purpose of this thesis is to develop a methodology that supports the blade designers during the design process and to enable them to interact with the design tools and assess design characteristics during the optimisation. The overall aim is to improve the design performance and speed. According to the proposed methodology, blade designers are called during intermediate stages of the optimisation to provide information about the designs, and then this information is input in the algorithm. The goal is to steer the optimisation to an area of the design space with feasible Pareto designs, based on the designer\u27s preference. Since there are objectives and constraints that cannot be quantified with the available computational tools, keeping the "human in the loop" is essential, as a means to obtain feasible designs and quickly eliminate designs that are impractical or unrealistic.The results of this research suggest that through the proposed methodology the designers have more control over the whole optimisation procedure and they obtain detailed Pareto frontiers that involve designs that are characterised by high performance and follow the user preference

A coupled electromagnetic / hydrodynamic model for the design of an integrated rim - driven naval propulsion system

This paper presents an analytical multi-physic modeling tool for the design optimization of a new kind of naval propulsion system. This innovative technology consists in an electrical permanent magnet motor that is integrated into a duct and surrounds a propeller. Compared with more conventional systems such as pods, the electrical machine and the propeller have the same diameter. Thus, their geometries, in addition to speed and torque, are closely related and a multidisciplinary design approach is relevant. Two disciplines are considered in this analytical model: electromagnetism and hydrodynamics. An example of systematic design for a typical application (a rim-driven thruster for a patrol boat) is then presented for a set of different design objectives (efficiency, mass, etc). The effects of each model are commente

An early-stage approach to optimise the synthesis, design and operation of a marine energy system for liquefied natural gas carriers

Since decisions of the greatest impact are made in early stages of ship design, developing design tools to make more information available sooner is desirable. Moreover, there is still room for improvements on the optimisation of energy system selection considering an integrated approach. Therefore, the present work aims to provide a comprehensive early-stage approach to perform the optimisation of design, synthesis and operation, considering economic and technical aspects as well as route weather. Constraints are used to avoid propellers that could present issues concerning strength, cavitation and vibration. Various propellers, sixteen engines and four operational profiles are assessed. A differential evolution optimisation algorithm whose objective function to be maximised is the net present value is applied. The case study is designed using a liquefied natural gas carrier of 175,000 m3 sailing between Lake Charles (USA) and Tokyo Bay (Japan), via Panama Canal. All suitable matchings for 15,023 propellers are found. The approach shows a gain of 22% between the worst individual of the initial population and the worst individual of the final population. The required brake power is approximately 22% higher for rough weather than for still water. A difference of over 120% was found by comparing varied matchings of economic scenes and fuel profiles. The approach shows a significant gain and highlights the value of exploring a broad range of energy system configurations in an integrated manner, considering the weather condition.Uma vez que as decisões de maior impacto são feitas nos primeiros estágios do projeto do navio, o desenvolvimento de ferramentas de projeto para disponibilizar mais informações mais cedo é desejável. Além disso, ainda há margem para melhorias na otimização da seleção do sistema de energia, considerando uma abordagem integrada. Portanto, o presente trabalho visa proporcionar uma abordagem preliminar e abrangente para a otimização de projeto, síntese e operação, considerando aspectos econômicos e técnicos, bem como o estado do mar ao longo da rota. Para evitar hélices que possam apresentar problemas de resistência, cavitação e vibração, são usadas restrições. Vários hélices, dezesseis motores e quatro perfis operacionais são avaliados. Um algoritmo de otimização do tipo evolução diferencial, cuja função objetivo a ser maximizada é o valor presente líquido, é aplicado. O estudo de caso foi projetado usando um transportador de gás natural liquefeito de 175,000 m3 que navega entre Lake Charles (EUA) e Tokyo Bay (Japão), através do Canal do Panamá. Todas as combinaçõe adequadas para 15,023 hélices são encontradas. A abordagem mostra um ganho de 22% entre o pior indivíduo da população inicial e o pior indivíduo da população final. A potência no freio necessária é aproximadamente 22% maior para mar agitado do que para água parada. Uma diferença de mais de 120 % foi encontrada comparando combinações variadas de cenas econômicas e perfis de combustível. A abordagem mostra um ganho significativo e destaca o valor de explorar uma ampla gama de configurações de sistemas de energia de forma integrada, considerando a condição climática

Propeller optimization by interactive genetic algorithms and machine learning

Marine propeller design can be carried out with the aid of automated optimization, but experience shows that a such an approach has still been inferior to manual design in industrial scenarios. In this study, the automated propeller design optimization is evolved by integrating human–computer interaction as an intermediate step. An interactive optimization methodology, based on interactive genetic algorithms (IGAs), has been developed, where the blade designers systematically guide a genetic algorithm towards the objectives. The designers visualize and assess the shape of the blade cavitation and this evaluation is integrated in the optimization method. The IGA is further integrated with a support-vector machine model, in order to avoid user fatigue, IGA\u27s main disadvantage. The results of the present study show that the IGA optimization searches solutions in a more targeted manner and eventually finds more non-dominated feasible designs that also show a good cavitation behaviour in agreement with designer preference

Design optimisation of Propeller Boss Cap Fins for enhanced propeller performance

Economic pressures and regulatory requirements have brought about a great interest in improving ship propulsion efficiency. This can be exercised by installing Energy Saving Devices (ESD) such as Propeller Boss Cap Fins (PBCF). This paper demonstrates an approach for optimising PBCF by using Computational Fluid Dynamics (CFD) analysis. The conducted Reynolds-averaged Navier-Stokes (RANS) CFD open water model tests were validated by comparison with experimental data until the simulation was deemed satisfactory within the capabilities and limitations of the model. A design and optimisation procedure was defined to analyse the impact of ESDs on propeller efficiency and then used to evaluate the influence of alternative geometric parameters and locations of the PBCF on the hub. This analysis was done at full scale using high fidelity CFD-based RANS methods. Outcomes of the study include a design and optimisation process that can be used for the analysis of other ESDs on the market. The influences of various PBCF geometry were examined with optimal solutions presented for the analysis case. Results indicated a net energy efficiency improvement of 1.3% contributing to a substantial minimisation of cost and energy consumption. A reduction in the hub vortex was also clearly identified and presented

Optimisation model for a ship's hybrid energy system with a Flettner rotor

This thesis attempts to investigate the effect of the implementation of Flettner rotors in the topology of the cruise ship Silja Serenade, which, in the year of this thesis dissertation, travels from Helsinki to Stockholm. The aim is the implementation of simulation models written in Matlab that simulate the behaviour of the ship topologies’ components, with the goal of minimising the global fuel consumption. The models refer to a particular time period defined by the provided data, but the structure is completely general and can be applied to the most different data and time periods, and for every ship. The topologies will consider the presence of a battery and a shaft generator. In the first part of this work, the literature part is described, covering the reasons of fuel consumption’s restrictions, the Flettner rotor’s old and recent history, the fundamentals of the ships’ topologies and a brief introduction to the optimisation theory. Those chapters are essential in order to comprehend what are the motivations for the research topic and how the work is developed. The second part includes the building of the optimisation models, the logic that they follow and the results. Each component of the topologies is explained separately, clarifying the assumptions taken over them and explaining why they are reasonable. The optimisation models are explained step by step, discussing why each decision is taken and how they influence the final results. In the final part, final conclusions are drawn. Results compare the case of different topologies in order to establish firmly the impact of the various topologies arrangements on the total fuel consumption, with a special focus on the effects that the Flettner rotors’ implementation has on it