A solution for improved simulation efficiency of a multi-domain marine power system model

Integrated Full Electric Propulsion (IFEP) marine power systems offer increased design flexibility and operational economy by supplying ship propulsion and service loads from a common electrical system. Predicting the behaviour of IFEP systems through simulation is important in reducing the design risk. However, the prevalence of power electronics and the potential for interaction between large electrical and mechanical systems introduce significant simulation challenges. This paper presents an integrated simulation tool, which brings together electrical, mechanical, thermal and hydrodynamic models, facilitating a holistic simulation capability. Approaches adopted for model validation and computational efficiency together with two case studies are discussed

Point absorber wave energy converters in regular and irregular waves with time domain analysis

A discrete control of latching is used to increase the bandwidth of the efficiency of the Wave Energy Converters (WEC) in regular and irregular seas. When latching control applied to WEC it increases the amplitude of the motion as well as absorbed power. It is assumed that the exciting force is known in the close future and that body is hold in position during the latching time. A heaving vertical-cylinder as a point-absorber WEC is used for the numerical prediction of the different parameters. The absorbed maximum power from the sea is achieved with a three-dimensional panel method using Neumann-Kelvin approximation in which the exact initial-boundary-value problem is linearized about a uniform flow, and recast as an integral equation using the transient free-surface Green function.The calculated response amplitude operator, absorbed power, relative capture width, and efficiency of vertical-cylinder compared with analytical results

[Report of] Specialist Committee V.4: ocean, wind and wave energy utilization

The committee's mandate was :Concern for structural design of ocean energy utilization devices, such as offshore wind turbines, support structures and fixed or floating wave and tidal energy converters. Attention shall be given to the interaction between the load and the structural response and shall include due consideration of the stochastic nature of the waves, current and wind

State of the Art in the Optimisation of Wind Turbine Performance Using CFD

Wind energy has received increasing attention in recent years due to its sustainability and geographically wide availability. The efficiency of wind energy utilisation highly depends on the performance of wind turbines, which convert the kinetic energy in wind into electrical energy. In order to optimise wind turbine performance and reduce the cost of next-generation wind turbines, it is crucial to have a view of the state of the art in the key aspects on the performance optimisation of wind turbines using Computational Fluid Dynamics (CFD), which has attracted enormous interest in the development of next-generation wind turbines in recent years. This paper presents a comprehensive review of the state-of-the-art progress on optimisation of wind turbine performance using CFD, reviewing the objective functions to judge the performance of wind turbine, CFD approaches applied in the simulation of wind turbines and optimisation algorithms for wind turbine performance. This paper has been written for both researchers new to this research area by summarising underlying theory whilst presenting a comprehensive review on the up-to-date studies, and experts in the field of study by collecting a comprehensive list of related references where the details of computational methods that have been employed lately can be obtained

De-risking Integrated Full Electric Propulsion (IFEP) vessels using advanced modelling and simulation techniques

Complex multi-domain engineering systems, where for example mechanical and thermal (sub)systems are connected to each other in some way, have increasingly become a vital part of our society. An example of such a system is the Integrated Full Electric Propulsion (IFEP) concept for the marine shipping industry. With this IFEP concept, as opposed to the more conventional marine power system, the power for the ship's propulsion and ship's services is provided by a common power plant. This offers advantages including fuel efficiency and design flexibility. However, due to its system complexity and capital costs, it is important that the overall dynamic behaviour of these systems can be predicted in the early stages of the design. Predicting the overall system behaviour can be obtained by employing an integrated end-to-end model, which combines detailed models of for example the mechanical and electrical (sub)systems. This allows for example ship designers to investigate disturbances and the primary and higher order responses across the system. However, present existing simulation tools do not easily facilitate such employment of a holistic approach. In this thesis the focus is on how advanced modelling and simulation techniques can be used to de-risk the design and in-service of complex IFEP systems. The state-of-the-art modelling and simulation techniques as well as the IFEP application area are considered. An integrated-model of an IFEP vessel was developed under the EPSRC collaborative AMEPS (Advanced Marine Electric Propulsion System) research project, which forms a major part of this thesis. In order to reduce the computational burden, due to a wide variety of time constants in the IFEP system, a multi-rate simulation technique was proposed. It was demonstrated that a reduction in simulation execution time between 10-15 times can be achieved. However, it was conceptually argued that multi-rate simulation could introduce errors, which propagates itself across the system thereby provoking potential unrealistic responses from other subsystems. Several case studies were conducted based on this model, which shows that such an integrated end-to-end model may be a valuable decision-support tool for de-risking the design and in-service phases of IFEP vessels. For example, it was demonstrated that a disturbance on the propeller could provoke a saturation of the gas turbine governor. Different power system architectures were proposed for IFEP power systems such as radial and hybrid AC/DC. For this thesis, an initial study was conducted to assess the relationship between the type of power system architecture and the vessel survivability. For this assessment an existing vessel survivability theory was further developed into a quantitative method. It was concluded that based on a comparative short circuit study and the proposed survivability method that the IFEP-hybrid AC/DC architecture offers the best vessel survivability.Complex multi-domain engineering systems, where for example mechanical and thermal (sub)systems are connected to each other in some way, have increasingly become a vital part of our society. An example of such a system is the Integrated Full Electric Propulsion (IFEP) concept for the marine shipping industry. With this IFEP concept, as opposed to the more conventional marine power system, the power for the ship's propulsion and ship's services is provided by a common power plant. This offers advantages including fuel efficiency and design flexibility. However, due to its system complexity and capital costs, it is important that the overall dynamic behaviour of these systems can be predicted in the early stages of the design. Predicting the overall system behaviour can be obtained by employing an integrated end-to-end model, which combines detailed models of for example the mechanical and electrical (sub)systems. This allows for example ship designers to investigate disturbances and the primary and higher order responses across the system. However, present existing simulation tools do not easily facilitate such employment of a holistic approach. In this thesis the focus is on how advanced modelling and simulation techniques can be used to de-risk the design and in-service of complex IFEP systems. The state-of-the-art modelling and simulation techniques as well as the IFEP application area are considered. An integrated-model of an IFEP vessel was developed under the EPSRC collaborative AMEPS (Advanced Marine Electric Propulsion System) research project, which forms a major part of this thesis. In order to reduce the computational burden, due to a wide variety of time constants in the IFEP system, a multi-rate simulation technique was proposed. It was demonstrated that a reduction in simulation execution time between 10-15 times can be achieved. However, it was conceptually argued that multi-rate simulation could introduce errors, which propagates itself across the system thereby provoking potential unrealistic responses from other subsystems. Several case studies were conducted based on this model, which shows that such an integrated end-to-end model may be a valuable decision-support tool for de-risking the design and in-service phases of IFEP vessels. For example, it was demonstrated that a disturbance on the propeller could provoke a saturation of the gas turbine governor. Different power system architectures were proposed for IFEP power systems such as radial and hybrid AC/DC. For this thesis, an initial study was conducted to assess the relationship between the type of power system architecture and the vessel survivability. For this assessment an existing vessel survivability theory was further developed into a quantitative method. It was concluded that based on a comparative short circuit study and the proposed survivability method that the IFEP-hybrid AC/DC architecture offers the best vessel survivability

Modeling and Real-Time Scheduling of DC Platform Supply Vessel for Fuel Efficient Operation

DC marine architecture integrated with variable speed diesel generators (DGs) has garnered the attention of the researchers primarily because of its ability to deliver fuel efficient operation. This paper aims in modeling and to autonomously perform real-time load scheduling of dc platform supply vessel (PSV) with an objective to minimize specific fuel oil consumption (SFOC) for better fuel efficiency. Focus has been on the modeling of various components and control routines, which are envisaged to be an integral part of dc PSVs. Integration with photovoltaic-based energy storage system (ESS) has been considered as an option to cater for the short time load transients. In this context, this paper proposes a real-time transient simulation scheme, which comprises of optimized generation scheduling of generators and ESS using dc optimal power flow algorithm. This framework considers real dynamics of dc PSV during various marine operations with possible contingency scenarios, such as outage of generation systems, abrupt load changes, and unavailability of ESS. The proposed modeling and control routines with real-time transient simulation scheme have been validated utilizing the real-time marine simulation platform. The results indicate that the coordinated treatment of renewable based ESS with DGs operating with optimized speed yields better fuel savings. This has been observed in improved SFOC operating trajectory for critical marine missions. Furthermore, SFOC minimization at multiple suboptimal points with its treatment in the real-time marine system is also highlighted

Operational tsunami modelling with TsunAWI – recent developments and applications

In this article, the tsunami model TsunAWI (Alfred Wegener Institute) and its application for hindcasts, inundation studies, and the operation of the tsunami scenario repository for the Indonesian tsunami early warning system are presented. TsunAWI was developed in the framework of the German-Indonesian Tsunami Early Warning System (GITEWS) and simulates all stages of a tsunami from the origin and the propagation in the ocean to the arrival at the coast and the inundation on land. It solves the non-linear shallow water equations on an unstructured finite element grid that allows to change the resolution seamlessly between a coarse grid in the deep ocean and a fine representation of coastal structures. During the GITEWS project and the following maintenance phase, TsunAWI and a framework of pre- and postprocessing routines was developed step by step to provide fast computation of enhanced model physics and to deliver high quality results

Development of horizontal axis hydrokinetic turbine using experimental and numerical approaches

“Hydrokinetic energy conversion systems (HECSs) are emerging as viable solutions for harnessing the kinetic energy in river streams and tidal currents due to their low operating head and flexible mobility. This study is focused on the experimental and numerical aspects of developing an axial HECS for applications with low head ranges and limited operational space. In Part I, blade element momentum (BEM) and neural network (NN) models were developed and coupled to overcome the BEM’s inherent convergence issues which hinder the blade design process. The NNs were also used as a multivariate interpolation tool to estimate the blade hydrodynamic characteristics required by the BEM model. The BEM-NN model was able to operate without convergence problems and provide accurate results even at high tip speed ratios. In Part II, an experimental setup was developed and tested in a water tunnel. The effects of flow velocity, pitch angle, number of blades, number of rotors, and duct reducer were investigated. The performance was improved as rotors were added to the system. However, as rotors added, their contribution was less. Significant performance improvement was observed after incorporating a duct reducer. In Part III, a computational fluid dynamics (CFD) simulation was conducted to derive the optimum design criteria for the multi-turbine system. Solidity, blockage, and their interactive effects were studied. The system configuration was altered, then its performance and flow characteristics were investigated. The experimental setup was upgraded to allow for blockage correction. Particle image velocimetry was used to investigate the wake velocity profiles and validate the CFD model. The flow characteristics and their effects on the turbines performance were analyzed”--Abstract, page iv

Time domain prediction of first- and second-order wave forces on rigid and elastic floating bodies

The application and development of a transient three-dimensional numerical code ITU-WAVE which is based on panel method, potential theory and Neumann-Kelvin linearization is presented for the prediction of hydrodynamics characteristics of mono-hull and multi-hull floating bodies. The time histories of unsteady motions in ambient incident waves are directly presented with regards to impulse response functions (IRFs) in time. The first order steady forces of wave-resistance, sinkage force and trim moment are solved as the steady state limit of surge radiation IRFs. The numerical prediction of the second order mean force which can be computed from quadratic product of first-order quantities is presented using near-field method based on the direct pressure integration over floating body in time domain. The hydrodynamic and structural parts are fully coupled through modal analysis for the solution of hydroelastic problem in which Euler-Bernoulli beam is used for the structural analysis. A stiff structure is then studied assuming that contributions of rigid body modes are much bigger than elastic modes. A discrete control of latching is used to increase the bandwidth of the efficiency of Wave Energy Converters (WEC). ITU-WAVE numerical results for different floating