1,720,966 research outputs found
Wear and Friction in a Controllable Pitch Propeller
No full textThe author is a naval architect and this book is his PhD thesis. In this research the author focuses on friction in a controllable pitch propeller (CPP), formation of wear in a CPP system, and their mutual dependence. Instead of going deeply only in tribology aspects, the author tries to get an overall description of the problem incorporating hydrodynamic and mechanical aspects of a CPP. By doing so, the author concludes that total wear is the result of several wear mechanisms but in the first place fretting and sliding wear. An attempt has been made to explain the existence of fretting as a consequence of too high oscillations in the wake speed when the ship is sailing in seaway. Wear experiments presented in this book show fretting wear to be more dangerous than other wear mechanisms in CPP. At the end, based on experiments and previous analysis, the author presents a total wear model for a CPP. This book is useful for marine engineers to better understand the properties and limits of a CPP in real service conditions. It further can be an example how to use a multi disciplinary approach in solving a specific problem. Also it can be useful for tribology experts to get an impression of the problems the marine people encounter and how these relate to their own expertise.Marine and Transport TechnologyMechanical, Maritime and Materials Engineerin
Dynamics of Energy System Behaviour and Emissions of Trailing Suction Hopper Dredgers
No full textReducing fuel consumption from dredge vessels is always one of the priorities of the ship builder and the dredge contractor. In addition there is an increased awareness worldwide regarding exhaust emissions. CO2, NOx and SOx currently are or will in future be regulated strictly by international legislation and local authorities. Looking at a dredge cycle of a Trailing Suction Hopper Dredger (TSHD), every stage is far from stationary and in fact the dynamic variations are very severe.. Its performance is strongly influenced by weather condition, hydrological condition, river/sea bed profiles, soil types and characteristics, discharge method and discharge pipeline configuration. Although, nowadays, sophisticated automation is employed on subsystems for optimizing the dredging process, the dredger is still mainly under control of operators. The knowledge, the skill, the attitude of the dredge operators determine the performance of a TSHD and make it even more dynamic. In order to reduce fuel consumption and exhaust emissions, the impact from said dynamics need to be taken into account. This research is therefore conducted in order to know, capture, understand and be able to predict the behaviour of the energy system of a TSHD under dynamic load. Comprehensive onboard measurements have been executed to collect real time data on the energy system behaviour and exhaust emissions. After post-processing, consisting of signal synchronization, correction of the NOx-sensor time lag, filtering, signal organization and unit conversion, the results are presented the very first time. It is observed that, at constant nominal engine speed transient loads push the fuel consumption, air consumption and NOx emission away from the stationary lines. However seen at a larger time scale (in the order of stages per dredging cycle), the effects from transient loads are neutralized. The most important conclusion is: that in terms of total fuel consumption and total exhaust emissions, a dynamic loading of the energy system is not resulting in a penalty. Nonlinear time domain simulation models of a TSHD energy system (for dredging and sailing) are built in Matlab/Simulink®. The main system components and their dynamics are included, which makes the scope of the simulation models wide enough to cover all required energy systems. By means of matching and validation, the precision of the simulation models is ensured on both component and system level. Most of the components are modelled based on first principle concepts. They provide the required level of detail for understanding the system behaviour and emissions. In addition, the simulation models are well structured, providing easy removal of non-needed components, addition of new components and improvement of existing components. Through onboard measurements and simulation models, the dynamics of the behaviour of energy systems and in particular the emissions of a TSHD was thoroughly investigated in the time domain. Using normalization and linearization, the response of the energy systems to external disturbances and control commands are also investigated in the frequency domain. The linear model requires only a limited number of normalized derivatives and time constants and they are relatively independent of physical dimensions of the components. In a block diagram as presented in the thesis it can be easily traced how the disturbances propagate through the energy system and the sensitivities of involved parameters can be judged. The linear model has several advantages when compared to the nonlinear model. In the first place a linear model is generic. Further the required normalized derivatives and time constants can often easily be estimated beforehand, also because their first principle origin is made explicit. So this makes it possible that the order of magnitude of the frequency bands of any system can be grasped, even before there is an actual design. Finally the dynamic response can be explored using classical control methods. This would be useful in deciding whether a control system is needed and to determine what kind of control strategy would be effective. In summary, the three approaches (onboard measurement, non-linear simulation model and linear model) presented in this thesis provide an exclusive database and practical tools to know, to capture, to understand and to be able to predict the behaviour of the energy system and emissions of a TSHD. By further development, such as: measurement from more vessels, extending the scope of the model, increasing the precision of the model and increasing the level of details of the model, these methods can eventually be used for optimizing the design of a TSHD and reducing operational cost (fuel and emissions).MTT-SPDOMechanical, Maritime and Materials Engineerin
Efficiency analysis and design methodology of hybrid propulsion systems
No full textA hybrid propulsion system features both a diesel engine and an electric motor for propulsion. The degrees of freedom with power generation raise the question how this division between power can be optimised in such a way that the engines are running with their optimal fuel efficiency. A generalised method to determine the power generation for all operating modes for a vessel, with a focus on the lowest fuel consumption of the diesel engines is developed.Ship Design, Production and Operation (SDPO)Marine & Transport TechnologyMechanical, Maritime and Materials Engineerin
Characterising Combustion in Diesel Engines: Using parameterised finite stage cylinder process models
No full textCharacterising combustion of diesel engines is not only necessary when researching the instantaneous combustion phenomena but also when investigating the change of the combustion process under variable engine operating conditions. An effective way to achieve this goal is to parameterize the combustion process using a finite combustion stage cylinder process model and then the parameters can be modeled to give a global description of diesel engine combustion. The main objective of this thesis is getting information how to calculate (simulate) the parameters defining the finite stage cylinder process model using both theoretical and experimental methods. The latter is essential but also complicated.Department of Maritime and Transport TechnologyMechanical, Maritime and Materials Engineerin
Helicopter-Ship Qualification Testing
No full textThe goal of this research project is to develop a novel test methodology which can be used for optimizing cost and time efficiency of helicopter-ship qualification testing without reducing safety. For this purpose, the so-called “SHOL-X” test methodology has been established, which includes the associated predictive software tool as developed in this dissertation. The test methodology consists of three distinctive phases. In phase I the ship-environment in which the helicopter will operate is determined by conducting wind tunnel measurements of the airflow in the take-off and landing paths of the ship. For the helicopter a ground assessment and shore-based hover trials are carried out to verify precisely the helicopter limitations, including aspects such as pilot workload in cross-wind conditions, engine performance and control margins. Thereafter, in phase II, the potential operational limitations are derived by combining the behaviour of the isolated helicopter and the environmental conditions for a particular ship type. This so-called “Candidate Flight Envelope” is used as starting point for sea trials. Finally, in phase III, a (partial) flight test campaign on board the ship is conducted preferably in a range of weather conditions by day and by night. This is to determine for the particular helicopter-ship combination the effects on the pilot workload from, for example, visual references, ship motion and turbulence. The main advantage of the new test methodology, aided by the presented predictive tool, is that the operator can perform early evaluation of safety limits for helicopters operating on ships in a wide range of in-service conditions. In this way the qualification process is less dependent on the successful outcome of solely qualitative assessed test points during dedicated sea trials. As such, the test methodology can be used to allow a well-considered assessment of the gap between the safe flight envelope, as determined by the helicopter manufacturer, and the user-defined operational flight envelope for a particular helicopter-ship combination. Additionally, the tool allows initial assessment of the impact of design changes to both helicopter and/or ship after the finally established operational limitations have been released to service with regard to flight performance and control capability. The newly developed predictive tool in this dissertation, is considered original, and can be seen as the most important novelty of this work. The innovative test methodology, including the associated predictive tool, has already been successfully applied between 2012 and 2014 during the helicopter-ship qualification process of the NH90 NFH across the entire Dutch fleet. The academic research is mainly performed somewhere between technology readiness level 2 (i.e. technology concept and/or application formulated) and technology readiness level 4 (i.e. model and/or sub-models validation). However, the validation sea trials at full-scale enabled the high ambition of this research project to be achieved: technology readiness level 7 (i.e. model demonstration in an operational environment). This high aim might seem ambitious for an academic research; although the reader should fully understand that the aim of this research is to reduce the number of flight hours for helicopter-ship qualification testing without reducing safety. The innovative test methodology enables the construction of operational limitations by two different options. The first and most common option is using dedicated sea trials in which the potential boundaries for the various take-off and landing procedures are validated. The second option, is the construction of the operational limitations for Hot & Heavy conditions by desk-top analysis alone, i.e., above approximately 25 °C outside air temperature (hot) with maximum weight of the helicopter (heavy). The construction of the operational limitations for Hot & Heavy conditions are based on the data gathered during shore-based hover trials and the flight test results for other referred weights (i.e. helicopter weight as a function of air density) on board the same ship type. The construction of operational limitations by desk-top analysis alone is a novel approach, and can be seen as the most important achievement of this work. Unfortunately, the establishment of helicopter-ship operational limitations is still considered a national responsibility, and there are no internationally agreed regulations or standard procedures. Consequently, the kind of interpretation given to such limitations differs strongly between countries. Therefore, as it is assumed that each country or operator aims for maximum operational flexibility of a particular helicopter-ship combination, with minimal expenses and without any concessions in flight safety, this dissertation has the ambition to function as the starting point for international regulations or standard procedures to conduct helicopter-ship qualification testing.Ship Design, Production and OperationsMechanical, Maritime and Materials Engineerin
A new technology for the reduction of particulate matter from diesel engines in ships
No full textIn this thesis the focus is on the particulate matter reduction of ships, as ships contribute significantly to the particulate matter concentration in ambient air. Because the fuel of sea ships contains a lot of ash, the emitted particulate matter will also contain a lot of ash. In car and truck applications the soot filters are cleaned by burning the particulate matter off of the filter. However, ash will not be burned off and accumulates in the filter. In the case of high-ash loads, like sea ships, a soot filter is not applicable, because the filters cannot be cleaned properly. The goal of the research was to develop a technology to reduce particulate matter that is fuel insensitive. In this thesis such a technology is described, tested and simulated for high-ash applications. The patented technology is based on coating particulate matter with water, and subsequently capturing by an electrostatic precipitator (ESP). In the present experimental set-up this was a two-stage ESP, which has a robust construction and a reduced risk of physical contact between the electrodes at different potential. The water-coated particles will flow off the collection plates, therefore allowing continuous operation of the ESP. The water stream needs to be cleaned before it is discharged in the surface waters. The required cleaning technology, however, is similar to the cleaning technologies used in sea water scrubbers. It is proven that the technology is capable of removing 80% of particulate matter, including the fraction of particulate matter smaller than 1 micrometer in (mobility) diameter. It was found that the new technology was rather insensitive to particle size and is thus very suitable to remove sub-micron particles.Mechanical Maritime and Materials Engineerin
On the application of network theory in naval engineering: Generating network topologies
No full textNetwork topology of technical systems (i.e. the way in which components of technical systems are connected to each other through connections like pipes, cables, shafts, etc.) in naval vessels is quickly fixed in current design methods. This means the vulnerability of these systems is also quickly fixed. Variation in network topology may lead to new, unknown topologies that have better survivability characteristics. Therefore a new approach to designing technical systems is explored in this paper. This approach applies mathematical network theory in a naval engineering context. Basic concepts of network theory are explained and then used to make automatic network topology generation possible. Preliminary results using a first version of a network topology generation algorithm are presented and discussed. Future work within the PhD research of which this network topology generation is one aspect is then described.Accepted Author Manuscript. Contribution P de Vos (see programme) in pdf-format, secured by password.Ship Design, Production and Operation
Linearisation of a ship propulsion system model
No full textThe 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.Accepted Author ManuscriptShip Design, Production and Operation
Control of Propeller Cavitation in Operational Conditions
No full textOff design conditions can have a severe impact on ship propulsion system behaviour. Resistance increase for instance leads to a 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 effect on engine loading and on propeller cavitation. This dissertation 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 has been tested extensively in a simulation environment before full scale trials took place in February 2008 onboard a frigate of the Royal Netherlands Navy. Results in terms of full scale propulsion system behaviour are presented, including photos showing the propeller cavitation behaviour in operational conditions.Maritime and Transport TechnologyMechanical, Maritime and Materials Engineerin
Three-Zone in-cylinder process model for DI diesel engines
No full textThe need to reduce harmful emissions to the environment is been addressed on different fronts. Diesel engines, as one of the prime movers in transport industry, has become an active research focus for several years in order to improve their efficiency while keeping the harmful emissions the lowest possible. The inclusion of more stringent regulations and emission control areas such as NECA in the north sea demands for a better understanding of the combustion process in the cylinder in order to reduce emissions. To study such problem an approach is to regard the cylinder as a perfectly mixed volume. This concept is very simple and allows for fast calculations but it lacks the physics and the resolution necessary to study pollutants formation. The main objective of this thesis is to propose a model where the cylinder volume is divided into a few volumes, so the cylinder process can be studied in more detail and some resolution is included to calculate NO emissions. A model with three control volumes, called zones, is introduced. One zone represents the liquid fuel in the cylinder and two zones represent the gas mixture. In one of the gaseous zones the mixture preparation and combustion reaction occur; the second gaseous zone provides the oxidant to the previous zone and the combustion products are further mixed with air. The detailed model and the equations necessary to simulate the process are introduced. The required sub-models are proposed and the implementation of the complete model is done in different steps. First the liquid volume is treated and tested under a set of different conditions. In a second step the gas phase is simulated by neglecting the existence of liquid fuel in the cylinder. Finally, the complete model is assembled and NO formation mechanism is coupled with the model, testing is done allowing to evaluate the concept.MSIMarine & Transport TechnologyMechanical, Maritime and Materials Engineerin
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