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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

An investigation of the response of an FPSOV structures to external air blast : a case study of FPSOV operating in the Niger Delta

Shittu, Kazeem Dolapo January 2014 (has links)
Floating production storage and offloading systems, otherwise known as FPSOs in the oil and gas industry, are high risk structures because of their exposure to hazardous and flammable hydrocarbons which they carry and in some situations, because of their vulnerability to terrorist attack especially in their areas of operation. These structures have been widely used for the development of offshore oil and gas fields all over the world, especially in most part of Africa, because of their attractive features such as large work area and storage capacity, relative lower cost of construction and good stability. They are either converted from existing tankers or bulk carriers or purposely built. However the recent wave of terrorism across the Nigerian Niger Delta has necessitated the study for the need for offshore structures especially FPSO to be protected from the activities of terrorist. One of the worst case scenarios that is likely to occur on an FPSO is an attack by terrorist resulting in an above water external air blast on the side plate of a midship section of an FPSO. The resulting damage effects that would be caused by this form of attack can be devastating in terms of loss of revenue to a nation, loss of life, assets and degradation to the local environment. This was tragically demonstrated in the North Sea with the loss of the Piper Alpha Platform mentioned by (lees, 1996), albeit initiated by an accidental internal blast, unrelated to terrorist activities. At present, most design methods on the midshipsection structural members of a merchant vessel are based on working stress design concepts that are safe and suitable for normal pre-commissioning and operating conditions and which emphasize the minimum acceptable requirement for the classification society. However, design under extreme air blast loading especially those typical of terrorist/Militant attack, whose magnitude would be far higher than ordinary operating load, are desirable. In order to make it a major design consideration, this study addressed this issue on minimizing the effects of blast overpressure through the evaluation of the 3 types of T stiffeners and 3 L stiffeners to local structural response of such blast pressure on the side shell of the midshipsection of a typical FPSO code named FPSO Nigeria. The Nigerian Niger Delta accounts for over 95% of Nigerian oil and foreign reserve earning, and has been a source of attack and insurgence by militant of the Niger Delta. The objective of this study is to examine an above water air blast pressure attack to the side plate of a midshipsection of an FPSO code named FPSO Nigeria. This blast pressure is converted to an equivalent amount of TNT explosive typical to that which may be used by the militants of the Nigeria Niger delta or other parts of the world and to v KAZEEM SHITTU-An Investigation Of The Response OF AN FPSOVStructure To External Blast: A Case Study Of FPSOV Operating In The Niger Delta recommend ways by which an FPSO operating in this area could be made more resilient to terrorist attack to a larger extent or at least to minimize terrorist caused damage to the barest minimum by the selection of the best of the 3 types of T and L stiffeners considered. Additionally, blast resistant anti-ballistic material was recommended and a cost benefit analysis carried out in order to justify the need and the importance of using such blast resistance anti-ballistic materials. In order to achieve the aim of the thesis, the study commenced with the investigation of the displacement and stresses of plates and stiffened plates using Abaqus software code and compared the results of displacement and stresses generated from Abaqus with that of classical theory in order to validate the accuracy of the Software code by considering different plate thickness and boundary conditions, frequency extraction analysis were generated for plates and stiffened plates in order to obtain frequencies at which resonance could occur and to prevent such. The results generated from Abaqus software code were found to correlates with those generated from classical theory. Actual FPSO Nigeria stiffened panel were then considered and subjected to non-linear blast analysis under different boundary conditions where effects of mesh refinement were considered in details. The mid ship section of the above water side of the FPSO Nigeria was then subjected to blast pressure attack considering the different type of stiffeners with a view to determine the best stiffener configuration and to determine the rupture strain consequently an anti-ballistic blast resistant material was recommended as an aftermath of Cost Benefit analysis was carried out to validate the need for such anti-ballistic blast resistance material on the above water side of FPSOs operating in the Nigeria Niger Delta and the cost savings to nigerian Government was highlighted vis a vis the loss that would have been incurred by the Government should such attack occurs. The research concentrates mainly on developing an appropriate methodology and an illustrating the behavior of typical ship structures to high rate transient air blast loading effects, rather than undertaking a specific detail design study as such. Consequently the research has made modest contribution to knowledge by the determination of all of the above including the cost benefit analysis carried out.
32

Component mode synthesis for ship structures : investigation into an alternative approach

Zoet, Petrus Gosse January 2013 (has links)
The main aim of this work is to help the shipbuilder to effectively assess a ships' structural design for its vibratory behaviour. For that purpose state of the art structural modelling techniques are reviewed for the validity of their basic principles, accuracy, practicality and required computation time when applied on typical marine structures. Full finite element modelling has been applied on a part of the structure of an LNG carrier on board which the author has taken vibration and noise measurements. Also fixed interface (Craig-Bampton) and free interface (Rubin's method) component mode synthesis sub structuring techniques have been applied. The aim of the analysis is to evaluate the effectiveness of finite element modelling through evaluation with measurement results, evaluate the accuracy of the sub structuring modelling techniques and to identify short comings of any of the tested methods. Two alternative component synthesis modelling sub structuring techniques are proposed in order to reduce required computation time; Zoet's method and the Rubin Zoet method. The Zoet method is tested using a section of the LNG carrier's structural model. The method is evaluated for accuracy (comparing obtained results with the results obtained through the full harmonic finite element analysis) and required computation time through comparison with the required computation time for: - full harmonic analysis - the classical modal reduction and mode superposition technique - the classical Rubin free interface component mode synthesis - and Rubin's method with interface reduction according to the IRS method (see section 6.5.3) - the Rubin-Zoet technique.
33

Ship collision and grounding performances

Abu Bakar, Anuar Bin January 2015 (has links)
This present thesis investigates the accidental load of ship collision and grounding performances. To achieve this objective the thesis is composed of several main tasks. The main tasks comprise the rupture prediction, validation of material failure, ship grounding analysis and ship collision analysis. To predict material rupture, FLD material failure was used and validated with available experimental and FEA data. The FLD was extended to established material failure scaling laws which consider onset failure at plane strain in relation to mesh sizes. This was accomplished by running mesh convergence studies at different mesh sizes and at different FLD0. The linear material damage evolution is adopted in this case until the convergence results were satisfied. The material damage was used for all of further analysis in ship collision and grounding and employed mild steel and high tensile steel material properties. The ship grounding structure damage was investigated by deploying conical rocks at different locations of the ship's double bottom structure. The analysis focused on vertical penetration and horizontal penetration which contributed to significant damage to the structure. The ship collision analysis was investigated in various types of structures arrangement and diverse ship striking scenarios to penetrate struck ship and collide rigid wall. Furthermore, the prediction of ship collision and grounding were extended by using simplified approaches that were capable to predict ship collision to rigid wall, rigid body striking ship collided with deformable struck ship and deformable collision of striking and struck ship. Finally, this substantial amount of research work achieved the objectives of the study when the results of accidental load were validated and correlate well with experimental, empirical and FEA simulations at more than a satisfactory level.
34

Operational practices to improve ship energy efficiency

Banks, Charlotte January 2015 (has links)
The aim of this research was to contribute towards energy efficiency in the shipping industry through improved operational practices that reduce fuel consumption, hence exhaust emissions and the amount of carbon dioxide released into the atmosphere. This is in line with meeting global emission reduction targets and the mitigation of Climate Change. A critical review is presented that was undertaken to understand Climate Change as a driver towards energy efficiency within the maritime industry. The regulations are reviewed along with existing operational practices and the enablers and barriers towards improvements. Several field studies that were undertaken to further examine current practices and barriers are described, including a questionnaire identifying the opinions and perceptions of seafarers. Based on conclusions from the review and field studies, a Framework for improving the energy efficiency of ship operations is presented. The proposed Framework identifies that for practical solutions in the industry, human factors must be addressed in parallel with technical advances. The following features of the Framework to enable improvements are identified to be: a) Ship Operational Performance Monitoring for performance feedback distribution and supporting operational strategic decisions and b) updates to existing Operating Procedures. However, it is proposed that these features cannot be achieved on a wide scale without first the development of the following elements: a) Maritime Education and Training on energy efficiency; b) Analysis of ship Operational Profiles; c) A Ship Operational Performance Prediction (SOPP) Model. These three elements were developed and are described in this thesis. The developments described in this thesis were enabled by the collection of operational datasets (namely Ship Reports, also commonly known as Noon Reports) and information for 21 case study ships; including tanker, container and bulk carrier ships. The collection of this data was enabled by field study visits. Regarding the development of Maritime Education and Training on energy efficiency, three course curriculums are proposed. The training material developed for the Energy Resource Management course is then described. The results from the analysis of Operating Profiles for the 21 case study ships are presented. Typical operating practices are identified along with the opportunities for energy efficiency improvements. The Ship Operational Performance Prediction Model was developed using the Ship Report dataset for a case study tanker ship. The model predicts the ship's main engine brake power and fuel consumption with adequate accuracy and allows for assessment of the impacts due to different operating conditions. Specifically, a function to account for time dependent performance changes is developed so that the hull and propeller surface degradation and fouling are taken into consideration. Finally, the utilisation of the developed elements within the proposed Framework to improve energy efficiency is discussed, so that the importance of methods utilising Ship Report operational datasets becomes evident.
35

A hydrodynamic analysis of deep-water moorings

Lin, Zi January 2015 (has links)
The move by the offshore oil & gas industry to deep water has an impact on the selection of mooring system configuration and design method. Methods of analysis need to be re-evaluated as water depth increases. The primary purpose of this thesis is to study the hydrodynamics of deep water moorings and the nonlinear dynamic response of the mooring line, which is representative of a Spar platform and a floating offshore wind turbine (FOWT). Emphasis is placed on the coupling effects between the floating body and mooring line and the nonlinear dynamic response of elastic mooring line. For a Spar platform, this thesis studied the behaviour of a 4-point mooring system in water depths from 300m to 3000m, using an indirect time-domain method. A panel method was applied for the hydrodynamics of the floating structures and a lumped mass and spring method for the dynamic response of the mooring lines. Coupled analysis results for intermediate water depth were compared with experimental data to check the validity of the numerical modelling. The results from coupled low frequency (LF) and fully coupled analysis are compared and discussed. Results from parametric studies are compared to offer guidance to mooring system designers on the suitability of particular approaches. For a floating wind turbine, three water depths-300m 600m and 900m were simulated in the time domain under both operational and shutdown conditions. A fully-coupled analysis was carried out to study the motion response of the FOWT under wave only and wave-plus wind condition. The aerodynamic modelling was based on the blade element momentum theory, while the mooring system global performance was simulated by the indirect time-domain method. By performing a comprehensive parametric study, the effects of the second-order wave drift force and the aerodynamic turbine thrust force on the motion response of the FOWT are studied and discussed. The performance of a polyester mooring line is non-linear and its elongation plays a significant role in the dynamic response of an offshore moored structure. Unlike chain, the tension-elongation relationship and the behaviour of elastic polyester ropes are complex. In this thesis, by applying a new stiffness model of the mooring line, the traditional elastic rod theory is extended to allow for large elongations, which are appropriate for simulating the static and dynamic response of both polyester lines and traditional chains. Galerkin's method was applied to discretise the equation of motion for the rod. One beneficial feature of the present method is that the stiffness matrix is symmetric; in non-linear formulations the element stiffness matrix is often non-symmetric. The static problem was solved by Newton-Raphson iteration whereas a direct integration method was used for the dynamic problem. The mooring line tension based on the enhanced model was validated against the proprietary software OrcaFlex. Results of mooring line top tension predicted by different elongation conditions were compared and discussed. The present method was then used in a time-domain simulation of a Spar-type platform, typical of those used for offshore wind turbines, moored by three taut lines in waves and currents. From a comparison between linear and non-linear formulations, it is seen that a linear spring model under-estimates the mean position when the turbine is operating, but over-estimates the amplitude of the platform response at low frequencies when the turbine has shut down.
36

Development of decision support tool for advising on selecting ballast water treatment system

Al Hababi, Hani H. M. H. January 2015 (has links)
In general, for shipping companies or any organisation the important decisions are made to deal with the selection of a particular alterative. This thesis presents a decision support tool for selecting a Ballast Water Treatment System (BWTS) for a given ship. A single decision has to be made between a number of given BWTS alternatives for a VLCC tanker under its voyage in the presence of a single decision maker. The decision support tool was developed using the Analytical Hierarchy Process (AHP) method, in order to help decision makers in shipping companies to select the most feasible BWTS for their ships. The ultimate aim of the developed decision support tool is to aid decision makers in shipping companies to make the right decisions when selecting between numbers of BWTS alternatives for their ships. In order to achieve the aim of this thesis several objectives were identified as follows: (1) To identify the influencing parameters and/or criteria related to both ballast water treatment system and ships parameters; (2) To evaluate the importance of the selected criteria for both BWTS and ship parameters/criteria; (3) To apply an appropriate Multi-Criteria Decision Making (MCDM) technique along with the above points; (4) To validate the develop decision support tool and investigate its applicability in actual case studies. The criteria were identified through the literature review and the semi-structured interviews with twelve senior staff or experts from three different trade shipping companies. The latter was an important step in finalising the new decision support tool, to evaluate the importance of the selection issues in shipping companies, and to evaluate the importance of the criteria used by the developed model. In addition, it helped framing the hierarchy structure of the Analytical Hierarchy Process (AHP) as a new model to support the selection of BWTS for ships. The comparisons between the case study, derived results, sensitivity analysis, robustness test, case study two and the validation interview with two experts from a well-known shipping company have supported the applicability and the validity of the model to help decision makers in shipping companies to select the most feasible BWTS for their ships. The model has also demonstrated its ability to aid decision makers or researchers in understanding the relationships between the different processes and their consequences on their BWTS selection.
37

Hydrodynamic interaction between ships travelling or stationary in shallow waters

Yuan, Zhi-Ming January 2014 (has links)
This thesis presents the development and application of a numerical method that associates the Rankine source method with double Doppler shift to predict the hydrodynamic interactions between two ships travelling or stationary in shallow waters. Firstly, a 3-D Rankine source panel method was developed to predict the hydrodynamic properties of a single ship travelling with a wide range of forward speeds. Double Doppler shift was taken into consideration in the boundary condition of the control surface. A Wigley III hull travelling with different forward speeds was considered to validate this radiation condition. Comparing with the experimental data, both the hydrodynamic coefficients and motion responses were well predicted by the present method. Then, the method for single ship was extended to ship-to-ship without forward speed problem. Comparing the present calculations of the hydrodynamic coefficients, wave excitation forces and motion responses with the experimental data, as well as with the numerical results from Green function method, a very good agreement was achieved which illustrated that the present program was a useful tool to predict the hydrodynamic behaviours of two ships arranged side by side without forward speed. The effects of mooring and fender system were also discussed based on the linear assumption. Based on the same framework, the 3-D Rankine source panel method associated with double Doppler shift was applied to ship-to-ship interaction with forward speed problem. The validations were established through two pairs of models. The computed dynamic responses of both models in heave and pitch motions showed a good agreement with the published experimental results. However, the prediction of the roll motion was full of challenges due to the inviscid assumption in the potential flow theory. The comparison between the present and Sommerfeld radiation condition was made at τ< 0.25, while the comparison between the present and upstream radiation treatment was made at τ> 0.25. It was shown that the present treatment could obtain a better wave pattern without reflections from the truncated control surface, which confirmed the effectiveness of the present radiation condition as a wave-pattern prediction tool for the ships travelling with a wide range of forward speed. After the validations of the present method, the parametric study about the forward speed and configurations was carried out in order to develop recommendations for ship designers and operators for maximum speed and distance between two ships in given environmental conditions for safe operation. The analytical expression of the semi-wedge angle based on double Doppler shift theory was derived to obtain the wake and quiescent region of the free surface. Based on the semi-wedge angle, the analytical formulation was established to obtain the optimal transvers distance between two travelling ships.
38

Three dimensional time domain simulation of ship motions and loads in large amplitude head waves

Hizir, Olgun Guven January 2015 (has links)
This PhD thesis presents the development of a practical computational tool named Large Amplitude RESponse (LARes), based on 3D quasi-non-linear time-domain technique, to predict ship motions and loads in large amplitude waves which can be accessible to ship designers. Firstly, a linear 3-D Green source panel code (LARes L1) was developed to perform linear time-domain analysis ship motion and internal load simulations based on the frequency-domain hydrodynamic coefficients which were calculated in the linear PRECAL software. Linear simulations are validated with the linear time-domain PRETTI software results using rectangular barge geometry. The motions, internal loads, global and sectional hydrodynamic forces were agreed well with the linear PRETTI model results in zero and forward speed simulations. Then, non-linear time-domain panel code (LARes L2) was developed in order to predict ship motions and loads in large amplitude waves using the Froude-Krylov nonlinearity level. At each time step, the exact wetted area of the ship surface under the wave profile was calculated and fed in the time-domain motion and load equations while the diffraction and radiation forces were kept as linear. The present program achieved good agreement with the non-linear PRETTI model results both for the barge and S175 container geometries at zero and forward speed conditions in small amplitude waves. Moreover, the S175 container ship results are compared with the available experimental data and agreed well with the experimental results in forward speed case. It has been observed that PRETTI code is over-estimating motion and load responses especially around the resonant frequency due to the surge motion influence in the memory forces evaluations. In the Froude-Krylov nonlinear level predictions, it has been observed that PRETTI diverges from the experimental results when the wave steepness is higher than 0.08 due to the linear radiation and diffraction forces. Based on the same framework, a more advanced nonlinear time-domain panel code (LARes L3) was developed in order to investigate the effects of quasi-non-linear diffraction and radiation forces in large amplitude ship simulations. A new mesh generator was introduced in order to cut and correct the original panels under the still water level in the updated position of the ship after displacements and rotations. The quasi-non-linear diffraction and radiation forces were calculated at the pre-defined position cases and stored in a database. In order to lower the computational cost multi-dimensional integration and interpolation codes were generated. The S-175 containership was tested in 120 different position cases and resulting hydrodynamic coefficients and forces were stored in the database. The results of the LARes L3 model were compared with the available experimental data using the S-175 containership in forward speed. The computed motion responses showed a good agreement with the experimental data. Moreover, three of the developed models are compared with the experiments and their performances were investigated with respect to the increasing wave slope. In addition to that, the effect of the wave length and ship speed in large amplitude waves are investigated in detail. Non-linear behaviors of the codes were compared with the experimental results which showed a good agreement. Finally, the Vertical Shear Force (VSF) and Vertical Bending Moment (VBM) responses were investigated in large amplitude motions. It was observed that, in the validation section, numerical model peak amplitudes showed well agreement with the experimental results, but they were observed to be shifted to the higher frequencies compared to the experimental results. The reason for that was attributed to the longitudinal mass distribution on the ship in the experimental setup which had not been provided in detail in the published experimental results.
39

Potential flow and CFD-based hydrodynamic analyses of mono- and multi-hull vessels

Tezdogan, Tahsin January 2015 (has links)
The majority of current techniques used for predicting ship motions rely on assumptions from the potential flow theory. However, this approach is not ideal, since potential flow theory ignores important effects such as breaking waves, turbulence and viscosity, which are significant in problems involving high Froude numbers, those involving large amplitude motions, shallow water problems and problems involving multi-hull ships. These effects should therefore be included in seakeeping and resistance calculations. Reynolds-Averaged Navier-Stokes (RANS) approaches are excellent alternatives to potential flow theory, as they can directly account for viscous effects in their calculations. Towing tank tests are used widely around the world, giving very accurate results. However, these may be costly and time-consuming. Towing tank experiments are also hampered by a limited availability of suitable facilities. Computational simulations offer a fast, low cost alternative to towing tank experi ments. Continued technological advances offer ever-increasing computational power, which can be harnessed for viscous flow simulations to solve the Navier-Stokes equations. Computational Fluid Dynamics (CFD) methods are rapidly gaining popularity for naval architecture, ocean and marine engineering applications. The application of CFD techniques to seakeeping problems allow designers to assess the seakeeping performance of a vessel whilst it is still being designed, enabling any necessary corrective action to be taken before the vessel is actually built. This work mainly aims to perform hydrodynamic analyses of mono- and multi-hull ships, and to develop a CFD-based unsteady RANS numerical model to predict the hydrodynamic performance of these ships. This model will cover seakeeping and resistance calculations in both deep and shallow water regions. Firstly, a detailed literature review of the existing numerical methods which have been developed to solve seakeeping problems of ship is performed. This review also looks in detail at the differences between seakeeping analysis techniques; the reasons for these differences are investigated. Following this, unsteady RANS simulations are performed for various seakeeping and resistance applications. In each specific study, the results obtained using a commercial RANS solver are compared to the results obtained using a potential flow theory code and the available towing tank experiments. Finally, the results drawn from each chapter of this thesis are summarised and discussed, and recommendations are made for future research.
40

An investigation into LCA as a complementary utility to regulatory measures of shipping efficiency

Blanco-Davis, Eduardo January 2015 (has links)
The IMO has recently developed technical and operational measures aimed at enhancing shipping environmental efficiency, i.e. the EEDI and the EEOI, respectively. The purpose of this exploratory research work is to investigate the Life Cycle Assessment (LCA) methodology as a complementary tool to these metrics, capable of not only serving as a widespread accepted environmental performance indicator, but also able to competently highlight energy efficiency. The EEDI and EEOI methodology is reviewed, while also using two case vessels as sample implementation case studies. An LCA model formulation is developed and also applied on the two case studies, utilising them for validation, and additionally for comparing the LCA approach to the IMO regulatory metrics. One of the case vessels comprises the evaluation of a proposed retrofit, in order to emphasise on the different metrics' potential to assess changes in the results, with regards to the retrofit's before and after phases. Results show that aside from the environmental score of CO₂ emissions per unit of work - documented by the current regulatory metrics -, LCA can also offer NOx and SOx scores, along with other hazardous releases. Moreover, LCA - aside from showing compliance to the formulation of both IMO regulatory metrics - is able to present material and energy utilisation throughout different stages within the vessel's lifetime. Lastly, it is demonstrated that LCA can be used in parallel to the regulatory metrics, in order to efficiently emphasise detailed environmental information, pertaining to specific substance release or phase improvement/redesign as required. It is concluded that LCA could serve in aiding to monitor and report maritime transport emissions with an already widely accepted methodology. Furthermore, LCA could be recognised between industry and international stakeholders - including shipping and shipbuilding and repair -, as a common performance marker capable of consistent implementation not only across shipping divisions, but also across different industry sectors.

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