A computer program, WINPOST-MULT, is developed for the dynamic analysis of a multiple-body floating system coupled with mooring lines and risers in the presence of waves, winds and currents. The coupled dynamics program for a single platform is extended for analyzing multiple-body systems by including all the platforms, mooring lines and risers in a combined matrix equation in the time domain. Compared to the iteration method between multiple bodies, the combined matrix method can include the full hydrodynamic interactions among bodies. The floating platform is modeled as a rigid body with six degrees of freedom. The first- and second-order wave forces, added mass coefficients, and radiation damping coefficients are calculated from the hydrodynamics program WAMIT for multiple bodies. Then, the time series of wave forces are generated in the time domain based on the two-term Volterra model. The wind forces are separately generated from the input wind spectrum and wind force formula. The current is included in Morison's drag force formula. In case of FPSO, the wind and current forces are generated using the respective coefficients given in the OCIMF data sheet. A finite element method is derived for the long elastic element of an arbitrary shape and material. This newly developed computer program is first applied to the system of a turret-moored FPSO and a shuttle tanker in tandem mooring. The dynamics of the turret-moored FPSO in waves, winds and currents are verified against independent computation and OTRC experiment. Then, the simulations for the FPSO-shuttle system with a hawser connection are carried out and the results are compared with the simplified methods without considering or partially including hydrodynamic interactions.

The purpose of this report is not only to improve the cage volume deformation problem during typhoon attack but also to perform the risk analysis for a single-point-mooring (SPM) net cage system when employed in the open sea. This SPM cage system has advantages over the traditional multi-mooring lines cage system, especially when the water depth is deeper than 50m, which may prohibit divers from checking the security of anchors as well as installing the mooring system at a precise position due to the difficulty in deploying anchors in the deep and restless ocean. But the SPM cage system has no such deploying problems, and yet offers some benefits such as: (1) having environmental eco-friendly feature, the uneaten feeds could spread in a vast area and thus reduce the intensity of pollution, (2) employing only one mooring line means saving a lot of construction cost, (3) a precise location is not required and thus relatively easier to be installed at any sites, and (4) easier to connect or remove cages from the mooring system. So far the SPM cage systems have become one of the most potential cage systems in the world. For example, Israel and Canada have individually developed their own SPM cage systems. This study also follows this trend and focuses on developing a new system which is suitable to Taiwan marine environment. The numerical model for cage motion equations are solved based on the lumped mass method which produces the maximum mooring line strength and the minimum of the volume deformation. As for the risk analysis for mooring line consists of two procedures: at first to form a loading probability density function, which is based on the recent data records forming significant wave probability density function and its corresponding mooring tension probability density function of rope through beta distribution technique; secondly to form a strength capacity probability density function, which is given by a rope manufacture company. Finally, the breaking risk of mooring lines is obtained by calculating the intersection area of loading and strength capacity probability density functions. The results show that the cage with a portal frame has good performance in general, especially when the sea states are rigorous. In other words, the frame-cage could maintain about 2 times net volume compared with the cage without a frame. However, the advantage of frame-cage is not obvious when the sea states are mild. Besides, the distance of frame ropes to the cage will also affect the net volume deformation, the trend shows that the net volume deformation increases with the decreasing of the distance of frame ropes. Finally assuming there are four typhoons per year attacking on the net cage system, the recommended replacing period of nylon mooring line (diameter 55 mm)is about 7 years, while for PET mooring line (diameter 50 mm)is about 13.4 years. The failure risk probability of nylon and PET mooring lines at the recommended replacing years are about 0.49 and 0.48~0.49 respectively. Therefore, we strongly recommend marine farmers to use PET ropes instead of nylon and have to replace those ropes before the failure occurs.

A computer program, WINPOST-MULT, is developed for the dynamic analysis of a multiple-body floating system coupled with mooring lines and risers in the presence of waves, winds and currents. The coupled dynamics program for a single platform is extended for analyzing multiple-body systems by including all the platforms, mooring lines and risers in a combined matrix equation in the time domain. Compared to the iteration method between multiple bodies, the combined matrix method can include the full hydrodynamic interactions among bodies. The floating platform is modeled as a rigid body with six degrees of freedom. The first- and second-order wave forces, added mass coefficients, and radiation damping coefficients are calculated from the hydrodynamics program WAMIT for multiple bodies. Then, the time series of wave forces are generated in the time domain based on the two-term Volterra model. The wind forces are separately generated from the input wind spectrum and wind force formula. The current is included in Morison's drag force formula. In case of FPSO, the wind and current forces are generated using the respective coefficients given in the OCIMF data sheet. A finite element method is derived for the long elastic element of an arbitrary shape and material. This newly developed computer program is first applied to the system of a turret-moored FPSO and a shuttle tanker in tandem mooring. The dynamics of the turret-moored FPSO in waves, winds and currents are verified against independent computation and OTRC experiment. Then, the simulations for the FPSO-shuttle system with a hawser connection are carried out and the results are compared with the simplified methods without considering or partially including hydrodynamic interactions.

Wave energy generation is a promising renewable energy source but it faces certain challenges before it can become commercially viable. In comparison to conventional energy generation it is expensive, furthermore it has been plagued by reliability challenges due to the harsh operating demands of the marine environment. This Thesis investigates the reliability of wave energy devices, and specifically focuses on mooring system reliability. Two major themes are developed: Firstly, an assessment is conducted on a conventional mooring component, reviewing safety factors suggested in mooring system design guidelines and investigating whether there is a potential to reduce these safety factors (and in so doing, reduce system costs). Numerical modelling, laboratory testing and field testing demonstrate that excessively large safety factors are published in design guidance for static loading scenarios. However, when considering fatigue loading regimes (a critical aspect of wave energy generation), the proposed safety factors are found to be appropriate. In fatigue design, the importance of selecting an appropriate stress concentration factor for use with generic S-N curves is highlighted. These findings indicate the publication of additional stress concentration factors and a standard approach for mean stress adjustment would be a valuable addition to mooring system design guidance for fatigue. The second theme introduces a novel mooring component, The Exeter Tether, designed to reduce mooring loads and thus reduce system costs. The introduction of any novel technology brings new reliability considerations, and a reliability assessment of the tether and sub-components is presented in this Thesis. Following a failure modes and effects analysis, a bespoke range of physical tests is developed to investigate reliability concerns unique to this novel component. Laboratory testing of the tether assembly shows promising fatigue performance, however field trials highlight concerns regarding bio-fouling and marine debris ingress. Sub-component testing of the EPDM (Ethylene propylene diene monomer) polymer core suggests an increase in material stiffness with both marine ageing and repeated compression cycles. This finding supports results from assembly trials in the laboratory and at sea, where tether assembly dynamic axial stiffness is observed to increase over time. The overarching design philosophy behind the Exeter Tether is to reduce mooring system loads, so establishing the `worked' operating profile of the tether is crucial for the design intentions to be realised without compromising the reliability of the overall mooring system. Trials on the anti-friction membrane establish optimum performance when using two layers of UHMWPE (Ultra high molecular weight polyethylene) tape. Further areas requiring research are highlighted, and suggestions are made to improve the reliability of future design iterations of The Exeter Tether. The two reliability approaches presented demonstrate the potential for cost reduction in mooring system design and highlight the importance of physical component testing, both in the field and in laboratory conditions, to optimise component design whilst ensuring overall system reliability.

The design of a mooring system for a floating structure is a significant challenge; the choice of line structure and layout determine highly non-linear hydrodynamic behaviors that, in turn, influence the dynamics of the whole system. The difficulty is particularly acute for Self-Reacting Point Absorber Wave Energy Converters (SRPA WEC) as these machines rely on their movements to extract useful power from wave motions and the mooring must constrain the SRPA WEC motion without detracting from power production. In this thesis this topic has been addressed in an innovative way and new ideas on how these devices should be moored were investigated. As part of the study, an optimization routine was implemented to investigate the optimal mooring design and its characteristics. In this process, different challenges were faced. To evaluate the different mooring configurations, a high fidelity representation of the system hydrodynamics is necessary which captures the non-linearities of the system. Unfortunately, high-fidelity modeling tends to be very computationally expensive, and for this reason previous studies based mooring design largely relies on simplified representations that only reflect part of the mooring design space since some physical and hydrodynamic properties are dropped. In this work, we present how a full hydrodynamic time domain simulation can be utilized within a Metamodel-Based Optimization to better evaluate a wider range of mooring configurations spanning the breadth of the full design space. The method uses a Metamodel, defined in terms of the mooring physical parameters, to cover the majority of the optimization process a high fidelity model is used to establish the Metamodel in a pre-processing stage. The method was applied to a case study of a two-body heaving SRPA WEC. Survivability constrains where introduce into the model using a new statistical approach which reduces the execution time, and allowed the optimization routine. The analysis results lead to the conclusion that for SRPA WEC the mooring loads have a significant impact on how the body reacts with the waves, affecting both the energy that enter the system as well as the energy that is extracted as power. This implies that, in some cases, the mooring lines need to be considered in early stages of the designs as opposed to an afterthought, as is typically done. Results indicate that an optimal mooring design can result in a 26% increase in total annual power production. In addition, the mooring lines impact on mitigating parasitic pitch and roll were analyzed. It was established that in regular waves, the mooring lines can reduce the parametric excitations and improve the power extraction up to 56% for a particular sea state. By applying a computationally efficient iterative design approach to a device's mooring, parasitic motions and suboptimal device operation can be reduced, ultimately making WECs a more competitive source of energy. / Graduate / 0346 / 0537 / 0548 / 0547 / jortiz@uvic.ca

Förtöjningsarbete är ett rutinarbete ombord på de flesta fartyg vid ankomster och avgångar men det är även sett som ett riskfyllt arbete med olyckor till följd. Syftet med det här examensarbetet är att undersöka varför det fortätter ske allvarliga olyckor i samband med förtöjning trots att det är ett rutinjobb. Genom att göra dokumentanalys av olycksfallsrapporter med hjälp av analysmodellen HFACS-MA har 24 olycksfallsrapporter analyserats. Modellen är framtagen som en ram för mänskliga och organisatoriska orsaker och faktorer. Faktorerna från rapporterna placerades i fem olika nivåer. Resultatet av analysen visar att den största bidragande faktorn är förutsättningarna, i arbetet även kallat ”Preconditions”, för besättningarna. Bland annat förtöjningstrossar som varit i dåligt skick och därför brustit, vilket i vissa fall lett till dödsfall eller allvarliga skador. Resultatet visar också att faktorer som misstag och bristande uppmärksamhet har lett till allvarliga olyckor. För att se vad som reglerar förtöjningsarbetet undersöktes gällande regelverk och rekommendationer. Det konstaterades att som det är idag finns inte tillräckligt utförliga bestämmelser om hur ett säkert förtöjningsarbete ska gå till. / Mooring is an routine work onboard most vessels when arriving or departing a port but it is also considered a hazardous work task that have led to some very serious accidents. The purpose of this paper is to try to understand why these serious accidents continue to happen. 24 accident reports have been analysed using the HFACS-MA model. The model is developed as a framework for human and organisational causes and factors, where the causes and factors were placed in five different levels. The result shows that the largest contributing factor is the ”Preconditions”, especially considering the material such as mooring ropes that were in poor condition and therefore leading to failure and in some cases the rope parted and killed or seriously injured the crew member. The result also shows that human factors such as mistakes and lack of attention have caused serious accidents. Additionally this study examines the existing regulations and recommendations concerning mooring operations and it becomes clear that these are not thorough enough to ensure a safe working routine onboard.

The main inquiry for this research is to identify the reasons that contribute to customer switching intention decisions. In addressing this enquiry, two theories - the theory of migration and theory of planned behaviour - were identified as the theoretical framework underpinning the study. Two main objectives of the study were (i) to identify the push-pull and mooring factors and (ii) to measure the relationship between the push-pull and mooring factors towards switching intention. The investigation focused on the impact of with push-pull-mooring factors on switching intention. Early research into switching behaviour studies focused largely on variables that contribute to the switching intention decision, mainly due to the critical incidents encountered by customers that push them from their origin or pull them to another destination or mooring factors that might inhibit or mitigate their switching decision. In view of this, a combination of push-pull and mooring variables were used to measure the switching intention behaviour. A multiple method approach was used to study the issues in two different stages. In the first stage qualitative data collection was used to support and confirm the identification of factors from the literature. For the main quantitative methods, using a hypothetical deductive testing approach, this study (N=2018) used survey data collected via a self-administered, voluntary online survey, to develop switching intention behaviour model. The results indicated that situational factors, positive attachments, perceived switching benefits, positive attitudes towards switching and positive beliefs of others towards switching emerged as consistent push factor while availability of alternatives emerged as the pull factors. Interestingly poor pricing, poor service incidents, positive ability to switch and switching barriers were not supported in this study indicating that there is no relationship between poor pricing, poor service incidents, positive ability to switch and switching barriers towards switching intention.

There are four types of oyster aquaculture such as oyster plug rod, horizontal hanging scaffold, pontoon-style longline, and floating raft system. This study is to investigate the mooring tension of an oyster floating raft system under environmental loadings. According to the hydrodynamic experimental test, the horizontal fluid velocity has a retarded phenomenon when encountering the front part of structure, and then gradually reduces to a stable situation after the second floating rod. The phenomenon is identified as shielding effect for the raft system and has been used as a shielding coefficient to modify the fluid velocity in the computation program. The dynamic analysis of floating raft system under random wave interaction is investigated numerically and experimentally. The lumped mass method is applied to divide the structure into many nodes and elements. A modified Morison equation dealing with moving structure components is used to calculate the environmental forces on the elements. Further, the forces on elements are divided equally into neighboring nodes to form the equation of motion based on Newton¡¦s second law. Finally, the 4th-order Runge-Kutta (RK4) method is used as a time marching scheme to predict the displacement and velocity of nodes for the next time step. The results of time series and spectrum analysis of mooring tension show good agreement between numerical predictions and experimental data. This paper has further expanded to predict the field oyster raft system in an open sea, and offers some useful information to the oyster farmers in terms of improving the structure safety.

Abstract This research is to develop a new compound cage system that not only has the benefit of the traditional cage system but also has a series of oyster containers hanged on the circumference of the floating collar to add economic value to the cage aquaculture industry. The purpose of this study is to investigate the cage net deformation rate and the maximum mooring tension at the anchor under three types of Liuchiu sea states. The results of numerical simulation could be used as valuable guide for fish farmers and aquacultural cage designers. The developed numerical method is based on a lumped-mass approach to build a system of motion equations, and then utilizes the fourth order Runge-Kutta method to solve the motion equations. The numerical results reveal that under regular wave conditions, the cage net deformation rate for the compound cage system is slightly less than that of the traditional cage system, but the maximum mooring tension has reversed effect, i.e., the compound cage system has higher mooring tension than that of traditional one. As for the cases of irregular waves, the numerical results indicate that the cage net deformed so seriously that the fish can¡¦t survived at the sea condition of typhoon 50-year return period. To overcome this net shrinkage problem, an improved scheme is necessary to be implemented before a real compound cage system is installed in the open sea.

This study presents the applications of plastic limit analysis to offshore foundations and anchors, including the drag embedment anchors (DEAs) for mobile offshore drilling units (MODU’s) and spudcan foundations for jack-up platforms. In deep waters, drag embedment anchors are an attractive option for mooring of semisubmersible platforms due to low installation cost and high holding capacity; on the other hand, jack-up platforms are more stable than semisubmersible platforms but only can be placed in shallow waters. The analyses of anchor capacities are developed for an idealized anchor comprising a rectangular fluke, a cylindrical shank, and a metal chain connected to the shank at the padeye. The anchor trajectory prediction during drag embedment is also developed by considering anchor behavior in conjunction with the mechanics of the anchor line. The results of simulations show that anchors approach at equilibrium condition rapidly during the embedment and both the normalized holding capacity and the anchor line uplift angle remain constants in this stage. Besides the geometry of the fluke, the properties of the shank and soil are also crucial factors in the anchor-soil interaction behavior. Partial failure of mooring systems for floating structures will subject drag anchors to loads having an appreciable component outside of the intended plane of loading. Partial failure of mooring systems during hurricanes in recent years have generated an interest in understanding drag anchor performance under these conditions. The analysis presents the simulations of three dimensional trajectories of an anchor system subjected to an out-of-plane load component. For the conditions simulated in the example analyses, the anchor experienced a modest amount of continued embedment following partial failure of the mooring system; however, the ultimate embedment and capacity of the anchor is much less than what would have developed if the anchor had continued in its original trajectory within the plane of intended loading. The analyses of the spudcan foundation of jack-up units include preloading, bearing capacity, and the displacement assessment. When the contribution of the soil moment resistance is considered, a three-stage assessment procedure is recommended: superposing environmental forces on the plot of yield surface, determining the value of yield function corresponding to the external forces, and computing the factor of safety of the spudcan. The results of the assessment may be ambiguous while the different yield functions are employed to analyze the spudcan in soft clay.