In 2012 106 vessels over 100 gross tonnes were lost. During the damage incidents many of these vessels required assistance from shore based emergency response services with regards to their damaged strength to stabilise the situation, preserve life, prevent environmental disaster and limit financial costs to owners and insurers. The research work presented in this Engineering Doctorate Thesis surrounds the strength assessment of damaged steel ship structures, the influence of damage on the strength of steel-plated structures and methods for assessing the residual strength of a vessel in an emergency. The focus of the work is to improve the modelling of damaged steel ship structures within an emergency situation, in order to improve guidance provided to a stricken vessel during a damage incident or salvage process. Literature study has shown that structural idealisation through the use of interframe progressive collapse analysis, to be the current state of the art method for the rapid assessment of intact and damaged ship structures. However, a number of weaknesses have been identified in the method when applied to damage assessment. The literature study has also shown a lack of understanding of the effect of damage on steel-plated structures as specific analysis has not been performed previously. Significant research has been undertaken into the influence of damage, in the form of a hole, on the ultimate collapse strength of steel-plated structures. Three levels of structural modelling have been used, stiffened-plate, stiffened panel and grillage. Comparison of the predicted ultimate collapse strength by finite element analysis (FEA) with predictions using the interframe progressive collapse idealisation, has shown the calculated results to be conservative for the assessment of damaged structure when the failure mode remains in the interframe collapse form. However, changes in the failure mode lead to the interframe progressive collapse method over predicting the ultimate collapse strength. The analysis shows that even small damage events can lead to significant changes to the failure mode and resulting ultimate collapse strength of the structure. Such influences must be accounted for in any simplified method. A new method for the assessment of damaged ship structures is proposed that is capable of modelling a damage scenario more accurately. Demonstration of the method has shown the results to be less conservative than the current state of the art, when compared to FEA, for local analysis of damaged steel-plated structure. The ability of the method to account for the influence of damage, and the resulting failure modes, that may significantly influence the ultimate bending strength of the structure has also been demonstrated. The method implements a compartment level progressive collapse analysis with structural data captured through the use of the response surface method ‘kriging’, using data points provided from FEA. This method allows the critical damage variables to be captured and strength data accessible quickly for use in the analysis. The time to provide a solution to the damage scenario is equivalent to the existing interframe progressive collapse method. Therefore, the method is suitable for application within an emergency response or salvage service.

The acoustic remote sensing of subsea gas leakage, applied to the monitoring of underwater gas discharges from anthropogenic and natural sources, is becoming increasingly important. First, as the oil and gas industry is facing increasing regulation, there is a need to put more control in the industrial process and to assess the impact on the marine environment. The applications are diverse, including: early warnings of "blow-out" from offshore installations, detection of leaks from underwater gas pipelines, gas leakage detection from Carbon and Capture and Storage facilities (a process aimed at mitigating the release of large quantities of CO2 in the atmosphere), and seabed monitoring. Second, this technology has a role to play in oceanography for a better understanding of natural occurrences of gas release from the sea floor such as methane seeps. This is of major importance for the assessment of the exchange of gas between the ocean and the atmosphere with application to global warming. All those phenomena involve the formation and release of bubbles of different sizes. These are strong sources and scatterers of sound. Within this context, this thesis draws on a two part study. The first part experimentally addresses the accuracy of a passive acoustic inversion method for the quantification of gas release. Such a technique offers the advantage of lower power requirements for long term monitoring. It is common practice for researchers to identify single bubble injection events from time histories or time frequency representations of hydrophone data, and infer bubble sizes from the centre frequency of the emission. This is well suited for gas release at a low flow rate, involving solitary bubble release. However, for larger events, with overlapping of bubble acoustic emissions, the inability to discriminate each individual bubble injection events makes this approach inappropriate. Using an inverse method based on the spectrum of the acoustic emissions allows quantification of such releases with good accuracy. The inverse scheme is tested using data collected in a large test tank and data collected at sea during the QICS (Quantifying Impacts of Carbon Storage) project. The second part of the thesis addresses the problem of quantifying gas releases using active acoustics. Single beam echosounders are commonly used instruments in fisheries acoustics. When investigating gas release from the seafloor, they are frequently employed to study the spatial distribution of the gas releases. However, few studies make use of these data to quantify the amount of gas being released. Here, using the common multi-frequency ability of these systems, an inverse method aimed at determining gas volumes is developed. This is tested against simulated data and the method shows good performances in scenarios with limited data sets (data collected at limited number of frequencies). Then, using data collected at sea from methane seeps to the west of Svalbard (from two research cruises), the method is applied and compared to independent measurements of gas fluxes.

No description available.

A Finite Element Method (FEM) is developed to calculate rotationally symmetric acoustic propagation over short range intervals (0-5 km) in shallow oceans (0-200 m deep) at low frequencies (0-50 Hz). The method allows full two-way wave propagation in range dependent environments and includes coupling to a full elastic seabed. Numerical results from a computer program are presented for propagation upslope, downslope, over seamounts and across trenches in the seabed. The seabed is modelled as a pressure release surface, a fluid halfspace and an elastic, solid halfspace and the implications of each type of model are discussed. The halfspaces, being represented by a new set of infinite elements, are modelled without truncation. The results are presented primarily as plots of transmission loss against range for a fixed depth receiver. Subsidiary results show the effect of depth averaging the receiver location, and extract mode amplitude data to reveal the strength of mode coupling and backscatter in different environments.

Anthropogenic structures fragment river connectivity, impeding the migration of diadromous fish between essential habitats. Tide gates are used worldwide primarily for flood protection and land reclamation by closing under hydraulic pressure during the flood tide and opening when head differential is sufficient during the ebb. Although tide gates are known to decrease fish species richness, abundance, and movement, their impacts on the migration of ecologically and socioeconomically important diadromous fish in terms of passage efficiency and delay have not been reported elsewhere. Acoustic and passive integrated transponder telemetry revealed that passage efficiencies of upstream migrating adult brown trout, Salmo trutta (92%), and downstream migrating juvenile sea trout smolts (96 - 100%) and adult European eel, Anguilla anguilla (98%), were high at top-hung tide gates in two small English streams. However, these fish experienced delay at the gates (adult brown trout, median = 6.0 h; sea trout smolts, mean = 6.5 and 23.7 h; eels, mean = 66.2 h) when compared to migration through unimpeded reaches. The percentage of time the gates were closed and mean angle of opening were positively related to delay in both species and life stages. Diel periodicity also influenced delay for smolts and eels, which were more active at night. For adult trout, water temperature was positively associated with delay. Upstream and downstream water temperature and salinity were influenced by the temporal operation of the gates. Orifices installed in the gates did not mitigate delay for adult or juvenile trout. For adult eels, delay was decreased when an orifice was operational, although this coincided with more eels first approaching the gates when open, higher tides and greater saline intrusion upstream of the gates. When gates were open, fish would not pass immediately through, indicating the potential influence of a behavioural avoidance component. To examine the effect of hydrodynamics created by top-hung tide gates with different aperture sizes, wild sea trout smolt behaviour was observed by video cameras in an experimental flume at night. Avoidance responses occurred within an average of 1.4 fish body lengths upstream of the gate. Fish were more likely to exhibit avoidance (switch in orientation from negative to positive rheotaxis, increased tail beat frequency and/or retreat upstream) in the vicinity of a model gate with a smaller angle of opening and passage aperture. Overall, top-hung tide gates delayed the migration of diadromous fish, potentially increasing energy expenditure and predation risk. Delay was not decreased by orifices. Modifying or replacing top-hung tide gates with designs that allow them to open wider and for longer could reduce migratory delay and improve the environmental conditions that cause behavioural avoidance.

A typical irrigation scheduling problem is one of preparing a schedule to service a group of outlets. These outlets may either be serviced sequentially or simultaneously. This problem has an analogy with the classical earliness/tardiness machine scheduling problems in operations research (OR). In previous published work integer programme were used to solve such problems; however, such scheduling problems belong to a class of combinatorial problems known to be computationally demanding (NP-hard). This is widely reported in OR. Hence integer programme can only be used to solve relatively small problems usually in a research environment where considerable computational resources and time can be allocated to solve a single schedule. For practical applications meta-heuristics such as genetic algorithms, simulated annealing or tabu search methods need to be used. However as reported in the literature, these need to be formulated carefully and tested thoroughly. This thesis demonstrates how arranged-demand irrigation scheduling problems can be correctly formulated and solved using genetic algorithms (GA). By interpreting arrangeddemand irrigation scheduling problems as single or multi-machine scheduling problems, the wealth of information accumulated over decades in OR is capitalized on. The objective is to schedule irrigation supplies as close as possible to the requested supply time of the farmers to provide a better level of service. This is in line with the concept of Service Oriented Management (SOM), described as the central goal of irrigation modernization in recent literature. This thesis also emphasizes the importance of rigorous evaluation of heuristics such as GA. First, a series of single machine models is presented that models the warabandi (rotation) type of irrigation distribution systems, where farmers are supplied water sequentially. Next, the multimachine models are presented which model the irrigation water distribution systems where several farmers may be supplied water simultaneously. Two types of multimachine models are defined. The simple multimachine models where all the farmers are supplied with identical discharges and the complex multimachine models where the farmers are allowed to demand different discharges. Two different approaches i.e. the stream tube approach and the time block approach are used to develop the multimachine models. These approaches are evaluated and compared to determine the suitability of either for the irrigation scheduling problems, which is one of the significant contributions of this thesis. The multimachine models are further enhanced by incorporating travel times which is an important part of the surface irrigation canal system and need to be taken into account when determining irrigation schedules. The models presented in this thesis are unique in many aspects. The potential of GA for a wide range of irrigation scheduling problems under arranged demand irrigation system is fully explored through a series of computational experiments.

Natural rubber has a good potential to be used as a material for the development of wave energy converters (WECs). Generally, rubber has the ability to withstand very large strains without permanent deformation or fracture and is not much affected by exposure to water. This makes it ideal for applications related to wave energy converter (WECs). However, there is a need to predict the efficiency of performance over the full lifetime of such an application given that WECs will represent large, expensive and novel products that must remain operational in an at-sea environment for 10-15 years. Pertaining to that criterion, fracture mechanics of rubber is an important aspect as well as strain-history and environmental effects. The objective of this study is to gain a fundamental understanding of several factors that contribute to service lifetime: the effect of ozone and oxidation, stress-strain behaviour including hysteresis, set, and cyclic stress relaxation, mechanical fatigue and the possible role of poorly dispersed filler agglomerates in nucleating failure. The work includes studies of the effect of protective coating layers and of naturally aged rubber artefacts using a mathematical model for diffusion limited oxidation. A literature review has been performed to address rubber science and associated technology, including, the durability of rubber. Experiments encompassing the effect of ozone, cyclic stress-strain behaviour and crack growth & fatigue of rubber were performed to interpret the relevant properties for the consideration of the development of wave energy converters. New parameters for characterizing macro dispersion in rubber are introduced in an attempt to seek a correlation with the life span of rubbers. All these observations and outcomes give an opportunity to enhance our understanding of the factors that determine long-term mechanical properties of rubber, to the general benefit of rubber science and technology.

No description available.

The erosion of mixed sediment deposits is described, under the action of unidirectional steady currents and (simulated) waves, separately, and in combination. The experiments were undertaken using a rectangular recirculating flume, incorporating an oscillating tray. The mixtures consisted of angular fine-grained quartz sands (D50=152.5 m and 215 m) combined with a very cohesive estuarine mud. Time-averaged erosion threshold current speeds, during the unidirectional and combined flow experiments, were measured. In addition, pore (water) pressure measurements, during the oscillatory and combined flow experiments, have been monitored. The results obtained under the action of currents show that there is an incremental increase, with clay content, in critical erosion shear stress. This increase is small for clay percentages lower than 11% (dry weight); it is larger for clay contents in excess of 11-14%. The quantity and cohesive nature of the clay fraction are suggested as the mechanisms to explain the bi-modal pattern of sediment erodibility. When the mixtures were subjected to different pre-threshold current speeds, together with various time-periods of flow, the critical erosion shear stress was higher than the original. In this process, current velocity is more important than flow duration. Data obtained under the influence of simulated wave action show that, for clay contents 11%, sediment erodibility is unaffected by the increasing clay concentrations. However, with clay contents in excess of 11-14%, a positive linear function may describe the variation in erosion threshold with clay content. Results obtained under the co-linear combined action of waves and currents demonstrate a significant and positive linear relation between erosion threshold and the cohesive additive. Furthermore, waves protect the sediment/water interface from the eroding competence of the steady currents. The resistance to erosion increases with a decrease in wave period (from 10 s to 6 s).

No description available.