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An above water centre bow in wave piercing catamarans provides additional reserve buoyancy for minimising deck diving in following seas. The centre bow entry in waves, however, contributes to the severity of the wet-deck arch slam loads and slam induced bending moments. In this thesis, the effects of the centre bow length and wet-deck height/tunnel clearance on the motions and slam loads in large wave piercing catamarans are investigated through model tests to establish a framework for the preliminary design analysis. The model tests were performed in regular waves in head seas using a 2.5 m hydroelastic segmented catamaran model designed with an adjustable wet-deck and a changeable centre bow segment. Five different centre bow and wet-deck configurations were considered and over 500 towing tests were performed at two model speeds, in three wave heights and for various wave encounter frequencies. The catamaran model was comprehensively instrumented to measure the pitch and heave, centre bow loads, centre bow accelerations, wet-deck arch slam pressures and the vertical bending moments at two segment cuts located in each port and starboard demihull. Motion analyses showed that both heave and pitch increased over a wide range of encounter wave frequency as the wet-deck height of the catamaran model increased. Increasing the length of the centre bow showed an increase in the pitch but a decrease in the heave for a particular range of encounter wave frequency. The vertical motions along the model length indicated that the position of minimum vertical displacements and accelerations were aft of the LCG, between 20% and 38% of the overall length from the transom. The increase in wet-deck and consequently the archways clearance also resulted in an increase in relative vertical displacement in the centre bow area. This indicated that although the wet deck height had been increased, the consequent increase in motion still caused slamming to occur. In dynamic analyses, the maximum force acting on the centre bow segment during a slam event was decomposed into a bow entry force and a slam force. It was found that the slamming force, the centre bow entry force and slam induced bending moment increase as the centre bow length increases. Increasing the wet-deck height reduced the maximum slam load and pressure in moderate waves, but not in large waves. A correlation analysis between the slam force and slam pressure showed that the slam loads increase in the longer centre bows because of the increase in the impact area. The location of maximum pressures along the centre bow length was more related to the encounter wave frequency rather than the centre bow configurations. The distribution of the peak pressures within the centre bow archways showed that the inboard peak pressures were higher than the top arch and outboard peak pressures. The slam occurrence and severity for different centre bow and wet-deck configurations were analysed by considering the centre bow immersion depth and relative velocity at slam using the undisturbed water profile. It was found that the undisturbed immersion depth for severe slam loads was greater than the immersion depth at the wet-deck level. Therefore, the cross structure between the demihulls and the centre bow can be modified to reduce the slamming pressure. The results obtained by the comparison of the various centre bow and wet-deck configurations demonstrate the significance of considering the effect of the centre bow and archway slamming in structural design and suggest that the class rules currently available for wave piercing catamarans with a flat deck structure could be modified accordingly. Amongst the tested centre bow configurations, the shortest centre bow was the best design for slam load alleviation. Ideally, a trade-off amongst the centre bow buoyancy in waves, slam load and the catamaran motions should be made to optimise the centre bow design according to the vessel‚ÄövÑvºs operating conditions.

An onboard monitoring system can measure features such as stress cycles counts and provide warnings due to slamming. Considering current technology trends there is the opportunity of incorporating machine learning methods into monitoring systems. A hull monitoring system has been developed and installed on a 111 m wave piercing catamaran (Hull 091) to remotely monitor the ship kinematics and hull structural responses. Parallel to that, an existing dataset of a geometrically similar vessel (Hull 061) was analysed using unsupervised and supervised learning models; these were found to be beneficial for the classification of bow entry events according to the kinematic parameters. A comparison of different algorithms including linear support vector machines, naïve Bayes and decision tree for the bow entry classification were conducted. In addition, using empirical probability distributions, the likelihood of wet-deck slamming was estimated given vertical bow acceleration thresholds.

Thermal insulation test methods approach their lower limits as thermal resistance falls below 0.1 m2⋅K/W. This is the minimum value specified in ASTM C 518 (ASTM International, 2010b) while ASTM C 177 (ASTM International, 2010a) proposes about 0.06 m2⋅K/W. Nevertheless these are the test methods, along with their ISO equivalents, required by Australasian building codes and directed at many products and materials with thermal resistance on the low side of 0.1 m2⋅K/W. Alternatives, such as ASTM E 1530 (ASTM International, 2011), cover much lower resistances but require carefully prepared small specimens and very-high contact pressures and are therefore largely unsuitable for both technical and compliance reasons. For these low resistances, the insulation test methods face large errors because of interface resistance between specimen and the apparatus hot and cold plates. Staying with C 518, the problem can be avoided by using direct measurement of the test specimen surface temperatures, but this is difficult, has its own accuracy issues, and is often impractical for commercial laboratories. This technique is generally used in conjunction with interface materials such as flexible foam between the specimen and the hot and cold plates, to enhance contact and also provide an access path for temperature sensors. The alternative prospect of using these interface materials to ensure good specimen contact has been studied, in conjunction with a simple two-step thermal resistance determination based on the difference between presence and absence of the test specimen. This article presents results of a study using this difference approach for the measurement of 12 highly conducting materials, including sheets of aluminum, phenolic, HDPE, MgO, bonded rubber and cork granules, PMMA, and compressed wood fiber. For each material, repeated measurements have been performed with four different interface or “buffer” materials: PVC, silicone, EVA, and nitrile. Silicone sponge provides the most uniform results, consistent with a measurably lower hysteresis. The difference technique yielded a lower indicated thermal resistance than direct measurement by between 0.003 and 0.01 m2⋅K/W, with some variation depending on the specimen surface characteristics and to a lesser extent on the choice of buffer. Larger differences were associated with bowed, uneven or roughly surfaced specimens. The difference-technique results have greater variability, but they may be seen as better estimates of the actual specimen resistance, as contact resistance is much lower for soft-surface interfaces. An interface resistance of up to 0.01 m2⋅K/W is large enough to be of significance in many thermal measurements.

The 2007 season yielded significant new insights into settlement expansion into the land north of the line of the Gorgan Wall and the later abandonment of these sites in the steppe, prior to the construction of the Wall. It also provided us with a better understanding of Sasanian hydraulic engineering and the date and strategic role of large square fortifications south of this linear barrier. Via underwater archaeology, we explored installations associated with the Tammishe Wall and now submerged in the Caspian Sea. A detailed study of the pottery from a variety of sites associated with the Walls, as well as of settlements in thehinterland, is beginning to provide us with a clearer picture of pottery typology and the sequence of building projects and settlement patterns in the Gorgan Plain.