Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Kevin LeRoy Johnson. / M.S.

The goal of this thesis is to develop a test platform for measuring surface effect ship (SES) response to wave loads. The platform is designed and built incorporating a self-propelled vehicle with data acquisition and navigation capabilities. Theoretical analysis is performed, various hardware and electronic parts are designed and built and software applications developed. Wave tank experiments are conducted for test platform evaluation and determination of vehicle response to a range of wave conditions. Furthermore, a three-dimensional model of the AIRCAT scale model SES is created. The theoretical analysis shows that the scale effects in some cases are great, so resonance phenomena cannot be observed. The experimental results clearly show that the heave, pitch and aircushion excess pressure fluctuations increase as the air-blower input level increases. The bow skirt arrangement needs improvements and further experimentation is necessary in order to draw conclusions about the wave loads applied on the skirt. / by Nicholas Kouvaras. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Complex oscillations including chaotic motions have been identified in off-shore and submerged mooring systems characterized by nonlinear fluid-structure interactions and restoring forces. In this paper, a means of controlling these nonlinear oscillations is addressed. When applied, the controller is able to drive the system to periodic oscillations of arbitrary periodicity. The controller applies a perturbation to the nonlinear system at prescribed time intervals to guide a trajectory towards a stable, periodic oscillatory state. The controller utilizes the pole placement method, a state feedback rule designed to render the system asymptotically stable. An outline of the proposed method is presented and applied to the fluid-structure interaction system and several examples of the controlled system are given. The effects of random noise in the excitation force are also investigated and the subsequent influence on the controller identified. A means of extending the controller design is explored to provide adequate control in the presence of moderate noise levels. Meanwhile, in the presence of over powering noise or system measurements that are not well defined, certain filtering and estimation techniques are investigated for their applicability. In particular, the Iterated Kalman Filter is investigated as a nonlinear state estimator of the nonlinear oscillations in these off-shore compliant structures. It is seen that although the inclusion of the nonlinearities is theoretically problematic, in practice, by applying the estimator in a judicious manner and then implementing the linear controllers outlined above, the system is able to estimate and control the nonlinear systems over a wide area of pseudo-stochastic regimes. / Graduation date: 2006

A vector form intrinsic finite element method ( plane frame element ) is developed and applied to study the dynamic responses of offshore template platform under wave force. The horziontal, vertical and rotational motions at each node in the finite element model also were analyzed by the developed solution procedure of offshore structures. Besides, this paper also discussed the application of viscoelastic dampers on the offshore structures. A design for the dampers incorporated in the template structure were presented, and dynamic analyses were carried out to observe the effect of the vibration mitigation on the structures .

The purpose of the work described here is to analyse vortex induced vibration VIV) effects on marine risers and unorthodox forms of suppression of this phe¬nomenon. which can cause structural failure through metal fatigue. Two suppression methods are explored: flex joints and buoyancy modules. Flex joints. which act like a hinge at a point on the riser due to the large reduction in bending stiffness. can suppress higher modes of vibration from propagating along or appearing in the riser. Buoyancy modules, with their local 100% increase in riser diameter. can decorrelate vortex shedding along the span of the riser and reduce the resonant effect of VIV. The numerical finite element cable model and rigid body model developed at the University of Victoria were modified and used as a foundation for the research. The modifications include an algorithm to estimate the forces clue to ocean surface interaction with rigid bodies and a model to produce the appropriate VIV response in the numerical cable model. The resulting VIV model was calibrated and validated with analytical. experimental, and numerical data available in the literature. In general. the model produces qualitative effects of VIV. including its self-starting and self-limiting nature, frequency lock-in. multi-mode response. and limited structural response on the order of one diameter. A simulation of a testbed riser in a variety of ocean currents was generated to observe the effects of installing flex joints and buoyancy modules at various locations along the riser span. The performance of the testbed riser was gauged by comparing the time series of von Mises stress and the associated safety factor, ns. from fatigue failure at many points along the span to an unmodified testbed riser. The stress fluctuation was drastically reduced within the flex joints for all water currents studied, which greatly increases fatigue performance. Flex joints placed at the top of the testbed riser had less impact. as the stresses are dominated by the large and unavoidable tensions found there. Flex joints placed in the bottom region of the riser did not affect the ns,. of the remaining riser span until very high modes of vibration were present. At these higher modes. some testbed riser configurations changed their vibration envelope and frequency. which indicates that a possible alternate and less damaging mode of vibration was induced. Flex joints therefore act effectively as a local patch against poor fatigue performance and placement of several flex joints does not negatively impact the behaviour of the rest of the riser in the cases examined. However. the explicit relationship between placement and spacing of flex joints with environment conditions remains unknown. Buoyancy modules introduced spatial fluctuations in the entire nu profile of the testbed riser, unlike flex joints. In addition. the buoyancy modules decreased n, performance due to the hydrodynamic load concentrations induced by their large diameters. However, the 16% coverage case increased n.,. elsewhere along the riser, though the 10% covered riser did not match this performance. Since in both cases the modules were evenly spaced along the riser. performance benefits from increased coverage implies a minimum coverage of 16% needed for significant improvement in fatigue performance for devices of this type. This coverage requirement may apply to traditional VIV suppression devices such as helical strokes. since they decorrelate vortex shedding along the span of the riser albeit in a different manner than buoyancy modules. Finally. the buoyancy modules changed the stress oscillation frequency more than the flex joint cases from the unmodified riser. This is desirable since lowering the frequency of oscillation also increases the fatigue performance of the riser.

The interaction of steep waves with structures is a complex problem which is still not fully understood, and is of great importance for the design of offshore structures. A particular problem of interest is the phenomenon of ringing which is highly nonlinear. In this thesis a number of inviscid free surface flow problems are simulated using a finite element model. The free surface boundary condition is fully nonlinear, meaning nonlinear effects up to very high order can be simulated, depending on mesh resolution. The model uses a fully automatic unstructured mesh generator; this allows the mesh to change its shape and structure as the free surface deforms. Two unstructured mesh generators have been developed, one based on the advancing front method, the other on the Voronoi technique. Variations of each method are examined. Both methods give good quality meshes. The advancing front technique is found to be faster, but the Voronoi method is more robust and reliable. In addition to the standard finite element method, a sigma transformed version of the finite element formulation has been developed as an alternative. Both techniques have been used for the numerical simulations. The sigma transformation involves stretching of the mesh between the bed and free surface, and so has the advantage that remeshing is avoided. The standard finite element method is straightforward to apply to problems involving submerged arbitrary shaped bodies. Simulations have been performed of a number of test cases, such as a standing wave of large amplitude, a base excited tank and steep travelling waves. Convergence tests were carried out and results found to be in close agreement with analytical and alternative numerical solutions of Wu and Eatock Taylor (1994), Wu et al. (1998) and Chern et al. (1999). The force on a submerged horizontal cylinder due a travelling wave has been calculated. First and second order components have been obtained by Fourier analysis. The results have been compared with the theoretical predictions of Ogilvie (1963), Vada (1987) and Wu and Eatock Taylor (1990) and the experimental results of Chaplin (1984).

This Thesis will consider the development of the traditional bill of lading from its origins, which appear to be much older than previously considered, up to the present day. The development of the bill of lading will be examined in order to answer basic questions: what is a traditional bill of lading, and what functions does it perform. In Part I of the Thesis the development of the three main functions of the traditional bill will be considered, namely receipt, contract, document of title. It will conclude with observations on the nature of the traditional bill of lading and how it differs from the early form of the bill of lading. Part II of the Thesis will then consider the development and nature of related shipping documents (charterparty bills, received for shipment bills, non-transferable bills), how far these documents perform the functions of the traditional bill of lading, and whether they can be truly described as bills of lading. Part II will then go on to consider the development and nature of electronic bills of lading and assess how well such bills perform the functions of the traditional bill of lading. The Thesis will conclude that although most of the functions of the traditional bill are in effect performed by electronic bills, electronic bills are in fact a new type of bill of lading and not merely a traditional bill in an electronic format. Conclusions will then be drawn as to what effect the development of new types of bill of lading will have on the future of the traditional bill of lading in the maritime industry.

Suction caissons are a foundation system for offshore structures which offer a number of advantages over traditional piled foundations. In particular, due to the method of installation used, they are well suited for deep-water applications. The suction caisson consists of an open ended cylindrical shell, which is installed below the seabed in a sequence which consists of two loading phases. The caisson is first installed part way under self weight, with the installation being completed by lowering the pressure within the cylinder and thus allowing the ambient water pressure to force the caisson into the ground. This thesis examines a number of structural issues which result from the form of the caisson — essentially a thin walled cylinder — and the interaction of the caisson with the surrounding soil during installation. To do this, variational analysis and nonlinear finite element analysis are employed to examine the buckling and collapse behaviour of these cylinders. In particular, two issues are considered; the influence of the open end, and the interaction between the cylinder and soil on the buckling and collapse loads. First, the behaviour of open ended cylinders is considered, where the boundary condition at the open end is allowed to vary continuously from completely free to pinned, by the use of a variable lateral spring. This lateral spring restraint may be considered to represent the intermediate restraint provided by a ring stiffener which is not fully effective. The effect of various combinations of boundary conditions is accounted for by the use of a multiplier on the lower bound to the buckling load of a cylinder with classical supports. The variable spring at the open end may also be considered to be an initial, simple representation of the effect of soil restraint on the buckling load. More complex representations of the soil restraint are also considered. A nondimensional factor is proposed to account for the influence of this spring on the buckling load. One combination of boundary conditions, where the upper end of the caisson is pinned, and the lower end free (referred to as a PF boundary condition), is found to have buckling and collapse behaviour which is unusual for cylindrical shells. Buckling loads for such shells are much lower than would be found for cylinders with more typical boundary conditions, and of similar dimensions. More unusually however, PF cylinders are shown to have positive postbuckling strength. The behaviour is found to be a result of the large flexibility which results from the low restraint provided by the PF boundary conditions. This is shown by continuously decreasing the flexibility of the cylinder, by increasing the axial restraint at the pinned end. It is shown that this results in a large increase in buckling load, and a return to more usual levels of imperfection sensitivity. In particular, with an intermediate level of axial restraint, buckling loads and imperfection sensitivity are intermediate between those of PF shells with no, and with full, axial restraint. Overall however, collapse loads for PF cylinders with no additional restraint are well below those of cylinders with stiffer boundary conditions, for equal geometries. Eigenvalue buckling of cylinders fully and partially embedded in an elastic material are examined, and two analytical solutions are proposed. One of these is an extension of a method previously proposed by Seide (1962), for core filled cylinders, to pin ended cylinders which have support from both a core and a surrounding material. The second method represents the elastic support as a two parameter foundation. While more approximate than the first method, this method allows for the examination of a wider range of boundary conditions, and of partial embedment. It is found that the buckling load of the shell/soil system decreases as the embedment ratio decreases. Collapse of fully and partially embedded cylinders is also examined, using nonlinear finite element analysis. The influence of plasticity in the soil is also considered. For cylinders with small imperfections, it is found that the collapse load shows a large increase over that of the same cylinder with no soil support. However, as the size of initial geometric imperfections increases, it is found that the collapse load rapidly approaches that of the unsupported cylinder. In particular, in weak soils the gain in strength over the unsupported shell may be minimal. The exception to this is again PF cylinders. As these have relatively low collapse loads, even very weak soils are able to offer an increase in collapse load over the unsupported case. Finally, a summary of these results is provided in the form of guidance for design of such structures.

[Truncated abstract] The axial performance of piles in sand remains an area of great uncertainty in geotechnical engineering. Over the years, database studies have shown that the existing method for offshore piles (e.g. API 2000) is unreliable. There is therefore a clear need for an improved predictive method, which incorporates the state-ofthe- art understanding of the underlying controlling mechanisms. This Thesis is dedicated to address the factors influencing the end bearing performance of displacement piles in siliceous sand with a view to proposing and justifying an improved design formulation. Firstly, a database of displacement pile load tests in sand with CPT data was compiled in collaboration with James Schneider (Schneider 2007). It features the widest database with also the latest available pile load test data (e.g. Euripides, Ras Tanajib, Drammen etc) in electronic form. Evaluation of the three new CPTbased methods (Fugro-05, ICP-05 & NGI-05) against this database has revealed a broadly similar predictive performance despite their end bearing formulations being remarkably different. This anomaly promoted the author to extend the database to include additional tests with base capacity measurements to form new base capacity databases for driven and jacked piles, which resulted in the UWA- 05 method for end bearing of displacement piles in sand. This method accounts for the pile effective area ratio, differentiates between driven and jacked piles, and employs a rational qc averaging technique. ... Field tests were performed in Shenton Park, Perth to supplement the database study and, in particular, to examine the effect of the incremental filling ratio (IFR). 10 open-ended and 2 closed-ended piles were tested in compression followed by tension. The test results provide strong support for the UWA-05 method for base capacity evaluation employing the CPT qc values and the effective area ratio. A series of jacked pile tests was carried out on the UWA beam centrifuge, to further explore the factors affecting pile base response. In total, four uniform and four layered centrifuge samples were prepared and tested at various stress levels and relative densities using three separate pile diameters. The resistance ratio (qb0.1/qc,avg) is found to be independent of the absolute pile diameter, effective stress and soil relative density. The tests in layered soil enabled quantification of the reduction in penetration resistance when a pile/cone approaches a weak layer and revealed the significant influence on base stiffness of underlying soft clay layers. The stiffness decay curves (G/GIN vs. w/D, where GIN is initial operational shear stiffness) measured in static load tests were found to vary with ratios of GIN/qc, while there was a unique relationship between G/GIN and qb/qc. A detailed parametric study was carried out (using the FE code PLAXIS) by idealising pile penetration using a spherical cavity expansion analogue in layered soil. The numerical predictions compare well with the centrifuge results and their generalization enabled guidelines to be established for end bearing in layered soil.

Thesis (Ph. D.), Memorial University of Newfoundland, 1998. / Bibliography: leaves 264-272.