The two aims of this work were: (1) to develop a theoretical technique for determining the conditions where a broach would occur, and (2) to identify the principal factors affecting the liability of a ship to broach. The first step was to develop a mathematical model based on the conventional manoeuvring equations with coefficients which were functions of the ship's longitudinal position in the wave, but independent of encounter frequency. Next, a theoretical method for calculating the values of some of the coefficients as functions of wave position was developed using a strip theory approach and the results compared with those obtained experimentally. The experimental technique involved using a planar motion mechanism to oscillate a constrained model balanced on a wave created by a wave dozer in a circulating water channel. Although the agreement was poor and experimental scatter high for some of the coefficients, the more important ones were predicted quite well using the theory. Constrained model experiments were also --carried out in calm water in order to determine the approximate value of the roll coupling terms and it was found that, since they were small, the roll equation could be ignored as a first approximation. It was then possible to study the stability of the lateral and longitudinal motions separately for various wavelengths and to determine that the principal factor causing a broach was the large wave induced yaw moment combined with the small restoring moment available from the rudder operating with reduced effectiveness. The lateral and longitudinal equations were then combined using a digital/analogue hybrid simulation permitting the conditions which caused a broach to be determined. When the results from the simulation-were compared with results which had already been carried out by the Admiralty Marine Technology Establishment at Haslar there was fairly good agreement, implying that this method could be used to determine whether a proposed design would meet an acceptable standard. Finally, possible improvements to the simulation were suggested and guidelines for reducing the liability to broach were given both for the operator and the designer.

This thesis is based on the application of hydraulic modelling techniques to the study of river rehabilitation schemes. River channelization and rehabilitation techniques are reviewed and the restoration of the River Idle is detailed. The rehabilitation of the Idle, consisting principally of the installation of a number of flow deflectors, forms the basis of the modelling work carried out. Open channel modelling techniques are reviewed and the packages ISIS, HEC-RAS, SSIIM and CFX are applied to the River Idle. Results from SSIIM (two dimensional) and CFX (three dimensional) are validated against site measured velocities. SSIIM predicted velocities calibrate poorly against site data whilst CFX results are considerably more encouraging. Reasons for the increased accuracy of the three dimensional results are discussed. The effect of the installation of the flow deflectors on aquatic habitat is simulated using the techniques underlying the Instream Flow Incremental Methodology (IFIM). The results from the one dimensional model ISIS and the three dimensional package CFX are used to make available habitat predictions. Results indicate an improvement in habitat for adult and spawning chub but a worsening of habitat for roach fry. However, habitat for roach fry can be expected to improve with time as the geomorphology of the river responds to the installation of the deflectors. The results from the habitat modelling exercise also indicate significant discrepancies between the results obtained by applying the one and three dimensional models. Greater improvements in habitat are indicated in the results from the three dimensional modelling approach. This can be attributed to a number of factors but most significantly the fact that the three dimensional model, in solving two further momentum balance equations, accurately simulates a plume of higher velocity which is produced by the narrowing of the channel width at the deflector. This plume of higher velocity is propagated downstream for some distance beyond the deflector and is associated with improved habitat suitability in the case of adult and spawning chub. The effect of the deflectors on the movement of sediments in the Idle is simulated using ISIS Sediment, a module of the ISIS package, and SHEAR. SHEAR is a FORTRAN program, written for this thesis, which calculates bed shear stresses from the vertical velocity distribution predicted by CFX. The predicted bed shear stresses are compared with a critical shear stress for erosion which is calculated from the Shields criteria. Deposition areas can be implied from zones of reduced bed shear stress. Thus, SHEAR is able to describe the spatial detail of erosion and deposition, for any given sediment particle size, at a specific discharge. Results from ISIS Sediment and SHEAR are compared qualitatively with site measurements of bed erosion that has taken place at a single deflector site. Results indicate that the programs have successfully reproduced the major features of the movement of sediments observed on site. These consist of the erosion of a scour pool adjacent to the deflector tip and deposition in the lee of the deflector leading to the development of a bank of sediment. Overall, significant benefits are indicated in a three dimensional approach over the more traditional one dimensional models. These are evident in both improved calibration with site measured velocities, better available habitat prediction and the ability to describe the spatial detail of erosion and deposition.

The thesis is concerned with an investigation of the possibilities of generating metric information and carrying out topographic mapping operations from side-looking radar images acquired from Earthorbiting satellites, as exemplified by the synthetic aperture radar (SAR) system flown onboard the Seasat satellite, Besides the theoretical analysis of the problem, several images covering test areas with different topographic characteristics have been used for extensive and comprehensive tests of the geometric accuracy of the SAR system; for experiments with digital monoplotting techniques applied to the SAR images; and for tests concerned with the detection and"interpretation of objects appearing on these images. The results show that metric information of a limited accuracy can be obtained from satellite SAR images. This could act as the basis for reconnaissance-type mapping at scales of 1: 250,000 and smaller. The geometric accuracy actually achieved does, however, depend heavily on the method used initially to process the SAR image data. In this respect, the results obtained with the digitally processed images are superior to those obtained with the optically processed images. The influence of the topographic relief present on the ground is also noticeable and various techniques have been devised and used to eliminate or substantially reduce this effect. The use of digital monoplotting techniques did not produce as good or as complete a rectification as expected due to the difficulties experienced with the interpretation of the terrain objects recorded on the SAR images. These result partly from the constraints in imaging direction that are an inherent feature of SAR imaging and which make the detection and interpretation of certain objects on an SAR image rather arbitrary. A further difficulty is the presence of background clutter on all the Seasat SAR images but which is especially noticeable on the optically processed images tested. At the present stage of the development and application of satellite SAR imagery for mapping, the limitations are centered around shortcomings in the image resolution and quality rather than the geometric characteristics of the imagery or the rectification techniques which have been devised and implemented for mapping purposes.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

No description available.

The beachface evolution in the swash zone under different single swash events is investigated by fully coupled simulations. Two fully coupled models (bed-load-only and combined load models) comprising the one dimensional shallow water equations and bed evolution equation are developed. The two coupled systems are solved by the specified time interval method of characteristics (STI MOC) (Kelly and Dodd, 2009, 2010), which can resolve shocks very accurately. The fully coupled bed-load-only simulations with six different sediment transport formulae for a single Peregrine and Williams (2001) (PW01) swash over an erodible plane beach all yield net erosion all over the swash zone. Consistent with Kelly and Dodd (2010), however, full coupling yields significantly less erosion for all the q=q(u) (q instantaneous sediment flux and u water velocity) formulae compared to the equivalent uncoupled results. It is also shown that including a dependence on h (water depth) in q can result in net deposition in the upper swash, and that with such a formula q the shoreline motion over a plane mobile beach is ballistic in the uprush. Bed shear stress described by the Chezy law is further included in fully coupled simulations, and much reduced maximum inundation and net offshore sediment transport are predicted both for q=q(u) and q=q(h,u). Although the net sediment flux at x=0 under one PW01 event is still offshore, deposition in the middle or upper swash may be predicted when bed shear stress is included. The fully coupled bed-load-only simulation with q=q(u) for a single Hibberd and Peregrine (1979) (HP79) swash event predicts considerable deposition in the swash zone. A backwash bore develops, associated with which a bed step forms when the shoreline catches up with the backwash bore. The subsequent shoreline movement is obtained by the Riemann solution for a wet-dry dam-break problem with a bed step. A bed step also occurs under a solitary wave simulation; its height is much larger than that under the HP79 simulation. Bed step height is found to depend largely on the water depth on the seaward side of the step, which is related to the swash event and the step position. The PW01 and HP79 swash events are also examined by the combined load model. Results show that suspended load results in deposition in the upper swash and erosion in the lower swash. However, pre-suspended sediment results in deposition in the lower swash, implying that net bed change due to suspended load in the lower swash could be depositional. The inclusion of suspended load has much smaller effect on the maximum inundation and swash hydrodynamics than bed load. The inclusion of bed load reduces the maximum inundation significantly; importantly, bed load results in the formation of a bed step and dominates the beach change near the bed step even when suspended load is dominant in the overall beach change.

It is common for field models of tight gas reservoirs to include several wells with hydraulic fractures. These hydraulic fractures can be very long, extending for more than a thousand feet. A hydraulic fracture width is usually no more than about 0.02 ft. The combination of the above factors leads to the conclusion that there is a need to model hydraulic fractures in coarse grid blocks for these field models since it may be impractical to simulate these models using fine grids. In this dissertation, a method was developed to simulate a reservoir model with a single hydraulic fracture that passes through several coarse gridblocks. This method was tested and a numerical error was quantified that occurs at early time due to the use of coarse grid blocks. In addition, in this work, rules were developed and tested on using uniform fine grids to simulate a reservoir model with a single hydraulic fracture. Results were compared with the results from simulations using non-uniform fine grids.

This project is a research into the effect of gas condensate damage in hydraulically fractured wells. It is the result of a problem encountered in producing a low permeability formation from a well in South Texas owned by the El Paso Production Company. The well was producing a gas condensate reservoir and questions were raised about how much drop in flowing bottomhole pressure below dewpoint would be appropriate. Condensate damage in the hydraulic fracture was expected to be of significant effect. Previous attempts to answer these questions have been from the perspective of a radial model. Condensate builds up in the reservoir as the reservoir pressure drops below the dewpoint pressure. As a result, the gas moving to the wellbore becomes leaner. With respect to the study by El-Banbi and McCain, the gas production rate may stabilize, or possibly increase, after the period of initial decline. This is controlled primarily by the condensate saturation near the wellbore. This current work has a totally different approach. The effects of reservoir depletion are minimized by introduction of an injector well with fluid composition the same as the original reservoir fluid. It also assumes an infinite conductivity hydraulic fracture and uses a linear model. During the research, gas condensate simulations were performed using a commercial simulator (CMG). The results of this research are a step forward in helping to improve the management of gas condensate reservoirs by understanding the mechanics of liquid build-up. It also provides methodology for quantifying the condensate damage that impairs linear flow of gas into the hydraulic fracture.

No description available.