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In an attempt to contribute the efforts for the robust and effective numerical tools concerning ship motions in astern seas, this thesis presents the development of a coupled non-linear 6-DOF model with frequency dependent coefficients, incorporating memory effects in random waves with a new axis system that allows straightforward combination between seakeeping and manoeuvring model whilst accounting for extreme motions. A combination of seakeeping and manoeuvring is achieved through the adoption of relatively new "horizontal body axis system" which accounts for large vertical motions as well. Furthermore, the frequency dependent terms are incorporated in order to improve the accuracy of the numerical model for non-zero encounter frequencies which are experienced especially when the ship has large heading angle. The effect of encounter frequency and so called "memory effects" are calculated in terms of radiation forces using convolution integrals. Equations of motions and external forces are described in terms of a new axis system. The wave forces are calculated through incident and diffraction wave forces. The incident wave forces are calculated using the instantaneous wave surface while low encounter frequency model is adopted for the calculation of diffraction forces. Finally, the whole numerical model is expressed in random sea environment including the convolution terms to carry out the simulations in more realistic sea environments. The validation of the numerical model with the results of benchmark tests commissioned by ITTC Specialist Group on Stability, showed reasonably satisfactory agreement while the inclusion of frequency dependent terms affected the accuracy of the numerical model. Parametrical studies were carried out to investigate the effect of different environmental and operational parameters to ship motions in extreme astern seas along with the effects of degrees of freedom and encounter frequency. In order to enhance the numerical model and to obtain further information about the coupling of the motions and the adequacy of the numerical model to carry out further simulations regarding dangerous situations during ship motions in random following and quartering seas, extensive captive and free running model tests were carried out. The numerical model provided good agreement with the experiments. The terms resulting from the coupling of vertical motions and large heeling angle to wave forces are obtained. It is believed that the numerical model has a good potential for providing a more rational basis for predicting the dangerous conditions which a ship could face in extreme astern seas, and for offering insights about the link of behaviour with the design parameters of a ship in the light of the validation with the experiment results and parametrical studies.

The United States Navy Meteorology and Oceanography (METOC) community routes ships for weather evasion using advanced meteorological modeling and satellite data, but lacks a tool to enable fewer ship routers to make better routing decisions faster. Limited resources and rising costs are impacting the frequency and duration of current naval operations. The Commander, Naval Meteorology and Oceanography Command has ordered the community to find efficiencies and automation possibilities in order to meet lower manning levels, reduce waste, and increase savings. Outside of the Navy, Ocean Systems Incorporated in Alameda, CA developed the Ship Tracking and Routing System (STARS) software package to calculate optimum sea routes based on weather model data. However, METOC ship routers are reluctant to adopt this complex software. To help solve this, we modeled Optimum Track Ship Routing (OTSR) for U.S. Navy warships using a network graph of the Western Pacific Ocean. A binary heap version of Dijkstra's algorithm determines the optimum route given model generated wind and seas input. We test the model against recent weather data to verify the model's performance, and to historical divert route recommendations in order to validate against routes developed by OTSR personnel.

Three sets of algorithms are formulated for use in a variety of models :- * Ship performance algorithms. * Optimisation algorithms. * Environmental data. Optimisation models are constructed for deterministic minima, with time, fuel and cost objective functions. Models are constructed for an actual ship, (M. V. DART ATLANTIC), and realistic working solutions are obtained based on real-time weather information, simulating an actual on-board, computer based system, using dynamic programming. Several combinations of algorithm types are used in the the models, enabling comparisons of effectiveness. Thus, the ship performance algorithms incorporate severally; simple ship speed loss curves, ship resistance, ship motions and ship motion criteria databases devised from a linear seakeeping model. Limitations of the models are discussed from the routeing examples given. State space restrictions and originally devised methods to aid convergence in the models are discussed. Extension of the forecasted environmental data is achieved by a variety of methods and comparisons sought. In particular ECMWF surface pressure files are interrogated to produce sea wave fields over the extended period, establishing main disturbance centres. The variety of algorithms formulated in this work has facilitated real-time comparisons, this is particularly effective in route-updating. The development of these models and the methods used to extend the forecast period, and the comparisons and associated results stemming from these models are viewed as an original contribution to real-time weather routeing of ships.

In the present study, 3 wake parameters are semi-automatically measured in 63 composite-labeled images of a surface piercing propeller tested at yaw angles 0-30 degrees, pitch angles 0-15 degrees, propeller immersion ratios of 0.33 and 0.50 and scaled advance ratios 0.656-1.927. A fourth wake parameter is measured in four composite labeled images of yaw angles 0-30 degrees, pitch angle 0 degrees, immersion ratios of 0.33 and 0.50 and scaled advance ratios 1.363-1.927. Measurements are plotted against propeller's angular position. Major findings include the behavior of wake parameters as the values of scaled advance ratio, yaw angle, pitch angle, and immersion ratio vary. / by Luis Altamirano. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

This thesis deals with the squat of a moving ship; that is, the downward displacement and angle of trim caused by its forward motion. The thesis is divided into two parts, in which the ship is considered to be moving in water of constant depth and non-constant depth respectively. In both parts, results are given for ships in channels and in open water. Since squat is essentially a Bernoulli effect, viscosity is neglected throughout most of the work, which results in a boundary value problem involving Laplace's equation. Only qualitative statements about the effect of viscosity are made. For a ship moving in water of constant depth, we first consider a one-dimensional theory for narrow channels. This is described for both linearized flow, where the disturbance due to the ship is small, and nonlinear flow, where the disturbance due to the ship is large. For nonlinear flow we develop an iterative method for determining the nonlinear sinkage and trim. Conditions for the existence of steady flow are determined, which take into account the squat of the ship. We then turn to the problem of ships moving in open water, where one-dimensional theory is no longer applicable. A well-known slender-body shallow-water theory is modified to remove the singularity which occurs when the ship's speed is equal to the shallow-water wave speed. This is done by including the effect of dispersion, in a manner similar to the derivation of the Korteweg-deVries equation. A finite-depth theory is also used to model the flow near the critical speed. For a ship moving in water of non-uniform depth, a linearized one-dimensional theory is derived which is applicable to unsteady flow. This is applied to simple bottom topographies, using analytic as well as numerical methods. A corresponding slender-body shallow-water theory for variable depth is also developed, which is valid for ships in channels or open water. Numerical results are given for a step depth change, and an analytic solution to the problem is discussed. / Thesis (Ph.D.)--Applied Mathematics, 2000.