Ships--Hydrodynamics

Linear and non-linear hydrodynamic coefficients of single and multiple hulls are
obtained using the boundary-integral method. For linear frequency-domain analysis, the
boundary-integral method based on a simple source distribution (Yeung [50] was used.
The nonlinear time domain simulations were carried out using a boundary-integral
algorithm based on the mixed Eulerian-Lagrangian (MEL) formulation (Longuet-Higgins
and Cokelet (19] ). Also, linear time domain simulations were carried out by utilizing a
simplified mixed Eulerian-Lagrangian formulation and the steady-state results compared
with that obtained from linear-frequency domain analysis. Both 2D and 3D results were
obtained for a range of parameters such as beam/draft, hull-separation/beam ratios and
frequency and amplitude of hull motions. The results shed light on complex wave-body
interactions involved in multi-hull ships and identifY critical hydrodynamic and
geometric parameters affecting their sea keeping performance. The computational tools
developed and the findings thus contribute to design of multi-hull ships for improved atsea
performance.

Numerical simulations of waterjet inlets have been conducted in order to understand inlet performance during ship turning maneuvers. During turning maneuvers waterjet systems may experience low efficiency, cavitation, vibration, and noise. This study found that during turns less energy arrived at the waterjet pump relative to operating straight ahead, and that the flow field at the entrance of the waterjet pump exhibited a region of both low pressure and low axial velocity. The primary reason for the change in pump inflow uniformity is due to a streamwise vortex. In oblique inflow the hull boundary layer separates when entering the inlet and wraps up forming the streamwise vortex. These changes in pump inflow during turning maneuvers will result in increased unsteady loading of the pump rotor and early onset of pump rotor cavitation.

The hydrodynamic interactions between ships in confined waters, restricted in width and depth, is analysed using a numerical surface singularity method called the Panel method. Based on potential flow and rigid free surface assumptions, a source distribution is utilized over the boundary surfaces to model the flow. The strength of the source distribution is obtained on satisfying the normal kinematic boundary conditions, i.e. as a solution of an integral equation. Discretization of the boundary surfaces yields a system of linear algebraic equations corresponding to the boundary integral equation, which then is solved numerically. From the singularity distribution, the velocity components, pressure coefficients and finally the interaction loads are calculated.

Technology movement toward deeper waters necessitates the control of vertically tethered systems that are used for installing, repairing, and maintaining underwater equipment. This has become an essential ingredient for the future success of the oil industry as the near-shore oil reservoirs are nearly depleted. Increased operation depths cause large oscillations and snap loadings in these longer cables. Research on this topic has been limited, and includes only top feedback control. The controllers developed in this thesis utilize top, bottom and combined top and bottom feedback. They are implemented on a discrete finite element lumped mass cable model. Comparison between PID, LQG and H infinity for all feedback combinations reveal that the Hinfinity controller with both top and bottom feedback has the best performance, while LQG has a more consistent and reliable performance for all feedback cases.