Thesis
Hydrodynamics of an unconstrained cylinder in forced roll
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2012
- Thesis identifier
- T13260
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- The research summarised in this thesis addresses the problem of determining the hydrodynamic properties of damaged ships subjected to forced oscillations in calm water. Traditionally forces of hydrodynamic reaction acting on a rigid body moving through a fluid are derived either analytically or numerically. The former approach is usually restricted to small amplitude motions of the body moving through an unbounded domain of ideal fluid. The methodology is relatively simple and computationally effective but, as experimental results suggest, accuracy of the prediction, particularly for roll motion is unsatisfactory even for intact ships. The advanced CFD-based techniques are more suitable in addressing this problem, particularly the case of a damaged ship, but they are computationally demanding. Therefore, in order to tackle the issue efficiently, there is a need for high-quality experimental data for validation of the numerical results. However, the experiments, particularly in roll, are very difficult and there is very little data available for the simpler case of intact ships and virtually none for damaged ships. As the problem involves complex nonlinear phenomena, the physical tests should be performed in a controllable environment and therefore, the 'classical' sea-keeping tests have very limited applicability in this respect. Furthermore, the calm-water experiments are usually performed with oscillations about a fixed axis and the adequacy of such an approach for investigating hydrodynamic properties of damaged ships can be questioned. That is, the physical tests on partially restricted models are of great value, particularly for validating analytical / numerical approaches, but the presence of constraints may introduce artificial conditions affecting the dynamical characteristics of the system. Accounting for this, the approach adopted in this thesis involves a freely-floating body subjected to harmonic excitations generated by an internal forcing mechanism. It is postulated that by removing all kinematic constraints the system can be analysed in the most realistic (achievable in calm water) and controllable configuration. Although use of gyroscopic moment generators for forced roll experiments is not a novelty, this methodology has never been fully exploited for measurements of hydrodynamic reaction forces acting on an unconstrained model of a damaged ship. As the experiments were unprecedented, they resulted in a modest amount of collected data but provided great opportunity for examining the nature and scale of the underlying phenomena. Furthermore, in the course of the research the methodology has been refined and has eventually reached the point at which it can be utilised to produce large amount of experimental data in an accurate and efficient way. From this perspective, the research is prenormative.
- Resource Type
- DOI
- Date Created
- 2012
- Former identifier
- 948158
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