Hydrodynamic Interaction Of Fixed And Floating Bodies Theoretical And Experimental Investigations Of The Heave Resonance Phenomenon

This report describes the analytical method and numerical procedure for the calculation of the wave pressure distribution and resulting induced forces and moments acting on large displacement bodies in the sea. The added mass and damping coefficients for the structure oscillating in all six degrees of freedom is computed. Then, the hydrodynamic coefficients associated with both the wave/structure interaction and the oscillation of the structure are determined by use of a Green's function method using quadralateral elements of constant source strength which applies to large structures of rather general shape. The analysis is based on linear theory and viscous effects are neglected on the basis that the size of the structure is large in relation to the amplitude of the incident wave. Also, the equations of motion for a free-floating body are developed which yields the dynamic response of a floating body with linear mooring line forces. Finally, the computer program capable of carrying out the numerical calculations is outlined and the input/output is discussed in some detail. (Author).

(Uncorrected OCR) Abstract of thesis entitled "Hydrodynamic interaction between a fixed and a moving cylinder" submitted by Imam, Kazi Hassan for the degree of master of philosophy at the University of Hong Kong in August, 1995. The present experimental investigation concerns hydrodynamic interaction phenomenon between two bodies in fluid. It is a basic study of two-body problem. It focuses on the interaction phenomenon that takes place when a cylinder, rectangular or circular, is convected by the free stream toward another fixed circular cylinder. Emphasis is given over the effect of interaction on the velocity of the floating cylinder and the resulting force on the fixed cylinder. Cylinders of three geometric shapes, i.e. rectangular, circular and square, and six sizes are used as floating cylinder in combination with one fixed circular cylinder. The floating cylinders are made up of wood, PVC and Plexiglas. The fixed cylinder's material is Nylon. A load balance is designed to measure the force on the fixed cylinder. Details of its design and calibration are given. Video recording of the floating cylinder's motion is used to measure the change in its velocity. Details of the technique are provided. Expected interaction force on the fixed cylinder and retardation of the floating cylinder's velocity are found to exist, These quantities are studied in terms of the gap distance between the floating and the fixed cylinders as well as time. The change in velocity of the floating cylinder is found to agree well with the theoretical result. The force on the fixed cylinder is somewhat less than expected in the near field while it seems to agree in the far field though it is not absolutely conclusive due to the presence of noise in the force signals. The reason for the discrepancy in the results obtained in the near field is attributed mainly to viscous effects and the reason for the noises is attributed to different sources of vibration.

This book covers the basics of the hydrodynamics and vibration of structures subjected to environmental loads. It describes the interaction of hydrodynamics with the associated vibration of structures, giving simple explanations. Emphasis is placed on the applications of the theory to practical problems. Several case studies are provided to show how the theory outlined in the book is applied in the design of structures. Background material needed for understanding fluid-induced vibrations of structures is given to make the book reasonably self-sufficient. Examples are taken mainly from the novel structures that are of interest today, including ocean and offshore structures and components. Besides being a text for undergraduates, this book can serve as a handy reference for design engineers and consultants involved in the design of structures subjected to dynamics and vibration.

After determining a need to further investigate the hydrodynamic behavior of the side-by-side floating bodies at a close proximity, model scale experiments were conducted. This experiment changed parameters such as the gap width and wave heading to examine the effects of hydrodynamic interaction. Two initial gap widths, 300 and 450 mm, and four wave headings, 90°, 60°, 30° and 0°, were examined. Each experimental setup was examined over a range of wave frequencies, while free surface elevation and vessel motion responses were monitored and recorded. Analysis of the data showed the narrow gap resonance phenomena. However, the experiment did show little variation of the frequency where gap resonance occurred. Beam seas cases showed one peak frequency where values were significantly amplified compared to surrounding frequencies, while other wave headings showed two peak frequencies. There was little variation of the frequency where resonance occurred for each case. However, the magnitude of amplification did show significant variation over each case. The vessel motion response showed significant amplification over quite broad frequency bands. Beam seas cases showed very little pitch motion but head seas cases showed significant roll motion.

Challenges remain in the prediction of hydrodynamic interactions of multiple floating bodies in close proximity, such as side-by-side offloading and ship replenishment. During such operations, large free-surface elevations in the gap and body motions may occur, impacting operation and crew safety. In this thesis, numerical and experimental studies are presented, focusing on the two-body interactions in waves. Linear potential-flow based seakeeping programs have been widely employed to solve hydrodynamic interaction problems due to their high efficiency. However, these methods over-predict body motions, free surface elevations in the gap, and hence low-frequency loadings on the bodies. To suppress the over-predictions, artificial damping is required as input, which is typically obtained from model tests. With objectives of investigating the effects of viscosity and dynamic gap changes in the two-body interaction problem and developing a systematic approach to estimate the artificial damping for use in potential-flow tools, an immersed-boundary method based finite volume method solver has been implemented in the OpenFOAM framework. The pressure implicit with splitting of operators (PISO) algorithm is applied for velocity-pressure coupling. Free surface is captured using the geometrical volume of fluid method. The relaxation zone method is utilized for wave generation and absorption. To provide high-quality experimental data and to validate the numerical method, model tests on two identical box-like FPSO models arranged side-by-side in head waves at zero forward speed have been conducted in the towing tank of Memorial University. Besides, sources of uncertainties in the model test were identified, and comprehensive uncertainty analysis on the test results was conducted. A combined experimental and numerical approach has been developed to estimate uncertainties due to model geometry, model mass properties, and test set-up. Validation studies on the present flow solver were conducted by firstly simulating the present experiment for two-body interactions in head seas without forward speed. Further, the solver was validated by simulating the underway replenishment of a frigate and a supply vessel at a moderate speed. Simulations were also performed using a panel-free method based potential-flow program in the frequency domain. The numerical results from both methods were compared with each other and with the experimental data to identify sources of the discrepancies in potential-flow predictions. A quasi-steady approach, which accounts for the gap changes due to transverse drift forces at zero speed, was adopted to improve the potential-flow simulations.

The International Conference on Hydrodynamics is an increasingly important event at which academics, researchers and practitioners can exchange new ideas and their research findings. This volume contains papers from the 2004 conference covering a wide range of subjects within hydrodynamics, including traditional engineering, architectural and mechanical issues as well as significant new technologies and methodologies such as bio-fluid mechanics and computational fluid mechanics.

This book presents the proceedings of the Symposium on Fluid-Structure-Sound Interactions and Control (FSSIC), (held in Tokyo on Aug. 21-24, 2017), which largely focused on advances in the theory, experiments on, and numerical simulation of turbulence in the contexts of flow-induced vibration, noise and their control. This includes several practical areas of application, such as the aerodynamics of road and space vehicles, marine and civil engineering, nuclear reactors and biomedical science, etc. Uniquely, these proceedings integrate acoustics with the study of flow-induced vibration, which is not a common practice but can be extremely beneficial to understanding, simulating and controlling vibration. The symposium provides a vital forum where academics, scientists and engineers working in all related branches can exchange and share their latest findings, ideas and innovations – bringing together researchers from both east and west to chart the frontiers of FSSIC.