Guo-ping Miao

A Time Domain Investigation on the Hydrodynamic Resonance Phenomena of 3-D Multiple Floating Structures

A 3-D time domain method is developed to investigate the gap influence on the wave forces for 3-D multiple floating structures. Special hydrodynamic resonance due to small gaps between multiple floating structures on wave forces is examined. Strong and complicate hydrodynamic interactions between the floating bodies are observed and the numerical computations have proved the existence of the sharp peak force response on each floating body at some special resonant wave numbers. By comparison with the results from the frequency domain technique, the results obtained from the time domain method reveal the similar resonant phenomena and hydrodynamic interaction. The resonant wave numbers are also proved around kL=nπ(n = 1, 2,...,∞) with a corresponding frequency shift. The strong hydrodynamic interaction feature is practically significant for the design of module structures and the links (connection) in whole the floating body system.

A Multi-Body Space-Coupled Motion Simulation for A Deep-Sea Tethered Remotely Operated Vehicle

A multi-body coupled dynamic model is developed to simulate the motion of a Tethered Remotely Operated Vehicle (TROV) system. A strong nonlinear coupling motion between umbilical tether and ROV is discussed.The movement of ROV is considered as six-degrees of freedom. The lumped mass model is applied and an averaged tangential vector technique is included in the three-dimensional dynamic response equations of the cable-segments. The model can simulate the three-dimensional transient coupled motion of the complex multi-body system in typical ship maneuvering conditions and can be used in either a towing problem or a tethered underwater vehicle problem. Simulation results are seen to fit well with the experiment.

ANALYTICAL MODELS OF FLOATING BRIDGES SUBJECTED BY MOVING LOADS FOR DIFFERENT WATER DEPTHS

There are two types of floating bridge such as discrete-pontoon floating bridges and continuous-pontoon floating bridges. Analytical models of both floating bridges subjected by moving loads are presented to study the dynamic responses with hydrodynamic influence coefficients for different water depths. The beam theory and potential theory are introduced to produce the models. The hydrodynamic coefficients and dynamic responses of bridges are evaluated by the boundary element method and by the Galerkin method of weighted residuals, respectively. Considering causal relationship between the frequencies of the oscillation of floating bridges and the added mass coefficients, an iteration method is introduced to compute hydrodynamic frequencies. The results indicate that water depth has little influence upon the dynamic responses of both types of floating bridges, so that the effect of water depth can be neglected during the course of designing floating bridges.

The Radiation and Diffraction of Water Waves by a Bottom-Mounted Circular Cylinder in a Two-Layer Fluid

An analytical method was proposed to analyze the radiation and diffraction of water waves by a bottom-mounted circular cylinder in a two-layer fluid. Analytical expressions for added mass and damping coefficients, as well as the wave excitation forces of the circular cylinder were obtained by an eigenfunction expansion method. The hydrodynamic forces on the bottom-mounted circular cylinder in a two-layer fluid include not only the added mass and damping coefficients, but also the wave forces of the surface and internal-wave modes. This is different from the case of a homogenous fluid. Some examples were given, showing that density stratification can have a relative large effect on these hydrodynamic forces over a wide range of frequencies

The radiation problem of multiple structures with small gaps in between

Influence of gaps on hydrodynamic interactions of multiple floating structures is considered in the present investigation. Strong and complicate hydrodynamic interactions between the floating bodies are observed and the numerical computations have showed the existence of the sharp peak force response on each floating body at some special resonant wave numbers, which are also proved to be around kL=nπ (n=1, 2, …, ∞) with a corresponding frequency shift. Width and depth of a gap also give influences on the resonant frequency and resonant amplitude of added mass and damping forces due to the radiation motions of the multiple bodies. The strong hydrodynamic interaction feature may have a big influence on the integrated loads of multiple floating structures system.

Numerical simulation for green water occurrence

Abstract A technique of dynamic mesh is specially introduced in a 2-D numerical wave tank to simulate the green water incident on a fixed FPSO model in head waves and oscillating vessels in beam sea conditions, respectively. Numerical results agree well with the corresponding experi- mental ones. It indicates the present numerical scheme and method can be used to actually simulate the phenomenon of green water on deck, and to predict and analyze the impact forces on floating structures due to green water. It is of great significance to further guide the ship design and optimization, especially for ship bow and its strength design. The mechanism may also help seaman to impose operation restrictions to avoid severe green water incidents.

FLOW NOISE MEASUREMENT OF SURFACE SHIP WITH TOWED MODEL

In this article, a new acoustic test technique using towed model was introduced to study flow noise caused by a surface ship. The project of model test was be properly designed for acoustic signal collecting and with the help of appropriate data processing method different kinds of acoustic sources could be successfully identified. A lot of work about fuid noise could be carried on with the towed model, and the noise corresponding to low frequency which is especially interested for its long distance radiating with small attenuation could also be studied in this way.

A linear hybrid model of MSE and BEM for floating structures in coastal zones

A linear hybrid model of Mild Slope Equation (MSE) and Boundary Element Method (BEM) is developed to study the wave propagation around floating structures in coastal zones. Both the wave refraction under the influence of topography and the wave diffraction by floating structures are considered. Hence, the model provides wave properties around the coastal floating structures of arbitrary shape but also the wave forces on and the hydrodynamic characteristics of the structures. Different approaches are compared to demonstrate the validity of the present hybrid model. Several numerical tests are carried out for the cases of pontoons under different circumstances. The results show that the influence of topography on the hydrodynamic characteristics of floating structures in coastal regions is important and must not be ignored in the most wave period range with practical interests.

The wave forces and moments on a floating rectangular box in a two-layer fluid

A comprehensive set of computational formulations is presented for the hydrodynamic forces on a floating rectangular box in a two-layer fluid by matching eigen functions of the interior and exterior problems. Some examples are given and the results indicate that density stratification can have a relative large effect on the hydrodynamic forces on the floating rectangular box over a wide range of frequencies.