Wave Pressure Distributions Along the Midship Transverse Section of a VLCC

The external wave pressure distributions along the transverse section in the midship region of a VLCC are evaluated in this paper. The commercial hydrodynamic code WASIM issued by DnV has been adopted to perform the hydrodynamic computation. The ship hulls have been discretized with coarser and finer mesh to investigate the effect of panel size on the hydrodynamic pressures. It is found that the difference between these two mesh finenesses is small. It is also found that the roll damping has a significant influence on the wave pressure of vessel especially in beam sea. A sensitivity analysis is carried out in the sense of assessing the influence of the roll damping on the wave pressure. Finally, the long term prediction of the wave pressure has been compared for different roll damping values.

Experimental Study on New Wave Measurement Using Passive Underwater Acoustics

The passive acoustic-based wave measurement via hydrophones is presented in this paper. It has the potential to measure non-intrusively, implement with low cost and with higher resolution. Details of experiments, real-time data recording and processing are described respectively. Particularly, the portable data acquisition system based on virtual instrument technique is designed to make the in situ measurement convenient and user-friendly. Special emphasis is put on FFT filtering technique to band pass the signal fast and efficiently. The key wave parameters, i.e. the mean wave period and the significant wave height, can be obtained from the comparatively safe and stable underwater by means of submerged hydrophones. Considering the pressure sensor has been widely used in the ocean wave measurement, it is deployed simultaneously to test the feasibility of the new system. The result shows that the present measuring system can give satisfactory measurement of significant wave heights and average wave periods in shallow water despite of the little deviation.

3D Numerical Modelling of the Wave-Induced Response Around the Circular Caisson Founded on the Seabed

Wave-induced liquefaction is one of the main factors influence the stability of marine structures. However, the investigation on this phenomenon is complicated as the dynamic interaction between soil, pore fluid and the structure is closely coupled. In order to obtain a better understanding of the wave-induced response around the circular caisson founded in the seabed, three dimensional numerical analyses have been performed using the 3D finite element program DYNE3WAC in order to investigate the wave-induced response around the circular caisson.

Prediction of Longshore Sediment Transport Using Soft Computing Techniques

An important task for coastal engineers is to predict the sediment transport rates in coastal regions with correct estimation of this transport rate, it is possible to predict both natural morphological or beach morphology changes and the influence of coastal structures on the coast line. A large number of empirical formulas have been proposed for predicting the longshore sediment transport rate as a function of breaking wave characteristics and beach slope. The main shortcoming of these empirical formulas is that these formulas are not able to predict the field transport rate accurately. In this paper, an Adaptive-Network-Based Fuzzy Inference System which can serve as a basis for consulting a set of fuzzy IF-THEN rules with appropriate membership functions to generate the stipulated input-output pairs, is used to predict and model longshore sediment transport. For statistical comparison of predicted and observed sediment transport, bias, Root Mean Square Error, and scatter index are used. The results suggest that the ANFIS method is superior to empirical formulas in the modeling and forecasting of sediment transport. We conclude that the constructed models, through subtractive fuzzy clustering, can efficiently deal with complex input-output patterns. They can learn and build up a neuro-fuzzy inference system for prediction, while the forecasting results provide a useful guidance or reference for predicting longshore sediment transport.

Performance of Perforated Wall for the Conditioning of the Flow in an Ocean Basin

This paper discusses the investigations conducted to develop the hydraulic design of the flow conditioner of the current generation system of LabOceano. The performance of different flow conditioner configurations were numerically investigated by means of computational fluid dynamics techniques. The numerical results were validated against experimental data, showing a good performance of the numerical model in predicting the main flow characteristics. It was observed that undesirable high angles of incidence of the flow occur upstream of the flow conditioner, indicating that the culvert geometry is not of much help to contribute to the conditioning of the flow. However, the results demonstrate that, in spite of such an adverse inflow conditions, the classical solution based on the perforated plate concept works very well.

Dynamic Simulation of Immersion of Tunnel Elements for Busan – Geoje Fixed Link Project

Construction of an 8.2km motorway between Busan — Korea’s southernmost, second largest city — and the island of Geoje, called the Busan-Geoje Fixed Link Project, is currently underway. As part of this four-lane fixed link, there will be a submerged tunnel section of 3.2km in length. COWI and Daewoo Engineering Co. have formed a joint venture (CDJV) to carry out the design of the immersed tube tunnel (Busan-Geoje Fixed Link Immersed Tunnel). The Immersed Tunnel consists of 18 Tunnel Elements and will be constructed from East to West. The immersed tunnel will become one of the longest in the world to date, especially in an area of significant seismic activity. Each of the 18 elements is identical, although they will be placed in water depths varying from 15m up to 50m subjected to waves and current. The prefabricated tunnel section will be brought to the site in a submerged condition, where it will be suspended from immersion rigs by four wire ropes. Each tunnel section will be lowered and connected to the previously installed element. The immersion rig pontoons and the submerged tunnel element will be moored to stay in position using as many as 14 wire ropes. This paper describes the unique immersion concept specially developed for this project, the salient features of each phase of analysis and the major conclusions. The findings in this study are expected to aid designers of similar immersion process concepts to ensure safe installation.

Comparison of Measured and Back Estimated Cone Penetration Resistance of Sand

The application of cavity expansion theory in the back estimation of cone penetration tests conducted in calibration chambers has been carried out by many researchers. However, the theory is seldom employed by centrifuge modelers. Based on the work of spherical cavity expansion of previous researchers, this study proposed an analytical solution that incorporates the effects of cone geometry and surface roughness and the effect of compressibility to estimate the cone tip resistance. The calculated results are compared with the measured cone penetration resistance of four cone penetration tests performed in the centrifuge. The cone penetration tests were conducted in granular soil specimens having relative densities ranging between 54% and 89%. The comparison demonstrates the capacity of the cavity expansion theory in the prediction of the centrifuge cone penetration resistance.

Nonlinear Crest Height Distribution in Three-Dimensional Ocean Waves

The interest and the studies on nonlinear waves are increased recently for their importance in the interaction with floating and fixed bodies. It is also well known that nonlinearities influence wave crest and wave trough distributions, both deviating from Rayleigh law. In this paper a theoretical crest distribution is obtained taking into account the extension of Boccotti’s Quasi Determinism theory, up to the second order for the case of three-dimensional waves, in finite water depth. To this purpose the Fedele & Arena [2005] distribution is generalized to three-dimensional waves on an arbitrary water depth. The comparison with Forristall second order model shows the theoretical confirmation of his conclusion: the crest distribution in deep water for long-crested and short crested waves are very close to each other; in shallow water the crest heights in three dimensional waves are greater than values given by long-crested model.

Experimental Study and Analysis of Different Air-Injecting Segment on the Separation Performance of Air-Injected De-Oiling Hydrocyclone

Developing state-of-the-art and separating principle of deoiling hydrocyclones are introduced. By theoretical analysis, the ways to enhance hydrocyclone’s separation efficiency are described. One way is to inject air into the hydrocyclones so as to combine with oil to form oil-gas compound body, and then increase de-oiling efficiency. By means of injecting air into large cone segment, or fine cone segment of the hydrocyclone, experiments were carried out. It is found that the best injecting part is fine cone segment. Further experimental studies were continued for confirming detail part in fine cone segment, which includes one-third segment and two-thirds segment for the sake of research. Results show that the best air-injecting part is the first one-third segment of fine cone segment. This conclusion would be useful for understanding of air-injected de-oiling hydrocyclone’s separating process, and for its design and applications.

Separated Flow About a Slender Body in Forward and Lateral Motion

This paper presents a solution method for obtaining the hydrodynamic forces and moments on a submerged body translating at a yaw angle. The method is based on the infinite-fluid formulation of the Free Surface Random Vortex Method (FSRVM), which is re-formulated to include the use of slender-body theory. The resulting methodology is given the name: Slender-Body FSRVM (SB-FSRVM). It utilizes the viscous-flow capabilities of FSRVM with a slender-body theory assumption. The three-dimensional viscous-flow equations are first shown to be reducible to a sequence of two-dimensional viscous-fluid problems in the cross-flow planes with the lowest-order effects from the forward velocity included. The theory enables one to analyze effectively the lateral forces and yaw moments on a body undergoing prescribed forward motion with the possible occurrence of flow separation. Applications are made to several cases of body geometry that are in steady forward motion, but at a yawed orientation. These include the case of a long “cone-tail” body. Comparisons are made with existing data where possible.