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Results
Finite Water Depth Effect On Two Ship Interactions In Waves
Li, Lin (Advanced Analysis Department, American Bureau of Shipping) | McTaggart, Kevin (Virtual Naval Platforms Group, Defence Research and Development Canada โ Atlantic) | Hsiung, C.C. (Department of Mechanical Engineering, Dalhousie University)
ABSTRACT A numerical seakeeping prediction including the influence of finite water depth on two ship interactions in waves is presented. An algorithm is developed to solve the zero-forward speed free surface Green function for finite depth water by combining both the integral form and John's conventional expansion series form of the Green function. The effect of water depth on the double-body flow and associated m-terms is also considered. For the effect of water depth on two ship interactions in waves with forward speed, the coupled motions and the coupled hydrodynamic forces are solved by using a three-dimensional panel method which is based on the zero-forward speed free-surface Green function in finite depth of water with forward speed correct. The results have been verified through limited published data and show excellent agreement and consistency. INTRODUCTION Most studies examining ship to ship interactions assume deep water. Warship replenishment at sea is an example of a situation for which the deep water assumption is appropriate. Other ship interactions, such as vessel traffic in congested harbors, are often significantly influenced by finite depth of water, particularly in the case of interaction between a super-tanker and the passing-by small supply vessels. Accurate modeling of phenomena such as collisions and stranding can require full consideration of the effects of finite depth of water. Ship to ship interactions in finite depth of water have been investigated in recent decades, but, only few studies are published in the early time which including Dand (1975), Fujino (1976), and King (1977). However, most of these studies are based on two-dimensional flow in finite depth of water, using slender-body theory. Furthermore, treatment of the free surface is often simplified. Unsteady flow effects are typically ignored when examining ship to ship interactions in finite depth of water.
- North America > Canada > Nova Scotia (0.28)
- North America > United States > California (0.28)
- Transportation > Marine (0.88)
- Energy > Oil & Gas > Upstream (0.66)
Application of the Complementary Volume Method to Simulation of Flows On an Unstructured Grid
Zhao, Gang (Environmental Fluid Mechanics Laboratory Department of Civil and Environmental Engineering, Stanford University) | Kitanidis, Peter K. (Environmental Fluid Mechanics Laboratory Department of Civil and Environmental Engineering, Stanford University) | Street, Robert L. (Environmental Fluid Mechanics Laboratory Department of Civil and Environmental Engineering, Stanford University)
ABSTRACT The complementary volume (co-volume) method is used to discretize the horizontal viscous terms of the Navier-Stokes equation on a triangular unstructured grid. With the co-volume method, the horizontal viscous terms can be discretized without any interpolation. And the covolume method is less expensive than higher-order interpolation schemes. The co-volume method is implemented within the UnTRIM code. Simulation results of test cases show that the co-volume method is less diffusive than the first-order interpolation scheme used in the original UnTRIM code. INTRODUCTION Unstructured grids are being used more and more in numerical simulations, as they have the attractive property that they can be applied to complex geometries while smoothly following the boundaries. Also, an unstructured grid can be easily refined locally, which enables more resolution in regions of interest. One of the challenges from using an unstructured grid is the discretization of the horizontal viscous terms in the Navier-Stokes equations. Since the locations where the velocity components are stored are not aligned, interpolations are usually carried out to obtain the required velocity components or gradients to discretize the horizontal viscous terms (Mavriplis, 1997). First-order interpolation introduces too much numerical diffusion, while higher-order interpolation schemes are extremely expensive on unstructured grids. In the current work, the complementary volume (co-volume) method (Choudhury and Nicolaides, 1990) is used to discretize the horizontal viscous terms on the triangular unstructured grid. Using the co-volume method, the viscous terms can be discretized without any interpolation, and the cost of the co-volume method is less than other standard higher-order interpolation schemes. NUMERICAL SCHEMES The UnTRIM model The co-volume method is implemented within UnTRIM (Casulli and Zanolli, 2002). UnTRIM is a three-dimensional hydrodynamic model with a free surface solver. The governing equations are the Navier- Stokes equations and the depth-integrated continuity equation (Eqs. 1~4).
Mathematical Model of Spit Growth In Serayu Estuary, Central Java, Indonesia
Salim, HangTuah (Department of Ocean Engineering, Bandung Institute of Technology) | Kusuma, Syahril Badri (Department of Ocean Engineering, Bandung Institute of Technology) | Nazili, Nazili (Department of Ocean Engineering, Bandung Institute of Technology)
ABSTRACT Due to the economic crisis struck the South Asian State in 1997, Indonesia experience the worst impact among other Nations in the region, the construction of power plant has been slowing down. In order to catch up with the power demand, several coal power plants are being constructed. One of them is Cilacap Coal Fire Power plant sited near Serayu river mouth. The morphology of the river mouth is very dynamic; it changes accordingly due to waves, tides, and upland flow. A mathematical model which incorporates all the driving forces caused by waves, tides, and upland flow was developed in order to predict the morphological changes caused by the construction of power plant facilities such as cooling water intake, water discharge, and coal unloading terminal. The input of the model are tidal elevations, wave climate predicted by hind casting, upland flow, bathymetry, and sediment properties. The model was verified and calibrated by the actual morphological change taking place in the river mouth. The model was used to predict the morphological changes, sedimentation in the harbor basin of coal unloading terminal, and the bathymetric changes. This model has helped the engineer in planning and designing the coastal protection measures. INTRODUCTION State electric power company PT PLN is responsible for providing the electricity to the public. Increasing demand for power has forced PT PLN to allow private company own the power plant and its power will be bought by PT PLN with prenegosiated price. High cost of fossil fuel caused the government to transform the diesel power plant to more economical coal fired power plant and to promote the third party to build new power plants. Private sectors have strong interest in this business and one of the private power plant is being built in the estuary of Serayu river whose
- Asia > Indonesia > Sumatra (0.41)
- Asia > Indonesia > Central Java (0.40)
- North America > United States > California (0.29)
- Energy > Power Industry > Utilities (0.54)
- Water & Waste Management > Water Management > Water Supplies & Services (0.49)
ABSTRACT Submerged breakwaters are becoming popular alternative to coastal protection where a moderate degree of energy transmission is acceptable. Such situations induce a complicate wave field because of non-linear wave-structure interactions. In front and behind the structures local scour and changes of the bottom topography may take place due to the wave field. This paper will present some results from large scale model tests conducted at the "Grosser WellenKanal" of Hannover, Germany. The decomposition phenomenon of nonlinear wave trains passing over a submerged breakwater has been investigated. Spectral energy distribution and total amount of energy within the spectra of mono-component wave trains shows a significant dependency on the position of wave gages in the wake of the barrier since all Fourier based analysis techniques are incapable to identify non-stationary processes. The Hilbert-Huang Transformation (HHT) is chosen to operate as a more appropriate tool to better understand the nonlinear processes of the transmitted transient waves induced by the presence of the obstacle. Results of this technique are shown and prove that the non-stationary sea states behind the structure are essentially composed of individual dispersive waves which are phase shifted in the wake of the structure and propagating individually to generate a beat effect. INTRODUCTION Real sea waves are non-linear and non-stationary and their profile is asymmetrical with regarding the zero level. The existence of small ripples riding longer waves, as well as the creation of many small waves resulting from wave breaking, complicates considerably the sea surface profile. The wave data records are a mixture of various wave systems with different periods and energy, generated by different sources. In general, water surface records in Coastal and Ocean Engineering are predominantly examined with time series analysis methods and Fourier analysis techniques.
- North America > United States > California (0.28)
- Europe > Germany > Lower Saxony > Hanover (0.25)
Mooring Method of Very Large Floating Structure
Nagai, Baku M. (Study Group of Hexa-FloatTM, Faculty of Engineering, University of the Ryukyus) | Ameku, Kazumasa (Study Group of Hexa-FloatTM, Faculty of Engineering, University of the Ryukyus) | Nagai, Yoshioki (Study Group of Hexa-FloatTM, Faculty of Engineering, University of the Ryukyus) | Izumikawa, Tatsuya (Study Group of Hexa-FloatTM, Faculty of Engineering, University of the Ryukyus)
ABSTRACT Mooring method of very large floating structure (VLFS) is one of the most important subjects in ocean engineering, since a practical, realistic method has not yet been developed. Authors have reached to a new mooring method after the experience of severe drifting of the VLFS. Proposed new systems are combinations of an inter-sinker, an inter-buoy and an anchor-sinker. Since the motion of VLFS and acting any forces acting on it are of oscillating nature even in the wild wave conditions, the up and down motions of the inter-sinker and the inter-buoy could store the swaying energy of the float and release it periodically. Then, the system prevents the drift of the anchor-sinker or from breaking the mooring chain. INTRODUCTION Authors have constructed a multi-purpose Hexa-FloatTM made of concrete, the surface shape of which is hexagonal with sides of 10 m in length and the height is 2.5 m. Hexa-Floats could be connected each other with ropes and rubber and cover the sea surface in any desired shapes. Since the multi-connected Hexa-Floats has better wave resistance performance than any other rigid large structures by their flexibly connecting method. It can be used for many purposes such as the base of sea diving, fishing, and swimming pool on the ocean, cultivation of marine products and the wind power stations. Figure 1 is a concept of multi-connected Hexa-floats making floating islands, and figure 2 shows the first prototype of Hexa-Float constructed in 2002. The weight of the first Hexa-Float is 480 tonf in air and anchored by a steel chain and a concrete sinker, which weighted 16.3 tonf in seawater. Sea depth is about 20 m at the point and the length of the chain is 50 m.
- Asia (0.31)
- North America > United States > California (0.30)
Advanced Evacuation Simulation of Emergency Preparedness For FPSO Conversion
Kim, Hyunseok (Naval Architecture and Marine Engineering, Universities of Glasgow and Strathclyde) | Vassalos, Dracos (Naval Architecture and Marine Engineering, Universities of Glasgow and Strathclyde) | Zhou, Yili (Marine and Offshore Engineering, Ngee Ann Polytechnic)
ABSTRACT This paper focuses on testing the applicability of the Advanced Evacuation Analysis to a FPSO conversion in a Singapore shipyard and examines the applicability of the information derived for use in emergency preparedness during shipbuilding and ship repair and for the effective deployment of human resources whilst accounting for ease of evacuation. One FPSO has been modelled to illustrate the practical usage of the advanced evacuation simulation application in the offshore industry. The results also have been checked via evacuation drills to verify the accuracy of the computer simulation. INTRODUCTION During shipbuilding and ship repair activities, fire on board a ship constitutes the principal hazard that may lead to people evacuation. If this hazard develops into an uncontrollable situation, it must be ascertained a priory that all people on board can be evacuated safely. Evacuation analysis should therefore be aimed at developing a system that guarantees this assertion to an acceptable level by utilising advanced consequence analysis tools for fire and evacuation within a risk assessment framework. Evacuability in this respect represents a risk measure of evacuation of people on board expressed as an index, for a given pertinent scenario, environment, distribution and demographics of human resources and initial response time. Developing such a system will ensure focus on safety of human resources in a systematic and all embracing way that safeguards against the consequences from principal hazards, such as fire, leading to abandoning a ship or mustering to a safe refuge onboard. As a part of safety regulations implemented in Singapore yards, there is a requirement to perform evacuation drills twice a year to identify any problems or further improvements for safety aspects. This involves a reasonable mount of manpower and time, and thus the need of using a proper simulation model of such activities becomes apparent.
- Asia > Singapore (0.70)
- North America > United States > California (0.28)
- Transportation > Marine (0.67)
- Commercial Services & Supplies > Security & Alarm Services (0.60)
- Energy > Oil & Gas > Upstream (0.48)
The Effect of Wave Radiation Stresses On Tidal Current
Wang, Shipeng (State Key Laboratory of Coastal and Offshore Engineering. Dalian University of Technology) | Liang, Shuxiu (State Key Laboratory of Coastal and Offshore Engineering. Dalian University of Technology) | Sun, Zhaochen (State Key Laboratory of Coastal and Offshore Engineering. Dalian University of Technology)
ABSTRACT The effect of wave radiation stresses on tidal current is studied by adding wave radiation stress terms in 2D depth-averaged hydrodynamic model. To avoid the shortcomings of Longuet-Higgins' radiation stress computation, this model used the parabolic mild slope equation to calculate wave parameters. Wave shoaling and wave breaking effect can be included in nearshore region in this model. Wave radiation stress can be calculated by wave parameters over wave period. The results show that wave radiation stresses have little effect on tidal elevation, but a significant effect on tidal current with wave amplitude increasing. Wave-induced current will affect the current system when waves break in nearshore region. INTRODUCTION Wave and tide are the most important dynamic factors in nearshore region. They have effect on sediment transportation and concentration diffusion. In the last several decades there has been significant progress in the understanding and numerical simulating of ocean surface waves (e.g. Phillips 1977; Booij 1999a, 1999b) and similar progress has been made in ocean tidal current model (e.g. Blumberg and Mellor 1987). But wave and current compose a very complicated system in the nearshore region because of their interaction. Wave breaking when wave shoaling occurs will induce current in the nearshore. By far, most of the researches on this system still focus on single factor, rather than coupling effect. Tide effect was neglected when wave propagation is studied, and vice versa. Therefore the study on wave and current interaction is needed in this region. Wave and current interaction is a very difficult subject to study because they are in different scales in both spatial and temporal domain. The first approach is to simplify the periodic tidal current as a steady current with wave propagating in or opposite direction (Thomas, 1981, 1990; Simons, 1982, 1983; Li, 1990).
- Asia > China (0.30)
- North America > United States > California (0.28)
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.49)
Effect of Air-Injection Means On Separating Performance of De-Oil Hydrocyclone
Zhao, Lixin (School of Mechanical Science & Engineering, Daqing Petroleum Institute) | Jiang, Minghu (School of Mechanical Science & Engineering, Daqing Petroleum Institute) | Li, Feng (School of Mechanical Science & Engineering, Daqing Petroleum Institute) | Liu, Shumeng (School of Environmental Science & Engineering, Shanghai Jiaotong University)
ABSTRACT Experiments were carried out to study the effect of different air-injection means on the separating performance of de-oil hydrocyclone. Two kinds of air injection facilities, gas-liquid pump and air compressor, were adopted. The experiments show that the separation performance of the hydrocyclone with air injection through micro-pore section is the optimum, the efficiency can be enhanced up to 96.5%, while 85% for the hydrocyclone without air injection under the same other conditions, and the effect of different air-injection means varies. The split ratio of the air-injection hydrocyclone should be larger than normal. INTRODUCTION Since 1980s, hydrocyclonic separation technologies have been widely applied in petroleum, chemical, and environmental fields, especially on offshore application, where space is limited and valuable. When the hydrocyclones were used to treat oily sewage, the high speed rotation of mixed fluid inside hydrocyclones is very necessary for high efficient separation (Jiang, Zhao, Li, and Wang, 2000), but if the rotation speed is too high, the oil droplets will be sheared to much smaller that are difficult to be separated, for hydrocyclones are not very effective for fine droplets separation (Zhao, and Jiang, 2000; Jiang, Zhao, and Wang, 2002). For floatation oil-water separation, gas bubble is produced in or introduced to the mixed fluid. The bubble adheres with oil droplets to form oil-gas compound body, and then float up to the liquid surface by the function of floatation, so as to clean oily sewage. For the normal used floatation facility, due to the limitation of gas-dissolved capability, the dissolved gas amount is lacking, which results in the gas-liquid ratio can only reach about 10%. On the other hand, the diameter of gas bubble is larger, normally 0.2~2.5 mm. Therefore, the oil concentration range of oily sewage that the floatation facility can treat is limited
- Asia > China > Heilongjiang Province (0.29)
- North America > United States > California (0.28)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Gas-injection methods (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring (1.00)
- Facilities Design, Construction and Operation > Processing Systems and Design (1.00)
Motion of Float Collar of Gravity Fish Cage
Zheng, Y.N. (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Dong, G.H. (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Gui, F.K. (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Teng, B. (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Li, Y.C. (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology)
ABSTRACT This investigation focuses on the motion of the floating circle collar of the gravity fish cage exposed to the open ocean waves. Both numerical computation and physical experiment were conducted. Regular waves were experimented at the water depth of 20 m. Wave height is 4, 5.5, or 7 m, and wave period is from 5 to 9 s. The comparison between the computed results and the experimental data has verified the numerical method proposed in the paper. INTRODUCTION The problem of the demands for seafood has been becoming more and more severe in the world due to the expansion of the global population and the decline in the fishery supply. This problem of supply and demand has been solved, or rather, has been alleviated in the past two decades through the marine aquaculture in shallow water. Thus, the near-shore marine aquaculture has brought many achievements. Bessonneau and Marical (1998) simulated the dynamic behavior of some submerged flexible reticulated surfaces. Lee and Wang (2000) studied the dynamic behavior of the tension-leg platform with the netcage system and derived a set of equations of motion of a simplified two-dimensional case. Colbourne and Allen (2001) measured the waveinduced mooring line forces on a full-scale cage and the wave-induced loads and motions of a model cage. Fredriksson (2001) physically and numerically modeled the open ocean fish cage and the mooring system dynamics. Recently, the amount of the near-shore marine aquaculture has been decreased, because the near-shore marine aquaculture is not beneficial to the dispersion of wastes and the multipurpose utilization of the coastal line. These problems, by contrast, can be simply avoided by moving aquaculture into the deep sea. It is evident that the deep-sea aquaculture has many advantages, especially in the sense of the environmental protection and the near-shore development.
Evaluation of Wave-induced Liquefaction In a Porous Seabed: Using an Artificial Neural Network And a Genetic Algorithm -based Model
Cha, Daeho (Fred) (School of Engineering, Griffith University, Gold Coast Campus Gold Coast Mail Centre) | Zhang, Hong (School of Engineering, Griffith University, Gold Coast Campus Gold Coast Mail Centre) | Dong-Sheng, Jeng (Department of Civil Engineering, The University of Sydney) | Blumenstein, Michael (School of Information and Communication Technology, Griffith University, Gold Coast Campus Gold Coast Mail Centre)
ABSTRACT The evaluation of wave-induced liquefaction is one of the key factors for analysing seabed characteristics and the design of marine structures. Numerous investigations of wave-induced liquefaction have been proposed. However, most previous research has focused on complicated mathematical theories and laboratory work. In this study, we contribute an alternative approach for the prediction of the wave-induced liquefaction using an Artificial Neural Network (ANN) and a Genetic Algorithm (GA)-based model. Combined ANN and GA-based models are still a newly developed area in coastal engineering. In this study, a Genetic Algorithm-based approach is proposed to find optimal weights for the ANN model. It reduces the training time, and improves the forecasting accuracy for wave-induced maximum liquefaction depth, compared to using the normal ANN training procedure. Simulation results demonstrate the capacity of the proposed ANN model for the prediction of wave induced maximum liquefaction depth in addition to the proposal of GAs for training the ANN model. INTRODUCTION In the last few decades, various investigations of wave-induced seabed liquefaction have been carried out. The reason for the numerous research studies focused on this topic is that vertical movement of sediment, might cause the instability of the structure. Bjerrum (1973) is possibly the first person that considered the wave-induced liquefaction occurring in saturated seabed sediments. Later, Nataraja et al. (1980) suggested a simplified procedure for ocean wave-induced liquefaction analysis. Recently, Rahman (1991) established the relationship between liquefaction and characteristics of wave and soil. He concluded that liquefaction potential increases the degree of saturation with an increase of wave period. Jeng (1997) examined four different criteria of the wave-induced liquefied state, together with Zen and Yamazaki's (1991) field data. He also conducted a parametric study and concluded that no liquefaction occurs in a saturated seabed, except in very shallow water.