Numerical calculation and model experiment of a novel external buoy type wave energy converter for navigation lighted buoys numerical study of a novel wave energy converter
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Abstract A novel external buoy type wave energy device with hydraulic conversion system used for navigation lighted buoys, named floating external double buoys wave energy device, is put forward and investigated by numerical calculations and model experiments. The hydrodynamic performance of the device under regular waves is numerically calculated based on linear potential flow theory and boundary element method. The generalized modal method is used to solve the hydrodynamic problems of multi‐buoy with hinged constraints. The model experiments are carried out in a 2D wave tank with a depth of 0.9 m. The wave height is set to 1/40 of the wavelength. The influence of wave period and damping loads on the hydrodynamic performance of the device is tested. The results of numerical calculations and model experiments have shown that the appropriate selection of hydraulic damping coefficient is of great significance to improve the capture width ratio of the device, and this device has good capture performance in a certain wave range, and it is expected to effectively solve the problem of continuous power supply for middle and small types of navigation lighted buoys.Keywords:
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Energy transformation
Single Buoy Moorings Inc. has designed and built a new tanker terminal which is being used by Societe Nationale des Petroles d'Aquitaine in the Ashtart field off the coast of Tunisia. A 70,000 ton tanker is used as the storage tank; the single-buoy mooring is anchored by six lines, and an articulated loading arm connects the buoy with the storage tanker. The arm is free to rotate. The storage facilities are connected to a production platform by a three mile long, 10 in, dia line which lines on the bottom of the ocean, about 70 m below the surface. Ships to be loaded approach the terminal from the rear and are secured by the mobile mooring lines. The ship can drift with the current during loading operations.
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The two Tension Leg Buoy (TLB) mooring system is a new type of early production system and has been designed to open up the oil fields in South China Sea. The system consists of two tension leg buoys and a mooring tanker, the mooring tanker is connected with the TLBs by wires, this mooring is a slack one, while the TLB is the taut mooring. The system is operating in a water depth of 40 m. In order to confirm the behaviour of this system in various combinations of wind wave and current, model tests were conducted in the wave tank of China Ship Scientific Research Center (69x46x4 m). During the test, the local current and wind generating facilities were used. Model tests of this system were performed for 9 different kinds of combination of wind, wave and current. In this paper, experimental results of the moored tanker and tension leg buoy, as well as those of tension variation in the leg of TLB are given. The behaviour of the system is analysed at the end of the report.
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The influence of the central platform on hydrodynamic performance of a wave energy converter (WEC) has remained elusive. To approach this dearth of relevant theoretical research, this paper presents a semi-submerged multi-buoy WEC and the results of the numerical analysis at different dimension parameters of the central platform of the WEC. The WEC consists of three oscillating buoys hinged with a central platform through multiple actuating arms. Numerical analysis revealed that there exists a relationship between the hydrodynamic performance of device and the geometry of the central platform. At the given wave condition, different central platform size would obviously affect the hydrodynamic performance and wave energy capture width ratio of the semi-submerged multi-buoy WEC. Additionally, appropriately increasing central platform draft would help to improve the wave energy capture capability of the oscillating buoys.
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A lot of research has been carried out regarding variations in mooring systems, one of which is the addition of buoys to the mooring system. In analyzing variations in mooring system designs, what needs to be considered is the reliability of the mooring lines. Therefore, in this research will analyze reliability on the effect of subsea buoy to the tension of mooring line with a variation position of subsea buoy. The variations on the position of one subsea buoy is arranged at the distance of the anchor 605 m, 577.5 m, 550 m, 522.5 and two subsea buoys at the distance from the anchor 605 m and 467.5 m. The analysis was performed for stand alone and offloading conditions with wave directions of 0 °, 45 °, 90 °, 135 °, 180 °. In this study to find the reliability of mooring lines, the author uses the Mean Value First Order Second Moment (MVFOSM) method. The results from this study, the probability of failure in the offloading condition without subsea buoy is 4.897E-17 and with subsea buoy (522.5 m) is 4.018E-17. Probability of failure in the stand alone condition without subsea buoy is 2.763E-16 and with subsea buoy (522.5 m) is 1.881E-16. From the probability of failure, the reliability of mooring lines in the offloading condition and stand alone condition without subsea buoy and with subsea buoy (522.5 m) is 1.00. The reliability calculation determined by DNV-OS E301, the results obtained meet the specified reliability criteria.
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Due to the ever increasing size of tankers and the inadequate facilities in the United States to accommodate these large vessels, a case is presented for the construction of offshore terminals utilizing the single buoy mooring system. Background information on the increase in size of tankers since 1961 is given, and a comparison of the single buoy mooring system to the offshore island terminal concept is also included. Reasons are given for preference of the single buoy mooring system over the offshore island, and several varied uses of the single buoy mooring system are also included in the discussion.
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Wave energy converter (WEC) designs are always discussed in order to find an optimum design to generate power. The power output from wave energy converters may be increase by controlling the oscillation in order to approach an optimum interaction between the WEC and the incident wave. However, in order to control the oscillation of the heave buoy, the wave profile and the device's response must be examined and fully understood. Analysis carried out by study heave buoys response on Malaysian water using MathCAD software. The results shows that the heave buoy give a good heave response with regards of the wave phase. In this particular area, it is estimated that the wave force can produce as much as 4x105 kW/m. From the response, the strategies to optimize power output can be proposed in order to maximize the active power to generate an optimum power output.
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This paper presents the design and analysis of the Ocean Sentinel instrumentation buoy mooring system, including numerical modeling and experimental validation testing during the summer of 2013. The intent of this study is to gather mooring data for the Pacific Marine Energy Center – North Energy Test Site (PMEC-NETS), and increase the understanding of numerical mooring models, which will contribute to improved designs of wave energy converter (WEC) mooring systems. The Ocean Sentinel instrumentation buoy (Ocean Sentinel) was configured in a three-point moor, with load cells on each mooring line, and the system was modeled using OrcaFlex. The model predictions of the mooring line loads are compared with actual experimental loads experienced during the summer 2013 deployment and the results are presented. Based on the results of the field testing, mooring system design improvements are proposed. This paper also includes wave data recorded during the deployment that was used in the numerical model to simulate the deployed conditions, as well as the simulated power output for a WEC array installation located at PMEC-NETS.
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To investigate the dynamic behavior of a mooring buoy installed in an open shore, a simplified simulation model is developed, which consists of the surging and heaving motions of a mooring buoy.
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A numerical model of two-buoy and single-buoy floating wave energy converters (WECs) is developed based on a modified nonlinear version of WEC-Sim. The model is validated against experimental data from a 1:5 geometric scale model of a two-buoy floating WEC. Nonlinear behavior is primarily attributed to viscous damping and mechanical friction effects. It is found that the modified WEC-Sim by correcting the phase of the wave excitation force in the source code provides an accurate representation of a two-buoy WEC operating in linear or nonlinear mode. An equivalent single-buoy WEC is modelled by locking the two-buoys together. The two-buoy WEC exhibits more than double the predicted maximum energy capture efficiency than its single-buoy counterpart within the range of numerical tests considered. Simulations of idealized floating WECs in conditions representative of Zhaitang Island, China indicate that the maximum energy capture efficiency may be enhanced by 13% when using a two-buoy system instead of a single-buoy WEC. The findings should be useful to practitioners involved in the design of floating wave energy converters.
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