A finite element model for efficiency of a moored floating OWC device in regular waves (original) (raw)
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Ocean Engineering, 2004
This paper attempts to provide a better understanding of the hydrodynamic behaviour of a floating multi-resonant oscillating column wave energy device which combines the concept of a floating breakwater and a wave energy device. Experiments were conducted on a 1:20 scale model of the floating wave energy device moored by six mooring lines to study the dynamics of the device under regular waves for various scopes. The effect of non-dimensionalized wave frequency parameter on the motion response and mooring force are reported and discussed in detail in this paper.
Developing a Formula to Represent the Second-Order Wave Effects on Moored Floating Structures
2010
The effects of wave direction, frequency and the waterline shape of floating structures on the wave mean drift force formula have been considered separately by several authors but there isn't a general formula to take into account all of these effects. In this regard, Faltinsen's wave drift force formula has been modified by adding finite draft coefficient. The results obtained from this formula which is dependent on wave frequencies, has been compared with Helvacioglu's experiments favorably in high wave frequencies. Moreover, the influence of the current on the wave mean drift force has been taken into account by considering the current coefficient derived from the ship added resistance formula. In addition, the formula for the calculation of the wave drift damping has been extended to cover high wave frequencies as well as low wave frequencies. The results compared with asymptotic formula showed good agreement in the high frequency band.
Energies
This paper describes experimental research on a floating moored Oscillating Water Column (OWC)-type Wave-Energy Converter (WEC) carried out in the wave flume of the Coastal Engineering Research Group of Ghent University. This research has been introduced to cover the existing data scarcity and knowledge gaps regarding response of moored floating OWC WECs. The obtained data will be available in the future for the validation of nonlinear numerical models. The experiment focuses on the assessment of the nonlinear motion and mooring-line response of a 1:25 floating moored OWC WEC model to regular waves. The OWC WEC model motion has 6 degrees of freedom and is limited by a symmetrical 4-point mooring system. The model is composed of a chamber with an orifice on top of it to simulate the power-take-off (PTO) system and the associated damping of the motion of the OWC WEC model. In the first place, the motion response in waves of the moored floating OWC WEC model is investigated and the wat...
Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, 2004
A combined experimental/numerical investigation of a moored floating structure response to incoming waves to incoming waves is proposed. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used for ships and submarines in special docking operations. The dynamic wave response is investigated by performing experiments in a towing tank equipped with a wave maker. Experimental results are compared with numerical simulations in regular and irregular waves, showing a good agreement. In regular waves the predicted time histories of pitch, heave and surge motions of the three-body structure and of the mooring line forces, bear very satisfactorily the experimental results. The case of irregular waves is also encouraging, since the statistics of the response is correctly kept up to the fourth order statistical moments. This confirms that the theoretical model proposed in this paper is a suitable tool to predict the actual behaviour of a complex moored structure at sea.
2018
Floating Oscillating Water Column (OWC) type Wave Energy Converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave dissipation of a nearshore location. The performance of floating OWC WECs has been widely studied using both numerical and experimental methods. However, due to the complexity of fluid-structure interaction of floating OWC WECs, most of the available studies focus on 2D problems with limited Degrees-Of-Freedom (DOF) motion while 3D mooring effects and multiple-DOF motion have not been extensively investigated yet. Therefore, in order to gain a deeper insight of these problems, the present study focuses on wave flume experiments to investigate the motion and mooring performance of a 1:25 scaled floating OWC WEC model. As a preparatory phase for the MaRINET2 EsfLOWC (Efficiency & survivability of floating OWC) project completed by the end of 2017, the main ...
Ships and Offshore Structures, 2020
A reliable simulation model to calculate the motion and force responses of wave energy converters (WECs) is imperative to ensure the reliability and long-term performance of WEC systems; these aspects are fundamental to achieving full commercialisation of wave energy. A simulation model was developed and validated concerning the simulated WEC buoy motions in a previous study; this study validated the mooring force calculations for the same model. The example WEC system comprises a buoy, a power takeoff (PTO) system, and a three-leg mooring system wherein each leg is divided into two taut segments joined by a submerged float. A 1:20 physical model was built and tested in the Deepwater Offshore Basin at Shanghai Jiao Tong University. Numerical models were developed to simulate the coupled hydrodynamic and structural responses of the WEC system, primarily using potential flow theory, the boundary element method, the finite element method, and the Morison equation. The simulated and measured axial force results at the top ends of the six mooring segments were compared; the results agreed best in the lower segments of each mooring leg and in the moorings on the downwind side because of the PTO system uncertainties and the uncalibrated damping in the numerical model. Nonetheless, the numerical model reasonably predicted the moorings' accumulated fatigue damage, demonstrating that the model can be reliably used for mooring structural analyses. The study also used the validated numerical model to simulate a full-scale WEC system installed in Runde, Norway. A comparison of the results from the full-scale measurements and simulations shows that the numerical simulation model exhibited a good predictive capability for the mooring forces of the full-scale WEC system.
Performance Prediction of an OWC Wave Power Plant with 3-D Characteristics in Regular Waves
2012
The primary wave energy conversion by a three-dimensional bottom-mounted oscillating water column (OWC) wave power device in regular waves has been studied. The linear potential boundary value problem has been solved following the boundary matching method. The optimum shape parameters such as the chamber length and the depth of the front skirt of the OWC chamber obtained through two-dimensional numerical tests in the frequency domain have been applied in the design of the present OWC chamber. Time-mean wave power converted by the OWC device and the time-mean second-order wave forces on the OWC chamber structure have been presented for different wave incidence angles in the frequency-domain. It has been shown that the peak period of for the optimum damping parameter coincides with the peak period of the time-mean wave drift force when = 0.
Science Progress, 2022
A moored floating platform has great potential in ocean engineering applications because the mooring system is necessary to keep a floating platform in the station. It relates directly to operational efficiency and safety of a floating platform. This study presents a comprehensive assessment of the dynamics of a moored semi-submersible in waves by performing model test and numerical simulation. First, a three-dimensional panel method was used to estimate the motion of a moored semi-submersible in waves. A semi-submersible is modelled as a rigid body with six degrees-offreedom (6DOF) motion. Dynamic response analysis of a semi-submersible is performed in regular wave and irregular wave. Second, the model test is performed in various wave directions. An Optical-based system is used to measure 6DOF motion of a semi-submersible. Numerical results are compared with the experimental results in various wave directions. Wavelength and wave direction showed significant effects on the motion response of a semi-submersible in regular wave. Third, to obtain a better understanding of response frequencies, the time histories of motion responses in irregular wave are converted from the time domain to the frequency domain. Effects of the wave frequency component on motion responses and mooring dynamics are analyzed. Motion spectrum in irregular wave has a strong response to the natural frequency of a moored semi-submersible and the peak of wave frequency. Finally, exceedance probability is estimated to predict probable extreme values of motion responses of a moored semi-submersible as well as mooring dynamics.