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Design and evaluation of linear and rotational generator scale models for wave tank testing
Published in C. Guedes Soares, Developments in Renewable Energies Offshore, 2020
Zahra Shahroozi, Mikael Eriksson, Malin Göteman, Jens Engström
Small-scale experiments in a controllable wave tank environment are important to assess wave energy technologies from technical, performance, risk and reliability, and power maximization points of view. The challenging design problems in the power take-off system in scale model includes high friction, unwanted inertia, cogging, etc. In this paper some of these issues have been addressed. The study presents design and dry-testing experiment for rotatory and linear PTO systems. Since the motion of the PTO during the dry-testing does not represent an oscillatory motion expected in the ocean waves, the calculated absorbed power can rather be viewed as an upper bound for the absorbed power during a wave cycleThe rotatory system based on eddy current damping shows promising system characteristics due to its non-contact nature of the damping. The damping increases with increased applied current, and is independent of the mass. From the power absorption point of view, a higher damping would be optimal, which could be obtained by increasing the number of magnet pairs (coils).The linear PTO with friction has depicted satisfactory results concerning its braking force. The design is simple and robust, and useful for scale experiments such as the intended one presented here, with the aim to study risk and reliability rather than power maximizing and control.
VIV of four cylinders in side by side configurations – experimental and CFD simulations
Published in Noor Amila Wan Abdullah Zawawi, Engineering Challenges for Sustainable Future, 2016
A.M. Al-Yacouby, V.J. Kurian, M.S. Liew, V.G. Idichandy
In this study, the VIV of four flexible cylinders with outer diameter D = 42 mm, at different center to center spacing have been investigated. The range of Re Number achieved in this study varied between 4.96E+03-2.48E+04. This study consists of 3D LES, with Smagorinsky subgrid scale turbulence model. The CFD simulation was validated using, wave tank model tests. From this study, the following concluding remarks can be drawn: The analysis of the results indicates that, in a group of four cylinders in tandem arrangement, with different center to center spacing, the cylinders which are in the wake of the leading cylinders have comparatively smaller drag coefficients and comparatively higher lift coefficients and St Numbers.The analysis of the results also indicates that the center to center spacing between the cylinders has a major influence on drag and lift coefficients as well as on St Number.Generally, the CFD simulation results are in good agreement with the experimental results.
CFD investigation of pitch-type wave energy converter-rotor based on RANS simulations
Published in Ships and Offshore Structures, 2020
Sunny Kumar Poguluri, Haeng Sik Ko, Yoon Hyeok Bae
To compare the CFD results, a model test was conducted in a wave flume at Jeju National University. The length of the wave tank was 20 m, width 0.8 m, and water depth 0.6 m. The wave tank was equipped with an inclined porous wave absorber and a piston-type wave maker capable of generating regular and irregular waves, as shown in Figure 2. A 1:11 scale WEC-rotor was fabricated using acrylic material. The model was allowed to rotate upward and downward about its own COR by means of a shaft passing through the rotor centre, and both ends of the shaft were connected to vertical rods that were attached to the wave flume by using clamps (see Figure 2). To reduce frictional force, a bearing mechanism was used between the shaft and the vertical rods, which allowed the rotor to pitch smoothly about the COR. The rotor could be fixed at the required draft by moving the vertical rods. Figure 2 shows a schematic diagram of the test facility and the experimental model setup.
Simulation on tsunami-like solitary wave run-up around a conical island using a modified mass source method
Published in Engineering Applications of Computational Fluid Mechanics, 2019
Zhe Ma, Ting Zhou, Jiawen Sun, Gangjun Zhai
Recently, three types of methods have been widely employed to generate waves in a numerical wave tank (NWT): source wave generating; static boundary wave generation; and moving boundary wave generation (Higuera, Losada, & Lara, 2015). Among these methods, it is innovative to generate waves numerically by using a source function inside the computational region. Only the radiation boundary conditions are needed at the boundaries because the source function is designed not to interact with reflected waves (Lin & Liu, 1999). Depending on the position where the source term is added, it is also made up of two sub-methods: the momentum source wave method; and the mass source wave method (Zhang, Fan, Liang, & Hua, 2019). Ha, Lin, and Cho (2013) and Liu, Lin, and Shao (2015) pointed out that the mass source wave method is more widely used and suitable for both deep and shallow waters; consequently it is inserted in the wave-generating module of DUT-FOAM, which is our in-house solver developed to meet the specific needs of research. A typical numerical wave tank with an internal mass source is shown in Figure 2. Three modules, including wave generation, wave absorption, and percolation in porous media are realized in DUT-FOAM. The third module is a technical application, which is not mentioned in this paper. The former two models are specially used to establish an effective numerical wave tank to generate and absorb waves, which plays a foundational role in this paper. However, the original mass source wave method tends to obtain smaller wave heights than expected ones. Therefore, a modified mass source wave method is proposed by transforming the source term in this paper. It is aimed to be more suited for highly nonlinear solitary waves. The Navier-Stokes equations are employed as the governing equations for the two-phase fluid and the volume-of-fluid (VOF) method is used for the free surface capturing. The present numerical wave tank also has a complete system for wave generating, wave damping, and wave probes for collecting the wave elevations, and different types of wave (e.g. linear wave, stokes second wave, focus wave, and others) can be realized in this tank.