Design and fabrication of wave generator using an oscillating wedge

Use your smartphone to scan this QR code and download this article ABSTRACT In this paper describes the design and fabrication of a wave flume and associated equipment. The water wave generation by a triangle wedge is examined in this paper. Wave flume is fabricated by a concrete flumewhich is 0.75-meter-wide, 1.3-meter-tall and 11meters long. One sideof the flume is made of concrete and the other side ismade of clearmica sheets for observe thewaterwave profile. Wave flume is equipped with a triangle wedge which located at one end of the wave flume, and this trianglewedge can bemove along the rail of thewave flume. The passivewave absorberwhich is made of honey comb which is located at the other end of the wave flume for absorbing energy waves generated from the wave maker. The wedge is controlled by a desktop computer through mathlab sofware. The wedge can be controlled move up and down at a prescribed speed and oscillation amplitude corresponding to the desiredwave height andwave frequency. At themiddle flume is equipped micro laser distance sensor which provides data-logging capability. Micro laser distance sensor can collect wave height and wave period through a small ball which is motioned in the tube which is assembled on the water surface and the small ball is very slight to avoid kinetic inertia energy. At the wave maker is equipped an Eccentricity Sensor which is used to measure the wedge position to feed back for desktop computer. Wave flume can generate the largest waves are about 0.2 meter high, a period about 1 second, and a wavelength about 1.5 meters. The waves generated by a oscillating wedge have been measured, analyzed to consider the generated wave energy.


INTRODUCTION
Ocean wave energy is the natural resource to be exploited as a renewable source of energy, while also coinciding with the aim of reducing our reliance on fossil fuel sources. The concept of harnessing ocean wave energy is by no means a new idea. Modern research into harnessing energy from waves was stimulated by the emerging oil crisis of the 1970s 1 . With global attention now being drawn to climate change and the rising level of CO 2 , the focus on generating electricity from renewable sources is once again an important area of research. At present, many countries in the world use wave energy as a source of clean and renewable energy 2,3 (Figure 1). Therefore, experimental wave flumes are very useful to test the performance of wave energy conversions. The wave generation is made through a wave-maker animated with a prescribed motion with specified amplitude and frequency 4 . Three main classes of mechanical type wavemakers are utilized in laboratory: The first is the movable wall type generators 5 , including piston and paddle-type wavemaker, which generates waves by a simple oscillatory motion in the direction of wave propagation (Figure 2). The movable wall type generators are used where the water is shallow compared to the wavelength of the waves. Here the orbital particle motion is compressed into an ellipse and there is significant horizontal motion on floor of the tank. This type of paddle is used to generate waves for modelling coastal structures, harbours and shore mounted wave energy devices. The second is the plunger-type wavemakers 5 , which generates waves by oscillating vertically in the surface of water (Figure 3). The plunger-type wavemakers are commonly used in wave flumes because they can be fabricated as fairly long wave machines and they easily relocated within the flumes. The machine is very compact, furthermore, as the shape is wedge, the flume can be designed to work with water behind the wave maker with almost no generation of back waves 4 .  The third is the flap-type wave-maker, which is located at one end of the tank 6 , and hinged on a sill (Figure 4), waves are generated by oscillation of the flap about the sill, flap-type wave-maker is used to produce deep water waves where the orbital particle motion decays with depth and there is negligible motion at the bottom. This paper describes the design and fabrication of a wave flume with the plunger-type wavemakers and associated equipment, the waves generated by a sinusoidal oscillating wedge have been measured and analyzed.

DESIGN AND FABRICATION Wave Flume
Experiments were performed in a concrete wave flume which is 0.75-meter-wide, 1.3-meter-tall and 11 meters long (Figure 5a). The water depth was maintained at 0.97 meters. The one side of the flume is made of 1-cm-thick clear mica sheets for observe the water waveform, mica sheets are supported by steel structural frames, the other side is the concrete wall (Figure 5b).

Wave Gauges and Data Acquisition
A Micro Laser Distance Sensor (HG-C1400-Panasonic) is used for measuring the wave height. This sensor is located at the middle of the tank and it isn't contacted with water so not affect parameters of the wave. This is also the advantage of this design. Additionally, an Eccentricity Sensor is used to measure the wedge position (Figure 6a).

Wave-Maker
Waves were generated using a wedge shaped plunger device, the 35 degree wedge has been chosen for the wave-maker because 35 degree wedge is so good for wave-maker performance in 7 . It is set at one end of the tank (Figure 6b) and is made of 1-mm-thick Inox sheets, it can generate regular waves. The wedge has a 0.418 m base and 0.566 m height, with a mean submergence height of 0.375 m (Figure 7). The wedge is

Wave Absorber
Wave absorber is the most important part in a wave flume. A great variety of designs and materials have been used throughout the world for the construction of wave absorbers. Wave absorbers could be classified into two main categories: active and passive absorbers. Active absorbers owning to its high cost is still very limited, except in a few cases where the wave board itself is programmed to absorb the reflected wave. In this design uses passive absorbers, the wave absorber has 1:4 slopes 9 . It is located at the end of the tank opposite to the wave-maker (Figure 6c). The waves generated are absorbed using a honey comb which is set at the other one end of the tank (Figure 8).

THEORETICAL APPROACH
Many models can be used to try to describe the evolution of the surface elevation in time and space. One of the most used, because of the simplicity that results of assuming linearity of the potential flow function, is the one related to the linear wave theory 10 .
The main parameters that define a wave are amplitude (A), period (T) and wavelength (L), represented in Figure 9. The amplitude corresponds to half of the wave height (H), the vertical distance between the highest and the lowest surface elevation in a wave. The time interval between the start and the end of the wave is what is known as the period of a wave. Finally, the wavelength is the distance between two successive peaks or two consecutive troughs. Table 1 and Figure 9 summarize a commonly used wave energy nomenclature.  Energy and power density: The energy density of a wave is the mean energy flux crossing a vertical plane parallel to a wave's crest. The energy per wave period is the wave's power density and can be found by dividing the energy density by the wave period.

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Power per meter of wave front: A wave resource is typically described in terms of power per meter of wave front (wave crest). This can be calculated by multiplying the energy density by the wave front velocity.

RESEACH METHOD, RESULT AND DISCUSSION
The research method is used in this paper is experiment method. We experiment with many difference parameters of system to consider the generated wave energy.
The list of experimental tests are presented in Table 2.
These tests were chosen to show the wave height range of 12 mm to 200 mm, wavelength range of 0.7m to 14m. The water depth was maintained at 0.97 meters. From Table 2, we draw Figure 10. According to Figure 10, we find that the wave's power density is related to eccentricity, which can be predicted linearly. May be, the experimental system is not good. So, there are many places that do not follow the linear relationship. Table 3, we draw Figure 11. According to Figure 11, we see that the wave's power density is related to the RPM, which can predict as a second order. When RPM is greater than 68r/m; the waves are interrupted. Table 4, we drawFigure 12. According to Figure 12, when increasing eccentricity (e = 100mm); the wave's SI106      power density increases. When RPM is greater than 66 r/m; the waves are interrupted.  Table 5, we draw Figure 13. In Figure 13, when e= 120, the graph has more fluctuation, due to the influence of reflectivity. When RPM is greater than 60r/m; the waves are interrupted    Table 6, we draw Figure 14. In Figure 14, when increasing eccentricity longer; fluctuation as much, due to the influence of reflectivity so much. When RPM is greater than 58r/m; the waves are interrupted.

CONCLUSION
In this paper, the system wave flume is described and fabrication for a study and built with a limited budget, however, it is well-suited to educational and research studies about wave energy. The performance of the physical wave maker and wave absorber was evaluated over a range of frequencies and eccentricity. The results also show that the wave's power density significantly affected by RPM and Eccentricity. The affected of reflectivity is so much, further work, we will improve the performance of the wave absorber in the wave flume to minimize the reflected waves.