The comparative results of the hydraulic model tests and the numerical analysis show that the viscous damping is about 5% of the critical damping of the vertical motion of the float in the wave channel. It was also found that the viscous damping increases as the channel width decreases.
INTRODUCTION
LITERATURE SURVEY
- Wave Energy Resource
- Overview of Wave Energy Converter
- Installed WECs with Project
Although useful, this classification is subject to limitations due to the wide variety of wave energy device designs. One of the best descriptions of a linear inductance wave energy conversion device is in an article by Omholt (1978).
RESEARCH OBJECTIVES
If the system is applied to the existing caisson breakwater, not only the cost of the supporting structure of the system can be saved, but also the efficiency can be improved because the waves reflected from the breakwater can be used as the excitation sources of the float. By using a wave channel in front of the existing breakwater, the reflected waves can be reduced as much as the emitted wave power, which is useful for fishing environments to slow the mixing of the upper layers of the sea like a perforated breakwater.
SCOPE OF THIS STUDY
FORMULATION OF THE PROBLEM
Governing Equation and Boundary Conditions
In general, a wave train will cause the floating body to oscillate in the six modes corresponding to wave, sway, heave, roll, pitch and yaw. However, the float movement in the wave channel is only permitted in the direction along the wave channel.
Wave Forces
The component of the wave force on the float, , can be obtained as where = float bottom. 13), represents the hydrodynamic exciting force associated with. On the other hand, is related to the radiated wave potential, , and is conveniently described in the usual way by the added mass coefficient, , and the damping coefficient, , as e.g.
FLOATER MOTION
- Equation of Motion
- Resonant Frequency
- Frequency-Domain Analysis of the Heaving Body
- Extracting Wave Power and Energy Relations
- Discretization of the Fluid Region
- Finite and Infinite Elements
This equation can be plotted to give a dimensionless measure of the amplitude and phase angle of the response as a function of frequency ratio. This shows that if the forcing frequency is less than the natural frequency, the response tends to the static response and the displacement is controlled by stiffness of the spring and not by the mass or the damping. If the forcing (excitation) frequency is close to or equal to the natural frequency of the PTO, the response can be much larger than the static deflection, especially if the structural damping is low, and is mainly controlled by damping force.
The increase in amplitude at resonance with respect to static displacement follows from Eq. In the case of the high pressure frequency range, the response is reduced and controlled by mass rather than the stiffness or damping of the PTO shaft. The complex-valued amplitudes of the float motion and the relative motions between the float and the LEG can be obtained as
To solve the boundary value problem defined as equations (1) ~ (4) and (7) in the standard finite element way, it is necessary to describe the unknown potential, , in terms of the nodal value vector with complex value. , , and the shape function vector, , as follows.
PERFORMANCE ANALYSIS
FINITE ELEMENT MESH
Figure 3-2 shows the finite element mesh, in which 2418 finite elements and 20 infinite elements are used to discretize the fluid region. The minimum element number used to discretize the fluid region per wavelength is 54, which is sufficient for interpolating the wave potential behaviors.
NUMERICAL RESULTS
- Resonance in Wave Channel
- Time-averaged Power & Efficiency
- Wave Reflection
In order to investigate the influence of the damping due to the liquid viscosity around the wave channel and float, two damping ratios of float () were considered. 3-6 show the time-averaged powers and efficiencies for the tested cases with 0% damping ratio with respect to normalized periods by resonant period of the wave channel. This therefore means that the efficiency of the PTO system can be improved by using resonant phenomena in the wave channel, float and LEG.
And they are greatly affected by the damping ratio of the generator, which is related to the amount of energy extracted from the waves. These results imply that the viscous damping produced in the vicinity of the wave channel and float is significant. It can be seen that these curves are similar to those of a typical perforated breakwater and have the maximum wave absorption effect near the resonant state of the wave channel.
Ignoring the effect of viscosity, it is indicated that the reflection coefficients () should be the minimum in the maximum efficiency condition.
CONCLUDING REMARKS
HYDRAULIC MODEL TEST
WAVE FLUME AND MODEL SETUP
- Wave Flume
- Model Setup
- Testing Conditions and Method
- Structure Displacement Measurement System Using Video
Wave energy absorption facilities are installed at the rear of the wave generator and at the downstream end of the wave tank. In order to effectively estimate the hydraulic properties of the caisson-type breakwater with WEC, some downstream parts of the breakwater were separated into two channels. Wave pressure was measured on the front walls of the breakwater at a sampling rate of 25 Hz.
In addition, the video recording was performed to measure the vertical displacement of the driver in the wave channel. In order to use multi-resonance, the shape of the wave channel is diversified with the opening and closing of the wave channel as in Fig. 4 shown. The side of the wave tank was shot by the video camera (Samsung SV-H66) to measure the vertical displacement of the driver in the wave channel, and analyzed the dynamic displacement using the image processing technique based on the video.
Lee et al (2006a, 2006b) studied to minimize the image processing area by introducing a ROI (Region of Interest) concept and using a set of pixels that expected the motion of the structure.
EXPERIMENTAL RESULTS
- Floater Motion
- Wave Run-up
- Wave Reflection
3-wave height meters (W1 ~ W3) were used to calculate the reflection coefficients of this system and displayed the time series data of the meters in the image. Using the technique of separating incident and reflected waves using the method of least squares (Park et al, 1992), the reflection coefficients, were shown for example with a draft of 7.0 cm and 9.5 cm in the figure. Also shown is a tendency to have a lower level near the resonant period of the wave channel, such as the rise of the free surface in front of the caisson wall in Fig.
Using the float offset, the viscous attenuation caused by the float can be determined quantitatively, and the reflection coefficients can be compared qualitatively with the damping caused by the float and the wave channel. 4-13, in the event that only the wave channel without the float is shown, it is possible to check the influence of only the wave channel. The width of the wave channel is affected differently, a detailed analysis will be discussed in the next section.
COMPARISON WITH NUMERICAL AND EXPERIMENTAL
- Resonance in Wave Channel without a Floater
- Wave Reflection
To investigate the resonant response of the floater in the wave channel and to quantify the viscous damping of the WEC, the hydraulic model test results were compared with the numerical results considering proper floater damping. The normalized amplitude of the floater motion for regular waves with a height of 0.02 m are shown in Fig. In the numerical analysis, the damping is assumed to be 5% of the floater's critical damping.
In addition to the viscous damping of the float, the damping effect of the shape of the wave channel is more dominant. If there is the float in the wave channel, the energy dissipation occurs due to the viscous damping with the shape of the float and the inlet channel, relatively, in case of. The difference in the results between with and without the float increases as the width of the wave channel increases, especially for resonant conditions.
Thus, to improve the efficiency of the WEC, minimizing the damping source of the wave channel is required.
CONCLUDING REMARKS
CONCLUSION
FUTURE WORKS
Hydrodynamic characteristics of two-dimensional wave energy absorbers, Journal of the Society of Naval Architects of Korea, 20(1), pp. Control strategies for a simple point absorber coupled to a hydraulic power lift, In Proceedings of the 8th European Conference on Wave and Tidal Energy. 2014) Damage of hollow steel composite SFT under fires, Journal of the Korea Academia-Industrial Society, 15(7), pp. 2014) Damage rate of reinforced concrete submerged floating tunnels under fire scenarios, Journal of the Korean Society, 14 (4), pp. 2014) Numerical analysis of wave reflection characteristics drilled with resonant channel, Journal of the Korean Institute of Navigation and Port Research, 38 (5), p. 2014) Wave Power Extraction System with Multi-Resonators Attached to Vertical Waves, Proceedings of the Twenty-Fourth International Conference on Ocean and Polar Engineering (2014), Busan, Korea.
Caisson Breakwaters Having Multiple Resonance Channels with Perforated Plates, Proceedings of the Korean Society Hazard Mitigation 2014 Conference, 1(13), pp Damage Analysis of Submerged Floating Tunnel Section by Fire Scenario, Proceedings of the Korean Society of Civil Engineers 2014 Conference, pp. 2013) Performance Analysis of Wave Energy Harvesting System by Using a Linear Electric Generator in Wave Channel, Proceedings of the Korean Society of Civil Engineers 2014 Conference, str. 2013) Wave Reflections from Breakwaters Having Resonance Channels with Perforated Plates, Proceedings of Korean Institute of Navigation and Port Research, str. 2014) Axial Compressive Behavior of Circular Steel Tube under High Temperature, Proceedings of the Korean Society of Civil Engineers Conference 2014 Conference, str. 2014) Evaluation of Enhanced Performance for Caisson-type Breakwaters Using Interlocking System, Proceedings enajstega (2014) simpozija mehanike na morju v Pacifiku/Aziji, Šanghaj, Kitajska. 2014) Omejevanje prečnih ojačitev za krožni kompozitni votli AB steber z notranjo cevjo, Zbornik druge avstralazije in. 2014) Učinkovitost odseka potopljenega plavajočega predora z uporabo jeklene kompozitne votle RC strukture, zbornik konference OCEANS'14 MTS/IEEE, St. 2014) Vedenje kompozitnega votlega RC SFT pod ognjem, zbornik konference Korejskega združenja gradbenih inženirjev 2014, Str. 2014) Preiskava plavajočega pomola korejskega pristanišča, zbornik letne konference Korejskega društva Korejskega društva za preprečevanje obalnih nesreč, str. 2013) Značilnosti razpršitve valov na prepletenih kesonskih valobranih, zbornik Korejskega društva Korejskega društva za obalne Letna konferenca o preprečevanju nesreč, str. 2013) Metoda gradnje modularnih votlih RC stebrov iz jekla in kompozita, zbornik konference Korejskega združenja za akademsko in industrijsko sodelovanje, str. 2010).
Detailed batimetry image of that summit area of Dokdo, Proceedings of the Korean Society of Oceanography Conference, pp. 2010) Neashore Bottom Surface Image Processing vir die Neashore Benthic Hapbitat.
