Oscillating Water Column Type Research Articles

Experimental Study of the Relationship between Slope and Opening Height of OWC Type Wave Breaker Model on Wave Reflection

Breakwater is a very effective wave dampening building to be used as a coastal protection against coastal abrasion by destroying wave energy before it reaches the coast. The working mechanism of the OWC type is the rise and fall of ocean waves which will push the air in the OWC column, then will rotate the turbine connected to the generator to produce electricity. This study aims to determine the effect of slope and opening height on breakwater on wave reflection. Then analyze the parameters that affect the amount of wave reflection and compare the resulting wave parameters. This research was conducted at the Hydraulics Laboratory, Department of Civil Engineering, Faculty of Engineering, Hasanuddin University. The method used was experimental based. The resulting wave characteristics consist of three depth variations, three period variations and three stroke variations. The research model used is an Oscillating Water Column (OWC) type breakwater with slope variations of 45°, 60° and 90° and open wall variations as high as 5 cm, 10 cm and 15 cm. The reading of the water level fluctuation is done electronically through the reading of the wave monitor. The results showed that the magnitude of the reflection coefficient is influenced by structural parameters, namely the slope and height of the model opening and hydraulic parameters, namely depth, period and wave height. The effect of the model slope on the reflection coefficient is that the greater the slope, the greater the reflection coefficient value. The effect of the model opening height is that the greater the opening height, the smaller the reflection coefficient value.

Research on Wave Energy Converters

With the acceleration of the global warming process, the clean energy crisis is becoming serious; conventional energy is unlikely to solve the current crisis, so people pay attention to new energy. As wave energy is widely distributed, renewable, and clean, hundreds of wave energy converters emerge. In order to understand the research progress of wave energy converters better, this paper divides wave energy converters into overtopping type, oscillating water column type, and oscillating body type according to the working principle and divides the oscillating body type into oscillating float type and oscillating pendulum type by different ways of energy capture. Based on the classification, various types of engineering cases, physical tests and digital simulation, and other academic research results are summarized, especially the generation power and energy conversion efficiency of various devices, and some shortcomings and suggestions are put forward, hoping to provide help for readers to study wave energy generation converters.

Hydrodynamic performance of an elastic capsule oscillating water column type WEC: An experimental study

Wave energy represents a promising and sustainable source of energy with substantial potential. To promote the utilization of wave energy resources as well as develop new wave energy converters (WECs) with application prospects, an innovative elastic capsule oscillating water column (EC-OWC) WEC is proposed, and an initial experimental investigation is conducted on the device. Besides, the expansion characteristics of the elastic capsule and the motion characteristics of the free bulge wave are investigated through bulge wave tests. Moreover, the hydrodynamic performances of the device on the condition that coupled with traveling regular waves are investigated through wave tests, as well as the damping characteristics of the impulse turbine model and the ring-opening as power take-off (PTO) systems in the EC-OWC. It indicates that the variation in the speed of the free bulge wave is consistent with the one-dimensional longitudinal wave theory, that the ring-opening model with an opening ratio of 0.76 percent has comparable operating characteristics to the impulse turbine, and that the impulse turbine model has outstanding operating characteristics in the EC-OWC system. The maximum primary hydrodynamic efficiency of the system is approximately 0.475. When the relative water depth is in the interval of approximately 0.07-0.09, the efficiency can reach 0.4. Furthermore, the efficiency increases and subsequently decreases with the variation of the relative hydraulic head, and the efficiency reaches the maximum value when the relative tube length is around 1.6. The results indicate that the one-dimensional longitudinal wave theory can provide support for the design of the elastic capsule. When the capsule length is close to half a wavelength and the internal and external oscillation periods are matched, the system reaches a near-resonant state, and the level of efficiency is optimized. The bulge wave contained within the EC-OWC is a half-wavelength standing wave.

Geometrical Design of the L-shaped Oscillating Water Column Using Artificial Neural Network

Among the various wave energy converters available, the oscillating water column (OWC) shows a number of advantages in terms of implementation and maintenance. In dealing with the survivability issues, incorporating OWCs into reinforced concrete constructions, like breakwaters, is more cost-effective and can endure the effects of seawater impact and erosion. This paper focuses on optimizing the geometrical design of a novel OWC type, the L-shaped OWC, by establishing a general design procedure to achieve higher energy-capturing efficiency. The performance of the OWC is influenced significantly by the OWC’s geometry under a specified wave condition. It is found that the dimension of the air chamber and water duct is critical in determining OWC’s performance. We develop the chamber and duct design procedure based on the artificial neural network approach by establishing a collection of two-dimensional RANS simulations as the training database. In the end, the performance of the optimal design is compared with the design of a previous paper. The result shows that the capture factor of the optimized chamber geometry of the L-shaped OWC is 12% more than the former design.

Passive flow control via tip grooving and stall fencing mechanisms of a marine energy harvesting turbine

Remarkable advancement in wave energy conversion technology has taken place in recent years. Due to its simplicity, the Wells turbine has been one of the most widely used power take-off mechanisms in an oscillating water column type wave-energy conversion device. However, the turbine suffers from several challenges due to its narrow operating range, which hinders the commercial feasibility of the system. Several aerodynamic applications have successfully used passive control methods to modify the flow conditions. This work applied a combination of stall fences and casing grooves for passive flow control of a Wells turbine. The computational fluid dynamics (CFD) technique is used to analyze the modified turbine numerically. The casing groove modified the tip-leakage vortices, interacted with local vortices created by the stall fences, and helped reattach the flow at higher flow coefficients. As a result, the modified turbine increases the operating range up to 33.3%. In addition, the peak-to-average (PTA) power ratio decreased by up to 27.7%.

Effect of the installation position on the primary conversion performance of an oscillating water column wave energy converter attached on double slit caisson break water

A ouble-slit breakwater has two water columns, one at the sea side and the other at the land side. an oscillating water column type wave energy converter has been proposed to utilize these chambers. In this presentation, the performance of a wave generator installed in both or one of the two chambers was evaluated in a water tank experiment. In the experiment, a 1/25 scale model of the actual system was used to evaluate the performance in regular waves. The regular waves ranged from 0.6 to 2.4 seconds with a wave height of 5 cm. Air chambers were installed on both the sea and land sides, and it was found that the water level amplitude of the seaward air chamber was larger at the short periods of 0.6 and 0.8 seconds, while the amplitude of the land side air chamber increased as the period increased. In other words, more energy is absorbed in the seaward air chamber in waves with short periods, and more energy is absorbed by the land-side air chamber in waves with long periods. The phase difference between the two air chambers was found to decrease as the period becomes longer. It was also confirmed that when air chambers were installed only on the seaward side or only on the landward side, the air chambers exhibited characteristics similar to a dynamic damper.

Optimal Design of Impulse Turbine Prototype of Oscillating Water Column Type Wave Energy Power Generation Device

The Oscillating Water Column Type is currently the most widely used wave energy generation device. The impulse turbine with fixed guide vanes has the advantages of high peak efficiency and excellent aerodynamic performance. Using three-dimensional numerical simulation methods to analyze the impulse turbine, construct and optimize the design of the turbine prototype, and provide suggestions for the subsequent innovation and improvement of the performance and structure of the impulse turbine with fixed guide vanes.

Hydrodynamic Investigation of a Novel Concept of Oscillating Water Column Type Wave Energy Converter Device

AbstractThe hydrodynamic performance of a novel and efficient concept of a floating oscillating water column device has been investigated. The new concept consists of two chambers. These chambers are positioned on the upstream (fore chamber) and on the downstream (rear chamber) of the incident wave direction. The rear chamber acts mainly similar to a backward bent duct buoy system, while the design of the fore chamber follows conventional types of oscillating water column systems with the harbor plates (bottom plates and side plates) elongated outside of the fore chamber. The primary efficiency of the devised concept has been investigated in the frequency domain. In this context, to solve the corresponding diffraction and radiation problems due to the influence of the air pressure inside the chambers as well as motions of the body, an in-house code has been developed in two-dimensional using the boundary element method based on the linear wave theory. The obtained numerical results show that the introduced concept has advanced hydrodynamic efficiency in a broad range of waves.

An Experimental Study on Condition Diagnosis for Thrust Bearings in Oscillating Water Column Type Wave Power Systems.

In order to utilize wave energy, various wave power systems are being actively researched and developed and interest in them is increasing. To maximize the operational efficiency, it is very important to monitor and maintain the fault of components of the system. In recent years, interest in the management cost, high reliability and facility utilization of such systems has increased. In this regard, fault diagnosis technology including fault factor analysis and fault reproduction is drawing attention as an important main technology. Therefore, in this study, to reproduce and monitor the faults of a wave power system, firstly, the failure mode of the system was analyzed using FMEA analysis. Secondly, according to the derived failure mode and effect, the thrust bearing was selected as a target for fault reproduction and a test equipment bench was constructed. Finally, with the vibration data obtained by conducting the tests, the vibration spectrum was analyzed to extract the features of the data for each operating status; the data was classified by applying the three machine learning algorithms: naïve Bayes (NB), k-nearest neighbor (k-NN), and multi-layer perceptron (MLP). The criteria for determining the fault were derived. It is estimated that a more efficient fault diagnosis is possible by using the standard and fault monitoring method of this study.

Power Performance Analysis According to the Configuration and Load Control Algorithm of Power Take-Off System for Oscillating Water Column Type Wave Energy Converters

A power take-off (PTO) system for an oscillating water column (OWC) wave energy converter comprises a turbine-generator-power converter. In this study, only the topologies of the power converter that affect the load control algorithm are compared. A power converter for renewable energy is composed of a diode-dc/dc converter and a pulse-width modulation (PWM) converter operating at small and large capacities, respectively. However, selecting a power converter according to the capacity based on the characteristics of the wave energy converter, in which the input energy is highly fluctuating, can significantly reduce the power performance. Thus, to verify load control characteristics according to the topology of the power converter, the turbine-generator-power converter was incorporated in the modeling, and the power performance based on the power converter topology under various wave conditions was analyzed. Further, torque control to obtain the maximum power among load control algorithms was applied under irregular wave conditions, and the power performance and PTO system characteristics according to the torque coefficient were analyzed. The results of this study suggested an increase in the torque coefficient of the maximum power control for the operational stability of the OWC-WEC, and it was confirmed that the RPM characteristics of the PTO system were reduced.

Hydrodynamic optimisation of an axisymmetric floating Oscillating Water Column type wave energy converter with an enlarged inner tube

Wave Energy Converters (WECs) that are classified as Floating Oscillating Water Columns (FOWCs) of point absorber type are designed to achieve resonance, at frequencies that are favourable for wave energy extraction. The resonance frequency of a FOWC type WEC is highly dependent on the added mass of its OWC, which often requires a long spar tube to achieve well-performing hydrodynamics. A proposed measure for driving down the cost of the converter is to reduce its length, while finding another way of achieving the desired OWC added mass. Frequency-domain modelling and hydrodynamic optimisation of the Spar-buoy OWC was carried out for an enlarged spar tube segment inside the floater. Results are compared to those of buoys with equal spar and inner tube diameters. Frequency responses of optimised buoy geometries - with and without enlarged inner tubes - explore the differences in their hydrodynamics. Expanding the inner tube diameter of the Spar-buoy OWC may increase energy extraction by up to 6.7% and reduce the buoy mass by up to 11.4%, when operating in a Portuguese offshore location. A sensitivity analysis on mean annual pneumatic power to changes in inner tube diameter and spar tube length was performed.

Experimental Analysis of a Biplane Wells Turbine under Different Load Conditions

The oscillating water column type wave energy converters equipped with Wells turbine are one of the popular wave energy conversion devices. In most of the numerical and experimental studies, the Wells turbine characteristics are examined in no-load condition or with a fixed loading to achieve a fixed rotational speed. In the present work, a biplane Wells turbine is designed and tested in an experimental test facility. The test facility consists of a piston-chamber assembly that can generate sinusoidal airflow inside a duct. The turbine is placed inside the duct and tested for different stroke lengths and time periods of the piston, which produces a sinusoidal inlet airflow of different amplitude and time period. The turbine characteristics are studied at the no-load condition and for different values of resistive loading connected with the generator. The hysteresis behavior of the turbine is studied for two different flow coefficients based on experimentally observed and numerically calculated volume flow rates. Based on the experimental results, a detailed analysis of the turbine performance is presented for different operating conditions.

Parametric Study for an Oscillating Water Column Wave Energy Conversion System Installed on a Breakwater

This study focuses on the analysis of the parameters of an oscillating water column (OWC) wave energy conversion system and wave conditions. Interactions between the dimensions of the OWC chambers and wave conditions are all taken into account to design an alternative OWC converter, called caisson-based OWC type wave energy converting system. A numerical method using an unsteady Navier-Stokes equations theorem in conservation form is used to analyze the proposed analytical model. The objective of this study is to try to apply an OWC wave energy converter to a caisson breakwater, which has been constructed in a harbor. The structure proposed in this study is a series of sets of independent systems, in which each set of converters is composed of three chambers to capture the wave energy, while better ensuring the safety of the caisson breakwater. Responses to be analyzed related to the conversion efficiency of the caisson-based OWC wave energy converting system include the airflow velocity from the air-chamber, the pneumatic power and the conversion efficiency in terms of a ratio between the pneumatic power and the energy of the incident waves. Parameters examined in this study include the dimensions of the OWC chamber features such as the orifice of the air-chamber allowing airflow in/output, the chamber length along the direction of incident waves, the size of the opening gate for incident waves and the submersion depth of the air-chamber. As found from the results, a best conversion efficiency from incident waves of 32% can be obtained for the extreme case where the orifice is very small, but for most other cases in the study, the best efficiency is about 15%.

Wave-to-Wire Model Development and Validation for Two OWC Type Wave Energy Converters

The Tupperwave device is a closed-circuit oscillating water column (OWC) wave energy converter that uses non-return valves and two large fixed-volume accumulator chambers to create a smooth unidirectional air flow, harnessed by a unidirectional turbine. In this paper, the relevance of the Tupperwave concept against the conventional OWC concept, that uses a self-rectifying turbine, is investigated. For this purpose, wave-to-wire numerical models of the Tupperwave device and a corresponding conventional OWC device are developed and validated against experimental tests. Both devices have the same floating spar buoy structure and a similar turbine technology. The models include wave-structure hydrodynamic interaction, air turbines and generators, along with their control laws in order to encompass all power conversion stages from wave to electrical power. Hardware-in-the-loop is used to physically emulate the last power conversion stage from mechanic to electrical power and hence validate the control law and the generator numerical model. The dimensioning methodology for turbines and generators for power optimisation is explained. Eventually, the validated wave-to-wire numerical models of the conventional OWC and the Tupperwave device are used to assess and compare the performances of these two OWC type wave energy device concepts in the same wave climate. The benefits of pneumatic power smoothing by the Tupperwave device are discussed and the required efficiency of the non-return valves is investigated.

Use of the Mps method to estimate the energy conversion efficiency of the owc-wec (first report)

In recent years, ocean renewable energy has been increasingly in the spotlight due to global warming and energy issues etc. Research on ocean renewable energy devices is being carried out by many researchers, companies and countries. Additionally, many sea tests are being carried out by countries with real sea test sites. Ocean renewable energy devices still need to research about a power generation method, an energy conversion efficiency and costs etc. In this paper, Authors focus on the oscillating water column type wave energy converter (called below OWC-WEC). It is considered that the OWC-WEC is useful because a movable part which becomes a cause of trouble is few and can also be used as a breakwater device. In this study, the MPS (Moving Particle Semi-implicit) method is applied to the performance analysis of the OWC-WEC. It is because the performance analysis by various parameters and the reduction of an experimental cost is needed. In this paper, these following items are shown; 1) the development of analysis program code which can simulate the multiphase flow by three phases of gas, liquid and solid, 2) the development of air duct model, 3) verification of the usefulness of the improved MPS program code and 4) verification of the applicability to the performance analysis of the OWC-WEC. This program code was applied to the simulation of the fixed type OWC-WEC. Following this, the reproducibility of the primary conversion efficiency of the fixed type OWC-WEC by this program code was verified and discussed. Finally, the usefulness and applicability of this program code were discussed and recommendations for future work were made.

A wave energy system based on peristaltic pumping of air by sea waves

Oscillating water column type of wave energy converters have attracted researchers and engineers working on the field of renewable energy systems, despite the problems caused by the alternating direction of air flow through the turbines. This problem has been circumvented by the use of single direction of rotation turbines such as Wells, Denniss-Auld and omnidirectional impulse turbines, albeit with rather low efficiencies. The authors have considered the usage of near-sinusoidal (cnoidal) form of sea waves as the drivers for the linear peristaltic pumping of air along a channel. The conceived device is an inverted U-shaped channel on a barge, aligned in the direction of wave and serves as a channel for the progress of waveform. Air is driven through the channel by peristaltic action to achieve a unidirectional air flow at the leeward end of the channel. An end-wall operated by a float experiencing heaving and surging motions at the leeward side of the channel prevents the escape of pumped air, which instead is directed to an upward duct leading to a turbine. Since the air flow is unidirectional, the use of more convenient air turbines compared to the ones used in oscillating water column devices are enabled. Air flow parameters with wave amplitudes exceeding and less than channel height above the calm water line are analysed using the Airy wave to demonstrate the feasibility of the proposed system analytically. It was found that the optimum solution was achieved when the channel top is at the calm water level

Investigation on the hydrodynamic scaling effect of an OWC type wave energy device using experiment and CFD simulation

This paper presents a study of the effect of model scale on the performance of a fixed Oscillating Water Column (OWC) type Wave Energy Converter (WEC). Tank tests at two different scales, including the effect of scaling of the test tanks to minimise the bias introduced by different wave blockage effects. CFD simulations based on Reynolds Average Navier Stokes (RANS) method were then carried out for both scaled OWCs to investigate whether CFD simulation is able to reproduce the scale effect. Comparison between the tank test results and the CFD simulation results suggests that CFD simulation is capable of reproducing the hydrodynamic scaling effect with a good accuracy. Results also suggest that the hydrodynamic scaling effect is mainly introduced by the Reynolds number effect for cases investigated in the current study.

Basic Characteristics of the Primary Conversion of an Oscillating Water Column Type Wave Energy Converter Installed on a Wave-Dissipating Double Caisson

Several types of oscillating water column (OWC) type wave energy converters (WECs) are researched and developed in the world. They are floating types and fixed types. In case of a fixed type, wave-dissipating caissons could be replaced by WECs of an OWC type. In OWC types, installation of the projecting walls (PWs) is useful in order to improve power take-off (PTO) performance. In this study, a double-dissipating caisson was used as an OWC type WEC with PWs. A front caisson of the double caisson seems to be the area surrounded by PWs and a back caisson can be seen as an OWC. The paper studied the basic property of the primary conversion from wave power to pneumatic power from model tests in a wave tank. It was found that the wave height strongly affects the behaviors of OWC motion and air pressure. Finally, the primary conversion was affected by wave height. Besides, the concept of use of a double caisson was useful for the primary conversion over 80% evaluated using test data.

Parameter Governing of Wave Resonance in Water Chamber and Its Application

It has become known that the oscillating water column (OWC) device is very popular as one of wave energy extraction facilities installed in coastal and ocean structures. However, it has not been clarified sufficiently how to obtain an effective cross section design of the structure until now. This paper describes theoretical procedure to yield effective cross section of water chamber type of sea wall, which is similar to the OWC type structure in relation to wave period or wave length. The water chamber type sea wall has a water chamber partitioned by a curtain wall installed in front of part of the structure. This type of sea wall also can be applied to extract wave power same as of OWC function. When the wave conditions on site are known, the dimensions especially the breadth of water chamber type sea wall can be determined.

Exploration of power take off in wave energy converters with two-body interaction

The study explores a novel design of wave energy converter (WEC) that utilizes the interaction between an inside heaving vertical cylinder with an outside fixed hollow cylinder. This design originates from the oscillating water column (OWC) type WEC but replaces the pneumatic power take off (PTO) through the Wells turbine with the hydrodynamic PTO through the inside heaving cylinder. To effectively evaluate the maximum power output, the system has been modeled in the hydrodynamic software AQWA (developed by ANSYS Inc) that has accumulated extensive offshore industry users. Ranges of the PTO parameters have been examined to make sure that proper linear damping can be implemented to simulate the PTO force. Comparing the efficiency of the pneumatic PTO with the hydrodynamic PTO, it appears that the hydrodynamic PTO is more promising than the traditional Wells turbine for an OWC system.