Ocean wave energy is one of the most abundant energy sources in the world. There is a wide variety of wave energy conversion systems that have been designed and developed, resulting from the different ways of ocean wave energy absorption and also depending on the location characteristics. This paper reviews and analyses the concepts of hydraulic power take-off (PTO) system used in various types of wave energy conversion systems so that it can be a useful reference to researchers, engineers and inventors. This paper also reviews the control mechanisms of the hydraulic PTO system in order to optimise the energy harvested from the ocean waves. Finally, the benefits and challenges of the hydraulic PTO system are discussed in this paper.
This study is concerned with the application of two major kinds of optimisation algorithms on the hydraulic power take-off (HPTO) model for the wave energy converters (WECs). In general, the HPTO unit’s performance depends on the configuration of its parameters such as hydraulic cylinder size, hydraulic accumulator capacity and pre-charge pressure and hydraulic motor displacement. Conventionally, the optimal parameters of the HPTO unit need to be manually estimated by repeating setting the parameters’ values during the simulation process. However, such an estimation method can easily be exposed to human error and would subsequently result in an inaccurate selection of HPTO parameters for WECs. Therefore, an effective approach of using the non-evolutionary Non-Linear Programming by Quadratic Lagrangian (NLPQL) and evolutionary Genetic Algorithm (GA) algorithms for determining the optimal HPTO parameters was explored in the present study. A simulation–optimisation of the HPTO model was performed in the MATLAB/Simulink environment. A complete WECs model was built using Simscape Fluids toolbox in MATLAB/Simulink. The actual specifications of hydraulic components from the manufacturer were used during the simulation study. The simulation results showed that the performance of optimal HPTO units optimised by NLPQL and GA approaches have significantly improved up to 96% and 97%, respectively, in regular wave conditions. The results also showed that both optimal HPTO units were capable of generating electricity up to 62% and 77%, respectively, of their rated capacity in irregular wave circumstances.
This paper presents accurate control parameters estimation of the hydraulic Power Take-Off (PTO) model for the wave energy conversion system to maximise energy production. In general, the performance of the hydraulic PTO system depends on the parameters setting of hydraulic PTO system components such as hydraulic motor displacement setting, pre-charge of the hydraulic accumulator, and et cetera. Conventionally, it requires to manually obtain the optimal parameters of a hydraulic PTO system by repeating the simulation process. However, this estimation method exposed to human error and would easily be resulting in a non-optimal selection of hydraulic PTO parameters for the wave energy conversion system. Therefore, an easy and accurate approach of using the GA optimisation method for determining hydraulic PTO parameters was introduced in the present study. This approach is simple and more accurate compared to the conventional optimisation method. The hydraulic PTO model was developed in SIEMENS/Amesim environment using available components in the library. The specifications of the actual hydraulic PTO system components from the manufacturer were used during the simulation set-up. The complete hydraulic PTO system was optimised using a special genetic algorithm (GA) optimisation tools in the SIEMENS/Amesim software. The simulation results showed that GA was effective to determine the optimal configuration parameters of hydraulic PTO system. From the results, the optimal configuration parameters of hydraulic PTO system were successfully reduced about 38%. Consequently, the maximum force applied to the WEC devices was reduced up to 34%. This force reduction is important since it will enable the WECS to be operated during a smaller wave condition.
Ocean wave could convert the resource energy more than half of its potential capacity often over time, compared with wind or solar system, which is less than half of its capacity resource. However, the challenge rises on designing an ocean wave-capturing device that can achieve optimum efficiency. This paper addressed several topics including the overview of existing technology of wave energy converter with emphasis on wave-activated body category, current principle of energy harnessing, types of generators utilised to harness the wave energy and the current technologies of power electronics implemented to ocean wave devices. Wave energy converters (WEC) that are commercialised, under testing and still in prototype stage are all listed and divided into two different categories, namely, submerged and floating on the sea. The results reveal that, compared with submerged WECs, the floating WECs gain more attention for development. The key factor in choosing a float on device is to consider the fabrication cost, environmental impact especially for marine life, design and maintenance issue, installation site and the selection of power takeoff system.
This paper provides the investigation of the performance One-Degree-of-Freedom system to be implemented in tremors patient writing device to reduce human hand tremor. The One-Degree-of-Freedom of two springs and a mass is proposed to absorb the hand vibration for patients that suffered tremors disease while writing. The performance of development device is based on drawing Archimedes spiral that done by a tremor patient.
This paper presents the simulation and experimental results of the hydraulic system for wave energy converter application. The different input force applied from the pump unit will imitates the force of wave energy converter (WEC) produced by the ocean waves motion. The simulation conducted using the Hydraulic FluidSIM® 5th version, while the experiment was conducted at Festo-Hydraulic Laboratory. In FluidSIM®, the role of wave floater represented by a set of pump unit that will provide desired pressure to the hydraulic piston. The pump unit consists of a motor, pump, tank and pressure relief valve. The input pressure at the pump unit was adjusted in twelve different levels in the range of 5 Bar to 60 Bar. The different pressure will create a different oil velocity that caused the extension and retraction of the piston. The different pressure also will create a different speed (measured in RPM) of a hydraulic motor. An accumulator and four units of check valves used to drive the moving oil in unidirectional at a smooth flow rate. As a result, the rise of input pressure at the pump unit will increase the speed of a hydraulic motor. For this reason, to achieve the optimal electrical generation by a generator that mounted with hydraulic motor, the higher input pressure is needed. Furthermore, the simulation is validated by the physical experiment to determine the accuracy of generating data. The averaged accuracy of simulation data compared to experimental is 89.92%. After all, the finding from this study will be utilised as a reference in the estimation of the optimal dimension for the actual scale of a hydraulic system for application in the WEC.
This paper presents the wind energy potential at Kudat Malaysia by considering the Levelized cost of energy (LCOE) model for combined wind turbine capacities. The combination of small- and utility-scale wind turbines is the key to the success of the operation of a wind park in the lower wind speed region. In a combination approach, the small-scale wind turbines provide the power required by the utility-scale wind turbines to start the blade rotation. For this reason, the particular closed-form equation was modified to determine the LCOE of a wind park with combined turbine capacities. The modified LCOE model can be used as a basis for setting tariff rates or define the economic feasibility of wind energy projects with combined wind turbine capacities.
This paper presents an evaluation of experimental results of a prototype assistive device in suppressing hand tremor during sitting and standing conditions. The handheld instrument is capable of sensing and suppressing hand tremor or other unpredicted movement during writing. The assistive device incorporates an accelerometer, allowing the movement of the hand to be captured and computed. The tremor suppressing instrument design is carried out by placing two springs between a handheld casing and pen-point at one end of the device. Decomposition of acceleration was analyzed using power spectral analysis to compare the data captured by attaching an accelerometer to a regular pen. The findings show that the proposed assistive device is able to improve the legibility of the handwriting of all the tested subjects by more than 16%.
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