. Using the time-series of significant wave height and the peak period between 1979 and 2009 generated by SOWFIA project, some relevant statistical information about energy content available in ocean waves in Cape-Verde is obtained. The monthly and annual time-series of the average power are analysed and the confidence intervals for their values are defined. Considering all of the 31 years of data, the results show that the most energetic month, from the average power point of view is January (23.49 kW/m) and the least energetic month is July (15.04 kW/m). In fact, the monthly average power decays from January to July and increases from July to December (21.21 kW/m). The annual average power exhibits a clear attenuation over the 31 years analysed, the reason for which is not yet clear to us. However, using the appropriate Autoregressive Integrated Moving Average (ARIMA) model it is possible to estimate that future values of the annual average power tend to oscillate around 18.2 kW/m. Through the Coefficient of Variation of Power (COVP), obtained by dividing the standard deviation of the power time-series by the average power, it is possible to conclude that the wave resource is stable, with COVP between 0.46 and 0.66. The values of the Monthly Variation Index (MVI), the maximum range of the monthly mean wave power relative to the yearly mean level, show that the resource is relatively stable, with MVI

/pdf/statistical-analysis-of-wave-energy-resources-available-for-4rm235k2yk.pdf

Statistical Analysis of Wave Energy Resources Available for Conversion at Natural Caves of Cape-Verde Islands

Sumber daya energi yang sampai sekarang masih menjadi tumpuan
adalah sumber daya fosil. Sumber daya fosil memiliki sifat tidak terbarukan
sehingga sewaktu-waktu dapat habis. Gelombang air laut merupakan sumber daya
yang ketersediaanya melimpah sehingga perlu dilakukan penelitian mengenai
karakteristik pembangkit listrik tenaga gelombang laut (PLTGL) yang dilakukan
pada skala laboratorium.
Metode penelitian yang digunakan adalah eksperimen dan simulasi pada
mekanisme PLTGL tipe pengungkit generator linier dengan variasi titik tumpu
dan volume pelampung. Prinsip kerja mekanisme adalah memanfaatkan gerak
naik turun pelampung yang disebabkan gerakan gelombang air laut. Pelampung
yang bergerak naik turun akan menggerakkan lengan pengungkit sehingga lengan
pengungkit dapat menggerakkan magnet linier. Langkah pertama dalam
penelitiain ini adalah melakukan pemodelan mekanisme PLTGL tipe pengungkit
generator linier. Tahap selanjutnya adalah melakukan eksperimen terhadap
mekanisme PLTGL tipe pengungkit generator linier. Untuk mendapatkan hasil
pemodelan yang valid maka dilakukan validasi pemodelan terhadap hasil
eksperimen yang telah didapat. Tahap terakhir adalah mengembangkan model
mekanisme PLTGL dengan penambahan gearbox dan penggantian generator
linier menjadi generator rotary. Pengembangan dilakukan menggunakan metode
simulasi dengan variasi titik tumpu dan volume pelampung.
Hasil simulasi mekanisme PLTGL tipe pengungkit generator linier
didapat tegangan maksimum sebesar 5.338 volt dengan daya sebesar 0.0303 watt
pada variasi titik tumpu T2, volume pelampung P3, dan frekuensi f3. Hasil
eksperimen mekanisme PLTGL tipe pengungkit generator linier didapat tegangan
maksimum sebesar 2.057 volt dengan daya sebesar 0.014 watt pada variasi yang
sama dengan simulasi. Error rata-rata yang terjadi antara simulasi terhadap
eksperimen sebesar 38.522%, dengan efisiensi mekanisme sebesar 29.668%.
sedangkan. Untuk pemodelan generator rotary tegangan lisrik maksimum yang
dapat dibangkitkan sebesar 10.38676 volt dengan daya maksimum sebesar
0.02227 watt pada variasi titik tumpu T2, volume pelampung P3, dan frekuensi f3.

Studi karakteristik model pembangkit listrik tenaga gelombang laut (pltgl) tipe pengungkit- generator linier dan generator rotary dengan variasi volume pelampung

An Oscillating Water Column device (OWC) is a Wave Energy Converter (WEC) that harvests energy from sea waves, via the oscillation of seawater inside a chamber caused by incoming waves. It consists essentially of two parts: the chamber made of concrete and the turbine generator group used for energy conversion. This paper deals with a one dimensional modeling based on the resolution of the aero-hydrodynamic coupled equations of air and water in the OWC chamber. The objective is to improve the results of an existing linear model by including other physical effects such as: viscosity, friction, isentropic transformation, and the chamber height. In this study we are interested in the water oscillation motion inside the chamber resulting from the water level perturbation inside the chamber. This process similar to a mechanical oscillator system is characterized by its own natural frequency and global damping. Theoretically, the free water surface will oscillate vertically according to the natural frequency and its amplitude will decrease with a ratio relative to the global damping. Analyses are focused on the temporal variation of wave height inside OWC and the effect of parameters on this variation (gravity acceleration, submerged depth, turbine damping, base area, chamber height, viscosity, friction and initial conditions). For practical applications; this aero-hydrodynamic model will improve the characterization of the linear model during the design step, where the objective is to find values of parameters giving maximum efficiency, this scenario corresponds to the resonance domain where the damping is low and the frequency of incoming waves matches with the natural frequency of the OWC.

Analysis of Aero-hydrodynamic Equations Inside an OWC Device for Wave Energy Conversion

The research presented in this dissertation investigates the development and the performances of a new type of Wave Energy Converter (WEC) aimed to provide water delivery and energy storage in the form of potential energy. The Oscillating Water Column Wave Pump (OWCP) concept was proposed and tested through a series of experimental investigations supported by scientific theory. The OWCP was developed after an extensive study of the existing wave energy technology available, from which it emerged that the Oscillating Water Column (OWC) device could be further implemented for water delivery purposes. The existing theory of the OWC was employed to develop a mathematical theory able to describe the system wave response and water removal of the OWCP. In order to understand and validate the mathematical models of the OWCP, experimental investigations were carried out under the influence of incident linear waves in a two-dimensional (2D) and three-dimensional (3D) wave flume. The experimental equipment and methodology are outlined, including the description of wave flumes, models and data acquisition equipment. Experimental tests were used to verify the concept of the OWCP and assess its performances, investigating both the response of the device to the waves with and without water removal. In order to increase the efficiencies of delivery, array configurations of multiple OWCPs were adopted. The research demonstrated that up to 14% of the energy carried by the incoming waves can be converted into useful potential energy for a single device. Moreover a further increase of the efficiencies can be obtained with the array configuration improving the overall capability of the OWCP, for optimal separation distance between the array components. Further model tests are required to extended this research to validate the developed mathematical models as an effective prediction tool of the performances of the OWCP and further increase the efficiency of water removal that can be achieved.

Davide Magagna

Papers

Oscillating water column wave pump: a wave energy converter for water delivery