بررسی آزمایشگاهی کارایی هیدرودینامیکی ستون نوسانگر آب شناور در استحصال انرژی موج

امواج دریاها و اقیانوس‌ها از مهم‌ترین منابع انرژی تجدید پذیر هستند که می‌توانند در آینده جایگزین بخشی از سوخت‌های فسیلی شوند. جهت استفاده از انرژی امواج، روش‌ها و دستگاه‌های متعددی طراحی و ساخته شده است که غالباً دارای پیچیدگی‌های فراوان می‌باشند. ستون نوسانگر آب به دلیل ساختار ساده مکانیکی به یکی از متداول‌ترین ابزارهای استحصال انرژی امواج در دنیا تبدیل شده است. با توجه به پیچیدگی‌های مربوط به شرایط هیدرودینامیک جریان و هوا در داخل این سیستم، نیاز است که از مدل‌های آزمایشگاهی جهت بررسی دقیق‌تر آن استفاده شود. در این تحقیق تاثیر ارتفاع دیواره انتهایی، موقعیت قرارگیری دستگاه و فرکانس امواج بر روی میزان توان خروجی با استفاده از مدل فیزیکی مورد بررسی قرار گرفته است. جهت بررسی تاثیر مستقیم و متقابل پارامترهای مختلف از تحلیل واریانس استفاده گردید. نتایج به‌دست‌آمده نشان می‌دهد که هر سه پارامتر مورد بررسی تاثیر معنادار بر روی توان خروجی داشته ولی تاثیر فرکانس و دیواره انتهایی بیشتر بوده است. علاوه بر این اثرات متقابل مربوط به دیواره انتهایی، اختلاف معنادار در سطح 0.01 داشته است. استفاده از دیواره 5 و 10 سانتیمتری به ترتیب باعث افزایش توان خروجی به میزان 0.88 و 1.48 نسبت به حالت بدون دیواره شده است. علاوه بر این وجود اثر متقابل میان ارتفاع دیواره انتهایی و عمق کارگذاری، باعث کاهش کارایی دیواره 10 سانتیمتری در حالت قرارگیری سیستم در عمق زیاد گردید. این نشان می‌دهد که جهت به دست آوردن بهترین کارایی می‌بایستی علاوه بر ارتفاع دیواره انتهایی، عمق کارگذاری نیز لحاظ شود.

Experimental study of Hydrodynamic Performance of Floating Oscillating Water Column as Wave Energy Convertors

Introduction Population increasing along with the environmental crisis due to the use of fossil fuels has led humans to seek to use renewable energy sources. One of the most important sources of renewable energy is the waves of the seas and oceans, which can meet some of the human needs for energy resources. One of the key steps in the development of wave energy renewable technology is the design and validation of physical models. Although physical models can not accurately simulate all the details and performance of the original prototype, they can be a very valuable source of information for researchers, developers, and inventors in this area. Due to its simple mechanical structure, the oscillating water column has become one of the most common tools for converting wave energy in the world. The oscillating water column could be used as a breakwater on the shores in addition to generating energy from the waves. Due to the complexities related to the hydrodynamic conditions of air and airflow inside the system, it is necessary to use laboratory models to study it more precisely. Methodology In the present study, laboratory flume model GUNT HM162 with a length of 12.5 m, width 0.31 m, and height 0.47 m with glass walls and the metal floor was used. A centrifugal pump with a flow rate of 165 m3/h and a height of 16 meters was used for the experiments. A wave generator with a frequency of 0.5 to 1.11 Hz was applied to create a wave in the laboratory flume. All experiments were performed at a constant flow depth of 200 mm. Three values were chosen for the distance of the OWC device from the water surface in the normal state (d), according to the chamber length (B). Therefore, distances of 10%, 25%, and 45% of the OWC chamber length were used as parameter d. To investigate the effect of back wall height (Z) on OWC efficiency, three physical models were made in three modes without back wall and with 5 and 10 cm back wall. In this research, the power generated by the wave inside the device was performed to evaluate the performance of the OWC. In addition, a twoway analysis of variance test was used to investigate the effect of independent parameters such as back wall height, the depth of the system, and the frequency of waves on the output power to determine the main and interaction effects.Results and Discussion The results show that with increasing the installation depth of the system, initially the amount of output power increased but then had a decreasing trend. Accordingly, the depth with the best performance must be considered for OWC. In this study, it was found that 0.25 B (chamber length) installation depth has better performance than the other two cases. Comparison of the effect of the back wall on the performance of the device at a depth of 0.25B shows that the models with the back wall have better performance comparing with the model without a back wall. The performance of the two back walls at frequencies less than 0.8 is similar, but for higher frequencies, the 10 cm back wall has better performance than another back wall. All the main effects have a significant influence on the output power, which the frequency of the waves and the height of the back wall have a higher effect. The results related to the interaction effects of independent parameters show that the interaction effects have a high influences on the amount of output power. Among the interaction effects, (Z × d) and (Z × Frequency) have a significant effect on the output power, which indicates the effect of the back wall on the total power. The results of the margin averages show that at the maximum frequency used, the 5 and 10 cm back wall were increased the efficiency of the OWC by 98% and 182%, respectively, compared to the model without a back wall.Conclusions Based on the result of the experiments, the presence of the back wall has a high effect on the OWC output power so that in the best installation depth (d =0.25B) and frequency of 1.1 Hz, the 5 and 10 cm back wall, increases the output power by 1.18 and 1.83, respectively. Twoway analysis of variance was used to investigate the effect of different parameters on OWC efficiency. The result of twoway ANOVA shows that the frequency of the waves and the back wall had the greatest effect on the output power. On the other hand, the interaction of the back wall with the frequency and installation depth also had a significant difference at the level of 0.01. The performance of the two back walls used at low frequencies was similar, but for the higher frequencies, the 10 cm back wall performed better. Accordingly, it can be concluded that the presence of a larger back wall cannot produce more power in all frequencies.