| With the development of the economy and society and the improvement of people’s living standards,people’s demand for electricity is also growing.Traditional energy sources are not renewable,small stocks and serious pollution.It is difficult to meet the needs of high-quality development of society by these traditional fossil energy sources.Offshore wind power has the characteristics of clean,green,low carbon and sustainable development,which complements the shortcomings of traditional energy.Therefore,countries pay more and more attention to the planning and development of offshore wind farms.China’s coastal areas are rich in wind energy resources and have great advantages.Most of the offshore wind farms are concentrated in the area,but there are many rare marine lives in the surrounding sea areas,such as Fujian,Guangxi Chinese white dolphins,Liaoning spotted seals,etc.Many wind farms are built near the protected areas.The construction of offshore wind farms will generate a large amount of underwater noise,the most serious effect of which is underwater piling noise.Underwater piling noise has the characteristics of high strength,long duration and serious pollution,and it increases with the increase of pile diameter.Many studies have shown that piling noise can alter the behavior of marine mammals and fish,masking their communication,leading to hearing damage and even death,which greatly interferes with their habitat.With the rapid development of offshore wind farms,the pile diameter used in piling construction is also increasing,and the noise source is becoming stronger.At present,the pile diameter adopted by some wind farms has increased to 7.8 m,but the public large-diameter piles(>6 m)have less pile noise data,and it is difficult to accurately estimate the source strength of large-diameter piles.Therefore,it is necessary to analyze the source intensity of underwater piling noise of offshore wind farms to meet the scientific research needs of underwater acoustic ecological environment,and provide the basis for scientific construction and environmental assessment of offshore wind farms,so as to ensure the scientific and rational development of offshore wind farms.By collecting and arranging the data of piling noise at home and abroad,this paper analyzes the relationship between the source strength of pile driving noise and the pile diameter,and derives a more appropriate empirical formula,so that the construction party can take corresponding acoustic protection measures.The main research contents and results of this paper are as follows:1.Collect and organize the develop ment process of pile foundation for offshore wind farms,expound the construction plan of piling construction,briefly summarize the monitoring methods of underwater piling noise at home and abroad,summarize the research status of piling source strength and its impact on marine life in offshore wind farms.2.Taking the monitoring data of piling noise of eight piles and monopile of Dalian offshore wind farm as an example,the acoustic characteristics of time domain and frequency domain are analyzed,combined with the environmental factors of construction sea area,the propagation curve is fitted,and the sound source level is calculated.Comparing the piling noise of the two pile diameters,the measured data of the two types of pile diameters are provided for the study of the relationship between the sound source level and the pile diameter,which is used to verify the empirical formula of sound source estimation.3.The relationship between the sound source level of the piling noise and the pile diameter of piling noise in offshore wind farms is studied,and the empirical formula is given.Through the monitoring and analysis of the piling noise of offshore wind farms and the data of piling underwater noise at home and abroad in recent years,it can be seen that with the increase of large-diameter pile foundations used in offshore wind power sites,the sound source for such piling noise is used.The empirical formula of the level estimate has an;"overestimation" and does not apply to the current acoustic protection of offshore engineering construction.In order to carry out the marine acoustic environmental impact assessment during the construction process more effectively and accurately,it is necessary to re-evaluate the sound source level of the construction piling noise.This paper collects the underwater piling noise data of offshore wind farms at home and abroad,uses cftool in MATLAB to curve fit,compares the fitting results with the empirical formulas of Nedwell and Wyatt,and uses the data of the research group in the sea areas of Dalian and other places in China.The measured data is verified and the empirical formula is closer to the measured data.When the pile diameter is within 0-5 m,the fitting result is basically consistent with the measured data.When the pile diameter exceeds 5 m,the fitting result is slightly higher than the measured data,but the error is still less than the empirical formula estimates of Nedwell and Wyatt.When the diameter is 6.5 m,the estimated value is 6.5 dB higher than the measured value.4.Analyze the impact of underwater piling noise on different marine organisms.Piling noise can have multiple effects on marine life.The extent of impact are related to the sound source level,water depth and the threshold of marine life.In general,the deeper the water depth,the smaller the propagation loss factor F,the less the propagation loss,and the greater the impact range.According to the empirical formula and the environmental conditions such as the water depth of the construction sea area,the sound source level and the influence range can be estimated before the piling construction,and relevant suggestions can be made in a targeted manner to protect the ecological environment around the construction sea area.This paper takes the rms sound source level of the piling noise is 230 dB and the propagation loss factor are 15~22 as example to estimate the impact range of the pile driving activities on finfish and fish.5.For the underwater noise sources generated by large-diameter piling construction of offshore wind farms,the paper also summarizes several main methods of noise reduction,and compares these methods from the practicality of engineering to propose the choice of acoustic protection for marine life... |
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