高坝泄洪诱发低频声波的机理及环境危害评估方法研究

In China, the structure vibration, downstream scouring and atomization induced by flood discharge of high dam have been widely studied, while few studies have been done on the induced low frequency noise(lower than 10Hz of air pulsation) and its environmental hazards so far. In view of the fact that low frequency noise(LFN) has been actually measured in models and prototypes of Xiangjiaba and Jinping projects, and the possibility that the noise may cause environmental hazards such as the vibration of house doors and windows and the discomfort of residents to some extent in actual projects, we plan to carry out prototype observation, a series of physical model tests and theoretical analysis to investigate deeply the mechanism of LFN induced by flood discharge as well as the key influencing factors. We will establish a quantitative method for forecasting the intensity of induced LFN, and study the LFN transmission pattern, the range of environmental hazards, the control technique of LFN and the similarity criterion for the distortion of induced LFN in the physical models with various scales, etc. The study is to make up the relevant study by providing theoretical support for the design and operation of flood discharge structures to avoid the possible hazards caused by LFN.

高坝泄洪诱发结构振动、空蚀破坏、下游冲刷和雾化等工程灾害已被人们熟知和广泛研究，而高坝泄洪诱发的低频声波（10Hz以下气压脉动）及其对环境的危害在国内基本没人研究。鉴于向家坝、锦屏等工程原型和模型泄洪时都实测到低频声波，实际工程中会在一定范围内存在诱发房屋门窗振动、造成人体不适等环境危害，本项目拟通过原型观测、系列物理模型实验和理论分析，深入研究高坝泄洪诱发低频声波的机理、影响低频声波的关键因素，建立泄洪诱发低频声波强度的定量预测方法，研究泄洪诱发低频声波传播规律及环境危害影响范围、泄洪诱发低频声波振动的控制技术、系列比尺物理模型模拟泄洪诱发低频声波的变态相似性等，为高坝泄洪工程的设计和运行中避免低频声波危害提供理论依据，以填补我国在该领域研究的空白。

高坝泄洪诱发低频声波是近年来高坝泄洪工程中发现的新问题，低频声波会引起结构物振动，同时也会影响周边人员的健康；此外，低频声波传播速度快，大气对低频声波能量吸收难，低频声波衰减慢，因此其环境影响范围广。本项目通过原型观测分析了泄洪诱发的低频声波的空间分布、时域和频域特性，采用考虑了泄洪雾化影响的大气声吸收理论计算低频声波传播和衰减规律，计算得出雾化区的声衰减系数约为0.0327dB/m，非雾化影响区的声衰减系数约为0.000349dB/m，计算结果与实测结果相符；基于原型观测结果，对比底流消能与挑流消能两种泄洪消能型式诱发低频声波的不同，提出了挑跌流泄洪消能诱发低频声波的多振源发声机制；采用单通道盲源分离算法与声源识别与定位技术，验证了金安桥电站泄洪诱发的低频声波声源位于消力池消能区，为后续研究提供技术支持；结合紊流数值模拟和涡声理论，提出了高坝泄洪底流消能诱发低频声波强度定量预测数学模型，预测声压与实测声压的谱相关系数分布在0.645~0.717之间，数学预测结果与原观低频声波在能量谱的不确定性和复杂度上十分接近，数学预测模型预测效果较好；结合低频声波原型观测分析、气-液紊流模型、涡声理论模型、声学数值模型，首次提出从水垫塘淹没射流和挑流水舌空腔耦合振动两个角度出发研究高坝挑跌流泄洪消能诱发低频声波的多振源发声机理；同时开展了高坝挑跌流泄洪消能诱发低频声波的多振源影响分析，结果表明水垫塘淹没射流和挑流水舌空腔耦合振动均对现场低频声波能量有贡献。其中，水垫塘淹没射流诱发低频声波贡献比平均为0.619，挑流水舌空腔耦合振动诱发低频声波贡献比平均为0.785；采用有限元模态分析和瞬态动力学响应分析，证明了泄洪现场卷帘门的振动主要与低频声波有关，同时提出了相应的振动控制措施，为泄洪诱发低频声波环境危害控制提供了技术支持。