预测声屏障插入损失的抛物方程方法研究

发布时间：2018-09-13 14:26

【摘要】：声屏障可以有效地降低交通噪声和工业噪声对环境的影响。在将声屏障用于环境噪声控制的实际过程中,事先准确预测声屏障的插入损失可以有效地指导声屏障的几何尺寸和安装位置的选择以及声屏障的结构设计过程。声屏障插入损失的常用预测方法包括解析法、近似法、边界元法(BEM),但是上述这三类方法仅适合用于声速和地面阻抗等参数为常数的均匀环境中的插入损失预测。在实际情况下,这些参数常不稳定(即非均匀环境),例如,顺风时声速随着高度的增加而增加。忽略声速、地面阻抗等因素而直接使用上述三类方法进行预测会导致一定的误差。抛物方程方法具有兼容非均匀性的优点,可以用于更为接近实际的户外环境。Salomons首次提出将有限差分抛物方程(Crank-Nicholson Parabolic Equation:CNPE)用于非均匀环境中的声屏障的插入损失预测,但是Salomons建立的方法在声屏障与声源距离较近时会产生较大误差,并且对于声屏障距离接收点较远的情况,该方法计算网格点的数目巨大,计算所需时间长。这两个缺点限制了该方法的应用。本文针对这两个缺点开展研究,建立完善的用于预测声屏障插入损失的抛物方程方法。本文首先介绍了声屏障插入损失计算方法的研究进展,以及有/无声屏障时计算位于阻抗面上方的点源辐射声场的解析方法。解析方法的结果可以为检验抛物方程方法的有效性和准确性提供参考。然后,介绍了CNPE方法的理论,并通过分析发现CNPE方法在声源距离声屏障较近的情况下会产生较大误差的原因在于CNPE方法所使用的Gauss初始场仅适用于小仰角(10度以内)范围内的声波。为解决Gauss初始场引起的问题,本文推导了可以用于较大仰角声波的更高阶数的Gauss初始场。通过数值仿真对比了不同阶数的初始场在CNPE方法中的效果。结果表明:4阶初始场是最适合CNPE方法的初始场,将该初始场与CNPE方法相结合,可以准确预测当声屏障与声源距离较近时的插入损失。最后,针对CNPE方法在接收点与声屏障距离很远的情况下计算效率很低的缺点,提出了基于格林函数抛物方程(Green’s function parabolic equation:GFPE)的插入损失计算方法,并通过数值仿真验证了GFPE方法的正确性及其预测声屏障插入损失的可行性。CNPE和GFPE两种方法所需计算时间的对比表明GFPE方法可以明显的提高计算效率,尤其是在频率较高的情况下,GFPE方法的计算速度优势更加明显。
[Abstract]:Noise barriers can effectively reduce the impact of traffic noise and industrial noise on the environment. In the actual process of applying noise barrier to environmental noise control, accurately predicting the insertion loss of sound barrier in advance can effectively guide the choice of geometric size and installation position of sound barrier and the structural design process of sound barrier. The commonly used prediction methods for acoustic barrier insertion loss include analytical method, approximate method and boundary element method (BEM),). However, these three methods are only suitable for the prediction of insertion loss in uniform environment with constant acoustic velocity and ground impedance. In practice, these parameters are often unstable (I. e., non-uniform environments), for example, the velocity of sound increases with the height of the downwind. Ignoring the factors such as sound velocity and ground impedance and using the above three methods directly will lead to certain errors. The parabolic equation method has the advantage of compatibility with inhomogeneity. It can be used to predict the insertion loss of sound barrier in non-uniform environment by using the finite difference parabolic equation (Crank-Nicholson Parabolic Equation:CNPE) for the first time. However, when the distance between the sound barrier and the sound source is close, the method established by Salomons will produce great error. For the situation that the noise barrier is far away from the receiving point, the number of grid points calculated by the method is huge and the calculation time is long. These two shortcomings limit the application of this method. In this paper, a perfect parabolic equation method is developed to predict the insertion loss of noise barrier. This paper first introduces the research progress of the calculation method for the insertion loss of the acoustic barrier and the analytical method for calculating the radiation sound field of the point source located above the impedance surface when there is a / no barrier. The results of the analytical method can provide a reference for checking the validity and accuracy of the parabolic equation method. Then, the theory of CNPE method is introduced. It is found by analysis that the CNPE method has a large error when the sound source is close to the sound barrier because the Gauss initial field used by the CNPE method is only suitable for acoustic waves in the range of small elevation angle (less than 10 degrees). In order to solve the problem caused by Gauss initial field, the Gauss initial field with higher order can be used for large elevation acoustic waves. The effect of the initial field of different order in CNPE method is compared by numerical simulation. The results show that the initial field of the fourth order is the most suitable for the CNPE method. Combining the initial field with the CNPE method, the insertion loss can be accurately predicted when the sound barrier is close to the sound source. Finally, aiming at the disadvantage of the CNPE method with low computational efficiency when the distance between the receiving point and the noise barrier is very long, a method for calculating the insertion loss based on the Green function parabolic equation (Green's function parabolic equation:GFPE) is proposed. The correctness of the GFPE method and the feasibility of predicting the insertion loss of the noise barrier are verified by numerical simulation. The comparison between the calculation time required by the two methods shows that the GFPE method can obviously improve the computational efficiency. Especially in the case of higher frequency, the speed advantage of the GFPE method is more obvious.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB535

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