Based on nearfield sound pressure sensing to pick up error information, an approach for constructing active acoustic structure to effectively reduce radiated sound power at low frequency is proposed. The idea is that a nearfield pressure after active control is used as error signals and transformed into an objective function in adaptive active control process.Firstly sound power expression using near-field pressure radiated from a flexible structure is derived, and then three kind of nearfield pressure based active control strategies,i.e.minimization of radiated sound power, minimization of sound power for dominant radiation modes and minimization of sound power for modified dominant radiation modes are respectively presented and applied to active control of radiated single and broadband noise. Finally computer simulations on sound power reduction under three strategies are conducted and it is shown that the proposed active control strategies are invalid and considerable reduction in radiated sound power can be achieved.
针对多重分形分析很难估计有限长离散数据的多重分形谱这一问题,提出了一种基于奇异性分析的多重分形图像去噪算法。通过定义基于小波系数矩的配分函数,给出了一种有限长离散数据序列多重分形谱估计方法。图像去噪算法中图像的性质由多重分形谱决定,对噪声的类型没有提出任何假设条件,而是通过定义一个基于二维微局域(2 mi crolocal)分析的变换算子对每一点的Hausdorff指数进行处理,使处理后的图像中大多数点位于平滑区域的同时,谱的相对强度没有变化,从而取得最佳效果。实验结果表明,该方法在去除噪声的同时可很好地保留原始图像的纹理信息。
