【作者】 张道伟；

【导师】 张揽月；

【作者基本信息】 哈尔滨工程大学 ， 水声工程， 2011， 硕士

【摘要】 水下航行体在航行时,会产生各种各样的辐射噪声,主要分为三类：结构噪声、螺旋桨噪声和流噪声,这三类噪声严重影响了航行体的隐蔽性,而其中结构噪声的影响最为明显。为了提高水下航行体的隐蔽性,有必要对噪声特征线谱来源进行研究。论文主要针对壳体结构受激振动时产生的谐振特征线谱进行研究分析。提取水下航行体振动时产生的谐振信号,然后将振动信号转化为时间切片,分析不同频谱分辨率下的相位差随时间的变化情况,获取壳体结构振动与声辐射的线谱时移特征,为分析壳体受激振动产生的谐振特征,分辨水下航行体受激振动产生的谐振特征线谱来源,提供信息处理手段支撑。论文工作主要由以下几个方面展开：首先,论文对球壳进行理论计算和有限元仿真分析,验证通过有限元分析软件ANSYS求取壳体结构谐振频率的数值分析方法的正确性,然后对两边带半球帽的加肋圆柱壳进行模态分析和谐响应分析,求出其在水中受激振动的谐振频率。其次,论文研究了复调制细化频谱分析方法(Zoom FFT)和全相位FFT (apFFT)谱分析技术。对于窄带信号而言,Zoom FFT是一种有效的频谱细化手段。全相位FFT谱分析算法是一种优良的抑制频谱泄露的方法,在不进行频率校正的基础上,就可实现精确的相位估计,具有“相位不变性”。此外,apFFT还可以在噪声背景条件下,对多频信号的频率、相位以及幅度进行高精度估计。通过对两种算法的仿真研究,验证了两种算法的正确性和可行性。最后,设计试验,对两边带半球帽的加肋圆柱壳在水中进行单频激励和宽带激励,并采用复调制细化频谱分析方法(Zoom FFT)对谐振频率处的信号进行细化谱分析,同时提取谐振信号线谱细化后的相位信息,接着采用全相位FFT谱分析技术对细化前的谐振信号线谱进行分析,并提取其相位信息。然后,分析不同频谱分辨率下的相位差随时间的变化情况,提取壳体振动产生谐振时的时移特征,从而实现一种新的壳体结构谐振特征线谱的识别方法。更多还原

【Abstract】 Due to the large-scale shells navigating underwater, a variety of radiation noise would be produced, which can be segregate into the following three categories:structural noise, propeller noise and current flow noise. Not only the mobility but also the performance of concealment will be limited by the three types of noise, among which the structural noise is the most impactive. In order to improve the concealment property of marine large-scale shells, it is of great necessity to investigate the sources of noise line spectrum.In this thesis, the excited resonant vibration line spectra were mainly researched. The resonant signal generated by shell vibration was extracted and converted into time slices. Then the property of phase difference changing with time at different frequency resolution condition was analyzed, which characters the shell vibration and sound radiation characteristics and is named the time shift feature. That serves as a significant approach to distinguish the sources of resonance vibration line spectra. The main contents of this thesis are as follow:Firstly, numerical analysis was done for both the spherical shell and the cylindrical shell with a hemispherical cap at both sides. Then the Vibration modes and the resonant responses were analyzed with ANSYS through which the resonant frequencies were confirmed.Secondly, the complex modulation spectrum analysis (Zoom FFT) and the all phase FFT (apFFT) spectral analysis technique are analyzed in this thesis. Zoom FFT is an effective method of zooming spectra for narrow-band signals. As for the all phase FFT, it shows great advantage in suppressing the leakage of spectrum. Further more, accurate phase estimation can be achieved without any frequency correction, which benefits from the behavior of phase invariance. In addition, for the multi-frequency signals ruined by noise, high-precision estimations of frequency, phase and amplitude will also be obtained through the apFFT algorithm.Then the feasibility of both algorithms was demonstrated through the computer simulation.Finally, the underwater experiments were carried out. The cylindrical shell with a hemispherical cap at both sides was excited by both the single frequency and the broadband signal sources. Then the resonant frequency spectra were zoomed with the Zoom FFT transformation. Meanwhile, the original resonant signals were analyzed with the all phase FFT algorithm to obtain the phase information. Consequently, the feature that the phase difference changes with time at different frequency resolution condition could be extracted. Hence, the above signal processing provides a new promising method to identify the resonant line spectra of shell structures.更多还原