船舶侧斜螺旋桨空化噪声调制谱模型

针对侧斜螺旋桨船舶建立了一种螺旋桨空化噪声调制谱理论模型。将螺旋桨旋转过程中崩溃的空泡体积的周期性变化近似为空化噪声能量的变化,根据船尾伴流速度与空泡噪声体积成比例以及螺旋桨转速与空泡数量成比例的关系,推导出了空化噪声调制谱数学表达式。理论分析和仿真验证了桨叶之间的差异性是调制谱轴频线谱存在的主要原因,而影响调制谱叶频强度的主要因素为螺旋桨侧斜角度以及转速。研究结论为辐射噪声调制谱特征分析与提取提供了理论依据,同时对螺旋桨结构设计和船舶降噪也具有一定的参考价值。     

船舶侧斜螺旋桨空化噪声调制谱模型

针对侧斜螺旋桨船舶建立了一种螺旋桨空化噪声调制谱理论模型。将螺旋桨旋转过程中崩溃的空泡体积的周期性变化近似为空化噪声能量的变化,根据船尾伴流速度与空泡噪声体积成比例以及螺旋桨转速与空泡数量成比例的关系,推导出了空化噪声调制谱数学表达式。理论分析和仿真验证了桨叶之间的差异性是调制谱轴频线谱存在的主要原因,而影响调制谱叶频强度的主要因素为螺旋桨侧斜角度以及转速。研究结论为辐射噪声调制谱特征分析与提取提供了理论依据,同时对螺旋桨结构设计和船舶降噪也具有一定的参考价值。     

浅析水下高速航行体对转螺旋桨辐射噪声线谱建模

分析了某水下高速航行体辐射噪声线谱统计特性,指出对转螺旋桨水下高速航行体线谱主要由螺旋桨“叶片速率”线谱及其谐波频率线谱组成。在此基础上,以周期信号为模型建立了航行体辐射噪声线谱数学模型,并应用该模型对不同转速航行体辐射噪声线谱频率进行了预测。     

遗传算法优化变分模态分解提取舰船辐射噪声特征线谱方法

特征线谱提取是舰船目标识别的一个重要研究环节,常采用传统的DEMON谱分析方法,处理过程中,一般对舰船噪声时域信号未予抑噪,低信噪比情况下,传统DEMON谱分析性能差。对此,提出一种采用遗传算法优化变分模态分解方法,用于分解舰船噪声原时域信号,获得抑制噪声后的舰船噪声重构信号,进而有效提取了舰船目标噪声幅度调制特征线谱。该方法首先采用遗传算法优化变分模态分解的两个关键输入参数(分解所取模态个数和惩罚因子),对变分模态分解得到的各阶固有模态分量加以判别,去除噪声主导分量,保留信号主导分量,使重构舰船噪声信号显著抑制了干扰噪声,然后对降噪后的重构信号进行频谱分析,获得目标噪声调制特征线谱。理论分析、仿真和实验数据处理结果表明,相比传统DEMON谱分析法,基于遗传算法优化变分模态分解的舰船噪声特征线谱提取方法具有更好的噪声抑制能力,所获取的舰船噪声幅度调制特征线谱信噪比明显高于传统DEMON方法,具有一定优势,前景良好。     

Theoretical analysis of the ship noise demodulation spectrum harmonic clan feature

The structure law of the ship noise demodulation spectrum harmonic clan feature and corresponding applications to the recognition problem are studied by theoretical derivation and sample analysis.In order to recognize the propeller blade-number,the ship propeller cavitation noise model is established on the basis of five hypotheses.Further,the mathematical expressions of the structure law are deduced by the model.And the class space of the propeller blade-number is analysed mathematically.The results can be applied to target recognition as expert knowledge.Finally,the demodulation spectrum harmonic clans of experiment samples are obtained by using the wavelet packet.The structure law is validated by the statistic analysis of experiment samples.It is shown that the statistical average results of experiment samples are consistent very well with the theory structure law,and 78.6% of the samples basically accord with the theory structure law.     

舰船辐射噪声线谱的幅度起伏模型

本文讨论在海中传播的舰船辐射噪声线谱和海洋环境噪声的幅度起伏模型。当线谱信号模型取正弦波加窄带高斯噪声时,窄带检测系统的输出起伏满足2 BT个自由度的非中心卡埃平方分布,起伏方差为声源特性和传播过程造成的起伏方差与处理器引起的方差之和;而海洋环境噪声采用平稳的白色高斯噪声模型时,通过窄带处理系统后的输出起伏满足2 BT个自由度的卡埃平方分布,方差仅由处理器决定。最后给出相应的实验结果,与理论计算符合良好。     

Prediction and validation of tonal noise from underwater propellers

Prediction and validation of low-frequency line spectrum noise from ship propeller under non-cavitating condition is presented.The flow field is analyzed with potential-based panel method,which requires the hydrodynamic forces to be integrated over the actual blade surface,rather than over the mean-chord surface.Then the pressure data is used as the input for Ffowcs Williams-Hawkings formulation to predict the far field acoustics.At the same time,propeller unsteady force is measured in hull-behind condition in China Large Cavitation Channel(CLCC).Line spectrum noise of the 1st blade passage frequency(BPF) of a five-bladed propeller operating in a non-uniform flow field is got according to the calculated and measured unsteady forces,in which good agreement is obtained,and the 1st BPF noise difference is within 3.0 dB.The investigation reveals that prediction precision of the propeller's 1st BPF unsteady force with panel method have reached engineering practical degree,providing significant parameters for prediction of propeller line spectrum noise.     

Characteristic correlation between propellers cavitating wake and cavitation noise

The characteristic correlation between the propellers cavitating wake and their cavitation noise has been studied. Based on the viscous multiphase flow theory, the Navier–Stokes equations, a turbulence model and a cavitation model were applied to predict numerically the vapor volume fraction and the pressure in the wake. Compared with experimental results, the numerical predictions of the sheet cavitation and the tip vortex cavitation are in agreement with the corresponding experimental data, which indicates the numerical method in present paper is feasible. The characteristic of the low line spectra of the numerical pressure fluctuation signals and the measured noise signals for uniform inflow and wake flow is analyzed, and the characteristic correlation of the two line spectra is also validated. Therefore, it can be concluded that due to the wake and the radiated noise both modulated by the revolving propeller blades, the features of the low line spectra for noise signals and the pressure signals in the wake are close to each other.     

参数未知的舰船辐射噪声检测方法

舰船辐射噪声的检测方法已有广泛研究,其中线谱特征是检测的重要依据。基于线谱特征的舰船辐射噪声检测方法常需要线谱数目、频率等参数作为检测的先验信息,这些信息不准确或无法确知时,检测方法的性能会受到显著影响。针对实际应用中对于未知舰船无法获得其参数信息的情况,研究基于连续谱谱峰特征的更为一般性的信号存在性检测方法。将窄带信号瞬时频率分析的思想扩展到舰船辐射噪声这类宽带信号,从信号频率与能量分布的角度推导得到宽带信号"瞬时频率"的近似表示式。构建宽带信号的瞬时频率检测器,并对其性能进行理论分析,结果表明该检测器的性能主要受舰船辐射噪声瞬时频率方差以及接收信噪比影响。通过计算机仿真和实际数据对算法的性能进行了验证。     

参数未知的舰船辐射噪声检测方法

舰船辐射噪声的检测方法已有广泛研究,其中线谱特征是检测的重要依据。基于线谱特征的舰船辐射噪声检测方法常需要线谱数目、频率等参数作为检测的先验信息,这些信息不准确或无法确知时,检测方法的性能会受到显著影响。针对实际应用中对于未知舰船无法获得其参数信息的情况,研究基于连续谱谱峰特征的更为一般性的信号存在性检测方法。将窄带信号瞬时频率分析的思想扩展到舰船辐射噪声这类宽带信号,从信号频率与能量分布的角度推导得到宽带信号\