IMO批准《船上噪声等级规则》修订草案

  目的  单向周期加筋板在船舶结构中应用广泛，开展其声振特性理论研究可为加筋板的声振特性分析和优化提供理论参考。  方法  首先，考虑骨材对板的力和扭矩作用，以及流体声介质与板的耦合作用，分别建立无限大单、双周期加筋板的结构动力学模型；然后，通过傅里叶变换将空间域转换到波数域，应用构造函数、泊松公式及周期函数的性质推导加筋结构的振动方程，得到力激励和声波激励下加筋板振动位移的解析解，并利用稳相法给出加筋板的远场声压表达式；最后，通过具体算例讨论骨材扭矩、激励类型、激励位置、板厚、骨材参数等因素对周期加筋板结构声振特性的影响规律。  结果  骨材扭矩对加筋板声振特性的影响较小；对于周期加筋结构，可以利用骨材参数对声子晶体带隙的影响，衰减某些频率的振动；激励加载在强构件处可有效减弱振动；骨材的间距、尺寸等参数对声振特性的影响较为明显。  结论  对激励及骨材参数的合理设置，可以有效优化加筋板结构的水下声振特性。

Sound radiation from fluid loaded orthogonally stiffened plates

  Objectives  One-way periodic stiffened plates are widely used in ship structures, and their vibro-acoustic characteristics provide a theoretical reference for the analysis and optimization of the sound and vibration characteristics of stiffened plates.  Methods  Considering the force and torque of the stiffeners to the plate, along with the coupling effect between the fluid acoustic medium and the plate, a structural dynamic model of infinite one-dimensional and two-dimensional periodically stiffened plates is established. The spatial domain is transformed into a space wave number domain using the Fourier transforms method. The vibration equation of the stiffened structure is deduced using the constructor, Poisson's formula and periodic function. The analytical solution of the motion equations of typical periodic stiffened plates is obtained and calculated under a time-harmonic point force or harmonic excitation. Combined with the stationary phase method, the far field radiated sound pressure can be obtained. The influence of the torque of the stiffener, excitation types, excitation locations, plate thickness, periodicity spacing and parameters of stiffeners on the sound radiation characteristics of three different models of periodic stiffened plates are numerically quantified.  Results  The torque of the stiffener has a lesser effect on structural vibration characteristics. The influence of the stiffener parameters on the phonon crystal band gap can be used to attenuate the vibration at certain peak frequencies. The excitation load on the strong structural components can effectively weaken the vibration. The periodicity spacing and parameters of the stiffeners have obvious effects on structural vibration characteristics.  Conclusion  The underwater acoustic vibration characteristics of reinforced plate structures can be effectively optimized by the reasonable setting of the excitation types and parameters of the stiffeners.