【作者】 李凯；

【导师】 赵德有； 黎胜；

【作者基本信息】 大连理工大学 ， 船舶与海洋结构物设计制造， 2011， 博士

【摘要】 船舶结构振动与噪声控制是一项十分必要的研究课题,它涉及到船舶在运行过程中对环境的影响、舒适性、结构安全性和隐身性等方面。因此,有效减少振动和噪声已成为船舶结构设计的一个重要目标。在船舶设计的早期阶段就需要考虑到声振要求,针对舰船中存在的结构噪声源进行分析,研究声振动在船体结构中产生、传播和耗散的机理和规律,使所建造的舰船满足低振动、低噪声的要求。本课题正是围绕这一出发点开展理论和数值研究。介绍了结构声振动传递问题的主要研究方法：对国内外结构振动声强试验和计算方法的研究进行了系统的总结；归纳了角谱声学和科学计算可视化的研究现状；并进行了板梁组合结构有限元模型固有频率的分析。针对船舶结构中广泛使用的加筋板,基于结构声强法研究了加筋板振动能量的传输,分布和耗散特性。介绍了结构声强分量的计算可视化的相关理论,以及系统功率输入和输出的计算公式；在数值算例中,利用有限元法对三种常见的加筋板模型进行了简谐集中力作用下的动力计算,然后通过编制程序计算结构声强分量,进行结构噪声源的定位,实现能量传输和衰减的可视化；同时针对不同的加筋形式对能量传递路径的影响也进行了讨论；研究了不同加筋板阻尼器能量耗散特性。最后以舰船平台板架为例揭示了结构声强技术在舰船振动设计的应用价值。在振动声强计算程序的基础上将流线可视化和振动能量可视化技术集成起来,基于Matlab软件完成动力分析和数据计算的相互调用,实现振动能量流的集成可视化显示；编制了数值仿真交互可视化界面,通过后台的调用计算,从而取代人工重复性的工作,在实际工程问题中可以节省很多计算时间和成本。借助于集成可视化技术可以准确揭示振动能量在耦合板中的传递分布特性,分析振动波在复杂耦合结构中的传播机理及在进一步实施主/被动控制中提供更准确的科学依据。针对船舶与海洋工程中常见的开口结构,基于振动能量可视化技术进行了开口加筋板能量流动特性的研究和振动抑制的探索。推导了结构声强和振动能量的平衡关系；分析表明,结构开口的出现,显著影响了振动能量在加筋板结构中的传递和分布；振动能量主要集中于开口的边界位置,应变能的最大幅值大多位于激励点位置和开口的夹角处。基于能量传递和分布可视化图,准确的判定敷设约束阻尼层的位置和数量,有效的控制开口加筋平板结构的振动响应,同时显著降低结构声能量的传递。对于流体加载结构振动和声学特性研究,介绍了声振能量传递和声固耦合相关理论；给出了结构振动能量与声辐射能量的关系,并从能量的角度出发,探讨了流体载荷对振动能量流动的影响,其中包括流体参数,激励频率等。通过辐射声强矢量图可以明显的观察到结构声的近场效应,即振动能量会从空间流向板的表面,此时流体介质对结构的反作用力不断的将能量返回给振动板表面,这一个流动过程体现了能量在流体和结构表面之间的交换和守恒,能量在这一区域流出和流入趋于稳定,因此大部分的能量驻留在结构的近场。由理论公式可知,声能量的量级主要取决于板单元的响应贡献的叠加,而结构声强则取决于振动能量在板结构中的分布和大小。因此可以通过改变或耗散结构振动能量的方法,进而控制声辐射能量的大小；通过能量可视化技术可以清晰的揭示能量集中的区域,在能量输入点和能量聚集区域确定合理的能量耗散控制点,通过添加外部阻尼器的方法,探讨阻尼耗散对频段内声振动能量传递的影响,取得了一些有实用价值的结论。对于结构声振动传递问题,从波数域角度入手,从本质上研讨振动波在介质中传递的波矢分量特性。应用声学角谱法,推导了典型平面倏逝波相位空间分布的解析表达式；给出了有限声源辐射场的角谱函数公式和可视化表达；在波数域求解了流体加载无限大平板在集中力和分布线力作用下的振动响应问题,推导了简支矩形板的波数域模态速度响应解析表达式；给出了不同激励参数下简支平板波数域结构声强可视化图；同时计算分析了不同板厚和流体密度对流体加载板临界频率的影响。本文从声振能量可视化的角度,以数值仿真结合理论推导为主,从物理和波数空间共同揭示结构声振传递规律,为结构声辐射机理及控制研究提供简捷、准确的理论依据。更多还原

【Abstract】 Reduction of vibration and noise of marine structures has been an important issue to designers. In these fields the accurate investigation of vibration energy transmission and distribution is of particular importance for structural noise and vibration control. This dissertation addresses a study on numerical analysis of vibration and radiation intensity. The major contents of the dissertation are as follows.The various methods related to vibration and noise radiated problems are introduced. The advantages and disadvantages of the approaches are discussed. The basic principle and development status of structural vibration intensity measurement and calculation technology are explained. The research prospects of angular spectrum approach and Visualization of Scientific Computing (ViSC) are also discussed.Three typical stiffened plate models under harmonic point force exciting are calculated to predict the vibration intensity’s components by finite element approach. Then, the intensity vector map visualization is used to indicate the location of vibration source and the sinking position where the energy is dissipated. The effects of stiffeners on the changes of energy transmission path through plate are also discussed. Moreover the input energy at the exciting point and dissipated energy at the damper are investigated. Also, an application of structural vibration intensity technique towards the design for platform of ship is explored.Based on the Matlab software, the Vibration Energy Flow Graphical User Interface(VEF-GUI) is designed by combing the dynamic analysis and mathematical processing capabilities. Furthermore, the Interactive Visual Interface containing numerical simulation and engineering test module is developed, which can save a lot of work and costs in research and practical engineering applications. The transmission and distribution of vibration energy flow in coupled plates are studied by VEF-GUI. The intensity vector, streamline map and energy distribution of coupled plates subject to a point force excitation are calculated and visualized to predict vibration energy transmission. The vibrational energy flows are very complex and dependent on the excitation frequencies, junction forms and boundaries. The vibration intensity method together with visualization techniques provides a powerful tool for vibration control.The energy flow visualization and control in vibrating stiffened plates with a cutout are studied using finite element method. The vibration intensity streamline, vibration energy and strain energy distribution of stiffened plates with cutout at different excitation frequencies are calculated respectively and visualized for the various cases. The cases of different size and boundaries conditions of cutouts are also investigated. It is found that the cutout or opening completely changes the paths and distributions of the energy flow in stiffened plate. The magnitude of energy flow is significantly larger at the edges near the cutout boundary. The position of maximum strain energy distribution is not corresponding to the position of maximum vibrational energy. Furthermore, the energy-based control using constrained damping layer (CDL) for vibration suppression is also analyzed. According to the energy distribution maps, the CDL patches are applied to the locations that have higher energy distribution at the targeted mode of vibration. The present energy visualization technique and energy-based CDL treatments can be extended to the vibration control of vehicles structures.The vibration energy flow in a fluid-loaded stiffened plate and the structural-acoustic coupling from the energy flow point of view are investigated using intensity vector technique in this paper. The spatial distribution of the vibration and acoustic energy flow is visualized to show the position of energy source, the direction of flowing energy and the amount of radiation sound energy with visualization technique. The numerical results show that the fluid loading changes the vibrational and sound energy flows. The structural-acoustic energy flow under air loading condition is generally at a smaller rate than that of under water loading condition from the spectrum plot. From GUI plots the sound energy flow clearly shows the structural near field behavior where the intensity vectors bend back to the panel surface. Furthermore, significant discrepancy between the sound energy distribution near the surface of the plate and the vibration energy in the stiffened plate is observed. The external damper significantly influences the vibrational and sound energy flows and the damping control strategies are investigated. The visualizations of the energy clearly show that the damper should be placed close to the energy input source and more damping involved more energy dissipated.An efficient Fourier transform technique to address the vibration structural and sound characteristics of a fluid-loaded plate excited by a mechanical force is presented. The process is based on the formulation in the wave number domain of the transversal response of the plate and of the acoustic response in the fluid domain. Analytical expressions in wave number space is obtained for these fields in the case of an infinite plate with point force and unform line force and a simply supported plate with point force. The cases using the two-dimensional Fourier transform to deduce the wave number fields of simply supported plate are discussed concerning structural intensity results on the plate.The angular spectrum function of various limited radiation source is developed and visualized to model the propagation of a wave field. This technique provides an efficient tool to analyse the vibro-acoustic behaviour of the structure.The characteristic of structural and sound energy transmission and distribution is invested in detail. The application of the vibration intensity methods together with Graphical User Interface visualization technique has improved the quality of structure-borne noise diagnostics and has made it possible to visualize energy wave phenomena in a vibrating structure.更多还原