【作者】 王浩；

【导师】 黎胜；

【作者基本信息】 大连理工大学 ， 船舶与海洋结构物设计与制造， 2020， 硕士

【摘要】 在船舶与海洋工程领域,随着人们对船舰结构的安全性、先进性及生活的舒适性等要求的逐步提高,船舰的振动及噪声控制受到了研究人员的持续关注,其在工程实践和理论研究中具有十分重要的意义。而被动控制所敷设的阻尼材料应该具备阻尼性能好,减振频带宽,适用性强等诸多优点才能被广泛应用于大型船舶、舰艇、鱼雷等军用和民用工业的减振降噪措施中,因此研究分析影响阻尼材料减振降噪方面作用效果的因素就显得尤为重要。其中对于阻尼材料而言,材料的损耗因子是其耗散振动噪声能量的主要因素,其次不同的工作环境也会对阻尼材料的减振效果带来影响。所以本文主要就研究了敷设不同阻尼比的阻尼材料结构在不同工作环境中的结构振动模态以及声辐射响应特性,借助于有限元结构仿真模拟和声学边界元数值分析法联合计算实现对这一问题的理论求解分析,通过分析各个有限元结构模型的振动模态图与声功率级线谱图分析出阻尼层的阻尼比在数值上的差异对结构振动特性以及响应特性方面的抑制作用,在不同工作环境下对振动特性以及声辐射特性的影响效果,具有一定的工程实际应用价值和理论研究意义。首先讲解了振动噪声对于生产生活的危害性及人们应对措施措施,梳理了有关结构的模态分析理论以及声辐射传播理论的研究进展,整理归纳了现今对于阻尼材料研究的简化阻尼结构模型,对粘弹性阻尼材料性能和复合结构运动微分方程也做了相应简述。之后对阻尼结构的模态分析理论做出了详细的叙述,为下一步仿真模拟打下了坚实的理论基础。在实际仿真模拟时,利用有限元建模仿真计算对空气中和水下圆柱壳分别进行振动模态图的分析与比较工作,并和文献中给出的解析解结果进行了对比,所模拟仿真的结果与文献结果十分吻合,说明使用本文所采取的理论和操作方法可以用于分析阻尼结构的振动模态分析,为论文后期的研究工作做好了数值计算模拟的准备。本文首先以空气中的圆柱壳作为研究对象,利用有限元建模对五种自建结构模型进行模态计算,采取的是自下而上的建模方式,通过敷设不同阻尼比的阻尼材料来验证不同比对阻尼结构振动模态的影响。其次为了研究流体介质以及结构阻尼构型对结构复模态的影响,开展了对阻尼板的复模态研究分析。研究发现:单单依靠结构自身的阻尼无法到达减振降噪的目的,而阻尼比越高的阻尼层能让结构的振动幅值更加迅速的减小。但是过高的阻尼因子会改变结构的固有模态,改变结构的振型次序,反而使结构物更容易受到低频激励的干扰。与此同时也发现:由于现实中工程结构物的边界约束的不同很可能会诱发圆柱壳结构产生仅仅在端面处沿轴向方向上的振动而圆柱壳结构的周向侧面则未出现振动的振型模态出现。通过各个模型的结构阻尼与频率的关系曲线可以发现圆柱壳结构存着一种相对稳定的模态振型,而当振动频率跨越这个相对稳定的模态振型频率的时候,那么其结构阻尼比与固有频率会发生跨越式变化,就类似于曲线处于“断裂”的状态;而流体介质在结构振型方面的影响更多体现在固有频率的下降、振动幅值的减小以及振型次序变化上。从对阻尼结构复模态的影响来看:流体介质、敷设不均匀阻尼层会让相应结构产生复模态,且两者对振动结构的复模态实部影响是比较小的,而对振动质点相位的影响更大;流体介质对结构复模态的影响并不明显,而相比之下阻尼构型对阻尼结构复模态影响更大。阻尼板结构会在特定的复模态下MPC、MCC值突然减小或增大(变化值在一个数量级之上),特别是在当结构宽度(长度)方向的半波数固定,而结构的长度(宽度)方向半波数出现增减之时。从复杂度指标MCC和MPC可以看出,振动结构在接近高阶模态时不再是复模态振动了,对于高阶模态而言有更多实模态特性;而流体介质可以让均匀全敷设的阻尼板出现部分复模态振型;有时复杂度指标MPC值显示出结构是复模态振动,但是MCC值却无法很好地表明结构是复模态振动,所以在如何选取模态复杂度指标来衡量结构模态复杂度的方面还需进一步研究。对声辐射响应特性方面的研究,主要利用了边界元法计算了各个结构模型的声场,通过提取有限元建模仿真计算的结构外表面节点空间信息,结构外表面的节点振速、节点法向位移等响应信息,而后再利用边界元法进行声场计算分析,利用相应软件的直接边界元法的计算模块,计算圆柱壳结构的振动声学特征量——辐射声功率级曲线。研究发现:不同数值的阻尼比能够影响圆柱壳结构的振型次序,改变结构在低频振动下的模态振型,增加声辐射的模态复杂度;与此同时阻尼层的敷设,特别是较高阻尼因子的阻尼材料层的敷设,可以有效降低圆柱壳声辐射的辐射功率;在空气中敷设了阻尼材料层的圆柱壳在降低声辐射的声功率方面,其降噪效果要比在水中敷设了相同阻尼材料层的圆柱壳更为明显;宏观把握整个声功率级曲线的线谱特征可以发现在低频振动阶段声功率级曲线的变化是比较缓慢的,但是在振动频率到达了某一阶的振型模态之后,声功率级会迅速变大;对于本文所计算的0-600Hz的计算频率范围中的相对高频段,声功率级——频率曲线的幅值变化的程度要小很多,但此时共振峰也更加杂乱密集了。因此根据上述有关不同的结构阻尼比和流体介质对阻尼复合结构振动模态特性和声辐射响应特性的结论分析,研究人员在对工程结构减振降噪方面进行设计的时候,不可一味追求高阻尼比的阻尼层敷设,否则很容易受到低频激励的影响而产生共振。尽可能在设计的时候使得结构“稳定模态”的频率范围更大,从而减小结构受激励影响而产生共振的可能性。同时设计时也兼顾该结构的日常工作环境的特点,结构强度、稳性;对于结构响应部分,则重点对内部激励源区域施加减振降噪的措施,防止产生了有指向性的远距离传播的声波而破坏了声隐身的需要。更多还原

【Abstract】 In the field of ship and ocean engineering,with the gradual improvement of people’s requirements on the safety,advancement and comfort of ship structure,the vibration and noise control of ship has been continuously concerned by researchers,and it also has very important significance in theoretical research and engineering application.Passive control and laying of damping materials should have good damping performance,vibration frequency band width,applicability,and many other advantages can be widely used in large ships,naval ships,torpedoes and other military and civilian industrial vibration noise reduction measures,so the analysis influence the effect of damping material reducing vibration noise reduction effects factor is particularly important.For damped materials,the loss factor of materials is the main factor that dissipates the energy of vibration noise.Secondly,different working environments will also influence the damping effect of damped materials.So this paper mainly studies the structure of damping materials with different loss factor in the structure vibration characteristics and response characteristics of different working environment,with the aid of finite element simulation and acoustic boundary element numerical analysis method combined computing implementation of solving this problem of theory analysis,through the analysis of the finite element model of structure vibration modal and sound power level line diagram analysis of loss factor of the damping layer on the numerical difference of structure vibration characteristics and response characteristics of inhibition,under different working conditions effects on the vibration and sound radiation characteristic,It has a certain engineering practical application value and theoretical research significance.First explained the vibration noise for production people about the dangers of life and response measures,combed the related theory of modal analysis of the structure and the research progress of sound radiation transmission theory,observes the current damping structure simplified model to the research of damping materials,performance of viscoelastic damping materials and composite structure movement differential equation also made the corresponding description.Then,the theory of modal analysis of damped structure is described in detail,which lays a solid theoretical foundation for further simulation.In actual simulation,finite element modeling and simulation calculation was carried out on the air and underwater cylindrical shell respectively vibration modal analysis and comparison of work,and compares the result with the analytic solution is given in the literature,the simulation results with the literature results perfectly,used in this paper,by use of theory and operation method can be used to analyze the damping of the structure of the vibration modal analysis,the late for paper work ready to the numerical simulation.In this paper,the cylindrical shell in the air is taken as the research object,and the modal calculation of five self-built structural models is carried out by finite element modeling.The bottom-up modeling method is adopted to verify the influence of different ratios on the vibration modes of damped structures by laying damping materials with different damping ratios.Secondly,in order to study the influence of the fluid medium and the structure damping configuration on the structure complex mode,the complex mode analysis of the damping plate is carried out.It is found that the damping layer with a higher damping ratio can reduce the vibration amplitude of the structure more rapidly.However,too high a damping factor will change the inherent mode of the structure and the mode order of the structure,making the structure more susceptible to the interference of low-frequency excitation.At the same time,it is also found that because of the different boundary constraints of the engineering structures in reality,the vibration of the cylindrical shell structure is likely to occur only along the axial direction at the end face,while the vibration mode of the circular side of the cylindrical shell structure does not appear.Through the model of structural damping and frequency of relation curve of cylindrical shell structure can be found in a relatively stable modal vibration mode,and when the vibration frequency across the relatively stable frequency,modal vibration mode then the structural damping ratio and natural frequency changes by leaps and bounds,is similar to the curve is in a state of "rupture";The influence of the fluid medium on the vibration pattern is mainly reflected in the decrease of the natural frequency,the decrease of the vibration amplitude and the change of the order of the vibration pattern.From the perspective of the influence on the complex modes of the damped structure,the fluid medium and the unevenly damped layer laid on the structure will produce complex modes of the corresponding structure,and the influence of the two on the real part of the complex modes of the vibration structure is relatively small,but the influence on the phase of the vibration particle is greater.The influence of fluid medium on the complex mode of structure is not obvious,while the influence of damped configuration on the complex mode of damped structure is greater.Under certain complex modes,the MPC and MCC values will suddenly decrease or increase(the change value is over an order of magnitude),especially when the half-wave number in the width(length)direction of the structure is fixed,while the half-wave number in the length(width)direction of the structure will increase or decrease.From the complexity indexes of MCC and MPC,it can be seen that the vibration structure is no longer complex mode vibration when approaching the high order mode,but has more real mode characteristics for the high order mode.The fluid medium can make the uniformly laid damping plate appear partial complex mode.Sometimes the MPC value of the complexity index shows that the structure is complex mode vibration,but the MCC value cannot well show that the structure is complex mode vibration.Therefore,further study is needed in how to select the modal complexity index to measure the modal complexity of the structure.Study of acoustic radiation response features,mainly using the boundary element method to calculate the various structural model of sound field,by extracting the structure of simulation calculation of finite element modeling surface node space information,method of structure vibration velocity,the surface node to the displacement response information,and then using the boundary element method for calculating and analyzing the sound field using the direct boundary element method of corresponding software calculation module,calculation of cylindrical shell structure vibration acoustic characteristics of radiated acoustic power level curve.It is found that the damping ratios of different values can affect the mode order of the cylindrical shell structure,change the mode mode of the structure under low frequency vibration,and increase the modal complexity of acoustic radiation.At the same time,the laying of the damping layer,especially the laying of the damping material layer with high damping factor,can effectively reduce the radiation power of the acoustic radiation of the cylindrical shell.In terms of reducing sound power of acoustic radiation,the noise reduction effect of cylindrical shell with damping material layer laid in air is more obvious than that of cylindrical shell with the same damping material layer laid in water.By grasping the line spectrum characteristics of the whole sound power level curve macroscopically,it can be found that the change of the sound power level curve is relatively slow in the low-frequency vibration stage,but after the vibration frequency reaches a certain mode of mode,the sound power level will increase rapidly.For the relatively high frequency band in the 0-600 hz calculation frequency range calculated in this paper,the amplitude of the sound power level-frequency curve changes much less,but at this time,the formant is also more disorderly and dense.So according to the structural damping ratio and different fluid on vibration modal damping composite structure features and acoustic radiation response characteristic analysis of the conclusions,the researchers in the design of engineering structure vibration noise,not blindly pursue high damping ratio of damping layer,laying or easily affected by the low-frequency excitation and produce resonance.As far as possible,the frequency range of the "stable mode" of the structure should be designed so as to reduce the possibility of resonance caused by excitation.At the same time,the design also takes into account the characteristics of the structure’s daily working environment,structural strength,stability;For the structural response part,the measures of vibration reduction and noise reduction are mainly applied to the internal excitation source region,so as to prevent the generation of directional long-distance propagation of sound waves and destroy the need of acoustic stealth.更多还原