基于谱元法的加筋双层板声透射分析

首先应用谱元法(SEM)建立简支加筋双层板结构在简谐平面声波激励下的振动响应分析模型,将所得结果与有限元法(FEM)计算结果对比,表明谱元法(SEM)在求解该类问题时具有精度高和求解速度快的优点。然后应用Rayleigh积分求解加筋双层板结构路径传声的透射声功率。在筋板截面面积不变的约束条件下,研究筋板倾角与面板间距在声波正入射情况下对透射侧面板辐射声功率的影响。结果表明:筋板倾角越大,加筋双层板的透射声功率越小;在倾角小于22o的情况下,隔声性能随着面板间距的减小而提高。分析结果对加筋双层板的结构设计与隔声优化具有一定的指导意义。     

阻尼夹芯复合材料加筋板的振动分析与数值模拟

以阻尼夹芯复合材料加筋板为研究对象,依据一阶剪切变形理论(FSDT)和Hamilton原理,推导板和加强筋的应变能、动能表达式,采用变分原理建立控制微分方程,根据相关边界条件和傅里叶级数求解方程。建立了ANSYS阻尼夹芯复合材料加筋板的有限元模型,该模型考虑到阻尼夹芯复合材料加筋板中阻尼材料与纤维预浸料间的结合方式,用模态应变能有限元数值模拟方法研究了结构的动力学性能,并通过对数值模拟结果与理论解的比较,验证了模型的合理性和有效性。探讨了不同的筋条尺寸、不同的筋条数量、不同的筋条分布方式对阻尼夹芯复合材料加筋板动力学性能的影响,得出了阻尼夹芯复合材料加筋板的一阶模态频率和损耗因子随不同参数的变化曲线,其结论为阻尼夹芯复合材料加筋板的优化设计提供参考。     

声学黑洞原理的双层加筋板⁃腔系统降噪研究EI北大核心CSCD

双层加筋板在现代交通运输工具中被广泛应用,这类结构的声振抑制问题一直是难点。声学黑洞(ABH:Acoustic BlackHole)作为一种新型的波操纵技术,为结构振动噪声控制提供了新思路。提出将ABH应用于双层加筋板中,开发有良好机械特性,特别是能实现减振降噪的结构。设计含有ABH的双层加筋板⁃腔系统,搭建实验平台并在点载荷激励下进行效果测试。结果表明截止频率以上腔体的宽频噪声可降低1.5~8 dB。基于有限元方法建立耦合数值模型,多角度量化了系统的动力学特性,分析揭示了ABH在腔室降噪中具有增加系统阻尼和降低内壁板和声腔的耦合强度的双重物理机制。针对降噪效果欠佳的低频段,提供优化设计方案,拓宽有效频率,实现了全频带的控制。进一步验证了复杂载荷作用下ABH双层加筋板⁃腔声振系统的减噪普适性。     

钢材与复合材料多形式加筋平板透声性能消声水池实测分析

以复合材料声呐导流罩加筋板结构多目标综合优化为工程背景,开展消声水池模型插入损失测试,横向对比分析钢制桁架筋材与四种复合材料筋材加筋板近场透声特性,综合讨论了筋材材质、筋材结构形式以及入射角度对加筋板近场透声性能的影响。测试及分析结果表明:桁架式加筋板近场透声性能优异且稳定;细矮型筋材可提高加筋板整体透声性能。研究结果为声呐导流罩复合材料加筋板结构的优化设计提供了参考。     

斜入射下水中隐身夹芯复合材料附体结构声学设计

摘 要：将隐身夹芯复合材料代替附体结构钢质壳板,建立了斜入射条件下水中隐身夹芯复合材料结构的声学模型;从水声波动方程出发,推导了二维空间声波斜入射时的传递矩阵,及带空腔水附体结构的声反射系数和吸声系数表达式;对带空腔水附体结构模型进行了垂直入射声学试验,试验结果与传递矩阵法数值计算吻合较好;对试验模型进行了斜入射下声学性能数值计算,分析了入射角对反射系数和吸声系数的影响;考虑斜入射下夹芯层厚度、密度、损耗因子、及水层厚度等对隐身附体结构声学性能的影响,应用数值方法对水中隐身夹芯复合材料附体结构进行了声学设计,分析了各层材料参数和几何参数对隐身结构反射系数和吸声系数的影响规律。     

考虑重流体耦合效应的双层板-腔结构振动与声辐射分析

考虑半空间声场内重流体的声振耦合效应，对有限大双层板-腔结构的振动与声辐射特性进行研究。采用改进傅里叶级数描述薄板位移和腔内声压，通过Rayleigh积分建立辐射板表面辐射声压和辐射板位移的关系，基于Hamilton原理，提出采用Rayleigh-Ritz法分析耦合系统声振特性的半解析方法，并通过和有限元结果对比验证方法的收敛性和准确性。分析单位简谐力激励下，声腔厚度和腔内流体介质对双层板-腔结构声辐射特性的影响。结果表明：重流体的耦合效应使薄板（奇，奇）模态振型显著变化，声腔较薄时声辐射对声腔厚度变化较敏感。相较于腔内流体声速，腔内流体密度对声辐射有较大影响。     

爆炸荷载作用下复合材料加筋板的动力响应

为了减轻抗爆结构质量,采用玻璃纤维增强聚合物基复合材料（SMC）与碳纤维增强聚合物基复合材料（CFRP）预浸料,通过数值模拟和等效计算理论,对传统加筋抗爆板结构进行轻质高强设计。利用LS-DYNA有限元数值模拟软件进行分析,发现在爆炸荷载作用下加筋板的运动以弹性运动为主,该种复合材料具有较好的抗爆性能。对复合材料加筋板结构进行参数化分析,发现在爆炸荷载作用下横筋对加筋板结构最大位移值影响最大,纵筋和面板对加筋板的影响依次减小。结合刚度折算方法,建立了爆炸荷载作用下正交异性加筋板结构动力响应分析理论。利用该理论计算得到板结构在爆炸荷载作用下的最大位移,与数值模拟对比发现两者结果较为接近,为加筋抗爆板的设计提供了一种简化有效的计算方法。     

连接界面不定性对于加筋板结构振动能量传递特性的影响分析

加筋板结构有着极为广泛的工程应用,准确预测振动能量(结构声)在加筋板中的传递特性是对于工程结构进行有效、合理声学设计的一个极为重要的环节。本文以板-筋-板组合系统为研究对象,将加强筋视为板件结构的中间连接件,通过仿真分析计算,研究了加筋板的参数不确定性对筋板组合系统的功率流传递特性影响。考虑到加强筋与所连接板件通常具有较大的动态特性差异,仿真模拟以中频混合分析法(Hybrid FE-SEA method)为主。研究表明:在长短波并存的中频域,加筋板中的结构声传递特性受加强筋刚度和边界条件变化的影响较大,而受其材料属性和连接自由度数量变化的影响较小。     

船舶结构建模及水下振动和辐射噪声预报

船舶动力系统的振动通过壳板向水下辐射的噪声的预报一直是非常关键的问题。船舶的声学设计建立在一体化的概念下，本文基于船体与周围声学流体介质耦合作用，建立了带有浮筏结构的动力装置的整个双层壳体船舶的FEM／BEM数学模型。首先利用有限元软件ANSYS建立了水下船舶结构的振动和声场耦合的模型，计算在模拟动力设备激励下船舶壳板的振动，然后利用边界元软件SYSNOISE，对轻外壳面上的法向声强进行预报。     

复合材料加筋壁板鸟撞动响应分析

考虑复合材料蜂窝夹芯结构的冲击损伤,采用接触碰撞耦合方法研究了复合材料加筋壁板的抗鸟撞性能。鸟撞方式包括垂直冲击和斜冲击两种,复合材料的冲击损伤模型采用Chang-Chang模型,分析了三种鸟撞速度下鸟撞性能参数如复合材料壁板的失效单元数、鸟体剩余动能和筋条的变形,以及复合材料壁板和筋条在某一鸟撞速度下应力随筋条数的变化规律。计算结果表明：垂直冲击和斜冲击下复合材料加筋壁板的抗鸟撞性能不同,并非筋条越多越有利于改善抗鸟撞性能,筋条有时还可能起反作用。     

Sound transmission loss characteristics of unbounded orthotropic sandwich panels in bending vibration considering transverse shear deformation

A theoretical study on the sound transmission loss (STL) characteristics of unbounded orthotropic sandwich panels considering the transverse shear deformation is presented. With the transverse shear deformation taken into account, the governing equation of bending vibration for unbounded orthotropic sandwich panels is derived and implemented to the sound transmission problem. The expressions for impedance and transmission coefficient are also derived. The accuracy of the theoretical predictions is checked against available experimental data. The influence of several key parameters on the sound insulation properties of the orthotropic sandwich panel is then systematically studied, including shear rigidity of the core, face sheet thickness, and core thickness. Numerical analysis shows that shear rigidity has evident effect on coincidence critical frequency and STL property, and should not be neglected when predicting STL. Increasing face sheet thickness can move coincidence critical frequency to lower frequency region and improve STL, which is much more effective than increasing the core thickness.     

Thermo-mechanical load interactions in foam cored axi-symmetric sandwich circular plates – High-order and FE models

This work presents analytical and finite element analysis (FEA) results of the thermo-mechanical non-linear response of an axi-symmetric circular sandwich plates with a compliant foam core. The study investigates the load–thermal interaction response of a sandwich panel where the properties of the core are temperature dependent and degrade as the temperatures are raised. It presents briefly the governing equations for a sandwich plate based on the principles of the high-order sandwich panel theory (HSAPT) which incorporates the effects of the vertical flexibility of the core material as well as the effects of temperature independent/dependent mechanical properties of the foam core. The effects of the thermal degradation of core material on the thermo-mechanical non-linear response of a simply supported circular sandwich plate are studied through the analytical and FE models. The difficulties involved in non-linear geometrical FE modeling of sandwich panels with a compliant “soft” core with temperature-dependent mechanical properties are discussed. The HSAPT model predictions are compared very well with FE result. An important conclusion of the study is that the interaction between mechanical loads, temperature induced deformations, and degradation of the mechanical properties due to elevated temperatures, may seriously affect the structural integrity of foam cored sandwich plates.     

直升机舱室声学超材料壁板的低频隔声性能分析

在直升机飞行过程中,旋翼、尾桨等噪声源在舱室内产生强烈的低频噪声,严重影响直升机的驾乘舒适性,长时间的噪声暴露会危及驾驶安全。直升机舱室常用的夹层壁板结构可有效隔绝中、高频噪声,但其低频隔声性能一般较弱。为有效降低直升机舱室内低频噪声,将局域共振型声学超材料与舱室夹层壁板结合,建立直升机舱室声学超材料壁板模型,采用有限元法分析平面波入射激励下声学超材料壁板的低频隔声性能,并探索局域振子质量、层间结构对隔声性能的影响规律。结果表明:相比敷设阻尼材料、布置动力吸振器等传统舱内降噪方法,声学超材料壁板能有效隔离低频噪声,形成380 Hz~620 Hz的宽低频带隙。增加局域振子质量可有效拓宽带隙宽度并增强带隙内声透射损失,增加纵向加强筋数目可增强结构整体刚度,使振动衰减。声学超材料内饰的引入可为解决直升机舱室低频噪声问题提供技术路线。     

Noise reduction capability of hybrid flax fabric-reinforced polypropylene-based composites

In recent years, natural fiber polymer composites have demonstrated great potential for reducing noise. This study reports sound transmission loss (STL) of hybrid flax fabric-reinforced polypropylene composites. The STL values were determined by the BSWA impedance tube and evaluated by ISO 10534 standard test procedure in the frequency range of 64 to 1600 Hz. Measurements show that the STL per areal density of flax/polypropylene is two times higher compared to aluminum. A noteworthy result is that upon hybridization with 13% carbon fibers (carbon-flax/polypropylene), the STL per areal density increases by 2.4 times. This study also presents the finite element (FE) simulation of sound transmission through the composites. Good agreement between FE predicted and experimentally measured STL is obtained. Moreover, parametric sensitivity studies are performed using the developed FE model to examine the effect of possible variation in the mechanical properties of the natural fiber composites on the STL performance. It is found that within 15% variation, no significant effect on STL is obtained and that STL is only sensitive to the in-plane elastic moduli.     

Loss behavior of viscoelastic sandwich structures: A statistical-continuum multi-scale approach

This work presents a multi-scale model of viscoelastic constrained layer damping treatments for vibrating plates/beams. The approach integrates a finite element (FE) model of macro-scale vibrations and a statistical-continuum homogenization model to include effects of micro-scale structure and properties. The statistical-continuum homogenization model makes the micro- to macro-scale transition to approximate the effective behavior of the heterogeneous core by using n-point probability functions. A simple sound transmission model is used to show the effect of material microstructure on the sound transmission loss of the sandwich structure. The damping behavior resulting from the presence of voids and negative stiffness regions in the core material is modeled. This study clearly shows that, it is of high interest to research either material structures or processing techniques which lead to negative stiffness behavior. The results also poignantly show that the proposed multi-scale model yields insight on heterogeneous material behavior leading to increased damping properties and ultimately enhances the ability to design sandwich beam/plates.     

水下多孔吸声材料夹层板隔声分析

利用结构弯曲波法,并结合Biot理论和Bolton多层板理论,推导了水下多孔吸声材料夹层板的隔声量理论计算公式,分析了（Binding-Binding,BB）型、（Binding-Unbinding,BU）型和（Unbinding-Unbinding,UU）型三种结构的隔声性能。将入射域、辐射域和中间空腔域中的声波以相应的速度势函数形式表达,多孔吸声材料的传声过程采用Biot理论和Bolton理论描述,再结合相应模型的边界条件,即可求解出结构的理论隔声量。在BB型、BU型和UU型三种模型中,UU型的隔声性能最好,BB型的隔声性能最差。夹层板中多孔吸声材料能有效避免空腔驻波共振的发生,并能显著提高结构高频的隔声性能。多孔吸声材料厚度和空腔空气层厚度的增加,能有效地促进结构的隔声性能。     

梁模型三明治板的隔声预报

提出一种针对有限大三明治蜂窝板的隔声预报方法。在一定条件下,三明治蜂窝板被看成是正交各向异性的,通过对蜂窝板正交方向上切割下来梁的简单测 试,可以得到三明治蜂窝板的等效刚度,结合正交各向异性板的振动方程,把板的振动展开成模态叠加的形式并求解,最终可以得到一块有限大三明治蜂窝板的理论隔声公式,理论预报结果与实验室测量结果对比良好。     

Ballistic resistance of hybrid-cored sandwich plates: Numerical and experimental assessment

The impact responses and ballistic resistance of sandwich plates having three different types of hybrid cores are investigated. The hybrid cores include metallic pyramidal lattice trusses, metallic pyramidal lattice trusses with ceramic prism insertions, and metallic pyramidal lattice trusses with ceramic prism insertions and void-filling epoxy resin. Three-dimensional (3D) finite element (FE) simulations are carried out for each sandwich type impacted by a hemispherical projectile. Upon validating the FE simulation results with experimental measurements, the ballistic limit velocity, energy absorption and failure mechanisms for each type of the sandwich as well as the influence of key material, structural and topological parameters are investigated systematically. Sandwich plates having metallic pyramidal lattice core with ceramic insertions and epoxy resin filling void spaces are found to outperform the other two sandwich types. It is also demonstrated that the back face-sheet plays a more significant role than the front face-sheet in resisting ballistic impacts.     

Behaviour of sandwich panels subject to intense air blasts – Part 2: Numerical simulation

Finite element simulation is employed to analyse the behaviour of clamped sandwich panels comprising equal thicknesses mild steel plates sandwiching an aluminium honeycomb core when subject to blast loadings. Pressure-time histories representative of blast loadings are applied to the front plate of the sandwich panel. The FE model is verified using the experimental test results for uniform and localised blast loading in the presence of a honeycomb core and with only an air gap between the sandwich plates. It is observed that for the particular core material, the load transfer to the back plate of the panel depends on the load intensity, core thickness and flexibility of the sandwich panels.