Snap-through behaviors and nonlinear vibrations of a bistable composite laminated cantilever shell:an experimental and numerical study

The snap-through behaviors and nonlinear vibrations are investigated for a bistable composite laminated cantilever shell subjected to transversal foundation excitation based on experimental and theoretical approaches.An improved experimental specimen is designed in order to satisfy the cantilever support boundary condition,which is composed of an asymmetric region and a symmetric region.The symmetric region of the experimental specimen is entirely clamped,which is rigidly connected to an electromagnetic shaker,while the asymmetric region remains free of constraint.Different motion paths are realized for the bistable cantilever shell by changing the input signal levels of the electromagnetic shaker,and the displacement responses of the shell are collected by the laser displacement sensors.The numerical simulation is conducted based on the established theoretical model of the bistable composite laminated cantilever shell,and an off-axis three-dimensional dynamic snap-through domain is obtained.The numerical solutions are in good agreement with the experimental results.The nonlinear stiffness characteristics,dynamic snap-through domain,and chaos and bifurcation behaviors of the shell are quantitatively analyzed.Due to the asymmetry of the boundary condition and the shell,the upper stable-state of the shell exhibits an obvious soft spring stiffness characteristic,and the lower stable-state shows a linear stiffness characteristic of the shell.

Vibration transmissibility characteristics of smart spring vibration isolation system

The objective of this work was to study the vibration transmissibility characteristics of the undamped and damped smart spring systems. The frequency response characteristics of them were analyzed by using the equivalent linearization technique, and the possible types of the system motion were distinguished by using the starting and ending frequencies. The influences of system parameters on the vibration transmissibility characteristics were discussed. The following conclusions may be drawn from the analysis results. The undamped smart spring system may simultaneously have one starting frequency and one ending frequency or only have one starting frequency, and the damped system may simultaneously have two starting frequencies and one ending frequency. There is an optimal control parameter to make the peak value of the vibration transmissibility curve of the system be minimum. When the mass ratio is far away from the stiffness ratio, the vibration transmissibility is small. The effect of the damping ratio on the system vibration transmissibility is significant while the control parameter is less than its optimal value. But the influence of the relative damping ratio on the vibration transmissibility is small.

Analysis of the hull girder vibration by dynamic stiffness matrix method

Dynamic stiffness matrix method is applied to compute vibration of hull girder in this paper. This method can not only simplify the computational model, but also get much higher frequencies and responses accurately. The analytical expressions of dynamic stiffness matrix of a Timoshenko beam for transverse vibration are presented in this paper. All effects of rotatory inertia and shear deformation are taken into account in the formulation. The resulting dynamic stiffness matrix combined with the Wittrick-Williams algorithm is used to compute natural frequencies and mode shapes of the 299,500 DWT VLCC, and then the vibrational responses are solved by the mode superposition method. The computational results are compared with those obtained from other approximate methods and experiment, and it indicates that the method is accurate and efficient.

Vibrations of tandem cold rolling mill: coupled excitation of rolling force and variable stiffness of fault-free back-up roll bearing

Vibration issues of a five-stand tandem cold rolling mill were found in the steel production practice,and the experimental observation and numerical analysis indicated that the vibrations were related to the back-up roll bearing.The results were validated by replacing the back-up roll bearing with the new bearing resulting in 30%decline in vibration amplitude.Models describing the four-row cylindrical roller bearing and the vertical system of the cold rolling mill including the bearing were established.Moreover,the mechanisms of periodic excitation and amplified vibrations of fault-free bearing were explained theoretically,along with the analysis of bifurcation behaviors of the motion states of the roller bearing and rolling mill system.It is found that the energy transmitted between vibrations with different frequencies if multiple excitation frequencies in the rolling mill system were close.

Design and Performance Study of Clutch Disc Assembly of Wide-Angle, Large-Hysteresis, Multistage Damper

The clutch is an important component of the vehicle driveline system.One of its major functions is to attenuate or eliminate the torsional vibration and noise of the driveline system caused by the engine.Based on experiments of vibration damping under different vehicle conditions,the structure and functional principle of a clutch-driven disc assembly for a wide-angle,large-hysteresis,multistage damper is investigated in this study using an innovative combined approach.Furthermore,a systematic integration of key technologies,including wide-angle low-stiffness damping technology,large-hysteresis clutch technology,a novel split pre-damping structure technology,damping structure technology for component cushioning,and multistage damping structure technology,is proposed.The results show that the total torsional angle of the wide-angle large-hysteresis,multistage damper is more than twice that of the traditional clutch damper.The multistage damping design allows a better consideration of various damping requirements under different vehicle conditions,which can effectively address problems of severe idle vibrations and torsional resonance that occur under idled and accelerated conditions.Meanwhile,the use of a large-hysteresis structure and wear-resistant materials not only improves the vibration damping performance,but also prolongs the product service life,consequently resulting in multi-faceted optimization and innovative products.

高频变压器电磁场-结构力场-声场求解及特性分析

大容量高频变压器结构紧凑,工作频率为数百Hz到几十kHz,工作波形为方波等非正弦的特殊激励波形。高频变压器电磁、结构、声等多场耦合紧密,运行时出现严重的振动与噪声问题,对高频变压器振动与噪声特性进行精细分析对于其减振降噪具有重要意义。为此,该文首先建立高频变压器电磁场-结构力场-声场3维仿真求解模型,明确各物理场的载荷传递过程以及电磁和力学性能参数;然后,采用有限元法得到不同电压激励下变压器铁芯表面时域振动波形与噪声频域特性,并定量评估了纳米晶切割铁芯对受力特性的影响程度;最后,对1台5 kHz/10 kVA高频变压器的振动和噪声进行试验测试,得到正弦和方波电压激励下铁芯振动和噪声数据。由仿真与试验结果可知,高频变压器铁芯拐角处振动较为剧烈且周围产生的噪声也较大;相比于正弦波激励,非正弦波激励下的振动不仅集中发生在2倍频,还存在许多高次谐波分量,同时各个频率段声压级明显增加;不同波形激励下测量点声压级相对误差均在10%以内,验证了仿真模型的准确性。

装配工艺参数对止口螺栓连接结构力学特性的影响分析

以航空发动机转子系统中止口螺栓连接结构为研究对象,基于单螺栓连接结构分析弯曲刚度的非线性特征,利用ANSYS实体单元建模方法分析连接结构的弯曲刚度,重点讨论了有无止口连接、预紧力、螺栓直径、止口过盈量等装配工艺参数对连接结构弯曲刚度的影响规律,并分析了止口连接结构对转子系统固有特性的影响.研究结果表明:止口连接结构的弯曲刚度呈现分段特性;增大预紧力、螺栓直径以及止口过盈量能提高连接结构弯曲刚度;有无止口连接结构的转子系统前三阶固有频率的相对误差小于2%,止口连接结构能够降低转子系统的最大振动幅值.

基于振动分析的钢筋桁架混凝土楼板等效计算模型研究

利用数值模拟对钢筋桁架混凝土楼板进行振动特性分析时,建立实体模型较为繁琐,特别是针对大跨度楼盖结构,实体模型单元数目众多,给有限元分析带来困难。为了简化建模过程,采用刚度等效的原则提出了建立等效简易模型的新方法,分别建立了钢筋桁架混凝土单向板的各向同性等效模型和双向板的各向同性等效模型,将有限元模拟结果和楼板试验结果对比分析,验证等效模型的可行性。结果表明:两种模型求得的结果具有很好的一致性,各向同性等效模型能完全满足精度需求;使用各向同性等效模型求解所需的计算时间仅为三维实体模型的1%左右,大大节省计算资源和提高建模效率。

柴油机油底壳穿孔板隔声罩优化设计

以某型柴油机的油底壳作为研究对象,对其声振特性进行识别与分析,确定设计穿孔板隔声罩的共振频带范围。使用粒子群算法针对共振频率进行穿孔板参数的优化设计,再通过阻抗管试验确定小孔分布对吸声性能的影响,并对穿孔板隔声罩进行多目标形貌优化设计以避开共振及激励频率。目标柴油机上加装优化的油底壳穿孔板隔声罩后,整机总声压级降低0.5 d B,降噪效果较好。

基于MATLAB的六极并联齿轮泵优化设计及分析

针对普通外啮合齿轮泵流量脉动品质差、质量大、成本高等问题,设计一种六极并联齿轮泵。分析六极并联齿轮泵的结构及其工作原理;对六极并联齿轮泵的瞬态流量特性进行分析,推导其单周期内的流量曲线函数;建立基于流量脉动系数、流量脉动频率和泵体体积的数学模型,选取设计变量,确定约束条件,并利用MATLAB优化工具箱中fmincon函数对目标函数进行参数优化。最后对相同理论流量和额定进出口压差下的六极并联齿轮泵及普通外啮合齿轮泵进行瞬态流量仿真和齿轮泵特性计算,并将结果进行对比分析。仿真结果表明:在结构设计合理的情况下,六极并联齿轮泵在减小流量脉动,降低振动、噪声、质量和制造成本,提高工作性能和使用寿命方面具有重要作用。

考虑机组弹性的双层隔振系统刚度匹配方法

为解决柴油发电机组对不同类型和功率发电机的连接套与隔振系统刚度匹配问题,提出以广义弹性力做功为基础的能量解耦法来量化刚度匹配对双层隔振系统固有特性的影响.基于某内燃动力总成双层隔振系统建立3自由度和18自由度动力学模型进行分析.结果表明:3自由度模型能够反映系统耦合的主要特点,机组弹性模态频率与低阶刚体振动模态频率比大于2.96时可以降低刚体振动对弹性模态的影响;考虑惯性耦合和弹性耦合后,18自由度模型对应的频率比应大于4.10才可以显著降低该振动耦合.同一柴油机匹配不同惯性参数的发电机,均可参考小惯性参数发电机隔振设计时对应的频率比和刚度比进行双层隔振系统刚度匹配.

高铁箱梁桥顶板纵向加筋对其声振特性的影响

伴随着高速铁路箱梁桥的大规模建设,列车经过时引起的高架桥低频声辐射问题已成为限制其发展重要因素之一。为了缓解列车经过箱梁桥时的声辐射问题,有必要开展桥梁降噪措施研究。以高速铁路箱梁桥为研究对象,对箱梁桥顶板增设纵向筋板,采用多体系统动力学软件UM及有限元-边界元方法建立车辆-轨道-桥梁耦合动力学模型和声学预测模型,对原结构箱梁桥和加筋板箱梁桥的振动加速度、辐射声功率、线性声压级和声场分布等进行分析,研究顶板纵向加筋对箱梁桥声振特性的影响。研究结果表明:增设纵向筋板后箱梁桥各个板件振动加速度都明显减小,在顶板处减幅最大;增设纵向筋板后箱梁桥的辐射声功率和声压级明显降低,降噪效果良好;其对桥上声场的降噪效果好于桥下和桥侧声场。

船用合流型三通调节阀声流固耦合声学特性研究

针对合流型三通调节阀噪声声压频谱、声指向性等声学特性规律不明确的问题,基于声流固耦合理论,以PN50 DN250三通调节阀为研究对象开展声学特性研究。基于k-ε模型分析阀门定常流动,在定常流动收敛的基础上开展LES非定常流动分析,并导出流固耦合面及流体域内的时域脉动信息作为噪声激励源,开展三通调节阀不同工况下的声学特性研究。搭建三通调节阀流噪声试验台,试验工况下数值模拟噪声与实测噪声声压仅相差1.85 dB(A),验证声流固耦合数值模拟方法的准确性。分别数值模拟阀门实际工况下80%及60%开度下的噪声声学特性,总结出阀门噪声声压级分别为51.18和54.13 dB(A),验证三通调节阀噪声满足使用要求,提出的声流固耦合数值模拟方法可为合流型三通调节阀声学特性分析提供一定参考。

变反激励力作用下齿轮箱减振降噪方法研究

从主动振动控制原理出发,通过改变反激励力的方式研究齿轮箱减振降噪效果。建立齿轮箱系统动力学模型,分析获取轴承支反力,采用有限元方法对齿轮箱进行振动特性分析,并建立箱体振动实验平台,结合有限元分析与实验测试结果确定次级力源布放位置;基于主动振动控制方法,在次级力源上施加不同激励力抑制其振动,分析在不同激励力作用下的减振效果;将获取的箱体表面振动数据作为边界条件导入LMS Virtual.Lab声学软件中计算齿轮箱向外声场辐射的噪声。研究结果表明:施加相位相反、振幅相同的反激励力减振效果最佳,相比于无控制状态平均位移减小0.18mm,施加抑制主导模态的反激励力时降噪效果最佳,在1191Hz处最高降噪量达到50.13dB。

空气弹簧隔振器样机垂向刚度特性建模与实验

空气弹簧隔振器被广泛用于精密仪器和生产设备隔振,其刚度-重力平衡点位置关系,即刚度特性是分析其与其他新兴隔振技术相互作用的重要依据。依据理想气体状态方程建立了某型空气弹簧隔振器样机的垂向刚度特性模型。综合整机振动实验结果与密封橡胶膜的刚度特性测量结果,间接测量了实物样机中空气弹簧的刚度特性。基于实验数据修正了模型,采用幂多项式拟合了气室体积-重力平衡点位置改变量的非线性曲线。减少了模型的刚度计算误差,为后续技术改造奠定了基础。

螺栓隔振结构在鱼雷噪声控制中的应用

为进一步研究隔振结构在鱼雷噪声控制中的作用,文中通过建立基于梁模型的隔振材料动力特性识别实验台,对聚醚醚酮材料的弹性模量和阻尼进行了识别和验证。同时建立了螺栓隔振结构的有限元模型,并验证了模型的精确性。将该模型应用于鱼雷发动机与壳体连接处,首次结合隔振圈建模理论和螺栓隔振结构,建立了鱼雷动力的整机隔振仿真模型。仿真结果揭示,综合使用隔振圈结合螺栓连接的隔振措施可使鱼雷振动噪声降低3.64 dB。研究结果为鱼雷振动噪声控制提供了有力的理论支撑。

偏载作用下菱形负刚度隔振系统的刚度特性

为探究偏载对菱形负刚度隔振系统刚度的影响,课题组基于力学分析方法,建立了偏载作用下隔振系统的数学模型,得到其无量纲刚度-位移非线性曲线,分析了偏载对其准零刚度特性的影响。利用Simulink进行仿真实验,给偏载作用下的隔振系统振动基座施加激励,得到了不同激励下隔振系统的时变刚度;结合傅里叶变换,探讨了隔振系统刚度的时变特性和幅频特性。结果表明:偏载越大,低刚度区间越窄,准零刚度特性越弱;时变刚度波动范围与峰值随偏载的增加而变大,但时变刚度的波动趋势不受偏载的影响;时变刚度幅值主要集中在低频区间,随频率的增加而减小,最终趋近于0。研究表明偏载对隔振系统的刚度会产生一定的影响。

基于AMESim的多液缸合流式压裂泵流量脉动特性研究

传统的机械式压裂泵存在冲次高、冲程短、曲轴易于失效等问题,为此,提出了一种多液缸合流式液压驱动压裂泵,并对其产生流量脉动的机理进行了研究。首先,详细阐述了多液缸合流式压裂泵的工作原理,基于液压流体力学等理论,建立了多液缸合流式压裂泵的数学模型,并进行了理论分析;其次,采用AMESim仿真软件搭建了多液缸合流式压裂泵工作仿真模型,选择了合理的仿真参数设置,进行了变负载压力下的仿真研究;最后,对液压动力传递链中的活塞-柱塞运动特性、泵腔流量特性、输出流量和压力脉动特性进行了研究,并对仿真结果进行了分析。研究结果表明:在25 MPa工况下,多液缸合流式压裂泵的输出压力和流量脉动率分别为36.8%和20.61%,冲次只有42次/min,符合实际工况;多液缸合流式压裂泵输出流量脉动的主要原因是各组液缸的频繁换向、泵送行程和吸入行程的切换,导致活塞-柱塞做减速停止运动和加速启动运动。

含裂纹两级人字齿轮传动系统弯-扭-轴-摆模型建立及振动特性影响

为揭示裂纹对两级人字齿轮传动系统的振动特性的影响规律,建立了考虑裂纹、时变啮合刚度、退刀槽和误差等因素的48自由度的弯-扭-轴-摆耦合动力学模型。模型中,采用势能法计算了含裂纹的两级人字齿轮传动系统中各齿轮副的时变啮合刚度,分析了裂纹对系统时变啮合刚度的影响。利用Runge-Kutta数值积分法进行求解,得到了表征振动特性的时域、频域、相图和Poincare图,并分析了裂纹对两级人字齿轮传动系统振动影响。通过试验,对比分析了正常齿轮与裂纹齿轮对系统振动特性的影响。结果表明,当齿轮出现裂纹时,系统的时变啮合刚度减小,并且随着裂纹的加剧,时变啮合刚度进一步降低;在裂纹的影响下,系统出现周期性冲击现象,在啮合倍频附近会出现明显的边频带,且随着裂纹的加剧系统的振动越来越明显;试验结果与理论分析一致性较好,能够为系统动态设计提供理论依据。

电动助力转向系统NVH特性数据采集与性能评价

针对汽车电动助力转向系统NVH特性数据存在多点位异步采样误差较大,且选取性能评价依据单一的问题,设计一种二十四通道NVH特性数据同步采集与多角度特性分析系统;采用多个数据采集模块联结、同步动态随机存储器读写、高速串行计算机扩展总线融合的方式,实现二十四通道NVH特性数据的同步精确采集与快速传输;从机械性能与声振特性方面对电动助力转向系统NVH特性进行多角度分析与评价。结果表明,与传统测试方法相比,所提方法可实现多点位同步高精度采样与多角度信号时频域分析,每个通道数据采集速率可达200 kHz/s,时频域分析依据更丰富、更全面。