Optimal design of composite multilayered plated and shell structures

For multilayered plated and shell structures the formulation of the optimization problem is strongly dependant on the definition of the design variables. Therefore, the first part of the work is devoted to the definition of design variables and the forms of objective functions. Then, two numerical examples have been solved to demonstrate the effectiveness of the proposed formulations and the optimization algorithm (the modified evolutionary strategy). They deal with thickness and shape optimization problems subjected to dynamic and static constraints, respectively.     

曲线轨道空间振动响应特性研究

曲线轨道空间振动存在平面内振动、平面外弯扭耦合振动,通过建立曲线轨道空间振动频域解析模型,对曲线轨道动力响应特性进行研究。将曲线轨道视为圆形结构的一部分,利用圆形结构周期性的特性,在一个基本元之内求解曲线轨道的动力响应。通过引入移动谐振荷载作用下轨梁动力响应的频域数学模态,得出曲线轨道轨梁频域响应的级数表达。在频域内采用数学模态叠加法表示曲线轨梁的纵向、横向、垂向及扭转振动,进而求解得到基本元内轨梁的频域动力响应。经计算表明,文中提出的频域解析模型能够得到精确的曲线轨道频域响应。通过分析速度、半径、超高等因素,得到以下结论：准静态激励下单个移动轴荷载对曲线轨梁的垂向、横向及扭转振动的影响范围在作用点两侧±5m左右;轴荷载移动速度对曲线轨梁横向位移、扭转变形具有显著的影响,随着速度的增加,曲线轨道由过超高状态逐渐过渡到理想超高状态,最终进入欠超高状态,轨梁横向位移、扭转变形方向发生改变,响应幅值先减小后增加;半径、超高和速度对曲线轨梁垂向位移、横向位移及扭转变形影响较大;随着半径的增加,速度对位移响应的影响程度降低;准静态移动轴荷载列作用下曲线轨梁垂向、横向及扭转频域响应主要集中在40Hz以内的频段;横向振动、扭转振动频谱分布范围较宽。     

正交加劲柱形壳自由振动的结构相似性分析

采用相似理论对自振正交加劲柱形壳进行分析,提出了其相似的必要条件,即相似率。结构建模中采用了Donnell非线性应变-位移关系曲线和Smearing理论。然后采用虚功原理分析加劲壳体的自由振动。在使用相似理论对推导的公式进行无量纲化后提出了相似率的概念。采用不同的算例从数值和试验角度论证了相似率的有效性。结果验证了推导公式的有效性。     

多轴应力响应下结构振动疲劳寿命预估的时域方法研究

应用Von Mises应力准则将多轴应力响应等效合成为单轴应力,给出了基于功率谱输入和时域输入的多轴应力响应振动疲劳寿命预估方法,时域输入法的求解过程没有丢失应力分量相位的相互信息,较功率谱输入法更完备。针对激励载荷是以功率谱密度函数形式表达的,提出了Monte-Carlo伪随机历程模拟将激励功率谱转换到时域激励中,再通过时域输入法进行寿命预估的求解思路,保证了等效合成的Von Mises应力的相位信息具有实际的物理意义,可指导多轴应力响应下结构振动疲劳寿命的精确预估以及声疲劳试验研究。     

弧齿锥齿轮箱动态特性分析及辐射噪声预估

以升船机同步系统用弧齿锥齿轮箱为研究对象,综合考虑锥齿轮副刚度激励、误差激励和啮合冲击激励等内部动态激励,建立了包含弧齿锥齿轮副、传动轴、轴承和箱体等的齿轮系统动力有限元模型,采用ANSYS对齿轮系统进行动态响应分析,得到齿轮箱的振动位移、振动速度及振动加速度;以箱体表面节点振动位移为边界激励条件,在SYSNOISE中建立箱体声学边界元模型,采用直接边界元法进行辐射噪声预估,得出箱体表面的声压云图及场点的辐射噪声。结果表明:齿轮箱动态响应及辐射噪声的峰值频率均出现在啮合频率及其倍频处。     

频率修正在超声变幅杆设计中的研究与应用

超声变幅杆在沿轴线方向作纵向振动时,由于存在泊松效应,纵向振动会引起变幅杆沿径向方向的横向振动。传统变幅杆在设计过程中,忽略横向振动的影响则会导致计算出的谐振频率高于实际频率。为了让变幅杆理论设计谐振频率与实际频率相符合,分别对简单圆柱杆和阶梯形变幅杆进行研究,推导出常用半径比范围内简单阶梯形变幅杆的频率修正公式,使其满足设计和使用要求,并可以减少能量传输过程中的能量损耗。     

周转斜盘发动机模态分析及减振方案设计

针对周转斜盘发动机结构复杂,有限元模型规模大且分析效率较低等问题,引入子结构模态综合法用于发动机振动特性分析和减振设计。基于Ansys软件建立了发动机模态综合法分析模型,计算了发动机模态。分析了发动机振动激励源和振动传递路径,讨论了发动机结构减振措施,提出了发动机关键轴承处采用柔性支撑的减振方案,拟定了柔性支撑减振器可行结构形式。基于模态综合法计算模型,将减振器作为子结构建立采取减振措施的动力学分析模型。谐响分析表明:减振方案在低频段很好的效果。     

Nonlinear Dynamic Response of Cylindrical Roller Bearing–Rotor System with 9 Degree of Freedom Model Having a Combined Localized Defect at Inner–Outer Races of Bearing

This article presents a nonlinear dynamic model for a cylindrical roller bearing–rotor system with interaction forces between the inner race, outer race, and roller. Roller–race contacts are modeled predicting nonlinear stiffness (Hertz contact theory) and nonlinear damping for a rotor–cylindrical roller bearing system. Here a shaft–rotor bearing system is modeled with 9 degrees of freedom with one defect on the inner race and one defect on the outer race for a case of combined localized defects. In the mathematical formulation, contacts between rolling elements and inner and outer races are considered as nonlinear springs and nonlinear damping is taken into consideration. Contact force calculations with nonlinearity are solved using the Newton-Raphson method for n unknown nonlinear simultaneous equation. The Newmark-β implicit integration technique coupled with the Newton-Raphson method is used to solve the differential equations. The results are obtained in the form of a time domain plot, frequency domain plot, and phase plot/Poincare map. The validity of the proposed model is compared with experimental results. A bifurcation graph of speed versus peak amplitude predicts the behavior of the system.     

Transverse and longitudinal vibrations of a frame structure due to a moving trolley and the hoisted object using moving finite element

This paper aims at presenting a technique to replace the moving load by an equivalent moving finite element so that both the transverse and the longitudinal inertial effects due to the moving mass may easily be taken into account simultaneously. Where the mass, damping and stiffness matrices of the moving finite element are determined by the transverse () inertia force, Coriolis force and centrifugal force of the moving mass, respectively. From the numerical examples illustrated, it has been found that, in addition to the conventional transverse () responses, the inertial effects of the moving load also affect the longitudinal () responses of the portal-frame structure significantly.     

Non-linear free vibrations of Kelvin–Voigt visco-elastic beams

A full visco-elastic non-linear beam with cubic non-linearities is considered, and the governing equations of motion of the system for large amplitude vibrations are derived. By using the method of multiple scales, the non-linear mode shapes and natural frequencies of the beam are then analytically formulated. The resulting formulations for amplitude, non-linear natural frequencies and mode shapes can be used for any type of boundary conditions. Next, method of Galerkin is used to separate the time and space variables. The equations of motion show the presence of a non-linear damping term in addition to the ones with non-linear inertia and geometry. As it is known, the presence of non-linear inertia and the geometric terms make the non-linear natural frequencies to be dependent on constant amplitude of vibration. But, when damping non-linearities are present, it is seen that the amplitude is exponentially time-dependent, and so, the non-linear natural frequencies will be logarithmically time-dependent. Additionally, it is shown that the mode shapes will be dependent on the third power of time-dependent amplitude. The analytical results are applied to hinged–hinged and hinged–clamped boundary conditions and the results are compared with numerical simulations. The results match very closely for both cases specially for the case of hinged–hinged beam.