分数阶黏弹性Pasternak地基上两端固支Timoshenko梁的动力响应

本文研究了放置在黏弹性Pasternak地基上的Timoshenko梁在移动载荷作用下的动力响应行为．首先,引入分数阶导数,将整数阶标准固体黏弹性地基模型推广为分数阶标准固体黏弹性模型．对于Pasternak地基,考虑压缩层是黏弹性的而剪切层仍是弹性的情况,给出了地基反作用力．然后,求解了Timoshenko梁的自由振动解,获得含黏性耗散信息的复固有频率及振型函数．在此基础上用振型叠加法分析了在移动简谐荷载作用下梁的位移响应．在数值算例中,给出了不同分数阶导数、地基黏性系数以及载荷移动速度下梁的动态响应,讨论了黏弹性地基对梁的动态响应的影响规律．     

实用黏弹性阻尼耗能系统非均匀非平稳巴斯金谱地震响应的一般精细解析解

针对设置支撑的实用黏弹性阻尼器耗能减震系统,结合虚拟激励法,构建非均匀调制非平稳巴斯金谱地震响应的一般精细解析解.首先对于设置支撑的单自由度实用黏弹性阻尼耗能减震结构模型,利用扩阶的方法得到耗能体系的状态方程.然后在高效的虚拟激励法基础上,提出多项式-指数-简谐精细积分一般格式,得到8种常见均匀与非均匀调制非平稳巴斯金谱随机地震激励下的响应具体解析解.算例分析表明:本文方法与传统方法计算结果一致,且一般格式可表示多种精细积分格式,具有广泛的适用性,为进一步研究该耗能减震系统的抗震动力可靠度和抗震设计方法提供了理论依据.     

NON-LINEAR FORCED VIBRATION OF AXIALLY MOVING VISCOELASTIC BEAMS

The non-linear forced vibration of axially moving viscoelastic beams excited bythe vibration of the supporting foundation is investigated. A non-linear partial-differential equa-tion governing the transverse motion is derived from the dynamical, constitutive equations andgeometrical relations. By referring to the quasi-static stretch assumption, the partial-differentialnon-linearity is reduced to an integro-partial-differential one. The method of multiple scales isdirectly applied to the governing equations with the two types of non-linearity, respectively. Theamplitude of near- and exact-resonant, steady state is analyzed by use of the solvability conditionof eliminating secular terms. Numerical results are presented to show the contributions of foun-dation vibration amplitude, viscoelastic damping, and nonlinearity to the response amplitude forthe first and the second mode.     

对不可压黏弹材料非线性本构关系的探讨

运用张量分析,证明了适合描述不可压缩黏弹性材料非线性本构关系的3种理论：BKZ理论、Lianis理论和Chirstensen理论,运用到各向同性材料中它们的单轴拉伸具有一样的表现形式,同时也验证了3种理论在解释非线性本构关系时具有统一性．     

求解弯曲矩形板受迫振动的混合变量法

应用混合变量最小作用量原理,求解了两邻边固定、另两邻边自由弯曲矩形板在均匀谐载作用下的受迫振动问题,得到其受迫振动的稳态解．所获得的计算结果,跟现有文献进行比较,证明其给出的方法是正确的,因此不仅具有重要的理论价值,而且可以为工程实际直接采用．     

FORCED VIBRATIONS WITH INTERNAL RESONANCE OF A PIPE CONVEYING FLUID UNDER EXTERNAL PERIODIC EXCITATION

Applying the multidimensional Lindstedt-Poincaré (MDLP) method, we study the forced vibrations with internal resonance of a clamped-clamped pipe conveying fluid under external periodic excitation. The frequency-amplitude response curves of the first-mode resonance with internal resonance are obtained and its characteristics are discussed; moreover, the motions of the first two modes are also analyzed in detail. The present results reveal rich and complex dynamic behaviors caused by internal resonance and that some of the internal resonances are decided by the excitation amplitude. The MDLP method is also proved to be a simple and efficient technique to deal with nonlinear dynamics.     

轴向变速运动粘弹性弦线的横向振动分岔

研究轴向运动弦线横向振动的分岔.弦线轴向速度为常平均速度带有简谐涨落,其粘弹性材料由Kelvin模型描述.建立系统的动力学方程并应用2阶Galerkin截断进行简化.计算了弦线中点的Poincare截面映射对平均轴向速度、轴向速度涨落幅值和弹性模量的分岔图.     

端承粘弹性桩纵向振动的轴对称解析解

将桩和土体视为粘弹性介质,在频率域求得了桩轴对称纵向振动时动力响应的解析解,进而得到桩头复刚度的解析表达式.通过数值计算,给出了桩头动刚度因子和等效阻尼随激励频率的响应,考察了土层粘性、桩长径比、桩土模量比、桩泊松比和粘性等参数对桩头刚度因子和等效阻尼的影响.研究表明:由于考虑了桩的径向变形效应以及土层对桩的径向力作用,轴对称解析解的桩头动刚度因子和等效阻尼与经典Euler杆模型桩的桩头动刚度因子和阻尼有较大区别.因此,经典Euler杆模型桩的适用范围具有一定的局限性,在若干情形下应采用基于三维粘弹性的桩纵向振动轴对称模型进行分析.     

功能梯度材料的黏弹性断裂问题

功能梯度材料(FGM)是一种不同于传统复合材料的新型工程复合材料 [1], 国内外关于FGM的断裂力学方面的研究发展非常迅速. 关于FGM静态裂纹问题,学者们研究了不同类型裂纹尖端场的应力强度因子 [2-5], 探讨了有限长裂纹在不用载荷作用下的传播等问题. 而关于动态裂纹问题,也已经取得很大成就 [6-9]. FGM一个很重要的应用是高温结构材料,在强大的热环境中,很多材料都呈现出黏弹性. 因此,研究FGM的黏弹性断裂力学非常具有实际价值.对此,众多研究 [10-14]提出不同的分析模型,并在不同受载条件,通过理论计算,分析了黏弹性裂纹尖端场的力学 行为.本文考查了功能梯度材料板条中界面裂纹垂直于梯度方向时的黏弹性断裂问题,首先利用有限元法求解线弹性功能梯度材料板条的裂纹尖端场,然后根据黏弹性的对应性原理,求解出黏弹性功能梯度材料板条裂纹问题的应力场强度因子.      

EXACT SOLUTIONS FOR FREE IN-PLANE VIBRATIONS OF RECTANGULAR PLATES

All possible exact solutions are successfully obtained in terms of 10 sets of distinct eigensolutions for the free in-plane vibration of isotropic rectangular plates. The plates have simply supported condition at two opposite edges and any combination of classical boundary conditions at the other two edges. The exact solutions are validated through both mathematical proof and comparisons with the solutions of differential quadrature method. Some unusual phenomena are revealed in free in-plane vibrations of rectangular plates due to one of the eigenvalues being zero. This work constitutes an improved version of very recent corresponding work by the same authors [Int. J. Mech. Sci., 2009, 51: 246-255]. Both the solution forms and solving procedures in the previous work are substantially simplified. Some new results are also given, which are useful for validation purpose in future.     

变水深坝—库系统耦振分析的边界元—有限元混合法

常用的混合元法解变水深坝－库系统的耦振，需要对变水深部分的流场进行域离散，计算工作量大，该文利用Ｆｒｉｅｄｍａｎ的算子函数理论，构造了势流问题在无限长带形域中的Ｇｒｅｅｎ函数，从而使流场的边界元剖分只限于变水深区域的边界，关于坝体仍采用有限元离散，最后借助所导出的有限元－边界元格式对坝－库系统的实例作了数值计算，结果证明了它的有效性。     

圆截面弹性细杆的平面振动

基于Kirchhoff理论讨论圆截面弹性细杆的平面振动．以杆中心线的Frenet坐标系为参考系建立动力学方程．杆作平面运动时,其扭转振动与弯曲振动解耦．讨论任意形状杆的扭转振动和轴向受压直杆在无扭转条件下的弯曲振动,证明直杆平衡的静态Lyapunov稳定性与欧拉稳定性条件为动态稳定性的必要条件．考虑轴向力和截面转动惯性效应的影响,导出弯曲振动的固有频率．