DYNAMIC SUBSTRUCTURE METHOD FOR PROPAGATION OF ELASTIC-PLASTIC WAVE INDUCED BY IMPACT

通过建立弹塑性碰撞动态子结构模型,推导了模态坐标下的控制方程,提出了模拟柔性结构碰撞激发弹塑性波传播的动态子结构方法,并对其中的主模态的存在性和主模态截断的收敛性进行了证明.通过对柔性杆纵向碰撞和柔性梁横向碰撞两个算例的计算,并将计算结果与理论解和三维动力有限方法计算结果进行了对比,验证了该方法的数值收敛性和计算碰撞弹塑性波传播的有效性.     

碰撞激发弹塑性波传播的动态子结构方法

通过建立弹塑性碰撞动态子结构模型, 推导了模态坐标下的控制方程,提出了模拟柔性结构碰撞激发弹塑性波传播的动态子结构方法, 并对其中的主模态的存在性和主模态截断的收敛性进行了证明. 通过对柔性杆纵向碰撞和柔性梁横向碰撞两个算例的计算, 并将计算结果与理论解和三维动力有限方法计算结果进行了对比, 验证了该方法的数值收敛性和计算碰撞弹塑性波传播的有效性.      

力锤敲击作用下内嵌自主移动钢球欧拉梁碰撞减振性能研究

结合内嵌自主移动质量子系统梁／板实验平台实验结果,对力锤敲击作用下,内嵌自主移动钢球欧拉梁碰撞减振系统进行研究。采用线性弹簧-阻尼模型模拟钢球与梁之间的碰撞机制,通过分析建立了整个碰撞系统的分段线性动力学方程;运用无量纲化、假设模态法及高阶模态截断等方法导出系统的状态空间方程。数值计算结果表明,内嵌自主移动钢球对欧拉梁...     

用模态法识别结构弹性碰撞载荷的可行性

本文在探讨杆的纵向和横向碰撞问题基础上，论证了用模态叠加法求解结构弹性撞击载荷的可行性。发展了识别撞击载荷的数值方法。用波传播理论、弹性接触理论和模态理论等有关知识对载荷历程进行了分析和解释，并验证了所给方法的精度和实用性。     

弹性地基梁损伤诊断研究

利用试验得到的振动参数评估结构的破损情况，是当前结构工程学科十分活跃的领域。由于弹性地基梁的振动模态受地基和梁两方面因素的影响，其损伤诊断问题变得十分复杂。本文通过对两靖自由弹性地基梁的灵敏性分析发现弹性地基梁的前两阶自由模态主要与地基有关，利用这一特性构造了两级识别的方法，并引入优化领域寻优能力极强的遗传算法进行识别，找到了令人满意的答案。     

具有非线性支撑和弹性边界约束的轴向载荷梁结构动力学行为研究

弹性梁结构作为一种基本单元被广泛于建筑、航空、航天、船舶等工程领域. 为有效降低弹性梁结构的振动水平, 深刻理解其振动特性、动力学行为显得尤为重要. 本文建立了具有非线性支撑和弹性边界约束的轴向载荷梁结构动力学分析模型, 并采用伽辽金截断法预报梁结构的动力学响应. 在伽辽金截断法的求解过程中, 选取具有弹性边界约束的轴向载荷梁结构的模态振型函数作为伽辽金截断法的试函数与权函数. 首先, 研究截断数对伽辽金截断法稳定性的影响, 并采用谐波平衡法研究伽辽金截断法的可靠性. 在此基础上, 研究谐波激励扫频方向、非线性支撑参数对具有非线性支撑和弹性边界约束的轴向载荷梁结构动力学响应的影响规律. 研究结果表明, 具有非线性支撑和弹性边界约束的轴向载荷梁结构的动力学响应具有初值敏感性且非线性支撑参数对梁结构动力学响应的影响显著. 相关非线性支撑参数使得梁结构出现复杂动力学行为. 合适的非线性支撑参数能够抑制具有非线性支撑和弹性边界约束的轴向载荷梁结构的复杂动力学行为并对梁结构边界处的减振具有有益效果.      

基于静力柔度灵敏度的网架结构损伤识别

采用模态参数来组集网架结构的柔度矩阵面临较多困难,如所需模态数量较多、测点数量有限和密集模态识别精度较低等．相比之下,基于静力测试的柔度矩阵具有测试精度较高、无截断误差的优点．文中提出一种基于静力柔度灵敏度、先定位后定量的网架结构损伤识别方法．首先,针对柔度灵敏度方程容易产生病态解的问题,构造一种奇异值贡献指标以合理截断柔度灵敏度矩阵的奇异值,从而提高解的精度．其次,结合前述奇异值截断策略,在不更新刚度矩阵的前提下,通过多次计算来逐步缩减疑似损伤杆件,从而降低未损杆件的干扰和实现损伤杆件的定位．最后,仅保留灵敏度矩阵中已定位损伤杆件对应的列,在迭代计算中不断更新刚度矩阵来进行损伤杆件的定量识别．以某网架结构为例进行数值分析．结果表明：提出的奇异值贡献指标具有明显的突变位置,可方便地指出灵敏度方程奇异值截断位置;提出的两步识别法在仅利用竖向自由度的情况下具有较好的抗噪能力,可有效定位和定量识别损伤杆件．     

振型一阶导数的高精度截尾模态展开法

模态展开法是计算振型一阶导数的常用方法,然而,当高阶模态被截断时,它不能给出精确解,甚至会产生很大的截断误差。本文研究被截断的高阶模态对振型导数贡献的定量计算问题,证明了被截断模态的贡献可以用已知的低阶模态和系统矩阵来显式表达,给出了计算方法,并用数值例子说明了本文方法的有效性和正确性。     

基于时间响应函数的结构阻尼识别方法比较

研究了3种基于时间响应函数的结构阻尼识别方法, 包括对数衰减法、希尔 伯特方法和小波方法. 给出了3种方法的实现算法, 分析了对密集模态的识别能力. 构造仿真算例, 采用3种方法识别了5{\%}, 10{\%}和30{\%}噪声条件下的模态阻尼. 结果表明, 小波方法比对数衰减法和希尔伯特方法具有更好的噪声鲁棒性. 采用小波方法分析了润扬大桥结构健康监测系统获得的实测数据, 识别出了润扬大桥悬索桥前6阶模态参数, 第2阶和第3阶模态频率相差仅为0.015\,Hz. 研究表明, 小波方法具备噪声条件下密集模态的识别能力, 是工程中阻尼识别的优选方法.     

改进的直接部件模态综合法

Yee和Tsuei提出的直接部件模态综合法将自由界面模态综合法与频响函数相结合 ,简化了计算过程、减少了计算量 ,并便于与实验模态分析相结合。本文在其基础上利用矩阵级数展开的方法将被截断高阶模态的贡献用保留模态和系统物理特性矩阵精确表达 ,结合分块计算方法 ,进一步减少了计算量并有效地提高了计算精度 ,且确定了模态截断准则。数值算例表明其行之有效     

两柔性梁碰撞振动类型的实验研究

基于对两弹性部件碰撞振动的理论及数值研究,设计了两柔性梁碰撞实验来研究碰撞振动类型．在实验中观察到亚谐、超谐、概周期、混沌等多种碰撞振动类型．此外,发现系统存在类似“频率锁定”性质的碰撞振动,以及同时存在性质相异的碰撞行为,如谐碰撞与混沌振动共存现象     

Fuzzy-logic control of parametrically excited impacting flexible system

Summary In this article, the control of a repetitive impacting elastic link with parametrically excited base in rotational motion is considered. A fuzzy-logic controller is designed and employed to suppress the vibrations resulting after the impact with an external rigid body. The momentum balance method and an empirical coefficient of restitution is used in the collision of the two bodies. The controller is applied successfully to reduce the vibrations of the parametrically excited impacting flexible system. Simulations for several combinations of excitation and rotation parameters are provided. Received 21 April 1997; accepted for publication 12 September 1997     

在质量块冲击作用下刚架大挠度响应的实验研究

本文报道刚架跨中受到以不同速度运动的质量块冲击时动态大挠度响应的实验研究工作,实验测取了冲击点位移、速度随时间变化的曲线及某些关键点的动态应变历史,由此描述了在响应过程中,质量块与刚架间动量动能的传递过程,找出了塑性区域形成和扩展的规律。研究表明:初始撞击接近于理想非弹性,动态荷载不宜简化为瞬时冲量,此时初始冲击动能与刚架所能吸收的最大弹性能之比即便很大,响应中弹性成分仍占有很大的比例,能量比率作为判断是否宜于采用刚塑性解答的条件已不再充分;刚架在初始撞击中吸收的能量和冲量与初始动能和动量之比,仅与刚架承受初始撞击的相当质量和冲击物质量之比有关,而与冲击速度无关,文中给出了二者的关系式。     

Experimental investigation on large deflection response of a frame impacted by a moving body

This paper reports on the experimental investigation of the dynamic large deflection response of a portal frame impacted at its midspan by a body moving at a certain speed. Both the deflection and velocity vs. time curves of the midspan and the dynamic history of a number of desired locations were recorded during the process of response. On the basis of the test data, the momentum and kinetic energy conversion between the frame and the moving body in the impact process are realized, and the occurrence and expansion of plastic regions are described. Investigation results show that the initial collision is approximately ideally inelastic, and that the elastic deformation plays a considerable role in the response though the input energy is much larger than the maximum elastic energy capacity of the beam member; therefore, in a general impact, the energy ratio should not be regarded as a sufficient criterion for a rigid—plastic solution. The ratios of the impulse transferred to and the energy absorbed by the frame in the initial collision to that carried by the moving body before impact is only related to the ratiobetween the equivalent mass of the frame paticipating in the initial collision and the mass of the impacting body, having nothing to do with the impacting velocity to a certain extent.     

碰撞振动及其典型现象

综述了机械系统碰撞振动的近期研究成果和碰撞振动的某些典型现象．对碰撞振动的几何与数值分析,以及实验研究作了评述,内容侧重于稳定性、奇异性,擦边诱发分叉,非线性模态等问题．最后,指出了今后研究中面临的一些问题      

Control techniques for impacting flexible systems

Summary In this article, a comparative study of the control for the repetitive impacting elastic link with parametrically excited base in rotational motion is considered. First, a sliding mode control strategy based on linearized inverse model is designed and employed to suppress the vibrations of the elastic beam after the impact. The control concept involves the usage of an adaptive plant inverse model as controller in feedforward configurations. Next, a linear controller is designed via Lyapunov-Floquet transformation. In this approach, the time-periodic equations of motion are transformed into a time-invariant form, which is suitable for the application of standard time-invariant controller-design techniques. Finally, a fuzzy logic controller is applied for the nonlinear model of the impacting system. The momentum balance method and an empirical coefficient of restitution is used in the collision. Received 27 January 1999; accepted for publication 3 June 1999     

结构多点弹性正撞问题的解法

以多个质点和梁碰撞为例给出了结构多点弹性正撞问题的求解方法．并用算例说明方法的可行性．     

On the impact of a rigid–plastic missile into rigid or elastic target

Here we carry out a systematic parametric study of a uniform cylindrical missile impacting rigid or elastic structures. We give an analytical result for the impact force in case of rigid target. A new parameter, the damage potential is introduced and it is shown that this single dimensionless combination of the parameters describes the course of the impact in this simplest case. For elastic target structures, we also show numerically that the course of the reaction force, the maximum target displacement and the duration of the impact depend primarily on the same dimensionless parameter with a secondary effect of the missile to target mass ratio and the relative stiffness of the target. The rigid target assumption is not always conservative with regard to the reaction force due to target vibration. We find a resonant effect in the maximum target displacement as the function of the missile to target mass ratio. The motivation of our work is rooted in the investigation of aircraft fuselage impact into robust structures like the containment of a nuclear power plant.     

Multiple impacts of two concentric hollow cylinders with zero clearance

The impact problem of two concentric, hollow, circular, elastic cylinders of same materials with zero clearance is studied, where the interior hollow cylinder is subjected to different uniformly distributed, exponentially decaying, interior pressures. The structural sizes and material parameters of the impacting system are unchanged. The influences of multiple collisions and multiple separations on interface impact pressures, dynamic radial displacements and stresses, are considered in the present investigation. The global histories of interface impact pressure have similar decay tendencies, and there exist three types of interface impact pressure branches. A so called ‘group’ phenomenon occurs in the histories of interface impact pressure, where several collisions take place closely together to form a cluster of interface impact pressure branches. Two neighboring cluster have an approximately constant time interval. The quasi-periodic growing of clusters means the impacting system is stable, and will result in quasi-periodic motions. A main frequency exists in the impacting system as well, which is different from the natural frequencies of two hollow cylinders.     

弹性波CT在混凝土靶体冲击损伤实验中的应用

介绍了弹性波CT技术的原理、方法和优点。在弹丸冲击混凝土靶体实验中,应用弹性波CT技术对冲击前后的混凝土靶体进行CT成像分析,并根据成像剖面上冲击前后对应位置的速度对比情况,分析其在弹丸冲击作用下的宏观破坏和内部损伤。CT成像分析结论与实际观测结果有较好的一致性,这表明利用弹性波CT成像能很好地反映混凝土靶体冲击前的结构特征、冲击后的破坏状况和损伤情况。