【作者】 张月红；

【导师】 陆念力；

【作者基本信息】 哈尔滨工业大学 ， 机械设计及理论， 2007， 硕士

【摘要】 目前对起重机伸缩臂稳定性校核主要还局限于中国起重机设计规范《GB3811/83》。其伸缩臂的计算长度是在未考虑油缸影响下采用能量方法推导而得,未免不够精确;而最近重新修订的新规范的计算模型采用的是变截面阶梯柱,在理论上更精确一些,但也没有考虑油缸的影响。含有各种形式油缸支承的伸缩臂的稳定性计算校核一直是困扰设计者的难题,吸引了众多专家学者做了大量研究,各自取得一些进展,但至今仍然没有给出完整的解决方案。起重机伸缩式吊臂通常由多节变截面的箱形臂组成,各臂节间轴向可相对滑动,在忽略摩擦力的情况下,油缸的作用力是非保向力,箱形伸缩臂的部分或全部臂节不直接承受轴力,其轴力由布置于吊臂内部的油缸承受。此时,吊臂的轴压临界力计算与简单的受压变截面阶梯柱的计算不同,所得临界力亦有所区别。考虑油缸时,伸缩臂的临界力取决于吊臂的截面惯性矩和油缸的支承形式,油缸的支承形式不同,其临界力也不同,本文将着重讨论此问题。本文在考虑了油缸的支承作用下,采用微分方程法和精确有限元法两种方法求起重机伸缩臂在起升平面外的欧拉临界力的精确解。微分方程法:适用于臂节数较少时(2～3节),不需要有限元知识,为设计人员提供便捷的计算公式,求解精确,但有局限性;精确有限元方法:适合于臂节数较多的情况,此时,失稳特征方程的求解较繁锁,又没有特殊规律可寻,不易采用手工计算,该方法为设计人员提供相应的计算理论,但需要有计算机软件与硬件的支持。本文给出单个油缸支承在顶部时伸缩臂欧拉临界力精确解的递推公式;通过比较用微分方程法、弹性支座法、有限元法三种方法确定伸缩臂的临界力;并求出了伸缩臂在不同支承情况下的失稳特征方程;同时给出了伸缩臂的变截面系数;详细的阐述了采用精确有限元法求解伸缩臂的临界力。对应《GB3811/83》规范的有关计算参数和图表,用本研究成果给出更为精确的计算参数,进而得出油缸对箱形伸缩臂整体稳定性的影响,在理论上更为严密。并将之与没考虑油缸支承作用的不同计算模型进行比较,分析结果表明,考虑油缸时伸缩臂的临界力大于不考虑油缸时伸缩臂的临界力。以往中国起重机设计规范《GB3811/83》和新规范中用忽略油缸支承作用的变截面阶梯柱力学模型计算起重机多节伸缩臂之稳定性,总体上是偏保守的。本文提出了考虑油缸之后的精确数据,相信这部分数据将为修改完善《起重机设计规范》提供重要参考依据。希望本研究所做的这些工作能够在这一领域起到某些补充以及能够对理论发展起到一定的推动作用。更多还原

【Abstract】 At present, stability analysis for telescopic boom still limitation to the design rules for cranes《GB3811/83》national standards of People’s Republic of China.In the original design rules for cranes, effective length of telescopic boom is confirmed by energy method without considering effect of cylinder, which is not precise; In the new revised design rules for cranes, considering the model as tapered stepped column, the result is more precise in theory,and still not considering effect of cylinder. Stability analysis and checking for telescopic boom with cylinder is still puzzling the designer, though many expert and scholar have done much research, till now, there is no accurate conclusion.Crane telescopic boom is made up of many tapered box sections which can axially slip relatively, only the boom is subject to bending moment, while supporting cylinder in boom bears axial force, which offers a non-conservative force, and the friction between booms is not taken account, therefore, its mechanical model cannot be equivalent to tapered stepped column’s, and Euler’s critical load is different. In the precondition of stability for cylinder, loading capability of telescopic boom depends on section inertia moment of boom and supporting form. As different placement and supporting form of cylinder for various telescopic booms, effective length coefficients are different too. The capability is irrespective with inertia moment of cylinder. The paper will emphasis this problem.The two method of differential equation and precise theoretical solution of Euler’s critical load at out-of-lifting-plane for crane multi-telescopic-boom with cylinder supporting is provided in this paper. Differential equation applicable for less pitch number(two-three),that doesn’t need finite element knowledge, provide a portable formula; precise finite element method applicable for multi-telescopic-boom, because it’s trouble to calculation and have no regularity, so this method provide the designer corresponding theory, but that need software and hardware to support.In the precondition of stability for cylinder in the paper, deduced a recurrence formula with single cylinder supporting at the top; and the critical force of telescopic boom is calculated with three different methods, including differential equation method, elastic support method and finite element method; getting destabilizing characteristic equation with different supporting type; meanwhile, solved variable cross-section length coefficient; then detailed represent using precise finite element method to solve critical force of telescopic boom.Corresponding to parameter and graph table about the rules for cranes GB3811-83,the paper give more accurate parameter, and then get the effect of cylinders to global stability, which is more accurate in theory. The result is compared with that of methods which did not take account of the effect of cylinders using the model of tapered stepped column. Euler’s critical load of the model considering the effect of supporting cylinder is greater than those neglecting it. In the previous design rules for cranes national standards of People’s Republic of China, the mechanical model to calculate crane multi-telescopic-boom’s stability is tapered stepped column neglecting the effect of supporting cylinder, thus the result generally incline to safety. The paper provide accurate data, and believe this can provide reference to the rules for cranes perfectly. The author really hope this can complement and motivation the theory developing in this realm.更多还原