共查询到19条相似文献，搜索用时 765 毫秒
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蜻蜓拍翼前飞中模型翼动态柔性变形的气动效应研究 总被引：1，自引：0，他引：1
根据蜻蜓拍翼前飞激发的流场具有St>>1/Re的特点，在理论模化框架下，本文采用势流假设，用二维变形体前、后缘脱涡的面元法研究了前飞模型蜻蜓翼在周期性拍动中动态柔性变形引起的气动力响应。通过比较柔性模型翼和刚性模型翼气动力随时间的变化，发现在下拍行程中动态柔性变形显著地提高了升力和推力；值得注意的是，蜻蜓前飞时，翼的实际柔性变形幅值恰处于一个最佳范围内，它大幅地提高了升力，同时使消耗的气动功率趋近于最低，有利于蜻蜓维持前飞状态。 相似文献
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变体飞行器可以在飞行中主动改变自身气动外形以在不同飞行环境中始终保持良好性能。本文针对一种伸缩翼结构变体飞行器模型进行了动态气动力测量,并采用烟线技术实时显示伸缩机翼区域流场。结果表明变体运动时飞行器气动特性存在着一定的非定常迟滞效应,且运动速度越大,迟滞效应越明显。出现这种非定常现象的原因是气体对模型运动的动态响应迟滞,随后进行的烟线试验证明了伸缩翼运动对翼尖涡瞬时结构具有显著影响。 相似文献
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扑翼驱动系统运转时,由于惯性和气动阻力矩的变化将引起系统速度的周期性波动,从而影响驱动效率和气动性能,因此速度波动的分析是研究扑翼微型飞行器动力学中的一个重要研究方向.基于拉格朗日方程,对一种常用的扑翼机构,建立了动力学方程,并求解其真实运动规律,进而为扑翼微型飞行器研究提供理论基础. 相似文献
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采用非线性有限单元法和非定常面元法,实现了正交各向异性矩形薄膜在拍动中的流固耦合数值模拟,并研究薄膜在小攻角沉浮运动时,在惯性力和气动力共同作用下的非定常变形响应及对应的气动特性.结果显示,在相同的沉浮运动条件下,薄膜的柔性有助于改善其气动性能,即薄膜弦向、展向弹性模量减小,引起柔性变形幅度的较大增加,则作用于膜上的平均气动升力也相应显著增高,而平均升力与平均气动功率的比值仅略有降低. 相似文献
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本文基于SST k-w模型对平板翼型的动态失速问题展开数值模拟研究,以翼型的1/2弦长处为转动中心,分析翼型在不同俯仰角速度下的气动性能,探究动态失速对平板翼型气动性能的影响。 相似文献
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对于不同结构形式的栅格翼,采用了分块结构网格生成策略,通过求解N-S方程对栅格翼子弹翼身组合体的亚声速和跨声速绕流流场进行了数值模拟,获得了栅格翼子弹翼身组合体在不同类型尾翼影响下的亚声速和跨声速气动特性,并与刀形翼子弹翼身组合体的气动特性进行了对比。计算结果表明：栅格翼子弹翼身组合体的飞行稳定性和法向力特性优于刀形翼子弹翼身组合体,其中斜置栅格翼模型的飞行稳定性和法向力特性均为最优;栅格翼子弹翼身组合体的轴向力系数大于刀形翼子弹翼身组合体,斜置栅格翼模型轴向力最大。 相似文献
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桥梁变形可分为静态变形和动态变形。静态变形通常是指变形观测的结果只表示在某一期间内的变形值。动态变形是指在外力影响下而产生的变形,它是以外力为函数来表示的动态系统对于时间的变化,其观测结果是表示桥梁在某个时刻的瞬时变形。基于各种原因,桥梁在修建施工过程中和使用期间,会出现变形,如果这种变形超过规定的限度,就会影响正常运营,而且严重时还会危及桥梁的安全寿命。为此,对桥梁进行变形监视观测是十分必要的。 相似文献
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本文探讨了动态-独立坐标系的建立过程，阐述了其在复杂地形线路工程中的优势，并结合青海某燃气管线项目，重点分析了动态-独立坐标系中不同高度抵偿坐标系间的搭接精度及其适用范围。结果显示：(1)在复杂地形、长距离线路控制测量项目中，地势起伏对地表长度投影变形影响较大，构建“动态-独立坐标系”不仅能够满足投影变形的相关规范要求，还对后续测绘及施工提供了极其便捷的工作条件；(2)根据搭接带检测边的拼接精度分析结果，“动态-独立坐标系”中相互搭接的独立坐标系，需在同一中央子午线分带下进行解算，不同中央子午线下解算的抵偿坐标系之间禁止相互拼接。 相似文献
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《科技通报》2017,(11)
提出一种基于有限元法的薄壁柔性零件的防变形冷加工技术研究方法。该方法先利用层次分析方法对薄壁柔性零件加工变形的影响因素进行提取,得到薄壁柔性零件加工变形影响因素提取属性,通过计算提取属性对目标层的影响程度矢量,得到每个薄壁柔性零件的加工变形影响因素的重要度值,在此基础上采用误差补偿方法计算出薄壁柔性零件的防变形冷加工铣削深度,并结合薄壁柔性零件变形预测模型对薄壁柔性零的切削参数进行优化设计,以最小化所有薄壁柔性零件切削工位的加工误差为目标函数。实验结果表明,所提方法能够有效提高薄壁柔性零件的形位精度,同时对同类的其他薄壁柔性零件的变形控制具有一定的参考价值。 相似文献
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The effect of rotational and translational support flexibility on the fundamental frequency of both an almost-clamped-clamped beam and a flexibly supported cantilever beam is considered. In each case the effect of a rotationally flexible support becomes more pronounced for decreasing values of the length-to-depth ratio. It is shown that the effect of end-fixity on the fundamental frequency can be of a magnitude equal to or greater than that due to the effect of shear deformation or rotatory inertia. Results using Bernoulli-Euler beam theory and Timoshenko beam theory are compared. Expressions are formulated that give the fundamental frequency as a function of the support flexibility, length to depth ratio and fundamental frequency for a rigid support. 相似文献
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Wenxi Zhang 《Journal of The Franklin Institute》2018,355(9):3968-3989
A new principle, run with flexible deformation, for avoiding vibration throughout trajectories of a flexible robot manipulator is proposed. It comprises the hysteretic and leading mechanisms to maintain a steady pace of flexible (neutral surface) evolution with rigid (joint axis) advance, with the surface staying on a single side of the axis for constant deformation. A simple proportional–derivative (PD) controller is presented to realize the mechanisms, capable of adapting deformation into an invariant set that the single-sided pace-keeping is dependable over a steady or transient period. Analytically this set is the dynamic equilibrium target, in which negativeness of the Lyapunov function’s derivative is uncertain, and is proven globally uniformly asymptotically stable via a generalized Lyapunov and LaSalle’s argument. Further, the desired deformation is same stable in the sense of Lyapunov theorem due to recursive slowdown by the controller. The theoretical work is validated by the numerical simulations, which shows that the desired performance is well achieved. Significant advantages such as vibration-free servo control of a flexible-axis-based trajectory are demonstrated. 相似文献
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人脸由于其非刚性明显,受到运动背景变化、形变程度复杂、特征丢失等因素的影响,使得在进行三维动态人脸形变估计时,面临着估计不准,误差较大的问题。为了解决这些问题,提出一种基于特征缺失修复的人脸三维运动形变估计算法,将非刚体人脸运动的形变估计过程中,运用特征补偿方法,补偿由于噪声、形变程度复杂带来的特征丢失缺陷,运用较多的人脸形变特征进行形变分析,准确计算人脸的形变程度。实验结果表明,这种方法得到的解误差较小,效果明显。 相似文献
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A.V. Balakrishnan Amjad M. Tuffaha Iylene Patino Oleg Melnikov 《Journal of The Franklin Institute》2014
We present a methodology for calculating flutter speeds of a high aspect ratio flying wing articulated with point masses in inviscid air flow. This highly flexible wing configuration typically models a HALE (High Altitude Long Endurance) UAV (Unmanned Aerial Vehicle) type aircraft. To demonstrate the procedure, we perform flutter analysis on an actual articulated wing model and we investigate the dependence of the flutter speed on the number of loads mounted onto the structure and the number of panels comprising the flying wing for both varying and constant span. The results show that the flutter speed decreases as more panels and point masses are incorporated into the flying wing. On the other hand, the number of point masses mounted onto the structure has a small effect on the flutter speed if the wing span is kept constant. 相似文献
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《Journal of The Franklin Institute》2021,358(14):6941-6961
This paper addresses the cooperative output feedback control of a mobile dual flexible manipulator, which is mounted at a moving platform to grasp and move a rigid object. We derive the distributed parameter model with geometric constraints for the dual flexible manipulator system by utilizing the Lagrange multiplier method and the Hamilton’s principle, which avoids the problem of control spillover. This paper considers a case where the states of system are difficult to measure directly and exploits the high gain observer theory to design the state observers for estimating the unavailable states. Then the cooperative output feedback control scheme is developed by the Lyapunov’s method, which enables the cooperative control of the flexible manipulator system. Furthermore, under the cooperative output feedback control scheme, we prove that the states of the system are uniformly bounded. Finally, the feasibility of the designed cooperative output feedback controllers is verified by numerical simulation. 相似文献
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To perform repetitive tasks, this paper proposes an adaptive boundary iterative learning control (ILC) scheme for a two-link rigid–flexible manipulator with parametric uncertainties. Using Hamilton?s principle, the coupled ordinary differential equation and partial differential equation (ODE–PDE) dynamic model of the system is established. In order to drive the joints to follow desired trajectory and eliminate deformation of flexible beam simultaneously, boundary control strategy is added based on the conventional joints torque control. The adaptive iterative learning algorithm for boundary control scheme includes a proportional-derivative (PD) feedback structure and an iterative term. This novel controller is designed to deal with the unmodeled dynamics and other unknown external disturbances. Numerical simulations are provided to verify the performance of proposed controller in MATLAB. 相似文献
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M. Madani 《Journal of The Franklin Institute》2011,348(6):999-1012
In this paper, simultaneous position/force control of a closed-chain planar manipulator with the last link flexible is studied when the manipulator is in contact with an environment. The proposed manipulator consists of a flexible link connected to three rigid linkages whichare optimized for kinematic and force manipulability in the region of interest. The flexible link is modeled as a series of rigid links connected by virtual torsion springs. A hybrid position/force control algorithm is developed and implemented on the manipulator. Experimental results are presented to verify the performance of the controller. 相似文献