机翼颤振模型梁架加工变形研究

机翼颤振模型对模拟飞机动力学特性、刚度分布、质量分布与气动外形具有重要意义.其梁架的性能对飞机模拟颤振试验有着重要的影响.机翼颤振模型梁架由于尺寸大、结构复杂、刚度差,在铣削加工中变形较大,其精度难以控制.为此,借助有限元软件对其进行铣削加工仿真,获得已加工表面残余应力,进而预测梁架铣削时的加工变形.在此基础上,对梁架加工工艺进行优化,提高加工精度.     

基于流固耦合方法的运载火箭安全阀颤振问题研究

安全阀是运载火箭增压输送系统所属重要单机,用于保护推进剂贮箱免受过压,在地面测试中曾出现安全阀在启闭过程中主阀颤振现象,导致零件受损并影响产品性能.基于动网格下的N-S流动方程和非线性接触下的刚体运动控制方程的流固耦合方法,采用Realizable k-ε湍流模型和显式动力学算法分析了阀门的气动载荷,进而分析出阀门颤振产生的机理为流场压力脉动与结构频率耦合和活塞在冲击响应作用下与阀杆都产生了塑性变形,据此提出增大运动部件尺寸来改善结构频率的措施,并对改善后的产品开展抽样试验验证,测试结果表明采取的改善措施有效地解决了阀门颤振问题,具有实际的工程价值.     

Nonperiodic flutter of a buckled composite panel

The nonlinear vibrations of a composite panel subjected to uniform edge compression and a high-supersonic coplanar flow is analysed. Third-order piston theory aerodynamics is used and the effects of in-plane edge restraints, small initial geometric imperfections, transverse shear deformation, and transverse normal stress are considered in the structural model. Periodic solutions and their bifurcations are determined using a predictor-corrector type Shooting Technique, in conjunction with the Arclength Continuation Method for the static state. It is demonstrated that third-order aerodynamic nonlinearities are destabilizing, and hard flutter oscillations (both periodic and quasiperiodic) of the buckled panel are obtained. Furthermore, chaotic motions of an uncompressed panel, as well as a buckled-chaotic transition, and chaos via period-doubling are possible, and the associated Lyapunov exponents are computed. A coexistence of the buckled state with flutter motion may also occur. Results indicate that edge restraints parallel to the flow do not significantly affect the immediate post-critical response, and that a higher-order shear deformation theory is required for a moderately thick/flexible-in-transverse-shear composite panel.     

桥梁颤振临界风速的概率密度演化计算

针对桥梁结构自身特性以及外部环境的随机性(如刚度、质量、阻尼比、气动导数等因素)所造成的桥梁的颤振临界风速不确定,难以衡量桥梁颤振稳定性问题. 将概率密度演化方法与桥梁颤振多模态耦合分析方法相结合,以江阴长江大桥作为实例,通过考虑桥梁结构自身的不确定性及气动导数的不确定性,给出不同模态阻尼比及频率的概率密度演化过程. 研究表明:结构模态阻尼比及频率在低风速情况下的概率密度分布可近似认为服从正态或对数正态分布,高风速下的概率密度则无法用单一的概率分布来描述,概率分布会出现双峰甚至多峰的情况;与按确定性方法到的颤振临界风速相比,按概率密度演化方法得到的颤振临界风速较小.     

风致静力扭角对桥梁颤振性能影响的节段模型试验研究

自由振动试验识别得到的气动参数已包含了一定的、但与实桥不严格相似的风致静力扭角的影响.为了在颤振分析中能精确考虑风致静力扭角的影响,首先必须消除节段模型试验中风致静力扭角对气动导数识别结果的影响.通过在试验过程中使节段模型作受控反向旋转可以消除平均风附加攻角,然后以象山港大桥为背景,将消除平均风附加攻角后的试验结果与常规试验结果相比较,对风致静力扭角对节段模型系统的阻尼比、气动导数和临界风速的影响进行了初步讨论.研究结果表明:风致静力扭角对模型扭转阻尼比和与扭转有关的气动导数有明显的影响.象山港大桥节段模型在+3°攻角发生颤振时风致静力扭角约为0.32°,攻角修正以后节段模型颤振临界风速识别结果提高了7%.     

复合材料曲壁板与平壁板热颤振特性的对比

对比研究了层合复合材料曲壁板和平壁板热颤振特性.分别建立三种铺层方式的曲壁板和平壁板的有限元模型.采用分步求解方法,首先计算热效应引起的附加刚度,然后将其引入到壁板颤振模型中进行颤振分析.分析了不同铺层方式曲壁板和平壁板的热颤振特性,结果表明壁板颤振临界速度随温升近似呈线性下降,正交各向异性铺设的曲壁板与准各向同性铺设的曲壁板相比,其颤振临界速度下降率更大,而平壁板情况刚好相反;不同铺层方式曲壁板的热颤振危险模态不同,而平壁板热颤振危险模态不受铺层方式的影响.     

Aeroelastic stability predictions for a MW‐sized blade

Classical aeroelastic flutter instability historically has not been a driving issue in wind turbine design. In fact, rarely has this issue even been addressed in the past. Commensurately, among the wind turbines that have been built, rarely has classical flutter ever been observed. However, with the advent of larger turbines fitted with relatively softer blades, classical flutter may become a more important design consideration. In addition, innovative blade designs involving the use of aeroelastic tailoring, wherein the blade twists as it bends under the action of aerodynamic loads to shed load resulting from wind turbulence, may increase the blade's proclivity for flutter. With these considerations in mind it is prudent to revisit aeroelastic stability issues for a MW‐sized blade with and without aeroelastic tailoring. Focusing on aeroelastic stability associated with the shed wake from an individual blade turning in still air, the frequency domain technique developed by Theodorsen for predicting classical flutter in fixed wing aircraft has been adapted for use with a rotor blade. Results indicate that the predicted flutter speed of a MW‐sized blade is slightly greater than twice the operational speed of the rotor. When a moderate amount of aeroelastic tailoring is added to the blade, a modest decrease (12%) in the flutter speed is predicted. By comparison, for a smaller rotor with relatively stiff blades the predicted flutter speed is approximately six times the operating speed. When frequently used approximations to Theodorsen's method are implemented, drastic underpredictions result, which, while conservative, may adversely impact blade design. These underpredictions are also evident when this MW‐sized blade is analysed using time domain methods. Published in 2004 by John Wiley & Sons, Ltd.     

大型圆筒混合机筒体制造工艺设计分析与论证

圆筒混合机的制造成功是大型机械设备国产化的新成果。混合机筒体的制造质量,直接关系整台设备运行的稳定性和使用寿命,是该设备制造技术重点、难点及核心。本文在分析这种超大型筒体结构特征及其关键制造技术的基础上,阐述了筒体的分段组合制造工艺方案的合理性,并详细论述了关系筒体强度和使用寿命各筒节焊接工艺的措施及关系筒体整体制造质量各关键筒节的制造工艺、工艺施工中的关键技术措施。通过筒体制造精度的检测结果验证了确保筒体最终制造质量的筒体组焊工艺、工艺装备及其调整、齿圈架法兰精整加工工艺设计是成功的。     

某无人机机翼颤振模型试验研究

推导了相似率比例关系 .依据机翼几何尺寸、风洞特性 ,确定了试验模型缩比比例系数 .计算了机翼振动特性、颤振临界速度的理论值 .通过用梁的动力相似模型模拟机翼振动特性 ;用框段模拟机翼外形 ,论述了颤振吹风试验模型研究的过程     

悬臂输流管的颤振和浑沌运动分析

研究了具有弹性支承和运动约束的悬臂输流管的稳定性问题。在分析参数对系统稳定性影响的同时，特别研究了动态失稳区域内的不同运动。结果表明，在一定条件下该系统不仅因颤振而动态失稳，在某些参数域内还可发生浑沌运动。本文用数值分析的方法确定了浑沌发生区域。