分布式通风消声板特性研究*

在隔声板结构中,分布式内嵌大量小型消声单元,在入射声波被消声单元有效衰减的同时,气流可均匀通过整个板结构,形成一种分布式消声板结构。利用平面波理论和修正传递矩阵法,建立消声板简化模型,并预测模型传递损失。加工消声板样件,实验室内测试并验证其声学及通风性能。对比隔声测试结果与预测结果,验证修正传递矩阵法针对该结构的准确性,同时验证消声板结构的实际效果。结果显示,该分布式消声板结构具有良好的声学效果,修正传递矩阵法可应用于该结构的声学性能预测以及结构设计。     

Computational aeroelastic investigation of a transonic limit-cycle-oscillation experiment at a transport aircraft wing model

Aeroelastic measurements of a three-dimensional wing model, the so-called Aerostabil wing, were conducted in the Transonic Windtunnel Göttingen. This clean, backward-swept wing allowed the experimental investigation of limit cycle oscillations in a certain transonic parameter range. In this paper, a detailed insight into the observed physical phenomena, especially the measured limit cycle oscillations, is presented by means of CFD–CSM coupled simulations. These simulations on the basis of a detailed structural finite element model reveal the specific properties of the Aerostabil wing and furthermore allow investigating the unstable behavior of this windtunnel model for transonic flow settings. The aerodynamic characteristics include a two-shock system and large flow separation areas, further increasing the complexity of the aeroelastic problem. A structural single degree-of-freedom system is used for the prediction of the experimental stability range and the limit cycle oscillation investigations. Due to the good agreement of simulation and experiment the limit cycle oscillations can be explained by means of nonlinear aerodynamic effects.     

现金持有动态调整机制——基于动态面板模型的实证分析

本文通过建立动态面板数据模型,系统地研究了中国企业现金持有的动态调整机制。发现:第一,企业存在最优目标现金持有水平,现金持有策略倾向于围绕这一目标进行动态调整,但是我国资本市场动态调整的成本较高;第二,现金持有不足企业的调整速度快于超额现金持有企业的调整速度,这说明,相对于超额现金持有带来的代理成本负面影响,企业更加倾向于关注现金持有不足所产生的流动性短缺风险。并且统计过程表明系统广义矩方法在动态面板模型估计中具有合理性。     

中国居民消费的特征分析——中基于两阶段面板分位回归

本文结合实际问题,提出一种两阶段面板数据分位回归方法,并使用该方法分析我国居民的消费特征。通过横向和纵向比较揭示三种不同收入人群的边际消费倾向的变化趋势。文章认为中等收入者的边际消费倾向趋于稳定,低收入者和高收入者的边际消费倾向都有上升的趋势。中国居民的边际消费倾向呈现"U"型,所以提高低收入者的消费不仅在于提高他们的收入,更重要的是缩小当前的贫富差距。     

Parametric studies on relationships between flutter derivatives of slender bridge (Ⅱ)

Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter deriva-tives of flexible structure, the change of flutter derivatives of slender bridge cross-section with respect to its aerodynamic center, rotational speed and angle variation is studied using a parametric method. The calculated results are compared with the measured ones, and expressions of flutter derivatives of the Messina Straits Bridge are derived. The in-trinsic relationships existing in flutter derivatives are validated again. It is shown that the influence of the rotational speed on flutter derivatives is not negligible. Therefore, it provides an additional semi-analytical approach for analyzing flutter derivatives of the bridge with streamlined cross-section to get its aerodynamic information.     

CHAOTIC MOTIONS AND LIMIT CYCLE FLUTTER OF TWO-DIMENSIONAL WING IN SUPERSONIC FLOW

Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contains both structural and aerodynamic nonlinearities. Hopf bifurcation theory is used to analyze the flutter speed of the system. The effects of system parameters on the flutter speed are studied. The 4th order Runge-Kutta method is used to calculate the stable limit cycle responses and chaotic motions of the aeroelastic system. Results show that the number and the stability of equilibrium points of the system vary with the increase of flow speed. Besides the simple limit cycle response of period 1, there are also period-doubling responses and chaotic motions in the flutter system. The route leading to chaos in the aeroelastic model used here is the period-doubling bifurcation. The chaotic motions in the system occur only when the flow speed is higher than the linear divergent speed and the initial condition is very small. Moreover, the flow speed regions in which the system behaves chaos axe very narrow.     

壁板颤振的分析模型、数值求解方法和研究进展

研究壁板颤振问题需要计及大挠度变形下结构的几何非线性效应,不仅涉及气动弹性稳定性,而且关心结构的非线性颤振响应.该文回顾了飞行器壁板颤振问题的国内外研究情况,评述了在壁板颤振研究中采用的分析模型、数值求解方法以及在理论分析和试验方面的研究成果,并提出了今后壁板颤振问题的4个研究方向.      

Limit Cycle Oscillations of a Wing Section with a Tip Mass

This paper presents an investigation into the limit cycleoscillation phenomenon for a nonlinear aeroelasticsystem under unsteady aerodynamics. The system consists of a sweptbackwing section carrying a tip mass with one degree of freedom. Thejunction stiffness considered between the wing and the tip mass istrilinear. The method of harmonic balance, which can be very practicalin the study of nonlinear flutter, is used for the theoretical analysisof limit cycle oscillations. Stable, unstable and semi-stable limitcycles are predicted in the system for both cases of hardening andsoftening springs. Results found by numerical simulation provide theamplitudes of limit cycles. The experimental results in wind tunneltests agree well with the predictions obtained both theoretically andnumerically.     

翼型厚度对气动弹性特性的影响

结合基于$k$-$\omega$的SST两方程湍流模型,求解雷诺平 均Navier-Stokes方程获得定常和非定常气动力,耦合翼型弹性运动方程,在时间 域内模拟了不同厚度对称翼型在不同迎角下的气动弹性动态过程, 并重点研究了较大迎角下的不同厚度翼型流场特征和气动弹性的性质,研究结果表明：在论 文所涉及的参数情况下,对于迎角从零到大迎角范围,翼型颤振临界速度随迎角的变化不是 单调的. 翼型颤振临界速度迅速下降的起始迎角比最大升力系数对应的迎角小很多.     

Numerical modelling of the stability of loaded shells of revolution containing fluid flows

A mixed finite-element algorithm is proposed to study the dynamic behavior of loaded shells of revolution containing a stationary or moving compressible fluid. The behavior of the fluid is described by potential theory, whose equations are reduced to integral form using the Galerkin method. The dynamics of the shell is analyzed with the use of the variational principle of possible displacements, which includes the linearized Bernoulli equation for calculating the hydrodynamic pressure exerted on the shell by the fluid. The solution of the problem reduces to the calculation and analysis of the eigenvalues of the coupled system of equations. As an example, the effect of hydrostatic pressure on the dynamic behavior of shells of revolution containing a moving fluid is studied under various boundary conditions. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 185–195, March–April, 2008