基于摄影测量的飞机静弹性风洞模型刚度识别方法

气动弹性风洞实验对飞行器研制不可或缺。为此,作者基于摄影测量技术,提出静弹性风洞实验模型刚度分布识别方法,即利用作用在模型机翼各个截面的已知弯矩、扭矩,结合摄影测量技术测得机翼各个截面受载变形前后的3D坐标,识别出模型的抗弯刚度和抗扭刚度分布。数值仿真和地面刚度实验研究表明:所建立的刚度识别方法能真实反映模型结构刚度特性,同时,较传统接触式测量方法,提出的方法对气动弹性风洞实验模型测量无附加刚度,既可提高刚度识别精度,又大幅缩短了刚度识别周期,故具有使用价值。

静气动弹性模型高速风洞试验研究

对采用复合材料玻璃纤维、碳纤维加工的静气动弹性模型进行了高速风洞试验研究,测试了模型的柔度矩阵、气动力、表面压力、弯/扭应变信号及弯/扭变形,为静气动弹性模型刚度试验、弯/扭应变信号测量、模型变形视频测量(VMD)及风洞总压控制等静气动弹性风洞试验能力的提高积累了经验,为飞行器静气动弹性研究提供了良好的试验平台。研究表明:静气动弹性模型较刚性模型升力线斜率及襟副翼效率下降、气动焦点前移;静气动弹性模型与刚性模型表面压力差异明显;在小迎角范围内,静气动弹性机翼模型弯/扭应变信号随迎角增加基本呈线性变化;在正迎角时,大展弦比后掠机翼静气动弹性模型的剖面扭转变形使有效迎角减小,剖面越靠近翼尖弯/扭变形越大。

静气动弹性模型的设计和风洞试验

介绍了静气动弹性模型的设计和风洞试验,并提出了利用弹性测力模型在风洞试验中测量到的变形求弹性压力分布的新看法。

一种基于光固化快速成型的飞机静弹性风洞试验模型设计方法

高速风洞静弹性模型设计和制造是静弹性风洞试验的一个关键。为解决模型设计周期长、制造费用高等问题,提出了一种基于立体光固化快速成型面向高速风洞大展弦比机翼静弹性模型研制方法。基于机翼刚度分布相似参数,采用机翼钢梁骨架和树脂蒙皮组合结构,通过优化结构尺寸完成静弹性模型结构设计;使用机械加工和快速成型技术完成模型制造,并通过地面刚度试验对加工模型进行了刚度分布验证。风洞试验结果表明:基于立体光固化成型技术设计和制造的静弹性风洞试验模型工程实用、可行,与传统静弹性模型研制过程相比,具有研制周期短、成本低而且不存在因填充物带来附加刚度的显著优势。

2UPR-RPU过约束并联机构刚度性能评价

运用螺旋理论和应变能方法研究了具有2R1T三自由度的2UPR-RPU过约束并联机构的静弹性刚度性能,模型考虑了杆件和关节的柔度。首先,基于螺旋理论得到分支的约束螺旋系;其次,基于材料力学得到分支中杆件的应变能,通过映射分支约束螺旋系到铰空间得到关节的应变能,通过汇总杆件、关节的应变能和卡氏定理得到与约束螺旋系对应的分支紧凑刚度矩阵;最后,通过虚功原理得到机构的总体刚度矩阵。采用有限元商业软件建立了有限元模型,并与理论模型进行对比,验证了理论模型的正确性。定义弹性元件存储的应变能与总应变能之比作为应变能因子指标,给出了应变能因子指标在规则工作空间的四维切片分布图,从应变能的角度定量评价了各弹性元件对机构刚度性能的影响程度,给出了不同载荷作用下的全局应变能因子指标。本研究为定位对机构刚度性能影响最大的弹性元件提供了新的思路。

Firmness evaluation of melon using its vibration characteristic and finite element analysis

The “Huang gua” melons were measured for their physical properties including firmness and static elastic modulus. The vibrational characteristics of fruits and vegetables are governed by their elastic modulus (firmness), mass, and geometry. Therefore, it is possible to evaluate firmness of fruits and vegetables based on their vibrational characteristics. Analysis of the vibration responses of a fruit is suggested for measuring elastic properties (Firmness) non-destructively. The impulse response method is often used to measure firmness of fruits. The fruit was excited using three types of balls (wooden, steel and rubber) and the vibration is detected by an accelerometer. The Instron device was used to measure the static elastic modulus of the inner, middle and outer portions of melon flesh. Finite element (FE) technique was used to determine the optimum excitation location of the chosen measurement sensor and to analyze the mode shape fruits. Four types of mode shapes (torsional or flexural mode shape, first-type, second-type spherical mode and breathing mode shape) were found. Finite element simulation results agreed well with experimental results. Correlation between the firmness and resonant frequency (r2=0.91) and between the resonant frequency and stiffness factor (r2=0.74) existed. The optimum location and suitable direction for excitation and response measurement on the fruit were suggested.

Wind-induced responses of super-large cooling towers

Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.

Macro Model Study for Nonlinear Spring of Tense Torsion Bar in Gap-Closing Type Electrostatic Micromirror

Nonlinear spring characteristics of the tense torsion bar in the gap-closing type electrostatic micromirror are examined. The macro model is introduced for the experimental study. The tension applied in the torsion bar is well controlled using the electromagnetic attraction. This controllability is suited for clearing the nonlinear nature. The tension is confirmed to have the effect to widen the controllable angle range of the mirror suppressing the pull-in. The pull-in angle is observed to increases to about 74% of the mechanical limit angle at the tension of 0,96 N. This is significantly larger than 44% of the case with the linear spring. The larger resonant frequency is maintained. The hardening of the spring can keep the balance with the electrostatic force over the limit of the linear spring. The observed features are explained reasonably with the combination of twisting and bending displacements of the torsion bar.

The Micro-foundations of the Environmental Kuznets Curve

This paper presents a simple and straight-forward static model of the micro-foundations of the environmental Kuznets curve, in which the relationship between income and pollution depends on the relative magnitudes of the diminishing income-compensated price elasticity of environmental amenity and increasing marginal propensity to earn environmental amenity out of non-environment income. The smaller the income-compensated price elasticity and the larger the marginal propensity to earn out of non-environment income, the earlier the turning point emerges. This key feature of our model generalizes the specific features of many existing models and generates many of their implications.