大展弦比夹芯翼大攻角颤振分析

首先导出大展弦比复合材料梁弯扭耦合模态的半解析解，对具有NACA0012翼型的大展弦比的夹芯翼，在模态空间内建立了运动方程。然后采用半经验的ONERA非线性气动力模型描述空气动力，形成了对大展弦比夹芯翼大攻角气动弹性问题的描述。通过结构求解器和空气动力求解器联合求解来完成非线性颧振边界的计算。为了验证非线性颤振边界的求解方法，还利用ONERA气动力模型中的线性部分建立了夹芯翼的线性颤振方程。结果表明：零翼根攻角时，线性颤振速度与用非线性颧振边界求解方法得到的颧振速度完全一致；颤振速度随翼根攻角的增加而迅速减小；复合层铺设方式对颤振速度有较大影响。     

地效翼的颤振特性研究EI北大核心CSCD

地面效应是指当机翼贴近地面飞行时,由于受到地面的干扰作用而引起升力增加和阻力降低的现象。研究地面效应对颤振的影响规律。建立基于计算流体力学/计算结构力学耦合的颤振计算方法,采用标模AGARD 445.6机翼对颤振计算方法进行验证。在此基础上,以贴近地面的三维机翼为研究对象开展颤振分析,研究指出地面效应增强了非定常气动力的幅值,而且离地越近这种效果就越明显,从而导致颤振速度随着离地高度的降低而减小。然后重点讨论了攻角对地效翼颤振的影响,与不考虑地效的经典线性颤振理论不同,指出地效翼的颤振速度与攻角有关,在地效区域内,增加机翼的攻角会使发生颤振时的静变形变大,导致机翼抬起和离地高度增加,地效减弱,使得颤振速度随攻角的增大而提高。     

用当地流活塞理论计算大攻角翼面超音速颤振

本文应用当地流活塞理论，推导了弹性振动翼面的非定常压力分布以及用模态坐标表示的广义气动力系数矩阵，相应的颤振运动方程和特征方程，提出了可用于大攻角、有限厚度翼面超音速颤振计算的一种新的工程计算方法。算例表明方法的可行性和工程实用价值。     

基于非线性气动力的失速颤振计算与试验研究

飞行器大攻角飞行过程中的动态失速会导致结构自激扭转或俯仰运动,造成非线性失速颤振现象,直接影响飞行器飞行安全与结构安全。该文对标准Leishman-Beddoes (L-B)非线性非定常气动力模型进行马赫数修正,使其适用于低速不可压情形的动态失速气动力计算,然后基于二元翼段气动弹性模型,采用Newmark时域推进方法进行工程失速颤振计算。依据计算结果设计并完成了二元翼段失速颤振风洞试验。试验结果表明,多数试验状态,基于L-B模型的失速颤振计算结果与试验结果均吻合较好。结果验证了修正的L-B模型可以用来进行低速大展弦比平直翼段翼型的失速颤振工程分析与极限环振荡评估,同时,失速颤振速度与极限环幅值受初始攻角的影响很大。     

基于多项式修正片条气动力的跨音速颤振分析方法及其试验验证

提出一种基于多项式修正片条气动力的跨音速颤振分析方法,以片条内升力和力矩随攻角变化斜率为修正目标,采用多项式方程模拟片条力矩分布,使整个翼面的气动力大小和分布都与目标相符,进而使用修正后的气动力进行跨音速区的颤振分析.计算结果经跨音速颤振风洞试验验证,该方法对翼吊发动机构型的机翼颤振型、带操纵面的尾翼颤振型都有较高的计...     

桥梁断面颤振稳定性的直接计算法

利用通用CFD软件进行桥梁断面颤振稳定性的直接数值计算对于初步设计阶段估计桥梁断面的颤振临界风速具有重要意义。本文基于CFD软件Fluent,发展了桥梁断面颤振稳定性的直接计算方法。利用直接计算方法对典型矩形断面和典型流线形断面的颤振稳定性进行了数值计算,并将计算结果与风洞试验结果进行了对比。对比结果表明了本文计算方法的正确性。     

桥梁主梁端部翼板颤振主动控制流固耦合计算

安装主动控制翼板是提高大跨度桥梁颤振稳定性的一种有效方法。运用流固耦合技术对桥梁颤振主动控制进行计算分析,可以考虑气动翼板的大幅度扭转以及气动翼板和主梁端部的气动干扰效应。通过对商用软件FLUENT二次开发,建立了竖弯和扭转流固耦合数值仿真计算模型,并对主梁端部安装了主动控制翼板的大海带桥的颤振稳定性进行了数值仿真计算分析。系统地研究了前后翼板相对于主梁的角速度对颤振性能的影响。数值仿真计算结果表明:没有采用主动控制翼板时,颤振临界风速计算值和风洞实验值吻合良好。采用主动控制翼板后,当前翼板角速度与主梁反向,后翼板角速度与主梁同向时控制效果良好。且随着气动翼板角速度增大,主梁扭转位移减小。旋涡脱落图表明:作用在翼板的流场和作用在主梁的流场相互干扰,因此作用在整个系统上的力矩变化不仅来源于气动翼板的力矩,而且来源于流场形态的改变。计算表明在上述良好的控制时,气动翼板提供反向力矩,且与作用在主梁上的力矩相位相反,最大限度地平衡了作用在主梁上的力矩,使作用在主梁系统上的力矩均值减小,这是主动控制翼板提高桥梁颤振稳定性的原因之一。最后研究了气动翼板合适长度,计算表明:当气动翼板长度为主梁宽度的10%~15%时,颤振主动控制效果较好。     

超音速飞行器翼—身组合体的颤振研究

飞行器的颤振是结构在高速气流中发生的一种自激振动现象,而这种现象在超音速和高超音速飞行器上极易发生。由于飞行器自身结构的复杂性,传统的组合体结构颤振分析在这种工况下会产生较大误差。利用特别适合复杂结构建模的动态子结构方法,针对飞行器在超音速飞行状态下高超音速流与飞行器自身结构的特点,考虑机翼、机身组合布局在颤振形态上产生的复杂情况,利用动态子结构中自由界面模态综合法,将整个飞行器分成机身、机翼子结构,基于非线性气动理论结合有限元计算软件,计算气动力分布情况并建立飞行器翼—身组合体系统的振动微分方程,对其进行颤振特性分析,得到飞行器在所设工况下的振动与颤振特性与颤振临界状态,实现全机气动弹性问题的仿真计算。为动态子结构方法应用于超音速飞行器的颤振研究提供理论基础,拓展了超音速飞行器组合体颤振的计算方法。     

增设主梁下风侧翼板抑制悬索架桥设阶段颤振的研究

本文首先建立了下风侧附加翼板桥梁主梁截面的自激气动力模型。以某悬梁桥设计方案为工程背景，应用多模态颤振分析方法，分析了该桥架设阶段颤振临界风速的发展趋势。以其中最危险的架设阶段为例，研究了主梁下风侧设置翼板这种控制措施对系统颤振的控制效果。分析表明，主梁下风侧附加翼板对于悬索桥架设阶段的颤振是一种有效的气动控制措施。     

基于弯扭耦合理论的颤振频率计算方法

首先,该文基于颤振研究的频率重合理论,对两组悬臂壳体结构进行了弯扭耦合模态的颤振规律研究,提出一种简便的颤振频率预估方法,并进行了两组模型校检。第一组模型控制均质梯形薄板掠角作为单一变量,对颤振模态与耦合模态进行了规律性研究,并对颤振频率计算方法进行试算,为带掠角的梯形翼颤振参数初选提供了参考。第二组模型以单向铺层结构的矩形悬臂薄板的铺层角度作为基本变量,给出颤振方向性对颤振参数的影响规律,同时也检验了复合材料薄板的颤振频率预算结果,为复合材料机翼设计提供相应参考依据。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.