Three-dimensional nonlinear flutter analysis of long-span suspension bridges during erection

In this work, the aerodynamic stability of the Yichang Suspension Bridge over Yangtze River during erection was determined by three-dimensional nonlinear flutter analysis, in which the nonlinearities of structural dynamic characteristics and aeroelastic forces caused by large deformation are fully considered. An interesting result obtained was that the bridge was more stable when the stiffening girders were erected in a non-symmetrical manner as opposed to the traditional symmetrical erection schedule. It was also found that the severe decrease in the aerodynamic stability was due to the nonlinear effects. Therefore, the nonlinear factors should be considered accurately in aerodynamic stability analysis of long-span suspension bridges during erection. Project supported by National Natural Science Foundation of China(No. 598954410), and China Postdoctoral Science Foundation (No. 2002031245)     

Aerodynamic stability of cable-stayed bridges under erection

INTRODUCTION Long-span cable-stayed bridges under service andparticular construction conditions are very susceptibleto wind action due to their great flexibility, so thewind stability (aerodynamic stability or flutter stabil-ity) is becoming a major concern in the design andconstruction phrases. As compared with the servicecondition, although the period of erection is not toolong, the structural stiffness of cable-stayed bridgesunder erection is greatly reduced, and consequentlythey be…     

Aerodynamic stability of cable-supported bridges using CFRP cables

To gain understanding of the applicability of carbon fiber reinforced polymer (CFRP) cable in cable-supported bridges, based on the Runyang Bridge and Jinsha Bridge, a suspension bridge using CFRP cables and a cable-stayed bridge using CFRP stay cables are designed, in which the cable’s cross-sectional area is determined by the principle of equivalent axial stiffness. Numerical investigations on the aerodynamic stability of the two bridges are conducted by 3D nonlinear aerodynamic stability analysis. The results showed that as CFRP cables are used in cable-supported bridges, for suspension bridge, its aerodynamic stability is superior to that of the case using steel cables due to the great increase of the torsional frequency; for cable-stayed bridge, its aerodynamic stability is basically the same as that of the case using steel stay cables. Therefore as far as the wind stability is considered, the use of CFRP cables in cable-supported bridges is feasible, and the cable’s cross-sectional area should be deter-mined by the principle of equivalent axial stiffness.     

Aerodynamic stability of cable-stayed-suspension hybrid bridges

INTRODUCTION The cable-stayed-suspension (CSS) hybridbridge is developed from the traditional cable-stayedbridge and suspension bridge, and has some advan-tages of the two bridge types described as follows: 1. As compared with the suspension bridge of thesame span length, the suspension portion is greatlyshortened, so the tensional forces in the main cablesare greatly decreased, which helps to decrease theconstruction costs of the main cables and the massiveanchors, and the difficulty of…     

小展弦比超音速飞机机翼气动特性分析

基于采用对称翼型的小展弦比三角形机翼模型,对其在亚音速状态和超音速状态时的升力特性、阻力特性、升阻比特性、稳定性特性进行了理论计算分析。并针对该模型进行数值模拟,分析其超音速流场特性,与理论分析结果进行对比,发现相差不大。得出结论:该翼型机翼在飞机巡航速度为Ma=2时气动性能较好。     

Mechanism of Breakdown in Laminar-Turbulent Transition of Incompressible Boundary Layer on a Flat Plate

Temporal mode direct numerical simulation was done for the process of laminar-turbulent transition in an incompressible boundary layer on a flat plate. The analysis of the results showed that during the breakdown process of laminar-turbulent transition, the modification of the mean flow profile by the disturbances led to a remarkable change in its stability characteristics, manifested in the significant enlargement of the linear unstable zone and the maximum amplification rate, and led to that many more disturbances were excited and enhanced rapidly, correspondingly the turbulent energy also increased rapidly, and the mean flow profiles evolved swiftly from laminar to turbulent. It was also found that if the oblique waves in the initial disturbances did not form symmetrical pairs, the subsequent span-wise mean velocities would, in general, be nonzero due to nonlinear interaction, which would have a great effect on the stability characteristics and also implied that the turbulence obtained by direct numerical simulation might not be fully a random process.     

Numerical study on the aerodynamic performance and safe running of high-speed trains in sandstorms

The influence of sandstorms on train aerodynamic performance and safe running was studied in response to the frequent occurrence of sandstorm weather in north China. An Eulerian two-phase model in the computational fluid dynamic (CFD) software FLUENT, validated with published data, was used to solve the gas-solid multiphase flow of a sandstorm around a train. The train aerodynamic performance under different sandstorm levels and no sand conditions was then simulated. Results showed that in sandstorm weather, the drag, lift, side forces and overturning moment increase by variable degrees. Based on a numerical analysis of aerodynamic characteristics, an equation of train stability was also derived using the theory of moment balance from the view of dynamics. A recommended speed limit of a train under different sandstorm levels was calculated based on the stability analysis.     

Multi-objective optimization design method of the high-speed train head

With the continuous improvement of the train speed, the dynamic environment of trains turns out to be aerodynamic domination. Solving the aerodynamic problems has become one of the key factors of the high-speed train head design. Given that the aerodynamic drag is a significant factor that restrains train speed and energy conservation, reducing the aerodynamic drag is thus an important consideration of the high-speed train head design. However, the reduction of the aerodynamic drag may increase other aerodynamic forces （moments）, possibly deteriorating the operational safety of the train. The multi-objective optimization design method of the high-speed train head was proposed in this paper, and the aerodynamic drag and load reduction factor were set to be optimization objectives. The automatic multi-objective optimization design of the high-speed train head can be achieved by integrating a series of procedures into the multi-objective optimization algorithm, such as the establishment of 3D parametric model, the aerodynamic mesh generation, the calculation of the flow field around the train, and the vehicle system dynamics. The correlation between the optimization objectives and optimization variables was analyzed to obtain the most important optimization variables, and a further analysis of the nonlinear relationship between the key optimization variables and the optimization objec- tives was obtained. After optimization, the aerodynamic drag of optimized train was reduced by up to 4.15%, and the load re- duction factor was reduced by up to 1.72%.     

一个特殊的相对转动非线性动力学模型的近似解

研究了一个特殊的相对转动非线性动力学模型,分别用同伦摄动法和同伦近似对称法给出近似解。通过对近似解进行数值模拟并进行比较,分析说明了同伦近似对称法的一阶近似解具有更好的准确度。     

Basic parameters of the static stability,loads and strength of the vital parts of a bucket wheel excavator’s slewing superstructure

Determining a bucket wheel excavator (BWE)’s slewing superstructure weight and its center of gravity (COG) is of extreme importance not only in the design phase, but also after the completion of the erection process and during the operation of the machine. This paper presents a critical comparative analysis of the basic parameters of the static stability of a BWE 1600 superstructure, with the parameters being obtained by both analytical and experimental procedures. The analysis shows that a relatively small difference in superstructure mass, obtained by calculation, leads to a relatively large unfavorable shifting of its COG, necessitating a significant increase in counterweight mass for balancing. A procedure for superstructure 3D model mass correction is presented based on results obtained by weighing after the completion of the erection process. The developed model provides enough accuracy to determine the superstructure’s COG in the entire domain of the bucket wheel boom inclination angle, and enables accurate load analysis of the superstructure’s vital parts. The importance of this analysis is reinforced by the finding that the procedure prescribed by standard DIN 22261-2 gives results which are not on the side of safety, as shown by an example of strength analysis of a bucket wheel boom stays’ end eyes.     

Study on effect of segments erection tolerance and wedge-shaped segment on segment ring in shield tunnel

INTRODUCTION Shield tunnel method has become the most pre- ferred method in city tunnel construction because of its excellent attributes: little effect on surrounding environment, fast and safe construction, outstanding performance in earthquake resistance, etc. (Zhang et al., 2004). In different shield tunnels, the arrangement and number of segments are different, but the whole assembling process is generally the same. The as- sembling process begins with A2P, then A1P, A3P, BP, CP, …     

某型空地导弹机动性分析

针对某型空地导弹机动性分析时气动参数的非线性特性,提出采用逐步逼近最终达到力矩平衡求解最大平衡攻角及可用法向过载的方法,解决了具有非线性气动特性导弹的可用法向过载计算问题,通过弹道仿真,对需用法向过载和可用法向过载进行了计算和对比．计算结果表明该导弹具有足够的机动能力,为总体设计和控制系统设计提供了依据．     

Exponential stability for networked control systems based on the model of nonlinear discrete-time system with time-varying delay

1.IntroductionAsthecomplexityofmoderncontrolsystems,itsdimensionbecomesmoreandmorevast.Actuators,sensorsandcontrollersinsystemsareusuallydistributed.Theclose-loopfeedbackcontrolsystemscanbeestablishedviaconnectingthesenodeswithcommunicationnetwork.Thesesystemsareoftencallednetworkedcontrolsystems(NCSs).TheNCSsbasedonfieldbusnetwork,suchasCANbus,havebeenwidelyusedinvariousindustrialareasinrecentyears.Therearemanynewissueswhenusingnewsystems.Thefirstissueisthenetwork-induceddelay(sensor-to-…     

具有时滞和非线性接触率的SIS传染病模型的稳定性分析

研究了一类具有时滞和非线性接触率的SIS传染病模型,讨论了系统平衡点的局部稳定性,根据比较定理讨论了无病平衡点的全局稳定性,并证明了地方病平衡点的一致持续性及全局稳定性。     

非线性森林系统的稳定性

考虑一类具有密度制约作用的森林系统,研究了该系统均稳定性．     

企业集群形成机理的进化博弈分析

企业集群的形成机理一直是企业集群理论研究和实践中最受重视和值得关注的问题之一。企业集群的形成实质上是一个网络外部化的过程，而其形成过程本质上类似于有限理性下复制动态进化博弈。并在此基础上建立了企业集群形成的进化博弈模型，由此得出企业集群形成的机理：当某个区位具有较强的网络外部化效应时，在其作用下，企业通过学习、调整和模仿会相继进入该区位，则该区位比较容易形成企业集群；如果某个区位具有较弱的网络外部化效应时，只有在区位已有的企业不设防下，随着进入区位的企业数量增加，或者依靠外部力量，特别是政府的政策作用，使得该区位的网络外部化效应增大时，该区位才能逐渐形成为企业集群。     

6061-T4铝合金方管压弯构件平面内稳定性研究

为研究6061-T4铝合金方管压弯构件平面内稳定力学性能,建立ANSYS有限元模型,分析初始缺陷幅值和单元划分精度对数值计算稳定承载力的影响,并通过现有试验数据对ANSYS有限元模型加以验证。在此基础上,进一步分析构件长细比和荷载偏心率对构件稳定承载力的影响。将《铝合金结构设计规范》GB50429-2007压弯构件面内稳定计算公式得到的相关曲线与数值计算的相关曲线进行比较,发现规范公式偏保守较多。基于大量参数分析,建议对于强硬化铝合金,GB50429相关公式中修正系数η1改取0.8,将文中建议结果和数值计算结果进行比较,较原公式吻合更好。     

Use of bionic inspired surfaces for aerodynamic drag reduction on motor vehicle body panels

Inspired by the successful applications of biological non-smoothness, we introduced bionic non-smooth surfaces as appendices into vehicle body design, aiming to further reduce aerodynamic drag. The size range of the non-smooth units with pits and grooves was determined according to our analysis with the mechanisms underlying non-smooth unit mediated aerodynamic drag reduction. The bionic non-smooth units reported here were designed to adapt the structure of a given vehicle body from the point of boundary layer control that reduces the burst and the loss of turbulent kinetic energy. The engine cover lid and vehicle body cap were individually treated with the non-smooth units, and the treated vehicles were subjected to aerodynamic drag coefficient simulation tests using the computational fluid dynamics (CFD) analysis method. The simulation results showed that, in comparison with smooth surfaces, properly designed non-smooth surfaces can have greater effects on drag reduction. The mechanism underlying drag reduction mediated by non-smooth surfaces was revealed by further analyses, in which the effects of non-smooth and smooth surfaces were directly compared.     

Short-term changes in responsiveness to models inBetta splendens

In an experiment attempting a detailed analysis of the habituation of aggression in blue male Siamese fighting fish, the fish viewed their mirror images for varying lengths of time, and then the duration of gill-cover erection was measured during a 60-sec presentation of a simplified model. Tests were separated by 24 h. Responsiveness was lower on the first day of testing than on any subsequent day. There was a peak of responsiveness to a blue model following 5-sec mirror exposure, with a decline in responsiveness after longer mirror exposures. Mirror exposure did not affect responsiveness to a green model. These results suggest that there are incremental and decremental effects of responding in this situation, both of which are stimulus-specific.     

非线性电路稳定性和非稳定性的分析

通过对非线性电路的理论分析,得出了非线性电路平衡状态的稳定性准则。即在非线性电路中,若平衡点处的动态电阻Rd为正,或当Rd为负时满足RdR1,则该点所表示的平衡状态是不稳定的。