Debris flow impact on flexible barrier: effects of debrisbarrier stiffness and flow aspect ratio

Conventionally,flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy.However,there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact.In this study,a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type,barrier stiffness,and flow aspect ratio(flow height to flow length)on the reaction force between the impacting medium and flexible barrier.Results show that,in contrast to flexible barriers for resisting rockfall,the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness.This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing,and only a small portion is forwarded to the barrier.Furthermore,a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder,and a flexible barrier.Under the circumstance of an extremely elongated debris flow event,i.e.,low aspect ratio,the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.

Flexible Calibration Method for 3D Laser Scanner System

In this paper, a flexible high-precision calibration method suitable for industrial field was proposed. The complexity of the coordinate transformation was simplified by choosing the camera coordinate system as the unified reference coordinate system. A flexible planar calibration pattern was introduced to the calibration process, which can be arbitrarily placed and from which the known feature points can be extracted to construct other unknown feature points. With the known intrinsic parameters, the laser projector plane equation was fitted by the multi-noncollinear points, which were acquired through the principle of triangulation and the projective invariance of cross ratio. With this method, the strict alignment and multiple times of coordinate transformation can be avoided. Experimental results showed that the arithmetic mean of the root mean square(RMS) error of distance was 0.000 7 mm.

Optimization of structural parameters for spatial flexible redundant manipulators with maximum ratio of load to mass

Optimization of structural parameters aimed at improving the load carrying capacity of spatial flexible redundant manipulators is presented in this paper. In order to increase the ratio of load to mass of robots, the cross-sectional parameters and constructional parameters are optimized respectively. The cross-sectional and configurational parameters are optimized simultaneously. The numerical simulation of a 4R spatial manipulator is performed. The results show that the load capacity of robots has been greatly improved through the optimization strategies proposed in this paper.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅰ)-GOVERNING EQUATION AND GENERAL SOLUTION

The overall bending of circular ring shells subjected to bending moments and lateral forces is discussed. The derivation of the equations was based upon the theory of flexible shells generalized by E.L. Axelrad and the assumption of the moderately slender ratio less than 1/3 (i.e., ratio between curvature radius of the meridian and distance from the meridional curvature center to the axis of revolution). The present general solution is an analytical one convergent in the whole domain of the shell and with the necessary integral constants for the boundary value problems. It can be used to calculate the stresses and displacements of the related bellows. The whole work is arranged into four parts: (Ⅰ) Governing equation and general solution; (Ⅱ) Calculation for Omega_shaped bellows; (Ⅲ) Calculation for C_shaped bellows; (Ⅳ) Calculation for U_shaped bellows. This paper is the first part.

Effect of Mass Ratio on Hydrodynamic Response of a Flexible Cylinder

The effect of the mass ratio on the flow-induced vibration （FIV） of a flexible circular cylinder is experimentally investigated in a towing tank. A Tygon tube with outer and inner diameters of 7.9 mm and 4.8 mm, respectively, was employed for the study. The tube was connected to a carriage and towed from rest to a steady speed up to 1.6 m/s before slowing down to rest again over a distance of 1.6 m in still water. Reynolds number based on the cylinder＇s outer diameter was 800-13,000, and the reduced velocity （velocity normalized by the cylinder＇s natural frequency and outer diameter） spanned from 2 to 25. When connected, the cylinder was elongated from 420 mm to 460 mm under an axial pre-tension of 11 N. Based on the cylinder＇s elongated length, the aspect ratio （ratio of the cylinder＇s length to outer diameter） was calculated as 58. Three mass ratios （ratio of the cylinder＇s structural mass to displaced fluid mass, m＊） of 0.7, 1.0, and 3.4 were determined by filling the cylinder＇s interior with air, water, and alloy powder （nickel-chromium-boron matrix alloy）, respectively. An optical method was adopted for response measurements. Multi-frequency vibrations were observed in both in-line （IL） and cross-flow （CF） responses; at high Reynolds number, vibration modes up to the 3rd one were identified in the CF response. The mode transition was found to occur at a lower reduced velocity for the highest tested mass ratio. The vibration amplitude and frequency were quantified and expressed with respect to the reduced velocity. A significant reduced vibration amplitude was found in the IL response with increasing mass ratios, and only initial and upper branches existed in the IL and CF response amplitudes. The normalized response frequencies were revealed to linearly increase with respect to the reduced velocity, and slopes for linear relations were found to be identical for the three cases tested.

Seismic earth pressures on flexible cantilever retaining walls with deformable inclusions

In this study, the results of 1-g shaking table tests performed on small-scale flexible cantilever wallmodels retaining composite backfill made of a deformable geofoam inclusion and granular cohesionlessmaterial were presented. Two different polystyrene materials were utilized as deformable inclusions.Lateral dynamic earth pressures and wall displacements at different elevations of the retaining wallmodel were monitored during the tests. The earth pressures and displacements of the retaining wallswith deformable inclusions were compared with those of the models without geofoam inclusions.Comparisons indicated that geofoam panels of low stiffness installed against the retaining wall modelaffect displacement and dynamic lateral pressure profile along the wall height. Depending on the inclusioncharacteristics and the wall flexibility, up to 50% reduction in dynamic earth pressures wasobserved. The efficiency of load and displacement reduction decreased as the flexibility ratio of the wallmodel increased. On the other hand, dynamic load reduction efficiency of the deformable inclusionincreased as the amplitude and frequency ratio of the seismic excitation increased. Relative flexibility ofthe deformable layer （the thickness and the elastic stiffness of the polystyrene material） played animportant role in the amount of load reduction. Dynamic earth pressure coefficients were compared withthose calculated with an analytical approach. Pressure coefficients calculated with this method werefound to be in good agreement with the results of the tests performed on the wall model having lowflexibility ratio. It was observed that deformable inclusions reduce residual wall stresses observed at theend of seismic excitation thus contributing to the post-earthquake stability of the retaining wall. Thegraphs presented within this paper regarding the dynamic earth pressure coefficients versus the wallflexibility and inclusion characteristics may serve for the seismic design of full-scale retaining walls withdeformable polystyrene inclusions. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Study on Running Performance of Flexible Wheels for Lunar Rovers： Relation between Stress Distribution of Flexible Wheel and Running Performance

On lunar exploration missions, the rovers which can move and explore directly are considered by various agency like NASA （National Aeronautics and Space Administration）, JAXA （Japan Aerospace Exploration Agency）, ESA （European Space Agency）. Lunar rovers are required to move on rough terrains such as craters and rear cliffs where it is scientifically very important to explore. However, there is a problem that the rovers have possibility of stack because of the lunar surface is covered with loose soil named Regolith. Therefore, this paper investigates a mechanism of kinetic behavior between the wheels of the exploration rovers and loose soil. And then, this paper proposed a flexible wheel to solve like that problems. The flexible wheel has the surface which can be changed flexibly toward rough terrain. Running experiments on loose soil which imitated regolith were carried out to observe the traversability of the flexible wheel using slip ratio. Traversality of flexible wheel was better than the circular rigid wheel. The authors believe that stress distribution is important. The stress distribution of the flexible wheels is horizontally long and stress value is small. However, the stress distribution can be changed by loaded more weight. Therefore, the relationship between the stress and the running performance was considered using this differential stress distribution. In experiments, the authors used the flexible wheel with simple structure （3 limbs）. From these considerations, the relationship between the stress of the flexible wheel and the running performance was described.

基于限流电抗器两侧特定频段暂态能量比的MTDC电网单端量保护方案

柔性直流输电技术有利于未来大量分布式能源接入电网,而配置快速、可靠的保护方案是柔性直流技术发展的关键。基于直流电网等效模型,提出一种基于限流电抗器两侧电压特定频段暂态能量比差异性的单端量故障区域识别方法。该方法依据贝瑞隆等效模型计算出限流电抗器两侧电压比,通过广义S变换提取限流电抗器两侧特定频段电压,根据故障时正负极限流电抗器的电压幅值差的差异性实现故障选极。最后在PSCAD/EMTDC平台搭建仿真模型,分析出发生区内外故障时差异性明显,具备较强的耐过渡电阻与抗噪声干扰能力。

面向新型电力系统的柔性直流换流器统一控制架构

新型电力系统的发展对柔性直流输电技术提出了更高需求,随着异构串联型直流换流器拓扑架构的提出,柔直换流器已在拓扑层面实现结构统一。然而,在控制层面,传统柔直换流器控制虽然具备功率解耦控制能力,但交流电压、直流电压和子模块电容电压之间存在紧密耦合,难以发挥柔直换流器全控型器件运行灵活性高的优势。首先,基于现有直流换流器控制架构,提出控制自由度的概念,并引入调制比的表征方法,构建模块化多电平换流器(modular multilevel converter,MMC)的多自由度控制体系;然后,通过分析MMC换流器内部的电压耦合机理及其与调制比的关系,系统地揭示了现有MMC换流器的各种控制策略之间的关联性,形成具备“功能统一、结构统一”的MMC换流器的4自由度统一控制架构。并针对柔直系统中不同控制目标的MMC换流器分析4自由度控制架构的应用及其控制潜能;最后,在单端MMC物理动模实验系统中对MMC换流器4自由度控制在典型应用场景下的性能进行实验验证。

复杂多边形蜂窝柔性蒙皮非线性行为数值分析

对复杂多边形蜂窝柔性蒙皮结构进行数值仿真,研究在拉伸、剪切、扭转以及弯曲载荷下的柔性蜂窝非线性变形行为,并对无橡胶表层、单侧橡胶表层和双侧橡胶表层的变形及强度进行分析。结果表明:无橡胶表层蜂窝可能在较小载荷下产生较大变形;单侧橡胶表层易使结构不对称,可能导致剪切载荷、扭转载荷下的变形不对称;双侧橡胶表层对抑制结构变形有明显作用;加入橡胶表层可能会使原本零泊松比或负泊松比效应的蜂窝柔性蒙皮表现出正泊松比的情况。

超临界660 MW机组直流锅炉动态特性仿真研究

为提升煤电机组灵活性,锅炉需具备良好的可控性和适应负荷快速变化的能力。锅炉灵活性与控制系统性能密切相关,而后者是基于动态特性设计的。为研究锅炉的动态特性,在Dymola平台中建立了某超临界660 MW机组直流锅炉的动态模型。结果表明:当锅炉入口参数发生扰动时,蒸汽温度的响应时间比蒸汽流量更长;当给水温度、给水量与燃料量分别阶跃增加5%时,主蒸汽温度分别变化10.2℃、-28.5℃和35.7℃;在锅炉的水煤配比调节过程中,给水量和燃料量变化时间不同会对主蒸汽温度产生不同的影响;当给水量比燃料量延迟约100 s作用时,主蒸汽温度在瞬态过程中的最大偏差相对于二者同时变化的情况减少了27.4℃;当变负荷幅度相同时,变负荷速率越大,主蒸汽参数的波动越剧烈,趋于稳定所需的时间越长。

计及改进阶梯型碳交易和热电联产机组灵活输出的园区综合能源系统低碳调度

为了进一步降低园区综合能源系统(park-level integrated energy system,PIES)碳排放量,优化热电联产(combined heat and power,CHP)机组出力的灵活性,提出一种考虑改进阶梯型碳交易和CHP热电灵活输出的PIES低碳经济调度策略。首先,将遗传算法与模糊控制相结合,设计一种遗传模糊碳交易参数优化器,从而对现有阶梯型碳交易机制进行改进,实现该机制参数的自适应变化;其次,在传统CHP中加入卡琳娜(Kalina)循环与电锅炉(electricboiler,EB),构造CHP热电灵活输出模型,以同时满足电、热负荷的不同需求;然后,提出一种柔性指标——电、热输出占比率,进而计算出电、热输出占比率区间,以衡量CHP运行灵活性;最后,将改进阶梯型碳交易机制和CHP热电灵活输出模型协同优化,以系统运行成本和碳交易成本之和最小为目标,构建PIES低碳经济优化模型。算例分析表明,所提策略可有效降低经济成本和碳排放量,同时还可扩展CHP灵活输出调节范围,能够为PIES低碳经济调度提供参考。

基于IAGA的多行设施布局优化方法

针对横向和纵向通道位置和数量均不确定的多行设施布局问题,提出一种基于IAGA的多行设施布局优化方法。考虑设施最大纵横比约束,建立以物流成本、搬运设备空载成本及占地面积成本的加权平均值最小化为优化目标的布局优化模型;设计基于柔性隔间结构编码的改进自适应遗传算法(IAGA)对模型进行求解。算法中设计了自适应调整交叉概率、自适应选择交叉算子(双点交叉算子和单亲单点交换算子)及分别针对隔间结构和设施编号排列的基本位变异算子,提高了其收敛速度和搜索能力。最后,通过案例分析验证了IAGA算法的有效性。

穿越非均匀土体综合管廊振动台试验研究

在建设综合管廊的过程中,难以避免地会穿越水平不均匀土体,此场地不利于管廊的抗震。该研究基于振动台试验,对地震作用下水平非均匀土体与综合管廊的动力变形响应及相互作用进行了系统性研究。深入分析了管廊的土压力增量、加速度、位移和应变,包括加速度峰值沿竖向分布情况以及管廊变形的直接影响因素,发现由于地下结构的存在,土体对加速度放大效应发生衰减;在大震时土体与管廊发生了相对滑移,此现象对管廊的变形产生较大影响;随着加速度的增大,土压力增量分布近似呈抛物线形;结构的柔度比越大,变形越大。基于振动台试验研究了管廊穿越非均匀土体的简化计算方法,通过调整变形比来实现土体分界对管廊变形的影响,为管廊的抗震设计提供参考。

柔性石墨接地材料工频热稳定性能试验研究

针对电力系统中广泛使用的金属接地材料在运行中存在的腐蚀严重、运维费用高等问题,新型耐腐蚀型柔性石墨非金属接地材料成为一个较为热门的研究方向。柔性石墨接地材料的电气及热特性与传统的金属接地材料差异较大,其在工频电流下的热稳定性能也与金属材料有所区别,成为了制约柔性石墨接地材料截面选取以及结构设计的主要因素。为了得到较为准确的柔性石墨接地材料热稳定性能,文中针对柔性石墨接地材料在不同短时工频电流作用下的电气及热特性变化展开实验研究,获得了相应的热稳定温度阈值和热稳定系数参考值。研究结果表明:柔性石墨接地材料最高允许工作温度(即热稳定温度阈值)约为300℃,与传统金属接地材料较为接近;而其热稳定系数约为2.94,相比金属接地材料较低,因此在设计接地体时,柔性石墨材料的接地体截面应超过金属接地材料接地体截面,才能保证通流容量满足实际需要。

基于现场试验的CFG桩复合地基桩帽与垫层效应分析

【目的】柔性垫层和桩帽对CFG桩复合地基的桩土应力比、荷载分担比和沉降均有较大影响,但目前柔性垫层与桩帽在现场试验中如何共同影响复合地基特性仍有待进一步的研究。【方法】以CFG桩复合地基软基处理的某路段作为工程背景,在土工格栅层数不变的情况下,对垫层厚度为100 mm、200 mm、300 mm,桩帽尺寸为0.8 m、1.0 m、1.2 m组合下的形式进行了现场原位试验,研究了CFG桩复合地基的桩土应力比、荷载分担比和沉降特性。【结果】现场试验表明:随着垫层厚度由100 mm增大到300 mm,桩土荷载比减小了51.5%,桩土应力比减小了52.5%,总沉降量增大了7.9%;随着桩帽直径由0.8 m增大到1.2 m,桩土荷载比增大了29.0%,桩土应力比减小了29.2%,总沉降量10.4%.本文区域地质条件,宜选用垫层厚度100 mm、桩帽直径为1.2 m的CFG桩复合地基形式。

On a Flexible Loan Repayment Method Depending on Borrower's Asset with an Early Termination Clause

Aiming at the problem that the asset’s fluctuation influences the borrower’s repayment ability,a loan with a new and flexible repayment method is designed,which depends on the asset value of the borrower.The repayment method can reduce the loan default probability,but it causes the uncertainty of the pay off time.Because the repayment term is related to the regular repayment amount in this method,a boundary for the regular repayment amount is set up in order to avoid too long repayment term.This will balance the benefit of borrowers and lenders and improve the applicability of this method.By establishing a mathematical model of the residual value of the loan,this model can be transformed into an initial-boundary problem of a partial differential equation.The analytic solution and the expected time to pay off the loan are obtained.Finally,numerical analysis are shown.

展弦比对NACA0012弹性平直机翼颤振临界特性影响研究

展弦比是飞行器机翼设计的重要参数,研究其对机翼颤振临界特性的影响具有重要的工程应用价值。本文采用三维雷诺平均N-S方程和S-A湍流模型求解NACA0012弹性平直机翼的非定常气动力,结合由模态法建立的机翼结构动力学方程,发展了计算流体力学(CFD)/计算结构力学(CSD)颤振时域数值模拟方法。利用该方法研究了不同展弦比条件下机翼的颤振临界速度和频率。结果表明,由于展弦比较大且材质轻柔,机翼会出现一定幅度的垂向静弯曲变形。展弦比的增大不会影响机翼模态固有振型,但是会导致机翼颤振临界速度、颤振频率和模态固有频率的降低。

五边形柔性芳纶纸蜂窝的制备及性能

为满足大曲率部件对蜂窝材料柔性的要求,丰富国产芳纶纸蜂窝的种类,进一步拓展国内外蜂窝市场,在传统正六边形芳纶纸蜂窝制造工艺的基础上,优化工艺技术,研制了一种孔格为五边形结构的新型柔性芳纶纸蜂窝ACCH-2I-2.75-48D(孔格边长为2.75 mm,密度为48 kg/m^(3))。测试了三种国产芳纶纸制备的柔性蜂窝的物理性能、力学性能、泊松比及阻燃性能,参照了欧洲复材(EC)相同规格的柔性芳纶纸蜂窝力学性能指标值,且与现有相同规格的正六边形芳纶纸蜂窝(ACCH-2I-2.75-48)和过拉伸芳纶纸蜂窝[ACCH-2I-2.75-48(OX)]的力学性能指标进行了对比。测试结果表明,五边形柔性蜂窝孔格规整,外观无缺陷,物理性能稳定,平面压缩强度、剪切强度和剪切模量达到了EC柔性蜂窝的指标值要求,力学性能达到批次间稳定,蜂窝在纵向和横向均具有良好的柔性且阻燃性能优异。结果证明,五边形柔性芳纶纸蜂窝的制造工艺已完备,研制的五边形柔性蜂窝具有优异和稳定的综合性能,满足作为夹层结构材料芯材的基本要求。

柔性尾鳍的形状对仿生机器鱼水动力学特性的影响研究

研究了仿生机器鱼不同形状柔性尾鳍的水动力学特性。根据仿生学观测结果,研制了4种形状的仿生机器鱼尾鳍,通过开展水动力学实验,对比分析了尾鳍外形、结构、材料和运动参数对水动力学参数的影响。结果表明,增大尾鳍的摆角幅度和摆动频率有利于提高推进力,但会引起游动的不稳定性;柔性强的新月形尾鳍具有较好的推进性能;展弦比越小的无鳍条尾鳍,高频游动性能越好,鳍条会降低尾鳍的高频游动性能。