不同高宽比并列双幅箱梁气动升力的干扰效应

为了给实际工程中并列双幅变截面箱梁的气动升力取值提供参考,针对不同高宽比的双幅箱梁,通过刚性模型测压风洞试验,测试了多个不同风攻角和间距时双幅箱梁的升力系数,并与单幅箱梁的升力系数进行了对比分析。引入干扰因子对下游箱梁的干扰效应进行定量表示。研究结果表明：与单幅箱梁相比,上游箱梁的气动升力变化不大,下游箱梁的气动升力变化显著;在大多数正向风攻角下,下游箱梁气动升力的干扰效应表现为明显的减小效应;在负向风攻角下,气动干扰使下游箱梁承受向下的升力,升力值随着风攻角的增大而增大,随着间距和箱梁高宽比的减小而增大。     

扁平流线型箱梁涡激振动及气动力特性分析

为了研究扁平流线型箱梁涡激振动及气动力特性受附属构件的影响,选取某准流线型桥梁主梁为研究对象,通过增减模型的附属构件来模拟裸梁和非裸梁2种断面,进行了不同风攻角下的风洞测压和测振试验。结果表明：扁平流线型箱梁的涡激振动特性受模型附属构件的影响较大,栏杆断面在正攻角下更易发生涡激振动;在相同攻角和风速情况下,栏杆断面存在更为明显的卓越频率,说明模型附属构件会对扁平流线型箱梁的旋涡脱落产生较大影响;扁平流线型箱梁平均风压系数受模型断面的影响较大,但脉动风压系数受模型断面和风攻角的共同影响;不同模型断面会对扁平流线型箱梁的平均三分力系数造成影响,但其变化趋势主要与风攻角有关。     

串联圆柱体气动噪声特性研究

采用分离涡模拟方法和Ffowcs Williams-Hawkings方程相结合的声类比方法对串联圆柱体气动噪声进行了仿真计算研究。以美国航空航天局兰利研究中心的基准模型为计算模型,对比相关试验数据,验证了计算方法的正确性,并进一步探究了不同间距比、不同圆柱体直径、不同来流速度、不同攻角对串联圆柱体湍流流场和气动噪声的影响。研究发现:在低马赫数下串联圆柱体气动噪声具有明显的偶极子特性,下游圆柱体是主要噪声源;圆柱体间存在产生最大噪声的临界间距比;增大下游圆柱体直径是有效降低串联圆柱体气动噪声的方法;来流速度对串联圆柱体气动噪声特性的影响非常强烈且呈现出一定的规律;在合适的攻角下,串联圆柱体的气动噪声能够有一定程度的降低。     

翼型厚度对风力机叶片翼型气动特性的影响

建立了预测翼型气动特性的理论模型并进行了数值计算,研究了翼型厚度对风力机叶片翼型的气动特性影响,给出了翼型厚度对翼型的升力系数、阻力系数、升阻比和流场、压力系数的影响。研究结果表明,对于同一弯度不同厚度的NACA系列翼型,在较小攻角时,较小厚度翼型可获得较大的升阻比,在大攻角时,增加厚度翼型可以提高翼型的升阻比,扩宽大升阻比范围,而且较大厚度翼型的分离点前移速度较缓慢,涡分布范围较小。     

一种预计机翼跨音速抖振边界的高精度方法

在用定常气动参数对机翼跨音速抖振边界进行仿真预计时,由于有些流场条件下的气动参数在抖振始发攻角附近变化不明显,给抖振边界的准确预计带来困难。因而提出了确定抖振始发攻角的气动参数曲线最大曲率法,通过求解机翼不同攻角下的定常流场N-S方程,获得机翼的升力系数、俯仰力矩系数和后缘压力系数,用四次多项式分别对这些气动参数进行曲线拟合,得到各种曲线的曲率方程,由曲率的极大值点确定抖振始发攻角。用该方法对一个NACA0012翼型在0.775马赫下的抖振始发攻角的仿真预计结果与风洞试验得到的抖振始发攻角对比表明具有较高的预计精度。     

空气动力制动风翼板气动干扰效应研究

基于三维定常可压缩N-S方程和Realizable k-ε双方程湍流模型,采用有限体积法对空气动力制动风翼板气动干扰效应规律进行了研究,结合某高速列车车型,分别对列车安装两排风翼板和三排风翼板两种情况进行研究,在每种情况下通过调整风翼板之间的轴向间距进行多工况对比分析。结果表明:当两排风翼板轴向间距不断增大时,后排风翼板产生的制动阻力逐渐增大,气动干扰效应不断减弱;当两排风翼板的轴向间距小于15 m时,前排风翼板对后排风翼板的气动干扰明显,当两排风翼板轴向间距超过20 m后,气动干扰效应基本消失;在消除前排风翼板对后排风翼板气动干扰的前提下,第2排风翼板产生的制动阻力相对第1排下降明显,第3排风翼板产生的制动阻力相对第2排下降幅度变缓,第2排风翼板和第3排风翼板产生的制动阻力相对第1排均较小。     

开口状态及干扰对柱面结构风荷载的影响

为满足储煤量、工艺及环保的要求,柱面煤棚结构常常成对出现且在端部和两侧采用不同形式的开口,煤棚间的相互干扰和开口状态对风荷载的影响效应目前尚不明确。针对此问题,通过刚性模型测压试验,研究了端部、两侧开口状态以及煤棚间距对其结构表面风荷载的影响,通过对比结构整体力系数、体型系数分布及脉动风压系数,给出了风向角、开口状态及间距对风荷载的影响规律,分析了其产生机理,并给出了该类结构的风荷载建议。结果表明:半封闭的端部开口方式能有效减小结构整体风荷载,且脉动风压值最小;两侧30%开孔率的开口形式,结构表面的风荷载分布更均匀,减小结构的脉动风压;煤棚之间的干扰对平均风荷载主要为遮挡效应,对脉动风荷载影响不显著。     

翼型厚度对风力机翼型气动特性的影响

在Re=3×106下,基于k-w SST两方程湍流模型对两种不同厚度的NREL风力机专用翼型进行了数值模拟,重点研究了-5°～15°攻角下不同厚度对翼型气动特性的影响规律。非定常计算结果表明:不同厚度对翼型气动性能影响显著,在某一小攻角范围,较小厚度值可获得较大升阻比,在大攻角翼型发生失速时,较大厚度值可提高翼型的升阻比,拓宽高升阻比的攻角范围,有效改善翼型的分离流动特性。     

襟翼相对长度对翼型流场结构影响

以NACA0018为基准翼型,采用Fluent数值模拟的方法,对比研究了襟翼相对长度和翼缝相对宽度对翼型流场结构及升、阻力特性的影响;文章分别选取了襟翼相对长度分别为0.2、0.3和0.4和翼缝相对为1.0%,分析襟翼相对长度对翼型气动性能的影响。数值结果表明:由于襟翼对翼型周围主涡发展和变化的影响,不仅改善了翼型的失速特性,同时也提高了翼型的气动性能。襟翼翼型的失速攻角在此次研究范围内均大于基准翼型,在攻角小于失速攻角时,襟翼翼型的升力系数均小于基准翼型,阻力系数均高于基准翼型,但升力系数的最大值均高于基准翼型;随着襟翼相对长度增大,翼型临界攻角逐渐减小;在攻角接近翼型失速攻角时,升力系数先增大后减小;襟翼长度相同时,随着翼缝相对宽度的增大,升力系数逐渐减小。     

单、双类圆柱型杆件绕流的大涡模拟研究

通过建立不同拔模角的渐变截面正圆柱型、斜体圆柱型杆件以及阶梯圆柱杆件模型,包括单杆件与双杆件,采用大涡模拟的数值方法,采取涡粘性亚格子Smagorinsky模型封闭方程,对高雷诺数下类圆柱型杆件的绕流流动进行研究。在增加横向速度的条件下,分析了各类杆件模型气动载荷的时域、频域特性,得到了阻力系数、升力系数、周向压力系数的分布规律;分析了尾流漩涡的变化规律,以及由于涡的交替脱落导致的杆件壁面压力的变化。计算结果表明单杆件模型中当拔模角增大时阻力系数的幅值在时间周期上延后出现且幅值减小;双杆件模型中则是拔模角为3°的工况,但斜体放置时拔模角为1°主频最大,同时存在低频的峰值。周期内涡旋脱落产生一个周期升力变化的同时,产生1.5个周期的阻力变化。在气动载荷中升力系数受复杂工况的影响最大,阶梯圆柱型杆件的气动力稳定性较好。拔模角及横向风速影响杆件尾流的分布规律,使得涡的脱落点沿倾角及横向风速的下游方向偏移。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.