Flow structures around a butterfly-shaped low-aspect-ratio wing

In the present study, we numerically investigate three-dimensional flow structures around a butterfly-shaped low-aspect-ratio wing and their effect on the aerodynamic force at the Reynolds number of 1000 based on the wing chord length and free-stream velocity. When the angle of attack is less than 10°, the flow is steady and fully attached to the upper-wing surface, by which the lift force increases almost linearly with the angle of attack. As the angle of attack further increases, the flow around the wing becomes unsteady and contains the leading-edge, trailing-edge, wing-tip, and hairpin vortices. At these angles of attack, the drag force increases rapidly with increasing angle of attack due to massive separation at the leading edge, but the lift force increases gradually without abrupt fall-off. This is because the wing-tip vortices induce a strong downward flow interacting with the flow separated from the leading edge and delay subsequent vortex roll-up in the downstream. The wing-tip vortices themselves also produce low-pressure regions on the upper-wing surface and thus provide an additional lift force. The flows separated from the leading and trailing edges are eventually combined into pairs of hairpin vortices which travel downstream in the wake. The formation of the hairpin vortices above the upper-wing surface also generates lowpressure regions, and they are another source of the lift force.     

Flow around a pipeline and its stability in subsea trench

Offshore subsea pipelines must be stable against external loadings, which are mostly due to waves and currents. To determine the stability of a subsea pipeline on the seabed, the Morrison equation has been applied with prediction of inertia and drag forces. When the pipeline is placed in a trench, the force acting on it is reduced considerably. Therefore, to consider the stability of a pipeline in a trench, one must employ reduction factors. To investigate the stability of various trenches, we numerically simulated flows over various trenches and compared them with experimental data from PIV (Particle Image Velocimetry) measurements. The present results were produced at Reynolds numbers ranging from 6×10³ to 3×10⁵ based on the diameter of the cylinder. Quasi-periodic flow patterns computed by large-eddy simulation were compared with experimental data in terms of mean flow characteristics for typical trench configurations (W/H=1 and H/D=3, 4). The stability for various trench conditions was addressed in terms of mean amplitudes of oscillating lift and drag, and the reduction factor for each case was suggested for pipeline design.     

Flow characteristics around a row of circular and wavy cylinders

The near-wake and flow interference around a row of five circular cylinders, staggered wavy cylinders and nonstaggered wavy cylinders are investigated experimentally by using PIV and LIF techniques. The effects and characteristics of employing wavy cylinders instead of circular cylinders are discussed. The cylinders were arranged atT/d=1.5 withRe ranging from 125 to 40000. Results showed the staggered wavy cylinders give rise to a more stable flow pattern with less fluctuation and longer wake vortex closure length.     

A study on thick plate forming using flexible forming process and its application to a simply curved plate

In this study, design and fabrication of a flexible forming machine are carried out for the purpose of manufacturing a prototype of curved plate block for hull structure used in shipbuilding industry. Flexible forming dies which consist of numbers of punches in an array form for upper and lower sides are designed in view of thick plate forming. A punch has formation of male and female screws to adjust its length with regard to a given surface, and all punches are supported by each other in punch housing. Software for process configuration and punch control are developed to operate the novel flexible forming machine. The software are composed of the punch height calculation part which uses an offset surface scheme. Prior to manufacturing of a prototype, numerical simulations for a saddle-typed thick plate forming process including metal forming and spring-back analyses are carried out to predict the forming performance. Experiments are also carried out to validate and confirm the feasibility of flexible forming technology in view of practical application of thick plate forming process. Curvature radii observed in the simulation and experiment are investigated and compared. Consequently, development and practical application of flexible forming technology to the thick plate forming process are described from design of the forming machine to manufacturing of the prototype. It is confirmed that the flexible forming technology suggested in this study has enough feasibility in new application of thick plate forming in shipbuilding structures which has been formed through expensive and laborious conventional line heating.     

Control of flow around a square cylinder at incidence by using a splitter plate

Passive control of vortex shedding behind a square cylinder at incidence has been conducted experimentally by using a stationary splitter plate for the Reynolds numbers of 3.0×10⁴. The splitter plate was located at the center of the rear face of the square cylinder in tandem. The width of the cylinder and the plate were both chosen to be 30 mm and the incidence angle of the square cylinder was rotated between 0° to 45°. In this study, the combined effects of the splitter plate and angle of incidence on the pressure distributions and vortex-shedding phenomenon were investigated. Vortex shedding frequency was obtained from velocity measurements and aerodynamic force coefficients acted on the cylinder were calculated from pressure distributions. Characteristics of the vortex formation region and location of the flow attachments, reattachments and separation were observed by using the smoke–wire flow visualization technique. For the case with the plate, there is a sudden jump in the Strouhal number in the vicinity of 13° which corresponds to a minimum value of the drag coefficient. At zero angle of incidence, Strouhal number and a drag coefficient of the square cylinder decreased about 20% by means of the splitter plate. Drag reduction was minimum at about 13° and reached its maximum value at about 20°.     

Flow time analyses of a simulated flexible job shop by considering jockeying

It has been essential to include flexibility in manufacturing policy making since variability in demand and products are considerably increasing. However, it is important to know and to monitor the proper level and type of flexibility that is required to obtain full benefits from it. This paper analyses the effects of flexibility on flow time performance of a simulated job shop. For that purpose, several scenarios are developed under four flexibility levels with two different machine selection rule and three types of dispatching rules. Furthermore, effect of jockeying as a queuing policy on the flow time performance is also investigated through simulation modeling. Results indicated that full flexibility is a preferable state for most of the cases. However, in some cases, chain configurations perform similar results since it combines the benefits of pooling and specialization. In addition, it is observed that a queue control mechanism like jockeying is an effective way to improve performance even though it may increase complexity of controlling policy.     

扑翼飞行的绕流升力与阻流升力及其估算

针对扑翼飞行比固定翼飞行气动特性更为复杂、升力计算更加困难问题,从绕流物体的基本气动特性出发,将飞行升力分成绕流升力与阻流升力。分析了扑翼飞行模式下绕流升力与阻流升力作用特点,解释了动物飞行中绕流升力与阻流升力的变化规律。在此基础上,建立了扑翼飞行运动模型,推导出扑翼最大绕流升力与阻流升力理论估算模型。实验算例表明,分类升力估算方法是可行的,绕流升力与阻流升力占比与扑翼实际飞行规律趋势一致。     

舰船螺旋桨非定常粘性流场与空化数值预报

基于粘性流理论,在均匀入流条件下,利用非结构网格和滑动网格技术数值求解非定常雷诺平均方程（URANS）来研究螺旋桨随边至下游两倍螺旋桨直径区域的尾流场压力和蒸汽体积分数等物理量。计算结果显示,螺旋桨空泡数值计算结果与INSEAN的实验观察结果基本一致,尾流场物理量的计算结果很好地预报了螺旋桨叶频和轴频等参数,梢涡对近尾流场的压力形成具有重要作用。     

Flow around a freely falling square shape particle in a channel using direct-forcing fictitious domain method

This paper presents a numerical investigation of the flow characteristics around a freely falling square shape particle in a two-dimensional channel. The FSI (fluid-solid interaction) has been realized by using the direct-forcing/fictitious domain (DF/FD) method. In order to identify the effect of fluid property on the flow characteristics and solid motion by FSI, a wide range of the fluid viscosity has been considered, which introduces various Reynolds numbers to this study. In addition, the off-centered distance of the square particle has been imposed to research the effect of the initial position. The centered particle is freely falling without rotation and transverse motion. However, the motion of the off-centered particle is significantly depended on the Reynolds number, so it is classified into the four regimes by the flow and moving characteristics of the particle. Quantitative information about the drag coefficient on the square particle is highlighted.     

On the stress concentration around a hole in an infinite plate subject to a uniform load at infinity

In this paper stress concentration around a hole in an infinite plate that is subjected to a uniform load at infinity is considered. The stress is calculated by using a modified Muskhelishvili complex variable method. The method is illustrated by several examples of stress distribution around polygonal holes of a complex geometry utilizing the Schwartz-Chistoffel mapping function.     

基于LBM方法的钝体绕流数值模拟

在生活中高雷诺数的钝体绕流现象普遍存在,但准确计算其流场特性却并不容易。针对这一问题采用多松弛时间格子Boltzmann方法(LBM)与壁面自适应局部涡黏(WALE)模型相结合的方法(MRT-LBM-WALE),对定常流下雷诺数90 000的二维圆柱绕流进行数值模拟,同时应用增强壁面函数对壁面附近湍流黏性进行修正,测算了其阻力系数、升力系数、涡脱落频率和表压。计算结果与已有实验比较表明,阻力系数、升力系数以及涡街的脱落频率均跟实验值吻合较好,同时在涡街捕捉上也表现出较高的稳定性和精度。     

Fundamental studies on free stream acceleration effect on drag force in bluff bodies

This paper describes fundamental studies on free stream acceleration effect on drag force in bluff bodies. The flow with gradual velocity increase assumed an accelerated flow. The wind tunnel tests were conducted in order to investigate the difference of aerodynamic characteristics between non-accelerated flow and accelerated flow. The experimental models were a circular cylinder and a square cylinder. In an accelerated flow, the condition of free stream was an acceleration of about 3.6m/s². Experimental Reynolds number varied between form 4.0×10⁴ to 1.64×10⁵. The pressure distributions and the aerodynamic force were measured in both case of nonaccelerated flow and accelerated flow. In case of a circular cylinder, the drag of accelerated flow is lower than that of non-accelerated flow in the low Reynolds number regime. Then, it becomes higher than that of non-accelerated flow in the high Reynolds number regime. On the other hand, in case of a square cylinder, the drag of accelerated flow is higher than that of non-accelerated flow in the whole Reynolds number regime. If a separation point can be movable such as the circular cylinder, the additional momentum due to flow acceleration leads to delay separation and to decrease the drag in the low Reynolds number regime. If a separation point is nearly fixed such as a square cylinder, the additional momentum due to acceleration always affects to increase the drag than that of non-accelerated flow. Based on this research, it is expected that the roof shape of high speed train where the separation point is movable has the advantages to reduce the effect of accelerated flow such as strong crosswind/gust.     

Flow measurement using free overfall in inverted semi-circular channel

Free overfall at the abrupt end of a channel offers a method for measurement of discharge. This paper presents a theoretical end-depth–discharge (EDD) relationship for free overfall in an inverted semi-circular channel. The theoretical procedure applied to compute the discharge over a weir is applied to the free overfall to get the EDD relationship. The pressure at the brink is assumed to be zero. The available experimental data are used to verify the proposed EDD relationship. The calculated discharges, using the proposed EDD relationship, show excellent agreement with the experimental values in subcritical flows; however, the agreement is not so good in supercritical flows.     

Tensionless contact of a flexible plate and annulus with a smooth half-space under axisymmetric loads by integral equations

In this paper, a new hybrid method of analysis is presented for the problem of a frictionless circular plate or annulus in tensionless contact with a half-space. By virtue of a set of analytically explicit Green's functions for the two interacting continua, an exact but compact integral equation formulation with closed-form kernels is derived. With the incorporation of a newly developed adaptive-gradient (AG) element capable of capturing regular-to-singular solution transitions smoothly, an accurate numerical procedure is developed and validated in a number of benchmark cases of nonlinear plate–annulus–half-space interaction. From the simplicity and rate of convergence demonstrated, the hybrid method is apt to be an attractive analytical–numerical platform that can be extended to a large class of contact problems.     

轿车门外板自由曲面的反求

为了获得已有自由曲面的CAD模型，这里通过对自由曲面的测量、特征提取及曲面构造的方法来定义出自由曲面的几何形状，并用该方法实现了对轿车门板自由曲面的反求，构造出该零件的CAD模型。     

Flow velocity pattern around trapezoidal piano key side weirs

In general, the side weirs are the structures installed along a channel or river. When the flow depth rises above the weir crest, the overflow passes through these weirs and enters the lateral canal. Nowadays, piano key weirs are considered as an important alternative to labyrinth weirs to modify the weirs encountering with difficulty to pass the maximum flow discharges. The present study investigates the hydrodynamic performance and the effect of the uniformity of velocity field on the resultant kinetic energy in the trapezoidal piano key side weirs with 90° installed laterally in the main channel wall. These weirs are classified as A-Type piano key weirs and two approaches (main: Mode 1 and adverse: Mode 2) were used to investigate the effect of the weirs' placement on their performance. The results showed that for velocity vectors in both modes, on average, the maximum flow discharge through the side weir occurred in the x and y directions (V_x and V_y) at Z*<0.2 and 0.2<Y*<0.7. The results also showed that at the control surface of X* = 1, the maximum values of α occur due to existing the inverse flow and increasing the deflection angle of the velocity vectors. The performance of the weir in Mode 2 was more appropriate Mode 1 due to the lack of weir base at the flow inlet, which is an obstacle for the deflection angle of the velocity vectors.     

On the free vibration analysis of a plate with an oblique inelastic line constraint

The free vibration of a rectangular plate with an oblique inelastic line constraint under various boundary conditions is analytically investigated. A double Fourier sine series is employed for the modal displacement functions and the method of stationary potential energy is applied for the analysis to obtain the general analytical solution. The geometric boundary conditions and interior oblique melastic line constraint are enforced by means of Stokes' Transformation and the Lagrange multipliers. The normalized frequency parameters and mode shapes are obtained for various boundary conditions and the results are cross-checked with those by MSC/NASTRAN Finite Element package.     

基于视频流的车牌识别研究及系统设计

该文深入研究从视频流中提取运动车辆进行车牌识别的问题,提出了一种车牌识别算法,根据该算法开发了基于MFC的视频流车牌识别可视化系统。算法采用三帧差分与背景消减相结合的方法提取含有运动车辆的关键帧,对关键帧进行灰度化,采用Sobel算子进行边缘检测,融合形态学处理对关键帧进行去噪,从而实现车牌的定位,用投影法结合字符特征对车牌字符进行精确分割,采用BP神经网络算法提取字符特征,输出字符识别结果,由此完成车牌字符识别。通过对50组不同的车辆视频进行检测识别,识别率(包含汉字)达到96%以上。     

Flow visualization of microscale effusion cooling within mainstream boundary layer on a flat plate

Effusion cooling can be one of the attractive methods of cooling in a current high-efficiency gas turbine which has a very hot gas temperature above 1600 °C. For higher effectiveness of the air cooling for a gas turbine vane and blade, the air-cooled flow through effusionholes should not overshoot into the mainstream flow but still remain within the mainstream boundary layer. The present study is intended to examine flow structure of a microscale effusion cooling for gas turbine applications through flow visualization which is highly effective to obtain better understanding of the flow physics. The air flow through effusion-holes can be visualized with an oil atomized droplets, a laser-sheet and a high-speed CCD imaging system. The qualitatively visualized results show their flow patterns and characteristics with different effusion hole size and blowing ratio for effusion cooling. A series of vortical structure can be observed within the boundary layer along the microscale effusion flat plate which provided that the effusion cooling can be a plausible candidate up to the effusion-hole size of 0.7 mm.