The investigation of a compressible laminar boundary layer past an elliptical cone

The self-similar boundary layer on a sharp circular cone was calculated first by Vvedenskaya[1]. The boundary layer equations were solved in a plane containing an outflow line which lies in this case in the symmetry plane at the leeward side, and after that a solution was constructed by using a marching method along a circumferential coordinate. The calculation results for the boundary layer on an elliptic cone were presented in Bashkin's papers [2–4]. However, only the middle angles of attack (30–50°) were considered. where the outflow line of an external stream is located in the windward symmetry plane, and the flow pattern in the boundary layer is analogous to that of the circular cone. In the present the laminar boundary layer on an elliptic cone is studied for a wide range of angles of attack. The boundary layer has been calculated at small incidence when the outflow of an external flow were located out of the symmetry plane. In this case the equations are solved first in the plane containing the outflow line and then the solutions were constructed by a marching method along a circumferentialcoordinate to the windward and leeward symmetry planes. The distribution of the skin-friction coefficients and the Stanton's numbers on a cone surface was given. The similarity solution of a set of boundary layer equations was obtained for thin cones at large incidence when the stream on the windward side of the cone was directed to the cone nose. The calculations of the laminar boundary layer at hypersonic velocities were carried out to include the real equilibrium properties of the air.     

A new algorithm for simulating flows of conducting fluids in the presence of electric fields

We propose an algorithm based on dissipative particle dynamics (DPD) for simulations of conducting fluids in the presence of an electric field. In this model, the electrostatic equations are solved in each DPD time step to determine the charge density at the fluid surfaces. These surface charges are distributed on a thin layer of fluid particles near the interface, and the corresponding interfacial electric forces are added to other DPD forces. The algorithm is applied to the electrospinning process at the Taylor cone formation stage. It is shown that, when the applied voltage is sufficiently high, the algorithm captures the formation of a Taylor cone with analytical apex angle 98.6°. Our results demonstrate the potential of the presented DPD algorithm for simulating two-phase problems in the presence of an electric field with non-periodic boundary conditions.     

均匀流场中四边形锥柱的压力试验研究

通过水池试验研究了在雷诺数Re为3.19×104~1.15×106,攻角为0°~180°,以15°为间隔,表面倾斜且前后不对称的四边形锥柱状结构在均匀流场中所受的压力载荷。分析了模型所受的周向压力和斯特劳哈尔数Sr随Re和攻角的变化趋势。结果表明:与圆柱绕流相比,倾斜壁面和攻角使压力在背压区和边界层分离点发生变化,同时,Sr也由0.2降到0.13。     

Size matters: Improved color‐difference estimation for small visual targets

Abstract— A long‐standing problem in color science is the accurate estimation of color differences for visual targets of small angular subtense. For instance, “What is the magnitude of a 0.5° color difference that will be as discriminable as a given 2° color difference?” Or, “What is the reduced angular subtense (or increased distance) at which two visual fields of given colors will become appreciably less discriminable than they were at larger subtense (or smaller distance)?” Past attempts at solving this problem have been specific to a particular color‐difference equation and, as such, the work lost relevance as improved color‐difference formulae were developed. This article proposes a structural model based upon the response of retinal cone cells to small‐subtense symbol images scattered by the ocular media. The method is demonstrated to be applicable without alteration to very different contemporary color‐difference equations, to be practical with a wide range of surround intensities, and to have high correlation with human search performance involving small color symbols on an electronic information display.     

Computation of supersonic inviscid flow around wings with a detached shock wave

The numerical method for computing inviscid supersonic flow around the front part of the arbitrary planform wings was presented in [1,2]. The aim of this paper, which is the extension of the previous ones, is to present a numerical method for computing the flow field above the remaining parts of the wing—the wingtip section and the central section of the wing. Here the problems are formulated for a three-dimensional steady gas-dynamic system of equations written in special curvilinear coordinates. Complicated physical domains of the solution are mapped on simple computational domains. For approximation of the differential equations the finite-difference second-order implicit schemes are used. The approximation of the wing surfaces is made with the help of the local cubic splines. According to the obtained algorithms calculations were made for the wing with elliptical planform and thick airfoil at M_∞ = 2 and M_∞ = 3.5 with the angle of attack α = 5°.     

A directional backlight with narrow angular luminance distribution for widening the viewing angle for an LCD with a front‐surface light‐scattering film

Abstract— A directional backlight unit has been developed to widen the viewing angle of a TN‐LCD with a front‐surface light‐scattering film/layer. The novel directional backlight has a diagonal of 34 cm and is structured by light‐direction‐control optical micro‐features and an inverted prism film. The backlight has a symmetrical round luminance cone of ±9° and a uniform spatial distribution of 88%. By using this backlight unit in combination with an LCD, the narrow cone resulted in widening of the TN‐LCD's viewing angle up to 120° at full width at half‐maximum.     

Analysis of TerraSAR-X data and their sensitivity to soil surface parameters over bare agricultural fields

The sensitivity of TerraSAR-X radar signals to surface soil parameters has been examined over agricultural fields, using HH polarization and various incidence angles (26°, 28°, 50°, 52°). The results show that the radar signal is slightly more sensitive to surface roughness at high incidence (50°–52°) than at low incidence (26°–28°). The difference observed in the X-band, between radar signals reflected by the roughest and smoothest areas, reaches a maximum of the order of 5.5 dB at 50°–52°, and 4 dB at 26°–28°. This sensitivity increases in the L-band with PALSAR/ALOS data, for which the dynamics of the return radar signal as a function of soil roughness reach 8 dB at HH38°. In the C-band, ASAR/ENVISAT data (HH and VV polarizations at an incidence angle of 23°) are characterised by a difference of about 4 dB between the signals backscattered by smooth and rough areas.Our results also show that the sensitivity of TerraSAR-X signal to surface roughness decreases in very wet and frozen soil conditions. Moreover, the difference in backscattered signal between smooth and rough fields is greater at high incidence angles. The low-to-high incidence signal ratio (Δσ° = σ_26°–28°/σ_50°–52°) decreases with surface roughness, and has a dynamic range, as a function of surface roughness, smaller than that of the backscattering coefficients at low and high incidences alone. Under very wet soil conditions (for soil moistures between 32% and 41%), the radar signal decreases by about 4 dB. This decrease appears to be independent of incidence angle, and the ratio Δσ° is found to be independent of soil moisture.     

一类旋转弹在高空中的锥形运动稳定性

为揭示弹箭在高空飞行过程中由于重力持续作用产生大攻角的物理本质,建立了弹道平面内时变参数的弹体运动数学模型,并推导了弹体在高空飞行段的攻角响应方程.同时,为了分析弹道顶点附近锥形运动的稳定性,综合考虑弹体姿态运动和位移运动建立了旋转弹锥形运动的动力学模型.针对大攻角引起显著气动非线性效应的情况,采用李雅普诺夫一级近似方法,给出了弹道顶点附近弹体锥形运动的稳定判据,并通过数值仿真验证了其正确性.     

基于FADS/IMU信息融合的大气数据测量方法研究

对飞行器大气数据进行估计是获取飞行状态的重要一环,是实现飞行器控制和稳定飞行的基础。通过研究嵌入式大气数据传感(FADS)系统,提出了基于容积卡尔曼滤波的惯性测量元件(IMU)数据和FADS数据融合算法。该算法对飞行器运动状态建立高阶滤波模型,使用容积点加权求和逼近的方法估计非线性运动模型,滤波输出值经处理后得到马赫数、攻角、侧滑角等大气数据。经仿真实验,算法计算的大气数据较为准确,马赫数误差小于0.01,攻角和侧滑角的误差小于0.1°。     

Hysteresis in flow past a NACA 0012 airfoil

Computations for two-dimensional flow past a stationary NACA 0012 airfoil are carried out with progressively increasing and decreasing angles of attack. The incompressible, Reynolds averaged Navier–Stokes equations in conjunction with the Baldwin–Lomax model, for turbulence closure, are solved using stabilized finite element formulations. Beyond a certain angle of attack the flow stalls with a sudden loss of lift and increase in drag. Hysteresis in the aerodynamic coefficients is observed for a small range of angles of attack close to the stall angle. This is caused by the difference in the location of the separation point of the flow on the upper surface of the airfoil during the increasing and decreasing angles of attack. With the increasing angle, the separation point moves gradually towards the leading edge. With the decreasing angle, the movement of the separation point away from the leading edge is abrupt.     

Multi-incidence angle RISAT-1 Hybrid Polarimetric SAR data for large area mapping of maize crop – a case study in Khagaria district,Bihar, India

Analysis of hybrid polarimetric synthetic aperture radar data has gained importance in the last couple of years with the availability of spaceborne data from Radar Imaging Satellite-1 (RISAT-1). RISAT-1 provides right circular transmit and linear receive data in Fine Resolution Stripmap-1 (FRS-1) mode with a swath of 25 km approximately covering 625 km² areas. But an administrative unit, like a district, in India cannot be covered in single FRS-1 acquisition. In this article, the possibility of acquisition of multi-incidence angle FRS-1 data to cover a larger area in three consecutive days over Khagaria district of Bihar State, India, for maize crop discrimination and mapping was investigated. It was assumed that the difference of 3 days in imaging does not affect the backscatter response from maize crop as there will not be much change in the maize crop characteristics in 3 days. The backscatter response of maize crop, which is in maximum vegetative stage, was studied at three incidence angles (viz. 28°, 42°, and 52°). The analysis was carried out for the discrimination of maize crop at each incidence angle in Raney derived hybrid decomposition parameters viz. Odd bounce, Double bounce, and Volume scattering mechanisms. The result shows that there is a slight difference in the backscatter response from maize crop due to the changes in incidence angle from 28° to 42° and has not shown any significant difference from 42° to 52°. However, the maize crop got well discriminated in the scatter plots of volume and double bounce scattering at both 28° and 42° and with odd and volume scattering combinations at 52°. The classification of the multi-incidence angle data resulted in 47,732 ha of maize cropped area in Khagaria district during rabi (winter season), 2014–15 with the producer’s accuracy of 92.00%.     

Elasto-plastic response of uniformly loaded sector plates: full-section yield model predictions and spread of plasticity

The governing equations for an elasto-plastic large deflection analysis of pressure loaded sector plates, based on the Ilyushin full-section yield criterion and the flow theory of plasticity, are presented. An outline of the solution of these equations using a finite difference implementation of the dynamic relaxation algorithm is given. Numerical results are presented for uniformly loaded slender and stocky sector plates with a 60° sector angle. In particular, first yield data are presented as well as the results of two parameter studies. The first study shows the effects of flexural and in-plane edge conditions on the deflections and stress resultants/couples at the centre of the sector plate and the second contrasts the spread of plasticity in slender sector plates with simply supported and clamped in-plane fixed edges.     

The FEM based liquid transfer model in gravure offset printing using phase field method

The velocity control of a roller is crucial in gravure offset printing for determining the quality of the printed images such as width and thickness of an electric circuit. The velocity control also affects mass printability, especially when using micro-scale liquid of high conductivity ink. In this work, a liquid transfer model for gravure offset printing is developed using the phase field method to investigate interfacial dynamics. As a numerical scheme, the finite element method is used for discretization of the partial differential equation. The interfacial layer governed by the phase field variable is embodied by the Cahn–Hilliard equation for a convection–diffusion problem. The numerical results are compared with those from the literatures for their validation. The results were found to be in good agreement with both analytical and experimental results in the literatures. After the validation, the effects of several key factors in gravure offset printing, such as velocity, gravity, surface tension and viscosity on liquid transfer are studied with respect to the contact angle of the upper plate. The ranges of the velocity and contact angle are varied from 0.01 to 0.25?m/s and from 30° to 70°, respectively. Also, the values of the surface tension and viscosity are changed from 0.5 to 1.5?N/m and from 0.05 to 0.15 N?s/m², respectively. The simulation result showed that at α?=?β?=?60° regardless of gravity, the liquid transfer rate (R _%) is increased as the velocity of the upper plate is increased at velocities below 0.01?m/s for liquid with low density, whereas the liquid transfer rate is decreased as the velocity is increased for liquid with high density. Also, the liquid transfer rate is increased as the surface tension is increased until the contact angle (α?≤?β?=?60°) approached 60°. Whereas the liquid transfer rate is decreased as the surface tension is increased until the contact angle (α?≤?β?=?60°) is increased to 60°.     

胶囊内窥镜倾角传感式磁跟踪系统的设计

为了提高胶囊内窥镜的跟踪精度,增强实时性,提出了倾角传感与磁场传感相结合的无线跟踪方法。推导了倾角传感模块在跟踪系统中的角度测量原理,基于坐标旋转和空间磁场理论,建立了倾角传感式磁跟踪数学模型,获得了胶囊方位与磁场信号的数学关系式。根据倾角传感的磁跟踪方案,设计开发了系统样机,包括:磁场发生装置、倾角式无线磁传感模块、无线数据接收装置、数据处理平台。跟踪实验表明,角度跟踪平均误差为4.2°、4.5°,标准偏差为2.2°、2.4°;x分量、y分量、z分量的平均位置误差为0.011 3 m、0.012 1 m、0.010 4 m,标准偏差为0.008 2 m、0.007 5 m、0.006 8 m。倾角传感器的引入减少了励磁源的个数,减小了每轮跟踪的采样数据量和采样时间,简化了非线性方程组的求解,进一步提高了跟踪精度。     

磁阻式传感器在角度测量中的应用

介绍一种利用磁阻式传感器构成的非接触角度自动测量系统。分析了非接触角度测量系统的结构、原理以及信号处理方法,给出了角度测试结果,系统的角度测量范围为0°~180°,测量精度为±0. 5°。     

MEMS无线数显角度测量仪设计

针对双轴或单轴高精度角度测量的工况需要,采用8位单片机为主控芯片,高精度数字MEMS为传感器芯片设计了一种体积小、功耗低的无线数显角度测量仪.远端上位机通过ZigBee无线模块对测量仪进行操作和三维显示,同时集成OLED屏可就地显示测量数据.具有双轴±90°倾角测量和单轴绝对式0°~360°转角测量功能.测试结果表明:该测量仪测量精度为0.1°,具有较高的推广应用价值.     

Application of the method of integral relations to boundary layer flows over blunt bodies

Calculations of boundary layer flows past blunt bodies at angles of incidence are presented. Using the method of integral relations together with the method of lines, the full three-dimensional boundary layer equations are reduced to a system of first order ordinary differential equations. The streamwise shear stress function θ and the cross-flow velocity component V are represented as suitable functions of the streamwise velocity component U. The role of the zone of dependence is automatically satisfied by the choice of differencing in the method of lines. Solutions correct to the second order are obtained in the positive shear region for flow over an ellipsoid at 30° incidence. The results are compared with corresponding finite difference solutions.     

机头结冰对大气数据系统测量影响研究

大气数据传感器安装于机头部位的飞机在遭遇结冰气象时,机头结冰会影响大气参数的测量精度。采用计算流体力学方法,对某两型运输飞机的大气数据系统进行模拟,考虑在机头结冰情况下的大气数据系统静压系数和迎角测量值的变化,获得了机头结冰对高度测量和速度测量的影响差量。研究表明,在两型运输飞机机头结冰状态下,中小迎角对大气数据系统静压和迎角测量的影响较小;大迎角对大气数据系统静压和迎角测量的影响较大,对应的高度测量影响量超过了10 m,速度测量影响量超过了2 kn。研究结果对于同类型飞机类似方向的研究具有一定的参考意义。     

Numerical solution of the three-dimensional boundary layer on a spinning sharp body at angle of attack

Numerical solutions for the laminar, compressible, three-dimensional boundary layer on general, sharp bodies of revolution at angle of attack with moderate axial spin are described. Unique solutions to the boundary layer equations are obtained by a finite-difference technique which properly treats the elliptic nature of the flow in a crossflow plane. Results are presented and compared with experiment for a tangent ogive-cylinder at four degrees angle of attack with and without spin. The results indicate that viscous flow solutions for spinning bodies at angle of attack can be obtained within the framework of conventional boundary layer theory. These solutions are free from the anomalies observed in a previous investigation.     

融合惯导与飞控系统信息的飞行大气全参数估计算法

针对嵌入式大气数据系统高空飞行精度低、跨大气层易失效等问题,提出一种融合惯导与飞控系统信息的 飞行大气全参数估计算法.基于飞行器气动模型及动力学方程,建立惯导信息与大气参数之间的函数 关系,进而利用扩展卡尔曼滤波实现大气参数的实时精确估计.仿真结果表明,该方法具有较高的 精度、良好的稳定性和鲁棒性,而且可以提高大气数据系统的测量范围和可靠性,能够适用于全 飞行包线下攻角、侧滑角、真空速的测量.