Influence of different data fusion methods on the accuracy of three-dimensional displacements field

Combining multi-source data can improve the accuracy and the spatial resolution of the three-dimensional (3-D) displacements field. How to effectively integrate multi-source data to obtain high-precision and high spatial resolution 3-D displacements field is worthy of further study. The stochastic model and fusion model of integrating multi-source data affect the accuracy of data fusion. In this paper, based on the least squares method, the effects of different stochastic models and data fusion models on the 3-D displacements field’s accuracy are studied. The optimal method for estimating large-scale 3-D displacements field from integrated InSAR, leveling and GPS measurements is obtained. Then we realize the integrating InSAR, leveling and GPS measurements to obtain the high-precision 3-D displacements velocity field in Tianjin (China) from 2016 to 2018. The results are validated with GPS measurements at 6 independent stations, with the root mean squares (RMS) residuals of the discrepancies being 2.39 mm/yr, 2.54 mm/yr and 2.83 mm/yr in eastern, northern and vertical directions, respectively. By comparing different stochastic models, the 3-D displacements field obtained from multi-source data is optimized by the variance component estimation-least squares method, which is better than weighted least squares (WLS) method. By comparing different data fusion models, the accuracy of the horizontal displacements velocity is better than that of interpolated GPS results. The horizontal displacements component has a great influence on the vertical displacements velocity accuracy in the process of acquiring the 3-D displacements velocity by integrating InSAR, GPS and leveling measurements. This study provides a reference method for integrating multi-source data to obtain 3-D displacements field. This method effectively utilizes the advantages of GPS, InSAR and leveling measurements, and extends the limitations of single technical in describing surface-time scale applications. The 3-D displacements information with a large spatial scale and high spatial resolution provide a reliable data basis for studying the crustal movement and its dynamic mechanism.     

基于超声多普勒与电导环的油水两相流流速测量

两相流动现象广泛存在于众多工业领域中,其流动过程参数如流速的准确测量对量化体积/质量流量及优化生产工艺和过程设备有重要意义。针对水平油水两相流流速测量问题,提出了一种同侧双晶连续波超声多普勒（CWUD）与电导环传感器相结合的测量方法。非侵入式超声多普勒传感器为双晶超声换能器,由2个倾角相同且中心频率为1 MHz的压电陶瓷晶片组成,两者之间使用隔声材料防止声波干扰,其中发射晶片向流体连续发射超声波,同时接收晶片接收经流体中离散液滴散射的超声波,测量区间覆盖管道横截面的整个径向范围。动态实验在50 mm管径的水平油水两相流装置上完成,通过分析油水两相流多普勒频移响应特性,发现在测量区间内,平均多普勒频移与总表观流速之间随连续相不同而呈现2种线性关系。因此,根据电导环传感器的电学敏感原理,获得无量纲电压参数判断两相流的连续相,继而选取相应流动状态下的测量模型,计算流体总表观流速。实验结果表明:总表观流速估计值均方根误差为0.01 m/s,平均相对误差为3.09%,其中相对误差小于5%的置信概率为70%。      

Surface tension-driven flows in horizontal liquid metal layers

The problem of surface tension-driven flows in horizontal liquid layers has been studied experimentally, and theoretically by direct numerical simulation and small perturbation analysis. We focus our attention on situations in which the depth of the fluid (liquid tin; small Prandtl number, Pr=0.015) is small enough to ensure the predominance of the surface tension forces over those due to the buoyancy. The surface velocity has been experimentally obtained for liquid tin layer with various aspect ratio (length to height) in the range 5<A<83. The thermal gradients are ranged from 5 to 40°K/cm. In the numerical study, the Navier-Stokes and energy equations are solved by an efficient finite difference technique. The parameters governing the flow behaviour in the liquid are varied to determine their effects on thermocapillary convection: the Reynolds number 10<Re<210⁴ and the aspect ratio 2<A<25; with Pr kept constant at Pr=0.015. The linear eigenequation resulting from small spatial disturbances of the Couette flow solution is solved using an Tau-Chebyshev approximation. A notable feature of the theoretical study is the totally different end circulations. In the region near the cold wall a multicell structure is evident. This agrees with the eigensolution which is of complex type, indicating spatial periodicity. In the hot wall region the flow is accelerated to reach the velocity value for the fully-developed Couette flow which is reached under conditions such as Re/A<20. The transition from viscous to boundary layer regime occurs for a critical value (Re/A)_c of nearly about 200, as deduced from the numerical and experimental results.     

开放空腔壳体入水流场结构及流体动力特征研究

基于混合介质雷诺平均Navier-Stokes方程,对开放空腔壳体垂直入水运动过程开展了数值研究,得到了压力场、速度场分布,空泡波动、闭合特征,空腔气体涨缩规律,以及流体动力变化规律,并分析了空腔结构在入水运动过程中对流场结构和流体动力的影响。结果表明:液体随气体涨缩同步进出开放端;开放端局部形成波动的压力源和周期性的压力场、速度场分布;入水空泡呈现波动形态,其扩展程度与开放端液体流速相关;空泡内形成气体漩涡,随空腔涨缩往返进出空泡,对空泡闭合具有抑制作用;流体动力呈波动变化规律,频率与气体涨缩频率一致,幅值与气体涨缩程度成正比。开放空腔结构在入水过程中空腔内气体发生涨缩运动,对流场结构和流体动力产生周期性扰动作用,在一定程度上可以减缓冲击、维持空泡及运动的稳定性。      

机载中空纤维膜组件壳程气体流动数值模拟

机载惰化用中空纤维膜组件具有分离效率高、安全稳定、结构紧凑等优点,是目前较为经济高效的飞机燃油箱惰化设备。采用计算流体力学(CFD)方法对某中空纤维膜组件壳程气体流动进行数值模拟,通过更改膜丝束间距、膜丝束入口速度、膜丝束流量、膜丝束排布方式及飞行高度,得到了不同工况下的组件轴向各截面的气体流动分布,并提出无量纲参数截面平均速度比来描述气体流动分布规律。仿真结果表明:在保持入口气体流动速度一定时,平均速度比值随着膜丝束间距的减小先减小后增大,在膜丝束间距为1.5倍膜丝半径时达到最小值, 在保持入口流量一定时,壳程气体流动有着相同的规律;在保持膜丝束填充数量不变时,均匀排布比不均匀排布的平均速度比值更小;保持膜丝束间距不变时,入口速度对平均速度比值影响不大;飞行高度对组件壳程气体分布的影响作用主要体现在膜组件内壁处。      

Ion dynamics associated with Alfven wave in the near-Earth magnetotail: Two-dimensional global hybrid simulation

Ion dynamics in the near-Earth magnetotail region is examined during periods of fast Earthward flow with a two-dimensional (2-D) global-scale hybrid simulation. The simulation shows that shear Alfven waves are generated at x ∼ −10R_E, where the strong earthward flow is arrested by the dipole field, and propagate along field lines from the equator to both southern and northern polar ionosphere. Non-gyrotropic ion velocity distributions occur where the large-amplitude Alfven waves are dominant. The simulation indicates that the Alfven waves are generated by interaction of the fast earthward flow with the stationary near-Earth plasma. Beam ions are found to be pitch-angle scattered and trapped in the wave field, leading to the non-gyrotropic ion distributions in the high-latitude plasma sheet boundary. In addition, significant particle heating and acceleration are found to occur behind the dipolarization front due to the effect of wave turbulence.     

不同重力条件下水平管内气液两相流流型及空隙率分布的数值模拟

基于VOF方法建立了不同重力条件下水平管内气液两相流动的三维非稳态数学模型并进行了数值求解, 研究了10^-4g₀, 0.17g₀, 0.38g₀, 1g₀ (g₀=9.8m·s^-2)四种重力条件下水平管内气液两流型及变化规律, 比较了不同重力条件下管内截面空隙率的分布和波动规律. 研究结果表明, 该模型能够正确预测不同重力条件下水平管内气液两相流的流型、截面空隙率和滑速比等重要参数; 同一气液两相表观速度工况下, 随着重力水平的升高, 气相更容易在水平管的上部积聚合并, 致使流型发生变化, 同时, 气液两相滑速比增大, 截面空隙率波动峰值的平均值下降, 波动频率降低; 而随着气液两相表观速度的增大, 两相混合工质内惯性力作用也随之增强, 这将削弱重力变化的影响.     

空间计量中长度单位和距离测量

长度单位定义是建立在光直线传播、光速在真空中为常数,以及光速各向同性的理论基础上,二维球面上的直线,在三维空间中是弯曲的测地线;三维空间的直线,在四维时空中也是弯曲的测地线。长度单位的定义是否适用四维时空呢？SI秒和SI米的定义适用于全域时空,但使用它们必需明确原时和坐标时的区别。爱因斯坦的狭义相对论以及光速不变原理只适用于惯性系,不适用于非惯性系。本文以转盘上的非惯性坐标系为例,利用广义相对论的坐标变换和时空度规运算,揭示了非惯性坐标系上的时空弯曲和光的非直线传播现象。计算了非惯性坐标系上Sagnac效应对卫星和地面站双向测距的影响,初步研究表明空间测量范围从局域推广到全域的话,诸如引力红移、相对速度效应、Sagnac效应等将会成为空间长度测量不确定度的影响因素,因此空间计量理论必须建立在广义相对论基础之上,用四维时空观念理解空间距离测量问题。     

Current collection through the transport of electrons across magnetic field lines

Collection of electrons by a long conducting cylinder in a flowing plasma is studied by means of numerical simulations. The plasma flow simulates the relative motion between a spacecraft and plasma. The sheath structures and the levels of electron current collections for the cases with and without an ambient magnetic field ( ) are studied. It is found that for the flow perpendicular to the magnetic field, the current is considerably enhanced depending on the relative drift velocity. In the case of a non-zero magnetic field perpendicular to the cylinder axis, the potential structure is a two-dimensional double layer with dimensions L L_|, where L and L_| are the dimensions perpendicular and parallel to , respectively. L is found to be the current limiting radius given by the Parker-Murphy model. For the flow along , the electron current is found to be smaller than that for the flow perpendicular to . This is explained in terms of the potential structures.     

Convective motions in liquid metals for material processings. Numerical simulation of oscillation regimes and effect of rotation

The paper is concerned with the numerical simulation and the analysis of some kinds of flow regimes which can develop in Bridgman and Czochralski systems for material processings. The flows in the liquid phase are investigated considering two-dimensional and axisymmetric models. The time-dependent regimes were studied for a zero-Prandtl-number fluid layer confined inside a two-dimensional cavity of aspect ratio (length-to-height) A=4, involving a stress-free upper surface and submitted to a horizontal temperature gradient. The range of Grashof number was varied up to the conditions at which the flow goes from oscillatory to chaotic type behaviours. The combined influence of the temperature gradients and of the rotations of the crucible and of the seed/crystal was investigated for a Czochralski model. The axisymmetric regimes were studied for a Pr_m=0.015 liquid melt confined inside a cylindrical crucible of aspect ratio (height-to-radius) A_m=2, and coupled to a viscous encapsulant liquid layer (10<Pr_e<1200) of aspect ratio A_e=0.5. A number of steady and (transient) time-dependent flow patterns are identified.     

固体火箭发动机燃烧室三维流动数值计算

采用k-ε双方程湍流模型,以SIMPLE计算程式求解翼柱型装药固体火箭发动机燃烧室内三维非定常不可压流N-S方程.在建立翼柱型装药简化模型的基础上采用边界标志法来表达燃面推移,采用从二维到三维的初场给定方法结合多重网格法求出了多个时间步的非稳态流场结构.计算结果表明燃烧室内旋涡运动呈现一定的空间与时间分布,周向加质导致燃气通道横断面上轴向速度分布的极不均衡.      

Natural convection driven by buoyancy and surface tension forces under external magnetic field

Two-dimensional natural convection driven both by buoyancy and surface tension in the horizontal layer of an electrically conducting liquid which is subjected to a horizontal temperature gradient and a vertical magnetic field is studied theoretically. The flow and temperature distribution in the liquid layer is analysed for two cases; (1) the top surface is free and the bottom is a rigid wall, and (2) both surfaces are rigid. The effect of the magnetic field on the flow velocity and the temperature distribution is made clear and the simple expressions are obtained for two extreme cases of the sufficiently large magnetic field and the small magnetic field.     

One dimensional blood flow in a planetocentric orbit

All life on earth is accustomed to the presence of gravity. When gravity is altered, biological processes can go awry. It is of great importance to ensure safety during a spaceflight. Long term exposure to microgravity can trigger detrimental physiological responses in the human body. Fluid redistribution coupled with fluid loss is one of the effects. In particular, in microgravity blood volume is shifted towards the thorax and head. Sympathetic nervous system-induced vasoconstriction is needed to maintain arterial pressure, while venoconstriction limits venous pooling of blood prevents further reductions in venous return of blood to the heart. In this paper, we modify an existing one dimensional blood flow model with the inclusion of the hydrostatic pressure gradient that further depends on the gravitational field modified by the oblateness and rotation of the Earth. We find that the velocity of the blood flow V_B is inversely proportional to the blood specific volume d, also proportional to the oblateness harmonic coefficient J₂, the angular velocity of the Earth ω_E, and finally proportional to an arbitrary constant c. For c = −0.39073 and ξ_H = −0.5 mmHg, all orbits result to less blood flow velocities than that calculated on the surface of the Earth. From all considered orbits, elliptical polar orbit of eccentricity e = 0.2 exhibit the largest flow velocity V_B = 1.031 m/s, followed by the orbits of inclination i = 45°and 0°. The Earth’s oblateness and its rotation contribute a 0.7% difference to the blood flow velocity.     

减压直流非转移弧等离子体射流速度的静电探针测量

组建了一套利用静电探针诊断技术测量减压直流非转移弧等离子体射流速度的实验系统。对以纯氩为工质的等离子体,在气流量1．25×10^-1kg/s、弧电流80A、真空室压力165Pa的条件下,测量了射流的速度及其分布。结果表明射流在发生器出口处中心最高速度约为1200m／s,在半径20mm处减小到635m／s。沿射流轴线方向的速度梯度约为10（ms^-1）／mm。射流速度随着弧电流增加而缓慢单调增加;当真空室压力从165Pa提高到2kPa时,发生器出口轴线上的射流速度从1200m／s降至570m／s。     

Dynamic particle accumulation structure (PAS) in half-zone liquid bridge – Reconstruction of particle motion by 3-D PTV

Three-dimensional (3-D) velocity field reconstruction of oscillatory thermocapillary convections in a half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3-D particle tracking velocimetry (PTV). Simultaneous observation of the particles suspended in the bridge by two CCD cameras was carried out by placing a small cubic beam splitter above a transparent top rod. The reconstruction of the 3-D trajectories and the velocity fields of the particles in the several types of oscillatory-flow regimes were conducted successfully for sufficiently long period without losing particle tracking. With this application the present authors conducted a series of experiments focusing upon the collapse and re-formation process of the PAS by mechanically disturbing fully developed PAS.     

Displacement monitoring performance of relative positioning and Precise Point Positioning (PPP) methods using simulation apparatus

Besides the classical geodetic methods, GPS (Global Positioning System) based positioning methods are widely used for monitoring crustal, structural, ground etc., deformations in recent years. Currently, two main GPS positioning methods are used: Relative and Precise Point Positioning (PPP) methods. It is crucial to know which amount of displacement can be detected with these two methods in order to inform their usability according to the types of deformation. Therefore, this study conducted to investigate horizontal and vertical displacement monitoring performance and capability of determining the direction of displacements of both methods using a developed displacement simulator apparatus. For this purpose, 20 simulated displacement tests were handled. Besides the 24?h data sets, 12?h, 8?h, 4?h and 2?h subsets were considered to examine the influence of short time spans. Each data sets were processed using GAMIT/GLOBK and GIPSY/OASIS scientific software for relative and PPP applications respectively and derived displacements were compared to the simulated (true) displacements. Then statistical significance test was applied. Results of the experiment show that using 24?h data sets, relative method can determine up to 6.0?mm horizontal displacement and 12.3?mm vertical displacement, while PPP method can detect 8.1?mm and 19.2?mm displacements in horizontal and vertical directions respectively. Minimum detected displacements are found to grow larger as time spans are shortened.     

带肋变截面回转通道内流动与换热的数值模拟

开发了三维流动换热的通用计算程序,数值研究了带肋变截面回转通道内流动与换热的特性.湍流模型采用低雷诺数k-ε模型.通道肋间距为25mm,肋高分别为1mm,1.5mm,2mm,冷气进口雷诺数Re分别为7500,12500,18500,25000.计算结果表明:①通道的平均努赛尔数均随进口雷诺数的增大而增大;②对于Re=7500和12500,肋高越高,换热越强;对于Re=18500和25000,肋高为1.5mm的通道换热最强;③局部雷诺数的不同和离心力的影响导致通道内各区域的局部换热随肋高的变化趋势并不一致;在进口段,肋高越高,换热越强;在出口段,当Re=7500和12500时,肋高越高,换热越强,而当Re=18500和25000时,存在最佳肋高1.5mm.     

压电式高速开关阀控液压缸位置系统

针对开关阀控液压缸位置分辨率低、响应慢的问题,设计了压电式高速开关阀控液压缸位置系统。首先,建立开关阀控液压缸位置系统模型,分析了PWM载波频率对开关阀流量特性的影响规律,采用基于差动流量的双阀结构,实现液压缸负载流量的非线性补偿,减小开关阀死区对系统静、动态性能的影响。然后,分析双阀控制式液压缸系统负载脉冲流量的影响因素,得到了开关阀控液压缸位置抖振的产生机理,比较基于脉冲流量的PWM、PAM、PFM控制方法。最后,依据压电式高速开关阀流量特性,提出了PWM+PAM的复合控制方法,根据误差信号及其变化,调节占空比和流量幅值,实现液压缸位置的快速、精确控制。仿真及实验结果表明:系统定位精度将近1%,为高速开关阀及其控制系统应用提供了理论基础。      

DORIS and GPS monitoring of the Gavdos calibration site in Crete

Due to its specific geographical location as well as its geodetic equipment (DORIS, GNSS, microwave transponder and tide gauges), the Gavdos station in Crete, Greece is one of the very few sites around the world used for satellite altimetry calibration. To investigate the quality of the Gavdos geodetic coordinates and velocities, we analyzed and compared here DORIS and GPS-derived results obtained during several years of observations. The DORIS solution is the latest ignwd11 solution at IGN, expressed in ITRF2008, while the GPS solution was obtained using the GAMIT software package. Current results show that 1–2 mm/yr agreement can be obtained for 3-D velocity, showing a good agreement with current geophysical models. In particular, the agreement obtained for the vertical velocity is around 0.3–0.4 mm/yr, depending on the terrestrial reference frame. As a by-product of these geodetic GPS and DORIS results, Zenith Tropospheric Delays (ZTDs) estimations were also compared in 2010 between these two techniques, and compared to ECMWF values, showing a 6.6 mm agreement in dispersion without any significant difference between GPS and DORIS (with a 97.6% correlation), but with a 13–14 mm agreement in dispersion when comparing to ECMWF model (with only about 90% correlation for both techniques). These tropospheric delay estimations could also provide an external calibration of the tropospheric correction used for the geophysical data of satellite altimetry missions.     

重力对R134a在矩形小通道内冷凝过程的影响

为研究重力对小通道冷凝过程的影响,采用VOF模型对制冷剂R134a在水平放置的边长1mm方形截面小通道内的冷凝换热过程进行数值模拟.模拟过程考虑重力、表面张力和界面剪切力的综合作用,表面张力采用CSF模型.结果表明：重力对矩形小通道冷凝换热的影响不明显,蒸气在通道横截面上呈近似圆形分布;通道较短时重力对液膜的汇聚作用不明显,达到一定长度后重力作用凸显.研究结果为天舟一号货运飞船搭载的蒸发与冷凝科学实验研究项目冷凝空间实验方案设计提供了理论依据.