3D Numerical Simulation of Overbank Flow in Non-Orthogonal Curvilinear Coordinates

The velocity field in meandering compound channels with overhank flow is highly three dimensional. To date, its features have been investigated experimentally and little research has been undertaken to investigate the feasibility of reproducing these velocity fields with computer models. If computer modeling were to prove successful in this context, it could become a useful prediction technique and research tool to enhance our understanding of natural river dynamics. A 3-D k-E turbulence hydrodynamic model in curvilinear coordinates is established to simulate the overhank flow. The bodyfitted coordinate is adopted in the horizontal plane, the part grid is adopted in the vertical direction, and the wall-function method is employed to simulate the bed resistance. The model is applied to the simulation of the meandering channel with straight flood plain banks, and the main velocities and secondary velocities for both the longitudinal and cross sections are presented. Comparison and analysis show that the results of simulation are fit to reflect the results of experiment. These results show the application value of the model to 3D overhank flow.

Covariant Anomaly and Hawking Radiation from Kerr-Newman Black Hole in Dragging Coordinates Frame

In the light of Robinson and Wilczek's new idea,and motivated by Banerjee and Kulkarni's simplified method of using only the covariant anomaly to derive Hawking radiation from a black hole,we generally extend the work to Kerr-Newman black hole in dragging coordinates frame.It is shown that the flows introduced to cancel the anomaly at the event horizon are equal to the corresponding Hawking radiation in dragging coordinates frame,which supports and extends Robinson and Wilczek's opinion.

Characteristics of a Terrain-Following Sigma Coordinate

This study quantifies the main characteristics of a terrain-following, G-coordinate through mathematical analyses of its covariant and contravariant basis vectors as well as the vertical coordinate of σ. A 3-D schematic of the σ-coordinate in a curvilinear coordinate system is provided in this study. The characteristics of the basis vectors were broken down into their ＂local vector charac- teristics＂ and ＂spatial distribution characteristics＂, and the exact expressions of the covariant; in addition, the con- travariant basis vectors of the G-coordinate used to eluci- date their detailed characteristics were properly solved. Through rewriting the expression of the vertical coordi- nate of G, a mathematical expression of all the cr-coor- dinate surfaces was found, thereby quantifying the so- called terrain-following characteristics and lack of flexi- bility to adjust the slope variation of G-coordinate sur- faces for the classic definition of G. Finally, an analysis on the range value of the vertical coordinate demonstrated that the general value range of G could be obtained by eliminating the G-coordinate surfaces below the Earth＇s surface. All these quantitative descriptions of the charac- teristics of G-coordinate were the foundation for improv- ing the G-coordinate or creating a new one.

Defining the We-map Reference Frames and Providing Mathematical Expressions for Transformation Relations

We-map is an interactive mobile map that can be easily communicated and applied on personal electronic devices,such as personal computers and mobile phones.Therefore,the study of direction systems and coordinate systems is critical,and exploring reference frames is essential in direction and coordinate systems.Despite its significance,existing research on We-map lacks specific solutions for the exploration of reference frames is indispensable for the establishment of accurate direction and coordinate systems.In this paper,we endeavor to address this gap by elucidating the significance of We-map reference frames,defining them with mathematical constraints,summarizing their nature and characteristics,deriving their transformation relationships and representing them through mathematical formulars and equations.Our work contributes to the fundamental theory of We-map and provides valuable systems and support for the mathematical foundation of We-map,map production,and platform development.Ultimately,this research serves to advance the development of We-map.

Automatic Method for Synchronizing Workpiece Frames in Twin-robot Nondestructive Testing System

The workpiece frames relative to each robot base frame should be known in advance for the proper operation of twin-robot nondestructive testing system. However, when two robots are separated from the workpieces, the twin robots cannot reach the same point to complete the process of workpiece frame positioning. Thus, a new method is proposed to solve the problem of coincidence between workpiece frames. Transformation between two robot base frames is initiated by measuring the coordinate values of three non-collinear calibration points. The relationship between the workpiece frame and that of the slave robot base frame is then determined according to the known transformation of two robot base frames, as well as the relationship between the workpiece frame and that of the master robot base frame. Only one robot is required to actually measure the coordinate values of the calibration points on the workpiece. This requirement is beneficial when one of the robots cannot reach and measure the calibration points. The coordinate values of the calibration points are derived by driving the robot hand to the points and recording the values of top center point（TCP） coordinates. The translation and rotation matrices relate either the two robot base frames or the workpiece and master robot. The coordinated are solved using the measured values of the calibration points according to the Cartesian transformation principle. An optimal method is developed based on exponential mapping of Lie algebra to ensure that the rotation matrix is orthogonal. Experimental results show that this method involves fewer steps, offers significant advantages in terms of operation and time-saving. A method used to synchronize workpiece frames in twin-robot system automatically is presented.

The Explanation of the Michelson-Morley Experiment Results by Means Universal Frame of Reference

It is commonly thought that the Michelson-Morley experiment from 1887 and Kennedy-Thorndike experiment from 1932 demonstrated that the universal frame of reference (ether) does not exist and that the velocity of light in vacuum is absolutely constant. The analysis of this experiment led to the creation of the Special Theory of Relativity (STR). The article explains why Michelson-Morley and Kennedy-Thorndike experiments could not detect the universal frame of reference. In this article, a different transformation of time and position than the Lorentz transformation is derived on the basis of the geometric analysis of the Michelson-Morley and Kennedy-Thorndike experiments. The transformation is derived based on the assumption that the universal frame of reference (UFR) exists. UFR is a frame of reference in which the velocity of light is constant in every direction. In inertial frames of reference moving in the UFR, the velocity of light may be different. The article has derived the formula for relative speed and patterns for the maximum and minimum speed of light that can be measured in the inertial system. Finally, the anisotropy of the microwave background radiation has been explained by using the presented theory. According to the body kinematics model presented in this article, anisotropy of cosmic microwave background is the Doppler effect for observer moving in the UFR.

框指令FRAME在数控铣削齿块中的应用

通过对框指令操作的分析提出一种新方法,用以替代在数控镗铣床回转工作台上加工大模数齿块中,齿块中心与工作台回转中心不重合时所需进行的大量的坐标参数计算。

CGCS2000框架下县级测绘基准服务升级改造研究应用

2000国家大地坐标系的全面推广使用,加快了城市现代测绘基准体系和服务的升级改造建设工作。苏州2000坐标系启用后,市本级现代测绘基准体系完成了升级改造。在此基础上,以常熟市为例分析了县级现有独立坐标系应用面临的问题和苏州2000坐标系的适宜性后,从总体思路、控制网升级改造、坐标转换平台等方面研究并实施了县级现代测绘基准服务升级改造;在苏州2000坐标系推广使用和市域一体化高质量发展建设背景下,实现了市级基准体系在常熟的加密扩展和应用。可为国内同类城市测绘基准服务的升级改造提供参考。

基于坐标时间序列的地心运动分析与预测

地心运动会影响地球参考框架原点的准确性,是地球参考框架进行非线性维持必须考虑的因素之一,因此提出对地心运动进行多尺度的建模和预测,以实现毫米级地球参考框架的建立和维持。采用网平移法计算的地心运动、全球地球物理流体中心(global geophysical fluids center,GGFC)和国际GNSS服务(international gnss service,IGS)第三次重处理(IGSR03)提供的3组地心运动数据,首先对其一致性和差异进行了分析,然后分别利用谐波模型和Diff-LSTM模型对地心运动进行了长期和短期的建模与预测,结果显示,GGFC地心运动的预测精度优于1.5 mm,而Diff-LSTM模型的地心运动预测结果在短期内优于谐波模型,当预测步长为17时,GGFC和IGSR03的地心运动预测精度均能达到甚至优于1 mm。表明地心运动的预测精度能够满足基于地球质量中心(center of mass of the total earth system,CM)的瞬时地球参考框架的建立与维持。

一种游动傅科机械编排的捷联惯性间接极区导航算法

针对指北方位、游移方位等机械编排的惯性导航系统在极区附近出现计算溢出、导航误差发散、方向基准缺失等问题,本文提出了一种基于游动傅科机械力学编排的捷联惯性间接极区导航算法。首先,推导了传统坐标系和横向坐标系下的游动傅科机械编排位置、速度和姿态转换关系,并设计了完整的捷联惯性极区导航流程。其次,在详细分析载体沿经线穿越极点时的导航解算性能基础上,提出了一种游动傅科机械编排的捷联惯性间接极区导航算法。实验结果表明,该算法能够实现传统导航与横向导航方式的平滑切换,并借助横向导航信息解决载体穿越极点时无法导航的难题。

Energy Efficiency Maximization for Cooperative NOMA with Hardware Impairments

The massive connectivity and limited energy pose significant challenges to deploy the enormous devices in energy-efficient and environmentally friendly in the Internet of Things(IoT).Motivated by these challenges,this paper investigates the energy efficiency(EE)maximization problem for downlink cooperative non-orthogonal multiple access(C-NOMA)systems with hardware impairments(HIs).The base station(BS)communicates with several users via a half-duplex(HD)amplified-and-forward(AF)relay.First,we formulate the EE maximization problem of the system under HIs by jointly optimizing transmit power and power allocated coefficient(PAC)at BS,and transmit power at the relay.The original EE maximization problem is a non-convex problem,which is challenging to give the optimal solution directly.First,we use fractional programming to convert the EE maximization problem as a series of subtraction form subproblems.Then,variable substitution and block coordinate descent(BCD)method are used to handle the sub-problems.Next,a resource allocation algorithm is proposed to maximize the EE of the systems.Finally,simulation results show that the proposed algorithm outperforms the downlink cooperative orthogonal multiple access(C-OMA)scheme.

高速公路顺层边坡锚索框架梁和抗滑桩联合支护体系变形特征研究

以贵州省乌长高速公路某顺层高边坡为例,建立有限元模型,对锚索框架梁-抗滑桩支护体系的变形规律进行研究。结果表明:对各排锚索施加相同的预应力值不合理,存在锚索框架和抗滑桩顺序破坏的风险,应根据各排锚索随桩顶位移的变化规律,设置差异化的预应力值,使锚索框架和抗滑桩两种支护形式同时达到最佳支护效果;靠近桩顶位置,应设置较低的预应力值,远离桩顶位置,应设置较高的预应力值。提出基于变形协调条件下的锚索预应力值计算方法,得到的锚索预应力值与数值模拟计算结果误差在6%以内,满足设计精度要求。

喷雾测量系统坐标架三维位移控制研究

为解决航天发动机试验中,通过三维PDA(Phase Doppler Anemometry)测量系统研究燃料喷注器雾化效果中对测量点精确定位的问题,采用自适应模糊神经网络PID控制算法实现对测量系统三维坐标架的步进电机进行控制。建立了一个步进驱动电机进行位置控制的传递函数模型,通过Matlab的Simulink仿真平台对步进驱动电机位移的PID控制、模糊PID控制及模糊神经网络PID控制的三种算法进行仿真。模拟实验结果表明:模糊神经网络PID控制将响应时间提升到0.05 s,并且大幅减小超调。相比于传统PID此方法可大幅提高坐标架定位的速度和精度。

火箭部段对接孔的数字量协调加工误差分析与控制方法研究

针对火箭部段对接孔数字量协调的难点,分析数字量协调加工的影响因素确定要因,并通过对比试验和理论分析的方法分析测量误差和定位误差两种要因对加工精度的影响。在此基础上,提出数字量协调加工控制方案,并以典型部段端框为对象开展协调制孔试验,试验结果表明,数字量协调加工孔位精度符合装配协调要求,与工装平台试对协调,为端框数字量协调加工的工程化应用奠定了基础。

Leader-Following Entrapping Control of AUVs Using Bearing Measurements in Local Coordinate Frames

In this paper,the entrapping control problem of discrete-time AUVs with local coordinate frames is studied.To achieve entrapment in arbitrarily shaped orbits and formations,we design a bearingbased leader-following framework fully in the discrete-time domain with four parts:the orientation estimation unit,estimator unit,controller unit and parameters tuning unit.With bearing measurements and communication information,the orientation estimation unit can estimate orientations of local coordinate frames infinite time,and the estimator unit can achieve local localization.Based on estimation,the controller unit can drive each AUV to track the desired orbit or formation with an arbitrary shape.We present su±cient conditions under which stability of the overall system is proved using the theorem offinite-time stability and LaSalle's theorem for the discrete-time system.Moreover,the parameters tuning unit can calculate optimal parameters to improve overall performance.Additionally,we extend our schemes to nonholonomic AUVs with unicycle models.Finally,simulation results demonstrate the effectiveness of the proposed scheme.

某大跨度现浇楼盖结构中框架边梁裂缝原因分析

通过对某大跨度现浇楼盖结构中框架边梁破坏现象的观察和计算结果的分析,得出以下结论:框架边梁与楼盖次梁整体现浇时,端部存在嵌固约束作用,特别是支承多根大跨度次梁的框架边梁始终处于弯剪扭复合受力状态。框架边梁两端1/3跨度内协调扭转嵌固约束作用显著,应高度重视,不可折减或忽略,设计时应考虑抗扭作用;框架边梁中部约1/3跨度内次梁的嵌固约束作用不显著,可不计边梁的约束影响,边梁的最大扭矩变化较小,中部约1/3跨度内次梁可按照两端简支梁设计。

A Note on Natural Coordinates and Frenet Frames

This paper discusses the relationship between natural coordinates in fluid mechanics and orthogonal curvilinear coordinates. Since orthogonal curvilinear coordinates have some excellent mathematical properties, natural coordinates can be applied more widely if they can be transformed to orthogonal curvilinear coordinates. Frenet formulas which describe the differential properties of natural coordinates were compared with the derivative formulas of orthogonal curvilinear coordinates to show that natural coordinates are not generally orthogonal curvilinear coordinates. A method was introduced to transform natural coordinormal planes of the natural coordinates about the streamlines. The transformation is true as long as the natural coordinates satisfy several equations. Vorticity decomposition in the natural coordinates is used to show that these conditional equations are satisfied only if the streamlines are perpendicular to the vortexlines on every given point in the flow field. These equations apply in both planar flows and axisymmetric flows without a circumferential velocity component, but do not apply in some 3-D flows such as Beltrami flow.

组态视角下产业链和创新链耦合协调多元路径研究

产业链和创新链协调发展对区域高质量发展具有重要意义。通过测算2012—2021年31个省份双链耦合协调度,采用核密度估计描述全国双链耦合协调度的变化趋势和差异;采用必要条件分析(NCA)与模糊集定性比较分析(fsQCA)相结合的方法,挖掘TOE框架下6个前因变量与双链耦合协调度提升的复杂因果关系。结果表明:全国双链耦合协调度不断提升,但省际差距不断增大;单个要素并不构成双链高耦合协调水平的必要条件,高数字产业建设在产生双链高耦合协调水平方面发挥着普遍作用;驱动双链高耦合协调水平的路径具有“殊途同归”特征,产生双链高耦合协调水平的路径分别为数字产业-教育驱动型、数字经济驱动型和数字设施-数字产业-教育均衡驱动型。

基于整网解和分区解的铁路沿线基准站CGCS2000坐标确定

基于现有高铁线路控制测量或监测需求,在沿线布设卫星导航定位连续运行基准站(CORS)作为控制基准。对于较长的线路监测,对沿线基准站坐标采用整网解与分区解进行差异比较,并设计了多种比较方式。研究结果表明,对于计算铁路沿线基准站的国际地球参考框架(ITRF)2020坐标,整网处理与分区处理的差异较小;对于CORS站的2000国家大地坐标系(CGCS2000)的坐标计算,两者差异大部分在框架转换精度范围内,但仍有12%的点差异较大,超过了CGCS2000框架转换的2倍误差。在实际计算过程中,需要考虑整网处理与分区处理的差异。

省级区域CORS标准化运行维护技术研究

本文基于湖北省北斗地基增强系统运行维护实际经验和故障情况统计分析,从坐标框架维护、基准站维护和观测数据维护三方面展开讨论。首先,采取频率为每年一次的全网坐标更新,保持坐标框架的稳定;其次,针对基准站的维护,设定每个基准站的全年巡检频率为2~3次,并对电力故障及网络故障等常见故障进行预防和处理;最后,在数据维护方面,每年进行数据质量分析,确保数据利用率及多路径效应等技术指标满足要求。结果表明,本维护策略的实施,能够确保湖北省北斗地基增强系统全年可利用率保持在95%以上,全年正常运行率达到98%以上。这些经验和方法为湖北省北斗地基增强系统的稳定运行提供有力保障,也可为其它省级区域基准站网的运行维护提供参考。