Three-Dimensional Velocity Distribution Measurement Using Ultrasonic Velocity Profiler with Developed Transducer

This study describes an ultrasonic velocity profiler that uses a new ultrasonic array transducer with unique 5-element configuration, with all five elements acting as transmitters and four elements as receivers. The receivers are designed to reduce the amount of uncertainty. As the fluid moves through this setup, four Doppler frequencies are obtained. The multi-dimensional velocity information along the measurement line can be reconstructed. The transducer has a compact geometry suitable for a wide range of applications, including narrow flow areas. The transducer’s basic frequency and sound pressure are selected and evaluated to be compatible with the application. First, to confirm the measurement ability, the measurement of the developed system in two-dimensional flow is validated by comparing it to the theoretical data. The uncertainty of measurement was within 15%. Second, the three-dimensional measurement in turbulent and swirling flow is proved experimentally to check the applicability of the proposed technique.

Particle Velocity Sensor and Its Application in Near-Field Noise Scanning Measurement

The Particle Velocity Sensor (PVS) is a kind of acoustic transducer which measures the particle velocity directly with figure-of-eight directivity. This paper proposes a near-field noise scanning technology based on the research of PVS, pressure-particle velocity (P-U) probe, and its application in noise source identification. Firstly, the principle and characteristics of PVS are presented. Secondly, a P-U probe is designed on the basis of PVS development. Finally, the noise measurement experiment for a single source is arranged and conducted. The result shows that the proposed P-U probe performs well in near-field noise source identification and localization.

A Study of Lift Force and Instantaneous Velocity Field Around an Oscillating Circular Cylinder

Force measurements of oscillatory flow acting on a single circular cylinder have been carried out. The experiments were done by oscillating a circular cylinder in still water. Instantaneous forces and velocity fields around the cylinder were measured by Particle Image Velocimetry (PIV). The Keulegan-Carpenter number (KC) varied in the range from 5 to 20 and the viscous parameter beta = Re / KC was set at 500 (Re is Reynolds number). It was found that the strength and frequency of the lift force increased with KC number, the main frequency of the lift force being three times the frequency of the oscillatory flow at KC = 20. The movement and strength of the vortices around the cylinder are discussed for different KC numbers.

Characterizing ship-induced hydrodynamics in a heavy shipping traffic waterway via intensified field measurements

Ship-induced hydrodynamics play an important role in shaping the cross-sectional profile of inland waterways and produce a large amount of pressure on the fluvial environment.This study aimed at quantifying the characteristics of ship-induced waves and currents in a heavy shipping traffic waterway via intensified field measurements conducted in the Changzhou segment of the Grand Canal,in Jiangsu Province,China.Based on the processed hydrodynamic data,waves and currents caused by single ships and multiple ships were investigated.For single ships,the shipinduced wave heights estimated with empirical formulas were not consistent with the observations.Categorized by the loading conditions of barges,the drawdown height was characterized by the ratio of ship speed to its limit speed.The maximum non-dimensional ship-induced wave height was parameterized by a nonlinear combination of the depth Froude number and a blockage coefficient.For multiple ships,when ships closely followed each other or interlaced each other's paths,it was difficult to characterize the superposition of several ship wakes.The magnitudes of current velocities induced by single ships and multiple ships were respectively nine and six times as large as those of natural flow.This may result in more severe sediment(re)suspension than natural flows.©2020 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

EXPERIMENTAL INVESTIGATION FOR THE EFFECT OF ROTATION ON THREE-DIMENSIONAL FLOW FIELD IN FILM-COOLED TURBINE

An experimental investigation of three-dimensional flow field in a film-cooled turbine model is carried out by using particle image velocimeter （PIV） in a low-speed wind tunnel. The effects of different blowing ratios （M=1.5, 2） on the flow field are studied. The experimental results reveal the classical phenomena of the formation of kidney vortex pair and secondary flow in wake region behind the jet hole. And the changes of the kidney vortex pair and the wake at different locations away from the hole on the suction and pressure sides are also studied. Compared with the flow field in stationary cascade, there are centrifugal force and Coriolis force existing in the flow field of rotating turbine, and these forces bring the radial velocity in the jet flow. The effect of rotatien on the flow field of the pressure side is more distinct than that on the suction side from the measured flow fields in Y-Z plane and radial velocity contours. The increase of blowing ratio makes the kidney vortex pair and the secondary flow in the wake region stronger and makes the range of the wake region enlarged.

Internal Flow Field Measurement of Gas Turbine Based on Optical Flow Method

The in-cylinder flow field of the internal combustion engine is an important factor affecting the quality and combustion quality of the fuel mixture in the cylinder. In order to calculate the high-precision flow field, the paper presents a flow field calculation method based on the optical flow algorithm. The motion of the point was calculated using the change in pixel intensity within two temporally adjacent frame images. The results show the high accuracy and resolution of the flow field at small displacement conditions.

An improved multidirectional velocity model for micro-seismic monitoring in rock engineering

An improved multidirectional velocity model was proposed for more accurately locating micro-seismic events in rock engineering. It was assumed that the stress wave propagation velocities from a micro-seismic source to three nearest monitoring sensors in a sensor's array arrangement were the same. Since the defined objective function does not require pre-measurement of the stress wave propagation velocity in the field, errors from the velocity measurement can be avoided in comparison to three traditional velocity models. By analyzing 24 different cases, the proposed multidirectional velocity model iterated by the Simplex method is found to be the best option no matter the source is within the region of the sensor's array or not. The proposed model and the adopted iterative algorithm are verified by field data and it is concluded that it can significantly reduce the error of the estimated source location.

Geodetic constraints on contemporary three-dimensional crustal deformation in the Laji Shan—Jishi Shan tectonic belt

The Laji Shan—Jishi Shan tectonic belt(LJTB),located in the southern part of the northeastern Tibetan Plateau(NETP),is a tectonic window to reveal regional tectonic deformation in the NETP.However,its kinematics in the Holocene remains controversial.We obtain the latest and dense horizontal velocity field based on data collected from our newly constructed and existing GNSS stations.Combined with fault kinematics from geologic observations,we analyze the crustal deformation characteristics along the LJTB.The results show that:(1)The Laji Shan fault(LJF)is inactive,and the northwest-oriented Jishi Shan fault(JSF)exhibits a significant dextral and thrust slip.(2)The transpression along the arc-shaped LJTB accommodates deformation transformation between the dextral Riyue Shan fault and the sinistral west Qinling fault.(3)With the continuous pushing of the Indian plate,internal strains in the Tibetan Plateau are continuously transferred in the northeast via the LJTB as they are gradually dissipated near the LJTB and translated into significant crustal uplift in these regions.

Three-Dimensional Analytical Modeling of Axial-Flux Permanent Magnet Drivers

In this paper, the axial-flux permanent magnet driver is modeledand analyzed in a simple and novel way under three-dimensional cylindricalcoordinates. The inherent three-dimensional characteristics of the deviceare comprehensively considered, and the governing equations are solved bysimplifying the boundary conditions. The axial magnetization of the sectorshapedpermanent magnets is accurately described in an algebraic form bythe parameters, which makes the physical meaning more explicit than thepurely mathematical expression in general series forms. The parameters of theBessel function are determined simply and the magnetic field distribution ofpermanent magnets and the air-gap is solved. Furthermore, the field solutionsare completely analytical, which provides convenience and satisfactoryaccuracy for modeling a series of electromagnetic performance parameters,such as the axial electromagnetic force density, axial electromagnetic force,and electromagnetic torque. The correctness and accuracy of the analyticalmodels are fully verified by three-dimensional finite element simulations and a15 kW prototype and the results of calculations, simulations, and experimentsunder three methods are highly consistent. The influence of several designparameters on magnetic field distribution and performance is studied and discussed.The results indicate that the modeling method proposed in this papercan calculate the magnetic field distribution and performance accurately andrapidly, which affords an important reference for the design and optimizationof axial-flux permanent magnet drivers.

Power Law Exponents for Vertical Velocity Distributions in Natural Rivers

While log law is an equation theoretically derived for near-bed region, in most cases, power law has been researched by experimental methods. Thus, many consider it as an empirical equation and fixed power law exponents such as 1/6 and 1/7 are generally applied. However, exponent of power law is an index representing bed resistance related with relative roughness and furthermore influences the shapes of vertical velocity distribution. The purpose of this study is to investigate characteristics of vertical velocity distribution of the natural rivers by testing and optimizing previous methods used for determination of power law exponent with vertical velocity distribution data collected with ADCPs during the years of 2005 to 2009 from rivers in South Korea. Roughness coefficient has been calculated from the equation of Limerinos. And using theoretical and empirical formulae, and representing relationships between bed resistance and power law exponent, it has been evaluated whether the exponents suggested by these equations appropriately reproduce vertical velocity distribution of actual rivers. As a result, it has been confirmed that there is an increasing trend of power law exponent as bed resistance increases. Therefore, in order to correctly predict vertical velocity distribution in the natural rivers, it is necessary to use an exponent that reflects flow conditions at the field.

On the Reversal Effects of the Velocity Quotient on the Directions of Changes of Finishing Results of Conventional and Flexible Grinding

The paper presents the problem of right direction of changes of the velocity quotient in view of getting advantageous smoothing results of material finishing using a compact elastic wheel. In fact the problem has been considered reversely in comparison with the change direction of the velocity quotient on the grounds of knowledge on grinding using ceramic wheels. The specifics of performance of the elastic wheels are considered. The investigation was carried out on the effect of their peripheral velocity on the directions of smoothing. The problem is considered by presenting it on the background of determined results of grinding using a ceramic wheel. The dependence of a determined roughness measure of the smoothed surface on the velocity quotient is delivered. The forms of a function approximating experimental dependences of the subject roughness measure on the mentioned quotient have been derived. Furthermore, the results coming out of the performed experimental studies have been presented.

Precise 3D shape measurement of three-dimensional digital image correlation for complex surfaces

Three dimensional-digital image correlation （3D-DIC） is a widely used optical metrology in the experimental mechanics community because of its reliability, practicality, and flexibility. Although the precision of digital image correlation （DIC） has been thoroughly studied theoretically and numerically, verification experiments have seldom been performed, especially fbr complex surfaces with a small field of view （FOV）. In this work, the shape of a 1-yuan coin was measured using 3D-DIC; the shape was complex due to the presence of many fine details, and the FOV was relatively small because the coin diameter was only 25 mm. During the experiment, a novel strategy for speckle production was developed： white paint was simply sprayed onto the surface. Black paint was not used; instead, taking advantage of the reflective nature of the coin surface, polarized light and a Polaroid filter were introduced, and the polarization direction was carefully adjusted, ensuring that the spray pattern was extremely thin and that high-quality speckle images with significant contrast were captured. The three-dimensional coin shape was also successfully determined for comparison using a stylus profiler. The results demonstrate that 3D-DIC provides high precision in shape measurement even for complex surfaces with small FOV. The precision of 3D-DIC can reach 1/7000 of the field of view, corresponding to about 6 ~tm in this experiment.

曲面仿生复眼测速技术研究

曲面仿生复眼相机具有大视场,对运动目标敏感等特点,在广域探测、内窥导管、精确制导等国防、医学及民用工业领域中有着广阔的应用前景,该文报道了基于曲面仿生复眼相机的高速运动目标测速技术研究。首先建立了基于曲面仿生复眼成像原理的测速模型;然后利用霍夫圆检测算法在原始复眼图像上找出每个子眼所在位置,并通过图像分割对相邻子眼之间重叠视场进行分析;最后再结合SIFT算法对相邻2个子眼的子图像进行特征点提取与图像配准,由提取出的特征点像素坐标计算出重叠区域像素数目,从而得到汽车的运动速度。设计了相关测速实验进行验证,实验中拍摄距离控制在6 m~10 m之间,对以8.33 m/s速度做匀速直线运动的汽车进行测试,测试结果表明,可将速度测试的相对误差控制在4%以内。与单孔径成像系统测速结果相比,曲面仿生复眼测速技术具有更高的准确性和重复性。

冲击实验中复杂流场的准静止区检测

颗粒流场特征检测通常采用粒子图像测速(PIV)技术测得速度场,再对多帧连续图像进行人工识别,检测结果存在一定的主观误差。因此,提出了一种在单帧流场图像中识别准静止区的DC-UNet++网络。首先,通过电荷耦合器件(CCD)采集小球冲击颗粒床形成的流场图像,再用PIV技术分析并制作数据集。然后,在多组数据集上训练CNN模型、UNet++模型和提出的DCUNet++模型,验证分析其在单帧图像上检测准静止区的可行性与准确性。最后,讨论了该模型在非透明和透明两类颗粒材料中的低速冲击流场上的泛化能力。实验结果表明:DC-UNet++网络在非透明和透明颗粒材料上的准确率分别达到87.76%和72.91%。DC-UNet++网络实现了在单帧图像上检测目标特征的任务,且对透明颗粒材料复杂流场下的特征仍具有较为准确的检测结果。

高超声速流场激光测速技术研究进展

高超声速气流条件下飞行器内/外部流动中存在强湍流及脉动、边界层转捩、激波-边界层干扰和高温真实气体效应等耦合效应,表征该非定常流动现象对飞行器气动力、气动热以及目标光电特性等产生的影响是高超声速流动研究中的前沿课题.速度作为表征流动过程最重要的参数之一,准确的速度测量对于深入理解上述复杂流动-传输机理以及高超声速飞行器设计具有重要指导意义.文章针对高超声速流场速度测量中几种常用的非接触式激光测试技术进行了综述,主要包括基于空间法的粒子图像测速,基于激光吸收光谱、激光诱导荧光和瑞利散射的多普勒测速,基于飞行时间法的分子标记测速,以及基于流场折射率的聚焦激光差分干涉测速技术.首先简要介绍每种激光测速技术的基本原理,然后进一步介绍该技术在高超声速自由流、层/湍流边界层、激波/边界层干扰、尾流或其他复杂流动区域的速度及其脉动度测量等方面的典型应用,分析各种技术环境适用性及面临的局限性和挑战.最后对基于激光技术的高超声速流场速度测量进行了总结及发展趋势展望.

巷道平均风速单点测试方法误差研究

为验证巷道平均风速单点测试方法可行性,提高巷道平均风速单点测试方法精度,采用Fluent数值模拟方法,计算各种断面形状、断面尺寸及支护方式巷道断面上平均风速单点测试误差分布。研究结果表明:在任意断面形状、断面尺寸及支护方式巷道断面上任意测点,巷道平均风速单点测试误差均小于6%,因此,巷道平均风速单点测试方法可行。根据巷道断面上平均风速单点测试误差分布情况,尽可能将风速传感器布置在误差小的位置,可进一步提高巷道平均风速单点测试方法精度。研究结果可为解决巷道平均风速快速精准测试问题,进而推进矿井通风智能化发展提供参考。

超声速差法平面叶栅流场试验和数值研究

针对平面叶栅狭小通道中流场非接触测量难题,提出一种基于超声速差原理的二维流场测量方法。设计一种2×4超声波斜、平口换能器组合阵列,研制一套多通道超声法测量和气流速度场重建系统。开展平面叶栅流场测量试验,成功获取了3种不同进口速度条件下流道二维速度场。利用COMSOL Multiphysics中CFD模块同步开展叶栅流场数值模拟,并与试验结果对比。结果表明:超声测量与数值模拟结果较为接近,速度大小和偏转角误差均在5%以内,较好地反映叶栅通道的流动特点。提出的超声测量技术有望进一步用于高马赫数流场研究。

干式铁芯电抗器振动特性数值模拟及试验研究

振动是影响干式铁芯电抗器运行状态的关键因素之一。在考虑铁芯夹件、垫块等结构件的影响下,采用有限元法实现了10 kV干式铁芯电抗器的3维瞬态电磁-结构多物理场仿真分析,研究了电抗器在磁致伸缩力、麦克斯韦力与洛伦兹力3者共同作用下的振动位移及速度分布特性。仿真结果表明,正常运行状态下,干式铁芯电抗器铁芯夹件的振动位移及速度显著大于其他部位,尤其是用于固定绕组的穿心螺杆。其次,结合干式铁芯电抗器模态仿真分析,获得了其模态特性及固有频率,并进一步分析了其振动机理。最后,采用多普勒激光测振仪测量了某10 kV干式铁芯电抗器的振动特性。试验结果表明,干式铁芯电抗器的振动频率以100 Hz及其倍频为主,其中300 Hz的振动响应最显著,其与其固有频率较接近,存在一定的共振风险。同时,试验结果与仿真结果一致性较好,验证了该文所述仿真分析方法的正确性和有效性。

基于Tomo-PIV技术的螺旋桨三维强旋转流动的实验研究

流体机械以及水力发电过程中的流动通常是具有强旋流的三维空间流动,此类流动的实验测量具有较大的难度。本文以水下伺服电机搭载三叶螺旋桨产生强的三维强旋转流动为例,采用四台CMOS摄像机同步对流场进行拍摄,并利用搭载了目前国际上最先进的层析粒子图像测速技术(Tomo-PIV)算法的德国LaVision公司的软件Davis 10.2.0对拍摄得到的图像进行空间重构,得到瞬时的三维空间速度场。基于得到的速度场,对螺旋桨三维强旋流结构的瞬时特性和时均特性进行了深入分析,并从速度、涡量和压力的变化上阐述了流场结构变化特点,证明了Tomo-PIV技术具有很高的测量精度和实际应用意义,在流体机械流场测量和水力发电领域三维空间流场的精细测量有广阔的应用前景。

西南印度洋中脊热液区岩石声学特性

西南印度洋中脊(Southwest Indian Ridge,SWIR)热液区具有潜在发育的大规模硫化物矿床,当前正在开展SWIR硫化物矿产资源评价。测量分析硫化物和不同围岩的声速等物性特征是硫化物近底地震勘探资料处理和解释的基础。该文对西南印度洋中脊热液区的硫化物和围岩等样品进行了系统的物性测量,结合岩石物性(包括密度、孔隙度、P波速度)与矿物组成,深入分析了西南印度洋中脊热液区岩石声速变化特性及其影响因素。结果表明,SWIR热液区围岩的P波速度受到岩石骨架矿物、孔隙和围压的影响。由于岩石孔隙度总体偏小,对P波速度的影响并不显著,但围压的增加使岩石微裂缝和孔隙逐渐闭合,P波速度呈非线性指数变化。蚀变作用导致了矿物成分改变,是影响围岩声速的最关键因素。单一物性参数测量结果可能存在多解性,联合波速、密度、磁性和电性等多物性参数测量有利于岩性区分。该研究成果有助于识别硫化物和围岩,为我国西南印度洋合同区多金属硫化物地震勘探工作提供重要支撑。