Monitoring shear deformation of sliding zone via fiber Bragg grating and particle image velocimetry

Monitoring shear deformation of sliding zones is of great significance for understanding the landslide evolution mechanism,in which fiber optic strain sensing has shown great potential.However,the cor-relation between strain measurements of quasi-distributed fiber Bragg grating(FBG)sensing arrays and shear displacements of surrounding soil remains elusive.In this study,a direct shear model test was conducted to simulate the shear deformation of sliding zones,in which the soil internal deformation was captured using FBG strain sensors and the soil surface deformation was measured by particle image velocimetry(PIV).The test results show that there were two main slip surfaces and two secondary ones,developing a spindle-shaped shear band in the soil.The formation of the shear band was successfully captured by FBG sensors.A sinusoidal model was proposed to describe the fiber optic cable deformation behavior.On this basis,the shear displacements and shear band widths were calculated by using strain measurements.This work provides important insight into the deduction of soil shear deformation using soil-embedded FBG strain sensors.

Particle image velocimetry (PIV) measurements of tip vortex wake structure of wind turbine

Large-view flow field measurements using the particle image velocimetry （PIV） technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented q53.2 m wind tunnel. The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine. The results show that the tip vortex first moves inward for a very short period and then moves outward with the wake expansion, while its vorticity decreases with time after being trailed from the trailing edge of the blade tip, and then increases continuously with the rapid rolling-up to form a strong tip vortex. The measurements also indicate that the downstream movement of the tip vortex is nearly linear in the very near wake under the test condition.

TWO-DIMENSIONAL PARTICLE IMAGE VELOCIMETRY(PIV) MEASUREMENTS IN A TRANSPARENT CENTRIFUGAL PUMP

A special transparent centrifugal pump is designed. Detailed opticalmeasurements of the flow inside the rotating passages of a five-bladed shroud centrifugal pumpimpeller have been performed by using two-dimensional particle image velocimetry (PIV). The flow issurveyed at three load conditions q_V/q_(Vd) = 0.4, q_V/q_(Vd) = 1.0, q_V/q_(Vd) = 1.5,respectively. As a result, phase averaged PIV velocity vector maps on three planes between hub andshroud of the impeller are presented. At design load, the mean field of relative velocity ispredominantly vane congruent, showing well-behaved flow without separation. The distributions of therelative velocity on different plane along the pump shaft are very different and there is always alow velocity zone near the pressure-side of the blade at both low and design flow rate, but thelow-velocity-zone at the low flow rate is much larger than that at the design one. The studydemonstrates that the PIV technique is efficient in providing reliable and detailed velocity dataover a full impeller passage.

Measurement on soil deformation caused by expanded-base pile in transparent soil using particle image velocimetry (PIV)

A new small-scale geotechnical physical model in 1-g and unconfined condition, combining the transparent soil, close-range photogrammetry and particle image velocimetry(PIV), was employed, which provides a non-intrusively internal deformation measurement approach to monitor the internal deformation of soil caused by expanded-base pile jacking with casing. The transparent soil was made of fused quartz and its refractive index matched blended oil, adding reflective particles(glass beads). Closerange photogrammetry was employed to record the images of the process of casing jacking and extraction in transparent soil, allowing the use of Matlab-based Geo-PIV to figure out the displacement field converted from image space to object space. Analysis of test results indicates that the maximum displacement caused by casing jacking for expandedconical-base pile is decreased by 29% compared with that for expanded-flat-base pile. The main movement happens at the early stage of casing extraction. The maximum displacement caused by casing extraction for the conical base is about 43% of that for the flatbase, while the affected zone caused by casing extraction for the conical base accounts for about 1/3 of that for the flat base. The contraction for horizontal displacements tends to decrease with the depth increasing. By contrast, the contraction under pile base decreases with the increasing of displacement. The displacements generated by jacking a conventional pile having a diameter equal to the casing diameter of the expanded-base pile were comparable to the net displacement taking place due to expanded-base pile installation for the conical base pile.

Study of Diesel Spray Particle Velocity Field Using a Particle Image Velocimetry Setup

Aim To investigate the spray particle velocity and its distribution characteristics. Methods\ A set of PIV (particle image velocimetry) system was developed and used to observe and analyze the spray particle velocity field. Results and Conclusion\ Double exposure image of the spray particle within the region of 10-50 mm from the nozzle tip was recorded and analyzed by the IBAS2000 analysis system. Some characteristics of the spray particle velocity and its distribution were obtained.

Particle image velocimetry and numerical simulations of the hydrodynamic characteristics of an artificial reef

This article reports a particle image velocimetry study and the comparative results of a numerical simulation into the hydrodynamic characteristics around an artificial reef.We reveal the process of flow separation and vortex evolution,and compare the force terms generated by our artificial reef model.The numerical simulation agrees well with experimental results,showing the applicability of computational fluid dynamics to the hydrodynamics of an artificial reef.Furthermore,we numerically simulate the hydrodynamics of the reef model for seven velocities.The results show that the drag coefficient is approximately 1.21 in a self-modeling region for Reynolds numbers between 2.123×104and 9×104.Therefore,the upwelling height and current width of the flow field do not change significantly when the inflow velocity increases.Our study indicates that computational fluid dynamics can be applied to study the hydrodynamics of an artificial reef and offer clues to its construction.

Particle Image Velocimetry Measurement of the Flow Field in the Play of the Drilling Pump Valve

The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry（PIV） technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in ＇various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics（CFD） simulations.

3D Particle Image Velocimetry Test of Inner Flow in a Double Blade Pump Impeller

The double blade pump is widely used in sewage treatment industry,however,the research on the internal flow characteristics of the double blade pump with particle image velocimetry（PIV） technology is very little at present.To reveal inner flow characteristics in double blade pump impeller under off-design and design conditions,inner flows in a double blade pump impeller,whose specific speed is 111,are measured under the five off-design conditions and design condition by using 3D PIV test technology.In order to ensure the accuracy of the 3D PIV test,the external trigger synchronization system which makes use of fiber optic and equivalent calibration method are applied.The 3D PIV relative velocity synthesis procedure is compiled by using Visual C＋＋ 2005.Then absolute velocity distribution and relative velocity distribution in the double blade pump impeller are obtained.Test results show that vortex exists in each condition,but the location,size and velocity of vortex core are different.Average absolute velocity value of impeller outlet increases at first,then decreases,and then increases again with increase of flow rate.Again average relative velocity values under 0.4,0.8,and 1.2 design condition are higher than that under 1.0 design condition,while under 0.6 and 1.4 design condition it is lower.Under low flow rate conditions,radial vectors of absolute velocities at impeller outlet and blade inlet near the pump shaft decrease with increase of flow rate,while that of relative velocities at the suction side near the pump shaft decreases.Radial vectors of absolute velocities and relative velocities change slightly under the two large flow rate conditions.The research results can be applied to instruct the hydraulic optimization design of double blade pumps.

Investigation of Unsteady Flow Fields for Flow Control Research by Means of Particle Image Velocimetry

Unsteady three-dimensional flow phenomena must be investigated and well understood to be able to design devices to control such complex flow phenomena in order to achieve the desired behavior of the flow and to assess their performance, even in harsh industrial environments. Experimental investigations for flow control research require measurement techniques capable to resolve the flow field with high spatial and temporal resolution to be able to perceive the relevant phenomena. Particle Image Velocimetry (PIV), providing access to the unsteady flow velocity field, is a measurement technique which is readily available commercially today. This explains why PIV is widely used for flow control research. A number of standard configurations exist, which, with increasing complexity, allow capturing flow velocity data instantaneously in geometrical arrangements extending from planes to volumes and in temporal arrangements extending from snapshots to temporarily well resolved data. With increasing complexity these PIV systems require advancing expertise of the user and growing investment costs. Using typical problems of flow control research, three different standard PIV systems will be characterized briefly. It is possible to upgrade a PIV system from a simple planar to a “high end” tomographic PIV system over a period of time, if sufficient PIV expertise can be built up and budget for additional investments becomes available.

A Review of Particle Image Velocimetry for Fish Migration

Understanding the flow characteristic in fishways is crucial for efficient fish migration. Flow characteristic measurements can generally provide quantitative information of velocity distributions in such passages;Particle Image Velocimetry (PIV) has become one of the most versatile techniques to disclose flow fields in general and in fishways, in particular. This paper firstly gives an overview of fish migration along with fish ladders and then the application of PIV measurements on the fish migration process. The overview shows that the quantitative and detailed turbulent flow information in fish ladders obtained by PIV is critical for analyzing turbulent properties and validating numerical results.

3D particle tracking velocimetry for the determination of temporally resolved particle trajectories within laser powder bed fusion of metals

Within this work,we present a system for the measurement of the three-dimensional(3D)trajectories of spatters and entrained particles during laser powder bed fusion(L-PBF)of metals.It is comprised of two ultrahigh-speed cameras and a reconstruction task specific processing reconstruction algorithm.The system enables an automated determination of 3D measures from the trajectories of a large number of tracked particles.Ambiguity evolving from an underdetermined geometrical situation induced by a two-camera setup is resolved within the tracking using a priori knowledge of L-PBF of metals.All processing steps were optimized to run on a graphics processing unit to allow the processing of large amounts of data within an appropriate time frame.The overall approach was validated by a comparison of the measurement results to synthetic images with a known 3D ground truth.

基于粒子图像分割的混合PIV-PTV算法

粒子图像测速法(particle image velocimetry,PIV)因其非接触场测量的特性,已成为空气动力学领域的主要测量工具。复杂流动的速度场往往具有非均匀性,示踪粒子难以在待测空间均匀分布。因此,在应用PIV互相关算法处理粒子稀疏区时,需要采用更大的查询窗口以降低测量的不确定度,但会带来空间分辨率低的实际问题。而粒子追踪测速法(particle tracking velocimetry,PTV)追踪单个示踪粒子的跨帧位移,具有比PIV更高的空间分辨率,但难以适用于粒子浓度高的稠密区。针对PIV、PTV各自的优点,本文发展了一种基于粒子图像分割的混合PIV-PTV测速技术。首先定义了基于维诺多边形的粒子局部浓度量度,用以计算示踪粒子在粒子图像上的局部浓度场;其次通过设定的浓度阈值对粒子进行二分类,使用基于高斯核函数的支持向量机寻找出最优的分类边界,从而实现对粒子图像的粒子稀疏区和稠密区的划分;最后对两个区域分别使用PIV和PTV进行速度场计算,并合并为完整的速度场输出。仿真结果表明,上述方法可实现对粒子图像中的示踪粒子稀疏区和稠密区的自动划分,有效提高速度场测量的空间分辨率。将该方法应用在马赫数Ma=6的湍流边界层近壁测量中,可有效解决高速条件下粒子因强剪切难以进入边界层近壁区的问题,显著提高对近壁流动的解析能力。

基于粒子图像测速(PIV)技术的圆盘桨搅拌槽湍流动能耗散率研究

在边长L为220 mm的方形搅拌槽内,采用高解析率的二维粒子图像测速(PIV)技术在搅拌雷诺数Re=1300下对圆盘桨形成的流场进行研究,得到Kolmogorov尺度下的高解析流场。基于流场数据和各向同性假设得到湍流动能分布,并比较了直接定义法和大涡PIV法计算的湍流动能耗散率。结果表明:当离底高度C=0.15L时,圆盘桨的流型呈现出独特的单循环流型,流体主要旋涡为单旋涡结构;搅拌槽内湍流动能的最大值出现在桨叶排出流的末端;在Kolmogorov空间解析尺度下直接定义法计算得到的湍流动能耗散率大于大涡PIV法,并且湍流动能耗散率的峰值位于桨叶端和排出流区域。直接数值模拟的验证结果表明,这两种计算方法中使用的各向同性假设是合理的。

冲击波流场的PIV速度场修正算法研究

粒子图像测速(particle image velocimetry,PIV)技术是研究分析流动现象产生机制和物理规律的1种重要手段。针对击波管实验中产生的平面冲击波流场,开展了冲击波波阵面及波后速度场图像测量实验,设计并实现了1种结合高斯拟合亚像素与连续性方程的复合图像修正算法,利用该算法对实验原始数据进行了处理分析。结果表明:经本文所提出的算法修正后,波阵面前PIV速度场矢量信息连续,可显示出由于粒子不均匀而不能正确测量的区域信息,提高了速度场信息测量精度,该方法可有效修正存在强间断面的速度场中,由记录图像质量差、粒子播撒不均匀或流动跟随性差等问题带来的速度场计算偏差,为冲击波速度场错误矢量的检测与修正提供了1种简单高效的算法。

Experimental study on movement of particles in centrifugal impeller

The slurry pump is the key component of a dredger. Solid particles have strong influence on the performance of a slurry pump. The movement of solid particles in a centrifugal impeller was studied using particle image velocimetry(PIV) measurement. The experiments were conducted in a dredging pump model at Hohai University. Some transparent glass spheres with diameter of 0. 2-0. 4 mm were used as solid particles. The concentration and relative velocities of the particles were analyzed to investigate the particle trajectory. The results show that the concentration of the particles on the pressure surfaces of the blades is higher than on the suction surfaces,and the particles tend to move towards the suction surfaces. Moreover,the particles have faster relative velocities than the liquid phase through the flow channels of the impeller.

基于PIV/PTV的平板裂缝支撑剂输送试验研究

为了解水力压裂过程中水力裂缝内支撑剂的铺置规律,基于平板裂缝开展了支撑剂输送试验,分析了泵注排量、压裂液黏度、注入位置、支撑剂类型对支撑剂铺置过程的影响;运用PIV/PTV技术,测试了压裂液-支撑剂两相运动速度,从颗粒运动角度分析了不同因素对最终砂堤形态的影响。试验发现:平板单缝内支撑剂铺置存在“裂缝前端先堆积至平衡高度,再稳定向后端铺置”和“砂堤整体纵向增长,稳定向后端铺置”2种典型模式,2种模式可以在泵注的不同阶段出现并转换;砂堤不同位置形态主控因素存在差异,注入位置与排量主要控制前缘形态,黏度与排量主要控制中部形态,黏度主要控制后缘形态;在裂缝远端,支撑剂沉降存在“回流式”和“直接式”2种模式,前者受涡流控制,后者则仅依靠重力沉降;现场施工时可考虑“定向射孔+大排量中高黏70/140目石英砂(主体支撑剂)+40/70目陶粒架桥+大排量中高黏70/140目石英砂长距离输送+排量尾追40/70目陶粒”,兼顾缝长方向远距离铺置和近井地带裂缝与井筒的高连通性。平板裂缝内支撑剂运移与铺置规律试验结果可以为页岩储层压裂主裂缝内支撑剂高效铺置及储层改造工艺参数优化提供参考。

Flow of Steel in Mold Region During Continuous Casting

The particle image velocimetry （PIV） technique was used to study the fluid flow phenomena that occurred during continuous casting, using a water model with dimensions of 1 840mm× 280 mm. Two types of solidified shells, i. e. , the smooth type and the coarse type, were used to characterize the dendrite in order to simulate different liquid-solid interfacial conditions. The influence of the nozzle angle and the immersion depth of nozzle, as well as the casting speed on the flow behavior was investigated quantitatively. The results were as follows： （1） There are two large recirculations above and below the fluid jet in the mold, respectively, under the smooth interface condition. However, in the case of the dendrite solidified shell, it was found that the flow velocity of the fluid decreased and more smaller vortices appeared in the upper region of the mold. （2） The angle and the immersion depth of nozzle are two important factors affecting the flow pattern, and they are also capable of bringing about the change in the flow direction. （3） The higher the casting speed, the higher are the jet stream and the impacting point on the narrow face. However, the high casting speed causes serious fluctuation of the meniscus, and correspondingly leads to various defects.

基于PIV的渐变地表粗糙度对坡面流水动力特性的影响

粗糙度是影响坡面流水动力特性的关键因子,为探究渐变粗糙度影响下坡面流水力特性,采用粒子图像测速技术(particle image velocimetry, PIV)观测并分析3组流量下渐变粗糙床面下坡面流的流速轮廓线、紊动强度、雷诺应力和壁面切应力的变化规律。结果表明:(1)流速随粗糙度增加而减小;拟合无量纲流速得到流速分布对数公式,粗糙度增大与拟合常数A成反比,与积分系数B成正比。(2)渐变地表粗糙度流向紊动强度与光滑床面坡面流变化趋势相似。流向紊动强度随相对水深的增大而减小。随着粗糙度增大,流向紊动强度大小出现非显著性差异。渐变粗糙床面下流向紊动强度符合Nezu经验公式,流量与经验系数成正比。(3)不同流量下,渐变粗糙床面的雷诺应力分布与光滑床面相似。在粗糙度影响下,雷诺应力最大值出现在y/H=0.2~0.4处。随着粗糙度逐渐增加,壁面切应力逐渐增大。综合表明,增加PIV分辨率方法可以适用于坡面流水力特性的研究。探究渐变粗糙度对坡面流的影响,探讨坡面流水动力学特性,为水土保持理论研究提供新思路。

大尺度类波形壁面湍流边界层TR-PIV实验研究

针对传统波形壁面因尺度微小所引发的加工困难、维护费用昂贵等问题,设计了一种大尺度的类波形壁面.对虎鲸的皮肤嵴结构进行放大和形貌改良,得到的大尺度类波形壁面可以更好地适用于工程实际;研究了大尺度类波形壁面对湍流边界层的影响,分析了其减阻效果及减阻机理.采取高时间分辨率粒子图像测速(TR-PIV)技术,对光滑壁面和振幅与波长之比分别为2a1/λ=0.033、2a2/λ=0.050、2a3/λ=0.066的3种大尺度类波形柔性壁面湍流边界层流场进行了实验测量,对流场中的时空相关函数进行计算.分析一个波长范围内流向、法向速度及压力分布,发现波形结构下坡段附近的逆压梯度使得流动减速,爬坡段附近的顺压梯度则加速了流动,减速效果最强位置位于波谷,加速效果最强位置位于波谷始末,流场中的速度在两个极值内变化.对不同工况下类波形壁面末尾凹槽下游紧邻平板区域各阶统计量进行了对比,结果表明3种类波形壁面的平均速度剖面于对数区表现出不同幅度的抬升,近壁区平均速度均有不同程度增大;近壁区流场雷诺切应力具有明显的降低,近壁区湍流脉动被抑制,雷诺应力的峰值相对壁面略有外移;3种类波形壁面均具有一定减阻效果,最大减阻率为23.0%.

The Criterion of Choosing the Proper Seeding Particles

This paper is focused on the problem of the ability of seeding particles to follow the flow field. One of the most important factors influencing the resultant accuracy of the measurement is using the proper seeding particles for feeding the flow when measuring by PIV （Particle Image Velocimetry） method. The aim of the paper is to provide comprehensible instruction for choosing the proper type of seeding particles with regard to the flow characteristics and required measurement accuracy. The paper presents two methods with the help of which it is possible to determine the seeding particles＇ ability to follow the flow field. The first method is based on the direct calculation of the phase lag and amplitude ratio between the particle and the fluid. The calculation is based on solution of the BBO （Basset Boussinesq Oseen） equation for spherical particle. The other method results from the calculation of the particle time response, which defines the maximum frequency of disturbances, which are to be followed by the particle. In the conclusion, the method of choosing the seeding particles is proposed, depending on the required measurement accuracy.