scholarly journals Extracting Crowd Velocities at High Density

2020 ◽  
Vol 5 ◽  
pp. A110
Author(s):  
Muhammad Baqui ◽  
Rainald Löhner
Keyword(s):  
Particle Image ◽  
Fundamental Property ◽  
Manual Tracking ◽  
Traffic Dynamics ◽  
Surveillance Camera ◽  
Flow Monitoring ◽  
Piv Technique ◽  
Quantitative Accuracy ◽  
Image Velocimetry ◽  
Velocity Extraction

Velocity is a fundamental property of foot traffic flow. Monitoring the change of velocity patterns at high pedestrian densities may provide valuable insights on foot traffic dynamics. In this paper, a closer look is taken to explore the capability of the Particle Image Velocimetry (PIV) technique on extracting crowd velocities from surveillance camera images. Experiments are performed to report the accuracy of pedestrian velocity extraction with PIV. Quantitative accuracy is reported with manual tracking of pedestrians, surveying correlation misses at different window sizes and compute times. The results indicate that the PIV algorithm can be a good candidate for velocity extraction in real-time.

Simultaneous Measurement of Temperature and Velocity in Turbulent Buoyant Plume by Combined LIF and PIV Technique

2006 ◽  
Author(s):  
Yoshie Watanabe ◽  
Yuji Hashizume ◽  
Nobuyuki Fujisawa
Keyword(s):  
Simultaneous Measurement ◽  
Particle Image ◽  
Fluorescent Dyes ◽  
Buoyant Plume ◽  
Thermal Flow ◽  
Piv Technique ◽  
Image Velocimetry ◽  
Wide Range ◽  
High Temperature Sensitivity ◽  
Surrounding Fluid

An experimental technique for simultaneous measurement of temperature and velocity in a thermal flow is described. This technique is based on the two-color laser-induced fluorescence technique combined with the particle image velocimetry. Illumination is provided from Nd:YAG laser and the fluorescent dyes are chosen as Rhodamine B and Fluorescent Sodium, which combination allows the accurate velocity measurement in a wide range of flow velocity and high temperature sensitivity in temperature measurement. The measurement of temperature and velocity in turbulent buoyant plume is carried out by this method, and the structure of the plume is studied in connection with the entrainment of surrounding fluid at the interface.

scholarly journals Novel analysis for large strains based on particle image velocimetry

2017 ◽  
Vol 54 (7) ◽  
pp. 933-944 ◽  
Author(s):  
Núria M. Pinyol ◽  
Mauricio Alvarado
Keyword(s):  
Particle Image Velocimetry ◽  
Slope Failure ◽  
Particle Image ◽  
Large Strains ◽  
Software Packages ◽  
Piv Technique ◽  
Standard Procedures ◽  
Image Velocimetry ◽  
Sandy Slope ◽  
Piv Analysis

Over the last few decades, the particle image velocimetry (PIV) technique has become an interesting tool used to measure displacements in the field of experimental mechanics. This paper presents a procedure to interpret PIV displacements, measured following an Eulerian scheme, with the purpose of providing accumulated displacements, velocities, accelerations, and strains on points representing physical particles. Strains are computed as the gradient of displacements. When compared with other standard procedures already published, the presented methodology is especially well suited to interpret large strains. The basis of the procedure is to map displacement increments measured through PIV analysis on the subset (or patch) centres into numerical particles that are defined as portions of the moving masses whose deformation is analyzed. The implementation of the method is explained in detail, highlighting its simplicity. The procedure can be used as a post-processor of currently available PIV software packages. The methodology is first applied to synthetic cases of rectangular samples in which known displacements are imposed and also to a sandy slope failure experiment involving large displacements. The method reproduces satisfactorily the recorded images.

scholarly journals Measurement of Velocity and Temperature Profiles in the 1/40 Scaled-Down CANDU-6 Moderator Tank

2015 ◽  
Vol 2015 ◽  
pp. 1-9
Author(s):  
Hyoung Tae Kim ◽  
Jae Eun Cha ◽  
Han Seo ◽  
In Cheol Bang
Keyword(s):  
Particle Image ◽  
Laser Induced Fluorescence ◽  
Test Facility ◽  
Temperature Profiles ◽  
Cfd Analysis ◽  
Tank Model ◽  
Piv Technique ◽  
Image Velocimetry ◽  
Potential Problems ◽  
Accident Conditions

In order to simulate the CANDU-6 moderator circulation phenomena during steady state operating and accident conditions, a scaled-down moderator test facility has been constructed at Korea Atomic Energy Institute (KAERI). In the present work an experiment using a 1/40 scaled-down moderator tank has been performed to identify the potential problems of the flow visualization and measurement in the scaled-down moderator test facility. With a transparent moderator tank model, a flow field is visualized with a particle image velocimetry (PIV) technique under an isothermal state, and the temperature field is measured using a laser induced fluorescence (LIF) technique. A preliminary CFD analysis is also performed to find out the flow, thermal, and heating boundary conditions with which the various flow patterns expected in the prototype CANDU-6 moderator tank can be reproduced in the experiment.

Effect of inlet port on the flow in the cylinder of an internal combustion engine

2006 ◽  
Vol 220 (1) ◽  
pp. 73-82 ◽  
Author(s):  
A Yasar ◽  
B Sahin ◽  
H Akilli ◽  
K Aydin
Keyword(s):  
Particle Image Velocimetry ◽  
Velocity Distribution ◽  
Particle Image ◽  
Combustion Engine ◽  
Flow Characteristics ◽  
Intake Port ◽  
Intake Valve ◽  
Piv Technique ◽  
Image Velocimetry ◽  
Image Density

In this study, the characteristics of flow emerging from the inlet of the intake port in the cylinder were investigated experimentally. A particle image velocimetry (PIV) technique was used to measure the velocity distribution in order to observe and analyse the flow behaviour. High-image-density PIV provided acquisition of patterns of instantaneous and averaged vorticity and velocity, revealing the detail of the flow characteristics in the cylinder cavity. With this measuring technique, it is possible to study the effect of intake valve geometry on the flow behaviours. The results showed that the flow structure changed substantially along the cylinder stroke due to the geometry of the intake valve port.

Experimental Study of the Characteristics of Gas Impinging Streams Using PIV Technique

2013 ◽  
Author(s):  
Wei Wei ◽  
ZhiYi Li ◽  
Fengxia Liu ◽  
Zhijun Liu
Keyword(s):  
Mass Transfer ◽  
Experimental Study ◽  
Flow Field ◽  
Flow Rate ◽  
Particle Image ◽  
Velocity Fields ◽  
Experimental Equipment ◽  
Piv Technique ◽  
Tracer Particles ◽  
Image Velocimetry

Impinging streams technology has been widely used in many applications in recent years because of its enhancement to the heat and mass transfer between phases. In this paper, in order to investigate the influences of the impinging distance and flow rate on the characters of the flow field, gas-gas impinging streams flow fields are tested experimentally and analyze qualitatively with particle image velocimetry (PIV). The experimental equipment consists of two opposite nozzles which are the same axis. A PIV system is used to measure the characters of the 2-D flow field between two opposite nozzles. The gas is delivered by a compressor through two opposite jets which could be seeded with oil droplets as tracer particles. The effects of the flow rate and impinging distance on the velocity fields of impinging zone are investigated in detail. As the flow rate increases from 0.2 m3/h to 0.8 m3/h, the width of impinging zone increases from 0.25 to 0.5. However, the range of impinging zone does not change significantly as the impinging distance increases from 61mm to 94mm. The results indicate that the PIV technique is an effective method to measure and analyze the characters of impinging streams.

Characteristics of Turbulent Flows Over Forward Facing Steps in Adverse Pressure Gradients Based on Two-Point Analyses

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Hassan Iftekhar ◽  
Martin Agelin-Chaab
Keyword(s):  
Particle Image Velocimetry ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Particle Image ◽  
Adverse Pressure Gradient ◽  
Pressure Gradients ◽  
Physical Size ◽  
Piv Technique ◽  
Image Velocimetry ◽  
Point Velocity

This study reports the results of turbulent flows forward facing steps (FFS) in pressure gradients using a particle image velocimetry (PIV) technique to obtain data up to 68 step heights downstream. The contours of two-point velocity correlations indicate that regardless of the pressure gradients, the physical size of the coherent structures characterized by the autocorrelations grows as the flow develops downstream along the step. Additionally, adverse pressure gradient (APG) elevates the size of the autocorrelations.

scholarly journals Experimental Investigation of Flow Structures Around side-by-side Yawed Cylinders in Shallow Water

2019 ◽  
Vol 2 (3) ◽  
pp. 1138-1151
Author(s):  
Ebubekir Kütük ◽  
Umutcan Olmuş ◽  
Tahir Durhasan ◽  
Hüseyin Akıllı
Keyword(s):  
Shear Stress ◽  
Shallow Water ◽  
Vector Fields ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Flow Structures ◽  
Piv Technique ◽  
Gap Ratio ◽  
Image Velocimetry ◽  
Yaw Angle

The aim of this experimental study is to investigate the flow behaviour around two equally yawed side-by-side cylinders in shallow water. Time averaged velocity vector fields, Reynolds shear stress distrubutions and streamline patterns were obtained using Particle Image Velocimetry (PIV) technique. The gap ratio between the cylinders were in the range of G/D=0.25-1.25 with an increment of 0.25 where G is the distance between the cylinders and D is the cylinder diameter. Five different yaw angles of cylinders were employed during the experiment. The results showed that the yaw angle, α had an important effect on the flow structures of the downstream of the cylinders. Reynolds shear stress and vortex structures were decreased, the intensity of the jet like flow were significantly attenuated for the gap ratios of G/D=0.25, 0.50 and 0.75.

Investigation of Streaming Flow Patterns in a Thermoacoustic Device Using PIV

2010 ◽  
Author(s):  
Hadi Babaei ◽  
Kamran Siddiqui
Keyword(s):  
Particle Image ◽  
Velocity Fields ◽  
Two Dimensional ◽  
Cold Side ◽  
Velocity Magnitude ◽  
Piv Technique ◽  
Image Velocimetry ◽  
Streaming Velocity ◽  
The Difference ◽  
Streaming Flow

We report on an experimental study conducted to study the streaming velocity fields in the vicinity of the stack in a thermoacoustic device. Synchronized Particle Image Velocimetry (PIV) technique was used to measure the two-dimensional streaming velocity fields. The streaming velocity fields were measured at both sides of the porous stack over a range of pressure amplitudes (drive ratios). The results show that the streaming flow structure is significantly different on hot and cold sides of the stack. The hot side of the stack experienced higher magnitudes and higher spatial variability of the streaming velocities compared to the cold side. The difference in the velocity magnitude between the hot and cold sides of the stack showed a significant increase with an increase in the drive ratio.

Fuel Composition Effects on the Velocity Field in a Lean Premixed Swirl-Stabilized Combustor

2003 ◽  
Author(s):  
Donald M. Wicksall ◽  
Ajay K. Agrawal ◽  
Robert W. Schefer ◽  
Jay O. Keller
Keyword(s):  
Velocity Field ◽  
Atmospheric Pressure ◽  
Particle Image ◽  
Velocity Fields ◽  
Fuel Composition ◽  
Composition Effects ◽  
Piv Technique ◽  
Image Velocimetry ◽  
Lean Premixed ◽  
Recirculation Zones

Fuel composition effects on the flow-field of a lean premixed swirl-stabilized burner were studied. Methane (CH4) was enriched with hydrogen (H2) to vary the fuel composition. The burner inlet had 28-degree swirl vanes located in the annulus around a centerbody. Combustion occurred in an air-cooled quartz chamber at atmospheric pressure. The measurements were obtained, using the particle image velocimetry (PIV) technique, which allowed the 2-D velocity and vorticity fields to be examined for different fuels. The average velocity field was significantly altered, including the shape of the central and corner recirculation zones in the H2 enriched flames. The instantaneous velocity fields showed corresponding differences as well. The length scales and vorticity levels of the time-averaged velocity field differed from those for the instantaneous fields, indicating the importance of temporally resolved measurements.

Study on Improvement of the Suction Valve Using PIV Technique

2005 ◽  
Author(s):  
Eitaro Koyabu ◽  
Tetsuhiro Tsukiji ◽  
Yoshito Matsumura ◽  
Taizo Sato
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Vibration Reduction ◽  
Flow Analysis ◽  
Particle Image Velocimetry System ◽  
Test Model ◽  
Reciprocating Compressor ◽  
Air Conditioner ◽  
Piv Technique ◽  
Image Velocimetry

The simplified test model of the commercial reciprocating compressor for an automotive air-conditioner is used to measure the displacement of the suction valves using a strain gauge and to investigate the velocity distributions of the discharge flow from the valves using the particle image velocimetry system. This paper is focused on the effects of shape of the suction valve on the vibration-reduction. The size of the suction valve hole and the width of the tip of the suction valve are changed as main parameters of the valve shape. First, the size of the conventional valve hole and the width of the tip of the conventional valve are changed and seven new valves are manufactured to reduce the vibration of the valve. Consequently, it is found that one shape of the new valves is the most effective for the vibration-reduction. Next, the influence of the natural frequency on the vibration-reduction is investigated using one shape of the new valves by changing the material and the thickness of the valve. In addition, the relation between the conventional valve and the new valves are also estimated by the pressure loss. Finally, the reason of the vibration-reduction for one shape of the new valves is discussed from the results of the flow analysis around the valve. The vibration-reduction for one shape of the new valves is confirmed by measurement of the displacement of the valve in the reciprocating compressor for the automotive air-conditioner.

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