scholarly journals Probabilistic Evaluation and Filtering of Image Velocimetry Measurements

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2206
Author(s):  
Evangelos Rozos ◽  
Katerina Mazi ◽  
Antonis D. Koussis
Keyword(s):  
Camera Calibration ◽  
Moving Objects ◽  
Probabilistic Approach ◽  
Video Recording ◽  
Calibration Procedure ◽  
Frame Rate ◽  
Acceptable Error ◽  
Practical Applications ◽  
Image Velocimetry ◽  
The Impact

The recent technological advances in remote sensing (e.g., unmanned aerial vehicles, digital image acquisition, etc.) have vastly improved the applicability of image velocimetry in hydrological studies. Thus, image velocimetry has become an established technique with an acceptable error for practical applications (the error can be lower than 10%). The main source of errors has been attributed to incomplete intrinsic and extrinsic camera calibration, to non-constant frame rate and to spurious low velocities due to moving objects that are irrelevant to the streamflow. Some researchers have even employed probabilistic approaches (Monte Carlo simulations) to analyze the uncertainty introduced during the camera calibration procedure. On the other hand, the endogenous uncertainty of the image velocimetry algorithms per se has received little attention. In this study, a probabilistic approach is employed to systematically analyze this uncertainty. It is argued that this analysis may not only improve the performance of the image velocimetry methods but it can also provide information regarding the impact of the video recording conditions (e.g., low density of features, oblique camera angle, low resolution, etc.) on the accuracy of the estimated values. The suggested method has been tested in six case studies of which the data have been previously made publicly available by independent researchers.

scholarly journals Collision of water drops with a thin cylinder

2021 ◽  
Vol 2057 (1) ◽  
pp. 012034
Author(s):  
A I Fedyushkin ◽  
A N Rozhkov ◽  
A O Rudenko
Keyword(s):  
Stainless Steel ◽  
High Speed ◽  
Video Recording ◽  
Frame Rate ◽  
Drop Diameter ◽  
Outer Diameter ◽  
Stainless Steel Capillary ◽  
Thin Cylinder ◽  
Water Drops ◽  
The Impact

Abstract The collision of water drops with a thin cylinder is studied. The droplet flight trajectory and the cylinder axis are mutually perpendicular. In the experiments, the drop diameter is 3 mm, and the diameter of horizontal stainless-steel cylinders is 0.4 and 0.8 mm. The drops are formed by a liquid slowly pumped through a vertical stainless-steel capillary with an outer diameter of 0.8 mm, from which droplets are periodically separated under the action of gravity. The droplet velocity before collision is defined by the distance between the capillary cut and the target (cylinder); in experiments, this distance is approximately 5, 10, and 20 mm. The drop velocities before the impact are estimated in the range of 0.2–0.5 m/s. The collision process is monitored by high-speed video recording methods with a frame rate of 240 and 960 Hz. The test liquids are water. Experiments and numerical simulation show that, depending on the drop impact height (droplets velocity) different scenarios of a drop collision with a thin cylinder are possible: a short-term recoil of a drop from an obstacle, a drop flowing around a cylindrical obstacle while maintaining the continuity of the drop, the breakup of a drop into two secondary drops, one of which can continue flight and the other one is captured by the cylinder, or both secondary droplets continue to fly, and the drop can be also captured by the cylinder, until the impact of the next drop(s) forces the accumulated drop to detach from the cylinder. Numerical modeling satisfactorily reproduces the phenomena observed in the experiment.

scholarly journals Estrus Detection Using Background Image Subtraction Technique in Tie-Stalled Cows

Animals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1795
Author(s):  
Shogo Higaki ◽  
Kei Horihata ◽  
Chie Suzuki ◽  
Reina Sakurai ◽  
Tomoko Suda ◽  
...  
Keyword(s):  
Moving Objects ◽  
Video Recording ◽  
Subtraction Technique ◽  
Image Subtraction ◽  
Estrous Cycles ◽  
Front View ◽  
Estrus Detection ◽  
Set Up ◽  
The Impact ◽  
Background Image

In this study, we determined the applicability of the background image subtraction technique to detect estrus in tie-stalled cows. To investigate the impact of the camera shooting direction, webcams were set up to capture the front, top, and rear views of a cow simultaneously. Video recording was performed for a total of ten estrous cycles in six cows. Standing estrus was confirmed by testing at 6 h intervals. From the end of estrus, transrectal ultrasonography was performed every 2 h to confirm ovulation time. Foreground objects (moving objects) were extracted in the videos using the background subtraction technique, and the pixels were counted at each frame of five frames-per-second sequences. After calculating the hourly averaged pixel counts, the change in values was expressed as the pixel ratio (total value during the last 24 h/total value during the last 24 to 48 h). The mean pixel ratio gradually increased at approximately 48 h before ovulation, and the highest value was observed at estrus, regardless of the camera shooting direction. When using front-view videos with an appropriate threshold, estrus was detected with 90% sensitivity and 50% precision. The present method in particular has the potential to be a non-contact estrus detection method for tie-stalled cows.

Particle motion with air resistance

2012 ◽  
Vol 8 (1) ◽  
pp. 1-15
Author(s):  
Gy. Sitkei
Keyword(s):  
Basic Equation ◽  
Initial Conditions ◽  
Equation Of Motion ◽  
Terminal Velocity ◽  
Dimensionless Form ◽  
Wood Industry ◽  
Acceptable Error ◽  
General Validity ◽  
Practical Applications ◽  
Air Resistance

Motion of particles with air resistance (e.g. horizontal and inclined throwing) plays an important role in many technological processes in agriculture, wood industry and several other fields. Although, the basic equation of motion of this problem is well known, however, the solutions for practical applications are not sufficient. In this article working diagrams were developed for quick estimation of the throwing distance and the terminal velocity. Approximate solution procedures are presented in closed form with acceptable error. The working diagrams provide with arbitrary initial conditions in dimensionless form of general validity.

scholarly journals Use of the AE Effect to Determine the Stresses State in AAC Masonry Walls under Compression

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3459
Author(s):  
Radosław Jasiński ◽  
Krzysztof Stebel ◽  
Paweł Kielan
Keyword(s):  
Ultrasonic Waves ◽  
Image Correlation ◽  
Masonry Walls ◽  
Acceptable Error ◽  
Compressive Stresses ◽  
Deformation State ◽  
Hydrostatic Stresses ◽  
Stress States ◽  
The Impact ◽  
Masonry Units

Safety and reliability of constructions operated are predicted using the known mechanical properties of materials and geometry of cross-sections, and also the known internal forces. The extensometry technique (electro-resistant tensometers, wire gauges, sensor systems) is a common method applied under laboratory conditions to determine the deformation state of a material. The construction sector rarely uses ultrasonic extensometry with the acoustoelastic (AE) method which is based on the relation between the direction of ultrasonic waves and the direction of normal stresses. It is generally used to identify stress states of machine or vehicles parts, mainly made of steel, characterized by high homogeneity and a lack of inherent internal defects. The AE effect was detected in autoclaved aerated concrete (AAC), which is usually used in masonry units. The acoustoelastic effect was used in the tests described to identify the complex stress state in masonry walls (masonry units) made of AAC. At first, the relationships were determined for mean hydrostatic stresses P and mean compressive stresses σ3 with relation to velocities of the longitudinal ultrasonic wave cp. These stresses were used to determine stresses σ3. The discrete approach was used which consists in analyzing single masonry units. Changes in velocity of longitudinal waves were identified at a test stand to control the stress states of an element tested by the digital image correlation (DIC) technique. The analyses involved density and the impact of moisture content of AAC. Then, the method was verified on nine walls subjected to axial compression and the model was validated with the FEM micromodel. It was demonstrated that mean compressive stresses σ3 and hydrostatic stresses, which were determined for the masonry using the method considered, could be determined even up to ca. 75% of failure stresses at the acceptable error level of 15%. Stresses σ1 parallel to bed joints were calculated using the known mean hydrostatic stresses and mean compressive stresses σ3.

scholarly journals U2-ONet: A Two-Level Nested Octave U-Structure Network with a Multi-Scale Attention Mechanism for Moving Object Segmentation

2020 ◽  
Vol 13 (1) ◽  
pp. 60
Author(s):  
Chenjie Wang ◽  
Chengyuan Li ◽  
Jun Liu ◽  
Bin Luo ◽  
Xin Su ◽  
...  
Keyword(s):  
Moving Objects ◽  
Object Segmentation ◽  
Contextual Information ◽  
Attention Mechanism ◽  
Moving Object ◽  
Feature Maps ◽  
Moving Object Segmentation ◽  
Practical Applications ◽  
Multi Scale ◽  
Spatial Redundancy

Most scenes in practical applications are dynamic scenes containing moving objects, so accurately segmenting moving objects is crucial for many computer vision applications. In order to efficiently segment all the moving objects in the scene, regardless of whether the object has a predefined semantic label, we propose a two-level nested octave U-structure network with a multi-scale attention mechanism, called U2-ONet. U2-ONet takes two RGB frames, the optical flow between these frames, and the instance segmentation of the frames as inputs. Each stage of U2-ONet is filled with the newly designed octave residual U-block (ORSU block) to enhance the ability to obtain more contextual information at different scales while reducing the spatial redundancy of the feature maps. In order to efficiently train the multi-scale deep network, we introduce a hierarchical training supervision strategy that calculates the loss at each level while adding knowledge-matching loss to keep the optimization consistent. The experimental results show that the proposed U2-ONet method can achieve a state-of-the-art performance in several general moving object segmentation datasets.

scholarly journals Stereoscopic PIV measurements using low-cost action cameras

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Theo Käufer ◽  
Jörg König ◽  
Christian Cierpka
Keyword(s):  
Continuous Wave ◽  
Low Cost ◽  
Frame Rate ◽  
Processing Scheme ◽  
Piv Measurements ◽  
Stereoscopic Piv ◽  
Cost Action ◽  
Image Velocimetry ◽  
Frequency Generator ◽  
Educational Applications

Abstract Recently, large progress was made in the development towards low-cost PIV (Particle Image Velocimetry) for industrial and educational applications. This paper presents the use of two low-cost action cameras for stereoscopic planar PIV. A continuous wave laser or alternatively an LED was used for illumination and pulsed by a frequency generator. A slight detuning of the light pulsation and camera frame rate minimizes systematic errors by the rolling shutter effect and allows for the synchronization of both cameras by postprocessing without the need of hardware synchronization. The setup was successfully qualified on a rotating particle pattern in a planar and stereoscopic configuration as well as on the jet of an aquarium pump. Since action cameras are intended to be used at outdoor activities, they are small, very robust and work autarkic. In conjunction with the synchronization and image pre-processing scheme presented herein, those cameras enable stereoscopic PIV in harsh environments and even on moving experiments. Graphic abstract

Geometry Design and Contact Ratio Analysis for Circular Arc Parallel-Axis Helical Gears

2016 ◽  
Author(s):  
Z. Chen ◽  
B. Lei ◽  
Q. Zhao
Keyword(s):  
Rolling Process ◽  
Helical Gear ◽  
Space Curve ◽  
Impact Factors ◽  
Contact Ratio ◽  
Circular Arc ◽  
Practical Applications ◽  
Geometry Design ◽  
Gear Mechanism ◽  
The Impact

Based on space curve meshing theory, in this paper, we present a novel geometric design of a circular arc helical gear mechanism for parallel transmission with convex-concave circular arc profiles. The parameter equations describing the contact curves for both the driving gear and the driven gear were deduced from the space curve meshing equations, and parameter equations for calculating the convex-concave circular arc profiles were established both for internal meshing and external meshing. Furthermore, a formula for the contact ratio was deduced, and the impact factors influencing the contact ratio are discussed. Using the deduced equations, several numerical examples were considered to validate the contact ratio equation. The circular arc helical gear mechanism investigated in this study showed a high gear transmission performance when considering practical applications, such as a pure rolling process, a high contact ratio, and a large comprehensive strength.

Estimation of Residual Stress in Cold Rolled Iron-Disks Using Magnetic and Ultrasonic Methods and Neutron Diffraction Technique

1994 ◽  
Vol 376 ◽  
Author(s):  
V.L. Aksenov ◽  
A.M. Balagurov ◽  
G.D Bokuchava ◽  
J. Schreiber ◽  
Yu.V. Taran Frank
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Sheet Metal ◽  
Diffraction Method ◽  
Calibration Procedure ◽  
Rolled Sheet ◽  
Forming Process ◽  
Practical Applications ◽  
Ultrasonic Methods ◽  
Cold Rolled

ABSTRACTVariation of internal stress states in cold rolled sheet metal can essentially influence the result of forming processes. Therefore it is important to control the forming process by a practicable in line testing method. For this purpose magnetic and ultrasonic nondestructive methods are available. However, it is necessary to calibrate these techniques. This paper describes a first step of such a calibration procedure making use of the neutron diffraction method. On the basis of the diffraction results an assessment of the magnetic and ultrasonic methods for the estimation of residual stress in the cold rolled iron-disks was made. Reasonable measuring concepts for practical applications to forming processes with cold rolled sheet metal are discussed.

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