Study on Vortex Structures and Intermittency in Two-Oscillating Grid Turbulence With Viscoelastic Fluids Based on Wavelet Analysis

2017 ◽  
Author(s):  
Yue Wang ◽  
Yongyao Li ◽  
Weihua Cai ◽  
Lu Wang ◽  
Fengchen Li ◽  
...  
Keyword(s):  
Wavelet Coefficient ◽  
Vortex Structures ◽  
Small Scale ◽  
Grid Turbulence ◽  
Multi Scale ◽  
Frequency Components ◽  
Scale Characteristics ◽  
Cetyltrimethyl Ammonium ◽  
Oscillation Frequencies ◽  
Oscillating Grid

In this paper, two-oscillating grid turbulence with/without viscoelastic additives was performed experimentally by particle image velocimetry. Two classical drag-reducing additives-polymer (Polyacrylamide, PAM) and cationic surfactant (cetyltrimethyl ammonium chloride, CTAC) were chosen. The experiments were carried out under the classical concentration (25ppm) and three different grid oscillation frequencies. Two-dimensional wavelet transform was utilized to investigate multi-scale characteristics of vortex structures and intermittency based on wavelet coefficient. The results showed that at the same decomposition level, the existence of viscoelastic additives attenuates the high-frequency components of fluctuation velocity. The small-scale intermittency is remarkably inhibited by viscoelastic additives especially for scale parameter smaller than 24. Besides, CTAC additives show different effect from PAM additives. Therefore, turbulent drag reduction with additives also happens in two-oscillating grid turbulence without wall effect.

scholarly journals MCSM-Wri: A Small-Scale Motion Recognition Method Using WiFi Based on Multi-Scale Convolutional Neural Network

Sensors ◽  
2019 ◽  
Vol 19 (19) ◽  
pp. 4162
Author(s):  
Ma ◽  
Huang ◽  
Li ◽  
Huang ◽  
Ma ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Recognition System ◽  
Letter Recognition ◽  
Small Scale ◽  
Motion Recognition ◽  
Multi Scale ◽  
Scale Characteristics ◽  
Scale Motion ◽  
Device Free ◽  
Fold Cross Validation

environmental perception technology based onWiFi, and some state-of-the-art techniques haveemerged. The wide application of small-scale motion recognition has aroused people’s concern.Handwritten letter is a kind of small scale motion, and the recognition for small-scale motion basedon WiFi has two characteristics. Small-scale action has little impact on WiFi signals changes inthe environment. The writing trajectories of certain uppercase letters are the same as the writingtrajectories of their corresponding lowercase letters, but they are different in size. These characteristicsbring challenges to small-scale motion recognition. The system for recognizing small-scale motion inmultiple classes with high accuracy urgently needs to be studied. Therefore, we propose MCSM-Wri,a device-free handwritten letter recognition system using WiFi, which leverages channel stateinformation (CSI) values extracted from WiFi packets to recognize handwritten letters, includinguppercase letters and lowercase letters. Firstly, we conducted data preproccessing to provide moreabundant information for recognition. Secondly, we proposed a ten-layers convolutional neuralnetwork (CNN) to solve the problem of the poor recognition due to small impact of small-scaleactions on environmental changes, and it also can solve the problem of identifying actions with thesame trajectory and different sizes by virtue of its multi-scale characteristics. Finally, we collected6240 instances for 52 kinds of handwritten letters from 6 volunteers. There are 3120 instances fromthe lab and 3120 instances are from the utility room. Using 10-fold cross-validation, the accuracyof MCSM-Wri is 95.31%, 96.68%, and 97.70% for the lab, the utility room, and the lab+utility room,respectively. Compared with Wi-Wri and SignFi, we increased the accuracy from 8.96% to 18.13% forrecognizing handwritten letters.

Investigation of Wire Effect in a Wire-Wrapped 37-Pin Fuel Assembly

2015 ◽  
Author(s):  
Jae-Ho Jeong ◽  
Jin Yoo ◽  
Kwi-Lim Lee ◽  
Kwi-Seok Ha
Keyword(s):  
Fuel Assembly ◽  
Relative Position ◽  
Large Scale ◽  
Vortex Structures ◽  
Secondary Flows ◽  
Vortical Flow ◽  
Small Scale ◽  
Multi Scale ◽  
Duct Wall ◽  
The Wire

The wire effect in a wire-wrapped 37-pin fuel assembly mock-up of a Japanese loop-type sodium-cooled fast reactor (SFR), Monju, has been investigated through a numerical analysis using a general-purpose commercial computational fluid dynamics (CFD) code, CFX. Complicated and vortical flow phenomena in the wire-wrapped 37-pin fuel assembly were captured by a Reynolds-Averaged Navier-Stokes (RANS) flow simulation with a shear stress transport (SST) turbulence model. The CFD results show good agreement with Rehme’s friction factor correlation model, which can consider the number of wire-wrapped pins in the fuel assembly. Three-dimensional multi-scale vortex structures start to be formed by an interaction between secondary flows around each wire-wrapped pin. Large-scale and small-scale vortex structures are generated in the corner and edge, and interior sub-channel, respectively. The behavior of the large-scale vortex structures in the corner and edge sub-channel are closely related to the relative position between the hexagonal duct wall and the wire spacer. Regardless of the relative position between the adjacent rod and wire spacer, a small-scale vortex is axially developed in the interior sub-channels. Furthermore, a driving force on each wire spacer surface is closely related to the relative position between the hexagonal duct wall and wire spacer. It is expected that the multi-scale vortex structures in the fuel assembly play a significant role in the convective heat transfer characteristics.

Wavelet analysis on the drag-reducing characteristics of turbulent channel flow with surfactant additive based on experimental data

2017 ◽  
Vol 95 (11) ◽  
pp. 1115-1121 ◽  
Author(s):  
Lu Wang ◽  
Zhi-Ying Zheng ◽  
Jia-Qi Bao ◽  
Tong-Zhou Wei ◽  
Wei-Hua Cai ◽  
...  
Keyword(s):  
Channel Flow ◽  
Coherent Structures ◽  
Turbulent Channel Flow ◽  
Discrete Wavelet ◽  
Two Dimensional ◽  
Solution Flow ◽  
Multi Scale ◽  
Turbulent Channel Flows ◽  
Scale Characteristics ◽  
Cetyltrimethyl Ammonium

Two-dimensional velocity fields for turbulent channel flows of water and 50 ppm CTAC/NaSal (cetyltrimethyl ammonium chloride/sodium salicylate) solution were experimentally obtained by particle image velocimetry. Multi-scale decompositions of the fluctuating velocity signals were performed by two-dimensional binary orthogonal discrete wavelet to analyze the influence of surfactant additives on the multi-scale characteristics of turbulent channel flow. From the results of wavelet multi-scale decompositions, it can be observed that the quantity of coherent structures near the wall in CTAC solution flow is decreased obviously. The results of the flatness factor show that the addition of drag-reducing additives inhibits the intermittency in turbulence. By analyzing the distribution of local intermittence measure and local Reynolds shear measure, it is found that the intermittency mainly concentrates near the wall, and the intermittent region distinctly reduces in CTAC solution flow compared with that in water flow. By combining the analysis of the motion of coherent structures in turbulent channel flow, it is shown that surfactant additives mainly and distinctly impact the coherent structures near the wall, especially in the viscous layer.

scholarly journals Experimental study on two oscillating grid turbulence with viscoelastic fluids based on PIV

2017 ◽  
Vol 95 (12) ◽  
pp. 1271-1277 ◽  
Author(s):  
Yue Wang ◽  
Wei-Hua Cai ◽  
Xin Zheng ◽  
Hong-Na Zhang ◽  
Feng-Chen Li
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Critical Concentration ◽  
Reduction Rate ◽  
Small Scale ◽  
Grid Turbulence ◽  
Viscoelastic Effect ◽  
Oscillating Grid

In this paper, to study the viscoelastic effect on isotropic turbulence without wall effects, a two oscillating grid turbulence is built to investigate this phenomenon using particle image velocimetry. In the experiments, the classical drag-reducing additives are chosen: polyacrylamide (PAM) and cetyltrimethyl ammonium chloride (CTAC), which have shown remarkable drag-reducing effect in wall-bounded turbulent flows. The results show that the existence of drag-reducing additives makes velocity field more anisotropic and reduces turbulent kinetic energy. We propose an intuitive and natural definition for a reduction rate of turbulent kinetic energy to show viscoelastic effect. It suggests that there exists a critical concentration for the reduction rate of turbulent kinetic energy in the CTAC solution case. Also, the small-scale vortex structures are inhibited, which suggests the drag-reducing mechanism in grid turbulence without wall effect.

Scale Characteristics and Effects on Spatial Variability of Soil Available Nutrients

2019 ◽  
Vol 35 (2) ◽  
pp. 221-230
Author(s):  
Gengxing Zhao ◽  
Chao Dong ◽  
Xiaona Chen ◽  
Baowei Su
Keyword(s):  
Spatial Variability ◽  
Spatial Autocorrelation ◽  
Soil Nutrients ◽  
Kriging Interpolation ◽  
Small Scale ◽  
Available Phosphorus ◽  
Multi Scale ◽  
Classical Statistics ◽  
Scale Characteristics ◽  
Patch Density

Abstract.The spatial variability of farmland soil nutrients on different scales is important for farming as it forms the basis for the efficient utilization of soil nutrients and precision fertilization. Survey points were distributed throughout the study area on three different scales (county, field, and block). Research on the scale effect of the spatial variability of available nitrogen (AN), available phosphorus (AP), and available potassium (AK) involved a combination of classical statistics, geostatistics, and Geographic Information System (GIS) techniques. Results indicated that the three kinds of nutrients presented moderate variation intensity on the three scales. All of the nutrients tested exhibited strong spatial autocorrelation, indicating that spatial variability was primarily affected by structural factors, including climate, soil type and topography. As the sampling scale decreased, the nutrients showing weak variation at the large scale exhibited great variation at the small scale; the spatial autocorrelation of these three nutrients first became greater and then weakened; the distance of the spatial autocorrelation shortened gradually. Furthermore, the patch density value of the soil nutrient map increased, which indicated that the distribution of nutrients tended to be more fragile. When combined, sampling methods on the multi-scale allowed us to obtain real and systematic soil information. This study explored scale characteristics and the effects of spatial variability with regards to the primary nutrients available on farmland and provided a theoretical basis to effectively understand the nutrient status of regional farmland and improve the efficacy of soil sampling. Keywords: Multi-scale, Geostatistics, Patch density, Fractal dimension, Kriging interpolation.

scholarly journals A new multi-scale backbone network for object detection based on asymmetric convolutions

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110113
Author(s):  
Xianghua Ma ◽  
Zhenkun Yang
Keyword(s):  
Object Detection ◽  
Image Features ◽  
Detection Accuracy ◽  
Mobile Platforms ◽  
Multi Scale ◽  
Backbone Network ◽  
Aspect Ratios ◽  
Pascal Voc ◽  
Scale Characteristics ◽  
Detection Speed

Real-time object detection on mobile platforms is a crucial but challenging computer vision task. However, it is widely recognized that although the lightweight object detectors have a high detection speed, the detection accuracy is relatively low. In order to improve detecting accuracy, it is beneficial to extract complete multi-scale image features in visual cognitive tasks. Asymmetric convolutions have a useful quality, that is, they have different aspect ratios, which can be used to exact image features of objects, especially objects with multi-scale characteristics. In this paper, we exploit three different asymmetric convolutions in parallel and propose a new multi-scale asymmetric convolution unit, namely MAC block to enhance multi-scale representation ability of CNNs. In addition, MAC block can adaptively merge the features with different scales by allocating learnable weighted parameters to three different asymmetric convolution branches. The proposed MAC blocks can be inserted into the state-of-the-art backbone such as ResNet-50 to form a new multi-scale backbone network of object detectors. To evaluate the performance of MAC block, we conduct experiments on CIFAR-100, PASCAL VOC 2007, PASCAL VOC 2012 and MS COCO 2014 datasets. Experimental results show that the detection precision can be greatly improved while a fast detection speed is guaranteed as well.

scholarly journals Multi-Scale Ionospheric Anomalies Monitoring and Spatio-Temporal Analysis during Intense Storm

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 215
Author(s):  
Na Cheng ◽  
Shuli Song ◽  
Wei Li
Keyword(s):  
Magnetic Storm ◽  
Large Scale ◽  
Temporal Dynamics ◽  
Ionospheric Disturbance ◽  
Ionospheric Scintillation ◽  
Small Scale ◽  
Electron Content ◽  
Total Electron ◽  
Multi Scale ◽  
Intense Storm

The ionosphere is a significant component of the geospace environment. Storm-induced ionospheric anomalies severely affect the performance of Global Navigation Satellite System (GNSS) Positioning, Navigation, and Timing (PNT) and human space activities, e.g., the Earth observation, deep space exploration, and space weather monitoring and prediction. In this study, we present and discuss the multi-scale ionospheric anomalies monitoring over China using the GNSS observations from the Crustal Movement Observation Network of China (CMONOC) during the 2015 St. Patrick’s Day storm. Total Electron Content (TEC), Ionospheric Electron Density (IED), and the ionospheric disturbance index are used to monitor the storm-induced ionospheric anomalies. This study finally reveals the occurrence of the large-scale ionospheric storms and small-scale ionospheric scintillation during the storm. The results show that this magnetic storm was accompanied by a positive phase and a negative phase ionospheric storm. At the beginning of the main phase of the magnetic storm, both TEC and IED were significantly enhanced. There was long-duration depletion in the topside ionospheric TEC during the recovery phase of the storm. This study also reveals the response and variations in regional ionosphere scintillation. The Rate of the TEC Index (ROTI) was exploited to investigate the ionospheric scintillation and compared with the temporal dynamics of vertical TEC. The analysis of the ROTI proved these storm-induced TEC depletions, which suppressed the occurrence of the ionospheric scintillation. To improve the spatial resolution for ionospheric anomalies monitoring, the regional Three-Dimensional (3D) ionospheric model is reconstructed by the Computerized Ionospheric Tomography (CIT) technique. The spatial-temporal dynamics of ionospheric anomalies during the severe geomagnetic storm was reflected in detail. The IED varied with latitude and altitude dramatically; the maximum IED decreased, and the area where IEDs were maximum moved southward.

Multi-scale characteristics of remote sensing lineaments

2019 ◽  
Vol 13 (2) ◽  
pp. 287-297
Author(s):  
Junlong Xu ◽  
Xingping Wen ◽  
Haonan Zhang ◽  
Dayou Luo ◽  
Lianglong Xu ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Multi Scale ◽  
Scale Characteristics
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