• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권2호
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• pp.391-411
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• 2023

Aggregates play the skeleton and supporting role in the construction field, high-precision measurement and high-efficiency analysis of aggregates are frequently employed to evaluate the project quality. Aiming at the unbalanced operation time and segmentation accuracy for multi-class segmentation algorithms of aggregate images, a Chaotic Sparrow Search Algorithm (CSSA) is put forward to optimize it. In this algorithm, the chaotic map is combined with the sinusoidal dynamic weight and the elite mutation strategies; and it is firstly proposed to promote the SSA's optimization accuracy and stability without reducing the SSA's speed. The CSSA is utilized to optimize the popular multi-class segmentation algorithm-Multiple Entropy Thresholding (MET). By taking three METs as objective functions, i.e., Kapur Entropy, Minimum-cross Entropy and Renyi Entropy, the CSSA is implemented to quickly and automatically calculate the extreme value of the function and get the corresponding correct thresholds. The image adaptive multi-class segmentation model is called CSSA-MET. In order to comprehensively evaluate it, a new parameter I based on the segmentation accuracy and processing speed is constructed. The results reveal that the CSSA outperforms the other seven methods of optimization performance, as well as the quality evaluation of aggregate images segmented by the CSSA-MET, and the speed and accuracy are balanced. In particular, the highest I value can be obtained when the CSSA is applied to optimize the Renyi Entropy, which indicates that this combination is more suitable for segmenting the aggregate images.

• 한국추진공학회지
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• 제4권4호
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• pp.18-25
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• 2000

유동장의 2차원 평면 속도 분포를 측정하기 위하여 two-color PIV 기법을 개발하였고, 마하 2.0 초음속 노즐에 적용하여 보았다 이 기법은 single-color PIV 기법과 유사하나 서로 다른 색의 두 레이저 빔을 사용하여 방향성의 문제를 해결하는 차이점을 갖는다. 녹색의 레이저 평면광 (532 nm)과 적색의 레이저 평면광 (619 nm)이 주입된 입자를 조사하기 위하여 사용되었고, 입자 위치가 고해상도 (3060${\times}$2036) 디지털 칼라 CCD 카메라에 기록되었다. 이러한 디지털 칼라 CCD 카메라론 이용한 two-color PIV 시스템은 사진 필름 현상 시간과 이에 따른 디지털화하는 시간 그리고 방향성의 문제론 해결하기 위해 사용되는 일반적인 image shifting 기법과 관련된 어려움을 제거해 준다. 또한 고속 유동장에서는 알맞은 입자 밀도의 주입이 어려워지는데, two-color PIV는 높은 신호 대 잡음비로 인하여 속도 벡터론 얻기 위해서 조사영역에 존재해야 하는 벡터쌍의 수가 줄어들게 된다. 따라서 다른 색의 두레이저 빔의 시간 간격을 조절함으로써 고속 유동장의 속도 분포를 쉽고 정확하게 측정할 수 있게 된다. 마하 2.0 초음속 노즐에서의 속도 분포가 측정되었으며, 속도장으로부터 변형률장을 구하여 과팽창 충격파 구조를 예측해 보았다. Two-color PIV에 의해 얻어진 속도 분포와 충격파의 위치 결과는 schlieren 사진과 비교 분석해 보았다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.901-905
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• 2005

Monte Carlo localization is known to be one of the most reliable methods for pose estimation of a mobile robot. Much research has been done to improve performance of MCL so far. Although MCL is capable of estimating the robot pose even for a completely unknown initial pose in the known environment, it takes considerable time to give an initial estimate because the number of random samples is usually very large especially for a large-scale environment. For practical implementation of the MCL, therefore, a reduction in sample size is desirable. This paper presents a novel approach to reducing the number of samples used in the particle filter for efficient implementation of MCL. To this end, the topological information generated off- line using a thinning method, which is commonly used in image processing, is employed. The topological map is first created from the given grid map for the environment. The robot scans the local environment using a laser rangefinder and generates a local topological map. The robot then navigates only on this local topological edge, which is likely to be the same as the one obtained off- line from the given grid map. Random samples are drawn near the off-line topological edge instead of being taken with uniform distribution, since the robot traverses along the edge. In this way, the sample size required for MCL can be drastically reduced, thus leading to reduced initial operation time. Experimental results using the proposed method show that the number of samples can be reduced considerably, and the time required for robot pose estimation can also be substantially decreased.

• 한국분무공학회지
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• 제10권1호
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• pp.17-23
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• 2005

Even though a relatively complete knowledge base has been established for diesel sprays, much of the knowledge cannot be directly translated to correlate the characteristics of gasoline spray. The macroscopic characteristics of gasoline impingement spray was investigated with photographic and image processing technique by Particle Motion Analysis System. The injector with single hole nozzle diameter of 0.28 mm was used in this experiment and the injection duration was selected as 10 msec. The injection pressure with 0.3, 0.35, and 0.4 MPa, impingement distance or 70, 100 and 130m, impingement angle or 0.15, 30 and $45^{\circ}$ were employed for the variables to affect the spray characteristics of impinging spray. It is clear that there is the analogy on the spray tip penetration between the gasoline impinging jet and diesel free jet. The spray tip penetration of impinging gasoline spray is proportional to the quarter power of the time after start of injection. The maximum height of impinging gasoline spray is also proportional to the quarter power of the time regardless of impingement distance, impingement angle and injection pressure. In addition, the effect of impingement angle on the spray tip penetration is significant according to the time after start of injection, even though there is minor effect in the initial stage of time after start of injection. Moreover, there is no remarkable effect of injection pressure on the spray tip Penetration under the experimental condition used in this study.

• 한국분무공학회지
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• 제1권1호
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• pp.63-75
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• 1996

The purpose of this study is to investigate the break-up characteristics by taking advantage of a two-phase coaxial nozzle. Air and water are utilized as working fluids and the mass ratio air/water has been controlled to characterize the atomization, diffusion and development of mixing process. By way of a photographic technique, conventional developing structures and diffusion angles have been analyzed systematically with variations of mass ratios. The turbulent flow components of the atomized particles were measured by a two channel LDV system and the data were treated by an on-lined measurement equipment. According to the photographic results the spreading angles decreased because the axial inertia moment was relatively higher than the lateral one with respect to the increase of mass ratio. It is found the jet flow diffuses linearly in a certain limit region while the atomizing characteristics, in terms of the distributions of particle diameters did not show particular differences. It may be expected that these fundamental results can be used as reference data in studying the atomization, breakup and diffusions.

• 대한기계학회논문집B
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• 제23권1호
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• pp.123-130
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• 1999

The objective of the current study is to understand steady 3-dimensional flow phenomena in a bifurcated duct experimentally. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. The gray level cross-correlation method is applied to the image processing algorithm. The subpixel and the area interpolation methods are used to obtain the final velocity vectors. The finite volume predictions are used to analyze the flow patterns in the bifurcation model. The results of the computer simulation and the PIV experiment for three-dimensional flow show the recirculation zone and the formation of the paired secondary flow distal to the apex of the bifurcation model. The results obtained with the two methods also show that the branch flow strongly strikes the inner wall due to the inertial effect and accompanied helical motion as it flows toward the outer wall.

• 전기학회논문지
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• 제65권6호
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• pp.1060-1069
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• 2016

In this paper, we introduce the fingerprint recognition system based on Radial Basis Function Neural Network(RBFNN). Fingerprints are classified as four types(Whole, Arch, Right roof, Left roof). The preprocessing methods such as fast fourier transform, normalization, calculation of ridge's direction, filtering with gabor filter, binarization and rotation algorithm, are used in order to extract the features on fingerprint images and then those features are considered as the inputs of the network. RBFNN uses Fuzzy C-Means(FCM) clustering in the hidden layer and polynomial functions such as linear, quadratic, and modified quadratic are defined as connection weights of the network. Particle Swarm Optimization (PSO) algorithm optimizes a number of essential parameters needed to improve the accuracy of RBFNN. Those optimized parameters include the number of clusters and the fuzzification coefficient used in the FCM algorithm, and the orders of polynomial of networks. The performance evaluation of the proposed fingerprint recognition system is illustrated with the use of fingerprint data sets that are collected through Anguli program.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.765-768
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• 2003

The objective of the present study was to visualize the pulsatile flow field in a branching model by using the high-resolution PIV system. A bifurcated flow system was built for the experiments in the pulsatile flow. Harvard pulsatile pump was used to generate the pulsatile velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow fields. Two consecutive particle images at several cross sections of the flow filed were captured by the CCD cameras ($1K{\ast}1K$ and $640{\ast}480$). The results after the image processing clearly showed the recirculation zones and the formation of the paired secondary flows from the distal to the apex in the bifurcated model. The results also indicated that the flow velocities in the inner wall moved faster than those in the outer wall due to the inertial force effects and the helical motions generated in the branch flows as the flow proceeded toward the outer wall. While the PIV images from the $1K{\ast}1K$ camera were closer to the simulation results thantheimagesfromthe640${\ast}$480camera,bothresultsofthePIVexperimentsusingthetwocamerasgenerallyagreed quitewellwiththeresultsfromthenumericalsimulation.

• 제어로봇시스템학회논문지
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• 제12권5호
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• pp.450-456
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• 2006

Monte Carlo localization is known to be one of the most reliable methods for pose estimation of a mobile robot. Although MCL is capable of estimating the robot pose even for a completely unknown initial pose in the known environment, it takes considerable time to give an initial pose estimate because the number of random samples is usually very large especially for a large-scale environment. For practical implementation of MCL, therefore, a reduction in sample size is desirable. This paper presents a novel approach to reducing the number of samples used in the particle filter for efficient implementation of MCL. To this end, the topological information generated through the thinning technique, which is commonly used in image processing, is employed. The global topological map is first created from the given grid map for the environment. The robot then scans the local environment using a laser rangefinder and generates a local topological map. The robot then navigates only on this local topological edge, which is likely to be similar to the one obtained off-line from the given grid map. Random samples are drawn near the topological edge instead of being taken with uniform distribution all over the environment, since the robot traverses along the edge. Experimental results using the proposed method show that the number of samples can be reduced considerably, and the time required for robot pose estimation can also be substantially decreased without adverse effects on the performance of MCL.

• 대한금속재료학회지
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• 제49권11호
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• pp.868-873
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• 2011

In this study, the fabrication of ultra fine grained Mo bulk was conducted. $MoO_3$ nanopowders were prepared by a high energy ball-milling process and then reduced at the temperature of $800^{\circ}C$ without holding time in $H_2$ atmosphere. The particle size of Mo nanopowder was ~150 nm and grain size was ~40 nm. The two-step process was employed for the sintering of Mo nanopowder to obtain fine grain size. The densification over 90% could be obtained by the two-step sintering with a grain size of less than 660 nm. For higher density, modified two-step sintering was designed. 95% of theoretical density with the grain size of 730 nm was obtained by the modified two-step sintering.