• Journal of Korean Society of Environmental Engineers
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• v.37 no.11
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• pp.607-618
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• 2015

This study was conducted to suggest hydraulic modification for improving evenness of inlet flow distribution into side stream type low-pressure MF (microfiltration) module using CFD (computational fluid dynamics) simulation and PIV (particle image velocimetry) techniques. From the results of CFD simulation for various typed inlet structure, it was investigated that installing internal orifice baffle in inlet the distribution channel could improve the evenness of inlet flow distribution over about 40%. Also, from the results of PIV measurements which were carried out for verifying the CFD simulation, it was observed that the momentum of the water body coming from the opposite side of the inlet was relatively larger. This momentum would generate strong shear force in the near of inlet side wall. On the other hands, occurrence of dead zone and eddy flow was confirmed in the opposite side.

• The Journal of the Korea Contents Association
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• v.6 no.8
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• pp.78-85
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• 2006

This study examined the stock return co-movement among Korean digital contents industry, American NASDAQ, and Japanese NIKKEI225. This is to identify the reaction of Korean digital contents industry on the movement of foreign stock market. To investigate the co-movements, during the period of 1999 to 2005, daily logarithm difference returns of each stock market indices are tested by the methodology of Granger(1963, 1969)'s causality test. The positive influence from NASDAQ index to Korean digital contents industry index are found, but not vice versa. It means that the market value of firms in Korean digital contents industry affected by the movement of American NASDAQ market which composite with digital IT firms. However, the co-movements with NIKKEI225 did not found.

• Journal of Korean Society of Transportation
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• v.26 no.5
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• pp.51-62
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• 2008

An innovative feature of this study is to propose a methodology for evaluating safety performance in real time based on vehicle trajectory data extracted from video images. The essence of evaluating safety performance is to capture unsafe car-following and lane-changing events generated by individual vehicles traveling within video surveillance area. The proposed methodology derived three indices including real-time safety index(RSI) based on the concept of safe stopping distance, time-to-collision(TTC), and the collision energy based on the conservation of momentum. It is believed that outcomes would be greatly utilized in developing a new generation of video images processing(VIP) based traffic detection systems capable of producing safety performance measurements. Relevant technical challenges for such detection systems are also discussed.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.1
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• pp.28-39
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• 2003

Effects of the orifice internal flow such as cavitation and hydraulic flip on transverse injection into subsonic crossflows have been studied. The liquid column breakup length and the liquid column trajectory were measured by changing the orifice diameter (d), the orifice length/orifice diameter (L/d), the injection pressure and the shapes (sharp and round) of orifice entrance, and were compared with previous results. It is found that cavitation bubbles, which occur inside the sharp-edged orifice, make the liquid jet very turbulent and especially in the orifices with L/d ＝ 5 hydraulic flip appear as cavitation bubbles are emitted from the orifice. The breakup length is shorter as cavitation bubbles grows and hydraulic flip appears. However, the liquid column trajectories normalized by the effective diameter and the effective momentum ratio have a similar tendency irrespective of cavitation and hydraulic flip.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.4
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• pp.402-410
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• 2004

In this paper, an optimal design method of clonal selection based Fuzzy-Neural Networks (FNN) model for complex and nonlinear systems is presented. The FNNs use the simplified inference as fuzzy inference method and Error Back Propagation Algorithm as learning rule. Also Advanced Clonal Selection (ACS) is proposed to find the parameters such as parameters of membership functions, learning rates and momentum coefficients. The proposed method is based on an Immune Algorithm (IA) using biological Immune System and The performance is improved by control of differentiation rate. Through that procedure, the antibodies are producted variously and the parameter of FNN are optimized by selecting method of antibody with the best affinity against antigens such as object function and limitation condition. To evaluate the performance of the proposed method, we use the time series data for gas furnace and traffic route choice process.

• Journal of the Korean Institute of Intelligent Systems
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• v.5 no.4
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• pp.41-55
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• 1995

In this paper, an optimal idenfication method using fuzzy-neural networks is proposed for modeling of nonlinear complex systems. The proposed fuzzy-neural modeling implements system structure and parameter identification using the intelligent schemes together wlth optimization theory, linguistic fuzzy implication rules, and neural networks(NNs) from input and output data of processes. Inference type for this fuzzy-neural modeling is presented as simplified inference. To obtain optimal model, the learning rates and momentum coefficients of fuzzy-neural networks(FNNs) are tuned automatically using improved modified complex method and modified learning algorithm. For the purpose of its application to nonlinear processes, data for route choice of traffic problems and those for activateti sluge process of sewage treatment system are used for the purpose of evaluating the performance of the proposed fuzzy-neural network modeling. The results show that the proposed method can produce the intelligence model with higher accuracy than other works achieved previously.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.495-501
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• 2012

Spray characteristics of liquid jets in crossflow, which can be observed in the liquid jet injection system of a gas turbine or ramjet engine, were experimentally investigated. By measuring liquid jet penetration in the case of single orifice and double orifice injectors, the experimental formula for jet penetration was modified to consider penetration distances greater than that considered in a previous study. The changes in spray characteristics resulting from changes in the liquid jet and crossflow pressure, including SMD and jet disintegration, were carefully studied. Specifically, the jet penetration was measured for different injector shapes, and in the case of a double orifice injector, the penetration of the rear orifice jet was found to be greater by approximately 20% ($L_h$ = 4 mm) compared to that in the case of a single orifice injector because of the influence of the front orifice.

• KIPS Transactions on Software and Data Engineering
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• v.3 no.6
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• pp.231-236
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• 2014

The transit time of contrast agents and the parameters of time-intensity curves in ultrasonography are important factors to diagnose various diseases of a digestive organ. We have implemented an automatic parametric imaging method to overcome the difficulty of the diagnosis by naked eyes. However, the micro-bubble noise and the respiratory motions may degrade the reliability of the parameter images. In this paper, we introduce an optimization technique based on MRF(Markov Random Field) model to enhance the quality of the parameter images, and present an image tracking algorithm to compensate the image distortion by respiratory motions. A method to extract the respiration periods from the ultrasound image sequence has been developed. We have implemented the ROI(Region of Interest) tracking algorithm using the dynamic weights and a momentum factor based on these periods. An energy function is defined for the Gibbs sampler of the image enhancement method. Through the experiments using the data to diagnose liver lesions, we have shown that the proposed method improves the quality of the parametric images.

• KIPS Transactions on Software and Data Engineering
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• v.9 no.2
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• pp.69-76
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• 2020

In this paper, we introduce a method to visualize the contrast diffusion patterns and the dynamic vascular patterns in a contrast-enhanced ultrasound image sequence. We present an imaging technique to visualize parameters such as contrast arrival time, peak intensity time, and contrast decay time in contrast-enhanced ultrasound data. The contrast flow pattern and its velocity are important for characterizing focal liver lesions. We propose a method for representing the contrast diffusion patterns as an image. In the methods, respiratory motion may degrade the accuracy of the parametric images. Therefore, we present a respiratory motion tracking technique that uses dynamic weights and a momentum factor with respect to the respiration cycle. Through the experiment using 72 CEUS data sets, we show that the proposed method makes it possible to overcome the limitation of analysis by the naked eye and improves the reliability of the parametric images by compensating for respiratory motion in contrast-enhanced ultrasonography.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.6
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• pp.466-473
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• 2011

The buoyancy and initial momentum fluxes make near-field dominated by buoyant jet when thermal discharge releases underwater. In order to estimate prediction capabilities of those near-field phenomena, non-hydrostatic RANS applied CFD(Computational Fluid Dynamic) model was used. Condition of model was composed based on past laboratory experiments. Numerical simulations carried out for the horizontal buoyant jet in the stagnant flow and vertical buoyant jet into crossflow. The results of simulation are compared with the terms of trajectory and dilution rate of laboratory experiments and analytic model(CorJET) results. CFD model showed a good agreement with them. CFD model can be appropriate for assessment of submerged thermal discharge effect because CFD model can resolve the limitations of near-field analytic model and far-field quasi 3D hydrodynamic model. The accuracy and capability of the CFD model is reviewed in this study. If the computational efficiency get improved, CFD model can be widely applied for simulation of transport and diffusion of submerged thermal discharge.