• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1088-1099
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• 2021

Time-frequency analysis technique is an effective analysis tool for non-stationary processes. In the field of reactor neutron noise, the time-frequency analysis method has not been thoroughly researched and widely used. This work has studied the time-frequency analysis of the reactor neutron noise experimental signals under bubble disturbance and control rod vibration. First, an experimental platform was established, and it could be employed to reactor neutron noise experiment and data acquisition. Secondly, two types of reactor neutron noise experiments were performed, and valid experimental data was obtained. Finally, time-frequency analysis was conducted on the experimental data, and effective analysis results were obtained in the low-frequency part. Through this work, it can be concluded that the time-frequency analysis technique can effectively investigate the core dynamics behavior and deepen the identification of the unstable core process.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.1736-1746
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• 2021

The results of full-scale numerical experiments of a hybrid thorium-containing fuel cell facility operating in a close-to-critical state due to a controlled source of fusion neutrons are discussed in this work. The facility under study was a complex consisting of two blocks. The first block was based on the concept of a high-temperature gas-cooled thorium reactor core. The second block was an axially symmetrical extended plasma generator of additional neutrons that was placed in the near-axial zone of the facility blanket. The calculated models of the blanket and the plasma generator of D-T neutrons created within the work allowed for research of the neutronic parameters of the facility in stationary and pulse-periodic operation modes. This research will make it possible to construct a safe facility and investigate the properties of thorium fuel, which can be continuously used in the epithermal spectrum of the considered hybrid fusion-fission reactor.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.36.3-37
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• 2015

4C39.25 (0923+392) is a distant radio loud AGN placed at redshift 0.695. The motivation of our work is peculiar properties 4C39.25. Firstly, it has a conspicuous distinction of jet direction between kilo-parsec scale observation made by VLA (Kollgaard et al. 1990) and the parsec scale observation by VLBA (Kellermann et al. 1998). This might indicate episodic-jet activity which recently turned on. This object currently shows two stationary compact parsec-scale components which are bright jet component on east and less luminous core on west. Also, it is known that there have been superluminal jet components which are flowing from the core toward east, and then merging with the bright jet component (Marscher et al. 1991, Alberdi et al. 2000, Lister et al. 2013). Although 4C39.25 seems to be a blazar-like source having broad emission lines (SDSS) and superluminal motion, its property that jet component is brighter than the core is different from ordinary blazars. Furthermore, it has young radio galaxy-like properties such as non-variation in total flux (Alberdi et al. 1997, 2000, MOJAVE database) and high frequency peak at spectral energy distribution (Orienti et al 2007). Such complex properties led us to make recent observations to reveal precise properties and new changes of the source. We used Korean VLBI Network (KVN) and VLBI Exploration of Radio Astronomy (VERA) Array (KaVA) which provide high-frequency (23GHz and 43GHz) and high spatial resolution (1.2mas and 0.6mas). Therefore, this system is suitable for morphological and physical research on parsec scale structure. We present results for several epochs observed during 2013 to 2014, mainly focusing on morphological changes of 4C39.25 using KaVA images.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.876-881
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• 2004

In this study, A special quality analysis and experiment for low power consumption type pneumatic on-off micro valve was performed. And flow characteristics of the micro valve by stroke change was numerically investigated. As a result, it is shown that magnetic force(2.4N) is exerted enough to move poppet with 0.3mm stroke with 0.01 seconds of response time, and that there is no magnetic force emitted by yoke. Under the condition of poppet stroke smaller than about 0.8mm, dynamic pressure acts to poppet wall up to supply pressure level. But, that is decreasing to 40% when poppet stroke is 0.8mm.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.2
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• pp.39-46
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• 2004

Modern users demand that the on and off type solenoid actuator should be smaller, lighter in weight, lower in consumption power, and higher in response time. The complete design satisfying such requirements can be achieved when electromagnetic theories and empirical knowledge are combined. This paper presents various types of empirical coefficients essentially needed for optimal design of a solenoid actuator. The values of these empirical coefficients are obtained through extensive experiments over a great length of time for various kinds of solenoid actuators. We have developed a design program that is composed by combination of governing equations and empirical coefficients, and have also manufactured a prototype solenoid actuator based on the final results of the design program. The propriety of the design program and empirical coefficients have been proven by experiments.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.223-226
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• 2003

In this paper, we propose new agent discovery and route discovery schemes to support Mobile IP (MIP) in Ad Hoc networks with wireless backbone. The wireless backbone consisting of stationary wireless routers and Internet gateways (IGs) is a kind of wireless access network of IP-based core network. The proposed scheme utilizes favorable features of wireless backbone such as stable links and no energy constraints. In the agent discovery scheme, backbone-limited periodic Agent Advertisement (AA) and proxy-AA messages are used, which reduce network-wide broadcasting overhead caused by AA and Agent Solicitation messages and decentralize MIP processing overhead in IGs. In order to reduce delay time and control message overhead during route discovery far the destination outside Ad Hoc network, we propose a cache-based scheme which can be easily added to the conventional on-demand routing protocols. The proposed schemes can reduce control overhead during agent discovery and route discovery, and efficiently support MIP in Ad Hoc network with wireless backbone.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.190-195
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• 2004

An exhaust brake system is composed of a gate valve, a pneumatic cylinder and an on-off solenoid valve. An on-off solenoid valve which is a key component of the exhaust brake system ought to have characteristics such as high reliability and long life for reducing the foot brake and tires damage, and for driver's fatigue relief of middle/large size vehicles running a long distance. In this paper, an on-off solenoid valve which is used for vehicle brake system was studied. For the performance evaluation of the on-off solenoid, electromagnetic characteristics and dynamic characteristics are analyzed. On the basic study for the performance improvement of exhaust brake system, pneumatic circuit and pneumatic valve of on-off solenoid type were suggested and the performance of pneumatic valve through the test procedure was evaluated.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.11
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• pp.874-882
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• 2003

The condition assessment of engineering systems has increased in importance because the manpower needed to operate and supervise various plants has been reduced. Especially, induction motors are at the core of most engineering processes, and there is an indispensable need to monitor their health and performance. So detection and diagnosis of motor faults is a base to improve efficiency of the industrial plant. In this paper, a model-based fault detection system is developed for induction motors, using steady state vibration signals. Early various fault detection systems using vibration signals are a trivial method and those methods are prone to have missed fault or false alarms. The suggested motor fault detection system was developed using a model-based reference value. The stationary signal had been extracted from the non-stationary signal using a data segmentation method. The signal processing method applied in this research is FFT. A reference model with spectra signal is developed and then the residuals of the vibration signal are generated. The ratio of RMS values of vibration residuals is proposed as a fault indicator for detecting faults. The developed fault detection system is tested on 800 hp motor and it is shown to be effective for detecting faults in the air-gap eccentricities and broken rotor bars. The suggested system is shown to be effective for reducing missed faults and false alarms. Moreover, the suggested system has advantages in the automation of fault detection algorithms in a random signal system, and the reference model is not complicated.

• Structural Engineering and Mechanics
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• v.56 no.6
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• pp.959-982
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• 2015

In this study, a non-stationary random earthquake Clough-Penzien model is used to describe earthquake ground motion. Using stochastic direct integration in combination with an equivalent linear method, a solution is established to describe the non-stationary response of lead-rubber bearing (LRB) system to a stochastic earthquake. Two parameters are used to develop an optimization method for bearing design: the post-yielding stiffness and the normalized yield strength of the isolation bearing. Using the minimization of the maximum energy response level of the upper structure subjected to an earthquake as an objective function, and with the constraints that the bearing failure probability is no more than 5% and the second shape factor of the bearing is less than 5, a calculation method for the two optimal design parameters is presented. In this optimization process, the radial basis function (RBF) response surface was applied, instead of the implicit objective function and constraints, and a sequential quadratic programming (SQP) algorithm was used to solve the optimization problems. By considering the uncertainties of the structural parameters and seismic ground motion input parameters for the optimization of the bearing design, convex set models (such as the interval model and ellipsoidal model) are used to describe the uncertainty parameters. Subsequently, the optimal bearing design parameters were expanded at their median values into first-order Taylor series expansions, and then, the Lagrange multipliers method was used to determine the upper and lower boundaries of the parameters. Moreover, using a calculation example, the impacts of site soil parameters, such as input peak ground acceleration, bearing diameter and rubber shore hardness on the optimization parameters, are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.687-692
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• 2015

A mold design for in-mold coating was developed to achieve simultaneous coating and injection molding of an automotive armrest. The developed mold includes one core and two cavities which are composed of a substrate cavity and a coating cavity. The core was attached to a movable plate and two cavities were mounted on a plate sliding in a stationary plate. In a two-step process, the part was first injection molded and subsequently, with the aid of a sliding table, was transferred to a second cavity. The materials used were PC/ABS for substrate and two-component polyurethane for coating. The experiments were conducted by changing the flow rate to investigate mixing characteristics. As the flow rate increased, the mixing improved. Additionally, the bubbles appeared over the substrate surface decreased with an increase of the weight of injected coating material.