• Steel and Composite Structures
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• v.35 no.6
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• pp.799-813
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• 2020

Fatigue cracks of rib-to-deck (RD) joints have been frequently observed in the orthotropic steel decks (OSD) using conventional U-ribs (CU). Thickened edge U-rib (TEU) is proposed to enhance the fatigue strength of RD joints, and its effectiveness has been proved through fatigue tests. In-depth full-scale tests are further carried out to investigate both the fatigue strength and fractography of RD joints. Based on the test result, the mean fatigue strength of TEU specimens is 21% and 17% higher than that of CU specimens in terms of nominal and hot spot stress, respectively. Meanwhile, the development of fatigue cracks has been measured using the strain gauges installed along the welded joint. It is found that such the crack remains almost in semi-elliptical shape during the initiation and propagation. For the further application of TEUs, the design curve under the specific survival rate is required for the RD joints using TEUs. Since the fatigue strength of welded joints is highly scattered, the design curves derived by using the limited test data only are not reliable enough to be used as the reference. On this ground, an experiment-numerical hybrid approach is employed. Basing on the fatigue test, a probabilistic assessment model has been established to predict the fatigue strength of RD joints. In the model, the randomness in material properties, initial flaws and local geometries has been taken into consideration. The multiple-site initiation and coalescence of fatigue cracks are also considered to improve the accuracy. Validation of the model has been rigorously conducted using the test data. By extending the validated model, large-scale databases of fatigue life could be generated in a short period. Through the regression analysis on the generated database, design curves of the RD joint have been derived under the 95% survival rate. As the result, FAT 85 and FAT 110 curves with the power index m of 2.89 are recommended in the fatigue evaluation on the RD joint using TEUs in terms of nominal stress and hot spot stress respectively. Meanwhile, FAT 70 and FAT 90 curves with m of 2.92 are suggested in the evaluation on the RD joint using CUs in terms of nominal stress and hot spot stress, respectively.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.2
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• pp.150-157
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• 2006

Spatially resolved remote identification and quantification of trace gases in the atmosphere is desirable in various fields of scientific research as well as in public security and industrial contexts. Environmental observations investigating causes, extent md consequences of air pollution are of fundamental interest. We present an Imaging-DOAS system, a ground based remote sensing instrument that allows spatially resolved mapping of atmospheric trace gases by a differential optical absorption spectroscopy(DOAS) with sun scattered light as the light source. A passive DOAS technique permits the identification and quantification of various gases, e.g., $NO_2,\;SO_2,\;and\;CH_2O$, from their differential absorption structures with high sensitivity. The Imaging-DOAS system consists of a scanning mirror, a focusing lens, a spectrometer, a 2-D CCD, ad the integral control software. An imaging spectrometer simultaneously acquires spectral information on the incident light in one spatial dimension(column) and sequentially scans the next spatial dimension with a motorized scanning mirror. The structure of the signal acquisition system is described in detail and the evaluation method is also briefly discussed. Applications of imaging of the $NO_2$ contents in the exhaust plumes from a power plant are presented.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.8
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• pp.2983-2988
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• 2010

The train control system used in Gyeongbu-line is classified in ATC, IXL and CTC. Domestic railway signaling systems are being developed by electrification. In these systems the electrification of interlocking reaches 57% and the safety equipments of railway crossings in trackside devices have completed their development into an integrated system. Block systems of all the existing sections have not yet electrified and integrated so that they need a number of complement in terms of construction and maintenance. For ABS currently used in existing domestic lines, and LEU being installed in Gyeongbu and Honam lines, although a train is controlled by the signaling information of the same train in the same location, the system is separately installed so that the same information is separately divided and transmitted at the each distinct system. Therefore, in the conventional ABS and LEU, there are a lot of duplicate installed compartments such as lamp detection and a power supply unit. Hence, we have a lot of problems: for maintenance, a lot of manpower and costs need to be invested and the overall manufacturing costs get higher, as well as the construction costs by duplicate. Therefore, this paper suggest design to develop an integrated electronic Block Control Unit by the integration of the currently used ABS, and communication and electronic technology. We are to monitor and manage the block systems in the corresponding station by integrating. And we are to transmit information together with LEU, which is an ATS wayside transmitter.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.254-260
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• 1999

Meteor Burst Communication can provide effective and economical means of communication where long distance VHF NLOS data transmission is needed; often ranges more than 1000 km. It has been, however, so far considered unsuitable for short distance application because of phenomenal decrease in burst durations, which leads to decreation of total duty rate of the system. This paper extensively analyzes characteristics of shot distance MB(Meteor Burst) path and shows the low duty rate may be improved by increasing burst rate through adapting antenna beam width to cover entire hot-spot region in the space and, by compensating effective burst length through cutting down man-made noises introduced by antenna. Based on the analysis, we are developed a small-opening-cavity antenna, especially designed for short distance MB path. In operation, the antenna is to be buried under ground surface so as to improve directivity and reduces noise introduction. The antenna exhibits power gain of 3 dB with 90 degree beam width and thus enables to illuminate entire hot-spot regions with the elevation angle of 8-90 degree which is the case of transmission less than 100 km. Directivity horizontal to earth surface is suppressed to minimum which enables to cut man-made noises from near-by sources down to more than 3 dB from the level reported with conventional 4 element Yagi. A series of experiments performed on 100 km MB paths have conformed that, with the antenna installed at receiving site, the burst rate and duration time have been noticed to increase by 10 and 20 percent respectively from the values obtained by conventional 4-element Yagi antenna under same testing condition.

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.554-560
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• 2017

Accurate altimetry is required for the reliable flight control of drones or unmanned air vehicles (UAVs), and the radar altimeter is commonly used owing to its accuracy for the ground level. Due to the limitation for size, weight and power consumption, the frequency modulated continuous wave (FMCW) radar is appropriate for drone because it has lower complexity than that of pulse Doppler (PD) radar. Especially, fast-ramp FMCW radar, which transmits linear FM signal during very short period, is generally utilized, because it is robust for the ego-motion of drone. Therefore, we present the design and implementation results of the radar signal processor (RSP) for fast-ramp FMCW radar system. The proposed RSP was designed with Verilog-HDL and implemented with Altera Cyclone-IV FPGA device. Implementation results show that the proposed RSP includes 27,523 logic elements, 15,798 registers and memory of 138Kbits and can measure the altimeter at the rate of 100Hz with the operating frequency of 50MHz.

• KIPS Transactions on Software and Data Engineering
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• v.6 no.9
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• pp.429-436
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• 2017

Unmanned Aerial Vehicles (UAV) that are piloted without human pilots can be commanded remotely via frequencies or perform pre-inputted missions. UAVs have been mainly used for military purposes, but due to the development of ICT technology, they are now widely used in the private sector. Teal Group's 2014 World UAV Forecast predicts that the UAV market will grow by 10% annually over the next decade, reaching $ 12.5 billion by 2023. However, because UAVs are primarily remotely controlled, if a malicious user accesses a remotely controlled UAV, it could seriously infringe privacy and cause financial loss or even loss of life. To solve this problem, a secure channel must be established through mutual authentication between the UAV and the control center. However, existing security techniques require a lot of computing resources and power, and because communication distances, infrastructure, and data flow are different from UAV networks, it is unsuitable for application in UAV environments. To resolve this problem, the study presents a lightweight UAV authentication method based on Physical Unclonable Functions (PUFs) that requires less computing resources in the ground Control and Non-Payload Communication (CNPC) environment, where recently, technology standardization is actively under progress.

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.483-490
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• 2003

We have analyzed theoretically optical pulse propagation in a coherent atomic medium for amplification without inversion (AWI), which is achieved by adding incoherent optical pumping to a typical EIT system. In order to explain experimental results [Kim et al., J. Phys. B, 36, 2671(2003)] to control the group velocity of the optical pulse by changing pumping power, we established a 5-level atomic system and applied density matrix equations. This AWI model system is different from previous AWI systems from the viewpoint of using two levels for incoherent optical pumping isolated optically from the EIT (electromagentically induced transparency) system so that more atoms can participate in pulse speed control. We have found that population transfer by collisions between ground states plays a decisive role for efficient AWI, and more atoms are effective for slowing the pulse. Our numerical results are in good agreement qualitatively with experimental results.

• Publications of The Korean Astronomical Society
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• v.30 no.1
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• pp.11-16
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• 2015

First light galaxies have predictable linear clustering, and are expected to produce fluctuations with a characteristic spatial power spectrum, which peaks at an angular scale of ~ 10 arcminutes and in the $1-2{\mu}m$ spectral regions. The Cosmic Infrared Background ExpeRiment 2 (CIBER2) is a dedicated sounding rocket mission for measuring the fluctuations in the extragalactic infrared background light, following up the previous successful measurements of CIBER1. With a 28.5 cm telescope accompanied with three arms of camera barrels and a dual broadband filter on each H2RG (${\lambda}_c=2.5{\mu}m$) array, CIBER2 can measure 6 bands of wide field ($1.1{\times}2.2$ degrees) up to 3 AB magnitudes deeper than CIBER1. This project is leaded by California Institute of Technology/Jet Propulsion Laboratory, collaborating internationally with Institute of Space and Astronautical Science in Japan, Korea Astronomy and Space Science Institute, Korea Basic Science Institute, and Seoul National University. The Korean team is in charge of 1) one H2RG scientific array, 2) ground station hardware and software, 3) telescope lenses, and 4) flight and test bed electronics fabrication. In this paper, we describe the detailed activities of the Korean participation as well as the current status of the CIBER2 project.

• Korean Journal of Construction Engineering and Management
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• v.13 no.2
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• pp.37-47
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• 2012

Engaged number in the construction industry is 45 percentage level against to manufacturing industry. And Induction -factor of Production is much the same to mfg. field, Value added Induction-factor is more higher than manufacturing industry, therefore we research again about workers' inferior working & personal life condition in our society in order to they feel happiness their life with pride for the job construction occupation. So construction companies & government will be contribute to strengthen their phase & to achieve more higher level of construction working culture for elevate competitive power. We have to prepare the basis to turn to the qualitative construction businesses by break away from only the amount of work volume in company with the system of workers' self-conceit on the ground of professional education/training, qualification system, social insurance benefits, working condition improvement, stable job. Our nations does not feel well-being senses, only 25 class level in the 30 countries of OECD. We draw the questions at issue with slough off old customs in order to qualitative improvement for profession & self-contentment of construction workers, and present the useful plan to contribute to international competitiveness with our construction firms in the globalize construction field under Government's & company's policy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.9
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• pp.825-837
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• 2017

This paper describes a novel type of a walking rehabilitation robot that applies robot technologies to crutches used by patients with walking difficulties in the lower body. The primary features of the developed robot are divided into three parts. First, the developed robot is worn on the patient's chest, as opposed to the conventional elbow crutch that is attached to the forearm; hence, it can effectively disperse the patient's weight throughout the width of the chest, and eliminate the concentrated load at the elbow. Furthermore, it allows free arm motion during walking. Second, the developed robot can recognize the walking intention of the patient from the magnitude and direction of the ground reactive forces. This is done using three-axis force sensors attached to the feet of the robot. Third, the robot can perform a stair walking function, which can change vertical movement trajectories in order to step up and down a single stair according to the floor height. Consequently, we experimentally showed that the developed robot can effectively perform walking rehabilitation assistance by perceiving the walking intention of the patient. Moreover we quantitatively verified muscle power assistance by measuring the electromyography (EMG) signals of the muscles of the lower limb.