• Smart Structures and Systems
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• 제25권3호
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• pp.265-277
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• 2020

Recently, the concept of "drive-by" bridge monitoring system using indirect measurements from a passing vehicle to extract key parameters of a bridge has been rapidly developed. As one of the most key parameters of a bridge, the natural frequency has been successfully extracted theoretically and in practice using indirect measurements. The frequency of bridge is generally calculated applying Fast Fourier Transform (FFT) directly. However, it has been demonstrated that with the increase in vehicle velocity, the estimated frequency resolution of FFT will be very low causing a great extracted error. Moreover, because of the low frequency resolution, it is hard to detect the frequency drop caused by any damages or degradation of the bridge structural integrity. This paper will introduce a new technique of bridge frequency extraction based on Hilbert Transform (HT) that is not restricted to frequency resolution and can, therefore, improve identification accuracy. In this paper, deriving from the vehicle response, the closed-form solution associated with bridge frequency removing the effect of vehicle velocity is discussed in the analytical study. Then a numerical Vehicle-Bridge Interaction (VBI) model with a quarter car model is adopted to demonstrate the proposed approach. Finally, factors that affect the proposed approach are studied, including vehicle velocity, signal noise, and road roughness profile.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집 특별세미나,특별/일반세션
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• pp.225-230
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• 2009

From the view point of railway vehicle dynamics, the interaction between wheel and rail have an huge effect on the behavior of the vehicle. This phenomenon is an unique motion, only for railway vehicles. Furthermore, close investigation of the backgrounds of the interaction is the key to estimate the dynamic behavior of the vehicle, successfully. To evaluate the model including flexible bodies such as car body and catenary system of the next generation express train, it is necessary to develop proper dynamic solver including a wheel rail contact module. In this study, wheel-rail contact module is developed using the general purpose dynamic solver. First of all, the procedure for calculation of the wheel-rail contact force has been established. Generally, yaw angle of the wheelset is ignored. Sets of information are summarized as tables and splined for further uses. With this information, normal force and creep coefficient can be extracted and used for FASTSIM algorithm, which has been shown good reliability over years. Normal force and longitudinal, lateral force at the contact surface are also calculated. Those data are verified by commercial railway simulation program 'VAMPIRE'. This procedure and program can offer a basic process for estimation of the dynamic behavior and wear of the wheel-rail system, even while running on the curved rail. Finally, multi-dimensional inspection tool will be developed including the prediction of the derailment.

• 한국식품영양학회지
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• 제21권4호
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• pp.562-571
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• 2008

The principal objective of this study was to assess dietitian's awareness and performance with regard to food suppliers' selection guidelines and purchase guidelines for the receipt of safe food materials. A questionnaire was administered to 203 dietitians working at an elementary school in Gyeonggi North province, and 190 responses were ultimately returned. Excluding responses with incomplete answers and significant missing data, 161 responses(79.3%) were ultimately utilized for data analysis. We determined that meat/poulty and seafood were purchased mainly by manufacturer's branch(59.8% and 78.3%), and processed food and kimchi were generally purchased by producer's cooperatives(47.7% and 44.9%). 78.3% of the contracts were made via informal purchasing and the frequency of contracts was less than 3 times per year(53.4%). Market studies were conducted individually(54.7%), and by group(47.2%). Dietitian and parents volunteered(50.3%) or dietitians, and school and foodservice staffs(45.3%) participated - together in receiving and inspection. School contracted with $4{\sim}5$(39.1%) and $6{\sim}8$ food suppliers(29.8%). Dietitians(42.3%) or school councils(40.2%) evaluated food suppliers once per semester(60.2%). The majority of dietitians(96.3%) conducted sanitary education for food suppliers once per semester (68.3%). All 13 guidelines which were usually used to evaluate food suppliers were thought to be important(more than 4) based on a 5 scale(1: never important, 5: very important). Among them, 'sanitary storage status of food products(4.85)', 'have a chill car(4.83)' and 'proper control of refrigerator, freezer and storage room(4.81)' were the most crucial guidelines. As dietitians evaluated food supplier's-observances of 13 guidelines, 'have a chill car(4.89)', 'hold medical examination of employees(4.89)' and 'hold liability insurance for handling product(4.80)' were fulfilled relatively well. The guidelines for conducting education for their employees(4.45) and keeping their establishment and equipment sanitary(4.79) were important, but were not observed well(3.39 and 3.37). Additionally, the difference between the importance and the observance score of the 'HACCP certificate' were fairly significant(4.44 and 3.54). Dietitians tended to report that purchasing management related to the removal of foodborne illness factors(4.71), return confirmation(4.50) and purchase specification(4.32) were important. The difference between importance and performance was highest in the process of changing food suppliers when the contracts were violated more than three times. Dietitian's age, education work experience and employment type had no observable effects on how important they considered purchase management to be, but their work experience significantly affected performance in terms of the removal of foodborne illness factors(p<0.05). As supplier management is the most critical factor, it is clearly desirable to educate suppliers at specialized training centers and to supervise suppliers in accordance with the established sanitary guidelines.

• 한국산학기술학회논문지
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• 제16권12호
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• pp.8516-8524
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• 2015

궤도틀림은 직접 궤도검측을 통해서도 평가가 가능하지만, 차체 진동가속도의 계측을 통해서도 간접적으로 관리상태를 파악할 수 있으며, 최근 이에 대한 연구가 활발히 진행되고 있다. 이러한 간접적인 방법을 통해 국내 경부고속철도 자갈궤도의 유지보수 수준을 조사하고 평가하기 위하여, 국내 경부고속철도와 프랑스 고속철도(TGV)의 차체 진동가속도 계측을 수행하고 UIC518 규격에 제시된 방법에 따라 차체 진동가속도 계측 데이터에 대한 신호처리를 수행하였다. 차체 진동가속도는 차량의 주행속도에 따라서도 영향을 많이 받으므로, 신호처리된 계측결과를 속도대역별로 구분하여 상하방향 차체가속도 및 좌우방향 차체가속도의 크기에 따른 빈도분포를 계산하였다. 이렇게 계산된 빈도분포로부터 차량 주행속도에 따른 차체 진동가속도의 분포특성을 조사하고 UIC518에 제시된 기준과 비교하였다. 또한, 경부고속철도와 프랑스 고속철도의 상하방향 및 좌우방향 차체가속도의 빈도분포에 대한 정량적 비교분석을 수행하고, 국내 경부고속철도 자갈궤도 구간의 궤도틀림 관리수준을 평가하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2011년도 추계학술대회
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• pp.475-478
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• 2011

차량 운전자는 안전을 위해 항상 자신의 차량의 상태를 점검하고 파악하는 것이 필수이다. 하지만 운전자가 차량의 상태를 알고자 한다면 전문 업체에게 의뢰하기 때문에 운전자는 시간과 금전적인 비용이 지불되어야 한다. 오늘날 빠르게 변화하는 IT기술의 발달로 인해 스마트폰의 다양한 기능을 이용하여 차량의 상태 점검을 할 수 있게 되었다. 하지만, 기존 스마트폰 자동차 진단 시스템은 자동차의 전문적인 지식을 학습해야 차량 상태를 알 수 있기 때문에 사용자들에게 진단기의 필요성이 부각되지 않는다. 이러한 점을 반영하여 스마트폰을 이용해 사용자들이 손쉽게 자신의 차량 상태를 한 번에 파악할 수 있는 시스템이 요구된다. 본 논문에서는 OBD-II 프로토콜 변환 WiFi 커넥터를 통해 받아오는 OBD-II 정보를 차량 운전자에게 필요한 차량 소모품 교체 주기의 점검, 차량 문제점 진단 정보를 사용자에게 실시간으로 보여주며 손쉽게 사용할 수 있는 자동차 소모품 구현을 IOS 기반 스마트폰에서 구현 하였다.

• 한국건설관리학회논문집
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• 제20권6호
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• pp.3-10
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• 2019

수년에 걸쳐 장기적으로 사업을 추진해야 하는 대형건설공사를 위해서는 단년도에 편성된 예산의 한도내에서 공사를 차수별로 계약체결하는 장기계속공사계약과 전체공사에 대한 예산을 편성해 두고 연차적으로 집행해 나가는 계속비사업계약이 있다. 장기계속공사계약의 경우 매년도 예산편성에 따라 공사를 진행하게 되므로 최초 예산을 산출할 때 전체 사업기간을 예상할 수 없다. 또한 장기계속공사계약과 관련해서는 하자책임과 관련된 법령, 계약이행과 관련된 법령이 체계적으로 정립되어 있지 못하고 있다. 그러므로 실제 건설현장에서는 장기계속공사계약과 관련하여 하자책임이나 계약의 이행과 관련하여 많은 문제점이 발생되고 있다. 이에 본 연구에서는 장기계속공사계약의 효율적인 운영을 위해 다음과 같은 개선방향을 제시하였다. 첫째, 하자담보책임은 법적책임이므로 시행령이 아닌 법에 명시하여야 한다. 둘째, 장기계속공사에서 차수별 계약당사자가 달라질 경우 시행령에서 특약을 정할 수 있도록 명시해야 한다. 셋째, 장기계속공사의 공기연장으로 인한 간접비가 발생될 경우 총사업비관리지침의 예비비항목을 활용할 수 있도록 해야 한다. 넷째, 공사계약일반조건의 경우 손해보험의 가입, 검사, 인수, 하자보수 및 하자검사와 관련된 조항을 보완해야 한다.

• 품질경영학회지
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• 제46권2호
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• pp.269-282
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• 2018

Purpose: The purpose of this study was to improve the FRP Van's durability by analyzing the problematic parameters, redesigning the rear van, and verifying the design drafts using the CAE analysis & Rig test. Methods: The collected data through the government quality inspection and field spot check were thoroughly analyzed through the characteristics diagram and the improvement suggestions were verified by performing CAE analysis, like the dynamic stiffness, Torsional stiffness, open/close condition's strength, Full car durability and Carrying out the actual test. Results: The results of this study are as follows; The output of CAE analysis shows that improvement suggestions have considerable effects on the reinforcement of FRP structure, and the actual torsion and open/close condition durability test prove that rear van may have durable life which is equivalent to vehicle life cycle. Conclusion: The structural weakness of KLTV's FRP rear van was overcome by applying the stiffener in rear van and changing the bonding method of each FRP pieces. That suggestions were proved using CAE analysis and Rig test.

• Structural Monitoring and Maintenance
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• 제1권1호
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• pp.131-157
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• 2014

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.

• 한국ITS학회 논문지
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• 제16권3호
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• pp.1-14
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• 2017

최근 자동차 산업은 자율주행자동차로 인해 빠르게 변화하고 있고 관련된 연구 또한 활발하게 진행되고 있다. 하지만 자율주행자동차의 기술에 관한 연구가 대부분이며, 도로교통 안전과 관련한 변화 예측과 개선방안에 대한 연구는 부족한 실정이다. 본 연구는 자율주행자동차의 도입에 따른 사업용 차량 도로교통 안전사업의 개선방안 제시와 우선순위 도출을 목적으로 수행하였다. 자율주행자동차 전문가를 대상으로 한 설문조사 결과와 AHP를 이용하여 분석한 결과 교통수단안전점검 법령 개정, 자율주행자동차 운전자 및 운영자 등에 대한 교육제도 개발 등이 가장 우선시 되어야 할 것으로 분석되었다.

• 방사선산업학회지
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• 제9권3호
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• pp.153-159
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• 2015

Reliability of printed circuit board (PCB), which is based on high integrated circuit technology, is having been important because of development of electric and self-driving car. In order to answer these demand, automated X-ray inspection (AXI) is best solution for PCB non-destructive test. PCB is consist of plastic, copper, and, lead, which have low to high Z-number materials. By using dual energy X-ray imaging, these materials can be inspected accurately and efficiently. Dual energy X-ray imaging, that have the advantage of separating materials, however, need some solution such as energy separation method and enhancing efficiency because PCB has materials that has wide range of Z-number. In this work, we found out several things by analysis of X-ray energy spectrum. Separating between lead and combination of plastic and copper is only possible with energy range not dose. On the other hand, separating between plastic and copper is only with dose not energy range. Moreover the copper filter of high energy part of dual X-ray imaging and 50 kVp of low energy part of dual X-ray imaging is best for efficiency.