• 한국항공우주학회지
• /
• 제40권6호
• /
• pp.536-541
• /
• 2012

새로 설계된 항공기 장착용 외장형 포드의 비행 시험용 계측포드를 설계하였다. 계측포드는 하중, 진동환경 및 공력 가열등 일반적인 항목뿐만 아니라 공력음향 환경에 대한 측정이 가능하도록 제작하였다. 특히 본 논문에서는 국내 최초로 수행 예정인 비행공력 음향 환경 측정에 대하여 집중적으로 다루었다. 계측포드는 MIL-HDBK-1763과 MIL-STD-810 Method 515에서 요구한 공력음향 시험요구 조건을 만족하도록 설계/제작되었다. MIL-STD-810에서 제시한 방법을 활용하여 공력음향 센서의 위치와 측정범위를 결정하였다. 센서는 혹독한 비행시험 환경을 고려하여 ENDEVCO 8510B-2를 사용하였다. 완성된 계측포드의 성능 시험을 위하여 KF-16 Sta. 5에 장착 후 지상 Run-Up 시험을 수행하여 자료를 획득하였다. 자료 분석결과 시스템은 정상적으로 작동하였으나, 공력음향 센서의 측정 범위를 상회하는 음압이 측정되어 비행 시험시 측정범위의 변경이 요구되었다.

• 한국산학기술학회논문지
• /
• 제21권1호
• /
• pp.426-438
• /
• 2020

본 연구의 목적은 방사선 노출 경험을 참여자의 관점에서 확인함으로써 수술실 간호사의 방사선 노출 경험에 대한 구성요소를 확인하고 의미구조를 밝히는 데 있다. 연구의 참여자는 일 광역시 종합병원 수술실에서 근무하는 간호사로 수술실 경력이 6개월 이상인 자 9명을 대상으로 하였다. 심층면담으로 자료를 수집하였고, Giorgi(2004)의 현상학적 분석 방법으로 분석하였다. 연구 결과 수술실 간호사의 방사선 노출 경험은 "반복되는 방사선 노출로 질환 발생을 걱정함", "육체적, 정신적으로 소진됨", "방사선 방어를 통해 자기보호를 하고자 노력함", "내적 혼란과 갈등을 느낌", "근무환경 개선을 요구함", "현실을 받아들이고 적응함"의 6개 구성요소로 도출 되었다. 결론으로 이들의 경험은 방사선 노출 수술에 참여하면서 질환 발생을 걱정하고 방사선 피폭과 관련된 신체적, 정신적 소진을 경험하고 갈등을 느끼면서 이직을 고려하기도 하지만 자기보호를 하고자 노력하고 현실을 받아들이고 적응하는 과정을 보였다. 본 연구결과의 바탕으로 방사선 안전 환경조성을 위해서는 조직적 차원에서 체계적으로 구체적인 해결 방법을 모색하는 것이 바람직하다고 볼 수 있다.

• Structural Engineering and Mechanics
• /
• 제81권5호
• /
• pp.565-574
• /
• 2022

The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (𝚫K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (𝚫K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation's Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).

• 한국방재학회 논문집
• /
• 제8권6호
• /
• pp.1-5
• /
• 2008

피복이 없는 FBG센서는 내구성이 매우 약하기 때문에 FBG센서 주위의 피복이 없이는, 많은 변수가 존재하는 실제 자연환경에서의 정확한 데이터수집이 어렵다. Steel sleeve packaged FBG 변형률 센서는 토목공학에서 널리 사용되고 있는 센서 중 하나이다. 변형률과 온도가 동시에 측정되는 FBG센서의 도입 이후로, 변형률과 온도의 정확한 보정은 필수적인 과정이 되었다. 이 논문에서는 FBG의 변형률과 온도의 측정 원리에 기초하여 steel sleeve packaged FBG센서의 온도보정 기술을 도출하였다. 그리고 두개의 FBG센서를 이용한 콘크리트 초기재령의 건조수축 실험을 통해 온도보정의 실행 가능성을 확인하였다.

• 한국주조공학회지
• /
• 제20권5호
• /
• pp.330-335
• /
• 2000

Functional metal prototypes are often required in numerous industrial applications. These components are typically needed in the early stage of a project to determine form, fit and function. Recent R/P(Rapid Prototyping) part are made of soft materials such as plastics, wax, paper, these master models cannot be employed durable test in real harsh working environment. Parts by direct metal rapid tooling method, such as laser sintering, by now are hard to get net shape, pores of the green parts of powder casting method must be infiltrated to get proper strength as tool, and new type of 3D direct tooling system combining fabrication welding arc and cutting process is reported. But a system which can build directly 3D parts of high performance functional material as metal park would get long period of system development, massive investment and other serious obstacles, such as patent. In this paper, through the rapid tooling process as silicon rubber molding using R/P master model, and fabricate wax pattern in that silicon rubber mold using vacuum casting method, then we translated the wax patterns to numerous metal tool prototypes by new investment casting process combined conventional investment casting with rapid prototyping & rapid tooling process. With this wax-injection-mold-free investment casting, we developed new investment casting process of fabricating numerous functional metal prototypes from one master model, combined 3-D CAD, R/P and conventional investment casting and tried to expect net shape measuring total dimension shrinkage from R/P pare to metal part.

• 설비공학논문집
• /
• 제17권11호
• /
• pp.1014-1021
• /
• 2005

Flow channels with non-circular cross-sections are encountered in a wide variety of heat exchangers. Accurate friction factor and Colburn j factor data are essential for the design and viable applications of such heat exchangers. In this study, an analysis is con ducted on heat transfer and pressure drop characteristics for tube-bundle heat exchanger with various arrangements of tubes, of which their geometry could easily be modified from a circular one in a harsh environment. The parameters investigated are aspect ratio, pitch, and inclined angle of tubes. The results obtained are: (1) Aspect ratio has larger influence on the j and f factor than pitch; (2) As aspect ratio increases, both j and f factors decrease; (3) The high performance is achieved when the pitch and aspect ratio are in the range of 1.5${\~}$2.5 and 1.25${\~}$2.0, respectively; and (4) the inclined arrangements of tubes show unfavorable results for both heat transfer and pressure drop characteristics in spite of the positive possibility of condensate removals in a latent heat recovery system.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
• /
• pp.303-310
• /
• 2011

This paper is focused on development of models for measuring lateral and vertical track irregularities from corresponding accelerometers of an in-service high-speed train. Generally, the track irregularity was measured by a special railway inspection vehicle or system with contact or non-contact sensors. However, the sensors are very expensive and vulnerable to a harsh environment. Displacement estimation from an inertial measurement unit and its wave-band filtering was already developed in the previous study, and it was found that their results included not only the track irregularities but also other information such as phase delay of the applied filters, and suspension and conicity of the wheel. To identify the track irregularities from those results, a compensation filtering method was proposed. Each directional compensation filter was derived by using a system identification method with the estimated directional displacement as input and the corresponding track irregularities as output. In this paper, they are integrated into a model for each direction and applied to the measured lateral and vertical acceleration data from the axle-box and bogie of an in-service high-speed train. Their results are compared with the data from the track geometry measurement system. From the comparison, the proposed models are a useful tool for the measurement of the track irregularities using accelerometers of in-service high-speed trains.

• 한국IT서비스학회지
• /
• 제14권1호
• /
• pp.159-173
• /
• 2015

This paper presents a study on the Internet of Things based low-power wireless sensor networks for remote monitoring of wildlife ecosystem due to climate change. Especially, it is targeting the wild vegetation communities ecological monitoring. First, we performed a pre-test and analysis for selecting the appropriate frequency for the sensor network to collect and deliver information reliably in harsh propagation environment of the forest area, and selected for sensors for monitoring wild vegetation communities on the basis of considerations for selecting the best sensor. In addition, we have presented the platform concept and hierarchical function structures for effectively monitoring, analyzing and predicting of ecosystem changes, to apply the Internet of Things in the ecological monitoring area. Based on this, this paper presents the system architecture and design of the Internet of Things based low-power wireless sensor networks for monitoring the ecosystem of the wild vegetation communities. Finally, we constructed and operated the test-bed applied to real wild trees, using the developed prototype based on the design.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2004년도 ICCAS
• /
• pp.1953-1957
• /
• 2004

The machine vision has been applied to a number of industrial applications for quality control and automations to improve the manufacturing processes. In this paper, the automation system using the machine vision is developed, which is applicable to the marking process in a steel production process line. The working environment is very harsh to workers so that the automatic system in the steel industry is required increasingly. The developed automatic marking system consists of several mechanical and electrical elements such as the laser position detecting sensor system for a structured laser beam which is projected to the billet in order to detect the geometry of the billet. An image processing algorithm has been developed to percept the two center positions of a camera and a billet, respectively, and to align two centers. A series of experiments has been conducted to investigate the performance of the proposed algorithm. The results show that two centers of the camera and the billet could be detected very well and differences between two center positions could be also decreased via the proposed tracking algorithm.

• Corrosion Science and Technology
• /
• 제12권5호
• /
• pp.239-244
• /
• 2013

Marine equipment exposed to harsh environments requires not only excellent corrosion resistance but also improvement of physical characteristics against natural material degradation. With growing interests in ocean energy resources, the higher reliability for marine equipment has become more important in terms of material characteristics. ALBC3 alloy represents excellent corrosion resistance and is widely used in corrosive environments. However, cavitation damage occurs frequently due to its poor durability in high flow rate of marine environment. In this research, shot peening technology was employed as a surface modification with shot peening stand-off distance to mitigate cavitation damage. The effects of shot peening on extent of cavitation damage and weight loss were evaluated for both shot peened and non-peened specimens. The results revealed that the application of shot peeing decreased cavitation damage for all experimental conditions in comparison with the non-peened specimens. The optimum stand-off distance was determined to be 10 cm, since more than 35 % of cavitation damage reduction was observed.