• 터널과지하공간
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• 제9권1호
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• pp.12-19
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• 1999

장약량, 측정거리 등과 같은 발파조건들이 지반진동에 미치는 영향을 조사하기 위하여 골프장 조성공사를 위한 지표발파와 고속도로 건설공사를 위한 터널발파에서 지반진동을 측정하였다. 지표발파에서 삼승근 환산거리방법으로 구한 입지상수 K와 n은 각각 74.1, 01.37로 나타났다. 측정거리가 멀어질수록 Khk n의 절대값은 증가하였다. 지표발파에서 주주파수 대역은 5~60 Hz 이었으며, 그 중에 80% 정도는 10~30 Hz의 범위에 분포하였다. 반면에 터널발파의 주주파수 대역은 25~98Hz로서 지표발파보다 크게나타났다.

• Current Optics and Photonics
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• 제4권4호
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• pp.330-335
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• 2020

We have investigated optimization of the working distance (WD) for a highly miniaturized imaging probe for endoscopic optical coherence tomography (OCT). The WD is the axial distance from the distal end of the imaging probe to its beam focus, which is demanded for dimensional margins of protective structures, operational safety, or full utilization of the axial imaging range of OCT. With an objective lens smaller than a few hundred micrometers in diameter, a micro-optic imaging probe naturally exhibits a very short WD due to the down-scaled optical structure. For a maximized WD careful design is required with the optical aperture of the objective lens optimally filled by the incident beam. The diffraction-involved effect was taken into account in our analysis of the apertured beam. In this study, we developed a simple design formula on the maximum achievable WD based on our diffraction simulation. It was found that the maximum WD is proportional to the aperture size squared. In experiment, we designed and fabricated very compact OCT probes with long WDs. Our 165-㎛-thick fiber-optic probes provided WDs of 3 mm or longer w ith reasonable OCT imaging performance.

• Ocean Systems Engineering
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• 제9권4호
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• pp.391-407
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• 2019

Tracking the location (position) of a surface or underwater marine vehicle is important as part of guidance and navigation. While the Global Positioning System (GPS) works well in an open sea environment but its use is limited whenever testing scaled-down models of such vehicles in the laboratory environment. This paper presents the design, development and implementation of a low energy ultrasonic augmented single beacon-based localization technique suitable for such requirements. The strategy consists of applying Extended Kalman Filter (EKF) to achieve location tracking from basic dynamic distance measurements of the moving model from a fixed beacon, while on-board motion sensor measures heading angle and velocity. Iterative application of the Extended Kalman Filter yields x and y co-ordinate positions of the moving model. Tests performed on a free-running ship model in a wave basin facility of dimension 30 m by 30 m by 3 m water depth validate the proposed model. The test results show quick convergence with an error of few centimeters in the estimated position of the ship model. The proposed technique has application in the real field scenario by replacing the ultrasonic sensor with industrial grade long range acoustic modem. As compared with the existing systems such as LBL, SBL, USBL and others localization techniques, the proposed technique can save deployment cost and also cut the cost on number of acoustic modems involved.

• 한국지반환경공학회 논문집
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• 제18권10호
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• pp.5-14
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• 2017

In recent years, world has witnessed many man-made activities related to both above and underground blasts. Details on behaviour of shallow foundations subjected to blast loads and induced liquefaction is scarce in literature. In this paper, typical shallow strip foundation in saturated cohesionless soils subjected to both above and underground blasting have been simulated by using finite difference based numerical model FLAC3D. Peak particle velocity (PPV) has been obtained to propose critical values for which bearing capacity failure for shallow foundations with soil liquefaction can occur. Typical results for pore pressure ratio (PPR) for various scaled distances are compared to PPR values obtained by using empirical equation available in literature which shows good agreement. Critical design values obtained in the present study for PPV and PPR to estimate the scaled distance, bearing capacity failure and liquefaction susceptibility can be used effectively for design of shallow strip foundation in cohesionless soil subjected to both above and under ground blast loads.

• 터널과지하공간
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• 제15권1호
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• pp.61-70
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• 2005

본 연구에서는 장대 터널 화재시 연기의 거동 특성 파악과 피난연락갱의 설치간격을 결정하기 위하여 축소 모형실험을 실시하여 그 결과를 분석하였다. Froude 상사를 기본으로 1/50로 축소하여 20 m의 모형 터널을 제작하여 실험하였다. 터널 내 20 MW의 화재가 발생 하였을 경우 CO의 전파 속도와 거리와의 관계를 이용하여 피난연락갱의 위치를 검토한 결과, 승객들의 피난시간은 6분이 적절하나 화재시 승객들의 심리적 상태를 고려하여 1분여의 지체시간을 생각하면 실제의 피난시간은 5분 정도가 될 것이므로 최대 간격 250m로 대인용 피난연락갱을 설치하는 것이 바람직할 것으로 판단되었다.

• 제어로봇시스템학회논문지
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• 제4권4호
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• pp.525-533
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• 1998

A conventional contact type brake system which uses a hydraulic system has mny Problems such as time delay response due to pressure build-up, brake pad wear due to contact movement, bulky size, and low braking performance in high speed region. As vehicle speed increases, a more powerful brake system is required to ensure vehicle safety and reliability. In this work, a contactless brake system of an eddy current type is proposed to overcome problems. Optimal torque control which minimizes a braking distance is investigated with a scaled-down model of an eddy current type brake. It is possible to realize optimal torque control when a maximum friction coefficient (or desired slip ratio) corresponding to road condition is maintained. Braking force analysis for a scaled-down model is done theoretically and experimentally compensated. To accomplish optimal torque control of an eddy current type brake system, a sliding mode control technique which is, one of the robust nonlinear control technique is developed. Robustness of the sliding mode controller is verified by investigating the braking performance when friction coefficient is varied. Simulation and experimental results will be presented to show that it has superior performance compared to the conventional method.

• 센서학회지
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• 제23권3호
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• pp.165-169
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• 2014

An existing infrared (IR) analysis system is generally composed of infrared source, IR focusing lenses, IR detector, and optical chopper. An optical chopper is widely used in combination with lock-in amplifier to improve the signal-to-noise ratio by periodically interrupting incident light beam. During recent years, a few researches on miniaturized optical chopper have been reported to apply to micro-scaled optical systems. In this paper, a micro optical chopper operated by electromagnetic actuation is proposed and applied to a miniaturized micro-scaled optical system operating in IR spectral range. Additionally, the fabrication method of the proposed micro chopper is demonstrated. The proposed micro optical chopper is composed of the polydimethylsiloxane (PDMS) membrane, solenoid, and permanent magnet. The permanent magnet is bonded on the PDMS membrane using an ultraviolet-activated adhesive. The operation of the chopper is based on the attractive and repulsive forces between permanent magnet and solenoid induced by an electrical current flowing through the solenoid. The fabricated micro optical chopper could operate up to 200 Hz of frequency. The maximum operating distance of the chopper with 7mm diameter membrane was $750{\mu}m$ at 100 Hz of frequency.

• 한국자기학회지
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• 제27권2호
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• pp.63-69
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• 2017

함정은 작전 운용관점에서 음향적 및 자기적으로 정숙성이 요구되며, 그 중에서 함정에서 발생하는 자기장 신호는 근거리에서 적의 감시체계 및 기뢰체계 등 위협세력에 의해 쉽게 노출되게 된다. 따라서 아함의 생존성 증대를 위하여 함정의 자기장 신호저감을 위한 다양한 기법이 연구되고 있으며, 최근에는 단순히 자기장 신호의 크기 감소 뿐 만 아니라 자기장 신호의 변화율 성분에 대한 감소까지 추가적으로 요구되고 있다. 본 논문에서는 상용 전자기 유한요소해석 도구를 이용하여 함정 축소모델에 대한 유도 자기장 신호를 예측하고, 소자코일을 배치하였다. 그리고 기울기 구속조건을 고려한 입자 군집 최적화 알고리즘을 적용하여 소자코일의 최적 소자전류를 도출하였다. 기울기 구속조건 유/무에 따른 소자 후 자기장 신호를 비교함으로써 최적 소자기법의 타당성을 해석적으로 검증하였다.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.3085-3099
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• 2021

Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to numerically assess the damage and vibrations of NPP buildings subjected to aircrafts crash. In Part I of present paper, two shots of reduce-scaled model test of aircraft impact on NPP were conducted based on the large rocket sled loading test platform. In the present part, the numerical simulations of both scaled and prototype aircraft impact on NPP buildings are further performed by adopting the commercial program LS-DYNA. Firstly, the refined finite element (FE) models of both scaled aircraft and NPP models in Part I are established, and the model impact test is numerically simulated. The validities of the adopted numerical algorithm, constitutive model and the corresponding parameters are verified based on the experimental NPP model damages and accelerations. Then, the refined simulations of prototype A380 aircraft impact on a hypothetical NPP building are further carried out. It indicates that the NPP building can totally withstand the impact of A380 at a velocity of 150 m/s, while the accompanied intensive vibrations may still lead to different levels of damage on the nuclear related equipment. Referring to the guideline NEI07-13, a maximum acceleration contour is plotted and the shock damage propagation distances under aircraft impact are assessed, which indicates that the nuclear equipment located within 11.5 m from the impact point may endure malfunction. Finally, by respectively considering the rigid and deformable impacts mainly induced by aircraft engine and fuselage, an improved Riera function is proposed to predict the impact force of aircraft A380.

• 한국지반환경공학회 논문집
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• 제15권12호
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• pp.117-128
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• 2014

일반적으로 기존 터널이나 공동 등에 근접하여 터널을 시공하는 경우에 기존 공동과 터널간의 간섭이 발생하며 이로 인한 영향을 최소화하기 위하여 이격거리를 터널의 폭 이상으로 유지하도록 일부시방서 등에 권고안이 제시되어 있는 상태이다. 이와같이 공동이나 구조물 등에 근접한 터널은 지반 상태 및 공동의 크기, 보조공법 등을 고려하여 결정하여야 하며, 지반이 연약한 상태에서는 근접도에 따라 민감한 반응을 나타내고 변형량도 크게 나타나므로 지반조건을 고려한 터널계획이 이루어져야 한다. 설계단계에서 공동이 터널의 안정성에 미치는 영향을 검토하기 위해 현장측정, 수치해석, 모형시험 등의 방법이 고려될 수 있으며, 이 중에서 모형시험(Scaled model test)은 결과를 가시적으로 나타낼 수 있을 뿐 아니라, 수치해석과 비교를 통해 거동을 보다 상세하고 현실적으로 예측 가능하다는 장점이 있다. 본 연구에서는 공동에 인접하여 터널 굴착이 이루어지는 경우, 계획단계에서 실제 거동을 예측하기 위한 모형시험 방법과 시험 시 고려사항들에 대해 고찰하고 실제 시험 결과와 수치해석 결과의 비교를 통해 제안된 기법의 적정성을 평가하였다. 또한 터널 굴착 시 터널 주변에 분포하는 공동의 이격거리에 따른 영향이 적절히 반영되는지 여부를 파악하기 위해 공동과 터널간 이격거리를 0.25D, 0.50D, 1.00D, Network 상태 분포 시로 가정한 일련의 모형시험을 수행하였으며, 공동이 없는 조건과 비교하여 제안된 방법의 적정성을 확인하였다. 추가적으로 축소모형시험 결과의 타당성 검증을 위한 목적으로 시험조건을 반영한 수치해석을 수행하였으며, 수치해석 결과와 모형시험 결과의 비교 검증을 수행하였다. 모형시험 및 수치해석 결과 이격거리 1.0D는 공동과 터널이 독립적인 거동을 보이는 한계거리로 평가되었다.