• 한국통신학회논문지
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• 제30권2A호
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• pp.66-79
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• 2005

본 논문에서는 스마트 무인항공기의 데이터 링크의 신뢰성 향상을 위하여 그것을 구성하는 RF 송수신 시스템의 성능 분석 및 통신링크 분석을 수행하였다. 시스템 분석은 데이터 링크의 개발 사양서 및 사용되는 부품의 data sheet를 참조하여 시스템 시뮬레이션 툴인 Agilent EEsof ADS(Advanced Design System)을 이용하여 수행하였고, 통신링크 분석은 스마트 무인항공기 운용 환경에 맞는 다양한 전파 모델들을 이용하여 분석하였다. 그 결과, 시뮬레이션 결과와 개발 사양서에서 나타난 문제점들을 제시하였고, 통신링크 분석을 통해 나타난 문제점 및 시스템 설계를 위한 고려사항에 대하여 제시하였다.

• Computers and Concrete
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• 제13권2호
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• pp.255-270
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• 2014

Impact performance of high-performance concrete (HPC) and SFRC at 28-day and 56-day under the action of repeated dynamic loading was studied. Silica fume replacement at 10% and 15% by mass and crimped steel fiber ($V_f$ = 0.5%- 1.5%) with aspect ratios of 80 and 53 were used in the concrete mixes. Results indicated that addition of fibers in HPC can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths and toughness of HPC. Variation of fiber aspect ratio has minor effect on improvement in impact strength. Based on the experimental data, failure resistance prediction models were developed with correlation coefficient (R) = 0.96 and the estimated absolute variation is 1.82% and on validation, the integral absolute error (IAE) determined is 10.49%. On analyzing the data collected, linear relationship for the prediction of failure resistance with R= 0.99 was obtained. IAE value of 10.26% for the model indicates better the reliability of model. Multiple linear regression model was developed to predict the ultimate failure resistance with multiple R= 0.96 and absolute variation obtained is 4.9%.

• Smart Structures and Systems
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• 제14권2호
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• pp.159-189
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• 2014

One of the most important requirements in the evaluation of existing structural systems and ensuring a safe performance during their service life is damage assessment. Damage can be defined as a weakening of the structure that adversely affects its current or future performance which may cause undesirable displacements, stresses or vibrations to the structure. The mass and stiffness of a structure will change due to the damage, which in turn changes the measured dynamic response of the system. Damage detection can increase safety, reduce maintenance costs and increase serviceability of the structures. Artificial Neural Networks (ANNs) are simplified models of the human brain and evolved as one of the most useful mathematical concepts used in almost all branches of science and engineering. ANNs have been applied increasingly due to its powerful computational and excellent pattern recognition ability for detecting damage in structural engineering. This paper presents and reviews the technical literature for past two decades on structural damage detection using ANNs with modal parameters such as natural frequencies and mode shapes as inputs.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.598-601
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• 2006

The radio signal in GNSS was intentionally designed with two frequencies in order to combat the dispersion error caused by trans-ionospheric propagation. By measuring the path delay independently at the two, widely spaced GPS frequencies, L1 & L2, the TEC along the path from satellite to receiver can be measured directly. The issue with dual frequency measurement of the ionosphere is the calibration of L1/L2 interfrequency biases. L1/L2 interfrequency biases are generated because physical electric signal paths of L1 and L2 circuits are different from each other for both satellites and receiver. Conventionally L1/L2 interfrequency bias is estimated and broadcasted by 2D ionospheric model. In this paper, we estimated IFB (interfrequency bias) by 2D & 3D ionospheric models including real time filter methods and compared the result of those and concluded the merit of 3D tomography model to recover the problem of 2D thin shell model. We confirmed our conclusion by experimental data.

• 한국해안해양공학회지
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• 제5권1호
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• pp.19-24
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• 1993

슈퍼컴과 워크스테이션을 사용하여 해양과정의 모델링 결과를 고화질의 컴퓨터 영상으로 제시할 수 있게 되었다. 본 연구에서는 근년에 발생한 지진진파(쯔나미)에 대한 수치모형을 적용하여 산정된 수위를 3차원적으로 연속적인 동화로서 제시하였다. 이 결과 광원, 반사 및 음영을 나타내는 최신 렌더링 기법에 의한 사진과 같은 효과를 갖는 영상들을 구축하였다. 비디오동화에 의한 수치모형의 결과는 실제적인 쯔나미의 파급거동을 잘 제시하였다.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.436-449
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• 2017

In this paper, the damage and failure behavior of triaxially braided textile composites was studied using progressive failure analysis. The analysis was performed at both micro and meso-scales through iterative cycles. Stress based failure criteria were used to define the failure states at both micro- and meso-scale models. The stress-strain curve under uniaxial tensile loading was drawn based on the load-displacement curve from the progressive failure analysis and compared to those by test and computational results from reference for verification. Then, the detailed failure initiation and propagation was studied using the verified model for both tensile and compression loading cases. The failure modes of each part of the model were assessed at different stages of failure. Effect of ply stacking and number of unit cells considered were then investigated using the resulting stress-strain curves and damage patterns. Finally, the effect of matrix plasticity was examined for the compressive failure behavior of the same model using elastic, elastic - perfectly plastic and multi-linear elastic-plastic matrix properties.

• International Journal of Automotive Technology
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• 제6권2호
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• pp.95-105
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• 2005

Diesel engines have low specific fuel consumption, but high particulate emissions, mainly soot. Diesel soot is suspected to have significant effects on the health of living beings and might also affect global warming. Hence stringent measures have been put in place in a number of countries and will be even stronger in the near future. Diesel engines require either advanced integrated exhaust after treatment systems or modified engine models to meet the statutory norms. Experimental analysis to study the emission characteristics is a time consuming affair. In such situations, the real picture of engine control can be obtained by the modeling of trend prediction. In this article, an effort has been made to predict emissions smoke and NO$_{x}$ using cylinder combustion derived parameters and diesel particulate filter data, with artificial neural network techniques in MATLAB environment. The model is based on three layer neural network with a back propagation learning algorithm. The training and test data of emissions were collected from experimental set up in the laboratory for different loads. The network is trained to predict the values of emission with training values. Regression analysis between test and predicted value from neural network shows least error. This approach helps in the reduction of the experimentation required to determine the smoke and NO$_{x}$ for the catalyst coated filters.

• 한국군사과학기술학회지
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• 제17권2호
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• pp.275-281
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• 2014

Although self-propelled artilleries are mobile equipment, they need their own covered-positions for survival against preemptive strikes. The most important military requirement is enough protective capacity against blast pressure caused by explosion. This paper aims to assess the protective capacity of the newly-placed concrete box-type artillery positions using accurate structural geometric models as well as soil-structure interaction analysis. The commercial program is used to model the structural geometry of the positions. In order to describe the correct wave propagation in the backfill along with soil-structure interaction, used parameters in shock equation of state are selected based on the related studies as well as theories and then their final results are verified with the ones calculated with empirical equations in the US Unified Facility Criteria. In sum, it could be concluded that the protective capacity of the newly-built positions satisfies the protective structural requirement.

• 융합신호처리학회논문지
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• 제10권2호
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• pp.127-131
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• 2009

디지털 도파관 모델은 파동 방정식의 일반해를 이용하여 진행파를 표현하고 이 진행파의 파동이동을 지연 라인으로 나타낸다. 일반적인 도파관 모델에서의 단일 지연은 샘플링 시간 간격을 의미하지만, 공간 기준 도파관 모델의 단일 지연은 샘플링된 공간의 거리를 의미한다. 이러한 차이점으로 인해 파동의 이동 거리를 직접적으로 조절할 수 있는 공간기준 도파관 모델이 비브라토 음과 같이 피치가 변하는 음을 합성할 수 있다고 알려져 있다. 본 논문에서는 지연라인의 길이의 비로서 피치가 변하는 음을 합성할 수 있는 시간 기준 디지털 도파관 모델을 제안하고 기존의 공간 기준 도파관 모델과의 성능을 비교하였다.

• Nuclear Engineering and Technology
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• 제50권2호
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• pp.280-291
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• 2018

In the framework of OECD/NEA Working Group on Fuel Safety, a RIA fuel-rod-code Benchmark Phase I was organized in 2010-2013. It consisted of four experiments on highly irradiated fuel rodlets tested under different experimental conditions. This benchmark revealed the need to better understand the basic models incorporated in each code for realistic simulation of the complicated integral RIA tests with high burnup fuel rods. A second phase of the benchmark (Phase II) was thus launched early in 2014, which has been organized in two complementary activities: (1) comparison of the results of different simulations on simplified cases in order to provide additional bases for understanding the differences in modelling of the concerned phenomena; (2) assessment of the uncertainty of the results. The present paper provides a summary and conclusions of the second activity of the Benchmark Phase II, which is based on the input uncertainty propagation methodology. The main conclusion is that uncertainties cannot fully explain the difference between the code predictions. Finally, based on the RIA benchmark Phase-I and Phase-II conclusions, some recommendations are made.