• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.235-239
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• 1996

분류가 모서리에 충돌할 때 발생하는 순음성 소리인 쐐기소리(edgetone)는 공력음향의 대표적인 현상으로서 지금까지 수많은 연구가 있어 왔으며 그 대부분의 특성이 규명되었다고 할 수 있다. 쐐기소리의 발생기구인 되먹임(feedback) 이론을 처음으로 제안한 이는 Powell로서 그는 되먹임사이클의 위상조건에 의하여 주파수특성에 관한 모델을 제안하였으며, 최근 그 모델의 위상인자에 관하여 Kwon은 새로운 값을 제안한 바 있다. 그런데, 쐐기소리의 이론은 주로 분류가 쐐기나 벽에 충돌할 경우에 집중되어 왔으며 분류가 원통에 충돌하여 발생하는 경우에 관한 연구는 Krothapalli의 초음속분류에 관한 연구와 Mochizuki등의 아음속분류에서 원통지름의 영향에 관한 연구를 들 수 있을 뿐이다. Mochizuki등은 원통의 지름이 노즐의 높이보다 작은 경우에 쐐기 소리의 주파수가 원통의 와류이탈(vortex shedding) 주파수와 같은 것을 관찰하였다. 그러나 분류와 원통이 작용하여 발생하는 쐐기소리의 주파수 특성에 관한 이론적 해석을 시도한 연구는 없으며 또한 방사음장의 특성에 관하여도 Han과 Kwon에 의한 모델이 발표된 바 있으나 실험적으로 입증되지 못하였다. 따라서, 본 연구의 목적은 2 fig.1과 같이 2차원 분류가 원통에 충돌할 때 발생하는 쐐기소리의 주파수특성의 정량적인 모델을 세우고 방사음장의 지향특성의 이론 모델을 확립하는 것이다. 먼저 주파수특성을 실험하고 되먹임이론을 적용하여 분석하므로써 유효음원의 위치를 구하고 또한, 수직벽에 작용하여 발생하는 충돌음(impinging tone)의 경우를 실험하여 주파수특성을 비교 고찰하므로써 유효음원의 위치에 관한 이론을 입증한다. 아울러 원통과 평면벽의 각 경우에 방사음장의 지향특성을 측정하고 고찰한다.2,5,6]을 단계별로 고찰하여, 점점 까다로워져 가는 선박 진동규제[3,4]에 대처하고 승무원의 안락성에 대한 욕구, 구조물의 안전성, 장비의 성능보존이 만족되는 저진동 선박의 건조를 위해 향후 해결해야할 과제들을 도출하여 선박진동분야이 연구개발 방향을 제시하고자 한다. 하는 것은 진단의 정밀도에 문제가 있을 것으로 생각된다. 따라서 언어적진리치가 도입되어 [상당히 확실], [확실], [약간 확실] 등의 언어적인 표현을 이용하여 애매성을 표현하게 되었다. 본 논문에서는 간이진단 결과로부터 추출된 애매한 진단결과중에서 가장 가능성이 높은 이상원인을 복수로 선정하고, 여러 종류의 수치화할 수 없는 언어적(linguistic)인 정보ㄷㄹ을 if-then 형식의 퍼지추론으로 종합하는 회전기계의 이상진단을 위한 정밀진단 알고리즘을 제안하고 그 유용성을 검토한다. 존재하여도 모우드 변수들을 항상 정확하게 구할 수 있으며, 또한 알고리즘의 안정성이 보장된 것이다.. 여기서는 실험실 수준의 평 판모델을 제작하고 실제 현장에서 이루어질 수 있는 진동제어 구조물에 대 한 동적실험 및 FRS를 수행하는 과정과 동일하게 따름으로써 실제 발생할 수 있는 오차나 error를 실험실내의 차원에서 파악하여 진동원을 있는 구조 물에 대한 진동제어기술을 보유하고자 한다. 이용한 해마의 부피측정은 해마경화증 환자의 진단에 있어 육안적인 MR 진단이 어려운 제한된 경우에만 실제적 도움을 줄 수 있는 보조적인 방법으로 생각된다.ofile whereas relaxivity at high field is not affected by τS. On the other hand, the change in τV does not affect low field profile but strongly in fluences on both

• Journal of Korea Water Resources Association
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• v.55 no.5
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• pp.333-343
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• 2022

For water resource management, the design flood is calculated using the flood frequency analysis technique and the rainfall runoff model. The method by design flood frequency analysis calculates the stochastic design flood by directly analyzing the actual discharge data and is theoretically evaluated as the most accurate method. Actual discharge data frequency analysis of the measured flow was limited due to data limitations in the existing flood flow analysis. In this study, design flood frequency analysis was performed using the measured flow data stably secured through the water level-discharge relationship curve formula. For the frequency analysis of design flood, the parameters were calculated by applying the bayesian inference, and the uncertainty of flood volume by frequency was quantified. It was confirmed that the result of calculating the design flood was close to that calculated by the rainfall-runoff model by applying long-term rainfall data. It is judged that hydrological analysis can be done from various perspectives by using long-term actual flow data through hydrological survey.

• Asian Journal of Turfgrass Science
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• v.20 no.2
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• pp.223-235
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• 2006

Soil testing laboratories unfamiliar with turfgrasses will often overestimate the plant's need for phosphorus and underestimate the need for potassium. This is partly due to differences in rooting between grasses and many garden plants and crops. The grasses are generally more efficient in extracting phosphorus from the soil, reducing their need for phosphorus fertilizer. The fact that crop yield is often the primary objective in field crop production, and is usually of little interest in turfgrass management, may affect soil test interpretation for potassium. Potassium levels above those required for maximum tissue yield of grasses may improve stress tolerance and turfgrasses will usually benefit from higher applications of this element. There are also diffrrences in soil testing philosophies. Some laboratories use the sufficiency level of available nutrients(SLAN) approach, whereas others prefer the basic cation saturation ratio(BCSR) approach. Some will use a combination of the two methods. The use of the BCSR theory easily lends itself to abuse and questionable fertilizer applications and products are sometimes recommended citing imbalances in cation ratios. The usefulness of the BCSR ratio theory of soil testing varies with soil texture and interpretations on tests performed on sand-based media are particularly a problem. Other soil testing problems occur when sand-based media used on sports fields and golf greens contain free calcium carbonate. The ammonium acetate extractant at pH 7.0 dissolves excessive amounts of calcium that can bias cation exchange capacity measurements and measurements of cation ratios. Adjusting the pH of the extractant to 8.1 can improve the accuracy of the testing procedure for calcareous media.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.573-590
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• 2020

This study presents the current status of DECOVALEX-2023 project Task G and our research results so far. Task G, named 'Safety ImplicAtions of Fluid Flow, Shear, Thermal and Reaction Processes within Crystalline Rock Fracture NETworks (SAFENET)' aims at developing a numerical method to simulate the fracture creation and propagation, and the coupled thermohydro-mechanical processes in fracture in crystalline rocks. The first research step of Task G is a benchmark simulation, which is designed for research teams to make their modelling codes more robust and verify whether the models can represent an analytical solution for displacements of a single rock fracture. We reproduced the mechanical behavior of rock and embedded single fracture using a three-dimensional grain-based distinct element model for the simulations. In this method, the structure of the rock was represented by an assembly of rigid tetrahedral grains moving independently of each other, and the mechanical interactions at the grains and their contacts were calculated using 3DEC. The simulation results revealed that the stresses induced along the embedded fracture in the model were relatively low compared to those calculated by stress analysis due to stress redistribution and constrained fracture displacements. The fracture normal and shear displacements of the numerical model showed good agreement with the analytical solutions. The numerical model will be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated using various experiments in a further study.

• Journal of Korean Society of Transportation
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• v.26 no.6
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• pp.113-122
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• 2008

This study extended Park et al.(2007c), which analyzed the efficiency of a hierarchical transit network, showed the result of a real data, and analyzed its applicability. Operating cost was estimated using a model which was established in this study, and minimum transit demand was derived from the operating cost. The minimum transit demand value is just a sample calculation, thus it varies by many inside and outside factors of the model. Looking at the inside of the model, operating cost and travel speed are major factors, and the possibility of introducing urban subway becomes high when the operating cost of the transit system is low and its travel speed is high. As far as the outside factors are concerned, according to the analysis on the network structure, transit demand, and transit mode share, the minimum transit demand value which was derived in this study will be the maximum value among the possible values. In the feasibility study, the benefit is likely to be overestimated and the cost is likely to be underestimated than those of this study. It could be concluded that the methodology of a feasibility study is appropriate in the field standard. This study analyzed the efficiency of introduction of urban subway using analytical approach, thus has many shortcomings and limitations. However the practical approach, like feasibility study, has some limitations as well. This study could be a basis on establishing an analysis framework that is more accurate and reasonable by comparing analytical approach and practical approach.

• Journal of Radiation Protection and Research
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• v.7 no.1
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• pp.34-48
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• 1982

The prime purpose of this study is to realize an index quantity, absorbed dose index, defined by the ICRU for the characterization of ambient radiation level at any location for the purpose of radiation protection. The experiment has been designed to be carried out in two phases, namely, preliminary and main experiment. In the primary study a 30cm diameter sphere of polyethylene was used, while in the main experiment that of tissue equivalent material was fabricated and used. Both experiments were performed in the gamma-ray fields of $^{137}Cs\;and\;^{60}Co$, and in a neutron beam of thermal column of the TRIGA MARK-II research reactor. In the measurement of gamma-ray absorbed dose TLD-700 $(^{7}LiF)$ chips were used, and for the neutron dose both Au activation foils and TLD chips (TLD-600 $(^{6}LiF)$ and TLD-700 for the discrimination of gamma-ray contribution) were used. Theoretical assessment of the absorbed dose in the sphere phantom has been carried out in accordance with the Ehrlich's idea that deduced on the basis of Burlin's cavity theory in the case of gamma-ray irradiation. For the analysis of neutron dose fluence-KERMA rate conversion method was used. The explanation on the dose assessment is given in detail. Results obtained were numerically and statistically analyzed and the depth dose distributions are presented in the graphic forms with normalized values. In the concluding remarks, the possibility and difficulty of realizing the index quantity, including questions and problems to be solved are mentioned.

• Journal of Korean Society of Transportation
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• v.26 no.3
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• pp.199-209
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• 2008

This paper is described the concepts and limitations for the traditional directional design hour volume estimation. The main objective of this paper is to establish an estimation method of probabilistic directional design hour volume in order to improve the limitation for the traditional approach method. To express the traffic congestion of specific road segment, this paper proposed the link travel time as the probability that the road capacity can accommodate a certain traffic demand at desired service level. Also, the link travel time threshold was derived from chance-constrained stochastic model. Such successive probabilistic process could determine optimal ranked design hour volume and directional design hour volume. Therefore, the probabilistic directional design hour volume can consider the traffic congestion and economic aspect in road planning and design stage. It is hoped that this study will provide a better understanding of various issues involved in the short term prediction of directional design hourly volume on different types of roads.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.4
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• pp.13-21
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• 2011

Seismic structure pounding between adjacent superstructures may induce the destruction of pier and bridge superstructures and cause local damage that leads to the collapse of the whole bridge system. The pounding problem is related to the expansion of joints, gap distance and seismic response of the abutments. In this research, methods of the contact element approach, the linear spring model, the Kelvin-Voigt model and the Hertz model were studied to analyse the pounding characteristics. The shaking table test for a model specimen such as a bridge superstructure with elastomeric bearings was performed to evaluate the contact element approach methods. Relationships between the time history response from the numerical analysis results and the measured response from the shaking table test are compared. The experimental results were not well matched with the numerical analysis results using the existing pounding stiffness models. Therefore, in this study, coefficients are proposed to calculate the appropriate pounding stiffness ratio.

• Communications for Statistical Applications and Methods
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• v.16 no.5
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• pp.803-812
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• 2009

The application of extreme value theory to financial data is a fairly recent innovation. The classical annual maximum method is to fit the generalized extreme value distribution to the annual maxima of a data series. An alterative modern method, the so-called threshold method, is to fit the generalized Pareto distribution to the excesses over a high threshold from the data series. A more substantial variant is to take the point-process viewpoint of high-level exceedances. That is, the exceedance times and excess values of a high threshold are viewed as a two-dimensional point process whose limiting form is a non-homogeneous Poisson process. In this paper, we apply the two-dimensional non-homogeneous Poisson process model to daily losses, daily negative log-returns, in the data series of KBW/USD exchange rate, collected from January 4th, 1982 until December 31 st, 2008. The main question is how to estimate extreme quantiles of losses such as the 10-year or 50-year return level.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.132-136
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• 2007

최근 지구온난화로 인한 이상기후의 영향으로 강우일수는 줄고 있으나 강수량은 예년과 비슷한 수준을 보이고 있다. 이로 인해 갈수기의 용수부족 현상은 더욱 심해지고. 장마철의 홍수피해와 게릴라성 집중호우로 인한 피해가 커지는 등 해가 갈수록 홍수 예경보의 중요성은 더욱 높아지고 있다. 그럼에도 불구하고 현재 홍수 예경보 체계는 몇 가지 문제를 가지고 있다. 기존 예경보 체계의 경우 한 번의 예측을 수행하기 위해 수반되는 전처리과정과 주계산과정을 거치는 동안 각 과정에서 발생한 오차들이 반복, 누적되어 최종 결과물(예측된 유출량) 속에 모두 포함된다. 또한 기존 체계에서는 유출모형을 적용하기 위해서 토양형. 피복상태 등에 관련된 매개변수들이 필요한데. 이러한 매개변수의 결정에 어려움이 있고. 불확실성을 갖고 있다. 본 연구에서는 불확실성을 적극적으로 인정하고 수학적으로 해석하려는 fuzzy 이론을 신경망 이론에 도입하여 홍수 예경보 시스템의 운영과정에서 발생하는 불확실성의 문제를 해결하고자 하였다. 본 연구에서 사용한 ANFIS(Adaptive Neuro-Fuzzy Inference System)은 data driven model(자료에 기반을 둔 모형)의 하나로 다음과 같은 장점을 가진다. 우선 data driven model은 유역의 물리적, 지형적 특성을 고려하지 않고(매개변수설정에서 발생하는 문제 해결 가능), 입력자료와 출력자료만을 고려하여 구축되는 모형이므로, 유역의 물리적 자료나 지형 자료와 같은 방대한 양의 자료 수집이 필요 없고, 일단 모형이 구축되면 자료의 입력만으로도 신뢰성 높은 결과를 단시간 내에 효율적으로 획득할 수 있다. 그리고 유역 내의 상황이 변화하더라도, 이들의 영향을 고려하여 쉽게 모형을 갱신할 수 있다. 마지막으로 모형의 구축 과정이 물리적 모형에 비해 비교적 간편하다는 장점이 있다. 본 연구에서는 ANFIS를 통해 탄천유역의 강수량 자료와 대곡교의 수위자료를 입력자료로 사용하여 대곡교의 수위를 예측하였다. 입력 자료는 시간차 계열의 강우량과 수위 자료를 사용하였으며 모형을 통하여 t+1, t+2, t+3 시간 후의 수위를 예측하였다.