• 지구물리와물리탐사
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• 제9권1호
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• pp.86-92
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• 2006

정규화된 파동장을 이용하는 탄성파 전파형 역산법은 기존의 전파형 역산법에서 필요로 하는 탄성파원 예측으로 인해 야기되는 잠재적인 역산오차를 피할 수 있다. 본 논문에서는 이러한 전파형 역산법에 가중 평활화제약을 추가하여 분해능을 높였으며, 모든 주파수성분을 동시에 역산하지 않고 주파수 별로 순차적으로 역산하도록 수정하였다. 새로운 방법은 간단한 2 차원 단층모델에 적용하여 검증하였다. 가장 큰 개선점은 적분감도에 기초하여 결정한 가중계수를 모델변수에 도입한 점이다. 모델변수에 가중계수를 적용하면 평활화제약을 선택적으로 완화할 수 있기 때문에 영상화 재구성 시 잘못된 영상을 줄이는데 효과적이다. 다중 단일주파수 역산은 다중주파수 동시역산을 대치할 수 있으며, 특히 작은 주파수부터 먼저 사용하는 순차적인 단일주파수 역산은 계산효율면에서 유용하다.

• Computers and Concrete
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• 제25권3호
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• pp.225-244
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• 2020

The influence of boundary conditions on the bending and free vibration behavior of functionally graded sandwich plates resting on a two-parameter elastic foundation is examined using an original novel high order shear theory. The Hamilton's principle is used herein to derive the equations of motion. The number of unknowns and governing equations of the present theory is reduced, and hence makes it simple to use. This theory includes indeterminate integral variables and contains only four unknowns in which any shear correction factor not used, with even less than the conventional theory of first shear strain (FSDT). Unlike any other theory, the number of unknown functions involved in displacement field is only four, as against five, six or more in the case of other shear deformation theories. Galerkin's approach is utilized for FGM sandwich plates with six different boundary conditions. The accuracy of the proposed solution is checked by comparing it with other closed form solutions available in the literature.

• 대한전자공학회논문지SP
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• 제38권1호
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• pp.54-68
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• 2001

본 논문은 2D 영상에서 겹쳐진 물체를 분리하기 위한 새로운 기법을 제안한다. 제안된 알고리즘은 겹쳐진 물체를 분리하는 보편적인 기법으로서의 매칭 알고리즘이 가지는 계산상의 부담을 줄이고자 하였다. 영상에서의 물체의 표현은 attributed graph를 사용하며, 각 node와 arc는 물체의 면과 면간의 관계에 각각 대응시킨다 또한, 각 arc는 그 parameter로서 관계계수를 가지며 이는 arc를 중심으로 양 끝에 존재하는 임의의 node의 상대 node에 대한 가려짐 상태에 의해 정의된다. 각 node는 이웃 node와의 관계에 의해 다양한 패턴으로 분류되며, 제안된 패턴을 이용하여 node들의 homogeneity를 검사한다. 끝으로, Homogeneity를 만족하는 node들을 하나의 집합(node set)으로 grouping함으로써, 가려진 물체와 가리는 물체를 분리하게 된다. 본 논문에서 제안한 알고리즘은 임의의 형태로 놓여있는 겹쳐진 물체를 효율적으로 분리하고 있으며, 매칭단계 이전에 물체를 분리함으로써 매칭에 필요한 시간부담을 크게 줄일 수 있음을 실험을 통해 보여주고 있다.

• Earthquakes and Structures
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• 제11권5호
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• pp.823-840
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• 2016

The plastic hinge lengths of beams and columns are a critical demand parameter in the nonlinear analysis of structures using the finite element method. The numerical model of a plastic hinge plays an important role in evaluating the response and damage of a structure to earthquakes or other loads causing the formation of plastic hinges. Previous research demonstrates that the plastic hinge length of reinforced concrete (RC) columns is closely related to section size, reinforcement ratio, reinforcement strength, concrete strength, axial compression ratio, and so on. However, because of the limitations of testing facilities, there is a lack of experimental data on columns with large section sizes and high axial compression ratios. In this work, we conducted a series of quasi-static tests for columns with large section sizes (up to 700 mm) and high axial compression ratios (up to 0.6) to explore the propagation of plastic hinge length during the whole loading process. The experimental results show that besides these parameters mentioned in previous work, the plastic hinge of RC columns is also affected by loading amplitude and size effect. Therefore, an approach toward considering the effect of these two parameters is discussed in this work.

• Structural Engineering and Mechanics
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• 제65권4호
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• 한국강구조학회 논문집
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• 제20권6호
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• pp.761-771
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• 2008

열차운행주파수가 철도교의 고유진동수와 일치하면, 철도교의 공진은 피할 수 없다. 또한, 열차가 교량을 매우 빠르게 통과하면, 계측 가능한 시간응답의 샘플 수는 매우 적다. 본 논문은 그러한 경우에 대하여 철도 교량의 동특성을 매우 효과적으로 추출할 수 있는 TDD기법과 SI기법을 소개한다. 열차통과 직후에 교량의 자유진동 시간응답구간의 상호상관을 이용하여 모드형상은 TDD기법으로 추출하고, 고유진동수 및 감쇠비 등의 시간변수들은 SI기법으로 추출한다. 경부고속철도 시스템에 위치한 2경간 강합성교량의 동특성 추출실험을 통하여 TDD기법과 SI기법의 현장 적용성이 검토되었다. 동특성 추정결과는 기존의 ERADC기법의 결과와 비교 검토되었다. 추정결과는 기존의 방법을 이용하여 획득된 결과와 매우 잘 일치한다.

• 대한기계학회논문집A
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• 제40권3호
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• pp.275-280
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• 2016

본 연구에서는 코일스프링의 동적 거동 분석을 위해 스프링 릴리즈 시험기를 설계하고 시험을 실시하였다. 시뮬레이션을 위해 집중 매개변수 스프링모델을 개발하였다. 실험계획법을 이용하여 코일스프링의 설계변수들을 최적화하였다. 2수준의 요인배치법을 사용하여 설계변수들의 민감도와 교호작용을 분석하였다. 민감도와 교호작용 분석결과를 통해 설계변수의 수준을 재배열하였다. 혼합수준 요인배치법을 이용하여 설계변수를 최적화 하였다. 최적설계 결과에 따르면, 스프링 조작기의 성능이 2.90 % 개선되었다.

• 대한기계학회논문집
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• 제13권2호
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• pp.287-298
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• 1989

본 수치적 해석에서는 H$_{w}$/H$_{g}$의 비가 5.0~16.7의 범위에서 수행된 실험결과를 바탕으로 기존의 ｋ-.epsilon. 난류모델을 사용하여, 고려하고자 하는 변수, 즉 유입유속, 입구 게이트의 높이, 수위, 배플의 유.무등에 따라서 액체의 유동형태가 어떻게 변하는가를 살펴 보고자 한다.다.

• Communications for Statistical Applications and Methods
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• 제25권3호
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• pp.245-261
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• 2018

Attempts have been made to define new classes of distributions that provide more flexibility for modelling skewed data in practice. In this work we define a new extension of the generalized gamma distribution (Stacy, The Annals of Mathematical Statistics, 33, 1187-1192, 1962) for Marshall-Olkin generalized gamma (MOGG) distribution, based on the generator pioneered by Marshall and Olkin (Biometrika, 84, 641-652, 1997). This new lifetime model is very flexible including twenty one special models. The main advantage of the new family relies on the fact that practitioners will have a quite flexible distribution to fit real data from several fields, such as engineering, hydrology and survival analysis. Further, we also define a MOGG mixture model, a modification of the MOGG distribution for analyzing lifetime data in presence of cure fraction. This proposed model can be seen as a model of competing causes, where the parameter associated with the Marshall-Olkin distribution controls the activation mechanism of the latent risks (Cooner et al., Statistical Methods in Medical Research, 15, 307-324, 2006). The asymptotic properties of the maximum likelihood estimation approach of the parameters of the model are evaluated by means of simulation studies. The proposed distribution is fitted to two real data sets, one arising from measuring the strength of fibers and the other on melanoma data.

• 한국농공학회논문집
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• 제49권4호
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• pp.13-22
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• 2007

The uncertainty in water quality model predictions is inevitably high due to natural stochasticity, model uncertainty, and parameter uncertainty. An integrated modeling system under uncertainty was described and demonstrated for use in watershed management and receiving-water quality prediction. A watershed model (HSPF), a receiving water quality model (WASP), and a wetland model (NPS-WET) were incorporated into an integrated modeling system (modified-BASINS) and applied to the Hwaseong Reservoir watershed. Reservoir water quality was predicted using the calibrated integrated modeling system, and the deterministic integrated modeling output was useful for estimating mean water quality given future watershed conditions and assessing the spatial distribution of pollutant loads. A Monte Carlo simulation was used to investigate the effect of various uncertainties on output prediction. Without pollution control measures in the watershed, the concentrations of total nitrogen (T-N) and total phosphorous (T-P) in the Hwaseong Reservoir, considering uncertainty, would be less than about 4.8 and 0.26 mg 4.8 and 0.26 mg $L^{-1}$, respectively, with 95% confidence. The effects of two watershed management practices, a wastewater treatment plant (WWTP) and a constructed wetland (WETLAND), were evaluated. The combined scenario (WWTP + WETLAND) was the most effective at improving reservoir water quality, bringing concentrations of T-N and T-P in the Hwaseong Reservoir to less than 3.54 and 0.15 mg ${L^{-1}$, 26.7 and 42.9% improvements, respectively, with 95% confidence. Overall, the Monte Carlo simulation in the integrated modeling system was practical for estimating uncertainty and reliable in water quality prediction. The approach described here may allow decisions to be made based on probability and level of risk, and its application is recommended.