• 대한원격탐사학회지
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• 제25권6호
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• pp.547-557
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• 2009

LIDAR (LIght Detection And Ranging) is an active remote sensing technology which provides 3D coordinates of the Earth's surface by performing range measurements from the sensor. Early small footprint LIDAR systems recorded multiple discrete returns from the back-scattered energy. Recent advances in LIDAR hardware now make it possible to record full digital waveforms of the returned energy. LIDAR waveform decomposition involves separating the return waveform into a mixture of components which are then used to characterize the original data. The most common statistical mixture model used for this process is the Gaussian mixture. Waveform decomposition plays an important role in LIDAR waveform processing, since the resulting components are expected to represent reflection surfaces within waveform footprints. Hence the decomposition results ultimately affect the interpretation of LIDAR waveform data. Computational requirements in the waveform decomposition process result from two factors; (1) estimation of the number of components in a mixture and the resulting parameter estimates, which are inter-related and cannot be solved separately, and (2) parameter optimization does not have a closed form solution, and thus needs to be solved iteratively. The current state-of-the-art airborne LIDAR system acquires more than 50,000 waveforms per second, so decomposing the enormous number of waveforms is challenging using traditional single processor architecture. To tackle this issue, four parallel LIDAR waveform decomposition algorithms with different work load balancing schemes - (1) no weighting, (2) a decomposition results-based linear weighting, (3) a decomposition results-based squared weighting, and (4) a decomposition time-based linear weighting - were developed and tested with varying number of processors (8-256). The results were compared in terms of efficiency. Overall, the decomposition time-based linear weighting work load balancing approach yielded the best performance among four approaches.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.288-288
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• 2018

점착성 유사는 응집 현상을 겪는 유사로, 응집 현상(Flocculation Process)는 응집 과정(Aggregation Process)와 파괴 과정(Breakup Process)의 경쟁으로 이루어진다고 여겨진다. 응집 현상을 통해 점착성 유사는 물과 점착성을 띠는 작은 입자들의 덩어리인 플럭(Floc)을 형성하여 흐름 내에서는 대부분이 플럭의 형태로 이동한다. 점착성 유사의 응집 모형 중 하나인 플럭 성장모형(Floc Growth Model, FGM)은 상미분 방정식으로 시간에 따른 플럭의 크기를 계산하는 모형이다. 응집과 파괴의 평형 상태에서 평균 입경을 얻는다. 이러한 FGM은 낮은 수치 계산 비용으로 합리적인 계산 결과를 얻을 수 있으며, 유사 이동 모형 혹은 흐름 모형과의 결합이 수월한 장점을 가진다. 또한, 닫힌 계(Closed System)에서 질량이 보존되는 특징이 있다. 반면, 결정론적인 특성을 띠면서 특정 플럭 크기만을 계산하기 때문에 점착성 유사의 입도 분포에 대한 정보를 얻을 수 없다. 결정론적 특성을 띠는 FGM에 추계학적 방법을 적용함으로써 특정 확률 분포형을 가지는 플럭의 입도 분포를 얻을 수 있다. 본 연구에서는 기 개발된 추계학적 FGM과 유사 이동 모형의 결합을 통해 변화하는 유수동역학적 조건에서 플럭의 입도 분포를 산정하고자 한다. 이전의 많은 실험실 실험 결과들은 부유가 발생한 상태를 유지하면서 수행되는 것으로, 특정 난류 특성(난류 소산 매개변수)와 특정 유사 농도 조건에서의 입도 분포를 얻는다. 그러나 하구부 및 하천의 하류는 조류의 영향을 받는 구간으로, 점착성 유사의 특성을 분석하기 위해서는 변화하는 유수동역학적 특성에 관한 고려가 필수적이라 할 수 있다. 결합된 점착성 유사 입도 분포 모형은 플럭의 침강과 재부유를 고려할 수 있는 특징을 가지며, 실측자료와의 비교를 통해 입도 분포를 합리적으로 모의하는 것으로 나타난다. 본 연구에서 개발된 점착성 유사 입도 분포 모형은 나아가 비점착성 유사의 입도 분포 모형과의 결합을 통해 두 종류의 유사가 혼재하는 구간에서도 합리적인 입도분포와 유사의 이동을 모의할 수 있을 것으로 예측된다.

• The Journal of Advanced Prosthodontics
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• 제11권3호
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• pp.179-186
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• 2019

PURPOSE. The purpose of this study was to compare two novel impression methods and a conventional impression method for edentulous jaws using 3-dimensional (3D) analysis software. MATERIALS AND METHODS. Five edentulous patients (four men and one woman; mean age: 62.7 years) were included. Three impression techniques were used: conventional impression method (CI; control), simple modified closed-mouth impression method with a novel tray (SI), and digital impression method using an intraoral scanner (DI). Subsequently, a gypsum model was made, scanned, and superimposed using 3D analysis software. Mean area displacement was measured using CI method to evaluate differences in the impression surfaces as compared to those values obtained using SI and DI methods. The values were confirmed at two to five areas to determine the differences. CI and SI were compared at all areas, while CI and DI were compared at the supporting areas. Kruskal-Wallis test was performed for all data. Statistical significance was considered at P value <.05. RESULTS. In the comparison of the CI and SI methods, the greatest difference was observed in the mandibular vestibule without statistical significance (P>.05); the difference was < 0.14 mm in the maxilla. The difference in the edentulous supporting areas between the CI and DI methods was not significant (P>.05). CONCLUSION. The CI, SI, and DI methods were effective in making impressions of the supporting areas in edentulous patients. The SI method showed clinically applicability.

• 디지털융복합연구
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• 제17권9호
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• pp.127-133
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• 2019

임의상환가능 상품은 옵션을 이용하여 수요창출과 리스크를 줄이는 서비스 파생상품의 일종이다. 본 논문은 임의상환가능 상품이 도입된 후, 예약 요청의 온라인승인 방법과 일괄승인 방법 둘의 성능을 비교한다. 최적의 예약관리법을 계산하기 위하여, 역행 동적계획법(Backward Dynamic Programming)과 확률적 최적화(Stochastic Optimization) 방법을 이용한다. 직관적으로는 공급자는 수요정보를 이용하여 일괄승인 방법으로 더 높은 수익을 올릴 것으로 예상되지만, 본 논문은 두 예약 요청 승인 방법의 예약관리전략과 수익은 동일하다는 것을 증명함으로써, 현행 예약 요청 승인 방법의 변화 없이 임의상환가능 상품을 빠르게 도입할 수 있다는 실무적인 기여도가 있다. 본 논문은 세 종류의 서비스 요금 클래스가 있을 경우 최적의 해를 정확히 구하였다. 향후 연구는 다양한 요금 모델에서 최적의 해를 구하는 것이다.

• Computers and Concrete
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• 제27권4호
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• pp.319-332
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• 2021

The performance of gene expression programming (GEP) in predicting the compressive strength of bacteria-incorporated geopolymer concrete (GPC) was examined in this study. Ground-granulated blast-furnace slag (GGBS), new bacterial strains, fly ash (FA), silica fume (SF), metakaolin (MK), and manufactured sand were used as ingredients in the concrete mixture. For the geopolymer preparation, an 8 M sodium hydroxide (NaOH) solution was used, and the ambient curing temperature (28℃) was maintained for all mixtures. The ratio of sodium silicate (Na2SiO3) to NaOH was 2.33, and the ratio of alkaline liquid to binder was 0.35. Based on experimental data collected from the literature, an evolutionary-based algorithm (GEP) was proposed to develop new predictive models for estimating the compressive strength of GPC containing bacteria. Data were classified into training and testing sets to obtain a closed-form solution using GEP. Independent variables for the model were the constituent materials of GPC, such as FA, MK, SF, and Bacillus bacteria. A total of six GEP formulations were developed for predicting the compressive strength of bacteria-incorporated GPC obtained at 1, 3, 7, 28, 56, and 90 days of curing. 80% and 20% of the data were used for training and testing the models, respectively. R2 values in the range of 0.9747 and 0.9950 (including train and test dataset) were obtained for the concrete samples, which showed that GEP can be used to predict the compressive strength of GPC containing bacteria with minimal error. Moreover, the GEP models were in good agreement with the experimental datasets and were robust and reliable. The models developed could serve as a tool for concrete constructors using geopolymers within the framework of this research.

• Steel and Composite Structures
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• 제38권3호
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• pp.337-353
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• 2021

Micro-electro-mechanical systems (MEMS) are widely employed in sensors, biomedical devices, optic sectors, and micro-accelerometers. New reinforcement materials such as carbon nanotubes as well as graphene platelets provide stiffer structures with controllable mechanical specifications by changing the graphene platelet features. This paper deals with buckling analyses of functionally graded graphene platelets micro plates with two piezoelectric layers subjected to external applied voltage. Governing equations are based on Kirchhoff plate theory assumptions beside the modified couple stress theory to incorporate the micro scale influences. A uniform temperature change and external electric field are regarded along the micro plate thickness. Moreover, an external in-plane mechanical load is uniformly distributed along the micro plate edges. The Hamilton's principle is employed to extract the governing equations. The material properties of each composite layer reinforced with graphene platelets of the considered micro plate are evaluated by the Halpin-Tsai micromechanical model. The governing equations are solved by the Navier's approach for the case of simply-supported boundary condition. The effects of the external applied voltage, the material length scale parameter, the thickness of the piezoelectric layers, the side, the length and the weight fraction of the graphene platelets as well as the graphene platelets distribution pattern on the critical buckling temperature change and on the critical buckling in-plane load are investigated. The outcomes illustrate the reduction of the thermal buckling strength independent of the graphene platelets distribution pattern while meanwhile the mechanical buckling strength is promoted. Furthermore, a negative voltage, -50 Volt, strengthens the micro plate stability against the thermal buckling occurrence about 9% while a positive voltage, 50 Volt, decreases the critical buckling load about 9% independent of the graphene platelet distribution pattern.

• Steel and Composite Structures
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• 제43권5호
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• pp.581-601
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• 2022

The main objective of this research work is to investigate the free vibration behavior of annular sandwich plates resting on the Kerr foundation at thermal conditions. This sandwich configuration is composed of two FGM face sheets as coating layer and a porous GPLRC (GPL reinforced composite) core. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the core thickness direction. To model closed-cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme is used, while the Poisson's ratio and density are computed by the rule of mixtures. Besides, the material properties of two FGM face sheets change continuously through the thickness according to the power-law distribution. To capture fundamental frequencies of the annular sandwich plate resting on the Kerr foundation in a thermal environment, the analysis procedure is with the aid of Reddy's shear-deformation plate theory based high-order shear deformation plate theory (HSDT) to derive and solve the equations of motion and boundary conditions. The governing equations together with related boundary conditions are discretized using the generalized differential quadrature (GDQ) method in the spatial domain. Numerical results are compared with those published in the literature to examine the accuracy and validity of the present approach. A parametric solution for temperature variation across the thickness of the sandwich plate is employed taking into account the thermal conductivity, the inhomogeneity parameter, and the sandwich schemes. The numerical results indicate the influence of volume fraction index, GPLs volume fraction, porosity coefficient, three independent coefficients of Kerr elastic foundation, and temperature difference on the free vibration behavior of annular sandwich plate. This study provides essential information to engineers seeking innovative ways to promote composite structures in a practical way.

• Structural Engineering and Mechanics
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• 제84권5호
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• pp.685-697
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• 2022

Nanotechnology has become one of the interesting technique used in material science and engineering. However, it is low used in civil engineering structures. The purpose of the present study is to investigate the static behavior of concrete plates reinforced with silica-nanoparticles. Due to agglomeration effect of silica-nanoparticles in concrete, Voigt's model is used for obtaining the equivalent nano-composite properties. Furthermore, the plate is simulated mathematically with higher order shear deformation theory. For a large use of this study, the concrete plate is assumed resting on a Pasternak elastic foundation, including a shear layer, and Winkler spring interconnected with a Kerr foundation. Using the principle of virtual work, the equilibrium equations are derived and by the mean of Hamilton's principle the energy equations are obtained. Finally, based on Navier's technique, closed-form solutions of simply supported plates have been obtained. Numerical results are presented considering the effect of different parameters such as volume percent of SiO₂ nanoparticles, mechanical loads, geometrical parameters, soil medium, on the static behavior of the plate. The most findings of this work indicate that the use of an optimum amount of SiO₂ nanoparticles on concretes increases better mechanical behavior. In addition, the elastic foundation has a significant impact on the bending of concrete slabs.

• 한국ITS학회 논문지
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• 제22권2호
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• pp.54-63
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• 2023

보행 교통사고를 예측하기 위해서는 보행 및 차량 통행량을 정확히 반영해야 한다. 그러나 보행량은 차량 통행량에 비해 측정에 어려움이 있다. 기존 연구는 직접 조사, 가구통행실태조사 등을 통해 추정하였지만 이는 많은 비용과 시간이 소요되며 정확도가 떨어진다. 이에 본 연구는 적은 시간과 비용으로 실시간으로 데이터를 수집 및 분석할 수 있는 스마트폰을 활용한 모바일 cctv를 대안으로 제시하였다. 본 연구는 사고로 발전할 수 있는 보행자-차량간 상충을 보행사고 노출로 정의하였다. 대구 동성로 일대의 40개 구간에 모바일 cctv를 설치한 후, 수집된 데이터를 활용하여 음이항 회귀분석을 통해 보행사고 노출을 추정한다. 분석 결과 보행사고 노출 변수들도 통계적으로 유의한 결과를 보인다. 분석 결과를 통해 보행사고 노출 추정 모형을 개발하였고, 이를 통해 잠재적으로 보행사고 발생할 수 있는 구간을 도출하는 것에 활용될 수 있음을 보여준다.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.516-525
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• 1994

TMI 및 Chernobyl 사고이후 향후 원전에 대한 안전성 향상을 강화하기위해 개량형 원전에 대해 여러가지 피동형 안전설비가 제안되고 있다. 피동냉각계통의 타당성을 검증하고 상세 설계자료를 제공하기 위해, 본 연구는 웨스팅하우스사의 AP-600 피동격납용기와 같은 한쪽 가열면을 갖는 폐쇄유로에 대한 공기 유입구 위치 및 외부영향이 자연순환 공기유량에 미치는 영향과 자연 및 강제대류하에서 대류열전달계수를 조사하였다. 본 실험은 AP-600 격납용기를 1/26로 축소한 segment 유형의 실험장치를 토대로 수행되었다. 자연 및 강제대류 조건하의 공기유로내 특정 위치에서 공기의 속도 및 온도를 측정하였다. 실험결과는 일차원 단순 모델과 비교하였으며, 좋은 일치점을 보였다.