• 수산해양기술연구
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• 제47권1호
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• pp.1-9
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• 2011

In order to investigate the cause and magnitude of scale effect occurring in the model experiments of fishing nets, five pairs of Nylon pyramid nets and one pair of PE ones in which all the two nets paired were equal each other in the factors determining their flow resistance, i. e., the ratio d/l of diameter d to length l of bars, the angle f between two adjacent bars, the attack angle q of nettings to the water flow, and the wall area S of nets, and different in the values of d and l were prepared. Then, the nets were attached to the circular steel frame alternately and their flow resistances with shapes in water were measured on the sea ascribing no turbulent flows by using the tension meter made of a block bearing for the experiment. All the Nylon nets were spreads out easily in water to form a circular cone at relatively low velocity of water and showed the resistance smaller a little in the nets with larger d and l than them with smaller d and l, because the filtration of water through meshes become easier in nets especially with larger l. But PE nettings were not spread out sufficiently on account of their small flexibility and showed higher resistance especially in them with thicker twines. Therefore, the difference in bar length or mesh size and flexibility of nettings between prototype and model nets are regarded to become factors ascribing scale effect. Especially the influence of the difference in mesh size may become large significantly in actual model experiments because the mesh size of model nets is decided at much larger value than that given by scale ratio and so the difference of mesh size between the two nets become much larger than that between nets used in this experiment.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.337-342
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• 2011

A roller rig has been widely used in the study about dynamic stability and railway safety. However, the cost for constructing the roller rig and the difficulty in adjusting the design parameters for vehicle systems lead to the development of a small scale simulator which is cheaper than the large scale test systems and easy to control the parameters affecting dynamic characteristics of the railway vehicle. For the operation of the small scale test system called a small scale simulator, it is required to investigate the performance and characteristics of the system. This could be achieved by a comparative study between an analysis and an experiment. This paper presented the analytical model which could be used for verifying of the test results and understanding of the physical behavior of the dynamic system comprising the small scale bogie and the simulator.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2000년도 춘계공동학술대회 논문집
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• pp.235-238
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• 2000

This article presents an adaptive decision tree algorithm for dynamically reasoning machine failure cause out of real-time, large-scale machine status database. On the basis of experiment using semiconductor etching machine, it has been verified that our model outperforms previously proposed decision tree models.

• 한국해양공학회지
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• 제32권5호
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• pp.351-360
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• 2018

The construction of large scale harbor structures at Maengbang beach, which is located on the eastern coast of Korea, is of great concern because it may cause disastrous beach erosion in the vicinity. Therefore, a hydraulic model experiment was conducted to examine the morphological changes after such construction. The water depth was scaled using the method of Van Rijn (2010), which is a well-known scale law, but the results appeared to be overestimated. The present study developed a new scale law that applies an equilibrium beach profile formula to scale the model evolution to the prototype scale. When compared with survey data observed at Maengbang beach, the proposed method showed better agreement than the method of Van Rijn (2010).

• Asian Journal of Atmospheric Environment
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• 제7권3호
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• pp.161-168
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• 2013

In this study, an investigation was conducted to assess the washout mechanism of Asian dust particles through both laboratory-scale experiment and model calculation. To artificially simulate Asian dust particle, $CaCO_3$ particles were generated inside an experimental chamber. They were then scavenged by the artificial rain drops. The abundant $CaCO_3$ particles scavenged on a rain drop were successively identified by SEM observation. The concentrations of Ca in residual $CaCO_3$ particles on individual droplet were quantified by PIXE analysis. There was a tendency toward a high accumulation of Ca on a relatively small drop (e.g., <1.0 mm diameter). It is thus suggested that smaller rain drops can effectively scavenge a significant amount of Asian dust particles in ambient atmosphere. The numerical estimation can account for 92.1% and 83.2% of Ca that were measured in small (<1.0 mm diameter) and large (>2.0 mm diameter) size drops, respectively.

• Geomechanics and Engineering
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• 제31권5호
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• pp.529-543
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• 2022

The lattice-spring-based synthetic rock mass model (LS-SRM) technique has been extensively employed in large open-pit mining and underground projects in the last decade. Since the LS-SRM requires a complex and time-consuming calibration process, a robust approach was developed using the Response Surface Methodology (RSM) to optimize the calibration procedure. For this purpose, numerical models were designed using the Box-Behnken Design technique, and numerical simulations were performed under uniaxial and triaxial stress states. The model input parameters represented the models' micro-mechanical (lattice) properties and the macro-scale properties, including uniaxial compressive strength (UCS), elastic modulus, cohesion, and friction angle constitute the output parameters of the model. The results from RSM models indicate that the lattice UCS and lattice friction angle are the most influential parameters on the macro-scale UCS of the specimen. Moreover, lattice UCS and elastic modulus mainly control macro-scale cohesion. Lattice friction angle (flat joint fiction angle) and lattice elastic modulus affect the macro-scale friction angle. Model validation was performed using physical laboratory experiment results, ranging from weak to hard rock. The results indicated that the RSM model could be employed to calibrate LS-SRM numerical models without a trial-and-error process.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.380-391
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• 2014

In this study, the scale effect on the performance of the podded propeller of tractor type is investigated. Turbulent flow computations are carried out for Reynolds numbers increasing progressively from model scale to full scale using the CFD analysis. The result of the flow calculation for model scale Reynolds numbers agrees well with that of the experiment of a large cavitation tunnel. The existing numerical analysis indicates that the performance of the podded propeller blades is mainly influenced by the advance coefficient and relatively little by the Reynolds number. However, the drag of pod housing with propeller in operation is different from that of pod housing without propeller due to the acceleration and swirl of propeller slipstream which is altered by propeller loading as well as the pressure recovery and friction according to Reynolds number, which suggests that the pod housing drag under the condition of propeller in operation is the key factor of the scale effect on the performance between model and full scale podded propellers. The so called 'drag ratio', which is the ratio of pod housing drag to total thrust of podded propeller, increases as the advance coefficient increases due to accelerated flow in the slipstream of the podded propeller. However, the increasing rate of the drag ratio reduces continuously as the Reynolds number increases from model to full scale progressively. The contribution of hydrodynamic forces, which acts on the parts composed of the pod housing with propeller operating in various loading conditions, to the thrust and the torque of the total propeller unit are presented for a range of Reynolds numbers from model to full scales.

• Structural Engineering and Mechanics
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• 제53권3호
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• pp.393-410
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• 2015

Two dimensional numerical models and physical models have been developed to study the highly nonlinear interactions between waves and breakwaters, but several of these models consider the effects of the structural dynamic responses and the shape of the breakwater axis on the wave pressures. In this study, a multi-material Arbitrary Lagrangian Eulerian (ALE) method is developed to simulate the nonlinear interactions between nonlinear waves and elastic seawalls on a coastal rubble mound breakwater, and is validated experimentally. In the experiment, a solitary wave is generated and used with a physical breakwater model. The wave impact is validated computationally using a breakwater - flume coupling model that replicates the physical model. The computational results, including those for the wave pressure and the water-on-deck, are in good agreement with the experimental results. A local breakwater model is used to discuss the effects of the structural dynamic response and different design parameters of the breakwater on wave loads, together with pressure distribution up the seawall. A large-scale breakwater model is used to numerically study the large-scale wave impact problem and the horizontal distribution of the wave pressures on the seawalls.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 1998년도 추계학술대회 논문집
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• pp.36-39
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• 1998

It is very difficult for the large-scale retailers, who deal with tens of thousands of items, to price all the items dynamically reflecting all the constraints and policies. In spite of its importance, the prices are determined by human experts because the process of setting the prices of all the items is not established yet. To solve this problem, we adopt a mixed model that combines three typical pricing models: cost-plus model, competition-oriented model, and demand-oriented model. Since each model an be converted to a set of constraints in point and interval forms, solving the pricing problem with the three groups of models requires an algorithm which can solve the problem with weighted constraints of intervals and points. So we have devised an algorithm named “Point Determination Algorithm”. From the rules that represents tile models, the constraints are extracted to be solvable by tile Point Determination Algorithm. A prototype KAPA (Knowledge Assisted pricing Advisor) is developed with this idea using the expert system environment UNIK - a tool developed by KAIST. According to the experiment with 76 items in comparison with 53 human pricing experts we confirmed that the KAPA can perform highly consistent with human experts. This implies KAPA system is applicable to pricing millions of items dynamically.

• 한국정보전자통신기술학회논문지
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• 제13권4호
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• pp.306-311
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• 2020

본 논문은 대량의 데이터를 활용한 모델 개발 시 다양한 라이브러리를 갖춘 파이썬 언의의 성능 향상방법을 다룬다. 파이썬 언어는 엑셀과 같은 스프레드시트 형태 데이터 처리 시 Pandas 라이브러리를 사용한다. 데이터 처리 시파이썬은 기가단위 이하 데이터 처리 시에는 인-메모리로 연산하여 성능 측면에서 크게 이슈가 없다. 하지만 기가단위 이상 데이터 처리 시 성능 이슈가 발생한다. 이에 본 논문은 데이터 처리 시 Pandas와 같이 사용할 수 있는 Dask 라이브러리를 활용하여 단일 클러스터 및 다중 클러스터에서 실행 작업을 분산처리 가능한 방법을 소개한다. 실험은 동일 사양의 하드웨어에서 간단한 지수산출 모델을 Pandas만 사용해서 처리하는 속도와 Dask를 같이 사용해서 처리하는 속도를 비교한다. 본 논문은 파이썬의 장점인 다양한 라이브러리를 쉽게 사용할 수 있다는 점을 유지하면서 성능측면에서도 대량의 데이터를 CPU 코어들이 분산 처리하여 모델을 개발할 수 있는 방법을 제시한다.