• 한국안전학회지
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• 제28권1호
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• pp.12-17
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• 2013

Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was exposed for the blade safety. Plain woven CFRP instead of GFRP was inserted into the layer of the box spar for improving the strength and blade life. DCB(Double Cantilever Beam) specimen was used for evaluating fracture toughness and damage evaluation of interlaminar delamination. The material used in the experiment is a commercial material known as CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.) and UD glass fiber prepreg(Hyundai Fiber Co.). From the results, crack growth rate is not so different according to the variation of the initial crack length. Mode I interlamainar fracture toughness of fiber direction $0^{\circ}$ is higher than that of $45^{\circ}$. Interlaminar fracture has an effect on fiber direction and K decreased with lower value according to increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness is under the mixed mode loading condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode.

• 한국항해학회지
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• 제4권2호
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• pp.7-38
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• 1980

Nowadays researchers attach a great importance to the problems concerned with scientific information in the field of science and engineering. There are some reasons for it, that is, ⅰ) the amount of scientific information increases in proportion to the activities of scientists and engineers, so it is difficult to pick up a real valuable information ⅱ) it becomes more important to use a variety of information in proportion to the spread ofthe branch of science ⅲ) since the medium of scientific information is mostly technical papers, it is very difficult to mechanically transact these papers and to keep all documents and scientific informations for a long time. To cope with these difficult situations, many technical skills have been developed, for example, data-base, automatic information retrieval, micro-film and so on. But there are comparatively few investigation on the matter how the researchers who are users and producers think about the systematization of scientific information usage, so this paper investigates the thought and information needs of researchers, and proposes a basis of a method for systematization of scientific information usage. The author inspects the actual conditions of scientific information, reconsider the method which has been used and investigates the matter of how researchers whose interest is closely related to the study of marine affairs think about problems of scientific information usage by thequestionarie of Fuzzy-DEMATEL method. Also, FSM which is method for structuring hierarchy for the several complex problems on the basis of fuzzy sets theory is adopted as a tool of analysis. We can understand the key problems and make a story to solve the systematization of scientific information usage from the results of the analysis and those results will be directly applicable to construct a new system for scientific information usage.

• 한국치위생학회지
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• 제6권4호
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• pp.263-282
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• 2006

The purpose of study was to offer devices to activate the dental health class of community health center and to evaluate the present programs and to propose adequate guidelines for future public dental health program of dental health care in health center. For this study, the mail quastionnaire survey was carried out from the 116 dental hygienists who are working in community health center. Present condition and direction of public dental health service are as follows: dentist's office was 90% by area and work department. Dental health department was equipped in 91.7% of 'public health center', but 'health branch office' was 57.9%. Dental hygienist education condition of Public health center was the most frequency in 'At large city'. 'Have no entirely' of dental health education number of times was 35.8% in 3 years. That is 44.5% in supplement insturction. Most Dental hygienist's business was most 'teeth-sealant' and 'Old man false teeth prosthetic dentistry business'. Therefor, The Obstacle factors of dental health service activity were 'manpower tribe(average 3.92)', and next 'lack of understanding and support insufficiency of law(average 3.47)'. Curriculum for educational practice should be also designed for brightening the dental health service business. The most important thing for dental health service is 'expanding and improving the facilities Legal system' and next 'Opportunity enlargement and activation that can take dental hygienist's residency'.

• 상하수도학회지
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• 제20권6호
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• pp.799-811
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• 2006

As an alternative measure to replace reactive stance with proactive one, a risk based management scheme has been commonly applied to enhance public satisfaction on water service by providing a higher creditable solution to handle a rehabilitation problem of pipe having high potential risk of leaks. This study intended to examine the feasibility of a simulation model to predict a recurrence probability of pipe leaks. As a branch of the data mining technique, probabilistic neural network (PNN) algorithm was applied to infer the extent of leaking recurrence probability of water network. PNN model could classify the leaking level of each unit segment of the pipe network. Pipe material, diameter, C value, road width, pressure, installation age as input variable and 5 classes by pipe leaking probability as output variable were built in PNN model. The study results indicated that it is important to pay higher attention to the pipe segment with the leak record. By increase the hydraulic pipe pressure to meet the required water demand from each node, simulation results indicated that about 6.9% of total number of pipe would additionally be classified into higher class of recurrence risk than present as the reference year. Consequently, it was convinced that the application of PNN model incorporated with a data base management system of pipe network to manage municipal water distribution network could make a promise to enhance the management efficiency by providing the essential knowledge for decision making rehabilitation of network.

• 대한기계학회논문집A
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• 제36권9호
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• pp.1103-1108
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• 2012

주증기관은 보일러와 터빈을 연결하는 주요계통이다. 운전조건으로 인한 배관시스템에 손상을 제한 할 수 있기 때문에 수격현상 해석은 중요하다. 배관시스템의 불안정한 유동에 의해 생성되는 수격현상은 압력의 과도한 변화, 진동 및 소음을 일으킬 수 있다. 주증기관 구조는 운전환경아래 압력맥동 및 여러 진동 등을 안전하게 견딜 수 있도록 설계되어야 한다. 본 논문에서는 정지 및 정상 운전기간 동안 배관에 유입되는 수격현상을 과도조건에 적용하여 ASME 피로수명 방법론과 유한요소해석에 따라 주증기관의 구조건전성을 평가하였다. 계산된 교번응력 및 피로응력 평가 결과, ASME 피로수명의 허용요건을 만족하였다.

• 한국항해항만학회지
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• 제32권6호
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• pp.453-458
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• 2008

원형실린더에 크기가 다른 제어봉을 부착하여 2차원 단면 유통특성에 대해서 시간평균유동장을 계측하여 근접후류 제어에 관하여 PIV기법을 적용하여 연구를 수행하였다. 모델시험은 각각 크기가 다른 제어봉을 적용하였으며($d/D=0.1{\sim}d/D=0.5$) 레이놀즈수는 원형실린더의 직경을 기준으로 Re=15,000으로 적용하였다. 유동장의 속도분포론 획득하기 위해 2프레임 상호상관법을 이용하였다. 실험에 적용된 원형실린더(D=50mm)에 제어봉을 부착한 결과를 상호 비교함으로서 시간평균속도분포와 제어봉에 의한 유동제어 효과를 알 수 있었다.

• Earthquakes and Structures
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• 제18권6호
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• pp.691-707
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• 2020

One of the most important issues in structural systems is evaluation of the margin of safety in low and mid-rise buildings against the progressive collapse mechanism due to the earthquake loads. In this paper, modeling of collapse propagation in structural elements of RC frame buildings is evaluated by tracing down the collapse points in beam and column structural elements, one after another, under earthquake loads and the influence of column removal is investigated on how the collapse expansion in beam and column structural members. For this reason, progressive collapse phenomenon is studied in 3-story and 5-story intermediate moment resisting frame buildings due to the corner and edge column removal in presence of the earthquake loads. In this way, distribution and propagation of the collapse in progressive collapse mechanism is studied, from the first element of the structure to the collapse of a large part of the building with investigating and comparing the results of nonlinear time history analyses (NLTHA) in presence of two-component accelograms proposed by FEMA_P695. Evaluation of the results, including the statistical survey of the number and sequence of the collapsed points in process of the collapse distribution in structural system, show that the progressive collapse distribution are special and similar in low-rise and mid-rise RC buildings due to the simultaneous effects of the column removal and the earthquake loads and various patterns of the progressive collapse distribution are proposed and presented to predict the collapse propagation in structural elements of similar buildings. So, the results of collapse distribution patterns and comparing the values of collapse can be utilized to provide practical methods in codes and guidelines to enhance the structural resistance against the progressive collapse mechanism and eventually, the value of damage can be controlled and minimized in similar buildings.

• 지질공학
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• 제29권3호
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• pp.237-249
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• 2019

본 연구에서는 지하수의 이동에 영향을 주는 암반의 균열에 대해서 고온하에서의 다단계 압력실험을 통해 균열면의 거칠기 변화에 대한 분석을 실시하였다. 연구에 사용된 시료는 지표에서 지하 500 m 구간에서 획득한 조립질 화성암과 세립질 화성암 시료 중 심도 약 40 m와 270 m의 시료를 실험에 사용하였다. 압력은 최대 120 MPa 까지 가압을 하였으며, 단계적으로 10 MPa씩 증가하면서 실험을 수행하였다. 각 단계에서의 표면 변화를 관측하기 위해서 고분해능 3차원 다초점 레이저 스캔 현미경(Confocal Laser Scanning Microscope, CLSM)을 사용하였으며, 이를 통해서 미세한 표면의 거칠기를 확인할 수 있었다. 거칠기의 변화에 대해서는 거칠기 인자값을 기준으로 변화된 양을 계산하였다. 본 실험에 사용된 시료는 $20{\times}40{\times}5mm$ 크기를 가지고 있으며, 가압장치는 나사방식으로 압력을 가할 수 있도록 제작한 챔버를 활용하여 실험을 수행하였다. 실험결과 단계적으로 압력이 가해지는 조건에서 압력에 따른 균열면의 거칠기는 입자의 크기에 따라 다른 변화를 보이는 것으로 확인되었으며, 이러한 자료는 추후 암석의 균열면을 따라 이동할 수 있는 지하수의 흐름에 대한 예측을 위한 기초자료로 활용 될 수 있을 것으로 기대한다.

• 산업경영시스템학회지
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• 제38권4호
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• pp.64-71
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• 2015

In this paper, we present a multi-period 0-1 knapsack problem which has the cardinality constraints. Theoretically, the presented problem can be regarded as an extension of the multi-period 0-1 knapsack problem. In the multi-period 0-1 knapsack problem, there are n jobs to be performed during m periods. Each job has the execution time and its completion gives profit. All the n jobs are partitioned into m periods, and the jobs belong to i-th period may be performed not later than in the i-th period, i = 1, ${\cdots}$, m. The total production time for periods from 1 to i is given by $b_i$ for each i = 1, ${\cdots}$, m, and the objective is to maximize the total profit. In the extended problem, we can select a specified number of jobs from each of periods associated with the corresponding cardinality constraints. As the extended problem is NP-hard, the branch and bound method is preferable to solve it, and therefore it is important to have efficient procedures for solving its linear programming relaxed problem. So we intensively explore the LP relaxed problem and suggest a polynomial time algorithm. We first decompose the LP relaxed problem into m subproblems associated with each cardinality constraints. Then we identify some new properties based on the parametric analysis. Finally by exploiting the special structure of the LP relaxed problem, we develop an efficient algorithm for the LP relaxed problem. The developed algorithm has a worst case computational complexity of order max[$O(n^2logn)$, $O(mn^2)$] where m is the number of periods and n is the total number of jobs. We illustrate a numerical example.

• 산업경영시스템학회지
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• 제42권1호
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• pp.143-150
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• 2019

We focus on the weapon target assignment and fire scheduling problem (WTAFSP) with the objective of minimizing the makespan, i.e., the latest completion time of a given set of firing operations. In this study, we assume that there are m available weapons to fire at n targets (> m). The artillery attack operation consists of two steps of sequential procedure : assignment of weapons to the targets; and scheduling firing operations against the targets that are assigned to each weapon. This problem is a combination of weapon target assignment problem (WTAP) and fire scheduling problem (FSP). To solve this problem, we define the problem with a mixed integer programming model. Then, we develop exact algorithms based on a dynamic programming technique. Also, we suggest how to find lower bounds and upper bounds to a given problem. To evaluate the performance of developed exact algorithms, computational experiments are performed on randomly generated problems. From the results, we can see suggested exact algorithm solves problems of a medium size within a reasonable amount of computation time. Also, the results show that the computation time required for suggested exact algorithm can be seen to increase rapidly as the problem size grows. We report the result with analysis and give directions for future research for this study. This study is meaningful in that it suggests an exact algorithm for a more realistic problem than existing researches. Also, this study can provide a basis for developing algorithms that can solve larger size problems.