• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.8
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• pp.897-904
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• 2012

The rifling design problem has continuous-type shape variables and an integral number of riflings. In addition, it requires considerable time for analysis because its behavior should be described by a nonlinear finite element model (FEM). Therefore, this study presents an efficient design process for rifling based on a design of experiment (DOE) approach. First, Bose's orthogonal array is used to represent 25 runs for four design variables including three shape variables and one integer variable. Then, nonlinear FE analyses are performed. Next, to minimize the bullet resistance without affecting the bullet velocity and bullet rotational angle immediately before a bullet leaves the gun barrel, a what-if design is performed. In the proposed what-if design, a functional including the design objective and constraints is constructed and effect analysis is performed by using the functional. It is found that the new design obtained from the what-if design shows better results than the current one.

• Journal of Navigation and Port Research
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• v.32 no.3
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• pp.223-228
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• 2008

As most of small fishing boats made of FRP have been constructed by experience in Korea, some structural safety problems have been occurred occasionally. To improve the structural strength and reduce the costs for construction and operation, optimum design for small fishing boat was carried out in this study. The weight of fishing boat and the main dimensions of structural members are chosen as objective function and design variables, respectively. By the combination of global and local search methods, a hybrid optimization algorithm was developed to escape the local minima and reduce CPU time in analysis procedure, and finite element analysis was performed to determine the constraint parameters at each iteration step in optimization loop. Optimization results were compared with the real existing fishing boat, and the effects of optimum design were examined from points of view; structural strength, material cost, etc.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.60.1-60.1
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• 2016

태양과 같은 별의 형성기작은 질량이 큰 별의 형성기작에 비해 비교적 잘 연구되어 왔다고는 하지만, 이 또한 온전한 이해와는 거리가 먼 상황이며 여전히 논란의 대상이다. IRAS, Spitzer와 같은 적외선우주망원경으로 얻어진 원시성의 광도함수는 일반적으로 받아들여졌던 별탄생 이론으로 설명되지 못한다는 것이 밝혀졌고, 이에 새로운 별탄생 이론이 필요하게 되었다. 새롭게 받아들여지고 있는 별탄생 모델은 Episodic Accretion 모델로서, 원시행성계원반에서 원시성으로 질량 강착이 간헐적이면서 폭발적으로 일어난다는 것이다. 이러한 모델의 관측적 증거의 하나는 FU Orionis와 같은 천체로서, T-Tauri 단계에 있는 원시성이 본래의 밝기보다 약 100배, 즉 가시광에서 5등급 이상 폭발적으로 밝아진 천체이다. 질량강착의 과정은 행성형성의 초기조건을 결정하는 원시행성계원반의 물리적, 화학적 특성을 결정하므로, 그 이해가 중요하다. 따라서 본 연구팀은 Episodic Accretion이 원시행성계원반과 원시항성풍의 형성과 진화에 어떤 역할을 하는지 연구하기 위하여, 보현산 천문대의 고분산 분광기인 BOES를 이용하여, 최근에 폭발을 일으킨 원시성인 HBC 722와 2MASS J06593158-0405277을 모니터링 관측을 해왔으며, 이전에 알려진 6개의 FU Orionis 형 천체들도 관측하였다. 여기서는 그 결과를 발표하고자 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.63-71
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• 2006

This study presents the effective stiffness-based optimal technique to control Quantitatively lateral drift for shear wall-frame structure system using sensitivity analysis. To this end, the element stiffness matrices are constituted to solve the compatibility problem of displacement degree of freedom between the frame and shear wall. Also, lateral drift constraint to introduce the approximation concept that can preserve the generality of the mathematical programming and can effectively solve the large scaled problems is established. And, the section property relationships for shear wall and frame members are considered in order to reduce the number of design variables and differentiate easily the stiffness matrices. Specifically, constant-shape assumption which is uniformly varying in size during optimal process is applied in frame structure. The thickness or length of shear wall can be changed depending on user's intent. Two types of 20 story shear wall-frame structure system are presented to illustrate the features of the stiffness-based optimal design technique.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.258-265
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• 2017

At the early stage of the development of high speed propulsion systems, the designers suffer from the lack of both the quantity and the quality of test data. In that situation, the associated uncertainties could not be modeled as probabilistic distribution since probabilistic modelling requires large amount of data. In this paper, instead, the information provided by experts based on their experience and engineering knowledge was used to model uncertainty using the evidence theory. In designing the DCR(Dual Combustion Ramjet) engine, the combustion efficiencies, not well understood and little data existing, are assumed to have been provided by experts. And the uncertainties are quantified by Evidence theory. The quantified uncertainties are incorporated into the optimization. The design variables, area of inlet and area of combustor exit, have been found while satisfying reliability margins of thrust and thermal choking. The results show a reasonable design of the engine under the uncertain circumstances.

• Journal of the Korean Wood Science and Technology
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• v.35 no.1
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• pp.11-16
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• 2007

This study was carried out to investigate the effect of Vapor-dam treatment on drying drying rates, prevention of checks and V-shaped split during air circulating oven drying bamboo (Phyllostachys pubescens Mazel et Z) tube. It was shown that the drying time from green to around 7~8 % of moisture content was required less as drying schedule was more severe, and distinctly dominated by the drying rate during the initial drying stage. Area shrinkages in cross section and thickness shrinkages measured during air circulating oven drying test were very large. Surface checks and V-shaped splits were occurred in untreated samples just after the beginning of drying, while sixty seven percentages of all the Vapor-dam treated samples could be produced without drying defects. The V-shaped splits occurred in the Vapor-dam treated samples were influenced more by the sealing of the vapor evaporation through the cross section than drying schedule.

• Journal of Korea Water Resources Association
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• v.51 no.7
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• pp.575-584
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• 2018

An increase in heavy rainfall and floods have been observed over South Korea due to recent abnormal weather. In this perspective, the high-resolution weather forecasts have been widely used to facilitate flood management. However, these models are known to be biased due to initial conditions and topographical conditions in the process of model building. Theretofore, a bias correction scheme is largely applied for the practical use of the prediction to flood management. This study introduces a new mean field bias correction (MFBC) approach for the high-resolution numerical rainfall products, which is based on a Bayesian Kriging model to combine an interpolation technique and MFBC approach for spatial representation of the error. The results showed that the proposed method can reliably estimate the bias correction factor over ungauged area with an improvement in the reduction of errors. Moreover, it can be seen that the bias corrected rainfall forecasts could be used up to 72 hours ahead with a relatively high accuracy.

• Tunnel and Underground Space
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• v.22 no.4
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• pp.284-295
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• 2012

Abrasiveness of rock plays an important role on the wear of rock cutting tools. In this study, Cerchar abrasiveness tests were carried out to assess the abrasiveness of 19 different Korean rocks. Cerchar abrasiveness test is widely used to assess the abrasiveness of rock because of its simplicity and inexpensive cost. This study examines the relationship between Cerchar Abrasiveness Index (CAI) and mechanical properties (uniaxial compressive strength, Brazilian tensile strength, Young's modulus, Poisson's ratio, porosity, shore hardness of rock), and the effect of quartz content, equivalent quartz content, which was obtained from XRD analysis. As a result of test, CAI was more influenced by petrographical properties than by the bonding strength of the matrix material of rock. CAI prediction model which consisted of UCS and EQC was proposed. CAI decreased linearly with the hardness of the steel pin. Numerical analysis was performed using Autodyn-3D for simulating the Cerchar abrasiveness test. In the simulations, most of pin wear occurred during the initial scratching distance, and CAI increased with the increase of normal loading.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.5
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• pp.579-586
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• 2019

Pilot Point Method (PPM) is one of the popular methods to search hydraulic conductivities in the inverse method using groundwater flow equations. In this study, the Simultaneous Search based Pilot Point Method (SSBM) was applied with diverse information (e.g. hydraulic heads and/or tracer concentration) applications over previously developed sensitivity based Pilot Point Method (e.g. D-optimality based Pilot Point Method: DBM). In the case of DBM, due to the minimized the variance size, tracer concentration can be recognized as a tool to control the searching space of hydraulic conductivities. SSBM reduced the procedure of hydraulic conductivity searching, though it produced more variance for exploring hydraulic conductivities. In addition, SSBM was dependent on the initial hydraulic conductivity values for search finalized hydraulic conductivities. When tracer concentration was applied, searching hydraulic conductivities was more preferable than only when hydraulic head was applied. Applications of various data for searching hydraulic conductivities is recommended as a more efficient way.

• Journal of the Korea Society of Computer and Information
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• v.15 no.9
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• pp.47-55
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• 2010

Linear constraint satisfaction optimization problem is a kind of combinatorial optimization problem involving linearly expressed objective function and complex constraints. Integer programming is known as a very effective technique for such problem but require very much time and memory until finding a suboptimal solution. In this paper, we propose a method to improve the search performance by integrating local search and integer programming. Basically, simple hill-climbing search, which is the simplest form of local search, is used to solve the given problem and integer programming is applied to generate a neighbor solution. In addition, constraint programming is used to generate an initial solution. Through the experimental results using N-Queens maximization problems, we confirmed that the proposed method can produce far better solutions than any other search methods.