• The Korean Journal of Applied Statistics
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• v.14 no.1
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• pp.13-24
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• 2001

In this paper, we investigated mean estimation methods in two-phase sampling. Under the fixed expected cost we reviewed the optimal sample sizes, minimum variances and approximate unbiased variance estimators for usual ratio estimator, stratified sample mean with proportional allocation and Rao's allocation of the second phase sample. Also we proposed combined ratio estimator, which uses both ratio estimation and stratification and derived optimal sample size, minimum variance and unbiased variance estimator. Through a limited simulation study, we compared estimators by design effects and came to know that ratio estimator is more efficient than stratified sample mean in some cases and inefficient in the other cases, but combined ratio estimator is more efficient than others in most cases.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.12
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• pp.67-74
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• 2004

Linear motor has been considered to be the most suitable electric machine for high speed and high precision linear motion control. Thrust of linear motor is one of the important factor to specify motor performance. Maximum thrust can be obtained by increasing the current in conductor and is relative to the sizes of conductor and magnet. But, the current and the size of conductor have an effect on temperature of linear motor. Therefore, it is practically important to find design results that can effectively maximize the thrust of linear motor within limited range of temperature. Finite element analysis was applied to calculate thrust and numerical solutions were compared with experiment. The temperature of the conductor was calculated by the thermal resistance which was measured by experiment. The optimum design process was coded by the ADPL of ANSYS which is a commercial finite element analysis software. Design variables and constraints were chosen based on manufacturing feasibility and existing products. As a result, it is shown that temperature of linear motor plays an important role in determining optimum design.

• Journal of Biosystems Engineering
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• v.24 no.4
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• pp.301-308
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• 1999

Path planning for field operation of agricultural machinery is an indispensible part for precision farming or autonomous field operation. In this study, two algorithms (I, II) of generating a time-based shortest operation path were suggested to plan an optimal operation of an agricultural tractor-implement in a rectangular shaped field. The algorithms were based on modification of a minimum spanning tree algorithm, and applied for tractor-implement operations. the generated path was consisted of round operation and returning operation sections. The number of round operation was determined from the condition that a tractor can turn smoothly at headlands. The performance of the algorithms was evaluated by the calculation number for path generation and the total path length generated. Their stability was affected by the number of returning operation, but the algorithm II was considered to be more stable. In addition, the performances of the developed algorithms were compared with those of the conventional field operations at selected field sizes and shapes. The results showed that the algorithms could reduce field operation time greatly. For a 100m$\times$40m field, the reduced path length was 78m. The study also included an user interface program for implementing the algorithms and generating GPS coordinates that could be used in GIS softwares for precision farming.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.6 no.3
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• pp.162-167
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• 2013

The variation of S11 depending on the ground sizes of circular planar monopole UWB antenna was studied. And optimal ground structure and size in UWB application devices are proposed. Radius R of circular monopole UWB antenna as a reference antenna was designed for UWB frequency band, and the measured results of this antenna on the horizontal ground plane was good agreed with the simulated results. When radius R is small, optimal size of ground plane is proposed, and when radius R is more large, minimum size of ground plane is proposed.

• Journal of Information Processing Systems
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• v.13 no.2
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• pp.305-320
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• 2017

The selection of subset size is of great importance to the accuracy of digital image correlation (DIC). In the traditional DIC, a constant subset size is used for computing the entire image, which overlooks the differences among local speckle patterns of the image. Besides, it is very laborious to find the optimal global subset size of a speckle image. In this paper, a self-adaptive and bidirectional dynamic subset selection (SBDSS) algorithm is proposed to make the subset sizes vary according to their local speckle patterns, which ensures that every subset size is suitable and optimal. The sum of subset intensity variation (${\eta}$) is defined as the assessment criterion to quantify the subset information. Both the threshold and initial guess of subset size in the SBDSS algorithm are self-adaptive to different images. To analyze the performance of the proposed algorithm, both numerical and laboratory experiments were performed. In the numerical experiments, images with different speckle distribution, different deformation and noise were calculated by both the traditional DIC and the proposed algorithm. The results demonstrate that the proposed algorithm achieves higher accuracy than the traditional DIC. Laboratory experiments performed on a substrate also demonstrate that the proposed algorithm is effective in selecting appropriate subset size for each point.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11C
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• pp.1066-1072
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• 2007

In this paper, we propose a fast multiple reference frame selection method for motion estimation and compensation in video coding. Reference frames selected as an optimal reference frame by variable block sizes motion estimation have the statistical characteristic that was based on block size. Using the statistical characteristic, reference frames for smaller block size motion estimation can be selected from reference frame which was decided as an optimal one for the upper layer block size. Simulation results show that the proposal method decreased the computations about 60%. Nevertheless, PSNR and bit rate were almost same as the performances of original H.264 multiple reference motion estimation.

• Korean Journal of Computational Design and Engineering
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• v.19 no.2
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• pp.91-102
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• 2014

The outer surface of an irregular structure contains panels with two-directional curvature called NURBS. To construct these forms of exterior materials, complex geometric surface should be divided into forms and sizes that can be manufactured and constructed. Because the bigger the curvatures of these divided exterior panel, the more expensive the construction costs, these complex two-directional curvatures should go through optimal process of reinterpretation to minimize the curved surfaces with complex two-directional curvatures. Yet, to gain higher ground in technological competition in the field of irregular structure construction, companies do not share know-how that they obtained. Accordingly, small construction and design companies have trouble calculating even rough estimate and cannot adjust expected construction cost based on comparison of design alternatives. Given this situation, this study conducted the research that can support decision-making in the design stage of the construction and provide basic material for optimal range to reduce manufacturing cost by the minimizing the distorted plane of the irregular structure.

• Fisheries and Aquatic Sciences
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• v.12 no.4
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• pp.342-349
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• 2009

The purpose of the current study was to optimize shrimp-pot design to allow greater control over the size of captured individuals for the purposes of shrimp resource management. Tank experiments were conducted to determine the optimal slope length and slope angle by analyzing the sizes of shrimp that entered 25 model pots with combinations of five different slope lengths and five different angles. Shrimp size was measured using carapace length. The results showed that as the slope angle of the pot increased, the size of individuals that entered the pot increased. Furthermore, as the slope length increased, each of the five different slope angles of the pot increased, and the size of individuals entering also increased. The data indicated that the optimum pot design for reducing the capture of immature individuals had a $75^{\circ}$ slope angle and a 35.4 cm slope length.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.138-143
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• 2007

The leading-cab (high energy absorption area) of rolling stock directly is impacted on the frontal crash unlike other cabs. Thus, leading-cab has a structurally complex shape to solve getting concentrated loads. However, in order to enhance structural performance and to achieve the weight reduction of cab, changing the sizes and adjusting the distance of members do not take an effective result. Therefore, in design phase, to find the material arrangement which helps structural capacity be better should be done. This research applies the topology optimization to concept design of protective shell frame on strategy of crush energy absorption with considering pressure and vertical loads acting on the principal part of leading-cab. In this research, topology optimization method focuses on structural design, and which yields optimal material arrangement under given loads and boundary conditions using density method which has the density of material as design variables. Finally, this research presents optimal material arrangement and structure of protective shell frame on given loads with applying topology optimization.

• Journal of Hydrogen and New Energy
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• v.24 no.5
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• pp.386-392
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• 2013

Polymer electrolyte membrane (PEM) fuel cell stacks are constructed by stacking several to hundreds of unit cells depending on their power outputs required. Fuel and oxidant are distributed to each cell of a stack through so-called manifolds during its operation. In designing a stack, if the manifold sizes are too small, the fuel and oxidant would be maldistributed among the cells. On the contrary, the volume of the stack would be too large if the manifolds are oversized. In this study, we present a three-dimensional computational fluid dynamics (CFD) model with a geometrically simplified flow-field to optimize the size of the manifolds of a stack. The flow-field of the stack was simplified as a straight channel filled with porous media to reduce the number of computational meshes required for CFD simulations. Using the CFD model, we determined the size of the oxidant manifold of a 30 kW-class PEM fuel cell stack that comprises 99 cells. The stack with the optimal manifold size showed a quite uniform distribution of the cell voltages across the entire cells.