• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.352-355
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• 2004

The objective of this work is to develop a new design method to find optimal coils, especially the optimal coil configuration of an optical pickup actuator. In designing actuator coils, the developed Lorenz force in the coils along the desired direction should be made as large as possible while forces and torques in other directions should be made as small as possible. The design methodology we are developing is a systematic approach that can generate optimal coil configurations for given permanent magnet configurations. To consider the best coil configuration among all feasible coil configurations, we formulate the design problem as a topology optimization of a coil. The present formulation for coil design is noble in the sense that the existing topology optimization is mainly concerned with the design of yokes and permanent magnets and that the optimization of actuator coils is so far limited within shape or size optimization. Though the present design methodology applies to any problem, the specific design example considered is the design of fine-pattern tracking and focusing coils.

• Steel and Composite Structures
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• v.45 no.4
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• pp.547-554
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• 2022

This paper studies the static stability of an axially graded column with the power-law gradient varying along the axial direction. For a nonhomogeneous column with one end linked to a rotational spring and loaded by a compressive force, respectively, an Euler problem is analyzed by solving a boundary value problem of an ordinary differential equation with varying coefficients. Buckling loads through the characteristic equation with the aid of the Bessel functions are exactly given. An alternative way to approximately determine buckling loads through the integral equation method is also presented. By comparing approximate buckling loads with the exact ones, the approximate solution is simple in form and enough accurate for varying power-law gradients. The influences of the gradient index and the rotational spring stiffness on the critical forces are elucidated. The critical force and mode shapes at buckling are presented in graph. The critical force given here may be used as a benchmark to check the accuracy and effectiveness of numerical solutions. The approximate solution provides a feasible approach to calculating the buckling loads and to assessing the loss of stability of columns in engineering.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.932-938
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• 2001

This study is concerned with the shape optimization of stem for the artificial hip prosthesis with unbonded cement mantle. The artificial hip prosthesis with unbonded cement mantle allows a stem to slip on cement mantle because of polished stem surface. Unbonded cement mantle type has several advantages compared with bonded cement mantle type, for example, small micro motion, preventing stress shielding and so on. In this study, 2-dimensional axisymmetric model was developed with considering characteristics of unbonded cement mantle. Moreover, optimal shape of stem was obtained by using feasible direction method. The objective of this optimization is maximizing supported vertical loading. The slip motion and stresses of stem, cement mantle and bone is used for constraints. The optimal shape which obtained by this study has slope of 0.15 in proximal part and maintains the width about 5mm in distal part In addition, simplified 3-dimensional analysis which applying optimal shape is carried out. The result of 3-dimensional analysis showed that optimal shape has some advantages for cement mantle stress. However, more realistic 3-dimensional analysis which including bending effect, complex geometries etc. is needed in further research.

• Journal of the Korean Regional Science Association
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• v.33 no.3
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• pp.49-59
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• 2017

The piezoelectric energy harvester is recently being developed and catching on as a way to achieve low carbon green growth. The practical application of the piezoelectric energy harvester is expected to contribute not only to the reduction of greenhouse gas emissions but also to the improvement of residents' welfare. This paper conducted a cost-benefit analysis for the installation of piezoelectric energy harvester on the highway focusing on its impacts on the public. The results showed that the installation of piezoelectric energy harvester on the gyeongbu highway is economically feasible in that it could increase the social welfare for the residents. Finally, this paper suggests policy direction for the practical use of the piezoelectric energy harvester, based on the results obtained.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.12
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• pp.1272-1277
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• 2014

This article describes a path planning algorithm for fixed-wing UAVs when a real terrain should be considered. Nowadays, many UAVs are required to perform mission flights near given terrain for surveillance, reconnaissance, and infiltration, as well as flight altitude of many UAVs are relatively lower than typical manned aerial vehicles. Therefore, real terrain should be considered in path planning algorithms of fixed-wing UAVs. In this research, we have extended a spline-$RRT^*$ algorithm to three-dimensional planner. The spline-$RRT^*$ algorithm is a $RRT^*$ based algorithm, and it takes spline method to extend the tree structure over the workspace to generate smooth paths without any post-processing. Direction continuity of the resulting path is guaranteed via this spline technique, and it is essential factor for the paths of fixed-wing UAVs. The proposed algorithm confirm collision check during the tree structure extension, so that generated path is both geometrically and dynamically feasible in addition to direction continuity. To decrease degrees of freedom of a random configuration, we designed a function assigning directions to nodes of the graph. As a result, it increases the execution speed of the algorithm efficiently. In order to investigate the performance of the proposed planning algorithm, several simulations are performed under real terrain environment. Simulation results show that this proposed algorithm can be utilized effectively to path planning applications considering real terrain.

• Journal of the Korean Wood Science and Technology
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• v.24 no.4
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• pp.22-31
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• 1996

Air permeabilities for both sapwood and heartwood of the three softwoods(Picea jezoensis, Larix gmelini, Pinus sylvestris), imported from the Russian Far East, in the three different structural directions were measured using steady-state rotameter method. After measuring permeability, the liquid absorption into the longitudinal permeability specimens was measured, and then related with the measured permeability. The longitudinal permeability was overwhelmingly greater than the transverse permeability, with the radial direction showing higher permeability than the tangential direction. There appear to be species differences in permeability of the three softwoods. The mean longitudinal sapwood permeability of P. jezoensis(3.300darcy) and P. sylvestris(3.028darcy) were considerably greater(ca. 25times) than that of L. gmelini(0.134darcy). Also the average longitudinal heartwood permeability of P. jezoensis(0.300darcy) was about 10 times as great as that of P. sylvestris(0.029darcy) and L. gmelini(0.024darcy). The average calculated radius of pit openings in the heartwood was $0.101{\mu}m$ for L. gmelini, $0.152{\mu}m$ for P. sylvestris for and $0.703{\mu}m$ for P. jezoensis. Heartwood permeability increases with the increase in radius of pit pore and the decrease in ring width and in extractive content, even though the correlation between permeability and its affecting factors was dependent on species. However, there was an inverse relationship between specific gravity and permeability, showing poor correlation between them. The correlation between air permeability and liquid retention was fairly high, so it was revealed that prediction of liquid absorption into the wood by using permeability was feasible.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.122-129
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• 2002

An optimization of satellite honeycomb platforms under sever space environment is performed. There are many optimization constraints for space environment to be considered. A modified method of feasible direction and a genetic algorithm are used to optimize the satellite platform structures. The design constraints are concerned with bearing stresses at joints and natural frequencies. The results from the optimization methods are compared. The numerical results show that natural frequency constraints are dominant to reach the optimum design. This study verifies the design of satellite honeycomb platforms and suggests an optimal platform design.

• ETRI Journal
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• v.5 no.3
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• pp.3-8
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• 1983

In the area of computer network planning, a location-allocation-size problem is involved. Since multi-facility location-allocation-size problems are very complex in formulating a mathematical model, it is a usual practise to adopt alternative approaches, which give no optimal results, instead of the optimal solution by mathematical approach. In this article, however, an attempt is made to formulate a mathematical model for the decision making problem of computer network design.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.2
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• pp.23-38
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• 1990

In this study, decompositive optimization method of two levels was selected to optimize effectively the geometry of the truss which takes the multi-loading condition, and the allowable stress, bucking stress, displacement and natural frequency constraints into consideration. The algorithm of this study is made up of sectional optimization using the feasible direction method in level 1, and geometrical optimization employing Powell's one-direction search method which menimizes only objictive function in level 2. The results of this study acquired by beenning applied to structural model of the truss are as follows : 1. It is verified that the algorithm of this study effectively converges, independent of the initial geometry of the truss and the applied various constraints. 2. The optimum goemetry of the truss varies more considerably according to the constraints selected. 3. Under the condition of the same design, the weight of the truss can be decreased more considerably by means of optimizing even the geometry of truss than by means of optimizing the section of truss while fixing geometrical configuration of it, even though there might be a little difference according to the initial geometry of the truss and the design condition.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.8
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• pp.1-6
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• 2010

We report on the electrical properties of Ti/Al/Ni/Au (20 nm/ 150 nm/ 30 nm/ 100 nm) Ohmic contacts and the anisotropic conductivity of n-type ${\alpha}$-plane ([11-20]) GaN grown on $\gamma$-plane ([1-102]) sapphire substrates. The Ti/Al/Ni/Au Ohmic contacts and their sheet resistances are characterized by using the transfer length method (TLM) as a function of azimuthal angles. It is found that the specific contact resistance does not depend on the axis orientation and there are significant electrical anisotropy in ${\alpha}$-plane GaN films on $\gamma$-plane sapphire substrates, and the sheet resistance varies with azimuthal angles. The sheet resistance values in the direction parallel to m-axis [1-100] are 25% ~ 75% lower than those parallel to c-axis [0001] directions. Thus, Basal stacking faults (BSFs) are offered as a feasible source of the anisotropic mobility in defected m-axis direction because the band-edge discontinuities owing to the differential band gap structure.