• Journal of Magnetics
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• v.18 no.3
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• pp.370-374
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• 2013

This paper introduces an innovative hybrid array consisting of both permanent and electro magnets. It will enable us to develop an active control mechanism for underdamped electro-dynamic suspension (EDS) Maglev systems. The proposed scheme is based on the Halbach array configuration which takes the major technical advantage from the original Halbach characteristics: a strongly concentrated magnetic field on one side of the array and a cancelled field on the opposite side. In addition, the unique feature of the proposed concept only differs from the Halbach array with permanent magnets. The total magnetic field of the array can be actively controlled through the current of the electro-magnet's coils. As a result, the magnetic force produced by the proposed hybrid array can also be controlled actively. This study focuses on the magnetic characteristics and capability of the proposed array as compared to the basic Halbach concept. The results show that the proposed array is capable of producing not only an equivalent suspension force of the basic Halbach permanent magnet array but also a controlled mode. Consequently, the effectiveness of the proposed array confirms that this study can be used as a technical framework to develop an active control mechanism for an EDS Maglev system.

• Journal of Drive and Control
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• v.17 no.4
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• pp.113-124
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• 2020

Most of the work of construction equipment and agricultural machinery is done in off-road conditions. Autonomous driving required in these conditions uses GPS sensors, and PID controllers to control their speed and position. The hydrostatic steering, which is composed of a PSU, hydraulic hoses, and cylinders, rather than a mechanical coupling is used in these equipments. The PSU plays a key role in hydrostatic steering. Precise control of the position under various conditions requires detailed behavioral analysis of the basic components and operation. Two Gerotor PSU is now a commonly used safer option. The components of the PSU can be divided into mechanical and hydraulic actuating elements by its behavior. Since the system is combined by mechanical and hydraulic elements, the modelings are performed using Amesim, which is one of the most effective for the multi-domain dynamic system analysis. To confirm the validity of the model, input torque and pressures are checked with varying steering speed. The opening and the steering speed of normal and newly designed control valve set is investigated with the effect of centering spring force and friction. Finally, simulation results with fully detailed model with two gerotors are analyzed and compared with simple model.

• Journal of Korean Society of Forest Science
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• v.88 no.4
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• pp.490-497
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• 1999

The objectives of this study were to identify aroma characteristics of Tricholoma matsutake(S. Ito et Imai) Sing. growing in different geograghic ranges in South Korea. Mushrooms were collected from 11 major sites which included four sites(Bonghwa, Uljin, Goryung and Chungdo) in Kyongbuk Province, three sites(Changnyung, Hadong and Hamyang) in Kyongnam Province, two sites(Yangyang and Inje) in Kangwon Province, one site(Goisan) in Choongbuk Province, and one site(Namwon) in Chonbuk Province. One of three mushrooms from each site were used for measurements of aromatic characteristics. Aromatic compounds were identified using a dynamic headspace trap method at $40^{\circ}C$ and GC-MSD(gas chromatograph-mass spectrometric detector) method. A total of 25 aromatic compounds were identified. Large variations in the composition and amount of aromatic compounds were noticed. Major aroma compound was 1-octen-3-ol, while methyl cinnamate known as the major aroma compound in matsutake was not detected at all. The total amount of aromatic compounds was highest in Bonghwa, and decreased in the order of Chungdo, Inje, Hamyang, Uljin, and Yangyang. Based on the total amount, kinds and amounts of individual aromatic compounds, the mushrooms from 11 major sites were grouped into following four types : 1) Bongwha Type : the total amount of aromatic compounds was highest, with major compound being 3-methyl 1-butanol. 2) Hamyang Type including Chungdo, Yangyang and Inje : 1-octen-3-of comprised 2/3 of total aromatic compounds, with second major being 3-methyl butanal. 3) Uljin Type : 1-octen-3-ol comprised 94% of total aromatic compounds, with other compounds being almost nothing. 4) Goisan Type including Goryung, Namwon, Changnyung, and Hadong : the total amount of aromatic compounds was lower than other three types.

• Korean Journal of Agricultural Science
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• v.31 no.2
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• pp.105-114
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• 2004

This study was performed to examine the physical and mechanical properties of eco-concrete using soil, natural coarse aggregate, soil compound and polypropylen fiber. The mass loss ratio was decreased with increasing the content of coarse aggregate and soil compound. The compressive strength, flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity were increased with increasing the content of coarse aggregate, soil compound and polypropylene fiber. The compressive and flexural strengths were showed in 8.07 MPa and 2.641 MPa at the curing age 28 days, respectively. The coefficient of permeability was decreased with increasing the content of coarse aggregate and soil compound, but it was increased with increasing the content of polypropylene fiber. The lowest coefficent of permeability was showed in $5.066{\times}10^{-9}cm/s$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.1
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• pp.31-40
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• 2017

Absolute nodal coordinate formulation was developed in the mid-1990s, and is used in the flexible dynamic analysis. In the process of deriving the equation of motion, if the order of polynomial referring to the displacement field increases, then the degrees of freedom increase, as well as the analysis time increases. Therefore, in this study, the primary objective was to reduce the analysis time by transforming the dimensional equation of motion to a non-dimensional equation of motion. After the shape function was rearranged to be non-dimensional and the nodal coordinate was rearranged to be in length dimension, the non-dimensional mass matrix, stiffness matrix, and conservative force was derived from the non-dimensional variables. The verification and efficiency of this non-dimensional equation of motion was performed using two examples; cantilever beam which has the exact solution about static deflection and flexible pendulum.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1067-1074
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• 2010

In this study, a loosely coupled fluid-structure interaction (FSI) analysis was conducted for a low-pressure (LP) final-stage rotor blade. Preliminary FSI analyses of a $15^{\circ}$ sweptback wing and a NASA Rotor 37 compressor blade were performed for verifying the boundary conditions. The results were compared with the established literatures for each model. The FSI analysis of the $15^{\circ}$ sweptback wing was carried out under both stable and unstable conditions. The excessive deformation of the wing was observed within 0.05 s under the unstable condition which is higher than the divergence speed of a wing compared with the stable condition. On the basis of the results of a steady-state study, an unsteady state FSI analysis was conducted for a NASA Rotor 37. Different deformations were observed at trailing edge of the blade in the static FSI and dynamic FSI analysis. A 3D FE model of a LP rotor was generated from the span-wise section data. In order to develop a reasonable model, an impact test was performed and compared to the FE model. Using this FE model, the steady-state FSI analysis was performed successfully.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.601-607
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• 2012

In this study, we performed computational fluid dynamic simulations to explore how the detailed design of drug-eluting stents affects both the flow field in the vicinity of the stent as well as the concentration of the eluted drug at the endothelial cell surface. Simulations were performed on three idealized stent geometries we developed and on geometries approximating three commercial stents,: Medtronic's Aurora stent, Cordis's BX Velocity stent, and Boston Scientific's Wallstent. An important contribution of the present study is the introduction of the stent effectiveness index (EI), which provides a quantitative assessment of stent performance and an objective basis for comparing the performance of different stents. Among the three commercial stents studied, our simulations have revealed that the BX Velocity stent is associated with the lowest in-stent EI values for the range of flow Reynolds numbers studied ($200{\leq}Re{\leq}800$). In addition to commercial stent designs, we investigated the EI in three idealized stents and determined that a spiral stent provides excellent performance (low EI) under all flow conditions investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.415-422
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• 2016

When shock acceleration is applied to a mechanical system, it may cause malfunctioning and damage to the system. Hence, to prevent these problems when developing a gimbal structure system for observation reconnaissance, the MIL-STD-810G shock standard must be satisfied as a design specification. Rubber vibration isolators are generally assembled on the base of the system in order to reduce the shock transferred from the aircraft. It is difficult to analyze the transient behavior of the system accurately, because rubber has a nonlinear load-deformation curve. To treat the nonlinear characteristic of the rubber, bilinear approximation was introduced. Using this assumption, transient responses of the system under base shock acceleration were calculated by the finite element method. In addition, experiments with a true prototype were performed using the same conditions as the analytical model. Compared with experimental data, the proposed numerical method is useful for the transient analysis of gimbal structure systems, including rubber vibration isolators with nonlinear stiffness and damping.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.11
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• pp.759-765
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• 2017

In this study, a three-dimensional least-square, level-set-based two-phase flow code was developed for the simulation of three-dimensional sloshing problems using finite element discretization. The code was validated by solving some benchmark problems. The proposed method was found to provide improved results against other existing methods, by using a coarser mesh. The results of the numerical experiments conducted during the course of this study showed that the proposed method was both robust and accurate for the simulation of three-dimensional sloshing problems. Using a substantially coarse grid, historical results of the dynamic pressure at a selected position corresponded with existing experimental data. The pressure history with a finer grid was similar to that of a coarse grid; however, a fine grid provided higher peak pressures. The present method could be extended to the analysis of a sloshing problem in a complex geometrical configuration using unstructured meshes owing to the features of FEM.

• Journal of KIISE
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• v.44 no.10
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• pp.1026-1033
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• 2017

In this paper a Bayesian modeling and duration-based prediction method is proposed for health clinic time series data using the Hierarchical Dirichlet Process Hidden Markov Model (HDP-HMM). HDP-HMM is a Bayesian extension of HMM which can find the optimal number of health states, a number which is highly uncertain and even difficult to estimate under the context of health dynamics. Test results of HDP-HMM using simulated data and real health clinic data have shown interesting modeling behaviors and promising prediction performance over the span of up to five years. The future of health change is uncertain and its prediction is inherently difficult, but experimental results on health clinic data suggests that practical long-term prediction is possible and can be made useful if we present multiple hypotheses given dynamic contexts as defined by HMM states.