• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1249-1261
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• 2018

The quantitative representation for the magnetic force of a cylindrical permanent magnet acting on a ferromagnetic cylindrical object was derived on the basis of magnetization theories, and the Gilbert and Ampere models of magnetism. The magnetic force derived in this study is directly proportional to the remanent magnetization magnetic field, the cross-sectional area of the permanent magnet, the saturation magnetic field, and the cross-sectional area of the ferromagnetic object and is inversely proportional to the square of the quantity related to the distance between the permanent magnet and the ferromagnetic object. The magnetic forces of an AlNiCoV cylindrical permanent magnet and a Ferrite cylindrical permanent magnet, both with a radius of 0.4 cm and a length of 7 cm, acting on ferromagnetic objects at distances farther than the radius were calculated to be less than 3.6711 N and 0.1857 N, respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.111-119
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• 2022

The increasing sectional stiffness and inducing prestress method of continuous steel box girder using modular CFT members use the restoring force of the CFT module generated from removing the prestressing bars in the CFT module after integrating the prestressed CFT module with the lower steel plate of the steel box girders as a prestressing force. The integrated CFT module in the steel box girder can improve the sectional stiffness of the continuous steel box girder section. To examine the applicability of the introduction of prestressing to the integrated steel box girder using the CFT module, in this study, inducing prestressing tests were conducted using CFT modules for steel plate specimens simulating the lower steel plate of the continuous steel box girder, and FE analyses were conducted for inducing prestressing tests. In addition, to confirm the effect of inducing prestress to the actual steel box girder and increasing sectional stiffness by the CFT modules, FE analyses for the actually applicable continuous steel box section were carried out depending on prestressing force and sectional conditions of the CFT modules, FE analysis results were compared.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.3
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• pp.409-422
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• 2016

A parametric study based on an unsteady mathematical model of a pyrotechnically actuated device was performed for design optimization. The model simulates time histories for the chamber pressure, temperature, mass transfer and pin motion. It is validated through a comparison with experimentally measured pressure and pin displacement. Parametric analyses were conducted to observe the detailed effects of the design parameters using a validated performance analysis code. The detailed effects of the design variables on the performance were evaluated using the one-at-a-time (OAT) method, while the scatter plot method was used to evaluate relative sensitivity. Finally, the design optimization was conducted by employing a genetic algorithm (GA). Six major design parameters for the GA were chosen based on the results of the sensitivity analysis. A fitness function was suggested, which included the following targets: minimum explosive mass for the uniform ignition (small deviation), light casing weight, short operational time, allowable pyrotechnic shock force and finally the designated pin kinetic energy. The propellant mass and cross-sectional area were the first and the second most sensitive parameters, which significantly affected the pin's kinetic energy. Even though the peak chamber pressure decreased, the pin kinetic energy maintained its designated value because the widened pin cross-sectional area induced enough force at low pressure.

• Bulletin of the Society of Naval Architects of Korea
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• v.14 no.3
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• pp.13-22
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• 1977

The hydrodynamic forces acting on a forced oscillating 2-dimensional cylinder on a free surface of a fluid of a finite depth are calculated by distributing singularities on the immersed body surface. And the Haskind-Newman relation in a fluid of a finite depth is derived. The wave exciting force of the cylinder to an oscillation is also calculated by using the above relation. The method is applied to a circular cylinder swaying in a water of finite depth, and then, to a rectangular cylinder heaving, swaying, and rolling. The results of above cases give a good agreement with those by earlier investigators such as Bai, Keil, and Yeung. Also, this method is applied to a Lewis form cylinder with a half beam-to-draft ratio of 1.0 and a sectional area coefficient of 0.941, and to a bulbous section cylinder which is hard to represent by a mapping function. The results reveal that the hydrodynamic forces in heave increase as the depth of a water decrease, but in sway or roll, the tendency of the hydrodynamic forces is difficult to say in a few words. The exciting force to heave for a bulbous section cylinder becomes zero at two frequencies. The added mass moment of inertia for roll is seemed to mainly depend on the sectional shape than the water depth.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.955-962
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• 2000

Scanning Probe Microscope (SPM) such as Scanning Tunneling Microscope (STM) and Atomic Force Microscope (AFM) was shown to be the powerful tool for nano-scale characterization of a fracture surface . AFM was used to study cross sectional profiles and dimensions of fatigue striations in 2017-T351 aluminum alloy. Their widths (SW) and heights (SH) were measured from the cross sectional profiles of three-dimension AFM images. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) Coincidence of the crack growth rate with the striation width was found down to the growth rate of 10-5 mm/cycle. (2) The relation of SH=0.085(SW)1.2 was obtained. (3) The ratio of the striation height to its width SH/SW did not depend on the stress intensity factor range K and the stress ratio R. (4) Not only the SW but also the SH changed linearly with the crack tip opening displacement (CTOD) when plotted in log-log scale. From these results, the applicability of the AFM to nano-fractography is discussed.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.2 s.2
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• pp.103-114
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• 2001

As the results of comparison with several anchorage design methods of PSC box girder, stress superposition effect by the order of prestressing force can't be considered in the case of multi-anchorage design with existing design methods. In anchorage design by 3-D finite element analysis, estimation of stress concentration region and stress flow are correctly defined, but the estimation of sectional forces in anchorage is very complicated. In the case of anchorage design by strut-tie model method, the stress superposition effect can be considered and sectional forces in anchorage are easily calculated. Therefore, strut-tie model method is remarkably suitable to anchorage design if geometrical conditions of the truss members are carefully considered.

• Journal of Korea Foundry Society
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• v.26 no.2
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• pp.85-91
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• 2006

Inclusions in Ti investment castings are generally known to have detrimental effects on the performance of the castings. However, actual inclusions are infrequent and hard to be located. As a result, it is extremely difficult to obtain sufficient amount of fatigue test specimens of titanium investment castings having inclusions in the gage section. Thus, in-depth research of the adverse influence of inclusions is also hindered. To address this problem, a new casting methodology of specimens containing hard alpha inclusions was developed in this study. To guarantee successful introduction of an inclusion and casting, a carefully designed mold with 8 legs and a special tool were employed. After solidification, castings were cut, and X-ray radiography determined that the inclusions were successfully incorporated into the castings. The castings were further prepared to obtain multiple test specimens and they were fatigue-tested consecutively. Fractography analysis confirmed that fatigue cracks initiated at the hard alpha inclusion. In a nonlinear regression model, the fatigue life can be modeled as an exponential function with a negative exponent of the cross-sectional area of an inclusion. The fatigue life of Ti specimens containing inclusions is inversely proportional to the cross-sectional area of an inclusion.

• Korean Journal of Applied Biomechanics
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• v.25 no.4
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• pp.371-381
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• 2015

Object : The purpose of this study was to investigate aging-related changes of intrinsic and extrinsic hand muscles in their strength, cross-sectional area and volume, force control, and multi-digit synergies. It was hypothesized that aging would negatively affect distal muscles (intrinsic muscles) more than proximal muscles (extrinsic muscles). Method : Nine young and eleven older right-handed participants underwent MRI scans of the hand and forearm. Muscle cross-sectional areas and volumes of the intrinsic and extrinsic hand muscles were determined. Result : Muscle volume of the intrinsic muscles were larger in the younger group than the older group while muscle volume of the extrinsic muscles did not differ. For the cross-sectional area, both the intrinsic and extrinsic muscles of the younger group were larger than the older group. The maximum strength of the intrinsic muscles of the young group was 31% greater than the older group ($399.1{\pm}26.4$ vs $270.2{\pm}22.9Ncm$, p < 0.05) while the extrinsic muscles showed no significant difference. Although the elderly group showed a trend of decreased force control and multi-digit synergies, no statistical differences were found. These findings indicate aging-related decreases in hand muscle size and strength affect intrinsic muscles more than extrinsic muscles, thus supporting the hypothesis that sarcopenia affects the muscle size and strength of distal muscles more than proximal muscles. Conclusion : The aging-related decreases in hand muscle size and function were more apparent in intrinsic hand muscles, located more distally, than extrinsic muscles, located more proximally.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.2
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• pp.27-36
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• 2010

It is well known that the shear strength of an RC column subjected to a lateral force decreases with the increase of the displacement ductility of column. This decreasing rate of shear strength is quite dependent on the initial shear strength. Therefore, the evaluation of the initial shear strength is important to predict the shear strength with reasonable accuracy. The shear behavior is complex because many parameters, such as the sectional shape, aspect ratio, axial force, longitudinal bars and ductility, are mutually interactive. In this study, the initial shear strength has been investigated by experiments varying parameters such as the aspect ratios, void ratios, ratio of longitudinal bars and sectional types. A new empirical equation for the initial shear strength, considering the ratio of the longitudinal bars, has been proposed and its validity has been assessed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.139-150
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• 2006

ILM(incremental launching method) bridge is one of the prestressed concrete bridge construction methods widely adopted owing to its effectiveness for the quality control. The sections of the launched superstructure pass every position of the bridge spans. This launching process causes the bridge sections to be experienced in the quite different stress states with the stress state occurred after construction completely. Due to the self weight of sections, particularly, the superstructure sections(deck) experience maximum positive and negative moment as well as maximum shear force during launching process. To minimize the temporarily caused sectional forces, launching nose is generally used in the construction method. Therefore, the magnitude of this sectional forces should be checked for the safety of super structure in construction and it is dependent on the structural characteristics of launching nose. In this study, the simplified formulas to analyze the sectional force occurred by the nose-deck interaction in ILM construction are developed. The considering parameters are the span length ratio, stiffness ratio and weight ratio between the launching nose and the super structure. In particular, the developed formulas can consider the tapered sectional shape of launching nose and the diaphragm wall in the superstructure. Additionally, the sensitivity analysis is performed to analyze the effects of nose-deck interaction according to the design parameters.