• 대한기계학회논문집B
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• 제23권8호
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• pp.969-977
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• 1999

A similarity solution of a steady laminar flow of micropolar fluids past wedges has been studied. The similarity variables found by Falkner and Skan are employed to reduce the streamwise-dependence in the coupled nonlinear boundary layer equations. Numerical solutions of the equations are then obtained using the fourth-order Runge-Kutta method and the distribution of velocity, micro-rotation, shear and couple stress across the boundary layer are obtained. These results are compared with the corresponding flow problems for Newtonian fluid past wedges with various wedge angles. Numerical results show that, keeping ${\beta}$ constant, the skin friction coefficient is lower for a micropolar fluid, as compared to a Newtonian fluid. For the case of constant material parameter K, however, the velocity distribution for a micropolar fluid is higher than that of a Newtonian fluid.

• 동력기계공학회지
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• 제15권3호
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• pp.58-64
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• 2011

As well known, the friction stir welding is a novel welding process which is a solid state welding process for sheet or plate using the friction stir phenomenon. This paper describes the effect of welding condition such as the rotation speed and the travelling speed during the friction stir welding process on the micro Virkers hardness and the microstructure of friction stir welded joints in AI-7075-T651 plate. From those investigations, the highest hardness of stir zone was observed at the welding condition of SO-3. The microstructures of the friction stir welded joints was not dependent on the welding conditions, but in the SO-4 specimen, the friction stir welding defect like tunnel shape was found in stir zone.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 학술대회 논문집 정보 및 제어부문
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• pp.318-319
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• 2008

In this paper, a steering feel simulator is designed and implemented using a steering wheel with a rotation angle sensor, torque sensor, and an ac motor for the generation of the required torque. The controller in the simulator consists of a 16-bit micro-controller, a D/A converter and A/D converters. The main objective of the controller is to perform torque control where the reference torque is calculated from the torque map for both the vehicle velocity and the wheel sensor cutout. It is shown via the experimentation using the proposed simulator that the simulator output performance can be easily understood for the variation of vehicle parameters or controller parameters.

• Computers and Concrete
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• 제7권4호
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• pp.303-315
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• 2010

In this paper, we present a new finite Timoshenko beam element with a model for ultimate load computation of reinforced concrete frames. The proposed model combines the descriptions of the diffuse plastic failure in the beam-column followed by the creation of plastic hinges due to the failure or collapse of the concrete and or the re-bars. A modified multi-scale analysis is performed in order to identify the parameters for stress-resultant-based macro model, which is used to described the behavior of the Timoshenko beam element. The micro-scale is described by using the multi-fiber elements with embedded strain discontinuities in mode 1, which would typically be triggered by bending failure mode. A special attention is paid to the influence of the axial force on the bending moment - rotation response, especially for the columns behavior computation.

• Structural Engineering and Mechanics
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• 제15권3호
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• pp.315-329
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• 2003

As shear occurs along a soil-structure interface, a localized zone with a thickness of several grain diameters will develop in soil along the interface, forming an interfacial layer. In this paper, the behaviour of a soil-structure interface is studied numerically by modelling the plane shear of a granular layer bounded by rigid plates. The mechanical behaviour of the granular material is described with a micro-polar hypoplastic continuum model. Numerical results are presented to show the development of shear localization along the interface for shearing under conditions of constant normal pressure and constant volume, respectively. Evolution of the resistance on the surface of the bounding plate is considered with respect to the influences of grain rotation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.213-216
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• 1996

This paper studies a class of in-parallel manipulators with special geometry where the forward displacement analysis problem can be solved easier than the fully parallel manipulators. Three horizontal links of this mechanism provide 3DOFs(Degrees of Freedom), which are one degree of orientational freedom and two degrees of translatory freedom. Three vertical links of this mechanism provide 3DOFs, which are two degrees of orientational freedom and one degree of translatory freedom. The main advantages of this manipulator, compared with the Stewart platform type, are the capability to produce pure rotation and to predict the motion of the moving platform easily. Since this manipulator has simple kinematic characteristics compared with the Stewart platform, controlling in real-time is possible due to less computational burden. The purpose of this investigation is to develope an analytical method and systematic method to analyze the basic kinematics of the manipulator. The basic kinematic equations of the manipulator are derived and simulation is carried out to show the performance of the mechanism.

• 한국결정학회지
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• 제12권1호
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• pp.5-9
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• 2001

Nd/sub 0.05/Y/sub 0.95/Ca₄O(BO₃)₃(Nd:YCOB) single crystals were grown by the Czochralski method using a iridium crucible under N₂ atmosphere. Optimum growth parameters to get high quality of single crystals were 1.5∼2 mm/hr of growth rate and 10∼20 rpm of rotation rate. The grown crystals were transparent with light purple color and well-developed in cleavage planes. The crystal structure of Nd;YCOB were identified to monoclinic by XRD method. Crystal defects acting as light scattering centers, such as micro-pores, secondary phases, inclusions and cracks were not observed under the He-Ne laser illuminations. Three red, green, blue laser devices for the RGB laser oscillations were designed and then fabricated from the grown Nd:YCOB crystals according to the phase-matching angles of negative type-I which were φ=16.40°, 33.95° and θ=22.59° with the flatness of λ/6 at least, respectively.

• 한국공작기계학회논문집
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• 제11권5호
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• pp.58-64
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• 2002

Mirror surface finish of Si-wafers has been achieved by rotary in-feed machining with cup-type wheels in ELID grinding. But the diameter of the workpiece is limited with the diameter of the grinding wheel in the in-feed machining method. In this study, some finding experiments by the rotary surface grinding machine with straight type wheels were conducted, by which the possible grinding area of the workpiece is independent of the diameter of the wheels. For the purpose of investigating the grinding characteristics of large scale diametrical silicon wafer, grinding conditions such as rotation speed of grinding wheels and revolution of workpieces are varied, and grinding machine used in this experiment is rotary type surface grinding m/c equipment with an ELID unit. The surface ground using the SD8000 wheels showed that mirror like surface roughness can be attained near 2~6 nm in Ra.

• 한국공작기계학회논문집
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• 제16권1호
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• pp.80-85
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• 2007

High speed cutting is a machining process which cuts materials with the fast movement and rotation of a spindle in a machine tool. High speed cutting leaves a plastically deformed layer on the machined surface. This deformed layer affects in various forms to the surface roughness of machined parts such as the dimensional instability, the micro crack. The surface roughness is called surface integrity which is very important in precision cutting. This paper aims to study on the machined surfaces characteristics of aluminum alloy and brass by AFM(Atomic force microscope) measurement. The objective is contribution to ultra- precision cutting by exhibit foundation data of surface roughness and tool wear when parts are cutting with diamond tool at the factory.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.133-144
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• 2020

This investigation is to study the effect of gravitational field and diffusion on a microstretch thermoelastic medium heating by a non-Gaussian laser beam. The problem was studied in the context of the dual-phase-lag model. The normal mode analysis is used to solve the problem to obtain the exact expressions for the non-dimensional displacement components, the micro-rotation, the stresses, and the temperature distribution. The effect of time parameter, heat flux parameter and gravity response of three theories of thermoelasticity i.e. dual-phase-lag model (DPL), Lord and Shulman theory (L-S) and coupled theory (CT) on these quantities have been depicted graphically for a particular model.