• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.452-455
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• 2005

The cutting characteristics of hardened steel by a PCBN tool is investigated with respect to workpiece surface roughness, cutting force and tool flank wear of the vision system. Backpropagation neural networks (BPNs) were used for detection of tool wear. The neural network consisted of three layers: input, hidden and output. The input vectors comprised of spindle rotational speed, feed rates, vision flank wear, and thrust force signals. The output was the tool wear state which was either usable or failure. Hard turning experiments with various spindle rotational speed and feed rates were carried out. The learning process was performed effectively by utilizing backpropagation. The detection of the abnormal states using BPNs achieved 96.4% reliability even when the spindle rotational speed and feedrate were changed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.83-86
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• 2002

Numerical simulations are conducted for laminar flow past a sphere rotating In the transverse direction, in order to investigate the effect of the rotation on the characteristics of flow over a sphere. The Reynolds numbers considered are Re=100, 250 and 300 based on the free-stream velocity and the sphere diameter, and the rotational speeds are in the range of $0{\leq}{\omega}{\leq}1$, where ${\omega}^{\ast}$ is the maximum velocity on the sphere surface normalized by the free-stream velocity. At ${\omega}^{\ast}=0$ (without rotation), the flow past the sphere experiences steady axisymmeoy, steady planar-symmetry and unsteady planar-symmetry, respectively, at Re=100, 250 and 300. However, with rotation, the flow becomes planar-symmetric for all the cases investigated and the symmetry plane is orthogonal to the axis of the rotation. The flow is also steady or unsteady depending on both the Reynolds number and the rotational speed, and the vortical structures behind the sphere are significantly modified by the rotation. For example, at Re=300, hairpin vortices completely disappear in the wake at ${\omega}^{\ast}=0.4\;and\;0.6$, and at ${\omega}^{\ast}=1$ vortical structures of a high frequency are newly generated due to the shear layer instability. It is also shown that with increasing rotational speed, the time-averaged drag and lift coefficients increase monotonically.

• ETRI Journal
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• 제41권6호
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• pp.838-849
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• 2019

We present a permanent magnet-based spherical wheel motor that can be used in omnidirectional mobility applications. The proposed motor consists of a ball-shaped rotor with a magnetic dipole and a hemispherical shell with circumferential air-core coils attached to the outer surface acting as a stator. Based on the rotational symmetry of the rotor poles and stator coils, we are able to model the rotor poles and stator coils as dipoles. A simple physical model constructed based on a torque model enables fast numerical simulations of motor dynamics. Based on these numerical simulations, we test various control schemes that enable constant-speed rotation along arbitrary axes with small rotational attitude error. Torque analysis reveals that the back electromotive force induced in the coils can be used to construct a control scheme that achieves the desired results. Numerical simulations of trajectories confirm that even without explicit methods for correcting the rotational attitude error, it is possible to drive the motor with a low attitude error (<5°) using the proposed control scheme.

• 한국유체기계학회 논문집
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• 제13권1호
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• pp.23-28
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• 2010

A draft tube which has impeller to elevate bottom water and spread it over surface of lake water, induces convective circulation of lake water, a Long-Distance Circulation (LDC). Circulation of lake water make stratified water mixed and enhance DO (Dissolved Oxygen) of bottom water. Circulation rate of water is determined by draft rate of the tube, which is dependent on design parameters of the draft tube system, i. e. dimension of impeller and diffuser, inclined angle of impeller, impeller shape, and rotational speed. In this study, change in draft rate and power consumption of circulation equipment was investigated numerically with changing impeller dimension, angle and rotational speed. It was found that flowrate of draft water was increased as the dimensions of draft tube and impeller, and rotational speed and inclined angle of impeller increased. The power consumption was also elevated with increasing parameter values, and final selection of parameter values was made to satisfy target flowrates and power consumption.

• Structural Engineering and Mechanics
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• 제17권6호
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• pp.789-817
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• 2004

This paper deals with the modal analysis of rotational shell structures by means of the numerical solution technique known as the Generalized Differential Quadrature (G. D. Q.) method. The treatment is conducted within the Reissner first order shear deformation theory (F. S. D. T.) for linearly elastic isotropic shells. Starting from a non-linear formulation, the compatibility equations via Principle of Virtual Works are obtained, for the general shell structure, given the internal equilibrium equations in terms of stress resultants and couples. These equations are subsequently linearized and specialized for the rotational geometry, expanding all problem variables in a partial Fourier series, with respect to the longitudinal coordinate. The procedure leads to the fundamental system of dynamic equilibrium equations in terms of the reference surface kinematic harmonic components. Finally, a one-dimensional problem, by means of a set of five ordinary differential equations, in which the only spatial coordinate appearing is the one along meridians, is obtained. This can be conveniently solved using an appropriate G. D. Q. method in meridional direction, yielding accurate results with an extremely low computational cost and not using the so-called "delta-point" technique.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권1호
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• pp.87-97
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• 2014

In this study, the model tests were conducted on the short piles installed in sands under a horizontal pullout load to investigate their behavior characteristics. From the horizontal loading tests where dimensions of the pile diameter and length, and loading point were varied, the horizontal pullout resistance and the rotational and translational movement pattern of the pile were investigated. As a result, the horizontal pullout resistance of the pile embedded in sands was dependent on the pile length, diameter, loading point, etc. The ultimate horizontal pullout load tended to increase as the loading point (h/L) moved to the bottom from the top of the pile, regardless of the ratio between the pile length and diameter (L/D), reached the maximum value at the point of h/L = 0.75, and decreased afterwards. When the horizontal pullout load acted on the upper part above the middle of the pile, the pile rotated clockwise and moved to the pullout direction, and the pivot point of the pile was located at 150-360mm depth below the ground surface. On the other hand, when the horizontal pullout load acted on the lower part of the pile, the pile rotated counterclockwise and travelled horizontally, and the rotational angle was very small.

• International Journal of Aeronautical and Space Sciences
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• 제14권1호
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• pp.11-18
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• 2013

Human spaceflight experience in extra-vehicular activity (EVA) is limited to two regimes: the micro-gravity environment of Earth orbit, and the lunar surface environment at one-sixth of Earth's gravity. Future human missions to low-gravity bodies, including asteroids, comets, and the moons of Mars, will require EVA techniques that are beyond the current experience base. In order to develop robust approaches for exploring these small bodies, the dynamics associated with human exploration on low-gravity surface must be characterized. This paper examines the translational and rotational motion of an astronaut on the surface of a small body, and it is shown that the low-gravity environment will pose challenges to the surface mobility of an astronaut, unless new tools and EVA techniques are developed. Possibilities for addressing these challenges are explored, and utilization of the International Space Station to test operational concepts and hardware in preparation for a low-gravity surface EVA is discussed.

• Design & Manufacturing
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• 제17권2호
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• pp.33-41
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• 2023

Metal raw materials and chemical additives, which are raw materials for secondary batteries, are pulverized by the high-speed rotation of the Grinding Disc of the Classifier Separator Mill (CSM). Grinding discs are required to withstand abrasion, corrosion, high-speed rotational force and impact. In order to analyze the stability of domestic and foreign grinding discs, quality tests including surface roughness, surface lubrication, surface state measurement, and surface 3D shape measurement were analyzed. When producing developed products, it shows that excellent products can be produced.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.365-366
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• 2002

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on a novel low temperature degradation-free zirconia/alumina composite material and conventional alumina and zirconia ceramics used for femoral head in total hip joint replacement. The wear of UHMWPE pins against these ceramic disks was evaluated by performing linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in bovine serum. The weight loss of polyethylene against the novel low temperature degradation-free zirconia/alumina composite disks was much less than those against conventional ceramics for all tests. The mean weight loss of the polyethylene pins was more io the linear reciprocal sliding test than in the repeal pass rotational sliding lest for all kinds of disk materials. Neither the coherent transfer film nor the surface damage was observed on the surface of the novel zirconia/alumina composite disks during the test. The observed r,'stilts indicated that the wear of the polyethylene was closely related to contacting materials and kinematic motions. In conclusion, the novel zirconia/alumina composite leads the least wear of polyethylene among the tested ceramics and demonstrates the potential as lhe alternative materials for femoral head in total hip joint replacement.

• 한국기계가공학회지
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• 제9권3호
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• pp.83-88
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• 2010

This study aimed to enhance the durability by distributing the stress concentration at the contact and increasing the mechanical characteristics, as well as by changing the surface shape for LIP in the low-pressure seal among oil seals installed to the power steering of automotive. Accordingly, results were derived from comparisons and reviews with oil seals under the existing mass production by carrying out the performance tests after designs and productions are done with the addition of embo shapes on the surface of LIP in the low-pressure seal. As a result of this study, it has been identified that the durability of oil seals with the addition of embo shapes was enhanced with higher radial force and less variation in the internal diameter for the LIP. In addition, it was seen that the sealing ability for those oil seals is superior to the existing oil seals as their rotational torque values are less than those of the existing oil seals.