• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.595-608
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• 1998

A diffuser an important equipment to change kinetic energy into pressure energy has been studied for a long time. Though experimental and theoretical researches habe been done the understanding of energy transfer and detailed mechanism of energy dissipation is unclear. As far as numerical prediction of diffuser flows are concerned various numerical studies have also been done. On the contrary many turbulence models have constraint to the applicability of diffuser-like flows with expansion and streamline curvature. In order to obtain the reliability of k-$\varepsilon$ turbulence model modified combination turbulence models composed of the anisotropic k-$\varepsilon$model modified combination turbulence models composed of the anisotropic k-$\varepsilon$ model with Hanjalic-Launder's preferential normal strain and Pope's vortex stretching mechanism are proposed. The results of the present proposed models prove the fact that the coefficient of pressure and the shear stress are well predicted at the diffuser flow.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2598-2604
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• 2002

Robots that can move along the narrow and rough tube are very important as the request for the inspection increases. It is necessary for the inspection robots to have a capability to move successfully at even overturned situation and have a simple mechanism to reduce the unexpected failure possibility fer the successful completion of the given mission. Through this paper, the authors propose a novel and simple mechanism using a combination cam device to generate the locomotive motion of multi-legs. This robot uses one DC motor and one combination cam shaft to generate the locomotive motion and can move rough tubes without failure even at the overturned situation. The robot also shows enough fragging force fer the connected line that is very important for a wired inspection robot. Kinematics analysis to design the specification of the robot will be followed and several applications show this robot's potential capabilities.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.295-296
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• 2006

We developed wire frame drive unit based on SMA for the 3D Shape display. Our basic concept is wire frame combination connected with a chain form which can create various shapes and it compared with pin array mechanism which is not able to display mushroom shape. It imitates antagonist mechanism of human musculoskeletal system. we create similar motion using repair-relaxation mechanism and locking mechanism by SMA. Therefore, in this paper, we propose SMA control solution for actuating repair-relaxation mechanism and locking mechanism. In our control system. we use optical sensor and quantitative angle between wire frames for closed loop control. And we supply amplified current for SMA by circuit composed of transistor and apply PWM signal to circuit for efficient control. So, wire frame drive unit enable diversity angle control based on sensor data. And then combination of wire frame drive units will create various objects.

• Geomechanics and Engineering
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• v.22 no.3
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• pp.255-264
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• 2020

With the ongoing development of deep mining of coal resources, some coal mine dynamic disasters have exhibited characteristics of both coal-gas outbursts and rockbursts. Therefore, research is required on the mechanism of rockburst-outburst coupling disaster. In this study, the failure characteristics of coal-rock combination structures were investigated using lab-scale physical simulation experiments. The energy criterion of the rockburst-outburst coupling disaster was obtained, and the mechanism of the disaster induced by the gas-solid coupling instability of the coal-rock combination structure was determined. The experimental results indicate that the damage of the coal-rock structure is significantly different from that of a coal body. The influence of the coal-rock structure should be considered in the study of rockburst-outburst coupling disaster. The deformation degree of the roof is controlled by the more significant main role of the gas pressure and the difference in the strength between the rock body and the coal body. The outburst holes and spall characteristics of the coal body after the failure of the coal-rock structure are strongly affected by the difference in strength between the roof and the coal body. The research results provide an in-depth understanding of the mechanism of rockburst-outburst coupling disasters in deep mining.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.8
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• pp.3626-3635
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• 2011

The modular robots are a kind of system that was developed to overcome the limitation of the movement for the mobile robot with wheels or legs. In legs type mobile robot case, they are limited for velocity and balance during moving at the uneven terrain. In wheeled mobile robot case, they are also limited to overcome dump, stair and so on. The modular robots can overcome moving limitation because of their transforming ability. However, they are researched not only driving mechanism but also combination mechanism. In this paper we proposed four kinds of unique structure for the combination and separation and also its algorithm. The effectiveness of the structure is verified with building the real structure and taking experiments to the designed modular robot

• The Journal of Korea Robotics Society
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• v.7 no.2
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• pp.83-91
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• 2012

In this paper, we propose a cable climbing robot which can climb up and down the cables in the bridges. The robot mechanism consists of three parts: a wheel based driving mechanism, adhesion mechanism, and safe landing mechanism. The wheel based driving mechanism is driven by tooth clutches and motors. The adhesion mechanism plays the role of maintaining adhesion force by a combination of pantograph, ball screw, and springs even when the power is lost. The safe landing mechanism is developed for guaranteeing the safety of the robot during operations on cables. It can make the robot fall down with reduced speed by dissipating the gravitational forces. The robot mechanism is designed and manufactured for validating its effectiveness.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.118-121
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• 1999

Multicast addresses cannot be permanently assigned to particular application or group combination, but need to be available for re-use. So, this requires a dynamic multicast address allocation and release mechanism. For a dynamic multicast address allocation and release mechanism, we must consider low blocking probability, low delay, low control traffic overhead. In this paper, we suggest a efficient dynamic multicast address allocation and release mechanism based on the multicast scope

• International Journal of Automotive Technology
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• v.7 no.4
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• pp.501-508
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• 2006

The effect of chemical additives, such as dimethyl ether(DME), ethanol, carbon disulfide on the soot formation were examined numerically. ill this study, the Frenklach soot mechanism was used as a base mechanism to predict the soot formation in the ethane flame. The combination of Westbrook's DME mechanism, Marinov's ethanol mechanism, and chemical kinetic mechanism for hydrogen sulfide and carbon disulfide flames was made with the base mechanism because the DME, ethanol, $CS_2$ additives are added into the ethane fuel. CHEMKIN code was used as a numerical analysis software to simulate the effect of chemical additives on reduction of the polycyclic aromatic hydrocarbons(PAH's) which are soot precursors. From the numerical results it is observed that addition of DME, ethanol and $CS_2$ into ethane fuel can reduce PAH species significantly. That means theses additives can reduce soot formation significantly. Results also strongly suggest suppression of soot formation by these additives to be mainly a chemical effect. Hand OH radicals may be the key species to the reduction of PAH species for additives.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.5
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• pp.102-111
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• 2010

This paper presents a design of seat mechanism for multi-postures controllable wheelchair. The possible seat postures are reclining, tilting, standing, which are controlled by four seat mechanisms using four linear actuators. The seat mechanisms designed in this study are reclining, tilting, forward-tilting, and elevation mechanism. Three postures except standing are controlled by corresponding mechanisms, but the standing posture is performed by combination of the reclining and the forward-tilting mechanism. Posture control system is composed of PID controllers and a planner to determine a feasible posture based on a posture transition diagram. Simulation results show that the seat mechanism and its control system are applicable to a multi-postures controllable wheelchair.

• Geomechanics and Engineering
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• v.24 no.2
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• pp.179-191
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• 2021

In this study, the strength and failure mechanism of red sandstones with combined defects were investigated by uniaxial compression tests on red sandstones with different crack angles using two-dimensional particle flow code numerical software, and their mechanical parameters and failure process were studied and analyzed. The results showed that the mechanical characteristics such as peak strength, peak strain, and elastic modulus of the samples with prefabricated combined defects were significantly inferior than those of the intact samples. With increasing crack angle from 15° to 60°, the weakening area of cracks increased, elastic modulus, peak strength, and peak strain gradually reduced, the total number of cracks increased, and more strain energy was released. In addition, the samples underwent initial brittle failure to plastic failure stage, and the failure form was more significant, leading to peeling phenomenon. However, with increasing crack angle from 75° to 90°, the crack-hole combination shared the stress concentration at the tip of the crack-crack combination, resulted in a gradual increase in elastic modulus, peak strain and peak strength, but a decrease in the number of total cracks, the release of strain energy reduced, the plastic failure state weakened, and the spalling phenomenon slowed down. On this basis, the samples with 30° and 45° crack-crack combination were selected for further experimental investigation. Through comparative analysis between the experimental and simulation results, the failure strength and final failure mode with cracks propagation of samples were found to be relatively similar.