• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2008.02a
• /
• pp.29-32
• /
• 2008

DMB가 출범한지 2007년을 기준으로 3년을 맞이했다. DMB에 대해서는 일반적으로 많이 알려졌으며 새로운 방송 시스템으로 분명 뛰어난 기술이다. 하지만 방송 현업 종사자의 시각에서 볼 때 시청자들의 호응도는 답보상태에 머물고 있다고 판단된다. 방송위원회의 2007년 12월 조사 결과를 보면 DMB는 국민의 60% 이상이 향후에도 구입할 의향이 없다고 조사되었다. 그 이유는 기존방송을 재전송 하고 있는 상황에서 DMB에 맞는 영상 콘텐츠의 부족함으로 볼만한 콘텐츠가 없다는 것과, 작은 화면으로 인한 시각적 불편함 때문이라는 것이다. 또한 방송 초기 유료와 무료 여부에 대한 국가의 정책결정 등의 문제점이 복합적으로 작용하고 있다. 그 외의 불만 사항으로는 서비스 만족도에서 수신가능 지역에 대한 불만이 63.7%로 가장 많았고 배터리 수명의 한계에 대한 불만 54.4%와 단말기 가격에 대한 불만사항 등이 뒤를 이었다. 이런 상황을 종합해 볼 때 DMB는 당초 예상했던 것처럼 황금 알을 낳는 거위가 아니라는 것과, 신규미디어로서 새로운 콘텐츠의 수요창출에 그다지 성공적이지 못 함을 알 수 있다. DMB의 성패는 시청자의 활용도에 따라 판가름 난다고 본다. DMB 기존의 방송을 재전송하고 있다. 하지만 기존의 방송과는 다르게 DMB 자체의 특성에 적합한 콘텐츠로 제작되어야 할 것이다. 이러한 재전송의 문제점을 개선하고 보다 나은 제작방안을 제시하여 시청자들의 DMB 방송 접근 확대화와 활성화가 본 논문의 연구 목적이다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.5
• /
• pp.489-495
• /
• 2016

This study focuses on a detailed ball-bearing model for spur gears. The nonlinear ball-bearing stiffness with radial clearance is derived and calculated. The bearing stiffness is used to the 3-degree-of-freedom (DOF) spur gear system model. The mode characteristics of the gear system model are analyzed and verified by performing finite-element analysis (FEA). From the results, the bearing stiffness on the radial clearance was more sensitive under low-load conditions compared to high-load conditions. The bearing stiffness significantly affected the gear dynamics in the low-frequency region, while the mesh stiffness affected the high natural frequency.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.7 no.4
• /
• pp.63-72
• /
• 2003

The combustion characteristics of the KSR-III engine were investigated numerically from the viewpoint of performance and combustion field. For numerical analysis of KSR-III engine with hub-and-spoke baffle, 3-D calculation was performed about $30^{\cire}$ section and the prediction of performance was in a good agreement with hot-firing test result. As a result of baffle installed, the performance of KSR-III engine was reduced in comparison with no baffle case and local high temperature region appeared on injector plate, combustion wall and baffle wall, This calculation was used practically as basic data for designing injector plate with film cooling holes and predicting the performance of KSR-III final flight test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11a
• /
• pp.297-303
• /
• 2001

This research presents an analytical model to characterize the ball bearing vibration due to the waviness in a rigid rotor supported by multi-row ball bearings considering centrifugal force and gyroscopic moment of ball. The effects of centrifugal force and gyroscopic moment are introduced to the kinematic constraints and force equilibrium equations. The waviness of ball and races is modeled by the superposition of sinusoidal function and it is introduced to position vectors of race curvature center to use the Hertzian contact theory in order to calculate the elastic deflection and nonlinear contact force resulting from the waviness while the rotor has translational and angular motion. They can be determined by solving the nonlinear equations of motion with five degrees of freedom by using the Runge-Kutta-Fehlberg algorithm. The accuracy of this research is validated by comparing with the results of the prior researches. It characterizes the vibration frequencies resulting from the various kinds of waviness in rolling elements, the harmonic frequencies resulting from the nonlinear load-deflection characteristics of ball bearing resulting from the waviness interaction.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.33 no.4
• /
• pp.330-335
• /
• 2013

Since real-time monitoring system like a fault early detection has been very important, infrared thermography technique as a new diagnosis method was proposed. This study is focused on the damage detection and temperature characteristic analysis of ball bearing using the non-destructive infrared thermography method. In this paper, for the reliability assessment, infrared experimental data were compared with the frequency data of the existing. As results, the temperature characteristics of ball bearing were analyzed under various loading conditions. Finally it was confirmed that the infrared technique was useful for real-time detection of the bearing damages.

• Transactions of the Korean hydrogen and new energy society
• /
• v.26 no.4
• /
• pp.386-392
• /
• 2015

Flow characteristics inside a 10 inch ball valve have been analyzed using three-dimensional numerical analysis and experiments. Continuity and three-dimensional Reynolds-averaged Navier-Stokes equations have been used as governing equations for the numerical analysis. The numerical model has been constructed through the grid dependency test and validation with the results of experiments to ensure reliability and numerical effectiveness. The shear stress transport (SST) model has been used as the turbulence closure. The experimental test-rig has been constructed to measure pressure, temperature and flow rate along the pipeline. Some valve opening angles have been tested to evaluate the flow characteristics inside the ball valve and pipeline. The results show that the rapid pressure variations is observed while the valve opening angle decreases, which caused by flow separation at the downstream of the ball valve.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.10
• /
• pp.1297-1303
• /
• 2013

A nonlinear finite element analysis is performed to evaluate the sealing capability and stress of dust covers for the ball joint of an automotive steering system. The analysis is performed for two types of dust covers: wrinkle type and pot type. The assembly condition and operation condition are analyzed, and the maximum stress and contact normal stress at the ribs are evaluated. It is confirmed that the sealing capability of both types is fairly good, but the wrinkle type is better than the pot type in terms of the maximum stress.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.9
• /
• pp.1669-1680
• /
• 1992

This paper deals with the prediction of cutting force and tool deflection and it's application in the flexible ball end milling process. Machining accuracy is determined by the static stiffness of tool system and the instantaneous cutting force. The static stiffness of tool system consists of the stiffness of holer and the stiffness of ball end mill. The stiffness of holder was obtained from the experimental result, and the stiffness of ball end mill with two flutes was theoretically analyzed by the finite elements method. In cutting process, the instantaneous cutting force is dependent upon the instantaneous feed and pick feed(radial depth of cut) which are varied by tool deflection. For the calculation of cutting force and deflection of ball end mill, iteration method is used with the linear interpolation to the data of cutting force obtained from rigid ball end mill and the data of tool deflection. In this paper, a for enhancing accuracy is discussed. And the selection of helix angle for minimizing machining error is also discussed.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2005.04a
• /
• pp.415-419
• /
• 2005

대수층 저장 및 회수(ASR)기술의 현장 적용성을 평가하기 위하여 경상북도 울릉군 울릉읍 저동천 상류부근에서 양수시험 및 주입시험을 실시하였다. 양수시험결과 투수계수는 $48.7m^2/day$ 이고, 저류계수는 0.009이며, 비양수량은 $158.2m^2/day$로 계산되었다. 또한 시험정과 관측정은 거의 위상차 없이 같은 수위강하 경향을 보여주며 취수정은 관측정보다 평균적으로 10cm 정도 더 높은 수위강하 폭을 보여주는 것으로 미루어 볼 때 시험정과 관측정의 두 지점은 서로 수리지질학적으로 긴밀히 연결되어 있는 하나의 시스템임을 강하게 시사한다. 이외에도 주입시험 결과 암반구간 대수층은 낮은 투수계수를 가질 뿐만 아니라 낮은 저류계수를 가지기 때문에 ASR에 불리한 조건을 가짐을 알 수 있다. 그러나 상부 충적층 구간에서 실시한 주입시험 결과, 두 지점은 긴밀히 연결된 하나의 시스템으로 두 지점의 심부 암반층과의 연결성은 없고, 대신 상부의 높은 투수계수를 가지는 충적층 구간이 두 지점사이에 서로 긴밀히 연결되어 있는 것으로 파악된다. 또한 잔류 수위가 0으로 떨어지는 것으로 볼 때 주입된 주입수는 저장되지 않고 인근의 저동천으로 빠져나가는 것으로 사료된다. 이상의 사실로 볼 때 본 연구지역은 ASR에 불리한 조건을 가지는 지역으로 최종적으로 판단된다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.11
• /
• pp.1315-1321
• /
• 2013

This study presents a prognostic technique for the damage state of a ball bearing. A stochastic bearing fatigue defect-propagation model is applied to estimate the damage progression rate. The damage state and the time to failure are computed by using RMS data from noisy acceleration signals. The parameters of the stochastic defect-propagation model are identified by conducting a series of run-to-failure tests for ball bearings. A regularized particle filter is applied to predict the damage progression rate and update the degradation state based on the acceleration RMS data. The future damage state is predicted based on the most recently measured data and the previously predicted damage state. The developed method was validated by comparing the prognostic results and the test data.