• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.244-249
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• 2000

Recently, composite material which has much excellent mechanical characteristics has been applied in many industries. However, it has a brittle characteristic under impact event. Especially, its invisible characteristics of the damaged area has been the motivation of many engineers investigation, and the nonlinearity of the impact mechanism is one of the main reason to assume the damaged area too simple. The damage mechanism of the composite laminated plate subjected to low velocity impact using ABAQUS/Standard & user subroutine was presented here.

• Tribology and Lubricants
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• 제37권3호
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• pp.112-116
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• 2021

Appropriate friction model usage is important for impact analysis because the relative motions between parts that are in contact for very short durations can vary greatly depending on the friction model. Vehicle seat components that have significant effects on impact analysis are also considered. This paper presents an experimental investigation of various material contact pairs to obtain the friction parameters of the Benson exponential friction model for impact simulation. The Coulomb friction model has limitations for impact analysis because of singularity at zero velocity. Metal/nonmetal materials are prepared, and friction tests are conducted for various sliding speeds, loads, and lubrication conditions. The obtained data are used in the friction model to implement finite element analysis. The parameters of the friction model are obtained by the curve-fitting method. The experimental results show that the friction coefficient with metal/nonmetal contact pairs is stable regardless of the working conditions. The friction model used in this study can also be applied for finite element analysis of the crash conditions, where the friction changes abruptly at the contact interface; the obtained friction parameters are also expected to be more accurate with more precise tests under different working conditions. These results can help improve the accuracy of the finite element analysis.

• Journal of Information Technology Applications and Management
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• 제21권2호
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• pp.15-29
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• 2014

This study analyzes the influence factors of IPTV users on the purchase of paid contents. This study carries out a web-log analysis of the actual users of the service provided by the domestic IPTV providers and classifies the influence factors on the purchase of paid contents largely into VOC, switching barriers, and content consumption pattern to conduct an empirical analysis. As analysis procedure, first, this study analyzes the preceding researches related to the core influence factors and content-purchasing patterns, and second, conducts a basic statistics analysis of the distribution of basic characteristics of the logs used, as presented in the above. Third, this study carries out a multiple regression analysis as an estimating equation of the number of purchasing the paid content depending on switching barriers of IPTV service, VOC, and content consumption pattern. As a statistical package, Stata version 11.2 was used. Through the empirical analysis, this study found that of the service use logs, VOC and content consumption pattern had a multi-dimensional impact on the purchase of premium contents. On the other hand, this study also found that the impact of switching barriers such as combination state with other products and current status of holding a point did not have a significant impact on the purchase of paid contents.

• 대한기계학회논문집A
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• 제33권1호
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• pp.1-26
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• 2009

Cylindrical shells of isotropic and composite laminated materials are being used many engineering applications. This paper reviews the literature focusing on various aspects of shell research. The aspects of research receiving interest here are the cylindrical theory being used, the stress, buckling analysis and the impact analysis. The vibration analyses and stiffening characteristics of the cylindrical shell are investigated. The design optimizations of the cylindrical shell are reviewed. The studies on the conical and spherical shell are also reviewed. This review aticles contain 236 referencees.

• 소음진동
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• 제6권4호
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• pp.447-456
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• 1996

Dynamic characteristics of the bell-type structure including acoustic effects and transient dynamic problems were analyzed numerically. Natural frequencies, mode shapes and transient dynamic analysis used the finite element method with 3-D general shell element. Mode shapes and stress distributions of transient dynamic analysis were expressed by computer graphics. The method using this study was evaluated by comparision of theoretical results at reference papers(14), (15) and the experimental test using Fast Fourier Transform analyzer. Vibrational modes governing acoustic characteristics of the typical bell-type structure depended on the first flexural mode(4-0 mode) and the second flexural mode(6-0 mode). Asymmetric effects by Dangiwas, acoustic holes gave rise to beat frequencies, and the Dangjwa was found to be most effective. When impact load acted on the bell, stress concentration occured at the rim part of bell. It was found that the bell type structure should be designed thickly at the rim part in order to prevent impact load from stress concentration.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 추계학술대회 논문집
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• pp.640-645
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• 2004

In this thesis, the impact analysis for the shunting procedure using the dynamic buffer characteristics of the coupler was developed. In this study, each car was modeled as one dimensional element by using the equivalent system. After the impact, the slip exists only between wheel and rail in the braked trainset. For this analysis the analysis code named the POTAS-MSM (Power Transmission Analysis Software Multi Slip Mechanism) which was developed for the numerical analysis of dynamic system is developed. The validation of this analysis was proven by comparing the numerical results with the results of world-famous S company which is located in Europe.

• The Journal of Asian Finance, Economics and Business
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• 제6권1호
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• pp.59-69
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• 2019

The auditor, an important instrument of corporate governance, ensures the transparency and accountability of the firm to the stakeholders. The objective of this paper is to explore the impact of audit characteristics on firm performance. In this study, external audit quality (BIG4), frequencies of audit committee meetings, and audit committee size are used as the proxies of audit characteristics and firm performance is measured through ROA, profit margin and EPS. A total of 503 firm years are considered as sample size from the listed manufacturing firms of Dhaka Stock Exchange (DSE) during the period of 2013 to 2017 to find out the impact of audit characteristics on firm performance. In this study, multivariate regression analysis is conducted using the pooled OLS method. Moreover, time dummy and lag model of multivariate analysis are also analyzed as robust check. The multivariate regression results find that external audit quality (BIG4) and audit committee size are significantly positively associated with firm performance. This study also finds that there is a significant negative relationship between audit committee meeting and firm performance. This study recommends that the regulatory authority and audit committee should review the frequencies of audit committee meeting to make it more effective to ensure better firm performance.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.846-853
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• 2008

Maglev System is expected to be a new public transportation for future because of its special characteristics. Sleepers of railway role on transferring the lateral load to guideway for Maglev and controlling the distance between rails. Variation of distance of sleepers can affect dynamic responses for maglev guideway. In this paper, Daejon maglev guideway is analyzed to find proper tie spacing of a maglev system. The analysis included using a maglev trainload and also the dead load as the primary forces on bridges. Not only the dynamic behavior of bridges is investigated under sleeper conditions, but also impact factor about vertical displacement on the guideway is produced. This guideway is analyzed in four cases followed by changing spacing of sleeper and then obtained dynamic characteristics such as displacements, acceleration and impact factor by Finite Element Analysis.

• 한국소음진동공학회논문집
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• 제16권7호
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• pp.754-761
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• 2006

This paper presents the dynamic characteristics of MR impact damper for vehicle collision system. Various types of mechanism have been proposed to reduce force transmitted to the vehicle chassis and finally to protect occupants from injury. In the case of head-on collision, the bumper makes main role of isolation material for collision attenuation. In this study, the proposed bumper system consists of MR impact damper and structures. The MR impact damper utilizes MR fluid which has reversible properties with applied magnetic field. The MR fluid operates under flow mode. The bellows is used for generation of fluid flow. A mathematical model of the MR impact damper is derived incorporating with Bingham model of the MR fluid. Field dependent damping force is investigated with time and frequency domain. The MR impact damper is then incorporated with vehicle crash system. The governing equation of motion of vehicle model is formulated considering occupant model. Dynamic characteristics of vehicle collision system investigated with computer simulation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.147-152
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• 2006

This paper presents the dynamic characteristics of MR impact damper for vehicle collision system. Various types of mechanism have been proposed for reduce transmitted force to vehicle chassis and finally protect occupants from injury. In the case of frontal collision, the bumper make main role of isolation material for collision attenuation. In this study, proposed bumper system composed of MR impact damper and structures. The MR impact damper is to adopted MR fluid which has reversible properties with applied magnetic field. MR fluid operates under flow mode with Bingham flow and bellows is used for generation of fluid flow. Mathematical model of MR impact damper incorporated with MR fluid is established. Field dependent damping force is investigated with time and frequency domain. The MR impact damper is then incorporated with vehicle crash system. The governing equation of motion of vehicle model is formulated considering occupant model. Dynamic characteristics of vehicle collision system investigated with computer simulation.