• Journal of Advanced Marine Engineering and Technology
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• 제11권2호
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• pp.51-60
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• 1987

Recently, the problem of the axial vibration for the marine diesel engine shafting has become important due to the increased exciting forces resulting from high supercharging and large output, and the reduced natural frequencies resulting from long stroke and show speed. The effects of the axial vibration on the propulsion shafting induce cracks of the connecting point of crankpin and crankarm, the severe wear of thrust bearing, the fatigue failure of each fixing bolt and jointed parts, the hull and local hull vibrations, and also the wear and the noise due to intense hammering phenomena of thrust collar. Therefore, each classification society requires the calculation of natural frequencies and their amplitudes and also measurements of the forced damped axial vibration. At present, the technical and theoretical level is at the stage of estimating the resonant points and their maximum displacements, but the estimated displacements of the resonant points are not so reliable as the torsional one. In this study, induced stresses and amplitudes of the forced damped axial vibration are calculated. For this purpose, the equation of forced axial vibration with damping for the propulsion shafting is derived and its steady-state response is calculated by the mechanical impedance method. A computer program for above calculations is developed. The measured values are analyzed and the calculated results are compared with the measured ones. They show fairly good agreements and the reliability of developed program is confirmed.

• The Journal of Asian Finance, Economics and Business
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• 제7권4호
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• pp.247-258
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• 2020

The study investigates the influences of different factors on revisit intention to Korea of Vietnamese tourists. A mixed-method including qualitative and quantitative methodologies were utilized. A focus group of 9 experts was carried out for reviewing and exploring different factors and the conceptual model. An in-depth interview with 19 participants was developed with an aim to develop and correct measurement items. The conceptual model was tested and developed using data collected by a questionnaire, from a sample of 473 respondents, who have visited Korea by both electronic and paper surveys with non-probability and convenience sampling techniques. The questionnaire in this research applied a 5-point Likert scale and was distributed both electronically using Google form and by questionnaire paper. The Bootstrap model was used for estimating the model parameters for retesting the reliability of the estimates. Factor analysis and Structural Equation Modelling are employed to analyze the data. Results showed that 427 tourists traveling by groups organized by travel companies and 46 tourists traveling on their own. The reliability, tangibility, empathy, and assurance had influences on tourists' intention to revisit a destination, especially through satisfaction mediating construct. Destination image, self-congruity, and the emergence of Hallyu had influences intension revisit through attitude and tourist motivation.

• 한국대기환경학회지
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• 제11권3호
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• pp.273-278
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• 1995

This study is to estimate the ventilation volume by the traffic that originated from driving automobiles for two tunnels (Kugi tunnel and Kumhwa tunnel) that adopted natural ventilation system among tunnels of Seoul, and on the basis of which, we estimated the ventilation velume at various conditions. With the result of the estimation, we will present the basic method that can be operated with the optimum condition for the ventilation system. Estimating the predicted ventilation volume in the tennel by the pollutant concentration, we used traffic volume and CO emission data by the automobile speed and CO concentration in the tunnel. And, when we estimated the traffic ventilation volume by natural and traffic ventilation force, we used traffic volume, automobile speed, tunnel area, automobile area data and so on. As the result of simple regression between predicted ventilation volume and traffic ventilation volume, we attained the regression coefficient 0.88, and achieved the relation form that predicted ventilation volume equal 0.12x traffic ventilation volume-92, 000. Using this equation, we estimated the ventilation volume to satisfy the enviromnental standards of several space, and calculated the required volume for mechanical ventilation. Incase of Kumhwa Tunnel, there is a need of mechanical ventilation all day long to satisfy air quality standard 9 ppm for 8 hours average and 10 ppm for the indoor air quality standard of public facilities.

• 품질경영학회지
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• 제43권3호
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• pp.383-396
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• 2015

Purpose: This study was to identify the structural relationships among suitability of entertainer advertising model, relationship quality and brand loyalty in coffee shop. Methods: This study collected data from those who visited two reputed franchised coffee shops. A variety of statistical methods were used; descriptive analysis, exploratory factor analysis, confirmatory factor analysis and structural equation modelling analysis. Results: The research results from this study are as follows: First, only credibility factor has a positive impact on relationship quality; second credibility and expertness factors positively influence brand loyalty; and third, there is a positive relationship between relationship quality and brand loyalty. Conclusion: The results of this research are useful for identifying the role of advertising models's suitability in estimating relationship quality and brand loyalty and strategies for strengthening brand loyalty for coffee shops.

• Tribology and Lubricants
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• 제25권4호
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• pp.256-260
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• 2009

Fretting is a kind of wear which effects on reliability and durability. When machine parts are joined joint in parts such as a bolt or a rivet or a pin, fretting phenomenon is occurred by micro relative movement. When fretting occurs in joint parts, there is wear which is the cause of fatigue crack. Recently, although the ways of assessment of fatigue and damage tolerance are established, there is no way to evaluate fatigue crack initiation life by fretting phenomenon. Consequently, the prediction of life and prevention plan caused by fretting are needed to improve reliability. The objective of this paper is to predict fretting wear by using a experimental method and contact analysis considering wear process. For prediction of fretting wear volume, systematic and controlled experiments with a disc-plate contact under gross slip fretting conditions were carried out. A modified Archard equation is used to calculate wear depths from the contact pressure and stroke using wear coefficients obtained from the disc-plate fretting tests.

• 한국정밀공학회지
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• 제19권1호
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• pp.196-203
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• 2002

Generally, non-uniformity and removal rate are important factors on measurements of both wafer and die scale. In this study, we verify the effects of the pressure and relative velocity on the results of the chemical mechanical polishing and the effect of pattern density on inter layer dielectric chemical mechanical polishing of patterned wafer. We suggest an appropriate modeling equation, transformed from Preston\`s equations which was used in glass polishing, and simulate the removal rate of patterned wafer in chemical mechanical polishing. Results indicate that the pressure and relative velocity are dominant factors for the chemical mechanical polishing and pattern density effects on removal rate of pattern wafers in die scale. The modeling is well agreed to middle and low density structures of the die. Actually, the die used in Fab. was designed to have an appropriate density, therefore the modeling will be suitable for estimating the results of ILD CMP.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1302-1310
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• 2001

This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

• Communications for Statistical Applications and Methods
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• 제25권3호
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• pp.321-328
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• 2018

In clinical trials with repeated measurements, the time-averaged difference (TAD) may provide a more powerful evaluation of treatment efficacy than the rate of changes over time when the treatment effect has rapid onset and repeated measurements continue across an extended period after a maximum effect is achieved (Overall and Doyle, Controlled Clinical Trials, 15, 100-123, 1994). The sample size formula has been investigated by many researchers for the evaluation of TAD in two treatment groups. For the evaluation of TAD in multi-arm trials, Zhang and Ahn (Computational Statistics & Data Analysis, 58, 283-291, 2013) and Lou et al. (Communications in Statistics-Theory and Methods, 46, 11204-11213, 2017b) developed the sample size formulas for continuous outcomes and count outcomes, respectively. In this paper, we derive a sample size formula to evaluate the TAD of the repeated binary outcomes in multi-arm trials using the generalized estimating equation approach. This proposed sample size formula accounts for various correlation structures and missing patterns (including a mixture of independent missing and monotone missing patterns) that are frequently encountered by practitioners in clinical trials. We conduct simulation studies to assess the performance of the proposed sample size formula under a wide range of design parameters. The results show that the empirical powers and the empirical Type I errors are close to nominal levels. We illustrate our proposed method using a clinical trial example.

• 물과 미래
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• 제14권3호
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• pp.37-46
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• 1981

본 연구에서는 수문관측자료가 없는 지점에서도 확률홍수량을 구할 수 있는 확률홍수량의 산정공식을 유도하였다. 연구 대상유역으로는 한국의 주요하천인 한강, 금강, 영산강, 섬진강, 낙동강을 택하였고, 분석지점으로는 5대강 유역의 24개 수문관측소를 선정하여 여기서 얻은 홍수량자료를 Weibull-Plot와 Gumber-Chow 방법에 의한 분석을 통하여 T년 확률홍수량을 구하고 유역면적, 유로장, 유역형상계수, 유역평균경사, 하천경사를 확률홍수량에 영향을 미치는 지형인자로 하여, 이들 확률홍수량과 지형인자와의 상관관계를 분석하여 확률홍수량 공식을 유도하였다. Gumbel-Chow 방법에 의한 확률홍수량과 지형인자의 상관관계 분석결과, 유역면적 A의 상관이 너무 높게 나타나 위 방법에 따라 구한 확률홍수량과 지형인자와의 상관관계 분석결과에 의하여 재기년에 따른 확률 홍수량과 지형인자와의 상관관계 분석결과에 의하여 재기년에 따른 확률 홍수량 공식을 유도하였다.

• 한국측량학회지
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• 제30권6_2호
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• pp.593-605
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• 2012

LiDAR systems provide dense and accurate topographic information. A pre-requisite to achieving the potential accuracy of LiDAR is having a proper system calibration, which aims at estimating all the systematic errors in the system measurements and the mounting parameters relating the different components. This paper presents a rigorous and two approximate methods for LiDAR system calibration. The rigorous approach makes use of the LiDAR equation and the system raw measurements. The approximate approaches utilize simplified LiDAR equations using some assumptions, which allow for less strict requirements regarding the raw measurements. The first presented approximate method, denoted as quasi-rigorous, assumes that we are dealing with a vertical platform (i.e., small pitch and roll angles). This method requires time-tagged point cloud and trajectory position data. The second approximate method, denoted as simplified, assumes that we are dealing with parallel strips, vertical platform, and minor terrain elevation variations compared to the flying height above ground. Such method can be performed using the LiDAR point cloud only. Experimental results using a real dataset, whose characteristics deviate to some extent from the utilized assumptions in the approximate methods, are presented to provide a comparative analysis of the outcome from the introduced methods.