• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.363-367
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• 2009

Recently, the manufacturing of micro-cavity by means of laser surface texturing (LST) technique and low friction study by the LST have been in great progress. Most of current works have been dealing with the effect of cavity on friction and wear. The main objective of the present study was to investigate numerically two-dimensional lubrication characteristics of micro-dimple shapes fabricated on solid surfaces, and this study utilized the commercial CFD code (Fluent V.6.3). For the evaluation, preliminary simulation was conducted and numerical predictions were compared with the analytic solution obtained from the Reynolds's equation. Mainly, the present study investigated the influence of dimple depth, pattern shapes, and film thickness on lubrication characteristics related to the reduction of friction. It is found that the existence of micro-dimpled surface makes it possible to substantially reduce the friction forces exerted on the surfaces. In particular, substantial decrease in shear stresses was observed as the lubricant film thickness decreases. For instance, in the case of the film thickness of 0.01 mm, the estimated shear stress decreases up to about 40%. It indicates that the film thickness would be important factor in designing the micro-dimpled surfaces. Furthermore, it was observed that such a optimum dimple depth would be present because the dimple depth larger than the optimum value did no longer affect the reduction in shear stresses.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1352-1358
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• 2004

The mechanical spring is one of widely used machine elements. Among various kinds, flat-type spring loaded by a rotating pin was studied. A flat spring was simplified to a cantilever beam, and numerical analysis was attempted. Since the loading pin rotates about a separate axis from the fixed spring or vice versa, the location, direction, and magnitude of the contact force including normal contact and friction loads vary accordingly. Meanwhile, the spring is deformed substantially as the relative motion progresses. Therefore, this problem needs to be formulated taking the follower loading characteristics and geometrical non-linearity into account. Derived nonlinear differential equation was solved to yield the spring deflection, contact force and the torque to rotate the pin, and the result was compared with a finite element solution. Also, the influences of principal design parameters were studied. The proposed methodology is expected to be useful for the design of pin-loaded flat spring and the prevention of mechanical failures in the form of yielding or fatigue failure of spring or severe wear of the components.

• Journal of Mechanical Science and Technology
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• v.19 no.spc1
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• pp.265-271
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• 2005

Randomness exists in engineering. Tolerance, assemble-error, environment temperature and wear make the parameters of a mechanical system uncertain. So the behavior or response of the mechanical system is uncertain. In this paper, the uncertain parameters are treated as random variables. So if the probability distribution of a random parameter is known, the simulation of mechanical multibody dynamics can be made by Monte-Carlo method. Thus multibody dynamics simulation results can be obtained in statistics. A new concept called functional reliability is put forward in this paper, which can be defined as the probability of the dynamic parameters(such as position, orientation, velocity, acceleration etc.) of the key parts of a mechanical multibody system belong to their tolerance values. A flexible mechanical arm with random parameters is studied in this paper. The length, width, thickness and density of the flexible arm are treated as random variables and Gaussian distribution is used with given mean and variance. Computer code is developed based on the dynamic model and Monte-Carlo method to simulate the dynamic behavior of the flexible arm. At the same time the end effector's locating reliability is calculated with circular tolerance area. The theory and method presented in this paper are applicable on the dynamics modeling of general multibody systems.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.9 no.2
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• pp.19-31
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• 1999

Most breakthrough tests are conducted at higher concentration levels compared to those in the field of air-purifying respirator applications. For example, typical challenge concentrations for breakthrough tests agains tcarbon tetrachloride are ranged between 250-1000 ppm although applicable concentrations range for air-purifying cartridge is 5-50 ppm for carbon tetrachloride. However, no guarantee has been made that isotherms derived from the experiment at high challenge concentrations could estimate adsorption capacity at the lower concentration range where workers wear usually air-purifying respirators. Three models of adsorption isotherms (Freundlich, Langmuir and Dubinin/Radushkevich(D/R) isotherms) that have been commonly applied for respirator cartridge testing were evaluated. Adsorption capacity at each challenge concentration was calculated from the Reaction Kinetic equation fitted for the breakthrough data. These data were used for derivation of three isotherms. In general, the D/R isotherm has given the best agreement between estimated adsorption capacities and experimentally measured. If the challenge concentration of 100 ppm is included for derivation of models, Freundlich and D/R models could succes sfully produced good estimations for adsorption capacities at 50 ppm level. Estimated adsorption capacities by both models ranged in 94 - 109 % of the experimentally measured. However, Langmuir model gives underes timation in all cases.

• Laser Solutions
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• v.12 no.1
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• pp.25-33
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• 2009

In laser-assisted machining (LAM), laser beam is used to locally increase the temperature of a workpiece and thus to enhance the machinability. In order to set the temperature of the material removal area of a workpiece at an optimal value, process parameters, such as laser power, feed rate, and rotational velocity, have to be carefully controlled. In this work, the effects of laser power and feed rate on the temperature distribution of a silicon nitride rotating at a constant velocity were experimentally investigated. Using a pyrometer, temperatures at various locations of the silicon nitride were measured both in circumferential and axial directions. The measured temperatures were fitted to a quadratic equation to approximate the temperature at the cutting location. The machining results showed that cutting force and tool wear were decreased when the temperature at the cutting location was increased.

• Journal of the Korean Society of Clothing and Textiles
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• v.28 no.2
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• pp.252-261
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• 2004

In this complex marketing world, marketers find themselves having to grapple with difficult issues about branding and their brand management. In many cases, a deeper understanding of how consumers feel, think, and act could provide valuable guidance to address these brand-management challenges. The objective of this study is to conceptualize and test the framework of building fashion brand equity, utilizing Keller＇s CBBE Model as a theoretical framework and Kim and Lim＇s (2002) scale as a measurement model of fashion brand equity. We conducted a survey toward 696 university students using Kim and Lim＇s fashion brand equity scale. To test the hypothesized building paths of fashion brand equity, statistical analyses were performed with AMOS 4.1 program using confirmatory factor analysis and structural equation model. The results of this study were as follows. First, fashion brand equity was defined in terms of six components; customer-brand resonance, customer feeling, customer judgment, brand imagery. brand performance and brand awareness. Fashion brand equity was multi-dimensional brand attitude, which could be measured by 16 items. Consequently, Kim and Lim＇s scale acquired a statistical validity. Second, the proposed conceptual framework of this study was partially significant. We can provide an effectiveness of Keller＇s CBBE model to conceptualize the building process of fashion brand equity. Third, it was different between two brands to build fashion brand equity.

• Journal of the Korean Society of Clothing and Textiles
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• v.26 no.11
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• pp.1660-1671
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• 2002

The purpose of this study is to develop and test the casual brand equity measurement, utilizing Heller 5(2001) ‘CBBE(Customer Based Brand Equity) Model' as a theoretical framework. The research was conducted in three steps from May to November in 2001. In the exploratory step, focus-group interview was conducted 5 times for gathering responses related to fashion equity. In Pilot study, 945 university students were surveyed and the data were analyzed to identify the components of fashion brand equity and to develop questionnaires. In the main research, 696 university students evaluated three brands in order to compare their equity that were formed in customers' perception. Statistical analyses were performed with SAS and LISREL 8.12 program using factor analysis and covariance structural equation model. The results were as follows: First, casual brand equity was defined in terms of six components; customer-brand resonance, customer feeling, customer judgment, brand imagery, brand performance and brand awareness. Second, casual brand equity was multi-dimensional brand attitude, which could be measured by 23 items that were different from previous measurement such as Aaker's ‘Brand Equity Ten' and K-BPI.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.7
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• pp.677-684
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• 2010

Backlashes of gears provide gears for good lubrication and for removal of the interference between teeth by the wear and manufacturing errors. The backlash is the strong nonlinear factor to gears. This study deals with nonlinear modeling of helical gears with backlash. Excitation of helical gears comes from torque variation, the tooth surface error, and the periodical change of mesh stiffness. To study the effect of torque fluctuation, equation of motion for the single degree of freedom torsional model of helical gears with the periodical change of mesh stiffness and the backlash was derived. The Newmark beta method and the Newton-Raphson method were used to obtain the nonlinear behaviors of mesh forces of helical gears. All excitation frequencies initially caused the tooth separation and single-sided impacts of the gear pair and eventually led to the normal tooth contact. However, some special excitation frequencies caused the single-sided impacts in the entire time as well as the initial time. Damping increase reduced the duration of single-sided impacts, and the backlash increase caused those in the entire time domain.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.12
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• pp.519-528
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• 2021

The COVID-19 pandemic struck several countries in 2020. After the government officially announced that individuals will be working from home, shut public service agencies, and compelled people to wear masks and maintain social distance, several hundred business actors were forced to shut down their firms. The purpose of this study is to help companies determine the steps for a new marketing strategy for healthy food products in Indonesia. The number of samples was 500 respondents. The variance-based Structural Equation Modeling (SEM) method was used to conduct this investigation, which was similar to a marketing study. The findings show that in Indonesia, lifestyle and price perceptions influence healthy food product purchasing decisions. Meanwhile, brand awareness and customer attitudes had no bearing on healthy food products purchase decisions. The novelty of this study stems from the discovery of new opportunities for business players to market healthy food products during the current COVID-19 period. This opportunity arises as a result of changes in customer lifestyles and price perceptions, both of which must be taken into account by organizations to offer nutritious food items at reasonable rates in Indonesia.