• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.731-736
• /
• 2004

In this study, a linearized model of pneumatic cylinder position control system including transmission line is proposed. The transmission line using compressible fluid has a nonlinear transfer characteristics because that the frequency response of it is changed by the flowing state of the fluid. But, when the pressure difference between both sides of transmission line is low, the effect of resonance characteristics of it under high frequency range can be neglected because of the friction force and low pass characteristics of the position control system. Therefore, the transmission line can be modeled by second order transfer function and the natural frequency, damping ratio and gain are changed by the diameter and length of it. The effectiveness of the proposed model is proved by comparison of simulation results using proposed model with experimental results and simulation results using conventional model.

• 한국소음진동공학회논문집
• /
• 제22권4호
• /
• pp.358-364
• /
• 2012

This work dealt with dynamic characteristics of spur gear and helical gear system to understand the gear vibration and noise. To find out dynamic characteristics in the gear system, a finite element model and an analytic model for the gear system were used. Using the models, the natural frequency and mode-shape characteristics of spur gears and helical gears were calculated. Two models show that natural frequencies of helical gears were lower than those of spur gears. Mode-shape characteristics of gear pairs by analytical model and some issues of finite element modeling were also discussed. Impact test was used to validate the finite element model.

• Advances in nano research
• /
• 제5권1호
• /
• pp.61-67
• /
• 2017

A semi-empirical approach to model the temperature effects on I-V characteristics of Carbon Nanotube Field Effect Transistors (CNTFETs) is proposed. The model includes two thermal parameters describing CNTFET behaviour in terms of saturation drain current and threshold voltage, whose values are extracted from the simulated and trans-characteristics of the device in different temperature conditions. Our results are compared with those of a numerical model online available, obtaining I-V characteristics comparable but with a lower CPU calculation time.

• International Journal of Automotive Technology
• /
• 제5권3호
• /
• pp.145-153
• /
• 2004

Potential fuel economy improvements and environmental legislation have renewed interest in Gasoline Direct Injection (GDI) engines. Computational models of fuel injection and mixing processes pre-ignition are being developed for engine optimisation. These highly transient thermofluid models require verification against temporally and spatially resolved data-sets. The authors have previously established the capability of PDA to provide suitable temporally and spatially resolved spray characteristics such as mean droplet size, velocity components and qualitative mass distribution. This paper utilises this data-set to assess the predictive capability of a numerical model for GDI spray prediction. After a brief description of the two-phase model and discretisation sensitivity, the influence of initial spray conditions is discussed. A minimum of 5 initial global spray characteristics are required to model the downstream spray characteristics adequately under isothermal, atmospheric conditions. Verification of predicted transient spray characteristics such as the hollow-cone, cone collapse, head vortex, stratification and penetration are discussed, and further improvements to modelling GDI sprays proposed.

• 한국실내디자인학회:학술대회논문집
• /
• 한국실내디자인학회 2002년도 춘계학술발표대회 논문집
• /
• pp.66-70
• /
• 2002

The purpose of this study was to identify the Korean traditional housing design characteristics in apartment model houses. 37 floor plans of apartment model houses in Busan were collected and analyzed. Also, 31 design element check-lists were checked through the field study in apartment model houses. The results were as follows: 1) Korean traditional housing design characteristics in aspects of space organization, such as harmony with nature, hierarchy, focal space, flexibility, were founded in apartment houses. 2) Korean traditional housing design characteristics in aspects of scale, material, color, and motif were mostly founded in the master bedroom and the living room in apartment house. 3) Also, the larger the size of apartment houses were, the more Korean traditional housing design characteristics were founded.

• 중환자간호학회지
• /
• 제9권2호
• /
• pp.36-47
• /
• 2016

Purpose: The study examined core job characteristics and job preference to explain work performance among critical care nurses. The theoretical model was constructed based on the job characteristics model with core job characteristics as exogenous variables, and work performance and job preference as endogenous variables. Methods: A total of 228 hospital nurses participated in the study from May to September, 2015. Data were collected through structured questionnaires and analyzed using structural equation modeling. Results: The model showed a good fit to the data with $x^2/df=2.90$, goodness of fit index = .91, root mean square residual = .20, comparative fit index = .93, and incremental fit index = .93. The core job characteristics explained 64% of the variance in job preference. The core job characteristics and job preference explained 52% of the variance in work performance. Conclusions: The core job characteristics can explain the work performance among critical care nurses through job preference. Effective strategies to improve the work performance among critical care nurses should focus on the application of the core job characteristic into a productive work environment. Further studies are warranted to explore the role of job preference of critical care nurses in promoting their work performance.

• 소음진동
• /
• 제5권1호
• /
• pp.75-83
• /
• 1995

The fluctuation of the engine torque appears to be the major source of the torsional vibration of the automotive driveline. The reduction of this torsional vibration has become a significant problem, due to an increase in the fluctuation of the torque of recent light weighted and high powered engines, along with the requirements of higher performance. The torsional vibration of the automotive driveline can be reduced by smoothing the fluctuation by adjusting the torsional characteristics of the clutch-disc. This paper presents an experimental and theoretical research on the clutch-disc torsional characteristics for the reduction of the torsional vibration at driving. The effects of clutch-damper on diminishing the torsional vibration were investigated experimentally. A dynamic model for the automotive driveline was developed, and the engine torque of the model were evaluated with experimental data. By executing a simulation using the model, it has become possible to obtain the clutch-disc torsional characteristics and the clutch-disc torsional characteristics for reducing the torsional vibration has been suggested. The results are as follows: (1) By exceuting simulations using nonlinear model of four degrees of freedom, a design technique to determine the clutch-disc torsional characteristics for reducing the torsional vibration at driving was developed. (2) The influence of barious torsional characteristics of the clutch has been studied in examining design parameters, which indicates that the domain to minimize the torsional vibration at driving depends on the characteristics of the clutch-damper, i. e., spring constant and hysteresis.

• Wind and Structures
• /
• 제31권3호
• /
• pp.269-285
• /
• 2020

The statistical characteristics of typhoon wind speed records tend to have a considerable time-varying trend; thus, the stationary wind model may not be appropriate to estimate the wind characteristics of typhoon events. Several nonstationary wind speed models have been proposed by pioneers to characterize wind characteristics more accurately, but comparative studies on the applicability of the different wind models are still lacking. In this study, three landfall typhoons, Ampil, Jongdari, and Rumbia, recorded by ultrasonic anemometers atop the Shanghai World Financial Center (SWFC), are used for the comparative analysis of stationary and nonstationary wind characteristics. The time-varying mean is extracted with the discrete wavelet transform (DWT) method, and the time-varying standard deviation is calculated by the autoregressive moving average generalized autoregressive conditional heteroscedasticity (ARMA-GARCH) model. After extracting the time-varying trend, the longitudinal wind characteristics, e.g., the probability distribution, power spectral density (PSD), turbulence integral scale, turbulence intensity, gust factor, and peak factor, are comparatively analyzed based on the stationary wind speed model, time-varying mean wind speed model and time-varying standard deviation wind speed model. The comparative analysis of the different wind models emphasizes the significance of the nonstationary considerations in typhoon events. The time-varying standard deviation model can better identify the similarities among the different typhoons and appropriately describe the nonstationary wind characteristics of the typhoons.

• 상하수도학회지
• /
• 제13권2호
• /
• pp.74-81
• /
• 1999

In this study, the hydrological changes due to urbanization were investigated and fundamental theory and characteristics of typical urban runoff model such as CHICAGO Model was studied. Above model was applied for urbanizing Dongsucheon basin, Incheon. The main parameters(CI, CP, CS) which are included in this model depending on runoff results were determined, and dimensionless values such as total runoff ratio($Q_{TR}$), peak runoff ratio($Q_{PR}$), and runoff sensitivity ratio($Q_{SR}=Q_{TR}/Q_{PR}$) were estimated in order to evaluate and compare the characteristics of model based on relative sensitivity analysis. Finally, applied model was proposed based on understanding of work types and established urban runoff models which can simulate well for areal development patterns and urban river basin.

• 한국분무공학회지
• /
• 제24권4호
• /
• pp.171-177
• /
• 2019

This paper describes numerical study of combustion characteristics in CNG(compressed natural gas) DI(direct injection) engine using gaseous sphere injection model. Simulations were conducted using KIVA-3V Release 2 code. Gaseous sphere injection model, which is modified model of liquid fuel injection, was used to simulate the CNG direct injection. Until now, a very fine mesh smaller than the injector nozzle has been required to resolve the gas-jet inflow boundary. However, the gaseous sphere injection model simulates gaseous fuel injection using a coarse mesh. This model injects gaseous spheres as in liquid fuel injection and the gaseous spheres evaporate together without the latent heat of evaporation. Therefore, it does not require a very fine mesh and reduce calculation time. Combustion simulation were performed under various injection timings and injection pressures.