• International Journal of Highway Engineering
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• v.18 no.3
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• pp.109-114
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• 2016

PURPOSES : The demand for extending national highways is increasing, but traffic monitoring is hindered because of resource limitations. Hence, this study classified highway segments into 5 types to improve the efficiency of short-term traffic count planning. METHODS : The traffic volume trends of 880 highway segments were classified through R-squared and linear regression analyses; the steadiness of traffic volume trends was evaluated through coefficient of variance (COV), and the normality of the data were determined through the Shapiro-Wilk W-test. RESULTS : Of the 880 segments, 574 segments had relatively low COV and were classified as type 1 segments, and 123 and 64 segments with increasing and decreasing traffic volume trends were classified as type 2 and type 3 segments, respectively; 80 segments that failed the normality test were classified as type 4, and the remaining 39 were classified as type 5 segments. CONCLUSIONS : A theoretical basis for biennial count planning was established. Biennial count is recommended for types 1~4 because their mean absolute percentage errors (MAPEs) are approximately 10%. For type 5 (MAPE =19.26%), the conventional annual count can be continued. The results of this analysis can reduce the traffic monitoring budget.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.11
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• pp.705-710
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• 2011

Fault detection has to be proceeded by steady state filtering to get rid of transient effect associated with thermal capacity. Coefficient of variance (COV), ratio of standard deviation devided by moving average, was employed as steady-state filter. Engine speed and refrigerant pressures were selected as parameters representing system dynamics. The filtered values were registered as members of steady-state DB. They were found to show good functional relationship with ambient temperature. The relationship was fitted with a second order polynomial and the distribution bounds of the data around the fitted curve were expressed by visual inspection because of varying average and random data interval. Fault data were compared with the steady-state data obtained during normal operation. The fault data were easily isolated from the fault-free one. To make such isolation reliable, tests to construct good DB should be designed in a systematic way.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.163-172
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• 1993

A probabilistic approach for evaluation of prediction of the strains using Lade's single surface constitutive model was employed, based on first-order approximate mean and variance. Several experiments such as isotropic compression and drained triaxial compression tests were conducted to examine the variabilities of soil parameters for Lade's model. By taking into account the results of the experimental data such as mean values and standard deviations of soil parameter's, a new probabilistic approach, which explains the uncertainty of computed strains, is applied. The magnitude of the COV for each parameter and the correlation coefficient between the two parameters can be effectively used for reducing the number of the parameters for the model. It is concluded that Lade's single surface constitutive model is surperior model for the prediction of the strain, because the COV of strains is under the "0.51".

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.12 s.243
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• pp.1307-1312
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• 2005

Turbulent in-situ mixing process is a new material process technology to get dispersed phase in nanometer size by controlling reaction of liquid/liquid, liquid/solid and liquid/gas, flow and solidification speed simultaneously. In this study mixing, the key technology to this synthesis method will be studied by computational fluid dynamics. For the simulation of mixing of liquid metal, static mixers will be investigated. Two inlets for different liquid metal meet and merge like 'Y' shape tube. The tube has various shapes such as straight and curved. Also, the radius of curve will be varied. The performance of mixer will be evaluated with quantitative analysis with coefficient of variance of mass fraction. Also, detailed plots of intersection will be presented to understand effect of mixer shape on mixing.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.52-58
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• 1998

The spray characteristics of air-assisted fuel injection and its effects on the engine combustion was investigated in this study. The atomization characteristics of a Bosch fuel injector inserted into the air-assist adapter were measured using particle motion analysis system. Droplet size decreased with air supplied and fine spray with below $60\mu\textrm{m}$ of SMD was acquired under the conditions of air-assist pressure over 0.5bar. The lean combustion performance of a 1.8L DOHC engine equipped with air-assist adapters was tested on the dynamometer. When the assistant air pressure is 1.0bar, lean limit recorded the highest value, and CO, HC emissions were decreased at the pressure over 1.0bar.

• Korean Journal of Materials Research
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• v.17 no.1
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• pp.11-17
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• 2007

Turbulent in-situ mixing process is a new material process technology to get dispersed phase in nanometer size by controlling reaction of liquid/solid, liquid/gas, flow ana solidification speed simultaneously. In this study, mixing which is the key technology to this synthesis method was studied by computational fluid dynamics. For the simulation of mixing of liquid metal, static mixers investigated. Two inlets for different liquid metal meet ana merge like 'Y' shape tube having various shapes and radios of curve. The performance of mixer was evaluated with quantitative analysis with coefficient of variance of mass fraction. Also, detailed plots of intersection were presented to understand effect of mixer shape on mixing. The simulations show that the Reynolds number (Re) is the important factor to mixing and dispersion of $TiB_2$ particles. Mixer was designed according to the simulation, and $Cu-TiB_2$ nano composites were evaluated. $TiB_2$ nano particles were uniformly dispersed when Re was 1000, and cluster formation and reduction in volume fraction of $TiB_2$ were found at higher Re.