• Journal of the Korean Society of Combustion
• /
• v.4 no.2
• /
• pp.51-62
• /
• 1999

NOx formation in turbulent flames is strongly coupled with temperature, superequilibrium concentration of O radical, and residence time. This implies that in order to accurately predict NO level, it is necessary to develop sophisticated models able to account for the complex turbulent combustion processes including turbulence/chemistry interaction and radiative heat transfer. The present study numerically investigates the turbulent nonpremixed hydrogen jet flames using the laminar flamelet model. Flamelet library is constructed by solving the modified Peters equations and the turbulent combustion model is extended to nonadiabatic flame by introducing the enthalpy defect. The effects of turbulent fluctuation are taken into account by the presumed joint PDFs for mixture fraction, scalar dissipation rate, and enthalpy defect. The predictive capability of the present model has been validated against the detailed experimental data. Effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.

• 한국연소학회:학술대회논문집
• /
• 1999.10a
• /
• pp.93-104
• /
• 1999

NOx formation in turbulent flames is strongly coupled with temperature, superequilibrium concentration of O radical, and residence time. This implies that in order to accurately predict NO level, it is necessary to develop sophisticated models able to account for the complex turbulent combustion processes including turbulence/chemistry interaction and radiative heat transfer. The present study numerically investigates the turbulent nonpremixed hydrogen jet flames using the laminar flamelet model. Flamelet library is constructed by solving the modified Peters equations and the turbulent combustion model is extended to nonadiabatic flame by introducing the enthalpy defect. The effects of turbulent fluctuation are taken into account by the presumed joint PDFs for mixture fraction, scalar dissipation rate, and enthalpy defect. The predictive capability of the present model has been validated against the detailed experimental data. Effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.26 no.1
• /
• pp.109-116
• /
• 2001

The detection of corporate failures is a subject that has been particularly amenable to cross-sectional financial ratio analysis. In most of firms, however, the financial data are available over past years. Because of this, a model utilizing these longitudinal data could provide useful information on the prediction of bankruptcy. To correctly reflect the longitudinal and firm-specific data, the generalized linear model with assuming the first order AR(autoregressive) process is proposed. The method is motivated by the clinical research that several characteristics are measured repeatedly from individual over the time. The model is compared with several other predictive models to evaluate the performance. By using the financial data from manufacturing corporations in the Korea Stock Exchange (KSE) list, we will discuss some experiences learned from the procedure of sampling scheme, variable transformation, imputation, variable selection, and model evaluation. Finally, implications of the model with repeated measurement and future direction of research will be discussed.

• Journal of Integrative Natural Science
• /
• v.4 no.3
• /
• pp.210-215
• /
• 2011

Holographic quantitative structure-activity relationships (HQSAR) is a useful tool to correlates structures with their biological activities. HQSAR is a two dimensional (2D) QSAR methodology, which generates QSAR equations through 2D fingerprint and correlates it with biological activity. Here, we report a 2D-QSAR model for a series of fifty-one 3,4-dihydroxychalcones derivatives utilizing HQSAR methodology. We developed HQSAR model with 6 optimum numbers of components (ONC), which resulted in cross-validated correlation coefficient ($q^2$) of 0.855 with 0.283 standard error of estimate (SEE). The non-cross-validated correlation coefficient (r2) with 0.966 indicates the model is predictive enough for analysis. Developed HQSAR model was binned in to a hologram length of 257. Atomic contribution map revealed the importance of dihydroxy substitution on phenyl ring.

• Journal of Forest and Environmental Science
• /
• v.28 no.2
• /
• pp.63-67
• /
• 2012

Crown ratio is the ratio of live crown length to tree height. It is often used as an important predictor variable for tree growth equation. It indicates tree vigor and is a useful parameter in forest health assessment. The objective of the study was to develop crown ratio prediction models for Tectona grandis. Based on the data set from the temporary sample plots, several non linear equations including logistics, Chapman Richard and exponential functions were tested. These functions were evaluated in terms of coefficient of determination ($R^2$) and standard error of the estimate (SEE). The significance of the estimated parameters was also verified. Plot of residuals against estimated crown ratios were observed. Although the logistic model had the highest $R^2$ and the least SEE, Chapman-Richard and Exponential functions were observed to be more consistent in their predictive ability; and were therefore recommended for predicting crown ratio in the stand.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.622-627
• /
• 2001

Microjet flows are often encountered in many industrial applications of micro-electro-mechanical systems as well as in medical engineering fields such as a transdermal drug delivery system for needle-free injection of drugs into the skin. The Reynolds numbers of such microjets are usually several orders of magnitude below those of larger-scale jets. The supersonic microjet physics with these low Reynolds numbers are not yet understood to date. Computational modeling and simulation can provide an effective predictive capability for the major features of the supersonic microjets. In the present study, computations using the axisymmetic, compressible, Navier-Stokes equations are applied to understand the supersonic microjet flow physics. The pressure ratio of the microjets is changed to obtain both the under- and over-expanded flows at the exit of the micronozzle. Sonic and supersonic microjets are simulated and compared with some experimental results available. Based on computational results, two microjets are discussed in terms of total pressure, jet decay and supersonic core length.

• Geomechanics and Engineering
• /
• v.15 no.3
• /
• pp.919-925
• /
• 2018

Stress-strain responses of weak-to-strong carbonate rocks used for tunnel construction were studied. The analysis of applicability of exponential stress-strain models based on Haldane's distribution function is presented. It is revealed that these exponential equations presented in transformed forms allow us to predict stress-strain relationships over the whole pre-failure strain range without mechanical testing of rock samples under compression using a press machine and to avoid measurements of axial failure strains for which relatively large values of compressive stress are required. In this study, only one point measurement (small strain at small stress) using indentation test and uniaxial compressive strength determined by a standard Schmidt hammer are considered as input parameters to predict stress-strain response from zero strain/zero stress up to failure. Observations show good predictive capabilities of transformed stress-stress models for weak-to-strong (${\sigma}_c$ <100 MPa) heterogeneous carbonate rocks exhibiting small (< 0.5 %), intermediate (< 1 %) and large (> 1 %) axial strains.

• Earthquakes and Structures
• /
• v.17 no.6
• /
• pp.591-598
• /
• 2019

The most recent shaking experiences have demonstrated that the predictions of the seismic models are not always in agreement with the registered responses, especially in the face of extreme earthquakes. Records collected from 1960 to 2011 at a rock-like site are used to develop a neural network that permits to estimate peak ground accelerations via the magnitude, the focal depth, the site-source distance and a seismogenic zone. The neural model is applied to the 8th and 19th September 2017 events that hit Mexican territory and the obtained results show that the network is flexible enough to work appropriately to various conditions of intensity and sites-sources with remarkably predictive capacity. The neural-attenuation curves are compared with those obtained from Ground Motion Prediction Equations and their performance is assessed for events, in addition to the devastating Mexican events, from Japan, Taiwan, Chile and USA.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.09a
• /
• pp.3-10
• /
• 2002

The strong ground motion data recorded in the Sino-Korea Craton are analysed toobtain attenuation relations valid for 5 < M < 8, r < 400 km applicable to the Korean Peninsula. The result is logA : -1.83+0.386M- log${\gamma}$-0.0015${\gamma}$ where A is peak horizontal acceleration in g, M is surface-wave magnitude, and r is hypocentral distance in km. Our result is compared with the existing attenuation relations of Western North America and Eastern North America and the prior predictive equations for the Southern part of Korean Peninsula. Our result compares better with those of North America than those of the Southern part of the Korean Peninsula. More theoretical and empirical studies are required for better attenuation relations appropriate for the Korean Peninsula.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.11 no.3
• /
• pp.154-160
• /
• 2008

We investigated molecular polarity by using theoretical means and comparing empirical solvent polarity. Our approach employed electrostatic potentials at the molecular surface calculated by density functional methods. A number of molecular descriptors related to molecular polarities were computed from molecular surface electrostatic potentials. Among computed molecular descriptors, the most positive electrostatic potential provided the best correlation with the empirical solvent polarities. A regression equation was developed in order to predict molecular polarities of molecules whose experimental solvent polarities were unknown. The new regression equations were utilized in estimating solvent polarities of cubane derivatives which are considered important precusors of high-energy density meterials.