• Title/Summary/Keyword: logarithmic form

Search Result 46, Processing Time 0.033 seconds

Finite element analysis of planar 4:1 contraction flow with the tensor-logarithmic formulation of differential constitutive equations

  • Kwon Youngdon
    • Korea-Australia Rheology Journal
    • /
    • v.16 no.4
    • /
    • pp.183-191
    • /
    • 2004
  • High Deborah or Weissenberg number problems in viscoelastic flow modeling have been known formidably difficult even in the inertialess limit. There exists almost no result that shows satisfactory accuracy and proper mesh convergence at the same time. However recently, quite a breakthrough seems to have been made in this field of computational rheology. So called matrix-logarithm (here we name it tensor-logarithm) formulation of the viscoelastic constitutive equations originally written in terms of the conformation tensor has been suggested by Fattal and Kupferman (2004) and its finite element implementation has been first presented by Hulsen (2004). Both the works have reported almost unbounded convergence limit in solving two benchmark problems. This new formulation incorporates proper polynomial interpolations of the log­arithm for the variables that exhibit steep exponential dependence near stagnation points, and it also strictly preserves the positive definiteness of the conformation tensor. In this study, we present an alternative pro­cedure for deriving the tensor-logarithmic representation of the differential constitutive equations and pro­vide a numerical example with the Leonov model in 4:1 planar contraction flows. Dramatic improvement of the computational algorithm with stable convergence has been demonstrated and it seems that there exists appropriate mesh convergence even though this conclusion requires further study. It is thought that this new formalism will work only for a few differential constitutive equations proven globally stable. Thus the math­ematical stability criteria perhaps play an important role on the choice and development of the suitable con­stitutive equations. In this respect, the Leonov viscoelastic model is quite feasible and becomes more essential since it has been proven globally stable and it offers the simplest form in the tensor-logarithmic formulation.

Mixing effect on Properties of NTC Thermistor in Mn-Co-O System (Mn-Co-O계 NTC 써미스터의 물성에 미치는 혼합의 영향)

  • Yoon, Sang-Sik;Kim, Kyung-Sik;Yoon, Sang-Ok
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
    • /
    • 2001.11b
    • /
    • pp.459-462
    • /
    • 2001
  • Interface effects on properties of NTC thermistors having Mn-Co-O spinel crytal structure system are analyzed by a mixing rule in case of mixed types and layered types between CuO and $Al_{2}O_{3}$ added compounds. With adding CuO and $Al_{2}O_{3}$, The compounds form completely solid solution and their resistance and B constant are changed due to the variation of conduction electrons by their ionic substitutions. The properties of mixed NTC thermistors are depended on the logarithmic mixing rule by a dispersed phase and they show slightly lower values due to the lattice mixing affect in compared with calculated values. The resistance of layered NTC thennistors is depended upon the series mixing rule containing the value of an interface layer and effected by the variation of its thickness, and it is changed rapidly to the logarithmic mixing rule by the connection between two layers with increasing the interface layer.

  • PDF

AN APPROPRIATE INFLOW MODEL FOR SIMULTANEOUS DISSOLUTION AND DEGRADATION

  • Lee, Ju-Hyun;Kang, Sung-Kwon;Choi, Hoo-Kyun
    • Honam Mathematical Journal
    • /
    • v.31 no.1
    • /
    • pp.109-124
    • /
    • 2009
  • Based on the observed data for Clarithromycin released, three commonly used inflow models: the power, the exponential, and the logarithmic models are considered. Among them, the power model is used most in practice for simplicity. Using the numerical parameter estimation techniques, the parameters appeared in the model equations are estimated. Through the numerical estimation results using the several experimental data sets, the exponential model turns out to be best among the three models. More specifically, the sum of squares of absolute errors and the sum of squares of relative errors for the exponential model are reduced by 80-95 % for the experimental data sets and 60-90 % for the noise added data sets compared with those for the power and logarithmic models. A typical experimental data set is used in this paper to show the estimation method and its numerical results. The proposed numerical method and its algorithm are designed for estimating the parameters appeared in the model differential equations for which the exact form of the solution is unknown in general. The methodology developed can be applied to more general cases such as the nonlinear ordinary differential equations or the partial differential equations.

A Study on the Reliability Performance Evaluation of Software Reliability Model Using Modified Intensity Function (변형된 강도함수를 적용한 소프트웨어 신뢰모형의 신뢰성능 비교 평가에 관한 연구)

  • Kim, Hee Cheul;Moon, Song Chul
    • Journal of Information Technology Applications and Management
    • /
    • v.25 no.2
    • /
    • pp.109-116
    • /
    • 2018
  • In this study, we was compared the reliability performance of the software reliability model, which applied the Goel-Okumoto model developed using the exponential distribution, to the logarithmic function modifying the intensity function and the Rayleigh form. As a result, the log-type model is relatively smaller in the mean squared error compared to the Rayleigh model and the Goel-Okumoto model. The logarithmic model is more efficient because of the determination coefficient is relatively higher than the Goel-Okumoto model. The estimated determination coefficient of the proposed model was estimated to be more than 80% which is a useful model in the field of software reliability. Reliability has been shown to be relatively higher in the log-type model than the Rayleigh model and the Goel-Okumoto model as the mission time has elapsed. Through this study, software designer and users can identify the software failure characteristics using mean square error, decision coefficient. The confidence interval can be used as a basic guideline when applying the intensity function that reflects the characteristics of the lifetime distribution.

Early Strength Development of Concrete Cured with Microwave Heating Form (마이크로웨이브 발열거푸집을 적용한 콘크리트의 조기강도 발현특성)

  • Koh, Tae Hoon;Hwang, Seon Keun;Moon, Do Young;Yoo, Jung Hoon;Song, Jin Woo;Ko, Ji Soo
    • Journal of the Korean Society for Railway
    • /
    • v.17 no.5
    • /
    • pp.365-372
    • /
    • 2014
  • Technologies for rapid concrete curing using elevated temperature are important for saving cost and time when constricting concrete structures. Recently, a microwave heating form was developed. In this study the early strength of concrete cured by the developed form was experimentally investigated. Large scale mock up tests were conducted six times, and the results were analyzed based on the maturity theory. Logarithmic correlation curves were generated based on the measured strength and estimated maturity. It was confirmed that the strength development of the concrete cured by microwave heating form can be estimated by the equivalent age theory usually applied to steam-curing technology. By using the microwave heating form, one day at most is enough to get the required strength for the safe removal of forms, even in cold weather.

Development of Web-based Creep Property Database (웹기반 크리프 물성 데이터베이스 개발)

  • Huh, Yong-Hak;Baek, Un-Bong;Lee, Wan-Kyu;Park, Whi-Lib;Jung, In-Hyeon
    • Journal of the Korean Society of Safety
    • /
    • v.17 no.4
    • /
    • pp.19-24
    • /
    • 2002
  • User-friendly-web-based database system for searching creep property data was developed. This system includes about 38000 creep data for 270 different materials including low carbon steel, stainless steel and alloy steel. Data on creep rupture, creep deformation, creep crack growth and creeping materials can be searched through this system. Retrieved data is displayed in numeric form and also presented in graphical form for visualizing the data. Furthermore, the creep rupture data is designed to be fitted to a regression equation of logarithmic stress using time-temperature parameter(TTP). The degree of the regression equation, orthogonal polynomials, was determined using analysis of variance.

A study of parameter estimation of stochastic volatility model

  • Tsukui, Makiko;Furuta, Katsuhisa
    • 제어로봇시스템학회:학술대회논문집
    • /
    • 1991.10b
    • /
    • pp.1858-1863
    • /
    • 1991
  • The theory of stock option pricing has, recently, attracted attention of many researchers interested not only in finance but also in statistics and control theory. In this field, the problem of estimating stock return volatility is, above all, of great importance in calculating actual stock option value. In this paper, we assume that the stock market is represented by the stochastic volatility model which is the same as that of Hull and White. Then, we propose an approximation function of option value. It is a type of Black-Sholes option formula in which the first and the second order moments of logarithmic stock value are modified in a special form from the original model. Finally, an algorithm of estimating the parameters of the stochastic volatility model is given, and parameters are estimated by using Nikkei 225 index option data.

  • PDF

Quality Evaluation of Pharmaceutical Preparations( II ) -Dissolution of Prednisolone Tablets- (의약품(醫藥品)의 품질평가(品質評價)에 관(關)한 연구(硏究) (제 2 보)(第 2 報) -프레드니솔론 정제(錠劑)의 용출(溶出)에 관한 연구(硏究)-)

  • Kim, Hyung-Kook;Kim, Jae-Baek
    • Journal of Pharmaceutical Investigation
    • /
    • v.14 no.3
    • /
    • pp.122-130
    • /
    • 1984
  • The dissolution profiles of the seven branded prednisolone tablets were determined by means of available compendium. Those tablets were stored at $40^{\circ}C,\;50^{\circ}C\;and\;60^{\circ}C$ for 15, 30 and 60 days respectively. Under the stress conditions, the dissolution efficiency showed significant changes. It is considered that the determination of shelf life of drug from these aging effects is possible because the dissolution data followed a logarithmic distribution. There were no substantial differences of dissolution between two prednisolone formulations with different particle size not larger than $100\;{\mu}m$. The effect of two starches (corn and potato) on the rate of dissolution of prednisolone from dosage form was also investigated. All marketed tablets met the requirement of the established compendium.

  • PDF

GENERALIZED EULER PROCESS FOR SYSTEMS OF NONLINEAR DIFFERENTIAL EQUATIONS

  • Yu, Dong-Won
    • Journal of applied mathematics & informatics
    • /
    • v.7 no.3
    • /
    • pp.941-958
    • /
    • 2000
  • Euler method is generalized to solve the system of nonlinear differential equations. The generalization is carried out by taking a special constant matrix S so that exp(tS) can be exactly computed. Such a matrix S is extracted from the Jacobian matrix of the given problem. Stability of the generalized Euler process is discussed. It is shown that the generalized Euler process is comparable to the fourth order Runge-Kutta method. We also exemplify that the important qualitative and geometric features of the underlying dynamical system can be recovered by the generalized Euler process.

A Study on the Size Distribution of Trace Metals Concentrations in the Ambient Aerosols (대기부유분진 중 미량 금속원소의 입경별 농도분포에 관한 연구)

  • 신훈중;이태정;김동술
    • Journal of Korean Society for Atmospheric Environment
    • /
    • v.12 no.1
    • /
    • pp.67-77
    • /
    • 1996
  • Total suspended particulate matters (TSP) were collected based on a size segregation method by a cascade impactor for 6 consecutive years (form Dec. 1989 to sep. 1994) in the Kyung Hee University-Suwon Campus, and 6 trace metals (Ca, Si, Fe, Pb, Cu, Zn) were determined by an x-ray fluorescence spectroscopy. Total number of samples collected during the study are 118 sets and each set of sample comsists of 9 filters. The levels of TSP and 6 trace metals were then used to examine seasonal and annual variations with respects to their size distributions. For statistical analyses, raw data were initially transformed by both logarithmic and root transformating to approximately normalize them, and then size distribution functions for each trace element were separately developed season-to-season by a regression analysis in order to obtain maximum amount of physical information, Subsequently, each developed model was verified by comparing with supervised data collected on 1994. The result showed that each prediction model was in good agreement except the fall, partly due to lack of the data collected on fall, 1994.

  • PDF