• Architectural research
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• 제12권2호
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• pp.93-98
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• 2010

This paper describes a numerical method for estimating the elastic moduli of cement paste. The cement paste is modeled as a unit cell which consists of three components: the unhydrated cement grain, the gel, and the capillary pore. In the unit cell, the volume fractions of the constituents are quantified using a single kinetic function calculating the degree of hydration. The elastic moduli of cement paste are calculated from the total displacements of constituents when a uniform pressure is applied to the gel contact area. The cement paste is assumed to be a homogenous isotropic matrix. Numerical simulations were conducted through the finite element analysis of the three-dimensional periodic unit cell. The model predictions are compared with experimental results. The predicted trends are in good agreement with experimental observations. This approach and some of the results might also be relevant for other technical applications.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.193-200
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• 2009

Recently, there have been efforts to construct hybrids among the existing methodologies for multiphase flow such as VOF, Level Set, and Front Tracking with the intention of facilitating simulations of general three-dimensional problems. As one of the hybrid method, we have developed the Level Contour Reconstruction Method (LCRM) for general three-dimensional multiphase flows including phase change. The main idea was focused on simplicity and a robust algorithm especially for the three-dimensional case. It combines characteristics of both Front Tracking and Level Set methods. While retaining an explicitly tracked interface using interfacial elements, the calculation of a vector distance function plays a crucial role in the periodic reconstruction of the interface elements in the LCRM method to maintain excellent mass conservation and interface fidelity. In addition, compact curvature formulation is incorporated for the calculation of the surface tension force thereby reducing parasitic currents to a negligible level.

• 대한간호학회지
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• 제33권6호
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• pp.705-712
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• 2003

Purpose: The purpose of this study was to explore factors that influence care dependency of institutionalized patients with dementia. Method: This study utilized descriptive correlational design. The convenience sample was composed of 110 residents with dementia of two long-term care facilities in Korea. Stepwise multiple regression was used to identify significant factors influencing care dependency in patients with dementia. Care dependency was measured using the Care Dependency Scale, Korean version(CDS-K). Cognition was measured by the MMSE-K. Functional disability was measured by the PULSES Profile. Behavioral dysfunction was measured by the modified E-BEHAVE AD. Result: Care dependency was significantly influenced by cognition, functional disability, behavioral dysfunction, and duration of dementia. This regression model explained 61 % of the variances in care dependency. Cognition explained 37% of the variances, and functional disability explained 21% of the variances. Conclusion: Results of this study suggest that professional caregivers intervene more effectively in caring for their patients with dementia by recognizing the patients cognitive, functional, behavioral disability, and its periodic change. Individually, remaining abilities-focused intervention should be applied to enhance patient to be dependent and to prevent unnecessary independency.

• 한국환경보건학회지
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• 제17권2호
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• pp.1-8
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• 1991

The stochastic variance and structures of time series data on air quality were examined by employing the techniques of autocorrelation function, variance spectrum, fourier series, ARIMA model. Among the air quality properties of atmosphere, SO$_{2}$ is one of the most siginificant and widely measured parameters. In the study, the air quality data were included hourly observations on SO$_{2}$ TSP and O$_{3}$. The data were measured by automatic recording instrument installed in Kwanghwamoon during February and March in 1991. The results of study were as follows 1. Hourly air quality series varied with the domiant 24 hour periodicity and the 12 hour periodic variation was also observed. 2. The correlation coefficients between SO$_{2}$ and O$_{3}$ is -0.4735. 3. In simulating or forecasting variation in SO$_{2}$ ARIMA models are on a useful tools. The multiplicative seasonal ARIMA (1, 1, 0) (0, 2, 1)$_{24}$ model provided satisfactory results for hourly SO$_{2}$ time series.

• Journal of applied mathematics & informatics
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• 제29권5_6호
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• pp.1571-1581
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• 2011

In this paper, we construct inequivalent Hadamard matrices based on several new and old full orthogonal designs, using circulant and symmetric block matrices. Not all orthogonal designs produce inequivalent Hadamard matrices, because the corresponding systems of equations do not possess solutions. The systems of equations arising when we search for inequivalent Hadamard matrices from full orthogonal designs using circulant and symmetric block matrices, can be concisely described using the periodic autocorrelation function of the generators of the block matrices. We use Maple, Magma, C and Unix tools to find many new inequivalent Hadamard matrices.

• 소음진동
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• 제8권6호
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• pp.1086-1092
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• 1998

This paper presents a general analytical method for analyzing the instability of unbalanced electromagnetic forces produced in induction motors with an eccentric rotor. The equations to be solved are a set of second order differential equations which give matrices with periodic coefficients that are a function of time due to the unbalanced electromagnetic force. The method is based on an extension of the Floquet theory. A transfer matrix over one period of the motion is obtained. and the stability of the system can be determined with the eigenvalues of the matrix. The analysis results of instability zone were coincided upon comparing that of transfer matrix method with that of rotating frame. Two examples are given. including an industrial application. The results show that the method proposed is satisfactory.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.478-485
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• 1998

The interior of open cavities exposed to a grazing flow is known to experience, strong periodic pressure, oscillations sustained for a wide range of flow velocities. In this study, an original approach was followed to develop a describing function model for the flow-excitation mechanism, governed by the shedding of discrete vortices within the shear layer over the orifice. A feedback loop analysis was performed to predict the frequency and the amplitude of the interior pressure fluctuations. Furthermore, a limit cycle stability analysis based on the extended Nyquist Stability criterion allowed the predictions of the onset and termination velocities for various modes. The analytical model was verified experimentally.

• 설비공학논문집
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• 제14권3호
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• pp.199-205
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• 2002

In this paper, the optimum shape and arrangement of ribs in the channel of a plate heat exchanger are studied. The following dimensionless geometric parameters of ribs are selected as design variables: rib height ($H_R$), angle of attack ($\beta$), rib pitch ($P_R$), rib distance (L) and aspect ratio of rib (AR). The optimization is performed by minimizing the objective function consisting of the Nusselt number and the friction factor. The optimal values of design variables are as follows: $H_R$=0.263, $\beta$=0.290, $P_R$=3.142, L: 3.954, AR=0.342. The pressure drop and the heat transfer of the optimum model, compared to those of the reference model, are increased by 15.1% and 41.6%, respectively.

• Journal of the Korean Statistical Society
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• 제18권2호
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• pp.125-134
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• 1989

This paper presents optimum simple step-stress accelerated life test plans for the case where the test process is observed periodically at intervals of the same length. Two types of failure data, periodically observed complete data and periodically observed censored data, are considered. An exponential life distribution with a mean that is a log-linear function of stress, and a cumulative exposure model for the effect of changing stress are assumed. For each type of data, the optimum test plan which minimizes the asymptotic variance of the maximum likelihood estimator of the mean life at a design stress is obtained and its behaviors are studied.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.598-603
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• 2005

In this study, an adaptive control scheme with a pre-specified $H_{\infty}$ property is proposed for the tracking control of linear induction motor (LIM) drive system. Under the influence of uncertainties and external disturbances, by using nonlinear decoupling and parameter tuner, the robust performance control problem is formulated as a nonlinear $H_{\infty}$ problem and solved by a quadratic storage function. This new design method is able to track the step and several periodic commands with improved performance in face of parameter perturbations and external disturbances. Simulation and experimental results are provided to demonstrate the effectiveness of the proposed adaptive $H_{\infty}$ controller.