• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3709-3714
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• 2013

Based on the Debye-H$\ddot{u}$ckel equation, a semi-empirical equation for activity coefficients was derived through empirical and theoretical trial and error efforts. The obtained equation included two parameters: the proportional factor and the effective radius of an ionic sphere. These parameters were used in the empirical and regression parameter fitting of the calculated values to the experimental results. The activity coefficients calculated from the equation agreed with the data. Transforming to a semi-empirical form, the equation was expressed with one parameter, the ion radius. The ion radius, ${\alpha}$, was divided into three parameters, ${\alpha}_{cation}$, ${\alpha}_{anion}$ and ${\delta}_{cation}$, representing parameters for the cation, anion and combination, respectively. The advantage of this equation is the ability to propose a semi-empirical equation that can easily determine the activity coefficient with just one parameter, so the equation is expected to be used more widely in actual industry applications.

• Journal of the Korean Wood Science and Technology
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• 제28권4호
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• pp.72-82
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• 2000

Attempts were made to analyze the behavior of single and multiple-bolted connections through theoretical methods such as European yield theory, empirical approaching method, and semi-rigid theory instead of many experimental methods that have been actually inefficient and non-economical. In the case of a single-bolted connection, if accurate characteristic values of a material could be guaranteed, it would be more convenient and economical to perform the behavior analysis using a model based on the semi-rigid theory, instead of the existing complex yield model, or the empirical formula which produces errors, giving different results from the actual ones. If the variables of equation determining the load and deformation could be appropriately controlled, the analytical method in conjunction with a semi-rigid theory could be effectively applied to obtain the desirably predicted value, considering that the appropriate solution could be derived through a simpler equation using a less difficult method compared to the existing yield model. It is concluded that analytical method with semi-rigid theory can be used in the behavior analysis of bolted connection because our developed method showed excellent analysis ability of behavior until number of bolt is two. Although our analytical method has the disadvantage that the number of bolt is limited to two, it is concluded that it has the advantage than numerical method which complicated and time-consuming.

• Journal of electromagnetic engineering and science
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• 제18권2호
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• pp.136-140
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• 2018

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the small-roughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.

• 콘크리트학회논문집
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• 제11권3호
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• pp.69-80
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• 1999

The strengthening of reinforced concrete structures by externally bonded GFRP has become increasingly common in resent years. However the analysis and design method for GFRP plate strengthening of RC beams is not well established yet. The purpose of present paper is, therefore, to define the failure mechanism and failure behavior of strengthened RC beam using GFRP and then to propose a resonable method for the calculation of interface debonding load for those beams. From the experimental results of beams strengthened by GFRP, the influence of length and thickness, width of plate on the interfacial debonding failure behavior of beam is studied and, on the basis of test results, the semi-empirical equation to predict debonding load is developed. The proposed theory based on nonlinear analysis and critical flexural crack width, predicts relatively well the debonding failure load of test beams and may be efficiently used in the analysis and design of strengthened RC beams using GFRP.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.718-733
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• 2021

A prediction method, based on the Morison equation as well as Froude-Krylov formula, is presented to simulate the loads acting on the columns and caissons of the semi-submersible platform induced by Internal Solitary Wave (ISW) respectively. Combined with the experimental results, empirical formulas of the drag and inertia coefficients in Morison equation can be determined as a function of the Keulegan-Carpenter (KC) number, Reynolds number (Re) and upper layer depth h₁/h respectively. The experimental and calculated results are compared. And a good agreement is observed, which proves that the present prediction method can be used for analyzing the ISW-forces on the semi-submersible platform. Moreover, the results also demonstrate the layer thickness ratio has a significant effect upon the maximum horizontal forces on the columns and caissons, but both minimum horizontal and vertical forces are scarcely affected. In addition, the incoming wave directions may also contribute greatly to the values of horizontal forces exerted on the caissons, which can be ignored in the vertical force analysis.

• 대한기계학회논문집
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• 제13권5호
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• pp.991-998
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• 1989

본 연구에서는 충돌각을 변수로 한 실험적 연구를 수행하기 위하여 여타의 변수를 고정하였으며, 유속은 R$_{e}$=5.2*$10^{4}$의 결과를 제시하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.725-728
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• 2005

The scattering problem of the randomly rough surface is examined by the method of moments(MoM), small perturbation method (SPM), integral equation method (IEM) and the semi-empirical polarimetic model. To apply the numerical technique of the MoM to microwave scattering from a rough surface, at first, many independent randomly rough surfaces with a rms height and a correlation length are generated with Gaussian random deviate. Then, an efficient Monte Carlo simulation technique is applied to estimate the scattering coefficients of the surfaces.

• 한국음향학회지
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• 제37권4호
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• pp.163-173
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• 2018

본 논문에서는 비행 중 비행체 표면에 작용하는 음향하중 예측을 수행하였다. 비행 중 음향하중은 비행체 표면의 압력 변동에 의해 발생한다. 기존의 비행 중 음향하중 예측방법은 반경험적 방법으로 이론과 실험 결과를 기반으로 도출한 경험식을 활용한다. 하지만 경험식의 입력 값으로 사용되는 비행체 주변 유동특성 및 경계층 파라미터를 매번 실험을 통해 얻는 것에는 한계가 있다. 따라서 본 논문에서는 전산유체해석(Computational Fluid Dynamics, CFD) 결과를 반경험적 방법과 혼합하는 하이브리드 방법을 이용하여 비행 중 비행체에 작용하는 음향하중을 예측하였다. Cone-cylinder-flare 형상 비행체에 대해 아음속, 천음속, 초음속, 최대동압도달(Maximum dynamic pressure, Max-q) 시점의 비행 환경에 대한 음향하중 예측을 수행하였다. 하이브리드 방법 적용 시 전산유체해석결과를 기반으로 한 경계층 끝단 영역 판단 방법에 대해 비교하였고 여러 연구자에 의해 제시된 경험식에 따른 음향하중 예측결과를 비교하였다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.10-11
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• 2006

The use of hot gas in melt atomization has been widely reported, but little detailed experimental data on its precise effects and no satisfactory theory to explain them have been published. In this paper the authors present experimental data on the atomization of metals with gas at temperatures from ambient to 1000C, a semi-empirical equation relating particle size to gas temperature and flow rate, and an analysis of the gas dynamics of the atomization process that allows some insight into the process.

• Steel and Composite Structures
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• 제28권2호
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• pp.209-221
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• 2018

An empirical and efficient method is presented for calculating the dynamic increase factor to amplify the applied loads on the affected bays of a steel frame structure with semi-rigid connections. The nonlinear static alternate path analysis is used to evaluate the dynamic responses. First, the polynomial models of the extended end plate and the top and seat connection are modified, and the proposed polynomial model of the flush end plate connection shows good agreement as compared with experimental results. Next, a beam model with nonlinear spring elements and plastic hinges is utilized to incorporate the combined effect of connection flexibility and material nonlinearity. A new step-by-step analysis procedure is established to obtain quickly the dynamic increase factor based on a combination of the pushdown analysis and nonlinear dynamic analysis. Finally, the modified dynamic increase factor equation, defined as a function of the maximum ratio value of energy demand to energy capacity of an affected beam, is derived by curve fitting data points generated by the different analysis cases with different column removal scenarios and five types of semi-rigid connections.