• 한국소음진동공학회논문집
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• 제15권4호
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• pp.492-498
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• 2005

A linear motor damper based on the linear motor principle is developed to suppress structural vibration. This paper deals with the design, analysis, and manufacture of the linear motor damper. It is designed to be able to move the auxiliary mass of 1500kg, up to $\pm250mm$ stroke. The control algorithm was designed based on LQG control logic with acceleration feedback. Through performance tests, it was confirmed that the developed hybrid mass damper has reliable feasibility as a control device for structural control. In addition, the linear motor damper is more economical than both hydraulic and electric motor driving mass damper with respect to simple structure and low maintenance cost. A series of performance tests of the linear motor damper system were carried out on the full-scale steel frame structure in UNISON Corporation. Through the performance tests, it was confirmed that acceleration levels are reduced down 10dB for first mode of structure

• 대한산업공학회지
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• 제17권2호
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• pp.131-142
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• 1991

The concept of criterion function is proposed as a framework for comparing the geometric and computational characteristics of various nonlinear programming approaches to linear programming such as the method of centers, Karmakar's algorithm and the gravitational method. Also, we discuss various computational issues involved in obtaining an efficient parallel implementation of these methods. Clearly, the most time consuming part in solving a linear programming problem is the direction finding procedure, where we obtain an improving direction. In most cases, finding an improving direction is equivalent to solving a simple optimization problem defined at the current feasible solution. Again, this simple optimization problem can be seen as a least squares problem, and the computational effort in solving the least squares problem is, in fact, same as the effort as in solving a system of linear equations. Hence, getting a solution to a system of linear equations fast is very important in solving a linear programming problem efficiently. For solving system of linear equations on parallel computing machines, an iterative method seems more adequate than direct methods. Therefore, we propose one possible strategy for getting an efficient parallel implementation of an iterative method for solving a system of equations and present the summary of computational experiment performed on transputer based parallel computing board installed on IBM PC.

• Ocean Systems Engineering
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• 제12권2호
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• pp.143-157
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• 2022

In this study, the nominal wake field of a semi-displacement type high-speed vessel was computed at full scale by using CFD (Computational Fluid Dynamics) and GEOSIM-based approaches. A scale effect investigation on nominal wake field of benchmark Athena vessel was performed with two models which have different model lengths. The members of the model family have the same Fr number but different Re numbers. The spatial components of nominal wake field have been analyzed by considering the axial, radial and tangential velocities for models at different scales. A linear feature has been found for radial and tangential components while a nonlinear change has been obtained for axial velocity. Taylor wake fraction formulation was also computed by using the axial wake velocities and an extrapolation technique was carried out to get the nonlinear fit of nominal wake fraction. This provides not only to observe the change of nominal wake fraction versus scale ratios but also to estimate accurately the wake fraction at full-scale. Extrapolated full-scale nominal wake fractions by GEOSIM-based approach were compared with the full-scale CFD result, and a very good agreement was achieved. It can be noted that the GEOSIM-based extrapolation method can be applied for estimation of the nominal wake fraction of semi-displacement type high-speed vessels.

• 한국태양에너지학회 논문집
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• 제30권5호
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• pp.25-31
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• 2010

A Precision Spectral Pyranometer (PSP) is mainly used as a reference to calibrate other pyranometers due to its high accuracy and sensitivity in response to the spectrum wavelength range of 0.285 ${\mu}$ to 2.8 ${\mu}$, while the sensitivity of photovoltaic-type Li-Cor pyranometer is limited within a certain spectral range from 0.4 ${\mu}$ to 1.1 ${\mu}$. In this study, two Eppley PSPs($PSP_1$ and $PSP_2$) were first compared to the calibrated Eppley PSPs from National Renewable Energy Laboratory (NREL), resulting in two linear correction factors based on the comparison between the logger output (V) from the test PSP and the solar radiation (W/m2) from the NREL PSP. The Li-Cor pyranometer used in this study was then corrected based on the comparison of measured solar radiation ($W/m^2$) from the corrected $PSP_1$ and the Li-Cor pyranometer. In addition, instrument scale corrections were also performed for the PSPs and the Li-Cor from the transmitter to the data logger. From the comparisons, a linear correction factor (1.0214) with R=0.9998 was developed for the scale correction between$PSP_1$ and $PSP_2$, while the Li-Cor pyranometer has a scale(1.0597) and offset (32.046) with R=0.9998 against$PSP_1$. As a result, it was identified that there were good agreements within ${\pm}$ 10 W/ $m^2$ between Eppley $PSP_1$ vs. $PSP_2$ solar radiation and within ${\pm}$ 20 W/$m^2$ between$PSP_1$ vs Li-Cor solar radiation after the empirical scale corrections developed in this study.

• Agribusiness and Information Management
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• 제8권2호
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• pp.1-8
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• 2016

The present study has aimed at analyzing the technical and scale efficiencies of credit utilization by the farmer-borrowers in Chittoor district of Andhra Pradesh, India. DEA approach was followed to analyze the credit utilization efficiency and to analyze the factors influencing the credit utilization efficiency, log-linear regression analysis was attempted. DEA analysis revealed that, the number of farmers operating at CRS are more in number in marginal farms (40%) followed by other (35%) and small (17.5%) farms. Regarding the number of farmers operating at VRS, small farmers dominate the scenario with 72.5 per cent followed by other (67.5%) and marginal (42.5%) farmers. With reference to scale efficiency, marginal farmers are in majority (52.5%) followed by other (47.5%) and small (25%) farmers. At the pooled level, 26.7 per cent of the farmers are being operated at CRS, 63 per cent at VRS and 32.5 per cent of the farmers are either performed at the optimum scale or were close to the optimum scale (farms having scale efficiency values equal to or more than 0.90). Nearly 58, 15 and 28 percents of the farmers in the marginal farms category were found operating in the region of increasing, decreasing and constant returns respectively. Compared to marginal farmers category, there are less number of farmers operating at CRS both in small farmers category (15%) and other farmers category (22.5%). At the pooled level, only 5 per cent of the farmers are operating at DRS, majority of the farmers (73%) are operating at IRS and only 22 per cent of the farmers are operating at CRS indicating efficient utilization of credit. The log-linear regression model fitted to analyze the major determinants of credit utilization (technical) efficiency of farmer-borrowers revealed that, the three variables viz., cost of cultivation and family expenditure (both negatively influencing at 1% significant level) and family income (positively influencing at 1% significant level) are the major determinants of credit utilization efficiency across all the selected farmers categories and at pooled level. The analysis further indicate that, escalation in the cost of cultivation of crop enterprises in the region, rise in family expenditure and prior indebtedness of the farmers are showing adverse influence on the credit utilization efficiency of the farmer-borrowers.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2019년도 학술발표회
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• pp.154-154
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• 2019

Characterization of reliable field-scale root-zone soil moisture (RZSM) variability contribute to effective hydro-meterological monitoring. Although a promising cosmic-ray neutron probe (CRNP) holds the pontential for field-scale RZSM measurement, it is often restricted at deeper depths due to the non-unique sensitivity of CRNP-measured fast neutron signal to other hydrogen pools. In this study, a merging framework relied on coupling cosmic-ray soil moisture with a representative additional RZSM, was introduced to scale shallower CRNP effective depth to represent root-zone layer. We tested our proposed framework over a densely vegetated region in South Korea covering a network of one CRNP and nine in-situ point measurements. In particular, cosmic-ray soil moisture and ancillary RZSM retrieved from the most time stable location were considered as input datasets; whereas the remaining point locations were used to generate a reference RZSM product. The errors between these two input datasets and the reference were forecasted by a linear autoregressive model. A linear combination of forecasts was then employed to compute a suitable weight for merging two input products from the predicted errors. The performance of merging framework was evaluated against reference RZSM in comparison to the two original products and a commonly used exponential filter technique. The results of this study showed that merging framework outperformed other products, demonstrating its robustness in improving field-scale RZSM. Moreover, a strong relationship between the quality of input data and the performance merging framework in light of CRNP effective depth variation has been also underlined via the merging framework.

• 제어로봇시스템학회논문지
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• 제19권1호
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• pp.10-14
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• 2013

High precision machining technology has become one of the important parts in the development of a precision machine. Such a machine requires high precision positioning as well as high speed on a large workspace. For machining systems having a high precision positioning with a long stroke, it is necessary to examine the repeatability of reference position decision. Though ball-screw driven linear stages equipped linear scale have high precision feed drivers and a long stroke, they have some limitations for reference position decision if they have not equipped the accurate home sensor. This study is performed to experimentally examine the repeatability for home position decision of a magnetic sensor as a home switch of ball-screw driven linear stage by using capacitance probe.

• Journal of applied mathematics & informatics
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• 제28권1_2호
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• pp.351-361
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• 2010

The solution of large sparse linear systems is one of the most important problems in large scale scientific computing. Among the many methods developed, the preconditioned Krylov subspace methods are considered the preferred methods. Selecting a suitable preconditioner with appropriate parameters for a specific sparse linear system presents a challenging task for many application scientists and engineers who have little knowledge of preconditioned iterative methods. The prediction of ILU type preconditioners was considered in [27] where support vector machine(SVM), as a data mining technique, is used to classify large sparse linear systems and predict best preconditioners. In this paper, we apply the data mining approach to the sparse approximate inverse(SAI) type preconditioners to find some parameters with which the preconditioned Krylov subspace method on the linear systems shows best performance.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.359-362
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• 2003

The aerostatic stage. which is used in semiconductor process, is demanded higher velocity and more precise accuracy for higher productivity and integrated performance. So, in the case of XY stage, H type structure, which is designed two co-linear axis of guide-way, driving force in one surface, has advantage of velocity and accuracy compared to conventional tacked type XY stage. To analyze characteristics of H type aerostatic stage, H type aerostatic surface XY stage is made, which is driven by linear motor and detected position with precise optical linear scale. And, analyze characteristics of motion error, effect of angular motion on positioning accuracy error and effect of simultaneous control on variation of velocity.

• 제어로봇시스템학회논문지
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• 제20권4호
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• pp.463-467
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• 2014

High precision machining technology has become one of the most important parts in the development of a precision machine. Such a machine requires high precision positioning as well as high speed on a large workspace. For machining systems having high precision positioning with a long stroke, it is necessary to examine the repeatability of the reference position decision. Though ball-screw driven linear stages equipped with linear scale have high precision feed drivers and a long stroke, they have some limitations for reference position decisions if they have not been equipped with an accurate home sensor. This study is performed to experimentally examine the repeatability for home position decision of a photo micro sensor as a home switch of a ball-screw driven linear stage by using a capacitance probe.