• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.47-50
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• 2006

In the aeroacoustic application of computational fluid dynamics, the physical phenomena like the crackle in the unsteady compressible jets should be based on very time-accurate numerical solution. The accuracy of the present numerical scheme is extended to the fifth order, using the WENO filter to the sixth-order central difference computation. However, the computational capacity is very restricted by the environment of computational power, so therefore the quadrilateral adaptive grids technique is introduced for this high-order accuracy scheme. The first problem is the multi-dimensional interpolation between fine and coarse grids. Some general benchmark problems are solved to show the effectiveness of this method.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.2
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• pp.93-99
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• 2016

In this paper, higher order coupler using small size waveguide which applicable for mobile Ku-band multimode monopulse satellite tracking antenna system, has been designed, implemented and tested. Proposed higher order mode coupler adopts a coaxial structure for low profile characteristic considering installation property to mobile satellite terminal system. In addition, by using proposed coupler, extracted tracking error signal pattern has measured and confirmed that required tracking accuracy is satisfied in desired frequency band. In the future, proposed coupler could utilize for multimode monopulse satellite tracking system for high tracking accuracy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.424-431
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• 2004

An implicit direct-time integration method for obtaining transient responses of general dynamic systems is described. The conventional Newmark method cannot be directly applied to state-space first-order differential equations, which contain no explicit acceleration terms. The method proposed here is the state-space Newmark method that incorporates the average velocity concept, and can be applied to an analysis of general dynamic systems that are expressed by state-space first-order differential equations. It is also readily coded into a program. Stability and accuracy analyses indicate that the method is numerically unconditionally stable like the conventional Newmark method, and has a period error of 2nd-order accuracy for small damping and 4th-order for large damping and an amplitude error of 2nd-order, regardless of damping. In addition, its utility and validity are confirmed by two application examples. The results suggest that the proposed state-space Newmark method based on average velocity be generally applied to the analysis of transient responses of general dynamic systems with a high degree of reliability with respect to stability and accuracy.

• Journal of the Korean Operations Research and Management Science Society
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• v.23 no.3
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• pp.185-207
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• 1998

This research investigates computer generated hybrid second-order model of two numerically based approaches to risk classification : discriminant analysis and neural networks. The hybrid second-order models are derived by rule induction using the ID3 and tested in the several different kinds of data. This new hybrid approach is designed to combine the high prediction accuracy and robustness of DA or NN with perspicuity of ID3. The hybrid model also eliminates the problem of contradictory inputs of ID3. After doing empirical test for the validity of hybrid model using small and medium companies' bankrupt data, hybrid model shows high perspicuity, high prediction accuracy for bankrupt, and simplicity for rules. The hybrid model also shows high performance regardless the type of data such as numeric data, non-numeric data, and combined data.

• Journal of computational fluids engineering
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• v.21 no.2
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• pp.1-11
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• 2016

Considerable efforts are required to develop a monotone, robust and stable high-order numerical scheme for solving the hyperbolic system. The discontinuous Galerkin(DG) method is a natural choice, but elimination of the spurious oscillations from the high-order solutions demands a new development of proper limiters for the DG method. There are several available limiters for controlling or removing unphysical oscillations from the high-order approximate solution; however, very few studies were directed to analyze the exact role of the limiters in the hyperbolic systems. In this study, the performance of the several well-known limiters is examined by comparing the high-order($p^1$, $p^2$, and $p^3$) approximate solutions with the exact solutions. It is shown that the accuracy of the limiter is in general problem-dependent, although the Hermite WENO limiter and maximum principle limiter perform better than the TVD and generalized moment limiters for most of the test cases. It is also shown that application of the troubled cell indicators may improve the accuracy of the limiters under some specific conditions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1376-1383
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• 2001

Modem technology depends on the reliability of extremely high technology equipments. In the production of semiconductor wafer, optical and electron microscopes, ion-beam, laser device must maintain their alignments within a sub-micrometer. This equipment requires a vibration free environment to provide its proper function. Especially, lithography and inspection devices, which have sub-nanometer class high accuracy and resolution, have come to necessity for producing more improved giga and tera class semiconductor wafers. This high technology equipments require very strict environmental vibration standard, vibration criteria, in proportion to the accuracy of the manufacturing, inspecting devices. The vibration criteria of high sensitive equipment should be represented in the form of 'exactness' and 'accuracy', because this is used as basic data for the design of building structure and structural dynamics of equipment. This paper deals with the properties of time and frequency domain in order to obtain more improved vibration criteria for high sensitive equipment.

• International Journal of Control, Automation, and Systems
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• v.6 no.2
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• pp.180-185
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• 2008

A new method for relative error continuous and discrete time model order reduction is proposed. The reduction technique is based on two recently developed methods, namely frequency domain balanced truncation within a frequency bound and inner-outer factorization techniques. The proposed method is of interest for practical model order reduction because in this context it shows to keep the accuracy of the approximation as high as possible without sacrificing the computational efficiency. Numerical results show the accuracy and efficiency enhancement of the method.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.91-98
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• 2005

This study has been focused on the development of a high speed feeding type three-dimensional bending machine. It is designed for manufacture of copper pipe for heat exchangers. For the purpose of design of the machine, analysis of bending process, structural analysis and reliability evaluation of the machine by a laser interferometer are carried out. The analysis is carried out by FEM simulation using commercial softwares, DEFORM, MARC and CATIA V5. In addition, the machine has attained high accuracy and repeatability. In order to improve the accuracy of this machine, the maximum speed, positioning accuracy and repeatability of feed are measured by the laser interferometer. The final results of analysis are applied to the design of a high speed feeding type three-dimensional bending machine and the machine is successfully developed.

• Current Optics and Photonics
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• v.7 no.6
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• pp.692-700
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• 2023

We present a method for improving the accuracy of the modal wavefront reconstruction in the radial shearing interferometers (RSIs). Our approach involves expanding the reduced radial terms of Zernike polynomials to high-order, which enables more precise reconstruction of the wavefront aberrations with high-spatial frequency. We expanded the reduced polynomials up to infinite order with symbolic variables of the radius, shearing amount, and transformation matrix elements. For the simulation of the modal wavefront reconstruction, we generated a target wavefront subsequently, magnified and measured wavefronts were generated. To validate the effectiveness of the high-order Zernike polynomials, we applied both low- and high-order polynomials to the wavefront reconstruction process. Consequently, the peak-to-valley (PV) and RMS errors notably decreased with values of 0.011λ and 0.001λ, respectively, as the order of the radial Zernike polynomial increased.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.11a
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• pp.101-104
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• 1991

Bal1 screw systems has been used for positioning elements of machine tools. In order to maintain high rigidity and accuracy, preload is applied between nut and screw. However, large amount of preload increases frictional heat. Temperature rises remarkably at high speed notion, Thermal expansion degrades positioning accuracy, In this paper, finite differance method is applied to compute temperature distributions and thermal expansions of ball screw systems according to preload condition and rotational steed. Some simulation results show that the developed methodology is good to study thermal expansion of ball screw systems.