• Journal of the Korean Society of Combustion
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• v.20 no.1
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• pp.24-31
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• 2015

Flame structure, which contains a useful information for studying combustion instability of the flame, is often quantitatively visualized with PLIF (planar laser-induced fluorescence) and/or chemiluminescence images. The latter, a line-integral of a flame property, needs to be preprocessed before being inverted, mainly due to its inherent noise and the axisymmetry assumption of the inversion. A preprocessing scheme utilizing multi-division of ROI (region of interest) of the chemiluminescence image is proposed. Its feasibility has been tested with OH PLIF and $OH^*$ chemiluminescence images of SNG (synthetic natural gas) swirl-stabilized flames taken from a model gas turbine combustor. It turns out that the multi-division technique outperforms two conventional ones: those are, one without preprocessing and the other with uni-division preprocessing, reconstructing the SNG flame structure much better than its two counterparts, when compared with the corresponding OH PLIF images. It is also found that the Canny edge detection algorithm used for detecting edges in the multi-division method works better than the Sobel algorithm does.

• Economic and Environmental Geology
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• v.27 no.5
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• pp.479-489
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• 1994

In this paper, the iterative least-squares inversion method is used to determine shapes and density contrasts of 2-D structures from the gravity data. The 2-D structures are represented by their cross-sections of N-sided polygons with density contrasts which are constant or varying with depth. Gravity data are calculated by theoretical formulas for the above structure models. The data are considered as observed ones and used for inversions. The inversions are performed by the following processes: I) polygon's vertices and density contrast are initially assumed, 2) gravity are calculated for the assumed model and error between the true (observed) and calculated gravity are determined, 3) new vertices and density contrast are determined from the error by using the damped least-squares inversion method, and 4) final model is determined when the error is very small. Results of this study show that the shape and density contrast of each model are accurately determined when the density contrast is constant or vertical density gradient is known. In case where the density gradient is unknown, the inversion gives incorrect results. But the shape and density gradient of the model are determined when the surface density contrast is known.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.2
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• pp.176-184
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• 2013

Quantification of road noise is a challenging issue in the development of tire noise since its transfer paths are complicated. In this paper, a simplified model to estimate the road noise is developed. Transfer path of the model is from wheel to interior. The method uses the wheel excitation force estimated throughout inverse method. In inversion procedure, the Tikhonov regularization method is used to reduce the inversion error. To estimate the wheel excitation force, the vibration of knuckle is measured and transfer function between knuckle and wheel center is also measured. The wheel excitation force is estimated by using the measured knuckle vibration and the inversed transfer function. Finally interior noise due to wheel force is estimated by multiplying wheel excitation force in the vibro-acoustic transfer function. This vibro-acoustic transfer function is obtained throughout measurement. The proposed method is validated by using cleat excitation method. Finally, it is applied to the estimation of interior noise of the vehicle with different types of tires during driving test.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.2
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• pp.127-132
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• 2003

Cryptosystems have received very much attention in recent years as importance of information security is increased. Most of Cryptosystems are defined over finite or Galois fields GF($2^m$) . In particular, the finite field GF($2^m$) is mainly used in public-key cryptosystems. These cryptosystems are constructed over finite field arithmetics, such as addition, subtraction, multiplication, and multiplicative inversion defined over GF($2^m$) . Hence, to implement these cryptosystems efficiently, it is important to carry out these operations defined over GF($2^m$) fast. Among these operations, since multiplicative inversion is much more time-consuming than other operations, it has become the object of lots of investigation. Recently, many methods for computing multiplicative inverses at hi호 speed has been proposed. These methods are based on format's theorem, and reduce the number of required multiplication using normal bases over GF($2^m$) . The method proposed by Itoh and Tsujii[2] among these methods reduced the required number of times of multiplication to O( log m) Also, some methods which improved the Itoh and Tsujii's method were proposed, but these methods have some problems such as complicated decomposition processes. In practical applications, m is frequently selected as a power of 2. In this parer, we propose a fast method for computing multiplicative inverses in GF($2^m$) , where m = ($2^n$) . Our method requires fewer ultiplications than the Itoh and Tsujii's method, and the decomposition process is simpler than other proposed methods.

• The Bulletin of The Korean Astronomical Society
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• v.33 no.1
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• pp.71.2-71.2
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• 2008

• Bulletin of the Korean Space Science Society
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• 2000.04a
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• pp.32-32
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• 2000

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1496-1499
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• 1996

A nonlinear tracking control technique developed for the control of nonlinear systems has been applied to the autopilot design of missile system. The difficulties in the application of inversion based control methods such as input-output feedback linearization and sliding mode control due to nonminimum phase characteristics are discussed. To avoid the stability problem associated with unstable zero dynamics, the input-output feedback linearization is applied with output-redefinition method to normal acceleration control. The output-redefinition method gives an indirect way to apply the nonlinear controls to nonminimum phase plants by redefining the plant output such that the tracking control of the modified output ensures the asymptotic tracking of the original output. The numerical simulation shows satisfactory results both for nominal and for slightly perturbed missile systems adopting the sliding mode control technique. However, the robustness problem in this method is briefly investigated and verified with the simulation.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.6
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• pp.598-606
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• 1990

Common problems encountered when orthogonal functions are used in system analysis and state estimation are the time consuming process of high order matrix inversion required in finding the Kronecker products and the truncation errors. In this paper, therefore, a method for the analysis of bilinear systems using Walsh, Block pulse, and Haar functions is devised, Then, state estimation of bilinear system is also studied based on single term expansion of orthogonal functions. From the method presented here, when compared to the other conventional methods, we can obtain the results with simpler computation as the number of interval increases, and the results approach the original function faster even at randomly chosen points regardless of the definition of intervals. In addition, this method requires neither the inversion of large matrices on obtaining the expansion coefficients nor the cumbersome procedures in finding Kronecker products. Thus, both the computing time and required memory size can be significantly reduced.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.782-788
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• 2008

In this paper, a comparison about two representative Transfer Path Analysis(TPA) methods for air-borne noise based on, matrix inversion method and pressure transmissibility, are presented on the view point of crosstalk effect between sources. In order to assess accuracy of two methods according to path models between virtual airborne noise sources, experiments are made for two cases, weak and strong crosstalk effect condition, by using acrylic vehicle model. Based on this assessment, the paper presents a reasonable application criteria for TPA method according to the circumstances of air-borne noise sources.

• Geophysics and Geophysical Exploration
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• v.7 no.1
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• pp.19-24
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• 2004

Frequency-space domain full-wave tomography is a promising technique for delineating detailed subsurface structure with high resolution. However, this method requires criteria for the selection of a set of optimal temporal frequency components, to achieve stability in the sequence of inversion processes together with computational efficiency. We propose a method of selecting optimal temporal frequencies, based on wavenumber continuity. The proposed method is tested numerically and is shown to be able to select an optimal set of frequency components that are sufficient to image the anomalies.