• International Journal of Control, Automation, and Systems
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• v.6 no.4
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• pp.506-514
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• 2008

This paper presents an intelligent model; named as free model, approach for a closed-loop system identification using input and output data and its application to design a power system stabilizer (PSS). The free model concept is introduced as an alternative intelligent system technique to design a controller for such dynamic system, which is complex, difficult to know, or unknown, with input and output data only, and it does not require the detail knowledge of mathematical model for the system. In the free model, the data used has incremental forms using backward difference operators. The parameters of the free model can be obtained by simultaneous perturbation stochastic approximation (SPSA) method. A linear transformation is introduced to convert the free model into a linear model so that a conventional linear controller design method can be applied. In this paper, the feasibility of the proposed method is demonstrated in a one-machine infinite bus power system. The linear quadratic regulator (LQR) method is applied to the free model to design a PSS for the system, and compared with the conventional PSS. The proposed SPSA-based LQR controller is robust in different loading conditions and system failures such as the outage of a major transmission line or a three phase to ground fault which causes the change of the system structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.490-495
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• 2007

This research aims to examine accuracy and efficiency of the first four moments corresponding to mean, standard deviation, skewness, and kurtosis, which are estimated by a function approximation moment method (FAMM). In FAMM, the moments are estimated from an approximating quadratic function of a system response function. The function approximation is performed on a specially selected experimental region for accuracy, and the number of function evaluations is taken equal to that of the unknown coefficients for efficiency. For this purpose, three error-minimizing conditions are utilized and corresponding canonical experimental regions constructed accordingly. An interpolation function is then obtained using a D-optimal design and then the first four moments of it are obtained as the estimates for the system response function. In order to verify accuracy and efficiency of FAMM, several non-linear examples are considered including a polynomial of order 4, an exponential function, and a rational function. The moments calculated from various coefficients of variation show very good accuracy and efficiency in comparison with those from analytic integration or the Monte Carlo simulation and the experimental design technique proposed by Taguchi and updated by D'Errico and Zaino.

• Geophysics and Geophysical Exploration
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• v.4 no.3
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• pp.70-79
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• 2001

The integral equation method is a powerful tool for numerical electromagnetic modeling. But the difficulty of this technique is the size of the linear equations, which demands excessive memory and calculation time to invert. This limitation of the integral equation method becomes critical in inverse problem. The conventional Born approximation, where the electric field in the anomalous body is approximated by the background field, is very rapid and easy to compute. However, the technique is inaccurate when the conductivity contrast between the body and the background medium is large. Quasi-linear, quasi-analytical and extended Born approximations are novel approaches to 3-D EM modeling based on the linearization of the integral equations for scattered EM field. These approximation methods are much less time consuming than full integral equation method and more accurate than conventional Born approximation. They we, however, still approximate methods for 3-D EM modeling. Iterative series methods such as modified Born, quasi-linear and quasi-analytical can be used to increase the accuracy of various approximation methods. Comparisons of numerical performance against a full integral equation and various approximation codes show that the iterative series methods are very accurate and almost always converge. Furthermore, they are very fast and easy to implement on a computer. In this study, extended Born series method is developed and it shows more accurate result than that of other series methods. Therefore, Iterative series methods, including extended Born series, open principally new possibilities for fast and accurate 3-D EM modeling and inversion.

• Archives of Plastic Surgery
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• v.38 no.2
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• pp.143-147
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• 2011

Purpose: A Tessier classification number 7 cleft is an uncommon malformation that results from a failure of mesenchymal fusion within the maxillary and mandibular prominences of the 1st pharyngeal arch. Many operative techniques of the number 7 cleft repair have been proposed to restore function and improve aesthetics. Fifteen patients underwent repair of a number 7 cleft over 13 years by a modification of the surgical Technique, and an appraisal of the operative outcome is reported herein. Methods: A retrospective review was conducted involving 15 patients with number 7 clefts who underwent surgery from 1996 to 2009. The changes in surgical technique included skin closure, attachment of the orbicularis oris muscle, and position of the repaired commissure; the changes were analysed with a review of the medical records and the outcomes of surgery were analysed via photographs. Specifically, the technique of skin closure was changed from the a Z-plasty to a linear closure, the orbicularis oris muscle overlapped attachment was replaced by a side-to-side approximation with horizontal mattress sutures, and the position of the repaired commissure was changed from 1 mm laterally to 1 mm medially in reference to the non-cleft side. Results: A Z-plasty caused additional cutaneous scarring, an overlapped attachment of the orbicularis oris muscle caused a thick oral commissure, and the repaired commissure migrated to the lateral side, so a 1 mm, laterally-positioned commissure caused asymmetry. The altered procedure included a linear skin closure, a side-to-side orbicularis oris muscle approximation, and a 1 mm, medially-positioned commissure, which together resulted in a good outcome. Conclusion: The altered procedure for repair of a number 7 cleft as described herein, yields a short scar, no functional problems with the orbicularis oris muscle, a thin oral commissure, and symmetry of the repaired commissure.

• Proceedings of the ESK Conference
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• 1995.04a
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• pp.25-29
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• 1995

When we design a product, we need to consider human sensibility for the product. In this study, we developed a technique to measure human sensibility for a product. Because human sensibility for a product is very subjective and fuzzy, it is hard to measure easily. To deal with this difficulty effectively, we used fuzzy-weighted checklist to this problem. The fuzzy- weighted checklist presents a fuzzy version of the weighted checklist technique computerized for evaluating or comparing complex system (or subjects). In this technique, we used pairwise comparison to get the relative weights of wensibility factors. Also, we used linguistic ratings to get the scores of sensibility factors for a product. Then, we synthesize the scores of sensi- bility factors to get fuzzy composite score (and linguistic approximation). If there are several alternatives, we can conduct alternative comparison. Finally, we wrote the program of this technique by Quick Basic software. As an example, this technique applied to car. The results show that we can use this technique effectively to the quantitative evaluation of human sensibility

• Journal of the Ergonomics Society of Korea
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• v.15 no.1
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• pp.15-26
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• 1996

When a product is designed, it is important to consider its image on consumers. In this study, we developed a technique to measure product image. Because human image of a product is very subjective and fuzzy, it is difficult to measure easily. To deal with this difficulty effectively, we used fuzzy- weighted checklist. The fuzzy-weighted checklist presents a fuzzy version of the weighted checklist technique for evaluating or comparing complex systems or subjects. In this technique, we used a pairwise comparison method to obtain the relative importance weights of image factors. Also, we used linguistic ratings to obtain the scores of image factors for a product. Then, we synthesized the scores of image factors to obtain a fuzzy composite score and its linguistic approximation. The entire procedure of this technique was written in quick Basic. As an example, this techinque is applied to car evaluation. The results show that this technique can be effectively used to the quqntitative evaluation of huamn image.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.5
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• pp.914-922
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• 1987

An image coding technique based on a segmentation, which utilizes a simplified description of regions composing an image, is investigated in this paper. The proposed coding technique consists of 3 stages: segmentation, contour coding. In this paper, emphasis was given to texture coding in order to improve a quality of an image. Split-and-merge method was employed for a segmentation. In the texture coding, a linear predictive coding(LPC), along with approximation technique based on a two-dimensional polynomial function was used to encode texture components. Depending on a size of region and a mean square error between an original and a reconstructed image, appropriate texture coding techniques were determined. A computer simulation on natural images indicates that an acceptable image quality at a compression ratio as high as 15-25 could be obtained. In comparison with a discrete cosine transform coding technique, which is the most typical coding technique in the first-generation coding, the proposed scheme leads to a better quality at compression ratio higher than 15-20.

• Proceeding of KASS Symposium
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• 2006.05a
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• pp.110-117
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• 2006

This study presents an effective stiffness-based optimal technique to consider floor rigid diaphragm action and a technique to evaluate the structural behavior characteristics and efficiency for tall shear wall outrigger system subject to horizontal loads. To this end, isoparametric plane stress element with rotational stiffness is used for shear wall element and stiffness gradient is calculated. Also, the approximation concept to solve effectively the large scaled problems, member grouping technique and resizing technique are considered. To verify the effectiveness and usefulness of this technique, the efficient evaluation method for three types of 50 story model with core and outrigger system is presented.

• Journal of the Korean Operations Research and Management Science Society
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• v.33 no.1
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• pp.107-115
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• 2008

We consider the discrete-time GI/G/1/K queue under the early arrival system. Using a modified supplementary variable technique(SVT), we obtain the distribution of the steady-state queue length. Unlike the conventional SVT, the modified SVT yields transform-free results in such a form that a simple two-moment approximation scheme can be easily established.

• East Asian mathematical journal
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• v.30 no.3
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• pp.327-334
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• 2014

In this paper, we construct extrapolated expanded mixed finite element approximations to approximate the scalar unknown, its gradient and its flux of semilinear Sobolev equations. To avoid the difficulty of solving the system of nonlinear equations, we use an extrapolated technique in our construction of the approximations. Some numerical examples are used to show the efficiency of our schemes.