• Computational Structural Engineering
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• v.7 no.4
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• pp.57-67
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• 1994

It is usual that underground structures are constructed within a multi-layered medium. In this paper, an efficient numerical modelling of multi-layered structural systems is studied using coupled analysis of finite elements and boundary elements. The finite elements are applied to the area in which the material nonlinearity dominates, and the boundary elements are applied to the far field where the nonlinearity is relatively weak. In the boundary element modelling of the multi-layered medium, fundamental solutions are not readily available. Thus, methods which can utilize existing Kelvin solutions are sought for the interior multi-layered domain problem. The interior domain problem which has piecewise homogeneous layers is analyzed using boundary elements with Kelvin solution, by discretizing each homogeneous subdomain and enforcing compatibility and equilibrium conditions between interfaces. Developed methodology is verified by comparing its results with those from the finite element analysis and it is concluded that coupled analysis using boundary elements and finite elements can be reasonable and efficient.

• Korean Journal of Cognitive Science
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• v.13 no.1
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• pp.23-40
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• 2002

This study is to examine brain regions that are involved in picture encoding in normal adults using fMRI methods. In Scan 1, the picture encoding was studied during a semantic categorization task in comparison with word. In Scan 2 task type effects were studied both during a picture naming task and during a semantic categorization task with pictures. Subjects were asked to make decision either by pressing a mouse button (Scan 1) or by responding subvocally (naming or saying yes/no) (Scan 2). Regardless of stimulus type, left prefrontal, bilateral occipital, and parietal activations were observed during semantic processing in comparison with fixation baseline. Processing of word stimulus relative to picture resulted in activations in prefrontal and parieto-temporal regions in the left side while that of picture stimulus relative to word resultd in activations in bilateral extrastriatal visual cortices and parahippocampal regions. In spite of the same task demands, stimulus-specific information processings were involved and mediated by different neural substrates; the word encoding was associated with more semantic/lexical processings than pictures and the picture processing associated with more perceptual and novelty related information processings than word. Activations of dorsal part of inferior prefrontal region, i.e., Broca's areas were found both during the picture naming and during the semantic tasks subvocally performed Especially, during the picture naming task, greater occipital activations were found bilaterally relative to the semantic categorization task. indicating a possibility that greater and higher visual processing was involved in retrieving the name referred by picture stimuli.

• Journal of Korea Multimedia Society
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• v.13 no.7
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• pp.1044-1050
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• 2010

Endoscopic ultrasonography is a medical procedure in endoscopy combined with ultrasound to obtain images of the internal organs. It is useful to have a predictive pathological manifestation since a doctor can observe tumors under mucosa. However, it is often subjective to judge the degree of malignant degeneration of tumors. Thus, in this paper, we propose a feature analysis procedure to make the pathological manifestation more objective so as to improve the accuracy and recall of the diagnosis. In the process, we extract the ultrasound region from the image obtained by endoscopic ultrasonography. It is necessary to standardize the intensity of this region with the intensity of water region as a base since frequently found small intensity difference is only to be inefficient in the analysis. Then, we analyze the spot region with high echo and calcium deposited region by applying LVQ algorithm and bit plane partitioning procedure to tumor regions selected by medical expert. For detailed analysis, features such as intensity value, intensity information included within two random points chosen by medical expert in tumor region, and the slant of outline of tumor region in order to decide the degree of malignant degeneration. Such procedure is proven to be helpful for medical experts in tumor analysis.

• Korean Architects
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• no.10 s.450
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• pp.83-83
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• 2006

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.10
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• pp.919-926
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• 2011

The fin of high speed air vehicle is composed of skins and strong skeletons. In the flutter analysis, the eigenmodes of a fin are used for evaluating the unsteady aerodynamic force and the modal approach is applied for solving the flutter equation in both time and frequency domain. Therefore, the proper eigenmodes used for a modal flutter analysis should be chosen. For the appropriate choice of eigenmodes, when there exist local modes of a skin in the high modes, the effects of those modes on the unsteady aerodynamic force and flutter characteristics are anlalyzed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.4
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• pp.400-408
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• 2009

This work presents experimental results on vibration control of flexible structures using the squeeze mode electrorheological(ER) mount. An appropriate size of the squeeze mode ER mount is devised and its field-dependent damping force characteristics are experimentally evaluated. The ER mount is then applied to two different flexible structures : beam structure and frame structure. An optimal controller associated with displacement and acceleration signals is designed to suppress the imposed vibration and experimentally realized using the microprocessor. Vibration control responses of the flexible structures such as acceleration are evaluated in time and frequency domains.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.179-184
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• 2001

대부분의 제품 생산 시에는 시제품을 제작하여 이에 대한 성능 심사를 통해 미비한 부분을 보완하기 위한 재설계 작업과정을 필요로 한다. 설계 작업에 가장 중요한 부분인 특정 설계 변수에 대한 민감도의 파악은 설계 작업의 핵심적인 역할을 하고 있다. 대개의 경우 진동설계를 위한 설계변수로 구조물의 단위면적, 길이, 재료의 성질과 같은 물리적인 변수를 많이 활용하고 있으며 이러한 변수들에 대한 민감도 해석 기법들은 이미 많은 연구를 통해 실용화되고 있다. 그러나 이러한 변수만으로는 주어진 조건을 만족하도록 설계하기가 어려운 경우가 있다. 이런 경우는 부가구조물을 첨가하여 저진동 설계조건을 만족하는 구조물을 제작하는 것이 보편적이다. 한편, 구조물의 최적화 과정에서 고유진동수를 고려해야 하는 경우가 많다. 저주파 영역의 문제에서는 첫번째 고유진동수가 구조물의 진동량에 관계되는 중요한 요인이 되고, 또한 공진에 의한 문제가 발생했을 경우에는 고유진동수를 옮겨서 공진을 회피할 수 있기 때문이다. 본 연구에서는 에어컨 실외기의 진동을 저감하고 그로 인한 구조기인 소음을 저감하기 위하여 음압 레벨을 바탕으로 정한 관심 주파수 영역에 고유진동수가 존재하지 않도록 부가구조물을 최적화하였다. 최적화에 필요한 민감도는 신뢰성 있는 유한요소 모델을 구성하는 것이 쉽지 않으므로 실험으로 구한 주파수 응답함수를 이용하였다.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.35-42
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• 2004

Impact-echo is a method for non-destructive testing of concrete structure. This method is based on the use of impact-generated stress wave which is propagated and reflected from internal flaws within concrete structure and external surface. In this study, we performed non-destructive testing using impact-echo methods for safety diagnosis of civil engineering and building structures. There are testing cases for the three models having one-dimensional form ; The first case is the measurement of thickness change of the model, the second is the detection of cavity in the model, and the third is the predictions of the lining thickness and the position of the cavity under tunnel lining condition.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.89-95
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• 2003

In this paper, an algorithm to locate and size damage in a complex truss structure using the time domain response is presented. Sampled response data for specific time interval is spatially expanded over the structure to obtain the mean train energy for each element of the structure. The mean strain energy for each element is, in turn, used to build a damage index that represents the ratio of the stiffness parameter of the pre-damaged to the post-damaged structure. The validity of the methodology is demonstrated using data from a numerical example of a space truss structure with simulated damage. Also in the example, the effects of noisy data on the proposed algorithm are examined by adding random noised to the response data.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.65-73
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• 2008

Retaining large stability margin is essential in designing a feedback control system to deal with the uncertainties inherently existing in the mathematical model and the control apparatus. The LQG controller in general loses the stability margin due to the embed Kalman filter. The performance of a control system called LTR with a DUOX structure(LTR/DOUX) to overcome the demerit of LQG controller is to be investigated from the responses in both the time and the frequency domain. The results indicated that the LTR/DOUX recovered the gain margin of 30dB approximately 20 times more than that of LQG/DOUX, resulting in a robust stable control system.