• Title/Summary/Keyword: 직접행렬 개선법

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New Construction for Visual Cryptography Using the Cumulative Matrix (누적행렬을 이용한 ( k, n) 시각암호의 새로운 구성)

  • 김문수;박지환
    • Journal of the Korea Institute of Information Security & Cryptology
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    • v.11 no.6
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    • pp.15-26
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    • 2001
  • Visual cryptography is a simple method in which secret information can be directly decoded in human visual system without any cryptographic computations. When the secret image is scattered to n random shares(slides), this scheme has some week point such as pixel expansion and contrast degradation. Therefore, it is necessary to reduce the pixel expansion and improve the contrast in recovered image. In this paper, we propose a new construction method for (k, n) visual cryptography using the cumulative matrix. In case k is odd, we can construct the cumulative matrix perfectly. For even k, the contrast of special pair in decoded image can be achieved best by permitting multiple contract. The proposed method is more simple than that of S. Droste\`s in construction and the average contrast of decoded image is improved for the most part. Also, we show that the basis matrices depending on the cumulative matrix are able to be applied for the general access structure.

New Construction Scheme for Improving Contrast in Visual Cryptography (시각암호의 휘도 개선을 위한 새로운 구성법)

  • 양신석;김문수;박지환
    • Journal of Korea Multimedia Society
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    • v.4 no.2
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    • pp.136-144
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    • 2001
  • visual cryptography is a simple method in which secret information can be directly decoded in human visual system without any cryptographic computations. This scheme is a kind of secret sharing scheme in which secret of image type is distributed to n random image(we call it share). When the secret image is distributed to n shares, the original pixel is expanded as much as the size of column in basis matrix. It causes the deterioration of contrast in docoded secret image. Therefore, many researches have performed to reduce the size of pixel expansion and to improve the contrast by overlapping the row in basis matrix for (k, n) visual cryptography. In addition, we show that the proposed method can construct the (k, n) visual cryptography with multiple contrasts depending on selecting k out of n slides in a group.

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Structural Identification for Structural Health Monitoring of Long-span Bridge - Focusing on Optimal Sensing and FE Model Updating - (장대교량의 구조 건전도 모니터링을 위한 구조식별 기술 - 최적 센싱 및 FE 모델 개선 중심으로 -)

  • Heo, Gwanghee;Jeon, Joonryong
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.25 no.12
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    • pp.830-842
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    • 2015
  • This paper aims to develop a SI(structural identification) technique using the kinetic energy optimization technique(KEOT) and the direct matrix updating method(DMUM) to decide on optimal location of sensors and to update FE model respectively, which ultimately contributes to a composition of more effective SHM. Owing to the characteristic structural flexing behavior of cable bridges, which makes them vulnerable to any vibration, systematic and continuous structural health monitoring (SHM) is pivotal for them. Since it is necessary to select optimal measurement locations with the fewest possible measurements and also to accurately assess the structural state of a bridge for the development of an effective SHM, a SI technique is as much important to accurately determine the modal parameters of the current structure based on the data optimally obtained. In this study, the KEOT was utilized to determine the optimal measurement locations, while the DMUM was utilized for FE model updating. As a result of experiment, the required number of measurement locations derived from KEOT based on the target mode was reduced by approximately 80 % compared to the initial number of measurement locations. Moreover, compared to the eigenvalue of the modal experiment, an improved FE model with a margin of error of less than 1 % was derived from DMUM. Finally, the SI technique for long-span bridges proposed in this study, which utilizes both KEOT and DMUM, is proven effective in minimizing the number of sensors while accurately determining the structural dynamic characteristics.

Further Improvement of Direct Solution-based FETI Algorithm (직접해법 기반의 FETI 알고리즘의 개선)

  • Kang, Seung-Hoon;Gong, DuHyun;Shin, SangJoon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.35 no.5
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    • pp.249-257
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    • 2022
  • This paper presents an improved computational framework for the direct-solution-based finite element tearing and interconnecting (FETI) algorithm. The FETI-local algorithm is further improved herein, and localized Lagrange multipliers are used to define the interface among its subdomains. Selective inverse entry computation, using a property of the Boolean matrix, is employed for the computation of the subdomain interface stiffness and load, in which the original FETI-local algorithm requires a full matrix inverse computation of a high computational cost. In the global interface computation step, the original serial computation is replaced by a parallel multi-frontal method. The performance of the improved FETI-local algorithm was evaluated using a numerical example with 64 million degrees of freedom (DOFs). The computational time was reduced by up to 97.8% compared to that of the original algorithm. In addition, further stable and improved scalability was obtained in terms of a speed-up indicator. Furthermore, a performance comparison was conducted to evaluate the differences between the proposed algorithm and commercial software ANSYS using a large-scale computation with 432 million DOFs. Although ANSYS is superior in terms of computational time, the proposed algorithm has an advantage in terms of the speed-up increase per processor increase.

A Four-node General Shell Element with Drilling DOFs (면내회전자유도를 갖는 4절점 곡면 쉘요소)

  • Chung, Keun-Young;Kim, Jae-Min;Lee, Eun-Haeng
    • Journal of the Earthquake Engineering Society of Korea
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    • v.16 no.4
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    • pp.37-52
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    • 2012
  • In this study, a new 4-node general shell element with 6 DOFs per node is presented. Drilling rotational degrees of freedom are introduced by the variational principle with an independent rotation field. In formulation of the element, substitute transverse shear strain fields are used to avoid shear locking, while four nonconforming modes are applied in the in-plane displacement fields as a remedy for membrane locking. In addition, a direct modification method for nonconforming modes is employed in the numerical implementation of nonconforming modes to represent constant strain states. A 9-points integration rule is adopted for volume integration in the computation of the element stiffness matrix. With the combined use of these techniques, the developed shell element has no spurious zero energy modes, and can represent a constant strain state. Several numerical tests are carried out to evaluate the performance of the new element developed. The test results show that the behavior of the elements is satisfactory.

A Derivation of the Representative Unit Hydrograph from Multiperiod Complex Storm by Linear Programming (선형계획법(線型計劃法)에 의한 대표단위도(代表單位圖) 유도(誘導))

  • Kwon, Oh Hun;Ryu, Tae Sang;Yoo, Ju Hwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.2
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    • pp.173-182
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    • 1993
  • This paper presents an algorithm to derive the representative unit hydrograph for the real environment of a watershed. For a given watershed, the conventional methods give several different unit hydrographs by storm events. In this study the LP model is somewhat modified based on the previous study by Mays et also as follows: the objective function is designed to minimize the sum of weighted residuals. An additional constraint of moving average is added to prevent the unit hydrograph from the occurence of oscillation which was not active in Mays's paper. Configuration of rainfall matrix was improved to reduce its dimension in accordance with Diskin's review point. In spite of the superiority of LP approach in terms of representativeness, all the methods were very sensitive to the validity of baseflow separation and rainfall-loss. Several methods of the separations for rainfall excesses and direct runoffs were applied and no preferred methods were identified. This is the matter of judgement considering catchment and rainfall characteristics. This algorithm was applied to a real watershed of the Wi stream in the Nak-dong river. Compared with the IHP results by conventional methods, this optimized representative unit hydrograph demonstrated relatively smaller and shorter values in terms of the peak discharge and the basin lag respectively, and the oscillation of its falling limb successfully eliminated owing to the additional constraints of moving averages.

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