• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.34 no.2
• /
• pp.71-75
• /
• 2021

Despite the development of computational resources, the need to analyze models is increasing. The size of model has been increased to analyze the entire structure more accurately and precisely. As the analysis model becomes larger and more complex, the computation time increases exponentially. Various industries use many structures that have repeated patterns. We focus on these structures with repeated patterns and propose a dynamic analysis method to efficiently calculate these repeated structures. To devise an efficient method for repeated structures, the substructuring scheme and the degree of freedom-based reduction method are used in this study. We modify the existing reduction method in consideration of the characteristics of the repeating structure. In the proposed method, the entire structure was expressed as a combination of substructures, where each substructure was represented as an unit cell of repeated structures. The substructures were condensed and assembled using the substructuring scheme and the modified condensation method. Finally, numerical examples were demonstrated to verify the efficiency and accuracy of proposed method.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.21 no.5
• /
• pp.439-450
• /
• 2008

In this study, the reduced system for the dynamic analysis is proposed and the selection criterion of the primary degrees of freedom is presented considering the relation between natural frequency and external loading frequency. A well-constructed reduced system can assure the accurate representation of the dynamic behavior under arbitrary dynamic loads. For selecting the primary degrees of freedom of the reduced system, we employ the robust two-level condensation scheme of which the reliability has been proven through previous study. In the numerical examples, the reliability of the dynamic analysis based on the reduced system is demonstrated through comparing with those of global system.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.1
• /
• pp.65-73
• /
• 2007

In the inverse perturbation method, enormous computational resource was required to obtain reliable results, because all unspecified DOFs were considered as unknown variables. Thus, in the present study, a reduced system method is used to condense the unspecified DOFs by using the specified DOFs, and to improve the computational efficiency as well as the solution accuracy. In most of the conventional reduction methods, transformation errors occur in the transformation matrix between the unspecified DOFs and the specified DOFs. Thus it is hard to obtain reliable and accurate solution of inverse perturbation problems by reduction methods due to the error in the transformation matrix. This numerical trouble is resolved in the present study by adopting iterative improved reduced system(IIRS) as well as by updating the transformation matrix at every step. In this reduction method, system accuracy is related to the selection of the primary DOFs and Iteration time. And both are dependent to each other So, the two level condensation method (TLCS) is selected as Selection method of primary DOFs for increasing accuracy and reducing iteration time. Finally, numerical verification results of the present iterative inverse perturbation method (IIPM) are presented.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.4
• /
• pp.329-334
• /
• 2017

The structures, which are made up with the huge number of degrees-of-freedom and the assembly of substructures, have a great complexity. In order to increase the computational efficiency, the analysis models have to be simplified. Many substructuring techniques have been developed to simplify large-scale engineering problems. The techniques are very powerful for solving nonlinear problems which require many iterative calculations. In this paper, a modal derivatives-based model order reduction method, which is able to capture the stretching-bending coupling behavior in geometrically nonlinear systems, is adopted and investigated for its performance evaluation. The quadratic terms in nonlinear beam theory, such as Green-Lagrange strains, can be explained by the modal derivatives. They can be obtained by taking the modal directional derivatives of eigenmodes and form the second order terms of modal reduction basis. The method proposed is then applied to a co-rotational finite element formulation that is well-suited for geometrically nonlinear problems. Numerical results reveal that the end-shortening effect is very important, in which a conventional modal reduction method does not work unless the full model is used. It is demonstrated that the modal derivative approach yields the best compromised result and is very promising for substructuring large-scale geometrically nonlinear problems.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.37 no.1
• /
• pp.9-16
• /
• 2024

Using the proper orthogonal decomposition (POD) based intrusive reduced order model (ROM), the total degrees of freedom of the structural system can be significantly reduced and the critical time step satisfying the conditional stability increases in the explicit time integrations. In this study, therefore, the changes in the critical time step in the explicit time integrations are investigated using both the POD-ROM and Voronoi-cell lattice model (VCLM). The snapshot matrix is composed of the data from the structural response under the arbitrary dynamic loads such as seismic excitation, from which the POD-ROM is constructed and the predictive capability is validated. The simulated results show that the significant reduction in the computational time can be achieved using the POD-ROM with sufficiently ensuring the numerical accuracy in the seismic analyses. In addition, the validations show that the POD based intrusive ROM is compatible with the Voronoi-cell lattice based explicit dynamic analyses. In the future study, the research results will be utilized as an elemental technology for the developments of the real-time predictive models or monitoring system involving the high-fidelity simulations of structural dynamics.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.27 no.1
• /
• pp.193-200
• /
• 2021

In this study, an analysis technique using static condensation is proposed for an efficient local nonlinear static analysis. The static condensation method is a model reduction method based on the degrees of freedom, and the analysis model is divided into a target part and a condensed part to be omitted. In this study, the nonlinear and linear parts were designated to the target and the omitted parts, respectively, and both the stiffness matrix and load vector corresponding to the linear part were condensed into the nonlinear part. After model condensation, the reduced model comprising the stiffness matrix and the load vector for the nonlinear part is constructed, and only this reduced model was updated through the Newton-Raphson iteration for an efficient nonlinear analysis. Finally, the efficiency and reliability of the proposed analysis technique were presented by applying it to various numerical examples.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.5
• /
• pp.483-489
• /
• 2015

In this paper, we propose monocular visual simultaneous localization and mapping (SLAM) in the large-scale environment. The proposed method continuously computes the current 6-DoF camera pose and 3D landmarks position from video input. The proposed method successfully builds consistent maps from challenging outdoor sequences using a monocular camera as the only sensor. By using a binary descriptor and metric-topological mapping, the system demonstrates real-time performance on a large-scale outdoor dataset without utilizing GPUs or reducing input image size. The effectiveness of the proposed method is demonstrated on various challenging video sequences.

• Vending industry
• /
• v.2 no.5 s.6
• /
• pp.56-62
• /
• 2002

담배자판기의 신규설치를 금지하고 기존 설치된 자판기마저 전면철거하도록 하는 보건복지부의 초강력 규제안이 마침내 철회가 되게 되었다. 보건복지부는 올 들어 확대되는 금연정책에 편승, 기존 흡연 구역 내 담배자판기 신규설치를 금지하고, 기존 설치된 제품들마저 전면철거하는 규제를 담은 국민건강증진법 시행령 개정안을 지난 4월 공고하며 그 입법추진을 진행한 바 있다. 이 공고안은 그간 국무총리실 산하 규제개혁위원회 분과위원회에 상정되어 1,2차 심의를 진행해 오다 지난 9월 27일 본회의를 통해 '보건복지부의 흡연구역 내 담배자판기 신규설치 금지 및 기존 자판기 철거는 명백히 영업활동 자유 및 재산권 침해에 해당된다.'는 이유로 이를 철회토록 하는 결정을 진행했다. 이 결정을 담은 국민건강증진법 개정안은 조만간 법제처 심사 및 차관회의 등을 거쳐 최종 확정 되게 된다. 이같은 규제개혁위원회의 결정은 협회를 중심으로 한 산업의 적극적인 대응이 있었기에 가능했다. 성인인증장치 도입을 통해 청소년 흡연문제를 완전, 해결하겠다는 산업계의 적극적인 자율대책에도 불구하고 아예 담배자판기를 뿌리 채 뽑겠다는 보건복지부의 행정만능주의적인 발상은 도저히 수용하지 못할 부당한 처사라는 데 관련업계가 인식을 같이 했다. 따라서 이를 반대하는 산업계 입장을 분명히 하며 분명히 하며 적극적인 저지 대응을 최근까지 진행해 왔다. 협회에서는 1차적으로 보건복지부 건강증진과에 담배자판기 전면철거에 대한 산업계 반대 입장을 피력하는 소견서 제출하고 적극적인 산업계의 반대의지를 피력하는 작업을 진행했다. 또한 청소년보호위원회를 통해 청소년 흡연감소를 위한 성인인증 담배자판기 설치 활용방안 건의하며 담배자판기의 긍정적인 활용측면을 집중 부각시키기도 했다. 재정경제부를 통해서는 담배사업법 관련 담배자판기 설치기준에 대한 질의를 통해 현행 관련법 내에서의 설치기준을 명확히 하기도 했다. 이같은 대응에 있어서의 핵심 설득 논리는 담배자판기가 이제는 성인인증장치 부착을 통해 청소년 및 사회적 위해 요인을 극소화 할 수 있다는 점에 있었다. 과거와는 달리 담배자판기가 오히려 청소년의 담배 구입루트 차단이라는 긍정적 역할을 할 수 있는 시점에 있어 이를 전면규제하기보다는 합법적인 설치 환경을 확보하여 사회적으로 떳떳하게 존재가치를 평가받을 수 있게 해달라는게 산업계의 초지일관의 주장이었던 것. 협회는 이같은 주장이 결코 산업계의 이기만이 아니라 세계적인 추세라는 점, 또 담배자판기를 전면철거까지 하면서 과당규제를 할 명분이 부족하다는 점을 반대논리로 적극 내세웠다. 규제개혁위원회가 이번 공공 이용시설 중 흡연구역으로 지정된 장소 내에 담배자판기는 설치 금지 및 철거규제에 철회권고를 내리게 된 것은 이러한 산업계의 주장을 적극 수용함에 힘입은 바 크다. 규제개혁위원회는 이번 결정의 주된 이유로 우선 기설치된 자판기에 대한 철거는 재산권 침해로 위헌 소지가 있음을 들고 있다. 또한 흡연자를 위한 흡연구역내에서마저 자판기 설치를 금지하는 등의 규제는 과도하며 흡연자의 권익보호 역시도 필요함을 인정하고 있다. 따라서 전면적인 규제보다는 청소년 이용통제 가능한 흡연구역에 한하여 담배자판기를 설치토록한 현행규정의 실질적 관리를 강화하며, 전체적으로 흡연구역을 축소 제한하는 방향으로 추진함이 바람직하다는 의견을 제시했다. 규제개혁위원회의 이번 결정으로 흡연구역 내 담배자판기의 설치는 현행법의 적용을 받게 되며, 산업계의 자율대책대로 성인인증 장치를 부착한 담배자판기의 설치 확대가 크게 촉발될 수 있을 것으로 기대된다. 담배자판기가 적극적이고 능동적인 사회적 역할을 할 수 있을 때 자연 이를 반대할 수 있는 명분도 약해질 수 밖에 없다. 산업계는 보다 신뢰성 있게 청소년 이용을 차단할 수 있는 담배자판기 관련 기술 수준을 향상시켜야 할 것이며, 협회에서는 담배자판기의 공공성과 역할에 대한 지속적인 계몽 홍보를 통해 소비자 인식을 고양시켜 나갈 수 있게 해야 할 것이다. 비록 전면 규제 완화가 어렵고 힘든 길이기는 하지만 소비자에게 신뢰성을 부여하고 청소년의 담배 구입 루트 차단에 혁혁한 역할을 다할 수 있게 된다면 그 입지기반을 재평가 받을 수 있게 될 것이다. 담배자판기의 내일은 이제 암울함이 아닌 서서히 희망을 비치는 쪽으로 급선회되고 있다.