• Title/Summary/Keyword: numerical stability

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Static, Dynamic and Buckling Analyses of a Power Transmission Tower under Wind Load (풍하중을 받는 송전철탑의 정적, 동적 및 좌굴해석)

  • Jung, Hyung-Jo;Shin, Dong-Seung;Moon, Byoung-Wook;Park, Ji-Hun;Lee, Sung-Kyung;Min, Kyung-Won
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.19 no.4 s.74
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    • pp.369-374
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    • 2006
  • This paper describes dynamic characteristics of a power transmission tower consisting of lots of power lines and insulators. A numerical 3D modeling for the static, dynamic and buckling analyses of the power transmission tower is presented considering the case when the power lines are cut. Eigenvalue analysis indicates that the transmission tower shows different behavior comparing to usual structures governed by several low modes. The transmission tower is governed by lots of modes. It is verified that the transmission tower is structurally safe against the static wind and buckling loads. But the structural and buckling safety is not guaranteed when all power lines are cut, which comes to collapse the transmission tower. Further study is in need to overcome such case. Wind dynamic analysis shows that fluctuating wind loads increase the response of the tower.

The Dynamic Nonlinear Analysis of Shell Containment Building subjected to Aircraft Impact Loading (항공기 충돌에 대한 쉘 격납건물의 동적 비선형해석)

  • 이상진
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.15 no.4
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    • pp.567-578
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    • 2002
  • The main purpose of this study is to investigate the dynamic behaviour of containment building in nuclear power plant excited by aircraft impact loading using a lower order 8-node solid element. The yield and failure surfaces for concrete material model is formulated on the basis of Drucker-Prager yield criteria and are assumed to be varied by taking account of the visco-plastic energy dissipation. The standard 8-node solid element has prone to exhibit the element deficiencies and the so-called B bar method proposed by Hughes is therefore adopted in this study. The implicit Newmark method is adopted to ensure the numerical stability during the analysis. Finally, the effect of different levels of cracking strain and several types of aircraft loading are examined on the dynamic behaviour of containment building and the results are quantitatively summarized as a future benchmark.

Development of Grid Reconstruction Method to Simulate Drying/Wetting in Natural Rivers (II): Model Application and Comparison (자연하천에서 마름/젖음 처리를 위한 격자재구성 기법의 개발 (II): 모형의 적용 및 비교.검토)

  • Choi, Seung-Yong;Kim, Sang-Ho;Hwang, Jae-Hong;Han, Kun-Yeun
    • Journal of Korea Water Resources Association
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    • v.42 no.11
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    • pp.989-1004
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    • 2009
  • The objective of this study is to examine validation of Grid Reconstruction Method, which is developed to simulate drying/wetting in complex natural rivers with wetting and drying domain areas. To verify application of the developed model, the model was applied to natural rivers with wetting and drying domain areas such as Han river and Nakdong river. The simulation results have shown good agreements with observed data and the results for the developed model were more accurate and improved stability of numerical computation than those of RMA-2 model. If the analysis of contaminant advection-diffusion and sediment transport are performed with the study results, the results can be effectively applied to river flow analysis and ecological hydraulics.

A Study on the Geometric Optimization of Truss Structures by Decomposition Method (분할최적화 기법에 의한 트러스 구조물의 형상최적화에 관한 연구)

  • 김성완;이규원
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.29 no.4
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    • pp.73-92
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    • 1987
  • Formulation of the geometric optimization for truss structures based on the elasticity theory turn out to be the nonlinear programming problem which has to deal with the cross-sectional area of the member and the coordinates of its nodes simultaneously. A few techniques have been proposed and adopted for the analysis of this nonlinear programming problem for the time being. These techniques, however, bear some limitations on truss shapes, loading conditions and design criteria for the practical application to real structures. A generalized algorithm for the geometric optimization of the truss structures, which can eliminate the above mentioned limitations, is developed in this study. The algorithm proposed utilizes the two-levels technique. In the first level which consists of two phases, the cross-sectional area of the truss member is optimized by transforming the nonlinear problem into SUMT, and solving SUMT utilizing the modified Newton Raphson method. In the second level, which also consists of two phases the geometric shape is optimized utillzing the unindirectional search technique of the Powell method which make it possible to minimize only the objective functlon. The algorithm proposed in this study is numerically tested for several truss structures with various shapes, loading conditions and design criteria, and compared with the results of the other algorithms to examine its applicability and stability. The numerical comparisons show that the two- levels algorithm proposed in this study is safely applicable to any design criteria, and the convergency rate is relatively fast and stable compared with other iteration methods for the geometric optimization of truss structures. It was found for the result of the shape optimization in this study to be decreased greatly in the weight of truss structures in comparison with the shape optimization of the truss utilizing the algorithm proposed with the other area optimum method.

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Evaluation of Track irregularity due to Adjacent Excavation Work on Serviced Urban Transit (도시철도 인접굴착공사에 따른 운행선 궤도의 궤도틀림 분석)

  • Choi, Jung-Youl;Lee, Ho-hyun;Kang, You-Song;Chung, Jee-Seung
    • The Journal of the Convergence on Culture Technology
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    • v.6 no.2
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    • pp.481-487
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    • 2020
  • In this study, finite element analysis was performed to evaluate the track irregularity of the existing track system on urban transit according to the large-scale excavation work that is constructed adjacent to the serviced line. Based on the numerical analysis, the effect of track irregularity generated during the step-by-step construction process was analytically derived, and the stability in terms of track deformation was evaluated through comparison with related standards. As the results, in the case of track irregularity items evaluated based on the relative displacement difference at a certain distance, such as alignment and vertical irregularity, it occurred most clearly at the location where deformation of the existing structure begins, such as the end point of adjacent excavation work. On the other hand, the overall vertical and horizontal displacement of the track was the largest deformation at the center of the construction section. The vulnerable position of the deformed side of the existing structure due to adjacent excavation is analytically proven that the both of the end point section and the center of the construction can be a vulnerable position in terms of track irregularity.

Direct Inelastic Earthquake Design Using Secant Stiffness (할선강성을 이용한 직접비탄성내진설계)

  • 박홍근;엄태성
    • Journal of the Earthquake Engineering Society of Korea
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    • v.8 no.1
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    • pp.17-27
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    • 2004
  • A new earthquake design method performing iterative calculations using secant stiffness was developed. The proposed design method has the advantages of convenience and stability in numerical analysis because it uses elastic analysis. At the same time, the proposed design method can accurately estimate the strength and ductility demands on the members because it performs the analysis on the inelastic behavior of structure using iterative calculation. In the present study, the procedure of the proposed design method was established, and a computer program incorporating the proposed method was developed. Design examples using the proposed method were presented, and its advantages were presented by the comparisons with existing design methods using elastic or inelastic analysis. The proposed design method, as an integrated method of analysis and design, can address the earthquake design strategy devised by the engineer. such as ductility limit on each member, the design concept of strong column - weak beam, and etc. In addition, through iterative calculations on the structure preliminarily designed only with member sizing, the strength and ductility demands of each member can be directly calculated so as to satisfy the given design strategy. As the result. economical and safe design can be achieved.

Development of non-fragile $H_{\infty}$ controller design algorithm for singular systems (특이시스템의 비약성 $H_{\infty}$ 제어기 설계 알고리듬 개발)

  • Kim, Jong-Hae
    • Journal of the Institute of Electronics Engineers of Korea SC
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    • v.42 no.6
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    • pp.9-14
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    • 2005
  • In this paper, we consider the synthesis of non-fragile $H_{\infty}$ state feedback controllers for singular systems and static state feedback controller with multiplicative uncertainty. The sufficient condition of controller existence, the design method of non-fragile $H_{\infty}$ controller, and the measure of non-fragility in controller are presented via LMI(linear matrix inequality) technique. Also, the sufficient condition can be rewritten as LMI form in terms of transformed variables through singular value decomposition, some changes of variables, and Schur complements. Therefore, the obtained non-fragile $H_{\infty}$ controller guarantees the asymptotic stability and disturbance attenuation of the closed loop singular systems within a prescribed degree. Moreover, the controller design method can be extended to the problem of robust and non-fragile $H_{\infty}$ controller design method for singular systems with parameter uncertainties. Finally, a numerical example is given to illustrate the design method.

Characteristics of Soil-Nailing Applied to Extension-Grouting Method (확장그라우팅 공법이 적용된 쏘일네일링의 거동특성)

  • Lee, Hyoungkyu;Lee, In
    • Journal of the Korean GEO-environmental Society
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    • v.11 no.3
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    • pp.53-62
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    • 2010
  • In the early 1990s, it was first introduced the soil nailing method for the slope stability and ground excavation and widely used as method of reinforcement. Also the application of soil nailing has been improved and developed. Most recently used for grout soil nailing greatly improve the methods and techniques for self-improvement techniques are classified as soil nailing. As the representative for the grout pressure method to improve the join method pressure grouting and improved method for the self-drilled soil nailing, removable soil nailing, extension grout method. Three dimensional finite difference analysis was used to evaluate characteristics of pull-out behavior of extension grout method. In this paper, it was described a characteristics of pull-out behavior of soil nailing with extension grout method through the result of numerical method.

Wave-Induced Soil Response around Submarine Pipeline (파랑작용에 의한 해저파이프라인 주변지반의 응답특성)

  • Hur, Dong-Soo;Kim, Chang-Hoon;Kim, Do-Sam
    • Journal of Ocean Engineering and Technology
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    • v.21 no.1 s.74
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    • pp.31-39
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    • 2007
  • Recently, the nonlinear dynamic responses among waves, submarine pipeline and seabed have become a target of analyses for marine geotechnical and coastal engineers. Specifically, the velocity field around the submarine pipeline and the wave-induced responses of soil, such as stress and strain inside seabed, have been recognized as dominant factors in discussing the stability of submarine pipeline. The aim of this paper is to investigate nonlinear dynamic responses of soil in seabed, around submarine pipeline, under wave loading. In order to examine wave-induced soil responses, first, the calculation is conducted in the whole domain, including wave field and the seabed, using the VOF-FDM method. Then, velocities and pressures, which are obtained on the boundary between the wave field and the seabed, are used as the boundary condition to compute the wave-induced stress and strain inside seabed, using the poro-elastic FEM model, which is based on the approximation of the Biot's equations. Based on the numerical results, the characteristics of wave-induced soil responses around submarine pipeline are investigated, in detail, inrelation to relative separate distance of the submarine pipeline from seabed. Also, the velocity field around the submarine pipeline is discussed.

Mechanical Characteristic Test of Architectural ETFE Film Membrane (크기최적화 이후에 나타나는 공간구조물의 후 좌굴 거동 변화에 대한 연구)

  • Lee, Sang-Jin;Jung, Ji-Myoung
    • Journal of Korean Association for Spatial Structures
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    • v.9 no.3
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    • pp.75-82
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    • 2009
  • This paper investigates the variation of post-buckling behaviours of spatial structures after sizing optimization with linear assumptions. The mathematical programming technique is used to produce the optimum member size of spatial structures against external load. Total weight of structure is considered as the objective function to be minimized and the displacement occurred at loading point and member stresses of structures are used as the constraint functions. The finite difference method is used to calculate the design sensitivity of objective function with respect to design variables. The post-buckling analysis carried out by using the geometrically nonlinear finite element analysis code ISADO-GN. It is found to be that there is a huge difference between the post buckling behaviours of the initial and optimized structures. Therefore, the stability of optimized spatial structures with linear assumption should be throughly checked by appropriate nonlinear analysis techniques. Finally, the present numerical results are provided as benchmark test suite for future study of large spatial structures.

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