• Title/Summary/Keyword: FE-based equations

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Local joint flexibility equations for Y-T and K-type tubular joints

  • Asgarian, Behrouz;Mokarram, Vahid;Alanjari, Pejman
    • Ocean Systems Engineering
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    • v.4 no.2
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    • pp.151-167
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    • 2014
  • It is common that analyses of offshore platforms being carried out with the assumption of rigid tubular joints. However, many researches have concluded that it is necessary that local joint flexibility (LJF) of tubular joints should be taken into account. Meanwhile, advanced analysis of old offshore platforms considering local joint flexibility leads to more accurate results. This paper presents an extensive finite-element (FE) based study on the flexibility of uni-planner multi-brace tubular Y-T and K-joints commonly found in offshore platforms. A wide range of geometric parameters of Y-T and K-joints in offshore practice is covered to generate reliable parametric equations for flexibility matrices. The formulas are obtained by non-linear regression analyses on the database. The proposed equations are verified against existing analytical and experimental formulations. The equations can be used reliably in global analyses of offshore structures to account for the LJF effects on overall behavior of the structure.

Numerical validation of burst pressure estimation equations for steam generator tubes with multiple axial surface cracks

  • Kim, Ji-Seok;Lee, Myeong-Woo;Kim, Yun-Jae;Kim, Jin-Weon
    • Nuclear Engineering and Technology
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    • v.51 no.2
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    • pp.579-587
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    • 2019
  • This paper provides further validation of the burst pressure estimation equations for multiple axial surface cracked steam generator tubes, recently proposed by the authors based on analytical local collapse load approach against systematic FE damage analysis results of Alloy 690 tubes with twin axial surface cracks. Wide ranges of the relative crack depth and multiple crack configurations are considered. Comparison shows good agreements, giving sufficient confidence of the proposed equations.

Alloying Effects of BCC-Fe Based Low-Alloy Steel on Mechanical and Thermal Expansion Properties for a Plant Engineering: Ab Initio Calculation (플랜트 엔지니어링을 위한 BCC-Fe 기반 저합금강의 기계적 및 열팽창 특성 합금 효과: Ab Initio 계산)

  • Myungjae Kim;Jongwook Kwak;Jiwoong Kim;Kyung-Nam Kim
    • Korean Journal of Materials Research
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    • v.33 no.10
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    • pp.422-429
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    • 2023
  • High-strength low-alloy steel is one of the widely used materials in onshore and offshore plant engineering. We investigated the alloying effect of solute atoms in α-Fe based alloy using ab initio calculations. Empirical equations were used to establish the effect of alloying on the Vicker's hardness, screw energy coefficient, and edge dislocation energy coefficient of the steel. Screw and edge energy coefficients were improved by the addition of V and Cr solute atoms. In addition, the addition of trace quantities of V, Cr, and Mn enhanced abrasion resistance. Solute atoms and contents with excellent mechanical properties were selected and their thermal conductivity and thermal expansion behavior were investigated. The addition of Cr atom is expected to form alloys with low thermal conductivity and thermal expansion coefficient. This study provides a better understanding of the state-of-the-art research in low-alloy steel and can be used to guide researchers to explore and develop α-Fe based alloys with improved properties, that can be fabricated in smart and cost-effective manners.

Non-Linear Fracture Mechanics Analyses for Axial Semi-Elliptical Surface Cracked Pipes (배관 내 축방향 반타원 표면균열에 대한 비선형 파괴역학 해석)

  • Kim, Jin-Su;Kim, Yun-Jae;Kim, Young-Jin
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.143-148
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    • 2003
  • This paper provides two types of engineering J estimation equations for cylinders with finite internal axial surface cracks under internal pressure. The first type is the so-called GE/EPRI type J estimation equation based on Ramberg-Osgood materials. Based on detailed 3-D FE results the GE/EPRI-type J estimation equation along the crack front is proposed and validated for Ramberg-Osgood materials. For more general application, the developed GE/EPRI-type solutions are then re-formulated based on the reference stress concept. The proposed reference stress based J estimation equation has good agreement between the FE results and the proposed reference stress based J estimation provides confidence in the use of the proposed method for elastic-plastic fracture mechanics of pressurised piping

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Seismic behavior of soft storey mid-rise steel frames with randomly distributed masonry infill

  • Quayyum, Shahriar;Alam, M. Shahria;Rteil, Ahmad
    • Steel and Composite Structures
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    • v.14 no.6
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    • pp.523-545
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    • 2013
  • In this study, the effect of presence and distribution of masonry infill walls on the mid-rise steel frame structures having soft ground storey was evaluated by implementing finite element (FE) methods. Masonry infill walls were distributed randomly in the upper storey keeping the ground storey open without any infill walls, thus generating the worst case scenario for seismic events. It was observed from the analysis that there was an increase in the seismic design forces, moments and base shear in presence of randomly distributed masonry infill walls which underlines that these design values need to be amplified when designing a mid-rise soft ground storey steel frame with randomly distributed masonry infill. In addition, it was found that the overstrength related force modification factor increased and the ductility related force modification factor decreased with the increase in the amount of masonry infilled bays and panels. These must be accounted for in the design of mid-rise steel frames. Based on the FE analysis results on two mid-rise steel frames, design equations were proposed for determining the over strength and the ductility related force modification factors. However, it was recommended that these equations to be generalized for other steel frame structure systems based on an extensive analysis.

A Study of Plastic Deformation Mechanisms in $Fe_3$Al Intermetallics Alloys by Inelastic Deformation Theory (비탄성 변형이론을 이용한 $Fe_3$Al 금속간화합물의 소성변형 기구 고찰)

  • 정호철
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.03b
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    • pp.180-183
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    • 1999
  • It is well known that Fe3Al intermetallic compound shows an anomalous peak of the yield strength at about 50$0^{\circ}C$ and then decrease at higher temperatures The dislocation structure was examined by transmission electron microscopy and high temperatures. The dislocation structure was examined by transmission electron microscopy and high temperature mechanical properties were examined by tensile and load relaxation tests. The flow stress curves obtained from load relaxation tests were then analyzed in terms of internal variable deformation theory. it was found that the flow curves consisted of three micro-deformation mechanisms -i. e inelastic deformation mode plastic deformation mode and dislocation creep deformation mode depending on both dislocation structure and deformation temperature. The flow curves could be well described by the constitutive equations of these three micro-deformation mechanisms based on the internal variable deformation theory.

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An iterative approach for time-domain flutter analysis of bridges based on restart technique

  • Zhang, Wen-ming;Qian, Kai-rui;Xie, Lian;Ge, Yao-jun
    • Wind and Structures
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    • v.28 no.3
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    • pp.171-180
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    • 2019
  • This paper presents a restart iterative approach for time-domain flutter analysis of long-span bridges using the commercial FE package ANSYS. This approach utilizes the recursive formats of impulse-response-function expressions for bridge's aeroelastic forces. Nonlinear dynamic equilibrium equations are iteratively solved by using the restart technique in ANSYS, which enable the equilibrium state of system to get back to last moment absolutely during iterations. The condition for the onset of flutter instability becomes that, at a certain wind velocity, the amplitude of vibration is invariant with time. A long-span suspension bridge was taken as a numerical example to verify the applicability and accuracy of the proposed method by comparing calculated results with wind tunnel tests. The proposed method enables the bridge designers and engineering practitioners to carry out time-domain flutter analysis of bridges in commercial FE package ANSYS.

A Study on Structural Integrity Assessment of Pipeline using Weight Function Solution (가중함수법을 적용한 파이프라인 구조건전성평가에 관한 연구)

  • Noh, Ki-Sup;Oh, Dong-Jin;Kim, Myun-Hyun
    • Journal of Welding and Joining
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    • v.35 no.1
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    • pp.55-60
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    • 2017
  • There are many Industry Code and Standard (ICS) for Structural Integrity Assessment (SIA) on welded structure with defect. The general ICSs, such as R6, BS 7910 and API 579-1/ASME FFS-1, provide equations to determine the upper bound residual stress profiles based on collections from many literatures. However, these residual stress profiles used in the SIA cause the conservative design for welded structures. In this study, the structural integrity assessment for girth weld in pipeline has been conducted based on fracture mechanics. In addition, thermo-elastic plastic FE analysis was performed for evaluating the residual stress of girth weld in pipeline. The weight function solution is used to determine the stress intensity factor using the residual stress profile obtained by the FE analysis. This approach can account for redistribution and relaxation of residual stress as the defects grow. In order to the evaluate quantitative comparison between BS 7910 and weight function solution, structural integrity assessment determining allowable crack size on cracked pipe was performed with failure assessment diagram.

Proposals for flexural capacity prediction method of externally prestressed concrete beam

  • Yan, Wu-Tong;Chen, Liang-Jiang;Han, Bing;Wei, Feng;Xie, Hui-Bing;Yu, Jia-Ping
    • Structural Engineering and Mechanics
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    • v.83 no.3
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    • pp.363-375
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    • 2022
  • Flexural capacity prediction is a challenging problem for externally prestressed concrete beams (EPCBs) due to the unbonded phenomenon between the concrete beam and external tendons. Many prediction equations have been provided in previous research but typically ignored the differences in deformation mode between internal and external unbonded tendons. The availability of these equations for EPCBs is controversial due to the inconsistent deformation modes and ignored second-order effects. In this study, the deformation characteristics and collapse mechanism of EPCB are carefully considered, and the ultimate deflected shape curves are derived based on the simplified curvature distribution. With the compatible relation between external tendons and the concrete beam, the equations of tendon elongation and eccentricity loss at ultimate states are derived, and the geometric interpretation is clearly presented. Combined with the sectional equilibrium equations, a rational and simplified flexural capacity prediction method for EPCBs is proposed. The key parameter, plastic hinge length, is emphatically discussed and determined by the sensitivity analysis of 324 FE analysis results. With 94 collected laboratory-tested results, the effectiveness of the proposed method is confirmed, and comparisons with the previous formulas are made. The results show the better prediction accuracy of the proposed method for both stress increments and flexural capacity of EPCBs and the main reasons are discussed.

Squeal Analysis of Disc Brake Using Analytical-FE Squeal Model (스퀼융합모델을 이용한 디스크 브레이크 스퀼 소음 연구)

  • Kang, Jaeyoung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.11
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    • pp.6406-6411
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    • 2014
  • This paper presents the analytical-FE (finite element) squeal model, which can provide the efficient simulation time and accuracy. The system geometry and the extraction of the vibration modes were constructed using the finite element method. Instead, the friction contact model was derived from theoretical contact kinematics of the rotating disc and the stationary pads. This modeling procedure was incorporated into the perturbed equations of motion based on the finite elements of the system. Throughout the analytical-FE squeal model, the accuracy of linear stability analysis and the simulation time of FE squeal analysis were improved. In addition, the sensitivity of contact stiffness on brake squeal and the mode-coupling mechanism were provided by the system parameter study.