A robust updated normal plane scheme for geometric non-linear structural analysis

In a conventional method of structural analysis, for modeling and analysis of jacket type offshore platforms, member connections are assumed to be rigid. In this method, members are rigidly connected which means there is no axial or rotational deformation at the end of brace member relative to chord axis. However in reality local deformations occur at chord surface due to applied loads from braces, which mean tubular joints are considerably flexible especially in non linear range of deformations. Therefore results of analysis based on rigid connections assumption differ from real behavior of the structure. Various research works have been carried out in the past on tubular joints and different methods have been presented in order to include the effect of joint flexibility in structural analysis. Most of these methods are just valid in elastic range but some non-linear methods have also been developed for simple tubular joints. In order to carry out a nonlinear analysis on a 3-D model of an offshore platform with multi-brace / multi-planar tubular joints, none of these simplified methods is applicable. In this case a complete model of tubular joints by non-linear shell elements is the most accurate one which is not only valid for non-linear analyses but also covers all type of tubular joints. In this paper two samples of offshore platforms are studied. These platforms are modeled using the following approaches: 1. No modeling of joints as structural elements (rigid connections). 2. Modeling of joint can with nonlinear shell elements (flexible connection). Different types of static non-linear analysis (Push over) are carried out and results are compared. In order to evaluate the results and compare this type of modeling with simplified methods included in professional software for the analysis of offshore structures, aforementioned platforms are also analyzed using the Fessler and MSL models to include effects of joint flexibility. The results of these types of modeling are also compared with the previous ones.

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NOVEL NON-LINEAR ELASTIC STRUCTURAL ANALYSIS WITH GENERALISED TRANSVERSE ELEMENT LOADS USING A REFINED FINITE ELEMENT

10.18057/ijasc.2015.11.2.6 ◽

2015 ◽

pp. 223-249

Author(s):

C.K. Iu ◽

◽

M.A. Bradford ◽

Keyword(s):

Finite Element ◽

Structural Analysis ◽

Linear Elastic ◽

Non Linear

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WHETHER WE ARE READY TO PROCEED TO A NONLINEAR ANALYSIS AT DESIGNING?

International Journal for Computational Civil and Structural Engineering ◽

10.22337/1524-5845-2017-13-3-86-102 ◽

2017 ◽

Vol 13 (3) ◽

pp. 86-102

Author(s):

Anatoly V. Perelmuter ◽

Victor V. Tur

Keyword(s):

Structural Analysis ◽

Linear Analysis ◽

Design Codes ◽

Limit States ◽

Advanced Method ◽

Additional Tool ◽

Special Cases ◽

Practical Design ◽

Non Linear ◽

Actual Design

Despite of the fact that in recent years the non-linear analysis is considered as an advanced method of structural analysis, the basic requirements, which are associated with this method in actual Design Codes, are often vague and declarative without clear comments. The main problems, which must be solved for implementation of the non-linear analysis in practical design, are discussed. It was shown, that currently non-linear analysiscan be considered as an additional tool, which is utilizing for limit states checking in special cases, for example, checking of the structural robustness in accidental design situation.

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On the Automation of Non-Linear Behavioral Structural Analysis. Guidance and Quality Control

Integrated Design and Manufacturing in Mechanical Engineering ’98 ◽

10.1007/978-94-015-9198-0_22 ◽

1999 ◽

pp. 175-182

Author(s):

J. P. Pelle ◽

D. Ryckelynck

Keyword(s):

Quality Control ◽

Structural Analysis ◽

Non Linear

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Advances in Offshore Structural Analysis Using Response-Based Time-Domain Approach

10.4043/31280-ms ◽

2021 ◽

Author(s):

Johyun Kyoung ◽

Sagar Samaria ◽

Jeffrey O’Donnell ◽

Sudhakar Tallavajhula

Keyword(s):

Structural Analysis ◽

Fracture Mechanics ◽

Time Domain ◽

Structural Strength ◽

Structural Response ◽

Life Extension ◽

Environmental Loads ◽

Analysis Methodology ◽

Non Linear ◽

The Time Domain

Abstract Demand for life extension assessments of floating offshore platforms continues to grow worldwide. Conventional structural analysis methods have limited ability to accurately capture non-linear environmental loading, non-linear loading by the mooring and riser systems, and resulting higher order hull responses. The uncertainties are typically managed by the factors of safety applied in the structural analysis. Time domain structural analyses have long promised to improve analysis accuracy and reduce these uncertainties. This paper describes a comprehensive and practical time domain structural analysis methodology applied to a deep-water semi-submersible-type floating platform including results for structural strength and fatigue. In addition, the time domain structural analysis was extended for use in fracture mechanics and the assessment of notional weld flaws to facilitate specification of impactful non-destructive examination (NDE). Present time domain structural analysis methodology employs a response-based finite element analysis (FEA) conducted in the time domain. All external environmental loads and inertial forces are converted to a response-based stress-time history. Previously, conventional time domain structural analysis involves massive computation resources to resolve solutions at every time interval. Present methodology significantly improves computational efficiency to be practical in real-world problems. The improvement is achieved by decomposing the structural response into a set of multiple load components selected on the bases of function for hull motion response and environmental loadings. Structural response in time domain is directly obtained by synthesizing the load components. An actual time domain structural response is captured effectively and efficiently to simulate the strength and fatigue criterion for the structure with consistent environmental loads and hull responses. Utilizing the level of detail provided by the time domain structural analysis methodology, a fracture mechanics evaluation of notional initial flaws (engineering criticality assessments – ECAs) can be conducted providing meaningful technical basis for in-service NDE and life extension assessments. The procedures for fatigue crack growth and fracture documented in BS 7910 were employed to derive the smallest initial flaws (critical initial flaws) that may result in structural failure during a facility's lifetime. A comparison indicates that conventional structural analysis methods provide conservative results for both structural strength and fatigue damage calculations resulting from the linear assumption of environmental loads and hull responses. Present time domain structural analysis methodology provides an innovative, cutting-edge approach providing accuracy and fewer uncertainties, which can be pragmatically used during a typical project.

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