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During service period, offshore wind turbines are subjected to both monotonic and cyclic loads, causing the rotation or translation of caisson foundations in the seabed. However, most of the existing studies focused on the performance of caisson foundations under monotonic static loading, and there are few studies about the effects of caisson-soil contact mode and soil strength reduction during installation in numerical simulations. This paper therefore systematically investigates the bending moment capacity and failure mechanism of caisson foundations under monotonic and cyclic loading in clay using finite element analyses. Three typical caisson-soil contact modes in different loading scenarios are considered, and the influence of soil strength condition, caisson aspect ratio on the bending moment capacity and failure mechanism of caisson foundations is explored. It is found that under monotonic loading, the bending moment capacity in the tensionless mode and the fully-bonded mode could be used as the lower and upper limit, respectively. Under cyclic loading, the fully-bonded mode always yields the highest moment capacity, while the frictionless mode and the tensionless mode produce the lowest in the case with small loading amplitude and the case with large loading amplitude, respectively. In addition, the behavior of cumulative angular displacement under combined load of wind and wave is also studied to provide insight for caisson foundation design. • The mechanical response of caisson foundation subjected to both monotonic and cyclic loading is numerically investigated. • Three typical caisson-soil contact modes in different loading scenarios are considered. • Recommendations in the design of caisson foundations under different loading conditions are provided. [ABSTRACT FROM AUTHOR]

Marine engineering structures may be subjected to various levels of vessel collisions, causing different degrees of damage to the RC piles. However, the influence of different combinations of impact mass and velocity under the same initial kinetic energy or momentum on the impact behavior of RC piles has not been explored. A numerical investigation of the impact responses of RC pile structures (including plumb piles and inclined pile groups) considering the material strain rate effect is carried out using the software ABAQUS/Explicit in this paper. Parametric studies are conducted based on the validated finite element models of RC piles subjected to horizontal impact. The internal force distributions, as well as the effect of the impact kinetic energy and the momentum (including different combinations of impact mass and initial velocity) on the impact response of RC piles, are discussed. The results indicate that the development path of the bending moment‒overall structural displacement curves in the plastic hinge regions of RC piles are almost identical under both impact and static loading conditions. Compared to momentum, the impact response of RC piles is insensitive to the variation of impact kinetic energy with different combinations of impact mass and velocity. Therefore, the impact kinetic energy is more suitable for evaluating the structural deformation of RC piles after impact. Finally, a performance-based impact-resistance design framework for RC piles is proposed. • A numerical investigation of the impact responses of RC pile structures is carried out. • The internal force distributions on the impact response of RC piles are discussed. • The effect of different combinations of impact mass and initial velocity on the response of RC piles is studied. • A performance-based impact-resistance design framework for RC piles is proposed. [ABSTRACT FROM AUTHOR]

Internal solitary waves with a huge amount of energy easily trigger the large dynamic responses of riser-wellhead system and threaten its structural safety. However, previous studies have only focused on the dynamic response of the riser under internal solitary waves. The riser may experience excessive traction from the platform, especially from the mooring platform, in response to the arrival of internal solitary waves. The bottom of the riser connects to the wellhead system, which in turn exerts a reaction force on the riser. To address this problem, a coupled dynamic model of deep-water drilling mooring platform-riser-wellhead system under internal solitary waves is developed in this paper. A dynamic response analysis method based on the fourth-order Runge-Kutta method and finite element method is also proposed for the mooring platform-riser-wellhead system. A dynamical solver for the coupled system is then developed using MATLAB. The dynamic response characteristics of the riser-wellhead system under internal solitary waves are calculated. Results show that the displacement and bending moment of the system initially increases and then decreases along with the propagation of internal solitary waves, and finally reach equilibrium position. The displacement and bending moment reach their peak before the trough of internal solitary waves passes through the riser-wellhead system. The dynamic responses of the riser-wellhead system under the influence of internal solitary wave loads are much larger than those without the effect of internal solitary wave loads. The riser system experiences shearing loads at the interface of internal solitary waves, which trigger a step-like bending moment variation. The bending moment of the conductor under the mudline is greatly increased by the internal solitary waves. • A coupled dynamic model of deep-water mooring platform-riser-wellhead system under internal solitary waves is developed. • A dynamic response analysis method for the coupled dynamic model is proposed. • The dynamic responses reach their peak with the influence of the trough of internal solitary waves. • The riser-wellhead system has much larger dynamic response under the internal solitary wave loads. • The bending moment of the riser at the interface of internal solitary waves has a "step"-like form. [ABSTRACT FROM AUTHOR]

This study reports a multi-scale structural analyses of a mainline floating double carcass marine hose (nominal diameter 508 mm, length 10.7 m, design pressure 2.1 MPa, weight 4100 kg). A material change in the reinforcement cords of the traditional hose is proposed, from polyester and polyamide to hybrid aramid/polyamide cords, allowing an improvement in design, reducing weight and increasing flexibility. Two models have been developed to obtain the hose responses. Firstly, a finite element model of the traditional system was built to perform a macro-scale analysis of global hydrodynamics loads in the hose line using Orcaflex™ software. Then, a non-linear finite element model was developed for meso-scale analysis using Abaqus™ software. Rubber and cords were modeled using hyperelastic models, and axial, bending and torsional stiffnesses were evaluated. Experimental tests were carried out to assess the mechanical response of an actual full-scale hose. The reduced number of layers of the hose using hybrid cords, compared to the traditional one, allowed a reduction in weight of 15%, and brought also a decrease in specific axial, torsional and bending stiffnesses of 43.9%, 52.2% and 21.6%, respectively. The multi-scale analysis predicted well the structural response of the hose line, and the reduced potential failure may increase life-time of the structure. [ABSTRACT FROM AUTHOR]

This paper concerns the fracture assessment of a clad pipeline subjected to large bending moment, and identifies different parameters influencing the fracture behaviors. The evolution of Crack Tip Opening Displacement (CTOD) of a pipeline containing a canoe shape crack on the external surface of the girth weld is studied under pure bending and combined pure bending and internal pressure through 3D elastic-plastic Finite Element (FE) simulations. Various parameters affecting the evolution of CTOD like crack depth, crack length to perimeter diameter ratio, internal pressure and the weld geometrical configurations have been investigated. It is observed that only the average width of the weld has a significant influence on the fracture response under pure bending, while the weld reinforcement height and fusion line slope have a moderate influence on the fracture behavior under biaxial loading. The crack at the interface between the weld and back steel has a similar fracture response to that of a crack located in the weld with equivalent effective crack depth. Finally, a strain based Failure Assessment Diagram (FAD) is proposed and compared with the fracture assessments produced by BS7910:2013, and 3D elastic-plastic FE simulations suggest that the British Standard is more conservative especially for deep cracks. [ABSTRACT FROM AUTHOR]

This paper addresses collapse behaviour of Very Large Floating Structure (VLFS) under extreme vertical bending moment. The study is performed as part of risk analysis to evaluate the consequence of a rare collapse event. Elastic and plastic deformation of VLFS develops under the extreme vertical bending moment while the deformation interacts with the fluid around VLFS. Therefore, hydro-elastoplasticity analysis need be developed taking account of these effects. In this study, the whole VLFS structure is modeled as two elastic beams with an elasto-plastic hinge embedded at the connection. The structural deformation is formulated by using finite element method (FEM). The hydrodynamic behaviour is modeled by using Rankine source panel method in time domain based on two-dimensional potential theory. The two models are coupled. A series of scaled model tests is performed for validation. Simulation and tank test results for the basic collapse behaviour of VLFS are presented and discussed. The numerical method is applied further to a realistic VLFS design to clarify its collapse behaviour. [ABSTRACT FROM AUTHOR]

Present article proposes improved assessment of the ultimate bending capacity (ultimate bending moment), i.e. enhancement of the ultimate limit state evaluation in the concept design of the monotonous thin-walled structures predominantly subjected to vertical bending loads during their exploitation. An alternative progressive collapse analysis method is proposed, which incorporates direct consideration of various relevant distributed load effects and consequently enables more sophisticated evaluation of the ultimate bending capacity and more accurate and reliable identification of the critical cross section and its collapse sequence. Relevant aspects of the employed approximate model for the cross sectional warping due to vertical bending are considered and determination of the (longitudinal) warping displacements and strains, shear strains and stresses, as well as the corrected longitudinal strains is described. Influence of the (ultimate) shear capacity on the (ultimate) bending capacity is discussed and detailed description and critical overview of the proposed method is given. Finally, various aspects of the considered problem and accuracy of the proposed approach are discussed and demonstrated on example of the thin-walled box-girder, whereby detailed comparison of the results obtained by the proposed approach and nonlinear finite element method analyses is given. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we propose a numerical procedure to analyze floating plate structures with multiple hinge connections in regular waves and investigate the maximum bending moment and deflection in the plate structures. The directly coupled equations of motion for the hydroelastic analysis are discretized by the boundary element method for fluid and the finite element method for plates. The hinge connection is modeled by releasing the rotational degrees of freedom of the plate finite elements, in which a complete condensation procedure is used considering structural mass and stiffness and fluid-structure interaction terms. Wave tank experiments have been performed to verify the numerical results. The modeling capability of the proposed numerical procedure is demonstrated through floating plate problems with 1- and 2-directional multiple hinge connections. The numerical analyses show the effect of the number of hinge connections used on the maximum bending moment and deflection of the floating plate structures according to the aspect ratio, bending stiffness and incident wavelength. [Copyright &y& Elsevier]

Abstract: This study proposes a new procedure for the estimation of stranding forces and their contact positions. The method is based on the measurement of a few characteristic on-site parameters, i.e., the draughts and bending moments acting on a stranded ship. A procedure that estimates penetration into the ship bottom based on knowledge of the resistance versus penetration relationship is also presented. The seabed topology is parameterized by a paraboloid. This geometry can, in principle, characterize a wide range of obstructions, from sharp rocks to large shoals. Nonlinear finite element analysis is used to simulate various stranding situations and to generate the corresponding resistance versus penetration curves. The present method provides insight into the identification of real stranding scenarios in terms of the location of obstructions, their possible shapes and the corresponding resistance-penetration curves. The proposed methodology represents a first step towards a tool for quick decision making during salvage operations. The ultimate goal is to allow near real-time prediction of the risk of penetration into cargo tanks and hull girder failure. To demonstrate the effectiveness of the proposed method, it is applied to a simulated trial stranding scenario. [Copyright &y& Elsevier]

Abstract: This is the second of two companion papers dealing with nonlinear finite element modelling and ultimate strength analysis of the hull girder of a bulk carrier under Alternate Hold Loading (AHL) condition. The methodology for nonlinear finite element modelling as well as the ultimate strength results from the nonlinear FE analyses was discussed in the companion paper (Part 1). The purpose of the present paper is to use the FE results to contribute towards developing simplified methods applicable to practical design of ship hulls under combined global and local loads. An important issue is the significant double bottom bending in the empty hold in AHL due to combined global hull girder bending moment and local loads. Therefore, the stress distributions in the double bottom area at different load levels i.e. rule load level and ultimate failure load level are presented in detail. The implication of different design pressures obtained by different rules (CSR-BC rules and DNV rules) on the stress distribution is investigated. Both (partially) heavy cargo AHL and fully loaded cargo AHL are considered. Factors of influence of double bottom bending such as initial imperfections, local loads, stress distribution and failure modes on the hull girder strength are discussed. Simplified procedures for determination of the hull girder strength for bulk carriers under AHL conditions are also discussed in light of the FE analyses. [Copyright &y& Elsevier]

Steel stiffened panels are widely used in engineering design and construction. However, numerical modeling and analysis effort for a three-dimensional (3D) stiffened panel may be notable, especially for the ultimate limit state of ship structures. Therefore, a homogenization method is outlined that transforms 3D stiffened panel into an Equivalent Single Layer (ESL) concerning the same mechanical behavior. ESL stiffnesses are obtained with a unit cell analyses based on stiffened panel where periodicity is imposed with boundary conditions based on a first-order shear deformation theory (FSDT). Stiffnesses were determined from the first derivative of a membrane force and bending moment obtained with numerical simulations. The effect of initial imperfection shape was included in the analysis to account for local and global buckling behavior. ESL with non-linear stiffness was implemented in Abaqus UGENS subroutine, allowing incremental evaluation of stiffness. Ultimate strength prediction of a steel grillage model with ESL finite element analysis was in excellent agreement with detailed 3D FEM analysis. The key in this analysis was consideration of non-linear ESL stiffness as linear analysis was unable to detect the point where ultimate strength capacity of the grillage was reached. • Homogenization method aims to transform the detailed 3D stiffened panel into an equivalent single layer (ESL). • Geometrical and material nonlinearities were considered in the stiffness calculation of ESL. • UGENS subroutine was invoked to involve the non-nonlinear membrane force and bending moment of ESL. • Ultimate strength of stiffened panel was accurately determined with current non-linear ESL approach. [ABSTRACT FROM AUTHOR]

Numerical research on the stress concentration factors (SCFs) in uniplanar tubular joints is abundantly reported in literature. However, it has been shown that SCF equations for uniplanar joints can lead to both under- or overestimation of the SCFs in multi-planar joints. In this paper, a parametric finite element study of 81 different three-planar KT joints subjected to five different in-plane bending loading conditions is performed. The effects of different non-dimensional geometrical parameters on the SCF values at the crown locations of the central and outer braces are studied. Based on nonlinear regression analyses of the finite element results, a new set of SCF equations is developed and presented. • Stress concentration factors at central and outer braces are studied for three-planar DKT joints. • Effects of non-dimensional geometrical parameters on the chord-side SCFs are quantified. • 81 FE models subjected to the five in-plane bending loading modes were studied. • 39 parametric formulas are presented for stress concentration factors. [ABSTRACT FROM AUTHOR]