A Consistent Analytical Model to Predict the Structural Behaviour of Flexible Risers Subjected to Combined Loads

2002 ◽  
Author(s):  
Roberto Ramos ◽  
Celso P. Pesce
Keyword(s):  
Analytical Model ◽  
Elastic Behaviour ◽  
Structural Behaviour ◽  
Element Analysis ◽  
Technical Literature ◽  
Combined Loads ◽  
External Pressures ◽  
Flexible Risers ◽  
Linear Elastic Behaviour ◽  
Ocean Environment

This work presents an analytical model for the structural analysis of flexible risers subjected to combined loads of bending, twisting and tension, as well as internal and external pressures applied to the riser. Flexible risers, either umbilical cables or flexible pipes, are complex structures used in offshore oil exploitation activities. Such structures are composed of several concentric polymeric and steel armour layers, which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. The complexity imposed mainly by geometry renders a finite element analysis of these structures practically unfeasible, even if we are to consider that all the materials obey a linear elastic behaviour. So, in order to calculate the stress distribution in the layers, as well as axial, torsional and flexural stiffness values of these structures, analytical methods have been proved to be, till now, a better choice. Using sets of equations, which comprise equilibrium conditions, constitutive equations and geometrical relations, it is possible to solve the problem for all the unknowns. This paper presents a consistent and comprehensive formulation leading to the solution in terms of stresses and deformation components in a flexible riser subjected to the above mentioned combined loads. It is based on the assumption of full-slip of the helically armoured layers after bending is imposed to the pipe. Other main modeling hypotheses are also highlighted in this work. The presented analytical model is, therefore, rather comprehensive and recovers, asymptotically, many results previously published in the technical literature. Comparisons between analytical results using the full-slip model and experimental results obtained in literature are shown and discussed. Some proposals leading to improvement of the presented model are drawn in the conclusions.

A New Analytical Expression to Estimate the Bending Stiffness of Flexible Risers

2003 ◽  
Author(s):  
Roberto Ramos ◽  
Celso P. Pesce ◽  
Clo´vis A. Martins
Keyword(s):  
Elastic Behaviour ◽  
Flexural Stiffness ◽  
Loop Formation ◽  
Structural Behaviour ◽  
Element Analysis ◽  
Flexible Risers ◽  
Linear Elastic Behaviour ◽  
Ocean Environment ◽  
Critical Regions ◽  
Offshore Oil

Flexible risers are complex structures used in offshore oil exploitation activities. Such structures are composed of several concentric polymeric and steel armour layers which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the equivalent flexural stiffness of such structures is an important task for the global structural analysis, since it provides a probable value that can be used in this analysis to predict the load distribution along the line (that is important in critical regions such as the TDP and the top). Besides that, estimates for the flexural stiffness are also important for predicting instabilities in the line (loop formation). However, the complexity imposed mainly by geometry and contact conditions renders a finite element analysis of these structures practically unfeasible, even considering that all the materials obey a linear elastic behaviour. So, in order to achieve this task, analytical methods have been proved to be, till now, a better choice. The aim of this work is to present the basis of a new analytical equation to estimate the flexural structural behaviour of flexible risers. Emphasis is given on the geometrical analysis of armour layers.

Some Further Studies on the Axial–Torsional Behavior of Flexible Risers

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Roberto Ramos ◽  
Clóvis A. Martins ◽  
Celso P. Pesce ◽  
Francisco E. Roveri
Keyword(s):  
Finite Element ◽  
Analytical Model ◽  
Experimental Tests ◽  
Analytical Models ◽  
Analysis Tool ◽  
Full Data ◽  
Technical Literature ◽  
External Pressures ◽  
Flexible Risers ◽  
Ocean Environment

Flexible risers are complex structures composed of several concentric polymeric and steel armor layers that withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the response of these structures when subjected to axisymmetric loadings (i.e., any combination of traction, torsion, and internal or external pressures) is an important task for the local structural analysis since it provides probable values for the loading distribution along the layers and, thus, allowing estimating the expected life of a riser using fatigue tools. Although finite element models have been increasingly used to accomplish this task in the last years, the simplicity and the reasonable accuracy provided by analytical models can be seen as reasons that justify their continued use, at least in the initial cycles of the design. However, any analytical model proposed for such a task must be checked with well-conducted experimental results in order to be considered as an acceptable analysis tool. The aims of this article are twofold: (i) to present the main results of experimental tests involving both internal pressure and traction loadings on a 63.5 mm (2.5 in.) flexible riser, carried out at the Institute for Technological Research of São Paulo (IPT), which can be used as a means of checking finite element or analytical models proposed by other researchers, and (ii) to compare some results obtained experimentally with those predicted by an analytical model which can also include any combination of axisymmetric loadings. Besides presenting full data concerning the internal structure of the riser, the experimental procedures used to perform the tests and the main results (e.g., Force × Displacement curves) are also presented. A brief discussion about the validity of some hypotheses that are usually assumed by analytical models found in the technical literature is made.

A Consistent Analytical Model to Predict the Structural Behavior of Flexible Risers Subjected to Combined Loads

2004 ◽  
Vol 126 (2) ◽  
pp. 141-146 ◽  
Author(s):  
Roberto Ramos, ◽  
Celso Pupo Pesce
Keyword(s):  
Structural Analysis ◽  
Analytical Model ◽  
Constitutive Equations ◽  
Structural Behavior ◽  
Slip Model ◽  
Flexible Riser ◽  
Equilibrium Conditions ◽  
Combined Loads ◽  
External Pressures ◽  
Flexible Risers

This work presents an analytical model for the structural analysis of flexible risers subjected to combined loads of bending, twisting and tension, as well as internal and external pressures applied to the riser. The proposed formulation, which comprises equilibrium conditions, constitutive equations and geometrical relations, leads to the solution of the problem in terms of the loads supported by the layers and deformation components of a flexible riser subjected to the above mentioned combined loads. All the modeling hypotheses are highlighted in the work. Comparisons between analytical results using the full-slip model and experimental results obtained in literature are shown and discussed. Some proposals leading to improvement of the presented model are drawn in the conclusions.

Generalised Beam Theory (GBT) for Shear Deformable Stiffened Sections

2014 ◽  
Vol 553 ◽  
pp. 600-605
Author(s):  
Gerard Taig ◽  
Gianluca Ranzi
Keyword(s):  
Cross Sections ◽  
Beam Theory ◽  
Element Model ◽  
Elastic Behaviour ◽  
Structural Behaviour ◽  
Thin Walled ◽  
Shell Finite Element ◽  
Linear Elastic Behaviour ◽  
Generalised Beam Theory ◽  
Shear Deformable

A Generalised Beam Theory (GBT) formulation is presented to analyse the structural behaviour of shear deformable thin-walled members with partially stiffened cross-sections located at arbitrary locations along their length. The deformation modes used in the formulation are taken as the dynamic eigenmodes of a planar frame representing the unstiffened cross-section. Constraint equations are derived and implemented in the GBT member analysis to model the influence of rigid stiffeners on the member response. The accuracy of the approach is validated against a shell finite element model developed in Abaqus. A numerical example describing the linear elastic behaviour of partially stiffened thin-walled member is provided to outline the usability and flexibility of the proposed method.

A Case Study on the Axial-Torsional Behavior of Flexible Risers

2008 ◽  
Author(s):  
Roberto Ramos ◽  
Clo´vis de Arruda Martins ◽  
Celso Pupo Pesce ◽  
Francisco E. Roveri
Keyword(s):  
Torsional Stiffness ◽  
Analytical Models ◽  
Analysis Tool ◽  
Full Data ◽  
Technical Literature ◽  
Static And Dynamic Loads ◽  
Flexible Risers ◽  
Ocean Environment ◽  
Technological Research Institute

Flexible risers are complex structures composed of several concentric polymeric and steel armor layers which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the axial and torsional stiffness values of such structures is an important task for the global structural analysis, since it provides a probable value that can be used in this analysis to predict the load distribution along the line and permitting, thus, to estimate the expected life of the structure. Although such stiffness values may be provided by the manufacturer, it is quite desirable that they can be estimated by analytical models instead. However, any analytical model proposed for such a task must be checked with well-conducted experimental results in order to be considered as an acceptable analysis tool. The aim of this work is to present the main results involving axial-torsional tests in a 2.5" flexible riser, carried out at the Technological Research Institute of Sa˜o Paulo (IPT). Besides presenting full data concerning the internal structure of the riser, this paper describes the experimental procedures used to perform the tests and the main obtained results (e.g., Force × Displacement and Twisting moment × Displacement curves). Tests involving internal pressure were also performed and the obtained results are also presented in this work. Comparisons between analytically calculated values of the axial and torsional stiffnesses with those obtained experimentally are made and discussed. A brief discussion about the validity of some hypotheses which are usually assumed by analytical models found in the technical literature is made at the end of the work.

Numerical and Analytical Modeling of Unbonded Flexible Risers

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
A. Bahtui ◽  
H. Bahai ◽  
G. Alfano
Keyword(s):  
Finite Element ◽  
Time Integration ◽  
Computational Cost ◽  
Element Model ◽  
Integration Scheme ◽  
Element Analysis ◽  
Axial Tension ◽  
External Pressures ◽  
Time Integration Scheme ◽  
Flexible Risers

This paper presents an analytical formulation and a finite element analysis of the behavior of multilayer unbonded flexible risers. The finite element model accurately incorporates all the fine details of the riser that were previously considered to be important but too difficult to simulate due to the significant associated computational cost. All layers of the riser are separately modeled, and contact interaction between layers has been accounted for. The model includes geometric nonlinearity as well as frictional effects. The analysis considers the main modes of flexible riser loading, which include internal and external pressures, axial tension, torsion, and bending. Computations were performed by employing a fully explicit time integration scheme on a parallel 16-processor cluster of computers. Consistency of simulation results was demonstrated by comparison with those of the analytical model of an identical structure. The close agreement gives confidence in both approaches.

Evaluation of web reinforcements in prestressed concrete box girders through shear-transverse bending domains

2020 ◽  
pp. 136943322098170
Author(s):  
Michele Fabio Granata ◽  
Antonino Recupero
Keyword(s):  
Analytical Model ◽  
Prestressed Concrete ◽  
3D Analysis ◽  
Box Girders ◽  
Element Analysis ◽  
Cross Sectional ◽  
Interaction Domains ◽  
Global And Local ◽  
Resultant Forces

In concrete box girders, the amount and distribution of reinforcements in the webs have to be estimated considering the local effects due to eccentric external loads and cross-sectional distortion and not only the global effect due to the resultant forces of a longitudinal analysis: shear, torsion and bending. This work presents an analytical model that allows designers to take into account the interaction of all these effects, global and local, for the determination of the reinforcements. The model is based on the theory of stress fields and it has been compared to a 3D finite element analysis, in order to validate the interaction domains. The results show how the proposed analytical model allows an easy and reliable reinforcement evaluation, in agreement with a more refined 3D analysis but with a reduced computational burden.

scholarly journals Extracting real-crack properties from non-linear elastic behaviour of rocks: abundance of cracks with dominating normal compliance and rocks with negative Poisson ratios

2017 ◽  
Vol 24 (3) ◽  
pp. 543-551 ◽  
Author(s):  
Vladimir Y. Zaitsev ◽  
Andrey V. Radostin ◽  
Elena Pasternak ◽  
Arcady Dyskin
Keyword(s):  
Experimental Data ◽  
Poisson Ratio ◽  
A Priori ◽  
Elastic Behaviour ◽  
Crack Model ◽  
Normal Compliance ◽  
S Wave ◽  
Linear Elastic ◽  
Non Linear ◽  
Linear Elastic Behaviour

Abstract. Results of examination of experimental data on non-linear elasticity of rocks using experimentally determined pressure dependences of P- and S-wave velocities from various literature sources are presented. Overall, over 90 rock samples are considered. Interpretation of the data is performed using an effective-medium description in which cracks are considered as compliant defects with explicitly introduced shear and normal compliances without specifying a particular crack model with an a priori given ratio of the compliances. Comparison with the experimental data indicated abundance (∼ 80 %) of cracks with the normal-to-shear compliance ratios that significantly exceed the values typical of conventionally used crack models (such as penny-shaped cuts or thin ellipsoidal cracks). Correspondingly, rocks with such cracks demonstrate a strongly decreased Poisson ratio including a significant (∼ 45 %) portion of rocks exhibiting negative Poisson ratios at lower pressures, for which the concentration of not yet closed cracks is maximal. The obtained results indicate the necessity for further development of crack models to account for the revealed numerous examples of cracks with strong domination of normal compliance. Discovering such a significant number of naturally auxetic rocks is in contrast to the conventional viewpoint that occurrence of a negative Poisson ratio is an exotic fact that is mostly discussed for artificial structures.

scholarly journals Safety Evaluation of the Combined Load for Offshore Wind Turbine Suction Foundation Installed on Sandy Soil

2021 ◽  
Vol 33 (5) ◽  
pp. 195-202
Author(s):  
Jeong Seon Park
Keyword(s):  
Wind Turbine ◽  
Sandy Soil ◽  
Wind Waves ◽  
Safety Evaluation ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Element Analysis ◽  
Combined Load ◽  
Combined Loads ◽  
Moment Load

Offshore wind turbine (OWT) receive a combined vertical-horizontal- moment load by wind, waves, and the structure’s own weight. In this study, the bearing capacity for the combined load of the suction foundation of OWT installed on the sandy soil was calculated by finite element analysis. In addition, the stress state of the soil around the suction foundation was analyzed in detail under the condition that a combined load was applied. Based on the results of the analyses, new equations are proposed to calculate the horizontal and moment bearing capacities as well as to define the capacity envelopes under general combined loads.

Sign in / Sign up

Export Citation Format

Share Document