Theoretical model for variable helical angle of tensile armour wires in bent flexible pipes

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives the lateral displacement of the wire, which is determined by minimizing the energy functional that consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is verified with a finite element (FE) simulation. Comparisons between the model predictions and the FE results in terms of the change in helical angle and transverse bending stress show good correlations. The verified model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear, and friction could significantly increase the stress at the end fitting compared with the frictionless case.

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Crushing of Flexible Pipes Under Traction: A Theoretical-Experimental Assessment

Volume 4: Pipeline and Riser Technology ◽

10.1115/omae2011-49524 ◽

2011 ◽

Cited By ~ 1

Author(s):

Guilherme R. Franzini ◽

Celso P. Pesce ◽

Fernanda C. M. Takafuji ◽

Rodolfo T. Gonc¸alves ◽

Rafael Tanaka ◽

...

Keyword(s):

Plastic Deformation ◽

Theoretical Model ◽

Sensitivity Analyses ◽

Experimental Comparison ◽

Concentrated Loads ◽

Flexible Pipe ◽

Experimental Assessment ◽

Helical Pitch ◽

Flexible Pipes ◽

Combined Action

The paper presents a theoretical-experimental comparison concerning standard crushing-traction tests of flexible pipe prototypes. The theoretical model for crushing is analytical and based on classic assumptions of equivalent pipes, applying model previously published in OMAE2003, and OMAE2010. Such a model considers the combined action of squeezing, concentrated loads due to the caterpillar shoes as well as the effect of initial ovalization. The experimental measures include a detailed internal geometrical mapping of the deformed carcass, until plastic deformation becomes evident. Discussion is made on the pertinence of modeling hypotheses. Sensitivity analyses, regarding initial ovalization and helical pitch of the pressure armor are also addressed.

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Reinforced Design of an Unbonded Flexible Flowline for Shallow Water

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 5, Parts A and B ◽

10.1115/omae2010-20179 ◽

2010 ◽

Author(s):

Qing-zhen Lu ◽

Qian-jin Yue ◽

Ming-gang Tang ◽

Jie-xin Zheng ◽

Jun Yan

Keyword(s):

Theoretical Model ◽

Shallow Water ◽

Tensile Property ◽

Low Cost ◽

Steel Wire ◽

External Pressure ◽

Radial Deformation ◽

Flexible Pipe ◽

Axial Tensile ◽

Flexible Pipes

Flexible pipeline has been widely used in offshore engineering. Comparing to steel pipe, flexible subsea pipeline has some merits such as anti-corrosive, easy laying and recycling. So it is suitable to be used as flowline in shallow water. Especially there are lots of marginal oil fields in shallow water of China. Different from deepwater dynamic riser, flexible pipe for shallow water applications has a low requirement of resisting external pressure. On the other hand, Flexible pipe need to satisfy the requirement of tensile property during installation. Therefore, a kind of simple and economical flexible pipe can be developed to meet the requirement of shallow water application. This paper presents an economical unbonded flexible pipeline, which is helically wound by steel wires. In order to guarantee the safety of the economical flexible pipeline under the laying, installation and working loads, a reinforced design of tensile property is necessary. A helically wounded flat-steel layer is introduced to constrain the steel wire radial deformation and strengthen the axial tensile stiffness of the pipeline. A theoretical model is established to analyze the tension behavior of the flexible pipes and some suggestions are proposed to strengthen the flexible pipe design. Additionally, tensile experiments are carried out for the original and reinforced flexible pipes, which verify the theoretical model and the effectiveness of the reinforced design. The results show that the reinforced pipeline not only meets the tensile requirement during installation for shallow-water applications, but also meets requirements of the minimum bend radius as well as hydrostatic collapse (resistance of the external pressure) with low cost.

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End Fitting Effect on Stress Evaluation of Tensile Armors in Unbonded Flexible Pipes Under Axial Tension

Volume 5A: Pipelines, Risers, and Subsea Systems ◽

10.1115/omae2017-62378 ◽

2017 ◽

Author(s):

Leilei Dong ◽

Qi Zhang ◽

Yi Huang ◽

Gang Liu ◽

Zhiyuan Li

Keyword(s):

Finite Element ◽

Lateral Displacement ◽

Supplementary Condition ◽

Bending Stress ◽

Stress Evaluation ◽

Axial Tension ◽

Flexible Pipes ◽

Helical Angle ◽

The Wire ◽

Unbonded Flexible Pipes

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives lateral displacement of the wire, which is determined by minimization of the energy functional consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is validated with a finite element simulation. Comparisons between the model predictions and the finite element results in terms of the change in helical angle and transverse bending stress show good correlations. The validated model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear and friction could significantly increase the stress at the end fitting compared with the frictionless case.

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Prediction of Internal Pressure of Flexible Pipe

Volume 5A: Pipelines, Risers, and Subsea Systems ◽

10.1115/omae2019-95458 ◽

2019 ◽

Author(s):

Qiangqiang Shao ◽

Ting Liu ◽

Shuai Yuan ◽

Peihua Han ◽

Yong Bai

Keyword(s):

Theoretical Model ◽

Oil And Gas ◽

Virtual Work ◽

Fluid Pressure ◽

Oil And Gas Industry ◽

Element Model ◽

Petroleum Products ◽

Burst Pressure ◽

Flexible Pipe ◽

Flexible Pipes

Abstract The flexible pipes are widely used in the oil and gas industry to transport petroleum products. The pipe might burst fails when a large internal fluid pressure acts on the pipe, and the consequences are disastrous. In order to ensure the security and reliability of flexible pipes in the application, the mechanical responses of the pipe subjected to high pressure loads should be carefully estimated. The main purpose of this paper is to investigate the burst pressure of the pipe. Based on the principle of virtual work, a theoretical model for stress and deformations of the pipe is established, which takes the material plasticity into consideration. In addition, a finite element model is developed by ABAQUS to verify the feasibility of the theoretical model. According to the verified model, it is efficient to predict the burst pressure and design its cross-section economically with its serving conditions.

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A theoretical model for understanding dentists' behavior in treating patients with AIDS

Journal of Dental Education ◽

10.1002/j.0022-0337.1991.55.11.tb02589.x ◽

1991 ◽

Vol 55 (11) ◽

pp. 708-716 ◽

Cited By ~ 1

Author(s):

MS Chen

Keyword(s):

Theoretical Model

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A Model for Analyzing Suicide Prevention

Crisis ◽

10.1027//0227-5910.21.2.80 ◽

2000 ◽

Vol 21 (2) ◽

pp. 80-89 ◽

Cited By ~ 3

Author(s):

Maila Upanne

Keyword(s):

Risk Factors ◽

Theoretical Model ◽

Protective Factors ◽

Suicide Prevention ◽

Suicide Risk ◽

Practical Work ◽

Individual Risk ◽

Self Assessment ◽

Prevention Project ◽

Individual Risk Factors

This study monitored the evolution of psychologists' (n = 31) conceptions of suicide prevention over the 9-year course of the National Suicide Prevention Project in Finland and assessed the feasibility of the theoretical model for analyzing suicide prevention developed in earlier studies [ Upanne, 1999a , b ]. The study was formulated as a retrospective self-assessment where participants compared their earlier descriptions of suicide prevention with their current views. The changes in conceptions were analyzed and interpreted using both the model and the explanations given by the subjects themselves. The analysis proved the model to be a useful framework for revealing the essential features of prevention. The results showed that the freely-formulated ideas on prevention were more comprehensive than those evolved in practical work. Compared to the earlier findings, the conceptions among the group had shifted toward emphasizing a curative approach and the significance of individual risk factors. In particular, greater priority was focused on the acute suicide risk phase as a preventive target. Nonetheless, the overall structure of prevention ideology remained comprehensive and multifactorial, stressing multistage influencing. Promotive aims (protective factors) also remained part of the prevention paradigm. Practical working experiences enhanced the psychologists' sense of the difficulties of suicide prevention as well as their criticism and feeling of powerlessness.

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