An Analytical Model for the Unbonded Flexible Pipe Stress Analysis With Consideration of Nonlinear Material Properties for Metal Layers

2010 ◽  
Author(s):  
Jian Liu ◽  
Zhimin Tan ◽  
Terry Sheldrake
Keyword(s):  
Stress Analysis ◽  
Analytical Model ◽  
Material Properties ◽  
Failure Modes ◽  
Nonlinear Material ◽  
Von Mises Stress ◽  
Stress And Strain ◽  
Flexible Pipe ◽  
Metal Layers ◽  
Plastic Stress

This paper presents an improved analytical model for the unbonded flexible pipe stress analysis with consideration of nonlinear material properties for metal layers. Analytical methods have often been used to analyse the stress and strain of flexible pipe systems because of their low cost and efficiency compared with detailed finite element modeling. Most of these kinds of models only consider the deformation of pipes within the elastic region. Such linear models can not be used directly to assess pipe failure modes such as the pipe burst strength, where the nonlinearity of the metallic material plays an important role in governing the pipe deformation and pipe structural capacity. The improved analytical model presented in this paper has fully considered the nonlinearity of metal layers such as the pressure armour and tensile armour layers because of their importance in resisting internal pressure and tension loads. Non-associative elasto-plastic stress strain curves obtained from experiments are used to simulate the metal layers. Von Mises stress is adopted in the model as the yield criterion of the metal layers. Radial return method (Simo and Taylor 1985 [1], Simo and Hughes 1998 [2]) is used to solve the plastic stress and strain of metal layers beyond the yield point. Due to its high nonlinearity from both system equations and material properties, Newton-Raphson method is adopted in the model as the solving method. The proposed study here considers tension, torque and pressure loads only for a straight pipe. The model predictions have been compared against measurements from Wellstream burst tests and failure tension tests performed over the full scale pipe samples. The prediction and experiment results agree.

Homogenization and Stress Analysis of Multilayered Composite Offshore Production Risers

2013 ◽  
Vol 81 (3) ◽  
Author(s):  
X. S. Sun ◽  
Y. Chen ◽  
V. B. C. Tan ◽  
R. K. Jaiman ◽  
T. E. Tay
Keyword(s):  
Stress Analysis ◽  
Elastic Constants ◽  
Material Properties ◽  
Axial Loading ◽  
Stress And Strain ◽  
Multilayered Composite ◽  
External Pressures ◽  
Complex Models ◽  
Composite Cylinders ◽  
Stress Analyses

An approach for stress analysis of multilayered composite cylinders is proposed for the analysis of new composite risers used in deep-water oil production of offshore petroleum industries. Risers essentially comprise long cylindrical sections connected end-to-end. In the formulation, only stresses and strains that are continuous through the thickness of the multilayered composite risers are taken to be equal to reported solutions for homogenous orthotropic hollow cylinders using homogenized material properties. These stress and strain solutions are then used to calculate the remaining discontinuous stresses and strains from the material properties of individual layers of materials. The homogenized elastic constants of cylindrically orthotropic composite risers are derived from force-deformation equivalence, taking into account the stress and strain distributions in each layer. Four typical loading conditions are considered in the stress analysis, namely, internal and external pressures, axial loading, bending, and torsion. Examples of homogenized elastic constants and stress analyses of composite cylindrical structures with different layups and materials are presented to demonstrate the application of the proposed method. The results compared very favorably with those from other solutions. This method provides practical benefits for the design and analysis of composite risers. Because there is no requirement to explicitly enforce interfacial continuity in this method, stress analyses of composite cylinders with many layers of different fiber angles or materials can be carried out efficiently. The homogenized elastic constants can greatly expedite the analysis of entire composite riser systems by replacing complex models of riser sections with homogenized riser sections.

Computational Mechanics of the Sclera and Optic Nerve Head (ONH): Effects of ONH Size and Pressure Range

2008 ◽  
Author(s):  
Lewis Waldman ◽  
Crystal Cunanan ◽  
Sanjay Asrani ◽  
Roy Kerckhoffs ◽  
Andrew McCulloch
Keyword(s):  
Optic Nerve ◽  
Optic Nerve Head ◽  
Material Properties ◽  
Pressure Range ◽  
High Pressures ◽  
Strain Differences ◽  
Temporal Variations ◽  
Nonlinear Material ◽  
Stress And Strain ◽  
Strain Components

Computational modeling was performed to study how loss of compliance of the eye and abnormally high pressures result in changes in stresses and strains that may impact the optic nerve in diseases such as glaucoma. Hemispherical finite element models of the eye were created in which scleral thickness varied from the equatorial region to the optic nerve head (ONH). Nonhomogeneous material properties were used to model the ONH as a continuous region softer than the adjacent sclera. The ONH and an adjacent buffer zone in the sclera were modeled with enough detail that the size of the ONH could be changed to account for variations observed in humans. The model was provided with appropriate dimensions typical of patients and nonlinear material properties with decreased compliance. Models with different ONH sizes were inflated in small steps to 55 mmHg (7.33 kPa), providing deformed configurations at intermediate pressures of 15, 30 and 45 mmHg, respectively. Color-coded maps of stress and strain components were rendered directly on deformed configurations of the eye model; and animations were produced that show both spatial and temporal variations of stresses and strains as internal pressure increases. Three-dimensional stresses and accompanying finite strains were similar for ONH sizes ranging form 1.5 to 2.5 mm in diameter. Stress and strain differences were estimated as pressure was increased from 15 to 25 mmHg, 30 to 40 mmHg, and 45 to 55 mmHg. Substantial changes occurred in stress and strain differences as the pressure range was varied with large changes occurring in the lowest pressure range for strain components and moderate increases in stress differences as pressures increase.

scholarly journals Evaluation of Bone–Implant Interface Stress and Strain Using Heterogeneous Mandibular Bone Properties Based on Different Empirical Correlations

2021 ◽  
Author(s):  
Mostafa Omran Hussein ◽  
Mohammed Suliman Alruthea
Keyword(s):  
Finite Element ◽  
Group Iv ◽  
Von Mises Stress ◽  
Patient Specific ◽  
Dental Arch ◽  
Stress And Strain ◽  
Bone Implant ◽  
Bone Properties ◽  
Group I ◽  
Von Mises

Abstract Objective The purpose of this study was to compare methods used for calculating heterogeneous patient-specific bone properties used in finite element analysis (FEA), in the field of implant dentistry, with the method based on homogenous bone properties. Materials and Methods In this study, three-dimensional (3D) computed tomography data of an edentulous patient were processed to create a finite element model, and five identical 3D implant models were created and distributed throughout the dental arch. Based on the calculation methods used for bone material assignment, four groups—groups I to IV—were defined. Groups I to III relied on heterogeneous bone property assignment based on different equations, whereas group IV relied on homogenous bone properties. Finally, 150 N vertical and 60-degree-inclined forces were applied at the top of the implant abutments to calculate the von Mises stress and strain. Results Groups I and II presented the highest stress and strain values, respectively. Based on the implant location, differences were observed between the stress values of group I, II, and III compared with group IV; however, no clear order was noted. Accordingly, variable von Mises stress and strain reactions at the bone–implant interface were observed among the heterogeneous bone property groups when compared with the homogenous property group results at the same implant positions. Conclusion Although the use of heterogeneous bone properties as material assignments in FEA studies seem promising for patient-specific analysis, the variations between their results raise doubts about their reliability. The results were influenced by implants’ locations leading to misleading clinical simulations.

scholarly journals Multi-stable composite twisting structure for morphing applications

2012 ◽  
Vol 468 (2141) ◽  
pp. 1230-1251 ◽  
Author(s):  
X. Lachenal ◽  
P. M. Weaver ◽  
S. Daynes
Keyword(s):  
Analytical Model ◽  
Material Properties ◽  
Degrees Of Freedom ◽  
Design Parameters ◽  
Engineering Structures ◽  
The Past ◽  
Wide Range ◽  
Morphing Structure ◽  
Low Mass ◽  
Unstable States

Conventional shape-changing engineering structures use discrete parts articulated around a number of linkages. Each part carries the loads, and the articulations provide the degrees of freedom of the system, leading to heavy and complex mechanisms. Consequently, there has been increased interest in morphing structures over the past decade owing to their potential to combine the conflicting requirements of strength, flexibility and low mass. This article presents a novel type of morphing structure capable of large deformations, simply consisting of two pre-stressed flanges joined to introduce two stable configurations. The bistability is analysed through a simple analytical model, predicting the positions of the stable and unstable states for different design parameters and material properties. Good correlation is found between experimental results, finite-element modelling and predictions from the analytical model for one particular example. A wide range of design parameters and material properties is also analytically investigated, yielding a remarkable structure with zero stiffness along the twisting axis.

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