An Investigation of the Bisymmetric Hydrostatic Collapse of Flexible Pipes Based on Equivalent Layer Approaches

The hydrostatic collapse strength of a flexible pipe is largely dependent on the ability of its carcass and/or pressure armor to resist radial loading and, therefore, its prediction involves an adequate modeling of these layers. Hence, initially, this work proposes a set of equations to estimate equivalent mechanical properties for these layers, which allows their modeling as equivalent orthotropic cylinders. Particularly, equations to predict the equivalent ring bend stiffness are obtained by simulating several two-point static ring tests with a three-dimensional finite element (FE) model based on beam elements and using these results to form datasets that are analyzed with a symbolic regression (SR) tool. The results of these analyses are the closed-form equations that best fit the provided datasets. After that, these equations are used in conjunction with a three-dimensional shell FE model (FEM) and a previously presented analytical model to study the bisymmetric hydrostatic collapse mechanism of flexible pipes. The predictions of these models agreed well with the collapse pressures obtained with numerical models and in experimental tests thus indicating the potential use of this approach in the design of flexible pipes.

A comparative analysis of air-jet yarn properties with the properties of ring spun yarns

Ring spinning is the most common method used among the short staple fibers spinning methods. Due to limitations of the production speed in the ring spinning, new spinning methods become more popular with each passing day. Air-jet spinning systems gathered attention with their market share in the new spinning methods. In this study, the properties of the air-jet yarns were comparatively analyzed with the properties of the equivalent Ring yarns, for both single and ply-twisted forms. It was found that the Rieter and Murata air-jet yarns do not show significant differences in terms of physical properties of yarns. Due to their special structure, air-jet yarns show lower hairiness and tenacity values when compared to the equivalent Ring yarns.

Novel Noncommutative Cryptography Scheme Using Extra Special Group

Noncommutative cryptography (NCC) is truly a fascinating area with great hope of advancing performance and security for high end applications. It provides a high level of safety measures. The basis of this group is established on the hidden subgroup or subfield problem (HSP). The major focus in this manuscript is to establish the cryptographic schemes on the extra special group (ESG). ESG is showing one of the most appropriate noncommutative platforms for the solution of an open problem. The working principle is based on the random polynomials chosen by the communicating parties to secure key exchange, encryption-decryption, and authentication schemes. This group supports Heisenberg, dihedral order, and quaternion group. Further, this is enhanced from the general group elements to equivalent ring elements, known by the monomials generations for the cryptographic schemes. In this regard, special or peculiar matrices show the potential advantages. The projected approach is exclusively based on the typical sparse matrices, and an analysis report is presented fulfilling the central cryptographic requirements. The order of this group is more challenging to assail like length based, automorphism, and brute-force attacks.

Prediction of Burst in Flexible Pipes

Usually when a large internal fluid pressure acts on the inner walls of flexible pipes, the carcass layer is not loaded, as the first internal pressure resistance is given by the internal polymeric layer that transmits almost all the loading to the metallic pressure armor layer. The last one must be designed to ensure that the flexible pipe will not fail when loaded by a defined value of internal pressure. This paper presents three different numerical models and an analytical nonlinear model for determining the maximum internal pressure loading withstood by a flexible pipe without burst. The first of the numerical models is a ring approximation for the helically rolled pressure layer, considering its actual cross section profile. The second one is a full model for the same structure, considering the pressure layer laying angle and the cross section as built. The last numerical model is a two-dimensional (2D) simplified version, considering the pressure layer as an equivalent ring. The first two numerical models consider contact nonlinearities and a nonlinear elastic-plastic material model for the pressure layer. The analytical model considers the pressure armor layer as an equivalent ring, taking into account geometrical and material nonlinear behaviors. Assumptions and results for each model are compared and discussed. The failure event and the corresponding stress state are commented.

Collapse Estimation of Interlocked Armour of Flexible Pipe With Strain Energy Equivalence

Deepwater environment brings unbonded flexible pipelines with collapse risk of interlocked armours, such as pressure armour and carcass. An effective and accurate prediction for collapse is required in design process. This paper presents a theoretical approach for estimating collapse of the interlocked armours based on strain energy equivalence principle of representative volume method. The strain energy with Dirichlet boundary is calculated using FEA software for the armours, which usually have complex cross-section. Meanwhile, an equivalent ring model is established as the representative volume, of which strain energy is acquired analytically. Equivalent thickness can be obtained by equivalence of both the two energys. And then the resistance to collapse of the flexible pipe can be carried out directly. Theoretical results from the approach presented in the paper are compared with numerical results proved by experimental ones from reference, which verifies the equivalence approach. This approach provides a new angle to process parametric design for critical collapse of the flexible pipe.

A Simplified Numerical Method of Composite Foundation for the Circular Basis

It is very difficult to analysis three-dimensional model of composite foundation because there are many unit numbers if piles, soil and plate unit are divided separately. three-dimensional problem is made into the axisymmetric finite element model and numerical analysis is more convenient as the periphery piles of the group piles into the pile system " equivalent ring " . Eamples shows the conclusion is reasonable and the simplified model is feasible.

Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

When subjected to large valued external pressures, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied to the internal polymeric layer that transmits the loading to the carcass layer. When the carcass layer fails due to this effect, the wet collapse occurs. This failure mode must be taken into account in the flexible pipe design. The study for this problem can be done neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to study the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed and compared with the purpose of calculating the critical value of the external pressure that causes carcass layer to collapse. The first and most complete study is done using a ring 3D FEM model that takes into account both the real pressure armor and carcass real profiles. In the second model, the pressure armor is considered adopting an equivalent ring simplification. The comparison of the results of both the models clarifies how the behavior of the pressure armor in the wet collapse situation is. Parametric studies of initial ovalization of the carcass and initial gaps in manufacturing of flexible pipes are made and discussed.

Crushing and Wet Collapse of Flowline Carcasses: A Theoretical-Experimental Approach

The present paper brings together theoretical predictions and experimental results, comparing crushing tests results as well as carcass wet collapse tests. The theoretical models are of two kinds: (i) numerical (FE) and (ii) analytical. The first kind is a restricted 3D version of a finite element model. The second kind is based on classic assumptions of equivalent ring behavior. Discussion is made on the real yield stress value to be adopted, as well as on the pertinence of geometric hypotheses. Sensitivity analyses, regarding ovalization and helical pitch are also presented.

Cotton Fabrics Produced with Twistless Wrap Spun Yarns

Properties of fabrics woven with wrap spun yarns and equivalent ring spun yarns of Upland cotton have been investigated. Experimental wrap spun yarns were made on a modern, special machine, which produces so-called twistless yarns from staple fibers that are held together by a fine multifilament wrap yarn. The filament wrap used for the experimental yarns was water soluble polyvinyl alcohol. Ring spun yarns were produced conventionally. Each kind of yarn was woven separately as both warp and filling into plain, twill, and sateen fabrics. The water soluble wrap of the wrap spun fabrics was removed during normal wet processing, yielding completely twistless cotton fabrics. The various fabrics were evaluated for their important mechanical properties. Results show that, compared to the ring spun equivalents, the tighter, plain-woven, twistless fabric (of typical average density) fared reasonably well in tensile breaking strength but was slightly weaker in tearing strength; the relatively looser twill and sateen twistless fabrics were significantly weaker in both tensile and tear strengths. Respective fabrics of the two yarn types, however, showed no significant difference in abrasion resistance, although the twill and sateen fabrics made with both yarns generally had lower flex abrasion resistance than the corresponding plain fabrics. Twistless fabrics, like their ring spun counterparts, maintained their tensile and tear properties after repeated laundering.