scholarly journals An Effective Multiscale Methodology for the Analysis of Marine Flexible Risers

2019 ◽  
Vol 7 (10) ◽  
pp. 340 ◽  
Author(s):  
B. D. Edmans ◽  
D. C. Pham ◽  
Z.-Q. Zhang ◽  
T. F. Guo ◽  
N. Sridhar ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Large Scale ◽  
Structural Response ◽  
Element Model ◽  
Life Extension ◽  
Scale Model ◽  
Flexible Pipes ◽  
Attractive Option ◽  
Flexible Risers ◽  
Global And Local

Life extension is an attractive option for subsea flexible risers nearing the end of their design lives. However, techniques for assessing accumulated fatigue damage in flexible risers are often associated with large uncertainties due to the simplified calculation approaches typically used. One approach to reducing uncertainties is the inclusion of nonlinearities in riser structural response and consistent linking between global and local models. In this article, we present the elements of a numerical multiscale procedure capable of predicting the stresses that lead to fatigue damage in flexible pipes, namely: a nonlinear beam element, a nonlinear section response model and a detailed finite element model; the consistent integration of models developed for different length scales; and finally a validation of the flexible riser large-scale model.

Whistling of Pipes With Narrow Corrugations: Scale Model Tests and Consequences for Carcass Design

2013 ◽  
Author(s):  
Joachim Golliard ◽  
Stefan Belfroid ◽  
Erik Bendiksen ◽  
Casper Frimodt
Keyword(s):  
Prediction Model ◽  
Gas Production ◽  
Scale Model ◽  
Small Scale ◽  
Operational Conditions ◽  
Flexible Pipes ◽  
Cavity Opening ◽  
Flexible Risers ◽  
Onset Velocity ◽  
Operational Envelope

Pipes for gas production and transport with a corrugated inner surface, as used in flexible pipes, can be subject to Flow-Induced Pulsations when the flow velocity is larger than a certain velocity. This onset velocity is dependent on the geometry of the corrugations, the operational conditions and the geometry of the topside and subsea piping. In this paper, small-scale tests performed on corrugated tubes are reported. The tested geometries include both “classical” profiles, similar to the inner profile of agraff flexible risers, and profiles with less typical variations, such as narrower and/or deeper cavities, or irregular pitch. These tests were performed in order to evaluate the validity of a prediction model developed earlier for the onset of pulsations, for corrugated pipes with these kinds of atypical variations, which are found on a new type of carcass designs. The mechanism of Flow-Induced Pulsations in corrugated pipes is discussed, as well as the principle of the prediction model. The experimental results show that the validity of the model remains reasonable in most cases, except when the cavities are very narrow. In this case, the model becomes overly conservative. This limitation can be attributed to the fact that, for very narrow cavities, the cavity opening becomes too small compared to the boundary-layer momentum thickness, effectively destroying any instability of the shear layer. Furthermore, the shift towards higher frequencies of the acoustic source term due to narrower cavities, and the possible coupling with higher acoustic modes, is considered. The results of the analysis are used to evaluate the onset velocity and whistling behavior of a newly developed carcass design of flexible risers. A previous analysis has indicated that the particular geometry profile of the new design improves the whistling behavior by pushing the onset velocity outside the typical operational envelope of flexible risers. The analysis confirms that the new design will be less prone to whistling than flexible risers with classical agraff carcasses.

On the Structural Response of a Flexible Pipe With Damaged Tensile Armor Wires

2011 ◽  
Author(s):  
Jose´ Renato M. de Sousa ◽  
George C. Campello ◽  
Antoˆnio Fernando B. Bueno ◽  
Eduardo Vardaro ◽  
Gilberto B. Ellwanger ◽  
...  
Keyword(s):  
Mechanical Response ◽  
High Stress ◽  
Three Dimensional ◽  
Structural Response ◽  
Experimental Tests ◽  
Element Model ◽  
Axial Stiffness ◽  
Stress Concentrations ◽  
Flexible Pipe ◽  
Flexible Pipes

This paper studies the structural response of a 6.0″ flexible pipe under pure tension considering two different situations: the pipe is intact or has five wires broken in its outer tensile armor. A three-dimensional nonlinear finite element model devoted to analyze the local mechanical response of flexible pipes is employed in this study. This model is capable of representing each wire of the tensile armors and, therefore, localized defects, including total rupture, may be adequately represented. Results from experimental tests are also presented in order to validate the theoretical estimations. The theoretical and experimental results indicate that the imposed damage reduced the axial stiffness of the pipe. High stress concentrations in the wires near the damaged ones were also observed and, furthermore, the stresses in the inner carcass and the pressure armor are affected by the imposed damage, but, on the other hand, the normal stresses in the wires of the inner tensile armor are not.

Numerical investigation of friction joint between Basalt Fiber Reinforced Composites and aluminum

2016 ◽  
Vol 231 (5) ◽  
pp. 543-551
Author(s):  
Andrei Costache ◽  
Christian Berggreen ◽  
Ion Marius Sivebæk ◽  
Kristian Glejbøl
Keyword(s):  
Finite Element ◽  
Basalt Fiber ◽  
Element Model ◽  
Fiber Reinforced ◽  
Pullout Force ◽  
Flexible Pipes ◽  
The Coefficient Of Friction ◽  
Flexible Risers ◽  
Offshore Oil Industry ◽  
Unbonded Flexible Pipes

Flexible risers are used in the offshore oil industry for exporting hydrocarbons from subsea equipment to floating production and storage vessels. The latest research in unbonded flexible pipes aims to reduce weight by replacing metal components with composite materials. This would result in lighter and stiffer flexible risers, which would be well suited for ultra deep water applications. This paper develops a new finite element model used for evaluating the efficiency of anchoring flat unidirectional fiber reinforced tendons in a mechanical grip. It consists two flat grips with the fiber reinforced tendon in between. The grips are pressed against the composite and the pullout force is ensured through friction. The novelty of the paper is represented by the detailed investigation of the influence between the coefficient of friction and the pullout force. By comparing numerical and experimentally obtained results, it is possible to show the importance of friction decay in the grip. Improper contact between the grips and composite is also taken into account and leads to good agreement between numerical and experimental results. This study shows how to avoid over-estimating the efficiency of such grip by using dry friction in finite element models.

Multi-Scale Analysis of the UHVDC Transmission Tower

2014 ◽  
Vol 680 ◽  
pp. 383-386
Author(s):  
Chun Cheng Liu ◽  
Wen Qiang Li ◽  
Shang Yu Hou ◽  
Zhao Wen He ◽  
Fan Gao
Keyword(s):  
Large Scale ◽  
Element Model ◽  
Beam Element ◽  
Scale Model ◽  
Scale Analysis ◽  
Transmission Tower ◽  
Gusset Plate ◽  
Multi Scale ◽  
Buckling Behavior ◽  
Scale Models

In order to analyze the mechanical properties of UHVDC transmission tower joint accurately, a multi-scale finite element model of the transmission tower is established with the interface between solid element model and beam element model. The model is applied to the nonlinear analysis of a key joint in a test condition .The results show that the tower destruction is caused by buckling behavior of the cross bracing member and the multi-scale model can simulate the force state of gusset-plate and the connected members realistically, which is superior to traditional large scale models. The analysis coincides with the experiment well and provides references for the transmission tower design.

Multiscale Finite Element Analysis of Unbonded Flexible Risers

2014 ◽  
Author(s):  
Ben Edmans ◽  
Dinh Chi Pham ◽  
Zhiqian Zhang ◽  
Tianfu Guo ◽  
Sridhar Narayanaswamy ◽  
...  
Keyword(s):  
Finite Element ◽  
Constitutive Model ◽  
Dynamic Analysis ◽  
Large Scale ◽  
Failure Modes ◽  
Life Extension ◽  
Equivalent Material ◽  
Analysis Model ◽  
Element Analysis ◽  
Flexible Risers

Unbonded flexible risers are a key technology in existing and proposed offshore developments. With increasing water depth, the demands on risers increase and the design against hydrostatic and tension loads becomes more of a challenge. In addition, many existing subsea production systems are approaching the end of their design life and operators need to know if they can remain in-service. To enable the benefits from deepwater production and life extension projects to be realized while minimizing risks to life, property and the environment, accurate modelling and analysis tools are required to improve the prediction of failure modes and to develop a better understanding of the conditions leading to progressive failure. In this work, a multi-scale approach is adopted whereby a global dynamic analysis model is employed to determine the overall displacements of the riser and this is linked with a local model that can provide accurate forces and stresses for the prediction of collapse, fatigue damage and buckling of tensile armour wires. Firstly, we describe a nonlinear constitutive model for use in large-scale dynamic analysis of flexible risers based on an analytical homogenization of composite cylinders using the analogy between slip between pipe layers and plastic flow in continua. The model is able to reproduce the bending hysteresis behaviour observed in flexible pipes and its dependence on internal and external pressure. Secondly, we show a procedure for obtaining equivalent material parameters for this model from finite element local analyses of a flexible pipe. Finally, we show the implementation of this constitutive model in a riser system using two-dimensional co-rotational hybrid beam finite elements.

scholarly journals Stochastic synchronization of dynamics on the human connectome

2020 ◽  
Author(s):  
James C. Pang ◽  
Leonardo L. Gollo ◽  
James A. Roberts
Keyword(s):  
Human Brain ◽  
Large Scale ◽  
Brain Network ◽  
Scale Model ◽  
Stochastic Perturbations ◽  
Stochastic Synchronization ◽  
Large Scale Model ◽  
Synchronization Effect ◽  
Global And Local ◽  
The Brain

AbstractSynchronization is a collective mechanism by which oscillatory networks achieve their functions. Factors driving synchronization include the network’s topological and dynamical properties. However, how these factors drive the emergence of synchronization in the presence of potentially disruptive external inputs like stochastic perturbations is not well understood, particularly for real-world systems such as the human brain. Here, we aim to systematically address this problem using a large-scale model of the human brain network (i.e., the human connectome). The results show that the model can produce complex synchronization patterns transitioning between incoherent and coherent states. When nodes in the network are coupled at some critical strength, a counterintuitive phenomenon emerges where the addition of noise increases the synchronization of global and local dynamics, with structural hub nodes benefiting the most. This stochastic synchronization effect is found to be driven by the intrinsic hierarchy of neural timescales of the brain and the heterogeneous complex topology of the connectome. Moreover, the effect coincides with clustering of node phases and node frequencies and strengthening of the functional connectivity of some of the connectome’s subnetworks. Overall, the work provides broad theoretical insights into the emergence and mechanisms of stochastic synchronization, highlighting its putative contribution in achieving network integration underpinning brain function.

A Real Time Fatigue Monitoring Platform for Flexible Risers

2021 ◽  
Author(s):  
Jiabei Yuan ◽  
Yucheng Hou ◽  
Eric Wilson ◽  
Zhimin Tan
Keyword(s):  
Service Life ◽  
Product Design ◽  
Real Time ◽  
Fatigue Damage ◽  
Input Data ◽  
Operating Conditions ◽  
Fatigue Performance ◽  
Life Extension ◽  
Service Life Extension ◽  
Flexible Risers

Abstract Fatigue life of flexible risers is a critical design factor in offshore riser system design. To estimate the fatigue damage, global and local analyses are performed inhouse with inputs from operators. Metocean data, riser properties, vessel or platform RAO data are typical inputs for the fatigue analysis. In addition to the conservatism inherited in the product design methodology and API safety factor 10 for fatigue estimation, the input data may also contain some additional conservatism compared to actual operational conditions as these were estimated/projected from limited time-span of observations or predicted purely from numerical modelling. In combination, these inheriated conservatism permits the feasibility of service life extension of the flexible riser systems. Many platforms or vessels already have real time monitoring of motions in multiple degrees of freedom and wave/current data. Furthermore, pipe internal operating conditions like pressure and temperature are usually recorded onboard. Compared to the typical input data/assumptions made in predictive analysis, these records are more precisely and directly related to the actual fatigue damage accumulation. With real time data, a more accurate estimation on fatigue performance of riser can be achieved, which could enable the service life extension without compromising the design safety factors. A special software tool has been developed to calculate the real time fatigue damage of flexible tensile wires. The software is based on product design tools which are calibrated and independently validated with over 30 years installed operational experience. Developed in Python, the software utilizes an OrcaFlex API and a local analysis algorithm in the background. The software can be customized towards different platforms and pipe systems, as well as input data types. Depending on clients’ needs, multiple fatigue hot spots like top end fitting, bend stiffener region or touch down zone can be monitored at the same time. Other parameters like riser real time extreme response or statistical results can also be checked in the software. This paper summarizes the development of the pipe monitoring system. It is believed that with real time inputs, the software can better assist clients to monitor the pipe fatigue performance and other related riser responses.

Optimization for Vibration Reduction in Final Phase of Automotive Body Structural Design

2001 ◽  
Author(s):  
Yasuaki Tsurumi ◽  
Toshiaki Nakagawa ◽  
Nobuyuki Mori ◽  
Hiroshi Yamakawa
Keyword(s):  
Structural Design ◽  
Degrees Of Freedom ◽  
Large Scale ◽  
Design Method ◽  
Element Model ◽  
Performance Criteria ◽  
Scale Model ◽  
Automotive Body ◽  
Large Scale Model ◽  
Noise Vibration

Abstract In automotive body structural design, Computer Aided Engineering (CAE) has been widely used in order to evaluate noise, vibration, harshness (NVH). A CAE engineer has usually used a large-scale finite element model exceeding 1 million degrees of freedom to improve NVH performance criteria in the final design phase. It is, however, difficult for a CAE engineer to propose the modification candidate for the NVH reduction to an automotive designer in the phase, while good accuracy of the analysis is obtained by using the large-scale model. Only the small modifications can be performed for the NVH performance since configurations of main frame structures are usually determined with respect to crashworthiness in the phase. Therefore, a CAE engineer cannot provide the designer with effective information on time. In this paper, a new optimal design method using a reduction scheme based on the physical coordinates under many design constraints regarding the crashworthiness is proposed in order to overcome above problems. Our proposed method finds out an optimal layout and stiffness value efficiently from the calculation results of the large-scale model. That is, we determine the appropriate location and additional scalar spring constants by minimizing the acceleration of the observation grid. The effectiveness and availability of this method are confirmed using an example.

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