Study of Seabed Trench Induced by Steel Catenary Riser and Seabed Interaction

2016 ◽  
Author(s):  
Kunpeng Wang ◽  
Ying Min Low
Keyword(s):  
Frequency Response ◽  
Static Analysis ◽  
Fatigue Damage ◽  
Surrogate Model ◽  
Unit Length ◽  
Low Frequency ◽  
Steel Catenary Riser ◽  
Cubic Polynomial ◽  
Seabed Interaction ◽  
Touchdown Point

Seabed trench profile has significant effect on the fatigue damage of steel catenary riser near touchdown point. This study briefly demonstrates an approach in literature to determine the seabed trench induced by wave frequency response based on the cubic polynomial model. In this approach, a criterion for the matching between catenary riser and seabed trench is proposed, which is an optimization problem, and needs iterative static analysis of catenary riser. Based on the criterion, the sensitivity of the trench length and position to three parameters is parametrically studied: riser mass per unit length, ratio of horizontal span to vertical span of catenary part, trench depth. The obtained data are employed to fit the equations of trench length and position, which is taken as surrogate model since the iterative static analysis is very complicated. For completeness, the validation against data obtained from hysteretic seabed model is also illustrated. Based on the surrogate model, this study investigates the effect of trench depth on the fatigue damage near touchdown and the effect of the low frequency response on the seabed trench, and some useful conclusions are obtained.

Sensitivity Study of Critical Parameters Influencing the Uncertainty of Fatigue Damage in Steel Catenary Risers

2010 ◽  
Author(s):  
Feng Zi Li ◽  
Ying Min Low
Keyword(s):  
Fatigue Damage ◽  
Cost Effective ◽  
Sensitivity Study ◽  
Structural Safety ◽  
Critical Parameters ◽  
Design Parameters ◽  
Steel Catenary Riser ◽  
Bending Stresses ◽  
Steel Catenary Risers ◽  
Touchdown Point

The most challenging aspect of a deepwater development is the riser system, and a cost-effective choice is the Steel Catenary Riser (SCR). Fatigue is often a governing design consideration, and it is usually most critical at the touchdown point (TDP) where static and dynamic bending stresses are highest. Unfortunately, it is also at this region that uncertainty is the maximum. The increased uncertainty casts doubt on the applicability of generic safety factors recommended by design codes, and the most consistent way of ensuring the structural safety of the SCR is to employ a reliability-based approach, which has so far not received attention in SCR design. As the number of basic random variables affects the complexity of a reliability analysis, these variables should be selected with caution. To this end, the aim of this paper is to draw up a comprehensive list of design parameters that may contribute meaningfully to the uncertainty of the fatigue damage. From this list, several parameters are selected for sensitivity studies using the commercial package Orcaflex. It is found that variations in seabed parameters such as soil stiffness, soil suction and seabed trench can have a pronounced influence on the uncertainty of the fatigue damage at the touchdown point.

Seabed Interaction Modeling Effects on the Global Response of Catenary Pipeline: A Case Study

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Hany Elosta ◽  
Shan Huang ◽  
Atilla Incecik
Keyword(s):  
Fatigue Damage ◽  
Interaction Model ◽  
Fatigue Performance ◽  
Random Waves ◽  
Floating Platform ◽  
Geotechnical Parameters ◽  
Steel Catenary Riser ◽  
Considerable Uncertainty ◽  
Interaction Modeling ◽  
Seabed Interaction

A steel catenary riser (SCR) attached to a floating platform at its upper end encounters oscillations in and near its touchdown zone (TDZ), which results in interaction with the seabed. Field observations and design analysis of SCRs show that the highest stress and greatest fatigue damage occurred near the touchdown point where the SCR first touches the seabed soil. The challenges regarding the fatigue damage assessment of an SCR in the TDZ are primarily because of the nonlinear behavior of SCR–seabed interaction and considerable uncertainty in seabed interaction modeling and geotechnical parameters. Analysis techniques have been developed in the two main areas: SCR–seabed interaction modeling and the influence of the uncertainty in the geotechnical parameters on the dynamic response and fatigue performance of SCRs in the TDZ. Initially, this study discusses the significance of SCR–seabed interaction on the response of an SCR for deepwater applications when subjected to random waves on soft clay using the commercial code OrcaFlex for nonlinear time domain simulation. In the next step, this study investigates the sensitivity of fatigue performance to geotechnical parameters through a parametric study. It is proven that employing the improved lateral SCR–seabed interaction model with accurate prediction of soil stiffness and riser penetration with cyclic loading enables us to obtain dynamic global riser performance in the TDZ with better accuracy. The fatigue analyses results prove that the confounding results indicated by the previous research studies on the SCR in the TDZ are due to different geotechnical parameters imposed with the seabed interaction model. The main benefit of employing nonlinear seabed approach is to capture the entity of realistic soil interaction behavior in modeling and analysis and to predict the likelihood of the fatigue damage of the SCR with seabed interaction, thereby minimizing the risk of the loss of the containment with the associated environmental impact.

Fatigue Damage Study of Helical Wires in Catenary Unbonded Flexible Riser Near Touchdown Point

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Kunpeng Wang ◽  
Chunyan Ji ◽  
Hongxiang Xue ◽  
Wenyong Tang
Keyword(s):  
Analytical Model ◽  
Fatigue Damage ◽  
Global Analysis ◽  
Axial Stress ◽  
Flexible Riser ◽  
Steel Catenary Riser ◽  
Finite Element Software ◽  
Seabed Stiffness ◽  
Touchdown Point ◽  
Unbonded Flexible Riser

This study presents an analytical model of flexible riser and implements it into finite-element software abaqus to investigate the fatigue damage of helical wires near touchdown point (TDP). In the analytical model, the interlayer contact pressure is simulated by setting up springs between adjacent interlayers. The spring stiffness is iteratively updated based on the interlayer penetration and separation conditions in the axisymmetric analysis. During the bending behavior, the axial stress of helical wire along the circumferential direction is traced to determine whether the axial force overcomes the interlayer friction force and thus lead to sliding. Based on the experimental data in the literature, the model is verified. The present study implements this model into abaqus to carry out the global analysis of the catenary flexible riser. In the global analysis, the riser–seabed interaction is simulated by using a hysteretic seabed model in the literature. The effect of the seabed stiffness and interlayer friction on the fatigue damage of helical wire near touchdown point is parametrically studied, and the results indicate that these two aspects significantly affect the helical wire fatigue damage, and the sliding of helical wires should be taken into account in the global analysis for accurate prediction of fatigue damage. Meanwhile, different from the steel catenary riser, high seabed stiffness may not correspond to high fatigue damage of helical wires.

scholarly journals Understanding the low frequency response of carbon nanotube thermoacoustic projectors

2021 ◽  
Vol 498 ◽  
pp. 115940
Author(s):  
Prashant Kumar ◽  
Rammohan Sriramdas ◽  
Ali E. Aliev ◽  
John B. Blottman ◽  
Nathanael K. Mayo ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Frequency Response ◽  
Low Frequency

Collective oscillations in bubble clouds

2011 ◽  
Vol 680 ◽  
pp. 114-149 ◽  
Author(s):  
ZORANA ZERAVCIC ◽  
DETLEF LOHSE ◽  
WIM VAN SAARLOOS
Keyword(s):  
Frequency Response ◽  
Acoustic Field ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Viscous Damping ◽  
Edge States ◽  
Bubble Cloud ◽  
Collective Oscillations ◽  
The Individual ◽  
Bubble Oscillations

In this paper the collective oscillations of a bubble cloud in an acoustic field are theoretically analysed with concepts and techniques of condensed matter physics. More specifically, we will calculate the eigenmodes and their excitabilities, eigenfrequencies, densities of states, responses, absorption and participation ratios to better understand the collective dynamics of coupled bubbles and address the question of possible localization of acoustic energy in the bubble cloud. The radial oscillations of the individual bubbles in the acoustic field are described by coupled linearized Rayleigh–Plesset equations. We explore the effects of viscous damping, distance between bubbles, polydispersity, geometric disorder, size of the bubbles and size of the cloud. For large enough clusters, the collective response is often very different from that of a typical mode, as the frequency response of each mode is sufficiently wide that many modes are excited when the cloud is driven by ultrasound. The reason is the strong effect of viscosity on the collective mode response, which is surprising, as viscous damping effects are small for single-bubble oscillations in water. Localization of acoustic energy is only found in the case of substantial bubble size polydispersity or geometric disorder. The lack of localization for a weak disorder is traced back to the long-range 1/r interaction potential between the individual bubbles. The results of the present paper are connected to recent experimental observations of collective bubble oscillations in a two-dimensional bubble cloud, where pronounced edge states and a pronounced low-frequency response had been observed, both consistent with the present theoretical findings. Finally, an outlook to future possible experiments is given.

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