Comparing Fatigue Reliability of Jack-Up Platforms Based on Selected Nonlinear Stress Models

2008 ◽  
Author(s):  
Naser Shabakhty
Keyword(s):  
Nonlinear Models ◽  
Nonlinear Behaviour ◽  
Fatigue Reliability ◽  
Offshore Structure ◽  
Advanced Technique ◽  
Stress Fluctuation ◽  
Nonlinear Stress ◽  
Exploration And Production ◽  
Offshore Industry ◽  
Jack Up

Jack-up is typically an exploration and production platform in shallow water operation. The possibility of moving this type of offshore structure from one location to other place and lifting up the deck above sea level made it attractive for offshore industry to use in deeper water and harsher environments. The jack-up structure consists of various components and behaves in a nonlinear and dynamic manner. Degradation phenomena such as fatigue may influence the structural performance and reduce strength of platform during its lifetime. Appropriate estimation of fatigue degradation strongly related to the suitable assessment of stress fluctuation, however, there are some uncertainties both in fatigue characteristics and environmental loads. These uncertainties can be taken into account in fatigue reliability framework. In this paper, several nonlinear models proposed by Wirsching and Light (W&L), Zhao and Baker (Z&L), Winterstein (Hermite model), in addition to the typical narrow banded model are utilized to specify nonlinearity in the stress fluctuation. The fatigue reliability is calculated based on these models and are compared with more advanced technique of rain flow counting method. The result shows a dependency between nonlinear behaviour of stress response and the selected model.

Reliability Analysis of Jack-Up Platforms Based on Fatigue Degradation

2002 ◽  
Author(s):  
Naser Shabakhty ◽  
Pieter van Gelder ◽  
Hotze Boonstra
Keyword(s):  
Service Time ◽  
Great Part ◽  
Fatigue Reliability ◽  
Original Design ◽  
Operational Conditions ◽  
Stress Fluctuation ◽  
The Difference ◽  
Offshore Industry ◽  
Jack Up ◽  
Load Conditions

Generally, jack-up structures are used for production drilling and exploration of hydrocarbons. The combination of mobility and the behavior as a fixed structure in operational conditions has made it an important structure in the offshore industry over the last 40 years. When a jack-up structure has been in operation for a great part of its original design-life and intention is there to extend the usage of this structure at a specific location, an investigation on fatigue degradation of the structure is an essential factor that has to be carried out before taking any decision. Fatigue is the process of damage accumulation in material due to stress fluctuation caused by variation of loads in service time. The fatigue failure occurs when accumulated damage has exceeded a critical level. In this paper, the remaining fatigue capacity of the jack-up structure is considered as an indicator for adequate use of the structure. It can be specified based on the difference between design-fatigue and fatigue experienced by the structure. The design-fatigue can be determined based on fluctuation of loads during the lifetime of the structure and experienced fatigue is specified by the load conditions, which the structure has experienced during its service time. When the information on the load conditions which the structure has experienced in its service time is available or known precisely, determination of the remaining fatigue capacity could be carried out by using the Palmgren–Miner’s rule. In practice, uncertainties are present in loads and characteristics of material. Hence it will be reasonable to determine the remaining fatigue reliability of the structure by the reliability methods. In this paper, based on a crack propagation approach and achieved information from inspection, it is shown that the remaining fatigue reliability of jack-up structures could be determined and updated by using a Bayesian procedure in the duration of the service time.

The Influence of Alternative Wave Loading and Support Modeling Assumptions on Jack-Up Rig Response Extremes

1996 ◽  
Vol 118 (2) ◽  
pp. 109-114 ◽  
Author(s):  
L. Manuel ◽  
C. A. Cornell
Keyword(s):  
Nonlinear Models ◽  
Random Wave ◽  
Force Model ◽  
Wave Loading ◽  
Force Modeling ◽  
Hydrodynamic Damping ◽  
Extreme Response ◽  
The Absolute ◽  
Non Gaussian ◽  
Jack Up

A study is conducted of the response of a jack-up rig to random wave loading. Steady current and wind load effects are also included. The effects of varying the relative motion assumption (in the Morison equation) and of varying the bottom fixity assumptions are investigated. One “fixity” model employs nonlinear soil springs. Time domain simulations are performed using linearized as well as fully nonlinear models for the jack-up rig. Comparisons of response statistics are made for two seastates. Hydrodynamic damping causes the rms response to be lower in the relative Morison case. The absence of this source of damping in the absolute Morison force model gives rise to larger resonance/dynamic effects—this tends to “Gaussianize” the response. Hence, the relative Morison model leads to stronger non-Gaussian behavior than the absolute Morison model. This is reflected in moments as well as extremes. The different support conditions studied are seen to significantly influence extreme response estimates. In general, stiffer models predict smaller rms response estimates, but also exhibit stronger non-Gaussian behavior. The choice of the Morison force modeling assumption (i.e., the relative versus the absolute motion formulation) is seen to have at least a secondary role in influencing response moments and extremes.

A Modified Matlock–Duffing Model for Two-Dimensional Ice-Induced Vibrations of Offshore Structures With Geometric Nonlinearities

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Hugh McQueen ◽  
Narakorn Srinil
Keyword(s):  
Oil And Gas ◽  
Numerical Models ◽  
Wedge Angle ◽  
Offshore Structures ◽  
Two Dimensional ◽  
Geometric Nonlinearities ◽  
Oil And Gas Exploration ◽  
Nonlinear Stress ◽  
Exploration And Production ◽  
Duffing Model

Oil and gas exploration and production have been expanding in Arctic waters. However, numerical models for predicting the ice-induced vibrations (IIV) of offshore structures are still lacking in the literature. This study aims to develop a mathematical reduced-order model for predicting the two-dimensional IIV of offshore structures with geometric coupling and nonlinearities. A cylindrical structure subject to a moving uniform ice sheet is analyzed using the well-known Matlock model, which, in the present study, is extended and modified to account for a new empirical nonlinear stress–strain rate relationship determining the maximum compressive stress (MCS) of the ice. The model is further developed through the incorporation of ice temperature, brine content, air volume, grain size, ice thickness, and ice wedge angle effects on the ice compressive strength. These allow the effect of multiple ice properties on the ice–structure interaction to be investigated. A further advancement is the inclusion of an equation allowing the length of failed ice at a point of failure to vary with time. A mixture of existing equations and newly proposed empirical relationships is used. Structural geometric nonlinearities are incorporated into the numerical model through the use of Duffing oscillators, a technique previously proposed in vortex-induced vibration studies. The model is validated against results from the literature and provides new insights into IIV responses including the quasi-static, randomlike chaotic, and locked-in motions, depending on the ice velocity and system nonlinearities. This numerical Matlock–Duffing model shows a potential to be used in future IIV analysis of Arctic cylindrical structures, particularly fixed offshore structures, such as lighthouses, gravity bases, and wind turbine monopiles.

Influencing Competence in Structural Integrity Management

2002 ◽  
Author(s):  
C. J. Billington ◽  
S. A. Caruana
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Safety Management ◽  
Oil And Gas Exploration ◽  
Operational Life ◽  
Exploration And Production ◽  
Management Context ◽  
Integrity Management ◽  
Offshore Industry ◽  
And Control

The offshore industry has experienced significant changes in the regulation and control of oil and gas exploration and production. The move away from the prescriptive approach towards a goal-setting regime gives Duty Holders greater control and accountability over the safety management of operations. Whilst this approach encourages greater ownership of safety by Duty Holders and provides greater flexibility, it also places greater demands and responsibility for ongoing integrity management, particularly when operational life is extended beyond the original specification with the need to account for the ageing mechanisms. Therefore it is increasingly important to ensure that those responsible for integrity management have all the necessary competences for this task and that the Duty Holder provides the necessary system competence to support this activity. This paper examines the factors which influence competence throughout the life-cycle of Structural Integrity Management (SIM) activities, and provides a model that relates this to a systematic safety management context.

Calculation of the Dynamic Positioning Capability of an Offshore Wind Farm Vessel During the Jack-Up Process in the Early Design Stage

2019 ◽  
Author(s):  
Maximilian Liebert
Keyword(s):  
Wind Farm ◽  
Offshore Wind ◽  
Design Stage ◽  
Force Model ◽  
Dynamic Positioning ◽  
The European Union ◽  
Early Design ◽  
Early Design Stage ◽  
Offshore Industry ◽  
Jack Up

Abstract As a consequence of the planned exit from fossil-based energy in the European Union the exploitation of renewable energies has become a major aspect of the Offshore Industry. Especially the construction and operation of offshore wind energy turbines pose a challenge which is met by the use of jack-up vessels with extendible legs. In order to dimension the vessel’s manoeuvring devices in the early design stage and to ensure a safe jack-up process for given environmental loads the dynamic positioning capability during the jacking including the influence of the legs has to be calculated. As part of the development of a holistic dynamic analysis this paper presents the implementation of the legs’ influence in an existing manoeuvring method. The manoeuvring method solves the equations of motion in three degrees of freedom (surge, sway, yaw). It is based on a force model which comprises various modular components. Therefore another component for the leg-forces is added. A Morison approach is chosen to calculate the hydrodynamic forces on the cylindrical legs. The legs’ hydrodynamic added masses are accounted for and added to the hull’s inertial terms. The benefit of the presented method is the possibility to calculate the dynamic positioning capability with extended legs without being dependent on the results of either time-consuming or non-specific model tests. Therefore the method represents a fast computing tool to design the vessel for the specific environmental conditions of the site of operation.

Dual Stiffness Approach for Polyester Mooring Line Analysis in Time Domain

2012 ◽  
Author(s):  
Arcandra Tahar ◽  
Djoni Sidarta ◽  
Alex Ran
Keyword(s):  
Traditional Method ◽  
Dynamic Stiffness ◽  
Performance Comparison ◽  
Mooring Line ◽  
Axial Stiffness ◽  
Analysis Tool ◽  
Floating Platform ◽  
Mooring Lines ◽  
Nonlinear Stress ◽  
Offshore Industry

Polyester mooring lines have been used in the offshore industry since the late ’90s. With increasing oil exploration and production in deeper waters, using polyester lines provides greater benefit than using traditional steel wires and chains. Some advantages of using polyester include a reduction of mooring line weight, a reduction in vessel offset and a reduction in the dynamics of the line tensions. However, unlike steel, polyester lines exhibit axial stiffness characteristics that are nonlinear and vary with time and loading history. Tahar (2001) developed a comprehensive theory and numerical tool to capture this behavior. The formulas allow relatively large elongation and nonlinear stress-strain relationships, as typically observed in polyester fibers. The mooring line dynamics are based on a rod theory and finite element method (FEM), with the governing equations described in a generalized coordinate system. Since this theory is computationally intensive, the benefits outweigh the costs less than they do for the practical approach recommended by API. Therefore, the fully coupled dynamic analysis tool CHARM3D has been modified to incorporate the API-recommended approach. Two axial stiffnesses (EA), post installation (static) stiffness and storm (dynamic) stiffness, have been convoluted into a dual stiffness to represent the total response of the floating platform in a single run. In the traditional method, the analyses are done twice, one run for each stiffness. Then, the extremes from each run are used as governing values for design. This paper presents the global performance comparison between the dual stiffness method and the traditional method. The effect of motions on SCR strength is also investigated using ABAQUS software.

Engineering Establishment of Living Quarters for Jack-Up Rig Structures

2016 ◽  
Author(s):  
Yeong Su Ha ◽  
Joo Shin Park ◽  
Jeong Bon Koo ◽  
Byung Jin Cho ◽  
Kuk Yeol Ma ◽  
...  
Keyword(s):  
Structural Engineering ◽  
Three Dimensional ◽  
Technical Specification ◽  
International Standards ◽  
Structural Safety ◽  
Fe Model ◽  
Wave Loads ◽  
Offshore Structure ◽  
Local Loads ◽  
Jack Up

The Living-Quarters (hereafter referred to as ‘LQ’) is one of the major structures for ship and offshore structure. The LQ gives safe living conditions to crews on board. Until now the structural design of LQ structure is based on simplistic beam calculation to determine the initial scantling under design load. These days, safety for people is a raising issue. It is needed to meet the high oil company’s needs as well as technical specification throughout offshore project. But, the engineering procedure for LQ structure is not clearly defined by classification of society rules and international standards. In this paper, the newly engineering procedure for LQ design is established considering LQ global loads with local loads for large equipment such as helideck structure, telecom mast and life saving appliances, and so on. To consider LQ global loads with local loads, the integrated three dimensional FE model and high technology engineering should be needed to require many kind of rules for equipment. Recently, the damage of LQ structure is occasionally reported during towing condition for jack-up rig structure. The LQ of jack-up rig is encountered such as slamming pressure and greenwater produced by harsh wave loads during towing condition because of small height of freeboard comparing to the wave height. To verify the structural safety under towing condition, the detailed non-liner analysis is performed to verify the load-carrying capacity against greenwater pressure. We newly propose a structural engineering procedure to improve the reliability of the LQ design in the jack-up rigs. From basis of this procedure, a more reasonable and optimized results are proposed as a practical manner as well as scientific approach.

scholarly journals Multiple states in river and lake ecosystems

2002 ◽  
Vol 357 (1421) ◽  
pp. 635-645 ◽  
Author(s):  
C. Lisa Dent ◽  
Graeme S. Cumming ◽  
Stephen R. Carpenter
Keyword(s):  
Linear Models ◽  
Nonlinear Models ◽  
Explanatory Power ◽  
Current Theory ◽  
Ecosystem Dynamics ◽  
Physical Factors ◽  
Nonlinear Behaviour ◽  
Positive Feedbacks ◽  
Lake Ecosystems ◽  
Physical Forcing

Nonlinear models of ecosystem dynamics that incorporate positive feedbacks and multiple, internally reinforced states have considerable explanatory power. However, linear models may be adequate, particularly if ecosystem behaviour is primarily controlled by external processes. In lake ecosystems, internal (mainly biotic) processes are thought to have major impacts on system behaviour, whereas in rivers, external (mainly physical) factors have traditionally been emphasized. We consider the hypothesis that models that exhibit multiple states are useful for understanding the behaviour of lake ecosystems, but not as useful for understanding stream ecosystems. Some of the best–known examples of multiple states come from lake ecosystems. We review some of these examples, and we also describe examples of multiple states in rivers. We conclude that the hypothesis is an oversimplification; the importance of physical forcing in rivers does not eliminate the possibility of internal feedbacks that create multiple states, although in rivers these feedbacks are likely to include physical as well as biotic processes. Nonlinear behaviour in aquatic ecosystems may be more common than current theory indicates.

Sensitivity Study of Wake Oscillator Parameters Influencing the Fatigue Damage of a Riser Undergoing VIV

2015 ◽  
Author(s):  
Ying Min Low ◽  
Narakorn Srinil
Keyword(s):  
Fatigue Damage ◽  
Structural Equation ◽  
Damping Ratio ◽  
Lift Coefficient ◽  
Sensitivity Study ◽  
Fatigue Reliability ◽  
Empirical Modelling ◽  
Wake Oscillator ◽  
Offshore Industry ◽  
The Impact

A great deal of attention has recently been paid to the semi-empirical modelling, nonlinear response prediction and estimation of stress and fatigue damage of marine risers undergoing vortex-induced vibrations (VIV). This is because when as the offshore industry move into deeper waters, the impact of VIV caused by ocean currents becomes detrimental being one of great concerns for offshore operators and riser engineers. For computational efficiency in time domain, the van der Pol wake oscillator, coupled with the structural equation of motion, has been an attractive approach. However, wake oscillator models rely on empirical coefficients, which have uncertainties whose effect on the fatigue reliability is not well understood. This study focusses on the wake oscillator proposed by Skop and Balasubramanian (1997). Using a top-tensioned riser model, a sensitivity study is performed on several random variables to determine their influence on the uncertainty of the fatigue damage. These variables include the maximum vibration amplitude, frequency ratio, damping ratio and lift coefficient. In addition, Monte Carlo simulations are conducted to predict the probability of failure.

Design of the University of New Orleans Ship-Offshore University Laboratory for Offshore Industry Support

1988 ◽  
Vol 110 (3) ◽  
pp. 133-140 ◽  
Author(s):  
R. Latorre
Keyword(s):  
New Orleans ◽  
Water Current ◽  
Offshore Structure ◽  
Water Research ◽  
Towing Tank ◽  
Calm Water ◽  
Tank Design ◽  
Offshore Industry ◽  
The University ◽  
University Laboratory

On July 23, 1987, the University of New Orleans (UNO) dedicated its new Engineering Building, which houses a 38.3 m×4.57 m×0–2.134 m deep ship-offshore university laboratory tow tank. This paper covers the initial stages of the project and summarizes the towing tank design for ship-offshore testing. The tank is configured for three purposes: 1) conventional ship research in deep water with calm water or waves; 2) offshore structure testing with provision for observation and anchoring; 3) shallow water research in calm water, current, and waves.

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