Friction, Contact Pressure and Non-Linear Behavior of Steel Tubes in Subsea Umbilicals

2013 ◽  
Author(s):  
Farzan Parsinejad ◽  
Chris Kassner ◽  
Mark Kurtz ◽  
Naiquan Ye
Keyword(s):  
Contact Pressure ◽  
Fatigue Damage ◽  
Cross Sections ◽  
Friction Stress ◽  
Stress Range ◽  
Steel Tubes ◽  
Load Variation ◽  
Linear Behavior ◽  
Non Linear ◽  
The Impact

Steel tube umbilical risers in deep water applications are subject to significant variable environmental loads during operation. These tubes are designed to carry high pressure fluids, up to 15,000 psi. The stresses accumulated in the walls consist of contribution from movement of the floating platform on which the umbilical is connected, axial tension due to the weight of umbilical and ancillaries, and internal pressure due to end cap effect. The helically wound steel tubes in umbilicals are un-bonded and can slip against adjacent layers. Therefore the stresses in these tubes experience a hysterical feature when the slip changes directions. It is known that in addition to bending stress, friction stress range has a major contribution in fatigue damage. If there is full slip, the friction stress range will be a constant value regardless of the load variation. However in many cycles the full slip is not reached and the stress range is proportional to load variation. This paper focuses on evaluating the impact of friction and contact pressure on helical steel tubes. The initial gaps between steel tubes and adjacent layers, friction coefficients and the contact stiffness are the main factors that affect such investigation. A novel methodology by using UFLEX2D (a MARINTEK product) has been applied for modeling complex umbilical cross sections and for the study of these parameters. Two cross sections for the same subsea application but with different designs have been investigated in the study. It has been shown how fatigue damage can be significantly impacted by different cross sectional design. For this study, non-linear moment/curvature relationship has been included in the analyses. Based on the findings of this study, more realistic results can be achieved by including the non-linear behavior in global analysis for fatigue damage calculations instead of using nominal bending stiffness supplied by umbilical manufacturer.

Friction, Contact Pressure, and Nonlinear Behavior of Steel Tubes in Subsea Umbilicals

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Farzan Parsinejad ◽  
Chris Kassner ◽  
Mark Kurtz ◽  
Naiquan Ye
Keyword(s):  
Contact Pressure ◽  
Fatigue Damage ◽  
Cross Sections ◽  
Contact Stiffness ◽  
Global Analysis ◽  
Nonlinear Behavior ◽  
Steel Tubes ◽  
Cross Sectional ◽  
Cross Sectional Design ◽  
The Impact

This paper focuses on evaluating the impact of friction and contact pressure on helical steel tubes. The initial gaps between steel tubes and adjacent layers, friction coefficients and the contact stiffness are the main factors that affect such investigation. A novel methodology by using UFLEX2D (a MARINTEK product) has been applied for modeling complex umbilical cross sections and for the study of these parameters. Two cross sections for the same subsea application but with different designs have been investigated in the study. It has been shown how fatigue damage can be significantly impacted by different cross-sectional design. For this study, nonlinear moment/curvature relationship has been included in the analyses. Based on the findings of this study, more realistic results can be achieved by including the nonlinear behavior in global analysis for fatigue damage calculations instead of using nominal bending stiffness supplied by umbilical manufacturer.

The Effects of Modelling Techniques and Data Uncertainty in Wellhead Fatigue Life Calculation

2012 ◽  
Author(s):  
Dara Williams ◽  
John Greene
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Environmental Data ◽  
Nonlinear Load ◽  
Soil Response ◽  
Load Response ◽  
Highly Nonlinear ◽  
Non Linear ◽  
The Impact

Offshore oil and gas exploration continues to move into deeper and more harsh environments and consequently the response of drilling riser systems and associated fatigue loading transmitted to the wellhead and conductor system are of key importance in the design of offshore wells. In addition the presence of ageing infrastructure in mature areas combined with requirements for future workover operations requires careful consideration of both past and future fatigue damage accumulation. In order to estimate remaining fatigue life for the wellhead and conductor the accumulation of damage from each stage of a drilling campaign and phase of operation of a well, including workover and completion operations, must be considered. Thus a detailed global finite element analysis of the impact of riser response, under wave and vortex induced vibration (VIV), on the conductor and wellhead structure is of critical importance. Traditional engineering evaluation methods to estimate fatigue of wellhead systems in offshore regions with limited availability of environmental data may result in an over estimation of fatigue damage accumulated in the wellhead. Any assumptions regarding fatigue current profiles can also lead to over-prediction of fatigue damage in the wellhead. This can have implications for the planning of future workover operations and may also lead to unnecessary over-design of the system. A further limitation of traditional wellhead fatigue evaluation criteria lies in the assumptions regarding riser tensioner system load response. These methods do not account for the highly nonlinear load response of the tensioner system and can thus significantly underestimate fatigue damage contribution. This paper presents a more detailed wellhead fatigue analysis methodology to incorporate new analysis techniques, as used for a number of recent applications, to assess with a greater level of refinement the impact of the riser motions on the wellhead fatigue. Specifically this methodology incorporates the generation of a detailed global finite element model of the riser and wellhead system to include detailed non-linear riser tensioner system models, accurate models of the wellhead and conductor, detailed non-linear soil response characteristics and the use of more refined current data as input to VIV calculations. The details of the riser and wellhead system model are presented and the conservatisms associated with traditional modeling methods with regard to VIV and riser tensioner load variations are discussed. A number of case studies are presented to illustrate the effects of various data assumptions and simplifications on estimated wellhead fatigue.

Modelling of Marine Riser Tensioner Load Variations and Implications for Minimum Top Tension Settings in Drilling Risers

2012 ◽  
Author(s):  
Conor Gallagher ◽  
Dara Williams ◽  
Donogh Lang
Keyword(s):  
Oil And Gas ◽  
Software Tool ◽  
System Response ◽  
Analysis Tool ◽  
Fe Model ◽  
Deepwater Drilling ◽  
Load Variation ◽  
Non Linear ◽  
The Impact ◽  
Water Depths

As the pace of deepwater oil and gas exploration continues to grow, so too does demand for modern drilling vessels with equipment capable of operating in water depths of 10,000ft or greater. These greater water depths place significant demands on the drilling riser and the riser tensioning system. Modern riser tensioners are complex hydro-pneumatic systems and far from applying a constant top tension, the stiffness and damping characteristics associated with the tensioner mean that the applied tension can vary substantially as the tensioner strokes in response to vessel heave. As a result it is critical that the riser tensioner system response be captured in sufficient detail when evaluating the loads on the drilling riser. Riser tensioner systems for deepwater drilling must be capable of supplying the required tension to satisfy the minimum stability tension requirement, as per API RP 16Q; however this recommended practice does not adequately account for dynamic tensioner load variation, which can be up to 50% of the nominal tension. For deepwater drilling riser systems, where riser load limits are being approached, accurate modeling of the tensioner system load variation is required to ensure that the riser does not experience compression or excessive stresses. Furthermore, as the dynamic tension variations are largely velocity dependent, they can be relatively independent of water depth. Thus larger percentage variations in tension are experienced at low tensions when compared to higher tensions. This is an important consideration when calculating minimum top tensions for deepwater drilling rigs in shallower water depths. This paper presents a comparison of the response of a direct-acting riser tensioner (DAT) system for a range of environments. The comparison is based on results from detailed tensioner models that include the individual hydraulic and pneumatic components of the tensioner system and that are fully integrated with a non-linear 3D structural FE analysis tool [1]. The FE model is based on a widely-validated-non-linear software tool [3]. The detailed tensioner model has been validated against manufacturer performance data for existing in-service tensioner systems. The detailed tensioner model has also been used as part of a drilling riser recoil analysis study [1] which provided a good comparison of recoil analysis results against a published recoil test case. The impact on the global riser response of accurately modeling the tensioner system behavior is demonstrated, while the implications for the calculation of minimum top tension are also discussed.

Effects of different parameters on inelastic buckling behavior of composite concrete-filled steel tubes

2019 ◽  
Author(s):  
Hossein Alimohammadi ◽  
Mohammadali Lotfollahi Yaghin ◽  
Mostafa Dalvi Esfahani
Keyword(s):  
Cross Sections ◽  
Concrete Surface ◽  
Horizontal Distance ◽  
Steel Tubes ◽  
Composite Columns ◽  
Buckling Behavior ◽  
Steel Sections ◽  
Concrete Filled Steel Tubes ◽  
The Impact ◽  
Box Columns

Composite columns are one of the most used cross-sections in various buildings and bridges. In this research, the impact of different parameters such as the effect of the eccentricity of loads or the change in the horizontal distance of the loading profiles in buckling of the composite columns with double IPE cross-sections as well as the impact of different value of slenderness on buckling of composite box columns has been investigated. Based on the results, the steel member's yielding will be delayed by filling the steel sections with concrete. Also, an increase in the amount of composite column capacity is directly related to the associative ratio of composite concrete. In other words, increasing the ratio of the concrete surface leads to greater capacity which is caused by being filled with concrete.

scholarly journals Failure of Slender Concrete Columns Due to a Loss of Stability

2019 ◽  
Vol 27 (1) ◽  
pp. 45-51 ◽  
Author(s):  
Vladimír Benko ◽  
Jakub Dobrý ◽  
Marek Čuhák
Keyword(s):  
Cross Sections ◽  
Linear Method ◽  
Bending Moment ◽  
Concrete Columns ◽  
Order Theory ◽  
Loss Of Stability ◽  
Non Linear ◽  
Calculation Results ◽  
European Code ◽  
The Impact

Abstract The European standard for the design of concrete structures that are likely to lose stability requires taking into account the effects of second order theory. This effect increases the impact of a bending moment due to member deformation and additional eccentricity. Slender members can be calculated by the use of a non-linear method. This approach shows a deficit in global reliability for cases where the concrete columns fail due to the loss of stability before reaching the design resistance in the critical cross-sections. Buckling is a brittle failure which occurs without any warning, and the probability of its formation is markedly influenced by the slenderness of the column. Here, the calculation results are presented and compared with the results from an experiment which was carried out in cooperation with STRABAG Bratislava LTD at the Central Laboratory of the Faculty of Civil Engineering SUT in Bratislava. The columns were designed according to the methods stated in STN EN 1992-1-1, namely, a general non-linear method. The focus of this study is to compare multiple approaches based on codes used in Germany (DIN 1045-1, 2001) and Austria (ÖNORM B 4700, 2001) with the present European code mentioned above. The paper aims to compare the global reliability of slender concrete columns with variable slendernesses of 90 and 160.

The efficiency of application of virtual cross-sections method and hypotheses MELS in problems of wave signal propagation in elastic waveguides with rough surfaces

2016 ◽  
pp. 3564-3575 ◽  
Author(s):  
Ara Sergey Avetisyan
Keyword(s):  
Half Space ◽  
Cross Sections ◽  
Classical Method ◽  
Signal Propagation ◽  
Elastic Half Space ◽  
Layered Systems ◽  
Surface Layers ◽  
Inhomogeneous Surface ◽  
Wave Signal ◽  
The Impact

The efficiency of virtual cross sections method and MELS (Magneto Elastic Layered Systems) hypotheses application is shown on model problem about distribution of wave field in thin surface layers of waveguide when plane wave signal is propagating in it. The impact of surface non-smoothness on characteristics of propagation of high-frequency horizontally polarized wave signal in isotropic elastic half-space is studied. It is shown that the non-smoothness leads to strong distortion of the wave signal over the waveguide thickness and along wave signal propagation direction as well.  Numerical comparative analysis of change in amplitude and phase characteristics of obtained wave fields against roughness of weakly inhomogeneous surface of homogeneous elastic half-space surface is done by classical method and by proposed approach for different kind of non-smoothness.

Nonlinear Time Series Analysis with R

2018 ◽  
Author(s):  
Ray Huffaker ◽  
Marco Bittelli ◽  
Rodolfo Rosa
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Particle Physics ◽  
Linear Time ◽  
Nonlinear Time Series ◽  
Nonlinear Time Series Analysis ◽  
Series Analysis ◽  
Linear Behavior ◽  
Non Linear ◽  
Scientific Principles

In the process of data analysis, the investigator is often facing highly-volatile and random-appearing observed data. A vast body of literature shows that the assumption of underlying stochastic processes was not necessarily representing the nature of the processes under investigation and, when other tools were used, deterministic features emerged. Non Linear Time Series Analysis (NLTS) allows researchers to test whether observed volatility conceals systematic non linear behavior, and to rigorously characterize governing dynamics. Behavioral patterns detected by non linear time series analysis, along with scientific principles and other expert information, guide the specification of mechanistic models that serve to explain real-world behavior rather than merely reproducing it. Often there is a misconception regarding the complexity of the level of mathematics needed to understand and utilize the tools of NLTS (for instance Chaos theory). However, mathematics used in NLTS is much simpler than many other subjects of science, such as mathematical topology, relativity or particle physics. For this reason, the tools of NLTS have been confined and utilized mostly in the fields of mathematics and physics. However, many natural phenomena investigated I many fields have been revealing deterministic non linear structures. In this book we aim at presenting the theory and the empirical of NLTS to a broader audience, to make this very powerful area of science available to many scientific areas. This book targets students and professionals in physics, engineering, biology, agriculture, economy and social sciences as a textbook in Nonlinear Time Series Analysis (NLTS) using the R computer language.

scholarly journals A note on the relations between elastic and inelastic interactions and increasing ratio σel(s)/σtot(s) at the LHC

2019 ◽  
Vol 34 (32) ◽  
pp. 1950259 ◽  
Author(s):  
S. M. Troshin ◽  
N. E. Tyurin
Keyword(s):  
Elastic Scattering ◽  
Energy Dependence ◽  
Impact Parameter ◽  
Cross Sections ◽  
Parameter Dependence ◽  
Slope Parameter ◽  
Short Notice ◽  
Inelastic Interactions ◽  
The Impact ◽  
Mode A

We comment briefly on relations between the elastic and inelastic cross-sections valid for the shadow and reflective modes of the elastic scattering. Those are based on the unitarity arguments. It is shown that the redistribution of the probabilities of the elastic and inelastic interactions (the form of the inelastic overlap function becomes peripheral) under the reflective scattering mode can lead to increasing ratio of [Formula: see text] at the LHC energies. In the shadow scattering mode, the mechanism of this increase is a different one, since the impact parameter dependence of the inelastic interactions probability is central in this mode. A short notice is also given on the slope parameter and the leading contributions to its energy dependence in both modes.

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