Contribution to the Evaluation of VIV Analyses Using Wake Oscillator and Vortex Tracking Models

2008 ◽  
Author(s):  
Daniel Lyrio Carneiro ◽  
Gilberto Bruno Ellwanger ◽  
Nelson Szilard Galgoul
Keyword(s):  
Degrees Of Freedom ◽  
Oil And Gas ◽  
Lateral Displacement ◽  
Three Dimensional ◽  
Low Frequency ◽  
Offshore Structures ◽  
Gas Production ◽  
Current Profile ◽  
Mooring Lines ◽  
Wake Oscillator

Fatigue due to vortex-induced vibrations (VIV) is one of the major uncertainties today in the design of slender offshore structures, such as risers, pipelines, umbilicals, tendons and mooring lines, required for oil and gas production in deep waters. The absence of reliable tools for quantitative analyses of this phenomenon is a technological barrier, which is being faced by several research groups. This paper presents valuable VIV results achieved by the author, using “wake oscillator” and “vortex tracking” models, when researching for his M. Sc. dissertation. Time domain analyses were performed using a commercial software. First results describe the response of the evaluated models for two degrees-of-freedom rigid cylinders by tracing lateral displacement versus flow velocity curves. These curves are plotted over others previously published in recognized recommended practices, articles and theses. Afterwards, VIV analyses results for a steel catenary 10-inch diameter riser in three-dimensional current profiles were compared to measured values. The considered riser, installed in 910m water depth offshore Brazil, is possibly the only monitored SCR with no VIV suppression devices in the world today. The results were considered satisfactory, despite some discrepancies: the model which appeared to be one of the most attractive for the rigid cylinder case, failed to predict VIV in the SCR under an irregular current profile, for example. Vortex tracking models presented excessive low frequency response in the SCR analyses. Authors believe that this response is unrealistic, and these frequencies can be dissipated by using a more adequate damping model than that employed by the utilized program.

VIM Simulation Method on a Cylindrical Floating Structure

2016 ◽  
Author(s):  
Toshifumi Fujiwara
Keyword(s):  
Fatigue Damage ◽  
Low Frequency ◽  
Safety Evaluation ◽  
Simulation Method ◽  
Offshore Structures ◽  
Dominant Factor ◽  
Floating Structure ◽  
Mooring Lines ◽  
Wake Oscillator ◽  
Low Frequency Motion

A cylindrical floating structure can basically experience Vortex-induced Motion (VIM) in strong current. Since the VIM on the structure with long term low-frequency motion causes fatigue damage of the structure’s mooring lines and risers, precise VIM assessment is needed for the safety evaluation of them. In the standard of the International Organization for Standardization ISO19901-7, ‘Specific requirements on stationkeeping systems for floating offshore structures and mobile offshore units’, for instance, a concrete method of assessing VIM displacement is not represented in the standard document, though the requirement on the VIM demands to do the assessment on the basis of proper ways. Then in this paper, a VIM simulation method on a floating structure with circular cylinder form, that is, for example a Spar, a MPSO (Mono-column type floating Production Storage and Offloading) and so on, is shown using the wake-oscillator model. Transverse VIM is only treated since it is dominant factor on the fatigue damage of the mooring lines and risers. The assessment quality of the simulation method on the transverse VIM of floaters in current is confirmed by model test data.

Evaluation of Methods to Predict Safe Welding Conditions and Maximum HAZ Hardness in Steel Welding

1995 ◽  
Vol 117 (1) ◽  
pp. 46-56 ◽  
Author(s):  
J. P. Tronskar
Keyword(s):  
Oil And Gas ◽  
High Strength Steels ◽  
Offshore Structures ◽  
Structural Steels ◽  
Gas Production ◽  
Carbon Equivalent ◽  
Chemical Compositions ◽  
International Institute ◽  
Empirical Formulas ◽  
Offshore Industry

During the last ten years new structural steels of improved weldability have been introduced. In particular, structural steels for the fabrication of offshore structures have been greatly improved in this respect throughout this period. These steels have lean chemical compositions which are generally outside the range for which the existing HAZ hardness criteria and the International Institute of Welding carbon equivalent (CEIIW) formula were originally developed. This paper presents the results from investigations of the weldability of three normalised (Re min 350 MPa) and three quenched and tempered (Re min 500 MPa) offshore structural steels. Weldability testing was conducted to study the relative performance of the different steels and to obtain a comparison between the capability of the different methods to predict safe welding conditions to avoid cold cracking in steel welding. It has become a widespread practice in welding high-strength steels to incorporate maximum HAZ hardness restrictions in fabrication specifications, particularly so in the offshore industry. Maximum HAZ hardness restrictions are often a point of contention between fabricators and their clients due to the difficulties often experienced in meeting these hardness requirements. Problems meeting maximum HAZ hardness requirements have been encountered for applications where maximum hardness HRC 22 or Vickers HV10 260 have been imposed for materials exposed to sour service in oil and gas production, processing and transportation. Many attempts have been made to develop empirical formulas for the estimation of maximum HAZ hardnesses. This paper presents some of the more successful approaches proposed to date and compares their performance.

Performance of Embedded Mooring Lines During Keying and Diving of Gravity Installed Anchors

2018 ◽  
Author(s):  
Yanbing Zhao ◽  
Haixiao Liu
Keyword(s):  
Finite Element ◽  
Drag Force ◽  
Parametric Study ◽  
Oil And Gas ◽  
Strain Softening ◽  
Three Dimensional ◽  
Frictional Coefficient ◽  
Mooring Lines ◽  
Soil Strain ◽  
The Relationship

Gravity installed anchors (GIAs) are the most recent generation of anchoring solution to moor floating facilities for deepwater oil and gas developments. After the installation of GIAs, the anchors are connected with the floating facility via the mooring lines, which interact with the anchors at the shackle and influence the keying and diving performance of GIAs. In the present work, a three-dimensional large deformation finite element (LDFE) model is established using the coupled Eulerian–Lagrangian method to investigate the performance of embedded mooring lines during keying and diving of GIAs. To verify the efficiency of the LDFE model, comparisons with the plasticity models are performed. Then, a parametric study is undertaken to quantify the relationship between the drag force Ta and drag angle θah at the shackle and the drag force T0 and drag angle θ0 at the mudline, in terms of the frictional coefficient, drag angle at the mudline and soil strain rate and strain softening. It is demonstrated that the drag angle at the mudline has the most significant effect on the performance of embedded mooring lines and hence the keying and diving of GIAs.

The Hydrodynamic Response and Frequency Domain Analysis of Deep Sea Truss Spar Platform

2013 ◽  
Vol 734-737 ◽  
pp. 1308-1312
Author(s):  
Song Sang ◽  
Xiao Shi ◽  
Chang Dong Li
Keyword(s):  
Frequency Domain ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Frequency Domain Analysis ◽  
Water Area ◽  
Calculation Model ◽  
Gas Production ◽  
Floating Body ◽  
Spar Platform ◽  
Oil And Gas Production

With the development of marine oil going to the deeper water area, SPAR platform with its many advantages has gradually become the mainstream of the offshore oil and gas production facilities. In this paper, the Spar platform three-dimensional hydrodynamic model establish is established firstly, then the floating body hydrodynamic is calculated by using the three-dimensional flow theory to get Spar platforms transfer function and hydrodynamic parameters of its motion response. At last, the frequency domain for floating body and mooring system coupling calculation model is analyzed.

scholarly journals Formulation of a Linearized Model for Vehicle-Track Interactions

2019 ◽  
Vol 2019 ◽  
pp. 1-16
Author(s):  
Fei Huo ◽  
Huanyun Dai
Keyword(s):  
Linear Model ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Safety Margin ◽  
Low Frequency ◽  
System Response ◽  
Energy Principle ◽  
Lateral Creep ◽  
Linearized Model ◽  
Random Vibration Analysis

In this paper, a fundamental wheel-rail interaction (WRI) element accompanied by its coupling matrices with other vehicle-track components have been derived taking into consideration the aspect of linearization. The key to the presented formulation is the use of the geometrical relationships of relative motions between degrees of freedom (DOFs) and energy principle. To the WRI element, both of the conditions of wheel-rail contacts and wheel-rail separations are allowed in the numerical computations; besides, the effects of the linear creepage and the gravitational restoring are considered in the description of wheel-rail interactions. By comparing with an advanced three-dimensional nonlinear model, the capability of the linear model in characterizing the response amplitude and frequency characteristic of vehicle-track systems is demonstrated. Moreover, the method for the random vibration analysis of the linear model is presented by treating the creep coefficients as the random sources, through which the safety margin of system response can be predicted well. From the numerical examples, it is, additionally, concluded that the lateral creep coefficient holds significant influence on wheel-rail lateral interactions and track vibrations, especially for the responses at low frequency ranges.

Study of Targeted Energy Transfer Inside Three-Dimensional Acoustic Cavity by Two Nonlinear Membrane Absorbers and an Acoustic Mode

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Xian Wu ◽  
Jianwang Shao ◽  
Bruno Cochelin
Keyword(s):  
Energy Transfer ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Low Frequency ◽  
Nonlinear Energy Sink ◽  
Acoustic Mode ◽  
Targeted Energy Transfer ◽  
Working Zone ◽  
Acoustic Cavity ◽  
Acoustic Cavities

As a new approach to passive sound control in low-frequency domain, the targeted energy transfer (TET) phenomenon has been investigated inside a three-dimensional (3D) acoustic cavity by considering a two degrees-of-freedom (DOF) system with an acoustic mode and a membrane nonlinear energy sink (NES). The beginning of TET phenomenon of the 2DOF system and the desired working zone for the membrane NES have been defined. In order to enhance the robustness and the effective TET range in acoustic cavities, a 3DOF system with two membranes and one acoustic mode is studied in this paper. We consider two different membranes and two almost identical membranes to analyze the TET phenomenon, respectively. The desired working zone which was obtained by the 2DOF system is applied to analyze the 3DOF system. We observe that two membranes can enlarge the desired working zone.

scholarly journals Effect of Water Depths on the Hydrodynamic Responses of an FPSO Platform

2018 ◽  
Vol 203 ◽  
pp. 01022
Author(s):  
Matthew Guan ◽  
Montasir Osman Ahmed Ali ◽  
Cheng Yee Ng
Keyword(s):  
Oil And Gas ◽  
Response Spectrum ◽  
Low Frequency ◽  
Mooring Line ◽  
Random Wave ◽  
Statistical Parameters ◽  
Mooring Lines ◽  
Line System ◽  
Wave Condition ◽  
Water Depths

Ship-shaped Floating Production Storage Offloading platforms (FPSO) are commonly used in the production of oil and gas in offshore deepwater regions. The vessel is held in place by mooring lines anchored to the seabed during operation, either in spread or turret mooring arrangement. When designing such systems, water depth is a main factor that needs to be considered. At greater depths, the hydrodynamic properties of mooring lines become important and may not be accurately predicted through traditional experiments or numerical quasi-static models. Numerical simulation using coupled dynamic analysis is thus recommended, as the hull-mooring behaviour is analysed simultaneously, and the damping and added mass properties of the entire mooring line system is taken into account. This paper investigates the motions and mooring line tensions of a turret-moored FPSO at various water depths ranging from 1000 m to 2000 m. The analysis focuses on numerical simulations in the fully coupled dynamic time domain. The study utilizes the commercial software AQWA, with the FPSO model subjected to a unidirectional random wave condition. The hull hydrodynamics is first solved using the 3D radiation/diffraction panel method, and the hull response equation is then coupled with the mooring line equation. The dynamic motions and mooring line tensions results are presented in terms of statistical parameters as well as response spectrum. The results highlight the significance of greater water depths on low frequency responses in surge motions and mooring line tensions, and provides insight on the increasing and decreasing trend of these responses.

scholarly journals Seismic Design of Offshore Structures under Simplified Pulse-Like Earthquakes

CivilEng ◽  
2020 ◽  
Vol 1 (3) ◽  
pp. 310-325
Author(s):  
Foteini Konstandakopoulou ◽  
George Papagiannopoulos ◽  
Nikos Pnevmatikos ◽  
Konstantinos Evangelinos ◽  
Ioannis Nikolaou ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Inelastic Behavior ◽  
Global Response ◽  
Wind Actions ◽  
Near Fault Earthquakes ◽  
First Time

Oil and gas offshore structures are essential infrastructures which are subjected to several categories of environmental loads such as wave and wind actions. These loads commonly designate the structural design of offshore platforms. Additionally, several offshore platforms are founded in earthquake-prone areas and the design of them is intensely affected by seismic ground motions. To be sure, various investigations have studied the earthquake response of offshore structures under the action of far-field seismic events. However, the inelastic behavior of platforms under the action of simple pulses has not been examined yet, where the latter loads can successfully simulate near-fault earthquakes. This work investigates, for the first time to our knowledge, the dynamic inelastic response of offshore platforms subjected to triangular, exponential, sinusoidal, and rectangular pulses. Thus, three-dimensional offshore structures are examined also considering the dynamic soil-pile-platform interaction effects, satisfying all the pertinent provisions of European Codes and taking into account geometric and material nonlinearities as well as the effects of the different angles of incidence of seismic waves on the overall/global response of offshore platforms.

scholarly journals Resonant Motions of Dynamic Offshore Structures in Large Waves

Fluids ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 352
Author(s):  
Ove Tobias Gudmestad
Keyword(s):  
Drag Force ◽  
Oil And Gas ◽  
Offshore Structures ◽  
Gas Production ◽  
Mass Force ◽  
Oil And Gas Production ◽  
Damped System ◽  
Loading Function ◽  
Non Linear ◽  
Marine Engineering

In marine engineering, the dynamics of fixed offshore structures (for oil and gas production or for wind turbines) are normally found by modelling of the motion by a classical mass-spring damped system. On slender offshore structures, the loading due to waves is normally calculated by applying a force which consists of two parts: a linear “inertia/mass force” and a non-linear “drag force” that is proportional to the square of the velocity of the particles in the wave, multiplied by the direction of the wave particle motion. This is the so-called Morison load model. The loading function can be expanded in a Fourier series, and the drag force contribution exhibits higher order harmonic loading terms, potentially in resonance with the natural frequencies of the system. Currents are implemented as constant velocity terms in the loading function. The paper highlights the motion of structures due to non-linear resonant motion in an offshore environment with high wave intensity. It is shown that “burst”/“ringing” type motions could be triggered by the drag force during resonance situations.

Modeling Solid Particle Erosion in Elbows and Plugged Tees

2001 ◽  
Vol 123 (4) ◽  
pp. 277-284 ◽  
Author(s):  
Jeremy K. Edwards ◽  
Brenton S. McLaury ◽  
Siamack A. Shirazi
Keyword(s):  
Flow Field ◽  
Particle Deposition ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Gas Production ◽  
Particle Trajectories ◽  
Oil And Gas Production ◽  
Erosion Prediction ◽  
Yield Trends ◽  
Model Equations

Predicted erosion patterns on the surface of a pipe fitting can now be obtained using a technique implemented into a computational fluid dynamics (CFD) code. This comprehensive erosion prediction procedure consists of 1) generation of a flow field simulation, 2) computation of a large number of particle trajectories inside the flow field, and 3) erosion model equations applied as particles impinge the walls of the geometry. Other quantities related to erosion, namely the particle deposition rate as well as local average impingement angle and velocity components, are also stored in the procedure. All predicted quantities (flow solution, particle trajectories, and erosion profiles) are analyzed using a three-dimensional visualization tool that was also developed. The current work focuses on two pipe fittings commonly used in the oil and gas production industry: elbows and plugged tees. First, the flow field and erosion predictions are evaluated through comparisons with experimental data. Erosion predictions yield trends and locations of maximum wear that are consistent with experimental observations. Next, two 90-deg pipe elbows with centerline curvature-to-diameter ratios of 1.5 and 5.0 are analyzed under prescribed erosive conditions. Predicted erosion results are presented in the form of surface contours. Finally, a simulated plugged tee geometry placed under erosive conditions is studied and erosion rates are compared to that of the two elbow test cases.

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