Numerical Simulation on Mooring Performance of LNG-FPSO System in Realistic Seas

2005 ◽  
Author(s):  
Yoshiyuki Inoue ◽  
Md. Kamruzzaman
Keyword(s):  
Time Domain ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Analysis Tool ◽  
Motion Response ◽  
Non Linear ◽  
Floating System ◽  
Exciting Forces ◽  
The Time Domain

The LNG-FPSO concept is receiving much attention in recent years, due to its active usage to exploit oil and gas resources. The FPSO offloads LNG to an LNG carrier that is located close to the FPSO, and during this transfer process two large vessels are in close proximity to each other for daylong periods of time. Due to the presence of neighboring vessel, the motion response of both the vessels will be affected significantly. Hydrodynamic interactions related to wave effects may result in unfavorable responses or the risk of collisions in a multi-body floating system. Not only the motion behavior but also the second order drift forces are influenced by the neighboring structures due to interactions of the waves among the structures. A study is made on the time domain analysis to assess the behavior and the operational capability of the FPSO system moored in the sea having an LNG carrier alongside under environmental conditions such as waves, wind and currents. This paper presents an analysis tool to predict the dynamic motion response and non-linear connecting and mooring forces on a parallel-connected LNG-FPSO system due to non-linear exciting forces of wave, wind and current. Simulation for the mooring performance is also investigated. The three-dimensional source-sink technique has been applied to obtain the radiation forces and the transfer function of wave exciting forces on floating multi-bodies. The hydrodynamic interaction effect between the FPSO and the LNG carrier is included to calculate the hydrodynamic forces. For the simulation of a random sea and also for the generation of time depended wind velocity, a fully probabilistic simulation technique has been applied. Wind and current loads are estimated according to OCIMF. The effects of variations in wave, wind and current loads and direction on the slowly varying oscillations of the LNG and FPSO are also investigated in this paper. Finally, some conclusions are drawn based on the numerical results obtained from the present time domain simulations.

Time-Domain VIV Prediction of Marine Risers

2012 ◽  
Author(s):  
Peter Ma ◽  
Wei Qiu ◽  
Don Spencer
Keyword(s):  
Experimental Data ◽  
Time Domain ◽  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Time Domain Analysis ◽  
Analysis Tool ◽  
Time Step ◽  
Marine Risers ◽  
Hydrodynamic Damping ◽  
High Reynolds

Vortex Induced Vibration (VIV) of marine risers poses a significant challenge as the offshore oil and gas industry moves into deep water. A time-domain analysis tool has been developed to predict the VIV of marine risers based on a forcing algorithm and by making full use of the available high Reynolds number experimental data. In the formulation, the hydrodynamic damping is not treated as a special case but simply an extension of the experimentally derived lift curves. The forcing algorithm was integrated into a mooring analysis program based on the global-coordinate based finite element method. At each time step, the added mass, lifting force and drag force coefficients and their corresponding loads are computed for each element. Validation studies have been carried out for a full-scale rigid riser segment and a model-scale flexible riser. The numerical results were compared with experimental data and solutions by other programs.

scholarly journals Effect of Wave-Current Interaction on Structural Responses of a Very Long and Side-Anchored Floating Bridge

2020 ◽  
Author(s):  
Jian Dai ◽  
Bjørn Christian Abrahamsen ◽  
Bernt Johan Leira
Keyword(s):  
Time Domain ◽  
Transfer Functions ◽  
Computational Study ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Bridge Model ◽  
Structural Responses ◽  
Floating Bridge ◽  
Current Interaction ◽  
The Time Domain

Abstract This paper is concerned with a computational study on the hydroelastic response of a long, straight and side-anchored fjord-crossing floating bridge accounting for the wave-current interaction. The effect of this interaction on a single bridge pontoon is investigated by using the three-dimensional potential solver VERES3D. The frequency-dependent hydrodynamic coefficients and excitation force transfer functions are presented and compared with WAMIT results where the current effect is ignored. Based on the frequency domain results, an approach to account for the wave-current interaction in time domain analysis is proposed. Next, a generic straight and side-anchored floating bridge model is put forward to examine the stochastic structural responses in the time domain. For the purpose of comparison, the bridge responses under waves and current without interaction are also investigated. This study attempts to quantify the wave-current interaction effect on the structural responses of a floating bridge and provide useful recommendations and suggestions to researchers and engineers for their study of similar structures.

Time-Domain Analysis of Wind-Induced Response of a Suspension Bridge in Comparison With the Full-Scale Measurements

2017 ◽  
Author(s):  
Jungao Wang ◽  
Etienne Cheynet ◽  
Jasna Bogunović Jakobsen ◽  
Jónas Snæbjörnsson
Keyword(s):  
Standard Deviation ◽  
Time Domain ◽  
Measurement Data ◽  
Suspension Bridge ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Full Scale ◽  
Buffeting Response ◽  
Non Linear ◽  
The Time Domain

The present study compares the buffeting response of a suspension bridge computed in the time-domain with full-scale measurement data. The in-service Lysefjord Bridge is used as a study case, which allows a unique comparison of the computational results with full-scale buffeting bridge response observed during a one year monitoring period. The time-domain analysis is performed using a finite element approach. Turbulent wind field is simulated according to the governing bridge design standard in Norway for three different terrain categories. The time-domain analysis indicates that the non-linear components of the wind loading are of limited importance in the present case, contributing by less than 5% to the standard deviation of the lateral displacement. The contribution of the buffeting loads on the main cables, hangers and towers to the lateral dynamic response of the bridge girder is about 6%. With the time-domain method, mode coupling as well as the influence of cables and towers are well captured in the simulation results. The buffeting response, estimated in terms of the standard deviation of acceleration, is found to be in good agreement with the field measurement data. Comparison suggests that the proposed numerical method, with the non-linear force model, is able to predict the bridge response reasonably well.

scholarly journals The Use of Frequency Analysis as a Complementary and Explanatory Element for Time Domain Analysis in Measurements of the Ability to Maintain Balance

2021 ◽  
Vol 76 (1) ◽  
pp. 117-129
Author(s):  
Jacek Jurkojć ◽  
Piotr Wodarski ◽  
Robert Michnik ◽  
Wojciech Marszałek ◽  
Kajetan J. Słomka ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Sagittal Plane ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Sensory Conflict ◽  
Cyclical Component ◽  
Human Balance ◽  
Analysis Of Results ◽  
The Time Domain

Abstract Assessment of human balance is one of the most common diagnostic tests, both in medical applications and during sports training. Many new methods of measuring are introduced in these studies; however, the analysis of results is still carried out mainly based on the values determined in the time domain – the average COP speed or the ellipse field of the prediction. The aim of the current work is to present the possibilities for the practical application of frequency analyses in assessment of the ability to maintain body balance as a method supplementing standard analyses. As part of the study, measurements of the ability to maintain balance in sensory conflict conditions introduced in the form of an oscillating, three-dimensional, virtual scenery were carried out. 27 healthy volunteers (13 women and 14 men) took part in the study. The three-dimensional scenery, presented by means of the Oculus system, oscillated in the sagittal plane with frequencies equal to 0.7 Hz and 1.4 Hz. The frequency value during the measurement was constant or changed in the middle of the test. Measurements were conducted on the FDM Zebris platform. The results were analyzed using developed coefficients determined on the basis of the Short-time Fourier transform (STFT). The use of frequency-domain analyses confirmed that in the COP movement, one can observe a cyclical component corresponding to following the scenery, as well as the appearance of other cyclical components whose observation is important in terms of assessing the ability to maintain balance. It has been shown that the changes in the average COP speed that occur during the measurement can result from changes related to the movement of following the scenery as well as additional body movements indicating a greater or lesser loss of balance. It has been shown that there are differences in the COP movement provoked by the movement of the surrounding scenery, which depend on the parameters of the introduced disturbances – something that can only be observed in results obtained in the frequency domain. The conducted research shows that in measurements involving the ability to maintain one’s balance conducted in sensory conflict conditions, standard time-domain analyses should be supplemented with other types of data analysis, e.g. frequency domain analyses.

scholarly journals Aeroelastic Stability of Idling Wind Turbines

2016 ◽  
Author(s):  
Kai Wang ◽  
Vasilis A. Riziotis ◽  
Spyros G. Voutsinas
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Linear Time ◽  
Operation Mode ◽  
Time Domain Analysis ◽  
Eigenvalue Analysis ◽  
Eigenvalue Stability ◽  
Non Linear ◽  
Aeroelastic Simulations ◽  
The Time Domain

Abstract. Wind turbine rotors in idling operation mode can experience high angles of attack, within the post stall region that are capable of triggering stall-induced vibrations. In the present paper, rotor stability in slow idling operation is assessed on the basis of non-linear time domain and linear eigenvalue analyses. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First, the flow conditions that are likely to favour stall induced instabilities are identified through non-linear time domain aeroelastic simulations. Next, for the above specified conditions, eigenvalue stability simulations are performed aiming at identifying the low damped modes of the turbine. The eigenvalue stability results are evaluated through computations of the work of the aerodynamic forces under imposed harmonic motion following the shape and frequency of the various modes. Eigenvalue analysis indicates that the asymmetric and symmetric out-of-plane modes have the lowest damping. The results of the eigenvalue analysis agree well with those of the non-linear work analysis and the time domain analysis.

scholarly journals The time domain numerical method of three-dimensional conductors including radiation with lumped parameter circuit

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Souma Jinno ◽  
Shuji Kitora ◽  
Hiroshi Toki ◽  
Masayuki Abe
Keyword(s):  
Numerical Method ◽  
Time Domain ◽  
Maxwell Equations ◽  
Three Dimensional ◽  
New Formalism ◽  
Vector Potentials ◽  
Lumped Parameter ◽  
Radiation Theory ◽  
Stable Solutions ◽  
The Time Domain

AbstractWe formulate a numerical method on the transmission and radiation theory of three-dimensional conductors starting from the Maxwell equations in the time domain. We include the delay effect in the integral equations for the scalar and vector potentials rigorously, which is vital to obtain numerically stable solutions for transmission and radiation phenomena in conductors. We provide a formalism to connect the conductors to any passive lumped-parameter circuits. We show one example of numerical calculations, demonstrating that the new formalism provides stable solutions to the transmission and radiation phenomena.

Concrete Modeling for Extreme Wave Slam Events

2017 ◽  
Author(s):  
Kasper Wåsjø ◽  
Terje P. Stavang ◽  
Tore H. Søreide
Keyword(s):  
Time Domain ◽  
Linear Time ◽  
Limit State ◽  
Material Model ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Capacity Control ◽  
Extreme Wave ◽  
Conventional Design ◽  
Non Linear

Experience from model tests has initiated a growing attention towards extreme wave slam as a critical load situation for offshore large volume structures. Most of the problem is related to the local slam pressure, which may go up to several MPa’s for 100-year and 10 000-year waves. The paper deals with modeling techniques for marine concrete structures under extreme slam loading from waves where dynamic effects together with material softening play a major role for the response. Different analysis approaches for ultimate limit state (ULS) and accidental limit state (ALS) controls are discussed in view of reliability philosophy as basis for conventional design approach. The present paper is devoted to the local impact scenario and the alternative approaches for response and capacity control involving non-linear time domain analyses. Conventional design schemes as based on linear elastic models for response calculation together with code specified capacity control often come out more conservative than non-linear approach. The paper demonstrates by case studies how softening of the structure in general reduces the response in terms of section forces. A key issue when going from conventional linear approaches into non-linear techniques is to still keep an acceptable reliability level on the capacity control. Load and material factors are normally based on structures with limited non-linearity where linear response modeling is representative. Implementing non-linear material model in time domain analysis has a major challenge in limiting the sensitivity in response and capacity calculation. The paper demonstrates the way material model of concrete affects the section forces to go into local capacity control, and concludes on needed sensitivity analyses. Practical approaches on the concrete slam problem together with resulting utilizations from the control are demonstrated. The full non-linear technique by response and capacity control in one analysis is also handled, using average material parameters and justifying safety factors for the effect of implementing characteristic lower strength of concrete in the capacity. The paper ends up in a recommendation on non-linear time domain analysis procedure for typically slam problems. A discussion is also given on applicable design codes with attention to non-linear analysis.

Sign in / Sign up

Export Citation Format

Share Document