Development of a FPSO Motion Simulator

2015 ◽  
Author(s):  
Dexin Zhan ◽  
Worakanok Thanyamanta ◽  
Jason McDonald ◽  
David Molyneux
Keyword(s):  
Control System ◽  
Wind Waves ◽  
Line Tension ◽  
Weather Conditions ◽  
Mooring Line ◽  
Restoring Force ◽  
3 Dimensional ◽  
Motion Simulator ◽  
Heading Control ◽  
Time Domain Response

This paper presents the development of a motion simulator for a moored FPSO, which includes numerical prediction of the FPSO motions in wind, waves and current. It also presents the resulting mooring line tension, 3-dimensional visualization of the FPSO motion, and summary analysis of the resulting motion parameters. The FPSO motion in waves was simulated using an in-house seakeeping code, MOTSIM. A spread mooring line routine, based on catenary theory, was developed and added to MOTSIM to calculate the restoring force of each mooring line. The visualizer (or animator) was developed in-house from open source software, including Ogre, Hydrax and Skyx. It can playback a 3-dimensional view of the simulation (above and below water). The user can view the results in a movie-like format, and change viewing position during the play-back. The user can also run a new simulation from the animator by inputting the required parameters. The program for analyzing the time dependent responses generated by MOTSIM was developed as a stand-alone program using MATLAB. The analyzer can conduct statistical analysis of time-domain response signals. A heading control system and a DP control system were also developed in the simulator and can be activated to help control the FPSO motion if required. A validation of the ship motion prediction and mooring tension was conducted against model experiments using 100-year return period environments with different combinations of wave, wind and current directions. The simulator was developed as a forecasting tool to help operators predict platform performance based of forecast weather conditions.

Route to Chaos of an Articulated Offshore Loading Platform

2004 ◽  
Author(s):  
A. P. Shashikala
Keyword(s):  
Wind Waves ◽  
Nonlinear Behavior ◽  
Mooring Line ◽  
Response Analysis ◽  
Mooring Lines ◽  
Restoring Force ◽  
Highly Nonlinear ◽  
Waves And Currents ◽  
Time Domain Response ◽  
The Time Domain

Articulated Loading Platforms are compliant structures which undergo excessive displacements due to large hydrodynamic loads produced by wind, waves and currents. Prediction of nonlinear behavior of these complex structures in the nonlinear environment is extremely difficult. The discontinuity in the mooring line stiffness at the equilibrium position due to slackening of the mooring line between tower and tanker introduces nonlinearity in the equation of motion. An attempt to study the effect of the highly nonlinear restoring force and hydrodynamic forces on the system was performed. The time domain response analysis was done on the basis of approximate analytical investigations. The solution of the nonlinear simultaneous equations was performed and the results were interpreted by means of phase plots and poincare mapping. The effect of forcing amplitude on the behavior of the system was studied by varying the frequency ratio. Possible occurrence of sub harmonic and chaotic responses and hence different routes to chaos were also identified. These results can be made use of in the design of mooring lines to avoid structural instabilities in the evolving offshore environment.

FPSO Transient Responses During Cyclonic Storms

2007 ◽  
Author(s):  
Dusan Curic ◽  
Yong Luo
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Wind Waves ◽  
Rapid Change ◽  
Line Tension ◽  
Green Water ◽  
Mooring Line ◽  
Sea Waves ◽  
Transient Responses ◽  
Cyclonic Storm

This paper presents the key results and conclusions of the study of FPSO transient responses in the cyclonic storm. The measured wind, wave and current data of recent cyclonic events are utilized to simulate the FPSO responses in terms of mooring loads, vessel yaw motion and relative FPSO heading to waves as it weathervanes in the wind, waves and current, input as time series. The primary objectives are to check the FPSO responses as the cyclone (eye or fringe) passes over it, causing rapid changes in the intensity and the direction of environmental loads, and to confirm the adequacy of the present mooring system design criteria. The results of the study serve as a good benchmark of the current industry standard for mooring design and address industry’s concern of the safety of FPSO platforms in the event of cyclonic storm. This study has used the hindcast data to inspect the event of a strong cyclonic storm passing over an FPSO. Despite the fact that the wind direction changes for about 140° in only one hour in the path of the cyclone eye, higher mooring line tension has not been observed due to reduced wind speed in the eye of the storm. The extreme mooring line tension is still governed by the responses in the path of cyclone fringe due to its maximum wind speed. Note that the transient analysis has shown that, during the rapid change of wind direction, the vessel can potentially be exposed to beam sea waves. Although this does not correspond with the highest tension in mooring legs, it can lead to critical green water impact.

Dynamic Modeling of Deepwater Offshore Wind Turbine Structures in Gulf of Mexico Storm Conditions

2006 ◽  
Author(s):  
Thomas Zambrano ◽  
Tyler MacCready ◽  
Taras Kiceniuk ◽  
Dominique G. Roddier ◽  
Christian A. Cermelli
Keyword(s):  
Gulf Of Mexico ◽  
Wind Turbine ◽  
Wind Waves ◽  
Line Tension ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Offshore Structure ◽  
Force Coefficient

A Fourier spectrum based model of Gulf of Mexico storm conditions is applied to a 6 degree of freedom analytic simulation of a moored, floating offshore structure fitted with three rotary wind turbines. The resulting heave, surge, and sway motions are calculated using a Newtonian Runge-Kutta method. The angular motions of pitch, roll, and yaw are also calculated in this time-domain progression. The forces due to wind, waves, and mooring line tension are predicted as a function of time over a 4000 second interval. The WAMIT program is used to develop the wave forces on the platform. A constant force coefficient is used to estimate wind turbine loads. A TIMEFLOAT computer code calculates the motion of the system based on the various forces on the structure and the system’s inertia.

Less=Moor: A Time-Efficient Computational Tool to Assess the Behavior of Moored Ships in Waves

2017 ◽  
Author(s):  
Yijun Wang ◽  
Alex van Deyzen ◽  
Benno Beimers
Keyword(s):  
Dynamic Response ◽  
Research Effort ◽  
Equations Of Motion ◽  
Line Tension ◽  
Mooring Line ◽  
Induced Response ◽  
Wave Forces ◽  
Computational Tool ◽  
The Time Domain ◽  
Nonlinear Equations Of Motion

In the field of port design there is a need for a reliable but time-efficient method to assess the behavior of moored ships in order to determine if further detailed analysis of the behavior is required. The response of moored ships induced by gusting wind and/or waves is dynamic. Excessive motion response may cause interruption of the (un)loading operation. High line tension may cause lines to snap, introducing dangerous situations. A (detailed) Dynamic Mooring Analysis (DMA), however, is often a time-consuming and expensive exercise, especially when responses in many different environmental conditions need to be assessed. Royal HaskoningDHV has developed a time-efficient computational tool in-house to assess the wave (sea or swell) induced dynamic response of ships moored to exposed berths. The mooring line characteristics are linearized and the equations of motion are solved in the frequency domain with both the 1st and 2nd wave forces taken into account. This tool has been termed Less=Moor. The accuracy and reliability of the computational tool has been illustrated by comparing motions and mooring line forces to results obtained with software that solves the nonlinear equations of motion in the time domain (aNySIM). The calculated response of a Floating Storage and Regasification Unit (FSRU) moored to dolphins located offshore has been presented. The results show a good comparison. The computational tool can therefore be used to indicate whether the wave induced response of ships moored at exposed berths proves to be critical. The next step is to make this tool suitable to assess the dynamic response of moored ships with large wind areas, e.g. container ships, cruise vessels, RoRo or car carriers, to gusting wind. In addition, assessment of ship responses in a complicated wave field (e.g. with reflected infra-gravity waves) also requires more research effort.

Validation of Mooring Simulations (for Mooring Integrity Assessment) With In-Service Tension Measurements

2021 ◽  
Author(s):  
Willemijn Pauw ◽  
Remco Hageman ◽  
Joris van den Berg ◽  
Pieter Aalberts ◽  
Hironori Yamaji ◽  
...  
Keyword(s):  
Numerical Models ◽  
Weather Conditions ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Data Set ◽  
Integrity Assessment ◽  
Motion Data ◽  
Load Cells ◽  
Line Loads

Abstract Integrity of mooring system is of high importance in the offshore industry. In-service assessment of loads in the mooring lines is however very challenging. Direct monitoring of mooring line loads through load cells or inclinometers requires subsea installation work and continuous data transmission. Other solutions based on GPS and motion monitoring have been presented as solutions to overcome these limitations [1]. Monitoring solutions based on GPS and motion data provide good practical benefits, because monitoring can be conducted from accessible area. The procedure relies on accurate numerical models to model the relation between global motions and response of the mooring system. In this paper, validation of this monitoring approach for a single unit will be presented. The unit under consideration is a turret-moored unit operating in Australia. In-service measurements of motions, GPS and line tensions are available. A numerical time-domain model of the mooring system was created. This model was used to simulate mooring line tensions due to measured FPSO motions. Using the measured unit response avoids the uncertainty resulting from a prediction of the hydrodynamic response. Measurements from load cells in various mooring lines are available. These measurements were compared against the results obtained from the simulations for validation of the approach. Three different periods, comprising a total of five weeks of data, were examined in more detail. Two periods are mild weather conditions with different dominant wave directions. The third period features heavy weather conditions. In this paper, the data set and numerical model are presented. A comparison between the measured and numerically calculated mooring line forces will be presented. Differences between the calculated and measured forces are examined. This validation study has shown that in-service monitoring of mooring line loads through GPS and motion data provides a new opportunity for mooring integrity assessment with reduced monitoring system complexity.

On the Probability Distribution of Mooring Line Tensions in a Directional Environment

2011 ◽  
Author(s):  
Jan Mathisen ◽  
Siril Okkenhaug ◽  
Kjell Larsen
Keyword(s):  
Time Series ◽  
Probability Distributions ◽  
Extreme Value Distribution ◽  
Line Tension ◽  
Extreme Value ◽  
Mooring Line ◽  
Large Set ◽  
Short Term ◽  
Reliability Method ◽  
Line Design

A joint probabilistic model of the metocean environment is assembled, taking account of wind, wave and current and their respective heading angles. Mooring line tensions are computed in the time domain, for a large set of short-term stationary conditions, intended to span the domain of metocean conditions that contribute significantly to the probabilities of high tensions. Weibull probability distributions are fitted to local tension maxima extracted from each time series. Long time series of 30 hours duration are used to reduce statistical uncertainty. Short-term, Gumbel extreme value distributions of line tension are derived from the maxima distributions. A response surface is fitted to the distribution parameters for line tension, to allow interpolation between the metocean conditions that have been explicitly analysed. A second order reliability method is applied to integrate the short-term tension distributions over the probability of the metocean conditions and obtain the annual extreme value distribution of line tension. Results are given for the most heavily loaded mooring line in two mooring systems: a mobile drilling unit and a production platform. The effects of different assumptions concerning the distribution of wave heading angles in simplified analysis for mooring line design are quantified by comparison with the detailed calculations.

scholarly journals Dynamic Response of Floating Wind Turbine Under Consideration of Dynamic Behavior of Catenary Mooring-Lines

2017 ◽  
Author(s):  
Shuangxi Guo ◽  
Yilun Li ◽  
Min Li ◽  
Weimin Chen ◽  
Yiqin Fu
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Nonlinear Dynamic ◽  
Ocean Waves ◽  
Wave Frequency ◽  
Mooring Line ◽  
Mooring Lines ◽  
Restoring Force ◽  
Dynamic Behaviors ◽  
Floating Wind Turbine

Recently, wind turbine has been developed from onshore area to offshore area because of more powerful available wind energy in ocean area and more distant and less harmful noise coming from turbine. As it is approaching toward deeper water depth, the dynamic response of the large floating wind turbine experiencing various environmental loads becomes more challenge. For examples, as the structural size gets larger, the dynamic interaction between the flexible bodies such as blades, tower and catenary mooring-lines become more profound, and the dynamic behaviors such as structural inertia and hydrodynamic force of the mooring-line get more obvious. In this paper, the dynamic response of a 5MW floating wind turbine undergoing different ocean waves is examined by our FEM approach in which the dynamic behaviors of the catenary mooring-line are involved and the integrated system including flexible multi-bodies such as blades, tower, spar platform and catenaries can be considered. Firstly, the nonlinear dynamic model of the integrated wind turbine is developed. Different from the traditional static restoring force, the dynamic restoring force is analyzed based on our 3d curved flexible beam approach where the structural curvature changes with its spatial position and the time in terms of vector equations. And, the modified finite element simulation is used to model a flexible and moving catenary of which the hydrodynamic load depending on the mooring-line’s motion is considered. Then, the nonlinear dynamic governing equations is numerically solved by using Newmark-Beta method. Based on our numerical simulations, the influences of the dynamic behaviors of the catenary mooring-line on its restoring performance are presented. The dynamic responses of the floating wind turbine, e.g. the displacement of the spar and top tower and the dynamic tension of the catenary, undergoing various ocean waves, are examined. The dynamic coupling between different spar motions, i.e. surge and pitch, are discussed too. Our numerical results show: the dynamic behaviors of mooring-line may significantly increase the top tension, particularly, the peak-trough tension gap of snap tension may be more than 9 times larger than the quasi-static result. When the wave frequency is much higher than the system, the dynamic effects of the mooring system will accelerate the decay of transient items of the dynamic response; when the wave frequency and the system frequency are close to each other, the displacement of the spar significantly reduces by around 26%. Under regular wave condition, the coupling between the surge and pitch motions are not obvious; but under extreme condition, pitch motion may get about 20% smaller than that without consideration of the coupling between the surge and pitch motions.

scholarly journals Instrument and Control. Development of 3-Dimensional Edge Cutting Control System for Billets.

DENKI-SEIKO ◽  
2000 ◽  
Vol 71 (3) ◽  
pp. 213-220 ◽  
Author(s):  
Naoki Fuse ◽  
Kaoru Nakamura ◽  
Tsutomu Kojima ◽  
Toshio Endo
Keyword(s):  
Control System ◽  
3 Dimensional ◽  
And Control

scholarly journals An Approximate Method for Calculation of Mean Statistical Value of Ship Service Speed on a Given Shipping Line , Useful in Preliminary Design Stage

2015 ◽  
Vol 22 (1) ◽  
pp. 28-35
Author(s):  
Katarzyna Żelazny
Keyword(s):  
Wind Waves ◽  
Parametric Method ◽  
Weather Conditions ◽  
Economic Effects ◽  
Design Stage ◽  
Design Parameters ◽  
Preliminary Design ◽  
Screw Propeller ◽  
Calm Water ◽  
Preliminary Design Stage

Abstract During ship design, its service speed is one of the crucial parameters which decide on future economic effects. As sufficiently exact calculation methods applicable to preliminary design stage are lacking the so called contract speed which a ship reaches in calm water is usually applied. In the paper [11] a parametric method for calculation of total ship resistance in actual weather conditions (wind, waves, sea current), was presented. This paper presents a parametric model of ship propulsion system (screw propeller - propulsion engine) as well as a calculation method, based on both models, of mean statistical value of ship service speed in seasonal weather conditions occurring on shipping lines. The method makes use of only basic design parameters and may be applied in preliminary design stage.

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