Effect of Mooring Line Azimuth Angle on the Hydrodynamic Performance of a Moored Fpso in Ultra-Shallow Water (original) (raw)
Related papers
2018
Non-ship shaped FPSO has more advantages than ship-shaped FPSO. It has more efficient storage shape, smaller sloshing forces, allows for larger freeboard and simple block construction. In addition, round shape FPSO is designed to have similar motion characteristics from all directions and eliminate yaw excitation. This eliminates the need for a costly turret and swivels, minimizes the bending loads and fatigue and increases the storage capacity per plated area. Mooring line configuration is critical for floating structure. Mooring designer need to ensure the mooring system can maintain the position and limit the motion of floating structures due to the environment loads such as wave loads, wind loads and current forces. A study on effect of mooring arrangement to the dynamic response of cylinder FPSO has been conducted. The main objective of this research is to predict the mooring forces as well as to simulate moored motion of cylindrical FPSO in different mooring arrangement. In th...
Analysis of motion on FPSO in shallow water with a non-collinear environment
2013
The ship-shaped floating structures like FPSO has an ability to produce, storage and offloading the oil but it is does not have the drilling capability. Usually the FPSO in shallow water is connected with the single point mooring systems such as Vertical Anchor Leg Mooring (VALM) buoy systems. The objective of this paper is calculate the response amplitude operators (RAO) of spread moored FPSO with two mooring configuration and with the effect of non-collinear environment of wave and current. The analyses done by using ANSYS AQWA (version 14) software with runs two types of analysis which is hydrodynamics diffraction and hydrodynamics time response. The analysis also focuses to calculate the RAO and normalized hawser line force of FPSO and VALM systems. The result from the software has been compared with the experiment result to validate it. The different in meshing elements size also are taken into account. The analysis also focuses to compare the RAO between single leg mooring FPSO and spread moored FPSO with the same loading condition. From the analysis, the RAO for 4 mooring FPSO is higher compared than 8 mooring FPSO but the 8 mooring FPSO shows high value of cable forces than 4 mooring FPSO. It also shows the value of RAO of single leg mooring FPSO is higher compared to the spread moored FPSO.
Dynamic Analysis of Mooring Lines for Deep Water Floating Systems
Volume 3: Materials Technology; Jan Vugts Symposium on Design Methodology of Offshore Structures; Jo Pinkster Symposium on Second Order Wave Drift Forces on Floating Structures; Johan Wichers Symposium on Mooring of Floating Structures in Waves, 2011
Efficient dynamic analysis of mooring lines and risers is necessary for deepwater floating systems that typically consist of a number of mooring lines and risers. In deepwater, the interactions between the floater motions and the large number of risers and mooring lines become significant and must be considered for accurate prediction of floater motions as well as line dynamics. Time-domain coupled dynamic analysis procedures have been proposed which can account for the coupling effects and consider most of the nonlinearities present in the problem. These methods have been shown to give more accurate results compared to traditional de-coupled analysis methods although they tend to be computationally more expensive. If the system has a large number of mooring lines and risers, it becomes very difficult and impractical to perform time domain coupled analysis. A number of efficient methodologies have therefore been proposed in the past to balance the accuracy of results with computatio...
Mooring Analysis of a Weathervaning FPSO in Bi-Directional Sea-States
Volume 6: Materials Technology; C.C. Mei Symposium on Wave Mechanics and Hydrodynamics; Offshore Measurement and Data Interpretation, 2009
Experimental studies were carried out at the Institute for Ocean Technology, Canada, in collaboration with the University of Western Australia (UWA) to assess the response of a moored 1:60 scaled Floating Production Storage and Offloading (FPSO) model in bi-directional seastates. The seastates comprise of a regular swell approaching in the head sea condition, and a JONSWAP wind sea approaching at various angles. The FPSO was moored in position by four spring-loaded mooring lines attached to an internal turret about which the model could weathervane. Previous papers by the authors have described the unpredictable yaw instability of the FPSO driven by long period swells, which was evidenced in the experiments. This creates difficulties in comparing motions from unidirectional and bi-directional seas, because the headings alter the response. However, the mooring tensions are relatively immune to yaw instabilities and this paper discusses effects of bi-directional seas on the mooring tensions. Numerical simulations are conducted using a time domain analysis software which simulates the motions of floating and moored structures in response to irregular seas. Simulations based on the software when compared with model tests at 45, 60 and 90 deg separation between the sea and swell shows reasonable agreement in terms of mooring tensions. Simulations are then conducted for a range of separation angles, and the effects of bi-directionality are further evaluated. It is found that a linear addition of the individual seastates can produce non-conservative results, which reinforces the fact that bi-directional seastates are important considerations for offshore operations of an FPSO.
Journal of Marine Science and Engineering, 2022
The behavior of different mooring line materials has a significant influence on the behavior of the mooring system and, consequently, the dynamic responses of the floating platform. Although there have been previous studies on FPSOs and their mooring systems, the influence of mooring line failure scenarios associated with different mooring materials has received less attention, particularly for turret-moored FPSOs with taut moorings. Thus, this paper investigates the behavior of different mooring line materials in intact, single-line, and double-line damaged conditions on the hydrodynamic responses of the FPSO, restoring behavior, mooring, and riser tensions considering wave conditions in the Gulf of Mexico. Mooring lines including Aramid, HMPE, polyester, and steel wire were considered in the middle segment, which was the segment of interest in this study. The restoring forces of the mooring system were found to increase with increasing mooring stiffness, and a higher stiffness res...
Dynamics of mooring systems in ocean engineering
Archive of Applied Mechanics (Ingenieur Archiv), 2003
The computation of restoring forces on floating platforms caused by mooring systems in ocean engineering is usually performed by means of quasi-static procedures. Thereby, nonlinear phenomena produced by the motion of the mooring line or the interaction between fluid and line are not considered. For lines in deep water, these effects may cause a tremendous increase in the tension force, which cannot be predicted by simplified models. Therefore, it is mandatory to determine the dynamics by means of a more precise mathematical model. In this paper, a model is presented for the analysis of the dynamic behavior of mooring systems taking into account the hydrodynamic forces exerted by the surrounding fluid. The mathematical description of the real mooring line is performed using a multibody system approach. Furthermore, a comparison of results of a quasi-static and a dynamic analysis is presented in order to stress the importance of a dynamic analysis of mooring lines.
Proceedings of the 4th International Conference on Civil, Structural and Transportation Engineering (ICCSTE'19), 2020
Restoring behaviour of a mooring system is majorly dictated by several factors including, pretension, mooring line material, azimuth angle, mooring line diameter and fairlead angle. Mooring line behaviour plays significant role in controlling the dynamic motions of floating offshore platforms. Hence, studying the parameters affecting mooring line responses is a very important aspect in the hydrodynamic analysis of FPSO. The primary aim of this paper is to investigate the influence of mooring line configurations in different wave headings and mooring line diameter on the restoring behaviour of a Turret-Moored FPSO. Force-excursion relationship of the mooring system is determined using an in-house developed MATLAB code, named MLQSC. Catenary mooring line was adopted in the study, consisting of Chain-Steel wire-Chain, and analyse using Quasi static analysis approach. Four (4) mooring configurations considered are Evenly distributed, 3x4, 4x3 and 6x2 in all cases with respect to 30,35,40 and 45-degree wave headings. The restoring behaviour of mooring configurations considered (consisting of 12 mooring lines) was observed to decrease with an increasing wave heading. Furthermore, the restoring behaviour was observed to decrease with increase in mooring line diameter which by implication increases the corresponding permissible excursion.
Vessel/mooring/riser coupled dynamic analysis of a turret-moored FPSO compared with OTRC experiment
A vessel/mooring/riser coupled dynamic analysis program in time domain is developed for the global motion simulation of a turret-moored, tanker based FPSO designed for 6000-ft water depth. The vessel and line dynamics are solved simultaneously in a combined matrix for the given environmental and boundary conditions. The vessel global motions and mooring tension are tested at the OTRC wave basin for the non-parallel wind–wave–current 100-year hurricane condition in the Gulf of Mexico. The same case is also numerically simulated using the developed coupled dynamic analysis program. The numerical results are compared with the OTRC 1:60 model-testing results with truncated mooring system. The system's stiffness and line tension as well as natural periods and damping obtained from the OTRC measurement reasonably match with numerically simulated static-offset and free-decay tests. The numerically predicted global vessel motions are also in good agreement with the measurements.
Appropriate Model for Mooring Pattern of a Semi-Submersible Platform
Exposure to environmental conditions at sea for a floating structure is inevitable. Environmental conditions that wave forces are the most important of them have a big impact on floating structures as well. Due to the nature of semi-submersible Platforms that they are exposed to the wave forces, therefore minimizing of tension force in mooring lines and choosing an appropriate mooring system always has been discussed. This article investigate the tension force on mooring lines of a semisubmersible platform when that it has been exposure to 0, 45 and 90 degrees of sea wave direction with the environmental conditions of the Caspian Sea with using Flow-3d (version10.0.1) software. Also the seven symmetric mooring systems in the form of 4 and 8 numbers of mooring lines' systems have been used to choosing the best modes.
Motion Response Analysis of Multi-point Moored FPSO
Firstly, ANSYS software was adopted in modeling and meshing. And then the characteristic of motion response to regular waves has been analyzed in frequency domain by using AQWA-LINE. Considering the coupling effect between FPSO and its mooring lines, time history of mooring line tension in time domain has been attained by utilizing AQWA-DRIFT. Then dichotomy was used to search the secure incident angels of joint wave, wind and current which meet both the tension limitations and the motion limitations. And investigations have been made on the impact that the total length of each mooring line has on the maximum tension of mooring line.