Evaluation of the dynamic responses of truss spar platforms for various mooring configurations with damaged lines

Ahmed, Montasir Osman; Yenduri, Anurag; Kurian, V.J.

doi:10.1016/j.oceaneng.2016.07.004

Cited by 29 publications

(5 citation statements)

References 13 publications

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“…In the fatigue analysis example of the API-recommended practice 2SK [34], the wind, wave, and current are assumed colinear. In addition, Ahmed et al [25,35] investigated the response of a truss spar under the unidirectional waves, current, and wind loads based on the observation that waves are accompanied by the current and the wind in practical situations.…”

Section: Environmental Conditionsmentioning

confidence: 99%

“…Qiao et al [24] investigated the corrosion effect on fatigue life of two mooring systems. Ahmed et al [25] was apparently the first to evaluate the dynamic response of truss spar platforms for various catenary mooring configurations with the damage levels of the mooring lines and simplified these lines as springs. However, to investigate the effect of the damage levels of the fiber ropes on the mooring performance, it is important that the nonlinear behavior of the fiber ropes should be considered, for example, by introducing the empirical equation of dynamic stiffness [15,23,26].…”

Section: Introductionmentioning

confidence: 99%

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Effects of Damaged Fiber Ropes on the Performance of a Hybrid Taut-Wire Mooring System

Lian

Yim

Zheng

et al. 2019

Journal of Offshore Mechanics and Arctic Engineering

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In this study, effects of damage levels of fiber ropes on the performance of a hybrid taut-wire mooring system are investigated. The analysis is performed using a numerical floating production storage and offloading (FPSO) model with a hybrid mooring system installed in 3000 m of water depth. An in-depth study was conducted using the numerical model, the dynamic stiffness equation of damaged fiber ropes, the time-domain dynamic theory, the rainflow cycle counting method, and the linear damage accumulation rule of Palmgren-Miner. Results indicate that, in a mooring line with an increasing damage level, the maximum tension decreases, while the offset of the FPSO increases. Particularly, when a windward mooring line failure occurs, in addition to the significant increase in the offset of the FPSO, the maximum tension, tension range, and annual fatigue damage levels of the remaining lines adjacent to the failed also increase significantly. The present work can be of great benefit to the evaluation of the offset of the floating platform, the tension response, and the service life of the hybrid mooring systems.

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Section: Environmental Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Damaged Fiber Ropes on the Performance of a Hybrid Taut-Wire Mooring System

Lian

Yim

Zheng

et al. 2019

Journal of Offshore Mechanics and Arctic Engineering

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“…To date, there has not yet been research working on the effect of ocean depths on manipulator dynamics. Ahmed et al [25] presented that the water particle force on the oceanic structure depends on the ocean depth. Hence, this paper investigates the effect of ocean depth variations on the manipulator joint torque with contributions as follows:…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of the effect of ocean depth variations on the dynamics of a ship mounted two-DoF manipulator system

Ramadiansyah¹,

Yazid²,

Ng³

2022

J. Mechatron. Electr. Power Veh. Technol.

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The dynamics of a ship need to be considered in the development of a manipulator system that will be applied to the ocean-based operation. This paper aims to investigate the effect of ocean depth variations on the ship motion as disturbances to a ship-mounted two-DoF (Degrees of Freedom) manipulator joint torque using an inverse dynamics model. Realization is conducted by deriving the mathematical model of a two-DoF manipulator system subject to six-DoF ship motion, which is derived by using Lagrange-Euler method. It is then combined with numerical hydrodynamic simulation to obtain the ship motions under ocean depth variations, such as shallow (50 m), intermediate (750 m), and deep (3,000 m) waters. Finding results show that randomness of the ship motions appears on the manipulator joint torque. In the azimuth link, maximum joint torque is found in shallow water depth with an increment of 8.271 N.m (285.69 %) from the undisturbed manipulator. Meanwhile, the maximum joint torque of the elevation link is found in intermediate water depth with an increment of 53.321 N.m (6.63 %). However, the difference between depth variations is relatively small. This result can be used as a baseline for sizing the electrical motor and developing the robust control system for the manipulator that is mounted on the ship by considering all ocean depth conditions.

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“…RAOs are used in the design of ships, oil, and gas installations and more recently, for floating offshore renewable energy device platforms [1][2][3][4]. They have a potential to be an effective marker for structural health monitoring (SHM) since a change in the shape of RAO is related to a change in the behavior of a device [5,6].…”

Section: Introductionmentioning

confidence: 99%

Comparison of Response Amplitude Operator Curve Generation Methods for Scaled Floating Renewable Energy Platforms in Ocean Wave Basin

O’Donnell

Murphy

Pakrashi

2020

ASME Letters in Dynamic Systems and Control

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Response Amplitude Operator (RAO) curves are commonly employed to assess the dynamic behaviour of floating offshore structures in the frequency domain. There are multiple methods used to obtain RAOs for numerical models, scaled physical models and full-scale tests. While for numerical modelling many studies detail the precise methods used, the literature around experimental RAO curves often do not detail them or leave methodological information incomplete. There exists inadequate experimental evidence in assessing the differences in results obtained by following different RAO generation methods from scaled physical testing. This paper addresses this gap by comparing two most popular RAO generation methods: the Energy Spectra (ES) and the Cross Spectral Auto Spectra (CSAS) method. These are experimentally compared on scaled semi-submersible and spar buoy platforms in an ocean wave basin. Differences of heave and pitch RAOs generated by different methods are investigated. A method for reasonably collating multiple tests to create a representative RAO is also presented. RAO amplitudes vary significantly and how they decay off beyond certain frequencies is dependent on the method adopted to create them. This variation can be a source of significant uncertainty for floating structures for further analysis, design, control or repair. Some RAOs (e.g. pitch) are sensitive to scaling and should be considered when converting scaled tests to full-scale equivalent. Detailing methods of RAO generation and comparing approaches of developing them can be important for crucial decisions from scaled physical testing of floating structures at design/development stages.

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Evaluation of the dynamic responses of truss spar platforms for various mooring configurations with damaged lines

Cited by 29 publications

References 13 publications

Effects of Damaged Fiber Ropes on the Performance of a Hybrid Taut-Wire Mooring System

Effects of Damaged Fiber Ropes on the Performance of a Hybrid Taut-Wire Mooring System

Numerical investigation of the effect of ocean depth variations on the dynamics of a ship mounted two-DoF manipulator system

Comparison of Response Amplitude Operator Curve Generation Methods for Scaled Floating Renewable Energy Platforms in Ocean Wave Basin

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