Dynamic design optimization of an equivalent truncated mooring system

Ferreira, Francirosy Campos Barbosa; Lages, Eduardo Nobre; Afonso, Silvana Maria Bastos; Lyra, Paulo Roberto Maciel

doi:10.1016/j.oceaneng.2016.06.021

Cited by 20 publications

(4 citation statements)

References 25 publications

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“…An algorithm was developed and applied to optimise the design of a scaled truncated mooring system using lines of different weights, and it was found that the static restoring force of the truncated mooring system matched well with the original mooring system. Ferreira et al [14] mentioned the problem of mooring system similarity due to the water depth condition in the model test and proposed a design optimisation technique to find the ideal truncated design considering dynamic effects. The calibration method was applied to adjust the design parameters to optimally fit the truncated mooring system to the full-depth mooring system in order to minimise the differences in motion response and tension for two mooring systems, catenary and semi-taut.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Low-Frequency Pitch Motion Characteristics for KRISO Standard Offshore Structure (K-Semi) Moored with a Truncation Mooring System

Park,

Jung,

Seo

et al. 2023

JMSE

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In this study, a model test was carried out to evaluate the station-keeping performance of Korea Research Institute of the Ships and Ocean Engineering (KRISO) standard semi-submersible, K-Semi in the Deep Ocean Engineering Basin (DOEB). The test was performed using a 1/50 scaled model with 12 mooring lines. The water depth was set to 3.2 m using a moveable bottom structure and truncated mooring lines. The dynamic behavior of the K-Semi was examined using a free decay test and regular wave as well as irregular wave tests of 1800. Large surge, heave and pitch due to drift motion from second-order effect were observed. The reason for the excessive low-frequency pitch motion is attributed to the restoring force and moment related to the mooring system as excessive surge occurred. The numerical model of K-Semi with the truncated mooring system was tuned and calibrated using model test results such as free decay and regular wave tests. Through numerical analysis, the motion characteristics of the K-Semi were compared with irregular model test results. In the case of a semi-submersible using a mooring system, it is observed that excessive pitch motion due to vertical restoring force and moment may occur when large horizontal displacement occurs. The effect of low-frequency pitch motion related to surge motion is an important factor in upwell estimation as well as second-order motion in referred DNV-GL OTG13.

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Section: Introductionmentioning

confidence: 99%

Investigation of Low-Frequency Pitch Motion Characteristics for KRISO Standard Offshore Structure (K-Semi) Moored with a Truncation Mooring System

Park,

Jung,

Seo

et al. 2023

JMSE

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“…Lastly, time-domain simulations can be used for evaluating the performance of the mooring system within the optimization process [11]. Although this is the most computationally expensive of the approaches, it will lead to the most accurate results.…”

Section: Introductionmentioning

confidence: 99%

“…Although this is the most computationally expensive of the approaches, it will lead to the most accurate results. Researchers have also experimented with screening the designs which time-domain simulations are run on to avoid wasting computational time on poor designs [10,11].…”

Section: Introductionmentioning

confidence: 99%

Development of a Multi-Objective Optimization Tool for Screening Designs of Taut Synthetic Mooring Systems to Minimize Mooring Component Cost and Footprint

et al. 2021

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As the offshore wind industry develops, more lease sites in the intermediate water depth (50–85 m) are being released to developers. In these water depths floating wind turbines with chain catenary systems and fixed-bottom turbines with jacketed structures become cost prohibitive. As such, industry and researchers have shifted focus to floating turbines with taut or semi-taut synthetic rope mooring systems. In addition to reducing the cost of the mooring systems, synthetic systems can also reduce the footprint compared to a chain catenary system which frees areas around the turbine for other maritime uses such as commercial fishing. Both the mooring systems component cost and footprint are pertinent design criteria that lend themselves naturally to a multi-objective optimization routine. In this paper a new approach for efficiently screening the design space for plausible mooring systems that balance component cost and footprint using a multi-objective genetic algorithm is presented. This method uses a tiered-constraint method to avoid performing computationally expensive time domain simulations of mooring system designs that are infeasible. Performance metrics for assessing the constraints of candidate designs are performed using open-source software such as Mooring Analysis Program (MAP++), OpenFAST and MoorDyn. A case study is presented providing a Pareto-optimal design front for a taut synthetic mooring system of a 6-MW floating offshore wind turbine.

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“…Starting from a statically-equivalent system, Ferreira et al [12] suggested to achieve dynamic equivalence by jointly varying the diameter and mass of the segments, while keeping the submerged weight constant, and the static properties of the system unchanged. Based on a numerical case study, they concluded that the truncated setup was able to replicate the dynamic line tensions in sea-states with comparable strength to the ones used in the calibration.…”

mentioning

confidence: 99%

Real-Time Hybrid Model Testing of a Top Tensioned Riser: A Numerical Case Study on Interface Time-Delays and Truncation Ratio

Sauder

Sørensen

Larsen

2017

Volume 2: Prof. Carl Martin Larsen and Dr. Owen Oakley Honoring Symposia on CFD and VIV

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This paper investigates the applicability of real-time hybrid model testing (ReaTHM testing) to the study of offshore systems in deep water. The focus is in particular on slender marine structures connecting floating structures to the seabed, and on how they could be truncated so that a model test setup at a reasonable scale could fit existing hydrodynamic laboratory infrastructures. In this context, ReaTHM testing consists in “substructuring” the slender structures in two parts. At the lower part of the water column, the first substructure is numerical, simulated using a nonlinear finite element method. On the upper part of the water column, the other substructure is physically modelled in an ocean basin. Both substructures interact in real-time through a set of sensors and actuators. This paper addresses through a case study the important issue of accuracy of ReaTHM testing, that is how the behavior of the substructured system varies from that of the emulated system. A top-tensioned riser in 1200m water depth is considered, with two truncation locations: 240m and 600m below the free surface. It is assumed that an artefact is introduced by the ReaTHM test setup, namely a time delay induced by e.g. the numerical calculations, or the actuation system. It is first shown how this artefact influences the accuracy of the setup, and then how the truncation ratio influences the tolerance of the ReaTHM test setup to such an artefact.

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Dynamic design optimization of an equivalent truncated mooring system

Cited by 20 publications

References 25 publications

Investigation of Low-Frequency Pitch Motion Characteristics for KRISO Standard Offshore Structure (K-Semi) Moored with a Truncation Mooring System

Investigation of Low-Frequency Pitch Motion Characteristics for KRISO Standard Offshore Structure (K-Semi) Moored with a Truncation Mooring System

Development of a Multi-Objective Optimization Tool for Screening Designs of Taut Synthetic Mooring Systems to Minimize Mooring Component Cost and Footprint

Real-Time Hybrid Model Testing of a Top Tensioned Riser: A Numerical Case Study on Interface Time-Delays and Truncation Ratio

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