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Research Papers: Offshore Technology

Using Design of Experiments and Design Optimization to Determine Statically Equivalent Mooring System on Truncated Water Depth

[+] Author and Article Information
Fábio M. G. Ferreira

Laboratório de Computação
Científica e Visualização,
Centro de Tecnologia,
Universidade Federal de Alagoas,
Maceió 57072-900, AL, Brazil
e-mail: fabio.ferreira@lccv.ufal.br

Eduardo N. Lages

Laboratório de Computação
Científica e Visualização,
Centro de Tecnologia,
Universidade Federal de Alagoas,
Maceió 57072-900, AL, Brazil
e-mail: enl@lccv.ufal.br

Silvana M. B. Afonso

Departamento de Engenharia Civil,
Universidade Federal de Pernambuco,
Recife 50670-901, PE, Brazil
e-mail: smb@ufpe.br

Paulo R. M. Lyra

Departamento de Engenharia Mecânica,
Universidade Federal de Pernambuco,
Recife 50670-901, PE, Brazil
e-mail: prmlyra@padmec.org

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received April 18, 2016; final manuscript received March 16, 2017; published online May 16, 2017. Assoc. Editor: Muk Chen Ong.

J. Offshore Mech. Arct. Eng 139(4), 041302 (May 16, 2017) (16 pages) Paper No: OMAE-16-1042; doi: 10.1115/1.4036376 History: Received April 18, 2016; Revised March 16, 2017

Several procedures have been proposed and developed to overcome the challenge in ultradeepwaters testing. A realistic alternative approach uses a hybrid passive methodology through equivalent truncated mooring systems. Often, the searching for equivalent systems involves using a trial-and-error. As an alternative, researches on the use of optimization techniques to establish truncated mooring system with the required properties have been attempted in recent years. In the literature, it is available only approaches considering nongradient-based algorithms. These algorithms usually involve several parameters which require appropriate tuning to provide good performance. Our approach involves optimization algorithms based on gradient. We use a calibration method to perform a static adjustment of design variables to optimally fit truncated mooring system to full-depth mooring system, which proved efficient. A further feature of this work is related to the study of the influence of design variables on the response, through a methodology based on design of experiments (DOE), avoiding the use of irrelevant variables. It should be emphasized that to the authors' knowledge this DOE methodology presented was not seen in other works in this field. We will show that the methodology proposed in this work makes easy to find an equivalent mooring system on truncated water depth. We will present and discuss two fictitious cases, one case based on the literature and another case based on a real scenario. The results show a good agreement between truncated mooring system and full-depth mooring system for the static adjustment.

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References

Figures

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Fig. 1

The hybrid passive system verification procedure [4]

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Fig. 2

Illustration of the mooring system with four catenary mooring lines

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Fig. 3

Full-depth versus truncated mooring system for the case of catenary mooring system

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Fig. 4

Comparison of the normalized maximum error between the restoring force and the line tension, varying weighting parameter (v)

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Fig. 6

Illustration of the coupling of dakota and dynasim

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Fig. 7

Configurations of different mooring systems

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Fig. 8

Optimization history of case 1

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Fig. 9

Comparison between the response in the full-depth and truncated systems for case 1

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Fig. 10

Percentage error between the response of truncated and full-depth systems for case 1

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Fig. 11

Comparison between the restoring force of full-depth system and both truncated systems (water depth of 900 m and 450 m) for case 1

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Fig. 12

Comparison between the percentage error of truncated system at water depth of 900 m and 450 m for case 1

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Fig. 13

Illustration of the taut-leg mooring system

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Fig. 14

Full-depth versus truncated mooring system for the case of the taut-leg mooring system

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Fig. 15

Optimization history for the case of the taut-leg mooring system

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Fig. 16

Comparison between the response of full-depth and truncated systems for case 2

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Fig. 17

Comparison between the response of full-depth and truncated systems considering the offsets in the orthogonal direction of that used in the optimization process for case 2

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Fig. 18

Percentage error between the response of truncated and full-depth systems for case 2

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Fig. 19

Maximum percentage error between the response of truncated and full-depth systems for all lines of case 2

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Fig. 20

Illustration of the mooring system with 12 catenary mooring lines of the work by Ji and Xu [23]

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Fig. 21

Optimization history of case 3

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Fig. 22

Comparison between the restoring force of full-depth system and both truncated systems for case 3

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Fig. 23

Comparison between line 1 tension of full-depth system and both truncated systems for case 3

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Fig. 24

Percentage error between the response of the truncated and full-depth systems for case 3

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Fig. 25

Maximum percentage error of line tension of the truncated system for all lines of case 3

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Fig. 26

Comparison between line 1 tension of full-depth system and both truncated systems (homogenous and nonhomogenous)

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Fig. 27

Comparison of maximum percentage error of line tension of both homogenous and nonhomogenous truncated systems for all lines

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Fig. 28

Illustration of the mooring system with 24 semitaut mooring lines

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Fig. 29

Optimization history for the case of the semitaut mooring system

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Fig. 30

Comparison between the response of full-depth and truncated systems for case 4

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Fig. 31

Comparison between the response of full-depth and truncated systems considering the offsets in the orthogonal direction of optimization process for case 4

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Fig. 32

Percentage error between the response in the truncated and full-depth systems for case 4

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Fig. 33

Maximum percentage error between the response of truncated and full-depth systems for all lines of case 4, for the offset in x-axis

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Fig. 34

Maximum percentage error between the response of truncated and full-depth systems for all lines of case 4, for the offset in y-axis

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