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Research Papers: Structures and Safety Reliability

Hydrodynamical Aspects of Pontoon Optimization for a Side-Anchored Floating Bridge

[+] Author and Article Information
Arnt G. Fredriksen

Multiconsult AS,
Kvaløyvegen 156,
Tromsø, 9013, Norway
e-mail: arnt.fredriksen@multiconsult.no

Mads F. Heiervang

Entail AS,
Gøteborggata 27b,
Oslo, 0566, Norway
e-mail: mads@entail.no

Per N. Larsen

Johs Holt AS,
Plogveien 1,
Oslo, 0679, Norway
e-mail: PerNorum.Larsen@johsholt.no

Pål G. Sandnes

Entail AS,
Gøteborggata 27b,
Oslo, 0566, Norway
e-mail: paal@entail.no

Bernt Sørby

Entail AS,
Gøteborggata 27b,
Oslo, 0566, Norway
e-mail: bernt@entail.no

Basile Bonnemaire

Lerøy Seafood Group,
Postboks 2123,
Tromsø, 9767, Norway
e-mail: basile.bonnemaire@leroy.no

Anders Nesteby

Multiconsult AS,
Storgata 35,
Fredrikstad, 1607, Norway
e-mail: anders.nesteby@multiconsult.no

Øyvind Nedrebø

Norwegian Public Road
Administration Region vest,
Postboks 43,
Leikanger, 6861, Norway
e-mail: oyvind.nedrebo@vegvesen.no

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received December 6, 2017; final manuscript received December 21, 2018; published online January 22, 2019. Assoc. Editor: Robert Seah.

J. Offshore Mech. Arct. Eng 141(3), 031603 (Jan 22, 2019) (9 pages) Paper No: OMAE-17-1211; doi: 10.1115/1.4042420 History: Received December 06, 2017; Revised December 21, 2018

Long floating bridges supported by pontoons with span-widths between 100 m and 200 m are discrete hydro-elastic structures with many critical eigenmodes. The response of the bridge girder is dominated by vertical eigenmodes and coupled horizontal modes (lateral) and rotational modes (about the longitudinal axis of the bridge girder). This paper explores the design principles used to reduce the response with regards to these eigenmodes. It is shown for a floating bridge with 200 m span-width that by inserting a bottom flange the vertical eigenmodes can be lifted out of wind-driven wave regime. It is also shown that selecting a pontoon length that leads to cancelation of horizontal excitation forces is beneficial, and that the geometrical shaping of the pontoon can be efficient to decrease the bridge response.

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References

Xiang, X. , Viuff, T. , Leira, B. , and Øiseth, O. , 2018, “Impact of Hydrodynamic Interaction Between Pontoons on Global Responses of a Long Floating Bridge Under Wind Waves,” ASME Paper No. OMAE2018-78625.
Cheng, Z. , Gao, Z. , and Moan, T. , 2018, “Wave Load Effect Analysis of a Floating Bridge in a Fjord Considering Inhomogeneous Wave Conditions,” Eng. Struct., 163, pp. 122–141. [CrossRef]
Giske, F. I. G. , Kvåle, K. A. , Leira, B. J. , and Øiseth, O. , 2018, “Long-Term Extreme Response Analysis of a Long-Span Pontoon Bridge,” Mar. Struct., 58, pp. 154–171. [CrossRef]
Viuff, T. , Xiang, X. , Leira, B. , and Øiseth, O. , 2018, “Code-to-Code Verification of End-Anchored Floating Bridge Global Analysis,” ASME Paper No. OMAE2018-77902.
Norwegian Public Roads Administration, 1864, “Design Basis Metocean,” Statens Vegvesen, Oslo, Norway, Report No. sbj-01-c3-svv-01-ba-001.
Keulegan, G. , and Carpenter, L. , 1956, “Forces on Cylinders and Plates in an Oscillating Fluid,” Nat. Bureau Standards, 60(5), pp. 423–440. [CrossRef]
Berthelsen, P. A. , and Faltinsen, O. M. , 2008, “A Local Directional Ghost Cell Approach for Incompressible Viscous Flow Problems With Irregular Boundaries,” J. Comput. Phys., 227(9), pp. 4354–4397. [CrossRef]
Newman, J. N. , 1977, Marine Hydrodynamics, The MIT Press, Cambridge, UK.
OrcaFlex 10.1, 2018, “OrcaFlex,” Orcina Ltd., Daltongate, Cumbria, accessed May 17, 2018, https://www.orcina.com/softwareproducts/orcaflex/

Figures

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Fig. 1

Overview drawing of the preliminary design of the straight floating bridge. North is directed approximately 10 deg of the longitudinal axis of the bridge.

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Fig. 2

Overview sketches of pontoons founds from the optimization process. A diamond shape on top, circtangle shape in the middle, and elliptical shape on bottom.

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Fig. 3

Longest eigenmode of floating bridge with frequency-dependent added mass for the circtangle shaped pontoon. X-axis in meters.

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Fig. 4

Longest rotational eigenmode for the floating bridge with frequency-dependent added mass for the circtangle shaped pontoon. X-axis in meters.

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Fig. 5

Shortest mainly rotational eigenmode for the floating bridge with frequency-dependent added mass for the circtangle shaped pontoon. X-axis in meters.

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Fig. 6

Longest vertical eigenmode for the floating bridge with frequency-dependent added mass for the circtangle shaped pontoon

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Fig. 7

Shortest mainly vertical eigenmode for the floating bridge with frequency-dependent added mass for the circtangle shaped pontoon

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Fig. 8

Added mass in heave for the circtangel geometry with and without flange

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Fig. 9

Potential flow damping in heave for the circtangel geometry with and without flange

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Fig. 10

Sway linear potential flow wave excitation force

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Fig. 11

Sway potential flow damping

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Fig. 12

Ratio of wave excitation force to damping

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Fig. 13

Weak axis moment from global analysis. The high tower is located at axis (A2), the cable stay bridge between axis A2 and A3. Larger pontoons in axis A3–A5 due to ship collision. A6–A21 have the same pontoon which are varied in this study.

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Fig. 14

Strong axis moment from global analysis (see Fig. 13 for additional description)

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Fig. 15

Torsional moment from global analysis (see Fig. 13 for additional description)

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