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Frontiers of Structural and Civil Engineering

ISSN 2095-2430

ISSN 2095-2449(Online)

CN 10-1023/X

Postal Subscription Code 80-968

2018 Impact Factor: 1.272

Front. Struct. Civ. Eng.    2021, Vol. 15 Issue (5) : 1111-1127    https://doi.org/10.1007/s11709-021-0757-1
RESEARCH ARTICLE
Floating forest: A novel breakwater-windbreak structure against wind and wave hazards
Chien Ming WANG1, Mengmeng HAN1(), Junwei LYU1, Wenhui DUAN2, Kwanghoe JUNG3
1. School of Civil Engineering, The University of Queensland, Queensland 4072, Australia
2. Department of Civil Engineering, Monash University, Victoria 3168, Australia
3. Hyundai Engineering and Construction, Technology Research Centre, Seoul 03058, Korea
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Abstract

A novel floating breakwater-windbreak structure (floating forest) has been designed for the protection of vulnerable coastal areas from extreme wind and wave loadings during storm conditions. The modular arch-shaped concrete structure is positioned perpendicularly to the direction of the prevailing wave and wind. The structure below the water surface acts as a porous breakwater with wave scattering capability. An array of tubular columns on the sloping deck of the breakwater act as an artificial forest-type windbreak. A feasibility study involving hydrodynamic and aerodynamic analyses has been performed, focusing on its capability in reducing wave heights and wind speeds in the lee side. The study shows that the proposed 1 km long floating forest is able to shelter a lee area that stretches up to 600 m, with 40%–60% wave energy reduction and 10%–80% peak wind speed reduction.

Keywords floating structure      breakwater      windbreak      hydrodynamic      CFD     
Corresponding Author(s): Mengmeng HAN   
Just Accepted Date: 16 September 2021   Online First Date: 10 November 2021    Issue Date: 29 November 2021
 Cite this article:   
Chien Ming WANG,Mengmeng HAN,Junwei LYU, et al. Floating forest: A novel breakwater-windbreak structure against wind and wave hazards[J]. Front. Struct. Civ. Eng., 2021, 15(5): 1111-1127.
 URL:  
https://academic.hep.com.cn/fsce/EN/10.1007/s11709-021-0757-1
https://academic.hep.com.cn/fsce/EN/Y2021/V15/I5/1111
return period (years) significant wave height Hs (m) peak period Tp (s) design scenarios
1 4.5 9.4–14.0 for wave breaking performance
100 8.4 13.9 for ultimate limit state design
Tab.1  Wave design conditions
Fig.1  Bird’s-eye view of floating forest.
parameter value
length of each segment of floating forest, L 360 m
depth of each segment, D 22 m
circular arch angle, α 84°
sloping angle of deck, θ 25°
height of the upper part, H 15 m
diameter of the tube, dt 2.5 m
height of the highest tube measured from deck, h 31 m
Tab.2  Dimensions of floating forest
Fig.2  Sketch of (a) plan view and (b) section view of breakwater segment, external geometry only.
Fig.3  Divisions of hull.
Fig.4  Module placement plan.
Fig.5  Drawing of 3-tube sections.
Fig.6  Drawing of 4-tube sections.
Fig.7  Mooring system for floating forest (dimensions of fenders and caissons are not to scale).
Fig.8  BEM panel mesh.
parameter value
xl1 ?165.47 m
xl2 ?149.84 m
xl3 ?134.21 m
yl1 43.17 m
yl2 26.96 m
yl3 10.78 m
zl1 0 m
zl2 0 m
zl3 0 m
xc 0 m
yc 67.59 m
zc 0.5 m
θf 45°
m 2.06×108 kg
rxx 99.45 m
ryy 14.40 m
rzz 104.58 m
rxy 0 m
ryz ?3 m
rxz 0.8194 m
Krad 106 kN/m
Ktan 106 kN/m
β 225° or 270°
Tab.3  Parameters for hydrodynamic analysis
Fig.9  Distribution of wave elevation at lee side for (a) floating breakwater and (b) stationary breakwater at T = 9.4 s, in beam sea conditions.
Fig.10  Distribution of wave elevation at lee side for (a) floating breakwater and (b) motionless breakwater in oblique sea conditions. (45° with respect to longitudinal line of the breakwater).
Fig.11  Distribution of wave elevation for floating breakwater case, t = 9.4 s. (a) ?200 m < y < 100 m; (b) ?500 m < y < ?200 m; (c) ?800 m < y < ?500 m.
Fig.12  Wave transmission coefficients. (a) RAO, oblique sea; (b) RAO, beam sea; (c) transmitted wave spectra, oblique sea; (d) transmitted wave spectra, beam sea.
Fig.13  Wave excitation force and overturning moment RAO, oblique sea. (a)Fx; (b)Fy; (c)Fz; (d)Mx; (e)My; (f)Mz.
Fig.14  Wave excitation force and overturning moment RAO, beam sea. (a)Fx; (b)Fy; (c)Fz; (d)Mx; (e)My; (f)Mz.
Fig.15  Rigid body motion RAO for floating breakwater under oblique sea. (a) Surge; (b) sway; (c) heave; (d) roll; (e) pitch; (f) yaw.
Fig.16  Rigid body motion RAO for floating breakwater under beam sea. (a) Surge; (b) sway; (c) heave; (d) roll; (e) pitch; (f) yaw.
stress and motion resultants oblique sea beam sea
Fx (N/m) 1.79 × 107 3.11 × 107
Fy (N/m) 3.13 × 107 6.44 × 107
Fz (N/m) 6.19 × 107 1.17 × 108
Mx (N·m/m) 1.11 × 109 1.07 × 109
My (N·m/m) 7.94 × 109 1.76 × 109
Mz (N·m/m) 7.66 × 109 6.21 × 109
surge (m/m) 0.71 1.28
sway (m/m) 0.74 0.88
heave (m/m) 0.53 1.20
pitch (°/m) 0.46 0.06
roll (°/m) 0.28 0.15
yaw (°/m) 0.04 0.05
Tab.4  Summary of maximum RAOs in oblique sea and beam sea conditions
Fig.17  Added mass RAO for floating breakwater modules. (a) Sway; (b) roll; (c) yaw; (d) sway-roll; (e) sway-sway, B1-B2; (f) roll-roll, B1-B2.
Fig.18  Distribution of hydrodynamic pressure on breakwater body.
Fig.19  Instant wave surface shape corresponding to maximum sway force (vertical displacement amplified for clarity).
Fig.20  Computational domain and boundary conditions in CFD simulations.
Fig.21  Inlet profiles of normalized mean wind speeds and normalized standard deviation (numerical: results from the simulation; theoretical: results from Eqs. (11) and (12)).
Fig.22  Overview and close-up view of mesh for aerodynamic analysis.
Fig.23  Illustration of sections taken for presenting results (the plane sections are highlighted by the green color). (a) Four tube section; (b) gap section; (c) three tube section.
Fig.24  Contour of Uˉx,z/ Uˉ0,z.
Fig.25  Contour of σux,z/ Uˉ0,z.
Fig.26  Contour of (Uˉx,z+σux,z)/(Uˉ0,z+σu0,z).
distance behind floating forest peak wind speeds
Vw = 40 m/s Vw = 50 m/s Vw = 60 m/s
100 m 11 m/s 14 m/s 17 m/s
200 m 21 m/s 27 m/s 32 m/s
300 m 28 m/s 36 m/s 43 m/s
400 m 32 m/s 41m/s 49 m/s
500 m 35 m/s 44 m/s 52 m/s
600 m 36 m/s 46 m/s 55 m/s
700 m 37 m/s 47 m/s 56 m/s
800 m 38 m/s 48 m/s 57 m/s
Tab.5  Peak wind speeds at 10 m height above mean sea level behind floating forest (Vw: incoming wind speed)
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