FLOATING BREAKWATER PERFORMACE FOR MARINA …

FINAL PROJECTPUTU YUNIK TRI WEDAYANTI

4205 100 015

FLOATING BREAKWATERS PERFORMANCE FOR MARINA

PROTECTION

1

INTRODUCTIONS

2

BACKGROUND

Floating Breakwaters belong to this specific categoryfor wave protection and restoration of semi-protectedcoastal regions.

入射波HI 反射波HR 通過波HT

透過率KT＝HI/HTThe breakwater generates a radiated wavewhich is propagated in offshore andonshore direction 3

Two-dimensional flow characteristics of waveinteractions with a fixed rectangular structure. (byKwang Hyo jung, 2005)

Ct (coeff. Transmition) was measured before the reflectionfrom the beach while the Cr(coeff. Reflection) wasmeasured after the quasi-steady state was achieved.Therefore, in this research the amount of energydissipated may not exact.

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CONTENTS

Research aim

Harms assumption

Laboratory Experiments

Numerical Simulations

Conclusions

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• To develop horizontal 2D wave model consideringthe energy dissipation behind the Double BarrierFloating Breakwater (DBFB).

• Modeling the new source term in wave-actionbalance equations relating to floating breakwatermotion.

• To calculate the value of CD (coeff. Drag) term andCM (coeff. Inertia) term and thus to confirm theharm’s assumption that CD is much larger than CMterm.

Research aim

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Harms assumption

⎟⎠⎞

⎜⎝⎛ −=

nLB

LH

PC

HHC iD

i

tt

13

4exp π

Laboratory measurements indicate that Floating Tire Breakwater(FTB) function predominantly as wave-energy dissipators,transforming into turbulence far more of the incident wave energythan they reflect.

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On Harm assumption CD term is much larger than CM term, sothe CM term can be omitted in the transmits coefficientcalculation. The harms assumption were generated bylaboratory experiments using Floating Tire Breakwater (FTB)

Ct = the transmitted wave L = wave length

energy B = breakwater width

Hi = incident wave height P = Porosity

Ht = transmitted wave height

CD = drag coefficient

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LABORATORY EXPERIMENTS

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BL

HiL : wave length

Hi : wave height

h : water depth

B : width of DBFB

d : draft

dh

DOUBLE BARRIER FLOATING BREAKWATER (DBFB)

• The Double Barrier FloatingBreakwater (DBFB) has arectangular body and doublevertical plates.

2cm

25cm

22.5m

17cm

5cm

1.25m 10

Experimental conditions

The experiments were conducted in the wave flume with thedimensions of the flume are 18m length, 0.6m width, and 0.8m depth

Two configurations were examined in the experiments as follows :(a) Heave motion DBFB; (b) Fixed DBFB

There are four variations on the experiments as follows: water depth,wave height, wave period, and wave length

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8.52m 6.22m 3.0m

1.0m以上

0.4m 0.3m 1.4m 0.4m

0.25m

斜面（砂）

造波板C

h1

Ch2

Ch3

Ch4

Ch5

Ch7

Ch8

18.0m

0.8m

0.6m

Illustration of experimental

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Heave motion DBFB Fixed DBFB

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Experimental data

Channel 3

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Calculations of CD and CM

( ) ( ){ ( ) ( )}Ax

ttutFtuttFCD ρΔ+−Δ+

=&&2

( ) ( ) ( ) ( ) ( )}{Vx

tuttFttuttutFCM ρ

Δ+−Δ+Δ+=

Morison et al. (1950)DtDuVCuAuCF MD ρρ +=

21

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Where: CD = drag coefficient

CM = inertia coefficient

= horizontal component of water particles velocity and

acceleration, respectively

t = time series

= time difference

F = wave force

= mass density of water

V = volume

A = Area

uu &,

ρ

tΔ

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Heave motion

18

19

20

531 8 8 11 10DC . exp( . Re)−= × − × ×

CD term is more larger than CM term based on the experimental results usinｇ the wave flume. Therefore, CM term can omit in this study.

Hokamura et al., 2008Tsujimoto et al (2009)

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NUMERICAL SIMULATIONS

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Extended Energy-Balance Equation with Diffraction (ExEBED)

Directly introduced a diffraction term, formulated from a parabolicapproxiamation wave equation, into the energy balance equation(Mase 2001)

A simple equation of estimating wave energydissipation number behind DBFB is proposed innumerical simulation

( ) ( ) ( ) ( ){ } SSCCSCCSv

ySv

xSv

byygyygyx εθθ

ωκθ −−=

∂∂

+∂

∂+

∂∂ 22 cos

21cos

223

Energy Balance Equation with Diffraction (ExEBED) is one ofwave model to estimate near shore wave condition

Two condition of incident wave was examined. Thoseconditions are normal distribution and oblique distribution.

Calculation of The spatial distributions of relative error,(Err)ij between the experimental and numerical results

Numerical conditions

Calculation of the horizontal distributions of wave heightusing the uniform Ct variations along the lee side of DBFB

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Numerical results

Normal incident condition

0o wave angle

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25o wave angle

Oblique incident condition

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The Relative error

( )( ) ( )

( ) ( )%100exp

exp×

−=

ij

ijijij H

HcalHErr

Spatial distributions of relative error between the experimental andnumerical wave height using the uniform Ct variations along the leeside of DBFB

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The Relative error

-7-6.5

-6-5.5

-5

-5-4

.5

-4.5

-4.5

-4

-4-3.5

-3.5

-3

-3

-2.5

-2.5

-2

-2

-2

-2

-2

-2

-2

-2

-1.5-1.5

-1.5

-1.5

-1.5

-1.5

-1.5

-1.5

-1

-1

-1

-1

-1

-1-1

-1-1

-1-1

-1

-0.5 -0.5 -0.5

-0.5

-0.5

-0.5

0

normal

200 250 300 350 400 450 500 0

50

100

150

200

250

300

350

Cross-shore direction (cm)

Longshore

direction(cm

)

Normal incident distribution

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-8-7.5-7

-6.5

-6.5

-6-6

-5.5

-5.5

-5

-5

-4.5

-4.5

-4

-4

-3.5

-3.5

-3

-3

-3

-2.5

-2.5

-2.5

-2

-2

-2-1.5

-1.5

-1.5 -1

.5

-1.5

-1.5

-1.5

-1

-1

-1

-1

-1

-1-1

-1 -1

-1

-0.5

-0.5

-0.5

-0.5-0.5

-0.5

-0.5

0

0

0

00

0

0

0

0

0.5

0.5

0.5

oblique

200 250 300 350 400 450 500 0

50

100

150

200

250

300

350

Cross-shore direction (cm)Long

shoredirection

(cm)

Oblique incident distribution

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CONCLUSION• Harms assumption is fairly good to used in the numerical

simulation based on the laboratory experiment results.

• the calculated horizontal distributions of wave height using the uniform Ct variations were reduced with changing the incident wave angle.

• The spatial distributions of relative error, (Err)ij are generated fairly good accuracy.

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Thank you for your attention

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Fixed DBFB

32

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35

36

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