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Simulation of the Wave Field Around a
Submerged Breakwater in a Numerical Wave Tank
By: Jiwon Mun & Firat Y. Testik, PhD
Glenn Department of Civil Engineering
Clemson University, Clemson, SC 29634, USA
The 25th Annual National Conference on Beach Preservation Technology
Hutchinson Island Marriott, Stuart, Florida
February 8-10, 2012
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Outline
Motivation & Background
Numerical Setup & Procedure
Experimental Setup & Procedure
Validation of the Numerical Wave Tank
Conclusions & Future Work
Motivation
Offshore breakwaters are regularly employed to provide
defense to important coastal areas. Submerged breakwaters
has become more common in recent years.
Submerged breakwaters:
+ often more aesthetically pleasing than emerged breakwaters
+ maintain the landward flow of water
- usually transmit more wave energy than emerged breakwaters
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Motivation
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Offshore morphology
Scour around breakwater
Wave field around the breakwater Incident Wave
Dissipated Wave
Reflected Wave
Transmitted Wave
Beach erosion
Scour around structures
Waves in the protected area
Main Goal
To construct an experimentally validated numerical wave tank
using computational fluid dynamics tools to study wave reflection and
transmission characteristics around submerged breakwaters.
Background
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Wave Reflection, Dissipation, and Transmission
Cr2 + Cd
2 + Ct2 = 1
(Cr = Hr / Hi & Cd = Hd / Hi & Ct = Ht / Hi)
Submerged Breakwater Types:
Vertical
Rubble Mound
Semi-Circular
Geotubes
Berm
….
Background – Reflection study by Young & Testik (2011)
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
0
0.5
1
0 0.5 1 1.5 2
Cr
a/Hi
(a)
Vertical Breakwater
Cr-vertical = 0.53e-0.85
a
Hi
æ
èç
ö
ø÷
Hi
a
Background – Reflection study by Young & Testik (2011)
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
0
0.5
1
0 0.5 1 1.5 2
Cr
a/Hi
(b)
Semi-Circular Breakwater
Cr-semicircular = 0.53e-1.4
a
Hi
æ
èç
ö
ø÷
Background – Reflection study by Hornack & Testik (2012)
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
0
0.5
1
0 0.5 1 1.5 2
Cr
a/Hi
BW-1 (1:1)
BW-2 (2:3)
BW-3 (1:2)
0
0.5
1
0 0.5 1 1.5 2
Cr
a/Hi
BW-4 (0.49)
BW-5 (0.39)
Permeable Trapezoidal Breakwater Impermeable Trapezoidal Breakwater
Numerical Set-up & Procedure
The numerical wave tank (NWT) was constructed using ANSYS-
FLUENT software.
The NWT simulations were: Turbulent (RNG k-ε model)
Unsteady
Incompressible
Multiphase [Volume of Fluid, VOF]
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Geometry & Boundary Conditions
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Numerical Set-up & Procedure
A C
B B
B 1:20
B
B
Boundary conditions: A - Velocity Inlet, B – No-slip Wall, C - Pressure Outlet
Quadrilateral mesh elements
Statistics – 70704 nodes and 70070 elements; Size: 0.01 – 0.02 m,
Meshing
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Numerical Set-up & Procedure
Mesh Size Sensitivity Analysis
4
6
0 2 4 6
H(cm
)
Distance from the wave-maker (m)
Mesh size (MS) =0.6cm 0.8cm 1cm 3cm 5cm Expt.
Wave Generation
Stokes 2nd Order Waves & Open Channel Wave BC
Numerical Set-up: Typical NWT Simulations
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Experimental Set-up & Procedure
Laboratory Wave Tank (12 m x 0.6 m x 0.6 m) (1) linear actuator and motor, (2) breakwater, (3) wave paddle, (4) sloping beach, (5) wave absorber, (6) moveable cart assembly with wave gauges.
(1)
(2)
(3)
(4) (5)
ε, T Hi a
(6)
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Experimental Set-up & Procedure
Measured & Calculated Data
Wave elevation data Averaged over 40 wave periods
Reflection Coeff. (Cr) Goda & Suzuki (1976)
Transmission Coeff. (Ct) Ct= Ht/Hi
Experimental Set-up: Typical Laboratory Waves
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Visual Comparison of Breaking Waves
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
NWT Simulations: Experimental Validation
(a) 0 s (b) 0.01 s (c) 0.23 s (d) 0.33 s
(e) 0.5 s (f) 0.63 s (g) 0.66 s (h) 0.76 s
Wave Elevation (without breakwater)
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
NWT Simulations: Experimental Validation
Offshore of Wave Break
-10
0
10
0.00 0.25 0.50 0.75 1.00η (
cm)
t/T
2.5m from the wave-maker
Experiment Simulation
-10
0
10
0.00 0.25 0.50 0.75 1.00η (
cm)
t/T
3.5m from the wave-maker
Onshore of Wave Break
-10
0
10
0.00 0.25 0.50 0.75 1.00η (
cm)
t/T
4.7m from the wave-maker
Wave Elevation (with breakwater)
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
NWT Simulations: Experimental Validation
Offshore of Breakwater
-10
0
10
0 0.25 0.5 0.75 1η (
cm)
t/T
2.5m from the wave-maker Experiment Simulation
-10
0
10
0.00 0.25 0.50 0.75 1.00η (
cm)
t/T
3.5m from the wave-maker
Onshore of Breakwater
-10
0
10
0.00 0.25 0.50 0.75 1.00η (
cm)
t/T
4.7m from the wave-maker
Wave Reflection From a Submerged Vertical Breakwater
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
NWT Simulations: Experimental Validation
Wave Reflection From an Emerged, Rigid, Vertical Wall
0.0
0.5
1.0
0 0.5 1 1.5 2
Cr
a/Hi
Simulated
As expected Cr is close to 1.
Wave Dissipation over a Submerged Vertical Breakwater
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
NWT Simulations: Ct and Cd Values
Wave Transmission over a Submerged Vertical Breakwater
0
0.5
1
0 0.5 1 1.5 2
Ct
a/Hi
0
0.5
1
0 0.5 1 1.5 2
Cd
a/Hi
Conclusions
A Numerical Wave Tank was developed using a two-phase CFD model.
The NWT was validated using experimental measurements from a
laboratory wave tank.
To validate the NWT, experimental and numerical wave elevation data
at different locations along the tanks were compared. Comparisons
showed good agreement in general.
Reflection coefficient values calculated using the NWT simulation
results for:
(i) waves impinging on an emerged, rigid, vertical wall, and
(ii) waves breaking over a submerged vertical breakwater
were compared with the expected wave reflection coefficient values.
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
Future Work
Energy dissipation effects due to roughness of the sandy bottom and the breakwater walls will be incorporated in the NWT.
The NWT will be calibrated to account for the dissipation due to wave
breaking more accurately.
Wave field around a variety of submerged breakwaters will be studied using the NWT.
Coupled non-cohesive sediment transport and wave field simulations
around submerged breakwaters will be conducted to study sediment erosion/deposition patterns.
…
The NWT will be tailored to serve as an effective and efficient tool for breakwater design purposes.
J Mun & FY Testik*
Wave Field Simulation around a Submerged Breakwater
J Mun & FY Testik* Wave Field Simulation around a Submerged Breakwater
Thank You!
QUESTIONS ?
*Contact:
+1.864.6560484
ACKNOWLEDGMENTS This research was supported by the funds provided by the PADI Foundation Grant #
5039 and College of Engineering and Science at Clemson University.
