6110ENG Wave Modeling and Coastal Structure Design at Coast GC

This report presents a wave modeling and coastal structure design project focused on constructing an impermeable rock groyne at Coast GC. Utilizing DHI MIKE 21 SW model, the project predicts design wave conditions based on available bathymetry and historical wind data, since no historical wave monitoring data was available. The design development involves spectral wave model analysis, simulations, and in-depth analysis of wave height/direction, period distributions, wave characteristics at the construction site, and wave spectral parameters. The report details the key model parameters, including bathymetry data, ARI design winds, and MIKE 21 SW parameters, and presents simulation results, design wave height calculations, and stability coefficient determination using Hudson's formula. The analysis integrates wave parameters to simulate wave characteristics, simulating decay, growth, and transformation of wind-generated waves, ultimately providing essential data for coastal structure design and safety.

Wave Modeling and Coastal Structure Design (Report) 1
WAVE MODELING AND COASTAL STRUCTURE DESIGN
(REPORT)
by[Name]
Course
Professor’s Name
Institution
Location of Institution
Date

Wave Modeling and Coastal Structure Design (Report) 2
Wave Modeling and Coastal Structure Design
1.0 Introduction and Background.
Project
The impermeable rock gryone structure to be constructed at the Coast GC is a structure
that will consist of steel reinforcement and cast in place concrete – the standard design of a
majority of civil and structural engineering. The project is to be undertaken at a construction site
identified as shown in Figure 1. The location of the project has no historical wave monitoring
data; however, the bathymetry data and the historical wind data for the area are available and
were useful in the development of the design. Table 1 presents the 50 year ARI design wind in
the research domain for the area. The design project applied DHI MIKE 21 SW model to predict
the design wave conditions using the provided design wind conditions.
Model and Design Formula
The design was done through spectral wave model analysis using relevant parameters as
indicated in the ‘Key Model Parameters’ section. The design development involved complete
simulations of the area using design wind conditions and wave output parameters. This was
followed by an in-depth analysis wave data of three key design aspects: (1) the developed wave
height/direction and period distributions, (2) the wave characteristics at the construction site, and
(3) the developed wave spectral parameter at the construction site. The results section of the
report presents the critical design wave and wave characteristics.
Key Model Parameters
Figure 1 below is satellite map showing the location of the project – where the
construction will take place. Next to the figure are the Bathymetry data (in meters) that was used.

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Figure 1: The map of Coast GC and the construction site.
Other important design data/parameters utilized in the project are the 50 year ARI design
wind in th research domain. The data is represented in Table 1 below.
Table 1: 50 Year ARI Design Winds at the Coast GC.
Wind direction N NW S SE

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Wind speed (m/s) 20.2 22.1 20.6 28.8
Accurate prediction of design waves is essential when determining design data for coastal
structures (Torum & Gudmestad, 2012). The safety of structures, as well as the possibility of
developing an economic design, relies above all on the reliability and accuracy of the underlying
design data.
The following data information was used in design development:
(i) Bathymetry data, from the pre-generated file of “CoastGC_Bathy.mesh”
The domain has Northern, Southern and Eastern open boundaries. “Lateral
boundary” applies to all of them. The coastal structure toes is at (Easting 550000,
Northing 6890000) with a water depth of 8.80 m.

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(ii) The MIKE 21 SW parameters applied include the following:
 Time: No of time steps 100, Time step interval: 1800 s
 Basic equations: Fully spectral formulation and Instationary formulation
 Spectral discretization: 25 frequencies and 16 directions
 No water level and current variations
 Diffraction – no diffraction
 Energy transfer - Include quadruplet wave interaction
 Wave breaking – Specified gamma, constant, value = 0.8
 Bottom friction - D50 sand size is 0.0002 m
 White capping – no white capping
 Structure – no structure

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 Initial condition - default JONSWAP fetch growth expression
Modeling part of the design gave:
Wind Direction N NW S SE
Wind speed 20.2 22.1 20.6 28.8
Signi.wave
height
4.523 4.368 4.07 4.79
Peak Wave
period
12.55 11.169 11.96 14.29
Methodology and formulas
The following were used in a pre-generated ‘CoastGC_bathy.mesh” file opened in MIKE 21 SW
and the simulation run:
i. Time up, 100 steps and 1800 sec.
ii. Given wind speeds and directions,
iii. Boundary conditions as lateral boundary.
iv. Point series,
v. Area series
vi. Spectral series

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2.0 Results
The spectral wave model was established using the MIKE 21 SW. the application is a 3rd
generation spectral wind wave model, a development of DHI. The model was applied in the
simulation of the growth, decay and transformation of wind generated waves and swells with the
CoastGC, construction site. Both a full spectral and directional decoupled parametric
formulations were included in this analysis.
The figures below show the simulation results from MIKE 21 SW model based on the
key model parameters specified for the project:
Figure 1. Spectral Wave Model
Figure 2. Wave Height and Wave Direction Distribution

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Figure 3. Wave period Distributions

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Figure 4. Wave Spectral Parameter
Formula and solution:
Design wave height,
H10 %=Hrms √−ln ( 0.1 )
Wave height at the breakwater,
Hb =γ b hb
Where γb – Break criteria

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-❑b HB−water depth at thetoe of Breakwater .
Hudsons Formula
Stability number,
Ns = H
∆ Dn 50
=(K D cot α ¿ ¿
1
3
 D50= H
∆ ¿ ¿
 ∆= ρs
ρw
−1
 W n 50= ρs g Dn 503
Calculations:
From the result maximum height is for the south-east direction-design height
Therefore,
Significant height, Hs =4.7912 m
Peak wave period, T p=14.289 s
For:
Break criteria,γb=0.8
Water depth breakwater, hb =8.8 m
Slope, tanα
Density of BW,ρs=2650 kg /m3

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The density of waterρw =1026 kg/m3
Find H10 %
For finding this, we need Hrmsvalue:
We can find it on the Raleigh distribution chart given below:

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For H10 %=1.42
We know that
Hs=4.7913
∴ Hrms= 4.7913
1.42 =3.374m
H10 %=Hrms √−ln (001)
=>5.12m
We need to find break water criteria
γb=0.8, Hb=γb hb =7.04
Since Hb > H BW; so it is an unbroken one