ENG6110 Coastal Engineering And Modelling

• 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

• Initial condition - default JONSWAP fetch growth expression

Modeling part of the design gave:

Methodology and formulas

The following were used in a pre-generated ‘CoastGC_bathy.mesh” file opened in MIKE 21 SW and the simulation run:

1. Time up, 100 steps and 1800 sec.
2. Given wind speeds and directions,

• Boundary conditions as lateral boundary.

1. Point series,
2. Area series
3. Spectral series

• Results

The spectral wave model was established using the MIKE 21 SW. the application is a 3^rd 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

Formula and solution:

Design wave height,

Wave height at the breakwater,

Where-

Hudsons Formula

Stability number,

Calculations:

From the result maximum height is for the south-east direction-design height

Therefore,

Significant height,

Peak wave period,

For:

Break criteria,

Water depth breakwater,

Slope, tan

Density of BW,

The density of water

Find

For finding this, we need value:

We can find it on the Raleigh distribution chart given below:

Conclusion

The models in MIKE21 are presented in a wave action density. Two governing equations are used to compute the full spectral formulation and the directional decoupled parametric formulation.

      The wave height, period distributions, wave direction and wave spectral parameter over the CoastGC were an integration to investigate the coastal wave process associated with the area. The MIKE 21 SW by DHI was used. The simulation coupled a spectral wave model with other wave parameters as shown to simulate the wave characteristics.

In addition, the model simulated decay, growth and the transformation of the waves simulated by the wind. The analysis used both the directionally-decoupled and quasi-stationary formulations. All the components used in the model took place at each time step. The MIKE 21 SW zipped files have a detailed description of the formulations and the coupled model spectrums.

            The MIKE 21 SW results gave the results which were used to calculate stone weight and trunk. Also, the wave wind energy is highest away from the ocean and low at the bed level

References

Torum, A., & Gudmestad, O. T. (2012). Water wave kinematics (Vol. 178). Springer Science & Business Media.

Lin, P., 2014. Numerical modeling of water waves. CRC Press