Numerical study of solitary wave interaction with a vegetated platform

Significance 

Climate changes and increase in the sea levels have led to the occurrence of extreme sea events such as tsunamis, coasting erosions and flooding. Being a global emergency, it requires urgent and effective solutions. Research has shown that coastal vegetation systems can be effectively used in the management of the coastal ecosystem due to their ability to attenuate the incident wave energy attributed to good wave damping efficiency. For example, the recently developed Martin Ecosystems BioHaven Floating Breakwater, comprising of a simple platform, vegetation stems, and vegetation roots, has been effective in protecting the shoreline and stabilizing the banks. Coastal vegetation can be classified as suspended, emergent and submerged vegetation.  Wave attenuation by submerged and emergent vegetation has been studied numerically. However, the interaction between the vegetated platform and extreme sea events has not been fully explored.

In a recent paper, Yanxu Wang (Ph.D. student), Professor Zegao Yin, and Professor Yong Liu from the Ocean University of China investigated the solitary wave interaction with vegetated platforms. In particular, a two-dimensional numerical model based on the microscopic approach was developed. The feasibility of the model was validated using data obtained from the existing literature. The research work is currently published in the research Ocean Engineering journal.

Numerical simulations based on the OlaFlow solver was conducted to evaluate the solitary wave interaction with the vegetated platforms. The wave damping efficiency of the vegetated platform being greater than that for the simple platform, the simple platform played a significant role while the vegetation played a supportive role in the wave damping. On the other hand, the vegetation roots exhibited better performance than stems for reducing wave transmission. However, the stems always contribute to diminishing the wave elevation oscillation and sub-peak in the undulating tails.

The individual drag coefficients for vegetation stems and roots were determined by investigating the velocity distributions of the green water and the underflow above and below the platform. This required a better understanding of the effects of various parameters: incident wave height, vegetation density, stem height, root height and platform width on the hydrodynamic coefficients. For green water, a self-similar velocity behavior is observed along the platform. The maximum velocity occurred at the green waterfront while the minimum velocity occurred at the seaside edge of the platform. However, the velocity of the underflow maintained almost constant along the platform and the maximum water velocity of the underflow occurred earlier than that for green water, especially for larger platform widths. Generally, an increase in the platform width led to an increase in the maximum velocity of the green water while that for the underflow followed the opposite trend.

In a nutshell, Ocean University of China scientists developed empirical formulas for predicting solitary wave transmission and reflection over simple and vegetated platforms. Overall, even though the study insights are limited to mainly solitary waves, it provides a useful approach for further numerical investigation regarding the effects of irregular waves on the vegetated platforms. Therefore, Professor Zegao Yin, in a statement to Advances in Engineering, observed that the study will advance the coastal environmental management strategies.

Numerical study of solitary wave interaction with a vegetated platform - Advances in Engineering
Fig. 1. Definition sketch of solitary wave interaction with the numerical vegetated platform model.
Numerical study of solitary wave interaction with a vegetated platform - Advances in Engineering
Fig. 2. Surface elevations after the vegetated platform for (a) various hs for hr = 0 m and (b) various hr for hs = 0 m.
Numerical study of solitary wave interaction with a vegetated platform - Advances in Engineering
Fig. 3. Comparisons between simulated and estimated (a) transmission coefficient and (b) reflection coefficient.

About the author

Yanxu Wang is currently a Ph.D. student in College of Engineering at Ocean University of China. He received the master’s degree in College of Engineering from Ocean University of China in 2017. He has published 10 peer-reviewed journal papers and won the National Scholarship in 2018.

His research interests include: multiphase flow; wave-structure interactions; marine energy utilization.

About the author

Zegao Yin is currently a professor in College of Engineering at Ocean University of China. He received the Ph.D. degree from Zhejiang University, China (2005). He worked at the University of Alberta (Canada) as a visiting professor in September 2011-September 2012. He has been in charge of 3 projects funded by National Natural Science Foundation of China and several provincial projects.

He has published more than 50 peer-reviewed journal papers and held about 20 patents. His research interests include: hydrodynamics of coastal and ocean engineering; marine energy utilization; environmental fluid dynamics.

About the author

Yong Liu is currently a professor in College of Engineering at Ocean University of China. He received the Ph.D. degree in Port, Coastal and offshore Engineering at Dalian University of Technology, China, in 2007. He has published more than 50 peer-reviewed journal papers.

His research interests include: hydrodynamic analysis and design methods for coastal structures; wave interaction with floating structures; sloshing in water tanks; boundary element method for wave-structure interactions.

Reference

Wang, Y., Yin, Z., & Liu, Y. (2019). Numerical study of solitary wave interaction with a vegetated platform. Ocean Engineering, 192, 106561.

Go To Ocean Engineering

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