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postgraduate thesis: Understanding and mitigating wave effects in fluid
| Title | Understanding and mitigating wave effects in fluid |
|---|---|
| Authors | |
| Advisors | Advisor(s):Chow, KW |
| Issue Date | 2023 |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Citation | Cheung, Y. Y. [張悅熒]. (2023). Understanding and mitigating wave effects in fluid. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. |
| Abstract | Surface waves play a significant role in distributing energy over the oceans, and extreme events—such as rogue waves and typhoon-generated waves—have been studied extensively recently. This thesis considers theoretical and computational approaches. Through two studies, it aims to explore unconventional modulation instability and also analyse the performance of floating breakwaters.
Study I discusses the modulation instability of plane waves of the Hirota equation, an integrable system with third-order dispersion, where finite amplitude disturbances cannot be accounted for by conventional analysis. The study considers exact doubly periodic solutions expressed through Jacobi elliptic functions, where wavy profiles at the intensity minima are interpreted as finite amplitude disturbances amplified and saturated at the intensity maxima. Such periodic states and breathers can be generated from finite amplitude disturbances with wavenumbers falling outside the linear instability band, qualifying as an unconventional or extraordinary modulation instability.
Study II investigates the feasibility, merits, and possible deficiencies of multiple-row floating breakwaters with specific designs through experimental and numerical methods. This deployment serves as a protective measure against extreme weather, storms, and typhoons in the southern part of Hong Kong Island. The project aims to study the potential of multiple-row breakwaters in enhancing wave cancellation capability and protecting coastal areas. Various design configurations are compared in terms of the number of rows and spacings between breakwaters. The results show improvements in wave attenuation capability for multiple-row floating breakwaters, as compared with the singlerow case. The study demonstrates that the longer the wave period, the higher the transmission coefficient would be. Large-scale domain numerical simulations are conducted to evaluate the performance of multiple-row breakwaters under real-world oceanic conditions. The implementation of multiple-row floating breakwaters shows improvements in reducing transmitted wave heights in normal and typhoon conditions.
By discussing the aspects of modulation instability in a non-traditional way and the configurations that can mitigate strong typhoon-generated waves, both studies contribute to the broader understanding of wave phenomena and the configurations that can be used to mitigate their effects. Additional testing and also exploration of other equations could further enhance our understanding, while addressing inherent factors in floating breakwater configurations could
help achieve better performance. |
| Degree | Master of Philosophy |
| Subject | Ocean waves |
| Dept/Program | Mechanical Engineering |
| Persistent Identifier | http://hdl.handle.net/10722/332108 |
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | Chow, KW | - |
| dc.contributor.author | Cheung, Yuet Ying | - |
| dc.contributor.author | 張悅熒 | - |
| dc.date.accessioned | 2023-10-04T04:53:36Z | - |
| dc.date.available | 2023-10-04T04:53:36Z | - |
| dc.date.issued | 2023 | - |
| dc.identifier.citation | Cheung, Y. Y. [張悅熒]. (2023). Understanding and mitigating wave effects in fluid. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. | - |
| dc.identifier.uri | http://hdl.handle.net/10722/332108 | - |
| dc.description.abstract | Surface waves play a significant role in distributing energy over the oceans, and extreme events—such as rogue waves and typhoon-generated waves—have been studied extensively recently. This thesis considers theoretical and computational approaches. Through two studies, it aims to explore unconventional modulation instability and also analyse the performance of floating breakwaters. Study I discusses the modulation instability of plane waves of the Hirota equation, an integrable system with third-order dispersion, where finite amplitude disturbances cannot be accounted for by conventional analysis. The study considers exact doubly periodic solutions expressed through Jacobi elliptic functions, where wavy profiles at the intensity minima are interpreted as finite amplitude disturbances amplified and saturated at the intensity maxima. Such periodic states and breathers can be generated from finite amplitude disturbances with wavenumbers falling outside the linear instability band, qualifying as an unconventional or extraordinary modulation instability. Study II investigates the feasibility, merits, and possible deficiencies of multiple-row floating breakwaters with specific designs through experimental and numerical methods. This deployment serves as a protective measure against extreme weather, storms, and typhoons in the southern part of Hong Kong Island. The project aims to study the potential of multiple-row breakwaters in enhancing wave cancellation capability and protecting coastal areas. Various design configurations are compared in terms of the number of rows and spacings between breakwaters. The results show improvements in wave attenuation capability for multiple-row floating breakwaters, as compared with the singlerow case. The study demonstrates that the longer the wave period, the higher the transmission coefficient would be. Large-scale domain numerical simulations are conducted to evaluate the performance of multiple-row breakwaters under real-world oceanic conditions. The implementation of multiple-row floating breakwaters shows improvements in reducing transmitted wave heights in normal and typhoon conditions. By discussing the aspects of modulation instability in a non-traditional way and the configurations that can mitigate strong typhoon-generated waves, both studies contribute to the broader understanding of wave phenomena and the configurations that can be used to mitigate their effects. Additional testing and also exploration of other equations could further enhance our understanding, while addressing inherent factors in floating breakwater configurations could help achieve better performance. | - |
| dc.language | eng | - |
| dc.publisher | The University of Hong Kong (Pokfulam, Hong Kong) | - |
| dc.relation.ispartof | HKU Theses Online (HKUTO) | - |
| dc.rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works. | - |
| dc.rights | This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. | - |
| dc.subject.lcsh | Ocean waves | - |
| dc.title | Understanding and mitigating wave effects in fluid | - |
| dc.type | PG_Thesis | - |
| dc.description.thesisname | Master of Philosophy | - |
| dc.description.thesislevel | Master | - |
| dc.description.thesisdiscipline | Mechanical Engineering | - |
| dc.description.nature | published_or_final_version | - |
| dc.date.hkucongregation | 2023 | - |
| dc.identifier.mmsid | 991044723912903414 | - |