Bore Generation, Propagation, and Impact on Coastal Structures

  • Jiaqi Liu

Student thesis: Doctoral ThesisDoctor of Philosophy


Generation and propagation of bores due to dam-break, initial mound of water, and solitarywave breaking and the impact on coastal structures are studied in this research by employing three different theoretical approaches. The theoretical models are based on three sets of equations, namely the Reynolds-Averaged Navier-Stokes (RANS) equations, the GreenNaghdi (GN) equations, and the Saint-Venant (SV) equation.

First, free surface flows of two and three dimensional bores generated by breaking of a water reservoir are studied. Two types of bore generations are considered, namely (i) bore generated by dam-break, where the reservoir water depth is substantially larger than the downstream water depth, and (ii) bore generated by an initial mound of water, where the reservoir water depth is larger but comparable to the downstream water depth. Each of these conditions correspond to different natural phenomena. This study shows that the relative water depth play a significant role on the bore shape, stability and impact. Various initial mounds of water and dam-breaks are considered, and the resulting bore generation and propagation are examined. Results obtained using the three different models are compared with each other, and with available laboratory experiments and analytical approximations where possible. Discussion is provided on the applicability of these methods to the problem of bore generation and propagation, noting the assumptions and limitations of each approach.

Second, the bore pressures on horizontal and vertical surfaces are studied. Effect of fluid viscosity on the bore pressure is studied by using different turbulence closures in the RANS model. Both two and three dimensional computations are performed to study their effects on the bore dynamics. Results of the theoretical models are compared with each other, and with available laboratory experiments. Information is provided on bore kinematics and dynamics predicted by each of these models.

Third, impact of bore on horizontal decks of coastal structures in shallow water is studied by using the RANS equations and the GN equations. Bores are generated by breaking of water reservoirs, and by breaking of solitary waves to resemble tsunami impact on coastal structures. Discussion is provided on (i) the fundamental characteristics and differences of bores generated through these two mechanisms, (ii) bore loads on horizontal decks and their variations with environmental conditions. Results are compared with other approaches used in the literature to study tsunami impact.

In summary, this study shows that the SV equation substantially simplified the physics of the problem, while results of the GN equations compare well with the RANS equations, with incomparable computational cost. RANS equations provide further details about the physics of the problem. All models agree in that the initial downstream water depth plays a key role on the bore generation and its stability. It is also shown that bore loads on coastal structures may be larger than equivalent solitary wave loads, and hence it is recommended to also consider bore impact at the design and analysis stages.
Date of Award2020
Original languageEnglish
SupervisorMasoud Hayatdavoodi (Supervisor) & Ian Mackie (Supervisor)

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