This study is a basic study on the analysis of the flow field surrounding the bubble curtain induced by releasing the air bubble underwater, the generation of the circular circulation mechanism, and the wave energy attenuation effect of induced artificial flow. To achieve the presented purpose, this study focused on the following two main contents. First, the formation and artificial flow characteristics induced by air bubbles were quantitatively evaluated according to air source depth and airflow rate as installation parameters of the bubble curtain. Then, major forming factors and hydraulic characteristic factors were derived. Second, the wave energy attenuation performance of the pneumatic breakwater was evaluated through a two-dimensional wave hydraulic model experiment and numerical analysis modeling. Then, a correlation analysis was performed between the wave field and the induced artificial flow among the external forces that should be considered the most when applying the marine environment. Finally, the relationship between the installation parameters of the bubble curtain and the wave energy attenuation performance was quantitatively established. The results of this study are summarized as follows.
1) The numerical analysis model was established to analyze the bubble curtain induced by releasing air bubbles underwater. Two-way coupling was considered for motion reproduction between gas-liquid phases in model construction, and the multiphase flow was treated with the relative velocity for a single-phase mixture according to air aeration. To analyze the dispersion effect of the turbulence field caused by the release of air bubbles underwater, the RNG k-e turbulence model was applied to construct a numerical analysis model that can economically simulate multiphase flow accompanied by strong turbulent flow.
2) Forming factors according to installation parameters were considered in relation to the formation of the bubble curtain induced by the release of air bubbles through the constructed numerical analysis model. Forming factors were developed and presented based on the results of this study to deal with the very complex phenomenon induced by the release of air bubbles underwater in a simple and engineering.
3) To analyze the flow characteristics induced by the bubble curtain in an engineering analysis method, hydraulic characteristic factors of the flow field were derived using the PIV hydraulic model experiment and numerical analysis model. For theoretical establishment of hydraulic characteristic factors, the theoretical equations were organized and presented, focusing on the characteristics of artificial flow induced by generating the bubble curtain underwater.
4) In the experiment and numerical analysis model results, the effect on the wave energy attenuation of the pneumatic breakwater was clearly confirmed, and the wave interacted with the bubble curtain and the surface wave energy dissipation occurred around the pneumatic breakwater.
5) The wave energy attenuation performance of a pneumatic breakwater is closely related to the period of the incident wave and airflow rate. As the airflow rate increased, the wave energy attenuation rate increased. For long period incident waves(), the bubble curtain has little effect on the propagating waves.
6) The scale effect was estimated through a dimensionless comparison of the wave energy attenuation performance of the pneumatic breakwater. In addition, a relational expression for deriving the airflow rate condition when the bubble curtain is used for attenuating wave energy is presented.