Numerical Simulation Of The Hydrodynamic Behavior Of A Pneumatic Breakwater

Breakwaters are critical structures which are very essential to protect harbors and coastal areas against wave attack.In recent years,pneumatic breakwaters attract considerable attraction as a special coastal protection structure.Compared to traditional breakwaters,the pneumatic breakwater was proposed due to several advantages.Firstly,the pneumatic breakwater is one kind of mobile breakwater with several specific advantages,such as mobility,temporality,and low cost.Secondly,the pneumatic barriers are easy and quick in construction and they are not limited by water depths and local geology conditions.In addition,the pneumatic breakwater does not affect the exchange of the water,sediment and the maritime traffic.Thus the air curtain breakwater has good prospects in water transportation,military application and the aquaculture industry.In order to improve the wave damping performance of pneumatic breakwater,it is essential to study the hydrodynamic behavior of a pneumatic breakwater more comprehensively.The hydrodynamic performance of pneumatic breakwater is analyzed through numerical simulations by CFD tools.The Reynolds Averaged Navier-Stokes(RANS)equations combined with the Shear Stress Transport(SST)k-omega turbulence model are used to simulate the flow field of the pneumatic breakwater.And the VOF method is used to track the interface between the air and the water.The paper is organized as follows:Firstly,an existing physical model test performed in a PIV wave flume is used to validate the numerical model,indicating that the numerical model can be used to analyze the hydrodynamic behavior of the pneumatic breakwater.The flow field generated by ascending air bubbles in static water is analyzed,and then the wave dissipating performance of the pneumatic breakwater is also analyzed,considering different wave periods,wave heights,airflow rates and layout patterns.The results indicate that wave heights,wave periods and the airflow rates all have certain influences on the wave dissipating performance of a pneumatic breakwater.Secondly,as for the pneumatic breakwater with double air discharging pipes,the rows of air curtains and the distance between aerial barriers are considered to study its wave attenuation performance.The results indicate that an appropriate distance between two rows of aerial curtains combined with adequate airflow rates could improve the wave dissipating capacity of pneumatic breakwater,especially for longer waves.Finally,a composite breakwater composed of pneumatic breakwater and submerged breakwater is proposed to damp longer waves.And the numerical model of the submerged breakwater is validated by an existing physical model conducted by Yuichi Iwagaki.The pneumatic breakwater has limited effect on damping longer waves and the submerged breakwater will affect the water resources exchange as its height is too high.Thus it is reasonable to conduct a composite breakwater to improve the wave damping performance.Then the wave dissipating performance of the composite breakwater is analyzed considering different submersion depths and layout patterns.The result indicates that the wave attenuation capacity for longer waves will be improved for composite breakwater as the air barrier is located on the leeward side of the submerged breakwater.