| Floating breakwaters play an important role in protecting the safety of marine structures.Compared with the traditional fixed breakwater,floating breakwaters have the advantages of being suitable for various foundation conditions,convenient installation and removal,and less interference to water circulation and fish migration.Among them,the Box-type FB is widely used because of its simple shape,and the existing researches show that the water ballast Box-type FB has good wave dissipation performance than other ballast types.In this paper,the following research is done on the water ballast Box-type FB:(1)The wave dissipation mechanism of tensely type water ballast Box-type FB is studied in detail by model experiment and numerical simulation to explore the correlation between flow field,turbulent kinetic energy distribution,motion response and mooring force,and summarize the shortcomings of Box-type FB.Then,based on the wave-attenuating mechanism of FB,the shape of Box-type FB is optimized,and a new type of water ballast I-shaped FB is proposed.(2)Under the same conditions,the wave-attenuating performance,the changes of flow field,motion response,internal ballast water movement and mooring force of I-shaped FB and Box-type FB are compared.Compared with Box-type FB:The transmission coefficient of the I-shaped FB decreased by 7.8%-15.2%within the scope of the experiment,the increases in sway,heave and roll are 15%,21%and 12%respectively.Under waves with wave heights of 0.03 m,0.05 m and 0.07 m,the maximum offshore mooring force is reduced by an average of 13.1%,11.1%and 7.2%,and the maximum onshore mooring forces are reduced by an average of 5.7%,6.1%and 5.7%.(3)Experimental studies are carried out for two connection modes(catenary type and tension type),and the wave-attenuating performance,motion response,internal ballast water movement and maximum mooring force of tensely type water ballast I-shaped FB and catenary type water ballast I-shaped FB are compared.The results show that the catenary type water ballast I-shaped FB can reduce the maximum mooring force by 21.7%-71.7%under the wave-attenuating performance is basically unchanged.(4)The effects of initial submerged depth and wings length on wave-attenuating performance are studied through model experiment.The results show that when the initial submerged depth is 2/3 times of the height of the FB(h),the wave-attenuating performance is better than that of initial submerged depth is 1/2 and 5/6 times of the height of the FB,and the reduction is 14.1%.For the mooring force,the average reduction of the maximum offshore side mooring force is 8.7%and 36.5%,and the average reduction of the maximum onshore side mooring force are 3.6%and 15.3%,respectively.Under the operating conditions of an initial immersion depth of 2/3 h,the study of wing length parameters shows that when the wing length is 7.5 cm,that is,the length of single side wing is 18%of the overall width of I-shaped FB,the value of transmission coefficient(K_t)reaches the minimum in the test range,which means that the wave-attenuating performance of FB is the best.Therefore,within the research scope of this paper,when the lower edge of the upper wing of I-shaped FB is flush with the water surface(the initial submerged depth is 2/3 times the height of I-shaped FB),and the length of one wing is 18%of the overall width of I-shaped FB,the catenary type water ballast I-shaped FB has the best wave-attenuating performance,and the maximum is the least.This paper can provide a reference for the optimal design of FB. |
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