| The environment of the ocean is complex and changeful and the vertical stratified fluid environment is universal around the world.In the process of developing marine resources,ocean stratification effect has become an important factor which cannot be ignored.When the floating structure is moving on the surface of the stratified fluid,it causes fluctuation on the internal interface,which affects the prediction of the force and the response of the structure.In the condition of two-layer fluid,a towing experiment of floating box is introduced in this paper,in order to study on the drag resistance and characteristics of the wave in the interface in a two-layer fluid.The towing experiment of floating box was carried out in a two-layer fluid with density stratification in the gravity stratified flow tank of PLA University of Science and Technology.In the experiment,three variables were set up to study the characteristics and changing laws of drag resistance and internal waves on the interface.The experimental results on the resistance show that the added resistance Fsd and the relevant resistance coefficient Csd reach its local maximum for special towing speed.Under the same interface position,the Froude number corresponding to the local maximum of Csd is very closed,reducing slightly with the draft.In addition,when the Froude number Fr exceeds 0.8,Csd/(b/h1)2depends on the Froude number only,irrespective of the box draught.Compared with the hull,the variation of added resistance and relevant resistance coefficient with different velocity is different,such as the value of maximum and the Froude number corresponding to the local maximum.Based on the wave making condition on the interface,the towing process is further analyzed: The experimental results show that under the same draught,the length λ and amplitude A of internal wave crest part reach their maximum for special towing speed.The local maximums are independent of draft depth;rather,the corresponding Fr depends on the draft.When the internal wave crest contacts with the after of the structure,which causes the turbulent mixing on the interface,the internal wave resistance increases to the maximum value.In addition,single-width energy of internal wave are deduced,which is used to analyze drag resistance and internal waves according to energy theory. |
