Research Study Of Offshore Duck Mouth Type Floating Marine Litter Collection Device And Its Related Hydrodynamics

With the development of marine industry and the increase of maritime activity,the offshore environment has been affected by the floating marine litter more and more.In addition,the floating marine litter is mainly located in the tourism and leisure area,the fishery area,the port and shipping zone,and the bathing beach zone,which has strong impacts on the coastal landscape,the ship navigation,the marine organism,and the human health.In recent years,the disposal of floating marine litter is becoming an important topic in the marine environment protection.However,the floating marine litter is primarily disposed by manpower,whose methods are relatively simple and crude.Moreover,due to the complicated offshore hydrodynamic environment,there is a lack of an effective,automatic method to clean the floating marine litter.In this study,a reasonable structural style of the collection device of floating marine litter is developed based on its related hydrodynamic characteristics research.In addition,the method to calculate wave force on the collection device of floating marine litter is analyzed,and the feasibility of the collection device of the floating marine litter proposed in this study is discussed according to the prototype test,which has enriched the method to collect the floating marine litter in the offshore area.Firstly,the distribution and classification of the floating marine litter is investigated to predict drifting trajectory of the floating marine litter,and the effective method and device to collect the floating marine litter are proposed on the basis of topographical,hydrological and geological conditions of layout location.After that,the hydrodynamic performance of collection device of the floating marine litter is analyzed in details through the theoretical analysis,numerical simulation,physical modelling test and prototype test,which mainly include:1.Based on the numerical model of ocean circulation(FVCOM)and the offshore wave propagation model(SWAN),the trajectory prediction model of the floating marine litter is developed.The movement routine of the floating marine litter is numerically obtained,and then the site selection problem of the collection device can be solved.2.The structural style and collection method of the floating marine litter are developed,and the prototype test of the collection device is also conducted.The floating marine litter collection device includes the barrier and the collection device.It is arranged in the sea with a layout of "duck mouth".By using the collection device,the floating marine litter can be automatically collected under any weather condition without the need of extra energy input.3.The theoretical analysis on the calculation method of the hydrodynamic loads on the“Duck Mouth,is presented The barrier mainly includes the horizontal circular cylinder and the submerged skirt.The modified Morison equation and the asymptotic analysis method are proposed to calculate the hydrodynamic loads on the small and the large horizontal circular cylinder with a small submerged depth.4.The wave hydrodynamic characteristics of barrier with a submerged skirt is investigated by numerical simulation and physical model test,and then the empirical formula of the wave force on the horizontal circular with a submerged skirt is proposed.Simplified method for line force calculation based on the empirical formula of wave force is verified by model test.It indicates that the line force obtained by this method is more conservative than test results,which could be a basis of engineering design or used to testify calculation results of line force by dynamic analysis.5.In order to check the practicability of the "Duck Mouth",the collection rate of floating marine litter and the motion response of the collection device is analyzed through the prototype test which shows that the "Duck Mouth" performs well in the sea.The results indicate that the intercepting rate can up to 93%and the collection rate is 60%in the normal environmental condition,and the maximum heave motion is 0.2 m.It provides a key reference to the engineering design of the floating marine litter disposal device.