| Mudflat shellfish aquaculture is an important part of China’s fisheries,and harvesting is a key part of mudflat shellfish culture production.To solve the problems of serious damage to mudflats,soil erosion,poor selectivity of shellfish harvesting and high labor cost,mechanized mudflat harvesting is promoted.The mudflat shellfish was taken as the research object in this paper,and the design and development of vibratory harvesting equipment were completed through vibration harvesting dynamics analysis,shellfish discrete element modeling,simulation analysis and experimental verification.The main research contents are as follows.(1)The kinetic equations of shellfish on the vibrating screen were established,and the exponential mathematical models of upward sliding,downward sliding and jumping of the mixture on the screen surface of the vibrating screen were deduced.The main parameters that affect the movement state of shellfish on the vibrating screen are crank length,crank speed,vibrating screen surface inclination and swing direction angle,etc.,and analyze and determine the structural parameters of the vibrating screen:crank length r=0.01m,crank speed n=720rpm,screen surface inclination angleα=8°for the first layer of vibrating screen,swing direction angleεis greater than 40°;screen surface inclination angleα=5°for the second layer of screen.The range of swing direction angleε:35°～45°.(2)Taking the manila clam(Ruditapes philippinarum)as an example,a clam discrete element method(DEM)particle shape was established,which is based on 3D scanning and EDEM software.The DEM contact parameters of clam-stainless steel,and clam-acrylic were calibrated by combining direct measurements and test simulations(slope sliding and dropping).The accuracy of the calibrated clam DEM model was evaluated in a clam seeding verification test by comparing the average error of the variation coefficient between the realistic and simulated seeding tests.The results showed that:(a)the static friction coefficients of clam-acrylic and clam-stainless steel were0.31 and 0.23,respectively;(b)the restitution coefficients of clam-clam,clam-acrylic,and clam-stainless steel were 0.32,0.48,and 0.32,respectively.Furthermore,the results of the static repose angle from response surface tests showed that when the contact wall was acrylic,the coefficient rolling friction and static friction of clam-clam were 0.17 and 1.12,respectively,and the coefficient rolling friction of clam-acrylic was 0.20.When the contact wall was formed of stainless steel,the coefficient rolling friction and static friction of clam-clam were 0.33 and 1.25,respectively,and the coefficient rolling friction of clam-stainless steel was 0.20.(3)The discrete element simulation of mudflat shellfish vibration harvesting was completed.A mudflat simulation environment was established and a vibratory harvesting mechanism was introduced to conduct vibratory harvesting simulation of mudflat shellfish.Through single-factor and response surface simulation experiments,the analysis obtained that the forward speed of the harvesting machine has a significant effect on the harvesting results.The key structural parameters of the harvesting machine were determined:vibrating screen amplitude of 1.4mm,spiral rolling steel brush to spindle speed ratio of 32,forward speed of 9.9m/min,and brush speed of 18rpm.It was found that the brush speed and the reciprocating motion displacement of the vibrating screen had a significant effect on the number of clams harvested,and the brush speed had a significant effect on the clam crushing rate.(4)The experimental research on mudflat harvesting of buried shellfish was carried out.The results show that:the spindle speed and forward speed of the harvesting machine have significant effects on the harvesting weight and crushing rate of clams;the best forward speed range of the harvesting machine is 7～8m/min,and the spindle speed(or vibration frequency)range is800～900rpm.The optimal operating parameters of the harvesting machine were determined as follows:forward speed range 7～8m/min,spindle speed(or vibration frequency)range800～900rpm,operating area of the harvesting machine about 0.06 hm~2/h,harvesting efficiency about 400kg/h,shellfish crushing rate≤7.34%,sand content≤0.49g,surface mud content≤3.09%,selectivity about 82%.By comparing the penetration force of vibratory harvesting and hydraulic harvesting on the mudflats after harvesting,it was found that vibratory harvesting could loosen and improve the substrate,reduce the degree of slabbing and decrease the loss of surface sediment,which is beneficial to the protection of mudflat shellfish ecological environment.This study proposes a new method of mudflat shellfish harvesting,the test determined the structure and operating parameters of the vibratory harvesting,and provides new options for mudflat shellfish harvesting. |
PDF Full Text Request