Research On Mechanical Properties Tests Of Clam And Key Issues Of Dredge Machinery

There are several problems existing on this kind of clam harvested by current hydraulic dredge,including high sand content,high damage rate,poor selectivity,etc.To solve the above problems,the manila clam(Ruditapes Philippinarum),one of the four main cultured shellfish in China,was taken as an example,the key issues such as the mechanical properties of the clam shell,the mechanical modeling of the clam cultured sediments,the oscillation softening of the sediment,the fluid-solid coupling model of tines and sediment,and the multidisciplinary collaborative design optimization for the clam dredge were researched by using the methods of the computer simulation,design optimization theory and experiment.A chain-tine clam dredge with oscillation mechanism has been developed,and the dredging performance experiments have been carried out.The main research work and achievements are displayed as follows:(1)The research on biomechanical properties of clam shell.The structure and morphological size distribution of clam shell could be known according to observed of macroscopic and microscopic morphological traits of the clam shell.It was found that the shell is made up of pure aragonite phases,and the inner,middle and outer layers are the composite prismatic structure,crossed-lamellar structure,and homogeneous structure,respectively.The hardness,tensile strength,three-point bending strength and compressive strength of the shell were tested using hardness testers and universal testing machine.The results showed that the inner layer of the shell is the hardest,and the hardness of each layer is anisotropy.The three-point bending strength is significantly higher than the tensile strength of shell.The quasi-static compressive strength of the whole shell fitted the Weibull distribution,and the lowest strength was found with beak vertical loading orientation(Z orientation).The age of the clam is a principal factor of the fracture force variation,and the fracture force varies from ca.100-400N.The results provide constraint conditions for the design and optimization of the clam dredge.(2)The research on physical and mechanical properties of clam cultured sediment.The basic physical properties of the tidal flat sediment and subtidal sediment were measured by standard geotechnical test methods.The results showed that subtidal sediment has higher moisture content,porosity and particle size than that of tidal flat sediment.The shear property and pressure-sinkage property of the two kinds of sediments were studied by in-situ shear tests and circular platen compress experiments in laboratory,respectively.It revealed the law that the shear strength of both sediments increases logarithmically with depth.By identifing the characteristic parameters of the sediment models,the applicability of applying Bekker model to describe the pressure-sinkage relationship of both sediments were discussed.It could provide a theoretical basis for determining the minimum grounding area of the walking mechanism.(3)The design and experiment research of sediment oscillation mechanism.A crank-rocker oscillation mechanism was designed,and the dynamic simulation model was established based on ADAMS software.The relationship between crank rotational frequency,towing velocity,amplitude,oscillation tines velocity ratio λ,minimum velocity angle y,draft force was researched.The results showed that it is beneficial to reduce draft force when the λ is more than 1,and the y is less than 90°.The simulation model were verified by the tidal flat sediment softening experiments using the oscillation mechanism prototype,the effect of towing velocity,frequency and amplitude on the sediment softening were revealed.It was found that the most important factor affecting the sediment softening is the amplitude.The results provide a technical support for the dredge design.(4)The design and simulation of chain-tine clam dredge.The overall design scheme of the clam rotating elastic tine excavating combined with the jitter chain net conveying and the sediment oscillation softening was put forward.The fluid-solid coupling model of tines,sea warer and sediment was established and solved based on LS-DYNA software.The effects of towing velocity,tines’ angular velocity and cutting depth on the tines’ cutting resistance and maximum equivalent stress were discussed.The results showed that the angular velocity had a significant effect on the tines’ cutting resistance and the maximum equivalent stress.Through regression analysis,the average cutting resistance and maximum equivalent stress models of tines were established.It could provide a reference for the construction of constraint functions in the dredge optimization.(5)The multidisciplinary design optimization of chain-tine clam dredge.According to the actual conditions of the designed dredge,some models were derived,including the tines kinematic model,the tines’ cutting power consumption model,the tines maximum equivalent stress model,the collision model between the clam and the tine,as well as the clam’s mechanical model.The constraint functions were established using above-mentioned models and the mechanical parameters of the clam shell and the sediment.The mathematical model of the dredge design optimization problem was established with the highest dredging efficiency.The optimization problem was disciplinary decomposed and solved by design space decrease collaborative optimization method.(6)The performance experiments of chain-tine clam dredge.Using the chain-tine dredge,the performances of clam dredging efficiency,dredging rates,damage rates,sand content rates and selectivity were tested in the clam cultured area of Dalu Island in Dandong.When the towing velocity was 1.028m/s and the tines’ angular velocity was 1.57rad/s,the clams’ sand content and damage rates of the chain-tine dredge decreased by 83.3%and 84.8%respectively,compared with that of the dive propeller dredge,has reached the expected design objective.