Kinematics Analysis And Structure Optimization Design And Development Of A Trash-cleaning Grab In The Low Head Hydropower Station

Using water resources and developing hydropower are important aspects of energy development.As an important means of hydropower generation,hydropower station takes the function of generating electricity,flood control,drought resistance,irrigation,shipping and so on.During the operation of the hydropower station,trashracks are usually arranged in front of the turbine inlets to intercept trash in the stream which might enter the headrace and to protect the units.The trash would pile up in front of trashracks if it cannot be cleared up in time.With the accumulation of trash,water flow in the headrace will be impeded,the operating head will fall,output of hydraulic turbine will reduce and the amount of generated energy will gradually decrease.Moreover,it is likely to crush the trashrack and hazard the generators.The trash accumulation will form waterhead,which causes the head loss.For the low head hydropower station discussed in this paper,head loss caused by trash must not be allowed.One of the effective means to decrease or avoid the head loss is to clear up the trash in front of the trashrack.The frequently-used cleaning method is mechanical clean.In this paper,the hydraulic trash-cleaning grab is used in the low head hydropower station.However,due to the debris in river,such as tree trunks and branches and bamboo branches,which will soon pile up in front of trashracks,the improper design of the machine,its bad kinematic and dynamic characteristics and its low efficiency cannot meet the requirements of frequent and efficient work demands.Analyzing the kinematics and dynamics characteristics of the cleaning grab,finding the problems of its structure design and optimizing and designing new cleaning grab are important and urgent to solve the existing problems of the hydropower station.Force analysis and theoretical calculation are first carried out of grab closing and descending processes to provide theoretical basis for subsequent dynamic and kinematics analysis.Three-dimensional modeling software SolidWorks is used to model the grab model,and the virtual prototype model is created in ADAMS.Dynamic and kinematics analysis are carried out to get changing curves.By analyzing the deficiencies of cleaning grab in the simulation results,that is,the power of the hydraulic cylinder is not enough to provide the closing force of the grab and the installation position of the hydraulic cylinder is not reasonable,the solution to replace the hydraulic system and optimize the installation position of the hydraulic cylinder is proposed.Kinematics simulation of grab-descending process is carried out to analyze the problem of difficulty of grab to enter water,and the simulation of the improved scheme in the software confirms the rationality of optimization.Through parametric modeling and optimization analysis of the grab,the installation position of the hydraulic cylinder is optimized to get the optimal position of the hydraulic cylinder based on actual conditions.Compared the dynamic analysis of the closing process of the new grab with the original grab,the optimization results obviously meet the design requirement.To get the needed pump station,the hydraulic system that needs to be replaced is redesigned and selected,and the simulation of the hydraulic system is completed.During designing the new grab,key joints and weld structure are calculated and checked,which guarantees the strength,stiffness,security and stability of the machine.In this paper,the control system to increase descending depth of the cleaning machine is also discussed,which solves the problem that the descending depth of the cleaning grab is low owing to the trash blockage.After completing the design of the grab,acceptance and commissioning requirements of it are established,in order to standard the performance indicators of new manufactured cleaning grab.Through this research,the optimization design of the hydraulic trash-cleaning grab helps to develop a new efficient cleaning grab.