基于变密度法的油菜割晒机割台机架拓扑优化与试验

Topology optimization and test of the header frame of rapeseed windrower based on the variable density method

为减少履带式油菜割晒机割台在不同工况下的振动,应用Hypermesh软件建立割台拓扑优化空间,利用多体动力学方法建立基于RecurDyn的油菜割晒机虚拟样机模型,获得部件调试工况、转运工况和田间作业工况下割台运动副的动态载荷;采用折衷规划法构建割台静态刚度和动态频率的综合目标函数,根据层次分析法确定各子目标的权重;以体积分数、运动副极大值载荷为约束条件,得到割台空间结构的理想材料密度分布,综合考虑实际工程应用,对优化得到的割台机架进行规则化处理;建立优化后割台机架的有限元模型并开展有限元静力分析与模态分析,对比分析优化前、后割台测点处的振动幅值。结果显示:优化后最大应力值由107.99 MPa下降到65.45 MPa,最大变形量由0.82 mm下降到0.36 mm;前三阶固有频率有不同程度提高,第一阶固有频率提高到24.187 Hz。实际振动测试结果表明,优化后割台各测点振动幅值下降,割台整体振动减小,其中纵向切割器支架振幅值由4.83 m/s^(2)下降到1.49 m/s^(2)。

The truss structure of header in the caterpillar type rapeseed windrower is complex and changeable,which leads to the problem of large vibration of the header.Based on the variable density method,the multi-objective topology optimization of frame structure of the header was carried out to reduce the vibration of the header under different working conditions.The topology optimization model of header was established by using Hypermesh software.The virtual prototype model of rapeseed windrower based on RecurDyn was established by using multi-body dynamics method.The dynamic loads of the moving pair of the header under parts debugging conditions,transport conditions and field operation conditions were obtained.The comprehensive objective function of static stiffness and dynamic frequency of the header was constructed with the compromise programming method.The weight of each sub-object was determined according to the analytic hierarchy process(AHP).Taking the volume fraction and maximum load of moving pair as constraints,the ideal material density distribution of the header spatial structure was obtained.Considering the practical engineering application,the optimized frame of header was normalized.The finite element model of the optimized frame of header was established and the finite element static analysis and modal analysis were carried out.The vibration amplitudes at the measuring points of the header before and after optimization were compared and analyzed.The results showed that the maximum stress value decreased from 107.99 MPa to 65.45 MPa after optimization.The maximum deformation decreased from 0.82 mm to 0.36 mm.The natural frequencies of the first three orders were increased to varying degrees,and the natural frequency of the first order was increased to 24.187 Hz.The results of actual vibration test showed that the vibration amplitude of each measuring point of the header decreases after optimization.The overall vibration of the header decreased,in which the amplitude of the longitudinal cutter support decreased from 4.83 m/s~2 to 1.49 m/s~2.It will provide reference for the structure improvement and optimization of rapeseed windrower.