Frequency response analysis based on thermo-mechanical coupling was conducted on a gasoline engine exhaust manifold in order to study the effect of temperature and thermal stress on vibration characteristic and fatigue life of exhaust manifold.Results show that the stress range and peak frequency are significantly changed when thermal load is taken into consideration, since different distributions of temperature and thermal stress lead to different structure stiffness.The vibration fatigue life under thermo-mechanical coupling is 42% lower than that without considering thermal load.Therefore, the thermal-mechanical coupling has significant effect on fatigue life, which can't be ignored.Topology optimization and multi-objective topography optimization were carried out on the bracket of exhaust manifold to optimize the vibration characteristics and extend the working life.Topology optimization was carried out to find the best force transferring path.The multi-objective topography optimization was carried out to define the stiffener, and its objective function was established based on the exponential weighted method.The optimization goal is to extend the fatigue life of the exhaust manifold and the subgoals are to increase the structural natural frequency of 1st/2nd/3rd/6th order.The optimization effect is obvious;the optimized exhaust manifold's fatigue life is 31.2 % higher than that of the original design.%为了研究温度及热应力分布对排气歧管的振动特性及疲劳寿命的影响,对汽油机排气歧管进行基于热机耦合的频率响应分析.研究发现,由于温度及热应力的不均匀分布会改变结构的刚度,热载荷的存在对传递函数峰值频率及应力幅值均产生了较大影响.热载荷与机械载荷耦合作用下的振动疲劳寿命较不考虑热载荷的振动疲劳寿命低42%,热机耦合在疲劳寿命分析中有着显著的作用,不可忽视.为了优化排气歧管的振动特性并延长其使用寿命,对排气歧管支架进行拓扑优化及多目标形貌优化.通过拓扑优化寻找最佳传力路径;在拓扑优化的基础上以提高排气歧管疲劳寿命为总目标,以提高危险频率段内的1、2、3、6阶固有频率为子目标,通过加权指数法建立目标函数,对支架进行多目标形貌优化确定加强筋位置.进行多目标优化后的排气歧管支架对提高排气歧管振动疲劳寿命效果明显,疲劳寿命较优化前增加了31.2 %.
展开▼
