【作者】 王玮；

【导师】 高仁璟；

【作者基本信息】 大连理工大学 ， 车辆工程（专业学位）， 2019， 硕士

【摘要】 环境污染已经成为当今世界最为严重的环境问题之一,而汽车总量增加进一步造成环境污染加重。面对如此严峻的形势,汽车产业需要进行变革。除了发展新能源和智能车以外,利用变体技术改善汽车外部空气动力学特性以提高汽车的能量利用效率有着重要的研究意义和应用价值。因此需要研究改善外部空气动力学特性的汽车变体技术,基于变体技术的汽车减阻研究成为未来汽车变革的一个重要研究方向。本文开展了基于变体应用的蜂窝结构设计,首先研究了基于蜂窝结构的变体技术,针对已有八边形蜂窝结构应力集中问题,通过圆滑过渡改进使其最大应力降低,并利用遗传算法进行多目标优化,得到改进后结构的最佳尺寸参数。综合考虑结构的承载和变形能力,利用拓扑优化方法建立了多刚度蜂窝结构优化设计模型,得到新的蜂窝结构构型,并通过均匀化方法得到其等效参数,进而对等效结构的变形和承载能力进行验证。最后将所设计的变体结构应用于汽车尾部,实现整车减阻设计。论文具体内容如下:(1)针对已有八边形蜂窝结构应力集中问题,通过倒圆角对原结构进行改进,并且推导得到其等效杨氏模量和等效剪切模量的理论表达式,通过与有限元分析结果对比验证其准确性。最后基于遗传算法得到了改进结构的最优几何参数并且通过变形分析提取局部应力,进一步验证该结构有助于减小应力集中。(2)综合考虑结构的承载和变形能力需求,通过拓扑优化设计方法建立了多刚度结构优化设计模型,并且改变不同的约束参数,得到了不同的结构构型,通过有限元分析得到不同构型水平方向的等效杨氏模量和面内等效剪切模量,通过比较选择最优构型。为了便于分析,利用等效均匀化理论得到上述构型的等效参数,通过分析等效结构变形和承载能力,验证了其力学性能的提升。(3)基于设计的新型蜂窝构型,分析研究整车空气动力学性能。通过改变汽车尾部的上倾角以及横向收缩率的方式,降低压差阻力实现整车减阻设计。通过建立整车外流场仿真模型,得到不同参数下整车的阻力系数,进而得到了最佳变体方式,验证了该方式的减阻效果。更多还原

【Abstract】 Environmental pollution has become one of the most serious environmental problems in the world,and with the increase of the total number of cars environmental pollution is further aggravated.Faced with such a grim situation,the automobile industry needs to be reformed.In addition to the development of new energy and intelligent vehicles,it is of great research significance and application value to improve the external aerodynamic characteristics of vehicles by using variant technology to improve the energy utilization efficiency of vehicles.Therefore,it is necessary to study the vehicle variant technology to improve the external aerodynamic characteristics.In this paper,we study the drag reduction performance of automobile based on morphing technology.Firstly,the morphing technology based on honeycomb structure is studied.The stress concentration problem of octagonal honeycomb structure is solved by smooth transition,and then the optimization parameters of the improved structure are obtained using genetic algorithm.Considering the bearing capacity and deformation capacity of the structure comprehensively,the optimization design model of multi-stiffness honeycomb structure is established by using topology optimization method.Then the equivalent parameters of the new honeycomb structure configuration are obtained by homogenizing method,and the deformation and bearing capacity of the equivalent structure are verified.Finally,the designed variant structure is applied to the rear end of the vehicle to realize the whole vehicle drag reduction.The main research of this paper is as follows:(1)Aiming at the stress concentration problem of the reference octagonal honeycomb structure,the reference structure is improved by rounding the corners,and the theoretical expressions of the equivalent Young’s modulus and equivalent shear modulus are derived,which is verified by using finite element analysis.Finally,based on genetic algorithm,the optimal geometric parameters of the improved structure are obtained.The local stress is extracted by deformation analysis and then further verifies that the structure can reduce the stress concentration.(2)Considering the bearing capacity and deformation capacity of the structure,the optimization design model of multi-stiffness honeycomb is established and a new honeycomb structure is obtained.Different optimization configurations of honeycomb are obtained by changing constraint parameters.By using finite element analysis,equivalent Young’s modulus and shear modulus of different configurations are obtained,Finally,using homogenization method the equivalent parameters of the honeycomb structure are obtained,which can be usedto verify the structure’s deformation and bearing capacity.(3)The aerodynamic performance of the vehicle is analyzed based on the design of the new honeycomb configuration.By changing the vertical diffuser angle and lateral diffuser angle of the vehicle,the vehicle drag is reduced.By establishing the simulation model of the vehicle’s external flow field,the drag coefficient of the vehicle under different parameters is obtained,and then the best morphing mode is obtained and the drag reduction effect of this mode is verified.更多还原