尾部扩散器对某跑车气动性能的影响

以某跑车模型为研究对象,探讨尾部小型扩散器对于车身气动性能的影响。在初始模型的基础上,进行CFD(Computational Fluid Dynamics)数值模拟计算,并对比风洞试验数据,验证仿真的可靠性。对初始模型的扩散器进行改进设计,加大扩散器的工作区域,研究其对于气动力的影响,并将改进后的扩散器与带有仿生凹坑型非光滑扰流器结合起来,通过数值模拟方法,得出压力和速度等流场参数,比较不同形式的扩散器对于气动性能的改进效果,分析气动力改善的原因。结果表明:通过对扩散器与非光滑扰流器的优化组合,能有效地提高气动负升力,减小气动阻力,达到了调谐车辆气动升力与气动阻力之间的耦合关系的目的。     

立体混合法制毡工艺及其对玻纤增强热塑性材料力学性能的影响

为了改进玻纤增强热塑性复合材料中基体树脂对玻璃纤维的浸渍效果,从而提升制品的力学性能,本文研究开发出一种新型的制毡工艺——立体混合法。该工艺是将基体树脂与玻璃纤维分别拉制成丝束状,展纤后,经改进的开松、混合、气流成网设备制成三维立体结构的连续针刺毡。将制作好的基毡采用层合热压法制备成板材,并对其进行力学性能测试。研究结果表明,制成立体混合毡后的玻纤增强板材浸渍工艺适应性更强,基体树脂与玻璃纤维之间的浸渍距离缩短,接触面积增加,使增强材料浸渍透彻,由该工艺制作出的热塑性板材比传统工艺制作出的板材浸渍效果好。在同等克重和玻纤含量条件下,其拉伸强度、弯曲强度、抗冲击强度有了大幅度提升。     

Simultaneous Multi-vehicle Detection and Tracking Framework with Pavement Constraints Based on Machine Learning and Particle Filter Algorithm

Due to the large variations of environment with ever-changing background and vehicles with different shapes, colors and appearances, to implement a real-time on-board vehicle recognition system with high adaptability, efficiency and robustness in complicated environments, remains challenging. This paper introduces a simultaneous detection and tracking framework for robust on-board vehicle recognition based on monocular vision technology. The framework utilizes a novel layered machine learning and particle filter to build a multi-vehicle detection and tracking system. In the vehicle detection stage, a layered machine learning method is presented, which combines coarse-search and fine-search to obtain the target using the AdaBoost-based training algorithm. The pavement segmentation method based on characteristic similarity is proposed to estimate the most likely pavement area. Efficiency and accuracy are enhanced by restricting vehicle detection within the downsized area of pavement. In vehicle tracking stage, a multi-objective tracking algorithm based on target state management and particle filter is proposed. The proposed system is evaluated by roadway video captured in a variety of traffics, illumination, and weather conditions. The evaluating results show that, under conditions of proper illumination and clear vehicle appearance, the proposed system achieves 91.2% detection rate and 2.6% false detection rate. Experiments compared to typical algorithms show that, the presented algorithm reduces the false detection rate nearly by half at the cost of decreasing 2.7%–8.6% detection rate. This paper proposes a multi-vehicle detection and tracking system, which is promising for implementation in an on-board vehicle recognition system with high precision, strong robustness and low computational cost.     

丙酮-丁醇-乙醇(ABE)/汽油混合燃料对高速发动机性能影响的试验研究

以发动机4000r/min、节气门开度35%为试验工况,对纯汽油及不同掺混体积分数丙酮-丁醇-乙醇(acetone-butanol-ethanol,ABE)与汽油混合物开展了不同点火提前角和喷油量的试验研究。分析了不同ABE混合比、点火提前角和过量空气系数对发动机性能的影响,并对每种燃料发动机最大功率工况的性能参数进行了比较。结果表明：点火提前角和过量空气系数相同时,混合燃料中ABE含量越高,燃油流量越大,发动机功率越大,有效热效率越高;燃油流量的总热量增大和热-功转换效率提高是促使发动机功率增大的主要原因;随ABE掺混比增加,NO比排放明显降低,CO比排放略有增加,碳氢化合物比排放先增后减。浓混合气工况增加ABE含量比在当量空燃比状态下增加ABE含量,发动机的有效热效率增大更明显,发动机的NO比排放降低更加明显。研究表明高速汽油机掺混ABE燃料具有较好的应用前景。     

Effect of weld cooling rate on Laves phase formation in Inconel 718 fusion zone

Inconel 718 (2 mm thick) was welded using argon and helium gas shielded tungsten arc welding process with a filler metal. Both constant current and compound current pulse modes were applied and the cooling rates calculated. The dependence of Laves phase formation, dendrite arm spacing and niobium segregation ratios in fusion zone on the nature of shielding gases and current was studied. The maximum instantaneous weld cooling rate was achieved for the combination of Helium shielding gas and compound current pulse mode. This ultimately resulted in reduction of laves phase, segregation of niobium and dendrite arm spacing in the fusion zone.     

Microstructural evolution in NiTi alloy subjected to surface mechanical attrition treatment and mechanism

Both nanocrystalline and amorphous phases are observed from the near surface of nickel titanium shape memory alloy (NiTi SMA) with the B2 austenite phase after surface mechanical attrition treatment (SMAT). The microstructure and phase changes are systematically studied by cross-sectional and plane-view transmission electron microscopy. The strain induces grain refinement and it is accompanied by increased strain in the surface layer triggering the onset of highly dense dislocations and dislocation tangles (DTs), formation of the martensite plate via stress-induced martensite (SIM) transformation (B2 to B19′), and dislocation lines (DLs) as well as dense dislocation walls (DDWs) inside the martensite plate leading to the subdivision of the martensite plate. In addition, reverse martensite transformation (B19′ to B2) and amorphization take place concurrently in the surface region, and successive subdivision and amorphization finally result in the formation of well separated nanocrystalline and amorphous phases in the near surface. The average grain size of the nanocrystallites is about 20 nm. Owing to the almost complete reverse martensite transformation as well as thermal stability, the strain-induced nanocrystalline structure has the B2 austenite phase in the surface layer and no transformation occurs.     

柴油机壁流式过滤体非稳态捕集过程的计算模型

基于排气在柴油机壁流式过滤体内的流动特点,并在综合分析壁流式过滤体深床捕集阶段捕集特点和滤饼捕集阶段捕集特点的基础上,建立了壁流式过滤体非稳态捕集过程的计算模型.该模型通过提出容纳度的概念,有效地区分了深床捕集阶段和滤饼捕集阶段;通过提出微粒在过滤壁表面沉积效率的概念,定量地描述了沉积在过滤壁表面的微粒量.基于该模型,介绍了计算算法,并编制了相应的计算程序.使用该模型研究了过滤体的捕集效率、流动阻力以及沉积在过滤体内微粒质量的非稳态变化规律.计算结果与试验结果吻合得较好,表明该模型在工程实际应用中具有可行性.     

Application of Kriging and radial basis function in power electronic module wire bond structure reliability under various amplitude loading

This paper discusses life time prediction of wire bond structure in a power electronic module based on computational approach that integrates methods for high fidelity analysis, reduced order modelling, and life time prediction using reduced order model. This methodology is demonstrated for the design of a wire bond structure in a power electronic module with aim of reducing the chance of failure due to the wire bond lift off in power electronic module when a random load is applied to the aluminium wire. In particular, wire bond reliability of the power module related to the thermal fatigue material degradation of aluminium wire is one of the main concerns. In the power electronic module reliability, understanding the performance, reliability and robustness of wire bond is a key factor for the future development and success of the power electronic module technology, because wire bond lift off failure ignites other catastrophic failures.The main focus in this study is on the application of reduced order modelling techniques and the development of the associated models for fast evaluation and analysis. The discussion is on methods for approximate response surface modelling based on interpolation techniques using Kriging and radial basis functions. The reduced order modelling approach uses prediction data for the electro-thermo-mechanical behaviour of the power module wirebond design obtained through non-linear transient finite element simulations, in particular for the fatigue life-time of the aluminium wire attached to the silicon chip of the wire in the module. The reduced order models are used for the analysis of predicting the life time of the wire bond structure under random load. One of the widely used cycle counting algorithm, so called rainflow counting algorithm is utilised to count the cycles of temperature profile at the a specific point of the wire bond structure in a power electronic module. Using the cycle results from rainflow algorithm mean life time of the wire bond structure is predicted by a linear cumulative damage model such as Palmgren–Miner rule. This model is utilised to predict the mean fatigue life of the wire bond structure.     

Galvanic series of different stainless steels and copper- and aluminium-based materials in acid solutions

Galvanic series of AISI 304, 316, 316L, and 316Ti austenitic stainless steels, AISI 410 and 420 martensitic stainless steels, 63Cu37Zn brass, Cu, Al, and AlMg1 were established for 10% (wt.) hydrochloric, phosphoric, sulphamic, sulphuric, nitric, citric, acetic, and methanesulphonic (MSA) acids used as cleaners in order to predict galvanic corrosion when coupling these materials. It was found that each acid has a distinctive order of metallic materials in a galvanic series. The largest corrosion potential difference in all acids exists between Al-based materials and stainless steels, as well as Cu-based materials indicating the use of Al-based materials as sacrificial electrodes.     

Composite chiral structures for morphing airfoils: Numerical analyses and development of a manufacturing process

This paper investigates complex composite cellular structures featuring a chiral topology with the ability to undergo large overall displacements with limited straining of its components. Numerical analyses are performed to exploit such properties in the design of a morphing airfoil. The advantages associated with the use of composites are investigated by comparing the numerical results with those obtained with a metallic structure. A manufacturing process is then developed to assemble the considered structural configurations using composite materials. The novel process developed is described as applied to the manufacturing of macro chiral components that are tested to evaluate their ability to undergo large deformations. Finally, detailed numerical models of the manufactured structures are presented as a possible approach to evaluate the strength of the proposed configuration.