轿车外流场网格生成策略及数值模拟

采用3种网格策略对某轿车外流场进行数值模拟研究,并应用商业CFD软件STAR—CD进行求解。根据计算过程和结果,分析不同网格策略的效果,论述3种网格策略的特点。数值模拟中考虑了车轮旋转和车轮固定两种边界条件,并将数值计算结果与试验数据进行了对比分析,探讨了高雷诺数k-ε湍流模型的计算精度。     

单缸机械-液压约束活塞发动机外特性仿真

阐述了单缸轴向MHCPE的结构原理,建立了考虑系统液、固、气耦合的工作过程数学模型,给出了求解的初始条件,定义了MHCPE的液压能比率及“外特性”概念,并对研制的单缸轴向MHCPE的工作外特性进行了仿真。仿真结果显示：输出压力随着液压能比率增加明显升高,受转速变化影响较小;输出流量随转速增加先升高后降低,受液压能比率变化影响较小;转矩随着液压能比率降低明显升高,受转速变化影响不明显;燃油消耗率在转速和液压能比率较高时明显增加。总的有效功率随着液压能比率的升高,有轻微降低,转速较高时该趋势尤其明显。     

发展循环经济的若干经济学理论探讨

运用经济学相关理论,探讨了当前发展循环经济的理论和政策存在的主要问题,并提出建议和对策。     

The relative contributions of soil hydrophilicity and raindrop impact to soil aggregate breakdown for a series of textured soils

Soil aggregate breakdown is the first key factor that causes soil erosion. At present, research on the mechanisms of soil aggregate breakdown during rainfall is common. However, the research to on quantifying the relative contributions of internal and external forces to aggregate breakdown remains limited. This paper was conducted to analyse the relative contribution of internal and external forces to aggregate disintegration and the factors affecting aggregate stability during rainfall. Soil aggregates with a series of textures were selected as test soil samples; deionized water was employed as the soaking solution and rainfall material in static disintegration experiments and rainfall simulation tests. The effect of internal force (soil hydrophilicity) on aggregate disintegration was analysed by the static disintegration method, and the combined effects of internal force (soil hydrophilicity) and external force (raindrop impact) on soil aggregate breakdown were analysed by rainfall simulation experiments. The results indicated that external force caused more severe soil aggregate breakdown than internal force, and the crushed aggregate was mainly distributed in the range of 2–0.25 mm. With increasing rainfall kinetic energy, the degree of aggregate breakdown increased gradually, and the degree of aggregation of the soil particles decreased gradually. Furthermore, soil aggregates with a high clay content (> 30%) were more stable than medium-clay (20–30%) and low-clay (< 20%) soil aggregates, and the correlation coefficient provided a good representation of the relationship between the clay content and soil aggregate stability index (ASI). Therefore, external force contributed more to soil aggregate breakdown than internal force during rainfall, and clay plays an important role in aggregate stability. The results of this study are of great significance for elaborating the mechanism and factors affecting aggregate breakdown.     

国际生猪价格和国内生猪价格的动态关联性——基于外部冲击视角

中国生猪进口量逐年上升,国际生猪市场和国内生猪市场的联系日渐紧密。欧盟生猪市场成为中国生猪市场的主要关联市场。本文基于2011年1月至2020年11月的欧盟生猪价格和国内生猪价格数据,建立国际生猪价格和国内生猪价格的动态多元GARCH模型,考察国际生猪和国内生猪市场的波动溢出效应和动态关联性,并加入外部因素,探讨外部因素对国内外生猪市场联动性的介入效应。结果发现:欧盟的生猪价格与中国生猪价格长期来看具有部分同步性,更多阶段存在反向变化,且差距程度自2019年起明显扩大。中国生猪价格和欧盟生猪价格之间存在明显的双向溢出效应,但不具备长期持续性。中国生猪市场和欧盟生猪市场之间的动态相关程度均值约13.15%且波动较大;整体上外部冲击会降低中国生猪市场与欧盟生猪市场之间的动态关联性,全球经济政策不确定性使中国生猪市场与欧盟生猪市场之间的动态关联性略有下降,国际原油价格波动降低了中国生猪市场与欧盟生猪市场之间的动态关联性,影响幅度较大,而美元货币政策使中国生猪市场与欧盟生猪市场之间的动态关联性略有加强。据此本文提出加强生猪产业规模化、健全生猪安全防控机制、增强生猪抵抗风险能力等相关建议,从而保障国内生猪市场的健康发展、提高国内生猪市场的影响力。