Simulation of vehicle braking behavior on wet asphalt pavement based on tire hydroplaning and frictional energy dissipation

To investigate the influence of wet conditions on vehicle braking behavior,a numerical-analytical method was proposed for the simulation of tire hydroplaning and frictional energy dissipation. First, a finite element model of tire hydroplaning was established using the coupled EulerianLagrangian method,including a pneumatic tire model and a textured asphalt pavement model. Then,the frictional force on the tire-pavement interface at different speeds was calculated by the model. Based on vehicle braking mechanism and frictional energy dissipation,a calculation method for braking distance was proposed based on a three-stage braking process. The proposed method was verified by comparing the calculated hydroplaning speed and braking distance with field test results.Then,vehicle braking distances and wet friction coefficients were calculated under different conditions. The results show that thinner water film,a more complex tread pattern and higher tire inflation pressure all contribute to the vehicle braking performance; moreover, the pavement texture has obvious influence on vehicle braking behavior,especially at a high speed. The proposed method shows great effectiveness in predicting vehicle braking behavior on wet asphalt pavements.

Inflation, Deflation and Normal Price Adjustment

This paper thinks that the price of a commodity depends on both the value of the commodity and that of the currency. The change in either value will cause the change of the price of the commodity. Only the price rising caused by the decreasing of the currency value can be called inflation, and the price rising led by the increasing of the value of the merchandise can not be called inflation. Therefore, it is not proper, as defined by the modem economics, to think that any price increasing should be in general called inflation.

U.S.,not China, is culprit of global deflation, inflation

This paper is an outcome of comprehensive and systematic research on whether China exports deflation and inflation using the newly developed DAG technique. Our results indicate that in the international transmission of inflation, the United States, as the world's largest economy, plays a dominant role. In contrast, during both deflation and inflation periods, China has a minimal impact on the price levels of major trading partners. Thus China is not to be blamed for global deflation or inflation. This research has made use of DAG and some other techniques to yield reliable and reasonable conclusions.

Numerical simulation of tire/soil interaction using a verified 3D finite element model

The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at different soil strengths.With the increasing capacity of numerical computers and simulation software,finite element modeling of tire/terrain interaction seems a good approach for predicting the effect of change on the parameters.In this work,an elaborated 3D model fully complianning with the geometry of radial tire 115/60R13 was established,using commercial code Solidwork Simulation.The hyper-elastic and incompressible rubber as tire main material was analyzed by Moony-Rivlin model.The Drucker-Prager yield criterion was used to model the soil compaction.Results show that the model realistically predicts the laboratory tests outputs of the modeled tire on the soft soil.

A simple analytical method for deflation prediction of inflatable structures

The static performance of inflatable structures has been well studied and the dynamic deployment simulation has received much attention. However, very few studies focus on its deflation behavior. Although there are several dynamic finite element algorithms that can be applied to the deflation simulation, their computation costs are expensive, especially for large scale structures. In this work, a simple method based on classic thermodynamics and the analytical relationship between air and membrane was proposed to efficiently analyze the air state variables under the condition of ventilation. Combined with failure analysis of static bearing capacity, a fast incremental analytical method was presented to predict both elastic and post wrinkling deflation process of inflatable structures. Comparisons between simplified analysis, dynamic finite element simulation, and a full-scale experimental test are presented and the suitability of this simple method for solving the air state and predicting the deflation behavior of inflatable structures is proved.

Analytical solutions for inflation of pre-stretched elastomeric circular membranes under uniform pressure

Elastomeric membranes are frequently used in several emerging fields such as soft robotics and flexible electronics.For convenience of the structural design,it is very attractive to find simple analytical solutions to well describe their elastic deformations in response to external loadings.However,both the material/geometrical nonlinearity and the deformation inhomogeneity due to boundary constraints make it much challenging to get an exact analytical solution.In this paper,we focus on the inflation of a prestretched elastomeric circular membrane under uniform pressure,and derive an approximate analytical solution of the pressure-volume curve based upon a reasonable assumption on the shape of the inflated membrane.Such an explicit expression enables us to quantitatively design the material and geometrical parameters of the pre-stretched membrane to generate a target pressure-volume curve with prescribed peak point and initial slope.This work would be of help in the simplified mechanical design of structures involving elastomeric membranes.

An Exceptional Generalization of the Poisson Distribution

A new two-parameter count distribution is derived starting with probabilistic arguments around the gamma function and the digamma function. This model is a generalization of the Poisson model with a noteworthy assortment of qualities. For example, the mean is the main model parameter;any possible non-trivial variance or zero probability can be attained by changing the other model parameter;and all distributions are visually natural-shaped. Thus, exact modeling to any degree of over/under-dispersion or zero-inflation/deflation is possible.

某风洞充气密封系统设计与应用研究

某风洞充气密封系统用于试验期间隔离大门内外气压环境或填充移动部件间隙,保证风洞回路最高可以模拟2万米高空以下气压环境;密封围带基体材料采用植入增强纤维的硅橡胶,围带截面为“凹”型带两侧固定基座,采用直线型带芯分段模压硫化成型,成功研制了适用于高低温环境、长寿命、高膨胀、大尺度环状充气密封围带;充气/放气气路、电磁阀和变送器等基于集成块安装设计;充气/放气控制系统采用PLC+电磁阀+真空发生器;系统通过Profinet接入风洞测控光纤环网,实现本地/远程自动化控制;解决了围带结构、气密泄漏、大尺度密封面平面度和金属气嘴结构设计等问题;系统应用效果好,自动化水平高,有较大推广应用价值。

两种确定肺段间平面的胸腔镜精准肺段切除术的临床对照研究

目的 比较单纯动脉结扎法与改良膨胀萎陷法在胸腔镜精准肺段切除术中确定肺段间平面的应用效果。方法 前瞻性纳入2021年8月至2023年2月于本院行胸腔镜精准肺段切除术的80例患者,采用随机数字表法将患者分为观察组和对照组,每组40例。观察组患者采用单纯动脉结扎法确定肺段间平面,对照组患者采用改良膨胀萎陷法确定肺段间平面。比较2组患者围术期相关指标、肺功能指标、术后并发症及随访情况。结果 观察组患者手术时间及术中出血量均显著短/少于对照组(P<0.05);而2组患者段间平面显现时间、术后总引流量、引流管留置时间、术后住院时间及肺段切除分布情况比较,差异均无统计学意义(P>0.05)。术后2组患者用力肺活量占预计值百分比(FVC%pred)、第1秒用力呼气容积占预计值百分比(FEV1%pred)较术前均显著降低(P<0.05),且观察组患者术后FVC%pred、FEV1%pred显著高于对照组(P<0.05)。2组患者术后各并发症的发生情况比较,差异均无统计学意义(P>0.05)。随访期间所有患者均未出现死亡、肿瘤局部复发或远处转移情况。结论 在胸腔镜精准肺段切除术中应用单纯动脉结扎法确定段间平面较改良膨胀萎陷法具有操作简便、损伤小、对患者肺功能影响小等显著优势,安全性较高,是一种可行且有效的技术。

轮胎充气过程胎压自动预估方法

针对越野汽车轮胎充气过程胎压动态复杂变化情况,提出一种轮胎充气过程胎压实时预估方法。主要由数据采集与预处理模块、预标定轮胎气阻模块及轮胎胎压预估模块组成;根据测压工况轮胎胎压值估算出轮胎气阻值;在此基础上,轮胎胎压预估模块利用气动原理循环预估轮胎胎压;并通过轮胎中央充放气系统平台进行验证。结果表明:该算法预估的均方根误差不超过0.0843 MPa,极大提高了胎压预估的精度。

串联囊式压力脉动衰减器气压主动控制方法研究

针对现有串联囊式衰减器(囊式衰减器)压力适应范围窄的问题,提出了通过气压控制系统实现囊式衰减器气囊内部气压主动跟随液压系统工作压力变化的方法,使囊式衰减器在不同工作压力时均具有良好压力脉动抑制性能。在建立气动伺服控制系统数学模型的基础上,分别采用比例积分微分(proportional integral derivative,PID)及模糊PID控制方法实现了囊式衰减器气囊内部气压主动跟随系统工作压力的变化,分析了系统工作压力的变化频率、振幅、气瓶充气压力等因素对气囊内压力控制性能的影响,在理论上证明了所提出方法的可行性;分别通过声学仿真软件和试验研究了采用与不采用气压主动控制时囊式衰减器对压力脉动的抑制性能,研究结果均表明采用气压主动控制方法时囊式衰减器对液压管道系统压力脉动的衰减幅值更大、压力适应范围更广,进而验证了所提出气压主动控制方法的有效性与可行性。

胎压差影响下车辆并装双胎滑水特性教学仿真

载货车辆并装双胎滑水实验极具危险性,在高校车辆类专业教学中难以开展,且胎压差影响下的滑水机理至今尚未探明。针对该问题,基于流固耦合原理,建立车辆并装双胎-积水-路面流固耦合模型并验证有效性,探明胎压差对滑水动力学行为的影响机理,揭示不同胎压差下双胎运动状态、水膜厚度对双胎滑水特性的影响规律。结果表明:并装双胎滑水时双胎间隙存有大量积水,积水高度远超水膜厚度;并装双胎自由滚动状态时胎压差增加,滑水性能降低;相同胎压差下,防抱死制动系统(anti-lock braking system,ABS)控制状态较自由滚动状态更易发生滑水;水流竖向托举力随胎压差和水膜厚度的增大而增大。该研究可用于指导并装双胎车辆设计和使用,进一步提高湿滑路面上车辆行驶安全性,也为轮胎滑水动力学教学仿真与实验提供参考。

新型多工位工程机械轮胎硫化后充气定型机的设计

介绍新型多工位工程机械轮胎硫化后充气定型机的设计。研发的定型机主要由机架、动/定卡盘、十字头卡盘锁紧机构、上托机构和推动气缸等组成,采用双气源供气。每个工位可以单独控制,设有不同压力的进气管道,实现人工装胎、定型、锁紧充气、松锁放气、卸胎的全过程动作,提高了工程机械轮胎生产的机械化和自动化水平,降低了劳动强度,且大幅提高了轮胎质量。

THE CONFIGURATION OF QUASICRYSTAL UNIT CELL AND DEDUCTION OF QUASILATTICE

From the crystal chemistry and icosahedral phase, two kinds of coordinational polyhedron with 8-fold rotational symmetry——hexakaicahedra and bicapped antiprism were possibly suggested and their one- and two-dimensional quasilattices were deducted. According to the principle of Bravais in conventional crystallography, four kinds of two-dimensional unit cell have been defined in 5, 8, 10, 12-fold rotational symmetry quasicrystal. The authors considered that quasicrystal is a kind of crystal which possesses an incommensurable translational period. This kind of translation is carried out by inflation or deflation symmetry operation.

Does China have Inflationary Effects on the USA and Japan?

With China＇s share in global trade increasing rapidly, some argued in 2002-2003 that China was exporting deflation to other countries as it was dumping cheap goods in mature markets. Later, others argued that China was causing sharp increases in global prices. This paper uses several econometric techniques to assess the extent of the link between inflation rates between China and the USA and Japan. Only limited empirical evidence at the aggregate level is found for consumer price inflation in China leading to price changes in the USA and Japan. However, there is some evidence that inflation in the USA has an impact on Chinese inflation. The results seem consistent with the Federal Reserve and the Bank of Japan being concerned about inflation and, hence, adjusting policy such that inflation shocks have no significant effect on overall inflation. Recent Chinese price rises are unlikely to have a material effect on the USA or Japan.

轮胎包络特性及冲击特性的影响因素研究

以215/55R17轮胎为研究对象,研究不同的充气压力与负荷对轮胎包络特性及冲击特性的影响。结果表明:在低速包络试验中,轮胎的径向力峰值随充气压力的增大而增大,随负荷的增大而减小,纵向力峰峰值随充气压力和负荷的增大而增大,但变化幅度不大;在冲击试验中,轮胎的径向力峰值与纵向力峰峰值随充气压力的增大而增大,径向力峰值随负荷的变化受到速度的影响但变化幅度较小,纵向力峰峰值随负荷的增大而增大。

硫化后充气工艺条件对轮胎性能的影响

研究硫化后充气工艺条件对轮胎外缘尺寸、动平衡性、均匀性和滚动阻力的影响。结果表明:后充气压力和高度增大对轮胎外缘尺寸有一定的影响,但是影响程度不大;增大后充气压力可以降低轮胎滚动阻力;随着后充气时间延长,轮胎的静不平衡量呈减小的趋势,胎侧凹陷增大,胎侧凸起不明显;增大后充气高度有利于减小轮胎力偶不平衡量,改善动平衡性。

冷却工艺对轮胎外缘尺寸及性能的影响

研究冷却工艺对轮胎外缘尺寸及性能的影响。结果表明:自然冷却速率高于硫化后充气冷却速率,但硫化后充气冷却轮胎的尺寸均匀性、径向刚性和耐久性能均较高;延长硫化后充气时间、降低硫化后充气终点轮胎温度,有助于降低轮胎尺寸收缩率;单根帘线的张力需大于初始冷却温度下骨架材料的热收缩应力,随着硫化后充气压力提高,轮胎外缘尺寸呈增大趋势;硫化后充气轮辋宽度对轮胎的外缘尺寸影响较小;随着出模时间的延长,轮胎外缘尺寸减小,需要控制出模时间。

硫化后充气工艺对子午线轮胎性能的影响

研究硫化后充气时间和压力对轮胎性能的影响。结果表明,延长后充气时间和增大后充气压力会提升初始状态轮胎的外直径和断面宽。后充气时间和压力在不同范围内对轮胎静态接地印痕参数和径向刚度的影响规律不同。从无后充气到有后充气,滚动阻力系数减小;继续延长后充气时间和增大压力,滚动阻力系数不会继续减小。从无后充气到有后充气,侧偏刚度增大,回正刚度减小;随着后充气压力增大,侧偏刚度和回正刚度均增大;后充气时间对侧偏刚度和回正刚度的影响在不同后充气压力下呈现不同的规律。

硫化后充气压力和时间对航空轮胎性能的影响

选取27×7.7-15航空轮胎作为研究对象,研究硫化后充气压力和时间对航空轮胎性能的影响。分析胎体帘线张力与充气压力的关系以及帘线收缩率、收缩力与温度的关系,并通过热电偶测温法测量轮胎硫化后充气过程中温度随时间的变化情况,确定轮胎最小硫化后充气压力设为200 kPa,可以保证轮胎在胎体温度为160~170℃时出模胎体帘线不产生热收缩;硫化后充气时间设为1个硫化周期,可以保证轮胎冷却至环境温度。成品轮胎充气外缘尺寸及动态模拟试验验证了后充气压力和时间选取的合理性。