飞机起落架舱内轮胎爆破压力场测试研究

飞机轮胎爆破压力场分布模型对于飞机轮胎强度计算和起落架舱内防护设计至关重要。本文开展某型飞机起落架舱内轮胎爆破试验研究,利用高频动压传感器测试防护罩上关键点处的压力值,建立了轮胎爆破气流场压力分布模型,最后采用有限元方法对防护罩结构进行数值模拟并与试验结果对比分析。结果发现,航空轮胎爆破时间短暂但威力巨大,起落架舱内轮胎爆破最大压力值随初始压力和爆破距离呈指数关系衰减。根据试验结果分别提出了斜交胎、子午胎的爆破压力场分布模型并对防护罩进行了数值计算,所得应变值与数值结果误差在12%以内,说明所提出的压力场分布模型可用于起落架舱内防护罩设计。本文所提出的试验方法及爆破压力场分布模型为起落架舱内防护设计提供了参考依据。     

一维孔隙率浅水方程及其数值离散

通过孔隙率方法来描述挡水物对过水能力的影响建立了一维孔隙率浅水方程. 采用有限体积方法和Roe格式的近似Riemann解建立了孔隙率浅水方程的离散模式. 对底坡和孔隙率源项采用特性方向分解的方法进行处理,使模型精确满足C(Conservative)特性,增加了模型的稳定性. 通过算例模拟证明了模型可以对河道中的挡水物作用进行模拟,且计算结果表明模型具有和谐、稳定、分辨率高等优点.      

滚动轮胎表面红外成像测温的偏差及其修正

使用红外热像仪从三个方向测量了滚动轮胎的表面温度,结果表明从不同方向对同一表面的测温结果不相同。根据几何光学和热辐射原理,造成这一偏差有两个原因:一是轮胎表面点的像面照度按其辐射入射角α的余弦四次方定律变化;二是轮胎表面点的发射率与β(该点入射方向与其法向之间的夹角)有关。本文首先采用余弦四次方定律对三个方向下的轮胎表面红外测试结果进行了与α相关的修正,然后依据轮胎表面任意点温度的同一性(即与测量方向无关)进行了与β相关的进一步修正,并给出了一个轮胎表面发射率与β的经验关系。具体表现为发射率在法向上最大,当β在60°以内时其变化相对平缓,超过60°则急剧下降,最终得到了一个表征轮胎表面点红外像面照度下降的双角度(α和β)修正函数以及相应的温度修正公式。 修正后不同方向下的温度分布趋于一致,其平均结果即可视为轮胎表面真实的温度分布。     

橡胶复合材料结构大变形有限元分析

建立了一个橡胶复合材料结构有限元分析模型。在该模型中 ,考虑了轮胎变形的几何非线性、轮胎与地面和轮胎与轮辋的大变形非线性接触、轮胎材料的非均匀性和物理非线性及橡胶基复合材料的各向异性。此外 ,本文还利用该模型研制的有限元分析软件对全钢丝子午胎的变形轮廓进行了详细的分析。     

ANALYSIS OF GROUNDING CHARACTERISTICS AND STRAIN ENERGY OF RADIAL TIRES WITH RADIAL STIFFNESS1)

利用轮胎综合试验机对径向刚度下子午线轮胎进行性能试验,采用正交试验法针对不同胎压、垂向载荷下轮胎的接地特性进行分析,结合仿真软件ABAQUS与试验进行对比。结果表明,橡胶材料Mooney-Rivli模型也具有一定的适用性,胎压增大时径向刚度发生线性变化,胎面印痕由椭圆形转变成近似矩形,印痕面积略微增大;随着胎压的不断增大,胎面印痕的面积显著减小,接触面的压力主要集中在胎肩,胎冠处也有所增加;胎压一定时,垂向载荷逐渐增大时,整个印痕面的应力呈对称分布,印痕面应力由内高外低逐渐向外高内低变化。建立数学模型与有限元软件同时对轮胎进行应变能分析,发现在低胎压150 kPa下受载荷时轮胎容易发生微小侧向位移同时发生变形,此时极易引起迟滞损失并造成应变能急剧增加。     

轮胎非线性对汽车悬架系统的影响

本文首次运用现代非线性动力学与分岔理论对采用轮胎非线性模型的汽车悬架运动特性进行了研究。并仿真比较了轮胎线性悬架模型和非线性模型对路面激励的响应。结果表明轮胎的非线性特性对汽车悬架的动力学特性有很大影响,在一定条件下产生了Hopf分岔,并求出了产生Hopf分岔的条件。     

轮胎充气温度对光电里程仪标度因数影响的标定算法

为减小车辆轮胎充气温度对光电里程仪标度因数的影响,提高车载航位推算系统的定位精度,分析了航位推算系统的误差模型,提出了基于载波相位差分GPS的里程仪标度因数标定方法.基于CDGPS的高精度定位特性,结合SINS和里程仪的输出,利用卡尔曼滤波对里程仪标度因数随轮胎充气温度的变化进行标定.实验表明该方法可以精确标定里程仪标度因数随轮胎充气温度的变化特性,在给定初始充气压力情况下标度因数与充气温度呈线性关系.利用标定后的里程仪进行了跑车验证实验,在较良好的路况下,行驶里程78km,纬度误差由28 m减小到5 m,经度误差由65 m减小到10m.     

子午线轮胎接地特性和应变能分析试验与仿真研究

利用轮胎综合试验机对径向刚度下子午线轮胎进行性能试验,采用正交试验法针对不同胎压、垂向载荷下轮胎的接地特性进行分析,结合仿真软件ABAQUS与试验进行对比。结果表明,橡胶材料Mooney–Rivli模型也具有一定的适用性,胎压增大时径向刚度发生线性变化,胎面印痕由椭圆形转变成近似矩形,印痕面积略微增大;随着胎压的不断增大,胎面印痕的面积显著减小,接触面的压力主要集中在胎肩,胎冠处也有所增加;胎压一定时,垂向载荷逐渐增大时,整个印痕面的应力呈对称分布,印痕面应力由内高外低逐渐向外高内低变化。建立数学模型与有限元软件同时对轮胎进行应变能分析,发现在低胎压150 kPa下受载荷时轮胎容易发生微小侧向位移同时发生变形,此时极易引起迟滞损失并造成应变能急剧增加。     

基于实验的数值反演的滚动轮胎稳态温度场的有限元分析

根据轮胎温度场的单向解耦分析思想,形成了一个基于ABAQUS程序的轮胎稳态温度场的分析方法,单向解耦过程分为变形、损耗、热传导三个分析过程。变形分析中,采用了平衡态的超弹性材料模型;损耗分析中,依据变形分析获得的应力应变场,结合材料粘性损耗特性来获得损耗能量;热传导分析中,依据实测的轮胎胎侧温度场,提出了一种基于实验的数值反演方法来确定胎侧的对流热边界条件。由于轮胎胎侧的形状和结构细节,其对流热边界不同于旋转平圆盘的对流热边界,本文的数值反演方法避免了实测胎侧对流热交换系数的困难。     

MPS方法数值模拟楔形体入水问题

入水问题是船舶海洋工程中典型的流动问题。当船舶在恶劣海况中航行或海洋平台遭遇恶劣天气时,结构物和水体之间往往会出现剧烈的砰击作用。砰击发生时,伴随着结构物湿表面的变化、自由液面的翻卷和破碎等强非线性现象。本文采用本课题组自主开发的基于移动粒子半隐式法MPS(Moving Particle Semi-Implicit Method)的求解器MLParticle-SJTU对二维楔形体入水问题进行了数值模拟。选取斜升角为30°的楔形体模拟其入水过程,研究了不同粒子布置方式对于计算结果如垂向水动力和自由面变化的影响,并与MLM砰击模型(Modified Logvinovich Model)的结果进行了比较,吻合较好。在此基础上,进一步研究了不同斜升角对计算结果(垂向水动力和自由面变化)的影响,其中流动分离前的垂向水动力与MLM结果相近,表明了MPS方法能有效地模拟入水问题。     

Tire inflation and its influence on drawbar characteristics and performance – Energetic indicators of a tractor set

This work deals with the influence of tire inflation on tractive characteristics and performance-energetic parameters of a ploughing set. The test was conducted using two tire sets with different tire pressures under field conditions. Measurements of tractive properties were performed by setting travel speeds to 5, 8, and 10 kph, respectively. The ploughing set was operated at 8 kph, according to the manufacturer’s recommendation. The measurement results were processed graphically and mathematically into the Vehicle Traction Ratio, drawbar power, and slip characteristics. The tire inflation, reduced from 180 to 65 kPa and/or 75 kPa, of tires with wide treads (low-profile) resulted in increase of the front tire footprint by 24.7% and rear tire footprint by 31.1%. This change had a positive impact on the specific tractive fuel consumption that decreased in the range from 3.4% to 16.0%, depending on the travel speed. The results of performed measurements revealed that reducing the tire inflation of appropriate tires can improve the drawbar characteristics and consequently the fuel consumption.     

An investigation of intelligent tires using multiscale modeling of cord-rubber composites

A computational model based on the multiscale progressive failure analysis is employed to provide the theoretical predictions for damage development in the cord-rubber composites in tires. Vulcanized rubber, reinforcing belts, and carcass used in tire structures cause the anisotropic behavior under different loading conditions. Steel reinforcement layers made of steel wires combined with rubber complicate the macro-scale finite element modeling of tires. This paper presents a new three-dimensional model of the cord-rubber composite used in tires in order to predict the different types of damage including matrix cracking, delamination, and fiber failure based on the micro-scale analysis. Additionally, intelligent tires have the potential to be widely used to enhance the safety of road transportation systems, and this paper provides an estimation of the effects of void volume fraction, fiber volume fraction, and stacking sequence of the cord-rubber composites on the acceleration profile of the tire measured at the inner-liner.     

Development and validation of off-road tire-gravelly soil interaction using advanced computational techniques

This paper presents a novel modelling technique to compute the interaction between an 8x4 off-road truck and gravelly soil (sand with gravel soil). The off-road truck tire size 315/80R22.5 is modelled using the Finite Element Analysis (FEA) technique and validated using manufacturer-provided data in static and dynamic responses. The gravelly soil is modelled using Smoothed-Particle Hydrodynamics (SPH) technique and calibrated against physical measurements using pressure-sinkage and direct shear-strength tests. The tire-gravelly soil interaction is captured using the node symmetric node to segment with edge treatment algorithm deployed for interaction between FEA and SPH elements. The model setup consists of four tires presenting the four axles of the truck, the first tire is a free-rolling steering tire, the second and third tires are driven tires and the fourth tire is a free-rolling push tire. The truck tires-gravelly soil interaction is computed and validated against physical measurements performed in Göteborg, Sweden. The effect of gravelly soil compaction and truck loading on the tire performance is discussed and investigated.     

Measurement of contact area, contact pressure and compaction under tires in soft soil

This paper reports about measurements of the contact area of agricultuural tires in a soil bin. Four tires of the dimensions 12.5/80-18, 13.6–28, 16.9–34 and 16.9–26 were tested on a soft sandy loam. Because the existing models for predicting the footprint are complicated, a simplified model has been established, yielding good results. Measured different contact areas of all four tires are nearly constant related to wheel load except for a small increase at higher loads. Using rated loads and applying the appropriate inflation pressure, the ground pressure of a group of similar tires in loose sandy loam is independent of the tire dimensions. Measured soil compaction under at tire a various wheel loads is compared with results obtained by a mathematical model.     

Effects of central tire inflation systems on ride quality of agricultural vehicles

Instrumentation to collect ISO2631 ride data was installed on a CaseIH 8950 tractor equipped with a central tire inflation system (CTIS). Data were collected at two speeds on three courses representing degraded secondary roads, moderately rough fields, and the toughest of farming conditions. Reductions in tire pressures available with central tire inflation resulted in greater tire deflections and, consequently, a smoother ride. The CTIS improved the ride of the vehicle by 99% over properly inflated tires on average, and by 177% when not in resonance.     

A modified point contact tire model for the simulation of vehicle ride quality

The vertical response characteristics of several tire models were mathematically analysed by computer program. The results from the computation were compared with those from experiments. The tire models mentioned in this paper are evaluated. Finally, a modified point contact tire model has been proposed. The validity of it was then examined by experiment with tires 6.50–16 and 6.50R16.     

Finite element modeling of interfacial forces and contact stresses of pneumatic tire on fresh snow for combined longitudinal and lateral slips

Significant challenges exist in the prediction of interaction forces generated from the interface between pneumatic tires and snow-covered terrains due to the highly non-linear nature of the properties of flexible tires, deformable snow cover and the contact mechanics at the interface of tire and snow. Operational conditions of tire-snow interaction are affected by many factors, especially interfacial slips, including longitudinal slip during braking or driving, lateral slip (slip angle) due to turning, and combined slip (longitudinal and lateral slips) due to brake-and-turn and drive-and-turn maneuvers, normal load applied on the wheel, friction coefficient at the interface and snow depth. This paper presents comprehensive three-dimensional finite element simulations of tire-snow interaction for low-strength snow under the full-range of controlled longitudinal and lateral slips for three vertical loads to gain significant mechanistic insight. The pneumatic tire was modeled using elastic, viscoelastic and hyperelastic material models; the snow was modeled using the modified Drucker-Prager Cap material model (MDPC). The traction, motion resistance, drawbar pull, tire sinkage, tire deflection, snow density, contact pressure and contact shear stresses were obtained as a function of longitudinal slip and lateral slip. Wheel states - braked, towed, driven, self-propelled, and driving - have been identified and serve as key classifiers of discernable patterns in tire-snow interaction such as zones of contact shear stresses. The predicted results can be applied to analytical deterministic and stochastic modeling of tire-snow interaction.     

Tire-ice model development for the simulation of rubber compounds effect on tire performance

The material properties of the rubber compounds, which are highly dependent on temperature, have a vital role in the tire behavior. A comprehensive study on the effect of the rubber properties on tire performance, for different temperatures, as well as different road conditions is required to adequately predict the performance of tires on ice.In this study, a theoretical model has been developed for the tire-ice interaction. The temperature changes obtained from the model are used to calculate the height of the water film created by the heat generated due to the friction force. Next, the viscous friction coefficient at the contact patch is obtained. By using the thermal balance equation at the contact patch, the dry friction is obtained. Knowing the friction coefficients for the dry and wet regions, the equivalent friction coefficient is calculated. The model has been validated using experimental results for three similar tires with different rubber compounds properties. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal load, etc.     

Rolling deformation of truck tires: Measurement and analysis using a tire sensing approach

Measurements on rolling tire deformation provide deep insights into the mechanism of generating tire forces and moments. For free rolling tires, substantial attention has been given to the rolling resistance because of its significant impact on the fuel consumption and CO₂ emissions. This paper attempts to investigate the rolling resistance force through measurements of the rolling deformation of truck tires using a tire sensing approach. An optical tire sensor system is used to measure rolling tire deformation, which includes the deformed inner profile, sidewall deformation, and tread deformation. Measurements were conducted on a test truck for both new and used tires. In addition, the influences from operational factors such as wheel load and inflation pressure on tread deformation were examined and analyzed.