Hybrid soft soil tire model (HSSTM). Part III: Model parameterization and validation

Part I describes the tire structure model; part II the contact detection and contact interface models for rigid and deformable terrains; part III the model parameterization and validation. Model parameters are estimated using non-linear least-square optimization to minimize the error between the Hybrid Soft Soil Tire Model (HSSTM) predictions and experimental data. The parameterization routines’ initial conditions are estimated from modal analysis in radial and circumferential directions. The preliminary parameterized model is incorporated in the optimization routine to find tire sidewall and belt parameters in the radial direction using quasi-static cleat loading test data. The vertical force at the spindle and tire contact patch are used to study the model accuracy in the radial direction. FlatTrac tire longitudinal and lateral force test data are employed to estimate the parameters in these directions. The tire shear force and moment at the spindle are validated against experimental data for lateral dynamics performance.     

Experimental analysis of vertical soil reaction and soil stress distribution under off-road tires

In this study, the vertical soil reaction acting on a driven wheel was measured by strain gages bonded to the left rear axle of a 2WD tractor driven under steady-state condition on different soil surfaces, tractor operations, and combinations of static wheel load and tire inflation pressure. In addition, the measurements of radial and tangential stresses on the soil–tire interface were made simultaneously at lug’s face and leading side near the centerline of the left rear tire using spot pressure sensors. The experimental results indicate that the proposed method of vertical soil reaction measurement is capable of monitoring the real-time vertical wheel load of a moving vehicle and provides a tool for further studies on vehicle dynamics and dynamic wheel–soil interaction. Furthermore, the measured distributions of soil stresses under tractor tire could provide more real insight into the soil–wheel interactions.     

不同材料参数和内压的轮胎对单腹板轮毂变形的影响

将轮胎材料简化为各向同性超弹性材料特性，考虑轮胎与轮毂和地面之间的三维接触以及轮胎中钢丝圈的影响，建立飞机单腹板机轮整体结构有限元模型。主要分析不同轮胎材料参数和内压下，单腹板轮毂轮缘处的径向变形，结果表明；轮毂剖面上测点的应变值与实验结果基本一致。轮胎下沉量与轮毂测点的径向变形和轮毂所受的载荷基本呈线性关系；凸出一侧的轮缘变形最大；轮胎下沉量较大时。轮胎材料参数对轮毂的径向变形影响明显；轮毂测点径向变形在1-2.5mm时，相同的径向变形，轮毂受到的总载荷受轮胎材料参数变化而变化，而在变形较大或较小时，影响不明显。对于同一种轮胎材料，不同的内压，轮毂的变形减轻比较大，气压越高，对于相同的轮胎下沉量，轮毂受到总体荷载也越高。     

Velocity distributions in Taylor vortex flow with imposed laminar axial flow and isothermal surface heat transfer

Fully-developed flow in a concentric annulus formed by a stationary outer cylinder, which may be heated isothermally, and a rotatable inner cylinder has been studied experimentally by means of hot-wire anemometry techniques. Velocity profiles for the axial, tangential, and radial directions of flow have been obtained for adiabatic conditions and for wide and narrow annular gaps.It has been shown that the onset of Taylor vortex flow has a pronounced effect on the velocity profiles for all three directions. However, while the profiles for the axial and tangential directions are explicable, those for the radial direction are not so, at present. Also, it was found that heat transfer through the outer annular surface had a greater effect on the radial velocity profile than on the axial or tangential, but in the narrow gap case only.     

2D FE–DEM analysis of contact stress and tractive performance of a tire driven on dry sand

Normal and tangential stresses acting over a contact interface of a tire driven on dry sand were investigated to expand the applicability of our model incorporating 2D FE–DEM with proportional–integral–derivative (PID) control. A simple averaging method for contact reaction was introduced: computational segments were defined over the lower half part of the tire circumference that translates without rotation with the tire; then the contact stresses were calculated segment by segment. For the analysis, it was assumed that the tire was in rigid contact mode and that it would travel on the model sand terrain in stationary condition. The integration of normal and tangential contact stresses with respect to the angle of rotation was then applied to calculate the vertical contact load, gross tractive effort, net traction, and running resistance of the tire by parametric (or semi-empirical) analysis. The result of tractive performance obtained through the parametric analysis was found to be similar to the result of tractive performance obtained directly using FE–DEM analysis. A forward shift of the consistent angle of rotation for maximum normal contact stress and that for maximum tangential contact stress with the increase of slip from 22% was also observed in the FE–DEM result.     

Experimental determination of the diffusion coefficients of wood in isothermal conditions

The diffusion coefficients of frake (Terminalia superba) were determined in the radial, tangential, and longitudinal directions at tree different temperatures: 30°C, 35°C an 40°C. The longitudinal diffusion coefficient is larger than the transverse diffusion coefficient. In addition the radial coefficient is larger than the tangential coefficient.     

Damage detection method in complicated beams with varying flexural stiffness

A damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying flexural stiffness and an edge crack, the SSEM is used to detect the crack location effectively by numerical modal shapes. As a complicated beam, the glass fiber-reinforced composite model of a wind turbine blade is studied based on an experimental modal analysis. The SSEM is used to calculate the damage index from the measured modal parameters and locate the damage position in the blade model successfully. The results indicate that the SSEM based on the modal shapes can be used to detect the damages in complicated beams or beam-like structures for engineering applications.     

Experimental modal analysis of a synthetic composite femur

In this paper we describe the experimental characterization of the modal parameters of a synthetic composite femur model widely used in biomechanical research studies. The objective of the experimental procedure was to identify the natural frequencies and mode shapes of an unconstrained (free-free) femur. The experimental data were compared with the same obtained in an analog study performed with a fresh cadaveric femur bone. Other objective of the study was to investigate modal analysis as a technique to validate a finite element model of a composite femur with isotropic material properties.     

子午线轮胎接触变形的结构有限元分析

针对195／60R14子午线轮胎建立了三维非线性有限元模型，着重研究了额定充气压力及静载荷作用下帘线承受拉应力和剪应力的基本特征。计算结果表明，接地区域摩擦力呈斜对称分布，反映了轮胎中帘线-橡胶复合材料存在变形耦合效应；冠带层、带束层、胎体帘线应力分布较为复杂，载荷变化对其应力水平和分布影响较大；在胎肩部位应力较高，且随载荷变化局部帘线应力变化剧烈，在承受交变载荷时，易形成层间剥落。分析结果有助于预测轮胎的使用性能，可以针对性地应用于因轮胎结构设计引起的质量损坏，某些对轮胎使用性能不利的受力状态可通过结构的优化设计来克服。     

利用地脉动试验识别楼房结构的模态参数

论述了在地脉动对结构物的环境激励条件下,进行结构物地脉动响应测量的试验原理及方法,提出了固有频率识别与振型识别的互补较正法．通过对实际楼房结构的地脉动响应测量识别结构的模态参数．识别结果表明该理论及试验方法行之有效．     

安装蜂窝板动力学特性分析及主动控制试验研究

通过对蜂窝芯的等效化处理,建立了ANSYS的壳单元模型,并作有限元模态分析,然后与其试验模态分析结果比较,有限元分析结果和试验结果基本一致。通过ANSYS的PSD随机功率谱分析和模态分析所得振型确定了贴片位置,对蜂窝板进行了压电智能结构振动主动控制试验研究,得到了较好的振动抑制效果。分析结果为仪器安装蜂窝板的设计和实现智能结构控制提供了重要参考依据。     

Analytical and experimental modal analysis of nonuniformly ring-stiffened cylindrical shells

In this research, the free vibration analysis of cylindrical shells with circumferential stiffeners, i.e., rings with nonuniform stiffener eccentricity and unequal stiffener spacing, is investigated using analytical and experimental methods. The Ritz method is applied in analytical solution, while stiffeners are treated as discrete elements. The polynomial functions are used for Ritz functions. The effects of nonuniformity of stiffener distribution on natural frequencies are considered for free–free boundary conditions. Results show that, at constant stiffener mass, significant increments in natural frequencies can be achieved using nonuniform stiffener distribution. In experimental method, modal testing is performed to obtain modal parameters, including natural frequencies, mode shapes, and damping in each mode. Analytical results are compared with experimental ones, showing good agreement. Because of insufficient experimental modal data for nonuniform stiffener distribution, the results of modal testing obtained in this study could be a useful reference for validating the accuracy of other analytical and numerical methods for free vibration analysis.     

在椭圆横截面弹体正侵彻下有限厚铝靶的破坏模式及响应特性

基于30 mm口径弹道炮平台,开展了3种不同椭圆横截面弹体在200~600 m/s撞击速度范围内正侵彻2A12铝靶的实验,获得了2A12铝靶的破坏形貌及弹体的剩余速度。在此基础上,建立了相应的数值模型,结合实验结果验证了所建模型的有效性,并系统分析了弹体横截面长短轴长度比对靶体的破坏情况及响应特性的影响。研究结果表明:弹体最大横截面面积是影响弹体剩余速度的主要因素,而弹体横截面长短轴长度比对弹体剩余速度的影响较弱;在圆形横截面弹体侵彻下靶体背部形成的花瓣大小和形状一致,空间分布均匀,而在椭圆横截面弹体侵彻下,随着弹体横截面长短轴长度比的增大,靶体背部形成的花瓣数量增加、尺寸变小,且在短轴方向的花瓣数量和靶体表面隆起高度均大于长轴方向的;靶体在圆形横截面弹体侵彻下的径向位移、径向应力和切向应力与其在椭圆横截面弹体侵彻下的显著不同,前者沿周向方向各点的变化规律基本一致,靶体处于简单的压缩状态,切向应力为零,而后者各点的应力状态与弹体横截面长短轴长度比和周向角密切相关,靶体受到压缩和剪切应力的耦合作用。     

Agricultural tire deformation in the 2D case by finite element methods

The mechanical characteristics of the rubber tire and the interaction between a tire and a rigid surface were investigated by a two-dimensional (2D) finite element (FE) model. The FE model consists of a rigid rim and a rigid contact surface which interact with the elastic tire. Four distinct sets of elastic parameters are used to represent beads, sidewall, tread and lugs. Several sets of tire loads and inflation pressures were applied to the FE model as boundary conditions, together with various displacements and friction conditions. The deformation of the tire profile, the tire displacements in the vertical and lateral directions, the normal contact pressures, the frictional forces and the stress distribution of the tire components were investigated by the 2D FE model under the above boundary conditions. The calculated tire deflections were compared with the measured data. The results show a good fit between calculated and measured data, especially at high load and inflation pressure. The comparison shows that the FE analysis is suitable to predict aspects of the tire performance like its deflection and interactions with the contact surface. Compared with the experimental methods, the FE methods show many advantages in the prediction of tire deformation, contact pressure and stress distribution.     

Structure–property relations for balsa wood as a function of density: modelling approach

In order to find an alternative core material to balsa wood in composite sandwich structures, it is important to understand balsa’s elastic properties in relation to its complex microstructural organisation. In the present work, experimental data on the elastic constants and microstructural features of balsa wood were collected for different porosities (densities) and processed into structure–property relations. An inverse problem was solved to predict variation of the cell wall properties with density, such that the collected experimental structure–property relations were satisfied. The Young’s modulus of the cell wall material in the longitudinal direction was found to increase with balsa’s density, which is consistent with the knowledge that the cell wall material stiffens during tree maturation. The value reported in the literature falls in the middle of the predicted range. The proposed micromechanical model also accurately calculated elastic properties of balsa wood at the mesolevel including longitudinal, radial, and tangential directions. The model took into account the presence of ray cells. It was shown that the addition of 15 % of rays increased the radial Young’s modulus up to 4 times with only slight decrease in the longitudinal modulus.     

Effects of soil and operational parameters on soil-tire interface stress vectors

Normal and tangential stress vectors were measured at the soil-tire interface of a pneumatic tractor tire on firm and soft soils. Stress magnitudes were determined with a transducer which was designed to measure both normal and tangential stresses. The orientation of the transducer was determined using a 3-dimensional, sonic digitizing system which was mounted inside the air cavity of the tire. Data are presented from tests conducted at zero input torque, zero net traction, and 0.15 net traction ratio which show the effects of inflation pressure, dynamic load, and soil conditions on the stress vectors.     

结构健康监测系统中传感器优化布置组合算法

在对结构健康监测中的传感器优化布置方法进行调研和总结的基础上,针对薄板、壳结构开展传感器优化布置的研究.提出了一种有效的传感器优化布置组合算法,由模态动能法、模态保证准则、遗传算法组合而成.该方法所得的传感器位置主要位于动态响应比较大区域,有利于提高信噪比;同时能够有效地保证模态振型的独立性,可以较完整地获得结构模态信息.针对这种组合算法的有效性采用简易机翼模型从数值计算和实验两方面进行了验证.     

The experimental determination of velocity distribution in annular flow

In the study of the flow of a fluid through an annular gap, the outer surface of which is stationary while the inner surface may be rotated, it is necessary to be able to accurately determine the velocity profiles obtaining in the axial, tangential, and radial directions of flow.

A method is described for this purpose employing hot-wire anemometry techniques and typical profiles are presented for each of the above flow directions. In the case of pure axial flow, a comparison is made between experimental and theoretical results, showing a close correspondence.     

Experimental characterization of non-premixed turbulent jet propane flames

This paper reports an experimental study conducted on turbulent jet propane flames aiming at further understanding of turbulent structure in non-premixed slow-chemistry combustion systems. Measurements of mean and fluctuating velocity and temperature fields, mean concentration of major chemical species, correlation between velocity and temperature fluctuations, and dissipation of temperature fluctuations are reported in a turbulent round jet non-premixed propane flame, Re=20 400 and 37 600, issuing vertically in still air. The experimental conditions were designed to provide a complete definition of the upstream boundary conditions in the measurement domain for the purpose of validating computational models. The measured data depicts useful flow field information for describing turbulent non-premixed slow-chemistry flames. Velocity–temperature correlation measurements show turbulent heat fluxes tended to be restricted to the mixing layer where large temperature gradients occurred. Observations of non-gradient diffusion of heat at x/D=10 were verified. Temperature fluctuation dissipation, χ, showed the highest values in the shear layer, where the variance of temperature fluctuations was maximum and combustion occurred. The isotropy between the temperature dissipation in the radial and tangential directions was confirmed. By contrast, the observed anisotropy between axial and radial directions of dissipation suggests the influence of large structures in the entrainment shear layer on the production of temperature fluctuations in the flame region. The value of the normalized scalar dissipation at the stoichiometric mixture fraction surface, χ_st, was calculated, and ranges between 2 and 4 s⁻¹. The measured data were used to estimate the budgets in the balance equations for turbulent kinetic energy, Reynolds shear stresses, turbulent heat flux and temperature variance, quantifying the mechanisms involved in the generation of turbulence as well as in the transport of the temperature.     

Best achievable modal eigenvectors in structural damage detection

This paper reports a modal formulation of the original method presented by Lim and Kashangaky, based on the use of the best achievable eigenvectors in damage detection problems. The method requires the measurement of both frequencies and mode shapes. The structural damage is located by computing the Euclidean distances between the measured mode shapes and the best achievable modal eigenvectors. The method is able to detect loss of both stiffness and mass properties, even though in this paper only the loss of stiffness will be analyzed. A simple numerical example is reported to investigate the applicability of the modal formulation. Finally, an experimental validation is included using a 10-bay truss laboratory structure.