Statistical model of nearly complete elastic rough surface contact

In the area of homogeneous, isotropic, linear elastic rough surface normal contact, many classic statistical models have been developed which are only valid in the early contact when real area of contact is infinitesimally small, e.g., the Greenwood–Williamson (GW) model. In this article, newly developed statistical models, built under the framework of the (i) GW, (ii) Nayak–Bush and (iii) Greenwood’s simplified elliptic models, extend the range of application of the classic statistical models to the case of nearly complete contact. Nearly complete contact is the stage when the ratio of the real area of contact to the nominal contact area approaches unity. At nearly complete contact, the non-contact area consists of a finite number of the non-contact regions (over a finite nominal contact area). Each non-contact region is treated as a mode-I “crack”. The area of each non-contact region and the corresponding trapped volume within each non-contact region are determined by the analytical solutions in the linear elastic fracture mechanics, respectively. For a certain average contact pressure, not only can the real area of contact be determined by the newly developed statistical models, but also the average interfacial gap. Rough surface is restricted to the geometrically-isotropic surface, i.e., the corresponding statistical parameters are independent of the direction of measurement. Relations between the average contact pressure, non-contact area and average interfacial gap for different combinations of statistical parameters are compared between newly developed statistical models. The relations between non-contact area and average contact pressure predicted by the current models are also compared with that by Persson’s theory of contact. The analogies between the classic statistical models and the newly developed models are also explored.     

Comparison of the three-phase oil relative permeability models

A comparative study of seven different methods for predicting three-phase oil relative permeabilities in the presence of gas and water phases is presented. Predicted oil relative permeabilities from these correlations have been compared with published three-phase experimental data obtained in Berea sandstone core samples. Some of the correlations under study have been recently developed and have never been tested against the laboratory data.The comparison shows that the commonly used models such as Stones' often do not give accurate predictions of the experimental data. It is concluded that the recently developed models fit the experimental data as well as or better than the previously developed and widely used three-phase oil relative permeability models.     

Mathematical models of shape memory alloy behavior for online and fast prediction of the hysteretic behavior

In this contribution, a new closed form of a mathematical model of Nickel–Titanium (NiTi) shape memory alloy (SMA) and its thermo-mechanical wire hysteresis behavior is developed. The approach is based on experimental data. The behavior of the heated and naturally cooled wire is modeled by mathematical expression. The cycle of heating and cooling is performed under a constant load. The prediction of the hysteretic behavior is realized through models adaptation, as predetermination, or real time determination of the models values, is developed and presented in detail. Simulations for position control using PID controller is shown for comparison purposes. The developed approach is incorporated in a feed forward control scheme. A comparison between the actual position and the predicted models position shows promising results.     

Modeling of the 3D rocking problem

The rocking motion of a rigid rectangular prism on a moving base is a complex three dimensional phenomenon. Although, with very few exceptions, the previous models in the literature make the simplified assumption that this motion is planar, this is usually not true since a body will probably not be aligned with the direction of the ground motion. Thus, even in the case where the body is fully symmetric, the rocking motion involves three dimensional rotations and displacements.In this work, a three dimensional formulation is introduced for the rocking motion of a rigid rectangular prism on a deformable base. Two models are developed: the Concentrated Springs Model and the Winkler Model. Both sliding and uplift are taken into account and the fully non-linear equations of the problem are developed and solved numerically.The models developed are later used to examine the behavior of bodies subjected to general ground excitations. The contribution of phenomena neglected in previous models, such as twist, is stressed.     

Numerical simulation of turbulence suppression: Comparisons of the performance of four k-? turbulence models

The standard k-ε model and three low-Reynolds number k-ε models were used to simulate pipe flow with a ring device installed in the near-wall region. Both developing and fully developed turbulent pipe flows have been investigated. Turbulence suppression for fully developed pipe flows revealed by hot-wire measurements has been predicted with all three low-Reynolds number models, and turbulence enhancement has been predicted by the standard k-ε model. All three low-Reynolds number models have predicted similar distributions of velocities, turbulence kinetic energy, and dissipation rate. For developing pipe flows, the region of turbulence suppression predicted by the three low-Reynolds number models is much more extensive (up to 30 pipe diameters downstream of the device) than for full developed flow; whereas the standard k-ε model has only predicted turbulence enhancement.     

SMA本构模型及其应用的研究进展

形状记忆合金(SMA)是一类应用前景广阔的智能材料系统, 其最基本的宏观响应特性是在不同温度和应力条件下的相变超弹性和形状记忆特性.近年来, 形状记忆合金本构模型发展迅速, 其在工程结构振动控制领域中的研究和应用也得到了广泛地关注.与此同时, 许多学者将SMA用于当前迅速发展的智能材料结构,发展了一系列SMA复合材料本构模型, 成为目前SMA的应用研究的热点.本文针对形状记忆合金本构模型的发展状况, 首先回顾了近年来常用的和新发展的SMA本构模型, 并根据其包含的力学特点和基本理论将其进行了比较归类, 分析了各类模型特点和适用范围;其次从微/宏观角度介绍了有广阔应用前景的SMA智能复合材料的本构模型的发展状况;接着简要的综述了几类较为实用的SMA本构模型在实现结构的主/被控制、变形控制及结构裂纹诊断与控制等方面的应用现状.最后对目前本构模型的发展趋势、工程应用问题提出了一些看法和展望.      

Effect of Multi-Scale Porosity in Local Permeability Modelling of Non-Crimp Fabrics

The influence of multi-scale porosity of fibre reinforcements on local permeability is investigated, in order to determine the possibility of simplifying permeability models for more efficient permeability calculations. Unit cell models of a biaxial Non-Crimp Fabric are developed and used to investigate, whether or not the porous bundles can be excluded, when modelling the local permeability. Numerical accuracy of calculations is controlled to guarantee the quality of the results and the conclusions drawn from them. It is found that fibre bundles with high fibre density can be excluded from permeability models, while bundles with low fibre volume fractions need to be included. A new method to model the local permeability of multi-scale reinforcements is developed and verified for low fibre density in the bundles. In this method, the effects of the flow inside the fibre bundles are included through modifications of the boundary conditions of a single-scale model representing the interbundle regions. The local permeability of multi-scale reinforcements can, therefore, be calculated by models with simplified fluid domains for all fibre bundle porosities, instead of being calculated by models consisting of the entire multi-scale geometry.     

Characterization of hole-diameter in thin metallic plates perforated by spherical projectiles using genetic algorithms

The empirical and semi-empirical models available in literature for the estimation of hole-diameter in thin metallic plates by the strike of spherical projectile are mostly valid for the data for which these have been developed. This may be partly attributed to the form of the model employed for their development. The behavioural constraints and the limiting conditions are not satisfied by these models. In the present paper, some of the non-dimensional models have been developed that satisfy the behavioural constraints and limiting conditions. The data used in the development of earlier statistical models has been reanalyzed for the development of new models for the characterization of hole-diameter with a view towards seeing whether better characterization is possible. The genetic algorithm coupled with the penalty function method has been used for the constrained optimization of model parameters that result in low errors and high correlation coefficients.     

应力波衰减基础上的岩石爆破损伤模型

在TCK损伤模型基础上 ,考虑岩石冲击损伤过程的声波测试衰减规律 ,构造新的岩石爆破损伤模型。将该模型装进LS DYNA3D动态有限元程序 ,通过岩石冲击损伤实验验证该程序的计算结果 ,并用新模型实现了岩石台阶爆破数值计算。     

Parameterization and modelling of large off-road tyres for ride analyses: Part 2 – Parameterization and validation of tyre models

Every mathematical model used in a simulation is an idealization and simplification of reality. Vehicle dynamic simulations that go beyond the fundamental investigations require complex multi-body simulation models. The tyre–road interaction presents one of the biggest challenges in creating an accurate vehicle model. Many tyre models have been proposed and developed but proper validation studies are less accessible. These models were mostly developed and validated for passenger car tyres for application on relatively smooth roads. The improvement of ride comfort, safety and structural integrity of large off-road vehicles, over rough terrain, has become more significant in the development process of heavy vehicles. This paper investigates whether existing tyre models can be used to accurately describe the vertical behaviour of large off road tyres while driving over uneven terrain. [1] Presented an extensive set of experimentally determined parameterization and validation data for a large off-road tyre. Both laboratory and field test are performed for various loads, inflation pressures and terrain inputs. The parameterization process of four tyre models or contact models are discussed in detail. The parameterized models are then validated against test results on various hard but rough off-road terrain and the results are discussed.     

Multiple-integral viscoelastic constitutive equations

A class of nonlinear viscoelastic constitutive equations including the K-BKZ constitutive equations, linear viscoelasticity and the Green-Rivlin models is developed. A stored-energy functional is associated with each model in such a way that the energy dissipation rate is non-negative. The theory is developed for 1D viscoelasticity and extended to 3D viscoelastic media.     

The unification of hypo-plastic and elasto-plastic theories

A unifying theory of plasticity is developed that allows deducing models with either hypo-plastic, elasto-plastic or hyper-plastic constitutive structures. Elasto-plasticity is shown to be a singular case of hypo-plasticity. It is further demonstrated that certain conditions can be imposed to generate a new hierarchy of thermodynamically consistent hypo-plastic models, with a hyper-plastic structure as a singular case. The unifying theory is powerfully bridging between the tools created specifically for advancing models under either of those previous formulations.     

Response of epoxy oversized models of strands to axial and torsional loads

As part of an extensive investigation on strand and cable properties, epoxy oversized models of strands have been manufactured using a newly developed technique. Axial and torsional loadings have been applied to the models. Strains, stresses and displacements have been determined using mechanical and electrical strain gages, dial gages and brittle coatings. The results obtained are compared with calculations using a previously developed theory. The response of a reference structure in which each wire is assumed to act independently is also compared with the response of the strand. Several discrepancies with theory are pointed out. It is believed that these are the first systematic measurements taken on strands.     

可压缩多介质粘性流体和湍流的大涡模拟

在可压缩多介质粘性流体动力学高精度计算方法MVPPM(multi-viscous-fluid piecewise parabolicmethod)基础上,引入Smagorinsky和Vreman亚格子湍流模型,采用大涡数值模拟方法求解可压缩粘性流体NS(Navier-Stokes)方程,给出适用于可压缩多介质流体界面不稳定性发展演化至湍流阶段的计算方法和二维计算程序MVFT(multi-viscosity-fluid and turbulence)。在2种亚格子湍流模型下计算了LANL(Los Ala-mos National Laboratory)激波管单气柱RM不稳定性实验,分析了气柱的形状、流场速度以及涡的特征,通过与LANL实验和计算结果的比较可知,Vreman模型略优于Smagorinsky模型,MVFT方法和计算程序可用于对界面不稳定性发展演化至湍流阶段的数值模拟。     

Modeling of bubble coalescence and break-up considering turbulent suppression phenomena in bubbly two-phase flow

New mechanistic bubble coalescence and break-up models considering turbulent suppression phenomena, which can possibly occur in the high liquid velocity condition of turbulent bubbly two-phase flow, are presented. The energy exchange mechanism between a turbulent eddy and interfacial structure was taken into account in the efficiency terms. Numerical simulations of turbulent bubbly flow were conducted in a CFD code to evaluate the newly developed models, in comparison with other advanced models coupled with a bubble-induced turbulent effect for one-group interfacial area transport equation. Local measurements of the bubble characteristics on the bubble size evolution along a vertical pipe flow were performed at KAERI-VAWL test facility using the five-sensor conductivity probe method to provide database for models validation. Results from the calculation clearly show the improvements of the newly developed models.     

Analytical approach for the prediction of steady state tyre forces and moments under different normal pressure distributions

In general, all primary as well as disturbing forces acting on a vehicle (with the exception of aerodynamic forces) are generated at the tyre–road interface. The small size pneumatic tyres presented in this work are mostly used in lightweight vehicles like scooters, motor cycles and 3-wheelers that are extensively used for intercity transportation applications in India and other developing countries. Analytical approach is more advantage than experimental work due to many factors like it involves less cost, minimum time and little effort. Hence, Analytical tyre models are developed based on various normal pressure distributions with tyre contact patch as rectangle at the middle with part of circles at the ends. The tyre longitudinal and lateral force characteristic equations for proposed tyre models are developed. In addition, the equations for self – aligning moment and overturning moment characteristics for all tyre models are also derived. Results of proposed tyre models in the present study are compared with well-established earlier tyre models [4], [5], [6]. From the force and moment characteristics of all tyre models, unsymmetrical trapezoidal pressure distribution tyre model gives better performance than other models due to which better lateral stability of the vehicle can be obtained.     

Stress finite-element models with independent strains

Stress finite-element models with an independent expansion for strain are developed. By adding the constitutive law, which is satisfied on the average only, as a condition of constraint to the functional, the variational principle on which they are based is derived. A model which is stiffer can thus be constructed. As the equilibrium models lead to results which are too flexible, an independent assumption for strain should in many cases improve the accuracy. The strains can easily be eliminated on an element basis. A quadrilateral hybrid stress model with an independent assumption of strain is developed and tested on the level of an element and of the structural system.     

Numerical investigation of leading edge separated flow over cranked wings using a vortex lattice model

Numerical models based on the vortex lattice concept using free vortex lines have been developed for the calculation of separated flow about cranked wings. Various separated flow models are developed assuming the flow to be separated along the leading edges of (i) the inner wing, (ii) the entire wing and (iii) the inner wing and the outboard part of the outer wing. To illustrate the effects of separation, attached flow solutions are also obtained. Results are compared with available experimental results. Agreement with separated flow solutions is usually good except at very high incidence.     

Constitutive modeling of discontinuities by means of discrete and continuum approximations and damage models

In this paper the mathematical modeling of discontinuities using the discrete approximation and the continuum approximation with weak discontinuities is presented. First, the kinematics of discontinuities is discussed, then two constitutive models based on the continuum damage mechanics theory are developed. The first model is an isotropic damage model and is used in the discrete approximation. The second model is an anisotropic damage model and is used in the continuum approximation. These models are characterized for weighing the mode of failure in the failure criterion. An energy analysis is proposed to establish the equations that relate the parameters of both constitutive models; the fulfillment of the involved equations guarantee that both models are energetically equivalent. It is concluded that the proposed models are suitable to reproduce the constitutive behavior of discontinuities.     

Linear Mathematical Models for the Aerodynamics of Three-Dimensional Lifting Systems in an Unsteady Subsonic Gas Flow

A complex of linear mathematical models for the processes associated with unsteady compressible subsonic flow past three-dimensional lifting systems is developed. The models make it possible to determine the aerodynamic transfer functions over their entire range of definition with respect to Mach, Strouhal, and decrement numbers. The corresponding boundary value problems for the Laplace and Helmholtz equations are formulated and a technique of reducing them to systems of singular integral equations is developed. The questions of the construction and mathematical validation of numerical methods of solution of these systems are discussed. The technique developed is an outgrowth of the discrete vortex method, as applied to the class of the problems under consideration. Examples of calculations are presented.