深部节理岩体塑性损伤耦合微面模型

采用微面模型理论和损伤力学方法,建立了节理岩体的弹塑性损伤耦合微面模型.在节理岩体的微面上,将岩体视为由节理面与岩石组成的二元介质,以节理连通率作为岩体沿该方向的面积损伤变量,考虑微面法向拉应力和压应力下的不同塑性变形和损伤耦合作用机制,基于塑性理论建立了节理岩体的微面塑性损伤增量本构关系.采用微面物理量与宏观物理量的几何约束模型,根据微面方向积分导出了节理岩体的宏观弹塑性增量本构关系.编制了节理岩体微面模型的MARC有限元子程序,对节理岩体的单轴拉伸、压缩试验和泥浆压力作用下的井壁稳定问题进行了数值模拟研究.数值计算结果表明,该模型能很好地揭示载荷作用下节理岩体的各向异性非弹性变形和次生节理演化过程.

粗糙路面检测链路模型研究

粗糙路面的反射特性影响路面检测系统的性能和路面气象检测的准确性,根据传统微面元模型,提出了一种多参量半球形等效仿真模型,建立了基于无线激光的粗糙路面链路传输模型。通过采用蒙特卡洛统计方法,分析了反射光在不同入射角和粗糙度情况下接收光功率的变化以及光子的分布规律。基于该模型,设计并实现了一套850 nm波长的非接触式激光路面状况检测系统,并利用该系统验证模型的准确性。仿真及实验结果均显示,随着入射光与路面法线方向夹角(入射角)的增大,接收到的光功率逐渐减小。当入射角小于15°时,粗糙度的增加与接收的光功率负相关;入射角大于15°时,随着粗糙度的增加,接收到的光功率逐渐增加,粗糙度越大,接收光功率与入射角的衰减关系越接近线性;当入射角达到60°时,接收到的光功率趋于常数。实验结果与模型仿真结果相吻合,从而验证了粗糙路面光反射等效半球形模型的有效性,且接收的回波信号信噪比不受路面粗糙度影响。

基于改进的微面元偏振BRDF模型的粗糙表面偏振反射特性分析

为了表征粗糙表面反射光的偏振特性,基于微面元偏振BRDF模型,综合考虑镜面反射和漫反射,提出一种改进的多参量微面元偏振BRDF模型,并基于斯托克斯矢量与穆勒矩阵的关系,建立反射光偏振度数学模型。根据所建模型,使用最小二乘法对绿漆和铝表面的偏振度测量值进行参量反演,确定参量的最优组合。在此基础上分析了入射角、表面粗糙度以及相对方位角对反射光偏振度的影响。结果表明,与参考模型相比,绿漆表面和铝表面的偏振度均方根误差分别减小了67.11%和77.54%,模型与实测数据的吻合程度更高,证实建模时考虑漫反射能够提高模型的准确性。该模型可为粗糙表面偏振特征的提取与识别提供理论指导。

粗糙基底上涂层的极化双向反射分布函数

为了有效检测光学基底和镀膜后的光学元件质量,根据微面元电磁散射理论建立了一阶极化光散射模型,推导求解出其极化双向反射分布函数,获得了极化双向反射分布函数PP项与散射角和方位角的三维关系。数值模拟分析了入射角、基底粗糙度及不同涂层厚度对极化双向反射分布函数的影响。数值结果表明:极化双向反射分布函数与入射角、相关长度、均方根高度及涂层厚度均成反比。P极化入射产生的P极化双向反射分布函数强烈依赖于入射角、散射角和方位角。布鲁斯特角的位置随着入射角的增加逐渐向散射方位角小的方向移动。

Heat transfer model for microwave hot in-place recycling of asphalt pavements

In order to solve for temperature fields in microwave heating for recycling asphalt mixtures, a two-dimensional heat transfer model for the asphalt mixtures within the heating range is built based on the theory of unsteady heat conduction. Four onedimensional heat transfer models are established for the asphalt mixtures outside the heating range, which are simplified into four half-infinite solids. The intensity of the radiation electric field is calculated through experiment by using heating water loads. It is suggested that the mathematical model of boundary conditions can be established in two ways, which are theoretical deduction and experimental reverse. The actual temperature field is achieved by fitting temperatures of different positions collected in the heating experiment. The simulant temperature field, which is solved with the Matlab PDE toolbox, is in good agreement with the actual temperature field. The results indicate that the proposed models have high precision and can be directly used to calculate the temperature distribution of asphalt pavements.

Dynamic characteristics of gear system under different micro-topographies with the same roughness on tooth surface

The topography of gear meshing interfaces is one of the key factors affecting the dynamic characteristics of the gear transmission system.In order to obtain the contact characteristics of meshing gear pair with different surface micro-topographies,an interface feature model and a tribo-dynamics coupling model for the gear system are proposed in this paper.The effects of the gear tooth surface micro-topography on the oil film distribution,contact damping and friction are considered.The time-varying meshing stiffness and the static transmission error are included in the abovementioned models.An exemplary gear pair is analyzed using the proposed models to investigate the influence of the surface micro-topography on the dynamic characteristics of gear system under different micro-topographies and input torque conditions.Simulation results show that the effects of gear tooth micro-topography on the gear dynamic responses(including the friction and the vicious damping at the gear meshing interface and the vibration in the direction of offline of action)are highly dependent on the regularity of tooth surface.The vibration and noise can be significantly controlled by manufacturing a regular gear tooth profiles instead of random profiles.

CFD Simulation of Film Flow and Gas/Liquid Countercurrent Flow on Structured Packing

A mathematic model of two-phase flow and a physical model of two-dimensional (2D) vertical section for the plate-type structured packing Mellapak 250.Y were set up and verified. The models were used to study the influence of packing’s surface microstructure on the continuity of liquid film and the amount of liquid holdup. Simulation results show that the round corner shape and micro wavy structure are favorable in remaining the continuity of liquid film and increasing the amount of liquid holdup. The appropriate liquid flow rate was determined by investigating different liquid loadings to obtain an unbroken liquid film on the packing surface. The pressure difference between inlet and outlet for gas phase allowed gas and liquid to flow countercurrently in a 2D computational domain. The direction change of gas flow occurred near the phase interface area.

Fractal model of thermal elasto-plastic contact of rough surfaces

Without considering the influence of heat,existing fractal contact models are not applicable to analyze the contacts when the temperature changes.For this problem,the normal load model and the normal stiffness model of thermal elasto-plastic contact of rough surfaces are developed respectively in this paper.The proposed model is based on the normal contact mechanics model of fractal theory of anisotropic and thermal elasto-plastic contact theory which can be used to characterize the rough surface thermodynamic properties.Then the validity of the model is verified.Finally,the influence of main parameters on the total normal load and the whole normal stiffness of thermal elasto-plastic contact at the interface is analyzed by contact simulation.The results show that the total normal load of thermal elasto-plastic contact increases with the increases of temperature.The whole normal stiffness of thermal elasto-plastic contact increases with increasing coefficient of linear expansion,scale factor,temperature difference or fractal dimension,but decreases with increasing fractal roughness.This model expands basic theory and applications of traditional models,and can be used to calculate and analyze the contacts when the temperature changes.

Effect of Interaction Potential on Laser-assisted e-Ar Scattering

The interaction potentials between electron and atom play an important role in electron- atom scattering. Using three potential models, the absolute differential cross section has been calculated by the second Born approximation theory. Results show that these model potentials are successful in the laser-assisted e-Ar scattering system. The influence of static potential, exchange potential and polarization potential on the absolute differential cross section is also analyzed and discussed.

Theoretical Analysis of Neutron Double-Differential Cross Sections of n ＋^9Be Reactions

By using the nuclear reaction model for light nuclei, the calculations of the double-differential cross sections of outgoing neutrons from n ＋^9Be reactions are performed. The total outgoing neutrons are only come from the （n, 2n）2a reaction channel. The （n, 2n）2a reaction channel is achieved through six different reaction approach, which are illustrated in this paper. The calculated results agree very well with the measured data at En = 7.1, 8.09, 8.17, 9.09, 9.97 and 10.26 MeV, because the updated level schemes related to the n ＋ ^9Be reactions have been employed in this calculations.

Properties and interfacial microstructure of cement-based materials with composite micro-grains

Silica fume, fly ash and nano-fiber mineral materials (NR powder) are employed to incorporate into cement-based materials. According to the grain grading mathematical model of cement-based materials, two packing systems, namely, spherical grading system and nano-fiber reinforced system were designed. Properties and interfacial microstructure of the two systems were studied according to secondary interface theory. It was shown that nano-fiber mineral materials can improve the grain grading of the admixture, increase the density of the system, improve the microstructure of the interface and the hardened paste, and enhance the uniformity of cement-based materials mixed with composite micro-grains and greatly increase their wearable rigidity and flexure strength. In this paper, two kinds of interface models, including spherical grain model and nano-fiber reinforced interface model of the cement-based materials mixed with composite micro-grains, were brought forward.

Modeling bidirectional reflection distribution function of microscale random rough surfaces

The radiative properties of three different materials surfaces with one-dimensional microscale random roughness were obtained with the finite difference time domain method(FDTD) and near-to-far-field transformation.The surface height conforms to the Gaussian probability density function distribution.Various computational modeling issues that affect the accuracy of the predicted properties were discussed.The results show that,for perfect electric conductor(PEC) surfaces,as the surface roughness increases,the magnitude of the spike reduces and eventually the spike disappears,and also as the ratio of root mean square roughness to the surface correlation distance increases,the retroreflection becomes evident.The predicted values of FDTD solutions are in good agreement with the ray tracing and integral equation solutions.The overall trend of bidirectional reflection distribution function(BRDF) of PEC surfaces and silicon surfaces is the same,but the silicon's is much less than the former's.The BRDF difference from two polarization modes for the gold surfaces is little for smaller wavelength,but it is much larger for the longer wavelength and the FDTD simulation results agree well with the measured data.In terms of PEC surfaces,as the incident angle increases,the reflectivity becomes more specular.

Finite element simulation of lower limb injuries to the driver in minibus frontal collisions

Purpose： This study aims to explore the biomechanical mechanism of lower limb injuries to the driver by establishing a finite element （FE） simulation model of collisions. Methods： First a minibus FE model was integrated with a seat belt system. Then it was used to rebuild two collisions together with the total human model for safety （THUMS） provided by Toyota Motor Corporation： a rear-end collision between a minibus and a truck and a head-on collision of a minibus to a rigid wall. The impact velocities of both collisions were set at 56 km/h. The vehicle dynamic response, vehicle deceleration, and dashboard intrusion in the two collisions were compared. Results： In the minibus rear-end truck collision, the peak values of the yon Mises equivalent stress at the tibia and the femur were 133 MPa and 126 MPa respectively; while in the minibus head-on rigid wall collision, the data were 139 MPa and 99 MPa. Compared with the minibus head-on rigid wall collision, the vehicle deceleration was smaller and the dashboard intrusion was larger in the minibus rear-end truck collision. Conclusion： The results illustrate that a longer dashboard incursion distance corresponds to a higher yon Mises equivalent stress at the femur. The simulation results are consistent with the driver＇s autopsy report on lower limbs injuries. These findings verify that FE simulation method is reliable and useful to analyze the mechanisms of lower limb iniuries to the driver in minibus frontal collisions.

Stream Surface Theory of Bird-like Flapping Flight

Through analyzing the motion characteristics of bird-like flapping flight, it is considered that the wing angular acceleration is equal to zero at the point of maximum angular speed. Thus, the flapping flight is equivalent to a uniform rotating motion which can be analyzed by using the stream surface theory of turbomachinery during a micro period of time. In this article, the N-S equations of the motion are expanded in a non-orthogonal curvilinear coordinate system, and simplified on stream surfaces of the flapping flight model. By using stream function me- thod, the three-dimensional unsteady flow equations are simplified as a two-order partial differential equation with variable coefficients eventually and the equation＇s iterative solving method on S1 and $2 stream surfaces of the flapping flight model is presented. Through expanding the relatively steady equations of flapping flight at an arbitrary time point of a stroke on meridional plane of the flapping flight model, it can use a relatively steady mo- tion to approximate the real flapping flight at that time point, and analyze the flow stability influenced by the wing＇s flexibility. It can be seen that the wing flexibility is related to the higher pressurization capacity and the flow stability, and the pressurization capacity of flexible wing is proportional to the angular speed, angular distor- tion rate and radius square.

Localization and macroscopic instability in nanoporous metals

Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic behavior from that established for the same material with larger voids.For example,irradiation of metallic materials can generate a large number of voids at the nanoscale,leading to complex deformation behaviors.The present work advances the understanding of strain localization in nanoporous metallic materials,connecting both the microscopic(nano-)and macroscopic scales.To explore the physical mechanisms at the nanoscale,molecular dynamics(MD)simulations were here carried out,capturing multiple nanovoids explicitly.Then,a homogenized continuum theory based in Gurson's constitutive framework is proposed,which enables us to explore how localized behavior at the macroscopic scale evolves.The homogenized model incorporates the surface tension associated with nanosized void.The importance of this surface tension is illustrated by several parametric studies on the conditions of localization,when a specimen is subjected to uniaxial tension.Our parametric studies show that for smaller nanovoid sizes,and for a hardening matrix material,shear localization onset is delayed.Our proposed homogenization model was then used to predict localization behavior captured by our MD simulation.The yield stress and the localization strain predicted by our continuum model are in general agreement with the trends obtained by MD simulation.Moreover,based on our present study,experimental results of shear failure strain vs.dose of irradiation for several metals could be qualitatively explained rather successfully.Our model can therefore help shed light on prolonging the operation limits and the lifetime of irradiated metallic materials under complex loading conditions.