虚拟柔性体实时形变仿真模型研究

为了在虚拟现实柔性体力触觉交互研究中得到稳定、连续、真实的力触感,提出一种基于球面调和函数表达的虚拟柔性体实时形变仿真模型,利用球面调和函数的正交归一、旋转不变、多尺度等特性实现物体的快速准确表达.在变形体的密度、杨氏模量、泊松比等参数已知的情况下,基于径向基函数神经网络模型预测柔性体受力形变后的SH模型.仿真结果表明,该方法不仅可以准确表达柔性体的实时形变,而且使得基于SH表达的柔性体形变的视觉刷新描述与柔性体反馈力的触觉刷新描述同步,从而满足虚拟手术仿真训练等虚拟柔性体力触觉交互研究要求.     

Buckling and post-buckling behaviors of higher order carbon nanotubes using energy-equivalent model

This paper aims to investigate the size scale effect on the buckling and post-buckling of single-walled carbon nanotube (SWCNT) rested on nonlinear elastic foundations using energy-equivalent model (EEM). CNTs are modelled as a beam with higher order shear deformation to consider a shear effect and eliminate the shear correction factor, which appeared in Timoshenko and missed in Euler–Bernoulli beam theories. Energy-equivalent model is proposed to bridge the chemical energy between atoms with mechanical strain energy of beam structure. Therefore, Young’s and shear moduli and Poisson’s ratio for zigzag (n, 0), and armchair (n, n) carbon nanotubes (CNTs) are presented as functions of orientation and force constants. Conservation energy principle is exploited to derive governing equations of motion in terms of primary displacement variable. The differential–integral quadrature method (DIQM) is exploited to discretize the problem in spatial domain and transformed the integro-differential equilibrium equations to algebraic equations. The static problem is solved for critical buckling loads and the post-buckling deformation as a function of applied axial load, CNT length, orientations and elastic foundation parameters. Numerical results show that effects of chirality angle, boundary conditions, tube length and elastic foundation constants on buckling and post-buckling behaviors of armchair and zigzag CNTs are significant. This model is helpful especially in mechanical design of NEMS manufactured from CNTs.

     

Deformation of an elastic capsule in a microfluidic T-junction: settling shape and moduli determination

Microdevices involving a stagnation-point flow, such as cross- and T-junctions, are useful for particle manipulation and characterization. In contrast to the wide use of cross-junctions, T-junctions have received limited attention as a medium for capsule deformation and characterization. In the present study, we investigate computationally the settling shape of an elastic capsule in a T-junction microchannel for a wide range of flow rates. Our work reveals that the capsules show a rich deformation behavior including (inverse) swallow-cap, sit-on and whitewater kayak shapes. We also propose a new methodology for the simultaneous and accurate determination of the shear and area-dilatation moduli of the membrane of artificial capsules via a single experimental technique by utilizing the dependence of the settling capsule’s dimensions on the capillary number and the membrane hardness identified in our investigation. Our moduli methodology utilizes high flow rates (i.e., large capsule deformations) where the effects of the membrane hardness become prominent and thus capsules with different area-dilatation modulus can be identified. Our procedure has the additional advantage of not being influenced by the fluids’ viscosity ratio or the membrane viscosity.     

Modeling Seismic-Acoustic Fields in Axisymmetric Absorbing Media: the Finite Difference Scheme

The finite difference scheme for modeling seismo-acoustic field propagation in axisymmetric absorbing media excited by an emitter in the borehole fluid (a monopole, a dipole, or a quadrupole) during the acoustic logging, or by an emitter in an elastic medium (a concentrated force, a dipole, or a center of expansion) during the seismic prospecting is presented. The explicit finite difference scheme approximating the equations of the modified Biot’s model, which describes the acoustic wave propagation in an isotropic porous viscoelastic medium saturated with viscous fluid, is proposed.     

Measurement of Young’s modulus and residual stress of thin SiC layers for MEMS high temperature applications

Silicon carbide (SiC) is a promising material for applications in harsh environments. Standard silicon (Si) microelectromechanical systems (MEMS) are limited in operating temperature to temperatures below 130°C for electronic devices and below 600°C for mechanical devices. Due to its large bandgap SiC enables MEMS with significantly higher operating temperatures. Furthermore, SiC exhibits high chemical stability and thermal conductivity. Young’s modulus and residual stress are important mechanical properties for the design of sophisticated SiC-based MEMS devices. In particular, residual stresses are strongly dependent on the deposition conditions. Literature values for Young’s modulus range from 100 to?400?GPa, and residual stresses range from 98 to?486?MPa. In this paper we present our work on investigating Young’s modulus and residual stress of SiC films deposited on single crystal bulk silicon using bulge testing. This method is based on measurement of pressure-dependent membrane deflection. Polycrystalline as well as single crystal cubic silicon carbide samples are studied. For the samples tested, average Young’s modulus and residual stress measured are 417?GPa and 89?MPa for polycrystalline samples. For single crystal samples, the according values are 388?GPa and 217?MPa. These results compare well with literature values.     

Thick shells of revolution: Derivation of the dynamic stiffness matrix of continuous elements and application to a tested cylinder

This paper describes a procedure for calculating the dynamic stiffness matrix of tubular shells with free edge boundary conditions. Such an analysis forms the basis for the Continuous Element Method. The method is used to formulate a thick axisymmetric shell element which takes into account rotatory inertia, transverse shear deformation and non-axisymmetric loadings.     

舰船水下声场边界元法建模与计算机模拟

根据舰船声场的特性,将舰船水下声场简化为一特殊的半自由空间声辐射问题,利用边界元法(BEM)建立了舰船水下声场的数值计算模型。通过对声场边界条件的计算机仿真和计算,获得了部分计算结果。结果表明:由所建模型计算的舰船辐射声场与真实海域中的实测规律基本吻合,该文提出的方法是有效可行的。最后对存在的问题进行了讨论。     

Visual-Based Impedance Control of Out-of-Plane Cell Injection Systems

In this paper, a vision-based impedance control algorithm is proposed to regulate the cell injection force, based on dynamic modeling conducted on a laboratory test-bed cell injection system. The injection force is initially calibrated to derive the relationship between the force and the cell deformation utilizing a cell membrane point-load model. To increase the success rate of injection, the injector is positioned out of the focal plane of the camera, used to obtain visual feedback for the injection process. In this out-of-plane injection process, the total cell membrane deformation is estimated, based on the $X-Y$ coordinate frame deformation of the cell, as measured with a microscope, and the known angle between the injector and the $X-Y$ plane. Further, a relationship between the injection force and the injector displacement of the cell membrane, as observed with the camera, is derived. Based on this visual force estimation scheme, an impedance control algorithm is developed. Experimental results of the proposed injection method are given which validate the approach.      

Analyses of acoustofluidic field in ultrasonic needle–liquid–substrate system for micro-/nanoscale material concentration

The ultrasonic needle–liquid–substrate system, in which an ultrasonically vibrating steel needle is inserted into an aqueous suspension film of micro-/nanoscale materials on a nonvibration silicon substrate, has large potential applications in micro-/nanoconcentration. However, research on its detailed concentration mechanism and the structural parameters’ effect on concentration characteristics has been scarce. In this work, the acoustic streaming field and acoustic radiation force in an ultrasonic needle–liquid–substrate system, which are generated by a vibrating needle parallel to the substrate, are numerically investigated by the finite element method. The computational results show that the ultrasonic needle’s vibration can generate the acoustic streaming field capable of concentrating micro-/nanoscale materials, and the acoustic radiation force has little contribution to the concentration. The computation results well explain the experimental phenomena that the micro-/nanoscale materials can be concentrated at some conditions and cannot at others. The computational results clarify the effects of the distance between the needle center and substrate surface, the needle’s radius, the water film’s height and radius and the shape of the needle’s cross section on the acoustic streaming field and concentration capability.     

基于锁相放大技术的激光超声信号处理电路的设计

利用激光声表面波(SAW)技术对膜材料机械特性的测量(如杨氏模量、密度、厚度等)已得到了越来越广泛的应用。但激光激发激光检测声表面波(LG/LD-SAW)的频谱带宽较宽(达几百兆到GHz),一般的检测方法难以在如此高的带宽下对其进行检测。设计了一种基于锁相放大(LIA)原理的微弱信号处理电路,通过应用一特殊的去噪电路,能在很宽的频谱(GHz)范围检测微弱信号,并将其从噪声信号中提取出来。     

Nonlinear modeling of soil deformation modulus through LGP-based interpretation of pressuremeter test results

Soil deformation modulus is an essential parameter for the analysis of behavior of substructures. Despite its importance, little attention is paid to developing empirical models for predicting the deformation moduli obtained from the field tests. To cope with this issue, this paper presents the development of a new prediction model for the pressuremeter soil deformation modulus utilizing a linear genetic programming (LGP) methodology. The LGP model relates the soil secant modulus obtained from the pressuremeter tests to the soil index properties. The best model was selected after developing and controlling several models with different combinations of the influencing parameters. The experimental database used for developing the models was established upon several pressuremeter tests conducted on different soil types at depths of 3–40 m. To verify the applicability of the derived model, it was employed to estimate the soil moduli of portions of test results that were not included in the analysis. Further, the generalization capability of the model was verified via several statistical criteria. The sensitivity of the soil deformation modulus to the influencing variables was examined and discussed. Moisture content and soil dry unit weight were found to be efficient representatives of the initial state and consolidation history of the soil for determining its deformation modulus. The results indicate that the LGP approach accurately characterizes the soil deformation modulus leading to a very good prediction performance. The correlation coefficients between the experimental and predicted soil modulus values are equal to 0.908 and 0.901 for the calibration and testing data sets, respectively.     

Asymptotic numerical method for problems coupling several nonlinearities

The objective of this paper is to assess the efficiency of the asymptotic numerical method to solve problems coupling various nonlinearities. The 3D hemispherical stretching of a circular sheet, that involves geometrical, material and red unilateral contact nonlinearities is chosen as an example. An elastoplastic model based on the plasticity deformation theory is adopted. The structural discretization is performed by a shell finite element well adapted for problems involving large displacements and large rotations. The unilateral contact problem is identified to boundary conditions which are replaced by force–displacement relations and solved using a special algorithm. Comparisons with results obtained by the help of an industrial code establish the interest and the performance of the present method.     

非致冷双材料红外探测器模拟分析

非制冷双材料红外探测器具有高响应率和低噪声的特点,噪声等效温差接近理论极限。其灵敏度高的基本原理是基于一个比较大的双层材料热膨胀系数和杨氏模量差,通过双材料悬臂结构可以把热转换成机械运动。经过采用ANSYS软件进行有限元模拟,得出材料厚度比与灵敏度、极板位移与电容变化的关系曲线。同时,模拟分析了不同悬臂尺寸的几何模型,得出了相应的优化结构。     

Coupled twist–bending static and dynamic behavior of a curved single-walled carbon nanotube based on nonlocal theory

The static and dynamic behavior of a curved single-walled carbon nanotube which is under twist–bending couple based on nonlocal theory is analyzed. The nonlocal theory is used to model the mechanical behavior of structure in small scale. The obtained differential equations are solved using a simply supported boundary condition and Navier analytical method. Moreover the twisted vibration and bending of curved nanotube is analyzed and also the armchair model is assumed in this study. The following parameters were studied in this paper: the effect of nonlocal parameter, the curved nanotube’s opening angel, the Young’s modulus and the mode number is studied. The results were verified with the previous literature which showed an excellent agreement. The results of this paper can be used as a benchmark for future investigations.

     

基于SPH与FEM的结构入水分析方法

建立基于光滑粒子动力学（smoothed particle hydrodynamics, SPH）、有限元法（finite element method, FEM）和无反射边界耦合的结构入水分析方法,将无限水域利用无反射边界条件截断成有限水域,将有限水域分为流体变形大的SPH区域、流体变形小的FEM区域和声学流体FEM区域,结构用FEM离散。采用通用接触算法模拟SPH与FEM的耦合,采用声固耦合方法处理FEM区域之间的耦合,建立流固耦合的SPH FEM分析方法。该方法结合SPH模拟大变形的优点和FEM的高效性,可实现含自由液面变形、液体飞溅和无限水域等特点的流固耦合问题的模拟,为结构入水分析缩小离散区域、降低自由度和SPH粒子数等提供一种有效的分析方法。     

Laminated composite structures by continuum-based shell elements with transverse deformation

In this paper a first-order shear/fourth-order transverse deformation theory of laminated composite shells is presented. A nonlinear continuum-based (degenerated 3D) finite element model with a strain/stress enhancement technique is developed in such a way that the nonzero surface traction boundary conditions and the interlaminar shear stress continuity conditions are all satisfied identically. Analytical integration through the shell thickness is performed. The resultants of the stress integrations are expressed in terms of the laminate stacking sequence. Consequently, the shell laminate characteristics in the normal direction can be evaluated precisely and the computational cost of the overall analysis is reduced. The numerical results are compared with analytical solutions and other finite element solutions to demonstrate the effectiveness of the theory and the computational procedure developed herein.     

Modeling of mechanical resonators used for nanocrystalline materials characterization and disease diagnosis of HIVs

The modeling and performance of mechanical resonators used for mass detection of bio-cells, nanocrystalline materials characterization, and disease diagnosis of human immune-viruses (HIVs) are investigated. To simulate the real behavior of these mechanical resonators, a novel distributed-parameter model based on Euler–Bernoulli beam theory is developed. This model is equipped with a micromechanical model and an atomic lattice model to capture the inhomogeneity nature of the material microstructure. Compared with lumped-parameter model predictions, the results show that this developed model best fits with the real behavior of the mechanical resonators when detecting the mass of vaccinia virus. In terms of material characterization, the developed model gives very good estimations for the densities and Young’s moduli of the grain boundary of both the nanocrystalline silicon and nanocrystalline diamond. For disease diagnosis, it is shown that the number of human immune-deficiency virus particles in a liquid sample can be easily detected when using the proposed model. The results also show that the developed model is beneficial and can be used to design mechanical resonators made of nanocrystalline materials with the ability to control the resonators’ sizes and the material structure.     

A novel bonding method for fabrication of PMMA nanofluidic chip with low deformation of the nano-trenches

All PMMA-based nanofluidic chips are becoming increasingly important for biological and medical applications. To fabricate PMMA nanofluidic chips, the open nano-trenches should be sealed by thermal bonding method. However, the present thermal bonding method suffers from high deformation of nano-trenches due to PMMA softening near glass transition temperature. In this work, a novel bonding technique, based on acetone and ethanol (v:v, 8:2) treatment, is developed to adjust the Young’s modulus of PMMA in its surface layer. By optimizing nanoimprinting and bonding process, PMMA nanofluidic chip was fabricated without undesired nano-trench deformation. The integrity of the enclosed PMMA nanofluidic system was verified by a fluorescence filling experiment.     

含初应力复合材料柱壳结构的双稳态特性

为分析初应力对复合材料圆柱壳结构双稳态特性的影响,采用经典板壳理论建立复合材料圆柱壳力学模型,基于层合结构本构关系推导用双参数表达的系统应变能公式;根据最小势能原理得到双稳态产生的条件和稳态时的曲率表达式。利用Abaqus软件构建圆柱壳的有限元模型,通过附加边界弯矩对柱壳稳态跃迁过程进行模拟。理论计算结果与有限元结果的对比验证理论模型的正确性。分析结果表明：当初应力满足一定条件时,复合材料柱壳结构在其变形过程中有2个稳定平衡位置,并且在稳定平衡位置结构都不产生扭转变形;2个稳定平衡位置的曲率方向可以相同或相反,这与无初应力时反对称复合材料柱壳双稳态曲率方向只能相同的情况有区别。