Algorithmic tangent modulus at finite strains based on multiplicative decomposition简

The algorithmic tangent modulus at finite strains in current configuration plays an important role in the nonlinear finite element method. In this work, the exact tensorial forms of the algorithmic tangent modulus at finite strains are derived in the principal space and their corresponding matrix expressions are also presented. The algorithmic tangent modulus consists of two terms. The first term depends on a specific yield surface, while the second term is independent of the specific yield surface. The elastoplastic matrix in the principal space associated with the specific yield surface is derived by the logarithmic strains in terms of the local multiplicative decomposition. The Drucker-Prager yield function of elastoplastic material is used as a numerical example to verify the present algorithmic tangent modulus at finite strains.     

Nanoscale mass sensing based on vibration of single-layered graphene sheet in thermal environments简

Based on vibration analysis, single-layered graphene sheet （SLGS） with multiple attached nanoparticles is developed as nanoscale mass sensor in thermal environments. Graphene sensors are assumed to be in simplysupported configuration. Based on the nonlocal plate the- ory which incorporates size effects into the classical theory, closed-form expressions lot the frequencies and relative fre- quency shills of SLGS-based mass sensor are derived using the Galerkin method. The suggested model is justified by a good agreement between the results given by the present model and available data in literature. The effects of tem- perature difference, nonlocal parameter, the location of the nanoparticle and the number of nanoparticles on the relative frequency shift of the mass sensor are also elucidated. The obtained results show that the sensitivity of the SLGS- based mass sensor increases with increasing temperature difference.     

Flowing simulation of injection molded parts with micro-channel简

In the micro-molding of component with a micro-sized channel, the ability for polymer melt to flowing into the micro-channel in a macro-sized part is a big challenge. The multidimensional flow behaviors are included in the injection molding the macro-component with a micro-channel. In this case, a simplified model is used to analyze the flow behaviors of the macro-sized part within a micro-channel. The flow behaviors in the macro-cavity are estimated by using the finite element and finite difference methods. The influence of the injection rate, micro-channel size, heat transfer coefficient, and mold temperature on the flowing distance is investigated based on the non-isothermal analytic method. The results show that an increase in the radius of the micro-channel and mold temperature can improve effectively the flowing distance in the micro-channel.     

Vibration analysis of axisymmetric functionally graded viscothermoelastic spheres简

The present study focuses on the analysis of free vibrations of axisymmetric functionally graded hollow spheres. The material is assumed to be graded in radial di- rection with a simple power law. Matrix Frrbenious method of extended power series is employed to derive the analytical solutions for displacement, temperature, and stresses. The dispersion relations for the existence of various types of pos- sible modes of vibrations in the considered hollow sphere are derived in a compact form. In order to explore the character- istics of vibrations, the secular equations are further solved by using fixed point iteration numerical technique with the help of MATLAB software. The numerical results have been presented graphically for polymethyl methecrylate materials in respect of natural frequencies, frequency shift, inverse quality factor, displacement, temperature change, and radial stress.     

新型涡轮流量计的理论模型简

基于动量力矩定理和流体边界层理论,建立了一新型涡轮流量计的理论模型. 利用该理论模型可以分析叶轮几何参数对流量计计量性能的影响. 以一DN50 涡轮流量计为例,利用本文所建立的理论模型对该流量计的仪表系数进行了计算,并在一体积管标准装置对该流量计的仪表系数进行标定. 结果表明,计算值和实验值较为吻合,误差在±;3.5% 以内,验证了模型的有效性,从而为仪表的结构优化设计提供了理论依据.     

结构可靠性仿真方法研究简

可靠性仿真是对复杂结构系统进行可靠性分析计算最为有效的方法,引起了研究者越来越广泛的关注. 综合目前结构可靠性仿真方法研究现状,介绍了蒙特卡罗（Monte-Carlo,MC）法、极限状态方程重构法、随机有限元法（stochastic finite element method,SFEM）进行结构可靠性仿真计算的特点及发展现状,归纳了固体火箭发动机（solid rocket motor,SRM）结构可靠性的特点及当前进行仿真的方法;并在此基础上分析了目前结构可靠性仿真方法及对SRM 结构可靠性进行仿真分析计算时存在的不足及需要进一步研究的内容.     

串列风力机尾流干扰的研究简

广义致动盘方法是通过引入体积力代替叶片的致动盘技术与三维Navier-Stokes 方程相结合来获得风力机周围流场信息的一种方法. 该方法避免了花费大量网格与计算资源去求解风力机叶片的附面层,从而可以把更多的网格与计算资源用于风力机尾流流场的模拟,非常适合用于风力机尾流流场的研究. 以NH1500风力机为计算模型,将常规CFD (computational fluid dynamics) 方法与广义致动盘方法计算所得的叶片载荷分布进行比较,以验证广义致动盘方法的可行性. 然后使用广义致动盘方法对风场中串列风力机进行数值模拟,研究串列风力机之间间距变化时,上游风力机产生的尾流对下游风力机的干扰影响.     

Numerical methods for solving singular integral equations obtained by fracture mechanical analysis of cracked wedge简

The numerical solutions to the singular integral equations obtained by the fracture mechanical analyses of a cracked wedge under three different conditions are considered. The three considered conditions are: (i) a radial crack on a wedge with a non-finite radius under the traction-traction boundary condition, (ii) a radial crack on a wedge with a finite radius under the traction-traction boundary condition, and (iii) a radial crack on a finite radius wedge under the traction-displacement boundary condition. According to the boundary conditions, the extracted singular integral equations have different forms. Numerical methods are used to solve the obtained coupled singular integral equations, where the Gauss-Legendre and the Gauss-Chebyshev polynomials are used to approximate the responses of the singular integral equations. The results are presented in figures and compared with those obtained by the analytical response. The results show that the obtained Gauss-Chebyshev polynomial response is closer to the analytical response.     

Mechanical properties of double-stranded DNA biofilm with Gaussian distribution简

In microcantilever-based label-free biodetection technologies, deflection changes induced by adsorptions of double-stranded DNA （dsDNA） molecules on Au-layer surface are greatly affected by the mechanical, thermal and electrical properties of DNA biofilm. In this paper, the elastic properties of dsDNA biofilm are studied. First, the Parsegian＇s empirical potential based on a mesoscopic liq- uid crystal theory is employed to describe the interaction energy among coarse-grained DNA cylinders. Then, con- sidering a Gaussian distribution of DNA interaxial distance, the thought experiment method is used to derive an analyti- cal expression for Young＇s modulus of DNA biofilm with a stochastic packing pattern for the first time. Results show that Young＇s modulus of DNA biofilm is on the order of 10 MPa. These findings could provide a simple and effective method to evaluate the mechanical properties of soft biofilm on snbstrate.     

Determination of elastic and plastic mechanical properties of dentin based on experimental and numerical studies

The aim of this study is to investigate the change of mechanical properties of human dentin due to aging and spatial variation. Sections of coronal dentin are made from human molars in three groups: young, mid-aged, and old patients. A nanoindentation test is conducted from regions near the pulp to the dentin-enamel junction (DEJ) to evaluate the load-depth indentation response and determine Young's modulus and hardness. Based on the loading and unloading load-displacement curves in nanoindentation, a numerical model of plastic damage is used to study the plastic and the damage behaviors and the contribution to the degradation in the unloading stiffness. The experimental results show that Young's modulus of the inner dentin is significantly lower than that of outer dentin in each age group. Compared with the young dentin, the old dentin has greater hardness and Young's modulus with similar spatial variations. The magnitudes of the yield strength and the damage variable are also affected by aging and vary with spatial locations. In the same age group, the yield strength in inner dentin is lower than those in middle and outer dentin, more damage occurs with similar spatial variations, and the yield strength of young dentin is generally lower and causes more damage compared with those in both the mid-aged and old groups.     

On some topics for the numerical simulation of ductile fracture

In this work, we analyze some aspects of the macroscopic Gurson–Tvergaard–Needleman (GTN) constitutive model when it is addressed to solve ductile fracture problems by means of numerical simulations:     

Micromechanical consideration of tensile crack behavior based on virtual internal bond in contrast to cohesive stress

A modified version of the virtual internal bond model (VIB) is presented. This involves the introduction of a R-bond restricting the relative rotation freedom of pairwise mass particle. Such a modification allows the VIB model to consider arbitrary values of the Poisson ratio. A linear elastic cohesive law considering both the R-bond and L-bond are assumed. The constitutive relationship is derived using the Cauchy–Born rules. The derived constitutive associates the bond stiffness with the Young’s modulus and Poisson ratio of materials. This gives the bond stiffness in terms of the Young’s modulus and Poisson ratio of materials.The modified VIB model is then used to analyze the tensile crack behavior. In contrast to the cohesive stress method, the deformation-governed concept will be used. The local materials failure is assumed to coincide with the reduction of the bond density due to the local deformation rather than by the local cohesive stress. A phenomenological relationship between the bond density and the deformation is established. The criterion which is applied to determined crack initiation and propagation is built into the constitutive model. As an example, the method is used to study the crack initiation and propagation behavior under tensile loading.     

基于整体位移模式的平面裂纹结构数值模拟方法

对于平面裂纹问题,针对扩展有限元法和无网格伽辽金法的不足,从结构的整体位移模式出发,提出了一种新的数值模拟方法。在整个求解域内构造其试探函数,并引入裂纹修正项描述裂尖处的奇异性和裂纹面的强间断特性;同时,提出了一种新的强制边界条件施加方法,通过引入位移边界水平集函数,将位移边界条件包含在近似位移场的表达式中,有效地解决了位移边界条件问题,减小了刚度矩阵的阶数,非常方便地消除了刚度矩阵的奇异性,降低了线性方程组的求解难度。含裂纹矩形平板结构的数值算例验证了该方法的有效性。     

基于CT图像的细观混凝土模型中低应变率冲击下端部摩擦效应研究

基于微观X射线计算断层扫描（XCT）图像,采用单元替换像素的方法建立真实普通强度混凝土试件的细观有限元模型。该模型包含骨料、砂浆、界面过渡区和孔洞,并采用ABAQUS中的混凝土损伤塑性本构模型CDP来模拟各相材料。对20个基于XCT图像的细观模型进行了中低应变率（10^-5 s^-1~2 s^-1）冲击作用下的端部摩擦效应的蒙特卡洛模拟;并对模拟结果进行统计分析和曲线拟合,获得了动态抗压强度和端摩擦系数及应变率之间的定量关系式,以及无摩擦时抗压强度提高因子CDIF与应变率之间的关系式。结果表明,端摩擦能够提高混凝土的抗压强度,但当摩擦系数达到0.3后其影响不再明显;CDIF与应变率的对数（logε）呈二次抛物线关系;拟合的关系式与实验结果吻合良好。     

A study on the behaviour of high-order flux reconstruction method with different low-dissipation numerical fluxes for large eddy simulation

This work focuses on the numerical dissipation features of high-order flux reconstruction (FR) method combined with different numerical fluxes in turbulence flows. The famous Roe and AUSM+ numerical fluxes together with their corresponding low-dissipation enhanced versions (LMRoe, SLAU2) and higher resolution variants (HR-LMRoe, HR-SLAU2) are incorporated into FR framework, and the dissipation interplay of these combinations is investigated in implicit large eddy simulation. The numerical dissipation stemming from these convective numerical fluxes is quantified by simulating the inviscid Gresho vortex, the transitional Taylor–Green vortex and the homogenous decaying isotropic turbulence. The results suggest that low-dissipation enhanced versions are preferential both in high-order and low-order cases to their original forms, while the use of HR-SLAU2 has marginal improvements and the HR-LMRoe leads to degenerated solution with high-order. In high-order the effects of numerical fluxes are reduced, and their viscosity may not be dissipative enough to provide physically consistent turbulence when under-resolved.