HEMORRHEOLOGY, VISCO-ELASTICITY AND THIXOTROPY IN CEREBRAL THROMBOSIS

In this study, we used blood rheometer type HT-I to determine blood viscosity, plasma viscosity, hematocrit, blood red cell visco-elasticity and thixotropy in 70 cases with cerebral thrombosis, compared with normal control group in order to study the relationship between their alteration and cerebral thrombosis blood and plasma viscosity were higher in the patients than in normal control. Hysteresis loop analysis showed that the red blood cell’s visco-elasticity, thixotropy and deformity decrease.

Parameter Characterisation of Asphalt Mixtures for Visco-Elastoplastic Analysis

Asphalt mixtures exhibit strong viscous properties under repetitive loads. This phenomenon can be simulated in creep and recovery tests. By applying the visco elastoplastic model proposed, data recorded in the tests are interpreted. It is emphasised that applicability of the visco elastoplastic model depends on the proper method of characterising parameters involved in the constitutive equations. Since two or more strain components of elasticity and viscosity coexist during the loading or unloading, a measuring system of two loggers is introduced to decouple these components. Test data are analysed in three steps as elastic, visco elastic and visco plastic evaluations, using the records collected at the moment of unloading, during the periods of recovery and creep respectively. Factors that may influence the accuracy of data analysis are also discussed.

Heat and Mass Transfer in MHD Visco-Elastic Fluid Flow through a Porous Medium over a Stretching Sheet with Chemical Reaction

This paper presents the study of convective heat and mass transfer characteristics of an incompressible MHD visco-elastic fluid flow immersed in a porous medium over a stretching sheet with chemical reaction and thermal stratification effects. The resultant governing boundary layer equations are highly non-linear and coupled form of partial differential equations, and they have been solved by using fourth order Runge-Kutta integration scheme with Newton Raphson shooting method. Numerical computations are carried out for the non-dimensional physical parameters. Here a numerical has been carried out to study the effect of different physical parameters such as visco-elasticity, permeability of the porous medium, magnetic field, Grashof number, Schmidt number, heat source parameter and chemical reaction parameter on the flow, heat and mass transfer characteristics.

Vibration of Visco-Elastic Parallelogram Plate with Parabolic Thickness Variation

The main objective of the present investigation is to study the vibration of visco-elastic parallelogram plate whose thickness varies parabolically. It is assumed that the plate is clamped on all the four edges and that the thickness varies parabolically in one direction i.e. along length of the plate. Rayleigh-Ritz technique has been used to determine the frequency equation. A two terms deflection function has been used as a solution. For visco-elastic, the basic elastic and viscous elements are combined. We have taken Kelvin model for visco-elasticity that is the combination of the elastic and viscous elements in parallel. Here the elastic element means the spring and the viscous element means the dashpot. The assumption of small deflection and linear visco-elastic properties of “Kelvin” type are taken. We have calculated time period and deflection at various points for different values of skew angles, aspect ratio and taper constant, for the first two modes of vibration. Results are supported by tables. Alloy “Duralumin” is considered for all the material constants used in numerical

ONE-DIMENSIONAL CONSOLIDATION OF LAYERED AND VISCO-ELASTIC SOILS UNDER ARBITRARY LOADING

Based on the layered visco-elastic soil model, according to the Terzaghi's one dimensional consolidation theory, by the method of Laplace transform and matrix transfer technique, the problems about the consolidation of layered and saturated visco-elastic soils under arbitrary loading were solved. Through deductions, the general solution, in the terms of layer thickness, the modulus and the coefficients of permeability and Laplacian transform's parameters was obtained. The strain and deformation of the layered and saturated visco-elastic soils under arbitrary loading can be calculated by Laplace inversion. According to the results of several numerical examples, the consolidation of visco-elastic soils logs behind that of elastic soils. The development of effective stress and the displacement is vibrant process under cyclic loading. Finally, an engineering case is studied and the results prove that the methods are very effective.

Effect of Non-Homogeneity on Thermally Induced Vibration of Orthotropic Visco-Elastic Rectangular Plate of Linearly Varying Thickness

The analysis presented here is to study the effect of non-homogeneity on thermally induced vibration of orthotropic visco-elastic rectangular plate of linearly varying thickness. Thermal vibrational behavior of non-homogeneous rectangular plates of variable thickness having clamped boundary conditions on all the four edges is studied. For non–homogeneity of the plate material, density is assumed to vary linearly in one direction. Using the method of separation of variables, the governing differential equation is solved. An approximate but quite convenient frequency equation is derived by using Rayleigh-Ritz technique with a two-term deflection function. Time period and deflection at different points for the first two modes of vibration are calculated for various values of temperature gradients, non- homogeneity constant, taper constant and aspect ratio. Comparison studies have been carried out with non-homogeneous visco-elastic rectangular plate to establish the accuracy and versatility.

Settlement Analysis for An Embankment Considering Visco-Elasto-Plastic Characteristics

In the paper. a visco-elasto plastic constitutive model and a method for determining model parameters for soft clay are presented. In this model total strain of soft clay is assumed to be divided into three parts: instantaneous elastic, visco-elastic and visco-plastic. The characteristics of instantaneous and visco-elastic deformation of soft clay are simulated by Merchant's model, the plastic is by a model with two yield surfaces. And related constitutive equation is conducted. A number of stress-controlled triaxial tests are performed to calculated the model parameters. The visco-elasto-plastic model is used for analysis of the displacement of an embankment on soft ground by use of three-dimensional finite element method. The predicted settlements agree well with the measured data. It is indicated that the viscous characteristics should be taken into account in deformation analysis for soft clay.

Advances in structural vibration control application of magneto-rheological visco-elastomer

Magneto-rheological visco-elastomer （MRVE） as a new smart material developed in recent years has several significant advantages over magneto-rheological liquid. The adjustability of structural dynamics to random environmental excitations is required in vibration control. MRVE can supply considerably adjustable damping and stiffness for structures, and the adjustment of dynamic properties is achieved only by applied magnetic fields with changeless structure design. Increasing researches on MRVE dy- namic properties, modeling, and vibration control application are presented. Recent advances in MRVE dynamic properties and structural vibration control application including composite structural vibration mitigation under uniform magnetic fields, vibration response characteristics improvement through harmonic parameter distribution, and optimal bounded parametric control design based on the dynamical programming principle are reviewed. Relevant main methods and results introduced are beneficial to understanding and researches on MRVE application and development.

Visco-elastic fluid flow past an infinite vertical porous plate in the presence of first-order chemical reaction

An analysis has been developed to study the unsteady free convection flow of an incompressible visco-elastic fluid on a continuously moving vertical porous plate in the presence of a first-order chemical reaction. The governing equations are solved numerically using an implicit finite difference technique. The obtained numerical solutions are compared with the analytical solutions. The velocity profiles are presented. A parametric analysis is performed to illustrate the influences of the visco-elastic parameter, the dimensionless chemical reaction parameter, and the plate moving velocity on the steady state velocity profiles, the time dependent friction coefficient, the Nusselt number, and the Sherwood number.

THE POINTWISE ESTIMATES TO SOLUTIONS FOR 1-DIMENSIONAL LINEAR THERMO-VISCO-ELASTIC SYSTEM

In this paper, we study the linear thermo-visco-elastic system in one-dimensional space variable. The mathematical model is a hyperbolic-parabolic partial differential system. The solutions of the system show some decay property due to the parabolicity. Based on detailed analysis on the Green function of the system, the pointwise estimates of the solutions are obtained, from which the generalized Huygens’ principle is shown.

Rayleigh-type wave propagation in incompressible visco-elastic media under initial stress

Propagation of Rayleigh-type surface waves in an incompressible visco-elastic material over incompressible visco-elastic semi-infinite media under the effect of initial stresses is discussed. The dispersion equation is determined to study the effect of differ- ent types of parameters such as inhomogeneity, initial stress, wave number, phase velocity, damping factor, visco-elasticity, and incompressibility on the Rayleigh-type wave prop- agation. It is found that the affecting parameters have a significant effect on the wave propagation. Cardano＇s and Ferrari＇s methods are deployed to estimate the roots of dif- ferential equations associated with layer and semi-infinite media. The MATHEMATICA software is applied to explicate the effect of these parameters graphically.

Thermal Effect on Free Vibration of Non-Homogeneous Orthotropic Visco-Elastic Rectangular Plate of Parabolically Varying Thickness

A simple model presented here is to study the thermal effect on vibration of non-homogeneous orthotropic visco-elastic rectangular plate of parabolically varying thickness having clamped boundary conditions on all the four edges. For non-homogeneity of the plate material, density is assumed to vary linearly in one direction. Using the separation of variables method, the governing differential equation has been solved for vibration of non-homogeneous orthotropic viscoelastic rectangular plate. An approximate frequency equation is derived by using Rayleigh-Ritz technique with a two-term deflection function. Results are calculated for time period and deflection at different points, for the first two modes of vibration, for various values of temperature gradients, non-homogeneity constant, taper constant and aspect ratio and shown by graphs.

The Equilibrium of Fractional Derivative and Second Derivative: The Mechanics of a Power-Law Visco-Elastic Solid

This paper investigates the equilibrium of fractional derivative and 2nd derivative, which occurs if the original function is damped (damping of a power-law viscoelastic solid with viscosities η of 0 ≤ η ≤ 1), where the fractional derivative corresponds to a force applied to the solid (e.g. an impact force), and the second derivative corresponds to acceleration of the solid’s centre of mass, and therefore to the inertial force. Consequently, the equilibrium satisfies the principle of the force equilibrium. Further-more, the paper provides a new definition of under- and overdamping that is not exclusively disjunctive, i.e. not either under- or over-damped as in a linear Voigt model, but rather exhibits damping phases co-existing consecutively as time progresses, separated not by critical damping, but rather by a transition phase. The three damping phases of a power-law viscoelastic solid—underdamping, transition and overdamping—are characterized by: underdamping—centre of mass oscillation about zero line;transition—centre of mass reciprocation without crossing the zero line;overdamping—power decay. The innovation of this new definition is critical for designing non-linear visco-elastic power-law dampers and fine-tuning the ratio of under- and overdamping, considering that three phases—underdamping, transition, and overdamping—co-exist consecutively if 0 < η < 0.401;two phases—transition and overdamping—co-exist consecutively if 0.401 < η < 0.578;and one phase— overdamping—exists exclusively if 0.578 < η < 1.

Heat and Mass Transfer in Visco-Elastic Fluid through Rotating Porous Channel with Hall Effect

This paper examined the hydromagnetic boundary layer flow of viscoelastic fluid with heat and mass transfer in a vertical channel with rotation and Hall current. A constant suction and injection is applied to the plates. A strong magnetic field is applied in the direction normal to the plates. The entire system rotates with uniform angular velocity (Ω), about the axis perpendicular to the plates. The governing equations are solved by perturbation technique to obtain an analytical result for velocity, temperature, concentration distributions and results are presented graphically for various values of viscoelastic parameter (K2), Prandtl number (Pr), Schmidt number (Sc), radiation parameter (R), heat generation parameter (Qh) and Hall parameter (m).

基于任务驱动的多糖制备工艺对其黏弹性影响综合实验教学设计

基于科教融合和成果导向(OBE)教育理念,将生化领域的前沿科技成果转化为教学实验,培养学生的科研创新素质。引入科研项目“多糖的制备工艺对其黏弹性能的影响”并贯穿教学全过程,引导学生查阅文献并讨论“耐温耐盐、环境友好新型驱油剂开发”的热点问题,拓宽学生的学术视野,培养学生文献查阅能力;鼓励学生根据自己的知识体系设计个性化实验方案,培养学生分析问题、解决问题的能力;指导学生探究利用盐醇析法和Sevage法制备多糖的工艺并计算其得率,采用红外和紫外光谱对样品进行表征,探究不同制备工艺对黏弹性及驱替效果的影响,帮助学生搭建“生物—化工—能源”多学科知识体系,提升实践创新能力;开展数据分析、方案评价和成果路演,锻炼学生的科研探究能力。

具有细晶/混晶交替分布组织特征的AZ31镁合金轧板拉伸变形行为仿真

通过中等应变速率轧制获取细晶区和混晶区交替分布的AZ31镁合金轧制板材,构建不同组织特征的黏塑性自洽(VPSC)模型,预测板材在室温拉伸下的变形机制、织构演变和力学响应,研究细晶区与混晶区对塑性变形的贡献。结果表明:经410℃、平均应变速率1.9 s^(-1)、4.8 s^(-1)和7.8 s^(-1)制备的轧制板材中细晶区与混晶区呈现板织构特征,细晶区织构组分相较于混晶区更接近ND方向;随着轧制平均应变速率的增加,板材的细晶区与混晶区的织构组分差异逐渐减小。在室温拉伸塑性变形初期阶段,轧制板材的主要变形机制是基面滑移,次要变形机制是棱柱面滑移和锥面滑移,而拉伸孪生几乎不开启。压缩孪生启动时,部分晶粒向TD方向偏转56°,形成TD方向的织构组分。棱柱面滑移活性的降低,有利于增强锥面滑移的分离效应,促使ND方向织构极密度降低和双峰织构形成。轧制板材在拉伸过程中,由于细晶区的织构组分相较于混晶区更接近ND方向,使得在拉伸过程中细晶区相较于混晶区的基面滑移开启较少,非基面滑移开启较多,促使拉伸变形的过程中细晶区起强化作用,混晶区起弱化作用。织构组分差异逐渐减小,使得细晶区与混晶区的变形机制活性趋于一致,促使其在拉伸过程中对抗拉强度贡献也逐渐趋于一致。

基于Visco-SCRAM模型的侵彻装药点火研究

针对弹体侵彻过程中装药的安全性,基于黏弹性统计裂纹力学(visco-statistical crack mechanics,Visco-SCRAM)模型计算装药整体温升、装药裂纹摩擦生热以及弹体装药与壳体摩擦生热,考察这3种机制对装药温升的贡献以及侵彻装药的点火机制,得到了装药点火对应的弹体侵彻临界初始速度。结果表明:(1)装药与弹体内壁摩擦生热对装药温升有一定贡献,随着弹体初始撞击速度的提高,摩擦生热对温升的贡献逐渐增大;(2)黏性、损伤和绝热体积变化导致的装药整体温升对装药点火的作用有限;(3)裂纹摩擦形成热点是侵彻装药点火的物理机制;(4)采用Visco-SCRAM模型可预测低强度、长脉冲载荷作用下的装药点火响应。

两类混凝土动力黏损伤本构模型比较研究

在混凝土弹塑性损伤理论框架下,为反映材料力学行为的率相关性,对静力损伤演化进行了动力扩展。混凝土在动力加载下的损伤演化滞后于静力加载而引起强化现象,借鉴黏塑性理论,在损伤子空间建立了两类格式的动力黏损伤演化模型:Perzyna模型和Duvaut-Lions模型。分别从本构理论和数值计算结果上对两类黏损伤演化模型进行了对比研究。从理论上来看,两类模型具有不同的黏性化变量;从模拟结果上来看,两类格式的线性黏损伤模型的计算结果基本重合,而两类非线性的黏损伤模型得到的结果存在差异。另外,两类非线性的黏损伤模型预测的混凝土动力强度的提高与试验数据吻合较好,说明均可反映混凝土材料的率相关性。

基于P波斜入射海相软土区螺旋桩动力响应分析

在地震频发地区,越来越多建筑使用螺旋桩作为基础,此桩型具有良好的抗震能力。通过建立三维有限元模型,基于黏弹性人工边界,把地震作用等效为边界结点上的作用力。该研究考虑动静边界转换的影响,最后建立了具有黏弹性边界的螺旋桩-土体三维模型。探讨了处于海相软土场地下,不同种类地震波、地震强度、入射角度和螺旋叶片个数对螺旋桩轴力、弯矩和动力p-y曲线的影响。结果表明,相比较于弯矩,入射角度对轴力和动力p-y曲线的影响较大。除此之外,地震强度对弯矩的影响较大,而地震波频率和螺旋叶片个数对其影响较小。不同地面峰值加速度(0.05g,0.10g,0.30g)时,随着入射角度的改变,螺旋桩受到最大和最小弯矩的差值从144.1 N·m增加到了891 N·m。通过该研究结论,不仅可以得出软土场地下螺旋桩-土体的相互作用关系,也能为螺旋桩抗震设计提供依据。

应用保辛Stereo-modeling方法的振幅补偿逆时偏移成像

地震波数值模拟的精度很大程度上决定了逆时偏移结果的分辨率,文中采用保辛近似解析离散化方法,在Birkhoffian系统下求解黏滞声波方程,并进行振幅补偿的逆时偏移(RTM)。首先,将黏滞声波方程构造成一个Birkhoffian系统,对于该系统采用二阶保辛Runge-Kutta法进行时间推进,分别采用Stereo-modeling法(STEM)和传统有限差分法进行空间算子离散,相应得到SSM(Symplectic Stereo-modeling Method)和CSM(Conventional Symplectic Method)两种方法。之后,对SSM和CSM进行一系列数值性质分析,包括数值频散分析、与解析解比较、效率对比、稳定性测试等。结果显示,SSM的最大数值频散误差约为9%,而CSM约为26%;SSM的计算效率高且长时计算稳定,计算效率约为CSM的两倍。最后,应用三个模型进行了正演数值模拟和逆时偏移试验。对于衰减数据,与声波RTM相比,黏滞声波RTM成像振幅更高,能获得与无衰减数据声波RTM相近的成像振幅。对于油气藏模型,SSM比CSM的成像精度更高、数值频散更小。