衬砌与土相互作用的圆形隧洞分数阶热弹性动力响应

衬砌作为地下工程的重要支护结构,常受到一些苛刻环境的作用,例如高温和冲击。考虑衬砌结构与土的动力相互作用,研究了圆形隧洞衬砌-土系统在热源和力源共同作用下的瞬态热弹性动力响应。基于分数阶热弹性理论,采用Laplace变换和微分算子分解法得到了土体的温度增量、位移、应力的解析表达式。将衬砌结构视为均匀弹性介质,得到了衬砌的温度增量、位移、应力解析解。利用衬砌内边界及衬砌与土体界面处连续性条件,在Laplace变换域内给出了深埋圆形隧洞衬砌-土系统的热弹性动力响应解答。采用Laplace逆变换Crump数值反演方法,得到了时域内衬砌-土系统热弹性响应的数值解。结果表明:随着分数阶参数?的增加,径向位移、径向应力逐渐增大,而其对环向应力的影响较小。在突加荷载和阶跃荷载作用下,随着分数阶参数?的增加,温度增量逐渐增大。     

横向冲击作用下高桥墩的几何非线性动力稳定性

考虑大变形的影响,建立了高桥墩在横向冲击荷载作用下的非线性动力学基本方程式;通过位移形函数假设,采用伽辽金积分方法得到了时间变率的动力学控制方程;对时间变率的非线性微分方程进行数值求解,给出了不同冲击荷载作用下不同柔度高桥墩的位移响应曲线以及其从产生横向振动到失稳的全过程,得到了横向冲击时高桥墩失稳的临界冲击荷载和失稳时刻;通过数值算例比较了三角形和矩形冲击荷载作用下高桥墩的荷载-位移响应曲线;分析了横向冲击力幅值、冲击区域大小、冲击持续时间、高桥墩柔度、桥面质量大小对位移幅值响应曲线、临界冲击荷载、失稳时刻的影响。结果表明:无论是在矩形还是三角形形式横向冲击作用下,随着冲击区域的增大高桥墩的振动幅值变大;桥面简化质量越大,高桥墩失稳的临界冲击载荷越小;柔度越大时,高桥墩失稳的临界冲击荷载幅值越小;对于矩形冲击,当冲击持续时间大于1s后,冲击持续时间的增加对高桥墩的稳定性无明显影响;对于三角形冲击荷载,随着冲击持续时间的增大高桥墩的振动幅值变大。     

双层扁平绕带式压力容器的刚塑性动力响应分析

采用刚塑性模型对双层长扁平绕带式压力容器受径向矩形脉冲内压作用的动力响应进行了分析,给出了结构在中载和高载作用下的变形模态、极限压力、响应时间和残余位移的表达式。计算结果表明,该种容器的静态极限压力值低于整体式压力容器的相应值;绕带层残余位移远大于其内壳和整体式压力容器的残余位移;当所受高载小于24.5 MPa时比整体式压力容器具有更强的抗冲击能力。     

风沙冲击作用下涂层与基体界面应力、位移及破坏机理研究

应用界面力学镜像点法及断裂力学理论分析了风沙冲击作用下钢结构表面涂层与基体的界面问题。分析结果表明:冲击角度一定时,界面应力随着冲击速度的增大而增大;冲击速度一定时,界面正应力在冲击点附近较大,在冲击角度为45°时最大;界面切应力在冲击角度为30°时达到最大;冲击角度一定时界面位移随着冲击速度的增大而增大,界面水平位移在冲击角度为30°时最大,冲击速度一定时界面垂直位移随着冲击角度的增大而增大。界面破坏机理是因为界面存在应力集中现象,易发生破坏,切向破坏较为严重。     

物性与温度相关材料广义热弹性模型及渐近分析

计及材料物性与温度的相关性,基于Clausius不等式和L-S广义热弹性理论,通过对自由能公式的高阶展开,构建了具有变物性特征的广义耦合热弹性动力学模型.推导了各向同性材料表面受热冲击问题的线性化控制方程组,利用热冲击的瞬时特征,借助于Laplace正、逆变换技术及其极限性质,给出了变物性条件下一维热冲击问题的温度场、位移场和应力场的渐近表达式.通过算例,得到了热冲击作用下各物理场的分布规律以及材料物性与温度相关性对于热弹性响应的影响规律.结果表明:材料物性与温度相关性对于各物理场的阶跃位置、阶跃间隔以及阶跃峰值均产生不同程度地影响,相比于位移场和应力场的显著影响,其对温度场的影响效果并不明显.     

钢骨混凝土构件抗冲击性能试验研究

利用超重型落锤试验机对钢骨混凝土构件进行了侧向冲击试验,研究了落锤冲击钢骨混凝土构件的冲击全过程和最终的破坏形态;分析了钢骨混凝土构件冲击力、位移和轴力时程曲线的特性;对比了不同冲击速度、冲击能量、轴压和边界条件等因素对钢骨混凝土构件的动力响应的影响。结果表明:钢骨混凝土构件在落锤冲击作用下外侧混凝土破坏严重,且冲击能量越大,外侧混凝土越易出现剪切破坏,但内部钢筋和钢骨只发生了一定的弯曲变形,表明钢骨混凝土构件抗冲击性能整体良好。本次试验参数范围内,钢骨混凝土构件的冲击力和跨中位移随冲击速度增加而增大;轴压力增大使钢骨混凝土构件的冲力峰值增大,冲击持时和跨中位移减小;相对于固简支和两端简支的边界条件,两端固支的边界对于钢骨混凝土构件的抗冲击性能提升最好。     

轴向冲击下C型冷弯卷边槽钢构件的动力响应

针对轴向冲击载荷下C型冷弯薄壁钢构件的动力响应,采用商业有限元软件Abaqus建立了能够反映冲击过程的有限元模型。通过对比有限元模拟和落锤实验中利用数字散斑技术采集的数据以及试样残余变形,验证了数值模型的可靠性。采用该模型分析了在不同冲击速度下翼缘、腹板和卷边质点的轴向位移-时间曲线以及腹板横向挠度的变化,结果表明:在较低冲击能量的作用下,翼缘对卷边的约束作用明显;而在较高冲击能量的加载过程中,冲击端卷边的轴向位移和速度明显大于翼缘和腹板,卷边破坏严重;随着冲击速度的提升,C型冷弯薄壁钢构件的动态屈曲临界载荷相应提升。     

血管的位移波——脉象新释

本文根据赵润屋的超声波实验结果提出血管的整体忙位移是脉象的新的科学解释。假设挠动脉切脉处的血管是一个在非对称载荷作用下的弹性简支梁,文章导出了位移函数的分折表达式及力学和生理参数对位移波的影响,并将它和压力波进行了比较.结果表明,位移波和压力波具有相似的波形,但具体数值不同。     

瞬态热冲击下层合材料板界面的热弹性行为

基于带有两个热松弛时间的G-L广义热弹性理论, 利用有限元方法研究了零阻抗理想界面层合板在瞬态热冲击诱导的位移、应力和温度等通过界面时的热弹性行为. 通过比较不同层中材料的比热容、热导系数、热松弛时间和密度等对界面处的位移、应力和温度的影响, 研究了不同材料参数对复合材料热力学行为影响, 发现不同材料参数将导致热穿过界面时界面处温度、位移和应力发生突变, 研究结果可以为由热引起的层合板挠曲变形提供理论依据.      

齿轮系统传动轴受横向冲击的响应分析

将齿轮传动系统的齿轮轴承简化为具有集中质量的固支梁,将齿轮受到啮合齿轮的意外撞击看成是质量块对梁的冲击。给出弯扭组合的Mises屈服条件,指出传动轴受冲击时不能忽略扭矩作用。分析了弯曲和扭转作用下的结构响应,进行了应变率修正,给出特殊情况下弯扭响应的简化分析。算例表明,弯扭冲击下传动轴的横向位移和扭转角都较大,不可忽略应变率效应;传动轴直径是影响横向位移的重要因素。     

黏弹性准饱和土中球空腔动力特性

在频率域内研究了内水压力作用下分数导数型黏弹性准饱和土中球空腔的稳态动力响应. 通 过引入与孔隙率有关的应力系数合理地确定了介质和孔隙水共同承担的内水压力值. 将土骨 架和衬砌分别视为具有分数导数本构模型的黏弹性体和多孔柔性材料, 基于Biot两相介质模 型, 通过引入位移势函数解耦得到了内水压力作用下分数导数型黏弹性准饱和土中半封闭球 形空腔的位移、应力和孔隙水压力解析表达式. 考察了物性和几何各参数对球形空腔动力响 应的影响, 结果表明: 分数导数本构模型更合理地描述了土体的动力学行为; 饱和度对应力 和孔隙水压力影响较大, 而对位移影响较小.     

Heat transfer in supersonic flow over a single spherical cavity

The flow and heat transfer on a plate with a single spherical cavity has been experimentally investigated for M=4 and Re_,L=3.1 · 10⁶. The flow pattern over the cavity has been obtained. Zones of enhanced heat transfer have been detected, and the heat transfer coefficients in and near the cavity have been determined. It has been established that a single spherical cavity has almost no effect on the integral heat flux.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 48–52, September–October, 1991.The authors are grateful to V. N. Brazhko for assistance in carrying out the experiments and to T. A. Ershova for assistance in analyzing the results.     

Dependence of modulus of elasticity and thermal conductivity on reference temperature in generalized thermoelasticity for an infinite material with a spherical cavity

Introduction Thetheoryofgeneralizedthermoelasticitywithonerelaxationtimebasedonamodified Fourier’slawofheatconductionwasdevelopedbyLordandShulman[1].Thistheoryallowsfor theso_calledsecond_soundeffectsinsolids,hencethermaldisturbancespropagatewithfinite wavespeeds. Themathematicalmodelofthegeneralizedthermoelasticitytheoryisofacomplicatednature thathindersthepossibilityofderivingananalyticalsolution.Mostattemptsdealingwiththese equationsarebasedoneithershort_timesolution[2-4]. Modernstructur…     

Singular integral transforms for heat transfer problems in semi-infinite solids with coatings

This paper is devoted to singular integral transform method for non-stationary one-dimensional heat transfer problems in semi-infinite solids. Different geometries (semi-space, cylindrical channel and spherical cavity) are studied, and resulting temperature fields are compared. Special attention is given to multi-layer surfacing of solid as a means of heat defense. Kernel splitting method for these problems with non-stationary heat exchange conditions on free boundary is developed.     

SOLUTIONS FOR CYLINDRICAL CAVITY IN SATURATED THERMOPOROELASTIC MEDIUM

Based on the thermodynamics of irreversible processes, the mass conservation equation and heat energy balance equation are established. The governing equations of thermal consolidation for homogeneous isotropic materials are presented, accounting for the coupling effects of the temperature, stress and displacement fields. The case of a saturated medium with a long cylindrical cavity subjected to a variable thermal loading and a variable hydrostatic pressure （or a variable radial water flux） with time is considered. The analytical solutions are derived in the Laplace transform space. Then, the time domain solutions are obtained by a numerical inversion scheme. The results of a typical example indicate that thermodynamically coupled effects have considerable influences on thermal responses.     

Scattering of a pulsed Rayleigh wave by a spherical cavity in an elastic half space

The time-dependent scattering by a spherical cavity in an elastic half space is considered. The incoming wave is a pulsed Rayleigh wave. The stationary part of the problem is solved by the T-matrix method, and an integration in frequency is performed with a modified gaussian weight function. The displacement components at some points on the surface of the half space are computed and shown in a number of plots.     

Magneto-thermoelasticity for an infinite body with a spherical cavity and variable material properties without energy dissipation

The model of generalized thermoelasticity proposed by Green and Naghdi, is applied to study the electromagneto–thermoelastic interactions in an infinite perfectly conducting body with a spherical cavity. The modulus of elasticity are taking as linear function of temperature. By means of the Laplace transform and Laplace inversion, the problem is solved. The closed form solutions for displacement, temperature, and thermal stresses are represented graphically. A comparison is made with the results in the case of temperature-independent.     

热冲击载荷作用下的含球形空腔的广义热弹性功能梯度球形各向同性体

This paper is concerned with the determination of thermoelastic displacement, stress and temperature in a functionally graded spherically isotropic infinite elastic medium having a spherical cavity, in the context of the linear theory of generalized thermoelasticity with two relaxation time parameters （Green and Lindsay theory）. The surface of cavity is stress-free and is subjected to a time-dependent thermal shock. The basic equations have been written in the form of a vector-matrix differential equation in the Laplace transform domain, which is then solved by an eigenvalue approach. Numerical inversion of the transforms is carried out using the Bellman method. Displacement, stress and temperature are computed and presented graphically. It is found that variation in the thermo-physical properties of a material strongly influences the response to loading. A comparative study with a corresponding homogeneous material is also made.     

Generalized thermoelastic infinite transversely isotropic body with a cylindrical cavity due to moving heat source and harmonically varying heat

In this paper, the induced temperature, displacement, and stress fields in an infinite transversely isotropic unbounded medium with cylindrical cavity due to a moving heat source and harmonically varying heat are investigated. This problem is solved in the context of the linear theory of generalized thermoelasticity with dual phase lag model. The governing equations are expressed in Laplace transform domain. Based on Fourier series expansion technique the inversion of Laplace transform is done numerically. The numerical estimates of the displacement, temperature and stress are obtained and presented graphically. The theories of coupled thermoelasticity, generalized thermoelasticity with one relaxation time, and thermoelasticity without energy dissipation can extracted as special cases. Some comparisons have been shown in figures to present the effect of the heat source, dual phase lags parameters and the angular frequency of thermal vibration on all the studied fields.     

Thermoelastic interactions without energy dissipation in an unbounded body with a spherical cavity subjected to harmonically varying temperature

The present work is concerned with the thermally induced vibration in a homogeneous and isotropic unbounded body with a spherical cavity. The Green and Nagdhi model of thermoelasticity without energy dissipation is employed. The closed form solutions for distributions of displacement, temperature and stresses are obtained. The solutions valid in the case of small frequency are deduced and the results are compared with the corresponding results obtained in other generalized thermoelasticity theories. Numerical results applicable to a copper-like material are also presented graphically and the nature of variations of the physical quantities with radial coordinate and with frequency of vibration is analyzed.