振动摩擦机理及其非线性动力学特性

本文揭示了振动工况下散体物料的振动摩擦机理,给出了振动参数与土壤内摩擦力的关系曲线,并用数值试验方法模拟了复杂的振动摩擦压实过程,分别给出了振频和振幅对土壤孔隙比和轴向应力均值的关系曲线,验证了振动压实减摩机理的正确性.结果表明:松散物料在振动工况下,其颗粒间的摩擦力由静摩擦力转变为动摩擦力,随着振频和振幅的增加,摩擦阻力减小,从而土的内摩擦力减小,并且存在最优的振动强度使土壤在振动压实过程中的内摩擦力最小.建立了基于振动压路机的振动摩擦系统非线性动力学模型,利用渐进法得到了振动压实过程的共振响应和非共振响应.     

混沌振动压实动力学的仿真研究—（Ⅱ）压实性能

影响振压路机压实性的参数－压实参数,主要有：振动轮振幅Ａ、激振频率Ｗ,激振力Ｆｅ,力的传递比Ｒｒ（土壤受力Ｆｓ与激振力Ｆｅ之比）。本文通过对“混沌”与“普通”振动压路机压实参数的对比,来比较“混沌”与“普通”振动压路机的压实性能。结果表明：“混沌”振动压路机的压实优性能优于“普通”振动压路机。     

混沌振动压实动力学的仿真研究——（Ⅱ）压实性能

影响振动压路机压实性能的参数——压实参数，主要有：振动轮振幅A、激振频率ω、激振力Fs、力的传递比Rp(土壤受力Fs与激振力Fs之比)．本文通过对“混沌”与“普通”振动压路机压实参数的对比，来比较“混沌”与“普通”振动压路机的压实性能．结果表明：“混沌”振动压路机的压实优性能优于“普通”振动压路机．     

颗粒物质对风积沙压实特性影响研究

本文从颗粒物质的角度探讨了风积沙的压实特性和机理。研究表明,风积沙的重型击实试验曲线呈"双驼峰"形式,表明风积沙具有干压实的特性,水在风积沙的压实过程中扮演着不同的作用|室内振动试验表明振动加速度及振动时间影响着风积沙"巴西坚果效应"与"反巴西坚果效应"之间的转化,从而影响风积沙的振实密度,二者均存在一个产生最大振实干密度的最优值。现场试验通过控制机械参数(振幅A=0.4mm,频率f=48Hz)在压实5遍的时候,可使压实度达到96.8%,CBR值达到25.3,均能满足《公路路基设计规范》要求。     

复杂板-腔系统声振耦合机理分析

以敷设多层粘弹性层的复杂弹性板-声腔声振耦合模型为研究对象,结合多层介质声阻抗方法及波数扩展,采用模态展开法推导出点激励作用下耦合系统振动和声场形式解,通过数值计算探索了弹性板参数和粘弹性层参数对弹性板振动和腔内声场的影响规律,并进一步分析了粘弹性层的抑振降噪效果。结果表明:改变弹性板参数对结构振动影响较大;粘弹性层参数对振动和声场影响较显著,其抑振降噪效果主要集中在1000Hz以上中高频段。     

SMA纤维复合材料梁振动半主动控制

分析了一类形状记忆合金(SMA)纤维混杂层合粱用于振动控制的动力学模型和作用机理．采用多胞模型、形状记忆合金一维本构关系分析方法，同时考虑横向剪切的影响，建立了层合梁的数学模型．半主动控制是通过改变受控结构的参数来减小结构振动的响应．根据开关控制原理确定可变刚度系统的控制律，进行SMA纤维混杂层合粱的半主动控制的数值仿真．结果表明，将半主动控制应用于梁的振动控制是一种有效的方法．     

振动压路机的滑膜控制研究

振动压实中的跳振现象在压实过程中时有发生,跳振现象将造成路基压实质量难以保证,也会对振动压路机操作人员的身心健康产生不利影响。因此,本文从控制“振动压路机-土”系统动力学模型的减振系统阻尼力的角度进行分析,通过研究模糊PID控制和滑模控制对振动控制产生的影响,得到相较于模糊比例积分微分（proportional integral differential,PID）控制,滑模控制可消除系统抖振的影响,更有利于保证路基压实过程中的振动控制,为振动压实的施工作业提供理论支持。

     

CCL非线性平衡吸附条件下填埋场渗滤液运移过程数值分析

采用Langmuir等温吸附方程表示黏土对渗滤液中某种污染物的非线性吸附,依据污染物在多孔介质中运移机理,建立了渗滤液在饱和多孔介质运移的一维数学模型。在考虑填埋场采用压实黏土衬里防渗层、垃圾生物降解生成污染物的特性、在填埋场下含有一定厚度含水层等实际情况下,采用有限差分法求解控制方程。通过参数对比计算与分析表明,与线性吸附相比,非线性吸附使得污染物的穿透能力增强,污染物浓度随时间变化曲线尖锐而狭窄、峰值浓度出现时间提前、曲线有尾部拖长现象。组合参数Sl对污染物运移影响较大,当Sl取值较大时,可降低污染物浓度,"挫峰"能力增强,污染物浓度随时间变化曲线表现出线性吸附性质。参数K1对污染物运移影响较参数Sl小。压实黏土衬里的渗透系数较低时,弥散控制污染物运移,且弥散系数较大和较小时,穿透曲线分别表现出线性吸附性质和非线性性质。     

含水率梯度作用下填埋场压实黏土层开裂特性试验与机理分析

为探究压实黏土防渗层干缩开裂的力学机制,开展了压实黏土层含水率梯度变化与干缩裂隙演化规律试验研究,并构建了含水率梯度作用下压实黏土层开裂分析模型,研究结果表明:蒸发过程中,压实黏土层失水率随深度指数递减,高液限黏土含水率梯度明显高于低液限黏土.压实黏土层表层拉应力随含水率梯度的增加而增加.蒸发过程中,低液限压实黏土层含...     

基于局部移动Kriging无网格方法的层合板自由振动分析

利用基于局部移动Kriging插值无网格法对层合板自由振动进行了数值分析,基于一阶剪切层合理论导出了层合板振动的控制方程和边界条件,进一步得到了自由振动的离散化特征方程。由于Kriging插值函数具有Kronecker delta函数性质,可以直接施加本质边界条件。通过本文给出的方法,对不同边界条件、不同跨厚比、不同材料参数和铺设角度的层合板的振动频率进行了计算,均得到满意结果。最后用该方法对层合板的铺设角度进行优化设计,得到了与已有文献完全一致的优化结果。数值结果充分表明了无网格Kriging方法分析层合板自由振动问题的有效性和高精确度。     

Experimental investigation on the vibro-compacted of RCC

The vibro-compacting process and the structural mechanism of RCC layers are discussed in this paper. In the meantime, some of their dynamic characteristics, such as the effect on the lower layer when rolling on the upper layer, the attenuation pattern of vibro-compacting energy along layer depth, the relationship between rolling parameters of vibro-compactor etc., which were clarified by tests in laboratory and at construction site, are also explained.     

多层粘合圆筒型壳

本文对由若干个各向异性单层粘合而成的多层圆筒壳体,提出一种解析方法,是用各单层顶面和底面的位移作基本未知量,并从各单层的平衡方程及层间的应力平衡条件中事先消去层间应力,从而建立全部壳体平衡型控制微分方程。     

Convective heat transfer in porous media with columnar structure

An analysis is made of convective heat transport, produced by uniform heating from below, in a horizontal layer of a porous medium consisting of vertical slabs or columns of different permeabilities. Estimates of the heat flux are made on the assumption that flow in one column does not interact with flow in adjacent columns. The results are compared with those for a homogeneous layer, for which previous work is reviewed. It is found that an inhomogeneous layer transports less heat than a homogeneous layer for which the mean Rayleigh number is the same, if the Rayleigh number is supercritical throughout the layer. If the Rayleigh number is subcritical in part of the layer, the inhomogeneous layer may transport more heat than the equivalent homogeneous layer.     

Vibration effect on convection onset in a system consisting of a horizontal pure liquid layer and a layer of liquid-saturated porous medium

The onset of convection in a system of two horizontal layers (a pure liquid and a porous medium saturated with the same liquid) heated from below under the action of vertical vibration is investigated. For describing the free thermal convection, in the liquid layer the Boussinesq approximation and in the porous layer the Darcy-Boussinesq approximation are used. In the limiting case of a thin liquid layer, effective boundary conditions on the upper boundary of the porous layer with account for convection in the liquid layer are obtained and it is shown that vibration has a stabilizing effect, whereas the presence of a liquid layer leads to destabilization. For an arbitrary liquid to porous layer thickness ratio the onset of convection is investigated numerically. In the case of a thin liquid layer there are two (short-and long-wave) unstable modes. In the case of thick layers the neutral curves are unimodal. Vibration has a stabilizing effect on perturbations with any wave number but affects short-wave perturbations much more strongly than long-wave ones.     

Stability of a steady-state discontinuity of a fluid layer on the surface of an immiscible fluid

A new stable structure of the three-phase system formed by a gas, a horizontal liquid layer with a free upper surface and an underlying immiscible liquid substrate is investigated experimentally and theoretically. When the upper layer has a greater surface tension than the lower layer and its thickness is fairly small, a local deformation of its surface can lead to the development of a steady-state concentric discontinuity within whose limits the lower layer os in contact with the gas. The conditions of stability of such a phase system with a steady-state discontinuity are studied and the dependences of the discontinuity parameters on the vessel diameter, the upper layer thickness, and the liquid surface tensions are obtained for various pairs of liquids. The formulation of the analytic problem of the layer discontinuity is discussed. The experimental data are compared with the results of calculations carried out for a model of a discontinuity in an infinite layer.     

Shear-wave resonances in a fluid–solid–solid layered structure

An inhomogeneous solid layer is bounded on one side by a fluid half-space and on the other by a homogeneous solid half-space. An acoustic wave in the fluid is incident on the layer. Experiments suggest that some kind of shear-wave resonance of the layer exists. Here, the layer is modeled with exponential variations of the material properties (Epstein model). Solutions in terms of hypergeometric functions are found. Genuine resonances are found but only when the layer is not bonded to the solid half-space; these are analogous to Jones frequencies in fluid–solid interaction problems. When the solid half-space is present, the resonances become complex: they are scattering frequencies. Simple but accurate asymptotic approximations are found using known estimates for hypergeometric functions with large parameters.     

Turbulent flow in converging nozzles,part one: boundary layer solution

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer assumptions and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order Adams predictor-corrector method. The free vortex and uniform velocity profiles are applied for the tangential and axial velocities at the inlet region, respectively. Due to the lack of experimental data for swirling flows in converging nozzles, the developed model is validated against the numerical simulations. The results of numerical simulations demonstrate the capability of the analytical model in predicting boundary layer parameters such as the boundary layer growth, the shear rate, the boundary layer thickness, and the swirl intensity decay rate for different cone angles. The proposed method introduces a simple and robust procedure to investigate the boundary layer parameters inside the converging geometries.     

High accuracy non-equidistant method for singular perturbation reaction-diffusion problem

Singular perturbation reaction-diffusion problem with Dirichlet boundary condition is considered. It is a multi-scale problem. Presence of small parameter leads to boundary layer phenomena in both sides of the region. A non-equidistant finite difference method is presented according to the property of boundary layer. The region is divided into an inner boundary layer region and an outer boundary layer region according to transition point of Shishkin. The steps sizes are equidistant in the outer boundary layer region. The step sizes are gradually increased in the inner boundary layer region such that half of the step sizes are different from each other. Truncation error is estimated. The proposed method is stable and uniformly convergent with the order higher than 2. Numerical results are given, which are in agreement with the theoretical result.     

临近空间大气环境研究现状

临近空间指高度位于(20$\sim$100)\,km之间的地球大气层.简要综述临近空间的已有了解和研究前沿,包括基本状态、主要过程与控制因子.介绍了基于已有探测资料的经验模式的建立和基于基本物理定量规律和数值模拟方法的中层大气环流和化学气候数值模拟.最后从临近空间大气环境保障应用角度提出研究的新建议.      

对流边界层大涡自组织过程的数值研究

利用简化的边界层日变化干对流模式,结合非线性热力学观点,数值模拟并分析了日间对流边界层中大涡形成、发展及衰亡的动力和热力学特征.结果表明,对流边界层中大涡始终处于不稳定状态,大涡的自组织合并和破碎串级输送过程同时并存,前者与边界层系统的局部减熵相对应,后者与对流边界层的总体增熵效应对应;大涡的演变是对流边界层总体增熵这一稳定因素和局部减熵这一不稳定因素相互竞争的结果.