Acoustical method for determining thermal diffusivity and relative difference in molar heat capacities of tantalum and vanadium

An acoustical technique is proposed for determining the thermal diffusivity in solids and the relative difference between the molar heat capacities at constant pressure and at constant volume. The method, which consists essentially of measuring the damping of freely vibrating bars, allows determination of the thermal diffusivity with an accuracy better than ±5% and has the advantage of not requiring a heat source. It also largely eliminates the complications of precise temperature measurements and insulation of specimen holders. Results are given for tantalum and vanadium over the temperature range 60–300 K.     

Probabilistic Estimates for the Two-Dimensional Stochastic Navier–Stokes Equations

We consider the Navier–Stokes equation on a two-dimensional torus with a random force, white noise in time, and analytic in space, for arbitrary Reynolds number R. We prove probabilistic estimates for the long-time behavior of the solutions that imply bounds for the dissipation scale and energy spectrum as R.     

在玻璃转变温度及其以上温区聚苯乙烯/聚氧化乙烯共混物的动力学弛豫行为

用熔融共混法制备了不同组分的聚苯乙烯(PS)与聚氧化乙烯(PEO)共混物(PS/PEO).在玻璃转变温度T_g及其以上温区,利用相对能量耗散技术研究了该共混物的动力学行为.结果发现,在能量耗散-温度曲线上出现了两个弛豫型的耗散峰(α峰和α′峰).分析表明,α峰是与PS玻璃转变有关的特征耗散峰; α′峰则对应于一种“液-液转变”.两者的弛豫时间τ都不满足Arrhenius关系.此外,还研究了组分对这两个弛豫型耗散峰的影响,并给予了定性的解释. 关键词： 相对能量耗散 玻璃转变 力学弛豫     

一维液态泡沫渗流实验研究及表面能和粘性耗散分析

液态泡沫由大量气泡密集堆积在微量表面活性剂溶液中形成，是远离平衡态的软物质. 泡沫强制渗流在微观上是指以恒定流率输入的液体在气泡间隙内的微流动过程，是影响泡沫稳定的主要因素之一. 采用在表面活性剂溶液中添加微量色素以显示泡沫中液体流动的方法，确定了透射率与液体分率的对应关系，测量得到了一维液态泡沫强制渗流中渗流波传播规律以及液体分率的演变规律；理论推导了泡沫基本单元，即开尔文单元结构(Kelvin cell)的粘性耗散能表达式，并依据Surface Evolver软件计算得到了不同液体分率时开尔文单元结构对应的的表面能，并计算出了与实验系统对应的开尔文单元结构的表面能和粘性耗散. 基于开尔文单元结构内液体分率演变的准静态假设，分析了表面能和粘性耗散的演变规律.     

Study of nonlinear dissipative pulse propagation under the combined effect of two-photon absorption and gain dispersion: A variational approach involving Rayleigh’s dissipation function

We try to derive some explicit equations for predicting the laws which govern the evolution of different parameters of a propagating optical pulse in a nonlinear medium under the combined influence of two-photon absorption and gain dispersion. Using the generalized Euler-Lagrange equation, the dynamics of different pulse parameters are generated. The Rayleigh’s dissipation function is incorporated in order to take recourse to the dissipative part, with an analogy with the non-conservative frictional problem in classical mechanics. It appears from the study that the influence of the dissipative part can well be explained using the proposed model. The analytically predicted results are compared with the numerical data obtained from direct simulation of the Ginzburg-Landau equation and the results are found to be quite satisfactory, supporting the prediction.     

威远江水电站泄水建筑物消能方案试验研究

通过威远江水电站泄水建筑物的整体模型试验,研究了泄水建筑物消能工的消能效果,发现了其主要问题为溢洪道挑流坎挑流消能时,当泄流量较大时的挑距过大,挑流水舌不能与下游水流很好衔接.泄洪洞挑流坎挑流消能时,当泄流量较小时,挑距较短.经过试验研究提出了修改解决方案,并经试验验证得到较好的消能效果,为工程设计和施工提供了可靠的设计依据.     

有压管道孔口消能效率分析

在分析有压管道消能问题的基础上,提出了二种典型实用的孔口消能方式：末端式消能和在线式消能。在研究孔口基本水力特性基础上,结合山西省万家寨引黄工程流量调节阀工程实际,对孔口消能效率及其与孔口流量系数、孔口过流面积和输水管道出口水头的关系进行分析研究。研究结果为类似工程设计提供了技术参考。     

The concept of minimized integrated exponential error for low dispersion and low dissipation schemes

We devise two novel techniques to optimize parameters which regulate dispersion and dissipation effects in numerical methods using the notion that dissipation neutralizes dispersion. These techniques are baptized as the minimized integrated error for low dispersion and low dissipation (MIELDLD) and the minimized integrated exponential error for low dispersion and low dissipation (MIEELDLD) . These two techniques of optimization have an advantage over the concept of minimized integrated square difference error (MISDE) , especially in the case when more than one optimal cfl is obtained, out of which only one of these values satisfy the shift condition. For instance, when MISDE is applied to the 1‐D Fromm's scheme, we have obtained two optimal cfl numbers: 0.28 and 1.0. However, it is known that Fromm's scheme satisfies shift condition only at r=1.0. Using MIELDLD and MIEELDLD , the optimal cfl of Fromm's scheme is computed as 1.0. We show that like the MISDE concept, both the techniques MIELDLD and MIEELDLD are effective to control dissipation and dispersion. The condition ν²>4µ is satisfied for all these three techniques of optimization, where ν and µ are parameters present in the Korteweg‐de‐Vries‐Burgers equation. The optimal cfl number for some numerical schemes namely Lax–Wendroff, Beam–Warming, Crowley and Upwind Leap‐Frog when discretized by the 1‐D linear advection equation is computed. The optimal cfl number obtained is in agreement with the shift condition. Some numerical experiments in 1‐D have been performed which consist of discontinuities and shocks. The dissipation and dispersion errors at some different cfl numbers for these experiments are quantified. Copyright © 2010 John Wiley & Sons, Ltd.     

耗散Schrdinger-Poisson方程组解的渐近性

考虑耗散Schr dinger Poisson方程组的Cauchy问题 ,对吸引力情形 ,证明了该问题整体强解的存在唯一性和解的渐近性。     

Direct numerical simulation of stationary particles in homogeneous turbulence decay: Application of the k–ε model

This study focuses on understanding how the presence of particles, in homogeneous turbulence decay, affects the dissipation of dissipation coefficient within the volume averaged dissipation transport equation. In developing this equation, the coefficient for dissipation of dissipation was assumed to be the sum of the single phase coefficient and an additional coefficient that is related to the effects of the dispersed phase. Direct numerical simulation was used to isolate the effect of stationary particles in homogeneous turbulent decay at low Reynolds numbers (Re_L = 3.3 and 12.5). The particles were positioned at each grid point and modeled as point forces and a comparison was made between a 64³ and 128³ domain. The results show that the dissipation of dissipation coefficient correlates well with a dimensionless parameter called the momentum coupling factor.