Thermal Expansion Coefficients of Thin Crystal Films

The formulas for atomic displacements and Hamiltonian of a thin crystal film in phonon occupation number representation are obtained with the aid of Green's function theory. On the basis of these results, the formulas for thermal expansion coefficients of the thin crystal film are derived with the perturbation theory, and the numerical calculations are carried out. The results show that the thinner films have larger thermal expansion coefficients.

Decoupling coefficients of dilatational wave for Biot's dynamic equation and its Green's functions in frequency domain

Green＇s functions for Blot＇s dynamic equation in the frequency domain can be a highly useful tool for the investigation of dynamic responses of a saturated porous medium. Its applications are found in soil dynamics, seismology, earthquake engineering, rock mechanics, geophysics, and acoustics. However, the mathematical work for deriving it can be daunting. Green＇s functions have been presented utilizing an analogy between the dynamic thermoelasticity and the dynamic poroelasticity in the frequency domain using the u-p formulation. In this work, a special term ＂decoupling coefficient＂ for the decomposition of the fast and slow dilatational waves is proposed and expressed to present a new methodology for deriving the poroelastodynamic Green＇s functions. The correct- ness of the solution is demonstrated by numerically comparing the current solution with Cheng＇s previous solution. The separation of the two waves in the present methodology allows the more accurate evaluation of Green＇s functions, particularly the solution of the slow dilatational wave. This can be advantageous for the numerical implementation of the boundary element method （BEM） and other applications.

Prediction of Activity Coefficients for Mixed Aqueous Electrolyte Solutions from the Data of Their Binary Solutions

The simple equation relating the activity coefficient of each solute in mixed electrolyte solution to its value in binary solutions under isopiestic equilibrium was tested by comparison with the experimental data for the 18 electrolyte solutions consisting of 1：1, 1：2, and 1：3 electrolytes. The isopiestic measurements were made on the quaternary system BaCl2-NH4Br-NaI-H2O and its ternary subsystems NaI-NH4Br-H2O, NaI-BaCl2-H2O, and NH4Br-BaCl2-H2O at 298.15K. The results were used to test the applicability of the Zdanovskii＇s rule to the mixed electrolyte solutions which contain no common ions, and the agreement is excellent. The activity coefficients of the solutes in the above quaternary and ternary systems calculated from the above-mentioned simple equation are in good agreement with the Pitzer＇s equation.

GP断层破裂模型在青海门源M_(S)6.9地震强地面运动模拟的适用性研究

2022年1月8日青海省门源县发生M_(S)6.9地震,震中附近遭受了强烈地震破坏.为验证Graves和Pitarka开发的GP断层破裂模型在震前对中国地区地震动场的预测与评估能力,本文基于GP法,考虑不同上升时间系数(rc)的影响,对门源地震进行了确定性地震动模拟.将模拟结果在地震动衰减规律、波形与幅值和烈度分布三个方面分别与青藏地区的地震动峰值预测方程、强震观测记录和根据强震记录自动产出的烈度图进行了对比.结果表明,当rc为9.0时,模拟记录与实测记录和地震动峰值预测方程基本一致.本文较好的重现了门源地震的强震动场,在合理选取rc的情况下,GP法可以应用于中国地区震前强地震动场的预测和估计.

基于S函数的调节阀粘滞特性检测方法

调节阀粘滞特性引起的振荡是工业控制回路性能恶化的最常见来源。目前虽然已有许多检测调节阀粘滞特性的方法,但这些方法的复杂性或存在的缺陷限制着其在实际工况中的具体应用。本文提出了一种检测过程控制回路中调节阀粘滞故障的新方法。该方法将控制器输出(OP)和过程变量(PV)的变化(ΔPV)在相平面图中所构成变化趋势与标准S函数进行对比,根据实际函数趋势与标准S函数间的差异计算相关系数,通过相关系数的数值具体得出调节阀中是否存在粘滞特性。仿真实例和实际工业数据分析实验验证了提出方法的有效性。

具有稚虫迁徙机制的S型自适应混沌蜉蝣算法

针对蜉蝣优化算法(MA)全局搜索能力较弱,对子代优秀个体有效信息利用不够充分的缺点,以及在计算中后期易陷入局部收敛,进而影响优化效果的问题,提出一种具有稚虫迁徙机制的S型自适应混沌蜉蝣优化算法(S-AMA)。S-AMA算法首先采用Logistic混沌映射产生蜉蝣种群,增加算法初期种群的多样性;随后,将蜉蝣生命周期进行数学建模,并引入S型生命系数替换原有的重力惯性系数,动态调整算法探索能力和开发能力间的平衡性;最后,根据蜉蝣在缺氧环境下的种群活动,引入稚虫迁徙机制强化子代优秀个体摆脱局部最优的能力,进而更加充分地搜索最优解附近的区域,以增强算法的收敛精度。实验部分将S-AMA应用于标准函数测试集,并分别进行优化对比实验、Wilcoxon秩和检验。结果表明:与对比算法相比,S-AMA算法具有更好的寻优能力、收敛速度及鲁棒性。

基于FPGA的AES和ECC算法图像加密

随着数字图像的使用次数日益增多,保护机密图像数据免受未经授权的访问较为重要。针对数字图像在通信、存储和传输等领域存在的安全问题,文中基于对称算法模型和非对称算法模型的优点提出一种具有高安全性和高速度性的数字信封技术密码方案。该方案以AES(Advanced Encryption Standard)和ECC(Elliptic Curve Cryptography)为基础,经优化后用于对称密钥共享的ECC硬件架构来提高密钥的安全性。通过加入伪随机数、使用列移位替代列混淆运算以及三维S-box等方式对传统AES进行优化,在保持香农扩散和混淆原理的同时降低了时间复杂性。基于FPGA(Field Programmable Gate Array)实现AES算法的数字图像加密仿真以及性能测试。测试结果表明,所提密码方案具有快速性、高安全性和有效性等优点,能够有效地实现图像加密。

基于最大信息系数法和邓熵的D-S证据理论改进

物联网中大量传感器采集的数据存在不确定性,针对D-S证据理论在处理冲突证据时融合决策结果与事实相悖的问题,文章提出一种新的基于改进D-S证据理论的多传感器数据融合算法,首先使用最大信息系数法计算证据间的可信度;然后结合信息熵对证据的不确定度进行分析,以确定新的权重;最后使用Dempster组合规则得到融合结果。算例分析表明,文章所提方法能有效融合冲突证据,较经典算法有较高的基本概率分配。将所提方法用于传感器数据处理,不仅能降低数据中存在的不确定性,还能有效处理D-S理论中的冲突问题,从而得到较为准确的融合结果。

改进Dempster-Shafer证据与概率模型集成的变压器故障诊断

针对单个变压器故障诊断模型准确率有限的问题,提出基于kappa系数改进Dempster-Shafer(D-S)证据理论与概率模型集成的变压器故障诊断方法。首先,分别构建基于概率输出的支持向量机、贝叶斯神经网络、深度信念网络的变压器故障诊断概率模型,拟合诊断模型在样本上的基本概率分配函数。然后,建立D-S证据理论信息集成框架,提出基于kappa系数与准确率权重的证据修正方法,从子模型与故障类型两个角度对证据进行修正,进而融合概率模型诊断结果。最后,通过仿真验证本文所提方法的有效性。

基于Pearson相关系数与广义S变换的低压直流微电网的故障选线方法

针对低压直流微电网线路的故障选线方法的研究有限,提出一种基于Pearson相关系数与广义S变换的故障选线方法。首先,介绍了低压直流微电网的一般组成。在此基础上,研究了低压直流微电网的单极故障以及极间故障的故障特征,提出选线方法,对各线路正负极首末端电流差进行Pearson相关系数计算来确定故障线路。然后对所选故障线路正负线路首端的电流量进行广义S变换,计算出其能量和的比值判别故障极性或者极间故障。最后,在PSCAD/EMTDC中搭建出低压直流微电网模型以输出各线路电流数据,并利用Matlab对数据进行仿真。结果表明,所提选线方法直接有效,且耐受过渡电阻的能力较强。

基于格子Boltzmann方法的粘弹性流体圆柱绕流分析

将光滑界面法引入到格子Boltzmann方法中分析粘弹性流体绕流问题,分别采用单松弛模型和对流扩散模型求解运动方程和Oldroyd-B本构方程,针对圆形和椭圆内部边界条件,给出连续界面插值函数,在此基础上,运用光滑界面法将内部边界转换为作用力项施加到演化方程中。首先分析圆柱绕流问题,给出不同材料参数情况下的流场分布和阻力系数计算结果,比较发现与宏观数值模拟结果相吻合。将模型拓展到绕椭圆流动中,分析椭圆形状和材料参数对粘弹性流体绕柱流的影响,发现随着椭圆长轴与短轴比值的增加和维森伯格数的增加,阻力系数逐渐下降,并且长短轴比对迭代收敛有较大影响。

基于S-A模型的覆冰输电线绕流数值分析

基于Spalart-Allmaras湍流模型(S-A模型)封闭的雷诺平均N-S方程,采用沿均匀流线的三阶Runge-Kutta法和Galerkin法分别进行时间和空间离散,得到了湍流方程的有限元格式。采用自编Matlab程序,数值模拟了不同风攻角下覆冰输电线绕流问题,得到了覆冰输电线绕流瞬态和时均流场、气动力系数时程曲线和平均气动力系数随风攻角的变化关系,并与试验结果进行对比,验证了该算法的有效性。基于流场演化和平均压力分布,分析表明风攻角变化引起的边界层分离点转移是产生升力系数尖峰突跳现象的主要原因。

Lattice Boltzmann simulations of turbulent shear flow between parallel porous walls

The effects of two parallel porous walls are investigated, consisting of the Darcy number and the porosity of a porous medium, on the behavior of turbulent shear flows as well as skin-friction drag. The turbulent channel flow with a porous surface is directly simulated by the lattice Boltzmann method （LBM）. The Darcy-Brinkman- Forcheimer （DBF） acting force term is added in the lattice Boltzmann equation to simu- late the turbulent flow bounded by porous walls. It is found that there are two opposite trends （enhancement or reduction） for the porous medium to modify the intensities of the velocity fluctuations and the Reynolds stresses in the near wall region. The parametric study shows that flow modification depends on the Darcy number and the porosity of the porous medium. The results show that, with respect to the conventional impermeable wall, the degree of turbulence modification does not depend on any simple set of param- eters obviously. Moreover, the drag in porous wall-bounded turbulent flow decreases if the Darcy number is smaller than the order of O（10-4） and the porosity of porous walls is up to 0.4.

Study on roughness coefficient for unsubmerged reed in the Changjiang Estuary

The influence of density,foliage and stem flexibility on the roughness coefficients under unsubmerged conditions,such as Manning＇s n,is investigated experimentally.An instrumentation system has been developed for measuring the flow rate ranging from 0.1 to 0.3 L/s under the condition of different artificial foliated reeds.Based on the experimental results,the influence on the relationship between n with different density,foliage,flexibility and flow depth is discussed.It is found that the foliage and the density are the important factors affecting Manning＇s n.At a range of relatively low velocity and relatively large bending stiffness of stem,Manning＇s n is not influenced significanthy by the flexibility of stem.

Investigation on the Dielectric Properties of CO2 and CO2-Based Gases Based on the Boltzmann Equation Analysis

In this paper, the dielectric properties of CO2, CO2/air, CO2/O2, CO2/N2, CO2/CF4, CO2/CH4, CO2/He, C02/H2, CO2/NH3 and CO2/CO were investigated based on the Boltzmann equation analysis, in which the reduced critical electric field strength （E/N）cr of the gases was derived from the calculated electron energy distribution function （EEDF） by solv- ing the Boltzmann transport equation. In this work, it should be noted that the fundamental data were carefully selected by the published experimental results and calculations to ensure the validity of the calculation. The results indicate that if He, H2, N2 and CH4, in which there axe high ionization coefficients or a lack of attachment reactions, are added into CO2, the dielectric properties will decrease. On the other hand, air, O2, NH3 and CFa （ranked in terms of （E/N）cr value in increasing order） have the potential to improve the dielectric property of CO2 at room temperature.

Reaearch on Skempton’s coefficient B based on the observation of groundwater of Changping station

Based on isotropie linear poroelastic theory and under the undrained condition, we summarize three equations connecting the Skempton＇s coefficient B with the groundwater level. After analysis, we propose a method to calculate the Skempton＇s coefficient B according to the relationship between water level and tidal strain. With this method we can get the value of B without the earthquake occurrence, which can provide the high frequency waves for research. Besides, we can also get the in-suit Skempton＇s coefficient B without the experiment of rock physics. In addition, we analyze the observed data of Changping station recorded in groundwater monitoring network （abv., GMN） before and after the Wenchuan Ms8.0 with this method, and find out there＇s a slight change of the value of B after the seismic waves passed by, which implies that the propagation of seismic waves may have brought some variations to the poroelastic medium of the well.

On the Application of the Lattice Boltzmann Method to Predict Soil Meso Seepage Characteristics

In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity distribution of water flow.In particular,impermeability is considered as macroscopic boundary condition for the left and right domain sides,while the upper and lower boundaries are assumed to behave as pressure boundaries controlled by different densities.The micro-boundary conditions are implemented through the standard rebound strategy and a non-equilibrium extrapolation scheme.Matlab is used for the development of the related algorithm.Finally,the influence of porosity,permeability,osmotic pressure and other factors is assessed with regard to seepage characteristics and the ensuing results are compared with Darcy’s law.The computations show that,for fixed initial conditions,the pore structure has a certain influence on the local velocity of seepage,but the overall state is stable,and the average velocity of each layer is the same.The larger the pore passage is,the faster the flow velocity is,and vice versa.For low permeability,the numerical results are consistent with the Darcy's law.The greater the pressure difference between the inlet and outlet of seepage,the greater the seepage rate.The relationship between them is linear(yet in good agreement with Darcy’s law).

Performance Investigation of 2D Lattice Boltzmann Simulation of Forces on a Circular Cylinder

The lattice Boltzmann method (LBM) is employed to simulate the uniform flow past a circular cylinder. The performance of the two-dimensional LBM model on the prediction of force coefficients and vortex shedding frequency is investigated. The local grid refinement technique and second-order boundary condition for curved walls are applied in the calculations. It is found that the calculated vortex shedding frequency, drag coefficient and lift coefficient are consistent with experimental results at Reynolds nu...

Hydraulic model with roughness coefficient updating method based on Kalman filter for channel flood forecast

A real-time channel flood forecast model was developed to simulate channel flow in plain rivers based on the dynamic wave theory. Taking into consideration channel shape differences along the channel, a roughness updating technique was developed using the Kalman filter method to update Manning＇s roughness coefficient at each time step of the calculation processes. Channel shapes were simplified as rectangles, triangles, and parabolas, and the relationships between hydraulic radius and water depth were developed for plain rivers. Based on the relationship between the Froude number and the inertia terms of the momentum equation in the Saint-Venant equations, the relationship between Manning＇s roughness coefficient and water depth was obtained. Using the channel of the Huaihe River from Wangjiaba to Lutaizi stations as a case, to test the performance and rationality of the present flood routing model, the original hydraulic model was compared with the developed model. Results show that the stage hydrographs calculated by the developed flood routing model with the updated Manning＇s roughness coefficient have a good agreement with the observed stage hydrographs. This model performs better than the original hydraulic model.