Unsaturated elasto-plastic constitutive equations for compacted kaolin under consolidated drained and shearing-infiltration conditions

Transient process of water flow changes the equilibrium conditions of an unsaturated soil, resulting in volume change of a soil. The volume change alters the hydraulic properties of the soil and thus influences the transient process of water flow through the soil. Therefore, the interactive processes between stress-strain behavior and pore-water pressure are the primary processes affecting the mechanical behavior of unsaturated soils. This paper presents coupled elasto-plastic constitutive equations for unsaturated compacted kaolin under consolidated drained and shearing-infiltration conditions. The study focused on the development of the suction increase (SI) yield curve that incorporates changes in matric suction during transient processes. In addition, the relationship of change in specific water volume with respect to net mean stress and matric suction was also proposed by incorporating the hysteresis of soil-water characteristic curve. The simulated results by the proposed constitutive model were compared with those obtained from isotropically consolidated drained tests and shearing infiltration tests of compacted kaolin to verify the proposed model. The simulated results are in close agreement with the experimental results.     

Thermodynamics, stress release and hysteresis behavior in highly adhesive Pd-H films

We investigate the role of clamping on the thermodynamics of highly adhesive metal hydride thin films. Using Pd as a model system, we add Ti as an intermediate adhesion layer to increase the interaction with the substrate. We show that Pd/Ti films remain clamped during (de-)hydrogenation while the stress release occurs by means of rearrangement and pile-up of the material. The compressive stress build-up reaches a value of about 1.5 GPa during hydrogen absorption. The enthalpy of hydride formation and decomposition, measured using Hydrogenography is found to decrease and increase by about 2.7 and 1.3 kJ/mol H₂ respectively, as compared to buckled Pd films. A simple model confirms that the change in the thermodynamics and the asymmetric expansion of the hysteresis correlate with the mechanical work needed to accommodate the stress induced plastic deformations in clamped Pd/Ti films during the (de-)hydrogenation cycle.     

Contribution of accurate thermal measurements to the characterisation of thermomechanical properties of rubber-like materials

Abstract

Since the pioneer works of Gough and Joule, the thermal characterisation of elastomers under mechanical loading has been investigated by numerous research teams. This is not surprising as the thermal signature of rubber is very useful data to investigate the dissipation mechanisms as well as the thermodynamical variables and couplings. In former recent studies dealing with fatigue investigations, an experimental protocol was developed. This protocol imposes cyclic loading to hourglass shaped samples, takes into account the large displacements and permits dissociation between the intrinsic dissipation, responsible for the mean temperature variation (called heat build-up in the literature) and thermomechanical couplings responsible for the temperature variation around this mean value during one cycle. Up to now, the mean temperature has been investigated in order to feed an energetic fatigue criterion. The aim of the present study is to investigate the thermomechanical couplings and the ability of thermal measurements to exhibit some specific thermomechanical properties observed for rubberlike materials. The materials studied are natural rubber and styrene butabiène rubber compounds filled with several amounts of carbons blacks. The experimental data clearly exhibit interesting features such as the thermoelastic inversion point and difference in the temperature signal between mechanical loading and unloading. This rich database is analysed and correlated to other results from the literature. The main results obtained are dealing with the ability of accurate measurements to characterise the thermodynamic couplings and to detect the stress induced crystallisation.     

Hydrogen electrosorption into Pd-Pt-Au ternary alloys

Thin layers of Pd-Pt-Au alloys were prepared by metal codeposition at constant potential from chloride solutions. The process of hydrogen electrosorption into Pd-Pt-Au alloys was investigated in acidic solution (0.5 M H₂SO₄) using cyclic voltammetry and chronoamperometry, also coupled with the electrochemical quartz crystal microbalance. It was found that Pd alloying with both Pt and Au decreases the maximum hydrogen solubility, but improves the kinetics of absorbed hydrogen oxidation, which is mirrored in a negative shift of the potential of hydrogen desorption peak and shorter hydrogen desorption time. In Pd-Pt-Au alloys the effect of absorption/desorption hysteresis and the stresses connected with hydrogen absorption are reduced in comparison with pure Pd. After prior hydrogen absorption in Pd-Pt-Au alloys, surface oxides are formed and reduced at potentials even by 200 mV lower than before hydrogen treatment.     

Energy efficient control of a BTX dividing-wall column

Dividing-wall column (DWC) is considered nowadays the new champion in distillation, as it can bring substantial reduction in the capital invested as well as savings in the operating costs. This work presents the simulation results of energy efficient control and dynamics of a dividing-wall column (DWC). In order to allow a fair comparison of the results with previously published references, the case-study considered here is the industrially relevant ternary separation of the mixture benzene-toluene-xylene (BTX) in a DWC. Rigorous simulations were carried out in Aspen Plus and Aspen Dynamics. Several conventional control structures based on PID control loops (DB/LSV, DV/LSB, LB/DSV, LV/DSB) were used as a control basis. These control structures were enhanced by adding an extra loop controlling the heavy component composition in the top of the prefractionator, by using the liquid split as an additional manipulated variable, thus implicitly achieving minimization of energy requirements. The results of the dynamic simulations show relatively short settling times and low overshooting especially for the DB/LSV and LB/DSV control structures. Moreover, the energy efficient control proposed in this work allows the operation of DWC with minimum energy requirements or maximum purity of products.     

An Efficient Dynamic Formulation for Multibody Systems

The objective of this article is to present an efficient extension ofRosenthal's order-n algorithm to multibody systems containing closedloops. The equations of motion are created by using relative coordinatesand partial velocity theory. Closed topological loops are handled by cutjoint technique. The set of constraint equations of cut joints isadjoined to the system's equation of motion by using Lagrangemultipliers. This results in the equation of motion as adifferential-algebraic equation (DAE) rather than an ordinarydifferential equation. This DAE is then solved by applying the extendedRosenthal's order-n algorithm proposed in this article. While solvingDAE, violation of the kinematic constraint equations of cut joints iscorrected by coordinate projection method. Some numerical simulationsare carried out to demonstrate efficiency of the proposed method.     

基于PREISACH理论的电流互感器建模研究

提出了一种新型电流互感器（CT）数字化模型。该模型由CT电磁感应方程和基于Preisach理论的新型铁心磁化模型组成：基于Priesach理论的WIPING—OUT特性，提出了确定铁心运行所在磁化曲线的方法，并在新坐标系下分离Preisach函数的变量，得到了不同情况下铁心磁通密度的计算方法，由此建立了铁心磁化模型；提出了一种新的寻解算法，通过该算法将铁心磁化模型同CT电磁感应方程相耦合，建立了CT数字化模型。该模型只需极限磁滞回环下降支、一次电流和二次负荷等少量易被直接测得的参数，即可较准确地仿真铁心内部磁化过程，具有实现简便，仿真精度高等特点。采用文中CT模型对保护CT的饱和特性进行了仿真研究，仿真结果和实测数据的比较验证了模型的有效性。     

永磁电机有限元时步法的研究与应用

对有限元时步法在永磁电机中的应用进行了研究,阐述了基于二维场路耦合时步法的永磁电机模型。采用一台具有特殊转子磁路结构的永磁电机进行了仿真分析,结合试验结果证明了该模型的正确性并指出利用永磁电机的有限元模型结合控制策略是现代电机及其控制系统仿真的方向。     

多环电网方向保护整定计算中形成有向简单回路的新方法

在高压或超高压电网的距离保护和零序保护的整定计算过程中，首先要确定全网的最小断点集(MBPS)，然后在断点集的保护安装处打开断点，使得全网变为辐射网络。其中，多环复杂电网中有向简单回路的确定是求解最小断点集的关键，也是其必要步骤之一。为了最大限度地减少多环复杂电网中有向简单回路的计算复杂性，该文提出了一种保护依赖度和主／后备保护依赖集的新概念：将所有有向简单回路的形成过程归结为环网中所有保护依赖度大小的比较和保护依赖集的不完全深度优先搜寻过程。通过比较保护依赖度的大小来确定每次方向回路搜索的起始点，并通过对保护依赖集的深度优先搜索来确定所有有向简单回路。该方法能统一处理环网中的‘T’形接线、辐射线路等保护的配合问题。算例表明该方法简单有效，显著地降低了计算的复杂性，可方便地应用于高压或超高压电网的距离保护和零序保护的整定计算。