On the simultaneous estimation of model parameters used in constitutive laws for inelastic material behaviour

The paper deals with the simultaneous estimation of parameters used in constitutive laws for modeling inelastic material behaviour. Experimental data is obtained from specimens with a uniform distribution of stresses. Uniaxial evaluations of the constitutive laws are used. Due to the numerical stiffness of the constitutive equations, it is shown that it is necessary to use an implicit time-integration scheme. The model parameters are estimated from experimental data using a least-squares criterion. Stochastic and deterministic optimization methods are used. The algorithms are parallelized on the basis of the master-slave paradigm. Since a complete parameter estimation requires error estimates and confidence regions, statistic methods are implemented.     

A dynamic damage constitutive model for a rock mass with non-persistent joints under uniaxial compression

Most problems faced by the practicing rock mass engineering involve the evaluation of rock mass dynamic strength and deformability. As part of a rock mass, the mesoscopic flaws such as the microcracks and the macroscopic ones such as the joints both inherently affect the rock mass dynamic strength and deformational behavior. Nearly none of the existing models can handle the co-effect of these two kinds of flaws on the rock mass dynamic mechanical behavior. This study focusses on the rock mass with multi-sets of non-persistent joints and establishes a mathematical model accounting for the anisotropy in dynamic strength and deformability induced by the joints. Accordingly, an approach incorporating the existing models or methods to enable perfect simulation of the dynamic stress-strain relationship of a rock mass is proposed, in which the joint geometrical parameters such as the joint length and dip angle, the strength ones such as the joint internal friction and the deformational ones such as the joint normal and shear stiffness can all be taken into account. In order to investigate the validity of the proposed model, a series of calculation examples have been made and the results fits very well with the theoretical ones.     

Modeling for heat and mass transfer with phase change in porous wick of CPL evaporator

A mathematic model is developed to describe heat and mass transfer with phase change in the porous wick of evaporator of capillary pumped loop (CPL). This model with six field variables, including temperature, liquid content, pressure, liquid velocity, vapor velocity and phase-change rate, is closed mathematically with additional pressure relationships introduced. The present model is suitable to the numerical computation, as the established equations become comparatively easy to solve, which is applied to CPL evaporator. The numerical results are obtained and the parameter effects on evaporator are discussed. The study demonstrates that instead of an evaporative interface, there exists an unsaturated two-phase zone between the vapor-saturated zone and the liquid-saturated zone in the wick of CPL evaporator.