Tomáš Koudelka

Efficient computer implementation of coupled hydro-thermo-mechanical analysis

Hydro-thermo-mechanical analysis of reactor vessels based on the finite element method is a very demanding task due to its complexity as well as the large number of unknowns. This contribution deals with efficient computer implementation of the coupled analysis and attention is also devoted to domain decomposition methods which enable utilisation of parallel computers. The parallel processing leads to very good speedup and it also enables to solve significantly large problems in acceptable time. The proposed strategy is demonstrated on a coupled analysis of an existing reactor vessel.

Subdifferential‐based implicit return‐mapping operators in computational plasticity

The paper is devoted to numerical realization of elastoplastic problems. The main goal is to improve implementation of the related constitutive problems. This can be done if plastic flow rules are defined by subdifferentials of plastic potentials. Then just one plastic multiplier is used even if the plastic potentials are nondifferentiable for unknown stress tensors. Further, the implicit Euler time discretization scheme is considered and the standard elastic predictor plastic corrector method is used to find the discretized constitutive solution. Due to the presence of the one multiplier, it is possible to construct a unique system of nonlinear equations within the plastic correction regardless the unknown stress tensor lies on the smooth portion of the yield surface or not. Plastic criteria given by the Haigh-Westergaard coordinates are investigated in this paper (PART I). The suggested method is in detail studied on the problem containing the DruckerPrager criterion, a nonassociative plastic flow rule and a nonlinear isotropic hardening. It is shown that for this problem, one can a priori decide whether the unknown stress tensor will lie on the smooth portion or at the apex of the yield surface. The corresponding tangential (consistent) stiffness matrix is constructed and the elastoplastic problem is solved by the semismooth Newton method. The new method is implemented within the in house software SIFEL and several numerical experiments are introduced.

Coupled shrinkage and damage analysis of autoclaved aerated concrete

This paper is devoted to analysis of shrinkage and damage of autoclaved aerated concrete. Coupled hydro-thermo-mechanical analysis is used for detailed description of drying which causes the shrinkage and damage consequently. The heat and moisture transfer are fully coupled while the staggered approach is used between transports and mechanics. Material parameters were obtained from laboratory experiments and the results of numerical simulations correspond with measured data.

Numerical modelling of consolidation processes under the water level elevation changes

Abstract The paper presents a numerical model of coupled hydro-mechanical behaviour of soils. The micro-mechanics model is based on the effective stress concept which covers the theory of deformation of soils (soil skeleton) and other porous materials. The final set of equations is simplified and derived for the water flow in a porous media and the spatial discretization is performed by the finite element method. The model was implemented to the SIFEL software package and some numerical examples are presented.

Plasticity Calculation of Plates Using Layered Model

A layered model is used for nonlinear analysis of plates. Calculation is performed using DKT plate elements and considering plastic yielding of layers with the use of double Drucker-Prager yield criterion model for concrete and J2 plasticity model for reinforcement. Computation is done by the SIFEL solver using the Finite Element Method.

An improved return-mapping scheme for nonsmooth yield surfaces: PART I - the Haigh-Westergaard coordinates

The paper is devoted to numerical realization of elastoplastic problems. The main goal is to improve implementation of the related constitutive problems. This can be done if plastic flow rules are defined by subdifferentials of plastic potentials. Then just one plastic multiplier is used even if the plastic potentials are nondifferentiable for unknown stress tensors. Further, the implicit Euler time discretization scheme is considered and the standard elastic predictor plastic corrector method is used to find the discretized constitutive solution. Due to the presence of the one multiplier, it is possible to construct a unique system of nonlinear equations within the plastic correction regardless the unknown stress tensor lies on the smooth portion of the yield surface or not. Plastic criteria given by the Haigh-Westergaard coordinates are investigated in this paper (PART I). The suggested method is in detail studied on the problem containing the DruckerPrager criterion, a nonassociative plastic flow rule and a nonlinear isotropic hardening. It is shown that for this problem, one can a priori decide whether the unknown stress tensor will lie on the smooth portion or at the apex of the yield surface. The corresponding tangential (consistent) stiffness matrix is constructed and the elastoplastic problem is solved by the semismooth Newton method. The new method is implemented within the in house software SIFEL and several numerical experiments are introduced.

Modeling of damage due to shrinkage in autoclaved aerated concrete

The paper deals with numerical modeling of damage evolution in autoclaved aerated concrete (AAC) due to shrinkage. It represents coupled thermo-hydro-mechanical problem where the temperature and moisture transports are fully coupled. The mechanical problem is partially coupled with transport part because the AAC shrinkage is influenced by moisture evolution. These models were implemented to the SIFEL software package and they were used for numerical simulation of drying wall made from AAC blocks.

Moisture and salt transport coupled with damage mechanics

Durability and life time of porous building materials depend significantly on distribution of moisture and salt concentration. Transport of moisture and salt is affected by damage evolution caused by mechanical loading. The permeability grows with evolution of microcracks and microvoids. This paper describes coupled thermo-hydro-mechanical model which connects the damage parameter and permeability.

Effect of mechanical damage on moisture transport in concrete

This paper is devoted to the influence of mechanical damage on moisture transport in quasi-brittle materials, such as concrete. The mechanical analysis is based on the isotropic damage model with the equivalent strain suitable for concrete. The mechanical model is formulated in the rate form in order to connect it with the nonstationary moisture transport which is modeled by a simple diffusion model derived from convection approach. The moisture transport is based on the volumetric moisture content. Three different formulas are used for description of the change of permeability with respect to growing damage parameter. Numerical approach is tested on an example of four-point shear test.

Numerical simulation for the drying shrinkage of autoclaved aerated concrete

A mathematical model for the description of drying shrinkage of autoclaved aerated concrete (AAC) is presented, bringing together the hygrothermal and mechanical considerations. The verification of the model is done using an approximation of a real laboratory experiment. Then, the applicability of the model is demonstrated by a numerical simulation of drying shrinkage and wetting expansion of AAC under real weather data. The presented results showed that the model works precisely and the presumption was made to extend the model in subsequent research.