Analysis of rock massif based on the theory of damage

This paper deals with analysis of rock massif in connection with a planned deposit of nuclear waste. This problem has emerged with renessaince of nuclear power plants which are now considered as a stable and relatively clean source of electrical energy. The deposits are located deep in rock massif and analysis of stress redistribution caused by cave drifting and temperature changes is required. Difficulties with solution of systems of non-linear algebraic equations were discovered and two variants of the arc-length method were tested

Hygro-Thermo-Mechanical Analysis of a Reactor Vessel

Determining the durability of a reactor vessel requires a hygro-thermo-mechanical analysis of the vessel throughout its service life. Damage, prestress losses, distribution of heat and moisture and some other quantities are needed for a durability assessment. A coupled analysis was performed on a two-level model because of the huge demands on computer hardware. This paper deals with a hygro-thermo-mechanical analysis of a reactor vessel made of prestressed concrete with a steel inner liner. The reactor vessel is located in Temelín, Czech Republic

Hygro-Thermo-Mechanical Analysis of a Reactor Vessel

Determining the durability of a reactor vessel requires a hygro-thermo-mechanical analysis of the vessel throughout its service life. Damage, prestress losses, distribution of heat and moisture and some other quantities are needed for a durability assessment. A coupled analysis was performed on a two-level model because of the huge demands on computer hardware. This paper deals with a hygro-thermo-mechanical analysis of a reactor vessel made of prestressed concrete with a steel inner liner. The reactor vessel is located in Temelín, Czech Republic

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

The paper is devoted to the numerical solution of elastoplastic constitutive initial value problems. An improved form of the implicit return-mapping scheme for nonsmooth yield surfaces is proposed that systematically builds on a subdifferential formulation of the flow rule. The main advantage of this approach is that the treatment of singular points, such as apices or edges at which the flow direction is multivalued involves only a uniquely defined set of non-linear equations, similarly to smooth yield surfaces. This paper (PART I) is focused on isotropic models containing: $a)$ yield surfaces with one or two apices (singular points) laying on the hydrostatic axis; $b)$ plastic pseudo-potentials that are independent of the Lode angle; $c)$ nonlinear isotropic hardening (optionally). It is shown that for some models the improved integration scheme also enables to a priori decide about a type of the return and investigate existence, uniqueness and semismoothness of discretized constitutive operators in implicit form. Further, the semismooth Newton method is introduced to solve incremental boundary-value problems. The paper also contains numerical examples related to slope stability with available Matlab implementation.Comment: 25 pages, 10 figure

Approximation methods for post-processing of large data from the finite element analysis

The paper describes efficient methods to post-process results from the finite element analysis. Amount of data produced by the complex analysis is enormous. However, computer performance and memory are limited and commonly-used software tools do not provide ways to post-process data easily. Therefore, some sort of simplification of data has to be used to lower memory consumption and accelerate data loading. This article describes a procedure that replaces discrete values with a set of continuous functions. Each approximation function can be represented by a small number of parameters that are able to describe the character of resulting data closely enough

Selection strategy for fixing nodes in FETI-DP method

This paper deals with selection strategy of fixing nodes in the FETI-DP method. The FETI-DP method is one of non-overlapping domain decomposition methods. The method was published by Farhat and co-workers in 2001. Selection of the fixing unknowns in the FETI-DP, TFETI or BDDC domain decomposition method has strong influence on the method behavior. The selection itself is not straightforward in the case of irregular domains and subdomains. Three-step algorithm for the selection of the fixing unknowns is presented and some numerical examples are shown. The algorithm is based on nodal multiplicity, which is the number of subdomains sharing the node. If the three-step algorithm selects unsatisfactory number of fixing nodes, additional geometrical conditions are applied. These conditions lead to selection of additional fixing nodes. Moreover, higher number of the fixing nodes usually results in better convergence of the coarse problems

Numerical simulation of degradation of porous building materials caused by freeze-thaw cycles

Freeze-thaw cycles in porous building materials are studied in this contribution. Degradation and durability of many building materials as well as structural elements are tightly connected with the freeze-thaw cycles. The porosimetry curve and Gibbs-Thomson equation are used for estimates of volume changes caused by the freeze-thaw cycles. The volume changes are used in mechanical analysis based on the isotropic damage model. Numerical example documents the approach proposed