104,171 research outputs found
Acceleration of Uncertainty Updating in the Description of Transport Processes in Heterogeneous Materials
The prediction of thermo-mechanical behaviour of heterogeneous materials such
as heat and moisture transport is strongly influenced by the uncertainty in
parameters. Such materials occur e.g. in historic buildings, and the durability
assessment of these therefore needs a reliable and probabilistic simulation of
transport processes, which is related to the suitable identification of
material parameters. In order to include expert knowledge as well as
experimental results, one can employ an updating procedure such as Bayesian
inference. The classical probabilistic setting of the identification process in
Bayes's form requires the solution of a stochastic forward problem via
computationally expensive sampling techniques, which makes the method almost
impractical. In this paper novel stochastic computational techniques such as
the stochastic Galerkin method are applied in order to accelerate the updating
procedure. The idea is to replace the computationally expensive forward
simulation via the conventional finite element (FE) method by the evaluation of
a polynomial chaos expansion (PCE). Such an approximation of the FE model for
the forward simulation perfectly suits the Bayesian updating. The presented
uncertainty updating techniques are applied to the numerical model of coupled
heat and moisture transport in heterogeneous materials with spatially varying
coefficients defined by random fields
Probabilistic modeling of chloride penetration with respect to concrete heterogeneity and epoxy-coating on the reinforcement
The presented article demonstrates the probabilistic method based modeling of the 2D chloride ingress into reinforced concrete structures with respect to concrete heterogeneity and epoxy-coated steel reinforcement. Spatial change of concrete diffusion is assessed through the investigation of random variation of the ability of concrete to resist chloride ingress. Time-dependent chloride concentration at the reinforcement level in both homogeneous and heterogeneous models is comparatively considered taking into account of the influence of reinforcement protection as well as the defects and holidays of the coating. Expansion optimal linear estimation method is exploited to generate a random field for the structure at the mesoscale and correlation length is employed to simplify the modeling process. Preliminary analyses of the built model are conducted in both deterministic and probabilistic solutions under the scheme of the finite element method. Thus, possibility of such analyses is exploited.Web of Science1224art. no. 406
Probabilistic simulation for the certification of railway vehicles
The present dynamic certification process that is based on experiments has been essentially built on the basis of experience. The introduction of simulation techniques into this process would be of great interest. However, an accurate simulation of complex, nonlinear systems is a difficult task, in particular when rare events (for example, unstable behaviour) are considered. After analysing the system and the currently utilized procedure, this paper proposes a method to achieve, in some particular cases, a simulation-based certification. It focuses on the need for precise and representative excitations (running conditions) and on their variable nature. A probabilistic approach is therefore proposed and illustrated using an example.
First, this paper presents a short description of the vehicle / track system and of the experimental procedure. The proposed simulation process is then described. The requirement to analyse a set of running conditions that is at least as large as the one tested experimentally is explained. In the third section, a sensitivity analysis to determine the most influential parameters of the system is reported. Finally, the proposed method is summarized and an application is presented
Formal analysis techniques for gossiping protocols
We give a survey of formal verification techniques that can be used to corroborate existing experimental results for gossiping protocols in a rigorous manner. We present properties of interest for gossiping protocols and discuss how various formal evaluation techniques can be employed to predict them
Meta-models for structural reliability and uncertainty quantification
A meta-model (or a surrogate model) is the modern name for what was
traditionally called a response surface. It is intended to mimic the behaviour
of a computational model M (e.g. a finite element model in mechanics) while
being inexpensive to evaluate, in contrast to the original model which may take
hours or even days of computer processing time. In this paper various types of
meta-models that have been used in the last decade in the context of structural
reliability are reviewed. More specifically classical polynomial response
surfaces, polynomial chaos expansions and kriging are addressed. It is shown
how the need for error estimates and adaptivity in their construction has
brought this type of approaches to a high level of efficiency. A new technique
that solves the problem of the potential biasedness in the estimation of a
probability of failure through the use of meta-models is finally presented.Comment: Keynote lecture Fifth Asian-Pacific Symposium on Structural
Reliability and its Applications (5th APSSRA) May 2012, Singapor
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