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Numerical simulation of intact rock behaviour via the continuum and Voronoi tesselletion models
Teja Fabjan, Diego Mas Ivars, Vladimir Vukadin, 2015, izvirni znanstveni članek

Opis: The numerical simulation of intact rock microstructure and its influence on macro-scale behaviour has received a lot of attention in the research community in recent years. Generating a grain-like structure with polygonal area contacts is one of the avenues explored for describing the rock’s microstructure. A Voronoi tessellation implemented in the Universal Distinct-Element Code (UDEC) is used to generate models with a polygonal microstructure that represent intact rock. The mechanical behaviour of the Voronoi polygons is defined by micro-properties, which cannot be measured directly in the laboratory. A numerical calibration procedure is needed to produce the macroscopic response of a model that corresponds to the material behaviour measured during a laboratory experiment. In this research, Brazilian, direct tensile, uniaxial compressive and biaxial test models are constructed to simulate the intact rock behaviour under a standard laboratory stress. An extensive series of parametric sensitivity analyses are executed in order to understand the influence of the input micro-properties on every model test behaviour and predict the relation between the micro-properties and the model’s macro response. The results can be treated as general guidelines for a complete and efficient intact rock calibration procedure. In parallel, a continuum-based model using the Mohr-Coulomb constitutive relationship is running as a benchmark. It has been shown that the Voronoi-based models through their microstructure approach better reproduce the Brazilian to direct tensile strength ratio, and show a better representation of the dilation, crack pattern and post-peak behaviour in comparison to continuum models.
Ključne besede: distinct-element method, parametric sensitivity analysis, intact rock, Voronoi tessellation, micromechanical properties, standard laboratory test
Objavljeno: 15.06.2018; Ogledov: 670; Prenosov: 59
.pdf Celotno besedilo (1,57 MB)
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Efficiency analysis with non parametric method: illustration of the Tunisian ports
Arbia Hlali, 2018, izvirni znanstveni članek

Opis: This paper applies a non-parametric method to provide level technical efficiency for 7 Tunisian ports during 18 years (1998-2015). These ports represent different data set. The use of the model of variable returns to scale (VRS) has led to interesting results. The results show that the most ports are characterized by low levels of technical efficiency, with the exception port of Rades. In addition, the result shows the variation of variable returns to scale and constant returns to scale of technical port’s efficiency. Furthermore, we concluded that the panel data improves the efficiency estimates.
Ključne besede: technical efficiency, Tunisian ports, non parametric analysis
Objavljeno: 25.04.2018; Ogledov: 480; Prenosov: 319
.pdf Celotno besedilo (382,56 KB)
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Wave motion in infinite inhomogeneous waveguides
Igor Špacapan, Miroslav Premrov, 2003, izvirni znanstveni članek

Opis: The analysis of wave motion in infinite homogeneous waveguides, having a complicated cross-section and/or an irregular inclusion, is a rather difficult task for the majority of available methods, especially when striving for accurate results. In contrast, this presented procedure performed in the frequency domain, is simple to apply. It yields correct results because the radiation conditions are considerably accurately satisfied, and it offers a clear parametric insight into wave motion. This procedure uses the FE modelling of an analysed section of the waveguide. It is based on the decomposition of wave motion, distinguishing propagating and non-propagating wavemodes by solving the eigenvalue problem. The presented examples demonstrate the effectiveness of this procedure, whilst a comparison between computed and analytical results demonstrates its accuracy.
Ključne besede: waves, wavemodes, waveguides, inhomogeneity, finite element method, parametric analysis, radiation conditions, eigenvalue problem, frequency domain
Objavljeno: 01.06.2012; Ogledov: 1615; Prenosov: 48
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