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Combustion simulation in the secondary chamber of a pilot-scale incinerator
Niko Samec, Filip Kokalj, Jyh-Yan Chen, 2007, izvirni znanstveni članek

Opis: A numerical analysis of combustion in the secondary chamber (thermoreactor) ofa two-stage pilot scale incinerator using computational fluid dynamics (CFD)is presented in detail. Various versions of the CFD program package CFX were used, which offer different combustion models for specific types and forms of combustion processes. The present study was focused on those physicalconditions that assure complete combustion, that is, temperature, residence time, and turbulent mixing. The selection of an appropriate combustion model was based on a comparison of the numerical results and experimental values of some combustion macro parameters in a thermoreactor. Combustion models based on one-step bimolecular chemical reaction and models based on multistep reactions were used. These models enabled a more detailed prediction of the combustion process in the secondary chamber of a pilot-scaleincinerator. The products of incomplete combustion that are significantly important for the designing and optimization of combustion devices can be predicted by applying multistep reaction models more accurately, especially in a transient regime of combustion.
Ključne besede: waste incineration, numerical modeling, combustion models, incinerator chamber, CFX, CFD, computational fluid dynamics
Objavljeno: 31.05.2012; Ogledov: 1042; Prenosov: 13
URL Celotno besedilo (0,00 KB)

Critical plane modelling of fatigue initiation under rolling and sliding contact
Matjaž Šraml, Jože Flašker, Iztok Potrč, 2004, izvirni znanstveni članek

Opis: Contact fatigue is a phenomenon of important practical significance for engineering applications involving localized contacts, such as gears, rail wheel system and rolling bearings. The service lifetime of such components is related to damage, which results from the contact fatigue. The process in the material structure that causes this kind of failure is quite complicated. The aim of the present paper is to describe a contact fatigue initiation criterion, based on the critical plane approach for the general contact problem. On the basis of contact stress analysis with modified Hertzian boundary conditions, the loading cycle of characteristic material points in the contact area is determined. The Dang Van damage initiation criterion is based on the critical plane approach, which combines the largest allowable shearing and hydrostatic stresses (tensile and compressive), with an assumed elastic shakedown behaviour and it is used in this work. The material point of initial fatigue damage is then determined at the transition of the loading cycle stresses over the critical plane. The model assumed a homogeneous and elastic material model, without any imperfections or residual stresses, and elastic shakedown is considered. A proper determination of loading cycles and their characteristic values is of significance for contact fatigue initiation analysis. Finally, determination of the most critical material point on or under the contact surface and related number of loading cycles required for fatigue damage initiation is calculated with the strain-life (▫$epsilon$▫-N) method.
Ključne besede: machine elements, contact fatigue, crack initiation, strain life method, critical plane approach, numerical modeling
Objavljeno: 01.06.2012; Ogledov: 836; Prenosov: 4
URL Celotno besedilo (0,00 KB)

Numerično modeliranje mešanja v posodi z Rushtonovim mešalom
Matjaž Hriberšek, Matej Zadravec, 2005, strokovni članek

Opis: Prispevek obravnava numerično modeliranje mešanja newtonske tekočine v mešalni posodi, v kateri je nameščeno turbinsko Rushtonovo mešalo. Obravnavan je ustaljeni turbulentni tokovni rezim, opisan s časovno povprečnim Navier-Stokesovim sistemom enačb. Numerično reševanje temelji na uporabi dvoenačbnega modela turbulence in metode končnih prostornin. Posebna pozornostje namenjena modeliranju vrtenja mešala ter izračunu mehanske moči za mešanje, kakor tudi nekaterim poenostavitvam, ki omogočajo hitrejši izračun zahtevnih diskretnih modelov.
Ključne besede: Rushton impeller, numerical modeling, turbulent flow, flow conditions
Objavljeno: 10.07.2015; Ogledov: 255; Prenosov: 20
URL Celotno besedilo (0,00 KB)

Development of a conceptual material model for structured materials - S_BRICK
Vladimir Vukadin, Jakob Likar, Vojkan Jovičić, 2005, izvirni znanstveni članek

Opis: Materials known in literature as Soft Rocks & Hard Soils such as claystones, siltstones, flysh, hard soils, marls, etc. received a lot of attention in research community in recent years. It was demonstrated that some of these materials can be described through general theoretical framework (Cotecchia & Chandler [1]), which takes into account the structure as an intrinsic material property that is present in all natural geological materials. The influence of the structure is manifested as an increase in strength and stiffness in a material. Based on a laboratory results and existent theoretical frameworks, a further step was taken with the development of a conceptual constitutive model for structured materials. A model formulated in strain space named BRICK (Simpson [2]) was chosen as a base model and was further developed with the inclusion of structure and destructuring. The new model was named S_BRICK and was tested on a conceptual level where the results of numerical tests on structured and structure less (reconstituted) materials at different stress paths were compared. The results showed that S_BRICK was able to capture stress-strain behavior typical for structured material and could be potentially used for the modeling of Soft Rocks and Hard Soils.
Ključne besede: geomechanics, soft rocks, hard soils, constitutive material models, structure, destructuring, numerical modeling
Objavljeno: 15.05.2018; Ogledov: 73; Prenosov: 3
.pdf Celotno besedilo (586,91 KB)

New trends in rock mass characterisation for designing geotechnical structures
Drago Ocepek, 2005, izvirni znanstveni članek

Opis: The investigation on designing supporting measures for geotechnical structures consists of the proper selection of the input data for the stress – strain analysis of the excavation process and the selection of retaining measures. In the preliminary phase of investigation the area must be geologically mapped in detail, and discontinuities precisely measured, boreholes and their “in situ” tests listed and samples for laboratory examinations taken. The new method allows rock mass classification for different rock quality, from soft rocks to mixed rock masses, as well as determination of the geological strength index GSI. The limits for using the suggested method are persistent discontinuities in rock mass which lead to translation or rotation failure mechanisms, either in a single plane or as a wedge. In all cases where discontinuities play a significant role, the rock mass structure must be considered and kinematical analyses performed. In other circumstances, a rock may be uniform and reasonably isotropic due to the geometry of discontinuities and their mutual intersections. The value range of GSI is first determined in the beginning of investigation and later in the excavation phase by considering the disturbance factor D, which expresses disturbances caused by excavation methods and rock mass relaxation. The strength and deformability parameters of rocks of different quality are determined by the generalized Hoek-Brown failure criterion and applied to shallow and deep tunnels or slopes. Before the start of excavations work and after establishing the retaining measures, the analysis results are checked by monitoring. New methods include the determination of post peak strength parameters of rock mass after relaxation, and routine measurements. The newest measurement system however allows direct readings of displacements of the rock mass in both the elastic and post-peak states. With back analyses we determine the softening behavior of the rock mass and a possible need for increasing retaining measures. Such a design method enables the optimization of retaining measures and the reduction of investment costs.
Ključne besede: geological strength index – GSI, simulation of a triaxial large scale »in situ« test, numerical modeling, retaining measures, rock reinforcement, monitoring, back analyses, strain softening, rock mass relaxation
Objavljeno: 16.05.2018; Ogledov: 48; Prenosov: 0
.pdf Celotno besedilo (1,05 MB)

Modeling of the stress-strain behavior in hard soils and soft rocks
Vladimir Vukadin, 2007, izvirni znanstveni članek

Opis: The paper begins with a definition of hard soils and soft rocks (HSSR); this is followed by a short overview of the typical stress-strain behavior of HSSR. It is shown that in spite of the differences in the origin, type and strength of materials, similar stress-strain behaviors can be observed for different materials, ranging from soils to rocks. Based on this observed similarity a theoretical framework can be postulated, with which an appropriate constitutive model for HSSR can be formulated. This model includes the concepts of structure and destructurization as intrinsic material properties. A model named S_BRICK that takes into account the structure and destructurization has been developed and a comparison of this model’s predictions with laboratory results is presented.
Ključne besede: geomechanics, soft rocks, hard soils, stress-strain behaviour, constitutive modeling, structure, destructurization, numerical modeling
Objavljeno: 18.05.2018; Ogledov: 86; Prenosov: 3
.pdf Celotno besedilo (679,21 KB)

Modeling of a geocell-reinforced pavement
Samo Peter Medved, Bojan Žlender, Stanislav Lenart, Primož Jelušič, 2016, izvirni znanstveni članek

Opis: This article details how the serviceability of a flexural pavement structure is improved by incorporating the Cellular Confinement System (geocells). For this purpose, two different pavement structures, with and without embedded geocells, were manufactured in a laboratory and an accelerated traffic type of loading was applied. The vertical and horizontal cyclic loads were applied simultaneously to simulate the effect of principal stress rotation. A comparative study between the conventional flexible pavement and the geocell-reinforced flexible pavement is presented. Additionally, numerical models of the laboratory tests were built and the results were compared. The simulation of the experimental tests using the Traffic Load Simulator (TLS) are carried out using the FEM and advanced models that describe the permanent strain behavior of the unbound granular material. The development of permanent deformation within the pavement structure, with and without the geocells, is also presented through the numerical model, which was verified by the experimental results.
Ključne besede: flexible pavement, reinforcement, geocell, traffic load simulator, permanent deformation, numerical modeling
Objavljeno: 18.06.2018; Ogledov: 5; Prenosov: 0
.pdf Celotno besedilo (1,39 MB)

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