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Numerical study of Rayleigh-Bénard natural-convection heat-transfer characteristics of water-based Au nanofluids
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2013, izvirni znanstveni članek

Opis: The present work deals with the natural convection in a square cavity filled with a water-based Au nanofluid. The cavity is heated from the lower and cooled from the adjacent wall, while the other two walls are adiabatic. Theg overning differential equations have been solved with the standard finite volume method and the hydrodynamic and thermal fields have been coupled using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticlesć volume fraction on the heat-transfer characteristics of Au nanofluids at a given base-fluid (i.e., water) Rayleigh number Rabf. Accurate results are presented over a wide range of the base-fluid Rayleigh numbers (102 £ Rabf £ 105) and the volume fraction of Au nanoparticles (0 % £ j £ 10 %). It is shown that adding nanoparticles to the base fluid delays the onset of convection. Contrary to what is argued by many authors, we show, with numerical simulations, that the use of nanofluids can reduce the heat transfer instead of increasing it.
Ključne besede: Rayleigh-Bénard natural convection, water-Au nanofluid, heat transfer, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 435; Prenosov: 54
.pdf Celotno besedilo (282,00 KB)
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Numerical study of heat-transfer enhancement of homogeneous water-Au nanofluid under natural convection
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2012, izvirni znanstveni članek

Opis: A numerical analysis is performed to examine the heat transfer of colloidal dispersions of Au nanoparticles in water (Au nanofluids). The analysis used a two-dimensional enclosure under natural convection heat-transfer conditions and has been carried out for the Rayleigh number in the range of 103 < Ra < 105, and for the Au nanoparticles' volume-fraction range of 0 < j < 0.10. We report highly accurate numerical results indicating clearly that the mean Nusselt number is an increasing function of both Rayleigh number and volume fraction of Au nanoparticles. The results also indicate that a heat-transfer enhancement is possible using nanofluids in comparison to conventional fluids. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers.
Ključne besede: natural convection, nanofluid, heat transfer, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 475; Prenosov: 48
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Numerical modelling of crack growth in a gear tooth root
Srđan Podrug, Srečko Glodež, Damir Jelaska, 2011, izvirni znanstveni članek

Opis: A computational model for determination of crack growth in a gear tooth root is presented. Two loading conditions are taken into account: (i) normal pulsating force acting at the highest point of the single tooth contact and (ii) the moving load along the tooth flank. In numerical analysis it is assumed that the crack is initiated at the point of the largest stresses in a gear tooth root. The simple Paris equation is then used for a further simulation of the fatigue crack growth. The functional relationship between the stress intensity factor and crack length K=f(a), which is needed for determining the required number of loading cycles N for a crack propagation from the initial to the critical length, is obtained using a displacement correlation method in the framework of the FEM-method considering the effect of crack closure. The model is used for determining fatigue crack growth in a real gear made from case carburised and ground steel 14CiNiMo13-4, where the required material parameters were determined previously by appropriate test specimens. The results of the numerical analysis show that the prediction of crack propagation live and crack path in a gear tooth root are significantly different for both loading conditions considered.
Ključne besede: zobniki, utrujanje, širjenje razpoke, numerično modeliranje, gears, fatigue, crack growth, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 436; Prenosov: 45
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Advances and uncertainties in the design of anchored retaining walls using numerical modelling
Antun Szavits-Nossan, 2008, izvirni znanstveni članek

Opis: This paper describes research on the prediction of horizontal displacements and internal forces in an anchored wall for the protection of an excavation, using standard field and laboratory tests and a finite-element programme with a soil model that can simulate the key aspects of soil behaviour at a construction site. It is important to be acquainted with the constitutive model incorporated in the programme, and the selection of the appropriate soil parameters for the numerical analysis is a crucial part of the modelling. As a result, it is useful to carry out numerical simulations of standard laboratory tests with well-known soil behaviour in order to select the relevant parameters for the simulation of the actual construction process. It is shown in this paper that the measurements of the shear-wave velocities, which can provide the soil’s stiffness at very small strains, can also be useful for determining the static stiffness at a magnitude of the strains relevant for the geotechnical structure under consideration, for both cohesive and noncohesive soils. The research was carried out by a detailed analysis of a case history involving an anchored, reinforced concrete wall supporting the walls of an excavation in a relatively stiff soil. The wall displacements were monitored using an installed inclinometer. The major part of the paper is devoted to an analysis of the selection of parameters, especially the stiffness parameters. The simulation of the triaxial, consolidated, undrained tests was used in order to assess the reduction of the secant stiffness modulus with an increase of the relative mobilized shear strength for the hard clay layer according to the published empirical evidence. It is shown that by selecting the appropriate stiffness parameters for the soil model used in the numerical analysis, it is possible to get an acceptable prediction of the anchored-wall displacements. This is just one example of a successful analysis, but it is encouraging in the way that it shows how it is possible to make reliable predictions based on standard field and laboratory tests and with the use of an available computer programme with a realistic soil model.
Ključne besede: anchored wall, soil model, shear stiffness, numerical modelling, measured displacements
Objavljeno: 01.06.2018; Ogledov: 200; Prenosov: 20
.pdf Celotno besedilo (426,36 KB)
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A coupled thermo-hydro-mechanical model of expansive clays subjected to heating and hydratation
Nadia Laredj, Hanifi Missoum, Karim Bendani, Mustapha Maliki, 2011, izvirni znanstveni članek

Opis: The focus of this work is to provide a numerical formulation for coupled thermo-hydro-mechanical processes in unsaturated expansive clays, especially in compacted bentonite, with a multiphase fluid flow. The model is characterized by the presence of a deformable solid matrix filled with two fluid phases (liquid water and air). In the proposed model, both pore-water and air transfers are assumed to be governed by the generalized Darcy’s law. Fully coupled, nonlinear partial differential equations are established and then solved by using a Galerkin weighted residual approach in the space domain and an implicit integrating scheme in the time domain. The model has been validated against an experimental test from the literature, which involves bentonite under laboratory conditions. The calculated relative errors between the experimental and numerical results are 3% for the temperature and 7% for the stresses. Consequently, the developed numerical model predicts satisfactory results, when compared to the experimental test measures. The model is applicable to two-dimensional problems with various initial and boundary conditions; non linear soil parameters can be easily included in this model.
Ključne besede: thermo-hydro-mechanical process, unsaturated bentonite, finite element, numerical modelling, expansive clays
Objavljeno: 13.06.2018; Ogledov: 112; Prenosov: 13
.pdf Celotno besedilo (389,48 KB)
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Implementation and verification of a geosynthetic-soil interface constitutive model in the Geogrid element of FLAC$^{3D}$
Wu Haimin, Shu Yiming, Dai Linjun, Teng Zhaoming, 2015, izvirni znanstveni članek

Opis: Due to the complexity of geosynthetic-soil interactions, the simple interface constitutive models embedded in the geosynthetic elements of general computing software cannot satisfy the requirements for a numerical simulation of different geosynthetic-soil interface behaviours. Based on the direct shear test results of a composite geomembrane (CGM) and polyurethane (PUR) mixed crushed stones interface, a nonlinear elastic, perfectly plastic model was used to describe the interface behaviours. The method of incorporating an interface constitutive model into the Geogrid element of a fast Lagrange analysis of continua in three dimensions (FLAC3D) procedure was presented in detail through a user-defined program in the FISH environment. Then the incorporated model of the Geogrid element was used to simulate the direct tests of the CGM-PUR mixed crushed stones interface. The results of the numerical tests confirmed the validity and reliability of the incorporated model. The method and program flowchart for implementing the nonlinear elastic, perfectly plastic interface constitutive model into the Geogrid element can provide a reference for users who want to simulate other geosynthetic-soil interface behaviours with FLAC3D.
Ključne besede: geosynthetic-soil interface, constitutive model, numerical modelling, FLAC3D, geogrid element
Objavljeno: 14.06.2018; Ogledov: 220; Prenosov: 15
.pdf Celotno besedilo (269,05 KB)
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