1. Advancing nanofluid numerical modelling: A novel Euler–Lagrange method with experimental validationNejc Vovk, Blaž Kamenik, Elif Begum Elcioglu, Erdem Ozyurt, Ziya Haktan Karadeniz, Alpaslan Turgut, Jure Ravnik, 2025, original scientific article Abstract: We present a novel approach to numerical modelling of thermal nanofluids based on the Euler–Lagrange method. This approach overcomes the challenge of extremely fine temporal discretization, which previous Euler–Lagrange nanofluid numerical models struggled to address, while also avoiding the need for too many Lagrangian nanoparticles. A numerical uncertainty assessment method is adapted for the proposed approach. The model is validated with a simple verification case and applied to simulate a closed natural circulation loop heat exchanger operating with heating power ranging from 10 W to 50 W and nanoparticle volume fractions of 0.5% to 2%, using an Al2O3–water nanofluid. Results are compared with experimental temperature measurements and an Euler–Euler implementation of the same nanofluid. The model is also applied to simulate the natural convection inside a vertical enclosure, studied experimentally by other authors. The proposed novel approach demonstrates agreement with both experimental data and the Euler–Euler implementation, effectively capturing the overall behaviour of nanofluids. We establish, that the interplay of multiple transport phenomena, that occur in nanofluid operated devices, can be difficult to completely reproduce numerically within the framework of current modelling assumptions.
Keywords: Euler–Lagrange nanofluid modelling, numerical uncertainty assessment, natural convection loop simulation, nanoparticle concentration analysis, nanofluid heat transfer
Published in DKUM: 17.06.2025; Views: 0; Downloads: 7
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2. Numerical study on in-plane behaviour of light timber-framed wall elements under a horizontal load impactMiroslav Premrov, Erika Kozem Šilih, 2025, original scientific article Abstract: This study analyses the many different parameters of the in-plane flexibility problem regarding the lateral behaviour of light timber-framed (LTF) wall elements with different types of sheathing material (FPB, OSB, or even reinforced concrete), as well as the thickness of the timber frame elements (internal or external wall elements). The analysis simultaneously considers bending, shear, and timber-to-framing connection flexibility, while assuming stiff-supported wall elements as prescribed by Eurocode 5. Particular emphasis is placed on the sliding deformation between sheathing boards and the timber frame, which can significantly reduce the overall stiffness of LTF wall elements. The influence of fastener spacing (s) on sliding deformation and overall stiffness is comprehensively analysed, as well as the different bending and shear behaviours of the various sheathing materials. The results show that reducing the fastener spacing can significantly improve the stiffness of OSB wall elements, while it is less critical for FPB elements used in mid-rise timber buildings. A comparison of external and internal wall elements revealed a minimal difference in racking stiffness (3.3%) for OSB and FPB specimens, highlighting their comparable performance. The inclusion of RC sheathing on one side of the LTF elements showed significant potential to improve torsional behaviour and in-plane racking stiffness, making it a viable solution for strengthening prefabricated multi-storey timber buildings. These findings provide valuable guidance for optimizing the design of LTF walls, ensuring improved structural performance and extended application possibilities in modern timber construction.
Keywords: timber, structures, light timber-framed element, modelling, numerical analysis
Published in DKUM: 17.03.2025; Views: 0; Downloads: 11
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3. Numerical study of racking resistance of timber-made double-skin façade elementsErika Kozem Šilih, Miroslav Premrov, 2022, original scientific article Abstract: The use of a double-skin façade (DSF) is a quite new approach in the building renovation process, complementing conventional renovation strategies. A double-skin façade is an envelope wall construction that consists of two transparent surfaces separated by a cavity and can essentially improve the thermal and acoustic resistance of the building envelope. The main double-skin wall components are usually composed of a hardened external single glazing pane and a double or triple thermal insulating internal glass pane, which are connected to the frame structure. Recently, many studies have analysed the thermal and acoustic performance of DSF elements, but almost none in terms of structural behaviour, especially in terms of determining the racking resistance of such wall elements. Moreover, with a view to reduce the global warming potential, an eco-friendly timber frame instead of a commonly used steel, aluminium or plastic frame is studied in this analysis. However, structurally combining timber and glass to develop an appropriate load-bearing structural element is a very complex process involving a combination of two materials with different material properties, where the type of bonding can be selected as a crucial parameter affecting the racking resistance range. Since the costs of experiments performed on such full-scale DSF elements are very high and such experiments are time-consuming, it is crucial to develop special mathematical models for analysing the influence of the most important parameters. Therefore, the main goal of this paper is to develop the finite element mathematical model of the studied DSF structural elements with a highly ecological solution by using a timber frame. In the second step, the developed model is further implemented in the numerical analysis of racking stiffness and followed by a comprehensive parametric numerical study on different parameters influencing the horizontal load-bearing capacity of such DSF timber elements. The obtained results indicate that the new approach of the developed load-bearing prefabricated timber DSF elements can essentially improve racking resistance and stiffness compared with the widely studied timber-glass single-skin wall elements and can thus be fully recommended especially in the structural renovation process of old buildings.
Keywords: timber, glass, double-skin façades, racking resistance, mathematical modelling, numerical analysis, Finite Elements Methods (FEM)
Published in DKUM: 11.03.2025; Views: 0; Downloads: 7
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4. Analytical model and swapping policy assessment of a vertical lift module – buffer integrated storage systemJakob Marolt, Fabio Sgarbossa, Jesus A. Jimenez, Abhimanyu Sharotry, Tone Lerher, 2024, original scientific article Abstract: To meet the rising demands of global trade and e-commerce, efficient warehousing relies on inte-grated and cooperative material handling systems. This paper investigates the extension of VerticalLift Module (VLM) storage capability with a Buffer System and assesses the impact of this integra-tion on performance. We developed an analytical model to calculate the expected dual commandcycles, forming the basis for evaluating the VLM – Buffer integrated storage system’s performance.Our research emphasises minimising unnecessary swaps between the VLM and the Buffer Systemto enhance throughput performance. We introduce the Look Ahead Strategy (LAS) to minimiseinter-system swaps and develop a Binary Integer Program (BIP) to benchmark its performance. Theresults indicate that LAS performs on par with BIP, due to its ability to consider product popular-ity during the final selection of the outbound swapping tote. Through a comprehensive analysisof the analytical model with an empirical correction, utilising Pareto-based order sequences, theresults show deviations of less than 1% on average, affirming the analytical model’s accuracy. Ourresearch provides insights on using the VLM-Buffer integrated storage system, emphasising efficienttote swapping policies like LAS for enhanced warehouse operations, and allows managers to assesssystem performance through scenario-based analyses.
Keywords: automated warehouses, vertical lift module, toteswapping, analytical and numerical modelling, performance evaluation
Published in DKUM: 11.10.2024; Views: 0; Downloads: 36
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5. Numerical analysis of low-enthalpy deep geothermal energy extraction using a novel gravity heat pipe designUrban Gselman, Vid Peršak, Darko Goričanec, 2024, original scientific article Abstract: Geothermal energy, derived from the Earth’s internal heat, can be harnessed due to the
geothermal gradient between the Earth’s interior and its surface. This heat, sustained by radiogenic
decay, varies across regions, and is highest near volcanic areas. In 2020, 108 countries utilised
geothermal energy, with an installed capacity of 15,950 MWe for electricity and 107,727 MWt for
direct use in 2019. Low-enthalpy sources require binary systems for power production. Open-loop
systems face issues like scaling, difficult water treatment, and potential seismicity, while closed-loop
systems, using abandoned petroleum or gas wells, reduce costs and environmental impacts greatly.
The novel geothermal gravity heat pipe (GGHP) design eliminates parasitic power consumption by
using hydrostatic pressure for fluid circulation. Implemented in an abandoned well in north-east
(NE) Slovenia, the GGHP uses a numerical finite difference method to model heat flow. The system
vaporises the working fluid in the borehole, condenses it at the surface, and uses gravitational flow
for circulation, maintaining efficient heat extraction. The model predicts that continuous maximum
capacity extraction depletes usable heat rapidly. Future work will explore sustainable heat extraction
and potential discontinuous operation for improved efficiency.
Keywords: geothermal energy, geothermal gravity heat pipe, numerical modelling, single well closed-loop heat exchanger
Published in DKUM: 03.09.2024; Views: 41; Downloads: 17
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6. 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, original scientific article Abstract: 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.
Keywords: geosynthetic-soil interface, constitutive model, numerical modelling, FLAC3D, geogrid element
Published in DKUM: 14.06.2018; Views: 1558; Downloads: 84
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7. A coupled thermo-hydro-mechanical model of expansive clays subjected to heating and hydratationNadia Laredj, Hanifi Missoum, Karim Bendani, Mustapha Maliki, 2011, original scientific article Abstract: 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.
Keywords: thermo-hydro-mechanical process, unsaturated bentonite, finite element, numerical modelling, expansive clays
Published in DKUM: 13.06.2018; Views: 1170; Downloads: 82
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8. Advances and uncertainties in the design of anchored retaining walls using numerical modellingAntun Szavits-Nossan, 2008, original scientific article Abstract: 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.
Keywords: anchored wall, soil model, shear stiffness, numerical modelling, measured displacements
Published in DKUM: 01.06.2018; Views: 952; Downloads: 108
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9. Numerical study of heat-transfer enhancement of homogeneous water-Au nanofluid under natural convectionPrimož Ternik, Rebeka Rudolf, Zoran Žunič, 2012, original scientific article Abstract: 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.
Keywords: natural convection, nanofluid, heat transfer, numerical modelling
Published in DKUM: 10.07.2015; Views: 1363; Downloads: 153
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10. Numerical study of Rayleigh-Bénard natural-convection heat-transfer characteristics of water-based Au nanofluidsPrimož Ternik, Rebeka Rudolf, Zoran Žunič, 2013, original scientific article Abstract: 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.
Keywords: Rayleigh-Bénard natural convection, water-Au nanofluid, heat transfer, numerical modelling
Published in DKUM: 10.07.2015; Views: 1435; Downloads: 122
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