Opis: A new class of polyHIPE materials has been prepared using high internal phase emulsions (HIPEs) with monomers in both phases. Resulting materials, namely hybrid polyHIPE materials, are obtained consisting of hydrophobic matrix (consisted of styrene cross-linked with DVB or dicyclopentadiene) filled with hydrophilic polymer gel (polyacrylic acid or polyNIPAM) and exhibit morphology changes according to pH and temperature of the surrounding medium. Our focus with regards to the production of hybrid polyHIPE materials was the responsiveness of such materials used for flow control. This property is beneficial for controlling the flow of the solution through the monolithic polymers. Furthermore, polyHIPE materials have also been prepared by using ring opening metathesis polymerisation of monomers, such as dicyclopentadiene and norbornene. Obtained materials have Young’s moduli in the range of hundred times higher than standard polyHIPE materials with the same level of porosity which represents a very important improvement in the development of highly porous cellular polymeric materials.Najdeno v: ključnih besedahKljučne besede: emulsions, high internal phase emulsions, polymers, polyHIPEs, hybrid, hybrid polyHIPE materials, ROMP, flow-through, styrene, DVB, acrylic acid, NIPAMObjavljeno: 04.05.2011; Ogledov: 924; Prenosov: 45 Polno besedilo (3,71 MB)
Opis: The problem of unsteady compressible fluid flow in an enclosure induced by thermoacoustic waves is studied numerically. Full compressible set of Navier-Stokes equations are considered and numerically solved by boundary-domain integral equations approach coupled with wavelet compression and domain decomposition to achieve numerical efficiency. The thermal energy equation is written in its most general form including the Rayleigh and reversible expansion rate terms. Both, the classical Fourier heat flux model and wave heat conduction model are investigated. The velocity-vorticity formulation of the governing Navier-Stokes equations is employed, while the pressure field is evaluated from the corresponding pressure Poisson equation. Material properties are taken to be for the perfect gas, and assumed to be pressure and temperature dependent.Najdeno v: ključnih besedahKljučne besede: compressible fluid flow, boundary element method, thermoacoustic waves, velocity-vorticity fomulationObjavljeno: 31.05.2012; Ogledov: 237; Prenosov: 0 Polno besedilo (0,00 KB)
Opis: In this paper acceleration and computer memory reduction of an algorithm for the simulation of laminar viscous flows and heat transfer is presented. The algorithm solves the velocity-vorticity formulation of the incompressible Navier-Stokes equations in 3D. It is based on a combination of a subdomain boundary element method (BEM) and single domain BEM. The CPU time and storage requirements of the single domain BEM are reduced by implementing a fast multipole expansion method. The Laplace fundamental solution, which is used as a special weighting function in BEM, is expanded in terms of spherical harmonics. The computational domain and its boundary are recursively cut up forming a tree of clusters of boundary elements and domain cells. Data sparse representation is used in parts of the matrix, which correspond to boundary-domain clusters pairs that are admissible for expansion. Significant reduction of the complexity is achieved. The paper presents results of testing of the multipole expansion algorithm by exploring its effect on the accuracy of the solution and its influence on the non-linear convergence properties of the solver. Two 3D benchmark numerical examples are used: the lid-driven cavity and the onset of natural convection in a differentially heated enclosure.Najdeno v: ključnih besedahKljučne besede: boundary element method, fast multipole method, fluid flow, heat transfer, velocity-vorticity fomulationObjavljeno: 31.05.2012; Ogledov: 234; Prenosov: 0 Polno besedilo (0,00 KB)
Opis: Genetic programming is one of the most general evolutionary computation methods. It is an automated method for creating a working computer program from a problem's high-level statement. Genetic programming does this by genetically breeding a population of computer programs using the principles of Darwin's natural selection and biologically inspired operations. In our research, material was formed by drawing using different process parameters and then determining the tensile strengths (dependent variable) of the specimens. On the basis of experimental data, various different prediction models for the tensile stress were developed by the genetic programming method. To make a comparison, the models for tensile stress were also developed by the standard regression method. The accuracies of the best genetic programme models were proved by a testing data set and comparison between the genetic and regression models.Najdeno v: ključnih besedahKljučne besede: forming, flow curve, copper alloys, genetic programmingObjavljeno: 01.06.2012; Ogledov: 143; Prenosov: 2 Polno besedilo (0,00 KB)
Opis: Modern reversible hydro energetic systems are expected to have short operating regimes (pump - turbine) switching time. It is known, one the one side, that profit of reversible systems increases with rise of difference between buying and selling price of the produced electrical energy. When we reduce switching time, on the other side, the physical limitations connected with water hammer effect and pressure pulsations caused with flow inertia have to be considered. These limitations could lead to material erosion and to material damage. Use of the asymmetrical nozzle that is the simple but effective system for avoidance of water hammer effect in pipe systems is presented in the paper. For such nozzle types, different pressure drops and flow rates, for different flow directions are expected, respectively. This fact is used to omit the water hammer effects, during sudden stops of the system; regardless if the system operates in turbine or pump mode. Special attention should be given to design of the nozzles due to the recirculation flows which can be induced with inappropriate geometry. According to this, computational fluid dynamics was used for nozzle design and flow analyse for different operating examples. Numerical simulation results were compared to experimental results measured at reversible pump - turbine model. Based on results agreement (pressure and overall characteristics) correct flow pattern for both operating regimes can be concluded.Najdeno v: ključnih besedahKljučne besede: pipelines, water hammer effect, flow pressure, measurements, fluid dynamicsObjavljeno: 31.05.2012; Ogledov: 131; Prenosov: 1 Polno besedilo (0,00 KB)
Opis: Research results of how the precipitated water scale on heaters of small domestic appliances influences the consumption of electricity are presented. It shows that the majority of water scale samples are composed of aragonite, calcite and dolomite and that those components have an extraordinary low thermal conductivity. Also, the results show that at 2 mm thick deposit, depending on the chemical composition of water scale, the thermal flow is reduced for 10% to 40%; consequently, the consumption of electricity significantly increases.Najdeno v: ključnih besedahKljučne besede: electricity, heat transfer, heat flow, heat exchanger, water scaleObjavljeno: 31.05.2012; Ogledov: 173; Prenosov: 1 Polno besedilo (0,00 KB)
Najdeno v: ključnih besedahKljučne besede: therodynamics, statistical nano-mechanics, fluid flow, nanofluids, thermal conductivity, pure fluids, mathematical modelObjavljeno: 30.05.2012; Ogledov: 146; Prenosov: 0 Polno besedilo (0,00 KB)
Opis: The non-Newtonian fluid flow in a sharp 90 curved pipe is studied numerically to obtain the pressure loss coefficient prompted by disagreement between the existing empirical correlations and results obtained by computer codes. This disagreement results from presumption of fully developed flow throughout the curvature (correlations) while the actual flow is partially developed for the Newtonian and sharp 90 curved bend non-Newtonian flows, and fully developed for slightly bent 90 curvature non-Newtonian flow. The Quadratic model is employed to accommodate the shear-thickening behavior of an electrostatic ash and water mixture. Numerical results are obtained for different values of Reynolds number. Finally, results for local pressure loss coefficient are compared with values obtained for the Power law rheological model.Najdeno v: ključnih besedahKljučne besede: shear-thickening fluid, fluid dynamics, rheological model, pipe bend flow, numerical modelling, pressure lossesObjavljeno: 30.05.2012; Ogledov: 141; Prenosov: 0 Polno besedilo (0,00 KB)
Opis: A numerical method for the solution of the incompressible Navier-Stokes equations was developed using an integral representation of the conservation equations. The velocity-vorticity formulation is employed, where the kinematics is given with the Poisson equation for the velocity vector, while the kinetics is represented with the vorticity transport equation. Based on computational aspects, resulting from CPU time and memory requirements of the boundary domain integral method, a combined approach to the solution of the set of governing equations is proposed. Kinematics is solved using boundary element method (BEM), while kinetics is solved using finite element method (FEM). Lid driven flow in a cubic cavity was considered to show the robustnessand versatility of this formulation. Results of Re=100,400,1000 show a good agreement with benchmark results.Najdeno v: ključnih besedahKljučne besede: 3-D incompressible viscous fluid flow, boundary element method, velocity-vorticity, finite element method, lid driven cavityObjavljeno: 31.05.2012; Ogledov: 119; Prenosov: 0 Polno besedilo (0,00 KB)
Opis: An efficient 3D multidomain BEM for solving problems governed by the Laplace equation is presented. Integral boundary equations are discretized using mixed boundary elements. The field function is interpolated using a continuous linear function while its derivative in a normal direction is interpolated using a discontiuous constant function over surface boundaey elements. Using amultidomain approach, also known as the subdomain technique, sparse system matrices similar to FEM are obtained. Interface boundary conditions between subdomains leads to an over-determined system matrix which is solved using a fast iterative linear least square solver. The accuracy and the robustness of the developed algorithm is presented on a scalar diffusion problem using simple cube geometry and various types of meshes. The efficiency is demonstrated with potential flow around a complex geometry of a fighter airplane using a tetrahedral mesh with over 100.000 subdomains on a personal computer.Najdeno v: ključnih besedahKljučne besede: fluid mechanics, aerodynamics, multidomain boundary element method, Laplace equation, mixed boundary elements, potential flowObjavljeno: 31.05.2012; Ogledov: 360; Prenosov: 0 Polno besedilo (0,00 KB)
