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See detailNumerical Solution of Non-Isothermal Fluid Flows Using Local Radial Basis Functions (LRBF) Interpolation and a Velocity-Correction Method
Bourantas, Georgios UL; Skouras, Eugene; Loukopoulos, Vasilis et al

in Computer Modeling in Engineering and Sciences (2010), 64(2), 187-212

Meshfree point collocation method (MPCM) is developed, solving the velocity-vorticity formulation of Navier-Stokes equations, for two-dimensional, steady state incompressible viscous flow problems in the ... [more ▼]

Meshfree point collocation method (MPCM) is developed, solving the velocity-vorticity formulation of Navier-Stokes equations, for two-dimensional, steady state incompressible viscous flow problems in the presence of heat transfer. Particular emphasis is placed on the application of the velocity-correction method, ensuring the continuity equation. The Gaussian Radial Basis Functions (GRBF) interpolation is employed to construct the shape functions in conjunction with the framework of the point collocation method. The cases of forced, natural and mixed convection in a 2D rectangular enclosure are examined. The accuracy and the sta- bility of the proposed scheme are demonstrated through three representative, well known and established benchmark problems. Results are presented for high values of the characteristics non-dimensional numbers of the flow, that is, the Reynolds, the Rayleigh and the Richardson number [less ▲]

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See detailNumerical solution of the dynamical mean field theory of infinite-dimensional equilibrium liquids
Manacorda, Alessandro UL; Schehr, Grégory; Zamponi, Francesco

in Journal of Chemical Physics (2020)

We present a numerical solution of the dynamical mean field theory of infinite-dimensional equilibrium liquids established in [Phys. Rev. Lett. 116, 015902 (2016)]. For soft sphere interactions, we obtain ... [more ▼]

We present a numerical solution of the dynamical mean field theory of infinite-dimensional equilibrium liquids established in [Phys. Rev. Lett. 116, 015902 (2016)]. For soft sphere interactions, we obtain the numerical solution by an iterative algorithm and a straightforward discretization of time. We also discuss the case of hard spheres, for which we first derive analytically the dynamical mean field theory as a non-trivial limit of the soft sphere one. We present numerical results for the memory function and the mean square displacement. Our results reproduce and extend kinetic theory in the dilute or short-time limit, while they also describe dynamical arrest towards the glass phase in the dense strongly-interacting regime. [less ▲]

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See detailNumerical studies of magnetic particles concentration in biofluid (blood) under the influence of high gradient magnetic field in microchannel
Loukopoulos, Vassilios; Bourantas, Georgios UL; Lampropoulos, Demetrios et al

Scientific Conference (2016, July 15)

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See detailNumerical study of high impedance T-match antennas for terahertz photomixers
Juul, Lars UL; Mikulics, Martin; Pereira, Mauro F. et al

in Optical and Quantum Electronics (2015), 47

This paper outlines an efficient numerical method to design terahertz photomixers. The simulations are benchmarked using measured power levels from results published in the literature. Next, the method is ... [more ▼]

This paper outlines an efficient numerical method to design terahertz photomixers. The simulations are benchmarked using measured power levels from results published in the literature. Next, the method is applied to two new photomixer designs based on the high impedance T-match antenna with bias supply DC-blocking structures for either a uniplanar layout or amultilayer structure for improved device reliability. Manufacturability is favoured by avoiding the use of airbridges, substrate thinning or under-etching. The estimated output power of the improved design is 9.0μW, which is an improvement of three times over the reference photomixer. [less ▲]

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See detailNumerical study of magnetic particles concentration in biofluid (blood) under the influence of high gradient magnetic field in microchannel
Loukopoulos, Vassilios; Bourantas, Georgios UL; Labropoulos, Dimitrios et al

Scientific Conference (2016, June)

A meshless numerical scheme [1] is developed in order to simulate the magnetically mediated separation of biological mixture used in lab-on-chip devices as solid carriers for capturing, transporting and ... [more ▼]

A meshless numerical scheme [1] is developed in order to simulate the magnetically mediated separation of biological mixture used in lab-on-chip devices as solid carriers for capturing, transporting and detecting biological magnetic labeled entities [2], as well as for drug delivering, magnetic hyperthermia treatment, magnetic resonance imaging, magnetofection, etc. A modified one-way particle-fluid coupling analysis is considered to model the interaction of the base fluid of the mixture with the distributed particles motion. In details, bulk flow influences particle motion (through a simplified Stokes drag relation), while it is strongly dependent on particle motion through (particle) concentration. Due to the imposed magnetic field stagnation regions are developed, leading to the accumulation of the magnetic labeled species and finally to their collection from the heterogeneous mixture. The role of (i) the intensity of magnetic field and its gradient, (ii) the position of magnetic field, (iii) the magnetic susceptibility of magnetic particles, (iv) the volume concentration of magnetic particles (nanoparticles) and their size, (v) the flow velocity in the magnetic- fluidic interactions and interplay between the magnetophoretic mass transfer and molecular diffusion are thoroughly investigated. Both Newtonian and non-Newtonian blood flow models are considered, along with different expressions for the concentration and numerical results are presented for a wide range of physical parameters (Hartmann number (Ha), Reynolds number (Re)). A comprehensive study investigates their impact on the biomagnetic separation. For verification purposes, the numerical results obtained by the proposed meshless scheme were compared with established numerical results from the literature, being in excellent agreement. [less ▲]

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See detailNumerical study of particle mixing in a lab-scale screw mixer using the discrete element metod
Qi, Fenglei UL; Heindel, Theodore; Wright, Mark

in Powder Technology (2017), 308

This study employs the discrete element method (DEM) to simulate particulate flow and investigate mixing performance of a lab-scale double screw mixer. The simulation employs polydispersed biomass and ... [more ▼]

This study employs the discrete element method (DEM) to simulate particulate flow and investigate mixing performance of a lab-scale double screw mixer. The simulation employs polydispersed biomass and glass bead particles based on experiments conducted in previous studies. Visual examination of particle distribution and statistical analysis of particle residence times of experimental data served as model validation. Statistical analysis indicates a maximum 9.8% difference between the experimental and simulated biomass particle mean residence time, and visual observations suggest the simulation captures the particle mixing trends observed in the experiments. Results indicate that the particle mean mixing time, non-dimensionalized by ideal flow time in the plug flow reactor, varies between 1.008 and 1.172, and it approaches 1 with increasing biomass feed rate. The mixing index profile in the axial direction shows a mixing-demixing-mixing oscillation pattern. Increasing screw pitch length is detrimental to mixing performance; decreasing the solid particle feed rate reduces the mixing degree; and increasing the biomass to glass bead size ratio decreases mixing performance. A comparison of a binary, single-sized biomass and glass particles mixture to a multicomponent mixture indicates that the binary system has similar mixing pattern as a multicomponent system. These findings demonstrate that DEM is a valuable tool for the design and simulation of double screw mixing systems. [less ▲]

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See detailNumerical study of the influence of particle size and packing on pyrolysis products using XDEM
Mahmoudi, Amir Houshang UL; Hoffmann, F.; Peters, Bernhard UL et al

in International Communications in Heat and Mass Transfer (2016), 71

Conversion of biomass as a renewable source of energy is one of the most challenging topics in industry and academy. Numerical models may help designers to understand better the details of the involved ... [more ▼]

Conversion of biomass as a renewable source of energy is one of the most challenging topics in industry and academy. Numerical models may help designers to understand better the details of the involved processes within the reactor, to improve process control and to increase the efficiency of the boilers. In this work, XDEM as an Euler-Lagrange model is used to predict the heat-up, drying and pyrolysis of biomass in a packed bed of spherical biomass particles. The fluid flow through the void space of a packed bed (which is formed by solid particles) is modeled as three-dimensional flow through a porous media using a continuous approach. The solid phase forming the packed bed is represented by individual, discrete particles which are described by a Lagrangian approach. On the particle level, distributions of temperature and species within a single particle are accounted for by a system of one-dimensional and transient conservation equations. The model is compared to four sets of experimental data from independent research groups. Good agreements with all experimental data are achieved, proving reliability of the used numerical methodology. The proposed model is used to investigate the impact of particle size in combination with particle packing on the char production. For this purpose, three setups of packed beds differing in particle size and packing mode are studied under the same process conditions. The predicted results show that arranging the packed bed in layers of small and large particles may increase the final average char yield for the entire bed by 46 %. © 2015 Elsevier B.V. [less ▲]

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See detailNumerical study on design rules for minimum degree of shear connection in propped steel-concrete composite beams
Vigneri, Valentino; Odenbreit, Christoph UL; Romero, Alfredo UL

in Engineering Structures (2021), 241

This manuscript presents a numerical study on simply supported propped composite beams with ductile shear connectors subjected to uniformly distributed load. The aim is to assess the performance of the ... [more ▼]

This manuscript presents a numerical study on simply supported propped composite beams with ductile shear connectors subjected to uniformly distributed load. The aim is to assess the performance of the revised rules for the minimum degree of shear connection (CEN/TC250/SC4.T3) with respect to the occurring slip. First, a non-linear 3D finite element model was developed through the software ABAQUS 2017 and validated against analytical values of the elastic stiffness and plastic bending resistance. Then, 91 configurations were analysed for different degrees of shear connection η=0.2,0.4…1.0. The span ranges from 6 to 25 m while the geometrical and mechanical properties varied within their typical field of applicability. According to both current and revised rules, 16 configurations with relatively deep beam and “weak” concrete slab exhibited allowable slip values smax significantly higher than 6 m. Therefore, the authors proposed a reduction of the maximum degree of utilization to these special cases. If the proposed reduction is included in the revised rules, none of the considered cases exhibit a slip smax higher than 8 mm while few cases have smax between 6 and 8 mm. For the ease of use, a design proposal is reformulated as a conditional reduction of the plastic bending resistance of the composite section. [less ▲]

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See detailNumerical study on the load bearing capacity of a steel U section beam used as a formwork in constrcution stage
Turetta, Maxime UL; Khelil, Abdelouahab; Odenbreit, Christoph UL et al

Scientific Conference (2018, September 05)

For many categories of buildings, the structural elements must be fire resistant to allow people to evacuate and firefighters to intervene. A new type of steel-concrete composite solution dedicated to ... [more ▼]

For many categories of buildings, the structural elements must be fire resistant to allow people to evacuate and firefighters to intervene. A new type of steel-concrete composite solution dedicated to steel building structures is under development to resist against this fire situation. The solution is composed of a steel U section acting as a formwork for a reinforced concrete part that provides the fire resistance. In order to keep the habits of steel construction, the solution is unpropped in construction stage and the concrete is casted on site. Thus the solution has to resist against three majors situations: the construction stage without propping, the exploitation stage and the fire situation. The steel part of the composite beam is then designed to face the construction stage without propping. The present paper describes the numerical investigations carried out on the load bearing capacity of this steel section in construction stage. The objective of these investigations is to finally propose a steel solution stable and resistant for its use during construction stage. The numerical model of the steel section and its boundary conditions are presented. A first elastic calculation is used to determine the Eigen modes of the beam that give the shape of initials imperfections. Then analysis considering materials non-linearity and geometrical imperfections (GMNIA calculation) are carried out. A sensitivity study on the influence of the geometrical imperfections on the load bearing capacity of the beam is performed. Then, with the more conservative initial imperfection, a study on the global stability of the beam without any intermediate restraint is carried out. Finally, to overcome the problem of instability in construction stage, the restraint induced by the perpendicular steel decks is investigated. [less ▲]

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See detailNumerical study on the revised rules for minimum degree of shear connection in propped and unpropped steel-concrete composite beams
Odenbreit, Christoph UL; Vigneri, Valentino UL

in Proceedings of ICMS (2021, June 16)

The work presents a numerical study that focuses on steel-concrete composite beams using ductile headed stud shear connectors. The objective is to check the suitability of the proposed revised EN 1994-1-1 ... [more ▼]

The work presents a numerical study that focuses on steel-concrete composite beams using ductile headed stud shear connectors. The objective is to check the suitability of the proposed revised EN 1994-1-1 rules for the minimum degree of shear connection. Therefore, a non-linear 3D finite element model of simply supported composite beams was developed and validated against the analytical values of the plastic bending design resistance. The parametric study consists of 10 configurations where the relative slip at slab-beam interface was carefully investigated at different degrees of shear connection and propping conditions. Specifically, the slip at the minimum degree of shear connection shall not exceed the limit of 6 mm defined as the characteristic slip of ductile connector according to EN 1994-1-1. The results showed that the revised rules for unpropped beams delivers conservative results whereas one case with propped conditions exhibit a maximum slip significantly higher than 6 mm. [less ▲]

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See detailNumerical Time-Domain Modeling of Lamb Wave Propagation Using Elastodynamic Finite Integration Technique
Rappel, Hussein UL; Yousefi-Koma, Aghil; Jalil, Jamali et al

in Shock and Vibration (2014), 2014

This paper presents a numerical model of lamb wave propagation in a homogenous steel plate using elastodynamic finite integration technique (EFIT) as well as its validation with analytical results. Lamb ... [more ▼]

This paper presents a numerical model of lamb wave propagation in a homogenous steel plate using elastodynamic finite integration technique (EFIT) as well as its validation with analytical results. Lamb wave method is a long range inspection technique which is considered to have unique future in the field of structural health monitoring. One of the main problems facing the lamb wave method is how to choose the most appropriate frequency to generate the waves for adequate transmission capable of properly propagating in the material, interfering with defects/damages, and being received in good conditions. Modern simulation tools based on numerical methods such as finite integration technique (FIT), finite element method (FEM), and boundary element method (BEM) may be used for modeling. In this paper, two sets of simulation are performed. In the first set, group velocities of lamb wave in a steel plate are obtained numerically. Results are then compared with analytical results to validate the simulation. In the second set, EFIT is employed to study fundamental symmetric mode interaction with a surface braking defect. [less ▲]

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See detailNumerical validation of a κ-ω-κ θ -ω θ heat transfer turbulence model for heavy liquid metals
Cerroni, D.; Vià, R. Da; Manservisi, S. et al

in Journal of Physics: Conference Series (2015), 655(1), 012046

The correct prediction of heat transfer in turbulent flows is relevant in almost all industrial applications but many of the heat transfer models available in literature are validated only for ordinary ... [more ▼]

The correct prediction of heat transfer in turbulent flows is relevant in almost all industrial applications but many of the heat transfer models available in literature are validated only for ordinary fluids with Pr ≃ 1. In commercial Computational Fluid Dynamics codes only turbulence models with a constant turbulent Prandtl number of 0.85 — 0.9 are usually implemented but in heavy liquid metals with low Prandtl numbers it is well known that these models fail to reproduce correlations based on experimental data. In these fluids heat transfer is mainly due to molecular diffusion and the time scales of temperature and velocity fields are rather different, so simple turbulence models based on similarity between temperature and velocity cannot reproduce experimental correlations. In order to reproduce experimental results and Direct Numerical Simulation data obtained for fluids with Pr ≃ 0.025 we introduce a κ-ε-κ θ -ε θ turbulence model. This model, however, shows some numerical instabilities mainly due to the strong coupling between κ and ε on the walls. In order to fix this problem we reformulate the model into a new four parameter κ-ω-κ θ -ω θ where the dissipation rate on the wall is completely independent on the fluctuations. The model improves numerical stability and convergence. Numerical simulations in plane and channel geometries are reported and compared with experimental, Direct Numerical Simulation results and with results obtained with the κ-ε formulation, in order to show the model capabilities and validate the improved κ-ω model. [less ▲]

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See detailNumerical Velocity determination and Calibration Methods for CHAMP Using the Energy Balance Approach
Weigelt, Matthias UL; Sneeuw, N.

in Jekeli, Christopher; Bastos, Luisa; Fernandes, Joana (Eds.) Gravity, Geoid and Space Missions (2005, June)

More than two years of data of the champ satellite mission is available and the usage of the energy balance approach for global gravity field recovery has been successfully implemented by several groups ... [more ▼]

More than two years of data of the champ satellite mission is available and the usage of the energy balance approach for global gravity field recovery has been successfully implemented by several groups around the world. This paper addresses two important aspects of the data processing. First, high-quality gravity recovery requires numerical differentiation of kinematic positions. Two methods are investigated using simulated and real dynamic data. It is shown that a third order Taylor differentiator is sufficient to reach good results. Second drift due to the accelerometer bias has to be corrected. Two possible approaches are discussed: cross-over calibration on the one hand calibration w.r.t. a reference model on the other hand. Currently the crossover calibration fails due to the insufficient accuracy of the crossover determination whereas the calibration w.r.t. a reference model gives good results. [less ▲]

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See detailNumerically determined enrichment functions for the extended finite element method and applications to bi-material anisotropic fracture and polycrystals
Menk, Alexander; Bordas, Stéphane UL

in International Journal for Numerical Methods in Engineering (2010), 83(7), 805-828

Strain singularities appear in many linear elasticity problems. A very fine mesh has to be used in the vicinity of the singularity in order to obtain acceptable numerical solutions with the finite element ... [more ▼]

Strain singularities appear in many linear elasticity problems. A very fine mesh has to be used in the vicinity of the singularity in order to obtain acceptable numerical solutions with the finite element method (FEM). Special enrichment functions describing this singular behavior can be used in the extended finite element method (X-FEM) to circumvent this problem. These functions have to be known in advance, but their analytical form is unknown in many cases. Li et al. described a method to calculate singular strain fields at the tip of a notch numerically. A slight modification of this approach makes it possible to calculate singular fields also in the interior of the structural domain. We will show in numerical experiments that convergence rates can be significantly enhanced by using these approximations in the X-FEM. The convergence rates have been compared with the ones obtained by the FEM. This was done for a series of problems including a polycrystalline structure. [less ▲]

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See detailNumerical–experimental observation of shape bistability of red blood cells flowing in a microchannel
Guckenberger, A.; Kihm, A.; John, T. et al

in European Physical Journal E. Soft Matter (2018)

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See detailLa numérisation de l'argent liquide: fin ou résistance du "cash"?
Allemand, Frederic UL

in Revue de l'euro (2019), (54),

Dans cette synthèse des communications au colloque, il est proposé une mise en perspective des tensions qui se nouent autour des formes de la monnaie et de son utilisation. Quoique les espèces conservent ... [more ▼]

Dans cette synthèse des communications au colloque, il est proposé une mise en perspective des tensions qui se nouent autour des formes de la monnaie et de son utilisation. Quoique les espèces conservent une charge symbolique et une certaine importance pour les paiements de faible valeur, des restrictions multiples se sont développées sur les dernières années au nom de la lutte contre la fraude fiscale, le crime organisé ou le terrorisme. A quoi s'ajoutent la suppression de certaines valeurs, les billets de 500 euros et, à l'opposé, les pièces de 1 ou 2 cents. Cependant, une remise en cause plus substantielle s'affirme sous l'effet du développement de l'introduction des nouvelles technologies dans le secteur des paiements: la réalisation des paiements scripturaux approchent dorénavant l'immédiateté; de nouvelles monnaies, locales, virtuelles trouvent de nouveaux publics, et entrent en concurrence avec la monnaie légale. [less ▲]

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See detailNumerische Kompetenzen bei Kindern
Wantz, Marc UL

in Krus, Astrid; Hammer, Richard (Eds.) „Kleine Forscher – Große Entdecker Psychomotorische Bewegungsförderung im Kleinkindalter“ (2009)

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See detailNumerische Untersuchung zur Strömungsentwicklung im passiven Flutsystem des Reaktordesigns Kerena
Kaczmarkiewicz, Nadine UL

Doctoral thesis (2019)

In case of a loss-of-coolant accident in a nuclear power plant, the passive gravity-driven core flooding system recovers the reactor’s water inventory so that the core is covered at all times. It is ... [more ▼]

In case of a loss-of-coolant accident in a nuclear power plant, the passive gravity-driven core flooding system recovers the reactor’s water inventory so that the core is covered at all times. It is essential to estimate, when passive flooding valves open, whether reverse flow occurs and to which extent this may delay flooding or even lead to initial mass displacement from the reactor to the flooding pools. Experimental investigations including passive safety systems of the KERENA-design are performed in a scaled-down facility. Such so-called integral tests are carried out with initial and boundary conditions of different design basis accidents. The behavior of the passive core flooding system is analyzed proofing the influence through other passive safety systems. Evidence is shown that a stable two-phase reverse flow occurs, due to incomplete condensation at the outlet of the emergency condenser and to adiabatic evaporation in the flooding line. The hydrostatic column is reduced during reverse flow but regained in all considered cases. As a result the onset of flooding is delayed only moderately. The influence on the flow development of the containment pressure, of the geometry of the flooding line, and of other peculiar boundary conditions of the considered experiments is discussed. Results from numerical simulations are presented and confirm the experimental results. The considered numerical model of the flooding system can predict fundamental phenomena governing the flow development in the flooding line with satisfactory accuracy. [less ▲]

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