Iskanje po katalogu digitalne knjižnice

Opis: We propose a novel, demonstrably effective, utmost versatile and computationally highly efficient pseudo-rigid body approach for tracking the barycenter and shape dynamics of soft, i.e. nonlinearly deformable micro-particles dilutely suspended in viscous flow. Pseudo-rigid bodies are characterized by affine deformation and thus represent a first-order extension to the kinematics of rigid bodies. Soft particles in viscous flow are ubiquitous in nature and sciences, prominent examples, among others, are cells, vesicles or bacteria. Typically, soft particles deform severely due to the mechanical loads exerted by the fluid flow. Since the shape dynamics of a soft particle - a terminology that shall here also include its orientation dynamics - also affects its barycenter dynamics, the resulting particle trajectory as a consequence is markedly altered as compared to a rigid particle. Here, we consider soft micro-particles of initially spherical shape that affinely deform into an ellipsoidal shape. These kinematic conditions are commensurate with i) the affine deformation assumption inherent to a pseudo-rigid body and ii) the celebrated Jeffery-Roscoe model for the traction exerted on an ellipsoidal particle due to creeping flow conditions around the particle. Without loss of generality, we here focus on non-linear hyperelastic particles for the sake of demonstration. Our novel numerical approach proves to accurately capture the particular deformation pattern of soft particles in viscous flow, such as for example tank-treading, thereby being completely general regarding the flow conditions at the macro-scale and, as an option, the constitutive behavior of the particle. Moreover, our computational method is highly efficient and allows straightforward integration into established Lagrangian tracking algorithms as employed for the point-particle approach to track rigid particles in dilute viscous flow.
Ključne besede: soft particles, pseudo-rigid bodies, Barycenter and shape dynamics, Lagrangian particle tracking
Objavljeno v DKUM: 19.09.2024; Ogledov: 0; Prenosov: 11
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Ključne besede: lignin particles, pickering emulsions, vegetable oils, UV protection, synergic effect
Objavljeno v DKUM: 06.05.2024; Ogledov: 188; Prenosov: 14
Celotno besedilo (6,41 MB)
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Opis: Cavitation erosion is a problem that presents a challenge for the engineers in different industries, as it erodes the machinery which leads to lower efficiency and higher maintanance costs. An experimental investigation has been conducted to evaluate cavitation and cavitation erosion with and without the presence of solid particles in a Venturi channel. The methodology is based on observing and analysing the evolution of the vapour structures and occurence of cavitation erosion on the sample surface in the Venturi channel. To conduct experiments the cavitation tunnel was used, with the central component being a transparent test section with a Venturi-like channel (constructed from Plexiglass walls and a metal insert) to monitor the process of cavitation. To detect the damage caused by cavitation erosion and abrasion, the most effective solution was found to be an indicator in the form of black acrylic paint thinned with water (at a ratio of 1:2). On the sample surface, a self-adhesive aluminium tape was applied to protect the aluminium base from erosive characteristics from cavitation Furthermore, a comparison between cavitation with and without solid particles was made to determine the effects of solid particles on both cavitation and abrasion of the sample surface. The observation revealed that no matter the solid particles, damage from cavitation erosion appears at the separation point and in proximity to the location of the detached cloud collapse. The spherical glass particles with diameters between 40 µm and 70 µm added an abrasive effect on the sample surface only in the presence of cavitation structures. It was determined, that the intensity of cavitation erosion and abrasion increases when the cavitation number decreases and volumetric flow rate increases. Also, an economic analysis was conducted, to determine which is the more cost beneficial solution between replacement of the metal insert and application of protective coatings over the metal insert.
Ključne besede: cavitation erosion, solid particles, abrasion, experiment
Objavljeno v DKUM: 28.02.2024; Ogledov: 230; Prenosov: 29
Celotno besedilo (3,93 MB)

Opis: The 3D unsteady, cavitating, particle-laden flow through a radial divergent test section was simulated with the homogeneous mixture model and Discrete Phase Model (DPM) within the commercial CFD code ANSYS Fluent. For turbulence, a RANS approach was adopted with the Reboud’s correction of turbulent viscosity in the k-ω SST model. Cavitation erosion was predicted with the Schenke-Melissaris-Terwisga (SMT) model, while particle erosion was predicted with the Det Norske Veritas (DNV) model. Two distinct erosion zones were identified, one for pure cavitation erosion and one for pure particle erosion. The occurrence of the pure particle erosion zone downstream of the cavitation erosion zone was analysed. By observing the streamlines downstream of the cavitation structures, it was found that vortices form in the flow and redirect the particles towards the wall, causing a pure particle erosion zone on the wall. Particles under consideration in this study were not found to alter the flow to the extent that the cavitation erosion zone would be significantly altered compared with the results without solid particles which are reported in the literature.
Ključne besede: cavitation, Particles ANSYS Fluent, erosion, CFD, modelling, DPM
Objavljeno v DKUM: 30.10.2023; Ogledov: 285; Prenosov: 9
Celotno besedilo (2,04 MB)
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Opis: This study investigates the effect of particles roundness and morphology on the shear failure mechanism of soil. A strip footing was modeled under laboratory conditions. Calcareous soil was tested with three roundness classes: angular, rounded and well-rounded shapes with sizes of 0.30 mm to 4.75 mm. These were divided into six different groups at three relative densities of 30%, 50% and 70%. A series of photographs was taken during the tests and analyzed using the particle image velocimetry (PIV) method to understand the soil-deformation mechanism. The results showed that increasing the sample sizes increased the affected area of the soil. At the same time, increasing the relative density caused a punching failure mechanism that went towards the general failure. The shear failure mechanism of the soil changed from general toward punching shear failure with increasing particle roundness. This effect was larger with the smaller materials. Underneath the affected layers of soil, the angular samples were deeper than the rounded and well-rounded samples. The affected depth in the angular soil was approximately 1.5B in the smallest size group. This was more than 3B and near 4B in the largest size group. Both the sides and the underlying soil layers should be considered on angular soils. The area under the footing becomes more important than the side parts after increasing the roundness of the particles.
Ključne besede: particle roundness, morphology of particles, shear failure mechanism, strip footing, PIV method, ultimate bearing capacity
Objavljeno v DKUM: 11.10.2018; Ogledov: 1653; Prenosov: 532
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