1. A novel pseudo-rigid body approach to the non-linear dynamics of soft micro-particles in dilute viscous flowJana Wedel, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2024, izvirni znanstveni članek 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: 6
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2. Informacijska varnost v avtonomnih hotelih : diplomsko delo visokošolskega študijskega programa Informacijska varnostMatjaž Hriberšek, 2024, diplomsko delo Opis: V diplomskem delu sem želel raziskati kakšna je izkušnja uporabnika pametnega hotela in kakšno je zaupanje v hotelske storitve v takšnih hotelih, da bo varovalo informacije strank. Cilj je preučiti, kako sodobna digitalna tehnologija spreminja hotelirstvo in v kolikšni meri posega v posameznikovo zasebnost. Glede na to, da so pametni hoteli v zadnjih par letih prišli na tržišče, ogromno ljudi niti ne ve, da takšni hoteli obstajajo oz. še niso bivali v njem. V teoretičnem delu sem za lažje razumevanje razložil nekaj pojmov kot so informacijska varnost, pametni hotel. Nato sem predstavil kakšno tehnologijo lahko najdemo v pametnih hotelih. Omenil sem internet stvari, ki je eden od glavnih razlogov, da so se pametni hoteli sploh razvili. Varnost in zasebnost gostov je zelo problematičen del nudenja storitev v pametnih hotelih. Tu je je treba zelo paziti in skrbeti za pametne naprave, ki so na voljo gostu v hotelu ali v sami sobi. V zadnjem delu pa sem se dotaknil še osebnih podatkov in informacijske varnosti v samih hotelih. Zaupanje gosta v hotel, da bo varoval osebne podatke gostov je zelo pomembna naloga hotelskih organizacij. Gost namreč pričakuje, da bo organizacija skrbela za informacijsko varnost in odpravljala napake, ki bi jih sami zaznali, še predno pride do kakšnih resnejših incidentov. Pri raziskovalnem delu je bila z deskriptivno metodo preučena pretežno tuja literatura. V metodološkem delu naloge pa sem s pomočjo anketnega vprašalnika v elektronski obliki iskal odgovore na zastavljene hipoteze. Na podlagi zbranih informacij so se potrdile zastavljene hipoteze.
Ključne besede: informacijska varnost, pametni hoteli, zasebnost, diplomske naloge
Objavljeno v DKUM: 29.08.2024; Ogledov: 109; Prenosov: 28
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3. A coupled point particle two-phase heat and mass transfer model for dispersed flows based on Boundary Element MethodsTimi Gomboc, Matej Zadravec, Jure Ravnik, Matjaž Hriberšek, 2024, objavljeni znanstveni prispevek na konferenci Opis: In dispersed multiphase flow processes we encounter coupled heat, mass and momentum transfer between the disoersed and the continuous phase. In the context of the subdomain Boundary Domain Integral Method (BDIM) solution of the Navier-Stokes equations a two-way coupling model is presented based on the use of the elliptic fundamental solution and the Dirac delta function properties which leads to accurate evaluation of the heat and mass point particle source impacts on the continuous (air) phase. In addition, the two-phase flow case under consideration is extended to the case of porous spherical particle drying with internal moving drying front, which is solved by the Boundary Element Method (BEM).
Ključne besede: heat transfer, mass transfer, Boundary Element Methods
Objavljeno v DKUM: 01.07.2024; Ogledov: 113; Prenosov: 14
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4. Vial wall effect on freeze-drying speedMatjaž Ramšak, Matjaž Hriberšek, 2024, izvirni znanstveni članek Opis: The vial wall thermal conductivity and thickness effect on freeze-drying speed is simulated. A 2D axisymmetric numerical simulation of Mannitol freeze-drying is employed using the boundary element method. The originality of the presented approach lies in the simulation of heat transfer in the vial walls as an additional computational domain in contrast to the typical methodology without a vial wall. The numerical model was validated using our measurements and the measurements from the literature. Increasing the glass vial thickness from 1 mm to 2 mm has been found as the major factor in primary drying time, increasing the gravimetrical Kv up to 20 % for all the simulated chamber pressures. The effect of thermal conductivity was simulated using a polymer and aluminium vial replacing the standard glass vial of the same thickness. The polymer vial‘s decreased Kv value is 5.6 % at a low chamber pressure of 50 mTorr, and 12.2 % at 400 mTorr, which is in excellent agreement with the experiment. Using higher conductivity materials, for example, aluminium, only 3.7 % and 2.3 % Kv increase were computed for low and high chamber pressures respectively.
Ključne besede: freeze-drying, lyophilization speedup, vial heat conductivity, vial wall thickness, boundary element method
Objavljeno v DKUM: 16.04.2024; Ogledov: 264; Prenosov: 28
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5. A point particle source model for conjugate heat and mass transfer in dispersed two-phase flows by BEM based methodsTimi Gomboc, Jurij Iljaž, Jure Ravnik, Matjaž Hriberšek, 2023, izvirni znanstveni članek Ključne besede: boundary-domain integral method, dispersed two-phase flow, two-way coupling, spherical porous particles, drying
Objavljeno v DKUM: 28.03.2024; Ogledov: 217; Prenosov: 17
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6. A novel particle–particle and particle–wall collision model for superellipsoidal particlesJana Wedel, Mitja Štrakl, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2023, izvirni znanstveni članek Ključne besede: multiphase flow, Lagrangian particle tracking, superellipsoid, collision, friction
Objavljeno v DKUM: 28.03.2024; Ogledov: 171; Prenosov: 9
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7. Coefficient of tangential restitution for non-spherical particlesJana Wedel, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2024, izvirni znanstveni članek Opis: In various industrial and naturally occurring multiphase flows, whether dilute or dense, particle interaction plays a crucial role. In most cases, the particles are non-spherical, which poses a computational challenge in terms of particle motion and particle interaction, i.e. both particle–particle and particle–wall collisions. In this study, we present a novel frictional particle collision model to be used in general fluid flows. The model is derived for superellipsoidal particle shapes and thus allows consideration of frictional collisions of a wide variety of particle geometries. In this context, we derive an expression for the tangential coefficient of restitution applicable to arbitrarily shaped particles. Furthermore, we present the performance of the novel model by applying it to demonstrative examples ranging from two- to multi-particle systems.
Ključne besede: non-spherical particles, particle collision, tangential restitution coefficient, superellipsoids
Objavljeno v DKUM: 26.02.2024; Ogledov: 293; Prenosov: 32
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8. Development of an experimental Dead-End microfiltration layout and process repeatability analysisGorazd Bombek, Luka Kevorkijan, Grega Hrovat, Drago Kuzman, Aleks Kapun, Jure Ravnik, Matjaž Hriberšek, Aleš Hribernik, 2024, izvirni znanstveni članek Opis: Microfiltration is an important process in the pharmaceutical industry. Filter selection and validation is a time-consuming and expensive process. Quality by design approach is important for product safety. The article covers the instrumentalization and process control of a laboratory-scale dead-end microfiltration layout. The layout is a downscale model of the actual production line, and the goal is filter validation and analysis of process parameters, which may influence filter operation. Filter size, fluid pressure, valve plunger speed, and timing issues were considered. The focus is on the identification of the most influential process parameters and their influence on the repeatability of pressure oscillations caused by valve opening. The goal was to find the worst-case scenario regarding pressure oscillations and, consequently, filter energy intake. The layout was designed as compact as possible to reduce pressure losses between the filter and valve. Valve-induced pressure oscillations proved to be prevailing over the water hammer effect. Several filters in sizes between 3.5 cm2 and 6900 cm2 were tested, and some recommendations were suggested for the reduction of energy intake of the filter and to improve the repeatability of the process.
Ključne besede: filtration, pressure oscillations, repeatability, processes, parameters
Objavljeno v DKUM: 01.02.2024; Ogledov: 425; Prenosov: 24
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9. Modelling of downscale model design and parameters for filter validation extention : zaključno poročiloMatjaž Hriberšek, Jure Ravnik, Aleš Hribernik, Jurij Iljaž, Matjaž Ramšak, Matej Zadravec, Gorazd Bombek, Timi Gomboc, 2023, končno poročilo o rezultatih raziskav Ključne besede: mechanics, porous materials, hydraulic model, mechanical properties
Objavljeno v DKUM: 03.11.2023; Ogledov: 653; Prenosov: 11 |
10. Geometrijsko in fizikalno sklopljen numerični model sublimacijskega sušenja v liofilizatorju : doktorska disertacijaBlaž Kamenik, 2023, doktorska disertacija Opis: V doktorski disertaciji so predstavljeni rezultati raziskav na temo eksperimentalnega dela določanja kinetike sušenja med procesom liofilizacije in ovrednotenja procesne zmogljivosti naprave, ter razviti numerični modeli za celovito modeliranje procesa in rezultati le teh. V sklopu eksperimentalnega dela se je ovrednotila kinetika sušenja destilirane vode (sublimacija ledu), ter eksperimentalna določitev kinetike depozicije ledu, kjer se je za tok vodne pare, ki je v režimu dušenega toka, izmerilo masne tokove sublimata in tlake znotraj sušilne komore in kondenzatorja.\\
Rezultati eksperimentov so nato služili za validacijo razvitih numeričnih modelov. Simulacije, ki vključujejo RDT preračune so bile pripravljene v računalniškem programu ANSYS Fluent ali v programskem jeziku Fortran. Razvilo se je več modelov različnih kompleksnosti, prvi model je model za ovrednotenje vpliva geometrije gumastega zamaška in vrata viale na tlačni padec in vpliv na proces, kjer se je tok sublimata modeliral v RDT programu, medtem ko se je kinetika sušenja računala s pomočjo 0D modela (sklopljen 0D-RDT model). Na podlagi rezultatov, se je določilo empirično korelacijo za opis le tega pojava. Naslednji model je večnivojsko sklopljen model z uporabo TCP strežnika, ki povezuje 1D program za simuliranje kinetike sušenja znotraj viale (napisan v programskem jeziku Fortran) s komercialno kodo ANSYS Fluent, ki je uporabljen za izračun tokovnih polj skozi sistem. Kinetika sušenja produkta v vsaki viali je simulirana z 1D modelom, v katerem se tlačni padec vodne pare, med tokom skozi zgornji prostor viale, obravnava z empirično korelacijo. Masni tokovi sublimata in temperatura plina se posredujejo RDT modelu, ki jih uporabi kot robne pogoje na lokalnih vtokih. Po izračunu novega tokovnega polja, RDT model vrne nove tlake nad vsako vialo. Na ta način dobimo vpogled v hidrodinamske razmere znotraj liofilizatorja in kinetiko sušenja vseh vial. Naslednji del je modeliranje depozicije ledu, kjer se je modeliral tok sublimata skozi celoten sistem, depozicija na hladnih stenah kondenzatorja pa se modelira z dodatnimi členi za ponor mase, gibalne količine in energije. V tem primeru se torej meja modeliranja prestavi v kondenzator, kar nam omogoči vpogled v dogajanje znotraj kondenzatorja in vzorec depozicije ledu, ki se odvija v kondenzatorju.
Ključne besede: RDT, liofilizacija, večnivojski model, prenos toplote in snovi, depozicija
Objavljeno v DKUM: 27.10.2023; Ogledov: 508; Prenosov: 112
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