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1

Symulacje pękania materiałów o ziarnistej strukturze mikroskopowej : pierwsze uwagi

Dębski Wojciech

Przegląd Geofizyczny

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2022

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Z. 1-2

39--54

PL

Proces pękania i fragmentacji ciał stałych jest zjawiskiem niezwykle powszechnym, a równocześnie niezwykle skomplikowanym. W zakresie zainteresowania geofizyki manifestuje się on najczęściej w postaci trzęsień ziemi i pęknięć lodowców. Dotychczasowe próby jakościowego zrozumienia tych naturalnych procesów nie dały w pełni zadowalających wyników. Ciągle nie rozumiemy wielu aspektów fizycznych tych procesów, a w konsekwencji nie można w stanie ich przewidywać z akceptowalną wiarygodnością. Losowość trzęsień ziemi i zjawisk lodowcowych znacząco ogranicza możliwości ich badań eksperymentalnych. Z tego powodu istotnego znaczenia nabiera podejście komplementarne oparte na symulacjach komputerowych. W niniejszej pracy ilustrowane jest takie podejście, analizujące pękanie materiału o ziarnistej strukturze mikroskopowej w procesie rozciągania. Wykonane symulacje pokazały jak struktura mikroskopowa determinuje losowość procesu pękania i wpływa na takie elementy procesu jak lokalizacja obszarów o zwiększonej gęstości energii kinetycznej, a więc powstawanie centrów nukleacji pęknięcia materiału.

EN

Fragmentation of solid materials is a very common and simultaneously very complex physical process. From geophysical point of view the most interesting examples of such processes are earthquakes and glacial processes like icequakes. In spite of a huge effort of analyzing them these processes are still poorly understood for many reasons. One of them is their stochasticity. For these reasons more important become numerical simulations which allow to cast some light on physical mechanism leading to nucleation, development and finally arresting earthquakes or glacial breaking processes. In this paper we illustrate advantages of such approach analyzing a tensional breaking process of macroscopically homogeneous material of granular microstructure. Our simulations have revealed how microstructure determines the fragmentation process including its stochasticity and influences creation of hotpots - regions of high concentration of kinetic energy leading finally to creation of nucleation centers.

2

The Use of the Inverse Problem Methodology in Analysis of Fluid Flow Through Granular Beds With Non-Uniform Grain Sizes

Sobieski Wojciech, Trykozko Anna

Technical Sciences / University of Warmia and Mazury in Olsztyn

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2021

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nr 24(1)

83--104

EN

The pressure drop during water flow through two gravel beds with 2-8 and 8-16 [mm] grain size was measured across a wide range of filtration velocities, and the optimal method for calculating the coefficients for Darcy’s law and Forchheimer’s law was selected. The laws and the experimental data were used to develop a computational program based on the Finite Element Method (FEM). The results were compared, and errors were analyzed to determine which law better describes flow data. Various methods of measuring porosity and average grain diameter, representative of the sample, were analyzed. The data were used to determine the limits of applicability of both laws. The study was motivated by the observation that computational formulas in the literature produce results that differ by several orders of magnitude, which significantly compromises their applicability. The present study is a continuation of our previous research into artificial granular materials with similarly sized particles. In our previous work, the results produced by analytical and numerical models were highly consistent with the experimental data. The aim of this study was to determine whether the inverse problem methodology can deliver equally reliable results in natural materials composed of large particles. The experimental data were presented in detail to facilitate the replication, reproduction and verification of all analyses and calculations.

3

Transport of emulsions in granular porous media driven by capillary force

Shtyka O., Przybysz Ł., Sęk J.

Acta Innovations

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2018

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no. 26

38--44

EN

The transport of liquids driven by capillary suction-pressure and balanced by both viscous drag force and gravity acceleration is known as spontaneous imbibition. The prediction of spontaneous imbibition in porous media is of importance due to its relevance as a fundamental phenomenon in numerous industrial technologies as well as in nature. A vast majority of the experimental results and mathematical models concerning the imbibition process of single-phase liquids are considered and analyzed in the literature. The present research focuses on two-phase liquids transport in porous medium driven by capillary force. The penetrating liquids were surfactant-stabilized emulsions with the different dispersed phase concentrations. The discussed issues are the influence of porous bed composition and inner phase concentration on the height of an emulsion penetration, which allows to predict the velocity of imbibition process. From a practical point of view, the experimental results give the possibility to evaluate: productivity of granular sorbents applied to recover the environment, efficiency of building materials wetting with multiphase liquids, process of oil-derived pollutants migration in porous media, e.g. soil and other rock structures, etc.

4

Highly nonlinear solitary wave velocity measurement with a modified Michelson interferometer

Olivares I., Riveros G., Manriquez C., Labbé R., Vergara L.

Optica Applicata

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2017

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Vol. 47, nr 2

257--262

EN

We have measured the velocity of a highly nonlinear solitary wave, generated by the collision of a ball with a linear set of pre-compressed balls of the same material, using a double Michelson interferometer. One of the mirrors of each interferometer was mounted on one of two balls of the array. The measured soliton velocity was u = (346 ± 40) m/s for brass balls with pre-compression force F = (0.8 ± 0.1) N, and u = (102 ± 3) m/s for Teflon balls with pre-compression force F = (0.4 ± 0.1) N.

5

Modelowanie numeryczne termomechaniki przepływu w reaktywnym ośrodku ziarnistym

Grucelski A., Pozorski J., Kardaś D.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2013

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z. 101

41--42

PL

Praca stanowi próbę całościowego ujęcia zagadnienia przepływu i wymiany ciepła w ośrodku ziarnistym (granularnym) na poziomie szczegółowego (2D/3D) modelu w skali rozmiarów pojedynczych ziaren. Dodatkowo, ziarna ośrodka podlegają pirolizie (procesowi uwalniania gazów) pod wpływem wzrostu temperatury, a także dylatacji termicznej i deformacji. Jakkolwiek opracowywany model fizykalny i obliczeniowy bazują na pełnym opisie zjawiska, docelowym zamierzeniem Autorów w jest wykorzystanie uzyskanych wyników do stworzenia modelu uproszczonego (1D/2D, nieustalony) dla ośrodka potraktowanego jako jednorodny po uśrednieniu przestrzennym.

6

Metoda badania odkształcalności termicznej organicznych ośrodków sypkich składowanych w silosach

Prusiel J., Łapko A.

Budownictwo i Inżynieria Środowiska

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2012

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Vol. 3, no. 1

61-65

PL

W artykule opisano koncepcję stanowiska do wyznaczania liniowego współczynnika rozszerzalności termicznej organicznych ośrodków sypkich oraz procedurę badawczą umożliwiającą określenie wyżej wymienionych właściwości ziarna składowanego w silosach, w warunkach rzeczywistego stanu naprężenia (konsolidacji ośrodka). Zagadnienie to ma duże znaczenie w silosach zbożowych z uwagi na możliwość wystąpienia zjawiska samonagrzewu ziarna. W artykule przedstawiono założenia teoretyczne zaproponowanej metody badawczej. Badanie należy przeprowadzić w modelowej komorze pomiarowej wyposażonej w płytę dociążającą próbkę ośrodka sypkiego oraz metalowy rdzeń umieszczony centrycznie w modelu umożliwiający nagrzewanie ośrodka sypkiego. Model stanowiska badawczego został zastrzeżony w Urzędzie Patentowym.

EN

The paper presents a conception of measuring stand and testing procedure for evaluation of thermal expansion coefficient of organic granular media stored in silos under real consolidation stress state in grain. This problem is particularly important in organics solids where the biological process of self heating could occur. Theoretical assumptions of proposed experimental method are given. The measurements should be conducted in model silo chamber equipped with surcharge rigid steel plate consolidating the grains and with centrally located core that enables heating the grains. The described method was registered as the Patent Claim.

7

Force distribution in granular systems with and without friction

Błaszczuk J.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

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2009

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Vol. 8, nr 2

21-27

EN

Force distribution in granular media is discussed in this paper. The proper estimation of the force network has become a challenging issue because of a tendency to optimize packing processes. The aim of the study is numerical analysis of regular packings of grains in the frictionless and frictional 2D systems, as well as assessment of force distribution in static granular media and analysis of the influence of the load type and system size on force distribution.

8

Dynamic neutron radiography studies of water migration in beds of natural zeolite

Żołądek J., Milczarek J. J., Fijał-Kirejczyk I.

Nukleonika

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2008

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Vol. 53, suppl. 2

113--119

EN

The results of the experiments on water migration in unsaturated beds of natural zeolite (clinoptilolite) performed with a dynamic neutron radiography technique are presented. It was found that the migration of water in zeolites is much slower than in quartz sand composed of the same size grains. The effect is attributed to the enormous grain surface roughness of the zeolite. The influence of gravity was found to be significant only for beds formed by the coarsest grains. It was found that the water imbibition rate increases with time in finest grain zeolite beds. The results show the difficulties of the classical theory of adhesion driven motion of the liquid in the single capillary as a model of water imbibition by zeolite beds.

9

A comparative analysis of theoretical models of gravity movements of cohesionless granular media

Szczepiński W.

Engineering Transactions

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2007

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Vol. 55, iss. 2

181-192

EN

Three different theoretical models for the analysis of movements of granular media caused by the gravity forces only are critically discused. In each of them the motion is treated as a purely kinematical problem. It has been shown that in application to varoius practical problems, they lead to different displacements patterns (e.g. funnel or mass flow, formation of shear bands or a flow without such bands). Examples of applicaion illustrate the discussion.

10

Insight into the problems of mass transport modelling in granular layer

Adach A., Wroński S.

Archiwum Ochrony Środowiska

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2004

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Vol. 30, no. 1

3--20

EN

The short outlook at main problems related to pollutant migration modelling in the granular layer is critically discussed in the paper. The general model of pollutant migration in granular was transposed into dimensionless form. The general model was adapted to describe the examined decontamination technology and two operational models were differentiated due to the dominant mass transfer resistances in the system. The verification validated the functional effectiveness of the suggested model and its numerical implementation under different conditions. It approves the possibility of the practical application of the proposed method. The problem of influence of irregular distribution of negative mass sources (sorptive agglomerates) on mass transport in the granular layer was underlined.

PL

W pracy przedstawiono skrótowo problemy związane z modelowaniem migracji zanieczyszczeń w złożach ziarnistych. Ogólny model migracji przedstawiono w formie bezwymiarowej. Model podstawowy zaadoptowano do opisu praktycznej metody dekontaminacji, formułując dwa modele operacyjne, w zależności od dominujących oporów transportu masy w układzie. Weryfikacja modelu potwierdziła poprawność modelu i jego implementacji numerycznej w różnych warunkach. Potwierdza to możliwość praktycznego zastosowania metody do estymacji migracji zanieczyszczeń w złożach ziarnistych. Zasygnalizowano istotny wpływ nieregularności dystrybucji ujemnych źródeł masy na transport masy w układzie.

11

DEM simulations of quasi-static shear deformation of granular media

Thornton C.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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1998

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Vol. 2, No 3

461-472

EN

Results are presented of numerically simulated three dimensional quasi-static shear deformation of polydisperse systems of spheres. Results of axisymmetric compression test simulations are reported for both dense and loose systems. The versatility of numerical simulation is demonstrated by presenting results obtained from simulations of general radial deviatoric loading, a constant deviatoric strain test and a multi-axial plane strain test. In all cases, the simulated stress-strain dilation responses are in excellent qualitative agreement with the behaviour of granular materials observed in physical experiments.