Institute of Fundamental Technological Research
Polish Academy of Sciences


Kajetan Wojtacki, PhD

Department of Biosystems and Soft Matter (ZBiMM)
Division of Modelling in Biology and Medicine (PMBM)
position: assistant professor
telephone: (+48) 22 826 12 81 ext.: 468
room: 309
ORCID: 0000-0002-7520-8274

Doctoral thesis
2015-12-16 Coupling between transport, mechanical properties and degradation by dissolution of rock reservoir  (LMGC, Université de Montpellier, Montpellier, France)
supervisor -- Daridon Loïc, LMGC, CNRS UMR 5508, Montpellier, France / MIST, UM, CNRS, IRSN, France
supervisor -- Monerie Yann, LMGC, CNRS UMR 5508, Montpellier, France / MIST, UM, CNRS, IRSN, France

Recent publications
1.  Cantor D., Wojtacki K., Effects of Friction and Spacing on the Collaborative Behavior of Domino Toppling, Physical Review Applied, ISSN: 2331-7019, DOI: 10.1103/PhysRevApplied.17.064021, Vol.17, pp.064021-1-6, 2022

Inspired by the high-speed camera experiments of YouTuber Destin Sandlin (SmarterEveryDay) [D. Sadlin, Dominoes – hardcore mode (2021), [Online; accessed 15-Jul-2021].] on the toppling speed of dominoes over different surfaces, we performed discrete-element simulations of this process, varying the spacing between adjacent and evenly spaced blocks (dominoes). We also varied the block-block and block-surface friction coefficients over a wide range of values to have a complete picture of the behavior of these cooperative, dissipative mechanical systems. We found that a steady wavefront speed v exists for a specific interval of spacings between dominoes and coefficients of friction. Surprisingly, while v is more affected by the domino-domino friction, the domino-surface friction determines whether or not toppling anomalies can appear and stop the wave. Finally, our observations led us to propose a scaling law that is able to predict v based on the domino configuration and friction coefficients, and to correctly reproduce experimental tests.

Cantor D. - Polytechnique Montreal (CA)
Wojtacki K. - IPPT PAN
2.  Majkut M., Kwiecińska-Piróg J., Wszelaczyńska E., Pobereżny J., Gospodarek-Komkowska E., Wojtacki K., Barczak T., Antimicrobial activity of heat-treated Polish honeys, Food Chemistry, ISSN: 0308-8146, DOI: 10.1016/j.foodchem.2020.128561, pp.1-6, 2020

Bactericidal properties of honey depend on botanical and geographical origin, where thermal treatment can have a significant affect. The aim of this study was to investigate the effect of temperature on minimum bactericidal concentration (MBC), vitamin C content, total polyphenols content and antioxidant capacity of ferric reducing antioxidant potential (FRAP) of several nectar honey varieties from northern Poland (lime, rapeseed, multifloral and buckwheat). The honeys were subjected to thermal treatment at 22 °C, 42 °C, 62 °C, 82 °C and 100 °C for two exposure times. The results showed a significant reduction of antimicrobial properties (MBC 50%) at 82 °C and 62 °C after 15 and 120 min exposure time for most samples. Short time exposure reduced vitamin C content (50 %) but increased total polyphenols content (27%) and FRAP value (106%).

honey, vitamin C, polyphenols, antioxidant properties, antibacterial activity, temperature treatment

Majkut M. - UTP University of Science and Technology (PL)
Kwiecińska-Piróg J. - Nicolaus Copernicus University (PL)
Wszelaczyńska E. - UTP University of Science and Technology (PL)
Pobereżny J. - UTP University of Science and Technology (PL)
Gospodarek-Komkowska E. - Nicolaus Copernicus University (PL)
Wojtacki K. - IPPT PAN
Barczak T. - University Paris-Saclay - LIMSI laboratory (FR)
3.  Wojtacki K., Vincent P.G., Suquet P., Moulinec H., Boittin G., A micromechanical model for the secondary creep of elasto-viscoplastic porous materials with two rate-sensitivity exponents: application to a mixed oxide fuel, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/j.ijsolstr.2018.12.026, Vol.184, pp.99-113, 2020

This study deals with the secondary creep of a porous nuclear fuel. This material is composed of an isotropic matrix, weakened by randomly distributed clusters of pores. The viscous strain in the matrix is described by two power-law viscosities corresponding to two different creep mechanisms. The material microstructure is analyzed and appropriate descriptors of its morphology are identified. Representative Volume Elements (RVE's) are generated according to these descriptors. The local fields and overall response of these realizations RVE's are simulated within the framework of periodic homogenization using a full-field computational method based on Fast Fourier Transforms. An analytical model based on appropriate approximations of the effective potential governing the overall response of porous materials under creep is proposed. The accuracy of the model is assessed by comparing its predictions with full-field simulations and the agreement is found to be quite satisfactory.

porous media, viscoplasticity, FFT method, homogenization, mathematical morphology, microstructures

Wojtacki K. - IPPT PAN
Vincent P.G. - Institut de Radioprotection et de SûretéNucléaire (FR)
Suquet P. - Aix-Marseille Université (FR)
Moulinec H. - Aix-Marseille Université (FR)
Boittin G. - Aix-Marseille Université (FR)
4.  Wojtacki K., Daridon L., Monerie Y., Computing the elastic properties of sandstone submitted to progressive dissolution, INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, ISSN: 1365-1609, DOI: 10.1016/j.ijrmms.2016.12.015, Vol.95, pp.16-25, 2017

We present a numerical method for estimating the stiffness-to-porosity relationships for evolving microstructures of Fontainebleau sandstone. The proposed study is linked to geological storage of CO 2 and focuses on long-term and far field conditions, when the progressive degradation of the porous matrix can be assumed to be homogeneous at the sample scale. The method is based on microstructure sampling with respect to morphological descriptors extracted from microtomography. First, an efficient method of generation of accurate numerical media is proposed. The method is based on grain deposit, compaction and diagenesis and allows to reproduce user-defined morphological parameters. Second, two simple numerical models that mimic chemical degradation of porous aquifers are presented. Effective elastic properties are estimated within the framework of periodic homogenization and finite element approach. A fixed-point method on a self-consisted outer layer allows to consider non-periodic representative volume elements. Accurate predictions of elastic properties over a wide range of porosity are obtained. The overall evolutions of elastic behaviour due to the increase of porosity are in excellent agreement both, with experimental data and the results obtained by Arns et al. [1].

Porous media, X-ray microtomography, Numerical dissolution, Fontainebleau sandstone, Self-consisted numerical method, Homogenization

Wojtacki K. - other affiliation
Daridon L. - Université de Montpellier (FR)
Monerie Y. - Université de Montpellier (FR)
5.  Wojtacki K., Lewandowska J., Gouze Ph., Lipkowski A., Numerical computations of rock dissolution and geomechanical effects for CO2 geological storage, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.2316, Vol.39, pp.482-506, 2015

The paper is motivated by the long-term safety analysis of the CO2 geological storage. We present a methodology for the assessment of the geomechanical impact of progressive rock dissolution. The method is based on the use of X-ray tomography and the numerical dissolution technique. The influence of evolution of the microstructure on the macroscopic properties of the rock is analysed by using periodic homogenization method. The numerical computations show progressive degradation of all components of the stiffness (orthotropic) tensor. Moreover, the evolution of associated mass transfer properties (as tortuosity and conductivity tensors), by using the periodic homogenization method, is also calculated. The correlation between the mechanical parameters and the transfer properties during the dissolution process is presented. The results show that the highest increase of the hydraulic conductivity (in direction Y) is not associated with the highest decrease of Young modulus in this direction. Moreover, the highest decrease of Young modulus (in the direction X) is not associated with percolation in this direction. Finally, an incremental law to calculate settlement, in case of a rock with evolving microstructure, is proposed. The solution of the macroscopic settlement problem under constant stress and drained conditions showed that the geomechanical effects of the rock dissolution are rather limited.

CO2 storage, homogenization, chemo-mechanical coupling, microstructure, X-ray tomography, numerical computations

Wojtacki K. - other affiliation
Lewandowska J. - Université Montpellier 2 (FR)
Gouze Ph. - Université Montpellier 2 (FR)
Lipkowski A. - Gdańsk University of Technology (PL)

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