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20 results on '"Viitanen, Leevi"'

3. Machine learning and predicting the time dependent dynamics of local yielding in dry foams

Author

Viitanen, Leevi, Mac Intyre, Jonatan R., Koivisto, Juha, Puisto, Antti, and Alava, Mikko

Subjects
Condensed Matter - Soft Condensed Matter, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Materials Science
Abstract

The yielding of dry foams is enabled by small elementary yield events on the bubble scale, "T1"s. We study the large scale detection of these in an expanding 2D flow geometry using artificial intelligence (AI) and nearest neighbour analysis. A good level of accuracy is reached by the AI approach using only a single frame, with the maximum score for vertex centered images highlighting the important role the vertices play in the local yielding of foams. We study the predictability of T1s ahead of time and show that this is possible on a timescale related to the waiting time statistics of T1s in local neighborhoods. The local T1 event predictability development is asymmetric in time, and measures the variation of the local property to yielding and similarly the existence of a relaxation timescale post local yielding.

Published
2020

8. Bio‐Based Foams to Function as Future Plastic Substitutes by Biomimicry: Inducing Hydrophobicity with Lignin.

Author

Miranda‐Valdez, Isaac Yair, Mäkinen, Tero, Hu, Xiang, Lejon, Juha, Elamir, Mohamed, Viitanen, Leevi, Jannuzzi, Luisa, Koivisto, Juha, and Alava, Mikko Juhani

Subjects
RAW materials, CONTACT angle, METHYLCELLULOSE, WOOD, SURFACE morphology, FOAM, LIGNINS
Abstract

To replace common plastics, bio‐based alternatives are needed. Cellulose foams, as plant‐based materials, are the most attractive solution, being often biodegradable and inexpensive and having the potential for distributed production. Cellulose and its derivatives, as raw materials, present a fundamental challenge, as they are hydrophilic. Herein, this problem is solved by drawing inspiration from the hydrophobic barrier that lignin creates in wood and applying lignin to methylcellulose (MC) foams. The lignin (0.0–1.0 wt% being the range studied here) is applied directly to the suspension consisting of water and MC (1.8 wt%), which is then foamed and solidified to a dry 3D porous structure. By comparing different types of lignin and the resulting surface morphologies, it is shown that organosolv lignin (OL) most strongly self‐assembles to the air–foam interfaces, achieving area fractions up to 27%. Using different concentrations of OL, how hydrophobicity—described by the initial water contact angle and its time evolution—increases with increasing lignin concentration is then shown. Thus, significantly increased water resistance (up to 91 times higher compared to the pure MC foam), a crucial property for developing novel bio‐based materials that can compete with traditional plastics, is able to be achieved. [ABSTRACT FROM AUTHOR]

Published
2024
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16. Vibration controlled foam yielding

Author

Rinkinen, Oona, primary, Viitanen, Leevi, additional, Mac Intyre, Jonatan R., additional, Koivisto, Juha, additional, Puisto, Antti, additional, and Alava, Mikko, additional

Published
2020
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19. The flow of foam around an obstacle in Hele-Shaw cell

Author

Koivisto, Juha, Puisto, Antti, Perustieteiden korkeakoulu, Alava, Mikko, Viitanen, Leevi, Koivisto, Juha, Puisto, Antti, Perustieteiden korkeakoulu, Alava, Mikko, and Viitanen, Leevi

Abstract

This study investigates the flow of a two-dimensional foam between two parallel plates. The project includes building the appropriate experimental apparatus, which would allow studying the flow field around a circular obstacle by filming the bubbles with a regular camera. Furthermore, it has the required flexibility to study the effect of boundary conditions, induced by the cell, to the foam rheology are studied by varying the flow driving. The experiments show that the driving of the flow, whether it is by pressure or moving the obstacle, has a significant effect to the flow field and thus to the foam rheology. The distinct values of static and dynamic friction between the bubbles and the top and bottom plate are expected to be the cause of the difference in the data obtained with different boundary conditions. Also the foam flow around the obstacle is found to be influenced by the foam’s liquid-gas ratio. Finally, the velocity field is compared to the changes in the bubble contacts. Despite the difficulties in the analysis, the results indicate that bubbles rearrange more frequently at the parts of the device where the spatial variation of the velocity is rapid., Tässä työssä tutkitaan kaksiulotteisen vaahdon virtausta kahden yhdensuuntaisen levyn välissä. Työn osana rakennetaan kokeisiin soveltuva mittalaite, jolla vaahdon virtaamista pyöreän esteen ympärillä voidaan tutkia kuvaamalla kuplia tavallisella kameralla. Tämän lisäksi työssä tutkitaan kammion virtaukselle aiheuttamien reunaehtojen vaikutusta vaahdon reologiaan muuttamalla virtauksen aiheuttavaa mekanismia. Kokeet osoittavat, että virtauksen syntymekanismi, joko paine-ero tai esteen liike, vaikuttaa merkittävästi virtauskenttään ja siten vaahdon reologiaan. Syynä tähän pidetään kuplan ja seinämän välisen staattisen ja dynaamisen kitkan välistä eroa. Myös vaahdon muodostavien kaasun ja nesteen tilavuusosuuksien suhteen havaitaan vaikuttavan vaahdon virtaukseen esteen ympärillä. Lopuksi nopeuskenttää verrataan muutoksiin vaahdon kuplien järjestyksessä. Huolimatta analyysin haasteellisuudesta saadut tulokset viittaavat siihen, että kuplat uudelleen järjestyvät useammin alueilla, joissa nopeus kenttä muuttuu nopeasti paikan suhteen.

Published
2017

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