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3D analysis of deformation and porosity of dry natural snow during compaction
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.ORCID-id: 0000-0002-5943-1476
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.ORCID-id: 0000-0001-7395-3302
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
2019 (Engelska)Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 6, artikel-id 850Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The present study focuses on three-dimensional (3D) microstructure analysis of dry natural snow during compaction. An X-ray computed microtomography (micro-CT) system was used to record a total of 1601 projections of a snow volume. Experiments were performed in-situ at four load states as 0 MPa, 0.3 MPa, 0.6 MPa and 0.8 MPa, to investigate the effect of compaction on structural features of snow grains. The micro-CT system produces high resolution images (4.3 μm voxel) in 6 hours of scanning time. The micro-CT images of the investigated snow volume illustrate that grain shapes are mostly dominated by needles, capped columns and dendrites. It was found that a significant number of grains appeared to have a deep hollow core irrespective of the grain shape. Digital volume correlation (DVC) was applied to investigate displacement and strain fields in the snow volume due to the compaction. Results from the DVC analysis show that grains close to the moving punch experience most of the displacement. The reconstructed snow volume is segmented into several cylinders via horizontal cross-sectioning, to evaluate the vertical heterogeneity of porosity distribution of the snow volume. It was observed that the porosity (for the whole volume) in principle decreases as the level of compaction increases. A distinct vertical heterogeneity is observed in porosity distribution in response to compaction. The observations from this initial study may be useful to understand the snow microstructure under applied stress.

Ort, förlag, år, upplaga, sidor
MDPI, 2019. Vol. 12, nr 6, artikel-id 850
Nyckelord [en]
Tomography, snow grains, snow microstructure, Digital volume correlation, Porosity
Nationell ämneskategori
Annan materialteknik Teknisk mekanik Strömningsmekanik och akustik
Forskningsämne
Experimentell mekanik; Strömningslära
Identifikatorer
URN: urn:nbn:se:ltu:diva-68399DOI: 10.3390/ma12060850ISI: 000465025400010PubMedID: 30871235Scopus ID: 2-s2.0-85063445766OAI: oai:DiVA.org:ltu-68399DiVA, id: diva2:1198567
Forskningsfinansiär
Europeiska regionala utvecklingsfonden (ERUF), 20201424
Anmärkning

Validerad;2019;Nivå 2;2019-03-22 (johcin)

Tillgänglig från: 2018-04-18 Skapad: 2018-04-18 Senast uppdaterad: 2019-05-03Bibliografiskt granskad
Ingår i avhandling
1. Experimental investigation of snow metamorphism at near-surface layers
Öppna denna publikation i ny flik eller fönster >>Experimental investigation of snow metamorphism at near-surface layers
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Experimentell undersökning avsnömetamorfismen vid nära ytskikt
Abstract [en]

Snow metamorphism is a direct objective in many snow research areas, and its charac-terisation is a major challenge in areas including winter road maintenance, detection of icing on wind turbine blades, and snow quality mapping for skiing. A common effect of snow metamorphism is compaction, which can be investigated from the associated vari-ations in physical properties of snow. While the relation between snow metamorphism and physical properties of snow is fairly well-known, a method to quantify this relationis not extensively researched. This experimental based thesis focuses on the relationship between the physical properties of snow and its degree of metamorphism. The link isestablished and investigated by quantifying near-infrared (NIR) reflectance measure-ments and analysing the microtomographic data. Three experimental approaches are developed to record the NIR reflectance measurements and to understand the influence of compaction at near-surface layers of a snowpack. In addition, an X-ray microtomogra-phy (micro-CT) system is used to visualise the behaviour of snow microstructure during compaction. In this thesis, snow experienced compaction via aging, the melting-freezing process, uniaxial loading, settling and infiltration of liquid water.

A numerical tool based on the well-established Discrete Ordinates Radiative Trans-fer (DISORT) method is used to solve the radiative transfer equation (RTE) for aplane-parallel and semi-infinite snowpack. The numerical solver takes the reflectance measurements as input and returns the coefficients of a first order Legendre phase function of an investigated snowpack at a given wavelength of light. The results from the solver show consistency and strong correlation between the Legendre coefficient sand the physical properties of snow. Furthermore, the physical properties of snow such as specific surface area (SSA) and liquid water content (LWC) were estimated via parameterisation where the reflectance data is used as input. The results suggest that the parameterisation of LWC can provide a qualitative estimate of the LWC in a snowpack, while the parameterisation of SSA provides a quantitative estimate of the snow SSA. As a next step, the influence of compaction on snow microstructure is investigated from three-dimensional (3D) images obtained using the micro-CT system. In this case, compaction is initiated by applying uniaxial load on a snow sample and the effect of compaction is analysed based on digital volume correlation (DVC) and porosity distribution. The micro-CT observations further emphasise that near-surface layers of a snowpack experience a higher degree of impact during compaction.

In summary, this thesis presents experimental methods to quantify the link between snow compaction at near-surface layers, and the physical properties of snow. The mode observations show that the estimated Legendre coefficients can provide qualitative descriptions of snow grain distribution and surface texture. The parameterisation methods can provide the details about the LWC and the SSA of a snowpack. Further, the observations from the micro-CT study suggest that grains breakage and recrystallisation are the prevailing effects of snow compaction. All observations in this thesis are helpful in understanding the metamorphism in a snowpack for relevant research areas.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2018
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nyckelord
Snow metamorphism, NIR reflectance, Snow and Ice, Radiative transfer equation, Paramterization, Snow properties, Tomography, Snow microstructure
Nationell ämneskategori
Annan materialteknik Teknisk mekanik
Forskningsämne
Experimentell mekanik
Identifikatorer
urn:nbn:se:ltu:diva-68394 (URN)978-91-7790-116-7 (ISBN)978-91-7790-117-4 (ISBN)
Disputation
2018-06-18, E 231, Luleå University of Technology, Luleå, 14:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-04-18 Skapad: 2018-04-18 Senast uppdaterad: 2019-09-11Bibliografiskt granskad

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