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Evaluation of a steerable filter for detection of fibres in flowing suspensions
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. (Linné Flow Centre)
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. (Linné Flow Centre)
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. (Linné Flow Centre)ORCID iD: 0000-0003-3737-0091
(English)Manuscript (Other academic)
Abstract [en]

Steerable filters are concluded to be useful in order to determine the orientation of fibres captured in digital images. The fibre orientation is a key variable in the study of flowing fibre suspensions. Here digital image analysis based on a filter within the class of steerable filters is evaluated for suitability of finding the position and orientation of fibres suspended in flowing suspensions. In sharp images with small noise levels the steerable filter succeeds in determining the orientation of artificially generated fibres with well-defined angles. The influence of reduced image quality on the orientation has been quantified. The effect of unsharpness and noise is studied and the results show that the error in orientation is less than 1◦ for moderate levels. A set of images with fibres suspended in a shear flow is also analyzed. The fibre orientation distribution is determined in the flow-vorticity plane. In this analysis a comparison is also made to a robust, but computationally more expensive, method involving convolutions with an oriented elliptic filter. A good agreement is found when comparing the resulting fibre orientation distributions obtained with the two methods.

National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10003OAI: oai:DiVA.org:kth-10003DiVA: diva2:200957
Note
QC 20100706Available from: 2009-03-02 Created: 2009-03-02 Last updated: 2010-07-21Bibliographically approved
In thesis
1. Near wall fibre orientation in flowing suspensions
Open this publication in new window or tab >>Near wall fibre orientation in flowing suspensions
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with fibre orientation in wall-bounded shear flows. The primary application in mind is papermaking. The study is mainly experimental,but is complemented with theoretical considerations.The main part of the thesis concerns the orientation of slowly settlingfibres in a wall-bounded viscous shear flow. This is a flow case not dealt withpreviously even at small Reynolds numbers. Experiments were conducted usingdilute suspensions with fibres having aspect ratios of rp ≈ 7 and 30. It is foundthat the wall effect on the orientation is small for distances from the wall wherethe fibre centre is located farther than half a fibre length from the wall. Farfrom the wall most fibres were oriented close to the flow direction. Closer tothe wall than half a fibre length the orientation distribution first shifted to bemore isotropic and in the very proximity of the wall the fibres were orientedclose to perpendicular to the flow direction, nearly aligned with the vorticityaxis. This was most evident for the shorter fibres with rp ≈ 7.Due to the density difference between the fibres and the fluid there is anincreased concentration near the wall. Still, a physical mechanism is requiredin order for a fibre initially oriented close to the flow direction at about half afibre length from the wall to change its orientation to aligned with the vorticityaxis once it has settled down to the wall. A slender body approach is usedin order to estimate the effect of wall reflection and repeated wall contacts onthe fibre rotation. It is found that the both a wall reflection, due to settlingtowards the wall, and contact between the fibre end and the wall are expectedto rotate the fibre closer to the vorticity axis. A qualitative agreement withthe experimental results is found in a numerical study based on the theoreticalestimation.In addition an experimental study on fibre orientation in the boundarylayers of a headbox is reported. The orientation distribution in planes parallelto the wall is studied. The distribution is found to be more anisotropic closerto the wall, i.e. the fibres tend to be oriented closer to the flow direction nearthe wall. This trend is observed sufficiently far upstream in the headbox.Farther downstream no significant change in the orientation distribution couldbe detected for different distances from the wall.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. vi, 49 p.
Series
Trita-MEK, ISSN 0348-467X ; 2009:03
Keyword
fluid mechanics, fibre orientation, shear flow, wall effect, fibre suspension, papermaking
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-9995 (URN)978-91-7415-240-1 (ISBN)
Public defence
2009-03-27, E2, Lindstedsvägen 3, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20100706Available from: 2009-03-02 Created: 2009-02-26 Last updated: 2010-07-21Bibliographically approved

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Söderberg, L. Daniel

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