| 1. |
- Aitomäki, Yvonne, et al.
(författare)
-
Estimating material properties of solid and hollow fibers in suspension using ultrasonic attenuation
- 2013
-
Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010 .- 1525-8955. ; 60:7, s. 1424-1434
-
Tidskriftsartikel (refereegranskat)abstract
- Estimates of the material properties of hollow fibers suspended in a fluid using ultrasound measurements and a simple, computationally efficient analytical model are made. The industrial application is to evaluate the properties of wood fibers in paper pulp. The necessity of using a layered cylindrical model (LCM) as opposed to a solid cylindrical model (SCM) for modeling ultrasound attenuation in a suspension of hollow fibers is evaluated. The two models are described and used to solve the inverse problem of estimating material properties from attenuation in suspensions of solid and hollow polyester fibers. The results show that the measured attenuation of hollow fibers differs from that of solid fibers. Elastic properties estimates using LCM with hollow-fiber suspension measurements are similar to those using SCM with solid-fiber suspension measurements and compare well to block polyester values for elastic moduli. However, using the SCM with the hollow-fiber suspension did not produce realistic estimations. In conclusion, the LCM gives reasonable estimations of hollow fiber properties and the SCM is not sufficiently complex to model hollow fibers. The results also indicate that the use of a distributed radius in the model is important in estimating material properties from fiber suspensions.
|
|
| 2. |
- Broberg, Patrik, 1983-
(författare)
-
Towards Automation of Non-Destructive Testing of Welds
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- All welding processes can give rise to defects that will weaken the joint and can lead to failure of the welded structure. Because of this, non-destructive testing (NDT) of welds have become increasingly important to ensure the structural integrity when the material becomes thinner and stronger and welds become smaller; all to reduce weight in order to save material and reduce emissions due to lighter constructions.Several NDT methods exists for testing welds and they all have their advantages and disadvantages when it comes to the types and sizes of defects that are detectable, but also in the ability to automate the method. Several methods were compared using common weld defects to determine which method or methods were best suited for automated NDT of welds. The methods compared were radiography, phased array ultrasound, eddy current, thermography and shearography. Phased array ultrasound was deemed most suitable for detecting the weld defects used in the comparison and for automation and was therefore chosen to be used in the continuation of this work. Thermography was shown to be useful for detecting surface defects; something not easily detected using ultrasound. A combination of these techniques will be able to find most weld defects of interest.Automation of NDT can be split into two separate areas; mechanisation of the testing and automation of the analysis, both presenting their own difficulties. The problem of mechanising the testing has been solved for simple geometries but for more general welds it will require a more advance system using an industrial robot or similar. Automation of the analysis of phased array ultrasound data consists of detection, sizing, positioning and classification of defects. There are several problems to solve before a completely automatic analysis can be made, including positioning of the data, improving signal quality, segmenting the images and classifying the defects. As a step on the way towards positioning of the data, and thereby easing the analysis, the phase of the signal was studied. It was shown that the phase can be used for finding corners in the image and will also improve the ability to position the corner as compared to using the amplitude of the signal. Further work will have to be done to improve the signal in order to reliably analyse the data automatically.
|
|
| 3. |
- Carlson, Johan, et al.
(författare)
-
Projekt: SCOPE Norra
- 2011
-
Annan publikation (populärvet., debatt m.m.)abstract
- SCOPE Norra är ett samarbetskonsortium för forskning och utveckling tillsammans med massa- och pappersindustrin i Norrbotten och Västerbotten. Projektet koordineras av centrumbildningen ProcessIT Innovations.Inom SCOPE Norra pågår ett flertal delprojekt, uppdelat på ett antal fokusområden.Huvudfinansiär för konsortiet är Tillväxtverket genom medel från EU:s strukturfonder.
|
|
| 4. |
|
|
| 5. |
- Linder, Tomas, et al.
(författare)
-
Anisotropic light propagation in paper
- 2012
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:2, s. 500-506
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate anisotropic light propagation in paper using both a theoretical model and experiments. The theoretical model utilizes the Monte Carlo method to solve the photon transport equation numerically. It is assumed that wood fibres are represented by infinitely long, homogeneous and straight cylinders. The layer-like microstructure and anisotropic orientation of the fibres is considered in the model. The conical scattering by cylindrical objects, the wood fibres, is argued as the main source of anisotropic scattering. Simulations revealed that laterally resolved transmittance exhibits directional dependence. Experiments on light transmitted through a standard kraft liner product confirmed that light in fact do propagate more in the machine direction than in the cross direction. Reasonably good agreement was obtained between experimentally and numerically obtained iso-intensity patterns.
|
|
| 6. |
- Linder, Tomas, et al.
(författare)
-
Lateral light scattering in fibrous media
- 2013
-
Ingår i: Optics Express. - 1094-4087. ; 21:6, s. 7835-7840
-
Tidskriftsartikel (refereegranskat)abstract
- Lateral light scattering in fibrous media is investigated by computing the modulation transfer function (MTF) of 22 paper samples using a Monte Carlo model. The simulation tool uses phase functions from infinitely long homogenous cylinders and the directional inhomogeneity of paper is achieved by aligning the cylinders in the plane. The inverse frequency at half maximum of the MTF is compared to both measurements and previous simulations with isotropic and strongly forward single scattering phase functions. It is found that the conical scattering by cylinders enhances the lateral scattering and therefore predicts a larger extent of lateral light scattering than models using rotationally invariant single scattering phase functions. However, it does not fully reach the levels of lateral scattering observed in measurements. It is argued that the hollow lumen of a wood fiber or dependent scattering effects must be considered for a complete description of lateral light scattering in paper.
|
|
| 7. |
- Linder, Tomas, et al.
(författare)
-
Light scattering in fibrous media with different degrees of in-plane fiber alignment
- 2014
-
Ingår i: Optics Express. - 1094-4087. ; 22:14, s. 16829-16840
-
Tidskriftsartikel (refereegranskat)abstract
- Fiber orientation is an important structural property in paper and other fibrous materials. In this study we explore the relation between light scattering and in-plane fiber orientation in paper sheets. Light diffusion from a focused light source is simulated using a Monte Carlo technique where parameters describing the paper micro-structure were determined from 3D x-ray computed tomography images. Measurements and simulations on both spatially resolved reflectance and transmittance light scattering patterns show an elliptical shape where the main axis is aligned towards the fiber orientation. Good qualitative agreement was found at low intensities and the results indicate that fiber orientation in thin fiber-based materials can be determined using spatially resolved reflectance or transmittance.
|
|
| 8. |
- Linder, Tomas, et al.
(författare)
-
Monte Carlo simulation of photon transport in a randomly oriented sphere-cylinder scattering medium
- 2011
-
Ingår i: Applied physics. B, Lasers and optics (Print). - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 105:3, s. 659-664
-
Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo simulation tool for simulating photon transport in a randomly oriented sphere-cylinder medium has been developed. The simulated medium represents a paper pulp suspension where the constituents are assumed to be mono-disperse micro-spheres, representing dispersed fiber fragments, and infinitely long, straight, randomly oriented cylinders representing fibers. The diameter of the micro-spheres is considered to be about the order of the wavelength and is described by Mie scattering theory. The fiber diameter is considerably larger than the wavelength and the photon scattering is therefore determined by an analytical solution ofMaxwell’s equation for scattering at an infinitely long cylinder. By employing a Stokes–Mueller formalism, the software tracks the polarization of the light while propagating through the medium. The effects of varying volume concentrations and sizes of the scattering components on reflection, transmission and polarization of the incident light are investigated. It is shown that not only the size but also the shape of the particles has a big impact on the depolarization.
|
|
| 9. |
- Löfqvist, Charlotte, et al.
(författare)
-
First Steps towards Evidence-Based Preventive Home Visits: Experiences Gathered in a Swedish Municipality.
- 2012
-
Ingår i: Journal of Aging Research. - : Hindawi Limited. - 2090-2204 .- 2090-2212. ; 2012
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of preventive home visits is to promote overall health and wellbeing in old age. The aim of this paper was to describe the process of the development of evidence-based preventive home visits, targeting independent community-living older persons. The evidence base was generated from published studies and practical experiences. The results demonstrate that preventive home visits should be directed to persons 80 years old and older and involve various professional competences. The visits should be personalized, lead to concrete interventions, and be followed up. The health areas assessed should derive from a broad perspective and include social, psychological, and medical aspects. Core components in the protocol developed in this study captured physical, medical, psychosocial, and environmental aspects. Results of a pilot study showed that the protocol validly identified health risks among older people with different levels of ADL dependence.
|
|
| 10. |
- Löfqvist, Torbjörn
(författare)
-
Photoacoustic techniques applied in pulp quality measurements
- 2011
-
Konferensbidrag (refereegranskat)abstract
- The pulp and paper industry is constantly striving to increase product quality and lowering the production costs. These efforts requires new or improved measurement techniques that either performs better than existing techniques or determines process parameters that at present cannot be determined. In the presented study we review a new photoacoustic technique that may have an impact in these matters. The photoacoustic technique is presented for two basic settings. The first is based on the effect that light absorbed in the fibre suspension generates sound through a thermoelastic energy transformation process. The sound wave, while propagating through the suspension, is distorted and attenuated by the fibres and thus inherently carries information about the suspension. The acoustic wave propagation is described mathematically and the model is used in an inverse manner to determine properties of the suspension and of the fibres, such as the fibre material elastic properties. The second setting includes monitoring of the scattered light intensity as well as its time-of-flight through the suspension. By combining the optical measurements and measurements of acoustic attenuation and speed of sound we have found that the combination can be used to give a good estimate of the total mass fraction as well as fiber and fines mass fractions. The proposed photoacoustic technique has potential to become a valuable tool for pulp and paper manufacturers enabling production of a more consistent product quality and further develop the understanding of the fiber elastic properties impact on the finished product.
|
|
