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  • 201.
    Dehkharqani, Arash Soltani
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Amiri, Kaveh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Steady and transient pressure measurements on the runner blades of a Kaplan turbine model2015Conference paper (Refereed)
    Abstract [en]

    The development of renewable energy sources has increased the need for power regulation. Power system regulation is mainly performed by hydropower plants through load variations. Additional forces are exerted on the runner blades during these load variations. This paper deals with pressure measurement performed on the blades of a Kaplan turbine model under steady state and load variation conditions. Flow behavior and frequency content of the pressure are investigated and compared to find critical condition in terms of pressure fluctuation. The results show that at various operating points and conditions, different regions of the blade are important. During load rejection, a considerable amount of pressure fluctuations are exerted on the runner blades. These results will be used to define experiments to be performed on the corresponding prototype. On the prototype, the loads acting on the runner blades will be investigated at various operation points similar to the model. In addition, the relation between the frequency content on the blades and loads on the main shaft will be investigated. Comparing results from model and prototype eventually would be valuable to explore the flow characteristics in prototype since CFD simulation of prototype is challenging.

  • 202.
    Dittes, Nicholas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Capacitance measurement in a bearing2018Patent (Other (popular science, discussion, etc.))
    Abstract [en]

     A bearing arrangement includes a bearing having an inner race and an outer race and a plurality of rolling elements arranged between the inner and outer race such that the first race is rotatable relative the second race; bearing lubricant arranged within the bearing to lubricate the rolling elements. The bearing arrangement provides a first electrically conductive portion and a second electrically conductive portion, the first and second electrically conductive portion being electrically insulated and arranged such that at least a portion of the bearing lubricant is located between the first and second electrically conductive portion; and a capacitance meter having a first electrode connected to the first electrically conductive portion and a second electrode connected to the second electrically conductive portion, configured to measure a capacitance between the first ring and the second ring to determine a water content in the lubricant based on the measured capacitance.

  • 203.
    Dittes, Nicholas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sensors for Water Contamination in Lubricating Grease2019Doctoral thesis, comprehensive summary (Other academic)
  • 204.
    Dittes, Nicholas J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pettersson, Anders (Contributor)
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lang, Defeng (Contributor)
    SKF.
    Corrosion Sensor for Water Contamintated Grease2019In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397XArticle in journal (Refereed)
    Abstract [en]

    A simple and inexpensive corrosion sensor has been manufactured to study the corrosion rate of new and water contaminated grease using a galvanic cell. This paper shows the methodology in using this concept for any application which may require quantifying the corrosivity of a liquid or semisolid which could be applied to the surface of the sensor. Water contamination is a problem in many grease lubricated machine components, so a sensor concept was developed and a correlation between water content and the corrosion rate is shown. This method could be used to precisely study the corrosion rate of aged or contaminated lubricants and could potentially be used as a cheap and simple way to estimate water contamination of grease.

  • 205.
    Dittes, Nicholas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pettersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lugt, Piet M.
    SKF Engineering and Research Center, Nieuwegein.
    Optical Attenuation Characterization of Water Contaminated Lubricating Grease2018In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 61, no 4, p. 726-732Article in journal (Refereed)
    Abstract [en]

    Water-contaminated grease samples are investigated with attenuation spectra in the visible and near-infrared (NIR) regions in this article. The purpose of this investigation was to identify a model with optical attenuation spectra such that the water content of grease samples could be characterized with a simple measurement setup using common methodology from the field of instrumental chemistry. The ratio between two chosen wavelengths of light appears to approximate the water content of grease samples with an acceptable coefficient of determination using a methodology to show what can potentially be done to develop condition monitoring tools. To illustrate the outlined method, a prestudy of grease aging and oxidation levels is also investigated to show that other variables do not significantly change the measurement.

  • 206.
    Dittes, Nicholas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Pettersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lang, Defeng
    SKF Research & Technology Development Nieuwegein, the Netherlands.
    Automated Dielectric Thermoscopy Characterization of Water Contaminated Grease2019In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 62, no 5, p. 859-867Article in journal (Refereed)
    Abstract [en]

    Machine maintenance is important for improving machine uptime, reliability, and reducing costs. Grease is used in most rolling element bearings, and one common failure criterion is water contamination, so developing a sensor which can detect water content automatically without human input could be a useful endeavor. The temperature dependence on the dielectric properties of water-contaminated grease is investigated in this paper with computer logged instrumentation. This method has been termed Dielectric Thermoscopy (DT). Several off the shelf (two lithium, one lithium complex, and two calcium sulphonate complex) and one unadditivized lithium grease are tested with varying amounts of water contamination from 0% to approximately 5%. Another grease is tested with small increments of added water from 0% to 0.97% to test the resolution of the measurement. The purpose is to use the capacitance temperature slope (termed dielectric thermoscopy) to show correlations to the water content of the grease sample and investigate if any grease types will pose problems in the measurement. A small, custom made fringe field capacitance sensor with an integrated temperature sensor has been used for this characterization and data is logged automatically with laboratory equipment and a PC. A useable and positive correlation to water content and the DT measurement of roughly 0.5 pF per 10 °C and percentage of water is found, although it was found that some greases have different behavior than others.

  • 207.
    Duenas Dobrowolski, Jan
    et al.
    Department of Design Fundamentals and Fluid-Flow Machinery, Wrocaw University of Technology, Wrocaw, Poland.
    Gawlinski, Marek
    Department of Design Fundamentals and Fluid-Flow Machinery, Wrocaw University of Technology, Wrocaw, Poland.
    Paszkowski, Maciej
    Department of Fundamentals of Machine Design and Tribology, Wrocaw University of Technology, Wrocaw, Poland.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Experimental Study of Lubricating Grease Flow inside the Gap of a Labyrinth Seal Using Microparticle Image Velocimetry2018In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 61, no 1, p. 31-40Article in journal (Refereed)
    Abstract [en]

    In this study, the flow of lubricating greases in a labyrinth seal geometry is studied using microparticle image velocimetry (µPIV). The aim is to evaluate the grease velocity distribution inside the gap of a labyrinth seal and to find a relationship between the grease consistency and the transferred speed from the rotating ring in order to choose the correct grease as a sealing medium. In addition, the grease flow characteristics are important for the understanding of fracture due to grease layer displacement. For these purposes, four greases with different rheological properties were used in µPIV experiments. It was found that the grease consistency plays a crucial role in speed development as well as the grease composition and presence of a slip effect at the grease–rotating wall interface.

  • 208. Dumortier, L.
    et al.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Benckert, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kjellström, Björn
    Evaluation of particle tracking velocimetry for studies of the flow in a boiler furnace1999In: Applied Modelling and Simulation, International conference, 1999Conference paper (Refereed)
  • 209.
    Dunca, Georgiana
    et al.
    Polytechnic University of Bucharest, Romania.
    Bucur, Diana
    Polytechnic University of Bucharest, Romania.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sensitivity analysis on flow rate estimation using design of experiments: Application to the pressure-time method2017In: 2017 10th International Symposium on Advanced Topics in Electrical Engineering, ATEE 2017, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 533-538, article id 7905035Conference paper (Refereed)
    Abstract [en]

    The present work investigates the flow parameters influence over the accuracy of flow rate determination by means of Design of Experiments -a statistical procedure widely used for experiments. The method used for the estimation of the flow rate derives from the standard pressure-time method, modified and improved - the solution is obtained by solving the water hammer equations considering an unsteady friction factor. The influence of the following parameters over the final moment of the flow rate variation regime is determined: the time of valve closure, the Reynolds number of the flow and the type of the closure law. A 23 factorial design is chosen to test the manner the three parameters influence, separately and together, the time value that should be chosen for the end of the flow rate variation regime. The results will help understand the influence of these parameters and the way in which they should be modeled within the flow rate determination method.

  • 210.
    Dunca, Georgiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana
    POLITEHNICA University of Bucharest.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Proulx, Gilles
    Hydro-Québec Research’s Institute.
    Dostie, Matheiu Bouchard
    Hydro-Québec Research’s Institute.
    Investigation of the pressure-time method with an unsteady friction2013In: Hydro 2013: International Conference and Exhebition : Promoting the Versalite Role of Hydro, 2013Conference paper (Refereed)
    Abstract [en]

    The pressure-time method is used to determine the flow rate in hydraulic turbines. Over the years, developments of the method to improve its accuracy have been proposed, such as a time dependent friction (Jonsson) or a different upper integration limit (Adamkowski). The present work investigates these developments on measurements performed on a full-scale machine for different flow rates. The discharge computed values using pressure measurements are compared to ultrasound transit time measurements performed simultaneously. The results point out the significance of the developments on the final results; variations of 0.5% are obtained when combining Jonsson friction formulation and Adamkowski upper integration limit.

  • 211.
    Dunca, Georgiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Popa, Radu
    POLITEHNICA University of Bucharest.
    Discharge evaluation from pressure measurements by a genetic algorithm based method2015In: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 46, p. 49-55Article in journal (Refereed)
    Abstract [en]

    This paper presents an alternative to the Gibson method, for discharge estimation of a turbine inside a hydropower plant. The method proposes a genetic algorithm which includes an integration procedure for the water hammer equations using the method of characteristics. The decision variables are represented by the steady-state regime discharge before the valve closure and the pipe friction factor. The recordings of pressure/differential pressure in measuring sections are used.

  • 212.
    Dunca, Georgiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Iovanel, Raluca Gabriela
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    On The Use of the Water Hammer Equations with Time Dependent Friction During a Valve Closure, for Discharge Estimation2016In: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 9, no 5, p. 2427-2434Article in journal (Refereed)
    Abstract [en]

    The paper presents a new method for in site discharge estimation in pressured pipes. The method consists in using the water hammer equations solved with the method of characteristics with an unsteady friction factor model. The differential pressure head variation measured during a complete valve closure is used to derive the initial flow rate, similarly to the pressure-time (Gibson) method. The method is validated with a numerical experiment, and tested with experimental laboratory measurements. The results show that the proposed method can reduce the discharge estimation error by 0.6% compared to the standard pressure-time (Gibson) method for the flow rate investigation.

  • 213.
    Dunca, Gerogiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Jonsson, Pontus
    Pöyry.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Discharge measurements using the Pressure-Time Method: Different evaluation procedures2013Conference paper (Refereed)
    Abstract [en]

    This paper analyzes the pressure-time method and its developments. The pressure-time method used to determine the discharge in hydraulic turbines is described and applied in a generic test case in well controlled laboratory conditions. Developments of the method are presented: a time dependent friction factor (proposed by Jonsson) and a different upper integration limit (proposed by Adamkowski). Laboratory experiments are used to compute the discharge using the pressure-time method in the standard and modified versions and the results are compared. The precision of the methods is verified by comparing the computed discharge values to the values measured with a magnetic flowmeter.

  • 214.
    Dunca, Gerogiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Jonsson, Pontus
    Pöyry SwedPower AB.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Discharge measurements using the Pressure-Time Method: Different evaluation procedures2014In: Polytechnical University of Bucharest. Scientific Bulletin. Series D: Mechanical Engineering, ISSN 1454-2358, Vol. 76, no 4, p. 195-202Article in journal (Refereed)
    Abstract [en]

    This paper analyzes the pressure-time method and its developments. The pressure-time method used to determine the discharge in hydraulic turbines is described and applied in a generic test case in well controlled laboratory conditions. Developments of the method are presented: a time dependent friction factor (proposed by Jonsson) and a different upper integration limit (proposed by Adamkowski). Laboratory experiments are used to compute the discharge using the pressure-time method in the standard and modified versions and the results are compared. The precision of the methods is verified by comparing the computed discharge values to the values measured with a magnetic flowmeter.

  • 215. Ebermark, Sofia
    et al.
    Marjavaara, Daniel
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Pressning av SMC: numeriska tryckfältsberäkningar med hjälp av inversmodellering2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 74-Conference paper (Other academic)
  • 216.
    Edlund, G.
    et al.
    Luleå tekniska universitet.
    Wikander, G.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The visualization of modes in a circular cochlear model by hologram interferometry1978In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 59, no 22, p. 299-303Article in journal (Refereed)
    Abstract [en]

    This work has been carried out to study the possibilities of using hologram interferometry to examine the mechanical behavior of the inner ear. The purpose was to make a model of the cochlea with a curved and stiff basilar membrane and to look for both travelling wave and standing wave patterns. The level of excitation is approximately the same as found in actual hearing when scaled to model dimensions and hence much lower than in most previous model studies. Also in contrast to previous studies, curvature effects are investigated

  • 217.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Marklund, Birger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wood-chip formation in circular saw blades studied by high-speed photography2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 115-119Article in journal (Refereed)
    Abstract [en]

    Films of wood-chip formation were captured with a high-speed camera during rip sawing of wood with a circular saw blade. The saw blade diameter was 400 mm and the rotational speed was 3250 rpm. The saw blade had four teeth with rake angles of 0°, 10°, 20° and 30° to ascertain the influence of different rake angles. Wooden boards were cut along the side so that the camera could record the cutting sequence without any interference from material between the cutting teeth and the camera. Tests were made for green, dry and frozen green pine boards, for both counter-cutting and climb-cutting cases. In addition, some Mozambican wood species were cut. The films, recorded at 40,000 frames s−1, show the cutting sequence along the trajectory of the tooth in question and the creation of the wood chip. Details such as the compression of the wood chip in the gullet, the movement of the wood chip inwards and outwards in the gullet and finally the exit from the gullet are visible. The chip size and chip movement depend strongly on the rake angle and on whether the wood is green, dry, frozen or unfrozen.

  • 218.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Söderholm, Karl-Johan M.
    University of Florida.
    How filler properties, filler fraction, sample thickness and light source affect light attenuation in particulate filled resin composites2005In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 21, no 8, p. 721-730Article in journal (Refereed)
    Abstract [en]

    The way by which variables such as filler type, filler surface treatment and light source affect light attenuation in particulate filled resin composites was presented. Mixture of 50 wt% bisGMA and 50wt% TEGDMA consisting of a photo-initiatior and a co-initiator was prepared. Three different filler types, HBB, SBB, and KU, which were either silane surface treated or not, were added to that mixture in eight different volume percentage. It was observed that of the two light sources, more light was absorbed by the composite when the laser light was used. It was also observed that the HBB filler absorbed most light and the KU filler the least.

  • 219.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan
    Florida University.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Quantitative measurements of dental light beam (halogen versus LED)2005Conference paper (Other academic)
  • 220.
    Engström, T. Fredrik
    et al.
    Luleå tekniska universitet.
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Karlsson, Rolf
    Vattenfall Research & Development.
    Proceedings of Turbine-99 - Workshop 2: The second ERCOFTAC Workshop on Draft Tube Flow, Älvkarleby, Sweden, June 18-20 20012002Book (Other academic)
  • 221.
    Eppanapelli, Lavan Kumar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental investigation of snow metamorphism at near-surface layers2018Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 222.
    Eppanapelli, Lavan Kumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Estimation of specific surface area of snow based on density and multispectral infrared reflectanceIn: Journal of cold regions engineering, ISSN 0887-381X, E-ISSN 1943-5495Article in journal (Refereed)
    Abstract [en]

    This paper presents a multiple regression method for predicting snow SSA based on multispectral reflectance and snow density. Multispectral near-IR reflectance from snow was measured at wavelengths 980 nm, 1,310 nm and 1,550 nm. In total, 16 different artificially prepared snow samples were investigated using two optical sensors, a spectrometer and a Road eye sensor. Both the sensors measured backscattered radiance from snow and measurements were carried out in a climate chamber.  Snow types with variations in physical properties such as grain distribution, surface texture, SSA, density and depth are considered. Variations in snow density were obtained through compaction and aging process. Correlation between the snow density and reflectance is investigated and influence of snow density and multispectral reflectance on snow SSA is also investigated. A generalized linear model is developed to predict the snow SSA with a coefficient of determination equal to 98\%. The preliminary validation of results show that the SSA can be accurately estimated from the density and multispectral reflectance. The model results indicate that the snow density has minor effect on the variations in snow SSA. Results suggest that snow with varying physical properties can be qualitatively characterized based on the presented approach, which is of interest for applications such as winter roads classification and pistes classification.  

  • 223.
    Eppanapelli, Lavan Kumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Johan
    Norwegian University of Science and Technology.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Investigation of snow single scattering properties of snow based on first order Legendre phase function2017In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 91, p. 151-159Article in journal (Refereed)
    Abstract [en]

    Angularly resolved bidirectional reflectance measurements were modelled by ap- proximating a first order Legendre expanded phase function to retrieve single scattering properties of snow. The measurements from 10 different snow types with known density and specific surface area (SSA) were investigated. A near infrared (NIR) spectrometer was used to measure reflected light above the snow surface over the hemisphere in the wavelength region 900 nm to 1650 nm. A solver based on discrete ordinate radiative transfer (DISORT) model was used to retrieve the estimated Legendre coefficients of the phase function and a cor- relation between the coefficients and physical properties of different snow types is investigated. Results of this study suggest that the first two coefficients of the first order Legendre phase function provide sufficient information about the physical properties of snow where the latter captures the anisotropic behaviour of snow and the former provides a relative estimate of the single scattering albedo of snow. The coefficients of the first order phase function were com- pared with the experimental data and observed that both the coefficients are in good agreement with the experimental data. These findings suggest that our approach can be applied as a qualitative tool to investigate physical properties of snow and also to classify different snow types.

  • 224.
    Eppanapelli, Lavan Kumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    3D analysis of deformation and porosity of dry natural snow during compaction2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 6, article id 850Article in journal (Refereed)
    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.

  • 225.
    Eppanapelli, Lavan Kumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Friberg, Benjamin
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Estimation of a low-order Legendre expanded phase function of snow2016In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 78, p. 174-181Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to estimate the scattering phase function of snow from angularly resolved measurements of light intensity in the plane of incidence. A solver is implemented that solves the scattering function for a semi-infinite geometry based on the radiative transfer equation (RTE). Two types of phase functions are considered. The first type is the general phase function based on a low-order series expansion of Legendre polynomials and the other type is the Henyey-Greenstein (HG) phase function. The measurements were performed at a wavelength of 1310 nm and six different snow samples were analysed. It was found that a first order expansion provides sufficient approximation to the measurements. The fit from the first order phase function outperforms that of the HG phase function in terms of accuracy, ease of implementation and computation time. Furthermore, a correlation between the magnitude of the first order component and the age of the snow was found. We believe that these findings may complement present non-contact detection techniques used to determine snow properties.

  • 226.
    Eppanapelli, Lavan Kumar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lintzen, Nina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Johan
    Department of Civil and Transport Engineering, Norwegian University of Science and Technology.
    Estimation of Liquid Water Content of Snow Surface by Spectral Reflectance2018In: Journal of cold regions engineering, ISSN 0887-381X, E-ISSN 1943-5495, Vol. 32, no 1, article id 05018001Article in journal (Refereed)
    Abstract [en]

    This study measures the spectral reflectance from snow with known liquid water content (LWC) in a climate chamber using two optical sensors, a near-infrared (NIR) spectrometer and a Road eye sensor. The spectrometer measures the backscattered radiation in the wavelength range of 920–1,650 nm. The Road eye sensor was developed to monitor and classify winter roads based on reflected intensity measurements at wavelengths of 980, 1,310, and 1,550 nm. Results of the study suggest that the spectral reflectance from snow is inversely proportional to the LWC in snow. Based on the effect of LWC on the spectral reflectance, three optimum wavelength bands are selected in which snow with different LWCs is clearly distinguishable. A widely used remote sensing index known as the normalized difference water index (NDWI) is used to develop a method to estimate the surface LWC for a given snow pack. The derived NDWI values with respect to the known LWC in snow show that the NDWI is sensitive to the LWC in snow and that the NDWI and LWC are directly proportional. Based on this information, the NDWI is used to estimate the surface LWC in snow from measurements on a ski track using the Road eye sensor. The findings suggest that the presented method can be applied to estimate the surface LWC in order to classify snow conditions potentially for ski track and piste applications.

  • 227.
    Eriksson, Ingemar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    New high-speed photography technique for observation of fluid flow in laser welding2010In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 49, no 10Article in journal (Refereed)
    Abstract [en]

    Recent developments in digital high-speed photography allow us to directly observe the surface topology and flow conditions of the melt surface inside a laser evaporated capillary. Such capillaries (known as keyholes) are a central feature of deep penetration laser welding. For the first time, it can be confirmed that the liquid capillary surface has a rippled, complex topology, indicative of subsurface turbulent flow. Manipulation of the raw data also provides quantitative measurements of the vertical fluid flow from the top to the bottom of the keyhole.

  • 228.
    Eriksson, Ingemar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Haglund, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Holographic measurement of thermal distortion during laser spot welding2012In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 51, no 3Article in journal (Refereed)
    Abstract [en]

    Welding distortion is an important engineering topic for simulation and modeling, and there is a need for experimental verification of such models by experimental studies. High-speed pulsed digital holography is proposed as a measurement technique for out-of-plane welding distortion. To demonstrate the capability of this technique, measurements from a laser spot weld are presented. A complete twodimensional deformation map with submicrometer accuracy was acquired at a rate of 1000 measurements per second. From this map, particular points of interest can be extracted for analysis of the temporal development of the final distortion geometry.

  • 229. Eriksson, Martin
    et al.
    Lucchese, Riccardo
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Gustafsson, Jonas
    RISE - Swedish Institute of Computer Science.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mousavi, Arash
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Monitoring and Modelling Open Compute Servers2017In: Proceedings IECON 2017: 43rd Annual Conference of the IEEE Industrial Electronics Society, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 7177-7184Conference paper (Refereed)
    Abstract [en]

    Energy efficient control of server rooms in modern data centers can help reducing the energy usage of this fast growing industry. Efficient control, however, cannot be achieved without: i) continuously monitoring in real-time the behavior of the basic thermal nodes within these infrastructures, i.e., the servers; ii) analyzing the acquired data to model the thermal dynamics within the data center. Accurate data and accurate models are indeed instrumental for implementing efficient data centers cooling strategies. In this paper we focus on a class of Open Compute Servers, designed in an open-source fashion and currently deployed by Facebook. We thus propose a set of methods for collecting real-time data from these platforms and a control-oriented model describing the thermal dynamics of the CPUs and RAMs of these servers as a function of both manipulable and exogenous inputs (e.g., the CPU utilization levels and the air mass flow produced by the server's fans). We identify the parameters of this model from real data and make the results available to other researchers.

  • 230.
    Erjavec, Nika
    et al.
    CBZI, University of Nova Gorica, Vipava.
    Pinato, Giulietta
    CBZI, University of Nova Gorica, Vipava.
    Ramser, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Raman spectroscopy as a tool for detecting mitochondrial fitness2016In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 47, no 8, p. 933-939Article in journal (Refereed)
    Abstract [en]

    Raman spectroscopy allows the molecular chemical analysis of whole living cells by comparing them to known Raman signatures of specific vibrational bonds. In this work we used Raman spectroscopy to differentiate between wild type yeast cells and mutants characterized by increased or reduced mitochondrial fragmentation. To associate mitochondrial fragmentation with biochemical markers, we performed Linear Discriminant Analysis (LDA) of whole cell Raman spectra (~50–100 cells/spectrum). We show that the long-lived, less fragmented mutants fall into a significantly distant cluster from the wild type and short-lived, more fragmented mutants. Clustering depends on respiratory growth and coincides with that of membrane phospholipids and some respiratory chain components. Spectral clustering is supported by enzymatic activity measurements of OXPHOS Complexes. In addition, we find that NAD(P)H autofluorescence also correlates with mitochondrial fragmentation, representing another likely aging biomarker, besides phospholipids and OXPHOS components. In summary, we demonstrate that Raman spectroscopy has the potential to become a powerful tool for differentiating healthy from unhealthy aged tissues, as well as for the prognostic evaluation of mitochondrial function and fitness.

  • 231.
    Fabricius, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Miroshnikova, Elena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Darcy's law for flow in a periodic thin porous medium confined between two parallel plates2016In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 115, no 3, p. 473-493Article in journal (Refereed)
    Abstract [en]

    We study stationary incompressible fluid flow in a thin periodic porous medium. The medium under consideration is a bounded perforated 3D-domain confined between two parallel plates. The distance between the plates is \(\delta \), and the perforation consists of \(\varepsilon \)-periodically distributed solid cylinders which connect the plates in perpendicular direction. Both parameters \(\varepsilon \), \(\delta \) are assumed to be small in comparison with the planar dimensions of the plates. By constructing asymptotic expansions, three cases are analysed: (1) \(\varepsilon \ll \delta \), (2) \(\delta /\varepsilon \sim \text {constant}\) and (3) \(\varepsilon \gg \delta \). For each case, a permeability tensor is obtained by solving local problems. In the intermediate case, the cell problems are 3D, whereas they are 2D in the other cases, which is a considerable simplification. The dimensional reduction can be used for a wide range of \(\varepsilon \) and \(\delta \) with maintained accuracy. This is illustrated by some numerical examples.

  • 232.
    Fallahjoybari, Nima
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Maerefat, Mehdi
    Department of Mechanical Engineering, Tarbiat Modares University.
    Nimvari, Majid E.
    Department of Mechanical Engineering, Tarbiat Modares University, Faculty of Engineering Technologies, Amol University of Special Modern Technologies, Amol.
    Numerical Computation of Macroscopic Turbulent Quantities in a Porous Medium: an Extemsion to a macroscopic Turbulent model2016In: Journal of Porous Media, ISSN 1091-028X, E-ISSN 1934-0508, Vol. 19, no 6, p. 497-513Article in journal (Refereed)
    Abstract [en]

    A numerical study is conducted using a standard numerical model for a porous medium consisting of a staggered arrangement of square cylinders. Fully developed macroscopic turbulent kinetic energy and dissipation rate are derived and analyzed for different porosities of the medium at different Reynolds numbers. The results obtained are used to extend the applicability range of an existing macroscopic turbulence model in porous media to low-Reynolds-number turbulent flows. It is shown that the levels of normalized macroscopic turbulent kinetic energy and dissipation rate are not constant over the entire range of Reynolds number. These quantities increase from lower levels at low Reynolds numbers up to an asymptotic value being independent of Reynolds number. The constants in the closure expression of the macroscopic turbulence equations are modified using the present results. Finally, in order to highlight the importance of the present modifications, the results of the macroscopic turbulence model before and after the modifications are compared for two cases.

  • 233.
    Farré-Lladós, Josep
    et al.
    Department of Mechanical Engineering, UPC - Technical University of Catalonia.
    Casals-Terré, Jasmina
    Department of Mechanical Engineering, UPC - Technical University of Catalonia.
    Voltas, Jordi
    Department of Graphic Expression, UPC - Technical University of Catalonia.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The use of Rapid Prototyping techniques (RPT) to manufacture micro channels suitable for high operation pressures and µPIV2016In: Rapid prototyping journal, ISSN 1355-2546, E-ISSN 1758-7670, Vol. 22, no 1, p. 67-76Article in journal (Refereed)
    Abstract [en]

    Purpose– This paper aims to present a new methodology to manufacture micro-channels suitable for high operating pressures and micro particle image velocimetry (μPIV) measurements using a rapid-prototyping high-resolution 3D printer. This methodology can fabricate channels down to 250 μm and withstand pressures of up to 5 ± 0.2 MPa. The manufacturing times are much shorter than in soft lithography processes. Design/methodology/approach– The novel manufacturing method developed takes advantage of the recently improved resolution in 3D printers to manufacture an rapid prototyping technique part that contains the hose connections and a micro-channel useful for microfluidics. A method to assemble one wall of the micro-channel using UV curable glue with a glass slide is presented – an operation required to prepare the channel for μPIV measurements. Once built, the micro-channel has been evaluated when working under pressure and the grease flow behavior in it has been measured using μPIV. Furthermore, the minimum achievable channels have been defined using a confocal microscopy study. Findings– This technique is much faster than previous micro-manufacturing techniques where different steps were needed to obtain the micro-machined parts. However, due to current 3D printers ' resolutions (around 50 μm) and according to the experimental results, channels smaller than 250-μm2 cross-section should not be used to characterize fluid flow behaviors, as inaccuracies in the channel boundaries can deeply affect the fluid flow behavior. Practical implications– The present methodology is developed due to the need to validate micro-channels using μPIV to lubricate critical components (bearings and gears) in wind turbines. Originality/value– This novel micro-manufacturing technique overcomes current techniques, as it requires less manufacturing steps and therefore it is faster and with less associated costs to manufacture micro-channels down to 250-μm2 cross-section that can withstand pressures higher than 5 MPa that can be used to characterize microfluidic flow behavior using μPIV.

  • 234.
    Farré-Lladós, Josep
    et al.
    Department of Mechanical Engineering, UPC - Technical University of Catalonia.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casals-Terré, Jasmina
    Department of Mechanical Engineering, UPC - Technical University of Catalonia.
    New solution to preent excessive wear in wind turbine gears2014In: Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2014: Lake Buena Vista, United States, 18 - 22 May 2014, Society of Tribologists and Lubrication Engineers , 2014, Vol. 2, p. 548-550Conference paper (Refereed)
  • 235.
    Farré-Lladós, Josep
    et al.
    Department of Mechanical Engineering, UPC - Technical University of Catalonia, KIC InnoEnergy S.E. - Location Iberia, Barcelona.
    Casals-Terré, Jasmina
    Department of Mechanical Engineering, UPC - Technical University of Catalonia, KIC InnoEnergy S.E. - Location Iberia, Barcelona.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    New Lubrication Device to Minimize Wear at the Pitch Gear2015Conference paper (Refereed)
  • 236.
    Farré-Lladós, Josep
    et al.
    Department of Mechanical Engineering, UPC - Technical University of Catalonia, KIC InnoEnergy S.E. - Location Iberia, Barcelona.
    Casals-Terré, Jasmina
    Department of Mechanical Engineering, UPC - Technical University of Catalonia, KIC InnoEnergy S.E. - Location Iberia, Barcelona.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    New Lubrication Device to Minimize Wear at the Pitch Gear2015Conference paper (Refereed)
  • 237.
    Farré-Lladós, Josep
    et al.
    Department of Mechanical Engineering, UPC - Technical University of Catalonia.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casals-Terré, Jasmina
    Department of Mechanical Engineering, UPC - Technical University of Catalonia.
    Embedded Micro-nozzles in the Pitch Gear Deddendum to Minimize Wear at Zero Degree Position2015Conference paper (Refereed)
  • 238.
    Farré-Lladós, Josep
    et al.
    Mechanical Engineering Department, UPC - Technical University of Catalonia, Terrassa.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casals-Terré, Jasmina
    Mechanical Engineering Department, UPC - Technical University of Catalonia, Terrassa.
    New method for lubricating wind turbine pitch gears using embedded micro-nozzles2017In: Journal of Mechanical Science and Technology, ISSN 1738-494X, E-ISSN 1976-3824, Vol. 31, no 2, p. 797-806Article in journal (Refereed)
    Abstract [en]

    The increase of power generated by wind turbines has increased the stresses applied in all of its components, thereby causing premature failures. Particularly, pitch and yaw gears suffer from excessive wear mainly caused by inappropriate lubrication. This paper presents a novel method to automatically lubricate the wind turbine pitch gear during operation. A micro-nozzle to inject fresh grease continuously between the teeth in contact was designed, manufactured, and installed in a test bench of a 2 MW wind turbine pitch system. The test bench was used to characterize the fatigue behavior of the gear surface using conventional wind turbine greases under real cyclic loads. Measurements of wear evolution in a pitch gear with and without micro-nozzle show a decrease of 70 % of the wear coefficient after 2×104 cycles.

  • 239.
    Fernberg, Patrik
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    "Detect" - a new defect detection method and its use on sheet moulding compound (SMC) substrates2008In: Composites for sustainable progress: ECCM 13, 13th European Conference on Composite Materials ; June 2 - 5, 2008, Stockholm, Sweden, Stockholm, 2008Conference paper (Refereed)
    Abstract [en]

    A novel optical method for detection of surface porosities on SMC substrates is presented. Detection is facilitated by observation of how a liquid film on the surface evaporates. The method utilizes the fact that complete evaporation takes longer time in the pores than elsewhere. The rate of change of a laser speckle pattern gives a measure of the changes at the surface and indicates where pores causes prolonged evaporation. A pilot measurement unit was built that shows that the principle ideas of the system work. Attempts were made to develop the pilot unit so that it could provide quantitative numbers of actual defects on an SMC substrate. The results are encouraging in the sense that the unit can automatically identify areas with higher number of defects.

  • 240.
    Fernberg, S Patrik
    et al.
    Swerea SICOMP AB.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Fibre reinforced polymer composites based on nanostructured constituents2008In: White Book: Polymer Nanoscience and Nanotechnology, a European Perspective, 2008, p. 233-256Chapter in book (Other academic)
  • 241.
    Fernberg, S.P.
    et al.
    Luleå tekniska universitet.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sandlund, E.J.
    Öhgren, I.
    Particle Distribution Mechanisms in Infusion Moulded Composites2004In: From nano-scale interactions to engineering structures: ECCM 11, 11th European Conference on Composite Materials ; May 31 - June 3, 2004, Rhodes, Greece / [ed] Costas Galiotis, Rhodos, 2004Conference paper (Refereed)
  • 242.
    Fernberg, S.P.
    et al.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Sandlund, E.J.
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mechanisms controlling particle distribution in infusion molded composites2006In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 25, no 1, p. 59-70Article in journal (Refereed)
    Abstract [en]

    This article presents results from an experimental investigation in which two grades of aluminatrihydroxide (ATH) particles are added to liquid resin and used in infusion molding experiments. Based on the results, potential key mechanisms controlling resin flow and hence also the final particle distribution are proposed. A pore doublet model is proposed to explain the seemingly random spatial distribution of particle-dense regions within the final material. These dense regions are found within flow channels, at locations where local shear strain rates are low. This suggests that they are formed as a consequence of a Bingham type of viscosity behavior observed for the suspension and/or due to filtering of particles during fiber bundle impregnation.

  • 243.
    Field, J.E.
    et al.
    Physics and Chemistry of Solids, Cavendish Laboratory, Cambridge, Department of Physics and Chemistry of Solids, Cavendish Laboratory, University of Cambridge.
    Amer, Eynas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Zafar, M.A.
    Department of Physics, University of Dacca.
    Walley, Stephen M.
    Department of Physics and Chemistry of Solids, Cavendish Laboratory, University of Cambridge.
    High-speed photographic study of laser damage and ablation2015In: Imaging Science Journal, ISSN 1368-2199, E-ISSN 1743-131X, Vol. 63, no 3, p. 119-136Article in journal (Refereed)
    Abstract [en]

    This paper reviews earlier work and describes a photographic investigation of damage produced in glasses, polymers and crystals by Q-switched and non-Q-switched laser pulses. The cameras used in the study include a Wollensak Fastax WF3 camera, a Beckman & Whitley (model 189) rotating mirror camera, and a Beckman & Whitley (model 501) image converter camera. The formation of internal disc-type cracks with the non-Q-switched pulse was studied in detail. The use of these cracks for fracture energy studies is demonstrated. Photographic sequences show the production of micro-plasmas associated with damage, and stress waves formed during irradiation in both solids and liquids. A recent development is that of digital holography which adds phase and intensity information to the more conventional photographic techniques. This technique is used here to study laser ablation and wave propagation in water. The photographic data shows the processes taking place in the laser interaction with a wide range of materials and should be of interest to modellers.

  • 244.
    Finnström, Marie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jet formation in liquid impact1984Licentiate thesis, monograph (Other academic)
  • 245.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    3D analys av deformationer i inhomogena material med röntgenbaserad mikrotomografi och digital volymkorrelation2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 94-Conference paper (Other academic)
  • 246.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Optimeringsstudie av datortomografisystem för användning inom 3D bildkorrelation2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 65-Conference paper (Other academic)
  • 247.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    X-ray microtomography and digital volume correlation for internal deformation and strain analysis2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A material that is exposed to mechanical load or experience a variation in its immediate environment (temperature, pressure, humidity etc.) will to some extent be affected by these new conditions, which is reflected through structural movements in the material. In order to measure engineering properties related to these structural changes, such as for example deformation and strain, we need to gain information about them that are precise and reliable. There exist many different methods for such measurements, which in most cases are based on the pure surface response due to the deforming mechanism. As long as the material structure is reasonably homogeneous the surface information may be enough but as the complexity of the material structure increase it gets more important to obtain information from the inside of the material. Here, a method for full 3D imaging and quantitative analysis of internal deformation and strain in inhomogeneous materials is presented. 3D structural information from the deforming material is obtained through use of x-ray microtomography. The deformation of the structure is analysed with a 3D pattern recognition technique called digital volume correlation, which is a 3D extension of digital image correlation. A thorough theoretical description of both image formation through x-ray microtomography as well as 2D and 3D structural deformation analysis is given. Complimentary, more practical aspects of the different x-ray imaging systems used in the research are described together with the different methods used for image quality assurance. Four different applications are presented. The first is an example of how rapid processes such as internal granular flow can be imaged and analysed with this kind of methods. The temporal resolution needed to resolve the process yields a sacrifice of spatial information and the analysis is carried out in 2D with digital image correlation. Secondly, the deformation and strain in 3D micro-scale wood structure exposed to three-point-bending is measured by use of synchrotron x-ray microtomography and digital volume correlation. Thirdly, the 3D structural swelling in wood microstructure due to water exposure is analysed using the same methods. Finally, the motion and induced strain in a granular material due to compaction is measured in 3D. The results show good agreement with corresponding 2D measurements, carried out for comparison. The experiments show that the method successfully can be used for analysis of various kinds of deformations and materials and that the results are trustworthy.

  • 248.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hjortsberg, E.
    LKAB, Research & Development, 983 81 Malmberget.
    3D sequential imaging and analysis of iron ore pellets under reduction by X-ray microtomography2012In: 6th Int. Congress on the Science and Technology of Ironmaking 2012, ICSTI 2012: Including Proceedings from the 42nd Ironmaking and Raw Materials Seminar, and the 13th Brazilian Symp. on Iron Ore, 2012, Vol. 3, p. 1744-1753Conference paper (Refereed)
    Abstract [en]

    In this study, X-ray microtomography, combined with textural analysis, is used for 3D imaging of iron ore pellets and characterisation of interior cracks under a reduction process. The work is currently focused on the development of the methods and therefore the results mainly reflect the possibilities with the technique. Reduction experiments on a number of iron ore pellets were performed in 4 steps during the transformation from hematite to magnetite at 500°C. The pellet microstructure is imaged and visualized before reduction and after each subsequent reduction step using x-ray microtomography and the crack distribution characterized with image analysis. For the chosen pellet composition, networks of cracks are already visible in the unreduced state and show a successive growth during the first half of the reduction process. However, this growth stops during the second half of the process, and for the majority of the investigated samples a certain regression of the crack size is observed. Although further studies are needed, it can be concluded that the use of X-ray microtomography has the potential to become an important tool for material characterization in iron ore pellet research due to its ability to gather information from the bulk of the material at several different stages of a process.

  • 249.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hjortsberg, Erik
    LKAB.
    X-ray microtomography for sequential imaging and analysis of iron ore pellets under reduction2012In: Scanmet IV: 4th International Conference on Process Development in Iron and Steelmaking, Luleå: MEFOS , 2012, Vol. 2, p. 217-227Conference paper (Refereed)
    Abstract [en]

    This work has been a part of the development of a method where x-ray microtomography and image analysis are used to quantify the crack distribution and propagation in iron ore pellets during reduction.Reduction experiments on 7 pellets, were performed in 4 steps during the transformation from hematite to magnetite at 500 °C. The pellet microstructure is imaged and visualized at each step using x-ray microtomography and the crack distribution characterized with image analysis.For the chosen pellet composition, networks of cracks are already visible in the unreduced state and show a successive growth during the first 30 minutes of reduction. As the transformation to magnetite is complete, crack growth has stopped and in several cases a partial regression is observed.It can be concluded that the use of X-ray microtomography has the potential to become an important tool for material characterization in iron ore pellet research due to its ability to gather information from the bulk of the material at several different stages of a process.

  • 250.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mooser, René
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    Arnold, M.
    Wood Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    Hack, Erwin
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    Wyss, Peter
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    3D micro-scale deformations of wood in bending: synchrotron radiation μCT data analyzed with digital volume correlation2008In: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 164, no 3, p. 255-262Article in journal (Refereed)
    Abstract [en]

    A micro-scale three-point-bending experiment with a wood specimen was carried out and monitored by synchrotron radiation micro-computed tomography. The full three-dimensional wood structure of the 1.57 × 3.42 × 0.75 mm3 specimen was reconstructed at cellular level in different loading states. Furthermore, the full three-dimensional deformation field of the loaded wood specimen was determined by digital volume correlation, applied to the reconstructed data at successive loading states. Results from two selected regions within the wood specimen are presented as continuous displacement and strain fields in both 2D and 3D. The applied combination of synchrotron radiation micro-computed tomography and digital volume correlation for the deformation analysis of wood under bending stress is a novel application in wood material science. The method offers the potential for the simultaneous observation of structural changes and quantified deformations during in situ micro-mechanical experiments. Moreover, the high spatial resolution allows studying the influence of anatomical features on the fracture behaviour of wood. Possible applications of this method range from bio-mechanical observations in fresh plant tissue to fracture mechanics aspects in structural timber.

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