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  • 1.
    Carlsson, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Wiinikka, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Iisa, Kristiina
    National Renewable Energy Laboratory, Golden, Colorado.
    High-speed imaging of biomass particles heated with a laser2013Ingår i: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 103, s. 278-286Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work two types of lignocellulosic biomass particles, European spruce and American hardwood (particle sizes from 100 μm to 500 μm) were pyrolysed with a continuous wave 2 W Nd:YAG laser. Simultaneously a high-speed camera was used to capture the behavior of the biomass particle as it was heated for about 0.1 s. Cover glasses were used as a sample holder which allowed for light microscope studies after the heating. Since the cover glasses are not initially heated by the laser, vapors from the biomass particle are quenched on the glass within about 1 particle diameter from the initial particle. Image processing was used to track the contour of the biomass particle and the enclosed area of the contour was calculated for each frame.The main observations are: There is a significant difference between how much surface energy is needed to pyrolyses the spruce (about 75% more) compared to the hardwood. The oil-like substance which appeared on the glass during the experiment is solid at room temperature and shows different levels of transparency. A fraction of this substance is water soluble. A brownish coat is seen on the unreacted biomass. The biomass showed insignificant swelling as it was heated. The biomass particle appears to melt and boil at the front that is formed between the laser beam and the biomass particle. The part of the particle that is not subjected to the laser beam seems to be unaffected.

  • 2.
    Eppanapelli, Lavan Kumar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D analysis of deformation and porosity of dry natural snow during compaction2019Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 6, artikel-id 850Artikel i tidskrift (Refereegranskat)
    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.

  • 3.
    Hellström, Gunnar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andersson, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Leonardsson, Kjell
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundqvist, Hans
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Simulation and experiments of entrance flow conditions to a fishway2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    When migrating fish tries to pass around man made obstacles such as hydropower dams with the aid of fish passages it is important that the migrating path is constructed in an efficient manner. By designing the entrance of the fishway in a manner that gives attractive flow conditions for migrating fish, the overall passage efficiency can be increased. In this study two alternative design solutions have been studied with numerical simulations, lab-scale experiments and in-field testing to achieve such attractive flow. Designs studied are constructions yielding a submerged jet, in order to increase the velocity of the flow at the entrance, and a half-cylinder, in order to create vortices that the fishes can utilize when continuing their journey towards their spawning grounds. A combination of the previous mentioned setups was also investigated. A first result shows that the increase in velocity decreases the residence time downstream the fishway and increases the total passage efficiency while the result from the vorticity generation is inconclusive at this point. The combination of the two designs shows similar passage efficiency as with only velocity increase although it does not show the same decrease in residence time. Improvements on the design of the vorticity generator and shape optimization of the construction generating the jet could further improve the efficiency of the fishway

  • 4.
    Joffe, Roberts
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Swerea SICOMP.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjögren, Anders
    Lund University.
    Characterization of defects in polymer composites used in medical devices by means of x-ray microtomography2017Ingår i: 3rd International Conference on Tomography of Materials and Structures (ICTMS2017), 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a study on micro-structural characterization of carbon fibre-reinforced plastics used inmedical devices. The focus of the investigation is on determination of void content in the materials, since voids act asdefects and will affect the service life of the composites/devices. The results show that x-ray microtomography is anaccurate and powerful technique to identify defects in composites, and it is of great value in quality control.

  • 5.
    Khayamyan, Shervin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Transitional and Turbulent Flow in a Bed of Spheres as Measured with Stereoscopic Particle Image Velocimetry2017Ingår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 117, nr 1, s. 45-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Stereoscopic particle image velocimetry has been used to investigate inertia dominated, transitional and turbulent flow in a randomly packed bed of monosized PMMA spheres. By using an index-matched fluid, the bed is optically transparent and measurements can be performed in an arbitrary position within the porous bed. The velocity field observations are carried out for particle Reynolds numbers, (Formula presented.), between 20 and 3220, and the sampling is done at a frequency of 75 Hz. Results show that, in porous media, the dynamics of the flow can vary significantly from pore to pore. At (Formula presented.) around 400 the spatially averaged time fluctuations of total velocity reach a maximum and the spatial variation of the time-averaged total velocity, (Formula presented.) increases up to about the same (Formula presented.) and then it decreases. Also in the studied planes, a considerable amount of the fluid moves in the perpendicular directions to the main flow direction and the time-averaged magnitude of the velocity in the main direction, (Formula presented.), has an averaged minimum of 40% of the magnitude of (Formula presented.) at (Formula presented.) about 400. For (Formula presented.), this ratio is nearly constant and (Formula presented.) is on average a little bit less than 50% of (Formula presented.). The importance of the results for longitudinal and transverse dispersion is discussed.

  • 6.
    Khayamyan, Shervin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Measurements of Transitional and Turbulent Flow in a Randomly Packed Bed of Spheres with Particle Image Velocimetry2017Ingår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 116, nr 1, s. 413-431Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Particle image velocimetry (PIV) has been used to investigate transitional and turbulent flow in a randomly packed bed of mono-sized transparent spheres at particle Reynolds number, (Formula presented.). The refractive index of the liquid is matched with the spheres to provide optical access to the flow within the bed without distortions. Integrated pressure drop data yield that Darcy law is valid at (Formula presented.). The PIV measurements show that the velocity fluctuations increase and that the time-averaged velocity distribution start to change at lower (Formula presented.). The probability for relatively low and high velocities decreases with (Formula presented.) and recirculation zones that appear in inertia dominated flows are suppressed by the turbulent flow at higher (Formula presented.). Hence there is a maximum of recirculation at about (Formula presented.). Finally, statistical analysis of the spatial distribution of time-averaged velocities shows that the velocity distribution is clearly and weakly self-similar with respect to (Formula presented.) for turbulent and laminar flow, respectively

  • 7. Khayamyan, Shervin
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    PIV measurements within a randomly packed bed of spheres2016Konferensbidrag (Refereegranskat)
  • 8.
    Larsson, Sofia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Tomographic PIV of flow through ordered thin porous media2018Ingår i: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, nr 6, artikel-id 96Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pressure-driven flow in a model of a thin porous medium is investigated using tomographic particle image velocimetry. The solid parts of the porous medium have the shape of vertical cylinders placed on equal interspatial distance from each other. The array of cylinders is confined between two parallel plates, meaning that the permeability is a function of the diameter and height of the cylinders, as well as their interspatial distance. Refractive index matching is applied to enable measurements without optical distortion and a dummy cell is used for the calibration of the measurements. The results reveal that the averaged flow field changes substantially as Reynolds number increases, and that the wakes formed downstream the cylinders contain complex, three-dimensional vortex structures hard to visualize with only planar measurements. An interesting observation is that the time-averaged velocity maximum changes position as Reynolds number increases. For low Reynolds number flow, the maximum is in the middle of the channel, while, for the higher Reynolds numbers investigated, two maxima appear closer to each bounding lower and upper wall.

  • 9.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Digital holographic interferometry in a disturbed environment2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Digital holographic interferometry is an optical measurement technique that is capable of measuring the movement/deformation of an object surface with extremely high accuracy, spatial resolution and temporal resolution. But, because it is very sensitive to disturbances, it is mostly used in well controlled laboratory environments. An exciting new application of the method could be for process supervision in the manufacturing industry. But before it can be used in such an environment it must be made more insensitive to disturbances. The work in this thesis deals with post processing of data from holographic interferometry measurements to reduce the effects of mechanical vibrations and random refractive index fluctuations in the surrounding air. The first approach of using a purely temporal interference filter was successful in reducing the noise due to vibrations, but the noise from the air disturbance was only reduced over a very limited spatial region. A more complete spatio-temporal filter that is not of the interference type requires that the spatio-temporal statistics of the noise from the air can be measured. Therefore the rest of the work is devoted to this problem. The method developed is applied to the relatively simple case of locally homogenous/isotropic refractive index fluctuations generated in a small wind tunnel. There is a simple theory for these types of fluctuations for which the method was successfully verified.

  • 10.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Time resolved digital holographic interferometry through disturbed phase objects2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Digital holographic interferometry is an optical measurement technique based on the work by Powell and Stetson in 1965. The basic principle of the method is that the whole light wave (both amplitude and phase) from an opaque surface or transparent object can be captured and stored using a single camera. By comparing the phase of the light waves captured at different times it is possible to detect very small surface deformations (for opaque objects) or refractive index changes (for transparent objects). The fact that the method is sensitive also for transparent object is a problem when measuring surface deformations that occur on the same timescale as the random fluctuations in the surrounding medium (most often air) since these effects will be added together in the measurement. In a controlled laboratory environment the levels of air disturbances can often be kept at reasonably low levels, but an interesting new application of the technique would be for process supervision in the manufacturing and process industry where the levels of disturbances are much higher. The purpose of this research has been to develop methods for separating the effects of object deformations and air disturbances from each other by digital processing of the measured data. A large part of the work has consisted of constructing experimental setups, developing algorithms and performing numerical simulations. Air disturbances tend to have fluctuations on a very wide range of time scales. To capture the fast fluctuations a high-speed holographic imaging system has been used throughout this work. The slow fluctuations are captured using long time sequences. This creates an enormous amount of data and handling and pre-processing this data has been one of the initial challenges.Air disturbances are very different depending upon how they are generated. Much of the work has therefore been to gain some understanding of different types of air disturbances such as convection flows surrounding hot objects, gas ejection from heated material (black liquor) and more controlled channel flows with fully developed turbulence. The type of imaging system used will also influence how a certain air disturbance will affect a measurement. The difference between telecentric and conventional imaging systems has been discussed and in connection with that a method of depth-resolved velocity measurements in channel flows has been devised.

  • 11. Lycksam, Henrik
    et al.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Digital holographic interferometry in a disturbed environment2007Ingår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 86-Konferensbidrag (Övrigt vetenskapligt)
  • 12. Lycksam, Henrik
    et al.
    Gren, Per
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Digital holographic interferometry in a disturbed environment2006Ingår i: Speckle06: speckles, from grains to flowers ; 13 - 15 September 2006, Nimes, France ; [proceedings] / [ed] Pierre Slangen; Christine Cerruti, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2006, s. 634111-Konferensbidrag (Refereegranskat)
    Abstract [en]

    The problem of environmental disturbances in Digital Holographic Interferometry has been addressed in this investigation. Disturbances may be caused by vibrations, air turbulence or the presence of scattering particles and the effect of them might significantly prevent spread of the technique into a wider area of application. To handle the problem with air turbulence a temporal sequence of an event is analysed and the effect on the motion and phase of the speckles is analysed and described using statistical measures. The effect of the medium will be fed back to the sequence using an adaptive filter and the undisturbed phase evolution estimated. The principle is demonstrated using a heat source placed in between the object and the CCD camera as the disturbance on a simple tilt experiment. The presence of scattering particles is more intriguing and has to be dealt with separately. In this investigation we adopt the technique of low-coherence interferometry to depth-code the holographic images acquired. The seeding of the pulsed Nd:YAG laser source used is shut off that results in a coherence length of about one cm. The paper shows a few preliminary results from a simple wavepropagation experiment.

  • 13.
    Lycksam, Henrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Gren, Per
    Measurement of spatiotemporal phase statistics in turbulent air flow using high-speed digital holographic interferometry2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 8, s. 1314-1322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We describe a method of measuring spatiotemporal (ST) structure and covariance functions of the phase fluctuations in a collimated light beam propagated through a region of refractive index turbulence. The measurements are performed in a small wind tunnel, in which a turbulent temperature field is created using heated wires at the inlet of the test section. A collimated sheet of light is sent through the channel, and the phase fluctuations across the sheet are measured. The spatial phase structure function can be estimated from a series of images captured at an arbitrary frame rate by spatial phase unwrapping, whereas the ST structure function requires a time resolved measurement and a full three-dimensional unwrapping. The measured spatial phase structure function shows agreement with the Kolmogorov theory with a pronounced inertial subrange, which is taken as a validation of the method. Because of turbulent mixing in the boundary layers close to the walls of the channel, the flow will not obey the Taylor hypothesis of frozen turbulence. This can be clearly seen in the ST structure function calculated in a coordinate system that moves along with the bulk flow. At zero spatial separation, this function should always be zero according to the Taylor hypothesis, but due to the mixing effect there will be a growth in the structure function with increasing time difference depending on the rate of mixing.

  • 14.
    Lycksam, Henrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Gren, Per
    Mätningar av spatiotemporal statistik i ett turbulent luftflöde med höghastighets digital holografisk interferometri2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 60-Konferensbidrag (Övrigt vetenskapligt)
  • 15. Lycksam, Henrik
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Leblanc, James
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Wiener filtering of interferometry measurements through turbulent air using an exponential forgetting factor2008Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, nr 16, s. 2971-2978Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of imaging through turbulent media has been studied frequently in connection with astronomical imaging and airborne radars. Therefore most image restoration methods encountered in the literature assume a stationary object, e.g., a star or a piece of land. In this paper the problem of interferometric measurements of slowly moving or deforming objects in the presence of air disturbances and vibrations is discussed. Measurement noise is reduced by postprocessing the data with a digital noise suppression filter that uses a reference noise signal measured on a small stationary plate inserted in the field of view. The method has proven successful in reducing noise in the vicinity of the reference point where the size of the usable area depends on the degree of spatial correlation in the noise, which in turn depends on the spatial scales present in the air turbulence. Vibrations among the optical components in the setup tend to produce noise that is highly correlated across the field of view and is thus efficiently reduced by the filter. © 2008 Optical Society of America.

  • 16.
    Lycksam, Henrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Öhman, Marcus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    High-speed interferometric measurement and visualization of the conversion of a black liquor droplet during laser heating2012Ingår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 50, nr 11, s. 1654-1661Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Black liquor is a mix of organic and inorganic materials that is left after the kraft pulping process. In a modern pulp mill the pulping chemicals and the energy in the black liquor is recovered and used in the pulping cycle by burning the black liquor in a recovery burner. An alternative to the recovery boiler is to gasify the black liquor to produce an energy rich synthesis gas that can be upgraded into synthetic fuels or chemicals. Characterization of black liquor has mostly been done under conditions that are relevant for recovery boilers but the conditions in a gasifier differ significantly from this. In particular the droplets are much smaller and the heating rates are much higher. This paper presents an optical interferometric technique that has the potential to produce data under relevant conditions for gasification. In the paper, results are measured at atmospheric conditions and with relatively low heating rate. However, the method can be applied also for pressurized conditions and at heating rates that are only limited by the frame rate of the digital camera that is used to capture the transient event when the droplets are heated. In the paper the dynamic properties of the gas ejected from and the swelling during conversion of a single droplet are measured

  • 17.
    Neikter, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Pederson, Robert
    University West, Div. Welding Material .
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy2017Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The aim of this work has been to compare two different analysing methods;x-ray microtomography and light optical microscopy, when it comes to defects and microstructure of additively manufactured Ti-6Al-4V. The results showthat both techniqueshave theirpros and cons:microtomography is the preferred choicefor defect detectionby analysing the full 3D sample volume, while light optical microscopy is better for analysing finer details in 2D.

  • 18. Tatar, Kourosh
    et al.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Digital holographic interferometry for simultaneous orthogonal radial vibration measurements along rotating shafts2008Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, nr 18, s. 3269-3274Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A digital holographic interferometry setup used to measure radial vibrations along a rotating shaft is presented. A continuous Nd:YAG laser and a high-speed digital camera are used for recording the holograms. The shaft was polished optically smooth to avoid speckle noise from the rotating surface. The light reflected from the shaft was directed onto a diffuser which in turn was imaged by the holographic system. Simultaneous measurements with a laser vibrometer were performed at one point and comparisons between the signals showed good agreement. It is shown that different vibration components of a rotating shaft can be simultaneously measured with this technique.

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