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  • 51.
    Andersson, L. Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby.
    Andersson, Anders G.
    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.
    Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations2018In: Engineering, ISSN 1947-3931, Vol. 10, p. 399-416Article in journal (Refereed)
    Abstract [en]

    High Reynolds number flow inside a channel of rectangular cross section is examined using Particle Image Velocimetry. One wall of the channel has been replaced with a surface of a roughness representative to that of real hydropower tunnels, i.e. a random terrain with roughness dimensions typically in the range of ≈10% - 20% of the channels hydraulic radius. The rest of the channel walls can be considered smooth. The rough surface was captured from an existing blasted rock tunnel using high resolution laser scanning and scaled to 1:10. For quantification of the size of the largest flow structures, integral length scales are derived from the auto-correlation functions of the temporally averaged velocity. Additionally, Proper Orthogonal Decomposition (POD) and higher-order statistics are applied to the instantaneous snapshots of the velocity fluctuations. The results show a high spatial heterogeneity of the velocity and other flow characteristics in vicinity of the rough surface, putting outer similarity treatment into jeopardy. Roughness effects are not confined to the vicinity of the rough surface but can be seen in the outer flow throughout the channel, indicating a different behavior than postulated by Townsend’s similarity hypothesis. The effects on the flow structures vary depending on the shape and size of the roughness elements leading to a high spatial dependence of the flow above the rough surface. Hence, any spatial averaging, e.g. assuming a characteristic sand grain roughness factor, for determining local flow parameters becomes less applicable in this case.

  • 52. Andersson, Magnus
    et al.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Långström, R.
    Luleå tekniska universitet.
    Development of guidelines for the vacuum infusion process2000In: Proceedings of the 8th International Conference on Fibre Reinforced Composites, FRC 2000: Centre for Composite Materials Engineering, University of Newcastle, UK, 13 - 15 September 2000 / [ed] A. G. Gibson, Cambridge: Woodhead Publishing Materials , 2000, p. 113-120Conference paper (Refereed)
    Abstract [en]

    The current trend towards increased use of vacuum infusion moulding for large surface area parts has increased the interest for an advanced modelling of the process. This paper presents a detailed experimental investigation of laminate thickness and out-of-plane flow front shape during impregnation of high permeability reinforcement on top of a non-crimp fabric reinforcement lay-up. The goal with the experiments is to increase the understanding of the process and to provide accurate data that can later be used for validation of numerical models. The laminate thickness was measured during impregnation with a stereoscopic digital speckle photography system and the flow front shape was determined by tracking of colour marks in the stacking. The laminate lay-ups studied are different combinations of non-crimp fabrics and flow layers while the resin used was a polyester developed specifically for vacuum infusion moulding. Results are presented both for the instantaneous thickness and the flow front shape for several different material combinations. It was found that the skewness of the flow front became more pronounced with increasing number of flow layers when the number of non-crimp fabric layers was kept constant. As a first step towards a complete numerical model of the impregnation process a simplified model for the compressibility and a proven model for permeability was implemented in a commercial CFD package that can handle moving boundaries and moving flow fronts. Only a qualitative comparison with experiments was done but the conclusion was that the overall behaviour of the model was encouraging. A validation of the numerical model based on the measurements in this paper is under development.

  • 53. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Numerical model for vacuum infusion manufacturing of polymer composites2003In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 13, no 3, p. 383-394Article in journal (Refereed)
    Abstract [en]

    The focus is set on the development and evaluation of a numerical mgodel describing the impregnation stage of a method to manufacture fibre reinforced polymer composites, namely the vacuum infusion process. Examples of items made with this process are hulls to sailing yachts and containers for the transportation industry. The impregnation is characterised by a full 3D flow in a porous medium having an anisotropic, spatial- and time-dependent permeability. The numerical model has been implemented in a general and commercial computational fluid dynamic software through custom written subroutines that: couple the flow equations to the equations describing the stiffness of the fibre reinforcement; modify the momentum equations to account for the porous medium flow; remesh the computational domain in each time step to account for the deformation by pressure change. The verification of the code showed excellent agreement with analytical solutions and very good agreement with experiments. The numerical model can easily be extended to more complex geometry and to other constitutive equations for the permeability and the compressibility of the reinforcement.

  • 54. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Långström, R.
    Swedish Institute of Composites, Piteå.
    Flow-enhancing layers in the vacuum infusion process2002In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 23, no 5, p. 895-901Article in journal (Refereed)
    Abstract [en]

    The current trend towards increased use of vacuum infusion molding for large surface-area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow-enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through-thickness flow front was observed by making a number of color marks on the glass-mats forming the reinforcing stack, which became visible when the resin reached their position. The in-plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill-time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead-lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead-lag has a miximum close to the inlet.

  • 55. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Langhans, N.
    EADS Military Aircraft, Munich.
    Computational fluid dynamics applied to the vacuum infusion process2005In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 26, no 2, p. 231-239Article in journal (Refereed)
    Abstract [en]

    An all-purpose computational fluid dynamics software is used for simulations of the vacuum infusion process. The study comprises simulations of a full three-dimensional two-phase flow through a porous medium. The medium that has an anisotropic, spatial- and time-dependent permeability is located in a complex mold with moving boundaries. With this generalization, different material combinations, processing conditions, and even other manufacturing techniques can be evaluated. The strength of the presented approach is exemplified by simulations of mold filling of a real part, using a typical vacuum infusion set-up. In addition to the overall development of the model, a number of specific aspects and phenomena are investigated and evaluated. Local lead of the flow front and a minor influence in overall flow front lead-lag, with no influence on the fill time, is the result of simulations of edge effects due to poor preform fitting.

  • 56. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Langhans, N.
    Numerical simulation of the vacuum infusion process2006In: Experimental techniques and design in composite materials (ETDCM6): "Sixth International Seminar on Experimental Techniques and Design in Composite Materials" which was held at Padova in June 2003 / [ed] Marino Quaresimin, Amsterdam: Elsevier, 2006Conference paper (Refereed)
  • 57.
    Andersson, Robin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modelling flow over rough surfaces in hydropower waterways2018Doctoral thesis, comprehensive summary (Other academic)
  • 58.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Vattenfall Research & Development.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Grade of geometric resolution of a rough surface required for accurate prediction of pressure and velocities in water tunnels2014Conference paper (Refereed)
  • 59.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Burman, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby.
    Inlet Blockage Effects in a Free Surface Channel With Artificially Generated Rough Walls2018In: Proceedings of the 7th IAHR International Symposium on Hydraulic Structures / [ed] Daniel Bung ; Blake Tullis, 2018, p. 723-732Conference paper (Refereed)
    Abstract [en]

    When considering free surface flow in channels, it is essential to have in-depth knowledge about the inlet flow conditions and the effect of surface roughness on the overall flow field. Hence, we hereby investigate flow inside an 18m long channel by using Particle Tracking Velocimetry (PTV) and Acoustic Doppler Velocimetry (ADV). The roughness of the channel walls is generated using a diamond-square fractal algorithm and is designed to resemble the actual geometry of hydropower tunnels. Four different water levels ranging from 20 to 50cm are investigated. For each depth, the inlet is blocked by 25 and 50% at three positions each, at the centre, to the right and to the left in the flow-direction. The flow is altered for each depth to keep the flow velocity even throughout the measurements. PTV is applied to measure the velocity of the free water surface; four cameras are placed above the setup to capture the entirety of the channel. The results show a clear correlation between roughness-height and velocity distribution at depths 20-30 cm. The surface roughness proved effective in dispersing the subsequent perturbations following the inlet blockage. At 50cm, perturbations from the 50% blockage could be observed throughout the channel. However, at 20cm, most perturbations had subsided by a third of the channel length. The ADV was used to capture the velocity in a total of 375 points throughout the channel, at a depth of 50 cm with no inlet perturbations.

  • 60.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    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.
    Gävunda case studyManuscript (preprint) (Other academic)
  • 61.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall AB Research and Development, Älvkarleby Laboratory, Älvkarleby.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical investigation of a hydropower tunnel: Estimating localised head-loss using the manning equation2019In: Water, ISSN 2073-4441, E-ISSN 2073-4441, no 8, article id 1562Article in journal (Refereed)
    Abstract [en]

    The fluid dynamics within a water tunnel is investigated numerically using a RANS approach with the k-ε turbulence model. The computational model is based on a laser scan of a hydropower tunnel located in Gävunda, Sweden. The tunnel has a typical height of 6.9 m and a width of 7.2 m. While the average cross-sectional shape of the tunnel is smooth the local deviations are significant, where some roughness elements may be in the size of 5 m implying a large variation of the hydraulic radius. The results indicate that the Manning equation can successfully be used to study the localised pressure variations by taking into account the varying hydraulic radius and cross-sectional area of the tunnel. This indicates a dominant effect of the tunnel roughness in connection with the flow, which has the potential to be used in the future evaluation of tunnel durability. ANSYS-CFX was used for the simulations along with ICEM-CFD for building the mesh. 

  • 62.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Sofia
    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.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental Study of Head Loss over Laser Scanned Rock Tunnel2016In: Experimental Study of Head Loss over Laser Scanned Rock Tunnel: Hydraulic Structures and Water System Management, ISHS 2016, Portland, United States, 27 - 30 June 2016, Portland: Utah State University , 2016, p. 22-29Conference paper (Refereed)
    Abstract [en]

    Flow in hydropower tunnels is characterized by a high Reynolds number and often very rough rock walls. Due to the roughness of the walls, the flow in the tunnel is highly disturbed, resulting in large fluctuations of velocity and pressure in both time and space. Erosion problems and even partial collapse of tunnel walls are in some cases believed to be caused by hydraulic jacking from large flow induced pressure fluctuations. The objective of this work is to investigate the effects of the rough walls on the pressure variations in time and space over the rock surfaces. Pressure measurement experiments were performed in a 10 m long Plexiglas tunnel where one of the smooth walls was replaced with a rough surface. The rough surface was created from a down-scaled (1:10) laser scanned wall of a hydraulic tunnel. The differential pressure was measured at the smooth surface between points placed at the start and end of the first four 2 m sections of the channel. 10 gauge pressure sensors where flush mounted on the rough surface; these sensors measure the magnitude and the fluctuations of the pressure on the rough surface. The measurements showed significant spatial variation of the pressure on the surface. For example, sensors placed on protruding roughness elements showed low gauge pressure but high fluctuations. The differential pressure indicated a head loss through the tunnel that was almost four times higher than a theoretical smooth channel.

  • 63.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Burman, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby.
    Localised roughness effects in non-uniform hydraulic waterwaysIn: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079Article in journal (Refereed)
    Abstract [en]

    Hydropower tunnels are generally subject to a degree of rock falls. Studies explaining this are scarce and the current industrial standards offer little insight. To simulate tunnel conditions, high Reynolds number flow inside a channel with a rectangular cross-section is investigated using Particle Image Velocimetry and pressure measurements. For validation, the flow is modelled using LES and a RANS approach with k - ε turbulence model. One wall of the channel has been replaced with a rough surface captured using laser scanning. The results indicate flow-roughness effects deviating from the standard non-asymmetric channel flow and hence, can not be properly predicted using spatially averaged relations. These effects manifest as localized bursts of velocity connected to individual roughness elements. The bursts are large enough to affect both temporally and spatially averaged quantities. Both turbulence models show satisfactory agreement for the overall flow behaviour, where LES also provided information for in-depth analysis.

  • 64.
    Andersson, Urban
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    An experimental study of the flow in a sharp-heel Kaplan draft tube2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This research project was originally part of a package (Turbine-99 Draft Tube) that had a mutual goal, to improve the understanding of draft tube flow and establish Best Practise Guidelines for simulation of draft tube flow.The draft tube is situated after the runner in a Hydropower turbine to recover as much of the remaining head and kinetic energy as possible before the water leaves the turbine. The case is fully turbulent, and because of the adverse pressure gradient with risk for separation, periodic inlet conditions from the runner with different degrees of swirl causes the draft tube flow to be difficult to predict. Therefore, unambiguous design criterions are lacking, and the slightly contradicting recommendations indicate that the standard rules give conservative, rather than optimal, designs. This thesis gives some background on draft-tube flows in general and discusses the parameters and flow conditions relevant to the Turbine-99 draft tube in some detail. The main goal of the thesis is to provide extensive experimental data on a well-defined sharp-heel draft-tube flow. The data bank has served as validation data for the simulation challenge presented by the Turbine-99 workshops in Porjus (June 1999), Älvkarleby (June 2001) and Porjus (December 2005).The experimental data and some numerical results are also available as an application challenge in the Qnet database (managed by Ercoftac), as a validation case for flow simulations.The experimental data consists of visualisations, pressure measurements and velocity measurements. These methods give a good qualitative picture of the flow pattern in the draft tube with quantitative data at selected cross section that can be used to validate the flow simulations. The first two workshops focused on mean quantities of pressure and velocities; however, phase resolved measurements have been added to add value to the experimental data.In addition to the experimental validation case, there is one paper that deals with loads on the draft tube, which affect the construction lifetime. Since the hydropower stations are expected to have a long total technical lifetime with a number of refurbishments, these questions will grow in importance over the next decades.

  • 65.
    Andersson, Urban
    et al.
    Vattenfall Research & Development.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Phase resolved velocity measurements at the draft tube cone of the turbine-99 test case2008In: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Conference paper (Refereed)
    Abstract [en]

    The Turbine-99 test case, a Kaplan draft tube, has been studied extensively both experimentally and numerically. To further complete the experimental data of this test case, phase resolved velocity profiles in the draft tube cone are presented in this paper. The phase resolved velocity profiles have been measured with a 2-component LDA equipment measuring both the tangential and the axial velocity components of the flow. The measurements were synchronised with a pulse from the runner shaft that gives the angular position/phase of each velocity measurement. The result shows a clear impact of the runner blade wakes on the flow distribution in the draft tube cone. Further down in the cone the blade wakes are still visible, even if noticeable weaker, and they have increased their extent in the tangential direction.

  • 66. Andersson, Urban
    et al.
    Engström, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Karlsson, Rolf
    Vattenfall Research & Development.
    The Turbine-99 workshops - conclusions and recommendations2004In: 22nd IAHR Symposium on Hydraulic Machinery and Systems, Stockholm, Sweden, June 29 - July 2, 2004, Stockholm: IAHR , 2004Conference paper (Other academic)
  • 67.
    Andersson, Urban
    et al.
    Vattenfall Research & Development.
    Jungstedt, J.
    Vattenfall Research & Development.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A model experiment of dynamic loads on a draft tube pier2008In: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Conference paper (Refereed)
    Abstract [en]

    Cracks on the pier of large draft tubes have occurred causing stand-still and repair of two large twin stations Porjus G11 and G12. In order to understand the mechanism behind the formation of the cracks, a research programme was initiated at Vattenfall. Measurements were performed on a prototype as well structural analysis (FEM). In order to corroborate some findings, get detailed information of the load on the pier and identify critical operating conditions, model tests were performed at the Hydraulic Machinery Laboratory of Vattenfall Research and Development, Älvkarleby, Sweden. An adjustable draft tube pier with several pressure holes was used to estimate the load acting on the pier. The tests did not indicate any operating point that would cause direct braking, but possible fatigue problems. At part load the pressure was considerably higher on one side of the pier. The pressure difference decreases with increased flow, and change high-pressure side at full load. Efficiency measurements and visualization did not show any impact of the angle bars installed in the year 2000 to strength the structure.

  • 68.
    Atta, Khalid
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Cervantes, Michel J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Maximum power point tracking for micro hydro power plants using extremum seeking control2015In: 2015 IEEE International Conference on Control Applications (CCA 2015): Sydney, Australia, September 21-23 2015, Piscataway, NJ: IEEE Communications Society, 2015, p. 1874-1879, article id 7320883Conference paper (Refereed)
    Abstract [en]

    In this work, we propose using extremum seeking control (ESC) as a tool for maximum power point tracking in micro hydro power plants. The phasor ESC, which is based on estimating the phasor of the plant output at the perturbation frequency, was modified by stimating the phasors of multiple harmonics of this frequency. This modification will improve the performance of ESC by reducing the luctuations in control variables that may appear in noisy environments as a result of high-amplitude perturbation signals. A test rig was used to experimentally verify the proposed approach and to demonstrate the usability of ESC in hydro power plants.

  • 69.
    Atta, Khalid
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Andreas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Cervantes, Michel J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gustafsson, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Phasor Extremum Seeking and its Application in Kaplan Turbine Control2014In: 2014 IEEE International Conference on Control Applications (CCA 2014): Juan Les Antibes, France, 8 -10 October 2014, Piscataway, NJ: IEEE Communications Society, 2014, p. 298-303Conference paper (Refereed)
    Abstract [en]

    The Combinator is an important part in Kaplan turbine control. It ensures that the turbine will operate in an optimum way, in terms of maximum efficiency of the plant. This work suggests a new sinusoidal perturbation based extremum seeking algorithm based on the phasor of the output. We propose to use this algorithm for generating the required data to build and correct the combinator. Simulations are presented showing the applicability of the proposed methods.

  • 70.
    Autioniemi, J
    et al.
    Lapland University of Applied Sciences.
    Autioniemi, M
    Lapland University of Applied Sciences.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Konttaniemi, H
    Lapland University of Applied Sciences.
    Sukuvaara, T
    FMI-Arctic Research Centre, Sodankylä.
    Ylitalo, R
    FMI-Arctic Research Centre, Sodankylä.
    Intelligent Road2015Report (Other academic)
    Abstract [en]

    Project Intelligent Road is a common effort of four main partners: Rovaniemi University of Applied Sciences (RAMK), Luleå Technical University (LTU), Finnish Meteorological Institute (FMI), Kaakkois-Suomen ELY-keskus (KaS ELY) – and representatives of business sector of the region. The overall objective of the project is to support the development of business community in Northern Scandinavian region by testing and improvement of existing innovative products concerned with road safety provision in Nordic weather conditions. The specific objective of the project is to create a demo of sustainable and marketable Intelligent Road System providing location-based short-term road weather information to the road user passing by the area. Target Groups, which are directly and positively affected by the project are businesses and above mentioned project partners. All these actors have exclusive know-how in the area and are each equally important for the implementation of the project and its success. Final beneficiaries of this project are business community of the Northern Scandinavian Region; Ministry of Transport and Communications of Finland, represented by KaS ELY and Finnish Transport Safety Agency; Swedish Ministry of Enterprise, Energy and Communications; and of course local municipalities, as Luleå Municipality, and road users.

  • 71. Baart, Pieter
    et al.
    Green, Torbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Li, Jinxia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    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.
    Lugt, Piet
    SKF Engineering & Research Center, Nieuwegein.
    Contaminant particle migration in a double restriction seal2013In: Proceedings of the STLE Annual Meeting and Exhibition 2013, Detroit MI, USA., STLE , 2013, p. 125-Conference paper (Refereed)
    Abstract [en]

    Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile.In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication

  • 72. Baart, Pieter
    et al.
    Green, Torbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Li, Jinxia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    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.
    Lugt, Piet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of speed, grease type, and temperature on radial contaminant particle migration in a double restriction seal2011In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 54, no 6, p. 867-877Article in journal (Refereed)
    Abstract [en]

    Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile. In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication.

  • 73.
    Baart, Pieter
    et al.
    SKF Engineering & Research Center, Nieuwegein.
    Lugt, Piet
    SKF Engineering & Research Center, Nieuwegein.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Green, Torbjörn
    Li, Jinxia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sealing improvements by grease selection in double lip seals and labyrinth seals2012In: 17th ISC: International Sealing Conference ; Stuttgart, Germany, Sept. 13 - 14, 2012, Frankfurt am Main: Fachverband Fluidtechnik im VDMA e.V , 2012Conference paper (Refereed)
  • 74.
    Backman, Gunnar
    et al.
    Rainpower Norway AS.
    Billdal, J.T.
    Rainpower Norway AS.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Farhat, Mohamed
    EPFL LMH Laboratory, Switzerland.
    Zobeiri, A.R.
    EPFL LMH Laboratory, Switzerland.
    Increased need for hydro pumped-storage plants to guarantee the stability of the power grids2008In: HYDRO 2008, Progressing World Hydro Development: Ljubljana, Slovenina, 6-8 October 2008, 2008Conference paper (Refereed)
  • 75.
    Baidar, Binaya
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A sensitivity analysis of the Winter-Kennedy method2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hydropower is among the lowest-cost electrical energy sources due to its long lifespan and lower operation and maintenance cost. The hydro-mechanical components of hydropower plants generally last about four to five decades, then they are either overhauled or replaced. The major upgrades and refurbishments of the hydropower plants that are ongoing have also been motivated by the introduction of new rules and regulations, safety or environmentally friendly and improved turbine designs. Whatever are the drivers, the refurbishments are usually expected to increase efficiency, flexibility and more power from the plant.

    Efficiency measurement is usually performed after refurbishments. While it is relatively straightforward to measure efficiency in high head machines due to the availability of several code-accepted methods, similar measurements in low head plants remain a challenge. The main difficulty lies in the discharge/flow rate measurement. The reason is due to the continuously varying cross-section and short intake, as a result, the flow profile or parallel streamlines cannot be established. Among several relative methods, the Winter-Kennedy (WK) method is widely used to determine the step-up efficiency before and after refurbishment. The WK method is an index testing approach allowing to determine the on-cam relationship between blade and guide vane angles for Kaplan turbine as well. The method utilizes features of the flow physics in a curvilinear motion. A pair of pressure taps is placed at an inner and outer section of the spiral case (SC). The method relates discharge (Q) as Q=K(dP)^n, where K is usually called as the WK constant and n is the exponent whose value varies from 0.48 to 0.52. dP is the differential pressure from the pair of pressure taps placed on the SC.  

    Although the method has very high repeatability, some discrepancies were noticed in previous studies. The reasons are often attributed to the change in local flow conditions due to the change in inflow conditions, corrosions, or change in geometry. Paper A is a review of the WK method, which includes the possible factors that can influence the WK method. Considering the possible factors, the aim of this thesis is to study the change in flow behavior and its impact on the coefficients. Therefore, a numerical model of a Kaplan turbine has been developed. The turbine model of Hölleforsen hydropower plant in Sweden was used in the study. The plant is considered as a low head with 27-m head and a discharge of 230 m3/s. The 1:11 scale model of the prototype is used as the numerical model in this study, which has 0.5 m runner diameter, 4.5 m head, 0.522 m3/s discharge and 595 rpm at its best efficiency point. A sensitivity analysis of the WK method has been performed with the help of CFD simulations. The numerical results are compared with the previously conducted experiment on the model. The study considers four different WK configurations at seven locations along the azimuthal direction. The simulations have been performed with different inlet boundary conditions (Paper B and Paper C) and different runner blade angles (Paper C). The CFD results show that the WK coefficients are sensitive to inlet conditions. The study also concludes that to limit the impact of a change in inflow conditions, runner blade angle on the coefficients, the more suitable WK locations are at the beginning of the SC with the inner pressure tap placed between stay vanes on the top wall.

  • 76.
    Baidar, Binaya
    et al.
    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.
    Numerical Study of Wall Shear and Velocities Using a Commercial CFD Code: Some Crucial Aspects to Consider2017In: Hydro Nepal: Journal of Water, Energy and Environment, ISSN 1998-5452, Vol. 21, p. 45-49Article in journal (Refereed)
    Abstract [en]

    This paper presents the numerical prediction of wall shear and velocities in steady and superposed pulsatile turbulent flow in a pipe, the phenomena that can be observed in hydropower. The previously conducted experiment is a base for this study and some crucial aspects of CFD while using a commercial code have been emphasized. The widely-accepted grid convergence index approach is adopted to quantify the discretization uncertainty and the results are validated against the experiment. The influence of the wall functions applied in the code is also studied with two turbulence models: standard k-ε and kω based SST model. The time-averaged results of superposed flow with small amplitude unsteadiness are equivalent to results from the steady flow. The results and the method used in this paper may be useful for the CFD simulations in hydropower applications like penstock and bifurcations designs.

  • 77.
    Baidar, Binaya
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nicolle, Jonathan
    Institut de recherche d’Hydro-Québec, Varennes, QC, Canada.
    Gandhi, Bhupendra K.
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, India.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sensitivity of the Winter-Kennedy method to different guide vane openings on an axial machine2019In: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 68, article id 101585Article in journal (Refereed)
    Abstract [en]

    This work studies the effects of guide vane openings (GVOs) on the Winter-Kennedy (WK) flow measurement method using CFD. The dependence of the WK coefficient with GVOs and its physical mechanism are presented. Although the WK method is reported to be sensitive to different factors including GVO, it is still unclear to which extent the GVO can be changed without modifying the WK coefficient significantly and the mechanism leading to such modification, if any. A numerical model of a Kaplan model turbine with a semi-spiral casing is developed and used to such purpose. Previously conducted experiments on the model turbine are used to validate the numerical results. The magnitude and behavior of the secondary flow are investigated together with the WK coefficients. The GVO is found to have an impact on the WK method, and the impact increases with the GVOs as the flow structure change. A suitable location to minimize the impact of the GVO is suggested. Furthermore, the theoretical WK constant with a suitable location and configuration are also presented; this can be useful in the absence of the measured WK coefficient.

  • 78.
    Baidar, Binaya
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nicolle, Jonathan
    Institut de recherche d'Hydro-Québec.
    Gandhi, Bhupendra K.
    Indian Institute of Technology Roorkee.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sensitivity of the Winter-Kennedy method to inlet and runner blade angle change on a Kaplan turbine2019In: IOP Conference Series: Earth and Environmental Science, Institute of Physics (IOP), 2019, Vol. 240, article id 022038Conference paper (Refereed)
    Abstract [en]

    The Winter-Kennedy (WK) method is a widely used index testing approach, which provides a relative or index value of the discharge that can allow to determine the on-cam relationship between blade and guide vane angles for Kaplan turbines. However, some discrepancies were noticed in previous studies using the WK approach. In this paper, a numerical model of a Kaplan model turbine is used to study the effects of upstream and downstream flow conditions on the WK coefficients. Experiment on the model turbine is used to validate unsteady CFD calculations. The CFD results show that the inflow condition affects the pressure distribution inside the spiral case and hence the WK results. The WK coefficients fluctuate with high amplitude - suggesting to use a larger sampling time for on-site measurement as well. The study also concludes that to limit the impact of a change in runner blade angle on the coefficients, the more suitable WK locations are at the beginning of the spiral case with the inner pressure tap placed between stay vanes on the top wall.

  • 79.
    Baidar, Binaya
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nicolle, Jonathan
    Institut de recherche d'Hydro-Québec, Canada.
    Trivedi, Chirag
    Norwegian University of Science and Technology, NTNU, Norway.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical study of the Winter-Kennedy method: a sensitivity analysis2018In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 140, no 5, article id 051103Article in journal (Refereed)
    Abstract [en]

    The Winter-Kennedy (WK) method is commonly used in relative discharge measurement and to quantify efficiency step-up in hydropower refurbishment projects. The method utilizes the differential pressure between two taps located at a radial section of a spiral case, which is related to the discharge with the help of a coefficient and an exponent. Nearly a century old and widely used, the method has shown some discrepancies when the same coefficient is used after a plant upgrade. The reasons are often attributed to local flow changes. To study the change in flow behavior and its impact on the coefficient, a numerical model of a semi-spiral case (SC) has been developed and the numerical results are compared with experimental results. The simulations of the SC have been performed with different inlet boundary conditions. Comparison between an analytical formulation with the computational fluid dynamics (CFD) results shows that the flow inside an SC is highly three-dimensional (3D). The magnitude of the secondary flow is a function of the inlet boundary conditions. The secondary flow affects the vortex flow distribution and hence the coefficients. For the SC considered in this study, the most stable WK configurations are located toward the bottom from θ =30deg to 45deg after the curve of the SC begins, and on the top between two stay vanes.

  • 80.
    Baidar, Binaya
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nicolle, Jonathan
    Institut de recherche d’Hydro-Québec.
    Trivedi, Chirag
    Norwegian University of Science and Technology.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Winter-Kennedy method in hydraulic discharge measurement: Problems and Challenges2016Conference paper (Refereed)
    Abstract [en]

    Winter Kennedy (WK) method is a popular way to measure the relative discharge and thus efficiency in Swedish hydropower plants. This is largely motivated by the numerous low head turbines and low cost of the method. WK is an index testing method that provides relative values of hydraulic efficiency by measuring differential pressures in one or two pairs of pressure taps in radial planes of the spiral casing. The method is described in the IEC41 standard. Despite several limitations, it is generally used to verify the increment in efficiency for refurbishment projects and sometimes for the continuous flow rate monitoring. Uncertainties in the results reaching up to 5% have been reported in different researches. Those are often attributed to a change in flow conditions after the refurbishment or in the course of time. However, a proper error analysis has not been performed yet. This paper includes a review of the available literature related to the topic to understand its problems and possible ways to investigate its limitations systematically.

  • 81.
    Banaem, Hossein Yousefi
    et al.
    Department of Biomedical Engineering, Faculty of Advance Medical Technology, Isfahan University of Medical Science.
    Kermani, Saeed
    Department of Biomedical Engineering, Faculty of Advance Medical Technology, Isfahan University of Medical Science.
    Sarrafzadeh, Omid
    Department of Biomedical Engineering, Faculty of Advance Medical Technology, Isfahan University of Medical Science.
    Khodadad, Davood
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    An improved spatial FCM algorithm for cardiac image segmentation2013In: 13th Iranian Conference on Fuzzy Systems: IFSC 2013, Qazvin, Iran; 27-29 August 2013, Piscataway, NJ: IEEE Communications Society, 2013, article id 6675656Conference paper (Refereed)
    Abstract [en]

    Image segmentation is one of challenging field in medical image processing. Segmentation of cardiac wall is one of challenging work and it is very important step in evaluation of heart functionality by existing methods. For cardiac image analysis, Fuzzy C- Means (FCM) algorithm proved to be superior over the other clustering approaches in segmentation field. However, the nave FCM algorithm is sensitive to noise because of not considering the spatial information in the image. In this paper an improved FCM algorithm is formulated by incorporating the spatial domain neighborhood information into the membership function for clustering (ISFCM). In this paper we applied improved Fuzzy c-Means with spatial information for left ventricular wall segmentation. Obtained results showed that the proposed method can segment cardiac wall automatically with acceptable accuracy. The comparison of proposed method with nave FCM proved that ISFCM can segment with more accuracy than nave FCM.

  • 82.
    Barabash, Victoria
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ejemalm, Johnny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Molin, Sven
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Masters Programs in Space Science and Engineering in Northern Sweden2017Conference paper (Refereed)
  • 83.
    Benckert, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A method to resolve the 180° ambiguity in speckle photography1991In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 30, no 4, p. 376-378Article in journal (Other academic)
    Abstract [en]

    A new way of resolving the 180° ambiguity in speckle photography is presented. Results from a study of the deformation of a wooden block caused by drying illustrates the method

  • 84.
    Benckert, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    In-plane surface deformations measured by speckle photography: some examples1992In: Laser in der Technik: Vorträge des 10. Internationalen Kongresses Laser 91 = Laser in engineering / [ed] Wilhelm Waidelich, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1992, p. 50-54Conference paper (Refereed)
  • 85.
    Benckert, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    White light speckle photography as a tool to study deformations in wood caused by drying1990In: Experimental mechanics : 9th International conference : Papers, Lyngby: Technical University of Denmark , 1990Conference paper (Refereed)
  • 86.
    Benckert, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wood drying studies using white light speckle photography1992In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 10, no 1, p. 24-30Article in journal (Refereed)
    Abstract [en]

    White light speckle photography is a powerful tool for measuring displacement fields in the sub-millimetre range. Here it has been utilised to study deformation and crack development in a block of wood during drying. The use of a series of single exposures made it possible to monitor the changes of the wood's surface with time. By combining two of the negatives the displacements over a given time interval were obtained for, at least in principle, all points on the surface.

  • 87.
    Benckert, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Lars
    Molin, Nils-Erik
    Fresnel diffraction of a Gaussian laser beam by polished metal cylinders1990In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 29, no 3, p. 416-421Article in journal (Refereed)
    Abstract [en]

    A laser beam touching the periphery of a polished cylinder is subjected to both diffraction and reflection. Inthe area where diffracted light and reflected light interact the resulting intensity distribution differs from thepattern predicted by diffraction theory for a sharp edge. The difference increases with cylinder radius. Inthis paper it is shown that a good description of the resulting intensity pattern is obtained by adding thereflected light amplitude to the diffracted amplitude as predicted by the Fresnel-Kirchhoff theory for a sharpedge.

  • 88.
    Benckert, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsson, Mikael
    Molin, Nils-Erik
    Measuring 3-D displacement of a surface using the white light speckle technique1986In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, p. 207-210Article in journal (Refereed)
    Abstract [en]

    When measuring in plane surface deformation using white light speckle photography, errors will arise if an out of plane displacement is present. Here it is shown that stereoscopic photography resolves this problem and makes the measurement of true in plane displacements possible. A rigid body translation is also introduced to determine unambiguously the direction of the displacement

  • 89.
    Benckert, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsson, Mikael
    Molin, Nils-Erik
    Measuring true in-plane displacements of a surface by stereoscopic white-light speckle photography1987In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 26, no 2, p. 167-169Article in journal (Refereed)
    Abstract [en]

    When in-plane surface deformations are measured using white-light speckle photography, errors arise if an out-of-plane displacement is present. Stereoscopic photography resolves this problem and makes possible the measurement of true in-plane displacements. A rigid-body translation is introduced to determine unambiguously the direction of the displacement

  • 90.
    Benckert, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Molin, Nils-Erik
    White light speckle: a non-contact method for the measurement of strain- and velocity fields1985Report (Other academic)
  • 91.
    Bergan, Carl
    et al.
    Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim.
    Amiri, Kaveh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Department of Engineering Sciences and Mathematics, Luleå University of Technology.
    Cervantes, Michel J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim.
    Dahlhaug, Ole G.
    Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim.
    Preliminary measurements of the radial velocity in the Francis-99 draft tube cone2015In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 579, no 1, article id 12014Article in journal (Refereed)
    Abstract [en]

    Two-dimensional particle image velocimetry (PIV) measurements in the draft tube cone of the Francis-99 model have been performed to complete the actual experimental data set with radial velocity data. The velocity profiles obtained presented some variation, which reason has not yet been identified. The presented results are therefore presented as preliminary until the reason is assessed. The axial velocity profiles corroborate well with the ones previously measured with laser Doppler velocimetry (LDV) for all operating points investigated. The radial velocity measured is small in magnitude for all operating points compared to the axial velocity. A gyroscopic effect induced by the swirl leaving the runner and the draft tube bend seems to induce an asymmetry in the draft tube cone.

  • 92.
    Bergan, Carl
    et al.
    Waterpower Laboratory, Norwegian University of Science and Technology.
    Goyal, Rahul
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Indian Institute of Technology Roorkee.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Dalhaug, Ole Gunnar
    Waterpower Laboratory, Norwegian University of Science and Technology.
    Experimental Investigation of a High Head Model Francis Turbine During Steady-State Operation at Off-Design Conditions2016In: IOP Conference Series: Earth and Environment, ISSN 1755-1307, E-ISSN 1755-1315, Vol. 49, no 8, article id 062018Article in journal (Refereed)
    Abstract [en]

    Francis-99 is a set of workshops aiming to determine the state of the art of high head Francis turbine simulations (flow and structure) under steady and transient operating conditions as well as promote their development and knowledge dissemination openly. The first workshop (Trondheim, 2014) focused on steady state conditions. Some concerns were raised regarding uncertainty in the measurements, mainly that there was no clear vortex rope at the Part Load (PL) condition, and that the flow exhibited relatively large asymmetry. The present paper addresses these concerns in order to ensure the quality of the data presented in further workshops. To answer some of these questions, a new set of measurements were performed on the Francis 99 model at Waterpower Laboratory at the Norwegian University of Science and Technology (NTNU). In addition to PL, two other operating conditions were considered, for further use in transient measurements, Best Efficiency (BEP) and High Load (HL). The experiments were carried out at a head of 12 m, with a runner rotational speed of 333 revolutions per minute (rpm). The guide vane opening angle were 6.72 degrees, 9.84 degrees and 12.43 degrees for PL, BEP and HL, respectively. The part load condition has been changed from the first workshop, to ensure a fully developed Rotating Vortex Rope (RVR). The velocity and pressure measurements were carried out in the draft tube cone using 2D PIV and six pressure sensors, respectively. The new PL condition shows a fully developed rotating vortex rope (RVR) in both the frequency analysis and in the phase resolved data. In addition, the measurements confirm an asymmetric flow leaving the runner, as was a concern in the first Francis-99 workshop. This asymmetry was detected at both design and off-design conditions, with a stronger effect during off design.

  • 93.
    Berglund, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonoobi, Mehdi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu, Oulu, Finland.
    Promoted hydrogel formation of lignin-containing arabinoxylan aerogel using cellulose nanofibers as a functional biomaterial2018In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, no 67, p. 38219-38228Article in journal (Refereed)
    Abstract [en]

    In this work, three-dimensional (3D) aerogels and hydrogels based on lignin-containing arabinoxylan (AX) and cellulose nanofibers (CNF) were prepared. The effects of the CNF and the crosslinking with citric acid (CA) of various contents (1, 3, 5 wt%) were evaluated. All the aerogels possessed highly porous (above 98%) and lightweight structures. The AX-CNF hydrogel with a CA content of 1 wt% revealed a favorable network structure with respect to the swelling ratio; nanofiber addition resulted in a five-fold increase in the degree of swelling (68 g of water per g). The compressive properties were improved when the higher CA content (5 wt%) was used; when combined with CNF, there was a seven-fold enhancement in the compressive strength. The AX-CNF hydrogels were prepared using a green and straightforward method that utilizes sustainable resources efficiently. Therefore, such natural hydrogels could find application potential, for example in the field of soft tissue engineering.

  • 94.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Edlund, Ove
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Robust registration of surfaces using a refined iterative closest point algorithm with a trust region approach2017In: Numerical Algorithms, ISSN 1017-1398, E-ISSN 1572-9265, Vol. 74, no 3, p. 755-779Article in journal (Refereed)
    Abstract [en]

    The problem of finding a rigid body transformation, which aligns a set of data points with a given surface, using a robust M-estimation technique is considered. A refined iterative closest point (ICP) algorithm is described where a minimization problem of point-to-plane distances with a proposed constraint is solved in each iteration to find an updating transformation. The constraint is derived from a sum of weighted squared point-to-point distances and forms a natural trust region, which ensures convergence. Only a minor number of additional computations are required to use it. Two alternative trust regions are introduced and analyzed. Finally, numerical results for some test problems are presented. It is obvious from these results that there is a significant advantage, with respect to convergence rate of accuracy, to use the proposed trust region approach in comparison with using point-to-point distance minimization as well as using point-to-plane distance minimization and a Newton- type update without any step size control.

  • 95.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Fergusson, Michael
    Xtura AB, Kungsbacka.
    Folkesson, Patrik
    Xtura AB, Kungsbacka.
    Runnemalm, Anna
    University West, Department of Engineering Sciences, Trollhättan.
    Ottosson, Mattias
    University West, Department of Engineering Sciences, Trollhättan.
    Andersson, Alf
    Chalmers University of Technology, Department of Product and Production Development.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Automatic in-line inspection of shape based on photogrammetry2016In: SPS16, Lund: SPS16 , 2016, , p. 9Conference paper (Refereed)
    Abstract [en]

    We are describing a fully automatic in-line shape inspection system for controlling the shape of moving objects on a conveyor belt. The shapes of the objects are measured using a full-field optical shape measurement method based on photogrammetry. The photogrammetry system consists of four cameras, a flash, and a triggering device. When an object to be measured arrives at a given position relative to the system, the flash and cameras are synchronously triggered to capture images of the moving object. From the captured images a point-cloud representing the measured shape is created. The point-cloud is then aligned to a CAD-model, which defines the nominal shape of the measured object, using a best-fit method and a feature-based alignment method. Deviations between the point-cloud and the CAD-model are computed giving the output of the inspection process. The computational time to create a point-cloud from the captured images is about 30 seconds and the computational time for the comparison with the CAD-model is about ten milliseconds. We report on recent progress with the shape inspection system.

  • 96.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Khodadad, Davood
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hällstig, Emil
    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.
    Dual-wavelength digital holography: single-shot shape evaluation using speckle displacements and regularization2014In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 53, no 1, p. 123-131Article in journal (Refereed)
  • 97.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Khodadad, Davood
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hällstig, Emil
    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.
    Single shot shape evaluation using dual-wavelength holographic reconstructions and regularization2014In: Fringe 2013: 7th International Workshop on Advanced Optical Imaging and Metrology / [ed] Wolfgang Osten, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2014, p. 103-108Conference paper (Refereed)
    Abstract [en]

    The aim of this work is to evaluate the shape of a free form object using single shot digital holography. The digital holography results in a gradient field and wrapped phase maps representing the shape of the object. The task is then to find a surface representation from this data which is an inverse problem. To solve this inverse problem we are using regularization with additional shape information from the CAD-model of the measured object.

  • 98.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Michael, Fergusson
    Viospatia AB.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Virtual projective shape matching in targetless CAD-based close-range photogrammetry for efficient estimation of specific deviations2018In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 57, no 5, article id 053110Article in journal (Refereed)
    Abstract [en]

    A concept for targetless, computer-aided design (CAD)-based, close-range photogrammetry for online shape inspection is introduced. The shape of an object, which is arbitrarily located on a conveyor belt, is to be measured and compared with its nominal shape as defined by a CAD model. For most manufactured objects, deviations are only measured at a few given comparison points. These deviations can be estimated using local photogrammetry based on a priori geometrical information given by the CAD model and the comparison points. Our method results in faster output with higher precision, because we do not generate a shape representation of the entire measured object using typical photogrammetric methods. Images depicting the object from convergent angles are captured by an array of cameras in a precalibrated network, and the CAD model is matched and aligned, within the projective geometry of the camera network, to the depicted object in the images without the use of targets. An algorithm for solving this virtual projective targetless shape matching problem is presented.

  • 99.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Rosendahl, Sara
    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.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shape verification using dual-wavelength holographic interferometry2011In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 50, no 10, article id 101503Article in journal (Refereed)
    Abstract [en]

    In automotive industry there is an interest of controlling the shape of a large number of identical components on-line in the manufacturing process. We propose a method to do this by capturing a digital hologram of the object and then using information from its computer aided design (CAD) model to calculate the shape and determine the agreement between the manufactured object and the CAD-model. The holographic recording of the object is done using dual wavelengths with a synthetic wavelength of approximately 400 μm. The optical measurement results in a wrapped phase map with the phase values in the interval [−π, π]. Each phase interval represents a depth distance on the object of about 0.2 mm. The phase unwrapping is done iteratively using information from the CADmodel. This implies that it is possible to measure large discontinuities on the surface of the measured object. The method also gives a point-to-point correspondence between the measurement and the CAD-model which is vital for tolerance control.

  • 100.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Rosendahl, Sara
    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.
    Shape verification aimed for manufacturing process control2011In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 49, no 3, p. 403-409Article in journal (Refereed)
    Abstract [en]

    We describe a method to verify the shape of manufactured objects by using their design model. A non-contact measuring method that consists of a stereo-camera system and a single projected fringe pattern is used. The method acquires one image from each camera. Additional shape information from the design model is also used. This surface-measurement method gives an accuracy of about 45 µm. Deviations from the design model within ±1.6 mm can be correctly detected. The measured surface representation is matched to the design model using the ICP-method. Fast performance has been considered adapting the method for on-line use.

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