| 45291. |
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| 45292. |
- Synnegård, Erik
(författare)
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Dynamic modelling and analysis of vertical machines
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since Sweden’s hydropower plants are getting old and operating conditions have changed, there is a need for simulation tools to predict the functionality, durability and needs for maintenance. Also for breakdowns and major revisions, there is a benefit if dynamical problems could be predicted through simulations. The important parts in the modelling of hydropower machines are the interconnections (Bearings, Generator, Runner). Therefore, accurate and fast models are preferred to describe the interconnections and implement to the finite element model of the rotor. Since hydropower machines are oriented ertically the bearing coefficients needs to be described dynamically. This is due to the fact that vertical machines has no stationary operating point.In paper A simulations of a hydropower machine that suffered from resonance problems were performed. To reduce vibrations, a new type of viscoelastic supports was implemented between the supporting structure and bearing bracket. It was shown through simulations that this support would reduce the vibration levels and reduce the probability of resonance problems occurring when running at operating speed. In paper B the effect of cross-coupling bearing terms was investigated, commonly the cross-coupling terms are neglected since they are small in comparison to the radial components. This is shown to be true for some load cases, but if studying a vertical machine the load angle will change dynamically and for some load angles the cross-coupling terms cannot be neglected. Experiments on a vertical test rig with tilting pad bearings also agree well with the simulations performed. Since the tilting pad bearings in vertical machines introduce periodic coefficients in the bearing, studies in paper C shows that this periodic excitation can cause increased vibrations for certain operating conditions.
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| 45293. |
- Synnegård, Erik, et al.
(författare)
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Forced response of a vertical rotor with tilting pad bearings
- 2016
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Ingår i: Open archives of the 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery. - : Symposion on Rotating Machinery.
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Konferensbidrag (refereegranskat)abstract
- This paper evaluates how tilting pad bearings can aect the forced response of a vertical rotor. Thestiness and damping for a tilting pad bearing is dependent on the position in the bearing (load on pador load between pad) and the magnitude of the load. In a vertical machine the position of the shaft inthe bearing will change for each time-step and produce a periodic stiness and damping. This periodicstiness has shown to produce higher frequency components depending on the number of pads. For thefour pad bearing considered in this paper these frequency components are 3 and 5 in the stationarycoordinate system. The aim of this study is to evaluate if the periodic coecients in the bearing couldexcite the system and cause resonance problems. It is found that for high loads the system can be exciteddue to the bearing dynamics at =!n = 0:33 and =!n = 0:2. However at low loads this eect isnegligible.
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| 45294. |
- Synnegård, Erik, et al.
(författare)
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Influence of cross-coupling stiffness in tilting pad journal bearings for vertical machines
- 2016
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Ingår i: International Journal of Mechanical Sciences. - : Elsevier BV. - 0020-7403 .- 1879-2162. ; 111-112, s. 43-54
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Tidskriftsartikel (refereegranskat)abstract
- This paper evaluates how cross-coupling coefficients affects the dynamics of a vertical rotor with tilting pad journal bearings. For vertical machines, the bearing properties are dependent on the bearing load and direction. As a result, it generally requires that bearing properties are calculated at each time step using the governing fluid dynamic equations. This method gives a good representation of the bearing but computational time increases and can cause stability problems. In this study the bearing properties are instead modelled as a function of eccentricity and its direction. Hence, the bearing properties can be evaluated at each time step without solving Navier-Stokes or Reynold's equation. The main advantage of using this method is to decrease the computational time. The cross-coupling stiffness and damping coefficients are usually neglected since they are small compared to the radial stiffness and damping coefficients. In this paper, the simulated unbalanced response is compared to experimental results and it is seen that the cross-coupling stiffness for vertical machines can influence the dynamics. It is shown that the cross-coupling can be of the same order of magnitude as the radial stiffness component depending on the shaft angular position in the bearing. Including cross-coupling increases higher frequency components and the experiments show similar behaviour. Hence the cross-coupling stiffness and damping coefficients should be included when simulating vertical machines subjected to high loads or when the detailed dynamical behaviour is important to investigate.
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| 45295. |
- Synnegård, Erik, et al.
(författare)
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Modeling of visco-elastic supports for hydropower applications
- 2015
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Ingår i: Proceedings of the 9th IFToMM International Conference on Rotor Dynamics. - Cham : Encyclopedia of Global Archaeology/Springer Verlag. - 9783319065892 - 9783319065908 ; , s. 2189-2197
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Konferensbidrag (refereegranskat)abstract
- This paper presents a numerical model of how a visco-elastic support affects the dynamical response of a 42 MW Kaplan turbine that is experiencing resonance problems. The supports are placed between the bearing bracket and the supporting concrete structure. Since the supports are nonlinear, the nodal displacements are solved using a Runge-Kutta time integration method where the visco-elastic supports are implemented as a nonlinear force. To reduce calculation time the number of degrees of freedom of the rotor model is reduced using the Improved Reduction System. Excitation of the system is implemented as a stationary force in the runner with varying frequency. The resulting nodal displacement from the transient simulation is then compared to the system simulated without the supports to show how the machine dynamics are affected. The simulations show that the visco-elastic supports efficiently reduces the displacements in the lower vibration modes. The reduced vibration levels should decrease the probability of resonance problems occurring when running at operating speed.
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| 45296. |
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| 45297. |
- Synnergren, Per, et al.
(författare)
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Application of digital speckle photography to flash x-ray studies of internal deformation fields in impact experiments
- 1999
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 38:19, s. 4030-4036
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Tidskriftsartikel (refereegranskat)abstract
- A technique to measure two-dimensional deformation fields of a layer inside materials during dynamic events such as impact experiments is presented. Even optically opaque materials like cement can be evaluated when flash x rays are used. Blocks of polyester and cement were prepared with a layer of x-ray-absorbing lead particles. The specimens were then hit by a 9-mm-diameter steel sphere (ball bearing) fired from a 9-mm-bore gas gun at a velocity of 373.5 3.0 ms 1 . A 30-ns-long x-ray pulse exposed one radiograph before impact; another radiograph was exposed a short time after the impact on the specimen. The two-dimensional displacement field was obtained when the x-ray radiographs were digitized by a conventional flatbed scanner, and a digital speckle photography algorithm was used to calculate the displacements. The flash x-ray technique allowed examination of the deformation at the layer inside the material during failure, thus giving interesting data about the material flow field around the impactor.
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| 45298. |
- Synnergren, Per, et al.
(författare)
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Digital speckle photography : visualization of mesoflow through clustered fiber networks
- 2002
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 41:7, s. 1368-1373
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Tidskriftsartikel (refereegranskat)abstract
- Digital speckle photography (DSP) is used for velocity field measurements inside a fiber network. The width of the channels in which the flow is measured is typically less than 1 mm. Therefore a microscope is used to image the fiber network. When we sample 30 images/s and separate the moving parts of the images from the stationary parts, the velocity field can be deduced with DSP
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| 45299. |
- Synnergren, Per, et al.
(författare)
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Dynamic Measurements of Internal Three-Dimensional Displacement Fields with Digital Speckle Photography and Flash X rays
- 1999
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 38:28, s. 5956-5961
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Tidskriftsartikel (refereegranskat)abstract
- A metrology system is presented that measures internal three-dimensional (3-D) displacement fields. The system uses a stereo pair of flash x-ray heads and correlation analysis to measure the true deformation of a layer of x-ray-absorbent particles inside the specimen. The 3-D deformation field inside blocks of polyester was determined. The polyester blocks were impacted by a 9-mm steel ball bearing fired from a 9-mm-bore gas gun at a speed of 373.5 3.0 m s 1 . At a given time after impact, a short-duration (30 ns) flash x-ray pulse exposes the x-ray radiographs and freezes the events during impact. Thereafter, the x-ray radiographs are scanned into a personal computer and analyzed as in digital speckle photography.
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| 45300. |
- Synnergren, Per, et al.
(författare)
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Estimation of curl in paper using a combination of shape measurement and least-squares modelling
- 2001
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Ingår i: Optics and lasers in engineering. - 0143-8166 .- 1873-0302. ; 35:2, s. 105-120
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Tidskriftsartikel (refereegranskat)abstract
- Curl is a quality problem that makes paper less suitable for printing. A paper sheet that has structural variations in its thickness such as gradients of fibre orientation, density and filler content, will curl and hence assume a cylindrical shape when its humidity content is changed. We propose a method to measure curl that can be used for automated analysis of the paper quality. The shape of the curled paper is measured using a stereoscopic camera system, which is capable of viewing a random pattern that is projected onto the specimen. The shape of the object is found by calculating the perspective difference in the camera set-up using digital image correlation. The quality parameters that are searched for are the magnitude of curl, which is defined as the inverse of the radius of curvature and the orientation of the curled paper. These parameters are estimated by performing a least-squares fit of a cylindrical shape to the three-dimensional measurement
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