| 1. |
- Khodadad, Davood, et al.
(författare)
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Full-field 3D deformation measurement : Comparison between speckle phase and displacement evaluation
- 2016
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 55:27, s. 7735-7743
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to describe a full-field deformation measurement method based on 3D speckle displacements. The deformation is evaluated from the slope of the speckle displacement function that connects the different reconstruction planes. For our experiment, a symmetrical arrangement with four illuminations parallel to the planes (x,z) and (y,z) was used. Four sets of speckle patterns were sequentially recorded by illuminating an object from the four directions, respectively. A single camera is used to record the holograms before and after deformations. Digital speckle photography is then used to calculate relative speckle displacements in each direction between two numerically propagated planes. The 3D speckle displacements vector is calculated as a combination of the speckle displacements from the holograms recorded in each illumination direction. Using the speckle displacements, problems associated with rigid body movements and phase wrapping are avoided. In our experiment, the procedure is shown to give the theoretical accuracy of 0.17 pixels yielding the accuracy of 2 × 10-3 in the measurement of deformation gradients
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| 2. |
- Bjurström, Johan, 1985, et al.
(författare)
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Unified Modeling and Analysis of Vibration Energy Harvesters under Inertial Loads and Prescribed Displacements
- 2022
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417 .- 1454-5101. ; 12:19
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we extend the optimization analysis found in the current literature for single-degree-of-freedom vibrational energy harvesters. We numerically derive and analyze the optimization conditions based on unified expressions for piezoelectric and electromagnetic energy harvesters. Our contribution lies in the detailed analysis and comparison of both resonant and anti-resonant states while fully including the effect of intrinsic resistance. We include both the case of excitation by inertial load and prescribed displacement, as the latter has not been elaborated on in the previous literature and provides new insights. We perform a general analysis but also consider typical values of applied piezoelectric and electromagnetic energy harvesters. Our results improve upon previous similar comparative studies by providing new and useful insights regarding optimal load, load power and power input to output efficiency. Our analysis shows an exponential increase in the critical mechanical quality factor due to the resistive loss coefficient. We find that the ratio of mechanical quality factor to resistive loss coefficient, at resonance, increases drastically close to the theoretical maximum for load power. Under the same optimization conditions, an equivalent conclusion can be drawn regarding efficiency. We find that the efficiency at anti-resonance behaves differently and is equal to or larger than the efficiency at resonance. We also show that the optimal load coefficient at resonance has a significant dependence on the mechanical quality factor only when the resistive loss coefficient is large. Our comparison of excitation types supports the previous literature, in a simple and intuitive way, regarding optimal load by impedance matching and power output efficiency. Our modeling and exploration of new parameter spaces provide an improved tool to aid the development of new harvester prototypes.
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| 3. |
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| 4. |
- Girhammar, Ulf Arne
(författare)
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A simplified analysis method for composite beams with interlayer slip
- 2009
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Ingår i: International Journal of Mechanical Sciences. - : Pergamon Press. - 0020-7403 .- 1879-2162. ; 51:7, s. 515-530
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Tidskriftsartikel (refereegranskat)abstract
- A simplified static procedure is proposed for analysing and designing composite beams with interlayer slip. The method is parallel to the Eurocode 5 method, but it is general in nature and can be applied to arbitrary boundary and loading conditions. In contrast with Eurocode 5, a general and correct way of choosing the effective beam length of the problem is given by the present procedure, which is that the effective beam length equals the buckling length that is found in the corresponding column buckling problem. The procedure predicts the deflections and internal actions and stresses, in principle by replacing the fully composite bending stiffness (EI(infinity)) with the effective (partially) composite bending stiffness (EI(eff)) in the expressions for these quantities in the corresponding fully composite beam. This effective bending stiffness depends on two non-dimensional parameters: the composite action parameter (shear connection stiffness) and the relative bending stiffness parameter. The method is applied to a number of simple practical cases and the results obtained have been compared with the exact values. The applicability of the simplified analysis procedure was found to be very good, except for interlayer shear stresses. The error in the Eurocode 5 procedure, as compared with the method proposed in this paper, can in some cases be up to almost 30% depending on the boundary conditions.
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| 5. |
- Girhammar, Ulf Arne
(författare)
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Composite beam-columns with interlayer slip : approximate analysis
- 2008
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Ingår i: International Journal of Mechanical Sciences. - Oxford : Pergamon Press. - 0020-7403 .- 1879-2162. ; 50:12, s. 1636-1649
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Tidskriftsartikel (refereegranskat)abstract
- An approximate second order analysis procedure for composite beam-columns with interlayer slip subjected to transverse loading and axial compressive loads is developed. The magnification factors to be applied to the first order solutions in order to estimate the deflections and internal forces obtained by the second order analysis approach are presented. The method of applying magnification factors to internal axial forces is discussed. The approximate second order analysis procedure is developed for the four Euler cases with various transverse load conditions. The procedure is applied to and the accuracy is illustrated for simply supported partially beam-columns of steel and concrete, and timber and concrete with different bending stiffness and interlayer slip properties. The deflections and internal forces obtained by the approximate method compared extremely well, except for slip forces in case of very flexible shear connectors, with those obtained by the more rigorous second order analysis approach for different composite action (partial interaction) parameters (shear connector stiffness values). The study also shows that the magnification factor associated with the deflections can be utilized to estimate also the internal actions, except shear forces in case of very flexible shear connectors, in the second order case with minimal error for simply supported beam-columns. Thus. for members with shear connector stiffness of structural significance the proposed approximate method can be used in general for simply supported beam-columns. For other boundary and loading conditions, the approximate method needs to be re-evaluated. The approach of using one magnification factor greatly simplifies the analysis task for those components.
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| 6. |
- Girhammar, Ulf Arne, et al.
(författare)
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Exact static analysis of partially composite beams and beam-columns
- 2007
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Ingår i: International Journal of Mechanical Sciences. - Oxford : Pergamon Press. - 0020-7403 .- 1879-2162. ; 49:2, s. 239-255
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Tidskriftsartikel (refereegranskat)abstract
- The ordinary differential equations and general solutions for the deflection and internal actions and, especially, the pertaining consistent boundary conditions for partially composite Euler-Bernoulli beams and beam-columns are presented. Static loading conditions, including transverse and axial loading and first- and second-order analyses are considered. The theoretical procedure is applicable to general loading and boundary conditions for uniform composite beams and beam-columns with interlayer slip. Further, the exact closed form characteristic equations and their associated exact buckling length coefficients for composite Columns with interlayer slip are derived for the four Euler boundary conditions. It is shown that these coefficients are the same as those for ordinary fully composite (solid) columns, except for the Euler clamped-pinned case. For the clamped-pinned case, the difference between the exact buckling length coefficient and the corresponding value for solid Columns is less than 1.8%, depending oil the so-called composite action parameter and relative bending stiffness parameter. Correspondingly, the maximum deviation between the exact and approximate buckling load is at most 2.5%. These small differences can in most practical cases be neglected. Also, the maximum theoretical range for the relative bending stiffness for partially composite beams and beam-columns is derived. An effective bending stiffness, valuable in the determination of the critical buckling load for partially composite members, is derived. This effective bending stiffness is also Suitable for analysing approximate deflections and internal actions or stresses in composite beams with flexible shear connection. The beam-column analysis is applied to a specific case. The difference in the approaches to the first- and second-order analysis is illustrated and the results clearly show the magnification in the actions and displacements due to the second-order effect. The magnification of the internal axial forces is different from magnifications obtained for the other internal actions, since only that portion of an internal axial force that is induced by bending is magnified by the second-order effect.
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| 7. |
- Aidanpää, Jan-Olov, et al.
(författare)
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Developments in rotor dynamical modeling of hydropower units
- 2009
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Ingår i: Proceedings of the IUTAM Symposium on Emerging Trends in Rotor Dynamics. - Dordrecht : Encyclopedia of Global Archaeology/Springer Verlag. - 9789400700192
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Konferensbidrag (refereegranskat)
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| 8. |
- Khodadad, Davood, 1985-, et al.
(författare)
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Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements
- 2015
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 54:16, s. 5003-5010
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18 mm×18 mm.
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| 9. |
- Khodadad, Davood, 1985-, et al.
(författare)
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Shape reconstruction using dual wavelength digital holography and speckle movements
- 2013
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Ingår i: Optical Measurement Systems for Industrial Inspection VIII. - : SPIE - International Society for Optical Engineering. - 9780819496041
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Konferensbidrag (refereegranskat)abstract
- A new technique to measure depth based on dual wavelength digital holography and image correlation of speckle movements is demonstrated. By numerical refocusing of the complex optical field to different focus planes and by measuring the speckle movements caused by a wavelength shift both the object surface position and its local slope can be determined. It is shown how the speckle movement varies linearly with the surface slope, the wavelength shift and the distance of the numerical propagation. This gives a possibility to measure the slope with approximately the same precision as from the interferometric phase maps. In addition, when the object surface is in focus there is no speckle movement so by estimating in what plane the speckle movement is zero the absolute surface position can be measured.
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| 10. |
- Lundström, Niklas, et al.
(författare)
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Dynamic consequences of electromagnetic pull due to deviations in generator shape
- 2007
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 301:1-2, s. 207-225
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Tidskriftsartikel (refereegranskat)abstract
- Results from earlier measurements on hydropower generators have indicated relatively large eccentricities and shape deviations in the rotor and stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called unbalanced magnetic pull (UMP). The UMP force can produce large vibrations which can be dangerous to the machine. A mathematical model is developed to describe the shapes of the rotor and stator, and the corresponding UMP is obtained through the law of energy conservation. The target of the paper is to analyse the dynamics of a generator due to shape deviations in the rotor and stator. As rotor-model, a balanced Jeffcott rotor is used. A linearization of the UMP indicates the importance of considering the nonlinear effects. The stability of some attractors are analysed and the generator dynamics are further investigated by simulating the basin of attraction. The magnitudes are approximately obtained when the shape deviations become dangerous for the generator. It is concluded which shape deviations that are more dangerous than others. In hydropower generator maintenance the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and estimate the stability and robustness by simulations.
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