| 1. |
- Abedi, Hamidreza, 1979, et al.
(författare)
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Numerical modelling of neutral atmospheric boundary layer flow through heterogeneous forest canopies in complex terrain (a case study of a Swedish wind farm)
- 2021
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 180, s. 806-828
-
Tidskriftsartikel (refereegranskat)abstract
- This paper exposes the risk of generalization of wind conditions from a single met-mast measurement to be representative of the actual flow field in a wind farm situated in complex terrain. As a case study, Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow for a mid-western Sweden wind farm is performed. The site-specific complex topography and the forest properties like the Plant Area Density and the tree heights are extracted from the Airborne Laser Scanning (ALS) 3D data, thus the forest is heterogeneous. To emphasize the impact of the local topography and surface roughness on the wind field, the wind turbines are not included in the numerical simulations. The predicted wind speeds using LES are compared to wind speed from the nacelle-mounted anemometers taken from the wind farm's turbine SCADA data, focusing on the wake-free turbines. A sufficient degree of match is observed, supporting the accuracy of the numerical simulations. The results show that inflow variables i.e., mean wind speed, shear exponent and turbulence intensity vary at each wind turbine location justifying the need for turbine-specific assessment of the wind resource in a wind farm located in forested complex terrain. The inter-turbine (between turbines in the wind farm) differences in wind resource is quantified in terms of the difference in turbine-specific structural and mechanical loads by running wind turbine mechanical simulations using the extracting the wind fields predicted by the LES. The results show that not only inter-turbine loads varying significantly in the wind farm, but the turbine loads also differ significantly if a homogeneous assumption is made for the forest. Most importantly, it was found that the homogeneous forest assumption predicted a higher turbulence intensity compared to a heterogeneous forest resulting.
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| 2. |
- Boersma, Greta J., et al.
(författare)
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Altered Glucose Uptake in Muscle, Visceral Adipose Tissue, and Brain Predict Whole-Body Insulin Resistance and may Contribute to the Development of Type 2 Diabetes: A Combined PET/MR Study
- 2018
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Ingår i: Hormone and Metabolic Research. - : Georg Thieme Verlag KG. - 0018-5043 .- 1439-4286. ; 50:8
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Tidskriftsartikel (refereegranskat)abstract
- We assessed glucose uptake in different tissues in type 2 diabetes (T2D), prediabetes, and control subjects to elucidate its impact in the development of whole-body insulin resistance and T2D. Thirteen T2D, 12 prediabetes, and 10 control subjects, matched for age and BMI, underwent OGTT and abdominal subcutaneous adipose tissue (SAT) biopsies. Integrated whole-body 18F-FDG PET and MRI were performed during a hyperinsulinemic euglycemic clamp to asses glucose uptake rate (MRglu) in several tissues. MRglu in skeletal muscle, SAT, visceral adipose tissue (VAT), and liver was significantly reduced in T2D subjects and correlated positively with M-values (r = 0.884, r = 0.574, r = 0.707 and r = 0.403, respectively). Brain MRglu was significantly higher in T2D and prediabetes subjects and had a significant inverse correlation with M-values (r = -0.616). Myocardial MRglu did not differ between groups and did not correlate with the M-values. A multivariate model including skeletal muscle, brain and VAT MRglu best predicted the M-values (adjusted r2 = 0.85). In addition, SAT MRglu correlated with SAT glucose uptake ex vivo (r = 0.491). In different stages of the development of T2D, glucose uptake during hyperinsulinemia is elevated in the brain in parallel with an impairment in peripheral organs. Impaired glucose uptake in skeletal muscle and VAT together with elevated glucose uptake in brain were independently associated with whole-body insulin resistance, and these tissue-specific alterations may contribute to T2D development.
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| 3. |
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| 4. |
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| 5. |
- Rosqvist, Fredrik, 1985-, et al.
(författare)
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Overeating saturated fat promotes fatty liver and ceramides compared to polyunsaturated fat : a randomized trial
- 2019
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - : Oxford University Press. - 0021-972X .- 1945-7197. ; 104:12, s. 6207-6219
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Tidskriftsartikel (refereegranskat)abstract
- CONTEXT: Saturated fat (SFA) versus polyunsaturated fat (PUFA) may promote non-alcoholic fatty liver disease (NAFLD) by yet unclear mechanisms.OBJECTIVE: To investigate if overeating SFA- and PUFA-enriched diets lead to differential liver fat accumulation in overweight and obese humans.DESIGN: Double-blind randomized trial (LIPOGAIN-2). Overfeeding SFA vs PUFA for 8 weeks, followed by 4 weeks of caloric restriction.SETTING: General community.Participants: n=61 overweight or obese men and women.INTERVENTION: Muffins high in either palm (SFA)- or sunflower oil (PUFA) were added to the habitual diet.MAIN OUTCOME MEASURE: Lean tissue mass (not reported here). Secondary and exploratory outcomes included liver and ectopic fat depots.RESULTS: By design, body weight gain was similar in SFA (2.31±1.38 kg) and PUFA (2.01±1.90 kg) groups, P=0.50. SFA markedly induced liver fat content (50% relative increase) along with liver enzymes and atherogenic serum lipids. In contrast, despite similar weight gain, PUFA did not increase liver fat or liver enzymes or cause any adverse effects on blood lipids. SFA had no differential effect on the accumulation of visceral fat, pancreas fat or total body fat compared with PUFA. SFA consistently increased, while PUFA reduced circulating ceramides; changes that were moderately associated with liver fat changes and proposed markers of hepatic lipogenesis. The adverse metabolic effects of SFA were reversed by calorie restriction.CONCLUSIONS: Saturated fat markedly induces liver fat and serum ceramides whereas dietary polyunsaturated fat prevent liver fat accumulation, reduce ceramides and hyperlipidemia during excess energy intake and weight gain in overweight individuals.
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| 6. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Site-specific analysis of on wind turbines in complex terrain: A case study
- 2021
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Ingår i: WESC2021, Wind Energy Science Conference , The Conference Book (Intro) with the Book of Abstracts (Theme 01 - 10). ; Theme 02, s. 2-111-2-112
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study aims to analyse and understand how the structural and drivetrain loads on the turbines can vary within a wind farm situated in a complex terrain. To this end, the flow field is studied using computational fluid and aero-elastic simulations and a modified version of the FAST software is used to determine the turbine response Verification of the numerical results is performed by using data from turbine SCADA system for a case study of Röbergsfjället wind farm with 8 turbines located in the mid-western part of Sweden.
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| 7. |
- Wickström, Anders, et al.
(författare)
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Analysis of wind turbines under harsh operation conditions
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This project focuses on the harsh operational conditions that sometimes lead to gearbox and bearing failures before their expected lifespan have been reached. Individual wind turbines that are subjected to extreme wind conditions and other severe operational conditions have been identified in close cooperation with wind turbine operators. Methods for determining the operational severity from data acquired during operation have been developed. Raw measured data have been processed and compared to the assumed data that were used in the wind turbine design process. Feedbacks from maintenance reports have been used to strengthen the relevance of these indices. A generic V90 turbine model has been created for the simulations using both FAST and VIDYN aero elastic simulation codes. The wind turbine dynamical behaviour has been analysed in arbitrary wind conditions and grid dynamics. The assessment has been made using 17 wind turbines of same design but with different operational conditions. The data from these turbines have been compared and comparison has also been made using simulated data for complex and flat terrains. The results show that the complex terrain increases the fatigue on the gearbox shaft and the fluctuation of wind direction in the complex terrain is much higher than for the flat terrain, resulting in more destructive fatigue loads. Simulation also shows that de-rating of the turbine has a significant impact on the loads in the drive train but no significant impact on the fatigue loads on the nacelle. There are different systems running for capturing operational data during operation. Normally the system stores only one measurement data point at each 20 seconds, i.e. 0.05 Hz. Then it is difficult to observe any details related to loads based on turbulence or other environment or technical conditions. For that reason, the project has managed to get higher resolution measurement data, 1 Hz sample rate, for specific turbines in the available fleets. The complex topography of a specific wind farm was extracted from LASer data and it was imported into the Computational Fluid Dynamics (CFD) software, STAR-CCM+, to generate the computational wind grid for the numerical simulations. The on-site meteorology mast data, provided by project partners, were used to determine the dominant mean wind speed/direction and turbulence intensity. A system simulation model in FAST or VIDYN can reasonably well predict the hub forces and mechanical torque of a Vestas V90 turbine under different kind of wind load in operation. A turbine designer is allowed to use any specific wind conditions as input for the load calculations. It might be outside the wind classes specified in IEC-61400-1 and therefore denoted class S, where the specific input conditions are stated. Using the calculated data for the complex terrain, a class 3S turbine has been defined with turbulence intensity, TI=0.17, shear α = 0.34 in comparison with standard wind turbine class 3A with TI=0.16 and α = 0.20. When using these input conditions, a fatigue load comparison and evaluation has been done. It shows that both drive torque and tower top bending moment increase with about 6 percent when class3S is used.
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| 8. |
- Wramner, Lina, 1979, et al.
(författare)
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Vibration dynamics in non-linear dual mass flywheels for heavy-duty trucks
- 2018
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Ingår i: Proceedings of ISMA2018 International Conference on Noise and Vibration Engineering. ; , s. 1935-1947
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Konferensbidrag (refereegranskat)abstract
- A non-linear model for simulations of a dual mass flywheel (DMF) for heavy-duty applications is proposed. The model includes internal clearances and friction. LuGre friction model is used, which depends on normal force, relative velocity between the two surfaces and an internal deflection variable. Measurements on the DMF are performed in a test rig and the test rig properties are analysed. The correlation shows that the general behaviour of the DMF is reproduced by the proposed simulation model. The viscous part of the friction is dominant for the analysed cases with zero mean torque, and a conventional Coulomb friction model would not suffice for this application. Near resonances, the model also shows a high sensitivity to internal clearances and spring stiffness. This indicates that correlation could be improved further if the static stiffness was measured with good accuracy for the relevant range of deflection angles.
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| 9. |
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| 10. |
- Asadi, Saeed, 1987, et al.
(författare)
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Global Sensitivity Analysis of High Speed Shaft Subsystem of a Wind Turbine Drive Train
- 2018
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Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; 2018
-
Tidskriftsartikel (refereegranskat)abstract
- The wind turbine dynamics are complex and critical area of study for the wind industry. Quantification of the effective factors to wind turbine performance is valuable for making improvements to both power performance and turbine health. In this paper, the global sensitivity analysis of validated mathematical model for high speed shaft drive train test rig has been developed in order to evaluate the contribution of systems input parameters to the specified objective functions.Thedrive train in this study consists of a 3- phase induction motor, flexible shafts, shafts’ coupling, bearing housing, and disk with an eccentric mass.The governing equations were derived by using the Lagrangian formalism and were solved numerically by Newmark method. The variance based global sensitivity indices are introduced to evaluate the contribution of input structural parameters correlated to the objective functions. The conclusion from the current research provides informative beneficial data in terms of design and optimization of a drive train setup and also can provide better understanding of wind turbine drive train system dynamics with respect to different structural parameters, ultimately designing more efficient drive trains. Finally, the proposed global sensitivity analysis (GSA) methodology demonstrates the detectability of faults in different components.
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| 11. |
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| 12. |
- Asadi, Saeed, 1987, et al.
(författare)
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Multibody dynamic modelling of a direct wind turbine drive train
- 2020
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Ingår i: Wind Engineering. - 0309-524X .- 2048-402X. ; 44:5, s. 519-547
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Tidskriftsartikel (refereegranskat)abstract
- Wind turbines normally have a long operational lifetime and experience a wide range of operating conditions. A representative set of these conditions is considered as part of a design process, as codified in standards. However, operational experience shows that failures occur more frequently than expected, the costlier of these including failures in the main bearings and gearbox. As modern turbines are equipped with sophisticated online systems, an important task is to evaluate the drive train dynamics from online measurement data. In particular, internal forces leading to fatigue can only be determined indirectly from other locations’ sensors. In this contribution, a direct wind turbine drive train is modelled using the floating frame of reference formulation for a flexible multibody dynamics system. The purpose is to evaluate drive train response based on blade root forces and bedplate motions. The dynamic response is evaluated in terms of main shaft deformation and main bearing forces under different wind conditions. The model was found to correspond well to a commercial wind turbine system simulation software (ViDyn)
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| 13. |
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| 14. |
- Asadi, Saeed, 1987, et al.
(författare)
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STRUCTURAL DYNAMICS OF A WIND TURBINE DRIVE TRAIN HIGH SPEED SUBSYSTEM: MATHEMATICAL MODELLING AND VALIDATION
- 2015
-
Ingår i: In Proc. of the International Conference on Engineering Vibration, Ljubljana, 7 - 10 September ; [editors Miha Boltežar, Janko Slavič, Marian Wiercigroch]. - EBook. - Ljubljana: Faculty for Mechanical Engineering, 2015. - 9789616536974 ; , s. 553-562
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Konferensbidrag (refereegranskat)abstract
- The paper studies the dynamics of a wind turbine drive train high speed subsystem, both by modelling and experiments with focus on system torsional vibration and transient events which can reduce fatigue life of functional components (gearbox, bearings, shafts, couplings,others). A scaled down drive train high speed shaft test rig has been developed. Main components of the test rig are six-pole motor with variable frequency drive controller (up to 1000rpm), shafts’ disk coupling and flexible mounting structure representing gearbox housing with output high speed bearing. The test rig is equipped with measurement system comprising a set of accelerometers and displacement sensors, strain gauges and telemeter system, data acquisition hardware and software (SKFWindCon3.0). Mathematical and computational models of the test rig have been developed and went through validation tests. The system dynamic response is studied for different operational scenarios and structural parameters (run-shut down case with and without eccentric mass). The ultimate goal of the test rig is to get insight into interactionbetween internal dynamics of drive train mechanical and electrical functional components and to develop novel methods to detect, predict and prevent faults and failures in wind turbine drive trains arising due to misalignments and transient external loads.
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| 15. |
- Asadi, Saeed, 1987, et al.
(författare)
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Vibration dynamics of a wind turbine drive train high speed subsystem: Modelling and validation
- 2015
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Ingår i: ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, IDETC/CIE 2015, Boston, United States, 2-5 August 2015. - 9780791857182 ; 8
-
Konferensbidrag (refereegranskat)abstract
- Modern wind turbines are enormous large-scale electromechanical systems. They operate in complex conditions, determined by a turbulent wind field, by possible disturbances in the electricity grid and by the behavior of sea waves for offshore turbines. Guaranteeing the structural integrity of these machines during a lifetime of 20 years is an enormous challenge. In this paper the dynamics of a wind turbine drive train high speed subsystem is studied both by modeling and experiments with focus on system torsional and flexural vibrations and transient events which can reduce fatigue life of functional components (gearbox, bearings, shafts, couplings, others). A scaled down drive train high speed shaft test rig has been developed. Main components of the test rig are six-pole motor with variable frequency drive controller (up to 1000 rpm), shafts' disk coupling and flexible mounting structure representing gearbox housing with output high speed bearing. The test rig is equipped with measurement system comprising a set of accelerometers and displacement sensors, data acquisition hardware and software (SKF WindCon3.0). Mathematical and computational models of the test rig have been developed and went through validation tests. The system kinematic and dynamic responses are studied for different operational scenarios and structural parameters (ratio of shaft bending stiffness and stiffness of mounting structures, unevenly inertia load distribution, others). The ultimate goal of the test rig is to get insight into interaction between internal dynamics of drive train functional components to be used the results obtained in developing novel methods to detect, predict and prevent faults and failures in wind turbine drive trains arising due to misalignments and transient external loads.
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| 16. |
- Cappel, Ute B, et al.
(författare)
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Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells.
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:40, s. 34970-34978
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Tidskriftsartikel (refereegranskat)abstract
- ) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.
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| 17. |
- Chernoray, Valery, 1975, et al.
(författare)
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Projects in Applied Mechanics 2017
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The course TME131 Project in Applied Mechanics is a mandatory course within the AppliedMechanics Masters programme at Chalmers. The course was carried out during springsemester 2017. In total 7 projects were carried out, and 4 of these are collected here.
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| 18. |
- Danvind, Jonas, et al.
(författare)
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Calibration of a constitutive model for diffusive moisture transport in wood using data from X-ray CT-scanning and digital speckle photography
- 2004
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Ingår i: 5th Conference on Timber drying for value-added prducts, COST action E15 "advances in drying of wood". ; , s. 210-218
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An unsteady-state diffusion model is applied for studying wood drying below the fibre saturation point. The moisture diffusion coefficient in Fick's law for Norway spruce under isothermal drying conditions is determined. Using X-ray CT-scanning and Digital Speckle Photography, the wood density and moisture content are obtained in the radial direction of the wood samples. An optimization scheme is used to minimize the difference between observed and computed moisture content in order to calibrate the values of a set of parameters describing the diffusion coefficient. In this study the values of the parameters for a parameterization of Arrhenius' type are determined. The general idea discussed, however, is not limited to a specific model, butcan be used for a wide class of parameter identification problems. The results show a good agreement between observed and computed moisture content and it is concluded that the numerical realization of the optimization scheme works well. Nevertheless, the value of the diffusion coefficient is somewhat higher than expected. This is likely the consequence of a permeable coating of the samples.
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| 19. |
- Ekström, Andreas, 1980, et al.
(författare)
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Bayesian optimization in ab initio nuclear physics
- 2019
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Ingår i: Journal of Physics G-Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 46:9
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical models of the strong nuclear interaction contain unknown coupling constants (parameters) that must be determined using a pool of calibration data. In cases where the models are complex, leading to time consuming calculations, it is particularly challenging to systematically search the corresponding parameter domain for the best fit to the data. In this paper, we explore the prospect of applying Bayesian optimization to constrain the coupling constants in chiral effective field theory descriptions of the nuclear interaction. We find that Bayesian optimization performs rather well with low-dimensional parameter domains and foresee that it can be particularly useful for optimization of a smaller set of coupling constants. A specific example could be the determination of leading three-nucleon forces using data from finite nuclei or three-nucleon scattering experiments.
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| 20. |
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| 21. |
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| 22. |
- Eriksson, Cecilia, 1966, et al.
(författare)
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Studies by imaging TOF-SIMS of bone mineralization on porous titanium implants after 1 week in bone
- 2006
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 252:19, s. 6757-6760
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Tidskriftsartikel (refereegranskat)abstract
- Anodic oxidation was used to grow porous layers on titanium discs. Six different oxidation procedures were used producing six different surfaces. The implants were inserted in rat bone (tibia) for 7 days. After implant retrieval, mineralization (hydroxyapatite formation) on the implant surfaces was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Bone tissue around the implants was sectioned and stained. The amount of bone in close apposition to the implant was calculated. The porosity showed great variation between the surfaces. Hydroxyapatite was detected on all surfaces. A slight positive correlation between porosity and mineralization was found, although the most porous surface was not the best mineralized one. Bone had formed around all implants after 7 days. The bone-to-metal contact for the porous implants did not differ significantly from the non-porous control. Porosity is known to influence cellular events. The results indicate that porosity could have an initial, positive influence on bone integration of implants, by stimulating the mineralization process. The methods used were found to be suitable tools for investigation of initial healing around implants in bone.
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| 23. |
- Eriksson, John, 1973, et al.
(författare)
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A Mass-Transport Model for Drying Wood under Isothermal Conditions
- 2005
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Ingår i: 9th international IUFRO wood drying conference, Nanjing, China, August 21-26, 2005. ; 1:1, s. 51-56
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mass transport in wood during drying is often described in terms of different periods. Depending on the current moisture content (MC) and the structure of the wood, the driving forces behind the mass transport are essentially different. Above a certain level of MC, the fibres are partially saturated and the transport of liquid (free) water occurs mainly as a consequence of capillary action. On the other hand, below the fibre saturation point, bound water within the cell walls is conveyed by diffusion, and water vapour in the lumen moves under influence of pressures. In this contribution, a unified model is presented that takes into account the transport of the different water phases. Simulation of the drying of a Norway spruce sample from about 135% to 7% MC is carried out using the finite element method (FEM). The resulting mean MC is compared with experimental observations obtained from X-ray Computed Tomography showing reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation.
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| 24. |
- Eriksson, John, 1973, et al.
(författare)
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A Mass Transport Model for Drying Wood under Isothermal Conditions
- 2007
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Ingår i: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 25:3, s. 433-439
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Tidskriftsartikel (refereegranskat)abstract
- Mass transport in wood during drying can have different mechanisms at different periods of drying. Depending on the current moisture content (MC) and the structure of the wood, the driving forces for the mass transport are essentially different. Above the fiber saturation point (FSP), the lumens are partially saturated and the transport of liquid (free) water occurs as a consequence of capillary action. On the other hand, below the FSP, bound water within the cell walls is conveyed by diffusion, and water vapor in the lumens moves under influence of pressures gradient. Based on these considerations, a unified model is presented that takes into account the transport of the different moisture phases. Simulation of the drying of a Norway spruce sample at 50°C from about 135 to 7% MC is carried out using the finite element method (FEM). Comparison between the simulated average MC and the experimental observations obtained from X-ray computed tomography (CT) shows reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation. Finally, the influence of absolute permeability on the average MC is studied.
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| 25. |
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| 26. |
- Guglielmo, Priscilla, et al.
(författare)
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Validation of automated whole-body analysis of metabolic and morphological parameters from an integrated FDG-PET/MRI acquisition
- 2020
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Automated quantification of tissue morphology and tracer uptake in PET/MR images could streamline the analysis compared to traditional manual methods. To validate a single atlas image segmentation approach for automated assessment of tissue volume, fat content (FF) and glucose uptake (GU) from whole-body [18F]FDG-PET/MR images. Twelve subjects underwent whole-body [18F]FDG-PET/MRI during hyperinsulinemic-euglycemic clamp. Automated analysis of tissue volumes, FF and GU were achieved using image registration to a single atlas image with reference segmentations of 18 volume of interests (VOIs). Manual segmentations by an experienced radiologist were used as reference. Quantification accuracy was assessed with Dice scores, group comparisons and correlations. VOI Dice scores ranged from 0.93 to 0.32. Muscles, brain, VAT and liver showed the highest scores. Pancreas, large and small intestines demonstrated lower segmentation accuracy and poor correlations. Estimated tissue volumes differed significantly in 8 cases. Tissue FFs were often slightly but significantly overestimated. Satisfactory agreements were observed in most tissue GUs. Automated tissue identification and characterization using a single atlas segmentation performs well compared to manual segmentation in most tissues and will be valuable in future studies. In certain tissues, alternative quantification methods or improvements to the current approach is needed.
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| 27. |
- Irfan, Muhammad, 1986, et al.
(författare)
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Constrained Lagrangian Formulation for Modelling and Analysis of Transmission Synchronizers
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An engineering model of a generic synchronizer is considered. The generic synchronizeris modeled consisting of the selector sleeve with engaging teeth and frictional cone, thesynchronizing ring with blocker and the gearwheel with engaging teeth. It is assumed thatfor the sleeve and synchronizing ring translational and rotational motions are feasible, forthe gearwheel only rotational motion is feasible. The motion of the generic synchronizer isperformed under the external and internal loads. The external loads comprise the vehicleresistance torque and the control force applied to the sleeve and the drag torque due to theclutch. The internal loads comprise the forces and torques arises due to interactionbetween the sleeve, the synchronizing ring, the gearwheel as well as oil splash during thesynchronization process. A feasible synchronization process of a generic synchronizer isdivided into four main phases: pre-synchronization, main synchronization, blockertransition (indexing for the ring), and engagement. Pre-synchronization and blockertransition are further divided into several sub-phases. The generic synchronizer is fullyparametrized and together with description of all phases constitutes kinematics ofsynchronization process in question.Due to the nature of synchronization process in transmission system a motion of asynchronizer mechanism is subjected to unilateral or/and bilateral constraints imposed ongeneralized coordinates or/and generalized velocities of the synchronizer. ConstrainedLagrangian Formalism (CLF) has been proposed as an approach for developingmathematical and computational models of a generic synchronizer dynamics. The CLFgives possibility to formulate direct dynamics, semi-inverse dynamics and inversedynamics problems for a generic synchronizer in unified and efficient way. It is shown thatCLF can be promising and useful for advanced dynamic analysis of the existingsynchronizer mechanisms and to design novel optimized ones.In the present report mathematical and computational models of a generic synchronizerwith five degrees of freedom have been developed using CLF. Application of CLF on themodelling of the synchronization process gives system of differential-algebraic equations(DAE). Analysis of the generic synchronizer performance diagrams has shown that the CLFbased model is able to predict the synchronization process characteristics reasonably well.The developed model has been validated by using measurement data from test rig at CVAB Scania. Performance of the generic synchronizer is also analyzed in case of drivelinevibrations. Sensitivity analysis of the synchronizer mechanism performance with respect tocone angle, coefficient of friction, maximum value of shift force and rate of applying shiftforce has been done.Next, the developed models will be used to get further insight into synchronizer design andits performance diagrams with aid of global sensitivity analysis and Pareto optimization.
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| 28. |
- Irfan, Muhammad, 1986, et al.
(författare)
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Dynamics and Pareto Optimization of a Generic Synchronizer Mechanism
- 2016
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319300849 ; 8, s. 417-425
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Konferensbidrag (refereegranskat)abstract
- Transmission systems for passenger cars and trucks are equipped with synchronizer mechanism. It has a great impact on driving comfort and transmission efficiency. A synchronizer mechanism as a key component of a transmission system must be able to prevent gears from shocking and reduce the noise. Gear shifting improvement with respect to smooth, quick and energy efficient synchronizer's performance is still an important issue for automotive industry. This contribution studies the kinematics and dynamics of a generic synchronizer consisting of sleeve, blocker ring and gearwheel constituting a mechanical system with a set of time-varying constraints describing frictional contacts between system's components. The dynamic response is modelled using constrained Lagrangian formalism. Pareto optimization problem is stated and optimized the rate of the applied sleeve force, coefficient of friction and cone angle are found to attain a minimal synchronization time as well as speed difference between sleeve and gearwheel. One outcome of the study is that the obtained Pareto solution is characterized by the minimal admissible value of the cone angle of the synchronizer.
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| 29. |
- Irfan, Muhammad, 1986, et al.
(författare)
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Failure modes and optimal performance of a generic synchronizer
- 2018
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Ingår i: The 5th Joint International Conference on Multibody System Dynamics. ; , s. 1-22
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Konferensbidrag (refereegranskat)abstract
- The gear shifting mechanism is a crucial part of the gearbox which transmits the torque from engine to wheels with different transmission ratio. For smooth and comfortable gear changing the gear shifting mechanism is still a challenge for the engineers to adapt the different driving situations. In case of heavy vehicles particularly under certain circumstances optimized performance by avoiding failure modes of the gear shifting mechanism is also a challenge. In this paper failure modes and optimized values of the system parameters are identified to contribute for this challenge. A model of the gear shifting mechanism is developed in GT-Suite software. Failure modes are identified via sensitivity analysis. Four system response characteristics are plotted against the time and used to identify the failure modes. Optimization routine of the GT-Suite is applied on the model by taking seven parameters into account as independent variables and synchronization time as an objective function. Percentage changes of the variables from their initial values are calculated and analyzed. Finding of optimal values of parameters of the gear shifting mechanism is valuable contribution to design reliable and efficient transmission system for automotive industry especially for heavy vehicles.
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| 30. |
- Irfan, Muhammad, 1986, et al.
(författare)
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Minimizing synchronization time of a gear shifting mechanism by optimizing its structural design parameters
- 2020
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 234:2-3, s. 488-504
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Tidskriftsartikel (refereegranskat)abstract
- A gear shifting mechanism is modeled in GT-Suite software. The mechanism has three main bodies: sleeve, ring, and gear. Results obtained from the simulation show that GT-Suite model can predict gear shifting process. Synchronization processes for three conditions of nominal, road grade, and vibrational motion of the master are studied in six cases by considering the sleeve and the gear as a master alternatively. The optimization based on the GT-Suite model is performed for each case to find the minimum gear shifting time based on variations of 17 structural design parameters. Minimum synchronization time is found almost same in all cases. It is concluded from closeness of the optimization results that average of the parameter values can be considered as optimized values for all cases. At the end, robustness of the optimized structural design parameters are analyzed with respect to the road grade, amplitude, and frequency of oscillatory excitation of rotational motion of the master.
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| 31. |
- Irfan, Muhammad, 1986, et al.
(författare)
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Modelling of Heavy Vehicle Transmission Synchronizer using Constrained Lagrangian Formalism
- 2015
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Ingår i: In Proc. of the International Conference on Engineering Vibration, Ljubljana, 7 - 10 September ; [editors Miha Boltežar, Janko Slavič, Marian Wiercigroch]. - EBook. - Ljubljana: Faculty for Mechanical Engineering, 2015. - 9789616536974 ; , s. 28-37
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Konferensbidrag (refereegranskat)abstract
- Robust and efficient synchronizers are keys elements to ensure good gear shift in heavy vehicles. In order to improve existing as well as develop new synchronizers, efficient simulation tools are needed. In this contribution, a mechanical system with 5 degrees of freedom modelling a generic synchronizer consisting of engaging sleeve, synchronizer ring and gearwheel are considered.Due to the design of the different components and their interactions the synchronizing process is described in terms of different steps or phases; presynchronization, main synchronization, blocker transition and engagement. The four main phases are further divided into sub-phases.To study the whole process in a unified manner, Constrained Lagrangian Formalism (CLF) turns out to be a suitable method in which the interactions between components (sleeve,synchronizer ring and gearwheel) are described by unilateral or/and bilateral constraints imposed on generalized coordinates of the system during different phases. Using CLF a mathematical model of a generic synchronizer is developed and represented by the system of differential-algebraic equations. Kinematics and kinetics of the generic synchronizer are modelled for each sub-phase. The sleeve is considered as a master and thegearwheel is considered as a slave. The statement of the dynamics problem for a generic synchronizer is given and the numerical algorithm is implemented in Matlab for solving the differential-algebraic equations resulting from CLF. The generic synchronizer computational model is adapted to available experimental setup and validated using obtained measurement data. Sensitivity of the synchronization time is studied varying the cone angle, coefficient of dry friction and sleeve force. Effect of driveline vibrations on synchronization performance isalso studied.
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| 32. |
- Irfan, Muhammad, 1986, et al.
(författare)
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Performance improvement of a transmission synchronizer via sensitivity analysis and Pareto optimization
- 2018
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Ingår i: Cogent Engineering. - : Informa UK Limited. - 2331-1916. ; 5:1, s. 1-46
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Tidskriftsartikel (refereegranskat)abstract
- Gear-shifting mechanism has a key role in transmission system of a vehicle. During gear shifting, there is a risk of losing the engine optimal speed that will ultimately lead to more emission from the vehicle. It is demanded for optimal performance of transmission systems to increase quality of synchronizer used for gear shifting. Especially in the case of heavy vehicles, the synchronizer performance needs to be robust more even during different operating scenarios. Synchronization process varies by changing its parameters values. So one of the ways to improve performance of the synchronizer is to optimizing its parameters. In the paper, a generic synchronizer mechanism (GSM) is considered. Mathematical model of GSM is presented based on constrained Lagrangian formalism (CLF) and detailed kinematics of synchronization process in transmission system. Speed difference at the end of the main synchronization phase and synchronization time are chosen as two objectives. The following eight parameters of the synchronizer have taken as input parameters: cone angle, cone coefficient of friction, cone radius, rate of shift force, blocker angle, blocker coefficient of friction, gear moment of inertia, and ring moment of inertia. Influence of the parameters on objectives is studied. The values of the objective functions decrease with increasing some of the parameters and increase with increasing others. Not only the objective functions have opposite behavior between the parameters but also have opposite behavior with variation of the same parameters. For example, the synchronization time decreases but the speed difference increases with increasing cone coefficient of friction. The Matlab routine of multi-objective optimization is applied to obtain the optimized parameter values of the generic synchronizer at different operating conditions. In the first case, the sleeve is considered as a master, in the second case the gear is considered as master, and in the third case both sleeve and gear are considered as slaves. In each case, three different operating conditions are studied which are nominal, transmission vibrations, and road grade. The obtained results of biobjective optimization (Pareto fronts, Pareto sets, and corresponding performance diagrams) are analyzed and the most influencing synchronizer parameters have been identified.
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| 33. |
- Irfan, Muhammad, 1986, et al.
(författare)
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VERIFICATION OF A TRANSMISSION SYNCHRONIZATION MODEL
- 2017
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Ingår i: Svenska Mekanikdagarna, Uppsala, 12-13 juni 2017. ; , s. 48-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A computational model of the gearshiftingmechanism may speed up the development of anew gearboxes. However, such model should beverified against other models as well as validatedagainst experiments to ensure reasonableaccuracy. In this contribution, results from the previousdeveloped mathematical model of a genericsynchronizer (gearshifting mechanism) againstthe model developed at Scania is presented. The mathematicalmodel is based on constrained Lagrangianformalism (CLF) and the generic synchronizer isconsist of engaging sleeve, synchronizer ring andthe gearwheel with dimensions relevant to that ofa heavy truck.
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| 34. |
- Johansson, Emil, et al.
(författare)
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Whole-Body Imaging of Tissue-specific Insulin Sensitivity and Body Composition by Using an Integrated PET/MR System: A Feasibility Study
- 2018
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Ingår i: Radiology. - : Radiological Society of North America (RSNA). - 0033-8419 .- 1527-1315. ; 286:1, s. 271-278
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To develop, evaluate, and demonstrate the feasibility of a whole-body protocol for simultaneous assessment of tissue-specific insulin-mediated fluorine 18 (F-18) fluorodeoxyglucose (FDG) influx rates, tissue depots, and whole-body insulin sensitivity (referred to as the M value). Materials and Methods: An integrated positron emission tomography (PET)/magnetic resonance (MR) imaging system combined with hyperinsulinemic euglycemic clamp (HEC) was used. Dynamic whole-body PET imaging was used to determine the insulin-mediated F-18-FDG tissue influx rate (K-i) in the whole-body region by using the Patlak method. M value was determined with the HEC method at PET imaging. Tissue depots were quantified by using water-fat separated MR imaging and manual segmentations. Feasibility of the imaging protocol was demonstrated by using five healthy control participants and five patients with type 2 diabetes. Associations between M value and K-i were studied in multiple tissues by using the Pearson correlation. Results: Positive correlations were found between M value and K-i in multiple tissues: the gluteus muscle (r = 0.875; P = .001), thigh muscle (r = 0.903; P < .001), calf muscle (r = 0.825; P = .003), and abdominal visceral adipose tissue (r = 0.820; P = .004). A negative correlation was found in the brain (r = 0.798; P = .006). The MR imaging-based method for quantification of tissue depots was feasible for determining adipose tissue volumes and fat fractions. Conclusion: This PET/MR imaging protocol may be feasible for simultaneous assessment of tissue-specific insulin-mediated F-18-FDG influx rates, tissue depots, and M value. (C) RSNA, 2017
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| 35. |
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| 36. |
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| 37. |
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| 38. |
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| 39. |
- Johansson, Håkan, 1979
(författare)
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A posteriori error estimation of target control problems: Weak formulation of inequality constraints
- 2013
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Ingår i: 6th International Conference on Adaptive Modeling and Simulation, ADMOS 2013; Lisbon; Portugal; 3 June 2013 through 5 June 2013. ; , s. 362-364
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Konferensbidrag (refereegranskat)abstract
- This contribution considers the steering of movements of a mechanical system from an initial state to a target state (target control). Suitable FE-approximations for the state and control variables are discussed along with a goal-oriented a posteriori estimate of the discretization errors.
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| 40. |
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| 41. |
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| 42. |
- Johansson, Håkan, 1979, et al.
(författare)
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Application-specific error control for parameter identification problems
- 2011
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947. ; 27:4, s. 608-618
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Tidskriftsartikel (refereegranskat)abstract
- An often occurring scenario in the mathematical modeling of physical phenomena is that of a two-step computation consisting of, first, identifying a relevant parameter set from experiments (such as material parameters) and, second, carrying out a subsequent simulation using these parameters. In order to ensure the quality of the results from the simulation, the different sources of errors, for example, from discretization and inexact solution, must be traced and properly reduced. In this paper, a previously developed method for goal-oriented a posteriori error estimation for identification problems is extended to accommodate the combined identification and subsequent simulation. © 2009 John Wiley & Sons, Ltd.
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| 43. |
- Johansson, Håkan, 1979, et al.
(författare)
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Application-Specific Error Control in Inverse Identification
- 2008
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Ingår i: 8th World Concress on Computational Mechanics WCCM8, 5th European Congress on Computational Methods in Applied Sciences and Engineering ECCOMAS 2008 (Edited by B.A. Schrefler and U. Perego). - 9788496736559 ; :CD, s. 1p abstract-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 44. |
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| 45. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a class of non-linear viscoelasticity models with adaptive error control
- 2007
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 41:1, s. 107-119
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of constitutive models is considered as an optimization problem where parameter values are sought to minimize the discrepancy between measured and simulated response. Since a finite element method is used to solve an underlying state equation, discretization errors arise, which induce errors in the calibrated parameter values. In this paper, adaptive mesh refinement based on the pertinent dual solution is used in order to reduce discretization errors in the calibrated material parameters. By a sensitivity assessment, the influence from uncertainties in experimental data is estimated, which serves as a threshold under which there is no need to further reduce the discretization error. The adaptive strategy is employed to calibrate a viscoelasticity model with observed data from uniaxial compression (i.e., homogeneous stress state), where the FE-discretization in time is studied. The a posteriori error estimations show an acceptable quality in terms of effectivity measures. © 2007 Springer Verlag.
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| 46. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a class of non-linear viscoelasticity models with sensitivity assessment based on duality
- 2007
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 69:12, s. 2513-2537
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of constitutive models is based on the solution of an optimization problem, whereby the sought parameter values minimize an objective function that measures the discrepancy between experimental observations and the corresponding simulated response. By the introduction of an appropriate adjoint problem, the resulting formulation becomes well suited for a gradient-based optimization scheme. A class of viscoelastic models is studied, where a discontinuous Galerkin method is used to integrate the governing evolution equation in time. A practical solution algorithm, which utilizes the time-flow structure of the underlying evolution equation, is presented. Based on the proposed formulation it is convenient to estimate the sensitivity of the calibrated parameters with respect to measurement noise. The sensitivity is computed using a dual method, which compares favourably with the conventional primal method. The strategy is applied to a viscoelasticity model using experimental data from a uniaxial compression test. Copyright © 2006 John Wiley & Sons, Ltd.
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| 47. |
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| 48. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a Nonlinear Elastic Composite with Goal-Oriented Error Control Using a Sub-Scale Modeling Approach
- 2004
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Ingår i: Proc. of Second International Conference on Multiscale Materials Modeling, MMM-2, October 11-15, 2004. ; 1:1, s. 466-468
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A recently proposed technique for the calibration of constitutive models is based on the optimization problem expressed such that the state equation is incorporated via an additional costate field. A distinct advantage is that error control is formally straightforward. This technique is applied to calibration of a nonlinear elastic composite using a meso-macro-transition approach, whereby the RVE is analyzed using (in this case) Dirichlet boundary conditions. The numerical results show the effectivity of the error prediction.
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| 49. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a nonlinear viscoelasticity model with sensitivity assessment
- 2005
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Ingår i: Constitutive Models for Rubber IV, edited by P.-E. Austrell & L. Kari. - 0415383463 ; , s. 341-347
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Konferensbidrag (refereegranskat)abstract
- The calibration of constitutive models isbased on the solution of an optimization problem, where parameter values are sought such that optimal correspondence between measured and simulated response is achieved. The calibration problem is solved using a recently proposed strategy, which has the advantage that discretization errors induced in the simulated response, leading to errors in the optimal parameter values, isrelatively straightforward to estimate. Furthermore, it ispossible to estimate how sensitive the obtained solution is to uncertainties in the experimental data.
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| 50. |
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