| 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
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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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| 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
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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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