| 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. |
- 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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| 3. |
- 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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| 4. |
- 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
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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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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| 5. |
- 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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| 6. |
- Lind, Lars, et al.
(författare)
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Comparison of four non-alcoholic fatty liver disease detection scores in a Caucasian population
- 2020
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Ingår i: World Journal of Hepatology. - : Baishideng Publishing Group Inc.. - 1948-5182. ; 12:4, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUNDNon-alcoholic fatty liver disease (NAFLD) is a common disorder, with an estimated prevalence ranging from 20% to 35% in the general population. Several scores based on easily measurable biochemical and clinical parameters, including the fatty liver index (FLI), hepatic steatosis index (HSI), lipid accumulation product (LAP), and NAFLD liver fat score (LFS), have been developed for the detection of NAFLD. However, comparative information regarding the efficacy of these scores for predicting NAFLD in population-based samples comprising normal and high-risk individuals is lacking.AIMTo evaluate four NAFLD detection scores in two samples with different NAFLD risks.METHODSNAFLD screening was performed in a population-based sample of 50-year-old individuals in Uppsala, Sweden [n = 310; Prospective investigation of obesity, energy and metabolism (POEM) study] and a high-risk population comprising patients with a body mass index > 25 kg/m2 and either high plasma triglycerides (≥ 1.7 mmol/L) or type 2 diabetes (n = 310; EFFECT studies). NAFLD was defined as liver fat > 5.5% using magnetic resonance imaging-proton density fat fraction. FLI, HSI, LAP, and NAFLD LFS were assessed. A logistic regression model was used to evaluate the effectiveness of the different scores.RESULTSThe prevalence of NAFLD was 23% in POEM. FLI showed the highest receiver operating characteristic area under the curve (ROC AUC; 0.82) and was significantly better than the LAP score (P = 0.005 vs LAP, P = 0.08 vs LFS, P = 0.12 vs HSI) for detection of NAFLD. The other three indices performed equally in POEM (0.77-0.78). The prevalence of NAFLD was 74% in EFFECT; LFS performed best (ROC AUC 0.80) in this sample. The ROC AUC for LFS (0.80) was significantly higher than that for FLI (P = 0.0019) and LAP (P = 0.0022), but not HSI (P = 0.11). We performed a sensitivity analysis with stratification for the two high-risk subgroups (patients with diabetes or hypertriglyceridemia) from the EFFECT studies. LAP performed best in patients with hypertriglyceridemia. No major differences were observed between the other scores.CONCLUSIONThe four investigated NAFLD scores performed differently in the populationbased vs high-risk setting. FLI was preferable in the population-based setting, while LFS performed best in the high-risk setting.
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| 7. |
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| 8. |
- Lind, Lars, et al.
(författare)
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The Plasma Metabolomic Profile is Differently Associated with Liver Fat, Visceral Adipose Tissue, and Pancreatic Fat
- 2021
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - : Lippincott Williams & Wilkins. - 0021-972X .- 1945-7197. ; 106:1, s. e118-e129
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Tidskriftsartikel (refereegranskat)abstract
- CONTEXT: Metabolic differences between ectopic fat depots may provide novel insights to obesity-related diseases.OBJECTIVE: To investigate the plasma metabolomic profiles in relation to visceral adipose tissue (VAT) volume and liver and pancreas fat percentages.DESIGN: Cross-sectional.SETTING: Multicenter at academic research laboratories.PATIENTS: Magnetic resonance imaging (MRI) was used to assess VAT volume, the percentage of fat in the liver and pancreas (proton density fat fraction [PDFF]) at baseline in 310 individuals with a body mass index ≥ 25 kg/m2 and with serum triglycerides ≥ 1.7 mmol/l and/or type 2 diabetes screened for inclusion in the 2 effect of omega-3 carboxylic acid on liver fat content studies.INTERVENTION: None.MAIN OUTCOME MEASURE: Metabolomic profiling with mass spectroscopy enabled the determination of 1063 plasma metabolites.RESULTS: Thirty metabolites were associated with VAT volume, 31 with liver PDFF, and 2 with pancreas PDFF when adjusting for age, sex, total body fat mass, and fasting glucose. Liver PDFF and VAT shared 4 metabolites, while the 2 metabolites related to pancreas PDFF were unique. The top metabolites associated with liver PDFF were palmitoyl-palmitoleoyl-GPC (16:0/16:1), dihydrosphingomyelin (d18:0/22:0), and betaine. The addition of these metabolites to the Liver Fat Score improved C-statistics significantly (from 0.776 to 0.861, P = 0.0004), regarding discrimination of liver steatosis.CONCLUSION: Liver PDFF and VAT adipose tissue shared several metabolic associations, while those were not shared with pancreatic PDFF, indicating partly distinct metabolic profiles associated with different ectopic fat depots. The addition of 3 metabolites to the Liver Fat Score improved the prediction of liver steatosis.
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| 9. |
- Mandalenakis, Zacharias, 1979, et al.
(författare)
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Survival in Children With Congenital Heart Disease: Have We Reached a Peak at 97%?
- 2020
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Ingår i: Journal of the American Heart Association. - 2047-9980. ; 9:22
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Tidskriftsartikel (refereegranskat)abstract
- Background Despite advances in pediatric health care over recent decades, it is not clear whether survival in children with congenital heart disease (CHD) is still increasing. Methods and Results We identified all patients with CHD using nationwide Swedish health registries for 1980 to 2017. We examined the survival trends in children with CHD; we investigated the mortality risk in patients with CHD compared with matched controls without CHD from the general population using Cox proportional regression models and Kaplan-Meier survival analysis. Among 64396 patients with CHD and 639012 matched controls without CHD, 3845 (6.0%) and 2235 (0.3%) died, respectively. The mean study follow-up (SD) was 11.4 (6.3) years in patients with CHD. The mortality risk was 17.7 (95% CI, 16.8-18.6) times higher in children with CHD compared with controls. The highest mortality risk was found during the first 4years of life in patients with CHD (hazard ratio [HR], 19.6; 95% CI, 18.5-20.7). When stratified by lesion group, patients with non-conotruncal defects had the highest risk (HR, 97.2; 95% CI, 80.4-117.4). Survival increased substantially according to birth decades, but with no improvement after the turn of the century where survivorship reached 97% in children with CHD born in 2010 to 2017. Conclusions Survival in children with CHD has increased substantially since the 1980s; however, no significant improvement has been observed this century. Currently, >97% of children with CHD can be expected to reach adulthood highlighting the need of life-time management.
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| 10. |
- Milosevic, Marko, 1991, et al.
(författare)
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Condition Monitoring of Railway Crossing Geometry via Measured and Simulated Track Responses
- 2022
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 22:3
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents methods for continuous condition monitoring of railway switches and crossings (S&C, turnout) via sleeper-mounted accelerometers at the crossing transition. The methods are developed from concurrently measured sleeper accelerations and scanned crossing geometries from six in situ crossing panels. These measurements combined with a multi-body simulation (MBS) model with a structural track model and implemented scanned crossing geometries are used to derive the link between the crossing geometry condition and the resulting track excitation. From this analysis, a crossing condition indicator Cλ1-λ2,γ is proposed. The indicator is defined as the root mean square (RMS) of a track response signal γ that has been band-passed between frequencies corresponding to track deformation wavelength bounds of λ1 and λ2 for the vehicle passing speed (f = v/ λ). In this way, the indicator ignores the quasi-static track response with wavelengths pre-dominantly above λ1 and targets the dynamic track response caused by the kinematic wheel-cross-ing interaction governed by the crossing geometry. For the studied crossing panels, the indicator C1-0.2 m,γ (λ1 = 1 and λ2 = 0.2) was evaluated for γ = u, v, or a as in displacements, velocities, and accelerations, respectively. It is shown that this condition indicator has a strong correlation with vertical wheel–rail contact forces that is sustained for various track conditions. Further, model calibrations were performed to measured sleeper displacements for the six investigated crossing panels. The calibrated models show (1) a good agreement between measured and simulated sleeper displacements for the lower frequency quasi-static track response and (2) improved agreement for the dynamic track response at higher frequencies. The calibration also improved the agreement between measurements and simulation for the crossing condition indicator demonstrating the value of model calibration for condition monitoring purposes.
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