| 1. |
- Wallerstedt, Cecilia, 1976, et al.
(författare)
-
Socioculturally-informed Interaction Analysis (SIA): Methodology and theoretical and empirical contributions of an emerging research program in early childhood education
- 2022
-
Ingår i: International Research in Early Childhood Education. - 1838-0689. ; 12:1, s. 1-23
-
Tidskriftsartikel (refereegranskat)abstract
- Over the last decade, a Swedish research group has conducted several empirical studiesin the field of Early Childhood Education (ECE). These studies are examples of what is sometimes referred to as practice-based studies, and they are often conducted in collaboration with ECE personnel. In this meta-study, we review 37 publications from the research group to highlight key contributions in terms of methodological issues or challenges identified,as well as empirical findings and theoretical developments. We argue that these studies constitute an emerging research program, termed Socioculturally-informed Interaction Analysis(SIA). Key aspects of SIA are:examining learning as a process, using recordings to avoid bias, considering pragmatic validity when working with transcriptions, making claims closely aligned with what is studied (ecological validity), and viewing context as an analytical rather than as a descriptive concept,and generalising at a conceptual level, which affords empirical generalisation.
|
|
| 2. |
- Andersson, Svante, 1962-, et al.
(författare)
-
Sustainable development considerations in supply chains : Firms' relationships with stakeholders in their business sustainability practices—A triangular comparison
- 2022
-
Ingår i: Business Strategy and the Environment. - Oxford : John Wiley & Sons. - 0964-4733 .- 1099-0836. ; 32:4, s. 1885-1899
-
Tidskriftsartikel (refereegranskat)abstract
- This study aims to investigate focal firms' business sustainability relationships in connection with their stakeholders in supply chain networks. A questionnaire survey was sent to a sample consisting of large Swedish firms, with 107 usable questionnaires returned. The results reveal which stakeholders are of interest for firms in sustainability efforts. The results are compared with earlier findings from Norway and Spain in a triangular approach. The former is a similar country, while the latter is different to Sweden in several ways. In addition, the study uncovers which stakeholders in the supply chain network should be considered. The study also demonstrates how firms can implement business sustainability in their supply chain networks and shows the extent to which different stakeholders are considered in sustainability efforts. The study contributes to sustainability research and stakeholder theory in supply chain networks. Opposite to earlier findings, this study showed only minor influences from national culture and institutions on firms' sustainable business practices in supply chain networks. © 2022 The Authors. Business Strategy and The Environment published by ERP Environment and John Wiley & Sons Ltd.
|
|
| 3. |
- Andersson, Svante, 1962-, et al.
(författare)
-
Sustainable development—Direct and indirect effects between economic, social, and environmental dimensions in business practices
- 2022
-
Ingår i: Corporate Social Responsibility and Environmental Management. - Oxford : John Wiley & Sons. - 1535-3958 .- 1535-3966. ; 29:5, s. 1158-1172
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the direct and indirect effects between economic, social and environmental dimensions of triple bottom line (TBL), based on a questionnaire survey and cross-industrial sample in Sweden. The analyses apply partial least squares structural equation models. The study tests the direct and indirect effects between economic, social, and environmental dimensions of TBL and offers additional validity and reliability to establish the measurement and structural properties between the dimensions of TBL. The study extends earlier findings by explicitly discussing how the three TBL goals relate to each other and shows how the dynamic capability view can be a fruitful lens to investigate business sustainability. Some differences in sustainability business practices caused by differences in national cultures are identified. Sustainability reporting in a strong uncertainty avoidance (UA) country happens in accordance with regulations and laws. Conversely, for weak UA cultures, reporting and compliance with regulations are ways to build trust with stakeholders. That is, reporting is more transparent and widespread in weak UA countries. The study also provides a foundation to guide companies' actions of business sustainability. The model shows companies how to establish the order of actions undertaken across economic, social, and environmental dimensions. In addition, it clarifies that the economic dimension exerts an effect on the social and environmental dimensions. The model also grasps long-term economic performance by including competitiveness and brand value, while earlier research mainly has focused on more short-term measurements as return on assets. © 2022 The Authors. Corporate Social Responsibility and Environmental Management published by ERP Environment and John Wiley & Sons Ltd.
|
|
| 4. |
- Barregård, Lars, 1948, et al.
(författare)
-
Cadmium Exposure and Coronary Artery Atherosclerosis: A Cross-Sectional Population-Based Study of Swedish Middle-Aged Adults
- 2021
-
Ingår i: Environmental health perspectives. - 1552-9924 .- 0091-6765. ; 129:6
-
Tidskriftsartikel (refereegranskat)abstract
- The general population is ubiquitously exposed to the toxic metal cadmium through the diet and smoking. Cadmium exposure is associated with increased morbidity and mortality in myocardial infarction and stroke. Atherosclerosis is the main underlying mechanism of myocardial infarction. However, associations between cadmium and coronary artery atherosclerosis have not been examined.Our study sought to examine the hypothesis that blood cadmium (B-Cd) is positively associated with coronary artery calcification, as a measure of coronary artery atherosclerosis in the population-based Swedish SCAPIS study.Our analysis included 5,627 individuals (51% women), age 50-64 y, enrolled from 2013 to 2018. The coronary artery calcium score (CACS) was obtained from computed tomography. Blood cadmium was determined by inductively coupled plasma mass spectrometry (ICP-MS). Associations between B-Cd and coronary artery calcium score (CACS Agatston score) were evaluated using prevalence ratios (PRs) in models adjusted for sex, age, smoking, hypertension, diabetes, low-density cholesterol/high-density cholesterol ratio, and family history.The median B-Cd concentration was 0.24 μ g / L . The prevalence of positive coronary artery calcium ( CACS > 0 ) was 41% and the prevalence of CACS ≥ 100 was 13%. Relative to the lowest quartile (Q) of B-Cd ( < 0.16 μ g / L ), the highest quartile (median 0.63 μ g / L ) was associated with a small but significant increase in CACS > 0 (PR 1.1; 95% CI: 1.0, 1.3), and a greater relative increase in CACS ≥ 100 (PR 1.6; 95% CI: 1.3, 2.0). When restricted to 2,446 never-smokers, corresponding PRs were 1.1 (95% CI 0.9, 1.3) for CACS > 0 (63 cases in Q4) and 1.7 (95% CI 1.1, 2.7) for CACS ≥ 100 (17 cases in Q4).Blood cadmium in the highest quartile was associated with CACS in a general population sample with low to moderate cadmium exposure. This supports the hypothesis that atherosclerosis is an important mechanism underlying the associations between cadmium and incident cardiovascular disease. The findings suggest that public health measures to reduce cadmium exposure are warranted. https://doi.org/10.1289/EHP8523.
|
|
| 5. |
- Bremer, Johan, 1991, et al.
(författare)
-
Electric-Based Thermal Characterization of GaN Technologies Affected by Trapping Effects
- 2020
-
Ingår i: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 67:5, s. 1952-1958
-
Tidskriftsartikel (refereegranskat)abstract
- This article presents an electric-based methodology for thermal characterization of semiconductor technologies. It is shown that for technologies such as gallium nitride (GaN) high electron mobility transistors, which exhibit several field induced electron trapping effects, the thermal characterization has to be performed under specific conditions. The electric field is limited to low levels to avoid activation of trap states. At the same time, the dissipated power needs to be high enough to change the operating temperature of the device. The method is demonstrated on a test structure implemented as a GaN resistor with large contact separation. It is used to evaluate the thermal properties of samples with different silicon carbide suppliers and buffer thickness.
|
|
| 6. |
- Cheregi, Otilia, et al.
(författare)
-
Transcriptome analysis reveals insights into adaptive responses of two marine microalgae species to Nordic seasons
- 2023
-
Ingår i: Algal Research. - 2211-9264. ; 74
-
Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in algae-based biomass produced outdoors in natural and industrial settings for biotechnological applications. To predict the yield and biochemical composition of the biomass, it is important to understand how the transcriptome of species and strains of interest is affected by seasonal changes. Here we studied the effects of Nordic winter and summer on the transcriptome of two phytoplankton species, namely the diatom Skeletonema marinoi (Sm) and the eustigmatophyte Nannochloropsis granulata (Ng), recently identified as potentially important for biomass production on the west coast of Sweden. Cultures were grown in photobioreactors in simulated Nordic summer and winter, and the gene expression in two phases was quantified by Illumina RNA-sequencing. Five paired comparisons were made among the four conditions. Sm was overall more responsive to seasons since 70 % of the total transcriptome (14,783 genes) showed differential expression in at least one comparison as compared to 1.6 % (1403 genes) for Ng. For both species, we observed larger differences between the seasons than between the phases of the same season. In summer phase 1, Sm cells focused on photosynthesis and polysaccharide biosynthesis. Nitrate assimilation and recycling of intracellular nitrogen for protein biosynthesis were more active in summer phase 2 and throughout winter. Lipid catabolism was upregulated in winter relative to summer to supply carbon for respiration. Ng favored lipid accumulation in summer, while in winter activated different lipid remodeling pathways as compared to Sm. To cope with winter, Ng upregulated breakdown and transport of carbohydrates for energy production. Taken together, our transcriptome data reveal insights into adaptive seasonal responses of Sm and Ng important for biotechnological applications on the west coast of Sweden, but more work is required to decipher the molecular mechanisms behind these responses.
|
|
| 7. |
- Costa, Fabíola Paula, et al.
(författare)
-
Aerodynamic Analysis of Conventional and Boundary Layer Ingesting Propellers
- 2023
-
Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 145:1
-
Tidskriftsartikel (refereegranskat)abstract
- The boundary layer ingestion (BLI) concept has emerged as a novel technology for reducing aircraft fuel consumption. Several studies designed BLI-fans for aircraft. BLI-propellers, although, have still received little attention, and the choice of open-rotors or ducted propellers is still an open question regarding the best performance. The blade design is also challenging because the BLI-propulsors ingest a nonuniform flow. These aspects emphasize further investigation of unducted and ducted BLI-propulsors and the use of optimization frameworks, coupled with computational fluid dynamics simulations, to design the propeller to adapt to the incoming flow. This paper uses a multi-objective NSGA-II optimization framework, coupled with three-dimensional RANS simulations and radial basis function (RBF) metamodeling, used for the design and optimization of three propeller configurations at cruise conditions: (a) conventional propeller operating in the freestream, (b) unducted BLI-propeller, and (c) ducted BLI-propeller, both ingesting the airframe boundary layer. The optimization results showed a significant increase in chord and a decrease in the blade angles in the BLI configurations, emphasizing that these geometric parameters optimization highly affects the BLI-blade design. The unducted BLI-propeller needs approximately 40% less shaft power than the conventional propeller to generate the same amount of propeller force. The ducted BLI-propeller needs even less power, 47%. The duct contributes to the tip vortex weakening, recovering the swirl, and turning into propeller force, as noticed from 80% of the blade span to the tip. However, the unducted and ducted BLI-configurations presented a higher backward force, 26% and 46%, respectively, compared to the conventional propeller, which can be detrimental and narrow the use of these configurations.
|
|
| 8. |
- Costa, Fabíola Paula, et al.
(författare)
-
Coupled unsteady RANS and FW-H methodology for aeroacoustics prediction of high-speed propellers
- 2022
-
Ingår i: 28th AIAA/CEAS Aeroacoustics Conference, 2022. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- This work investigates the use of solid and permeable surfaces in the Ffowcs WilliamsHawkings (FW-H) analogy for predicting high-speed propeller noise. The CFD/CAA methodology encompasses unsteady Reynolds-Averaged Navier-Stokes simulations to compute the flowfield on the acoustic surface applied in the FWH analogy to obtain the noise signatures in the far-field. Furthermore, this manuscript also investigates the effects of the downstream end-cap position, on the propeller noise prediction, by using two permeable surfaces with different lengths to assess the propeller noise levels in each case. The former is a short SFW-H surface placed near the rotor, and the latter, namely the LFW-H, is a surface larger in length where the end-cap grid is placed farther downstream from the rotor. The results showed the capability of the permeable surface technique for predicting the noise with higher accuracy than the solid formulation, especially at the first blade passing frequency. Also, the larger LFW-H surface performed better than the SFW-H surface. A reason that could justify this is that the LFW-H end-cap surface is placed at a suitable distance downstream from the propeller. Therefore, the LFW-H surface can include more of the contributions of the non-linear effects or quadrupole sources enclosed within the permeable source surface region.
|
|
| 9. |
- Flyckt, Jonatan, et al.
(författare)
-
Detecting ditches using supervised learning on high-resolution digital elevation models
- 2022
-
Ingår i: Expert systems with applications. - : Elsevier Ltd. - 0957-4174 .- 1873-6793. ; 201
-
Tidskriftsartikel (refereegranskat)abstract
- Drained wetlands can constitute a large source of greenhouse gas emissions, but the drainage networks in these wetlands are largely unmapped, and better maps are needed to aid in forest production and to better understand the climate consequences. We develop a method for detecting ditches in high resolution digital elevation models derived from LiDAR scans. Thresholding methods using digital terrain indices can be used to detect ditches. However, a single threshold generally does not capture the variability in the landscape, and generates many false positives and negatives. We hypothesise that, by combining the digital terrain indices using supervised learning, we can improve ditch detection at a landscape-scale. In addition to digital terrain indices, additional features are generated by transforming the data to include neighbouring cells for better ditch predictions. A Random Forests classifier is used to locate the ditches, and its probability output is processed to remove noise, and binarised to produce the final ditch prediction. The confidence interval for the Cohen's Kappa index ranges [0.655, 0.781] between the evaluation plots with a confidence level of 95%. The study demonstrates that combining information from a suite of digital terrain indices using machine learning provides an effective technique for automatic ditch detection at a landscape-scale, aiding in both practical forest management and in combatting climate change. © 2022 The Authors
|
|
| 10. |
- Flyckt, Jonatan, et al.
(författare)
-
Explaining rifle shooting factors through multi-sensor body tracking
- 2023
-
Ingår i: Intelligent Data Analysis. - : IOS Press. - 1088-467X .- 1571-4128. ; 27:2, s. 535-554
-
Tidskriftsartikel (refereegranskat)abstract
- There is a lack of data-driven training instructions for sports shooters, as instruction has commonly been based on subjective assessments. Many studies have correlated body posture and balance to shooting performance in rifle shooting tasks, but have mostly focused on single aspects of postural control. This study has focused on finding relevant rifle shooting factors by examining the entire body over sequences of time. A data collection was performed with 13 human participants carrying out live rifle shooting scenarios while being recorded with multiple body tracking sensors. A pre-processing pipeline produced a novel skeleton sequence representation, which was used to train a transformer model. The predictions from this model could be explained on a per sample basis using the attention mechanism, and visualised in an interactive format for humans to interpret. It was possible to separate the different phases of a shooting scenario from body posture with a high classification accuracy (80%). Shooting performance could be detected to an extent by separating participants using their strong and weak shooting hand. The dataset and pre-processing pipeline, as well as the techniques for generating explainable predictions presented in this study have laid the groundwork for future research in the sports shooting domain.
|
|
| 11. |
- Ghosh, Debarshee, 1995, et al.
(författare)
-
Aerodynamic Analysis of Low-Pressure Axial Fans Installed in Parallel
- 2024
-
Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - 1528-901X .- 0098-2202. ; 146:5
-
Tidskriftsartikel (refereegranskat)abstract
- Ducted rotor-only low-pressure axial fans play an integral role in automotive thermal management. The tightly packed under-hood region and down-stream heat-exchanger shape limit the fan diameter. In order to circumvent this limitation, multiple cooling fans of small diameters are tightly packaged and placed in parallel. Currently, there is limited scientific work, that study the aerodynamics of low-pressure axial fans when installed in parallel. This work aims to quantify the aerodynamic performance and the flow-field as a result of installing low-pressure axial fans in parallel through computational fluid dynamics (CFD). Publicly available experimental data from Friedrich-Alexander University is used for the validation of the numerical setup. Three-dimensional, full-annulus, unsteady Reynolds-averaged Navier‐Stokes (URANS) analysis has been performed for both a single-fan and two-fans installed in parallel and their respective aerodynamic performance has been compared for the operation condition identified as the best efficiency point in experiments. Only small differences are observed in the overall aerodynamic performance of the two-fans in parallel compared to a single-fan. A circumferential nonuniformity in the form of a local high-pressure zone at the inlet of the fan is observed when the two-fans are placed in parallel. The resulting circumferential nonuniformity is quantified, both in space and time. A strong correlation is found between the pressure fields of the two-fans installed in parallel.
|
|
| 12. |
- Ghosh, Debarshee, 1995, et al.
(författare)
-
Computational Fluid Dynamics Simulations of Aerodynamic Performance of Low-Pressure Axial Fans with Upstream Blockage
- 2024
-
Ingår i: SAE Technical Papers. - 0148-7191 .- 2688-3627.
-
Konferensbidrag (refereegranskat)abstract
- Rotor-only ducted low-pressure axial fans play a crucial role in automotive thermal management of the tightly packed under-hood region. Most current scientific work concerning low-pressure axial fans investigate the aerodynamic performance of these fans while operating with uniform inlet flow conditions. This is rarely the case in real-world applications. This work aims to investigate the aerodynamic performance of low-pressure axial fans operating with upstream blockages. First, a validation study is performed in the absence of any upstream blockage. Numerical results are compared against publicly available experimental data. Steady-state, Reynolds-Averaged Navier Stokes (RANS) analysis is performed on a single-blade passage. The validation study also evaluates the choice of turbulence model and suggests the use of the k- ε turbulence model with wall functions for the best comparison against experimental data. To study the effect of upstream blockage, a generic blockage disc is positioned upstream of the fan inlet. Three different radial extents of the blockage disc is evaluated, such that different radial extents of the blade span is blocked. A strong influence of the upstream blockage is observed on the fan performance and flow distribution along the blade span. The total-to-static pressure coefficient and the total-to-static efficiency decrease proportionately to the extent of blockage in the radial direction. The peak total-to-static efficiency moves to a lower flow coefficient with increase in upstream flow blockage. This is deemed undesirable for automotive applications where it is desirable to have maximum aerodynamic efficiency at the highest possible flow coefficient.
|
|
| 13. |
- Lejon, Marcus, 1986, et al.
(författare)
-
The Impact of Manufacturing Variations on Performance of a Transonic Axial Compressor Rotor
- 2020
-
Ingår i: Journal of Turbomachinery. - : ASME International. - 1528-8900 .- 0889-504X. ; 142:8
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the impact of manufacturing variations on performance of an axial compressor rotor is evaluated at design rotational speed. The geometric variations from the design intent obtained from measurements were used to evaluate the impact of manufacturing variations on performance and the flow field in the rotor. The complete blisk is simulated using 3D computational fluid dynamics calculations, allowing for a detailed analysis of the impact of geometric variations on the flow. It is shown that the mean shift of the geometry from the design intent is responsible for the majority of the change in performance in terms of mass flow and total pressure ratio for this specific blisk. In terms of polytropic efficiency, the measured geometric scatter is shown to have a higher influence than the geometric mean deviation. The geometric scatter around the mean is shown to impact the pressure along the leading edge and the shock position. Furthermore, a blisk is analyzed with one blade deviating substantially from the design intent. It is shown that the impact of this blade on the flow is largely limited to the blade passages that it is directly a part of. It is also shown that the impact of this blade on the flow field can be represented by a simulation including three blade passages. In terms of loss, using five blade passages is shown to give a close estimate for the relative change in loss for the blade deviating substantially from the design intent and for the neighboring blades.
|
|
| 14. |
- Lindblad, Daniel, 1989, et al.
(författare)
-
Convergence Acceleration of the Harmonic Balance Method using a Time-Level Preconditioner
- 2020
-
Ingår i: AIAA Scitech 2020 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105951 ; 3
-
Konferensbidrag (refereegranskat)abstract
- The Harmonic Balance method is nowadays widely applied for numerically solving problems that are known to possess time-periodic solutions. Key reasons for its success are its wide range of applicability, relative ease of implementation, and computational efficiency compared to time-accurate approaches. The computational efficiency of the Harmonic Balance method is partly derived from the fact that it searches directly for a periodic solution, instead of integrating the governing equations in time until a periodic solution is reached. Convergence acceleration techniques such as multigrid, implicit residual smoothing and local time stepping may also be used to improve the efficiency of the Harmonic Balance method. This paper considers another option for accelerating convergence, namely a novel time-level preconditioner that can be applied to the Harmonic Balance residual locally in each computational cell. This preconditioner is derived from a rigorous stability analysis of the Harmonic Balance equations and is shown to give a speed-up factor of 2 when applied to simulations of laminar vortex shedding behind a circular cylinder.
|
|
| 15. |
- Lindblad, Daniel, 1989, et al.
(författare)
-
Convergence Acceleration of the Harmonic Balance Method using a Time-Level Preconditioner
- 2020
-
Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 58:11, s. 4908-4922
-
Tidskriftsartikel (refereegranskat)abstract
- The harmonic balance method is nowadays widely applied for numerically solving problems that are known to possess time-periodic solutions. Key reasons for its success are its wide range of applicability, relative ease of implementation, and computational efficiency compared to time-accurate approaches. The computational efficiency of the harmonic balance method is partly derived from the fact that it searches directly for a periodic solution instead of integrating the governing equations in time until a periodic solution is reached. Convergence acceleration techniques such as multigrid, implicit residual smoothing, and local time stepping may also be used to improve the efficiency of the harmonic balance method. This paper considers another option for accelerating convergence, namely, a novel time-level preconditioner that can be applied to the harmonic balance residual locally in each computational cell. The benefit of employing this preconditioner is analyzed both from a theoretical perspective, by performing a rigorous stability analysis based on the linearized Euler equations, and from a numerical perspective, by applying it to two test cases.
|
|
| 16. |
- Lindblad, Daniel, 1989, et al.
(författare)
-
Minimizing Aliasing in Multiple Frequency Harmonic Balance Computations
- 2022
-
Ingår i: Journal of Scientific Computing. - : Springer Science and Business Media LLC. - 0885-7474 .- 1573-7691. ; 91:2
-
Tidskriftsartikel (refereegranskat)abstract
- The harmonic balance method has emerged as an efficient and accurate approach for computing periodic, as well as almost periodic, solutions to nonlinear ordinary differential equations. The accuracy of the harmonic balance method can however be negatively impacted by aliasing. Aliasing occurs because Fourier coefficients of nonlinear terms in the governing equations are approximated by a discrete Fourier transform (DFT). Understanding how aliasing occurs when the DFT is applied is therefore essential in improving the accuracy of the harmonic balance method. In this work, a new operator that describe the fold-back, i.e. aliasing, of unresolved frequencies onto the resolved ones is developed. The norm of this operator is then used as a metric for investigating how the time sampling should be performed to minimize aliasing. It is found that a time sampling which minimizes the condition number of the DFT matrix is the best choice in this regard, both for single and multiple frequency problems. These findings are also verified for the Duffing oscillator. Finally, a strategy for oversampling multiple frequency harmonic balance computations is developed and tested.
|
|
| 17. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
An aeroacoustic study of the flow surrounding the front of a simplified ICE3 high-speed train model
- 2020
-
Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 160
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical study using IDDES is carried out to investigate the aerodynamic and the aeroacoustic response of a simplified ICE3 high-speed train model. The work focuses on the front part of the train and, in particular, on the first bogie cavity. The choice is justified by a literature survey which shows that this part of the train is the principal contributor of critical noise pollution created at pass-by in populated areas. Detailed CFD can provide useful insight and be of great importance in the identification of noise generation mechanisms and their relation with the flow structures. Results show the formation of two main aerodynamic structures with a clear relation to the aeroacoustic response calculated on the train and ground surfaces. Simulations were made at Re=1.8×105 and M=0.058 to match the experimental observations found in literature and generate a set of benchmark data for future investigations.
|
|
| 18. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Using horizontal sonic crystals to reduce the aeroacosutic signature of a simplified ICE3 train model
- 2021
-
Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 172
-
Tidskriftsartikel (refereegranskat)abstract
- The design of noise barriers for high-speed trains is challenging due to the flow interaction between the train body and barriers. A failed design could affect the flow that in turn introduces additional aerodynamic loads to the train and generates extra noise. This study is the first investigation to numerically explore the detailed effects of noise barriers on high-speed trains. In particular, horizontal sonic crystals are compared to vertical, closed at the ground barriers in order to investigate the detailed effects of different noise screens on high-speed trains. The compressible IDDES is used to simulate the flow. The focus of this study is twofold. The first is to test if an alternative barrier typology can effectively reduce the noise signature, without having an impact on the train’s aerodynamic performance. The second is to explore the connection between the near-field velocity fluctuations and the far-field noise. A few specific tonal frequency components have been commonly reported but not clearly explained in the literature. It is unclear if the specific tonal components are less dependent on the Reynolds numbers, although, in general, energetic flow structures are dependent on inflow speeds. Concerning the noise reduction, the results show that the sonic crystal barrier case has a significantly better performance. A modal analysis is used to explore the causes of the tonal peaks and the association of the underbody swirling vortices to the far-field noise is described.
|
|
| 19. |
- Montero Villar, Gonzalo, 1992, et al.
(författare)
-
Investigation of Phase-Lagged Boundary Conditions for Turbulence Resolving Turbomachinery Simulations
- 2020
-
Ingår i: AIAA AVIATION 2020 FORUM. - Reston, Virginia : American Institute of Aeronautics and Astronautics. ; 1
-
Konferensbidrag (refereegranskat)abstract
- The present work explores whether phase-lagged boundary conditions can be used to perform scale resolving simulations of turbomachines. The phase-lagged approach considered is based on storing the flow signal, both at the pitch-wise boundaries and the rotor-stator interface, as its temporal Fourier coefficients for a finite number of harmonics. The method is implemented in an in-house CFD solver, G3D::Flow, which can perform both URANS and hybrid RANS/LES simulations. In order to evaluate the performance of the phase-lagged boundary condition, a comparison is made with a sliding mesh simulation on a compressor cascade. Furthermore, the possibility of breaking an error feedback loop generated in the sampling process by including multiple blade passages is also investigated. It is found that this approach greatly improves convergence and accuracy of the sampling.
|
|
| 20. |
- Peretz-Andersson, Einav, et al.
(författare)
-
AI Transformation in the Public Sector : Ongoing Research
- 2021
-
Ingår i: 33rd Workshop of the Swedish Artificial Intelligence Society, SAIS 2021. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665442367 ; , s. 33-36
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Real-world application of data-driven and intelligent systems (AI) is increasing in the private and public sector as well as in society at large. Many organizations transform as a consequence of increased AI implementation. The consequences of such transformations may include new recruitment plans, procurement of additional IT, changes in existing positions and roles, new business models, as well as new policies and regulations. However, it is unclear how this transformation varies across different types of organizations. We study the effects of bottom-up approaches, such as pilot projects and mentoring to specific groups within organizations, and aim to explore how such approaches can complement the top-down approach of strategic AI implementation. Our context is the public sector. Our goal is to acquire an improved understanding of how and when AI transformation occurs in the public sector, which are the consequences, and which strategies are fruitful or detrimental to the organization. We aim to study public sector organizations in Sweden, Norway, New Zealand, Germany, and The Netherlands to learn about potential similarities and differences with regard to AI transformation.
|
|
| 21. |
|
|
| 22. |
- Siggeirsson, Elias, 1989, et al.
(författare)
-
Numerical and experimental aerodynamic investigation of an s-shaped intermediate compressor duct with bleed
- 2020
-
Ingår i: Proceedings of the ASME Turbo Expo. ; 2D-2020
-
Konferensbidrag (refereegranskat)abstract
- A series of CFD simulations are performed to analyse the effects a rotor off-take bleed has on the performance of an Intermediate Compressor Duct (ICD). To validate the CFD results, a comparison is made to measurements obtained from an experimental facility located at GKN Aerospace Engine Systems in Sweden. To achieve a deeper understanding of the flow physics, hybrid RANS/LES simulations are performed for a single operating condition. The CFD simulations are capable of predicting the behavior when extracting large amount of air through the bleed pipe, where an improved prediction is obtained with the hybrid simulation. The performance of the ICD is severely compromised with increased amount of bleed as the flow delivered to the downstream component is highly disturbed. The disturbed flow is caused by the extraction of axial flow through the bleed pipe, increasing the incidence into the low-pressure compressor’s outlet guide vanes resulting in unfavorable velocity profiles into the ICD. This behavior causes the flow to separate at the OGV blades, where the separation increases with increase bleed. Furthermore, when including the full bleed system, significant circumferential distortions are observed, showing the necessity of the integrated design.
|
|
| 23. |
- Siggeirsson, Elias, 1989, et al.
(författare)
-
Numerical and Experimental Aerodynamic Investigation of an S-Shaped Intermediate Compressor Duct with Bleed
- 2021
-
Ingår i: Journal of Turbomachinery. - : ASME International. - 1528-8900 .- 0889-504X. ; 143:10
-
Tidskriftsartikel (refereegranskat)abstract
- A series of computational fluid dynamics (CFD) simulations are performed to analyze the effects a rotor off-take bleed has on the performance of an intermediate compressor duct (ICD). To validate the CFD results, a comparison is made to measurements obtained from an experimental facility located at GKN Aerospace Engine Systems in Sweden. To achieve a deeper understanding of the flow physics, hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) simulations are performed for a single operating condition. The CFD simulations are capable of predicting the behavior when extracting large amount of air through the bleed pipe, where an improved prediction is obtained with the hybrid simulation. The performance of the ICD is severely compromised with increased amount of bleed as the flow delivered to the downstream component is highly disturbed. The disturbed flow is caused by the extraction of axial flow through the bleed pipe, increasing the incidence into the low-pressure compressor's outlet guide vanes (OGVs) resulting in unfavorable velocity profiles into the ICD. This behavior causes the flow to separate at the OGV blades, where the separation increases with increasing bleed. Furthermore, when including the full bleed system, significant circumferential distortions are observed, showing the necessity of the integrated design.
|
|
| 24. |
- Siggeirsson, Elias, 1989, et al.
(författare)
-
Off design simulations of an S-shaped intermediate compressor duct: Experimental validation of DDES and RANS using G3D::Flow
- 2020
-
Ingår i: AIAA Scitech 2020 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics. ; 1:PartF
-
Konferensbidrag (refereegranskat)abstract
- A comparison is made between measurements obtained in an experimental test rig at GKN Aerospace and simulations using the CFD solver G3D::Flow, developed and maintained at Chalmers University of Technology. The geometry represents an Intermediate Compressor Duct (ICD) of an aircraft engine. The aim is to validate the different CFD turbulence closure techniques with experimental data and to compare the CFD methods with each other. The turbulence techniques used are RANS, Unsteady-RANS (URANS) and Delayed-Detached Eddy-Simulation (DDES) models. The one-equation turbulence model, developed by Spalart and Allmaras, is used as the main model for the (U)RANS simulations and as the sub-grid-scale model for the DDES. To save computational resources, wall-functions are used to model the boundary layers. Overall, the CFD simulations are in a good agreement with the measured data, where some differences are observed when considering radial profiles of total pressure, downstream of the ICD. Furthermore, there are instabilities present in the DDES simulations at the inner wall of the ICD. Large instabilities were also observed in the experiments, represented by relatively large uncertainties. This behavior was not captured by the (U)RANS simulations. Additionally, the instantaneous DDES is capable of representing the true flow much better (if sufficiently small scales are resolved), where the (U)RANS results will never exist in reality, limiting the information acquired.
|
|
