| 1. |
- Bonitz, Sabine, 1985, et al.
(författare)
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Numerical investigation of crossflow separation on the a-pillar of a passenger car
- 2018
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Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - : ASME International. - 1528-901X .- 0098-2202. ; 140:11
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Tidskriftsartikel (refereegranskat)abstract
- The flow around passenger cars is characterized by many different separation structures, typically leading to vortices and areas of reversed flow. The flow phenomena in these patches show a strong interaction and the evolution of flow structures is difficult to understand from a physical point of view. Analyzing surface properties, such as pressure, vorticity, or shear stress, helps to identify different phenomena, but still it is not well understood how these are created. This paper investigates the crossflow separation (CFS) on the A-pillar of a passenger car using numerical simulations. It is discussed how the CFS and the resulting A-pillar vortex can be identified as well as how it is created. Additionally, the vortex strength is determined by its circulation to understand and discuss how the vortex preserves until it merges with the rear wake of the vehicle.
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| 2. |
- Bonitz, Sabine, 1985, et al.
(författare)
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Unsteady pressure analysis of the near wall flow downstream of the front wheel of a passenger car under yaw conditions
- 2018
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Ingår i: International Journal of Heat and Fluid Flow. - : Elsevier BV. - 0142-727X. ; 73, s. 188-198
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Tidskriftsartikel (refereegranskat)abstract
- The flow around passenger cars is complex and is characterized by many different structures and interactions. The occurring flow phenomena around a car determine crucial vehicle properties such as the driving stability, the noise level, the aerodynamic performance and the vehicle contamination. Therefore, it is of high importance to increase the understanding of the developing flow phenomena. Generic models are widely used to investigate flow structures and their interactions, but cannot serve to derive a general flow field for detailed full-scale vehicle models. A particularly complex area is the flow around the wheels and its interaction with the vehicle geometry. Studies on wheel-wheelhouse flow focus mainly on the geometrical influence of the wheel size, rim and tyre on the aerodynamic drag and the flow field close to the wheel. The present work investigates the flow behind the front wheel arch of a full-scale passenger car. Time resolved surface pressure measurements were taken to study the near wall flow under different yaw conditions. Based on the data obtained, flow structures are identified and their propagation speed is calculated. Further, characteristic frequencies observed are discussed. It is found that coherent structures are present behind the front wheel arch, one above the wheel centre height and one below it. These remain even under large yaw angles, no matter if the vehicle is yawed to lee- or windward. The investigation further shows that two characteristic frequencies can be found, St=0.03 and St=0.2, whereby the latter is caused by the wheel rotation. The same frequencies also occur under yaw conditions, but yawing the measurement area to leeward results in less pronounced frequency peaks.
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| 3. |
- Kounenis, Charlampos, et al.
(författare)
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Investigations of the Rear-End Flow Structures on a Sedan Car
- 2016
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamic drag, fuel consumption and hence CO2 emissions, of a road vehicle depend strongly on its flow structures and the pressure drag generated. The rear end flow which is an area of complex three-dimensional flow structures, contributes to the wake development and the overall aerodynamic performance of the vehicle. This paper seeks to provide improved insight into this flow region to better inform future drag reduction strategies. Using experimental and numerical techniques, two vehicle shapes have been studied; a 30% scale model of a Volvo S60 representing a 2003MY vehicle and a full scale 2010MY S60. First the surface topology of the rear end (rear window and trunk deck) of both configurations is analysed, using paint to visualise the skin friction pattern. By means of critical points, the pattern is characterized and changes are identified studying the location and type of the occurring singularities. The flow field away from the surface is then analysed using PIV measurements and CFD for the scale model and CFD simulations for the full scale vehicle. The flow field is investigated regarding its singular points in cross-planes and the correlation between the patterns for the two geometries is analysed. Furthermore, it is discussed how the occurring structures can be described in more generalized terms to be able to compare different vehicle geometries regarding their flow field properties. The results show the extent to which detailed flow structures on similar but distinct vehicles are comparable; as well as providing insight into the complex 3D wake flow.
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| 4. |
- Källström, Elisabeth, et al.
(författare)
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Analysis of Automatic Transmission Vibration for Clutch Slippage Detection
- 2015
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Ingår i: 22nd International Congress on Sound and Vibration 2015 (ICSV 22). - : Curran Associates, Inc.. - 9781510809031
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Konferensbidrag (refereegranskat)abstract
- Heavy duty construction equipment is generally equipped with automatic transmission enablingto change gear ratio automatically. The clutches in an automatic transmission transfer torquefrom the engine to the gearbox and clutch failures may result in costly downtime of constructionequipment. To prevent costly downtime of construction equipment, condition monitoring in com-bination with condition based maintenance may be utilized. Different sensor data are collectedon a machine that enables condition monitoring. Vibration have been measured on an automatictransmission in a construction equipment machine during controlled driving sessions, with andwithout clutch slippage, on a test track. An initial investigation of the vibration measured on theautomatic transmission have been carried out with the purpose to find out if the vibration maycontain reliable information related to clutch slippage considered to be abnormal. Initial signalanalysis of the data have been carried out using Spectrogram and Spectral Kurtosis methods. Theresults indicate that information related to abnormal clutch slippage may be extracted from vibra-tion measured on an automatic transmission in a construction equipment machine.
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| 5. |
- Källström, Elisabeth, et al.
(författare)
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On-board Clutch Slippage Detection and Diagnosis in Heavy Duty Machine
- 2018
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Ingår i: International Journal of Prognostics and Health Management. - : PHM Society. - 2153-2648. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- In order to reduce unnecessary stops and expensive downtime originating from clutch failure of construction equipment machines; adequate real time sensor data measured on the machinein combination with feature extraction and classification methods may be utilized.This paper, based on a study at Volvo Construction Equipment,presents a framework with feature extraction methods and an anomaly detection module combined with Case-Based Reasoning (CBR) for on-board clutch slippage detection and diagnosis in a heavy duty equipment. The feature extraction methods used are Moving Average Square Value Filtering (MASVF) and a measure of the fourth order statistical properties of the signals implemented as continuous queries over data streams. The anomaly detection module has two components,the Gaussian Mixture Model (GMM) and the Logistics Regression classifier. CBR is a learning approach that classifies faults by creating a new solution for a new fault case from the solution of the previous fault cases. Through use of a data stream management system and continuous queries (CQs), the anomaly detection module continuously waits for a clutch slippage event detected by the feature extraction methods, the query returns a set of features which activates the anomaly detection module. The first component of the anomaly detection module trains a GMM to extracted features while the second component uses a Logistic Regression classifier for classifying normal and anomalous data. When an anomalyis detected, the Case-Based diagnosis module is activated for fault severity estimation.
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| 6. |
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| 7. |
- Rytkönen, Paulina, 1961-, et al.
(författare)
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Utmaningar och möjligheter för små och medelstora företag i Stockholms skärgård
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport syftar till att inventera de utmaningar och möjligheter som företagarna i Stockholms skärgård står inför. Rapporten har skrivits inom ramen för Interreg-projektet Archipelago Business Development och omfattar en inventering av skärgårdsföretagarnas behov, utmaningar och möjligheter i Stockholms skärgård.Undersökningen har bland annat gjorts genom gruppintervjuer med företagare på Dalarö, Ornö, Sandhamn och Utö. Därutöver har enskilda intervjuer genomförts med företagare i fem olika kommuner. Geografiskt fördelas urvalet på Stockholms södra och mellersta skärgård.
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| 8. |
- Xu, Wenqian, 1992-, et al.
(författare)
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Media Representation of Life Stages : Analysis of Photographs Posted on Norrköping Municipal Facebook Accounts
- 2019
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Konferensbidrag (refereegranskat)abstract
- Aim: It has been found by researchers that older adults are statistically underrepresented and associated with negative stereotypes in the mass media. Older adults are generally viewed as incompetent from stereotyped media content, which may make them socially excluded from a set of opportunities and resources. The media portrayals are conceived as value-expressive and constructing the image of older adults and ageing. The purpose of this study is to investigate how Norrköping municipality portrays citizens at different life stages in social media with a special emphasis on the use of age stereotypes in the photos used.Method: The material consists of the photos collected from 32 Facebook accounts produced by municipal bodies during the entire year of 2018. The analysis is based on a categorization of various features of the photos in order to statistically describe the relation between signs, activities and contexts associated with distinct life stages. Further, the meaning of frequently-used symbols in the photographs is analysed.Result: The study concludes that old age persons are numerically underrepresented in the material. A number of signs and activities in the photographs, and contexts beyond the photographs, that stereotypically corresponded to five distinct life stages (infancy, childhood, adolescence, adulthood and old age) are identified. Old age is repetitively portrayed in the context of coffee drinking and foot bathing on Norrköping municipality’s Facebook page, while adolescence is depicted with practical training at high schools to an excessive degree. Besides, the result suggests that certain minorities of citizens did not show up in the municipal social media: people with disabilities, migrants, people with dementia and on forth.Conclusion: The municipality communicates stereotypical images of life stages through associating with specific contexts in the photographic coverage. Therefore, communication professionals need to be aware of the stereotypical construction of life stages in the media.
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