| 1. |
- Ou, Tinghai, et al.
(författare)
-
Changes in winter cold surges over Southeast China: 1961 to 2012
- 2015
-
Ingår i: Asia-Pacific Journal of Atmospheric Sciences. - : Springer Science and Business Media LLC. - 1976-7633 .- 1976-7951. ; 51:1, s. 29-37
-
Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the overall changes in occurrences of winter cold surges over Southeast China for the period 1961-2012, using instrumental observations, reanalysis and model simulation datasets. Based on objectively defined criteria, cold surges were classified into 3 types according to their dynamical origin as inferred from daily evolution patterns of surface pressure systems with a focus on the Siberian High (SH): type A with an amplification of a quasi-stationary SH associated with high-pressure anomalies over the Ural mountains, type B with a developing SH associated with fast traveling upper-level waves, and type C with a high-pressure originated in the Arctic. Examination of the long-term change in cold surge occurrences shows different interdecadal variations among the 3 types. During 1961-2012, type A events (37.8%) decreased, while type B events, accounting for the majority (52.5%) of total winter cold surges, increased slightly. The contribution by type C to the total occurrence of the cold surges was small (8.8%) compared to that of A and B, but it became more frequent in the latest decade, related to the tendency of the Arctic Oscillation (AO) being more in its negative phase. Overall, we found slightly increased occurrences of cold surges over Southeast China since the early 1980s, despite the weakened SH intensity and warmer mean temperature compared to previous decades. The climate model projections of the phase 5 of the Coupled Model Intercomparison Project (CMIP5) suggests similar trend in the late 21st century under warmer climate.
|
|
| 2. |
- Liao, Wenhui, et al.
(författare)
-
Impact of Synoptic Weather Types on Ground-Level Ozone Concentrations in Guangzhou, China
- 2021
-
Ingår i: Asia-Pacific Journal of Atmospheric Sciences. - : Springer Science and Business Media LLC. - 1976-7633 .- 1976-7951. ; 57, s. 169-180
-
Tidskriftsartikel (refereegranskat)abstract
- © 2020, Korean Meteorological Society and Springer Nature B.V. Although precursor concentrations were reduced by emission control in Guangzhou, southern China from 2006 to 2016, ground-level O3 concentrations increased, forming potential risks to human health. This study explored the impacts of large-scale synoptic weather circulations on O3 concentration in Guangzhou, in a particular focus on high O3 pollution episodes. Twelve local weather types were clustered based on Lamb-Jenkinson weather types (LWTs). Analyses showed that LWTs strongly impacted daily O3 concentrations: A, AS, CN, and N+ weather types were likely associated with high ozone concentrations, while the ozone levels were relatively low under C, CE, CS, and S+ types. LWTs could explain 30–40% of the inter-annual variability of O3 concentration during the dry season. Numerical model simulations further demonstrated that continuous type A weather was the leading LWT correlated with high O3 concentrations, while type C weather was the predominant type correlated with low O3 concentrations. CMIP5 model results showed that occurrences of weather type A would increase by about 25% in the high emission scenario over the 2020–2069 period, which might worsen the O3 pollution in Guangzhou in the future. The increase in frequency weather type A would not be significant under the low emission scenario during the same period. Therefore, we should strictly implement the global emission reduction plan to prevent the change of weather circulation caused by climate change from aggravating ozone pollution in the future. The strong link between O3 concentrations and LWT frequencies makes the daily occurrence of LWTs a useful predictor for episodes of high O3 pollution and makes annual frequencies of LWTs good indicators of the inter-annual variability of the O3 concentration. These results are useful in efforts to predict O3 concentrations, providing a reliable weather forecast is available.
|
|
| 3. |
- Sheridan, Sonja, 1952, et al.
(författare)
-
Competence to Teach a Point of Intersection for Swedish Preschool Quality
- 2020
-
Ingår i: Asia-Pacific Journal of Research in Early Childhood Education. - : Pacific Early Childhood Education Research Association. - 1976-1961. ; 14:2, s. 77-98
-
Tidskriftsartikel (refereegranskat)abstract
- This article aims to highlight preschool teachers’ teaching competence as one critical aspect of Swedish preschool quality. The study was based on quality evaluations using the Early Childhood Environment Rating Scale. Data was collected from 153 preschools and analysed with descriptive statistics for the subscales. The standpoint of the article is that children learn and develop by communicating and interacting with their environment, highlighting how intentions and circumstances between and within systems and contexts affect preschool teaching and conditions for children’s learning. To evaluate high-quality preschool education, two subscales with the lowest quality scores, Language and literacy and Learning activities, were chosen to explore teaching, as they embrace items and criteria that depend on teaching. The results highlight distinct patterns of variation in quality. The competence to teach is a point of intersection for the quality in preschool, and conditions for children’s learning. Areas in need of competence development are subject, and didactic knowledge competence in relating to children in dialogue, child-focused strategies, clarifying and communicating an object of knowledge by integrating play, care, and learning in teaching.
|
|
| 4. |
- Lipatnikov, Andrei, 1961
(författare)
-
Burning rate in impinging jet flames
- 2011
-
Ingår i: Journal of Combustion. - : Hindawi Limited. - 2090-1976 .- 2090-1968. ; 2011:737914, s. 11-
-
Tidskriftsartikel (refereegranskat)abstract
- A method for evaluating burning velocity in premixed turbulent flames stabilized in divergent mean flows is quantitatively validated using numerical approximations of measured axial profiles of the mean combustion progress variable, mean and conditioned axial velocities, and axial turbulent scalar flux, obtained by four research groups from seven different flames each stabilized in an impinging jet. The method is further substantiated by analyzing the combustion progress variable balance equation that is yielded by the extended Zimont model of premixed turbulent combustion. The consistency of the model with the aforementioned experimental data is also demonstrated. © 2011 A. N. Lipatnikov.
|
|
| 5. |
- Bolzon, Micheal, 1990, et al.
(författare)
-
Effects of Wheel Configuration on the Flow Field and the Drag Coefficient of a Passenger Vehicle
- 2019
-
Ingår i: International Journal of Automotive Technology. - : Springer Science and Business Media LLC. - 1976-3832 .- 1229-9138. ; 20:4, s. 763-777
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of wheel rotation, rim coverage area, fan spokes, spoke sharpness, and tread pattern on the flow field and drag coefficient of a passenger vehicle were investigated. Force measurements and wake surveys were taken on a 1/5th scale passenger vehicle at a Reynolds number of 2.0 × 106. The wake surveys were conducted at three planes. Vorticity, total pressure coefficient, and local drag coefficient plots are presented. Wheel rotation reduced the drag coefficient of all of the wheel configurations tested, which generally agrees with literature. Wheel rotation reduced the front wheel’s jetting vortex’s drag while increasing the drag from the center of the front wheel to the upper rim track. Reducing the rim coverage area increased the drag coefficient. This increase was attributed to an increased jetting vortex drag and a change in flow separation around the front wheel. The fan spoke rim performed the worst, regardless of rotation. Rounding the spoke edges reduced the drag coefficient of a rotating wheel. The tread pattern slightly reduced the shoulder vortex vorticity and slightly increased the separation around the front wheel.
|
|
| 6. |
- Chakraborty, N., et al.
(författare)
-
Statistics of conditional fluid velocity in the corrugated flamelets regime of turbulent premixed combustion: A Direct Numerical Simulation study
- 2011
-
Ingår i: Journal of Combustion. - : Hindawi Limited. - 2090-1976 .- 2090-1968. ; 2011:Article ID 628208
-
Tidskriftsartikel (refereegranskat)abstract
- The statistics of mean fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes (RANS) simulations have been studied using a Direct Numerical Simulation database of statistically planar turbulent premixed flame representing the corrugated flamelets regime combustion. Expressions for conditional mean velocity and conditional velocity correlations which are derived based on a presumed bimodal probability density function of reaction progress variable for unity Lewis number flames are assessed in this study with respect to the corresponding quantities extracted from DNS data. In particular, conditional surface averaged velocities ̄(u i ) Rs and the velocity correlations ̄(u i u j ) Rs in the unburned reactants are demonstrated to be effectively modelled by the unconditional velocities ̄(u i ) R and velocity correlations ̄(u i u j ) R , respectively, for the major part of turbulent flame brush with the exception of the leading edge. By contrast, conditional surface averaged velocities ̄(u i ) ps and the velocity correlations ̄(u i u j ) Ps in fully burned products are shown to be markedly different from the unconditional velocities ̄(u i ) P and velocity correlations ̄(u i u j u j ) P , respectively. © 2011 Nilanjan Chakraborty and Andrei N. Lipatnikov.
|
|
| 7. |
- Franzke, Randi, 1989, et al.
(författare)
-
Numerical Investigation of the Air Flow in a Simplified Underhood Environment
- 2022
-
Ingår i: International Journal of Automotive Technology. - : Springer Science and Business Media LLC. - 1976-3832 .- 1229-9138. ; 23:6, s. 1517-1527
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal management plays a crucial role for the energy efficiency of electrified vehicles. Using numerical flow simulations, the air paths and temperature distributions in the underhood can be identified and optimised early in the development process. However, the numerical method needs to be verified in its accuracy for capturing the important flow features in the underhood. In this study, a numerical approach is developed that is robust with respect to spatial and temporal resolutions as well as to different turbulence models. The methodology is validated against experimental data from LDA measurements. The geometric configurations investigated are representative of electrified vehicles, with one or two front opening designs, two different fans, and with or without a blockage behind. The results showed that for one of the fan installations, although the major flow field structures were well captured, the locations of the peak velocities did not match the experiments. For the second fan, the CFD results agreed well with the measurements.
|
|
| 8. |
- Gao, Shigen, et al.
(författare)
-
Fuzzy adaptive automatic train operation control with protection constraints : A residual nonlinearity approximation-based approach
- 2020
-
Ingår i: Engineering applications of artificial intelligence. - : Elsevier BV. - 0952-1976 .- 1873-6769. ; 96
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we present fuzzy adaptive control based on residual nonlinearity approximation in the presence of protection constraints for the target trajectory tracking problem observed in automatic train operation. Herein, protection constraints refer to a condition wherein the speed and position of a controlled train are not allowed to surpass the boundaries imposed by automatic train protection and moving authority. By defining proper coordinate transformation, the protection constraints are converted to an error-prescribed performance control problem that facilitates operational efficiency by reducing the margin with respect to target trajectories. Based on the prescribed performance control methodology, we present an improved scheme using fuzzy residual nonlinearity approximation and establish the uniformly ultimately boundedness (UUB) property. A novel feature therein is that the ultimate boundary of the proposed scheme is simultaneously characterized by the prescribed performance functions and control parameters, with rigorous and analytically mathematical expressions; while pioneering the prescribed performance control methodology, the ultimate boundary is characterized solely by the prescribed performance functions. To verify the effectiveness and advantages of the proposed scheme, the controllers are applied to the automatic train operation on the Beijing Yizhuang line, which contains 13 operational intervals. Finally, comparative and simulation results are presented to validate the proposed method.
|
|
| 9. |
- Huang, Chen, 1981, et al.
(författare)
-
Comparison of presumed PDF models of turbulent flames
- 2012
-
Ingår i: Journal of Combustion. - : Hindawi Limited. - 2090-1976 .- 2090-1968. ; 2012:564621, s. 15-
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past years, the use of a presumed probability density function (PDF) for combustion progress variable or/and mixture fraction has been becoming more and more popular approach to average reaction rates in premixed and partially premixed turbulent flames. Commonly invoked for this purpose is a beta-function PDF or a combination of Dirac delta functions, with the parameters of the two PDFs being determined based on the values of their first and second moments computed by integrating proper balance equations. Because the choice of any of the above PDFs appears to be totally arbitrary as far as underlying physics of turbulent combustion is concerned, the use of such PDFs implies weak sensitivity of the key averaged quantities to the PDF shape. The present work is aimed at testing this implicit assumption by comparing mean heat release rates, burning velocities, and so forth, averaged by invoking the aforementioned PDFs, with all other things being equal. Results calculated in the premixed case show substantial sensitivity of the mean heat release rate to the shape of presumed combustion-progress-variable PDF, thus, putting the approach into question. To the contrary, the use of a presumed mixture-fraction PDF appears to be a sufficiently reasonable simplification for modeling the influence of fluctuations in the mixture fraction on the mean burning velocity provided that the mixture composition varies within flammability limits.
|
|
| 10. |
- Kumar, Arun, 1991, et al.
(författare)
-
Improved Predictive Model of Drivers’ Subjective Perception of Vehicle Reaction under Aerodynamic Excitations
- 2023
-
Ingår i: International Journal of Automotive Technology. - 1976-3832 .- 1229-9138. ; 24:6, s. 1655-1664
-
Tidskriftsartikel (refereegranskat)abstract
- In vehicle development, rating vehicle reactions to external disturbances such as aerodynamic excitations are important for improving safety and comfort of passengers. Vehicle motion reactions under such conditions are dependent on both disturbance and drivers’ steering actions. A predictive model has been developed to correctly anticipate the drivers’ ability to identify unexpected external disturbances for straight-line, high-speed driving in a driving simulator. The measured variables were band-pass filtered to desired frequency ranges. Excess yaw and roll velocities, defined as the difference between actual rotations and rotations predicted with a dynamic model from the cause of actual steering, were calculated. The standard deviations of the measured variables in a time window around disturbances were used in a regression model to predict the driver responses. Replacing actual rotations with excess rotations reduced the importance of steering input as a predictor by approximately 2/3, thus improving the accuracy of the predictive model. The model showed the change in driver sensitivity to rotations at different frequency intervals. It also showed that only driver input in around 1 ∼ 2 Hz reduces driver sensitivity and that drivers are not necessarily sensitive to high rotational accelerations, but rather to large differences between actual vehicle yaw and roll and expected vehicle yaw and roll responses from the steering input The result from this study were later compared to succeeding on-road tests which confirmed that the predictive model was improved with the use of excess motion variables.
|
|
