| 1. |
- Sherratt, K., et al.
(författare)
-
Predictive performance of multi-model ensemble forecasts of COVID-19 across European nations
- 2023
-
Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Methods: We used open-source tools to develop a public European COVID-19 Forecast Hub. We invited groups globally to contribute weekly forecasts for COVID-19 cases and deaths reported by a standardised source for 32 countries over the next 1–4 weeks. Teams submitted forecasts from March 2021 using standardised quantiles of the predictive distribution. Each week we created an ensemble forecast, where each predictive quantile was calculated as the equally-weighted average (initially the mean and then from 26th July the median) of all individual models’ predictive quantiles. We measured the performance of each model using the relative Weighted Interval Score (WIS), comparing models’ forecast accuracy relative to all other models. We retrospectively explored alternative methods for ensemble forecasts, including weighted averages based on models’ past predictive performance.Results: Over 52 weeks, we collected forecasts from 48 unique models. We evaluated 29 models’ forecast scores in comparison to the ensemble model. We found a weekly ensemble had a consistently strong performance across countries over time. Across all horizons and locations, the ensemble performed better on relative WIS than 83% of participating models’ forecasts of incident cases (with a total N=886 predictions from 23 unique models), and 91% of participating models’ forecasts of deaths (N=763 predictions from 20 models). Across a 1–4 week time horizon, ensemble performance declined with longer forecast periods when forecasting cases, but remained stable over 4 weeks for incident death forecasts. In every forecast across 32 countries, the ensemble outperformed most contributing models when forecasting either cases or deaths, frequently outperforming all of its individual component models. Among several choices of ensemble methods we found that the most influential and best choice was to use a median average of models instead of using the mean, regardless of methods of weighting component forecast models.Conclusions: Our results support the use of combining forecasts from individual models into an ensemble in order to improve predictive performance across epidemiological targets and populations during infectious disease epidemics. Our findings further suggest that median ensemble methods yield better predictive performance more than ones based on means. Our findings also highlight that forecast consumers should place more weight on incident death forecasts than incident case forecasts at forecast horizons greater than 2 weeks.
|
|
| 2. |
- Mingione, G., et al.
(författare)
-
Airframe Noise Reduction Technologies applied to High-Lift Devices of Future Green Regional Aircraft
- 2014
-
Ingår i: Greener Aviation 2014: Clean Sky breakthroughs and worldwide status.
-
Konferensbidrag (refereegranskat)abstract
- Regional aircraft typically operate over airports located in the neighbourhood of densely populated areas, with high frequency of take-off / landing events and, hence, they strongly contribute to community noise and gaseous emissions. These issues currently limit further growth of traffic operated by regional airliners which, in the next future, will have to face even more stringent environmental constraints worldwide as prescribed by the civil aviation certification normative and local regulations as well.Therefore, in accordance with ACARE Vision 2020 toward a drastic reduction of air transport environmental impact over next decades, several mainstream technologies have been considered in the frame of Clean Sky JTI – Green Regional Aircraft (GRA) ITD project for application to next-generation regional aircraft. Such technologies are concerning: i) advanced aerodynamics and load control to maximise lift-to-drag ratio in both design and off-design conditions of the whole flight mission profile, thus reducing fuel consumption/ air pollutants emission and also allowing for steeper/ noise-abatement initial climb paths; ii) load alleviation to avoid loads from gust encounter and manoeuvre exceeding given limits, thus optimising the wing structural design for weight saving; iii) low airframe noise to reduce aircraft acoustic impact in approach flight condition.High-Lift-Devices (HLD) in fully-deployed settings represents one of the main sources of aircraft community noise during the approach flight phase and of consequent annoyance perceived by the resident population in the vicinity of airports. Therefore, in the overall scenario as above outlined, several HLD architectures, integrating either matured or more advanced low-noise concepts/technical solutions still preserving high-lift performances, have been investigated in the frame of the GRA ITD project. These HLD have been tailored to different classes/ configurations of future regional aircraft, ranging from high-wing 90-seat Turboprop to low-wing 130-seat Turbofan with different power-plant and engine installation.Technological studies of High-Lift Low-Noise devices carried out in the framework of the GRA ITD project have been presented. Both computational analyses and wind tunnel tests have been described in detail.Some passive acoustic devices have been firstly analysed with different numerical approaches. First of all, the use of conventional liners, as acoustic treatments carefully integrated with the wing, have revealed to be effective in noise detection for a wide range of frequencies. Also side-edge fences have demonstrated a promising aptitude in suppression of the turbulent vortex occurring around the flap side-edge. These encouraging results have been also confirmed during an extensive WT test campaign.Finally, multi-objective optimizations and the numerical assessment of several configurations have been performed by applying both aerodynamic and aeroacoustic methodologies. These studies have showed the successfully design of high-lift technologies with a low noise impact.The most promising among the addressed HLD technologies will be brought to the final demonstration phase within the GRA ITD work programme, in order to assess in a realistic experimental environment (TRL 5) the aircraft low-speed aerodynamic and aero-acoustic performances through WT tests on large-scale (say 1:6) complete A/C powered models.
|
|
| 3. |
- Mingione, G., et al.
(författare)
-
Landing gear noise reduction technology development for future green regional aircraft
- 2014
-
Ingår i: Greener Aviation 2014: Clean Sky breakthroughs and worldwide status.
-
Konferensbidrag (refereegranskat)abstract
- One of the main objectives of the CS-JTI GRA ITD project - Low Noise Configuration domain is the aircraft noise reduction. It is well known that landing gear is one of main sources of airframe noise and therefore several previous projects have been carried out in USA and Europe to investigate relevant low-noise technologies.Nevertheless these studies have addressed mainly wing-mounted main landing gear (MLG) architecture of low-wing large aircraft which is quite different from the fuselage-mounted MLG of high-wing aircraft. Therefore, an activity plan has been defined to address noise reduction of MLG, and of nose landing gear (NLG) as well, for high-wing turboprop regional aircraft, aimed at identifying TRL 3 technologies and increase their maturity level up to TRL 5.The plan includes both numerical and experimental activities with the participation of European industries, research centers, SMEs and universities, as either GRA ITD Members or Partners of projects in the frame of Calls for Proposals (CfP).In 2012 MLG and NLG baseline configurations, being realistic CAD models of actual architectures, have been jointly delivered by Alenia Aermacchi and Messier-Bugatti-Dowty. In the course of 2013 low-noise technologies development is performed, from state-of-art survey and preliminary studies based on semi-empirical approach, to CFD/CAA analyses and basic wind tunnel tests on simplified mock-ups. Technologies under investigation are fairings, wheels hub caps, bay and doors acoustic treatments, partial closure of bay cavity (after gear lowering), spoilers, vortex disintegrators, etc.The paper describes to-date results and the criteria adopted to down-select landing gear low noise devices leading to the choice of best solutions for WT test demonstrations.
|
|
