Efficient parameterization of waverider geometries

This paper summarizes the results of investigations into the development of parametric waverider geometry models, with emphasis on their efficiency, in terms of their ability to cover a large feasible design space with a sufficiently small number of design variables to avoid the “curse of dimensionality.” The work presented here is focused on the parameterization of idealized waverider forebody geometries that provide the baseline shapes upon which more sophisticated and realistic hypersonic aircraft geometries can be built. Three different aspects of rationalizing the decisions behind the parametric geometry models developed using the osculating cones method are considered. Initially, three different approaches to the design method itself are discussed. Each approach provides direct control over different aspects of the geometry for which very specific shapes would be more complex to obtain indirectly, thus enabling the geometry to more efficiently meet any related design constraints. Then, a number of requirements and limitations are investigated that affect the available options for the parametric design-driving curves of the inverse design method. Finally, the performance advantages that open up with increasing flexibility of the design-driving curves in the context of a design optimization study are estimated. This allows one to reduce the risk of overparameterizing the geometry model, while still enabling a variety of meaningful shapes. Although the osculating cones method has mainly been used here, most of the findings also apply to other similar inverse design algorithms

Parametric geometry models for hypersonic aircraft: integrated external inlet compression

In this paper we are investigating a method for the design and integration of 3D externalcompression inlet geometries on parametric geometries of air-breathing hypersonic aircraft.We view the geometries as the first stage of a mixed compression inlet. The investigations arebased on waverider geometries generated with the osculating cones waverider forebodydesign method. The osculating cones method is further utilized to create a secondcompression surface before the inlet cowl, essentially creating a second waverider geometryon the underside of the forebody. This way, we achieve greater compression for the part ofthe flow to be captured by the inlet cowl using a geometry that does not require sidewalls(like 2D ramps do), and has a potentially larger capture area than axisymmetric inletgeometries such as half-cones. The integration method is explained in detail, validated andfurther examined with CFD simulations. Those include measurements of the sensitivity ofthe flowfield to angle of attack, sideslip and Mach number changes. A number of options fordesigning the downstream internal compression part of the inlet are also discussed

Parametric geometry models for hypersonic aircraft components: blunt leading edges

In this paper we report the results of investigations into the efficient parameterization of blunt leading edge shapes for hypersonic aircraft geometries. The investigations mostly revolve around waverider geometries generated with inverse design techniques, such as the osculating cones waverider forebody design method. The shapes presented however, can be utilized to introduce bluntness to any wedge-like geometry with sharp leading edges. Initially, we present detailed descriptions of three different variations of the rational Bézier curve based parameterization that was developed, and the variety of shapes that can be obtained is demonstrated. Afterwards their performance is evaluated utilizing 2D CFD analysis. In our simulations, the rational Bézier curve leading edges outperform circular ones when it comes to minimizing both drag and peak heating rates or peak temperatures. Additionally, with higher order rational Bézier leading edge shapes, higher levels of geometric continuity can be achieved at the interface between the blunt part and the original wedge-like geometry, resulting in a smoother transition. Preliminary results indicate that this can potentially affect the receptivity and hence transition mechanisms. Finally, the 2D geometry formulations are extended to full 3D waverider forebody geometries

Shape optimization of a simplified car geometry using evolutionary algorithms and computational fluid dynamics

75 σ.Στην παρούσα διπλωματική εργασία υλοποιείται και αυτοματοποιείται μια μέθοδος αεροδυναμικής ανάλυσης (με λογισμικό υπολογιστικής ρευστοδυναμικής) και, στη συνέχεια, μια διαδικασία βελτιστοποίησης (με λογισμικό εξελικτικών αλγορίθμων) μιας απλοποιημένης μορφής αυτοκινήτου. Πρόκειται για μια χαρακτηριστική περίπτωση-benchmark, ευρύτατα χρησιμοποιούμενη από τις αυτοκινητοβιομηχανίες. Η βελτιστοποίηση στοχεύει στην ελαχιστοποίηση του αεροδυναμικού συντελεστή αντίστασής του οχήματος. Παρά την απλοποιημένη γεωμετρία, το πρόβλημα της ανάλυσης και της βελτιστοποίησης (αλλά ακόμη και αυτό της γένεσης πλέγματος) παρουσιάζει αρκετή πολυπλοκότητα, ιδίως επειδή κατά τη βελτιστοποίηση απαιτείται να γίνονται οι διαδικασίες αυτόματα, χωρίς την παρέμβαση του χρήστη-σχεδιαστή. Η εργασία παρουσιάζει με λεπτομέρειες όλα τα στάδια που απαιτούνται για την ανάλυση του προβλήματος ροής και τη βελτιστοποίηση. Στην εργασία αυτή γίνεται, πρώτα, αξιολόγηση ενός νέου κώδικα γένεσης πλέγματος καθώς είναι μια από τις τελευταίες προσθήκες στο πακέτο λογισμικού ανοιχτού πηγαίου κώδικα OpenFOAM (Field Operation and Manipulation, ειδικό τμήμα του οποίου αναπτύσσεται πλέον από την ΜΠΥΡΒ/ΕΜΠ) το οποίο χρησιμοποιείται για την επίλυση των εξισώσεων Navier-Stokes και τον υπολογισμό του συντελεστή αντίστασης του σώματος. Μεταξύ άλλων, εντοπίζονται διαφορές στην πρόλεξη των ροϊκών φαινομένων από διαφορετικά μοντέλα τύρβης. Πραγματοποιούνται και συγκρίσεις με πειραματικά αποτελέσματα για πιστοποίηση των υπολογιστικών αποτελεσμάτων. Στο πρόβλημα βελτιστοποίησης υιοθετείται κατάλληλη παραμετροποίηση της μορφής του πίσω-κάτω μέρους του οχήματος, ώστε να προκύπτει μια απλοποιημένη μορφή διαχύτη, και αναζητούνται οι βέλτιστες τιμές των έτσι οριζόμενων μεταβλητών σχεδιασμού με το λογισμικό βελτιστοποίησης EASY που έχει αναπτυχθεί από τη ΜΠΥΡΒ/ΕΜΠ.In this diploma thesis, an automatic process for the aerodynamic analysis (using CFD software) of a simplified car geometry is set up and, then, is also used for its shape optimization (by means of evolutionary algorithms). The problem studied is a popular benchmark case in car industries. The optimization task aims at minimizing the drag coefficient of the body. Despite the simplified shape of the body used, developing a quality mesh generation process and computing the characteristics of the flow is complex and computationally demanding, especially within an evolutionary optimization algorithm where all processes need to be automated and executed with no further human input. A complete presentation of all the necessary steps taken for the aerodynamic analysis and optimization process is given in this work. Firstly, an evaluation of a relatively new mesh generation tool, included in the open source CFD software package OpenFOAM (Field Operation and Manipulation), takes place. OpenFOAM, part of which is co-developed by the PCFD&O/NTUA, is also used for solving the Navier-Stokes equations for the computation of the flow characteristics and drag coefficient of the body. Over and above, results using different turbulence models are compared with experimental data available. The design variables are defined so as to control the shape of a simplified diffuser formed at the rear-lower part of the vehicle. The EASY optimization software, developed by PCFD&O /NTUA, is used to seek their optimal values (yielding the optimal shape of the diffuser) for minimum drag.Κωνσταντίνος Γ. Κοντογιάννη

First simultaneous SST/CRISP and IRIS observations of a small-scale quiet Sun vortex

Context. Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations. Aims. We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated upflows through the photosphere and chromosphere of a quiet Sun internetwork region. Methods. We analyzed high spatial and temporal resolution ground- and spaced-based observations of a quiet Sun region. The observations consist of high-cadence time series of wideband and narrowband images of both Hα 6563 Å and Ca II 8542 Å lines obtained with the CRisp Imaging SpectroPolarimeter (CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well as ultraviolet imaging and spectral data simultaneously obtained by the Interface Region Imaging Spectrograph (IRIS). Results. A small-scale vortex is observed for the first time simultaneously in Hα, Ca II 8542 Å, and Mg II k lines. During the evolution of the vortex, Hα narrowband images at −0.77 Å and Ca II 8542 Å narrowband images at −0.5 Å, and their corresponding Doppler signal maps, clearly show consecutive high-speed upflow events in the vortex region. These high-speed upflows with a size of 0.5–1 Mm appear in the shape of spiral arms and exhibit two distinctive apparent motions in the plane of sky for a few minutes: (1) a swirling motion with an average speed of 13 km s-1 and (2) an expanding motion at a rate of 4–6 km s-1. Furthermore, the spectral analysis of Mg II k and Mg II subordinate lines in the vortex region indicates an upward velocity of up to ~8 km s-1 along with a higher temperature compared to the nearby quiet Sun chromosphere. Conclusions. The consecutive small-scale vortex events can heat the upper chromosphere by driving continuous high-speed upflows through the lower atmosphere

Recurrent prurigo nodularis related to infected tonsils: a case report

This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

The flare likelihood and region eruption forecasting (FLARECAST) project: flare forecasting in the big data & machine learning era

The European Union funded the FLARECAST project, that ran from January 2015 until February 2018. FLARECAST had a research-to-operations (R2O) focus, and accordingly introduced several innovations into the discipline of solar flare forecasting. FLARECAST innovations were: first, the treatment of hundreds of physical properties viewed as promising flare predictors on equal footing, extending multiple previous works; second, the use of fourteen (14) different machine learning techniques, also on equal footing, to optimize the immense Big Data parameter space created by these many predictors; third, the establishment of a robust, three-pronged communication effort oriented toward policy makers, space-weather stakeholders and the wider public. FLARECAST pledged to make all its data, codes and infrastructure openly available worldwide. The combined use of 170+ properties (a total of 209 predictors are now available) in multiple machine-learning algorithms, some of which were designed exclusively for the project, gave rise to changing sets of best-performing predictors for the forecasting of different flaring levels, at least for major flares. At the same time, FLARECAST reaffirmed the importance of rigorous training and testing practices to avoid overly optimistic pre-operational prediction performance. In addition, the project has (a) tested new and revisited physically intuitive flare predictors and (b) provided meaningful clues toward the transition from flares to eruptive flares, namely, events associated with coronal mass ejections (CMEs). These leads, along with the FLARECAST data, algorithms and infrastructure, could help facilitate integrated space-weather forecasting efforts that take steps to avoid effort duplication. In spite of being one of the most intensive and systematic flare forecasting efforts to-date, FLARECAST has not managed to convincingly lift the barrier of stochasticity in solar flare occurrence and forecasting: solar flare prediction thus remains inherently probabilistic

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

On developing efficient parametric geometry models for waverider-based hypersonic aircraft

This work is focused on tackling the high dimensionality and complex nature of waverider based high speed aircraft design through the development of effective and efficiently parameterized parametric geometry models. The first part of the work is focused on the parameterization and handling of waverider forebody geometries. Different design approaches and a novel design method are presented, each offering direct control of different aspects of the geometry. This can be utilized to directly implement any design constraints or to enable straightforward interfacing with additional geometry components. The new three-dimensional leading edge waverider design method that is proposed is a step away from inverse and one towards direct waverider design. A series of requirements for designing valid three-dimensional leading edge curves are also highlighted. A method to compare different parameterization schemes in order to avoid over or under-parameterizing the geometries and assist in deciding on the number of degrees of freedom and control points for the design-driving curves of the inverse design methods is also presented. This enables the designer to make better educated decisions during the parametric model development phase and when parameterizing hypersonic-design-specific components for which we have limited experience and detailed data in the literature. Complementing the waverider forebody component of the aircraft are a series of blunt leading edge shape formulations. Their effectiveness and efficiency compared to other blunting approaches is highlighted. They are suitable for generating blunt shapes for any wedge-like geometry and they can also be used for inlet cowls, sidewalls, control surfaces, etc. They also offer second order continuity at the interface between the blunt part and the original geometry, which can have a favourable effect on the receptivity and turbulent transition mechanism. Finally, a parametric geometry model development framework consisting of a revised aerodynamic design process that involves design loops to better tune the parametric model, and a geometry engine developed to enable these early design loops, is presented. This is complimented by a number of implementation specific findings and proposed features such as an interactive GUI with real-time updates and dynamically controlled resolution of the generated geometries