• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 261
  • 65
  • 51
  • 32
  • 26
  • 16
  • 15
  • 13
  • 6
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • Tagged with
  • 628
  • 333
  • 140
  • 129
  • 62
  • 56
  • 45
  • 43
  • 43
  • 41
  • 39
  • 38
  • 37
  • 36
  • 35
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
511

Att spåra vägar : Hur de utvecklas, förändras eller försvinner. / To trace roads : How they develop, change or disappear

Lindblom, Peter January 2022 (has links)
This is a study of local roads in two villages in the interior of Småland to see how much of the older road network can be found by studying maps from the 19th century, today's digital maps with height shading and Fornsök's map service. The introduction will be a review of other people's studies and their results that are used to be able to answer three questions.1- How to distinguish older roads from newer ones?2 -Which method can be used to determine the age of roads using maps?3 -How can you distinguish older hiking trails or other guides in map material?Throughout the texts show that ancient monuments are often close to older roads and that our roads today go the same routes as before. Locally in the villages, the rural roads are fewer today than what is seen on the oldest map from 1814 and to get a grip on changes and events, a method used by Kalle Måhl used in Gotland villages will be used together with Edmund Husserl and Martin Heidegger phenomenology archaeological theory. The theory is based on the fact that we have the same spatial perception based on bodily experiences in terms of direction and scale. The method means that you look at today's roads and compare them with the 1843 map in my case, note changes and compare these with the older map from 1814. With facts from Fornsök, you can analyze the changes and get a result. The result in this case with Bodaryd, Uggleryd and their road network is that they existed at least in 1549 as two farms and that the emerging villages were split by law change 1814-1843 with a number of scattered farms and several smaller settlements in the forests that today only exist as ancient finds in Fornsök. In addition, the connection between a registered hollow road and the rural roads has been established, however, there is only a theoretical connection to an unregistered hollow road that is without connections on the maps.
512

Les formes de participations syndicales dans les cégeps

Garant, Mélanie 16 April 2018 (has links)
La réforme au collégial en 1993 a modifié les relations de travail dans le réseau collégial. La décentralisation d'une partie des matières négociables au niveau national vers le local apporte un changement dans les relations patronales-syndicales. Les syndicats et leur fédération doivent adapter leurs stratégies afin de demeurer actifs. La présente recherche a étudié deux collèges dans le réseau afin d'analyser le comportement des syndicats à la suite des restructurations qui ont modifié l'environnement interne et externe des collèges. Pour ce faire, nous avons utilisé le modèle du triangle du pouvoir de Levesque et Murray (2003) qui divise en trois composantes les ressources que les syndicats mobilisent (la capacité stratégique, la cohérence interne et la cohérence externe). L'analyse des résultats, combinée au cadre théorique, nous permet de démontrer que les éléments du triangle du pouvoir influencent le choix de la stratégie aux syndicats locaux. De plus, malgré les défis que pose le régime, certains syndicats locaux semblent peu enclins à faire valoir le droit de négocier localement. Finalement, il est intéressant de constater comment deux syndicats évoluant dans un même contexte et dans un même réseau peuvent avoir des positions syndicales diamétralement opposées. Les ressources et le contexte interne sont déterminants dans la stratégie adoptée et dans la manière de gérer les défis communs.
513

Les petites unités d'accréditation et la démocratie syndicale : le cas du syndicat des professionnèles des CLSC-CHSLD de Québec et de Chaudière-Appalaches CSN / Les petites unités d'accréditation et la démocratie syndicale

Bouchard, Olivier 11 April 2018 (has links)
Le présent mémoire vise à établir des bases, des critères de mesure de la démocratie syndicale, phénomène étonnamment peu étudié à travers les époques. Particulièrement, cette recherche s'intéresse à la démocratie syndicale perçue dans une petite unité d'accréditation, puisque la démocratie est avant tout la gouverne de la majorité. Ainsi, comment s'en tire une petite unité syndicale dans le concert des syndicats d'une centrale ? Plus précisément, nous tenons à étudier, d'une part, le degré de présence perçu de la démocratie syndicale auprès du Syndicat des professionnèles des CLSC-CHSLD de Québec et de Chaudière-Appalaches CSN (SPCLSC-CHSLD) et, d'autre part, de connaître la perception de ce syndicat de la démocratie syndicale présente dans certaines autres instances décisionnelles de la Confédération des syndicats nationaux (CSN). Notre hypothèse principale veut que le degré de présence perçu de la démocratie syndicale soit fort, c'est-à-dire que les quatre dimensions du modèle conceptuel développé se retrouvent au sein du SPCLSC-CHSLD lors de l'analyse. Le devis de recherche est double, puisque l'analyse porte sur trois niveaux distincts qui ne commandent pas et ne permettent pas une même expectative de conclusions et d'extrapolations. La méthodologie utilisée est quantitative et l'analyse s'est faite à l'aide de tests de statistiques déductives, appliqués à un questionnaire de sondage administré à un échantillon de membres du SPCLSC-CHSLD. Bien que l'analyse soit pragmatique et que le sujet abordé ait été grandement éclaté, il est constaté, d'une part, un haut taux de non-réponse aux questions à même les répondants et, d'autre part, une invalidation de l'hypothèse de la recherche. En effet, de façon très surprenante, une des dimensions du modèle conceptuel ne se retrouve pas être perçue comme présente de manière suffisamment forte pour prétendre à la présence complète - et forte - de la démocratie syndicale. Le second objectif de recherche, soit de connaître la perception des répondants de la démocratie syndicale présente aux autres instances décisionnelles de la centrale, permet d'orienter le futur propos de recherches ultérieures pouvant s'intéresser à la démocratie syndicale aux instances supérieures d'une centrale, puisque plusieurs constituantes inhérentes de la démocratie syndicale sont perçues comme étant absentes aux plus hauts niveaux décisionnels. / The present thesis aims at setting bases or criteria for the measurement of union democracy, amazingly enough a poorly studied phenomenon over time. This study focuses primarily on union democracy as perceived in a small accreditation unit, since democracy is the prerogative of those who are part of the majority. How does a small union get by among a chorus of unions in a confederation? On the one hand, we want to study more precisely the degree of perception of the existence of union democracy within the Syndicat des professionnèles of the CLSC-CHSLD of Québec and Chaudière-Appalaches CSN (SPCLSC-CHSLD). On the other hand, we want to study the perception of union democracy by this specific union within other decision-making structures of the Confédération des syndicats nationaux (CSN). Our main assumption is that the degree of perception of the existence of union democracy is high. In other words, the analysis shows that the four dimensions of the conceptual model developed are found within the SPCLSCCHSLD. Therefore, the mandate of this research is twofold, because the analysis is directed toward three different levels that do not require or allow the same conclusions and extrapolations expectancy. We used a quantitative methodology and the analysis was carried out with inferential statistics tests applied to a survey questionnaire completed by a sample of SPCLSC-CHSLD members. Although the analysis is pragmatic and the subject broached greatly fragmented, we noticed a high rate of non-response to the questions among respondents and an invalidation of the research hypothesis. Surprisingly, one of the dimensions of the conceptual model is not perceived as being strong enough to inspire a complete and influential presence of union democracy. The second objective of the study is to learn about respondents' perception of union democracy in other decision-making structures of the confederation. It allows orientation of future research subjects regarding union democracy in a confederation’s higher authority, given that several constituents inherent in union democracy are perceived as absent in higher levels of authority.
514

Développement d’un dispositif expérimental dédié à la mesure des sections efficaces de capture et de fission de l’233u dans le domaine des résonances résolues / Development of an experimental set-up for the measurement of the neutron-induced fission and capture cross section of 233U in the resonance region

Companis, Iulia 09 December 2013 (has links)
233 U est le noyau fissile produit dans le cycle du combustible 232 T h/233 U qui a été proposé comme une alternative plus sûre et plus propre du cycle 238 U/239 P u. La connaissance précise de la section efficace de capture de neutrons de cet isotope est requise avec une haute précision pour la conception et le développement de réacteurs utilisant ce cycle du combustible. Les deux seuls jeux de données expérimentales fiables pour la section efficace de capture de l’233 U montrent des écarts important allant jusqu’à 20%. Ces différences peuvent être dues à desincertitudes systématiques associées à l'efficacité du détecteur, la correction du temps mort, la soustraction du bruit de fond et le phénomène d’empilement de signaux causé par la forteactivité α de l’échantillon. Un dispositif expérimental dédié a la mesure simultanée des sections efficaces de fission et de capture des noyaux fissiles radioactifs a été conçu, assemblé et optimiséau CENBG dans le cadre de ce travail. La mesure sera effectuée à l’installation de temps de vol de neutrons Gelina de l’IRMM, où les sections efficaces neutroniques peuvent être mesurées sur une large gamme d’énergie avec une haute résolution énergétique. Le détecteur de fission se compose d’une chambre à ionisation (CI) multi-plaque de haute efficacité. Les rayons γ produits dans les réactions de capture sont détectés par un ensemble de six scintillateurs C6 D6entourant la CI. Dans ces mesures, les rayons γ de la capture radiative sont masqués parle grand nombre de rayons γ de fission, ce qui représente le problème le plus délicat. Ces γ parasites doivent être soustraits par la détection des événements de fission avec une efficacité très bien connue (méthode de VETO). Une détermination précise de cette efficacité est assezdifficile. Dans ce travail, nous avons soigneusement étudié la méthode des neutrons prompts de fission pour la mesure de l'efficacité de la CI, apportant un éclairage nouveau sur la méthode, ce qui a permi d’obtenir une excellente précision sur l'efficacité de détection des fission d’une sourcede 252 Cf. Avec cette même source, plusieurs paramètres (pression du gaz, haute tension et la distance entre les électrodes) ont été étudiés afin de déterminer le comportement de la CI et detrouver le point de fonctionnement idéal : une bonne séparation énergétique entre les particulesα et les fragments de fission (FF) et une bonne résolution temporelle. Une bonne séparationα-FF a également été obtenue avec une cible d’233 U très radioactive. De plus, l’analyse deforme de signaux entre les rayons γ et les neutrons dans les détecteurs C6 D6 a été observée àGelina dans des conditions expérimentales réalistes. Pour conclure, le dispositif expérimentalet la méthode de VETO ont été soigneusement vérifiés et validés, ouvrant la voie à la mesure future des sections efficaces de capture et fission d’233 U . / 233U is the fissile nucleus produced in 232T h/233U fuel cycle which has been proposed as asafer and cleaner alternative to the 238U/239P u cycle. The accurate knowledge of the neutroncapture cross-section of this isotope is needed with high-precision for design and developmentof this fuel cycle. The only two reliable experimental data for the capture cross-section of233U show discrepancies up to 10%. These differences may be due to systematic uncertaintiesassociated with the detector efficiency, dead-time effects, background subtraction and signalpile-up caused by the α-activity of the sample. A special experimental set-up for simultaneousmeasurement of fission and capture cross sections of radioactive fissile nuclei was designed,assembled and optimized at CENBG in the frame of this work. The measurement will be per-formed at the Gelina neutron time-of-flight facility at IRMM, where neutron cross sectionscan be measured over a wide energy range with high energy resolution. The fission detectorconsists of a multi-plate high-efficiency ionization chamber (IC). The γ-rays produced in cap-ture reactions are detected by an array of six C6 D6 scintillators surrounding the IC. In thesemeasurements the radiative capture γ-rays are hidden in large background of fission γ-rays thatrepresents a challenging issue. The latter has then to be subtracted by detecting fission eventswith a very well known efficiency (VETO method). An accurate determination of this efficiencyis rather difficult. In this work we have thoroughly investigated the prompt-fission-neutronsmethod for the IC efficiency measurement, providing new insights on this method. Thanks tothis study the IC efficiency was determined with a very low uncertainty. Using a 252Cf source,several parameters (gas pressure, high voltage and the distance between the electrodes) havebeen studied to determine the behaviour of the IC in order to find the ideal operation point:a good energy separation between α-particles and fission fragments (FF) and a good timingresolution. A good α-FF separation has been obtained with a highly radioactive 233U target.Also, the pulse-shape discrimination between γ-rays and neutrons in the C6D6 detectors wasobserved at Gelina under realistic experimental conditions. To conclude, the experimentalset-up and the VETO method have been carefully checked and validated, opening the way tofuture measurements of the capture and fission cross sections of 233U.
515

The Plastic Behaviour of Cold-Formed Rectangular Hollow Sections

Wilkinson, Timothy James January 2000 (has links)
The aim of this thesis is to assess the suitability of cold-formed rectangular hollow sections (RHS) for plastic design. The project involved an extensive range of tests on cold-formed Grade C350 and Grade C450 (DuraGal) RHS beams, joints and frames. A large number of finite element analyses was also carried out on models of RHS beams. The conclusion is that cold- formed RHS can be used in plastic design, but stricter element slenderness (b/t) limits and consideration of the connections, are required. Further research, particularly into the effect of axial compression on element slenderness limits, is required before changes to current design rules can be finalised. Bending tests were performed on cold-formed RHS to examine the web and flange slenderness required to maintain the plastic moment for a large enough rotation suitable for plastic design. The major conclusions of the beam tests were: (i) Some sections which are classified as Compact or Class 1 by current steel design specifications do not maintain plastic rotations considered sufficient for plastic design. (ii) The current design philosophy, in which flange and web slenderness limits are independent, is inappropriate. An interaction formula is required, and simple formulations are proposed for RHS. Connection tests were performed on various types of knee joints in RHS, suitable for the column - rafter connection in a portal frame. The connection types investigated were welded stiffened and unstiffened rigid knee connections, bolted plate knee joints, and welded and bolted internal sleeve knee joints, for use in RHS portal frames. The ability of the connections to act as plastic hinges in a portal frame was investigated. The most important finding of the joint tests was the unexpected fracture of the cold-formed welded connections under opening moment before significant plastic rotations occurred. The use of an internal sleeve moved the plastic hinge in the connection away from the connection centre- line thus eliminating the need for the weld between the RHS, or the RHS and the stiffening plate, to carry the majority of the load. The internal sleeve connections were capable of sustaining the plastic moment for large rotations considered suitable for plastic design. Tests on pinned-base portal frames were also performed. There were three separate tests, with two different ratios of vertical to horizontal point loads, simulating gravity and horizontal wind loads. Two grades of steel were used for comparison. The aims of the tests were to examine if a plastic collapse mechanism could form in a cold-formed RHS frame, and to investigate if plastic design was suitable for such frames. In each frame, two regions of highly concentrated curvature were observed before the onset of local buckling, which indicated the formation of plastic hinges and a plastic collapse mechanism. An advanced plastic zone structural analysis which accounted for second order effects, material non-linearity and member imperfections slightly overestimated the strength of the frames. The analysis slightly underestimated the deflections, and hence the magnitude of the second order effects. A second order plastic zone analysis, which did not account for the effects of structural imperfections, provided the best estimates of the strengths of the frames, but also underestimated the deflections. While cold-formed RHS did not satisfy the material ductility requirements specified for plastic design in some current steel design standards, plastic hinges and plastic collapse mechanisms formed. This suggests that the restriction on plastic design for cold-formed RHS based on insufficient material ductility is unnecessary, provided that the connections are suitable for plastic hinge formation, if required. A large number of finite element analyses were performed to simulate the bending tests summarised above, and to examine various parameters not studied in the experimental investigation. To simulate the experimental rotation capacity of the RHS beams, a sinusoidally varying longitudinal local imperfection was prescribed. The finite element analysis determined similar trends as observed experimentally, namely that the rotation capacity depended on both the web slenderness and flange slenderness, and that for a given section aspect ratio, the relationship between web slenderness and rotation capacity was non-linear. The main finding of the finite element study was that the size of the imperfections had an unexpectedly large influence on the rotation capacity. Larger imperfections were required in the more slender sections to simulate the experimental results. There should be further investigation into the effect of varying material properties on rotation capacity.
516

The Plastic Behaviour of Cold-Formed Rectangular Hollow Sections

Wilkinson, Timothy James January 2000 (has links)
The aim of this thesis is to assess the suitability of cold-formed rectangular hollow sections (RHS) for plastic design. The project involved an extensive range of tests on cold-formed Grade C350 and Grade C450 (DuraGal) RHS beams, joints and frames. A large number of finite element analyses was also carried out on models of RHS beams. The conclusion is that cold- formed RHS can be used in plastic design, but stricter element slenderness (b/t) limits and consideration of the connections, are required. Further research, particularly into the effect of axial compression on element slenderness limits, is required before changes to current design rules can be finalised. Bending tests were performed on cold-formed RHS to examine the web and flange slenderness required to maintain the plastic moment for a large enough rotation suitable for plastic design. The major conclusions of the beam tests were: (i) Some sections which are classified as Compact or Class 1 by current steel design specifications do not maintain plastic rotations considered sufficient for plastic design. (ii) The current design philosophy, in which flange and web slenderness limits are independent, is inappropriate. An interaction formula is required, and simple formulations are proposed for RHS. Connection tests were performed on various types of knee joints in RHS, suitable for the column - rafter connection in a portal frame. The connection types investigated were welded stiffened and unstiffened rigid knee connections, bolted plate knee joints, and welded and bolted internal sleeve knee joints, for use in RHS portal frames. The ability of the connections to act as plastic hinges in a portal frame was investigated. The most important finding of the joint tests was the unexpected fracture of the cold-formed welded connections under opening moment before significant plastic rotations occurred. The use of an internal sleeve moved the plastic hinge in the connection away from the connection centre- line thus eliminating the need for the weld between the RHS, or the RHS and the stiffening plate, to carry the majority of the load. The internal sleeve connections were capable of sustaining the plastic moment for large rotations considered suitable for plastic design. Tests on pinned-base portal frames were also performed. There were three separate tests, with two different ratios of vertical to horizontal point loads, simulating gravity and horizontal wind loads. Two grades of steel were used for comparison. The aims of the tests were to examine if a plastic collapse mechanism could form in a cold-formed RHS frame, and to investigate if plastic design was suitable for such frames. In each frame, two regions of highly concentrated curvature were observed before the onset of local buckling, which indicated the formation of plastic hinges and a plastic collapse mechanism. An advanced plastic zone structural analysis which accounted for second order effects, material non-linearity and member imperfections slightly overestimated the strength of the frames. The analysis slightly underestimated the deflections, and hence the magnitude of the second order effects. A second order plastic zone analysis, which did not account for the effects of structural imperfections, provided the best estimates of the strengths of the frames, but also underestimated the deflections. While cold-formed RHS did not satisfy the material ductility requirements specified for plastic design in some current steel design standards, plastic hinges and plastic collapse mechanisms formed. This suggests that the restriction on plastic design for cold-formed RHS based on insufficient material ductility is unnecessary, provided that the connections are suitable for plastic hinge formation, if required. A large number of finite element analyses were performed to simulate the bending tests summarised above, and to examine various parameters not studied in the experimental investigation. To simulate the experimental rotation capacity of the RHS beams, a sinusoidally varying longitudinal local imperfection was prescribed. The finite element analysis determined similar trends as observed experimentally, namely that the rotation capacity depended on both the web slenderness and flange slenderness, and that for a given section aspect ratio, the relationship between web slenderness and rotation capacity was non-linear. The main finding of the finite element study was that the size of the imperfections had an unexpectedly large influence on the rotation capacity. Larger imperfections were required in the more slender sections to simulate the experimental results. There should be further investigation into the effect of varying material properties on rotation capacity.
517

La presse et l'événement

Nobre-Correia, José-Manuel January 1980 (has links)
Doctorat en philosophie et lettres / info:eu-repo/semantics/nonPublished
518

Réactions de fusion entre ions lourds par effet tunnel quantique : le cas des collisions entre calcium et nickel / Heavy-ion fusion reactions through quantum tunneling : collisions between calcium and nickel isotopes

Bourgin, Dominique 26 September 2016 (has links)
Les réactions de fusion-évaporation et de transfert de nucléons entre ions lourds à des énergies proches de la barrière de Coulomb jouent un rôle essentiel dans l’étude de la structure nucléaire et des mécanismes de réaction. Dans le cadre de cette thèse, deux expériences de fusion-évaporation et de transfert de nucléons ont été réalisées au Laboratoire National de Legnaro en Italie : 40Ca+58Ni et 40Ca+64Ni. Dans une première expérience, les sections efficaces de fusion de 40Ca+58,64Ni ont été mesurées à des énergies au-dessus et en dessous de la barrière de Coulomb et ont été interprétées à l’aide de calculs en voies couplées et Hartree-Fock dépendants du temps (TDHF). Les résultats montrent l’importance de l’excitation à un phonon octupolaire dans le noyau 40Ca et les excitations à un phonon quadripolaire dans les noyaux 58Ni et 64Ni, ainsi que l’importance des voies de transfert de nucléons dans le système riche en neutrons 40Ca+64Ni. Dans une expérience complémentaire, les probabilités de transfert de nucléons de 40Ca+58,64Ni ont été mesurées dans le même domaine d’énergie que l’expérience précédente et ont été interprétées en effectuant des calculs TDHF+BCS. Les résultats confirment l’importance des voies de transfert de nucléons dans 40Ca+64Ni. Une description conjointe des probabilités de transfert de nucléons et des sections efficaces de fusion a été réalisée pour les deux réactions étudiées en utilisant une approche en voies couplées. / Heavy-ion fusion-evaporation and nucleon transfer reactions at energies close to the Coulomb barrier play an essential role in the study of nuclear structure and reaction dynamics. In the framework of this PhD thesis, two fusion-evaporation and nucleon transfer experiments have been performed at the Laboratori Nazionali di Legnaro in Italy : 40Ca+58Ni and 40Ca+64Ni. In a first experiment, fusion cross sections for 40Ca+58,64Ni have been measured from above to below the Coulomb barrier and have been interpreted by means of coupled-channels and Time-Dependent Hartree-Fock (TDHF) calculations. The results show the importance of the one-phonon octupole excitation in the 40Ca nucleus and the one-phonon quadrupole excitations in the 58Ni and 64Ni nuclei, as well as the importance of the nucleon transfer channels in the neutron-rich system 40Ca+64Ni. In a complementary experiment, nucleon transfer probabilities for 40Ca+58,64Ni have been measured in the same energy region as the previous experiment and have been interpreted by performing TDHF+BCS calculations. The results confirm the importance of nucleon transfer channels in 40Ca+64Ni. A simultaneous description of the nucleon transfer probabilities and the fusion cross sections has been performed for both reactions, using a coupled-channels approach.
519

The aeroelastic tailoring of a high aspect-ratio composite structure / Taeke Nicolai van den Bosch

Van den Bosch, Taeke Nicolai January 2014 (has links)
The aim of this investigation was to review literature for the most suitable aeroelastic tailoring analysis tools for long slender composite structures, and integrate them into an aeroelastic tailoring process. The JS1C Revelation is a high performance sailplane made from modern composites, mostly carbon fibre. This has the advantage of being more rigid than traditional engineering materials, thereby reducing the effects of the twisting deflections on these long slender structures due to aerodynamic loads. The implementing of aeroelastic tailoring can create bend-twist couples for performance improvements. Composites enable the use of aeroelastic tailoring to improve gliding performance. Flaperon 3 of the JS1C 21 m was used as the design problem for aeroelastic tailoring. Aeroelastic tailoring was done by analysing the flaperon structure at the different layup angles to determine the correct design point to tailor the structure to improve aerodynamic performance at thermalling and cruise, but mostly cruise since it accounts for 70% of the flight time. The composite structure analysis tool has the objective to get results during concept design. This directed the line of research of analysis tools to a solution method of two dimensional cross-section mesh properties projected onto a one dimensional beam. The literature of Hodges had good verification and published data on the analysis tools. The analysis tools comprised of three programs that were not very user friendly. Thus the author compiled a Matlab program as a user interface tool to run the three programs together. The aeroelastic tailoring process systematically works through the known design variables and objectives, which are given as inputs to the analysis tool. The analysis tool plots the coupling data versus layup angle. From this the best layup angles for a sought-after bend-twist couple is used to aeroelastically tailor the wing. The composite structure analysis tool’s accuracy was verified by analysing cantilever beam deflections and comparing the results with hand calculations and SolidWorks Simulation FEM results. The analysis tool’s accuracy was further verified by comparing the aerodynamic torsional load’s twist deflections with thin walled tube theory. The analysis tool was validated by applying a torsional load at the tip of a JS1C production Flaperon 3 in an experimental setup and then comparing this result with the Flaperon 3 modelled in the analysis tool. These comparisons also ensured that the model’s composite material properties and the meshing of the flaperon cross-sectional properties were correct. This aeroelastic tailoring was validated with the advantage of then being used to improve the aerodynamic performance of the JS1C Revelation 21 m tip’s flaperon. This improvement could be made by making use of a tailored bend-twist couple to reduce the effect of the aerodynamic load’s twist deflections. A test sample of the JS1C 21 m flaperon 3 was used to validate aeroelastic tailoring. The test sample was designed to be 1 m in length and have all the specified tailoring coupling characteristics that could improve the aerodynamic performance of the JS1C 21 m flaperon 3. The test sample was manufactured according to Jonker Sailplanes manufacturing standards and experimentally set up with the same applied deflections as in the analysis tool. The calculated bend-twist values and the experimental setup results were similar with a negligible difference, assuming small displacements and an aspect ratio greater than 13; this confirmed that the PreVABS/VABS/GEBT composite structure analysis tool could be used in aeroelastic tailoring to predict and design the bend-twist couple needed to improve the aerodynamic performance of the JS1C 21 m. While the twist behaviour of Flaperon 3 was improved by the tailored bend-twist couple, it was still necessary to add pre-twist as well, to fully address the effects of twisting by aerodynamic forces. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014
520

The aeroelastic tailoring of a high aspect-ratio composite structure / Taeke Nicolai van den Bosch

Van den Bosch, Taeke Nicolai January 2014 (has links)
The aim of this investigation was to review literature for the most suitable aeroelastic tailoring analysis tools for long slender composite structures, and integrate them into an aeroelastic tailoring process. The JS1C Revelation is a high performance sailplane made from modern composites, mostly carbon fibre. This has the advantage of being more rigid than traditional engineering materials, thereby reducing the effects of the twisting deflections on these long slender structures due to aerodynamic loads. The implementing of aeroelastic tailoring can create bend-twist couples for performance improvements. Composites enable the use of aeroelastic tailoring to improve gliding performance. Flaperon 3 of the JS1C 21 m was used as the design problem for aeroelastic tailoring. Aeroelastic tailoring was done by analysing the flaperon structure at the different layup angles to determine the correct design point to tailor the structure to improve aerodynamic performance at thermalling and cruise, but mostly cruise since it accounts for 70% of the flight time. The composite structure analysis tool has the objective to get results during concept design. This directed the line of research of analysis tools to a solution method of two dimensional cross-section mesh properties projected onto a one dimensional beam. The literature of Hodges had good verification and published data on the analysis tools. The analysis tools comprised of three programs that were not very user friendly. Thus the author compiled a Matlab program as a user interface tool to run the three programs together. The aeroelastic tailoring process systematically works through the known design variables and objectives, which are given as inputs to the analysis tool. The analysis tool plots the coupling data versus layup angle. From this the best layup angles for a sought-after bend-twist couple is used to aeroelastically tailor the wing. The composite structure analysis tool’s accuracy was verified by analysing cantilever beam deflections and comparing the results with hand calculations and SolidWorks Simulation FEM results. The analysis tool’s accuracy was further verified by comparing the aerodynamic torsional load’s twist deflections with thin walled tube theory. The analysis tool was validated by applying a torsional load at the tip of a JS1C production Flaperon 3 in an experimental setup and then comparing this result with the Flaperon 3 modelled in the analysis tool. These comparisons also ensured that the model’s composite material properties and the meshing of the flaperon cross-sectional properties were correct. This aeroelastic tailoring was validated with the advantage of then being used to improve the aerodynamic performance of the JS1C Revelation 21 m tip’s flaperon. This improvement could be made by making use of a tailored bend-twist couple to reduce the effect of the aerodynamic load’s twist deflections. A test sample of the JS1C 21 m flaperon 3 was used to validate aeroelastic tailoring. The test sample was designed to be 1 m in length and have all the specified tailoring coupling characteristics that could improve the aerodynamic performance of the JS1C 21 m flaperon 3. The test sample was manufactured according to Jonker Sailplanes manufacturing standards and experimentally set up with the same applied deflections as in the analysis tool. The calculated bend-twist values and the experimental setup results were similar with a negligible difference, assuming small displacements and an aspect ratio greater than 13; this confirmed that the PreVABS/VABS/GEBT composite structure analysis tool could be used in aeroelastic tailoring to predict and design the bend-twist couple needed to improve the aerodynamic performance of the JS1C 21 m. While the twist behaviour of Flaperon 3 was improved by the tailored bend-twist couple, it was still necessary to add pre-twist as well, to fully address the effects of twisting by aerodynamic forces. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

Page generated in 0.0259 seconds