• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 378
  • 153
  • 69
  • 59
  • 39
  • 30
  • 13
  • 11
  • 8
  • 6
  • 5
  • 4
  • 4
  • 3
  • 3
  • Tagged with
  • 973
  • 207
  • 170
  • 138
  • 105
  • 83
  • 68
  • 64
  • 63
  • 60
  • 59
  • 58
  • 57
  • 57
  • 55
  • 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.
691

Accepterat pris: -En studie om bakgrundentill införandet och om syftet uppnåtts ochhålls än idag? / Accepted price: -A study of background tothe introduction and the purpose achievedand if maintained today?

Karlsson, Zandra, Bergroth, Carl-Henrik January 2014 (has links)
Våren 2011 var det stora debattämnet i media, bland konsumenter och hos fastighetsmäklare lockpriser . Med lockpris avses att en bostad annonseras till ett väsentligt lägre pris än det bedömda marknadsvärdet på bostaden. Motivet var att locka till sig fler spekulanter till en eventuell budgivning. Innebörden av väsentligt är inte helt fastställt i lagen, vilket gör begreppet svårtolkat. I och med att utgångspriserna var satta så lågt jämfört med vad slutpriset blev så fick fastighetsmäklarna utstå mycket kritik. Mäklarbranschens anseende försämrades, och för att motverka detta bildades en arbetsgrupp av fastighetsmäklare från olika mäklarföretag i Stockholms innerstad. Detta mynnade ut i att istället för att använda sig av ett utgångspris så infördes begreppet accepterat pris. Ett accepterat pris innebär att det pris som annonseras ska vara på en sådan nivå att säljaren kan tänka sig att sälja bostaden till det priset. Dock med den kvarstående fria prövningsrätten som säljaren oavsett har, som innebär att tvång till försäljning inte råder, trots inkommit bud på annonserat pris. Som säljare har du rätt att sälja när du vill, till vem du vill och till vilket pris du vill. Syftet med uppsatsen är att redogöra för överenskommelsen av accepterat pris, vilka de bakomliggande faktorerna var vid införandet och vad målet var. Vidare vill vi klargöra om lockpriser är på väg tillbaka och utreda vilka andra bakomliggande faktorer som kan bidra till att ett pris uppfattas som lockpris. Resultatet av uppsatsen visar att en av tankarna bakom införandet av accepterat pris var att stärka mäklarbranschens anseende och öka transparensen till spekulanterna då dem skulle få en bättre uppfattning om bostadens slutpris redan vid annonseringen av objektet. Enligt de gjorda intervjuerna med mäklare så märks en viss tendens till att lockpriserna anses vara på väg tillbaka. Även den inhämtade statistiken visar att så skulle kunna vara fallet då skillnaden mellan accepterat pris/utgångspris och slutpris på senare tid har ökat. För att kunna dra någon mer definitiv slutsats är detta något man bör ta ställning till när mer data har insamlats över ett större tidsperspektiv framåt i tiden. / The great debate topic in media and among real estate agents in spring 2011 was specially reduced prices . Specially reduced prices means that a property is advertised at a considerably lower price than the evaluated current market value of the property. This is to attract more bidders in a potential bidding. It is in this case not completely established by law what is meant by considerably lower price, why this concept is difficult to interpret. Real estate agents got lot of criticism due to the output prices which were too low compared to the final prices. The real estate agents industry’s reputation became worse and to counter this, there was formed a taskforce of real estate agents in Stockholm. This resulted in that instead of making use of a starting price the concept of accepted price was introduced. The accepted price meant that the price that was advertised was going to be at such a level that the seller was willing to sell the property for that. With the free trial right the seller would not be compelled to sell anyhow. This study is about accounting for the emergence of accepted price and the factors behind the introduction and the concept. It also aims to clarify what the goal of accepted price was and to discuss if specially reduced prices are coming back. Finally to investigate if there can be some underlying factors that can contribute to that our perception increases as specially reduced prices. The results of the paper show that one of the ideas behind the introduction of the accepted price was to strengthen the real estate agent industry's reputation and increase transparency to bidders so they would get a further idea of the final price of the property already at the announcement. According to the interviews made with the real estate agents, it is noticed a certain tendency that specially reduced prices are considered to be on the way back. Although the collected statistics shows that such could be the case when the difference between starting- and final price has recently increased. To be able to make a more definite conclusion, this is something that could be considered when more data have been collected over a wider time frame in the future.
692

Viability, feasibility and Sustainability of emission reducing solutions for Nordic wood stoves: Testing and evaluation : Degree project for Master in mechanical engineering with focus on innovative and sustainable product development

Berg, Casper January 2022 (has links)
As of 2022 the European Union introduced a new Eco Design legislation which states emission limits for stoves sold in the EU. There are already requirements on emissions, but as both legislation are to be harder and there is a higher interest in Eco friendly products, there is an interest to study different ways to reduce the emissions from wood stoves. As stoves are today primarily seen as furniture that can provide some heat, easy usage is expected.  The objective of this report is to explore this connection between emission reduction and how viable, feasible and sustainable it might be if it where to be implemented in a real product. Using design thinking and the design thinking methodology, concepts where developed and tested using test stoves which where equipped to measure emissions of carbon monoxide and organic gaseous compounds. The testing was done in accordance with EN 16510 and the developed prototype was a catalytic filter mesh which was designed to be rotated so that air could flow around it instead of through it during startups and refueling. The theory behind it was that previous studies on similar catalytic mesh filters showed promising emission reductions. However, these test where done on static catalytic filters which where always in the path of the air in the flue system. That meant pressure drops due to restricted airflow in the stoves could result in impaired combustion and increased emissions.  The Testing showed promising result with the variable filter outperforming a stationary filter setup. The variable filter showed 16\% reduced carbon monoxide emissions and 25\% reduced organic gaseous compound emissions compared to the stationary filter setup. Furthermore the benefits of variable filters is believed to increase as the amount of filters stacked increase since it would in a stationary setup provide a lot of air restriction which could have serious effect on how easy the product would be to start and maintain. As for usability the setup is believed to be implementable in such ways that no additional work would be necessary from a user perspective and thus not discourage new users from choosing a stove which produces less emissions. / Från och med 2022 inför Europeiska Unionen Eco Design direktivet med utsläppsgränser som måste föjlas vid försäljning av kaminer i EU. Det finns redan liknande krav på usläpp, men då de troligen ökar i framtiden och intresset för miljövänliga produkter ökar, så finns det det intresse att studera lösningar som minskar utsläppen från vedkaminer. Eftersom vedkaminer i dagens läge inte bara behöver värma ett hus, utan ses också som en möbel så är användarvänligheten av ytersta vikt.  Syftet med denna raport att utforska kopplingen mellan minsking av utsläpp och hur det skulle kunna implementeras på ett rimligt sätt i en verklig produkt. Genom användning av Desing thinking och Design research methodology, utvecklades koncept och testades i en kamin som mätte bl.a kolmonoxid och organiskt gasformiga föreningar. Testerna gjordes i enlighet med EN 16510 och den utvecklade prototypen var ett katalytiskt filternät som var designat för att roteras så att luft kan strömma runt den istället för genom vid uppstart och påfyllning. Teorin var att tidigare studier på liknande katalytiska nätfilter visade på lovande utsläppsminskningar. Dessa tester gjordes dock på statiska katalytiska filter som alltid var i vägen för luften i rökkanalen. Det innebar att tryckfall på grund av begränsat luftflöde i kaminerna kunde resultera i försämrad förbränning och ökade utsläpp.  Testningen visade lovande resultat med det variabla filtret som överträffade en stationär filteruppsättning. Det variabla filtret visade 16 \% minskade kolmonoxidutsläpp och 25 \% reducerade utsläpp av organiska gasformiga föreningar jämfört med den stationära filteruppsättningen. Dessutom tros fördelarna med variabla filter öka när mängden staplade filter ökar då en stationär uppställning skulle ge en hel del luftbegränsningar som kan ha allvarliga effekter på hur lätt produkten skulle vara att starta och underhålla. När det gäller användbarhet tros installationen vara genomförbar på ett sådant sätt att inget ytterligare arbete skulle behövas ur ett användarperspektiv och därmed inte avskräcka nya kunder från att välja en kamin som har linkande lösning.
693

Unsteady Dynamics of Shock-Wave Boundary-Layer Interactions

Akshay Deshpande (11022453) 23 July 2021 (has links)
<div>Shock-wave/turbulent boundary-layer interactions (SWTBLIs) are characterized by low-frequency unsteadiness, amplified aerothermal loads, and a complex three-dimensional flowfield. Presence of a broad range of length and time-scales associated with compressible turbulence generates additional gasdynamic features that interact with different parts of the flowfield via feedback mechanisms. Determining the physics of such flows is of practical importance as they occur frequently in different components of a supersonic/hypersonic aircraft such as inlets operating in both on- and off-design conditions, exhaust nozzles, and control surfaces. SWTBLIs can cause massive flow separation which may trigger unstart by choking the flow in an inlet. On control surfaces, fatigue loading caused by low-frequency shock unsteadiness, coupled with high skin-friction and heat transfer at the surface, can result in failure of the structure.</div><div><br></div><div>The objective of this study is twofold. The first aspect involves examining the causes of unsteadiness in SWTBLIs associated with two geometries – a backward facing step flow reattaching on to a ramp, and a highly confined duct flow. Signal processing and statistical techniques are performed on the results obtained from Delayed Detached-Eddy Simulations (DDES) and Implicit Large-Eddy Simulations (ILES). Dynamic Mode Decomposition (DMD) is used as a complement to this analysis, by obtaining a low-dimensional approximation of the flowfield and associating a discrete frequency value to individual modes. </div><div><br></div><div>In case of the backward facing step, Fourier analysis of wall-pressure data brought out several energy dominant frequency bands such as separation bubble breathing, oscillations of the reattachment shock, shear-layer flapping, and shedding of vortices from the recirculation zone. The spectra of reattachment shock motion suggested a broadband nature of the oscillations, wherein separation bubble breathing affected the low-frequency motion and shear-layer flapping, and vortex shedding correlated well at higher frequencies. A similar exercise was carried out on the highly confined duct flow which featured separation on the floor and sidewalls. In addition to the low-frequency shock motions, the entire interaction exhibited a cohesive back-and-forth in the streamwise direction as well as a left-right motion along the span. Mode reconstruction using DMD was used in this case to recover complex secondary flows induced by the presence of sidewalls.</div><div><br></div><div>For the final aspect of this study, a flow-control actuator was computationally modeled as a sinusoidally varying body-force function. Effects of high-frequency forcing at F<sup>+</sup> =1.6 on the flowfield corresponding to a backward facing step flow reattaching on to a ramp were examined. Conditionally averaged profile of streamwise velocity fluctuations, based on reattachment shock position, was used for the formulation of spatial distribution of the actuator. The forcing did not change the mean and RMS profiles significantly, but affected the unsteadiness of the interaction significantly. The effects of forcing were localized to the recirculation zone and did not affect the evolution of the shear-layer. The acoustic disturbances propagating through the freestream and recirculation zone drove the motion of the reattachment shock, and did not alter the low-frequency dynamics of the interaction.</div>
694

Application des techniques de bases réduites à la simulation des écoulements en milieux poreux / Application of reduced basis techniques to the simulation of flows in porous media

Sanchez, Mohamed, Riad 19 December 2017 (has links)
En géosciences, les applications associées au calage de modèles d'écoulement nécessitent d'appeler plusieurs fois un simulateur au cours d'un processus d'optimisation. Or, une seule simulation peut durer plusieurs heures et l'exécution d'une boucle complète de calage peut s'étendre sur plusieurs jours. Diminuer le temps de calcul global à l'aide des techniques de bases réduites (RB) constitue l’objectif de la thèse.Il s'agit plus précisément dans ce travail d'appliquer ces techniques aux écoulements incompressibles diphasiques eau-huile en milieu poreux. Ce modèle, bien que simplifié par rapport aux modèles utilisés dans l'industrie pétrolière, constitue déjà un défi du point de vue de la pertinence de la méthode RB du fait du couplage entre les différentes équations, de la forte hétérogénéité des données physiques, ainsi que du choix des schémas numériques de référence.Nous présentons d'abord le modèle considéré, le schéma volumes finis (VF) retenu pour l'approximation numérique, ainsi que différentes paramétrisations pertinentes en simulation de réservoir. Ensuite, après un bref rappel de la méthode RB, nous mettons en oeuvre la réduction du problème en pression à un instant donné en suivant deux démarches distinctes. La première consiste à interpréter la discrétisation VF comme une approximation de Ritz-Galerkine, ce qui permet de se ramener au cadre standard de la méthode RB mais n'est possible que sous certaines hypothèses restrictives. La seconde démarche lève ces restrictions en construisant le modèle réduit directement au niveau discret.Enfin, nous testons deux stratégies de réduction pour la collection en temps de pressions paramétrées par les variations de la saturation. La première considère le temps juste comme un paramètre supplémentaire. La seconde tente de mieux capturer la causalité temporelle en introduisant les trajectoires en temps paramétrées. / In geosciences, applications involving model calibration require a simulator to be called several times with an optimization process. However, a single simulation can take several hours and a complete calibration loop can extend over serval days. The objective of this thesis is to reduce the overall simulation time using reduced basis (RB) techniques.More specifically, this work is devoted to applying such techniques to incompressible two-phase water-oil flows in porous media. Despite its relative simplicity in comparison to other models used in the petroleum industry, this model is already a challenge from the standpoint of reduced order modeling. This is due to the coupling between its equations, the highly heterogeneous physical data, as well as the choice of reference numerical schemes.We first present the two-phase flow model, along with the finite volume (FV) scheme used for the discretization and relevant parameterizations in reservoir simulation. Then, after having recalled the RB method, we perform a reduction of the pressure equation at a fixed time step by two different approaches. In the first approach, we interpret the FV discretization as a Ritz-Galerkine approximation, which takes us back to the standard RB framework but which is possible only under severe assumptions. The second approach frees us of these restrictions by building the RB method directly at the discrete level.Finally, we deploy two strategies for reducing the collection in time of pressuresparameterized by the variations of the saturation. The first one simply considers time as an additional parameter. The second one attempts to better capture temporalcausality by introducing parameterized time-trajectories.
695

Instabilités thermoacoustiques dans les moteurs à propergol solide / Thermo-acoustic instabilities in solid rocket motors

Genot, Aurélien 21 June 2019 (has links)
Dans un moteur à propergol solide, des instabilités thermoacoustiques auto-entretenues, induites par le couplage de la dynamique de la combustion des gouttes d’aluminium, libérées par la combustion du propergol, avec le champ acoustique peuvent induire des oscillations de pression.L’analyse menée tout au long de ce manuscrit repose sur un ensemble d’hypothèses simplificatrices: (i) la réponse de la combustion de gouttes d’aluminium aux perturbations acoustiques est contrôlée par l’écoulement local autour de la goutte, (ii) le processus de combustion peut être supposé quasi stationnaire pour la gamme de fréquences et les amplitudes acoustiques étudiées et (iii) la combustion de l’aluminium est brusquement arrêtée lorsque le diamètre de la goutte d’aluminium diminue en dessous d’un diamètre résiduel.L’instabilité thermoacoustique est étudiée au moyen de simulations numériques de l’écoulement dans un moteur générique et d’analyses théoriques. Le diamètre résiduel des gouttes d’aluminium après la combustion, l’amplitude de la perturbation acoustique et la durée de la combustion des gouttes d’aluminium figurent parmi les principaux paramètres modifiant l’instabilité. En outre, trois comportements de réponse de la combustion à l’acoustique sont identifiés : un comportement linéaire pour les faibles niveaux de pression acoustique puis un comportement quadratique (faiblement non-linéaire) et enfin un comportement fortement non-linéaire quand l’amplitude des oscillations augmente.Ensuite, deux aspects importants de la réponse des gouttes d’aluminium sont identifiés. Ils sont associés aux oscillations de la durée du temps de combustion des gouttes, identifiables à la frontière du nuage de gouttes, et aux fluctuations du taux d’évaporation contrôlées par la convection de l’écoulement gazeux autour de chaque goutte. Tenant compte de ces dynamiques,des expressions analytiques sont obtenues permettant de reproduire avec précision les résultats numériques des simulations de l’écoulement. Quatre nombres sans dimension qui régissent la dynamique de ces instabilités sont également identifiés. Inspiré de l’analyse théorique précédente, un modèle numérique d’ordre réduit faiblement non linéaire est finalement développé pour prédire des cycles limites. / In a solid rocket motor, self-sustained thermo-acoustic instabilities, induced by the coupling of the combustion dynamics of aluminum droplets released by the burning propellant with the acoustic field can induce pressure oscillations.The analysis conducted throughout this manuscript relies thus on a set of simplifying hypothesis by assuming (i) that the response of the combustion of aluminum droplets to acoustic perturbations is controlled by the oscillating drag exerted by the local flow around the droplet, (ii) that this unsteady combustion process can be assumed quasi-steady for the range of frequencies and acoustic amplitudes studied and (iii) that aluminum combustion is abruptly quenched when the aluminum droplet diameter falls below a residual diameter.The thermo-acoustic instability is studied first by numerical flow simulations in a generic solid rocket motor and theoretical analyses. The post-combustion residual diameter of the aluminum particles, the amplitude of acoustic perturbation and the lifetime of the burning aluminum droplets are among the main parameters altering the instability. Also, three combustion response behaviors to acoustics are identified : a linear behavior for small acoustic pressure levels followed by a quadratic behavior then a highly non-linear behavior when the pressure amplitude increases in the motor chamber. Moreover, two important features of the response of aluminum droplets are identified. They are associated to oscillations of the droplet lifetime at the boundary of the droplet cloud and to fluctuations of the droplet evaporation rate, controlled by convection. The dynamics of the droplets highly depends on gas and droplet velocity fields and on droplet diameter. Taking these features into account, yields analytical expressions that allow to reproduce with accuracy the numerical results from the flow simulations. Four dimension less numbers are then identified. They govern the dynamics of these instabilities. Inspired from the previous theoretical analysis, a weakly nonlinear low-order numerical model is finally developed to predict limit cycles.
696

Ověřování vlastností betonů s nanočásticemi / Verification of properties of concretes with nanoparticles

Pacltová, Klára January 2019 (has links)
This diploma thesis deals with the influence of addition of carbon nanoparticles on cement composites. The theoretical part of the diploma thesis is focused on the research of information about carbon nanoparticles, more precisely about carbon nanotubes and graphene oxide. There are summarized methods of dispersing carbon nanotubes and their effects on cement composites. The practical part follows the theoretical part of the research. In the first phase, the correct technique of graphene oxide dispersion was verified. Subsequently, the effects of graphene oxide on the mechanical properties of cement mortars were verified. In the final phase of the diploma thesis, the knowledge gained from the previous part was verified on concrete samples.
697

Generel bezbariérových tras v Bystřici pod Hostýnem / Generel plan of barrier-free routes in Bystrice pod Hostynem

Bakalová, Lucie January 2022 (has links)
The principal theme of this diploma thesis is a development of Generel for barrier-free routes in Bystřice pod Hostýnem. The thesis focuses on familiarization with a group of people with limited movement and orientation abilities, their comfortable and safe usage of road constructions and public spaces. Theoretical interpretation of this diploma thesis is based on the bylaw No. 398/2009 Coll., on general technical requirements ensuring barrier-free use of the buildings. Theoretical part of the thesis continues by familiarization with the way of movement and orientation of people with limited movement and orientation abilities and their use of features used to simplify pedestrian transportation in the city. The practical part of the thesis is focused on development of proposal for routes connecting important objects of civil amenities in the city of Bystřice pod Hostýnem. Practical part also provides valuation of current status of existing routes and their proposed changes to achieve compliance with bylaw No. 398/2009 Coll., to ensure the maximum safety of barrier-free routes in the city.
698

Enhancement of Light Emission from Metal Nanoparticles Embedded Graphene Oxide

Karna, Sanjay K. 05 1900 (has links)
A fully oxidized state of graphene behaves as a pure insulating while a pristine graphene behaves as a pure conducting. The in-between oxide state in graphene which is the controlled state of oxide behaves as a semiconducting. This is the key condition for tuning optical band gap for the better light emitting property. The controlling method of oxide in graphene structure is known as reduction which is the mixed state of sp2 and sp3 hybrid state in graphene structure. sp2 hybridized domains correspond to pure carbon-carbon bond i.e. pristine graphene while sp3 hybridized domains correspond to the oxide bond with carbon i.e. defect in graphene structure. This is the uniqueness of the graphene-base material. Graphene is a gapless material i.e. having no bandgap energy and this property prevents it from switching device applications and also from the optoelectronic devices applications. The main challenge for this material is to tune as a semiconducting which can open the optical characteristics and emit light of desired color. There may be several possibilities for the modification of graphene-base material that can tune a band gap. One way is to find semiconducting property by doping the defects into pristine graphene structure. Other way is oxides functional groups in graphene structure behaves as defects. The physical properties of graphene depend on the amount of oxides present in graphene structure. So if there are more oxides in graphene structure then this material behaves as a insulating. By any means if it can be reduced then oxides amount to achieve specific proportion of sp2 and sp3 that can emit light of desired color. Further, after achieving light emission from graphene base material, there is more possibility for the study of non-linear optical property. In this work, plasmonic effect in graphene oxide has been focused. Mainly there are two kinds of plasmon effects have been studied, one is long range (surface) and short range (localized) plasmon. For long range plasmon gold thin film was deposited on partially reduced graphene oxide and for short range plasmon silver nanoparticles have used. Results show that there are 10-fold enhancement in light emission from partial graphene oxide coated with gold thin film while 4-fold enhancement from reduced graphene oxide solution with silver nanoparticles. Chemical method and photocatalytic method have been employed for the reduction of graphene oxide for the study of surface plasmon and localized plasmon. For the characterization UV-Vis spectrometer for absorption, spectrofluorophotometer for fluorescent emission, Raman spectrometer for material characterization, photoluminescence and time resolved photoluminescence have been utilized. Silver and gold nanoparticles are spherical of average size of 80 nm and 40 nm have been used as plasmons.
699

Facile Fabrication of Functionally Graded Graphene Films for Transient Electronics

Bhatkar, Omkar S. January 2018 (has links)
No description available.
700

Machine Learning-Based Reduced-Order Modeling and Uncertainty Quantification for "Structure-Property" Relations for ICME Applications

Yuan, Mengfei 11 July 2019 (has links)
No description available.

Page generated in 0.0909 seconds