Thèses sur le sujet « Visco Elastici »
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1
Manfroni, Michele. « Controllo del flusso termico in convezione mista tramite fluidi visco-elastici ». Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/6107/.
Texte intégralRésumé :
L'obiettivo del lavoro è stato quello di valutare l'influenza di fluidi viscoelastici sullo scambio termico in flussi in convezione mista, tramite l'analisi di simulazioni numeriche dirette del campo. Si è osservato che il numero di Nusselt aumenta se il numero di Deborah della soluzione cresce, ma l'incremento della componente di convezione forzata inibisce tale effetto positivo.
2
Bertoni, Vanessa. « Analisi probabilistica e uso di controventi dissipativi in telai in accaio e composti acciaio - calcestruzzo ». Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4469.
Texte intégralRésumé :
2009/2010In questa tesi si indagano vari metodi per la protezione sismica delle strutture a partire da una corretta e realistica valutazione della loro risposta sismica attraverso un approccio probabilistico che tenga conto delle aleatorietà più significative. Se la risposta non soddisfa quanto atteso si può intervenire in vari modi come attraverso l’introduzione di controventi dissipativi. Si analizzano qui due tipologie: i controventi dotati di dispositivi visco elastici e quelli con dispositivi fluido viscosi. Di entrambi si presentano dei metodi di progetto completi con relativi confronti.
XXIII Ciclo
1977
3
Bella, Maurizio. « Modellazione numerica di strutture sismoresistenti e analisi probabilistiche di tipo montecarlo ». Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3460.
Texte intégralRésumé :
2008/2009Lo scopo della presente Tesi è lo sviluppo e la messa a punto di una serie di modelli numerici e codici di calcolo atti a modellare il comportamento di strutture sismoresistenti di tipo intelaiato sottoposte ad azione sismica al fine di poter effettuare una valutazione dell'affidabilità strutturale per mezzo di analisi probabilistiche di tipo Montecarlo. In particolare la modellazione dei giunti composti trave-colonna, è stata realizzata definendo un modello meccanico per componenti, atto a descrivere il comportamento del giunto modellato per mezzo di un insieme di elementi rigidi e deformabili, opportunamente connessi tra di loro e a cui sono stati assegnati opportuni modelli istertici. A tale scopo si è proceduto allo sviluppo ed implementazione all’interno del codice di calcolo ABAQUS e ADAPTIC di una serie di modelli isteretici reperiti in letteratura atti alla modellazione numerica delle principali componenti deformative individuabili nei giunti trave colonna e nei dispositivi viscoelastici utilizzati nella realizzazione di controventi dissipativi. Nello sviluppo del modello meccanico per la modellazione del comportamento dei giunti nodi trave colonna composti si è prestata particolare attenzione alla definizione degli elementi che descrivono l’interazione tra la soletta e la colonna. Per agevolare l’esecuzione dell’elevato numero di analisi numeriche richieste dalle analisi probabilistiche di tipo Montecarlo si è inoltre proceduto a sviluppare un pre-processore ed un post-processore in grado di interfacciarsi con i codici di calcolo utilizzati. Nel primo capitolo verrà introdotto il problema della valutazione dell'affidabilità delle strutture. Nel secondo capitolo verranno introdotti i metodi di analisi strutturale con particolare riferimento al metodo dell'analisi probabilistica di tipo montecarlo applicato alla valutazione dell'affidabilità delle strutture. Nel terzo capitolo si esaminerà la problematica della modellazione numerica delle strutture sismoresistenti. Nel quarto capitolo verranno illustrati i modelli numerici sviluppati e implementati nonchè i codici di calcolo sviluppati. Nel quinto capitolo verrà illustrato il processo di validazione dei modelli numerici sviluppati utilizzando i risultati forniti da una serie di indagini sperimentali condotte da vari autori e reperite in letteratura. Infine nel sesto capitolo si procederà alla valutazione dell'affidabilità strutturale di una struttura intelaiata campione. Più precisamente la struttura oggetto dell’indagine è il telaio testato nel European Laboratory for Structural Assessment (ELSA) del Joint Research Center (JRC) di Ispra (Varese). In particolare, per tale struttura verranno determinate le curve di fragilità con riferimento allo spostamento relativo di interpiano (IRDA) assunto come indice di danno strutturale.
XXII Ciclo
1979
4
Whiting, Andrew Ivan Melville. « Localized buckling of an elastic strut in a visco-elastic medium ». Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/37110.
Texte intégralRésumé :
Certain types of long, axially compressed structures have the potential to buckle locally in one or more regions rather than uniformly along their length. Here, the potential for localized buckle patterns in an elastic layer embedded in a visco-elastic medium is investigated using a strut-on-foundation model. Applications of this model include the growth of geological folds and other time-dependent instability processes. The model consists of an elastic strut of uniform flexural stiffness supported by a Winkler-type foundation made up of discrete Maxwell elements. Mathematically, this model corresponds to a nonlinear partial differential equation which is fourth-order in space and first-order in time. The nature of the buckling process is characterized by an initial period of elastic deformation followed by an evolutionary phase in which both elasticity and viscosity have a role to play. Two different formulations are studied: the first combines linear strut theory with a nonlinear foundation and is valid for small, but finite, deflections; the other incorporates the exact expression for curvature of the strut resulting in geometrical nonlinearities and is capable of modelling large deflections. The evolution of non-periodic buckle patterns in each system is examined under the constraint of controlled end displacement. Two independent methods are used to approximate the solution of the governing equations. Modal solutions, based on the method of weighted residuals, complement accurate numerical solutions obtained with a boundary-value solver. In either case, the results suggest that for the perfect system, localized solutions follow naturally from the inclusion of nonlinear elasticity with softening characteristics. Emphasis throughout is on the qualitative features displayed by the phenomenon of localization rather than specific applications. Nevertheless, the ideas and results are a step towards accounting for the rich variety of deformed shapes exhibited by nature.
5
Sandin, Joakim. « Analysis Methods for Structures with Visco-Elastic Damping Treatment ». Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-13250.
Texte intégralRésumé :
During aircraft development, the impact of vibrations is examined and how this affects the aircraft structure under different conditions. Those vibrations can damage electronic equipment that are installed within the fuselage and can even lead to material fatigue within the structure. To reduce vibrations there are two approaches that are preferred to use, installing vibration insulators attached between the structure and the electrical component or change the design of the structure to a stiffer one. Those methods are easiest to implement in an early stage of the development but in later stages, when vibration problems usually are detected, it is too difficult and expensive to do major changes of the structure and there is lack of space to implement vibration insulators. A third method is then to apply passive damping in form of damper mats to surfaces on structures where critical vibrations occurs. The effects on the structural behavior when damper mats are applied to a certain structure are studied in this thesis work. The purpose is to get deeper knowledge about how damper mats can be used to reduce vibrations in aircraft structures. The type of damper mat that is studied is known as Constrained Layer Damping, CLD, which is a sandwich of a visco-elastic material layer and a stiffer constraining material layer. Modelling and simulation methods that are based on commercial FE-software have been developed. The analysis method is based on doing a modal analysis with structural damping taken into account. This makes it possible to predict the overall global damping at each structural mode. The models for damper mats have in this project been verified with experimental testing using typical damper mats. The methodology can be used to predict the behavior of damped structures in order to obtain an effective and lightweight passive damping solution.Under utvecklingen av flygplan undersöks hur vibrationer påverkar flygplansstrukturen under olika förutsättningar. Dessa vibrationer kan skada elektronisk utrustning som är monterad i flygplanskroppen och kan även göra så att materialutmattning uppstår i flygplansstrukturen. För att motverka vibrationer finns det två metoder som är att föredra, antingen att montera vibrationsisolatorer mellan de elektroniska utrustningarna och strukturen eller att ändra designen på strukturer till en styvare. Dessa metoder är enkla att implementera i ett tidigt steg i utvecklingsprocessen men i senare steg, då vibrationsproblem ofta upptäcks, så är det för komplicerat och för dyrt att göra större ändringar på strukturen och så är det ont om plats för att kunna installera vibrations isolatorer. En tredje metod är istället att implementera passiv dämpning i form av dämpningsmattor på ytor av strukturen där kritiska vibrationer uppstår. Effekterna av det strukturella uppförandet när dämpningsmattor är applicerade på en viss struktur har studerats i det här examensarbetet. Syftet är att få en fördjupad kunskap om hur dämpningsmattor kan användas för att reducera vibrationer i flygplan strukturer. Den typ av dämpningsmatta som har studerats är känd som Constrained Layer Damping, CLD, vilken är en sandwich av ett visko-elastiskt lager samt ett styvare lager. Modellerings och simuleringsmetoder som är baserade på kommersiella FE-mjukvaror har utvecklats. Analysmetoderna är baserade på att utföra modalanalys tillsammans med strukturell dämpning. Detta möjliggör att förutse den övergripande dämpningen vid varje strukturell mod. Modellerna för dämpningsmattorna har i det här projektet verifierats med experimental testning av typiska dämpningsmattor. Metodiken kan användas till att prediktera beteendet av dämpade strukturer för att uppnå en effektiv och lättviktig passiv dämpningslösning.
6
Matar, Ali. « The mechano sorptive creep of softwood in bending ». Thesis, London South Bank University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288110.
Texte intégralRésumé :
This PhD research project mainly examined the important yet incompletely understood field of the mechano-sorptive creep of softwood. It included the acquisition of accurate creep data during constant and cyclic moisture conditions. The study only concerns the loading of softwood in the longitudinal, parallel to the grain direction in bending mode. Mechano-sorptive creep deformation takes place when the wood is subjected to load in varying humidity conditions, where the creep deformation is substantially higher than the creep deformation under constant humidity conditions. Visco-elastic creep is defined as the creep strain that is primarily dependent on time. Further analysis on the pseudo-creep, which is reversible with moisture changes, was also investigated. The Young's Modulus (E) and density (p) of the samples used in this research were measured and the ratio of (E/p) was used to characterise the quality of the wood specimen. A program was written in Quick-Basic for the computer to take readings from the creep machines at all times during all creep tests for acquiring maximum creep data possible for obtaining better results. A 'steaming' technique was implemented to accelerate creep recovery, in order to allow the re-use of the same sample for repeated creep testing, so reducing the effects of variability. Measurements of visco-elastic creep, mechano-sorptive creep limit and pseudo-creep rate as functions of percentage relative humidity and E/p were investigated and analysed. The mechano-sorptive creep limit was successfully reached by the load-reduction method. The pseudo-creep rate was similar for samples with the same values of E/p at different relative humidity. The higher the relative humidity, the larger the magnitude of visco-elastic and the 'reference' creep at the mechano-sorptive creep limit. A higher value of E/p produced lower pseudocreep rate, visco-elastic creep and mechano-sorptive creep limit. Equations were derived from the one week visco-elastic creep experimental data in order to extrapolate visco-elastic creep to longer time durations, (medium, long and permanent periods, and compared to the new European code of practice for timber design, namely the Draft Eurocode 5), and at two critical relative humidity conditions, (63% and 90%rh), which correspond to the Service Classes 1 and 2 in the Draft Eurocode 5. Also, an equation to predict the mechano-sorptive creep limit at various values of E/p for the two critical relative humidity conditions, (63% and 90%rh), was acquired. The prediction of creep at various relative humidities along the pseudo creep line was also quantified. The extrapolated visco-elastic creep along with the total upper-bound creep values were compared to the creep allowances of the Draft Eurocode 5 for both Service Classes 1 and 2. Moreover, a design scheme for estimating the upper-bound creep, consisting of the addition of visco-elastic, mechano-sorptive and pseudo creep for Draft Eurocode 5 Service Classes 1 and 2 was achieved. A study of the degree of interaction between visco-elastic and mechanosorptive creep was further investigated. Two different experiments were performed to reach some conclusion. The results of the first experiment showed that mechanosorptive creep acceleration decreases the visco-elastic creep rate and there was some kind of interaction between the two creep mechanisms. Hence the two creep mechanisms should not be considered as a separate phenomenon. On the other hand, the results of the second experiment showed that the visco-elastic and mechanosorptive creep are not a single process but are related processes. Moreover, it was deduced that the mechano-sorptive creep does not depend on the accumulation of the visco-elastic creep rate.
7
Brunetti, Carlotta. « Frequency-dependent response of snow in uniaxial compression and comparison with numerical simulation ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7820/.
Texte intégralRésumé :
La determinazione del modulo di Young è fondamentale nello studio della propagazione di fratture prima del rilascio di una valanga e per lo sviluppo di affidabili modelli di stabilità della neve. Il confronto tra simulazioni numeriche del modulo di Young e i valori sperimentali mostra che questi ultimi sono tre ordini di grandezza inferiori a quelli simulati (Reuter et al. 2013). Lo scopo di questo lavoro è stimare il modulo di elasticità studiando la dipendenza dalla frequenza della risposta di diversi tipi di neve a bassa densità, 140-280 kg m-3. Ciò è stato fatto applicando una compressione dinamica uniassiale a -15°C nel range 1-250 Hz utilizzando il Young's modulus device (YMD), prototipo di cycling loading device progettato all'Istituto per lo studio della neve e delle valanghe (SLF). Una risposta viscoelastica della neve è stata identificata a tutte le frequenze considerate, la teoria della viscoelasticità è stata applicata assumendo valida l'ipotesi di risposta lineare della neve. Il valore dello storage modulus, E', a 100 Hz è stato identificato come ragionevolmente rappresentativo del modulo di Young di ciascun campione neve. Il comportamento viscoso è stato valutato considerando la loss tangent e la viscosità ricavata dai modelli di Voigt e Maxwell. Il passaggio da un comportamento più viscoso ad uno più elastico è stato trovato a 40 Hz (~1.1•10-2 s-1). Il maggior contributo alla dissipazione è nel range 1-10 Hz. Infine, le simulazioni numeriche del modulo di Young sono state ottenute nello stesso modo di Reuter et al.. La differenza tra le simulazioni ed i valori sperimentali di E' sono, al massimo, di un fattore 5; invece, in Reuter et al., era di 3 ordini di grandezza. Pertanto, i nostri valori sperimentali e numerici corrispondono meglio, indicando che il metodo qui utilizzato ha portato ad un miglioramento significativo.
8
Thrower, Edward Neal. « Permanent deformation of flexible road pavements by visco-elastic analysis ». Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37877.
Texte intégral
9
Garnier, Erell-Isis. « Long waves in water over a visco-elastic muddy seabed ». Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67613.
Texte intégralRésumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 289-290).
The propagation of surface waves over a flat muddy seabed are studied. Mud is first considered as a Newtonian fluid. Water and mud equations are derived in order to obtain governing equation for surface and interface waves. By the method of multiple scales. nonlinear evolution equations are derived for the harmonic amplitudes. These equations are numerically solved for a finite number of harmonics to show the behavior of surface and interface motions. A drift current in mud is found at the second order., meaning that surface waves induce mud motion. Equation governing the total wave energy variation is derived and used to verify the accuracy of numerical solutions. The model is extended to viscoelastic mud, using the results of four experiments carried on different types of muds. These muds range from very elastic to rather viscous, allowing us to compare hie differences in behavior. Surface and interface variations. mud drift current and energy variations are plotted and compared to the results with Newtonian muds. A sloping muddy seabed is then considered. Mud is modeled as viscoelastic to avoid a constant static current that would happen with Newtonian mud. By the method of multiple scales and by introducing a space-dependent wavenumber, mud drift current and energy variation equations are derived again, taking into account the effect of the slope. An analytic stud v of the surface variations demonstrates that surface and interface waves, as well as drift current, exponentially decay to reach a zero value at the shore.
by Erell-Isis Garnier.
S.M.
10
Nicely, Clinton R. « Transverse Vibrations of Multi-Walled Nanotubes with Visco-Elastic Layers ». University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1227460546.
Texte intégral
11
Alrumaih, Wail Saad. « A novel tuned visco-elastic damper for floor vibration abatement ». University of Dayton / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1245387294.
Texte intégral
12
Al-Rumaih, Wail Saad. « A novel tuned visco-elastic damper for floor vibration abatement ». Dayton, Ohio : University of Dayton, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1245387294.
Texte intégral
13
Smith, Brennan M. « Functionality of corn and sorghum proteins in visco-elastic dough systems ». Diss., Kansas State University, 2012. http://hdl.handle.net/2097/13655.
Texte intégralRésumé :
Doctor of PhilosophyFood Science Institute
Fadi Aramouni
Scott Bean
Zein, the storage protein of corn, has been shown to form a wheat-like dough; however the exact mechanism is unknown since zein lacks the large polymeric proteins found in wheat. To understand how zein forms a dough, different reagents were added during mixing of zein. Salts from the Hofmeister series were used to determine how hydrophobic interactions influence zein’s dough forming ability. In addition, urea, ethanol, and beta mercaptoethanol (β-ME) were also tested to evaluate the effects of protein denaturation and disulfide bonds on zein dough formation and bread quality. Kosmotropic salts had a negative effect on zein dough formation indicating that increasing hydrophobic interactions prevented dough formation. Surface hydrophobicity was found to decrease significantly (p < 0.05) when zein was exposed to 1M or 2M of the kosmotropic salts. Conversely, chaotropic salts had a slight positive effect on zein dough formation as did urea and ethanol. Interestingly, -ME had little effect on zein dough formation demonstrating that disulfide bonds played no role in zein dough development, and that large disulfide linked polymeric protein complexes were not present as found in wheat dough. Specific volumes of zein-starch bread increased as NaCl content in the bread formula decreased. Likewise, including 5% ethanol (v/v) in the bread formula was found to increase bread quality. Experiments were also conducted to compare the functionality of isolated sorghum proteins (kafirins) to commercially available zein produced during wet milling of corn. The effect of steeping, the first step in wet milling, on kafirin functionality was investigated. Sorghum flour was steeped for 0, 72, or 96 hours. Unsteeped sorghum flour was digested with Alcalase for 90 min at 50°C. After steeping or digestion with Alcalase, kafirins were isolated from the remaining material. Both groups of Kafirins had the ability to form a zein-like visco-elastic resin when mixed with warm water by hand. This is the first time that kafirin has been reported to form a visco-elastic resin using only water as a plasticizer.
14
Ostberg, Martin. « Modelling tools for quieter vehicles : Waves in poro-and visco-elastic continua ». Phd thesis, Conservatoire national des arts et metiers - CNAM, 2012. http://tel.archives-ouvertes.fr/tel-00780673.
Texte intégralRésumé :
New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro- and visco-elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two di↵erent ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco-elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode-matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro-elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three-dimensional problem is split up into several, much smaller, two- dimensional ones, radically decreasing the computational load.Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures.The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.
15
Ren, Xiaoan. « The method of arbitrary lines in non-linear visco-elasticity ». Thesis, University of Westminster, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240413.
Texte intégral
16
Mortazavi, Shahriar. « Finite element visco-elastic analysis of permanent deformation in flexible road pavements ». Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38112.
Texte intégral
17
Östberg, Martin. « Modelling tools for quieter vehicles : Waves in poro-and visco-elastic continua ». Doctoral thesis, KTH, MWL Strukturakustik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95205.
Texte intégralRésumé :
New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro– and visco–elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two di↵erent ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco–elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode–matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro–elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three–dimensional problem is split up into several, much smaller, two– dimensional ones, radically decreasing the computational load. Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures. The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.QC 20120522
Centre for Eco2 Vehicle Design
18
Ravish, Masti Sarangapany. « Vibration damping analysis of cylindrical shells partially coated withconstrained visco-elastic layers ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31242169.
Texte intégral
19
Zheng, Li. « Temperature-dependent visco-elastic-plastic analysis of permanent deformation in bituminous pavements ». Thesis, London South Bank University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259911.
Texte intégralRésumé :
In this project the deformation behaviour of a rolled asphalt mixture is investigated, and the influence of temperature on the deformation mechanism of the mixture is assessed, based on a series of uniaxial creep and creep recovery experiments conducted under compressive stress and controlled temperature. Firstly, the experiments were conducted for various temperature levels, loading time, and number of load applications. It is found that the total strain consists of the elastic, plastic, viscoelastic and viscoplastic strain components. The temperature and number of load cycles hardly affects the elastic strain, but the plastic increases with temperature and decreases with number of load applications at constant stress levels. The timedependent (viscoelastic and viscoplastic) and the instant (elastic and plastic) deformation reduced respectively to viscoelastic and elastic deformation components at low temperature. Secondly the relationship between the total strain and the variables, time, temperature, stress and number of cycles are successfully modelled mathematically. After this, the model is introduced into the finite element method. Also an approximate approach for permanent deformation in a flexible pavement is presented and a non-linear finite element program "CEPVP" with consideration of the pavement temperature profile was devised. The calculation was conducted using program `CVEVP". It was found that there was a great agreement between the computation and the test. Finally, a general comparison of program 'CVEVP' and package ANSYS was conducted. Considering the effects of mechanical parameters of bituminous materials, time of loading, thickness of asphalt and granular layers and environmental temperature, calculation of permanent deformation of bituminous pavement was carried out using program `CVEVP'. Some findings were concluded. For example, it was found that the plastic properties of asphalt mixture are the important factor in calculating the permanent deformation of flexible pavements, particularly at the upper end of the temperature spectrum.
20
Rahemi, Hossein. « Thermal fracture service life analysis of a case bonded visco-elastic cylinder ». Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-172155/.
Texte intégral
21
Renault, Amélie. « Caractérisation mécanique dynamique de matériaux poro-visco-élastiques ». Thèse, Université de Sherbrooke, 2008. http://savoirs.usherbrooke.ca/handle/11143/1915.
Texte intégralRésumé :
Poro-viscoelastic materials are well modelled with Biot-Allard equations. This model needs a number of geometrical parameters in order to describe the macroscopic geometry of the material and elastic parameters in order to describe the elastic properties of the material skeleton. Several characterisation methods of viscoelastic parameters of porous materials are studied in this thesis. Firstly, quasistatic and resonant characterization methods are described and analyzed. Secondly, a new inverse dynamic characterization of the same modulus is developed. The latter involves a two layers metal-porous beam, which is excited at the center. The input mobility is measured. The set-up is simplified compared to previous methods. The parameters are obtained via an inversion procedure based on the minimisation of the cost function comparing the measured and calculated frequency response functions (FRF). The calculation is done with a general laminate model. A parametric study identifies the optimal beam dimensions for maximum sensitivity of the inversion model. The advantage of using a code which is not taking into account fluid-structure interactions is the low computation time. For most materials, the effect of this interaction on the elastic properties is negligible. Several materials are tested to demonstrate the performance of the method compared to the classical quasi-static approaches, and set its limitations and range of validity. Finally, conclusions about their utilisation are given.
22
Plog, Jan Philip. « Investigation of the visco-elastic behaviour of watersoluble cellulosic derivatives in uniaxial elongation ». [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975508008.
Texte intégral
23
Kang, JiJun. « Determination of elastic-plastic and visco-plastic material properties from instrumented indentation curves ». Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13509/.
Texte intégralRésumé :
Instrumented indentation techniques at micro or nano-scales have become more popular for determining mechanical properties from small samples of material. These techniques can be used not only to obtain and to interpret the hardness of the material but also to provide information about the near surface mechanical properties and deformation behaviour of bulk solids and/or coating films. In particular, various approaches have been proposed to evaluate the elastic-plastic properties of power-law materials from the experimental loading-unloading curves. In order to obtain a unique set of elastic-plastic properties, many researchers have proposed to use more than one set of loading-unloading curves obtained from different indenter geometries. A combined Finite Element (FE) analysis and optimisation approach has been developed, using three types of indenters (namely, conical, Berkovich and Vickers), for determining the elastic-plastic material properties, using one set of ‘simulated’ target FE loading-unloading curves and one set of real-life experimental loading-unloading curves. The results obtained have demonstrated that excellent convergence can be achieved with the ‘simulated’ target FE loading-unloading curve, but less accurate results have been obtained with the real-life experimental loading-unloading curve. This combined technique has been extended to determine the elastic and visco-plastic material properties using only a single indentation ‘simulated’ loading-unloading curve based on a two-layer viscoplasticity model. A combined dimensional analysis and optimisation approach has also been developed and used to determine the elastic-plastic material properties from loading-unloading curves with single and dual indenters. The dimensional functions have been established based on a parametric study using FE analyses and the loading and linearised unloading portions of the indentation curves. It has been demonstrated that the elastic-plastic material properties cannot be uniquely determined by the test curves of a single indenter, but the unique or more accurate results can be obtained using the test curves from dual indenters. Since the characteristic loading-unloading responses of indenters can be approximated by the results of dimensional analysis, a simplified approach has been used to obtain the elastic-plastic mechanical properties from loading-unloading curves, using a similar optimisation procedure. It is assumed that the loading-unloading portions of the curves are empirically related to some of the material properties, which avoids the need for time consuming FE analysis in evaluating the load-deformation relationship in the optimisation process. This approach shows that issues of uniqueness may arise when using a single indenter and more accurate estimation of material properties with dual indenters can be obtained by reducing the bounds of the mechanical parameters. This thesis highlights the effects of using various indenter geometries with different face angles and tilted angles, which have not been covered previously. The elastic-plastic material parameters are estimated, for the first time, in a non-linear optimisation approach, fully integrated with FE analysis, using results from a single indentation curve. Furthermore, a linear and a power-law fitting scheme to obtain elastic-plastic material properties from loading-unloading indentation curves have been introduced based on dimensional analysis, since there are no mathematical formulas or functions that fit the unloading curve well. The optimisation techniques have been extended to cover time-dependent material properties based on a two-layer viscoplasticity model, has not been investigated before.
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Ravish, Masti Sarangapany. « Vibration damping analysis of cylindrical shells partially coated with constrained visco-elastic layers ». Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23000867.
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Churchin, John Anthony. « A Study Of Visco-Elastic Properties Of Denture Liners And Classification Of Terminology ». Thesis, Faculty of Dentistry, 1992. http://hdl.handle.net/2123/4205.
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Ziegler, Daniel Alexander [Verfasser], et C. [Akademischer Betreuer] Wieners. « A parallel and adaptive space-time discontinuous Galerkin method for visco-elastic and visco-acoustic waves / Daniel Alexander Ziegler ; Betreuer : C. Wieners ». Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/120664690X/34.
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Tsunoda, Katsuhiko. « The role of visco-elasticity on the crack growth behaviour of rubber ». Thesis, Queen Mary, University of London, 2001. http://qmro.qmul.ac.uk/xmlui/handle/123456789/28950.
Texte intégralRésumé :
This thesis concerns crack growth phenomena in rubber. It is widely known that a relationship exists between the magnitude of the stored energy release rate available to drive a crack, called the tearing energy (7'), and the resultant crack growth rate. For rubbers this basic relationship is said to be a characteristic of the material. The magnitude of T is related to both the visco-elastic losses and the crack tip diameter (d) However the actual size of d and its relationship with the viscoelastic losses is not clear. This thesis examines the crack growth behaviour in relation to d and the visco-elastic losses for a wide range of rubbers, whose visco-elastic properties are altered either by swelling in a liquid, altering the test temperature or the cross-link density and by the incorporation of fillers. Static, constant T, crack growth tests were carried out. These revealed that two different crack growth processes exist. For the fast crack growth process, T is determined by variations in the visco-elastic losses alone. For the slow crack growth process, T is determined by variations in both the visco-elastic losses and d. It is proposed here that the factors, which alter d, are associated with cavitation ahead of the crack tip for unfilled materials and with strength anisotropy for carbon black filled materials. In cyclic crack growth tests, the crack growth per cycle, dc/dn, can be considered to result from the sum of time and cyclic dependent crack growth components. For the first time, the detailed magnitudes of the contribution of each of these components to dc/dn have been determined, for a wide range of materials and mechanisms responsible for this behaviour are postulated. Also crack growth tests, both static and cyclic, were extended to very large extensions. Lastly this investigation revealed that the tensile strength for both ciystallising and noncrystallising rubber can be predicted using the tearing energy concept for a variety of loading regimes.
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Jones, Ryan Edward 1974. « Thermally driven visco-elastic measurement technique via spectral variations in scanning probe microscopy cantilevers ». Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/27098.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 166-167).
Understanding how fluids respond to various deformations is of great importance to a spectrum of disciplines ranging from bio-medical research on joint replacements to sealing technology in industrial machinery. Specifically, this work addresses the need for probing interfacial rheology to understand how lubricants fail as system scales are reduced from bulk dimensions to molecular length scales. In the pursuit of interfacial rheology, one needs a platform capable of the temporal and spatial range and resolution required to quantify the visco-elastic fluid properties in the interfacial regime. With the availability and versatility of AFMs and the mounting models and data related to the performance of SPM probes in a fluid environment, the AFM is an attractive platform to exploit. This thesis will discuss the use of thermal oscillations of an SPM probe to quantify the visco-elastic properties of fluids via spectral variations. There exist theoretical models for the Fluid-Structure Interactions (FSI) of vibrating bodies in incompressible viscous mediums that have been validated. This thesis will discuss how these models have been extended to develop a new visco-elastic FSI model. The analytical results of these models will be quantitatively compared to thermally driven SPM cantilevers to extract fluid properties. The new theory required for modeling the probe dynamics is outlined and the present limitations, for both the analytical and experimental techniques, are discussed.
by Ryan Edward Jones.
Ph.D.
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Brown, Susan Jayne 1967. « Gravity, capillary and dilational wave mode resonance at a visco-elastic two-fluid interface ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/28931.
Texte intégralRésumé :
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.Includes bibliographical references (p. 222-226).
(cont.) space corresponding to experimental conditions to thereby interpret the experimental results. We tested this method on noisy simulated data sets and then applied it to published experimental data sets. We designed an experimental set-up to measure wave number, spatial damping coefficient, and wave slope data for a 3-10 hertz frequency range of transverse and longitudinal waves in a clean enclosed flume. We used kimball-mounted lasers whose beams passed through optical glass in the tank and lid to capture transverse wave motion. The experimental conditions included waves traveling on fatty acid monolayers on aqueous solutions and also waves traveling on a visco-elastic fluid at a variety of temperatures. In addition to the wave data we obtained, we also measured in-situ surface tension. Analyzing the experimental data, we demonstrated the effects of modulation of one wave mode on another. We obtained the rheological parameters for these experimental systems by the inverse method. We used the inverse method to construct the dispersion relation solution space corresponding to the experimental conditions. We used the diagnostic tools for root classification, spatial stability together with a graphical representation of the dispersion relation solution space to understand the physics underlying our experiments. We demonstrated resonance phenomena experimentally with the wave data from the visco-elastic fluid and confirmed this resonance numerically: gravity-capillary resonance near 4.2 hertz ...
This thesis is a study of first order resonance between gravity, capillary and dilational wave modes. Gravity, capillary and dilational waves, occurring at a visco-elastic interface between two fluids, are different modes described by a single linear dispersion relation. Gravity and capillary modes arise due to the restoring forces of surface tension and gravity and result in oscillatory motions transverse to the surface. The dilational, or Marangoni, modes arise due to the elastic nature of the interface and result in longitudinal motion along the interface. The visco-elasticity of the interface may be due to the interfacial nature of the two fluids or it may be due to the presence of a monolayer of surfactant, such as a film on the ocean surface. This visco-elasticity affects the interfacial stress balance and is accounted for in the dispersion relation via interfacial heological parameters. We described resonance as coalescence of the roots of the dispersion relation in complex frequency and wave number space. We used this description to explain numerical and experimental resonance phenomena noted in previous studies. We classified some of the roots of the dispersion relation as primarily gravity, capillary or dilational modes. We numerically determined the dependence on interfacial rheology of root coalescence (resonance) and the boundaries of spatial stability of the modes. We used these diagnostic tools to characterize the conditions for both gravity-capillary and capillary-dilational modal resonances. We developed an inverse method from which interfacial rheological parameters can be determined from experimental measurements of wave number, frequency and spatial damping coefficient. We used this tool to construct the dispersion relation solution
by Susan Jayne Brown.
Sc.D.
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Östberg, Martin. « Modelling Tools for Quieter Vehicles : Effective Vibro-Acoustical Modelling of Rotationally Symmetric Structures Consisting of Visco-Elastic and Poro-Elastic Media ». Licentiate thesis, KTH, VinnExcellence Center for ECO2 Vehicle design, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13251.
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Bragaglia, Massimiliano <1973>. « Studio del comportamento visco-elastico del conglomerato bituminoso con il metodo degli elementi distinti particellari ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/93/1/Tesi_dottorato.pdf.
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Bragaglia, Massimiliano <1973>. « Studio del comportamento visco-elastico del conglomerato bituminoso con il metodo degli elementi distinti particellari ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/93/.
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Blignaut, Caitlyn. « A Non-linear Visco-elastic Model for Dynamic Finite Element Simulation of Bovine Cortical Bone ». Master's thesis, Faculty of Engineering and the Built Environment, 2021. http://hdl.handle.net/11427/33433.
Texte intégralRésumé :
Modelling and simulation of the human body during an impact situation such as a car accident, can lead to better designed safety features on vehicles. In order to achieve this, investigation into the material properties and the creation of a numerical model of cortical bone is needed. One approach to creating a material model of cortical bone suitable for these situations is to describe the material model as visco-elastic, as reported by Shim et al. [1], Bekker et al. [2] and Cloete et al. [3]. The work by Shim et al. and Bekker et al. developed three-dimensional models, but do not accurately capture the transition in behaviour in the intermediate strain rate region, while Cloete et al. developed a phenomenological model which captures the intermediate strain rate behaviour in one dimension. This work aims to verify and extend these models. The intermediate strain rate regime (1 s−1 to 100 s−1 ) is of particular interest because it is a key characteristic of the behaviour of cortical bone and several studies have been conducted to gather experimental data in this region [3, 4, 5, 6]. The behaviour can be captured using non-linear viscoelastic models. This dissertation focuses on the development and implementation of a material model of cortical bone based on non-linear visco-elastic models to capture the intermediate strain rate regime behaviour. The material model was developed using uni-axial test results from cortical bone. The model by Cloete et al. has been improved and extended, and issues of local and global strain rate with regards to the viscosity have been clarified. A hereditary integral approach was taken in the analysis and implementation of discrete models and was found to be consistent with mathematical models. The model developed was extended to three dimensions in a manner similar to that of Shim et al. and Bekker et al. for implementation in commercial finite element software (LS-Dyna and Abaqus).
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Verma, Navin Prakash. « Viscous Dampers for Optimal Reduction in Seismic Response ». Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/43716.
Texte intégralRésumé :
To model dissipation of energy in vibrating civil structures, existence of viscous damping is commonly assumed primarily for mathematical convenience. In such a classical damper, the damping force is assumed to depend only on the velocity of deformation. Fluid viscous dampers that provide this type of damping have been manufactured to provide supplementary damping in civil and mechanical systems to enhance their performance. Some fluid dampers, however, exhibit stiffening characteristics at higher frequencies of deformation. The force deformation relationship of such dampers can be better represented by the Maxwell model of visco-elasticity. This model consists of a viscous dashpot in series with a spring, the latter element providing the stiffening characteristics. This study is concerned with the optimal utilization of such Maxwell dampers for seismic performance improvement of civil structures. The force deformation relationship of Maxwell dampers is described by a first order differential equation. Earlier studies dealing with these dampers, used an unsymmetric set of equations for combined structure and damper system. The solution of such equations for response analysis or for optimization calculation by a modal analysis approach would require the pair of the left and right eigenvectors. In this study, an auxiliary variable is introduced in the representation of a Maxwell damper to obtain symmetric equations of motion for combined structure and damper system. This eliminates the need for working with two sets of eigenvectors and their derivatives, required for optimal analysis.
Since the main objective of installing these dampers is to reduce the structural response in an optimal manner, the optimization problem is defined in terms of the minimization of some response-based performance indices. To calculate the optimal parameters of dampers placed at different location in the structure, Rosen's gradient projection method is employed. For numerical illustration, a 24-story shear building is considered. Numerical results are obtained for seismic input defined by a spectral density function; however, the formulation permits direct utilization of response spectrum-based description of design earthquake. Three different performance indices -- inter story drift-based, floor acceleration-based, and base shear-based performance indices-- have been considered to calculate the numerical results. A computational scheme is presented to calculate the amount of total damping required to achieve a desired level of response reduction. The effect of ignoring the stiffening effect at higher frequencies in the Maxwell model on the optimal performance is evaluated by parametric variation of relaxation time coefficient. It is observed that the models with higher relaxation time parameter show a decreased response reducing damping effect. Thus ignoring the stiffening effect when it is, indeed, present would provide an unconservative estimation of the damping effect. The effect of brace flexibilities on different performance indices is also investigated. It is observed that flexibility in a brace reduces the effectiveness of the damper.Master of Science
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Ames, Nicoli M. (Nicoli Margret) 1978. « An internal variable theory for isotropic visco-elastic-plastic solids : application to indentation of amorphous polymeric solids ». Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/33162.
Texte intégralRésumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (leaves 91-92).
A significant advance in modeling the plastic deformation of amorphous polymers has been made by Parks, Argon, Boyce, Arruda, and their co-workers (e.g. Parks, Argon, & Bagepalli, 1985; Boyce, Parks, & Argon, 1998; Arruda & Boyce, 1993), and by Wu and Van der Giessen (1993). Although these models phenomenologically capture the large deformation elastic-viscoplastic response of these materials in a reasonably accurate manner, they do not adequately account for the creep response of these materials at stress levels below those causing "macro-yield", as well as the Bauschinger-type reverse yielding phenomena at strain levels less than ~ 30% associated with the macro-yield transient. Anand (2003) has recently generalized the model of Anand and Gurtin (2003) to begin to capture these important aspects of these material's mechanical response. In this work, we summarize Anand's three-dimensional theory and then specialize the constitutive equations to an approximate one-dimensional form. Also, we describe our monotonic, cyclic and creep experiments on the amorphous polymeric solid poly(methyl methacrylate) (PMMA), at ambient temperature and stress states under which this material does not exhibit crazing, and we outline detailed procedures for material parameter determination from these experiments. We have implemented the three-dimensional constitutive equations in the finite-element computer program ABAQUS/Explicit (ABAQUS, Inc., 2002), and using this finite-element program, we show numerical results to some representative problems in microindentation, and compare them against corresponding results from physical experiments.
by Nicoli Margret Ames.
S.M.
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Janovjak, Harald. « Exploring the Mechanical Stability and Visco-elasticity of Membrane Proteins by Single-Molecule Force Measurements ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1135090167025-44737.
Texte intégralRésumé :
Relatively little is known about the folding and stability of membrane proteins. Conventional thermal or chemical unfolding techniques probe the average behavior of large numbers of molecules and thus cannot resolve co-existing minor and major unfolding pathways and intermediates. Here, I applied single-molecule force measurements based on an atomic force microscope (AFM) to characterize the stability of the membrane protein bacteriorhodopsin (BR). In these mechanical unfolding experiments, an external pulling force played the role of the denaturant and lead to unfolding of the three-dimensional structure of individual proteins. It was found that single BRs unfold step-wise in a well-defined sequence of stable intermediates and in different unfolding pathways. Although single [alpha]-helices were sufficiently stable to unfold in individual steps they also exhibited certain probabilities to unfold in pairs. These observations support the "two-stage" and the "helical-hairpin" model of membrane protein folding. Dynamic force measurements showed that [alpha]-helices and helical hairpins are relatively rigid structures, which are stabilized by narrow energy barriers and have stabilities between 100-10?000 seconds. These forced unfolding experiments were complemented with the development of new force measurement techniques. It is demonstrated that hydrodynamic effects need to be considered to obtain more complete kinetic pictures of single molecules. In addition, two force spectroscopy approaches to measure the complex visco-elastic response of single molecules are presented and applied to BR. These experiments revealed that the unfolding patterns of single proteins are dominated by purely elastic polypeptide extension and determined the dissipative interactions associated with the unfolding of single [alpha]-helices. In addition, it was found that kinks result in a reduced unfolding cooperativity of [alpha]-helices.
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Nguyen, Dang Dan. « Revêtements polymères sous contraintes environnementales couplées ». Phd thesis, Université de La Rochelle, 2012. http://tel.archives-ouvertes.fr/tel-01065519.
Texte intégralRésumé :
L'objectif de notre étude est de mettre en évidence les synergies existantes entre les différents facteurs de vieillissement lors de la dégradation d'un revêtement polymère modèle, représentatif d'une peinture anticorrosion.Notre travail a consisté à suivre le vieillissement hygrothermique du système DGEBA/TETA sous forme de film libre et de revêtement déposé sur substrat acier dans différentes solutions (eau pure et NaCl 3%) pour différentes températures et contraintes mécaniques visco-élastique appliquées. Nos résultats ont montré que le programme de cuisson affectait les propriétés physico-chimiques et mécaniques du système initial et que l'absorption d'eau, non homogène, suivait une loi non-Fickienne, suite à un phénomène de gonflement.La prise en eau et la diffusion ont été caractérisées par gravimétrie et spectroscopie d'impédance électrochimique. Nos résultats montrent que les propriétés barrière du revêtement diminuent avec la quantité d'eau absorbée et avec la température de vieillissement. Cependant, la contrainte plane appliquée sur le système tend à contrarier cet effet. La formalisation de nos observations expérimentales dans le cadre d'une approche thermodynamique a montré l'effet prépondérant de la partie entropique par rapport à la partie enthalpique de l'énergie d'activation des processus de transport de l'eau, en raison de l'orientation des chaînes sous l'action de la contrainte. De plus, une diminution de la permittivité relative du revêtement sec a été observée en fonction de la température et de la contrainte appliquée, indépendamment de son signe (tension ou compression). Dans ce cas, la contribution enthalpique semble être prépondérante.
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Grasso, Eva. « Modelling visco-elastic seismic wave propagation : a fast-multipole boundary element method and its coupling with finite elements ». Phd thesis, Université Paris-Est, 2012. http://tel.archives-ouvertes.fr/tel-00730752.
Texte intégralRésumé :
The numerical simulation of elastic wave propagation in unbounded media is a topical issue. This need arises in a variety of real life engineering problems, from the modelling of railway- or machinery-induced vibrations to the analysis of seismic wave propagation and soil-structure interaction problems. Due to the complexity of the involved geometries and materials behavior, modelling such situations requires sophisticated numerical methods. The Boundary Element method (BEM) is a very effective approach for dynamical problems in spatially-extended regions (idealized as unbounded), especially since the advent of fast BEMs such as the Fast Multipole Method (FMM) used in this work. The BEM is based on a boundary integral formulation which requires the discretization of the only domain boundary (i.e. a surface in 3-D) and accounts implicitly for the radiation conditions at infinity. As a main disadvantage, the BEM leads a priori to a fully-populated and (using the collocation approach) non-symmetrical coefficient matrix, which make the traditional implementation of this method prohibitive for large problems (say O(106) boundary DoFs). Applied to the BEM, the Multi-Level Fast Multipole Method (ML-FMM) strongly lowers the complexity in computational work and memory that hinder the classical formulation, making the ML-FMBEM very competitive in modelling elastic wave propagation. The elastodynamic version of the Fast Multipole BEM (FMBEM), in a form enabling piecewise-homogeneous media, has for instance been successfully used to solve seismic wave propagation problems in a previous work (thesis dissertation of S. Chaillat, ENPC, 2008). This thesis aims at extending the capabilities of the existing frequency-domain elastodynamic FMBEM in two directions. Firstly, the time-harmonic elastodynamic ML-FMBEM formulation has been extended to the case of weakly dissipative viscoelastic media. Secondly, the FMBEM and the Finite Element Method (FEM) have been coupled to take advantage of the versatility of the FEM to model complex geometries and non-linearities while the FM-BEM accounts for wave propagation in the surrounding unbounded medium. In this thesis, we consider two strategies for coupling the FMBEM and the FEM to solve three-dimensional time-harmonic wave propagation problems in unbounded domains. The main idea is to separate one or more bounded subdomains (modelled by the FEM) from the complementary semi-infinite viscoelastic propagation medium (modelled by the FMBEM) through a non-overlapping domain decomposition. Two coupling strategies have been implemented and their performances assessed and compared on several examples
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Barros, Renato Marques de. « Funções de Green e de influencia para meios visco-elasticos transversalmente isotropicos no dominio da frequencia ». [s.n.], 2001. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264035.
Texte intégralRésumé :
Orientador : Euclides de Mesquita NetoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-07-31T20:40:49Z (GMT). No. of bitstreams: 1 Barros_RenatoMarquesde_D.pdf: 12889106 bytes, checksum: ae50d7f1404dacf5b43d8e4007ad231d (MD5) Previous issue date: 2001
Resumo: O objetivo do presente trabalho é a síntese de Funções de Green e de Influência no domínio da freqüência para meios transversalmente isotrópicos visco-elásticos. Inicialmente são analisados problemas bidimensionais. A transformada integral de Fourier é aplicada no procedimento de solução, com inversão numérica. Soluções fundamentais para o espaço completo, semi-espaço e meios estratificados horizontalmente são consideradas. Na seqüência são considerados problemas tridimensionais em coordenadas retangulares e cilíndricas nos quais a transformada integral de Hankel com inversão numérica foi empregada. As soluções obtidas foram comparadas com as soluções disponíveis na literatura. Um conjunto de soluções axi-simétricas para o espaço completo, semi-espaço e meio multi-estratificado foi, também, sintetizado. O método da matriz de rigidez dinâmica foi, então, empregado para problemas axi-simétricos e bidimensionais. As soluções encontradas foram validadas com numerosos resultados disponíveis na literatura. As funções de Green e de Influência sintetizadas podem ser incorporadas tanto nas versões direta como indireta do Método dos Elementos de Contorno para a análise do comportamento dinâmico estacionário de meios transversalmente isotrópicos e visco-elásticos
Abstract: The present work synthesizes frequency domain Green and Influence Functions for transversely isotropic visco-elastic continua. Initially the two-dimensional case is treated. The Fourier integral transform is applied in the solution procedure, with numerical inversion. Fundamental solutions for full-space, half-space and horizontally layered media are considered. The stiffness matrix approach is used to obtain solutions for multi-layered media. In the sequence the three-dimensional case is considered. A series of axisymmetric solutions for for full-space, half-space and horizontally layered media are also synthesized. The matrix stiffness approach is also applied to the axisymmetric problem. The Hankel integral transform with numerica1 inversion is applied to the 3D cases. Numerical solutions are validated by comparisons whenever results are available in the literatura. The synthesized Green and Inf1uence Functions may be incorporated in the Direct or Indirect Versions of the Boundary Element Method to analyse the stationary dymanic behavior of transversely isotropic vico-elastic media
Doutorado
Mecanica dos Sólidos e Projeto Mecanico
Doutor em Engenharia Mecânica
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Thomazo, Luiz Henrique. « Formulação do metodo dos elementos de contorno indireto para resposta transiente em meios visco-elasticos 2D ». [s.n.], 2004. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263977.
Texte intégralRésumé :
Orientadores: Euclides de Mesquita Neto, Edson Antonio Capello SousaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-08-09T04:23:51Z (GMT). No. of bitstreams: 1 Thomazo_LuizHenrique_M.pdf: 1773463 bytes, checksum: e38435e9b18935ddc2edc19b8b2efac4 (MD5) Previous issue date: 2004
Resumo: Este trabalho apresenta uma metodologia para a realização de análises dinâmicas estacionárias e transientes em domínios visco-elásticos limitados ou ilimitados, utilizando-se o Método dos Elementos de Contorno. São utilizados como estados auxiliares soluções não-singulares de problemas do semi-espaço e do espaço completo de meios visco-elásticos. Os estados visco-elásticos auxiliares são sintetizados numericamente, tanto no domínio da freqüência, como no domínio do tempo. Os mencionados estados auxiliares são constituídos das soluções em tensão e deslocamento resultantes de cargas espacialmente constantes, aplicadas sob segmentos lineares tanto na superfície de semi-espaços, como no interior de espaços completos. Inicialmente os estados auxiliares são sintetizados numericamente no domínio da freqüência, dando origem à análise de problemas estacionários. Na seqüência estados auxiliares transientes são obtidos a partir da aplicação da transformada de Fourier rápida (FFT) sobre os estados estacionários mencionados. Os estados auxiliares são utilizados para a síntese de uma versão não singular Indireta do MEC (MEC-I) tanto no domínio da freqüência quanto no domínio do tempo. No trabalho ainda é formulada e implementada a inclusão de um corpo rígido interagindo com o meio discretizado pelo MEC-I. O comportamento visco-elástico do contínuo é introduzido pelo princípio da correspondência e são analisados os modelos de histerése constante e de Kelvin-Voigt
Abstract: The main purpose of the present work is to further develop a methodology to perform stationary and transient dynamic analysis of viscoelastic continua by the Boundary Element Method. Numerically synthetized stationary and transient, half-space and full-space auxiliary states are employed to render a non-singular implementation of the indirect version of the Boundary Element Method, IBEM. The auxiliary states used in this word are displacement and traction components stemming from the solution two stress bounary value problems. A constant traction distribution applied at a linear segment over the viscoelastic half-space surface and at the interior of the viscoelastic full-space describe the solutions applied to formulate the BEM. The IBEM is formulated and implemented to render the dynamic solution of bounded and unbounded domains. The interaction of the IBEM mesh with a massless rigid body is also formulated in the context of this work. Viscoelastic effects are included by means of the correspondence principle. The influence of the constant hysteresis and the Kelvin-Voigt damping models are studied.
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Schuchardt, Arnim [Verfasser]. « On the Mechanical Modeling, Visco-Elasticity and Application of Aerographite, a 3D Carbon Nano-Material / Arnim Schuchardt ». Kiel : Universitätsbibliothek Kiel, 2016. http://d-nb.info/1081366788/34.
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Taira, Claudio. « Avaliação do desempenho em laboratório de misturas asfálticas densas utilizando asfalto convencional (CAP-20) e asfalto modificado com polímero SBS (BETUFLEX B 65/60) ». Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/18/18137/tde-09052016-111805/.
Texte intégralRésumé :
Este trabalho teve por objetivo o desempenho de misturas asfálticas densas utilizando um ligante convencional (CAP-20) e o mesmo ligante modificado com polímeros tipo SBS, produzido sob o nome comercial de BETUFLEX B 65/60, através dos ensaios Marshall, fluência por compressão uniaxial estática e dinâmica, resistência à tração por compressão diametral e módulo resiliente pro compressão diametral dinâmica, em misturas compactadas com uma mesma faixa granulométrica e diferentes teores de ligantes. O ensaio Marshall apresentou, para as misturas preparadas com asfalto modificado, valores maiores de estabilidade para a maioria dos teores, apesar de valores elevados de fluência em todos os teores analisados. Os resultados de deformação do ensaio de fluência por compressão uniaxial não distinguiram claramente o efeito da adição de polímeros em misturas asfálticas, ao contrário do observado no ensaio dinâmico, onde as deformações foram consideravelmente menores para a maioria dos teores analisados. Os resultados do ensaio de resistência à tração por compressão diametral mostram um desempenho superior da mistura modificada. O ensaio de módulo resiliente por compressão diametral dinâmica indicou, à temperatura de 25ºC, valores menores para a mistura com asfalto modificado, não sendo notada, entretanto, uma diferenciação de desempenho nas temperaturas de 5ºC e 40ºC. A modelação matemática das curvas de fluência e de recuperação às equações constitutivas de alguns modelos visco-elásticos básicos detectou uma diferenciação entre os valores de alguns elementos constitutivos, tanto do ensaio dinâmico, quanto do estático.The purpose of this study is to evaluate the performance of asphalt mixes using conventional binder and the same binder modified with SBS polymer (Betuflex B 65/60) based on Marshall test, static and dynamic creep tests, indirect tensile strength test and resilient modulus by indirect tensile test, with the same granulometric composition and different binders contents. In Marshall test, polymer modified asphalt mixes presented better stability performance than conventional asphalt mixes in most of binders contents, despite of the higher flow values obtained for all binders contents. The static creep test results indicated that this test does not clearly distinguish the effect of polymer in asphalt mixes while the results of dynamic creep test indicated the opposite, i. e., polymer modified asphalt mixes deformations are smaller for most of the asphalt binders contents studied. The indirect tensile strength test results showed a better performance of modified asphalt. The results of resilient modulus by indirect tensile test at 25°C showed smaller values for modified asphalt, while the results at 5ºC and 40ºC did not show differences between the asphalt mixes. The mathematics modelling of the creep and recovering curves according to constitutive equations of some basic visco- elastic models showed a difference between the values of some constitutive elements in both cases, dynamic and static tests.
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Hamitou, Okba. « Efficient preconditioning method for the CARP-CG iterative solver for the solution of the frequency-domain visco-elastic wave equation ». Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAM087/document.
Texte intégralRésumé :
La résolution de l'équation des ondes acoustiques et élastiques en 3D dans le domaine fréquentiel représente un enjeu majeur dans le cadre de l'inversion des formes d'ondes pour l'imagerie haute résolution de cibles crustales (Virieux, 2009). Après discrétisation, ce problème revient à résoudre un système linéaire à valeurs complexes, creux, de grande taille non défini et mal conditionné. Les méthodes d'inversion sismique requièrent la solution de ce problème pour l'évaluation du problème direct pour un grand nombre de sources (plusieurs milliers voir dizaines de milliers). Dans l'approximation acoustique, les méthodes directes sont privilégiées. Cependant, le coût mémoire de ces méthodes les rendent aujourd'hui inutilisables pour résoudre les problèmes élastiques 3D. En raison de leur plus faible coût mémoire, les méthodes itératives pour les équations en fréquence peuvent être considérées pour l'élastodynamique. Cependant, une convergence rapide passe par des préconditionneurs adaptés pour les solveurs itératifs. Par ailleurs, les stratégies pour résoudre des systèmes linéaires avec des seconds membres multiples ne sont pas aussi efficaces que pour les méthodes directes. La modélisation dans le domaine temporelle quant à elle présente une importante complexité en coût de calcul et cette complexité croît linéairement avec le nombre de sources.Dans cette thèse, l'approche utilisant un solveur itératif est considérée. Le solveur itératif CARP-CG introduit par Gordon (2010) est considéré. Cette méthode est basée sur la méthode de Kaczmarz qui transforme un système linéaire mal conditionné en un système hermitien, positif et qui peut être résolu en utilisant les méthodes du type gradient conjugué (CG). Dans des configurations de forts contrastes et hétérogénéités, ce solveur s'est révélé être extrêmement robuste alors que les méthodes itératives standards basées sur les sous-espaces de Krylov telles que GMRES et BiCGSTAB nécessitent l'utilisation d'un préconditionneur pour converger (Li, 2015). Malgré les bonnes propriétés de la méthode CARP-CG, le nombre d'itérations nécessaires pour atteindre une précision suffisante reste néanmoins élevé. Je présente alors une stratégie de préconditionnement adaptée au problème de propagation des ondes et à la méthode CARP-CG. Ce préconditionneur est un inverse creux et approché d'un opérateur de propagation des ondes fortement amorti. Le calcul du préconditionneur est réalisé grâce un algorithme massivement parallèle pour les architectures à mémoire distribuée.La méthode développée est appliquée à des cas d'étude réalistes. Les applications sont faites sur des modèles synthétiques 2D dans l'approximation visco-acoustique pour des fréquences allant jusqu'à 40 Hz puis dans l'approximation élastique pour des fréquences allant jusqu'à 20 Hz. Ces études montrent l'efficacité de la méthode CARP-CG munie de la stratégie de préconditionnement. Le nombre d'itérations est fortement réduit (jusqu'à un facteur 9) permettant d'améliorer considérablement la complexité de la méthode CARP-CG. Des gains en temps de calcul allant jusqu'à un facteur 3.5 sont ainsi obtenus. La méthode est ensuite appliquée à un cas 3D synthétique et réaliste dans l'approximation visco-élastique pour des fréquences allant de 1.25 Hz à 7.5 Hz. Des résultats encourageants sont obtenus. Munie du préconditioneur, la méthode CARP-CG permet de résoudre ces systèmes linéaires deux fois plus rapidement.La stratégie de préconditionnement implique la nécessité de plus grandes ressources en mémoire pour le solveur itératif; cependant, elles ne constituent pas une limitation pour la méthode et restent très négligeables devant celles requises par les solveurs directs. La principale limitation réside dans le temps de calcul qui demeure assez significatif. Cependant, cette méthode constitue un solveur compétitif comparé aux autres solveurs en temps et direct utilisés aujourd'hui dans le cadre de l'inversion des formes d'ondesA robust and efficient wave modeling method is the cornerstone of high resolution seismic inversion methods such as the frequency-domain Full Waveform Inversion (Virieux, 2009). After discretization, frequency-domain wave modeling amounts to the solution of large (up to several billion of unknowns for realistic case studies), sparse, indefinite and ill-conditioned linear systems. Furthermore, seismic inversion methods require the solution of this problem for numerous sources (from several thousands up to tens of thousands). In the acoustic approximation, 3D real case studies can be handled efficiently using direct solvers. However because of their tremendous intrinsic memory requirements, they are not yet adapted to the solution of the 3D elastodynamics equations. Iterative solvers provide an alternative to direct solvers. However, they require a preconditioning strategy to ensure convergence for the frequency-domain wave equation. Besides, multiple right-hand sides linear systems are not treated as efficiently as direct solvers do.In this thesis, we are interested in the use of a robust iterative solver adapted to the solution of these systems called CARP-CG (Gordon, 2010). The CARP-CG method has shown robust convergence properties for 2D and 3D elastic problems in highly heterogeneous media compared to standard Krylov methods such as GMRES or Bi-CGSTAB which require the use of a preconditioner to ensure convergence (Li, 2015). Despite the good convergence properties of CARP-CG, the latter still requires a large number of iterations to reach sufficient accuracy. I introduce an efficient preconditioning strategy adapted to the CARP-CG method and the frequency-domain wave problem. This preconditioner is computed as a sparse approximate inverse of a strongly damped wave propagation operator. The computation of the preconditioner is performed in a massively parallel algorithm for distributed memory architectures.The efficiency of the preconditioner is evaluated on several case studies. First, applications are performed on realistic synthetic models in the 2D visco-acoustic approximation (up to $40$ Hz) and the 2D visco-elastic approximation (up to $20$ Hz). These studies show that the CARP-CG method together with the preconditioning strategy is robust and efficient. The number of iterations is significantly reduced (up to a factor $9$) enabling a speedup in the computation time by a factor up to $3.5$. Second, this method is investigated in the 3D elastic approximation on a realistic synthetic case study on the range of frequencies 1.25 to 7.5 Hz. Very encouraging results are obtained with a significant reduction in the number of iterations. A slow increase of the number of iterations with respect to the frequency is noted.This preconditioning strategy adapted to the CARP-CG method implies larger memory requirements. However, this extra memory cost remains one order lower compared to direct solver memory requirement, and should be affordable on standard HPC facilities. The main bottleneck preventing from the possible use of this iterative solver for 3D elastic FWI remains the computation time for the wave equation solves
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Akogyeram, Samuel. « Bonding and debonding mechanism of pressure sensitive adhesives ». Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/12765.
Texte intégralRésumé :
Pressure-sensitive adhesives (PSAs) are complex macromolecular-based blend formulations that, in dry form will adhere permanently to diverse surfaces with the application of mere finger pressure. This thesis addresses the bonding and debonding mechanisms of coated films of different commercially available PSAs by systemically investigating the film characteristics on multiple levels. The methods implemented involve a novel procedure in investigating viscoelastic properties with Dynamic Mechanical Analysis, film surface chemistry with Time-of-flight Secondary Ion Mass Spectrometry and film morphology, modulus and bonding characteristics with Atomic Force Microscope. The theoretical aspect invoked rubber elasticity, viscoelasticity and thermodynamic concepts in representation of film morphology with corresponding adhesion nature. The results indicate that the bonding and debonding behaviour of PSA films are of a viscoelastic nature, dictated mainly by two fundamental morphological elements. These elements are; (1) the formation of phase-separated self-assembly of polystyrene-richcopolymer nano-domains within the adhesive matrix and (2) the inter-linking of the nanodomains by elastically active elastomer segments into a physical crosslinked network system that is highly efficient in dissipating large strain energy. These morphological factors are manifested through a profound contribution to the peel strength of the adhesive films when either coated at high temperatures or annealed. Increasing the content of the polystyrene endblock-tackifier in the adhesive blend formulation increased the PSA’s performance sensitivity to the film coating temperature. Meanwhile increasing the cis-C=C bond concentration in the formulation reduced the film’s performance sensitivity to coating temperature, as polydienes are premised to promote the entropy-elasticity of the film matrix by contributing to the nano-domain interconnections. This thesis generates many qualitative similarities, despite the significantly different adhesive blends investigated and hopefully the results reported here are more universal than one might expect.
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Damarla, Gowrisankar. « Determination of Wear in Polymers Using Multiple Scratch Test ». Thesis, University of North Texas, 2004. https://digital.library.unt.edu/ark:/67531/metadc4627/.
Texte intégralRésumé :
Wear is an important phenomenon that occurs in all the polymer applications in one form or the other. However, important links between materials properties and wear remain illusive. Thus optimization of material properties requires proper understanding of polymer properties. Studies to date have typically lacked systematic approach to all polymers and wear test developed are specific to some polymer classes. In this thesis, different classes of polymers are selected and an attempt is made to use multiple scratch test to define wear and to create a universal test procedure that can be employed to most of the polymers. In each of the materials studied, the scratch penetration depth s reaches a constant value after certain number of scratches depending upon the polymer and its properties. Variations in test parameters like load and speed are also studied in detail to understand the behavior of polymers and under different conditions. Apart from polystyrene, all the other polymers studied under multiple scratch test reached asymptotes at different scratch numbers.
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Hadj, Mohammed el. « Applications des methodes multi-grilles aux calculs des structures elastique et visco-plastique ». Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0047.
Texte intégralRésumé :
Les methodes multi-grilles sont destinees a reduire le cout de resolution des systemes lineaires (temps de calcul et stockage) en particulier sur de petits calculateurs. L'application de la methode des elements finis pour l'etude des structures et la mise en forme de materiaux conduit a de tels systemes. Dans le premier chapitre de notre travail, nous presentons en premier lieu les principes generaux d'approximation par elements finis et les methodes de resolution. Ceci nous permet ensuite, de decrire dans le second chapitre, le principe algorithmique d'une methode deux-grilles et la generalisation aux methodes multi-grilles. Nous terminons ce chapitre par une etude bibliographique de ces methodes. Dans le troisieme chapitre, nous analysons plusieurs algorithmes de resolution pour le cas de l'elasticite lineaire en deux et trois dimensions, puis nous presentons un algorithme efficace qui conduit a des resultats tres interessants du point de vue cout de resolution. Dans le dernier chapitre de cette these, nous presentons l'application de ces methodes aux problemes visco-plastiques en formulation vitesse et pression utilisant la methode du lagrangien augmente
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Wood, Brian Henry. « Experimental validation of an integrated FRP and visco-elastic hardening, damping, and wave-modulating system for blast resistance enhancement of RC columns ». Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Wood_09007dcc80538e4c.pdf.
Texte intégralRésumé :
Thesis (M.S.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 28, 2008) Includes bibliographical references (p. 112-115).
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Gelineau, Pierre. « Caractérisation morphologique et homogénéisation élastique et visco-élastique de polymères renforcés de nano-plaquettes d'argile ». Thesis, Compiègne, 2015. http://www.theses.fr/2015COMP2193/document.
Texte intégralRésumé :
L'objectif de ce travail est de comprendre l'influence de nano-plaquettes d'argile sur le comportement mécanique de polymères nano-renforcés. Cette compréhension nécessite une caractérisation fine de la micro-structure mais aussi l'étude du comportement mécanique de ces matériaux (en élasticité et en visco-élasticité). A l’échelle microscopique, la taille des agrégats de plaquettes d'argile et la distribution spatiale de ces agrégats ont été observées au TEM. A l’échelle nanoscopique, le d-spacing entre plaquettes d'un agrégat a été mesuré en utilisant la XRD. Ces techniques expérimentales ont permis de mettre en évidence une micro-structure intercalée. A l’échelle macroscopique, des essais de traction monotones ainsi que des essais dynamiques (DMA) ont été réalisé afin d'étudier le comportement mécanique des matériaux. Pour prédire les propriétés élastiques macroscopiques, la combinaison de deux approches a été envisagée; modèles hybrides et modèles matrice-inclusion. Cet outil permet d'anticiper les propriétés de ces matériaux sans avoir à les fabriquer ainsi que de tester simplement l'influence de la micro-structure sur le comportement macroscopique. Le schéma d'homogénéisation mis en place permet de prendre en compte la micro-structure intercalée d'une matrice polymère renforcée par des empilements de sandwiches bi-couches (plaquettes d'argile et polymère). On observe, en élasticité, un bon encadrement des données expérimentales. Une extension de cette approche en visco-élasticité a été développée. Les prédictions en visco-élasticité comparées aux données expérimentales ont fourni une bonne estimation du module complexe et des modules de conservation et de perteThis work aims to understand the influence of nano-clay platelets on the mechanical behavior of nano–reinforced polymers. This understanding requires a good description of the micro-structure and a characterization of the mechanical behavior of these materials (elastic and visco-elastic). At the micro-scale, the size of the aggregates of nano-platelets and their spatial distribution were observed using TEM. At the nano-scale, the d-spacing between platelets within an aggregate was measured using XRD. These experimental techniques highlighted intercalated micro-structures. At the macroscale, monotonic tensile tests and Dynamic Mechanical Analysis (DMA) have been performed to study the mechanical behavior of the materials. To predict the macroscopic elastic behavior, the combination of two approaches has been considered; hybrid and matrix-inclusion models. This needed tool allows to anticipate the behavior of these materials without process them. By the consideration of the morphology into the modeling scheme, the influence of the micro-structure on the macroscopic behavior can be studied. The considered multiscale approach is able to estimate the macroscopic behavior of an intercalated nano-composite, in which a polymeric matrix is reinforced by stacks of bi-layers sandwiches (nano-clay platelets and polymer). It was observed from their comparison that the modeling predictions well bounded the experimental data in elasticity. This multi-scale approach was extended in the context of viscoelasticity and the predictions in this context were in good agreement with the experimental data for the complex modulus and for the storage and loss moduli
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Ramalho, Denise Alves. « Estudo da influência dos perfis de solo na resposta dinâmica de sistemas rotor-fundação ». [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264189.
Texte intégralRésumé :
Orientador: Katia Lucchesi Cavalca DediniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-09T21:40:12Z (GMT). No. of bitstreams: 1 Ramalho_DeniseAlves_M.pdf: 10823264 bytes, checksum: 8b25eba0e7c26b9c543a70020d208299 (MD5) Previous issue date: 2006
Resumo: O objetivo deste trabalho é estender e melhorar a análise dinâmica de um sistema rotorfundação-solo através da inclusão de modelos distintos de perfis de solo. Obtém-se a resposta desbalanceada de um rotor Laval (Jeffcott) simples bidimensional com mancais rígidos. O rotor é colocado sobre uma fundação de bloco rígido. Os perfis de solo incluem o modelo clássico de semi-espaço e o modelo de solo sobre base rígida. Em particular, uma camada sobre base rígida com diferentes valores de profundidade será considerada. A resposta dinâmica do solo é obtida no domínio da freqüência. O mecanismo de amortecimento interno do solo é considerado. Vários estudos paramétricos são realizados para avaliar o papel da espessura da camada do solo, do coeficiente de amortecimento do solo, da inércia da fundação e da altura dos mancais na resposta ao desbalancemento do rotor. Acredita-se que a análise deste modelo simples de rotor-fundação-solo ajudará a esclarecer o papel dos parâmetros mencionados na resposta dinâmica do rotor
Abstract: The aim of the present work is to extend and improve the dynamic analysis of a rotorfoundation-soil system by including the modelling of distinct soil profiles. The unbalance response of a simple two-dimensional Laval (Jeffcott) rotor with rigid bearings is performed. The rotor is attached to a rigid strip foundation (block foundation). The soil profiles, on the other hand, include the classical half-space but also stratified soils. In particular, a layer with various depths over a bedrock will be considered. The soil¿s dynamic response is furnished in terms of frequency dependent complex impedances. The soil internal damping mechanism is also addressed by making the soil a viscoelastic continuum. A series of parametric studies are perfomed to assess the role of soil layer thickness, soil internal damping coefficient, foundation inertia and bearing height on the rotor unbalance response. It is believed that the analysis of this simple otor-foundation-soil model will help to clarify the role of the mentioned parameters on the rotor dynamic response
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Li, Ying. « Digital Mix Design for Performance Optimization of Asphalt Mixture ». Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/72959.
Texte intégralRésumé :
Asphalt mix design includes the determination of a gradation, asphalt content, other volumetric properties, the evaluation of mechanical properties and moisture damage potentials. In this study, a computational method is developed to aid mix design. Discrete element method (DEM) was used to simulate the formation of skeleton and voids structures of asphalt concrete of different gradations of aggregates. The optimum gradation could be determined by manipulating the particle locations and orientations and placing smaller particles in the voids among larger particles. This method aims at an optimum gradation, which has been achieved through experimental methods. However, this method takes the mechanical properties or performance of the mixture into consideration, such as inter-aggregate contacts and local stability. A simple visco-elastic model was applied to model the contacts between asphalt binder and aggregates. The surface texture of an aggregate particle can be taken into consideration in the inter-particle contact model. The void content before compactions was used to judge the relative merits of a gradation. Once a gradation is selected, the Voids in Mineral Aggregate (VMA) can be determined. For a certain air void content, the mastics volume or the binder volume or the asphalt content can be determined via a digital compression test. The surface area of all the aggregates and the film thickness can be then calculated. The asphalt content can also be determined using an alternative approach that is based on modeling the inter-particle contact with an asphalt binder layer. In this study, considering the necessity of preservation of the compaction temperature, the effect of various temperatures on Hot Mix Asphalt (HMA) samples properties has been evaluated. As well, to evaluate the effect of this parameter on different grading, two different grading have been used and samples were compacted at various temperatures. Air voids also influence pore water pressure and shrinkage of asphalt binder and mixture significantly. The shrinkage is measured on a digital model that represents beams in a steel mold and is defined as the linear autogenous deformation at horizontal direction.Ph. D.