Dissertations / Theses on the topic 'Basse velocità'

Il presente elaborato propone un metodo di calibrazione alle basse velocità degli anemometri a filo caldo utilizzati nella galleria del vento presente al C.I.C.Lo.P.E. (Center for International Cooperation in Long Pipe Experiments) dell'Università di Bologna, potenzialmente estendibile ad applicazioni più generali. In seguito ad un'analisi teorica approfondita della fattibilità di una calibrazione alle basse velocità, si è dimensionato e realizzato un prototipo in P.V.C. a geometria convergente-divergente, ritenuto in grado di produrre un flusso uniforme in uscita tale da garantire una soluzione al problema della calibrazione all'interno della test-section della galleria. Completata la fabbricazione del componente si è condotta un'analisi sperimentale, con l'ausilio del C.A.T. (Coaxial Air Tunnel) presente nell'hangar della Scuola di Ingegneria, sede di Forlì, del flusso generato internamente al divergente del calibratore. Nonostante si sia rilevata, mediante lo studio sperimentale condotto, una non perfetta uniformità del flusso uscente dal componente, i risultati riscontrati hanno permesso di inquadrare approcci e soluzioni atti ad un'ottimizzazione del calibratore, lasciando ampio margine di miglioramento ai fini della calibrazione alle basse velocità mediante il metodo descritto.

Nel presente lavoro di tesi è stato studiato il comportamento all’impatto di laminati compositi di varia natura, valutando il danneggiamento ad impatti a bassa velocità. Il comportamento dei diversi campioni è stato osservato prendendo come riferimento un laminato in fibra di carbonio e resina epossidica. Al fine di studiare e migliorare la risposta dei materiali a questo tipo di sollecitazioni sono stati utilizzati diversi approcci: introduzione di strati eterogenei di natura differente e uso di tessuti ibridi (fibre di carbonio e fibre polimeriche). I campioni sono stati quindi sottoposti ad impatti a diversa energia, con lo scopo di valutare l’energia assorbita e la loro deformazione. I provini danneggiati sono stati quindi sottoposti ad analisi di caratterizzazione microscopica, termica e meccanica.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Afin de mieux comprendre et de mieux quantifier la formation des dommages d'impact et leurs conséquences sur la tenue de la structure composite, le recours à la simulation numérique semble être un complément indispensable pour enrichir les campagnes expérimentales. Cette thèse a pour objectif la mise au point d'un modèle d'impact pour la simulation numérique par éléments finis dynamique implicite, capable de prévoir les dommages induits.La première étape du travail a consisté à élaborer un modèle s'appuyant sur le modèle de comportement du pli " Onera Progressive Failure Model " (OPFM) et sur le modèle bilinéaire de zones cohésives proposé par Alfano et Crisfield, puis d'évaluer la sensibilité aux différentes composantes des lois de comportement de la réponse à un impact et des dommages prévus. Des essais d'impact et d'indentation sur des plaques stratifiées en carbone/époxy ont ensuite été réalisés, analysés et enfin confrontés aux résultats numériques, afin d'évaluer les performances à l'impact du modèle OPFM et ses limites.Ces travaux permettent d'aboutir à trois principales conclusions. Premièrement, l'usage de modèles de zones cohésives semble nécessaire pour prévoir la chute de force caractéristique de l'impact sur stratifiés. Deuxièmement, la prise en compte des contraintes hors plan, notamment les cisaillements, est indispensable pour prévoir correctement l'endommagement d'impact. Enfin, si le modèle OPFM est capable de prévoir qualitativement les dommages d'impact, l'absence de caractère adoucissant ou de viscoplasticité semble cependant limiter leur prévision quantitative.

In questo lavoro di tesi è stato elaborato un modello analitico al fine di ottenere una stima dell’ampiezza di delaminazione a seguito di impatti a bassa velocità in laminati in composito, in particolare carbon/epoxy. Nel capitolo 2 è descritto il comportamento meccanico di tali laminati (equazioni costitutive della singola lamina, dell’intero laminato e costanti ingegneristiche dell’intero laminato per qualsiasi sistema di riferimento). Nel capitolo 3 viene descritta la filosofia di progettazione damage tolerance per tali materiali sottoposti a low-velocity impact (LVI) e richiamato il concetto di structural health monitoring. In particolare vengono descritti i tipi di difetti per un laminato in composito, vengono classificati gli impatti trasversali e si rivolge particolare attenzione agli impatti a bassa velocità. Nel paragrafo 3.4 sono invece elencate diverse tecniche di ispezione, distruttive e non, con particolare attenzione alla loro applicazione ai laminati in composito. Nel capitolo 4 è riportato lo stato dell’arte per la stima e la predizione dei danni dovuti a LVI nei laminati: vengono mostrate alcune tecniche che permettono di stimare accuratamente l’inizio del danno, la profondità dell’indentazione, la rottura delle fibre di rinforzo e la forza massima di impatto. L’estensione della delaminazione invece, è difficile da stimare a causa dei numerosi fattori che influenzano la risposta agli impatti: spesso vengono utilizzati, per tale stima, modelli numerici piuttosto dispendiosi in termini di tempo e di calcolo computazionale. Nel capitolo 5 viene quindi mostrata una prima formula analitica per il calcolo della delaminazione, risultata però inaffidabile perché tiene conto di un numero decisamente ristretto di fattori che influenzano il comportamento agli LVI. Nel capitolo 6 è mostrato un secondo metodo analitico in grado di calcolare l’ampiezza di delaminazione mediante un continuo aggiornamento della deflessione del laminato. Dal confronto con numerose prove sperimentali, sembra che il modello fornisca risultati vicini al comportamento reale. Il modello è inoltre fortemente sensibile al valore della G_IIc relativa alla resina, alle dimensioni del laminato e alle condizioni di vincolo. É invece poco sensibile alle variazioni delle costanti ingegneristiche e alla sequenza delle lamine che costituiscono il laminato. La differenza tra i risultati sperimentali e i risultati del modello analitico è influenzata da molteplici fattori, tra cui il più significativo sembra essere il valore della rigidezza flessionale, assunto costante dal modello.

Nella pratica clinica la velocità del cammino è un parametro importante, largamente utilizzato sia come strumento predittivo di mortalità, disabilità e ulteriori avvenimenti avversi, sia singolarmente o all'interno di test motori per la misura oggettiva del cambiamento nello status dei pazienti, ad esempio prima e dopo una terapia. Le principali critiche alla misura della velocità all'interno degli ambienti clinici riguardano la mancanza di validità ecologica e le limitate distanze percorribili. Uno dei possibili strumenti utilizzabile per una valida e accurata misura di questo parametro anche in ambiente di vita reale, senza ad esempio vincoli su luogo e momento della misura o il bisogno di un continuo monitoraggio da parte di un esaminatore, è il GPS. L’impiego di questo dispositivo è stato fino ad ora limitato, per via delle basse prestazioni ottenibili in presenza di ostacoli come alti edifici o zone con una fitta vegetazione, migliorabili solo utilizzando dispositivi professionali dall'alto costo. Ad oggi invece questa spesa, con l’immissione sul mercato di moduli GNSS a basso costo capaci di misure differenziali RTK, è diminuita notevolmente rendendo questi ricevitori accessibili al consumatore medio. Lo scopo di questa tesi consiste, dunque, nella validazione della misura della velocità del cammino effettuata con uno di questi nuovi ricevitori, chiamato simpleRTK2B. Con questa finalità sono stati quindi stilati tre protocolli sperimentali che, utilizzando un cronometro e un sistema di fotocellule LED, consentissero la validazione della misura che simpleRTK2B fa della velocità media, sia in condizioni di utilizzo ottimale che in ambiente urbano.

Nel Novembre 2018, la startup spagnola ArduSimple ha lanciato sul mercato simpeRTK2B, il primo dispositivo a basso costo, che permette di acquisire in real-time dati su posizione, velocità e altre informazioni, con accuratezza centimetrica, grazie all’utilizzo della tecnologia RTK. In questo lavoro ci si soffermerà sull’uso del simpleRTK2B per la misura della velocità del cammino. Lo scopo sarà caratterizzare il dispositivo, studiando il suo comportamento in varie situazioni d’uso, reali o simulate. Attraverso acquisizioni statiche si analizzerà l’accuratezza del dato dell’altitudine e l’influenza sui dati dovuta a variazioni dell’orientamento dell’antenna rispetto al cielo. Poi, con acquisizioni dinamiche, si cercherà di capire se l’accuratezza cambia al variare di: posizionamento dell’antenna; condizioni atmosferiche; distanza del ricevitore dalla stazione base che invia le correzioni RTK; presenza o meno di una barra metallica come base per l’antenna; orario d’acquisizione. Questo elaborato inizierà con l’introduzione dei concetti fondamentali sul sistema globale di navigazione satellitare; successivamente verrà descritto il dispositivo simpleRTK2B in tutte le sue parti, a cui seguiranno alcuni richiami sui metodi di statistica inferenziale successivamente utilizzati nell’analisi dei dati. Saranno poi presentati i protocolli utilizzati per le varie acquisizioni, le elaborazioni effettuate sui dati e le relative analisi, corredate da una presentazione sistematica dei principali risultati ottenuti.

L'utilisation industrielle ou militaire des explosifs est largement répandue. La sécurité est devenue un axe majeur avec notamment l'ignition involontaire des explosifs composés de HMX lors des impacts à basse vitesse. L'objectif de cette thèse est de contribuer à la compréhension des mécanismes dissipatifs à l'origine des échauffements locaux dans le matériau. Le développement d'un essai aux barres d'Hopkinson a permis de coupler de grandes vitesses de déformations à des pressions élevées pour compléter les données expérimentales. Cet essai a montré un angle de frottement quasiment identique à celui obtenu en quasistatique mais une contrainte de cohésion supérieure d'environ 25 MPa. Ensuite, pour observer les mécanismes pouvant être sources d'échauffement, un essai de compression dans la tranche a été développé avec des observations en temps réel. Celles-ci ont permis de conclure qu'il y a très peu de frottements entre les gros grains et la matrice (l'ensemble des petits grains, du liant et de la porosité). De la plasticité des grains de HMX a pu être observée mais surtout beaucoup d'endommagement dans certaines zones y compris dans la matrice. Une microfissuration très intense de certains grains a été observée. Parallèlement, une représentation numérique biphasique (gros grains de HMX et matrice) de toute la microstructure du matériau a été considérée. Une confrontation entre les observations expérimentales et les simulations a permis de déterminer le seuil de plasticité du HMX. Le comportement de la matrice a été identifié pour prendre en compte l'effet de vitesse et l'endommagement observé. Enfin, les confrontations entre les essais et les simulations de ceux-ci ont montré que les échauffements devraient plutôt se localiser dans la matrice que dans les gros grains de HMX et que le mécanisme le plus probable est le frottement de lèvres de microfissures.

The flow distribution in the primary circuit of the pressurized water reactor was studied with experiments and Computational Fluid Dynamics (CFD) simulations. The main focus was on the flow field and mixing in the downcomer of the pressure vessel: how the different factors like the orientation of operating loops, the total loop flow rate and the asymmetry of the loop flow rates affect the outcome. In addition to the flow field studies the overall applicability of CFD methods for primary circuit thermal-hydraulic analysis was evaluated based on the CFD simulations of the mixing experiments of the ROCOM (Rossendorf Coolant Mixing Model) test facility and the mixing experiments of the Paks NPP. The experimental part of the work in work package 3 included series of steady state mixing experiments with the ROCOM test facility and the publication of results of Paks VVER-440 NPP thermal mixing experiments. The ROCOM test facility models a 4-loop KONVOI type reactor. In the steady-state mixing experiments the velocity field in the downcomer was measured using laser Doppler anemometry and the concentration of the tracer solution fed from one loop was measured at the downcomer and at the core inlet plane. The varied parameters were the number and orientation of the operating loops, the total flow rate and the (asymmetric) flow rate of individual loops. The Paks NPP thermal mixing experiments took place during commissioning tests of replaced steam generator safety valves in 1987-1989. It was assumed that in the reactor vessels of Paks VVER-440 NPP equipped with six loops the mixing of the coolant is not ideal. For the realistic determination of the active core inlet temperature field for the transients and accidents associated with different level temperature asymmetry a set of mixing factors were determined. Based on data from the online core monitoring system and a separate mathematical model the mixing factors for loop flows at the core inlet were determined. In the numerical simulation part of the work package 3 the detailed measurements of ROCOM tests were used for the validation of CFD methods for primary circuit studies. The selected steady state mixing experiments were simulated with CFD codes CFX-4, CFX-5 and FLUENT. The velocity field in the downcomer and the mixing of the scalar were compared between CFD simulations and experiments. The CFD simulations of full scale PWR included the simulation of Paks VVER-440 mixing experiment and the simulation of Loviisa VVER-440 downcomer flow field. In the simulations of Paks experiments the experimental and simulated concentration field at the core inlet were compared and conclusions made concerning the results overall and the VVER-440 specific geometry modelling aspects like how to model the perforated elliptic bottom plate and what is the effect of the cold leg bends to the flow field entering to the downcomer. With Loviisa simulations the qualitative comparison was made against the original commissioning experiments but the emphasis was on the CFD method validation and testing. The overall conclusion concerning the CFD modelling of the flow field and mixing in the PWR primary circuit could be that the current computation capacity and physical models also in commercial codes is beginning to be sufficient for simulations giving reliable and useful results for many real primary circuit applications. However the misuse of CFD methods is easy, and the general as well as the nuclear power specific modelling guidelines should be followed when the CFD simulations are made.

The flow distribution in the primary circuit of the pressurized water reactor was studied with experiments and Computational Fluid Dynamics (CFD) simulations. The main focus was on the flow field and mixing in the downcomer of the pressure vessel: how the different factors like the orientation of operating loops, the total loop flow rate and the asymmetry of the loop flow rates affect the outcome. In addition to the flow field studies the overall applicability of CFD methods for primary circuit thermal-hydraulic analysis was evaluated based on the CFD simulations of the mixing experiments of the ROCOM (Rossendorf Coolant Mixing Model) test facility and the mixing experiments of the Paks NPP. The experimental part of the work in work package 3 included series of steady state mixing experiments with the ROCOM test facility and the publication of results of Paks VVER-440 NPP thermal mixing experiments. The ROCOM test facility models a 4-loop KONVOI type reactor. In the steady-state mixing experiments the velocity field in the downcomer was measured using laser Doppler anemometry and the concentration of the tracer solution fed from one loop was measured at the downcomer and at the core inlet plane. The varied parameters were the number and orientation of the operating loops, the total flow rate and the (asymmetric) flow rate of individual loops. The Paks NPP thermal mixing experiments took place during commissioning tests of replaced steam generator safety valves in 1987-1989. It was assumed that in the reactor vessels of Paks VVER-440 NPP equipped with six loops the mixing of the coolant is not ideal. For the realistic determination of the active core inlet temperature field for the transients and accidents associated with different level temperature asymmetry a set of mixing factors were determined. Based on data from the online core monitoring system and a separate mathematical model the mixing factors for loop flows at the core inlet were determined. In the numerical simulation part of the work package 3 the detailed measurements of ROCOM tests were used for the validation of CFD methods for primary circuit studies. The selected steady state mixing experiments were simulated with CFD codes CFX-4, CFX-5 and FLUENT. The velocity field in the downcomer and the mixing of the scalar were compared between CFD simulations and experiments. The CFD simulations of full scale PWR included the simulation of Paks VVER-440 mixing experiment and the simulation of Loviisa VVER-440 downcomer flow field. In the simulations of Paks experiments the experimental and simulated concentration field at the core inlet were compared and conclusions made concerning the results overall and the VVER-440 specific geometry modelling aspects like how to model the perforated elliptic bottom plate and what is the effect of the cold leg bends to the flow field entering to the downcomer. With Loviisa simulations the qualitative comparison was made against the original commissioning experiments but the emphasis was on the CFD method validation and testing. The overall conclusion concerning the CFD modelling of the flow field and mixing in the PWR primary circuit could be that the current computation capacity and physical models also in commercial codes is beginning to be sufficient for simulations giving reliable and useful results for many real primary circuit applications. However the misuse of CFD methods is easy, and the general as well as the nuclear power specific modelling guidelines should be followed when the CFD simulations are made.

Ce travail s’inscrit dans la problématique de réduction de masse, de sécurité inhérent au domaine aéronautique, il concerne plus spécifiquement les sièges de pilotes d’avion de ligne. Un nouveau concept d’assise composite sandwich multifonctionnel est proposé. Il est composé d’une peau carbone, d’une âme nid d’abeille Nomex et d’une peau hybride Kevlar/lin. L’assemblage de plusieurs matériaux engendre des comportements parfois complexes et rend difficile la prédiction de la ruine de la structure. Une démarche expérimental/numérique est mise en place pour appréhender l’endommagement de l’assise et ainsi permettre un pré-dimensionnement via un outil numérique.Tout d’abord, des essais de caractérisation permettent d’élaborer les lois de comportement des différents matériaux constituant le sandwich. Le composite hybride présente un comportement élasto-plastique-endommageable-anisotrope. Le nida Nomex est représenté par un réseau de ressort et une loi couplant le comportement en compression et en cisaillement qui est implémentée dans ABAQUS. Des essais d’impacts permettent d’évaluer les modes de rupture et l’énergie dissipée par les concepts d’assises réalisés. Des simulations numériques intégrant les comportements matériaux identifiés sont mises en places pour corréler l’essai d’impact. L’analyse couplée des résultats expérimentaux et numériques permet d’identifier les couplages entre les différents mécanismes. Enfin, le modèle est utilisé pour dimensionner une assise composite qui s’avère sans optimisation fine, comparable à une assise existante en aluminium de l’A350
This work is part of the problem of mass reduction, safety inherent in the aeronautical field, it concerns more specifically the seats of pilots of airliner. A new multi-functional sandwich composite seat pan is proposed, composed by a carbon skin, a Nomex honeycomb core and a Kevlar/flax hybrid skin. The assembly of several materials generates complex behaviors and makes the ruin of the structure difficult to predict. An experimental/numerical approach is used to understand the damage mechanism of the seat and to create a pre-dimensioning numerical tool.Firstly, characterization tests allow identifying the mechanical behaviors of each material and constituting a database for the creation of material laws. The hybrid composite shows an elastoplastic-damaging-anisotropic behavior. The honeycomb is represented by a spring network and a law coupling the compression and shear behavior is implemented. Impact tests are used to evaluate the failure modes and the energy dissipated by the different concepts. The impact tests are correlates by numerical simulation using the identified material behaviors. The analysis of the experimental and numerical results makes it possible to identify the coupling between the different mechanisms. Finally, the model is used to design a new composite seat pan. This one is comparable to the existing aluminum seat pan without optimization phase

Lors d'une étude précédente, des prototypes destinés à transporter des matériels militaires lourds (600kg) par hélicoptère ont été produits. Reposant sur l'utilisation de matériaux composites à structure sandwich, ces structures ont convaincu par leur légèreté et leur résistance à la charge, mais ont montré des faiblesses lors de la sollicitation en impact basse énergie / basse vitesse. Lors de cette thèse, nous avons cherché à optimiser la résistance des structures sandwich à ce type d'endommagements en étudiant l'influence des paramètres d'élaboration par un procédé de mise-en-oeuvre industriel. Une étude bibliographique a permis la mise en évidence des paramètres critiques de faisabilité du projet. Le choix du procédé de fabrication a été arrêté à l'infusion de résine liquide, technique couramment utilisée dans l'industrie est facilement utilisable par des petites et moyennes structures. L'état de l'art a également révélé des pistes d'amélioration des structures sandwich via les conditions de fabrication. Un procédé particulier a du être mis en place afin de fabriquer des structures composites sandwich en une seule étape. Avec cette méthode, quatre jeux de paramètres ont été retenus pour l'étude : les températures de fabrication, la nature de la matrice, l'état de surface de l'âme, ainsi que la présence (ou non) d'additifs nano-dimensionnés dans la matrice. Diverses combinaisons de ces paramètres ont été utilisées pour fabriquer des panneaux sandwich ensuite découpés en échantillons afin d'être testés en impact à l'aide d'une tour de chute. Une première série de tests a permis de déterminer les conditions d'impact représentative des cas réellement rencontrés, les techniques permettant l'identification et la caractérisation des endommagements, ainsi que l'observation des comportements pendant l'impact. A partir des observations pendant et après l'impact, nous avons pu constater trois comportements et quatre types d'endommagements, sur l'ensemble des échantillons testés. Ces comportements et endommagements ont pu être reliées aux paramètres d'élaboration sélectionnés. [...]
In a previous study, prototypes for heavy military equipment (>600kg) transportation by helicopters were developed. Based on sandwich composite structures, these materials showed promising results in terms of weight reduction and load bearing capabilities, but weaknesses were observed during low velocity/low energy impact solicitations. During this PhD project, we aimed at optimizing sandwich structure's resistance to impacts, by studying elaboration parameter's influences of an industrial production method on impact behaviors. A bibliographic review showed critical parameters for this project's feasibility. We chose to use the Liquid Resin Infusion as the elaboration process; this technique is commonly used in the industry, and is suited for small production structures. State of the art also showed impact resistance improving methods for sandwich structures, in terms of processing conditions. A particular elaboration method was designed, to produce sandwich structures in a one-shot process. In this study, and with this method, four sets of parameters were selected: elaboration temperatures, matrix types, core's surface nature, and whether or not the matrix contained nanoscaled additives. Several combinations of these parameters were used to produce sandwich panels, which were cut in samples, to be impacted on a drop-weight tower. Preliminary testing allowed to determine representative impact conditions, similar to real-life situations, the observation and characterization techniques of damages, and behavior observation methods during impact. Based on that, we were able to identify three behaviors during impact, and four damage types, over all tested samples. These behaviors and damages were linked to the selected elaboration conditions and one set appeared very promising. The analysis of the parameters allowed us to understand the mechanisms occurring during the production of the panel. Residual resistance after impact was characterized by subjecting the samples to consecutive impacts. Four behaviors were observed, directly linked to the damages initially observed. The choice of an optimal structure was confirmed

Les traitements de materiaux par plasma sont actuellement largement utilises dans la plupart des industries bien que les processus physiques qui regissent ces decharges ne soient pas totalement maitrises. Avec l'essor de nouvelles sources optiques, le diagnostic de fluorescence laser, non perturbatif vis a vis du milieu, associe aux diagnostics electriques, permet la caracterisation de sources a plasma basse pression. Grace a cet outil, on peut ainsi comprendre la cinetique des ions (production, excitation, diffusion) et mesurer les parametres critiques influant sur la qualite du traitement (flux, directionalite, fonction de distribution en energie des particules bombardant la surface, temperature du substrat)

A period of cement hydration is one of critical in the life span of concrete structures. One of the reasons of collapse of concrete structural elements during and after construction is the error in determining the concrete characteristics at early age. Recently, non-destructive test emerged as a popular way to evaluate the properties of cement-based materials. This test offers continuous measurements of concrete properties as well as ability to monitor any changes in the current state of structural materials. In the existing research, some of these methods fail to capture well properties of the materials in the plastics stage. A new piezoelectric pulse testing device (Piezoelectric Ring Actuators Technique), (P-RAT ) was initially developed at the University of Sherbrook as a non-destructive test (NDT ) for soil. This technique is considered a completely new, versatile, advanced and accurate. The development of the new technique (P-RAT ) was done on two main bases: the first was the development of piezoelectric ring actuators set-up and the second is the development of the interpretation method. The setup is composed of two main units; emitter and receiver, and is capable of measuring shear and compression wave velocities in specimens. With this technique, many problems of pulse tests, which make interpretation of results difficult and ambiguous, were solved in soil. The P-RAT overcomes wave reflections at boundaries (end-caps and sides), sample disturbance, weak shear coupling between soil and device (interaction) as well as the fixation problems, low resonant frequency and limited input voltage of the existing device. The previous method is exploited forward to measure the hydration properties of cement-based material. To apply this test method, it is necessary to determine how the evolution of shear wave velocity can be related and sensitive to the hydration of cement-based materials. Validation of the P-RAT with four conventional test setups that can be used to monitor early setting and hydration of cement-based materials is carried out. These tests include penetration resistance to monitor initial and final setting respectively, calorimetric to monitor heat of hydration, electrical conductivity to monitor change in continuity of the pore structure and compressive strength at 24 hours. The phase one of this investigation included trial tests to investigate the possibility of employing the original setup used for soil (P-RAT ) to determine setting and hardening properties of cement-based material. Based on the results of the preliminary test, two modifications were conducted to the previous test device to fit with cement based material and to obtain adequate resonant frequency for cement-based materials. These modifications are the design of the container and changing the dimensions of the rings. The resultant version of P-RAT after the modification was referred to be as P-RAT2 . Calibration of the P-RAT2 with water specimen was undertaken using the compression wave velocity and resulted in 99.33% accuracy. One paste mixture was tested three times to determine the experimental error of the P-RAT2 . The repeatability carried out on the P-ART2 proved the ability of this setup to capture accurate results of the shear wave velocity. This relative error is limited to 9 %. A number of series of validation was performed on cement paste and mortar mixtures proportioned with various water cement ratios (w/cm ) as well as chemical admixtures. The w/cm ratio ranged between (0.35 and 0.50). The investigated chemical admixtures comprise of high-range water-reducing agent, viscosity-modifying agent, set-accelerating agent, and set-retarding agent. The presented validations examine the ability of a P-RAT2 to monitor the hydration of the cement-based materials. The hydration is characterized by setting time, heat of hydration, electrical conductivity, and compressive strength at 24 hours. The results obtained using the P-RAT2 was correlated to those obtained using the conventional tests and strength measurement. The results enable to validate the ability of P-RAT2 to accurately detect variations in the hydration of cement-based materials. In addition, the initial and final time of setting can be determined from the derivation of velocity vs. time curve. The results show that conductivity, resistivity, has a bilinear relationship to shear wave velocity. The compressive strength at 24 hours was correlated to both the shear wave velocity and shear modulus obtained using the P-RAT2 . Furthermore, analytical model was derived to estimate the w/cm in mortar mixture by measuring the shear wave velocity (V[subscript s] ) and the corresponding time (t )||Résumé : La période d'hydratation du ciment est l'une des périodes clé du cycle de vie des structures en béton. L'une des raisons de l'effondrement d'éléments structuraux en béton pendant et après la construction peut être attribuée à une détermination des caractéristiques au jeune âge erronée. Depuis quelques années, l’auscultation des structures est devenue une méthode très populaire pour évaluer les propriétés des matériaux cimentaires. Cette méthode permet d'obtenir les propriétés du béton en continue et possibilité un suivi de changements dans I'état des matériaux structuraux. Dans I'état actuel de la recherche dans ce domaine, certaines méthodes ne sont pas adéquates pour bien mesurer les propriétés des matériaux à I'état plastique. Un nouvel appareil d'essai à impulsions piezoélectriques (Piezoelectric Ring Actuators technique), (P-RAT) a initialement été développé à l’Université de Sherbrooke comme technique d'auscultation des sols. Cette technique est considérée complètement nouvelle, polyvalente, évoluée et précise. Le développement de cette nouvelle technique (P-RAT) a été effectué en deux volets : la première sole est le développement du dispositif de vérin de commande annulaire piezoélectrique et le deuxième est le développement d'une méthode d'interprétation. Le dispositif d'essai est composé de deux unités principales, un émetteur et un récepteur. Et permet de mesurer la vitesse de propagation des ondes de cisaillement et de compression. Grâce à cette technique, plusieurs des problèmes associés aux dispositifs d'essais par impulsion des ondes, qui rendent les résultats ambigus et difficiles à interpréter, ont été résolu pour les sols. Le dispositif P-RAT surmonte les problèmes de réflexion des ondes aux limites (embouts et côtés), la perturbation de l’échantillon, le couplage de cisaillement faible entre le sol et l'appareil (interaction) ainsi que les problèmes de fixation, la faible résonnance des fréquences et le voltage d'entrée limité du dispositif. La méthode décrite a été utilisée pour mesurer les propriétés d'hydratation des matériaux cimentaires. Pour pouvoir appliquer cette méthode, il faut déterminer comment l’évolution de la propagation des ondes de cisaillement peut être reliée à l'hydratation des matériaux cimentaires et être sensible à ces dernières. La validation de la méthode P-RAT est réalisée, à l'aide de quatre configurations conventionnelles que l’on peut utiliser pour faire le suivi de la prise et de l'hydratation des matériaux cimentaires. Ces essais consistent à la résistance à la pénétration afin de pouvoir déterminer la prise initiale et finale, la calorimétrie pour suivre l’evolution de la chaleur d'hydratation, la conductivité électrique pour effectuer le suivi de la structure des pores et la résistance à la compression à 24 heures. La phase 1 de l'étude comprend des essais pour évaluer la possibilité d'utiliser la configuration originale utilisée pour les sols (P-RAT) pour déterminer les propriétés de prise et de durcissement des matériaux cimentaires. Selon les résultats des essais préliminaires, deux modifications ont été effectuées à l'appareil original pour permettre son utilisation avec des matériaux cimentaires et pour obtenir une fréquence de résonnance raisonnable sur les matériaux cimentaires. Les modifications effectuées sont la conception du contenant et un changement de la dimension des anneaux. La version modifiée du P-RAT est designée P-RAT2. La calibration du P-RAT2 à l'aide d'échantillon liquide sous propagation d'ondes de compression a été menée, avec des résultats d'une précision de 99,33 %. Un mélange a été testé trois fois pour déterminer l'erreur expérimentale du P-RAT2. La répétitivité des essais sur le PART2 a démontré la capacité de cet appareil à produire des résultats de cisaillement de propagation des ondes de cisaillement très précis. L'erreur relative se limite à 9 %. Une série d'essais de validation a été menée sur des mélanges de pâte de ciment et de mortier de rapport eau/ciment variés (e/c) ainsi qu'avec des adjuvants. Le rapport e/c variait entre 0,35 et 0,50. Les adjuvants utilisés étaient des supers plastiflants (réducteur d'eau), des agents de viscosité, des agents accélérateurs de prise et des agents retardateurs de prise. Les validations présentées ont pour but de valider la capacité du P-RAT2 à suivre l'hydratation des matériaux cimentaires. L'hydratation est caractérisée par le temps de prise, la chaleur d'hydratation, la conductivité électrique et la résistance à la compression à 24 heures. Les résultats obtenus à l'aide du P-RAT2 ont été comparés à ceux obtenus à l'aide d'essais de mesure des caractéristiques physiques et de résistance traditionnels. Ces résultats permettent de valider la capacité du P-RAT2 à détecter avec précision les variations dans l'hydratation des matériaux cimentaires. De plus, le dispositif P-RAT2 peut avoir une correction avec mesure obteniez avec les appareils traditionnels. II est aussi possible de déterminer le temps de prise initial et final à l'aide d'une courbe de propagation vs le temps. Les résultats montrent que la conductivité et la résistivité ont une relation bilinéaire à la propagation des ondes de cisaillement. La résistance à la compression à 24 heures a été comparee à la fois à la propagation des ondes de cisaillement et au module de cisaillement obtenus avec le P-RAT2. De plus, un modèle analytique a été établi pour estimer le rapport e/c dans le mélange de mortier en mesurant la propagation des ondes de cisaillement (V) correspondant au temps (t).

Les explosifs sont des matériaux qui, bien que potentiellement sensibles, sont conçus pour être stables en conditions normales, ainsi que lors de sollicitations mécaniques, chimiques ou thermiques " faibles ". Pourtant, sous sollicitations mécaniques de faible intensité, comme les impacts basse vitesse, ils peuvent réagir de manière intempestive. Les propergols, et plus particulièrement la butalite, objet de notre étude, présentent ce caractère : on observe des " réactions " pour des vitesses d'impacts inférieures à 100 m.s-1, dont l'origine est probablement liée à l'endommagement microstructural du matériau. Dans ce contexte, le but ultime du CEA Gramat est d'obtenir un outil de prédiction de la vulnérabilité des matériaux énergétiques pour les impacts à basse vitesse de type " tour de chute ". Pour ce faire, il est essentiel de disposer de données sur la morphologie et le comportement (thermo)mécanique macroscopique du matériau considéré, de ses phases constitutives à l'échelle mésoscopique et de ses interfaces. Ainsi l'objectif de la thèse est de déterminer le type et le niveau de(s) endommagement(s) apparaissant(s) dans une " butalite inerte " suite à un impact mécanique dit " à basse vitesse " (i.e., inférieure à 100 m.s-1) réalisé à l'aide d'un dispositif de type tour de chute modifié, associant un suivi par vidéo numérique rapide et une analyse microtomographique ante- et post-essai, en étudiant le ou les phénomènes physiques à l'origine des réactions sous " faibles " sollicitations, leur évolution et leur(s) origine(s) physique(s). Les grains sont modélisés par une loi de comportement purement élastique et la matrice en PBHT est décrite par une loi visco-hyper-élastique (couplage d'une série de Prony et du modèle de Mooney-Rivlin).

Etude des proprietes de fatigue des superalliages contenant des inclusions de type ceramique. Determination, a temperature ambiante, des cinetiques de debut de propagation de fissures a partir des defauts presents dans la structure. Mise en evidence, d'un effet de "fissure courte". Il est demontre que deux parametres jouent un role, essentiel dans la differenciation des cinetiques de propagation des fissures courtes et longues : le caractere tridimentionnel des fissures naturelles et le phenomenes de fermeture de fissures

Les travaux de thèse sont axés sur les méthodes numériques pour les écoulements diphasiques, compressibles, à faible vitesse, avec apparition soudaine de forts gradients de pression. La vitesse matérielle de chacune des phases étant très petite devant la célérité des ondes acoustiques, le régime d'écoulement est dit à faible nombre de Mach. Dans ce travail, la loi d'état de la phase considérée contient toujours une information mesurant sa plus ou moins grande compressibilité. Ainsi, la faible compressibilité de l'eau peut produire un régime d'écoulement où des sauts de pression importants apparaissent même si le nombre de Mach est très faible. La première partie de la thèse s'est focalisée sur un modèle diphasique dit homogène-équilibré. Les deux phases de l'écoulement ont alors la même vitesse, pression, température et même potentiel chimique. Un premier travail a été la construction de solveurs de Riemann approchés dits tout-nombre-de-Mach. En l'absence de transitoire rapide, ces solveurs basent leur contrainte de pas de temps sur la vitesse des ondes matérielles lentes et sont donc précis pour suivre ces dernières. En revanche, lorsqu'une onde de choc rapide traverse l'écoulement, ces solveurs s'adaptent automatiquement afin de la capturer. La seconde partie de la thèse s'est focalisée sur la prise en compte du couplage convection-source dans le cadre des modèles en approche bi-fluides avec effets de relaxation pression-vitesse. Dans ces modèles, les deux phases de l'écoulement possèdent leur propre jeu de variables. Dans ce travail, un schéma implicite à mailles décalées, basé sur l'influence des termes sources dans des problèmes de Riemann linéaires, a été proposé
The present work focuses on numerical methods for low-material velocity compressible two-phase flows with high pressure jumps. In this context, the material velocity of both phases is small compared with the celerity of the acoustic waves. The flow is said to be a low-Mach number flow. In this work, the equation of state of the considered phase always contains information relative to its compressibility. For example, the low-compressibility of liquid water may lead to fast transients in which high pressure jumps are produced even if the flow Mach number is low. The first part of this work has leaned on two-phase homogeneous-equilibrium models. Thus, both phases have the same velocity, pressure, temperature and the same chemical potential. The construction of what is called an all-Mach-number approximate Riemann solver has been conducted. When no fast transients come through the flow, the above solvers enable computations with CFL conditions based on low-material velocities. As a result, they remain accurate to follow slow material interfaces, or subsonic contact discontinuities. However, when fast shock waves propagate, these solvers automatically adapt in order to capture them. The second part of the thesis has been dedicated to the design of numerical methods enhancing the coupling between convection and relaxation for two-fluid models containing pressure-velocity relaxation effects. In such models, both phases have their own set of variables. A time-implicit staggered scheme, based on the influence of relaxation source terms on linear Riemann problems has been proposed

Des essais de traction-compression dans le domaine de fatigue plastique ont revele la grande stabilite cyclique du materiau. Analyse des conditions d'amorcage et de propagation des fissures. Mise en evidence du role des defauts de frittage ou des inclusions. Des essais de fissuration sont effectues dans le domaine des moyennes et basses vitesses en considerant l'effet du rapport de charge et de l'environnement. Description par la mecanique lineaire de rupture du comportement des microfissures

In this thesis, we have explored the possibilities to realize a Graphene Based Hybrid structures (GBHs) by the functionalization of a graphene layer on both sides. The first chapter gives a general introduction about graphene and a literature review of different metal intercalations on graphene. The second chapter explains the experimental techniques used in this work. In chapter 3, we studied the functionalization of epitaxial graphene on SiC(0001) by gold intercalation. With the help of Scanning Tunneling Microscopy, we have evidenced and characterized different intercalation modes such as the formation of aggregates of individual gold atoms and the formation of a continuous gold layer between the top graphene and the buffer layer. The free standing nature of the intercalated gold atoms was examined by differential charge density plot, projected density of states calculations and further by X-ray photoelectron spectroscopy. The band structure modification of graphene due to these intercalated gold atoms was evidenced by Angle-resolved photoemission spectroscopy, which reveals a strong Van Hove extension and an increase of the Fermi velocity. Extend to this research, to obtain an extended Van Hove singularity usually observed in highly doped graphene; we studied highly electron donor molecules, TetraThioFullvalene (TTF) on pristine and gold intercalated graphene and on graphite (chapter 4). The dependence of charge transfer of these molecules with their conformation and the reactivity of photochromic with conjugated molecules on graphene were also discussed. To understand the structural properties of these molecules photophysical measurements were performed in chapter 5.

Face aux défis environnementaux actuels, les industriels ont mis en œuvre de nouveaux matériaux recyclables et permettant une réduction significative de la masse. Le développement de la résine thermoplastique Elium par ARKEMA s’inscrit dans cette problématique. L’utilisation de cette résine pour la fabrication de pièces composites qui peuvent être sujettes à des dommages d’impact, nécessite au préalable des études, dans le but de comprendre leurs mécanismes de ruine sous ce type de sollicitation. Ainsi, la présente thèse propose une contribution à l’analyse multi-échelle de la tenue à l’impact des composites stratifiés à base de la résine Elium. Une étude expérimentale préliminaire a permis de confirmer la meilleure résistance à l’impact des composites à matrice Elium acrylique, comparativement à celles des composites thermodurcissables conventionnels. Ensuite, les performances à l’impact des composites stratifiés ont été améliorées par l’introduction de copolymères à blocs dans la matrice. Ces derniers sont capables de former des micelles de tailles nanométriques et ainsi d’améliorer la ténacité de la matrice acrylique. Les effets de l’énergie d’impact, de la température et de la composition en nanocharges sur la réponse du matériau composite ont été analysés. Afin de proposer un outil d’aide à la prédiction de la réponse à l’impact des matériaux fibres de verre/Acrylique, deux stratégies de modélisation ont été retenues. La première modélisation (macroscopique) considère le pli tissé du stratifié comme un matériau homogène tandis que la seconde (mésoscopique) utilise une description géométrique de l’ondulation et de l’entrecroisement des torons noyés dans la résine Elium. Ces deux modèles considèrent des zones cohésives à l’interface entre les plis adjacents pour simuler le délaminage interlaminaire. Des essais de délaminage (expérimentaux et numériques) ont permis d’alimenter le modèle d’endommagement de l’interface interplis. D’autre part, des essais de caractérisation du comportement mécanique et de l’endommagement du matériau couplés à l’homogénéisation multi-échelle des matériaux par la Mécanique du Génome de Structure ont permis d’identifier les paramètres du modèle macroscopique. A l’échelle mésoscopique, le modèle géométrique a été réalisé grâce au logiciel Texgen. Ce logiciel permet d’obtenir une description approchée mais réaliste de l’ondulation des torons de fibres. La même description a servi à l’homogénéisation numérique multi-échelle des stratifiés étudiés. La simulation numérique de l’impact basse vitesse a été effectuée au moyen du logiciel d’éléments finis ABAQUS/Explicit. Les modèles de comportement du matériau ont été implémentés via la routine utilisateur VUMAT. Les résultats obtenus offrent une bonne corrélation avec les données expérimentales
In the race for light materials able of meeting modern environmental challenges, an acrylic resin (Elium) has been developed. Elium is a thermoplastic resin able to replace thermosetting matrices, which are widespread nowadays in the industrial world. The present study aims to evaluate the impact resistance and to understand the failure mechanisms of composite laminates based on acrylic matrix under impact loading. We provide a contribution to the multiscale analysis of the impact resistance of laminated composite.First, the impact resistance and the damage tolerance of the acrylic resin based composites were compared with those of conventional composites. Then, the impact performance of the laminated composites has been enhanced by adding copolymer blocks to the liquid acrylic resin. These copolymers are able to form micelles of nanometer sizes, which lead to the improvement of both the acrylic matrix fracture toughness and the impact resistance. The effects of the impact energy, temperature, and composition in nano-copolymers have also been investigated.In order to provide a numerical tool for the prediction of the impact response of the glass fiber/Acrylic laminates, two strategies have been analyzed. The first one, performed at the macroscopic scale, considers the woven ply of the laminate as homogeneous material, and the second one (at the mesoscopic scale), deals with a realistic geometrical description of the yarns undulation. Both models use cohesive zones at the interface between the adjacent plies, to simulate the delamination. For this purpose, experimental and numerical delamination tests were performed to feed the inter-ply damage model. Mechanical tests for material characterization were also performed on specimens in order to identify the ply-damage model parameters. The Mechanics of Structure Genome (MSG) and a finite element based micromechanics approaches were then conducted to evaluate the effective thermomechanical properties of the yarns and the plain woven composite laminate. The realistic topological and morphological textures of the composite were accounted through Texgen software. These numerical impact simulations were performed using the finite element software ABAQUS/Explicit. Both models were implemented through a user material subroutine VUMAT. The obtained results appear in a good agreement with the experimental data and confirm the relevance of the proposed approach

Une formulation de la densite electronique en fonction de l'altitude et de l'angle solaire est etablie pour la basse ionosphere, cette formulation est basee sur la resolution des equations differentielles relatives aux densites des charges caracteristiques du milieu ionise traite. La relation entre les problemes aeronomiques et les problemes de propagation des ondes electromagnetiques est etudiee en reliant la vitesse de phase des ondes tbf a certains parametres representatifs de l'atmosphere moyenne. Cette relation est ensuite utilisee pour evaluer les variations de l'altitude de reflexion des ondes tbf ainsi que pour la determination de la temperature dans la mesosphere

La sensibilité des méthodes acoustiques non-linéaires à la présence ainsi qu'à l'évolution des microendommagements a été prouvée dans différents travaux sur une large gamme de matériaux. Parmi les méthodes appliquées figure la résonance non-linéaire dont la sensibilité à l'endommagement est prouvée pour un seul mode de vibration à travers la décroissance de la fréquence de résonance ƒ et celle facteur de qualité Q en fonction de la déformation dynamique. Ainsi, les paramètres non-linéaires hystérétiques (NLH) ƒ et Q ne sont connus que dans une gamme fréquentielle réduite. Le présent travail de thèse propose l'utilisation d'une approche originale permettant de suivre la dispersion des paramètres ƒ et Q à travers la génération d'ondes guidées dans des plaques en composites à matrices polymère et métallique. De plus, l'approche en ondes guidées a également permis de définir un nouveau paramètre NLH V liée au mode de Lamb A0. L'un des résultats originaux de ce travail est que le rapport V/ƒ s'avère constant (~ 2) quelle que soit la fréquence considérée et ce pour les deux types de composites. Ce résultat prometteur montre pour la première fois qu'il est possible de généraliser le comportement NLH dans les structures en plaques moyennant le formalisme de Lamb. Finalement, le travail de thèse s'est également intéressé à la définition d'un nouveau paramètre NLH large bande, noté ∆S, afin de suivre la sensibilité du spectre de vibration à l'endommagement. Les mesures ont montré que ∆S pouvait se distinguer de par une réponse pouvant être nonlinéaire dès les premiers niveaux d'excitation ou à partir d'un niveau seuil. Ce résultat très prometteur montre à quel point il est important d'élargir le domaine fréquentiel pour une détection précoce de l'endommagement et ce même à des niveaux d'excitation où l'on croyait le matériau se comporter de façon linéaire.

Interpretation de l'abaissement de la pression de fusion lorsque la fusion est plus rapide que le temps de relaxation de la polarisation de **(3)he d'apres l'etude theorique de la morphologie de l'interface liquide-solide lors de la fusion de **(3)he solide polarise. Tendance au metamagnetisme de **(3)he liquide pour une polarisation de equiv. A 20 %, a 0,1 k, et absence d'anomalie dans la vitesse du son mesuree a ce taux de polarisation. Possibilite de refroidir le liquide polarise au-dessus de 0,1 k en un temps tres court compare a celui de la relaxation de polarisation. Etude experimentale des proprietes magnetoelastiques de composes a deux fermions lourds et analyse phenomenologique pour prevoir la magnetostriction, la vitesse du son sous champ magnetique de ces composes pesentant une forte tendance au metamagnetisme, et, aux frequences grandes comparees au taux de relaxation de la polarisation, la vitesse du son

碩士
國立臺灣大學
海洋研究所
98
Marine geophysical and geological/geochemical investigations in the area offshore of southwest Taiwan supported by the Central Geological Survey, MOEA, suggest the existence of a large amount of gas hydrate in that region. Because the formation of gas hydrate is controlled by temperature and pressure, gas hydrate is present only in the gas hydrate stability zone. Due to the differences of acoustic impedances of the sedimentary strata containing gas hydrate and with free gases across the base of gas hydrate stability zone (BGHS), the interface often shows a strong reflector on seismic profiles. This strong reflector is called bottom-simulating-reflector (BSR). The depth of BSR should coincide with the depth of BGHS, but earlier studies of BGHS depths derived from thermal probe data are often different from the BSR depths on seismic profile. Possible reasons include： (1) Inaccurate seismic velocities caused wrong BSR depth estimation; (2) thermal probe can measure only shallow thermal structure, if the thermal gradient calculated is not correct, the BGHS estimation could be wrong . To reduce the problem of limited heat flow measuring depths, this study uses P wave velocity to derive the change of porosity in sediments. Then, we used the estimated porosity value to calculate the change of thermal conductivities. To test this method, we first use an empirical velocity-depth relation to calculate the BGHS depth at 80 heat flow sites offshore southwest Taiwan. The results show abnormal BGHS depth at some sites. These sites are either with high sedimentation rates or covered by thick sediments, give lower in-situ heat flows than the BSR-based heat flows. At other sites, the BGHS depths are in general consistent with BSR depths. The result suggest that adding velocity information to the computation will improve the accuracy of the BGHS depth value . To study the effect of seafloor environments, this study uses gas hydrate phase boundary curve to get the temperature at the BSR, and the divided thermal conductivity value to calculate the heat flow at BSR depth. Comparing with the heat flow measured by heat probe, we can divide the study area into three zones based on their different surface environment：(1) Low heat anomaly zone：heat flow is hindered by soft sediment in lower/middle canyon、basin and accretionary wedge, so the heat flow value measured by the apparatus is lower than that at BSR depth (2) High heat anomaly zone：in area where submarine erosion is occurring, such as the upper canyon zone, higher measured heat flow value are obtained (3) No heat anomaly zone：between canyons, deposition and erosion processes on the seafloor is lower than either Low heat anomaly zone or High heat anomaly zone, so the heat flow measured by the apparatus coincide with BSR depth. Furthermore, this study uses the large-offset seismic data collected during the TAIGER survey at heat flow sites or near sites to derive the local P-wave velocities of the strata. The result shows that more accurate velocity can further decrease the discrepancy between the BSR depth and BGHS depth. We thus suggest that accurate velocity of the sediment strata is important in calculating acc BGHS depth and BSR depth.

碩士
國立體育大學
教練研究所
95
The purpose of this study was to investigate the effect of 20 days vibration training and jump rope training on baseball players’ lower limbs’ power (CMJ), take-off reaction time, base-running velocity from home to first after batting and 5m base-running velocity after batting of baseball players. Twenty-six adult baseball players (excellent university and substitute service of professional baseball teams) were involved in this study with the average age and height weight were 2.3±2.46yr、174.6±4.51cm、and 79.23±7kg, respectively. Pretest (T-1) included 4 tests. The CMJ and take-off reaction time was basic test of sport capacity, base-running velocity from home to first after batting and 5m base-running velocity after batting were specific test of sport capacity. Subjects was divided to group A (vibration training) and group B (jump rope training by CMJ performance in matched-pair designed ( each group have 13 people). Group A and B started 20 days training, there were 4 times training in 10 day and separated at least 1 day. Group A were stimulated by vibration frequency at 40Hz, and amplitude at 2mm, in 2 movements of vibration training and proceeded 5 sets, each set performed 60s, and set rested 40s. Group B proceed 2 sets × 5 times × 10s of jump rope training by personal best performance, set rest interval was 2 min, and each time rest 30s. Middle-test (T-2) was proceeded in 10 days and posttest (T-3) was proceeded after training. Results showed that CMJ of Group A and B had significant improvement after 20 days training (p<0.001、p<0.01), but there was no difference between groups. Reaction time of Group A and B were significant improvement (p<0.001), but there was no difference between groups. Base-running velocity from home to first after batting of group A and B were significant improvement (p<0.001) and group A was significant higher than group B to 0.32 m/s (p<0.05); 5m base-running velocity after batting of group A was significant improvement (p<0.01), but group B was not significant improvement and group A was significant higher Group B in 0.34 m/s (p<0.05). Conclusions of the study were vibration and jump rope training can improve CMJ, take-off reaction time, base-running velocity from home to first after batting, 5m base-running velocity after batting, but base-running velocity from home to first after batting and 5m base-running velocity after batting were significant different between groups.

碩士
國立中山大學
企業管理學系研究所
89
Based on the theories, such as the resources-based theory, new product development and Strategic alliances, we proposed the equity-building process of new ventures of Internet industry. We note that new ventures’ purpose of capital raising actions before going public is not simply to raising fund, those actions represents that organizations attempt to obtain rare resources, building core competence, through equity invested or conjoined. In other word, equity portion to the new venture can become a means not necessarily an end. Through several Internet new ventures’ interview, we discussed factors that affect the equity-building process, such as original core resources and primary exchanging resources. Four propositions have developed. First, original core resources of new ventures would affect equity-building process, especially on target selecting, conjoining timing, and interaction. Second, on the affection of single equity relation’s occurs, primary exchanging resource didn’t evidently a decisive factor, for, it’s hardly to tell it apart from original core resources. Third is our basic notion, we hold that equity-building process before IPO becomes a portion of growing strategy of emerging organization. Fourth, based on the observation of these selected cases, we conclude that characteristics of core resources of new ventures would affect their manners of acquiring resources, especially needed for organization growth. Due to the limitations of organization condition and capital market, new ventures’ equity-building process of Internet industry could not apply the financial views of analysis. For this reason, we proposed new analysis manner, tried to indicate that how to select and equity portion, and how to build-up competitive advantage during infant stage.

碩士
東南科技大學
電機工程研究所
102
The phenomenon of pulse beat is generated when heart press blood to vascular. Through the pulse beating can understand the function of the heart and blood vessels elastic. Typical pulse wave is mainly composed of P-wave and R-wave, its waveform is a regular oscillatory behavior. However, the actual pulse wave appears irregular oscillation due to abnormal of the physiological.This paper attempts to summarize the relationship between physiologic abnormalities and the pulse wave oscillation. In order to find another way to determine the physiological abnormalities, we construct pulse wave velocity, resonant bandwidth and three dimension phase plane to determine abnormal occurrence. This research also propose a new type of Chinese pulse diagnosis acquisition system, we use conductive polymer as a material made of sensors, because it has a soft, plastic characteristics can be made of non-rigid pulse diagnosis instrument.Finally,We use self-developed human-machine interface to perform pulse diagnosis signal capture and analysis.

abstract: A modeling platform for predicting total ionizing dose (TID) and dose rate response of commercial commercial-off-the-shelf (COTS) linear bipolar circuits and technologies is introduced. Tasks associated with the modeling platform involve the development of model to predict the excess current response in a bipolar transistor given inputs of interface (NIT) and oxide defects (NOT) which are caused by ionizing radiation exposure. Existing models that attempt to predict this excess base current response are derived and discussed in detail. An improved model is proposed which modifies the existing model and incorporates the impact of charged interface trap defects on radiation-induced excess base current. The improved accuracy of the new model in predicting excess base current response in lateral PNP (LPNP) is then verified with Technology Computer Aided Design (TCAD) simulations. Finally, experimental data and compared with the improved and existing model calculations.
Dissertation/Thesis
Masters Thesis Electrical Engineering 2017

Dissertação de mestrado integrado em Engenharia Civil
O principal objetivo do presente trabalho é a utilização de técnicas de Data Mining (DM) na previsão das propriedades mecânicas dos granitos. Este objetivo pretende responder às dificuldades encontradas na caraterização mecânica direta dos granitos presentes em edifícios antigos, nomeadamente devido à impossibilidade de extração de provetes para posterior análise laboratorial. Foi executada uma campanha experimental que abrangeu duas técnicas não destrutivas designadamente: (1) medição da velocidade de propagação de ultrassons (V PU) e (2) Martelo de Schmidt (MS). Estas duas técnicas foram aplicadas em diferentes tipos de granito com condições superficiais próximas das dos granitos encontrados em construções de pedra; (1) granito de um edifício de habitação e (2) blocos de diferentes tipos de granito retirados diretamente de pedreiras sem tratamento superficial. Posteriormente, estes blocos foram retificados para obtenção de superfícies lisas de modo que fosse possível comparar os resultados dos ensaios não destrutivos (END) em diferentes tipos de superfície. Desta campanha foi verificada com sucesso a eficácia da técnica de ultrassons na deteção da anisotropia dos granitos, ao contrário do MS, que se revelou ineficaz na mesma tarefa. Adicionalmente, verificou-se a eficácia de ambas as técnicas na avaliação do estado de desgaste dos granitos. Provetes cilíndricos extraídos dos granitos estudados sob a forma de blocos foram submetidos a ensaios laboratoriais com vista à obtenção das propriedades físicas, mecânicas e índices não destrutivos (IND). Entre as diferentes propriedades mencionadas foram analisadas as suas respetivas relações. Três bases de dados foram construídas com base em propriedades físicas e mecânicas obtidas num estudo anterior num conjunto diferenciado de granitos. Estas serviram como plataforma de aplicação de três técnicas de DM para a previsão de três propriedades mecânicas, nomeadamente a resistência à compressão (fc), resistência à tração (ft) e módulo de elasticidade (E). Globalmente, os modelos construídos apresentaram uma boa capacidade de previsão.
The main objective of the present work is the use of Data Mining (DM) techniques to predict the mechanical properties of granites. This objective intended to answering to the difficulties found on mechanical properties characterization of granites applied on ancient buildings, namely due the impossibility of extraction of samples for further laboratorial analysis. An experimental campaign was carried out using two non-destructive techniques (NDT), namely: (1) ultrasonic pulse velocity (UPV ) and (2) the Schmidt Hammer (SH). These two non-destructive techniques were applied in different types of granites with surface features close to the one found in granites applied in ancient constructions, namely in (1) granite blocks of an existing building and (2) blocks of distinct types of granites coming directly from different quarries without superficial treatment. Furthermore, the blocks were swan for obtaining plain surfaces in such way that a comparison of non-destructive techniques could be compared in different types of surfaces. In this campaign the good performance of the ultrassonic technique was found on the detection of anisotropy, contrarily to the SH technique, which was not efficient in detecting anisotripy. Additionally, a good performance was achieved in both techniques on the evaluation of the state of weathering and wearing of surfaces. Cylindrical samples extracted from the granite blocks were subjected to a laboratorial campaign which intended to obtain the physical and mechanical properties and also nondestructive indexes (NDI). The relation between the different properties mentioned above was analyzed. Three databases were built based on a previous mechanical characterization study of different types of granites. Using the information present in those databases three different DM techniques were applied aiming the prediction of three mechanical properties, namely the compressive strengh (fc), tensile strength (ft) and the elastic modulus (E). Globally, the models showed a good performance.

It has recently been recognized that abundant gas hydrates occur in localized zones of upwelling fluids, with concentrations much higher than in regional distributions associated with bottomsimulating reflectors (BSRs). We report a study of multi-channel seismic reflection data across such structures in the Ulleung Basin, East Sea backarc offshore Korea, an area with few BSRs. The structures are commonly up to several km across and a few hundred meters in depth extent, and are characterized by reduced reflectivity and bowed-up sediment reflectors on time-migrated sections. The seismic pull-up mainly results from higher velocities, although physical deformation due to folding and faulting is not ruled out. Some of the features extend upward close to the seafloor and others only partway through the gas hydrate stability zone. The base of gas hydrate stability zone (BGHSZ), calculated assuming a regional average constant heat flow of 110 mW/m2, is confirmed by the presence of gas inferred from reduced instantaneous frequencies and high instantaneous amplitudes, and from a decrease in seismic velocities. The vents are fed by upward migrating free gas or gas-rich fluids through near-vertical conduits probably due to regional, upward fluid flow caused by tectonic compression of the basin.

Splitter plates are passive flow control devices for reducing drag and suppressing vortex shedding from bluff bodies. Most studies of splitter plates involve the flow around an “infinite” circular cylinder, however, in the present study the flow around a surface-mounted finite-height circular cylinder, with a wake-mounted splitter plate, was studied experimentally in a low-speed wind tunnel using a force balance and single-component hot-wire anemometry. Four circular cylinders of aspect ratios AR = 9, 7, 5 and 3 were tested for a Reynolds number range of Re = 1.9×10^4 to 8.2×10^4. The splitter plates had lengths, relative to the cylinder diameter, of L/D = 1, 1.5, 2, 3, 5 and 7, thicknesses ranging from T/D = 0.10 and 0.15, and were the same height as the cylinder being tested. The cylinders were partially immersed in a flat-plate turbulent boundary layer, where the range of boundary layer thickness relative to the cylinder diameter was δ/D = 1.4 to 1.5. Measurements were made of the mean drag force coefficient, the Strouhal number at the mid-height position, and the Strouhal number and power spectra along the cylinder height. For all four finite circular cylinders, the splitter plates were effective at reducing the magnitude of the Strouhal number, and weakening or even suppressing vortex shedding, depending on the specific combination of AR and L/D. Compared to the case of an infinite circular cylinder, the splitter plate is less effective at reducing the mean drag force coefficient of a finite circular cylinder. The largest drag reduction was obtained for the cylinder of AR = 9 and splitter plates of L/D = 1 to 3, while negligible drag reduction occurred for the shorter cylinders.