Dissertations / Theses on the topic 'Stretch speed'

This thesis investigates the laminar flame speed of C₁-C₃ alkanes and their binary mixtures at conditions of interest in natural gas based gas turbines viz. high temperature, pressure and dilution. Laminar flame speed has been found useful not only for validating chemical kinetics mechanisms but also for developing empirical scaling laws for practical combustion systems. The thesis addresses the lack of laminar flame speed data of C₁-C₃ alkanes at preheat (300-650 K), pressure (1-10 atm) and significant oxidizer dilution (15-21 vol% O₂). Over 400 measurements are reported over a wide range of conditions along with comparison to predictions from leading chemical mechanisms. Unstretched flame speed measurements were performed using a modified Bunsen flame technique based on reaction zone area from chemiluminescence imaging, whereas the strain sensitivity measurements were performed using a bluff-body stabilized stagnation flame with high resolution PIV. These measurements are used to: (i) discern the uncertainties associated with the measurements, (ii) understand the effect of fuel mixture and vitiation on flame speed, and (iii) validate the performance of the leading chemical kinetics mechanisms. Extensive testing shows the unstretched flame speed measurements from the modified Bunsen technique are reasonably accurate. Vitiation studies for methane and propane flames at high preheat show the reduction in flame speed results primarily from the thermal effect of the diluent and that the relative change in flame speed from the undiluted mixture is well correlated to the fractional change in the adiabatic flame temperature over a range of conditions. Significant difference in the measured and predicted flame speeds were observed for rich, atmospheric pressure, propane and lean, high pressure, methane/ethane mixtures with dilution. This highlights possible avenues for improvements in the chemical kinetics mechanisms. Systematic errors were also identified in the Bunsen flame measurements at certain conditions, such as for rich flames with dilution, indicating a need for better understanding of the Bunsen flame technique at these conditions. The difference in the measured and predicted flame speed does not show any clear correlation with the flame height or the strain sensitivity of the mixture. Finally previously proposed mixing rules for estimating flame speed of fuel mixtures from pure fuel components are shown to be reasonably accurate over a range of pressure, reactant temperature and dilution conditions.

This study examined the short-term training effects of two volumes of a dynamic warm up performed 4 days per week over a 3 1/2-week period. A total of 25 Division III wrestlers volunteered for the study. Three participants either dropped out or were unable to attend post-testing, resulting in 22 total participants completing the study. Groups were divided into control, low volume, and high volume groups. All participants completed pre and poststudy performance tests including the standing long jump, proagility, start-stop-cut, and 30- meter sprint. The low and high volume training groups each performed the same dynamic warm up prior to each pre-season captain's practice. The control group did not participate in an organized warm up. The low volume group performed one set of each warm up exercise, and the high volume group performing two sets of each warm up exercise. Data analysis indicated significant increases in performance for the standing long jump (p = .011) and start-stop-cut (p = .000) measures among the entire sample population. However, there was no significant difference between the groups in these measures. No significant results were found either for the sample as a whole or between groups for the proagility and 30-meter measures. The increased performance of all groups, including the control group, fails to provide evidence for the effectiveness of training with either warm up volume. Further research is needed to address limitations of this study to determine effectiveness of various warm up volumes.

The laminar burning velocity is an important fundamental property of a fuel-air mixture at given conditions of temperature and pressure. Knowledge of burning velocities is required as an input for combustion models, including engine simulations, and the validation of chemical kinetic mechanisms. It is also important to understand the effect of stretch upon laminar flames, to correct for stretch and determine true (unstretched) laminar burning velocities, but also for modelling combustion where stretch rates are high, such as turbulent combustion models. A constant volume combustion vessel has been used in this work to determine burning velocities using two methods: a) flame speed measurements during the constant pressure period, and b) analysis of the pressure rise data. Consistency between these two techniques has been demonstrated for the first time. Flame front imaging and linear extrapolation of flame speed has been used to determine unstretched flame speeds at constant pressure and burned gas Markstein lengths. Measurement of the pressure rise during constant volume combustion has been used along with a numerical multi-zone combustion model to determine burning velocities for elevated temperatures and pressures as the unburned gas ahead of the spherically expanding flame front is compressed isentropically. This burning velocity data is correlated using a 14 term correlation to account for the effects of equivalence ratio, temperature, pressure and fraction of diluents. This correlation has been modified from an existing 12 term correlation to more accurately represent the dependence of burning velocity upon temperature and pressure. A number of fuels have been tested in the combustion vessel. Biogas (mixtures of CH₄ and CO₂) has been tested for a range of equivalence ratios (0.7–1.4), with initial temperatures of 298, 380 and 450 K, initial pressures of 1, 2 and 4 bar and CO₂ fractions of up to 40% by mole. Hydrous ethanol has been tested at the same conditions (apart from 298 K due to the need to vaporise the ethanol), and for fractions of water up to 40% by volume. Binary, ternary and quaternary blends of toluene, n-heptane, ethanol and iso-octane (THEO) have been tested for stoichiometric mixtures only, at 380 and 450 K, and 1, 2 and 4 bar, to represent surrogate gasoline blended with ethanol. For all fuels, correlation coefficients have been obtained to represent the burning velocities over wide ranging conditions. Common trends are seen, such as the reduction in burning velocity with pressure and increase with temperature. In the case of biogas, increasing CO₂ results in a decrease in burning velocity, a shift in peak burning velocity towards stoichiometric, a decrease in burned gas Markstein length and a delayed onset of cellularity. For hydrous ethanol the reduction in burning velocity as H₂O content is increased is more noticeably non-linear, and whilst the onset of cellularity is delayed, the effect on Markstein length is minor. Chemical kinetic simulations are performed to replicate the conditions for biogas mixtures using the GRI 3.0 mechanism and the FlameMaster package. For hydrous ethanol, simulations were performed by Carsten Olm at Eötvös Loránd University, using the OpenSMOKE 1D premixed flame solver. In both cases, good agreement with experimental results is seen. Tests have also been performed using a single cylinder optical engine to compare the results of the hydrous ethanol tests with early burn combustion, and a good comparison is seen. Results from tests on THEO fuels are compared with mixing rules developed in the literature to enable burning velocities of blends to be determined from knowledge of that of the pure components alone. A variety of rules are compared, and it is found that in most cases, the best approximation is found by using the rule in which the burning velocity of the blend is represented by weighting by the energy fraction of the individual components.

Increasingly stringent pollution and emission controls have caused a rise in the use of combustors operating under lean, premixed conditions. Operating lean (excess air) lowers the level of nitrous oxides (NOx) emitted to the environment. In addition, concerns over climate change due to increased carbon dioxide (CO2) emissions and the need for energy independence in the United States have spurred interest in developing combustors capable of operating with a wide range of fuel compositions. One method to decrease the carbon footprint of modern combustors is the use of high hydrogen content (HHC) fuels. The objective of this research is to develop tools to better understand the physics of turbulent flame propagation in highly stretch sensitive premixed flames in order to predict their behavior at conditions realistic to the environment of gas turbine combustors. This thesis presents the results of an experimental study into the flame propagation characteristics of highly stretch-sensitive, turbulent premixed flames generated in a low swirl burner (LSB). This study uses a scaling law, developed in an earlier thesis from leading point concepts for turbulent premixed flames, to collapse turbulent flame speed data over a wide range of conditions. The flow and flame structure are characterized using high speed particle image velocimetry (PIV) over a wide range of fuel compositions, mean flow velocities, and turbulence levels. The first part of this study looks at turbulent flame speeds for these mixtures and applies the previously developed leading points scaling model in order to test its validity in an alternate geometry. The model was found to collapse the turbulent flame speed data over a wide range of fuel compositions and turbulence levels, giving merit to the leading points model as a method that can produce meaningful results with different geometries and turbulent flame speed definitions. The second part of this thesis examines flame front topologies and stretch statistics of these highly stretch sensitive, turbulent premixed flames. Instantaneous flame front locations and local flow velocities are used to calculate flame curvatures and tangential strain rates. Statistics of these two quantities are calculated both over the entire flame surface and also conditioned at the leading points of the flames. Results presented do not support the arguments made in the development of the leading points model. Only minor effects of fuel composition are noted on curvature statistics, which are mostly dominated by the turbulence. There is a stronger sensitivity for tangential strain rate statistics, however, time-averaged values are still well below the values hypothesized from the leading points model. The results of this study emphasize the importance of local flame topology measurements towards the development of predictive models of the turbulent flame speed.

The thesis discusses the roads in lanes 2 + 1 arrangement in the country and abroad. It focuses primarily analogy of this type of arrangement in our situation, ie on stretches of roads I. classes with an increased number of lanes for slow vehicles to climb. Part of this work is to verify some of the traffic, including traffic flow characteristics compared to conventional two-lane roads, especially in terms of: sectional speed; overtaking; Accident and dependence longitudinal gradient. The work aims to evaluate the foreign experience and achievements of domestic communications options for application configuration 2 + 1 in the Czech Republic.

The goal of this project is to obtain quantitative images of the lens and the ciliary body to validate EVAS-II (Second generation Ex Vivo Accommodation Simulator). To accomplish this goal it was necessary to develop methods, instrumentation and image processing techniques to acquire 3D images in EVAS-II, using UBM (Ultrasound Bio Microscope), and to apply these techniques to non-human primate eyes. The lens studies included measurement of speed of sound in the lens to reconstruct accurate images of the lens, development of instrumentation to measure the un-distorted lens shape and development of a mathematical model to quantify the whole lens shape. Speed measurements showed that the speed of sound exhibits a gradient profile in the equatorial plane, similar to refractive index and protein distributions in the lens. Lens shape measurements showed that the UBM can be used to accurately measure thickness, diameter, cross-sectional area, volume and surface area of the lens. The ciliary body studies included development of instrumentation and algorithms to obtain 3-D images of tissue in EVAS-II and development of methodology to quantify ciliary body movement during stretching. Studies showed that the accommodation process in young baboon eyes in EVAS-II is comparable to the in vivo process in rhesus monkeys. The UBM can be used to obtain reliable quantitative information about the lens and the ciliary body. 3-D UBM enables monitoring of ciliary body motion of the entire accommodative apparatus.

Made available in DSpace on 2014-06-11T19:31:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-09-25Bitstream added on 2014-06-13T20:21:42Z : No. of bitstreams: 1 camara_ft_dr_jabo.pdf: 548163 bytes, checksum: a7f77b0a81b4b0e6e9ac1c242bc53422 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Funep
Biodiesel is a renewable fuel, biodegradable and produced from vegetable oil or from animal fat through transesterification. The viability of this product as a source of alternative energy depends on various factors, among which the mixture proportion and the stability during storage time stand out. This is because the availability of the raw material is seasonal and varies in accordance with the harvests of different cultures. The objective of the present work was to evaluate the operational performance of an agricultural tractor working with palm oil biodiesel while performing the operation of tillage with a chisel plow, also opacity, the density of the fuel and the outflow from the filling pump were studied regarding storage time and biodiesel/diesel mixture proportion. The experiment was conducted in the Department of Rural Engineering at UNESP, Jaboticabal, Brazil, in partnership with LADETEL/USP-Ribeirão Preto. Storage time was with new fuel (soon after production), three months and six months, and the percentage proportions used for biodiesel + diesel were B0 (0+100), B5 (5+95), B50 (50+50) e B100 (100+0). When comparing the treatments, we evaluated the fuel consumption, the real velocity of displacement, the sliding of the wheels, the strength of the traction bar, the fuel density, the outflow from the filling pump and the opacity of the fuel smoke. The results show an increase in consumption specific to a mixture starting from 25% biodiesel, although the storage time did not affect consumption. In relation to the opacity of smoke, there was a reduction, even with only 5% biodiesel in the mixture, again with the storage time having no influence.

Orientador: Afonso Lopes
Banca: Wilson José Oliveira de Souza
Banca: Carlos Alberto Alves de Oliveira
Banca: Newton La Scala Junior
Banca: Carlos Eduardo Angeli Furlani
Resumo:Biodiesel é um combustível renovável, biodegradável e produzido a partir de óleo vegetal ou de gordura animal por meio de transesterificação. A viabilidade desse produto como fonte alternativa de energia depende de vários fatores, entre os quais se destacam a proporção de mistura e a estabilidade durante o período de armazenamento, uma vez que a disponibilidade de matéria-prima é sazonal e varia de acordo com a safra de cada cultura. O presente trabalho teve como objetivo avaliar o desempenho operacional realizando a operação de preparo do solo com escarificador e a opacidade da fumaça de um trator agrícola funcionando com biodiesel de dendê, a densidade do combustível e a vazão da bomba de abastecimento, cujos fatores estudados foram o tempo de armazenamento e a proporção de mistura biodiesel/diesel. O experimento foi conduzido no Departamento de Engenharia Rural, da UNESPJaboticabal, em parceria com o LADETEL/USP-Ribeirão Preto. O tempo de armazenamento foi combustível novo (logo após ser produzido), três e seis meses, e as proporções percentuais de biodiesel + diesel foram B0 (0+100), B5 (5+95), B50 (50+50) e B100 (100+0). Para comparar os tratamentos, foram avaliados o consumo de combustível, a força de tração na barra, a velocidade real de deslocamento, a patinagem das rodas, a potência na barra de tração, a densidade do combustível, a vazão da bomba de abastecimento e a opacidade da fumaça de combustão. Os resultados evidenciaram aumento no consumo específico a partir da mistura com 25% de biodiesel, entretanto o tempo de armazenamento não influenciou no consumo. Com relação a opacidade da fumaça, houve redução, mesmo com apenas 5% de biodiesel na mistura, com o tempo de armazenamento não influenciando.
Abstract: Biodiesel is a renewable fuel, biodegradable and produced from vegetable oil or from animal fat through transesterification. The viability of this product as a source of alternative energy depends on various factors, among which the mixture proportion and the stability during storage time stand out. This is because the availability of the raw material is seasonal and varies in accordance with the harvests of different cultures. The objective of the present work was to evaluate the operational performance of an agricultural tractor working with palm oil biodiesel while performing the operation of tillage with a chisel plow, also opacity, the density of the fuel and the outflow from the filling pump were studied regarding storage time and biodiesel/diesel mixture proportion. The experiment was conducted in the Department of Rural Engineering at UNESP, Jaboticabal, Brazil, in partnership with LADETEL/USP-Ribeirão Preto. Storage time was with new fuel (soon after production), three months and six months, and the percentage proportions used for biodiesel + diesel were B0 (0+100), B5 (5+95), B50 (50+50) e B100 (100+0). When comparing the treatments, we evaluated the fuel consumption, the real velocity of displacement, the sliding of the wheels, the strength of the traction bar, the fuel density, the outflow from the filling pump and the opacity of the fuel smoke. The results show an increase in consumption specific to a mixture starting from 25% biodiesel, although the storage time did not affect consumption. In relation to the opacity of smoke, there was a reduction, even with only 5% biodiesel in the mixture, again with the storage time having no influence.
Doutor

For a wounded soldier to have as good a chance of survival as possible, an important variable during care is the time it takes for the wounded to get to a high-quality medical facility where there is expertise in surgery. If the injured person is to be transported with a stretcher carried by other soldiers, the speed for which this can be done is limited by the strength of the bearer in the hands and forearms.This study aims to explore how the speed and perceived ergonomics of those who carry a stretcher can change for a group if it is issued a relieving carrying system that redistributes the load of the stretcher to the hips, back and legs. The study is largely based on a study by Knapik et al (2000) where similar tests were done in a controlled indoor environment but where this study was done in a field environment with groups of 2 or 4 people carrying a stretcher.The study is done in the form of tests and experiments with conscripts from Skaraborg Wing, F 7. The conscripts carried a stretcher in a field-like environment where speed, comfort and usability were in focus. The study was also done with a questionnaire belonging to the experiments to value the experience.The study resulted in a relieving carrying system integrated in the Swedish Armed Forces' combat vest 2000 having an increased average speed with the median 30.7% when carrying a stretcher loaded with 100 kg. The analysis shows that it is above all women who benefit greatly from not carrying a stretcher with their hands. Something they are statistically worse at than men. The study also shows that there are tendencies that the comfort is improved for a soldier.
För att en sårad soldat ska ha så goda chanser till överlevnad som möjligt är en viktig variabel under omhändertagandet tiden det tar för den sårade att komma till en högkvalitativ sjukvårdsinrättning, där det finns expertis inom kirurgi. Om den skadade ska transporteras med sjukbår som bärs av andra soldater, är hastigheten för vilket detta kan göras begränsad av de bärandes styrka i händer och underarmar.Denna studie syftar till att utforska hur hastigheten samt den upplevda ergonomin för de som bär en sjukbår kan förändras för en grupp om den tillförs ett avlastande bärsystem som omfördelar lasten till höfter, rygg och benen. Studien baseras till stor del på en studie av Knapik med flera (2000) där liknande tester gjordes i en kontrollerad inomhusmiljö, men där denna studie är gjord i en fältmiljö med grupper om 2 eller 4 personer som bär en sjukbår.Studien är gjord i form av prov och försök med värnpliktiga ur Skaraborgs Flygflottilj, F 7, som bär en bår i en fältliknande miljö där hastigheten, komforten och användbarheten stod i fokus. Studien är även gjord med en enkätundersökning tillhörande försöken i syfte att skatta upplevelsen.Studien resulterade i att ett avlastande bärsystem integrerat i Försvarsmaktens stridsväst 2000 medförde en ökad snitthastighet, med medianen 30,7%, vid bärande av en sjukbår 2 lastad med 100 kg. Analysen påvisar att det framför allt är kvinnor som har stor nytta av att inte bära en sjukbår med händerna, något de statistiskt sett är sämre på än män. Studien visar även att det finns tendenser för att komforten förbättras för en soldat men användbarheten är oförändrad.

Comprendre et prédire les différents mécanismes en jeu dans les flammes prémélangées turbulentes est un enjeu crucial pour le dimensionnement ou l’optimisation de nombreux systèmes de combustion. Les écoulements réactifs turbulents se caractérisent par une interaction complexe entre les mouvements hydrodynamiques, le dégagement de chaleur produit par la flamme et la turbulence. Ce défi étant extrêmement difficile à relever, l’étude préalable des interactions entre une flamme plane et une structure tourbillonnaire fournit un cadre canonique idéal pour mieux appréhender et comprendre les mécanismes physiques à l’oeuvre. Dans cette perspective, des études expérimentales ont été réalisées utilisant un brûleur à jet impactant alimenté par un prémélange (méthane/air, propane/air, hydrogène/air). Un panel de techniques expérimentales ainsi que des outils numériques ont été utilisés pour caractériser finement les interactions entre une flamme de prémélange et un vortex toroïdal. En modifiant la richesse et la composition du mélange ainsi que l’intensité du vortex, le suivi temporel de l’interaction a permis d’extraire différentes informations telles que la dynamique de la surface de flamme, de l’étirement et de la courbure du front de flamme ainsi que les vitesses de déplacement/consommation. De surcroit, la structure interne du front de flamme a été étudiée en la décomposant en une zone de préchauffage et une zone de réaction
Understanding and predicting the different mechanisms at play in turbulent premixed flames is a tremendously difficult issue for sizing or optimizing many combustion systems. Turbulent reactive flows are characterized by a complex interaction between the fluid motion, the inherent heat generated by the flame and turbulence. This challenge being extremely difficult to meet, the study of the interactions between a flat flame and a toroidal vortex provide an ideal canonical framework to better understand the physical mechanisms at play. In this perspective, experimental studies were carried out using a stagnation burner fed by a premixed fuel and air (methane/air,propane/air, hydrogen/air). A panel of experimental techniques as well as numerical tools have been used to characterize thoroughly the flame/vortex interactions. By modifying the equivalence ratio, the mixture composition and the vortex intensity, the temporal evolution of the interaction enable the extraction of the flame surface, the flame front stretch and curvature as well as the displacement/consumption speeds. In addition, the internal flame structure is deeply investigated by decomposing the flame front into a preheat zone and a reaction zone

碩士
國立中央大學
機械工程研究所
92
This thesis investigates experimentally the effect of unsteady stretch on laminar premixed flames interacting with turbulent flows. Using a turbulent wake burner and a large cruciform burner, a von Kármán turbulent wake and near-isotropic turbulent flows can be generated, respectively. We applied high-speed particle image velocimetry (PIV) and the laser tomography to quantitatively measure the corresponding strain rate, curvature, stretch rate, and dilatation rate along the interacting flame front with turbulent wake and near-isotropic turbulence. Experiments in the turbulent wake burner were conducted to study the effect of radiative heat losses on stretching of premixed CH4 flames by using two diluting gases, CO2 (large radiative heat loss) and N2 (small radiative heat loss),respectively. Note that the laminar burning velocities for both CO2- and N2-diluted flames are kept constant with SL = 10 cm/s at a fixed equivalence ratio Φ = 0.7. Experimental results reveal that the maximum burning rate that may be indicated by the maximum dilatation rate occurs in regions of high positive curvature rates. This confirms that the reaction rate of Le＜1 flames is increased by the positive stretch, as already suggested by Law and many other researchers. The curvature team is more important than the strain rate term in the overall stretch consideration for the present lean CH4/air premixed flames with Le＜1, at least for the ratio of the mean tangential velocity of the staggered vortex pair of the wake to the laminar burning velocity, uθ/SL , up to 2. By comparing CO2- and N2-diluted flames, the wrinkled flame propagation speeds and the peak values of the dilatation rate are largely decreased by the increase of radiative heat loss. Experiments in the cruciform burner were conducted to investigate the effect of unsteady stretch for rich (Φ = 1.45) methane/air flames interacting with near-isotropic turbulence, where the root-mean-square turbulent intensity u'=32.3 cm/s and u'/SL = 2.2. The experimental data suggest that the reaction of rich CH4 flames (Le＞1) is strengthened by the negative strain rate, but the flame is burned more intensely near regions of the flame front whose curvature is positive. For the unsteady stretch of rich CH4 flames, the strain rate term plays a dominate role on the stretch rate in the beginning of the flame-turbulence interaction, but during the interaction the curvature term gradually becomes a dominate term.

碩士
崑山科技大學
機械工程研究所
101
Metal stretch net, featured by its diamond shape pores, is a product meeting the increasing ecological concerns. Metal stretch net is attracting more applications that require lightweight, good shielding, high transparency, and good ventilation. Stretch metal net is made from one piece of metal and exhibits high structure integrity. Due to the increasing awareness of energy consumption, lightweight design and energy saving in manufacturing become important research issues. Fine mesh metal net is especially gaining high acceptance, and in order to increase its applications, the processing speed has to be increased. The process of making stretch metal net consists of successive cutting and stretching. Process speed is limited by power, vibration, and positioning time for punch. High speed camera and time simulation will be used in this investigation.

碩士
國立成功大學
機械工程學系
88
Pendulum test is a common clinical technique for assessing spasticity on knee joints of stroke patients, but it has not been applied on elbow joints. The goal of this study is to design a simple instrument for performing pendulum tests on upper limbs. Based on biomechanical models of elbow, one can obtain the physiological parameters of the models by using a constrained optimization method (sequential quadratic programming) and the models are validated by using a sophisticated spasticity measurement system developed in previous researches. We hope that the simple pendulum test can assist neurologists to assess spasticity in stroke patients. Three biomechanical models are utilized in this study: (1) simple model: with removal of muscle stretch reflex mechanisms, only rotational stiffness and rotational damping coefficient of soft tissue of elbow joint are considered; (2) pure velocity-stretch-reflex model: by adding velocity-dependent stretch reflex component to the simple model; (3) additive model: by adding position-dependent stretch reflex component to the pure velocity- stretch-reflex model. The last one is a complete model from physiological point of view. Parameters of the models are estimated by using the sequential quadratic programming method. To explore global minimum solutions of the parameter estimation problem, genetic algorithm is employed and results are compared with those of sequential quadratic programming. 10 normal subjects and 10 stroke patients are recruited in this study. From results of parameter estimation, one may find that, in the simple model, intact side, affected side of stroke patients and normal group can be differentiated by using rotational damping ratios of the model. In the pure velocity-stretch-reflex model, the rotational damping coefficients of patients'' affected side are lower than values obtained in the simple model. It reveals that the contribution of velocity-dependent stretch reflex component is significant, however when attempting to separate the position-dependent and velocity-dependent components of spasticity, one gets multiple solutions from the optimization process. The problem of choosing an optimal solution remains open and parameters obtained by using the simple model might be valid for assessing spasticity. Statistical analyses show that, the rotational stiffness of both sides of patients is higher than that of normal group. For stroke patients, the rotational damping coefficient of affected side is slightly higher than that of intact side. In the pure velocity-stretch-reflex model, the velocity-dependent parameter of affected side is higher than that of intact side, but it shows no significant difference in the additive model. The contribution of position-dependent stretch reflex component is not significant and the dominant parameters are rotational damping coefficient and velocity-dependent parameter. In summary, based on our limited subjects and data, we can find that the complete biomechanical model might not be useful for assessments of spasticity due to the problem of multiple solutions. The rotational stiffness of both sides of patients is higher than that of normal group. This finding agrees with increased toughness of intact side found in clinical practice. The change of rotational damping coefficients of both elbows of stroke patients is not significant and the contribution of position-dependent stretch reflex to spasticity is not significant. One may conclude that spasticity is more dependent on stretch velocity, which agrees with physiological hypothesis on spasticity.

High-pressure experiments and chemical kinetics modeling were performed for laminar spherically expanding flames for methane/air, ethane/air, methane/ethane/air and propane/air mixtures at pressures between 1 and 10 atm and equivalence ratios ranging from 0.7 to 1.3. All experiments were performed in a new flame speed facility capable of withstanding initial pressures up to 15 atm. The facility consists of a cylindrical pressure vessel rated up to 2200 psi. Vacuums down to 30 mTorr were produced before each experiment, and mixtures were created using the partial pressure method. Ignition was obtained by an automotive coil and a constant current power supply capable of reducing the spark energy close to the minimum ignition energy. Optical cine-photography was provided via a Z-type schlieren set up and a high-speed camera (2000 fps). A full description of the facility is given including a pressure rating and a computational conjugate heat transfer analysis predicting temperature rises at the walls. Additionally, a detailed uncertainty analysis revealed total uncertainty in measured flame speed of approximately +-0.7 cm/s. This study includes first-ever measurements of methane/ethane flame speeds at elevated pressures as well as unique high pressure ethane flame speed measurements. Three chemical kinetic models were used and compared against measured flame velocities. GRI 3.0 performed remarkably well even for high-pressure ethane flames. The C5 mechanism performed acceptably at low pressure conditions and under-predicted the experimental data at elevated pressures. Measured Markstein lengths of atmospheric methane/air flames were compared against values found in the literature. In this study, Markstein lengths increased for methane/air flames from fuel lean to fuel rich. A reverse trend was observed for ethane/air mixtures with the Markstein length decreasing from fuel lean to fuel rich conditions. Flame cellularity was observed for mixtures at elevated pressures. For both methane and ethane, hydrodynamic instabilities dominated at stoichiometric conditions. Flame acceleration was clearly visible and used to determine the onset of cellular instabilities. The onset of flame acceleration for each high-pressure experiment was recorded.

碩士
淡江大學
電機工程學系
85
The low voltage IF (intermediate-frequency) limiting amplifier and received signal strenght indicator (RSSI) are widely used the FM modulation in communication systems. The main functions are amplification and limitation signal and measuring received signal strength. There are several IC's products realizing limiting amplifier and RSSI in bipolar technologies. Here we want to implement the low voltage IF limiting amplifier and received signal strength with CMOS technology. The differential amplifier and full wave rectifier circuit were adopted in this circuit. We have shown the results by the experiment. We provide three circuits of the high speed low voltage limiting amplifier, in order to improve the bandwidth. The first circuit is composed of the basic differential amplifier circuit, output stage, and voltage compensation circuit. In the second circuit, we utilize CSCG differential amplifier to improve the operation frequency. The relationship between, the frequency and the numbers of stages in limiting amplifier were discussed. Although the bandwidth of the high speed limiting amplifier is enough, the limiting amplifier just only amplifies the signal that system needed in actual usage. The actual usage of circuit will he improved, if the limiting amplifier needs the function of filter. We compare the performance of three circuits in the chapter 5 for limiting-filtering amplifier and try to implement them in a IC in the future. We have implemented four chips in this paper, each of them was implemented by TSMC 0.8um process, TSMC 0.6 process, UMC 0.8um process, and UMC 0.5 process. The chip of low voltage IF limiting amplifier and RSSI are in good working, others are partial working. The experiment results of the IF limiting amplifier are as follows: the smallest input signal is 15mv, total gain is 60dB, power dissipation is 3mw. The experiment results of RSSI are as follows: the range of the input signal is 15mv to 500mv, the power dissipation is 2mw and the total power dissipation of the chip is 5 mw.