Yes / This research work focuses on the wake flow region of a cylinder with a spoiler on a rough bed under steady flow conditions. The acoustic Doppler velocimetry was used for the measurement of three-dimensional velocity data for two Reynolds numbers in a fully developed turbulent flow around the cylinder with a spoiler. The mean flow velocities, second-order turbulence structures, and conditional statistics were investigated in the wake region of the spoilered cylinder. The flow was separated from the spoiler with the formation of two shear layers between free surface flow and recirculating flow. It is observed that the flow is reattaching to the bed at 11D irrespective of the Reynolds number. Downstream of the cylinder, the mean velocity distributions are asymmetric due to the wall–wake effect, and the point of inflection is observed for each velocity profile at z = 0.40ẟ. The turbulence intensities, Reynolds stresses, and TKE are highly enhanced in the wake region of the cylinder as compared to their respective upstream values for both runs. The turbulence intensities, Reynolds normal stresses, Reynolds shear stresses, and turbulent kinetic energy are attaining peaks at z = 0.4 ẟ for all the streamwise locations, and the peaks are found to be highest at x = 10D. The quadrant analysis results indicate that the sweeps are dominating bursting events in the inner and intermediate layers, while ejections are dominating in the outer layer of the wake region. As the hole size, H increases ejections stress fraction rises as compared to that of the sweeps in the wake region for z = 0.2–0.7 h.

The onset of fluid-elastic instability in cylinder arrays is usually thought to depend primarily on the mean flow velocity, the Scruton number and the natural frequency of the cylinders. Currently, there is considerable evidence from experimental measurements and computational fluid dynamic (CFD) simulations that the Reynolds number is also an important parameter. However, the available data are not sufficient to understand or quantify this effect. In this study we use a high resolution pseudo-spectral scheme to solve 2-D penalized Navier-Stokes equations in order to accurately model turbulent flow past cylinder array. To uncover the Reynolds number effect we perform simulations that vary Reynolds number independent of flow velocity at a fixed Scruton number, and then analyze the cylinder responses. The computational complexity of our algorithm is a function of Reynolds number. Therefore, we developed a high performance parallel code which allows us to simulate high Reynolds numbers at a reasonable computational cost. The simulations reveal that increasing Reynolds number has a strong de-stabilizing effect for staggered arrays. On the other hand, for the in-line array case Reynolds number still affects the instability threshold, but the effect is not monotonic with increasing Reynolds number. In addition, our findings suggest that geometry is also an important factor since at low Reynolds numbers critical flow velocity in the staggered array is considerably higher than the in-line case. This study helps to better predict how the onset of fluid-elastic instability depends on Reynolds number and reduces uncertainties in the experimental data which usually do not consider the effect of Reynolds number. / Thesis / Master of Science (MSc)

A generalized low order model (LOM) for the fluctuating lift coefficient caused by vortex shedding from a tandem cylinder pair is proposed to expand upon models from previous authors. This model could provide a reduced computational time method for collecting qualitative and quantitive data from a tandem shedding pair. A delay coupled system with sufficient bifurcation characteristics is developed to account for the different flow regimes (extended-body, reattachment, and co-shedding) which occur as cylinder spacing is varied. Coefficient and parameter fitting is performed to fit experimental data. Finally, results and physical interpretations of the interactions in the model are discussed. It was found that many aspects of the flow at varying L/D ratios could be modeled by the LOM, including vortex suppression in the forward cylinder at the critical spacing, and amplitude growth in the rear cylinder in the co-shedding regime.

No description available.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22416号 / 工博第4677号 / 新制||工||1730(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 八木 知己, 教授 清野 純史, 教授 高橋 良和 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Detta kandidatexamensarbete behandlar design och konstruktion av ett nytt avgassystem för en motorcykel. Utvecklingen grundar sig på resultat från en körning i bromsbänk av motorcykeln utrustad med original avgassystem, där det visar sig att det finns en påtaglig dipp i vridmoment mellan 4000 och 6500 rpm. Samt på resonemang kring avgassystemets geometri och dess inverkan på motorns egenskaper. Dessa resonemang grundar sig i sin tur på fysikaliska principer. Målet med projektet är att utveckla ett avgassystem som påverkar motorn på det sätt att vridet i motorns mellanregister ökar för att utradera den påvisade dippen i mellanregistret samtidigt som det fortfarande ska uppfylla de krav svensk lagstiftning ställer på motorcyklar angående ljudnivå. Resonemangen på vilka avgassystemet utformas behandlar cylinderspolning, lågtryckspulser, avgasernas hastighet, avgassystemskonfiguration och cylinderparning. Det beslutas att systemet ska utformas på så sätt att avståndet till kollektorer blir så långt som möjligt i tillgängligt utrymme, att avgassystemet ska vara av 4-2-1 konfiguration och att cylinder 4 och 1 respektive 2 och 3 ska paras ihop. Avgassystemet tillverkas med enbart handverktyg och består till största del av standarddelar. Efter konstruktion så testas det nya systemet med en körning i bromsbänk och en ljudmätning. Den resulterade grafen från körningen i bromsbänken visar att dippen i vridmoment mellan 4000 och 6500 varv utraderades samtidigt som momentet ökade lite genom hela registret. Maximala vridmoment ökade från 103,7 Nm (Newtonmeter) med original avgassystem till 106,6 Nm med det nya. Toppeffekten ökade från 115,7 hk (hästkrafter) till 122,5 hk. På grund av att tillgång till verkstad försvann i och med pandemiutbrottet våren 2020 så beslutades att inte tillverka någon ljuddämpare, istället inhandlades och monterades en standardiserad fullflödesljuddämpare. Ljudmätningar visar att målet med ljudnivån inte uppnåtts. För att vara lagligt så får den maximala ljudnivån vid 5200 rpm inte överstiga 93 dB (decibel). Det nya systemet uppmättes till 109,4 dB vid 5200 rpm och klarar därmed inte ljudnivåkravet. Projektet visar att det är möjligt att markant påverka motorkaraktären med ändringar i avgassystemets geometri och konfiguration. Detta projekt visar dock bara på vad summan av förändringarna åstadkommer och kan inte ge specifika svar på vilka ändringar som står för vilken del av resultatet. / This bachelor's thesis deals with the design and construction of a new exhaust system for a motorcycle. The development is based on the results on a dyno run of the motorcycle equipped with the original exhaust system as well on reasonings regarding the exhaust system geometry and its impact on engine characteristics. These reasonings, in turn, are based on physical principles. The dyno run with the original exhaust system showed a significant dip in torque between 4000 and 6500 rpm. The aim of the project is to develop an exhaust system that affects the engines performance in a way that results in the increase of the engines midrange torque in order to erase the detected dip in the midrange while still fulfilling the requirements Swedish legislation imposes on motorcycles regarding noise pollution. The reasoning on which the exhaust system is designed deals with cylinder scavenging, low pressure pulses, exhaust speed, exhaust system configuration and cylinder pairing. It is decided that the system shall be designed in such a way that the distance to collectors is as far as possible in the available space, that the exhaust system shall be of 4-2-1 configuration and that cylinders 4 and 1 and 2 and 3 shall be paired. The exhaust system is manufactured using hand tools only and consists mostly of standardized parts. After construction, the new system is validated with a dyno run and sound level measurements. The resulting graph from the dyno run of the motorcycle equipped with the new exhaust system shows that the dip in torque between 4000 and 6500 rpm was erased while the overall torque increased slightly throughout the register. Maximum torque increased from 103.7 Nm with the original exhaust to 106.6 Nm with the new. The peak power increased from 115.7 hp to 122.5 hp. Sound measurements indicate that the aim for the sound level has not been achieved. To be legal, the maximum noise level at 5200 rpm must not exceed 93 dB. The new system was measured at 109.4 dB at 5200 rpm and thus does not meet the sound level requirement. The project shows that it is possible to significantly influence the engine character with changes in the geometry and configuration of the exhaust system. However, this project only shows what the sum of the changes achieves and cannot provide specific answers as to which changes account for what part of the result.

<p>This dissertation describes an investigation into the free radical batch polymerization of methyl methacrylate to high conversion. The overall objective was to develop a kinetic model to accurately predict conversion and molecular weight distribution for the polymerization. The dissertation is divided into three self-contained parts.</p> <p>Part I describes the development and testing of the kinetic model. New gel permeation chromatograph (GPC) data interpretation methods (developed in Part I I), the free volume concept of diffusion theory, and newly obtained isothermal kinetic data, are combined with computer implemented optimization techniques, to show that classical kinetics apply to high conversions.</p> <p>Part II details the development of three new GPC interpretation techniques. The two most recent are evaluated in Part I.</p> <p>The third has been used by other workers. Other interpretation methods are also evaluated and discussed. Part I I I describes the development of a high shear concentric cylinder viscometer and its use with Newtonian standards. This is a prelude to future studies in polymer rheology and polymerization under shear conditions.</p> / Doctor of Philosophy (PhD)

<p>Amidst the increasing need to improve efficiency of fluid power systems for off-road vehicles, different architectures have been proposed in literature to reduce system throttling losses. Among the most cited ones, are architectures based on the use of common-pressure rails (CPR), which in some cases have been combined with multi-chamber cylinders to further reduce power losses. This kind of solution appears to be particularly attractive in systems with several actuators with many instances of overrunning loads, such as in earthmoving machines. In this scenario, a basic question arises concerning the maximum amount of energy that can be saved by adding extra pressure rails and/or cylinder chambers. Answering this question can be challenging given that many parameters such as cylinder areas, pressure levels and both actuator and supervisory level controls can affect the results for a given application. This work investigates energy savings potential of different architectures based on the previously mentioned concept. Based on the results of this investigation, a novel architecture combining multi-pressure rails and multi-chamber cylinders is proposed and investigated. The system is sized and simulated for the study case of an excavator. This work addresses controllers design, from the supervisory level power management control to the local cylinder actuation system. In addition, special care is taken in the area selection of the multi- chamber cylinder, with factors such as manufacturing cost and reliability being considered. The proposed design procedure allows the design of compact and efficient three-chamber cylinders on a wider range of applications. Results show the potential for power consumption reduction of up to 31% when compared to state-of-the-art machines available in the market. Additionally, the proposed cylinder design optimization allows a reduction of up to 25% in cylinder weight when compared to other design methods for multi-chamber cylinders. Within this scope, an experimental setup is designed for proof of concept of the proposed hydraulic circuit and cylinder control methods, with laboratory tests validating the feasibility of the proposed system. Test results demonstrated the ability of the proposed controller in efficiently controlling pressures within the actuator, while delivering stable speed tracking performance. Experiments also demonstrated the system capability in recovering energy and validated the expectation of obtaining hydraulic actuation with low pressure drop across control valves.</p>

The instability mechanism of the shear-thinning and shear-thickening fluids pasta circular cylinder is studied using linear theory. The shear-dependent viscosityis modeled by the Carreau-law where the rheological parameters, the power-index and the material time constant are chosen in the range 0.4 &lt; n &lt; 1.75 and0.1 &lt; λ &lt; 100. A second order finite-difference code is used for the simulationof cylinder flow in which the Immersed Boundary Technique is implemented torepresent the cylinder surface on a Cartesian mesh. The critical Reynolds num-ber for the onset of instability is reported for a range of rheological parameters.Structural sensitivity analysis based on the idea of ”wavemaker” is performedto identify the core of the instability. Perturbation kinetic energy budget is alsoconsidered to examine the physical mechanism of the instability. The charac-teristics of base-flow: drag coefficient, size of recirculation bubble and viscositydistribution are presented to provide useful knowledge about shear-thinning ef-fect in flow past a cylinder.