Yes / The bed slope and the tailwater depth are two important ones among the factors that affect the propagation of the dam-break flood and Favre waves. Most previous studies have only focused on the macroscopic characteristics of the dam-break flows or Favre waves under the condition of horizontal bed, rather than the internal movement characteristics in sloped channel. The present study applies two numerical models, namely, large eddy simulation (LES) and shallow water equations (SWEs) models embedded in the CFD software package FLOW-3D to analyze the internal movement characteristics of the dam-break flows and Favre waves, such as water level, the velocity distribution, the fluid particles acceleration and the bed shear stress, under the different bed slopes and water depth ratios. The results under the conditions considered in this study show that there is a flow state transition in the flow evolution for the steep bed slope even in water depth ratio α = 0.1 (α is the ratio of the tailwater depth to the reservoir water depth). The flow state transition shows that the wavefront changes from a breaking state to undular. Such flow transition is not observed for the horizontal slope and mild bed slope. The existence of the Favre waves leads to a significant increase of the vertical velocity and the vertical acceleration. In this situation, the SWEs model has poor prediction. Analysis reveals that the variation of the maximum bed shear stress is affected by both the bed slope and tailwater depth. Under the same bed slope (e.g., S0 = 0.02), the maximum bed shear stress position develops downstream of the dam when α = 0.1, while it develops towards the end of the reservoir when α = 0.7. For the same water depth ratio (e.g., α = 0.7), the maximum bed shear stress position always locates within the reservoir at S0 = 0.02, while it appears in the downstream of the dam for S0 = 0 and 0.003 after the flow evolves for a while. The comparison between the numerical simulation and experimental measurements shows that the LES model can predict the internal movement characteristics with satisfactory accuracy. This study improves the understanding of the effect of both the bed slope and the tailwater depth on the internal movement characteristics of the dam-break flows and Favre waves, which also provides a valuable reference for determining the flood embankment height and designing the channel bed anti-scouring facility. / National Natural Science Foundation of China (Grant No: 51879179, 52079081), the Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1809) and the Sichuan Science and Technology Program (No. 2019JDTD0007)

Yes / The Prandtl second kind of secondary current occurs in any narrow channel flow causing velocity dip in the flow velocity distribution by introducing the anisotropic turbulence into the flow. Here, a study was conducted to explain the occurrence of the secondary current in the outer region of flow velocity distribution using a universal expression. Started from the basic Navier-Stokes equation, the velocity profile derivation was accomplished in a universal way for both smooth and rough open channel flows. However, the outcome of the derived theoretical equation shows that the smooth and rough bed flows give different boundary conditions due to the different formation of log law for smooth and rough bed cases in the inner region of velocity distribution. Detailed comparison with a wide range of different measurement results from literatures (from smooth, rough and field measured data) evidences the capability of the proposed law to represent flow under all bed roughness conditions.

Better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation. Instead of spatial averaging, this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels. Velocity data were collected with a one dimensional laser Doppler velocimeter (LDV) under single layer emergent and submerged flow conditions, and through two layers of vegetation. The effects of dowel arrangement, density, and roughness are also examined under the single layer experiments. The results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it. The region immediately behind a dowel, where the vorticity and turbulence intensity are highest, is characterized by a velocity spike near the bed and an inflection point near the top of the dowel arrays. With two dowel layers, the velocity profile in the region behind a tall dowel exhibits multiple inflection points and the highest turbulence intensities are found there. / Master of Science

The aim of the thesis, is to find the transient force applied by an individual transient liquid slug on an elbow at the end of a horizontal line due to an impact. The liquid slug is driven by pressurized air in a tank located upstream of the pipeline. The time dependent pressure distribution along the elbow and a vertical extension segment after the elbow was solved, with a 1-D numerical approach along a curved line mesh. For this purpose / firstly, a 3-D axial turbulent velocity profile function was assumed for the slug, with its shape allowed to sway towards the convex side of the elbow along the curved mesh with the aid of a calibration tool. Then, the pressure values were calculated by using 1-D application of Reynolds Equations in cylindrical polar and cartesian coordinates for the elbow and the vertical extension segment, respectively. The transient force acting on the elbow and the following vertical extension segment was found by using these calculated pressure values and applying conservation of momentum principle over the volume elements selected along the elbow and the vertical extension segment. For the analysis of the slug motion from the pressurizer tank to the elbow, a previously written computer code BOZKUS-2 was utilized. Then, the elbow and the vertical extension segment calculations in this study were made with a new code KAYHAN, which is an improved version of BOZKUS-2. The calculated transient force and impact pressures at the elbow were also compared with those from previous studies.

As the greenhouse effect is an imminent concern, motivation for the development of energy efficient systems has grown fast. Today heavy-duty vehicles (HDVs) account for a growing part of the emissions from the vehicular transport sector. One way to reduce those emissions is by driving at short intervehicular distances in so called platoons, mainly on highways. In such formations, the aerodynamic drag is decreased which allows for more fuel efficient driving, meanwhile the roads are used more efficiently. This thesis deals with the question of how those platoons can be controlled without using communications between the involved HDVs. In this thesis, artificial neural networks are designed and trained to predict the velocity profile for an HDV driving over a section of road where data on the topography are available. This information is used in a model predictive controller to control the HDV driving behind the truck for which the aforementioned prediction is made. By having accurate information about the upcoming behaviour of the preceding HDV, the controller can plan the velocity profile for the controlled HDV in a way which minimizes fuel consumption. To ensure fuel optimal performance, a state describing the mass of consumed fuel is derived and minimized in the controller. A system modelling gear shift dynamics is proposed to capture essential dynamics such as torque loss during shifting. The designed controller is able to predict and change between the three highest gears making it able to handle almost all highway platooning scenarios. The prediction system shows great potential and is able to predict the velocity profile for different HDVs with an average error as low as 0.04 km/h. The controller is implemented in a simulation environment and results show that compared to a platoon without these predictions of the preceding HDV, the fuel consumption for the controlled HDV can be reduced by up to 6 %.

This master's thesis deals with pulsating flow of Newtonian and non-Newtonian fluid. Theoretical part represents necessary theoretical knowledge for pulsating flow and understanding of non-Newtonian behaviour. Furthermore the thesis focus is directed on numerical simulation of pulsating flow in straight, ideally rigid tube and in patient-specific model of human artery, more precisely in carotid. Two methods are used: numerical solution based on finite volume method (FVM) and also analytical solution using Bessel functions by Womersley. Results are validated against experimental measurements of velocity profiles by particle image velocity method (PIV). The agreement between numerical and experimental data with consideration of PIV inaccuracy was was very good from both point of views - qualitative and quantitative. Numerical solution also compare influence of turbulence and non-Newtonian behaviour towards base (laminar flow, Newtonian fluid). Developed methodology is then applied on patient-specific model of carotid, which was renovated from computed tomography. Measurements in vivo in human arteries is very expensive and often invasive. Because of that measurement outputs are limited, most of the time on pressure and flow. Computational fluid dynamics (CFD) is non-invasive and outputs are through whole domain. Due to these advantages CFD significantly contributes to understanding of hemodynamics influence in cardiovascular diseases.

Yes / When using point measurement for environmental or sediment laden flows, there is well-recognised risk for not having aligned measurements that causes misinterpretation of the measured velocity data. In reality, these kinds of mismeasurement mainly happen due to the misinterpretation of bed orientation caused by the complexity of its determination in natural flows, especially in bedload laden or rough bed flows. This study proposes a novel bed realignment method to improve the measured data benchmarking by three-dimensional (3D) bed profile orientation and implemented it into different sets of experimental data. More specifically, the effects of realignment on velocity profile and streamwise turbulence structure measurements were investigated. The proposed technique was tested against experimental data collected over a water-worked and an experimentally arranged well-packed beds. Different from the well-packed rough bed, the water-worked bed has been generated after long sediment transport and settling and hence can be used to verify the proposed bed-alignment technique thoroughly. During the flow analysis, the corrected velocity, turbulence intensity and Reynolds stress profiles were compared to the theoretical logarithmic law, exponential law and linear gravity (universal Reynolds stress distribution) profiles, respectively. It has been observed that the proposed method has improved the agreement of the measured velocity and turbulence structure data with their actual theoretical profiles, particularly in the near-bed region (where the ratio of the flow measurement vertical distance to the total water depth, z/h, is limited to ≤0.4).

In cycling, performance models are used to investigate factors that determine performance and to optimise competition results. We present an innovative and easily applicable mathematical model describing time-resolved approaches for both the physical aspects of tractional resistance and the physiological side of propelling force generated by muscular activity and test its validity to reproduce and forecast time trials in track cycling. Six elite track cyclists completed a special preparation and two sprint time trials in an official velodrome under continuous measurement of crank force and cadence. Fatigue-free force-velocity profiles were calculated, and their fatigue-induced changes were determined by non-linear regression analysis using a monoexponential equation at a constant slope. Model parameters were calibrated based on pre-exercise performance testing and the first of the two time-trials and then used to predict the performance of the second sprint. Measured values for power output and cycling velocity were compared to the modelled data. The modelled results were highly correlated to the measured values (R2>0.99) without any difference between runs (p>0.05; d<0.1). Our mathematical model can accurately describe sprint track cycling time trial performance. It is simple enough to be used in practice yet sufficiently accurate to predict highly dynamic maximal sprint performances. It can be employed for the evaluation of completed runs, to forecast expected results with different setups, and to study various contributing factors and quantify their effect on sprint cycling performance.

In track cycling sprint events, optimal cadence PRopt is a dynamic aspect of fatigue. It is currently unclear what cadence is optimal for an athlete’s performance in sprint races and how it can be calculated. We examined fatigue-induced changes in optimal cadence during a maximal sprint using a mathematical approach. Nine elite track cyclists completed a 6-s high-frequency pedaling test and a 60-s isokinetic all-out sprint on a bicycle ergometer with continuous monitoring of crank force and cadence. Fatigue-free force-velocity (F/v) and power-velocity (P/v) profiles were derived from both tests. The development of fatigue during the 60-s sprint was assessed by fixing the slope of the fatigue-free F/v profile. Fatigue-induced alterations in PRopt were determined by non-linear regression analysis using a mono-exponential equation at constant slope. The study revealed that PRopt at any instant during a 60-s maximal sprint can be estimated accurately using a mono-exponential equation. In an isokinetic mode, a mean PRopt can be identified that enables the athlete to generate the highest mean power output over the course of the effort. Adding the time domain to the fatigue-free F/v and P/v profiles allows time-dependent cycling power to be modelled independent of cadence.

Une « boue » est constituée de particules submillimétriques immergées dans un fluide. Nous étudions des boues concentrées (ou « pâtes granulaires »), où la concentration en particules est proche du maximum réalisable. Les particules peuvent être plus denses que le fluide, et sédimenter, ou être équilibrées en densité. Ces deux cas sont examinés, à l’aide d’une boue modèle. Nous étudions les écoulements de ces boues dans une cellule de Couette. Les expériences utilisent des méthodes innovantes, permettant de mesurer les vitesses des grains individuellement et collectivement, et les profils de concentration sous cisaillement. Les expériences apportent des informations nouvelles sur les écoulements, comme l’existence de courants de re-circulation. Les résultats sur les vitesses azimutales et concentrations sont en accord avec la théorie de Morris et Boulay d’équilibre des forces normales, pour un rapport convenable des coefficients viscométriques des forces tangentielle et normales. / Wet granular materials are made of solid particles in high concentration, immersed in a viscous fluid. We investigated particle dynamics in a model granular suspension in Couette geometry, at low Reynolds/Taylor numbers for density and non density matched suspension. We used innovated techniques such as: Single Particle Tracking (SPT), Multi Particles Video Trajectography (MPVT) and Concentration Photometry (CP). These experiments allow us to provide information about single and collective motion of grains as well as particle repartition (local volume fraction). We investigated fully 3D velocity profiles in concentrated suspensions, diffusion coefficients, particle fluctuations and recirculation motion, also differential flows. We observe that the flow of non density matched suspensions is localized near the inner cylinder in the low shear rate regime, resulting in a sheared layer only a few particle diameters in thickness, in a way very similar to sheared dry granular materials. At high enough angular velocity, the initially localized flow crosses over to full fluidization: in this regime the granular suspension nearly behaves as a density-matched suspension. Dependence between particles’ velocity and associated fluctuation amplitude is evidenced. Experiments as velocity and concentration profiles were compared with theoretical prediction based on the force balance model and different viscometric laws were investigated for normal and shear forces.