Thèses sur le sujet « Bed roughness »

Thèse sciences techniques, EPF Lausanne, no 2632 (2002), Faculté Environnement naturel, architectural et construit ENAC, Domaine du génie civil. Directeur: A. Schleiss ; rapporteurs: M. Altinakar, G.-R. Bezzola, J. Gessler.

Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, June 1998.<br>Thesis advisor(s): Gallagher, Edith L. ; Thornton, Edward B. "June 2000." Includes bibliographical references (p. 75-76). Also available online.

In practice, baffle blocks and sills are commonly being used to stabilize the location of a hydraulic jump and shorten the length of a stilling basin. On the other hand, gravels, corrugations and rectangular prismatic roughnesses which cover the entire length of the basin or placed in a staggered manner may be an alternative. The objective of this study is to determine the effects of these roughness elements on the characteristics of hydraulic jumps such as conjugate depth, jump length and energy dissipation using experimental data collected from the previous studies. The investigations show that the roughness elements have positive effects on the characteristics of hydraulic jumps. The tailwater depth reduction compared to classical jump is 2-10%. The length of the jump is reduced about by 30-50% by prismatic roughness elements, 40% by corrugations, and 30% by gravels. The roughness elements induce 3-15% more energy dissipation than that of classical jump. Therefore, these types of bed roughness elements should be considered as an effective alternative of accessory devices such as baffle blocks and sills.

Experiments have been performed to investigate the relationship between the geometry of an idealised bed roughness and the structure of the turbulent boundary layer above. This work has particular applications in relation to architecture and environmental health, designing comfort for pedestrians and managing environmental pollution. Experiments were carried out in a laboratory water flume to study the turbulence structure generated under both rough and smooth bed conditions. The relationship between small scale turbulent eddies formed between the elements of a two-dimensional bed roughness and the intermittent turbulent structure of the boundary layer was established in the form of roughness length scale and friction velocity using LDV measurements from the mean velocity profile. Turbulence production was also determined from measurements of the Reynolds stress and velocity gradient. This was compared with the diffusion characteristics of the flow. Spacing between the roughness slats was varied for different tests to produce isolated (k-type) bed roughness, skimming (d-type) flow, and wake interference flow for transitional roughness. Transition between these regimes was further investigated using flow visualisation, and a clear correlation established between the vortices at the bed and the turbulence characteristics of the boundary layer. The effect of sudden changes in bed geometry on the turbulence structure was investigated for flows aligned perpendicular to the roughness elements forming simulated urban environment. These results were compared for a similar model street canyon with and without a large scale upstream approach roughness. The turbulence generated as a result of the change in local bed geometry has a significant influence on the dispersion of dye tracer used to simulate pollutant. It was found that uniformity in height of buildings along parallel streets in an urban environment promotes shear at roof-level, thereby trapping fluid and pollution within the canyon. On the other hand, non-uniformity in building height and the presence of substantial upstream buildings promotes turbulence which helps in ventilation of street canyons.

It is demonstrated that the method for locating a velocity profile origin, or plane of zero velocity, by fitting log profiles to streamwise velocity measurements is applicable to a larger range of roughness scales than previously expected. Five different sets of detailed, experimental velocity measurements were analyzed encompassing sediment-scale roughness elements, roughness caused by rigid vegetation, and large-scale roughness elements comprised of mobile bedforms. The method resulted in similar values of normalized zero-plane displacement for all roughness types considered. The ratios of zero-plane displacement, dh, to roughness height, ks, were 0.20 and 0.26 for the sediment- and vegetation-scale experiments, respectively. The results for the two experiments with bedform dominated roughness were 0.34 and 0.41. An estimate of dh/ks ranging from 0.2 to 0.4 is therefore recommended for a range of roughness types with the higher end of the range being more appropriate for the larger, bedform-scale roughness elements, and the lower end for the sediment-scale roughness elements. In addition, it is demonstrated that the location of the plane of zero velocity is temporally constant even when the bed height is not. The effects of roughness element packing density were also examined with the identification of a possible threshold at 4%, above which zero-plane displacement is independent of packing density. The findings can be applied to field velocity measurements under mobile bed conditions, facilitating the calculation of turbulence parameters such as shear velocity, by using point measurements and providing guidelines for the estimation of an appropriate value for zero-plane displacement.<br>Master of Science

In the scope of the study, prismatic roughness elements with different longitudinal spacing and arrangements have been tested in a rectangular flume in order to reveal their effects on fundamental characteristics of a hydraulic jump. Two basic roughness types with altering arrangements have been tested. Roughness elements of the first type extends through the channel width against the flow with varying length and pitch ratios for different arrangements. The second type is of staggered essence and produced by piecing the roughness elements defined in the initial type into three parts which are equal in length. The doublet formed from the pieces on the sides is shifted to the consequent row to make two successive roughness rows encapsulate the channel span completely. Staggered roughness type is formed with the repetition of this arrangement along the flume. Independent of their type and arrangement, the entirety of roughness elements are embedded in the channel bed in order to avoid their protuberance into the flow, based on the presumption that the crests of the roughness elements levelled with the channel inlet would be less exposed to caving effects of flow than the protruding elements. In the study, influence of the proposed roughness elements on the fundamental engineering concerns as the length, height (tail water depth) and energy dissipation capacity of hydraulic jumps has been questioned in the light of empirical work and related literature on forced and smooth hydraulic jumps. At the final stage of the study, it was concluded that both strip and staggered roughness have positive effects on the characteristics of hydraulic jump given above. 3-7% more energy dissipation was observed in jumps on rough beds compared to classical hydraulic jumps. For tailwater dept reduction, whereas strip roughness provided 5-13%, staggered roughness led to 7-15% tailwater depth reduction compared to classical hydraulic jump. While strip roughness reduced jump length around 40%, 35-55% reduction was observed with staggered roughness when compared to classical hydraulic jump.

Thesis advisor: Gail C. Kineke<br>This study characterizes the bed of the Connecticut River estuary in terms of grain size and bedforms, and relates these to river discharge, tidal currents, and sediment transport. Over four field excursions, sediment cores were collected, in addition to bathymetry surveys, and water column measurements. A three-dimensional circulation and sediment transport model calculated boundary shear stress over the same time. The bed of the estuary is composed mostly of sand, with small amounts of fine sediments. Deposition of fine sediments is limited by the landward extent of the salt intrusion. Large bedforms are oriented seaward. The critical shear stress for the median grain size is exceeded each tidal cycle. Bedload transport is dominantly seaward during high discharge conditions, but varies during low discharge. Bathymetry surveys from previous studies and this study show consistent bedform fields over 25 years. Bedforms observed in the field reflect typical conditions rather than extreme events<br>Thesis (MS) — Boston College, 2015<br>Submitted to: Boston College. Graduate School of Arts and Sciences<br>Discipline: Earth and Environmental Sciences

Metal additive manufacturing (AM) can produce complex parts that were once considered impossible or too costly to fabricate using conventional machining techniques, making AM machines an exceptional tool for rapid prototyping, one-off parts, and labor-intensive geometries. Due to the growing popularity of this technology, especially in the defense and medical industries, more researchers are looking into the physics and mechanics behind the AM process. Many factors and parameters contribute to the overall quality of a part, one of them being the powder bed itself. So far, little investigation has been dedicated to the behavior of the powder in the powder bed during the lasering process. A powder spreading machine that simulates the powder bed fusion process without the laser was designed by Lawrence Livermore National Laboratory and was built as a platform to observe powder characteristics. The focus for this project was surface roughness and particle size distribution (PSD), and how dose rate and coating speed affect the results. Images of the 316L stainless steel powder on the spreading device at multiple layers were taken and processed and analyzed in MATLAB to access surface quality of each region. Powder from nine regions of the build plate were also sampled and counted to determine regional particle size distribution. As a comparison, a simulation was developed to mimic the adhesive behavior of the powder, and to observe how powder distributes powder when spread.

Study of turbulent flow over a rough bed is highly important due to its numerous applications in the areas of sediment transport and pollutant discharge in streams, rivers and channels. Over the past few decades, many experimental studies have been conducted in this respect to understand the underlying phenomenon. However, there is a scarcity in the number of computational studies conducted on this topic. Therefore, a Large Eddy Simulation (LES) of turbulent flow over a rough channel bed was conducted to contribute further understanding of the influence of bed roughness on turbulent flow properties. For this purpose, an efficient, second order accurate 'immersed boundary method' was implemented into the LES code Hydro3d-GT, and validated for flow past bluff bodies. LES results from the present study showed excellent agreement with previous experimental studies on flow over rough beds. An in-depth analysis of time varying turbulent quantities (like the velocity fluctuations) revealed the presence of coherent structures in the flow. Also, a three dimensional visualization of the turbulent structures provided a good picture of the flow, especially in the near bed region, which is quite difficult to accomplish using experimental studies.

Additive Manufacturing (AM) is an uprising manufacturing process for parts with complex geometries and low production quantities. Within the layer-wise building process, less additional processes are needed, to produce the parts. This allows a building of parts within a reasonable time- and costs-range. Especially industries, such as aerospace industry, can profit from AM. Electron beam – Powder bed fusion (EB-PBF) is a common technique, within AM, to produce metallic parts out of special alloys such as Alloy 718. This superalloy is a Nickle-Iron based alloy that has high mechanical properties, even in elevated temperatures (up to 650ºC). The combination of such material properties with high geometrical freedom creates new opportunities for the industry. However, it must be noted that a significant drawback of AM-techniques is the need for post-processing because of surface roughness- and microstructural characteristics. Commonly, the produced parts utilize mechanical post process such as milling to provide good surface roughness and dimensional accuracy. To reduce the surface roughness in the contour region, and therefore reduce the amount of mechanical post-processing, the present survey elaborates the effect of relevant parameters on contours such as the number of contours, scanning speed, focus offset and beam current. By using Design of Experiments (DOE), two batches were carried out: one screening batch and a two-level-full factorial design. In those batches, 15×15×15 mm cubes were printed with various parameters and, after that, analysed by using White light interferometry (WLI), Optical microscopy (OM) and Scanning electron microscopy (SEM). Furthermore, the program ImageJ was used to perform porosity and melt pool measurements. It had been observed that the number of contours had quite a considerable impact on the final surface roughness and the number of defects. Samples with two contours, instead of only one, tend to have a lower surface roughness. Nevertheless, the parameters and their interaction were found to have fundamental effects on the resulting surface roughness and microstructure.

Additive Manufacturing (AM), commonly known as 3D Printing, is a disruptive modern manufacturing process, in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology has opened up a design space that was not formerly accessible with conventional manufacturing processes. It is, now, possible to manufacture complex geometries, such as topology-optimized structures, lattice structures and intricate internal channels, with relative ease. PBF is comprised of Electron Beam Melting (EBM) and Selective Laser Melting (SLM) processes. Though AM processes offer several advantages, the suitability of these processes to replace conventional manufacturing processes must be studied in detail; for instance, the capability to produce components of consistent quality. Therefore, understanding the relationship between the AM process together with the post treatment used and the resulting microstructure and its influence on the mechanical properties is crucial, to enable manufacturing of high-performance components. In this regard, for AM built Alloy 718, only a limited amount of work has been performed compared to conventional processes such as casting and forging. The aim of this work, therefore, is to understand how the fatigue properties of EBM and SLM built Alloy 718, subjected to different thermal post-treatments, is affected by the microstructure. In addition, the effect of as-built surface roughness is also studied. Defects can have a detrimental effect on fatigue life. Numerous factors such as the defect type, size, shape, location, distribution and nature determine the effect of defects on properties. Hot Isostatic Pressing (HIP) improves fatigue life as it leads to closure of most defects. Presence of oxides in the defects, however, hinders complete closure by HIP. Machining the as-built surface improves fatiguelife; however, for EBM manufactured material, the extent of improvement is dependent on the amount of material removed. The as-built surface roughness, which has numerous crack initiation sites, leads to lower scatter in fatigue life. In both SLM and EBM manufactured material, fatigue crack propagation is transgranular. Crack propagation is affected by grain size and texture of the material.

Ce travail de doctorat examine l’effet de la rugosité du lit sur les couches de mélange peu profondes (SML) et l’évolution des structures cohérentes qui les peuplent, telles que les Structures Cohérentes de Kelvin-Helmholtz (KHCSs), les Courants Secondaires (SCs), les tourbillons de grande ou très grande taille (en anglais, Large ou Very-Large Scale Motions, LSMs et VLSMs respectivement). Deux scénarios de rugosité du lit sont considérés : un lit uniformément rugueux et une transition latérale d’un lit rugueux à un lit lisse. Le lit rugueux est constitué d’un gazon dense artificiel d’une hauteur de 5mm, tandis que le lit lisse est constitué de plaques de PVC. Les expériences sont réalisées dans un canal expérimental de 18m × 1.98m. Nous avons imposé à l’amont plusieurs répartitions de débit, obtenant ainsi des écoulements uniformes ou cisaillés transversalement. Dans ce manuscrit, nous explorons dans un premier temps les écoulements sur le lit uniformément rugueux, en comparant les données acquises aux mesures précédemment effectuées dans le même canal avec un lit hydrauliquement lisse. Les objectifs sont de valider la pertinence des paramètres identifiés précédemment dans l’étude des SMLs et KHCSs qui portait essentiellement sur des fonds lisses, d’évaluer l’effet d’un lit rugueux sur le champ turbulent des SMLs, et d’explorer l’interaction entre les KHCSs, LSMs et VLSMs. Dans un second temps, nous étudions l’évolution longitudinale des SMLs, KHCSs, SCs, LSMs et VLSMs sur un lit avec une transition latérale de rugosité. Nous évaluons les mécanismes d’échange latéral de quantité de mouvement et leur importance relative, en explorant finalement l’interaction entre les quatre types de structures cohérentes<br>This PhD investigates the effect of bed roughness on shallow mixing layers (SML) and the evolution of coherent structures that populate them, such as Kelvin-Helmholtz Coherent Structures (KHCSs), Secondary Currents (SCs), and Large and Very-Large Scale Motions (LSMs and VLSMs respectively). Two bed roughness scenarios are considered: a uniformly rough bed and a lateral transition from a rough bed to a smooth bed. The rough bed is made of artificial dense grass with a height of 5mm, while the smooth bed is made of PVC plate. The experiments are conducted in an 18m × 1.98m laboratory flume. The flow configurations explored include both initially spanwise sheared and uniform flows. First, we explore the flows over the uniformly rough bed, comparing the acquired data to previous measurements conducted in the same flume with a hydraulically smooth bed. The objectives are to validate driving parameters for SML and KHCSs observed in the literature, assess the effect of a rough bed on the turbulent field of SML, and explore the interactions between KHCSs, LSMs, and VLSMs. Second, we investigate the longitudinal evolution of SML, KHCSs, SCs, LSMs and VLSMs over a bed with a lateral roughness transition. We evaluate the mechanisms of lateral momentum exchange and their relative importance, ultimately exploring the interaction between all four types of coherent structures

The increased temperatures in the Arctic accelerate the loss of land based ice stored in glaciers. The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere and holds ~10% of all the freshwater on Earth, equivalent to ~7 metres of global sea level rise. A few decades ago, the mass balance of the Greenland Ice Sheet was poorly known and assumed to have little impact on global sea level rise. The development of regional climate models and remote sensing of the ice sheet during the past decade have revealed a significant mass loss. To monitor how the Greenland Ice Sheet will affect sea levels in the future requires understanding the physical processes that govern its mass balance and movement. In the southeastern and central western regions, mass loss is dominated by the dynamic behaviour of ice streams calving into the ocean. Changes in surface mass balance dominate mass loss from the Greenland Ice Sheet in the central northern, southwestern and northeastern regions. Little is known about what the hydrological system looks like beneath the ice sheet; how well the hydrological system is developed decides the water’s impact on ice movement. In this thesis, I have focused on radar sounding measurements to map the subglacial topography in detail for a land-terminating section of the western Greenland Ice Sheet. This knowledge is a critical prerequisite for any subglacial hydrological modelling. Using the high-resolution ice thickness and bed topography data, I have made the following specific studies: First, I have analysed the geological setting and glaciological history of the region by comparing proglacial and subglacial spectral roughness. Second, I have analysed the subglacial water drainage routing and revealed a potential for subglacial water piracy between adjacent subglacial water catchments with changes in the subglacial water pressure regime. Finally, I have looked in more detail into englacial features that are commonly observed in radar sounding data from western Greenland. In all, the thesis highlights the need not only for accurate high-resolution subglacial digital elevation models, but also for regionally optimised interpolation when conducting detailed hydrological studies of the Greenland Ice Sheet.<br>De ökade temperaturerna i Arktis påskyndar förlusten av landbaserad is lagrad i glaciärer och permafrost. Grönlands inlandsis är den största ismassan på norra halvklotet och lagrar ca 10% av allt sötvatten på jorden, vilket motsvarar ca 7 meter global havsnivåhöjning. För ett par decennier sedan var inlandsisens massbalans dåligt känd och antogs ha liten inverkan på dagens havsnivåhöjning. Utvecklingen av regionala klimatmodeller och satellitbaserad fjärranalys av inlandsisen har under de senaste decenniet påvisat en betydande massförlust. För att förutse vilken inverkan inlandsisen har på framtida havsnivåhöjningar krävs en förståelse för de fysikaliska processerna som styr dess massbalans och isrörelse. I de sydöstra och centrala västra delarna av inlandsisen domineras massförlusten av dynamiska processer i isströmmar som kalvar ut i havet. Massförlusten i de centrala norra, sydvästra och nordöstra delarna domineras av isytans massbalans. Ytterst lite är känt om hur det hydrologiska systemet ser ut under inlandsisen; hur väl det hydrologiska systemet är utvecklat avgör vattnets påverkan på isrörelsen. I denna doktorsavhandling har jag använt markbaserade radarmätningar för att kartlägga den subglaciala topografin för en del av den västra landbaserade inlandsisen. Denna kunskap är en viktig förutsättning för att kunna modellera den subglaciala hydrologin. Med hjälp av rumsligt högupplöst data över istjockleken och bottentopografin har jag gjort följande specifika studier: Först har jag analyserat de geologiska och glaciologiska förhållandena i regionen genom att jämföra proglacial och subglacial spektralanalys av terrängens ytojämnheter. Sedan har jag analyserat den subglaciala vattenavrinningen och påvisat en potential för att avrinningsområdena kan ändras beroende på vattentryckförhållandena på botten. Slutligen har jag tittat mer i detalj på englaciala radarstrukturer som ofta observerats i radardata från västra Grönland. Sammanfattningsvis belyser avhandlingen behovet av inte bara noggranna rumsligt högupplösta subglaciala digitala höjdmodeller, utan även regionalt optimerad interpolering när detaljerade hydrologiska studier ska utföras på Grönlands inlandsis.

The work presented in this thesis was conducted at Uppsala University and at Swerim AB. The study aims to broaden the knowledge about the corrosion of additively manufactured bioresorbable alloy WE43 in humanlike conditions for future applications. Biodegradable metal implants are implants meant to stay in the body and support the wounded bone for a certain time period, and then degrade as new, healthy bone forms in its place. Magnesium alloys have properties that are desired for these kind of implants as it is biodegradable, non-toxic and matches the mechanical properties of bone. Furthermore, magnesium alloy WE43, containing yttrium, neodymium and zirconium, already exist on the market as a powder extruded screw that treats Hallux valgus, thus proves the alloys compatibility as a bioresorbable implant. However, in order to optimize implants for specific situations, additive manufacturing can be a powerful tool. By utilizing the advantages of additive manufacturing, patient specific, complex designs implant can be manufactured rapidly in order to be used in a patient. On the other hand, additive manufacturing is a complex method with many aspects affecting the outcome. Therefore it is important to study the influence that different parameters have on the material's properties, especially the corrosion properties. This thesis aims to study different power settings on the laser in the manufacturing process and what effect it has on the microstructure as well as the corrosion properties of as built WE43 samples. Samples of three different parameters settings were manufactured with a Powder Bed Fusion-Laser Beam 3Dprinter. These samples were analyzed regarding surface roughness and microstructure with Light Optical Microscope, Scanning Electron Microscope, Energy Dispersive Spectroscopy, Electron Backscatter Diffraction and Alicona InfiniteFocus. Furthermore, the corrosion properties of the samples were investigated by collecting and measuring hydrogen gas that is released during the corrosion process. In addition, the electrolyte were examined regarding the change in ion concentration and electrochemical tests were performed. It was found that the samples did not differ substantially in microstructure as all three parameter settings exhibited a matrix of magnesium and precipitates of alloying elements. However, the sample manufactured at the lowest energy density had pores incorporated in the bulk. Despite the porous bulk this sample performed best in the immersion tests and exhibited the lowest corrosion rate over 28 days. The reason for this behavior is not determined, however possible causes are discussed and further studies are recommended.

The objective of this study is to determine the effect of different roughness types and arrangements on hydraulic jump characteristics in a rectangular channel. Three different types of roughness were used along experiments. All of them had rectangular prism shapes and that were placed normal to the flow direction. To avoid cavitation, height of roughness elements were arranged according to level of the channel inlet, so that the crests of roughness elements would not be protruding into the flow. The effects of roughness type and arrangement on hydraulic jump properties, i.e. energy dissipation, length of the jump and tail water depth were investigated. These properties were compared with the available data in literature and with the properties of hydraulic jump occurred on smooth bed.

Dans le cadre de ce travail, la génération des surfaces produites par le procédé de fusion laser sur lit de poudre LPBF a été étudiée. Le LPBF est un procédé de fabrication additive qui peut conduire à de nouvelles opportunités (fabrication de structures complexes avec canaux internes, structures lattices). Ce procédé attire donc une attention considérable en particulier dans l'industrie aéronautique. Une étude de l’influence des paramètres primaires du procédé LPBF sur la génération des surfaces a été réalisée. Au cours de cette étude, la relation entre la rugosité des surfaces supérieures et latérales et la densité du matériau a été établie. Cela a permis de déterminer la première fenêtre de paramètres optimaux.Une analyse de la dispersion de la rugosité et la reproductibilité du procédé ont ensuite été réalisées. Cette analyse a révélé une importante dispersion de la rugosité, notamment d'une face à l'autre. En conséquence, des recommandations sur les mesures de surface ont été proposées.L'effet de différents paramètres secondaires est également étudié afin de mieux comprendre la génération de la surface latérale et de l'optimiser. Cette étude a montré que les compensations et les réglages de contour sont des paramètres clés qui peuvent contribuent à la réduction de la rugosité des surfaces latérales. Sur la base des résultats de ces études, la rugosité a pu être diminuée d’un Sa de 40 µm à un Sa de 10 μm.Enfin, cette thèse présente une nouvelle approche de modélisation de génération des topographies des surfaces latérales. L’approche est basée sur la géométrie du cordon (rayons de courbure). Elle permet de prendre en compte la position des cordons et des couches et prédit la rugosité pour différentes stratégies de lasage et paramètres de compensation<br>In the current study, surface generation during additive manufacturing (AM), especially the laser powder bed fusion (LPBF) process was studied. LPBF is a progressive process that can lead to new opportunities, such as applications that require complex structures (internal channels or lightweight lattice structures). It has therefore attracted considerable attention, which has led to research and development in many industries, particularly in the aerospace industry.A surface generation study to optimize surface roughness and material density by examining the influence of the primary LPBF process parameters was therefore performed. During this study, the relationship between the roughness of the top and side surfaces and the density of the material was established. This made it possible to determine the first window of optimal parameters.An analysis of the roughness dispersion and process reproducibility were then carried out. This analysis revealed a significant roughness dispersion, especially from one side to the other. As a result, recommendations on surface measurements have been proposed.The effect of different process options (secondary parameters) are also studied in order to better understand the generation of the side surface and optimize it. This study showed that compensations and contour settings are key parameters that can help reduce the side surface roughness. Indeed, the geometric positioning of the different weld tracks is an important issue that must be addressed to reduce surface roughness. Based on the results of this study, it is possible to reduce the average surface roughness Sa from 40 to 10 μm.Finally, this thesis presents a new approach to modeling side surfaces roughness (at 0°). The approach is based on the weld track geometry (radii of curvature). It allows to take into account the weld tracks and layers position in relation to each other and thus to predict the roughness for different scanning strategies, compensation parameters

A study of the hydraulic jump on a trapezoidal prismatic channel and roughened beds is presented. Extensive measurements have been made regarding the characteristics of hydraulic jumps as sequent depths, wing fluctuations, energy dissipation and jump length on artificially roughened beds for Froude numbers between 4.16 and 14.58. Three different types of prismatic roughness elements and nine different roughness patterns were installed separately on channel bottom and side walls throughout the experiments to obtain rough surfaces. Strip roughness elements were built from fiberglass sheets and implemented perpendicular to the flow direction. To avoid cavitation, roughness elements were designed in that way that the crests of the elements are not protruding into the flow. The founded properties were compared with the available data in literature and with the properties of hydraulic jump occurred on smooth bed.

Sediment transport, and bedload transport in particular, is one of the most dynamic and complex hydraulic and geomorphologic processes in a river basin. Sediment supply is strictly dependent on erosion processes in the catchment which are highly controlled by primary factors such as: climate, basin area, geology and topography. Sediment transport influences the geomorphic responses of rivers and the equilibrium of the fluvial environment. The sampling devices and techniques used in the field to quantify bedload transport are very few. Difficulties liked to their efficiency, together with the request of large human and financial resources, have proven that bedload transport is one of the most difficult fluvial processes to measure. These difficulties have pushed scientists to develop physically based and empirical formulas to quantify bedload transport based on both laboratory and field studies. However, field measurements are very limited. Despite continued efforts, bedload transport equations still have limited application. Thus, understanding and quantifying sediment yield is becoming increasingly the center of attention of a variety of scientific and societal problems. Given the poor knowledge of river supplies at regional scale, this research aims at quantifying the bedload yield to the Romagna beaches through field investigations and measurements on two representative rivers to enlarge the actual dataset. By means of hydraulic and hydrological approach and, most of all, by means of bed load transport direct measurement campaigns in the field, this research aims at defining the quantity of sediment flux of the Fiumi Uniti and Savio rivers. They both flow from the northern Apennines to the Padan plain and outflow into the Adriatic Sea in the Ravenna province. Focusing particularly on bedload transport, the investigation took place in the last 10 kilometers of the rivers, i.e. in the vicinity of their mouths. Field campaigns have been carried out by means of the Helley-Smith bedload sampler. Field measurements started in 2005-06 by previous authors were revise and were integrated by the author in 2019. Repeated samplings carried out during different flood conditions have permitted to calculate bedload rating curves (and annual bedload yields). Bathymetric surveys carried out on the river downstream reaches, revealed the presence of bedforms. Since these play an important role in the interaction between flow and sediment transport, further investigation have been done on their role in controlling bedload. Important components affecting the bedload transport rates and its calculation using the classical bedload equations were also investigated. They include the threshold conditions of incipient bedload motion and the roughness component of dune bedforms. The field data indicate that bedload sediment yield to the Romagna beaches is highly variable and that the Fiumi Uniti bedload transport is higher than that of the Savio river. Finally, a comparison of the field data with the results of well-known criteria to predict bedload transport rate has been performed to define the best equation to be used at regional scale to quantify bedload supply to beaches in a mid-term scenario.<br>Il trasporto di sedimenti, e in particolare il trasporto solido (al fondo), è uno dei più dinamici e complessi risultati dei processi idro-climatici, idraulici e geomorfologici che si verificano all’interno di un bacino fluviale. La capacità di produzione sedimentaria dipende strettamente dalla fornitura di sedimenti dal bacino che è altamente controllata da fattori primari quali: clima, area del bacino, geologia e topografia. Ulteriormente influenzato da impatti antropici, il trasporto di sedimenti controlla le risposte geomorfiche dei fiumi che, a loro volta possono essere ulteriormente esacerbati dai cambiamenti climatici. Diversi sono gli strumenti e le tecniche di campionamento utilizzati sul campo per quantificare il trasporto solido. Le difficoltà connesse alla loro efficienza, assieme alla richiesta di grandi risorse umane e finanziarie, hanno dimostrato che il trasporto solido è uno dei processi fluviali più difficili da misurare. Negli ultimi cinquant'anni tali difficoltà hanno spinto gli scienziati a sviluppare modelli empirici per la stima del trasporto solido al fondo. Sono state proposte diverse formule basate fondamentalmente su studi di laboratorio e di campo, pur considerando che le misure dirette di campo sono molto limitate. Nonostante i continui sforzi compiuti, esistono ancora grandi limiti delle equazioni. Comprendere e quantificare il tasso dei sedimenti trasportati sta diventando sempre più importante per una varietà di problemi sia da un punto di vista scientifico che applicativo. Sebbene vi siano alcuni sporadici studi sperimentali sugli apporti solidi fluviali in regione Emilia-Romagna, i dati a disposizione sono estremamente esigui e, sfortunatamente, si riferiscono solo a un numero limitato di fiumi. Data la scarsa conoscenza degli apporti fluviali a scala regionale, questa ricerca mira a quantificare il trasporto solidi dei corsi d’acqua attraverso indagini sul campo e misurazioni dirette svolte su due fiumi rappresentativi con lo scopo di ampliare il dataset attuale a disposizione. Mediante un approccio di tipo idraulico ed idrologico e, soprattutto, mediante campagne di misura diretta del trasporto solido, si è quantificato il trasporto al fondo nei Fiumi Uniti e Savio. Entrambi i fiumi scorrono dall'Appennino settentrionale alla Pianura Padana, sfociando nel mare Adriatico in prossimità della provincia di Ravenna. Concentrandosi in particolare sul trasporto solido fluviale, l'indagine si svolge nei pressi degli ultimi dieci chilometri dei corsi d’acqua, a ridosso delle zone fociali. Le campagne sono state condotte con un approccio di misurazione diretta ( ossia tramite l’utilizzo del campionatore Helley-Smith) iniziato nel 2005-06 da autori precedenti ed esteso dall’autrice nel 2019. Campionamenti ripetuti effettuati in diverse condizioni di piena hanno permesso di calcolare le scale di deflusso degli apporti solidi (e il carico solido al fondo fluviale annuale). Ulteriori indagini batimetriche sono state condotte in prossimità delle sezioni di misura, rivelando la presenza di forme di fondo. Ulteriori approfondimenti sono stati svolti relativamente ai fattori che influenzano il trasporto solido, del quale è stata anche effettuata una stima analizzando alcune classiche equazioni presenti in letteratura. Sono state infatti considerate sia le condizioni di soglia del movimento dei sedimenti sia la componente di rugosità dovuta alla presenza delle forme di fondo, ed in particolare dovuta alle dune. I dati ottenuti indicano che l’apporto solido fluviale dei fiumi studiati è molto variabile ed in particolare il trasporto solido dei Fiumi Uniti è superiore a quello del fiume Savio. Infine, è stato eseguito un confronto tra dati misurati sul campo e quelli ottenuti da criteri ben noti di letteratura allo scopo di definire la migliore equazione utilizzabile a scala regionale per quantificare l’apporto solido fluviale alle spiagge romagnole.

碩士<br>國立中央大學<br>能源工程研究所<br>99<br>This study investigates experimentally the Brazil-nut effect in a quasi-2D vertical vibrated granular bed, the only difference lying in the surface roughness of the larger disks (or called intruders). The so-called “Brazil nut problem” means the larger particle rises to the top of the container and the smaller particles move to the bottom. The dynamics of the larger disk is recorded by using a high speed camera. The effects of vibration conditions and filling height of the granular bed on the dynamics of intruder are investigated in the study. The results show that the rising velocity decreases with increasing granular bed filling height. It also shows that the rising time becomes faster with the larger dimensionless vibration acceleration and smaller vibration frequency is applied in the granular system. However, the rise time of the rough disks is smaller than the smooth one because of the larger energy dissipation of the rough disks. Additionally, the difference in the rising time between the rough and smooth intruders is more significant with the smaller dimensionless vibration acceleration, higher vibration frequency and higher granular bed filling height.

Yes<br>A set of shallow-water equations (SWEs) based on a k-epsilon Reynold stress model is established to simulate the turbulent flows over a complex roughness bed. The fundamental equations are discretized by the second-order finite-difference method (FDM), in which spatial and temporal discretization are conducted by staggered-grid and leap-frog schemes, respectively. The turbulent model in this study stems from the standard k-epsilon model, but is enhanced by replacing the conventional vertical production with a more rigorous and precise generation derived from the energy spectrum and turbulence scales. To verify its effectiveness, the model is applied to compute the turbulence in complex flow surroundings (including a rough bed) in an abrupt bend and in a natural waterway. The comparison of the model results against experimental data and other numerical results shows the robustness and accuracy of the present model in describing hydrodynamic characteristics, especially turbulence features on the complex roughness bottom.<br>National Key Research and Development Program of China (Grant No: 2016YFE0122500, 2013CB036401 and 2013CB036402), China Postdoctoral Science Foundation (Grant No: 2016M591184) and Programme of Introducing Talents of Discipline to Universities (Grant No: BC2018038)<br>Research Development Fund Publication Prize Award winner, June 2019.

ABSTRACT A hydraulic jump is a phenomenon of hydraulics which is frequently observed in open channel flow such as rivers and spillways. The hydraulic jump depends on the initial fluid speed. If the initial speed of the fluid is below the critical speed, then no jump is possible. This project discusses about the behaviour of hydraulic jump on rough horizontal bed and its implementation in field. In the previous studies various types of roughness were used. For the present study to create roughness on bed by using, different sizes of wooden blocks with different spacing between them are used and seen its effect on hydraulic jump properties such as sequent depth ratio, roller length & the loss of energy etc. For this a large no. of experimental series were carried out with different cases. It was found that the rough bed dissipates more energy with a decrease in length of jump as compared to a smooth bed. To see the effect of roughness some relationships were also plotted. It was also found that sequent depth ratio is function of Froude no. Here with an increase in discharge the sequent depth ratio decreases. By plotted another relation between Froude No. and sequent depth, it was found that with increase in Froude No., the sequent depth ratio also increases rapidly. The ratio of spacing and height should be in proportionate manner; otherwise it will not serve as a rough bed. Because the increased height of roughness works as an obstruction not as a roughness. If the ratio of height decreases with their spacing, then it works as a smooth bed not rough bed. For this study some empirical equations & results were used which are helpful in estimation of Froude no. and other properties of hydraulic jump.

Yes<br>This work presents new water surface elevation data including evidence of the spatial correlation of water surface waves generated in shallow water flows over a gravel bed without appreciable bed forms. Careful laboratory experiments have shown that these water surface waves are not well-known gravity or capillary waves but are caused by a different physical phenomenon. In the flow conditions studied, the shear present in shallow flows generates flow structures, which rise and impact on the water-air interface. It is shown that the spatial correlation function observed for these water surface waves can be approximated by the following analytical expression W(rho) = e(-rho 2/2 sigma w2)COS(2 pi L-0(-1)rho). The proposed approximation depends on the spatial correlation radius, sigma(w), characteristic spatial period, L-0, and spatial lag, . This approximation holds for all the hydraulic conditions examined in this study. It is shown that L-0 relates to the depth-averaged flow velocity and carries information on the shape of the vertical velocity profile and bed roughness. It is also shown that sigma(w) is related to the hydraulic roughness and the flow Reynolds number.

A new theoretical analysis was developed that accounts for variable grain protrusion within self-formed, stable gravel armour layers. A key feature of the analysis is accounting for the variation in drag coefficient, drag force and critical dimensionless shear stress with grain protrusion above the virtual bed, which is defined here as the elevation at which the extrapolated logarithmic velocity profile becomes equal to zero. The central hypothesis is that self-formed stable armour layers develop through adjustment of grain protrusion such that all grains are at the threshold of motion, at least in a statistical sense. This represents the limiting case of equal mobility. Testing of the analysis using published flume data shows good agreement between observed and predicted roughness height, mean velocity and flow depth. Experimental work on simulating gravel-bed armouring was carried out to obtain more data and test the assumptions underlying the numerical model. Velocity profiles across and along the flume were measured with an acoustic Doppler velocimeter (ADV). To determine the reliability of ADV measurements in turbulent flows over rough boundaries, a thorough data analysis was undertaken. Shear stresses obtained from the force balance (pgYSj), from the velocity profiles, or from the Reynolds stress measurements were compared and showed a reasonable agreement. A unique study on individual grain protrusion was carried out, in which the armoured beds were scanned, digital elevation models (DEM) were developed, and then combined with photographs to obtain the information on protrusions. These measured protrusions are in good agreement with those calculated in the numerical mod

Yes<br>The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group (RNG) k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-ε model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning's roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.<br>National Natural Science Foundation of China (Grants No. 11361002 and 91230111), the Natural Science Foundation of Ningxia, China (Grant No. NZ13086), the Project of Beifang University of Nationalities, China (Grant No. 2012XZK05), the Foreign Expert Project of Beifang University of Nationalities, China, and the Visiting Scholar Foundation of State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, China (Grant No. 2013A011).

The marine industry has increased its adoption of pure-electric, diesel-electric, and other non-traditional propulsion architectures to reduce ship emissions and fuel consumption. While these technologies can improve performance, the design of a propulsion system becomes challenging, given that no single technology is superior across all vessel types. Furthermore, even identical ships with different operating patterns may be better suited to different propulsion technologies. Addressing this problem, previous research has shown that if key elements of a vessel's operational pro file are known, simulation and optimization techniques can be employed to evaluate multiple propulsion architectures and result in a better propulsion system design and energy management strategy for a given vessel. While these studies have demonstrated the performance improvements that can be achieved from optimizing clean marine propulsion systems, they rely on vessel operational profiles obtained through physical measurement from existing ships. From a practical point of view, the optimization of a vessel's propulsion system needs to occur prior to a vessel's construction and thus precludes physical measurement. To this end, this thesis introduces a marine simulation platform for producing vessel operational profiles which enable propulsion system optimization during the ship design process. Core subsystem modules are constructed for simulating ship motions in 3 degrees of freedom and result in operational profile time-series, including propulsion power. Data is acquired from a benchmark vessel to validate the simulation. Results show the proposed approach strikes a balance between speed, accuracy, and complexity compared with other available tools.<br>Graduate