Добірка наукової літератури з теми "Free settling"

In recent years, a range of computer simulation models leading to a better understanding of liquid phase sintering phenomena, have been developed with the aim of simulating the detailed evolution of microstructure during grain growth. Some liquid phase sintered materials show both macrostructural and microstructural effects associated with gravity force. Therefore we will develop a numerical procedure for the estimation of how much gravity will influence domain (two-dimensional particle representation) growth, domain boundary migration and solid skeleton formation due to gravity induced segregation during liquid phase sintering. The method used for the simulation of a gravity field will be based on the settling procedure. Gravity induced settling will be separated into two stages - Free Settling and Skeletal Settling. Isolated solid phase domains fall under gravity and slide down over the already settled domains (free settling). During settling they make point contacts with each other. Necks between them then form and start to grow until the equilibrium dihedral angle between the domain boundaries and the liquid is established. Thus a solid skeleton forms and skeletal settling of a connected solid structure takes place. .

Sediment settling velocity is an important parameter in particle suspension and indispensable link of hyperconcentrated flow as well as basic theory support for efficient sediment transport of Xiaolangdi Reservoir. This paper has adopted current sediment sample in Xiaolangdi Reservoir to take still water settling experiment, observed carefully silt sediment distribution during different settling duration under various initial concentrations, analyzed common settling velocity calculation method, and adopted settling duration curve method as calculation method to obtain a constant settling velocity of free settling section. Typical settling velocity that is obtained from experiments makes supplement and fitness to settling velocity formula of the existing groups of sediment sample, amends the formula coefficient, further explore the settling characteristics and settling velocity of fine particle mixed viscous sediment with water concentration change, and meanwhile this paper researched settling distance impact on settling velocity, existing sediment group settling transition to mesh settling critical transition silt concentration of Xiaolangdi Reservoir.

Settling velocity is an important parameter affecting the characteristics of sediment transport. Especially for cohesive sediment in estuarine or mangrove areas, determination of settling velocity is extremely complex. The study focuses on anlalyzing the relationship between settling velocity and sediment concentration. Based on the empirical formulas of Hwang (1989) and experimental data of Mehta and Li (2003), the settling velocity by concentration is considered with variation of four parameters a, b, m and n. The method is applied to calculate the settling velocity of cohesive sediment in Can Gio Biosphere Reserve, Ho Chi Minh city. From collected sediment samples in fieldwork, the settling column test is used to determine settling velocities. With 38 data of experimental settling velocity, the semi-empirical curve is determined. The results show that the settling velocity in free settling is about 0.28 × 10-5 m/s; the maximum velocity is about 0.99 × 10-3 m/s corresponding to the maximum concentration of 4.7 kg/m3. The resulting values of a, b, m and n are 0.05; 3.5; 3 and 3.2, respectively. The results are reliable to real applications.

Settling phenomenon of solid particles immersed in a turbulent fluid has been investigated, in a condition of free-stream turbulence. Since structures formed onto this condition are complex, it is difficult to predict exactly how particles move. It is thus appropriate to conduct deepen studies of the phenomenon and carry out simulations to describe particles’ settling velocity. In order to define a new correlation for the evaluation of particles’ settling velocity, different literature correlations and parameters have been exploited. Langevin dynamics has been used to describe fluid’s motion, and by considering several forces acting on particles (buoyancy, drag, gravitational and virtual mass), it has been possible to evaluate their settling velocity, through a computational approach. Data have been obtained by varying characteristic properties, such as kinetic energy, its rate of dissipation, and physical properties of fluid and particles. Aiming to find a reliable correlation which best explains the settling phenomenon, results in output from simulations have been compared with that deriving from proposed correlation. Encouraging results have been obtained over the range of operating conditions examined.

This thesis presents the first measurements of the velocities and orientation of nylon fibrous particles with length to diameter ratios of between 35 and 60 where the density ratio between the two phases is of order 1,000. One set of data was obtained with the fibres settling in air at a fibre Reynolds number in the range of 10 – 100 based on the fibres’ lengths under conditions that avoided any influence of secondary flows and at a mean volume fraction of 10-5. The other data were obtained with the fibres transported in a turbulent co-flowing jet at the jet Reynolds number of 70,000 in the super-dilute regime. These data are of relevance to the combustion of biomass particles in furnaces and boilers. As such, the data will contribute to the replacement of fossil fuels with biomass, which is an attractive fossil-fuel alternative because it is renewable and the net greenhouse gas emissions are lower than for fossil fuels. The measurements described above were undertaken with a novel implementation of Particle Tracking Velocimetry (PTV) in which a fibre’s orientation, the vertical and horizontal components of velocity, were measured simultaneously based on each fibre’s two end-points. The laser used in the experiments was a Quantel Brilliant Twins doublecavity pulsed Nd: YAG 10 Hz laser. The thickness of the light sheet was about 5 mm, which is a value found experimentally to provide a good compromise between a sufficiently high fraction of fibres fully within the light sheet and a reasonable spatial resolution. The one key feature of this method is that the “part-in” fibres within the laser sheet were detected and rejected through an assessment of the signal intensity and signal Abstract VI intensity gradients. The other key feature is that the volume fraction of the fibres was measured by counting the number of particles in the viewing volume. Firstly, the drag coefficient of long aspect ratio fibrous particles has been investigated experimentally. A “sphericity” parameter has been widely introduced in previous work to define the drag coefficient of fibrous particles. However it is not suitable for long aspect ratio fibres. In the present work, the relationship between the drag coefficient and a fibre’s Reynolds number based on the diameter for a long fibre was derived and investigated. An equation was proposed to describe the relationship between the volume fraction and settling velocity. It was also found that the scatter of horizontal velocity increases significantly with the volume fraction. The equivalent diameter of a settling fibre in air is reported. Two previous models of the drag coefficients of fibrous particles were also assessed. Secondly, the influence of volume fractions of the fibrous particles on their settling velocities and orientations was investigated. It was found that the mean settling velocities of the fibrous particles increased significantly with the number density of the fibres for the low volume fractions. This is attributed to the fibres’ orientation transition from the horizontal to the vertical state because of increasing interactions between the fibres, together with the influence of the cloud-like motion on the fibres. The volume fraction also has a strong influence on the mean orientations of the fibrous particles such that the fibres’ orientation tends to be more vertical with an increase in the number density of the fibres. Abstract VII Thirdly, for a bulk settling motion of the fibrous particles, it has been found that the distributions of the fibres’ vertical and horizontal components of settling velocity are nearly Gaussian. The bulk mean settling velocity of the fibres is much higher than that of a single fibre. This is attributed to the bulk motion effect and orientation transition mentioned above. The orientations of the majority of the fibrous particles are nearly horizontal. A key new finding is that the horizontal velocity of the fibres, whilst settling in air, is preferentially aligned with the major axis of the fibres, because a horizontal fibre moving horizontally in this direction has the minimum drag force. Furthermore it has been found that the majority of fibres exhibit rotation and tumbling while settling in air, which contrasts with the previous measurements in water. This is attributed to the fibre’s pressure centre being behind the mass centre whilst settling. It has also been found that the fibres’ tumbling is inhibited by a decrease in the aspect ratio. Angular velocities of the fibrous particles and their distributions for four types of the fibres are reported. Fourthly, the influence of the aspect ratio of the fibrous particles on their settling velocities and orientations was investigated for aspect ratios of 35, 48 and 60. For fibres with a constant diameter but different length, it was found that the settling velocity normalized by that of an equivalent sphere (Vcx/Veq-sph) decreases with an increase in fibre length. For fibres with the same length but different diameter, both the mean settling velocity and the normalized settling velocity (Vcx /Veq-sph) decrease with an increase in diameter. For fibres with the same aspect ratio but different length and diameter, the normalized settling velocity (Vcx /Veq-sph) decreases with an increase in particle size. Abstract VIII Lastly, the measurements in a turbulent jet found both that the fibres’ most probable orientation tends to be approximately 50° to the axial direction and that there are few fibres that are aligned with the direction of the flow at the centre-line of the jet, which is consistent with the simulation of inertial fibres in a turbulent channel flow. However it contrasts with the previous work of small fibres in a turbulent pipe flow, where the fibres were reported as being predominately aligned with the direction of the flows at the centre-line of a pipe. This difference is attributed to the fibres’ inertia. The fibres’ inertia is significant for the present jet flow because the density ratio between the particle and fluid phases for the present case is three orders of magnitude larger than that of the turbulent pipe flow. At the centre of the co-flowing jet, the fibres’ axial velocity and orientation were found to change little with an increase in volume fractions in the super-dilute regime, which contrasts with the findings of the free-falling cases in which the settling velocity and orientation change significantly with the volume fraction. These differences are attributable to a reduction in the relative significance in the interactions between the wakes of the proximate particles. The fibres’ vertical angular velocity is the lowest at the centre-line of the jet and increases significantly in the radial direction, which is consistent with the previous simulations. At the centre-line of the jet, the fibres’ normalized radial velocity is much higher than that of the spheres with a similar Stokes number based on diameter. This is attributed to the dual effects of significant orientation of the fibres to the flow and to their tumbling, both of which induce a radial velocity that does not occur with spheres.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2016

M.Sc. (Aquatic Health)
The increased supply of water to areas targeted for development and the concomitant increase in land use and waste disposal activities has lead to the deterioration in the quality of water in South Africa‟s freshwater systems (DWA, 2011a). In order to manage this, the South African Department of Water Affairs (DWA) has developed numerous water quality policies and management approaches. One such approach is the determination and use of Resource Water Quality Objectives (RWQOs) (DWAF, 2006a). Resource Water Quality Objectives are a set of instream water quality objectives that aim to ensure that water that is fit for use is supplied to downstream users through the management and control of upstream impacts (DWAF, 2006b). In this study, site specific RWQOs were determined for the Modder and Riet Rivers as a means of providing a basis for reporting on instream water quality. As with many of the freshwater catchments in South Africa, the Modder-Riet catchment, located in the Free State and Northern Cape Provinces, is a water limited catchment (Slabbert, 2007). Historically most of the Modder and Riet Rivers would typically have had low water yields, with dry periods and pools forming in large endorheic areas (Grobler and Davies, 1981). As the need to supply water for crop production and domestic use grew, various transfer schemes and reservoirs were developed between the Caledon, Orange and Modder-Riet River systems (DWAF, 2006a). In order to distribute this water, various canal systems and operating rules for the storage dams were developed to transport water to the predominantly agricultural and domestic water users in the various parts of the catchment. Much of the water that is used in the Modder-Riet catchment therefore originates from reservoirs and from outside the catchment, completely transforming it from its natural state. This change in land-use and hydrology of the Modder-Riet catchment resulted in a concomitant change in the water quality. Salinisation, microbial contamination and eutrophication have, in particular, been recorded as the most significant problems affecting the fitness for use of the water in the Modder-Riet catchment. In order to manage these water quality problems and the effects on downstream users, a Catchment Management Strategy (CMS) for the Modder-Riet catchment was developed in 2006 which identified the users in the catchment and put forth a set of catchment-wide RWQOs (DWAF, 2006a). Further studies in the area have also subsequently highlighted that, given the current growth in water use, the associated negative water balance and the potential for serious deleterious effects of increased return flows on the water users, the need for improved efficiency of water use and the management of water quality in this catchment (as well as in those catchments which support the Modder and Riet Rivers) will become ever increasingly important (DWA, 2006a; DWA, 2012a; DWA, 2013a). The aim of this study was to: 1) determine whether catchment characteristics, water quality and user requirements across the catchment differed enough to warrant the separation of the catchment into different Management Units (MUs) for which site specific instead of generic RWQOs should be set, 2) to set low confidence level 3 RWQOs for various sites which represent each MU and 3) to determine the implications for the future management of the water quality in the Modder-Riet catchment. Fourteen Level 3 RWQOs for the main constituents of concern, namely phosphate (PO4), ammonia (NH3), ammonium (NH4+), nitrate and nitrite (NO3 + NO2-N), Escherichia coliform (E. coli), Electrical Conductivity (EC), chloride (Cl), sodium (Na), the Sodium Adsorption Ratio (SAR), aluminium (Al) and fluoride (F), were determined at strategic sites within six water quality MUs. These MUs were roughly the same as those determined in the Modder-Riet CMS, with a few exceptions:  the Upper and Middle Riet MUs from the CMS were not found to be different enough in terms of land use and water quality to warrant their separation and in this study were lumped together to form the Upper Riet MU, and  the Lower Riet MU from the CMS did not take account of the operation of the Kalkfontein and Orange-Riet transfer schemes which, in this study, resulted in the delineation of the Middle Riet River MU from Kalkfontein Dam to the outlet of Kalkfontein Canal and the Lower Riet MU from below the Kalkfontein Canal end point on the Riet River and the transfer site on the Modder River (at Scholzburg Weir) to just above the zone of influence from the Vaal River on the lower Riet River below Soutpansdrift. As with the delineation of the MUs, the location of the RWQO sites were determined in consultation with the Modder-Riet Catchment Management Forum (CMF) and were based on 1) their ability to exercise control over the quality of water entering a MU (resulting from upstream water uses) and 2) the need to provide water that is fit for use for the downstream users in areas of similar land uses. Within each MU, additional sites were added that would ensure fitness for use at specific strategic points. Since the RWQOs that were set at these sites were based predominantly on the current state of the water quality in the Modder and Riet Rivers they varied widely, with the strictest RWQOs being set for the transfers from the Caledon River via Novo Transfer Scheme, at Mazelspoort Weir on the Modder River and within the Kalkfontein Canal at the outlet of Kalkfontein Dam on the Riet River. Whether the status quo should be maintained, improved or allowed to deteriorate was determined by considering the water quality management vision and goals for the catchment, the water quality needs of the downstream users and the potential impact on the upstream uses. Although the RWQOs in almost all cases were more stringent than those set for Modder and Riet Rivers in the. CMS, of greater significance was the variation between the RWQOs set at each of the sites. By using the current state of water quality as a reflection of fluvial processes (such as assimilation, deposition and dilution), the RWQOs in this study took account of the differences in the effects of the various land uses and allowed for the determination of objectives which were tailored to specific areas of the catchment. They therefore more accurately represented the user requirements and the need for interventions. The RWQOs set by the CMS on the other hand were applied at catchment scale (i.e. there was one set of RWQOs for the entire catchment) and as such may have been too lenient in some areas and too strict in others. Thus although broad scale objectives set by the CMS may be useful for water quality assessments in the Modder-Riet catchment, the need to account for differences in local factors which influence water quality across the catchment (such as the presence of multiple transfer systems and large dams, and variations in land and water use) would warrant the determination of level 3 RWQOs. Based on an assessment of the compliance to the RWQOs over the past three to five years, PO4, NH3, EC, E.coli and Al were identified as the major water quality variables which have the potential to impact on the downstream users and for which Source Management Objectives (SMOs) and water quality allocation, management and implementation plans for the urban and agricultural sectors will be required. This is especially evident in the middle Modder and lower Riet catchments as well as below the numerous small urban areas which occur throughout the catchment. Key factors which have been highlighted for consideration in the future management of water quality in these catchments include inter alia: the consideration of appropriate water quality models, the development and implementation of agricultural Best Management Practices (BMPs) and the improved management of Sewerage Treatment Works (STWs). In addition, Persistent Organic Pollutants (POPs) and metals such as Al, chromium and manganese have been identified as potential variables which may affect users and for which further investigations are required. In conclusion, the hypothesis that that “the characteristics of the Modder-Riet catchment were different enough to warrant the determination of level 3 RWQOs, where in the more impacted portions of the catchment, water quality stress would be evident and would require a number of source directed interventions” could be accepted. It was however also found that interventions to improve instream water quality should not only be based on Source Directed Controls (SDCs) in their strictest sense, but should also incorporate aspects of good governance and effective regulation. This includes improved co-ordination of water quality monitoring and data management and reporting, effective and sustained capacity building and community learning and the establishment of functional, multi-scale feedback mechanisms. The application of the principles of Strategic Adaptive Management (SAM) was also identified a key element in the future management of water quality in this catchment.

Franz Joseph Gall (1758–1828) viewed himself as a cutting-edge scientist, whose broad goals were to understand the mind and brain, and to be able to account for both group and individual behavioral traits in humans and animals. Starting in Vienna during the 1790s, he argued for many independent faculties of mind (e.g., music, calculation), ultimately settling on 27, with 8 being unique to humans. At the same time, he became the first person to provide evidence for cortical localization of function, the idea that the cerebral cortex is composed of specialized functional areas or organs, as he preferred to say. But although he utilized many acceptable methods in his multifaceted research program (e.g., dissections, studying people with brain damage, and observing behaviors over a lifetime), his doctrine was highly controversial from the start. For scientists and physicians, this was largely because he made cranioscopy his primary method, believing cranial bumps and depressions faithfully reflect the cortical organs and could be correlated with specific behaviors. In this book, Gall is shown to be a dedicated scientist with brilliant insights: a free-thinking naturalist of the mind and a visionary of the brain, yet a researcher with faults. Despite being frequently portrayed as a charlatan or comical figure, the authors also show how what others called his “phrenology” (a term he abhorred) helped shape the modern neurosciences and other disciplines. Maintaining that Gall’s impact deserves more recognition today, this book provides a fresh look at the man, his objectives, and his revolutionary doctrine.

AbstractLack of housing security is a major problem for rural migrant workers in China. This chapter explores the range and depth of housing problems facing rural migrants. These challenges include issues of affordability and poor housing quality and administrative barriers that inhibit access to commercial housing and housing welfare programmes. There is a big difference between the housing consumption pattern of migrant workers in the city and that in the countryside. This is due to large discrepancies in levels of access to good quality accommodation between migrants from rural areas and the established urban population. These inequalities are exacerbated by inherited forms of residential registration that adversely affect rural migrants settling in towns and cities. The situation is further exacerbated by land use regulations that restrict the construction of collective dormitories for rural migrant workers. The key is to promote the system reform of rural land and speed up the establishment of a free market homestead and rural housing. Policy responses over the past twenty years are evaluated, and recommendations for future policy development are proposed to improve housing conditions, including reform of land use regulations and improved property rights for migrants.

How is the word “immigration” defined? The Oxford English Dictionary states that “it is the action of entering into a country for the purpose of settling in it.” The definition conveys a sense of individual freedom. The settler arrives out of choice....

This chapter examines the novel A Free Life by Ha Jin in terms of (re) construction of Chinese Wen masculinity in a transnational context. The analysis suggests that while the story is mainly about the protagonist Nan’s journey to settle down in the U.S with his wife and son, the plot is parallel with another hidden thread that runs through it, which is his personal transformation from the loss of masculineness to the build-up of a new type of Wen masculinity. The analysis also finds out that the novel seems to use emasculation of the male characters as the signifier of the dark side of Chinese traditional culture and the current political system. Through depicting Nan’s struggle and success in settling down the novel embraces individualism as a remedy to Chinese masculinity, redefining the ideal of Wen Chinese intellectuals in American context.

Chapter 3 covers the years in which the Illinois state capital moved from Kaskaskia to Vandalia to Springfield, focusing on legislative and judicial debates surrounding the Black Code, which limited the rights of free blacks, and the euphemistic practices of indentured/involuntary servitude and apprenticeship contracts. As antislavery populations surged in northern Illinois, political and legal opinions about blacks shifted. The 1832 Black Hawk War, a land dispute involving the Sauk and Fox, led to the 1833 treaty that removed Native Americans from the state. The Illinois General Assembly, including in 1836–37 representatives Stephen Douglas and Abraham Lincoln, chartered state banks that failed; set up internal improvement schemes that indebted the state; and ultimately supported completion of the Illinois and Michigan Canal (1848).

After a second sojourn in Sierra Leone, where he continued his studies of the Qur’ān and Arabic, Rufino returns to Brazil. Before settling in Recife he spent some time in Rio de Janeiro and Bahia, from where he brought a teenaged son, Nicolau José. In Recife he settled on the Rua da Senzala Velha (Old Slave Quarters Street). Although a small community, the Yoruba-speaking popoulation of Recife were not an insignificant minority. They included slaves, freedmen, and free Africans, and some were Muslims like Rufino, while others practiced African and Afro-Brazilian religions. One of the Muslim Yoruba speakers was Mohammah Gardo Baquaqua, who arrived in Pernambuco in 1845.

Sometimes it is possible to deal productively with the subject matter of choosing and making decisions without actually settling upon any particular theory of choice. This is the case in the law of business organisations, which does not settle upon a theory of choice because it does not consider itself the ultimate decision maker. Rather, the law develops rules to allocate decision-making authority among the various parties. Utilising only a few basic principles of decision theory, the law of business organisation creates a structure for allocating decision-making responsibility on many different levels. However, it leaves the ultimate decision makers free not only to make substantive decisions for themselves but also to select from among the various theories of choice for doing so.

Complex networks are characterized by having a scale-free power-law (PL) degree distribution, a small world phenomenon, a high average clustering coefficient, and the emergence of community structure. Most proposed models did not incorporate all of these statistical properties and neglected incorporating the heterogeneous nature of network nodes. Even proposed heterogeneous complex network models were not generalized for different complex networks. We define a novel aspect of node-heterogeneity which is the node connection standard heterogeneity. We introduce our novel model “settling node adaptive model” SNAM which reflects this new nodes' heterogeneous aspect. SNAM was successful in preserving PL degree distribution, small world phenomenon and high clustering coefficient of complex networks. A modified version of SNAM shows the emergence of community structure. We prove using mathematical analysis that networks generated using SNAM have a PL degree distribution.

One of MacKinnon’s central claims is that pornography is not only words. Rather, pornographic speech subordinates and silences women. Using Austin’s speech act theory, Langton and Hornsby argue that pornographic speech has the power to silence women, thus depriving women of free speech rights. This silencing claim has attracted much philosophical interest over the past couple of decades. The chapter considers how we should understand the silencing claim by carefully dissecting the relevant literature. It further assesses the philosophical and practical tenability of the claim. The main philosophical lessons to arise from this chapter are as follows. First, even though some aspects of the silencing claim have pretheoretical plausibility, it remains to be established that pornographic speech is responsible for women’s silencing. Second, the silencing claim is often discussed by appealing to intuitive gut-feelings about specific cases. But (the chapter argues) this is not methodologically conducive to settling the matter.

The understanding of some physical phenomena involved in the transport of free particles such as fibers during injection processes is an important issue. To answer some of the questions arising in such problems, we study here numerically the quasi-steady kinematics of a free cylindrical solid particle moving in a Newtonian fluid confined between two parallel plane walls taking the hydrodynamic interactions into account. This is achieved by the use of the resistance matrix technique relating the kinematics of the particle to the forces and the torques exerted on the particle and to the dissipation induced by the motion of this particle. Our approach is confirmed by asymptotical developments and by a comparison with other authors in some cases. The solutions of three practical problems are given. In the first one, the sedimentation of the particle is studied. It is found that the maximum settling velocity of the free particle is obtained at a position off the symmetry plane. The cylinder is observed to rotate counter intuitively against the direction of rolling along the adjacent wall. Moreover the angular velocity has an influence on the settling velocity when the concentration is very high. The second problem concerns the transport of a neutrally buoyant cylindrical particle in a Poiseuille flow. This study reveals that there are relative translational and angular velocities between the free particle and the undisturbed fluid particle contrary to the commonly admitted hypothesis used in several models and numerical codes. Finally the third problem is a combination of the two previous situations: the transport of a non-neutrally buoyant particle in a Poiseuille flow. Depending on the ratio of the buoyancy forces to the viscous ones, different solutions are possible and exposed. Other problems can also be solved with this approach which is less time-consuming than complex methods such as DNS.

Abstract Many species of spiders move from one location to another using a remarkable aerial dispersal “ballooning”. By ballooning, spiders can reach distances as far as 3200 km and heights of up to 5 km. Though a large number of observations of spider ballooning have been reported, it remains a mysterious phenomenon due to the limited scientific observation of spider ballooning in the field, high uncertainties of the meteorological conditions and insufficient controlled laboratory experiments. Most of the ballooning spiders are spiderlings and spiders under 3 mm in length and 0.2 to 2 mg in mass with a few exceptions of large spiders (over 3 mm in length, over 5 mg in mass). What physical mechanism dominates the three stages of spider ballooning — take-off, flight, and settling? Many factors have been identified to influence the physical mechanism, including a spider’s mass, morphology, posture, the silken dragline properties, and local meteorological conditions (e.g., turbulence level, temperature and humidity). A thorough understanding of the roles of key parameters is not only of ecological significance but also critical to advanced bio-inspired technologies of airborne robotic devices. This work aims to determine how the dragline length and spider mass affect the interaction of the spider-dragline system in the free-fall scenario. Experiments using a thread of different lengths and a sphere of different masses to mimic the spider-dragline were carried out. The first sets of tests focused on the spider-dragline system, rather than the fluid flow. High-speed images of a spider-dragline falling in a closed container of air were recorded with 1500 frames per second at Reynolds numbers of several thousand, based on the spider dragline and the local relative velocity. Image data allow for tracking the vertical velocities and acceleration of the spider-dragline, as well as the drag force acting on the spider-dragline. Terminal velocities in the settling stage are compared with estimates using various fluid dynamics models in previous work. Such results under controlled laboratory conditions are expected to shed lights on the intriguing flow physics of spider ballooning at the settling stage and to inform future experiments and numerical models.

Abstract Drilling and completion fluids (muds) are complex suspensions that typically contain weight material (such as barite) to increase the density, and clay particles to increase the viscosity and provide yield stress. In a static column of fluid, barite will inevitably settle. The density of the mud column gradually increases, from free fluid at the top to a compact, and possible gas tight solid at the bottom. The separation mechanism into different phases is complex, thus detailed, systematic fluid experiments is needed to fully understand the properties of settled barite. Wave velocity, commonly used to determine the condition of the borehole (and annulus), could be used to characterize, and possibly identify the different sediment phases in a mud column. The current study investigates the evolution of acoustic wave velocity during compaction/gravity separation of mud. A laboratory setup which allows for a controlled drainage of fluid was used to resemble the sedimentation process. The study was performed on three drilling fluids: two synthetic and one commercial polymer, and three compacted barite samples using two test procedures. The first procedure focuses on investigating acoustic properties during settling. The second procedure was used to investigate the behavior of compacted barite. The result shows a decrease in the wave velocity during settling, whereas increase in the wave velocity in consolidated barite with compaction. The increase or decrease of velocity with compaction can be explained by the relative changes of modulus/stiffness and density of the studied material.

Abstract A stable cement slurry is critical to the success of a cementing job, from cement placement to long-term zonal isolation. Conventional anti-settling (AS) additives, such as clays and polysaccharides, are commonly applied to improve cement slurry stability, but they are only effective for low-to-mid temperature applications (up to 260°F) due to high temperature thermal thinning effects or thermal degradation. To compensate for such thermal thinning or thermal degradation effects, higher doses of AS additives are often applied, which inadvertently increase slurry placement difficulty with minimal improvement to slurry stability. This paper presents the performance of a novel, thermally activated, free-flowing, and easy-to-use temperature-triggered anti-settling (TTAS) agent that can help reduce the overall AS additive usage, prevent solids settling, and mitigate the formation of free fluid at 200-350°F or higher while having minimal effect on slurry rheology prior to activation. The performance of this novel TTAS agent was evaluated against conventional AS additives, including bentonite clay, diutan gum, and a commercial AS product in 16-lbm/gal and 18-lbm/gal Class H cement slurries. Static sedimentation (SS) and dynamic sedimentation (DS) tests revealed that the conventional AS agent-containing slurries exhibited mixability concerns, noticeable settling at downhole condition and gelation tendency. By contrast, the TTAS agent-containing slurries exhibited good mixability, no adverse effect on rheology at 80°F, and improved slurry stability, evidenced by less than ½ inch cone height and less than 1-lbm/gal differential density (Δρ) in dynamic sedimentation test using as low as 0.3% bwoc dosage.

Research being undertaken at the University of Leeds, as part of the DIAMOND university consortium, is exploring the effectiveness of various ultrasonic technologies as in situ probes to characterize and monitor nuclear waste slurries, such as the ‘Legacy’ Magnesium hydroxide sludges found in Sellafield, U.K. Through use of a commercial Acoustic Backscatter Sensor (ABS) with 1–5 MHz transducers, various properties of free-settling oxide simulant sludges were determined. Work was focused upon characterizing essentially ‘static’ sludges (to give prospective use as tools for the wastes in current deposits); although, the sensors also have potential as dispersion monitors during any future processing and storage of the Legacy wastes, as well as many other storage, clarifier or thickener systems across a wide range of industrial processing operations. ABS data of mixed glass powder dispersions was analysed and compared to scattering theory, to understand the correlations between acoustic attenuation and particulate concentration. The ABS was also calibrated to measure changes in average particulate concentration within a settling suspension over time, and showed the depth-wise segregation of the dispersion through the settling column at different particular time intervals. It was found that observed hindered settling also led to an increase in particulate concentration over the sludge zone and significant segregation occurred at moderate time intervals, due to the broad size distribution of the aggregates measured. It is hoped in future that these sensors may be able to be fitted to robotic handlers that have been installed onsite (and previously used for sampling), allowing fully automatic in situ sludge analysis.