10 research outputs found
Predictive control based on black-box state-space models
No full textElectrical Engineering, Mathematics and Computer Scienc
A numerical study of the effect of graphene nanoparticle size on brownian displacement, thermophoresis, and thermal performance of graphene/water nanofluid by molecular dynamics simulation
No full textBrownian motion, often known as BM, is an inherent characteristic of minute particles suspended in a fluid. It plays an important role in several physical and chemical processes. Thermophoresis refers to the process where particles in a fluid are carried along with a gradient in temperature (Temp). This feature has significant importance in several applications, including microfluidics, thermal control, and energy conversion. Through the examination of the thermophoresis phenomenon in water/graphene nanofluid (NF), researchers might get valuable knowledge on the potential uses of these materials. The current study examined the effect of various sizes of graphene nanoparticles (NPs) (5, 6, 9, and 10 Å) on the thermal behavior (TB), BM, and thermophoresis of water/graphene NF using molecular dynamics (MD) simulation. This study reported the changes in heat flux (HF), thermal conductivity (TC), average Brownian displacement (BD), and thermophoresis. It is concluded that by increasing the size of graphene NPs from 5 to 10 Å, the average BD and thermophoresis increased from 3.06 Å and 23.88 Å to 4.16 Å and 31.46 Å, respectively. Due to their higher kinetic energy (KE) and momentum, larger graphene NPs experienced more BM, enabling them to withstand random thermal fluctuations more effectively than smaller particles. In addition, as the size of graphene NPs increased, the HF and TC values increased from 39.54 W/m2 and 0.36 W/(m.K) to 47.19 W/m2 and 0.51 W/(m.K) after 10 ns. Therefore, the size-dependent changes in BD and thermophoretic effects led to a simultaneous increase in HF and TC of the NF, which was attributed to the larger heat transfer (HT) surface area, improved HT properties, and synergistic effects of larger graphene NPs. The maximum (Max) temperature increases from 1415 K to 1504 K. These findings were useful in a variety of industries, particularly for improving TB in different NFs. © 2024 The Author(s
Maximum allowable pressures during horizontal directional drillings focused on sand
No full textHorizontal directional drilling (HOD) is a rather simple installation technique for pipes for public infrastructure and it has therefore become increasingly popular. When HOD is started, a pilot drilling is made first; a small borehole is made in the soil along the trajectory. After the pilot drilling the borehole is enlarged with a reamer until the designed diameter is obtained and the product pipe is pulled in. Drilling fluid or mud is used for the stability of the borehole and to transport the excavated soil. A certain minimum mud pressure is needed to ensure a return flow and to ensure that the borehole does not collapse. In order to prevent soil failure, it is necessary that the pressure will not exceed a certain maximum. At present in the Netherlands and also abroad, in order to compute the maximum allowable mud pressures, it is assumed that the cavity expansion theory applies in the borehole at greater depth. The equations to calculate this pressure were first presented by Luger and Hergarden (L&H, 19881. This theory assumes plastic deformations, which lead to failure. However, recent research has shown that soil failure due to hydraulic fracturing is an important failure mechanism also. In the framework of BTL (Boren Tunnels & Leidingen) research was done to look at whether hydraulic fracturing was observed before in the context of liquid injection in softer soils like clay. The process of hydraulic fracturing in soil with cohesion (clay) was recognised in literature indeed and models were developed. However no literature was found on hydraulic fracturing in soils without cohesion (sand). This thesis research was done to improve the knowledge of the behaviour of sand and bentonite around a borehole in order to better determine the soil failure process under maximum pressures. New soil models to describe soil behaviour were developed for a cylindrical and a spherical cavity under fluid pressure. The soil model for a cylindrical cavity is comparable to the soil model at the basis of the equations derived by L&H. The soil models assume; \u95 the medium to be homogeneous and isotropic, \u95 to have infinite dimensions (gravity neglected) and therefore prior to the application of the load the entire soil mass has an isotropic effective stress, \u95 the soil behaves in the plastic zone as a compressible plastic solid, defined by Mohr-Coulomb shear strength parameters Ie, <pl. Beyond the plastic zone the soil is assumed to behave as a linearly elastic, isotropic solid defined by a modulus of deformation (E) and a Poisson's ratio (v). Next to that, in the derived models for this thesis it is possible to take dilatancy into account. It was tried to introduce failure and especially hydraulic fracturing into these 'new' models. The introduction of the criterion of a maximum strain instead of a maximum radius of plasticity (L&H) seems to satisfy better the results found in the mentioned BTL-experiments. However it is difficult to draw absolute conclusions as the model is not a full representation of the reality due to; \u95 the assumptions made for the soil model, \u95 the parameters that are used for calculation are difficult to determine, showing wide ranges of variation, \u95 stratified soil can not be introduced. It is therefore recommended to use the equations with a lot of precaution.Geo-EngineeringGeotechnologyCivil Engineering and Geoscience
Fundamental Electromagnetic Configuration for generating One-directional Magnetic Field Gradients
No full textIn this article, electromagnet layouts are presented, which generate a magnetic field with a magnitude gradient that does not vary significantly in a horizontal plane but decreases monotonically with the vertical height above the magnet. Such a one-direction magnetic field gradient is a specific requirement for magnetic density separation (MDS), a novel recycling technology that combines a vertical magnetic field gradient with a ferrofluid to separate a mixture of non-magnetic materials based on their mass density. We are assembling the first superconducting magnet to be used for this application. In contrast to other separation technologies that use ferrofluid, multiple products can be separated in a single process step. First, the idealized current distribution is introduced that produces such a magnetic field with a magnitude that decays only in one direction. This ideal field can be approximated with practical coil configurations, which are evaluated with a Fourier analysis to derive an optimal cross-sectional layout based on flat racetrack coils. The analysis concludes with a discussion of the effect of winding pack thickness on the value of the magnetic field above the magnet system and the peak field inside the winding pack. The conclusions of this study are applicable not just for MDS but for any application that requires a magnetic field gradient that changes only in one direction
An interpolation strategy for discrete-time bilinear MPC problems
No full textInput-output (I-O) feedback linearization suffers from a number of restrictions which have limited its use in model-based predictive control. Some of these restrictions do not apply to the case of bilinear systems, but problems with input constraints and unstable zero dynamics persist. The present note overcomes these difficulties by means of an interpolation strategy. Involved in this interpolation is a feasible and stabilizing trajectory, which is computed through the use of invariant feasible sets, and a more aggressive trajectory, which can be chosen to be either the unconstrained optimal trajectory or any alternative one
Two-phase analysis of heat transfer of nanofluid flow in a wavy channel heat exchanger: A numerical approach
No full textThe heat transfer improvement by using CuO/water nanofluid (NF) in a wavy channel is evaluated numerically using the turbulent two-phase mixture and the κ - ε models. The numerical work is a 2-dimensional model created and analyzed in Gambit and Ansys Fluent software, respectively. The flow Reynolds (Re) numbers of 8000 – 40,000, wavelength ranging from 0 – 0.4 m, and solid volume fraction (SVF) of 0 % to 4 % are investigated. In all cases, a constant heat flux of q′′=5000 W/m2 is applied on the outer surface of the heat exchanger. The heat transfer and fluid flow were analyzed by the flow visualization method and heat transfer evaluation indexes. The results show that by increasing the Re number, the vortices increase and more turbulence are generated in the vicinity of the waves near the channel inlet. As the amplitude of the channel waves increased, the velocity at the top of the wave increased, and the resulting pressure gradient behind the wave is intensified and the reverse flow is generated. The improving effect of using NF is more prominent where the effect of other enhancing factors is weak. For wall amplitude of 0.1 m, by increasing the SVF from 1 – 4 % the average Nu number (Nuavg) increased by 35 % and 22 % in Re = 8,000 and 40,000, respectively
Optimum Coil-System Layout for Magnet-Driven Superconducting Magnetic Density Separation
No full textThis article discusses the optimum layout of coils of a superconducting magnet system for magnetic density separation (MDS). MDS is a novel separation technology that combines a vertical magnetic field gradient with a ferrofluid to separate mixtures of non-magnetic particles based on their mass density. The MDS process can separate more than two types of particles in a single process step, thereby distinguishing it from other separation techniques using a ferrofluid. The authors are currently constructing a superconducting MDS demonstrator. Ideally, the gradient of the magnetic field magnitude should change only with the distance above the magnet but remain constant in a horizontal plane. In principle, such an ideal field profile can be generated with an infinite harmonic sheet current. In practice, edge effects appear due to the necessity of using a finite number of coils. These cause a horizontal component in the field gradient and also change the vertical component. We compare the vertical magnetic field gradient of various coil layouts to see which configuration performs best. To facilitate ease of production, the analysis is restricted to flat racetrack coils. The main result is that the specific shape of a racetrack coil has a larger influence on the vertical gradient than the number of coils. The feed particles need to be pushed through the separation chamber from the insertion to the collection point. One option to realize this is to use an MDS setup in which the magnet is inclined with respect to the horizontal plane. This tilting results in a horizontal magnetic force component, which drives feed particles through the fluid bed. We show that a three-coil layout provides the largest usable fluid bed depth for a wide range of tilt angles
Modeling and Characterization of a ReBCO HTS Degaussing Demonstrator
No full textThe magnetic modelling and experimental validation of a superconducting degaussing system for maritime vessels is discussed. Degaussing coils compensate for the distortion in the earths' magnetic field by the magnetized steel hull of a ship, thus rendering it 'invisible' for magnetic field sensors. Whereas typical power requirements with copper coils are of the order of 100 kW, a ReBCO HTS degaussing system in principle allows to reduce this by an order of magnitude. In order to validate such efficiency estimates and to demonstrate the required hardware, a table-top test setup was realized with magnetic ship steel. The vessel-imitating cylindrical demonstrator is equipped with six degaussing coils, grouped in three sets that act in two different directions, with each set consisting of one copper and one ReBCO coil, the latter one equipped with a sub-cooled forced-flow liquid nitrogen system. Static magnetic field measurements are reported and compared to both analytical and numeric finite element models. The results illustrate how even relatively simple analytical models can be used as a powerful tool to extrapolate design parameters and thus to predict the power requirements of large-scale degaussing systems.DC systems, Energy conversion & Storag
Bioavailability and biodistribution of differently charged polystyrene nanoparticles upon oral exposure in rats
No full textThe likelihood of oral exposure to nanoparticles (NPs) is increasing, and it is necessary to evaluate the oral bioavailability of NPs. In vitro approaches could help reducing animal studies, but validation against in vivo studies is essential. Previously, we assessed the translocation of 50 nm polystyrene NPs of different charges (neutral, positive and negative) using a Caco-2/HT29-MTX in vitro intestinal translocation model. The NPs translocated in a surface charge-dependent manner. The present study aimed to validate this in vitro intestinal model by an in vivo study. For this, rats were orally exposed to a single dose of these polystyrene NPs and the uptake in organs was determined. A negatively charged NP was taken up more than other NPs, with the highest amounts in kidney (37.4 µg/g tissue), heart (52.8 µg/g tissue), stomach wall (98.3 µg/g tissue) and small intestinal wall (94.4 µg/g tissue). This partly confirms our in vitro findings, where the same NPs translocated to the highest extent. The estimated bioavailability of different types of NPs ranged from 0.2 to 1.7 % in vivo, which was much lower than in vitro (1.6–12.3 %). Therefore, the integrated in vitro model cannot be used for a direct prediction of the bioavailability of orally administered NPs. However, the model can be used for prioritizing NPs before further in vivo testing for risk assessment. © 2015, The Author(s)
The Concept of Vacant Possession: Theory and Practice
No full textAbstract
To the everyday man or woman on the street, the term 'vacant possession' raises its head most noticeably in the residential sphere, with many everyday people buying and selling property and being obliged to give, or entitled to receive, vacant possession. Furthermore, the term is by no means limited to a 'lay' usage: a wide range of business and professional people use the expression 'vacant possession' on a daily basis, and the term is in the lexicography of judges, conveyancers, litigators, surveyors, estate agents, commentators and others connected to property, including property owning landlords and tenants. All these stakeholders make use of the term in a formal and professional sense, and with reference to legal transactions for which vacant possession is an essential element.
Although it is an everyday term that is used by many, a common feature of these usages of the term is a lack of attention to what it actually means. For example, estate agents, who invariably use the term in their advertising particulars, seem able to distinguish between 'full vacant possession', 'immediate vacant possession' or 'complete vacant possession', with ostensibly no real justification as to how the prefacing adjective in each case adds anything to the message that they are seeking to convey to prospective purchasers, as to what they can expect to obtain on completion. Lawyers talk about 'giving VP on completion', but few documents ever actually define what vacant possession means with a capitalised 'V' and 'P'. Furthermore, the courts have made decisions as to whether vacant possession was or was not given in a particular instance, but rarely found it necessary to explain what the term actually meant, or sought to explicitly apply an understanding of the concept to the facts of any particular case.
Indeed, behind the familiarity of this common expression, lie years of uncertainty, misunderstanding and general neglect of the development of a sound and coherent theoretical model of vacant possession. There is very little case law and even less judicial guidance available. In 1988, and in two editions of the Conveyancer and Property Lawyer, Charles Harpum wrote what probably remains the most insightful learned article on the subject, but since then the concept appears to have warranted very little scholarly or practitioner attention.
This thesis explores the concept of vacant possession and its meaning. Expounding the inconsistent evolution and development of the concept, the thesis explains the constituent elements of the concept of vacant possession, along with the practical manifestation of the term in everyday property cases. In doing so, it highlights the difficulties that lawyers, surveyors, judges and other third parties face on a day-to-day basis when seeking to interpret the nature, scope and extent of the obligation. Further, to link this work to wider theoretical debate in literature pertaining to possession, the thesis draws on other common property law concepts, those of actual occupation and adverse possession; such a discussion helps to explain why the inherently infra-jural concept of vacant possession cannot be 'tied down' to a precise legal definition or formulation.
In conclusion, and to facilitate understanding and usage of the term, the thesis draws on the analysis undertaken to promulgate a working articulation of the concept, and considers other provisions that can ameliorate the remedial entitlements for an injured party in the event of a breach of the obligation. These may go some way to assist all those who will encounter the concept in future legal transactions
