A numerical and experimental study on cavitation in positive displacement pumps and its application in valve design optimization

Appendix of "Technical sheets and drawings" appears in the online version only.This thesis was previously held under moratorium from 26/11/2015 to 15/06/2021.A comprehensive and transient Computational Fluid Dynamic model of a Positive Displacement reciprocating pump in cavitating condition was developed in order to study the main features and the causes of cavitation in this kind of device. Several sensitivity analyses were also carried out in order to identify the most influential parameters on cavitation; the design of the inlet valve as well as the operating conditions were found to be the main parameters playing an important role in cavitation. To complete the numerical study, a sensitivity analysis on the air content in the water was carried out.;This highlighted the importance of the physical properties of the working liquid in influencing the vapour generation during cavitation. The second part of the project was dedicated to the experimental analysis; a test rig replicating the numerical model was designed and built. The experimental tests were carried out and the results were compared to the numerical data obtained in the previous part. The comparison revealed a reasonable accuracy as well as good consistency although numerical problems were found in the way the cavitation model accounted for the influence of the air dissolved in the water which was overestimated. The validated numerical model was utilised to modify the design of the inlet valve.;A new model of the valve was presented and described, it was demonstrated capable of minimising the vapour generation under the same operating condition with respect to the initial valve design. The modification proposed was implemented in the design of new valves which are already being manufactured and tested in the field, they will be introduced into the market afterwards. The project is the demonstration that numerical tools based on CFD are nowadays ready to effectively support designers and industries in bringing down the cost of the engineering process of new and more efficient products.A comprehensive and transient Computational Fluid Dynamic model of a Positive Displacement reciprocating pump in cavitating condition was developed in order to study the main features and the causes of cavitation in this kind of device. Several sensitivity analyses were also carried out in order to identify the most influential parameters on cavitation; the design of the inlet valve as well as the operating conditions were found to be the main parameters playing an important role in cavitation. To complete the numerical study, a sensitivity analysis on the air content in the water was carried out.;This highlighted the importance of the physical properties of the working liquid in influencing the vapour generation during cavitation. The second part of the project was dedicated to the experimental analysis; a test rig replicating the numerical model was designed and built. The experimental tests were carried out and the results were compared to the numerical data obtained in the previous part. The comparison revealed a reasonable accuracy as well as good consistency although numerical problems were found in the way the cavitation model accounted for the influence of the air dissolved in the water which was overestimated. The validated numerical model was utilised to modify the design of the inlet valve.;A new model of the valve was presented and described, it was demonstrated capable of minimising the vapour generation under the same operating condition with respect to the initial valve design. The modification proposed was implemented in the design of new valves which are already being manufactured and tested in the field, they will be introduced into the market afterwards. The project is the demonstration that numerical tools based on CFD are nowadays ready to effectively support designers and industries in bringing down the cost of the engineering process of new and more efficient products

Reorganisation of sensorimotor function in children with brain disease

Introduction: In this study, paradigms were developed for the investigation of sensorimotor function in children using functional MRI (fMRI), somatosensory evoked potential (SEP) recordings and behavioural measures. These techniques were applied both to normal controls subjects and to children with brain disease. A major aim was to investigate the remarkable recovery of function that can take place following brain injury sustained early in life. Methods: Three fMRI paradigms were developed, namely active movement of the hand, passive flexion/extension movement of the fingers and median nerve stimulation. In addition, SEPs of functional cortical responses to stimulation of the median nerve were recorded at high temporal resolution. Finally, the extent of residual or recovered sensory and motor hand function was assessed using behavioural tests, including grip strength and double simultaneous stimulation. In one set of investigations, all three techniques were applied to children following hemispherectomy or children following vascular damage to the middle cerebral artery territory, to examine the pattern of residual sensorimotor function following brain injury. In a second study, fMRI was carried out in pre-surgical paediatric patients for mapping of the sensorimotor cortex in preparation for surgical resection of lesions in the vicinity of this cortical region. Results and Discussion: fMRI was successful in locating the hand cortical sensorimotor area in 11 out of 12 paediatric patients pre-operatively, and was of value to the neurosurgeon in helping to delineate the boundaries of subsequent cortical resection. In patients following stroke and hemispherectomy, a combination of fMRI, SEP and behavioural techniques provided evidence for inter-hemispheric reorganisation of sensorimotor function through ipsilateral sensorimotor pathways, and also suggested an increase in the involvement of ipsilateral secondary sensorimotor areas. The data also indicate that cortical sensorimotor reorganisation and functional recovery can be seen in patient both with congenital disease and with late-onset acquired disease, suggesting that factors additional to age at injury may influence the degree of residual function resulting from cerebral reorganisation. Informed consent was obtained for all patients and controls, and the study was approved by the Great Ormond Street Hospital for Children/Institute of Child Health Research Ethics Committee

Design of Electric Motors for a Hybrid Farming Tractor

In questa tesi viene presentato uno studio di fattibilità per l'elettrificazione del powertrain di un trattore agricolo da campo aperto. In particolare il lavoro di tesi si focalizza sul dimensionamento di tre motori SPM tramite il metodo della coppia termica equivalente. Una dettagliata analisi elettromagnetica è stata condotta per valuatare le prestazioni. Il comportamento termico è stato analizzato sia a regime sia in transitorio durante reali cicli di lavoro.ope

Pumps and water lifters for rural development

CER76-77ADW-JFR-EVR61.Includes bibliographical references (pages 167-178).June 1977

Simultaneous measurements of kinematics and fMRI: compatibility assessment and case report on recovery evaluation of one stroke patient

<p>Abstract</p> <p>Background</p> <p>Correlating the features of the actual executed movement with the associated cortical activations can enhance the reliability of the functional Magnetic Resonance Imaging (fMRI) data interpretation. This is crucial for longitudinal evaluation of motor recovery in neurological patients and for investigating detailed mutual interactions between activation maps and movement parameters.</p> <p>Therefore, we have explored a new set-up combining fMRI with an optoelectronic motion capture system, which provides a multi-parameter quantification of the performed motor task.</p> <p>Methods</p> <p>The cameras of the motion system were mounted inside the MR room and passive markers were placed on the subject skin, without any risk or encumbrance. The versatile set-up allows 3-dimensional multi-segment acquisitions including recording of possible mirror movements, and it guarantees a high inter-sessions repeatability.</p> <p>We demonstrated the integrated set-up reliability through compatibility tests. Then, an fMRI block-design protocol combined with kinematic recordings was tested on a healthy volunteer performing finger tapping and ankle dorsal- plantar-flexion. A preliminary assessment of clinical applicability and perspectives was carried out by pre- and post rehabilitation acquisitions on a hemiparetic patient performing ankle dorsal- plantar-flexion. For all sessions, the proposed method integrating kinematic data into the model design was compared with the standard analysis.</p> <p>Results</p> <p>Phantom acquisitions demonstrated the not-compromised image quality. Healthy subject sessions showed the protocols feasibility and the model reliability with the kinematic regressor. The patient results showed that brain activation maps were more consistent when the images analysis included in the regression model, besides the stimuli, the kinematic regressor quantifying the actual executed movement (movement timing and amplitude), proving a significant model improvement. Moreover, concerning motor recovery evaluation, after one rehabilitation month, a greater cortical area was activated during exercise, in contrast to the usual focalization associated with functional recovery. Indeed, the availability of kinematics data allows to correlate this wider area with a higher frequency and a larger amplitude of movement.</p> <p>Conclusions</p> <p>The kinematic acquisitions resulted to be reliable and versatile to enrich the fMRI images information and therefore the evaluation of motor recovery in neurological patients where large differences between required and performed motion can be expected.</p

Design of High Efficiency Brushless Permanent Magnet Machines and Driver System

The dissertation is concerned with the design of high-efficiency permanent magnet synchronous machinery and the control system. The dissertation first talks about the basic concept of the permanent magnet synchronous motor (PMSM) design and the mathematics design model of the advanced design method. The advantage of the design method is that it can increase the high load capacity at no cost of increasing the total machine size. After that, the control method of the PMSM and Permanent magnet synchronous generator (PMSG) is introduced. The design, simulation, and test of a permanent magnet brushless DC (BLDC) motor for electric impact wrench and new mechanical structure are first presented based on the design method. Finite element analysis based on the Maxwell 2D is built to optimize the design and the control board is designed using Altium Designer. Both the motor and control board have been fabricated and tested to verify the design. The electrical and mechanical design are combined, and it provides an analytical IPMBLDC design method and an innovative and reasonable mechanical dynamical calculation method for the impact wrench system, which can be used in whole system design of other functional electric tools. A 2kw high-efficiency alternator system and its control board system are also designed, analyzed and fabricated applying to the truck auxiliary power unit (APU). The alternator system has two stages. The first stage is that the alternator three-phase outputs are connected to the three-phase active rectifier to get 48V DC. An advanced Sliding Mode Observer (SMO) is used to get an alternator position. The buck is used for the second stage to get 14V DC output. The whole system efficiency is much higher than the traditional system using induction motor

Improving high-speed electrical machines by amorphous metals

This dissertation is about the application of an amorphous magnetic material (AMM) to a sleeve-free interior permanent-magnet (PM) rotor of high-speed synchronous motors. Currently, surface-mounted PM rotors are commonly used in the high-speed motors. In order to protect the high-speed rotors from centrifugal forces, high-strength non-ferromagnetic sleeves are required. This results in a reduced torque density, lowered flux-weakening ability, and highen losses of the motor caused by pulse-width-modulation (PWM) voltage. Hence, a sleeve-free rotor structure is beneficial. AMM has been used for transformers and inductors for decades. It is well-known due to its low core losses. However, because of its high hardness and brittleness, slotting becomes a key obstacle to its application in electrical machines. Hence, this material has not been widely applied in the electrical machines yet. An important property, the high mechanical strength of the AMM has been ignored eagerly. In this work, an interior PM rotor made from AMM for high-speed operation is studied. The high mechanical strength and the low core losses of the AMM are fully taken use of. Because of the difficulty in slotting of the AMM, this material is not used for the stator and a conventional silicon steel will be used. In order to fulfill the proposed high-speed rotor, the properties of the AMM in terms of electromagnetics and mechanics are experimentally studied. The influences of the mechanical stress and temperature on the electromagnetic properties of the AMM cores are well studied. Based on the measured data, a prototype is designed and optimized in terms of electromagnetics, mechanics and thermal behaviors. To ensure the success of the prototype, the slotting methods are also investigated and wire electrical discharge machining method is selected for manufacturing of the AMM rotor core. In order to show the advantages and disadvantages of the proposed high-speed AMM rotor, a surface-mounted PM rotor covered by a carbon-fiber sleeve is designed as a comparison. Since the influences of the PWM inverter on the losses of the high-speed motors are significant and this problem has not been thoroughly investigated before, the dissertation goes into a further research on it to fill the gap in this field. Finally, two prototypes are built and tested. The design results are verified through experiments. It is verified that by applying the AMM to the proposed rotor, the performance of the high-speed PM motor is significantly improved, such as better flux weaking ability, higher torque and power densities and higher efficiency. Based on the tested data of the prototypes, it is confirmed that the AMM has high potential in the application of high-speed high-power-density PM motors

Brain Microstructure: Impact of the Permeability on Diffusion MRI

Diffusion Magnetic Resonance Imaging (dMRI) enables a non invasive in-vivo characterization of the brain tissue. The disentanglement of each microstructural property reflected on the total dMRI signal is one of the hottest topics in the field. The dMRI reconstruction techniques ground on assumptions on the signal model and consider the neurons axons as impermeable cylinders. Nevertheless, interactions with the environment is characteristic of the biological life and diffusional water exchange takes place through cell membranes. Myelin wraps axons with multiple layers constitute a barrier modulating exchange between the axon and the extracellular tissue. Due to the short transverse relaxation time (T2) of water trapped between sheets, myelin contribution to the diffusion signal is often neglected. This thesis aims to explore how the exchange influences the dMRI signal and how this can be informative on myelin structure. We also aimed to explore how recent dMRI signal reconstruction techniques could be applied in clinics proposing a strategy for investigating the potential as biomarkers of the derived tissue descriptors. The first goal of the thesis was addressed performing Monte Carlo simulations of a system with three compartments: intra-axonal, spiraling myelin and extra-axonal. The experiments showed that the exchange time between intra- and extra-axonal compartments was on the sub-second level (and thus possibly observable) for geometries with small axon diameter and low number of wraps such as in the infant brain and in demyelinating diseases. The second goal of the thesis was reached by assessing the indices derived from three dimensional simple harmonics oscillator-based reconstruction and estimation (3D-SHORE) in stroke disease. The tract-based analysis involving motor networks and the region-based analysis in grey matter (GM) were performed. 3D-SHORE indices proved to be sensitive to plasticity in both white matter (WM) and GM, highlighting their viability as biomarkers in ischemic stroke. The overall study could be considered the starting point for a future investigation of the interdependence of different phenomena like exchange and relaxation related to the established dMRI indices. This is valuable for the accurate dMRI data interpretation in heterogeneous tissues and different physiological conditions