1,721,225 research outputs found
Modelling and computation of drops and bubbles in turbulence
No full textExistence of drops and bubbles in turbulence is granted by their interface. Interfaces are a macroscopic perception of molecular properties, are not property of the drop or the carrier fluid and their role is enormously important in a number of environmental and industrial processes: it is across interfaces that momentum, heat and mass transfer fluxes occur. In this talk, We will briefly review the physics modelling and the current computational methodologies used to track interfaces and we will focus on the phase-field approach, in which the phase distribution is a field described by the order parameter φ. We will present several flow instances and phenomena in which surface tension, density and viscosity are varied, and we will also cover the role of surfactants in altering topological changes of drops (breakage and coalescence) in connection with the characteristics of turbulence. Finally, we will examine the heat transfer between a dispersed phase of large deformable drops and a carrier fluid focusing on the flow structure inside the drops
Distributed Controller for the Parallel Operation of Power Converters with Small Output Filters
No full textAbsolute Two-tracked Optical Rotary Encoders Based on Vernier Method
Full text linkDriving synchronous machines requires early and accurate knowledge of the absolute position of the rotor; current solutions based on resolvers, sin-cos or absolute encoders are complex, bulky and costly. Hence, in this work two variants of absolute rotary encoder based on Vernier method are analyzed. One, already discussed in the literature, displays the Vernier scale across the whole circumference (full-Vernier), the other shows half Vernier traces over the entire perimeter (half-Vernier), which is an original feature. Both implementations are characterized by only two tracks and as many sensors: the proposed conditioning algorithms provide the absolute angular position as a function of the time delays between the wave edges generated by the two traces, thus being of easy implementation on low-cost MCUs. The Vernier encoders are also compared with state-of-the-art absolute and relative solutions, i.e. incremental, binary and Gray-code encoders. Experimental tests are carried out to assess the accuracy of the proposed sensors. The investigation shows that (i) the full-Vernier cannot provide, in practice, a reliable estimate of the direction of rotation and of the actual angular sector without resorting to a third sensor; (ii) the half-Vernier produces a trusty measurement of the absolute angle and velocity and (iii) can give a reliable position result with less than 30° shaft turn, but (iv) it can suffer from marginal performance degradation at low velocities in conjunction with high accelerations. Compared to the Gray encoder, the half-Vernier provides a simpler and more compact hardware for a given resolution, similar to that of an incremental encoder, at the expense of a small accuracy reduction at low speed
Model-based simulation of dynamic behaviour of electric powertrains and their limitation induced by battery current saturation
No full textThe wide-spread e-mobility revolution is asking for new software solutions capable of providing meaningful information not only for the mechanical part of the vehicle architecture, as in the past, but also for novel electric and hybrid driveline components. The objective of the paper is to provide a lightweight model for a fully electric vehicle powertrain, trying to assess the current constraints imposed by the battery to the whole driveline, and able to reflect this limitation throughout the transmission line, down to the electric motor and thus to the performance of the full vehicle. The model is suitable for real-time performances thanks to the effective computation of the powertrain via analytical solutions. Moreover, the whole system has been modelled following a model-based approach in Modelica language and is made part of the Altair activate car real-time library, in which both the electrical and mechanical parts integrate smoothly
Fluid Mechanics for Mechanical Engineers
No full textThis textbook describes the fundamentals of the phenomena of fluid dynamics in the context of engineering instances. It is designed to replace introductory books and notes on the subject for first-level engineering courses as well as higher-level courses or for professional use. The use of this book requires the basic knowledge of mathematics and physics normally delivered in the early years of undergraduate study. However, the extensive use of examples and solved exercises proposes a parallel intuitive route to understanding the necessary mathematical formalisms. It proves that a new fluid dynamics text should not contain new ideas or formalisms, but should present the material in a modern and intuitive way. The approach chosen is primarily practical, so that that readers can practice by solving the proposed problems and examples in order to be prepared to solve the new problems they will encounter in their academic and professional activities. It serves as a teaching tool for courses in basic fluid dynamics, advanced fluid dynamics, turbulence, and aerodynamics
Reliability Study on Front-end Capacitors in Boost PFC Architectures
No full textSingle-phase line rectifiers usually implement a PFC front-end to reduce the input current distortion; Power factor correction is often implemented using a boost converter. This topology demands bulky electrolytic capacitors necessary to achieve unity power factor and low output voltage ripple while maintaining restrained volumes, thereby reducing system lifetime since electrolytic capacitor is one of the main causes of failure in power electronics. An alternative control of the PFC boost converter allows reducing the required capacitance and enables the electrolytic capacitor substitution with a long-life low-ESR film one, reaching high power factor and low output voltage ripple. In this study, a thermo-electric model of the two different PFC methods allowed us to analyze the system behavior. Employing two commercial capacitors, an electrolytic and a film type, a full lifetime model has been derived, from which emerges that film capacitor lifetime is almost two times longer compared to electrolytic one
Appraisal of energy recovering sub-grid scale models for large-eddy simulation of turbulent dispersed flows
No full textCurrent capabilities of Large-Eddy Simulation (LES) in Eulerian–Lagrangian studies of dispersed
flows are limited by the modeling of the Sub-Grid Scale (SGS) turbulence effects on particle dynamics. These
effects should be taken into account in order to reproduce accurately the physics of particle dispersion since
the LES cut-off filter removes both energy and flow structures from the turbulent flow field. In this paper,
we examine the possibility of including explicitly SGS effects by incorporating ad hoc closure models in
the Lagrangian equations of particle motion. Specifically, we consider candidate models based on fractal
interpolation and approximate deconvolution techniques. Results show that, even when closure models are
able to recover the fraction of SGS turbulent kinetic energy for the fluid velocity field (not resolved in LES),
prediction of local segregation and, in turn, of near-wall accumulation may still be inaccurate. This failure
indicates that reconstructing the correct amount of fluid and particle velocity fluctuations is not enough to
reproduce the effect of SGS turbulence on particle near-wall accumulation
Soft-Body Modeling: A Scalable and Efficient Formulation for Control-Oriented Simulation of Electric Vehicles
No full textElectric vehicle (EV) modeling based on soft-body formulation is proposed as an alternative method suitable for the simulation of EVs and for the study of dynamic control strategies. This investigation strives to assess how this different formulation can be exploited to overcome the limitations of the traditional modeling methods. At this purpose, a soft-body tire model is created and tuned accurately; hence, the vehicle system founded upon the soft-body formulation is compared with two analytical models and with the result of an established opensource multibody simulator
Direct Numerical Simulation of the Interactions between Electrohydrodynamic Flows and Boundary-Layer Turbulence
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