1,721,135 research outputs found
Scienze dell'educazione e inclusione sociale. Un seminario per riflettere sulle disuguaglianze educative
No full textInclusione sociale e politiche nazional
La valutazione scolastica: letture e riflessioni. Un'antologia di testi sulle teorie della valutazione
No full textScienze dell'educazione e inclusione sociale
No full textConvegno su scienze dell'educazione e inclusione social
Reflections on Free-Piston Stirling Engines. Part 1. Cyclic Steady Operation
No full textIn spite of the conceptual simplicity, the design of the free-piston Stirling engines (FPSEs) is made difficult by the necessity to accurately foresee the effect of the various geometric, dynamic, and thermodynamic variables on their behavior. This paper describes a fully developed mathematical model able to characterize these machines taking into account all of the relevant physical aspects involved, including the casing motion. A closed-form solution of the governing equations is used, together with a theorem developed by the authors to derive a basic criterion for the FPSE cyclic steady operation. Because this criterion is expressed in an analytical form as a function of the different variables involved, it is possible to choose the engine design parameters to ensure a steady periodic state. The developed model may be used not only for design purposes but also to simulate theoretically the dynamic behavior of a built engine
La macchina di Stirling a pistone libero: studio del comportamento dinamico al variare del carico
No full textThe paper presents a mathematical model for the dynamic behavior prediction of free-piston Stirling machines. This model is used both to define some analytical relations useful in the design of the engine, in order to assure to it, in advance, a correct and stable operation, and to quantitatively evaluate its dynamic response to external load variations.La memoria presenta un modello matematico per lo studio del comportamento dinamico di motori Stirling a pistone libero. Tale modello è utilizzato, da un lato, per definire alcune relazioni utili in fase di progetto al fine di assicurare a priori alla macchina un funzionamento corretto e stabile e, dall'altro, per valutare quantitativamente la sua risposta dinamica al variare del carico esterno
Analysis of Free-Piston Stirling Engine/ Linear Alternator Systems. Part 1: Theory
No full textLinear alternators are frequently proposed and used as electric-energy-producing devices in connection with free-piston Stirling engines. However, while considerable research work has been done on this type of engine and on its dynamics and thermodynamics, there are only few studies dealing with the linear alternator and its interaction with both the engine and the load. The objective of this article is to provide a mathematical model able to describe a free-piston Stirling engine/linear alternator combination as a whole system, where the electric, dynamic, and thermodynamic aspects are linked together. The engine/alternator system drives through a tuning capacitor a static load. In particular the method is applied 1) to calculate the force resisting the piston motion produced by the alternator and the associated load and 2) to derive a criterion of electric, dynamic, and thermodynamic steady-state operation of the machine
Progettazione Ottimizzata di Motori Stirling a Pistone Libero
No full textThis paper presents an analytical-numerical procedure for the study of free-piston Stirling engines. The seeking of the dynamic stability conditions is the problem here considered in more detail. The presented method allows useful "design rules" to be defined that must be satisfied in order to guarantee a correct behavior of the engine. In the reported design example, such behavior is verified by means of a code, previously developed, performing a dynamic and thermodynamic simulation.Viene presentato un procedimento analitico-numerico per lo studio di motori Stirling a pistone libero. Si affronta in particolare il problema della ricerca delle condizioni di stabilità dinamica, pervenendo a definire opportune "regole di progetto" cui tali macchine devono soddisfare per avere un corretto funzionamento a regime. Nell'esempio di progetto riportato, tale funzionamento è verificato utilizzando un codice, precedentemente sviluppato, per la simulazione dinamica e termodinamica
On the Self-Regulation of Free-Piston Stirling Engines: Comparison of Theoretical and Experimental Results
No full textA general theory for the dynamic stability evaluation of a Free-Piston Stirling Engine/Load Device-Load System, partly presented by the authors in past studies, is furtherly considered and improved in this paper. Here the developed methodology is applied in order to achieve the following items: - to give an interpretation of the self-regulating capability of such systems; - to find and to quantitatively characterize all the elements that have a stabilizing effect on their dynamic behaviour; - to validate the mathematical model by means of comparison with experimental results
The Effect of Nonlinear Thermo-fluid-dynamic Terms on Free-Piston Stirling Machine Stability
No full textIn this work a new linearization technique of the dynamic balance equations of a free-piston Stirling machine is developed. It takes into account the nonlinear thermo-fluid-dynamic terms inherent in the machine, although keeping the linearity of the differential dynamic equations. This allows the equations of motion to be solved still analytically and, therefore, useful algebraic relations (already established by the authors in past studies) linking together the various machine parameters to be used. The advantages related to the proposed linearization methodology are the following: 1) it gives a right interpretation of the machine working when the operational parameters vary, because the considered nonlinear terms have a stabilizing effect; 2) it can be used to predict the machine performance not only with more accuracy, but especially in a more exhaustive way, allowing to estimate also the piston stroke and, therefore, the delivered power; 3) it enables to design the machine in such a way to enhance its stability, thus eliminating the necessity of power control systems
Reflections on Free-Piston Stirling Engines. Part 2. Stable Operation
No full textIn this paper a new linearization technique of the dynamic balance equations of a free-piston Stirling machine is developed. It takes account of the nonlinear thermo-fluid-dynamic terms inherent in the machine, while keeping the linearity of the differential dynamic equations. This allows the equations of motion to be solved analytically and, therefore, it allows the algebraic relations linking the various machine parameters, established in a companion paper, to be suitably used. The casing motion is also considered. The following advantages are related to the proposed linearization methodology: 1) It gives the correct interpretation of the machine response to variations in the operating conditions because the considered nonlinear terms have a stabilizing effect that cannot be ignored; 2) it can be used to predict the machine performance not only with more accuracy than conventional linear dynamic analyses that fully neglect the nonlinearities, but in a more exhaustive way, allowing the piston stroke and, therefore, the delivered power to be calculated; and 3) it enables the machine to be designed in the initial stages in such a way as to enhance its inherent stability. To illustrate these features, we have considered, as an example of a free-piston Stirling engine, the well-known Space Power Research Engine
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