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Correlation of powder flow properties to interparticle interactions at ambient and high temperatures

Particuology 2014年第1期12卷 90-99页

作者： Igino Tomasetta diego Barletta Massimo Poletto dipartimento di ingegneria industriale Università degli Studi di Salerno

A combination of a continuum approach and a particleparticle approach to describe the multiscale nature of the mechanical properties of bulk solids may be beneficial to scientific and engineering applica tions. In this paper, a procedure is proposed to estimate the interparticle forces beginning with the bulk flow properties as measured with standardized techniques. In particular, the relationship between inter particle forces and bulk solid tensile strength is adopted based on the microscale approaches of Rumpf （1970） and Molerus （1975）. The flow properties of fluid cracking catalyst （FCC）, corundum and glass bead powders were all characterized with a modified Schulze ring shear cell capable of operating at tempera tures up to 500 ~C. The powder test conditions were selected such that the van der Waals forces were the most significant particleparticle interactions. The model equations describe two cases, in which either elastic or plastic deformation of the contact points is assumed. The results indicate that the model pro vides the correct order of magnitude for the values of the tensile strength when proper values for the mean curvature radius at the contact points are taken into account. A sensitivity analysis for the main parameters in the model was performed. This analysis indicated that the assumption of plastic deforma tion at contact surfaces coupled with a decrease in porosity justified an increase of the tensile strength with consolidation stress. Furthermore, the effect of temperature on the measured flow behavior can be explained as a change in the strength of the material.

关键词： Shear testingYield locusvan der Waals forcelnterparticle interactionsPowder consolidationHigh temperature

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Study of geometric parameters for the design of short intakes with fan modelling

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Chinese Journal of Aeronautics 2022年第11期35卷 18-32页

作者： Andrea MAGRINI Ernesto BENINI dipartimento di ingegneria industriale Universitá degli Studi di PadovaPadova 35131Italy

The flow over a short intake is characterised by a strong interaction with the fan, that can only be captured when the rotor blades are modelled in the numerical simulations. In this paper, we use a coupled methodology to derive indications about relevant geometric variables affecting the high-incidence operation of an ultra-high bypass ratio turbofan intake with a length-to-diameter ratio of 0.35. By reproducing the effect of the fan through a body force model, we carry out a parametric study of the influence of the contraction ratio and the scarf angle at take-off conditions for a grid of 28 different three-dimensional shapes. The analysis of the selected performance metrics distributions at three angles of attack of 16., 24., and 28. reveals that a contraction ratio higher than 1.20 is needed to avoid separation at high incidence. While for an attached inlet the best performance is found with a moderate scarf angle, in presence of a developed separation the distortion level reduces as the scarf decreases up to negative values. We discuss the correspondence between the distortion indexes and the flow field, highlighting the origin of the detachment for the different geometries, according to the operating condition, and analysing the fan operation in the most distorted case. Finally, we assess the influence of modelling the rotor in the simulations, showing that its suppression effect on the separation at a given incidence depends on the intake geometric features.

关键词： Body force method Coupled methods Fan/intake interaction Nacelle aerodynamics Short intake UHBPR

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Semisolid lead-antimony alloys for cars batteries

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Transactions of Nonferrous Metals Society of China 2010年第9期20卷 1774-1779页

作者： A.POLA M.GELFI M.M OdiGELL R.ROBERTI dipartimento di ingegneria Meccanica e industriale Università degli Studi di Brescia Aachener Verfahrenstechnik Chair of Mechanical Unit OperationsRWTH Aachen University

The application of semisolid process was investigated on Pb-Sb alloys that are normally used for metallic parts in car batteries, in order to increase their mechanical properties and corrosion *** semisolid behaviour of a Pb-4%Sb alloy was analysed by means of rheological and calorimetry differential scanning *** alloy was melted, treated by ultrasound to obtain the semisolid state and then poured into permanent *** of these samples were also heated in semisolid temperature range and injected in thixo-casting *** poured and injected samples were characterized by metallographic analysis, mechanical test and electrochemical corrosion *** results show an improvement of mechanical and corrosion resistance with respect to samples obtained by conventional casting technique.

关键词： Pb-based alloys semisolid metal corrosion resistance viscosity

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Modeling of shear induced coarsening effects in semi-solid alloys

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Transactions of Nonferrous Metals Society of China 2010年第9期20卷 1696-1701页

作者： M.MOdiGEL L A.POLA AVT Chair of Mechanical Process EngineeringRWTH Aachen University dipartimento di ingegneria Meccanica e industriale Uni.degli Studi di Brescia

In long-term rheological shear experiments with semi-solid alloys, coarsening of the particles will falsify the interpretation of the experimental *** coarsening is intensified by the shear induced convection and the mean size of the particles is changed significantly during the experiments.A simple model has been set up which takes the influence of the convection into *** resulting growth law has been simplified for diffusion and convection dominated *** growth law was verified with shear experiments in a Searl-rheometer with A356 and tin-lead *** experiments demonstrated that under convection the growth follows a linear time law and that the rate constant depends on the root of the shear *** correction of experimental results to gain the true viscosity function is demonstrated for a shear jump experiment with A356.

关键词： microstructure coarsening Ostwald ripening flow function viscosity rheology semi-solid alloys

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Algorithms to Compute the Largest Invariant Set Contained in an Algebraic Set for Continuous-Time and discrete-Time Nonlinear Systems

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IEEE/CAA Journal of Automatica Sinica 2020年第1期7卷 57-69页

作者： Laura Menini Corrado Possieri Antonio Tornambè dipartimento di ingegneria industriale Universitàdi Roma Tor VergataRoma 00133Italy Istituto di Analisi dei Sistemi ed Informatica“A.Ruberti ”Consiglio Nazionale delle Ricerche(IASI-CNR)Roma 00185Italy dipartimento di ingegneria Civile e ingegneria Informatica Universitàdi Roma Tor VergataRoma 00133Italy

In this paper, some computational tools are proposed to determine the largest invariant set, with respect to either a continuous-time or a discrete-time system, that is contained in an algebraic set. In particular, it is shown that if the vector field governing the dynamics of the system is polynomial and the considered analytic set is a variety, then algorithms from algebraic geometry can be used to solve the considered problem. Examples of applications of the method(spanning from the characterization of the stability to the computation of the zero dynamics) are given all throughout the paper.

关键词： Asymptotic stability discrete-time systems invariance nonlinear systems

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AC ripple on DC voltage:Experimental and theoretical investigation of the impact on accelerated ageing in electrical insulation

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High Voltage 2024年第4期9卷 902-910页

作者： Giovanni Gardan Gian Carlo Montanari dipartimento di ingegneria industriale Universita degli Studi di PadovaPadovaItaly Center for Advanced Power Systems Florida State UniversityTallahasseeFloridaUSA

With the increasing penetration of DC systems into the high voltage and medium voltage power industry,DC voltage is becoming common for distribution/transmission and to supply different typologies of *** allowable extent of AC ripple superimposed to DC,and its effect on insulation ageing,is a long-term discussed *** most harmful phenomenon causing extrinsic ageing acceleration and insulation system premature failure is partial discharges(PD);thus,the risk of incepting PD due to AC ripple could become a primary issue for electrical asset equipment *** this work,the impact of AC sinusoidal ripple on insulation system life and reliability is dealt with,considering both intrinsic and extrinsic ageing but focusing on the latter,that is,the PD *** are performed to assess how the jump voltage(due to AC ripple)and the DC component impact on PD activity in terms of amplitude and repetition *** the first time,the correlation between the magnitude of jump voltage associated with ripple and PD inception is established,shedding a light on the allowable ripple extent which does not impact significantly on ageing and premature insulation *** approach can provide straightforward tools for design specification and ageing inference of insulation systems.

关键词： impact insulation electrical

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On “Over-Sized” High-Gain Practical Observers for Nonlinear Systems

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IEEE/CAA Journal of Automatica Sinica 2018年第3期5卷 691-698页

作者： Daniele Carnevale Corrado Possieri Antonio Tornambè dipartimento di ingegneria Civile e ingegneria Informatica Universita di Roma Tor Vergata

In this paper,it is shown that the performances of a class of high-gain practical observers can be improved by estimating the time derivatives of the output up to an order that is greater than the dimension of the system, which is assumed to be in observability form and, possibly, time-varying. Such an improvement is achieved without increasing the gain of the observers, thus allowing their use in a wide variety of control and identification applications.

关键词： Filtering properties nonlinear systems observability observer design

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Nonlinear Damped Oscillators on Riemannian Manifolds:Fundamentals

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Journal of Systems Science & Complexity 2016年第1期29卷 22-40页

作者： FIORI Simone dipartimento di ingegneria dell'Informazione Facolta di IngegneriaUniversita Politecnica delle Marche

The classical theory of mass-spring-damper-type dynamical systems on the ordinary flat space R^3 may be generalized to higher-dimensional Riemannian manifolds by reformulating the basic underlying physical principles through differential *** dynamical systems have been studied in the scientific literature because they arise naturally from the modeling of complex physical structures and because such dynamical systems constitute the basis for several modern applications such as the secure transmission of *** flows of nonlinear dynamical systems may evolve over time in complex,non-repeating(although deterministic) *** focus of the present paper is on formulating the general equations that describe the dynamics of a point-wise particle sliding on a Riemannian manifold in a coordinate-free *** paper shows how the equations particularize in the case of some manifolds of interest in the scientific literature,such as the Stiefel manifold and the manifold of symmetric positive-definite matrices.

关键词： Nonlinear(active/passive) damping nonlinear oscillator Riemannian manifold

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Effect of Heat Loss on Laminar Flamelet Species Concentration

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Journal of Thermal Science 2016年第5期25卷 418-423页

作者： Marco Boccanera diego Lentini dipartimento di ingegneria Meccanica e Aerospaziale Sapienza Università di Roma

The effects of heat loss on the structure of laminar flamelets,which are the constitutive elements of turbulent flames under the most common operating conditions,are investigated for typical aeronautical gas-turbine operating conditions at *** magnitude of heat loss is quantified via the "enthalpy defect" measured with respect to an adiabatic flame.A procedure to generate laminar flamelets with an assigned enthalpy defect at the boundaries is devised and applied to nonpremixed propane/air flames,as propane reproduces the essential features of higher hydrocarbon *** is found,contrary to commonly held beliefs,that the enthalpy defect has a significant effect on the concentration not only of minor species,but also of main reaction *** effects are found in general to be more pronounced for fuel-rich *** impact is anticipated on the formation rate of nitric *** effects of scalar dissipation rate are also discussed.

关键词： Turbulent Combustion Heat Transfer Laminar Flamelets Hydrocarbon Combustion Aeroengines Gas Turbines

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Addition of Thermoplastic Starch(TPS)to Binary Blends of Poly(lactic acid)(PLA)with Poly(butylene adipate-co-terephthalate)(PBAT):Extrusion Compounding,Cast Extrusion and Thermoforming of Home Compostable Materials

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Chinese Journal of Polymer Science 2022年第10期40卷 1269-1286,I0011页

作者： Clizia Aversa Massimiliano Barletta Università degli Studi Roma Tre Dipartimento di Ingegneria Industriale Elettronica e MeccanicaVia della Vasca Navale 7900146 RomaItaly

Development of home compostable materials based on bioavailable polymers is of high strategic interest as they ensure a significant reduction of the environmental footprint in many production *** this work,the addition of thermoplastic starch to binary PLA/PBAT blends was *** compounds were obtained by a reactive extrusion process by means of a co-rotating twin screw ***,physical and chemical characterization tests were carried out to highlight the effectiveness of the material design *** compounds were subsequently reprocessed by cast extrusion and thermoforming in order to obtain products suitable for the storage of hot *** extruded films and the thermoformed containers were further characterized to highlight their thermo-mechanical,physical and chemical ***-rheological,mechanical and physical properties of the material and of the cast film were analyzed thoroughly using combined technique as capillary rheometer,MFI,DSC,VICAT/HDT,XRD,FTIR,UV-Vis,SEM,permeability and,lastly,running preliminary chemical inertness and biodegradation *** attention was also devoted to the evaluation of the thermo-mechanical resistance of the thermoformed containers,where the PLA/PBAT/TPS blends proved to be very effective,also presenting a high disintegration rate in ambient conditions.

关键词： Thermoplastic starch(TPS) Poly(lactic acid)(PLA) Poly(butylene adipate-co-terephthalate)(PBAT) Extrusion Thermoforming Compostability

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