EXTENDED VALIDATION OF DYNAMIC IRREVERSIBLE THERMOPORATION: A NOVEL THERMAL PROCESS FOR MICROBIAL INACTIVATION

A novel thermal treatment for microorganism inactivation, characterized by a very rapid temperature increase (up to 30C/s) and a low final temperature (up to 65C) maintained for a relatively short holding time, has been recently presented and tested by the authors, showing microbial load reduction greater than 5 log units against several common bacteria and yeasts. With the aim of extending the possible use of the new thermal treatment to a wider microorganisms class, in this work the dynamic irreversible thermoporation (DIT) treatment was further tested on a well-known thermoresistant strain, the Enterococcus hirae: The results of these new experimental tests confirmed the reliability of t…

Helical Shift Mechanics of Rubber V-Belt Variators

A very common configuration of V-belt variators for motorcycles considers the correction of the belt tensioning depending on the resistant torque by means of suitable helical-shaped tracks allowing the driven half-pulleys to close/open. The theoretical model for belt-pulley coupling is rather complex for this configuration, where one half-pulley may run in advance and the other one behind with respect to the belt, and requires the repeated numerical solution of a strongly nonlinear differential system by a sort of shooting technique, until all the operating conditions are fulfilled (angular contact extent, torque, and axial force). After solving the full equations, the present study develop…

Power losses in power-split CVTs: A fast black-box approximate method

Abstract This paper addresses the mechanical losses of planetary transmissions, with particular attention to power-split CVTs in their hybrid electric versions. It provides unified layout-independent analytical relationships, which can be used for both analysis, design and control purposes, and a simplified approach; the latter overcomes the necessity to segment the operating range of the power-split CVT in order to keep its loss model physically consistent. An example of application to a real hybrid electric PS-CVT is performed to show the simplicity, accuracy and generality of the proposed method.

SOLUZIONE IN FORMA CHIUSA PER IL CALCOLO DELLE FREQUENZE NATURALI DI CILINDRI A PARETE SOTTILE E BORDI INCASTRATI

In questo lavoro si presenta un modello matematico che consente di calcolare in forma chiusa ed in maniera accurata le frequenze naturali dei gusci cilindrici circolari isotropi a parete sottile e bordi incastrati. L’equazione delle frequenze è stata determinata applicando il principio di Hamilton, mediante il metodo di Rayleigh, al sistema di equazioni indefinite del moto derivanti dalla versione di Reissner della teoria di Love, opportunamente modificata con le assunzioni di Donnell. La validazione del modello è stata effettuata mettendone a confronto i risultati sia con quelli derivanti dall’analisi modale realizzata agli elementi finiti, sia con dati sperimentali e teorici presenti in l…

Extended Validation of Dynamic Irreversible Thermoporation: A Novel Thermal Process for Microbial Inactivation

A novel thermal treatment for microorganism inactivation, characterized by a very rapid temperature increase (up to 30°C/s) and a low final temperature (up to 65°C) maintained for a relatively short holding time, has been recently presented and tested by the authors, showing microbial load reduction greater than 5 log units against several common bacteria and yeasts. With the aim of extending the possible use of the new thermal treatment to a wider microorganisms class, in this work the dynamic irreversible thermoporation (DIT) treatment was further tested on a well-known thermoresistant strain, the Enterococcus hirae: The results of these new experimental tests confirmed the reliability of…

Analysis of hybrid vehicle transmissions with any number of modes and planetary gearing: kinematics, power flows, mechanical power losses

Abstract This paper is focused on upgrading a unified parametric model, available in the literature, that can perform both the analysis and the design of Power-Split Continuously Variable Transmissions (PS-CVTs), which are particularly promising to deploy in the hybrid electric powertrain. In particular, this work is focused on the analysis of PS-CVTs and proposes a new matrix approach for identifying the basic functional parameters underlying the model from the constructive layout of the transmission. This new method does not rely on a case-specific formulation, thus befits any power-split transmission, regardless of the number of planetary and ordinary gear sets and their constructive arr…

Experimental model-based linearization of a S.I. engine gas injector flow chart:

Experimental tests previously executed by the authors on the simultaneous combustion of gasoline and gaseous fuel in a spark ignition engine revealed the presence of strong nonlinearities in the lower part of the gas injector flow chart. These nonlinearities arise via the injector outflow area variation caused by the needle impacts and bounces during the transient phenomena that take place in the opening and closing phases of the injector and may seriously compromise the air-fuel mixture quality control for the lower injection times, thus increasing both fuel consumption and pollutant emissions. Despite the extensive literature about the operation and modelling of fuel injectors, there are …

Model-based optimization of injection strategies for SI engine gas injectors

A mathematical model for the prediction of the mass injected by a gaseous fuel solenoid injector for spark ignition (SI) engines has been realized and validated through experimental data by the authors in a recent work [1]. The gas injector has been studied with particular reference to the complex needle motion during the opening and closing phases. Such motion may significantly affect the amount of injected fuel. When the injector nozzle is fully open, the mass flow depends only on the upstream fluid pressure and temperature. This phenomenon creates a linear relationship between the injected fuel mass and the injection time (i.e. the duration of the injection pulse), thus enabling efficien…

Experimental Evaluation of a New Thermal Process for Microorganisms Inactivation

A new thermal process for the inactivation of microorganisms in beverages has been studied and is presented in this paper. The treatment, not yet studied in the scientific literature, mainly consists of a thermal shock characterized by temperature increases up to 30°C/s, with final temperatures up to 65°C. This study presents the first experimental results obtained by the application of the new thermal treatment, with different combinations of the process parameters (rate of temperature rise, final temperature and holding time), on separate suspensions of Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Listeria innocua and Candida albicans. The required rapid temperature in…

Dielectric Characterization of Fruit Nectars at Low RF Frequencies

Dielectric properties of apple, apricot, peach, and pear nectars were studied in the frequency range from 15 kHz to 30 MHz and the temperature range from 25 to 60 degrees C. Both the relative dielectric constants and the dielectric loss factors decreased by increasing frequency and increased linearly with increasing temperature with values in the order 10(4)-10(2) and 10(5)-10(2), respectively. The power dissipation densities and the power penetration depths were found to increase linearly with temperature. Power dissipation densities remained essentially constant for all the samples while power penetration depths decreased significantly on increasing frequency. The dependence of each of th…

Hybrid electric vehicle powertrain design: Construction of topologies and initial design schemes

This paper introduces the generic representation and construction methods for the architectures of the four-wheel-drive hybrid electric vehicle (HEV) powertrain, which achieve the unified rules to represent and construct all types of HEV powertrains. To map the architecture into numerical variables and add it into optimization, the kinematic matrix of the HEV powertrain is extracted corresponding to the topological structure. Based on the torque distribution requirement of four-wheel-drive HEV, the initial design schemes (architecture and parameters) are created by charge-under-go feasibility inspection.

On the Birth and Growth of Pendulum Clocks in the Early Modern Era

Measuring the passage of time has intrigued humankind throughout the centuries. Ancient times witnessed the appearance and development of clepsydras and water clocks, whose place was subsequently taken by mechanical clocks in the Middle Ages. It is really surprising how the general architecture of mechanical clocks has remained almost unchanged in practice up to the present time. Yet the foremost mechanical developments in clock-making date from the 17th century, when the discovery of the laws of pendular isochronism by Galilei and Huygens permitted a higher degree of accuracy in the measuring of time.

Modello dinamico di iniettore di gas per motore ad accensione comandata

Nel presente lavoro si studia la complessa dinamica dell’otturatore di un iniettore di gas a solenoide per motori ad accensione comandata; come è noto, esso è sottoposto a spinte di diversa natura ed il suo moto ha un influenza determinante nei confronti della massa di combustibile erogata, la quale viene di norma modulata intervenendo sulla durata dell’intervallo di eccitazione del solenoide, chiamato “tempo di iniezione”. Ad otturatore completamente aperto, la massa di gas che attraversa la sezione di uscita dell’iniettore dipende esclusivamente dalle condizioni del fluido a monte dell’iniettore e dalla durata del tempo di iniezione: ciò rende lineare la caratteristica di funzionamento de…

Study on heat transfer coefficients during cooling of PET bottles for food beverages

The heat transfer properties of different cooling systems dealing with Poly-Ethylene-Terephthalate (PET) bottles were investigated. The heat transfer coefficient (Ug) was measured in various fluid dynamic conditions. Cooling media were either air or water. It was shown that heat transfer coefficients are strongly affected by fluid dynamics conditions, and range from 10 W/m2 K to nearly 400 W/m2 K. PET bottle thickness effect on Ug was shown to become relevant under faster fluid dynamics regimes.

On the beneficial effect of rotor suspension anisotropy on viscous-dry hysteretic instability

The destabilizing influence of the internal friction on the supercritical rotor whirl can be efficiently counterbalanced by other external dissipative sources and/or anisotropic suspension systems. The theoretical approach may take the internal dissipation into consideration either by dry or viscous models. Nevertheless, several numerical results and a new perturbation technique of the averaging type prove that similar rotor motions and stability limits are achievable by both models, whence the linear viscous assumption appears preferable. Thus, the internal hysteretic force may be expressed by the product of an equivalent viscous coefficient and the rotor centre velocity relative to a refe…

Shear coefficient determination in linear friction welding of aluminum alloys

In the present study, a combined experimental and numerical investigation on Linear Friction Welding (LFW) of AA2011-T3 aluminum alloy was carried out in order to find the temperature dependent shear coefficient to be used in a 3D numerical model of the process. Torque, oscillation frequency and pressure were acquired in order to calculate the shear stress at the interface. A numerical thermal model was used to calculate the temperature at the interface between the specimens starting from experimental temperatures acquired through a thermocouple embedded in the LFW specimens. Finally, the calculated shear coefficient was used to model the contact between the two specimens in a dedicated 3D,…

Experimental and Numerical Analysis of Microstructure Evolution during Linear Friction Welding of Ti6Al4V

Abstract Linear Friction Welding (LFW) is a solid state welding process used to joint bulk components. In the paper, an experimental and numerical study on LFW of Ti6Al4V titanium alloy is presented. A laboratory designed LFW machine has been used to weld the specimens with different contact pressure and oscillation frequency. The joint microstructure has been experimentally observed with SEM and EDS. A dedicated numerical model, able to predict temperature, strain and strain rate distribution as well as the phase volume fraction evolution, has been utilized to predict the final microstructure in the welded parts. It was found that complete transformation of the alpha phase into beta phase …

Hybrid Electric Vehicle Powertrain Design

L’attività di ricerca riguarda la progettazione, la modellistica ed il dimensionamento dellepowertraindestinateprincipalmente a veicoli elettrici ibridi.In tale ambito presentano interessanti caratteristiche e prestazioni, le trasmissioni del tipo power Split CVT, specie in virtù della loro capacità di consentire una migliore cooperazione dei propulsori

A closed-form solution for natural frequencies of thin-walled cylinders with clamped edges

Abstract This paper presents an approximate closed-form solution for the free-vibration problem of thin-walled clamped–clamped cylinders. The used indefinite equations of motion are classic. They derive from Reissner׳s version of Love׳s theory, properly modified with Donnell׳s assumptions, but an innovative approach has been used to find the equations of natural frequencies, based on a solving technique similar to Rayleigh׳s method, on the Hamilton׳s principle and on a proper constructions of the eigenfuctions. Thanks to the used approach, given the geometric and mechanical characteristics of the cylinder, the model provides the natural frequencies via a sequence of explicit algebraic equat…

On the linear friction welding process of aluminum alloys: Experimental insights through process monitoring

Abstract Linear friction welding is a solid-state joining process for non-axisymmetric components in which joining of materials is obtained through the relative motion of two components under pressure. In the process the heat source is given by the frictional forces work decaying into heat determining a local softening of the material and eventually bonding conditions. A dedicated fixture was equipped with sensors for the in-process acquisition of variables regarding kinematics, dynamics and temperature levels. The results of an experimental campaign aimed to weld AA6082-T6 aluminum alloy parts are presented and a process window is identified for the used alloy.

A mathematical model for the prediction of the injected mass diagram of a S.I. engine gas injector

A mathematical model of gaseous fuel solenoid injector for spark ignition engine has been realized and validated through experimental data. The gas injector was studied with particular reference to the complex needle motion during the opening and closing phases, which strongly affects the amount of fuel injected. As is known, in fact, when the injector nozzle is widely open, the mass flow depends only on the fluid pressure and temperature upstream the injector: this allows one to control the injected fuel mass acting on the “injection time” (the period during which the injector solenoid is energized). This makes the correlation between the injected fuel mass and the injection time linear, e…

Efficiency of Split-Way CVT's. A simplified model

ABSTRACT In this paper, a general formula is obtained for the efficiency of all types of Split-Way CVT, consisting of one or two epicyclic trains, a number of fixed ratio gears and one variable speed unit (CVU). It is based on the application of the principle of virtual works and on the simplifying hypothesis that all the dissipation is lumped inside the CVU. The comparison with some experimental results from the literature shows a surprisingly good fit, also in the neighbourhoods of zero speed ratio. INTRODUCTION The possibility of changing the speed ratio continuously between the primary and the secondary shaft of a mechanical transmission is a very interesting topic, mainly in the automo…

A new approach to the design of a speed-torque-controlled rubber V-belt variator

This paper presents a new model for a torque-speed-sensing rubber V-belt variator. The actuators are of the centrifugal roller kind on the driver side and a helical torque cam plus a compression-torsion spring on the driven side. The equations permit designing the actuator geometry in order to keep the transmissible torque as close as possible to the torque request in the whole operative field. Moreover, a procedure is suggested for the most proper design of an automatic variator of this kind. It permits choosing the required variogram of the transmission, i.e. the matching between the engine and the transmission, and designing the actuators: roller mass, housing shape, contact plate angle…

PROGETTAZIONE E VERIFICA SPERIMENTALE DI UNA MICROTURBINA IDRAULICA PER L’INDUSTRIA ALIMENTARE

In questo articolo sono descritte le attività di ricerca e sviluppo di una micro-turbina idraulica inserita all’interno di un macchinario che opera un nuovo processo di abbattimento della carica batterica applicabile nell’industria dell’imbottigliamento delle bevande. Peculiarità della turbina progettata è la geometria della palettatura della girante, dritta ed a sviluppo puramente assiale, che ne rende estremamente economica la realizzazione. Lo scambio di energia avviene grazie al moto vorticoso impresso al fluido (swirl) mediante opportuno posizionamento dei condotti di adduzione. Lo studio della turbina è stato condotto mediante classico approccio unidimensionale, mentre il dimensioname…

Global Efficiency of Power-Split Hybrid Electric Powertrain

The development of a proper energy management strategy in hybrid electric vehicles is crucial to pursue the best balance between emissions reduction and performance. In this respect, this paper addresses a straightforward method to investigate the behaviour of the hybrid powertrain in steady-state operation in terms of speeds and torques both of the thermal engine and the electric machines. The procedure takes into account the conversion power losses in the internal combustion engine and the electric unit and the mechanical power losses occurring in the power-split transmission. This enables the calculation of a set of maps describing the global efficiency of the hybrid powertrain and the p…

Effective Linear Friction Welding Machine Redesign through Process Analysis

Linear friction welding is a solid-state joining process developed for non-axisymmetric components in which the joining of the specimens is obtained through reciprocating motion and pressure. In the process, the friction forces work due to the high frequency oscillation and the pressure between the specimens is converted in thermal energy. In order to design an effective machine, relevant issues derive from the high frequency and the large inertial forces involved in the process. In this study, the authors describe the redesign of a preexisting prototypal machine for LFW processes. A machine redesign is needed when welding high resistant materials, i.e. steels or titanium alloys, with high …

Implicit regulation for automotive variators

A well-known practice uses mechanical variators to realize the so-called continuously variable transmissions (CVTs) for automotive application. A remarkable problem for one of the most used CVTs is given by the hydraulic control of the axial thrust on the half-pulleys that is necessary for torque transmission. It involves a heavy decrease in transmission efficiency. In the present paper, the possible production of the required axial thrust by a simple spring to eliminate hydraulic losses is analysed. It is shown that the power capacity of such a regulated variator is near to the maximum possible, and the belt torque loss is always considerably lower than the sum of the belt and pump losses…

BCD-9 OPERATIVE VARIATOR CHARACTERIZATION FOR CVT IMPROVEMENT(BELT AND CHAIN DRIVES)

Approximate Closed-Form Solutions for the Shift Mechanics of Rubber Belt Variators

The mechanical behavior of V-belt variators during the speed ratio shift is different from the steady operation as a gross radial motion of the belt is superimposed to the circumferential motion. The theoretical analysis involves equilibrium equations similar to the steady case, but requires a re-formulation of the mass conservation condition making use of the Reynolds transport theorem. The mathematical model of the belt-pulley coupling implies the repeated numerical solution of a strongly non-linear differential system. Nevertheless, an attentive observation of the numerical diagrams suggests simple and useful closed-form approximations for the four possible working modes of any pulley, o…

Functional design of power-split CVTs: An uncoupled hierarchical optimized model

Abstract This paper provides a new model for the preliminary design of compound power-split CVTs. Unlike the existing models, the presented method allows the engineers to prioritize functionality and efficiency of the transmission, while delaying the choice of the involved gear sets’ layout as long as possible. The design approach follows a specific priority order, and each step deals with one particular issue, without mutual interference. A smart design-chart eases the assessment and the comparison of the only eligible alternatives, and eventually leads to a final feasible constructive scheme, which can be an excellent concept for further optimization and implementation. Moreover, the mode…

Hysteretic whirl stabilization in rotor-shaft-bearing systems on dry friction suspension

SUMMARY. The undesired whirl of rotating machines can be reduced by elastic journal box suspension systems equipped with dry friction dampers. The critical speeds can be cut off by the adhesion of the friction surfaces and the whirl amplitude can be restrained throughout the remaining sliding range by a proper choice of the suspension-to-shaft stiffness ratio and of the support-to-rotor mass ratio. The dry friction forces counteract also efficiently the well known destabilising effect of the shaft hysteresis in the supercritical range. This lecture deals firstly with the natural precession speeds, investigates the steady response to unbalance and defines the ranges of adhesive or sliding co…

VALUTAZIONE DELLA TERMOPORAZIONE DINAMICA IRREVERSIBILE (DIT) COME STRUMENTO PER L’ABBATTIMENTO DELLA CARICA BATTERICA IN MATRICI ALIMENTARI

A theoretical approach to pneumatic muscle mechanics

The mechanical response of pneumatic artificial muscles is analyzed assuming the inextensibility of the sheathing braids and taking into account the stress field inside the rubber bladder, which is regarded as a Mooney-Rivlin hyperelastic material. The end effects are simulated by heuristically profiling the meridian section. After estimating the constitutive parameters by traction tests on rubber specimens, the theoretical results are compared with experiments and a satisfactory accordance may be detected.

Design of a Hybrid Electric Power-Split Transmission for Braking Energy Recovery in a Drilling Rig

Despite the promising potential of the hybrid electric power-split layout, its broader market penetration is prevented by the large number of feasible solutions and the constructive complexity, which overcomplicate the design process. Moreover, due to the lack of relevant literature references, the power-split transmissions design is even more difficult if concerning applications outside the automotive and agricultural sectors. In this paper, a general parametric model already available in the literature to design a single-mode power-split transmission with up to two planetary gear sets and six ordinary gear sets was applied to hybridize an oil drilling rig to recover energy braking during …

Direct analysis of power-split CVTs: A unified method

Abstract This paper provides a fast kinematic analysis method for compound power-split CVTs, which consents to identify their functional parameters. Such parameters permit the assessment of power flows, torques and efficiency, and the design of equivalent transmissions by the use of a recently published mathematical model. The same method can easily address either simpler or more complex transmissions by mean of kinematic equivalent parameters, without the need to arrange separate systems of equations. As a case study, we performed the kinematic analysis of the “Voltec” multi-mode GM transmission.

On the birth and growth of pendulum clocks in the Early on the History Modern Era

Measuring the passage of time has intrigued humankind throughout the centuries. Ancient times witnessed the appearance and development of clepsydras and water clocks, whose place was subsequently taken by mechanical clocks in the Middle Ages. It is really surprising how the general architecture of mechanical clocks has remained almost unchanged in practice up to the present time. Yet the foremost mechanical developments in clock-making date from the 17th century, when the discovery of the laws of pendular isochronism by Galilei and Huygens permitted a higher degree of accuracy in the measuring of time.

Experimental Evaluation of a New Thermal Process for Microorganisms Inactivation

A new thermal process for the inactivation of microorganisms in beverages has been studied and is presented in this paper. The treatment, not yet studied in the scientific literature, mainly consists of a thermal shock characterized by temperature increases up to 30°C/s, with final temperatures up to 65°C. This study presents the first experimental results obtained by the application of the new thermal treatment, with different combinations of the process parameters (rate of temperature rise, final temperature and holding time), on separate suspensions of Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Listeria innocua and Candida albicans. The required rapid temperature in…

Linear friction welding of dissimilar AA6082 and AA2011 aluminum alloys: microstructural characterization and design guidelines

This paper presents the results of an experimental and numerical campaign on Linear Friction Welding of dissimilar AA2011-T8 and AA6082-T6 aluminum alloys. Experimental tests were carried out with constant oscillation amplitude and process time. Varying oscillation frequency, interface pressure, specimen geometry and mutual position were used. Grain size measurements, HV tests and EDX analysis were considered to characterize the microstructure of the joints as a function of the input process parameters. A thermal numerical model was utilized to predict the temperature profiles in the joints during the process. The obtained results allowed the identification of four weld categories: sound jo…

Three-mode pneumatic management of marine U-tank systems

Abstract This paper deals with a new pneumatic control strategy for the roll damping enhancement of marine U-tank stabilizers. The proposed technique consists in a three-mode operation, where the control is active only within a limited resonant range around the ship natural frequency, whereas the control valves are kept closed in the remaining frequency range. Moreover the connection valve between the two air chambers is either closed or partially opened for the low or high frequencies, respectively. The pressurized air for the active control is fed by a turbo-blower set aboard and operates accelerating the motion of the water mass in the U-duct. The theoretical analysis is conducted in the…

Progetto preliminare di trasmissioni CVT con due vie in parallelo

Power Losses Minimization for Optimal Operating Maps in Power-Split HEVs: A Case Study on the Chevrolet Volt

The power-split architecture is the most promising hybrid electric powertrain. However, a real advantage in energy saving while maintaining high performance can be achieved only by the implementation of a proper energy management strategy. This requires an optimized functional design before and a comprehensive analysis of the powertrain losses after, which could be rather challenging owing to the constructive complexity of the power-split transmission, especially for multi-mode architecture with multiple planetary gearing. This difficulty was overcome by a dimensionless model, already available in the literature, that enables the analysis of any power-split transmission, even in full electr…

On the isochronism of Galilei's horologium

Measuring the passage of time has always fascinated the humankind throughout the centuries. It is amazing how the general architecture of clocks has remained almost unchanged in practice to date from the Middle Ages. However, the foremost mechanical developments in clock-making date from the seventeenth century, when the discovery of the isochronism laws of pendular motion by Galilei and Huygens permitted a higher degree of accuracy in the time measure.

Mappe di Lavorabilita’ per Giunti Misti di Alluminio Mediante Processo di Saldatura Linear Friction Welding

Il Linear Friction Welding è un processo di saldatura allo stato solido in cui una parte fissa è forzata contro una parte che si muove con moto lineare alternato per generare calore attraverso l’attrito. Nel presente lavoro viene descritto lo studio effettuato per la realizzazione della giunzione mista mediante processo di Linear Friction Welding tra due leghe di alluminio che presentano proprietà meccaniche differenti, come la lega AA2011 e AA6082. Lo studio è stato condotto analizzando due differenti configurazioni determinate dalla posizione relativa delle leghe costituenti i provini da saldare. Per la realizzazione del processo è stata utilizzata una macchina prototipale dotata di senso…

Ingegnerizzazione di una macchina prototipale per processi di saldatura linear friction welding

Experimental results for a belt variator in transient conditions

An Efficient Damping Technique for the Unstable Hysteretic Rotor Whirl by Proper Suspension Systems

This paper shows as the destabilising influence of the shaft hysteresis on the supercritical rotor whirl can be efficiently counterbalanced by external dissipative sources. After calculating the steady whirling paths of the rotor and the bearing due to unbalance, the stability is checked by the Routh-Hurwitz procedure, investigating the influence of the stiffness anisotropy of the supports. A fairly interesting result is that the instability phenomena can be conveniently prevented by different suspension stiffness in the horizontal and vertical planes.

Effective Linear Friction Welding Machine Redesign through Process Analysis

Linear friction welding is a solid-state joining process developed for non-axisymmetric components in which the joining of the specimens is obtained through reciprocating motion and pressure. In the process, the friction forces work due to the high frequency oscillation and the pressure between the specimens is converted in thermal energy. In order to design an effective machine, relevant issues derive from the high frequency and the large inertial forces involved in the process. In this study, the authors describe the redesign of a preexisting prototypal machine for LFW processes. A machine redesign is needed when welding high resistant materials, i.e. steels or titanium alloys, with high …

Control of hysteretic instability in rotating machinery by elastic suspension systems subject to dry and viscous friction

Abstract Most of the undesired whirling motions of rotating machines can be efficiently reduced by supporting journal boxes elastically and controlling their movement by viscous dampers or by dry friction surfaces normal to the shaft axis, which rub against the frame. In the case of dry dampers, resonance ranges of the floating support configuration can be easily cut off by planning a motionless adhesive state of the friction surfaces. On the contrary, the dry friction contact must change automatically into sliding conditions when the fixed support resonances are to be feared. Moreover, the whirl amplitude can be restrained throughout the speed range by a proper choice of the suspension-to-…

A simple method for the design of hybrid electric power-split cvts: A case study

A brief parametric method for the preliminary design of hybrid electric Power-Split CVTs is performed. The desired torque-speed characteristic is obtained, and general control and optimization criteria are introduced in order to minimize the size of the required electric machines. The optimization is performed by mean of scheme-independent functional parameters, while a specific constructive design is proposed only later, along with possible full electric operations.