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Several methodologies for the mesh stiffness calculation in spur gears have been found in the literature, in the last decades. Based on a bibliographical analysis and the research activities of the authors, attention has been devoted to three methodologies, which appeared as the most employed and cited. A critical review of such methodologies, FE-based method, hybrid analytical-FE method, and analytical approach, has been undertaken, highlighting some crucial aspects regarding the mesh stiffness estimation process. Within this framework, useful information related to the critical choice of parameters needed for the implementation of the methods are presented, in order to provide further guidelines for their application. Furthermore, the methods are compared in terms of results accuracy and computational time for full blank and lightweight gears. This comparison leads to useful guidelines regarding the definition of the most suitable approach depending on the specific requirements. Finally, two variants of an examined hybrid method are presented. They are based on linear, nonlinear FE analyses and analytical formulation. Their purpose is to compare the use of different analytical formulations against the FE formulation for the computation of the local deformation of gear teeth.

The mathematical model for evaluating the dynamic behavior of linear vibratory feeders is presented and discussed. The model is based on the Eksergian's equation of motion, with the aim at taking into account the effects of the main design parameters without unnecessarily increasing the complexity of the model. Deep emphasis is given to the procedure for the estimation of the external excitations applied to the driveline by proposing two procedures. The first one gives birth to a transcendent equation system, while the second procedure, based on more restrictive hypotheses regarding the geometry of the feeder, leads to a linear system. A dedicated experimental campaign for characterizing the dynamic behavior of a real machine is conducted under different operational conditions. Measured data are compared with simulated results obtained by applying both models; the experimental validation highlights the satisfactory quality of the model estimation, both in terms of torsional oscillations of the driveline and the global frame vibrations.

Noise and vibration control in mechanical systems has become ever more significant for automotive industry where the comfort of the passenger compartment represents a challenging issue for car manufacturers. The reduction of piston slap noise is pivotal for a good design of IC engines. In this scenario, a methodology has been developed for the vibro-acoustic assessment of IC diesel engines by means of design changes in piston to cylinder bore clearance. Vibration signals have been analysed by means of advanced signal processing techniques taking advantage of cyclostationarity theory. The procedure departs from the analysis of the Continuous Wavelet Transform (CWT) in order to identify a representative frequency band of piston slap phenomenon. Such a frequency band has been exploited as the input data in the further signal processing analysis that involves the envelope analysis of the second order cyclostationary component of the signal. The second order harmonic component has been used as the benchmark parameter of piston slap noise. An experimental procedure of vibrational benchmarking is proposed and verified at different operational conditions in real IC engines actually equipped on cars. This study clearly underlines the crucial role of the transducer positioning when differences among real piston-to-cylinder clearances are considered. In particular, the proposed methodology is effective for the sensors placed on the outer cylinder wall in all the tested conditions.

The gear fault diagnosis on multistage gearboxes by vibration analysis is a challenging task due to the complexity of the vibration signal. The localization of the gear fault occurring in a wheel located in the intermediate shaft can be particularly complex due to the superposition of the vibration signature of the synchronous wheels. Indeed, the gear fault detection is commonly restricted to the identification of the stage containing the faulty gear rather than the faulty gear itself. In this context, the paper advances a methodology which combines the Empirical Mode Decomposition and the Time Synchronous Average in order to separate the vibration signals of the synchronous gears mounted on the same shaft. The physical meaningful modes are selected by means of a criterion based on Pearson’s coefficients and the fault detection is performed by dedicated condition indicators. The proposed method is validated taking into account simulated vibrations signals and real ones.

Driveline components connected to internal combustion engines can be critically loaded by dynamic forces due to motion irregularity. In particular, flexible couplings used in engine test rig are usually subjected to high levels of torsional oscillations and time-varying torque. This could lead to premature failure of the test rig. In this work an effective methodology for the estimation of the dynamic behavior of highly flexible couplings in real operational conditions is presented in order to prevent unwanted halts. The methodology addresses a combination of numerical models and experimental measurements. In particular, two mathematical models of the engine test rig were developed: a torsional lumped-parameter model for the estimation of the torsional dynamic behavior in operative conditions and a finite element model for the estimation of the natural frequencies of the coupling. The experimental campaign addressed torsional vibration measurements in order to characterize the driveline dynamic behavior as well as validate the models. The measurements were achieved by a coder-based technique using optical sensors and zebra tapes. Eventually, the validated models were used to evaluate the effect of design modifications of the coupling elements in terms of natural frequencies (torsional and bending), torsional vibration amplitude, and power loss in the couplings.

Heavy duty wheels are used in applications such as automatic vehicles and are mainly composed of a polyurethane tread glued to a cast iron hub. In the manufacturing process, the adhesive application between tread and hub is a critical assembly phase, since it is completely made by an operator and a contamination of the bond area may happen. Furthermore, the presence of rust on the hub surface can contribute to worsen the adherence interface, reducing the operating life. In this scenario, a quality control procedure for fault detection to be used at the end of the manufacturing process has been developed. This procedure is based on vibration processing techniques and takes advantages of the results of a lumped parameter model. Indicators based on cyclostationarity can be considered as key parameters to be adopted in a monitoring test station at the end of the production line due to their not deterministic characteristics.

The development of a zero-dimensional model for analysing pressure phenomena in multiple stage external gear pumps is addressed in the present work. The tandem pump is composed of two coaxial stages: the high pressure one, made by spur gears, and the low pressure one, made by helical gears. The two stages have common shafts and a common case. The oil pressure course around the gearpair, as well as the suction/delivery pressure ripple, is estimated for both stages. Attention is focused on the description of the modelling approach: an original method is developed to model the helical gears and their effects on the determination of the geometrical parameters. The lumped parameter (LP) model takes advantage of a Computational Fluid Dynamic (CFD) model applied to different pump regions in order to estimate several internal flow features. Measured delivery pressure ripple and volumetric efficiency are used to evaluate the model reliability under different working conditions.

In modern industry, the wide use of reliable and sophisticated sensors with their connection to internet has introduced the phenomena of Big Data, especially in the field of condition monitoring systems (CMSs) in e-maintenance applications. In particular, in the case of vibration signals, high-performance acquisition systems are required, characterized by anti-aliasing filtering and high uniform sampling rate, in order to properly digitalize the meaningful frequency content of the signals. In this context, the capability of non-uniform random sampling (RS) is assessed in this work. While in different fields, such astronomy, structural and biomedical studies, the RS is a problem to be resolved, due to the unavailability of samples at specific instants (missing data problem), in the field of fault detection & diagnosis (FDD), RS can be a chosen sampling method thanks to its advantages: anti-aliasing property and low average sampling rate. Therefore, this paper focuses on studying the anti-aliasing property of the random sampled data, verifying the criterion proposed in literature for establish the Nyquist frequency, and analyzing its sensitivity to the sampling parameters. This study is carried out using simulated signals and computing the spectral window, giving the Nyquist frequency for different random sampling parameters; moreover, a spectral analysis method, the Schuster periodogram, is used to verify when the spectrum is actually free of alias. The results show that the Nyquist frequency depends on the numerical accuracy of the randomly generated time instants.

So far, the study of gear contacts in lightly loaded gears by means of vibration analysis has not been sufficiently addressed in the literature. Indeed, the complex nature of the physical phenomena involved makes the vibration analysis extremely challenging. This paper deals with the development and the validation of an approach for the contact pattern assessment in straight bevel gears within a pass/fail decision process. The proposed methodology is based on blending vibration-based condition indicators with classification algorithms in order to discriminate proper contact patterns from improper ones. Specifically, three different classification algorithms have been investigated: the Naive Bayes classifier, the weighted k-Nearest Neighbors classifier and a novel classifier proposed by the authors. The classifier accuracies are evaluated with a MC cross-validation that includes an extended experimental campaign consisting of more than one hundred different straight bevel gear pairs. The results show that the proposed classifier is superior to the other considered classifiers in terms of average accuracy. Finally, this manuscript proposes an original methodology that provides a reliable and quick assessment of the contact pattern in straight bevel gears considering different speeds, gear parameters and surface finish.

This paper addresses the use of first- and second-order cyclostationary (CS1 and CS2) tools to process the vibration signals picked up from internal combustion (IC) engines during cold tests. This type of analysis is needed in order to detect and diagnose irregular operations for quality control purposes. The effectiveness of indicators such as Mean Instantaneous Power (MIP), Degree of Cyclostationarity ( D C S α ) and Indicator of Cyclostationarity ( I C S n x ) in detecting assembly faults has been tested on real signals concerning three faulty conditions: inverted piston, connecting rod with incorrectly tightened screws, connecting rod without one bearing cap. In the past several authors have mainly used cyclostationary metrics for diagnostics purposes in rolling bearings and gear systems. Moreover, a signal model, qualitatively reproducing the features of actual cold test signals, has been formulated and used in order to preliminarily study the influence of signal parameters on the Indicators of Cyclostationarity. The results indicate that the cyclostationary tools – mainly CS2 tools – are effective in detecting and diagnosing all tested faulty conditions. In particular, indicator I C ⌢ S 2 x is highly sensitive to faults and it is suitable as pass/fail tool in quality control at the end of the engine assembly line. As a further second-order cyclostationary metric, the MIP is effective for detection, as well for fault identification, since it is able to localize regular and fault events within the engine cycle. In addition D C S α effectively characterizes the CS2 periodicities, giving the cyclic order distribution. Since these CS2 tools require a moderate computation cost, they can be considered ready for on-line industrial applications.

Classical design optimization procedures rely on the application of optimization algorithms upon system simulations. These algorithms need a large number of samples to converge on the optimal point. Hence design optimization needs large simulation time since each simulation has to be performed many times. In this paper an original and useful methodology to study and optimize mechanical systems is presented. The proposed methodology combines different techniques such as design of experiments, response surface models and evolutionary algorithms leading to larger time reduction with respect to the classical design optimization approach. On the one hand the proposed methodology gives the optimal combination of variables and on the other hand provides important results to understand the influence of each input to the system outputs. Moreover, a robust design process has been carried out in order to consider the manufacturing tolerances of the real mechanical system and assess their effect on the system performance. The results offer important information and design insights that would be very difficult to obtain without such a procedure. In order to demonstrate the methodology effectiveness, two case studies have been accounted: the optimization of the vibration level of a vane pump and a gear pump. To simulate the dynamical behaviour of the two pumps, mathematical models have been used. These models have been developed and validated by the authors in previous works. The mathematical models include the main important phenomena involved in the pumps operation and they have been validated on the basis of experimental data. The main operational and geometrical input variables have been taken into account in the optimization procedure of such pumps.

This work concerns external gear pumps for automotive applications, which operate at high speed and low pressure. In previous works of the authors (Part I and II, [1] , [2] ), a non-linear lumped-parameter kineto-elastodynamic model for the prediction of the dynamic behaviour of external gear pumps was presented. It takes into account the most important phenomena involved in the operation of this kind of machine. The two main sources of noise and vibration are considered: pressure pulsation and gear meshing. The model has been used in order to foresee the influence of working conditions and design modifications on vibration generation. The model experimental validation is a difficult task. Thus, Part III proposes a novel methodology for the validation carried out by the comparison of simulations and experimental results concerning forces and moments: it deals with the external and inertial components acting on the gears, estimated by the model, and the reactions and inertial components on the pump casing and the test plate, obtained by measurements. The validation is carried out by comparing the level of the time synchronous average in the time domain and the waterfall maps in the frequency domain, with particular attention to identify system resonances. The validation results are satisfactory global, but discrepancies are still present. Moreover, the assessed model has been properly modified for the application to a new virtual pump prototype with helical gears in order to foresee gear accelerations and dynamic forces. Part IV is focused on improvements in the modelling and analysis of the phenomena bound to the pressure distribution around the gears in order to achieve results closer to the measured values. As a matter of fact, the simulation results have shown that a variable meshing stiffness has a notable contribution on the dynamic behaviour of the pump but this is not as important as the pressure phenomena. As a consequence, the original model was modified with the aim at improving the calculation of pressure forces and torques. The improved pressure formulation includes several phenomena not considered in the previous one, such as the variable pressure evolution at input and output ports, as well as an accurate description of the trapped volume and its connections with high and low pressure chambers. The importance of these improvements are highlighted by comparison with experimental results, showing satisfactory matching.

A wind turbine is a very well-known archetype of energy conversion system working at non-stationary regimes. Despite this, a deep mechanical comprehension of wind turbines operating in complicated conditions is still challenging, especially as regards the analysis of experimental data. In particular, wind turbines in complex terrain represent a very valuable testing ground because of the possible combination of wake effects among nearby turbines and flow accelerations caused by the terrain morphology. For these reasons, in this work, a cluster of four full-scale wind turbines from a very complex site is studied. The object of investigation is vibrations, at the level of the structure (tower) and drive-train. Data collected by the on-board condition monitoring system are analyzed and interpreted in light of the knowledge of wind conditions and operating parameters collected by the Supervisory Control And Data Acquisition (SCADA). A free flow Computational Fluid Dynamics (CFD) simulation is also performed, and it allows one to better interpret the vibration analysis. The main outcome is the interpretation of how wakes and flow turbulences appear in the vibration signals, both at the structural level and at the drive-train level. Therefore, this wind to gear approach builds a connection between flow phenomena and mechanical phenomena in the form of vibrations, representing a precious tool for assessing loads in different working conditions.

This paper proposes an experimental methodology for the analysis of the lubrication regime and wear that occur between vanes and pressure ring in variable displacement vane pumps. The knowledge of the lubrication regime is essential for the improvement of the performance of high pressure vane pumps by reducing wear, increasing the volumetric efficiency and decreasing maintenance costs. Tests using pressure rings of different materials were carried out in order to identify the best material in terms of wear and friction. The proposed methodology is based on Archard's law and takes advantage of wear experimental measurements, an empirical model for the estimation of contact pressure forces and hardness standard tests. The results of the analysis state that low wear and reduced friction can be obtained if elasto-hydrodynamic lubrication between vanes and pressure ring is established. Results have been also verified by an analytical elasto-hydrodynamic model.

SUMMARYThis work presents the experimental validation and updating of a flexible multibody model ideated for taking into account installation conditions of industrial serial planar manipulators without resorting to cumbersome modeling. The flexibility of the frame, the manipulator is fixed, is modeled over the flexibility of joints, which is introduced as lumped stiffness. In particular, the flexible frame is included in the model by using the Component Mode Synthesis methodology, in which only the natural modes of vibration and the static constrain modes are accounted. The flexible multibody model has been developed because these commercial machines are mainly used to perform low-speed tasks, and they are designed by taking into account their flexibility at most in the joints. Unfortunately, there are particular installation conditions in which even low-speed tasks can generate low-frequency vibrations that highly interfere with the task. This aspect is considered here, and how to manage this problem is explained by using the developed multibody model. The model is validated through experimental measurements. The experimental tests consist of several modal analyses, together with acceleration and laser Doppler measurements in operational conditions. This methodology takes into account the installation conditions through the model of flexible frame, and gives a tool for studying ad hoc solutions which prevent the occurrence of unwanted low-frequency vibrations.

Before marketing external gear pumps are subjected to a running in process to increase their efficiency. However, this is one of the most time-consuming tasks of the entire manufacturing process. Therefore, a mathematical model for optimizing the running in process can be a useful tool for time-to-market reduction. In particular, in this paper a model for the analysis of the dynamic behaviour of external gear pumps, developed by the authors in previous works, is modified and used for simulating the running in process. The modified model is presented and validated via experimental data. A good correlation between simulation and test results guarantees the effectiveness of the model in determining the amount and the distribution of the removed material during the running in process. A meaningful reduction (16%) of the global running in time has been achieved with the introduction of a modified running in process drawn from simulation results.

This paper addresses the application of an image recognition technique for the detection and diagnosis of ball bearing faults in rotating electrical machines (REMs). The conventional bearing fault detection and diagnosis (BFDD) methods rely on extracting different features from either waveforms or spectra of vibration signals to detect and diagnose bearing faults. In this paper, a novel vibration-based BFDD via a probability plot (ProbPlot) image recognition technique under constant and variable speed conditions is proposed. The proposed technique is based on the absolute value principal component analysis (AVPCA), namely, ProbPlot via image recognition using the AVPCA (ProbPlot via IR-AVPCA) technique. A comparison of the features (images) obtained: (1) directly in the time domain from the original raw data of the vibration signals, (2) by capturing the Fast Fourier Transformation (FFT) of the vibration signals, or (3) by generating the probability plot (ProbPlot) of the vibration signals as proposed in this paper, is considered. A set of realistic bearing faults (i.e., outer-race fault, inner-race fault, and balls fault) are experimentally considered to evaluate the performance and effectiveness of the proposed ProbPlot via the IR-AVPCA method.

The inertia properties of an engine to be mounted on complex mechanical systems (e.g., cars, boats, etc.) are usually evaluated by considering the engine like a rigid-body (RB). These properties are mainly employed to design the geometry and the stiffness of the engine support, so as to build the dynamic model of the mechanical system the engine has to be mounted on. In this paper, two different techniques for measuring the RB inertia properties are compared: one in the time domain and the other in the frequency domain. The time-domain technique is based on the measurement of the oscillation period of a trifilar pendulum; whilst, the frequency-domain technique is based on the measurement of the Frequency Response Function (FRF) of the softly suspended RB. These techniques are applied to estimate the RB inertia properties both of an engine block and of a marine diesel engine. Eventually, their pros and contras are highlighted.

The present paper addresses the development of a lumped parameters model used to analyze the dynamic behavior of a so-called tandem gear pump. The pump is composed of two coaxial stages, both with external gears: a high pressure stage with spur gears and a low pressure one with helical gears. In particular, the paper deals with the modelling and the analysis of the phenomena bound to the pressure distribution around the gears, since they have the most important effect in the dynamic behavior of the pump. The pressure variation in the inlet and outlet chambers, the variable pressure in the trapped volume as well as the pressure evolution from the low to the high pressure chamber is estimated based on the Euler’s approach. The model is developed in Matlab environment. Attention is particularly focused on the description of the methodology adopted for modelling the low-pressure stage, constituted by helical gears, and its influence on the calculation of the pump geometrical parameters. The results provided by the numerical model are compared with experimental measurements in terms of outlet pressure ripple and volumetric efficiency under different working conditions. The results of the validation can be considered satisfactory. Predicted pressure ripple is shown and the effects of interconnections between stages are analyzed studying the outlet pressure ripple in the frequency domain as well.Copyright © 2015 by ASME

The conventional modal testing, hereafter referred as Displacement Modal Testing (DMT) is based on measurement of displacement, velocity or acceleration as well as excitation force. An enormous literature regards the DMT, on the contrary, a few papers address modal testing based on strain gauges or strain sensor, hereafter referred as Strain Modal Testing (SMT). The main reason of this scenario is due to practical problems in the use of strain gauges as calibration procedure, ground loop, sensitivity not adequate at high frequency, bonding quality. In this work, a novel piezoelectric strain sensor is used for SMT. It is demonstrated in the present work that this sensor overcomes the practical drawbacks related to the use of strain gauges. Thus, SMT based on piezoelectric strain sensors can be a valid alternative to DMT, usually based on accelerometers. Comparisons between the modal testing results concerning brackets with different constraint conditions using both accelerometers and strain sensors are given in terms of modal parameters, highlighting their pros and cons.Copyright © 2015 by ASME

This work concerns external gear pumps for automotive applications, which operate at high speed and low pressure. In previous works of the authors (Part I and II, [1] , [2] ), a non-linear lumped-parameter kineto-elastodynamic model for the prediction of the dynamic behaviour of external gear pumps was presented. It takes into account the most important phenomena involved in the operation of this kind of machine. The two main sources of noise and vibration are considered: pressure pulsation and gear meshing. The model has been used in order to foresee the influence of working conditions and design modifications on vibration generation. The model׳s experimental validation is a difficult task. Thus, Part III proposes a novel methodology for the validation carried out by the comparison of simulations and experimental results concerning forces and moments: it deals with the external and inertial components acting on the gears, estimated by the model, and the reactions and inertial components on the pump casing and the test plate, obtained by measurements. The validation is carried out comparing the level of the time synchronous average in the time domain and the waterfall maps in the frequency domain, with particular attention to identify system resonances. The validation results are satisfactory globally, but discrepancies are still present. Moreover, the assessed model has been properly modified for the application to a new virtual pump prototype with helical gears in order to foresee gear accelerations and dynamic forces. Part IV is focused on improvements in the modelling and analysis of the phenomena bound to the pressure evolution around the gears in order to achieve results closer to the measured values. As a matter of fact, the simulation results have shown that a variable meshing stiffness has a notable contribution on the dynamic behaviour of the pump but this is not as important as the pressure phenomena. As a consequence, the original model was modified with the aim at improving the calculation of pressure forces and torques. The improved pressure formulation includes several phenomena not considered in the previous one, such as the variable pressure evolution at input and output ports, as well as an accurate description of the trapped volume and its connections with high and low pressure chambers. The importance of these improvements are highlighted by comparison with experimental results, showing satisfactory matching.

Bearings play a pivotal role in the rotating machine scenario, due to their ubiquity and importance. A crowd of signal processing procedures have been developed in order to extract information about incipient localised faults in bearings from the measured acceleration signals. In the case of bearings for planetary gear applications, additional complexities are introduced. First, transducers may only be placed on the exterior of the gearbox, usually rather far from bearings. Second, the rotational axes of the planet gears are not fixed, i.e. they move with respect to the gearbox housing and thus to the transducers. As a result, the vibration signature of the planet gear bearings can be altered by the variable transfer path. In this condition, the standard signal processing techniques fail, and the characteristic bearing fault frequencies cannot be determined. On the other hand, global indicators of the bearing health may be used, but they are not able to specify where the fault is located. In this paper, a pre-processing technique is applied to the vibration signals of a planetary gearbox in order to highlight the planet gear bearing signatures. This technique is based on the McFaddens time synchronous averaging method to extract the vibration data relative to each planet. Then, cyclostationary techniques such as the Cyclic Power has be applied to extract the bearing signature.

Vibration signals can be successfully captured and analyzed for quality control at the end of the production line. Various signal processing techniques and their applications are presented in this paper. These applications demonstrate the importance of selecting proper signal processing tools in order to extract the most reliable information from the signals. The presented applications regards tooth fault detection in helical gears and the detection of assembly faults in diesel engines by means of cold test technology.

The paper presents a methodology for noise and vibration analysis of gear pumps and its application to an external gear pump for automotive applications. The methodology addresses the use of a combined numerical model and experimental analyses. The combined model includes a lumped-parameter model, a finite-element model and a boundary-element model. The lumped-parameter (LP) model regards the interior parts of the pump (bearing blocks and gears loaded by the pressure distribution and the driving torque), the finite element (FE) model regards the external parts of the pump (casing and end plates), while the boundary element (BE) model enables the estimation of the emitted noise in operational conditions. Based on experimental evidences, attention has been devoted to the modelling of the pump lubricant oil: the fluid-structure interaction between the oil and pump casing was taken into account. In the case of gear pumps all these important effects have to be considered in the same model in order to take their interactions into account. The model has been assessed using experiments: the experimental accelerations and acoustic pressure measured in operational conditions have been compared with the simulated data coming from the combined LP/FE/BE model. The combined model can be considered a very useful tool for design optimisation. (C) 2013 Elsevier Ltd. All rights reserved.

This paper assesses the application of different processing techniques on acceleration signals extracted from faulty heavy duty wheels. Heavy duty wheels are used in applications as automatic vehicles and are mainly composed of a polyurethane tread glued to a cast iron hub. The adhesive application between tread and hub is the most critical assembly phase, since it is completely made by an operator and a contamination of the link area may happen. Furthermore the presence of rust on the hub surface can contribute to worsen the adherence interface, reducing the operating life. Several wheels with different types of faults have been manufactured ‘ad hoc’ with anomalies similar to the ones that can really be originated. Synchronous average is calculated over the wheel rotation in order to highlight the phenomena that have the wheel rotation as periodicity (e.g. the contact between defect and test bench drum). Successively, cyclostationary theory is applied to extract information from the frequency/order domain of the processed signals. Eventually, well-suited indicators/coefficients are applied to the processed signals, objectifying the anomaly presence and defining pass-fail reference values based on the non-statistical Tukey’s method.

The free vibrations of circular cylindrical shells partiallyloaded by a distributed mass and rested on an elastic bed are studied in this paper. Both the mass-load and the elastic bed are assumed to be applied on limited arcs and with arbitrary distributions in circumferential direction,while they are considered to be uniformly distributed in longitudinaldirection on the entire shell length. Therefore, the problem is notaxisymmetric. The solution is obtained by using the development of theflexural mode shapes in a Fourier series, whose coefficients are determinedby rendering the Rayleigh quotient stationary, so a Galerkin equation isobtained. The proposed method is independent of the boundary conditionsat the shell ends. The results are satisfactorily compared to FEM results.Finally, the influence of the mass-load and of the bed stiffness on thenatural frequencies and mode shapes of a simply supported shell is shownand discussed.

Two models for the estimation of the pressure evolution in high pressure variable displacement vane pumps are proposed: a lumped parameter model and an empirical model. The former has full physical meaning and allows to simulate the behavior of a wide pump range, the latter, based on experimental measurements, can be applied only to a single family of pumps. Both the models can simulate the pressure evolution around the rotor in working conditions. These results are important for the structural design of the pump. Moreover, these models are the first element of a combined model aimed at the dynamic simulation of this type of pump, as a tool for vibro–acoustical optimization.Copyright © 2013 by ASME

Adulterations detection in concentrated rectified musts (CRM) could be strengthened by either making acceptance criteria capable of better reflecting the features of genuine samples or employing additional tracers suitable to ascertain the addition of exogenous sugars. In fact, thanks to their purity, CRM are an ideal substrate for adulterations with sugars of plants other than grape, in particular beet sucrose, able to emulate genuine samples. The present work shows that, moving from well-established standard methods like isotopic analysis of D/H and 13C/12C ratios and presence determination of myo-inositol, a better definition of genuineness characteristics could be achieved through a multivariate approach integrated with the measurements of myo-inositol and its isomer scyllo-inositol. The separation between adulterated and genuine samples has been obtained by implementing a multivariate version of the expectation−maximization (EM) algorithm, and the estimates have been later used to derive a classifica...

Vane pumps exhibit pressure ripple in the pressure evolution trend during a complete shaft rotation. Pressure ripple can determine oscillating forces within the system leading to vibration and noise generation. In this context, this paper is focused on the experimental measurement of the pressure evolution in vane pumps by using two different methodologies. Results of measurements are shown, highlighting advantages and disadvantages of both methodologies. In the first method a pressure transducer is directly facing the volume between two vanes, in the second method the sensor is located inside an external chamber where the oil is transferred via a duct suitably designed in the rotor shaft. Briefly, the first method gives better results in terms of pressure evolution but involves some practical problems in the setup: the measurements exhibit pressure offsets strongly dependent on the tightening torque used for sensor mounting and negative pressure values in the low pressure region. The second method is simpler to set up but the results are influenced by the dynamical behavior of the measurement duct carrying oil. In order to avoid resonances of this duct, a vibro-acoustical finite element (FE) model of the oil cavity has been developed. The numerical frequency response functions obtained by the FE model have been used in order to optimize the geometry of the measurement duct, reducing the effects of the resonances of the oil ducts. It is shown that, using this improved methodology, the dynamical components of the measured pressure are not significantly influenced by the frequency response of the measurement duct when the outlet pressures is higher than 50 bar, while for lower outlet pressure the first resonance of the measurement duct is close to the main vane harmonics.

This work addresses on a complete vibro-acoustic characterization of an axial compressor with the aim to foresee the rotor instability. The tests were performed on a turboshaft Allison 250-C18. The compressor is composed of six axial stages and one centrifugal stage. Four vibration signals were simultaneously measured by means of accelerometers, while the acoustic signals were measured by means of two microphones. Two different kinds of tests have been carried out on the compressor that operates at constant speed: in the course of the first test the six signals were acquired at different positions of the throttle opening, whereas during the second test, the signals were acquired while the throttle was gradually opened. The test results show a sensitive increase of the sub-synchronous activity in the accelerometers spectrum map, moreover, closing the throttle, the amplitude of the spectrum components increases. These phenomena can be related to the rotating stall behavior.Copyright © 2013 by ASME

This work addresses the elastodynamic modeling of vibratory bowl feeders and its experimental verification. The bowl feeder mainly consists of a bowl connected to a base by three or four inclined leaf springs. The springs constrain the bowl so that its vertical displacement causes a coupled rotation around its vertical symmetry axis. The feeder is actuated by electromagnets, while rubber mounts are positioned under the base for reducing the vibration transmission to the floor. The developed model is a linear lumped-parameter model for the prediction of the dynamic behavior of bowl feeders. The model has been experimentally verified by means of modal analyses and operational accelerations. Model parameters, such as the stiffness and damping of rubber mounts, leaf spring stiffness and time-varying excitation, have been experimentally estimated. The proposed model can be used for the analysis of feeder dynamics and for evaluating the effects of changes in design and operational parameters in terms of bowl and base vibration and dynamic forces transmitted to the floor.

In this work a combined model for the vibro-acoustic analysis of an external gear pump for automotive applications is presented and experimentally assessed. The model includes a lumped-parameter model, a finite-element model and a boundary-element model. The lumped-parameter (LP) model regards the interior parts of the pump (bearing blocks and gears), the finite element (FE) model regards the external parts of the pump (casing and end plates), while the boundary element (BE) model estimates the noise generation in operational conditions. Attention has been devoted to the inclusion of the oil effect inside the pump casing: the fluid-structure interaction between oil and pump casing was taken into account. The model has been assessed using experiments: the experimental accelerations and acoustic pressure measured in operational conditions have been compared with the simulated data coming from the combined LP/FE/BE model. Eventually, model results and limitations are presented.Copyright © 2013 by ASME

This paper shows the application of some processing techniques for the vibration analysis in working conditions of two different types of marine flexible couplings for boat propulsion. The flexible couplings are mounted between the flywheel of the marine diesel engine and the propeller shaft. The vibration signals are processed in time and frequency domain. Moreover, due to the presence of impulses in the signals, Continuous (CWT) and Discrete Wavelet Transform (DWT) are applied and compared with the conventional time and frequency domain methods. In this work the wavelet analysis is used for the impulse component extraction and the choice of different wavelet functions for this purpose is evaluated. The experimental comparison between two different types of couplings is also given. The results suggest that the wavelet transform techniques are effective to indicate which type of coupling provides a good vibrational behaviour especially in working condition when the angular speed of the propeller shaft is often inverted.

This paper deals with the detection of distributed faults in ball bearings. In literature most of the authors focus their attention on the detection of incipient localized defects. In that case classical techniques (i.e. statistical parameters, envelope analysis) are robust in recognizing the presence of the fault and its characteristic frequency. In this paper the authors focalize their attention on bearings affected by distributed faults, due to the progressive growing of surface wear or to low-quality manufacturing process. These faults can not be detected by classical techniques; in fact, in this case the signal does not contain impulses at the fault characteristic frequency, but more complex components with strong non-stationary contents. Distributed faults are here detected by means of advanced tools directly derived from the theory of cyclostationarity. In particular three metrics — namely Integrated Cyclic Coherence (ICC), Integrated Cyclic Modulation Coherence (ICMC) and Indicator of Second-Order Cyclostationarity (ICS2x) — have been calculated in order to condense the information given by the cyclostationary analysis and to help the analyst in detecting the fault in a fast fault diagnosis procedure. These indicators are applied on actual signals captured on a test rig where a degreased bearing running under radial load developed accelerated wear. The results indicated that all the three cyclostationary indicators are able to detect both the appearance of a localized fault and its development in a distributed fault, whilst the usual approach fails as the fault grows.Copyright © 2013 by ASME