Daniela Siano

Three-dimensional/one-dimensional numerical correlation study of a three-pass perforated tube

Abstract Automotive exhaust systems give a major contribution to the sound quality of a vehicle and must be properly designed in order to produce acceptable acoustic performances. Obviously, noise attenuation is strictly related to the internal gas-dynamic field that, on the other hand, needs to be optimised also in terms of pressure losses. In this work, the noise attenuation characteristics of a typical perforated muffler for automotive applications are investigated. Acoustic performances are quantified by the Transmission Loss (TL) parameter, which only depends on the geometrical characteristics of the device. Different numerical analyses are employed. At first, a one-dimensional (1D) simulation code (GT Power™) is used to predict the TL profile in a low frequency range. 1D simulation, in fact, may be only applied under the hypothesis of a planar wave propagation. A more complex 3D FEM/BEM approach is also realised using the VNOISE™ code, [17] , specifically designed for acoustic applications. Obviously, such analysis allows to obtain more accurate results at high frequency, depending on the mesh size. Different flow velocities and gas temperatures are investigated in both 1D and 3D models. The predicted TL profiles are compared and discussed in order to assess the potentiality and limitations of the employed numerical approaches.

Gerotor pump cavitation monitoring and fault diagnosis using vibration analysis through the employment of auto-regressive-moving-average technique

Abstract Gerotor pumps, as well known, are widely used in lubrication circuits of internal combustion engines for their simplicity, high efficiency and low costs. In this paper an experimental characterization of a Gerotor pump is shown. The research is a collaboration between the Hydraulic Power Research Group (HPRG) of the University of Naples “Federico II” and the Istituto Motori of CNR. The aim of this research is to investigate the possibility of using simple data to acquire, as vibrational data, on the pump under investigation to detect possible cavitation problem by implementing a proper mathematical procedure to this aim. As been demonstrated that these pumps are particularly subject to cavitation. The gerotor pumps are much subject to cavitate than expected, especially under particular operating conditions of the engine. Cavitation is also correlate to vehicle dynamics particularly with the recent tendency to reduce the mass of oil in the sump. Therefore, the research to avoid cavitation is crucial nowadays. Consequently this study has been firstly performed with an experimentation on the pump by monitoring the delivered oil flow-rate and the adsorbed torque on the pump shaft. An accurate analysis of the pressure oscillations in cavitation conditions, has been, also, conducted. Then, an accelerometer sensor has been properly located to study the cavitation with a fault diagnosis system based on vibration detection. The experimental tests have been performed on a test bench of the Hydraulic Laboratory of the University of Naples “Federico II” in Italy. The bench allows testing the pump working by varying the shaft speed, the oil temperature, the suction and the delivery pressure. The main measured parameters are shaft torque, oil flow rate, mean suction and delivery pressure and the instantaneous suction and delivery pressure. As expected, tests revealed the high influence of the suction pressure on the delivered oil flow rate, while no significant influence has been noted on the adsorbed torque. Furthermore, the pressure oscillations in the pump delivery are highly influenced by the suction pressure. A non intrusive accelerometer has been installed during the experimentation on the oil pump. Since the vibration due to cavitation is the main concern of this study, the accelerometer has been mounted at the suction port in the radial direction. More precisely, the paper presents a fault diagnosis system based on vibration detection. Firstly, a Fast Fourier Transform of the vibration signal has been computed. The investigation has been made with and without the presence of cavitation varying the pump rotation speeds. Limitations due to the detecting of the on line cavitation problems by monitoring the FFT vibration spectra have been overcame by implementing an alternative method based on stochastic approach. This diagnosis method of accelerometer time series analysis based on an Auto Regressive and Moving Average (ARMA) method has been used to determine the pump failure. The diagnosis results have demonstrated the ability of the proposed mathematical technique in the identification of cavitation phenomena proving that the proposed approach is a useful methodology to detect the presence of fault. The approach can predict, with good accuracy, pump failure in real time operation. In addition, a threshold vibration level in decibel scale is also fixed.

Elastic Multi Body Simulation of a Multi-Cylinder Engine

This paper analyzes the vibration behavior of an in-line 4-cylinder, 4-strokes, internal combustion turbocharged direct injection gasoline engine. A detailed multi-body numerical model of the engine prototype was used to characterize the whole engine dynamic behavior, in terms of forces and velocities. The crank train multi-body model was created starting from engine geometrical data, and the available combustion loads were employed for the Multi-Body Dynamic Simulation (MBDS). A combined usage of FEM and multi body methodologies were adopted for the dynamic analysis: both crankshaft and cylinder block were considered as flexible bodies, whereas all the other components were considered as rigid. The engine mounts were considered as flexible elements with given stiffness and damping. The hydrodynamic bearings were also modelling. The software LMS Virtual Lab (modules PDS and Motion) and ANSYS were used for the simulation.

Experimental vibro-acoustic analysis of the gear rattle induced by multi-harmonic excitation

The paper reports a wide vibro-acoustic experimental investigation of the gear rattle phenomenon induced by multi-harmonic excitation. The analysis is performed by using different measurement techniques which allow some of the significant parameters in this type of investigation to be acquired on a specific test rig: the angular rotations of the gears by using encoders; the accelerations obtained from a triaxial accelerometer; the sound pressure level determined by employing both acoustic microphones; the correct evaluation of the acoustic sources by utilizing a p–v sound intensity probe. Performance indices were adopted to compare the dynamic behaviours of the system with respect to some parameters, such as the speed of the pinion, the fluctuations in the speed of the pinion and the lubrication conditions. The results of the comparative analysis show very good agreement between the vibro-acoustic measurements and the results from the encoder-based method; this has helped us to interpret the physical behaviour of the gear pair with respect to the impacts occurring between the teeth during the different phases of the phenomenon. Moreover, the study indicates interesting aspects of the effects of multi-harmonic excitation on the rattle phenomenon, with particular attention to the influence of lubrication on the reduction in the rattle noise.