Mayank Tiwari

Transient response of a hydraulic engine mount

Abstract Linear and non-linear transient responses of a typical hydraulic engine mount are analytically and experimentally studied in this paper. First, a lumped parameter linear model is used to approximate the typical step response and to suggest parameters that must be experimentally determined. Various configurations as related to inertia track and decoupler are analyzed. Two bench experiments are constructed for the identification of non-linear compliances and resistances. One of the main non-linear characteristics, however, comes from the decoupler mechanism. To accurately predict the time events of the decoupler opening and closing, an equivalent viscous damper model is employed along with a multi-staged switching mechanism. Additionally, non-linear behavior arising due to the vacuum formation in the top chamber is studied by defining a bi-linear asymmetric stiffness curve. New transient experiments are conducted on an elastomer test system, and measured transmitted force and top chamber pressure signals are analyzed. Results of the proposed simulation model match well with measured responses when step up, step down and triangular waveforms are applied. Areas for future research are identified.

Analytical prediction of the breakout noise from a rectangular cavity with one compliant wall

This paper describes an analytical calculation of breakout noise by incorporating three-dimensional effects along with the acoustical and structural wave coupling phenomena. The breakout noise phenomena from cavities are important at low frequencies, and the coupling between acoustic waves and structural waves plays a critical role in prediction of the transverse transmission loss. The first step in the breakout noise prediction is to calculate the inside cavity pressure field and the normal cavity wall vibration by using an impedance-mobility approach, which results in a compact matrix formulation. The second step is to calculate the radiated sound power from an unbaffled plate formulation that poses formidable challenges on computational time. The proposed formulation helps in reducing the computational time substantially by converting quadruple integrals into single integrals using an appropriate coordinate transformation technique. Analytical results are validated with the finite element/boundary element numerical models.

Analytical prediction of break-out noise from a reactive rectangular plenum with four flexible walls.

This paper describes an analytical calculation of break-out noise from a rectangular plenum with four flexible walls by incorporating three-dimensional effects along with the acoustical and structural wave coupling phenomena. The breakout noise from rectangular plenums is important and the coupling between acoustic waves within the plenum and structural waves in the flexible plenum walls plays a critical role in prediction of the transverse transmission loss. The first step in breakout noise prediction is to calculate the inside plenum pressure field and the normal flexible plenum wall vibration by using an impedance-mobility approach, which results in a compact matrix formulation. In the impedance-mobility compact matrix (IMCM) approach, it is presumed that the coupled response can be described in terms of finite sets of the uncoupled acoustic subsystem and the structural subsystem. The flexible walls of the plenum are modeled as an unfolded plate to calculate natural frequencies and mode shapes of the uncoupled structural subsystem. The second step is to calculate the radiated sound power from the flexible walls using Kirchhoff-Helmholtz (KH) integral formulation. Analytical results are validated with finite element and boundary element (FEM-BEM) numerical models.

Bearing Wear Due to Mechanical Stresses and Electrical Currents

Passage of current through moving conductive contacts results in electrical discharge and then melting of the material, which leads to wear. Such kind of bearing wear is common in electrical machines. There are however certain patterns which are unique to this kind wear. This wear pattern is called ‘fluting’, which are repetitive in nature. Electrical discharge can create higher surface roughness. Also the thermal and rheological properties of the lubricant play a big role in the film thickness formation. The passage of current through the lubricant also changes this and is determined by the electrical properties of the lubricant. In this work effect of bearing currents on a 7204 angular contact ball bearing is studied. This is tested with and without different cage materials with an axial load and no radial load, rotating at 2700 rpm. Four experiments were done at different-level of voltage, lube and cage material. Type of lubricant was seen to play a significant role in fluting.Copyright

Use of Artificial Neural Network (ANN) to Determining Surface Parameters, Friction and Wear during Pin-on-Disc Tribotesting

In tribological analysis of machine elements (such as gears, ball/roller bearings etc.), surface roughness plays very important role, ultimately it affects the friction coefficient, wear, rolling contact fatigue (micro pitting) and other failure mechanisms. Surface geometry and topography changes with time (number of cycles) during rolling/sliding motion of contacting surfaces. So, it is important to show the variation of surface topography parameter during wear process. This work presents the evolution of roughness parameters, wear and friction coefficient during pin-on-disc tribotesting under dry condition. The test is performed using pin on disc apparatus under room temperature condition. The pin (25mm long, 6mm diameter) is made of medium carbon steel (AISI 1038) whereas the disc (165mm diameter, 8mm thickness) is made of high carbon steel (SAE 52100). This works demonstrates the potential of Artificial Neural Network (ANN) for prediction of roughness parameters, friction coefficient and wear coefficient. Experimental results obtained from wear testing are compared with those obtained using artificial neural network (ANN) analysis. A very good agreement in results suggests that a well trained neural network is capable to predict the parameters in wear process.

Effect of Rotary Inertia and Gyroscopic Moments on Dynamics of Two Spool Aeroengine Rotor

The main objective of the paper is to study the effect of rotary inertia and gyroscopic moments due to lumped masses on the dynamics of two spool aeroengine rotors. Since the rotary inertia effect is well established, the thrust of the paper is on the effect of gyroscopic moments. Quantitative as well as qualitative aspects are studied. Effect of gyroscopics and rotary inertia on rotor critical speeds and unbalance response are studied for several rotors with particular reference to relative LP and HP rotor speeds. A two spool rig which resembles an actual aeroengine has been designed and built. Experiments have been conducted on two configurations of the rig in order to verify the theoretical results obtained by a formulation developed using the method of extended transfer matrices, for the two spool rotor with two intershaft bearings. A reasonably good correlation between the theoretical and experimental results is observed.© 1993 ASME

Prediction of Breakout Noise from Acoustically Lagged Rectangular HVAC Ducts

Heating, ventilation and air-conditioning (HVAC) ducts are often lagged on the outside of the duct wall with a highly porous material, covered in turn with a thin impervious jacket. This arrangement is used to provide thermal insulation as well as the breakout noise reduction. In this paper, a prediction method based on the four-pole parameters is discussed to evaluate the lagged duct performance in terms of the breakout noise reduction in the plane-wave frequency range. Transfer matrix of the inner and outer duct walls in the transverse direction is calculated using the wall admittance as a function of the axial wave number. Assuming a common axial wave number ensures coupling between the acoustic waves and structural waves. It is a function of the wall admittance. Considerable difference between common axial wave number and the air acoustic wave number is observed near the coupling frequency region of the duct wall. The overall transfer matrix is developed in order to relate the inside plane wave pressure to the outer acoustic particle velocity. This is combined with the radiation impedance of the duct to predict the transverse transmission loss. Net Insertion loss of the lagged duct is calculated using the difference of the transverse transmission loss of the lagged duct and the corresponding bare duct. Predicted values of the insertion loss are compared with the measured values from literature. Finally, results of parametric studies are presented.