S. Fatima

Noise Control of Home Appliances — The Green Way

Material used for noise control applications should possess good sound absorption and dampening properties. In this work, the authors have focused on noise control applications of novel material made of jute which is a readily available, cheap and biodegradable natural fiber. Based on physical, flammable and acoustical properties, jute felt shows good sound absorption properties which has been used for noise control in a domestic clothes dryer and a vacuum cleaner. The noise sources in these appliances were ranked by measuring their radiated sound intensity levels. An overall reduction of radiated noise levels of 6 dB and 10 dB were obtained in the domestic dryer and the vacuum cleaner, respectively, by using the developed jute felt.

An Overview of Automobile Noise and Vibration Control

In this paper the current state-of-the-art techniques in automobile noise and vibration control are presented. Automobile designers and manufacturers have to pay attention to the global competition of their products, adherence to legislative regulations and passenger/driver comfort while designing an automobile and its components. Designers can take advantage of efficient numerical modeling techniques so that in before the prototype of the automobile is produced, the design can be tweaked and modified by using computer aided models to optimize the design with a target of achieving low noise and vibration levels in the prototype. Here, examples of some typical cases are provided where optimum levels of noise and vibration level are obtained in the design of automobile components using computer aided engineering techniques

Multiple Fault Classification Using Support Vector Machine in a Machinery Fault Simulator

The classification of various faults using a fault simulator and support vector machines (SVMs) has been studied. A database is created for number of faults by measuring vibration signals using seven accelerometers mounted on a machinery fault simulator (MFS). Statistical features are extracted in time domain from the vibration signals. Then, the sensitive features are selected using compensation distance evaluation technique. Multi-class SVMs ensemble algorithm is implemented for classification of the various faults by considering SVMs created by the possible combinations of sensitive features for each class of the fault. The effect of distance evaluation criterion for selection of sensitive features amongst the extracted twelve statistical features has been addressed. By using the developed algorithm, the effective location of accelerometer among seven accelerometers for better classification of the faults has been investigated. Measurements are done at five different rotational speeds. The robustness of the developed algorithm has been tested at different speeds.

Technique for optimal placement of transducers for fault detection in rotating machines

Online fault detection and diagnosis of rotating machinery requires a number of transducers that can be significantly expensive for industrial processes. The sensitivity of various transducers and their appropriate positioning are dependent on different types of fault conditions. It is critical to formulate a method to systematically determine the effectiveness of transducer locations for monitoring the condition of a machine. In this article, number of independent sources analysis is used as an effective tool for reducing the number of vibration sources within the system, which is then followed by principal component analysis to identify the incoherent transducers to be employed for fault detection. This experiment is conducted on a machine fault simulator for unbalanced rotor, misaligned shaft, and cracked shaft. The validation of the proposed selection process is illustrated using spectral analysis for each defect.

A misalignment detection methodology by measuring rate of temperature rise of shaft coupling using thermal imaging

Couplings used for connecting shafts allow for small amounts of misalignment between them. However, these misalignments give rise to additional vibrations at the bearing locations. And traditionally, misalignments in shafting systems have been determined by a vibration signature analysis. These misalignments are also responsible for temperature rise at the bearings and couplings. In this article, an experimental study has been made to detect early the presence of misalignment in systems, by measuring the temperature of the shaft couplings using a thermal imaging camera. The effects of load, speed and misalignment on the types of couplings and their temperature rise have been studied. It has been found that by monitoring the rate of temperature rise within the time constant of a coupling system, a misalignment in a system can be detected. In this study, the experimentally measured time constant is found to be in the range of estimated time constant of the system from one-dimensional heat transfer models. An approximate idea of the estimated thermal time constant of a system can be obtained by the theory reviewed in this article. In order to detect the misalignment in the system, the temperature measurement of the coupling has to be done before it reaches its steady-state value. Vibration measurements using both accelerometers and single-point laser vibrometer at the bearing locations under different load and speed conditions have also been done to correlate with the thermal imaging. It has been found that the measured transient spatial temperature distribution on the couplings also indicates the presence of misalignment in the shafting system. The methodology proposed in this article can be used in automated detection systems using thermography to detect misalignments from remote locations.

A new sound quality metric for the design of engine exhaust mufflers

In this paper, a study is made to determine the critical dimensions in the design of a family of reactive mufflers which significantly affect the sound quality of the tailpipe radiated noise. The sound quality parameters of the tailpipe noise such as the loudness level, the roughness and the tonality are measured, and a new sound quality metric is developed which can be used as an index to predict the performance of a muffler. The new sound quality metric was based on the evaluations of the synthesized tailpipe noise by a jury consisting of a few undergraduate and postgraduate students at the Indian Institute of Technology Kharagpur. Using the new sound quality metric, the parameters with the most influence on the design of the muffler can be determined. It was found that the length and the open area ratio of a concentric-tube resonator muffler have the highest impact on the tailpipe noise sound quality.