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Published Articles

The Volume 17, No 3, September 2012

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Sound Characteristics and Sound Prediction of the Traditional Musical Instrument the Three-Rattle Angklung

Waluyo Adi Siswanto, Lina Tam, and Md Zainorin Kasron


The three-rattle angklung is a traditional musical instrument made of bamboo. The objective of this research is to observe the unique sound characteristics of the three-rattle angklung. The sound characteristics data can be used for defining digital sound of angklung to be played in a digital synthesizer. One set of angklung from the big size C5 to the small size C6 is recorded and analyzed in terms of the frequency contents. The sound characteristics of angklung are represented by four dominant frequency contents and the corresponding relative amplitudes of each rattle bamboo tube. This paper also introduces an equation model to predict the sound produced by the bamboo of the three-rattle angklung. This research reveals that bamboo rattles 2 and 3 produce the fundamental note, and bamboo rattle 1 generates a higher octave with the same note. Each bamboo rattle produces fundamental frequency note, its harmonics, and overtones. It is also found that three-rattle angklung can produce an accurate frequency almost in every note.

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Coupled Lateral-Torsonal Vibration Analysis of a Geared Shaft Rotor System using a Complex Rotor Variable Approach

K. V. S. Seshendra Kumar, B. S. K. Sundarasiva Rao


Though there have been numerous studies on both rotor dynamics and gear dynamics, the studies on geared rotor dynamics have been rather recent. The study of the dynamic behavior of geared rotor systems usually requires that torsional and lateral vibration modes be coupled in the model, a problem not present for studies of rotors without gears. For rotor dynamics studies, the finite-element method seems to be a highly efficient modeling method. In the present work, a finite-element model of a geared rotor system on flexible shaft bearings has been developed. The whirling motion and critical speed of the system has to be found by considering all the rotors in the system as well as interactions between them. It is shown that the lateral vibrations have considerable effect when the natural frequencies of the lateral vibration and torsional vibration are close to each other, which is well expected. By studying the responses of the system with strong lateral-torsional coupling, the nature of the coupling effect is discussed.

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Second Generation Shock Tube Calibration System

David Wisniewiski


Meggitt Sensing Systems (formerly Endevco) pioneered the commercialization of a shock tube calibration system by taking an established laboratory tool capable of imparting near-instantaneous pressure stimulus and incorporating this capability into active product development for the purpose of providing quantifiable frequency response of pressure transducers. These activities commenced in 1996 in a cooperative effort with Texas Christian University, and results were reported extensively through 1998. After 15 years of successful new product introduction, empirical data has been used to model more accurately the 1-D compressible gas dynamics occurring within the shock tube so that the time interval of the reflected shock - the most critical parameter in determining the transfer function for the pressure transducer under test - can be optimized for varying amplitudes. The existing Meggitt Sensing Systems shock tube (102 mm diameter x 3.7 m length) operates up to a pressure of 6895 kilopascal gauge (kPag) and sustains up to 8 ms reflected shocks. Recent modelling suggests that these parameters can double. Accordingly, effort is currently under way to bring this enhanced capability to the marketplace, offering both increased performance and ease of user operation.

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On the Role of Higher-Order Evanescent Modes in End-Offset Inlet and End-Centered Outlet Elliptical Flow-Reversal Chamber Mufflers

A. Mimani, M.L. Munjal


This paper deals with the role of the higher-order evanescent modes generated at the area discontinuities in the acoustic attenuation characteristics of an elliptical end-chamber muffler with an end-offset inlet and end-centered outlet. It has been observed that with an increase in length, the muffler undergoes a transition from being acous- tically short to acoustically long. Short end chambers and long end chambers are characterized by transverse plane waves and axial plane waves, respectively, in the low-frequency range. The nondimensional frequency limit k0 (D1 /2) or k0 R0 as well as the chamber length to inlet/outlet pipe diameter ratio, i.e., L/d0 , up to which the muffler behaves like a short chamber—and the corresponding limit beyond which the muffler is acoustically long are determined. The limits between which neither the transverse plane-wave model nor the conventional axial plane-wave model gives a satisfactory prediction have also been determined, the region being called the interme- diate range. The end-correction expression for this muffler configuration in the acoustically long limit has been obtained using 3-D FEA carried on commercial software, covering most of the dimension range used in the design exercise. Development of a method of combining the transverse plane wave model with the axial plane wave model using the impedance [Z] matrix is another noteworthy contribution of this work.

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Suppression of Bending Vibration of Drill-Strings via an Adjustable Vibration Absorber

Hamed Moradi, Firooz Bakhtiari-Nejad, Mojtaba Sadighi


Vibration control of the drilling process in the gas and oil industries is of great importance. Applying an effective control system diminishes both costs and process time and increases work efficiency. Typically, the drill string vibrates in a combination of three distinct modes of transverse, torsional, and axial vibrations. Due to the impor- tance of torsional vibration and the associated stick-slip phenomenon, many works have been devoted to this area. However, transverse vibration is another major source of vibration arisen from the long length of the drill string structure. In this paper, a tunable vibration absorber as a semiactive controller is designed to suppress the transverse vibration. After modeling the drill string as an Euler-Bernoulli beam and formulating the problem, the optimum specifications of the absorber, such as spring stiffness, absorber mass, and its position, are determined using an algorithm based on the mode summation method. The effect of bit rotational speed under the non-resonance and resonance condition is studied. It is shown that the best position of the absorber depends on the spring stiffness and bit rotational speed.

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