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Published Articles

The Volume 19, No 3, September 2014

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A Two-Stage Fuzzy Piecewise Logistic Model for Two Different Harmonic Excitations

Ruan Miao


It is very important for a firm to be able to forecast the sales volumes of new products. However, current environments usually have uncertain factors and rapid changes, and decision makers must make forecasts in these fluctuating situations with minimal data. Previous studies combine scenario analysis and the technology substitution model to forecast the market share of multigenerational technologies, which is one kind of interpolation method. However, a technology substitution model based on a logistic curve does not always fit the S-curve well. Therefore, based on historical data and the data forecasted by the scenario and Delphi methods, a two-stage fuzzy piecewise logistic growth model is proposed. The piecewise concept is adopted in order to understand the market impact of a new product so that it will be possible to determine the effective length of sales forecasting intervals even when handling large-variation data. In order to demonstrate the model's performance, the researchers used Tseng et al.'s data from 2009, the market share of an organic light-emitting diode (OLED) television (TV), and four other TV technologies in three possible scenarios of the global market: optimistic, pessimistic, and most possible. The results show that the proposed model outperforms the technology substitution model.

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The Design and Performance of Feedback Controllers for the Attenuation of Road Noise in Vehicles

Jordan Cheer and Stephen J. Elliott


Active noise control systems offer a potential method of reducing the weight of acoustic treatments in vehicles and, therefore, of increasing fuel efficiency. The commercialisation of active noise control has not been widespread, however, partly due to the cost of implementation. This paper investigates the design and performance of feedback road noise control systems, which could be implemented cost-effectively by using the car audio loudspeakers as control sources and low-cost microphones as error sensors. Three feedback control systems are investigated, of increasing complexity: a single-input single-output (SISO) controller; a SISO controller employing weighted arrays of error sensors and control sources; and a fully-coupled multi-input multi-output (MIMO) controller. For each of the three controllers robustness and disturbance enhancement constraints are defined, and by formulating the three controllers, using an Internal Model Control (IMC) architecture and using frequency discretisation, the constrained optimization problems are solvable using sequential quadratic programming. The performance of the three controllers and the associated design methods are first evaluated in a simulated environment, which allows the physical limits on performance to be understood. Finally, to validate the results in the simulated environment, the performance of the three controllers has been calculated using data measured in a car cabin, and it has been shown that the fully-coupled MIMO controller is able to achieve significant low frequency road noise control, at the expense of increased implementation complexity compared to the SISO and SISO weighted transducer arrays feedback controllers.

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Numerical Investigation of Modal Parameter Statistics of Random Rods

Carlos H. Gomes, Samir N.Y. Gerges, Jorge P. Arenas


In this article, the ensemble statistics of the modal parameters of longitudinal rods with non-deterministic parameters were investigated through the statistical results of metric functions of the Random Matrix Theory (RMT). The levels of agreement with the Poisson and Gaussian Orthogonal Ensemble (GOE) models were evaluated for natural frequencies and corresponding mode shapes. The mean and relative variance values of kinetic energy density responses were calculated and compared to analytical predictions based on the Poisson and GOE models. The main effects on the energy response statistics due to incomplete establishment of GOE (or Poisson) statistics were systematically assessed for each modal parameter considering the single point-loading and spatially-averaged excitation. The numerical results also allowed the identification of the possible impact on the performance of analytical predictions of the relative variance when the modal parameter statistics do not conform completely to the GOE (or Poisson) model. An improved understanding was obtained regarding the relationship between the modal parameter statistics expected for one-dimensional engineering systems and those described by the GOE and Poisson models.

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A Novel Method to Minimize Torque Ripple, Mechanical Vibration, and Noise in a Direct Torque Controlled Permanent Magnet Synchronous Motor Drive

A.Sivaprakasam, T.Manigandan


The Direct Torque Control (DTC) technique of the Permanent Magnet Synchronous Motor (PMSM) receives increasing attention due to its simplicity and robust dynamic response compared with other control techniques. The classical switching table based DTC presents large flux, torque ripples, and more mechanical vibrations in the motor. Several studies have been reported in the literature on classical DTC. However, only limited studies exist that actually discuss or evaluate the classical DTC. This paper proposes a simple DTC method/switching table for PMSM, to reduce flux and torque ripples as well as mechanical vibrations and noise. In this paper, two DTC schemes are proposed. The six sector and twelve sector methodology is considered in DTC Scheme I and DTC Scheme II, respectively. In both DTC schemes, a simple modification is made in the classical DTC structure by eliminating the two-level inverter available in the classical DTC and replacing it with a three-level Neutral Point Clamped (NPC) inverter. To further improve the performance of the proposed DTC Scheme I, the available 27 voltage vectors are allowed to form different groups of voltage vectors such as Large-Zero (LZ), Medium-Zero (MZ), and Small-Zero (SZ), whereas in DTC Scheme II, all the voltage vectors are considered to form a switching table. Based on these groups, a new switching table is proposed. The proposed DTC schemes are comparatively investigated with the classical DTC and existing literatures from the aspects of theory analysis and computer simulations. It can be observed that the proposed techniques can significantly reduce the flux, torque ripples, mechanical vibrations, and noise and improve the quality of current waveform compared with traditional and existing methods.

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A Two-Step Model Reduction Method for a Strap-on Launch Vehicle

Liu Pan, Guo Shao-Jing, Cai Guo-Ping


In this paper, a two-step model reduction method is proposed using a strap-on launch vehicle as research object. In this method, the double-compatible free-interface modal synthesis method is first used for the modeling of the system, and the first step of reduction work is done by preserving the lower-order modes of flexible components of the system in the modeling process for the system. Then the second step of reduction is done for the established dynamic model of the system using the modal cost analysis method. After the two steps of order reduction, a low-order dynamic model of the system can be obtained. Simulation results indicate that this low-order model can reflect the characteristics of the original system effectively and the order is low enough as well.

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Study on Noise Reduction Using a Wavelet Packet for Ultrasonic Flaw Detection Signal of a Small Diameter Steel Pipe with a Thick Wall

Yongqiao Wei, Rui Tang, Li Hou, Fenglan Jia, Zhijun Sun and Bo Li


Ultrasonic detection technology is an important tool that is used to ensure the safe operation of equipment. However, when carrying out ultrasonic testing, especially in the ultrasonic detection of small-diameter steel pipes with thick walls, a mass of structural noise causes the useful information to get lost. This is problematic because the quality of ultrasonic echo signals is the foundation for the pipeline flaw-identification and feature extraction. At present, the wavelet packet thresholding method is the most widely used in signal de-noising processes. In this paper, a de-noising method of a wavelet packet based on the threshold is proposed for the limitation of both soft and hard thresholds. The ultrasonic wave pipeline detection signal that is often contaminated by noise is de-noised by this method. Moreover, the contrastive analysis is performed among the wavelet packet transform based on an adjusted threshold, the original ultrasonic echo signal, and the default threshold. Experiment results show that the noise reduction effect of the wavelet packet based on the adjusted threshold is the most reasonable one, and the signal-to-noise ratio (SNR) of the signals is also improved.

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Analysis on Multiple Perforated Plate Sound Absorber Made of Coir Fiber

Md. Ayub, Mohammad Hosseini Fouladi, Masomeh Ghassem, Mohd Jailani Mohd Nor, Hamidreza Soheili Najafabadi, Nowshad Amin and Rozli Zulkifli


Current studies are aiming to improve the sound absorption of coir fiber by implementing combinations of Perforated Plates (PPs) and air gaps. The Atalla and Sgrad model along with Johnson-Allard model and Acoustic Transmission Analysis (ATA) approach are used to estimate the absorption coefficient of the combination. Measurements are conducted in impedance tube to validate the analytical results. Outcomes show that the absorption coefficient of the panel is governed by the porosities of the implemented PPs. Reduction in the porosity of the face PP causes the incident sound to reflect back whereas higher porosity encourages the sound to enter and be absorbed gradually in the inner compartments. For the case of multilayer panels with two PPs, the best result is obtained when the inner PP has low porosity and is backed with an air gap. Absorption in high and low frequency bands are enhanced by having highly porous material and a thick layer of air gap in front of and behind the inner PP, respectively. This study shows that the high-frequency absorption is enhanced further in panels that include three PP layers. The study suggests fabricating panels containing two or three PPs with gradual reduction of porosity from the face PP to the inner ones, while the inner most PP has low porosity and is backed with air gap.

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