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The Volume 20, No 2, June 2015



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A Comparison Between National Scheme for the Acoustic Classification of Dwellings in Europe and in the U.S.

Umberto Berardi and Birgit Rasmussen


https://doi.org/10.20855/ijav.2015.20.2369


The classification of dwellings according to different building performances has been proposed through many schemes worldwide in recent years. The general idea behind these schemes relates to the positive impact a higher label, and thus a better performance, should have. In particular, focusing on sound insulation performance, national schemes for sound classification of dwellings have been developed in several European countries. These schemes define acoustic classes according to different levels of sound insulation. Due to the lack of coordination among countries, a significant diversity in terms of descriptors, number of classes, and class intervals occurred between national schemes. However, a proposal "acoustic classification scheme for dwellings" has been developed recently in the European COST Action TU0901 with 32 member countries. This proposal has been accepted as an ISO work item. This paper compares sound classification schemes in Europe with the current situation in the United States. Economic evaluations related to the technological choices necessary to achieve different sound classification classes are also discussed. The hope is that a common sound classification scheme may facilitate exchanging experiences about constructions fulfilling different classes, reducing trade barriers, and finally increasing the sound insulation of dwellings.


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A Vibration Energy Approach Used to Identify Temperature Trending in Railroad Tapered-Roller Bearings

Constantine Tarawneh, Rafael K. Maldonado, Arturo A. Fuentes, Javier A. Kypuros


https://doi.org/10.20855/ijav.2015.20.2370


Bearing temperature trending is a phenomenon that has plagued the railroad industry for decades and has resulted in costly train stoppages and non-verified bearing removals. Initial experimental studies conducted at The University of Texas-Pan American to explore this troubling phenomenon identified potential sources for the abrupt changes in temperature exhibited by some railroad bearings. The authors hypothesize that vibration-induced roller-misalignment is the root cause for bearing temperature trending. Hence, subsequent research focused on providing validation for the proposed hypothesis through vibration monitoring techniques. To that end, dynamic testers were used to run railroad bearings at the various speeds and loads that they experience in the field. A "trigger" bearing with a known cup raceway defect was used as a vibration source to induce roller misalignment on neighbouring defect-free bearings. Results show that the vibration energy of a bearing would decrease prior to an increase in temperature. In theory, misaligned rollers would vibrate less, leading to a decrease in the overall vibration energy, while also generating sufficient friction to account for the observed temperature increase. Typically, rollers realign themselves through geometrical thermal expansions or changes in the operating conditions, thus, returning to normal temperature and vibration levels. This paper outlines the research findings.


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Usage of Spectral Distortion for Objective Evaluation of Personalized HRTF in the Median Plane

Fabián C. Tommasini, Oscar A. Ramos, Mercedes X. Hug and Fernando Bermejo


https://doi.org/10.20855/ijav.2015.20.2371


Measuring the head-related transfer functions (HRTFs) for each subject is a complex process. Therefore, it is necessary to develop procedures that} allow the} estimation of} personalized HRTFs. It is common to estimate the weights of the principal component analysis (PCA) of a group of subjects based on some anthropometric parameters using multivariable regression modell}ing. Moreover, to objectively evaluate} the goodness of fit} between the original HRTFs and the personalized ones, the spectral distortion (SD) is usually used too. However, its suitability in the median plane, in which the spectral profiles are crucial to localize a sound source, has not yet been demonstrated. This paper analyses the validity of the} SD as a measure of the quality of the HRTF personalization in the median plane, from the localization point of view. The HRTFs were modell}ed from the} weights estimated by multiple linear regression and artificial neural networks (ANNs). The SD was used to compare the HRTFs measured with} those estimated. Likewise, the level of fitting accuracy of characteristic resonance and notches in the median plane was also compared. Despite the fact that the SD scores of ANNs are lower than those of the multiple linear regression and are similar to those reported by other studies, the errors obtained from analys}ing both central frequencies and levels for resonance and notches could be discriminated.


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Stability of a Nonlinear Quarter-Car System with Multiple Time-Delays

Raghavendra D. Naik and Pravin M. Singru


https://doi.org/10.20855/ijav.2015.20.2372


This paper examines the dynamical behaviour of a nonlinear oscillator which models a two-degree-of-freedom quarter-car system forced by the road profile. The influence of two time delays in the system, which is generally due to the inherent dynamics of the actuator, is studied. The asymptotic and technical stability domain is obtained by using Bogusz's stability criterion for a two-degree-of-freedom system. The results obtained from Lyapunov's and Bogusz's stability criterions are compared. The numerical results obtained are found to be in good agreement with the analytical predictions.


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Automatic Selection of the WPT Decomposition Level for Condition Monitoring of Rotor Elements Based on the Sensitivity Analysis of the Wavelet Energy

Cristina Castejón, María Jesús Gómez, Juan Carlos García-Prada, Alberto Junior Ordoñez and Higinio Rubio.


https://doi.org/10.20855/ijav.2015.20.2373


Vibration signals are a widely used technique for machine monitoring and fault diagnostics. However, it is necessary to select a suitable pattern that represents the condition of the machine. Wavelet Packet Transform (WPT) provides a high potential for pattern extraction. Several factors must be selected and taken into account in the wavelet transform application such as the level of decomposition, the suitable mother wavelet, and which frequency bands (obtained from the decomposition process) contain the necessary information for the diagnosis system. The selection of the parameters commented above is a complex task that depends on many factors. Most of the works found in the literature select these factors based on experience, graphical methods, or trial and error methods. In this work, a method based on the relative wavelet energy is developed in order to automatically select the parameter defined by the WPT. The selection allows for the efficient extraction of the most suitable patterns for a later classification and fault detection process. In order to prove the soundness of the method proposed, a Jeffcott rotor model with four crack levels will be developed, and the vibratory signals provided by this model will be used for the monitoring condition.


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Study of Automobile Suspension System Vibration Characteristics Based on the Adaptive Control Method

Ruqiang Mou, Li Hou, Yiqiang Jiang, Yong Zhao and Yongqiao Wei


https://doi.org/10.20855/ijav.2015.20.2374


An automotive suspension determines both the driving stability and comfort of the vehicle occupants. This paper establishes two kinds of two degrees of freedom for the automobile suspension vibration model and uses the PID controller to establish an automobile suspension adaptive open-loop and closed-loop control system. Respectively, by step interference, white noise and sinusoidal interference for the input, studying the vibration characteristics of the vibration model in the vertical direction. By numerical simulation, we obtain the suspension of the vertical displacement and acceleration-time graphs. The simulation results show that the vibration characteristics of the first model are more in accordance with the actual situation of the car, and the closed-loop control is better than the open-loop control. The adaptive closed-loop control system can reduce the output displacement of automobile suspension to around 1% of the interference road input displacement. The output acceleration value is small, and the acceleration changes smoothly. The results verify the rationality and validity of the automobile suspension model and adaptive control system, which provides a theoretical foundation for the design and optimization of the automobile suspension system.


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Vibrations of Completely Free Rounded Regular Polygonal Plates

C. Y. Wang


https://doi.org/10.20855/ijav.2015.20.2375


The vibrations of completely free polygonal and rounded polygonal plates are important for large floating or space platforms. The problem is solved by an improved Ritz method on a class of homotopy shapes. The first five frequencies are determined, and interesting evolutions of mode shapes are shown.


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