Numerical analysis of wave propagating in a periodic layered structure

Controlling sound fields is a key technology for noise removal, acoustic lenses, energy harvesting, etc. This study investigated the control of sound field by a periodic layered structure. At first, we formulated the wave propagation in a periodic layered structure and proved that the wave fields constructed by the periodic boundary conditions are limited to plane wave modes with discretely different propagation directions. Numerical calculations clarified that the desired plane wave mode can be obtained in the transmitted wave through an intermediate thin-plate stacked region in a periodic layered structure, in which Lamb waves travel in each plate at different phase velocities and create phase difference at the exit of the intermediate thin-plate region. Further numerical investigations revealed that tuning frequency and length of the thin-plate region provides wave field more dominantly with a single wanted plane wave mode.

Multipoint Wave Measurement in Tuned Liquid Damper Using Laser Doppler Vibrometer and Stepwise Rotating Galvanometer Scanner

Liquid dampers, such as tuned liquid dampers (TLDs), are employed to improve serviceability by reducing wind-affected building vibrations. In order to maximize the vibration suppression efficiency of the liquid damper, the tuning frequency of the liquid damper should match the natural frequency of the building. Experimental evaluation of the tuning frequency of a liquid damper performed in a factory prior to installation in a building is a critical task to ensure correct performance, and for this, multipoint measurement of the TLD is required. In this study, a novel liquid level measurement system combining Laser Doppler Vibrometer (LDV) and a stepwise rotating galvanometer scanner was developed to observe liquid sloshing in TLD. The proposed system can measure the liquid level at multiple points simultaneously with a single laser point. In the experimental phase, the liquid damper’s natural frequency and mode shape are experimentally evaluated utilizing the developed system. The performance of the proposed system was verified by comparison with the video sensing system.

Suppression of correlated interference by adaptive notch filters under pulse repetition period modulation

Introduction: We discuss the problem of correlated noise suppression by adaptive complex notch filters of various orders. In order to eliminate the dependence of the transmission coefficient of the useful signal on its frequency, the pulse repetition period is modulated. Purpose: Studying the influence of pulse repetition period modulation on the correlated noise suppression coefficient. Methods: The notch filter parameters were optimized with the criterion of minimum average dispersion of correlated noise at the output of the filters during the repetition period modulation. Results: Expressions are obtained for the variance of correlated noise at the output of complex adaptive filters of various orders when the repetition period is modulated. Relationships are given for finding the optimal values ​​of the tuning frequency and coefficients of the notch filters which minimize the correlated noise level at their output. Expressions are obtained for the coefficients of correlated noise suppression by notch filters in the context of pulse repetition period modulation. The graphs are presented showing how the correlated noise suppression coefficient depends on the relative value of the probing signal repetition period deviation for various values ​​of the correlated noise spectral density width at optimal or non-optimal values ​​of the tuning frequency and coefficients of the notch filters. It is shown that the use of probing pulse repetition period modulation leads to a decrease in the correlated noise suppression coefficient. On the other hand, the adaptation of the weighting coefficients for the adopted models of notch filters and correlated interference provides an increase in the suppression coefficient. Practical relevance: When developing or studying correlated noise suppression systems, the obtained results make it possible, taking into account the permissible losses of the suppression coefficient, to reasonably choose the input pulse repetition period deviation value in order to eliminate the effect of “blind” frequencies.

The magic of frequencies - 432 Hz vs. 440 Hz: Do cheerful and sad music tuned to different frequencies cause different effects on human psychophysiology? A neuropsychology study on music and emotions

The present study aims to see whether music (cheerful and sad) tuned to different frequencies (432 Hz vs. 440 Hz) cause different effects on the listener’s emotions. In the research, the effects of cheerful and sad music samples at different frequencies were examined within the framework of variables such as Heart Rate Variability (HRV), emotions felt and mood. The study was carried out with a total of 51 participants (31 women comprising 60.8% of the study group, and 20 men comprising 39.2% of the study group) who have not received music education. The average age of the participants is 22.19 (S = 1.08, range = 20-25). In the study, the activation levels of the autonomic nervous system were assessed using Heart Rate Variability (HRV), whereas the moods of the participants before listening music were assessed using the Profile of Mood States (POMS) scale. Finally, The Geneva Emotional Music Scales (GEMS) was used to assess the potential emotions and mood state to appear after listening music. All music samples used in the study (one cheerful and one sad per participant) were chosen by the relevant participant. The conversion of the samples recorded at 440 Hz tuning frequency, to 432 Hz was carried out with a Max/MSP patch designed specifically for the study. The findings of the study show that the cheerful and sad music tuned to different frequency levels (432 Hz vs. 440 Hz) do not induce significant variation in sympathetic and parasympathetic activation levels. However, regardless of the tuning, the participants who listened cheerful music reported higher levels of relaxation after listening. Moreover, again regardless of the tuning, according to GEMS results, the participants experienced higher levels of sublimity compared to unease, and also higher levels of unease compared to vitality. The analysis regarding cheerful music, in turn, found that the participants, this time, experienced higher levels of vitality compared to sublimity, and higher levels of sublimity compared to unease. In the most comprehensive analysis with no reference to the cheerful or sad character of the sample, the participants who listened 440 Hz pieces reported rather negative mood after listening music compared to the participants who listened 432 Hz pieces. Moreover, men were observed to report even higher levels of negative mood after listening 440 Hz pieces, compared to their mood after listening 432 Hz pieces. All the findings thus reached imply that different tunes lead to variation in reported moods, even though they do not bring about changes in sympathetic and parasympathetic activation levels. ​Extended English summary is in the end of Full Text PDF (TURKISH) file. Özet Bu çalışmanın amacı, 432 Hz ve 440 Hz frekanslara göre ayarlanmış müziklerin (neşeli ve hüzünlü) duygu oluşumunda bir fark yaratıp yaratmayacağını değerlendirmektir. Farklı frekanslardaki neşeli ve hüzünlü müzik örneklerinin yarattığı etkiler, Kalp Hızı Değişkenliği (KHD), hissedilen duygular ve duygu durumu gibi değişkenler çerçevesinde incelenmiştir. Araştırma, müzik eğitimi almayan 31'i (%60.8) kadın, 20'si (%39.2) erkek toplam 51 kişiyle gerçekleştirilmiştir. Katılımcıların genel yaş ortalaması 22.19’dur (S = 1.08, ranj = 20-25). Çalışmada otonom sinir sistemi aktivasyonunu değerlendirmek için Kalp Hızı Değişkenliği (KHD) ölçümü; müzik dinleme öncesi anlık duygu durumunu (mood) değerlendirmek için Duygu Durumu Profili Ölçeği (POMS) ve müzik dinleme sonrası oluşan muhtemel duyguları değerlendirmek için Cenova Duygu Müzik Ölçeği (GEMS) kullanılmıştır. Çalışmada kullanılan bütün müzik örnekleri (bir neşeli, bir hüzünlü) her bir katılımcının kendisi tarafından belirlenmiştir. 440 Hz akort frekansına göre kaydedilmiş örneklerin 432 Hz frekansa dönüştürülmesi çalışmaya özgü geliştirilmiş bir Max/MSP patch uygulaması ile yapılmıştır. Bulgular, farklı frekanslara (432 Hz ve 440 Hz) göre dinlenen neşeli ve hüzünlü müziklerin, sempatik ve parasempatik aktivasyon düzeyleri arasında anlamlı bir fark yaratmadığını göstermiştir. Ancak akort türünden bağımsız olarak, neşeli müzik dinleyen katılımcılar müzik dinleme sonrası daha fazla gevşeme hissettiklerini bildirmişlerdir. Bunun yanı sıra katılımcıların, akort türünden bağımsız olarak GEMS ölçeğine göre hüzünlü müzik dinleme sonrası yücelik (sublimity) duygusunu canlılık (vitality) ve huzursuzluk (unease) duygusundan daha fazla hissettiği; huzursuzluk duygusunu ise canlılık duygusundan daha fazla hissettiği belirlenmiştir. Neşeli müzik için yapılan analiz sonucunda katılımcıların neşeli müzik dinleme sonrası canlılık duygusunu yücelik ve huzursuzluk duygularından daha fazla hissettiği; yücelik duygusunu ise huzursuzluk duygusundan daha fazla hissettiği görülmüştür. En genel değerlendirmede müzik türünden bağımsız olarak, 440 Hz ile müzik dinleyen katılımcıların 432 Hz ile müzik dinleyen katılımcılara göre müzik dinleme sonrası olumsuz duygu durumunun daha yüksek olduğu; ayrıca erkeklerin kadınlara göre 440 Hz müzikleri dinleme sonrası olumsuz duygu durumunun 432 Hz müzikleri dinleme sonrası olumsuz duygu durumundan daha yüksek olduğu görülmüştür. Elde edilen tüm bulgular akort türünün sempatik ve parasempatik aktivasyon düzeyleri arasında bir farklılaşma yaratmasa da duygu durumu üzerinde bir farklılaşmaya neden olduğunu ima etmektedir.

Investigation on Acoustic Properties of Thruster Chamber with Coaxial Injectors and Plenum Chamber

Based on the URANS equation, a numerical simulation is carried out for acoustic properties of the thruster chamber with coaxial injectors and plenum chamber in a liquid rocket engine. Pressure oscillations with multiacoustic modes are successfully excited in the chamber by using the constant volume bomb method. FFT analysis is applied to obtain the acoustic properties of eigenfrequencies, power amplitudes, and damping rates for each excited acoustic mode. Compared with the acoustic properties in the model chamber with and without an injector as well as with and without the plenum chamber, it can be found that the injector with one open end and one half-open end still can work as a quarter-wave resonator. The power amplitudes of the acoustic mode can be suppressed significantly when its eigenfrequency is close to the tuning frequency of the injector, which is achieved by Cutting down the pressure Peak and Raising up the pressure Trough (CPRT). Compared with the acoustic properties in the model chamber with and without the plenum chamber, it can be found that 1L acoustic pressure oscillation is inhibited completely by the plenum chamber and other acoustic pressure oscillations are also suppressed in a different extent. The injector and plenum chamber have a little effect on the eigenfrequencies and damping rate of each acoustic mode. For multimode pressure oscillation, it is better for tuning frequency of the injector closing to the lower eigenfrequency acoustic mode, which will be effective for suppression of these multiacoustic modes simultaneously.

Design and test of a torsional vibration absorber in series with a planetary gearset

Traditional vibration absorbers have not often been a practical solution for attenuating low frequency drivetrain modes of vibration because of the combination of the large mass and inertia and/or low stiffness, required to tune to the desired frequency. With the goal of reducing the inertia and size of a torsional vibration absorber, a unique vibration absorber was developed. Using a planetary gearset, the effective inertia of the absorber was increased without changing its physical mass, and a torsional mode below 30 Hz was successfully attenuated with physically realizable inertia and stiffness parameters. By reducing the tuned mass, the total volume claimed by the vibration absorber and planetary gearset was up to three times less than an equivalent traditional vibration absorber. A lumped parameter torsional model was developed to determine the optimal configuration of the planetary gearset input, output, and absorber inertia as well as a method to predict the optimal tuning frequency of the planetary torsional vibration absorber. A drivetrain dynamometer setup which emulates a two-degree-of-freedom torsional system was used to experimentally test and validate the performance of two planetary torsional vibration absorber prototypes built based upon the results of the lumped parameter model. The dynamometer setup was designed to have a first torsional mode around 20 Hz in which the planetary torsional vibration absorber was designed to attenuate. Based upon the experimental results of the planetary torsional vibration absorber, a reduction of over 20 dB was achieved.