scholarly journals The Didjeridu: Lip Motion and Low Frequency Harmonic Generation

2000 ◽  
Vol 53 (6) ◽  
pp. 835 ◽  
Author(s):  
Lloyd C. L. Hollenberg
Keyword(s):  
Low Frequency ◽  
Striking Difference ◽  
Longitudinal Models ◽  
Damping Force ◽  
Impedance Function ◽  
Longitudinal Model ◽  
Brass Instruments ◽  
Resonance Frequencies ◽  
Case Characteristic ◽  
Generation Of Harmonics

The dynamic acoustics of the Australian didjeridu are studied by separately considering transverse and longitudinal lip vibration models in the context of highly non-sinusoidal lip motion. Timedomain computer simulations are performed based on these lip models coupled to the input impedance function of a straight pipe. For the purposes of direct comparison, detailed results are reported here for lip motion leading to both sinusoidal lip opening area functions (characteristic of higher frequency brass instruments) and the more complex non-sinusoidal (approximately half-closed cycle) case characteristic of the didjeridu. Over a range of lip resonance frequencies, the sounding frequency for the transverse (longitudinal) model is found to be below (above) both the lip and fundamental pipe resonance frequencies, in qualitative agreement with linear theory for these value types. A striking difference is found between the two models when comparing the effect of significant lip closure in the non-sinusoidal cycle—the sounding frequency in the transverse case is raised by up to 10%, whilst essentially unaltered in the longitudinal model. The effect the lips sticking during the non-sinusoidal cycle was considered by increasing the damping force upon closure, and was found in both transverse and longitudinal models to weaken significantly the generation of harmonics in the sound.

scholarly journals A Multi-Mode Broadband Vibration Energy Harvester Composed of Symmetrically Distributed U-Shaped Cantilever Beams

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 203
Author(s):  
Xiaohua Huang ◽  
Cheng Zhang ◽  
Keren Dai
Keyword(s):  
Energy Harvester ◽  
Low Frequency ◽  
Experimental Results ◽  
Vibration Energy ◽  
Cantilever Beams ◽  
Resonant Frequencies ◽  
Promising Alternative ◽  
Piezoelectric Energy ◽  
Straight Beam ◽  
Resonance Frequencies

Using the piezoelectric effect to harvest energy from surrounding vibrations is a promising alternative solution for powering small electronic devices such as wireless sensors and portable devices. A conventional piezoelectric energy harvester (PEH) can only efficiently collect energy within a small range around the resonance frequency. To realize broadband vibration energy harvesting, the idea of multiple-degrees-of-freedom (DOF) PEH to realize multiple resonant frequencies within a certain range has been recently proposed and some preliminary research has validated its feasibility. Therefore, this paper proposed a multi-DOF wideband PEH based on the frequency interval shortening mechanism to realize five resonance frequencies close enough to each other. The PEH consists of five tip masses, two U-shaped cantilever beams and a straight beam, and tuning of the resonance frequencies is realized by specific parameter design. The electrical characteristics of the PEH are analyzed by simulation and experiment, validating that the PEH can effectively expand the operating bandwidth and collect vibration energy in the low frequency. Experimental results show that the PEH has five low-frequency resonant frequencies, which are 13, 15, 18, 21 and 24 Hz; under the action of 0.5 g acceleration, the maximum output power is 52.2, 49.4, 61.3, 39.2 and 32.1 μW, respectively. In view of the difference between the simulation and the experimental results, this paper conducted an error analysis and revealed that the material parameters and parasitic capacitance are important factors that affect the simulation results. Based on the analysis, the simulation is improved for better agreement with experiments.

Compact 2DOF liner based on a long elastic open-neck acoustic resonator for low frequency absorption

2021 ◽  
Vol 69 (1) ◽  
pp. 1-17
Author(s):  
Frank Simon ◽  
Delphine Sebbane ◽  
surname given-names
Keyword(s):  
Low Frequency ◽  
Acoustic Resonator ◽  
Degree Of Freedom ◽  
Tube Length ◽  
Remarkable Feature ◽  
Absorption Frequency ◽  
Acoustic Liners ◽  
Quarter Wavelength ◽  
Resonance Frequencies ◽  
Double Degree

Passive acoustic liners, used in aeronautic engine nacelles to reduce radiated fan noise, have a quarter-wavelength behavior. The simplest systems are SDOF-type (single degree of freedom), consisting of a perforated sheet backed with a honeycomb, whose absorption ability is limited to frequencies near the Helmholtz frequency. Thus, to widen the absorption frequency range, manufacturers use a 2DOF (double degree of freedom) system, with an internal layer over another honeycomb (stack of two resonators). However, one constraint is the limited thickness of the overall system, which reduces the space allotted to each honeycomb. A possible approach, based on a previous concept called LEONAR (long elastic open-neck acoustic resonator), could be to link each perforated layer to hollow tubes inserted in each honeycomb layer, in order to shift resonance frequencies to lower frequencies by extending the air column lengths. The presence of an empty chamber on both sides of the internal perforated layer also allows the tube length to be increased through tubes crossing both cavities, preserving the liner thickness. The main aim of this article is to mathematically describe the principle of a 2DOF LEONAR and to show the relevance of the mathematical model through FEM simulations and experiments performed in an impedance tube. Moreover, its behavior is analyzed through a parametric study, in order to explore its potential for an aeronautic application. A remarkable feature of 2DOF LEONAR-type materials with insertion of bottom tubes in the higher cavity is the possibility of maintaining the low frequency band provided by the original LEONAR concept, while adding a second absorption peak at a higher frequency, by the second layer and the accompanying tubes. There is a fundamental difference from classical SDOF/2DOF resonators, for which the thicknesses are obviously different.

Development of a tunable low-frequency vibration energy harvester and its application to a self-contained wireless fatigue crack detection sensor

2018 ◽  
Vol 18 (3) ◽  
pp. 920-933 ◽  
Author(s):  
Suyoung Yang ◽  
Sung-Youb Jung ◽  
Kiyoung Kim ◽  
Peipei Liu ◽  
Sangmin Lee ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Energy Harvesting ◽  
Crack Detection ◽  
Energy Harvester ◽  
Low Frequency ◽  
Vibration Energy ◽  
Low Frequency Vibration ◽  
Resonance Frequencies ◽  
Energy Harvesting System ◽  
Fatigue Crack Detection

In this study, a tunable electromagnetic energy harvesting system, consisting of an energy harvester and energy harvesting circuits, is developed for harnessing energy from low-frequency vibration (below 10 Hz) of a bridge, and the harvesting system is integrated with a wireless fatigue crack detection sensor. The uniqueness of the proposed energy harvesting system includes that (1) the resonance frequencies of the proposed energy harvester can be readily tuned to the resonance frequencies of a host structure, (2) an improved energy harvesting efficiency compared to other electromagnetic energy harvesters is achieved in low-frequency and vibration, and (3) high-efficiency energy harvesting circuits for rectification are developed. Furthermore, the developed energy harvesting system is integrated with an on-site wireless sensor deployed on Yeongjong Grand Bridge in South Korea for online fatigue crack detection. To the best knowledge of the authors, this is the very first study where a series of low-frequency vibration energy harvesting, rectification, and battery charging processes are demonstrated under a real field condition. The field test conducted on Yeongjong Grand Bridge, where fatigue cracks have become of a great concern, shows that the proposed energy harvester can generate a peak voltage of 2.27 V and a root mean square voltage of 0.21 V from 0.18-m/s2 root mean square acceleration at 3.05 Hz. It is estimated the proposed energy harvesting system can harness around 67.90 J for 3 weeks and an average power of 37.42 µW. The battery life of the wireless sensor is expected to extend from 1.5 to 2.2 years. The proposed energy harvesting circuits, composed of the AC–DC and boost-up converters, exhibit up to 50% battery charging efficiency when the voltage generated by the proposed energy harvester is 200 mV or higher. The proposed boost-up converter has a 100 times wider input power range than a conventional boost-up converter with a similar efficiency.

scholarly journals Performance Analysis of an Electromagnetically Coupled Piezoelectric Energy Scavenger

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 845 ◽  
Author(s):  
Abdolreza Pasharavesh ◽  
Reza Moheimani ◽  
Hamid Dalir
Keyword(s):  
Energy Harvesting ◽  
Multiple Scales ◽  
Nonlinear Partial Differential Equations ◽  
Low Frequency ◽  
Primary Resonance ◽  
Excitation Amplitude ◽  
Load Resistance ◽  
Response Curves ◽  
Piezoelectric Energy ◽  
Resonance Frequencies

The deliberate introduction of nonlinearities is widely used as an effective technique for the bandwidth broadening of conventional linear energy harvesting devices. This approach not only results in a more uniform behavior of the output power within a wider frequency band through bending the resonance response, but also contributes to energy harvesting from low-frequency excitations by activation of superharmonic resonances. This article investigates the nonlinear dynamics of a monostable piezoelectric harvester under a self-powered electromagnetic actuation. To this end, the governing nonlinear partial differential equations of the proposed harvester are order-reduced and solved by means of the perturbation method of multiple scales. The results indicate that, according to the excitation amplitude and load resistance, different responses can be distinguished at the primary resonance. The system behavior may involve the traditional bending of response curves, Hopf bifurcations, and instability regions. Furthermore, an order-two superharmonic resonance is observed, which is activated at lower excitations in comparison to order-three conventional resonances of the Duffing-type resonator. This secondary resonance makes it possible to extract considerable amounts of power at fractions of natural frequency, which is very beneficial in micro-electro-mechanical systems (MEMS)-based harvesters with generally high resonance frequencies. The extracted power in both primary and superharmonic resonances are analytically calculated, then verified by a numerical solution where a good agreement is observed between the results.

Bandgap Properties of Two-Layered Locally Resonant Phononic Crystals

2020 ◽  
Vol 12 (07) ◽  
pp. 2050075
Author(s):  
Hongyun Wang ◽  
Heow Pueh Lee ◽  
Wei Xu
Keyword(s):  
Coating Thickness ◽  
Low Frequency ◽  
Phononic Crystals ◽  
Formation Mechanisms ◽  
Frequency Range ◽  
The Third ◽  
Resonance Frequencies ◽  
Rubber Coating ◽  
Lower Frequency Range ◽  
Mass Spring

Multi-layered locally resonant phononic crystals (LRPCs) with wider and multiple bandgaps (BGs) in low frequency range and small size of the unit cell have promising applications in noise and vibration controls. In this paper, a 2D two-layered ternary LRPC consisting of a periodical array of cylindrical inclusions embedded in an epoxy matrix is investigated by the finite element method (FEM), where the inclusion is comprised of two coaxial cylindrical steel cores with rubber coating. It is found that the size of the inclusion of the 2D two-layered ternary LRPC has significant effects on the BG properties. With the increase of the core radius and coating thickness, the first BG would shift to lower frequency range with its width decreasing, and the second BG width would become wider until the third BG appears. Especially, with the increase of the coating thickness, more bands and BGs would appear in the lower frequency range. Based on the formation mechanisms of the BGs, several mass-spring models to predict the frequencies of the first two BG edges are developed. The results calculated by these mass-spring models are in good agreement with those by the FEM except for the upper edge frequency of the second BG when the rubber coating thickness exceeds a certain value and the third BG is opened up. These proposed mass-spring models would allow for quick pre-estimation of the resonance frequencies, and facilitate the selection of possible parameters for the wider and lower frequency BGs to obtain the desired attenuation bands. The studies would also benefit the design of multiple BGs for some device applications.

scholarly journals A low-cost acoustic permeameter

2017 ◽  
Vol 6 (1) ◽  
pp. 199-207 ◽  
Author(s):  
Stephen A. Drake ◽  
John S. Selker ◽  
Chad W. Higgins
Keyword(s):  
Standard Deviation ◽  
Relative Error ◽  
Low Cost ◽  
Low Frequency ◽  
Environmental Noise ◽  
Intrinsic Permeability ◽  
Sampling Errors ◽  
Resonance Frequencies ◽  
The Mean ◽  
Frequency Approximation

Abstract. Intrinsic permeability is an important parameter that regulates air exchange through porous media such as snow. Standard methods of measuring snow permeability are inconvenient to perform outdoors, are fraught with sampling errors, and require specialized equipment, while bringing intact samples back to the laboratory is also challenging. To address these issues, we designed, built, and tested a low-cost acoustic permeameter that allows computation of volume-averaged intrinsic permeability for a homogenous medium. In this paper, we validate acoustically derived permeability of homogenous, reticulated foam samples by comparison with results derived using a standard flow-through permeameter. Acoustic permeameter elements were designed for use in snow, but the measurement methods are not snow-specific. The electronic components – consisting of a signal generator, amplifier, speaker, microphone, and oscilloscope – are inexpensive and easily obtainable. The system is suitable for outdoor use when it is not precipitating, but the electrical components require protection from the elements in inclement weather. The permeameter can be operated with a microphone either internally mounted or buried a known depth in the medium. The calibration method depends on choice of microphone positioning. For an externally located microphone, calibration was based on a low-frequency approximation applied at 500 Hz that provided an estimate of both intrinsic permeability and tortuosity. The low-frequency approximation that we used is valid up to 2 kHz, but we chose 500 Hz because data reproducibility was maximized at this frequency. For an internally mounted microphone, calibration was based on attenuation at 50 Hz and returned only intrinsic permeability. We found that 50 Hz corresponded to a wavelength that minimized resonance frequencies in the acoustic tube and was also within the response limitations of the microphone. We used reticulated foam of known permeability (ranging from 2 × 10−7 to 3 × 10−9 m2) and estimated tortuosity of 1.05 to validate both methods. For the externally mounted microphone the mean normalized standard deviation was 6 % for permeability and 2 % for tortuosity. The mean relative error from known measurements was 17 % for permeability and 2 % for tortuosity. For the internally mounted microphone the mean normalized standard deviation for permeability was 10 % and the relative error was also 10 %. Permeability determination for an externally mounted microphone is less sensitive to environmental noise than is the internally mounted microphone and is therefore the recommended method. The approximation using the internally mounted microphone was developed as an alternative for circumstances in which placing the microphone in the medium was not feasible. Environmental noise degrades precision of both methods and is recognizable as increased scatter for replicate data points.

An Advanced Test Method to Determine Viscous Damping of Floating Structures

2010 ◽  
Author(s):  
Z. J. Huang ◽  
B. J. O’Donnell ◽  
T. W. Yung ◽  
S. T. Slocum
Keyword(s):  
Low Frequency ◽  
Test Method ◽  
Total Force ◽  
Viscous Damping ◽  
Damping Force ◽  
Restoring Force ◽  
Viscous Forces ◽  
Motion Time ◽  
Research Company ◽  
Time Histories

ExxonMobil Upstream Research Company developed an advanced model test method to determine reliable damping values for predicting low frequency motions of an FLNG barge and an LNG carrier. Since viscous damping forces are a very small portion of the total force on the model, how to separate the viscous forces from the total forces is the key technical challenge. To better isolate viscous damping forces, an inertial compensation system consisting of springs was employed in the test. The spring stiffness was designed such that the restoring force cancelled the large inertial loads at the oscillation frequency. Furthermore, double-body models were built and were deeply submerged to minimize surface wave damping. With such an experimental setup, the total force measured was mainly the viscous damping force. Viscous damping was derived from the measured force and motion time histories.

A Novel Magnetorheological Concentric Spiral-Flow Damper

2015 ◽  
Author(s):  
Kai Hsiang Chang ◽  
Jing Long Tong ◽  
Chou Min Chia ◽  
Kuang Yuh Huang
Keyword(s):  
Heat Dissipation ◽  
Experimental Studies ◽  
Low Frequency ◽  
Mr Damper ◽  
Flow Channel ◽  
Spiral Flow ◽  
Damping Force ◽  
Fixed Space ◽  
Novel Design ◽  
High Range

In this article, a novel design of MR damper, concentric spiral flow MR damper, is proposed. It could improve the heat dissipation problem which is usually found in traditional MR damper. The proposed MR damper has a concentric spiral flow channel around the cylinder which not only separates coils from MR fluid, but also increases the length of flow channel in a fixed space. Experimental studies has been conducted to demonstrate the performance of the proposed MR damper, the result shows the MR damper generates the maximum damping force of 188 N without applying magnetic field and 1251 N when inputting 1.5 A at low frequency, which means the damper has high range of adjustable damping force. The CSF-damper can be used to systems or structures with low dynamic response.

Determination of Viscous Damping for Low Frequency Motions of Floating Structures

2011 ◽  
Author(s):  
Z. J. Huang ◽  
B. J. O’Donnell ◽  
T. W. Yung ◽  
S. T. Slocum
Keyword(s):  
Forced Oscillation ◽  
Low Frequency ◽  
Test Method ◽  
Irregular Waves ◽  
Viscous Damping ◽  
Damping Force ◽  
Near Resonance ◽  
Research Company ◽  
Decay Tests ◽  
Scale Motion

ExxonMobil Upstream Research Company developed an advanced model test method to determine reliable damping values for predicting low frequency motions of an FLNG barge and an LNG carrier [1]. An inertial compensation system was introduced in the test to confidently isolate the relatively very small viscous damping force from the total measured forces in the forced oscillation tests. In the system, the spring stiffness in the restoring mechanism was tuned such that the test was done near resonance. This method has been successfully applied to ExxonMobil forced oscillation tests to measure damping of deeply submerged, double body models. Three types of motions were generated in the tests: sinusoidal motions, decay motions and motions with multiple frequencies. In this paper, the authors attempt to correlate the damping obtained from decay tests and from tests with motions of multiple frequency components. Findings from this work help determine damping for predictions of full scale motion in irregular waves.

Saccade-related activity in monkey superior colliculus. I. Characteristics of burst and buildup cells

1995 ◽  
Vol 73 (6) ◽  
pp. 2313-2333 ◽  
Author(s):  
D. P. Munoz ◽  
R. H. Wurtz
Keyword(s):  
Superior Colliculus ◽  
High Frequency ◽  
Low Frequency ◽  
Striking Difference ◽  
Related Activity ◽  
Slow Increase ◽  
High Frequency Discharge ◽  
Optimal Direction ◽  
Saccade Onset ◽  
Increased Activity

1. In the monkey superior colliculus (SC), the activity of most saccade-related neurons studied so far consists of a burst of activity in a population of cells at one place on the SC movement map. In contrast, recent experiments in the cat have described saccade-related activity as a slow increase in discharge before saccades followed by a hill of activity moving across the SC map. In order to explore this striking difference in the distribution of activity across the SC, we recorded from all saccade-related neurons that we encountered in microelectrode penetrations through the monkey SC and placed them in categories according to their activity during the generation of saccades. 2. When we considered the activity preceding the onset of the saccade, we could divide the cells into two categories. Cells with burst activity had a high-frequency discharge just before saccade onset but little activity between the signal to make a saccade and saccade onset. About two thirds of the saccade-related cells had only a burst of activity. Cells with a buildup of activity began to discharge at a low frequency after the signal to make a saccade and the discharge continued until generation of the saccade. About one third of the saccade-related cells studied had a buildup of activity, and about three fourths of these cells also gave a burst of activity with the saccade in addition to the slow buildup of activity. 3. The buildup of activity seemed to be more closely related to preparation to make a saccade than to the generation of the saccade. The buildup developed even in cases when no saccade occurred. 4. The falling phase of the discharge of these saccade-related cells stopped with the end of the saccade (a clipped discharge), shortly after the end of the saccade (partially clipped), or long after the end of the saccade (unclipped). 5. Some cells had closed movement fields in which saccades that were substantially smaller or larger than the optimal amplitude were not associated with increased activity. Other cells tended to have open-ended movement fields without any peripheral border; they were active for all saccades of optimal direction whose amplitudes were equal to or greater than a given amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

Sign in / Sign up

Export Citation Format

Share Document