scholarly journals On the Optimisation of Multi-Degree-of-Freedom Acoustic Impedances of Low-Frequency Electroacoustic Absorbers for Room Modal Equalisation

2017 ◽  
Vol 103 (6) ◽  
pp. 1025-1036 ◽  
Author(s):  
Etienne Rivet ◽  
Sami Karkar ◽  
Hervé Lissek
Keyword(s):  
Low Frequency ◽  
Degree Of Freedom

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.

scholarly journals A Two-Degree-of-Freedom Cantilever-Based Vibration Triboelectric Nanogenerator for Low-Frequency and Broadband Operation

Electronics ◽  
2019 ◽  
Vol 8 (12) ◽  
pp. 1526 ◽  
Author(s):  
Gang Tang ◽  
Fang Cheng ◽  
Xin Hu ◽  
Bo Huang ◽  
Bin Xu ◽  
...  
Keyword(s):  
Output Voltage ◽  
Low Frequency ◽  
Degree Of Freedom ◽  
Triboelectric Nanogenerator ◽  
Energy Harvesters ◽  
Harvesting Technique ◽  
Wide Range ◽  
Operating Bandwidth ◽  
Self Powered ◽  
Two Degree Of Freedom

With the continual increasing application requirements of broadband vibration energy harvesters (VEHs), many attempts have been made to broaden the bandwidth. As compared to adopted only a single approach, integration of multi-approaches can further widen the operating bandwidth. Here, a novel two-degree-of-freedom cantilever-based vibration triboelectric nanogenerator is proposed to obtain high operating bandwidth by integrating multimodal harvesting technique and inherent nonlinearity broadening behavior due to vibration contact between triboelectric surfaces. A wide operating bandwidth of 32.9 Hz is observed even at a low acceleration of 0.6 g. Meanwhile, the peak output voltage is 18.8 V at the primary resonant frequency of 23 Hz and 1 g, while the output voltage is 14.9 V at the secondary frequency of 75 Hz and 2.5 g. Under the frequencies of these two modes at 1 g, maximum peak power of 43.08 μW and 12.5 μW are achieved, respectively. Additionally, the fabricated device shows good stability, reaching and maintaining its voltage at 8 V when tested on a vacuum compression pump. The experimental results demonstrate the device has the ability to harvest energy from a wide range of low-frequency (<100 Hz) vibrations and has broad application prospects in self-powered electronic devices and systems.

A two-degree-of-freedom string-driven rotor for efficient energy harvesting from ultra-low frequency excitations

Energy ◽  
2020 ◽  
Vol 196 ◽  
pp. 117107
Author(s):  
Qinxue Tan ◽  
Kangqi Fan ◽  
Kai Tao ◽  
Liya Zhao ◽  
Meiling Cai
Keyword(s):  
Energy Harvesting ◽  
Low Frequency ◽  
Degree Of Freedom ◽  
Efficient Energy ◽  
Two Degree Of Freedom

Two degree of freedom vibration based electromagnetic energy harvester for bridge health monitoring system

2020 ◽  
pp. 1045389X2095945
Author(s):  
Muhammad Masood Ahmad ◽  
Farid Ullah Khan
Keyword(s):  
Cantilever Beam ◽  
Energy Harvester ◽  
Low Frequency ◽  
Open Circuit ◽  
Electromagnetic Energy ◽  
Degree Of Freedom ◽  
Mode Shapes ◽  
Fixed End ◽  
Two Degree Of Freedom ◽  
Maximum Voltage

This paper presents an electromagnetic energy harvester to extract low frequency and low acceleration vibration energy available in a bridge environment. The developed harvester is a multi-mode oscillator with dual electromagnetic transduction mechanisms. The harvester consists of two cantilever beams. The first cantilever beam is split into two equal pieces along its length and the second beam placed in between them coming back to the fixed end and attached at outer end to the first beam. This way instead of a long conventional cantilever beam a compact harvester is fabricated. Two magnets as proof masses are attached to each free end of the beam making it a two degree of freedom system (2-DOF). The magnets are positioned to oscillate inside hand wound coils during operation. An analytical model was developed and COMSOL multiphysics was used to simulate the mode shapes of the harvester. The mathematical model was simulated for open circuit voltage in MATLAB and showed closely matching results with the experimental values. The harvester is characterized in lab for its performance under sinusoidal vibrations at low frequency (3 Hz–15 Hz) and low acceleration (0.01–0.09 g) levels. The 2-DOF harvester has two resonant frequencies of 4.4 Hz and 5.5 Hz and a volume of 333 cm3. It produces maximum voltage of 0.6 V at first resonance on coil-1 and maximum voltage of 1.2 V on coil-2 at second resonance at 0.09 g. At acceleration of 0.09 g the harvester produced 2.51 mW at first resonant frequency and 10.7 mW at second resonance. Moreover, the AC output voltage of the harvester is rectified to DC voltage by a three-stage Cockcroft-Walton multiplier type circuit. The DC power output at 0.05 g was 0.939 mW at first resonance and 0.956 mW at second resonance while maximum voltages of 5.4 V on coil-1 and 4 V on coil-2 were produced.

Multi-degree-of-freedom low-frequency electroacoustic absorbers through coupled resonators

2018 ◽  
Vol 132 ◽  
pp. 109-117 ◽  
Author(s):  
Etienne Rivet ◽  
Sami Karkar ◽  
Hervé Lissek
Keyword(s):  
Low Frequency ◽  
Degree Of Freedom ◽  
Coupled Resonators

Analytical Model Development and Model Reduction for Electromechanical Brake System

2004 ◽  
Author(s):  
Jaeho Kwak ◽  
Bin Yao ◽  
Anil Bajaj
Keyword(s):  
Analytical Model ◽  
Model Development ◽  
Low Frequency ◽  
Degree Of Freedom ◽  
Design Stage ◽  
Simplified Models ◽  
Contact Mode ◽  
Early Design Stage ◽  
Invaluable Tool ◽  
Electromechanical Brake

This paper presents a detailed analytical model development which can describe the dynamic behavior of the electromechanical brake-by-wire (BBW) system over the entire operating range. The complete model has 10 degree-of-freedom (DOF) and includes essential nonlinearities such as gear backlashes, Coulomb frictions, and disk gap clearance. Such a full model is reduced to 6 degree-of-freedom model in SIMULINK for simulation study of the effectiveness and the achievable performance of different hardware and controller designs, an invaluable tool in the early design stage of a product. Simulation results show that the model is able to reproduce various nonlinear characteristics including typical structural hysteresis as shown in real brake assembly. The linearized version of the full nonlinear model is then obtained for its modal properties to understand the modes that are critical to the low frequency dynamics of the overall system. The results of the modal analyses are subsequently utilized to obtain two simplified models, one for non-contact mode and the other for the contact mode of operation. The concepts of two simplified models well capture the dynamic characteristics of the system over the frequencies of interest and are being used in the controller (e.g., clamping force control) and estimator (e.g., gap clearance estimation) designs that are under investigation.

An Analytical and Experimental Study of Automobile Dynamics With Random Roadway Inputs

1977 ◽  
Vol 99 (4) ◽  
pp. 284-292 ◽  
Author(s):  
A. J. Healey ◽  
E. Nathman ◽  
C. C. Smith
Keyword(s):  
Experimental Study ◽  
Degrees Of Freedom ◽  
Low Frequency ◽  
Vertical Direction ◽  
Degree Of Freedom ◽  
Vehicle Body ◽  
Acceleration Response ◽  
Wide Range ◽  
Frequency Components ◽  
The Common

This paper presents the results of an analytical and experimental study of ride vibrations in an automobile over roads of various degrees of roughness. Roadway roughness inputs were measured. Three different linear mathematical models were employed to predict the acceleration response of the vehicle body. The models used included two, four, and seven degrees of freedom, primarily for vertical direction motion. The results show that the prime source of errors in predicting responses of this type lies in the common assumptions made for roadway roughness spectra. With adequate description of the roadway inputs, the results showed that the seven degree of freedom model accurately predicted the low frequency response (up to 10 Hz). Using the seven degree of freedom model, predicted accelerations compare well with measured data for a wide range of roadways in the low frequency range. Higher frequency components in the measured acceleration response are significant and are illustrated here.

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