Development of an Adaptive Helmholtz Resonator for Broadband Noise Control

2004 ◽  
Author(s):  
Simon J. Este`ve ◽  
Marty E. Johnson
Keyword(s):  
Helmholtz Resonator ◽  
Broadband Noise ◽  
Experimental Result ◽  
Helmholtz Resonators ◽  
Large Cylinder ◽  
Payload Fairing ◽  
Compact Design ◽  
High Level ◽  
Design Options ◽  
Control Application

This paper presents the development of adaptive Helmholtz resonators aimed at controlling broadband disturbance for the reduction of noise transmission into rocket payload fairing. Helmholtz resonators are commonly used for narrow band control application and so are designed to present the lowest amount of damping yielding maximum impedance. For this particular application however, optimal damping ratios usually superior to 4% are required. This relatively high level of damping permits more lightweight and compact design options to be considered that are not possible for low damping applications. Two design solutions are presented. The first tunes the resonator by varying the length of an accordion neck. The second varies the HR opening using an iris diaphragm. The characteristics of these two devices are measured, and a solution to maintain the damping level relatively constant is also proposed. Finally, experimental result obtained in a large cylinder representative of a payload fairing using 8 adaptive resonators is presented.

Second Paper: Lateral Helmholtz Resonator Silencer with Turbulence Absorption

1967 ◽  
Vol 182 (1) ◽  
pp. 60-72 ◽  
Author(s):  
Y. N. Chen
Keyword(s):  
Pipe Flow ◽  
Helmholtz Resonator ◽  
High Flow ◽  
Exhaust Pipe ◽  
Helmholtz Resonators ◽  
Intense Noise ◽  
Lateral Resonance ◽  
Fast Flow ◽  
High Level ◽  
Flow Velocities

Lateral Helmholtz resonators are ineffective for fast flow because of the turbulence caused by the movement of the gas mass from the resonator neck into the main pipe flow. The absorption of this turbulence at its source is an effective method for keeping the resonator silencing ability at a high level. Experimental results on an acoustic filter formed by resonators for flow velocities up to 80 m/s, so treated, are compared with the theory. There is evidence of lateral resonance of the gas column in the exhaust pipe at high flow velocities, detected as an intense noise of a discrete frequency (1000 Hz). The excitation of this resonance was found to be due to the pseudo-acoustic wave caused by the neck jets in the resonator. The influence of the flow upon the natural frequency of the resonator is also discussed. The Reynolds number of the flow seems to play an essential role on this point.

Nonlinear behavior of Helmholtz resonator with a compliant wall for low frequency, broadband noise control

2021 ◽  
pp. 1-29
Author(s):  
Maya Pishvar ◽  
Ryan L Harne
Keyword(s):  
Dynamic Response ◽  
Low Frequency ◽  
Nonlinear Behavior ◽  
Helmholtz Resonator ◽  
Broadband Noise ◽  
Sound Attenuation ◽  
Wall Material ◽  
Modeling Framework ◽  
Compliant Wall ◽  
Broadband Sound

Abstract Low frequency sound attenuation is often pursued using Helmholtz resonators (HRs). The introduction of a compliant wall around the acoustic cavity results in a two-degree-of-freedom (2DOF) system capable of more broadband sound absorption. In this study, we report the amplitude-dependent dynamic response of a compliant walled HR and investigate the effectiveness of wall compliance to improve the absorption of sound in linear and nonlinear regimes. The acoustic-structure interactions between the conventional Helmholtz resonator and the compliant wall result in non-intuitive responses when acted on by nonlinear amplitudes of excitation pressure. This paper formulates and studies a reduced order model to characterize the nonlinear dynamic response of the 2DOF HR with a compliant wall compared to that of a conventional rigid HR. Validated by experimental evidence, the modeling framework facilitates an investigation of strategies to achieve broadband sound attenuation, including by selection of wall material, wall thickness, geometry of the HR, and other parameters readily tuned by system design. The results open up new avenues for the development of efficient acoustic resonators exploiting the deflection of a compliant wall for suppression of extreme noise amplitudes.

scholarly journals Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects

2018 ◽  
Vol 8 (10) ◽  
pp. 1923
Author(s):  
Martin Dannemann ◽  
Michael Kucher ◽  
Eckart Kunze ◽  
Niels Modler ◽  
Karsten Knobloch ◽  
...  
Keyword(s):  
Polymer Films ◽  
Helmholtz Resonator ◽  
Broadband Noise ◽  
Acoustic Energy ◽  
Acoustic Damping ◽  
Acoustic Performance ◽  
Acoustic Liners ◽  
Flexible Polymer ◽  
Noise Absorption ◽  
Aero Engines

In aero engines, noise absorption is realised by acoustic liners, e.g., Helmholtz resonator (HR) liners, which often absorb sound only in a narrow frequency range. Due to developments of new engine generations, an improvement of overall acoustic damping performance and in particular more broadband noise absorption is required. In this paper, a new approach to increase the bandwidth of noise absorption for HR liners is presented. By replacing rigid cell walls in the liner’s honeycomb core structure by flexible polymer films, additional acoustic energy is dissipated. A manufacturing technology for square honeycomb cores with partially flexible walls is described. Samples with different flexible wall materials were fabricated and tested. The acoustic measurements show more broadband sound absorption compared to a reference liner with rigid walls due to acoustic-structural interaction. Manufacturing-related parameters are found to have a strong influence on the resulting vibration behaviour of the polymer films, and therefore on the acoustic performance. For future use, detailed investigations to ensure the liner segments compliance with technical, environmental, and life-cycle requirements are needed. However, the results of this study show the potential of this novel liner concept for noise reduction in future aero-engines.

Numerical study for increasement of low frequency sound insulation of double-panel structure using sonic crystals with distributed Helmholtz resonators

2019 ◽  
Vol 33 (14) ◽  
pp. 1950138
Author(s):  
Myong-Jin Kim
Keyword(s):  
Free Space ◽  
Transmission Loss ◽  
Numerical Study ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Sound Insulation ◽  
The Finite Element Method ◽  
Helmholtz Resonators ◽  
Sonic Crystal ◽  
Sonic Crystals

Numerical simulations of the sound transmission loss (STL) of a double-panel structure (DPS) with sonic crystal (SC) comprised of distributed local resonators are presented. The Local Resonant Sonic Crystal (LRSC) consists of “C”-shaped Helmholtz resonator columns with different resonant frequencies. The finite element method is used to calculate the STL of such a DPS. First, the STLs of LRSC in free space and the DPS with LRSC are calculated and compared. It is shown that the sound insulations of the local resonators inserted in the double panel are higher than that in free space for the same size of the SCs and the same number of columns. Next, STL of the DPS in which the SC composed of three columns of local resonators having the same outer and inner diameters but different slot widths are calculated, and a reasonable arrangement order is determined. Finally, the soundproofing performances of DPS with distributed LRSC are compared with the case of insertion of general cylindrical SC for SC embedded in glass wool and not. The results show that the sound insulation of the DPS can be significantly improved in the low frequency range while reducing the total mass without increasing the thickness.

scholarly journals Surface Air Movement: An Important Contributor to Ventilation of Isolated Subsurface Structures?

2019 ◽  
Vol 4 (2) ◽  
pp. 23 ◽  
Author(s):  
Thomas Neil McManus ◽  
Assed Haddad
Keyword(s):  
Air Flow ◽  
Helmholtz Resonator ◽  
Worker Safety ◽  
Time Base ◽  
Near Surface ◽  
Helmholtz Resonators ◽  
Subsurface Structures ◽  
Air Movement ◽  
Air Speed ◽  
Almost All

This study reports on near-surface airspeed measured using a fast-responding thermoanemometer during an investigation of ventilation of an isolated subsurface structure induced by natural forces. Air speed changes continuously, rapidly, and unpredictably when assessed on the time base of one or two seconds. Zero, the most common air speed, occurred in almost all tests throughout the year but especially during cool and cold months. The most probable non-zero air speed, 10.7 m/min (35 ft/min), occurred in all tests. This air speed is below the level of detection by the senses. The number of zero values and the height of the peak at 10.7 m/min follow a repetitive annual cycle. Isolated subsurface structures containing manhole covers share the characteristics of Helmholtz resonators. Grazing air flow across the opening to the exterior induces rotational air flow in the airspace of a Helmholtz resonator. Rotational flow in the airspace potentially influences the exchange of the confined atmosphere with the external one. Ventilation of the airspace occurs continuously and without cost and is potentially enhanced by the unique characteristics of the Helmholtz resonator excited by surface air movement. These results have immense importance and immediate applicability to worker safety.

Removal of Fission Products in the Spent Electrolyte Using Iron Phosphate Glass as a Sorbent

2010 ◽  
Author(s):  
Ippei Amamoto ◽  
Naoki Mitamura ◽  
Tatsuya Tsuzuki ◽  
Yasushi Takasaki ◽  
Atsushi Shibayama ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Phosphate Glass ◽  
Alkali Metals ◽  
Fission Products ◽  
Iron Phosphate ◽  
Experimental Result ◽  
Filtration Method ◽  
High Level ◽  
Filtration Experiment

This study is carried out to make the pyroprocessing hold a competitive advantage from the viewpoint of environmental load reduction and economical improvement. As one of the measures to reduce the volume of the high-level radioactive waste (HLW), the phosphate conversion method is applied for removal of fission products (FP) from the melt, referring to the spent electrolyte in this paper. Among the removing target chlorides in the spent electrolyte i.e., alkali metals, alkaline earth metals and rare earth elements, only the rare earth elements and lithium form the precipitates as insoluble phosphates by reaction with Li3PO4. The sand filtration method was applied to separate FP precipitates from the spent electrolyte. The iron phosphate glass (IPG) powder, which is a compatible material for the immobilization of FP, was used as a filter medium. After filtration experiment, it was proven that insoluble FP could almost be completely removed from the spent electrolyte. Subsequently, we attempted to separate the dissolved FP from the spent electrolyte. The IPG was being used once again but this time as a sorbent instead. This is possible because the IPG has some unique characteristics, e.g., changing the valence of iron, which is one of its network modifiers due to its manufacturing temperature. Therefore, it would be likely to sorb some FP when the chemical condition of IPG is unstable. We produced three kinds of IPG under different manufacturing temperature and confirmed that those glasses could sorb FP as anticipated. According to the experimental result, its sorption efficiency of metal cations was attained at around 20–40%.

scholarly journals Numerical Simulation and Experimental Investigation of the Preparation of Aluminium Alloy 2A50 Semi-Solid Billet by Electromagnetic Stirring

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5470
Author(s):  
Yongfei Wang ◽  
Shengdun Zhao ◽  
Yi Guo
Keyword(s):  
Numerical Simulation ◽  
Aluminium Alloy ◽  
Deep Understanding ◽  
Electromagnetic Stirring ◽  
Experimental Result ◽  
Maximum Speed ◽  
Operating Parameters ◽  
Average Grain Size ◽  
Semi Solid ◽  
High Level

Electromagnetic stirring (EMS) has become one of the most important branches of the electromagnetic processing of materials. However, a deep understanding of the influence of the EMS on the thermo-fluid flow of the aluminium alloy melt, and consequently the refinement of the microstructure is still not available. This paper investigated the influence of the operating parameters of EMS on the magnetohydrodynamics, temperature field, flow field, and the vortex-shaped structure of the melt as well as the microstructure of the aluminium alloy 2A50 billet by numerical simulation and experiments. The operating parameters were categorised into three groups representing high, medium, and low levels of Lorentz forces generated by EMS. The numerical simulation matched well with the experimental result. It was found that a high level of EMS can improve the uniformity of the temperature and flow fields. The maximum speed was observed at the radius of around 25 mm under all EMS levels. Both the depth and diameter of the vortex-shaped structure generated increased with the enhancement in the EMS level. The average grain size of the edge sample of the billet was reduced by 48.3% while the average shape factor was increased by 51.0% under the medium-level EMS.

Recent Studies of Adaptive Tuned Vibration Absorbers/Neutralizers

2009 ◽  
Vol 62 (6) ◽  
Author(s):  
Lari Kela ◽  
Pekka Vähäoja
Keyword(s):  
Piezoelectric Materials ◽  
Helmholtz Resonator ◽  
Primary System ◽  
Vibration Absorbers ◽  
Review Section ◽  
Helmholtz Resonators ◽  
Tuned Vibration Absorbers ◽  
Current Events ◽  
Year 2000 ◽  
Tuned Vibration Absorber

This article gathers together the most recent articles of adjustable tuned vibration absorbers. The tuned vibration absorber was invented over 100 years ago, and its adjustability is also already well-known. However, concentration of this review was only on articles published since the year 2000 in peer reviewed journals, except from certain elementary books and some previous review articles in order to keep up with the current events in this broad field. First a brief inspection of the theory of tuned vibration absorbers (TVAs) is presented. After that mechanical TVAs are presented more carefully. In the same chapter the following are also handled: virtual absorbers, absorbers with adjustable damping, and Helmholtz resonators. Own chapter is allocated for multiple TVAs whose idea is to replace adjustability by adding several TVAs to primary system to damp out vibrations in the wide frequency band. The review section is completed by presenting smart material TVAs, which include, e.g., piezoelectric materials, shape-memory alloys, electrorheological and magnetorheological materials of fluids. An adjustable Helmholtz resonator in a low pressure hydraulic system is presented in Sec. 5. Experiments verify the efficiency of the damping character of the adjustable Helmholtz resonator whose resonant frequency can be varied.

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