Reduction of the Sound Pressure Radiated by a Submarine by Isolation of the End Caps

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Mauro Caresta ◽  
Nicole J. Kessissoglou
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Axial Direction ◽  
Radial Component ◽  
Axial Motion ◽  
Low Frequencies ◽  
End Caps ◽  
Passive Isolation ◽  
Radiated Sound ◽  
Finite Cylindrical Shell

A passive isolation approach to reduce the sound pressure radiated by a submarine is presented. The submerged vessel is modeled as a stiffened cylindrical hull partitioned by bulkheads and with two end caps of conical shape. Fluctuating forces from the propeller are transmitted to the hull through the shaft and a rigid foundation, resulting in axisymmetric excitation of the hull. The hull surface motion is mainly in the axial direction with a small radial component due to the coupling between the two orthogonal shell displacements. The sound pressure resulting from the axial motion is radiated from the end caps of the submarine. This work investigates reduction of the far field sound pressure by passive isolation of the end caps from the main hull. Isolation of the axial motion of the end caps from the cylindrical hull results in significant reduction of the radiated sound at low frequencies. The fluid loading approximation for a finite cylindrical shell in the low frequency range is also discussed.

scholarly journals Theoretical and experimental study on a finite size vector sensor array with a cylindrically symmetric carrier

2019 ◽  
Vol 283 ◽  
pp. 07008
Author(s):  
Junyuan Guo ◽  
Shi-e Yang ◽  
Hongjuan Chen ◽  
Shengchun Piao ◽  
Longhao Qiu
Keyword(s):  
Finite Size ◽  
Low Frequency ◽  
Doa Estimation ◽  
Radial Component ◽  
Tangential Component ◽  
Low Frequencies ◽  
Cylindrically Symmetric ◽  
Noise Characteristics ◽  
Vector Sensor ◽  
Array Gain

In this work, a finite size acoustic vector sensor (AVS) array is designed and its performance is theoretically and experimentally studied. The two-dimensional AVS array is comprised of five vector sensors and configured as a cross, and the array carrier is a cylindrically symmetric structure. Theoretical analysis and simulation indicate that the proposed method considering structure scattering can widen the working bandwidth. Furthermore, the utilization of vector sensor enables a significant white noise gain improvement at low frequencies, which makes the array more robust and easier to realize. Experiments have been done to study the array performance from several aspects including sensor noise characteristics, the beampattern, the direction-of-arrival (DOA) estimation ability and the array gain. From the change of the sensor directivity patterns or the amplitude distortion of the noise field, we can clearly observe the scattering field intensity. Moreover, it shows that the influence of the structure scattering on the tangential component of the vector field is symmetric, while that of the radial component is asymmetric. Experimental results also demonstrate that, with the proposed method, the 2nd and the 3rd order beamformers can be obtained which could be further used for the estimation of target DOA. In addition, an array gain of at least 6 dB is obtained capable of detection of weak signals. Our results indicate that the proposed array with a physical size less than one meter, although affected by nearby scatterers, can effectively break the Rayleigh limit and realize the remote detection in low-frequency regime.

The Sound Environment of the Foetal Sheep

Behaviour ◽  
1982 ◽  
Vol 81 (2-4) ◽  
pp. 296-315 ◽  
Author(s):  
B.A. Baldwin ◽  
B.C.J. Moore ◽  
Sally E. Armitage ◽  
J. Toner ◽  
Margaret A. Vince
Keyword(s):  
Sound Pressure ◽  
Body Wall ◽  
Low Frequency ◽  
Sound Level ◽  
The Body ◽  
Human Foetus ◽  
Low Frequencies ◽  
Sound Environment ◽  
High Sound ◽  
Foetal Lamb

AbstractThe sound environment of the foetal lamb was recorded using a hydrophone implanted a few weeks before term in a small number of pregnant ewes. It was implanted inside the amniotic sac and sutured loosely to the foetal neck, to move with the foetus. Results differ from those reported earlier for the human foetus: sounds from the maternal cardiovascular system were picked up only rarely, at very low frequencies and at sound pressures around, or below, the human auditory threshold. Other sounds from within the mother occurred intermittently and rose to a high sound pressure only at frequencies above about 300 Hz. Sounds from outside the mother were picked up by the implanted hydrophone when the external sound level rose above 65-70 dB SPL, and the attenuation in sound pressure was rarely more than 30 dB and, especially at low frequencies, usually much less. However, attenuation due to the transmission of sound through the body wall and other tissues tended to change from time to time. It is concluded that the foetal lamb's sound environment consists of (1) intermittent low frequency sounds associated largely with the ewe's feeding and digestive processes and (2) sounds such as vocalisations from the flock, human voices and other sounds from outside the mother.

Low Frequency Calibration of Measurement Microphones

2009 ◽  
Vol 28 (3) ◽  
pp. 223-228 ◽  
Author(s):  
Gunnar Rasmussen ◽  
Kim M. Nielson
Keyword(s):  
Frequency Response ◽  
Sound Pressure ◽  
Low Frequency ◽  
Constant Force ◽  
Low Frequencies ◽  
Proportional Relation ◽  
Frequency Calibration ◽  
Large Piston

The calibration of measurement microphones below 100 Hz is not very well covered by the present IEC standards. The uncertainty increases rapidly and for very low frequencies it goes toward infinity. This paper approaches this issue and presents a unique way to verifying and calibrating the low-frequency response of measurement microphones. Using a small isolated calibration volume and applying a constant force to a large piston inside this volume, you obtain a direct proportional relation between force and sound pressure, allowing calibration of measurement microphones down to 0.01 Hz.

scholarly journals Design and Analysis of a Novel Microspeaker with Enhanced Low-Frequency SPL and Size Reduction

2020 ◽  
Vol 10 (24) ◽  
pp. 8902
Author(s):  
Ki-Hong Park ◽  
Zhi-Xiong Jiang ◽  
Sang-Moon Hwang
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Experimental Results ◽  
Multimedia Content ◽  
The Novel ◽  
Element Analysis ◽  
Low Frequencies ◽  
Acoustic Performance ◽  
Technological Developments ◽  
New Type

In the era of multimedia devices, smartphones have become the primary device for consuming multimedia content. As technological developments have facilitated a more immersive multimedia experience, enlarged displays and the use of several sensors have limited the allowable size of microspeakers. Although sound plays an important role when consuming multimedia content, the limited space for microspeakers in modern devices leads to poor acoustic performance, especially at low frequencies. To address this issue, this paper proposes a novel microspeaker structure that enhances the low-frequency sound pressure level (SPL), while also featuring reduced exterior dimensions. The structure was designed and analyzed using 3D finite element analysis. Through coupling analysis, the simulation results were verified on the basis of the experimental results. The novel microspeaker has one outer magnet surrounding the entire coil, unlike in prototype microspeakers, which have two outer magnets. The gap between the top plates and coil is reduced, and a new type of coil is introduced for the purpose of increasing electromagnetic force. The samples were manufactured, and their SPLs were tested in an anechoic chamber. The experimental results prove that the proposed microspeaker offers an improved SPL at low frequencies compared with prototype microspeakers.

scholarly journals Hearing in the African lungfish ( Protopterus annectens ): pre-adaptation to pressure hearing in tetrapods?

2010 ◽  
Vol 7 (1) ◽  
pp. 139-141 ◽  
Author(s):  
Jakob Christensen-Dalsgaard ◽  
Christian Brandt ◽  
Maria Wilson ◽  
Magnus Wahlberg ◽  
Peter T. Madsen
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
West African ◽  
Low Frequencies ◽  
Frequency Responses ◽  
Protopterus Annectens ◽  
Vibration Detection ◽  
Low Frequency Vibration ◽  
African Lungfish ◽  
Early Tetrapods

Lungfishes are the closest living relatives of the tetrapods, and the ear of recent lungfishes resembles the tetrapod ear more than the ear of ray-finned fishes and is therefore of interest for understanding the evolution of hearing in the early tetrapods. The water-to-land transition resulted in major changes in the tetrapod ear associated with the detection of air-borne sound pressure, as evidenced by the late and independent origins of tympanic ears in all of the major tetrapod groups. To investigate lungfish pressure and vibration detection, we measured the sensitivity and frequency responses of five West African lungfish ( Protopterus annectens ) using brainstem potentials evoked by calibrated sound and vibration stimuli in air and water. We find that the lungfish ear has good low-frequency vibration sensitivity, like recent amphibians, but poor sensitivity to air-borne sound. The skull shows measurable vibrations above 100 Hz when stimulated by air-borne sound, but the ear is apparently insensitive at these frequencies, suggesting that the lungfish ear is neither adapted nor pre-adapted for aerial hearing. Thus, if the lungfish ear is a model of the ear of early tetrapods, their auditory sensitivity was limited to very low frequencies on land, mostly mediated by substrate-borne vibrations.

scholarly journals Investigation of Low-Frequency Sound Radiation Characteristics and Active Control Mechanism of a Finite Cylindrical Shell

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Shaohu Ding ◽  
Chunyang Mu ◽  
Yang Gao ◽  
Hong Liu ◽  
Maoqiang Li
Keyword(s):  
Cylindrical Shell ◽  
Active Control ◽  
Physical Mechanism ◽  
Sound Power ◽  
Radiation Characteristics ◽  
Low Frequencies ◽  
Acoustic Control ◽  
Radiated Sound ◽  
Finite Cylindrical Shell ◽  
Structural Acoustic Control

In this paper, the radiation characteristics and active structural acoustic control of a submerged cylindrical shell at low frequencies are investigated. First, the coupled vibro-acoustic equations for a submerged finite cylindrical shell are solved by a modal decomposition method, and the radiation impedance is obtained by the fast Fourier transform. The modal shapes of the first ten acoustic radiation modes and the structure-dependent radiation modes are presented. The relationships between the vibration modes and the radiation modes as well as the contributions of the radiation modes to the radiated sound power are given at low frequencies. Finally, active structural acoustic control of a submerged finite cylindrical shell is investigated by considering the fluid-structure coupled interactions. The physical mechanism of the active control is discussed based on the relationship between the vibration and radiation modes. The results showed that, at low frequencies, only the first several radiation modes contributed to the sound power radiated from a submerged finite cylindrical shell excited by a radial point force. By determining the radiation modes that dominate the contribution to the radiated sound, the physical mechanism of the active control is explained, providing a potential tool to allow active control of the vibro-acoustic responses of submerged structures more effectively.

High-Intensity Acoustic Test Facility Using Hydraulics

1999 ◽  
Vol 42 (1) ◽  
pp. 46-50
Author(s):  
Paul Lieberman
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Fatigue Tests ◽  
Pressure Level ◽  
Test Facility ◽  
Hydraulic Control ◽  
Hydraulic Facility ◽  
Low Frequencies ◽  
Hydraulic Simulator

The hour-long duration acoustic fatigue tests at levels above 190 dB overall sound pressure level (OASPL) can be achieved with the required sound pressure level (SPL) spectrum using available test facilities with a hydraulic simulator, which operates at only 3 to 10 psi. Furthermore, the hydraulic control at the low frequencies is available, whereas there is a 50-Hz frequency cutoff for acoustic test facilities. Many structures have destructive low-frequency resonant modes which would be properly excited in the hydraulic facility and not in the acoustic facility.

The reaction of a captive herring school to playbacks of a noise-reduced and a conventional research vessel

2015 ◽  
Vol 72 (4) ◽  
pp. 491-499 ◽  
Author(s):  
Nils Olav Handegard ◽  
Alex De Robertis ◽  
Guillaume Rieucau ◽  
Kevin Boswell ◽  
Gavin J. Macaulay
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Clupea Harengus ◽  
Research Vessel ◽  
Frequency Noise ◽  
Atlantic Herring ◽  
Low Frequencies ◽  
Vessel Noise ◽  
Fish Avoidance

Fish avoidance of vessels can bias fisheries-independent surveys. To understand these biases, recordings of underwater radiated vessel noise from a noise-reduced and a conventional research vessel were played back at the same sound pressure levels (SPL) as experienced in situ to Atlantic herring (Clupea harengus) in a net pen at two different densities. The noise-reduced vessel recording was also scaled to the same SPL as the conventional vessel to test if characteristics other than SPL affected the reactions. Overall, only weak reactions were observed, but reactions were stronger in the low-density school, in the middle of the pen, and for the scaled silent vessel compared with the conventional vessel. These observations may be attributable to the lack of low frequencies (<50 Hz) in the playbacks, differential motivation for reaction driven by fish density, higher low-frequency noise in the middle of the pen (but lower overall SPL), and characteristics other than SPL. These results call into question the use of SPL as a proxy for fish reaction to vessels as used in standards for construction of research vessels.

scholarly journals Calculation of sound pressure level of marine propeller in low frequency

2018 ◽  
Vol 37 (1) ◽  
pp. 60-73 ◽  
Author(s):  
Mohsen Gorji ◽  
Hassan Ghassemi ◽  
Jalal Mohamadi
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Hydrodynamic Pressure ◽  
Pressure Level ◽  
Navier Stokes ◽  
Marine Propeller ◽  
Low Frequencies ◽  
Directivity Patterns ◽  
Good Agreement

The research performed in this paper is carried out to calculate the sound pressure level of the marine propeller by Reynolds-Averaged Navier–Stokes solver in low frequencies band. Noise is generated by the induced trailing vortex wake and induced pressure pulses. The two-step Fflowcs Williams and Hawkings equations are used to calculate hydrodynamic pressure and its performance as well as sound pressure level at various points around the propeller. The directivity patterns of this propeller and accurate explanation of component propeller noise are discussed. Comparison of the numerical results shows good agreement with the experimental data.

Reduction of Hull-Radiated Noise Using Vibroacoustic Optimization of the Propulsion System

2011 ◽  
Vol 55 (03) ◽  
pp. 149-192 ◽  
Author(s):  
Mauro Caresta ◽  
Nicole J. Kessissoglou
Keyword(s):  
Sound Pressure ◽  
Search Algorithm ◽  
Great Influence ◽  
Low Frequency ◽  
Pattern Search ◽  
Propulsion System ◽  
Stiffened Cylindrical Shell ◽  
Radiated Noise ◽  
End Plate ◽  
Radiated Sound

Vibration modes of a submarine are excited by fluctuating forces generated at the propeller and transmitted to the hull via the propeller-shafting system. The low frequency vibrational modes of the hull can result in significant sound radiation. This work investigates reduction of the far-field radiated sound pressure from a submarine using a resonance changer implemented in the propulsion system as well as design modifications to the propeller-shafting system attachment to the hull. The submarine hull is modeled as a fluid-loaded ring-stiffened cylindrical shell with truncated conical end caps. The propeller-shafting system is modeled in a modular approach using a combination of mass-spring-damper elements, beams, and shells. The stern end plate of the hull, to which the foundation of the propeller-shafting system is attached, is modeled as a circular plate coupled to an annular plate. The connection radius of the foundation to the stern end plate is shown to have a great influence on the structural and acoustic responses and is optimized in a given frequency range to reduce the radiated noise. Optimum connection radii for a range of cost functions based on the maximum radiated sound pressure are obtained for both simple support and clamped attachments of the foundation to the hull stern end plate. A hydraulic vibration attenuation device known as a resonance changer is implemented in the dynamic model of the propeller-shafting system. A combined genetic and pattern search algorithm was used to find the optimum virtual mass, stiffness, and damping parameters of the resonance changer. The use of a resonance changer in conjunction with an optimized connection radius is shown to give a significant reduction in the low frequency structure-borne radiated sound.

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