scholarly journals Study on Sound Generating Mechanism Using Vibrational Energy and Sound Energy. 2nd Report. Relationship between Structural Intensity Vortex Flow and Sound Field.

1996 ◽  
Vol 62 (593) ◽  
pp. 97-103 ◽  
Author(s):  
Noritoshi NAKAGAWA ◽  
Akihiko HIGASHI ◽  
Yasuhisa SEKIGUCHI
Keyword(s):  
Vortex Flow ◽  
Vibrational Energy ◽  
Sound Field ◽  
Sound Energy ◽  
Structural Intensity

General Theory of the Energy Relations in Halls with Asymmetrical Absorption

1998 ◽  
Vol 5 (3) ◽  
pp. 163-183 ◽  
Author(s):  
Higini Arau
Keyword(s):  
General Theory ◽  
Uniform Distribution ◽  
Decay Time ◽  
Sound Field ◽  
Reverberation Time ◽  
Sound Energy ◽  
Method Of Calculation ◽  
New Energy ◽  
Energy Relations

In this paper we describe a method of calculation of the energy relations in halls where the existence of a non-uniform distribution of absorptive material in the room results in a non-diffuse sound field. The cases of halls used for concerts and speech have both been treated in order to derive new energy relations that yield known expressions when applied to a diffuse sound field. The importance of the initial reverberation time corresponding to the first portion of the decay has been verified showing that the main subjective parameters relating to the sound energy are influenced strongly by this portion, which is called the Early Decay Time if it is measured in the first 10 dB of the decay.

Gyroscopic Effects of a Vibrationally Isolated Rotating Disk and Shaft

1997 ◽  
Author(s):  
Donald L. Margolis
Keyword(s):  
Vibrational Energy ◽  
Rotating Disk ◽  
Aircraft Engine ◽  
Energy Transmission ◽  
Sound Energy ◽  
Supporting Structure ◽  
Rotating Machine ◽  
Established Fact ◽  
Radiated Sound ◽  
Gyroscopic Effects

Abstract An aircraft engine is an example of a rotating machine whose rotating imbalance will be transmitted as vibrational energy into the structure to which it is attached. There is considerable interest in understanding this energy transmission in order to design mounting systems, both passive and active, which can control this transmission the best possible way in order to reduce structurally borne noise in the cabin. It is a well established fact in acoustics[1] that in order to reduce perceived sound at the listener, the noise transmission path must be severed by 1) eliminating the source of the disturbance (usually difficult if not impossible), 2) preventing propagation of energy into the structure and ultimately to structural surfaces, 3) preventing radiation of sound energy from vibrating surfaces, and 4) preventing radiated sound from reaching the listener. In this paper we address only the prevention of energy transmission from the source into the supporting structure through use of some type of mounting system.

scholarly journals A Prediction Method for Acoustic Intensity Vector Field of Elastic Structure in Shallow Water Waveguide

2020 ◽  
Vol 2020 ◽  
pp. 1-23
Author(s):  
Wenbo Wang ◽  
Desen Yang ◽  
Jie Shi
Keyword(s):  
Spatial Structure ◽  
Shallow Water ◽  
Transfer Functions ◽  
Source Parameters ◽  
Prediction Method ◽  
Sound Field ◽  
Elastic Structure ◽  
Superposition Method ◽  
Acoustic Intensity ◽  
Sound Energy

Compared with scalar sound field, vector sound field explained the spatial structure of sound field better since it not only presents the sound energy distribution but also describes the sound energy flow characteristics. Particularly, with more complicated interaction among different wavefronts, the vector sound field characteristics of an elastic structure in a shallow water waveguide are worthy of studying. However, there is no reliable prediction method for the vector sound field of an elastic structure with a high efficiency in a shallow water waveguide. To solve the problem, transfer functions in the waveguide have been modified with some approximations to apply for the vector sound field prediction of elastic structures in shallow water waveguides. The method is based on the combined wave superposition method (CWSM), which has been proved to be efficient for predicting scalar sound field. The rationality of the approximations is validated with simulations. Characteristics of the complex acoustic intensity, especially the vertical components are observed. The results show that, with constructive and destructive interferences in the depth direction, there could be quantities of crests and vortices in the spatial structure of time-dependent complex intensity, which manifest a unique dynamic characteristic of sound energy. With more complicated interactions among the wavefronts, a structure source could not be equivalent to a point source in most instances. The vector sound field characteristics of the two sources could be entirely different, even though the scalar sound field characteristics are similar. Meanwhile, source types, source parameters, ocean environment parameters, and geo parameters may have influence on the vector sound field characteristics, which could be explained with the normal mode theory.

Estimation of vibrational energy flow by sound energy in a vibrating rectangular plate

1996 ◽  
Vol 100 (4) ◽  
pp. 2596-2596
Author(s):  
Noritoshi Nakagawa ◽  
Akihiko Higashi ◽  
Yasuhisa Sekiguchi
Keyword(s):  
Rectangular Plate ◽  
Energy Flow ◽  
Vibrational Energy ◽  
Sound Energy ◽  
Vibrational Energy Flow

scholarly journals A Revised Sound Energy Theory Based on a New Formula for the Reverberation Radius in Rooms with Non-Diffuse Sound Field

2015 ◽  
Vol 40 (1) ◽  
pp. 33-40 ◽  
Author(s):  
Higini Arau-Puchades ◽  
Umberto Berardi
Keyword(s):  
Sound Absorption ◽  
Sound Field ◽  
Critical Distance ◽  
Sound Level ◽  
Reverberation Time ◽  
Sound Energy ◽  
Sound Fields ◽  
Energy Theory ◽  
New Interpretation ◽  
New Formula

Abstract This paper discusses the concept of the reverberation radius, also known as critical distance, in rooms with non-uniformly distributed sound absorption. The reverberation radius is the distance from a sound source at which the direct sound level equals the reflected sound level. The currently used formulas to calculate the reverberation radius have been derived by the classic theories of Sabine or Eyring. However, these theories are only valid in perfectly diffused sound fields; thus, only when the energy density is constant throughout a room. Nevertheless, the generally used formulas for the reverberation radius have been used in any circumstance. Starting from theories for determining the reverberation time in non- diffuse sound fields, this paper firstly proposes a new formula to calculate the reverberation radius in rooms with non-uniformly distributed sound absorption. Then, a comparison between the classic formulas and the new one is performed in some rectangular rooms with non-uniformly distributed sound absorption. Finally, this paper introduces a new interpretation of the reverberation radius in non-diffuse sound fields. According to this interpretation, the time corresponding to the sound to travel a reverberation radius should be assumed as the lower limit of integration of the diffuse sound energy

scholarly journals Effects of mount positions on vibrational energy flow transmission characteristics in aero-engine casing structures

2019 ◽  
Vol 39 (2) ◽  
pp. 313-326
Author(s):  
Yingqun Ma ◽  
Qingjun Zhao ◽  
Kai Zhang ◽  
Meng Xu ◽  
Wei Zhao
Keyword(s):  
Finite Element ◽  
Energy Flow ◽  
Vibrational Energy ◽  
Shell Element ◽  
Coupling Model ◽  
Transmission Characteristics ◽  
Structural Intensity ◽  
Aero Engine ◽  
Vibrational Energy Flow ◽  
Vibration Problems

The main goal of the study is to apply the structural intensity method to analyze the effects of positions of the main-mount and the sub-mount on the vibrational energy flow transmission characteristics in aero-engine casing structures, so as to attenuate the vibration of the casing and the whole aero-engine. Structural intensity method, indicating magnitude and direction of the vibrational energy flow, is a powerful tool to study vibration problems from the perspective of energy. In this paper, a casing-support-rotor coupling model subjected to the rotor unbalanced forces is established by the finite element method. Formulations of the structural intensity of a shell element and the structural intensity streamline are given. A simulation system consisting of the finite element tool and the in-house program is developed to carry out forced vibration analysis and structural intensity calculation. The structural intensity field of the casing is visualized in the forms of vector diagram and streamline representation. The vibrational energy flow behaviors of the casing at the rotor design rotating speed are analyzed, and the vibrational energy flow transmission characteristics of the casing with different axial positions of the main-mount and the sub-mount are investigated. Moreover, some measures to attenuate the vibration of the casing are obtained from the numerical results, and their effectiveness is verified in the frequency domain and the time domain. The results shed new light on the effects of the mount positions on the vibration energy transmission behaviors of the casing structure. The structural intensity method is a more advanced tool for solving vibration problems in engineering. Furthermore, it may provide some guidance for the vibration attenuation of the casing and the whole aero-engine.

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