scholarly journals Observations of the Stability of a Normal Mode Sound Field in an Intermediate Scale Model

1961 ◽  
Vol 33 (6) ◽  
pp. 831-831
Author(s):  
J. A. Scrimger
Keyword(s):  
Normal Mode ◽  
Sound Field ◽  
Scale Model ◽  
Intermediate Scale ◽  
The Stability

Active control of fan noise from high-bypass ratio aeroengines: a numerical study

2001 ◽  
Vol 105 (1053) ◽  
pp. 627-631
Author(s):  
P. Traub ◽  
F. Kennepohl ◽  
K. Heinig
Keyword(s):  
Active Control ◽  
Numerical Study ◽  
Active Noise Control ◽  
Sound Field ◽  
Primary Objective ◽  
Scale Model ◽  
Research Centre ◽  
Infinite Length ◽  
Circular Duct ◽  
Bypass Ratio

Abstract Under the national research project, dubbed Turbotech II, in which MTU Aero Engines, DLR Institute of Propulsion Technology and EADS Corporate Research Centre participate, active noise control (ANC) has been tested with a scale model fan of one metre diameter for a high bypass ratio aeroengine. MTU’s task in this project was to develop a computer code to predict the sound field in the intake duct of the fan-rig by the use of active control. The primary objective of the numerical study was to specify numbers of actuators (loudspeakers) and error sensors (microphones) and their positioning to control the harmonic sound power, radiated upstream to the duct intake. The computer model is based on the geometry of an annular or circular duct of rigid walls and infinite length, containing a subsonic axial uniform flow. The modal amplitudes of the primary sound field are input data. The actuators are modelled by acoustic monopoles. Two control algorithms have been used for achieving the control objective. The first consists simply in the reduction of the in-duct mean squared pressures. The second, so called modal control, is designed to cancel dominant modes selectively. Numerical results are presented using a typical configuration of wall mounted actuators and error sensors in the form of a number of rings uniformly distributed along the length of the intake duct. Guidelines have also been derived to design a favourable configuration of actuators and sensors. The findings of the numerical study are compared with the results of the ANC tests.

scholarly journals A Finite-Difference Wavenumber-Time Domain Method for Sound Field Prediction in a Uniformly Moving Medium

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Bichun Dong ◽  
Runmei Zhang ◽  
Chuanyang Yu ◽  
Huan Li
Keyword(s):  
Finite Difference ◽  
Time Domain ◽  
Sound Pressure ◽  
Sound Field ◽  
Time Domain Method ◽  
Practical Significance ◽  
Moving Medium ◽  
Domain Method ◽  
Aero Engines ◽  
The Stability

Sound field prediction has practical significance in the control of noise generated by sources in a flow, for example, the noise in aero-engines and ventilation systems. Aiming at accurate and flexible prediction of time-dependent sound field, a finite-difference wavenumber-time domain method for sound field prediction in a uniformly moving medium is proposed. The method is based on the second-order convective wave equation, and the wavenumber-time domain representation of the sound pressure field on one plane is forward propagated via a derived recursive expression. In this paper, the recursive expression is first deduced, and then numerical stability and dispersion of the proposed method are analyzed, based on which the stability condition is given and the correction of dispersion related to the transition frequency is made. Numerical simulations are conducted to test the performance of the proposed method, and the results show that the method is valid and robust at different Mach numbers.

Stability of parallel flow of a multi-component cylindrical plasma to electrostatic perturbations

1981 ◽  
Vol 26 (2) ◽  
pp. 369-383
Author(s):  
R. Lucas
Keyword(s):  
Normal Mode ◽  
Axial Velocity ◽  
Sufficient Conditions ◽  
Parallel Flow ◽  
Zeroth Order ◽  
Unperturbed State ◽  
Plasma Component ◽  
Cylindrical Plasma ◽  
The Stability ◽  
System Variables

Sufficient conditions for the stability of parallel flow of a warm N-component cylindrical plasma to electrostatic perturbations are obtained. In the unperturbed state the jth plasma component is assumed to have axial velocity Vj0(r), r being the radial co-ordinate, and the equilibrium quantities are permitted to be arbitrary functions of r consistent with the zeroth-order equations. The L2-norms of certain system variables are shown to be bounded uniformly in time. Circle theorems are obtained for the complex eigenfrequencies of any normal mode.

scholarly journals Experimental Study on City Road Collapse under Vibrating Load

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Yuxiao Wang ◽  
Gang Shi ◽  
Xiaowei Tian ◽  
Chaoyue Li ◽  
Huanyu Cheng
Keyword(s):  
Dynamic Load ◽  
Static Load ◽  
Soil Layer ◽  
Formation Time ◽  
Traffic Load ◽  
Scale Model ◽  
The Road ◽  
Ultimate Failure ◽  
The Stability ◽  
Collapse Process

Underground pipeline seepage and traffic load are the important factors causing city road collapse. In this paper, eight groups of indoor scale model experiments are used to study the road collapse caused by pipeline seepage, taking into account the load type, pipeline buried depth, the distance between pipeline and loss channel, the relative position of pipeline and loss channel, and the formation time of loss channel. The results show that when the erosion channel was formed later, the underlying erosion cavity was ellipsoid, while the other erosion cavities were funnel shaped. When only the static load is applied, the time to reach the ultimate failure is longer than that when only dynamic load is applied. The smaller dynamic load can increase the stability of the soil above the seepage pipeline, while the larger dynamic load can accelerate the collapse process. With the formation time of the erosion channel increasing, the erosion void size is larger and the surface is easier to collapse. With the increase of the distance between the loss passage and the pipeline, the damage time of the road surface is also increased. The larger the thickness of the soil layer above the pipeline, the smaller the size of the underground cavity and the surface subsidence.

Linearized theory of inhomogeneous multiple ‘water-bag’ plasmas

1973 ◽  
Vol 9 (2) ◽  
pp. 235-247 ◽  
Author(s):  
H. W. Bloomberg ◽  
H. L. Berk
Keyword(s):  
Boundary Conditions ◽  
Normal Mode ◽  
Normal Mode Analysis ◽  
Mode Analysis ◽  
Special Boundary ◽  
Finite Region ◽  
Trapped Particles ◽  
Linearized Theory ◽  
Beam Approximation ◽  
The Stability

The problem of the stability of inhomogeneous, electrostatic, multiple water-bag plasmas is considered. Equations are derived for general stationary water-bag equilibria, as well as for the corresponding perturbations. Particular attention is directed to systems with trapped particles in periodic equilibria, and special boundary conditions for the perturbation equations at the trapped-particle turning points are introduced. A normal-mode analysis is carried out for a configuration involving trapped particles occupying a finite region in the vicinity of the trough of an equilibrium wave (BGK mode). The results confirm the validity of the bunched-beam approximation.

Prediction of subjective properties of a sound field in a concert hall with tenth‐scale model

1999 ◽  
Vol 105 (2) ◽  
pp. 1197-1197
Author(s):  
Koji Ishida ◽  
Kiyoshi Sugino ◽  
Hideki Tachibana
Keyword(s):  
Sound Field ◽  
Scale Model ◽  
Concert Hall

The Prediction of Velocity Distribution of Plate Jet with a EMMS Model

2015 ◽  
Vol 799-800 ◽  
pp. 629-634
Author(s):  
Ke Zhi Yu ◽  
Hai Zhang ◽  
Yan Ling Liu
Keyword(s):  
Velocity Distribution ◽  
Viscous Dissipation ◽  
Energy Minimization ◽  
Scale Model ◽  
Stability Conditions ◽  
Multi Scale ◽  
Plane Jets ◽  
The Stability ◽  
Plane Jet

The energy minimization multi-scale model is applied to the plane jet. The stability conditions of plane jets is adopted to predict the velocity distribution of plane jet. When the ratio of total dissipation to viscous dissipation tends to the maximum is used as the optimization condition and entrancement factor is considered as a constant, the Gauss velocity distribution can be concluded in the plane jet.

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