Acoustic Design Sensitivity for Structural Radiators

1992 ◽  
Vol 114 (2) ◽  
pp. 178-186 ◽  
Author(s):  
K. A. Cunefare ◽  
G. H. Koopmann
Keyword(s):  
Velocity Distribution ◽  
Design Sensitivity ◽  
Characteristic Dimension ◽  
Surface Velocity ◽  
Element Formulation ◽  
Acoustic Intensity ◽  
Acoustic Design ◽  
Sensitivity Distribution ◽  
Maximum Value ◽  
Rigid Surfaces

An analysis technique designated as acoustic design sensitivity (ADS) analysis is developed via the numerical treatment of a discrete quadratic expression for the total acoustic power radiated by a three-dimensional extended structure. A boundary element formulation of the Helmholtz Integral Equation is the basis of the analysis leading to the quadratic power expression. Partial differentiation of the quadratic power expression with respect to a known surface velocity distribution leads to a sensitivity distribution, represented by a distribution of values on the surface of a structure. The sensitivity values represent a linear approximation to the change in the total radiated power caused by changes in the surface velocity distribution. For a structure vibrating with some portions of its surface rigid and such that the acoustic wavelength is long compared to a characteristic dimension of the structure, ADS analysis reveals that the rigid surfaces strongly influence the sensitivity distribution, as expected. Under such conditions, the rigid surfaces can exhibit the maximum value of the entire sensitivity distribution, even though the acoustic intensity is identically zero on a rigid surface. As the frequency increases, and the acoustic wavelength becomes comparable to a characteristic dimension of the structure, the position of the maximum value of the sensitivity distribution will coincide with the region of the maximum surface acoustic intensity.

Pure Design Method for Aerofoils in Cascade

1969 ◽  
Vol 11 (5) ◽  
pp. 454-467 ◽  
Author(s):  
K. Murugesan ◽  
J. W. Railly
Keyword(s):  
Exact Solution ◽  
Velocity Distribution ◽  
Design Problem ◽  
Design Method ◽  
Tangential Velocity ◽  
Surface Velocity ◽  
Normal Velocity ◽  
Blade Design ◽  
Blade Shape

An extension of Martensen's method is described which permits an exact solution of the inverse or blade design problem. An equation is derived for the normal velocity distributed about a given contour when a given tangential velocity is imposed about the contour and from this normal velocity an initial arbitrarily chosen blade shape may be successively modified until a blade is found having a desired surface velocity distribution. Five examples of the method are given.

An Energy Boundary Element Formulation for Predicting the Acoustic Field Around a Vehicle at High Frequencies Due to Airborne Noise Sources

2003 ◽  
Author(s):  
Aimin Wang ◽  
Nickolas Vlahopoulos ◽  
Jason Zhu ◽  
Mike Qian
Keyword(s):  
Energy Density ◽  
Boundary Element ◽  
Acoustic Field ◽  
Test Data ◽  
Acoustic Energy ◽  
Element Formulation ◽  
Acoustic Intensity ◽  
Numerical Predictions ◽  
Airborne Noise ◽  
Acoustic Energy Density

An Energy Boundary Element Analysis (EBEA) formulation is presented for calculating sound radiation from a source with arbitrary shape at high frequency. The basic integral equation for the EBEA is derived including a half-space boundary condition. The time and frequency averaged acoustic energy density and acoustic intensity constitutes the primary variables of the new formulation, and the corresponding Green’s functions are derived. The governing equations for the EBEA are established and the numerical formulae for the coefficients of the system matrix, the acoustic energy density, and the acoustic intensity are derived using a Gaussian quadrature. The EBEA formulation and the corresponding numerical implementation are validated by comparing EBEA results to test data for the acoustic field around a vehicle that originates from an airborne noise source. Good correlation is demonstrated between numerical predictions and test data.

An inverse design method of diffuser blades by genetic algorithms

1998 ◽  
Vol 212 (4) ◽  
pp. 261-267 ◽  
Author(s):  
H-Y Fan
Keyword(s):  
Neural Network ◽  
Genetic Algorithm ◽  
Velocity Distribution ◽  
Design Method ◽  
Back Propagation ◽  
Inverse Design ◽  
Surface Velocity ◽  
Target Velocity ◽  
Constant Height ◽  
Inverse Design Method

A genetic algorithm incorporating a neural network technique is proposed to search for a turbo-machinery diffuser blade profile that produces a given velocity distribution on its surface. Such a new inverse design method works through minimizing the error between the surface velocity distribution of candidate blades and the target velocity distribution. For ease of employing the genetic algorithm, the blade profiles to be searched are parameterized by Bezier curves. To fix the surface velocity distribution of a candidate blade, a special type of back propagation (BP) neural network is implemented. The proposed approach is illustrated by a diffuser having two-dimensional blades with constant height and thickness. The simulations show that the new method is not only feasible but also reliable and efficient.

A Method for Inverse Aerofoil and Cascade Design by Surface Vorticity

1982 ◽  
Author(s):  
R. I. Lewis
Keyword(s):  
Velocity Distribution ◽  
Incompressible Flow ◽  
Design Tool ◽  
The Body ◽  
Surface Velocity ◽  
Classical Solutions ◽  
Analysis Tool ◽  
Attached Flow ◽  
Turbomachine Blade

Surface vorticity theory, normally considered as an analysis tool, has been modified to operate as a design tool whereby the shapes of components may be found to produce a prescribed surface velocity in incompressible flow. The basis of the method is presented and checked against classical solutions for cylindrical and diamond shaped struts with fully attached flow. A procedure for turbomachine blade or aerofoil design is outlined and illustrated with back checks via Martensen’s method. The method allows specification of velocity distribution on either or both surfaces of the body. If only one surface of an aerofoil or blade is prescribed, the user is allowed to specify profile thickness also.

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