Elastic Response of a Submerged Plate Coated With Multiple Layers of Elastomeric Materials in the Presence of a Turbulent Boundary Layer

1999 ◽  
Author(s):  
Jeff M. Mendoza ◽  
Hoang Pham
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Material Properties ◽  
Theory Of Elasticity ◽  
Elastic Response ◽  
Water Medium ◽  
Coupling Mechanism ◽  
Submerged Plate ◽  
Elastomeric Materials ◽  
Shear Motion

Abstract This study addresses the elastic response of a submerged plate coated with multiple layers of elastomeric materials. of interest is the extent at which the mechanism of interaction between dissimilar elastomers can be modified through selection of material properties. Such modification can optimize the received signal response at the sensors in the presence of a turbulent boundary layer (TBL) as well as provide insight into advantageous TBL and structure-borne vibration decoupling configurations. The analytical model is an infinite multilayer composite of steel and viscoelastic materials separating the semi-infinite media of water (external) and air (internal). The theory of elasticity expedites the analysis of elastic response, governed by dilatational and shear motion, in each layer. The analysis considers excitation by an incident plane wave in addition to a fully developed TBL both in the water medium. A series of numerical simulations based on material properties of well-characterized elastomers quantify the degree at which this coupling mechanism can be optimized in applications of noise and vibration reduction.

scholarly journals THE DYNAMICS OF OSCILLATING SHEETFLOW

1986 ◽  
Vol 1 (20) ◽  
pp. 71 ◽  
Author(s):  
W.T. Bakker ◽  
W.G.M. Van Kesteren
Keyword(s):  
Boundary Layer ◽  
Numerical Model ◽  
Turbulent Boundary Layer ◽  
Analytical Model ◽  
Darcy Law ◽  
Elastic Response ◽  
Sheet Flow ◽  
Grain Interaction ◽  
Spherical Grains ◽  
Intrusion Depth

Two mathematical models for the simulation of the dynamics of sheetflow are presented, an analytical and a numerical one. In the analytical model the theory of Bagnold (1954) is implemented: a constant ratio between shear stress and normal stresses is assumed. In the numerical model the motion of each layer of grains is considered separately; each layer exists of a rigid rectangular structure of spherical grains. Grain- grain interaction between the successive layers occurs in two ways: on one hand viscous interaction forces, comparable with squeezing forces in lubrication problems and on the other hand direct contact with elastic response when the distance between the grains becomes less than .01 of the grain diameter. When the relative motion of adjacent layers results into compression or dilatation, a resistant force analogous to the Darcy law is assumed.The numerical model has been combined with the turbulent boundary layer model of Bakker and v. Kesteren (1984). Results of computations are compared with measurements of Bagnold (1954) and Horikawa et al (1982). The analytical model predicted the concentration in the sheet flow layer and the intrusion depth rather well, where the numerical model gave reasonable results with respect to the velocity pattern above the sheetflow layer. It is concluded, that up to now the more sophisticated assumptions of the numerical model do not lead as yet to higher accuracy with respect to the intrusion depth of the sheet flow, probably because the separation between sheet flow and the turbulent boundary layer above has been assumed too smooth.

Long-Range Acoustic Scattering by Surface Inhomogeneities Beneath a Turbulent Boundary Layer

1984 ◽  
Vol 106 (3) ◽  
pp. 376-382 ◽  
Author(s):  
D. G. Crighton
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Long Range ◽  
Fluid Layer ◽  
Acoustic Scattering ◽  
Acoustic Power ◽  
Coupling Mechanism ◽  
Fluid Loading ◽  
Low Frequencies ◽  
Homogeneous Surface

Low-frequency turbulent boundary layer eddies inject a power Ps into the elastic structure over which the boundary layer is formed which generally greatly exceeds the acoustic power Pa directly radiated by the eddies (acoustically equivalent to quadrupoles). The power Ps remains trapped in the surface and an adjacent fluid layer and propagates in subsonic surface wave modes until it encounters a rib, or edge, or other surface inhomogeneity, from which a power Pe is scattered to the far field. While Pe is again small compared with Ps, it may nonetheless greatly exceed Pa, and in that case the dominant acoustic mechanism is associated with the long-range coupling between the quadrupole eddy and the remote inhomogeneity via subsonic surface waves. That interaction, and the acoustic fields produced by it, are examined in detail in this paper for the inhomogeneities represented by a simple line support rib, a simple point support rib, and an edge to a plane elastic plate, either with or without an adjacent rigid baffle, and with a range of edge conditions. Under conditions of “light” fluid loading, the long-range coupling mechanism seems unlikely to be of importance, but at low frequencies and under “heavy” fluid loading it appears that, even for large separations between an eddy and an inhomogeneity, the long-range coupling generates an acoustic field far in excess of that radiated by the same boundary layer turbulence over a homogeneous surface.

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