Displacement Field Of Structure Research Articles

Experimental results on active structural acoustic control using fiber-optic strain sensors

A new strategy for the active control of the sound power radiated from a flexural vibrating beam is experimentally investigated. This strategy involves sensing the discrete structural strain using white-light interferometric multimode fiber-optic strain sensors. Two approaches are used to relate the radiated sound power to the structural strain. The first approach is based on the reconstruction of the transverse structural displacement field from the structural strain field using a finite-difference scheme, and a wave-number transformation of the structural displacement to obtain the radiated sound field. The second approach is based on an exact expression directly relating the radiated sound field to the wave-number transform of the structural strain. In both approaches, the wave-number transform is performed over the supersonic (radiating) components of the structural information. The dynamic strain measurements are first compared with polyvinylidene film strain sensors. As a second step, a straightforward control scheme is implemented into a multichannel filtered-x LMS algorithm to control the strain amplitudes on the beam actively. Finally, both strategies for using the strain information are implemented to perform the active control of the sound power radiated from the beam. Preliminary performance results of both strategies using four strain sensors are then presented.

Fractal surfaces and interfaces in structures. Methods and algorithms

The scope of the present paper is the study of structures involving interfaces of fractal geometry. This geometry is analysed here by a sequence of classical geometry problems formulated by means of an I.F.S. (iterated function system) or through a F.I. (fractal interpolation). These approximations of the fractal geometry are combined with the F.E.M. (finite element method) in order to calculate stress and displacement fields in fractal structures.

Acoustic radiation from fluid‐loaded structures with discontinuities

The presence of discontinuities, such as joints, in a fluid‐loaded structure results in far‐field acoustic radiation even when subsonic wave numbers prevail in the main body of the structure. The object of this study is to develop a rational model of this phenomenon using singular perturbation methods. When a flexural wave in a thin structure impinges on a joint, evanescent structural displacement fields are set up in the vicinity of the joint. It is proposed to show that these fields are associated with rotation‐dominated modes that are supported by shear‐corrected plate theories of the Timoshenko‐Mindlin‐type flexural mode. The method of matched asymptotic expansions will be used to obtain mode‐conversion coefficients, and it will be shown that the spatial wavenumber spectrum of the local field is instrumental in setting up an acoustic far field in the surrounding fluid. An important mathematic issue is the proper description of evanescent fields; this analysis will be based on results obtained previously in connection with acoustic waveguides.

Thin Shell Foundation Resting on Stochastic Soil

The paper presents an approximate elastic solution to the statical problem of a thin concrete shell foundation. The soil‐structure interaction follows the Winkler concept of soil with random subgrade modulus. The randomness of the soil subgrade modulus renders the problem stochastically nonlinear. The method of statical solution is based on the finite difference procedure in the variational formulation and, to account for the probabilistic nature of the problem, is combined with the method of realizations in one approach, and with the perturbation method (small random parameter method) in the other case. The shell foundation that is dealt with in this paper consists of four hyperbolic‐paraboloid (in short hypar or HP) shells and a set of straight ribs. For the illustrative problem, the results consist of the estimates for the expectations and standard deviations of the discrete values of the structural displacement and internal force fields.

Acoustic radiation from fluid-loaded structures with discontinuities

The presence of discontinuities, such as joints, in a fluid-loaded structure results in farfield acoustic radiation even when subsonic wavenumbers prevail in the main body of the structure. The object of this study is to develop a rational model of this phenomenon using singular perturbation methods. When a flexural wave in a thin structure impinges on a joint, evanescent structural displacement fields are set up in the vicinity of the joint. It will be shown that these fields are associated with rotation-dominated modes that are supported by shear-corrected plate theories of the Timoshenko-Mindlin type flexural mode. The method of matched asymptotic expansions will be used to obtain mode-conversion coefficients, and it will be shown that the spacial wavenumber spectrum of the local field is instrumental in setting up an acoustic farfield in the surrounding fluid. An important mathematical issue is the proper description of evanescent fields; the analysis will be based on results obtained previously in connection with acoustic waveguides.

Acoustic radiation from fluid‐loaded structures with discontinuities

The presence of discontinuities such as joints, in a fluid‐loaded structure results in farfield acoustic radiation even when subsonic wavenumbers prevail in the main body of the structure. The object of this study is to develop a rational model of this phenomenon using singular perturbation methods. When a flexural wave in a thin structure impinges on a joint, evanescent structural displacement fields are set up in the vicinity of the joint. This paper proposes to show that these fields are associated with rotation‐dominated modes that are supported by shear‐corrected plate theories of the Timoshenko‐Mindlin type flexural mode. The method of matched asymptotic expansions will be used to obtain mode‐conversion coefficients, and it will be shown that the spatial wavenumber spectrum of the local field is instrumental in setting up an acoustic farfield in the surrounding fluid. An important mathematical issue is the proper description of evanescent fields; this analysis will be based on results obtained previously in connection with acoustic waveguides.