Index of content:
Volume 129, Issue 2, February 2011
- STRUCTURAL ACOUSTICS AND VIBRATION 
129(2011); http://dx.doi.org/10.1121/1.3531807View Description Hide Description
Millions of miles of pipes are being used for the transportation, distribution, and local use of petroleum products, gas, water, and chemicals. Most of the pipes are buried in soil, leading to the significance of the study on the subject of guided wave propagation in pipes with soil influence. Previous investigations of ultrasonic guided wave propagation in an elastic hollow cylinder and in an elastic hollow cylinder coated with a viscoelastic material have led to the development of inspection techniques for bare and coated pipes. However, the lack of investigation on guided wave propagation in hollow cylinders embedded in infinite media like soil has hindered the development of pipe inspection methods. Therefore the influence of infinite media on wave propagation is explored in this paper. Dispersion curves and wave structures of both axisymmetric and nonaxisymmetric wave modes are developed. Due to the importance of the convergence of numerical calculations, the requirements of thickness and element number of the finite soil layer between hollow cylinder and infinite element layer are discussed, and an optimal combination is obtained in this paper. Wave structures are used for the mode identification in the non-monotonic region caused by the viscoelastic properties of coating and infinite media.
129(2011); http://dx.doi.org/10.1121/1.3531837View Description Hide Description
This work investigates composite plates and their ability to direct flexural intensity, which has important implications for noise and vibration control. It is well known that a composite plate supports a flexural wave whose wavenumber depends strongly on its angle of propagation. This suggests that a composite plate will direct more flexural intensity in some directions than others. The present work considers a thin multi-layered plate in which each layer is constructed from an orthotropic material and has a chosen orientation relative to the other layers. Such an approach may be used to design highly directive structures. An analysis is presented in which a two-dimensional Fourier transform is analytically applied to the equation of motion, yielding algebraic expressions for displacements and stress resultants. Next, a two-dimensional discrete inverse Fourier transform is applied to compute displacements and stress resultants at discrete locations. Flexural intensity is computed at these locations.
Smearing technique for vibration analysis of simply supported cross-stiffened and doubly curved thin rectangular shellsa)129(2011); http://dx.doi.org/10.1121/1.3523305View Description Hide Description
Plates stiffened with ribs can be modeled as equivalent homogeneous isotropic or orthotropic plates. Modeling such an equivalent smeared plate numerically, say, with the finite element method requires far less computer resources than modeling the complete stiffened plate. This may be important when a number of stiffened plates are combined in a complicated assembly composed of many plate panels. However, whereas the equivalent smeared plate technique is well established and recently improved for flat panels, there is no similar established technique for doubly curved stiffened shells. In this paper the improved smeared plate technique is combined with the equation of motion for a doubly curved thin rectangular shell, and a solution is offered for using the smearing technique for stiffened shell structures. The developed prediction technique is validated by comparing natural frequencies and mode shapes as well as forced responses from simulations based on the smeared theory with results from experiments with a doubly curved cross-stiffened shell. Moreover, natural frequencies of cross-stiffened panels determined by finite element simulations that include the exact cross-sectional geometries of panels with cross-stiffeners are compared with predictions based on the smeared theory for a range of different panel curvatures. Good agreement is found.