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In the present paper, a two-dimensional periodic curved panel which rests on an orthogonal array of equispaced simple line supports has been analyzed by a FEM. A periodic unit of the system is represented by an accurate high-precision curved triangular shallow shell finite-element model to find out frequencies of plane wave motion in terms of propagation constants for the two-dimensional periodic shell. The natural frequencies of vibration of a full cylindrical shell have been obtained for different propagation constants in the axial and circumferential directions. The propagation surface is found using the optimum periodic curved panel in the analysis. It is observed that the lowest frequency can be found out at the lower bound of first propagation surface, by choosing an optimum periodic angle of curved panel. All the natural frequencies of orthogonally multisupported open curved panel of ([N.sub.x] X [N.sub.y]) elements have been found out from the propagation surface and compared with NASTRAN results. It is shown that by this approach the order of the resulting matrices in the FEM is considerably reduced leading to a significant decrease in computational effort. CE Database keywords: Wave propagation; Panels; Vibration.

An investigation on stiffened isotropic and composite plates has been conducted to determine the geometric and material parameters for the plate, as well as the stiffener from experimental modal data and finite element predictions using a genetic algorithm (GA). The problem is formulated as a global minimization of the error function defined by the difference in undamped eigenvalues and eigenvectors, as predicted from the finite-element modeling to that obtained experimentally. The parameter estimation problem is solved using a GA implementing selection, crossover, and mutation operators to obtain the global minimum solution. Because stiffeners contribute substantially to the overall rigidity of the plate assembly, their position, physical properties, and orientation create considerable variation of the modal properties, as compared to the bare plate with similar construction. This makes each of the stiffened plate identification problems rather unique. GAs have been the subject of considerable interest in providing a robust search procedure for a global optimum solution for such difficult minimization problems. The method is demonstrated on a few simulated examples on stiffened plates to investigate the uniqueness and convergence of results. The methodology, although slow in execution, is found to be very robust, even in the presence of noise, for isolating interesting zones of the search space. Unlike many traditional optimization techniques, it does not get stuck at a particular local minimum due to its parallelism. DOI: 10.1061/(ASCE)0887-3801(2002)16:3(206) CE Database keywords: Plates; Stiffening; Algorithm; Parameters; Model analysis.

Research was conducted to determine plate and stiffener material property parameters derived from stiffened and unstiffened multilayered composite plates using numerical analysis and finite element method. Data indicate that the position, physical characteristics, and stiffener orientation exhibit large variations in the modal properties.

In the present study, 9 bacterial and 6 fungal endophytes were isolated from surface sterilized leaf, stem and root samples of the medicinal plant - Andrographis paniculata (Kalmegh). The endophytes were screened for plant growth promoting traits (IAA, phosphate solubilization and N2 fixation), enzymes (cellulase and amylase) and antimicrobial compounds against 3 potent human pathogens-E. coli, Staphylococcus sp. and Vibrio sp. The majority of the isolated endophytes produced the phytohormone - IAA (ranging 2-45μg/ml), and 1 endophyte solubilized phosphate and fixed N2. All the fungal endophytes possessed cellulase and amylase activity. In the preliminary screening, 4 bacterial and 4 fungal endophytic isolates extract showed antagonistic activity against the 3 potent human pathogens which are known causative agents of urinary tract, skin and gastrointestinal tract infections, respectively. The endophytes of A. paniculata exhibiting broad and specific antimicrobial activity make them ideal candidates in medical purposes. [ABSTRACT FROM AUTHOR]

Stiffened plates and shells often find wide application in bridge engineering, aircraft, ship and allied industries owing to its high strength to weight ratios. They are often subjected to dynamic loading such as air blast loading, for which detailed dynamic analysis is required to study the structure under these conditions. In the present approach, the dynamic response of stiffened plates and shells has been investigated by the finite element method employing a high precision arbitrary-shaped triangular shell element in which stiffeners may lie in any arbitrary direction within the element. This provides greater flexibility in the mesh generation. The governing undamped equations of motion have been solved by Newmark's method for direct time integration. The dynamic response of plates and shells with or without stiffeners, subjected to different kinds of load-history have been studied and results are compared with the published analytical results.