1,721,074 research outputs found
Dynamic response of sandwich shells to underwater blasts
No full textThis paper presents a general approach for analyzing the response of beam plates and shells to short duration pressure pulses typically encountered as a result of underwater explosions. The problem is formulated in terms of curvilinear coordinates and the resulting equations can then be specialized for each particular geometry. Results are presented for several examples
Dynamic response of sandwich shells to underwater blasts
No full textThis paper presents a general approach for analysing the response of beam, plates and shells to short duration pressure pulses typically encountered as a result of underwater explosions. The problem is formulated in terms of curvilinear coordinates and the resulting equations can then be specialized for each particular geometry. Results are presented for several examples
Free Vibrations of Doubly Curved Functionally Graded Shells
No full textFunctionally graded materials are composite materials with material properties varying in one or more directions. Most studies consider isotropic FGM that often consist of a metal matrix such as stainless steel or aluminium and spherical ceramic particles. The volume fraction of the particles then varies through the shell thickness. Anisotropic FGM have been considered more recently. These are fiber reinforced composite materials with through-the- thickness variation of the fiber volume fraction and/or the fiber orientation.
Previous studies [1,2] have shown that plates made out of isotropic FGM behave like homogeneous plates. Elastic coupling between in-plane and out of plane deformations can be eliminated from the equations of motion if the neutral surface is taken as the reference surface instead of the mid-plane. Thus, no new method need be developed and the natural frequencies of such functionally graded plates are directly proportional to those homogeneous plates with the same shape and support conditions. Based on results published by previous authors, it was shown that these results also hold for isotropic functionally graded shells [3] and for very thick shells [4]. For anisotropic FGMs the same relationship exists between graded and shells with constant fiber orientation and fiber volume fraction through the thickness.
The First-order Shear Deformation Theory (FSDT) is used to analyze moderately thick structural elements. In order to include the effect of the initial curvature a generalization of the Reissner-Mindlin theory [5] is adopted. The governing equations of motion, written in terms of stress resultants, are expressed as functions of five kinematic parameters, by using the constitutive and kinematic relationships. The solution is obtained by using the Generalized Differential Quadrature (GDQ) method [6] which leads to a standard linear eigenvalue problem. This simple and direct procedure can be applied to a large number of cases [5,7-10] to circumvent the difficulties of programming complex algorithms for the computer, as well as the excessive use of storage and computer time. Results are obtained taking the meridional and circumferential co-ordinates into account, without using the Fourier modal expansion methodology. GDQ results are validated with those obtained by using commercial programs.
Natural frequencies of panels made of isotropic FGMs with various shapes (cylindrical, spherical, hyperbolical, catenoidal) and boundary conditions were determined using the GDQ method. It was found that the natural frequencies of the graded shells were directly proportional to those of the same shell made out of isotropic materials and that ratio is independent of shape and boundary conditions. In spite of the asymmetric properties of the material with respect to the mid-plane, these shells behave as if they were homogeneous and isotropic. Using the neutral surface as the reference surface, elastic coupling between the in-plane and transverse deformations due to material properties varying through the thickness can be removed from the equations of motion. Non-dimensional parameters were developed to assess a number of complicating factors such as: the effect of transverse shear deformation and rotary inertia, aspect ratio and curvature. This allows to determine when these factors are important and when certain levels of refinement in the analysis are required
A Media Converter Prototype for 10-Mb/s Ethernet Transmission Over 425 m of Large-Core Step-Index Polymer Optical Fiber
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Large core Polymer Optical Fibers for aeromobile cabling: 100Mbps and 1Gbps transmission
No full textDYNAMIC RESPONSE OF FLEXIBLE WEDGES ENTERING THE WATER
No full textHydroelasticity is a phenomenon occurring during the interaction between water and a deformable structure.
Structural deformations can modify the fluid motion, introducing difficulties in the calculation of the impact-induced stresses.
Predicting the structural deformations and stresses during the water entry of flexible structures is a major challenge and suitable computer-aided design tools are currently being developed and validated. This work investigates the water impact of deformable wedges.
Experimental and numerical results on the parameters affecting hydroelasticity are evaluated for flexible plates with different boundary conditions. The occurrence of hydroelastic effects is shown to depend on the ratio between the natural frequency of the structure and the characteristic wetting time. The influence of the fluid-structure interactions is investigated by numerical simulations.
The conditions for which fluid-structure interactions are significant and must be accounted for in the analysis are identified, while outside this range the structure can be modeled as a rigid body. Pressure at the fluid-structure interface is found not to be influenced by the structural deformation, unless fluid is detaching due to cavitation of ventilation
A system and a method for measuring distances, displacements and mechanical actions
No full textAccording to the present invention there is provided an optical transducer adapted to detect external mechanical actions acting on said transducer, said transducer comprising at least one sensing optical path (5) adapted to transmit at least one sensing optical signal (b') and to emit at least one sensing output electrical signal (d) along with at least one reference path (4) adapted to emit at least one output electrical reference signal (e). Moreover, at least one portion (5') of said at least one optical path (5) is adapted to be exposed to external mechanical actions, so that the transmission of said sensing optical signal (b') through said sensing optical path can be modified as a result of said mechanical actions, so that a phase shift between said sensing electrical signal (d) and said reference electrical signal (e) is generated.; Furthermore, said at least one reference path (4) comprises phase shifting means (11) adapted to maintain the phase shift between said at least one output sensing electrical signal (d) and said at least one output reference electrical signal (e) at a constant value in absence of any mechanical action exerted on said at least one sensing optical path (5), resulting in the working point of the transducer being kept within a range centered o a predefined phase shift, thus allowing to improve the sensitivity pf the transduce
EFFECT OF THE BOUNDARY CONDITIONS ON THE HYDROELASTIC IMPACTS OF COMPOSITE PLATES
No full textHydroelasticity is a phenomenon occurring during the interaction between water and a deformable structure.
Structural deformations can modify the fluid motion, introducing difficulties in the calculation of the impact-induced stresses.
Predicting the structural deformations and stresses during the water entry of flexible structures is a major challenge and suitable computer-aided design tools are currently being developed and validated. This work investigates the water impact of deformable wedges.
Experimental and numerical results on the parameters affecting hydroelasticity are evaluated for deformable plates with different boundary conditions. The occurrence of hydroelastic effects is shown to depend on the ratio between the natural frequency of the structure and the characteristic wetting time.
The conditions for which fluid-structure interactions are significant and must be accounted for in the analysis are identified, while outside this range the structure can be modeled as a rigid body
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