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In this contribution, and as an extension of previous work, the simultaneous use of thin concrete shells for roofing and liquid containment is explored, with a particular focus on the bending and buckling behaviour of the shell. T...
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In this contribution, and as an extension of previous work, the simultaneous use of thin concrete shells for roofing and liquid containment is explored, with a particular focus on the bending and buckling behaviour of the shell. The concept of dual-purpose concrete shells is a novel one, and has the potential to revive the widespread use of elegant thin concrete shells once again. It is shown how excessive stresses due to water loading can be controlled through gradual thickening of the shell over the submerged region. Not only are membrane stresses lowered, but the bending stresses in the vicinity of the shell edge are also significantly moderated. Through a linear eigenvalue buckling analysis followed by a nonlinear Riks-type buckling analysis accounting for geometric imperfections, such thickening is also shown to be effective in enhancing the buckling resistance of the shell. The overall conclusion is that the concept of dual-purpose concrete shells is structurally viable, and deserves more attention.
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The paper reports year around rearing of eri (Philosamia ricini) under local agro-climate. Seven rearings were possible from 4 October 2004 to 7 October 2005 with the duration of rearing varying from 45--60 days depending upon sea...
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The paper reports year around rearing of eri (Philosamia ricini) under local agro-climate. Seven rearings were possible from 4 October 2004 to 7 October 2005 with the duration of rearing varying from 45--60 days depending upon season. Worm, weight varied from 5.116 to 5.700 g. Cocoon weight did not show much variation (2.51 to 2.69 g). Same was the case with shell weight fluctuating from 0.32 to 0.37 g. The commercial characters were at par with those attained in the northeast.
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In this paper, a computational model is proposed to simulate automatically a flexible membrane, with any shape, able to carry a larger number of loading conditions, including pressure loads and by the application of non-zero displ...
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In this paper, a computational model is proposed to simulate automatically a flexible membrane, with any shape, able to carry a larger number of loading conditions, including pressure loads and by the application of non-zero displacements prescription. Under the action of these loads the membrane is deformed reaching one of its equilibrium configurations, which will define the middle surface of the shell to be built. A relatively simple process to generate non-geometrical shells by means of mathematical programming combined with the finite element technique is presented.
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A three-dimensional (3D) method of analysis is presented for determining the free vibration frequencies of joined hemispherical-cylindrical shells of revolution with a top opening. Unlike conventional shell theories, which are mat...
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A three-dimensional (3D) method of analysis is presented for determining the free vibration frequencies of joined hemispherical-cylindrical shells of revolution with a top opening. Unlike conventional shell theories, which are mathematically two-dimensional (2D), the present method is based upon the 3D dynamic equations of elasticity. Displacement components u_r, u_θ and u_z in the radial, circumferential, and axial directions, respectively, are taken to be periodic in θ and in time, and algebraic polynomials in the r and z directions. Potential (strain) and kinetic energies of the joined shells are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four-digit exactitude is demonstrated for the first five frequencies. Natural frequencies are presented for different boundary conditions. The frequencies from the present 3D method are compared with those from 2D thin shell theories.
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In nature, mollusk shells have a role in protecting the soft body of the mollusk from predators and from the external environment, and the shells consist mainly of calcium carbonate and small amounts of organic matrices. Organic m...
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In nature, mollusk shells have a role in protecting the soft body of the mollusk from predators and from the external environment, and the shells consist mainly of calcium carbonate and small amounts of organic matrices. Organic matrices in mollusk shells are thought to play key roles in shell formation. However, enough information has not been accumulated so far. High toughness and stiffness have been focused on as being adaptable to the development of organic-inorganic hybrid materials. Because mollusks can produce elaborate microstructures containing organic matrices under ambient conditions, the investigation of shell formation is expected to lead to the development of new inorganic-organic hybrid materials for various applications. In this review paper, we summarize the structures of mollusk shells and their process of formation, together with the analysis of various organic matrices related to shell calcification.
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In this work, a new technique for the analysis of general bending resistant shells of revolution is proposed. The technique is based on dividing the shell into conical segments, and using Chebyshev series to convert the equilibriu...
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In this work, a new technique for the analysis of general bending resistant shells of revolution is proposed. The technique is based on dividing the shell into conical segments, and using Chebyshev series to convert the equilibrium equations of each segment into a system of algebraic equations. The complete system of equations of the whole shell is built-up by applying compatibility conditions between the conical segments, along with the boundary conditions at the shell ends. The proposed technique is validated by solving the problem of a composite spherical shell under uniform internal pressure by dividing it into cones. The technique is then applied to solve the problems of a composite laminated general shell and an isotropic conical shell with variable thickness under uniform internal pressure.
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This study develops a computational model of free-form shell generation in the design of roof structures that rely on the optimized behavior of the membrane theory of thin shells. For architects and engineers, the model offers a l...
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This study develops a computational model of free-form shell generation in the design of roof structures that rely on the optimized behavior of the membrane theory of thin shells. For architects and engineers, the model offers a low cost, fast, and relatively easy design solution. A computational model for structural free-form shell generation is presented to simulate physical models of shell optimization. This method of designing optimized structures is based on mathematical programming combined with the finite element technique, and is inspired by the laws of nature and, in particular, by the Heinz Isler methods of designing shells using physical models. A flexible membrane is simulated automatically, initially in the horizontal plane surface, with any shape and boundary conditions, and able to carry several specified loads. The membrane under the action of these loads is deformed until reaching one of its equilibrium configurations, which defines the middle surface of the shell to be built. By the principle of minimum total potential energy, the positions of steady equilibrium of the membrane correspond to the local minimum points of the total potential energy function. When the total potential energy function does not exist, it is advisable to use an incremental Newton-Raphson-type method to find the solutions for the nonlinear system of equations given by the equilibrium equations of the membrane in the space. Structural analysis of thin concrete shells with the final shapes of the optimized membranes demonstrates which displacements and principal stresses are optimal. The computational method presented in this paper could be integrated, for example, with Contour Crafting (CC), a layered fabrication technology that offers the potential to construct full-scale buildings directly from three-dimensional computer-aided design models (3D CAD). Structural behavior is in accordance with the membrane theory of thin shells and aesthetic appeal is a natural consequence of the forms generated for applications in architectural design and civil engineering.
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The Japanese quail (Coturnix coturnix japonica) is remarkable in terms of production potential for meat and eggs and as an alternative model for poultry research. Just like the layer chickens, the quail industry can also suffer fr...
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The Japanese quail (Coturnix coturnix japonica) is remarkable in terms of production potential for meat and eggs and as an alternative model for poultry research. Just like the layer chickens, the quail industry can also suffer from poor eggshell quality resulting in serious economic losses. While there are commercially available supplements manufactured to promote egg performance for chicken layers, these are often difficult to find specific for quails. Hence, this study was conducted to determine the effect of combined vitamins, minerals, and amino acid supplement on the external egg quality of Japanese quail eggs which can be used as baseline information to formulate supplements tailored for quail layers. Twenty birds per treatment were given different levels of supplement via the drinking water and external egg quality parameters were measured weekly and after supplementation, respectively. Our study clearly demonstrated an interaction between the levels of supplementation and the amount of time (in wk) the birds were on supplement on egg shell thickness (p ≤ 0.05). Egg shell thickness was highest between 1.5 g/L and 2 g/L at the fourth wk of supplementation and decreased after two wks the supplementation was withdrawn. Similar results were observed on the egg shell weight except for the overall egg weight which remained relatively unchanged.
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Thin shells are increasingly finding new applications under the sea. In this study, we consider a thin-walled shell-of-revolution assembly comprising a deep spherical shell dome (deeper than a hemisphere) axisymmetrically and tang...
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Thin shells are increasingly finding new applications under the sea. In this study, we consider a thin-walled shell-of-revolution assembly comprising a deep spherical shell dome (deeper than a hemisphere) axisymmetrically and tangentially joined to a steep-sided conical shell, the whole being a closed shell structure intended for stationary deployment beneath the surface of the sea in relatively shallow water. The closed shell structure, which might serve as an underwater observatory, is intended to operate at a constant depth, anchored to the seabed against flotation forces, with the thin steel shell walls being required to withstand the external hydrostatic pressure of the surrounding water. We use shell theory to investigate the discontinuity stresses that occur at the junction of the spherical shell and the conical shell, and employ FEM to explore the buckling behaviour of the thin shell. While discontinuity stresses are relatively small, they may influence the lower buckling modes of the shell, which are found to be largely confined to the region of the cone that is adjacent to the junction. Considerations are extended to a doubly-curved variant of the cone in the form of a paraboloid of revolution. As expected, double curvature enhances buckling capacity and also influences the mode shapes.
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The aeroelastic stability of a medium length cantilever cylindrical shell stiffened by an edge ring with the outer surface exposed to supersonic gas flow is investigated. The shell motion is described by the equations of the semi-...
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The aeroelastic stability of a medium length cantilever cylindrical shell stiffened by an edge ring with the outer surface exposed to supersonic gas flow is investigated. The shell motion is described by the equations of the semi-membrane theory for laminated shells and considered with various end conditions. The dependences of the critical flutter speed on the dimensions of the ring cross-section, the value of the structural damping coefficient, the flow parameters, and the type of boundary conditions are obtained.
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