| 1. |
- Ashwear, Nasseradeen, et al.
(författare)
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Optimization of modular tensegrity structures for high stiffness and frequency separation requirements
- 2016
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 80, s. 297-309
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Tidskriftsartikel (refereegranskat)abstract
- Tensegrities are cable-strut assemblies which find their stiffness and self-equilibrium states from the integrity between tension and compression. Low stiffness and coinciding natural frequencies are known issues. Their stiffness can be regulated and improved by changing the level of pre-stress. In vibration health monitoring, the first natural frequency is used as an indicator of better stiffness, but coinciding natural frequencies will be an obstacle in measuring and analysing the correct resonance. In this paper, the above two issues have been considered for modular tensegrity structures. The finite element model used considers not only the axial vibration of the components, but also the transversal vibration where non-linear Euler-Bernoulli beam elements are used for simulations. A genetic algorithm is used to solve the optimization problem, with a multi-objective criterion combination. The optimum self-stress of the tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others. Two approaches are used to find the optimal self-stress vector: scaling from a base module or considering all modules at once. Both approaches give the same optimum solutions.
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| 2. |
- Dhavale, Nikhil N., et al.
(författare)
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Finite Inflation Analysis of Two Circumferentially Bonded Hyperelastic Circular Flat Membranes
- 2014
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 81:9
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Tidskriftsartikel (refereegranskat)abstract
- A finite inflation analysis of two circumferentially bonded hyperelastic circular flat membranes with uniform internal pressure is presented. The governing equations of equilibrium are obtained using the variational formulation. By making a suitable change in the field variables, the problem is formulated as a set of two coupled nonlinear two point boundary value problem (TPBVP) and is solved using the shooting method. Membranes of identical and dissimilar material properties are considered in the analysis. For dissimilar membranes, asymmetric inflation, and remarkably, deflation (after an initial phase of inflation) in one of the membranes in certain cases, has been observed. The effect of inflation pressure and material properties on the geometry of inflated configuration, state of stress, and the impending wrinkling condition of the membranes are also studied. This work has relevance to tunable inflated reflectors and lenses among other applications.
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| 3. |
- Tamadapu, Ganesh, et al.
(författare)
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Modeling and parametric investigation of thick encapsulated microbubble's nonspherical oscillations
- 2016
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 140:5, s. 3884-3895
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Tidskriftsartikel (refereegranskat)abstract
- Numerous studies have been carried out in the past few decades to investigate the radial oscillations of encapsulated microbubbles (MBs). Nonspherical oscillations also have gained attention, being unavoidable in actual applications of these bubbles. The present paper is intended to describe the nature of resonance trends of such spherical and nonspherical modes of a thick encapsulated MB filled with air and suspended in water. The shell material is assumed to be linear viscoelastic and quasi-incompressible. The considered isotropic and spherically isotropic material parametric range is limited to thick polymer shelled MBs. For the case of an isotropic material, shell viscosity has a major influence on the fundamental modes with meridional wave number n = 0, 4, especially for thicker bubbles, unlike for the case of the spherically isotropic material case considered, where the viscosity has very little influence. For most of the parametric range, n = 2, 3 modes are underdamped and their frequency is found to be lower than the n = 0, 4 modes, for both material cases. An interesting case is found for a spherically isotropic quasiincompressible material case, where the first few nonspherical mode resonances are very close to radial mode resonance frequency.
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| 4. |
- Tamadapu, Ganesh, et al.
(författare)
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Resonances of a submerged fluid-filled spherically isotropic microsphere with partial-slip interface condition
- 2015
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 118:4
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the numerous applications of spherical shell models in micro and nano scales (such as microbubbles, bacterial cells, and viral capsids), we have considered the axisymmetric free vibrations of a spherically isotropic fluid-filled thick microspherical shell suspended in another unbounded fluid. A partial-slip condition is considered at the solid-fluid interface(s). Three-dimensional linear elasticity equations for the spherically isotropic shell dynamics and linearized Navier-Stokes equations for the two compressible viscous fluids are used in the analysis. The eigenvalue problem is discretized and solved to find the resonances and quality factors. A perfectly matched layer technique is used to separate the solid driven spectrum from the boundary reflecting spectrum. An example of air filled polymer shell suspended in water is presented. The added mass effect and partial-slip condition from water (air) on the frequencies and quality factors are found to be significant (negligible). Spherical isotropy is found to have major influence on the low frequency and large meridional wave number region of the resonance spectrum. High quality eigenmodes are observed due to very small viscous penetration depth compared to the shell size. In the thin-shell limit, the eigenvalue problem can have only two modes of vibration for any meridional wave number greater than or equal to two. This explains the reason for the second resonance frequency found for the quadrupole shape oscillations of various bacterium cells in the earlier work. The partial-slip condition is found to have very small influence on the first few modes of vibration. Surface tension is found to have significant influence only on the lowest frequency trend of the eigenspectrum. Perfectly matched layer technique used in the present analysis is found to be very effective in handling the boundary truncated problems.
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