1,721,017 research outputs found
METHOD AND APPARATUS FOR WAVE GENERATION AND DETECTION USING TENSEGRITY STRUCTURES
Full text linkThis disclosure relates to an apparatus based on tensegrity structures (referred to as tensegrity apparatus) for the transmission of special solitary waves with adjustable profile into a material or structure, and the detection of such waves from a material or structure
Stress wave mitigation in granular chains
No full textWe study stress wave mitigation in one- and two-dimensional granular media employing evolutionary algorithms to investigate the optimal design of composite protectors using granular chains composed of beads of various sizes, masses, and stiffnesses. We define a fitness function using the maximum force transmitted from the protector to a ``wall'' that represents the body to be protected and accordingly optimize the topology (arrangement), size, and material of the chain. We obtain optimally randomized granular protectors characterized by high-energy equipartition and the transformation of incident waves into interacting solitary pulses. We provide a quantitative characterization of dissipative effects using the propagation of highly nonlinear solitary waves as a diagnostic tool and develop optimization schemes that allow one to compute the relevant exponents and prefactors of the dissipative terms in the equations of motion. We thus propose a quantitatively-accurate extension of the Hertzian model encompassing realistic material dissipative effects. Experiments and computations with steel, brass, and polytetrafluoroethylene reveal a common dissipation exponent (for a discrete Laplacian of the velocities) with a material-dependent prefactor
On the Nonlinear Dynamics of Tensegrity Lattices
No full textIn the present work, we examine a novel application of tensegrity structures, exploring their use as networks supporting energy transport through solitary waves. We show that the elastic potential of a ‘regular minimal tensegrity prism’ (Skelton and de Oliveira, 2010) belongs to the class of nonlinear potentials analyzed in Friesecke and Matthies (2002), which characterize lattices supporting solitary waves with profile dependent on the wave speed. We numerically study the shape of such a profile over a wide range of wave speeds, showing that it localizes on a single lattice spacing (i.e., on a single prism) in the limit for the wave speed tending to infinity. This feature of tensegrity structures has not yet been investigated in the literature, and could pave the way to the use of ‘tensegrity lattices’ (or ‘crystals’) as novel materials to control stress propagation and produce energy trapping (cf., e.g., Fraternali et al. (2010a,b); Daraio et al. (2006) and therein references); innovative tendon- and strut-controlled structures for seismic applications (Skelton, 2002); as well as in novel acoustic devices, in order to create acoustic lenses capable of focusing pressure waves in very compact regions in space (Spadoni and Daraio, 2010)
Angular dependence of highly nonlinear pulse splitting in a two dimensional granular network
Full text linkShielding buildings from surface waves with “Seismic Metastructures”
No full textPhononic crystals and metamaterials constitute a broad class of artificially engineered materials able to manipulate the
propagation of acoustic/elastic waves at different lengths scale. Filtering and directivity properties of these materials can be controlled and tuned by designing their fundamental building blocks, usually referred as unit cells. Phononic crystals exploit periodicity to induce total wave reflection at selected frequencies. The obtained filtering properties emerge at wavelengths comparable to the periodicity. On the other hand, phononic metamaterials exploit the coupling between propagating waves and local resonators in the fundamental unit cells. As a result, propagation of waves with frequencies around the resonance is inhibited.
More recently the use of phononic crystals and metamaterials has been envisioned for large-scale applications in the field of civil engineering as a mean to shield buildings and infrastructures from natural or man-induced seismic waves. Among these, a solution based on metamaterial concepts and referred as “seismic metastructure” has been recently proposed by some of the authors. The proposed system is realized by an array of buried heavy-cylindrical steel units encased in cylindrical concrete pipes that constitute the metamaterial resonant units. The proper design and arrangement of these resonant units allows filtering longitudinal and shear waves in the typical frequency range of seismic waves (1-10Hz). In fact, analytical/numerical models as well as experimental evidences on a scaled setup proved the shielding capabilities of the proposed seismic isolation system with respect to bulk waves.
Building on the initial results on bulk waves, here we design “seismic metastructure” able to mitigate Rayleigh surface
waves. This is of special interest as they are considered the most harmful seismic threat. An analytical model to analyze the propagation of seismic surface waves through a soil engineered with seismic metastructures is developed. The analytical model allows predicting the frequency range within seismic Rayleigh waves are inhibited. A full 3D finite element model is used to numerically validate the prediction of the analytical model. Experimental evidences of the filtering properties of the designed metastructures are obtained on a scaled experimental setup. The excellent agreement of analytical/numerical and experimental results demonstrates the potential of this novel class of seismic isolation devices
Directional wave propagation in a highly nonlinear square packing of spheres
Full text linkWe studied the dynamic response of a twodimensional
square packing of uncompressed stainless
steel spheres excited by impulsive loadings. We developed
a new experimental measurement technique,
employing miniature tri-axial accelerometers, to determine
the stress wave properties in the array resulting
from both an in-plane and out-of-plane impact. Results
from our numerical simulations, based on a discrete
particle model, were in good agreement with the experimental
results. We observed that the impulsive
excitations were resolved into solitary waves traveling
only through initially excited chains. The observed solitary
waves were determined to have similar (Hertzian)
properties to the extensively studied solitary waves supported
by an uncompressed, uniform, one-dimensional
chain of spheres. The highly directional response of
this system could be used as a basis to design granular
crystals with predetermined wave propagation paths
capable of mitigating stress wave energy
Solitary waves on tensegrity lattices
Full text linkWe study the dynamics of lattices formed by masses connected through tensegrity prisms. By employing analytic and numerical arguments, we show that such structures support two limit dynamic regimes controlled by the prisms’ properties: (i) in the low-energy (sonic) regime the system supports the formation and propagation of solitary waves which exhibit sech2 shape, and (ii) in the high-energy (ultrasonic) regime the system supports atomic-scale localization. Such peculiar features found in periodic arrays of tensegrity structures suggest their use for the creation of new composite materials (here called ”tensegrity materials”) of potential interest for applications in impact absorption, energy localization and in new acoustic device
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