179 research outputs found
Modeling damaged wings: Element selection and constraint specification
The NASTRAN analytical program was used for structural design, and no problems were anticipated in applying this program to a damaged structure as long as the deformations were small and the strains remained within the elastic range. In this context, NASTRAN was used to test three-dimensional analytical models of a damaged aircraft wing under static loads. A comparison was made of calculated and experimentally measured strains on primary structural components of an RF-84F wing. This comparison brought out two sensitive areas in modeling semimonocoque structures. The calculated strains were strongly affected by the type of elements used adjacent to the damaged region and by the choice of multipoint constraints sets on the damaged boundary
Dynamics of a bouncing dimer
We investigate the dynamics of a dimer bouncing on a vertically oscillated
plate. The dimer, composed of two spheres rigidly connected by a light rod,
exhibits several modes depending on initial and driving conditions. The first
excited mode has a novel horizontal drift in which one end of the dimer stays
on the plate during most of the cycle, while the other end bounces in phase
with the plate. The speed and direction of the drift depend on the aspect ratio
of the dimer. We employ event-driven simulations based on a detailed treatment
of frictional interactions between the dimer and the plate in order to
elucidate the nature of the transport mechanism in the drift mode.Comment: 4 pages, 5 figures, Movies:
http://physics.clarku.edu/~akudrolli/dime
The anomalous behavior of coefficient of normal restitution in the oblique impact
The coefficient of normal restitution in an oblique impact is theoretically
studied. Using a two-dimensional lattice models for an elastic disk and an
elastic wall, we demonstrate that the coefficient of normal restitution can
exceed one and has a peak against the incident angle in our simulation.
Finally, we explain these phenomena based upon the phenomenological theory of
elasticity.Comment: 4 pages, 4 figures, to be appeared in PR
Simulation of deterministic energy-balance particle agglomeration in turbulent liquid-solid flows
An efficient technique to simulate turbulent particle-laden flow at high mass loadings within the four-way coupled simulation regime is presented. The technique implements large-eddy simulation, discrete particle simulation, a deterministic treatment of inter-particle collisions, and an energy-balanced particle agglomeration model. The algorithm to detect inter-particle collisions is such that the computational costs scale linearly with the number of particles present in the computational domain. On detection of a collision, particle agglomeration is tested based on the pre-collision kinetic energy, restitution coefficient, and van der Waals’ interactions. The performance of the technique developed is tested by performing parametric studies on the influence of the restitution coefficient (en = 0.2, 0.4, 0.6, and 0.8), particle size (dp = 60, 120, 200, and 316 μm), Reynolds number (Reτ = 150, 300, and 590), and particle concentration (αp = 5.0 × 10−4, 1.0 × 10−3, and 5.0 × 10−3) on particle-particle interaction events (collision and agglomeration). The results demonstrate that the collision frequency shows a linear dependency on the restitution coefficient, while the agglomeration rate shows an inverse dependence. Collisions among smaller particles are more frequent and efficient in forming agglomerates than those of coarser particles. The particle-particle interaction events show a strong dependency on the shear Reynolds number Reτ, while increasing the particle concentration effectively enhances particle collision and agglomeration whilst having only a minor influence on the agglomeration rate. Overall, the sensitivity of the particle-particle interaction events to the selected simulation parameters is found to influence the population and distribution of the primary particles and agglomerates formed
Dynamic buckling and fragmentation in brittle rods
We present experiments on the dynamic buckling and fragmentation of slender
rods axially impacted by a projectile. By combining the results of Saint-Venant
and elastic beam theory, we derive a preferred wavelength lambda for the
buckling instability, and experimentally verify the resulting scaling law for a
range of materials including teflon, dry pasta, glass, and steel. For brittle
materials, buckling leads to the fragmentation of the rod. Measured fragment
length distributions show two clear peaks near lambda/2 and lambda/4. The
non-monotonic nature of the distributions reflect the influence of the
deterministic buckling process on the more random fragmentation processes.Comment: 4 pages, 5 figures, submitted to Physical Review Letter
Platforming Equality: Policy Challenges for the Digital Economy
This is the final version. Available from Autonomy via the link in this recordWelcome to Autonomy’s ‘Platforming Equality’ document: a collection of papers on the challenges that the digital economy poses to policymakers, activists and researchers. We’ve invited a range of contributors to probe deeper into under-examined topics in the digital economy and to shed light on how they operate. Another aim of the collection is to explore policy options for alleviating a range of new challenges that have emerged within the digital economy.
Contributors move beyond theoretical discussion of the problems themselves and turn towards an analysis of responses that are open to activists, municipal authorities and government policy makers. Articles suggest a range of policy recommendations and discuss the strengths and weaknesses of different approaches. Each contributor examines a specific issue based on their own research and an analysis of the existing literature. They then provide their own perspective on the policies and approaches that would be most suitable to tackling the issue
Simulation of cohesive head-on collisions of thermally activated nanoclusters
Impact phenomena of nanoclusters subject to thermal fluctuations are
numerically investigated. From the molecular dynamics simulation for colliding
two identical clusters, it is found that the restitution coefficient for
head-on collisions has a peak at a colliding speed due to the competition
between the cohesive interaction and the repulsive interaction of colliding
clusters. Some aspects of the collisions can be understood by the theory by
Brilliantov {\it et al.} (Phys. Rev. E {\bf 76}, 051302 (2007)), but many new
aspects are found from the simulation. In particular, we find that there are
some anomalous rebounds in which the restitution coefficient is larger than
unity. The phase diagrams of rebound processes against impact speed and the
cohesive parameter can be understood by a simple phenomenology.Comment: 10 pages, 12 figures, submitted to PRE; revised content and added
reference
Simulation for the oblique impact of a lattice system
The oblique collision between an elastic disk and an elastic wall is
numerically studied.
We investigate the dependency of the tangential coefficient of restitution on
the incident angle of impact.
From the results of simulation, our model reproduces experimental results and
can be explained by a phenomenological theory of the oblique impact.Comment: 30 pages, 9 figures, submitted to J. Phys. Soc. Japa
Impact testing to determine the mechanical properties of articular cartilage in isolation and on bone
The original publication is available at www.springerlink.comNon peer reviewedPostprin
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