4,749 research outputs found
Development of ductile claddings for dispersion-strengthened nickel-base alloys Final report
Development of ductile oxidation-resistant cladding alloys for thoria dispersion, strengthened nickel and nickel-chromiu
Towards Gradient-Based Actuationof Magnetic Soft Robots Using a Six-Coil Electromagnetic System
Spatiotemporal chaos and the dynamics of coupled Langmuir and ion-acoustic waves in plasmas
A simulation study is performed to investigate the dynamics of coupled
Langmuir waves (LWs) and ion-acoustic waves (IAWs) in an unmagnetized plasma.
The effects of dispersion due to charge separation and the density nonlinearity
associated with the IAWs, are considered to modify the properties of Langmuir
solitons, as well as to model the dynamics of relatively large amplitude wave
envelopes. It is found that the Langmuir wave electric field, indeed, increases
by the effect of ion-wave nonlinearity (IWN). Use of a low-dimensional model,
based on three Fourier modes shows that a transition to temporal chaos is
possible, when the length scale of the linearly excited modes is larger than
that of the most unstable ones. The chaotic behaviors of the unstable modes are
identified by the analysis of Lyapunov exponent spectra. The space-time
evolution of the coupled LWs and IAWs shows that the IWN can cause the
excitation of many unstable harmonic modes, and can lead to strong IAW
emission. This occurs when the initial wave field is relatively large or the
length scale of IAWs is larger than the soliton characteristic size. Numerical
simulation also reveals that many solitary patterns can be excited and
generated through the modulational instability (MI) of unstable harmonic modes.
As time goes on, these solitons are seen to appear in the spatially partial
coherence (SPC) state due to the free ion-acoustic radiation as well as in the
state of spatiotemporal chaos (STC) due to collision and fusion in the
stochastic motion. The latter results the redistribution of initial wave energy
into a few modes with small length scales, which may lead to the onset of
Langmuir turbulence in laboratory as well as space plasmas.Comment: 10 Pages, 14 Figures; to appear in Physical Review
A Numerical Study of Penetration in Concrete Targets by Eroding Projectiles of Different Materials
Numerical simulations have been performed to examine the effect of three different eroding rod materials on the penetration in concrete targets. Same kinetic energy is delivered to concrete target using cylindrical rods of Aluminium, Iron, and Copper of identical size. Impact velocities have been varied to keep the kinetic energy the same. Penetration characteristics like centerline interface velocity, penetrator deceleration, plastic strain in the target, and energy partitioning during penetration have been studied for the three different penetrator materials. In all three cases, penetration proceeds nearly hydrodynamically. It is seen that even though the steady-state penetration ceases before reaching the hydrodynamic limit, the secondary penetration takes the total penetration beyond the hydrodynamic value. Plastic strain in the target material is a measure of damage beyond the crater produced by penetration. The lateral extent of plastic strain in target is more for Aluminium penetrator compared to the other two. Energy partitioning during penetration provides details of the rate at which energy is entering into the target. Kinetic energy delivered to the target during impact is partitioned into internal energy and kinetic energy of the target. Finally, the influence of target thickness on the extent of plastic strain has been studied. The result shows that Aluminium penetrators inflict maximum damage to targets of finite thickness
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