Residual Kinetic Energy Research Articles

Electronic Structure Calculations Using A Modified Thomas-Fermi Approximation

ABSTRACTWe have recently developed an accurate and easily implemented approach to many-electron calculations, based on a modified Thomas-Fermi approximation. Specifically, we derived an electron density approximation, the first term of which is the Thomas-Fermi result, while the remaining terms substantially corrected the density near the nucleus. In a first application, we used the new density to accurately calculate the details of the self-consistent ion cores, as well as the ionization potentials for the outer s-orbital bound to the closed-shell ion core of the Group III, IV and V elements. Next, we demonstrated that the new density expression allows us to separate closed-shell core electron densities from valence electron densities. When we calculated the valence kinetic energy density, we showed that it separated into two terms: the first exactly cancelled the potential energy due to the ion core in the core region; the second was the residual kinetic energy density resulting from the envelopes of the valence electron orbitals. These features allowed us to write a functional for the total valence energy dependant only on the valence density. This equation provided the starting point for a large number of electronic structure calculations. Here, we used it to calculate the band structures of several Group IV and Group III-V semiconductors. We emphasize that this report only provides a summary; detailed derivations of all results are in Reference 5.

Self-conditioned fields for large-eddy simulations of turbulent flows

An alternative foundation is developed for the large-eddy simulation (LES) of turbulent flows. It is based on ‘self-conditioned fields’, for example, the mean velocity field conditional on a discrete representation of the filtered velocity field. It is shown that the self-conditioned velocity field minimizes the residual kinetic energy, and that, with the ideal model, the method yields the correct one-time behaviour as determined by the Navier–Stokes equations. The approach is extended to the self-conditioned probability density function (PDF) of compositions. Compared to LES formulations based on the filtered velocity and the filtered density function, the self-conditioned field approach has several advantages: for laminar flow, and in the direct-numerical-simulation limit, the residual fluctuations are zero or exponentially small; full account is taken of the probability distribution of turbulent fields; there are no commutation issues; and there are no issues with filtering at walls, where the self-conditioned velocity is zero. The exact evolution equations for the self-conditioned velocity and composition PDF are derived. Basic models are presented, and the development of improved models is discussed.

A Low Cost Air Hybrid Concept

The air hybrid engine absorbs the vehicle kinetic energy during braking, stores it in an air tank in the form of compressed air, and reuses it to propel a vehicle during cruising and acceleration. Capturing, storing and reusing this braking energy to give additional power can therefore improve fuel economy, particularly in cities and urban areas where the traffic conditions involve many stops and starts. In order to reuse the residual kinetic energy, the vehicle operation consists of 3 basic modes, i.e. Compression Mode (CM), Expander Mode (EM) and normal firing mode. Unlike previous works, a low cost air hybrid engine has been proposed and studied. The hybrid engine operation can be realized by means of production technologies, such as VVT and valve deactivation. In this work, systematic investigation has been carried out on the performance of the hybrid engine concept through detailed gas dynamic modelling using Ricardo WAVE software. Valve timing optimization has been done for the more efficient operation of air hybrid operation and obtaining higher braking and motoring mean effective pressure for CM and EM respectively.

Post-failure behaviour of impulsively loaded circular plates

The dynamic plastic response of a simply supported circular plate is analysed. Emphasis is given to the plate behaviour after it has broken free from the supports due to a local material failure. The theoretical rigid plastic analysis predicts various features of the response such as the time to failure, residual kinetic energy and the critical velocity at failure. The residual kinetic energy of the plate could be significant enough to cause secondary impact damage. It is shown that the shape of the plate changes after breaking free from the supports, which is important for forensic investigations. The solution for various cases were proven to be exact in the context of the upper and lower bounds theorems of the theory of plasticity.

Effect of frame size, frame type, and clamping pressure on the ballistic performance of soft body armor

We analyze, with the computer code LS-DYNA, three-dimensional (3D) transient deformations of a 10-layer woven Kevlar armor held in a square steel frame and impacted at normal incidence by a 9 mm FMJ (full metal jacket), 124 grain projectile. The composite armor is discretized into weft and warp yarns to simulate its woven structure. The yarn is modeled as a 3D continuum. We consider failure of the yarn, and friction between adjoining layers and between the armor and the frame bars. For the armor perfectly bonded to the rigid frame bars, the computed residual speed and the residual kinetic energy of the projectile are found to increase with a decrease in the frame size implying thereby that the armor fixed in a smaller frame will have lower V 50 than that of the same armor clamped in a larger frame. (The V 50 of an armor equals the speed of a standard projectile that upon normal impact has 50% probability of just perforating the armor). For the armor allowed to slide between the frame bars, we have studied the effect of the pressure applied to the bars of the two- and the four-bar frames on the speed and the kinetic energy of the residual projectile. For both the two- and the four-bar frames, the speed of the residual projectile is found to increase with an increase in the applied pressure. Computed results also show that the armor fixed in the two-bar frame exhibits higher impact resistance than that held in the four-bar frame. The V 50 is found to be ∼270 m/s when the woven armor is held in a four-bar frame with a clamping pressure of 200 MPa. The V 50 decreases with an increase in the pressure applied to either the two-bar or the four-bar frames.

Shape stability and violent collapse of microbubbles in acoustic traveling waves

Acoustically driven bubbles can develop shape instabilities and, if forced sufficiently strongly, distort greatly and break up. Perturbation theory provides some insight as to how these nonspherical shape modes grow initially but loses validity for large deformations. To validate the perturbation theory, we use a numerical model based on the boundary integral method capable of simulating nonspherical, axisymmetric bubbles subject to acoustic driving. The results show that the perturbation theory compares well with numerical simulations in predicting bubble breakup and stability. Thereafter, we compare the peak temperatures and pressures of spherical to nonspherical bubble collapses by forcing them with standing waves and traveling waves, respectively. This comparison is made in parameter ranges of relevance to both single bubble sonoluminescence and multibubble sonoluminescence and sonochemistry. At moderate forcing, spherical and nonspherical collapses achieve similar peak temperatures and pressures but, as the forcing is increased, spherical collapses become much more intense. The reduced temperature of nonspherical collapses at high forcing is due to residual kinetic energy of a liquid jet that pierces the bubble near the time of minimum volume. This is clarified by a calculation of the (gas) thermal equivalent of this liquid kinetic energy.

Modes of energy loss on shearing of thin confined films

Analysis of friction versus time traces for stick-slip friction of mica surfaces across solidified films confined between them, reveals that most of the frictional dissipation occurs via viscous heating of the shear melted film during the part of the cycle where the surfaces slide past each other (slip). A much smaller part of the energy dissipation results from the loss of residual kinetic energy at the abrupt end of the slip.

Three‐dimensional Compressible Hydrodynamic Simulations of Vortices in Disks

We carry out three-dimensional, high resolution (up to $1024^2\times 256$) hydrodynamic simulations of the evolution of vortices in vertically unstratified Keplerian disks using the shearing sheet approximation. The transient amplification of incompressible, linear amplitude leading waves (which has been proposed as a possible route to nonlinear hydrodynamical turbulence in disks) is used as one test of our algorithms; our methods accurately capture the predicted amplification, converges at second-order, and is free from aliasing. Waves expected to reach nonlinear amplitude at peak amplification become unstable to Kelvin-Helmholtz modes when $\mid W_{\rm max}\mid\gtrsim \Omega$ (where $W_{\rm max}$ is the local maximum of vorticity and $\Omega$ the angular velocity). We study the evolution of a power-law distribution of vorticity consistent with Kolmogorov turbulence; in two-dimensions long-lived vortices emerge and decay slowly, similar to previous studies. In three-dimensions, however, vortices are unstable to bending modes, leading to rapid decay. Only vortices with a length to width ratio smaller than one survive; in three-dimensions the residual kinetic energy and shear stress is at least one order of magnitude smaller than in two-dimensions. No evidence for sustained hydrodynamical turbulence and transport is observed in three-dimensions. Instead, at late times the residual transport is determined by the amplitude of slowly decaying, large-scale vortices (with horizontal extent comparable to the scale height of the disk), with additional contributions from nearly incompressible inertial waves possible. Evaluating the role that large-scale vortices play in astrophysical accretion disks will require understanding the mechanisms that generate and destroy them.

Post-failure response of impulsively loaded clamped beams

This paper analyses the response of a clamped rigid, perfectly plastic beam subjected to an impulsive velocity loading throughout the span. A critical velocity is determined using a damage mechanics model, beyond which a beam fails at the supports. Attention is focused on the dynamics of the beam after failure. A transient phase of deformation develops after failure and leads to a change of the beam geometry after failure. Other parameters such as the residual kinetic energy and rigid body velocity are also determined. A comparison is made between the clamped case here studied and the simply supported one described elsewhere by the authors.

Protection capability of dual flying plates against obliquely impacting long-rod penetrators

The protection capability of dual steel flying plates against obliquely impacting tungsten heavy alloy long-rod penetrators was simulated using NET3D code. The major variables considered in this work include thickness ratios of front to rear plate (5/0, 3.3/1.7, 2.5/2.5, 1.7/3.3, and 0/5) and plate velocity (0.2 and 0.5 km/s) at obliquity of 60°. Based on the residual kinetic energy of the penetrator after perforating the plates system, the protection capability of the system increased with an increase in the ratio of rear plate thickness. Such a trend was confirmed at a normal ordnance velocity (1.5 km/s) as well as a hypervelocity regime (2.5 km/s) and was shown to be best exploited when the relative velocity between the penetrator and rear plate was appropriate. A design guideline for an effective flying plate protection structure was proposed.

Eect of the Velocity of a Single Flying Plate on the Protection Capability Against Obliquely Impacting Long-Rod Penetrators

The protection capability of a flying steel plate against obliquely impacting tungsten heavy alloy long‐rod penetrators was simulated using the NET3D code as a function of plate velocity ranging from −0.5 to 0.5 km/sec at an obliquity of 60°. The negativity in plate velocity was assigned if the plate had a velocity component in the direction of penetrator progress. Based on the residual kinetic energy of the penetrator after perforating the plate, the protection capability of the plate increased as the plate velocity decreased to a negative value at both a normal ordnance velocity (1.5 km/sec) and a hypervelocity (2.5 km/sec) impact. The defeat capability of the oblique plate increased as the impact velocity increased in the plate velocity range studied in this work. The interaction mechanisms between the penetrator and steel plate, responsible for these results, were investigated. The physical meaning of the results obtained in this work were discussed in the light of sensor‐activated and reactive armours.

Speed of particles ejected from animal skin by CO2 laser pulses, measured by laser Doppler velocimetry

During ablation of tissue with laser pulses rapid sublimation of matter occurs and high pressures are exerted within the tissue, resulting in steam, smoke and particles being expelled. In this paper we report the speed of particles ejected from animal tissue exposed to CO2 laser pulses measured directly by laser Doppler velocimetry (LDV). Speeds recorded just above animal skin were in the range of 9 to 18 m s−1 for laser pulses of 128 to 384 J cm−2 respectively. Aerodynamic turbulence slowed the particles down to a critical speed Vc of 4 m s−1 within a few millimetres above the laser ablation site. Once the particles reach this minimum speed, if no collisions occur, they will only decelerate by gravitational action and the residual kinetic energy will send the particles up to about 0.87 m from the skin surface. Since ejected particles may carry viable cells, acting as disease vectors during laser surgery, our results suggest that the LDV technique should be used to measure the speed of particles ejected from healthy or pathological human tissues, helping to establish safe conditions during laser surgery.

Transient flexural waves in a disk and square plate from off-center impact

Flexural waves in a disk and square plate produced by off-center impact are analyzed. The effects on maximum transient stress σmax of boundary shape, edge constraint, thickness, side of square plate or diameter of disk, and eccentricity of center of impact are studied. While prior analytical work has been confined to disks for simplicity, ballistic experiments were performed using square plates for practical reasons. The two geometries agree better for central impact or edges that are simply supported or clamped. Analytical results show some intensification as center of impact approaches the edge, but this is insufficient to explain the measured rise in residual projectile kinetic energy after penetrating a ceramic tile. This reveals the inadequacy of the crack initiation mechanism as the primary model of defeating the projectile by ceramic tiles.

Guided ion beam study of collision-induced dissociation dynamics: integral and differential cross sections

The low energy collision-induced dissociation (CID) of Cr(CO)6+ with Xe is investigated using a recently modified guided ion beam tandem mass spectrometer, in the energy range from 0 to 5 eV in the center-of-mass (CM) frame. The additions to the instrument, updated with a double octopole system, and the new experimental methods available are described in detail. Integral cross sections for product formation are presented and analyzed using our standard modeling procedure. A slightly revised value for the bond dissociation energy of (CO)5Cr+–CO of 1.43±0.09 eV is obtained, in very good agreement with literature values. Axial and radial velocity distributions for primary and product ions are measured at 1.3, 2.0, and 2.7 eV, in the threshold region for product formation. The resulting velocity scattering maps are presented and discussed. Evidence of efficient energy transfer is observed from angular scattering of CID products. Experimental distributions of residual kinetic energies are derived and extend to zero, the point of 100% energy deposition. This indicates that energy transfer is nonimpulsive and probably associated with transient complex formation. For the first time, the experimental residual kinetic energy distributions are compared with the predictions of the empirical model used in integral cross section analyses. Good agreement is observed within experimental uncertainties. A model for the distribution of deposited energy during collisional activation is derived on the basis of these experimental observations.

Electroless nickel plating on magnesium alloy

a traveling wave tube (TWT) for amplification of signals. In a TWT the collector is the main source of heat dissipation. The electrodes are heated by the residual kinetic energy of the collected electrons; however, the elec- trodes must be maintained at a rela- tively low temperature. There are two ways to dissipate this heat into cold space (see Fig. 1). 1. Heat conduction from the elec- trodes to the spacecraft radiator. This is called conduction cooling and is suit-

Effects of multiple blade interaction on the containment of blade fragments during a rotor failure

A finite element analysis is used to study the impact and the containment aspects of rotor blade fragments that are produced during a aircraft jet engine rotor failure. The impact and containment studies are performed on a ring-type containment structure and various fragment types are considered in this study. For each type of fragment, the ring thickness is varied incrementally and the ring response, residual kinetic energy level of the fragments, magnitude of impact forces and the overall containment or failure are determined. First, only a single fragment is considered and the rotor is assumed to contain no other blades. Next, the remaining blades are introduced and the effects of multiple collisions with the other blades on the containment are analyzed. The explicit, nonlinear finite element code Dyna3d is used for the numerical computations in this study and the results are compared with the experimental results performed on a T58 rotor at the spin facility of the Naval Air Propulsion Test Center.

A study of fragmentation in the ballistic impact of ceramics

Experiments in which both confined and unconfined ceramic targets are perforated by pointed and blunt projectiles are described, and a correlation is established between increased degree of fragmentation and reduced ceramic toughness. Front confinement of the ceramic results in greater overall fragmentation, however fewer, very fine fragments are produced for confined targets compared to unconfined targets. By attributing the fine fragments principally to crushing ahead of the impacting projectile, and coarse fragmentation to the interaction of stress relief waves, the effects of confinement can be qualitatively explained in terms of a simple model for loading and stress relief during perforation. The use of blunt projectiles increases the degree of fragmentation in those cases where the ceramic strength itself is insufficient to fracture the tip on impact. Measurements of fractured ceramic surface area and calculations of fracture work demonstrate that very little of the projectile kinetic energy is consumed in creating new ceramic fracture surface, and it is shown that a high proportion of the projectile impact kinetic energy is redistributed to residual kinetic energy of ejected ceramic debris. For cases where the projectile does not deform during penetration it is possible to derive a value for the average pressure resisting the penetrator. The ballistic efficiency of the ceramic increases with hardness for the lower strength ceramics, however, for the hard ceramics, where the principal influence of the ceramic is to destroy the projectile nose and create an inefficient penetrator, it is found in these tests that the residual penetration depths are similar, and ballistic efficiency is then unrelated to ceramic strength.

Head-on mergers of systems containing gas

Several simple mergers between model galaxy clusters containing a mixture of gas and dark matter are examined, testing the coupling of the gas to the underlying collisionless material. The gas is shocked, irreversibly dissipating the energy fed into it by the collisionless component and forms a resolved constant-density core. For the dark matter, however, admixture of phase space vacuum is not very efficient and a constant-density core is not produced. In the final state the central gas has little residual kinetic energy, indicating that streaming motions do not help to support the gas.

An engineering model to predict perforation damage to plates impacted by high velocity debris clouds

This paper describes experiments and the development of a model to predict damage to metallic plates impacted by high velocity, multi-particle debris clouds. The experiments involved single steel spheres fired at a steel shatter plate at speeds near 1.5 and 2.0 km/sec to generate the debris clouds. In each series of tests, the impact velocity was controlled, and a witness plate was placed at increasing distances behind the shatter plate to observe the effects of debris particle dispersion on plate damage. This paper focuses on the variations, with plate spacing, in the size of the central region removed from the witness plates. The central hole size model compares the post impact kinetic energy distribution in a witness plate impacted by a debris cloud to the free impact residual kinetic energy in an equivalent plate impacted by an L/D=1 steel cylinder, at the ballistic limit velocity. This approach permits extension of the model to other plate materials through utilization of existing ballistic limit velocity data.

Formation and evolution of X-ray clusters - A hydrodynamic simulation of the intracluster medium

view Abstract Citations (360) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Formation and Evolution of X-Ray Clusters: A Hydrodynamic Simulation of the Intracluster Medium Evrard, August E. Abstract The X-ray-emitting intracluster medium (ICM) in clusters of galaxies is studied using a combined three-dimensional hydrodynamic and N-body simulation algorithm with the assumption that clusters formed via hierarchical clustering in a cold dark matter-dominated universe with ICM fraction {OMEGA}_ICM_ = 0.1. The ICM is treated as an ideal γ = 5/3 gas undergoing shock heating within the self-consistency evolving dark matter potential. The evolution of a single, Coma-richness cluster is examined in detail. A core of ~ 10^13^ M_sun_ of gas collapses by z = 1 and grows through mergers and accretion of surrounding material. The process can be crudely defined by a shock front moving outward at ~ 400 km s^-1^ reaching a radius ~ 5h^-1^_50_ Mpc at the present epoch. The 2 x 10^14^h^-1^_50_ M_sun_ of gas within an Abell radius at z = 0 is close to isothermal at T = 7.2 keV with evidence for a modest temperature inversion in the cluster center. Polytropic models provide a poor description of the ICM thermodynamic state. The density profile of the cluster shows no resolved core radius, although a flattening of the logarithmic slope is apparent at radii r ~< 500h^-1^_50_ kpc. The total 2-10 keV luminosity of 7.5 x 10^44^h_50_ ergs s^-1^ is therefore subject to an uncertain core contribution. A Sunyaev-Zel'dovich central decrement of roughly 0.5 mK would be expected from this cluster at redshifts z ~< 0.25 at 1' resolution. The signal drops below 0.1 mK at z = 0.5 Investigation of the standard hydrostatic isothermal B-model shows that estimates of the specific energy ratio β = σ^2^/(kT/micron_p_) based on surface brightness profiles are systematically biased. The discrepancy arises from the existence of residual kinetic energy in the shock-heated gas and poor modeling of the underlying binding mass distribution. Simple binding mass estimates based on this model underestimate the actual binding mass within an Abell radius by ~ 30%. The mass contained within an Abell radius for Coma and A2256 is estimated to be 2.4 and 2.6 x 10^15^h^- 1^_50_ M_sun_, respectively, after correcting for these effects. Publication: The Astrophysical Journal Pub Date: November 1990 DOI: 10.1086/169350 Bibcode: 1990ApJ...363..349E Keywords: Cosmology; Galactic Clusters; Galactic Evolution; Interstellar Gas; X Ray Sources; Brightness Distribution; Dark Matter; Hydrodynamics; Many Body Problem; Universe; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: INTERGALACTIC MEDIUM; GALAXIES: X-RAYS; HYDRODYNAMICS full text sources ADS | data products SIMBAD (2)