Academic literature on the topic 'Energy absorbing boundaries'

The Earth’s atmosphere is far from equilibrium; it is constantly in motion from the combined effects of gravity and planetary rotation, is constantly absorbing and emitting radiation, and hosts ongoing chemical reactions which are ultimately fuelled by solar photons. It has fluxes of material and energy across its boundaries with the planetary surface, both terrestrial and marine, and also emits a continual outward flux of infrared photons to space. The gaseous atmosphere is manifestly a kinetic system, meaning that its evolution must be described by time dependent differential equations. The equations doing this under the continuum fluid approximation are the Navier–Stokes equations, which are not analytically solvable and which support many non-linear instabilities. We have also seen that the generation of turbulence is a fundamentally difficult yet central feature of air motion, originating on the molecular scale. Non-equilibrium statistical mechanics may offer insight into which steady states a system far from equilibrium as a result of fluxes and anisotropies may migrate, without the need for detailed solution of the explicit path between the states. However, it does not seem possible to demonstrate mathematically that such steady states exist for the atmosphere. A physical view of the planet’s past and probable future suggests that the past and future evolution of the sun and its outgoing fluxes of energy may mean that the air-water-earth system may never have been or will ever be in a rigorously defined steady state. Also, to the human population, the detailed, time-dependent evolution is what matters in many respects. Nevertheless, non-equilibrium statistical mechanics is a discipline which should be applicable in principle to yield information about approximate steady states. These steady states may as a practical matter be definable from the observational record, for example the ice ages and the intervening periods evident in the geological record, or between states with two differing global average abundances of a radiatively active gas such as carbon dioxide. There has been great progress recently in non-equilibrium statistical mechanics, stemming from recent work on the concept of the maximization of entropy production.

Abstract Additive manufacturing has enabled the production of intricate lattice structures that meet stringent design requirements with minimal mass. While many methods such as lattice-based topology optimization are being developed to design lightweight structures for static loading, there is a need for design tools for achieving dynamic loading requirements. Lattice structures have shown particular promise as low-mass energy absorbers, but the computational expense of nonlinear finite element analysis and the difficulty of obtaining objective gradient information has made their optimization

The Savannah River Site (SRS) has a need to transport Highly Enriched Uranium (HEU) within site boundaries. A Type A fissile package design similar to the General Electric (GE) RA-3 and the Westinghouse PATRIOT packages has been selected for these shipments. This package design involves the use of light gage steel shapes, oriented to absorb energy from deformation and friction bearing contact surfaces, in between a thin gage mild carbon steel inner and outer shell. The RA-3 and the PATRIOT2 were both qualified by testing rather than analysis. To validate the SRS specific design, an advanced AB

The current paper investigates the use of perfectly-matched layers (PML) as absorbing elements for a finite element (FE) model simulating a semi-infinite medium. This formulation is convenient for application of Craig-Bampton reduction (CBR), which significantly reduce the number active degrees-of-freedom in the model in an attempt to improve the computational efficiency. The results from this investigation suggest the PML elements worked seamlessly with the FE elements to approximate the elastodynamic response of a 2D layered halfspace subjected to a surface load; the wave energy appears to b

Traumatic brain injuries (TBI) due to blast are common in modern combat situations, and often lead to permanent cognitive impairment. Despite the prevalence and severity of blast-induced TBI, the condition remains poorly understood. Computer simulations of blast and blast injury mechanics offer enormous potential; however, computer models require accurate descriptions of tissue mechanics and boundary conditions in vivo. To gain insight into the mechanisms of blast injury, we applied direct (light) oscillatory pressure loading to the skulls of human volunteers, and measured displacement and str

This work is concerned with a method to generate pure traveling vibration waves in finite structures. Using progressing deformations, i.e. waves, is not common when dealing with forced vibration since structures are naturally vibrating in their, naturally occurring, normal modes. Indeed, natural vibration modes can be referred to standing waves. Since a structure does not lend itself to a traveling wave vibration, the generation of traveling waves in a structure becomes a challenging task. The boundary conditions or external forces must be carefully tuned in an iterative process that necessita