Numerical analysis of a sling support arrangement for grp composite pressure vessels

A flexible sling support arrangement for horizontal glass reinforced plastic pressure vessels is examined using advanced finite element methods. A mathematical model is produced employing a suitable analysis capable of representing the non-linear behaviour of a sling supported GRP vessel. This system is used to examine the phenomena occurring at the interface between the vessel and the supporting belt. Each component is initially considered some distance apart and then brought together using three-dimensional contact surfaces. External loads are thereafter applied to the combined model. Although several numerical difficulties arise due to the difference in flexibility between the vessel shell and the sling support, these are overcome and the resulting vessel strains and contact interface pressures show good agreement with experimental work. The magnitudes of the strains at the location of the saddle horn are significantly reduced. Results of a parameter study are also presented which show the effect of the sling position together with the influence of the wrap-round angle and a number of recommendations are made with respect to design

An experimental study of damage accumulation in balanced CFRP laminates due to repeated impact

The behaviour of balanced laminates (symmetric, antisymmetric and asymmetric) under repeated low energy hits of a 12.1 mm hemispheric impactor was evaluated. The resistance to the impulsive force was found to be influenced by the stacking sequence and the crack path through the laminate. The symmetric plate with different ply directions proved to have best resistance to impact. The rate of damage progression in the event was characterised by an equation from the energy profile that correlates the propagation energy and time. This was differentiated to give the rate of damage evolution. A comparison of the bending stiffness obtained from the force-displacement plot of the first impact, revealed that the symmetric composite had the highest stiffness. Noted at perforation were fibre breakage and matrix cracking

Impact characterisation of doubly curved composite structure

Under repeated impact composite domes subjected 6 J energy, changes locally with increasing drop height. The action of the dynamic load generates reactions at the support and bending moments at points on the surface of the composite. The peak loads were noted to increase and stabilise about some mean value; and the 150mm diameter shell was more damage tolerant compared to the 200 mm diameter one

A study of repeated impact loading on a symmetrical carbon fibre laminate

The behaviour of a symmetric laminate under repeated low energy hits of a 12.1mm hemispheric impactor was evaluated. The laminate was able to endure 20 collisions with the striker before perforation. The rate of damage progression was characterised by an equation from the energy profile that correlates the propagation energy and time. The function was represented by a sixth order polynomial. This was differentiated to give the rate of damage evolution. The contact time related to theimpact events with the same degree of polynomial. At perforation fibre breakage and matrix cracking were observed

A parametric study of alternative support systems for cylindrical GRP storage vessels

Paper presenting a parametric study of alternative support systems for cylindrical GRP storage vessels

Entropy Bounds and Dark Energy

Entropy bounds render quantum corrections to the cosmological constant $\Lambda$ finite. Under certain assumptions, the natural value of $\Lambda$ is of order the observed dark energy density $\sim 10^{-10} {\rm eV}^4$, thereby resolving the cosmological constant problem. We note that the dark energy equation of state in these scenarios is $w \equiv p / \rho = 0$ over cosmological distances, and is strongly disfavored by observational data. Alternatively, $\Lambda$ in these scenarios might account for the diffuse dark matter component of the cosmological energy density.Comment: 6 pages, Latex. Added discussion of non-cosmological limits on holographic dark energy. Version to appear in Physics Letters

Multi-Periodic Repetitive Control System: A Lyapunov Stability Analysis for MIMO Systems

A multi-input/output (MIMO) repetitive control problem of tracking and disturbance rejection is considered when both reference and disturbance signals are finite linear combinations of periodic but not necessarily sinusoidal signals. Lyapunov stability analyses under a positive real condition (and a natural relaxation) and exponential stability under a strict positive real condition are provided together with bounds on the induced L2 and RMS gains of the closed loop system. It is shown that similar Lyapunov stability results apply when the plant is a positive real state-delay system. Extension of the analyses to a class of nonlinear systems is discussed and indicates a good degree of robustness in the design

A New Anomaly Matching Condition?

We formulate ``Witten'' matching conditions for confining gauge theories. The conditions are analogous to 't Hooft's, but involve Witten's global SU(2) anomaly. Using a group theoretic result of Geng, Marshak, Zhao and Okubo, we show that if the fourth homotopy group of the flavor group $H$ is trivial ($\Pi_4(H) = 0$) then realizations of massless composite fermions that satisfy the 't Hooft conditions also satisfy the Witten conditions. If $\Pi_4 (H)$ is nontrivial, the new matching conditions can yield additional information about the low energy spectrum of the theory. We give a simple physical proof of Geng, et. al.'s result.Comment: 11 pages, LaTex, all macros include

Anthropic Distribution for Cosmological Constant and Primordial Density Perturbations

The anthropic principle has been proposed as an explanation for the observed value of the cosmological constant. Here we revisit this proposal by allowing for variation between universes in the amplitude of the scale-invariant primordial cosmological density perturbations. We derive a priori probability distributions for this amplitude from toy inflationary models in which the parameter of the inflaton potential is smoothly distributed over possible universes. We find that for such probability distributions, the likelihood that we live in a typical, anthropically-allowed universe is generally quite small.Comment: 12 pages, 2 tables. v3: Replaced to match published version (minor corrections of form

Relaxing the Cosmological Moduli Problem

Typically the moduli fields acquire mass m =C H in the early universe, which shifts the position of the minimum of their effective potential and leads to an excessively large energy density of the oscillating moduli fields at the later stages of the evolution of the universe. This constitutes the cosmological moduli problem, or Polonyi field problem. We show that the cosmological moduli problem can be solved or at least significantly relaxed in the theories in which C >> 1, as well as in some models with C << 1.Comment: 9 pages, 3 Postscript figure