Preliminary design of a test rig for combining passive nonlinear isolation with active control

Resilient elements are typically used to isolate delicate equipment from a vibrating host structure. Conventionally, these isolators are designed to operate in their linear region, but more recently nonlinear isolators have been employed to increase the frequency over which vibration isolation can be achieved. Another way of improving the performance of an isolator has been to use active control in conjunction with a passive linear system. The work presented in this paper concerns the development of an experimental rig for vibration isolation and is motivated by the intention to combine the advantages of passive nonlinear isolation with active control.The structure consists of a mass suspended on four tensioned wires to form a single-degree-of-freedom system. The nonlinear stiffness of the wires is such that the system behaves like a hardening Duffing oscillator. Firstly, a static analysis is carried out, both analytically and experimentally, where the nonlinearity of the system is determined by the tension, length, cross-sectional area and Young’s modulus of the wires. For the dynamic analysis, harmonic base excitation is considered. The magnitude of the base displacement is fixed for all excitation frequencies and the level of nonlinearity is adjusted by varying the tension in the wires, a higher tension leading to a milder system nonlinearity. Finally, the motion transmissibility of the system is measured and appears to agree with the theoretical result. The rig forms a suitable platform for subsequent incorporation of an active control system for combining the benefits of passive nonlinear isolation with, for example, skyhook damping

Association of five Austrodanthonia species (family Poaceae) with large and small scale environmental features in central western New South Wales

Twenty-eight natural populations of Wallaby Grasses, Austrodanthonia species, in central western New South Wales were sampled and species presence related to a suite of environmental characteristics. An average of 12 plants were selectively sampled from each population; most populations consisted of at least four out of five species, Austrodanthonia bipartita, A. caespitosa, A. eriantha, A. fulva and A. setacea. Numerous ecological factors allowed the widespread co-occurrence of these closely-related species. Large-scale rainfall and climatic factors were correlated with species-presence but no universal small-scale site environmental variables were important for all species. The most widespread species was Austrodanthonia caespitosa and environmental variations at a local site scale, depending on exposure to solar radiation, may at least partially overcome regional rainfall and climate influences

Be Star Disk Models in Consistent Vertical Hydrostatic Equilibrium

A popular model for the circumstellar disks of Be stars is that of a geometrically thin disk with a density in the equatorial plane that drops as a power law of distance from the star. It is usually assumed that the vertical structure of such a disk (in the direction parallel to the stellar rotation axis) is governed by the hydrostatic equilibrium set by the vertical component of the star's gravitational acceleration. Previous radiative equilibrium models for such disks have usually been computed assuming a fixed density structure. This introduces an inconsistency as the gas density is not allowed to respond to temperature changes and the resultant disk model is not in vertical, hydrostatic equilibrium. In this work, we modify the {\sc bedisk} code of \citet{sig07} so that it enforces a hydrostatic equilibrium consistent with the temperature solution. We compare the disk densities, temperatures, H$\alpha$ line profiles, and near-IR excesses predicted by such models with those computed from models with a fixed density structure. We find that the fixed models can differ substantially from the consistent hydrostatic models when the disk density is high enough that the circumstellar disk develops a cool ($T\lesssim10,000$K) equatorial region close to the parent star. Based on these new hydrostatic disks, we also predict an approximate relation between the (global) density-averaged disk temperature and the $T_{\rm eff}$ of the central star, covering the full range of central Be star spectral types.Comment: 25 pages; 11 figure

Generation of optimum vertical profiles for an advanced flight management system

Algorithms for generating minimum fuel or minimum cost vertical profiles are derived and examined. The option for fixing the time of flight is included in the concepts developed. These algorithms form the basis for the design of an advanced on-board flight management system. The variations in the optimum vertical profiles (resulting from these concepts) due to variations in wind, takeoff mass, and range-to-destination are presented. Fuel savings due to optimum climb, free cruise altitude, and absorbing delays enroute are examined

The lunar phases of dust grains orbiting Fomalhaut

Optical images of the nearby star Fomalhaut show a ring of dust orbiting the central star. This dust is in many respects expected to be similar to the zodiacal dust in the solar system. The ring displays a clear brightness asymmetry, attributed to asymmetric scattering of the central starlight by the circumstellar dust grains. Recent measurements show that the bright side of the Fomalhaut ring is oriented away from us. This implies that the grains in this system scatter most of the light in the backward direction, in sharp contrast to the forward-scattering nature of the grains in the solar system. In this letter, we show that grains considerably larger than those dominating the solar system zodiacal dust cloud provide a natural explanation for the apparent backward scattering behavior. In fact, we see the phases of the dust grains in the same way as we can observe the phases of the Moon and other large solar system bodies. We outline how the theory of the scattering behavior of planetesimals can be used to explain the Fomalhaut dust properties. This indicates that the Fomalhaut dust ring is dominated by very large grains. The material orbiting Fomalhaut, which is at the transition between dust and planetesimals, can, with respect to their optical behavior, best be described as micro-asteroids.Comment: Accepted for publication in A&

Novel applications for TAZ-8A

Recent needs in the non-aerospace industrial sector have revitalized interest in high performance alloys. TAZ-8A has a combination of properties that makes it unique: a high temperature strength, oxidation resistance, abrasion resistance, and exceptional thermal shock resistance. The major drawback for the utilization of this alloy is the relatively high cost compared with the more common iron base alloys. Reduced material consumption and lower costs are possible by using coatings of TAZ-8A on a low cost substrate. Coatings were applied using plasma spray techniques developed by NASA as well as modified plasma vapor deposition (PVD) techniques

Analysis of turbofan propulsion system weight and dimensions

Weight and dimensional relationships that are used in aircraft preliminary design studies are analyzed. These relationships are relatively simple to prove useful to the preliminary designer, but they are sufficiently detailed to provide meaningful design tradeoffs. All weight and dimensional relationships are developed from data bases of existing and conceptual turbofan engines. The total propulsion system is considered including both engine and nacelle, and all estimating relations stem from physical principles, not statistical correlations