Predicting material damping in composite blades - a novel low order approach and experimental validation

Fibre-reinforced polymer (FRP) composites are being used increasingly in turbomachinery components, due to their light weight and high specifi c strength. Bladed components are sensitive to vibrations, which are driven by the magnitude of excitation and their damping. Vibrations cause high-cycle-fatigue and eventual failure, so care must be taken to minimise vibration amplitude, through engineered damping if possible. Modelling material damping in composites is challenging due to their anisotropy but tailoring the layup of a laminate could potentially positively influence the material damping. This work presents a low-order modelling approach and experimental measurement technique, producing computationally efficient and simple damping predictions for composite components with arbitrary geometry and layup. This "smeared" approach, whilst similar to existing approaches, uses a strain energy computation to determine the material damping, but homogenises the effective properties of entire layups, rather than lamina properties, as typically used for macro-scale modelling. Initial experimental validation of the approach showed it to predict damping well for abstract single-layup specimens. Improved input damping parameters were produced through the development of a novel test rig, consisting of heavy tip masses attached to rectangular coupon specimens. This reduces extraneous damping contributions signifi cantly. The test rig facilitated further investigation into the scalability of smeared predictions, showing that the smeared elastic moduli and damping parameters can be used to represent the behaviour of thicker laminates effectively if out-of-plane stress and strain contributions are accounted for during modal loss factor computation. This investigation, coupled with input parameters gathered using the test rig, provided the con fidence to apply the smeared technique to geometrically complex, multilaminates. The technique predicted modal damping effectively, proven with full experimental validation. Throughout the work, the smeared approach is shown to produce equivalent, and sometimes superior, accuracy to the existing layered approach, with a signifi cant reduction in computational cost.Open Acces

Assessment of Error in Synoptic-Scale Diagnostics Derived from Wind Profiler and Radiosonde Network Data

A topic of current practical interest is the accurate characterization of the synoptic-scale atmospheric state from wind profiler and radiosonde network observations. We have examined several related and commonly applied objective analysis techniques for performing this characterization and considered their associated level of uncertainty both from a theoretical and a practical standpoint. A case study is presented where two wind profiler triangles with nearly identical centroids and no common vertices produced strikingly different results during a 43-h period. We conclude that the uncertainty in objectively analyzed quantities can easily be as large as the expected synoptic-scale signal. In order to quantify the statistical precision of the algorithms, we conducted a realistic observing system simulation experiment using output from a mesoscale model. A simple parameterization for estimating the uncertainty in horizontal gradient quantities in terms of known errors in the objectively analyzed wind components and temperature is developed from these results

NASA/DFRC Workshop on Climate Change Adaptation: Assessing Climate Variability and Change

This presentation was developed in the DFRC Climate Change Adaptation Workshop Aug 2-3, 2011 to address impacts of climate change to the center, and provide recommendations for adaptation/mitigation

Examination of the observed synoptic scale cirrus cloud environment: The December 3-6 FIRE cirrus case study

Recently, Sassen provided evidence for supercooled water droplets in cirrus uncinus cell heads at temperatures between 40 and -50 C. Chemistry related to volcanic aerosol of stratospheric origin was evoked as an explanation for this phenomenon. Sassen speculated that injections of sulfuric acid droplets into the upper troposphere were accomplished by tropopause folds associated with subtropical jet streams. He also postulated global climatic perturbations due to the effect of these cirrus microphysical perturbations on radiative fluxes. Using data processing and objective analysis techniques described by Mace and Ackerman, the synoptic scale environment was examined for evidence of tropopause folds that may have served as a source mechanism of stratospheric aerosol in the upper troposphere

A search for solar neutrons on a long duration balloon flight

The EOSCOR 3 detector, designed to measure the flux of solar neutrons, was flown on a long duration RACOON balloon flight from Australia during Jan. through Feb, 1983. The Circum-global flight lasted 22 days. No major solar activity occurred during the flight and thus only an upper limit to the solar flare neutrons flux is given. The atmospheric neutron response is compared with that obtained on earlier flights from Palestine, Texas

Smaller Saami Herding Groups Cooperate More in a Public Goods Experiment

Group living often entails a balance between individual self-interest and benefits to the group as a whole. Situations in which an individual’s vested interests conflict with collective interests are known as social dilemmas (Kollock 1998). More formally, a theoretical game becomes a social dilemma when an equilibrium of dominant strategies leads to worse outcomes for all players compared to a more cooperative but non-equilibrium strategy (Zelmer 2003; Cardenas and Carpenter 2008). For example, arms races, climate change, the Cold War, credit markets, eBay, exploitation of fisheries, irrigation scheduling, overpopulation, pollution, price wars, voting, water supply and welfare states all give rise to social dilemmas (Kollock 1998; Wydick 2008). Researchers have identified various mutually inclusive routes to solving social dilemmas, including interacting with kin and/or cooperative individuals, communication, coordination, exclusion, institutions, leadership, legislation, mobility, monitoring, parcelling out cooperation or access to resources, partner choice, partner control, policing, punishment, repeated reciprocal interactions, rewards, sanctions, and social norms (Trivers 2005; West et al.2007; Levin 2014; Raihani and Bshary 2015). Social dilemmas pervade the pastoralist way of life. Individual herders must balance their interests (e.g., generating income and managing the inherent risks of pastoralism) with the interests of their herding group and the wider community facing similar challenges (Næss et al.2012; Næss and Bårdsen 2015). Pastoralists such as Saami reindeer herders in Norway face social dilemmas across a range of scales and have a variety of individual and collective strategies for solving them

Airborne Science Program: Observing Platforms for Earth Science Investigations

This slide presentation reviews the Airborne Science Program and the platforms used for conducting investigations for the Earth System Science. Included is a chart that shows some of the aircraft and the operational altitude and the endurance of the aircraft, views of the Dryden Aircraft Operation Facility, and some of the current aircraft that the facility operates, and the varieties of missions that are flown and the type of instrumentation. Also included is a chart showing the attributes of the various aircraft (i.e., duration, weight for a payload, maximum altitude, airspeed and range) for compariso

Comment on 'Computation of choked and supersonic turbomachinery flows by a modified potential method'

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76485/1/AIAA-9485-236.pd

Kinship underlies costly cooperation in Mosuo villages

The relative importance of social evolution theories such as kin selection, direct reciprocity and need-based transfers in explaining real-world cooperation is the source of much debate. Previous field studies of cooperation in human communities have revealed variability in the extent to which each of these theories explains human sociality in different contexts. We conducted multivariate social network analyses predicting costly cooperation-labouring on another household's farm-in 128 082 dyads of Mosuo farming households in southwest China. Through information-theoretic model selection, we tested the roles played by genealogical relatedness, affinal relationships (including reproductive partners), reciprocity, relative need, wealth, household size, spatial proximity and gift-giving in an economic game. The best-fitting model included all factors, along with interactions between relatedness and (i) reciprocity, (ii) need, (iii) the presence of own children in another household and (iv) proximity. Our results show how a real-world form of cooperation was driven by kinship. Households tended to help kin in need (but not needy non-kin) and travel further to help spatially distant relatives. Households were more likely to establish reciprocal relationships with distant relatives and non-kin but closer kin cooperated regardless of reciprocity. These patterns of kin-driven cooperation show the importance of inclusive fitness in understanding human social behaviour

Population structured by witchcraft beliefs

Anthropologists have long argued that fear of victimization through witchcraft accusations promotes cooperation in small-scale societies1. Others have argued that witchcraft beliefs undermine trust and therefore reduce social cohesion2. However, there are very few, if any, quantified empirical examples demonstrating how witchcraft labels can structure cooperation in real human communities. Here we show a case from a farming community in China where people labelled zhu were thought capable of supernatural activity, particularly poisoning food. The label was usually applied to adult women heads of household and often inherited down the female line. We found that those in zhu households were less likely to give or receive gifts or farm help to or from non-zhu households; nor did they have sexual partnerships or children with those in non-zhu households. However, those in zhu households did preferentially help and reproduce with each other. Although the tag is common knowledge to other villagers and used in cooperative and reproductive partner choice, we found no evidence that this assortment was based on cooperativeness or quality. We favour the explanation that stigmatization originally arose as a mechanism to harm female competitors. Once established, fear that the trait is transmissible may help explain the persistence of this deep-rooted cultural belief