Use of elastomeric elements in control of rotor instability

The dynamic characteristics of elastomeric supports are discussed. Stiffness and damping characteristics for elastomers of various geometries including O-rings, buttons loaded in compression, and rectangular elements loaded in shear are presented. The effects of frequency, temperature, and amplitude are illustrated, as well as the effects of material and geometry. Empirical design methods are illustrated, and several examples are presented where elastomers have successfully controlled both synchronous and nonsynchronous vibrations

Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 4: Testing of elastomers under a rotating load

A test rig designed to measure stiffness and damping of elastomer cartridges under a rotating load excitation is described. The test rig employs rotating unbalance in a rotor which runs to 60,000 RPM as the excitation mechanism. A variable resonant mass is supported on elastomer elements and the dynamic characteristics are determined from measurements of input and output acceleration. Five different cartridges are considered: three of these are buttons cartridges having buttons located in pairs, with 120 between each pair. Two of the cartridges consist of 360 elastomer rings with rectangular cross-sections. Dynamic stiffness and damping are measured for each cartridge and compared with predictions at different frequencies and different strains

Effects of environmental changes on marsh vegetation with special reference to salinity

A literature survey primarily concerned with brackish and salt marshes located along the eastern coast of North America and the Gulf Coast was presented. The review concentrated upon the vegetation of the marshes, particularly in regard to distribution, composition, succession, and productivity. Special efforts were made to include major works concerned with the Louisiana and Mississipi coastal marshes. It appears that spring to early summer (weeks 18-34 of the year; April - mid-July) is the best period of time to categorize the communities. It is during this time of the year that the communities appear most stable in regard to species composition. This allows a strong correlation to be drawn between the salinity of the region and the dominant species of the community. As such, this would seem to be best period in which to sample the marsh via air or land for differences in vegetation and salinity

Subsynchronous vibrations in a high pressure centrifugal compressor: A case history

Two distinct aerodynamically excited vibrations in a high pressure low flow centrifugal compressor are documented. A measured vibration near 21% of running speed was identified as a nonresonant forced vibration which results from rotating stall in the diffuser; a measured vibration near 50% of running speed was identified as a self excited vibration sustained by cross coupling forces acting at the compressor wheels. The dependence of these characteristics on speed, discharge pressure, and changes in bearing design are shown. The exciting mechanisms of diffuser stall and aerodynamic cross coupling are evidenced. It is shown how the rotor characteristics are expected to change as a result of modifications. The operation of the compressor after the modifications is described

Development of procedures for calculating stiffness and damping properties of elastomers. Part 3: The effects of temperature, dissipation level and geometry

Effects of temperature, dissipation level and geometry on the dynamic behavior of elastomer elements were investigated. Force displacement relationships in elastomer elements and the effects of frequency, geometry and temperature upon these relationships are reviewed. Based on this review, methods of reducing stiffness and damping data for shear and compression test elements to material properties (storage and loss moduli) and empirical geometric factors are developed and tested using previously generated experimental data. A prediction method which accounts for large amplitudes of deformation is developed on the assumption that their effect is to increase temperature through the elastomers, thereby modifying the local material properties. Various simple methods of predicting the radial stiffness of ring cartridge elements are developed and compared. Material properties were determined from the shear specimen tests as a function of frequency and temperature. Using these material properties, numerical predictions of stiffness and damping for cartridge and compression specimens were made and compared with corresponding measurements at different temperatures, with encouraging results

Optimising digital nature for wellbeing

The global burdens of negative psychological states such as stress, anxiety, and burnout represent a growing public health concern. As the incidence of these conditions has risen so too has awareness that natural environments might provide cognitive and affective benefits. Yet unrelenting urbanisation, unprecedented species extinction, and rampant ecological degradation are fostering a creeping extinction of experience, straining the links between people and planet. In an increasingly technologically mediated world, growing emphasis is being placed on how digital forms of nature could impact health. Understanding how simulated contact with the natural world might be optimised for positive wellbeing outcomes is vital if ‘virtual nature’ is to be used as a therapeutic tool. This thesis consists of three original studies – conducted with large samples and as part of national broadcast initiatives – that aimed to address this burgeoning need. We first investigated nuances in the way natural soundscapes are experienced. Through an award-winning collaboration with the BBC Natural History Unit, a novel podcast series and experiment generated responses from 7,596 participants. Results indicated how the composition of nature-based soundscapes can affect their restorative potential, demonstrated the crucial role that memories play in these relationships, and suggested that appraisals of restoration can exert an important mediating effect on pro-environmental behaviour. Next, a similar level of granularity was applied to landscape aesthetics. An online experiment probed how ephemeral features such as sunrise, sunsets, and storms can impact appraisals of virtual environments. Data from 2,509 people supported the familiar urban-nature dichotomy yet revealed substantial momentary and diurnal heterogeneity in measures of beauty and awe. Changes in these metrics also partially mediated participants’ willingness to pay to visit these locations in the ‘real world’. Partnering again with the BBC on a multi-platform broadcast initiative called Soundscapes for Wellbeing, our third experiment assessed how the visual and acoustic elements of a digital nature experience, including music, might influence viewer emotions. Analyses from 7,636 respondents suggested that whilst music could enhance high arousal feelings such as excitement, natural sounds were integral to eliciting restoration, calmness, awe, and nostalgia. Again, these data revealed a substantial moderating effect of memories, underlining the importance of lived experiences in determining outcomes. Taken together, these findings reveal important distinctions in the way natural soundscapes are perceived, demonstrate the potential for both ephemeral features and natural sounds to elicit the complex emotions of awe and nostalgia, and highlight the profound moderating effects of personal memories. Future work might focus on expanding understanding of how awe, nostalgia, and memories could represent a hitherto under-recognised depth to the therapeutic potential of encounters with nature in both virtual and real settings.Wellcome Trus

Development of procedures for calculating stiffness and damping of elastomers in engineering applications. Part 5: Elastomer performance limits and the design and test of an elastomer damper

Tests were performed on elastomer specimens of the material polybutadiene to determine the performance limitations imposed by strain, temperature, and frequency. Three specimens were tested: a shear specimen, a compression specimen, and a second compression specimen in which thermocouples were embedded in the elastomer buttons. Stiffness and damping were determined from all tests, and internal temperatures were recorded for the instrumented compression specimen. Measured results are presented together with comparisons between predictions of a thermo-viscoelastic analysis and the measured results. Dampers of polybutadiene and Viton were designed, built, and tested. Vibration measurements were made and sensitivity of vibration to change in unbalance was also determined. Values for log decrement were extracted from the synchronous response curves. Comparisons were made between measured sensitivity to unbalance and log decrement and predicted values for these quantities

The ergonomics of command and control

Since its inception, just after the Second World War, ergonomics research has paid special attention to the issues surrounding human control of systems. Command and Control environments continue to represent a challenging domain for Ergonomics research. We take a broad view of Command and Control research, to include C2 (Command and Control), C3 (Command, Control and Communication), and C4 (Command, Control, Communication and Computers) as well as human supervisory control paradigms. This special issue of ERGONOMICS aims to present state-of-the-art research into models of team performance, evaluation of novel interaction technologies, case studies, methodologies and theoretical review papers. We are pleased to present papers that detail research on these topics in domains as diverse as the emergency services (e.g., police, fire, and ambulance), civilian applications (e.g., air traffic control, rail networks, and nuclear power) and military applications (e.g., land, sea and air) of command and control. While the domains of application are very diverse, many of the challenges they face share interesting similarities

A social goals perspective on bullying in schools

Contrasting approaches to explaining the social-cognitive contributors to bullying in schools have stressed the importance of a child‘s social goals in determining whether he or she will bully. In spite of this, the social goals of bullies and victims have not been adequately investigated in empirical research. This thesis aimed to address this issue by investigating the social goals associated with bullying/victimisation, determining whether these goals were able to predict bullying/victimisation even after other social processing biases and theory of mind had been taken into account, and considering the influence social goals have on children‘s response to provocation. In a series of six studies, 583 children from Primary schools in the UK completed several measures aimed at assessing their engagement in behaviours related to bullying and being victimised, their social goals (both as general interpersonal goals and also specific to hypothetical social scenarios), and other social-cognitive factors (including theory of mind). Although the pattern of results across studies was not always uniform, there was a general trend for bullying in boys to be associated with situation-specific goals that protected their physical dominance within their peer group, while bullying in girls was better predicted by an overall concern for maintaining an image of popularity. Interestingly, victimisation in boys was predicted by an inappropriate concern for others‘ feelings in certain scenarios, while victimisation in girls was associated with a low level of concern for behaving prosocially. Importantly, these kinds of social goals remained predictive of bullying and victimisation even after controlling for variance accounted for by theory of mind and other social information processing biases. Finally, social goals were found to mediate the relationship between bullying/victimisation and aggressive/submissive response strategies. Findings are discussed in relation to the existing literature as well as to their potential impact on intervention strategies