Design and testing of the Minotaur advanced grid-stiffened fairing

A composite grid-stiffened structure concept was selected for the payload fairing of the Minotaur launch vehicle. Compared to sandwich structures, this concept has an advantage of smaller manufacturing costs and lighter weight. To reduce weight the skin pockets are allowed to buckle visibly up to about 0.5 cm peak displacement.

Various failure modes were examined for the composite grid-stiffened structure. The controlling criterion for this design was a joint failure in tension between the ribs and skin of the structure. The identification of this failure mechanism and the assessment of bounding strains required to control it required extensive test and analysis effort. Increasing skin thickness to control skin buckling resulted in reduced strains between the skin and ribs.

Following the identification of the relevant failure criteria, a final design for the fairing was generated. The resulting 6 m tall fairing was constructed of a tow-placed carbon fiber composite grid structure that was over-wrapped to create a laminated skin. Upon completion of curing and machining, the fairing was cut in half to create the classic “clam-shell” fairing. Static qualification testing demonstrated the structural integrity of the fairing, thereby proving the design and manufacturing process. Loads were applied incrementally in a static loading scenario. The applied load envelope exceeded worst-case dynamic flight conditions with an added safety factor of 25%. At peak load the fairing maintained structural integrity while remaining within the required displacement envelope for payload safety.

Data were collected during the test from a variety of sensors including traditional displacement transducers and strain gages. In addition, full field displacement was monitored at critically loaded fairing sections by means of digital photogrammetry. This paper summarizes the test results, presents the overall performance of the fairing under the test loads, correlates test response and analysis, and identifies lessons learned.

Work continues at the Air Force Research Laboratory (AFRL) and Boeing to identify means of further controlling tensile failure of the un-reinforced polymer bonded joint between the ribs and skin. Stiffening of skin adjacent to the joints and introduction of lightweight foam jackets at the interior of the fairing both show promise of delaying joint failure to higher loads.     

The influence of gas velocity, salt type and concentration on transition concentration for bubble coalescence inhibition and gas holdup

The influence of gas velocity (3.5, 10, and 18 mm/s), salt type (NaCl, NaF, NaBr, NaI and CsCl) and salt concentration (0.001-3 M) on bubble coalescence in a small bubble column were studied. The bubble coalescence was determined by the relative change in the measured light intensities passing through the salt solutions and clean deionised water. It was shown that the transition salt concentration for bubble coalescence inhibition (determined at 50% of bubble coalescence) of all investigated salts decreases with increasing superficial gas velocity. The difference in the transition concentration between NaCl, NaF, NaBr and CsCl does not significantly change with the gas velocity. However that difference between NaI and the other salts significantly decreases with increasing the gas velocity. The gas holdup significantly increases with NaCl, NaF, NaBr and CsCl concentrations but does not significantly change with NaI concentration. These new results imply that the transition salt concentration for bubble coalescence and gas holdup depend not only on the salt properties (i.e. the ion type and their combination) as previously reported, but also on the hydrodynamic conditions.     

Supportive Housing: Justifiable Paternalism?

Scholars have long draw on neoliberalism and paternalism as theoretical frameworks to argue that states have become less generous in providing welfare and housing resources. These theories similarly demonstrate that the resources that are provided are characterized by conditional exchanges, whereby welfare recipients and social housing tenants are required to comply with behavioural conditions. Theoretical critiques of state intervention influenced by neoliberalism and paternalism are broad, but they generally agree that conditional welfare approaches, including social housing, focus on changing individuals living in poverty themselves and not sufficiently changing policy, economic, social and institutional forces that underpin poverty. In light of these theories of state intervention, this article draws on an Australian qualitative study with tenants and service providers in supportive housing. The article shows that supportive housing is positioned as a significant intervention to not only house disadvantaged groups, but rather as an optimistic mechanism to directly improve disadvantaged people’s lives. The article argues that when coupled with long-term housing, a weak form of paternalist welfare for people who have experienced chronic homelessness can be justified.     

Overview of underground coal gasification operations at Chinchilla,Australia

Underground coal gasification (UCG) is a process which converts deep, un-mineable or difficult to mine coal resources into syngas which can then be converted into valuable end products such as electric power, liquid fuels, synthetic natural gas and chemicals. This paper provides a summary of the UCG operations conducted at the Chinchilla Demonstration Facility in Australia, focusing on gasifiers constructed using directional drilling. A number of the experiences and key lessons learned from operating multiple underground gasifiers over several years at the facility are described. Implications for the implementation in commercial projects using UCG are also discussed. Finally, the potential of UCG as a method for producing syngas from deep coal is discussed and some of the challenges and opportunities are summarized.     

Structural modifications in stretch-induced crystallization in PVDF films as measured by small-angle X-ray scattering

The nanostructure of stretched and nonstretched PVDF samples was studied by small-angle X-ray scattering (SAXS). The crystallinity of the samples was determined by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC), and crystalline phases by Fourier transform infrared spectroscopy (FTIR). The nanostructure can be described by a lamellar stacking of crystalline and amorphous layers, with a fairly well defined long period D and a diffuse-boundary in the interface between the crystalline and amorphous phases. The crystallinity of the stretched sample was found to be greater than that of the nonstretched sample. The long period D and the thicknesses of the crystalline lamellae T_c were found to be greater in the stretched sample than those in the nonstretched sample. The thickness of the diffuse-boundary was evaluated as being ∼ 1.4 nm in the nonstretched sample and 1.1 nm in the stretched sample. It was concluded that the growth of the thickness of the crystalline layer induced by the stretching process (stretch-induced crystallization) occurs partially at expense of the diffuse boundary and also by the coarsening of the structure with the stretching process, because of the diminution in the surface area to volume ratio observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modelling and optimization of a wellhead gas flowmeter using concentric pipes

A novel configuration of a landfill wellhead was analysed to measure the flow rate of gas extracted from sanitary landfills. The device provides access points for pressure measurement integral to flow rate computation similarly to orifice and Venturi meters, and has the advantage of eliminating the problem of water condensation often impairing the accuracy thereof. It is proved that the proposed configuration entails comparable computational complexity and negligible sensitivity to geometric parameters. Calibration for the new device was attained using a custom optimization procedure, operating on a quadri-dimensional parameter surface evincing discontinuity and non-smoothness.     

A Pilot Study of the VirtuSphere as a Virtual Reality Enhancement

This pilot study assessed the utility and acceptability of the VirtuSphere, a cutting edge navigation platform designed to enhance presence in virtual environments. The VirtuSphere includes a 12-ft hollow sphere within which the user stands, and it rolls within a wheeled platform, in any direction, according to the user's steps. The pilot was a within-subject crossover design comparing the VirtuSphere to standard game controller navigation. The comparison was based on locomotion in Virtual Iraq, a virtual world resembling Iraqi war zones. Participants were 10 active duty soldiers not suffering from posttraumatic stress disorder. Results indicated that there were negligible differences in sense of presence, simulator sickness, and satisfaction across the two navigation systems. Although the VirtuSphere may provide entertainment value, these results do not provide initial support for the use of the VirtuSphere to improve constructs thought to be important to behavioral health applications of virtual reality. Potential improvements to the design of the VirtuSphere are discussed.     

Dynamics of safety performance and culture: A group model building approach

The management of occupational health and safety (OHS) including safety culture interventions is comprised of complex problems that are often hard to scope and define. Due to the dynamic nature and complexity of OHS management, the concept of system dynamics (SD) is used to analyze accident prevention. In this paper, a system dynamics group model building (GMB) approach is used to create a causal loop diagram of the underlying factors influencing the OHS performance of a major drilling and mining contractor in Australia. While the organization has invested considerable resources into OHS their disabling injury frequency rate (DIFR) has not been decreasing. With this in mind, rich individualistic knowledge about the dynamics influencing the DIFR was acquired from experienced employees with operations, health and safety and training background using a GMB workshop. Findings derived from the workshop were used to develop a series of causal loop diagrams that includes a wide range of dynamics that can assist in better understanding the causal influences OHS performance. The causal loop diagram provides a tool for organizations to hypothesize the dynamics influencing effectiveness of OHS management, particularly the impact on DIFR. In addition the paper demonstrates that the SD GMB approach has significant potential in understanding and improving OHS management.