High-solid-content hydroxyapatite slurry for the production of bone substitute scaffolds

Key to various bone substitute scaffold production techniques is the development of free-flowing ceramic slurry with optimum theological properties. The aim is to achieve a colloidal suspension with as high a solid content as possible while maintaining a low viscosity which easily penetrates the pores of relevant sacrificial templates. The following investigation describes the optimization of a hydroxyapatite slip and demonstrates its potential application in scaffold production. Using predominantly spherical particles of hydroxyapatite of between 0.82 mu m and 16.2 mu m, coupled with a 2 wt % addition of the anionic polyelectrolyte, ammonium polyacrylate, an 80 wt % (55.9 vol %) hydroxyapatite solid loaded slip with a viscosity of approximately 126 mPa s has been developed. Its ability to infiltrate and replicate porous preforms has been shown using polyurethane foam. The enhanced particle packing achieved has allowed for the production of scaffolds with highly dense and uniform grain structures. The results represent a significant improvement in current slurry production techniques and can be utilized to develop high-density ceramic bone substitute scaffolds.

The control of wave energy converters using active bipolar damping

A novel method for controlling wave energy converters using active bipolar damping is described and compared with current control methods. The performance of active bipolar damping is modelled numerically for two distinct types of wave energy converter and it is found that in both cases the power capture can be significantly increased relative to optimal linear damping. It is shown that this is because active bipolar damping has the potential for providing a quasi-spring or quasi-inertia, which improves the wave energy converter's tuning and amplitude of motion, resulting in the increase in power capture observed. The practical implementation of active bipolar damping is also discussed. It is noted that active bipolar damping does not require a reactive energy store and thereby reduces the cost and eliminates losses due to the cycling of reactive energy. It is also noted that active bipolar damping could be implemented using a single constant pressure double-acting hydraulic cylinder and so potentially represents a simple, efficient, robust and economic solution to the control of wave energy converters.

Fatigue performance of aircraft panels with novel skin buckling containment features

To increase structural efficiency of stiffened panels in an aircraft, it is plausible to introduce skin buckling containment features to increase the local skin stability and thus static strength performance. Introducing buckling containment features may also significantly influence the fatigue crack growth performance of the stiffened panel. This study focuses on the experimental demonstration of panel durability with skin bay buckling containment features. Through a series of fatigue crack growth tests on integrally machined aluminium alloy stiffened panels, the potential to simultaneously improve static strength performance and crack propagation behaviour is demonstrated. The introduction of prismatic buckling containment features which have yielded significant static strength performance gains have herein demonstrated potential fatigue life gains of up to + 63 per cent.

Aerodynamic performance of a bypass engine with fan nozzle exit area change by warped chevrons

Variation of the bypass nozzle exit area enables optimization of the turbofan engine operating cycle over a wider range of operational conditions resulting in improved thrust and/or fuel consumption. Two mechanisms for varying the nozzle area have been investigated. The first uses an array of chevrons which when closed, form a full body of revolution and when warped/curved, increase the exit area while forming a serrated trailing edge. The second technique incorporates an axially translating section of the nacelle shroud and uses the change in the nozzle boat-tail radial location with the axial location as a means to vary the nozzle exit area. To analyse the effects on a typical rotor/stator stage, computational fluid dynamics simulations of the NASA Rotor 67, Stator 67A stage integrated into a custom-built nacelle were performed. Nozzles with 8, 12, and 16 chevrons were simulated to evaluate the impact of the variation in geometry upon the nacelle wake and local forces. Gross thrust of the nacelle and the turbulent kinetic energy (TKE) variation through the wake is compared. The chevron nozzle attains a nearly 2 per cent maximum thrust improvement over the translating nozzle technique. The chevron nozzle also has significantly lower (nearly 8 per cent) peak TKE levels in the jet plume.

A numerical investigation of the flow structures and losses for turbulent flow in 90 degrees elbow bends

Computational fluid dynamic modelling was carried out on a series of pipe bends having R/r values of 1.3, 5, and 20, with the purpose of determining the accuracy of numerical models in predicting pressure loss data from which to inform one-dimensional loss models. Four separate turbulence models were studied: the standard k-epsilon model, realizable k-epsilon model, k-omega model, and a Reynolds stress model (RSM). The results are presented for each bend in the form of upstream and downstream pressure profiles, pressure distributions along the inner and outer walls, detailed pressure and velocity fields as well as overall loss values. In each case, measured data were presented to evaluate the predictive ability of each model. The RSM was found to perform the best, producing accurate pressure loss data for bends with R/r values of 5 and 20. For the tightest bend with an R/r value of 1.3, however, predictions were significantly worse due to the presence of flow separation, stronger pressure gradients, and high streamline curvature.

Alternative method to evaluate discharge coefficients. Part 2: case study

The purpose of this article is to apply an alternative method whereby discharge coefficients can be estimated for the flow through a poppet valve at various lifts. Presented is the development of an operational quasi-steady flow rig. An engine cylinder head poppet valve was used as the case study. The requirement to directly measure mass flowrates using a standard conventional steady flow apparatus has been eliminated. Transient mass flowrates, pressures and temperatures of air during an inflow test for a poppet valve at various lifts were measured. Mass flowrates were also calculated from measured cylinder gas pressures and corrected for heat transfer. Using both methods to determine the mass flowrates, isentropic discharge coefficients were calculated and shown to compare within +/- 4.0 per cent of steady flow data. A computational fluid dynamics (CFD) validation of the quasi-steady flow rig is also presented.

Thermoforming carbon fibre-reinforced thermoplastic composites

The use of carbon fibre composites is growing in many sectors but their use remains stronger in very high value industries such as aerospace where the demands of the application more easily justify the high energy input needed and the corresponding costs incurred. This energy and cost input is returned through gains over the whole life of the product, with for example, longer maintenance intervals for an aircraft and lower fuel burn. Thermoplastic composites however have a different energy and cost profile compared to traditional thermosets with notable differences in recyclability, but this profile is not well quantified or documented. This study considers the key process control parameters and identifies an optimal window for processing, along with the effect this has on the final characteristics of the manufactured parts. Interactions between parameters and corresponding sensitivities are extracted from the results.