1,640 research outputs found
Active Flow Control at Low Reynolds Numbers by Periodic Airfoil Morphing
Get PDFThis paper investigates the application of a periodically deforming airfoil surface for the purpose of flow control at low Reynolds numbers. A physical model has been fabricated by bonding Macro Fiber Composite (MFC) actuators to the underside of a NACA 4415âs suction surface. The results presented build on work by Jones et al.1 First, the behavior of the surface when actuated at a range frequencies is investigated through a combination of photogrammetric and laser sensor measurements. Second, the aerodynamic performance of this novel flow control technique is presented. It is shown that when the actuation frequency âlocks-inâ to the surface motion significant improvements in performance are observed in a flight regime notorious for poor airfoil behavior
On orbit validation of solar sailing control laws with thin-film spacecraft
Get PDFMany innovative approaches to solar sail mission and trajectory design have been proposed over the years, but very few ever have the opportunity to be validated on orbit with real spacecraft. Thin- Film Spacecraft/Lander/Rovers (TF-SL Rs) are a new class of very low cost, low mass space vehicle which are ideal for inexpensively and quickly testing in flight new approaches to solar sailing. This paper describes using TF- SLR based micro solar sails to implement a generic solar sail test bed on orbit. TF -SLRs are high area- to-mass ratio (A/m) spacecraft developed for very low cost consumer and scientific deep space missions. Typically based on a 5 ÎŒm or thinner metalised substrate, they include an integrated avionics and payload system -on-chip (SoC) die bonded to the substrate with passive components and solar cells printed or deposited by Metal Organic Chemical Vapour Deposition (MOCVD). The avionics include UHF/S- band transceivers, processors, storage, sensors and attitude control provided by integrated magnetorquers and reflectivity control devices. Resulting spacecraft have a typical thickness of less than 50 ÎŒm, are 80 mm in diameter, and have a mass of less than 100 mg resulting in sail loads of less than 20 g/m 2 . TF -SLRs are currently designed for direct dispensing in swarms from free flying 0.5U Interplanetary CubeSats or dispensers attached to launch vehicles. Larger 160 mm, 320 mm and 640 mm diameter TF -SLRs utilizing a CubeSat compatible TWIST deployment mechanism that maintains the high A/m ratio are also under development. We are developing a mission to demonstrate the utility of these devices as a test bed for experimenting with a variety of mission designs and control laws. Batches of up to one hundred TF- SLRs will be released on earth escape trajectories, with each batch executing a heterogeneous or homogenous mixture of control laws and experiments. Up to four releases at different points in orbit are currently envisaged with experiments currently being studied in MATLAB and GMA T including managing the rate of separation of individual spacecraft, station keeping and single deployment/substantially divergent trajectory development. It is also hoped to be able to demonstrate uploading new experiment designs while in orbit and to make this capability available to researchers around the world. A suitable earth escape mission is currently being sought and it is hoped the test bed could be on orbit in 2017/18
Topological optimization of compliant adaptive wing structure
Get PDFLoad-path-based topology optimization is used to synthesize a compliant adaptive aircraft wing leading edge, which deforms in a prescribed way when subject to a single point internal actuation. The load-path-based optimization method requires the specification of a parent lattice. Increasing the complexity of this lattice means the number of parameters required for a complete representation of the structure in the topology optimization becomes prohibitive, although it is desirable to enable a full exploration of the design space. A new method based on graph theory and network analysis is proposed, which enables a substantial reduction in the required number of parameters to represent the parent lattice. The results from this load-path-based approach are compared with those obtained from the better-known density-based topology optimization method
Experimental FSI study of adaptive shock control bumps
Get PDFThe shock stabilisation and wave drag reduction potential of a two-dimensional adaptive shock control bump has been studied in the Imperial College supersonic wind tunnel. The bump was modelled as a flexible aluminium alloy plate deformed through spanwise actuation, and several bump heights were tested beneath a Mach 1.4 transonic shock wave. Schlieren images and static pressure readings along the flexible plate allowed the study of the λλ-shock structure generated by the bifurcation of the normal shock for a range of shock positions. All bumps tested were found to increase shock stability, but wave drag reduction was only observed for shocks close to the leading edge of the flexible plate. Positive deformations of the flexible plate for downstream shocks are believed to reduce supersonic flow reacceleration, and hence the strength of the rear leg of the λλ-shock and wave drag, in comparison to a solid bump with the same shape. The position of the rear leg of the λλ-shock was found to exhibit a bistable behaviour, and this is hypothesised to be caused by a complex coupling of aerodynamic and structural instabilities
Wind Tunnel Experiments with Flexible Plates in Transonic Flows
No full textThe evolution of adaptive shock control bump (SCB) design has seen the system flexibility increase to a point where the aerodynamic loading can affect the deformation of the plate. By studying the effects of a flexible plate subject to transonic flow the fluid structure interaction can be investigated. In this study an array of thin plates (0.4 and 0.6 mm) with different aspect ratios (1 and 1.33) are exposed to a Mach 1.4 normal shockwave. PIV is used in combination with Schlieren imaging to provide a detailed view of the flow curvature surrounding the plate as well as the global shock structure. A technique that extracts the plate deformation from the PIV images is also presented which provides fluid and structural information for each test. The relationship between plate and flow angle is discussed as well as the effect of plate stiffness and free stream influence of each plate configuration
Rigid-foldable parabolic deployable reflector concept based on the origami flasher pattern
Get PDFThis paper presents a novel deployable reflector concept based on the origami flasher pattern. The proposed folding architecture achieves rigid foldability for flasher patterns applied to doubly curved surfaces, allowing parabolic reflectors to be divided into a number of rigid panels for efficient stowage. Such an architecture provides an intermediate solution between current rigid-surface and flexible-surface reflectors, offering both surface precision and stowage compactness. The proposed patterns have a positive-finite degree of mobility, and so reliable and deterministic deployment is realized through suitable actuation. A Bayesian optimization approach is used in conjunction with kinematics and collision models in order to find optimal stowage patterns that accommodate finite thickness panels and supporting structures. For the generated optimal patterns, panel split line geometries are designed analytically to eliminate gaps while avoiding collision at panel edges during folding
âIt's like the bad guy in a movie who just doesn't dieâ : a qualitative exploration of young people's adaptation to eczema and implications for selfâcare
Get PDFBackground
Eczema is a common childhood inflammatory skin condition, affecting more than one in five children. A popular perception is that children âoutgrow eczemaâ, although epidemiological studies have shown that, for many, eczema follows a lifelong episodic course.
Objectives
To explore the perceptions of young people about the nature of their eczema and how these perceptions relate to their selfâcare and adapting to living with eczema.
Methods
This is a secondary inductive thematic analysis of interviews conducted for Healthtalk.org. In total 23 interviews with young people with eczema were included. Of the 23 participants, 17 were female and six male, ranging from 17 to 25 years old.
Results
Participants generally experienced eczema as an episodic longâterm condition and reported a mismatch between information received about eczema and their experiences. The experience of eczema as long term and episodic had implications for selfâcare, challenging the process of identifying triggers of eczema flareâups and evaluating the success of treatment regimens. Participantsâ experiences of eczema over time also had implications for adaptation and finding a balance between accepting eczema as long term and hoping it would go away. This linked to a gradual shift in treatment expectations from âcureâ to âcontrolâ of eczema.
Conclusions
For young people who continue to experience eczema beyond childhood, a greater focus on selfâcare for a longâterm condition may be helpful. Greater awareness of the impact of early messages around âgrowing out ofâ eczema and provision of highâquality information may help patients to manage expectations and support adaptation to treatment regimens
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