61 results found
Murphy R, Imediegwu C, Hewson R, et al., 2021, Multiscale structural optimisation with concurrent coupling between scales, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, ISSN: 1615-147X
A robust three-dimensional multiscale structural optimization framework with concurrent coupling between scales is presented. Concurrent coupling ensures that only the microscale data required to evaluate the macroscale model during each iteration of optimization is collected and results in considerable computational savings. This represents the principal novelty of this framework and permits a previously intractable number of design variables to be used in the parametrization of the microscale geometry, which in turn enables accessibility to a greater range of extremal point properties during optimization. Additionally, the microscale data collected during optimization is stored in a re-usable database, further reducing the computational expense of optimization. Application of this methodology enables structures with precise functionally-graded mechanical properties over two-scales to be derived, which satisfy one or multiple functional objectives. Two classical compliance minimization problems are solved within this paper and benchmarked against a Solid Isotropic Material with Penalization (SIMP) based topology optimization. Only a small fraction of the microstructure database is required to derive the optimized multiscale solutions, which demonstrates a significant reduction in the computational expense of optimization in comparison to contemporary sequential frameworks. In addition, both cases demonstrate a significant reduction in the compliance functional in comparison to the equivalent SIMP based optimizations.
Nightingale M, Hewson R, Santer M, 2020, Multiscale optimisation of resonant frequencies for lattice based additive manufactured structures, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, ISSN: 1615-147X
This paper introduces a novel methodology for the optimisation of resonant frequencies in three-dimensional lattice structures. The method uses a multiscale approach in which the homogenised material properties of the lattice unit cell are de fined by the spatially varying lattice parameters. Material properties derived from precomputed simulations of the small scale lattice are projected onto response surfaces, thereby describing the large scale metamaterial properties as polynomialfunctions of the small scale parameters. Resonant frequencies and mode shapes are obtained through the eigenvalue analysis of the large scale -finite element model which provides the basis for deriving the frequency sensitivities. Frequency tailoring is achieved by imposing constraints on the resonant frequency for a compliance minimisation optimisation. Asorting method based on the modal assurance criteria allows for specific mode shapes to be optimised whilst simultaneously reducing the impact of localised modes on the optimisation.Three cases of frequency constraints are investigated and compared to an unconstrained optimisation to demonstrate the algorithms applicability. The results show that the optimisation is capable of handling strict frequency constraints and with the use of the modal tracking can even alter the original ordering of the resonant mode shapes. Frequency tailoring allows for improved functionality of compliance minimised aerospace components by avoiding resonant frequencies and hence dynamic stresses.
Soltani Z, Santer M, 2020, The determination and enhancement of compliant modes for high-amplitude actuation in lattices, International Journal of Solids and Structures, Vol: 206, Pages: 124-136, ISSN: 0020-7683
This paper details the nonlinear design of adaptive lattices by determination and enhancement of compliant modes and optimizing the designed structure for delivering high amplitude actuation. The particular focus is the kagome lattice geometry—a pattern with some unique and useful actuation properties. Developing a novel design tool, the stiffness matrix of the beam assembly is calculated using a developed second-order geometrically nonlinear beam finite element formulation allowing large rotations. Based on this formulation in conjunction with singular value decomposition of the stiffness matrix, the modal optimization technique reduces the continuous structure with many degrees of freedom to a small number of low energy modes, which form the basis of designing the adaptive structure. For delivering high-amplitude actuation, the designed structure needs to be re-optimized due to changes in the nonlinear stiffness matrix under large deformation. This is performed via Bayesian optimization and by removing some internal members of the lattice. The integrity and feasibility of the optimum design is guaranteed via defining some constraints on removed members.
Thillaithevan D, Bruce P, Santer M, 2020, Stress constrained optimization using graded lattice microstructures, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, ISSN: 1615-147X
In this work we propose a novel method for predicting stress within a multiscale lattice optimization framework. On the microscale, a scalable stress is captured for each microstructure within a large, full factorial design of experiments. A multivariate polynomial response surface model is used to represent the microstructure material properties. Unlike the traditional solid isotropic material with a penalisation based stress approach of penalising stress values or using the homogenized stress, we propose the use of real microscale stress components with macroscale strains through linear superposition. To examine the accuracy of the multiscale stress method, full-scale finite element simulations with non-periodic boundary conditions were performed. Using a range of microstructure gradings, it was determined that 6 layers of microstructures were required to achieve periodicity within the full-scale model. The effectiveness of the multiscale stress model was then examined. Using various graded structures and two load cases, our methodology was shown to replicate the von Mises stress in the centre of the unit lattice cells to within 10\% in the majority of the test cases. Finally, three stress-constrained optimization problems were solved to demonstrate the effectiveness of the method. Two stress constrained weight minimization problems were demonstrated, alongside a stress constrained target deformation problem. In all cases, the optimizer was able to sufficiently reduce the objective while respecting the imposed stress constraint.
Gramola M, Bruce P, Santer M, 2020, Off-design performance of 2D adaptive shock control bumps, Journal of Fluids and Structures, Vol: 93, ISSN: 0889-9746
Adaptive shock control bumps can exploit the on-design drag-reducing potential of 2D bumps, while mitigating their off-design performance deterioration through geometric modifications. In this study, experiments and simulations have been employed to investigate the wave-drag reducing potential of (actuated and unconstrained) 2D adaptive shock control bumps over a wide range of shock positions. Experiments were carried out in the Imperial College supersonic wind tunnel, modelling the adaptive bump as a flexible surface placed beneath a Mach 1.4 shock wave. 2D RANS CFD simulations of the flow in a parallel channel with a solid bump complement experiments. Wave drag was demonstrated to be proportional to the ratio of inlet to exit stagnation pressure in a blow-down wind tunnel for a given shock position. The shock exhibits a hysteretic behaviour when travelling in the wind tunnel working section, governed by the wave drag reducing potential of the bump. The actuated adaptive bump tested reduces wave drag over a wider operational envelope than solid bumps as experiments revealed the presence of three preferred structural configurations, which lead to a significantly enlarged hysteresis region. Finally, tests on unconstrained bumps were shown to increase wave drag, both on- and off-design, due to the unfavourable bump shapes that result from (only) passive actuation, suggesting that some constraints are required to achieve desirable surface deformations.
Murphy R, Imediegwu C, Hewson R, et al., 2020, Multiscale concurrent multi-objective structural optimization of a goose neck hinge
© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. A robust multiscale concurrent optimization framework, which enables the precise functional-grading of mechanical properties within structures over two-scales, is presented within this paper and applied to a practical aerospace application — the mass minimization of a Goose Neck Hinge. The novelty of this framework lies in the concurrent nature of the response surface which enables the efficient calculation of small-scale mechanical properties during large-scale optimization. The efficacy of this approach permits a large number of design variables to be used in the parameterization of the small-scale without incurring a significant computational expense. The mass minimization of the Goose Neck Hinge constitutes a multi-objective optimization problem, constrained by a single maximum displacement constraint. Optimization of the Goose Neck Hinge was undertaken using both the framework presented within this paper and a density based topology optimization, to understand the relative performance of the multiscale framework to an industry standard method for structural optimization. The optimized multiscale geometry was able to satisfy the maximum displacement constraint using 20% less material than the density based topology optimization. This indicates that this framework has the potential to deliver a new generation of optimized aerospace structures.
Garland MGC, Santer MS, Morrison JF, 2019, Control of cellular separation using adaptive surfaces, Journal of Fluids and Structures, Vol: 91, ISSN: 0889-9746
We report results from an experimental investigation of the three-dimensional separation produced by a high-lift aerofoil at moderate incidence, with constant section, where the separation is controlled by the implementation of an adaptive surface. Mean and time-resolved measurements are made using a NASA GA(W)-1 aerofoil with AR=6 at Re c =3.5×10 5 . Surface oil visualisation and stereo Particle Image Velocimetry (PIV) are used to explore the flow field. The mean topology of the flow identifies characteristic spanwise periodic behaviour, “stall cells” along the surface of the model. Analysis of the time-dependent surface pressure shows two distinct frequencies within the flow field. The higher frequency appears at a Strouhal number, St≈0.2, representative of vortex shedding, and the typical von Kármán vortex street. The lower frequency appears at St≈0.02, observed as a global fluctuation in stall-cell extent. This lower frequency is apparent in many separated flows, but in the present context, appears to have received only little attention. It correlates with widely observed low-frequency unsteadiness in the wing loading around stall. While this mode is analogous to that observed in other types of separation, here the streamwise extent of the separation varies because the flow is separating from a curved surface rather than from a sharp edge; the width of the separated region also varies. We show that fully-reversible point actuations of an actuated surface with auxetic structure, introduced immediately upstream of the saddle point at the leading edge of the stall cell, reduce the extent of the separated region.
Imediegwu C, Murphy R, Hewson R, et al., 2019, Multi-scale structural optimization towards three-dimensional printable structures, Structural and Multidisciplinary Optimization, Vol: 60, Pages: 513-525, ISSN: 1615-147X
This paper develops a robust framework for the multiscale design of three-dimensional lattices with macroscopically tailored structural characteristics. The work exploits the high process flexibility and precision of additive manufacturing to the physical realization of complex microstructure of metamaterials by developing and implementing a multiscale approach. Structures derived from such metamaterials exhibit properties which differ from that of the constituent base material. A periodic microscale model is developed whose geometric parameterization enables smoothly changing properties and for which the connectivity of neighboring microstructures in the large-scale domain is guaranteed by slowly changing large-scale descriptions of the lattice parameters. A lattice-based functional grading of material is derived using the finite element method with sensitivities derived by the adjoint method. The novelty of the work lies in the use of multiple geometry-based small-scale design parameters for optimization problems in three-dimensional real space. The approach is demonstrated by solving a classical compliance minimization problem. The results show improved optimality compared to commonly implemented structural optimization algorithms.
Peacocke L, Bruce P, Santer M, 2019, Coupled aerostructural modelling of deployable aerodecelerators for Mars entry, Journal of Spacecraft and Rockets, Vol: 56, Pages: 1221-1230, ISSN: 0022-4650
Analysis of deployable aero-decelerators has been performed using a developed 6 degree-of-freedom entry trajectory simulator coupled with a structural model of the deployable structural members, or ribs, to investigate the effect of aero-decelerator flexibility on the trajectory and configuration design. The Modified Newtonian method is used in the entry trajectory simulator, and the deployable ribs are modelled as Euler-Bernoulli beams. It is shown that, although flexibility is beneficial in reducing mass and volume of the deployed ribs, an increase in peak heat flux will result. However, if mass savings from flexible ribs can be reallocated towards increasing the diameter of the entry vehicle, significant benefits can be gained.
Gramola M, Bruce PJK, Santer M, 2019, Experimental and numerical study of 2D adaptive shock control bumps, 3AF International Conference
Gramola M, Bruce PJ, Santer MJ, 2019, FSI study of 2D adaptive shock control bumps, AIAA Scitech 2019 Forum, Publisher: American Institute of Aeronautics and Astronautics
Murphy RD, Imediegwu C, Hewson R, et al., 2019, Multiscale concurrent optimization towards additively manufactured structures, AIAA Scitech 2019 Forum, Publisher: American Institute of Aeronautics and Astronautics
This work establishes a robust concurrent multiscale optimization framework which facilitates the precise functional-grading of mechanical properties within structures, over two scales.The novelty lies in the concurrent nature of the response surface which connects the small-scalegeometry to the large-scale domain. A concurrent implementation enables an efficient application of computational resources, such that a large number of design variables can be usedwithout a significant computational penalty. This framework also takes advantage of the process flexibility and precision of additive manufacturing techniques to ensure that all optimizedstructures are manufacturable and suitable for an aerospace based application. A complianceminimization case is compared against a standard topology optimization algorithm, resultingin superior functional values and demonstrates the efficacy of the presented approach. A further application of this framework is highlighted through a target deformation case, where acomplex deformation field is obtained through simple loading conditions. Results from both ofthe example problems indicate that this framework has potential within the field of adaptivestructures, to inspire a new generation of multifunctional designs.
Gramola M, Bruce PJK, Santer M, 2019, Photogrammetry for accurate model deformation measurement in a supersonic wind tunnel, Experiments in Fluids, Vol: 60, ISSN: 0723-4864
The interest in adaptive devices for high-speed applications leads to the need for an accurate and reliable technique to obtain model deformation measurements during experiments. Point-tracking photogrammetry has been applied to supersonic wind tunnel testing, using four Phantom high-speed cameras placed on either side of the working section, where coded targets were applied to the surface of interest. Calibration experiments on a solid plate beneath a =1.4 normal shock and a =2 oblique shock allowed the quantification of the sources of optical distortion, namely the wind tunnel glass windows and aerodynamic effects (the lower pressure in the working section and the interaction between shock waves and the boundary layer). A correction matrix was applied to account for the optical distortion due to the glass, and the root-mean-square error due to aerodynamic effects (<0.03 mm) is believed to be negligible for applications with significant displacements (of the order of 1 mm). The application of photogrammetry to a flexible shock control bump has shown that the bump shape can be detected accurately, while disclosing some complex 3D effects that could not have been revealed by spanwise-averaged techniques such as schlieren photography.
Gramola M, Bruce P, Santer M, 2018, Experimental FSI study of adaptive shock control bumps, Journal of Fluids and Structures, Vol: 81, Pages: 361-377, ISSN: 0889-9746
The 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.
Imediegwu C, Murphy R, Hewson RW, et al., 2018, Multiscale structural and thermal optimization towards 3D printable structures, The 9th International Conference on Computational Methods
Bird J, Santer M, Morrison J, 2018, Experimental control of turbulent boundary layers with in-plane travelling waves, Flow, Turbulence and Combustion, Vol: 100, Pages: 1015-1035, ISSN: 1386-6184
The experimental control of turbulent boundary layers using stream-wise travelling waves of spanwise wall velocity, produced using a novel activesurface, is outlined in this paper. The innovative surface comprises a pneu-matically actuated compliant structure based on the kagome lattice geometry,supporting a pre-tensioned membrane skin. Careful design of the structureenables waves of variable length and speed to be produced in the flat surfacein a robust and repeatable way, at frequencies and amplitudes known to havea favourable influence on the boundary layer. Two surfaces were developed,a preliminary module extending 152 mm in the streamwise direction, and alonger one with a fetch of 2.9 m so that the boundary layer can adjust to thenew surface condition imposed by the forcing. With a shorter, 1.5 m portionof the surface actuated, generating an upstream-travelling wave, a drag re-duction of 21.5% was recorded in the boundary layer withReτ= 1125. Atthe same flow conditions, a downstream-travelling produced a much smallerdrag reduction of 2.6%, agreeing with the observed trends in current simula-tions. The drag reduction was determined with constant temperature hot-wiremeasurements of the mean velocity gradient in the viscous sublayer, while si-multaneous laser Doppler vibrometer measurements of the surface recorded thewall motion. Despite the mechanics of the dynamic surface resulting in someout-of-plane motion (which is small in comparison to the in-plane streamwisemovement), the positive drag reduction results are encouraging for future in-vestigations at higher Reynolds numbers.
Imediegwu C, Murphy R, Hewson RW, et al., 2018, The design of a lattice-based periodic microstructure model towards 3D printable optimized structures, 10th European Solid Mechanics Conference
Bird J, Santer M, Morrison J, 2018, Compliant kagome lattice structures for generating in-plane waveforms, International Journal of Solids and Structures, Vol: 141-142, Pages: 86-101, ISSN: 0020-7683
This paper details the design, manufacture and testing of an adaptive structure based on the kagome lattice geometry – a pattern with well documented interesting structural characteristics. The structure is used to produce in-plane travelling waves of variable length and speed in a flat surface. The geometry and dimensions, as well as the location and compliance of boundary conditions, were optimized numerically, and a pneumatically-actuated working demonstrator was manufactured. Static and dynamic photogrammetric and force measurements were taken. The structure was found to be capable of producing dynamic planar waveforms of variable wavelength with large strains. The lattice structure was then surfaced with a pre-tensioned membrane skin allowing these waveforms to be produced over a continuous plane.
Jinks E, Bruce P, Santer M, 2018, Optimisation of adaptive shock control bumps with structural constraints, Aerospace Science and Technology, Vol: 77, Pages: 332-343, ISSN: 1270-9638
This paper presents the results from a study to design an optimal adaptiveshock control bump for a transonic aerofoil. An optimisation frameworkcomprising aerodynamic and structural computational tools has been used toassess the performance of candidate adaptive bump geometries based on a novelsurface-pressure-based performance metric. The geometry of the optimal resultantdesign is a unique feature of its adaptivity; being strongly inuencedby the (passive) aerodynamic pressure forces on the exible surface as well asthe (active) displacement constraints. This optimal geometry bifurcates theshock-wave and carefully manages the recovering post-shock ow to maximisepressure-smearing in the shock-region with only a small penalty in L=D for theaerofoil. Short adaptive bumps (with small imposed displacements) generallyperform better than taller ones, and maintain their performance advantage fora wide range of bump positions, suggesting good robustness to variations inshock position, which are an inevitable feature of a real-world ight application.Such devices may o er advantages over conventional ( xed geometry) shockcontrol bumps, where optimal performance is achieved with taller devices, atthe expense of poor robustness to variations in shock position.Keywords: Shock Control Bumps; Aeroelastic Optimisation
Jones G, Santer M, Debiasi M, et al., 2017, Control of flow separation around an airfoil at low Reynolds numbers using periodic surface morphing, Journal of Fluids and Structures, Vol: 76, Pages: 536-557, ISSN: 0889-9746
The paper investigates experimentally the low Reynolds number flow () around a model that approximates a NACA 4415 airfoil and the control of separation using periodic surface motion. Actuation is implemented by bonding two Macro Fiber Composite patches to the underside of the suction surface. Time-resolved measurements reveal that the peak-to-peak displacement of the surface motion is a function of both the amplitude and frequency of the input voltage signal but the addition of aerodynamic forces does not cause significant changes in the surface behavior. The vibration mode is uniform in the spanwise direction for frequencies below 80 Hz; above this frequency, a secondary vibration mode is observed. The flow around the unactuated airfoil exhibits a large recirculation region as a result of laminar separation without reattachment and consequently produces relatively high drag and low lift forces. Various actuation frequencies were examined. When actuated at , the spectra in the vicinity of the trailing edge and near-wake were found to be dominated by the actuation frequency. Sharp peaks appear in the spectra suggesting the production of Large Coherent Structures at this frequency. The increased momentum entrainment associated with these enabled a significant suppression of the separated region. The result was a simultaneous increase in and decrease in and therefore a large increase in the ratio. In addition, a delay in the onset of stall results in a significant increase in the maximum achievable lift.
Papadakis G, Santer M, Jones G, 2017, Control of low Reynolds number flow around an airfoil using periodic surface morphing: a numerical study, Journal of Fluids and Structures, Vol: 76, Pages: 95-115, ISSN: 0889-9746
The principal aim of this paper is to use Direct Numerical Simulations (DNS) to explain the mechanisms that allow periodic surface morphing to improve the aerodynamic performance of an airfoil. The work focuses on a NACA-4415 airfoil at Reynolds number Rec=5×104 and 0° angle of attack. At these flow conditions, the boundary layer separates at x∕c=0.42, remains laminar until x∕c≈0.8, and then transitions to turbulence. Vortices are formed in the separating shear layer at a characteristic Kelvin–Helmholtz frequency of Sts=4.9, which compares well with corresponding experiments. These are then shed into the wake. Turbulent reattachment does not occur because the region of high turbulent kinetic energy (and therefore mixing) is located too far downstream and too far away from the airfoil surface to influence the near-wall flow. The effect of three actuation frequencies is examined by performing the simulations on a computational domain that deforms periodically. It is found that by amplifying the Kelvin–Helmholtz instability mechanism, Large Spanwise Coherent structures are forced to form and retain their coherence for a large part of the actuation cycle. Following their formation, these structures entrain high momentum fluid into the near-wall flow, leading to almost complete elimination of the recirculation zone. The instantaneous and phase averaged characteristics of these structures are analyzed and the vortex coherence is related to the phase of actuation. In order to further clarify the process of reduction in the size of recirculation zone, simulations start from the fully-developed uncontrolled flow and continue for 25 actuation cycles. The results indicate that the modification of airfoil characteristics is a gradual process. As the number of cycles increases and the coherent vortices are repeatedly formed and propagate downstream, they entrain momentum, thereby modifying the near wall region. During this transient period, the separa
Garland M, Santer M, morrison J, 2017, Optimal Aero-Structural Design of an Adaptive Surface for Boundary Layer Motivation Using an Auxetic Lattice Skin, Journal of Intelligent Material Systems and Structures, Vol: 28, Pages: 2414-2427, ISSN: 1530-8138
The aero-structural design of an adaptive vortex generator for repeatable, elastic, deployment and retraction from anaerodynamically clean surface is presented. A multidisciplinary objective function, containing geometrically nonlinear nite element analysis and large eddy simulation, is used to derive the optimal adaptive geometry for increasing themomentum of the near wall uid. It is found that the rapid increase of in-plane membrane stress with de ection is asigni cant limitation on achievable deformation of a continuous skin with uniform section. Use of a 2D auxetic latticestructure in place of the continuous skin allows signi cantly larger deformations and thus a signi cant improvement inperformance. The optimal deformed geometry is replicated statically and the e ect on the boundary layer is validatedin a wind tunnel experiment. The lattice structure is then manufactured and actuated. The deformed geometry isshown to compare well with the FEA predictions. The surface is re-examined post actuation and shown to return tothe initial position, demonstrating the deformation is elastic and hence repeatable.
Johnson M, McCann J, Santer M, et al., 2017, On orbit validation of solar sailing control laws with thin-film spacecraft, The Fourth International Symposium on Solar Sailing, Publisher: Japan Space Forum
Many 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-SLRs) 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 μm 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 μm, are 80 mm in diameter, and have a mass of less than 100 mg resulting in sail loads of less than 20 g/m2. 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
Bird J, Santer M, morrison J, 2016, The determination and enhancement of compliant modes for actuation in structural assemblies, International Journal of Solids and Structures, Vol: 106-107, Pages: 264-273, ISSN: 0020-7683
Linear algebra methods for determining modes of kinematic and static indeter-minacy in jointed frames are extended to reveal modes of compliance in oth-erwise rigid assemblies. These modes are extracted from a structural model,based on nite elements, via a singular value decomposition and yield the waysin which a structure can be most easily deformed. This modal approach alsoallows for the formulation of a reduced-order structural model, whereby relevantmodes are selected and used as the basis for the optimisation of a complaintstructure. The method detailed is shown to be a useful design tool, demon-strated by its application to a structure based on the Kagome lattice geometry.For certain frameworks, rst order e ects produce tightening under actuation.As a result, a scheme to adjust the modes to take nonlinear e ects into accountis also given.
Jinks E, Santer M, bruce P, 2016, Aero-Structural Design Optimization of Adaptive Shock Control Bumps, 54th AIAA Aerospace Sciences Meeting, Publisher: American Institute of Aeronautics and Astronautics
Shock control bumps (SCB) are a transonic flow control device that aim to reduce theoverall drag due to a normal shock on a typical passenger jet at cruise. The concept of adaptiveSCB which can be deployed for best use are investigated through an aero-structuraldesign tool that produces optimal geometries. The optimizer uses a surface based performancemetric to highlight the importance of the flow quality around the SCB as wellas including a structural element that is required to provide the necessary flexibility todeform. The performance metric produces the target pressure distribution and successfullysmears the shock. It is found that the structural constraint does not inhibit bumpheight and global airfoil performance is not significantly a↵ected, L/D varies < 0.6%. Theaerodynamic pressure loading can be utilised to produce a new family of SCB geometriesthat are unachievable with mechanical actuation alone. The study shows that adaptiveSCB that exploit the naturally occurring pressure field around an airfoil in a passive wayare a feasible technology to mitigate the poor o↵-design performance of static SCB.
Jinks E, bruce P, Santer M, 2016, Wind Tunnel Experiments with Flexible Plates in Transonic Flows, 54th AIAA Aerospace Sciences Meeting, Publisher: AIAA
The evolution of adaptive shock control bump (SCB) design has seen the system flexibilityincrease to a point where the aerodynamic loading can affect the deformation of theplate. By studying the effects of a flexible plate subject to transonic flow the fluid structureinteraction 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 flowcurvature surrounding the plate as well as the global shock structure. A technique thatextracts the plate deformation from the PIV images is also presented which provides fluidand structural information for each test. The relationship between plate and flow angleis discussed as well as the effect of plate stiffness and free stream influence of each plateconfiguration.
Jones G, Santer M, Papadakis G, et al., 2016, Active Flow Control at Low Reynolds Numbers by Periodic Airfoil Morphing, 54th AIAA Aerospace Sciences Meeting, Publisher: American Institute of Aeronautics and Astronautics
This paper investigates the application of a periodically deforming airfoil surface for thepurpose of flow control at low Reynolds numbers. A physical model has been fabricatedby bonding Macro Fiber Composite (MFC) actuators to the underside of a NACA 4415’ssuction surface. The results presented build on work by Jones et al.1 First, the behavior ofthe surface when actuated at a range frequencies is investigated through a combination ofphotogrammetric and laser sensor measurements. Second, the aerodynamic performanceof this novel flow control technique is presented. It is shown that when the actuationfrequency ‘locks-in’ to the surface motion significant improvements in performance areobserved in a flight regime notorious for poor airfoil behavior.
Yasin R, Cui Y, Santer M, 2016, Reconfigurable Deployable CubeSat Solar Arrays Usin Thin Composite Flexures, 3rd AIAA Spacecraft Structures Conference
Cui Y, Santer M, 2015, Characterisation of tessellated bistable composite laminates, Composite Structures, Vol: 137, Pages: 93-104, ISSN: 0263-8223
Tessellated surfaces consisting of both unsymmetric composite elements with opposite layups, and unsymmetric composite elements in combination with symmetric composite elements, are investigated. It is shown that in simple cases these continuous surfaces only exhibit bistability due to the strong interaction between the connected elements. Strategies to mitigate against this interaction are proposed and implemented to achieve surfaces with high degrees of multistability up to the theoretical maximum.
Johnson M, 2015, TWIST: High performance thin film small satellite subsystems with a twist, Centre for Earth Observation Instrumentation Final Report, JA - PS - 184.108.40.206.5.1R1
The core goal of TWIST is to demonstrate that a multifunctional thin-filmdeployable small satellite subsystem can be stowed in the same volume as a traditional nanosatellite solar array, yet achieve 2-32x increase in likefor like available surface area when deployed, enabling novel spaceapplications hitherto impossible or non-viable due to power, communications or orbit constraints.
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