bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parametric studies of aerofoil-vortex interaction; a numerical approach using LES
Authors: Ilie M. , Nitzsche F. , Matida E. 
Published: February 2016

AbstractThe influence of angle-of-attack and vortex-aerofoil vertical miss-distance on the aerofoil-vortex mechanism of interaction is investigated numerically using the large-eddy simulation approach. The study concerns the aerofoil-vortex interaction (AVI) phenomena encountered in the rotorcraft aerodynamics. The studies are performed for a Reynolds number of 1·3 × 106 based on the chord (c = 0·2m) of the aerofoil and free-stream velocity U = 100ms−1. The studies are conducted for three different angles-of-attack (α = 0°, and α = 5°, α = 10°) and vertical miss-distances (h = 0·0m, h = −0·01, h = −0·02m) respectively. The present study shows that the magnitude of lift coefficient and flow separation, at the instant of interaction, decay with the increase of angle-of-attack and vertical miss-distance.
A neuro-fuzzy approach to the weight estimation of aircraft structural components
Authors: Hannon C. , Toropov V. V. , Querin O. M. 
Published: February 2016

AbstractThis paper explores the issues related to the application of fuzzy logic techniques to aid the process of weight estimation for aircraft structures at preliminary design stages. The focus lays on the design of a neuro-fuzzy system for the weight analysis, through the use of the Neuro-Fuzzy Function Approximator (NEFPROX) algorithm. The paper introduces a three-level process designed around Mamdani fuzzy systems derived through NEFPROX and analyses its application to the sizing and weight estimation of spoiler attachment ribs. Problems such as structure parameterisation, variable selection and model optimisation are explored as part of the process validation phase on the selected structural case study. The model performance is evaluated with respect to modelling accuracy, generalisation capabilities and the interdependencies between the variables the model is able to derive from the analysis of the given structural examples. The results are then compared to the performance obtained from the application of Takagi-Sugeno-Kang (TSK) fuzzy models derived using Adaptive Network-based Fuzzy Inference System (ANFIS) on the same sample of spoiler attachment ribs. Results highlight the benefits of adopting NEFPROX for the derivation of fuzzy systems to be applied in structural weight estimation problems, from the point of view of both accuracy of the approximation provided and the quality and interpretability of the final rulebase derived by the system.
Damage arrest design approach using stitched composites
Authors: Velicki A. , Thrash P. 
Published: February 2016

AbstractAlthough the deployment of carbon fibre structural components has enjoyed wide success on smaller aircraft, their acceptance on larger transport airframes is less sanguine – especially in the case of primary structure applications where the increasing out of plane loads found on the larger airframes have exposed the weak interlaminar properties of the layered material system. This has led to an overreliance on mechanical attachments to suppress these through thickness failures, which ultimately degrades structural performance and increases manufacturing costs. Until these resin dominated failure modes can be dealt with more effectively, without adversely affecting the in plane properties of the laminate, the true weight-savings potential afforded by carbon fibre material systems will be difficult to attain. This paper describes how researchers at NASA-LaRC and The Boeing Company are working to develop a next generation stitched composite design solution that addresses the fundamental challenges in achieving improved structural performance and reduced fabrication costs for large carbon fibre airframe structures.
Robust geometric sizing of a small flying wing planform based on evolutionary algorithms
Authors: Rodríguez-Cortés H. , Arias-Montaño A. 
Published: February 2016

AbstractIn this paper a geometric sizing method for a small electric powered flying wing is proposed. The geometric sizing method aims to reduce the effects of variations in the power plant characteristics on endurance. This results in a single-objective design optimisation problem where the sensitivity to power plant characteristics of the endurance equation is minimised, constrained to Reynolds number, wing load, wing taper ratio, aircraft size and wing sweep angle. As a result, geometric characteristics of the flying wing such as span, tip chord and root chord are obtained. Flying wing aerodynamic characteristics are obtained by means of an inviscid fluid flow analysis program of the type low-order panel methods, known as CMARC. The optimisation problem involves a non convex function so that it is necessary to rely on heuristic programming methods. In particular an Evolutionary Algorithm based on differential evolution is considered.
An optimal control approach for alleviation
of tiltrotor gust response
Authors: Muro D. , Colella M. Molica , Serafini J. , Gennaretti M. 
Published: February 2016

AbstractThe alleviation of gusts effects on a tiltrotor in
aeroplane and helicopter operation modes obtained by
an optimal control methodology based on the
actuation of elevators, wing flaperons and
swashplate is examined. An optimal observer for
state estimate is included in the compensator
synthesis, with the Kalman-Bucy filter applied in
the presence of stochastic noise. Tiltrotor dynamics
is simulated through an aeroelastic model that
couples rigid-body motion with wing and proprotor
structural dynamics. An extensive numerical
investigation examines effectiveness and robustness
of the applied control procedure, taking into
account the action of both deterministic and
stochastic vertical gusts. In addition, a passive
pilot model is included in the aeroelastic loop and
the corresponding effects on uncontrolled and
controlled gust response are analysed.
Performance of Glare panels subjected to
intense pressure pulse loading
Authors: Soutis C. , Mohamed G. , Hodzic A. 
Published: February 2016

AbstractA robust and efficient computational model has been
developed which is capable of modelling the dynamic
non-linear behaviour of Glare panels subjected to
blast loadings. High strain rate material
characterisation and modelling of interfacial
debonding between adjacent sublaminates have been
taken into consideration. Numerical model validation
have been performed considering case studies of
Glare panels subjected to a blast-type pressure
pulse for which experimental data on the back face-
displacement and post-damage observations were
available. Excellent agreement of mid-point
deflections and evidence of severe yield line
deformation were shown and discussed against the
performed blast tests. A further parametric study
identified Glare as a potential blast attenuating
structure, exhibiting superior blast potential
against monolithic aluminium plates. The results
were normalised and showed that for a given impulse,
Glare exhibited a smaller normalised displacement,
outperforming monolithic Aluminium 2024-T3 plates.
It was concluded that further work needed to be
carried out to take into account the influence of
geometry (cylindrical structures),
pre-pressurisation effects and boundary
conditions
Parametric damage tolerance design of metallic aeronautical stiffened panels
Authors: Molinari G. , Meneghin I. , Melega M. , Troiani E. 
Published: February 2016

AbstractOn the basis of well-known literature, an analytical tool named LEAF (linear elastic analysis of fracture) was developed by the authors to predict the damage tolerance (DT) proprieties of aeronautical stiffened panels. The tool is based on the linear elastic fracture mechanics and the displacement compatibility method. By means of LEAF, an extensive parametric analysis of stiffened panels, representative of typical aeronautical constructions, was performed to provide meaningful design guidelines. The effects of riveted, integral and adhesively bonded stringers on the fatigue crack propagation performances of stiffened panels were investigated, as well as the crack retarder contribution using metallic straps (named doublers) bonded in the middle of the stringers bays. The effect of both perfectly bonded and partially debonded doublers was investigated as well. Adhesively bonded stiffeners showed the best DT properties in comparison with riveted and integral ones. A great reduction of the skin crack growth propagation rate can be achieved with the adoption of additional doublers bonded between the stringers.
Implementation of vision-based automatic guidance system on a fixed-wing unmanned aerial vehicle
Authors: Lee C-S , Hsiao F-B 
Published: February 2016

AbstractThis paper presents the design and implementation of a vision-based automatic guidance system on a fixed-wing unmanned aerial vehicle (UAV). The system utilises a low-cost ordinary video camera and simple but efficient image processing techniques widely used in computer-vision technology. The paper focuses on the identification and extraction of geographical tracks such as rivers, coastlines, and roads from real-time aerial images. The image processing algorithm primarily uses colour properties to isolate the geographical track of interest from its background. Hough transform is eventually used to curve-fit the profile of the track which yields a reference line on the image plane. A guidance algorithm is then derived based on this information. In order to test the vision-based automatic guidance system in the laboratory without actually flying the UAV, a hardware-in-the-loop simulation system is developed. Description regarding the system and significant simulation result are presented in the paper. Finally, an actual test flight where the UAV successfully follows a stretch of a river under automatic vision-based guidance is also presented and discussed.
Improved extrapolation of steady turbulent aerodynamics using a non-linear POD-based reduced order model
Authors: Zimmermann R. , Görtz S. 
Published: February 2016

AbstractA reduced-order modelling (ROM) approach for predicting steady, turbulent aerodynamic flows based on computational fluid dynamics (CFD) and proper orthogonal decomposition (POD) is presented. Model-order reduction is achieved by parameter space sampling, solution space representation via POD and restriction of a CFD solver to the POD subspace. Solving the governing equations of fluid dynamics is replaced by solving a non-linear least-squares optimisation problem. The method will be referred to as LSQ-ROM method. Two approaches of extracting POD basis information from CFD snapshot data are discussed: POD of the full state vector (global POD) and POD of each of the partial states separately (variable-by-variable POD). The method at hand is demonstrated for a 2D aerofoil (NACA 64A010) as well as for a complete industrial aircraft configuration (NASA Common Research Model) in the transonic flow regime by computing ROMs of the compressible Reynolds-averaged Navier-Stokes equations, pursuing both the global and the variable-by-variable POD approach. The LSQ-ROM approach is tried for extrapolatory flow conditions. Results are juxtaposed with those obtained by POD-based extrapolation using Kriging and the radial basis functions spline method. As a reference, the full-order CFD solutions are considered. For the industrial aircraft configuration, the cost of computing the reduced-order solution is shown to be two orders of magnitude lower than that of computing the reference CFD solution.
Simulating the environment at the helicopter-ship dynamic interface: research, development and application
Authors: Hodge S. J. , Forrest J. S. , Padfield G. D. , Owen I. 
Published: February 2016

AbstractThis paper presents highlights from research conducted at the University of Liverpool to determine suitable fidelity criteria and guidelines for the modelling and simulation of the helicopter-ship dynamic interface environment. The paper begins by describing the characteristics of the helicopter-ship dynamic interface, explaining the motivation behind the research and reviewing the state-of-the-art in dynamic interface simulation. The development of a dynamic interface research environment based on an existing research simulator operated by the University of Liverpool is then described, before key results from a number of piloted simulation experiments are presented. These experiments were specifically designed to address fidelity sensitivity issues, such as, are unsteady airwake models necessary, or can a steady airwake model induce appropriate levels of pilot workload? What influence does the modelled ship geometry, or choice of atmospheric wind conditions have on the airwake model and on pilot workload? Finally, the paper concludes by briefly describing the relevance of these research findings to current and future industry programmes.
Computation of stress intensity factors in functionally graded materials using partition-of-unity meshfree method
Authors: Muthu N. , Maiti S. K. , Falzon B. G. , Guiamatsia I. 
Published: February 2016

AbstractThis paper describes the computation of stress intensity factors (SIFs) for cracks in functionally graded materials (FGMs) using an extended element-free Galerkin (XEFG) method. The SIFs are extracted through the crack closure integral (CCI) with a local smoothing technique, non-equilibrium and incompatibility formulations of the interaction integral and the displacement method. The results for mode I and mixed mode case studies are presented and compared with those available in the literature. They are found to be in good agreement where the average absolute error for the CCI with local smoothing, despite its simplicity, yielded a high level of accuracy.
The influence of surface ply fibre angle on the compressive strength of composite laminates containing delamination
Authors: Rhead A. T. , Butler R. , Liu W. , Baker N. 
Published: February 2016

AbstractA combination of uniaxial compression tests and Strip Model and Finite Element analyses of laminates artificially delaminated to create circular (±θ) sublaminates is used to assess the influence of fibre angle on the compressive strength of composite laminates.Sublaminates with 0° < θ < 40° are found to fail by sublaminate-buckling-driven delamination propagation and provide poor tolerance of delamination. This is a consequence of their relatively high axial stiffnesses, low sublaminate buckling strains, Poisson’s ratio induced compressive transverse strains and extension-twist coupling which produces unexpected sublaminate buckling mode shapes. Sublaminates with 40° < θ < 60° are most tolerant to delamination; axial and transverse stiffnesses are minimal, formation of sublaminate buckles is resisted, high laminate buckling strains reduce interaction between laminate and sublaminate buckling mode shapes and extension-twist coupling is minimal. Sublaminates with 60° < θ < 90° are shown to produce varied tolerance of delamination. Sublaminate buckling is generally prevented owing to transverse tensile strains induced by mismatches between laminate and sublaminate Poisson’s ratios but may occur in laminates with low Poisson’s ratios.
Aerodynamic studies over a manoeuvring UCAV 1303 configuration
Authors: Chandrasekhara M. S. , McLain B. K. 
Published: February 2016

AbstractThe flow past an unmanned combat air vehicle (UCAV) 1303 was investigated in a water tunnel in an effort to understand the complex flow field. The UCAV 1303 is characterised by a non slender, 47° swept-leading-edge delta wing, with a cranked trailing edge, a cropped wing tip and a fuselage. It also has no vertical tail. Dye visualisation pictures and five-axis strain gage load data were obtained on a 1:72 scale model in both steady flow and while the model executed preprogrammed manoeuvres. From the strain gage data, body axis force and moment data were derived. In addition to some similarities, comparison of the flow features observed with those of more well known slender delta wing flows showed some remarkable differences such as tip-stall, the presence of two like-sense vortices on the same side of the wing, their simultaneous spiral and bubble bursting. This paper predominantly discusses the flow visualisation results and attempts to correlate the load data to some of the observed flow features.
A finite-volume gas-kinetic method for the solution of the Navier-Stokes equations
Authors: Righi M. 
Published: February 2016

AbstractGas-kinetic theory is also valid in the continuum regime: the Euler and Navier-Stokes equations can be obtained as projection of the Boltzmann equation on to the physical space (x,t). The numerical schemes derived from gas-kinetic theory are computationally more expensive than Navier-Stokes based ones, but offer advantages which have been attracting a growing level of attention: they can (i) accommodate discontinuities at cells interface, (ii) provide high-resolution fluxes, (iii) provide advantages in the simulation of turbulence, (iv) handle hypersonic and/or rarefied flows. This study extends the validation of gas-kinetic schemes investigating a few turbulent flow cases. At a slightly higher computational cost, gas-kinetic schemes provide results comparable to those obtained with well-validated Navier-Stokes schemes using the same turbulence model, grid and reconstruction order. In the case of shock-separated flows, the results obtained with the gas-kinetic scheme are even closer to experimental data. These findings are consistent with the idea that gas-kinetic theory is a physically more consistent framework for investigating the mechanics of fluids.
Robust and computational efficient autopilot design: A hybrid approach based on classic control and genetic-fuzzy sliding mode control
Authors: Babaei A. R. , Mortazavi M. , Menhaj M. B. 
Published: February 2016

AbstractThe purpose of this paper is developing an efficient flight control strategy in terms of time response characteristics, robustness with respect to both parametric uncertainties and un-modeled nonlinear terms, number of required measurements, and computational burden. The proposed method is based on combination of a classic controller as principal section of the autopilot and a multi-objective genetic algorithm-based fuzzy output sliding mode control (FOSMC). FOSMC not only modifies robustness of the classic controller against uncertainties and external disturbances, but also modifies its time response for wide range of commands. FOSMC is a single input-single output controller that is based on the system output instead of the system states. In this situation, the proposed autopilot does not require measurement of other variables and observer, and also it is practicable because of considerable reduction in rule inferences then computational burden. As a critical application, the proposed method is applied to design the altitude hold mode autopilot for an UAV which is non-minimum phase, uncertain, and nonlinear.
Guided wave propagation in composite laminates using piezoelectric wafer active sensors
Authors: Gresil M. , Giurgiutiu V. 
Published: February 2016

AbstractPiezoelectric wafer active sensors (PWAS) are lightweight and inexpensive transducers that enable a large class of structural health monitoring (SHM) applications such as: (a) embedded guided wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays; (b) high-frequency modal sensing, i.e., electro-mechanical impedance method; and (c) passive detection. The focus of this paper is on the challenges posed by using PWAS transducers in the composite laminate structures as different from the metallic structures on which this methodology was initially developed. After a brief introduction, the paper reviews the PWAS-based SHM principles. It follows with a discussion of guided wave propagation in composites and PWAS tuning effects. Then, the mechanical effect is discussed on the integration of piezoelectric wafer inside the laminate using a compression after impact. Experiments were performed on a glass fibre laminate, employing PWAS to measure the attenuation coefficient. Finally, the paper presents some experimental and multi-physics finite element method (MP-FEM) results on guided wave propagation in composite laminate specimens.
Validation of endurance estimates for battery powered UAVs
Authors: Traub L. W. 
Published: February 2016

AbstractAn experimental investigation is presented to validate endurance estimates for a battery powered flight vehicle. In this study a radio controlled model aircraft was ‘flown’ inside a wind tunnel. Various Lithium Ion batteries were used to power the model. Battery electrical characteristics were recorded during each run to assess battery discharge behaviour. Theoretical estimates based upon battery characteristics yielded endurance estimates within 3% of that measured experimentally. The discharge characteristics of the batteries were found to be the largest source of uncertainty for endurance estimates.
The optimum aeroplane and beyond
Authors: Poll D. I. A. 
Published: February 2016

AbstractA summary of the ways in which aviation impacts the environment is presented and the ratio of the energy liberated during a flight to the revenue work done (ETRW) is identified as a key indicator in the assessment of environmental impact. Using the ‘Breguet’ range equation, a number of theorems relating to ETRW are derived and discussed. This is followed by an approximate analysis to produce estimates for the ETRW of aircraft currently in service. It is found that the global fleet average value for ETRW is much higher than those estimated for existing individual aircraft. An explanation of the difference is presented, with the contributions from airline operations and air traffic management identified and quantified. Consideration is then given to the potential for future reduction in ETRW through advances in materials, alternative fuels, structures, aerodynamics and propulsion technologies and the likely benefits are quantified. The improvement in ETRW that could be achieved if this parameter was minimised in the design process with the current level of technology is also considered. Finally, the likelihood of performance improvements being introduced in the short, medium and long term is briefly discussed.
Rigid body separation dynamics for space launch vehicles
Authors: Rao B. N. , Jeyakumar D. , Biswas K. K. , Swaminathan S. , Janardhana E. 
Published: February 2016

AbstractThis paper presents a systematic formulation for the simulation of rigid body dynamics, including the short period dynamics, inherent to stage separation and jettisoning parts of a satellite launcher. This also gives a review of various types of separations involved in a launch vehicle. The problem is sufficiently large and complex; the methodology involves iterations at successively lower levels of abstraction. The best choice to tackle such problems is to use state-of-the-art programming technique known as object oriented programming. The necessary classes have been identified to represent various entities in the launch vehicle separation process (e.g., gravity, aerodynamics, propulsion and separation mechanisms etc.). Simple linkages are modelled with suitable objects. This approach helps the designer to simulate a launch vehicle separation dynamics and also to analyse separation system performance. To examine the influence of the design variables on the separating bodies, statistical analyses have been performed on the upper stage separation process and pull out of ongoing stage nozzle from the spent stage of a multistage rocket carrier using retro rockets.