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The Direction Zone of Engineless UAVs in Dynamic Soaring
Get PDFThis paper mainly analyzes the dynamic soaring of UAV utilizing gradient wind. Dynamic soaring is an efficient path in which UAV absorbs energy from environment to enhance its flight endurance. A set of three-dimensional point dynamic equations for a soaring aircraft in three degrees of freedom is used in calculations. To simplify the calculation, the gradient wind’s direction is taken into decomposition. The notion of trajectory subsection analysis is applied to account for the energy transformation mechanism during the dynamic soaring, and the zone of direction is converted into cutting-in angle, which is regarded as initial limiting condition in the optimization of dynamic soaring trajectory. Then, the relationship between energy gain/loss and cutting-in angle is acquired. Three dynamic soaring styles corresponding to three typical cutting-in angles are selected to be analyze intensively, and the explicit characters of trajectories, airspeed, attitude angles and energy variation are presented. All these results reveal the zone of direction and validate the method of control for a dynamic soaring UAV soaring in gradient wind field without thrust
Analytical Method for Simulation of Buckling and Post-buckling Behaviour of Curved Pates
Get PDFShips, ship-shaped offshore structures, land-based structures and aerospace structures typically consist of various curved plate components. It is difficult to simulate the buckling and post-buckling of curved thin and/or thick plates that have characteristics of nonlinear structural mechanics, such as nonlinear behaviour when loading is applied. The elastic post-buckling behaviour of a curved plate is very complex, and accompanied by mode changes due to the occurrence of secondary buckling behaviour. Therefore, it is very important to clarify the elastic post-buckling behaviour when subjected to axial loading. The aim of this study was to derive an analytical calculation based on the formulation of the total potential energy, and a mathematical solution to simulate the elastic buckling and post-buckling behaviour of cylindrically curved plates under axial compression. The accuracy of the proposed method with the aforementioned modelling techniques was verified through comparison with finite element analyses of various curved plate configurations
Long Endurance and Long Distance Trajectory Optimization for Engineless UAV by Dynamic Soaring
Get PDFThe paper presents a comprehensive study on the performance of long endurance and long distance trajectory optimization of engineless UAV in dynamic soaring. A dynamic model of engineless UAV in gradient wind field is developed. Long endurance and long distance trajectory optimization problems are modelled by non-linear optimal control equations. Two different boundary conditions are considered and results are compared: (i) open long endurance pattern, (ii) closed long endurance pattern, (iii) open long distance pattern. In patterns of (i) and (ii), the UAV return to original position with the maximum flying time in pattern (ii) , and in patterns of (ii) and (iii), the maximum distance and minimum flying time occur in pattern (iii). The energy variations trends of three patterns have shown a fairly similar pattern. In the gradient wind field, long endurance and long distance are two independent flight patterns for engineless UAV by dynamic soaring
Texture Segmentation based on Multivariate Generalized Gaussian Mixture Model
Get PDFTexture Analysis is one of the prime considerations for image analysis and processing. Texture segmentation gained lot of importance due to its ready applicability in automation of scene identification and computer vision. Several texture segmentation methods have been developed and analysed with the assumption that the feature vector associated with the texture of the image region is modelled as Gaussian mixture model. Due to the limitations of the Gaussian model being meso kurtic, it may not characterise the texture of all image regions accurately. Hence in this paper, a texture segmentation algorithm is developed and analysed with the assumption that the feature vector of the texture associated with the whole image is characterised by multivariate generalized Gaussian mixture model. The generalized Gaussian mixture model includes several lepto kurtic, platy kurtic and meso kurtic distributions as particular cases. The model parameters are estimated through EM algorithm. The segmentation algorithm is developed using maximum likelihood under Bayesian framework. The performance of the proposed algorithm is evaluated through segmentation quality metrics and conducting experimentation with a set of 8 sample images taken from Brodatz texture database. A comparative study of the proposed algorithm with that of Gaussian mixture model revealed that the proposed algorithm outstandthe existing algorithms
A Framework for Comprehensive Impact Assessment in the Case of an ExtremeWinter Scenario, Considering Integrative Aspects of Systemic Vulnerability and Resilience
Get PDFIn northern regions, society can be seriously interrupted by a prolonged electricity network blackout due to a winter storm that cuts off power, communication and road networks. Due to hard winter weather it is essential to enhance the resilience of society to avoid danger to life. This can be achieved by developing new models to enhance preparedness for coming disaster events and to support rescue and other authorities to focus their resources on the most vulnerable targets in actual cases of emergencies. This paper presents a part of the results of activities performed within the EU project ‘CRISMA – Modelling crisis management for improved action and preparedness’. It focuses on improved resilience by proposing a framework for systemic vulnerability and impact analyses. The described work is conceptually based on risk-hazard and socio-constructive approaches. It is illustrated by means of a scenario consisting of a prolonged blackout together with an extreme winter storm in northern Finland. Scenario components include the integrative analysis of rapidly cooling houses and exposed vulnerable people as well as estimations of the potential costs of the crisis situation. The model can be extended to handle passable routes and the deployment of available rescue and snow ploughing equipment
Dynamic Response and Oscillating Behaviour of Fractionally Damped Beam
Get PDFThis paper presents the numerical solution of a viscoelastic continuous beam whose damping behaviours are defined in term of fractional derivatives of arbitrary order. Homotopy Perturbation Method (HPM) is used to obtain the dynamic response with respect to unit impulse load. Obtained results are depicted in term of plots. Comparisons are made with the analytic solutions obtained by Zu-feng and Xiao-yan (2007) to show the effectiveness and validation of the present method
A Practical Engineering Approach to the Design and Manufacturing of a mini kW BladeWind Turbine: Definition, optimization and CFD Analysis
No full textA practical engineering approach to the design of a 60 kW wind generator with improved performances is presented. The proposed approach relies on the use of a specific, "ad hoc'' developed software, OPTIWR (Optimization Software), expressly conceived to define an
"optimum'' rotor configuration in the framework of the blade-element-momentum theory. Starting from an initial input geometric configuration (corresponding to an already existing 50 kW turbine) and for given values of the wind velocity Vwind and of the advance ratio X = Vwind/ΩR (where Ω is the blade rotational speed and R is the propeller radius), this software is used to determine iteratively the optimized distributions of chords and twists which can guarantee a constant value of the socalled axial induction factor a = 1/3 along the blade. The output configuration is then converted into a CAD model to be used, in turn, as input data for a CFD commercial software. With this tool the relative rotational motion between the fluid and the wind turbine simulated resorting to a MRF (Moving Reference Frame) technique (for which continuity and momentum equations are solved in a rotating reference frame). The outcomes of the numerical simulations are then used to verify the improved performances of the optimized configuration and to which extent the CFD data agree with "expected'' behaviours (i.e. performances predicted on the basis of the simplified model). Finally, some details about the construction technique used to turn the optimized configuration into an effective working prototype are provided, in conjunction with a critical discussion of suitable production methods for composite components
Experimental and Numerical Investigations on Multicellular GFRP Bridge Deck Panels
Get PDFThe maintenance, upgrading and replacement of existing bridges have become urgent requirement and a challenging task for the construction sector. Bridge decks made of fibre reinforced polymers (FRP), have been widely adopted both in new construction and replacement of existing bridge decks. This paper reports the studies carried out hand lay-up multicellular glass fibre reinforced polymer. Multicellular bridge deck panels with various cross sectional profiles have been analysed using a general purpose finite element software ANSYS. A cross sectional profile that satisfied the deflection criteria with minimum weight was selected for analysis and fabrication. Six multicellular GFRP composite bridge deck panel of size 1250mm × 333mm × 150mm (l×b×d) were fabricated by hand lay-up process using various materials. The responses have been compared with analytical and numerical solutions and found to be they are in good agreement with each other
Effect of An Initial Stress on SH-Type GuidedWaves Propagating in a Piezoelectric Layer Bonded on A Piezomagnetic Substrate
Get PDFPropagation of SH-type guided waves in a layered structure with an invariant initial stress is studied, where a piezoelectric thin layer is perfectly bonded on a piezomagnetic substrate. Both the layer and the substrate possess transversely isotropic property. The dispersion relations of SH waves are obtained for four kinds of different electro-magnetic boundary conditions. The effects of initial stress, thickness ratio and electro-magnetic boundary conditions on the propagation behaviors are analyzed in detail. The numerical results show that: 1) The positive initial stresses make the phase velocity increasing, while the negative initial stresses decrease the phase velocity; 2) The smaller the thickness ratio of a piezoelectric layer to a piezomagnetic substrate, the larger the phase velocity of SH-type guided wave propagating in the corresponding layered structure; 3) The electrical boundary conditions play a dominant role in the propagating characteristics. Moreover the phase velocities for the electrically shorted surface are smaller than that for the open case. The obtained results are useful for understanding and design of the electromagnetic acoustic wave and microwave devices
Analysis of Symmetry Breaking Bifurcation in Duffing System with Random Parameter
Get PDFThe symmetry breaking bifurcation (SBB) phenomenon in a deterministic parameter Duffing system (DP-DS) is well known, yet the problem how would SBB phenomenon happen in a Duffing system with random parameter (RP-DS) is still open. For comparison study, the results for DP-DS are summarized at first: in short, SBB in DP-DS is just a transition of response phase trajectories from a single self-symmetric one about the origin into two mutual symmetric once, or vice versa. However, in DP-DS case, the two mutual symmetric phase trajectories are never commutable. In view of every sample of RP-DS is a DP-DS, we think that SBB phenomenon might also happen in a RP-DS as an ensemble mean behavior. Since the orthogonal polynomial approach is a practical method to study the dynamical behavior of nonlinear system with random parameters, so we apply the Chebyshev polynomials approach to reduce the RP-DS to an equivalent deterministic system (EDS) to study its dynamical behavior in ensemble average mean. Numerical simulations on both DP-DS and EDS show that though SBB may happen in similar apparent forms, but for EDS the two coexisting symmetric phase trajectories are occasionally commutable. We cannot but resort to study the different features of attractive basins for these two kind of mutual symmetric phase trajectories. We found that the boundary of attractive basins in EDS case is fractal-like, while that in DP-DS case is smooth