Browsing by Author "Zbikowski, Rafal"
Now showing 1 - 12 of 12
Results Per Page
Sort Options
Item Open Access Aeroservoelastic modelling and control of a slender anti-air missile for active damping of longitudinal bending vibrations(Elsevier, 2017-03-07) Verhaegen, Anatole; Zbikowski, RafalSlender anti-air missiles experience longitudinal bending in supersonic flight and yet their autopilots are designed under the rigid-body assumption. Such autopilot design employs notch filters to remove the modal frequencies of the elastic airframe but this approach limits the autopilot bandwidth. In this paper, aeroservoelastic modelling and control of the ASTER 30 missile is proposed to enable autopilot design with extended bandwidth. The aeroservoelastic model combines missile flight dynamics, actuator dynamics and airframe elasticity, the latter focusing on longitudinal bending treated as a continuous Euler–Bernoulli beam problem. The beam is discretised leading to a nodal model and the modal analysis is then performed. The modal model is expressed in the state-space form and its order is reduced to enable optimal sensor placement and active damping control. The aeroservoelastic model of the ASTER 30 missile is further refined for control purposes by optimally choosing actuator inputs together with the number and position of sensors to be mounted on the missile airframe. Once these choices are made, several variants of active vibration damping control are proposed and analysed in order to enable an extended bandwidth for the autopilot by countering the airframe deformation measured by these sensors.Item Open Access Airborne mapping of complex obstacles using 2D Splinegon(2008-06-04T00:00:00Z) Lazarus, Samuel B.; Shanmugavel, Madhavan; Tsourdos, Antonios; Zbikowski, Rafal; White, Brian A.This paper describes a recently proposed algorithm in mapping the unknown obstacle in a stationary environment where the obstacles are represented as curved in nature. The focus is to achieve a guaranteed performance of sensor based navigation and mapping. The guaranteed performance is quantified by explicit bounds of the position estimate of an autonomous aerial vehicle using an extended Kalman filter and to track the obstacle so as to extract the map of the obstacle. This Dubins path planning algorithm is used to provide a flyable and safe path to the vehicle to fly from one location to another. This description takes into account the fact that the vehicle is made to fly around the obstacle and hence will map the shape of the obstacle using the 2D-Splinegon technique. This splinegon technique, the most efficient and a robust way to estimate the boundary of a curved nature obstacles, can provide mathematically provable performance guarantees that are achievable in practice.Item Open Access Bioinspired symmetry detection on resource limited embedded platforms(2017-07) Elliott, Alexander William; Zbikowski, RafalThis work is inspired by the vision of flying insects which enables them to detect and locate a set of relevant objects with remarkable effectiveness despite very limited brainpower. The bioinspired approach worked out here focuses on detection of symmetric objects to be performed by resource-limited embedded platforms such as micro air vehicles. Symmetry detection is posed as a pattern matching problem which is solved by an approach based on the use of composite correlation filters. Two variants of the approach are proposed, analysed and tested in which symmetry detection is cast as 1) static and 2) dynamic pattern matching problems. In the static variant, images of objects are input to two dimentional spatial composite correlation filters. In the dynamic variant, a video (resulting from platform motion) is input to a composite correlation filter of which its peak response is used to define symmetry. In both cases, a novel method is used for designing the composite filter templates for symmetry detection. This method significantly reduces the level of detail which needs to be matched to achieve good detection performance. The resulting performance is systematically quantified using the ROC analysis; it is demonstrated that the bioinspired detection approach is better and with a lower computational cost compared to the best state-of-the-art solution hitherto available.Item Open Access Computational Optimal Control of the Terminal Bunt Manoeuvre(Cranfield University, 2007) Subchan; White, Prof B A; Zbikowski, RafalThis work focuses on a study of missile guidance in the form of trajectory shaping of a generic cruise missile attacking a fixed target which mu ·t be struck from above. The problem is reinterpreted using optimal control theory resulting in two formulations: I ) minimum time-integrated altitude and 2) minimum flight time. Each formulation entails nonlinear, two-dimensional missile flight dynamics, boundary conditions and path constraints. Since the thus obtained optimal control problems do not admit analytical solutions, a recourse to computational optimal control is made. The focus here is on informed use of the tools of computational optimal control, rather than their development. Each of the formulations is solved using a three-stage approach. In stage I, the problem is discretised, effectively transforming it into a nonlinear programming problem, and hence suitable for approximate solution with the FORTRAN packages DIRCOL and NUDOCCCS. The results of this direct approach are used to discern the structure of the optimal solution, i.e. type of constraints active, time of their activation, switching and jump points. This qualitative analysis, employing the results of stage I and op- timal control theory, constitutes stage 2. Finally, in stage 3, the insight of stage 2 are made precise by rigorous mathematical formulation of the relevant two-point boundary value problems (TPBVPs), using the approach private theorems of optimal control theory. The TPBVPs obtained from this indirect approach are then solved using the FORTRA package B DSCO and the results compared with the appropriate solutions of stage I. For each formulation (minimum altitude and minimum time) the influence of boundary conditions on the structure of the optimal solution and the performance index is investigated. The results are then interpreted from the operational and computational perspectives. Software implementation employing DIRCOL, NUDOCCCS and BNDsca, which produced the results, is described and documented. Finally, some conclusions are drawn and recommendations made.Item Open Access Computational optimal control of the terminal bunt manoeuvre(2016-10-10) Subchan, A; Zbikowski, Rafal; White, Prof B AThis work focuses on a study of missile guidance in the form of trajectory shaping of a generic cruise missile attacking a fixed target which must be struck from above. The problem is reinterpreted using optimal control theory resulting in two formulations: I) minimum time-integrated altitude and 2) minimum flight time. Each formulation entails nonlinear, two-dimensional missile flight dynamics, boundary conditions and path constraints. Since the thus obtained optimal control problems do not admit analytical solutions, a recourse to computational optimal control is made. The focus here is on informed use of the tools of computational optimal control, rather than their development. Each of the formulations is solved using a three-stage approach. In stage I, the problem is discretised, effectively transforming it into a nonlinear programming problem, and hence suitable for approximate solution with the FORTRAN packages DIRCOL and NUDOCCCS. The results of this direct approach are used to discern the structure of the optimal solution, i.e. type of constraints active, time of their activation, switching and jump points. This qualitative analysis, employing the results of stage I and optimal control theory, constitutes stage 2. Finally, in stage 3, the insight of stage 2 are made precise by rigorous mathemati cal formulation of the relevant two-point boundary value problems (TPBVPs), using the appropriate theorems of optimal control theory. The TPBVPs obtained from this indirect approach are then solved using the FORTRAN package BNDSCO and the results compared with the appropriate solutions of stage I. For each formulation (minimum altitude and minimum time) the influence of boundary conditions on the structure of the optimal solution and the performance index is investigated. The results are then interpreted from the operational and computational perspectives. Software implementation employing DIRCOL, NUDOCCCS and BNDSCO, which produced the results, is described and documented. Finally, some conclusions are drawn and recommendations made.Item Open Access Effectiveness of autonomous decision making for unmanned combat aerial vehicles in dogfight engagements(AIAA, 2018-02-07) Ramírez López, Nelson; Zbikowski, RafalThe main objective of this work is to perform a study of the utility of unmanned combat aerial vehicles (UCAVs) in dogfighting (DF) engagements, with DF defined as an aerial battle between two fighter aircraft taking place at close range. The key problem is to assess effectiveness of UCAVs in DF combat when using autonomous decision making based on a representative guidance law and a game-theoretic algorithm. The UCAV DF problem is considered here as a two-player (two fighters), zero-sum, sequential-interaction game with limited information (i.e., each fighter only knows the last three positions of its opponent every time a decision needs to be made). A software simulator has been developed to represent a one-versus-one, clear-sky, close-range aerial battle involving three-dimensional trajectories with high-angle-of-attack (AOA) maneuvers for fighters with similar/dissimilar performance capabilities, considered under four initial conditions: offensive, defensive, neutral, and opposing engagements. Different “levels of intelligence” of the enemy are implemented to validate the performance of the UCAV autonomous decision making against diverse opponents. The simulation-based parametric study elucidates the influence of fighters’ performance capabilities and the fighters’ skill on the outcome of the engagement.Item Open Access Experimental investigation of some aspects of insect-like flapping flight aerodynamics for application to micro air vehicles(Springer Science Business Media, 2009-05-31T00:00:00Z) Ansari, S. A.; Phillips, Nathan; Stabler, G.; Wilkins, P. C.; Zbikowski, Rafal; Knowles, KevinInsect-like flapping flight offers a power-efficient and highly manoeuvrable basis for micro air vehicles for indoor applications. Some aspects of the aerodynamics associated with the sweeping phase of insect wing kinematics are examined by making particle image velocimetry measurements on a rotating wing immersed in a tank of seeded water. The work is motivated by the paucity of data with quantified error on insect-like flapping flight, and aims to fill this gap by providing a detailed description of the experimental setup, quantifying the uncertainties in the measurements and explaining the results. The experiments are carried out at two Reynolds numbers-500 and 15,000-accounting for scales pertaining to many insects and future flapping-wing micro air vehicles, respectively. The results from the experiments are used to describe prominent flow features, and Reynolds number-related differences are highlighted. In particular, the behaviour of the leading-edge vortex at these Reynolds numbers is studied and the presence of Kelvin-Helmholtz instability observed at the higher Reynolds number in computational fluid dynamics calculations is also verified.Item Open Access An indicial-polhamus model of aerodynamics of insect-like flapping wings in hover(2011-10-14) Pedersen, C B; Zbikowski, RafalAs part of the ongoing development of Flapping-Wing Micro Air Vehicle (FMAV) prototypes at RMCS Shrivenham,a model of insect-like wing aerodynamics in hover has been developed, and implemented as MATLAB code.The model is intended to give better insight into the various aerodynamic effects on the wing, so is as close to purely analytical as possible. The model is modular, with the various effects treated separately.This modularity aids analysis and insight, and will allow future refinement of individual parts. However,it comes at the expense of considerable simplification,which requires empirical verification. The model starts from quasi-steady inviscid flow around a thin 2D rigid flat wing section,accounting for viscosity with the Kutta-Joukowski condition,and the leading edge suction analogy of Polhamus. Wake effects are modelled using the models of Kussner and Wagner on a prescribed wake shape,as initially used by Loewy. The model has been validated against experimental data of Dickinson's Robofly, and found to give acceptable accuracy.Some empirically inspired refinements of the Polhamus effect are outlined, but need further empirical validation. This thesis comprises of six main parts: Part I is introductory material, and definitions, including an overview of what insect-like Rapping flight actually entails, and detailed definitions of the variables and terms used later. Part 2 describes the new theoretical model, and a simple scaling analysis of the forces and moments predicted. Part 3 deals with the MATLAB implementation of the above theory, and the considerations re-quired when adapting the theory for computational use. Part4 shows and discusses the results of the above code, against experimental measurements on Dickinson's Robofly. Part 5 is the conclusions, including a comprehensive list of all assumptions made in the theory. Part6 , the appendices, contain useful mathematical identities,and a copy of the code that was developed.Item Open Access Non-linear unsteady aerodynamic model for insect-like flapping wings in the hover. Part 2: implementation and validation(Professional Engineering Publishing, 2006-06-30T00:00:00Z) Ansari, S. A.; Zbikowski, Rafal; Knowles, KevinThe essence of this two-part paper is the analytical, aerodynamic modelling of insect-like flapping wings in the hover for micro-air-vehicle applications. A key feature of such flapping-wing flows is their unsteadiness and the formation of a leading-edge vortex in addition to the conventional wake shed from the trailing edge. What ensues is a complex interaction between the shed wakes, which, in part, determines the forces and moments on the wing. In an attempt to describe such a flow, two novel coupled, non-linear, wake integral equations were developed in the first part of the paper. The governing equations derived were exact, but did not have a closed analytical form. Solutions were, therefore, to be found by numerical methods and implemented in Fortran. This is the theme of the second part of the paper. The problem is implemented by means of vortex methods, whereby discrete point vortices are used to represent the wing and its wake. A number of numerical experiments are run to determine the best values for numerical parameters. The calculation is performed using a time- marching algorithm and the evolution of the wakes is tracked. In this way, both flow field and force data are generated. The model is then validated against existing experimental data and very good agreement is found both in terms of flow field representation and force prediction. The temporal accuracy of the simulations is also noteworthy, implying that the underlying flow features are well captured, especially the unsteadiness. The model also shows the similarity between two-dimensional and three-dimensional flows for insect-like flapping wings at low Reynolds numbers of the order of Re similar to 200.Item Open Access Non-linear unsteady aerodynamic model for insect-like flapping wings in the hover. Part 1: Methodology and analysis(Professional Engineering Publishing, 2006-12-31T00:00:00Z) Ansari, S. A.; Zbikowski, Rafal; Knowles, KevinThe essence of this two-part paper is the analytical, aerodynamic modelling of insect-like flapping wings in the hover for microair vehicle applications. A key feature of such flapping-wing flows is their unsteadiness and the formation of a leading-edge vortex in addition to the conventional wake shed from the trailing edge. What ensues is a complex interaction between the shed wakes which, in part, determines the forces and moments on the wing. In an attempt to describe such a flow, two-novel coupled, non-linear, wake-integral equations are developed in this first part of the paper, and these form the foundation upon which the rest of the work stands. The circulation-based model thus developed is unsteady and inviscid in nature and essentially two-dimensional. It is converted to a ‘quasi-three-dimensional' model using a blade-element-type method, but with radial chords. The main results from the model are force and moment data for the flapping wing and are derived as part of this article using the method of impulses. These forces and moments have been decomposed into constituent elements. The governing equations developed in the study are exact, but do not have a closed analytic form. Therefore, solutions are found by numerical methods. These are described in the second part of this paper.Item Open Access On mathematical modelling of insect flight dynamics in the context of micro air vehicles(IOP Publishing, 2006-07-10) Zbikowski, Rafal; Ansar, Salman A.; Knowles, KevinThis paper discusses several aspects of mathematical modelling relevant to the flight dynamics of insect flight in the context of insect-like flapping wing micro air vehicles (MAVs). MAVs are defined as flying vehicles ca six inch in size (hand-held) and are developed to reconnoitre in confined spaces (inside buildings, tunnels etc). This requires power-efficient, highly-manoeuvrable, low-speed flight with stable hover. All of these attributes are present in insect flight and hence the focus of reproducing the functionality of insect flight by engineering means. This can only be achieved if qualitative insight is accompanied by appropriate quantitative analysis, especially in the context of flight dynamics, as flight dynamics underpin the desirable manoeuvrability. We consider two aspects of mathematical modelling for insect flight dynamics. The first one is theoretical (computational), as opposed to empirical, generation of the aerodynamic data required for the six-degrees-of-freedom equations of motion. For these purposes we first explain insect wing kinematics and the salient features of the corresponding flow. In this context, we show that aerodynamic modelling is a feasible option for certain flight regimes, focussing on a successful example of modelling hover. Such modelling progresses from first principles of fluid mechanics, but relies on simplifications justified by the known flow phenomenology and/or geometric and kinematic symmetries. In particular, this is relevant to six types of fundamental manoeuvres, which we define as those steady flight conditions for which only one component of both the translational and rotational body velocities is non-zero (and constant). The second aspect of mathematical modelling for insect flight dynamics addressed here deals with the periodic character of the aerodynamic force and moment production. This leads to consideration of the types of solutions of nonlinear equations forced by nonlinear oscillations. In particular, the existence of non-periodic solutions of equations of motion is of practical interest, since this allows steady recitilinear flight. Progress in both aspects of mathematical modelling for insect flight will require further advances in aerodynamics of insect-like flapping. Improved aerodynamic modelling and computational fluid dynamics (CFD) calculations are required. These theoretical advances must be accompanied by further flow visualisation and measurement to validate both the aerodynamic modelling and CFD predictions.Item Open Access Vulnerability analysis of GPS receiver software(IEEE, 2019-07-04) Gonzalez, G. Mori; Petrunin, Ivan; Zbikowski, Rafal; Voutsis, K.; Verdeguer Moreno, RicardoSatellite navigation systems such as the Global Positioning System (GPS)makes it possible for users to find their relative or absolute position. Thanks to its mobility and reliability, the GPS is used in many civil and military applications. However, the GPS does not provide an advanced level of security. Therefore, it could be potentially a target of attacks. With the development of new GPS attacks, the security knowledge has to grow at the same rate, so existing attacks can be detected by updated versions of receiver software or hardware. In this paper, a comparative analysis of GPS receiver resilience to software attacks is performed with the help of GNSS simulator from Spirent. The main objective of this work is to perform a sensitivity analysis of variables involved in calculation of position of the GPS receivers from different price bands that might be targeted by existing or future GPS attack. Variables making the biggest impact on calculated position are determined using the model. Experimentation validation of their influence is performed using selected receivers and corrupted signals generated by GNSS simulator. The testing is based on tuning the selected variables in order to simulate the theoretical error obtained from the sensitivity analysis. The results obtained from testing are discussed in order to analyse the behaviour of the considered GNSS receivers (including the premium class ones)and establish whether they provide a protection from existing or potential GPS attacks.