Browsing by Author "Zolotas, Argyrios C."
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Item Open Access Evaluation and selection of video stabilization techniques for UAV-based active infrared thermography application(MDPI, 2021-02-25) Pant, Shashank; Nooralishahi, Parham; Avdelidis, Nicolas Peter; Ibarra-Castanedo, Clemente; Genest, Marc; Deane, Shakeb; Valdes, Julio J.; Zolotas, Argyrios C.; Maldague, Xavier P. V.nmanned Aerial Vehicles (UAVs) that can fly around an aircraft carrying several sensors, e.g., thermal and optical cameras, to inspect the parts of interest without removing them can have significant impact in reducing inspection time and cost. One of the main challenges in the UAV based active InfraRed Thermography (IRT) inspection is the UAV’s unexpected motions. Since active thermography is mainly concerned with the analysis of thermal sequences, unexpected motions can disturb the thermal profiling and cause data misinterpretation especially for providing an automated process pipeline of such inspections. Additionally, in the scenarios where post-analysis is intended to be applied by an inspector, the UAV’s unexpected motions can increase the risk of human error, data misinterpretation, and incorrect characterization of possible defects. Therefore, post-processing is required to minimize/eliminate such undesired motions using digital video stabilization techniques. There are number of video stabilization algorithms that are readily available; however, selecting the best suited one is also challenging. Therefore, this paper evaluates video stabilization algorithms to minimize/mitigate undesired UAV motion and proposes a simple method to find the best suited stabilization algorithm as a fundamental first step towards a fully operational UAV-IRT inspection system.Item Open Access Facilitating autonomous systems with AI-based fault tolerance and computational resource economy(MDPI, 2020-05-11) Deliparaschos, Kyriakos M.; Michail, Konstantinos; Zolotas, Argyrios C.Proposed is the facilitation of fault-tolerant capability in autonomous systems with particular consideration of low computational complexity and system interface devices (sensor/actuator) performance. Traditionally model-based fault-tolerant/detection units for multiple sensor faults in automation require a bank of estimators, normally Kalman-based ones. An AI-based control framework enabling low computational power fault tolerance is presented. Contrary to the bank-of-estimators approach, the proposed framework exhibits a single unit for multiple actuator/sensor fault detection. The efficacy of the proposed scheme is shown via rigorous analysis for several sensor fault scenarios for an electro-magnetic suspension testbed.Item Open Access On-line learning and updating unmanned tracked vehicle dynamics(MDPI, 2021-01-15) Strawa, Natalia; Ignatyev, Dmitry I.; Zolotas, Argyrios C.; Tsourdos, AntoniosIncreasing levels of autonomy impose more pronounced performance requirements for unmanned ground vehicles (UGV). Presence of model uncertainties significantly reduces a ground vehicle performance when the vehicle is traversing an unknown terrain or the vehicle inertial parameters vary due to a mission schedule or external disturbances. A comprehensive mathematical model of a skid steering tracked vehicle is presented in this paper and used to design a control law. Analysis of the controller under model uncertainties in inertial parameters and in the vehicle-terrain interaction revealed undesirable behavior, such as controller divergence and offset from the desired trajectory. A compound identification scheme utilizing an exponential forgetting recursive least square, generalized Newton–Raphson (NR), and Unscented Kalman Filter methods is proposed to estimate the model parameters, such as the vehicle mass and inertia, as well as parameters of the vehicle-terrain interaction, such as slip, resistance coefficients, cohesion, and shear deformation modulus on-line. The proposed identification scheme facilitates adaptive capability for the control system, improves tracking performance and contributes to an adaptive path and trajectory planning framework, which is essential for future autonomous ground vehicle missionsItem Open Access Robust dynamic CPU resource provisioning in virtualized servers(IEEE, 2020-01-15) Makridis, Evagoras; Deliparaschos, Kyriakos M.; Kalyvianaki, Evangelia; Zolotas, Argyrios C.; Charalambous, ThemistoklisWe present robust dynamic resource allocation mechanisms to allocate application resources meeting Service Level Objectives (SLOs) agreed between cloud providers and customers. In fact, two filter-based robust controllers, i.e. H∞ filter and Maximum Correntropy Criterion Kalman filter (MCC-KF), are proposed. The controllers are self-adaptive, with process noise variances and covariances calculated using previous measurements within a time window. In the allocation process, a bounded client mean response time (mRT) is maintained. Both controllers are deployed and evaluated on an experimental testbed hosting the RUBiS (Rice University Bidding System) auction benchmark web site. The proposed controllers offer improved performance under abrupt workload changes, shown via rigorous comparison with current state-of-the-art. On our experimental setup, the Single-Input-Single-Output (SISO) controllers can operate on the same server where the resource allocation is performed; while Multi-Input-Multi-Output (MIMO) controllers are on a separate server where all the data are collected for decision making. SISO controllers take decisions not dependent to other system states (servers), albeit MIMO controllers are characterized by increased communication overhead and potential delays. While SISO controllers offer improved performance over MIMO ones, the latter enable a more informed decision making framework for resource allocation problem of multi-tier applications.Item Open Access Sustainable cities: the relationships between urban built forms and density indicators(Elsevier, 2020-07-03) Ahmadian, Ehsan; Sodagar, Behzad; Mills, Glen; Byrd, Hugh; Bingham, Chris M.; Zolotas, Argyrios C.The paper introduces a novel indicator of urban built form termed Form Signature. Generic models of four urban built forms are developed including pavilion, terrace, court and a newly introduced tunnel-court which are used to compare and contrast their land-use performance and density characteristics. Selecting plot ratio and site coverage as the most popular and appropriate density indicators, the simultaneous relationship to each of the considered urban built forms is shown graphically with the number of storeys, plan depth and cut-off angle as the main variables of interest. For existing urban areas, the resulting graphs provide a robust tool for statistical analysis of contexts such as climate, economy, energy and crime potential and establish their relationship to form and density. To show the value of the contribution, analysing 32 case studies from 19 cities in different global locations showed an insignificant relationship between climate and form/density of urban areas, while practically depicting that urban areas built in court form acquire higher cut-off angle compared to terrace form urban developments. For the planning of future urban areas, the resulting relationships provide an application-oriented urban planning tool to facilitate the most effective land-use method in order to achieve sustainable cities. Examples showing the potential of the tool for future statistical energy and social analysis of urban areas are provided. Finally, a relative comparison shows that the newly-introduced tunnel-court form achieves the greatest density while pavilion achieves the lowestItem Open Access Wing tilt scheduling in tandem-wing VTOL configurations(Vertical Flight Society (American Helicopter Society), 2021-01) Grzędziński, Kacper; Stéphan, Valentin; Zolotas, Argyrios C.The effect of scheduling wing tilt angle in tandem tilt-wing vertical take-off and landing (VTOL) aircraft is investigated with respect to both the static and dynamic longitudinal stability; a first-principles three degree of freedom model of longitudinal motion is derived and simulated with aerodynamic coefficients from a conventional subsonic aerofoil profile. Model trimming through readily available optimisation software is used to determine the values of thrusts and tilts needed for trimmed flight; at airspeeds that correspond to hover and cruise flight modes. The resulting equilibria are discussed qualitatively and compared to equilibria resulting from a model that accounts for the interaction between propeller slipstream and wing aerofoils. Through simulations, it is shown that propeller slipstream influences the dynamic longitudinal modes of the aircraft, under the parametric assumptions of this paper.