1,721,119 research outputs found
Drilling Damage of GFRP and Residual Mechanical Behavior - Part II: Static and Cyclic Bearing Loads
No full textThe damage generated during the drilling of Glass Fiber Reinforced Plastics (GFRP) laminates can be detrimental for the mechanical behavior of the material around the hole, especially when the hole surface is subjected to a bearing load. The present work is the second part of a study aiming to investigate the effect of drilling conditions on the residual mechanical behavior of GFRP laminates subjected to a bearing load. To address this aim, holes drilled in different conditions were tested with static and cyclic bearing loads. The results of these tests were characterized through quantitative parameters and through microscopic observations of hole sections. Results indicate that for the range of the experimental conditions investigated, the main cause of mechanical failure is the micro damage generated at the inner part of the hole surface, while delamination plays a minor role. Therefore, despite the general attention paid during drilling to reduce delamination, the optimal drilling conditions should avoid the onset of microcracks distributed in the inner part of the hole
POF bandwidth measurements using OTDR
No full textThe experimental measurements of the modal bandwidth on POF cables is today an important issues for fiber manufacturers, whenever new types of fibers are designed and/or commercialised, and for any research center working with POF for high-speed transmission applications. In this paper we focus on a measurement techniques using an high resolution Optical Time Domain Reflectometer (OTDR
Marburg type and Balò's concentric sclerosis: rare and acute variants of multiple sclerosis.
No full text
Design of Sliding Mode Techniques for a CMG-based Testbed Attitude Control System
Full text linkPrecise pointing accuracy and rapid maneuvering are two key features for attitude control missions of small spacecraft. Control moment gyroscopes (CMGs) are applied as ideal actuator for large torque output capability but are usually limited due to the problem of inherent mechanical singularity. This paper proposes a robust attitude control methodology, based on Sliding Mode Control (SMC) techniques, in presence of CMG practical restrictions and disturbances. Two second-order SMC techniques are designed, to guarantee accuracy and limited convergence time. Moreover, attitude control torques are generated by means of four single gimbal CMGs in pyramidal configuration, considering the design of an experimental testbed. The effectiveness of the proposed methodologies are shown in simulations, for different mission scenarios, including singularity points
Leader-Following Coordination of Heterogeneous Multi-Agent Systems via Displacement Feedback
No full textThis paper deals with heterogeneous second-order multi-agent consensus, for attitude coordinated control of spacecraft. A robust consensus for undirected and connected graph is shown, with dynamic weight interaction and only displacement measurements available. Leader-following coordination is proposed, with proof of internal stability. Flexible appendages, external disturbances and uncertainties are included in the model. A space maneuver is considered to show the achievement of the consensus
Constrained Formation Control Framework for Spacecraft Proximity Formation Flight
Full text linkThis paper presents an analytical framework for designing Artificial Potential Field (APF) gains for spacecraft formation control within the Circular Relative Orbit framework. While APF methods are effective for formation shaping, they often overlook system dynamics and constraints, risking instability. The proposed method ensures Lyapunov stability through a systematic gain design and the definition of an operational bound. Stability is verified using Structured Singular Value μ-analysis. Numerical simulations confirm the robustness and scalability of the approach, supporting safe and reliable proximity operations for future multi-satellite missions inEarth orbit
Sliding Mode Control with Chattering Attenuation and Hardware Constraints in Spacecraft Applications
Full text linkModelling of the Transient Thermal Field in Laser Surface Treatment Test
No full textprinted on line (2008), will be published soon (2009
Proximity operations with obstacles avoidance based on artificial potential field and sliding mode control
No full textThis paper combines Guidance and Control (GC) algorithms for spacecraft proximity operations in presence of multiple obstacles. The proposed guidance algorithm is based on Artificial Potential Field (APF) theory, while the adopted control strategies are first-order Sliding Mode Control (SMC) algorithms. The position control problem is addressed by considering two different first-order methods: the simplex-based and the component-wise SMC. Both control strategies result to be effective and suitable to be implemented by the mono-directional actuation system. These algorithms are suitably designed for a ground test-bed for spacecraft rendezvous and docking experiments, developed within the STEPS project (Systems and Technologies for Space Exploration). The selected algorithms are suitable for autonomous, real-time control of proximity maneuvers with a minimum on-board computational effort. Moreover, the presented strategy is able to avoid obstacles and to manage issues related to the presence of local minima in APF algorithms
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