1,721,134 research outputs found
Mathematical analysis of models of non-homogeneous fluids and of hyperbolic equations with low regularity coefficients
Full text linkThe present thesis is devoted to the study both of strictly hyperbolic operators with low regularity coefficients and of the density-dependent incompressible Euler system. On the one hand, we show a priori estimates for a second order strictly hyperbolic operator whose highest order coefficients satisfy a log-Zygmund continuity condition in time and a log-Lipschitz continuity condition with respect to space. Such an estimate involves a time increasing loss of derivatives..
A note on non-homogeneous hyperbolic operators with low regularity coefficients
Full text linkIn this paper we obtain an energy estimate for a complete strictly hyperbolic operator with second order coefficients satisfying a log-Zygmund-continuity condition with respect to , uniformly with respect to , and a log-Lipschitz-continuity condition with respect to ,uniformly with respect to
The well-posedness issue for an inviscid zero-Mach number system in general Besov spaces
Full text linkThe well-posedness issue in Sobolev spaces for hyperbolic systems with Zygmund-type coefficients
Full text linkIn this paper we study the well-posedness of the Cauchy problem for first order hyperbolic systems with constant multiplicities and with low regularity coefficients depending just on the time variable. We consider Zygmund and log-Zygmund type assumptions, and we prove well-posedness in H^infty respectively without loss and with finite loss of derivatives. The key to obtain the results is the construction of a suitable symmetrizer for our system, which allows us to recover energy estimates (with or without loss) for the hyperbolic operator under consideration. This can be achievied, in contrast with the classical case of systems with smooth (say Lipschitz) coefficients, by adding one step in the diagonalization process, and building the symmetrizer up to the second order
A Dynamic Manipulation Strategy for an Intervention Autonomous Underwater Vehicle
Full text linkThis paper presents the modelling and the control architecture of an Autonomous Underwater Vehicle for
Intervention (I-AUV). Autonomous underwater manipulation with free-floating base is still an open topic of research,
far from reaching an industrial product. Dynamic manipulation tasks, where relevant vehicle velocities are required
during manipulation, over an additional challenge. In this paper, the accurate modelling of an I-AUV is described,
not neglecting the interaction with the fluid. A grasp planning strategy is proposed and integrated in the control
of the whole system. The performances of the I-AUV have been analysed by means of simulations of a dynamic
manipulation task
Single axis FOG aided attitude estimation algorithm for mobile robots
No full textThis paper is focused on an attitude estimation method for Autonomous Underwater Vehicles (AUVs).
Data acquired by a commercial Micro-Electro-Mechanical Systems (MEMS) Inertial Measurement Unit
(IMU), equipped with magnetometers, and a Fibre Optic Gyroscope (FOG) are fused to estimate the
attitude of the vehicle. One of the most used attitude estimation filter, a Nonlinear Complementary
Filter (NCF), is proposed as the basis of this work; then, some adaptations to the original formulation of
the filter are illustrated to better suit it to the field of underwater robotics. The proposed improvements
include the online tuning of the gains of the filter to cope with sensor disturbances and the employment
of the data acquired by a FOG. In addition, a fast procedure for the calibration of a magnetometer
is introduced to increase the reliability of its readings. The resulting filter is used to estimate the
attitude of an AUV; the performances of the proposed solution are tested and evaluated, in particular
when unpredictable magnetic disturbances are present, highlighting the improvements that the applied
changes allow to achieve in the specific field of application
An Attitude Estimation Algorithm for Mobile Robots under Unknown Magnetic Disturbances
Full text linkAttitude estimation is a crucial aspect for navigation and motion control of autonomous vehicles. This concept is particularly true in the case of unavailability of localization sensors when navigation and control rely on dead reckoning strategies; in this case, indeed, the orientation estimate is also used along with speed measurements to update the position estimate. Among the different approaches proposed in the literature, the de facto state of the art in this field is represented by nonlinear complementary filters: they fuse the measurements of angular rate obtained through gyroscopes, and a measurement of gravity and Earth's magnetic field vectors respectively obtained through accelerometers and magnetometers. This paper is focused on an attitude estimation strategy for autonomous underwater vehicles (AUV). The proposed novelty includes the identification of some critical issues that arise when AUV attitude estimation algorithms are applied in practice. They are mainly due to the use of low-accuracy low-cost microelectromechanical systems (MEMS) sensors and on different sources of magnetic disturbances. Some strategies to overcome the identified issues are proposed, including the integration of a single-axis fiber optic gyroscope (FOG) that ensures a considerable performance improvement with a moderate cost increase. The proposed strategies for detection of issues and sensor fusion have been experimentally tested and validated in a real application scenario estimating the attitude of an AUV performing a lawn mower path. The expected performance improvement is confirmed; the obtained results are described and analyzed in this paper
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