Search results for "CATIONS"
showing 10 items of 10791 documents
Accurate keyframe selection and keypoint tracking for robust visual odometry
2016
This paper presents a novel stereo visual odometry (VO) framework based on structure from motion, where a robust keypoint tracking and matching is combined with an effective keyframe selection strategy. In order to track and find correct feature correspondences a robust loop chain matching scheme on two consecutive stereo pairs is introduced. Keyframe selection is based on the proportion of features with high temporal disparity. This criterion relies on the observation that the error in the pose estimation propagates from the uncertainty of 3D points—higher for distant points, that have low 2D motion. Comparative results based on three VO datasets show that the proposed solution is remarkab…
Real time UAV altitude, attitude and motion estimation from hybrid stereovision
2012
International audience; Knowledge of altitude, attitude and motion is essential for an Unmanned Aerial Vehicle during crit- ical maneuvers such as landing and take-off. In this paper we present a hybrid stereoscopic rig composed of a fisheye and a perspective camera for vision-based navigation. In contrast to classical stereoscopic systems based on feature matching, we propose methods which avoid matching between hybrid views. A plane-sweeping approach is proposed for estimating altitude and de- tecting the ground plane. Rotation and translation are then estimated by decoupling: the fisheye camera con- tributes to evaluating attitude, while the perspective camera contributes to estimating t…
A macroscale FEM-based approach for selective laser sintering of thermoplastics
2017
A numerical approach to model the selective laser sintering (SLS) of polypropylene is proposed. A 3D thermal model was developed and thus enables the prediction of the temperature fields and the extension of the sintered area in the powder bed taking into account the phase change during multiple laser passes. Powderâliquid, liquidâsolid and solidâliquid phase changes were modelled during the SLS and the subsequent cooling processes. Then, a 3D thermomechanically coupled model was set up based on the temperature results of the thermal model in order to predict the distortion of the produced parts after cooling down. Different pre-heating temperatures were considered, highlighting their…
The application of the random balance method in laser machining of metals
2008
International audience; Features peculiar to laser technology offer some advantages over more traditional processes, but, like all processes, it has its limitations. This article studies the limitations of laser machining of metals, and quantifies, through an experimental design method, the influence of operating parameters on productivity and on the quality of the machined surface. Three study materials were used: an aluminium alloy, stainless steel and a titanium alloy. An initial reading of the results indicates that productivity depends mainly on the frequency of the laser pulse and that the aluminium alloy behaves differently from the other two. The quality of the machined surface, jud…
A numerical model for Wire integrity prediction in Friction Stir Extrusion of magnesium alloys
2017
Abstract A numerical model for the prediction of the wire quality produced by the novel direct machining chip recycling technique known as Friction Stir Extrusion (FSE) is presented. Wire microstructure and wire integrity have been predicted by embedding in the code the equations enabling the calculation of the Zener-Hollomon parameter as well as the W parameter of the Pivnik-Plata solid bonding criterion. The proposed model, developed for the AZ31 magnesium alloy using the commercial simulation package DEFORM, is 3D Lagrangian, thermo-mechanically coupled with visco-plastic material behavior. The model was first validated against experimental temperature measurements and then used to predi…
Single block 3D numerical model for linear friction welding of titanium alloy
2018
A two-stage approach for the simulation of Linear Friction Welding is presented. The proposed model, developed using the commercial simulation package DEFORM, is 3D Lagrangian, thermo-mechanically coupled. The first phase of the process was modelled with two distinct workpieces, while the remaining phases were simulated using a single-block model. The Piwnik–Plata criterion was set up and used to determine the shifting from the dual object to the single-block model. The model, validated against experimental temperature measurements, is able to predict the main field variables distributions with varying process parameters. Titanium alpha and beta phases evolution during the whole process has…
In-process control strategies for friction stir welding of AZ31 sheets with non-uniform thickness
2017
Two different in-process control strategies were developed and compared with the aim to produce AZ31 magnesium alloy joints by friction stir welding on sheet blanks with a non-uniform thickness. To this purpose, sheets with dip or hump zones were welded by either changing the rotational speed or the tool plunging in order to keep constant the value of the vertical force occurring during the welding stage of the process. The influence of the main process parameters on the tool force, the micro- and macromechanical properties, and the joints microstructures in the dip and hump zones were analyzed. The results showed that using the rotational speed change-based approach, the hump zones are sub…
Energy harvesting using piezoelectric transducers for suspension systems
2020
Abstract Energy harvesting by using functional materials in suspension systems bear potential to win-back certain (even if low) amounts of vibrational energy, otherwise dissipated via the conventional (passive) dampers. Piezoelectric (PE) ceramics are functional materials that can be used for transforming mechanical energy into electrical and vice versa. In this paper, we study the capabilities and efficiency of energy harvesting (EH) with PE transducers under two different kinds of external excitation: i) Periodic and ii) stochastic. An appropriate nonlinear lumped parameter electromechanical model (LPEM) is brought into the two-port network notation. Laboratory experiments were conducted …
Contactless generation of cavitation in high temperature liquid metals and its impact on particle dispersion in solidified iron and steel samples
2021
Abstract A recently developed method for the contactless magnetic generation of cavitation is demonstrated for high-melting-point metals. The approach is based on the floating-zone technique, which is truly contactless and crucible-free as it uses electromagnetic forces. Using this method, ultra-high-temperature ceramic particles, such as TiN, TiB2 and TiC, are admixed in liquid iron and 316L steel. The dispersion and particle refinement caused by cavitation treatment during melting and solidification are investigated. Magnetic fields up to 8 T that correspond to pressure oscillation amplitude of 0.83 MPa are used. The signal emitted by the collapsing bubbles is captured and visualized for …
The numerical simulation of heat transfer during a hybrid laser–MIG welding using equivalent heat source approach
2014
International audience; The present study is dedicated to the numerical simulation of an industrial case of hybrid laser-MIG welding of high thickness duplex steel UR2507Cu with Y-shaped chamfer geometry. It consists in simulation of heat transfer phenomena using heat equivalent source approach and implementing in finite element software COMSOL Multiphysics. A numerical exploratory designs method is used to identify the heat sources parameters in order to obtain a minimal required difference between the numerical results and the experiment which are the shape of the welded zone and the temperature evolution in different locations. The obtained results were found in good correspondence with …