Obstacle

About: Obstacle is a research topic. Over the lifetime, 9517 publications have been published within this topic receiving 94760 citations. The topic is also known as: impediment & barrier.

Collision avoidance for quadrotor using stereo vision depth maps

Abstract: A collision avoidance algorithm for a quadrotor unmanned aerial vehicle using a stereo vision sensor is proposed. A mathematical model for the quadrotor is developed, and the underactuated problem of the quadrotor is treated by introducing virtual inputs. Stereo vision is used to obtain depth map information, which is used to detect an obstacle. The collision cone approach is adopted to avoid collisions between the quadrotor and the detected obstacle. The collision prediction is conducted by using the relation between the velocity vector of the quadrotor and the collision cone. Information of the detected obstacles is accumulated to determine the location and size of the obstacles, which is used to prevent the quadrotor from colliding with the obstacle. Multiple obstacles can also be managed by creating obstacle clusters in the image plane. A waypoint guidance law and controller are designed using a feedback linearization scheme and a linear quadratic tracker. Numerical simulations are performed to demonstrate the performance of the proposed algorithm.

Dynamic Obstacle Avoidance for Unmanned Underwater Vehicles Based on an Improved Velocity Obstacle Method.

Abstract: In view of a dynamic obstacle environment with motion uncertainty, we present a dynamic collision avoidance method based on the collision risk assessment and improved velocity obstacle method. First, through the fusion optimization of forward-looking sonar data, the redundancy of the data is reduced and the position, size and velocity information of the obstacles are obtained, which can provide an accurate decision-making basis for next-step collision avoidance. Second, according to minimum meeting time and the minimum distance between the obstacle and unmanned underwater vehicle (UUV), this paper establishes the collision risk assessment model, and screens key obstacles to avoid collision. Finally, the optimization objective function is established based on the improved velocity obstacle method, and a UUV motion characteristic is used to calculate the reachable velocity sets. The optimal collision speed of UUV is searched in velocity space. The corresponding heading and speed commands are calculated, and outputted to the motion control module. The above is the complete dynamic obstacle avoidance process. The simulation results show that the proposed method can obtain a better collision avoidance effect in the dynamic environment, and has good adaptability to the unknown dynamic environment.

A mimetic discretization of elliptic obstacle problems

Abstract: We develop a Finite Element Method (FEM) which can adopt very general meshes with polygonal elements for the numerical approximation of elliptic obstacle problems. These kinds of methods are also known as mimetic discretization schemes, which stem from the Mimetic Finite Difference (MFD) method. The first-order convergence estimate in a suitable (mesh-dependent) energy norm is established. Numerical experiments confirming the theoretical results are also presented.

Hydrodynamic interactions of ships with fixed obstacles

Abstract: The hydrodynamic interactions of a slow-moving vessel with a shoreline or an obstacle in shallow water are investigated using slender-body theory. With the assumption that the free surface is rigid, the problem is shown to be equivalent to studying the flow about a porous airfoil moving near an irregular boundary in the horizontal plane. A numerical procedure is developed based on the availability of an "obstacle Green function." Theoretical results indicate that the vessel experiences an attractive force and a bow-in moment during the approach toward a wedge-shaped obstacle, such as a pier or a breakwater, regardless of the angle of approach. For a vessel approaching a side bank at an angle, the theory yields results consistent with the so-called "bank-rejection" phenomenon.