Obstacles In Space Research Articles

A direct imaging method for half-space inverse elastic scattering problems

We propose a direct imaging method based on reverse-time migration in order to reconstruct extended obstacles in the half space with finite aperture elastic scattering data at a fixed frequency. We demonstrate the resolution of the reconstruction method in terms of the aperture and the depth of the obstacle embedded in the half space. The resolution analysis is studied via the point spread function and implies that the imaginary part of the cross-correlation imaging function always peaks on the upper boundary of the obstacle. Numerical examples are included to illustrate the effectiveness of the method.

A manipulator control in an unknown environment

An algorithm for a n-link manipulator movement amidst unknown static obstacles in a continuous space is presented. Given theorem stating that if the manipulator moves according to the algorithm will be discovered in a finite number of steps whether a given target configuration is reachable or not. The number, shapes and dispositions of obstacles may be arbitrary.

Effect of obstacle strength and spacing on the slope of Haasen plot

ABSTRACTThe rate sensitivity of multiple obstacle aluminium alloy system was measured using the stress relaxation method. A discrepancy was observed between the slope of the Haasen plot (rate sensitivity of dislocation–dislocation interaction) in pure metals and in alloys strengthened by multiple obstacles. Considering a simplifying assumption of the constant obstacle force–distance profile, it is suggested that slope of the Haasen plot is governed by glide dislocations’ length taking part in a thermally activated event. The relative strength and spacing of obstacles (forest dislocations, solutes and precipitates) is proposed to affect the thermally activated dislocation length, which in turn manifests as the difference in slope of the Haasen plot.

Workspace analysis of the bogie 6-degree-of-freedom dynamic simulation test bench

The bogie 6-degree-of-freedom dynamic simulation test bench can simulate various operating conditions of the bogie through coordinated movement of the three parallel 6-degree-of-freedom motion platforms; however, the motion of the platforms will be interfered by some space obstacles. In order to obtain the collision-free workspace of the 6-degree-of-freedom motion platforms, a limit boundary–search method based on the collision-detection model is proposed. The structure of three parallel 6-degree-of-freedom motion platforms is analyzed, and its inverse kinematics model is established. Considering its internal constraints, the constraint models of the actuators’ stroke and the spherical hinges angle are established. Based on the collision-detection method between convex polygons, the minimum distance-detection models between platforms and obstacles as well as between actuators and obstacles are established. Then the limit boundary–search method is used to search for all boundary points that satisfy the constraint conditions. Finally, the correctness and feasibility of the proposed method and models are verified by some simulation examples. The proposed research avoids collisions effectively and provides a reference for the optimal design of the test bench.

Atomistic modeling of dislocation cross-slip in nickel using free-end nudged elastic band method

Cross-slip of screw dislocations plays an important role in the plastic deformation of face-centered cubic (FCC) metals and alloys. Here we use the free-end nudged elastic band (FENEB) method to determine the atomistic reaction pathways and energy barriers of cross-slip in an FCC single crystal of Ni. We focus on the cross-slip process mediated by an array of pinning vacancy clusters in the form of stacking fault tetrahedra. We also study a competing process of screw glide by direct cutting of those pinning obstacles on the original slip plane. The activation energies of both cross-slip and obstacle-cutting are determined for different stresses, obstacle spacings and sizes. Using FENEB-calculated energy barriers, we construct dislocation mechanism maps to reveal the effects of resolved shear stress, obstacle spacing and size on the rate-controlling dislocation process for plastic deformation. We further evaluate the activation volumes of cross-slip and obstacle-cutting. The latter result emphasizes the notion of finite strength of the atomically sized pinning obstacles to dislocation motion and also validates the Nabarro scaling law of the linear dependence of activation volume on obstacle spacing.

Robot Motion Planning in an Unknown Environment with Danger Space

This paper discusses the real-time optimal path planning of autonomous humanoid robots in unknown environments regarding the absence and presence of the danger space. The danger is defined as an environment which is not an obstacle nor free space and robot are permitted to cross when no free space options are available. In other words, the danger can be defined as the potentially risky areas of the map. For example, mud pits in a wooded area and greasy floor in a factory can be considered as a danger. The synthetic potential field, linguistic method, and Markov decision processes are methods which have been reviewed for path planning in a free-danger unknown environment. The modified Markov decision processes based on the Takagi–Sugeno fuzzy inference system is implemented to reach the target in the presence and absence of the danger space. In the proposed method, the reward function has been calculated without the exact estimation of the distance and shape of the obstacles. Unlike other existing path planning algorithms, the proposed methods can work with noisy data. Additionally, the entire motion planning procedure is fully autonomous. This feature makes the robot able to work in a real situation. The discussed methods ensure the collision avoidance and convergence to the target in an optimal and safe path. An Aldebaran humanoid robot, NAO H25, has been selected to verify the presented methods. The proposed methods require only vision data which can be obtained by only one camera. The experimental results demonstrate the efficiency of the proposed methods.

EFFECTS OF STREET FURNITURE TOWARDS THE LESSENING OF PEDESTRIAN AREA IN BRAGA STREET

Abstract- Bandung has revitalisation plans stretching throughout the city to promote “smart” and “sustainable” living. One of these projects falls on jl. Braga revitalisation project that has shown significant difference in outlook and in visitor count. The popularity of the street may in return cause discomfort for visitors, as the space allowance per person becomes smaller. This assumption has already been made by Carmona (2003) where he stated that “an unfriendly environment’s pedestrian flow may be increased significantly if the space becomes more pedestrian friendly”. The aim of this study is to evaluate the physical changes made by the revitalisation process in correlation to overcrowding. The discussion will begin by identifying elements withing the street that cause obstructions (obstacles), and a simulation of the circulation space acquired by the obstacle (or the activity it generates) is made in order to calculate the resultant circulation space and measure its overcrowding level. Overall, results show the overcrowding level of the street is constrained and congested. Witihin six out of seven obstructions analysed, it is proved that overcrowding is caused by the acquisition of space of obstacles, whether by itself or by the activities it generates. Key Words: obstacle, obstruction, overcrowding, jl. Braga

EFFECTS OF STREET FURNITURE TOWARDS THE LESSENING OF PEDESTRIAN AREA IN BRAGA STREET

Abstract- Bandung has revitalisation plans stretching throughout the city to promote “smart” and“sustainable” living. One of these projects falls on jl. Braga revitalisation project that has shown significantdifference in outlook and in visitor count.The popularity of the street may in return cause discomfort for visitors, as the space allowance perperson becomes smaller. This assumption has already been made by Carmona (2003) where he stated that “anunfriendly environment’s pedestrian flow may be increased significantly if the space becomes more pedestrianfriendly”.The aim of this study is to evaluate the physical changes made by the revitalisation process incorrelation to overcrowding. The discussion will begin by identifying elements withing the street that causeobstructions (obstacles), and a simulation of the circulation space acquired by the obstacle (or the activity itgenerates) is made in order to calculate the resultant circulation space and measure its overcrowding level.Overall, results show the overcrowding level of the street is constrained and congested. Witihin six outofseven obstructions analysed, it is proved that overcrowding is caused by the acquisition of space ofobstacles,whether by itself or by the activities it generates.Key Words: obstacle, obstruction, overcrowding, jl. Braga

Probabilistic Model of Random Encounter in Obstacle Space

Based on probabilistic time-geography, the encounter between two moving objects is random. The quantitative analysis of the probability of encounter needs to consider the actual geographical environment. The existing encounter probability algorithm is based on homogeneous space, ignoring the wide range of obstacles and their impact on encounter events. Based on this, this paper introduces obstacle factors, proposes encounter events that are constrained by obstacles, and constructs a model of the probability of encounters of moving objects based on the influence of obstacles on visual perception with the line-of-sight view analysis principle. In realistic obstacle space, this method provides a quantitative basis for predicting the encountering possibility of two mobile objects and the largest possible encounter location. Finally, the validity of the model is verified by experimental results. The model uses part of the Wuhan digital elevation model (DEM) data to calculate the encounter probability of two moving objects on it, and analyzes the temporal and spatial distribution characteristics of these probabilities.

Efficient Lazy Theta* Path Planning over a Sparse Grid to Explore Large 3D Volumes with a Multirotor UAV.

Exploring large, unknown, and unstructured environments is challenging for Unmanned Aerial Vehicles (UAVs), but they are valuable tools to inspect large structures safely and efficiently. The Lazy Theta* path-planning algorithm is revisited and adapted to generate paths fast enough to be used in real time and outdoors in large 3D scenarios. In real unknown scenarios, a given minimum safety distance to the nearest obstacle or unknown space should be observed, increasing the associated obstacle detection queries, and creating a bottleneck in the path-planning algorithm. We have reduced the dimension of the problem by considering geometrical properties to speed up these computations. On the other hand, we have also applied a non-regular grid representation of the world to increase the performance of the path-planning algorithm. In particular, a sparse resolution grid in the form of an octree is used, organizing the measurements spatially, merging voxels when they are of the same state. Additionally, the number of neighbors is trimmed to match the sparse tree to reduce the number of obstacle detection queries. The development methodology adopted was Test-Driven Development (TDD) and the outcome was evaluated in real outdoors flights with a multirotor UAV. In the results, the performance shows over 90 percent decrease in overall path generation computation time. Furthermore, our approach scales well with the safety distance increases.

The effect of the contaminant emission rate on the velocity field and contaminant distribution with the presence of an obstacle in a large space

In the industrial field, the prediction of the contaminant gas distribution is very meaningful. However, when the leakage is high, not only the contaminant distribution will not follow the pattern of the original flowfield, but the contaminant buoyancy or negative buoyancy will affect the flowfield conversely. In this study, we focus on the effect of the contaminant emission rate on the velocity field and contaminant distribution with an obstacle in a large space by means of CFD simulation. Two leaking positions and five emission rates of the source have been taken into consideration. When the emission rate is high enough, the flowfield structure will be altered and new vortexes will appear. The contaminant dimensionless concentration distribution is totally different from the low-emission-rate conditions. The flammable region becomes significant, which leads to the potential risk of explosion.

Optimal Control of a Swarming Multi-agent System through Guidance of a Leader-Agent

Control of a large group of individuals that form a collective has applications in the fields of swarm robotics, biology, economics and in control of human crowd motion. In this study, a leader-agent guides a group of autonomous agents with limited information to desired objectives. The basic idea of the leader-agent concept is that only the leader-agent knows the predetermined objective of the group and the environment. The leader tries by optimal interventions to steer the entire swarm towards objectives. For this purpose, we utilize an optimal control strategy. Possible objectives for the group include moving to a target position, tracking of a given trajectory, and avoiding collisions with obstacles in the two-dimensional space.

A real-time framework for kinodynamic planning in dynamic environments with application to quadrotor obstacle avoidance

The objective of this paper is to present a full-stack, real-time motion planning framework for kinodynamic robots and then show how it is applied and demonstrated on a physical quadrotor system operating in a laboratory environment. The proposed framework utilizes an offline–online computation paradigm, neighborhood classification through machine learning, sampling-based motion planning with an optimal cost distance metric, and trajectory smoothing to achieve real-time planning for aerial vehicles. This framework accounts for dynamic obstacles with an event-based replanning structure and a locally reactive control layer that minimizes replanning events. The approach is demonstrated on a quadrotor navigating moving obstacles in an indoor space and stands as, arguably, one of the first demonstrations of full-online kinodynamic motion planning, with execution cycles of 3 Hz to 5 Hz. For the quadrotor, a simplified dynamics model is used during the planning phase to accelerate online computation. A trajectory smoothing phase, which leverages the differentially flat nature of quadrotor dynamics, is then implemented to guarantee a dynamically feasible trajectory.

Effect of wall-mounted V-baffle position in a turbulent flow through a channel

PurposeThe purpose of this paper is to carry out a numerical study on the dynamic and thermal behavior of a fluid with a constant property and flowing turbulently through a two-dimensional horizontal rectangular channel. The upper surface was put in a constant temperature condition, while the lower one was thermally insulated. Two transverse, solid-type obstacles, having different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel and fixed to the top and bottom walls of the channel, in a periodically staggered manner to force vortices to improve the mixing, and consequently the heat transfer. The flat rectangular obstacle was put in the first position and was placed on the hot top wall of the channel. However, the second V-shaped obstacle was placed on the insulated bottom wall, at an attack angle of 45°; its position was varied to find the optimum configuration for optimal heat transfer.Design/methodology/approachThe fluid is considered Newtonian, incompressible with constant properties. The Reynolds averaged Navier–Stokes equations, along with the standard k-epsilon turbulence model and the energy equation, are used to control the channel flow model. The finite volume method is used to integrate all the equations in two-dimensions; the commercial CFD software FLUENT along with the SIMPLE-algorithm is used for pressure-velocity coupling. Various values of the Reynolds number and obstacle spacing were selected to perform the numerical runs, using air as the working medium.FindingsThe channel containing the flat fin and the 45° V-shaped baffle with a large Reynolds number gave higher heat transfer and friction loss than the one with a smaller Reynolds number. Also, short separation distances between obstacles provided higher values of the ratios Nu/Nu0 and f/f0 and a larger thermal enhancement factor (TEF) than do larger distances.Originality/valueThis is an original work, as it uses a novel method for the improvement of heat transfer in completely new flow geometry.

Mobile Robot Path Planning with a Non-Dominated Sorting Genetic Algorithm

In many areas, such as mobile robots, video games and driverless vehicles, path planning has always attracted researchers’ attention. In the field of mobile robotics, the path planning problem is to plan one or more viable paths to the target location from the starting position within a given obstacle space. Evolutionary algorithms can effectively solve this problem. The non-dominated sorting genetic algorithm (NSGA-II) is currently recognized as one of the evolutionary algorithms with robust optimization capabilities and has solved various optimization problems. In this paper, NSGA-II is adopted to solve multi-objective path planning problems. Three objectives are introduced. Besides the usual selection, crossover and mutation operators, some practical operators are applied. Moreover, the parameters involved in the algorithm are studied. Additionally, another evolutionary algorithm and quality metrics are employed for examination. Comparison results demonstrate that non-dominated solutions obtained by the algorithm have good characteristics. Subsequently, the path corresponding to the knee point of non-dominated solutions is shown. The path is shorter, safer and smoother. This path can be adopted in the later decision-making process. Finally, the above research shows that the revised algorithm can effectively solve the multi-objective path planning problem in static environments.

Coupling minimization with obstacles avoidance of free-floating space robots based on hybrid map in configuration space

To avoid the saturation of momentum wheels and the harm due to the thruster plume during the on-orbital manipulation, space robots usually stay in a free-floating state which follows the linear and angular momentum conservation leading to a kinematic coupling effect of the satellite base and the space manipulator. Emphasizing the stability of satellite base and execution safety, it is significant to minimize the kinematic coupling effect as well as avoid obstacles in the environment. Nevertheless, coupling minimization and obstacles avoidance are considered separately in previous work. By applying a hybrid map in the Configuration space, this article proposes a unified method dealing with the above two problems together. First, coupling factors are defined to evaluate the kinematic coupled effect which can be described by a coupling map; second, an obstruction map is generated by transforming obstacles in the Cartesian space to the Configuration space; the proposed hybrid map is finally generated from an overlay of a coupling map and an obstruction map. Numerical simulations verify the effectiveness of the method on a two degree-of-freedom planar space robot.

Flame acceleration and deflagration-to-detonation transition in narrow channels with thin obstacles

The entire process of deflagration-to-detonation transition (DDT) in narrow channels with thin obstacle configurations is studied through high-resolution simulations. The results show that the confinement and disturbance of obstacles promote considerably the flame acceleration and DDT. There exist two modes of DDT associating with obstacle spacing S. For small spacing S, the flame acceleration depends on strong confinement and jet flow between obstacles; eventually DDT occurs due to early burning amplified by shocks in front of the flame. However, for large spacing S, the flame acceleration is mainly attributed to turbulence; DDT results from the interaction of reflection shock with turbulent flame. It is found that the run-up distance of DDT in the obstructed channels shortens significantly, as compared with that in the smooth channel.

Automatic Manipulation of Magnetically Actuated Helical Microswimmers in Static Environments.

Electromagnetically actuated microswimmers have been widely used in various biomedical applications due to their minor invasive traits and their easy access to confined environments. In order to guide the microswimmers autonomously towards a target, an obstacle-free path must be computed using path planning algorithms, meanwhile a motion controller must be formulated. However, automatic manipulations of magnetically actuated microswimmers are underdeveloped and still are challenging topics. In this paper, we develop an automatic manipulation system for magnetically actuated helical microswimmers in static environments, which mainly consists of a mapper, a path planner, and a motion controller. First, the mapper processes the captured image by morphological transformations and then labels the free space and the obstacle space. Second, the path planner explores the obstacle-free space to find a feasible path from the start to the goal by a global planning algorithm. Last, the motion controller guides the helical microswimmers along the desired path by a closed-loop algorithm. Experiments are conducted to verify the effectiveness of the proposed automatic manipulation. Furthermore, our proposed approach presents the first step towards applications of microswimmers for targeted medical treatments, such as micromanipulation, targeted therapy, and targeted drug delivery.

Reachable region query and its applications

In this paper we study the reachable region queries for objects moving in obstacle space. Loosely speaking, given any one of moving objects and many other information, we are asked to return the whole region in which each location has the non-zero probability to be reachable for the moving object. To solve this problem, this paper presents an efficient algorithm that runs in O(nlog n) time and consumes O(nlog n) space, where n is the number of vertices of obstacles. Moreover, this paper establishes the lower bound for the proposed problem, showing that our solution essentially is optimal in terms of random access memory (RAM) model. Empirical study based on both real and synthetic datasets demonstrates the effectiveness and efficiency of our solution.

Intelligent Guide Cane design Based on Ant Colony Algorithm

The traditional guide cane for blind people is designed for visually impaired people, which can alert the blind to obstacles on the road. But it can not warn other walking hazards and obstacles in space above the waist. Therefore, due to the narrow search scope, it is not suitable for the current actual needs of the blind. And with the application of computer technology, the blind man navigation system can be designed by single-chip computer based on ant colony algorithm. This article mainly uses traditional walking stick as carrier, 51 single-chip computer as core, using infrared technology, the speech module to realize the goal of the blind person to avoid obstacles. Then the ant colony algorithm for blind guide is introduced and the simulation results in the software show that the method of introducing ant colony algorithm into blind guide is feasible.