Random Obstacles Research Articles

Adaptive Dynamic Path Planning Algorithm for Interception of a Moving Target

Most of the 3D curve path planning is used to build static path planning. For intercepting of a moving target, the path planning has to be set in a dynamic condition. L+Dumo algorithm which is based on curve is used to intercept a moving target. In the real situations, the Unmanned Aerial Vehicle (UAV) has possibility to intercept a moving target from all direction. It is assumed that environment of the UAV is in 3D Euclidean Space. It means that the UAV has to adapt for all quadrants for interception of a moving target. This research develops a path planning algorithm which enhances the previous L+Dumo algorithm to encounter the possibility quadrants. The enhancement would be simulated in C++ language to determine the accuracy of the algorithm. The simulation is conducted using one UAV and one moving target with random obstacles of cylindrical shape in between both objects. The result shows that the system accuracy is 81.0876%, a level which is able to encounter all possibility quadrants.

Modular ventilation with twin air curtains for reducing dispersed pollution

The optimal solution for reducing the level of pollutants remains their trapping close to source. When this possibility is absent, the high degree of pollutant dispersion makes difficult and expensive any process of pollutant trapping and cleaning. This work suggests a new approach regarding the ventilation of urban road tunnels, based on the necessity for such spaces to take advantage of ventilation means which permanently direct the air towards cleaning filters while constraining uncontrolled pollutants dispersion. A concept of a modular ventilation is proposed, in which the air flow is not only induced by intake and/or exhaust fans and random obstacles inside the boundaries, but also confined by means of air curtains generated by cross flow fans. The expected result is a higher efficiency of the ventilation and of the subsequent air cleaning process. To illustrate the concept, a case study was undertaken. The investigations were focused on the behavior of twin air curtains generated by two cross flow fans and forming virtual walls inside an urban road tunnel. The results presented indicate how the distance between the curtains should be chosen, so that they remain stable, how the curtains interact with moving vehicles, and how the vents placed on the tunnel ceiling for exhausting polluted gases should be designed.

Ultrastable neuroendocrine robot controller

The work of a simulated neuroendocrine controller with ultrastable neurons and glands is sketched and tested in terms of stability and adaptability. The artificial neurons connect to each other and to motors, while hormones produced by behaviour-related glands regulate their output. The ultrastable nature of the cells allows them to maintain their homeostasis by random reconfiguration of their connections and parameters without reference to the global goal of the system. Interactions of these ultrastable components cause individual robot behaviours to emerge to certain extents. The presented results show that the controller as a whole is capable of not only configuring itself to perform random walk, obstacle avoidance, mineral collection and recharging, but also to stay robust or adapt to a number of environmental and body perturbations without a need for a body model.

Effect of Polydispersity on Diffusion in Random Obstacle Matrices

The dynamics of tracers in disordered matrices is of interest in a number of diverse areas of physics such as the biophysics of crowding in cells and cell membranes, and the diffusion of fluids in porous media. To a good approximation the matrices can be modeled as a collection of spatially frozen particles. In this Letter, we consider the effect of polydispersity (in size) of the matrix particles on the dynamics of tracers. We study a two dimensional system of hard disks diffusing in a sea of hard disk obstacles, for different values of the polydispersity of the matrix. We find that for a given average size and area fraction, the diffusion of tracers is very sensitive to the polydispersity. We calculate the pore percolation threshold using Apollonius diagrams. The diffusion constant, D, follows a scaling relation D~(φ(c)-φ(m))(μ-β) for all values of the polydispersity, where φ(m) is the area fraction and φ(c) is the value of φ(m) at the percolation threshold.

Implementation and Comparison the Dynamic Pathfinding Algorithm and Two Modified A* Pathfinding Algorithmsin a Car Racing Game

problem of pathfinding and it also be one of the most popular algorithm used for the game's development (10). Assuming a path exists between the starting point and the ending point; then the A* algorithm guarantees to find the best path. Although the A* algorithm is efficient, it still can consume considerable CPU cycles, especially if you want to simulate pathfinding for a large number of game characters. The chief shortcoming of the A* algorithm in a racing game is that it can not solve the problem of random dynamics obstacles avoidance. In this paper, we will first study the A* algorithm in a car racing game, and then proposes two modified A* algorithm to do pathfinding. After that, we propose a more general dynamic pathfinding algorithm to solve the problem of random dynamics obstacles avoidance. All the three algorithms are able to find the path for a car racing game and can save the most import resource in game, CPU cycles.

Game AI: Simulating Car Racing Game by Applying Pathfinding Algorithms

In this paper, two modified A* algorithms to effectively solve the pathfinding problem in a static obstacles racing game are proposed. Three real speedways of Formula one (F1) are selected as our game speedways, to simulate and analyze our study. The first modified A* algorithm uses a line-of-sight algorithm to reduce the waypoints found by the original A* algorithm; about 97% waypoints in the speedways of F1 in Turkey, Italy and Hungary could be removed. The second modified A* algorithm improves the performance of original A* algorithm by heuristically considering the truth that the game-controlled car should steer itself towards. That is to say, we could reduce the lap times by only checking three waypoints in front of the car, instead of checking four waypoints (up, down, left and right) in the original A* algorithm. Finally, a more general dynamic pathfinding algorithm which can solve the random obstacles avoidance problem in a racing game is also proposed.

Minimum toe clearance adaptations to floor surface irregularity and gait speed

Toe speed during gait generally nears its maximum while its height reaches a local minima approximately halfway through swing phase. Trips are thought to frequently occur at these local minima (minimum toe clearance or MTC events) and trip risk has been quantified using the minimum distance between the toe and ground here (MTC). This study investigated MTC on floor surfaces with and without multiple small obstacles. After shoes and floor surfaces were digitized, 14 unimpaired subjects (half women) each traversed a 4.88 m walkway 4 times at slow, preferred, and fast speeds across surfaces with no obstacles, visible obstacles, and hidden obstacles. Both surfaces with obstacles had the same random obstacle configuration. Shoe and body segment motions were tracked using passive markers and MTC and joint kinematics calculated. All MTC and kinematic variables tested significantly increased with faster instructed gait speed except the likelihood of MTC event occurrence (local minima in minimum toe clearance trajectory when foot is in upper quartile of speed). MTC events were less frequent for swing phases on surfaces with obstacles (80% vs. 98% for no obstacles). MTC values, when present, were doubled by the presence of visible obstacles (22.2±7.3 mm vs. 11.1±5.7 mm) and further increased to 26.8±7.1 mm when these obstacles were hidden from view (all comparisons p≤0.0003). These substantial floor surface-related changes in MTC event occurrences and values resulted from alterations in toe- and heel-clearance trajectories caused by subtle but significant changes in joint kinematics that did not exceed 10% each joint's swing phase range of motion.

Impact of random obstacles on the dynamics of a dense colloidal fluid

Using molecular dynamics simulations we study the slow dynamics of a colloidal fluid annealed within a matrix of obstacles quenched from an equilibrated colloidal fluid. We choose all particles to be of the same size and to interact as hard spheres, thus retaining all features of the porous confinement while limiting the control parameters to the packing fraction of the matrix, φ(m), and that of the fluid, φ(f). We conduct detailed investigations on several dynamic properties, including the tagged-particle and collective intermediate scattering functions, the mean-squared displacement, and the van Hove function. We show the confining obstacles to profoundly impact the relaxation pattern of various quantifiers pertinent to the fluid. Varying the type of quantifier (tagged-particle or collective) as well as φ(m) and φ(f), we unveil both discontinuous and continuous arrest scenarios. Furthermore, we discover subdiffusive behavior and demonstrate its close connection to the matrix structure. Our findings partly confirm the various predictions of a recent extension of mode-coupling theory to the quenched-annealed protocol.

Two-Dimensional Continuum Percolation Threshold for Diffusing Particles of Nonzero Radius

Lateral diffusion in the plasma membrane is obstructed by proteins bound to the cytoskeleton. The most important parameter describing obstructed diffusion is the percolation threshold. The thresholds are well known for point tracers, but for tracers of nonzero radius, the threshold depends on the excluded area, not just the obstacle concentration. Here thresholds are obtained for circular obstacles on the continuum. Random obstacle configurations are generated by Brownian dynamics or Monte Carlo methods, the obstacles are immobilized, and the percolation threshold is obtained by solving a bond percolation problem on the Voronoi diagram of the obstacles. The percolation threshold is expressed as the diameter of the largest tracer that can cross a set of immobile obstacles at a prescribed number density. For random overlapping obstacles, the results agree with the known analytical solution quantitatively. When the obstacles are soft disks with a 1/r12 repulsion, the percolating diameter is ∼20% lower than for overlapping obstacles. A percolation model predicts that the threshold is highly sensitive to the tracer radius. To our knowledge, such a strong dependence has so far not been reported for the plasma membrane, suggesting that percolation is not the factor controlling lateral diffusion. A definitive experiment is proposed.

Aperiodic fractional obstacle problems

We determine the asymptotic behavior of (bilateral) obstacle problems for fractional energies in rather general aperiodic settings via Γ-convergence arguments. As further developments we consider obstacles with random sizes and shapes located on points of standard lattices, and the case of random homothetics obstacles centered on random Delone sets of points. Obstacle problems for non-local energies occur in several physical phenomena, for which our results provide a description of the zeroth order asymptotic behavior.

Multi-dimensional backward stochastic differential equations with one reflecting lower barrier of Itô diffusion type

This paper investigates a class of multi-dimensional stochastic differential equations with one reflecting lower barrier (RBSDEs in short), where the random obstacle is described as an Itô diffusion type of stochastic differential equation. The existence and uniqueness results for adapted solutions to such RBSDEs are established based on a penalization scheme and some higher moment estimates for solutions to penalized BSDEs under the Lipschitz condition and a higher moment condition on the coefficients. Finally, two examples are given to illustrate our theory and their applications.

Non-existence of positive stationary solutions for a class of semi-linear PDEs with random coefficients

We consider a so-called random obstacle model for the motion of a hypersurface through a field of random obstacles, driven by a constant driving field. The resulting semi-linear parabolic PDE with random coefficients does not admit a global nonnegative stationary solution, which implies that an interface that was flat originally cannot get stationary. The absence of global stationary solutions is shown by proving lower bounds on the growth of stationary solutions on large domains with Dirichlet boundary conditions. Difficulties arise because the random lower order part of the equation cannot be bounded uniformly.

Two-Dimensional Continuum Percolation Threshold as a Function of the Radius of the Diffusing Particles

Lateral diffusion in the plasma membrane is obstructed by proteins bound to the cytoskeleton. The most important parameter describing diffusion in the presence of immobile obstacles is the percolation threshold, where long-range conducting paths disappear and the long-range diffusion coefficient therefore goes to zero. The thresholds are well-known for point diffusing particles on various lattices or the continuum. But for diffusing particles of nonzero radius, the threshold depends on the excluded area, not just the obstacle concentration. For the triangular lattice, the threshold is known to be highly sensitive to the size of the diffusing particle [Saxton, Biophys J 64 (1993) 1053], but lattice calculations give very low resolution. Here high-resolution results are obtained for circular obstacles on the continuum. Random obstacle configurations are generated by Brownian dynamics or Monte Carlo methods, and tested for percolation by examining bond percolation on the Voronoi diagram of the obstacles. The percolation threshold is expressed as the diameter of the largest diffusing particle that can cross a set of obstacles at a prescribed number density. For the simplest case, random overlapping obstacles, the analytical solution is known and the Monte Carlo results agree with it quantitatively. When the obstacles are disks with a 1/r⊥12 repulsion, the percolating diameter is around 10% lower than for overlapping obstacles. Disks with a 1/r⊥6 or 1/r⊥18 repulsion behave similarly. The results are used to find the thresholds for lipids, and for proteins of various diameters. (Supported by NIH grant GM038133)

Homogenization of Random Fractional Obstacle Problems via Γ-Convergence

Γ-convergence methods are used to prove homogenization results for fractional obstacle problems in periodically perforated domains. The obstacles have random sizes and shapes and their capacity scales according to a stationary ergodic process. We use a trace-like representation of fractional Sobolev norms in terms of weighted Sobolev energies established in [9], a weighted ergodic theorem and a joining lemma in varying domains following the approach by [2]. Our proof is alternative to those contained in [7, 8].

Large-Eddy Simulation of Flows over Random Urban-like Obstacles

Further to our previous large-eddy simulation (LES) of flow over a staggered array of uniform cubes, a simulation of flow over random urban-like obstacles is presented. To gain a deeper insight into the effects of randomness in the obstacle topology, the current results, e.g. spatially-averaged mean velocity, Reynolds stresses, turbulence kinetic energy and dispersive stresses, are compared with our previous LES data and direct numerical simulation data of flow over uniform cubes. Significantly different features in the turbulence statistics are observed within and immediately above the canopy, although there are some similarities in the spatially-averaged statistics. It is also found that the relatively high pressures on the tallest buildings generate contributions to the total surface drag that are far in excess of their proportionate frontal area within the array. Details of the turbulence characteristics (like the stress anisotropy) are compared with those in regular roughness arrays and attempts to find some generality in the turbulence statistics within the canopy region are discussed.

Geometrical and Taylor dispersion in a fracture with random obstacles: An experimental study with fluids of different rheologies

The miscible displacement of a Newtonian or shear‐thinning fluid by another one of same rheological properties has been studied optically in a flat transparent model fracture with a random distribution of identical cylindrical obstacles on one of the walls. At the local scale, the concentration variation on individual pixels satisfies a Gaussian convection‐dispersion relation with local transit time (x, y) and dispersivity ld(x, y). The variation of ld with the Péclet number Pe shows that it results from a combination of geometrical and Taylor dispersion, respectively dominant at low and high Pe values. Using shear‐thinning solutions instead of a Newtonian fluid enhances the velocity contrasts (and therefore geometrical dispersion) and reduces Taylor dispersion. At the global scale, the front geometry is studied from the isoconcentration lines c = 0.5 (equivalent to lines of constant (x, y) value): beyond a transition travel time, their width in the direction parallel to the flow reaches a constant limit varying linearly with Log(Pe) with a slope increasing with the shear‐thinning character of the fluid. These characteristics are compared to previous observations on other model fractures with a self‐affine roughness displaying channelization effects.

Effect of obstacles in the road profile on the dynamic response of a vehicle

The simulation study is aimed at explaining the effect of large obstacles (bumps and potholes) appearing on a road surface on the response of a vehicle passing the obstacle. For the tyre representation, the simplest point-follower model was used. Only the random obstacle modelled by cosine waves of variable height and constant height-to-length ratio was applied. For the traversing vehicle, two models were considered: a planar model of a personal car with a driver and one passenger, and a planar model of a three-axle truck. Vertical accelerations acting on the travelling people and dynamic tyre forces were estimated. In the first part of this paper, the dependences of the extreme values of the vehicle responses when passing an isolated obstacle on the obstacle height and the travel speed were evaluated. In the second part of this paper, the r.m.s. values of the same quantities were evaluated when the vehicle passes a road section with a standard pure random profile on which a number of randomly distributed obstacles were superimposed. The dependences of all quantities in question on the ‘obstacle density’ and on the travel speed were estimated.

Effect of the distribution of sorption sites on transport diffusivities: A contribution to the transport of medium-weight-molecules in polymeric materials

The detailed transports of both small and large molecules in heterogeneous media including either random disorder or periodic obstacles are known to decrease the value of macroscopic diffusion coefficients. This work proposes to analyze the successive displacements of medium-sized molecules in polymer materials according to the dispersion and topology of sorption sites from a modified application of the transition state theory. In absence of available information on the dispersion of rate constants between sorption macrosites for such molecules, their transport mechanisms at molecular scale is related to their sorption properties, which are more likely to be available. Simulations by kinetic Monte Carlo (KMC) techniques are presented for different distributions of occupancy values randomly allocated in space or distributed in self-similar clusters. Network structures are generated from the equilibrium occupancy on the basis of transition-state theory formulation on 2D lattice approximations. Different reconstruction strategies on 2D hexagonal lattices are examined regarding maximum likelihood principles including maximization of obstruction effects and minimization of either local or global variance of conductances between sorption sites. Effects of short time scales are assessed by comparing results obtained with networks verifying reversible and non-reversible random walks.

Effect of obstacles on the indicators of road unevenness

A simulation study of the effect of a large obstacle (a bump or a depression) on standard parameters of the road unevenness power spectral density (PSD) is presented. Two basic types of obstacles are considered. The so-called technological obstacle is modelled by a trapezoid of length 1 m and variable height. The random obstacle is modelled using cosine waves of variable height and constant height/length ratio. In both cases, the density of obstacles on a 1024-m-long road section is also considered. It appears that even a small obstacle on a high-quality surface causes significant deformation of the PSD, the effect being greater on the unevenness index. Profiles with a large number of randomly distributed cosine obstacles with random heights result in the PSD with two straight lines intersecting at the circular spatial frequency of 4-6 rad/m. It appears that this could be a good model for a deteriorated road. Thus, the aim of the work presented in this paper is to show the value of the simulation approach used and the practical value of particular results obtained, especially as an initial impulse to further extensive research activities in this field.

Properties of linear polymer chains in porous media

A simple model of linear polymer chains in porous media was developed, with model chains consisting of identical united atoms (beads) restricted to vertices of a simple cubic lattice. The macromolecules were confined between two parallel and impenetrable surfaces with a set of random obstacles. The excluded volume was the sole interaction among polymer beads (an athermal system). The model’s properties were determined with Monte Carlo simulations employing a Metropolis-type sampling algorithm with local changes of chain conformation. The mean dimensions of the chain were shown to depend strongly on the concentration of obstacles, while the polymer’s instantaneous shape remains constant. It was found that during migration in obstacle-dense environment the chain can be trapped in the region of local lower density of obstacles (a ‘cavity’), leave it after a period of time and move on to another cavity.